Water-energy nexus in the combined cycle power plant using energy, exergy, economic and environmental analyses

The growing demand for water and energy and the limitation on their resources necessitate comprehensive studies on the water-energy nexus from different aspects in large industries, especially power plants. In the present study, the water-energy nexus has been analyzed using energy, exergy, economic, and environmental analyses for the retrofit scenarios in a combined cycle power plant. The injection of boiler blow-down into the condenser will save 47809.5 m3 of make-up water and 1.115 million m3 of natural gas per year. Replacing the Maisotsenko evaporative cooler with the fogging system increases the revenue index and the water consumption index by 2.7%. The raw water is replaced with high-quality water. The output power of the combined cycle power plant is reduced by 2.1 MW (0.83%) due to the steam injection from the heat recovery boiler into the combustion chamber of the gas unit, while its exergy degradation rate is reduced by 8.5 MW (2.42%). Also, the efficiency of the first and second laws have been decreased by 0.49% and 0.4%, respectively. The results show that the recovery of boiler blow-down for condenser or steam injection into the combustion chamber of the gas unit from heat recovery of the boiler reduces water consumption and exergy destruction simultaneously. Using Maisotsenko cycle and steam injection into the combustion chamber of the gas unit from the heat recovery of boiler reduces the exergy destruction and NOx emissions. The present study provides useful insights to quantify the water-energy nexus for decision-makers in the industry to reach proper decisions according to the opportunities and limitations.

Automated summary

The present study analyzes the water-energy nexus in a combined cycle power plant using energy, exergy, economic, and environmental analyses. The injection of boiler blow-down into the condenser and the replacement of the evaporative cooler with the fogging system result in significant water and natural gas savings. The steam injection from the heat recovery boiler into the combustion chamber of the gas unit has both positive and negative impacts on the power plant's performance.