成型生物质流化床气化及结渣影响因素研究

为提高生物质气化产物的品质,采用成型桉树皮和成型玉米秸秆2种典型农林废弃物,并选取稻壳和木屑作为对比,在中试规模的流化床实验台上进行气化实验,得到成型桉树皮、成型玉米秸秆、稻壳和木屑的最佳空气当量系数,分析了成型生物质在气化中出现结渣现象的原因。结果表明：在实验条件下,成型桉树皮、稻壳和木屑的最佳空气当量系数为0.20,其燃气热值分别为5.5 MJ/m³、5.5 MJ/m³、6 MJ/m³,气化效率分别为60%、45%、52%;成型玉米秸秆由于其高灰分、低热值,所需空气量更大,最佳空气当量系数为0.24,燃气热值为4 MJ/m³,气化效率为35%;气化温度提高可促进不同生物质的气化反应,碱金属、碱土金属含量较多的成型生物质在气化过程中更易结渣。     

玉米秸秆循环流化床热解气化试验

采用循环流化床气化中试装置对玉米秸秆进行了气化试验,分别在常温空气与250℃预热空气条件下,研究了空气当量比（ER）和原料含水率对气化特性的影响规律。结果表明：随着ER的增大,循环流化床气化炉内的反应温度升高,气化燃气中的CO₂含量增加,焦油与CO含量及燃气热值降低,气化效率随ER的增大呈先增大后减小的趋势;随着气化原料含水率的增加,循环流化床气化炉内的平均温度下降,燃气中的CO₂与H₂及焦油含量逐渐升高,CO含量下降,CH₄与C_nH_m含量均为先增加后减少。与常温空气工况相比,预热空气工况下的燃气热值与气化效率均有一定程度的提高。采用预热空气为气化介质,提高气化剂温度,可显著促进玉米秸秆的气化反应,提升气化效率。     

废轮胎整胎与生物质共气化实验研究

以树枝秸秆及废轮胎整胎为原料,在"反烧"式固定床气化炉中以空气为气化剂进行气化实验研究。结果表明,随着空气当量比ER的增加,炉内气化温度升高,气化效率提升,当ER为0.30时,炉内温度达到750℃,气化效率为56.45%,气体热值为4.68 MJ/m3;随着原料中废轮胎比例的增加,气化效率有所提高,燃气热值升高,当废轮胎质量含量为44%时,气化效率达到60.21%,气体热值为5.34 MJ/m3;气化温度是影响气化效率和气体热值的最重要因素,提高空气当量比可以使炉内温度升高,强化气化效果;同时原料中废轮胎比例也对气化效率及气体热值有较大影响,废轮胎质量含量为40%~50%较为适宜。废轮胎以整胎形式与生物质共气化是废轮胎处置与资源化利用的有效方式。     

市政污泥循环流化床气化特性的模拟研究

运用Aspen Plus分析软件对市政污泥进行循环流化床气化模拟计算,分析了空气当量比、预热空气温度和污泥含水率对污泥气化特性的影响。结果表明：空气当量比对气化特性影响较大,在选定的污泥含水率下,最佳空气当量比在0.3左右;预热空气温度的提高可以提高气化温度和燃气热值;随着污泥含水率的升高,气体产物中CO₂、CH₄含量升高,燃气热值和气化温度明显降低,在流化床气化反应时干污泥含水率不宜高于20%。模拟研究结果可为污泥气化耦合燃煤发电工程方案提供一定的数据支撑和依据。     

生物质流化床富氧气化过程热平衡模型

基于元素守恒、化学反应平衡和能量守恒,考虑碳不完全转化因素,建立生物质流化床富氧气化的热平衡模型。采用非平衡当量因子对气化反应平衡常数进行修正,修正后的模拟数据与文献数据吻合良好。利用该模型模拟富氧浓度和原料含水率对气体组分、气体热值和气化效率的影响。模拟工况下的结果表明:富氧浓度从21%增至100%,可燃组分含量增多,气体热值从6.37 MJ/m~3增至11.44 MJ/m~3,气化效率不断增大;原料含水率从零增至35%,气化炉温不断降低,可燃组分减少,气体热值从5.45 MJ/m~3降至4.65 MJ/m~3。     

