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Exhaust gas heat exchangers

Exhaust gas heat exchangers

Our exhaust gas heat exchangers are primarily used in combined heat and power (CHP) plants. Combined heat and power plants produce both heat and electricity, making them particularly energy efficient in comparison to other technologies. Thus CHP plants also play an important role in the future energy mix.

In an exhaust gas heat exchanger, the hot exhaust gas from the CHP engines or CHP gas turbines is cooled, in the process heating water, a water-glycol mixture or thermal oil. This thermal energy can be used in a local or district heating system or for other industrial purposes.

The maximum possible cooling of the exhaust gas depends on the fuel gas used in the respective CHP plant. If it is possible to ensure a high fuel quality, then an additional efficiency increase can be realized by using condensing technology.


Since our exhaust gas heat exchangers are designed and constructed on a project-specific basis, we can offer highly customized solutions and thus an ideal match for the technical and structural framework conditions.

The most common designs are shown below.


The standard design, which is used for most of our heat exchangers. The exhaust gas connections can be implemented radially or axially.

It is also possible to provide the heat exchanger without exhaust gas chambers or with flange-mounted exhaust gas chambers.


A bypass can be used to decouple the heat exchanger whenever the thermal output isn't needed. The bypass is typically located above the heat exchanger, but can also be mounted on the side.

The bypass flaps can be equipped with electric or pneumatic actuators and/or can be operated manually. We also supply separate bypass T-connectors.

Catalyst chamber

In this design a catalytic converter can be installed into the heat exchanger inlet chamber. This is often required for applications in which oxidisation catalysts are required for emissions reduction reasons.

The catalytic converter can be mounted either via the chamber cover or via a side inspection opening.

Safety technology

The safety technology systems are designed in close cooperation with our customers, the planners and the operators in order to meet the respective project requirements and are fitted with the required controls and instruments.

The exact implementation can vary widely and depends on whether the application involves warm water, hot water or thermal oil.


A vertical design is also possible if this is necessitated by system space considerations. The heat exchanger can be equipped with a floor plate, side feet or with brackets.

Special designs

In theory, there are countless possibilities for exactly how an exhaust gas heat exchanger is designed.

For example with two inlet connections in case of split exhaust gas routing after the CHP engine, as dual-stream version or with different fittings and measurement ports.


Fields of use

The most common fields of use for our exhaust gas heat exchangers:


Natural gas CHP plants

Natural gas CHP plants are used in industrial applications, for example in the automotive and food industries, in municipal utilities and energy suppliers or in schools, hospitals, hotels, airports and swimming pools.

In most cases the gases in the exhaust gas heat exchanger are cooled to between 120 °C and 100 °C. In order to increase the overall efficiency of the plant, additional downstream heat exchangers can be installed to reduce the exhaust gas temperature.

If the temperature drops below the dew point, the latent heat can be used in addition to the sensible heat (condensing technology). In the process, the water vapour in the exhaust gas is condensed. In greenhouses these condensing heat exchangers are used in addition to CO2 fertilization of the plants.

Biogas CHP plants

There are currently about 10,000 biogas plants in Germany, in which biogas is produced in digesters by fermenting biomass. The biogas can be used in a CHP plant to produce electricity and heat or processed into biomethane and fed into the natural gas network.

When designing exhaust gas heat exchangers for biogas CHP plants, great care is taken to ensure that the exhaust gas temperatures are selected so that they don't drop below the dew point. Failure to do so could otherwise result in the formation of harmful sulphuric acid which can damage the heat exchanger.

A noteworthy part of the enkotherm product portfolio is the "Energy Tower", which allows the latent heat to be captured even in biogas plants.

Sewage gas CHP plants

Sewage gas, like biogas, is also one of the renewable fuels. It is produced in sewage treatment plant digesters and has a higher methane content than biogas.

The sewage gas is converted to electricity and heat in a CHP plant and can be used to supply the sewage treatment plant itself and nearby properties.

The exhaust gas outlet temperature in sewage gas applications also has to be selected so that no damaging sulphuric acid forms in the heat exchanger, which could damage it.

Landfill gas CHP plants

In landfills the garbage which is buried there produces so-called landfill gas as it rots. This cannot simply be allowed to enter the environment and is therefore particularly well suited for and should be used in a combined heat and power plant.

The CHP plants are often set up in containers in the immediate vicinity of the landfill, allowing them to be moved to a different location easily once the landfill no longer produces sufficient gas.

We design the exhaust gas heat exchangers for landfill applications to allow for reliable long-term operation.

Mine gas CHP plants

The mine gas which forms in the vicinity of coal mines can be extracted and delivered to a CHP plant in order to produce electricity and heat.

This allows the greenhouse gas effect to be reduced many times over, since the methane which otherwise escapes into the environment unused from the mines is turned into energy.

Our exhaust gas heat exchangers are also suitable for the somewhat less common mine gas applications.

Wood gas CHP plants

In wood gas CHP plants, gas is produced from wood pellets and then converted to electricity and heat in a CHP plant. Wood gas CHP plants are primarily found in Southern Germany, Austria, Italy and Switzerland, but also in Eastern Europe and Japan.

enkotherm has many years of expertise in this field and supplies leading manufacturers in the wood gas industry.

Our exhaust gas heat exchangers are designed for the special requirements of wood gas applications and feature the required materials and wall thicknesses for these applications.

Hydrogen CHP plants

Hydrogen will play an important role in the future energy mix. Excess electricity from renewable energies such as wind energy can be converted to hydrogen through electrolysis, and the hydrogen can then be fed into the existing natural gas network or storage systems.

Some CHP plant manufacturers already offer solutions which allow CHP plant engines to run on or be retrofitted for hydrogen.

enkotherm can also supply suitable heat exchangers for this application.

Other CHP plants

In addition to the aforementioned types of gas, there are many other fuels such as liquid gas, syngas, heating oil, palm oil or diesel, which can be used to fuel combined heat and power plants.

The waste heat from the engines can also be captured with an exhaust gas heat exchanger in these applications.

Our exhaust gas heat exchangers are designed, planned and constructed specifically for the respective application. 

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