The Experimental Study And Numerical Simulation On The Occurrence And Migration Mechanism Of Alkali During Coal-Fired Process

Coal-fired combined cycle power generation technology is one of the trends of clean coal power generation technology. However, alkali vapors easily deposited on heat exchanger surfaces to lead to slagging, and in gas turbines they caused high-temperature corrosion of turbine blades. Although tolerance limit of alkali vapors in the flue gas was usually given under 0.024 ppm by weight at the inlet of gas turbines, it was actually one or more orders of magnitude than that of the limit. Research for the occurrence and migration mechanism of alkali metal will play an important role in the development of coal-fired combined cycle power generation technology.Based on the Gibbs free energy minimization principle of chemical equilibrium, two models of coal-fired process and alkali occurrence and migration were developed using Aspen Plus software. Conclusions were drawn about the occurrence and migration mechanisms of alkali under the factors of Cl-containing in coal, reactor temperature and pressure, Ca/S, the ratio of air and coal, etc., and the results for adding limestone compared with those without limestone. Moreover, the conditions for limit level of alkali vapors were predicted.For studying and validating the occurrence and migration models of alkali, equipments for coal combustion and alkali sampling were designed and got the data of alkali occurrence and migration for different coals and under different conditions. After comparing the results of experimentation with those of computing, two results were approach, especially near 1130 K. It was found that under an atmospheric pressure, the amount of alkali vapors was decreased to 0.024 ppm by weight in 1044 K for Xuzhou coal, and for coal GBW11119 and coal GBW11120 the temperature should be increased to 1003 K and 973 K to the same level, respectively. While the reactor pressure was 10~6 Pa, the temperature should be1082 K, 1040 K and 1000 K for these coal samples, respectively. The results provided an important reference for the design of Coal-fired combined cycle power generation, the plan of alkali control and produce operation. Meanwhile, it is important for studying alkali slagging on the heat surface.