Thermodynamic analysis of a condensing evaporator in an evaporative gas turbine cycle

Aleksi Mankonen,Esa Vakkilainen,Juha Kaikko,Vitaliy Sergeev,A Borodinecs,N Vatin,V Sergeev

doi:10.1051/matecconf/201824507007

Abstract

Low efficiency is the main stumbling block preventing the widespread adoption of small-scale gas turbines in distributed energy production. The evaporative gas turbine cycle has been proposed as a way to improve efficiency, but the large number of components required make the configuration complex and expensive. The condensing evaporator is a component that simplifies the evaporative gas turbine cycle. The heat and mass exchanger device is designed for an externally fired application, which means that the flue gas stream is replaced by moist air. The air-water mixture condenses inside a tube bank, releasing heat to the evaporating water film on the other side of the tubes. Similar inventions include the tubular humidifier and the Maisotsenko compressed air saturator, which also aim to make the evaporative gas turbine cycle more economically feasible. Available theory focuses on either humidification towers or evaporative condensers in HVAC applications. The tubular humidifier has been analyzed in a similar manner as humidification tower since the flow configurations of the two components are similar. However, the theory of humidification towers is not directly applicaple to the condensing evaporator. This study proposes a method of analysis of the condensing evaporator in power generation.

Highlights

Distributed generation of electricity allows rapid reaction to demand, provides better power quality under many circumstances and offers an alternative to investment in distribution capacity [1]
The simulations suggest that when the cold fluid is very dry, the latent heat of condensation can be utilized
Once the cold fluid contains more water, the temperature level needed for further humidification becomes higher than the condensation temperature on the other side

Summary

Introduction

Distributed generation of electricity allows rapid reaction to demand, provides better power quality under many circumstances and offers an alternative to investment in distribution capacity [1]. The electrical efficiency of an externally fired microturbine (EFMT) is only 17 % [3] Such efficiency can be achieved by feeding the hot exhaust air to the combustor [4]. In an evaporative gas turbine cycle, there are usually two heat exchangers for preheating the injection water: a compressor aftercooler and an economizer in the turbine exhaust. The Maisotsenko compressed air saturator [10] combines all of the components of an evaporative cycle into one tube-shell heat exchanger and evaporator. The device uses the heat of the hot gas directly to evaporate water and achieve humidification. It is designed for an externally fired application. A numerical model is developed in this study to determine the expected performance of a condensing evaporator

Model development

Results

Discussion