COMPARING SIMPLE CHARCOAL
PRODUCTION TECHNOLOGIES
FOR THE CARIBBEAN
by
Jeffrey L. Wartluft
and
Stedford White
MONTSERRAT
FUELWOOD/CHARCOAL/COOKSTOVE PROJECT
A cooperative effort by
the
GOVERNMENT OF MONTSERRAT, MINISTRY OF
AGRICULTURE (GOM)
CARIBBEAN DEVELOPMENT BANK
(CDB)
VOLUNTEERS IN TECHNICAL
ASSISTANCE (VITA)
and
UNITED STATES AGENCY FOR INTERNATIONAL
DEVELOPMENT (USAID)
VITA
1600 Wilson Boulevard, Suite
500
Arlington, Virgnia 22209
USA
Tel: 703/276-1800 * Fax:
703/243-1865
Internet:
pr-info@vita.org
March 1984
[C] 1984, Volunteers in Technical
Assistance, Inc.
TABLE OF CONTENTS
Acknowledgements
1.
Introduction
Objectives
2.
Procedures
Selection of techniques
Efficiency tests
Economics
Acceptability
Raw material
3.
Results and discussion
Efficiency
Economics
Acceptability
Raw material
Charcoal quality
4.
Conclusions
Appendixes
I.
Construction and use of carbonizing techniques
Montserration coal pit
3-pipe Mini CUSAB kiln
Montserratian kiln
Tongan kiln
New Hampshire (Black Rock) kiln
Jamaican retort with tar condenser
Jamaican retort with gas ports
II.
Relative efficiency testing procedures for charcoal kilns
III.
Charcoal kiln test data sheet
IV.
Species of wood commonly used in charcoal production
Bibliography
ACKNOWLEDGEMENTS
The
information presented here is the result of the cooperation
of many
people in several organizations. A
partial list includes:
C.T. John,
John Pitman, Nymphus Meade, and Franklyn Margetson of
the
Government of Montserrat; Dan Chalmers, Jeffrey Dellimore,
Carolyn
Cozier, and David Moore of the Caribbean Development Bank
(CDB); and
Richard R. Fera, John M. Downey, Jane Kenny, Margaret
Crouch, and
Julie Berman of VITA.
The people
directly involved with the authors at the project site
were Joseph
Daniel, Meredith White, and James Silcott.
Gratitude is
extended to the many secretaries, coal burners,
craftsmen,
and others that made this project possible.
1.
INTRODUCTION
Before the
energy crisis of 1973, the majority of people in
Montserrat
used liquid petroleum gases (1pg) for cooking.
Since
then, many
households have switched to more traditional fuels to
combat the
resulting price hikes and scarcities of 1pg, with the
result that
the 1980 Commonwealth Caribbean Population Census
(GOM, 1980)
estimated that 40 percent of Montserratian households
cooked with
wood and charcoal. In 1981 the
Government of Montserrat
(GOM) was
spurred into action by these revelations.
Realizing
that a
massive return to traditional fuels could have
disastrous
effects on the local environment, and suspecting that
traditional
pit methods of converting wood into charcoal were
inefficient,
the GOM acted to put together the resources and
expertise to
study ways to increase the efficiency of charcoal
production.
This effort would help assure a future
supply of
local
renewable fuel from forest resources.
With
financial and supervisory help from the Caribbean Development
Bank (CDB)
and financial and managerial help from Volunteers
in Technical
Assistance (VITA), the Montserrat Fuelwood/Charcoal/
Cookstove
Project began in 1982. [1]
The Project was an integrated
approach to
finding the best ways to substitute local
renewable
energy for imported, liquid-based fuels.
This report
presents the
findings of the charcoal portion of the project.
Montserrat is
a small island in the Caribbean with an area of 39
square miles
and a population of 11,606 (GOM, 1980).
Approximately
270 tons of
charcoal are produced each year by about 150 part-time
producers
(Wartluft, 1983). All of this charcoal
is produced
in pits dug
into the earth.
The world
literature on charcoal production presents the pit
method as
inefficient. For example, several
publications report a
maximum
efficiency of 15 percent for pits (Agarwal, 1980; Roos,
1979; Earl,
1975). One goes so far as to state that
for this kind
of yield on a
dry weight basis the carbonization has to be perfect,
and the pit
fitted with a vent pipe. Deal reports a
much
higher
efficiency of 20 percent (20 stacked cubic yards of wood
yields 1 ton
of charcoal) on a green weight basis for earth kilns
in Uganda
(Earl, 1974). In these publications,
all other types of
kilns are
reported to give higher yields than earth pits, averaging
around 25
percent on a wet or air-dry weight basis.
