生物质流化床气化炉气化过程的实验研究

在流化床生物质气化炉内 ,采用空气作气化剂 ,对七种农、林废弃物进行了气化实验研究。生成的燃气成分 :CO在 1 4 %～ 1 7%之间 ,H2 含量一般低于 1 0 % ,甲烷含量为 5%～ 1 0 %。燃气热值多数在 53 0 0～ 6 50 0 k J/ Nm3 ,气化效率 72 .6 %。实验结果表明 ,流化床生物质气化炉可用于生物质气化。     

流化床作为生物质气化反应器试验研究

在流化床生物质气化炉内 ,用空气进行气化生物质 (花生壳 )的试验研究 ,分析的参数是当量比ER 0 .2— 0 .4 5 ,气化床的温度 75 0— 85 0℃和加入二次风。当ER在 0 .2 5— 0 .33,气化燃气热值为 6 .2— 6 .8MJ/m3 ,气体产量在 2 6 0— 390m3 /h ,生物质燃烧时比气化产量在 1.2 8— 2 .0 3m3 /kg之间 ,炭转化率在 5 3%— 80 %。并对 7种农、林废弃物进行了初步气化试验研究 ,生成的燃气体积分数 :CO为 14 %— 18% ,H2 一般低于 6 % ,甲烷 4 %— 12 %。燃气热值在 4 70 0— 710 0kJ/m3 。试验结果表明 ,在流化床生物质气化炉中 ,通过在悬浮空间加入二次风 ,可使燃气热值得到提高。     

生物质的流化床转化

综述了生物质的流态化特性及生物质的流化床利用,内容包括：生物质在流化床中燃烧,气化以及在流经床中的热解,并介绍了煤与生物质共气化燃烧的最新进展。     

流化床生物质气化过程的中试研究

随着社会对能源需求的日益增长，作为主要能源来源的化石燃料却迅速地减少，因此，寻找一种可再生的替代能源便成为社会普遍关注的焦点。生物质能源是一种理想的可再生能源，每年都有大量的工业、农业及森林废弃物产出，它来源广泛。其具有以下特点：（1）可再生性。（2）低污染性（硫含量和氮含量低，燃烧过程中产生的SOX、NOX较低）。生物质作为燃料时，由于它在生长时需要的二氧化碳量相当于它燃烧时排放的二氧化碳量，因而对大气的二氧化碳净排放量近似于零，这可有效地减少温室效应。（3）广泛的分布性。缺乏煤炭的地域可充分利用生物质能源。世界上87％的能源需求来源于化石燃料，这些燃料燃烧时，向大气中排放出大量的CO2、SOX、NOX。生物质中硫的含量极低，基本上无硫化物的排放，所以，利用生物质作为替代能源对改善大气酸雨环境、减少大气中二氧化碳含量从而减少“温室效应”都有极大的好处。全世界目前正面临着资源和环境的挑战，要做到环境和能源的持续发展，就必须合理有效地开发利用新能源，以尽可能减少对自然环境的破坏和污染。生物质的低硫和CO2的零排放使生物质成为能源生产的又一研究热点。     

气化剂参数对流化床生物质气化指标影响的模型研究

以典型生物质资源麦秆为原料,采用流化床气化方法,通过建立热力学平衡模型,计算并分析气化剂参数对气化指标的影响,理论优化了以蒸汽+空气为气化剂时的气化指标,得出了空气中氧气浓度的增加能够显著提高气化指标,降低消耗;气化剂预热温度的增加可以增加气化炉操作温度,降低气化过程无用的热负荷,降低消耗;空气中氧气浓度和蒸汽/空气质量比与气化反应温度近似成线性关系,即氧气浓度增加,气化炉温度增加,蒸汽/空气质量比增加,气化炉温度降低;蒸汽/空气质量比能够调节气化炉反应温度和气体组成,当该值在0.05时,气化温度为1 270 K,合成气中CO+H2+CH4体积分数为25.7%,气化指标较好。     

新型流化床式生物质热裂解液化设备设计与试验

设计并研发了5 kg/h处理量的新型流化床式生物质热裂解液化设备,将不可冷凝气体作为循环流化气体替代昂贵的惰性保护气,整体结构简单、紧凑,各个关键系统设计完善。以山杨木木材为原料进行热裂解液化试验表明,新型流化床式热裂解液化设备工作的基本优化工艺参数为反应温度500~600℃、物料粒径0.5~0.9 mm、物料含水率10%以下。     

生物质循环流化床气化炉运行特性

我国生物质循环流化床气化炉的商业应用仍处在初始阶段,相关方面的公开报道还极少,因此研究其运行特性和控制方法对该炉型气化炉的商业化发展意义重大.以江苏某米厂5 t/h生物质循环流化床气化炉为例,针对气化炉运行过程中不同阶段的床层压降、床层温度、流化风量、返料风及返料蒸汽量等关键参数的变化规律及控制方法进行了分析讨论.结果...     

