H2S removal from air stream 12

[jtritts2]

I need to remove H2S from some off gasses. The air flow rate is approximately 25,000 cfm and the concentration of H2S is 800 ppm. Iron sponge has been suggested as a solution, but the technology is old and I have not been able to locate any technical info for sizing and or feasibility. Is iron sponge a good solution? Where can I get info for design? Are there any new/better technologies.

 

[TD2K]

Iron sponge is a non-renewable method of removing H2S. The H2S reacts with the iron to form iron sulfide. When all/most of the iron is used up, H2S starts to break through and you need to remove the old bed and install new sponge. There are also liquids that do similar things but if I remember rightly, they are all for trace amounts of H2S because otherwise the solvent consumption gets excessive (a search on google should find lots). Sorry, I don't have sizing information for any of these to give you.

25,000 cfm (let's assume standard conditions) at 800 ppm is almost 2600 lb per day of H2S. That's a lot of H2S, I don't think I'd look at a process like iron sponge or any other 'single use' solution.

Is this 25,000 scfm or is this actual cfm? What are the process temperature and pressure? How low do you need to remove the H2S to?

 

[jproj]

I've seen activated carbon used to scrub H2S from air (more specifically sewer gas). I can't give you any details, though and I doubt it was 25,000 cfm. Depending on the conditions, biological H2S removal might also be an option.

jproj

 

[butelja]

NaOH can be used in a packed tower to scrub the H2S. If your plant is near a paper mill, they use lots of NaHS, and may be able to purchase your scrubber effluent.

 

[barilko]

Be wary of activated carbon scrubbers.... industry experience has shown that the heat of reaction in the carbon scrubber with H2S can reach the ignition point. You need to take the heat away to maintain thermal equilibrium. A continuous flow may achieve this.
If the flow stops, the H2S will form sulphur on the bed and will accelerate the need for replacement or regeneration.

This can be especially dangerous if it comes in contact with an explosive atmosphere.

 

[tblaser]

Refineries deal with large amounts of H2S gas. They traditionally absorb the H2S with Amine solutions, regenerate the solution to remove the H2S gas, which then is sent to a sulfur plant for conversion to elemental sulfur. It is not cheap but the technology is proven.

 

[DeltaCascade]

Try the GPSA Engineering Data Book

http://gpsa.gasprocessors.com/databook.html

 

[KernOily]

The H2S removal technology selected is based on rate, concentration, and operational considerations. In this area, we use the SulFerox process to scrub about 2500 lb/hr H2S from an inlet gas stream of about 2.5 MMscfd and 10,000 - 15,000 ppmv [H2S]. SulFerox is a licensed Dow-Shell process currently handled by Westfield Engineering. Do a Google search. It converts H2S to solid elemental sulfur using an iron redox reaction via a regenerable iron chelant solution and is a continuous process. The solid sulfur is sold as a soil amendment. A SulFerox competitor is the LoCAT process, another proprietary licensed process.

Others use the Sulfa-Treat process for this same stream. Sulfa-Treat is a solid adsorbent that looks a lot like black kitty litter. It is a once-through product and is non-hazardous when spent.

There are once-through liquid processes like Sulfa-Scrub, Sulfa-Rid, etc. that are atomized into the line containing the gas. They work well but you have to dispose of the spent solution.

The caustic scrubbers work well too but I think your rate is too small for those. I'd have to check further.

The processes like Claus, amine, Stretford, etc. are for much larger rates and concentrations than you have. I think if I was in your shoes I would first look at the Sulfa-Treat process. Low capital cost, good removal efficiency, no nasty hazwaste issues. The Sulfa-Treat people are very helpful and will give you a ton of free selection and sizing information if you call them.

