煤粉加压密相输送特性研究

煤粉加压密相输送系统作为粉煤气化工艺的上游系统,直接影响气化炉的稳定、可靠及安全运行。当气化原料煤种发生改变或进行掺混配煤,其煤粉输送特性可能随之改变,对煤粉输送过程的平稳运行有一定影响。为研究干煤粉气化炉供煤系统的工作特性,针对某气化装置混配后的原料煤粉,利用HR指数和FF函数对粉体流动性进行分级表征,然后在内径25和15 mm管径下进行背压2、4和5 MPa的加压密相输送试验,考察了表观气速、输送压力对煤粉流量的影响规律,最后采用煤粉流量的平均波动幅度和最大波动幅度作为煤粉输送过程稳定性的评价指标,对各工艺参数间的波动相关性进行比较分析。结果表明:该原料煤粉的HR指数为1.42,FF函数为2～4。结合流动性分级表,该原料煤粉的流动性位于黏结区,但靠近易流动区;随着表观气速的增大,煤粉流量先增大后减小,在临界气速处煤粉流量最大。当表观气速超过临界气速后,由于气相压降占主体,颗粒相压降减小导致煤粉流量开始降低;输送压力对煤粉流量和流态转换有一定影响。在相同表观气速下,输送压力提高,煤粉流量有下降趋势,在小管径15 mm管道中该规律更为明显。输送压力越高,密相到稀相的流态转换越急剧,根据背压2和4 MPa的输送相图,在临界气速处,25 mm管径下相图曲线的曲率约为15 mm管径下的2倍;煤粉流量的平均波动和最大波动幅度可作为输送稳定性的评价标准。试验范围内,煤粉流量的平均波动幅度小于3%,最大波动幅度小于10%,煤粉流量最大波动幅度约为平均波动幅度的3.4倍,两者间的相关系数为0.948。 As the upstream system of coal gasification process,the dense phase conveying of pulverized coal at high pressures directly affects the stabilization,reliability and safe operation of gasifier. The conveying characteristics of pulverized coal may be accordingly changed when the coal type of gasification is changed or blended with other types,which has a certain impact on the smooth operation of the pulverized coal conveying process. To study the operating characteristics of coal-providing system for a coal gasification unit,based on the mixed raw materials of a coal gasification unit,the characterization experiments were conducted on the powder fluidity through HR index and FF function. Then,the dense phase conveying experiments were done in the pipeline with inner diameter of 25 mm and 15 mm pipeline under the back pressure of 2,4 and 5 MPa.The influence law of the superficial gas velocity,and back pressure on the pulverized coal flow was discussed. Finally,the average fluctuation and maximum fluctuation of mass flow rate of the pulverized coal were used as evaluation index of stability for the pulverized coal conveying process and the fluctuation correlation between the various process parameters was compared and analyzed. The results show that the HR index of the raw coal is 1.42 and the FF function is 2-4. Combined with the fluidity classification table,the fluidity of the pulverized coal is located in the bonding area,but close to the easy fluidity area. With the increasing of superficial gas velocity,the mass flow rate of the pulverized coal first increases and then decreases,reaching the largest flow at the critical gas velocity. The pressure drop of particle phase decreases because the gas-phase pressure drop occupies the main body and the mass flow rate of pulverized coal starts to decrease after the apparent gas velocity exceeding the critical gas velocity. The back pressure has certain influence on