Variety-duty Characteristic Analysis and Optimal Operation of Cold-End System of 600MW Direct Air-cooled Thermal Power Unit

Abstract

The operating backpressure of the direct air-cooled unit is a significant economic parameter, and the optimal backpressure is corresponding to the best efficiency of the unit, which is mainly affected by ambient temperature, steam turbine exhaust flow, and face velocity in the operation of the cold-end system. A calculation model of the condenser of a 600MW direct air-cooled unit using the ε-NTU method was established to analyze the off-design performance. Compared with the characteristic curve provided by the manufacturer, the maximum error of the calculation results is 1.68%, meeting the engineering accuracy requirements. In order to obtain the optimal backpressure and optimal face velocity under off-design conditions, a cold-end optimization calculation model based on genetic algorithm is established with the maximum net power output as the objective function. The influence of the exhaust steam flow, ambient temperature and face velocity on the pressure of condenser is analyzed. In addition, the changing rules of the net power output with face velocity and backpressure under different conditions are studied. The results indicated that the working pressure of the condenser increases with the increment in ambient temperature and exhaust steam flow, and decreases with the rise of face velocity. The net power output of unit increases first and then decreases with the increment in backpressure and face velocity. Moreover, the higher the ambient temperature, the larger optimal face velocity and optimal backpressure of the unit, as well as the more cooling air volume is required under the optimal air face velocity. Keywords: Direct air-cooled unit, Off-design condition, Characteristic analysis, Optimal backpressure, Genetic algorithm DOI: 10.7176/JETP/13-1-02 Publication date: January 31 st 2023