The John M. Campbell Co. has a really good course on Gas Treating and Sulfur Recovery where they address this very issue. Thanks!
Pete
pjchandl@prou.com

 

We (Westfield Engineering & Services) are the licensor's of SulFerox Technology. This process, is a very cost-effective solution to removing H2S from a gas stream (even if the stream contains oxygen or carbon dioxide) down to ultra-low levels (less that 0.5 ppm), and in the sulfur production range from 0.2 to 10.0 LTPD. Above this level, other technologies become more cost-effective. Below this level, more than likely, iron sponge is more cost effective (although we are developing a Low-Production SulFerox design, which we would expect to be more cost-effective in ultra-low sulfur production designs).

j.dickinson@westfieldengineering.com

http://www.westfieldengineering.com.

John Perry Dickinson - Manager of SulFerox Technology.

 

[yorkjim]

This is a large amount of H2S.

Another option is biological treatment - Thiobacillius is a reduced sufur scavanger.

We have experience in designing up to 200 ppm, a possible solution here could be a bioscrubber stage to reduce concentration, followed by traditional chemical scrubbing (caustic/hypochlorite - caustic only will only solubolize the H2S).

Also note - we will recommend a design of a traditional wet scrubber that will be the smallest possible without sacrifice in efficiency in industry today.

http://www.lantecp.com

eldridge@lantecp.com

 

[STEK]

Any one-use absorbent will be prohibitively expensive for your sulfur rate. Several processes are available for scrubbing out the H2S and converting it to elemental sulfur, typically of low value. Your application is a good fit for a process offered by ThioSolv for converting the sulfur to ATS. I heard about it from Mike at mfray1@msn.com

 

[KernOily]

"Any one-use absorbent will be prohibitively expensive for your sulfur rate."

I guess my experience has been different. Having done a number of these projects, I've found that only a rigorous total life-cycle cost economics analysis will reveal which process represents the best investment. It's really hard to say a priori which process is the 'best' without having first done the homework. Sometimes these projects are not economic at all, i.e. they generate no positive cash flows per se. Usually the chelate/redox processes, which are usually the process of choice for small rates, are only economic beyond a certain rate due to the capital cost.

For "small" rates and "small" H2S concentrations I've found that usually the batch processes are more economic than the continuous processes. The best advice I can give is to talk to a number of process owners to get the straight skinny on operating cost and capital cost before you start your economics. This is because the vendors/process licensors/engineering contractors (that's me) don't usually have all the facts in regard to the life cycle cost. They can usually give you pretty good data on installed cost, and they can usually provide ballpark numbers for things like $ chemical used per lb S removed, but the real op cost is totally another issue. A good basic reference here is "Gas Treating and Sulfur Removal" published by Campbell, as I mentioned earlier.

You can always do a pilot test. The SulfaTreat, SulfaChek etc. batch guys will set you up on a pilot for free. That would give you a snapshot of usage and op cost. I do not know if the bioprocesses or the iron chelate processes will do a pilot; you'd have to contact them. Good luck! Thanks!
Pete

 

[dfman]

Hi there

For high airflow volume & high level H2S removal (>100 ppm H2S) your main options will be either chemical or biological treatment.

At this specification activated carbon is going to be very expensive to buy & dispose of waste material every 12 months

If you have chemicals available you can assess:
1) Caustic Scrubber, with waste being disposed to aerated area to complete oxidation of H2S
2) Traditional Packed Bed - Caustic Hypochlorite system
3) Catalytic Scrubbing - Hypo/Caustic with catalyst (Synetix)

These solutions are very established & as the proven option.

The other option of H2S scrubbing, the "new kids on the block", are biological technologies, such as BioTrickling Filters and BioFilters.

At this level of H2S you would need to pretreat the air prior to a BioFilter to less than 30 ppm H2S for cost-effective capital, operating & space considerations, using either a Caustic Scrubber or BioTrickling Filter.

The BioTrickling Filter can be designed to treat H2S down to less than 1ppm H2S. This would be cheaper than chemical scrubbing in both capital & operating costs atributable to nutrient addition.

If you have secondary effluent available you can reduce this operating cost further.

BioFilters or Activated Carbon could then be used to "polish" the emission for odour if needed at high loading rates.

Contact Clean TeQ in Melbourne, Australia for further details.

Hope this helps.

ctairman
info@cleanteq.com