Cogeneration is a technology that allows two types of energy to be produced simultaneously in the same installation: mechanical and thermal, from a single fuel (coal, fuel oil, natural gas, wood, biomass, etc.). While cogeneration has already proven its effectiveness in industry, horticulture and in the heating of large buildings, it is gradually being developed for private individuals. This is known as micro-cogeneration. How it works, its uses, its advantages and disadvantages, find out everything there is to know about this 2-in-1 technology.
In order for a power plant to generate electricity, it must produce heat from the combustion of different resources (coal, oil, natural gas, wood, biomass…) which then supplies a turbine to produce electricity. During the production of electricity, heat is generated. This heat is not reused and is therefore considered to be lost.
A cogeneration plant is capable of producing both electricity and heat from a single source of fossil energy (oil, gas, etc.) or renewable energy (wood, biogas, etc.). As in a “conventional” thermal power plant, cogeneration is based on the combustion of energy resources to produce electricity. However, unlike a fossil-fired power plant, the heat released during combustion and electricity production is used to heat large buildings, such as a factory, hospital, etc. Still quite marginal, cogeneration currently provides 11% of the electricity and 15% of the heat at European level. However, this process favours the use of the recovered heat as energy. If this technique were to become widespread in France, it is estimated that up to 20% of the total energy consumed in the country could be saved and greenhouse gas emissions drastically reduced.
How cogeneration works
Understanding how a cogeneration plant works is quite simple and follows the following steps
a single energy source, either fossil or renewable, turns a motor or turbine;
the engine or turbine then triggers an alternator which creates electricity;
This is then collected and stored;
When set in motion, the alternator heats up and to prevent it from overheating, a coolant is used to vaporise the heat;
the steam is then recovered by a heat exchanger which uses it to produce hot water;
the hot water produced is used to supply industrial systems, the heating system of companies and public buildings or sanitary installations.
The different types of cogeneration installations
There are different types of cogeneration systems.
Combustion turbine cogeneration
The thermodynamic principle of a gas turbine is used here. A compressor sucks in and compresses air. This air, into which a gaseous fuel (natural gas, butane, propane, biogas, etc.) is injected, is transferred to a combustion chamber. The turbine then has the role of expanding the hot, high-pressure combustion gases. This is then converted into electrical energy by means of an alternator. The heat produced by the combustion of the gases is then collected by a boiler, which sends it to a heat transfer fluid, usually water.
This type of installation is mainly found in industry, or in a combined cycle power plant. Its electrical efficiency varies between 25 and 40%. Its overall efficiency is close to 100%.