Numerical heat transfer analysis of Maisotsenko Humid Air Bottoming Cycle – A study towards the optimization of the air-water mixture at bottoming turbine inlet

Abstract

Maisotsenko Humid Air Bottoming Cycle (MHABC) is a recently proposed waste heat recovery unit for gas turbine topping cycle. An air saturator is used for the waste heat recovery and air humidification purposes in the bottoming cycle. The humid air is used in bottoming cycle turbine. In this work, detailed heat transfer analysis of the MHABC is proposed along with the evaluation of degree of humidification and energy recovery. The air saturator is numerically simulated after the development of governing ordinary differential equations for the temperature and humidity distribution of the working air. The governing differential equations of air saturator are discretized using first order accurate finite difference scheme and simulated using MATLAB. The results for the air saturator are initially validated using inlet ambient pressure conditions at standard atmospheric conditions. The upper section of the bottoming cycle is modeled using analytical NTU method. The overall performance of the plant with MHABC is also compared with results reported in literature. Temperature and humidity levels for working air is presented. These results show that the proposed MHABC configuration gives maximum work output (58 MW) and efficiency (∼34%) at the air saturator exit relative humidity of 70%. Corresponding to the maximum system output conditions, the dew point effectiveness of the air saturator is noted at 0.8 with 32% relative humidity at the bottoming turbine inlet. While the air split ratio of 50% between lower air saturator and heat exchanger gives more than 8 MW of waste heat recovery.