Selecting working fluids in organic Rankine cycle (ORC) for waste heat applications and optimal cycle parameters for different hot source temperatures

The high-temperature gas flows into the environment from many industries. Utilizing the Organic Rankine cycle (ORC) to generate electricity from this energy is worthwhile. In this study, the best thermodynamic conditions of ORC with 27 working fluids are presented. The considered temperatures for the heat sources were divided into low, medium, and high, with values of 50-90 degrees C, 95-190 degrees C, and 195-280 degrees C, respectively. The optimization was carried out to get the maximum power through a genetic algorithm in MATLAB software. The optimization parameters included the inlet temperature of the turbine (T-tur), the pressure of the (P-cond), the pressure of the boiler (P-boil), and the outlet temperature of hot air (T-hf,T-out). The results indicated that in low-temperature heat sources, R170 (144.13-209.87 kW) was the best fluid, and in the medium- and high-temperature heat sources, R227ea (1372.31-1533.86 kW) and R141b (6640.97-7524.6 kW) were the optimal fluids. Moreover, considering environmental issues and flammability, R744 (low-temperature), R1234ze (medium-temperature), and R245ca (high-temperature) were the best working fluids. In the low- and medium-temperature heat sources, T-cri/T(hf,in )for optimal fluids were 0.46-0.6 and 0.55-0.88, respectively. However, in the high-temperature heat source, this ratio was 0.72-0.78. As working fluids were selected, if T-hf,T-in - T-cri was above 100 degrees C or lower than 20 degrees C, these working fluids were left out. In the future scope, finding a temperature for the heat source above which water is the suitable fluid compared to organic fluids and investigating the effect of changing heat carrier from air to combustion gases are proposed.

Automated summary

This study presents the best thermodynamic conditions and optimal working fluids for the Organic Rankine cycle (ORC) to generate electricity from high-temperature gas. The optimization was carried out using a genetic algorithm, and the results showed the optimal fluids for different temperature ranges of the heat sources. Additionally, environmental issues and flammability were considered in selecting the best working fluids.