Alternatives to Venting: Final Report

Abstract:

This document is a closedown report for the project titled 'Alternatives to Venting '.

Planned venting can arise from a number of sources around the network, including venting at compressor sites and pipeline decommissioning for repair, replacement or modification. Planned venting at compressor sites is monitored and recorded through the on-line control system. For 2011/12, this was reported as 2984 tonnes of natural gas.

For pipeline decommissioning current best practice employed by the Pipeline Maintenance Centre (PMC) involves transfer of gas from the decommissioned section to an active section by means of a compressor but this is only feasible until the decommissioned section pressure reaches 7 bar. At this pressure the Portable Recompression Equipment operation cannot increase the pressure sufficiently to transfer the gas to the active section. So the final operation during decommissioning is to then vent the remaining gas. To improve the environmental performance of final stages of the decommissioning process several options are available including:

Collect the gas and use either on the decommissioned site or elsewhere with the network.

Flare the gas. Methane is recognised as having a significantly greater "Global Warming Potential" (GWP) than carbon dioxide, approximately twenty times. Thus flaring will reduce the environmental impact.

The programme of works looks to address some of these issues arising from the need for National Grid to vent either pipelines or compressor pipe sections as part of the normal operation either for maintenance requirements or as part of the normal control sequence. Its scope looks to cover the following areas:

Developed a venting decision/logging support tool.

Conduct trials to demonstrate mobile recompression equipment.

To develop and test the suitability of large scale adsorbed natural gas (ANG) technology to constructively reuse gas that would otherwise been vented to atmosphere.

This report covers the project's:

Scope

Objectives

Success Criteria

Performance Compared to the Original Project Aims, Objectives and Success Criteria

Required Modifications to the Planned Approach During its Course

Lessons Learnt for Future Projects

Outcomes

Planned Implementation

Author(s):

National Grid Gas Transmission