[permaculture] Bio digester percieved dangers

Lawrence F. London, Jr. venaurafarm at bellsouth.net
Fri May 27 21:16:15 EDT 2011

On 5/25/2011 3:42 PM, DGilsen at aol.com wrote:
> Hi there guys I have used a biogas digester off and on for years.   They
> use them on poor farms built by undereducated farmers in India and they  make
> there biogas plants out of brick.  I had kids and so I dug a pit and  placed
> the tank I used in there.  Even with five kids and a neighbor  hood full of
> vandals I never had a problem.  Bio gas is very forgiving, but  even when
> the kids fooled with my system I never had any problems.  Those  kids heard
> form my kids that I was cooking and heating my water with farts. They  opened
> valves and fooled with every valve they could they ripped off the  hoses
> and pipes to smell the "farts"!  and no explosions!They drained my  gas tank
> several times to the air.  Finally I called all the kids and  parents in the
> neighbor hood and we had a "class" on the biogas system I had and  finally
> the little turkeys quit screwing around with my biogas tanks I also  fenced
> it off to limit access.
> Bio gas  is explosive but not as bad as I have heard it was, and if  any
> system should have exploded mine should have ,but it didn't  Don't  worry
> about it.  Place the storage tank in a pit and fence it off, with  chain link.
> If it does explode the explosion is directed upward .
> Carol

To back you up, Carol, here is feedback from David House; take note of 
the last paragraph about not installing the tank in the ground (unless 
it is really well insulated with spray-on hard-setting waterproof foam 
insulation - then again animals and insects may degrade it - my 
suggestion). - LL

-------- Original Message --------
Subject: Re: [permaculture] Bio digester percieved dangers
Date: 	Thu, 26 May 2011 18:27:25 -0700
From: 	David <david at h4c.org>

I have been surprised in the workshops that I have given to learn that
many folks don't realize that biogas/methane *cannot* explode /unless/
it is mixed with air. Calling biogas/methane "explosive" is likely the
source of confusion.

Plan old water, after all, is *explosive*, if it is heated up enough--
plenty of boilers have exploded, after all-- and it is in fact water
that caused the explosion at the Japanese nuclear reactor. (What
happened there, however, was only partially a steam explosion. It was
primarily caused by the fact that at very high temperatures, water
disassociates into hydrogen and oxygen, and /that/ mixture explodes.)

So my point, again, is that biogas *cannot* explode, *will not* explode, 
and will not even /burn/ (!), unless it is mixed with air/oxygen. If 
folks would keep a positive pressure in their biogas systems, then such 
explosive mixtures very rarely occur, and then only in the air 
surrounding the digester, not in the digester itself.

As a final point, I would not suggest putting a biogas tank in the
ground, if you have a tank. It just steals heat from it, in temperate

David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

"Make no search for water. But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)


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