Project Details
- SCR Technology for Severn Trent
- United Kingdom
There are 12 water/sewerage companies across the UK (England, Scotland, Wales, and Northern Ireland), Severn Trent being one of the largest covering a region from the Bristol Channel to the Humber and from the Welsh Border to the East Midlands providing two billion litres of water their eight million customers every day.
With Carbon Emissions and Net Zero being at the forefront of the UKs environmental Policies in
recent years, Severn Trent in 2019 set themselves a bold ambition, which they named as their “Triple Pledge” which was to achieve Net Zero Carbon Emissions, transfer to 100% renewable energy/resources and convert their entire fleet to clean vehicles all by 2030.
With Carbon Emissions and Net Zero being at the forefront of the UKs environmental Policies in
recent years, Severn Trent in 2019 set themselves a bold ambition, which they named as their
“Triple Pledge” which was to achieve Net Zero Carbon Emissions, transfer to 100% renewable
energy/resources and convert their entire fleet to clean vehicles all by 2030.
As part of their pledge Severn Trent also committed to upgrade 12 of their standby power
generating sets over 10 sites throughout 2020/21. The arial photograph below shows the
Netheridge Site in Gloucestershire in the far south of the region which was the first to be
upgraded (See list of all 12 generating sets upgraded below).
Phase 1 – 2020
Netheridge 2 x MTU20V4000
Mythe 1 x MTU20V4000
Tittesworth 1 x Cummins KTA38
Tittesworth 1 x Cummins KTA50
Leek 1 x Cummins KTA38
Bellington 1 x Volvo TWD1643
Childswickam 1 x Volvo TWD1640
Neachley 1 x Paxman 12YHX
Phase 2 – 2021
Shelton 1 x MTU20V2000
Sugarbrook 1 x MTU20V4000
Monkmoor 1 x Cummins KTA50
There were a total of 4 sets of MTU20V4000 generating sets that needed to be upgraded with SCR
Emissions Reduction Technology to comply with MCPD (Medium Combustion Plant Directive)
requirements to meet NOx Levels of no more than 190mg/Nm3@15%O2 to allow them to continue
being operated, engine details and existing silencer layout on top of the enclosures shown below:
View below shows the 2 off SCR Systems with mixer pipe, SCR Reactor, and silencer on the two
sets at Netheridge together with a 5,000 Ltr AdBlue Bulk Tank that feed adblue to both sets.
The SCR/Silencer designs were the same across all 3 sites with the exception that where there
were single sets on a site the AdBlue Bulk Tank was only 2500 Ltr..
When commissioned the NOX was reduced from 1225ppm (NOx 1) to just 130ppm(NOx 2) which is
equivalent to 160mg/Nm3@15%O2 a total NOx reduction of -89%.
There were a total of 2 x KTA38 and 2 x KTA50 generating sets that needed to be upgraded with
SCR Emissions Reduction Technology to comply with MCPD (Medium Combustion Plant Directive)
over 3 sites.
each other inside of a plantroom. The photograph on the left shows the original setup of the
The other two KTA38 AND KTA50 SCR Systems were Leek and Monkmoor sites. The photograph on
the left below shows the KTA38 SCR System being installed on the canopy roof where we also
installed a DOC (Diesel Oxidation Catalyst) to improve the performance of the SCR System as this
was a particularly old engine.
The photograph on the right is of the original 40ft Container at Monkmoor that housed a KTA50
Engine which shows the existing silencers (The next page shows the SCR System on the
Monkmoor site).
The illustration below shows the SCR System with Collector Box, Mixer Pipe and SCR Reactor on
the enclosure roof followed by the existing silencer. The Electronic Control Panel along with a
small AdBlue Buffer Tank was mounted on the outside of the enclosure. The main adblue bulk tank
is shown adjacent to the enclosure.
Once commissioned the KTA50 Engine at Monkmoor Site was seen to have reduced Engine Out NOx (NOx1) from 1655ppm to 88ppm (NOx2) at Tailpipe (99mg/Nm3@15% O2) a reduction of almost 95%.
The total allowable limit for MCPD is 190mg/Nm3@15%O2 which meant we were almost 50% below the allowable limit. Similar results were seen at Tittesworth and leek with NOx reductions between -90% to -95% on all of the KTA38 & KTA50 Engines.
The Bellington Generator was a SDMO with Volvo 1640 Engine sited with the plantroom SCR Design as below:
For The Childswickham Project with another Volvo Engine (1643) of almost identical size, the SCR
Reactor with Mixer Pipe was mounted directly on top of the roof on an external canopy. The
photograph below the SCR Replacement.
Once commissioned the Volvo Engine at Childswickham was seen to have reduced Engine Out
NOx (NOx1) from 606ppm to 137ppm (NOx2) at Tailpipe (168mg/Nm3@15% O2) a reduction of
around -78%.
One reason that the NOx reductions were not as high was because running at 100% load the
engine only reached between 325-350C whereas other sets on the Severn Trent Sites operated
between 400-450C.
Another reason was that we wanted to conserve as much adblue as possible so as the set was
already achieving below the allowable limit for MCPD of 190mg/Nm3@15%O2 which decided that
there was no need to increase the adblue dosing further.
