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00548 Experimental and numerical assessment of NOx reduction and char burnout of various South African utility feedstocks
09 Experimental and numerical assessment of NO, 98100548 reduction and char burnout of various South African utility feedstocks Fortsch. D. er al. VDI-Ber., 1997, 1313, (Verbrennung und Feuerungen), 21-26. Five South African domestic coals were investigated with respect to both NO, reduction by air staging and char burnout. The char burnout experiments were conducted at Eskom using a drop tube furnace in order to adjust the parameters for the char combustion model which is currently used in the MOLOS 3D combustion code. Furthermore, the response of the aforementioned coals to air-staged combustion was investigated. The NO, tests were carried out at a 20 kW furnace at the Australian Combustion Technol. Center (ACTC). The behaviour of the tested coals varied significantly. In order to study the special behaviour of the coals. a new NO, model, tested against the experimental data, was applied for mathematical modelling using the AIOLOS code. Experimental research of pressurized coal 98100549 pyrolysis Xiong, Y. et al. Ranshao Kexue Yu JishLl. 1997, 3, (2) 135-142. (In Chinese) The paper studies the effects of pressures (101-1317 kPa) on the coal pyrolysis process under inertial atmosphere (Nz) and the process of coal particle devolatilization in different pressures. A pressurized thermogravimetric analyser was used to examine the effects of coal particle sizes on the process of coal pyrolysis devolatilization. Kinetic equations of pressurized coal pyrolysis are obtained, and a mathematical model of pressurized coal pyrolysis based on the kinetic equations is presented. The model calculation agreed with experimental results. Experimental study of coal combustion under 98/00550 fluidized bed conditions Weber, T. et al. DGMK Tagungsber., 1997, 9703. (Proceedings ICCS ‘97, Volume Z), 963-966. A laboratory-scale bubbling fluidized bed system was used to study the combustion behaviour of anthracite coals and Iignites. Carried out in batch mode, the experiments varied in fuel properties and combustion conditions. The global combustion rates and the char combustion kinetics were evaluated for the four fuels under investigation. An extended high temperature coal particle com98100551 bustion model Jones, J. M. er al. DGMK Tugungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 931-934. Coal combustion models currently use simplified devolatilization and combustion steps to meet present day computational limitations. However, the availability of more advanced computers make the use of more complicated steps possible, especially coal particle devolatilization and the use of more realistic char combustion processes. The present work is concerned with the development of a mathematical model which describes devolatilization, the formation of a mobile and plastic coal, and the subsequent formation of a porous char or cenosphere, and its loss of hydrogen atoms and carbonization. This process can be interpreted in terms of the properties of the initial coal and can be modelled to some extent by the FG-DVC code. Consideration is also given to the influence of the initial coal composition on subsequent NO, production. Flash pyrolysis of single coals 98100552 Kellerhoff, T. er al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 569-572. A small entrained flow reactor, where the particles were quickly heated to >lSOO”C, was used to investigate the influence of residence time and gas temperature on the pyrolysis of coal. The studies include the determination of the correct volatile matter content, the calculation of the N distribution between the residual char and the volatiles, the release rates and the ratio of NHs and HCN as intermediates for the NO, formation. The determination of the composition of pyrolysis gases by FTIR. CH4, CzH4, CO, and NHa were determined in the pyrolysis gas. The influence of the parameters on NHs formation is rather low and longer residence times implicate higher CO concentrations. However, the concentrations of CH4 and CzH4 do not permit further predictions. Fluidized-bed incineration of solid pellets: combus98100553 tion and co-combustion Saxena, S. C. Energy Conwrs. Mgmf. 1998, 39. (l/Z). 127-141. The author describes the IJIC experimental facility for combustion of materials in a fluidized-bed combustor. The combustion and co-combustion studies made in a heated inert bed of wood refuse-derived fuel, peanut-hull, paper, cellulose and cardboard pellets are reviewed and discussed. Coal and propane are used as auxiliary fuels. The emission of carbon monoxide in the flue gas is monitored and, for most conditions, its value is well within the Illinois Environmental Protection Agency limit. The carbon combustion efficiency values are found to be quite high (99.8 + percent) validating the thermal degradation capability of the fluidized-bed incinerator. Furthermore, the thermal combustion efficiencies are also equally high, which reinforces the concept of waste-to-energy generation.
