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4th International Symposium of South-East European Countries (SEEC) on FLUIDISED BEDS IN ENERGY PRODUCTION, CHEMICAL AND PROCESS ENGINEERING AND ECOLOGY

ROMANIAN EXPERIENCE AND POSSIBILITIES FOR FLUIDISED BED COMBUSTION OF COAL AND CO-COMBUSTION OF BIOMASS AND PETROLEUM WASTES

L. Dragos, C. Flueraru, N. Scarlat, M. Macavescu

OVM-ICCPET 236 Vitan Street, Sector 3, 74369 Bucharest

Tel: + 40 21 346 42 47 // Fax: + 40 21 346 43 70 // E-mail: [email protected] Abstract Several research programmes has been carried out in Romania for fluidised bed combustion of different solid fuels. The paper presents the activities of OVM-ICCPET for the development of the stationary fluidised bed combustion (SFBC) technology. The results obtained in Romania in some SFBC thermal plants were quite encouraging. The paper presents some of the results obtained in Thermal Plant Motru. Furthermore, OVM-ICCPET developed and patented a circulating fluidised bed combustion technology (CFBC) and built a 1 MWt CFBC pilot plant, that was used for the performance of combustion and desulphurisation test programme using different coals, biomass and industrial wastes. Combustion tests were performed for the development of a technology for the co-combustion of petroleum waste and biomass in fluidised bed. The tests, performed on a 100 kW experimental plant, allowed to obtain the data regarding the co-combustion of petroleum waste and biomass. Keywords: fluidised bed combustion, co-combustion, coal, biomass, petroleum waste. 1. INTRODUCTION The power sector in Romania is in a re-organisation process since 1990, with the aim to improve its efficiency, in the general context of the transition to a market economy, taking into consideration the influence of energy sector on the economy. The actual stage of development of Romanian energy system requires the refurbishment of a coal-based boilers, due to their long lifetime and low efficiency. This could be done through the implementation of the fluidised bed combustion technology, having high efficiency and low pollutant emissions, low investment and operating costs, in the conditions of using different kind of fuels. Accordingly to the EU policy for promotion of coal utilisation for energy production with high efficiency, for the introduction of advanced energy production systems, OVM-ICCPET has been carried out research programmes aiming the implementation of circulating fluidised bed combustion plants, for the refurbishment of coal-based boilers. Nowadays, we are trying to promote a national programme for the applications of CFBC boilers in coal based power plants. Several options and locations have been investigated for the implementation of the CFBC technology since 1994 together with Coal Research Establishment – UK, aiming to cover the energy demand on a local scale, and to build a clean demonstration plant, with high efficiency and low pollutant emissions. 2. ROMANIAN EXPERIENCE REGARDING FLUIDISED BED TECHNOLOGY 2.1. Achievements in the field of stationary fluidised beds Research and experiments were performed in OVM-ICCPET for the development of the fluidised bed combustion technology since the 70’s. The research activity included combustion and desulfurisation experiments and tests on laboratory and pilot scale facilities. A semi-industrial 2 MWth stationary fluidised bed combustion plant was design and commissioned as a test facility for the development of combustion and desulphurisation technologies. The activities performed during 20 years have lead to the development and designing, by our own conception, a range of small capacity boilers for steam (2 t/h and 10 t/h) and hot water between 2

April 3-4, 2003 Thessaloniki, Greece


and 12 MWth, which were implemented in thermal plants in Romania (Motru, Filipesti de Padure, Filiasi, etc.). About 50 SFBC boilers have been implemented in industrial power plants. In the conditions of an adequate maintenance and operation, the results obtained in Romania in some SFBC thermal plants were quite encouraging, like the good results obtained in operation in Thermal Plant Motru which is in operation for 20 years. Furthermore, the research programme focussed the development of the circulating fluidised bed combustion technology and its implementation in power plants. OVM-ICCPET developed and patented a CFBC technology. For this aim, a 1 MWth CFBC pilot plant was designed and commissioned to be used for the performance of research and experiments regarding the combustion of different fuels in order to be demonstrated on a pilot scale. The research works is continuing now by identification of the implementation possibilities of our own CFBC technology in Romania in the first demonstrative installation to certify its advantages in long time operation for local and imported coals and different wastes. Combustion tests have been also performed for the development of a technology for the co-combustion of petroleum waste and biomass in fluidised bed. The tests performed on a 100 kW experimental plant, allowed to obtain the necessary data regarding the possibilities of combustion of the mixture for energy production. 2.2. FBC Thermal Plant Motru The FBC Thermal Plant Motru, fitted with a stationary fluidised bed boilers was built based on the research and design of OVM – ICCPET, being into operation with very good results since 1983; during the time several improvements were made to the boilers, based on the acquired experience.

