太阳能CO_2煤气化反应器玻璃窗清洁度的数值模拟

Numerical simulation of cleanliness of glass window in solar CO_2 coal gasification reactor

太阳能二氧化碳煤气化拥有减少CO_2排放,清洁、节能地制取高品质高纯度气体燃料的优点.作为太阳能热化学制备清洁燃料的核心部件,旋风流反应器便于输运、液态排渣、效率高、易实现,然而直接式反应器的一个主要问题是煤颗粒会沾染反应器玻璃窗口,影响反应器效率和安全性.针对三维直接辐照旋流太阳热化学反应器,并考虑能流椭球型分布及聚光边界条件,本文采用欧拉-拉格朗日方法建立了气固两相流数学模型并耦合煤颗粒、气体的参与性介质辐射和化学反应动力学模型.与苏黎世联邦理工学院的实验结果对比验证之后,研究了CO_2进气质量流量配比和煤颗粒质量流量对石英玻璃窗表面沉积煤颗粒的影响规律.计算结果表明,保持玻璃窗口清洁主要取决于进气质量流量配比,当CO_2与煤颗粒的摩尔比在1.3～1.8的范围内,腔体、清扫玻璃和输送煤颗粒气体质量流量分别占总CO_2进气质量流量的范围为71.9%～78.2%,15.7%～20.7%和5%～10%,玻璃窗口清洁度最优.煤颗粒质量流量对石英玻璃窗表面沉积煤颗粒的影响不大,但会显著影响煤颗粒运动轨迹.

Solar CO2 coal gasification technology uses highly concentrated solar radiation to generate high temperature above 1000℃, so that the pulverized coal particles can react with CO2 to generate CO in the solar reactor. Compared with common industrial coal gasification tech no logy, solar CO2 coal gasification has the advantages of reducing CO2 emissions and producing high quality and high purity gaseous fuels in a clean and energy efficient manner. Solar coal gasification stores intermittent and unstable solar energy in clean fuels, which has promising application and has attracted the interest of many researchers around the world. As the core component of solar thermochemical, solar reactors are mainly divided into direct and indirect types. The direct reactor is easy to realize and has many advantages,which is convenient for transport and liquid slagging. However, a major problem of the direct solar reactor is that coal particles may contaminate the reactor glass window which will affect the efficiency and safety of the reactor. So keeping the reactor quartz glass clean is the key to increase reactor efficiency and safety. The reactor windows are typically purged with argon to avoid contamination by coal ash and tar, but this also results in reducing thermal efficiency and difficulties of separating from the gas. In this paper, CO2 gas is used as the reactant and also used to clean the quartz glass window in a solar gasification reactor. This paper establishes a three dimensional mathematical model of a directly-irradiated cyclone-flow solar thermochemical reactor. UDF is used to realize the flux ellipsoid distribution and concentrating in fluent software.A gas-solid two-phase flow model is established and the participating media radiati on and chemical reaction kinetic models of coal particles and gases are coupled by Euler-Lagrange method. The numerical results are validated by comparing with the experimental results of ETH cyclone reactor. Then the effect of CO2 intake mass flow ratio and coal particle mass flow on the deposition of coal particles on the quartz glass window surface was studied. The calculation results show that maintaining the glass window cleaning mainly depends on the intake mass flow ratio of the sweeping glass and the cavity. When the sweeping glass window intake CO2 mass flow is too small, coal particles are easy to contaminate the glass. When the sweeping glass window intake CO2 mass flow is too large, the molar ratio of C02 to coal particles will increase which reduce CO2 conversion. The coal particle inlet CO2 mass flow accounts for a small amount of total intake gas mass flow, mainly as a gas for transporting coal particles. When the molar ratio of CO2 to coal particles is in the range of 1.3-1.8 and the mass flow rate of the cavity, sweeping glass and conveying coal particles takes the percentage of the total CO2 in take mass flow rate in the range of 71.9%-78.2%, 15.7%-20.7% and 5%- 10%, respectively, the glass window cleanliness is optimal. The increase of mass flow rate of coal particles (1.5×10^-4×10^-4 kg/s) can significantly reduce the molar ratio of CO2 to coal particles, but the turbulence of coal particle trajectory will increase, which causes a small amount of coal particles to move toward the glass window through the opening aperture.