在流化床气化炉中生物质与煤共气化的研究(Ⅰ)以空气-水蒸汽为气化剂生产低热值燃气

在600kW流化床气化炉工业示范装置上以空气.水蒸汽为气化剂,将生物质/煤按不同比例进行了共气化的实验研究.在实验研究的运行条件下,得到了生物质/煤混合比例对气化炉工作温度、燃气热值、气体产率和气化效率等重要技术参数的影响.对玉米芯/煤的比例为81/19时的典型实验结果表明:气化炉工作温度869℃,空气当量比ER=0.21,S/B=0.20时,气体产率1.96m3/kg,燃气热值6.4MJ/m3,气化效率71.3%,燃气中焦油含量小于10mg/m3,该炉经过连续运行考核,运行平稳,工况稳定.     

典型生物质流化床气化中试试验研究

在中试规模流化床上研究稻壳与木屑、空气当量比ER及气化温度(650-800℃)对气化特性的影响。结果表明:木屑、稻壳在ER为0.2左右时达到最佳气化工况,热值分别为5.39 MJ/m~3、6.04 MJ/m~3,气化效率分别为46.15%、51.91%;随着ER的增大,气化炉温度呈现先增加后减小趋势,过高或过低的ER都不利于生物质气化反应;随着温度的增加,合成气可燃组分增加,CO_2组分减小,气体热值、气化效率上升。     

两级下吸式生物质气化炉气化性能的研究

在自行设计的两级下吸式生物质气化炉中,研究了空气当量比(ER)对气体组成、气体热值、气化效率以及焦油含量的影响。试验结果表明,该新型两级气化炉能够产生焦油含量较低的燃气;在空气预热的条件下,焦油含量更低,可达238 mg/m3。该新型两级气化炉的最佳ER为0.33~0.35,当ER=0.34时,气化气低位热值(LHV)最高为4 409 kJ/m3,气化效率为63.7%,焦油含量低于300 mg/m3。     

在流化床气化炉中生物质与煤共气化的研究（I）以空气-水蒸汽为气化剂生产低热值燃气

在600kW流化床气化炉工业示范装置上以空气-水蒸汽为气化剂,将生物质／煤按不同比例进行了共气化的实验研究。在实验研究的运行条件下,得到了生物质／煤混合比例对气化炉工作温度、燃气热值、气体产率和气化效率等重要技术参数的影响。对玉米芯／煤的比例为81／19时的典型实验结果表明：气化炉工作温度869℃,空气当量比ER=0．21,S／B=0．20时,气体产率1．96m^3／kg,燃气热值6．4MJ／m^3,气化效率71．3％,燃气中焦油含量小于l0mg／m^3,该炉经过连续运行考核,运行平稳,工况稳定。     

典型生物质及木质素水蒸气气化制富氢合成气的试验研究

选取稻壳、木屑、小麦秸秆及玉米秸秆四种典型生物质及木质素，以管式炉为反应器，将每种实验样品3 g放入陶瓷方舟，通入0.4 MP、150℃的水蒸气，流量为3 g/min,选取550℃、650℃、750℃、850℃、950℃进行水蒸气气化实验，探究典型生物质水蒸气气化产物、热值及固体转化率随温度变化规律。实验结果表明：木屑产生H₂含量在750℃可达60.17%。提高水蒸气气化温度可以有效降低CH₄含量，提高H₂的体积分数。在实际工程应用时，如果要获得较高的氢气纯度，温度至少在750℃以上；如果使可燃气含量最高时，建议将温度控制在750℃左右。     

下吸式固定床的生物质H2O/CO2气化数值模拟研究

利用Aspen Plus 软件建立干桦木屑在下吸式固定床气化炉中的气化模型,模拟值与文献实验值吻合良好。利用Aspen Plus的灵敏度分析模块模拟分别以水蒸气（H₂O）和二氧化碳（CO₂）为气化剂时气化剂/生物质碳比（GC值）对气化结果的影响,并结合H₂O、CO₂各自的特点研究其复合气化。结果表明,H₂O气化时可获得富氢煤气,但其净CO₂排放量较高;CO₂气化时碳转化率及冷煤气效率较低,但净CO₂排放量较低;H₂O、CO₂复合气化使碳转化率及冷煤气效率略有降低,但可有效减少气化系统中的净CO₂排放量。     

