煤热解制备高品质焦油反应定向方法与机理

Pyrolysis for high-quality tar and gas is the core technology for value-added cascade utilization of coal. The critical problem that causes the difficulty in industrial applications of coal pyrolysis technology is the formation of too many heavy species. Addressing this problem, this project is devoted to the control of pyrolysis reactions and in turn the intentional manipulation of pyrolysis product. It investigates the approach and mechanism of reaction control from both molecule/particle and particle/reactor scales. In the molecular scale the free radical stabilization reaction will be optimally controlled by adding external free radicals to obtain the expected primary pyrolsyis products, while in the reactor scale the secondary reactions occurring to the primary pyrolysis product will be manipulated through optimizing the mutual matching conditions and manners among the product flow, gas-solid transfer and the secondary reactions. The use of some particular internals in the pyrolsyis reactor will be employed as the major means for implementing the control in the latter case, which is in fact determinative of the quality of the finally pyrolysis product. In addition, this study will also test the possibility and its implied mechanics for upgrading the pyrolsyis product through the in-situ catalysis of coal char material. As a consequence, the study is expected to provide a solid support from both practical approach and theoretical justification for the pyrolsyis reactor innovation that leads to the production of high-yield pyrolysis oil rich in light fractions and lean in heavy components.

煤热解制备高品质焦油和热解气是煤炭高效分级利用的核心技术之一。本项目针对阻碍煤热解技术工业应用的重质组分大量生成难题，提炼调控热解反应、定向热解产物的关键科学问题，分别从分子/颗粒和颗粒/反应器尺度研究热解反应的一次产物定向、反应器中产物流动传递与二次反应匹配及最终产物定向的调控方法与作用机制。通过半焦气化及其催化裂解/重整碳氢烷烃强化外部自由基供给而调控自由基稳定反应和一次热解产物组成；探索反应器中一次产物流动及其与物料、反应场温度的作用关系，明确定向调控热解二次反应和最终热解产物的措施与作用机制；并研究热解反应器内煤半焦原位催化一次及二次热解产物，定向提升热解产品品质的可能性与反应机理。本项目的实施将为创新反应器，建立抑制重质组分生成、提高轻质组分含量及产率的热解新工艺提供方法与理论支撑。

影响煤热解技术工业化应用的关键问题是焦油产率低、焦油中重质组分和粉尘含量高。针对这些问题，本项目致力于研究煤热解制备高品质焦油的反应控制方法和机理。研究了热解反应气氛对热解产物分布的影响、热解器中内构件对产物流动传递与二次反应匹配的调控作用、半焦基催化剂对热解油气的原位催化提质，获得了以下主要结果。. (1) 采用输送床反应器研究了温度和气氛对煤快速热解行为的影响。合成气中的氢气是导致焦油产率增加的主要原因，它能提高H自由基含量，抑制焦油的聚合反应以及与芳香族化合物发生加氢反应。焦油分析结果表明在较高的温度下含水蒸气的合成气气氛结合了合成气和水蒸气的优势，即合成气能提高轻质焦油和重质焦油的产率，而水蒸气能降低重质焦油的产率。. (2) 建立了具有传热板和中央集气管的内构件移动床新型热解反应器。与传统的反应器相比，内构件反应器中煤热解时间缩短，焦油产率提高，焦油中轻质组分的含量增加。随着外炉加热温度升高，传统的反应器中焦油产率下降，而内构件反应器的焦油产率升高。传热板以强化传热为主要作用，可显著提高煤升温速率；而中央集气管通过改变气相产物的流动方向由高温区向低温区，通过减少焦油的二次热解反应而提高焦油产率，并对焦油中的重质组分进行原位截留和再裂解，提高焦油中轻质组分的含量，提高焦油的品质。. (3) 采用两段式固定床，获得了煤热解油气产物二次原位催化裂解对焦油的提质作用。以半焦为催化剂载体，通过添加不同活性金属和助剂进行催化剂筛选，发现Ce-Ni/char催化剂既具有较好的焦油裂解活性又能抑制积炭，焦油中轻质焦油的含量和轻质焦油产率显著提高。Ce的添加可改变催化剂的酸性位分布并使催化剂上负载的金属Ni分布更加均匀，避免了Ni颗粒聚集而产生强的酸性位。. 通过以上研究揭示了煤热解反应中的过程调控机制，为创新煤热解反应器、解决煤热解油重质组分含量高的技术难题提供了可行的方法和理论依据。