[Gasification] Compression question: lime water

[Zietsman, Rex]

Jim wrote:
"the other thing i have read for this is filtering through lime water. i
understand this is a common tactic in indian digester units.  A relevant
link on this is: http://www.green-trust.org/2000/biofuel/methane.htm of
course you can have an activated charcoal bed to scrub the co2 too."

Jim,
Lime works well as it forms calcium carbonate with the CO2 and picks up
acid gases at the same time - H2S is a case in point. The difficulty is
that you end up with a solid end product that has to be regenerated.
This can be done by heating up the calcium carbonate to above 900degC,
950 being a good number, to allow it to thermally decompose back to lime
(CaO) and CO2. The lime you add to water where it hydrates to Ca(OH)2.
The hydrated lime is then a good common alkali which will capture CO2
again. In the case of H2S, it will absorb to form a sulphite which, in
an oxidising environment will become sulphate otherwise known as gypsum.
Gypsum cannot realistically be regenerated (the economics are against
you as you need a reductant, controlled heating, etc) but is a very good
soil conditioner - the calcium is taken up by plants while sulphate is a
very good migratory or salts that tend to accumulate in tilled soil.

Have fun!
Rex