Dual Mech seal for styrene monoper application

[reallyme00]

Dear All, I would like to hear from someone who has experienced leakage problems with dual mech seal that is designed for pumping styrene monomer.we are having seal reliability issues as the seal fails very frequently say 2 times a year due to various reasons such as i/b bellow tear during start up due to polymerization and subsequent sticking of sealing faces prior to start up, o/b coking and etc...we were able to eliminate the O/B coking issue,,...but i/b polymerization has been unresolved yet...can anybody share their knowledge as how u avoid the polymerization and what seal is being used in your plant? the pumping is being switched every two weeks in order to avoid long stand by period...do anybody actually use a pusher seal...i'm interested to know coz i would like to eliminate the bellow design which i feel is not robust enough...the pumping temp is 35 deg c...barrier fliud is EB...having a 10 lit bladder and air fin cooler....BF temp is around 40 to 50 deg c...

Thanks in advance... Please dont hesitate to ask me should u need more details...

 

[flexibox]

I think you will find that the bellows seal is there because of Oring compatibility issues. Does the bellows bore clog up with polymerized product? What temperatures do you need for the product to polymerize? I do not understand the coking of the O/B seal at 50C you normally require much higher temperatures. What is barrier fluid EB? Can you inject a product flush (plan 11 & 53B)to cool the I/B seal which may prevent Polymerization? Do you have more information on the Seal system, how it is topped up (auto or manual) because often the seal is blamed for the failure and it may be related to operations. If you have seal drawing and P&ID would help make better assessment

 

[reallyme00]

Dear Flexibox,

Thanks for reply. The bellow does not clog up but it shear off as the faces stick together.

As per operation, it is best to keep the temperature below 40 to avoid polymerization. O/B coking mainly caused by high pressure(15bar) temperature as the seal system(53B) uses air fin cooler. EB= ethyl benzene....ethyl benzene reduces the tendency of polymerizaton. the mistake we did is that we removed plan and now are reinstalling the plan11 piping. The seal system is 53 B and it is filled manually and directly from the header.

Now we decided to install pusher seal with perfluro elastomer as secondary seals and introducing plan 14 to have better circulation around the I/B seal.

Trust it will solve the problem....please provide if u have better solution.