A National Grid worker on the phone surrounded by screens displaying data

Compressor upgrade project hits new milestone

A vital project to upgrade two compressor stations on the Gas National Transmission System (NTS) has reached a significant milestone with the appointment of Costain Oil and Gas as main works contractor. The Huntingdon and Peterborough compressor upgrade is the single largest capital project currently being undertaken on the gas network.

The upgrade project currently in progress at Huntingdon and Peterborough is part of a major capital delivery programme that will see National Grid replace or upgrade a series of compressor stations on the NTS to bring them into line with strict environmental limits laid down under the Industrial Emissions Directive (IED).

The two sites are part of a network of 64 gas-driven compressors around Great Britain that act as the ‘engines’ of the NTS, making sure that gas is pumped to where it is needed 24/7. However, legislation to cut emissions of carbon dioxide (CO₂) and oxides of nitrogen (NOx) mean that ageing technology must be replaced with newer, low emission alternatives.

Design and construction phase begins

Under the main works contract, which is valued at £113m, Costain Oil and Gas is responsible for detailed design, construction and commissioning at the two sites. Central to the success of the project will be the installation of four new gas turbine compressors – two at each site – which feature the latest combustion technology.

The new units, each 15.3MW in size, are manufactured by Solar Turbines. They are gas turbine driven compressors that use dry low emissions (DLE) technology, recognised as the next generation of ‘green’ compressors and feature computer-controlled combustion systems, together with low emission burners. They will replace existing infrastructure – the Peterborough units were commissioned in the 1970s and those at Huntingdon in the late 1980s.

Once operational, the compressors will reduce NOx emissions by around 95% over 20 years, with a 16% reduction in CO2 over the same timeframe. The carbon dioxide saving is equivalent to the amount of CO2 produced by driving over 28 million miles in a medium-sized car per year.

The improvements will ensure that the sites meet emissions limits laid down under IED legislation, which is divided into a number of directives, including the Integrated Pollution, Prevention and Control Directive; this is what is driving the investment at both Huntingdon and Peterborough.

Keeping the gas flowing

One of the biggest challenges for the National Grid project team overseeing the upgrade is the fact that the two compressor stations are adjacent on the NTS. With both being heavily used, they cannot be taken out of service at the same time, or be offline during the colder winter months.

Lead Project Manager Paul Emmett explains:

“In an ideal world we would take each site off the network for around 18 months and complete the entire upgrade before turning the site back on, but that is simply not possible. Each site must be in a position where it can be turned back on each year by 1 November and go back into service.

“To achieve this we’ve had to develop a managed delivery programme with defined outages between April and October over consecutive years to minimise any impact on the NTS. This avoids any outages during the winter months when gas demand is higher.”

The delivery programme

An early priority for Costain Oil and Gas will be the start of detailed design and procurement of items that will take longer to deliver. They will start at Huntingdon – the lead site – in summer 2017, with the two compressors being delivered by Solar Turbines in September 2017.

A two-year construction period will then follow, including installation of the new compressors and supporting equipment, as well as the new station control building. The site is due to be up and running by the end of 2019 with Peterborough to follow the same path but a year later.

FEED study and early works

This is the third phase of emissions-related projects on the NTS, with phase 1 leading to new units being installed at St Fergus and Kirriemuir in Scotland, and phase 2 placing a new unit at Hatton in Lincolnshire.

Within phase 3, work has already been completed to upgrade the compressor station at Aylesbury in Buckinghamshire, with Huntingdon and Peterborough next in line. National Grid has employed a different strategy at Huntingdon and Peterborough to previous projects of the same type.

Paul Emmett says: “This time we undertook a front end engineering design (FEED) study for both sites between February 2014 and October 2015. Also, we procured the compressor directly from the manufacturer, Solar Turbines, rather than as part of the main works contract to allow us to manage directly any design and compliance issues. Working with Solar, we’ve been able to finalise and lock in the compressor design much earlier.

“The FEED study allowed us to identify all the necessary supporting equipment and to conduct an ‘asset health’ check that identified any items such as valves or flow meters that needed replacing. This has meant we got a very clear handle on costs to deliver these projects.”

One of the big successes for the project team in 2016 has been the early works programme at Huntingdon. Working with chosen contractor J. Murphy & Sons, the team developed a project charter to guide how the various parties would work together.

With collaboration between National Grid’s Operations and Capital Delivery teams, the early works focused on three key activities – replacing the station valves, removing the after-coolers and replacing the station vent stack. The compressor station has now been brought back online, paving the way for the Costain team to tackle the next phase of the project.

Paul adds: “What we’ve been able to do is remove all assets from the location where the new compressors will be housed so that there is a sterile area ready for Costain to hit the ground running when they arrive on site. It’s been a really good springboard for the next stage of the project.”