A project of Volunteers
in Asia
Fuel Gas from Cowdung
by B.R.
Saubolle and A.
Bachmann
Published by:
Szhayogi Press
Tripureshwar
Kathmandu
NEPAL
Available from:
UNICEF
P.O. Box 1187
Kathmandu
NEPAL
Reproduced
by permission.
Reproduction of this microfiche document in any
form is subject to the samerestrictions
as those
of the original document.
B.R. SAUBOLLE
. ~A~~~A~N
FUEL GAS FROM CO
THIRD
E3.R.SAUBOLLE
EOITION
AN0
A.BACHMANN
SAHAYOGI
PRESS
KATHMANOU
Published
by:
Sahayogi
Press
Tripureshwar
Kathmandu
First
Edition
: April
1976
Second Edition
: April
1980
Third
: September
Edition
1983.
the
authors,
reserved
by
Copyright
is
granted
for
hereby
but
permission
is
or
the
reproduction
of
any
part w text
publication;
non-profit
drawing,
for
however,
tile
whole
booklet,
or any major
without
portion
should
not
be reproduced
permission.
Anyone making
use of material
herein
should
acknowledge
presented
the
authors
submit
to
the
source
and
a copy of the excerpt.
Printed
in Nepal
at Sahayogi
Press
THIS
BOOKLET
IS DEDICATED
TO THE MILLIONS
OF VILLAGERS
IN THE HIMALAYAN
KINGDOM OF NEPAL
WHOSE NEED FOR FUEL
HAS BEEN THE AUTHORS’
1
SOLE REASON
FOR WRITING
IT,
GRANT
COWDUNG.
YOU
YOU ARE TO BAKE Y3UR BREAD ON THAT,
EZEKIEL
4.15
Rev.
Saubolle
is
the
pioneer
of
biogas
in
Nepal.
His
oil
drum
built
plant,
in 1960 at St. Xavier's
School
in Godavari,
twenty
kilometers
south-east
of Kathmandu,
was used for
boiling
which
tea,
"Father"
offered
to his
guests.
The biogas
plant
offered
brilliant
demonstration
of
fuel
from waste long 'before
it became "fashionable".
Many of
us
here
in
Nepal
were
inspired
by his pioneering
work.
Late
Rev.
B.R. Saubolle,
1904 - 1982
S.J.
Rev.
B.
Saubolle
came to Nepal
in
the
fifties,
and
early
loved
this
country.
A versatile
man
and
a
thinker
great
of things
small and beautiful.His
interests
ranged
from
bee-keeping,
roses,
solar
heating,
to orchid
cultivation.
To many
Godava,r..i
)
“Pn+her”
villagers
of
w -i--eWBS
a man they
were proud
to call
a friend
and one of their
own kind.
BIOGAS NEWSLETTER
CONTENTS
9
Preface
Introduction
Gas Production
10
-.
11
Slurry
11
Pit
12
Volume
output
and Temperature
Output
and Pressure
13
-
15
-
16
Gas
18
Consumption
Nature
of
Points
to be considered
constructing
before
a Plant
19
Sheet
21
Gas Drums
24
Data
Constructing
- The Pit
a Plant
25
25
- Input
- Paddle-Wheel
Mixer
- Gas Outlet
L Moisture
Release
27
29
30
= Gas Drums
34
- Flame
37
Trap
- Gas Pipe
Using
the
Line
Dimensions
38
Gas
- Burners
40
-Lamps
47
- Running
Engines
50
Double
Chamber
Construction
Gas in Bags
Stirrer
or No Stirrer?
Gas from
Night
A Biogas
Demonstration
Chinese
Biogas
A Nepali
Version
A Comparison:
Possible
Temperature
54
-.__.__--
62
_
64
67
Soil
Plant
70
73
Technology
of
Chinese
the
vs.
Chinese
Design
Indian
Troubles
Table
-
---
94
99
101
102
PREFACE
more
than
a quarter
century
It
was slightly
ago
biogas
plants
first
appeared
as a practical
that
renewable
alternative
The
source
of
energy.
idea
took
time to catch
on and to be accepted,
but these
use.
In a recent
fiveplants
are now in world-wide
itself
the
task
of installing
year
plan
India
set
gas plants
a year.
China
claims
at
25,000
cowdung
the
present
moment
to have
some 7,000,000
present
scattered
all
over the country,
ranging
biogas
plants
from small
family
plants
to huge government
installations
for
running
buses,
trucks
and diesel-electric
besides
steadily
providing
a collosal
generators,
rich
fertilizer
and
humus
for
field
and
amount
of
garden.
The welcome given
to FUEL GAS FROM COWDUNG by readers
Since
been
very
heartening.
the
world
has
around
it
first
appeared
it has several
times
been reprinted
at the special
request
of UNICEF. We have the pleasure
third
edition,
the
public
the
present
in
offering
more useful
to readers
which
we hope will
be still
in developing
countries.
borrowed
rather
edition
we have
this
In
preparing
the
appeared
in
which
have
from
articles
freely
to
do
For
permission
BIOGAS NEWSLETTER of
Nepal.
also
We wish
the
Editors.
grateful
to
so we are
Services
Consulting
Development
and
the
to
thank
for
kindly
allowing
us
Nepal,
of
Butwal,
(D.C.S.)
produced
appliances
designs
of
several
include
to
and perfected
by them.
B.R. Saubolle,
S.J.
Andreas Bachmann
INTRODUCTION
areas
of
South-East
Asia,
remote
living
in
People
sub-tropical
countries,
where
tropical
or
other
or
is
hard
to
not
available
and fuel
electricty
is
abundant
and efficient
fuel
have a very
cheap,
get,
This
from
ordinary
cowdung.
produced
the
in
gas
is
generated
with
the
(marsh
gas or methane)
gas
a slurry
of cowdung
by letting
greatest
ease simply
and water
ferment
in a ;Yell-like
pit
without
exposure
LO
the
surface
and
collects
The gas rises
to air.
is piped
to the kitchen
stove.
in a drum, whence it
A farmer
with
a couple
of bulls
or buffaloes
for
ploughing
and one or two cos for
milk
gets
enough
sufficient
to produce
gas for
all
every
dung
day
family
of six.
The
the
cooking
needs
of a village
and hygienic,
the pots
do not
get
cooking
is clean
and the gas is
there
is no smoke or smell,
black,
the
gas
to
cook
extracting
after
non-toxic.
And
and to light
his house at night,
the farmer
his food,
well
fermented
and
the
left,
has
all
still
dung
to fertilize
his fields.
rotted,
11
GAS PRODUCTION
TIME
animal
dung
(from
horses,
Fresh
cowdung,
or other
pou3try)
buffaloes,
donkeys,
mules,
yaks,
Pigs,
diluted
with
water
and fermented
by bacterium
methanodelivers
exposure
to
air,
90% of
without
genes,
within
a
period
of
four
weeks,
its
potential
gas
more than half
of it
within
the first
eight
or ten
Six
weeks of fermentaticn
produces
about
98%.
days.
the
fermenting
pit,
in which
daily
additions
Hence
enter
at the
bottom
and gradually
raise
\,f
slurry
should
be large
enough
to
at
the
top,
to overflow
addition
for
a minimum of four
weeks
hold
each day's
or a maximum of six,
i.e.
from
30 to 40 days.
In
volume
of
the
pit
should
be at
the
other
words,
or better
40 times,
the volume
of
least
30 times,
siurrjr
added daily.
SLURRY
dilution
of
fresh
dung with
water
for
The optimum
one that contains
from
7% to
slurry
is
the
making
readings
the peak being 896, Hydrometer
9% solid
matter,
1.030
for
approximately
gravity
of
show a specific
The
around
1.100.
8% falls
7% and 1.190
for
9%.
automatically
by mixing
right
percentage
is obtained
a given
volume
of dung with
from
one to one-andthat
the
volume
of
water.
The fact
times
a-half
plants
have
been
thousands
of
upon
thousands
gas
without
the
use
decades
satisfactorily
for
working
that
this
instrument,
useful
of an hydrometer
proves
necessary.
A good
though
it
may be, is not strictly
slurry
is one in which the dung is broken up thoroughly
even mixture
having
the consistency
and makes a smooth,
If
the slurry
is too thin,
the solid
of thin
cream.
bottom
instead
the
separates
and
falls
to
matter
thick,
too
of
remaining
in
suspension;
if
it
is
freely
to the surface.
In either
the gas cannot
rise
case the output
of gas is less.
It
has been found
that
the optimum
pH for
digesting
slurry
is around
8. When starting
a plant,
the early
fermentation
is
acid
and
much
carbon
dioxide
is
off;
given
but
the
acidity
gradually
diminishes,
the
contents
of
the
pit
become alcaline,
and once
methane
generation
predominates.
If
the pit
is overloaded,
or the slurry
too
thick,
acidity
increases,
carbon
dioxide
is
much
formed,
and the
gas won't
burn,
users
prefer
a
proportion
of
1:l
l/4
May
(4 parts
dung to 5 parts
water)
and enjoy
troublefree operation.
The acidity
of the effluent
is measured
with
pH paper
(narrow-range:
6-9).
It
should
read
from 8 - 8.5,
which
is slightly
more alkaline
than
the effluent
of a municipal
sewage plant.
VOLUME OF
PIT
As was said
above,
a volume
from 30 to
Thus:
PROPORTION
1:l
1:l
1:l
DUNG
l/4
l/2
2.5
2.5
2.5
cft
cft
cft
l/4
l/2
75 ltr
75 1tr
75 1tr
the
fermenting
40 times
the
WATER
2.5
3.1
3.75
cft
cft
cft
SLURRY
(x 30 or
5
cft
5.6
cft
6.25 cft
pit
slurry
should
have
added daily.
VOLUME OF PIT
40)
=
or
150
168
187
or
or
4500
5100
5610
or
or
200 cft
224 cft
250 cft
OR
1:l
1:l
1:l
It
is
the pit
150
170
187
ltr
1tr
ltr
recommended
to use 1:l
40 times the daily
slurry.
or
75 ltr
94 1tr
112 ltr
=
=
=
1:
1
l/4
or 6000 ltr
6800 ltr
7480
ltr
and
lnake
Experience
has
shown
that
Indian
villagers
consume
on an average
15 cft
(425
ltr)
of gas per person
per
day.
So for
a family
of six
about
100 cft
(say
3000 litres)
of gas would
suffice.
This
output
would
require
a pit
of
at
least
double
that
volume,
200
cft
or 6000 litres,
say 5 ft
(1.5
m) diameter
by
11 ft
(3.40
m) dep,
tkaing
2 l/2
cft
or 75 litres
of
fresh
dung
every
day.
12 litres
Allow
fresh
dung per person per day.
13
BACTERIA
For
may
a new Plant,
from one of the
starting
be
obtained
the
necessary
bacteria
following
sources:
a) Spent slurry
from another
gas plant;
b) Either
sludge or overflow
water from a
septic
tank;
c) Horse dung or pig dung, both rich in bacteria;
d) Oooze from the bottom of any dirty
pool.
Without
a month
added
to get
OUTPUT AND
bacteria
started.
fermentation
may
take
about
TEMPERATURE
At a temperature
of 85 OF ( 30 OC), 1 cft
of dung
so
that
if,
delivers
40 cft
of gas in four
weeks;
5 cft
are added daily,
the daily
output
for
example,
of gas
will
be about
200 cft.
This
is not a matheaverage
depending
on
constant:
it
is
an
matical
At higher
temperatures
the health
and feed
of COWS.
the
output
is greater,
being
50 cft
or more at 90
it
drops
to
about
20 cft.
while
at
55O
degrees F,
MEAN TEMPERATURE
DURING MONTH
85oF 1 29W or over
75°F 1 24%
65oF 1 18%
55OF , 12oC
OUTPUT OF GAS
(cft/lb.dung)
(ltr/kg
dung)
1.5
92.7
1.0
61.8
0.8
49.5
0.5
30.8
REMARKS
Excellent
Good working average
Serviceable
Hardly worthwhile
In
places
where
for
the
greater
part
of the
year
the mean temperature
is 18
OC (65
OF) or more,
a
gas plant
is
really
worthwhile.
In winter
the
gas
diminish
unless
something
is done to warm the
will
digesting
slurry.
Several
methods
are commonly recommended:
is
a help.
1 - DEPTH - Depth
In
the
tropics
and lower temperature
latitudes,
even in the
Himalayas
at 5000 ft.;
the
temperature
at 4 m below ground,
hardly
drops
lower
than
15
OC. especially
if
the
slurry
is added hot, and some gas can be produced.
14
INSULATION
Fermenting
2 slurry
generates
practically
no heat (only
about
3 *C>. Pit
temperature
slightly
higher
only
than
the outside
air.
is
Yet
if
the little
heat generated
is prevented
from dissipating
by conduction,
something
is gained.
The insulamaterial
must be kept
quite
dry.
ting
If
damp, it
instead
CEUI
chill
of keeping
warm.
In
the
tropics
it
should
also
be something
that
white
will
ants
not eat.
3 - HOT SLURRY - This
helps
a little.
The daily
in the order
of only
2.5% of pit
volume,
input
is
so that
it
cannot
make very
much difference,
but
certainly
it
is
more helpful
if
the
slurry
is hot
(35 OC) rather
than chillingly
cold.
4 - HEATING COIL - When building
a pit,
a coiled
2"
pipe
of
diameter
can
be
installed
inside.
It
recommended
1000 cm2 of coil
area
per
is
to allow
3 m3 of pit
volume
(1 sq.ft./lOO
cft.).
The
coil
should
be heated
with
water
not
more than
60
OC
(140 OF) or the slurry
will
cake on the coil
surface,
A thermostat
set at 35 OC (95 OF) should
be installed
in
the
slurry.
The gas used
in
heating
coil
the
is repaid
three times over by the increase
of output.
Heating
could also be done by solar
collectors.
5
around
in it.
matter
-
COMPOST TROUGH the upper
half
of
The heat
generated
keeps the pit warm.
Some users
build
a trench
the
pit
and make compost
by the composting
organic
6 - PLASTIC TENT - If
the pit
and a couple
of
metres
of
ground
all
around
it
enclosed
in
a
are
clear
glass
or
plastic
structure,
the
hot-house
effect
keeps
the
slurry
warm.
A few years
ago it
was claimed
that
this
system kept gas plants
functioning
in Korea
in
but
the midst
of
snow and ice;
on the
our
own investigation
has
led
us to
spot
its
doubt
that
efficacy.
However,
we do believe
in
milder
winters
(above
plastic
freezing),
the
tent
may really
be useful.
