Fw: DIG-L: energy conversion

["renertech" <renertech@xtra.co.nz>]

Oops!   Forgot to add the attachment.  So Sorry.  I also added in a few more comments to the message below.  Ken C.

----- Original Message -----

From: renertech

To: digestion@crest.org

Sent: Monday, April 08, 2002 10:48 PM

Subject: Re: DIG-L: energy conversion

Dear Michael, I had replied to a couple of other requests off line, but it looks as if the New Zealand Farmer biogas system is interesting to many more, so I am replying to you on the network.  Because the first guy as from the US of A, I did the figures in Imperial rather than metric.  If you can't decipher them then I guess I could do a rerun??    Because of the low prices for petroleum fuels over the last 15 years, there are not too many plants still working, but those that are will be watching the present OPEC price hikes with great interest.  Most of these farmers take the intermediate pressure methane of stripped biogas and  use a long stroke hydraulic cylinder to compress it up to 3000psi in one compression stroke.  Then they have the usual  CNG conversion kit on their motor vehicles and run around on their own homemade CNG.  I might also say that  using the UASB technique, you don't need to use up half of your gas to heat the system to mesophyllic temperatures.  Biogas can be made at temperatures as low as 10-15oC   If you look at the publications page on my website,  you will see a report there on making biogas from coffee wastes which gives most of the details.  

Sincerely,

Ken Calvert.
Renertech.
159 St.Andrew St.
Invercargill.
New Zealand. 9501
Phone. +64 3217 7015
Fax.      +64 3217 7032
E-Mail   renertech@xtra.co.nz
Webs   www.coffee.20m.com
----- Original Message -----

From: Michael Köttner

To: renertech

Sent: Monday, April 08, 2002 8:17 PM

Subject: Re: DIG-L: energy conversion

Dear Ken,

 

I would be more interested in your system of gas stripping, especially to take out the CO2 under low pressure. How is it done and is it still done in New Zealand as in Germany we are looking always at very complicated devices when it comes to CO2 stripping ? Could you send some more information, bacause farmers here are interested in low tech approaches.

 

---

• To: "sigma" <sigma@ix.netcom.com>
• Subject: Re: biogas stripping etc.
• From: "renertech" <renertech@xtra.co.nz>
• Date: Mon, 8 Apr 2002 22:32:38 +1200
• References: <001701c1de91$03d501c0$0ed0f7a5@ix.netcom.com>

