A New Concept of Steam-Injection Inverted Gas Turbines For Efficient Power Generation From High-Temperature Waste Gases

Abstract High-temperature waste heat gases above 700°C represent a recoverable heat source for power cycles. Conversion efficiency is governed mainly by temperature. Still, it can be enhanced by systematically formulating the cycle. This paper proposes a new concept for efficiency improvement of inverted gas turbines through ejector-assisted steam injection. Hereby, the waste gas enters an ejector, where it is compressed using high-pressure, high-temperature steam. The resulting mixture expands from higher-than-atmospheric to sub-atmospheric pressure in a turboexpander. The low-pressure mixture is cooled first in steam-generating heat exchangers. Then, an additional heat exchanger is proposed to cool the wet waste gases below the water saturation temperature, where the injected steam condenses. This reduces turbocompressor flow rate, resulting in lower power consumption. Finally, the condensed water is pressurized in a pump and heated and evaporated in the steam generator. The high-pressure steam is used in the ejector. To analyze system performance under varying conditions of waste gas inlet temperature, vacuum intensity, steam pressure, and steam injection fraction, a thermodynamic model is developed. Results show that thermal efficiency of 0.3 at 1300°C waste heat temperature, 0.26 at 1100°C, 0.21 at 900°C, and 0.17 at 700°C is achievable. Recommendations are provided for vacuum and steam parameters that maximize thermal efficiency. In this way, the study makes a broader scientific contribution by establishing a conceptual framework applicable to advanced cycle investigations for the systematic integration of waste heat.