For UK gas distribution networks, gas venting remains a necessary part of normal operations, for maintenance and safety purposes which can be either manual or automatic. Gas venting results in unburned natural gas being released into atmosphere. This has an environmental impact as the main constituent of natural gas, methane, has approximately 28 times the global warming potential of carbon dioxide (based on the IPCC Fifth Assessment Report (AR5) over a 100-year period).
Depending on the source of venting, varying quantities of gas will be released and there is limited understanding of the environmental impact this causes. Additionally, vented gas results in shrinkage, defined as the volume of gas that is lost from the network which cannot be accounted for. GDNs have an obligation under Special Condition 1F.14 to improve the Shrinkage and Leakage Model (SLM) by improving the accuracy and calculation of Shrinkage Gas reporting.
Currently, there are varying methods to different degrees of sophistication, to quantify and forecast the extent and impact of venting.
Objectives
Following the 3 stage approach to the project, the objectives of each stage are:
Stage 1 objectives
Identify and detail current venting processes and equipment which release gas. Include literature review of previous projects and identify the lessons learnt.
Provide an assessment of the frequency at which gas is released (considering variation through periods of high and low demand).
Provide a detailed understanding of the volume of gas being vented annually from equipment and operations.
Provide an assessment of the environmental impact of current venting processes.
Stage 2 objective
Identify safe, environmentally friendly alternative processes and technologies that could be adopted by the networks.
Stage 3 objective
Quantify the benefits associated with the options identified and highlight the most appropriate.
Learnings
Outcomes
Data was gathered to give an understanding of the venting that occurs across each network. Once the key operations had been identified and amount of gas quantified, solutions were identified through research. Solutions were ranked based upon the cost benefit analysis and estimated saving in emissions of natural gas to atmosphere. A brief explanation behind the rank is included:
1. Pipeline commissioning updated procedure and concept idea – this is the second highest environmental savings of emissions and low cost to implement. Could be partially implemented with no technology solution. This area is seen as a major ‘quick win’
2. Valve control systems, VRG and Emerson Shafer – very high cost to implement but very large potential saving in emissions to atmosphere. A multiple of approximately x3 (NGN) and x9 (WWU) greater volume of annual emissions in comparison to the other areas of gas venting
3. Pipeline decommissioning, GECO – Lower cost to implement than the zero emissions odorant injection system although the lowest in terms of natural gas emission savings
4. Gas analysers, VE technology – lower cost to implement than the ZEO system for a similar saving in emissions
5. Odorant injection, ZEO – more expensive to implement than VE technology or GECO for a similar saving in emissions. However, the existing equipment only has a finite lifespan; this technology could therefore be programmed in as the replacement to the current automatically venting equipment.
Lessons Learnt
Data capture/engaging staff internally takes longer than expected and future projects should always allow plenty of time for this.