Some
mention is
made of the high variability of yields from the pit
methods.
In some cases percent efficiencies are given
with no
reference to
the base used (dry, air-dry, or wet weight) or
whether
measurements were actually taken.
[1]
CDB and VITA funds in this project were from
USAID's renewable
energy
project.
When wood is
converted to charcoal, over half of the energy value
is lost.
Why then even consider charcoal if
efficiency is the
issue?
The most convincing reason is that charcoal
is preferred.
It is
preferred because it is lighter and less bulky, making it
easier to
transport. Charcoal stores
indefinitely, whereas wood
is attacked
by insects and fungi that reduce its energy value.
And charcoal
is a more concentrated heat source and puts out less
smoke than
wood. A less obvious reason is that
carbonization of
wood is an
easy way to break down large pieces to a size easy to
use for
cooking. Otherwise, the large pieces
might rot on the
forest floor
(FAO, 1983).
OBJECTIVES
The
objectives of the project were to:
1.
substitute local renewable fuel for imported fuel,
2.
use the forest resource wisely, and
3.
create local industry and employment.
More
specifically for the charcoal portion of the project, we
wanted to
find the best charcoal production techniques in terms
of
efficiency, economics, and acceptability.
An efficient technique
would produce
the greatest quantity of good quality charcoal
from the
smallest amount of wood and labor input.
But it
would have to
be economical as well. And regardless
of efficiency
or economics,
to make an impact the technique would have to be
acceptable to
the charcoal producers.
2.
PROCEDURES
To meet these
objectives, we selected eight designs to compare
with the
standard 'coal pit." Our research marked the first time
that so many
simple charcoal technologies were scientifically
tested by the
same team in the same location and under the same
conditions.
SELECTION OF
TECHNIQUES
Several
criteria were used in selecting carbonization techniques
for
comparative testing. We wanted simple,
inexpensive techniques
using
equipment that was capable of being fabricated locally.
To
save time, we
selected techniques that had already been tried and
reported on
in the literature.
At the
outset, five designs were selected:
* the 12-pipe mini CUSAB (Little, 1978),
* Costa Rican kiln (Instituto Tecnologico
de Costa Rica),
* Tongan kiln (BuLai and Rocholson),
* New Hampshire kiln (Baldwin, 1958), and
* Jamaican retort with tar condenser
(VITA, 1978) (Jamaica
Scientific Research Council) (Appendix
I).
Of these, two
were modified before testing. The
round, tapered
New Hampshire
kiln was built with straight sides and in an octagonal
shape due to
shop limitations. The 90-cubic-foot
size was
dictated by
the size of steel sheets available. The
Jamaican
retort as
presented in the literature is built with six or eight
used 50-gallon
oil drums. For our research purposes,
and to make
the retort
more portable, we used just two drums welded together.
Other
modifications were made in order to improve the operation
of the
equipment. Our first modification was
to the Costa Rican
kiln, which
took too long to carbonize wood, and produced many
brands (not
fully carbonized pieces of wood). We
dropped the
Costa Rican
model, and dubbed our modified kiln the "Montserratian."
In place of
two 6-inch square holes in the drum bottom,
we put one
round 6-inch diameter hole in the center of the
bottom.
To eliminate having to turn the drum upside
down to seal
it off for
cooling, we left a 1-1/2-inch lip around the edge when
cutting out
the top. On this, a full top from
another drum or a
round piece
of galvanized sheet metal rested. Sand
was piled on
top of this
to seal any openings. The operating
procedure was
also
changed. Rather than cutting all wood
to 17 inches and
stacking the
bottom half solidly, wood was cut the length of the
drum and stacked
vertically, leaving a 6-inch diameter full-length
opening in
the center for ignition and air flow.
The 12-pipe
mini CUSAB was very troublesome to operate, with tin
cans falling
off and air leaking from cracking clay.
From the
literature we
found a modification using just three pipes instead
of
clay-filled tin cans to seal the pipe ends.
The pipes were
threaded and
end caps were simply screwed on by hand.
We also
sealed this
model in the same way as the Montserratian to eliminate
the necessity
of turning the drum upside down. The
12-pipe
model was
discontinued in favor of the 3-pipe model.