下吸式固定床的生物质O2/CO2分段气化流程模拟

建立干桦木屑在下吸式固定床气化炉中的Aspen Plus气化模型,该模型预测煤气组成和煤气热值,与文献试验结果吻合良好。利用灵敏度分析模块模拟了氧碳比、CO₂/C对气化结果的影响,并提出O₂/CO₂分段气化流程,对比常规的CO₂气化特征,分析了CO₂/C对气化结果的影响。结果表明,纯氧气化时可获得高H₂和CO浓度的气化气,但其净CO₂排放量较高,氧碳比增加使碳转化率逐渐增加、冷煤气效率先增加后降低;CO₂作为气化剂时,随着CO₂/C的增加,净CO₂排放量逐渐减少,但碳转化率及冷煤气效率大幅降低;与常规CO₂气化相比,O₂/CO₂分段气化在保持低CO₂排放量的同时,可有效增加气化过程中的碳转化率及冷煤气效率。     

上吸式生物质秸秆气化炉的设计与试验研究

设计一台上吸式生物质秸秆气化炉,并进行热解气化试验,分析不同气化剂量对炉内温度的影响以及温度和秸秆种类对产气成分的影响。试验结果表明：气化剂量对炉内温度及炉内温度对产气成分含量的影响均较大;秸秆种类也对产气的热值有较大的影响,稻草热解可燃气热值4．1MJ／m^3,油菜秆热解可燃气热值4．9MJ／m^3,玉米秆热解可燃气热值5．5MJ／m^3。     

Pilot scale autothermal gasification of coconut shell with CO2-O2 mixture

This paper explored the feasibility and benefit of CO₂ utilization as gasifying agent in the autothermal gasification process. The effects of CO₂ injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO₂/C ratio from 0.6 to 1.6. O₂ was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO₂ injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO₂-O₂ gasification with a CO₂/C ratio of 0.6–1.2. The progress of the expected CO₂ to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO₂/C ratio increased. The producer gas heating value of CO₂-O₂ gasification was consistently higher than that of air gasification. These results show the potential of CO₂-O₂ gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.     

生物质混流式固定床气化炉运行特性分析

以桉木为原料,对1.5 t/h生物质混流式固定床气化炉运行特性进行了测试分析与评价,与文献报导报道的相关炉型包括上吸式、下吸式、两段式等炉型运行结果进行了比较。实验以气化炉空气通入量作为主要控制变量,对有或无水蒸气条件下的气化炉温度及压力分布、燃气组成、焦油与飞灰含量、气体产率等参数进行了较长周期的测试,结果表明：气化炉运行效果符合设计要求,各项指标相当于或优于传统的下吸式气化炉;气化炉运行温度与压力比较稳定;以冷燃气计算的燃气热值一般约为4 900 ~ 5 500 kJ/Nm3;气化效率约为70% ~ 78%;燃气焦油含量约600 ~ 3 500 mg/Nm3,运行负荷在50%以上时,焦油含量一般低于1 500 mg/Nm3。研究结果有望为混流式气化炉的改进和操作提供优化建议,同时可为其他气化工艺设计提供参考依据。     

Hydrogen-rich gas production from biomass air and oxygen/steam gasification in a downdraft gasifier

Biomass gasification is an important method to obtain renewable hydrogen. However, this technology still stagnates in a laboratory scale because of its high-energy consumption. In order to get maximum hydrogen yield and decrease energy consumption, this study applies a self-heated downdraft gasifier as the reactor and uses char as the catalyst to study the characteristics of hydrogen production from biomass gasification. Air and oxygen/steam are utilized as the gasifying agents. The experimental results indicate that compared to biomass air gasification, biomass oxygen/steam gasification improves hydrogen yield depending on the volume of downdraft gasifier, and also nearly doubles the heating value of fuel gas. The maximum lower heating value of fuel gas reaches 11.11 MJ/N m³ for biomass oxygen/steam gasification. Over the ranges of operating conditions examined, the maximum hydrogen yield reaches 45.16 g H₂/kg biomass. For biomass oxygen/steam gasification, the content of H₂ and CO reaches 63.27–72.56%, while the content of H₂ and CO gets to 52.19–63.31% for biomass air gasification. The ratio of H₂/CO for biomass oxygen/steam gasification reaches 0.70–0.90, which is lower than that of biomass air gasification, 1.06–1.27. The experimental and comparison results prove that biomass oxygen/steam gasification in a downdraft gasifier is an effective, relatively low energy consumption technology for hydrogen-rich gas production.     