Figure 1: SFB boiler at Power Plant Motru

The Plant is fitted with 2 x 50 t steam /h boilers constructed in 1969 and a SFBC hot water boiler of 11,6 MWt commissioned in 1983 (Figure 1). The plant delivers hot water for district heating and local industry in Motru. The used fuel is lignite with a lower heating value of 6,7 MJ/kg extracted from a nearby coal mine. The furnace of the SFVBC boiler has a 60 m3 inside volume and a 130 m2 heat transfer surface. The fuel, local lignite with 0 – 5 mm particle size is introduced by two screw feeders with variable speed. The convective part is of membrane walls type, with two flue gas ways (ascending and descending), with a 490 m2 total heat transfer surface. The main fans ensure the primary and secondary fluidising air flow and the combustion air for the start-up burners. Obtained Results

maximum / minimum load: 13.9 / 10.5 MWt input / output water temperature: 70 / 1500C boiler efficiency: 80% air minimum temperature: - 100C fluidising primary air flow: 15,000 Nm3/h fluidised bed regime temperature: 750 – 8500C burning gas temperature at furnace output: 1700C

The boiler, designed and installed by OVM-ICCPET is in operation for more than 20 years, that proves that the fluidised bed combustion technology is a well developed and competitive technology, leading to with good results, in the conditions of an adequate operation, exploitation and requirement for keeping the plant into operation for energy production necessary for local area.



3. RESEARCH PROGRAMME FOR CIRCULATING FLUIDISED BED COMBUSTION OF COAL 3.1. Experimental activities A research programme for the coal combustion in circulating fluidised bed was also performed. The experiments performed on the 1 MWth CFBC pilot plant aimed to establish the parameters of the combustion process and the conditions for obtaining low pollutant emissions. Figure 2 presents the 1 MWth CFBC pilot plant used in the research programme. The experimental facility is equipped with a furnace of 12m height and with an internal diameter of 550mm at top, being also fitted with heat exchange surfaces. The plant is fitted with solid particles' recirculation line (cyclone, air valve and an external heat exchanger). The main operating parameters for temperature, air, flue gas and water flows are recorded using a data acquisition system.

Figure 2: 1 MWth CFBC Pilot Plant

The experiments on the pilot plant used different sorts of coals for the establishment of their behaviour during combustion and desulphurisation. The selection of the coal for experiments and tests (Table 1) was based on their share in the energy production system. Three lignite from surface exploitation from Oltenia Basin, a brown coal from Comanesti and two types of hard coal were used. Table 1: Ultimate coals analysis

Symbol U. M. Surface exploitation Coal mines Hard coal Lignite

type 1 Lignite type 2

Lignite type 3

Comanesti Romania Australia

WtI % 33.40 35.60 44.10 12.60 9.70 11.20

AI % 33.20 27.10 20.40 48.70 9.50 20.90 CI % 20.95 23.70 21.76 25.20 64.15 56.00 HI % 1.83 2.23 1.94 2.20 4.85 3.33 Sc

I % 0.80 0.60 0.80 1.45 2.00 0.55 OI % 9.22 10.12 10.29 9.20 8.84 7.20 NI % 0.60 0.65 0.71 0.65 0.96 0.82 LHV kJ/kg 6,365 7,688 7,461 9,368 25,481 21,817

The used lignite had a lower heating value (LHV) between 6300 – 7500 kJ/kg, an ash content between 20 – 35 % and a sulphur content between 0.6 – 0.8 %. The brown coal from Comanesti was also tested, with LHV of 9300 kJ/kg, an ash content of 48% and a sulphur content of 1.45 %. It was also tested Romanian and Australian hard coal with a LHV between 21800 – 25400 kJ/kg, an ash content between 9,5 – 20 % and a sulphur content between 0.55 – 2%. Detailed measurements of the operating parameters were performed during tests. The furnace temperature was between 820 – 880 ˚C, obtaining a thermal efficiency between 85 – 88 %. The combustion tests were followed by desulphurisation tests using different limestone for desulphurisation. The desulphurisation efficiency varied between 88 – 92 % for Ca/S molar ratio



