co-utilization of coal & municipal wastes

8/3/2019 Co-utilization of Coal & Municipal Wastes

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CO-UTILISATION OF COAL

AND MUNICIPAL WASTES

Report No. COAL R212

DTI/Pub URN 01/1302

by

Optimat Limited

The work described in this report was carried out under contract as part of theDepartment of Trade and Industrys Cleaner Coal Technology Transfer Programme. The

Programme is managed by ETSU. The views and judgements expressed in this report are

those of the Contractor and do not necessarily reflect those of ETSU or the Department of

Trade and Industry.

Crown Copyright 2001

First published December 2001


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CO-UTILISATION OF COAL AND MUNICIPAL WASTES

by

Optimat Limited

SUMMARY

Continuous growth in global municipal solid waste (MSW) arisings, increasing government

environmental legislation to reduce landfill disposal and energy policy initiatives are

generating worldwide interest in the recovery of energy from municipal solid wastes.

Although less common in the UK, energy from waste plants are common in most European

countries and elsewhere. These are currently based on direct combustion of MSW, or

partially processed MSW on specially designed combustion grates or fluidised bed

combustors.

There is also growing interest in the development of advanced technologies for the thermal

processing of MSW, with heat recovery and power generation, as an alternative to

conventional incineration technologies. These more novel thermal processing technologies are

based principally on gasification or pyrolysis, and these are covered in other DTI

programmes. MSW, however, is a poor and inconsistent fuel and, for a number of years, there

has been interest in the co-utilisation of pre-processed MSW, or refuse derived fuel (RDF)

with coal in combustion and other systems, which were originally designed for processing of

coal. In most case this involves partial replacement of coal with waste material in existing

capital plant. In principle, the co-utilisation option has the potential to increase power and

energy generation from waste materials relatively quickly, at low capital cost and at low risk.

This approach may also help to reduce important non-technical barriers to the development

of energy from waste projects and help create a market for refuse-derived fuels. There are,

however, a number of concerns about the risks associated with co-utilisation, including

concerns about the quality of the delivered RDF, about the effects on existing plant

integrity/efficiency and about the environmental/ regulatory issues. Much of the recent

research and development work worldwide has been aimed at addressing these risk areas, and

significant progress has been made.

The technical and economic feasibility of the co-utilisation of MSW and RDF with coal at

industrial and utility scale was assessed under this project, which was fully supported by the

DTI under its Cleaner Coal Technology Transfer Programme. The overall aim of the study

was to evaluate the commercial viability of co-utilisation and potential export opportunities

for UK manufacturers of combustion plant, ancillary equipment and support services.

Specific objectives of the study were:

To assess global market opportunities for co-utilisation of coal and municipal waste To review the current international status and level of commercialisation of technologies

for co-utilisation of coal and municipal waste. This included identification of future

technology transfer and R&D requirements for combustion plant and ancillary equipment.


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To identify municipal waste supply infrastructure requirements, economic andtechnology barriers to successful co-utilisation

To increase UK industry awareness of potential markets and export opportunities forequipment and services

To identify initiatives that would facilitate development, transfer and exploitation of co-utilisation of coal and municipal waste technology by UK industry

Technology Status

The composition of MSW varies significantly from country to country, due to cultural

differences and generally reflects the level of industrialisation and level of paper and plastics

used in packaging. MSW is a poor quality fuel and in a number of countries, pre-processing of

MSW to prepare an RDF is practised to improve its consistency, storage and handling

characteristics, combustion behaviour and calorific value. Production of RDF generally

involves one of two basic approaches, viz:

Wet floc-type RDF preparation by shredding, screening, magnetic and eddy currentseparation, and possibly air classification, and

The preparation of a dry densified RDF by intensive processing of MSW followed bydrying and compaction into a pellet or cube.

Production methods most favoured in the UK have been in densified RDF. A typical RDF

production layout is shown below.

Municipal Waste

PrimaryShredder

Magnetic

Separation

Prim.Disc

Screen

Sec.Disc

Screen

Residue

Air

Classifier

Secondary

Shredder

Eddy Current

Classifier

compactor

Refuge Derived Fuel

composting landfi ll cement

production

Iron

Production

power

generation

heavy

plastics

glassferrous

metals

non-ferrousmetals

floc

RDF Production Facility

It is worth noting in this context that ASTM developed a classification for physical and

chemical characteristics of RDF in the 1980s, ASTM E 83, defining seven types of RDF.


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During the 1980s and 1990s a series of combustion trials were carried out in the UK on

small industrial boilers, principally using stoker-fired units and fluidised beds. Significant

problems incurred, particularly with combustion behaviour and tendency to form fouling

deposits on heat exchanger surfaces. More recently a few new and existing facilities are opting

for floc-type RDF production. RDF production plants currently in operation in the UK

including at Newcastle, Slough, Hastings and Isle of Wight, which either supply fuel locally or

produce power for the grid.

The prospects for utilisation and co-utilisation of RDF in Europe are illustrated by future

plans in Finland, where one of the key objectives of the National Waste Management Plan is

to discontinue disposal of untreated MSW to landfill by 2005 by developing advanced source

separation, resource recovery and the production/utilisation of recovered fuel (REF) in both

existing and new plant. The plan is to expand production and markets for REF to around 1

million tonnes/yr by 2005. There has also been wider international interest in the USA and

elsewhere, in the preparation of a refuse derived boiler fuel containing a blend of pre-

processed MSW with coal suitable for combustion in pulverised coal and fluidised bed

boilers.

There are a number of widely employed industrial and utility scale coal utilisation

technologies that have the potential for co-utilisation with waste materials. The following

technologies may offer the most promising prospects for large-scale co-utilisation of coal with

RDF:

Pulverised coal-fired boiler plant for generation of power and heat from coal, and, as such,represents the largest potential market for coal/waste co-utilisation, worldwide.

Fluidised bed boiler plants for power and heat generation at the large industrial and utilityscale, particularly in Europe and North America; there is significant potential for co-firing

of waste materials in this type of plant.

Cement kilns are relatively large-scale users of coal in most developed countries and thereis significant potential for co-firing in this type of plant.

A typical layout of a fluidised bed power generation is shown in below.


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RDF silo

dolomit sand

Turbogeneratorsteam

grid

ash separator bag house filter

bottom ash cyclone ash fly ash

Combustor

(e.g fluidised

bed)

bottom ash

lime

Small Scale Fluidised Bed Power Generation

In all three cases, near term markets will be in retrofitting of existing plant to permit co-firing.

In the longer term there may be emerging markets in the supply of plant with multiple fuel

firing capability, including RDF materials.

Also of growing government interest is embedded power generation and dealing with waste at

a local level. There has been a number recent developments in the UK on firing RDF directly

in small-scale purpose built integrated recycling power generation plant using shell boilers

and grate-fired technology. Although co-utilisation with coal is not involved, there is

significant potential in low coal consumption markets where the main driver is dealing with

waste materials.

Economic Analysis

Full commercialisation of co-utilisation technologies for municipal waste will not happen

unless economic viability can be demonstrated, particularly where significant capital

investment is required. In consideration of opportunities involving electricity sales, there is

uncertainty regarding the sustainable prices that can be achieved for wholesale electricity.

Considerable geographic variation in landfill disposal costs currently exists for MSW.

Economic models were used to assess commercial feasibility in four different applications:

Direct co-utilisation of RDF with coal in large utility scale power generation Small scale integrated recycling RDF power generation plant using fluidised bed and

custom built shell boiler technology

In-direct co-utilisation of RDF in dedicated combustion systems in large-scale powergeneration

Co-utilisation of RDF in cement kilns


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Results from the analysis highlighted two near market applications, which are considered to

be technically and economically feasible. Co-utilisation of coal and RDF in cement kilns and

small scale integrated recycling and power generation directly firing RDF were assessed to

commercially attractive. In both models, pre-processing MSW on-site, which would attract

landfill disposal levies and remove costs of transporting RDF are key factors for economic

viability. Direct co-firing of RDF in large utility scale power generation or in-direct co-

utilisation in dedicated combustion boilers would be uneconomic at the present time with the

models used. The purchase price of RDF and its relatively low calorific value are the main

factors. However, co-utilisation of RDF and coal in large scale power generation may become

viable if RDF is produced on-site, or if government incentives/ tax credits were available. It

should be noted that considerable regional variation of landfill costs for MSW exist and that

current low landfill costs in some territories will be a major barrier to commercial feasibility.

