Understanding how to reduce compressor emissions in the natural gas industry can not only help the environment, but can also improve overall industry efficiency.
Methane and volatile organic compounds (VOCs) are pollutants that are emitted from the oil and natural gas industry. These pollutants are on the rise and it harms our ecosystem and the people living in it.
On the other hand, compressors are one of the major sources of these pollutants during oil and gas production, processing, transmission, and storage.
As such, knowing how to reduce compressor emissions in the natural gas industry comes with a lot of benefits – it can provide a cost-effective way of reducing VOC and methane waste and emissions.
In 2011, it was estimated that there are 504,000 producing gas wells in the U.S. and each of these takes advantage of a compressor to aid its processes.
There are expectations that the number of oil and natural gas exploration and production industry will continue to increase, thereby surging air emissions from oil and natural gas sources.
Nonetheless, the latter can be curbed by controlling how these pollutants are exposed to the atmosphere.
Why Is a Compressor Used for Natural Gas?
A compressor is a mechanical device that increases the pressure of a gas and are used during natural gas processing, transmission, and storage in the natural gas industry.
Reciprocating and centrifugal compressors are the most common types of compressors used in the oil and gas industry.
Either of these machines can be employed to transport natural gas from the production site, through the supply chain, and to the final consumer. However, during this process, compressors emit vented VOC and methane into the atmosphere.
And this vented emission comes from the seals or the packing surrounding the mechanical compression components of the machine.
Generally, compressor emissions can come from many components including:
- Compressor seals
- Pressure relief valves
- Starter open-ended line
- Blowdown open-ended line
What’s more, these emissions from the compressor tend to increase over time as the components of the machine start to degrade.
How to Reduce Emissions in The Natural Gas Industry
The emissions from reciprocating compressors used in the oil and gas industry can be reduced by adopting control techniques that reduce the leaking of natural gas beyond the piston rod packing.
In some cases, certain replacements may be required including:
- Replacement of the piston rod
- Refitting or realignment of the piston rod
- Replacement of the compressor rod packing
Similarly, new technologies can be used to ensure that the emission from these compressors can be captured and routed to a combustion device or reused in another process.
In contrast, the emissions from a centrifugal compressor can be reduced by limiting the leak of natural gas across the rotating shaft using a mechanical dry seal.
1. Replacement of the Compressor Rod Packing
Control techniques can be used to reduce the potential emission of pollutants in reciprocating compressors. These techniques limit the leaking of natural gas past the piston rod packing.
Reciprocating compressor rod packing features a series of flexible rings. These rings fit around the shaft to create a seal against leakage.
However, compressor emissions can still occur around the rings due to the slight movement of the rings in the cups as the rod moves. In addition, the packing rings may deteriorate with time and as such, more natural gas can escape around the piston rod.
Accordingly, this VOC and methane emissions can be reduced by replacing the compressor rod packing. These replacements should be carried out regularly.
2. Replacement of Piston Rod
Another way of reducing emissions is through the refitting or realignment of the piston rod and replacement of the piston rod as it is also possible for the piston rods on reciprocating compressors to deteriorate.
These rods can wear out if they are improperly aligned and when that happens, it can affect the fitting of the packing rings against the shaft.
Furthermore, the piston rods can be coated with tungsten carbide or chrome, which helps to prolong its lifespan.
3. Gas Recovery for Reciprocating Compressors
There is also another way of reducing gas emissions from reciprocating compressors used in the oil and gas industry. In this case, it involves the use of control techniques that recover natural gas leaking past the piston rod packing.
This means that the gas that would have been released into the atmosphere is captured and routed back to the compressor engine. This gas is transported through the valve train before it is injected into the engine intake air after the air filter.
Similarly, emissions from reciprocating compressor rod packing vents can be captured to manifold the vent line to a vapor recovery unit (VRU) system.
The VRU is made up of a compressor and scrubber, and its installation at a facility with a compressor allows the vent streams to be routed to tanks. This allows the vented rod packing gas to be captured by the VRU.
Uses of Captured Gas Emissions
The captured gases from a reciprocating compressor can be put to good use. Here, it can either be sold or routed for fuel, thereby reducing energy expenses for the site.
Nonetheless, this gas can be sent to a flare system if the gas cannot be used productively.
4. Dry Seals for Centrifugal Compressors
In centrifugal compressors, dry seals can help to reduce emissions.
In line with that, it can reduce the operating costs and at the same time, enhance compressor efficiency.
Conclusion
Compressors are useful in the oil and gas industry, however, they emit gases that can be harmful to humans and the environment. Nonetheless, it is worth noting that there are several ways to reduce compressor gas emissions in the natural gas industry.
All it will take is to replace the piston rod, realign the piston rod, and even replace the compressor rod packing.
What’s more, emitted natural gas can be captured and routed to be used as fuel in compressors.
In the case of centrifugal compressors, a dry seal can be used to reduce the emission of gases from these compressors.
