energy efficiency in meat processing

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THESIS FOR THE DEGREE OF LICENTIATE OF ENGINEERING Energy Efficiency in the Meat Processing Industry Opportunities for Process Integration ANNA FRITZSON Department of Energy and Environment Heat and Power Technology CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden, 2005 Work performed at SIK – The Swedish Institute for Food and Biotechnology

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CHALMERS UNIVERSITY OF TECHNOLOGY - PhD Thesis

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Page 1: Energy Efficiency in Meat Processing

THESIS FOR THE DEGREE OF LICENTIATE OF ENGINEERING

Energy Efficiency in the Meat Processing Industry Opportunities for Process Integration

ANNA FRITZSON

Department of Energy and Environment Heat and Power Technology

CHALMERS UNIVERSITY OF TECHNOLOGY

Göteborg, Sweden, 2005

Work performed at SIK – The Swedish Institute for Food and Biotechnology

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Energy Efficiency in the Meat Processing Industry Opportunities for Process Integration

ANNA FRITZSON

Anna Fritzson, 2005

Department of Energy and Environment

Heat and Power Technology

ISRN CTH-VOM-PB-09/05-SE

ISSN: 1404-7098

Chalmers University of Technology

SE-412 96 Göteborg

Sweden

Telephone Chalmers +46 (31) 772 10 00

Telephone SIK +46 (31) 335 56 00

Printed by Chalmers Reproservice

Göteborg, Sweden 2005

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Energy Efficiency in the Meat Processing Industry – Opportunities for Process Integration

ANNA FRITZSON

SIK – The Swedish Institute for Food and Biotechnology and

Department of Energy and Environment, Heat and Power Technology

Chalmers University of Technology

ABSTRACT

There are a number of trends in the food industry that will make energy-related issues more important in food processing plants in the future. For example, the energy use in the plants is increasing due to a growing consumption of industrially processed food and a growing demand for a greater range of different products. These changes in customer behavior, together with raised energy prices, policy instruments and harder price competition, enhance the interest in saving energy in the food industry.

In the first part of this thesis the potential to reduce energy-related costs and CO2 emissions in two existing modern slaughter and meat (SMP) plants was investigated using process integration methods. In the case studies the opportunities for extended heat-exchanging and heat pumping were examined. A potential to reduce external heating and cooling demands by using heat pumps was found using heat pinch analysis. In one of the studied plants installation of an additional heat pump was shown to reduce the external heat demand, excluding process steam, to almost zero. The use of a shaftwork targeting method in one of the studied plants shows a potential for reducing the electricity demand in the refrigeration systems of the plant by 10%.

In the second part of the work the economic and technical potentials for reducing CO2 emissions and fuel-related costs in plants of different size and level of heat recovery were studied for different possible future energy markets. Different energy efficiency measures, such as extended heat integration, switching fuels in boilers, integration of heat pumps or a CHP plant, and an integrated energy utility system in an ecocyclic industrial park were examined in four fictitious plants. It was found that all measures are more or less advantageous in different future energy markets. However, heat integration and heat pumps are robust solutions that are profitable in all studied energy markets. The integration of a CHP plant was shown to be a profitable option for an SMP plant when the energy market develops towards a more sustainable state, especially when the plant is part of an ecocyclic industrial park.

It was also concluded that the options studied in the second part of the thesis can save large amounts of CO2 emissions from the plants. The cheapest investment per kg CO2 reduction was shown to be a switch from fuel oil to natural gas in the boilers in the plants. Other efficient ways of reducing CO2 emissions is using wood chips instead of oil in boilers, extended heat recovery, and installation of heat pumps.

Keywords: Process integration, heat pinch analysis, food processing, slaughter and meat processing, shaftwork, heat recovery, heat pump, combined heat and power

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LIST OF PUBLICATIONS

This thesis is based on the following papers, referred to in the text by their Roman numerals.

I. Fritzson, A., Berntsson, T. and Vamling, L., 2004. Energy conservation in the food industry using process integration – methodologies and case study. To be published in Proceedings of ICEF9 International Congress on Engineering and Food, Montpellier, France.

II. Fritzson, A. and Berntsson, T., 2005. Efficient energy use in a slaughter and meat processing plant – opportunities for process integration. Journal of Food Engineering, in press.

III. Fritzson, A. and Berntsson, T., 2005. Energy efficiency in the slaughter and meat processing industry – opportunities for improvements in future energy markets. Accepted for publication in Journal of Food Engineering.

Anna Fritzson is the main author of the three appended papers. Lennart Vamling supervised and contributed to the study presented in Paper I with some calculations. Thore Berntsson supervised the work with all three papers.

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TABLE OF CONTENTS ABSTRACT

LIST OF PUBLICATIONS

1 INTRODUCTION ...................................................................................................... 1

1.1 FOOD AND ENERGY .................................................................................................... 1

1.2 THE INDUSTRIAL BACKGROUND .............................................................................. 2

1.3 OUTLINE OF THE THESIS............................................................................................. 3

2 THE AIMS AND OBJECTIVES OF THE STUDY...................................................... 5

3 ENERGY UTILITY SYSTEMS IN SLAUGHTER AND MEAT PROCESSING PLANTS .................................................................................................................... 7

3.1 INTRODUCTION............................................................................................................ 7

3.2 STEAM........................................................................................................................... 8

3.3 WATER.......................................................................................................................... 8

3.4 ELECTRICITY................................................................................................................ 9

3.5 REFRIGERATION SYSTEM........................................................................................... 9

3.6 ENERGY CONSERVATION SYSTEMS......................................................................... 10 3.6.1 Heat Integration................................................................................................................ 10 3.6.2 Heat Pumps ....................................................................................................................... 11 3.6.3 Combined Heat and Power (CHP)................................................................................. 11

4 PREVIOUS WORK................................................................................................. 15

4.1 ENERGY USE IN THE FOOD INDUSTRY ................................................................... 15

4.2 ENERGY EFFICIENCY STUDIES IN THE FOOD INDUSTRY ...................................... 16 4.2.1 Continuous Food Processes ............................................................................................. 17 4.2.2 Manufacturing Food Industry ......................................................................................... 18

4.3 HEAT PUMPS IN FOOD PROCESSING PLANTS ......................................................... 19

4.4 COMBINED HEAT AND POWER PLANTS IN THE FOOD INDUSTRY ....................... 19

5 METHODOLOGY – TOOLS ................................................................................... 21

5.1 HEAT PINCH ANALYSIS ............................................................................................ 21

5.2 BATCH PINCH ANALYSIS .......................................................................................... 23

5.3 PROCESS INTEGRATION OF HEAT PUMPS AND CHP PLANTS............................... 25

5.4 SHAFTWORK TARGETING......................................................................................... 27

5.5 SIMULATION AND THE USE OF HYSYS ................................................................ 29

5.6 ENERGY SCENARIOS ................................................................................................. 30 5.6.1 Fuel ..................................................................................................................................... 32 5.6.2 Electricity ........................................................................................................................... 33

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6 RESULTS................................................................................................................ 37

6.1 PROCESS INTEGRATION CASE STUDIES IN SMP PLANTS...................................... 37 6.1.1 Introduction....................................................................................................................... 37 6.1.2 Reduction in External Heat Demand in SMP Plants – Papers I and II ..................... 38 6.1.3 Reduction of Shaftwork Need in an SMP Plant – Paper II.......................................... 43

6.2 FUTURE OPPORTUNITIES FOR ENERGY SAVING IN SMP PLANTS – PAPER III .. 46 6.2.1 Introduction....................................................................................................................... 46 6.2.2 Non-Integrated Plants ...................................................................................................... 47 6.2.3 Ecocyclic Industrial Park ................................................................................................. 49 6.2.4 Integrated Plants ............................................................................................................... 50 6.2.5 CO2 Emissions................................................................................................................... 51 6.2.6 Summary ............................................................................................................................ 53

7 DISCUSSION .......................................................................................................... 55

8 CONCLUSIONS ...................................................................................................... 57

9 FUTURE OUTLOOK.............................................................................................. 59

10 ACKNOWLEDGEMENTS ....................................................................................... 61

11 NOMENCLATURE AND ABBREVIATIONS.......................................................... 65

12 REFERENCES ........................................................................................................ 67

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INTRODUCTION

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1 INTRODUCTION

1.1 FOOD AND ENERGY The food system accounts for a significant share of the total energy use in society. In fact, 20% of the total energy use in society can be attributed to the food system (SEPA, 1997). The energy use arises in all parts of the life cycle of food products. The consumption sector, including households, restaurants and the catering trade, is the largest user of energy in the Swedish food chain, 38-45% (Uhlin, 1997). Processing of food uses 17-20%, agriculture 15-19%, and distribution and retail 20-29% of the energy consumption in the Swedish food system. In an American study (Heller and Keoleian, 2000), home refrigeration and preparation were shown to consume 31% of the energy use in the United States food system, agricultural production 21%, processing 16% and transport 14%. The production of packaging material, the commercial food service and food retail are also part of the food system.

Even though the industrial energy use is not the largest part of the energy consumption in the food chain, increased energy efficiency or alternative ways of producing heat in a plant can be important for the profitability of a plant, especially as energy prices probably will increase in the future. Decreasing the

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energy use in food plants has previously not been highly prioritized in Swedish food industry, as the plants have concentrated on their core business of making food, and electricity prices have historically been low in the Swedish industry. Currently, there is an increased focus on reducing greenhouse gases and saving fossil fuels in society through different policy instruments, such as CO2 permit trading, which creates economic incentives for industry to reduce fossil fuel use and to reduce greenhouse gas emissions.

There are also a number of trends in the food industry that will make energy-related issues more important in food processing plants in the future. The consumption of industrially processed food is increasing in Sweden – see Eidstedt, Svensson and Wikberger (2004) – as well as in other countries: see for example Olsson (2003). As the demand grows for products that can be prepared quickly and simply, the food processing industry carries out a higher level of processing and packaging combined with cooling and freezing. This leads to a larger energy use in the food processing plants, while the energy usage in households is changed and to some degree transferred to the industry (Sonesson, Mattsson, Nybrant and Ohlsson, 2005).

Additionally, there is a growing demand for greater flexibility in the food processing plants. Consumers want a greater range of different products. This, in turn, increases energy use in the plants e.g. through increased warm water usage due to increased cleaning. These changes in customer behavior, together with raised energy prices, policy instruments and harder price competition from a more global market enhance the interest in saving energy in the food industry.

1.2 THE INDUSTRIAL BACKGROUND The food industry consumes large amounts of energy both because of its size and because of the amount of energy-demanding processes that are normally used. In Sweden, for example, the food processing plants used approximately 5.75 TWh fuel and electricity (Statistics Sweden, 2002) out of the approximately 160 TWh used by all industry in 2000 (EUROSTAT, 2005). The overall energy use in Swedish food processing plants consists on average of 45% electricity and 55% purchased fuels, not including fuel for transports (SEPA, 1997). Within the food industry, the dairy and cheese and the slaughtering and meat processing industries are particularly electricity-demanding. The sugar industry and drink production plants are particularly fuel-demanding.

In addition to an increasing production of industrially processed food, there is also a trend in the European countries towards fewer and larger slaughter and meat processing (SMP) plants. For individual plants, the larger units might be expected to result in lower energy consumption per unit of produced meat product at the plant. In practice, however, this does not seem to be the case

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(European Commission, 2003b). Still, as plant sizes increase there is an increased potential for saving energy, and thereby decreasing the CO2 emissions associated with energy use in the plants – by means of, for example, extended internal heat exchange, installation of a heat pump, or a combined heat and power (CHP) plant.

