Reducing Storage Tank Thief Hatch Emissions

Regulations on emissions for process manufacturers and producers have continued to grow ever stringent. Storage tanks in oil and gas production sites account for a sizable percentage of volatile organic compound (VOC) emissions. To address these regulations, you may have seen last week’s news, New ultra-tight thief hatch reduces storage tank emissions, conserves tank contents.

Emerson's Steve Attri

I caught up with Emerson’s Steve Attri about these developments for this new Enardo Model ES-665 spring-loaded thief hatch. He noted that this solution was designed to help meet emissions regulations such as the U.S. Environmental Protection Agency’s (EPA’s) Quad O regulations.

Thief hatches, also referred to as gauge hatches, provide both access to tanks as well as pressure control. Technology has advanced over the years from simple dead weight hatches to today with spring loading and advanced seal designs. Enforcement of emission levels has gotten high-tech as well.

Inspectors often use optical gas imaging infrared (IR) cameras to detect leaks. Detectable emissions from hatches and other pressure relief devices can result in significant fines and stopped production.

Steve explained the difference between tank venting and leakage. If a tank needs to relieve overpressure or vacuum conditions, it opens to normalize pressure.

Thief Hatch Leaks versus Venting

The ES-665 provides sealing technology that significantly reduces vapor emissions and product loss. Its performance is rated at 0.1 standard cubic foot per hour (SCFH) at 90% of pressure setpoint. This is based on testing at ambient conditions in accordance with API (American Petroleum Institute) 2000. This tighter gauge hatch solution is designed to help meet today’s more stringent emissions regulations.

Enardo ES-665 RetrofitSteve noted that the center assembly on the hatch was designed to be able to upgrade the Enardo ES-660 and 660 thief hatch center assemblies. The retrofit was designed so no tools or special skill sets would be required. Here is an illustration of the three-step process.

This retrofit process is also much faster than installing a whole new thief hatch unit, resulting in less time for personnel in these hazardous locations, less tank downtime, and better emissions control.

Steve explained that it’s important to remember that in a retrofit, the emissions may not match levels of a brand-new ES-665 thief hatch due to the condition of the existing base.

An upgraded ES-660 or 660 can be expected to perform somewhere in between that of the ES-660 (1 SCFH at 90% setpoint) and ES-665. It is more likely that the performance would be nearer to the ES-665 side of the range.

Given the use of high-tech inspections and enforcement, tighter thief hatch seals are required to help oil & gas producers maintain compliance with stringent emissions requirements.

You can connect and interact with other pressure regulation experts in the Regulators group in the Emerson Exchange 365 community.

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