Thermodynamic analysis and performance optimization of organic rankine cycles for the conversion of low-to-moderate grade geothermal heat

Abstract

The present study considers a thermodynamic analysis and performance optimization of geothermal power cycles. The proposed binary-cycles operate with moderately low temperature and liquid-dominated geothermal resources in the range of 110 o C to 160 o C, and cooling air at ambient conditions of 25 o C and 101.3 kPa reference temperature and atmospheric pressure, respectively. A thermodynamic optimization process and irreversibility analysis were performed to maximize the power output while minimizing the overall exergy destruction and improving the First-and Second-law efficiencies of the cycle. Maximum net power output was observed to increase exponentially with the geothermal resource temperature to yield 16-49 kW per unit mass flow rate of the geothermal fluid for the nonregenerative ORCs, as compared to 8-34 kW for the regenerative cycles. The cycle First-law efficiency was determined in the range of 8-15% for the investigated geothermal binary power cycles. Maximum Second-law efficiency of approximately 56% was achieved by the ORC with an IHE. In addition, a performance analysis of selected pure organic fluids such as R123, R152a, isobutane and n-pentane, with boiling points in the range of -24 o C to 36 o C, was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for non-regenerative cycles. The regenerative ORCs, however, require organic fluids with lower vapour specific heat capacity (i.e. isobutane) for an optimal operation of the binary-cycle.

Simulation analysis of cooling methods of an on-board organic Rankine cycle exhaust heat recovery system

“…The vehicle weight, the transmission parameters and the tire parameters of the truck, the fuel injection quantity, and the speed of the engine were set in the model. The ambient pressure and temperature was set as 99.5 kPa and 298.15 K …”

“…The vehicle weight, the transmission parameters and the tire parameters of the truck, the fuel injection quantity, and the speed of the engine were set in the model. The ambient pressure and temperature was set as 99.5 kPa and 298.15 K. 41 The ORC system models were also developed in GT suite. 42 Shell and tube, plate, and tube fin heat exchanger models were used to simulate the evaporator, the condenser, and the radiator, respectively.…”

Fluid-to-fluid scaling of heat transfer to mixed convection flow of supercritical pressure fluids

“…With the development of the use of renewable energy and waste heat, supercritical ORCs are attracting more and more attention as a promising energy‐to‐power transition technology . In recent years, the focus of ORC research has gradually shifted from thermodynamic studies for working fluids and system optimization to experimental and components studies, which has raised more pressing requirements for fluid‐to‐fluid scaling methods. So many kinds of working fluids are used for various heat sources in ORC systems that it is impossible to conduct experiments with every fluid.…”

Thermodynamic Performance Analysis of Turbine-Bleeding Organic Rankine Cycle with and without Regeneration

“…Meinel et al [10] carried out simulations of a two-stage ORC concept where the extracted vapor from the first turbine stage is used to recuperated the fluid to saturated liquid before the liquid is pressurized to the evaporation pressure with feed pump. Yekoladio et al [11] presented a thermodynamic performance analysis of ORC using turbine bleeding for the recovery of geothermal heat sources in the range from 110°C to 160°C to maximize power output and improve the first and second law efficiencies.…”