Economic Options for H2S Removal - Biogas Plant

[mechjason]

I'm looking into options for scrubbing H2S from biogas and trying to determine which is the most economically sound (both capex and opex). The gas may have concentrations up to 5,000ppm H2S and a large volume (up to 150,000m3/week). Need to scrub it down to around 600ppm. What would be the best technology for this?

 

[georgeverghese]

Typical information you'll need to have:
a) Peak hourly rate?
b) Min / max operating pressure / temp at the absorber ?
c) Any other sulphur bearing contaminants - COS, CS2?
d) Since this is biogas, almost all of this would be methane and saturation water vapor, and no CO2?

Given you dont need high removal eff, possible options would be, at either end of the spectrum :a physical sorbent like Selexol (Dow / UOP); chemical sorbent - the more popular activated MDEA / piperazine blends - many licensors for this.

The physical sorbent schemes are simpler and more stable (flash regen might do), and may save you on CAPEX for materials of construction also, while the chemical sorbents may enable lower sorbent circ rates, but you may need better materials of construction if you want to minimise corrosion related operating issues later.

 

[EmmanuelTop]

The process would be removing ~500 kg of Sulfur per week so you are definitely looking at regenerative processes such as those mentioned by George. Scavengers and non-regenerative adsorbers are probably not economical for these conditions.

Great disadvantage of physical solvents is their affinity towards Hydrocarbons and the need for higher operating pressures, which leaves you with chemical (Amine) solvents: MDEA, DEA, etc. I see you are based in Australia so perhaps you can shoot an inquiry directly to Huntsman Co. or to Worley Parsons so you can obtain the EPC quotation/proposal.

http://www.huntsman.com/performance...B7B06/files/GasProcessingBrochureEN201312.pdf

http://www.worleyparsons.com/Contact/Pages/OfficeListings.aspx

Dejan IVANOVIC
Process Engineer, MSChE

 

[MortenA]

You might want to take a look at the LO-CAT process suited for low/ambient pressure gas:

http://www.merichem.com/gas/upstream/natural-gas/lo-cat

 

[MortenA]

BTW i have seen a unit once and its quite low tech and should fit right in with bio-gas (i saw a unit in a paper recycle plant that had H2S problems). The finished waste product is elemental sulphur that may be a little more difficult to handle than e.g. gypsum.

 

[EmmanuelTop]

See also the links below - some of them contain discussion on alternative processes:

http://www.eco-tec.com///pdf/brochures/gPur Brochure0411.pdf

http://cdn.intechopen.com/pdfs/2286...s_and_co2_from_biogas_by_amine_absorption.pdf

http://www.eco-tec.com///pdf/TP - 186 Biogas Purification - PowerGen 2007.pdf

Dejan IVANOVIC
Process Engineer, MSChE

 

[mechjason]

thanks guys; I'll talk to some suppliers and see what they say in regards to costings

 

[georgeverghese]

There are some other physical sorbents that may be of interest, since this biogas would be low on C2plus, and low hydrocarbon dewpoint:
N-methyl pyrrolidone - Lurgi license
Morphiline based derivative - Uhde license

Obviously, you'll need a game plan for what you'll do with this H2S stream from the regen unit flash drum and / or stripper - that may have some bearing on a favourable process scheme.

 

[georgeverghese]

Another simple scheme for this lower removal efficiency for H2S would be scrubbing with plain water - Henry's Law absorption values for H2S in water are tabled in Perry Chem Engg Hansdbook, chapter 2 on physical props

 

[MortenA]

Nah to much H2S - would require hge amounts of water that would get contamited with a lot of other "shit" - and the regen would have to be stripping by air i assume? That would then mean that you would emit all that H2S. It might be allowed since its biogas (it would have gone that way anayway - but you cant be sure.

I think that the OP should consider that a lot of the H2S solutions are geared towards much higher throughputs at much higher pressure (and generally better economy) than what is the case for biogas in general. 150,000 m3/week biogas may be a lot for biogas, but its a tiny gas field. I would still look at the LO-CAT solution