Exergy and economic analysis of using the flue gas injection system of a combined cycle power plant into the Heller Tower to improve the power plant performance

Natural Draft Dry Cooling system (Heller Tower) is regarded as one of the frequently used cooling systems in steam power plants. The performance of these towers depends heavily on environmental conditions. Under wind conditions, due to the lack of symmetry in pressure distribution around the tower and the formation of wind cover phenomena on the top of the tower, the inlet flow rate to the tower drops and accordingly, the heat rejected by Heller Tower reduces almost by 40%, leading to a reduction in the power and efficiency of cooling tower and entire power plant. The injection of flue gas dissipated by the recovery boiler, which has the temperature of about 130 degrees C, into a cooling tower at the combined cycle power plant is regarded as one of the recent methods proposed to improve the cooling tower efficiency under wind conditions. The present study aimed to examine various dimensions of the effect of flue gas injection into the cooling tower of a combined cycle power plant on the entire power plant, as well as its efficiency in terms of exergy and economic analysis. For this purpose, a Heller Tower was modeled by the CFD method. In addition, the amount of the cooling tower heat was calculated by the results of numerical analysis and used for the thermo-exergy simulation of various components of a combined cycle power plant in states of with and without flue gas injection under the tower design and crosswind conditions. The results indicated that the power generated by the steam cycle increased by a maximum of 7.92 MW due to the flue gas injection and under wind conditions. Finally, the results of the economic analysis represented the return on investment rate of 81.18 and 91.17% for two states of permanent and economic use, respectively, and the payback period of about one year. (C) 2019 Elsevier Ltd. All rights reserved.