Help - My gas won't burn.

[northern installer]

Re: co 2 removal,I think divers at one time used a simple dry filter to remove exhaled co 2 within a closed 'rebreather' system;is there anyone here can tell us what chemical was used? my guess is potassium or sodium hydroxide,but I am not sure;is this system still used?

[JMALW]

On the pressure theory Ivan suggested - very good one and to this end I decided to use the bunsen burner since it is very versatile in its use as a tool to play with - I can alter the jet size, turn the pressure up or down by a simple tap and also vary the in going air mix. I remove most of the moisture by condensing it - I place a container into another submerged in cold water, it has a glass fitted to the bottom so that I can see any deposit and then drain it off. Since I heat the digester the gas is warm and so contains quite a bit of moisture but it is easy then to remove it this way.  What Ivan said is is evident when one tries to light a propane or acetalene torch when you can see how the pressure tends to blow the flame out, however, usually hitting the gas flow at the right distance from the nozzle eventually ignites it. I spent quite a bit of time playing with mine to no avail. I tried the soapy bubble last night and got some pretty impressive bubbles but they showed no sign of ignition. As a starting point I use 24mbars (Propane is 34mbars) (Natural gas 22mbars) and I use a manometer to monitor this.

[Eleanor]

We used calcium hydroxide in solid form for CO2 removal in instrument air but this was only for relatively small amounts. I don't how much waste material would be produced in this case but quite a lot I would have thought. Could probably be used for liming the garden.

I was thinking of drying the gas with something like this but don't know how much they cost. Also, I don't know how wet the gas is and if it would be worth it.

http://www.permapure.com/Products/ME/ME.htm

You seem to have got the drying sorted but another way could be to run a coil of the gas pipe through a fridge and install a drain in the lowest point of the pipe. Probably a bit dangerous unless you're running a gas fridge which maybe you will be if you can ever get it to light! Waffling now.

There also seems to be a lot of research into CO2 selective membranes for carbon capture schemes. Older technology uses cellulose acetate. They seem to need a reasonable pressure though which could be an issue for home systems.

I still can't help thinking that you need to know the rough composition of the gas 

[SteveH]

 An idea for a simple test:

 Put a small lit candle into the bottom of a tin can & trickle your gas in... If it's combustible you will get a "woof"... If it's not the candle will go out...

 Not sure about the relative mass of CO2 & Methane, I know both gasses are heavier than air. Might it be possible to use a tall tube (Drain pipe) & gravity to split the gasses...

 There you go, that just proves how little I know about Chemistry...

[JMALW]

I'm not sure if the methane is heavier or lighter than air but I thought I would try the one they demonstrated when i was at college - upturned treacle tin
with hole in top - fill with gas , light the gas at the hole and stand back - when the gas in the tin got to the right stoichimetric mix it exploded ensuring the tin hit the roof.  Mine would not even light.

[JMALW]

We used calcium hydroxide in solid form for CO2 removal in instrument air but this was only for relatively small amounts. I don't how much waste material would be produced in this case but quite a lot I would have thought. Could probably be used for liming the garden.

I was thinking of drying the gas with something like this but don't know how much they cost. Also, I don't know how wet the gas is and if it would be worth it.

http://www.permapure.com/Products/ME/ME.htm

You seem to have got the drying sorted but another way could be to run a coil of the gas pipe through a fridge and install a drain in the lowest point of the pipe. Probably a bit dangerous unless you're running a gas fridge which maybe you will be if you can ever get it to light! Waffling now.

There also seems to be a lot of research into CO2 selective membranes for carbon capture schemes. Older technology uses cellulose acetate. They seem to need a reasonable pressure though which could be an issue for home systems.

I still can't help thinking that you need to know the rough composition of the gas  

I second that Eleanor

[Ivan]

I'd say you've done enough to show that your gas is mostly CO2. An anaerobic digester can't produce mostly CO2, unless it has an air supply. Think you'll now need to start looking for the source of the air entering your digester

[northern installer]

if you put a co 2 scrubber of large enough capacity in the system,if there is no gas left at the outlet you have proved its all  co 2? not all that scientific,but enough to point you in the right direction?

[wyleu]

Could you not put a sample in a large plastic syringe and suck up a little liquid that absorbs CO2. Cap the syringe and make a note of where it is on the scale, leave it overnight and that might tell you what proportion is CO2.

[JMALW]

I have been focusing on these very points and trying to work out how I can (1) measure the contents/sample (2) avoiding any air intake with the digestate (3) maintaining temperature.  On the air ingress point - the sytem is always in positive pressure of at least 20mbars therefore it is not possible for air to get in via joints etc only digestate if any. So I'm ensuring that it is chopped up small them soaked in water for an hour before putting it in.  Eleanor suggested
 calcium hydroxide so I'm getting some. Strange, no one else seems to go to this trouble.

[sleepybubble]

fascinating topic, this is going to be my big project for next year, so I am following this one now with interest. I have access to plenty of pig pooh/bedding/ and about forty black bin sacks of grass clippings a day, if wanted.

Somebody gave me a gas hob which has natural gas jets fitted but they also gave me the propane jets.... I had thought that knocking up a methene generator might be a bit simplier than all this though, didn't expect all this washing of gas and stuff.

[Rooster]

I wonder if part of the issue is the digestate itself.

Didn't see any poo in JMALWs input for instance! Having the right mix going in must help the quality of the gas.

I could be wrong but I didn't think the dairy farmers who have digesters do that much to process the gas.

So I think part of the solution is to get some POO in the thing, nice and regular like!!

[desperate]

It brings a whole new meaning to "sitting on the can", judging by the flare that we used to see at our local sewage farm it may be worth a try.

Desp

[JMALW]

During the Fall (American for Autumn) I collected all the leaves and filled 15 jumbo bags and also as many grass cuttings and have loads left - probably last me untill spring with other food I stuff in.  Now I did read that animal poo is not as good as the latter since the animal uses a great deal of the energy taken between eating and sh........g it. What I do takes the raw material and cuts out the animal bit.  There may be more to the way I've been applying it though - I may not have been breaking it down enough in size and probably not warm enough for methanogens compared to those that produce CO2.  But I can assure you there is plenty of gas  of sorts coming out. Before you guys go and spend dosh on this wait until I get a result. Problem is It's getting colder and I am having a problem keeping it warm enough.

[daftlad]

Now I did read that animal poo is not as good as the latter since the animal uses a great deal of the energy taken between eating and sh........g

I saw a small feature on telly, it wat about the ARTI biogas digester and the fella said just that, poo has already been digested by bacteria which means most of its food value (to the bacteria) is gone, he suggested that food waste was something like 4 times better.
Rooster may have a point, maybe there is none of the right bacteria in the digester? I have read that the best place to find the right bacteria is the bottom of a pond that has bubbles coming to the surface? Or go and find some road kill, really mankey road kill. 
My book on such things has about 10 pages on biogas, would you like me to scan them and email them to you? if so PM me with your email address.
ta ta