Abstract
This paper summarizes the results of an engineering study of partial substitution of an air cooler, which cools a process stream from 140 °C to 45 °C meantime dissipates heat of 32 MW into the environment, with an organic Rankine cycle (ORC). Aims were to investigate the application of different working fluids, and ranking them based on the following criteria maximum achievable power output, efficiency of the cycle, amount of the heat recovered, required heat exchanger area, attainable CO2 emission reduction, and payback time of the investment. Results showed that in case of the applied working fluids and design parameters the efficiency of the system obtained at the highest power generated (WT) varied between 9.8 % and 10.2 %. The maximum calculated power output was in the range of 1.63 –2.11 MW. Additionally, it was determined that the maximum turbine power and cycle efficiency not coincided for n-pentane, isopenatane and n-butane working fluids. The waste heat (QH) recovered in the evaporator varied between 16.10 MW and 18.70 MW. Results also displayed that the maximum power generated by the turbine and the maximum waste heat recovery did not coincide for every working fluid applied in the design boundaries. The attainable reduction in the CO2 emission was in the range of 2600-3400 t/y based on production of electricity by natural gas. The preliminary economic calculation showed that the payback time is between 6.3-7.0 y. Based on the techno-economic evaluation of the ORC system most appropriate working fluid could not be selected at the given process conditions. But the butanes gave higher turbine power, efficiency and CO2 emission reduction at same heat recovery level.