Other general trends which may influence the future consumption of resources in the slaughtering industry include increasing demand for better food safety, which leads to a higher intensity of cleaning and disinfection operations. The growing requirement of good eating quality can lead to increased need for cooling, as the control of chilling processes can improve tenderness. The need to improve the working environment affects the energy use in slaughtering plants through, for example, increased automation of processes in the plant (European Commission, 2003b). None of these trends are discussed further in this thesis.

Process integration is defined by the International Energy Agency (IEA) as “Systematic and general methods for designing integrated production systems, ranging from individual processes of total sites, with special emphasis on the efficient use of energy and reducing environmental effects” (Gundersen, 2002).

Process integration methods can be used when designing and retrofitting industrial processes to obtain a complete plant with optimal use of resources, such as energy, raw materials and process equipment. The focus of the methods has traditionally been on efficient energy use (heat pinch analysis), but recently other parameters, such as water use, have been studied. Implementation of process integration methods in different sectors of industry has shown a large potential for fuel savings.

In this thesis, process integration methods are used to find the potential to save on energy-related costs and CO2 emissions in modern existing SMP plants. The profitability and CO2 reduction potential for energy efficiency measures that can be made in an SMP plant are also studied and compared for different possible energy markets.

1.3 OUTLINE OF THE THESIS Chapter 1 gives a background to trends and energy use in the Swedish food industry. In Chapter 2, the objectives and system boundaries of this work are presented and in Chapter 3 the energy utility systems in SMP plants are described. A presentation of previous energy studies in different branches of the food processing industry is made in Chapter 4 and a description of the methodologies used, as well as a literature review of the methods, is made in Chapter 5. The results from the papers included in the thesis are presented in Chapter 6. In Chapters 7 and 8 the results in and the conditions for this work are

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discussed and conclusions are drawn. A future outlook is given in Chapter 9, where further research and work are suggested.

The thesis is based on three papers describing energy efficiency measures in the SMP industry. The papers are included in the thesis. In Paper I process integration methods are described and the potential for decreasing external heating and cooling demand by increased heat integration or heat pumping is examined at an SMP plant. In Paper II the potential for decreasing external heating and cooling demands at another SMP plant is examined. The potential for reducing the electricity demands in the refrigeration systems in the plant is also studied in Paper II.

Paper III describes four different fictitious SMP plants with different production sizes and different external heating and cooling demands. The economic profitability and the CO2 emission reduction potential are studied and compared for different energy investment projects: increased heat integration, heat pumping, changing fuel in the boiler, and a combined heat and power plant. The comparison is made for four different future energy market parameter sets.

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THE AIMS AND OBJECTIVES OF THE STUDY

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2 THE AIMS AND OBJECTIVES OF THE STUDY In slaughter and meat processing (SMP) plants, animals are slaughtered and the meat is butchered and packaged or processed in the meat processing part of the plant. Some of the changes discussed in this thesis have an impact on the energy use in other parts of the life cycle of a food product than industry. For example, one trend described is increased size of plants, which means changes in transportation of both animals for slaughter and finished products. However, only the energy use in industry is considered here.

♦ The main objective of the thesis was to study the SMP industry to find and quantify the potential for saving external energy, and thereby energy-related costs, and for reducing CO2 emissions, without changing the food process or decreasing the quality of the food product.

♦ A further objective has been to study and compare the profitability and CO2 reduction potential for energy efficiency measures that can be made in an SMP plant for different possible energy markets.

The primary aim was to use existing Swedish SMP plants as case studies to examine the energy utility systems in such plants. In the case studies, the aim has been to use process integration methods to study the potential for reducing

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external heating and cooling demands by increasing heat integration or installing heat pumps in a systematic way, i.e. using heat pinch analysis. Another aim was to examine systematically, using a shaftwork targeting method, the potential for reducing shaftwork and thereby electricity demand in refrigeration systems in existing SMP plants.

An additional the aim has been to acquire a broader view of energy utility systems in SMP plants, currently and in an economy more conscious of climate change. The intention was also to study the economic and technical potential for reducing CO2 emissions and fuel-related costs in plants of different size and level of energy savings for different possible future energy markets. There are several ways to reduce CO2 emissions in a plant e.g. increased heat recovery, heat pumping of waste heat, integration of combined heat and power (CHP), increased component energy efficiency, and switching to fuels with lower CO2 emissions. The purpose in this thesis was to consider all of these options except for increased component energy efficiency, and an integrated energy utility system together with an adjacent food plant in an ecocyclic industrial park.

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3 ENERGY UTILITY SYSTEMS IN SLAUGHTER

AND MEAT PROCESSING PLANTS

3.1 INTRODUCTION Most of the larger Swedish slaughterhouses have some kind of meat processing part including production of meat (e.g. cutting and deboning and fat removal), preservation of meat (e.g. freezing, curing and smoking) and production of meat products (e.g. sausages, formed meats and meat-based ready meals). The slaughter and meat processing parts have fairly different characteristics from both a process and an energy standpoint. In addition, the energy use in a slaughterhouse is different for different types of animals. Common steps for all kinds of slaughter are dressing, rapid chilling of the slaughtered animal, and cold storage. In the slaughterhouse a large part of the energy from fuel is used to heat water. The warm water is used primarily for cleaning purposes. Other areas that consume fair amounts of fuel are heating of buildings, melting of fat, and (when slaughtering pigs) the singeing oven. Electricity use is largest in the cooling and freezing compressors and other engines.

In the meat processing part of the plant the process differs greatly depending on which kinds of products are produced. Common important processing steps are

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those in boiling vessels, smoking cabinets, roasting ovens and cooling and freezing of meat and meat products. Heating of water, heating of buildings and cooling and freezing compressors are the largest energy users. Generally, the specific energy use is lower for slaughter than for meat processing (Nyström and Franck, 2002b).

Some kind of direct and indirect heat recovery is common at least in Swedish slaughterhouses. A normal example is recovery of heat from the refrigeration system both directly and by means of heat pumps.

3.2 STEAM The steam in a slaughter and meat processing (SMP) plant is used to increase the temperature of water and, in plants with heat recovery, to heat the water that has been preheated by heat recovery to its final temperature. The steam is also used for process needs, such as boiling equipment or frying equipment, where the heating needs to be done with steam. The steam in the SMP plants studied in this thesis is produced in boilers operating on fuel oil, electricity or LPG. The temperature of the steam in the plants is approximately 180°C.

3.3 WATER The largest heat demand in an SMP plant is the need for heated water. In many cases, five temperature levels of water are used. Hot water, approximately 85°C, is mainly used for disinfection of equipment; warm water, approximately 55°C, is primarily used for cleaning and tap water; approximately 40°C is mainly used for hygienic purposes such as for sinks where employees wash their hands. Some of the water brought into the plant is chilled by the refrigeration system. Such “iced water” has a temperature of approximately 1°C and is used as cooling medium in some of the processes. There is also cold water which is used without changing its temperature, approximately 10°C. Additionally, other water temperatures can be needed in the plant. For example, when slaughtering pigs, water at approximately 60°C is needed for scalding.

Warm water is also used for comfort heating of offices etc. during the colder part of the year.

In a studied Danish cattle slaughterhouse, 54% of the energy consumed for heating was used to produce warm water, while 17% of the total heat demand was acquired through heat recovery (European Commission, 2003b).

In the SMP plants in this thesis all fresh water that is to be used for hot and warm water is preheated by heat recovery. Since the use of heated water varies, e.g. during running of tap water and washing of equipment, it is difficult to keep

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an even temperature of the water. This means that the steam production has to match temperature and heat quantity demands when large volumes of heated water are needed but little or no recovered heat is available. As most of the heated water is needed when there is little recovery heat available, e.g. cleaning at night when there is no production, several tanks for heated water are needed at the plants.

3.4 ELECTRICITY In most SMP plants, electricity is bought from the national grid and used for equipment such as compressors in the refrigeration systems, compressed-air compressors and other engines, heat pumps, on-site transport and lighting. The largest consumers of electricity in the plant are usually the compressors in the refrigeration plants. Background information from one of the plants studied in this thesis shows that more than 35% of the electricity used in the plant is used in the refrigeration plant (excluding electricity needs for the heat pumps). Data from a Danish cattle slaughterhouse show that approximately 45% of its electricity consumption was in the refrigeration plant (European Commission, 2003b).

3.5 REFRIGERATION SYSTEM In an SMP plant there are many different cooling needs. Numerous areas, such as butchering areas, need cooling for hygienic reasons; storage areas need refrigeration; warm products from the meat processing plant and slaughtered animals need to be cooled fast; and there is a need for cold storage of frozen products. The SMP plants studied in this thesis both have two multi-stage ammonia refrigeration plants to meet the cooling demands. The outline of a two-stage refrigeration plant is shown in Figure 1. In the areas of the plant where ammonia is not permitted, brine or glycol heat exchangers are used.

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SUPERHEATERCONDENSER

REFRIGERATORS

-40°C

REFRIGERATORS

-10°C

FLASH CHAMBER

FLASH CHAMBER

Figure 1 – A two stage refrigeration plant.

It is reported that most refrigeration plants in the European Union can be improved to save up to 20% of their energy consumption by surveying the plants, good housekeeping, monitoring of the plants, and good maintenance and control (European Commission, 2003b). This can mean, for example, a defrost-on-demand system that initiates defrosting in the freezing rooms when needed, curtains at regularly used doors, and avoidance of heat sources such as personnel, lights and motors in refrigerated areas. These ways of reducing energy consumption are not included in this thesis.

3.6 ENERGY CONSERVATION SYSTEMS There are several ways of reducing the external heat and cooling demand in SMP plants. Heat integration and heat pumps to reduce fuel and cooling needs are used in the Swedish plants studied in this thesis. For more information about other ways to reduce heat and cooling demands, see for example Smith (2005).

3.6.1 Heat Integration Instead of using steam to meet all the heat demands, and instead of using cold utility to meet all the cooling demands in the plants, streams that need to be cooled can be used to warm streams that need to be heated – so-called heat integration. In the SMP plants studied in this thesis, several streams are integrated and a rather small part of the heat demand is met by steam. The

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integrations currently made in the plants are heat recovery from cooling of compressed-air compressors and refrigeration compressors, heat recovery from the refrigeration plants in condensers and superheaters, and, finally, heat recovery from the singeing flue gases. The heat recovered is used to warm water for use in the plant or as heating of buildings.

3.6.2 Heat Pumps In SMP plants the condenser heat from the refrigeration plants is considerable. Therefore, installation of heat pumps using this heat as a heat source, heating water for cleaning and comfort heating, is an interesting option for most plants. The SMP plants studied in this thesis both have two heat pumps. The heat pumps all use compressed ammonia from the refrigeration systems and compress it to higher pressures. The ammonia is condensed in superheaters and condensers, heating water. The condensed ammonia is brought back to the refrigeration systems where the pressure is lowered and the liquid is distributed to the freezing and cooling rooms in the refrigeration plant where it is evaporated and compressed; see Figure 2. The heat excess in the refrigeration systems in an SMP plant is usually large enough for installing several heat pumps to cover a part of the heat demand of the plant.

SUPERHEATER CONDENSER

REFRIGERATION AND COOLING ROOMS

COMPRESSOR

COMPRESSORS

FLASH CHAMBER

Figure 2 – An outline of one of the heat pumps in the studied SMP plants.

3.6.3 Combined Heat and Power (CHP) A combined heat and power (CHP) plant can be designed in many ways. In this thesis, two CHP alternatives for an SMP plant are investigated: a steam turbine operated together with a boiler, and a gas turbine with a heat recovery steam generator (HRSG). Another CHP option that may be interesting for the food industry, a gas engine, is not considered.

