Table Of ContentMethane
Production
System
Jemmett Engineering
8 Hallam Gardens
Hatch End
Pinner
Middlesex
HAS 4PR
© Jemmett Engineering 1996
BASIG PROPERTIES a
ethene is a colorless, oderies4 gig in the group of hydrocarbons.
Tr i of course, @ fiaumable gaa. its chenies! representation is Ciy.
Depending on the area found, Methane gas makes up to 85 to 908 of of
natural gue reserves.
Since natural gaz le conposed aainly of nethane, the to gases in se-
parate states Offer similar themal characteristies » A cubic foot of
Natura gas ylelds a thepaal value of about 1000 British Therual Units.
The gaa Produced by the following procedure will have other “diluters”
within if, "shonefore having 2" lover thermal value, this type of Ketbane
ge actually offers ebout 00 BT's per cubic foot,
In Vohicles, about 220 cubic fect of gas equals 1 gallon of gasoline.
Intemal combustion engines require 18 cuble feet of nethane gas per
horsepower per hours
The concept of profucing Methane gas ty the process of Annerobic
Digestion tg not a new ones Netxane was produce by thie process as
eafly ao 1870, with methana productions pregrans set-up in Tidia as
early as the tum of the century, Of courge the secand Wornd Yar
notlveted Germany to produce bewhane gaz in digesters. This gue waa
then usel to mun tractors and other vehicles, and the final fy-product
which asker a good fertilizer yao spread upon the fields. Digestion to
produce methane gae also can occur in natural conditions, often being
Produced in murky eranp vatere. This has Drougts abort the tem ‘svaip
gee" in reference to nethane, There ape currently thousands of digest
fro in use all over the world, Varying fron extremely conDlex com
Rereial plante to backyard farm unite. Comtrics that ara prodaminant
in tne area ares India, South africa, France and several others in
Arica,
ANAEROBIC DIGESTION
Anaerobic Digestion is one of the most common biological procedures in
nature. Ae the nane implies, it means decay or breakdown in the ab-
sence of air (more specifically oxygen). This procsea ig similar to
fermentation, eince tiny micro-organions called ansercbes bring about
the transfornation, Like in the preduction of ethanol, digestian oF
fermentation must take place in two steps. Firstly, in the mediur of
digestion, certain micra-organiane break down the materiale into simple
sugars, alcohol, glycerol and peptides. When these conponents ate pre-
sent in the correct anounts and the conditions are correct, 8 second
group of aicro-organisme convert these simpler; broken dom molecules
Into methane ges, These methane producing uicro-orgenisns are particu~
larly sensitive to environmental conditions.
Tenperature and acidity are two areas thet require close attention.
Anaerovic digestion occurs within a temperature range fron 32° F to
Bhout 150°F. However, there are optimum conditions of teapereture
that promote naximin activity of the micro-organisms. This will pro-
duce more methane gas, Tenperatures below 60°F produce little gaz.
The best temperature to operate the digester at’ is the range betwean
83 and 950F, Tn acme Climates, this will be difficult to maintain, 30
efforts 0 get as close to tiie range as possible is all you can do.
Acidity in Anaerobic Digestion is important as well, AM range of 7
408 ig desired. Adding too tuch raw material to an existing
digestar that is producing gas, may slow the procedure down until
the bacteria can digest enough of it to create an environnent with
a BH range of 7 to 8. Gas production should then ocour,
On the other hand, a fermenting solution with a low acid Level will
cause the fermenting process to slow down until the becterla can
Produce enough acid (acidic carbon dioxide) to restore @ balance.
The two variables can ba measured of course; a thermeneter for
temperature and a simple acid nescuring ayster like Litmus paper
to deterzine the pi level in the solution. A low pi implies too
much seid, whereas a high BH implies 2 low level of acid.
Two other conponents that are important in the digeeter are the elements
Carbon and Nitrogen. Hoth elements are required ty the bacteria to
live in the digester. However, the bacteria consumes Carbon at the rate
bf about 30 tines ‘that of Nitrogen. Consequently, the system wil)
produce maximum anounts of gaa when the material put in the digester
haa a carbon/nitrogen ratio of about 30 to 4, As in the case of the
acidity, the bacteria will veually compensate for the imbalances and
ereate this ratio it needs. This ocours at the expense of a low gas
Produeing rate until this ratio is achieved.
The gas produced in these sinple digesters is not pure methene, Tt nor-
nally contains } parts methane to 1 part carbon dioxide, with trace
amounts of hydrogen, nitrogen and other elenents characteristic to the
original materials used in the digester.
me slurry that is nomally left after the digestion is complete,
ig nagnly conpoced of organig humus, with smaller avounts of nitrogen,
Phoapraten and potash. This final wy-product ie a valuable source of
fertilizer for furthur productions on fare of vegetation.