Combustion
(burners, combustion
systems)
98100554 Formation and destruction mechanisms of nitrogen oxides during coal combustion in circulating fluidized beds Barrel, C. and Lecuyer. I. Collect. Notes Internes Dir. Etud. Rech.: Prod. Energ. (Hydra&., Therm. Nucl.), 1997, (97NB00055) l-237. (In French) NO, formation and decomposition in circulating fluidized combustion of coal was examined in a small-scale experimental unit. The unit was equipped with solids re-injection, under industrial conditions, in order to develop a numerical set of chemical reactions involving NO,. Using a laboratory-scale combustor, a model was developed to calculate NO, concentrations during coal combustion. The calculated NO and NzO concentrations wore correlated with experimental data independent of C-O ratio. The model could be modified by adding information on the solids distribution in the reactor, the particle energy balance, as well as the composition of the gas resulting from devolatilization. A refined numerical model was validated for Provence coal, and may be used in more significant numerical computer codes modelling hydrodynamics and combustion of a 250 MW unit. Formation of N2 in the fixed-bed pyrolysis of low 98/00555 rank coals and the mechanisms Wu, Z. and Ohtsuka, Y. Sehitan Kagaku Kaigi Happy0 Ronbunshu, 1996, 33, 205-208. (In Japanese) An increase in coal nitrogen conversion to NZ during the fixed bed pyrolysis of low rank coals accompanies increasing temperature in the range of hOO1200°C. At 1200°C it reaches 6%70%. In contrast, char nitrogen decreases with temperature. Nz formation is suppressed dramatically with demineralization by HCI washing, with the corresponding increase in char nitrogen, and mainly Fe- and/or Ca-containing species are removed from these coals. The addition of a nanophase iron catalyst promotes N: formation from the demineralized coals. Fe species inherently present in the ion-exchangeable forms were discovered to be responsible for the remarkable formation of Nz. The findings also show Nz arises mostly from iron-catalysed solid-phase reactions of char nitrogen and precursors. Fragmentation of coal particles at high temperature 98100556 environment Dacombe, P. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 923-926. An experimental study in a high-temperature drop tube furnace was performed with regard to the fragmentation nature of large, granular coal particles during combustion. The influence of furnace temperature, particle size and type of coal on the fragmentation of these particles was determined. The extent of fragmentation increased with an increase in furnace temperature, particle size and volatile matter content. This correlation was due to the strength of the coal particles and the thermal stress that the particle is subjected to as it is heated within the furnace. The mode of fragmentation varied with the coal type. Low and high-volatile coals tend to break up into a few large fragments only. Medium volatile coals tend to break up to produce a few large fragments and many small fragments. 98iOO557 Gas concentration profiles and NO, formation in circulating fluidized bed combustion Zhao, J. et al. Fuel, 1997, 76, (Y), 853-860. NO, formation and destruction reactions were experimentally studied to better understand their behaviour in circulating fluidized bed combustion. Both longitudinal and lateral gradients were measured for NO,, Oz, CO and CHI during combustion of solid fuels of differing reactivity in a CFBC pilot unit. Anthracitic, bituminous, sub-bituminous and lignitic coals and petroleum coke were tested as fuels. Significant lateral and longitudinal gradients of gaseous species were witnessed under all the conditions studied. NO, profiles were correlated to a large degree with those of oxygen and local char concentration, which in turn were coupled to the CFB hydrodynamics. NO, formation reactions are improved with high partial oxygen pressures at the unit’s base and in the char-lean core. Low oxygen partial pressures, however, favour NO, reduction in the solid-rich annulus and towards the top of the unit. When NO, formation and destruction are limited to the char, profiles are readily interpreted. The addition of volatile nitrogen makes the profiles considerably more complex. Depending on the percentage volatile matter of the fuel, limestone used for sulfur capture can augment or reduce overall NO, formation.
98lOOS58 Heavy metal emissions from a bituminous coal and lignite combustion Can, B. et oi. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 1063-1066. Combustion of a 7236 kcal/kg bituminous coal and a 5782 kcalika oowdered lignite was carried out in two industrial-scale boilers, The -4.65 MWt bituminous coal-fired system had a moving grate and 3.7 MW lignite-fired system had a stationary grate and bath of them are mechanical feed. The flue gases were monitored using a MRU 95/3CD gas analyser for Oz. CO, SOz, NO, and NOz. Particulate emissions were sampled using an Anderson Universal Sampler. The results are presented.
