select seal to coal tar

[adula29]

Hi.
What kind of mechanical seal I must to use for coal tar (max 80deg C).
I know that it must be double mechanical seal, with API Plan 53. But construction of this seal? Back-to-Back or tandem; bellows or springs. Maby some example from Burgmann or J.Crane.

 

[longeron]

Just curious- what kind of pump are you using in this service?

At first glance a dual seal does seem to be a good option. A high viscosity service like this one makes start-up extraordinarily difficult for a seal lubricated by the process fluid. Not that start-up isn't going to be difficult for a dual pressurized seal.

Is it possible to heat the process fluid inside the pump? Perhaps with a steam jacket to lower the viscosity of the tar in the seal chamber?

My first choice for this would be a single spring seal with elastomer bellows. This is a low temperature application for which a single spring is ideal, especially because of the viscosity. Your vendor can look at the seal chamber to determine the best arraignment for your application.

What kind of utilities are available around the asset? Nitrogen, plant air, water, steam? How would you support a pressurized seal support system?

 

[bk19702]

A single seal, with API Flush Plan 02 / 62 would be the most economical option. A stationary metal bellows works well with the Plan 62 (steam quench) as a baffle can be incorporated into the seal design to direct steam flow at the entire bellows I.D. Ideally, you would have a steam jacket around the seal chamber and the quench on the seal to keep this area warm. If you elect to use a API Plan 02 flush (dead-ended seal chamber), then it would be recommended to leave the throat of the seal chamber open to promote more fluid circulation in the cavity. When properly designed with the correct materials, a single seal with the above flush plans can function well in services such as these.

Before you get too far into the seal design, you need to verify with your seal vendor the cavity dimensions you have will accommodate a cartridge seal, single, dual, etc. A dual pressurized system will work but you still need to address viscosity of the proecess fluid at startup as longeron stated. Of course, if you are mandated to limit leakage externally than the pressurized dual may be one of your few options, but the utilities required and installation costs will be much greater than a single. You would still need to address whether or not leakage of your barrier fluid into the process could be tolerated and what type of barrier fluid will be compatible with your process, unless of course you use a pressurized gas seal with steam barrier, which is another option available. I think the dual seals is overkill unless you really need it.

As you can see, many questions to be addressed that can't be given proper justice on the internet. Hopefully the information helps somewhat.