Methods Research On Heat Economy Evaluation For Sliding Pressure Operation Of 300MW Turbine

With the economy development and people consumption level increment, the proportion consuming electricity in life is more and more larger. The changing range of electric load in day and night is more and more, which causes the 300MW units operating in original base-load have to participate the peak-load regulation. So the operating time of 300MW units in low load is increasing. The operating way of steam turbines under low load for long time deviates from its design condition, which decreases the heat economic performance greatly. But only the operation mode can be possible to be artificially adjusted in the primary factors that influence the economic performance of steam turbines. Therefore, in researching steam turbine operation in sliding pressure with low load, operation modes have great influence upon the heat economy of coal-fired power plant.According to the International Formulation 1997 of the International Association for the Properties of Water and Steam (IAPWS-IF97), the program for calculating the thermodynamics properties of water and steam is introduced and designed firstly in this paper. Considering the complexity of enthalpy and entropy subprogram, the mathematical model is given to solute pressure and temperature by means of specific enthalpy and entropy. And in the new algorithm the pressure value is obtained by using Golden Mean Method. Then the calculating program for a 300MW steam turbine in constant pressure and variable pressure operation condition is given. And a series of indexes such as governing valve pressure loss, exit temperature in high pressure casing, relative internal efficiency of governing stage, consumed power of feedwater pump, heat rate, ideal cycle thermal efficiency have been calculated. Through the comparison and analysis of the above indexes, the optimal sliding pressure operation mode is obtained. Moreover, the optimal operation mode in low load of a 300MW unit is determined. After calculating theheat economy performance for a 300MW steam turbine in different sliding pressure operation, the conclusion is obtained that reducing the numbers of governing valve all to open is helpful to increase heat economy performance when 300MW steam turbine operates in low loads with sliding pressure operation. At the same time, the influence upon safety of steam turbine with sliding pressure operation is analyzed in this paper.