Are there any steps we can take to reduce vapour emissions in crude oil storage and pumping operations?Jan-2022
Jake Gotham, InSite Technical Services, email@example.com
To add to Lawrence’s answer:
1. If you have existing floating roof tanks, it is good practice to use a FLIR camera to check for rim seal leaks. An experienced FLIR operator can identify tanks with abnormal rim seal leaks.
2. As Lawrence says, even a good floating roof will allow some vapour to escape. The next option to consider is an aluminium dome roof (ADR). Adding an ADR can significantly reduce emissions, and is becoming industry standard for crude oil and gasoline storage.
3. This can be further developed by installing a small purge stream that takes vapour from between the floating roof and the ADR and passes it through a vapour recovery unit or charcoal bed. This is rarely considered necessary, but has been done in specific situations where there was increased sensitivity to low-level emissions.
4. Regarding pumping operations, pump seals and control valve stems are likely emission points. Again, an experienced FLIR operator can identify bad actors.
Lawrence Chen, KBC (A Yokogawa Company), firstname.lastname@example.org
The most common types of storage tanks are fixed roofs and floating roofs. Fixed roofs are permanently affixed to the top of the tank. During the process of storing crude oil, light hydrocarbons such as natural gas liquids, volatile organic compounds, and hazardous air pollutants vaporise and collect between the liquid level and the fixed roof tanks. As the liquid level in the tank varies, these gases slowly release out to the atmosphere. Installing vapour recovery units (VRU) can help to prevent this from occurring. A VRU is an engineered compression package, which aims to lower emissions levels coming from the vapours of crude, gasoline or other fuels. It is typically designed to capture about 95% of Btu-rich vapours, recovering gasoline vapours to be used as fuel and thus reducing emissions.
Floating roofs are much better at reducing emissions than fixed roof free-vented tanks. The tank roof floats on the top of the liquid, eliminating vapour space between the liquid and the roof. However, they are not totally emissions proof as vapour seals (aka primary seal) around the tank rim can fail, and most seals have a loss factor based on tank diameter and environmental factors. Liquid droplets can also stick to the tank shell when liquid exits the tank and the roof descends, which then evaporate to the atmosphere, resulting in emissions similar to hydrocarbon leaving the fixed roof tanks. This can be mitigated by installing a secondary seal that is fixed at the top of the rim plate on the floating roof. The seal acts as an excellent secondary vapour barrier containment that also protects the tank contents and primary seal against weather elements and debris.