A steam turbine can be operated with various types of boilers and fuels. Heavy fuel oil, natural gas and two types of biofuels are considered in the studies. In

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the steam turbine design considered in this thesis the steam produced in the boiler either goes through the turbine or is reduced to the pressure needed for process steam. A steam turbine with steam extraction is technically possible, but is not considered in this thesis since it entails a more complicated technical solution and therefore a larger investment cost. Expanded steam from the turbine heats water in a condenser and the produced electricity is either used in the plant or sold to the electricity grid; see Figure 3.

ELECTRICITY

STACK

CONDENSATE

STEAM TO TURBINEFUEL

STEAM TO PLANT

WARM WATERTO PLANT

BOILER

Figure 3 – An outline of a steam turbine used in the thesis.

The gas turbine unit considered is a natural gas-driven gas turbine with an HRSG that produces steam by using the heat in the exhaust gases from the turbine. The HRSG can be supplementary-fired with natural gas to be able to meet all the heat demand at the plant. In this way, there is no need for an additional boiler to produce steam. The exhaust gas from the turbine is cooled down to 130°C in the HRSG; see Figure 4.

GT

NATURAL GAS

AIR

ELECTRICITY

EXHAUST

STACK

WATER STEAM

NATURAL GAS

ELECTRICITY

HRSG

Figure 4 – An outline of a gas turbine with an HRSG.

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With such relatively small heat demands as in the studied SMP plants, only rather simple steam or gas turbines with relatively low efficiencies are available. Larger turbines generally have higher isentropic efficiency. A higher admission pressure to a steam turbine also gives a larger isentropic efficiency. Increased heat integration or heat pumping in a plant decreases the heat demand in the plant and therefore also the possibility to install a CHP plant economically.

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4 PREVIOUS WORK

4.1 ENERGY USE IN THE FOOD INDUSTRY The food industry is dependent on energy in the form of electricity and heat for different types of unit operations. Different energy-demanding operations are used for different food products and include disinfection, cooling/freezing, smoking, frying, boiling and baking. For example, energy usage for heating accounts for almost 30% while cooling and freezing use approximately 15% of the total energy input in the American food industry (Okos, Rao, Drescher, Rode and Kozak, 1998). According to Drescher et al (1997) the meat industry is the third most energy-demanding sector of the food industry in the United States.

In a study of energy use in the Swedish food industry, Nyström and Franck (2002b) identified the most energy-intensive segments of the food industry. They found that the slaughter and meat processing (SMP), dairy, bakery, beverage and sugar industries are large users of energy. It was also shown that the energy use per kg slaughtered animal in the SMP industry in 2002 was only 60% of what it was in 1980. Almost 60% of the energy demand in SMP plants is met with electricity, followed by fuel oil, natural gas and LPG. The use of some

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heat integration and heat pumps is common in the SMP plants communicated within the study.

In a study by Sonesson, Mattsson, Nybrant and Ohlsson (2005) the environmental impact of three meatball meals prepared differently (home-made, semi-prepared and ready-made) was quantified with life cycle assessment (LCA) methodology. The differences between the total emissions and between the energy uses for the preparation of the meals were shown to be small. However, the industrial energy use in the life cycle of the semi-prepared and ready-made meals represented a larger part of the total energy use than was the case for the home-made meal. For the semi-prepared meatball meal, the dominating energy consumer in the life cycle of the product was agriculture, accounting for 33% of the energy use. Industry (26%), consumers’ home transports (16%) and packaging (11%) were also found to contribute significantly.

In a similar study, Sonesson and Davies (2005) compared the environmental impact of different meals consisting of chicken. For the semi-prepared meal consisting chiefly of chicken and potatoes, the energy use in industry was 26% of the life cycle energy use of the product, while agriculture accounted for only 18%. The difference in energy use between the chicken meal and the meatball meal is due to the larger energy demand for raising cattle. For both the meatball and the chicken meals, important factors for the energy consumption were raw material utilization, energy efficiency in industry and households, packaging and residue treatment.

When agriculture uses the most energy in the life cycle of a meat product, there is a lot of energy that can be saved in agriculture. This also indicates that the raw material efficiency in the rest of the food chain (industry, retail and households) is important. The raw material has caused a substantial environmental impact on its way to industry, retail and household. Thus, every piece of lost food has caused an environmental impact that must be carried by the remaining food, making each kg of food consumed environmentally “more expensive”. In her studies, Berlin (2002, 2005) conclude that identifying and minimizing the losses of raw material in the process decrease the economic and environmental cost without affecting the final product. Heller and Keoleian (2000) estimated that 26% of edible food in the US is wasted along the life cycle of the food products.

4.2 ENERGY EFFICIENCY STUDIES IN THE FOOD INDUSTRY

In the 1970s when the cost of oil increased, energy-saving techniques in the food industry became an interesting topic. The discussion concentrated on new processing techniques but also energy accounting methods; for example, see

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Singh (1978). After the introduction of heat pinch analysis, several scientific papers describing case studies using this method in the food industry have been published. Most of them, however, describe industries such as sugar refineries, dairies and breweries that are similar to the continuous chemical process industry where the pinch technology was developed. Relatively few studies have been published in the part of the food industry where the production is mainly batchwise and related to the manufacturing industry, rather than the processing industry represented by the SMP industry in this thesis. A few examples of process integration studies performed in continuous food process plants as well as in food processing plants with production similar to that in the manufacturing industry are presented below. To read more about heat pinch analysis, see Chapter 5.

4.2.1 Continuous Food Processes Using heat pinch analysis in a Brazilian soybean extraction plant, Ravgnani, Cardoso and da Silva found a large potential to save energy (2001).

In a heat pinch analysis study of an American wet corn milling plant producing high-fructose corn syrup, different options for energy cost reduction were evaluated. The payback periods for heat recovery, process modification, cogeneration and heat pumping in the plant were compared and it was found that extended heat recovery was the most profitable measure and that it had a payback period of less than one year. It was also found that by studying the whole plant, an existing heat pump could have been installed in a more profitable way (McMullan, 1991).

The use of heat pinch analysis throughout the whole design phase when building a new edible-oil processing factory in the UK reduced the energy use by 35% and a payback period of less than three years was obtained (Van den Bergh Oils Ltd, 1997). Spriggs, Shah and Eastwood (1987) showed how heat pinch analysis can find a potential to reduce the process heating bill by 24% at a brewery through better integration of process heat sources and heat sinks. The analysis for the process shows the possibility of integrating a CHP plant based on a natural gas engine with an estimated payback period of three years.

A heat pinch analysis of parts of a US cheese plant is described in a paper by Zehr, Mitchell, Reinemann et al (1997). Through composite curves of an evaporation system, a large reduction potential for cooling (97% reduction potential) and heating demand (48% reduction potential) is found. Additionally, a heat exchange system in a drying part of the plant is shown to produce significant savings in energy costs. In a study in a Lithuanian dairy, some savings with short payback periods (1.5-3 years) were also shown (Nagevicius and Mikaliunas, 1998). A heat pinch analysis in a Swedish dairy showed several opportunities for reducing the external heat demand in the

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plant, such as extended internal heat recovery and installation of a heat pump. The study resulted in a biogas plant using waste products from the dairy and reducing the fuel oil demand by 2000 m³ per year as well as the load on the municipal sewage treatment plant (Nyström and Franck, 2002a).

In the sugar industry, steam and power costs are major cost elements and CHP plants are common. Several heat pinch analysis studies have found energy-saving potential in the sugar industry. Energy-saving options were found, in addition to an enhanced CHP scheme, in a sugar refinery in the UK (Sinclair, 1992) as well as a 9% energy reduction potential in an Indian sugar factory (Ram and Banerjee, 2003). In a report edited by Wamsler (2001), a heat pinch analysis study in a Swedish sugar mill is shown to find energy efficiency measures saving approximately 10% of the current energy demand at the plant, all with an estimated payback period of less than one year. A larger energy-saving potential is also found if some of the process temperatures are changed to some extent.

4.2.2 Manufacturing Food Industry An energy investigation at a relatively large ready-made meal producer in Sweden has shown ways to conserve energy such as recovering heat from compressed-air compressors (Gierow, 2004). Process-integration thinking in a chocolate factory in Lithuania (Akelaitis, 1998) lead to considerable economic savings. Most of these savings, however, come from improvement of the use of utilities such as repair of cooling towers and insulation of pipes.

A few examples of energy savings in the meat industry can also be presented. Herbert, Anderson and Buhot et al (1984) describe how electricity can be saved in an Australian slaughterhouse by operating the refrigeration plant intermittently instead of continuously. During weekends this can save around half of the electricity use in the plant. Similarly, Chmiel and Clemens (1997) show in their study of the German meat industry that money can be saved by trying to operate during off-hours when energy costs are low. It is shown that it is profitable to invest in insulation of freezing and refrigeration rooms and by installing double doors preventing warm air from entering the refrigerated rooms.

Bowater (1990) analyzes whether there is an economic advantage to use the waste heat from a refrigeration plant in a meat processing plant. Three plants of typical international production sizes are considered and it is found that in the largest plant the payback period of a heat pump is less than two years.

In 1995, Chadderton (1995) showed that heat pinch analysis can be a useful design tool for meat plants. Significant savings in utilities were found in hypothetical beef and sheep meat plants in New Zealand. The possibility of

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introducing heat pumps is also investigated in the sheep plant, finding that there is a potential of reducing the need for utilities.

Dalsgård proposes a simplified heat pinch analysis for medium-sized plants (Dalsgård, Petersen and Qvale, 2002) and presents a case study using this method from a Danish chicken processing plant (Dalsgård, Munkøe and Qvale, 2002). Dalsgård suggests that the process should be divided into sub-problems that are optimized separately. Streams that are considered unimportant are discarded and the objective of the studies is not to reach the best economic solution, but to design a simple network rather quickly without losing too much opportunity for energy savings. With this method important matches may be lost and sub-optimization can be made since integration is only made in subsystems. It also requires the person carrying out the study to have experience with similar studies. A potential for a heat recovery system in the chicken processing plant producing hot water is found with an estimated payback period of 2.2 years.

4.3 HEAT PUMPS IN FOOD PROCESSING PLANTS The use of heat pumps in the food processing industry is quite common. Below, a few examples of papers describing this are presented.

Already in 1985 two heat pumps installed in an edible-oils plant and in a dairy production plant, both in Canada, were described (Wright and Steward, 1985). The payback periods for these installations were found to be 2.3 and 4.8 years respectively, depending largely on the operating time of the installation. Rowles (1986) described the installation of a heat pump in a Canadian poultry processing plant with a payback of 1.7 years. The payback periods calculated in these studies cannot be directly correlated with current payback periods since the electricity prices have been considerably increased since then.

Korfitsen and Kristensen (1998) show the potential for installing ammonia heat pumps in two Danish plants; a poultry slaughterhouse and in an ice cream factory. Both cases show an acceptable payback period (1.25 and 3.36 years respectively) for heat pumps using condenser heat from the refrigeration systems as a heat source. Similarly, an energy investigation at a Swedish ready-made meal producer has shown that it is profitable to install a heat pump also using heat excess from the refrigeration plants (Gierow, 2004).

