稻秆的烘焙预处理及其固体产物的气化反应性能

摘要

稻秆资源分散、水分含量高且密度低、热值低,烘焙预处理技术能够降低收集运输的物流成本,获得的固体产物能量密度高、可磨性好,适于气流床气化.在固定床热解装置上通N2保护,稻秆分别经过2000℃、2500℃、3000℃烘焙300min,得到的固体产物在热重分析仪中与CO2进行非等温气化实验,升温速率200℃/min,终温102000℃.实验结果表明,稻秆烘焙产物以固体剩余物和不凝结气体为主,还有少量可凝结液体(水分和焦油).气体产物中CO2所占比例超过80%,其次为CO和微量CH4.预处理温度越高,固体剩余物越少、气体产物越多,可凝结性液体变化不大.稻秆烘焙过程的能量产率为40%～60%,随温度升高经历了急剧下降和缓慢降低两个阶段.固体剩余物的可磨性相比原始稻秆有了很大的提高,易于制细粉用于气流床气化.烘焙温度升高,所得固体产物气化反应性提高.根据Coats-Redfern法确定烘焙稻秆焦-CO2气化反应机理符合二维扩散模型,求得反应活化能730kJ/mol～880kJ/mol.%Torrefaction is a main pretreatment technology for improving the properties of rice straw in order to deal with such problems as dispersed resource, high moisture content, high bulk volume and low heating value.The straw after torrefaction was gasified in an entrained flow gasifier because of high heating value and good grindability.Straw samples were torrefied in a fixed bed reactor at 200 ℃, 250 ℃ and 300 ℃ for 30 min under nitrogen atmosphere.The non-isothermal gasification was carried out in a thermogravimetry analyzer (TGA) with heating rate of 20 ℃/min and final temperature of 1 200 ℃.The results show that the products are mainly solid product and gases, as well as a mount of condensable liquid ( water and tar).The ratio of CO2 in gases is up to 80％ remaining a little CO and CH4.The total weight of solid product decreases with increasing temperature of torrefaction, accordingly that of gas products increases; the liquid products changed little at different temperatures.The energy efficiency of torrefaction is about 40％ to 60％ and decreases sharply then drops slowly with increasing reaction temperature.The grindability of solid product is improved by torrefaction and easy to be pulverized for utilization in an entrained flow gasifier.The results of TGA indicate the biomass sample pretreated at higher torrefaction temperature has higher gasification reactivity.The mechanism of reaction between torrefied straw and carbon dioxide could be simulated by a two dimension distribution model (2D).The apparent activation energy calculated by Coats-Redfern method is about 73 kJ/mol ～ 88 kJ/mol.