内构件移动床热解反应器空腔介尺度结构机制及其对气固作用影响

By mounting a central gas collection channel, numbers of heat-transfer enhancement internals connecting to heating wall and recycling pyrolysis gas into the reactor from the heating wall, a newly devised moving bed reactor with internals has shown to be highly effective in directing the coal pyrolysis reactions and breaking through the technical difficulties of coal pyrolysis for producing high-quality pyrolysis tar and gas at high yields. Of this new reactor, the part between the walls of the reactor and central channel forms actually a moving bed with the cross flow of the recycled pyrolysis gas so that the so-called gas cavity, the meso-scale flow structure of this type of reactors to be possibly formed to lower the gas-solid reaction performance inside the reactor. The growth and breakage of gas cavity represents the meso-process of the reactor. Although there are lots of literature studies about gas cavity, the quantitative analysis of its mechanism of formation and variation has been mostly based on the force balance of the particle layer above the cavity, making it difficult to predict the structure or boundary of the gas cavity and its dynamic variations with the flow conditions. The research contents of this program include the matching between flow, temperature and transfer in pyrolysis reactor and the control methods of pyrolysis products. This study proposes that the existence of a gas cavity in the moving bed is subject to a characteristic pressure that can be formulated from experimentally measured data based on particle force balance analysis. In turn, CFD simulation of the flow field is performed to get the iso-pressure contours that are then correlated with the estimated characteristic pressure for an existing gas cavity to define the boundary of the cavity. Via this way, it is also possible to investigate the dynamic variations of the boundary and structure of the gas cavity through CFD simulation. Furthermore, the study defines the particle-fluid interaction factor, which shows in fact the probability of particle-fluid interaction, to be the product between the gas flux through an elemental bed volume and the particle volume in such a bed element. Based on CFD simulation this study will for the first time investigate the distribution of the interaction factor inside the reactor. The study will also systematically investigate the effects of the perpendicular heat-transfer internals on the formation and variations of gas cavity and on the distribution of particle-fluid interaction factor. It is expected that the results from the study will greatly support the further optimization of the moving bed reactor without the gereration of gas cavity, which will be benefitial to the development of the corresponding reactor and its application to coal pyrolysis.

内构件移动床反应器通过设置中心集气通道、与壁面直交传热强化构件和从反应器壁循环热解气实现热解反应和产物的定向、突破煤热解制备高品质油气技术难题。反应器壁与中心集气通道壁之间形成错流移动床反应器，循环热解气流动可能导致气体空腔介尺度结构及其成长与破裂演变的介尺度过程。文献研究通常基于颗粒床力平衡分析研究空腔形成机制，不能预测空腔结构边界及其演变特性。本项目研究热解产物流动-温度-传递场匹配与产物调控方法，在此基础上提出错流移动床的流体空腔受控于特征压力机制，通过建立特征压力方程，基于CFD模拟反应器全流场，进而结合特征压力计算而预测气体空腔边界，研究其随操作条件的演变。定义任意单元在单位时间内流过的流体体积与单元内颗粒体积之积为颗粒流体作用因子，根据CFD模拟定量颗粒流体作用强度的空间分布。该研究将为进一步优化移动床煤热解反应器结构、避免产生气体空腔现象提供理论支持。

为了解决煤炭热解制备高品质油气技术难题,内构件移动床反应器设置中心集气通道,与壁面直交传热强化构件和从反应器壁循环热解气,实现产物的定向热解。反应器壁与中心集气通道壁之间形成错流移动床反应器，循环热解气流动可能导致气体空腔介尺度结构及其成长与破裂演变的介尺度过程。.本项目开展了热解产物流动-温度-传递场匹配与产物调控方法研究。此外，实验和模拟结果表明在移动床热解反应器中介尺度空腔结构极难发生，因此，本项目对于移动床空腔介尺度问题不再研究，而进行了内构件固定床及移动床反应器内广义介尺度结构特征的模拟研究。（1）通过在固定床热解反应器的内外层分别加入石英砂的对比实验，清楚的解析了中心集气管内构件的加入确实改变了反应器内部的产物流动方向，大大减少了热解产物的二次反应，提高了固定床反应器中油页岩热解的页岩油收率；（2）采用上下两段加热的方式，上段产生热解油气，通过调节下段的温度场考察热解油气二次反应与温度场的关系，进而阐明内构件调控产物从高温区向低温区流动实现了温度分布和二次反应的匹配，同时挥发分携带的热量也加热了内层的油页岩，提高了热效率。（3）通过两段反应器分离了煤热解和二次反应过程，研究了不同温度的半焦对先锋褐煤热解产物分布和品质的影响。（4）基于煤热解固定床反应器的CFD模型，同时考虑煤热解反应和焦油的二次裂解反应，对内构件的影响机制进行考察，并且通过模拟优化了操作参数和内构件反应器的结构参数，模拟结果表明，中心集气管通过加强气体对流传热增强了床层的径向传热，传热板通过提高床层内的辐射传热增强了床层内的传热，相比集气管，传热板强化传热的效果更显著。.本项目为实现热解过程的可控调节提供了理论依据。