Environmental and thermoecological comparative assessment of improved humid air waste heat recovery configurations

Abstract

This paper provides a comprehensive assessment of the humid air turbine-based waste heat recovery system with respect to different flow configurations in the air saturator. The novelty of this work is to provide a holistic approach to the environmental and thermoecological assessment of Maistosenko cycle-based waste heat recovery units by considering three configurations of air saturator namely, counter-flow, cross-flow, and mixed-flow configuration. In other words, the assessment is carried out to evaluate the performance improvements while comparing the environmental as well as thermoecological perspectives. This provides a broader and wholesome perspective allowing a wider application of these configurations, especially in different climatic conditions experiencing varying ambient temperatures. The ambient temperature is particularly important when air is used as working fluid and routed in three different configurations within the heat recovery unit i.e., air saturator. The addition of humidity in the air saturator tends to improve the performance of bottoming cycle depending on the air direction within the saturator which has a counter, cross and mixed flow configurations. Moreover, ambient or dead state temperature is considered one of the influencing parameters on the performance of considered heat recovery configurations. With the rising ambient temperatures up to 50 °C, owing to intensive heat waves and sustained droughts; the performance indicators of power generation units indicate as much as 25% reduction in the sustainability index along with 10% lowering of energy and exergy efficiencies. In this regard, the flow configuration and efficiency of air saturators become critically important especially as a heat recovery unit while working in intense operating conditions. The results have suggested that counter configuration can offer the highest among of net-work marking 51.9 MW whereas the cross-flow configuration can mark only 49.78 MW. Thermoecological assessment has suggested that the ambient temperature of this type of powerplant can be less than 40 °C. It is concluded that the optimal configuration is counter-flow configuration for the waste heat recovery in gas turbines based upon second law and thermoecological assessment.