5 replies to this topic

[suresh77babu]

Dear All,

I am operating Deaerator at 1.5kg/cm2 and temp 130deg c. If suddenly cold makeup of DM water  is given to deaerator what will be effect to my BFW pump.  We have LP steam injection always to deaerator. If suction temperature of BFW  pump drops to minimum very sharply what will happen to my pump. How i can maintain NPSHr for this pump at this time.  Any suggestions please.

[thorium90]

I doubt the temperature will drop sharply. Firstly, the cold demin will get stripped in the deaerator dome where it will be heated up and the oxygen gets removed due to its lower solubility at higher temperatures. Secondly, i assume your lp steam acts as the pegging steam to maintain your deaerator temperature and pressure. Thirdly, your deaerator cant be that small that the temperature drops that sharply..
Anyway, there is a reason why the pumps are always located below the deaerator. Also, when the water gets colder, it is further away from its boiling point.

Edited by thorium90, 19 October 2013 - 08:15 PM.

[samayaraj]

Sudden injection of cold DM water into deaerator causes sudden decrease in deaerator pressure (due to sudden condensation of steam space). Ultimately this reduces the NPSH required for the pump and one of the running pump got failed due to this issue. So, there is a need for gradual injection of cold DM water. To avoid failure of feed pump due to low NPSH problem, continuous cold DM water to be injected at the suction of feed pump.

 

 

 

Regards,

Samayaraj

[thorium90]

I believe Samayaraj experienced trip of the feed pump because he injected too much cold water into the deaerator without maintaining the pressure using pegging steam. This caused the pressure at the pump suction to drop below NPSH causing cavitation and tripping of the pump. Although if the deaerator is 10m above the pump you would already have 1bar and you would have to cool it down to a vacuum to trip your pump and that would be a misoperation which i assume operators would not do to a pressurized vessel..
Low suction temperatures does not trip the pump. NPSH depends strongly on pressure not temperature. Sudden injection of cold water does not trip the pump but rather, poor control and operation of deaerator pressure does..

Edited by thorium90, 20 October 2013 - 08:35 PM.

[breizh]

Hi ,

 

Probably a good resource to consider .Google Spiraxsarco , a lot of good tutorial .

 

Breizh

Edited by breizh, 20 October 2013 - 09:47 PM.

[suresh77babu]

I am very thankful to all  for above suggestions and explanations.