Sundyne Pumps Mechanical seals 3

[SENGUTTUVAN]

For one of the Sundyne Pump for the wash water service, the Engineering feed document asks for seal plan 31,52.The pump capacity if 56m3/hr and the discharge pressure is 98 kg/cm2.The pumping temperature is 45 deg c. The service being wash water ( without any solids or hazardous chemicals) , i am not able to understand why recommended seal flush plan is for double mech seal? Sundyne clarifies that the seal plan will be as per the client reqt. Since the pressure is high should we go for double mech seal with seal plan 31 & 52 or stop with 31 which is the standard seal plan for Sundyne. Is there any other crieteria for opting for double mech seal other than for hazardous service?

 

[bk19702]

Another trigger for dual seals would be containment for environmental concerns; with this being wash water I'm not sure what the trigger would be for a dual seal. I'm finding more and more that most engineering contractors now seem to default to dual seals even if they are not necessarily required. A full review of the process and plant standards would be in order to determine why dual seals were selected. Keep in mind the Plan 52 is unpressurized, so process leakage will be out to the reservoir (which must be vented to the flare, I might add), so if there are truly hazardous materials present a pressurized system may be more appropriate. Also, from personal experience I would ask for either a plan 13 or 14 for your inboard seal flush, depending on what your pressure differentials look like between suction , seal cavity, and discharge pressure. The plan 31 standard by Sundyne is integral to the casing and by their own admission cannot be easily serviced or monitored. As the separator internals wash out, which they will, you are going to have issues down the line. A traditional recirculation flush like I've mentioned should be more than adequate for the service. Again, you want to fully evaluate what the seal cavity pressure is so you are sure the flow rate will be adequate into / out of the cavity and that you have adequate vapor suppression of the process fluid at the faces.

 

[JJPellin]

We have 10 or 12 pairs of wash water pumps that are Sundynes. All of them use API Plan 31. About half of our pumps use stripped sour water and the other half use cold condensate. SSW could be considered to carry some hazard and may be the reason for recommending a dual seal. If there is any scenario where you could have H2S break through into the SSW system, this would represent a great enough hazard to justify the dual seal. But, for the sake of reliability, Plan 31 seems to work well in our applications. What is the temperature and pressure of your water supply? What is the source?

Johnny Pellin

 

[SENGUTTUVAN]

This pump is in the VGO unit of the refinery plant . The wash water source to the Wash water break tank ( from where it feeds the said wash water pumps)is from the cold condensate header , stripped non phenolic wash water header and product fractionator receiver. The suction pressure for the pumps are 12.3 kg/cm2g max and rated 0.4 kg/cm2g.

 

[bk19702]

Sounds like you could go with a single seal, unless a possibility exists for H2S carryover like JJPellin suggests. I would still have a preference for API plan 14; 13 at minimum, over the Plan 31 internal cyclone.

 

[SENGUTTUVAN]

Thanks to all for the suggestions. Will look into the suggestions.

 

[SENGUTTUVAN]

Finally the client want to have 31,53B seal flush plan. Before going to sundyne, I want to know ,what would be the impact on the bearing loads and other factors because of the inclusion of seal flush plan 53B where the seal chamber needs to be pressuried. Will there be any change required in the model of the Pump itself? Thanks for advise.

 

[bk19702]

The seal chamber won't be pressurized, the cavity between the inboard and outboard seals will. Dual seals on a sundyne will be piped to Ports 2 & 7 on the casing (barrier in / barrier out). I'm curious - why the 53B? Is there a requirement on not having the barrier fluid in direct contact with the source of pressurization (i.e. nitrogen like in a Plan 53A)? You'll need to make sure you have a makeup line in place for the barrier fluid you are going to use. One big drawback with the 53B is the low volume of barrier fluid you can have in the reservoir. You need to make up whatever fluid you lose over time as a result of leakage into the process past the inboard seal. You'll also want to make sure the bladder material is compatible with the barrier fluid you choose; any exotic materials required for this component will drive the price up. If a dual pressurized seal is required, the 53A will be less of a headache and in the same price range as the 53B (or a little cheaper) in my opinion.

 

[JJPellin]

A pressurize double seal is a standard option for a Sundyne pump. No modifications to the pump are necessary. There will be a different combination of sleeves and seal faces used, but no other parts are affected. As noted by BK19702, the pressure is between the two product seals. The two seals are configured in such a way that this pressure will have a negligible affect on thrust loads. It will have no affect on the bearings.

Johnny Pellin

 

[SENGUTTUVAN]

Thanks JJ and BK19702. I will study the option of 53A.