中型流化床中的生物质气化实验研究

以空气为气化介质,在中型流化床反应器上进行了生物质(木屑)气化实验研究。考察了当量比ER(0.20～0.34)、气化温度(670～820℃)对气化结果的影响,初步探讨加入二次风对气化的影响。在实验研究的条件范围内,煤气热值在5650～6665kJ/m3范围内变化,生物质产气率在1.51～2.26m3/kg之间变化,碳转化率在74.3%～90.8%之间变化,气化效率达到61.8%～78.1%;加入适量二次风可以提高气化效率和碳转化率,减少焦油含量。实验结果表明:此流化床气化炉当气化温度在720～770℃之间,当量比ER在0.24～0.28之间时,气化效果最好,此时煤气热值可达到6400～6600kJ/m3,产气率为1.75～1.95m3/kg,碳转化率为83%～89%,气化效率高达71%以上。     

竹材流化床气化试验研究

利用自制的小型流化床气化炉,在400～700℃、过量空气系数0.2～0.8的范围内对竹材进行了气化试验研究。当气化温度为700℃、过量空气系数为0.2时,气化气热值最高,达到7200 kJ/Nm3左右;当气化温度为700℃、过量空气系数为0.4时,气化效率最高,达到60%左右;气化气产率与过量空气系数呈线性正相关,几乎与反应温度无关;当过量空气系数达到0.6以上、反应温度达到500℃以上时,碳转化率可达到85%以上。     

基于ASPEN PLUS模拟生物质气流床气化工艺过程

基于ASPEN PLUS模拟平台,对热解后半焦气化与生物质原料直接气化分别进行了模拟计算,得出如下结论:热解方法作为生物质气流床气化工艺的前处理手段是可行的。热解终温为300℃时对气流床气化是最合适的;O/C摩尔比在0.9～1.1之间比较合适;气化温度和碳转化率随着O/C摩尔比的增加而升高;对于300℃半焦进行气化,空气温度预热到550℃比较合适,气化温度可达到1056℃,煤气热值可达到5958kJ/Nm~3,碳转化率也可达到99.59%。     

反应温度对木屑炭水蒸气气化产物的影响

以木屑炭为原料,在固定床反应器中进行了水蒸气气化试验。试验在水蒸气流量为0.854 g/min,温度为800～1 000℃条件下,反应15 min。主要考查气化反应温度对碳转化率、合成气产率、燃气热值及燃气组成的影响。研究结果表明,在高温条件下木屑炭与水蒸气具有很高的反应活性,燃气产率为0.9～3 L/g;在气化温度为1 000℃时,碳转化率最高达到80%;燃气热值为8.9～9.4 MJ/m3,合成气(H2+CO)比例为68%～79%,H2/CO为4.02～6.32。     

内在碱金属钠对稻秆与塑料PE共气化产气特性的影响

为研究稻秆内在碱金属钠对稻秆与塑料PE共气化产气规律的影响,文章选取稻秆和塑料PE为研究对象,通过水洗和浸渍法对稻秆进行预处理,在研究温度和PE含量对气化产气影响的基础上重点研究了二者共气化过程中钠对气化产气的影响。结果表明:随着钠含量的增加,H2的最大瞬时产量表现出增多的趋势,钠含量为0.11%,0.49%,0.97%时H2的体积分数对应为4.5%,8.5%,9.5%;钠含量由0.11%增至0.97%时,总产气组分中H2和CO的体积分数分别提高了1.64倍和1.35倍,热值和碳转化率分别提高了1.8倍和2.3倍。     

石油焦的气化反应特性

针对3种不同的石油焦，在热天平上考察了不同的化学反应条件，包括温度、压力和气氛等因素对气化反应的影响．研究结果发现，在水蒸气气氛下石油焦具有良好的气化反应活性，而在二氧化碳气氛下石油焦气化反应进行得相当缓慢，相同条件下的C-H2O反应速率是C-CO2反应速率的十几倍，在60％水蒸气的实验温度条件下，每升高50℃，平均气化反应速率提高1倍；1000℃时，水蒸气分压对平均气化反应速率的影响不均匀，分压增加，影响减小．随着反应的不断进行，气化反应速率存在最大值，而出现最大值时的转化率不受反应温度和压力的影响，而与气化介质有关．根据实验结果，分析得到了3种石油焦在水蒸气条件下反应速率与温度、水蒸气分压和转化率的关系式，并得到了3种石油焦气化反应的活化能。     