We have not experimented
with this ourselves.
15
SURFACE DIGESTER A horizontal
digester
built
above ground
on an east-west
axis
and painted
black
would
heat
up in the sun, more so if
covered
sheeting.
with
plastic
If
it
gets
too
hot
in the
and white wash the digester.
summer, remove the plastic
7
Rather
than
bother
with
any measures
outlined
above,
it is far
simpler
to be content
with whatever
amount
of gas
forms
in
the
cold
months
and 'replace
the
with
some other
fuel.
One will
shortage
then
have
cooked
on free
cowdung
gas for
nine
months
of the
ye= l which is not at all bad.
It is good to remember that
cows' urine
also
ferments
and forms
If
a little
of
this
is
gas.
used with
water
for
making
the
slurry,
the
output
of gas is
But
too
thereby
increased.
much urine
is
harmful:
it
increase
the
ammonia
content
would
more
than
the bacteria
can tolerate.
About
one-third
of
the
water required
can be replaced
by urine.
OUTPUT AND
PRESSURE
The output
of gas varies
with
the pressure
to which
the fermenting
slurry
is subjected.
Taking
atmospheric
pressure
as normal
(the
drum being
perfectlycounterit
has been found
that
under
a pressure
balanced),
of 4" water
head the production
drops
by 596, while
under a negative
pressure
of 4!', production
is about
10% above normal.
In practice
, however,
a little
gas may be sacrificed
the
drum not
being
to convenience,
counterbalanced
but
left
floating
on the slurry.
There
is
at all,
steady
pressure
at
slight
all
times
caused
thus
a
weight
of
the
drum,
and the
gas is
ready
by the
for
use
at
any moment without
one's
having
to go
remove
balance
outside
and
weights.
However,
in
colder
climates
where gas formation
is less
abundant,
wiser
to
counterbalance
the
drum
and thus
it may be
facilitate
the
production
of
gas.
But
it should
be
noted
that
a negative
pressure
could
be dangerous
if
there
is
a slight
leak
in the gas drum on the
delivery
pipeline.
Air
is
drawn
in and the air-gas
mixture
may attain
explosive
proportions
(596 - 15%).
16
All
it
then needs is a careless
match or a backfire
with
no flame
arrester
in the
line.
We know of one
such drum which shot up in the air like
a rocket.
A simple
way of measuring
gas pressure
is to disconnect
the gas pipe
at
a lamp or stove
and push
into
a
tumbler
of water till
the gas ceases to bubble
through,
the
depth
then
measure
of water
that
just
balances
the flow of gas.
CONSUMPTION
of
for
A pressure
s-afficient
pressure
8
2”
10 cm (4")
I-S-CL
V" b&L lighting
gas
rir.g
water
and
CcnsuEes
head has
heating280
lif*es
--
--
been found
u'7der this
il
(10
cf+-)
of gas per hour
and boils
4.5
ltr
(1 imp.
gall.)
of water
in under
20 minutes.
Lamps using
40 candlepower
mantles
take
2.75
cft
(78
ltr)
per
mantle
a high
pressure,
of course,
stoves
per hour.
Under
hotter
and
'Turn
burn
lamps
brighter.
For
working
combustion
internal
engines
the
consumption
gas
per h.p.
is about
15 cft
(425 ltr).
*Some authors
give a slightly
higher
figure.
A
NOTE
ON OUTPUT, TEMPERATURE AND
CONSUMPTION
In this
book the calculations
for pit
size
and output
on a temperature
of 27c29 oC
of gas are based
(800,
85
OF), As the temperature
rises,
production
increased,
is
greatly
being
double
or
more
when
the slurry
in the
pit
is
35
OC. In our tropical
summers,
in places
where for
days no end the ambient
temperature
is over
38 OC (100
OF),
a family
size
pit
calculated
to serve
6 persons
may very
easily
produce enough gas to cook for 12 or 15.
We say (p. 20 > that
we need 15 cft
gas per person
This
is
an average
when meals
are cooked
per day.
for
6 to 8 persons.
15 cft.
(425 ltr)
will
suffice
one burner
for
1 - 1 l/2
hours
depending
on its
* Sathianathan:
Biogas
Achievements
and Challenges,
p.74
17
obviously
This
amount
is
far
size
and efficiency.
too little
for the cooking
needs of one person
alone.
On the other
hand,
the greater
the number of people
lower
is
the
cooked
for,
the
Per
gas consumption
of 20 persons,
it
takes
When one is cooking
person.
cook
for
25 or
28
additional
gas to
little
very
in the same pot.
output
at
the
mentioned
above,
viz.,
Both
points
consumption
average
temperatures,
and
the
higher
are well illustrated
by the installaof gas per person,
Bihar,
tion
at Holy
Family
Hospital,
Patna,
India.
The digester
there
has a volume
of 80 m3. Applying
for
family
plants,
this
pit
is ought
the guidelines
to prodclcz
40 m3 of gas per d=xr
-=-v 9 wh i c h at 425 1itres
per person
would
suffice
for
94 persons.
As a matter
already,
in summer, four
for
several
years
of fact,
meals a day have been cooked for
400 persons
entirely
on cowdung
Tn winter,
and sometimes
even
in
gas.
the
number
of
persons
increases,
summer whenever
heating
with
bottled
gas or with
some supplementary
coal is necessary.
From all
1)
21
this
two facts
stand
out
clearly:
the summer temperature
(37 OC - 45 OC) greatly
increases
the output
of gas;
when large numbers are cooked
for,
the average
much
person
is
very
consumption
of
gas per
lower.
measuring
the
gas.
The hospital
has
no means
of
Some is lost
because
at night
gas bubbles
out from
under
the drum (30 m3 capacity)
and is lost
to the
Another
the
air.
very
interesting
point
is
that
pit
is not being
used to capacity.
The daily
input
of slurry
is
a trifle
over
1 m3, whereas
the pit
ought to receive
2 m3. So this
particular
installation
could
produce
it
actually
very
much more gas than
The
half
the
does.
input
approximately
represents
daily
contribution
of
the
animals
and birds
on the
small hospital
farm (cows, buffaloes,
pigs,
chickens).
,
18
NATURE
O'r
GAS
with
a clear,
Cowdung gas burns
pale
electric-blue
with
or
without
the
flame,
admixture
of
air.
The
flame
is invisible
in bright
daylight.
It
is hotter
gas or oil
gas,
than
coal
having
a BTU value
of
approximately
600 per cft (or 5380 cal per litre),
authors
though
no two
seem to agree
on the
exact
Probably
the
gas
varies
somewhat
from
plant
figure.
plant*
Analyses
of
to
cowdung
show that
its
gas
composition
is,
with
slight
variations,
65% methane,
25% carbon
dioxide
and
10% other
gases,
in
very
small
quantities.
The gas is non toxic
and virtually
Mixtures
odourless.
of methane
and air
are explosive
if the methane content
is from 5% to 14%.
MANURE
Spent slurry
dried
in the sun constitutes
an excellent
which
manure,
appears
from
tests
to
be richer
in
nitrates
thsn
ordinary
farmyard
manure,
and slightly
superior
to it.
In liquid
form
too
it
is good if
diluted;
but dried
slurry
is preferable.
CONCLUSION
Anyone with
a few head of cattle
can provide
enough
for
his
daily
cooking
needs
and
still
have
manure
gas
for
his
garden
and fields,
better
manure
than
he
otherwise
would
have
be
merely
dung
letting
the
rot aerobically
in an open pit.
Fermenting
and fermented
slurry
gives
off
no odour.
Insects
and small
animals
falling
into
it
cannot
survive.
Dried
slurry
is
as clean
and fresh
as sawdust
and be be stowed
away in sacks till
needed for use or for sale.
POINTS TO BE CONSIDERED BEFORE' CONSTRUCTING A PLANT
For what
purpose
is
the
plant
required?
a)
In
GAS FOR COOKING ONLY this
case
the
height
of
the
gas drum is
usually
one-third
the
depth
of
the
since
pit,
has to hold
more gas than
for
it
never
a couple of hours'
use at a time.
bj
ONLY GAS FOR LIGHTING
For
this
the
be large
enough
to
drum must
hold
all
generated
in
the
24 hours
to
be
gas
able
to deliver
it
in four
or five
hours.
A pit,
at 30 C, generates
half
its
volume
in
a day.
So the
drum must
hold
half
the volume of the pit.
cl
GAS TO RUN A GENERATOR EIGHT HOURS A
DAY FOR A SMALL INDUSTRY - Here
again
the
drum
must
have
at
least
half
the
pit volume.
d;
RICH FERTILIZER
FOR A GARDEN OR FARM
Gas not
needed.
Here
the
drum
can be
eliminated,
and the gas allowed
to escape
into
the
atmosphere
through
a
water
seal.
4
BOTTLING OF GAS FOR RUNNING CARS - Find
out how many cft
of gas, when compressed,
can fill
the
size
of bottle
you intend
to
use.
drum
The
should
be
at
least
large enough to hold that amount.
20
How large
should
the
plant
be?
The average
oriental
villager
uses 15 cft
(425 ltr)
of gas per day.
This
amount
is generated
from
10.6
ltr
fresh
dung
(at
30
oc).
Western
cuisine
would
require
more,
perhaps
500
ltr
from
12.5
ltr
gas
dung per person.
The volume of fresh
dung available
every day multiplied
the
volume
of
the
pit
most
suitable
by 80 gives
to handle
that
amount of dung. The pit
volume divided
b Y 2 glVeS
the
volume
of
gas generated
daily
(at
divided
by 425 (or 500) gives
the
30 w ; and this
number of persons
served.
Whence:
D
x
80= P/2
= G/425
(or
Or beginning
with
the
number
the size
of pit
and the amount
work the formula
backwards,
thus:
Pers.
x 425 (or
500)
=
This
formula
is
correct
if
the proportion
1:1.
The total
regardless
of
its
proportions,
the pit volume.
Having found
turn
to the
most suitable.
G
500)
=
Persons
of
of
persons,
to
find
dung needed daily,
x
2 =
P/80
=
D
the
slurry
is made in
daily
input
of slurry,
of
should
be l/40
the approximate
volume
Data Sheet and select
of pit you require,
the size
of plant
21
2 z a3 0 Ln 0
v I I . . . .
tn
ln c4: 0r’
22
23
l
In
the
40-day
slurry
is l/40
cycle
the pit
the volume
volume.
of
daily
a
In
the
30-day
slurry
is l/30
cycle
the pit
the volume
volume.
of
daily
e
The
the
l:l,
e
At temperatures
of 85OF (3OOC)
the
gas produced
is 40 times
daily
of
dung.
This
figure
used in Lhe calculations.
and above,
the volume
has
been
e
IF
die
above
calculations,
there
t 1-e figure
has been slightly
off
for the sake of convenience.
here
and
rounded
double
figures
volume
obtained
and second,
from
for
gas show first,
from
g slurry
of
a slurry
of 1:l l/2.
It
is
worth
noting
from
the
above mentioned
table
that the management of a gas plant
is somewhat elastic:
it
leaves
the owner a useful
latitude.
For example,
if
it
is required
initially
to cook for
10 persons,
but it
is foreseen
that
at a future
date
food will
have to be prepared
for
18 or 20
a No. 4 plant
could
be built
and run at first
on a 40-day
cycle
with
a slurry
of
I:1
l/2.
It
will
then
serve
10
or
12 persons.
When the
need
for
gas
increases,
the pit
can be run on a 30-day
cycle
with
a slurry
of 1:l.
The output
will
then suffice
for 18-20 persons.
The change
over
from one cycle
to another,
or from
should
be done
one density
of
slurry
to
another,
volume
the
increasing
or
diminishing
gradually,
little
by
its
proportions,
altering
of
slurry,
or
taking
a week or ten
days for
the complete
little,
A sudden alteration
is likely
to affect
change over.
the pH and produce dioxide
instead
of methane.
24
Volumes
Diameter,
cm
Area, sq.cm.
Depth, cm
Volume, litres
Burners
Hours (280/hr/b)
Refill,
ltr/hr.
40-cycle,
Refill,
30-cycle,
The
that
ltr/hr.
GAS DRUMS
of different
sizes
recommended
1:l
110
9498.5
120
1140
1
4
76.6
140
15386
120
1846
2
3.3
125
165
21371.6
120
2564
3
3
186.6
190
28338.5
120
3400
3
4
250
1:l
103
166
250
333
above rates
of refill
the temperature
in the
pit
are correct
on condition
is 85 OF (30 OC).
A size-l
4 hrs
at
drum will
one filling,
pit
will
most
probably
not
be used
for
a stretch;
may be for
only
2 hrs.
So the
hold
enough
gas for
two meals
with
only
and more gas will
fill
in between.
The other
at a time.
sizes
Their
will
owner
surely
not use all
the
will
learn
to economize.
burners
People
to build
pits
are advised
tc choose
wanting
a size
larger
than
need
(provided
strictly
they
they have enough dung).
This
will
make up for slower
production
of
gas
in
lower
Any extra
temperatures.
gas could be used for lighting.
25
SUGGESTIONS FOR CONSTRUCTING A
PLANT
Many different
shapes
and styles
of gas plants
have
horizontal,
vertical,
cylindribeen experimented
with:
cubic.
The design
won overwhelming
that
has
cal,
its
reliable
for
performance
in
popularity
many
countries
is
Indian
different
the
pit
design,
of
which
over
70,000
plants
are in use in India
alone,
Korea,
and many
25,000
in
in
Taiwan,
the
Japan,
Philippines,
Vietnam,
Indonesia,
Pakistan,
Iran,
Thailand,
and who knows
Africa,
Papua New Guinea,
This
else.
is
proof
enough
of its
efficiency
where
and outstanding
worth.
This
is the design,
basically,
that we recommend here.
We describe
below the construc2-size
plant.
of
a No.
For
other
sizes
tion
see
the Data Sheet.
l-
THE
PIT
Make the
inside
diameter
of
the
pit
5 ft
and its
inside
depth
11 ft
4".
Of this
depth
2 ft are above
ground
level
and 9 ft
4" below.
Cement construction
is not necessary:
baked brick
bound with
lime mortar
or with
clay
is
sufficient.
Any porousness
in
the
construction
is very
soon blocked
with
the
cowdung
itself.
At
two-thirds
the
height
of
the
pit
from
the
bottom,
a ledge
or cornice
is
made some six
in wide
for
the
drum to rest
on when empty.
This
also
serves
to direct
into
the drum any gas forming
near
the
circumference
of
the
pit,
and
prevents
it
from escaping
between
the drum and the pit
wall.
