Experimental research on agglomeration in straw-fired fluidized beds

Agglomeration is a major problem in straw combustion in a fluidized bed. This paper presents the results of rice straw combustion experiments carried out under different operating conditions in a bubble-fluidized bed (BFB). The influences of bed material size and type, feeding mode, temperature, and fluidization number on agglomeration were discussed, and the mode of alkali accumulation in the bed was analyzed. The results indicated that low bed temperature, short fuel in-bed residence time, high fluidization number, and small bed material particles are conducive to agglomeration prevention. Successful extended combustion in a small BFB and in a bench-scale circulating fluidized bed was carried out without agglomeration under selected parameters. This work suggests the possibility for combusting high-alkali straw using fluidization technology.     

Reactivity tests of the water–gas shift reaction on fresh and used fluidized bed materials from industrial DFB biomass gasifiers

The dual fluidized bed gasification process, offers various advantages for biomass gasification as well as the utilization of other solid feedstocks. In order to improve the knowledge of the reactions in fluidized bed gasifier, different types of bed material used in the gasifier were tested in a micro-reactivity test rig. It has been previously observed that during long-term operation, the surface of the bed material used (calcined olivine) undergoes a modification that improves catalytic activity. The main reaction of interest is the water–gas shift reaction. Olivine taken from long-term operation at the 8 MW biomass gasifier at Güssing (Austria), fresh olivine as a reference, and calcite, which is commonly used for enhancing in-bed catalytic tar reduction, were tested using the micro-reactivity test rig. Tests were carried out at temperatures of 800, 850, and 900 °C and space velocities of 40,000 to 50,000 h⁻¹ were applied. CO conversions of up to 61.5% were achieved for calcite. Used olivine showed a similar behavior, representing a large improvement compared to fresh olivine, which had CO conversion rates of less than 20%.     

降低流化床水煤气炉飞灰含碳量的方法与实验研究

介绍了降低流化床水煤气飞灰含碳量的方法及实验研究结果。实验研究包括在现场进行的飞灰停留时间的冷态实验以及在实验室进行的飞灰反应性的实验。     

A numerical model of a fluidized bed biomass gasifier

A one-dimensional, steady state, numerical model was developed for a fluidized bed biomass gasifier. The gasifier model consists of a fuel pyrolysis model, an oxidation model, a gasification model and a freeboard model. Given the bed temperature, ambient air flow rate and humidity ratio, fuel moisture content and reactor parameters, the model predicts the fuel feed rate for steady state operation, composition of the producer gas and fuel energy conversion. The gasifier model was validated with experimental results. The effects of major mechanisms (fuel pyrolysis and the chemical and the physical rate processes) were assessed in a sensitivity study of the gasification model. A parametric study was also conducted for the gasifier model. It is concluded that the model can be used for gasifier performance analysis.     

Integrating biomass gasification with solid oxide fuel cells: Effect of real product gas tars,fluctuations and particulates on Ni-GDC anode

The aim of this work was to experimentally assess the feasibility of feeding real biomass product gas to solid oxide fuel cells (SOFC) for efficient and clean power production. The impact of tars on Ni-GDC anode was the main focus of the experiments. Planar SOFC membranes were operated at two gasification sites: (a) autothermal fixed-bed downdraft gasifier and (b) allothermal bubbling fluidized bed gasifier. In all cases the gas was hot-cleaned from particulates, HCl and H₂S.     

Experimental analysis of biomass gasification with steam and oxygen

Parametric tests are performed on an indirectly heated, fluidized bed biomass gasifier. The test system allows feedstock, oxygen, nitrogen, and steam flow rates, and temperature to be controlled independently. Gas residence time, temperature, equivalence ratio, and steam:biomass ratio are varied, and product gas composition and select gasification parameters are evaluated and compared with theoretical predictions.     

