Steam quenching of the Stuffing box 1

[maintennance]

For the process pumps in a refinery, where high temperature process fluids are used ( 260 deg C and upto 340 Deg C) , one of the pump vendor is requiring LP steam quenching in the stuffing box in their design and claims that this will reduce the heat soak for better life of the mechanical seal and the bearings as these will operate at much lower temperature . But further queried, the vendor says the same pump can also perform without any problem if the purchaser cannot provide steam.
Basically steam is a poor thermal conductivity and i am not convinced with the reply of the vendor.

Other vendors does not say this requirement for the same pump .

Thanks to clarify to have steam quenching design and its advantages and disadvantages.

 

[flexibox]

If you are using a mechanical seal at these temperatures it will most likely be a Metal Bellows seal. Pipining Plan can be Plan 11+ 62 (LP Steam) or Plan 02 + 62 (LP Steam)
Putting steam into the jacket is rather unusual for this type of application, cooling water is normally used to cool rather than steam. Stean is used with high viscous product like bitument to keep the product liquid.
As far as the seal is concerned I would recommend no Steam or cooling water to the Jacket. Make sure that you have a high temperature metal bellows seal with Steam quench. If steam is not available then use Nitrogen quench. Plan 62 prevents coking that is why we use it.

 

[JJPellin]

I am not sure about your terminology. A steam quench (Plan 62) is generally a good idea for hot, heavy streams. It can extend seal life by reducing coke formation at the atmosphere side of the seal faces. But, this would not be described as steam to the stuffing box. If, you are referring to steam passing through a jacket around the stuffing box, or a jacket in the seal gland, then that is another matter. We use steam jacketed glands for heavy streams. But not for the purpose implied. We use it to keep the seal faces hot and the product between the faces liquid for start-up. Once the pump is up and running, the steam is a poor cooling media. But, it can help to keep the seal from starting up with the faces stuck together with cooled product. We use this method for asphalt pumps in tank farm applications. Please clarify if you are asking about a steam quench or a steam jacket.

Johnny Pellin

 

[ione]

To go deeper into this matter, have a read to the link below and to the attached paper

http://www.mcnallyinstitute.com/17-html/17-09_api_gland.htm

 

[maintennance]

Sorry flexibox I have not made the point clear. JJ had striked it . Yes I am asking about the steam letting it through the stuffing box jacket which vendor is saying that for service temperatures above 260 deg C, they recommend this steam jacketting where the LP steam has to be used and they say this is required to reduce the heat soak in the stuffing box due to high service temperatures.They also claim better life of the seal and the bearings By the by the seal flush plan is 32,52. The pumps are used in the Delayed coker unit pumps for like HCGO like serivces. Is the vendor claim is correct?

 

[JJPellin]

I have never used a steam jacket in an application of the sort you are describing. However, I have also never used a Plan 52 in a service this hot. I don't know what you would use for the barrier fluid. For heavy coker gas oil, coker charge or fractionator bottoms service, we would use a Plan 32 with cooled (~120 °C), filtered heavy gas oil as flush. We would use a Plan 62 steam quench. We would steam trace the pump using 250 psi saturated steam to prevent it from setting up. We would insulate the pump very well for the same reason. I don't see an advantage with the steam jacket. The running pump has no need for it and the standby pump better be hot and ready to run by the use of a drilled check valve or warm-up line bypassing the check valve.

As Flexibox already noted, you had better have a high temperature metal bellow seal.


Johnny Pellin

 

[maintennance]

Thank U JJ. Will follow the advice of Flexibox. Thanks Flexibox. But can we not use 32,52 seal flush plan. 32 seal flushing liquid is like what JJ indicated.

JJ, with regard to warm up arrangement vendors have quoted for Overhanging type Pump (OH2 type) and hence they are not requiring any warm up arrangement for their pumps they claim. Then we need to specifically ask for warm up arrangement only for the system requirement . Am I correct?

 

[JJPellin]

The pump manufacturer may claim that warm up piping is not needed. But it is. These streams can set up or become extremely viscous at ambient temperatures. If you expect the pump to start automatically on loss of the main pump, it must be hot. If you expect operators to be able to start it up within minutes, it must be hot. And even for an overhung pump, excessive thermal shock can result in rubs, leaks, bearing or seal failures. I would consider warm up arrangements to be mandatory at these process temperatures.

I am confused about the seal flush plan. If you are asking if you can use a low temperature seal because you have seal flush that is only ~120 °C, then the answer is no. If flush is lost, the seal would fail dramatically and catastrophically, which would be guaranteed to start a fire. Even with flush, you should use a high temperature seal (metal bellows) and a steam quench.


Johnny Pellin