small biogas system linked with CHP to produce electricity

  • wini
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small biogas system linked with CHP to produce electricity

Dear All,

i am working in productive sanitation for IDP settlements in South Darfur. i was looking for technology options to produce electricity from shared and public latrines. Does anyone have an idea about low cost biogas plant and CHP systems. or any studies regarding the topic.

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Wini
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  • JKMakowka
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Re: small biogas system linked with CHP to produce electricity

There has been some success using plugflow plastic bag digesters, coupled to small generators. There are some Chinese made ones specifically adapted for running on pure biogas, but often it is easier to use one that starts with petrol and just substitute part of the fuel with a biogas injection.

However my honest recommendation is to not even try... all these are complicated and maintenance intensive setups. And people used to running generators on petrol will always complain that the gas produced is insufficient.

Why not look into solar? There are many ready made and quite cheap systems that include battery, converters and all that in a nice box and the maintenance needed is minimal. In my experience people also have different expectation if it is a solar system and will not complain as much about insufficient power to run a electric stove or something like that.

Krischan Makowka
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  • Marijn Zandee
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Re: small biogas system linked with CHP to produce electricity

Dear Wini,

To add to what Kris mentioned above.

I would guess that from public latrines you could have quite reasonable biogas output, if they are used by something like 200 people per day or more. However, I would advise not to go for electrification.

The amount of gas you are likely to produce will only allow to use fairly small generators (rough guess is 3 kWh). I have some experience with these. You can get fairly reliable ones from China, which are LPG generators with the carburetor set up differently to allow them to run on biogas. As long as your Methane content is above 55-60%, they seem to work ok. However, you will probably still need some de-sulfurising and de-watering installation for the gas. Which adds to the complexity of the system.

My main objection to the small generators is that they are air cooled, and as such cannot be used for capturing the heat energy (which you propose to do with a CHP system). Therefore, the efficiency of the system is very low.

For the electricity, I would agree with Kris that a solar set-up is probably better. If you can use a lot of hot water (for cleaning or cooking?) you could still consider a biogas installation.

Perhaps the people from (B)energy could help you further. www.be-nrg.com/b-products/

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Marijn

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  • sanjayg111
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Re: small biogas system linked with CHP to produce electricity

In my experience, if you are planning a biogas then perhaps using the same for cooking is fine but electricity is a more complicated process and not very suitable for IDP set up. THese require regular maintenance. So even if you are able to procure one, getting timely services and repair will be tough. You will usually not find these services locally.
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Re: small biogas system linked with CHP to produce electricity

Dear All,

sorry for belated response; i have very limited access to internet. thank you very much for your contributions. the thing is my project objective is to have cleaner environment using productive sanitation systems to recycle domestic waste (fecal sludge, animal dunk, solid waste and etc.), my idea behind using biogas electrification came from the context;electricity price is very high compare to other cities in Sudan (0.7$ in Kass to 0.03$ in Khartoum) and the service is provided by informal sellers specially in the camps. plus, many houses are made of straws thus people are scared of using gas for cooking.

Thanks,
Wini
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  • wini
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Re: small biogas system linked with CHP to produce electricity

The biogas plant could be at public latrines or school latrines. my first model will be based on school latrines fecal mixed with donkey dunk. if possible to provide me with the links of good suppliers for biogas plants and generators, i would be very thankful.

about B energy products; does anyone has an experience with their backpack.
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Re: small biogas system linked with CHP to produce electricity

We had a lengthy discussion about biogas in schools, just do a quick search. It is definitely feasible for cooking (but not for electricity) if supplemented with additional feed material. Cow dung is best, but donkey dung might work (although if I remember correctly, horse dung is generally considered to not work that well, maybe too dry and bad c:n ration?).

For generator supply, its better so look at what's available in the nearest central market. Just ask some shops with typical Chinese import generators what they can get. And as I said before, a sufficiently robust generator can be carefully fed with biogas as alternative fuel after starting.

About the be-energy back-pack: yeah I know the people behind it and have seen it as a working sample. The original creator (Katrin) is based in Addis and will probably be glad to give you some tips and help you out. However I am not sure what you want to do with it, as uncompressed biogas really is only suitable for small scale cooking.

Krischan Makowka
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Re: small biogas system linked with CHP to produce electricity

Anyways, here some documents about running regular generators in dual-fuel mode (but again, not really recommended over maintenance concerns).

The "gtz volume 1" document has short instructions on how to do the dual-fuel conversion on page 23pp.

In the likely case that you will have H2S engine corrosion problems, have a look at the purification of biogas document.

And last but not least, a short hands on guide on plastic-bag biodigestors which is probably the easiest and most fail-proof way of getting some biogas (but they have a relatively short lifespan).

Krischan Makowka
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  • Marijn Zandee
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Re: small biogas system linked with CHP to produce electricity

Dear Wini,

I have seen the backpacks, they appear to be well made. But you should really think about how you would want to use them. Would you try to sell the gas?

I don't know of any biogas companies that work in your area.

Dear Kris,

Do you have personal experience with the dual fuel option? I have never tried it myself, but many people I talked with had a "don't bother", it is too much hassle kind of attitude about them. Would be nice to hear some positive experience.

The old GTZ/Gate publication about biogas purification should be updated some time. I like it in a way, but it is all a bit too based on DIY recipes for this day and age (in my view). I would suggest buying a few sacks of iron oxide pellets. ( gyhongchang.en.alibaba.com/productgroupl...as_Desulfurizer.html ) It would be nice to find some systematic research on the topic, including a financial analyses.

Marijn Zandee

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Re: small biogas system linked with CHP to produce electricity

About the dual fuel option, well kinda... I have seen it being used in relatively makeshift solutions but with compressed natural gas. Definitely don't try this indoors though ;)

But I agree that if you can get your hands on a proper gas run generator that allows running on low pressure biogas feeds, that is definitely preferrable in general. However for critical installations like a hospital a backup generator that runs on diesel is necessary then. I guess a properly build dual-fuel generator (for diesel, biogas and compressed natural gas, maybe also methanol or ethanol) would be nice to have for such situations.

About the GTZ purification doc: yeah true... but than again, big difference between most of Asia and rural Africa.

Krischan Makowka
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