Market Survey

Global markets were provisionally prioritised in terms of market needs and ease of marketentry. Potential opportunities considered for energy from municipal waste included co-

utilisation of RDF with coal in large scale power generation (direct and indirect co-utilisation),

direct combustion of RDF in small-scale integrated recycling & power generation plant and

RDF as a co-fuel in cement production and metal production. Based on the economic

analysis, priority short to medium term opportunities identified were; small-scale integrated

recycling and power generation plant firing RDF; and cement production. Co-utilisation in

large-scale coal boilers for power generation could offer longer-term opportunities, but will

rely largely on future technology development to improve economic feasibility.

The market potential for small scale integrated recycling power generation plant was based oncomparisons between a number of econometric factors, including capturing a 10% share of

MSW disposed in seven key territories and capital costs for fluidised bed plant (~35m),

public sector capital spend and generation sectoral spend:

Territory Estimate (M) Nature of Estimate

Brazil 1,267 Sector spend, EFW estimates (mean)

Chile 250 Sector spend, EFW estimates (mean)

China 1,900 Public sector capital spend (10% of mean estimate)

India 4,402 Sector spend, EFW estimates (mean)

Japan 7,390 Sector spend, EFW estimates (mean)Korea 2,531 Sector spend, EFW estimates (mean)

Malaysia 1,534 EFW estimates (concurs with public capital spend)

A large proportion of these potential markets will involve a percentage of local content,

although opportunities for UK suppliers may include plant design, build/operate and

consultancy. In some European countries integrated recycling and incineration account for

90% of municipal waste disposal.

With global cement production estimated to be around 1.5 billion tonnes per annum,

significant opportunities and interest exist to replace fossil fuels with RDF. Alternative fuels

currently supply on average around 12% of thermal energy consumption in the UK and


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Europe, equivalent to 2.5 million tonnes of coal per year. If 50% of thermal energy

requirements from the European cement industry was produced from RDF this would equate

to 10 million tonnes of coal valued at over 250 million per annum. On a global level, 50% of

thermal energy from RDF would be equivalent to replacing 75 million tonnes of coal, worth

around 1.9 billion with 75-150 million tonnes to of RDF. This would require 750 (100kt/yr)

RDF production plants. The top 15 cement producing countries, accounting for 70% of global

production, have been ranked below in terms of their relative overall potential:

Territory Overall Potential

China High

India High

Japan High

S. Korea High

Brazil High

Turkey High

Thailand Med

US Med

Italy Med

Germany Med

Spain Med

Mexico Med

Russia Low

Indonesia Low

Taiwan Low

Short to medium term opportunities may exist for UK companies to supply design and

supply integrated waste handling plant to cement manufacturers for on-site RDF production.

All application areas e.g. power generation; combined recycling & power generation and

cement production are currently being tested on a number of potential export markets.

Feedback from Chile indicated interest for direct co-utilisation of RDF in power generation,

dedicated stand alone RDF combustion systems, combined recycling-power generation

systems and RDF production/handling equipment in cement production. Although this only

covered a small number of potential users, it highlighted relative attractiveness, applications

and important factors. It also indicated a low level of end-user awareness of the technologiesinvolved and suppliers. This could provide future export opportunities for UK suppliers of

thermal processing plant, equipment and support services. Wider opportunities for co-

utilisation of RDF and coal include metal production. This will require further detailed

assessment.

The results of the study were presented at a workshop at ETSU in June 2001 which was

attended by delegates from various UK organisations closely involved/interested in this area.

The main conclusions arising from the study are as follows:

1. Co-utilisation of RDF in large-scale pulverised coal boilers was assessed to be uneconomicwith the financial models used. Co-utilisation of RDF and coal in large-scale power


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generation may become viable if RDF is produced on-site, or if government incentives/ tax

credits were available. This will require development of more advanced technology for

waste separation at source and the production/utilisation of recovered fuel both in new

and existing plant.

2. Cement production, using RDF as a co-fuel was an economically viable option to reducefuel costs and reduce landfill disposal. Although this will depend on cost of capital, coal

and landfill disposal prices.

3. Multi-billion pound export opportunities may exist for UK companies to supply designand supply new or retrofitted integrated waste handling plant, on-site RDF production

systems, dedicated RDF combustion technology and ancillary equipment to cement

producers.

4. Small scale purpose built integrated recycling and power generation plant using fluidisedbed and shell boiler combustion technologies also look commercially attractive. Breakeven

to cover operational costs would be possible at electricity prices of around 0.025/KWh

with the financial models used.

5. Future research and development will need to address concerns about the risks of co-utilisation of environmental regulatory concerns relating to plant emissions.


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CONTENTS

Page No

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

1.1 Background.............................................................................................................11.2 Study Objectives....................................................................................................1

1.3 Methodology..........................................................................................................2

2 TECHNOLOGY REVIEW.......................................................................................2

2.1 The fuel characteristics of MSW and RDF materials.............................................4

2.2 Technology and Systems.....................................................................................11

2.3 UK Technological Capability...............................................................................29

2.4 Opportunities for R&D.......................................................................................33

2.5 Opportunities for Technology Transfer..............................................................36

3. MARKET SURVEY...............................................................................................37

3.1 Municipal Waste Arisings....................................................................................38

3.2 Energy Production and Consumption..................................................................41

3.3 Coal Imports and Exports....................................................................................54

3.4 Socio-Economic Trends........................................................................................58

3.5 Market Drivers and Barriers................................................................................66

3.6 Receptive Markets For Co-Utilisation................................................................66

3.7 Prioritised Markets For Export Development.....................................................69

3.8 Market Testing.....................................................................................................89

3.9 Market Conclusions.............................................................................................90

4 ECONOMIC ANALYSIS.......................................................................................92

4.1 Direct Co-combustion in Large-scale Power Generation.....................................92

4.2 Small-scale Integrated Recycling and Power Generation......................................93

4.3 Dedicated Combustion Systems in Large Scale Power Generation......................97

4.4 Co-combustion in Cement Production.................................................................98

4.5 Other Opportunities............................................................................................99

4.6 Qualifying Opportunities.....................................................................................99

5 OPPORTUNITIES...............................................................................................100

5.1 Integrated Recycling and Power Generation......................................................100

5.2 Co-utilisation of RDF in Cement Production....................................................102

6. CONCLUSIONS...................................................................................................104

7. RECOMMENDATIONS.....................................................................................105

8. ACKNOWLEDGEMENTS..................................................................................106

9. LIST OF PUBLICATIONS CONSULTED.........................................................106


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10. EXPORT MARKET CONTACTS......................................................................112


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1 INTRODUCTION1.1 Background

Continuous growth in global municipal waste arisings, increasing legislation and an acute

shortage of suitable landfill sites is having a serious impact on waste disposal costs and a

sustainable environment. Furthermore, spiralling landfill charges will have a considerableaffect on the international competitiveness of UK manufacturing industry, compared with

other economies where regulations are not fully implemented. In the UK for example, only

8% of the 25 million tons of domestic waste arisings in 1998 were treated or reclaimed with

the bulk going to landfill. Apart from Western nations, municipal waste arisings are rapidly

becoming a serious global problem in emerging industrialised countries in the Far East,

Middles East, Central America etc as economic growth gathers pace and populations increase.

As opportunities to export waste decline, governments will face increasing pressures to find

solutions to the municipal waste disposal question. Soiling and contamination are major

reasons for the relatively low reclamation rates of municipal waste as cleaning, separation and

transport costs are financially prohibitive. Energy recovery using municipal waste as a co-

fuel with coal is one potential solution. Although less common in the UK, energy from

municipal waste schemes is more widely used in some European countries, where the bulk of

municipal waste is burnt. Special purpose equipment is used for co-firing, which is based on

a variety combustion technologies such fluidised bed etc. Potential applications for co-firing

municipal waste range from small scale domestic / community heating plant e.g combined

heating and power (CHP) units to large scale power generation. This study focused on

applications for co-firing combustion plant and ancillary equipment. The combined benefits

of minimising environmental impact, reduced landfill charges and fuel costs may provide an

attractive proposition to local authorities and industrial energy consumers.

