Plan 74 vs Plan 52 1

[hemvig]

Lean amine Pump
flow: 90 gpm
head: 329 ft
temp 150 F
sp. gravity: 0.994
Vapor pr: 2.02 psia

Can someone help me with the seal selection which one is good Plan 74 or Plan 52? If so Why? Explain.

Thanks in advance

 

[ciise]

hemvig- I recently came across similar application- I was under training at the time and my senior selected plan 74. When I asked why, the answer was that Lean Amine has poor lubricity in which case Plan 74 is a better selection.

I am not giving an advice here-just stating a fact. I am sure the experts will give you more relevant advise..

Good luck

 

[NGLENGR]

The 52 is an unpressurized liquid secondary seal. The 74 is a dual pressurized (gas) seal.

The plan 74 will always leak the buffer gas into the process and atmosphere, as the between seal space is maintained at a higher pressure than process. Depending on your tolerance for gas (nitrogen, CO2, air, whatever), the plan 74 is quite tolerant to cavitation, low VP margin, air entrainment, or other off-design conditions for a pump.

The plan 52 can be as simple as an atmospheric pot with oil and as complicated as a cooled reservoir with instrumentation and a pumping ring in the seals. In my facility, our amine pumps (rich and lean) are plan 52s. The lubricity of amine isn't great as ciise pointed out, but with adequate cooling the seals have fared well.

If your process is a condensing fluid, you'll need to monitor the collection of process into the barrier fluid in the pot. This can cause problems with environmental leakage past the secondary seal.

In any case, be aware of using Viton or any other similar material for O-rings in amine service as they will fail due to embrittlement. I would suggest Kalrez or similar material.

 

[JJPellin]

We have had much greater success with 74 as compared to 52 in lean amine services. I have a few points that I think may explain that result. Lean amine would tend to be a service where outside flush (Plan 32) is not possible. We are not allowed to dilute the amine with any water stream. And, there is no cleaner source of amine available that is at suitable pressure to use. The lean amine stream itself has some unfortunate properties that make it undesirable as a seal face lubricant. It can be very corrosive of some materials. It is saturated with dissolved gas which includes H2S. It tends to produce crystalline by-products under some conditions that can build up on the faces or on the atmosphere side of the seal.

A Plan 52 can address this last problem if the proper barrier fluid is selected. Our most common barrier fluid is #1 fuel oil in most other services. This doesn’t work well with amine. A water/glycol mixture would do better because the amine can dissolve into the barrier fluid to some extent. But, the poor lubricating properties of the amine are still a problem in this case. Flashing and plating out of by-products will still tend to occur.

We had many amine (lean and rich) pumps with Plan 11 or 52 and were generally dissatisfied with the reliability. We started converting them to gas seals more than 10 years ago. We have been very happy with the result. I can only think of one exception. We have one pair of lean amine pump that are piped in an unfortunate way. The tiny amount of nitrogen from the gas seal on the standby pump builds up in the pump case and causes a problem when they attempt to run their spare. This requires the operators to vent the case and re-flood the pump before starting it up. This is only a problem in this one pair since the others tend to have top suction arrangements or piping arranged such that the vapors do not build up.

I would strongly prefer Plan 74 for lean amine service over Plan 52.


Johnny Pellin