Steam Question 1

[JoeChem]

I have a small laboratory direct steam injection distillation system tied into a plant steam system. This usually works very well but occasionally I get a yellowish precipitate in the condensate. This material is insoluble in water and ties up with an oil product making it very difficult to separate the oil from the water. Lately I've been having this problem very consistently.

I think the material is definately coming from the steam as I've cleaned my distillation still and condensers and run just steam through the system for several days now. I am running the condensate through a paper filter as it comes out of the separators and I am still collecting the precipitate. I talked to the boiler treatment representative and he swears that it would be impossible for his chemicals to introduce this material into the steam system (what else is he going to say?).

The precipitate looks and smells a whole lot like elemental sulphur. The boiler treatment chemicals are:

Ondeo-Nalco 2828 Plus
Diethylethanolamine
Potassium hydroxide
Sodium tripolyphosphate
Sodium sulfite
Anionic polymer

Ondeo-Nalco 2584
Potassium hydroxide
Sodium hydroxide

Ondeo-Nalco 1720
Sodium bisulfite

I have gone beyond trying to figure out what is causing the contaminated steam and what to do to fix it. As the rest of the facility does not use direct steam injection this problem doesn't seem to concern them - I'm the only one that is actually using the steam directly. Has anyone seen this before or know what this yellow stuff is?

I have contacted the local Spirax/Sarco folks and they are recommending an Iron Separator device that they say will knock the precipitate out of the system. I initially went looking for a steam filter but these folks say the iron separator will do the job at considerably less cost. The guy's premise is that the precipitate will be carried by the moisture in the steam and if the separator removes the moisture it will also get the crud.

Does anyone have any experience with this style of separator?


Thanks in advance.

JoeChem.

 

[Cormoran]

The steam carry same chemical products for water "ever". More or minus. If you require clean steam, you require an aditional evaporator or boil your water without chemicals.
Alfredo

 

[spereira]

Hi
JoeChem, I have the same problem in our plant. we use direct steam for heating process water. sometimes they become yellowish. I've also spoken to the people responsible for our water/condensate treatment and they say that it is possible that contact with iron can lead to this. I've measured the amount of DEHA on our steam condensate, together with the iron content of our process water and there seems to be an increase in the colour intensity of these waters when it's iron content increases. So far I haven't been able to find what it is due to but fortunately we have a decolorizing step by activated carbon after the direct steam injection so it's not such a problem for the production department. Do you have more inforamtion regarding this iron separator? is it on their website?
Susana

 

[kenvlach]

The boiler treatment representative must be a saleman rather than a technical rep.
All of the chemicals, except the diethylethanolamine, protect the steel boiler from corrosion due to oxygen and carbon dioxide in the feedwater. The polymer aids removal of precipitates from the boiler during blowdown.

The diethylethanolamine is specifically meant to volatilize with the steam. It protects steam lines (and condensate system, if there is one) from corrosion. And, it has a faint yellow color (except at reagent grade purity). It forms a messy liquid by reaction with CO[sub]2[/sub]. Not surprised if diethylethanolamine also forms an oily complex with whatever you are distilling.
Yellow color also comes from dissolved iron and rust, a likely precipitate.
From the smell, you are also getting some vapor byproduct of the sodium (meta)bisulfite.

You cannot clean the steam of a volatile by mechanical means such as a separator. Either use a reboiler as suggested by Cormoran or activated carbon (GAC), as suggested by spereira. However, if cleaning the steam, separate out the condensate before and after the GAC.