Conversion And Optimization Of Low Grade Heat In Fluid Catalytic Cracking Absorption Stabilization Processes

Huge amount of low grade heat in petroleum chemical engineering process was released directly to the environment without recovery.Take Fluid catalytic cracking absorption and stabilization?FCCAS?process as example,plenty of low grade heat with temperature of 100-140°C was cooled by cold utility or repeatedly heated,which led to energy wasting and even caused to pollution to the environment.Therefore recovering these low grade heat sources in the processes had important socio-economic and ecological significance.According to the characteristics of low grade heat in the FCCAS process,this study established the methodology of developing the integrated system to incorporate ORC system into FCCAS process to up-cycle and reuse the process low grade heat.The integrated system thermodynamic model was built by Aspen plus software.The performance evaluation criteria of the integrated system including the system net work(W_net),electricity production cost?EPC?and total annual profit?TAP?,was put forward for optimization of operation conditions.After investigated systematically,this study concluded as followings:There will be an upper bound value for mass flow rate of each working fluid,the reason is different for high critical temperature?HCT?and low critical temperature?LCT?working fluids.The Wnet increased with the increase of mass flow rate for all working fluids.But the change of Wnet along with evaporation pressure was different for two different kinds of working fluids.After optimization,R124 and R227ea were the best candidates due to their highest output net work in HCT and LCT working fluids.With the increase of mass flow rate,the EPC and TAP will reached an optimal value for all working fluids.But evaporation pressure exerted different influence on the EPC and TAP for HCT and LCT working fluids similarly.For the HCT working fluids,the use of working fluid of R245fa allowed the EPC to be the lowest,while the application of R124 obtained the highest TAP.For the LCT working fluids,R227ea was the best choice due to its lowest EPC and highest TAP.The working fluids R124 and R227ea with better system performance were selected to compose mixture working fluids.The effect of mass flow rate and evaporation pressure on the system performance was different for mixture working fluids with various mass fractions.After system performance optimization,the mixture working fluids R124/R227ea?0.5/0.5?was the best.In this study,the methodology of developing the integrated system and optimization of pure and mixture working fluids selection and operation conditions,can also be applied to other petrochemical processes for low grade heat recovery.