Help - My gas won't burn.

[desperate]

Hi JMALW

I've been reading quite a lot over the hols about gas plants, similar to yours, as it is something I am quite interested in.
The book has a chapter all about homestead size digesters for four cows output or thereabouts, and a few points caught my eye especially after taking interest in this thread.
 Firstly they say that the Carbon/Nitrogen ratio should be 30/1 for ideal methane production, they go on to discuss the various ratios for a variety of raw materials and how a complication is the values of Ammoniacal and Nitrate type nitrogen are misleading,as they are not equally available to the Bacteria, so a chemical analysis is not that usefull on its own.
Second, they say that plant materials do indeed produce a lot more gas than a mixture of animal and plant materials, but it has a lot lower CH4 content and a higher CO2 content, 40%/60%, if I recall correctly you are feeding in mainly plant waste, whereas here they are recommending 50/50 plant and animal waste proportions for the highest CH4 content.
Third, they do also say that the ph value needs to be allowed time to stabilize to about 8-8.5 at a temperature of 35-40c or 7.5-8.0 at a temp of 50-55c as there are 2 predominant types of bacteria that we are interested in. They seem to agree that it is better to utilise a lower temperature as it is less energy costly even though it is a little less productive.
Fourth they say that a lot of co2 is always produced first and it requires patience to see the production of 60-70% CH4 from the digester.
The book I am quoting is called "Producing your own power" Published by Vintage Books 1975, so it may be a little out of date and almost certainly out of print, but I have borrowed it from my Father in law and am happy to look up further info. At some stage in the not too distant I may well have a go at something similar to your set up, the soil pipe from our bog goes down through my garage/playpen

All the best,

Desperate

[JMALW]

Hi Desperate
That was very interesting and starts to make more sense with my set up.  Currently the weather is against me for critical experimenting but on the other hand it is showing me what happens when it's colder. For your kind interest this is what I get.   The gassing  is still going on quite strong with very little external heating - just adding waste into the well lagged digester. This seems to produce some exothermic heat - enough to still convert.  I'm interested in the notion that it needs some other ingredient to ferment more CH4 so maybe adding some cow poo may do it.  Now it becomes more interesting if I knew how to separate the two main gasses - CO2 for my greenhouse and CH4 for heat or power since I could seriously use both for my projects. I have an enclosed standby diesel generator which is connected permanently in case of power outages and I experiment with a petrol genset converted to LPG which I hope to trial with suitably cleaned up Methane - just a few modifications to the gas regulator.  I just seem to be very close to a successfull outcome.

I would add that I have redesigned my original digester to remove the hazard of H2S spilling out of the filler when adding waste. Although H2S is heavier than air it does waft around the filler  - the first you know is when you get eye irritation which is a sure sign it's there.  To over come this I have made the drain sealer into a plunger operated from a lever and made a pipe connection from a waste disposal unit which chomps up the digestate into a slurry then passed to the neck of the filler with a bypass to remove excess water used by the disposal unit.  This set up effectively removes any contact with H2S. Do not rely on smell since you only get one whiff and you lose your sense of smell very quickly - it is a very dangerous gas and lethal in small doses.

Happy new year to all
John

[noelsquibb]

ahh, chemistry
if only I had listened 

ave a pat, you certainly deserve one for effort -

[desperate]

Its that Cheech and Chong joke again.

Desp

[JMALW]

Hi all
Just saying hello and to let you know I'm still trying.  The weather hit my project like most others I guess.  I'm working on modifications to the digester and hope to have it working again in the spring. The water pumping system is working flawlessly except it's just pumping air at the minuite but I hope to be able to store about 7 cu mtrs of gas replenished as quick as required when I fathom out how to split the CO2 and CH4.  I'll be back.

John

[desperate]

Good stuff.....don't give up.........a good fart always takes a little longer to brew.......

am eagerly awaiting an update.

