热态原位半焦催化脱除煤焦油机理及其气化活性受损评估

The problem caused by tar is a major technical barrier for developing the clean and effective coal gasification technology. Many researches have demonstrated that char is a good catalyst for tar removal, due to its obvious property, such as wide and cheap material sources, reusing easy by gasification and combustion if deactivated. However, the existing reports mainly focus on the feasibility research on tar removal by char and the improvement of tar removal efficiency. Researches about the mechanism of tar catalytic removal by char and the evolution of char's reactivity in this process are very few, strongly inhibiting the rapid development of this novel tar removal technology. In this study, a two-stage reaction apparatus consisting a coal pyroyzer and a tar cracker will be adopted. Tar produced in the pyrolyzer is transported into the cracker which is filled with the hot in-situ char bed layer, and then the tar removal property of char and the evolution of tar components will be examined systematically. An apparent kinetics model about tar removal by char will be proposed. The effect of tar removal on the change of char's specific surface area, pore structure and carbon matrix is also analyzed fully. And then a novel micro fluidized bed reactor is adopted to examine the change of gasification behavior and kinetics in the atmospheres of CO2 and steam for the char used in tar removal. Finally a kinetics model of char gasification considering the effect of tar inhibiting effect will be deduced. On the basis of this study, we hope to fill the gasps of the mechanism of tar removal by char, probe the inhibiting effect of tar removal on the structure and gasification behavior of char, and also guide the development of novel coal gasification technology.

煤焦油是清洁、高效煤气化技术开发过程中迫切需要解决的技术难题。研究表明，半焦能有效地脱除焦油，且具有来源广、成本低、失活后可继续用于气化等优势。然而，现有的相关研究大多集中在半焦脱除焦油的可行性论证和焦油脱除效率的改进上，而对半焦脱除焦油的机理和焦油脱除过程中半焦气化活性的变化规律研究很少，严重制约着该技术的发展。本研究拟在两段反应器内系统地研究热态原位半焦对煤焦油的脱除性能和焦油组分的演变规律，建立煤焦油脱除的宏观动力学模型；同时全面分析焦油脱除过程对半焦的孔道结构、碳微观结构等的影响，进而揭示半焦对煤焦油的脱除机理；最后，利用新型的微型流化床反应分析仪来研究焦油脱除过程对半焦与CO2/水蒸汽气化活性和动力学的影响，建立含焦油抑制效应的半焦气化反应模型。本研究可以填补半焦催化脱除焦油机理的空白，并揭示焦油脱除过程对半焦气化活性和动力学数据的影响，为新型气化工艺的开发提供理论依据。

煤焦油是煤中、低温气化过程中不可避免的液体副产物，其遇冷凝结，易堵塞管路、腐蚀设备、引起催化剂中毒、带来酚水等二次污染，对气化工艺影响严重。半焦属于非金属催化剂，能有效脱除焦油，且原料廉价易得，再生容易，有效避免硫/氯等元素引起的中毒等特点。目前，有限的文献研究多基于冷态半焦进行，未能真正反应气化炉内的真实情况。.基于此，本课题利用原位（热态）半焦来研究半焦的脱焦油特性，并评估其自身活性受损情况。主要开展以下几个方面的研究：原位半焦的制备方法，原位半焦和非原位（冷态）半焦的脱焦油性能比较、半焦催化焦油后气化活性评价、半焦脱除焦油的潜在工业应用等。研究发现，同等制备条件下，原位半焦比非原位半焦具有更大的比表面积和更发达的孔结构，且碳微晶结构有序度较低，碳原子的活性较高，具有更强的脱焦油性能，生成气体中焦油含量更低。分析焦油裂解过程中，热裂解作用、部分氧化作用和半焦的催化重整作用发现，部分氧化和半焦催化重整在焦油脱除和气体改质方面较热裂解方法更有效，且具有选择性，在部分氧化作用下半焦的积碳明显变弱。半焦的比表面积越大，对焦油的催化重整效果越好。半焦中的微孔和介孔对焦油脱除都有贡献，其中微孔的贡献更大。半焦用后比表面积下降，尤其是微孔的比表面积，而介孔的比表面积大幅增加。通过在脱灰半焦中负载金属氧化物发现，不同种类的金属氧化物对焦油的脱除效果不同，钙和铁氧化物的活性较好。EDS分析表明，催化裂解焦油后的半焦在900℃与水蒸气发生部分气化反应后，其表面得到有效更新，碱金属和碱土金属元素进一步富集，有助于半焦催化活性的恢复。针对原位半焦的气化行为和反应动力学，采用微型流化床反应分析仪，构建了原位半焦的气化分析分析方法，建立反应动力学模型。在上述研究的基础上，形成了流化床两段气化技术，充分利用热态原位半焦的催化重整作用来脱除焦油，该技术广泛应用于煤、生物质等含碳原料的气化利用，具有重要的经济、社会和环保效益。