4.4 COMBINED HEAT AND POWER PLANTS IN THE FOOD INDUSTRY

In the Swedish food industry, CHP plants exist almost solely in the sugar industry. In the rest of Europe, CHP plants are commonly applied in the sugar

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industry (European Commission, 2003a) and, according to Colonna and Gabrielli (2003), CHP plants are “rather common” in the rest of the European food industry. This difference compared to Sweden is probably due to generally larger plant sizes and historically higher electricity prices in the rest of Europe. In addition, some installations of trigeneration plants that use steam for cooling as well as for power production have been introduced in plants in Europe (Colonna and Gabrielli, 2003). In the US, gas turbine plants in the food industry are reported by Axford and Bailey (1992) for large cold warehouses, a fruit processing plant and a large cheese plant.

Calderan, Spiga and Vestrucci (1992) describe a model of a CHP plant including a gas turbine with a waste heat recovery unit to be installed in an Italian poultry plant. The electricity demand of the CHP plant is the limiting factor for the size of the turbine and the payback period is calculated to be about 5 years.

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5 METHODOLOGY – TOOLS The focus of process integration methods has traditionally been on efficient energy use, and this is also the case in the present thesis. To read more about the basic aspects of process integration methods as well as some of the recent and advanced elements of these methods, see Gundersen (2002).

5.1 HEAT PINCH ANALYSIS Heat pinch analysis is the single most important process integration concept and the one that originally gave birth to the field. The concept was developed into an industrial technology by Bodo Linnhoff and his group at UMIST in Manchester in the 1980s. The methodology is based on thermodynamic principles. Using heat pinch analysis, it is possible to identify appropriate changes in the core process conditions that can have an impact on energy savings. Some questions that can be answered by pinch analysis are: What are the minimal external heating- and cooling demands, the so-called energy targets, for a particular process? What is the maximal heat recovery through internal heat exchangers? How should a heat exchanger network be constructed so that internal heat-exchanging is optimized?

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Before performing a heat pinch analysis it is important to define the studied system. The aim of study should be well defined so that a method which is appropriate for that aim can be chosen and an appropriate level of detail is chosen for the study. It is also important to find the limitations that exist in the energy flows in the system. For example, any heat pinch analysis should separate the temperature demands that are crucial for the process, e.g. the temperature of the water being used for hygienic reasons, from those that can be allowed to vary.

The heat pinch analysis starts with the heat and material balance for the process. Streams that need to be heated (cold streams) or cooled (hot streams) are identified and, with these in mind, graphical representations of the energy flows of a process can be produced. Some examples of these graphs are Composite Curves (CC) and the Grand Composite Curve (GCC). When constructing a GCC, the hot and cold streams from the process are divided into temperature intervals. In each interval, the loads from the streams in the interval are added together. The load for hot streams is added as a negative number. In this way, temperature intervals with negative or positive loads are created. These intervals are plotted consecutively with temperature on the y-axis and load on the x-axis. The pinch temperature is seen where the curve touches the y-axis. In Figure 5 a simple GCC is shown. The GCC shows the size of the demands at the different temperatures of the process, the minimal external heating and cooling demands, the amount of heat that can be exchanged internally, and the pinch temperature; see Figure 5. In this way targets for energy saving can be set prior to the design of the heat exchanger network for the process.

0

50

100

150

200

0 20 40 60 80 100Load (kW)

t (°C)

Minimal external cooling demand

Minimal external heating demand

Pinchtemperature

Heat available

Heat needed

Figure 5 – A GCC for a process.

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The pinch divides the process into two separate parts, one above and one below the pinch temperature. In the part above the pinch temperature, there is a net heat deficit and external heating is needed. In the part below the pinch temperature there is a net surplus of heat that needs to be removed by cooling the streams. The existing steam consumption is compared with the minimal steam consumption for that process; the difference between them is the potential saving. This potential saving exists because streams in the plant are heated or cooled against the three “pinch rules”: no external heating below the pinch temperature where there is a net heat surplus, no external cooling above the pinch temperature where there is a net heat deficit, and no heating across the pinch temperature.

Since energy savings in one part of a plant are counterproductive if they lead to an equal or larger energy increase in another part of the plant, it is important to include the whole site in a process integration study.

When performing process integration studies, i.e. using heat pinch analysis, in a food processing plant there are several difficulties that need to be overcome. In the food industry, energy is only a small part of the total cost of production and is not considered a core business. As a consequence, many food processing plants do not submeter their energy bills, and therefore limited data on energy are available. Additionally, the demands in the plants vary, not only with the seasons and during the day, but also with the production mix, which creates difficulties in data gathering.

Batchwise production is another characteristic feature of food production which complicates energy recovery. It can be difficult to use all available heat sources for heat recovery as they are usually not continuous and are only available during production times. Contrary to the heat sources, the heat sinks at the site usually occur when there is little or no production, e.g. warm water for cleaning.

5.2 BATCH PINCH ANALYSIS Heat pinch analysis was developed as a method for continuous processes. The area of heat recovery in batch production is more complicated since the process parameters for batch processes are time-dependent. In other words, the transfer of heat from a hot batch stream to a cold one is constrained not only by temperature (the hot stream must have a higher temperature than the cold stream it is supposed to heat) but also by time (the hot and cold streams must coincide). This makes batch processes more difficult to heat-integrate than continuous processes. There are a number of different methods for identifying the energy target for a batch process. There are both methods that use temperature as the major constraint, e.g. the Time Average Model, the Time Slice Model and Cascade Analysis, and methods that use time as the major

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constraint, e.g. Time Pinch Analysis. The targets obtained from these methods will all be different, and the described methods can be used for different purposes.

The Time Average Model (TAM) described by Linnhoff, Ashton and Obeng (1987) is analogous to pinch analysis for continuous processes, since heating and cooling duties are “time-averaged” over a convenient period. This means that the analysis is made with an average heat duty for a time period resulting in the minimum energy consumption for a batch process assuming cyclic batches and unlimited ideal heat storage for that period. The target obtained can be used as an absolute lowest level and can point to the potential for improving energy efficiency. The target cannot be used to distinguish between direct measures, through heat exchangers and indirect measures through heat storage and heat transfer, which is important information when estimating total cost.

In the Time Slice Model (TSM), described by Ashton (1993), the batch cycle is divided into time intervals where each interval is limited by the time at which a batch operation starts or finishes. The heat recovery is considered separately in each time interval. As the number of intervals increases, the external energy target is less equal to the target obtained with TAM, targeting the amount of heat recovery that is feasible without heat storage.

A more systematic way to consider the time aspect is to use a two-dimensional heat Cascade Analysis (CA) producing a three-dimensional cascade plot (Kemp and Deakin, 1989). In the cascade analysis, heat can be transferred to a lower temperature by direct heat exchange in the same time interval, or to a later time interval via indirect heat exchange using storage. Different strategies can be used in the CA and, for larger problems, graphical diagrams have been developed similar to the GCC.

Another graphical method that has been developed for use with batch processes is the Time Pinch Analysis (Wang and Smith, 1995). Assuming that the scheduling of the operations of the process is defined, this method uses the time as a primary constraint for identifying the time pinch of the processes. Composite curves and a grand composite curve are drawn showing when indirect heat recovery is needed and indicating the total heat recovery for the process. This is done for all the temperature intervals in the process, thus using temperature as a secondary constraint.

In Papers I and II in this thesis, the Time Average Model is used. The reasons for this are both the lack of time data in the studies and the irregularity of some of the streams that are studied, i.e. the use of tap water. Therefore, it is difficult to model with any of the methods described above. As already mentioned, the TAM gives energy targets that might not be achievable, but can be used to study

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the gross potential for saving energy in the plant and to find the absolute minimum external heat demand for a batch process.

The TAM analysis will overestimate the potential for saving external heat and cooling demand, since the heat sources and sinks are seemingly present at the same time. If this overestimation does not indicate any potential for energy saving, there is no reason to spend time finding more data or making a more thorough analysis of the plant. If there is a large enough potential found in the TAM study, there is an incentive to make a more detailed study with more extensive data, including detailed information about when different heat demands and sources occur.

There are also methods for process integration using energy storage in batchwise production. For a review of some of these methods and techniques, see Mikkelsen (1998).

5.3 PROCESS INTEGRATION OF HEAT PUMPS AND CHP PLANTS

The GCC constructed in a heat pinch analysis can be used to study how a heat pump or a combined heat and power plant should be integrated with the rest of the process to reduce the total external energy demand. The need for external heat and its temperature level are shown above the pinch temperature in the GCC. Correspondingly the need for cooling and its temperature level are shown below the pinch. Therefore, an analysis of how to satisfy the heating and cooling demands can be carried out using these curves.

A heat pump raises heat from a low temperature level (heat source) to a higher temperature level (heat sink) by means of primary energy. A heat pump should be integrated with the process so that the net surplus of heat below the pinch temperature is used in the evaporator in the heat pump, and so that the heat deficit above the pinch temperature is covered by the excess heat in the condenser. In other words the heat pump is integrated across the pinch temperature; see Figure 6.

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Load (kW)

t (°C)

Condenser

Evaporator

Figure 6 – Integration of a heat pump with a process.

In a plant with a combined heat and power (CHP) plant with a steam turbine like the one studied in this thesis, the steam that has been expanded in the turbine is used to heat water in a condenser. The water can be used directly in the plant or as a heating medium in heat exchangers in the plant. Integration of a steam turbine in a process can be visualized as in Figure 7.

Load (kW)

t (°C)

Steam condenser

Figure 7 – Integration of a simple steam turbine with a process.

In a plant with a gas turbine, the exhaust gases from the turbine are used for heating in the process. Usually, the heat is transferred from the CHP plant to the process indirectly by making steam in an HRSG.

In Figure 8 it is shown how the exhaust gases from a gas turbine are cooled producing steam in an HRSG. The slope of the exhaust gas line is inversely

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proportional to exhaust mass flow and specific heat capacity. The size of a certain type of gas turbine is proportional to its exhaust mass flow.

Load (kW)

t (°C)

Steam level

Exhaust gases

Figure 8 – Integration of a gas turbine with a process.

For more information about how to integrate heat pumps and CHP plants in a process, see Wallin, Strömberg, Franck et al (1992).

5.4 SHAFTWORK TARGETING The largest energy demand in an SMP plant is usually electricity due to the refrigeration needs in the plant; see section 4.1. Using traditional heat pinch analysis, electricity demand is not included in the scope of the analysis. Linnhoff and Dhole (1992) described a way to visualize the shaftwork of a refrigeration plant with curves analogous to the heat pinch analysis curves. By doing this, targets for the minimal amount of shaftwork needed for a certain refrigeration plant can be identified from basic process data. An Exergy Grand Composite Curve (EGCC) is constructed, replacing the temperature on the y-axis with the Carnot factor, ηC=1-Ta/T, where Ta is the ambient temperature.

When using the targeting procedure, an EGCC is constructed for the freezers and refrigeration rooms in the studied plant. The required temperatures in these rooms are reduced by half of the smallest temperature difference (∆Tmin) that can be accepted between the refrigeration medium and the required temperature of the air in the freezers and refrigeration rooms. In rooms where the refrigeration medium used is not permitted, additional temperature difference is added to allow for intermediate heat exchange such as a brine heat exchanger. The Carnot factors are calculated for the air temperatures and plotted against the cooling loads. A utility curve (UC) describing the Carnot factors, increased by half of ∆Tmin, versus heat load for the temperature levels

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that are used in the refrigeration system is also constructed. For an example of a UC and an EGCC, see Figure 9. The area between the UC and the EGCC represents an exergy loss and it is directly proportional to the excess shaftwork required in the refrigeration plant due to excessively large temperature differences in heat exchangers in the freezers and refrigeration rooms. This means that a decrease in the area between the curves generates a decrease in the shaftwork requirement for the refrigeration plant. In other words, the least possible shaftwork for the refrigeration can be achieved when the EGCC and the UC are perfectly aligned. This, however, usually leads to a refrigeration plant with too many refrigeration levels and therefore a system which is too complex in reality.

