Peak Load Regulation Of Gas-steam Combined Cycle Heating Power Plants

With the rapid development of the national economy and the changes in the consumption of residents,great changes have taken place in the social power structure.The peak-valley gap is increasing greatly and the power grid dispatching situation become increasingly grim.Compared to the coal-fired units,the cycle unit has the characteristics of quick stopping speed,high energy efficiency and high peak capacity,which are very suitable for the power grid dispatching.The ambient temperature has great influence on the gas turbine,so it’s very important to analyze the change of ambient temperature in the whole working condition and the regulation of peaking capacity of the combined cycle system.At present,most of the combined cycle unites are heating units,and the amount of heat extraction exerts a great influence on the peaking capacity.Therefore,it’s also of great significance to analyze the regulation of the exhaust volum and master the capacity of the unit to optimize the operation of the combined cycle and the safety of the grid.The specific contents of this artical are as follows:(1)Establish the variable condition model of PG9171 E gas-steam combined cycle unit.In this paper,variable conditions modeling is for relatively advanced and more widely used E-class gas turbine combined cycle unit based on the literature research.The traditional superposition method is used to establish the compressor working condition model.The heat balance equation is used to establish the combustion chamber model.Flugel formula is used to establish the turbine working condition model.A simple method was used to establish a dual-pressure non-reheat boiler model,which laid the foundation for further study on the characteristics of gas-steam combined cycle.(2)Analyze the influence of ambient temperature on the performance of full-scale gas-steam combined cycle and peaking capacity.Based on the PG9171 E gas turbine system,the thermodynamic performance of all the main components was analyzed by changing the ambient temperature and the corresponding boundary conditions.And then the temperature range throughout the year peaking margin combined cycle unit is calculated.The results show that,basing the performance guarantee condition as the benchmark condition,with higher temperature the unit exhibits a better off-design performance,with the efficiency increment of 1.69%~3.75%,and its net power output will increase by 11.48%~11.57%.On the contrary,the unit with lower temperature has lower off-design performance with the efficiency decrement of 2.56%~5.08%,and its net power output will decrease by 10.44%~10.58%.For the peaking load capacity of the unit,with higher temperature the capacity is less and the maximum and minimum generating loads are 47.63 MW and 242.62 MW at-20℃;at 40℃ are 39.14 MW and 172.12 MW respectively;and the peak load in the whole year temperature range is 132MW~194MW.(3)Analysis of different heating extraction steam combined cycle unit peak shaving.Based on PG9171 E gas turbine system,by adjusting the amount of heat extraction and the corresponding boundary conditions,the calculation of the peak extraction capacity of the unit under different extraction volumes is carried out.With the increase of steam extraction volume,the minimum power generation load of steam turbines and gas turbines are increasing.The maximum power generation load of steam turbines is decreasing while the maximum power of gas turbines is maintained.As can be seen,the maximum output of the combined cycle unit is gradually reduced,the minimum output is increasing,and the peak adjusting ability is gradually reduced.In the heat pumping capacity of 15-135 t / h range,unit peak shaving margin range 32.16-213.65 MW.