requirments in boiler water treatment 1

[bdmiller]

Can someone give me some general guidleins as to requirments for boiler water pre-treatment. specifically I am looking for what is the norm for oxygen scavenging in boiler water treatment. How low do you need to go? do all boilers have to worry about this? Ever considered a membrane device or other technology over chemical treatment for this?

any input is appreciated...
thanks,
Brian Miller

 

[cdcosta]

Those requirements are a function of your process requirements and system metallurgy... a steam turbine etc. has more stringent requirements than other process uses.
Also your feedewater temp. will affect this. O2 is less soluable in water at higher temps.
Typically a mechanical dearator is used along with sulphite to scavenge the excess O2. Typically 50 - 100 ppm sulphite residual is targetted.

As far as membrane usage... it depends on makeup water feedrate. RO units can be costly and require membrane replacement. You could also consider Di's or softeners in the overall comparison...

 

[cub3bead]

Spray-tray type deaerators are generally capable of producing water with a DO2 level of 7 ppb. Chemical scavenging can take you down to < 1 ppb.

Sulfite dosing depends on the boiler operator pressure. It is not used in high pressure boilers.

Oxygenated water chemistry has been imported from Europe and is finding applications in supercritical steam generators. Oxygen is actually fed into the boiler feed water. There have been a number of papers wrtitten on this topic, you might try looking at past papers from the Internation Water Conference for details.

You might try looking at

http://www.liqui-cel.com

for more info on the gas transfer membranes that can be used to degas boiler feedwater.

I think the Liqui-Cel might be an interesting replacement for forced draft degassifiers in makeup IX systems. If you could maintain low DO2 levels in the IX product you could consider the use of less exotic materials for storage tanks, etc.

 

[countryham]

I have been challenging past methodology and thinking about oxygen scavenger applications in deaerators for a long time. Current knowledge suggests that it is advantageous to carry a 5ppb dissolved oxygen residual in deaerators and consequently all feed water equipment.Lower oxygen residuals promote GREATER corrosion--NOT LESS. See the May 2005 EPRI Report(Electric Power Research Institute Report). That recommends ORP values between (-300Mv)and(+150Mv) in boiler feed water.-- Something that is diffult, if not impossible, to do when you operate a scavenger system based upon residuals in boilers.--As recommended by chemical vendors over the world--There are a number of technical errors that have been recognized as validated postulates by vendors' hand books for fifty years without challenge.