The co-firing of biomass and coal plays an important role in increasing the biomass power capacity and reducing greenhouse gas (GHG) emissions. The challenges of the large percentage biomass co-firing (over 20% on energy basis) in existing pulverized coal boilers are keeping the same steam parameters and having a high boiler efficiency and a stable operating. The primary goal of this thesis is to develop a combustion concept for coal-fired boilers to enablea large percentage of biomass co-firing with up to a 100% fuel switch; these changes should increase the combustion efficiency, reduce CO2  and NOx emissions, improve the process efficiency, while maintaining the same steam parameters after switching fuels. To achieve these goals,  a  typical  biomass  pretreatment technology  called  torrefaction  has  been  employed to upgrade  the  biofuel  quality  in  terms  of  both  energy  density  and  chemical  properties. Consequently, a torrefaction based co-firing system has been proposed. In addition, a novel biomass combustion method called volumetric combustion has been designed; this process involves intense mixing and flue gas internal recirculation inside the combustion chamber, increasing the residence time of the biomass particles and making the temperature and gas species more uniform. In this thesis, a series of studies based on experiments, CFD modelling, and process simulations have been performed. First, the raw material was palm kernel shells (PKS) that were torrefied over same residence time but at different temperatures in a laboratory-scale torrefaction reactor, producing three torrefied biomasses with different degrees of torrefaction. The devolatilization kinetics and char oxidation kinetics were determined based a series of high-temperature high-heating-rate tests in an isothermal plug flow reactor (IPFR), the obtained kinetic parameters were adopted for CFD modeling. Continually, the numerical investigations on the flame properties of the torrefied biomass and a 220 MWe coal-fired boiler performance were conducted, to understand the predicted results of the coal-fired boiler performance at varying biomass co-firing ratios. Afterward, analyses of the impacts of the degree of torrefaction and the biomass co-firing ratio on process operation, performance and electricity efficiency of a torrefaction based co-firing power plant were performed. Finally, the properties of the pollutants emitted from biomass volumetric combustions under various combustion modes and co-firing ratios were studied using Aspen Plus. According to the results, the following conclusions can be reached: 1) a high heating rate enhances the yields of the volatiles for biomass devolatilization processes with the same final temperature; 2) the enhanced drag force on the biomass particles causes a late release of volatile matter and delays the ignition of the fuel-air mixture. Furthermore, oxidizers with lower oxygen concentrations normally generate larger flame volumes, lower peak flame temperatures and lower NO emission; 3) the co-firing simulation reveals that a boiler load reduction of less than 10% is observed when firing 100% torrefied biomass; 4) deep torrefaction is not recommended because the energy saved during biomass grinding is lower than that consumed by the additional torrefaction process; the electrical efficiency of power plant is reduced when increasing either the degree of torrefaction or the biomass substitution ratio; 5) the amount of flue gas that needs to be recycled for NOx reduction decreased when the percentage of co-fired biomass increased. Overall, from the perspective of combustion, both the torrefaction process and volumetric combustion are promising steps toward realizing large percentage biomass co-firing in coal-fired boilers with high efficiency and reduced emissions. / <p>QC 20140130</p>

