【作者】 齐国利；

【导师】 谈和平； 董芃；

【作者基本信息】 哈尔滨工业大学 ， 动力工程及工程热物理， 2010， 博士

【摘要】 在生物质能源的利用技术中,生物质热解气化技术是一种通过热化学反应将固态生物质转换为气体燃料的过程。但是传统的气化技术存在着燃气中焦油含量高、废水难以处理等问题,特别是焦油含量高是目前生物质热解气化技术面临的主要问题。目前能有效解决焦油问题方法之一是高温热裂解法,它是一种简单易行、具有工程应用前景的焦油脱除方法。本文针对生物质利用过程中焦油含量高的问题,提出了生物质热解及焦油高温热裂解的技术路线,通过实验和数值模拟,研究了生物质热解特性,分析了生物质油和焦油的热裂解特性,得到如下结果:(1)利用热重分析法研究了典型生物质稻壳、玉米秸秆和白桦木屑的热解过程,分析生物质热解的一般规律。通过比较慢速升温和快速升温条件下生物质热解过程的差异,发现热重法可以定量预测粒径小于0.2mm生物质的热解过程,能够定性描述粒径小于1mm生物质的热解过程。(2)设计研制了一种生物质热解及焦油高温热裂解实验系统,该系统将生物质热解和焦油的高温裂解分开,通过改变燃烧器的供热量和蓄热式陶瓷裂解器的截面积,来调节焦油裂解的温度环境和停留时间。实验运行结果表明本文设计的生物质热解及焦油高温热裂解系统不仅能够提供焦油裂解所需的高温温度场,而且能够准确测定焦油在此温度场的停留时间。(3)在生物质热解及焦油高温热裂解实验台上考察了裂解温度对焦油种类、热解产物、气体产物成分、焦油中化合物成分的影响以及停留时间对焦油裂解率的影响。结果表明随着温度的升高液体产物产率经历了先升高后减少的过程,温度为500℃时,液体产物产率最高,之后随着温度的提高,液体产物产率逐渐减少,当温度达到1200℃时,生物质气中焦油含量已达到11.7mg/Nm~3;当温度达到1200℃时,焦油含量中的成分主要是三环、四环的芳香族有机物,焦油种类从129种下降到18种;增加停留时间可以明显降低生物质气中的焦油含量,但当温度达到1200℃时,停留时间为0.5s时焦油量急剧下降,再增加时间则焦油量变化不明显。(4)建立了生物质热解及液体产物高温热裂解的化学反应动力学模型,该热解模型根据液体产物的特点将可凝挥发份分为生物质油和焦油。将化学反应动力学方程和能量方程耦合,通过数值模拟,分析温度、停留时间、粒径和压力等参数对生物质热解及焦油高温热裂解的影响。结果表明:热解反应的吸热效应对温度场和反应进程有较大的影响,大颗粒在靠近中心的几层在热解反应区出现一段温度近似维持恒定的水平段,在该阶段前后则是纯物质受热升温物理过程中常见的指数温升曲线,预测结果与实验值基本吻合。更多还原

【Abstract】 Among biomass energy utilization technologies, biomass pyrolysis and gasification technology is a process which is to convert solid biomass into gaseous fuel through thermal chemical reaction whose gas products of biomass pyrolysis can be used for power generation, gas supply and central heating. But there are some problems for traditional gasification technology, such as high tar content in biomass fuel gas and waste water difficult to treat. In particular, high tar content in fuel gas is the main problem for biomass pyrolysis and gasification technology. At present, one of the most effective methods to thoroughly solve the problem is high-temperature thermal cracking which is simple and feasible and has the engineering application promise. This dissertation aiming at the high tar content in biomass utilization, proposed a technique route of biomass pyrolysis and tar thermal cracking, and experimentally and numerically investigated biomass pyrolysis characteristics and analyzed thermal cracking characteristics of bio-oil and tar. The main results are as follows:(1) Pyrolysis process of typical biomass, such as rice husk, corn straw and birch is investigated by thermogravimertric analytical method. The general rule of biomass pyrolysis is analyzed. Comparing slow heating rate with fast heating rate for biomass pyrolysis process, thermogravimetry may be used to quantitatively predict biomass pyrolysis process of small particles whose diameters are less than 0.2mm, and qualitatively describe biomass pyrolysis process of larger particles whose diameters are less than 1mm.(2) The experimental system of biomass pyrolysis and tar high-temperature thermal cracking was developed, and biomass pyrolysis and tar high temperature cracking were separated by changing heat output of combustor and cross-section area of regenerative ceramic cracker to adjust temperature environment and residence time for tar cracking. Results show that experiment system not only can supply the required high temperature field for tar cracking, but also accurately measure the residence time of tar in the temperature field.(3) The effect of cracking temperature on species of tar compounds, pyrolysis products, pyrolysis products composition and substance in tar, and the effect of residence time on ratio of tar cracking were studied. Results show that the liquid product yield experiences from an increasing process to a decreasing one. Liquid product yield reaches maximum when pyrolysis temperature is 500℃. Liquid product yield gradually decreases as temperature increasing; tar content of biomass fuel gas reaches 11.7mg/Nm~3 when temperature reaches 1200℃; tar composition is the main aromatic compounds with 3-rings and 4-rings, and tar species reduce from 129 to 18 when pyrolysis temperature reaches 1200℃. Tar content in biomass gas is obviously reduced, but when pyrolysis temperature is 1200℃, tar content of biomass gas sharply declines as residence time is 0.5s. Further increasing residence time, tar content will not change significantly.(4) A chemical reaction kinetics model of biomass pyrolysis with liquid product high-temperature thermal cracking was established. Based on characteristic of liquid products, the condensable volatile is divided into two parts: tar and biomass oil. The effects of temperature, residence time, particle size, velocity, pressure and other parameters on biomass pyrolysis and tar high-temperature cracking were numerically investigated. Results show that the effect of endothermic of pyrolysis reaction on temperature field and reaction process is great; the pyrolysis reaction zone appears a constant temperature period in several layers near the center of large biomass particles; before or after the period, pure physical process of material heated is observed according to the index curve of temperature; the simulation results agree with the experimental well.更多还原