Coal conversion submodels for design applications at elevated pressures. Part II. Char gasification

This paper surveys the database on char gasification at elevated pressures, first, to identify the tendencies that are essential to rational design of coal utilization technology, and second, to validate a gasification mechanism for quantitative design calculations. Four hundred and fifty-three independent tests with 28 different coals characterized pressures from 0.02 to 3.0 MPa, CO₂ and steam mole percentages from 0 to 100%, CO and H₂ levels to 50%, gas temperatures from 800 to 1500 °C, and most of coal rank spectrum. Only a handful of cases characterized inhibition by CO and H₂, and only a single dataset represented the complex mixtures of H₂O, CO₂, CO, and H₂ that arise in practical applications. With uniform gas composition, gasification rates increase for progressively higher pressures, especially at lower pressures. Whereas the pressure effect saturates at the higher pressures with bituminous chars, no saturation is evident with low-rank chars. With fixed partial pressures of the gasification agents, the pressure effect is much weaker. Gasification rates increase for progressively higher gas temperatures. In general, gasification rates diminish for coals of progressively higher rank, but the data exhibit this tendency only for ranks of hv bituminous and higher.

These tendencies are interpreted with CBK/G, a comprehensive gasification mechanism based on the Carbon Burnout Kinetics Model. CBK/G incorporates three surface reactions for char oxidation plus four reactions for gasification by CO₂, H₂O, CO and H₂. Based on a one-point calibration of rate parameters for each coal in the database, CBK/G predicted extents of char conversion within ±11.4 daf wt% and gasification rates within ±22.7%. The predicted pressure, temperature, and concentration dependencies and the predicted inhibiting effects of CO and H₂ were generally confirmed in the data evaluations. The combination of the annealing mechanism and the random pore model imparts the correct form to the predicted rate reductions with conversion. CBK/G in conjunction with equilibrated gas compositions accurately described the lone dataset on complex mixtures with all the most important gasification agents, but many more such datasets are needed for stringent model evaluations.

Practical implications are illustrated with single-particle simulations of various coals, and a 1D gasifier simulation for realistic O₂ and steam stoichiometries. The rank dependence of gasification rates is the determining factor for predicted extents of char conversion at the gasifier outlet. But soot gasification kinetics will determine the unburned carbon emissions for all but the highest rank fuels. Only gasification kinetics for gas mixtures with widely variable levels of H₂O, H₂, and CO are directly relevant to gasifier performance evaluations.     

Modelling of biomass gasifier and microturbine for the olive oil industry

The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small‐scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm^?3) and the CHP system provides 30 kW_e and 60 kW_th. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle‐Tempo software^®. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of fly ash and H2S on a Ni-based catalyst for the upgrading of a biomass-generated gas

The main concern about the technology for the production of hydrogen and transport fuels by biomass gasification is the presence of contaminants (H₂S, tars, fly ash, alkali, and heavy metals, ammonia) that are poisonous for the catalysts used for upgrading the biomass-generated gas. The impact of the main contaminants on a Ni/MgAl(O) reforming catalyst was studied in a laboratory environment, by exposing the studied sample to H₂S, NH₃, K₂SO₄, KCl, ZnCl₂, and a solution derived from biomass fly ash. Lastly, the catalyst was also streamed with a gas produced by a bench-scale downdraft gasifier. The extent of deactivation was examined in the methane steam reforming reaction, under different operational conditions. The main effect of the treatments was a decrease in the bulk surface area and in the metal dispersion. Streaming H₂S quickly deactivated the catalyst; however, the activity was recovered by increasing the inlet temperature or by adding O₂ to the stream. In further laboratory tests, the performances of the catalyst seemed not to be greatly affected by either the above treatments or by the presence of ammonia in the fed water. The catalyst produced a syngas composition close to that predicted at equilibrium even after being streamed with the biomass-generated gas.