Experimental study on coal multi-generation in dual fluidized beds

An atmospheric test system of dual fluidized beds for coal multi-generation was built.One bubbling fluidized bedis for gasification and a circulating fluidized bed for combustion.The two beds are combined with two valves:one valve to send high temperature ash from combustion bed to the gasification bed and another valve to sendchar and ash from gasification bed to combustion bed.Experiments on Shenhua coal multi-generation were madeat temperatures from 1112 K to 1191 K in the dual fluidized beds.The temperatures of the combustor are stableand the char combustion efficiency is about 98%.Increasing air/coal ratio to the fluidized bed leads to theincrease of temperature and gasification efficiency.The maximum gasification efficiency is 36.7% and thecalorific value of fuel gas is 10.7 MJ/Nm3.The tar yield in this work is 1.5%,much lower than that of pyrolysis.Carbon conversion efficiency to fuel gas and flue gas is about 90%.     

内循环流化床煤气化炉的试验研究和设计

介绍了一种内循环流化床煤气化炉，它由气化室和燃烧室组成，采用蒸汽和空气鼓风，可产生中热值煤气。在小型试验台上对运行参数和结构尺寸对物料循环的影响进行了试验，提出了合理的运行设计参数，并建立了颗粒通过水平孔口物料循环模型。在此基础上，进行100kg／h小型内循环流化床气化炉设计。图10表4参9     

Some theoretical aspects of mixing in the British coal twin-bed combustor/pyrolyser

British Coal, in collaboration with Senior Green Ltd., has incorporated a novel twin-bed coal-fired combustor into a 2.8 MW_t water tube boiler. The firing system comprises two interconnected shallow fluidized beds operated as a pyrolyser and a char combustor, respectively. Gas temperatures well in excess of bed temperatures are achieved when the hot gas streams from the two beds are mixed in a common chamber. Particular attributes of the system are high combustion intensity (without in-bed tubes), inherently low NO_x emission levels and wide turndown range (up to 10: 1). As part of the ongoing R&D programme, mathematical modelling techniques are being applied to provide a sound theoretical understanding of the physical and chemical processes occurring within the system. In order to assess the factors affecting scale-up of the twin-bed unit, Gloucestershire College of Arts and Technology (GLOSCAT), in collaboration with the Coal Research Establishment of British Coal, is currently developing a comprehensive mathematical model of the system. The paper describes one aspect of the system model, namely solids mixing. The application of simple analytic methods has been found useful to describe the process. Assuming uniform conditions in the vertical plane, mixing of coal and sand within a bed has been regarded as a diffusion process, and a system of ordinary differential equations have been established to predict carbon concentration and temperature profiles for each bed. Although a number of simplifying assumptions have been made, the models provide useful sensitivity analyses, allowing an assessment of the factors influencing scale-up, e.g. the effect of mixing rate and char particle size on temperature profiles. Analytic solutions are presented, and the sensitivity analyses are illustrated using standard computer graphics.     

A mathematical model for exit gas composition in a 10 MW fluidized bed coal combustion power plant

A mathematical model has been developed for the oxygen mass balance for a 10 MW fluidized bed coal combustion power plant operated at Jamadoba (TISCO, India). Assuming the three phase theory of fluidization, the fluid bed is considered to consist of a number of equivalent stages in series. Within each stage, an exchange of gas takes place between the bubble, cloud-wake, and emulsion phases. An effective chemical reaction rate of char combustion has been derived considering the single film theory of char combustion for shrinking particles. The model has been used to predict the consumption of oxygen in the fluidized bed combustor, the outlet gas composition, variation of oxygen concentrations in different phases and also the variation of average oxygen concentration along the bed height. Model predictions were compared with plant data, and reasonable accuracy was obtained.     

Experiments on chemical looping combustion of coal with a NiO based oxygen carrier