Several
modifications were made to the retort.
A serious problem
was that nuts
oxidized onto the bolts when heated, making them
difficult to
loosen. First we tried welding a
1/2-inch rebar
around the
drum opening, to which the cover bolt heads were then
welded.
This prevented the bolts from turning with
the nuts. But
our second
modification with tabs, slots, and wedges was most
effective.
The reinforcing ring was retained as a
sturdy base on
which to weld
the slotted tabs.
Because so
little tar was produced--about 1 pint per charge--we
tried and
preferred the retort with gas ports.
There was about a
50 percent
savings in the scrap fuel and labor time needed to run
the process
with gas ports, but little similar advantage to tar
production.
We found the best placement for gas pipes
was in the
front third
section of each drum. Another effective
innovation
with the gas
port model was the use of a piece of tin to cover
the firebox
opening once the gas ports were lit.
This helped keep
heat in and
cool breezes out. Without this, the
retort produced
more brands
near the cover.
The last
modification to the retorts was an insulated cement
block and
poured, reinforced concrete housing over the retort.
The drums,
mounted on one foot high legs, slide in or out for
repair or
replacement. This was done after the
eighth burn on one
retort burned
out the tin that supported the earth insulation.
The cost of
replacing the tin every eight burns represented about
half the
value of the product. The economics of
this modification
remains to be
proven, as it was built near the end of testing.
However,
cement and cement blocks hold up well under heat in
Montserrat.
EFFICIENCY
TESTS
At least five
tests were made on each kiln and retort design.
Tests were
made to measure the yield in pounds of marketable
charcoal in
terms of the oven-dry weight of wood used.
Marketable
charcoal was
that which did not pass through a 1-inch mesh
screen.
To arrive at oven-dry weights of wood, we
determined the
moisture
content of sample disks that were cut from the wood
going into
each test charge (Appendixes II and III).
The same wood
supply, location, and operators were used for all
tests except
for those on "coal pits." Measurements were made on
actual coal
pits being operated by Montserratian "coal burners."
Results of
these tests were expressed as percent yield on an
oven-dry
basis: the number of pounds of charcoal produced from
each 100
pounds of oven-dry wood used. As a
matter of interest,
they were
also expressed as the percent net heat value; that is,
the Btu's of
charcoal yielded from each 100 Btu's of wood input.
ECONOMICS
In order
to determine the economics of using the different
carbonizing
techniques,
records were kept on labor and materials
costs to
build equipment, any maintenance costs
incurred during
operation,
and the number of person hours of work involved in
operating the
equipment. Along with data from yield
tests on the
average
amount of charcoal per burn, the number of burns possible
in a year,
and equipment life, we were able to calculate the
proceeds per
dollar of investment, with and without labor costs.
Proceeds over
the life of the equipment were calculated by using
the average
yield of charcoal per burn, times the estimated burns
per year (50
weeks) for full-time operation, times the estimated
number of
years of equipment life, times the price of charcoal,
estimated at
EC$.50 per pound. Since charcoal is
sold by volume
at EC$5 per
tin (9 x 9 x 14 inches), its price per pound varies
with the bulk
density of charcoal. A typical tin of
charcoal
weighs from
10 to 12 pounds (EC$.50 to $.42 per pound).
Investment
over the life of the equipment was figured as the
total
purchase cost plus any maintenance costs incurred during
the life of
the equipment. Investment and labor
costs included
the above
plus the person hours needed to operate the equipment
times EC$3
per hour labor rate.
The
comparative figures used were the proceeds divided by investment
plus
labor. The results showed the expected
income derived
from each
dollar of expenditure with and without labor costs.
ACCEPTABILITY
Feedback from
field tests of different techniques with Montserratian
coal burners
helped us judge the relative acceptance of
the
techniques. To introduce the techniques
to coal burners, we
held a
well-advertised demonstration of all models.
To help
assure an
audience we sent a letter to each known coal burner,
and offered lunch
and bus fare. During the demonstration
we
offered to
lend kilns and retorts to interested parties in exchange
for feedback
on what they liked or disliked about the
different
techniques, and why.
RAW MATERIAL
From
observations of local methods of charcoal production and
conversation
with coal burners, we gained an appreciation for the
preferred
species, sizes, and moisture conditions of the wood
used.