The ledge
should
never
be more than
2 ft
(60 cm)
below
ground
level.
In
this
case
its
should
top
be 7 ft 4" above pit bottom.
Do not construct
the
water
well
or spring.
it is better
to cement
2-
pit
within
40
If
the water
the inside.
ft
of
table
a drinking
is reached
INPUT
An ordinary
10 cm (4"')
rain
pipe
will
do, beginning
90 cm (3')
above ground
level
at the base of a mixing
trough
and ending
in
the pit
at least
60 cm (2')
above the bottom.
26
I/--scu M
BREAKING
9
RODS
hOTTOM
A SM4PLE
SINGLE
CLOSED
CHAMBER
PIT
THE MIXING
TROUGH - Villagers
are
often
careless
the
proportions
of
dung
and
about
water
in
the
They
go
by
guesswork
slurry.
rather
than
by actual
measurements,
making
the
slurry
too
thick
or
too
thin.
This
infallibly
alters
the
pH and produces
too much carbon
dioxide.
It
helps
accuracy
to have
markers
in the trough,
one showing
the correct
level
of water,
and another
nearer
the
showing
the
top
level
of
the
slurry
after
the dung has been
total
The markers
added.
could
be grooves
or
ridges
in
sticking
out
a trifle.
To
the plaster,
or a brick
avoid having to build
a very large
trough,the
dimensions
to hold
just
could
be calculated
half
the
volume
need(:d
daily.
Then the owner
of
slurry
knows that
he has to put in two trough-fulls
every day.
A useful
improvement
to
the
mixing
trough
is
to
give
the bottom
a slight
slope
away from
the inlet
Any sand or dirt
that
drops
down during
the
hole.
mixing
is
then
not
drawn
into
the pit
but
remains
in the trough
to be washed out through
a small
hole
in the wall at the lowest point.
THE PADDLE-WHEEL MIXER - In
a biogas
digester,
as
the bits
in any compost
heap,
of raw material
are
their
all
over
surface
by microbes.
attacked
The
greater
the
surface
area exposed,
the more thorough
the
decomposition.
Where vegetable
matter
is
used,
e.g.
straw,
leaves,
crop
grass,
stalks,
the
finer
it
is
chopped
up before
being
put
into
the
pit,
the better.
In a cowdung-gas
plant
the slurry
should be thoroughly
mixed
to
make it
homogeneous
and smooth
flowing.
The dung should
not
be used
in a lumpy
condition.
Though such lumps would,
of course,
ultimately
decomtheir
breakdown
is
easier
and
more
rapid,
pose,
and their
gas sooner
obtained,
if
they
are
first
broken up.
It
is not
too
difficult
to break
them up by hand
for small
family-size
plants,
but for larger
installations,
where the volume of daily
slurry
may be quite
considerable,
hand mixing
is
far
too
fatiguing
and
time
consuming.
It
is much more practical
and rapid
mixer.
to use a mechanical
The accompanying
diagram
shows one such mixer.
Dimensions
vary with
the volume
of slurry
to be prepared.
working
While
the
paddles,
place
(it
ought
not
to),
could
be fixed
over them to
'clothing.
if
any
splashing
takes
a half-cylinder
of
tin
safeguard
the operator's
-.
,-?._
/
I,
I,,--5
7 _-.v
-i lj
II
Pi,-
.*
&
.Y'
'L
A pacidie-wheel
mixer- in
use. Notice the ugly,
old-style
outlet
through
hose pipe.
The dung and water
are put
into
the trough
and the
handle
is
cranked.
The paddles
help
to break
up
the
lumps
and mix the dung with
the water.
In the
beginning
the lumps may be too large
to pass through
the screen,
so the mixer
could
be used for
a while
without
it.
Then as the
lumps are redated
in size,
the
screen
can be placed
in
position.
Lumps that
get stuck
are scraped
off and made to pass the paddles
Soon the
again.
slurry
flows
through
The
easily.
plug
is then
drawn and the slurry
allowed
to enter
the
pit.
We think
a screen
of l/2"
mesh would
be
suitable,
though
a
finer
slurry
passing
through
a l/4*' screen would be still
better.
29
dung
to the bottom
of
the
pit
Lumps of
may sink
rise
to
float
on
the
surface.
With
a
very
fine
or
slurry
the dung remains
in suspension,
and decomposes
and produces
gas much faster.
3-
-THE OVERFLOW
from
or
two
the
topmost
Remove a brick
layer
of
the pit
wall.
The space left
will
serve as overflow.
The spent
slurry
is led
away in a drain
to a long
narrow
trench
!':O cm (20")
or more wide with
a porous
bottom.
Here
the
water
seeps out
and the fermented
to be collected
and stored
dung dries
in
the
sun,
There
should
be two or
for
use as manure.
three
one filling
while
another
is
drying
such
trenches,
slurry
has no smell whatever.
out. The dried
4-
GAS OUTLET
The original,
primitive
method
of gas take-off
(one
still
comes across
occasionally)
is
a short
length
of
metal
with
the
main
gas valve
attached,
pipe,
welded
to
the
of
the
drum.
To this
is
fixed
top
a rubber
or plastic
hose
long
enough
to allow
the
drum to rise
and fall,
whose free
and is attached
to the moisture
release.
This method is not recommended
has proved
unsatisfactory.
nowadays
as it
The floppy
hose
pipe
is
ungainly
and
awkward
and sooner
or
later
cracks
and leaks
and has to be replaced.
It
has
been
superceded
in
Nepal
by
the
centre-guide
take-off.(cf.
diagram).
This
modern method
uses the centre-pipe
as the gasoutlet.
Gas collecting
in
the drum passes
into
the
slide
pipe
through
holes
near
the
top of the
drum.
Since
the top of the slide
pipe
is closed,
the gas
passes
on into
the guide
pipe
and leaves
it
through
a connecting
pipe
at the bottom
which
leads
it
out
of the pit.
This method is neat,
strong
and permanent.
Furthermore,
it
has
been
observed
that
since
air
and rain
cannot
enter
the slide
pipe and guide
pipe,
corrosion
of
these
pipes
is eliminated,
or
if
any
does occur,
it
is
so extremely
little
as to cause
no trouble
whatever.
5 - MOISTURE RELEASE
The gas in the plant
is moist
and warm. On its
way
to
the
kitchen
it
passes
through
piping
which
in
winter
may be
quite
chill
and
cause
moisture
to
condense
inside
the
pipe.
This
condensed
moisture
will
accumulate
and may eventually
block
the
flow
of gas. So a moisture
release
device
should
be installed at the
lowest
point
of the delivery
line.
Four
methods
of
moisture
disposal
are
illustrated
in
the
accompanying
diagram.
The
first
is
simply
a length
of pipe
in a bottle
of water.
The moisture
trickles
down the pipe
into
the bottle
and overflows
onto
the ground.
It
is quite
automatic
and requires
no attention
beyond
seeing
that
the bottle
is always
full.
The end of the pipe
should
be 15-20 cm below
the surface
of the water.
MOISTURE
container
TRAP
U-pipe
DEVICES
moisture
tap
is the same in principle,
The second
its
shorter
arm 15-20 cm long.
The
be full
of water.
The
end,
out.
third
is a length
of
which
is
occasionally
DCS
trap
a
pipe
moisture
device
U-pipe
with
must always
pipe
with
a valve
at the
opened
to let
the water
Where
there
is
a high
water
table,
with
perhaps
danger
of
occasional
mild
flooding
during
monsoon,
these
three
devices
have the disadvantage
that
water
may enter
the pipeline
through
them instead
of leaving
it.
Sucn a contingency
is
with
the
DCS
impossible
Moisture
Trap.
31
In hot
moisture
the pipe
climates
one
since
trap,
is chilled.
THE DCS
may possibly
get
moisture
condenses
MOISTURE
TRAP
by
with
no
only
when
DEVICE
The Development
and Consulting
Services
of
Butwal,
Nepal,
have
produced
a moisture
trap
of
entirely
new design.
It
is
in
essence
a U-pipe
with
long
to
which
arms
the gas pipe
is attached.
The moisture
in
the
U, to the
collects
middle
of which
another
long
pipe
is
fixed
called
"the
dipper
pipe".
The
U must always
some water
contain
in order
to form
sT:sal which
a wate?
forces
the
gas to rise
up the
first
down the
via
arm and flow
second
the
main
gas valve
which
is
just
above
ground.
The rest
of
can be below ground.
the device
The top of the dipper
pipe
too
is
above
ground.
It
is kept
covered
with
the pipe
is the dipper,
a small
a screw cap. Inside
metal cup attached
to a long wire.
DIAGRAM
OF WATER
TRAP
front
dtpper
p,pe cover-.
DEVICE
DETAIL
stde
-.\
,motn
gas
-i
OlPPEli
valve
, grotlnd
level
-L--- -~--
n
rhandle
I
’ ,
olDe’A!L”d’
r--dtooer
keep dipper
dapper pipe
not In uee.
/
,,*r
,,f’ ,”
,q&)
.’
,, ,: ’ ’
,‘,,:,
/,.. ,: ,:, 9-J
; I , i,‘,
,’ I / ,,’ / / , “,,
Excess
moisture
with the dipper
continues
till
is then left
in
f
-,
,,
,.
I,,’
,‘.’
,. I
’
,’ ;
,’ “,
InsIde
when
’
I
,
6 mm Q
’ .‘,,/
<I
.,’ , ” ;” ‘J
I,,,. /
, ~‘:/,/
, ,./ ,
o-r--
11
?L
1, 1
rcontalner
for
ing out water
ltft-
collecting
in
the
U is
taken
out
and thrown away. Extraction
of moisture
no
more
enters
dipper,
which
the
tihe pipe and screwed shut.
32
pit-digester
designs,
most
the
In
must
gas
Pipe
the
pit
not
leave
lower
than
60 cm below
ground
-qal-iJe and
level,
otherwise
the
main
the
moisture
release
cannot
be
conveniently
manipulated:
they
would
be beyond
reach.
With
the
D.C.S.
moisture
trap
this
trouble
is
avoided.
The main
gas valve
is
always
conveniently
above ground.
The gas outlet
and even
the
top
of the
pit
could
be much lower
if
desired.
Another
advantage
of
this
design
.
that
it
is
so neat
and simple
and self-containeds
To adapt
it
to lower
or higher
gas outlet
all
thai
is needed
is to shorten
or lengthen
the dipper
pipe
and the arm of the U.
depth
make the
making
moisture
realease,
In
this
cup 5 cm more than the gas pressure.
of the dipper
is
10 cm the
cup should
be
if
the
pressure
Thus,
15 cm deep. Join
the gas pipe
to the U-arms at double
in this
case 30-35 cm above
the height
of the cup,
seal
will
thus never
the bottom
of the U. The water
and
the
gas
will
have
be less
than the gas pressure
in the U also
to go round
the right
way. The water
through
the dipper
pipe;
prevents
gas from escaping
so there is no need for its closure
to be gas-tight.
satisfactorily
This
working
DCS moisture
trap
is
in Nepal wherever
it has been installed.
THE
NEPAL1
SLIMLIME
There is yet one more design
of trap worth describing,
the
consists
Nepali
Slimline.
While
the
DCS trap
of
one
connected
one
for
three
pipes
gas inlet,
for
gas outlet
and the
third
for
water
collection
and
one
pipe:
extraction,
Slimline
has
only
the
or so it
seems.
In reality
there
are two, one inside
inner
the
other,
the
outer
one
for
agas
and the
for
water.
the pit
and the kitchen
Condensate
from
trap,
in
the
pipeline
trickles
d0W.n
and
gathers
whence
it
is
the
extracted
with
a dipper,
as in
DCS trap.
33
The two pipes can be of any diameter
the owner desires.
on the volume
of the digester
and the
Much depends
of
the
main
gas pipe.
The only
point
to
diameter
that
there
be sufficient
space between
the
mind is
full
and free
passage
of
two pipes
to
allow
the
depends
of
the
pipes
on
how
deep
The
length
gas.
in the ground
the gas comes out of the pit.
As for
a
15
cm
depth
ought
collection,
the “Sump" for water
to be enough for household
plants
with
a gas pressure
This
determines
the position
of 10 cm water
column.
outlet
should
be just
inlet
pipe.
The
the
Of
gas
at ground
level
or slightly
below,
so that
the main
gas valve is conveniently
accesible.
GROUND
LEVEL
[ i-
1
I
m
COVER
( LOOSLY
to prevent
dirt
v---
-REDUCER,
---I\11
r
/r
In making
a perfect
a perfect
top.
DIPPER,
CAP,
FITTED
)
from
entering
gastight
handle
gastight
and
fitted
cup
/'//
fitted
the
Slimline
it
is
necessary
to ensure
bottom,
and
watertight
the
closure
at
gastight
fitting
of the two pipes
at the
6-
THE GAS DRUM
steel
sheeting
or galvanizedThis
is made of mild
from
SWG 16 to SWG
sheeting
of
any thickness
iron
favours
the heavier
30 (1.63
mm - 0.32
mm). India
further
strengthened
with
angle
iron
or iron
swiw
Taiwan often
uses gauge 30 fixed
to a rectangular
rods;
(their
fermenting
for
rigidity
wooden
framework
There
is no point
tanks
too are often
rectangular).
then
having
to
heavy
and
the
drum
too
in making
where
the whole
in plants
Except
counterbalance
it,
be stored
for
use at
one time,
gas has
to
day's
to make the drum one-third
the depth
it
is customary
and its
diameter
10 cm less
than
that
of the
pit,
almo5.t
double
the
height
of the pit.
A 2 l/2"
pipe*
md is welded
to the
through
it
of the drum passes
held
firmly
by thin
lower
end is
its
centre;
top
pipe
(called
the
top
of
this
The
tie-rods.
iron
drilled
A few holes
are
closed.
pipe")
is
"slide
below
the
drum
and
just
inside
the
in
the
pipe,
top. (see diagram).
This
pipe
slips
onto
a 2it pipe*
held
perfectly
in
the dead centre
of the pit
by two strong
cross-bars,
or imbedded
in
a ferro-concrete
beam.
As the
drum
fills
and empties
it rides
up and down on this
centre
guide
pipe,
the top of which
should
stand
at least
half
the
of
the
drum above overflow
level.
height
Make sure that
the drum is perfectly
airtight.
Attach
handles
to the outside
for
lifting.
Weld four
metal
rods
from
the
tie-rods
to the
slide
pipe.
Stagger
them.