A chemical looping combustion process for coal using interconnected fluidized beds with inherent separation of CO₂ is proposed in this paper. The configuration comprises a high velocity fluidized bed as an air reactor, a cyclone, and a spout-fluid bed as a fuel reactor. The high velocity fluidized bed is directly connected to the spout-fluid bed through the cyclone. Gas composition of both fuel reactor and air reactor, carbon content of fly ash in the fuel reactor, carbon conversion efficiency and CO₂ capture efficiency were investigated experimentally. The results showed that coal gasification was the main factor which controlled the contents of CO and CH₄ concentrations in the flue gas of the fuel reactor, carbon conversion efficiency in the process of chemical looping combustion of coal with NiO-based oxygen carrier in the interconnected fluidized beds. Carbon conversion efficiency reached only 92.8% even when the fuel reactor temperature was high up to 970 °C. There was an inherent carbon loss in the process of chemical looping combustion of coal in the interconnected fluidized beds. The inherent carbon loss was due to an easy elutriation of fine char particles from the freeboard of the spout-fluid bed, which was inevitable in this kind of fluidized bed reactor. Further improvement of carbon conversion efficiency could be achieved by means of a circulation of fine particles elutriation into the spout-fluid bed or the high velocity fluidized bed. CO₂ capture efficiency reached to its equilibrium of 80% at the fuel reactor temperature of 960 °C. The inherent loss of CO₂ capture efficiency was due to bypassing of gases from the fuel reactor to the air reactor, and the product of residual char burnt with air in the air reactor. Further experiments should be performed for a relatively long-time period to investigate the effects of ash and sulfur in coal on the reactivity of nickel-based oxygen carrier in the continuous CLC reactor.     

循环流化床锅炉燃煤着火特性

在电加热的小型流化床燃烧系统上,采用热烟气炉下点火方式研究了7个煤种的着火点,并分析了粒径、床温、挥发分、水分等因素对着火特性的影响．提出了煤颗粒在流化床内着火点测定的实验规范,并在TGA上测量着火点,与实际电厂锅炉投煤温度进行了比较．结果表明,在流化床实验台上测得的着火温度可以通过修正来表示实际锅炉上的投煤温度．     

Experimental Study on Oxy-Fuel Combustion and NO Emission in a Spouted-Fluidized Bed with under Bed Feeding

The spouted-fluidized bed is modified from the classical fluidized bed device, which combines the features of spouted and fluidized beds. In the present work, the performance of oxy-fuel spouted-fluidized bed combustion with under bed feeding and its effect on NO emission were systematically investigated. The results revealed that it was feasible to use a spouted-fluidized bed combustor for oxy-fuel combustion with real flue gas recycling. The transition from air combustion to oxy-fuel combustion was smooth and the concentration of CO_2 in the flue gas could be as high as 90% steadily(dry base). Increasing the reaction temperature exhibited a negative effect on NO emission. Compared with that under the shallow bed, the concentration of NO in the flue gas was lower under the deep bed condition. Besides, the utilization of crush particles was favorable for suppressing NO emission because of the promoted mixing between coal particles and solid bed materials. Furthermore, the addition of limestone was proven to undesirably increase the NO emission during oxy-fuel spouted-fluidized bed combustion.     

增压流化床锅炉床下点火启动过程的研究与应用

分别在实验室规模常压模拟增压流化床燃烧室和１５ＭＷｅ ＰＦＢＣ－ＣＣ联合循环中试电站６０ｔ／ｈ蒸 发量的ＰＦＢＣ锅炉上进行了增压流化床锅炉床下点火启动特性的试验研究和应用实践．试验了热烟气点 燃流化床的煤种适应性;研究了加煤床温、埋管受热面、热烟气温度和流化风量等参数对床层冷启动和热 启动过程的影响规律．验证了为增压流化床锅炉设计的启动系统中带有气封结构风室的可靠性和烟气分 布的均匀性。考察了增压流化床在深床运行中实施压火后,能再次热启动的条件及所需的燃油量和煤量 的变化。将热烟气床下点火技术和热烟气与主燃风的同风室结构应用于中国第一座ＰＦＢＣ－ＣＣ中试电站, 取得了点火过程稳定可靠和安全的效果．     

Modeling and countermeasures of combustion characteristics of char particles in CFBC

INTRAODUCTIONAsahigh-efficiencyandcleancoalcombustiontechnology,circulatingfluidizedbed(CFB)combustiontechnologyachievesrapiddevelopmentinChinaforburningvariouslow--gradefuels.ThescalerupofCFBboilersbecomesakeypointconcernedbytheCFBboilerdesigners.At...     

双燃料煤粉流化床复合燃烧锅炉的物质平衡与热量平衡

本文分析了双燃料粉流化床复事燃烧锅炉的物质平衡及热量平衡,得到了炉腔及空气预热器的物质平衡方程,沸腾层及煤粉炉膛的热平衡方程主炉膛出口过量空气系数,锅炉气体及未完全热损失,固体未完全损失的计算公式。     

粉煤流化床燃烧_PC_FBC_炉膛烟温试验研究

针对新型高效、清洁煤燃烧方式,即粉煤流化床（ＰＣ－ＦＢ）,在一座０．３ＭＷ的试验台上,系统而详细地研究了ＰＣ－ＦＢ炉膛空间烟气温度的分布特性。主要研究内容包括：ＰＣ－ＦＢ炉膛空间内烟流的稳定性与均匀性;床层温度、流化速度、床料的平均粒径、二次风率、二次风的投入位置对炉膛内烟温分布的影响,并总结出合理的炉膛烟温分布。     

