【作者】 成功；

【导师】 肖波；

【作者基本信息】 华中科技大学 ， 环境工程， 2012， 博士

【摘要】 合成气是以H2和CO为主要组分供化学合成用的一种原料气,它可以作为中间体用于石油化工行业或通过费托合成制备各种高品质液体燃料和化学品,如氢气、甲醇和二甲醚等。目前绝大多数合成气制备工艺仍是采用煤气化或天然气气化的方式,随着化石能源的日益枯竭和不断严重的环境问题,发展以可再生资源为原料的合成气生产工艺对缓解世界能源短缺和环境污染具有重要的意义。生物质是一种来源广泛、成本低廉、环境友好的可再生能源,通过热化学的方法将生物质转化为高品位、高附加值的化学品将成为未来研究的焦点。本文以生物质作为原料,采用水蒸汽催化气化技术制取合成气。对生物质催化气化合成气制备工艺展开了系统的研究,主要研究内容及成果如下：(1)选用常见的生物质——松木锯末作为气化原料。采用工业分析和元素分析对原料样品的理化特性及元素组成进行分析。结果表明：松木锯末含有很高的挥发分及少量的固定碳,而灰分极低；其元素组成主要为C和O,N和S的含量分别为0.41%和0.06%。样品的热重分析显示松木锯末的热裂解分为脱水、挥发分释放和缓慢热解三个阶段。使用等转化率法求解了松木锯末热解动力学参数,样品热解的表观活化能E值在200-258kJ/mol范围之间。松木锯末是一种具有代表性的生物质原料,在利用过程中会产生较少量的有害气体和固体残渣,是环境友好的生物质资源。(2)在自制的两段式生物质催化气化固定床反应装置上,开展了生物质水蒸汽催化气化制备合成气的小试研究。本装置导热性能良好、进料连续稳定、进出料质量平衡精度可靠。实验主要探讨了气化温度、固相停留时间、水蒸汽生物质质量比(S/B)以及催化温度对气化产物分布、气体成分及合成气组分的影响。结果表明：随着气化温度从750℃升高至900℃,气体产物的产量快速增长,气体中合成气组分(H2和CO)的含量从61.7%增加至65.96%,此外H2/CO比也逐渐从1.16增加到1.80；延长固相停留时间有助于气体产物的生成、合成气含量的提高以及H2/CO比的增长,然而当固相停留时间大于26s后气体成分的变化逐渐较小,固相停留时间的影响已不明显；对于制备合成气而言,最佳的S/B值为0.4-0.6,此时气体中H2+CO的含量为约70%,H2/CO比在2.0-2.5之间；催化剂能大大降低气体产物中焦油和CH4的含量,最优化的催化温度为650℃。(3)在小型管式固定床反应器上分别对不同温度下,生物质气化过程中挥发分释放及半焦气化两个阶段的气体产物释放行为进行了研究。结果表明：提高反应温度有利于两个阶段气体产物的释放及合成气组分(CO和H2)的生成,温度对半焦气化阶段气体产量的影响更大。高温条件下(>750℃),气体产物主要来自于半焦气化反应,同时,该反应是影响气体成分中H2/CO比的重要环节。热重分析表明：生物质在水蒸汽气氛下的失重过程表现出明显的“两段性”,第一阶段(221-351℃)为挥发分析出,受水蒸汽的影响较小；第二阶段(710-805℃)为半焦与水蒸汽发生气化反应的阶段。两个阶段可分别用二级动力学反应模型和缩核反应模型描述,计算得到的活化能分别为87.10kJ/mo1.(?)(?)80.45kJ/mol。(4)采用热重分析(TGA)、热重-质谱联用仪(TG-MS)和气相色谱-质谱联用仪(GC-MS)对生物质焦油的热解动力学特性及热解机制进行了研究。利用Flynn-Wall-Ozawa法(FWO)和Kissinger-Akahira-Sunose法(KAS)计算得到焦油热解活化能E值在53-73kJ/mol之间,通过主曲线法判断出焦油的热失重过程可用单一的机理函数描述,焦油热解反应动力学方程可以表示为：焦油热解气体中主要轻质组分的释放温度区间和焦油主要失重的温度区间相吻合,气体产物集中释放的温度在150℃以内,随着温度的升高大多数气体的释放速率逐渐降低,温度超过400℃之后,析出的组分主要为CO和CO2,以及少量的H2O和CH4。随热解时间的延长,焦油中化合物种类呈先增加后减少的趋势,其中单环芳烃和小分子含氧化合物的含量不断降低,而PAHs逐渐形成。反应120s后,焦油热解产物形成蜂窝状固体碳化物,主要成分为大于4环的PAHs及碳链在C20左右的长链脂肪烃。(5)开发了基于生物质微米燃料外加热的生物质催化气化制备合成气工艺,并进行了中试规模的研究。采用生物质微米燃料作为外部热源能够提供较高的气化反应温度,并且燃烧烟气中NOx和S02等有害气体的含量极低。在最佳的工况条件下,气体产量达到1.31Nm3/kg,其中合成气(H2+CO)含量达到70.1%,H2/CO比为2.07。对该中试气化装置的能量评估表明：其冷气效率、能源回收率和能耗比分别为48.57%、60.04%和2.40。生物质微米燃料外加热的生物质催化气化制备合成气工艺具有高效、低成本和低污染的优势。更多还原

