pH for removal of NH3 from exhaust with dilute H2SO4 Scrubbing? 2

[AUSLK]

I can calculate the required amount of H2SO4 required to react with the ammonia (in a verticle packed tower scrubber). But I also need to know what "optimal" pH to operate at and also calculate my H2SO4 consumption to reach that point.
Thanks for the help.

 

[9741411]

Recommend maintaining scrubber pH nuetral. 2 advantages are 1) can use mild steel, 2) won't have to nuetralize afterwards.

ammonia is easliy scrubbed, even in a venturi-type scrubber

 

[glennpan]

Your best bet is to contact the manufacturer of the packing material who can tell you the pH where you will have the best efficiency.

The chances are that you will need an acidic pH, so a PVC scrubber will probably be the best choice.

 

[jppmj]

The best way to remove ammonia from air is to use a scrubber with structured or random packing like Pall Rings in PP The scrubber can be built in plastic like PVC or PP or PE.
The diameter of the scrubber is calculated from air velocity (about 1.5 to 2 m/s).
The packing height depends on ammonia concentration in and ammonia concentration out (2 to 4 m heigh).
The liquid flow rate is about 12 to 20 m3/m2/h.
The pH is 2 to 4.
Be carefuul : with high ammonia concentration you can have serious heating due to heat of reaction.
H2SO4 consumtion is one mole H2SO4 per ole NH3.
The salt producted Ammonium sulfate

 

[jppmj]

The best way to remove ammonia from air is to use a scrubber with structured or random packing like Pall Rings in PP The scrubber can be built in plastic like PVC or PP or PE.
The diameter of the scrubber is calculated from air velocity (about 1.5 to 2 m/s).
The packing height depends on ammonia concentration in and ammonia concentration out (2 to 4 m heigh).
The liquid flow rate is about 12 to 20 m3/m2/h.
The pH is 2 to 4.
Be carefuul : with high ammonia concentration you can have serious heating due to heat of reaction.
H2SO4 consumtion is one mole H2SO4 per ole NH3.
The salt producted Ammonium sulfate

 

[AUSLK]

All,

The scrubber is an existing FRP scrubber from a previous acid scrubbing application. NH3 scrubbing is much easier than acid scrubing so the scrubber size should not be an issue (per vendor). Main challenge is balancing water consumption versus H2SO4 consumption to keep pH of wastewater above 2.5 going down the drain. Thus my question for optimal pH. I understand that higher pH's require more water makeup (less acid) and a bigger drain load, while lower pH's conserve water. Mainly what I am hearing is can run anywhere between pH=2 to 5 and have no problem scrubbing 99%+ NH3.

Data:
15000 scfm with 3 lbs/day NH3 loading
500 gpm scrubbing solution circulation rate
8ft tower dia x 10ft packed section, Jaeger 3.5"Tripak

It appears from the 1:1 NH3 to H2SO4 value that I will only consume about 2 gal/day of 96% sulfuric (at any pH). So qualitatively speaking I believe I can run at pH close to 5 with no problems.

Make sense?

 

[AUSLK]

jppmj,

I am curious about your 1 mole H2SO4 to 1 mole NH3.

I was using the following chemical reaction equation:

2NH3 + H2SO4 = (NH4)2SO4

Is this not the correct equation to use?

Thanks,
AUSLK

 

[25362]

AUSLK, your reaction shows 2 moles of NH[sub]3[/sub], not one, per mole of acid. Is that what you mean ? Sulphuric acid is one of the cheapest in the market.
By the way, ammonium sulphate is used as a rice field fertilizer, and as a supplier of nitrogen in fermentation processes.

 

[AUSLK]

25362, yes jppmj advised 1:1 moles H2SO4:NH3, I am using 1:2 and was hoping to get verification on the correct number. I have known about the various uses of ammonium sulphate, my local water district injects it in our potable water supply as a nitrogen source. Unfortunately my production rate will be meager, such that it's not economically viable to segregrate it from the other industrial waste streams.

 

[25362]

AUSLK, do you mean ammonium sulphate is added to non-potable water, as a nitrogen source ? Is it not toxic to humans if added to drinking water ?

 

[AUSLK]

25362,

Yes that is what I mean, and apparently not toxic (at least at the concentrations they are using).

Do you agree with the 1:2 ratio of sulfuric acid to ammonia?

 

[oxilume]

Recommend you decommission the verticle packed tower scrubber. Install a horizontal radial entrained gas to fluids mass transfer unit. You can find a description of the technology on US Patent & Trademark website by searching for Inventor Tom Grisham.

http://www.revextechnologies.com

 

[25362]

AUSLK, although stoichiometry calls for half the acid, actual (not chemical) consumption may be driven by efficiency factors (I've seen brochures showing two scrubbers in series for better results), lower pH values, higher possible temperatures, ammonium hydrogen sulphate formation, better mass transfer, etc. may ask for twice the dosage. Better ask again jppmj on this subject.

 

[Profaic]

Ammonia and amines are all highly soluble in an acid environment. The equilibrium is however driven by the concentration of the wash liquor and oprating temperature.

At higher temperatures, the vapour pressure of the contaminant overcomes its solubility. Remember, at equilibrium the reaction can go both ways.

The reaction you describe at ambient would tend to go to completion forming ammonium sulphate and NOT the bisulphate.

profaic