Biogas - experimental scale Anaerobic Digestor and collector

[wooliver]

Mr. or Dr. Karve from Idia has came upon a paradignm jump in the respect that, it seems you can yield much methane from table scraps and less dung. The idea is, as i grasp it, you are making an artificial intestine of sorts. Where the stomach has digestive acids, the intestine is where the beneficial bacteria convert food to fuel. By the time food is digested, what is excreted is mostly, if not completely, bacteria. Remeber this. In most farms and city water sewage treament plants, the idea is to dilute and disarm the bacteria. The methane they produce is a by-product of a process to rid of the manure. Karve wants to produce methane firstly. Feeding the digestor like an animal, with table scraps and organics that still have higher caloric values. He starts the process with some dung but if the process is controled well, more dung, need not be added, as the initial bacteria is kept well fed and is able to propegate. Also mentioned, there are two types of methanogenic bacteria, low temp. 50-60F to 100F, and thermophilic or high temperature bacteria that thrive between 105-115F. Reviewing the fact that pastuization occurs at around 145F, so 130F would be plenty hot.

Once methane starts to produce, a small amount may be used to heat the digestor. As mentioned last time i'm using a 50w heating pad presently to keep the temp up overnight. I can see it will be a battle to efficiently heat a digestor in the winter in cold climates. Using black poly or black painted tanks in the sun seems wise. I've not come up with a solution for heat transfer in the winter. If there is enough gas production for to heat itself, then it is only a matter of insulating.

Thus far in actuality i've filled a 5 gallon barrel with both dry and green grasses, that are abundant now, and a few pounds of fresh cattle manure. Within 24hrs. it has produced a .2 cubic feet of CO2. Meaning the process is starting.

Another problem that bothers me, is the need for the process to be continuos. The digestion must remain free of air, yet must be able to be replenished or fed. And effluence must be drained off as well. There are many designs to choose from, but i've not come across best solution.  

I live close to a rural ethenol plant. I think it would be poetic to charge this digestor alternately with distillers grain. But one must always consider calories are calories and protien has been much removed from the grain. But like our relatives the sewage treament plants, the job of more completely consuming that which has not yet been adequately consumed, should also be a part of the mission.

[Bruce S]

There is a lot of good info in what you've done and learned. You are correct, the idea of not loading so much dung into the digestor seems to allow a quicker start, less of a load to the little buggers to get to working with.

One of the things that will also help is knowing that while using the grains and such you'll get a faster start, but not a long term output without constant feeding.

This was part of the Dr.'s design decission. He wants them to get a good quick high daily output , mostly for 1 to 3 meals worth of out put, so feeding it his way is perfect for this.

One of the co-combined ideas is to go this route along with the addition of feeding the "roadside" manure to help in long term production, which in side studies seems to also have the added function of being able to handle some cold spells without killing the entire runs. This also goes a long way into getting the files and other nasties into the digestor instead of bugging animals and humans alike.

In your setup, you could let the setup cook itself out then go back and rework it to become a continous unit , OR build a second one while this cooks and use part of it as a starter for the new one.

A small water column will help you with a constant pressure as well as a safety valve in case the digestor get to working too well or you run out of storage room.

For continous use setups, you'll need a loader side that will have an entry that is about 1/3rd from the top of the water line ALWAYS. air getting into it as you know will make it dangerous.

The bucket in bucket method is a good teaching one and can easily be adapted for constant recharging and even a pretty easy way to adapt to allow the bottom solids to be pushed by the addition of more charge.

A couple other things , let go of that CO2; it has air in it and can become a problem. What mods are you doing to engines or items to burn this?

Cheers;

Bruce S

 

[wooliver]

It started with a 1 lb. cylinder of propane, a gas grill regulator, and a needle valve. The engine was a yamaha 50cc (2 cycle) moped engine.

 I simply pryed open the rubber than fits between the air cleaner and carburator. Then shoved the 1/4" clear plastic tubing down into the airway. Upstream is the needle valve and regulator, then the LP bottle.

 The engine is started on gasoline. The needle valve is turned on slightly. It doesn't take much to smother the engine with too much propane replacing the air.

So once you get the engine to start and run on gasoline with just a little propane (running the engine quite rich)i shut the gasoline supply off. First the float bowl must run ampty before the engine truely runs on propane but it soon does. Now i have achieved running the engine, but at only one speed. This is  gas grill regualtor, not a regulator designed for engine throttling. They do make them. I don't have one yet. That type of regulator can completely shut off if there is no vacuum across the output ventury. This experiment, combine with what i've learned about engine specific regulators was enough to satisfy me.

You need to know your engine displacement(divided by 2 four a 4 cycle)and the intended r.p.m. and know that it takes 10% gas to air. From that you can derive your cubic footage of gas production needed for a given time. (remember you're calculating for 1 atmosphere) If i take a 20# tank and compress to 250lbs. i can run a 50cc moped for 7.4hrs @ 2000rpm. or an 80" v-twin for 33 minutes @ 2000rpm. More than enough for the days commute.

 Mind, you need to know something about propane and natural gas. Propane is liquified and the vapor above the gas can reach 250lbs. Natural gas (roughly the same properties as biogas) liquifies at much higher pressure(and lower temp). I'm not going to liquify the biogas, but for the experiment i used propane. This is the reason for the regulator. Bringing the cylinder pressure down to inches of water collumn instead of psi. Know your regulators, and know your stuff, when messing with gaseous fuel. In my estimation they never would have legalized gasoline by today's safety standards. I'm much more comfortable working with natural gas, be it petroleum or bio. Propane expands more than 600 to 1 yet is heavier than air, so it can linger on the ground unnoticed waitng for a spark. Methane is lighter than air, so it disipates up. Also i am not going to compress it that much so the expansion is less as well.

I can see by the combination of technologies why people have not adopted biogas, but it's nothing new. It's more of a lost technology. This is old fuel waiting to be harvested. The only reason we're burning gasoline today is purely political.

I'm an electronic engineer by trade. Electricity is a fine thing that has made much possible, But we've also spent way too much to simply extract it and pump it. The fine folks that build wind generators, pumps and mills have a grasp as well on an old energy source. I'm glad there are other people that ask questions.  

P.S. on filteration - bubbling through water cleans most of the acid out of the gas. CO2 of course, can't completely be removed but is heavier than methane, hence the reason for the valve on the top of the holding tank. This gas, biogas, isn't 100% methane, but neither is petroleum natural gas. It's "good enough" gas.  

 

[kurt]

you mite find this page useful  http://tinyurl.com/2vpn2x

[Bruce S]

I like the common sense grasp you have on this...

Shows you've done a lot of research, testing and thought.

The propane regulator is a good one to use, will be very helpful/cheap if you get to using a good small engine for emergency genset. Perfect for a 5hp 4cycle that sits and runs at a specific rpm.

What are your long term goals?

Bruce S

 

[elvin1949]

  Kurt

 That is one of the most informative pages i have read in a looong time.

 One thing most people need to be reminded of is that LNG--Propane--Butane--Methane used in I.C.E.

devices like high compression ratios 19 to 1 up to 22 to 1.

 Thank you

later

Elvin

[Bruce S]

Elvin;

   You are so correct.. they actually get more efficent when up in the 10 - 12 compression areas. I haven't seen any of the buses here that run LNG up in the high ranges of 19 but would be possible I think.

For standard I.C.E.s the 10.5 of old days would be easy to work with.

Cheers

Bruce S

[elvin1949]

   Heck of a lot better than the crap we have to work with today.

 later

Elvin