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

0 50 100Load [kW]

ηC

EGCC

UC

Figure 9 – An example of a Utility Curve and an Exergy Grand Composite Curve.

Assuming no changes in the refrigeration demands in the food processing plant, the area between the curves can be changed by modifying the cooling load at existing temperature levels in the refrigeration system. This represents a case where the cooling demands are achieved with a decreased temperature difference. This, however, results in a decrease in driving force in the coolers, and therefore larger heat exchanger areas are needed.

Another way of decreasing the area between the EGCC of the process and the UC is to increase the temperature of one or more of the temperature levels in the refrigeration plant to fit the process needs more closely. In an existing refrigeration system this leads to an increased capital cost through increased heat exchanger areas and costs for changes in compressors etc. to enable the change in temperature.

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The shaftwork targeting method helps to identify changes in the refrigeration system that are interesting to study more closely without having to model every possible design. It also gives an overview of the whole refrigeration system so that changes in shaftwork for the whole system can be seen when temperatures or cooling loads are changed, for example in refrigeration rooms. Thus, the time needed to find solutions to decrease the shaftwork usage in a refrigeration plant is significantly reduced, and the possibility to find a design of the whole refrigeration system with low shaftwork is increased.

5.5 SIMULATION AND THE USE OF HYSYS Once the duties of the heat exchangers and the temperatures of the refrigerant are specified by the shaftwork targeting method described above, the compressors, condensers and flash drums in the refrigeration plant can be designed. Process simulators can be used to simulate the refrigeration systems to determine required refrigerant flow rates and the resulting compressors’ capacities and shaftwork needs. The simulator used in this thesis is HYSYS version 3.1, a graphic-oriented simulator developed by Hyprotech Limited. In a HYSYS model, blocks representing heat exchangers, compressors etc. can be used to simulate refrigeration plants. HYSYS has a feature which calculates the flow rate of refrigerant in an exchanger if the duty is specified together with the inlet and outlet temperature. This is convenient when simulating a refrigeration system where the duty is the refrigeration needed, the conditions at the outlet of the exchanger can be specified as saturated vapor of the refrigerant, and the temperature of the refrigerant is the cooling temperature defined for the refrigeration system. This means that only real equipment is included in the model and the only data that need to be entered are the specifications of the refrigerant exchangers, including the refrigeration demands and the efficiencies for the equipment.

One part of a refrigeration plant in an SMP simulated in HYSYS can be seen in Figure 10.

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Figure 10 – Part of a refrigeration plant simulated in HYSYS.

5.6 ENERGY SCENARIOS SMP plants consume both heat and electricity in their different processes. Extended heat integration and other energy-saving measures would reduce the fuel and electricity needs in this type of industry. However, as the plants are connected to a changing energy market, the long-term outcome of energy-saving projects when it comes to economy and CO2 emissions is hard to forecast. Analysis of energy projects must therefore not be limited to technical studies in the plant but also include likely future development of the energy market.

Assessing the development of the energy market is usually difficult given the fluctuations of fuel and electricity prices. Further uncertainty arises when cost resulting from energy policy instruments aiming at reducing greenhouse gas emissions must be taken into account.

In order to gain a better understanding of the long-term economic and environmental consequences and to enable analysis and evaluation of different energy efficiency projects, Ådahl and Harvey (2004) developed four possible energy market parameter sets. These “blocks” are based on the Nordic energy market and reflect different climate policies. The assumed key parameters for the blocks are: - Fuel prices and availability (including both fossil and biomass fuels) - Base electric power prices

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- Marginal power production technology; generation costs and associated CO2 emissions - Economic value of CO2 emissions reduction These parameters are not independent of each other, i.e. many parameters are closely linked. Ådahl and Harvey identify such links and consistent sets of parameters that can be used for conducting “packaged” sensitivity analyses for energy-related investment projects. The evolution of the parameters is strongly influenced by changes in energy demand, political target levels for reduction of CO2 emissions, availability of new technology in the energy sector, and availability of renewable energy resources and technology.

The parameter sets build upon different assumptions regarding evolution over time of energy demand in the stationary sector, target levels for the reduction of CO2 emissions, and availability of new technology in the energy sector. The assumptions are presented briefly below. No attempt is made to speculate as to when in the future the different sets of parameters could be valid, even though an indicative time period is presented. The intention is that the blocks can be used to assess the economic and climate-change impact of industrial energy system investment projects carried out in different energy markets. Different combinations of blocks and their periods of validity can be said to represent scenarios of energy market development paths or energy market scenarios. However, such scenarios are not essential in this thesis, since the evaluation of the energy efficiency projects is a ranking between alternatives under different possible future conditions.

The models have been developed primarily for evaluating energy utility system investment options in the Swedish pulp and paper industry. The results, however, can be used in other industries if the blocks are adapted accordingly. If energy policy instruments are harmonized within the EU in the future, it is reasonable to assume that the proposed values can also be used for evaluating investment options in other EU countries as well. It should also be noted that the proposed prices do not include environmental policy instruments, such as sulphur taxes, that are not related to CO2 emissions.

The four blocks of parameters identified by Ådahl and Harvey are presented below and the values of their parameters are shown in Table 1. Block I corresponds to the Swedish energy market in the near future. This block uses energy prices from 2003 to a large extent and includes current Swedish taxation rules for industry. A low cost for CO2 emissions associated with electric power generation is also included, reflecting the EU-wide CO2 emission rights trading system that started on January 1st, 2005. Block II corresponds to a “business as usual” evolution of society, i.e. focus on high economic growth with corresponding high energy usage. Costs associated with CO2 emissions are assumed to be low and harmonized between sectors.

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The indicative time period for this set of parameters is 2010-2030. Given current trends in Swedish energy and environmental policy, Block II is improbable, but when compared to Block I it can show the effect of switching from current Swedish taxation rules for industry to minimum levels in the EU-wide CO2 emission rights trading system. Block III corresponds to a “moderate change” evolution of society, i.e. a balance between economic growth, reduced energy usage, and reduction of CO2 emissions. Block III conditions may occur in the medium-term future (i.e. 2010-2030) if society has ambitious long-term targets for CO2 emission reduction, or in the more distant future (2030-2050) if society has reduction targets that are less far-reaching. Block IV corresponds to a “sustainable” evolution of society, i.e. CO2 emissions are reduced to levels estimated to be sustainable. Conditions for this case are likely to occur in the more distant future provided that ambitious emissions reduction targets are set up and fulfilled by society.

By using the four blocks, energy efficiency projects studied can be evaluated for different sets of energy prices and emission levels, and it can be seen which energy efficiency projects are favored in different blocks.

5.6.1 Fuel The fuels considered in this thesis are heavy fuel oil, natural gas, and biofuels in the form of wood chips and pellets.

The oil prices in the blocks reflect price levels as available in oil price statistics for 2003 (Block I). This value was assumed to be valid also for medium-term cases (Blocks II and III) whereas an increase was assumed for the long-term case (Block IV). It should, however, be noted that current oil prices are substantially higher than the values proposed by Ådahl and Harvey.

The natural gas prices are assumed to follow the oil prices and are assumed to be 80% of oil prices. The price does not include transmission costs which may be substantial for countries such as Sweden. It is also assumed that natural gas is an available fuel for all studied plants.

The price for biofuel is the most difficult to forecast since the international biofuel market is currently rather undeveloped. Biofuel is also a regional fuel for which the market price is very dependent on local supply and demand. As a renewable, CO2-neutral fuel it is clearly influenced by energy policy instruments. Biofuel prices and associated CO2 emission consequences are assumed to be defined by the marginal technology, i.e. the last application demanding biofuels. In this way, biofuel pricing is assumed to be related to the electricity price, rather than to the fossil fuel price as has been assumed previously. The maximum price an electricity producer is willing to pay for

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biofuel is given by the short-run marginal benefits from electricity income. For Block I, current biofuel prices in Sweden were assumed. For the other blocks it was assumed that biofuel will be primarily used in the electrical power generation sector in the future, which is a possible scenario since co-firing is already common in power plants. Thus, biofuel prices are linked to electricity prices in the future blocks. There are evidential data in several energy market studies which show that the electricity/biofuel price ratio can be assumed approximately constant.

Fossil fuels emit CO2 when refined, transported and combusted. There are no net CO2 emissions from combustion of biofuel since the amount of CO2 emitted when burning biofuel is the same as the CO2 absorbed by the biofuel when growing. However, there are CO2 emissions during production and distribution of the biofuel; see Uppenberg, Almemark, Brandel et al (2001). The CO2 emission amounts used in the thesis are presented in Table 1.

5.6.2 Electricity The electricity prices in the blocks are based on marginal production costs. The build margin approach is used and makes a best guess as to what type of electricity generation facility would have been built (or built sooner) if the energy efficiency project had not been implemented. The build margin cases considered are: advanced coal power plants built with current best available technology (BAT) (Block II), natural gas combined cycle built with current BAT (Block III), and coal power plants with CO2 separation and storage (Block IV). The current operating marginal generation technology in the Nordic area has been identified as coal-fired power plant technology (Block I).

The CO2 emissions associated with electricity generation are also based on the marginal power production technology. The difference in CO2 emissions in the blocks is due to the fuel, the efficiency of the marginal technology, and whether the emitted CO2 is separated and stored or not.

The base electricity price in Block I is based on marginal production costs in existing coal-fired power plants. Grid transmission cost for the purchased power is not included. For the long-term blocks, electricity prices are assumed to be equal to generation costs estimated on the basis of available estimations of investment costs, operation and maintenance costs, efficiencies and assumed fuel costs for the marginal generation technology.

In certain blocks (Blocks I and III) a premium value for electric power generation from renewable energy sources is assumed, based on the Swedish Renewable Electricity Certification system. This provides an extra income for electricity production based on biofuel, and an extra charge for purchased electricity since the electricity certificates must be paid for by all electricity

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consumers. Therefore, when electricity production is based on biofuel it is advantageous to sell the electricity to the grid. In Blocks II and IV it is more profitable to use the electricity in the plant than to sell it to the grid since a large part of the electricity cost, such as grid transmission costs, is thereby avoided. The value for the certificates in Block I corresponds to the average value since the system was initiated. The value in Block III is lower, reflecting the higher assumed value for CO2-permits in this block.

When studying the SMP plants in this thesis, the electricity price is a sum of the base electricity costs in the blocks and several other costs. Included in the price are grid transmission costs and part of the price of renewable electricity certificates. The grid transmission costs are assumed constant. The total electricity price for Block I has been checked against the price of electricity in Swedish SMP plants to make sure that it is reasonable for the industry.

For more information about the conditions and prices used to calculate the energy prices and emissions in the blocks, see Ådahl and Harvey (2004), Harvey, Ådahl and Berntsson (2004), Harvey and Ådahl (2004) and Paper III.

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Table 1 – Prices and CO2 emission for fuels and electricity in the blocks (Ådahl and Harvey, 2004; Uppenberg et al, 2001; Marbe, Harvey and Berntsson, 2003). Original prices and costs have been converted: 9.13 SEK = €1 (European Central Bank, 2005).