This master thesis describes the co-firing concept, benefits and opportunities of pretreated biomass in pulverized coal boilers for industrial use. Burning fossil fuels, i.e. coal is under immense political pressure as European Union (EU) and other countries are trying to bring down the CO2 emission. Biomass combustion is already a proven technology and it plays a greater role in reducing CO2 emission. The main objective of this thesis is the brief study of computational fluid dynamics (CFD) modelling to examine the co-firing of greater amount of pretreated biomass and pulverized coal in a 200MWe pulverized coal boiler. Here, we exchange around 50 % of existing fuel in pulverized coal boiler with torrefied biomass. Torrefied biomass aids to increase the efficiency of existing coal boiler and cut down the CO2 emission. In this work, two cases of co-firing of pretreated biomass and coal have been investigated by CFD. Firstly, an experimental work was done in a laboratory scale to have few different types of torrefied biomass with different degrees of torrefaction. The devolatilization kinetics and char oxidation kinetics were also determined by experiments and other parameters have been calculated. One important aspect of this work has been to evaluate the performance of torrefaction based co-firing. Therefore, co-firing case has been compared to the 100 % coal feed case to understand the performance of torrefaction based co-firing. Furthermore, fluid flow, particles trajectories, heat transfer, and different emission behaviors have been studied. In addition, mechanisms of corrosion during co-firing have been studied and a guideline has been provided for corrosion model for analyzing the characteristics of alkali metals and their effects in co-firing coal boiler. The outcome from the CFD simulation indicated that boiler efficiency increases and the net CO2 emission reduced with increasing the biomass percentage in the co-firing system.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21373号 / 工博第4532号 / 新制||工||1706(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 前 一廣, 教授 河瀬 元明, 教授 佐野 紀彰 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Co-firing is a combustion process in which more than one type of fuel is used. In many cases, co-firing reduces fuel costs and/or reduces the environmental impact. The objective of this research was to test the hypothesis that adding biogas to be co-fired with biomass in a traditional cookstove reduces indoor air pollution and increases the combustion efficiency. The impact of co-firing on indoor air pollution is assessed by comparing the concentrations of carbon monoxide and particulate matter in the exhaust stream of a co-fired cookstove to a cookstove fueled with biomass alone. The concentrations of each of these pollutants were measured using a portable emissions monitoring system. Combustion efficiency is defined as the ratio of energy released by combustion to energy in the fuel. Instead of combustion efficiency, the impact of co-firing was assessed on the modified combustion efficiency, which is defined as CO2/(CO2+CO) on a molar basis. This is because CO and CO2 concentrations can be measured. In addition, the impact of cofiring on other parameters such as thermal efficiency, specific fuel consumption rate, and specific emission of CO, CO2, and PM were assessed. Previous investigation of biomass combustion in traditional cookstoves indicates that power harvested using a thermoelectric generator can be used to drive a fan and increase the amount of air flowing into the combustion zone. The impact of using a fan on indoor air pollution and combustion efficiency was also assessed. It was found that co-firing biomass with optimum amount of biogas reduced the emission of CO by 32 % and PM by 33 % and increased the modified combustion efficiency by 1.3 %. It was found that using a fan reduced the emission of CO by 35 % and PM by 39 % and increased the modified combustion efficiency by 1.1 %. Finally, the combination of co-firing and use of a fan reduced the emission of CO by 58 % and PM by 71 % and increased the modified combustion efficiency by 2.8 %.

No description available.

A preservação ambiental e o uso de combustíveis fósseis para geração de energia têm estimulado a realização de pesquisas na busca de alternativas para a redução das emissões de gases poluentes como CO2, CO, SO2 e NOx. O uso da biomassa em sistemas de co-combustão em leito fluidizado é mencionado como uma destas alternativas. O presente trabalho utilizou biomassa residual da indústria de extração de tanino, o Resíduo de Cascas de Acácia Negra (RCAN), em conjunto com carvão mineral da Mina de Candiota – RS com o objetivo de estudar a fluidodinâmica entre diferentes composições destes materiais em sistema de leito fluidizado com areia em escala de laboratório e em uma unidade piloto. Também foi realizada a avaliação dos parâmetros operacionais e das emissões dos gases gerados na co-combustão das misturas em planta piloto com reator de leito fluidizado borbulhante. Durante a fluidização no sistema de escala laboratorial, os valores da velocidade mínima de fluidização, Umf, variaram consideravelmente com o aumento da concentração de RCAN no leito em relação à fluidização utilizando-se somente o carvão mineral Da mesma forma, a queda de pressão, ΔP, diminuiu com o aumento da concentração da biomassa no leito. Nas operações de co-combustão em planta piloto, as misturas de carvão mineral e RCAN necessitaram de menores porcentagens de excesso de ar (99,7% a 65,2%) no reator em comparação à queima apenas de carvão mineral (108,4% a 107,5%) para que se atingisse a temperatura de operação do leito. Em particular, a condição de maior quantidade de biomassa na alimentação pode se observar a menor porcentagem de excesso de ar (50,8%). Ainda, a co-combustão do RCAN com carvão mineral favoreceu a diminuição das concentrações de SO2 nos gases gerados em mais de 90%, mantendo as emissões em níveis aceitáveis conforme os limites de emissão estabelecidos pela resolução CONAMA Nº 436, de 22/12/2011 e Resolução SEMA Nº 016 de 2014. / The environmental issues brought by the use of fossil fuels for power generation have led to the development of research in the exploration for alternatives to reduce emissions of greenhouse gases or pollutants such as CO2, CO, SO2, and NOx. The biomass use in cofiring systems with fluidized bed has been mentioned as one of these alternatives. The present work used biomass waste from tannin extraction industry, Black Wattle Bark Waste (BWBW), jointly with coal for the purpose of studying the fluid dynamics biomass mixtures with coal and sand in different proportions of the materials in laboratory scale fluidized bed system. Also, operational parameters and emissions generated in a cofiring pilot plant with bubbling fluidized bed reactor were evaluated. The fluidization tests performed on a bench scale showed that the values of the minimum fluidization velocity, Umf, varied considerably with increasing concentration of BWBW compared with the fluidization of coal. Likewise, the pressure drop through the bed, ΔP, decreased with increasing concentration of biomass in the bed. In the cofiring operations, coal and mixtures BWBW required smaller percentages of excess air in the reactor (99,7% a 65,2%) in comparison with the pure coal (108,4% a 107,5%) burning to obtaining the bed operating temperature. The burning of the mixture with higher amounts of biomass in the reactor feed had the lowest percentage of excess air (50.8%). It was also evidenced a decrease of SO2 generation in more than 90% for the flue gas generated in the coal with BWBW cofiring keeping emissions at acceptable levels in comparison with emission limits of current legislation CONAMA Nº 436, from 22/12/2011 and legislation SEMA Nº 016 of 2014.

