Thermal electricity

Beyond generating electricity by so-called “conventional” power plants, ENGIE operates combined cycle and cogeneration plants which use natural gas, resulting in diversified electricity production with a low level of CO2 emissions. These plants provide improved energy efficiency and help secure the power supply. Moreover, they are very flexible allowing a very rapid response to peaks in electricity consumption.

ENGIE operates a diversified range of assets that ensure a secure and reliable supply of electricity as well as increasingly low-carbon sources of energy, such as natural gas and renewable energies. For ENGIE, this entails more than merely a transition; it is an energy revolution.

The thermal electricity supplied by ENGIE in numerous countries is based on a variety of technologies:

• Traditional thermal power plants: also called combustion power plants, they operate with energy produced by a steam boiler fueled by coal, natural gas, heating oil, as well as by biomass. The steam activates a turbine which, in turn, drives an alternator to produce electricity.

• Combined cycle gas power plants (or steam-gas turbine plants): these combine a gas turbine and a traditional thermal plant to generate electricity. Unlike conventional thermal power plants, the residual energy of the gases is used for another cycle. This is one of the reasons for which these kind of plants are more efficient (by 56%), also meaning that they produce lower CO₂ emissions than conventional plants.

Initially, gas is injected into the combustion turbine. It generates steam, which is then supplied to another turbine. The combustion turbine and steam turbine work in tandem to turn one or more alternators, which produce electricity.

• Recovery of blast furnace gas: electricity production can also be obtained by recovering and recycling gases from iron and steel production (blast-furnace gas, coking plant gas, steel plant gas), using a traditional boiler (a comparable technology to traditional thermal power plants) or in a heat recovery boiler in a combined cycle gas plant.

• Gas turbines and turbojets: mostly used to supplement the electricity production of other thermal plants, gas turbine and turbojet units can take over very rapidly in the event of a failure of other power plants or of unexpected peaks in consumption.

Gas turbine and turbojets: the compressor draws in air, compresses it and injects it into the combustion chamber. Natural gas (gas turbine) or kerosene (turbojet) is injected into the chamber to be burned. The hot combustion gases rotate the turbine, which drives an alternator to produce electricity.

• Cogeneration units: these produce heat (their principal role) simultaneously with electricity (their secondary role) in a single installation and employing a single fuel. It is a highly energy-efficient solution. By recovering thermal energy normally lost in power generation, these plants are able to produce electricity and heat with efficiency of close to 90%, which is of great interest for industrial sites.

Co-generation: a gas-powered generator drives an alternator that produces electricity. Heat recovered from the cooling of the motor and the combustion gases heats a water circuit thanks to heat exchangers.

Towards an increasingly decarbonized electricity generation mix

ENGIE is aiming to be a leader in the energy transition. The Group’s strategy is based on the development of businesses with low carbon emissions, gas infrastructures and integrated solutions designed for its customers.

ENGIE is restructuring its portfolio of businesses, and is progressively divesting assets involving coal-fired generation. The Group is repositioning its thermal power plants towards gas and cogeneration, complementing its development in renewable energies. Combined cycle gas plants contribute to ensuring the stability of the grid during peaks in electricity consumption (e.g. in severe freeze-ups) or when there are falls in the production of renewable energies, which are by nature intermittent (hydroelectricity, solar, wind, biomass and geothermal).

A flexible, efficient fuel that is easy to store and transport, natural gas will be required to play a major part in electricity supply in a period of heavy demand. It is the cleanest fossil fuel, with CO₂ emissions half those of coal. ENGIE is involved in all phases of the natural gas chain. Thanks to its great proficiency and expertise in the cycle, it is able to work on improving both the energy efficiency and environmental performance of natural gas.