The devolatilization of coal and a comparison of chars produced in oxidizing and inert atmospheres in fluidized beds

This is a study of the devolatilization of coal in a laboratory-scale bed of silica sand, fluidized with either air or N₂ and electrically heated to 750 or 900°C. Coal particles (diameter 1.4–1.7 or 2.0–2.36 mm) were fed in batches to the surface of the bed and allowed to devolatilize in either an oxidizing atmosphere of air or inert N₂. In the first case, combustion of the volatiles occurred, but there was only thermal decomposition (pyrolysis) in the second situation. The resulting chars were recovered and analyzed for composition and structure, so that comparisons could be made between the effects of devolatilization with combustion and of pyrolysis in an inert atmosphere. It was found that the fractions of C and H in the char were only slightly sensitive to the type of fluidizing gas used. The amount of nitrogen in the recovered char and also the devolatilization time showed no dependence on the type of fluidizing gas, whereas BET areas were slightly larger after combustion in air. It is concluded that these effects are small relative to other errors, inherent in experiments on coal combustion, so that chars prepared in a bed fluidized by hot N₂ are very similar to those formed during coal combustion at nominally the same temperature. Equally, the overall composition of the volatile matter released during combustion in a fluidized bed is the same as in pyrolysis in nitrogen. The effects of other parameters, such as the temperature of the bed, the flow rate of the fluidizing gas and the size of the coal particles are also discussed in detail. It is concluded that most of the volatiles burn in a fluidized bed (at or less than 900°C) far away from the original coal particle. Also, NO_x is in effect a primary product of devolatilization, being produced in appreciable amounts when coal is heated in inert N₂. The ratio of C/N in the volatiles is found to be a constant during the latter stages of devolatilization, but beforehand at lower temperatures, carbon species are preferentially released. Overall, devolatilization of small particles (< 2.4 mm) in a fluidized bed at 900°C is kinetically controlled. The activation energy is small, being 15 ± 6 kJ/mol.     

116MW水冷方形分离循环流化床热水锅炉的运行经验

城市燃煤集中供暖对洁净燃烧技术的需求是循环流化床热水锅炉发展的动力。介绍了首台运行的最大容量的116MW循环流化床热水锅炉的运行情况。实践表明：采用水冷方形分离器的116MW循环流化床热水锅炉运行稳定,可用率高,燃烧效率高,满足严格的大气排放标准,密封性好,占地面积小,可以很好地适应城市集中供暖频繁启动和压火的需要。图6表5参6     

褐煤在鼓泡流化床和循环流化床燃烧的汞迁移试验研究

对褐煤在小型电加热鼓泡流化床和小型电加热循环流化床中燃烧时的汞迁移特性进行了对比试验研究,重点考察了不同燃烧工况对汞迁移特性的影响。试验结果表明,炉膛温度和给煤量增加,鼓泡流化床和循环流化床的烟气总汞HgT均增加,飞灰颗粒汞含量Hg(p)均减少,并且循环流化床的烟气总汞HgT值均低于相同燃烧工况的鼓泡流化床值,循环流化床的飞灰颗粒汞含量Hg(p)值均高于相同燃烧工况的鼓泡流化床的值;流化风速增加,循环流化床的烟气总汞HgT减少,飞灰颗粒汞含量Hg(p)增加,鼓泡流化床烟气总汞HgT增加,飞灰颗粒汞含量Hg(p)减少。     

Description,applications and numerical modelling of bubbling fluidized bed combustion in waste-to-energy plants

The use of the fluidized bed combustor (FBC) has increased. It began in the 20th century as coal combustion and gasification, which then developed into catalytic reactions. Only recently, the application field has been extended to the incineration of biomass and pre-treated waste, for either power generation or waste disposal. The success of fluidized bed combustion is due to high combustion efficiency, great flexibility when it comes to the heating value of the fuel and reduction in pollutants emitted with the flue gas.     

