pump station design

[ehsank1358]

Dear Friends
My project is regarding design of a pump station for a condensate terminal.
condensate is available in one tank.i am going to design a pump(one spare will be considered) which is capable to transfer 1500 m3/h condensate via 300 meter pipe to a carrier(ship).
no diameter for pipe size and pump is available since this is a cost estimating
design.
my procedure is as below.please review it and let me know if it is wrong:
first of all i assumed that pressure at ship inlet shall be about 2.5 bar.
i have not considered any pressure drop between tank and suction of pump,actually
i toke minimum liquid level of tank(e.g. 1 meter level of condensate in tank)
as pump suction pressure ,then i used HYSYS for determining the pressure drop across
300 meters pipe.
i used maximum ambient temperature for incoming fluid from tank as worse case of pump design.
also i used minimum ambient temperature for determing of pipe pressure.
then i change pump duty(delta P) and pipe diameter to meet pressure of 2.5 bar at
ship inlet.
from this method several scenarios were defined for evaluation cost of project.
please let me know if you can help and improved this method of evaluation.
also please check the following questions and let me know your reply.please
mention reference for each response:
1-is it required to considered any piping section before suction of pump for such basic design?
if so, how length of pipe is logical?can i consider same diameter for both suction
and discharge of pump?
2-what is maximum velocity for discharge(suction if required) of pump for condensate fluid?
i have taken a maximum velocity of 2 m/s for pipe.
3-what is worse temperature for pump design and pressure drop through pipe?i used maximum ambient temperature for incoming fluid from tank for pump design and minimum ambient temperature for piping design.
thanks in advanced

 

[roker]

Hello,

You should consider the condensate temp since with condensate the temp is usually near boiling which brings us to the NPSHavail versus the NPSH rquired by the pump (you can select from catalogs or in the internet) this will determine the height of tank above the pump suction.

regards,
roker

 

[devaxrayz]

Ehsank,

first i will answer your question

1. It is not only required but also a must to consider any piping section for a suction for pump design. This is because one of the important thing in pump design is to calculate the available NPSH (NPSHa). The suction pipe length should be as small and as straight as possible to minimize pressure drop which will reduce your NPSHa. There is no guidance for this suction pipe length. You have to estimated it based on where is your tank and where will u located your pump and imagine the pipe routing. Many thing should be consider for pump location but most consideration it should be easy accessible for operation and maintenance.
You already on the right track if you use maximum condensate temperature from the tank for suction design because at maximum temperature you will get your maximum condensate vapor pressure which will lead to your minimum NPSHa (worst case, while using minimum temperature to determine the piping pressure in most case will not give any significant impact (especially when you talking abount maximum and minimum AMBIENT temperature).

Yes you can consider the suction diameter is the same with your discharge diameter, it can happen. The reality it will depend on your suction design which intend for enough NPSHa, and discharge design which intend for economic.
Most common for your application is your suction will be 1 or 2 size larger than your discharge diameter. Let say your discharge is 16", your suction probably 18" or 20"

2. For pump suction, the maximum velocity is not depend on what is your liquid (water, condensate etc) but it is depend on what is the condition of your fluid. If your fluid is at boiling point it is up to 4 ft/s, for subcooled liquid (40 F below boiling point) it is up to 8 ft/s. However for suction, the most important is the design provide enough NPSHa (NPSHa should be larger than pump NPSH required with 2 - 4 ft margin). The more velocity, the more pressure drop and you got less NPSHa.

For Pump discharge the maximum velocity is depend on your erosional velocity (it can goes up to 25 ft/s). However when we are talking about pumped liquid you should talk about economic velocity. higher velocity means less pipe diameter (less capital cost) but higher pump power due to high pressure drop (more operational cost). The common economic velocity of discharge is 12-15 ft/s.

3. The worst temperature for pump design (in operation side) is the boiling point temperature.

Back on your procedure, i think there is no problem with it. But instead of changing the pumpduty and trial and error with pipe dia to match the destination pressure. It is more easier to change the pipe dia (base on standard market pipe) and then calculate the pump disharge pressure/head/duty (disch press = destination pressure + pipe pressure drop).
One more thing is since you are doing cost estimating, you better select your pipe class correctly. Looking at your pressure and discharge pipe length, It is seem that you will use class 150 pipe means you will use sch 40 for pipe 2 to 6 inch, sch 20 for 8 to 12 inch and sch 10 for 14 inch and larger. Selected thicker pipe will increase your estimate.

-rayz-

 

[rrrewagad1]

Dear friends,
Can anyone please tell me How much percentage of steam (flash steam) allowed in condensate line to avoid corrosion/erosion problems due to slug flow conditions.
System-
Line- 2'', 500m
Flow of condensate- 6500 Kg/hr
Press.- 3.3 kg/cm2g,
Temp- 136oC