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The gas turbine engine has many advantages such as low investment costs, low emissions and a low water consumption. This fact allows its application in many power engineering systems, for example as parts of gas and oil transport systems. It is possible to increase the efficiency of gas turbines through the use of combined cycles. For this purpose, the steam cycle is used most frequently. These systems are highly efficient in terms of energy, but they are very complex and have a high water consumption. An alternative to steam cycles are gas-air systems, referred to as the ABC’s (Air Bottoming Cycles), which use hot combustion gases as a heat source for the air cycle. ABC’s are composed of a gas turbine powered by natural gas, an air compressor and an air turbine coupled to the system by means of a heat exchanger, referred to as the AHX (Air Heat Exchanger). The paper presents an application of gas-air systems with example configurations, together with thermodynamic characteristics. Two technological structures are taken into consideration — a simple system of the ABC and an ABC with air intercooling. A parametric analysis of these systems is performed using a special computer program with real gas properties for enthalpy and entropy calculations. A basic comparative analysis of gas turbine air bottoming cycle and combined gas-steam cycle has been also done. Other important calculations are related to the heat exchanger, which is one of the most important components in this system because it couples the gas and air parts. The efficiency of the whole cycle depends on a rationally designed heat exchanger. The calculations are performed for a shell-and-tube exchanger, as well as for a plate heat exchanger. For all investigations an purchase cost of machines and devices is also determined.

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The use of air-bottoming cycle as a heat source for the carbon dioxide capture installation of a coal-fired power unitThe installations of CO2capture from flue gases using chemical absorption require a supply of large amounts of heat into the system. The most common heating medium is steam extracted from the cycle, which results in a decrease in the power unit efficiency. The use of heat needed for the desorption process from another source could be an option for this configuration. The paper presents an application of gas-air systems for the generation of extra amounts of energy and heat. Gas-air systems, referred to as the air bottoming cycle (ABC), are composed of a gas turbine powered by natural gas, air compressor and air turbine coupled to the system by means of a heat exchanger. Example configurations of gas-air systems are presented. The efficiency and power values, as well as heat fluxes of the systems under consideration are determined. For comparison purposes, the results of modelling a system consisting of a gas turbine and a regenerative exchanger are presented.