循环流化床返料阀结构对循环流率动态响应特性的影响
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摘要
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75 t/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. 30 m/s,循环流率从50 kg/(m~2·s)提升到60 kg/(m~2·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67 s。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 0.14,0.3 m/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.
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 0.14,0.3 m/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.
引文
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[22] PRABIR Basu,JAMES Butler.Studies on the operation of loopseal in circulating fluidized bed boilers[J]. Applied Energy,2009,86(90):1723-1731.
[23] DONG Li,JI Wenfeng,ZHAO Zhigang,et al.Elimination of stagnant particles from a N-valve with side aeration in circulating fluidized bed[J]. Advanced Powder Technology,2014,25(3):1155-1161.
[2]吴优福.循环流化床锅炉SO2超低排放技术研究[J].洁净煤技术,2017,23(2):108-113,118.WU Youfu.Study on SO2ultra low emission technology on circulating fluidized bed boiler[J].Clean Coal Technology,2017,23(2):108-113,118.
[3]刘晓娟,殷卫峰.国内外生物质能开发利用的研究进展[J].洁净煤技术,2008,17(4):7-9.LIU Xiaojuan,YIN Weifeng. Biomass energy and its application technology in China and the world[J]. Clean Coal Technology,2008,17(4):7-9.
[4] LIU Zhongyuan,MA Suxia,PAN Xiongfeng,et al. Experimental study on the load response rate under the dynamic combined combustion of PC coal and CFB coal in a CFB boiler[J].Fuel,2019,236(15):445-451.
[5] GAO Mingming,HONG Feng,LIU Jizhen,et al.Investigation on the energy conversion and load control of supercritical circulating fluidized bed boiler units[J].Journal of Process Control,2018,68:14-22.
[6]李金晶,吕俊复,岳光溪,等.循环流化床锅炉热惯性分析[J].热能动力工程,2009,24(5):609-613,681.LI Jinjing,LYU Junfu,YUE Guangxi,et al. An analysis of thermal inertia of a CFB(circulating fluidized bed)boiler[J]. Journal of Engineering for Thermal Energy&Power,2009,24(5):609-613,681.
[7]陈俊.循环流化床原煤—煤粉动态复合燃烧的污染物排放特性研究[D].太原:太原理工大学,2018.
[8]潘雄峰.循环流化床低热值煤—高热值煤粉动态复合燃烧负荷响应特性研究[D].太原:太原理工大学,2018.
[9]朱昊凌.大型CFB机组调峰性能优化技术研究[D].昆明:昆明理工大学,2015.
[10]刘朝阳.CFB锅炉效率与机组变负荷速率特性研究[D].南京:东南大学,2017.
[11]刘吉臻,洪烽,高明明,等.循环流化床机组快速变负荷运行控制策略研究[J].中国电机工程学报,2017,37(14):4130-4137,4292.LIU Jizhen,HONG Feng,GAO Mingming,et al. Research on the control strategy for quick load change of circulating fluidized bed boiler units[J]. Proceeding of the CSEE,2017,37(14):4130-4137,4292.
[12]刘云飞.循环流化床锅炉最佳风煤比模型研究[D].保定:华北电力大学,2017.
[13]宋畅,吕俊复,杨海瑞,等.超临界及超超临界循环流化床锅炉技术研究与应用[J].中国电机工程学报,2018,38(2):338-347,663.SONG Chang,LYU Junfu,YANG Hairui,et al. Research and application of supercritical and ultra-supercritical circulating fluidized bed boiler technology[J].Proceeding of the CSEE,2018,38(2):338-347,663.
[14]柯希玮,蔡润夏,吕俊复,等.钙基脱硫剂对循环流化床NOx排放影响研究进展[J].洁净煤技术,2019,25(1):1-11.KE Xiwei,CAI Runxia,LYU Junfu,et al.Research progress of the effects of Ca-based sorbents on the NOxreaction in circulating fluidized boilers[J].Clean Coal Technology,2019,25(1):1-11.
[15]柯希玮,蔡润夏,杨海瑞,等.循环流化床燃烧的NOx生成与超低排放[J].中国电机工程学报,2018,38(2):390-396,669.KE Xiwei,CAI Runxia,YANG Hairui,et al.Formation and ultralow emission of NOxfor circulating fluidized bed combustion[J].Proceeding of the CSEE,2018,38(2):390-396,669.
[16] HUANG Yiqun,ZHANG Man,LYU Junfu,et al. Effects of gas leakage on the separation performance of a cyclone.Part 2:Simulation[J]. Chemical Engineering Research and Design,2018,316:906-915.
[17] LIU H,CATTOLICA R J,SEISER R,et al. Three-dimensional full-loop simulation of a dual fluidized-bed biomass gasifier[J].Applied Energy,2015,160:489-501.
[18] DING J,GIDASPOW D.A bubbling fluidization model using kinetic theory of granular flow[J]. AICHE Journal,1990,36(4):523-538.
[19] HARRIS S E,CRIGHTON D G.Solitons,solitary aves,and voidage disturbances in gas-fluidized beds[J]. Journal of Fluid Mechanics,1994,266:243-276.
[20]丁瑞锋.Loop seal阻力特性研究[D].北京:清华大学,2015.
[21]邢文崇.循环流化床锅炉N型返料阀的研究开发[D].北京:清华大学,2014.
[22] PRABIR Basu,JAMES Butler.Studies on the operation of loopseal in circulating fluidized bed boilers[J]. Applied Energy,2009,86(90):1723-1731.
[23] DONG Li,JI Wenfeng,ZHAO Zhigang,et al.Elimination of stagnant particles from a N-valve with side aeration in circulating fluidized bed[J]. Advanced Powder Technology,2014,25(3):1155-1161.