Simulation Analysis On Low Calorific Value Gas-steam Combined Cycle

The gas turbine combine cycle(GTCC)generator unit is used to recover by-product gas generated from steel plant due to its own many advantages including high operating efficiency,starting sharply and high operating reliability.However,the combined cycle often runs at part-load or off-design conditions because it is sensitive to environment condition and the fluctuating in flow rate and lower heating value(LHV)of by-product gas.This causes the low energy efficiency of GTCC and blast furnace gas recovery capacity and increases the electricity cost of steel mill itself.Therefore,it is important to investigate the design and off-design parameters and their corresponding performance,which can elevate the thermal efficiency of GTCC and decrease the pollutant emissions and electricity cost of steel mill.In this thesis,an off-design model of M701SF gas turbine combined cycle unit is established,and then it’s off-design characteristics during part-load and maximum output operating conditions are studied,and its operational strategy and operational scheme are optimized.The detailed research contents as follow:(1)An off-design model of the M701SF gas turbine and its corresponding bottoming cycle system was established,and a new solution method was proposed for the complex off-design model of the bottom cycle system.The effectiveness of the method is verified by solving the off-design model of the dual-pressure bottom cycle system.(2)The off-design characteristics of the gas turbine are analyzed.With decrease in value of gas turbine load,the gas turbine energy efficiency decreases and the decline rate decreases at the same time as the ambient temperature increases.In additton,the operational reliability of gas turbine decreases as the ambient temperature and gas turbine load increase.(3)The off-design characteristics of the bottom cycle system matched with the M701SF gas turbine are analyzed.With the gas turbine load decreases,the energy efficiency and output power of the bottom cycle system decrease and drop sharply in range of 90%～100%of load rate,at the same time,the operational reliability of heat recovery steam generator(HRSG)decreases.The performance of the bottom cycle system decreases under constant pressure operation,however,the local reliability of HRSG increases.With the ambient temperature increases,the performance and the reliability of the HRSG increases,however,the performance of the bottom cycle system decreases due to the increase in exhaust back pressure of the low-pressure cylinder.(4)The operational strategy of GTCC is studied,and the off-design characteristics of GTCC at a certain combine cycle load is analyzed.An improved strategy is proposed,compared to traditional operational strategy,the energy efficiency of GTCC increases by 0.31%and the gas volume flow decreases by 11562Nm~3 under the control of the improved strategy.When the combine cycle load is set,the energy efficiency of GTCC decreases with increase in value of ambient temperature and LHV of gas,the maximum energy efficiency loss respectively caused by ambient temperature and LHV of gas are 2.12%and 0.73%.(5)The operational schemes of GTCC in condition of maximum power output are studied and optimized.With the LHV of gas and inlet air temperature decrease,the maximum power output of GTCC is elevated.Therefore,considering both inlet air cooling and LHV adjustment of gas is the best operation scheme.Under the control of the best operation scheme,the maximum output of GTCC increased by30.28MW,however,it’s energy efficiency only decreased by 0.53%.