Ammonia Scrubber Particulates 1

[shiek]

Our facility wet scrubs ammonia through a packed bed with muriatic acid. On occasion, a visible plume of ammonium chloride appears. We are looking for a solution to this problem, short of a new scrubber.

We are considering:

1. H2SO4 as a scrubbing solution.
2. Crack and burn the NH3.
3. Post Scrub
4. Improve pH control.

 

[yorkjim]

Your solution #1 is best - as HCl is supporting the formation of ammonium chloride - the scrubbing solution needs to be altered.

 

[PeterAB]

I wonder if substituting sulfuric for hydrochloric acid won't simply substitute ammonium chloride with ammonium sulfate particulate. However, sulfuric acid has a lower vapor pressure than hydrochloric, so switching may be helpful.
Ordinarily I would expect the aqueous ammonium chloride to stay in solution. Ammonium chloride particulate might be formed in the gas phase if there is HCl vapor in the gas phase. In that case your temperature might be too high. Note that the reaction between ammonia and HCl is highly exothermic - a concern at higher concentrations.
If high temperature is the cause, you may want to consider using a more dilute scrubbing solution and/or recirculate it through a heat exchanger -- or try the lower vapor pressure (dilute) sulfuric acid.

 

[dfman]

We have looked at this problem theoretically.

Problem with packed bed scrubbers is that they will block up with particulate very quickly.

One solution might be Fluid Bed Scrubbers, with turbulent packing for the scrubbing of gases and particulates in one phase.

Contact Clean TeQ in Australia if you would like further details.

Hope this helps
ctairman
info@cleanteq.com

 

[AUSLK]

If you don't have a "mist eliminator" after the packed bed and scrubbing solution distributor (if a verticle packed tower), but within the scrubber, this could be a inexpensive solution. We scrub with Sulfuric acid, form ammonium sulfate which is soluble (up to about 38%) in water and then blow down the scrubbing solution based on conductivity. Scrubber temperature is ambient and pressure is about 20 inches of water column negative with induced draft fans pulling the exhaust through the scrubbers.

Improved pH control will help too, if you experience wide excursions.

 

[saumian]

Auslk,

We considering to build simple bubble chamber to absorb ammonia vapours from our bulk storage tank, needed during fill ups.

Can you give me some advice or any other leads to learn more about this.

Saumian

 

[Andremor]

How can project of column (gas cleaner) for absorved amine and isopropanol ?
I have flow of gas and % molar the component´s but, i not have flow of liquid.(counter-flow)

How i can find that data ?:

diameter column ?
NUT ?
HTU ?

sorry i dont speak very well

André

 

[siretb]

It is possible to use HCl, but you need to avoid inside the column a dangerous area, in terms of pH, concentrations. This can be don by adjusting the L/G rates, and careful process control.
sulfuric is another option that should work, as peterAB states.
I do not think that a demister will work, aerosols of NH4Cl are too fine
Unless you have a very high concentration of non soluble particles, packings will not be a problem.

 

[yorkjim]

ctairman's comment here that packed bed scrubbers:

"block up with particulates very quickly quickly"

is not an absolute truth. Older tower packings, such as saddles, do have histories of fouling and plugging, often times within relatively short time frame.

But retrofit to a modern, open design packing can very likely solve this problem. I am familiar with a number of towers that fouled quarterly, and by retrofitting to a modern packing, rather than simply replacing the packing that was fouling, these towers now have operated for years - and continue to operate today - with no fouling as well as no loss in efficiency.

 

[dfman]

Yorkjim

I was offering advice, not stating an "absolute truth" or being a smart arse.

Instead of stating someone is wrong, why don't you try and make sure you are right first? And, by the way, keep to the topic.

Following the line of argument about ammonium chloride particulate in packed bed scrubbers if you can't keep the compounds in the aqueous phase, yes particulate blockage WILL be a problem.

And yes, sure, if you change to a more open packing, sure, you will have less problems with particulate.

But the trade-off will be less transfer power to remove the pollutant from the air to the liquid phase & less oxidisng ability (hence more chemical use).

Fluid Bed Scrubbers will allow you to do achieve both objectives, and are effective particularly in retrofitting to packed bed scrubbers where you will not need prescrubbing with venturi scrubbers, increase the size of the scrubber or use more chemicals.

This was the point I was making.

ctairman

 

[yorkjim]

Hi ctairman,

I apologize if I offended you. But I also point out, my statement regarding your comment was a qualified statement, I did not say that you were incorrect. I do therefore stand by my post. Your previous post, as written, more than implies, it indeed predicts, particuate buildup, and this may - but it also may not, be true.

And, at the risk of offending you again as well as getting a bit out of the thread track, I have to do it again, because in your response to me you state that a more open packing will be less efficient (per your comment that more pollutant will exit the stack after repack to a more open packing, with possible higher chemical consumption). I also point out that we do not know the current packing in this NH3 scrubber. But as an example if the current packing is saddles, Pall Rings or similar old style random packing, a modern packing will have far superior HTU in this application. So efficiency will improve, not degrade, after repack, and the particulate will much more likely pass out of the tower. I have the data is you want it.

I also never stated anything about the Fluid Bed scrubber option you are trying to sell. Indeed, it is an option that should be explored and compared to other options.

 

[siretb]

I support what Yorkjim writes. We use packed beds for scrubbing in application involving a lot of solids. What you have to do is to select a good, second or third generation packing, and irrigate it enough.
Returning to your original post, the plume observed is due to very fine areosols, created inside the scrubber in an area where NH3 is still present in the gas phase.
As I stated in my former reply, changing the operating conditions (concentrations, L/G, ....) may help a lot. It that is not possible, plainly switching to sulfuric should do.
What kind of inlet ammonia concentrations are we talking about ?

 

[yorkjim]

Hi siretb,

Thanks, I am most familiar with NH3 concentrations as high as several hundred ppm.

Another point that has not been mentioned is the H2SO4 is generally less expensive than muriatic acid. Sulfuric acid is the most produced and used process chemical.

It would be interesting if sheik would post how this all worked out.

 

[shiek]

The final story; we have improved the pH control which has helped but not completely solved the problem.