8 replies to this topic

[tsrc8204]

Dear all experts,

I am starting to calculate and sizing a propylene loading pump which was transferred from the storage tank to truck. The operating conditions are as following:

1. Suction Pressure: 15 kg/cm2
2. The height between tank and pump is around 3 M (evelation)
3. Pumping length is around 300 M
4. Discharge head (elevation): 7 M
5. if set the capacity of pump is 50 m3/hr (density is 524 kg/m3)
6. Pipe size: 3"
7. Loading Arm : 2" for liquid, 1" for vapor balanced

According to these data, my calculation result for NPSH is 125 M; actual pumped head is 45 M. Please help me to identify what I missed or did incorrect in this case, thank you all.

tsrc8204

[Art Montemayor]

TSRC:

Your description is not complete and flawed. The best and most accurate way to transmite a hydraulic or pumping problem description is to do it with an engineering sketch. This can easily be done in an Excel spreadsheet - in which you can also input all your calculations.

Be SPECIFIC. What do you mean by NPSH? Is is NPSH available (NPSHa) - or NPSH required (NPSHr)? Where is the suction pressure taken at? What is the length and configuration of the loading arm? Where are the detailed hydraulic calculations?

50 m3/hr (220 gpm) is a little too much for a 2" pipe. I think something is wrong with your calculations. Please submit them in an Excel spreadsheet - with a detailed and accurate engineering sketch as I requested above.

[tsrc8204]

Dear Art Montemayor,

Tks for your correction, I sketched a simple drawing for you further comments. Please help me to check and let me know the results. Sorry, I am a new engineer and hane no fully experiences on this, so if you can support I will very appreciate, thank you.

Attached Files

•  pump_head.xls   94.5KB   59 downloads

[fallah]

For suction head, simply stated:

NPSHA=P+L-V-H
as:
P = Pressure on surface of liquid in closed suction tank, in meter absolute
L = Minimum static suction head,in meter
V = Vapor pressure of the liquid at maximum pumping temperature,in meter absolute
H = Friction loss in meter in suction pipe at required capacity

If P = 16 Kg/cm2 (15+1), provided that 15 kg/cm2 would be gauge pressure, and considering V equal to around 9 Kg/cm2 (at 15 C), H equal to around 1 m:

Estimated NPSHA = 160 + 3*0.524 - 90 - 1 = 70.5 mwc

[ankur2061]

Fallah,

A correction is required in your calculation:

(16*10/0.524)+3-(9*10/0.524)-1
= 305+3-172-1
= 135 m

Regards,
Ankur.

[fallah]

Ankur,

If you note in my calculation, you will see that the result (70.5) based on mwc (meter water column), simply could be coverted to meter propylene column by 70.5/.524 = 135.

Thus, my result is the same as yours but different in descriptions.

Regards

[tsrc8204]

Dear Ankur and Fallah,

Thanks for sharing your experience, but I don't understand why you set the P = 15+1 (kg/cm2.G) I thought it should be 15 due to this is a closed vessel, if this vessel is opened system maybe as you said P=16, so that is why my calculation for NPSHa is 125M. Could you please tell me your concerning for this case? thank you!

tsrc

[fallah]

Dear Ankur and Fallah,

Thanks for sharing your experience, but I don't understand why you set the P = 15+1 (kg/cm2.G) I thought it should be 15 due to this is a closed vessel, if this vessel is opened system maybe as you said P=16, so that is why my calculation for NPSHa is 125M. Could you please tell me your concerning for this case? thank you!

tsrc

Dear tsrc,
As i described:
P = Pressure on surface of liquid in closed suction tank, in meter absolute
If 15 Kg/cm2 would be absolute pressure you are right,otherwise you should get 16 Kg/cm2 as pressure on surface of the liquid in your calculation.
Hope this clarify

[clkuoa]

Dear TSRC,
As for actual pump head calculation, the result I calculate was about 34 m. This value is needed to multiply by one safety factor ~ 1.25 to get pump head = 42.5 m. This value is approximate to your calculation (45m).