Considerable developments have taken place in combustion technology for biomass and coal

co-utiIisation, which has been the subject of a number of DTI projects. The use of municipal

wastes as a co-fuel will not be realised without similar development of new, or adaptation of

existing coal combustion plant and ancillary equipment. Commercial exploitation of these

new technologies will provide potential export opportunities for UK suppliers of equipment

and services, especially in markets where there is a combination of high consumption of coal

and growing municipal waste problems.

1.2 Study Objectives

The overall objective of this study was to assess market potential for co-utilisation of coal

and municipal wastes. Its aims to identify important co-utilisation technology requirements

and corresponding export market opportunities for UK manufacturers of combustion plant

and ancillary equipment. Specific objectives of the study are:

1. To review the current international status and level of commercialisation of technologiesfor co-utilisation of coal and municipal waste. This included identification of future

technology transfer and R&D requirements for combustion plant and ancillary equipment.

2. To assess global market opportunities for co-utilisation of coal and municipal waste.


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3. To identify municipal waste supply infrastructure requirements, economic andtechnology barriers to successful co-utilisation.

4. To increase UK industry awareness of potential markets and export opportunities forequipment and services.

5. To identify initiatives that would facilitate development, transfer and exploitation of co-utilisation of coal and municipal waste technology by UK industry.

1.3 Methodology

To achieve the study objectives the following programme of was carried out in four phases,

designed to identify attractive technologies and opportunities for commercialisation that could

be exploited by UK based equipment and service supply companies. It was based on desk

research to the status of relevant co-utilisation technology, a capability assessment of the UK

supplies industry, primary and secondary market research using published information and

cost/benefit analytical tools. This included:

Activity 1. Technology Review

Identifying important technologies, plant and equipment categories required for successfulco-utilisation of coal and municipal waste based on desk research.

Assessing UK supplier capabilities based on telephone interviews with suppliers andtechnology experts.

Prioritising key technologies using capability mapping techniques.

Identifying areas for technology transfer and future R&D using gap analysis. Identifying company interest in export development based on telephone interviews with

suppliers and relevant trade associations.

Activity 2. Market Survey

Quantifying potential markets based on national waste arisings and coal consumption Identifying receptive markets for co-utilisation of coal and municipal wastes based on a

results from a market testing programme

Prioritising markets for export development using an opportunity assessment toolActivity 3. Cost/Benefits Analysis

Demonstrating cost benefits of co-utilisation using a case example for comparison withconventional energy production routes.

Activity 4. Dissemination

Maximising industry awareness using workshop events, editorials in trade journals andpublication of a dissemination report.

2 TECHNOLOGY REVIEW


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Over the past 10-20 years there has been increasing interest worldwide in the development of

more advanced technologies for the thermal processing, with heat recovery and power

generation, ofmunicipal solid waste (MSW), as alternatives to conventional incineration

technologies. At the present time, the conventional MSW incineration technologies are based

on the direct combustion of the MSW, or of partially processed MSW, on specially designed

combustion grates and in fluidised bed combustors. Much of the work on novel thermal

processes for MSW has been concerned with the development of specific novel thermal

processing techniques, and these are based principally on gasification or pyrolysis

technologies. In the majority of cases, the waste-to-energy projects have involved the

installation of new, purpose-designed energy conversion plants. These plants have tended to

be relatively small, generally less than 50 MWe.

There has also been, however, some interest in the co-utilisation of MSW or, more

commonly, a pre-processed MSW or refuse-derived fuel (RDF), with coal in combustion and

other systems, which were originally designed for the processing of coal. This is an option

which is increasingly being pursued in Europe and North America. In most cases, this

involves the partial replacement of coal with the waste material in existing coal-fired plant. In

principal, the co-utilisation option can offer the attraction of making use of existing capital

plant, and as such has the potential to lead to a significant increase in the level of power and

heat generation from waste materials relatively quickly, at low capital cost and at low risk.

This approach may also assist in the removal of some of the more important non-technical

risks on the development of energy from waste projects by helping to create a market in

refuse-derived fuels and to promote the establishment of secure fuel supply chains.

To date, the experience in the co-utilisation of MSW and refuse-derived fuels with coal hasnot been extensive, and has involved, in the main, research and development activities and

pilot plant trials a relatively small number of industrial-scale demonstration projects. In

most advanced industrial countries, these developments have been in response to a number of

government initiatives in environmental and energy policy, viz:

Policies aimed at reducing the quantities of MSW and other wastes which are sent todisposal by landfill, and

Government targets and policies aimed at increasing the level of power generation fromrenewable energy sources.

These government initiatives have generated significant interest within the electricity supply

industry and in other sectors in the co-utilisation of waste materials and biomass with coal in

existing plant. There are, however, some concerns within the industry about the risks

associated with co-utilisation, and these can be considered under three categories, viz:

The concerns about the control and specification of the delivered fuel quality with MSWand other waste materials,

The concerns about the technical risks to the integrity and operation of the existing coal-fired plant introduced by the co-utilisation of waste materials, and

The environmental and regulatory concerns.


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Much of the research and development work over the past few years has been aimed at

addressing these concerns and at developing the means of quantifying and minimising the

technical risks. There has been significant progress in Europe, North America and Japan on

the co-utilisation of waste materials with coal over the past few years. This part of the report

provides a status review of these developments, world wide, with particular emphasis on the

co-utilisation of MSW and RDF materials in the electricity supply industry and in other

industrial sectors.

2.1 The fuel characteristics of MSW and RDF materials

MSW is a very poor and inconsistent fuel and a very unpleasant material, which cannot be

stored for any significant period of time. It is notoriously difficult to handle and to feed to

combustion plant.

The composition of MSW varies significantly from country to country, due to cultural

differences and to the level of source separation and other recycling and processing of wastes

carried out in different countries. In general terms, the quality of the MSW also reflects the

level of industrialisation, and the quantities of paper and plastic sheet used in packaging. The

MSW quality also varies with time e.g. the inclusion of grass cuttings hedge trimmings and

other plant materials during the summer months can have a significant impact.

The average analysis data for British MSW are presented in Tables 1 and 2. In Britain, very

little source separation and recycling of waste components is done, and the analysis data in

these tables represent an essentially raw MSW material. The principal components of the

category assay In Table 1 are paper and board, putrescibles and fine, non-categorisablematerial (


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Units Low CV Average

CV

Design

C.V

1. Materials Composition

Paper % 26.0 30.7 35.0

Plastic Film % 3.0 4.6 5.0

Dense Plastics % 2.0 3.4 4.0

Textiles % 4.0 3.3 5.0

Miscellaneous Combustibles % 6.0 5.2 8.0

Glass % 7.0 7.9 10.0

Putrescibles % 20.0 22.5 12.0

Ferrous Metal % 6.0 7.5 9.0

Non Ferrous Metal % 1.0 1.2 2.0

Fines, less than 10mm % 19.0 11.1 8.0

2. Proximate Analysis

Moisture % 32.7 31.4 26.1

Ash % 30.3 27.8 30.5

Volatile Matter % 33.3 36.8 39.5

Fixed Carbon % 3.9 4.1 4.2

3. Ultimate Analysis

Moisture + Ash % 63.0 59.2 56.6

Carbon % 19.8 22.1 23.7

Hydrogen % 2.81 3.18 3.38

Nitrogen % 0.66 0.61 0.58

0xygen (by difference) % 13.2 14.2 15.0

Sulphur % 0.13 0.12 0.12

Chlorides % 0.41 0.55 0.63

Lead ppm 133 133 114

Cadmium ppm 19 21 25

Mercury ppm 0.3 0.3 0.3

4. Gross Calorific Value MJ/kg 8.30 9.39 10.10

Table 1 Typical composition of British MSW

Category Weight (%,

as received)

Moisture(%,

as received)

Ash(%, as

received)

GCV(MJ kg-

1

, as rec.)Paper 33 30 8 12

Plastic film 3 25 9 27

Dense plastic 3 15 6 30

Textile 4 25 8 15

Misc. combustible 5 25 1 12

Misc. non-comb. 5 15 85 -

Glass 9 10 90 -

Ferrous metal 7 15 85 -

Non-ferrous 1 10 90 -

Putrescible 20 65 40 6


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< 10 mm fines

Unseparated 100 33 29 8.4

Table 2 Average category assay for British MSW

The combustion of MSW is carried out in purpose-designed incineration plants, basedconventionally on grate or fluidised bed combustors. The nature of the waste is such that the

combustion process is less than perfect and this has both technical and environmental

impacts.