Bench-scale bubbling fluidized bed systems around the world - Bed agglomeration and collapse: A comprehensive review

Thermochemical conversion by gasification process is one of the most relevant technologies for energy recovery from solid fuel, with an energy conversion efficiency better than other alternatives like combustion and pyrolysis. Nevertheless, the most common technology used in the last decades for thermochemical conversion of solid fuel through gasification process, such as coal, agriculture residues or biomass residues are the fluidized bed or bubbling fluidized bed system. For these gasification technologies, an inert bed material is fed into reactor to improve the homogenization of the particles mixture and increase the heat transfer between solid fuel particles and the bed material. The fluidized bed reactors usually operate at isothermal bed temperatures in the range of 700–1000 °C, providing a suitable contact between solid and gas phases. In this way, chemical reactions with high conversion yield, as well as an intense circulation and mixing of the solid particles are encouraged. Moreover, a high gasification temperature favours carbon conversion efficiency, increasing the syngas production and energy performance of the gasifier. However, the risk of eutectic mixtures formation and its subsequent melting process are increased, and hence the probability of bed agglomeration and the system collapse could be increased, mainly when alkali and alkaline earth metals-rich biomasses are considered. Generally, bed agglomeration occurs when biomass-derived ash reacts with bed material, and the lower melting temperature of ash components promotes the formation of highly viscous layers, which encourages the progressive agglomerates creation, and consequently, the bed collapse and system de-fluidization. Taking into account the relevance of this topic to ensure the normal gasification process operating, this paper provides several aspects about bed agglomeration, mostly for biomass gasification systems. In this way, chemistry and mechanism of bed agglomeration, as well as, some methods for in-situ detection and prediction of the bed agglomeration phenomenon are reviewed and discussed.     

流化床煤气化技术的工业应用

介绍了几种典型的流化床煤气化炉 ,重点阐述了一种自主开发的流化床水煤气发生炉的工艺、结构、水煤气的组成和污染物的排放等 ,分析了流化床煤气的特点并与流化床燃煤技术进行了比较。认为流化床煤气化技术的开发值得我国锅炉制造行业的重视。     

Characterization of particulate matter in the hot product gas from atmospheric fluidized bed biomass gasifiers

This study compares the characteristics of particulate matter (PM) in the hot product gas from three different atmospheric fluidized bed biomass gasifiers: a bubbling fluidized bed (BFB) gasifier, a circulating fluidized bed (CFB) gasifier, and an indirect BFB gasifier (the latter integrated with a CFB boiler). All gasifiers displayed a bimodal particle mass size distribution with a fine mode in the <0.5 μm size range and a coarse mode in the >0.5 μm size range. Compared with the mass concentration of the coarse mode the mass concentration of the fine mode was low in all gasifiers. For both the BFB and CFB gasifiers the fine-mode PM had a similar inorganic composition, indicating an origin from the ash and the magnesite bed material used in both gasifiers. In the indirect BFB gasifier the fine-mode PM was instead dominated by potassium and chlorine, and the tar fraction properties evoked tar condensation in the sampling system that affected mainly the fine-mode PM. The coarse-mode PM in the BFB gasifier was dominated by char fragments abraded from the pyrolyzed wood pellets. In the CFB gasifier the coarse-mode PM was mainly ash and magnesite bed material that passed through the process cyclone. In the indirect BFB gasifier the coarse-mode PM was mainly ash, probably originating both from the BFB gasifier and the CFB boiler.     

Chemical‐looping combustion — an overview and application of the recirculating fluidized bed reactor for improvement

This paper propose recirculating fluidized bed (RCFB) reactor for chemical‐looping combustion (CLC) to overcome some of the issues associated with the existing interconnected reactors arrangements like low residence time of bed material in the air reactor, high attrition of bed material in the cyclone separator, cluster formation in the air reactor, complex operation involving loop seals and high heat losses. RCFB has high solid circulation rate, long residence time, efficient fuel–oxygen carrier contact, low heat losses and low gas leak in between the reactors, as compared to the existing reactor configurations. A cold model study was performed on a Perspex made, semicircular, transparent RCFB reactor. A single RCFB reactor was operated in the alternate oxidation and fuel burning cycles to simulate the interconnected reactors arrangement for CLC. The generated experimental data has been used to predict the optimal RCFB reactor configuration for a RCFB‐based CLC power plant. Copyright © 2014 John Wiley & Sons, Ltd.     