I II III IVCO2

Indicative CO2 emission target (% rel. 1990) -5 -5 -25 -50CO2 value in heating sector (€/t) 20.3 5.5 27.4 54.8CO2 value in electricity sector (€/t) 5.5 5.5 27.4 54.8

Fossil fuelsPrice heavy fuel oil (€/MWhfuel) 16.4 16.4 16.4 18.6Price heavy fuel oil, incl. CO2 cost (€/MWhfuel) 22.0 18.0 24.0 33.6Total CO2 emissions for heavy fuel oil (kg CO2/MWhfuel) 297 297 297 297Price natural gas (€/MWhfuel) 13.1 13.1 13.1 14.9Price natural gas incl. CO2 cost (€/MWhfuel) 17.3 14.2 18.7 26.0Total CO2 emissions for natural gas (kg CO2/MWhfuel) 215 215 215 215

BiofuelsPrice wood-fuels (€/MWhfuel) 13.7 14.1 17.6 24.3Total CO2 emissions for wood-fuels (kg CO2/MWhfuel) 10.8 10.8 10.8 10.8Price refined biofuels, e.g. pellets (€/MWhfuel) 21.4 21.8 25.3 32.0Total CO2 emissions for pellets (kg CO2/MWhfuel) 4.3 4.3 4.3 4.3

ElectricityEl marginal prod cost incl. CO2 (€/MWhel) 31.7 33.0 42.9 62.3Grid transmission costs (€/MWhel) 5.5 5.5 5.5 5.5Price renewable electricity certificate (€/MWhel) 21.9 0.0 11.0 0.0Required market share for renewable electricity [%] 7.4 0.0 16.9 0.0Total electricity cost incl. CO2 (€/MWhel) 38.8 38.4 50.3 67.8Net income from sales of renewable electricity to grid (€/MWhel) 53.6 33.0 53.9 62.3

Marginal (baseline) electricity CO2 emissions incl. 7% grid losses (kg/MWhel) 834 778 374 97

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6 RESULTS

6.1 PROCESS INTEGRATION CASE STUDIES IN SMP PLANTS

6.1.1 Introduction In Papers I and II, case studies have been made in two relatively modern Swedish slaughter and meat processing (SMP) plants with relatively extensive heat integration. There are two main purposes of the studies: to identify the potential of saving external heat demand at the plants through heat pinch analysis (Papers I and II) and to find the potential to reduce the electricity use in the refrigeration plants (Paper II). There is limited energy-data availability in both plants and for the heat pinch analysis the TAM model is used. Therefore the studies can only point to the potentials to save external heat demand in the plants, and further studies are needed to confirm the obtained results. In Paper I the time average over a production period of one day is used, while in Paper II a whole production year is evaluated. For more details on the studies, see Papers I and II. For some economic calculations related to these studies, see Paper III.

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It is important in any energy analysis to separate temperature demands that are crucial for the process, e.g. the temperature of water being used for hygiene reasons, from those that can be allowed to vary. The main heat demands found in the plants were those of hot water, scalding water, tap water, heating of buildings and processing steam. Main cooling demands included the heat excesses found in the refrigeration systems. Heat excesses that can be used in the plant include heat from heat pumps and singeing flue gases.

6.1.2 Reduction in External Heat Demand in SMP Plants – Papers I and II

In Paper I, an SMP plant producing meat from the slaughterhouse and cured meats, sausages and tinned products from the meat processing plant is studied. There are two heat pumps used for recovering excess heat from the refrigeration systems and in the plant and approximately 60% of the external heat demand, excluding process steam, is obtained through heat recovery by the heat pump and internal heat-exchanging.

In Paper I, a production period where the production mix and volume are fairly representative is chosen as the basis of the pinch analysis. Due to low data availability, the period only includes the part of the day that involves normal production which means that the study does not show warm water demands for the non-productive hours of the day.

The GCC of the plant in Paper I is shown in Figure 11. The heat excess from the refrigeration systems is not included in the energy balance. Instead the refrigeration demands are included at the actual temperature levels in the GCC. Such an analysis can show whether the heat excess from the condensers in the refrigeration systems may be used in a heat pump.

The temperature level of the excess heat from the condensers in one of the two refrigeration systems in the plant is shown in Figure 11. From this figure it can be seen that only 450 kW of the available 2,100 kW from the heat excess of the refrigeration system can be utilized if no heat pumps are available. A large amount of the heat excess can be used, however, if the temperature in the condensers is elevated 28°C by a heat pump. If such a heat pump is installed it is possible to use all of the available excess heat from this refrigeration system and to cover more than 60% of the heat demands in the plant excluding process steam.

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Figure 11 – The GCC of the SMP plant studied in Paper I. The refrigeration needs are included at their different temperature levels. The temperature levels of the condensers in one of the refrigeration plants are included as horizontal dashed lines.

Generally it can be seen in the study that, to recover larger amounts of excess heat, it has to be available at relatively high temperatures. Since the cleaning periods are not included in the analysis, a smaller heat demand than is really the case is shown in the GCC. In order to obtain an external heat demand similar to an optimum case, heat storage is needed.

Various measures already taken in the SMP plant in Paper I have saved rather large amounts of energy. In the heat pinch analysis, it was shown that one heat pump, elevating the excess heat from one of the refrigeration plants to the right condenser temperature, can decrease the external heat demand to the same level as do the two heat pumps that are already installed. This illustrates the benefit of using heat pinch analysis for studying a process before investing in energy efficiency measures since one heat pump has a lower investment cost than two. Additionally, as can be seen in Figure 12, the existing heat pump has a higher temperature lift than the suggested pumps leading to an approximately 25% lower electricity demand for the suggested heat pump in the plant.

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Figure 12 – The GCC of the SMP plant studied in Paper I. The gray curve describes the heat excess from the existing heat pumps

In Paper II, an SMP plant with products such as meat from pork, beef and lamb, ready-made meals and semi-manufactured products is studied. As in the plant studied in Paper I, this plant has two installed heat pumps using excess heat from the refrigeration system.

Average data from the control system of the plant and manual measurements, as well as some calculated data, are used in the analysis of the plant. All the data included in the analysis are checked in a model of the utility system in the plant, in such a way that the data are realistic for an average 24-hour period with production in the plant.

In Paper II, all streams above ambient temperatures are included in the analysis of the possibilities for extended internal heat-exchanging. A GCC is constructed for the SMP plant, excluding excess heat from the heat pumps but including excess heat from the condensers in the refrigeration plants. The GCC is constructed so that the external heat and cooling demands in the GCC are the same as in the real plant (see Figure 13); this is achieved when ∆Tmin is approximately 7°C. The large excess heat that can be seen below the pinch is the heat from the condensers in the refrigeration plants. The rather low ∆Tmin indicates that there is not a very large potential for saving external heat and cooling demands by increasing internal heat recovery in the plant. If countercurrent liquid/liquid heat exchangers are used, a good industrial practice is to set the temperature difference in the heat exchangers no lower than 5°C. There is a potential for saving approximately 70 kW in the SMP plant if the

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internal heat-exchanging is increased so that ∆Tmin is reduced from 7°C to 5°C. This potential would be rather expensive to achieve in the plant, since several more heat exchanger units are needed to improve the heat recovery. This probably also holds true if more exact data are used in the analysis, and there is therefore no reason to make a more detailed study of the plant.

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Figure 13 – The GCC for the SMP studied in Paper II. The grey curve shows the temperature versus heat load for the heat pumps that are already installed in the plant. The dashed line shows the opportunity to install an extra heat pump using the excess heat from the condensers in the refrigeration plant.

After constructing the GCC, it is possible to study the potential for an additional heat pump in the plant. There is a rather large part of the heat demand that can be covered by installing a new heat pump, approximately 1 MW. The suggested condenser temperature of this new heat pump is 62°C.

In the SMP plant studied in Paper II, almost 30% of the heat demand is covered by the internal heat-exchanging already installed. Including the installed heat pumps, less than 65% of the heat demand excluding process steam is currently covered by steam from the boilers. If another heat pump is installed in the plant, as suggested above, almost all of the heat demand, excluding process steam, can be supplied by internal heat-exchanging and heat pumps.

The studies show that the excess heat from the refrigeration plant is large enough to be used in the suggested heat pump. There is also a large enough potential for using the energy from a new heat pump, and thereby reducing external heating and cooling demands, to motivate further studies. The exact size of the heat pump needs to be evaluated in greater detail in order to deliver the load needed during peak hours if there is no possibility of thermal storage. More exact data are needed to make a good economic evaluation of the results in these studies, but the new suggested heat pump can be expected to be no less profitable than the two that are already installed in the plant.

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In modern plants with extensive existing heat recovery, there is a low potential for extended heat recovery by internal heat-exchanging, as seen in the studies presented in Paper II. In a plant similar to the SMP plants studied in Papers I and II, but with limited heat recovery, there is of course a greater potential for reducing external heat and cooling demands. In that case, the measures already taken in the studied SMP plants are good first steps in reducing external energy demands.

If a new plant were to be built with a GCC similar to the SMP plant described in Paper II, it might be justified to install two heat pumps with larger heat loads than the existing ones, thus better satisfying the heat needs in the process. Hereby, together with heat integration, the use of heat pumps reduces the fuel demand in the plant, and steam is only needed for covering peaks in heat demand and for the production of processing steam. For the results for the plant in Paper II, see Figure 14.

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Figure 14 – The results for the SMP plant studied in Paper II show that two heat pumps can be integrated with the existing SMP plant or a plant with a similar GCC.

The heat pinch analyses in Papers I and II are done in somewhat different ways. In Paper I the heat excess from the condensers in the refrigeration plants is not included in the GCC while in Paper II the heat excess is included. This shows how including or excluding different streams in the GCC can highlight different potentials for energy savings in a plant. By not including the heat excess from the condensers, it is possible to study whether a small change in temperature can reduce the external heat demand, perhaps even without a heat pump. By including the heat from the condensers, it is accepted that the temperature of the heat excess from the refrigeration plants is fixed and cannot be changed.

Another difference between the heat pinch analyses in Papers I and II is the time period over which the analysis is made. Due to lower data availability, one “time slice”, the productive period of the day, is chosen in Paper I while in

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Paper II a “time average” is made over a whole production year. This means that the potential found in Paper I is applicable during the studied time frame, while there is no information about the other possible time periods in the production year. In Paper II, on the other hand, the resulting potential is an average for the whole year and a more detailed analysis is needed to show the economic potential of the suggested changes.

6.1.3 Reduction of Shaftwork Need in an SMP Plant – Paper II The SMP plant studied in Paper II has two two-stage ammonia refrigeration plants with four refrigeration levels (-10, -12, -25 and -40°C). In the areas of the plant where ammonia is not permitted, brine heat exchangers are used.

Using the shaftwork targeting method (see Chapter 5) to analyze the SMP plant in Paper II it is found that there is a potential for reducing shaftwork in the refrigeration systems; see Figure 15. The current shaftwork need is 15% larger than the lowest possible shaftwork realized with a refrigeration system designed for the smallest possible temperature difference in all refrigeration and freezing rooms. Some of this potential can be fulfilled by using the temperature levels in the refrigeration plant in a more energy-efficient way. This can be done by adjusting the cooling loads of the temperature levels, from the highest to the lowest, so that they better fit the EGCC. In this way, as large a part of the total load as possible is on a high temperature level, and shaftwork is saved in the refrigeration plant. Modeling such changes in HYSYS shows a potential for a shaftwork saving of approximately 5%. This reduction can be accomplished in the plant by increasing the areas of some heat exchangers in the freezers and refrigeration rooms. After these changes, the shaftwork need is reduced to a level exceeding the lowest possible shaftwork by 10%. It should be noted that the air temperature in the freezing and cooling rooms is not changed by these changes.

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-0.3

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Figure 15 – The EGCC for the refrigeration system needs in the SMP plant in Paper II (shown in grey) and the utility curve describing the current temperatures and loads used in the refrigeration plant. A large area can be seen between these curves indicating a potential to save shaftwork in the refrigeration plant.

