Supercritical Pressure Boiler Superheated Steam, Reheat Steam And Temperature Change Working Condition

Superheated steam temperature and reheated steam temperature has an important influence on safe and economic operation of the unit. Because no drum is required in a supercritical pressure boiler, there is no fixed boundary among the hot-water heating surface,evaporation heating surface and superheating heating surface. When running conditions are changing, the length of each heating surface is varied. So, steam temperature characteristic of the supercritical pressure boiler is different from the drum boiler's, and it is of significance to study each running factor of supercritical pressure boiler affecting the boiler steam temperature. Steam temperature control equation for the supercritical pressure boiler is presented and the measure to analyze the rule of steam temperature change with steam temperature control equation is presented. Taking a 660MW supercritical pressure boiler as the subject, quantitative calculation and qualitative analysis are done when running conditions are changing in this article.Coal-water ratio is the fundamental reason which causes the change of steam temperature, and intermediate point's temperature is used as the control signal for coal-water ratio regulation. When intermediate point temperature is not controlled and coal-water ratio is not varied, steam temperature change is contrary to drum boiler's, which is resulted from changes of feed water temperature,excess air coefficient and coal equality.In the case that intermediate point temperature is controlled, steam temperature changes are calculated quantitatively when feed water temperature decreases and superheated steam pressure decreases, and steam temperature changes are analyzed qualitatively when load increases and excess air coefficient increases. Steam temperature changes because coal-water ratio varies. So, when the running conditions are changed, even at the same load, coal-water ratio should be changed appropriately. When the running conditions are changed largely, it is necessary to change intermediate point temperature so as to decrease fluctuation of the desuperheater spray water.Steam temperature characteristic is presented when intermediate point temperature is evolved in steam temperature adjustment and steam temperature characteristic is also presented when intermediate point temperature is not evolved in steam temperature adjustment. There is a remarkable difference between them. The former is presented as the static characteristic of supercritical pressure boiler, and the later is used to. analyze direction and amplitude of steam temperature in the dynamic course of temperature adjustment until coal-water ratio is varied.Steam temperature control equation is useful for operators to judge and analyze the direction of superheated steam temperature change and reheated steam temperature change and to calculate steam temperature changes local quantitatively in many conditions when running conditions are changing.