Deaerator 3

[res2002]

Hi:
I am upgrading a system wherein the client wants to install a deaerator in the existing system. The present system has a consensate return tank, with LP steam supply to it and the feed water is pumped to the boiler. The deaerator is to be installed about 80' away from the condensate tanks. The new system will be as follows:
Condensate returns to the existing tank. It will be pumped to the deaerator and then from deaerator to the boiler.
Any suggestions or tips for designing the system?

 

[arunb]

It is not clear why the condensate tank is being retained, otherwise as such it is not required when a deaerator is being considered and could simplify the system.I presume the condensate pressure is not adequate to bring it to the new deaerator.In any case it may not be necessary to heat in the condensate tank since deaeration itself requires steam heating.

As I do not know about your system, I can't say how the system could be designed.The deaerator system design is fairly standard, perhaps you could get some information from the supplier's themselves.

The make up water to the deaerator could have a control control valve which regulates it so that the condensate from the condensate tank is utilized fully. You could examine the possibility of using the existing BFP (relocating from condensate tank to deaerator outlet) and existing feed control stations.

Hope this helps.

 

[nstress]

The Deaerator is normally a pressurised vessel, while the condensate tank is an atmopheric tank only. The low pressure steam connection must be given to the deaerator, where the steam heats the water to expel the dissolved oxygen in the water.

good luck

 

[jproj]

res2002:

First of all, to pump directly from the deaerator is just asking for trouble. Deaerators are normally designed to empty into a storage tank, which provides the required head for the pump. The receiver tank also provides storage volume in the case the inlet water is stopped (gives you some extra time to shut the boiler feed pumps off so you don't run them dry).

It would be a whole lot more efficient to install the deaerator on top of the existing condensate tank. Condensate return can be pumped directly to the deaerator where it can be deaerated with the LP steam (you could even leave the LP Steam inlet in the condensate tank if it is above the normal water level). After being deaerated, the condensate drains to the existing condensate receiver (by gravity) where it can be pumped directly to the boiler.

This setup would require some re-work on the existing condensate tank, but would save you the money in buying another storage tank and additional pumps (though you may have to replace the existing pumps anyway).

Good Luck!

jproj

 

[DeltaCascade]

A boiler feedwater dearator will take steam condensate and make-up water (likely about 7-10 ppm dissolved O2), and scrubbing steam, and produce water essentially at its boiling point with about 7 ppb dissolved oxygen. This water is dropped by gravity into a deaerator storage section. Deaerator scrubber and storage sections are essentially one unit and typically operate at about 5 psig. The storage section is a pressurized vessel, typically designed for about 20 minutes of residence time (as stated above). This residence time also allows for chemical oxygen scavenger to reduce dissolved oxygen content further, to about zero (producing a reducing vs an oxidizing atmosphere) .. eg: catalyzed sodium sulfite or other oxygen scavenging agent is typically used, primarily to minimize oxygen pitting in downstream economizer and steam condensate systems.

As the stored deaearated water is at it's boiling point, the boiler feedwater pump immediately downstream of it is subject to cavitation ... hence, deaerators are must be above, typically about 30 feet in the air, above the pumps, to provide NPSH.

Good luck...

 

[INBCPE]

I second DeltaCascade.

I used to work in a very old chemical plant that had a Blue Seal boiler plant. Except for leaking seals every now and then, everything ran fine, 24 hours a day, for decades.

Our condensate recovery system consisted of traps draining into headers that drained into Sarco condensate pumps, which then pumped everything into another series of small condensate recovery tanks and Sarco pumps, which then pumped condensate directly into our DA (a simple packaged integral spray head dearator and storage tank). The DA tank outlet was 4.5' above the inlet of our turbine pumps. The pumps themselves were below the NOWL of the boilers. And as long as we kept up with our water treatment program and annual maintenance, everything ran right as rain.

 

[Amsterdam]

Everheard of the Stork Type Sprayer De-Aerator, I think that is the solution of your problem.