Conceptual design of a super-critical CO2 brayton cycle based on stack waste heat recovery for shazand power plant in Iran

Conceptual design of a waste heat recovery cycle is carried out in attempt to enhance the thermal efficiency of a steam power plant. In the recovery system, super-critical an CO2 is employed as the working fluid operating in a Brayton cycle. Low grade heat rejected by the flue gases through the stack is used as the primary heat source, while a secondary heat exchanger utilizes the hot gases leaving the economizer to heat of CO2 up to desired temperature. In the present work, a case study for a 325 MW steam power plant of Shazand in Iran is carried out and a thermodynamic model is developed to predict the performance of the system. Regarding that the proposed recovery cycle may lead to less effective air preheating and affecting the combustion efficiency, an optimization process has been conducted to determine the optimum conditions. It’s been also considered that excessive decline in flue gas temperature leaving the stack may result in the condensation and accumulation of corrosive substances on the inner surface of the stack. The results demonstrate that this waste heat recovery system can deliver up to 18 MW of net power which corresponds to an increase of 1.58 percent in thermal efficiency of the power plant. Obtained results magnify the importance of this innovative design, consequently illustrate the necessity for using waste heat recovery system.