中药渣水蒸气气化制备合成气研究

以中药渣为原料进行水蒸气气化实验,研究气化温度、水蒸气与生物质质量之比(S/B)对产气流量、气体产率、产气组分、碳转化率、燃气热值以及气化效率的影响。研究结果表明:气化温度的升高能够促进气化反应的进行,提高产气品质和气化效率;一定量的气化剂水蒸气可提高气化效率,但是过量的水蒸气会影响气化效果;气化温度为800℃,S/B为1.0时,气化效果最佳,气化效率高达72.91%;中药渣具备良好的水蒸气气化特性。研究结果可为中药渣资源利用提供理论参考。     

CO2气氛下生物质气化制氢的数值分析

生物质气化制氢有重要的工业应用价值,本文采用ASPEN PLUS软件数值模拟了稻壳在流化床中的气化过程。本次模拟运用吉布斯自由能最小化原理,选择RGibbs和RYield模块,采用CO2作为气化剂,计算获得了气化温度、CO2质量流量、CO2和稻壳质量比和碳转化率对产氢率的影响规律。结果表明：在CO2质量流量为200kg/h时,H2的生成率高达43%。随着CO2/B增加,CO和CO2体积分数逐渐升高,CH4体积分数下降,H2体积分数在不同的气化温度下趋于平稳（600~700℃）或下降（800~1000℃）。随着气化温度升高,碳转化率增加;随着CO2和稻壳质量比的升高,碳转化率下降。     

生物质快速热解及水蒸气气化实验研究

对生物质气流床气化过程进行了小型台架实验研究,建立生物质气流床气化小型实验台架,进行生物质快速热解和水蒸气气化的实验,实验表明:温度提高有利于提高产品气的产率、气化过程的碳转化率和气化效率,但温度过高会促进CH_4的重整反应、水气变化反应、降低CO、甲烷含量,从而影响产品气热值。粒径对气化结果有着一定影响,粒径对气化结果的影响主要体现在固相内部升温速率和最终温度上,粒径越小,颗粒升温越快,能达到的最终温度越高。水蒸气气化过程中,适当的水蒸气的通入能大量提高产气中的H_2、CO的占比,提高碳转化率和H_2/CO的比值,碳转化率在S/B比为1.4时达到最大值96%,此时气化效率也高达94%,水蒸气的通入过量会导致炉内温度下降,各项评价指标均开始下降,降低燃气品质。     

煤焦气化反应动力学研究

气流床气化技术是煤炭清洁、高效转化的重要途径和发展方向之一。利用热天平,采用等温热重法对抽样选出的煤种在800℃～1 400℃温度范围内进行了煤焦CO2气化反应动力学特性研究。研究结果表明:高温下煤焦的气化反应特性不同于低温时的反应特性,在900℃～1 000℃时气化反应逐步由化学反应控制过渡到过渡区控制,在1 100℃～1 300℃时气化从反应过渡区控制逐步到扩散区控制;不同粒径的煤粉气化反应,在相同的时间内,1 000℃时的碳转化率、气化反应速率比950℃时的碳转化率、气化反应速率高很多,950℃时的碳转化率、气化反应速率比900℃时的碳转化率、气化反应速率高。     

生物质加压气化技术的研究与应用现状

生物质气化气可以替代化石燃料用于发电、供热和用于生产合成反应的化工原料,解决日益严重的能源短缺和环境污染等问题.加压气化具有生产能力大、效率高,可降低单位投资成本,减少焦油的产生,有利于后续发电及合成工艺等诸多优点.文章介绍了压力对气化的影响,加压气化存在的主要问题,加压在生物质和劣质煤等联合气化、定向气化制备合成气、IGCC上应用的研究和应用现状.     