Fuel and Energy Abstracts
January 1998
47
Combustion
(burners, combustion
systems)
98100554 Formation and destruction mechanisms of nitrogen oxides during coal combustion in circulating fluidized beds Barrel, C. and Lecuyer. I. Collect. Notes Internes Dir. Etud. Rech.: Prod. Energ. (Hydra&., Therm. Nucl.), 1997, (97NB00055) l-237. (In French) NO, formation and decomposition in circulating fluidized combustion of coal was examined in a small-scale experimental unit. The unit was equipped with solids re-injection, under industrial conditions, in order to develop a numerical set of chemical reactions involving NO,. Using a laboratory-scale combustor, a model was developed to calculate NO, concentrations during coal combustion. The calculated NO and NzO concentrations wore correlated with experimental data independent of C-O ratio. The model could be modified by adding information on the solids distribution in the reactor, the particle energy balance, as well as the composition of the gas resulting from devolatilization. A refined numerical model was validated for Provence coal, and may be used in more significant numerical computer codes modelling hydrodynamics and combustion of a 250 MW unit. Formation of N2 in the fixed-bed pyrolysis of low 98/00555 rank coals and the mechanisms Wu, Z. and Ohtsuka, Y. Sehitan Kagaku Kaigi Happy0 Ronbunshu, 1996, 33, 205-208. (In Japanese) An increase in coal nitrogen conversion to NZ during the fixed bed pyrolysis of low rank coals accompanies increasing temperature in the range of hOO1200°C. At 1200°C it reaches 6%70%. In contrast, char nitrogen decreases with temperature. Nz formation is suppressed dramatically with demineralization by HCI washing, with the corresponding increase in char nitrogen, and mainly Fe- and/or Ca-containing species are removed from these coals. The addition of a nanophase iron catalyst promotes N: formation from the demineralized coals. Fe species inherently present in the ion-exchangeable forms were discovered to be responsible for the remarkable formation of Nz. The findings also show Nz arises mostly from iron-catalysed solid-phase reactions of char nitrogen and precursors. Fragmentation of coal particles at high temperature 98100556 environment Dacombe, P. et al. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2). 923-926. An experimental study in a high-temperature drop tube furnace was performed with regard to the fragmentation nature of large, granular coal particles during combustion. The influence of furnace temperature, particle size and type of coal on the fragmentation of these particles was determined. The extent of fragmentation increased with an increase in furnace temperature, particle size and volatile matter content. This correlation was due to the strength of the coal particles and the thermal stress that the particle is subjected to as it is heated within the furnace. The mode of fragmentation varied with the coal type. Low and high-volatile coals tend to break up into a few large fragments only. Medium volatile coals tend to break up to produce a few large fragments and many small fragments. 98iOO557 Gas concentration profiles and NO, formation in circulating fluidized bed combustion Zhao, J. et al. Fuel, 1997, 76, (Y), 853-860. NO, formation and destruction reactions were experimentally studied to better understand their behaviour in circulating fluidized bed combustion. Both longitudinal and lateral gradients were measured for NO,, Oz, CO and CHI during combustion of solid fuels of differing reactivity in a CFBC pilot unit. Anthracitic, bituminous, sub-bituminous and lignitic coals and petroleum coke were tested as fuels. Significant lateral and longitudinal gradients of gaseous species were witnessed under all the conditions studied. NO, profiles were correlated to a large degree with those of oxygen and local char concentration, which in turn were coupled to the CFB hydrodynamics. NO, formation reactions are improved with high partial oxygen pressures at the unit’s base and in the char-lean core. Low oxygen partial pressures, however, favour NO, reduction in the solid-rich annulus and towards the top of the unit. When NO, formation and destruction are limited to the char, profiles are readily interpreted. The addition of volatile nitrogen makes the profiles considerably more complex. Depending on the percentage volatile matter of the fuel, limestone used for sulfur capture can augment or reduce overall NO, formation.
98lOOS58 Heavy metal emissions from a bituminous coal and lignite combustion Can, B. et oi. DGMK Tagungsber., 1997, 9703, (Proceedings ICCS ‘97, Volume 2) 1063-1066. Combustion of a 7236 kcal/kg bituminous coal and a 5782 kcalika oowdered lignite was carried out in two industrial-scale boilers, The -4.65 MWt bituminous coal-fired system had a moving grate and 3.7 MW lignite-fired system had a stationary grate and bath of them are mechanical feed. The flue gases were monitored using a MRU 95/3CD gas analyser for Oz. CO, SOz, NO, and NOz. Particulate emissions were sampled using an Anderson Universal Sampler. The results are presented.
Fuel and Energy Abstracts
January 1998
47