【Abstract】 Syngas consisting mainly of H2and CO is applied to chemical synthesis. It can find a wide range of applications including use as feedstock for chemical elements in the petrochemical industry and as liquid fuels based on the Fischer-Tropsch process to produce high grade chemicals such as hydrogen, methanol or dimethyl ether. Now, syngas production process is based on the gasification of coal or natural gas. With the fossil energy exhausting and serious environmental problems, the development syngas production from renewable biomass would be significant for solving the shortage of fossil and environmental pollution. Biomass is aboundant, low-cost, environmental friendly. Biomass converted to high grade and high value-added chemicals by thermochemical processes will become the focus of further study.In this study, catalytic gasification of biomass feedstock with steam was used for syngas production. The main results were as follows:(1) Pine sawdust was employed as biomass feedstock. The results of ultimate and proximate analyses showed that pine sawdust was rich in volatile matter and it contained fewer contents of fixed carbon and ash. The thermalgravitic analysis (TGA) indicated three stages (dehydration, volatile release and slow pyrolysis) during the decomposition. The activation energy of pine sawdust pyrolysis was calculated to be200-258kJ/mol using iso-conversion methods. Pine sawdust was beneficial for the environment, as a common biomass, because it would produce less hazardous gases and solid residues.(2) Catalytic gasification of biomass with steam for syngas production was performed in a two-stage fixed bed gasifier. The self-manufacture gasifier had well thermal conductivity, continuous feeding and high currency. The effects of gasification temperature, solid residence time (SRT), steam to biomass ratio (S/B) and catalytic temperature on catalytic gasification were investigated. The results showed that the gas yield and syngas concentration increased with the increasing gasification temperature from750℃to900℃. The value of H2/CO also increased from1.16to1.80. Furthermore, prolonging SRT resulted in the high gas yield, syngas concentration and H2/CO value. However, the changes in gas composition would be neglected when SRT was above26s. The optimum S/B was found to be0.4-0.6for syngas production. At the optimum value, the H2+CO concentrations in gas product reached about70%and the H2/CO value was from2.0to2.5. Moreover, the optimum catalytic temperature was650℃for tar cracking and CH4reforming.(3) Syngas production from in volatile release stage and char gasification stage were studied in a lab-scale fixed bed. The results showed that high temperature was in favour of gas and syngas (H2, CO) yields in the two stages. When the reactot temperature was above750"C, gas yield and H2/CO were depended on the char gasification reaction. The thermalgravitic analysis revealed the mass loss of the sample in steam atmosphere was divided into two stages (221～351℃and740-805℃). The two stages were respectively described by second reaction model and random nucleation model. The calculated activation energy values in two stages were87.10kJ/mol and80.45kJ/mol, respectively.(4) TGA, TG-MS and GC-MS were used to study kinetic and mechanism of tar decomposition. The activation energy of tar decomposition was determined to be53-73kJ/mol at different conversions using FWO and KAS methods. The decomposition of tar was described by single order of reaction function and the reaction kinetic equation estimated by master plots method. With the prolonging pyrolysis time, the contents of compounds in the tar decreased. The temperature range of light components in gas product from tar decomposition was corresponding to the temperature range of mass loss. Main gas product released within150℃. When the temperature was above400℃, released gas product included CO, CO2, H2O and CH4. Compounds in tar increased with the prolonging reaction temperature, and then decreased. The contents of monocyclic aromatic hydrocarbons and oxy-compounds decreased, while PAHs gradually formed. After120s, the tar was converted to porous solid carbide. The main composition was PAHs more than4-ring and aliphatic hydrocarbon about C20.(5) Allothermal catalytic gasfication of biomass for syngas production using biomass micron fuel (BMF) was developed, and studies on a pilot-scale gasification system were carried out. Combustion of BMF could provide the higher temperature for gasfication reactions and the flue gas from the combustor contained less NOX and SO2. Under the optimum conditions, the gas yield reached1.31Nm3/kg with H2+CO concentrations of70.1%and H2/CO value of2.07. The energy evaluation on the pilot-scale gasification system suggested that cold gas efficiency, energy recovery and energy consumption ratio were48.57%、60.04%and2.40, respectively. The gasification process was high efficiency, low-cost and low contamination emission.更多还原