View Full Version : Methane Digestor/Production
12-06-2007, 04:22 PM
Annabella's post in another area got me thinking. I'd like to try producing some methane. I have another guy interested in it as well.
I've read up on basically two different methods. One using composted raw materials and the other using manure of one form or another. At this stage I believe we are going to attempt the manure method. Just something small to start with and see how it works and learn the basics.
Has anyone experimented with methane production? How about digestor plans?
Any thoughts and input would be great. If we get things in order and it seems feasible, we will try powering a small engine like a generator or wood splitter. My end goal would be to convert my propane boiler and possibly a vehicle. Ambitious perhaps but why not.
12-07-2007, 05:01 PM
Some info I've found out:
Natural Gas is 97% methane
Most digestors using animal waste and/or vegetation actually produce biogas which is about 65% methane, the balance is mostly carbon dioxide and hydrogen sulfide. *The hydrogen sulfide damages normal ic engines so it must be removed. *The carbon dioxide is an impurity that doesn't allow a clean burn. *Both can be removed by using lime water and iron filing filters.
Compressing natural gas by mechanical means doesn't appear to be cost effective and can add a ton of complication for the homestead.
Air introduced to methane production can be very dangerous so a closed system that is purged must be attained
I'm still learning however I'll post more info as long as there is an interest. *
12-07-2007, 05:22 PM
I gave up on the idea of methane years ago....I decided it's just too dangerous!
12-08-2007, 04:32 AM
Did you produce any?
12-08-2007, 03:54 PM
I've never built a digester, but I worked with a friend who built one back in the 80's.
When he abandoned the idea, so did I.
12-09-2007, 06:38 AM
May I ask what was the reason it was abandoned? Did it get finished? Did it actually work? What were the reasons that it didn't become a viable source of energy?
I myself was involved in ethanol production a few years back. I was working with 5 gallon batches in the kitchen. The books describe how much glucose, nutrients, and yeast should be present that will produce X amount of ethanol. In practice, what I found was that I only produced about half as much alcohol as I should have, which was disappointing. That is the difference between what the books say and what you can actually do!
12-09-2007, 11:42 AM
The digester worked, but because of the carbon dioxide the gas only had maybe half the energy value of natural gas....even so...it's quite dangerous to store in useful quantities for anything other than heating a burner for cooking or something like that....there are many more practical ways to accomplish that.
12-09-2007, 01:27 PM
Did you try lime water filtering to remove the carbon dioxide? Additionally, what methods did you use or plan on using for storage? One last question, what more practical ideas did you have as an alternative or replacement and was it just the storage issue that made you consider it not practical or lack of devices or something else?
Sorry to bombard you but I figured you would have at least tried it at some point and have some solid info on it.
12-09-2007, 01:34 PM
He did the filtering but that just adds to the amount of labor and the cost.
The gas was stored in innertubes.....safer than anything that's solid, but still a concern
A wood fire or even a wood-gas burner is more practical for cooking, IMHO.
12-09-2007, 02:14 PM
I have a small Well Mate pressure tank downstairs that I thought I may be able to use for a small storage. I would be able to fill the bladder with methane and then apply water pressure to achieve the level of methane pressure I want to attain.
As far as the carbon dioxide removal, I figured I would run the output of the digester directly into a container with the lime water, possibly through an air stone like an aquarium would use. This would eliminate any additionaly work needed. I also plan on running the gas through the iron filings to remove some other impurities. This should give me 97 to 98% methane.
We'll see how it goes obviously. My chickens will get me started and if it works out, I'll talk to the neighbors that own a miniature horse farm and some other close neighbors with dairy farms.
12-09-2007, 04:21 PM
12-28-2007, 05:41 AM
Great let me know how it goes. The only problem I see is using the manure process, yes it produces methane but for a much shorter time than using vegatation process. Are you going to use a batch (sump) digester or a continuous digester? I think that if you are using the manure process it would be better to use a continuous digester. If you use the lime water to eliminate the co2, then the iron filings for the hydrogen sulphide I would recommend mixing the iron filings with sawdust, to help remove the moisture from the gas that has passed through the lime water. make sure you purge all the air out of your systemI don't want to hear that you blew yourself up ::)
12-29-2007, 01:42 AM
For starters we are just doing a one time setup with a watercooler container. Start slow and small and see how we make out.
I like Jean Pain's plans better as well mainly because I'd love to incorporate the heating ability into my existing system. I'm not sure on what level I'd have to get to although I had a farmer neighbor mow our fields last year and he took the bails for mushroom farms. It was mostly grown up for a couple years with some multifloral rose and so on. These bails weren't the small size but more like 900 lbs or so, big rectangular monsters. So, I was thinking that perhaps I could have them come and bail again but position the bails close to the house and build my compost pile with them or break them down and build them. We'll see....
As far as purging the system I have read about it and will keep it in mind as well. I also did some research with our Chemistry teacher and she informed me that hydrogen sulfide is water soluble so it would probably be removed during the limewater phase. Again, we are starting small to test these types of theory's out and see what kind of output could be expected.
Instead of a continuous digester, I think I would use multiple setups that would run in parallel. This way one or more would always be producing but removing one a week to recharge wouldn't affect the overall output and also require less maintenance.
12-30-2007, 08:42 PM
I like the idea of the parallel batch digesters, it does take a couple of weeks or more to start producing methane. So you may want to start your second batch even before the first one starts producing. There is also a chance of spontaneous combustion in your bales or loose hay. I don't know if I would stack it too close to the house maybe run underground water lines after they run through the aerobic composting area?
12-30-2007, 10:48 PM
Running underground lines would be an interesting idea. Maybe some quick disconnect fittings would help matters.
As far as spontaneous combustion goes, here are some items I found that briefly discuss the issue:
By the sounds of things, I probably won't leave the bales in tact but pull them apart and shred them further. Another option may be to have the neighbors chop them into haylage wagons and then just dump them in location. I can finish everything with a skidsteer.
Great thread, I have been very interested in this.
Mad I was thinking of your idea of using a water tank with a bladder. I think I would try getting a large container like a 55 gal drum with a pipe though the bottom about 3 foot long. Then place a smaller container like a 35 gal trash can over the pipe and fill the drum with your lime water. Put the air stone in the drum. When there is no methane the trash can will be sitting on the pipe and be full of water so very little air in the system. As the methane bubbles though the air stone it will be captured by the trash can. The can will then float higher making more space for the gas. The output will be though the pipe. You could adjust the presser by adding mass to the top of the can.
01-24-2008, 11:19 PM
Mmm There is a book out called ? The Three Cubic Meter Methane Digester" Which I know I have read and think I might still have. It gave designs for an in ground digester. instead of outside storage it used a weighted domed floating lid that raised up as the gas was produced and dropped as it was used. It was a continuous feed two chambered pipe/tank. This is one of my first projects on my list when I do get to move to my property. The other big one is building a wind Generator.
There are all sorts of web postings on this,,, or at least there were a number of years ago when I fell in love with the idea. It was written about a long time ago by the original Mother Earth News when they built a Batch Digester that really worked good.
04-01-2008, 12:18 PM
The EPA has a great free book about the production of methane. It was written for waste water treatment, but the source can be modified. The price is right and it contains a ton of useful info.
04-01-2008, 07:21 PM
Annabella's post in another area got me thinking. *I'd like to try producing some methane. *
well, beer, beans and hard-boiled eggs works for me, but, i do get into a lot of trouble with swmbo -
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