Silencers for Gas Engines and CHP Plants: Why the Exhaust Needs a Different Approach

In Short

Gas engine and CHP silencers differ from diesel ones because the exhaust gas is more corrosive, heat recovery equipment shares the exhaust path and treatment stages sit downstream. Copying a diesel silencer specification often leads to early rust, a blocked treatment stage or a missed sound limit, so gas plants need their own approach.

A gas engine and a diesel engine can sit side by side in the same hall, rated for the same output, and still need quite different exhaust silencers. People often assume a silencer is a silencer and copy the specification from the diesel set next door. That is how a gas plant ends up with a unit that rusts early, clogs a treatment stage downstream or does not meet the sound limit it was bought for. This guide explains in plain words why gas engines and CHP plants are a separate case.

A Different Kind of Exhaust

A diesel set starts, runs for a while and stops. A gas engine in a CHP plant is usually built to run for long periods, often day and night, and the whole plant is designed around that. The exhaust leaves the engine hotter and cleaner-looking than diesel smoke, but it carries more moisture, and it behaves differently when it cools. The silencer is no longer just a noise part at the end of a pipe. It is one item in a chain that also recovers heat and cleans the gas.

The sound itself is different too. Gas engines tend to have a strong low-frequency note that carries a long way, and a plant that runs through the night is judged against the quietest hours of the neighbourhood, not the working day.

Heat Recovery Changes the Picture

In a CHP plant the exhaust is a source of useful heat. A heat exchanger takes energy out of the gas before it reaches the stack, so the gas arrives at the silencer cooler than it left the engine, and that is exactly where trouble can begin. Cooler gas means moisture can condense inside the silencer, and what condenses is not harmless water.

This is the main reason the silencer for a CHP plant is chosen together with the heat recovery section and not after it. Where the silencer stands in the chain, before or after the exchanger or on both sides, changes what it has to put up with and how long it lasts.

Treatment Stages Share the Path

Many gas engines also have an exhaust treatment stage in the chain to meet emission rules. These stages are sensitive to dirt and to back pressure, and they need the gas to arrive in a calm, even stream. A silencer placed next to them has to support that, not disturb it. It also has to keep its own material from shedding into the stream that follows.

The practical lesson is that the silencer, the heat exchanger, the treatment stage, the pipe route and the stack are one system. Each has its own pressure drop, and the engine has one back pressure limit for all of them together.

What to Settle Early

Because so many parts share the path, the order and position of the items should be agreed before the silencer is detailed. The choice of type, the grade of attenuation, the protection against condensate and the arrangement of drains and supports all follow from the layout of the plant, not the other way round.

AXON supplies exhaust silencers for gas engines and CHP plants as part of the complete exhaust system, matched to the engine, the heat recovery equipment and the sound limit. Send the engine data, the plant layout and the sound requirement, and the proposal covers the whole chain instead of a single part.

What the selection covers

Silencer type and grade for the character of a gas engine's noise
Position in the chain relative to the heat recovery section and any treatment stage
Protection against moisture that forms when the gas cools
Drains, supports and access for a plant that runs for long periods
Combined pressure drop of the whole exhaust path within the engine limit
Noise from the pipe, the shell and the stack outlet

What to send with an enquiry

Engine model and fuel, and whether it is a gas engine or a CHP unit
Plant layout drawing or a sketch of the exhaust route
Details of any heat recovery equipment and exhaust treatment stage
Sound limit, its location and the hours it applies
Indoor or outdoor installation and the space available
Expected running pattern: continuous, daily or peak duty

Send an enquiry Send us files

Questions we are often asked

Can I use a diesel generator silencer on a gas engine?

Sometimes, but it should not be assumed. The exhaust, the running pattern and the equipment around it are different, so the silencer should be selected for the gas plant and not copied from a diesel specification.

Why does a CHP plant need special attention?

Because the exhaust gives up heat to a heat recovery section, the gas reaches the silencer cooler. That changes what happens to the moisture inside and affects how long the silencer lasts.

Does the silencer affect an exhaust treatment stage?

Yes. Both share the same path and the same back pressure limit, and the silencer must not disturb the gas flow or release material into it. The two should be planned together.

Is noise from a gas engine different from a diesel set?

It often has a strong low-frequency content, and plants that run at night are held to the quietest hours of the day. The silencer grade is chosen with that in mind.

What does AXON need to propose a silencer for a gas plant?

The engine data, the plant layout, details of the heat recovery and treatment equipment, the sound limit and the available space. AXON then proposes a silencer matched to the whole exhaust chain.