Theoretical performance analysis of the multi‐stage gas–solid fluidized bed air preheater

The multi‐stage fluidized bed can be used to preheat the combustion air by recovering the waste heat from the exhaust gas from industrial furnaces. The dilute‐phase fluidized bed may be formed to exclude the excessive pressure drop across the multi‐stage fluidized bed. But, in this case, the solid particles do not reach to the thermal equilibrium due to relatively short residence time in each layer of fluidized bed. In this study, a theoretical analysis on the dilute phase multistage fluidized bed heat exchanger was performed. A parameter related to the degree of thermal equilibrium between gas and solid particles at the dilute‐phase fluidized beds was derived. Using this parameter, a relatively simple expression was obtained for the thermal efficiencies of the multi‐stage fluidized bed heat exchanger and air preheater. Copyright © 2001 John Wiley & Sons, Ltd.     

Production of hydrogen in an autothermal fluidized gasifier

Production of hydrogen has gained increasing importance because of its use as a clean fuel and also for various industrial uses. For this purpose a laboratory scale fluidized bed autothermal gasifier has been designed to gasify the solid carbonaceous materials with steam. The heat required for the steam-carbon reaction is provided by the partial oxidation of the hydrocarbon gases. Highly reactive carbonaceous materials like charcoal and lignite have been gasified with steam in the presence of a high temperature flame produced by the partial oxidation of acetylene/natural gas with oxygen. About 95% carbon gasification and 40% steam decomposition have been achieved. The product gases contain about 80% synthesis gas (carbon monoxide and hydrogen). Further investigations with non-caking high ash Indian coals and agricultural wastes are planned to be carried out.     

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．     

Co–gasification of coal/biomass blends in 50 kWe circulating fluidized bed gasifier

This paper reports gasification of coal/biomass blends in a pilot scale (50 kWe) air-blown circulating fluidized bed gasifier. Yardsticks for gasification performance are net yield, LHV and composition and tar content of producer gas, cold gas efficiency (CGE) and carbon conversion efficiency (CCE). Net LHV decreased with increasing equivalence ratio (ER) whereas CCE and CGE increased. Max gas yield (1.91 Nm³/kg) and least tar yield (5.61 g/kg of dry fuel) was obtained for coal biomass composition of 60:40 wt% at 800 °C. Catalytic effect of alkali and alkaline earth metals in biomass enhanced char and tar conversion for coal/biomass blend of 60:40 wt% at ER = 0.29, with CGE and CCE of 44% and 84%, respectively. Gasification of 60:40 wt% coal/biomass blend with dolomite (10 wt%, in-bed) gave higher gas yield (2.11 Nm³/kg) and H₂ content (12.63 vol%) of producer gas with reduced tar content (4.3 g/kg dry fuel).     

喷动流化床煤气化试验研究

以空气和水蒸汽为气化剂，在一内径为60mm的V型布风板喷动流化床工业煤气炉内对动力烟煤的气化进行了系统的试验研究，考察了V型布风板床料的流化特性，研究了操作参数对气化过程的影响，测量了煤气成分沿床高和径向的变化，分析了影响煤气成分和热值的有关因素，提出了合理的运行条件和参数，研究结果对工业装置的放大设计，改造现有燃烧设备并降低对环境的污污具有指导意义。     

生物质富氧气化特性的研究

富氧气化是先进的中热值气化方法之一，具有设备体积小，运行稳定等优点。从富氧气化的原理出发，分析氧气浓度，气化当量比等因素对气化结果的影响，并在实验的基础上，分析讨论提高了富氧气化经济性和实用性的途径，总结得到的循环流化床富氧气化的最佳运行条件：氧气浓度，气化当量比约０．１５。     

空气鼓风流化床煤部分气化炉煤气成分与热值试验

在内径100mm，高4．2m的常压流化床气化炉试验装置上进行试验，考察了气化炉温度，空煤比，汽煤比等影响因素对煤气成分和热值的影响，并对其气化机理进行了分析。结果表明，流化床煤部分气化炉内存在较佳气化温度，汽煤比和空煤比区域。图7表3参4     

温度对中试规模的喷动流化床煤部分气化行为的影响

在构建的热输入2MW的中试规模加压喷动流化床部分气化试验装置上,对徐州烟煤的加压部分气化行为进行了研究.重点考察了气化温度对煤气成分、煤气热值、碳转化率和煤气产率等气化指标的影响.研究结果表明,煤气各组分的浓度,特别是甲烷浓度对气化温度非常敏感,碳转化率和煤气产率随温度的升高而增加,在试验的温度区间内,温度对煤气热值影响不大.部分气化炉所产生的煤气和半焦的热值均满足第二代增压流化床联合循环发电系统的要求.     

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.     

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