Len Hi there,
                       The New Zealand farmers biogas program was originally
worked out back in the 70s, by the Invermay Ag Research Station at Mosgiel,
close to where I live.
The biogas comes off the digester by its own pressure and comes through the
Sulphide stripper, which I shall describe in a moment, and is collected in a
gas bag which has a air pressure switch gotten from an automatic washing
machine, which clicks in at about 12" water guage and out at about 2-3".
When the gas bag is full the switch clicks in and starts a  simple air
compressor which only needs to pump the gas up to   around  50-60psi.
although the compressor can go much more than that.  The compressed gas is
then bubbled into the base of a vertical standing length of  6-10" pipe
about 4-6metres high and 2/3 full of water. The pipe can be anything though
PVC looks nice and clean.  If you are lucky enough to have a high mains
pressure for your supply, you just feed that in through a partially opened
tap.  The water level is controlled  by an exit float valve  which bleeds
off the highly gas charged water when the level gets beyond 2/3 to 3/4 way
up the pipe.  That water, when the pressure is released, will fiz just like
soda water.  The gas then comes off the top of the vertical pipe through a
pressure release valve which controls the whole operation, and goes into a
pressure cylinder for storage at what we call intermediate pressure. If your
water supply is at low pressure, then  you will have to use an old piston
water pump or any type of positive displacement pump which can work at its
limit, say 150psi. It should be switched off and on along with the gas
compressor.  This means that the gas compressor can also work up to that
figure, and the whole system shifts up a cog in terms of its efficiency and
the gas comes out the stripping column for storage at that much higher a
pressure and correspondingly less volume.  We liked to get hold of old 500
litre LPG  cylinders from hotels and the like. One farmer I knew got hold of
 an old railway locomotive boiler and used that.  He actually had two. One
alongside the biogas plant and another alongside his grain drier which was
about half a mile away.  They were connected together by 3/4" pvc water
pipe, which gave adequate gas transfer when the grain drier was working.
Just make sure that you have a water drain tap on the bottom of your storage
cylinder because everything gets warm and the gas will drop a lot of
moisture as it cools.
  Now to come back to the sulphide stripper.  Probably the best thing to use
is a pair of old  200litre/44gallon drums.  They will corrode fairly quickly
and have to be replaced, but that is cheaper than the hasstle of keeping
plastic drums from melting in the heat.
Fill the drums with steel turnings or bashed up rusty tin cans or anything
that is iron or steel.  The easiest way to do that is to  chop out the  3/4
bung in the top and weld in a  4" or larger pipe fitting.   The 2" bung on
the other side should have a length of the largest size of steel pipe that
you can fit inside a 2" pipe nipple, and that goes nearly to the bottom of
the drum and that is the gas inlet from the gas bag.  The new and larger
bung should be the gas outlet  from the top of the drum with a 2" reduction
to plastic pipe, with which  everything is connected. The wet biogas will
flow slowly through the drum and the metalic iron and the rust will react
with the Hydrogen sulphide to make ferrous sulphide.  You should have two of
these drums made up and rotate them at suitable intervals to make sure that
no H2S gas is getting through the system, or your intermediate gas
compressor will not last for very long.
To regenerate the sulphide stripper all you have to do is to unscrew the 4"
bung on the used drum and let the air into the drum, as slowly as possible.
The best way is to let the air just diffuse into the drum through the open
bung over several days.  The air will react with the iron sulphide to
produce flowers of sulphur, metallic iron again, and lots of heat.   Enough
heat to melt a plastic drum and to also create a rising current of air
through the drum to speed up the reaction should it get away on you.   When
you swop the drums, the process will cycle  again until the drum is half
full of  elemental sulphur and is so corroded from the inside out, that its
time to replace the drum.
At this point I think its time to stop and you can ask some more questions
to direct the thinking to what you haven't  caught up with.   Cheers!   Ken
C.









    .


----- Original Message -----
From: "sigma" <sigma@ix.netcom.com>
To: "renertech" <renertech@xtra.co.nz>
Sent: Monday, April 08, 2002 12:04 PM
Subject: biogas stripping etc.


> Hello Ken:
>
> You said: "Gas stripping is not difficult.  You can do it with a column of
> water under low pressure, and you can take out the sulphide with a drum of
> crushed rusty tin cans.   Come back to me if you want more details."
>
> Could you explain in more detail how to do these two things.  Also, some
> time in the past, I read that New Zealand dairy farmers (with digesters, I
> assume) separate the CO2 out by compressing the biogas, in some manner.
Can
> you shed some light on this too?
>
> Many thanks for you help.
>
> Best wishes,
>
> Len
>
>
>
>
>

---

Digestion List Archives:
http://www.crest.org/discussion/digestion/200202/

Digestion List Moderator:
Paul Harris, paul.harris@adelaide.edu.au
http://www.roseworthy.adelaide.edu.au/~pharris
List-Post: <mailto:digestion@crest.org>
List-Help: <mailto:digestion-help@crest.org>
List-Unsubscribe: <mailto:digestion-unsubscribe@crest.org>
List-Subscribe: <mailto:digestion-subscribe@crest.org>

Other Digestion Events and Information:
http://www.bioenergy2002.org
http://crest.org/discussiongroups/resources/biomass/biogas/BIOGASMK.pdf
http://www.crest.org/articles/static/1/1010424940_7.html

Beginners Tour of Biogas
http://WWW.roseworthy.adelaide.edu.au/~pharris/biogas/beginners