Eliminating Pig Trap Blowdown Emissions at a Remote Site with No Grid Power

Pig trap depressurization is one of the larger sources of unmitigated methane and VOC emissions in the midstream sector. Blowdown of launchers before loading a pig, and of receivers before recovering one, is standard practice across the industry. On gathering lines prone to condensate formation, pigging frequency is high, which multiplies the emissions impact of every blowdown cycle.

Methane reduction commitments have put that practice under scrutiny. Mitigation options exist, flaring among them, but the real difficulty is executing them safely, quickly, and cost-effectively at sites that were never built to support extra equipment. This site presented two constraints that ruled out most conventional answers: no grid access and the presence of liquids, which prevents the use of traditional compressors.

 "The operator sought to achieve 100% mitigation without adding significant costs to the operation or the use of combustion-based equipment."

High Pigging Frequency on Condensate-Prone Lines

Lines that form condensate require very frequent pigging. Each launch and each receipt means another trap blowdown, so the emissions burden compounds quickly over a year of operation.

No Grid Access at a Remote Site

The facility has no electrical service. Any solution requiring electrical power, VFDs, or fuel delivery would have meant building new infrastructure at a location where that cost is difficult to justify.

Liquids Present in the Trap Contents

Condensate in the recovered stream prevents the use of traditional compressors, which cannot tolerate liquid ingestion. The mitigation equipment had to handle gas and liquid alike.

Partial Mitigation Was Not Enough

An existing equalization practice had already lowered blowdown pressure, reducing released volume. But reduction is not elimination, and the operator's commitment required a path to 100% mitigation.

An initial site visit produced the key insight. The facility already contained both high-pressure (1,000 psig) and low-pressure (150 psig) pigging equipment, tied together by existing jumper headers, piping, and valves. That arrangement was already being used to equalize high-pressure equipment down to the lower pressure before venting. It was also, unrecognized until then, a ready-made source of differential pressure sitting inside the fence.

The ZD3 harnesses differential pressure as the sole driving force for its linear transfer compressor. It requires no electrical power, no VFDs, no fuel, and no external energy source of any kind. At a remote site with no grid access, the dP that already existed between the two pressure systems was enough to run the entire mitigation process. A short sequence of manual ball valves gives pigging operators the ability to fully depressurize any equipment on site before opening a trap door.

The system captures and eliminates emissions from both the high-pressure and low-pressure traps during pigging operations. What was previously a reduced but ongoing release is now a closed loop, with trap contents recompressed back into the pipeline instead of vented.

The safety improvement is an associated benefit alongside the emissions result. Keeping gas and liquids inside the pipeline keeps workers away from pressure, flammability, and chemical hazards during what is otherwise one of the more exposed routine tasks at a gathering facility. The noise and odors that accompany a blowdown are gone as well.

Methane and VOC emissions from high-pressure and low-pressure trap depressurization fully captured

Workers kept away from pressure, flammability, and chemical hazards during pigging operations

Noise and odors from blowdowns eliminated, improving relations with neighboring properties

Achieved at a remote site with no grid access, using only differential pressure already present on site

No combustion-based equipment introduced and no significant added operating cost

Manual controls keep the system simple for pigging crews to operate without specialized training

The value of this installation extends past the single facility. Any site with both high-pressure and low-pressure piping inside the fence is a candidate for the same approach, and the operator is treating this deployment as the first step in a broader program.

Duplicate the system at a second site

Replicate the installation at a comparable facility to confirm the approach transfers cleanly and to establish a standard configuration.

Survey facilities without an existing jumper line

Examine sites that lack a high to low jumper but do have both high-pressure and low-pressure piping inside the fence, where a jumper could be added to create the required dP.

Aggregate capture data for reporting

Collect recovered volume data across installations to support air permit documentation and greenhouse gas reporting obligations.

Build a prioritized fleet-wide installation plan

Rank and schedule dP-driven equipment installations across all sites where high pressure, low pressure, and usable differential pressure exist in proximity.

The ZD3 is ZEVAC's permanently installed closed vent system, built for facilities that need continuous or on-demand emissions capture without an energy supply to support it. Differential pressure between two points in the customer's own system powers a linear transfer compressor, with no electronics, no combustion, and no rotating components in the flow path. That makes it particularly well suited to remote gathering sites, and its liquid tolerance handles the condensate that would disable a conventional compressor.

Whether a facility can run a ZD3 on existing differential pressure comes down to a handful of site conditions. These are the questions worth answering before a site visit.

Do high and low pressure systems coexist on site?

The essential precondition is two pressure systems in proximity, ideally already tied together by jumper headers. Where a jumper does not exist but both systems do, adding one may be the lowest-cost path to enabling capture.

What differential pressure is reliably available?

Confirm the typical dP between the two systems under normal operating conditions, including the low end of the range. The dP is the power source, so its availability determines whether the system runs when operators need it.

Are liquids present in the recovered stream?

Condensate-prone lines produce liquid alongside gas. Confirm expected liquid content so the system is configured appropriately, and note that liquid tolerance is what rules conventional compressors out of these applications.

Manual or automatic controls?

Manual ball valve sequences keep the system simple and transparent for pigging crews who are already following a procedure. Automatic controls suit installations where capture needs to happen without an operator present.

How will captured volume be documented?

Determine early how recovered volumes will be measured and recorded. That data supports air permit documentation and greenhouse gas reporting, and it builds the case for the next installation.