基于离散颗粒单元法的流化床生物质气化过程研究

Study on the Biomass Gasification Process in Fluidized Bed Based on Discrete Element Method

基于离散颗粒单元法提出气相和颗粒相控制方程,结合化学反应动力学方法建立生物质气化模型,通过模拟空间液滴在湿空气中的蒸发过程验证了模型的可靠性,数值模拟流化床内生物质气化过程。模拟结果给出生物质颗粒在反应器内的流动特性与反应特性瞬时分布情况,床层内气泡周期性地产生、上浮最终破裂,进入反应器内的生物质随着床料颗粒一同周期性上浮和下沉,最终与床料充分掺混,并且均匀分布于床料中。燃料颗粒进入反应器后会迅速热解析出挥发分,并由气流从顶部出口带出。模拟给出气体产物质量分数瞬时分布,CH4、CO、CO2、H2这4种产物质量分数分布基本一致,都是集中分布于左壁面,CO和CO2的占比稍高;N2和O2的分布与前4种分布规律正好相反;H2O的分布则稍有不同,在进料口附近的浓度梯度较小。

Based on discrete element method, the control equations of gas and solid phases were proposed. The reliability of the model was verified by simulating the evaporation process of droplets in wet air, and the model was presented for simulating the biomass gasification process in the fluidized bed. The simulation results show the instantaneous distribution of the flow and reaction characteristics of biomass particles in the reactor, and the bubbles periodically generate and float up and eventually break in the bed. The biomass particles entering the reactor periodically floated up and sink with the bed particles, then biomass is fully mixed with the bed material and evenly distribute in the bed materials. After the fuel particles entered the reactor, it would pyrolysis the volatiles rapidly and be carried out by the air flow from the top outlet. The simulations show the instantaneous distribution of mass fraction of gas products. The gas species CH4, CO, CO2, and H2 are basically the same distribution, and the proportion of CO and CO2 is slightly higher. The distribution of N2 and O2 was contrary to the former four distribution rules. The distribution of H2 O gas species was slightly different, and the concentration gradient near the inlet was lower.