Optimal waste heat recovery through humidification in 2-spool micro gas turbines: A comparative study of advanced humidified cycles

Incorporating water into a micro Gas Turbine (mGT) has proven effective in recovering waste heat, significantly enhancing electrical efficiency. Techniques such as steam injection, preheated water addition, and the use of a saturator in the Humid Air Turbine (HAT) concept show great potential for waste heat recovery. However, these methods have not been applied in 2-spool small-scale gas turbine systems. This study proposes a systematic approach to optimize 2-spool advanced humidified mGT cycles for heat recovery. A two-step method was used, starting with a black-box model to determine thermodynamic limits, achieving an 8.3% absolute efficiency increase by injecting 400 g/s of water. Several advanced humidified cycles were analyzed. The REVAP® cycle, identified as optimal, reduced stack temperature to 49.6 °Celsius, achieving a 4.1% efficiency increase and an 11.2% reduction in fuel consumption. Despite its complexity, REVAP® outperformed cycles with saturation towers (HAT and mHAT) by maximizing heat recovery. HAT achieved the highest water injection with a 4% efficiency gain. However, none of the advanced simulated cycles reached the theoretical exergetic limit. This highlights the importance of cycle layout and design, especially under constraints like the number of heat exchanger units and water phase change dynamics.