permaculture

[dwoodard@becon.org]

Natural gas as it comes from the well contains basically methane (CH4)
mixed with propane, butane and other gases (ethane?) and sometimes
hydrogen sulphide, plus some carbon dioxide. Depending partly on relative
prices
the other gases may be removed before the natural gas is distributed for
sale.

I understand that biogas contains a large amount of CO2. That's why its
BTU value is less than that of methane.

Natural gas is usually stored under pressure in old wells or salt caverns.
Liquifying it takes more energy and more costly equipment. On a farm scale
it might be cheaper and more efficient to store the manure.

Lora, I think you may have misread your bill. 200 cubic feet of natural
gas would have a producer price arounf US$1, at retail maybe 2 or 3
dollars.
I expect you would need a good deal more manure than you calculated.
Natural gas price are usually quoted per million BTU content, or per
thousand cubic feet.

Doug Woodard
St. Catharines, Ontario, Canada


> "Lawrence F. London, Jr." wrote:
>
> Can't methane from digesters be compressed and liquified?
>
> Lora wrote:
>
> I'm no expert but I thought I'd throw my two cents in on this one. I read
> alot about biogas digesters awhile back and kept simplifying
> what I was finding until I reached these conclusions. I may not have
> carried my decimals correctly so correct me if I'm wrong but to
> the best of my understanding biogas (methane was what I was looking at the
> numbers for) of 1 therm amount = 2 cubic feet (because it
> burns half as hot as natural gas) and it was my understanding that 1 lb of
> manure would get you 1 cubic foot or 1/2 therm. I looked at
> my natural gas bills for the last couple years and I use 200 cubic
> feet/200 therms per year on average (for hot water heater,
> cookstove and furnace - about 70% is the furnace.) and thus I would need
> 400 lbs of manure per year. That's not much over 1 lb per
> day. I believe a certain amount of any other carbon matter could also be
> added (shredded newspaper, junk mail, food and yard waste,
> etc. And that I could divert the urine to go direct to mixing with
> greywater for watering plants and it would not affect the biogas
> production significantly). If you could rig up your non-flush or low flush
> toilet to go into the digester even a one or two person
> household might be enough. If one had a cow or pig or chickens then yahoo.
> I don't have very good insulation in my home but I live in
> Arizona so it doesn't get too cold and only 6 months a year - so your
> mileage may vary...
>
> Natural gas is twice as high in btu's as un-monkey-ed with methane.

[snip]

It can be compressed and
> liquified, etc. but you needn't bother unless you are a big farm and
> are selling it and using vast quantities of animal manure or crop waste or
> you want to make alot all at once and store it in a smaller
> tank I suppose.

[snip]