Transient behavior investigation of a regenerative dual-evaporator organic Rankine cycle with different forms of disturbances: Towards coordinated feedback control realization

Highlights: • Regenerative dual-evaporator ORC with R1234ze is designed to recover solid bulk waste heat. • Novel coordinated feedback control system including two PI controllers is proposed. • Transient behaviors are studied under step, sinusoidal and random oscillations. • The steadiness and efficient sliding pressure operation of RDORC system are realized. This study utilizes an innovative regenerative dual-evaporator organic Rankine cycle (RDORC) with R1234ze to recover solid bulk waste heat by using air as heat transfer medium. A comprehensive transient model for RDORC is constructed based on finite volume method. Furthermore, a novel coordinated feedback control system for RDORC including two PI controllers is proposed to remain turbine inlet main vapor and resupplied vapor superheat degrees constant. The transient behaviors of RDORC and simple ORC (SORC) are compared under external disturbances of heat source inlet temperature. The results indicate that under 10 °C step decrease disturbance, the RDORC presents a 0.5 °C larger undershoot and a 164s longer setting time of superheat degree than that of SORC. Compared with SORC, the exergy efficiency enhancement of RDORC increases from initial value 4.13% to final value 4.51% after the step disturbance. Under sinusoidal disturbance with amplitude of 10 °C in RDORC, the peak amplitude of turbine main vapor inlet pressure (3.6%) is far higher than that of turbine resupplied vapor inlet pressure (0.82%). Besides, under random disturbance with variance of 1, the system exergy efficiency and thermal efficiency fluctuate around the design values of 35.67% and 7.65% with maximum deviations of 2.2% and 0.37%, respectively.