Experimental study of dual fixed bed biochar-catalytic gasification with simultaneous feed of O2-steam-CO2 for synthesis gas or hydrogen production

The catalytic gasification of biochar was investigated in the presence of a Ni/SiO₂ catalyst in a fixed bed reactor with an O₂-steam-CO₂ gas feed. The effects of operating temperature, catalyst nickel loading and composition of O₂-steam-CO₂ feed gas on biochar carbon conversion and gas products were investigated. The results indicate that the highest biochar carbon conversion could be obtained at approximately 800 °C, whilst the 10% Ni/SiO₂ catalyst was shown to produce the greatest syngas yields. The presence of O₂ in the feed gas can result in slightly more CO in the gas product, whilst a higher steam content leads to more H₂ in the gas product. The CO₂ offered a benefit as an adjusting agent for achieving a desired H₂/CO ratio. No evidence of coke deposition on the catalyst was found under any of the tested conditions.     

Mechanisms of Thermochemical Biomass Conversion Processes. Part 2: Reactions of Gasification

Abstract

Gasification as a thermochemical process is defined and limited to combustion and pyrolysis. The gasification of biomass is a thermal treatment which results in a high proportion of gaseous products and small quantities of char (solid product) and ash. Biomass gasification technologies have historically been based upon partial oxidation or partial combustion principles, resulting in the production of a hot, dirty, low Btu gas that must be directly ducted into boilers or dryers. In addition to limiting applications and often compounding environmental problems, these technologies are an inefficient source of usable energy. The main objective of the present study is to investigate gasification mechanisms of biomass structural constituents. Complete gasification of biomass involves several sequential and parallel reactions. Most of these reactions are endothermic and must be balanced by partial combustion of gas or an external heat source.     

Techno-economic analysis and life cycle assessment of hydrogen production from different biomass gasification processes

The paper presents techno-economic analyses and life cycle assessments (LCA) of the two major gasification processes for producing hydrogen from biomass: fluidized bed (FB) gasification, and entrained flow (EF) gasification. Results indicate that the thermal efficiency of the EF-based option (56%, LHV) is 11% higher than that of the FB-based option (45%), and the minimum hydrogen selling price of the FB-based option is $0.3 per kg H₂ lower than that of the EF-based option. When a carbon capture and liquefaction system is incorporated, the efficiencies of the EF- and FB-based processes decrease to 50% and 41%, respectively. The techno-economic analysis shows that at a biomass price of $100 per tonne, either a minimum price of $115/tonne CO_2e or a minimum natural gas price of $5/GJ is required to make the minimum hydrogen selling price of biomass-based plants equivalent to that of commercial natural gas-based steam methane reforming plants. Furthermore, the LCA shows that, biomass as a carbon-neutral feedstock, negative life cycle GHG emissions are achievable in all biomass-based options.     

Syngas yield during pyrolysis and steam gasification of paper

Main characteristics of gaseous yield from steam gasification have been investigated experimentally. Results of steam gasification have been compared to that of pyrolysis. The temperature range investigated were 600–1000 °C in steps of 100 °C. Results have been obtained under pyrolysis conditions at same temperatures. For steam gasification runs, steam flow rate was kept constant at 8.0 g/min. Investigated characteristics were evolution of syngas flow rate with time, hydrogen flow rate and chemical composition of syngas, energy yield and apparent thermal efficiency. Residuals from both processes were quantified and compared as well. Material destruction, hydrogen yield and energy yield is better with gasification as compared to pyrolysis. This advantage of the gasification process is attributed mainly to char gasification process. Char gasification is found to be more sensitive to the reactor temperature than pyrolysis. Pyrolysis can start at low temperatures of 400 °C; however char gasification starts at 700 °C. A partial overlap between gasification and pyrolysis exists and is presented here. This partial overlap increases with increase in temperature. As an example, at reactor temperature 800 °C this overlap represents around 27% of the char gasification process and almost 95% at reactor temperature 1000 °C.     

Characteristic of hydrogen and syngas evolution from gasification and pyrolysis of rubber

The characteristics of syngas evolution during pyrolysis and gasification of waste rubber have been investigated. A semi-batch reactor was used for the thermal decomposition of the material under various conditions of pyrolysis and high temperature steam gasification. The results are reported at two different reactor temperatures of 800 and 900 °C and at constant steam gasifying agent flow rate of 7.0 g/min and a fixed sample mass. The characteristics of syngas were evaluated in terms of syngas flow rate, hydrogen flow rate, syngas yield, hydrogen yield and energy yield. Gasification resulted in 500% increase in hydrogen yield as compared to pyrolysis at 800 °C. However, at 900 °C the increase in hydrogen was more than 700% as compared to pyrolysis. For pyrolysis conditions, increase in reactor temperature from 800 to 900 °C resulted in 64% increase in hydrogen yield while for gasification conditions a 124% increase in hydrogen yield was obtained. Results of syngas yield, hydrogen yield and energy yield from the rubber sample are evaluated with that obtained from woody biomass samples, namely hard wood and wood chips. Rubber gasification yielded more energy at the 900 °C as compared to biomass feedstock samples. However, less syngas and less hydrogen were obtained from rubber than the biomass samples at both the temperatures reported here.     