Desperate

[desperate]

Hi JMALW

was boning up on CCS technology the other day and something rang a bell I know someone who wants to capture some co2, apparently they use some kind of Ammonium salts in aqueous solution at a lowish temp to capture the co2 in the flue gas, and then heat it to drive it off again. Unfortunately they didn't say which ammonium salts but maybe Mr Pontiff knows, he seems to be a chemical wizard. Or maybe a Googling??

seeya

Desperate

[northern installer]

CO 2 absorbtion:I mentioned this before but it raised no comment (except from Eleanor who suggested calcium hydroxide) Divers use, or used to use, rebreathing apparatus,that uses the same gasses over and over again,replenishing the (relatively small )oxygen consumption,and absorbing the (larger) co 2 production with a chemical filter;one of these filters should be able to cope with a reasonable flow of co 2,,but I am unable to quote the chemistry without knowing the material used for the filter(which may ,of course,be the calcium hydroxide used in Eleanors instruments)
Surely there are some divers on this forum that know where such a filter can be obtained,and what chemicals are used in it?

[pontiff]

CO 2 absorbtion:I mentioned this before but it raised no comment (except from Eleanor who suggested calcium hydroxide) Divers use, or used to use, rebreathing apparatus,that uses the same gasses over and over again,replenishing the (relatively small )oxygen consumption,and absorbing the (larger) co 2 production with a chemical filter;one of these filters should be able to cope with a reasonable flow of co 2,,but I am unable to quote the chemistry without knowing the material used for the filter(which may ,of course,be the calcium hydroxide used in Eleanors instruments)
Surely there are some divers on this forum that know where such a filter can be obtained,and what chemicals are used in it?

I think they use a type of sodalime which is mainly calcium hydroxide , with a bit of sodium and potassium hydroxides too. The apollo space programme used lithium hydroxide scrubbers on the moon missions. Both are limited in the concentrations of CO2 they can deal with, as the apollo 13 crew found out when they squashed 3 astronauts in a spaceship designed for 2....buts that's a story for another day...

Desperate, kind words indeed! (but sadly not true I'm afraid) Using solid calcium hydroxide is the best bet for a test to see if the CO2 is the problem. I would also experiment with drying it too by passing through/storing with silica gel or calcium oxide. Small scale stuff to find the problem.

If the issue is CO2 then it will be tough to find a large scale solution going down the scrubber route. The technology to deal with it in large amounts is still in its infancy though there are some very promising new lines of research going on. In the past it's been regarded as an engineering issue but now the chemists are becoming more heavily involved real progress is being made.

Wish I could be of more help.  

[Rooster]

I'm sure there's some mileage in improving the quality of the gas produced before needing to think about scrubbers.

Get that Poo in there!!

[JMALW]

Hi folks
I'm giving it a lot thought, I know now what the pioneers of the iron, bronze and steel age must have gone through and I know that a lot of stuff was developed in a back yard or shed even of recent times and I take my hat off to all of them. They had the ideas which could not be implemented until some other detail was cleared. It's seems unbelievable that with all the technology and knowledge around today that this simple concept of separating two gases is not widely available.  Could it be that innovation is dead.javascript 

[JMALW]

Hi
I've found some interesting stuff on membranes - apparently a lot of work going on by boffins to crack this issue of separating CO2 and CH4. So far I've found out that Cellulose Acetate has been found to be the best to work in filtration.  I've turned my basement into a laboratory and I'm going to find out how to build a filtration unit. 

[daftlad]

I have been looking at the ARTI website
 http://www.arti-india.org/index.php?option=com_content&view=article&id=45:arti-biogas-plant-a-compact-digester-for-producing-biogas-from-food-waste&catid=15:rural-energy-technologies&Itemid=52
and maybe it is temperature rather than gas mix? (India is a hot country)
I was actually thinking of going on one of there courses but running out of time.
Anyway keep up the good work and hopefully you will have fire come the good weather.
ta ta

[JMALW]

Hi
Regardless of how to separate the gas I found that temperature is key to making the system sustainable IE producing any gas at all. My tank inhabitants go into sleep mode when the temperature drops below 16 C and trying to maintain the 30 C optimum is hard to do without using some of the gas to keep it warm here in Blighty should I be so lucky- luck defined as " when preparation meets opportunity". But I have to say even if the gas production fails to yield, the ability to decompose all our waste and consume other waste is worth the trouble with the rising cost of fertiliser and the proposals to start charging more for waste disposal.   

[northern installer]

I have found the soda lime formula for removing co2 in closed circuit diving apparatus:94% Ca(OH)2  2-4% NaOH  1-3% KOH @ 14-19% water content....I am not a chemist,its from a 1952ish navy manual!