基于CPFD方法的流化床生物质气化数值模拟

基于计算颗粒流体动力学(CPFD)建立了三维鼓泡流化床水蒸气-空气混合气化的数值模型,并进行了模型验证,结果表明模拟和实验具有良好的一致性。在该模型的基础上,研究了气化炉内气体分布以及温度分布;同时探究了生物质属性(颗粒粒径、含水率、种类)以及操作条件(气化温度、床料高度)对气化特性的影响。结果表明,生物质颗粒粒径对气化性能的影响存在一个最优值,平均粒径为0.6 mm是最佳的;较高的含水率会降低可燃气体产量,不利于气化反应的进行;四种生物质中,锯末气化的效率最高、可燃气体产量最大、气体热值最高,稻壳仅次于锯末但其碳转化率高于锯末;提高气化温度可以增加可燃气体的比例、提高气化效率;而初始床层高度的变化可以改变H₂/CO的比例。本实验为生物质水蒸气/空气气化提供了理论参考,有助于生物质原料的选取和处理,也有助于气化炉的放大和优化。     

生物质流化床空气-水蒸气气化模型研究

根据流化床反应器特点,结合生物质气化动力学反应机理,建立了生物质在流化床内气化的等温稳态、一维二相动力学模型。该模型所做的主要假定如下:流化床分为气泡相和乳相,在气泡相和乳相内均存在化学反应,考虑二相内的轴向气体扩散,生物质热解过程瞬时完成,主要考虑焦碳以及CO,CO2,H2,H2O,CH4等在流化床内发生的8个主要化学反应。数学模型属于常微分方程组边值问题,利用数值计算软件M atlab7.0进行编程求解。以木粉为原料,将模型结果与实验结果进行了对比,模拟结果与试验数据符合良好,在一定程度上证明了模型的有效性和可靠性。     

生物质废物蒸汽气化高效制取富氢燃气的研究

本文利用固定床管式炉将木屑气化转化为富氢燃气,考察反应温度、注水流量和催化剂用量对气体组分和产量的影响规律。实验结果显示,生物质气化的总产气量和H₂占比随反应温度的升高而增加,随注水流量和催化剂用量的增大先增加后减小。生物质蒸汽气化的最佳条件为反应温度850℃、注水流量15 mL/h和原料/催化剂投加比50%,此时总产气量为1835.18 mL/g_木屑,其中CO为796.61 mL/g_木屑,占比43.54%,而H₂也达到最大值724.92 mL/g_木屑,占比接近40%。研究结果可以为生物质废物向富氢燃气的高效转化提供数据支撑。     

A mathematical model of fluidized bed biomass gasification

A mathematical model of biomass gasification in a fluidized bed has been developed. It considers axial variations of concentrations and temperature in the bubble and emulsion phases. The mass balance involves instantaneous oxidation and equilibrium devolatilization of the biomass, kinetics of solid-gas gasification reactions as well as of gaseous phase reactions and interphase mass transfer and gas convection. The energy balance is solved locally for each vertical volume element, and globally on the reactor by iteration on the temperature at the bottom of the bed. Three parameters have been adjusted based on the experimental results: the heat transfer coefficient at the wall, the weighting of the kinetics of the water-gas shift reaction and the fraction of biomass carbon remaining as char after devolatilization. The model is used to simulate a pilot scale (50 kg/h) biomass gasifier, and its predictions compared to experimental measurements. The temperature and gaseous concentrations are estimated with good accuracy for the experiments using a wood feedstock, except for the concentration of hydrogen which is overestimated.     

