【作者】 马强；

【导师】 王勤辉； 程乐鸣；

【作者基本信息】 浙江大学 ， 热能工程， 2010， 硕士

【摘要】 能源危机与温室效应使高效低污染的近零排放系统备受关注。以生物质为原料的无氧气化制氢系统不但能够利用废弃的生物质制取高纯度氢气,而且可以同时获得便于后续存储和利用的高浓度C02。基于、CaO吸收体气化法是生物质无氧气化制氢技术的核心。本文对CaO存在条件下生物质的热解反应以及生物质半焦的富氧燃烧反应这两个工艺中的重要过程开展了实验研究,为下一步生物质无氧气化技术的研究和开发提供参考。利用热重-傅立叶变换红外分析联用(TG-FTIR)与XRD分析相结合的方法研究了生物质木屑在CaO存在条件下的常压热解反应特性,并获得CaO添加量、升温速率对生物质常压热解失重过程和挥发份的析出过程的影响特性。实验结果表明CaO吸收剂的加入改变了生物质木屑的热解特性,在低温热解阶段CaO能够吸收部分生物质热解产生的CO2,产生CaCO3,同时能够吸收H20产生Ca(OH)2,在高温热解阶段CaCO3和Ca(OH)2又分解生成CaO、CO2和H2O。CaO的添加量越大,对热解过程的影响越显著。同时CaO吸收剂的加入还降低了热解气中H2O、CO、CH4以及羰基、芳香烃和酚等焦油类物质的析出。升温速率提高,热解初始失重温度变大,造成热解曲线失重部分整体向高温方向移动,且半焦产率增加。利用加压热重分析仪(PTGA)、气相色谱分析仪以及XRD分析相结合研究了压力对CaO存在条件下生物质热解反应的影响特性。结果表明压力对木屑热解过程有明显的影响。随压力的提高,热解初始失重温度变大,造成热解曲线失重部分整体向高温方向移动,热解半焦产率提高。对于CaO存在条件下的木屑热解过程,提高压力能够促进CaO吸收CO2的碳酸化反应,同时提高所产生CaCO3的煅烧分解温度,有利于生物质无氧气化制氢系统气化炉中CO2的吸收固定。热解压力的提高还可以抑制热解焦油类物质的挥发,增加焦油类物质通过CaO吸收剂的停留时间,有利于生物质无氧气化过程中焦油的去除和分解。利用加压热重分析仪(PTGA)、扫描电镜(SEM)技术相结合研究了生物质木屑热解半焦的加压富氧燃烧特性,考察不同热解条件和不同燃烧气氛对热解半焦燃烧特性的影响。结果表明加压或CaO存在的条件下所获得的半焦反应活性变差,使得半焦的燃烧着火温度升高,半焦燃烧稳定性变差。在压力不变的条件下,随着O2浓度的增加,燃烧初始失重温度变小,造成燃烧曲线失重部分整体向低温方向移动,燃烧着火温度降低,燃烧稳定性整体提高。保持O2浓度不变时,在常压-1.3MPa范围内提高反应压力力,对半焦的燃烧特性有类似的影响。保持O2分压不变,提高反应压力,降低O2浓度,燃烧初始失重温度变大,造成燃烧曲线失重部分整体向高温方向移动,着火温度升高,燃烧稳定性降低,不利于燃烧反应进行。说明O浓度对半焦燃烧反应的影响比压力更明显。更多还原

【Abstract】 There is an increasing attention on the high-efficiency and low-pollution near zero emission system due to the energy crisis and greenhouse effect. Adopting iste biomass as feedstock, the zero emission system can produce not only high purity hydrogen but also high concentration CO2 that easier to be stored and utilized. Biomass anaerobic gasification based on the methodology of CaO absorbent gasification is the core unit for biomass near zero emission system. This article gives experimental study of both biomass pyrolysis in presence of abundant CaO sorbents and biomass char oxygen-enriched combustion at elevated pressures. The results are expected to provide reference material for the utilization of biomass anaerobic gasification in future.Adopting thermogravimetric Fourier transform infrared (TG-FTIR) analysis and X-ray diffraction (XRD) technology, sawdust atmospheric pyrolysis in presence of abundant CaO sorbents is studied. Effects of CaO amounts and heating rates on weight loss process and volatile evolution for sawdust atmospheric pyrolysis are analyzed. Results shows that CaO sorbents can transform the mechanism of sawdust pyrolysis. At lower temperatures, CaO absorb CO2 and H2O in the volatiles, forming CaCO3 and Ca(OH)2, respectively. The produced CaCO3 and Ca(OH)2 then decompose in higher temperatures. The effect of CaO on sawdust pyrolysis is increased with increasing CaO amounts. Moreover, the evolutions of tar species such as CO, CH4, carbonyl groups, aromatics and phenols are also reduced. Additionally, the pyrolysis reaction moves to higher temperatures and the char yield is enhanced with increasing heating rates.Utilizing a Thermax 500 pressurized thermogravimetric analyzer (PTGA) combined with Gas chromatographic (GC) and XRD technology, effect of pressure on sawdust pyrolysis in presence of abundant CaO sorbents is examined. Pressure conditions influence the pyrolysis apparently. Firstly, the pyrolysis reaction moves to higher temperatures and the char yield is enhanced with increasing pressures. Secondly, The CaO carbonation reaction is enhanced and the decomposition temperature of CaCO3 is elevated at pressurized conditions, which are favorable for CO2 capture in the gasifier. Further, residence time of tars species is prolonged at pressurized conditions due to the restrained diffusion. As a result, high pressure pyrolysis is more favorable for tar reduction and decomposition.Using the PTGA and scanning electron microscopy (SEM) analysis, effects of char production and combustion conditions on biomass char pressurized oxygen-enriched combustion are both surveyed. Sawdust chars produced at pressurized conditions or in presence of CaO sorbents have worse reactivity. The ignition temperature increase and the value of combustion stability become lower. With increasing oxygen volume concentrations at steady total pressure, the combustion reaction move to lower temperatures, meanwhile, the ignition temperature decrease and the value of combustion stability become higher. At a steady oxygen volume concentration, the same conclusions can be obtained as above with increasing total pressures from 0.1 MPa to 1.3MPa. Moreover, increasing total pressure at a steady oxygen partial pressure will make the combustion reaction moving towards higher temperature as the oxygen volume concentration decreasing. Correspondingly, the ignition temperature increase and the value of combustion stability become lower. Oxygen volume concentration has larger influence on char pressurized oxygen-enriched combustion than the total pressure.更多还原