We took a
number of moisture content samples of fresh-cut wood to
determine
which species were the driest, and therefore more
efficient for
carbonizing without seasoning. For
three of the
most popular
species, we took periodic moisture content samples
from piles
seasoning under roof for 10 months.
This was to indicate
the amount of
time necessary to season these species to air
dry
condition, about 20-25 percent moisture content (green basis).
3.
RESULTS AND DISCUSSION
EFFICIENCY
Out of the
16.56 oven-dry tons of wood processed in 51 tests, the
most
efficient carbonization technique in terms of yield was the
retort.
The retort with tar condenser averaged 34
pounds, and the
retort with
gas ports averaged 33 pounds of charcoal per 100
pounds of
oven-dry wood (see Table 1.)
Table 1.
Average Yields of Charcoal by Carbonization Method
Yield
Average
Wood
Yield
Moisture
Oven-dry
Net
Content
Oven-dry
Yield Heat
Carbon-
(percent)
Weight
Coefficient Value
ization
No. of
(green Basis
of
Basis
Method
Trials
basis) (percent)
Variation
(percent)
Retort
11
21 34
.22 51
with tar
condenser
Retort
7
25 33
.29
50
with gas
ports
Montser-
7
32 29
.10
45
ratian
coal pit
New
6
27 26
.37
40
Hampshire
kiln
Tongan
6
24 23
.45
36
kiln
Mini
5
27 22
.24
35
CUSAB
kiln
Montser-
9
26 21
.35
32
ratian
kiln
Among the
kilns, the yields decreased with decreasing kiln size.
The largest
kiln, the coal pit, had an average yield of 29 pounds
and the three
small single-drum kilns had yields averaging 22
pounds of
charcoal per 100 pounds of oven-dry wood. In between
these was the
New Hampshire kiln yield of 26 pounds for every 100
pounds of
oven-dry wood. It is interesting to see
that the coal
pit yields
varied less than any of the others.
This is most
likely due to
the extensive experience of coal pit operators.
With the
exception of the coal pits, our results were comparable
to results of
trials in other parts of the world. Our
Mini CUSAB
and Tongan
models were within 1 percent of the yields found for
these models
in Fiji (Rocholson and Alston). The New
Hampshire
kiln yield of
approximately 24 percent in a cold climate compares
with our
average yield of 26 percent (Baldwin, 1958).
The well
known
Tropical Products Institute (TPI) kiln of similar design
and capacity
had yields averaging 26 percent in trials from seven
countries
(Paddon and Parker, 1979; FAO, 1983).
And in Ghana a
similar kiln
had yields from 22 to 26 percent (Lejeune, 1983).
Retorts have
higher yields because all of the wood is converted
to
charcoal. In kilns, some of the wood is
burned away to provide
process heat,
while any scrap fuel can be used to carbonize the
wood in the
retort. For instance, during our tests
we used coconut
husks, scraps
from a neighboring wood working shop, drift
wood, wood
from species not suited for conversion to charcoal
such as
flamboyant, branches of acceptable charcoal species that
were too
small to be marketable, and cardboard scraps from the
supermarket.
Retorts use the gases coming out of the
wood, while
kilns waste
most of these gases. In the model with
the tar condenser,
gases are
condensed into tar, which is useful in preserving
wood and
metal and in patching roofs. In the
model with
gas ports,
the gases become part of the fuel for the process.
Even though
the retort extends the usable resource and gives
higher
yields, it requires more work gathering fuel.
About 350
pounds of
scrap wood fuel were used per five-hour firing of the
retort with
tar condenser. Close to half that much
fuel and
person hours
were used by the retort with gas ports.
Three hundred
fifty pounds
of 1- to 6-inch diameter wood is less than half
of a pick-up
load. The same weight of light branches
could take
up to two
pick-up loads. The typical pick-up load
of crooked
green wood
weighed 1500 pounds.
The
"coal pit" earth kiln did much better than expected.
The
slower
carbonizing process and lower temperatures used in the
coal pit did
not drive off as many volatiles from the wood as the
faster,
higher temperature kilns and retorts.
As a result, the
charcoal from
coal pits was heavier than that from kilns and
retorts.
We operated our kilns and retorts fast, as
one of the
advantages
was supposed to be a shorter turnaround time giving
potential for
greater production. Since the greater
weight per
volume of
coal pit charcoal was due to volatiles, the heat value
per volume
was greater. One tin of coal pit
charcoal weighed 12
pounds,
whereas the kiln and retort charcoal from our tests
weighed about
10 pounds per tin. Kilns and retorts
can be operated
more slowly,
yielding charcoal of greater weight.
