Option to resolve acceleration head loss
Option to resolve acceleration head loss
(OP)
Hi,
I am new here and need some guidance.
A new pump skid needs to be fabricated and fitted in a ready location at my gas platform. From what I heard, the old pump never worked - did not know a lot of details. Did a calculation to determine if NPSHa > NPSHr so there won't be repeat incidents. (suspect pump didn't work because of cavitation).
This pump skid is for well equalization purpose. Liquid service is diesel, from a 2000L tank, routed through a long piping to a pump (2 decks down), to be pumped to individual well to equalize the SCSSV.
I considered pressure of the tank (which is atmospheric), static head (fluid elevation from tank to pump suction), friction loss and acceleration head. from calculation, if taking into account the acceleration head, NPSHa will be < NPSHr, which mean that heavy cavitation occurs.
Acceleration head, Ha, formula I used:
Ha = LVNC/gk, where
L=actual suction pipe length (metres)
V=mean flow velocity in suction line (m/s)
N=pump speed (rpm)
C=pump constant factor. I used C=0.016
g=9.81 m/s2
k=liquid factor (a constant)
I want to explore ways to resolve the acceleration head loss issue, to ensure NPSHa > NPSHr. Options:
1. Reduce actual suction pipe length, L by reroute whole piping to make it shorter/more straightforward between pump suction and tank. But this will be a tremendous work, possibility of welding (which means potential of production downtime)
2. Increase suction pipe diameter to reduce suction piping flow velocity, V but maintain piping routing configuration. More reasonable option but need major piping work, which may cause more time
3. Install a small tank (100L) near the pump suction. But need to see if space constraint is an issue.
I am more inclined to Option #3. However, my question is, by putting in that small tank as intermediate tank, will that negate the actual suction pipe length from big 2000L tank to pump suction, and L is now considered to be length between 100L to pump suction instead?
In short, if original L = 25 metres, but by installing the intermediate tank, L= 2 metres? Thus reducing the acceleration head loss?
Need guidance. Thanks so much!
I am new here and need some guidance.
A new pump skid needs to be fabricated and fitted in a ready location at my gas platform. From what I heard, the old pump never worked - did not know a lot of details. Did a calculation to determine if NPSHa > NPSHr so there won't be repeat incidents. (suspect pump didn't work because of cavitation).
This pump skid is for well equalization purpose. Liquid service is diesel, from a 2000L tank, routed through a long piping to a pump (2 decks down), to be pumped to individual well to equalize the SCSSV.
I considered pressure of the tank (which is atmospheric), static head (fluid elevation from tank to pump suction), friction loss and acceleration head. from calculation, if taking into account the acceleration head, NPSHa will be < NPSHr, which mean that heavy cavitation occurs.
Acceleration head, Ha, formula I used:
Ha = LVNC/gk, where
L=actual suction pipe length (metres)
V=mean flow velocity in suction line (m/s)
N=pump speed (rpm)
C=pump constant factor. I used C=0.016
g=9.81 m/s2
k=liquid factor (a constant)
I want to explore ways to resolve the acceleration head loss issue, to ensure NPSHa > NPSHr. Options:
1. Reduce actual suction pipe length, L by reroute whole piping to make it shorter/more straightforward between pump suction and tank. But this will be a tremendous work, possibility of welding (which means potential of production downtime)
2. Increase suction pipe diameter to reduce suction piping flow velocity, V but maintain piping routing configuration. More reasonable option but need major piping work, which may cause more time
3. Install a small tank (100L) near the pump suction. But need to see if space constraint is an issue.
I am more inclined to Option #3. However, my question is, by putting in that small tank as intermediate tank, will that negate the actual suction pipe length from big 2000L tank to pump suction, and L is now considered to be length between 100L to pump suction instead?
In short, if original L = 25 metres, but by installing the intermediate tank, L= 2 metres? Thus reducing the acceleration head loss?
Need guidance. Thanks so much!





RE: Option to resolve acceleration head loss
Ha = v2/2g
where Ha = acceleration head in metre of flowing liquid
v = velocity in m/s
g = gravity in m/s2
Generally the acceleration head can be disregarded in NPSH calculations because it is recovered in the pump.
