Navigating green pathways
Published by Bella Weetch,
In response to climate concerns, most countries around the world have goals to reach net zero by 2050. This means that all greenhouse gas (GHG) emissions produced are balanced by an equal amount of emissions that are eliminated. As a result, governments are establishing more stringent regulations to encourage companies to accelerate their decarbonisation efforts. For example, the US Environmental Protection Agency (EPA) announced forthcoming regulations that will usher a path for companies to increase the urgency to reduce their carbon footprints – primarily GHG emissions.
So, how can energy companies bring new and existing equipment into compliance? What impact will green technology and alternative fuels have? Energy companies will have to address these and other difficult questions in order to determine their best pathway to decarbonisation. This article will explore two potential paths – emission reduction and hydrogen fuel – and how new technologies are being developed to support energy companies as they navigate these decisions.
In the natural gas sector, piston rod packing on reciprocating compressors is a major source of methane emissions. In 2019, the Pipeline Research Council International (PRCI) determined that, on average, compressors in storage and transmission emit 2458 and 3012 ft3/d of methane gas per unit, respectively.
Methane emissions at the rod packing tend to come from one of three sources. The first and most conspicuous is leakage that occurs along the piston rod past the seal rings. Some gas loss here is expected, as packing rings shuttle back and forth with the reciprocating action, but this can increase greatly as the packing wears over time, or possibly due to process upsets that damage the wear components.
Second, leakage can occur between cups in a rod packing case. Damage to cup faces over time, poor repair procedures, or insufficient clamping force can result in a loss of cup-to-cup contact. Though less attention is paid here, research has shown that emissions between cups can equal or exceed those past the rod rings. Finally, the nose gasket seal can be a significant leak source if there is damage or a loss of clamping force.
In addition to emission sources during operation, rod packing can leak significantly when in standby mode. This can be addressed with standby seals, which activate a positive seal upon shutdown of a compressor. One natural gas distributor recently recorded a reduction in standby emissions of 86% by employing a standby seal on multiple units. However, these standby seals are optional packing case features that are utilised on only a small fraction of units in the field.
Methane emissions from reciprocating compressors have been subject to increasing levels of regulation in recent years. Following a joint resolution by the US Congress in June 2021, the EPA has proposed revisions to the new source performance standards under the Clean Air Act for the oil and natural gas sector, aimed at more comprehensive emissions reductions. The existing OOOO and OOOOa standards established in 2016 require rod packing to be replaced on or before three years, or 26000 run hours. The new rules will shift to a performance-based standard of 2 ft3/min. The new subparts, OOOOb and OOOOc, would require monitoring on an annual basis (8760 run hours), with replacement and/or repair of the packing in order to maintain the required emission rate. Alternatively, a vapour recovery system can be implemented to capture and re-route these emissions.
Written by Craig Martin, Paul Modern and Juan Moreno, Cook Compression.
This article was originally published in the February 2023 issue of Hydrocarbon Engineering magazine. To read the full article, sign in or register for a free subscription.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/06022023/navigating-green-pathways/
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