This is by far the oldest engine that we have ever retrofitted with SCR Technology where the
58Ltr/515Kw engine which as first installed in 1973 (over 50 years old) within a plantroom as shown
below was still able to meet the latest MCPD Levels of a modern-day engine.
In actual fact as can be seen by the screen shot of the IMS-eco SCR Software, NOX was reduced
from 736ppm (NOx 1) to just 56ppm(NOx 2) which is equivalent to just 67mg/Nm3@15%O2 a third
of the maximum allowable limit and a total NOx reduction of -92%.
The photograph below shows the MTU20V2000 Sets at Shelton Site adjacent to its fuel tank in
the corner of the complex. The SCR Reactor was designed to be installed on the roof of the
enclosure with the silencer downstream as shown below:
When commissioned the NOX was reduced from 1050ppm (NOx 1) to just 130ppm(NOx 2) which
is equivalent to 160mg/Nm3@15%O2 a total NOx reduction of -88%.
Phase 1 of the Severn Trent Project was received in April 2020 for delivery and commissioning all
9 systems by December 2020.
The second phase of the remaining 3 units was received in April 2021 for delivery by October
2021
Both phases of the project was delivered and commissioned on time, and all met the MCPD
Emissions Regulations for NOx as required.
The IMSeco SCR System is a “Closed Loop” controlled Dosing and Monitoring Package with NOx,
Temperature and Back Pressure Sensors, Airless Injectors and an ECU housed within a Control
Panel that not only guarantees to meet the MCPD Emission Levels but because of its configurable
AdBlue Dosing Strategy can be set to provide the most economical adblue consumption.
The SCR system comprises of the following components:
- SCR+ASC Catalysts
- MAP Sensor (Air Intake Pressure) or CanBus!
- Exhaust Temperature Sensor
- NOx sensors (Engine Out and Tailpipe)
- ECU
- AdBlue Pump – RPU
- AdBlue Injector
- Backpressure Sensor
- AdBlue Buffer Tank
- Speed Sensor (RPM) or CanBus Signal
The SCR System injects a measured amount of the AdBlue Solution (32.5% Urea in Water) under
pressure which is hydrolyzed to produce an ammonia gas that is required forthe NOx (NO/NO2)
reduction across the SCR catalysts. There needs to be a sufficient number of SCR catalysts to
provide enough surface area and catalyst volume to be able to obtain the NOx conversions
required on each engine.
In the unlikely event that too, much ammonia is produced in the dosing process, IMS always uses a
bed of ASC (Ammonia Slip Catalysts) after the SCR Catalysts to prevent any excess ammonia gas
from exiting the tailpipe.
The “Closed Loop” system utilizes two NOx sensors that measures “Engine out” and “Tailpipe NOx”
which gets stored within the ECU for downloading to provide “Real-Time” NOx reduction
reporting of emissions reductions.
The following parameters are logged in the SCR systems ECU (note this is not an extensive list,
more parameters can be monitored) and can be visually checked on the Digital Display on the
front of the Control Panel
- Date/Time/Work Time
- Exhaust Gas Temperatures
- Air Intake Pressure / Air Intake Temp
- AdBlue Level/AdBlue Injection Pressure / Ad Blue Consumption
- Injection Status – On or Off and Pump Status – On or Off
- Injection Time On/Injection Time Off
- NOx – Engine Out/Tailpipe
- Airflow In/Airflow Out (Exhaust)
- Any Error Codes
As well as the parameters listed above the ECU also records pressure drop, RPM, turbo pressure
and engine operation time with exhaust gas flowrate.
If errors occur the ECU records them, all of which are date/time stamped so that they can be
downloaded at a later date and reviewed/updated for maintenance or warranty purposes.
The system is supplied with a Bunded AdBlue Tank which is fitted with a KUS Type Level Sensor
(Pump and In-line Filter) that draws the AdBlue from within the tank and delivers it to a pressure
rail where it gets pressurized for injection into the exhaust. The amount of adblue that is dosed is
determined by the exhaust flowrate and other information obtained from the engines CanBus
System by the ECU along with the NOx Levels and Exhaust Temperatures that the ECU obtains
from the pre/post NOx Sensors and Temperature Sensors so only the correct amount of AdBlue is
consumed to provide the amount of NOx reduction required. The ECU will self-adjust the dose
rates depending on the parameters measured.
The Level Sensors within the tanks measure the adblue levels and provides several warnings
should the adblue levels get low. If the AdBlue is not replenished water will be recirculated from a
closed loop water system with small tank to prevent the Injectors from overheating.
Where possible as much of the SCR installation was carried out at the IMS Facility in Shepshed
Leicestershire before being shipped to site. However, with some of the systems that was not
possible, and a lot of the installation had to be carried out on site due to the bespoke nature of
this project especially with the systems being fitted above the engines within the plantroom, or
on the plantroom roof as in the case of the very old Paxman Engine.
For commissioning to take place the engines had to have been commissioned and shown to be
running stable and that there were sufficient levels of Adblue/Urea within the Tanks before we
could begin to undertake the initial checks of the systems including electrics, instruments, and
pipe connections to ensure that they were all functioning correctly and that there were no
exhaust leakages within the system. On completion reports were provided to the customer to
validate compliance.
