A Perspective Evolution Methodology of Energy Management in a Subcritical Regenerative Organic Rankine Cycles Operate at Two Temperature Levels

Abstract

The waste energy recovery and management philosophy represent a great challenge for scientists. This article outlines a scheme to utilize two different source temperature levels in the range of (160–200) °C. Two regenerative organic Rankine cycles (RORC) were implemented to construct a compound regenerative organic Rankine cycle (CRORC) to improve the energy management of the sources. The method of energy management for these cycles was accomplished by extracting a certain amount of energy from the high-temperature cycle and rejecting it to the working fluid in an economizer at the low-temperature level. R-123 was circulated in the high-temperature cycle due to its high critical temperature at evaporation and condensation temperatures of 150 °C and 50 °C respectively. R-123, R-245fa, R-1233zd-E, and the hydrocarbon R-600a were used as working fluids for the low-temperature cycle at evaporation and condensation temperatures of 130 °C and 35 °C respectively. This technique showed that the first law of thermodynamics efficiency was augmented by (3–5)% for the low-temperature mini-cycle of the (CRORC). The energy consumption at the low-temperature cycle was also reduced by (3–5)%. The latter reduction range accounts for 2% for the total extracted energy for the independent system where both high-temperature and low-temperature cycles were utilized separately. The data showed that increasing the superheat degree from 10 °C to 20°C has enhanced the thermal efficiency of the compound (CRORC) system by (2–4)%. The (CRORC) system of R-123/R600a, R-123/R-123, and R-123/R-245fa fluid pairs exhibited higher thermal efficiency than that of R-123/R-1233zd-E pair by (4.5–6)%, (4–6)% and (3–4)% respectively. The net thermal efficiency of the compound (CRORC) system fell in the range (12–13)% and the low-temperature mini-cycle of the (CRORC) system had a range of (12–14)% for all of the examined operating conditions. Keywords: compound cycle, regenerative, energy management, energy recovery