4 replies to this topic

[yoonee]

Hello. I'm Yoon, assistant engineer in process team. 

This is my first posting and chance for basic engineering of  power generation plant. It means I'm newbie.

As I mentioned in topic, I really wondering the elevation of condensate pump(CP), height from hotwell of condenser.

For setting high heat drop in TBN, I'v setted vacuum of condenser about 0.07ata, then the useful driving force from hotwell to CP is just gravity force. 

I think enough suction pressure and elevation include line friction loss should be considered with NPSHa of CP. 

How can I calculate the length of line to CP? Is there any criteria to design this stuff?  

 

[thorium90]

I would suggest simply placing the pump just beside the condenser, minimizing the distance between pump and hotwell. Whats of importance is the line size which you can get from the typical line sizing equations.

Edited by thorium90, 15 October 2013 - 12:56 AM.

[NAP]

Typically for fluids at boiling point (like condensate), the elevation of pump is set such that the difference between NPSHa and NPSHr is about 2 meters to avoid severe cavitation issues. The value of 2 meters is from what I have seen in standards of two EPC companies and most of the client specified standards. Your client may have more or less stringent requirement

 

What this means is either the condenser bottom tangent line elevation goes up if the pump sits at grade OR the pump goes down in the ground like a can pump

 

NPSHr value can be estimated during basic design stage with an assumed value of NSS (your mech engg. can help you with this)

[fallah]

yoonee,

 

Considering the limitations to elevate the power plant's condensers due to their huge sizes, the NPSHA for condensate pumps is usually extremely low. Then vertical can type pumps are normally being applied to do the job. In such applications of can type pumps, considering near zero absolute pressure in the condenser, the NPSHA is limited to the elevation between the water level in the condenser hotwell and the centerline of the first stage impeller of the pump. To keep the friction losses on minimum value, the suction piping is to be sized such that the velocity in the pump suction piping and within the suction can of the pump to be around 1 m/s and not greater than 1.2 m/s.

Edited by fallah, 15 October 2013 - 02:32 AM.

[samayaraj]

NPSHA should be at least greater than 1m than NPSHR. As you know, NPSHA is function of height between the hotwell to center of pump and length of piping. As you increase the length of pipe, head will increase & the frictional loss will increase. So, by increasing the pipe dia, you can reduce the velocity thus reducing the frictional loss. Its better to keep the suction velocity less than 1 m/sec. With this velocity, find the pipe size and estimate the length required by keeping NPSHA as 1 or 2m.