CCGT power plant
Combined Cycle Gas Turbine (CCGT) is a gas turbine generator in a combined system that is designed to produce electricity. This is a modern method of energy production, which, on the one hand, reduces the emission of harmful substances into the atmosphere and, on the other hand, increases the efficiency of conventional gas power plants. From the following article you will learn what it is, how it works and what are the advantages of a combined cycle gas-steam power plant (CCGT).
What is the Combined Cycle Gas Turbine system?
A gas turbine operating in a combined system uses two technologies operating on the energy market that produce electricity: gas and steam, combining them into one unit. Therefore, the combined cycle energy production process involves recovering temperature from exhaust gases and using this heat to produce additional energy. Thanks to this, a significant improvement in the efficiency of the thermal energy used is achieved compared to a conventional steam power plant.
In the Combined Cycle Gas Turbine system, a gas and steam turbine are coupled to one generator. Thanks to this system, operating efficiency increases by approximately 50-60%, thanks to the discharge of exhaust gases from the gas turbine to the steam generator with heat recovery. However, the heat recovered in the combined gas combustion process is sufficient to drive a steam turbine with an electrical power of nearly 50% of the power of the gas turbine generator.
Principle of operation of CCGT
The operation of gas turbines in the combined cycle can be divided into few stages.
The first is the same as in the case of an installation with a gas turbine operating in a standard system. A simple open cycle gas power plant is equipped with a compressor, a combustion chamber and a turbine. In this type of cycle, the entry temperature to the turbine, like the exit temperature of the exhaust gases, is very high. This is therefore a temperature sufficient to be used in the second cycle, in which steam is used as the working factor, using the operating principle known from thermal power plants.
It is worth noting that the air sucked into the system is cleaned, cooled and controlled. In contrast, modern gas turbines are able to successfully operate in a wide variety of climates and environments thanks to inlet air filtration systems that are specifically designed for the plant's location.
The purified air is then compressed and mixed with natural gas and ignited, causing it to expand. The pressure created by expansion rotates the turbine blades, which are attached to the shaft and generator, producing electricity.
In the second stage, the exhaust heat produced in the gas turbine is used to generate steam by passing it through a Heat Recovery Steam Generator (HRSG). The steam temperature in this case is from 420 to 580°C.
In a heat recovery steam generator, highly purified water flows in pipes and hot gases circulate around it, thus generating steam. The steam then turns a turbine and a coupled generator to produce electricity. The hot gases leave the HRSG at a temperature of approximately 140°C and are vented to the atmosphere.
To sum up, a gas-steam power plant works as follows:
- By burning natural gas, the turbine of a gas power plant is driven, producing electricity.
- Water vapor is produced by using hot exhaust gases from the combustion process.
- The produced steam drives the turbine of a steam power plant, generating additional energy.
CCGT systems
Advantages of using modern gas turbine generators
The main advantages of power plants with a CCGT system include:
- Increased production efficiency of the plant - an increase of approximately 50%.
- Lower investment costs - up to 30% lower compared to a conventional steam power plant.
- Reduced water demand.
- Possibility of installation divided into stages.
- Fully automated operation - no large number of personnel are required to operate the CCGT.
- High reliability and operational flexibility - the CCGT system can start and stop quickly.
- Lower impact on the environment - compared to other conventional power plants, it has the lowest impact on global warming.
- Short investment implementation time.
Disadvantages of Combined Cycle Gas Turbine
Despite many advantages, it should be noted that this solution also has its disadvantages. These include:
- CCGT is a modern but still expensive technology, which increases the cost of the initial investment.
- The efficiency of the steam turbine decreases with lower load on the gas turbine.
- More expensive, dedicated materials (e.g. steel of appropriate quality) are required to work at high temperatures and pressures.
- Limited possibility of changing the gas turbine fuel.
Why is it worth using the CCGT system?
A combined cycle gas power plant is a very efficient energy generation unit. CCGT is a modern, environmentally friendly and highly effective solution. It should be noted that combined cycle power plants are also much more economically efficient compared to conventional power plants.