Humidification Impact on the Performance Improvement of a Novel Two-Shaft Micro Gas Turbine: Thermodynamic Cycle Performance Assessment

Despite appearing as a promising technology for small-scale decentralized Combined Heat and Power (CHP), the relatively low electrical efficiency of micro Gas Turbines (mGTs) prevents them from being attractive to users with variable heat demand. Transforming the cycle into a micro Humid Air Turbine (mHAT) by adding a saturation tower in the cycle allows for an increase in the electrical efficiency of these units in moments of low heat demand. Although humidification is well studied and proven effective on the simple recuperated Brayton cycle mGTs, its potential for cycle performance improvement when applied on more advanced mGT cycles is currently unknown. Therefore, the numerical study presented in this paper aims to assess the impact of humidification on the performance of a novel two-shaft mGT from MITIS, exploiting the intercooled regenerative reheat gas turbine cycle concept. The benefits of water injection mostly rely on the increased heat capacity of the air-vapor mixture, and the more significant amount of heat recovered in the recuperator, both resulting a the lower fuel consumption. Simulation results show indeed that by introducing a saturation tower in this two-shaft turbogenerator system, waste heat is recovered, leading to increased electrical efficiency from 35.12% for the mGT cycle to 36.31% for the mHAT cycle while providing a flexible heat and power output. This rise in the efficiency is maybe small, but could be increased further by going towards more advanced cycle configuration (aftercooling) as well as by less limiting the TIT.