14 SCR roof skids for the containerised gensets of a power plant

The challenge

A power plant in South America generates with fourteen containerised diesel gensets of 1,100 kWe each, driven by Cummins KTA50-G3 engines at 1,500 rpm. Untreated, each engine emits about 4,500 mg/Nm³ NOx at 15% O₂. The plant needed NOx after-treatment on every genset, designed for a target of 225 mg/Nm³.

The after-treatment had to handle 4,011 l/s of exhaust at up to 525 °C within the engine’s back-pressure allowance of 68 mbar, and leave room for a particulate filter to be added later.

Our approach & engineering

Axces engineered one vertical roof skid per genset that combines the SCR catalyst, the exhaust silencer and a spark arrestor in a single housing, and supplied fourteen identical sets. Apart from the control cabinet and one central urea tank, everything for each genset sits in or on its own container.

Catalyst and dosing

The catalyst uses vanadium (V₂O₅) elements of 150 × 150 × 500 mm, set 4 × 6 per layer in two layers, and works between 265 °C and 515 °C. An air-assisted dosing system injects urea solution through a 1,500 mm lance into a static mixing pipe of AISI 316Ti, which gives the urea the length it needs to mix with the gas before the catalyst. Each container has its own 60-litre AdBlue day tank, filled from one central 30-tonne urea tank through pre-filters. NOx sensors on every set feed the dosing control.

Silencer and spark arrestor in the same housing

Downstream of the catalyst the gas passes straight through the silencer section, designed for 30–40 dB(A) of attenuation, and the spark arrestor before it leaves the skid. The housing is 316L and 16Mo3, designed for 550 °C, with bellows compensators and insulation mattresses on the hot connections.

Ready for a particulate filter

Each skid also carries a filter housing, delivered empty. A diesel particulate filter can be fitted into it later without rebuilding the exhaust or the skid.

• One standard skid, repeated across all 14 gensets
• SCR, silencer and spark arrestor in one housing
• Each genset’s equipment in or on its own container
• Air-assisted urea dosing from a central tank through day tanks per container
• Filter housing in place for a later particulate filter

Scope of supply

• 14 × combined SCR, silencer and spark-arrestor housings with catalyst
• 14 × static mixing pipes, bellows compensators and insulation mattresses
• 14 × filter housings prepared for a later particulate filter
• 14 × dosing cabinets with NOx sensors
• Installation support: a first set built together with the customer’s team, and remote support for the rest

Results

All fourteen skids were shipped in January 2026, in five containers with a total weight of 33.6 tonnes. Installation starts with one set that the customer’s team builds together with Axces as the example for the other thirteen, which follow with remote support. Emission measurements follow commissioning.

• 14 identical SCR, silencer and spark-arrestor skids, one per genset
• Designed to bring NOx from about 4,500 to 225 mg/Nm³ at 15% O₂
• One central urea tank feeding day tanks in every container
• Prepared for a particulate filter without rebuilding the exhaust

Related reading

• NOx reduction with SCR: how the catalyst, urea dosing and mixing work
• Retrofitting emission control on existing generator fleets: adding SCR to gensets already in service
• Soot and particulate reduction: DPF and filtration for diesel exhaust
• Exhaust silencers explained: absorptive, reactive and combination designs