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Small scale sulfur removal

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Jobst

Chemical
Mar 5, 2008
32
I have a gas stream as follows:

CO: 22%
H2: 19%
CO2: 56%
N2: 3%
H2S: 500 ppm

The stream is water saturated, 37 C, 4 barg. Flow is approx 380 Nm3/hr.

I want to reduce the sulfur to below 10 ppm. Recovery of the sulfur is not required.

I've spoken to one vendor of iron oxide based adsorbant, and apparently the performence of this technology in a reducing environment is unknown. I assume this can be extended to the more traditional iron sponge tech as well.

From what I understand ZnO based tech requires higher temperatures.

Does anone have any insight as to who to get in touch with next? The big players tend to laugh off this kind of scale...
 
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Yes I can understand. 380 Nm3/hr is soooo small!

Consider as first option the use of strong oxidants
H2O2, permanganate, Sodium hypochlorite; I like H2O2.
sodium carbonate has been considered, avoid caustic soda (scaling issues, and carbonation)
iron based systems work well, but for this kind of scale are not appropriate.
Beware of thiols R-SH are they present? They are more difficult to scrub and contribute a lot to odors.

for the design, the regular chemical engineering approach, with NUT's HTU's and esuilibrium data will do.
My guess (no guarantee, I did NOT perform the calculations )is that some 2.5-3 m of a good packing would do.
A batch where you control the redox in the sump is probably a good option for your flowrates.
 
What kind of reformer is this syngas coming from? Usually you do the ZnO adsorption while the stream is still hot.

Don't forget that when you oxidize H2S under acid aqueous conditions (i.e. with H2O2 or the like) you get SOLID sulphur and sulphate. Alkaline conditions (where you get sulphate only) are out due to the CO2 in your stream. 500 ppm isn't much, but do a mass balance and see how much sulphur your packing will have to deal with and have a means to mitigate that before you go with the packed scrubber.

ZnO does require high temperatures. If the stream is alerady cool, what you're talking about in this case is a cross exchanger, an electric heater for trimming and start-up, and a fairly small bed of ZnO material. Its H2S affinity is huge so it doesn't take much.
 
Thanks for responses.

I was indeed worried about all the CO2 -- maintaining alkalinity in a solution in contact with that stream seems like a no-go. Solid formation in a packed tower is definitely not the design intent!

The stream isn't actually syngas (rather, it hasn't originated in a place gases of that composition usually do...).

There is another place in the process with some heat I could steal, so I'll send out some inquiries to the ZnO people. At this scale I definitely favour a semi-batch type scavenger so it seems to fit the bill.

Still welcome any more suggestions if there's something that has been overlooked!
 
The flow is indeed small and the H2S content is low.
I should suggest to use activated carbon.
Use a capacity of 400 kg H2S/m3 activated carbon.

Dirk
 
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