For these reasons, significant effort has therefore been expended, in a number of countries, on

the development of refuse-derived fuels (RDF) prepared by the processing of MSW. In

general terms, there are basically two approaches to the production of a refuse-derived fuel,

viz:

The preparation of a wet, floc-type RDF by shredding, screening, magnetic separationand perhaps air classification, of the MSW is practised in a number of countries.

The preparation of a dry, densified RDF, in pellet or cube form by intensive processing ofMSW is practised in Britain and in one or two other places.

The selection of the appropriate level of MSW pre-processing is based on cost, the yield of

RDF required and the thermal processing technology proposed for the RDF. Clearly, a more

intensely pre-processed RDF is more expensive to produce, and the yield is lower than for a

wet, floc-type RDF.

The basic approach to the production of refuse-derived fuels can best be described by

examination, in the first instance, of the category assay for British MSW in more detail. The

basic data are presented in Table 2. This shows the moisture and ash contents and the

calorific values of the major constituents of British MSW. The objective in a refuse-derived

fuel preparation process is to remove the materials towards the bottom of the table, such as

the glass, metals, miscellaneous non-combustibles, fines and putrescibles, which have low

calorific value, and to concentrate in the fuel product the higher calorific value materials

towards the top of the table. The consequences of the removal of specific MSW components

on the yield and the quality of the RDF product are illustrated in Table 3.

Degree of

sorting

Mass yield

(%)

Ash content

(%)

Moisture

content (%)

GCV

(MJ kg-1)

Raw MSW 100 29 33 8.4

- metals, glass,

misc. comb.

78 13 39 10.8

- 10 mm fines 68 9 26 11.8

- putrescibles 48 9 28 14.2

Plastic alone 6 8 20 28.5

Table 3 The effect of sorting on the properties of RDF


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In industrial RDF production plants, the processing of the MSW is by a combination of

screening, shredding, magnetic separation and air classification, and where a high grade RDF is

produced, drying and densification. The detailed approach varies from case to case,

depending on the requirements of the RDF thermal processing and heat recovery plant. In this

context, it is relevant to note that ASTM developed a classification of RDF materials in the

1980s, ASTM E 856 83 (re-approved 1998) Standard Definitions of Terms and

Abbreviations relating to Physical and Chemical Characteristics of Refuse Derived Fuel.

This Standard defines seven types of RDF material, and these are listed in Table 4.

Class Form Description

RDF-1 Raw Municipal solid waste (MSW) with minimal processing to

remove oversize bulky waste.

RDF-2 Coarse MSW processed to coarse particle size with or without ferrous

metal separation such that 95% by weight passes through a 6inch square mesh screen.

RDF-3 Fluff Shredded fuel derived from MSW processed for the removal of

metal, glass, and other entrained inorganics; particle size of this

material is such that 95% by weight passes through a 2 inch

square mesh screen.

RDF-4 Powder Combustible MSW fraction processed into powdered form

such that 95% by weight passes through a 10-mesh (0.035

inch) screen.

RDF-5 Densified Combustible MSW fraction densified (compressed) into

pellets, slugs, cubettes, briquettes or similar forms.RDF-6 Liquid Combustible MSW fraction processed into a liquid fuel.

RDF-7 Gas Combustible MSW fraction processed into a gaseous fuel

Table 4 - ASTM Classification of RDF materials. (ASTM E856, 83 re-approved

1998)

It is instructive to examine in more detail one or two approaches to the preparation and

utilisation of RDF materials worldwide, and to discuss the potential for wider replication of

this approach. One of the largest RDF production and utilisation facilities in the world is at

the Palm Beach Resource Recovery facility in West Palm Beach, Florida, USA (Gittinger and

Arvan, 1998). In this facility, the raw MSW is processed to yield recoverable or recyclable

materials and the remaining mixed waste is shredded into a relatively consistent RDF material,

at an RDF yield of around 83%. The facility has been in commercial operation since 1989

and was initially designed to process 566,000 tonnes of MSW per annum, through three RDF

processing lines. Throughout the 1990s, the plant throughput has increased significantly to a

current level in excess of 750,000 tonnes p.a. The RDF produced is of the wet, floc type,

described above, with a net calorific value of around 11 MJ kg-1. The efficiency of the

recovery of saleable ferrous and non-ferrous metals from the raw MSW has increased

significantly since the RDF production plant was first built. The RDF product is combusted

in two large stoker-fired boilers, each designed to produce 128 tonnes per hour of steam at

400C and 52 bar. The fuel is introduced to the boiler furnace through multiple air-swept


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feed spouts arranged in the furnace front wall. Up to around 50% of the RDF is burned in

suspension and the unburned material is combusted on a travelling grate. The electricity

generation capacity of the plant is 61.4 MWe.

In Britain, throughout the 1970s and 1980s, there was significant development of the

technology for the production of a high quality, palletised RDF. It was considered at that

time that the preparation of a pelletised RDF from MSW offered the promise of providing a

relatively low cost waste processing, recycling and disposal option at a scale appropriate to

British conditions and provided a readily stored and transported fuel for the large number of

small stoker-fired industrial boilers that were then in operation in Britain. Initial pilot plant

trial work was carried out at Warren Spring Laboratories in the mid-1970s and two RDF

production plants were built, viz:

Byker in Newcastle upon Tyne, which was designed to process 30 tonnes per hour ofMSW, and

Doncaster, which was designed to process 10 tonnes per hour.These plants were originally envisaged as resource recovery facilities, with the recycling of

metals and other materials in addition to the RDF production. Further RDF production

plants were built in Eastbourne, Glasgow, Birmingham, Liverpool, Hastings and the Isle of

Wight. In all cases, the plants produced a dried, pelletised RDF, which was intended as fuel

to replace coal in small industrial boiler plants. In at least one case, the palletised RDF was

co-fired with coal in a purpose-designed, small shell boiler fitted with a coking stoker. The

analysis data for three of the RDF products, from the Byker, Castle Bromwich (Birmingham)

and Govan (Glasgow) plant are listed in Table 5 (Livingston, 1991). It is clear from thesedata that these are relatively high-grade fuels compared to MSW. The ash contents are

generally between 10-15%, and the moisture contents are in the range 5-15%, depending on

the operation of the drying equipment and the history of the sample. The RDF materials have

relatively high volatile matter contents, and the Gross Calorific Values are typically in the

range 15-20 MJ kg-1, on an as received basis.

Sample Castle

Bromwich

Byker Govan

Proximate Analysis (%, as rec.)

Moisture 7.6 9.2 7.0Volatile matter 65.6 67.0 68.9

Fixed carbon 12.9 9.6 11.6

Ash 13.9 14.2 12.5

Ultimate analysis (%, as rec.)

Moisture 7.60 9.20 7.00

Carbon 40.96 40.78 39.54

Hydrogen 6.37 5.57 5.62

Sulphur 0.27 0.31 0.21

Chlorine 0.45 0.45 0.39Nitrogen 0.66 0.75 0.71


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Oxygen 29.79 28.70 34.03

Ash 13.90 14.24 12.50

Gross Calorific Value MJ kg-1 (as

rec.)

17.80 16.78 18.95

Table 5 Analysis data for palletised British RDF materials (after Livingstone, 1991)

During the late 1980s and the early 1990s, a series of combustion trials were carried out in

the UK on small industrial boilers, principally stoker-fired units and fluidised beds.

Significant problems, particularly with the combustion behaviour of the fuel and with the

tendency to form fouling deposits on heat exchange surfaces. These problems proved difficult

to resolve, and rendered the pelletised RDF less attractive as a boiler fuel than was originally

anticipated. In the early 1990s the market for RDF as a boiler fuel declined markedly as

many small coal-fired units were brought out of service and natural gas became the preferred

fuel for industrial boilers. A number of the RDF production plants closed during the late

1980s and 1990s, including Govan, Liverpool, Castle Bromwich, Eastbourne and Doncaster.The current situation is that the plant at Byker is still operating and supplies fuel to a small,

local power plant. A new waste processing and RDF production plant, with a capacity of

50,000 tonnes of RDF per annum, has been built in Sykes Road on the Slough Trading Estate.

The dried, densified RDF product, Fibre Fuel, is prepared from mainly waste paper materials,

and is co-fired with coal in two circulating fluidised bed boilers operated by Slough Heat and

Power Ltd. This will be discussed in more detail later in this section.

