Even though the best practice for tank blanketing regulator installations is to install the regulator on top of the tank to minimize outlet piping and sensing line lengths, many refinery and chemical plants install their regulators at grade (on the ground). The primary reasons for this are ease of maintenance and troubleshooting; a pressure regulator at grade is typically easier to access and does not require additional equipment such as a large crane to pull the regulator if a repair is required. Additionally, it minimizes safety risks by keeping mechanics and operators off of tank tops.
From my past experience working in refineries I completely understand the desire to make equipment easy to working on and access. However, when it comes to blanketing regulators there are some things engineers need to keep in mind when trying to decide if an installation at grade is really going to be better for maintenance. Of course, we recommend you contact your local Emerson sales representative to discuss the implications and best practices for using your tank blanketing regulator at grade installations. Our sales representatives can provide expert guidance to help choose the best equipment and installation position for your particular application.
There are 3 key things to think about if you are considering installing your blanketing regulator at grade:
The sensing line will need to be as large as possible
Due to the sensing line length, the time it takes for the regulator to register the vapor space pressure will be dampened. For installations on top of a tank the rule of thumb is to increase the sensing line size 1 NPS for every 10 feet, but this is not practical for grade level installations on tanks that are 40 to 60 feet tall. The key take away is that a ½” or even a 1” sensing line for a grade level installation may not be large enough to adequately register the vapor space pressure at the regulator.
Low point drains will need to be installed AND maintained
The sensing line and outlet piping will need to have low point drains in order to remove any condensate that may build-up over time. Not removing this condensate can cause an even more delayed regulator response or even render the regulator inoperable if condensate fills a portion of the line. Equally important is the proper processes and procedures required to ensure the lines are drained on a regular interval.
Performance testing after installation will be required
Every blanketing regulator should be tested after installation and commissioning, but this is especially important for a blanketing regulator installed at grade to ensure the regulator meets your specific performance requirements. Because blanketing regulators are designed to be mounted as close to the tank top as possible it is almost impossible to guarantee any level of performance for a regulator at grade prior to installation. This is especially true for set pressures below 1-inch of H2O. After testing additional changes to the sensing line, outlet piping—or even the regulator—may be required if the regulator is not meeting your pressure control requirements.
I wanted to share some additional comments & insights from my LinkedIn status update sharing this post.
Hamza BEN AMARA: Dealing with tank blanketing regulators is quite sensitive in terms of the safety of products stored inside. But the big advantage,I think is to avoid the collapsing of the tank's walls when a vacuum pressure occurs, especially the position of the regulator for the ease of maintenance.
Michael Calaway responded:
Yes Hamza you are absolutely correct, one of the reasons for tank blanketing is adding blanketing gas to the tank vapor space when required for normal tank operation such as filling or product cooling. If we want to avoid O2 entering the tank though conservation vents or pressure vacuum relief valves (PVRVs) then the blanketing must be able to response quickly and have the required capacity to keep a tank from being exposed to a vacuum.
Hamza added:
Indeed, I have had to deal with tank blanketing for produced water storage. This is intended not only for vacuums but also to avoid the corrosion and solids build-up within the tank and facilities by O2 contamination. Putting on the ground the regulators, it really depends on the application: crude, petroleum products or water and essentially the operating conditions apart the dimensions of the tank.