Exhaust and SCR Systems for Generator Sets

The exhaust system starts at the engine flange and ends at the top of the stack. In between it carries gas at several hundred degrees, takes up the thermal growth of the pipe, keeps the back pressure within what the engine maker allows, brings the noise down and, more and more often, cuts NOx before the gas reaches the air.

Drawn for one engine

Every system starts from one engine data sheet: the exhaust gas flow, the temperature and the back pressure limit, together with the route the pipe has to take on site. Piping, flexible connectors, expansion joints, supports, insulation, rain caps and stacks are then selected as one system, in carbon steel or stainless steel.

Back pressure is where an exhaust most often goes wrong: a few extra bends or a longer run than planned, and the engine loses output. That is why we ask for the real route, not only the connection sizes.

Silencers chosen for the site

The exhaust silencer is chosen for the sound level the site needs rather than by a grade name. Together with the enclosure and the air silencers it decides what is heard at the boundary, so when a noise limit is given we look at all three.

SCR for NOx

Selective catalytic reduction doses a urea solution into the exhaust ahead of a catalyst, where nitrogen oxides are converted to nitrogen and water vapour. It is the usual answer when a permit sets NOx limits that the engine cannot meet on its own. The reactor, the dosing and the controls are built into the exhaust line and the package.

An SCR needs exhaust temperature to work, so the operating profile matters. A standby set that runs at low load for short tests behaves very differently from a prime power unit - tell us how the set will actually run.

What AXON supplies

Exhaust piping, flexible connectors and expansion joints
Exhaust silencers
Thermal insulation, supports, rain caps and stacks
SCR systems with dosing and controls
Carbon steel or stainless steel construction
Integration into AXON containers or stand-alone installation

What to send with an enquiry

Engine make, model and rating
Exhaust gas flow, temperature and back pressure limit from the engine data sheet
NOx limit and the reference conditions in the permit
Noise limit at the exhaust outlet or at the site boundary
The route: pipe length, bends and stack height
Operating profile: standby, prime or continuous

Send an enquiry Send us files

Questions we are often asked

What is an SCR system on a generator?

An exhaust after-treatment that reduces nitrogen oxides. A urea solution is dosed into the exhaust and reacts on a catalyst, leaving mainly nitrogen and water vapour.

Does SCR work on a standby generator?

It can, but it needs exhaust temperature. Short, low-load test runs are the difficult case, so the operating profile has to be part of the design.

Which materials do you use?

Carbon steel with corrosion protection or stainless steel, depending on the gas temperature, the site and the customer specification.