Technical and Economic Analysis of the Gas Turbine Air Bottoming Cycle

Abstract

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.

Analysis of Maisotsenko open gas turbine bottoming cycle

“…Nevertheless, water addition reduction in the air saturator degrades its capability to fully recover the waste heat available in the topping turbine exhaust gases. This can be verified by calculating the air saturator outlet air temperature from Equation (9). If the calculated value of the air saturator outlet temperature is greater than the exhaust gases inlet temperature, air saturator would not be able to cool down the exhaust gases to the mentioned temperature and the actual exhaust gases temperature dumped into the atmosphere is greater than the calculated value.…”

“…Selecting a proper value for ASDH allows designers to determine temperature of humid air leaving the air saturator from Equation (9). Nevertheless, water addition reduction in the air saturator degrades its capability to fully recover the waste heat available in the topping turbine exhaust gases.…”

Comparative analysis of power augmentation in air bottoming cycles

“…Other advantages of ABC over CCC are low start-up time, high flexibility, compact size, and low pollutant emission (Chmielniak, Czaja, and Lepszy 2012;Khaldi 2011). In 1988, ABC was patented by W. Farrell of the General Electric Company (Farrell 1988).…”

Thermodynamic and economic comparative analysis of air and steam bottoming cycle

“…The ABC also improves the performance of the new combined engine in the offdesign mode [15,16]. It is expected that the ABC will require much lower investment expenditures compared to the CCPP [17].…”