The prospects for the utilisation and co-utilisation of RDF materials in a modern, European

country are illustrated by the future plans in Finland, as described in the National Waste

Management Plan 2005, which was approved by the Finnish government in 1998 (Sipila,Lohiniva and Rantasalo, 2000). One of the key objectives of the plan is to discontinue the

disposal of untreated MSW to landfill by the year 2005. The proposed approach involves

the development of advanced source separation of MSW and industrial waste materials, for

resource recovery and for the production of recovered fuel (REF) materials, and the utilisation

of the recovered fuels in both existing and new CHP plants. Three classes of REF have been

identified and standard specifications have been defined. These are listed in Table 6.

Parameter Unit REF

Construction

wood

REF II

Commercial

waste

REF III

Domestic

wasteFinnish Standard

Chlorine %, w/w < 0.15 < 0.50 < 1.50

Sulphur %, w/w < 0.20 < 0.30 < 0.50

Nitrogen %, w/w < 1.00 < 1.50 < 2.50

Potassium+sodium

(water soluble)

%, w/w < 0.20 < 0.40 < 0.50

Metallic aluminium %, w/w < 0.01 < 0.01 Agreed

separately

Mercury Mg/kg < 0.1 < 0.2 < 0.5Cadmium Mg/kg < 0.1 < 4.0 < 5.0


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Typical properties

Moisture %, w/w 14 9 29

Ash %, w/w 3 6 10

GCV MJ/kg (dry

basis)

20 25 23

Carbon %, w/w 49 56 53

Hydrogen %, w/w 6 7 7

Nitrogen %, w/w 0.7 0.6 0.7

Chlorine %, w/w 0.06 0.2 0.7

Sulphur %, w/w 0.07 0.16 0.13

Table 6 Properties of Finnish recovered fuel (REF) materials (after Sipila, 2000)

The plan is to expand the production and markets for the recovered fuels to around 1 million

tonnes by the year 2005. The key technologies for the utilisation of these materials are:

Co-firing with more conventional fuels, i.e. principally waste wood and coal, in fluidisedbed and grate-fired boilers, and

Gasification, with fuel gas clean-up, and firing in existing coal, oil or gas-fired power plantboilers.

In Finland, it is proposed to build around ten new CHP plants over the next five to ten years

for the co-firing of the recovered fuels. This is perceived as being a key element of the

countrys plans for compliance with EC and other international commitments on waste

management and environmental issues.

There has also been interest, in the USA and elsewhere, in the preparation of a refusederived

boiler fuel, which contains a blend of material derived by the processing of MSW with coal.

One interesting development of this type has been the SlurryCarb process, which has been

developed EnerTech Environmental Inc. in the USA. The initial development work on the

process was carried out in collaboration with the Energy and Environmental Research Centre

(EERC) in Grand Forks, North Dakota, and was described by Klosky and Anderson (1995).

The concept involves the treatment of an aqueous slurry containing the blended RDF and

lignite fuels at 1200-2100 psi and 250-350C. Under these conditions, the oxygen in the

fuels is released as CO2, leaving a carbonised product, which contains around 95-98% of the

original calorific value of the unprocessed feed materials. The objectives of the development

work were to produce a pumpable slurry fuel from lignite and RDF materials, with high solids

loading and high calorific value, which is suitable for combustion in pulverised coal and

fluidised bed boilers. The results of batch experiments at EERC are presented in Table 7.

ULTIMATE

ANALYSIS

(%, DRY

BASIS)

Raw

RDF

Raw

lignite

Carbonised

RDF

Carbonised

lignite

Carbonised

RDF/lignit

e blend

(50:50)

Carbon 47.6 61.9 68.0 66.0 67.4Hydrogen 6.6 4.5 7.2 4.6 5.8


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Nitrogen 0.2 0.9 0.5 0.9 0.8

Sulphur 0.2 1.8 0.1 1.5 1.1

Oxygen 38.7 20.8 13.1 16.7 15.0

Ash 6.7 9.4 11.1 10.3 9.9

Chlorine 0.4 N.D. 0.02 N.D. 0.02Rheology

Solids % w/w 9.4 35.9 44.4 55.2 56.4

Viscosity cP 816 495 250 825 815

GCV

(MJ kg-1)

Dry basis 20.1 25.4 33.0 27.2 29.5

Slurry 1.9 9.1 14.7 15.0 16.6

Table 7: Fuel properties of the raw and carbonised slurry fuels from the SlurryCarb process

(after Klosky and Anderson, 1995)

The carbonised RDF/lignite slurry was considered to have acceptable properties and the

results of small scale combustion tests at EERC were sufficiently encouraging to justify

proceeding to the demonstration of the concept in a 280 kg h-1 continuous process pilot

plant, which provided fuel for further larger scale combustion trials. The SlurryCarb process

is currently entering the commercialisation phase, both in the USA and in Japan. In 1999,

Enertech Environmental Inc. entered into a co-operative agreement with the US Department

of Energy to build a process development facility, with a capacity of 100 tonnes per day to

allow demonstration of the process. This plant is intended to demonstrate the capability of

the process to produce E-fuel from a range of feedstocks, including sewage sludges, RDF and

low rank coals. The E-fuel is intended for direct combustion in biomass, pulverised coal and

oil-fired boilers and as a feedstock for gasifiers and fluidised bed combustors. Enertech have

also entered a licence agreement with Mitsubishi Corporation of Japan, who have constructed

a 20 tonne per day SlurryCarb unit in Ube City, Japan, to permit further demonstration of

the capabilities of the system.

2.2 Technology and Systems

This section of the review builds on the ETSU technology status report Co-utilisation of

coal and biomass / waste. Two technology areas are discussed direct combustion

technologies and indirect combustion technologies together with equipment classifications

relevant to energy from waste projects.

Combustion Technologies / Applications

In this section conventional direct combustion technologies are considered. The nature and

status of the relevant technologies are considered, followed by a summary technical

competitiveness review.

Technology Suitability/issuesStoker systems Have been applied to co-firing of specific wastes, including refuse


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Technology Suitability/issues

derived fuels (RDF).

However, not considered the most appropriate technology, and too

small-scale, for co-firing applications emissions control can be

uneconomic.Cement kilns Considerable use of alternative waste fuels (especially waste chemical

and tyre derived fuels), but limited experience with municipal waste.

Blast furnaces No extant studies of municipal waste, coarse or densified RDF in steel

making. Current blast furnace technologies focused upon the

incorporation of coal and natural gas with coke; need for controlled

process militates against poor quality / inconsistent fuels, although

plastics have been employed in some instances.

Atmospheric

fluidised bed

combustion(AFBC)

Appropriate to a number of waste fuels, some extant examples of

municipal waste usage.

Could handle suitably processed municipal wastesMedium sized applications, typically district heating and CHP.

Circulating

fluidised bed

combustion

(CFBC)

Has been applied to RDF and coal co-firing in the UK.

Similar range of applications to AFBC


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Technology Suitability/issues

Pressurised

fluidised bed

combustion

(PFBC)

Some extant examples of commercial co-utilisation plant.

Installations are under development, but outside of the UK.

Cyclone

furnaces

Have been employed in co-firing applications with waste / biomass

fuels such as TDF and wood chips.

Potential for usage with municipal waste without comminution

New installations unlikely to be built high NOx output

Some potential for retrofitting waste handling equipment for co-firing

in existing installations.

Pulverised fuel

boilers

Most widely applied technology for utility-scale power generation.

Potential co-firing applications involving premixed or co-prepared

fuels.

No specific experience with municipal wastes.

Incineration Mass burn (moving grate) systems in use around the UK, employing

unprocessed fuels.

Coarse RDF (shredded material) and densified RDF (pelletised) based

co-fuels viable, but low coal prices make dRDF unviable as a

commercial fuel.

Table 8: Combustion Technologies Technical Overview:

Technology: international position UK position

Stoker systemsMany makers of sole-fuel equipment.

One principal manufacturer of co-combustion systems (James

Proctor Ltd). Many makers of

sole-fuel equipment.

Cement kilns

No current examples of municipal waste usage.

Chemfuels, tyres and plastics have been employed.

Cement process useful for the absorption of acid

gas pollutants and trace metals.

Many instances of use of tyre

based fuels, waste chemical fuels

and plastics.

Blast furnaces / steel making

Plastics have been explored as blast furnace fuels inChina and Japan relatively clean, well

characterised waste streams from industrial sources.

