煤慢速热解过程交联反应动力学特性与化学渗透热解模型

To support the development of coal liquifaction, a practical model for slow pyrolysis is necessary to be developed based on the mechanism of coal pyrolysis. The chemical percolation model for devolatilization (CPD) is good to predict the volatile yields during the rapid pyrolysis in coal combustion. However, the agreement of this model with experiments is not good during slow pyrolysis. It is mainly because the cross-linking reaction is too simplified. The influence of crosslinking reaction on the amount of bridges is neglected in CPD model. The kinetic parameters of crosslinking reaction are constant for all coals, and do not change with changing function group structure. The influence of the radicals generating from the cleaving of unstable bridges and side chains on crosslinking reaction rate is not be considered. The char with more side chains and fewer unstable bridges will be produced from maceral during rapid pyrolysis. Then the rapid pyrolysis char and the mixture of maceral with its rapid pyrolysis char will be pyrolyzed respectively again in fixed bed reactor slowly. Through the change of the bridge amount during the slow pyrolysis, the effect of cleaving of side chains and unstable bridges on crosslinking reaction will be studied. A correlation between the kinetic parameters of crosslinking reaction and the function group structure parameters will be established. Moreover this correlation will be introduced into CPD model, and the crosslinking reaction path will be added to improve the accuracy of CPD model for slow pyrolysis.

为促进煤液化技术发展，需要建立能够反映煤热解机理，并能应用于工程实践的煤慢速热解模型。目前广泛应用于煤燃烧领域的煤化学渗透热解（CPD）模型，在慢速热解条件下与实验吻合不好，其主要原因是模型中交联反应计算方法过于简化，不能反映交联反应对煤内桥键数量变化影响，不能反映交联反应动力学特性随煤官能团组成的变化，不能反映慢速热解条件下，不稳定桥链、侧链裂解生成自由基对交联反应速率的影响。本项目通过快速热解制备不稳定桥链含量较少，侧链含量较多的半焦。通过分析煤显微组分快速热解半焦以及显微组分与其快速热解半焦混合物，在固定床反应器慢速热解过程中桥链数量的变化，并结合自由基生成原理，研究交联反应与侧链裂解的关系，分析不稳定桥链裂解对交联反应速率的影响，拟合计算关联式，通过煤分子结构计算交联反应动力学参数。并将关联式引入CPD模型，在模型反应框架中补充交联反应路径，建立适用于煤慢速热解的化学渗透热解模型。

煤化学渗透热解（CPD）模型中交联反应计算方法过于简化，因而不适用于煤慢速热解过程，为解决该问题，本项目对煤热解过程交联反应动力学特性与自由基作用关系进行了研究，主要研究工作与成果如下：1.为获得准确的煤结构信息，通过分离CP/MAS 13C固体核磁共振中H原子向C原子的连接和非链接磁化转移，建立了煤结构定量表征方法；2.利用快速热解消耗煤中部分易反应桥链，制备侧链含量较多的半焦，并建立了利用桥、侧链及脂肪结构数量计算煤热解过程孔隙结构演变模型;3.快速热解半焦与原煤混合慢速共热解，分析侧链数量与官能团组成对交联反应的影响，发现在不同混合比例下共混热解半焦中都出现了脂肪桥和醚键数量增多形成交联桥链的现象，不同温度下共混热解半焦中稳定自由基浓度的分析表明，煤热解过程自由基间的聚合反应路径很大程度上取决于自由基间的数量关系；4.修正了CPD模型中的反应路径，按稳定性将煤内官能团分为三类，并拟合了三类官能团的反应动力学参数，利用三类官能团裂解的重合度反映热解过程自由基间数量关系随加热速率变化对交联反应的影响，建立了适用于慢速热解的化学渗透热解模型。