With
a slight
rotation
of
the drum,
or with
its
mere rise
and fall,
these
break
up troublesome
scum that
forms
on the
slurry
and tends
to harden
and prevent
the passage
of gas.
Protect
the outside
and inside
of the drum with a coat of paint.
+
This
diameter
is
suitable
for
small
family-size
require
course
Larger
installations
of
plants.
sturdier
pipes of bigger
diameter.
,35
front
/
side
cross
TOP
-HOLES,
DRUM,
/
CLOSED-~
INSIDE
GAS EXIT
-7
.r
HANDLES
10 MM@
M.S. ROD--
-BARS
FOR CONSTANT BREAKING OF SCUM
i-7
-PIPE.
BOTTOM
OPEN
/ cross
\
! !
’ LDRUM
OPEN BELOW
\
CROSS
BARS
Gas drum showing scum-braking
rods fixed
all helter-skelter,
not as recommended
in the text.
36
A
NEAT
AND
eliminating
:/IODERN
the
ugly,
SCHEME
--
WAY
OF
GAS
old-style,
TAKE - OFF
flexible
pipe
OF PRINCIPLES
front/cross
full of gas
floating
gas drum
front/cross
___---.__
empty/no
gas availabIe
sitting
gas drum
inside
open
pipe
?
I
\
hooks
6 Nos
outer pipe:
top closed
/
I
/
,-ho[es,inside
drum:gasexit
ii
1
I overflow
1
GAS
DRUM
2
SLiDE
PIPE (G.I.
3
CENTER AND GAS EXIT
4
CROSS SUPPORTS
9
MAIN GAS VALVE
6
MOISTURE TRAP
Note:
3.70
the
drum
increase
diameter,
moisture
trap
the
76 /
keep
ground.
is
not
21/Z” 0)
PIPE
2"0
height
low,
so that
the
too
deep
in
37
Note:
0
e
0
steel
cold-rolled
drums,
making
For
hot-rolled.
preferable
to
sheeting
is
It resists
corrosion
better.
dung
suffer
cattle
using
only
Plants
those
whose
corrosion
than
from
less
slurry
is augmented with human waste.
the
where
night
soil
is
Plants
only 9
material
are
raw
predominant,
the
or
This
corrosion.
may be
most
liable
to
due to increased
hydrogen
suphide.
whether
drums,
iron,
with
of plain
followed
by a coat
all
I)
T+z is wiser
to paint
sheeting
or
of G.I.
red
oxide
of
a coat
of bituminous
paint.
e
Corrosion
of concrete
too,
or of brickwork,
Chinese-model
plant
drumless
in
a
gas
is prevented
by bituminous
paint.
7 - THE
FLAME
TRAP
(Not
shown in plant
diagram)
safety
device
that
should
arrester
is
a
A flame
It
is commonly
be incorporated
into
every
gas line.
main
gas valve
near
after
the
just
placed
either
or
just
before
a gas stove
or lamp.
the
digester,
It
is safer
to have one in both places.
Its
purpose
to
prevent
back-fire,
accidental
case
of
is,
in
running
down the
gas pipe
into
the
the
flame
from
collecting
drum and causing
an explosion.
CROSS
CROSS
LFLAME
ARRESTER
38
of
fine
mesh
or roll
The arrester
can be a ball
which would
not galvanized
wire
wire
(copper,
copper
rust
away) inserted
into
the gas pipe.
It is sometimes
not realised
that
this
necessarily
forms an obstruction
It
is therefore
to the
free
and full
flow
of gas.
placed
in
arrester
be
flame
the
that
recommended
a length
of pipe
of
slightly
larger
diameter
than
is
placed
near
the
especially
if
it
the gas pipe,
a l/2"
main
gas pipe
use a 3/4"
For
main valve.
arrester.
arrester,
for a 1" pipe a 1 l/4"
An arrester
could
wire disc at either
into the pipe line.
also
end
be made by brazing
a copper
of a short
bit
of pipe joined
GAS PIPE LINE DIMENSIONS FOR LOW PRESSURE GAS (10 CM)
HEAD
APPR.
100mm
WATER
COLUMN
1.41
50
2.83
100
4.24
5.66
200
167
152
ti
137
E
L
5
z
122
106
z
76
h
c
IL
0
I
ri
91
61
45
30
15
0
DISCHARGE mJ/ h 0
ft3Ih
0
150
203
250
8.&9
300
DIAGRAM BASED ON A FALL OF 3/16 WATER GAUGE FOR
FOR ORDINARY LOW PRESSURE GAS SUPPLY
39
PIPE
Q) short
MAIN
distance
GAS VALVE
b)
medium----_---distance
c)
long
d)
hillside
a,t
a
distance
15.12.78
INSTALLATIONS
SLOPE
=
1 cm/mtr
40
Ideally,
the
shorter
the
line
the
better,
pipe
the gas pit
being
as near
the kitchen
as possible.
sometimes
this
is
not
practicable.
But
The greater
the distance,
the larger
should
be the pipe diameter,
unless
one uses
a P-P.
For a distance
of
150 m
Khadi
and
Village
Industries
Commission
(Bombay)
recommends
a 1 l/2'!
pipe.
At
a college
in
Patna
a 2" pipe line,
too big in our opinion,
was installed
for
a distance
of 160 m. It has worked
with
entire
satisfaction
for several
years.
Galvanized
iron
water
pipes
have proved
to be the
best.
Plastic
could
be used;
however,
field
tests
have shown that
due to various
factors
(poor
quality
material,
ill-fitting
adapters,
&c.
this
is
not
as satisfactory
as metal
piping).
G.I.
laid
pipes
underground
should
be
protected
against
corrosion
with
durable
paint
(bitumen)
wrapped
around
with
a bitumen-soaked
cotton
bandage.
Plastic
pipes
should
not
their
mechanical
resistance
for
gas-tightness
should
never with an open flame.
USING
be used
indoors
because
is not
reliable.
Testing
be done
with
soap
water
THE
GAS
The first
drumful
of gas will
probably
contain
so
much carbon
dioxide
that
it
will
not burn.
It
may
also,
just
possibly
contain
some methane
and a lot
air
of
in
just
the
right
proportion
to explode
if
DON‘T ATTEMPT TO LIGHT THE FIRST DRUMFUL
ignited.
OF GAS. Void
it
into
the air
and let
the drum fill
again.
COOKING
In India
special
stoves
are made for
burning
cowdung
gas.
This
gas,
coming
at
low pressure
of
7-10
cm
will
not burn
in stoves
built
for
high
water
head,
pressure
use.
However,
a llPrimusls
or other
pressure
stove
burner
will
work
satisfactorily
if
the centre
there
nipple
in
the
burner
is
removed,
or where
41
if
the needle-thin
jet hole
is enlarged
is no nipple,
to 1.5 mm (l/16").
On the other
hand a burner
made
water
pipe
allows
too much
at home out of half-inch
The
pipe
should
be choked
with
a metal
disc
gas.
centre
having
the
hole
of
diameter
1.5
to
2 mm.
An efficient
burner
is a tin
can, filled
with
stones
to balance
it,
having
half
a dozen
1.5
mm holes
in
the
top.
The gas enters
at
the bottom
through
a pipe choked to a 2 mm orifice.
Cooking
I-
G.I. PIPE
on gas
FLEXIBLE
L-LAME
TRAP
GAS VALVE
PIPE
BURNER
L
HOSE
CLAMP
Though
cowdung
gas burns
well
with
or without
air
it is advantageous
to use a burner
with
an adjustable
air
inlet,
as such
stoves
burn
hotter
with
less
gas.
42
.
E
WE
E
al
2
ul
z
.-L
2
=i
s
.z
Tii
0
”IW
-
-
-.,
El
I
Y
961
_--.-
------691
Cooking
with
flat-bottomed
in a pot
Cooking
with
round
.,
.‘.<
I.
..,.
”
\
; x, . .
I ,
I,
pot
bottom.
.,
‘.
810
-GAS
450 W/h
= 16 cft /h
for
pressure
low
CAST
BURNER
IRON)
18 Not
HOLE s
ASmm@
NOZZLE
-HOtES
VILLAGE
\
8 mm *
IN
A
2.5 mm9
PIPE
AND
COLLAR
-61.
LG.1.
ELBOW
PIPE l/I’6
2*-l/2”
- MODEL STOVE
A simple
solution
to the
stove
problem
is
to use
the
existing
village
"chulo"
or
stove.
Insert
a
pipe
into
it
and fill
the
stove
with
stones.
This
works
quite
satisfactorily
if
fitted
with
a choked
inlet
(2 mm) and an air control.
45
A
CHINESE
GAS STOVE
the
stove
and
into
sunk
deep
pot
is
The cooking
in
the
centre,
Below it,
off
the bottom.
rests
just
is a hole through
which is directed
a gas jet sufficito
let
air
be drawn in
the
hole
ently
distant
from
thus
ensuring
a
proper
gastogether
with
the
gas,
hiss.
The flame
It
makes
an audible
mixture.
air
licks
the bottom
of the pot,
and the heat that
rises
being
blown
away
and
lost
instead
of
up the sides,
exposed
on top
of
pots
sits
when the
( as happens
and directed
against
enclosed
totally
is
a stove)
the pot by the tapering
configuration
of the stove.
novel
design
is
therefore
more fuel
efficient
This
than a normal open gas ring.
AERATION
PASSAGE
NOZZLE
FIXATION
GAS SUPPLY
A
REFRIGERATOR
BURNER
of a kerosene
flame
A fridge
that
runs
on the heat
can be run on cowdung
gas with
a suitable
burner.
The burner
whose design
is presented
here has given
conducted
in Nepal.
With
results
in tests
ve ry g00d
8 cm and a consumption
of
100
a gas pressure
of
this
burner
has successfully
worked
a fridge
ltr/hr,
of 12 cft capacity
over a test period
of eight
months.
simple,
elegant
and inexpensive,
It
is
To fit
it
into
the space provided,
the stand can be made taller
The
nozzle
can
shorter.
or
be slightly
adjusted
a little
higher
or lower,
and
fixed
as may be -found
necessary.
7 NOS.
HOLES,
C.I.
PIPE l/2"
(15,'21
mm 0)
2 mm 0
0
2 NOS. AIRHOLFS
AT 6 mm 0
r
--
RRONZE-PIECE,
NOZZLE = 1 I"," 0
HEIGHT ADJUSTABLE
zzz--I
/
7
/--
S T A :i 10 M 5
18 x ; mm
i
\I
\I
\
\ I
\I
measurements
a,ba
in mm
13 1278
This
burner
has also
run a kerosene
incubator
(100
egg capacity),
and can serve
very
well
as a low
or
for
any
other
application
temperature
bunsen burner,
smokeless
req~irixg
small
0
continuous:
clean,
a
flame.
47
LIGHTING
when burnt
white
light
Cowdung gas gives
a soft,
much
like
the
very
incandescent
mantle,
with
an
and
not
quite
as
bright
lamp,
light
from an Alladin
lantern
or
a Petromax.
and glaring
as a Coleman
are
manufactured
styles
and sizes
Lamps of various
for
use
with
cowdung
gas.
They
India
expressly
in
to
four
or
more mantles,
each
from
one
may have
2.75
cft
(80
ltr)
gas per
approximately
consuming
Each mantle,
at a pressure
of 4"
hour per
mantle.
water head burns about as bright
as a 40 watt electric
bulb. At higher
pressure
they burn brighter.
For lighting,
where
many lamps
are
needed,
it
is
more efficent
to run a generator
gas and have electric
lights
in
gas lamps.
than
to burn
the
gas direct
A 40-watt
mantle
consumes
about
80 litres
per hour
so 25 mantles
would
require
2000
litres.
On
an
to
produce
average
it
takes
only
750
litres
gas
1 kW/hr
of electricity,
enough
to light
25 Nos. 40watt
cheaper
bulbs.
And wiring
a house
is easier,
and safer
than installing
gas pipes with the possibilty
of cracking
and the danger of leakage.
A
SIMPLE
CHINESE
GAS
LAW
The 0.8
mm nozzle
is
suitable
in China
where
gas
pressure
is high
(up to 100 cm). For a 10 cm pressure
the diameter
should be about 2 mm.
front/cross
&-
HANGER / THIN
MIRE
GLASS PIPE
8/10 mm 0, HEIGHT
ADJUSTABLE,
DEPENDING ON GAS PRESSURE
/--
J
TYO HOLES, 5 mm 0
FOR HANGER
METAL
14/16
tUBE
mm 0
4 HOLES, 6 mm D
FOR AIR MIXTURE
g-8
'v'
I
DIFFUSER
BAKED CLAY
NOZZLE,
0.8mm
49
metal
glass
tube
tube
INlO mmO
14116 mma
rN
-
nozzle=
0.8 mm9
diffuser
measurements
in mm
Kathmondu,16.9.78
a,ba
3/4”B plumbing
thread;
tne same rootstock head can be used for industrial
purposes,
when fixed
in a row on a
pipe with 3/4”0 inside threads (branch).
RUNNING
ENGINES
combustion
engine
can
be
adapted
to
Any internal
on cowdung
run
gas.
For
petrol
engines,
drill
a
hole in the carburetor
just
near the choke and intro1/4H (7 mm> tube connected
to the gas supply
duce a
through
a control
valve.
The engine
may be started
and then
switched
over
to methane
while
on petrol
running,
or vice
versa.
For
smooth
running
of
the
the
shod d flow
engine
at
a steady
pressure
gas
can be maintained
which
for
stationary
engines
by
adjusting
weights
on the gas drum, or in automobiles
through
a metering
device sold commercially.
It is commonly recommended
that
when running
internal
combustion
engines
on cowdung
gas the gas be first
be purified.
This
is done by ridding
it of moisture,
of
carbon
dioxide
and
of
hydrogen
sulphide.
But
at least
one experienced
authority*
maintains
that
engines
after
years
of
running
on un-purified
gas
have shown no appreciable
ill
attributable
effects
to the gas as a such.
"L.
Fry:
Methane
Digesters
for
Fuel
Gas and Fertilizer.
51
(Ruston,
engines
diesel
manufacturers
of
Several
adapt
easily
others)
can
Kirloskar
and
Crossley,
It
is
engines
for
the
use of
cowdung
gas.
their
agent
experienced
and
have
a recognized
wiser
to
the
attempt
than
to
changes
necessary
the
effect
This
remark
and risk
ruining
the engine.
job oneself
applies
to petrol
engines
too.
