Selective Catalytic Reduction

The introduction of more stringent environmental legislation, via the Industrial Emissions Directive (IED) meant our gas turbine driven compressors didn’t meet the required standards. To overcome this, Gas Transmission (GT) had two options; replace the older equipment with newer, lower emission gas turbines, or retrofit emission reduction systems to cut the emissions to appropriate levels.

So, in 2016 the team began a project looking at whether a Selective Catalytic Reduction (SCR) system could be used to help us meet our emissions obligations.

SCR is an emissions abatement system that’s fitted to the exhaust of a gas turbine. Ammonia (in the form of aqueous ammonia or urea) is injected into the exhaust and reacts with nitric oxide (NO) and nitrogen dioxide (NO2), causing the nitrogen and oxygen to separate. This reaction is assisted by a catalyst and allows for the release of nitrogen and water into the atmosphere, instead of nitrogen oxide (NOx).

The team developed the conceptual design for an SCR scheme that would work on the GT compressor fleet. Following this, the gas turbines across our sites were screened, to see which units were best suited to having the system installed. As part of this, three units were identified. For each, a Best-Available Technique (BAT) study was conducted, to understand the cost and environmental benefits of installing SCR.

The project helped to identify that SCR could be a viable solution for all unit types – our results showed that as a solution SCR meets the required emissions standards and would result in significant cost savings when compared to installing new gas turbines. However, several next steps were required before we could apply SCR to a gas transmission network compressor unit.

As a continuation of the project, a Strategic Options Paper (SOP) was developed and approved to investigate the strategic, commercial, and engineering options available to GT, and to progress with the development of a Front-End Engineering Design (FEED) for the chosen solution.

This was closely followed by an investment paper to secure funds to design, build and commission two SCR units on two gas turbines at Aylesbury Compressor Station, to reduce carbon emissions to levels which comply with the Industrial Emissions Directive (IED). All work was completed in early 2020.