Figure 41 Conpodstion of Gas Produced ond Reaultant py-Product
Shteage elengnte Gas Produced+
Hy Ny ete. 658 Methane
30R Garbon Dioxide
race Elementi
— itydrogen, Nit
rogan, etc.
Figure 1 Cont'd: Resultant By-product after Digestion
21S variable elements relate? to original
nator
2 1 potach,
\<——— 18 phosphates
| ———~ oft nitrogen
75% organic
humus
Incidentally, the time factor involved in starting this type of syaten
ean be as lang a8 a month, wut often requires 2 to 3 weeks. A great
Geal of patience 1s reguired when starting un this type of systen.
Don't geb too discouraged remember, the bacteria will require time to
break dom the meteaites in tho slurry inte alcohole ent cugars, before
the Seaond type of baoteris cer produce gas. “actly, it may bo hoceceary
for the Second bacteria type (the gac prodveing oned. ++) to adjust the
Garbon/itrogon level or the soidity before substantial amounts of gas
san ba produced.
SIMPLE ANAEROBIC DIGESTER
A Digester yan ba a vary simple systen, The main component required
‘to meke a simple digester is the vescel that wilt contain the slurry,
in order to produce gas within. There must be @ way of filling
the vessel, ag well as a way of extracting the eae aa well. 0 page 5
ig a simple digester, shown purely for denonstrative purposes only,
and is not recommendad for construction in ite caact state. Although
correct in coneapt, it lacks a method of gas storage in a safe manner.
GAS STORAGE
Qnee the gas ig produced, a practical and SAFE meane of storing it
ig essential. Ary container that hae air in It will mix with the
Methane gaa ac it onters it, producing an EXPLCSIVE combination,
It 4a therefore neceesary to construct a containor with ABSOLUTELY
Nig AIR inside of it, before the mathano gas is introduced into the
storage vessel.
Figure 2+ Basic Anaerobic Digester
eas.
ovtrur =|
service door
presgure valve
‘Thig baste digester will produce a modest amount o7 Methane gas,
It is a good model to try cut, in order to familiarize yousel? with
the coticept of methane production, A simply container for storing the
gas ie still required. This must be done of course is a safe manner.
This digester is called a batch-feed system, where @ slurey ta
introdaged Into the digester by way of a service door, and then
Sealed. After a couple of weeks, nen the conditions within the
tank have been adjuoted by the bacteria, fermentation commences.
An airapace must be left at the top for two Yeaaons: Firstly, the
Sivet group of bueteria (the aerobes) require come oxygen to broak
dom the slurry into simple walectles, Secondly, foaning usually
oecure during the digestion process, especially in the aerobic atage.
Ge the space is not alequate, foam will, travel ito the pipes above,
After a couple of wonthe, the batch will no Longer produce gsc, At thie
point, the drain valve ndy be opened, and the decouposed natter re—
Boved: the container aay be flushed out through the service door, but
leaving a small amount of 014 slurry in the container will speedup
fermentation when the new batch is introduced.
Tae following page outLines the construction of the basic
Anaerobic Ligester, on a batch feed basis
LEGAL WAIVER
‘These plans are your guidelines only. de take no responsibility
tn regarés to the success or safety of this project. Acceptance of
those Plana warrants thie on your Part. Proceed with this project
entirely at your own risk.
Remeubor that methane gas ig a very Slammable gas. Always use con-
nop eenge whan dealing with the protuction, storage and cunsunption
of methane gas. Methane gas ix equivalent to 120 Cotane gasoline.
When mixed with alr it beoones and explosive conbination! Alvays
wear proteative eyewear when near the digester, or when handling
the gas in any manner. Like propane and natural gas, methane
ean asphyziate a person in wn enclosed area.
BATCH DIGESTER CONSTRUCTION
Thie Little digester will preduce encveh Treo gas to provide heat
oh e. stove for wt least { meal per day, Modest applications, 1iko
Uignting snall reons by Way of lantems era caazing are ideal for
this system. It esa te built for a very epall amount of money as well.
A'sinple imer tube fron a lerge tractor tire will make a perfect
container for the gas becavaer
= 4t 4s relatively inexpensive and eusy to obtain
2 4 may be purged* easily by rolling into x tight mass
= it antonatically creates a pressure for feeding inte
appliances, which is safe
- Eells stout the right volume that this generator can
produce, therefore waking it compatible to the digester.
