Question about chemical composition of biogas

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marc91
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Question about chemical composition of biogas




by marc91 » 16/02/13, 07:58

Hello
I read a lot about biogas
relatively easy to produce, it seems that this one
contain a lot of CO2, hydrogen sulfide
and a lot of humidity.
I also found in a document that by filtering it through a metal sieve (iron wool) and wood shavings we managed to remove the hydrogen sulfide, what is it?
for humidity is there a way to dry the gas?
and what to do for CO2

please :D
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by Christophe » 16/02/13, 10:19

This purification is called "linearization of biogas" in order to best approach the properties of natural gas.

The CO2 diffuses in the water, a bubbling makes it possible to remove a large part of it.
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by chatelot16 » 16/02/13, 13:36

CO2 dissolves in water, but the amount of absorbed CO2 is limited, so you have to replace the water

problem dissolved water also methane ... so this water system makes a significant loss of methane ... fortunately CO2 is more soluble than methane but dissolution in simple water loses too much methane

solution, find a product that absorbs much more CO2 than methane: water and limestone

passing the methane through a column filled with limestone gravel and watered with water ... this water will dissolve the CO2 become acidic and eat the limestone, which allows it to absorb even more CO2

the water which leaves the bottom of the column is very rich in limestone and C02: it suffices to run it off into the open air so that it loses its CO2 and limestone, like a petrifying fountain, and can be reused closed circuit

thanks to limestone we can remove all the CO2 with a lower water flow rate, therefore lose less methane, than with pure water

another remark bubbling a gas in a liquid is not practical: it causes a loss of pressure which must be compensated by a pump ... passing the gas through a column of gravel sprayed with water lets the gas pass without loss pressure
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by marc91 » 17/02/13, 09:57

chatelot16 wrote:CO2 dissolves in water, but the amount of absorbed CO2 is limited, so you have to replace the water
..............

thanks to limestone we can remove all the CO2 with a lower water flow rate, therefore lose less methane, than with pure water

another remark bubbling a gas in a liquid is not practical: it causes a loss of pressure which must be compensated by a pump ... passing the gas through a column of gravel sprayed with water lets the gas pass without loss pressure


in a text on the installation made by Jean Pain, the author says that this one "filtered" the gas through pebbles ...

the biogas being VERY wet, this one would it not be enough to dissolve the limestone?, or to envisage a drip irrigation?
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by bidouille23 » 18/02/13, 20:44

End

a molecular sieve to dry the gas does it perhaps?

http://fr.wikipedia.org/wiki/Tamis_mol%C3%A9culaire
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by chatelot16 » 18/02/13, 23:04

yes the molecular sieve is the modern solution in the laboratory ... but is it a profitable solution for biogas?

I am wary of too expensive modern solutions to be profitable

I like the good old calcium chloride: rubson granules or other brands

the calcium chloride absorbs a lot of water, becomes a liquid still very greedy for water ... it is necessary to preserve this dilute solution of calcium chloride to dry it with the heat of a hearth, or of the sun to reuse it

similarly for the absorption of CO2, limestone is an old method, there are other more modern but more expensive solutions
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by bidouille23 » 19/02/13, 00:08

I don't know I say that it is to help if possible by giving a solution after knowing if it is the best or not ....

As for the molecular sieve just ask here for example they make calcium chloride and molecular sieve ...

it must have turned into 40 euros / Kg the sieve seen that in 2008 it was around 20 I think ... good not with them but we must not be far from this approximation .. for the chloride it is how much ?

And small detail the molecular sieve also dries and is reused ... same ...

Asked the manufacturer is therefore perhaps the solution to find out which of the screen or chloride is the best solution;) ...

I can not say anything more on the subject, I become reader again after having made my small contribution ... :) ;)
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by chatelot16 » 19/02/13, 01:00

calcium chloride is 1 or 2 euro per kg ... so cheap that often we throw away the diluted solution without trying to recycle it

in addition 1 kg of calcium chloride absorbs several kg of water since the concentrated solution continues to be hungry for water until it is strongly diluted

calcium chloride is a waste from some chemical industry ... its value is almost zero and costs only the price of packaging and transport

the problem with calcium chloride is that you need a large enough absorber so that the gas speed is very low, and the gas does not cause this slightly corrosive product

the molecular sieve is better suited to high throughput

beware of current sources of information that always forget the old ways often more profitable in small dimensions
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by bidouille23 » 19/02/13, 13:06

It is not false ...
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