DIRECT
INTAKE
MIXER
FOR
DIESEL
J-WAY
BIOGAS
CHOKE
(BALL
VALVE)
3/L”
FRONT
INTAKE
ENGINE
LREAR
PIPE1
PIPE
INTAKE
PIPE
Carbon dioxide
is removed by bubbling
the gas through
hydrogen
sulphide
by passing
it
through
lime water;
a tube containing
ferric
oxide,
which is later
renovato air
or by gentle
heating;
ted merely
by exposure
by passing
it
through
a quantity
of
and moisture
very dry wood shavings.
DIESEL
ENGINE
WORKING
WITH
BIO-GAS
SCHEME
EIOGAS
CHOKE7
,-INTAKE
PIPE
rEXHAUST
--
AIR -FI
usually
Engines
of gas per h-p.
LTER
consume
per hour.
approx.
550
ltr
(20
cft)
engine
to
run
on gas
Rather
than
alter
a diesel
alone,
it is far simpler
and cheaper
and more practical
It
can then
to convert
it
to a dual-fuel
engine.
be run
either
entirely
on diesel
oil
as usual
or
on 20% oil and 80% gas.
52
The gas is
fed
in between
the
air
intake
and the
engine
and the mixture
of air
and gas is drawn into
cylinder.
The engine
is
the
started
on diesel
oil
with
the
gas valve
closed,
and when running
steady
under full
load,
the gas valve
is opened very gradually.
Because
the
explosive
mixture
is
now richer
than
with
oil
the engine
alone
tends
to run faster,
but
governor
the
automatically
controls
the
speed
by
d,minishing
the
diesel
oil
If
the
gas
is
supply.
fed in either
too
suddenly
or too much,
the engine
may begin
to knock
and run
irregularly.
The valve
then
be closed,
should
ever
so little
at a time,
*the
till
running
becomes
quite
smooth.
The amount
will
take
depends
on its
of gas an engine
make and
the efficiency
of its governor.
The average requirement
of oil
is between
30% and 20% with
a corresponding
gas consumption
of from 70% - 80%, sometimes
slightly
more. The saving in oil is considerable.
Agro processing
with combustion
engine:
4/5 biogas and l/5 diesel
fuel
A dual-fuel
engine
works
best
under
a steady
load.
If
the
load
varies
much and
frequently,
the
gas
valve
requires
constant
adjustment
unless
equipped
with
its
own governor.
Small
infrequent
variations
are taken
care of by the engine
governor
which allows
more or less dies1 oil as required.
53
I
I
I
I
I
zCA
2
I
/<
\
\
/
-y,
/.,,’
@
,
--
.’ I,
L’
4.’
0
F
//
l---J
OEL
-
If
in
the middle
of a long
steady
run the engine
the
suddenly
begins
to
knock,
it
is
a sign
that
load
has suddenly
/lropp.zd
and the gas input
is now
It silould
be adjusted.
tot rich.
engine
to run on gas there
a diesel
When adapting
to
lower
the
compression
ratio,
is no need whateve:r*
advisable
to alter
the injection
timing.
nor
is
it
to maintain
the
running
it
is essential
smooth
For
gas pressure
as ste:l.iy
as possible.
DOUBLE
CHAMBER CONSTRUCTION
light,
insoluble
or
indigestible
matter
in
Since
the
slurry
tends
to rise
with
the gas bubbles
for
first
couple
of
weeks
of
violent
fermentation
the
to
fall
to
and thereafter
the
bottom
and form
a
troublesome
sludge,
an improved
model
of the Indian
divided
into
now being
used which
is
-fermenter
is
two compartments
up to the ledge top having
a combined
of 40 time:;
the
daily
input
of slurry.
The
volume
2 ft
(60 cm) above the bottom
input
pipe ends about
The output
is
through
a pipe
of
one compartment.
beginning
about
6" (15 cm) above
the floor
of ty;
ground
4"
above
ending
compartment
and
second
cm) lower
than
the drum top when the drum is resting
on the ledge.
improved
model
is that
since
I,his
The advantage
of
daily
flow
oi' slurary
gclc::s up the
first
side,
the
and
down
the
second
rises,
when the insoluble
matter*
where this matl,er
n'.turaliy
tends to fall,
the outgoing
found
at
sludge
with
any
out
draw:'
daily
slurry
out
the pit,
if
to clean
T i-lus , having
the
bottom.
becomes ;i comparatively
rare necessity.
at all required,
two-compartmerlt
This
size,
pits
of
any
for those of larger
used
on
construction
can
be
is
particularly
recommended
but
volume than 200 cft
(6000 ltr).
55
such
a pit
for
the
first
time,
pour
When filling
slurry
into both halves
equally
to balance
the pressure
inner
wall,
or
it
thin
collapse.
The
on the
may
need
not
to
be thicker
dividing
wzll
than
3"
(8
the smallest
dimension
of a brick.
cd,
Indian
pit
design,
two chamber
construction
If
the
input
pipe.
It
is better
to have a straight
in
by
curved,
sticks
dropped
pipe
is
and
stones
playful
boys jam at the bend and cannot
be removed
without
emptying
With
a straight
the
whole
pit.
such
through
or
be
objects
can
fall
right
pipe,
pushed out with a bamboo.
To exclude
foreign
matter
with
1 cm (l/2")
strainer
the input
and output
pipes.
from
the pit
fix
a wire
holes
at
the
mouth
of
56
TWO
CHAMBER
CONSTRUCTION
57
One of the first
private
gas plants
in Kathmandu nearing
completion.
It is five metres
deep and 180 cm in diameter.
Notice the mixing trough behind pit,
outlet
(right
foreground) and gas pipe to kitchen.
The same plant
in operation
58
A biogas
plant
in the hills
This picture
shows the dividing
wall in the pit,
the fixture
of
the vertical
guide pipe, and
the gas outlet.
59
FUEL
GAS FROM
COWDUNG
/ GOBAR
GAS PLANTS
-----c
FOR SMALLER SIZES THE ONE -COMPARTMENT
CONSTRUCTIONS
ARE WORKING SATISFACTORILY
IMPROVEMENT:
CENTRE- PLACED
GIAS- OUTLET PIPE.
SIZE DAILY GAS- IPIT Dir AMETER
PIT DEPTH
DRUM DIAMETER
SLURRY/DAY
PRO[
E
a
2i
.ax
in
I
:
0
L
”
DRUM
DIAMETER
TOP OF PIPE 2’/2”#
(90cm)
ABOVE
-OVERFLOW-LEVEL
2” d PIPE 8’ LONG
DRUM OF 16 SWG
1.6 mm OR 2.0 mm MS. -I.
MiLD STEEL
HOLES FOR GAS EXIT
(ON TOP, INSIDE, --IN 2’/2”8 PIPE )
------
---
x
z
0
.2bib PIPE 7’-2”
(215 cm) LONG
TOP TO BE PERFECTLY
CLOSED
Y
L
Q
n
L
Q)
CROSS - SUPPORTS.
:
=I
c
CENTRE GUIDE
= GAS PIPE
BOTTOM CLOSED
moisture
tap main- gasvalve - -
ii
mixing
trough
(2’xZ’x
1’)
r
.K
w
5
b
=
3
L
C
c
0
.*ad
ii
ul
4
0
b
lz
design:
a,b a
8. Saubolle
76 / 3.78 / 11.79
PIT-
DIAMETER
--
overflow
4” x 4”
10 x 10 cm
60
FUEL GAS FROM
SlZE
DAILY
COWGUNG
GAS - -P!T!eMET,kfis
1
-------
2
3
4
/ GOBAR
t ;_QEPTH
DH.lJ_M_Dl.jif4~TER
c1f-j
’ ‘+I’
t m r ‘.+ ”
3' 8"
._~330 -__.. 10
_-_ --110
340
11
140
7
8”
380
11
165
5' 8"
15
382
DF<ll’vl T)c 16 SW3
‘Ic
nCTTCC
-Jnmm
,.P
DC,
I Lr,
L.”
llllll
DRUM
e
--- - \
GAS PLANTS
190
DIAMF’ER
--fir--
8"
I SLURRY/DAY
30 DAY CYCLE
125 LITERS
200 LITERS
300 LITERS
400 LITRES
:
5'
.
TOP OF PIPE 2l/2”d
(30 cm1 ABOVE
STEEL
MILD
HOLES FOR GAS EXIT
(ON TOP, INSIDE DRUMIN 2’/2”9’ PIPE)
CROSS -SUPPORTS
-2a;!
moistur ‘e taof 11I
1.
main
g,ai VdiV e
_--.
1’1
mixing trouqh I2'x2'x
--2 c-.I?7
i
_. -
_ .- -._
--
CENTHE f-dJIDE
= GAS PIPE
-BOTTOM
CLOSED
- I Lr)
sludge
u s . C.C.PIPE
. . --
Iii
dez;i.jn:
a,t-,ti
H.34
76:
I!,.lllr
2 Ti‘lll.79
PIT - DIAMETER
+----------T
I
tank
61
FUEL
GAS FROM
/ GOBAR
GAS
PLANT
1
2
FOR PLACES WITH HIGH WATERTABLE
= REDUCED PIT
DEPTH,
BIG6 iER DIAMETER,
RED. DRUM HEIGHT- BIGGER 0
PIT DEPTH
DRUM DIAMETER
SLURRY/DAY
DAILY GAS- ]PI T DIAMETER
PRODUCTIOI u ’ cm
’+”
I*”
’ l ”
30 DAY CYCLE
cm
2cLmg1 8’-2”
2.5 m3 90 cft
140
4’- 8”
130
1 4’- 4”
125 LITERS
4 rn3 148cftl
170 1 5’-8” 1 265 ] I&101
160
1 S-4”
1200 LITERS
1
3
4
! 6 m3 218cft
I8 m3290cft
u
5
f-
:
I
DRUM OF 16 SWG
16
20mm. . . . . .
-...- OR
-.. -.MILD STEEL
TYPE \j’
SIZE
.
'II1
COWOUNG
1
200
230
6’- 8”
7’- 8”
287
290
9’-7”
9’-0”
190
220
6’- 4”
7’- 4”
300 LITERS
400 LITERS
IJKU
\
HOLES FOR GAS EXIT
(ON TOP, INSIDE DRUM
IN 2?2b PIPE ).
-_--
r
Ix+“-
OVERFLOW-LEVEL
OF DRUM HAS
-ACONICAL
cow7
w s*
-5I -.--_
c
ROSS-SUPPORTS
CENTRE-, GUIDE =
GAS PIPE 2”d
LENGTH=
6’ (180 cm)
moisture
main qas valve--_mixing
trough(
FIX
-uLL
\
-TO
L-----
2’x 2’xl’I
RED.ELBOW
2”xl”
THE BOTTOM
L
Z
C
0
.a
Y
u
C.C.PlPE
--“6 --..--
s
ii
0
L
0
I
cl
b
7
;;
design:
a,ba
B. Saubolle
2, 76 /Il.79
DIAMETER
-I
i
d
62
GAS
IN
BAGS
the
most expensive
single
In
constructing
a plant,
the
storage
drum.
item
is
Its
cost
may amount
to
expenditure.
total
Villagers
balk
at
it.
half
the
One alternative
is the Chinese
drumless
plant;
another
is the bag collector.
This may be made of hyphalon,
or
of
reinforced
synthetic
rubber.
In
of neoprene
Tibet
one sees cars
and buses
with
what
looks
like
baloon
on the roof,
containing
several
an elongated
for
two to four
hours
metres
of
cubic
gas f enough
depending
on
the
size
of
the
bag
and
running,
of
the
vehicle.
In
China
gas
is
the
horse
power
of
taken
in bags by trailer
or hand cart
to the fields
where
it
is
needed
for
working
irrigation
pumpsin the Pacific
they
are simply
used
In many islands
for normal gas storage
at the plant
itself.
To be sure these bags are costly,
but not as expensive
advantage
the
further
have
drums.
They
as metal
rolled
up and transported,
that
they
can be folded,
solution
for
gas plants
which
makes them a possible
While
gas
cannot
be
compressed
in far away hilly
places.
into
them
(methane
is
very
difficult
to
compress
cylinders),
strong
oxygen
even
into
into
anything,
a
pressure
of
withstand
to
they
can be expected
which
is more than
double
the
25 cm water
column,
working
pressure
normally
needed.
)-
Bag gas holders
can serve another
very useful
purpose
digesters.
with
Chinese
conjunction
used
in
when
high
pressure,
very
under
hold
gas
digesters
These
through
the
the
gas
forces
1000 mm, which
up to
concrete
cover unless
this
is rendered
very thoroughly
liable
to
also
high
pressure
is
Such
leak-proof.
The
pit
walls
or cover.
the
fine
cracks
in
cause
pressure
in
a
dealing
with
excess
normal
way of
to void
some of the gas into
the
plant
is
Chinese
of so much
iiieai-is a dead loss
which
of coiirse
air,
are
obviated
by
the use
drawbacks
three
These
gas.
Excess
metal)
even
a bag
(or
of
gas
gas holder.
The
pressure
stored.
it
can be
need not be wasted;
being
Zc)wtr bt:cause
of the
increased
storage
space,
pit,
or of
danger
of damage to the
is
less
there
leakage
through
the cover.
Capacity
100 m3/Walser
Biogas Reservoir
/
Capacity
75 m3
As plastic
and rubberoid
suffer
under adverse
climatic
conditions
(fierce
tropical
sun,
heavy
monsoon rain)
bag digesters
and gas holders
should
be kept
under
also
protect
them from
which
will
shelter,
adequate
damage by playful
children.
Bag holders
and digesters
may be had from:
Kunststoffwerk
Istighofen,
- Fa. E. Walser,
CH- 8575 Buerglen
/ TG, Switzerland
- Lokestoke
Developments,
Eastbourne
Lane,
Sussex GU 29 9AB, Erlgland
Midhurst,
64
STIRRER
OR NO
STIRRER ?
have shown that
cowdung
slurry
fermented
Lab tests
its
delivers
90% of
potential
anaerobically
gas
in four
weeks at a temperature
of 27-40 C. To obtain
two more weeks.
If
the temperature
another
8% takes
will
the
whole
process
take
very
much lower,
is
temperature
it
is
more
at
a higher
much longer;
does
not
produce
more
The temperature
rapid.
gas
A given
amount
merely
speeds
up the production.
it
only
a certain
amount of gas.
of dung can generate
place
in
a few
days
or maw,
this
takes
Whether
than
it
can.
