High pressure PD pump low emission seal?

[ywchua]

Hi all,

We currently have a PD pump on our Hydrotreater pumping high concentration H2S (above 2000 ppm)water at 6 m3/h. It pumps from a suction of 3.7 kg/cm2 to 70 kg/cm2. Unfortunately we are only using single packing on this service, which I believe is specified wrongly during design. Any recommendation/experiences in similar situation on seals to use?

Pump is not reliable at all because of its service, valves keep damaging causing severe water hammering (believe a pipe elbow failed once due to fatigue), but thats another matter.

 

[flexibox]

With H2S you should use dual seals but if you have pump reliability issues then you will most like experience pre mature seals failures. I would recommend a dual pressuized seal for this application with API Plan 53B however with damaging valves due to water hammer I would hate to see what will happen tot he seal. This seal will guarantee zero emmission of H2S to atmosphere if operated correctly. The other issue you will be faced with is will a dual seal fit in the seal chamber of a PD Pump?

trust this helps.

 

[ywchua]

Thanks flexibox. Like you mentioned will a dual seal fit into a PD pump? Im not very experienced with PD pump seals, more towards centrifugal and we have quite a few 53Bs on site. Recently we just resolved a 53B issue on a hot pump in excess of 300 C. It was a design flaw with the tab holders on the cartridge which allowed the shaft sleeve to pull outwards, overcompressing seal faces when the tertiary seal is tightened. New thicker tabs resolved the issue.

 

[flexibox]

Can you provide information on the pD pump? I may have a come across them in the past. If you want more information happy to look for it if I can assist.

cheers.

 

[ywchua]

Its a triplex piston pump, pistons are 60mm diameter. Full speed is 273 rpm, but we normally run it at 170 rpm. Theres an inverter on the electric motor. They have poppet valves, suction and discharge. Suction pressure 3.6 kg/cm2, dishcarge pressure 70kg/cm2 rated, flow at 6 m3/h (170rpm). Its a Peroni Titano.

The pump should work well in clean water service, but our process design information given to the manufacturer was wrong, it was listed as clean water.

Current fluid is H2S concentrated water, usually below 30 C, sulphide 500 - 2000 ppm, there are some abrasives in the water, havent measured quantity and size yet. Sometimes we find crystalised fine abrasives on the packing and valves. Apparently its sulphur from the H2S when mixed with air. Im guessing because packing are not meant to be sealed tight it could possible go in through there. Let me know if you need more info.

Thanks a lot flexibox

 

[bk19702]

If you are able to fit an dual seal in this service, you need to verify that the circulation rate of barrier fluid would be adequate based off of that low shaft speed. Plan 53A, B, C rely on shaft rotation for barrier fluid circulation - depending on the heat load on the seal you may be ok, but it would be one more variable to review as you progress with the application. Forced barrier fluid circulation (Plan 54) may be the way to go depending on the mechanical seal circulation rate requirements.

 

[ywchua]

we're trying to steer away from barrier seal systems to be honest. We do not have automatic top up systems, we rely on the operator to drag the top up trolley to the system and use a hand pump. Im currently look at different pumps as well for the application. Seems like process plants/refineries which has a Wash Water Injection service has issues with their pumps. Hoping to have a centrifugal pump that elminates all vibration issues, when it comes to sealing should be able to go back to a secondary containment seal. Looking at pitot tube pumps, anyone fitted mechanical seals on those before? Service has fine abrasives, not able to quantify size/volumetric percentage at this point, its tested before and results show either iron sulphide or elemental sulphur.

 

[flexibox]

yechua
I could not find any information on these pumps and doubt whether you can fit dual mechanical seals. Sorry canot help. Yes you can fit seals in pilot tube pumps just trying to remember the brand name of such pumps to send you something. I will check this too.

 

[ywchua]

I've got some data on Pitot tube pumps, just wondering because its more of a centrifuge thing, does it take long for it to respond? Anyone has experience with these pumps? This may not be a suitable question for this forum sorry.

 

[bk19702]

The Pitot tube pumps I have come across in the past were made by RotoJet, which I believe is under the Weir umbrella. They come equipped with single or dual mechanical seals, if I recall. They will be an internal component design, similar to a Sundyne application however - not a cartridge seal.

 

[ywchua]

Alright thanks for that bk19702. Very useful information. Do you have experience with the operation of pitot tube pump?

 

[bk19702]

One of our sister refineries has had experience with these pumps in wash water service for a desulphurization unit. Initially there were pitot tube issues due to low suction pressure and dirt in the water. The original tube material was 17-4PH, which was found to be erodded away at the tip due to silt in the water. An upgraded tube material (thicker wall Inconel with Stellite insert) was installed and remedied the situation. So, if you have a dirty service, you may want to keep this in mind if you go with the Rotojet. A cutaway of the Rotojet pump is attached; you can see what I was talking about regarding the location of the mechanical seal.

 

[bk19702]

Attachment didn't work the first time. Trying again.

 

[ywchua]

Thanks! The pumps Im currently dealing with is wash water on a desulphurisation unit. So far I've heard of 1 of our sister refineries in US having this issue and another in Holland as well. Our contacts in a refinery in UK went to a Warren Hydracell pump. They've had a test run so far and it went alright and they'll get back to me once they've ran it for a while. We have warren pumps in our dye injection systems and they seem to work very well. Obviously thats considered a clean service compared to wash water.