多孔CaO颗粒脱硫过程中硫酸盐化特性的数值模拟
Numerical simulation of sulfation characteristics of porous CaO particles during desulfurization
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摘要: 在循环流化床炉内喷钙控制SO2的过程中，新生成的CaSO4会堵塞CaO颗粒的孔隙，导致脱硫效率的降低。通常认为CaSO4堵塞CaO颗粒孔隙有2种形式：其一是CaSO4产物层覆盖在颗粒的外表面造成堵塞孔隙出口；其二是SO2进入孔隙内部生成CaSO4形成均匀堵塞。这种处理方法忽略了孔隙内部的SO2浓度差异，与实际情况相差甚远。针对此问题，建立了离散化的收缩孔隙随机孔模型对CaO颗粒与SO2的反应过程进行数值模拟。模型考虑了生成的CaSO4对有效扩散系数的影响，孔隙内部SO2浓度差异对于CaO颗粒转化速率的影响，以及反应过程中孔隙结构收缩对于颗粒整体转化的影响。通过Fortran自主编程并计算，结果表明模型与实验数据吻合较好。CaO颗粒反应过程中，由于颗粒外部SO2浓度高而率先反应并堵塞颗粒孔隙，导致颗粒内部大量CaO没有参与反应。CaO硫酸盐化的最佳环境温度为800~900 °C，过高和过低都会对其硫酸盐化产生负面影响。颗粒粒径越小，CaO硫酸盐化率越高。Abstract: In the process of controlling SO2 by injecting calcium into the circulating fluidized bed furnace, the newly formed CaSO4 will block the pores of CaO particles, resulting in the reduction of desulfurization efficiency. Most researchers believe that there are two ways for CaSO4 to block the pores of CaO particles. One is that the CaSO4 product layer is covered on the outer surface of particles, causing blockage of the outlet of the pores. The second is that SO2 enters the pores and generates CaSO4 to form a uniform blockage. This method ignores the difference of SO2 concentration in the pore, which is far from the actual situation. To solve this problem, a discrete shrinkage pore stochastic pore model was established to numerically simulate the reaction process of CaO particles with SO2. The effect of the generated CaSO4 has been considered by the new model, and the influence of inner pore SO2 concentration difference on the transformation rate of CaO particles, and the reaction process of pore structure influence on the overall transformation of the particle shrinkage. Through independent programming and computing by fortran, the results show that the new model is in good agreement with the experimental data. In the process of CaO particle reaction, because of the high concentration of SO2 outside the particles, the reaction takes place first and blocks the pores of particles, resulting in a large amount of CaO in the particles which is not involved in the reaction. The optimum environmental temperature of CaO sulfation is from 800 to 900 °C, too high and too low will have a negative impact on sulfation. The smaller the particle size is, the higher the sulfur retention efficiency of CaO is.
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