That
is
cannot
produce
more gas
it
what we mean with potential.
very vast majority
of gas plants
throughout
The very,
the world
are built
to deliver
their
full
potential
For this
the pits
are
in 30, 40, 50 or more days.
the
times
the
given
a volume
30,
40,
50,
or more
Pit
size
is determined
daily
slurry.
volume
of the
range
given
the
local
it
takes,
time
also
by the
potential
of
the
full
exhaust
temperature,
to
of
is achieved,
nothing
we do, whether
the dung. Once it
or heat
or
beat
it,
or
stirr
it,
it,
we compress
any more of what it no longer
will
make it given
it,
has.
through
the
slurry
into
the floating
The gas rises
tend
matter
solid
tiny
particles
of
Since
drum.
the
slurry
in
the pit
is
the
bottom,
to
fall
to
and
denser
at
the
top
than
at
thinner
necessarily
It
is denser
here
also because
the daily
the bottom.
input
enters
at the bottom
and fresh
slurry
is heavier
than partially
exhausted
slurry.
For these two reasons
that
gas forming
at the very
bottom
we may expect
hampered
rising
up.
It
is
difficulty
in
has more
We
may
say
it
is
partially
trapped
in its
movement.
will
But
it
free
itself.
to
struggle
to
and has
and does ultimately
escape within
the pre-set
number
of days without
our
having
to do anything
to help
it.
In fact
it is naturally
helped
by the disturbance
inrush
of fresh
at the botttom
caused
by the daily
slurry.
65
experiments
of
observed
in
the
been
has
It
may
that
if
occident,
especially
in
the
owners,
plant
at
the
very
bottom
are
stirred
and sludge
the slurry
around,
"trapped"
swirled
the
gas which
is
and
UP
released.
This
has
led
some to
there
is
promply
use
of
a stirrer
the
produces
that
more
believe
to obtain
more rapidly
merely
helps
it
gas 9 whereas
already
There
is
that
been
produced.
gas
has
the
truth
in the statement
that
the microbes
undoubtedly
they
could
could
produce
more gas if
at the bottom
freely
and
particles
more
attack
more
move about
of
dung.
But
let
us remember
that
they
are daily
and
swirled
around
by the
swamped and s~~rrounded
flood
of frcsk‘
rich
slurry
shot at them by the daily
input.
is
used,
it
If
a stirrer
would
be reasonable
to
since
full
potential
of
the
build
a smaller
pit,
in a shorter
time,
the daily
dung would
be obtained
and there
would be no need to have such a long retention
as is required
to get
the same amount of gas
It's
a matter
of choice.
Occidentals
without
a stirrer.
are very
conscious
of time.
They want
to do things
quickly,
to spend money on a stirrer,
and are ready
every
day in working
it.,
Orientals
and spend energy
more
happy-go-lucky.
Why buy
Why
are
a stirrer?
give
oneself
the
added
daily
drudge
of
having
to
manipulate
it,
when
the
same amount
of
will
gas
be obtained
if
one sits
down and waits
patiently
for
a few more days?
Time
is
of
no consequence,
and it. costs nothing.
Each day':;
slurry
rises
a little
nigher
up the gas
and giving
lighter
by decomposing
pit
as it
gets
inputs,
off
more r',as and is pushed up by subsequent
fjJ;3!
y,
its
potentill
by the time it has exhausted
the outlet
and is thrown
out.
This
tia! ) .j i !.t:aches
a plant,
.t;L-1
e tlit!Ory
of
operation
of
is
t'passive"
as dist.ingui.shed
from "active"
stirring.
If a stirrer
fresh
as well
in the pit,
is used : al 1 the slurry
as CIXI;:ctisi,t.:d, i:; mixed up. It is there-fore
inevitable
:fcii i y :;omc fresh
that
out together
slurry
is thrown
SUlli@
This
is
definately
with
I;hat
is
exhausted.
a loss.
66
There
is another
disadvantage
to stirring
the slurry
These contain
10% of human waste,
in Chinese
plants.
eggs present
in
parasite
this
lie
at
the
and the
That is why the effluent
take-off
in approved
bottom.
is
half
way up the
Chinese
plants
digester
where
non-existant.
This is importhese
eggs are virtually
tant
where the effluent
is used in vegetable
gardens.
rise
and fall
of
slurry
due to
The constant
gas
pressure
barely
affects
the bottom.
mentioned
loss
of
above,
and the
danger
The
gas
parasites,
are
present
only
in
from
single-pit
installations
where
output
larger
the
plants.
In
flows
into
a covered
sedimentation
tank,
the unexhausted thrown-off
slurry
continues
to ferment
and produce
which
is
connected
by pipe
to
the
main
its
gas,
outlet.
installations
Some
have
third
even
a
gas
for
effluent.
storage
of
the
By prolonging
tank
from
first
time
input
to
final
extraction
and use
of
the
effluent,
these
extra
tanks
serve
a further
important
purpose.
It
takes
ninety
day for
parasite
to
be
totally
destroyed
and
rendered
harmless.
eggs
If
the
volumes
of
the
second
and third
tanks
are
so calculated
as to allow
the slurry
to take ninety
days for processing
from start
to finish,
the health
hazard
is
eliminated.
But
such
are
installations
very costly
and far beyond the means of villagers.
In conclusion
we may say that:
l-
A stirrer
2-
It
is
an
complication;
3-
It
may lessen
the
cost
of
a
making
it
smaller,
the
since
obtained
more rapidly
and the
time can be shorter
;
4-
It
causes
a loss
causing
unexhausted
out;
does not
added
produce
more gas;
expense
in
gas
slurry
and
an
added
plant
by
gas
is
retention
production
by
to
be thrown
67
5-
a health
hazard
It
creates
iut!' 1.t: human waste
is
part
input;
6-
It
of
in
of
any
the
plant
daily
is unnecessary,
since
the total
amount
with
or without
a stirrer
gas produced,
potential
the
more
than
never
be
CEUI
of the cowdung.
must
not
be
above
we have
discussed
The stirrer
confounded
with
the scum breaker.
This latter
consists
break
up the
the
drum which
attached
to
of rods
falls
or
rises
or
drum
scum automatically
as the
plants
with
the
cowdung
All
rotated.
is
slightly
floating
drum should incorporate
a scum breaker.
GAS
FROM NIGHT SOIL
Human waste,
though
its
C/N ratio
is not ideal*
does
produce
an amount
of
methane
that
can be useful.
In China
tons
of night
soil
are gathered
in tank
trucks
every
day and fermented
in huge installations
outside
the towns,
the chief
aim being
the production
of first
grade
soil
conditioner.
The gas produced
is abundant
because
of the proportions
of tht? plants,
and
is
used
for
running
electric
generators
and
and lighting.
Pumps9 or for cooking
Such large
plants
running
primarily
exclusively
or
on night
soil
have
place
in
a booklet
on
little
cowdung
gas.
However,
it
is
quite
common to
add
human waste
to
a cowdung
gas plant.
The digester
is
simply
used as a septic
tank,
the
toilet
wastes
being
piped
directly
to
the
fermenting
pit.
Where
this
is
done,
attention
should
be paid
to one or
two important
points.
should
be
seats
The toilet
*
Useful
in the
Volume
topic
information
on this
MINI
present
authors @ booklet
Press,
Tripureshwar,
I, Sahayogi
may be found
TECHNOLOGY
Kathmandu.
68
one metre
above
the
pit
about
overflow
level,
and
the inlet
pipe
from the toilet
should
end immediately
below
the ledge.
If
it
goes deep down, solid
matter
inside
and is
accumulates
hard
to clean
out.
Then,
disinfectants
should
not be used in the toilet
bowls.
would
kill
They
the bacteria
needed
for
fermenting
slurry.
Too much water
the
should
not
be flushed
The amount
of water
used in flushing
into
the pit.
could
be deducted
from
the volume
needed for
making
The actual
slurry
would
then be thicker,
the slurry.
but
the total
amount of water
entering
the pit
per
day would be about right.
Biogas production
from
septic
tank
For night
soil
gas,
what
can be done,
and has been
two
is
to use an ordinary
done with
good results,
+-jr tp&r@c- nnmhf3mtmnnt
Make it absolutely
septic
tak.
vuurp-‘*
“...~~I”
except
for the gas outlet
pipe,
and collect
gastight,
from
which
drum,
the
gas
in
a separate
floating
In building
this
it
can be piped
to points
of use.
tank
make sure
that
the
outlet
pipe
begins
septic
and that
the
input
pipe
15 cm below
water
level,
5
cm
(2"')
lower
than
the
toilet
from
ends
about
the mouth of the outlet
pipe,
so that
in the event
in
the
tank
the gas may
of
too
high
gas pressure
than
back
up
off
rather
the
outlet
blow
through
into the toilet.
69
too
produce
far
tanks
septic
family-size
Private
Only those of big institulittle
gas to be worthwhile.
prisons,
schools,
boarding
hospitals,
like
tions
input
to produce
a reasonable
would have enough daily
gas.
The waste
of one adult
gives
amount of useable
28-30 litres
(1 cft)
of gas.
Biogas digester combined with
digester
- below ground level)
middle:
latrine,
front:
turret
latrine
(fixed
dome type
left:
mixing trough,
of biogas digester.
in human waste
to produce
There
is
enough
nitrogen
carbonaceous
matter
is added.
very much more gas if
It has been proved
that
if
500 grams of wheat
straw
the output
of gas is
is added per person
per day,
coming (at the right
temperature)
increased
seven fold,
But with
such a bulk
of
to 200 litres
per person.
the plant
cannot
very well
dry matter
in the input,
be flow fed. Tt should be batch loaded.
70
A
BIOGAS
DEMONSTRATION PLANT
experimentation
one
research
and
purposes
of
For
to
work
with
a small
size
prefer
sometimes
would
than
a
full
size
installation
of
several
plant
rather
quantities
requiring
large
capacity
cubic
meter
Experiments
in
effects
the
day.
slurry
every
of
variation,
different
slurry
densities,
of temperature
etc.,
can
often
be more
output,
insulation,
gas
conducted
on
a
small
scale
before
being
conveniently
tried
on a full
size plant.
For demonstration
purposes
too,
and for the instruction
plant
is
often
preferable.
learners,
a small
of
biogas
popularization
programme
in
the
Nepali
For
far
away villages
scattered
over
the hills
of this
that
five
minutes
of demoncountry,
we soon realized
could
the
villagers
actually
see
when
stration,
small
pan
of
and
perhaps
even
bring
a
gas burn,
impressive
boil,
could
be far
more
the
water
to
We had a number
and convincing
than hours of talking.
attached
for
handles
plants
made with
of
these
from one village
to another.
of carrying
convenience
Though
ours
were
made from
were
a success.
They
plant
can
very
easily
be
sheet
metal,
a similar
made from a 200-litre
oil drum.
not
produce
will
course,
A 200-liter
digester,
of
do any steady
and useful
work
like
enough
gas to
It
may
light
a
stove
for
some
15
cooking
a meal.
minutes
once a day, and that
is all.
But demonstration
just
to show that
the gas does burns
(does not take
more than one minute.
a daily
slurry
would
require
digester
size
of
This
If
a little
more gas
6 litres.
of at least
(1:l)
increased
to
could
be
input
daily
the
is
wanted,
But
then
the
full
gas potential
of the
10 litres.
dung will
not be obtained.
The effluent
will
continue
this
But
rejected.
being
after
slowly
fermenting
not
to
get
our
purpose
is
since
not matter,
does
but to have a sufficient
quantity
all
the gas possible,
for a proper demonstration.
.
zz
JI
u
a
‘\
’ “&-
_, .---+
..- -
--
-..
:
\
--t... ---.
.
.T:;
4
6
0
8
-a--*---
-..- _.
SOL
L.--
-------1st
011
__ _.
._.--_.-- A ..- I
I..- .-.-.-.--__.-_ ..
I
--
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--
w
’ rij
t
L
._ cJ.:..
73
CHINESE
BIOGAS
TECHNOLOGY
For
building
a gas
plant,
a villager
can
always
dig
the
pit;
manage to
he can generally
make and
bake bricks
on his
own land;
but
the
expense
of
buying
a huge metal
drum he more often
than
not
just cannot afford.
The Chinese
have
thought
up a way of
eliminating
They seal
the fermenting
pit
with
a dome
the drum.
or a slab
of concrete.
For
the
input
and outflow
of the slurry,
in place
of a pipe,
they have a broad
chamber.
As the
forms,
instead
of
pushing
a
gas
drum up it
pushes
the
slurry
down,
forcing
it
into
the
Side
chambers e When the
gas is
drawn
and the
pressure
diminishes,
the
slurry
flows
back
into
the main pit.
The only
advantage
of
this
model,
apart
from
its
fertilizer
value,
is
that
it
does
away with
the
expensive
drum,
thus
substantially
reducing
the
cost
of
the
installation.
Since
the
whole
plant
is below
ground
level,
it
is
not
designed
to let
the exhausted
slurry
flow out by itself.
It is either
pumped out or drawn out with
a bucket.
This is labour
intensive.
There is always slurry
in the inlet
and outlet
chambers
and whatever
gas is formed
in these
is lost
to the
air.
for
the
But
Chinese
this
is
no loss.
Their
main
objective
in
installing
a gas plant
is
top
grade
fertilizer,
the
being
taken
merely
as
gas
a useful
by-product.
A gas plant
for
them is first
and foremost
a private
fertilizer
factory.
However,
if
the pit
is large
enough,
the gas produced,
even
if some is lost,
is quite
sufficient
for the family's
cooking
and lighting
needs.
There
are
said
to be
seven million
of these plants
all over the country.
Most
even
of
plants,
family
size,
but
especially
the larger
ones, are run on the batch
loading
system.
But
pure
cowdung
plants,
loaded
with
daily
input
of dung
and slurry
alone,
run
just
as well.
The
typical
average
input
of a pit
is stated
as comprising
10% human
waste,
30% animal
dung 9 10% vegetable
matter
(chopped
crop
stalks,
dry leaves,
grass
clip-
74
etc.)
pings,
human excreta
and 50% water.
In
family
plants
the
directly
flow
into
the
gas pit,
no
required.
manipulation
being
The
animal
dung
is
put
in as a slurry.
The vegetable
matter
is first
composted
for
a fortnight,
so
that
decomposition
already
set
in
and
fermentation
has
can begin
at
once
in
the
The vegetable
pit.
matter
forms
much
acid,
which
has to be balanced
organic
with
regular
additions
of
lime
or
ashes
in
order
to maintain
the
pH between
7 and 8.
So working
a Chinese
gas
entails
quite
a lot
of labour
and attention,
plant
model;
but the Chinese
far more, than does the Indian
all
manage
right,
and
their
plants
give
perfect
satisfaction.
