Newhouse Farm

Chrisf · Posted: Fri Jul 10, 2009 2:15 pm Post subject: Biogas production

I had a brain wave this morning (I can hear the wife groaning already). I have been mulling over the idea of making biogas and looking into the kit involved. I have read the chinese biogas manual which is very useful, the basic idea being sinking a large lined pit in the ground, putting a cap on it and filling it with organic waste to bubble away. My eureka moment came when it occured to me that as I live in the country, I have a sceptic tank. This lead me to think 'well its a big pit in the ground into which organic waste goes'. Hope you're all still with me, I have a tendency to ramble. So all I need to do is seal it and continue the process to produce methane, which I can collect and use for fuel. The contents of the tank thus being removed to be used as a fertiliser.

Ok so that's the plan, does anyone wish to comment, advise, or otherwise poke fun!!??

retrotecchie · Posted: Fri Jul 10, 2009 4:47 pm Post subject:

You will produce some methane, but as it's a septic tank and I assume you flush the loo with water, I'm afraid your contents will be far too diluted to produce useable amounts of biogas
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Mike&Penny · Posted: Fri Jul 10, 2009 5:15 pm Post subject: also

Also -- the major design issues are around the collector, not the digestor itself. A collector is not too difficult to cobble up in a climate where it doesn't freeze hard. But the only "simple" designs are the counterweighted floating "bell jar" type. If you ever took chem class and in lab collected a gas in an ionverted jar originally filled with water you'll have the general idea -- though in this case the "jar" starts out with its top at the surface of the pool of water and gradually rises as it fills with gas.

The design problem to be solved is holding a largish volume of gas at a constant rather low pressure.
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DMc · Posted: Fri Aug 21, 2009 11:44 am Post subject: Re: Biogas production

Mike&Penny · Posted: Fri Aug 21, 2009 2:46 pm Post subject: alternative collector

An alternative to the "floating" type of collector and what I would have to try to use (it freezes hard here) is the "bladder" type. Picture a giant plastic (or rubber?) bag sandwiched between a deck and flat top that can rise up and down counterweighted so that the pressure will be as desired. Usually a retining wall around so that the bag can't spread sideways. For example, if that top had an areas of 100,000 sq cm and the net weight was 10,000 Nt then the gas in the bag would be at a pressure of 10 Nt/sq cm whenever that tp was between resting on the deck (bag empty) or so high that all give in the bag eliminated so that the bag skin itself was acting as a ballon. The hard part here is arranging that the "top" and the deck remain parallel.

The point is that any practical home biogas unit still needs a collector with a capacity of several cubic meters. The gas is being generated over 24 hours but used in bursts for cooking, etc.

PS -- I used to have plans for te various sorts, but alas, that was pre fire and I can't remember the sources. Going back to the 60's used to be a bunch of "homesteading" and/or "far off the grid" publications that had stuff like tis.
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b.steadman · Posted: Fri Aug 21, 2009 3:03 pm Post subject:

Have you seen these?

Jean Pain You Tube Part 1
Jean Pain You Tube Part 2
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DMc · Posted: Fri Aug 21, 2009 3:12 pm Post subject:

b.steadman · Posted: Fri Aug 21, 2009 3:16 pm Post subject:

I was thinking about you possibly using the tyre inner tubes as a storage facility as per the films. Its what I imagined when Mike was talking about the collector.
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DMc · Posted: Fri Aug 21, 2009 4:24 pm Post subject:

We don't know much about the gas side of things as yet, and that isn't our main focus. We are primarily interested in producing heat from compost. The gas is, for us, a bonus by-product and we are not really sure what to do with it or even whether to collect it at all.

aurangzeb · Hazel Seedling Joined: 18 May 2009 Posts: 22

Production of bio gas using natural waste is OK in principle.

However in order to get useful amounts of gas a household would normally need 2-5 human waste PLUS two animal waste (cows/ buffalo dung). Additionally you need green (grass cuttings shed leaves) and brown (twigs) waste, PER DAY. All this can generate biogas for cooking for 2-3 persons. For heating you will require much much larger quantities of the above.

Here is a link
http://www.panda.org/wwf_news/features/?95320/Biogas-saving-nature-naturally-in-Nepal

Aurangzeb

DMc · Posted: Thu Aug 27, 2009 3:58 am Post subject:

You may well be right - I wouldn't know - but I think you are talking about a different approach, Your comments suggest a continual composting of waste.I am basing my approach on the videos that b.steadman linked to. These don't use any human or animal waste, just chipped up brush wood, and use a batch approach rather than a continual process of feeding in new material. If that works here in Finland it is very interesting because we have a lot of forests so it should be possible to source large quantities of suitable material. The gas output is a secondary interest at the moment though; we are more concerned with heat output obtained by running loops of pipe through the compost heap.
You do address a key question though: how much output is there per input. On the gas side of things I don't have a clue. On the heat side I have done some calculations but need to try it in practise to check these.

cadfael · Posted: Thu Aug 27, 2009 10:30 am Post subject:

Another link for you! http://www.adelaide.edu.au/biogas/resources/skproj.pdf
Depending on how much gas you get, JPs idea of using old tyre inner tubes is good as you can connect them easily
Mike.
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Mike&Penny · Posted: Thu Aug 27, 2009 12:40 pm Post subject: I would think

I would think that if you were pumping the gas into inner tubes (and then regulating output) this might be useful but you'd still need quite a few inner tubes or a few very large ones. But say inner tubes sandwiched between flat surfaces (one moving) to provide a significant amount of constant (low) pressure storage? That'd be a lot of inner tubes and a rather large area for these surfaces.

That's why I described "bags" which can be constructed out of plastic or rubber sheet for this application. Or the counter weighted floating cylinder with open bottom (aka giant "bell jar"). Not that hard with these to have capacities of the order of of thousands of liters. Keep in mind that at atmospheric pressure methane is less than one gram/liter. You need a good sized collector to hold a kg of this fuel.
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cadfael · Posted: Fri Aug 28, 2009 9:23 am Post subject:

OOPS!! Should have specified large truck or better yet, tractor inner tubes!!
Thanks M&P!
Dead easy to make up a manifold using plastic tubes and jubilee clips.
Mike.
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Minds are like parachutes, they only work when open.
I don't bodge, I improvise and innovate.
Dogs, logs and chainsaws.

Chrisf · Posted: Fri Aug 28, 2009 4:25 pm Post subject:

Hi all

Sorry haven't been on for a while so I didn't realise there were more replies. Firstly I got the book as a birthday present (I ask for some strange things), but I think it came from ecologic books.

From my understanding biogas is the product made from anaerobic digestion of any organic matter. So it would include animal waste (and I include humans in that, remember folks, we are animals too) and vegetable waste. So anything that you would stick on the compost can go in which is essentially what I was thinking as well as our waste and the waste from our other animals (poultry, cats, dog and anything else).

I have read about Jean Pain and their seems to be arguments for and against. The main issue I have is the apparent quantities used in this method. I recall he describes using 50 tonnes of material.

The chinese system of storage basically has a chamber above the digestion soup to trap the gas with a pipe from the top to the cooking or heating device. Off the top of my head I can't remember any sizes but this method was more a community facility so there would be plenty of inputs and outputs.

Something which could be utilised in a collector is to work a hydraulic accumulator which may help but I haven't time to go into it just now. I'll maybe go into that another time...