Friday, January 15, 2010

Threads on Compressing Biogas I found interesting

Ken Calvert <renertech at> wrote:
  Dear Michael etal, I think you have found the figures for LNG not CNG. The 
only way to liquify Methane is at a very low temperature. If you strip the 
CO2 and H2S out of biogas then to all intents you have Natural Gas, and CNG 
or compressed natural gas equipment operates at around 3,500psi, but it is 
still a gas. If you are going to compress biogas at all, then it is best 
to stick to the usual figures and then you can run you car cook your food 
and warm your house with standard mass produced Global standard equipment 
from off the shelf of any hardware/heating store. If you, and anyone else 
wants some plans as to how to do it as economically as possible then send me 
a private email and I will return mail you some brochures put out by our 
Ministry of Agriculture for small farm and hobby farm Biogas plant.
In brief, you collect the gas in a plastic bag, and monitor the pressure 
with the filler guage out of a auto washing machine. The pressure switches 
on a two cylinder air compressor which sucks the gas through one of a pair 
of barrels filed with rusty bashed up tin cans which are alternated one in 
line and the other left open to the air. The Iron sulphide in air then 
reverts to iron metal for reuse of the barrel, and the sulfur is left as 
elemental flowers of sulfur which is useful stuff. (beware heat problems) 
At around 150psi the gas is bubbled through a vertical water column 
consisting of a six meter length of 6" 150mil plastic pipe. 2metres as 
someone suggested is not enough. Natural gas at 150psi can then be used in 
liu of LPG if it is metered through an LPG reduction valve and the jets in 
LPG stuff are opened out a smidgeon. Storing a reasonable volume of methane 
at this pressure takes some ingenuity but it can be done. To drive your 
car on CNG requires a pair of old double acting hydraulic cylinders off a 
bulldozer or some such. You can't use one cylinder with a floating piston, 
because as already mentioned lubricating oil will take up methane under 
pressure and hydraulic pumps don't work too well with oil foaming out the 
tank. A single 3 ft stroke will take you up to 3000psi + in one stroke, 
and normal DIY hydraulic equipment from Northern Tool or other DIY stores 
operate at just the right pressures to make a rather neat setup. However,
let me say it again spending the money to go this far is crazy if you do 
not clean up your gas first and convert it into the Natural Gas which is a 
world wide commodity with so many appliances and equipment matched to its 
Ken C.
Scrubbing and compressing biogas makes sense only if you want to use it as
fuel in an internal combustion engine. If you want fuel just for heating,
burn the biomass as it is, and make use of its full calorific value. When
you convert biomass into biogas, you lose at least 75% of the energy in the
process of conversion.
Michael etal,   coming back for a second bite at the cherry.  There used to 
be on the market ,out of Europe,  a micro cng compressor by which an urban 
person, could take natural gas from their household supply, and pump it up 
to the required pressure straight into the tank of their car overnight.  It 
was quite small and operated at about 1/3 to 1/2 hp.  It would sit in the 
corner of ones garage and got around all the OSH regulations by not storing 
permantly anything dangerous under pressure in ones house.
    I once talked to someone else who had hooked a  hand operated grease gun 
to a 1/4 hp motor. A lever grease gun will take you up to 7000psi. 
However, he had his pressures and compression ratios all wrong  and it was 
even more painfully slow than one might imagine.   Happy compressing.
O.K. here it is!

If you scrub your biogas to the quality of natural gas, 
then you can  fill a CNG converted  car in your garage over night, 
with no problems of HP storage because the car provides the HP storage.  
I would go more and say that an enterprising person could  also use the 
CNG gas tank
of their car as storage to run ones household in the evening too. 
Bolt on CNG conversion kits are readily available from Europe.
Especially from Italy.   You might have problems in  getting it approved 
without a operators certificate as well, 
but thats a bureacratic problem not a technical one.   ATB Ken C.   