Whatever you decide to do you are shooting in the dark if you do not find out why the original pump did not perform to design.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Option to resolve acceleration head loss
htt
RE: Option to resolve acceleration head loss
I was referring to the website that ione was talking about, as well as the research paper here, dated 2008. Please refer page 54:
ht
RE: Option to resolve acceleration head loss
RE: Option to resolve acceleration head loss
Are you able to give opinion on the option #3 I asked about?
RE: Option to resolve acceleration head loss
I have used dampers on the delivery side to smooth flow from reciprocating pumps for process control reasons, but never on the suction side. However, I think having one on the suction side (your option #3) would be a good choice for you because your suction line is relatively long. The friction loss would have to be calculated over the entire suction line length but the acceleration losses would be reduced as per the recommendations in your paper.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: Option to resolve acceleration head loss
RE: Option to resolve acceleration head loss
What would you be doing, if you knew that you could not fail?
RE: Option to resolve acceleration head loss
Using formula Ha = LVNC/gk, which expression will be affected if dampener is used? Appreciate your comment.
RE: Option to resolve acceleration head loss
What do you mean by 'provide the full head using the LVNC equation'? Does it mean, reduce the acceleration head loss by reducing L (Option 1 and 3) or V (Option 2)?
RE: Option to resolve acceleration head loss
Best first solution in this case is to try increasing the available head, probably by making the suction pipe diameter larger, or ... shorter.
What would you be doing, if you knew that you could not fail?
RE: Option to resolve acceleration head loss
ht
RE: Option to resolve acceleration head loss
What would you be doing, if you knew that you could not fail?
RE: Option to resolve acceleration head loss
Regards,
SNORGY.
RE: Option to resolve acceleration head loss
To size a suction side flow stabilizer you need different formulas. With a properly sized suction flow stabilizer you can practically eliminate acceleration head completely.
RE: Option to resolve acceleration head loss
Regards,
SNORGY.
RE: Option to resolve acceleration head loss
1) Contact a GOOD pulsation dampener company that REALLY knows what they are talking about. 95% of them do not truly understand what they are doing. A good company is Performance Pulsation. Their owner (John) is a pulsation wiz. John recommends a "maintenance free" flow-through style dampener. He also claims that other technologies may dampen pulsations on the suction, but they will not assist with regaining lost NPSHa. I never asked him to elaborate on why, so I could not tell you. NOTE: The article Ione attached disagrees with this concept.
Dampener to be mounted as close as possible to pump suction.
2) Lighten the spring rate on the suction side of the pump. The pressure difference between the suction and the cylinder pressure is what actuates the valve. There must be a sufficient pressure difference to open it.
3) Of course, run the pump slower as a result of #2, but also to assist with NPSHa issues.
4) It is interesting to notes that all fluids are slightly compressible. Therefore, if you have a 100[ft] of suction line then the equation you use should not account for all 100[ft]. It has been awhile since I have done this, but I seem to think that it is uncommon to see pulsation 30+ [ft] ahead of the pump suction.
RE: Option to resolve acceleration head loss
Sorry, I was mistaken. The k should not be 0.016. I have modified my k to be 0.2 (equiv to duplex single acting pump type).
0.016 was used by our vendor, which is using another formula to calculate acceleration head loss: Ha = 0.016LQN/d^2. This was suggested by Milton Roy pump but I have never seen this formula used other places in other papers or internet.
What was really strange is that both formulas, a) Ha = LVNC/gk and (b) Ha=0.016LQN/d^2 , gave vastly different results.
Using equation a) will give NPSHa > NPSHr, ie no cavitation. But b) will result in NPSHa < NPSHr , ie heavy cavitation will be exhibited.
I read in some papers that equation a) will begin to lose validity if length of suction piping >50ft. (In my case, the suction piping is 82ft). But how valid is eq b)? In the end we had a discussion and concluded that there will be no cavitation. But I am still a bit weary.
RE: Option to resolve acceleration head loss
0.2 is o.k. for your pump type. What acceleration loss do you get when using formula a)?