Shaping the future of the Gas Transmission Network

Compressor Strategy

Welcome to our dedicated webpage for the Industrial Emissions Directive (IED) - Compressor Strategy for the Gas Transmission System (NTS). This webpage was established to enable us to engage with you, our stakeholders, to provide a single point of contact and information to you as we work together to develop our compressor strategy.

For any additional enquiries or further information, please direct your enquiries to Craig Dyke at Craig.Dyke@nationalgrid.com or by phone to 01926 653397.

Legislation is placing stricter controls on our industrial emissions, encompassing seven directives which have been bought under a single clear legislative instrument.

The Industrial Emissions Directive (IED) came into force on 6th January 2011 and was transposed into UK law as the Pollution Prevention and Control (Scotland) Regulations in 2012, effective from 7th January 2013 and the Environmental Permitting (England and Wales) (Amendment) Regulations in 2013, effective from 27th February 2013.

Over the past two years we have been working with you, our stakeholders, to develop a strategy for our compressors to ensure that they meet the new requirements of the Industrial Emissions Directive (IED).

The most stringent impacts of the IED on National Grid are:

  • a new limit for the emissions of carbon monoxide (CO).
  • a more stringent limit for the emissions of oxides of nitrogen (NOx) for all of our large combustion plant (LCP).

Our large combustion plant had previously been exempt from the LCP Directive limit for NOx by virtue of its age. The IED is now removing this age related exemption and the limit for NOx will now apply to all of our large combustion plant. As a result a number of the larger gas turbines operated by us will need modifying or replacing in order to meet the new and revised limits. Compliance with the new emissions limit is now mandatory. However, we have entered a number of the machines in our fleet which are not compliant into a limited life derogation, allowing the continued operation of those non-compliant machines until either 31st December 2023, or when the machines have accumulated a total of 17,500 operating hours (whichever is soonest).

Why is IED important?

Gas compressors maintain the pressure on the National Transmission System (NTS) and ensure that gas reaches the desired location when required.

Currently we have 24 compressor sites on the NTS. At these compressor sites, 17 individual units are impacted by IED and as a result we will not be able to operate them as we currently do by 2023, which will impact our network capability.

In order to address these changes we have been developing an investment plan for each of our non-compliant units, to ensure that we can continue to provide the levels of network capability required by you, our customers, at an acceptable cost.

In developing our strategy there are many factors to take account of and potential solutions to consider. We have already seen a significant change in the way gas flows around our system, in addition to increasing uncertainty over supply locations and volatility in demand.

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Changes in the flow of gas through the UK during the last ten years

For background purposes, the figures below illustrate how much the flows have changed in the past ten years, moving from a predominant flow from north to south to a greater flow from east to west.

The coloured arrows indicate where there has been a decline in supplies (red arrows) or an increase in supplies (green arrows) between the winters of 2002/3 and 2012/13.

Although the flows into the Bacton gas terminal have remained relatively consistent, the sources of gas have evolved. In 2002/03, Bacton was supplied by only UKCS gas, but by 2012/13 it was mostly continental European supplies entering the terminal through the IUK and BBL interconnectors.

Not only have the predominant flows of gas changed but also the flows seen day to day. The figure below illustrates just two of the possible supply patterns that can occur on the national transmission system.

Winter 2010/11 was dominated by high LNG flows through the Milford Haven and Isle of Grain terminals. By contrast, winter 2012/13 saw high flows through Bacton from continental Europe and Easington from Norway, as a result of LNG being diverted to other markets in South East Asia.

The reduction in supplies from the west in 2012/13 has a direct influence on the amount of capacity that can be offered to South Wales, the south west and West Midlands, since the gas has to be transported further distances from supplies in the north and east. This, in turn, has an impact on compressor usage.

In general, these changes in entry flow locations and sources of gas have an impact on the system operator in terms of the need for network capacity, flexibility and how the network must be operated. Compressors are key components in delivering a full and flexible operational capability.

Supporting Information

Workshop Materials

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