A preservação ambiental e o uso de combustíveis fósseis para geração de energia têm estimulado a realização de pesquisas na busca de alternativas para a redução das emissões de gases poluentes como CO2, CO, SO2 e NOx. O uso da biomassa em sistemas de co-combustão em leito fluidizado é mencionado como uma destas alternativas. O presente trabalho utilizou biomassa residual da indústria de extração de tanino, o Resíduo de Cascas de Acácia Negra (RCAN), em conjunto com carvão mineral da Mina de Candiota – RS com o objetivo de estudar a fluidodinâmica entre diferentes composições destes materiais em sistema de leito fluidizado com areia em escala de laboratório e em uma unidade piloto. Também foi realizada a avaliação dos parâmetros operacionais e das emissões dos gases gerados na co-combustão das misturas em planta piloto com reator de leito fluidizado borbulhante. Durante a fluidização no sistema de escala laboratorial, os valores da velocidade mínima de fluidização, Umf, variaram consideravelmente com o aumento da concentração de RCAN no leito em relação à fluidização utilizando-se somente o carvão mineral Da mesma forma, a queda de pressão, ΔP, diminuiu com o aumento da concentração da biomassa no leito. Nas operações de co-combustão em planta piloto, as misturas de carvão mineral e RCAN necessitaram de menores porcentagens de excesso de ar (99,7% a 65,2%) no reator em comparação à queima apenas de carvão mineral (108,4% a 107,5%) para que se atingisse a temperatura de operação do leito. Em particular, a condição de maior quantidade de biomassa na alimentação pode se observar a menor porcentagem de excesso de ar (50,8%). Ainda, a co-combustão do RCAN com carvão mineral favoreceu a diminuição das concentrações de SO2 nos gases gerados em mais de 90%, mantendo as emissões em níveis aceitáveis conforme os limites de emissão estabelecidos pela resolução CONAMA Nº 436, de 22/12/2011 e Resolução SEMA Nº 016 de 2014. / The environmental issues brought by the use of fossil fuels for power generation have led to the development of research in the exploration for alternatives to reduce emissions of greenhouse gases or pollutants such as CO2, CO, SO2, and NOx. The biomass use in cofiring systems with fluidized bed has been mentioned as one of these alternatives. The present work used biomass waste from tannin extraction industry, Black Wattle Bark Waste (BWBW), jointly with coal for the purpose of studying the fluid dynamics biomass mixtures with coal and sand in different proportions of the materials in laboratory scale fluidized bed system. Also, operational parameters and emissions generated in a cofiring pilot plant with bubbling fluidized bed reactor were evaluated. The fluidization tests performed on a bench scale showed that the values of the minimum fluidization velocity, Umf, varied considerably with increasing concentration of BWBW compared with the fluidization of coal. Likewise, the pressure drop through the bed, ΔP, decreased with increasing concentration of biomass in the bed. In the cofiring operations, coal and mixtures BWBW required smaller percentages of excess air in the reactor (99,7% a 65,2%) in comparison with the pure coal (108,4% a 107,5%) burning to obtaining the bed operating temperature. The burning of the mixture with higher amounts of biomass in the reactor feed had the lowest percentage of excess air (50.8%). It was also evidenced a decrease of SO2 generation in more than 90% for the flue gas generated in the coal with BWBW cofiring keeping emissions at acceptable levels in comparison with emission limits of current legislation CONAMA Nº 436, from 22/12/2011 and legislation SEMA Nº 016 of 2014.

