Optimization Of Gas Turbine Waste Heat Power Cycle In Compressor Station Of Natural Gas Transmission Pipeline

Along the natural gas pipeline,a series of gas turbine driven compressor units operate to pressurize the natural gas.During the working process of gas turbine,a large amount of flue gas waste heat with an initial temperature of 400-500°C is generated,and its recycling can bring significant benefits of energy saving and carbon emission reduction.Considering that there is generally a lack of suitable heat users around the compressor station,and the waste heat has a certain grade and quantity,it is appropriate to use the power recovery method.It is important to carry out the optimization research on waste heat power recovery technology of gas turbine,and obtain the system design scheme with the optimal technical and economic performance.Existing research work mostly takes the maximum net output power of the system,or the highest cycle thermal efficiency,or the lowest EPC（electricity production cost）under the condition of given waste heat source as the optimization goal.In the previous research of our group,a new optimization objective function-MPC（The maximum power output with the restraint on EPC≤EPC₀.EPC₀:EPC of fossil energy power generation system）was proposed.That is,the pursuit of the maximum net output power under the premise of ensuring the total energy and total resource utilization efficiency of the system can better guide the system optimization compared with the existing simple thermodynamic or economic optimization objectives.In this paper,MPC is taken as the optimization objective function,and the simulation optimization mean is established,including the optimization algorithm model framework,the system model,the thermodynamic performance calculation and the system cost estimation module.Among them,the variable turbine efficiency model is coupled in the thermodynamic performance analysis and the thermal stability limitation of working fluid is considered.System cost estimation are based on Aspen PEA software.Under the condition of waste heat source of gas turbine in Quzhou and Hongliu two actual compressor stations,the simulation and optimization research of power recovery system aiming at MPC was carried out for a variety of suitable primary cycle forms and working fluids.Considering that various price fluctuation factors will lead to the change of EPC₀ value,the influence law of EPC₀ value on optimization results is analyzed.The relationship between the similarities and differences between MPC and existing objective functions with the EPC₀ value is discussed.The results show that:（1）The technical economy of the flue gas waste heat power recovery system is related to the EPC₀ value,the heat source conditions and the thermodynamic cycle-working fluid-cycle parameters of the system.Given EPC₀=0.041$/k Wh,under the condition of waste heat source of Quzhou compressor station（the initial temperature of flue gas is 400℃,mass flow rate is 26kg/s）,the Rankine cycle with cyclopentane as the working fluid is the optimal working fluid-cycle combination;under the optimal cycle parameters,the system gives the highest MPC=2195.34k W,which provides an additional 11.8%power for the compressor station.Under the condition of waste heat source in Hongliu Compressor Station（initial flue gas temperature 470℃,mass flow rate 74kg/s）,split-flow heating CO₂ trans-critical cycle is the optimal working fluid-cycle combination;under the optimal cycle parameters,the system gives the highest MPC=9307.6k W,providing additional 33.2%power to the compressor station.The optimal cycle-working fluid-cycle parameters and technical economy are obviously different under the conditions of the two waste heat sources.（2）The relationship between MPC and the existing optimization objective function is related to the EPC₀ value.Combined with the possible variation range of EPC₀ value and the analysis of the EPC variation range of the waste heat power system under the condition of a given heat source,when the lower limit of EPC of the system is higher than the upper limit of EPC₀,the system has no application value.The minimum EPC is consistent with MPC;when the upper limit of EPC of the system is lower than the lower limit of EPC₀,the maximum net output power is consistent with MPC.