between 1.8 – 2.2. The pollutant emissions were also reduced, with SO2 concentrations between 130 – 290 ppm and the NOx concentration between 35 – 105 ppm. 3.1. Lignite combustion The results obtained during lignite and hard coal combustion experiments are shown in Table 2. Each presented data represents average values for the registered parameters for a longer operating period for one test. The grain size distribution of lignite was between 0-10 mm for all experiments, with an average diameter between 0.83 and 1.19 mm. The parameters value show that the average temperature in the furnace was for all lignite types between 820 and 880 ˚C, which corresponds to typical operation regimes for circulating fluidised bed combustion. In spite of the quite high ash and moisture content, the combustion efficiency was high, as shown in Table 2. The primary air fraction was in the experiments between 50 - 70%, and the flue gas velocity was between 6 – 6.5 m/s. The sorbent used in experiments was limestone with a grain size of 0-1 mm and average diameter 0,090 - 0,100 mm. Ca/S molar ratio was between 1.8 and 2.2, which are optimum values from the economic point of view. The tests used Ca/S molar ratio of 1 – 3, and the results showed that a Ca/S molar ration larger than 2.4 is not necessary, considering the desulphurisation efficiency. Table 2: Experimental results for lignite combustion in the 1 MWth CFBC pilot plant Parameters U.M. Test 1 Test 2 Test 3 Test 4 Test 1 Test 2 Coal type — Lignite

type 1 Lignite type 2

Lignite type 3

Comanesti Romania Hard Coal

AustraliaHard Coal

Load MWt 1.05 0.94 1.10 1.15 1.05 1.02 Fuel flow kg/h 798 600 706 582 165 186 Limestone flow kg/h 44 22.5 35 47.5 28 9 Excess air ratio — 1.19 1.25 1.22 1.15 1.18 1.105 Furnace temperatures °C 820 825 860 880 860 880 Thermal efficiency % 86.8 85.3 87.5 88.2 90.4 90.8 Ca/S molar ratio — 2.2 1.8 2.0 2.0 2.5 2.5 SO2 theoretical conc. Ppm 1812 1144 1656 3044 1632 575 O2 concentration % 3.4 4.3 3.8 2.8 3.0 2.1 CO2 concentration % 16.1 15.1 15.8 16.3 15.7 15.8 SO2 concentration Ppm 180 134 137 289 114 70 NOx concentration Ppm 58 77 34 105 48 55 CO concentration Ppm 48 54 52 60 44 71 Desulphurisation efficiency % 90.06 88.30 91.70 90.50 93 88 3.2. Hard coal combustion The average parameters of the main parameters, obtained during experiments using Romania and Australia mentioned hard coals, are also presented in Table 2. The coal particles were as for lignite, between 0-10 mm. The primary air fraction was kept around 75 %, and the fluidisation velocity about 5.5 m/s. The combustion process was more stable in case of hard coal combustion, but the bed material decreased in time, requiring the inert material addition in the bed. The temperature in the furnace was around 900 ˚C but, due to the lower air excess by 10-15 than in case of lignite, the NOx content in flue gas was kept at about circa 50 ppm. The other pollutant emissions had low values, maximum 71 ppm CO, and below 120 ppm SO2 when limestone was added for desulphurisation. The desulphurisation efficiencies were between 88 and 93% with Ca/S molar ratio of 2.5 – 2.8. The measurements revealed a lower self-desulphurisation for hard coal combustion (10-12%) compared to the self-desulphurisation level obtained for lignite, due to the lower ash content. 4. PETROLEUM WASTE AND BIOMASS CO-COMBUSTION IN FLUIDISED BED A research programme was performed for the development of a technology for the co-combustion of petroleum waste and biomass (sawdust) in fluidised bed. The tests were performed on a 100 kW experimental plant and allowed to obtain the data regarding the mixture combustion. The results of the combustion trials allowed the establishment of the characteristics and combustion parameters of the co-combustion of biomass and petroleum wastes with high efficiency



and low pollutant emission. The research programme lead to the identification and development of technical solutions of systems and auxiliary components including fuel preparation and feeding system. 4.1. The 100 kW fluidised bed combustion experimental plant The 100 kW fluidised bed combustion experimental plant (Figure 3) is fitted with air box, fuel (coal. Biomass, petroleum wastes) and limestone feeding systems, recirculation system, cyclone, ash evacuation system, convective pass and an operating parameters measuring system. The furnace, with an internal diameter of 219 mm at the bottom and 245 mm at top, is constructed from 7 parts and has a height of 3120. The experimental plant construction was adopted in such a way in order to be able to use the plant for gasification, stationary and circulating fluidised bed combustion, biomass and different waste combustion. Two of the furnace parts are cooled with water to keep the temperature in furnace at the desired level.