The plant
should
be built
the
above
water
table
to
avoid
all
possibility
of
seepage,
which
might
dilute
the
slurry
too
much.
It
should
preferably
bz sited
in full
sun.
The volume
of
a pit
built
to supply
gas for
both
cooking
and lighting
is
given
as 2 m3 per person.
For a family
of six
the pit
could
be 3 m deep
x
2m
x
2m.
It should have a strong
well-compacted
The floor
and walls
are usually
of concrete,
base.
but
baked
brick
and cement
mortar
could
also
be
While we would use iron
rods for
re-inforcing,
used.
the
Chinese
use
sticks
or
bamboo
strips
painted
with
tar.
Special
attention
is paid
to all
joints
between
floor
and walls,
and between
wall
cover.
All
parts
interlock
very
securely,
particularly
round the cover and the gas outlet.
Unbelievable
as
it
through
escapes
may seem,
gas
concrete!
It
is
therefore
absolutely
necessary
to
plaster
the
chiefly
inside,
the
upper
portion
and
the
cover.
Four
plasterings
are
insisted
upon.
The
first
is of concrete
with
10% lime.
The second
is
a 3-5
mm layer
of
sand/lime
3:7.
After
this
the
whole
interior
surface
is
tapped
with
a stick
to
discover
hollow
spots
or
air
bubbles.
If
any
are
found,
those
are
parts
re-plastered
out
and
dwz
solidly.
The
third
plastering
is cement/lime/fine
in
the
ration
P:2:1.
sand
Last
of
all
comes a 23 mm coat
of lime/sand
1:l.
in the above
The lime
75
it
makes a denser
plaster.
plasterings
is necessary:
often
form.
The whole
air
bubbles
it
tiny
Without
throrough
or
the
and
to
be painstaking
has
work
A
suggested
Indian
substitute
gas will
surely
escape.
for
all
this
plastering
is to cover
the whole inside
with
acrylic
working
Nepal
is
paint.
with
enamel
plastic
emulsion.
*
lflfl
I
-50
>-LO
:
1[<
cc
fLA5,.
==I==
-34
-
_ -.
-,,I
GLASS
I.D.
TUDES
IO old 0
-- 10 t
TO REAO PRESSURE
A00 LEFT COLUMN
FIGURE TO RIGHT
COLUMN FIGURE.
1
THUS:
-Oi
20
(LEFT)
+ 20
(RIGHT)
= 10 CM WATERCOLUNN
- 10”
1
- 2oc
2
;z
,--*
c
-
COLOUREO WATER
-3o!
-4o’
An alternative
procedure
is
recommended
by Guangshu
Acadmey
of
Institute
of
Energy
Sources,
Chinese
The first
plastering
is of
common cement
Sciences.
mortar:
second,
of
cement
mortar
with
5% by
the
weight
of
polyvinyl
the
third,
of
acetate
latex;
a cement paste with
10% PAL. Finally
a coat of bituminous
paint
is
applied
to
protect
the
cement
from
corrosion.
This
employed
for
procedure
been
has
years
with
Not
a single
the
utmost
satisfaction.
leak has yet been reported.
76
the
amount
of meticulous
care
and technical
Seeing
and
the
cost
of
concrete
construction,
skill
required,
would
not
be preferable
if
it
one wonders
to buy
a steel
drum and build
the far
simpler
Indian
style
However,
in
mountainous
of
gas pit.
country
where
unweildy,
metal
drums cannot
be carried
huge y heavy,
*up and down steep pathways
and across
raging
torrents
on
tree-trunk
bridges,
the
Chinese
model
becomes
a very practical
solution.
There
is
no single
"Chinese
model"
gas plant.
The
idea
is
a
digester
closed
on
the
top
and
having
basic
a broad
outlet
chamber
instead
of merely
an outlet
The input
may be through
a pipe
or a chamber.
pipe.
idea
is
The basic
modified
ad lib,
each
Province
the
design
of its
choice,
adopting
which
is
often
dictated
by the
nature
of
the
soil,
the height
cf
the water
table,
or the availability
of construction
materials.
In some places
the plants
are rectangular
in design,
other
though
in
parts
of
the
this
country
shape
could
be considered
outmoded
and cylindrical
tanks
are
preferred.
Sechuan
Province
favours
a shallow
digester
of
large
diameter
completely
below
ground
It
is essentially
a straight
shallow
cylinder
level.
about
1 m deep with
a dome about
50 cm high
and
a concave
bottom
about
35 cm deep,
though
a flat
bottom
is also
allowed.
The lower
end of the input
is about
half
way up the cylinder.
The output
begins
at about
the same level,
so as to draw slurry
from
the
rather
than
from
the bottom.
middle
There
are
virtually
none
in
This
is
the
middle.
important
when the effluent
is used in vegetable
gardens.
The gas pressure
in a Chinese
plant
is always
high,
but
it
should
never
be allowed
to
exceed
100 cm
water
column,
or
In
construction
the
may crack.
each
which
China
plant
has
a homemade manometer
doubles
as a saftey
valve.
It
is made of two glass
tubes
100 cm long
and 1 cm in diameter
connected
by a rubber
tube at the bottom.
One end is connected
to the
gas mains
through
a tee.
The difference
in
between
coloured
water
level
the
two
columns
of
shows the gas pressure.
Pressure
over
100 cm pushes
water
out of the tubes
into
a receptacle
safeguarding
thus
allows
gas to escape,
the
water
flows
When the
pressure
drops,
the tubes.
above and
the
plant.
back into
are
generally
emptied
and reloaded
plants
Batch
20-25%
of
the
months.
four
three
or
every
loaded
is
left
to innoculate
the new material.
old
slurry
for
thorough
emptied
entirely
ever
pit
is
If
the
must be taken
against
precautions
cleaning
or repair,
methane
concentration
of
A
30%
inside.
fumes
the
while
70% can
anaesthezise
a person,
air
can
in
A 5.15% mixture
is explosive.
asphyxiate.
Ccnstr
:, tion
materials
LIME - CLAY
22%)
hardens
and long curing.
commonly
(1 lime,
slowly,
employed
in
China
are:
9-19
clay,
moisture
about
requires
firm
compacting
LIME - CONCRETE (1 lime,
3 sand,
or bricks)
tamped layer by layer.
6 crushed
stones
CONCRETE
compressive
usually
of
strength
400
kg/cm2
(called
No.
400)
No.
150,
(150
kg/cm2)
for
covers
and
connections,
in
special
cases
No. 100, and for most parts No. 30.
MASONRY (of
brick,
stone,
cement-lime-sand
a mortar
of
50 kg/cm2,
cobbles,
slate)
of
strength
with
10 -
recommended
construction
plans
below
three
We give
Industrial
Institute
of
Sechuar
Provincial
the
by
for
one
construction,
ir
lime-clay
Design,
one
and one for
ordinary
cement
concrete.
lime-concrete,
Chinese
ball
intriguing
In
addition
we give
the
and a slightly
modified
design
successfully
digester,
tried
out in Nepal.
The digester
wall is only 6-7 cm thick,
the
smallest
dimension
of a brick.
The bricks
are laid vertically.
Notice
the shoulder
from which the dQme rises
to strengthen
its
base.
Beginning
the dome. Ericks
(Photos:
laid horizontally.
Mrs. S.L. Maskeyl
79
Approaching
cal,
the manhole. Bricks
first
row half-bricks.
again
verti-
Second row of bricks
for manhole are full
size. Notice how dome, only just laid,
is
strong enough to be trod upon.
CPhohos: Mrs. S,L. Maskey)
80
<
.
fl
77
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c‘0
E/’
c
lz
‘,,i
,?
C
4
SYMBOLS
jYMBOL5
-__
Tqq
f/
5
8
--
-
.-___
5
A
8
NATURAL
SOIL
-.~
Rl
R,
R3
RADIUS
----
TAMPED
SOIL
SAND, LIME
CLAYsPLASTERING
0
Dl
DIAMETER
L
L,
LENGTH
--
LIME
!-I H,
CONCRETE
h, h,
HEIGHT
SLATES
d
(ROCK)
THICKNESS
-
----._
------.~--
RISE
GROUTED
fl
COBBLES
f2
-.-
I
m2
m3
SQUARE
(M2)
(M31
CUBIC
BRICKS
--._.
- .----~~~ ._.. _
THE LOWER SYMBOL OF SMALL
SCALE
WITH
Ng 5
SEE PAGE
DETAILS
SYMBOLS
A
METER
METER
1:2:3
0
DETAIL (DRAWING
FIGURE
FOR
DETAIL
N-O
-t
LOCATION
SECTION
1
DETAIL
Na 5
MEANS
IN THIS
PAGE
.-.__-----___---.
__
--YcT.;
RATIO
1:2:3
CONCRETE
DETAIL
FOR A
f.lLfi
2
1
OF
BOLD LINE
LOCATION
$--J4
4
/ CONVENTIONS
FIGURE
SECTION
FOR
FOR
87
moveable
cover
05
outlet
cover
4
outlet
opening
0
1. covers
opening
for moveable cover
in mm
g. 76
of q 150 concrete
2. gas tubes are of steel, plastic
about 25 mm inside diameter,
3.
measurements
copied: a,be
are made
inlet pipes and their
made of concrete.
connections
or slates.
or bamboo,
5OOmm long
are
-82
loo lm
concrete
/----
z
-+’
---
&
z-
.Ej?+qj
-
2
z
7
two grz
corm
43
L
II
l
c-.-q-g-_
--
--
f
L,
inlet
pipe
3
0
We
pipe
length
81
f32
63
2000
1500
1000
I
I
83
1-3 mm
tamped
thick parting
agent of fine sand
backfill
300 mm at least in thickness
bamboo (branches) mat
earth tormwork
and its umbrellashaped
support (il members
resting
in shoes for convenirnut ef removal.)
dome
as designed
tov
/
I
/----support
/
h
6
mats
-
-
masonery
wall
center tied
with wires
together
-
OVERALL
EXCAVATION
DOME ON lIMf3ER’BAMBOO)
opied:
a,ba
9.76
,-----tamped
backfill
-L
,r
traversed
strips
shoes
WITH CAST SUPPORT
84
central
pole
,-dotted
line shows
rope as radius
to
curvature.
/ control
-7
\
CASTING
bF DOME
ACC. TO NUMBERS
tOD
brick
+
+
t stakes f
LAY I N&OUT
bearing
l
EXCAVATING
OF 6OTfOM
ACC. TO NUMBERS
l-1
section
1
--il
lOQ-u -SO
measurements
copied:
a,ba
in mm
9.78
D
I’ 100
s
86
2-2
note:
section
dome, wall and bottom
are of Il 30 concrete,
when
dome is made of P 100 concrete,
see detail 1
inlet
and
outlet
6, 8, 10 + 12 m3
are
made
CONCRETE
of lime-clay.
TANKS
87
’ 01
/ 5:
1
I 2
f
-1
it
C'>:
.I.
.-
l-l
SECTION
__
-f
,
m
lJ.-.-
-
1----
~~~~=~
100,
580
k---.-..
~~
250
__----cl
L-
TOP
measurements
copied:
a,be
in mm
9.78
m
..I
900
100
88
2-2
section
concrete
430
con
note:
6.8,
all parts
are of lime concrete
If the bottom and
dome are madeof
other materials,
see details
1,2
10, 12 m3
LIME
CONCRETE
TANKS
89
----. -._-_____
j- 1 section
measurements
copied: e,ba
in mm
9.76
90
2-2
SECTION
,3 / I. / B ( H 1R1/ fl / D / H1/ R / f2 1
f-----t-+----t----k---
6
-
8
~580 3064 2530 1740 i f&O 2~00 1000 2550 300 i
I
I
I
I
1
1
I
#
I
L880 3360 2630 1960 540 2700 1000 2860 34O
10
5180 3660 2730 2100
600
3000
1000 3180
12
5380 3860 2790 2320
6&O
3200
1000 3GO0 LOO
I
lime concrete i-
c‘/
note.
380
cl50
Pi-*---
rl5O
-----w---
02
03
all parts of tank are of ltme clay. If the
and dome are made of other
materials,
see details,
a.@.@
bottom
6,8,10+12m3
LIME
- CLAY
TANKS
91
gas
pipe,
measurements
copied:
a,ba
in
cm!
9. 78
moveable
inlet
pipe
92
3
1. .di.g out half
the spheroid
2. lay
of
concrete
3. build
top half
of spheroid
of
build
top of
construction
sphere
without
procedure
of
wooden
the
frame
spheroid
1.
Cower half of sphere
1: 2: 4 cement,
sand, gravel.
gravel
to be of lo-15 mm P.
concrete
thickness
4 mm
2.
top of sphere
is brick work, with a coat of cement
and sand.
if no bricks
ate used:
1:2:5 cement,
sand plaster
8-10 mm thickness
ou?side
3.
inside
to coat three
times:
1 st. 1:2.5 cement+sand,8mm
thick
2nd. I:1
cement + time, 3 mm thick
3 rd.
coating
3mm thick
6.
dig out another
deeper pit, fi!I this
with
water,
and float
the spheroid
into
right
position.
5.
fill
spheroid
its position
and the pit
6.
fit
inlet
THE
with
empty
pipe
and
water; when
both, spheroid
outlet
CHINESE
BALL
-W@ESMR
in
chamber.
i
93
OUTLET
A "Cast-in-place"
digester,
A trench
200 cm
deep x 6 cm wide is dug with special
tools.
Concrete is poured in and tamped down to
Digester
top center is
make digester
wall.
dome shaped with mud. Concrete is cast over
this.
When hard, the mud of dome support
and of hole pit is removed through manhole.
Picture
shows manhole construction.
Photo: Elm. S.L.Maskey)
94
A
NEPALESE-MADE "CHINESE"
Producing
100 cft
of
GAS PLANT
gas per
day
This
is a local
modification
of the Chinese
design.
It eliminates
the manhole
in the centre
of the dome.
This
certainly
abolishes
the
need
for
a gastight
seal
that
has to be checked
every
time
the manhole
opened
for
cleaning
or
repairing
the
pit.
is
The
dome is
completey
cast
and plastered
and rendered
gastight
once at for
all.
So far
so good.
But when
unless
cleaning
has to
be done,
a forced
draught
is provided
with
a fan
or air
pump,
the fumes in
such a confined
space might be overpowering.
The technique
of making
this
version
of the Chinese
design
depends
on making
the
gas dome of concrete
The digester
pit
is dug from
over
a mould.
spread
This
technique,
dry.
once
it
is
the
dome,
under
labour
charges
slightly
more
in
costs
although
it
the need for
heavy wood
saves
than
other
versions,
otherwise
need
to
would
form
work
that
Or
metal
This
version
of the
be carried
to the
plant
site.
