pH control without using caustic
pH control without using caustic
(OP)
I am currently working at a refinery were we have a problem with ammonia in our waste water this is due to partly to direct release to our holding basin and performance problems with slop water processing. we hae identified one of our problems as the presence of Organic acids that are trapping ammonia in the ammonium ion form. i have looked in to caustic but i doun't want to use it because of caustic cracking issues at process temps over 50 decC any suggestions on another way of neutralizing these organic acids





RE: pH control without using caustic
RE: pH control without using caustic
From what I know from refinery wastewater experience is that ammonia source is primarily stripped sour water. Ammonia levels in wastewater directly depend on the SWS efficiency for this pollutant. Normally, the wastewater is subjected to stripping by elevating stream pH. If you have any issues with caustic, you can try other bases too. Lime has been proven one but generates sludge.
Regards
TechV
RE: pH control without using caustic
"lime soap" sludge. MgO will not raise the pH high enough to convert the ammonium salts into ammonia to any great extent.
I second the suggestion to consider sodium carbonate if caustic is unacceptable. There are also zeolites that selectively adsorb ammonium ion, such as clinoptilite.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: pH control without using caustic
thanks
Gareth
RE: pH control without using caustic
If this is a possibility there are a few questions you should ask yourself. Does your sour water skimmer(s) provide adequate residence time for good oil recovery from their sour water stream? Do your sour water tanks, and the level you run them at, provide adequate residence time for additional oil water separation, and are you set up well to skim those tanks if necessary?
The potential consequences include upsetting your sour water strippers, hydrocarbon fouling in your sour water strippers, consuming sulfur plant capacity with excess hydrocarbon in acid gas, and maybe even elevated CO emissions from your final incinerator. So this option should not be considered lightly, but it may be worth looking into if your ammonia problems are bad enough.
Good luck.
RE: pH control without using caustic
Na2CO3 + 2H2O à H2CO3 + 2 NaOH
and
pushing oil through would not reduce the amount of ammonia in the effluent which is the aim if increasing the stripper efficency. as iam trying to process crude water draw water which has been in contact with cude so im not sure werther Jason5000 what you proposed works.
thanks for posting guys its getting closer to a soulution
RE: pH control without using caustic
2 Na(OH) + H2CO3 -> Na2CO3 + 2 H2O
This reaction does not reverse.
You are definitely not going to get caustic by neutralizing an organic acid with sodium carbonate.
RE: pH control without using caustic
RE: pH control without using caustic
The overall equation for the reaction between sodium carbonate solution and dilute hydrochloric acid for example is:
Na2CO3 (aq) + 2 HCl (aq) >>>> 2NaCl (aq) + H20 + CO2 (g)
RE: pH control without using caustic
Thanks. I had figured it was some metallurgical issue beyond my understanding.
Perhaps, there are some kinds of stainless steel, in which intergranular corrosion will be promoted by sodium hydroxide. But, I don't know of any, and caustic soda is one of the friendliest materials to metal (if not to human flesh) that there is.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: pH control without using caustic
The Feed contains mainly contains water, ammonia, H2S, Acetic acid, Propionic acid and Formic acid.
so im unsure as to how the Sodium carbonate will affect the system.
RE: pH control without using caustic
When you said "organic acids" I was thinking you meant fatty acids, like stearic, palmitic, etc.
The calcium salts of acetic, formic, and propionic acids are soluble in water. So, perhaps a lime slurry is a good choice for you. But, you need to have very good agitation in the reaction tank, lime is very prone to settle out in dead spots, unreacted.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: pH control without using caustic
Neutralization doesn't involve a concentrated caustic solution nor would it be occurring with a high pH. Neutralization involves taking the solution pH to a neutral pH of 7. In addition, if you had high pH, you would be experiencing scaling from the other components in the water.
Intercrystalline cracking of steel caused by exposure to caustic solutions above 70°C while under tensile stress; once common in riveted boilers. Also known as caustic cracking. Your temperature does not appear to be high enough either to be concerned with.
Caustic usage will allow you to use the least amount of chemicals. If you use lime, you will also get volumes of waste sludge. Sodium Carbonate will also give you fizzing due to the off gassing of CO2.
--------------------------------------------------------------------------------
RE: pH control without using caustic
The caustic problem is due to possible build up of caustic in heat exchangers and the bottom of the tower which are at 70-120 degC.
ive been told by our inspections department that 5wt% caustic would count as a high concentration in this process, which i think is wrong. So the problem still stands!
I think 5Wt% caustic would be perfectly safe with an inline mixer down stream of the injection point along with an anlyzer to stop over doseing and it would be perfectly safe.
RE: pH control without using caustic
The 5% wt caustic is in the chemical feed line, not in the vessel itself.
The temperature is not that high either.
Don't see where you inspections department came up with this Caustic Crackin / Corrosion arguement.
RE: pH control without using caustic
The 5% wt caustic is in the chemical feed line, not in the vessel itself.
The temperature is not that high either.
Don't see where you inspections department came up with this Caustic Crackin / Corrosion arguement."
I don't either. I've seen equipment made of similar materials give reliable service for many years, on electroplating lines.
I recall, for example, a mild steel tank used to contain a steel blackening bath, 50+% sodium hydroxide, at 150+ degrees C for at least three years.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.