PURGING a container or Line mesng to remove all the air from it.
this is important fron a safety viewpoint to prevent an explosion
of methane and air, ag nentioned earlier, There are two simple ways
of doing this:
“Collapsing the container, and exhausting the air from it
“Displacing the air with another eubstance in rigid lines and
containers
The container ueed in this aysten will be @ atandard 44 gation of
drum. Bake cure that the one you get is relatively elean, with no
rust whatsoever, Tf there were any toxic chemicals, like cleaning
fivids, solvents, ete., flush out the tank several tines with soap
and water, followed bya flush with cold water for several minutes.
2
A agoura bape can be made out of a few concrete building blocks. It te
‘vent to Keep the container off tha ground a few inches, to provant
uoisture underneath the container from forming rust.
‘There ave nomally two vent holes, about 23" wide on the top of the
dyum. Those alone may be adequate for filling the drum with your
elurty mixture, Reuember that these met be in good condition and
peal gne tight. If a larger acoses door is required, 9 gas tight plate
gan be added after cutting out the appropriate hole. an autonotive
air fivter housing wakes a perfect, easy to find plata for this purpose.
Binoe they are normally secured with one or tro bolts to the top of
the auto's cartoretar; 2 small bracket will Rave ta be fustened acrose
the botton of the housing, with « bolt te fucliitate attacheuent of
the plate.
Figure 31 Opticnel Access Pate Configuration
original mount hole
cover Plate
bolt
“sattached strip, nuts
nousing
Pigure ‘1 Houmting the Accass plate inte
‘tha Top of the Drur
top of drum
A
angle iron nowsing
peveral
1" angle irons
to attach to
the top of the
ve yun, and sold-
swhen cutting out the mole \+ er the sean to
in the top of the drum, make {1 L—1 make a gastient
fltees
sure that tt isa tignt fit,
so that the joint can ulso
‘be soldered.
a,
Lastly, driti a snug fitting hole of 3/4" into the tep of the drum
at sons convendent Location and install the followings
Figure 51 Fressure Valve Configuration
a
3" pipo~ elue
faith epoxy te
> GAS OUSTUT
|_— pressure varve
ip: goint- the fitting to the inner tube is
quite eal, Therefore an adap-
for ‘T! joint is the ansyer.
The main’ Line should be #"./A
standart serew-on tire hoco
will fit with the aid of sone
epoxy glue.
‘tire hose, 4
Figure 61 Coupleted Digester
> sas oveeur
output Lino with valve
service door
avain valve
___ brick base
inner tube
For larger,cutpute, this unit can be joined to another in » series
contigveation, For double gas outme, Stnee these digesters are
simple to tuiid, three or four can be employed for added output.
OPERATION OF DIGESTER
The composition of the slurry, of course will determine the degree
of success of your new digester. As nevtioned earlier, a carbon/
attregen ratio in the slurry of 30 to 1 {9 what is needed. Tha
alaget foolproof substanca for this systen is sone sort of manure (1)
whether it is from cows, pigs, chickens, horses or whatever.
Adding other material ilke grass cuttings or leeves is acceptable,
however by themselves they contain almost no nitrogen. They will
therefore not ferment, or fement at an insignifiesrt rate. With
unimown anteriais, At'#ill be inpossible to determine the curbon
to Mitroger. pation without the aid of a lab analysi. The other
alternative is to go akead by tria) and error.
on the farm, nanure of sone gort should be readily available. As a
reault, apetating a aysten Like this one showd bequite eagy.
In the city and cuburban areas, manure ic of course not readily
available. However, Leaver ard’ grasa clippings can be ued from
the backyaml. These Substances san be stixed with Host of your
organic garbage that 1 normally discarded as trash, The erly
garbaga that in useless is the group of dry goos like paper,
bareal boxes, cellophane plastica ete. with a good varlety of
trash, 18 is quite probable that the systen will eventually deliver
free fethane gas. You'd be surprised at the ancint of organic waste
‘that the average household produces in just one day. Moreover, a
high degree of variety in the nature of thesa organic conpmnds
wi}1 more than likely offer the correct acidity and earken to nitragen
ponditions that are required.
Ideally, the slurry that works the best in the digester consists oft
= 3 to 4 gallone of liguified ssnure
= 40 gallone of water
= enough gress cuttings and leaves (a 50-50 retio)
to fL11 the container to within a foot of the top.
Then stir the alxture well.
This systan, with solids will produce gas after about 2 weeke;
peak in produotion after about 6, and then diminish in obtput. There
will be little, if any, significant production after about 12 weeks.
Tigu4d aninal wastes offer good output after only about 1 week of
ingubation, howaver Liguid waste 1s diffieblt to accumilate and
handle on the farm,
Shut the pressure vatve off, and place the tube normally leading to
the inner tractor tube Anto's glass of water, When bubbles begin to
vccur ata steady rate, the system is generating gaa.
