稻草烘焙过程和后续热解过程中氯和钾的迁移机制

发布时间：2018-04-20 02:34

  本文选题：稻草 + 烘焙　； 参考：《华东理工大学》2017年博士论文

【摘要】：生物质多富含氯和碱金属,在热化学转化过程中部分氯和碱金属将释放至气相,导致设备和运行问题以及环境污染问题。本文以稻草、木屑、马尾藻和玉米秆为生物质原料,研究了生物质烘焙过程中氯和钾的迁移行为。同时本文结合烘焙稻草高温热解焦的物理化学性质,进一步研究了烘焙预处理对稻草高温热解过程中氯和钾迁移行为的影响。主要研究结论如下:(1)研究了生物质烘焙过程中氯和钾的释放及赋存形态转化规律,并考察了烘焙生物质的化学组成、表面形貌和孔隙结构。结果表明,当烘焙温度低于250—时,烘焙对生物质孔隙结构的影响较小;当烘焙温度为300—时,中孔和大孔的比表面积略有增大,微孔比表面积则显著增加。氯的释放与脱挥发分同步,并且无机氯部分转化为有机氯赋存在烘焙生物质中。钾的释放率小于氯的释放率,水溶态钾部分转化为离子交换态钾,同时颗粒粒径对钾的迁移影响较小。烘焙稻草表面还存.在富含氯和钾元素的颗粒物。(2)研究了烘焙预处理对稻草800-1200℃高温热解焦表面形貌、孔隙结构和石墨化程度的影响,考察了烘焙稻草高温热解焦的气化反应活性。结果表明,烘焙预处理导致稻草高温热解焦的比表面积减小。稻草烘焙过程中挥发分脱除越多,则高温热解焦的比表面积越小。300℃烘焙预处理导致水洗稻草高温热解焦的比表面积显著增大。当烘焙温度高于250℃时,烘焙导致稻草热解焦的石墨化程度降低。随着烘焙温度的升高,水洗稻草热解焦的石墨化程度则升高。烘焙均导致稻草和水洗稻草热解焦的气化反应活性降低。(3)研究了稻草原料及烘焙稻草在800-1200℃热解过程中氯和钾的释放及赋存形态转化规律,分析了烘焙预处理对稻草高温热解过程中氯和钾迁移规律的影响。结果表明,随着烘焙温度的升高,热解过程中氯的释放率存在减小趋势。当热解温度低于900℃时,烘焙导致稻草烘焙和热解整个过程中钾的总释放率大于稻草原料的钾释放率;当热解温度高于1000℃时,烘焙稻草的钾总释放率与稻草原料的钾释放率相近。烘焙对稻草高温热解过程中氯和钾迁移行为的影响主要包括五个方面:①烘焙过程中形成有机氯;②烘焙过程中水溶态钾转化为离子交换态钾;③烘焙过程中稻草的挥发分含量降低;④烘焙减弱了高温热解焦的多孔特性;⑤烘焙过程中氯和钾在稻草表面富集。
[Abstract]:Biomass is rich in chlorine and alkali metals, some of which will be released to gas phase in the process of thermochemical conversion, resulting in equipment and operation problems and environmental pollution. The migration behavior of chlorine and potassium during biomass baking was studied using straw, sawdust, sargassum and cornstalk as biomass raw materials. At the same time, combined with the physical and chemical properties of high temperature pyrolysis of baked straw, the effects of baking pretreatment on the migration of chlorine and potassium during the high temperature pyrolysis of straw were further studied. The main conclusions are as follows: (1) the release and transformation of chlorine and potassium during biomass baking were studied, and the chemical composition, surface morphology and pore structure of roasted biomass were investigated. The results showed that when the baking temperature was lower than 250 -, the effect of baking on the pore structure of biomass was small, and when the baking temperature was 300 -, the specific surface area of mesoporous and macroporous increased slightly, while the specific surface area of micropore increased significantly. The release of chlorine is synchronized with the devolatilization, and the inorganic chlorine is partly converted into organic chlorine, which is stored in roasted biomass. The release rate of potassium is smaller than that of chlorine. The water-soluble potassium is partially transformed into ion-exchange potassium, and the particle size has little effect on the migration of potassium. The baking straw remains on the surface. The effects of baking pretreatment on the surface morphology, pore structure and graphitization degree of rice straw pyrolyzed at 800-1200 鈩，

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