Some process fundamentals of biomass gasification in dual fluidized bed

The dual fluidised bed gasification technology is prospective because it produces high caloric product gas free of N₂ dilution even when air is used to generate the gasification-required endothermic heat via in situ combustion. This study is devoted to providing the necessary process fundamentals for development of a bubbling fluidized bed (BFB) biomass gasifier coupled to a pneumatic transported riser (PTR) char combustor. In a steam-blown fluidized bed of silica sand, gasification of 1.0 g biomass, a kind of dried coffee grounds containing about 10 wt.% water, in batch format clarified first the characteristics of fuel pyrolysis (at 1073 K) under the conditions simulating that prevailing in the gasifier intended to develop. The result shown that via pyrolysis more than 60% of fuel carbon and up to 75% of fuel mass could be converted into product gas, while the simultaneously formed char was about 22% of fuel mass. With all of these data as the known input, a process simulation using the software package ASPEN then revealed that the considered dual bed gasification plant, i.e. a BFB gasifier + a PTR combustor, is able to sustain its independent heat and mass balances to allow cold gas efficiencies higher than 75%, given that the fuel has suitable water contents and the heat carried with the product gas from the gasifier and with the flue gas from the char combustor is efficiently recovered inside the plant. In a dual fluidized bed pilot gasification facility simulating the gasification plant for development, the article finally demonstrated experimentally that the necessary reaction time for fuel, i.e. the explicit residence time of fuel particles inside the BFB gasifier computed according to a plug granular flow assumption, can be lower than 160 s. The results shown that varying the residence time from 160 to 1200 s only slightly increased the gasification efficiency, but the reaction time available in the PTR, say, about 3 s in our case, was too short to assure the finish even of fuel pyrolysis.     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases — a bubble and an emulsion phase — with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model. __________ Translated from Chemical Engineering (China), 2007, 35(10): 23–26 [译自: 化学工程]     

Modeling and simulation of biomass air-steam gasification in a fluidized bed

By considering the features of fluidized-bed reactors and the kinetic mechanism of biomass gasification, a steady-state, isothermal, one-dimensional and two-phase mathematical model of biomass gasification kinetics in bubbling fluidized beds was developed. The model assumes the existence of two phases – a bubble and an emulsion phase – with chemical reactions occurring in both phases. The axial gas dispersion in the two phases is accounted for and the pyrolysis of biomass is taken to be instantaneous. The char and gas species CO, CO₂, H₂, H₂O, CH₄ and 8 chemical reactions are included in the model. The mathematical model belongs to a typical boundary value problem of ordinary differential equations and its solution is obtained by a Matlab program. Utilizing wood powder as the feedstock, the calculated data show satisfactory agreement with experimental results and proves the effectiveness and reliability of the model.     

Numerical simulation of 3D fluidized bed biomass gasification based on CPFD

Based on computational particle fluid dynamics (CPFD), a three-dimensional bubbling fluidized bed steam-air mixed gasification numerical model was established, and it was verified with experiment trials. The results show that the simulation and experiment have good consistency. Based on the model, the gas distribution and temperature distribution in the gasifier were studied; meanwhile, the biomass properties (particle size, water content, types) and operating conditions (gasification temperature, bed height) were investigated. The results show that there is an optimal value for the impact of biomass particle size on gasification performance, with an average particle size of 0.6 mm being the best; a higher water content will reduce the output of combustible gas and is not conducive to the gasification reaction. Among the four types of biomass, sawdust gasification has the highest efficiency, the largest combustible gas production, and the highest gas calorific value. Rice husk is second only to sawdust but its carbon conversion rate is higher than that of sawdust; increasing the gasification temperature can increase the proportion of combustible gas and increase gasification efficiency; while the change of initial bed height can change the ratio of H₂/CO. This experiment provides a theoretical reference for biomass steam/air gasification, which is helpful for the selection and processing of biomass raw materials, and also facilitates the amplification and optimization of the gasifier.     

流化床煤气化试验研究

为研究温度和煤的煤焦反应性对流化床煤气化特性的影响,在小型电加热鼓泡床试验装置上,对4种高灰劣质粉煤——石沟驿煤、大塘煤、洋江煤和玉带煤进行空气为气化剂的煤气化试验研究。研究结果表明:随着温度的升高,各煤种气化得到冷煤气的热值、产气率、冷煤气效率和碳转化率均升高,在1 000℃时,石沟驿煤气化得到煤气的热值、产气率、冷煤气效率和碳转化率分别达到4.65 MJ/m3,2.21 m3/kg,47.8%和65.7%;4种煤的煤焦反应性均较差,其中石沟驿煤相对较高,其他煤的煤焦反应性低且相近;在相同温度水平下,气化得到煤气有效成分和热值与煤的煤焦反应性成正相关关系,煤的煤焦反应性最高的石沟驿煤气化得到的冷煤气的有效成分、热值均明显高于其他煤种。