A Process Of Integrating Gas-steam Combined Cycle With Furnace And Its Optimum Design

In order to improve the energy efficiency of the gas-steam combined cycle of cogeneration station and the process furnace of large-scale industrial enterprises,a new process of integrating gas-steam combined cycle and its adjacent furnace is proposed.In this new process,flue of gas turbine is used to heat the feed of process furnace,and then split,part of it mixes with the furnace's air and burns at the furnace's burner,the other part of it is sent to the heat recovery steam generator?HRSG?as the existing process does.In this way,the temperature of furnace's exhaust will increase,thus the exhaust is sent to the evaporation or overheating section of HRSG and discharges at the chimney of HRSG,which means the chimney of furnace can be shut down.The benefits of the new process are as follows.Firstly,the new process upgrades the utilization of the waste heat of the gas turbine's flue because it can save fuel consumption at the cost of less production of medium-pressure steam in HRSG.Secondly,it helps to upgrade the utilization of furnace's exhaust by sending the exhaust into HRSG to produce steam,which just needs to ensure the pinch point and approach temperature point belonging to HRSG are within the reasonable ranges.Thirdly,since part of the turbine's flue is used as the combustion promotor in furnace,its energy along with high temperature and abundant oxygen is utilized,and fuel consumption of furnace can get a further drop.Further investigation is done based on the existing and new process.Firstly,with the help of exergy analysis and?-H diagram,it is proved that the exergy loss of the new process is less than that of the existing process.Secondly,program the new process in MATLAB,including air compressor,combustion,gas turbine,heat exchanger,furnace,HRSG,steam turbine,deaerator,etc.Thirdly,based on the MATLAB model,fuel consumption of furnace(m_f2),flow rate of the furnace's air(m_a2),material's preheat temperature from the heat exchanger(T_y2),the flow rate of turbine's flue to furnace(m_g4c),HRSG's pinch point(?T_pp)and approach temperature point(?T_ap)are set as the design variables,and genetic algorithm is adopted to optimize the model with extra-fuel power generation efficiency as objective function.Fourthly,apply the proposed new process to the case which consists of a furnace of a 12Mt/a crude oil distillation unit and 240MW gas-steam combined cycle unit,the optimal result is 51.56%,which is 1.54%higher than that of the existing process.Although the total power generation decreases by 15.92MW,the annual economic benefit of the system increases by 32.07 million yuan because the fuel consumption of furnace drops by 3821.6kg/h.Also,the total exergy loss of the new integrated process reduces by 19.04%compared with the existing process.