Deaerator Design 2

For a Fire Tube Steam Boiler Application with Pressure Rating 150 PSI,
1. Should we need Deaerator - is it economical.
2. If so, how should we design Deaerator for my application.

Please share your knowledge.

 

[quark]

KPS!

Whether you require deaerator or not depends upon the dissolved oxygen levels in the boiler feed water. If it is morethan 5ppm, then you have to have. If you have condensate mixing arrangement, then Spirax has one good system which efficiently mixes condensate and cold water as well as deaerates.

One simple technic is to use steam sparger in the bottom of the tank and keep open the lid.

Note: You have to check DO levels.

Regards, Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[jproj]

K.P.S.

As quark stated, if you have high levels of dissolved gas in your feed water, you will need to remove it before sending this water to the boiler to avoid corrosion problems. You can remove the dissolved gas either chemically or mechanically. Considering chemical treatment is an on going process, it will become uneconomical very quickly. A deaerator, on the other hand, can be strategically placed to recover lost heat or steam (depending on your system) making it an economical decision.

Regarding deaerator design:
Designing for the flowrates required is a simple material & energy balance:
mass in = mass out
energy in = energy out

The actual unit design is a little more complicated than that, though and I would recommend contacting a deaerator design company (there are several). On top of designing the unit for you, they will guarantee the unit's performance, which limits your liability should a problem develop. If there is a problem, most deaerator manufacturers will come and fix it for you. I recommend Sterling Deaerator. I have worked with them in the past and they make a quality product.

http://www.sterlingdeaerator.com/

Best of Luck!

jproj

 

[MJCronin]

KPS

You DO NOT need a deaerator....if, of course you have barrels of money and do not mind replacing the entire boiler, condensate and steam piping every third year.

You see, deaerators are not real.....they perform no real function...... they really do nothing for the steam system. They are a myth...... a dream propogated by mechanical/power engineers only interested in selling more equipment.

This silly business about keeping oxygen out of your system is just one big lie.....Oxygen, is smart and knows enough to stay away from steam and condensate systems....it does't go where it is not wanted.....

Go ahead.... start up your system and enjoy it!!!!!!...... It works well does't it???? (at first anyway)

And, about that oil in your automobile, and that stupid oil filter......you don't really need them either.....

For more lies, try

http://www.kansascitydeaerator.com/

http://www.craneco.com/ourbiz/ourbiz_fluid.cfm

http://www.powersourcing.com/se/deaerators.htm

Also use that gift from God, "GOOGLE" and search "Deaerator why needed"

MJC

 

[TD2K]

ROTFLMOA

MJC, whatcha got? Gotta be good stuff.

 

[Narasimha]

If the Boiler capacity is small something like 2/3 tph, I feel chemical dosing is more economical. Rarely we find small boilers with dearators.

 

I admit that Need of Deaerator is must.
Please provide me your knowledge regarding,

1...To what temperature the feed water should be heated and what factor decides the Temperature of Deaerated Water.
2...Relation between Deaerator StorageTank and BoilerCapacity.
3... What factors decides the pressure of Steam and its mass Rate for deaerator.
4...At what Height from Pump Deaerator Storage Tank should be placed.

Awating your sugessions.
K.P.S

 

[jproj]

KPS:

1) Depends on your system and where the deaerator is located. Some deaerators are located on the condenser and operate under a vacuum. Other deaerators are placed on the LP drum and operate at much higher pressures. Some deaerators are just connected to the storage tank and pump directly to the boiler. The operating pressure (temperature) depends on how your boiler is designed and how your system is set up. If your boiler was designed for 100ºC inlet water, and there is no pre-heating from the deaerator to the boiler, then the DA must operate at or above 100ºC. If there are heaters between the DA and boiler, the DA can operate at a lower temperature.

2)Can't help you there. Most deaerator storage tanks are designed for 10 minutes storage time (from normal water level) at the maximum boiler feed rate. Some have higher storage times (I've seen as much as 30 min) and some have lower.

3) Steam flow rate is determined from the material and energy balance. You may use anything from wet to superheated steam to heat the inlet water (It just depends on what you have available). Once you have the steam conditions, you can determine the steam's enthalpy from steam tables and solve for the flow rate through material / energy balances (don't forget the vent!)

4) The height that the storage tank needs to be above the pump suction is only dependant on the NPSHR for your pump.

Good Luck!

jproj

 

[MJCronin]

KPS

All right..... I will not be sarcastic and rude..... (I will also try not to drink a six-pack just before I go on line) I promise........

jproj seems to hit the nail on the head with all of his answers... I would like to add that you must perform a system mass-energy balance ( just like you learned at the university) and......

Secondly, deaearators are typically sold rated at 15, 30 and 50 psig...... you should design your system around these commmercially available sizes

The NPSHa is an area where you can make big "screw-ups" if you do not elevate the deaearator.....You can ruin several expensive boiler feed pumps............jproj is right.... however, I would like to add, take the NPSHr for the pump and add 50% ( or 6 feet, whichever is more) to layout your system.......Check the Hydraulic Institute Standards for more detailed information

Here is a wild idea............ contract with apower engineer to specify and design your system !!!!


MJC

 

[KernOily]

MJC - you suggest to add 6' or 50% to the manufacturer's published NPSHr. I've always heard (and used) that 3' is the number. Is 6' more suited to boiler feed pumps, and 3' OK for ANSI pumps? Thanks!
Pete

 

[MJCronin]

74Elsinore,

Based on everything I have read,(including the Pump Handbook) there is some controversy on this number.

The best and most recently published guideline on this topic is contained in the "Hydraulic Institute" Standards.....try Standard 9.6.1 entitled "Centrifugal Vertical NPSH Margin (ANSI/HI 9.6.1)

Try

http://www.pumps.org

for more information

Obviously, a higher deaerator is better....... but there are limits on building height and boiler room design

Everything comes down to money

MJC