An optimization for water requirement in natural gas combined cycle power plants equipped with once-through and hybrid cooling systems and carbon capture unit

Abstract

A water-energy nexus analysis for a Natural Gas Combined Cycle power plant equipped with Post-Combustion Carbon Capture unit was studied. Once-through and hybrid indirect dry and wet cooling systems were considered. An optimization model was developed to minimize the water requirement in each of the cooling system. The model and numerical method were validated with previously reported experimental measurements. In once-through cooling system, the optimized mass flow rates were slightly less than the original operating condition. For hybrid cooling system, the effects of air to water ratio, humidity content, air wet bulb temperature, and the number of cycles of concentration on the water requirements were studied for a wide range of cooling load split factors. The difference in water requirement becomes insignificant when the cooling load exceeds 60%. It was shown that the increase in the number of cycles of concentrations reduces water losses within 5–6 cycles. It is recommended to consider dynamic control for the cooling system using the developed optimization algorithm to maintain optimum operating conditions. For the once-through cooling system, maintaining the least water withdrawal while protecting aquatic life is suggested. For hybrid cooling systems, keeping the split factor below 0.5 and optimizing water consumption and power penalty are recommended.