流化床炉内温度场的虚拟表示

介绍了以VC^ 6．0为平台，结合Intra3D技术，研究流化床锅炉燃烧温度场的三维动态可视化虚拟表示．在流化床锅炉燃烧温度场的动态全面仿真的基础上，运用计算机图形学的理论和方法，利用数字仿真的大量数据，借助粒子运动系统的规律，建立流化床虚拟火焰，并实现动态显示和基本的人机交互，该技术的研究，可拓展热力系统性能研究的思路，弥补试验或中试研究投资大和周期长的不足，开拓出新型热力系统的虚拟再现研究手段。     

循环流化床中石油焦与煤混合燃烧SO2排放特性研究

在一座0．5MW1循环流化床热态试验装置上进行了石油焦与煤混合燃烧试验，研究了烟气中SO2的排放特性．对于石油焦与煤不同燃料配比，不同锅炉运行参数，如过量空气系数、床温、一次风率、Ca／S比等对烟气中SO2排放浓度的影响规律进行了研究．试验表明：对不同配比的燃料，随过量空气系数和一次风率的增大，SO2排放浓度降低；对于床温有一最佳温度，其SO2排放浓度最低；随Ca／S增大，SO2排放浓度降低。     

Gasification of lignocellulosic biomass in fluidized beds for renewable energy development: A review

A literature review on gasification of lignocellulosic biomass in various types of fluidized bed gasifiers is presented. The effect of several process parameters such as catalytic bed material, bed temperature and gasifying agent on the performance of the gasifier and quality of the producer gas is discussed. Based on the priorities of researchers, the optimum values of various desired outputs in the gasification process including improved producer gas composition, enhanced LHV, less tar and char content, high gas yield and enhanced carbon conversion and cold gas efficiency have been reported. The characteristics and performance of different fluidized bed gasifiers were assessed and the obtained results from the literature have been extensively reviewed. Survey of literature revealed that several industrial biomass gasification plants using fluidized beds are currently conducting in various countries. However, more research and development of technology should be devoted to this field to enhance the economical feasibility of this process for future exploitations.     

A proposed scheme for coal fired combined cycle and its concise performance

For IGCC, the primary investment is too high due to the demand of high gasification efficiency. For PFBCC, the thermal efficiency is too low due to the relatively low turbine inlet temperature and the hot working medium of the gas turbine is not easy to clean. A new scheme is proposed for coal fired combined cycle to overcome the main drawbacks of IGCC and PFBCC. The research targets are developing a new cycle construction of coal fired combines cycle to raise the efficiency and reduce the primary investment. Actually, the new scheme is a synthesis of some existing proposals. It adopts partial gasification to reduce the primary investment of the gasification equipment. The un-gasified surplus solid is then feed to a pressurized fluidized bed boiler, but adopting Curtiss Wright type external combustion to lower the ash content in the working medium. The gas fuel from the partial gasifier is combusted in a top combustor to further increase the working medium temperature. An extremely concise performance estimation method for the new scheme and its equations is proposed in order to easily understand the basic physical meaning of the new system. Some typical calculations based on this concise method are given. Then, a more detailed computation is accomplished with Aspen Plus code. The basic feasibility of this scheme is proven to be favorable. The efficiency is higher than the existing coal fired IGCC plants. The advantage of the new scheme comes from the better utilization of coal energy. Almost all the energy of coal is first utilized in the top cycle, and then the bottom cycle, just like the gas fueled combined cycle does. The primary investment is lower than the ordinary IGCC due to the lack of air separation unit and the adoption of partial gasification. The ash content is much lower than that of the existing PFBCC plants. If no any harmful ash in working medium is required, the atmospheric fluidized bed can be applied rather than the pressurized fluidized bed. A similar proposal with atmospheric fluidized bed and its performance estimation are also given. However, its efficiency will be lower than the pressurized fluidized bed scheme.     

Physicochemical properties and gasification reactivity of the ultrafine semi-char derived from a bench-scale fluidized bed gasifier

Zhundong coalfield is the largest intact coalfield worldwide and fluidized bed gasification has been considered as a promising way to achieve its clean and efficient utilization.The purpose of this study is to investigate the physieochemical properties and gasification reactivity of the ultrafine semi-char,derived from a bench-scale fluidized bed gasifier,using Zhundong coal as fuel.The results obtained are as follows.In comparison to the raw coal,the carbon and ash content of the semi-char increase after partial gasification,but the ash fusion temperatures of them show no significant difference.Particularly,76.53％ of the sodium in the feed coal has released to the gas phase after fluidized bed gasification.The chemical compositions of the semi-char are closely related to its particle size,attributable to the distinctly different natures of diverse elements.The semi-char exhibits a higher graphitization degree,higher BET surface area,and richer meso-and macropores,which results in superior gasification reactivity than the coal char.The chemical reactivity of the semi-char is significantly improved by an increased gasification temperature,which suggests the necessity of regasification of the semi-char at a higher temperature.Consequently,it will be considered feasible that these carbons in the semi-char from fluidized bed gasifiers are reclaimed and reused for the gasification process.