Setting of safety valves in crude oil electrodehydrators
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SY/T 0045-2008, Design Specifications for Electrical Dehydration of Crude Oil, stipulates as follows: 7.8 A closed-type safety valve and a sampling valve shall be installed before the shut-off valve of the drain pipeline of the electrical dehydrator. By common understanding, aren’t safety valves usually designed to be located at the top of a container? What are the main considerations behind this rule? Which friend is familiar with this and can discuss it? Thank you!
I checked the explanatory notes for this standard again today, and the explanation is as follows: Regarding the provision in 7.8 under B.6.3, once a safety valve is installed on the drain line of the electric dehydrator, it is no longer necessary to install another safety valve at its top. The liquid discharged by the safety valve should not be released on-site to avoid environmental pollution and potential accident risks. I still don’t quite understand why it isn’t placed at the top of the container
If it is designed at the top of the container, after the safety valve activates, oil is discharged from the outlet of the safety valve, while water is discharged through the drain line installed on the dehydrator.
This is one reason, but it seems that the safety valve cannot be moved from the top to the bottom just because crude oil is escaping from it. For example, the discharged crude oil can be poured into an accident tank; in addition, in accordance with the provisions of GB150.1: B.9.1, the discharge device should be installed at a location on the container body or its connecting pipelines where it is easy to install, inspect, and maintain. The valve body of the safety valve should be located at the top of the container or pipeline, oriented vertically upward.
The safety valve of the electric dehydrator is located at the top; when this valve activates, the oil at the top is discharged through it. However, in production facilities, when the safety valves related to crude oil activate, the oil is usually directed to a closed discharge tank or a flare skid, so environmental incidents generally do not occur.
I have come across different installation methods for electric relief valves; some are installed at the top while others are in the aqueous phase at the bottom. Personally, I think it’s better to install them at the top.
I personally agree with your view. I still have doubts regarding the understanding of the standards; it’s not sufficient to place the safety valve at the bottom just because the fluid discharged is crude oil ； If that’s the only reason, then there are many petrochemical plants equipped with devices for releasing crude oil or other oils!
My personal understanding may not be correct; in petrochemical equipment, the top part is usually filled with gas. When a safety shutdown occurs, releasing the gas from that top portion is generally sufficient to control pressure. Compared to liquids, less gas needs to be released, and it can be directly sent to the flare system. The electrical dehydrator operates with the tank always full on a daily basis; when pressure release is needed, the volume of fluid to be released is large. Is installing it at the bottom convenient for releasing the fluid into the closed drainage system?
This post is very meaningful. A year has passed – do people have any new insights?
I hadn’t considered this before； If it is designed at the top of the container as mentioned earlier, after the safety valve activates and pressure is released from its outlet, the crude oil can only be discharged into the crude oil storage tanks; however, the distance between these tanks is too great ； Under normal conditions, what is discharged through the drain line installed on the dehydrator is water, which can then be poured into the sewer.
A safety valve must be installed at the top of the electrodesalination tank in atmospheric-pressure systems. If the safety valve activates, fluid can flow into the flash tower of such systems; however, it is feasible from a design perspective to provide heating for the outlet pipeline. Our company’s 5 million tons per year atmospheric pressure plant was designed in this way, and it has been operating without any problems for 10 years.