Research in
Germany has shown that it takes more energy to drive
moisture from
wood during fast carbonization than it does in slow
carbonization.
[2]
This energy savings in slower-burning coal
pits
contributes to their good yields too.
Another
difference in the operation of the coal pits versus the
kilns and
retorts in terms of our research, was the operator
[2]
Personal communication with Dr. Arno
Fruhwald.
experience.
Coal pits were operated by veteran coal
burners,
while the
kilns and retorts were operated by first timers.
With
more
experienced operators, the metal kilns could probably be
expected to
give better yields.
In order to
find out the strength of fire needed under a retort
to raise the
internal temperature to the optimum 900 degrees F
(USDA Forest
Service, 1961), we used a pyrometer with thermocouple
placed in the
center of the charge. When we fired the
retort as
hard as we could, the internal temperature reached a
maximum of
1250 degrees F at the end of the burn, five hours
after
ignition. From this we learned that a
vigorous but not all-out
fire was
necessary.
Regarding
efficiency in terms of person hours, there was less
wood cutting
for coal pits, but more hard work gathering grass
and shoveling
"mold" or dirt, and then separating the mold from
the finished
product. All metal kilns required
several well-timed
adjustments.
The operation of the New Hampshire kiln was
relatively
controllable.
Any adjustments were definite and stayed
that way
until the next adjustment was made.
Adjustments to the
coal pit were
less definite as the mold could shift at any moment
and create an
unwanted vent hole, or close an intentional one.
The
single-drum kilns required the most constant attention.
Adjustments
such as shaking the drum were only temporary and had
to be
repeated frequently.
In contrast
to kiln operation, all that was necessary in retort
operation was
to stoke the fire. The successive
stages of carbonization
were easy to
discern in the retorts, which gave a
sense of
confidence in the expected results. A
group of 8- to 14-year-old
boys
successfully operated a retort on their first try
without
supervision.
ECONOMICS
With
practically no initial investment, the coal pit was clearly
the most
economical (see Table 2). Including the
cost of labor,
the coal pit
returned an estimated US$8.60 for every dollar
spent.
The next closest method, the New Hampshire
kiln, returned
an estimated
US$4.60 per dollar of expenditure.
Single drums
because of
low yields, and retorts because of short lives, managed
to earn only
$1.34 and $1.05 respectively for each dollar of
outlay.
None of the methods lost money according to
our estimates.
These
comparisons were done on one unit of each type.
Some favorable
adjustments could
be made to several of the techniques.
Simultaneous
operation of several units of the smaller drums with
very little
addition to labor cost should increase returns.
In
the case of
the retorts, a favorable change in economics could be
made by
increasing the size of the unit.
Table 2. The Economics of
Different
Charcoal Techniques
Coal
New
Single
Item
Pit
Hampshire
Drums Retort
Charcoal
product/charge 654
285
41 77
(pounds)
[a]
No.
charges/week for a 1
3
5 3
single unit
Charcoal
proceeds/year 16,350
21,375
5,125 5,775
(EC$)
[a]
Initial
investment 5/burn
3,000
40 400 [c]
(EC$)
Equipment
life 10
2
.05 0.1
(years)
Proceeds/dollar
of 65
14
64 3
investment (EC$)
Person
hours/week to 11
21
25 25
operate a single unit [d]
Proceeds/dollar
of 8.60
4.60
1.34 1.05
investment and labor
(EC$)
[a] Charcoal
yields based on 5-18 trials per technique.
[b] Charcoal
price = EC$.50/pound.
[c] First
installation, thereafter EC$150.
[d] Labor
rate = EC$3/hour; exchange rate: EC$2.70 = US$1.00.
ACCEPTABILITY
The time
available to spend with coal burners while they field-tested
kilns and
retorts was limited. However, we were able to
get some
feedback from Montserratians who tried them. Approximately
half the
island's coal burners (74) were present at our
day-long
demonstration. After the demonstration, six Montserratian
kilns, four
retorts, one Tongan kiln, and one New Hampshire
kiln were
lent for field testing.