Dear biogas workers,
I wish all of you a happy new year. I take this opportunity 
to report some of my findings and poremises based on actual 
field experiences and observations.
Use of human food for generating biogas: Because the methanogens are
found universally in fecal matter, the faeces are considered by everybody to
be their food. The intestines of animals house a large variety of bacteria. 
It is my premise, that because these bacteria, including the methanogens, live in the
guts of animals, they eat what the animals eat. They are found in the faeces
because they are thrown out of the body along with faeces. The fecal matter 
represents the residual matter that can be digested neither by the digestive system of the concerned animal nor by any of the bacteria residing in its gut. The fecal matter can be digested only by a cascade reaction starting from hydrolysis to acetogenesis to methanogenesis, with a different bacterial species acting at each step. This process is analogous to biphasic systems, in which aerobic bacteria are employed for achieving partial digestion of the biomass, which is later acted upon by the methanogens under anaerobic conditions. The rapid generation of biogas from sugar or starch is most probably due to the fact that these substances are directly digested by the methanogens, without taking help of any other bacterial species. Especially in the case of sugars, biogas starts emanating from the biogas plant within two hours of introducing the feedstock into the biogas
plant, and it is digested and converted completely into biogas within 24
hours. Starch takes just a little longer. I do not advocate the use of  good
quality grain or crystalline sugar as feedstock for biogas generation. 
One should  use urban food waste for this purpose. In fact, its disposal is looked
upon as a problem by the municipal authorities. Our technology offers a
solution to this problem.
Failure of biogas technology in India: India has about 145 million rural
families. Even after 60 years of efforts on the part of the Government of
India, we have in this country only about 3 million working biogas plants. 
The low penetration of the biogas technology in India is primarily due to the 
high cost of the dung based biogas plant and also due to the fact that the
government promoted  biogas only as cooking fuel. Had it been made known to 
the villagers that biogas could be used as fuel in an internal combustion engine
for generating electricity or for pumping water, the villagers would have accepted 
the biogas technology wholeheartedly. 
Biogas as fuel in an internal combustion engine: volunteers of a U.K based NGO 
called Engineers Without Borders standardised this system in collaboration 
with our scientists. In this system, unpurified biogas is used as fuel 
in an internal combustion engine..A large number of people, including us, 
are making use of this technology. We use one internal combustion engine for
generating electricity at our campus, and another internal combustion engine 
for driving our char briquette extruder. 
In the area where our R & D centre is located, we get electricity only for a
period of 12 hours in a day. Several farmers and restaurant owners in our
neighbourhood now generate their own electricity by using this technology.
They use biogas generated by them in their own biogas plants. 
Farmers use cattle dung as feedstock, whereas the restaurant owners use food waste.

Failure of biogas plant at Approvecho: A team from Approvecho had visited 
our campus and seen with their own eyes the working of our biogas plants
made from two water tanks. I was with Approvecho only for a period of 4 days.
It was the beginning of February. The temperature at that time was below zero. I
had sent to them, in advance, our video CD and a list of the hardware needed
for fabricating a biogas plant. I was informed that everything was available 
in the local shops and that the hardware would be purchased after my arrival
at Approvecho. When we actually tried to buy the hardware, we found that
the tanks of specified sizes were not available in any of the shops.
They were listed in the catalogues of the manufacturing firms but not 
available off the shelf. Therefore we had to improvise, 
using discarded barrels obtained from grocery shops.
Therefore, instead of a moving drum model, 
I constructed a fixed dome biogas plant with the available material.
With the short time available to me, I could only assemble the hardware 
and leave without actually commissioning the plant. 
I heard later that the plants fabricated by me at Approvecho did not work,
but there was nothing I could do about it as I could not visit USA again 
just to repair the biogas plants.
Efficiency of a biogas plant: 
If, instead of fermentation taking 40 days, 
I got the same amount of biogas within 24 hours, 
I would consider the process to be 40 times efficient. 
If, instead of using daily feedstock weighing 40 kg, 
I got the same amount of biogas with just 2 kg feedstock (e.g. stale bread),
I would consider the process to be 20 times as efficient.
Multiplication of the two process efficiency figures gives you the 
total efficiency figure of  800.
Use of effluents as fertilizer: 
The effluent of a biogas plant contains most of the
minerals required by plants and it should therefore go back to the fields.
There is however a problem in an urban environment, 
because there are no fields in the vicinity. 
The slurry from our domestic biogas system is generally poured by the users 
into the toilet and flushed away.
Compact biogas system gives insight into agriculture: 
There is universal agreement among soil scientists that there exists a
positive correlation between the microbial population density in the soil 
and soil fertility. The reason for this correlation is that the
soil micro-organisms can make minerals in the soil available to the plants.
Agronomists recommend applying organic matter to the soil in the form of compost
in order to feed the soil micro-organisms. Our work on biogas showed that 
high calorie organic matter worked much better as feedstock in a biogas plant 
than a substance like dung, having a relatively low nutritional value. 
I tested the same concept in agriculture and got excellent results, 
when I applied sugar or green leaves to the soil. Just 10 kg (dry weight) 
per acre (25 kg per hectare), applied to a field, once every 3 months, 
gives as high yield as a field receiving the full recommended dose of 
inorganic fertilizers. Literally thousands of farmers in my state are now 
using this technology. Critics call this method soil mining,
but one should keep in mind the fact that just 1 meter layer of 
soil contains enough minerals to support agriculture continuously 
for 25000 years. The earth's crust is 100 km thick. 
A.D.Karve, Jan 01, 2009



aaron said...

i saw this post, but it is kind of tedious for a layperson to get into. im an environmental science student and researching anaerobic digestion. i would love to make an anaerobic digester and be able to utilize the biogas for cooking/heating/ etc. i would like to also try and compress it for vehicle use or pass it through a generator. do you have any experience with this???

Biogas Plant in Bangalore said...

This is a fantastic post,very well authored and easy to understand.
Domestic Biogas Plant in Bangalore