A preservação ambiental e o uso de combustíveis fósseis para geração de energia têm estimulado a realização de pesquisas na busca de alternativas para a redução das emissões de gases poluentes como CO2, CO, SO2 e NOx. O uso da biomassa em sistemas de co-combustão em leito fluidizado é mencionado como uma destas alternativas. O presente trabalho utilizou biomassa residual da indústria de extração de tanino, o Resíduo de Cascas de Acácia Negra (RCAN), em conjunto com carvão mineral da Mina de Candiota – RS com o objetivo de estudar a fluidodinâmica entre diferentes composições destes materiais em sistema de leito fluidizado com areia em escala de laboratório e em uma unidade piloto. Também foi realizada a avaliação dos parâmetros operacionais e das emissões dos gases gerados na co-combustão das misturas em planta piloto com reator de leito fluidizado borbulhante. Durante a fluidização no sistema de escala laboratorial, os valores da velocidade mínima de fluidização, Umf, variaram consideravelmente com o aumento da concentração de RCAN no leito em relação à fluidização utilizando-se somente o carvão mineral Da mesma forma, a queda de pressão, ΔP, diminuiu com o aumento da concentração da biomassa no leito. Nas operações de co-combustão em planta piloto, as misturas de carvão mineral e RCAN necessitaram de menores porcentagens de excesso de ar (99,7% a 65,2%) no reator em comparação à queima apenas de carvão mineral (108,4% a 107,5%) para que se atingisse a temperatura de operação do leito. Em particular, a condição de maior quantidade de biomassa na alimentação pode se observar a menor porcentagem de excesso de ar (50,8%). Ainda, a co-combustão do RCAN com carvão mineral favoreceu a diminuição das concentrações de SO2 nos gases gerados em mais de 90%, mantendo as emissões em níveis aceitáveis conforme os limites de emissão estabelecidos pela resolução CONAMA Nº 436, de 22/12/2011 e Resolução SEMA Nº 016 de 2014. / The environmental issues brought by the use of fossil fuels for power generation have led to the development of research in the exploration for alternatives to reduce emissions of greenhouse gases or pollutants such as CO2, CO, SO2, and NOx. The biomass use in cofiring systems with fluidized bed has been mentioned as one of these alternatives. The present work used biomass waste from tannin extraction industry, Black Wattle Bark Waste (BWBW), jointly with coal for the purpose of studying the fluid dynamics biomass mixtures with coal and sand in different proportions of the materials in laboratory scale fluidized bed system. Also, operational parameters and emissions generated in a cofiring pilot plant with bubbling fluidized bed reactor were evaluated. The fluidization tests performed on a bench scale showed that the values of the minimum fluidization velocity, Umf, varied considerably with increasing concentration of BWBW compared with the fluidization of coal. Likewise, the pressure drop through the bed, ΔP, decreased with increasing concentration of biomass in the bed. In the cofiring operations, coal and mixtures BWBW required smaller percentages of excess air in the reactor (99,7% a 65,2%) in comparison with the pure coal (108,4% a 107,5%) burning to obtaining the bed operating temperature. The burning of the mixture with higher amounts of biomass in the reactor feed had the lowest percentage of excess air (50.8%). It was also evidenced a decrease of SO2 generation in more than 90% for the flue gas generated in the coal with BWBW cofiring keeping emissions at acceptable levels in comparison with emission limits of current legislation CONAMA Nº 436, from 22/12/2011 and legislation SEMA Nº 016 of 2014.

The topic of this diploma thesis is to design the co-firing of blast furnace gas and coke-oven gas. First, the stoichiometric calculation for the gas mixture was made. It is followed with the determination of basic measures of heating surfaces and with their thermal calculation. The part of the work is also the drawing documentation of the boiler.

The thesis aims at current issues of using renewable resources here in the Czech Republic, mainly on biomass co-firing with fossil fuels in large combustion plant. The introduction provides an overview of systems for biomass co-firing. Further the using of optimization for solution problem of integration biomass fuels into existing large combustion plants and planning its operation conditions is presented. The main point of this thesis lies in creating of a user interface for modeling and optimization tool. Its functionality will be proved by solving a case study involving the analysis of possibilities for replacing fossil fuels due to the limited availability of coal in the market.