In order to decrease additional shaftwork, the temperature of one of the temperature levels in the refrigeration plant must be changed in order to make the UC better fit the EGCC. A test of several different temperatures for the highest temperature level shows that if the highest temperature is set to -3°C and the loads of the temperature levels are adjusted, the smallest area, and therefore shaftwork, is achieved. Modeling this case in HYSYS shows a potential for a shaftwork saving of more than 10% compared to the current refrigeration plant, although not cumulative with the 5% saving mentioned above. This reduction in shaftwork can be accomplished by necessary changes in compressors and other equipment to enable the change in temperature level, and by increasing heat exchanger areas in refrigeration rooms. After these changes the shaftwork need is reduced to only 3% larger than the lowest possible shaftwork; see Figure 16.

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Figure 16 – In order to save shaftwork in the refrigeration plant in Paper II the area between the EGCC and the utility curve is decreased by changing the temperature of the first refrigeration level from -10°C to-3°C and changing the load of all the refrigeration levels to fit the EGCC.

It might be interesting to change more than one temperature level in a refrigeration plant to save additional shaftwork. In this case, however, the difference between the shaftwork used and the lowest possible shaftwork after changing the temperature of the highest level is small, and can be further reduced only by introducing additional temperature levels in the refrigeration plant. This is probably not profitable in the studied plant, but could be an option when designing a new plant with the same refrigeration needs.

If changes in the room temperatures are possible, an even larger shaftwork saving can be achieved.

The changes in the refrigeration plant suggested above that enable a 5-10% decrease in shaftwork might not be profitable as a stand-alone measure in an existing plant. A 10% saving of shaftwork in the refrigeration system yields a decrease of €40,5001 per annum at typical Swedish electricity prices in 2004 (€35 per MWh). As part of a process change or a retrofit project this change is probably cost-effective and as the price of electricity will probably increase in the future, the changes will be even more profitable. In a less modern plant 16% of the electricity need in the refrigeration systems can be saved; see Paper II.

1 €1 = 9.13 SEK. This corresponds to the average exchange rate between March 2002 and March 2005 (European Central Bank, 2005).

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6.2 FUTURE OPPORTUNITIES FOR ENERGY SAVING IN SMP PLANTS – PAPER III

6.2.1 Introduction Three factors are important when studying different energy efficiency measures for a plant: the development of the energy market (e.g. the energy costs and policy instruments) the size of the plant and its energy demands, and the types of energy efficiency measures that have already been applied. In Paper III, the profitability and the changes in CO2 emissions for different opportunities to save external heat and cooling demand in SMP plants in current and future energy markets are compared. The plants are also combined with heat demands from other plants investigating the opportunities for saving energy demand in ecocyclic industrial parks. The energy market parameter sets, or “blocks”, described in the methodology section are used. The oil price is currently higher than forecasted in the blocks. This means that the profitability when decreasing the heavy fuel oil or switching to another fuel is underestimated in this study. As for oil, the natural gas price has increased a bit more than forecasted in the blocks.

Based on the SMP plants studied in Papers I and II, four different fictitious SMP plants are studied. Two of the plants have approximately the same production capacity as the SMP plant studied in Paper II. As the trend in the Swedish SMP industry is towards larger plants, two of the fictitious plants have a production capacity, and corresponding cooling and heating demands, that are twice as large as in the SMP plant in Paper II. It is also interesting to study a larger plant since energy-saving opportunities are more advantageous when the plant size is larger. To be able to study the difference in profitability for different energy efficiency measures when the plant is already integrated, the plants also have different heating and cooling demands. One plant of each size is set to be non-integrated, filling all its heat and cooling demands with external utilities, and one plant of each size is set to be integrated to the extent of the SMP plant studied in Paper II. The four fictitious plants studied are described in Table 2.

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Table 2 – The plants studied in Paper III (NIP = Non-integrated Plant, IP = Integrated Plant).

Case NIP1 NIP2 IP1 IP2SMP production [kg] xa 2x x 2xPlant heat demand [MW] 2.9 5.9 2.9 5.9Integrationb [MW] 0 0 1.0 2.1Heat excess from heat pumps [MW] 0 0 0.9 1.8Process steam demand [MW]c 0.9 1.8 0.9 1.8Total steam demand [MW]d 3.8 7.7 1.9 3.8Fuel demand [GWh/year] 26.7 53.3 13.2 26.3Electricity demand [GWh/year] 31 62 32.2 64.3

a x corresponds to slaughter of approximately 700 000 animals per year, the greatest part of which is pigs, plus processing meat into different meat products. b Integration in this context means a reduction of external heat demand by increasing internal heat exchanging in a plant. c The steam demand is used for process needs, i.e. excluding steam demand for heating needs that in reality do not need steam. d The total steam demand for a plant is the process steam demand + the plant heat demand that is not covered by heat integration or heat excess from heat pumps.

Changes are made to save external heat demand in the fictitious plants and to reduce emissions associated with the energy use at the plant. The changes considered are: - increasing heat integration by an extended heat exchanger network, - integrating one or more heat pumps, - replacing existing heavy fuel oil boiler with boilers using other fuels, - installing a steam turbine using different types of fuels and - installing a gas turbine using natural gas.

For details of investment costs, pay-back periods (PBP), CO2 emissions etc., see Paper III.

6.2.2 Non-Integrated Plants One way of decreasing the external energy demand in the non-integrated plants is by heat recovery through installation of heat exchangers for heat-exchanging between heat excesses and demands; another way is to install one or more heat pumps. The PBP for increasing the degree of integration in the non-integrated plants to the same level as the integrated plants is interesting in all future energy markets studied. The reduction in operational cost is greater with a heat pump than for increased heat-exchanging, but the investment cost for a heat pump is greater than for increased heat-exchanging. This has the result that the PBP for installing two heat pumps in a non-integrated plant is about the same as for increased heat exchange.

It has been found that the PBP for replacing the old heavy fuel oil boiler by a new natural gas-fired boiler is short. This is because the price of natural gas is

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lower than the price of oil in all blocks, the boiler efficiency is higher for a natural gas boiler than for an oil boiler, and the investment cost for a natural gas boiler is fairly low. On the other hand, the PBP for investing in a biofuel boiler is too long to be interesting in any of the future energy markets since the investment cost for a biofuel boiler is quite large and the biofuel price is not low enough. This means that much larger CO2 emission fees on fossil fuels than suggested in the energy market “Blocks” used in this study are needed if biofuel is to be an interesting fuel for the studied industry.

In a plant with external heat demand it is also interesting to study integration of a CHP unit instead of investing in heat pumps or heat integration in the plant. For the smaller non-integrated plant, there is no reasonable PBP for investing in either a steam turbine for any of the studied fuels or a gas turbine with an HRSG. For the larger non-integrated plant, all turbines are more advantageous than the same units for the smaller plant. However, investment in a steam turbine is only interesting with a wood chip boiler in Block I, and investment in a gas turbine is only interesting in the future energy market Block IV.

As a conclusion, it is more profitable to install heat pumps or increase the heat recovery than to install turbines for both non-integrated plants. However, it is even more profitable to change fuels to natural gas, i.e. invest in a new natural gas boiler, for both plants.

The results for the largest non-integrated plant are shown in Figure 17.

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Figure 17: Payback period for energy efficiency options for the larger non-integrated plant (NIP2). The ratios between the payback periods for these options in the smaller non-integrated plant are similar to the ones in NIP2.

6.2.3 Ecocyclic Industrial Park To obtain even larger energy utility systems it can be profitable to locate several different food processing plants or other industrial plants in the same area, so-called ecocyclic industrial parks, so that different companies can “co-own” a utility system. Nearby residential areas can also be included, as the production of district heating can represent an extra profit to the plants. Integration of the energy utility system of several plants in district heating systems can enable investments that would not be profitable for a stand-alone plant, for example a CHP plant. Several plants together represent a total heat demand large enough to buy a larger steam or gas turbine with a better efficiency and a lower investment cost per kWh electricity.

If another food processing plant is located so that the energy utility systems of the largest non-integrated plant can be integrated with it, the PBP for a CHP unit is short compared to a stand-alone SMP plant. For example, the PBP for installing a steam turbine with a heavy oil boiler is very long for a stand-alone plant, while it is realistic in some future energy markets for an ecocyclic industrial park. The PBP for steam turbines with natural gas or wood chips is also short enough to be interesting in some energy markets, and a gas turbine is also an attractive alternative; see Figure 18.

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Figure 18: Payback period for installing turbines in an ecocyclic industry park compared to a stand alone plant (NIP2) (ST = steam turbine, GT = gas turbine).

6.2.4 Integrated Plants In the integrated plants, heat recovery is large enough to make increased heat-exchanging too expensive. However, installation of an additional heat pump is shown to be worthwhile in all future energy markets, especially in the larger plant; see Figure 19.

In the smaller integrated plant, the external heat demand is not large enough to make CHP a beneficial option and, even if a steam turbine is technically possible in the larger integrated plant, it is not economically advantageous. However, a gas turbine may be profitable in the energy market in the most distant future due to high electricity prices.

As for the non-integrated plants, the PBP is short for investing in a new boiler using natural gas in both of the integrated plants.

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Figure 19 – The payback period for installing a new heat pump in IP1 and IP2.

6.2.5 CO2 Emissions The base case for the CO2 emission reduction calculations is the original fuel demand satisfied with heavy fuel oil. In the calculation of total CO2 emissions, only the emissions associated with the use of electricity and fuels at the plant are included.

The products from the plants also cause CO2 emissions from transports and packaging. Also, the total global CO2 emissions can be reduced by sending slaughter waste from the plant to a waste treatment plant that produces heat and/or power replacing fossil fuels. All these emissions remain unchanged for a particular studied plant after energy efficiency measures suggested, and are therefore not included in the study.

It is found that reductions of between 5 and 35% of the total CO2 emissions in a large non-integrated plant can be made by the studied measures. Looking at only the reduction in CO2 emissions for the options studied in Paper III, the best case for a stand-alone plant is a new biofuel boiler; however, this is not reasonable from an economic point of view.

In Figure 20, the investment per kg CO2 reduction for the most economically interesting options studied in the paper is presented. Changing fuel from heavy fuel oil to natural gas gives the smallest investment per kg CO2 reduction. Also changing fuel to wood chips gives a rather small investment cost per kg CO2 reduction per year.

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Figure 20 – The investment cost per CO2 emission reduction [€/(kg/year)] for some of the options for NIP2 studied in Paper III. The blocks represent different future possible energy markets with Block IV being the one occurring in the most distant future.

Installing heat pumps in a plant generally reduces the total amount of CO2 emissions per year more than increasing the heat exchanger network in the plant. When considering investment per kg CO2 emission reduction, heat pumps are also generally the least costly. Investment in a gas turbine gives a reasonable cost per reduced CO2 in the energy markets likely to occur in the nearest future, but is very costly in the more distant future markets where the CO2 emissions from the electricity in the grid are lower than the CO2 emissions from the turbine.

The electricity consumption causes the largest part of the CO2 emissions from the plant. Therefore, it is possible to reduce CO2 emissions by saving electricity in the plant. The potential of saving 10% of the electricity use in the refrigeration plants identified in Paper II can be realized by decreasing the temperature difference between refrigeration media and the needed temperatures in the refrigeration and freezing rooms.

In the SMP plants studied in this thesis, reduction of external heating demand means that the external cooling need is also reduced. For example, the heat pumps suggested in the studies use excess heat from the refrigeration systems that would have been cooled in condensers by air and/or water cooling. The cost reduction by doing this is considered negligible compared to the cost of fuel for steam and for electricity, refrigeration and equipment. In a case with large water

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and electricity costs, the savings when reducing external cooling demand can be considerable.

