28 SCR systems for the backup gensets of a Dutch datacenter

The challenge

A datacenter in the Netherlands is backed by twenty-eight diesel gensets of 2,500 kWe each, built into containers by a genset builder. The gensets run for emergencies and for scheduled test runs, and the NOx limit for the site applies to those test runs: 190 mg/Nm³ at 15% O₂, dry, at the reference load. A diesel engine at full load produces several times that, so every genset needed selective catalytic reduction.

The genset builder asked for a plug-and-play solution. The SCR had to sit on the roof of the genset container, in series with the exhaust silencer, and work from a minimum ambient temperature of -10 °C. It had to carry a C5 coating and lagging, and twenty-eight identical sets had to arrive in batches that kept pace with the builder’s own production line.

Our approach & engineering

Axces combined the SCR reactor and the exhaust silencer in one housing and mounted it, with the mixing pipe and outlet elbow, on a galvanised skid frame that sets down on the container roof. One design was engineered, proven on a first unit and then repeated twenty-eight times.

Reactor, mixing and dosing

Exhaust gas from the engine enters a curved mixing pipe, where a dosing system injects urea solution at up to 57 kg/h. The pipe gives the urea the length it needs to evaporate and mix with the gas before it reaches the catalyst. In the reactor, catalyst elements convert the nitrogen oxides to nitrogen and water. NOx sensors before and after the catalyst control the dosing and show the operator what the system removes.

Silencer in the same housing

Downstream of the catalyst the gas passes straight into the integrated exhaust silencer and leaves through the outlet elbow. Building the silencer into the SCR housing replaces a separate silencer on the roof and keeps the assembly to one skid per genset.

Built to ship and lift

Each set travels in four parts: the mounting frame, the inlet and mixing pipe, the SCR housing with its silencer, and the outlet elbow. The housings and elbows were fabricated at Axces Production in Poland.

• One standard design, repeated across all 28 gensets
• SCR reactor and exhaust silencer in a single housing
• Urea dosing up to 57 kg/h, controlled by NOx sensors before and after the catalyst
• Designed for -10 °C, with C5 coating and mineral-wool lagging
• Shipped in four parts per set, ready to set down on the container roof

Scope of supply

• 28 × SCR reactors with integrated exhaust silencer
• 28 × mixing pipes, outlet elbows and galvanised skid frames
• 28 × urea dosing units, compressors and day tanks
• 28 × sets of NOx sensors before and after the catalyst, with pressure and level sensors
• Factory acceptance test of the first set on a test yard, support with its installation, and commissioning support
• Delivery in four batches of seven

Results

The first complete set passed its factory acceptance test and hot commissioning on a test yard in September 2022, before the batch deliveries began. At full load the system’s own NOx sensors read 994 ppm before the catalyst and 91 ppm after it, a reduction of about 91%. All twenty-eight sets were delivered to the genset builder’s yards and are in service at the datacenter.

• 28 identical SCR and silencer sets on the genset container roofs
• Each genset built to a NOx limit of 190 mg/Nm³ at 15% O₂
• About 91% NOx reduction at full load at first-unit commissioning
• One skid per genset instead of a separate SCR and silencer

Related reading

• Data center backup power and emission regulations: the Dutch, German and Swiss rules for emergency gensets
• 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
• Meeting environmental noise limits at data centers: how exhaust silencing fits the site limit