Complete, Portable Units Available in US?

Digester design and construction info

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Mike D.
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Complete, Portable Units Available in US?

Postby Mike D. » Wed Oct 15, 2008 11:42 am

Hello all! I'm new to the forum and had a question. I've been doing a ton of online research on biogas digesters the last couple of weeks, with an eye towards the feasibility of setting up one or a series of small biogas digesters in the US to generate green electricity, with the electricity generated covering the costs of the digester(s) and generator(s).

One of the first stories I saw on the internet, from several publications (example) was about a company called Sintex creating self-contained biogas digesters for use in rural India to turn human and animal waste into cooking fuel. I checked out Sintex's web site, and they do have several models of a all-in-one digester that appears to be somewhat portable. The articles mentioned that these digesters were available in India for roughly $425 US, but the web site contained no information about pricing or availability in the United States.

Does anyone have any knowledge about these Sintex digestors, or any other digestors that are self-contained and available in the US? I emailed Sintext a few days ago, but have not heard back.

Thanks for your comments and assistance, and thank you to Mr. Crosby for creating this very informative and helpful site! I'm trying to work through my plans in my head, and I'm sure I'll have a bunch more questions!

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Bob
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Re: Complete, Portable Units Available in US?

Postby Bob » Fri Oct 17, 2008 10:39 am

Hi, Mike,

I'll be interested to hear what you learn about the Sintex unit. It looks interesting.

From my own experience, the digester itself ($425) is a small part of the total installed cost of a complete operating system. The total cost will depend to some extent, on how much daily maintenance people would be willing to do. This is probably different in the US than in rural India. I also note that they are using the gas for cooking, which is far simpler and cheaper than generating electricity from it.

Mike D.
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Re: Complete, Portable Units Available in US?

Postby Mike D. » Mon Oct 20, 2008 8:41 am

Thanks for the comments, Bob.

So far no word from Sintex. I'll probably try them again in a few days.

The more I think about making this viable, the more I think that a single large system would probably be more cost-effective than a distributed system. The higher cost of the non-digester items as you suggest seems to back this theory up. The key in that senario is finding a consistant supply of materials to feed the digestor.

I'd love to get your thoughts on the the non-digestor parts of the system you'd need and their rough costs. One of the things I'm having trouble wrapping my head around is getting materials in and out of the digestor. I imagine most of the materials I'd be dealing with would be solids, to which water would be added for ideal digestion. Is the material that would come out of the digestor liquid, then? I'd think that having it a solid would make it easier to store and distribute as fertilizer.

BTW, this past weekend I was pressing apple cider. It reminded me that about a year ago at this time was when I first really thought about biogas. We were pressing cider at my friend's house, and last year he didn't have a compost area set up yet, so we were temporarily storing the crushed and pressed apple waste in large black plastic trash bags. It was amazing watching those sealed bags swell with gas after just a couple days in the sun.

I'd imagine that cider-making waste would make a nice fuel for a digester!

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Bob
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Re: Complete, Portable Units Available in US?

Postby Bob » Mon Oct 20, 2008 10:42 am

The more I think about making this viable, the more I think that a single large system would probably be more cost-effective than a distributed system.

I agree. You can't get enough gas from a small (e.g. single family) system to justify the added expense of automation, gas scrubbing and/or compression and electric generation. But if you have a need for a small amount of gas for cooking or heating water, and if you can use the gas as it is generated (avoiding the added cost & complexity of storing it), it makes more sense.

I'd love to get your thoughts on the the non-digestor parts of the system you'd need and their rough costs.

As noted before, it depends. Can you say more about what degree of automation (or conversely, what amount of daily maintenance) would be acceptable?

I'd imagine that cider-making waste would make a nice fuel for a digester!

Yes, I would expect so. Being a one-time, or seasonal load, it would probably lend itself to a batch feed, or hybrid system.

Mike D.
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Re: Complete, Portable Units Available in US?

Postby Mike D. » Mon Oct 20, 2008 11:50 am

Thanks again Bob for your response.

I'm thinking a fairly automated system would probably be most realistic. I'm sure that adds to the cost, but the time savings would be key to keeping the system up and running.

I think adding materials to the digester could be fairly manual, but from that point on, the more automated the process, the better. Again, I'd probably be dealing with mostly solids...animal manure/bedding, agricultural waste, food waste, etc.

Is the "spent fuel" in most systems a liquid or predominately solid? As I said before, how the spent materials are removed from the digestor is one of the things I haven't quite wrapped my head around fully.

I'm still kind of trying to determine exactly what fuel sources I'd be able to acquire in the neccesary quantity. I don't own a farm myself, but the area I'm looking at has many small horse, cow, and other livestock farms, in addition to some small-scale agricultural farms.

I suppose the possibility of actually having someone pay to dump certain materials (food and agricultural waste?) as a possible source of both fuel and additional funding towards the bottom could be explored. Also, there may be a market for the solid or liquid byproducts as fertilizer.

Sorry for the mix of technical and economic feasibility thoughts above...I'm just kind of trying to noodle through the whole process in my head, and any input you have on any of it is very much appreciated, even if it's just to say "man, you're nuts!". :D


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