增压富氧锅炉高温对流受热面换热规律研究

Study on Heat-transfer Behavior of High-temperature Convective Heating Surfaces in a Pressurized Oxy-fuel Boiler

以某台300 MW燃煤锅炉为研究对象,运用Aspen Plus软件确定煤粉在常规空气、常压富氧和增压富氧燃烧气氛下生成的烟气物性,采用Fluent软件,结合离散坐标辐射模型(DOM),对3种燃烧气氛下高温再热器和高温过热器处的烟气流速、对数平均温差、传热系数、管壁温度分布和管圈内蒸汽焓增等参数进行数值模拟.结果表明:燃烧气氛由常规空气变为常压富氧再到增压富氧的过程中,换热器的传热系数均增大;与常规空气燃烧气氛相比,常压富氧和增压富氧燃烧气氛下换热器的管圈间热偏差较小;换热器的弯管处可能存在超温现象;随着烟气流速的增大,实现相同换热量,换热器所需换热面积逐渐减小,且变化幅度也减小,为保证锅炉安全稳定运行,需要将部分省煤器移入炉膛上部.

Taking a 300 MW coal-fired boiler as the object of study, physical properties of the boiler flue gas were studied using Aspen Plus software respectively under air, oxy-fuel and pressurized oxy-fuel combustion conditions, while the gas velocity, logarithmic mean temperature difference, heat-transfer coefficient, temperature distribution among tube coils and steam enthalpy rise in tube coils were numerically simulated for areas around the high-temperature reheater and superheater using Fluent software combined with discrete-ordinates radiation model （DOM）. Results show that the heat-transfer coefficient of above heat exchangers increases in the process of changing combustion atmospheres step by step from conven- tional air to oxy-fuel and to pressurized oxy-fuel conditions. Compared with the air atmosphere, smaller thermal difference exists in tube coils under oxy-fuel and pressurized oxy-fuel combustion conditions, when local overheating may occur at tube bends of the heat exchanger. With the rise of gas flow rate, the heating area required for the same amount of heat exchange reduces, and the trends of heating surface variation reduces as well, under the pressurized oxy-fuel combustion conditions, in which case, some of the heat exchangers have to be moved up to the furnace top to achieve safety and stable operation of the boiler.