基于生物质气化耦合发电的气化特性实践研究

在10 MW级生物质气化耦合燃煤发电工程项目上,考察了当量比、添加蒸汽、掺混秸秆对稻壳气化特性的影响。在当前的实验条件下,随着当量比在0. 14～0. 20的范围内增加时,CO、H_2和CH_4的体积分数均随之减少,燃气热值和气化效率也随当量比的增大而降低;添加适量蒸汽可以促进CO、H_2和CH_4及燃气热值的提高,气化效率则随蒸汽量的增加而升高;当秸秆掺混比例逐渐增加时,CO、H_2和CH_4的体积分数和燃气热值出现了不同程度的下降,气化效率也不断降低。     

Characteristics of syngas from co-gasification of polyethylene and woodchips

Gasification of polyethylene (PE) and woodchips (WC) mixtures have been investigated in a semi-batch reactor, using high temperature steam as the gasifying agent. The reactor temperature was maintained at 900 °C. The ratio of PE–WC was varied from 0% to 100% in 20% intervals. Characteristics of syngas were evaluated based on the yield of syngas, hydrogen, energy, ethylene, total hydrocarbons and apparent thermal efficiency of the process. Results show that properties of syngas evolved during gasification of PE–WC blends cannot be determined from the weighted average syngas properties obtained from separate gasification of WC and PE. Superior results in terms of syngas yield, hydrogen yield, total hydrocarbons yield, energy yield and apparent thermal efficiency from PE–WC blends were obtained as compared to expected weighed average yields from gasification of individual components. Results confirm synergistic interaction between PE and WC during high temperature steam gasification of these mixtures. These results also provide the importance of mixing two or more compounds on the performance of stream gasification of wastes.     

Characteristics of cardboard and paper gasification with CO2

Evolutionary behavior of syngas chemical composition and yield have been examined for paper and cardboard at three different temperatures of 800, 900 and 1000 °C using CO₂ as the gasifying agent at constant flow rate. Specifically the evolution of syngas chemical composition with time has been investigated. Pyrolysis of the sample was dominant at the beginning of the gasification process as observed from the high initial devolatilization of the sample followed by char gasification of material to form syngas for a long period of time. Results provided the role of gasification temperature on kinetics of the CO₂ gasification process. Increase in gasification temperature provided increased conversion of the sample material to syngas. Thus the sample conversion to syngas was low at the low temperature of 800 °C while at elevated temperatures of 900 and 1000 °C substantial enhancement of the kinetics process occurred. The evolution of extensive reaction rate of carbon-monoxide was calculated. Results show that increase in temperature increased the extensive reaction rate of carbon-monoxide. The global behavior of syngas chemical composition examined at three different temperatures revealed a peak in concentration of H₂ to exhibit after few minutes into the gasification that changed with gasification temperature. At 800 °C gasification temperature peak in H₂ was displayed at 3 min into gasification while it decreased to only 2 min, approximately, at gasification temperatures of 900 and 1000 °C. The effect of reactor temperature on CO mole fraction has also been examined. Increase in the gasification temperature enhances the mole fraction of CO yields. This is attributed to the increase in forward reaction rate of the Boudouard reaction (C+CO₂2CO). The results show important role of CO₂ gas for the gasification of wastes and low grade fuels to clean syngas.     

煤的气化技术及其应用

煤气化技术是环境友好的现代煤化丁的关键技术。介绍了当今世界主要的煤气化技术,着重介绍了已工业化生产的鲁奇、Transport、壳牌、德士古、康菲气化炉及我国自主开发的华东理工大学气化炉等技术,并且介绍了煤气化技术在煤气化联合循环发电和在煤化丁的合成油、合成氨、合成甲醇、合成烯烃等方面的应用。重点介绍了我国煤化工发展的具体情况。