Reducing methane emissions:
Transmission, storage, LNG terminals and distribution
- Prevent emissions whenever possible
- Reduce emissions that cannot be prevented
- Identify and repair equipment that is not working properly
- Track emissions and mitigation activities
Methane emissions in the natural gas supply chain arise from venting, fugitive emissions and incomplete combustion (methane slip). Best practice for reducing or eliminating emissions from these sources has been described in guides developed by the signatories to the Methane Guiding Principles (MGP). However, the technical and economic characteristics of the best practice may vary depending on the characteristics of the part of the supply chain the best practice is applied in.
This synopsis describes ‘mitigation measures’ to reduce methane emissions in transmission, storage, LNG terminals and distribution. These measures may require different practices to other parts of the supply chain. For example, leaks from buried pipelines can be more difficult to identify and quantify than leaks from sources above the ground, and the cost of repairs will be higher.
Mitigation measures include approaches used across the full natural gas supply chain and methods that are specific to transmission, storage, LNG terminals and distribution. Sources which mitigation measures are applied to include the following.
- Compressors (convert wet seals to dry seals, address rod-packing seals, reduce emissions from gas starts)
- Pneumatics (convert to be powered by electricity or compressed air, replace high-bleed devices)
- Dehydrators (switch to low-emission or no-emission dehydration, optimize glycol dehydrators, and route flash gas to flare or use as fuel)
- LNG truck loading (dry connects, use nitrogen to purge lines, vapor balancing)
- Pipeline maintenance (pump down, recompress and reroute, use hot taps, flare residual gas, use in-line inspection technologies)
- Pipeline commissioning (vacuum instead of purge)
- Third-party damage (damage-prevention programs, install excess-flow valves in lines)
- Storage systems (monitoring, well-integrity monitoring and reviews)
- Boil-off gas in LNG terminals
- Equipment leaks (implement leak detection and repair programs, replace equipment prone to leaks)
- Energy use (reduce methane from incomplete combustion of fuel by having automated air/fuel ratio controls, minimizing the number of start-ups and increasing combustion efficiency of equipment)
- Flares (minimize flaring, improve efficiency, avoid pilot failure)
Continual improvement in reducing emissions should be achieved across all parts of the supply chain
Case studies with features unique to this sector
Pipeline draw-down and pump-down
Operators can lower gas pressure in sections of pipeline that need maintenance work by blocking it off and allowing customers to withdraw gas, before venting. Operators can also reduce venting using a mobile compressor that removes gas from the pipeline section to be vented and recompresses it into a nearby section.
Recovering blowdown gas with permanent compressors
Install electrically driven compressors in compressor stations to reroute and not vent blowdown gas, with temporary tank storage.
Flare residual blowdown gas
If gas cannot be moved into another pressurized system, or there is residual gas left after a recompression operation, flaring reduces the methane in the vented gas.
Hot tapping for pipeline connections
Hot tapping makes a new connection to a pipeline while the pipeline remains in service. This avoids the need to depressurize and vent the pipeline to make the connection.
Monitoring underground storage
Implement well-integrity management systems.
Replace dehydrators in storage systems with lower-emission alternatives
Vapor-compression refrigeration and Joule-Thompson expansion can be used to condense water in gas streams, reducing emissions compared to glycol dehydrators.
Minimizing emissions through the design of LNG terminals and LNG truck- loading systems
A variety of mitigation practices reduce venting and fugitive emissions in LNG terminal operations.
Commissioning with vacuum pumps
Constructing and commissioning a new section of distribution network gives rise to methane emissions during the purging process and pressurization of the new section. Emissions can be avoided by using a vacuum pump to remove the air in the new section.
Avoid emissions caused by third-party damage
Civil work around gas networks can cause damage to service lines, resulting in emissions. Work with third parties to prevent damage events.
Install excess-flow valves in service lines
When damage arises in service lines or inside customer premises, gas is released into the atmosphere. The resulting flow of gas can be detected and stopped with an automated cut-off valve.