1. furnace; 2. cyclone; 3. Convective pass; 4. recirculation loop; 5. Ash cooler; 6. Air preheater; 7. bunkers; 8. Secondary air inlet

Figure 3: FBC Experimental Plant The coal, petroleum waste and limestone feeding systems comprise storage bunkers fitted at the bottom with screw feeders. The screw feeders use continuous current electric motors to allow a speed variation an easier control of the fuel flows. For the control and study of the combustion and desulphurisation processes, the experimental facility is equipped with apparatus for the measurement of operating parameters: flue gas, air and water temperatures, the pressure and pressure drop in the facility, air, flue gas, fuel and limestone flows. The experimental facility could operate with different air, fuel and limestone flows through the utilisation of variable voltages. The plant heat-up is made through the use of a natural gas burner with a separate combustion chamber, which provides hot air for fuel ignition. The measured operating parameters with specialised devices are visualised and stored with a data acquisition system through an electronic interface connected to a computer. 4.2. Combustion tests The experiments and combustion tests for the co-combustion of biomass and petroleum sludge (Table 3) were performed on the 100 kW fluidised bed combustion experimental plant for the establishment of the behaviour, combustion condition and process characteristics. Table 3: Petroleum sludge and biomass analysis

Fuel WtI AI Vi HI CI Sc

I LHV [%] [%] [%] [%] [%] [%] KJ/kg

Petroleum sludge 19.46 32.52 30.35 4.45 32.85 0.71 13,390 Biomass 9.60 0.31 75.17 5.86 45.29 0.25 17,145



The combustion trials established a solution for the utilisation of a mixture of petroleum sludge and biomass (10 – 50 % weight) that was very adequate for this type of petroleum waste. The combustion experiments were performed after complete tests related to the mixing and feeding facility. The fuel ignition and the bed heat-up were obtained using a natural gas burner, as presented before. The necessary air for the burner is provided through separate air ducts, and then introduced in the furnace, in the air box, below the grate. The temperature was continuously monitored. After the temperature in the furnace reaches 250 – 300 ˚C, the mixture started to be fed into the furnace. After starting the fuel feeding, the natural gas burner was shut down. During tests, the concentrations of the pollutant emissions were monitored: CO, NO2, and SO2 using a gas analyser. A very low pollutant emission was maintained, with the following values: SO2 between 0 – 300 ppm, NOx between 120 – 150 ppm and CO emissions between 350 – 760 ppm.

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Figure 3: Main temperatures for biomass and

petroleum sludge combustion – test 1

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Figure 4: Main temperatures for biomass and petroleum sludge combustion – test 2

The temperature variation in Figure 4 and Figure 5 is mainly due to the air flow and fuel flow which were varied to obtain an optimum operating system, as well as for studying the influence of different factors on the combustion process. The combustion diagrams revealed, after the sludge and biomass ignition in the furnace, a quite steady temperature level, over 800 - 900 and even 950 °C. The combustion process was further improved through the increase of the secondary air inlet, leading to a very high decrease of the CO emission level, improvement that was also noticed when looking to the flue gas at the stack exit, which became much less perceptible. The experiments on the experimental plant were necessary for the establishment of the characteristics and combustion parameters in real operating conditions. They allowed the establishment of the adequate co-combustion technology for the implementation in Romania of industrial plants for petroleum sludge and biomass combustion for energy production. 5. CONCLUSIONS The results obtained in Romania in some SFBC thermal plants, in the conditions of an adequate maintenance and operation, were quite encouraging, such as the good results obtained in operation in Thermal Plant Motru. The implementation of fluidised bed combustion technology in Romania, considering the obtained results in operation and experimental tests, is real possibility for the application of clean energy production technology through the valorisation of local coal resources. OVM-ICCPET has also performed a research programme for the development of a technology for the co-combustion of petroleum waste and biomass in fluidised bed. The tests performed on a 100 kW experimental plant, allowed to obtain the necessary data regarding the possibilities of combustion of the mixture for energy production. The research programme lead to the identification and development of technical solutions of the systems and auxiliary components of the plant, including the fuel preparation and feeding system. Combustion tests have been performed for the development of a technology for the co-combustion of petroleum waste and biomass in fluidised bed. The tests performed on a 100 kW experimental plant, allowed to obtain the necessary data regarding the possibilities of combustion of the mixture for energy production.


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