What is a combined cycle gas turbine power plant?

We use electricity countless times a day. Right now, the screen you’re reading is powered by it! But how often do you stop to question how or where your electricity is produced? It’s quite possible a CCGT () can take the credit, but what is a CCGT, and how does it work?

What is a CCGT (combined cycle gas turbine)?

Put simply, a CCGT is a power plant with two cycles. Gas is burned to power gas turbine generators, which produce electricity. Then, waste heat from that process is recovered and used to heat water, powering a steam turbine generator, which produces more electricity.
The same amount of gas can produce far more electricity in this way.

How is electricity produced at a CCGT?

Let’s look at the process step-by-step:

1. Burning hot gas

Gas is mixed with air and accelerated through the gas turbine compressor before being fed to the combustion system. Here, the fuel mix is ignited, creating a high-temperature, high pressure gas stream. The rapidly expanding gas turns the turbine which spins a generator to produce electricity.

2. Heat recovery

In a regular gas turbine power plant, that’s pretty much the full story. However, a combined cycle gas turbine puts the waste gas from the first process to good use. A heat recovery steam generator (HRSG) takes the hot exhaust gas and supplies it to a steam turbine.

3. Full steam ahead

The gas is used to heat water, converting it to steam which drives a turbine. This turbine, much like the one in the first stage, spins a generator to produce additional electricity.

The advantages of CCGTs

That second cycle makes fantastic use of heat energy, which would otherwise go to waste. Instead of being discharged through the exhaust stack, the energy is converted into electricity with some reporting they produce up to 50% more electricity than a gas turbine alone.

With more electricity generated from the same amount of gas, fuel costs, and greenhouse gas emissions both go down. CCGTs are one way for power plants to .

The disadvantages of CCGTs

The main disadvantage of a CCGT is that the initial setup is complex and expensive. The additional equipment needed for heat recovery and the second cycle of generating electricity is also large and heavy. If space is limited, installing a combined cycle power plant may not be possible.

The alternative to installing a CCGT

Using waste heat seems like a great idea, but you may not be willing or able to convert your gas turbine at this time. Fortunately, there are ways to ensure you are making the best possible use of the equipment you already have.

Ensuring your gas turbine compressor is kept clean ensures maximum efficiency and lower greenhouse gas emissions. The equipment and chemicals to facilitate regular washes are a far cheaper alternative to a CCGT upgrade.

Get in touch

At Rochem, we specialize in gas turbine compressor cleaning products. With over 40 years of experience, we have developed a range of market-leading equipment and which are trusted at sites around the world.

Whether you are responsible for a gas turbine or a combined cycle gas turbine, if you’d like to discuss how we can help.