In addition experience of natural gas / coal usage,

especially in USA. Potential to employ product of

gasified MSW in blast furnaces

No experience of MSW or any

waste streams (such as industrialplastic wastes) as co-fuel in blast

furnaces


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Fluidised bed combustion (AFBC / CFBC / PFBC)

Most experience resides in Scandinavia / Japan,

especially for PFBC. Foster Wheeler is installing a

CFBC municipal waste system in Japan. CRDFtechnologies using fluidised beds are well

established for waste throughputs of 75,000 to

200,000 tonnes/year. There are hundreds of small

coal fired AFBC units in China.

Several large UK players in AFBC

(Mitsui Babcock, ABT Holther ,

ICL and others) but technology

is licensed-in from outside the UK.No UK experience of other types

designs and installations all

overseas.

Cyclone furnaces

There are over 100 units, mainly in the USA and in

Germany. None have been commissioned since

1980s, because of the high NOx formation.

No operational units in the UK.

Perhaps opportunities for waste

handling / pre-treatment equipment

for retrofitting installations.

(Mitsui) Babcock experience with

contaminated waste disposal usingCF.

Pulverised fuel boilers

Most commonly used coal combustion technology

world-wide, decades of experience in all markets.

Osterreichische Draukraftwerke have demonstrated

10% waste co-firing as part of the CADDET

programme.

Mitsui Babcock already active in

biomass firing plant development,

several firms capable of retrofitting

services.

Incineration

Mass burn systems are essentially stoker boilers

in use for over a century world-wide.

Perhaps some potential for

exploitation of existing base, if

innovations in emissions controlare available.

Table 9: Combustion Technologies Competitive Technical Status

Indirect Combustion Systems

In this section indirect combustion technologies are considered. The nature of the relevant

technologies is considered, followed by a summary technical competitiveness review.

Technology Suitability / issues

Gasification systems Some experience with coal-only systems in the UK.

British Coal experience at pilot scale with sewage sludge as a

co-feedstock.

No extant examples of municipal waste as a co-feedstock in

the UK.

International experience with the sole processing of municipal

waste.

Pyrolysis systems Suitable for processing biomass / waste alone.

Some gasification systems incorporate pyrolysis cycle.

Carbonisation Potential for waste material usage as fillers in coke

production.


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Technology Suitability / issues

Technology not developed.

Hybrid systems Separate boiler systems for straw, and biomass generated fuel

in-line are both extant technologies.

Gasification combined with pulverised fuel systems haspotential for development.

Table 10: Indirect Combustion Systems Technical Overview


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16


Gasification systems

Some coal-fired demonstration units, around 250 MW size,

are being operated in Europe and the USA. European plantswere part of the Thermie programme, and US plants are

funded by the DOE. Organic Power have developed a full-

scale multi fuel (biomass / waste) gasification plant in

Norway. Co-gasification of coal and waste demonstrated by

Rheinbraun AG and Krupp Udhe as part of the ECs

Thermie programme

Number of firms involved

in waste-only gasification

developments, none in co-gasification with coal.

Potential for use as

retrofitted adjunct fuel

source?

Pyrolysis systems

Small-scale combined pyrolysis / incineration system for

RDF developed by Saxlund in Norway. Similar system for

municipal waste installed by Tricil.

No UK installations or

experience in RDF

pyrolysis.

Carbonisation

Commercial feasibility needs to be investigated.

Commercial feasibility

needs to be investigated.

Hybrid systems

Osterreichische Draukraftwerke have demonstrated 10%

waste co-firing (through separate CFB pyrolysis unit) in

Austria.

UK experience in coal-

only and waste-only

systems may be suitable

for retro-fitting

applications (discussed

under gasification above).

Table 11: Indirect Combustion Systems Competitive Technical Status

Energy From Waste Equipment

In this section the equipment types relevant to energy from waste systems are considered.

The James and James classifications (see references) have been applied to this analysis. The

status of the relevant technologies is considered, followed by a summary technical

competitiveness review with insights from recent journal and business press reports.

Equipment Technical points / issues

Incinerators / combustors - Used for disposal-only as well as waste-to-energy projects.- Technology well established.- Emissions cleanup required.

Compactors - Includes range of densifying equipment producing DRDFranging in scale from briquettes to pellets.

- Cost of producing DRDF from municipal wastes can beuneconomic.

Disintegrators / shredders - Mature technologies such as granulators, shredders,grinders and so on

- Usually offered separately rather than as part of integratedsolution.

Feeding systems - Mature technologies such as conveyors, screw feedersystems and so on.


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Equipment Technical points / issues

- Often delivered as part of integrated systems by companies few companies supplying feeding systems separately.

Gasifiers - Discussed under gasification in section 2.2Storage systems -

Usually offered as part of an integrated solution

- Classification also includes digestion plants; perhaps sometechnology transfer opportunities in terms of materials?

Turbines - Biomass / waste systems suppliers principally offer gasturbines for biogas or syngas applications.

- Potential for gas turbine installations in co-gasificationplants designs? requires R&D.

Table 12: Energy from Waste Technical Overview

Technology / international position UK position

Incinerators / combustorsSignificant international expertise and experience, as

in the Lausanne municipal heating project and the

Siemens retrofit project in Slovakia.

Specialist waste companies,equipment suppliers and

consultancies active in the sector.

Many small firms compared to

competitors.

Compactors

Generalist suppliers in many competitor territories.

Low IP technology.

Some evidence of focus and

specialisation in small UK firms,

with respect to waste.

Disintegrators / shredders

USA and Germany strong in equipment manufacture.

Technologies are proven with low IP content.

UK presence dominated by small

number of specialist firms, some

just suppliers rather than OEMs.

Feeding systems

Some firms offering specialist feeding / handling

systems, especially in USA and Germany. May

others offering such systems as part of integrated

solutions.

Feeding systems generally only

offered as part of an integrated

solution by UK firms.

Gasifiers

Specialist gasification and generalist firms in USA

(such as Foster Wheeler, particularly active

internationally), mostly generalist firms supplying

gasification equipment in other territories, although

Organic Power (Norway) have been active in a

number of recent projects in Europe.

Specialist, generalist and

consultancy firms active in

gasification systems supply and

technology development.

Storage systems

Generally offered as part of integrated solutions

Generally offered as part of

integrated solutions.

Turbines (biogas / syngas)

Significant specialist presence in USA, some

specialists in Germany. Mostly supplied through

generalists / as part of integrated solutions in other

territories.

Specialists and generalists active in

the UK gas turbine sector.

Table 13: Energy from Waste Competitive Technical Status


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Of the considered technology areas, three areas were considered to have the most potential:

Pulverised coal-fired boiler plants are by far the most popular technology for thegeneration of power and heat from coal, and, as such, represent the largest potential

market for coal/waste co-utilisation, worldwide.

Coal-fired fluidised bed boilers are also popular for power and heat generation at the largeindustrial and utility scale, particularly in Europe and North America, and there is

significant potential for the co-firing of waste materials in this type of plant.

Cement kilns are relatively large-scale users of coal in most developed countries, and thereis significant potential for the co-firing of waste materials in this type of plant.

These three technologies represent the most promising markets for the large-scale co-

utilisation of coal and MSW. In all three cases, however, the tendency has been, and will

continue to be, to co-utilise a fuel prepared from MSW, rather than raw MSW. There are also

smaller potential markets associated with a number of other coal utilisation technologies, i.e:

The co-combustion of RDF with coal in stoker-fired industrial boilers, and The co-gasification of RDF with coal.These technologies will also be discussed in this section, albeit at a lower level of detaiI. Each

of these co-utilisation options will be described in turn, with particular emphasis on the

industrial experience to date and the scope for further replication of co-firing projects. Each of

these areas is considered in further detail below, in sections 2.2.1 to 2.2.5

2.2.1 Pulverised Coal-Fired Boilers

Looking, in the first instance, at the direct co-utilisation of RDF with coal in large pulverised

coal-fired boilers, a number of important demonstration projects should be considered. There

is a good deal of interest in the co-utilisation of RDF with coal in Europe, and particularly in

Italy, and this is the subject of a number of demonstration projects supported by the EC

Thermie programme.