6.2.6 Summary In the studies of different energy efficiency measures in four fictitious SMP plants evaluated for four future combinations of energy market parameters, it was found profitable to invest in an increased heat exchanger network or heat pumps in the non-integrated plants. Additionally, reductions of between 5 and 35% of the total CO2 emissions in a large non-integrated plant can be made by these measures. The most cost-effective reduction of CO2 emissions is achieved by switching fuel from heavy fuel oil to natural gas.

For the already integrated plants investing in a new heat pump was found to be economically interesting under conditions corresponding to some of the future energy market parameter sets.

The profitability of investing in a CHP plant was found to be small compared to other energy efficiency or CO2 emission-reducing options. In the integrated plants, the payback period for a CHP plant was long. The payback period for a steam or gas turbine installed at an ecocyclic industrial park was found to be short enough to be interesting.

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7 DISCUSSION The majority of slaughter and meat processing (SMP) plants do not have submetering of energy consumption. Thus it is difficult to find data for a detailed energy analysis of a plant. This is also one of the reasons why many companies are not fully aware of the energy utility systems in their plants. A good way of increasing such knowledge is to make studies similar to those in the present thesis. These system-oriented studies also encourage studying the whole plant instead of concentrating on a certain piece of equipment. A greater understanding of the energy system, in addition to submetering of the energy consumption, makes it possible to decrease the energy use for the entire plant and thereby the energy-related costs and emissions.

The large variation in energy demand in an SMP plant makes heat recovery more difficult than for plants with continuous demands. The payback period for an energy-saving project is also longer since the operating time per year is shorter than for other process industries. By means of heat storage and a detailed analysis, there is a potential to save external energy also in these types of plants. When studying the economic potential of energy-saving projects it is important to use energy data that are valid not only in the current energy market but also in the future energy markets when the project is installed.

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The potential for reduction of energy-related cost and CO2 emissions in the modern SMP plants studied in this thesis is not as large as the potential in less modern plants. When studying a plant without heat recovery, the methods used in this thesis are of great value. Through these systematic methods, opportunities for energy savings are found in plants where there seem at a first glance to be none. The study of the whole plant also avoids sub-optimization and finds a design of the heat recovery system that saves the most energy for the whole plant. Process integration methods can be a valuable tool in decreasing the fuel demand in the SMP industry, especially as the size of the plants increases.

In this thesis it is assumed that natural gas is a readily available fuel for all plants. In plants that are not connected to a natural gas pipeline network this is not true. For these plants the environmental impact of using natural gas is marginally underestimated since LPG will have to be used and there are additional emissions from trucks transporting the fuel.

When undertaking a study like the present one, it is advantageous to coordinate the work between university, industry and industrial research institute. In this thesis, this collaboration makes it possible to use the research experience from the academic world, the industrial experience and contacts with industry and academia from the institute, and the application of the research in a real plant from the participation of industry. Through this kind of collaboration knowledge about technical, economic, industrial and energy system experience can be drawn from all sources.

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8 CONCLUSIONS In this thesis, the potential for reducing fuel demand and energy-related CO2 emissions in the slaughter and meat processing (SMP) industry, without changing the food process or decreasing the quality of the food product, is quantified. The profitability and CO2 reduction potential for energy efficiency measures that can be made in an SMP plant for different plausible energy markets are also compared.

♦ From the case studies of existing Swedish SMP plants it can be concluded that the energy-saving measures already made in the plants reduce the external heat demand in a satisfactory way. However, by using heat pinch analysis a further potential to save energy, by e. g. extended heat pumping, can be found. These changes reduce the external heat demand, excluding process steam, to almost zero. Through heat pinch analysis suggestions such as how to place heat pumps in similar plants without heat recovery can also be made. In both case studies, a decrease in cooling demand can also be achieved.

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The potential for reducing shaftwork, and thereby electricity demand, in refrigeration systems in existing SMP plants was also studied by using a shaftwork targeting method. A potential for reducing the electricity demand in the refrigeration systems of the plant by 10% is demonstrated. The potential to save external heat demand and electricity in the studied SMP plants does not make a large impact on the total energy use in society. However, increased energy efficiency in a plant is important for the profitability of the plant, especially as energy prices rise.

♦ Additionally, a broader outlook on energy utility systems in SMP plants, currently and in an economy more conscious of climate change, was explored. In the four fictitious plants studied, different energy efficiency measures, such as extended heat integration, switching fuels in boilers, integration of heat pumps or a CHP plant, and an integrated energy utility system in an ecocyclic industrial park, are more or less advantageous in different future energy markets. However, heat integration and heat pumps are robust solutions that are profitable in all studied energy markets. It can also be concluded that the studied options can save large amounts of CO2 emissions from the plants. The cheapest investment per kg CO2 reduction was shown to be a switch from fuel oil to natural gas in the boilers in the plants. The use of a CHP plant can be an economically interesting option for an SMP plant when the energy market develops towards a more sustainable state, even for small plants. As the investment costs for small CHP plants can be anticipated to decrease as the demand for them increases, the profitability of such an investment will increase.

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9 FUTURE OUTLOOK In this thesis several ways of saving energy-related costs and emissions in one part of the food processing industry are studied. However, there is still much to be studied further to decrease energy use in the food industry.

To broaden the results from this study, additional real plants can be examined in more detail to accomplish energy savings. It is also of interest to study other parts of the food processing industry, such as the bakery industry, to find ways to reduce the external energy demand. Designing a whole new plant from an energy-saving perspective and, for example, designing refrigeration rooms to decrease cooling need and minimize shaftwork and designing energy utility systems to enable maximum energy recovery can result in a potential for energy savings not found in an existing plant. Moreover, it is worthwhile to investigate how the energy efficiency measures studied in the thesis can be combined in an economically optimal way.

It is also interesting to use other process integration methods in the meat processing industry and other parts of the food processing industry. For

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example, water pinch analysis can be used to find the potential to decrease water usage at a plant and thereby, in some cases, also the energy usage.

In order for the food processing industry to be as energy-efficient as possible, research on how to design energy-effective processing equipment is needed. It can also be valuable to study the dynamic behavior of the combined heat and power plants and heat pumps suggested in this thesis in greater detail. In this way, the economic effects of these options can be calculated more exactly. An additional dynamic affect that is important to study is how to store heat in the best way in order to match the heat excesses and heating needs over a production period. Another challenge would be to study the economic and technical potential for installing a gas engine in plants similar to the ones studied in the thesis.

When considering energy prices in the future, one can be even more visionary than in this thesis and try to look farther into the future. It can be relevant to include new types of policy instruments but also to study what the ratio between, for example, fossil fuel price and biofuel price would have to be before the payback for a change to a sustainable fuel is beneficial, and what type of policies can be found to bring this about.

It is also important to expand the system boundaries in this thesis and study, for example, the consequences for the global energy system of the trends seen in the slaughter and meat processing industry. For instance, how do the emissions from transports change due to consolidation of smaller plants into larger plants and how are the emissions from the global energy system affected when solid slaughter waste is transported to large combined heat and power plants?

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10 ACKNOWLEDGEMENTS I want to thank all the people who contributed to this thesis and helped make my time as a Ph.D. student an (almost always) enjoyable one.

First of all the Swedish Energy Agency is gratefully acknowledged for its financial support without which the work presented in this thesis would not have been possible.

Secondly, many thanks to my supervisors who form a team that is hard to beat. Thank you for you supervision and valuable input to my work. To my head supervisor Professor Thore Berntsson, thank you for giving me the opportunity to work with this project. Your ability to recognize what is important from all that is not made my work much better.

To my co-supervisors: Dr. Berit Mattsson, thank you for introducing me to the field of Ph.D. studies, helping me to keep everything in perspective and not abandoning me. Dr. Per-Åke Franck, thank you for squeezing me into your busy schedule and for our interesting discussions about how to interpret different types of curves. Katarina Lorentzon, M. Sc., thank you for your

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encouragement, especially during the past six months, and all the time you spent reading my manuscripts and giving me constructive criticism. Dr. Lilia Ahrné was part of the team during the first part of my studies and introduced me to the wonderful world of food processing.

Docent Simon Harvey and Dr. Anders Ådahl, thank you for sharing your thoughts about energy scenarios with me. Professor Lennart Vamling gave me my first experience of process integration in the meat industry and shared interesting discussions with me. Thank you also to Thomas Ohlsson for reviewing and providing valuable comments on the thesis.

Many thanks also go to everyone who helped me with information and data for the case studies. I would especially like to thank the staff at the plants used in the studies. Thank you for kindly answering all my “stupid” questions and going out of your way to provide me with the answers. Thank you also for teaching me more than most people want to know about slaughter… I hope you can find something useful in this thesis. Thank you also, Lars-Göran Vinsmo, for helping me with measurements and Helena Röshammar for finding all the articles I needed, fast!

Eva, Maria, Lars, Per, Johanna, Fredrike, Norman and the rest of the Ph.D. crew at SIK: thank you for lots of fun and seriousness during coffee breaks, long late nights and weekends, Ph.D. trips and conferences. Thanks also to Ulf, Britta, Thomas A., Anna Fö, Jennifer and all other present and past members of MIL, for letting me take part in your environmental perspective on food. Thanks also to all my other colleagues at SIK, especially POM and the people on “the shelf”.

To my colleagues at Chalmers who always made me feel welcome at “fikarum VoM” – Bengt (no, I’m not having meatballs for lunch), Ulrika, Roger, Miriam, Åsa, Marcus O., Erik A., Eva, Marcus E., Erik H., Jörgen, Mathias, Lennart P- E., “seniors” and all other old and new Ph.D. students (who are not so new anymore) and who spent time at the department with me – I’ll miss coming to visit you regularly, having Friday “coffee” and discussing ways to save energy (and the world).

I would also like to thank Borealis AB for giving me the opportunity to finish this thesis and my new colleagues there for allowing me to be away from work so much. Thank you for your encouraging words and interest in my studies (“aren’t you done with your thesis yet?!”). I look forward to working with you 100%.

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My friends, thank you for putting up with my unsocial behavior. I have not been able to give you as much time as I have wanted lately, but I hope to make it up to you!

My dear family, what would I do without you? Thank you for loving me and helping me in the ways you can, being a come-to-life dictionary for example.

Mathias, without your support this thesis would never have been written. Thank you for not letting me take the easy way out. I love you so much for loving me, even during these past six months. I hope you won’t tire of me now when I’ll actually be able to spend whole weekends away from work!

Jesus, you never said it would be easy, you only said that I'd never go alone.

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11 NOMENCLATURE AND ABBREVIATIONS BAT Best available technology

CAHP Compression/Absorption Heat Pump

CC Composite Curve

CHP Combine Heat and Power

COP Coefficient of Performance

EGCC Exergy Grand Composite Curve

HRSG Heat Recovery Steam Generator

GCC Grand Composite Curve

IP Integrated Plant

NIP Non-Integrated Plant

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PBP Pay-back period = project) to due cost loperationa of (Reduction

project of Cost

[years]

SMP Slaughter and Meat Processing

T Temperature [K]

t Temperature [°C]

Ta Ambient temperature, 293.15 K

∆Tmin Smallest accepted temperature difference

UC Utility curve

Q Heat/cooling load [kW]

α Efficiency for a CHP, production heat Total

production yelectricit Total [%]

ηT The isentropic efficiency of the turbine. It describes the capacity of the turbine to transfer the energy content of the steam to mechanical work [%].

ηtot Total efficiency for a CHP, nconsumptio fuel Total

production heat)ty(electrici Total + [%]

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REFERENCES

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