循环流化床返料阀结构对循环流率动态响应特性的影响

Effect of loop seal structure of circulating fluidized bed on the dynamic response characteristics of circulating flow rate

循环流化床锅炉燃烧技术是一种洁净煤燃烧技术,其应对负荷变化的灵活性未来会得到更多的关注。但目前对于负荷变化的研究集中于调峰策略优化,缺乏提升CFB本身变负荷速率的影响因素研究。在CFB锅炉负荷变化时,循环流率也随之变化,并达到新的平衡态,而返料阀的结构是循环流率的重要影响因素。因此,为了研究CFB锅炉变负荷响应速率的影响因素,基于CPFD方法对某75t/h循环流化床锅炉立管及返料阀内在循环流率变化时的流动行为进行模拟,研究不同返料阀结构对循环流率变化的响应速度。结果表明,在立管远离回料阀侧及回料阀水平横段底部存在一定的流动死区,返料阀及立管内物料仅在较小的区域内有较大的移动速度。当循环流率增加时,较小的颗粒移动区域限制了其达到更大流量平衡的时间,减弱了系统变负荷的响应速率。在松动风、流化风分别为0.14和0.30m/s,循环流率从50kg/(m2·s)提升到60kg/(m2·s)时,随着水平横段长度的增加,系统响应时间先急剧减小后缓慢上升;返料阀水平横段长度与立管直径之比为3.5时,最短响应时间为67s。保持流化风量不变并改变松动风大小,系统响应时间随松动风量的增加而减小,但不同返料阀结构下系统响应时间的规律相似。返料阀对循环流率变化的响应速度与返料阀内的流动死区大小密切相关。

The boiler combustion technology of circulating fluidized bed (CFB) is a kind of clean coal combustion technology,and its flexibility to cope with load change will attract more attention in the future.Recent studies about load change are focused on the optimization of peak shaving,which lack the research of influence factors on CFB boiler itself.The circulation rate will change and reach a new equilibrium state as load of CFB boiler changes.The structure of loop seal is an important factor on the circulation state.Therefore,in order to investigate the influence factors on CFB boiler response rate to load change,the flow behavior of a 75 t/h in standpipe and loop seal of a CFB boiler with circulating rate change was simulated based on CPFD method.The dynamic response rate to circulating flow rate change under different loop seal structure was studied.The results indicate that there are some “flow-dead zone” on the away-recycle-valve side of the standpipe and the bottom of the loop seal.The gas-solid flow in that zones have relatively high moving velocity only in restricted areas,so the moving area of small particle limits the time to reach a higher flux equilibrium state when the circulation rate increases.The flow-dead zone decreases the response rate to the load change.When the loosening air and fluidizing air are 0.14,0.3m/s respectively and the circulating flow rate increases from 50 kg/(m 2·s) to 60 kg/(m 2·s),the system response time decreases sharply first and then increases moderately with the increase of horizontal section length.The shortest response time is 67 s,when the ratio of loop seal horizontal section length to the standpipe diameter is 3.5.Keeping the fluidizing air and adjusting the loosening air,the system response time decreases with the increase of loosening air while the relation between system response time and the loop seal structure keeps similar.The response rate of loop seal to circulating flow rate change is closely related to the size of flow-dead zone in the loop seal.