The island's
largest charcoal producer field-tested the New Hampshire
kiln. It took
him several burns, one with our kiln operator,
to learn how
to operate it. He has slowed the
process down
by closing
all vent holes almost entirely and using just two of
four
chimneys. This has given his customers
the heavy charcoal
they
want. They complained about the lighter
charcoal he made
when he
burned it within 12 hours. He maintains
that they are
starting to
prefer the metal kiln charcoal to the coal pit charcoal
because it
lights more easily. This, he figures,
is because
he does not
need to douse embers with water as he does with the
coal pit
product. The only problem is that it
does not carbonize
well pieces
of wood over 6 inches in diameter. In
the coal pit,
he fully
carbonizes pieces up to 16 inches in diameter.
He claims
that his
yield is better with less work with the New Hampshire
kiln.
He has purchased a used chain saw, and wood
cutting is no
problem.
Before the chain saw, he tried our bow saw
and saw horse
and liked
them very much.
For coal pit
modification, we had some 4-inch diameter pipe made
into 6-foot
long chimneys with tripod legs welded on the bottom
to keep them
upright. This same coal burner has
tried and likes a
chimney at
the end of his coal pit. He claims that
the process is
speeded up,
the product is more uniform, and the yield is better
than without
the chimney. The chimney changes the
air flow by
removing
smoke from the bottom of the pit rather than the top.
This forces
more heat lower into the charge and results in fewer
brands at the
bottom of the pile.
The retorts
have been well received; one man tried 11 successful
burns, and
the boys at the Boy's Home ran successful burns, too.
It was not
necessary to have project personnel help operate
retorts.
one man found out, though, that large, green
pieces did
not carbonize
well in the retort. The tar-condensing
feature has
not been
embraced by any field tester--all have gas port models.
The
single-drum kilns were solicited by a number of Montserratians
who wanted to
make charcoal for their own use. To
date,
we have not
received any enthusiastic response from field testers
of these
models. Problems seem to be smoke in
the eyes, and too
much
attention needed compared to a small coal pit.
Again, we
have not had
the time needed to meet with these people to help
get them
started.
At the outset
of the project, portability of kilns was to be of
major
importance. We learned, however, that
the great majority of
coal pits are
near the coal burner's houses so they can control
them
better. They told us of the wasted
efforts of setting a pit
in the forest
only to have it "blow" to ashes because it could
not be
monitored well. Coal burners routinely
pay for transporting
wood to their
houses. The distance is rarely more
than three
miles.
They do their own cutting and piling at the
roadside.
RAW MATERIAL
From years of
experience, coal burners have found out which
species are
most suitable for charcoal production.
These appear
in a list in
Appendix IV in approximate order of priority.
The moisture
in wood has a negative effect on charcoal yield,
both in
quantity and in time. Coal burners know
this, but much
green wood is
carbonized for reasons of expediency.
Fresh-cut
moisture
contents are listed in Appendix IV for the species we
measured.
Three of the most common species dried to
optimum
conditions in
about two months (Figure 1). After this
time,
2ap12.gif (600x600)
drying slowed
considerably and insect destruction built up.
Montserratian
coal burners
often season their wood for two to four
weeks,
sometimes more. We calculated the
effect of seasoning on
charcoal
yield. For those trials where the wood
was above 35
percent
moisture content (green basis), the average yield was 24
percent.
For wood with less than 20 percent moisture
content
(green
basis), the average yield was 28 percent.
These measurements
were taken
over all the different kiln models.
For converting
green weight of wood to stacked cubic volume and
vice versa, a
number of measurements were made during the resource
assessment
phase of the project. Table 3 gives the
results
for the
species listed in Appendix IV.
Table 3.
Conversion Factors for Green Weight of Wood
to Stacked Cubic Volume
Conversion
(green pounds
Type of Wood
per stacked cubic foot)
Suitable for charcoal --
22
less than or equal to 3. 8 inches
diameter breast height (dbh)
Greater than 3.8 inches dbh
27
Not suitable for charcoal
19
Overall
23
These
conversion factors may be helpful in estimating yields
where no
scales are available. Or they can be
used to convert
commonly used
forestry measurements of stacked volume to weight
for fuel
value or charcoal conversion estimates.
CHARCOAL
QUALITY
What is good
quality for cooking? Montserratians like
charcoal in
big, heavy
pieces. The higher density gives more
"substance" or
heat content
per volume, and so lasts longer in a stove.
It also
does not
readily break up into fines. Because it
has a relatively
high
percentage of volatiles, it lights more easily too.