One of the most important and well-documented of these projects involves the demonstration

of the direct co-combustion of RDF in a 320 MWe tangentially-fired, pulverised coal boiler atFusina Unit 4 near Venice in Italy (Bonfanti, Pasini and Pintus, 2000). The boiler has been

retrofitted with a 9 tonne per hour RDF handling and firing system, designed to permit firing

of RDF at up to 5% of the total heat input to the furnace. The handling system is designed to

process both floc-type and pelletised RDF materials. The RDF is produced by CSRBF-

Udine, by the processing of Italian MSW, and is manufactured to comply with the

requirements of the Italian legislation on RDF quality (DM. No. 72 5th February 1998).

These requirements are listed in Table 14. Limits have been placed on the general quality of

the RDF, i.e. on the moisture and ash contents and the calorific value, and on the heavy metal

concentrations. These limits are intended to ensure efficient combustion of the RDF

materials, in an environmentally acceptable fashion.


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Parameter Unit Limit

Net Calorific Value MJ kg (as received) >15

Moisture content % w/w (as received)


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In this context, the use ofcyclone burners has been of interest, particularly in the USA, for

the co-firing of RDF materials with coal in large boilers. This approach has some attractions

since the comminution requirements for the fuel are less exacting than for pulverised coal

firing, and a significant portion of the fuel ash is retained within the cyclone burner and is

drained from the cyclone as a fused slag. This may help to alleviate some of the downstream

problems associated with mixed RDF-coal ashes. The most relevant experience at industrial

scale in the USA with cyclone burners has been at the Otter Tail Power, Big Stone plant in

South Dakota, USA, where a range of waste materials including tyre-derived fuels and refuse-

derived fuels have been co-fired with lignite in a 440 MWe boiler, fitted with 12 cyclone

burners. Significant results from these trials, which promote co-firing of RDF and coal, are as

follows:

Emissions of SO2, NOX and CO were reduced, PCDD and PCDF levels were well belowfederal or state requirements and, the emission levels of PCBs, BTX and PAH

compounds were either reduced or not detected.

CO2, HF and HBr emission levels were unchanged compared to coal only. Addition of lime to the RDF helps to produce a better pellet, capable of extended storage,

and contributes to the control of acid gases.

Although the emissions of HCl were increased, compared to coal only, they were stillwithin acceptable regulatory levels.

In general terms, the use of a cyclone burner for RDF-coal co-firing has a number of potential

attractions however, there are relatively few cyclone-fired systems compared to conventional,

pulverised coal-fired boilers, worldwide.

During the 1970s and early 1980s, a number of electricity utility companies in the USA

were involved in the co-utilisation of RDF materials in large coal-fired boilers. One of the

results of this experience was the preparation of a series of guidelines for the co-firing of

RDF, produced by the Electric Power Research Institute (EPRI) in the late 1980s, (Fiscus et

al., 1988). These Guidelines were prepared in response to a number of proposals which

involved the co-combustion of MSW or, more commonly, RDF in existing coal-fired boiler

plants. The guidelines were intended to assist utility engineers to evaluate and to respond to

these proposals, to identify the boiler units, which are most amenable to RDF co-firing, and

to assess the significance of the likely impacts of RDF co-firing on the operation andperformance of the boilers. In the event, very few such projects were implemented and most

of the projects at that time which involved RDF co-firing were discontinued. The guideline

documents, however, are still of some value in the assessment of potential RDF co-firing

projects, although much of the advice on economic, environmental and institutional matters is

now out of date.

The key results of the EPRI evaluation indicate:

The selection of the unit for RDF co-firing should focus on plants operating as baseloadunits with at least 15 years remaining operating life.


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The units should operate at high capacity and load factors and should be of sufficient sizeto consume the available RDF stream, at a reasonable co-firing ratio.

The selected boiler units should not exhibit significant operating problems with coal alone,and in particular should have no boiler slagging and fouling problems.

The ash handling and flue gas particulate collection equipment should have sufficientcapacity to cope with the additional burdens associated with RDF co-firing.

The co-firing of RDF has the effect of increasing the flue gas volumes and the ash burdens,and there will be a significant reduction in the boiler efficiency.

In retrofit situations, significant derating of the unit, resulting from limitations on boilergas velocities, induced draft fan capacities or electrostatic precipitator capacity is common

experience, depending on the RDF:coal co-firing ratio.

Throughout the 1990s, the interest in the co-firing of RDF in utility boilers in the USA has

decreased, and it has been a relatively uncommon practice. This is, in the main due to the

technical problems associated with RDF co-firing and to concerns about the impacts on the

environmental performance and regulation of the plants, when co-firing RDF. These issues

have also influenced the level of interest in RDF co-firing in electrical utility companies in

Europe and elsewhere. It is only in the past 5 years or so, when there has been increasing

interest in the reduction of fossil fuel utilisation in power plants due to concerns about the

Greenhouse Effect, and the costs of landfill and other waste disposal routes have increased

substantially, that the interest in the replacement of coal with biomass and waste fuels in

utility boilers has increased once again. In this context, a successful outcome to the EC

demonstration project at Fusina in Italy will be significant step forward in providing solutions

to the technical problems associated with RDF co-firing and opening the path to successful

replication of this approach elsewhere. In the main, the market will involve principally theretrofitting of existing coal-fired boilers with the capability of co-firing the waste fuels. In the

longer term, it may be the case that new utility boiler plants will be designed and built with a

co-firing capability.

2.2.2 Fluidised Bed Fired Boilers

Looking, in the first instance, at the direct co-utilisation of RDF with coal in large Fluidised

bed-fired boilers are widely used for the combustion of coal at both utility and industrial

scale, and a number of operating plants have been involved in the co-firing of coal with a range

of biomass and waste materials. The most common waste materials co-fired in this type ofplant are waste wood and bark materials, principally in Scandinavia and North America. The

co-firing of MSW and RDF materials is less common, however there are a number of

historical examples and a number of important new projects, which may point the way to the

future.

The co-firing of RDF with coal in a fluidised bed-fired boiler is one of the technologies being

demonstrated under the EC Thermie co-firing programme (Amorino, 2000). The project is

located in the Sulcis area in Sardinia, Italy, and the project partners are Societa Tecnologie

Avanzate Carbone SpA (Sotocarbo), a specialist clean coal technology development

company, Sondel Societa Nordelettrica SpA, an Italian Independent Power Company andAustrian Energy Energietechnic GmbH, who are the boilermaker. The project involves the


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design, construction and operation of a 10 MWe demonstration plant, based on an

atmospheric internal circulating fluidised bed boiler for the co-combustion of coal, RDF and

sewage sludge. The plant will fire 72,500 tonnes p.a. of RDF, 17,000 tonnes p.a. of sewage

sludge and up to 26,000 tonnes p.a. of imported coal. The project is currently in the design

phase. The waste materials comprise:

52,500 tonnes p.a. of urban MSW from 25 small towns in the region around the plant, and 20,000 tonnes p.a. of dry wastes.The MSW is first separated into wet and dry fractions. The wet fraction is sent for biological

stabilisation. The dry fraction is mixed with the dry waste stream, and is further processed

to recover metals and to reduce the non-combustible fraction. The product is a pre-treated

waste stream (PTMSW). The composition of the PTMSW is as follows:

Organic fraction 22%

Cellulose 44%

Plastic 20%

Metal 4%

Non-combustibles 9%

A briquetting plant will also be installed to permit long-term storage of the PTMSW material.

The PTMSW and coal will be co-combusted in a purpose-designed fast, internally circulating,

fluidised boiler to be supplied by Austrian Energy, in a 60:40 mixture on a heat input basis.

The boiler will generate steam at 450C and 60 bar, which is supplied to the turbo-generator.

The gross power production will be 12.2 MWe with 10.2 MWe available for export. Theoverall net electrical efficiency of the system will be around 24%. The project developers

consider that the selected approach to the co-utilisation of waste materials and coal has the

following attractions:

Power production with low CO2 emissions, Low levels of generation and emission of dioxins due to the good combustion conditions

associated with co-combustion,

The co-combustion with coal provides a high degree of operational flexibility, The use of local resources for power generation, and a cost-effective route for the disposal

of sewage sludges, and The co-firing approach provides an economically attractive means of compliance with

Italian legislation with respect to the recovery of energy from waste materials.

