Gas Turbine Cycle

Gas turbine generator can be divided into some classifications. One of its classifications is based on cycle.  The following below is classification of gas turbine generator based on cycle:

1. Open Cycle Gas Turbine

In this cycle, gas from combustion process after passed and expanded through turbine generator, will be directly discharged into atmosphere. This installation has simple structure which consists of compressor, furnace and turbine as a drive of compressor and load. The structure and composition of gas turbine installation with open cycle can be seen in the Figure 1.

Figure 1: Open Cycle Gas Turbine Generator

Caption:

F          = furnace

C         = compressor

T          = turbine

G         = generator

2. Closed Cycle Gas Turbine

Gas turbine can be designed with closed system. In this cycle, the working fluid is not connected to surrounding atmosphere, thereby can be maintained its purity. This is advantageous in terms of prevention of damage caused by erosion and corrosion. This system can be also used in high pressure up to 40 atm like installation of steam generator but its work does not experience phase change. The scheme closed cycle gas turbine installation can be seen in Figure 2.

Figure 2: Closed Cycle Gas Turbine Generator

Caption:

F          = furnace

C         = compressor

T          = turbine

G         = generator

HE       = heat exchanger

Closed cycle gas turbine has more complicated construction because it need larger heater and inter cooler equipment before enter compressor. The following below is advantageous of closed cycle gas turbine:

-          For the same power, this turbine has smaller size

-          Can work at high pressure

-          More efficient in the use of fuel

3. Combined Cycle Gas Turbine

Because of the energy is lost along with waste flue gas, it has made several attempts to use flue gas by adding some kind of new process after additional equipment. Therefore, the energy which should be discharged can be utilized again for particular process and thus can improve efficiency of the system. But along with additional process and equipment, the required of investment cost will be higher. In terms of economic, gas turbine with combined cycle has some advantageous if gas turbine is performed in base/primary load and continuously.