Study On Coupling Modeling Of External Heat Exchanger And Main Bed Of Circulating Fluidized Be

Circulating fluidized bed boilers have a wide range of load adaptability and coal quality adaptation characteristics,and because of its medium temperature combustion and furnace desulfurization characteristics,has a unique advantage in the control of pollutants,environmental impact,a period of time will be as a specific regional power system power supply in the main form,its single capacity and parameters of ultrasupercritical can make its aforementioned advantages to better play,which is bound to be accompanied by the boiler body heating surface Structural design changes.The addition of an external heat exchanger effectively reduces the arrangement of the furnace heating surface and enhances the flexibility of bed temperature,steam temperature and boiler load regulation of circulating fluidized boilers,and is widely used in the design and manufacture of large circulating fluidized bed boilers.Circulating fluidized bed boilers have a wide range of load adaptability and coal quality adaptation characteristics,and because of its medium temperature combustion and furnace desulfurization characteristics,has a unique advantage in the control of pollutants,environmental impact,a period of time will be as a specific regional power system power supply in the main form,its single capacity and parameters of ultra-supercritical can make its aforementioned advantages to better play,which is bound to be accompanied by the boiler body heating surface Structural design changes.The addition of external heat exchangers effectively reduces the arrangement of the furnace heating surface and enhances the flexibility of bed temperature,steam temperature and boiler load regulation of circulating fluidized boilers,which is widely used in large circulating fluidized bed boilers by design and manufacturing departments.This design is also adopted in the Weihe 2×660MW ultra-supercritical circulating fluidized bed boiler coal-fired power generation project,which is listed as a demonstration project during the 13 th Five-Year Plan period,with six external heat exchangers on the left and right sides of the furnace chamber.External heat exchanger is essentially a non-combustion solid particle bubble type fluidized bed composed of one or more heat exchange chambers.The installation of external heat exchanger increases the arrangement of the heating surface of the boiler body,solves the problem of balancing the arrangement of evaporative and superheated heating surfaces,and ensures a reasonable distribution of the heat transfer ratio of the fuel combustion release on the premise of satisfying the boiler load,superheated steam and reheated steam indicators,but it also brings about the complexity of the boiler system structure and operation and maintenance.CFB boilers are faced with large changes in load and heavy deterioration in coal quality during operation,and the accompanying internal disturbances such as changes in steam and water parameters and changes in air volume within the generating unit have become common problems.Therefore,it is necessary to explore the effect of external heat exchanger on bed temperature variation,fuel combustion and steam quality of CFB boilers after ultrasupercriticalization in complex processes under multi-disturbance conditions.In the paper,numerical simulations of the thermal state of the boiler under BMCR conditions were carried out based on the computational particle fluid dynamics method with the Weihe 660 MW ultra-supercritical circulating fluidized bed boiler as the research object to investigate the effects of the external heat exchanger return flow rate and boiler coal quality variation on the boiler bed temperature.The results show that the variation range of boiler bed temperature is about 20°C by adjusting the circulating ash flow rate of the external heat exchanger within the normal opening range of the tapered valve.When the boiler burns temporary transitional coal,its low heat content and high ash content result in a slightly lower chamber temperature than that when the design coal and calibration coal are burned.Afterwards,Aspen Plus software,which is based on process simulation,was used to establish a 660 MW ultra-supercritical circulating fluidized bed boiler simulation model and to conduct a study on the effect of external heat exchanger on steam temperature.The results show that,to a certain extent,the steam temperature can be adjusted by adjusting the circulating ash flow rate into the external heat exchanger;the circulating ash flow rate into the external heat exchanger shows a linear variation law with the load in the process of boiler variable load;in the case of coal quality change,the ratio of radiation and convection heat absorption of the boiler can be adjusted by changing the heat absorption of the heating surface in the external heat exchanger to meet the boiler The requirements of steam parameters.