In Britain, the co-firing of coal with an RDF prepared from packaging wastes in a circulating

fluidised bed boiler is practised by Slough Heat and Power Ltd. The power plant in the

Slough Trading Estate has been operated by Slough Heat and Power Ltd. since the 1920s. In

the 1980s, the plant was modernised, and two multi-solids fluidised bed boilers, based on the

Battelle Institute design, were installed. These boilers can generate 180 tph of steam at 509C

and 87 bar. The power plant has the capability to generate 35MWe and to supply heating and

process steam to local industrial customers. The plant now co-fires coal and a densified RDFmaterial, which is prepared from waste paper and non-PVC plastic materials at a local waste


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processing and recycling plant. This plant has the capacity to process 65,000 tonnes p.a. of

waste, and to produce up to 50,000 tonnes p.a. of RDF. The densified RDF product has a

GCV of around 18 MJ kg-1 and is co-fired with coal at a co-firing ratio of 40:60 on a heat

input basis. Slough Heat and Power Ltd regard the RDF-coal co-firing system as an

environmentally attractive and cost-effective approach to the generation of both electricity

and heat from waste materials.

Austria Energy and LLB Lurgi Lentjes Babcock Energietechnik GmbH have recently installed

a 110 MW th circulating fluidised bed boiler plant in Lenzing, Austria, for the co-combustion

of a range of waste materials with coal (Rosenauer, Holblinger and Cleve, 1997). The waste

fuels include RDF, wood waste, sewage sludge and a range of specific industrial wastes. The

plant is integrated with the Chemical Production Plant Lensing AG, and in addition to

disposing of a number of specific solid waste materials, the boiler will also incinerate waste

exhaust gases from the viscose fabric production plant. The boiler generates 129 tonnes per

hour of high pressure process steam at 500C and 80 bar for the chemical plant. The plant,

and in particular the fuel handling and feeding system and the combustor, have been designed

to provide the maximum degree of fuel flexibility. The fuels of lower bulk density, i.e. the

RDF, wood waste, and the specific industrial wastes are injected pneumatically into the

combustion chamber. The coal and sewage sludge are fed into the return leg from the seal

pot. The CFB combustor is completely refractory-lined, and has been designed for maximum

fuel flexibility. The hot flue gases pass through the refractory lined cyclone, which separates

much of the ash to the secondary combustion chamber and then to the waste heat boiler. The

residence time of the flue gases in the secondary combustion chamber is 2 seconds, and there

are support oil/gas burners to ensure maintenance of the required flue gas temperatures.

Overall, the new boiler project at Lensing provides a very good example of the co-combustionof coal with a range of waste materials including RDF, process wastes, waste wood and

sewage sludges, with the incineration of gaseous waste streams from an industrial process,

with the cost-effective generation of process steam for the factory.

A recent project in Thailand is worthy of consideration in this context. The project is in

Chiang Mai, the second largest city in Thailand, and will be operated by the Provincial

Electricity Authority of Thailand, and the boiler plant has been supplied by Kvaerner

Enviropower of Sweden. The boiler co-fires RDF with lignite. The plant is designed to handle

up to 160,000 tonnes p.a. of raw MSW from the city of Chiang Mai. The waste is processed

in three stages to prepare a wet, floc-type RDF, viz:

Removal of bulky waste, Screening and size reduction, and Ferrous metal recovery.The RDF is co-fired with crushed lignite in a circulating fluidised bed boiler, which has the

capacity to generate 98.2 tonnes per hour of steam at 450C and 43 bar. The steam is

supplied to a turbo-generator with the capacity to generate 20 MWe.

Overall, it is clear that there is increasing activity worldwide involving the co-combustion ofRDF materials with coal in fluidised bed boilers for the production of electricity and/or heat.


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In the main, the market will involve the installation of new plant, specifically designed to

allow sufficient flexibility in operation for RDF co-firing.

2.2.3 Cement Kilns

There are a large number of cement kilns in operation worldwide, many of which fire coal as

the primary fuel. However, there has been increasing interest in recent years in the co-firing

of waste materials with coal, principally to reduce the fuel costs, since most of the waste

materials considered for co-firing in cement kilns attract significant disposal credits. A cement

kiln is a long rotary kiln fired from one end by a long suspension flame, with the raw material

(principally limestone and clay) introduced at the other end. The raw material is dried,

calcined and burned as it passes down the length of the kiln, and the clinker product is

produced at the burner end of the kiln.

Cement kilns have a number of inherent advantages in the co-firing of waste materials with

coal, viz:

They operate at relatively high temperatures and have long residence times, whichpromote the efficient destruction of organic compounds present in the waste.

The kiln has relatively high thermal inertia and good thermal stability. The strongly alkaline environment of the kiln helps to reduce acid gas emissions by

absorption of significant levels of the acid gas species into the cement.

Residual ash and much of the trace metals content of the waste materials are absorbed andfixed into the structure of the final cement product.

Solid, liquid or gaseous waste materials, with a wide range of physical characteristics, canbe co-utilised as alternative fuels with coal, although the interest has been mainly on theco-firing of waste liquids and, more recently petroleum cokes and shredded tyres.

Although a number of trials involving the co-firing of RDF materials have been performed,

none of them appears to have been developed into commercial operations. One of the most

technically successful trials of co-firing RDF with coal was carried out at Blue Circles

Westbury Works in the late 1980s. In this case, a shredded, floc-type RDF was prepared

by the processing of MSW, and this was co-fired with pulverised coal into the kiln.

Technically the trial work was reasonably successful, however the trials were discontinued,

due to changes in the operational requirements of the plant, and because of the relatively

modest savings in fuel costs associated with RDF co-firing. Although there were disposalcredits associated with the raw MSW, these were relatively modest since at that time landfill

disposal costs for MSW were relatively low. There were also significant costs associated with

the preparation of the RDF.

The significant increase in landfill costs in recent years in most industrial countries is likely to

have the effect of making the co-firing of RDF with coal more economically attractive to the

operators of cement kilns, and this may lead to an increase in the interest in co-firing

techniques. There is, however, significant public concern in most developed countries about

the use of cement kilns for the thermal processing of waste materials. The environmental

regulation of these activities has proved to be sensitive and problematic, and this may


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continue to represent a significant barrier to the expansion of co-utilisation activities within

the cement industry.

2.2.4 Stoker-Fired Boilers

Stoker-fired boilers are designed to feed solid fuel on to a grate, through which a portion of the

combustion air is passed. The term is used to describe a wide range of different types of

combustion plant, including

Underfeed stokers and static grates, Chain grates and travelling grates, and Spreader stoker systems.Stoker-fired boilers have been historically the most widely applied commercial process for the

combustion of coal in small-scale plant (up to around 80MWth) to generate steam for

electricity production or for heating. The stoker firing principle is also widely applied for

the incineration of MSW, and other waste materials. Although stoker-fired systems have been

applied to a wide range of solid fuels, and can provide reasonably good and efficient

combustion, they are not particularly suited to the combustion of fuels with high moisture

content, or low calorific value. They are also not particularly suited to the combustion of

fuels that are inconsistent and of variable quality. This can result in poor ignition, high levels

of unburned material in the solid residues and high levels of emission of CO, and other

gaseous and gas-borne pollutants.

The co-firing of RDF with coal in stoker-fired boilers has been the subject of a number of

trials and demonstration projects, both in Britain and overseas e.g.

The Argonne National Laboratory (Illinois, USA) successfully co-fired RDF with coal ontheir 20 MWe travelling grate spreader-stoker unit, and

The co-firing of pelletised RDF with bituminous coal was demonstrated successfully in alarge travelling grate-fired boiler at Fort Dunlop in Birmingham, England in the late 1980s.

Neither of these demonstration projects, however, was taken forward to long-term

commercial operation. One of the barriers to the co-utilisation of RDF materials with coal in

combustion equipment designed for coal firing is associated with the environmental

regulations applied in this situation. In most industrial countries, RDF co-firing would besubject to the operating standards appropriate to the incineration of waste materials rather

than those appropriate to the combustion of coal, and these are much more exacting. In many

circumstances, the costs of compliance with the environmental control standards appropriate

to waste incineration would outweigh any fuel cost savings associated with RDF co-firing,

particularly at industrial scale.

2.2.5 Indirect Co-utilisation

The indirect co-utilisation of MSW and RDF is also of interest in the current context.

Relevant technologies include:


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The co-gasification of the waste materials with coal in entrained flow gasifiers, The co-gasification of the waste materials in fluidised bed gasifiers, and The co-gasification of wastes in fixed bed gasificatio

co-utilization of coal & municipal wastes

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