Chinese
design
is therefore
considered
to be easier
to make in the hilly
regions
of Nepal,
where transport
is difficult.
CONSTRUCTION PROCEDURE
a hole,
2 m deep by 2 m diameter
1.
Dig
2.
or branches
and form
utiards
with
Cover
hole
a mud mould for
the cement dome -top
at ground
and fit
Dig trench
with
a ,-jig.
levelshaped
outlet
fit
asbestos
cement
pipe
pipe,
gas
and scum breaker
support
pipe.
3.
Pour
that
dome.
supports
The
the
forms
thicker
edge
dome on undug earth.
4.
Build
slurry
inlet
pit.
a
collar
95
5.
Dig
outlet
6.
While
concrete
7.
Build
outlet
masonry
turret
and scum breaker
8.
Dig
under
dome to
plaster
against
wail.
form
digester
9.
Clean
underside
of dome
the
who 1e plaster
coat
one time, w.ithout
stopping.
carefully
must
access
arch.
hole
beside
is
second
of
do
pILpe
*
hardening,
10. Plaster
coat
second
with
acrylic
mixed
(20 litres
cement
to
to give stiff
paste).
11. Plaster
walls.
position
coat
on dome
pipes.
to
slurry
fitting.
support
gas
and
and
pit
and plaster,
be
applied
at
under
dome -using
plastic
emulsion
1 liter
paint,
with
on
digester
12. Paint
inside
of
dome with
mixture
plastic
emulsion
and
cement
with
give a brushable
consistancy.
cement
paint
water
floor
of
and
acrylic
water
to
13. Build
slurry
reservoir
tank
of brick
or stone
masonry.
Plaster
inside
of
tank
if
soil
is
porous.
Cover
dome with
soil
to depth
of 42
cm.
14. Fit
scum breaker,
fill
with
slurry
of
1:l
cowdung
and water
and wait
for
gas production
to start
(about
15 days).
Let the first
drumfull
of gas escape.
Once the plant
is producing
add
60
kg
of
dung
per
day
mixed
1:l
with
gas
water,
cleaned
of
all
straw
and
vegetable
matter.
(Ref: Bhgcls Neasktter,
No, 10, D,. FuZford,
DC'S1
96
lo.
I..11.1
I
97
DETAIL
A
OF
GAS
SECTION
DOME
60 mn Concrete
1:6; cement: small Aggregate (as dry as possible
4 parts water to 1 part cement
8 mm Plaster
1:2 (cement
coat
: sand)
emulsion. /
3 rmn Plaster
coat with acrylic
plastic
20 litres
cement to 1 litre
paint with water to a
thick paste. Paint with acrylic
plastic
emulsion
mixed with cement and ,watered to a brushable
consistancy.
SECTION
OF
DETAIL
B
DIGESTER
PIT
WALLS
AND
FLOOR
15 mm Plaster
Coat
1:6
cement:sand
10 mm Plaster
Coat
1:3
cement:sand
2 coats
ter-paste
on.
Mud Wall
cement:wabrushed
98
3
Pouring
Pounding
concrete
the mud mould
on dome
for the dome
IPhotos: Kluu?u oititl
99
A
COMPARISON
We are often
asked questions
like
"What do you think
is better,
of Chinese
technology?l'
or "Which gas plant
Chinese?"
To this
we can only
the
the
Indian
or
that
both
are better.
The Indian
is better
answer
in some respects
and the Chinese
is better
in others.
Both have definative
advantages,
and both have snags.
Nothing
in
this
world
is perfect.
We list
for
you
of both
some 9.f’ the good and some of the bad points
could
be
said
for
and against
More
technologies.
have
touched
on
the main
but we hope we
both
sides,
plant
choice
of
the
Your
differences.
may often
materials
available,
conditions,
be guided
by local
and other
similar
circumstanthe skill
of the builder,
plan't
you build,
if it
is properly
ces. But whichever
give
will
operated,
installed
and
YOU excellent
service.
EFFICIENCY:
The Indian
gas plants
are very
satis'actory
INDIAN:
and serviceable.
They are simple
to build
and maintain,
and if
intelligently
operated
are virtually
troubleThey
are
highly
recommended,
for
especially
free.
beginners.
The Chinese
pl,a.nts
too give
perfect
satisCHINESE:
high
builders.
The
Require
faction.
mwl-ewed
gas pressure
in the di,gester
poses the biggest
problem
cracks
leaks,
construction
is
net
perfect
(gas
if
of gas:
and walls,)
g&what
wasteful
in cover
gas
excess
pressure
.iS
lost,
side
formed
in
chmkw%j
is reduced
by releasing
gas to atmosphere.
So relativThe exhausted
slurry
ely
larger
plants
are needed.
and sludge
of each batch m&es richer
and more abundant
soil
conditioner
than .that of Indian
pit.
The digester,
insulated
better
totally
because
undergrmmd,
is
against
winter
cold.
r-l
,--GAS
--?I~
INLET
DRUM
MOVEA@LE
EFFLUENT
I
-INLET
COVER
-FERMENTING
--
SLURRY
--DOME
AS SEGMENT
OF SPHERICAL
SHELL
PIPE
- -PUMP
\\
r,s T,A.CE
-CFF
I
THROUGH
I
CENTRE
PIPE.
FLAT
i
BOTTOM
ahal
BOTTOM-
i
OUT
’
AS INVERiED
SEGMENT
OF
FROM
Ml DDLE.
SPHERICAL
CHINESE-
IKDIAN
ertilizer
concrete
tank with adjacent
effluent
chamber.
Requires
skill
to render
gastight.
Can be built
anywhere.
build
but hard to install
where drum cannot be made
or easily
be carried
INPUT
may serve
as septic
lants
tank
exclusively
OPERATION
- virtually
ond mixing
no attention
and feeding
- height
float
of
bey-
shows
GAS PRESSURE
- low: 70 - 150 mm water
- steady,
due to floating
drum
COST
high because
of metal
and its
fixture
APPEARANCE
presentable,
neat
gas
col.
drum
gas
in
sealed
- gas volume and pressure
shown by slurry
height
digesin
up to 1000 mm water- high:
column maximum
- constantly
varying
lower
cost
neat,
clean,
because
no metal
unobstrusive.
THE
SHELL
101
POSSIBLE
DEFECT
No gas.
rise.
Drum won't
-.
No gas at
plenty
in
stove;
drum.
TROUBLES
,
MAY BE CAUSED BY
REMEDY
a) no bacteria
Add some.
b)
lack
Patience!
Without
it may take four
weeks..
c)
slurry
d)
insufficient
e)
leak
f)
hard scum on slurry
blocks
gas.
of
time
is
in
too
cold
Use warm water.
Cover plant
with plastic
tent or use
heating
coil.
input
Add right
daily
drum or pipe
amount
Open escape
b)
insufficent
pressure
Increase
c)
gas
blocked
slurry
taps
Remove drum; clean
slurry
surface.
With sliding-drum
plants
turning
drum slightly breaks
crust.
blocked.
water.
inlet
of
Check seams, joints,
with soap water.
a) gas pipe is
by condensed
scum
bacteria
to five
by
cock.
weights
on drum.
!
Remove drum and clean inlet.
Close all
gas-taps;
fill
the gas line
with water;
apply pressure
through
moisture escape.
Drain water out,
increase.
Counterbalance
to 2 mm diameter.
"MAY BE THE CARBURETTOR IS JAMMED..."
TEMPERATURE TABLE
69
20.6
a9
31.7
145
62.7
70
21.1
90
32.2
150
65.5
06
=
(OF-32
“F=(OC
)
x
x
.0.5556
1.8
) + 32
-.
INFORMATION
AVAILABLE
ON APPROPRIATE
/
MINI
TECHNOLOGY - VOLUME I
and A. Bachmann
by B.R. Saubolle
TECHNOLOGY
Second Edition
Contains
36 low-key
projects
to make life
more livable:
water
heaters,
biogas,
sawdust
solar
stoves,
room
corn
and cooling,
sheller,
heating
crow
trap,
fly
and
much
more.
Abundantly
illustrated.
trap,
A real jewel!
MINI
TECHNOLOGY and
by A. Bachmann
VOLUME II
B.R. Saubolle
continues
volume
second
the
information
on
This
technology
for
rural
areas
and developing
countries,
not
available
where
electricity
is
from
the
yet
suggestions
based on experience
power grid.
It
gives
on fuel
efficient
stoves,
smokeless
kitchens,
energy
from
water.
Explains
also
methods
of rat'
disposal,
A welcome
addition
to the literature
in this
etc.
field!
BEEKEEPING,
by
B.R.
Saubolle
and
A. Bachmann
An introduction
to modern beekeeping
in Nepal.
Written
expressly
for
the
Apia
indica,
this
booklet
will
render
great
service
all
over South-East
Asia.
Clear,
to
the
point,
practical.
Treats
also
of
wall
and
log hives and of the African
Top-Bar Hive.
A treasure!
MULTI-PURPOSE
by A.M. Nakarmi
POWER-UNIT - With
and A. Bachmann
horizontal
water
wheel
This
booklet
explains
in a few words,
but with
many
diagrams
and photgraphs,
one of the latest
developments
in the field
of micro hydro-power
in Nepal.
In essence
it
is based on traditional
technology
and can provide
from two to five or ten horse power.
comes
in
The modular
design
standard
that
sizes
manufactured
in
porterable
are
loads,
so that
it
can
be
transported
easily
even
to
remote
areas.
This
device
aroused
has
considerable
interest
in
The booklet
provides
useful
information
many places.
of
alternative
and
renewable
energy
resources
in
rural
areas.
Published
Sahayogi
by:
Press,
Tripureshwar,
Kathmandu
7 04
FROM THE SAME PUBLISHER
ENERGY RESOURCES AND LOCALLYSMALL SCALE RENEWABLE
FEASIBLE TECHNOLOGY IN NEPAL
and G.R. Shakya
by A. Bachmann
provides
a collection
of
booklet
the
recent
This
achievements
in the field
of locally-feasible
technosome of
the
traditional
technology
also
logy
and
The combination
of
the
booklet,
that
of
in
Nepal.
the photographs
and the directory
will
the
article,
prove
to be a useful
tool
for people
activley
involved
in improvement
of rural
living.
A good pathfinder!
HOME BREW, by
B. Remi
A delightful
booklet,
explaining
how to make beers
Written
in a light
vein,
it
is profusely
and wines.
Advocates
only low-alcohol
and humorously
illustrated.
no destillation.
beverages:
A charming
production!
DRINKING WATER INSTALLATIONS
AND DRAINAGE REQUIREMENTS
by A. Bachmann
IN BUILDINGS IN NEPAL,
This
book
is based
on many years
of experience
in
The collection
includes
instalsanitary
engineering.
medium-pressure
water
lowand
lations
of
supply,
also is valuable
experienwaste water and gas. Included
The
solar
water
heaters.
locally
produced
ces
of
and has many technical
drawings
presentation
is clear
architects
and
planners
as well
and
is
made for
working
at
building
technicians
sites;
all
as for
conditions
to
Nepal
and useful
with
reference
to
to many other countries.
Several
times reprinted,
revised
edition.
MOUNTAIN ENVIRONMENT AND DEVELOPMENT
occasion
published
on the
A collection
of
papers
Swiss
Association
the
20th
anniversary
of
of
the
for
Technical
Assistance
in Nepal,
1976. This booklet
has been reprinted
several
times
and found
worldwide
distribution!
RENEWABLE ENERGY RESOURCES IN
NEPAL
Kathmandu
the
Workshop-Seminar,
Proceedings
of
Sahayogi
Press
and
April
published
by
l-4
1981,
Tribhuvan
University.
Recast,
view
of
overall
pi:ovides
a good
This
collection
solutions
for
urban
and rural
problems
and possible
populations
in Nepal.
BOOK REVIEW
FUEL
GAS
FROM COWDUNG
directed
to
people
who
This
booklet
is
wish to build
a biogas
plant
for
supplying
gas for cooking,lighting
and other
household
Detailed
constructions
are
purposes.
given
for
constructing
plants
of
several
Two general
designs
are presented.
sizes.
that
commonly
used
design
is
first
The
India,
which
is based
on the use of
in
collection.
The
for
drum
a metal
gas
(who
used
by the
Chinese
second
design,
do not
have easy
access
to metal
drums)
pressure-tight
use
of
the
based
on
is
the
space
enclosures
for
gas collection,
being
provided
my
the
for
needed
gas
chamber
being
connected
auxiliary
an
to the bottom
of the main pit,
into
which
part
of the slurry
flows
as gas is accumulated
in the top of the main enclosure.
While
the main trust
of" the booklet
deals
use
of
manure
from
the
with
cowdung,
dealt
with,
and
animals
is
also
other
also
the possible
use of
sanitary
wastes
that
the
noted
dwellings.
It
is
from
India
and
in
Nepal,
emphasis
in
chief
is
on the
book
was written,
the
where
gas
as
a
fuel.
Besides
production
of
slurry
effluent
the
gas production,
the
from the plant
is an excellent
fertilizer,
of
the
value
of
the
most
retains
which
this
purpose.
This
for
original
cowdung
the
plant.
By
usage
of
is
a secondary
that
the
primary
noted
contrast,
it
is
biogas
units
is
the
Chinese
purpose
of
with
fertilizer,
the
production
of
for
gas
as
a secondary
the
production
of
objective.
this
book
should
be
most
summary,
In
wish
to
helpful
to
those
readers
who
small-scale
install
practical
design
and
systems
for
producing
gas and fertilizer.
sufficiently
The
instructions
given
are
detailed
to provide
guidance
in the planning
and construction
of such plants
for specific
capacities.
SUNWORLD / Vol.6
/ No.
2 / 1982
a
FUEL
B.R.
GAS
FROM COWBUNG
Third
Edition
bY
and
Saubolle
An
excellent,
in
simple
of
methane
dung
-
clear
succint,
1Language
gas
abundant,
of
clear
diagrams
with
has
already
and
has
It
in
has received
principles
animal
This
distribution
the
from
in
booklet
exposure
production
measurements
and helpful
A. Bachmann
metric
and British
proved
several
systems.
gained
worldwide
very
practical
developing
countries.
much praise!
L
.
Booklets available fr0m3
U I’! 1 CEF
P. 0. Box 1184
Kathmandu 1 Nepal
.
Printed
at
in
Sahayogi
Nepal
Press,
Tripureshwar,
Kathmandu.