Process Control Of Low Grade Waste Heat Recovery

With the rapid development of economy,the problem of energy crisis and environmental pollution is becoming more and more serious.It is very effective by using Rankine cycle which can recover low temperature waste heat to reduce industrial energy consumption and greenhouse gas emissions.In recent years,many scholars have done research on transcritical cycle by using CO₂ as refrigerant,which can not only recycle energy but also protect environment.This paper analyzes thermodynamic model of CO₂ transcritical cycle.Based on Aspen HYSYS software,the CO₂ transcritical cycle model consists of evaporator,expander,condenser,pump.Under a rated condition,the system performance is studied by adjusting system working parameters.Based on the equations of mass and energy conservation and reasonable simplifying assumptions,it is used to build CO₂ transcritical cycle model of evaporator,expander,condenser,pump.The whole dynamic system,which is control-oriented,is established by connecting these subcomponents.Two control schemes are proposed to make the best of low temperature waste heat.Firstly,feedforward decoupling（FD）method is studied to deal with multivariable coupling and particle swarm optimization（PSO）algorithm is used to optimize PID controller parameters.Simulations demonstrate the controller can obtain satisfactory set-point tracking and disturbance suppression performance.Secondly,by incorporating linear quadratic regulation（LQR）strategy with PI controller,multivariable control system is designed based on CO₂ transcritical cycle waste heat recovery system.Through matlab simulation,the control scheme can achieve good control effect and anti-disturbance ability.