Article summary: Successful closed vent systems are built on sound decisions made long before construction begins. This article explores four critical decision points that influence compliance, design performance, and long-term reliability for oil and gas storage facilities.
In the oil-and-gas compliance world, regulatory changes often don’t fully take shape until they’re tested in the field. That’s when the conversation merits a fresh look.
Two years ago, we wrote about how new federal regulations for closed vent systems (CVS) would soon apply to more oil and gas storage vessels. That has played out largely as expected. Operators in the crude oil and natural gas storage industry are tasked with implementing new or redesigned CVS to comply with the U.S. Environmental Protection Agency’s New Source Performance Standards. In many cases, that means merging regulatory interpretation, design decisions, and operational realities all at once, often for the first time at a given site. The challenge: designing a system today that will hold up to real-life conditions next year and beyond.
That is where site-specific thinking matters. Facilities that look similar on paper can behave very differently in real time. Staying ahead of those differences depends on working through several critical design decisions early in the project. Here are four that appear in almost every CVS design.
1. Define a rigid regulatory scope
A workable CVS design starts with a clear understanding of what actually falls inside the regulatory scope. If that boundary is off, the project team gets bogged down solving the wrong problem or misses the part of the system that really needs attention.
On a recent project, the initial review focused on facility components beyond the scope of the rule—the storage vessels and the associated closed vent system. In another case, the initial request focused on one part of the system, even though the rule pointed our team elsewhere. Requests like that are common, especially when requirements are new, evolving, and unfamiliar. That’s why early scope definition matters so much. It is important for the engineering team to collaborate early with the environmental team to align design decisions with regulatory requirements. Even well-intentioned approaches can drift away from what the regulation actually requires.
Working meticulously through the scope at the front end keeps the effort focused, helps the design team spend time where it counts, and reduces the chance that the project burns money on work that was never required in the first place. Go beyond what the rule actually requires, you’ll add cost and no clear benefit.
2. Align operation to permitting
This is a common design-phase pitfall. A CVS is neither solely a permitting exercise nor solely an equipment exercise.
Once the scope is clear, the next step is to verify that the design, controls, and day-to-day operating plan align with the permitting assumptions.
This is a common design-phase pitfall. A CVS is neither solely a permitting exercise nor solely an equipment exercise. Ideally, an integrated team of permitting and design experts determines how the system will be controlled and operated, and whether the specified equipment will perform in a manner consistent with the assumptions used in the air calculations and the CVS analysis. If those pieces are addressed independently, the gap between permitting assumptions and reality will only widen.
On a recent project, we needed to keep our client below the 100-ton-per-year threshold for air permitting. The initial concept would not have met that goal, so we revisited the design and adjusted it to remove a portion of the gas stream before it reached the storage tanks. By routing that gas back into the pipeline instead of sending it to storage, the project reduced emissions at the tanks and created an opportunity for product recovery. That kept the system aligned with both permitting assumptions and operational goals, improved tank emissions performance, and generated product recovery value by returning gas to the pipeline.
When permitting assumptions, design choices, and operating realities are considered together, the system is more likely to perform as intended without costly adjustments later.
3. Design for today, tomorrow, and beyond
A CVS design that works at startup can still create trouble later if production changes were never built into the original design basis. At a well site, production usually declines over time. But at a compressor station or similar facility, throughput can increase as more wells come online. Either way, equipment sized for a single point in time can become the wrong equipment later.
We recently encountered a system that was designed only for initial production levels. As production declined over time, the flow to the combustor dropped to the point that the unit was no longer operating within its intended range, resulting in performance and efficiency issues. We also see oversized combustors that can’t reach optimal temperature and don’t provide the required destruction efficiency. At another site, a unit started up, smoked for about 45 seconds, and shut down. These issues arise when the future production picture never really makes it into the equipment decision.
The answer is not always the same, though the process should be. Operators may choose to evaluate a vapor recovery unit rather than combustion. They may plan for equipment changes over time. They may stage completions so new wells help offset the decline from older ones. What matters is that the project answers a key question: “What will this system need to handle in five years, not just on day one?”
The answer helps turn a complex challenge into a manageable design choice.
4. Use sampling to inform design
Sampling should be treated as a critical design input rather than a task to close out on a schedule.
Sampling decisions shape the quality of every subsequent decision. If the data is weak, incomplete, or not representative, the design can look sound on paper but fail in practice.
On a recent project, we were tasked with finding representative data for wells that were not yet in production. The initial approach relied on historical area data, but new samples yielded results that did not align with expectations. Rather than forcing those results into the design, we re-evaluated the sampling approach, collected additional data, and ultimately developed a dataset that better reflected site conditions.
On another project, a sample was collected from the wrong location, and the incorrect analysis was run, requiring additional coordination between operations and measurement teams before the data could be trusted. In both cases, the extra work up front helped prevent costly design mistakes.
That’s why sampling should be treated as a critical design input rather than a task to close out on a schedule. Good teams use judgment when the numbers do not line up with field reality. They ask whether the sample is representative, whether it was collected from the right location, and whether the analysis supports the design decisions riding on it. That kind of discipline saves time later, even when it slows the project down for a moment up front.
Bring these decisions together
CVS projects rarely run into trouble because of a single decision. More often, issues arise when several reasonable decisions fail to align.
That’s why scope, permitting assumptions, future production, and field data are worth considering early, as interconnected components. Together, they play a significant role in determining how the system performs in the real world.
For help turning closed vent system requirements into practical design solutions, contact our team.
About the authors
For more than 30 years, senior mechanical engineer Dawn Kopecky has provided engineering, operations, and construction services to the power and petrochemical industries. Zie provides assistance on all phases of projects from permitting support, engineering, and procurement through construction, startup, operations, and maintenance. Dawn has worked with a variety of power generation processes, including combustion-turbine combined cycles, fluidized beds, pulverized-coal steam cycles, reciprocating engines, and cogeneration systems. Zir petrochemical background covers distillation, scrubbing, absorption, and various reaction processes. (Note: Dawn uses the pronouns zie/zir/zirs.)
Tony Shoberg, vice president and senior chemical engineer, has more than 20 years of experience working for oil and gas clients. His work involves developing environmental permitting strategies, preparing permit applications and notifications required to site and construct new facilities and expand existing facilities, performing audits, and developing compliance management plans and systems.
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