[Digestion] Measuring the gases produced

[David Fulford]

Frank, Hi

I tried Paul Harris's very simple idea recently. Fill a disposable plastic 
syringe with gas, up to about 80% i.e. a 50 ml syringe should be filled to 
40 ml. Then draw in a solution of a hydroxide so the plunger comes to the 
maximum reading (50 ml means drawing in 10 ml of solution). Sodium 
hydroxide is probably the best, but lime water, calcium hydroxide, will do. 
Close the end of the syringe. There are rubber caps that are available for 
this. Using a finger tip means that you get corrosive hydroxide on it. 
Shake the syringe, so the carbon dioxide dissolves in the solution and the 
syringe plunger is pulled in. You can press gently on the plunger to 
overcome friction, but not so hard as to push the solution out. The new 
volume reading is the volume of biogas less that of carbon dioxide 
(probably mainly methane).

The group in India to whom I showed this idea were very pleased. They now 
have a low tech method of measuring methane content of the gas.

I normally use a methane analyser that I bought second hand when British 
Gas were replacing their old ones. It has a thermal conductivity cell. 
Methane will transfer heat more easily than air or carbon dioxide. It was 
calibrated on methane/air mixes, but it should be OK for methane/carbon 
dioxide mixes, if not completely accurate.

Cheers,

David

At 12:15 24/09/2007 -0700, frank wrote:

>Hi Methane producers,
>
>Are there standard procedures for measuring the gas make up coming from
>the digester? I am thinking the most will be CH4 and CO2 with some
>ammonia and nitrogen.  I am thinking the CO2 can be scrubbed out using
>NaOH and titrated or determined by the gas reduction. Perhaps the CH4
>can be by difference? or measured using a SnO2 cell?
>
>We have set up a pilot plant for experimenting with different feedstock
>and are ready for testing the trapped gas.
>
>Any suggestions is appreciated.
>Thanks
>Frank
>
>--
>Frank Shields
>Soil Control Lab
>42 Hangar way
>Watsonville, CA  95076
>(831) 724-5422 tel
>(831) 724-3188 fax
>frank at compostlab.com
>www.compostlab.com
>
>
>
>
>_______________________________________________
>Digestion mailing list
>Digestion at listserv.repp.org
>http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org
>Beginner's Guide to Biogas
>http://www.adelaide.edu.au/biogas/
>http://info.bioenergylists.org

*** Dr David Fulford, MSc Renewable Energy, Engineering Building ***
***     School of Construction Management and Engineering        ***
***      The University of Reading, Whiteknights,                ***
***    Reading RG6 6AY, UK      Tel: +44-(0)118-378 8563,        ***
***                 Mob: 07746 806401                            ***
*** Fax: +44-(0)118-931 3327 E-mail: D.J.Fulford at Reading.ac.uk   ***