The fact
that it
smokes a bit more is of lesser importance.
This type of
charcoal
comes from coal pits in the way they are normally operated,
but with
experience, can come from kilns and retorts too.
4.
CONCLUSIONS
Our testing
shows that, in spite of the energy losses incurred in
converting
wood, charcoal is a worthy cooking fuel for Montserrat
and that
traditional production methods are not unnecessarily
wasteful.
The traditional Montserratian coal pits can
provide
yields of
charcoal that are comparable to the yields from larger
metal kilns
and retorts, and are superior in yield to single-drum
kilns.
They are the least expensive method of
carbonizing wood.
Moreover, the
coal pits can be modified with a simple chimney to
increase charcoal
yield and uniformity.
Metal kilns
and retorts can be burned at a slower rate to improve
yield and
charcoal quality, according to our tests, but require
extra wood
cutting, although less overall physical work than coal
pits.
We also found
that large, green pieces of wood do not give good
results in
metal kilns or retorts. Seasoning wood
before carbonizing
does give
better yields, with two months as the optimum
time for
seasoning.
Our research
experience also leads us to the following suggestions
for future
research and other programs:
*
A retort made with steel sheet (3/16 or 1/8
inch thick) rather
than used drums might favorably alter its
economics.
*
Clean, bagged charcoal could replace the
small amount of
imported charcoal briquettes.
*
More information should be gathered on
species' green moisture
contents, seasoning rates, specific
gravities, and conversion
factors for weight to stacked cubic volume.
*
A dissemination program should be mounted to
get maximum exposure
of the past year's results.
The theme should be "charcoal
is an alternative fuel for everybody."
*
Additional work on the use of simple
chimneys to improve coal
pit performance could be beneficial.
Yield measurements should
be used to help judge the effectiveness of
chimneys.
*
An educational program should be set up on
"good forest
harvesting practices" for coal
burners.
APPENDIX I
CONSTRUCTION AND USE OF CARBONIZING
TECHNIQUES
MONTSERRATIAN COAL PIT
02p03z.gif (600x600)
CONSTRUCTION
Tools
*
shovel (spade), cutlass (machete)
Materials
*
loose dirt, green leaves and/or grass
Method
Excavate a
pit four to six feet wide by five to 100 feet
long, by one
to four feet deep in the ground. Orient
the pit
length
parallel to the prevailing winds.
Provide for drainage
by digging a
small canal as deep as the pit and sloping away
from the
pit. Lay two parallel stringers (sticks
or poles)
about three
to four inches in diameter and three fee apart on
the bottom,
along the length of the pit. On top of
and perpendicular
to the
stringers, pile the wood to be carbonized.
All the wood
should be cut to the same length. Pile
the wood
tightly to
minimize void spaces. Short cut-offs
can be used
to fill in
void spaces. Leave three or four inches
of clearance
between the
piece ends and the sides of the pit.
Put two
five feet
long stakes into the ground at each end of the
stringers at
stringer width. These stakes will hold
up the
ends of the
pile and will be used to help control the draft
when the kiln
is in operation. Stack larger and
smaller
diameter
pieces together, but most of the larger pieces
should be in
the top half of the kiln. At the end
chosen for
lighting
(usually the windward end), stack dry sticks and
brands from
previous burns. This will help the burn
get
started.
After stacking, cover the entire pile with
green
grasses and
leaves so that the wood canot be seen.
About a
two inch
layer will do. Then shovel about three
inches of
dirt over top
of the entire pile. The four stakes
should be
sticking
about six inches above the dirt. In
pits longer than
10 feet,
stakes can be jammed into each side of the pit so
they stick
into the wood pile and protrude from the dirt on
the outside.
They can be supported by a Y shaped stake on
the
outer end for
stability. At the bottom center of the
windward
end where the
pile will be lighted, leave a one foot square
opening in
the dirt and grass.
To light the
kiln build a small fire, and when well underway
with good
coals, shovel the coals into the base of the pile
at the
lighting point. Alternate ways of
lighting are to use
a kerosene
soaked rag or a few hand-size pieces of old rubber
tire inserted
in a hole under the lighting point and lit.
In
a matter of
minutes smoke will be seen coming out the opposite
end of the
pit (or part way along the sides in a long
pit).
A small opening can be left near the top at
the leeward
end to help
promote an initial draft. After 15
minutes or so
when the smoke
is readily coming out of the leeward end of
the kiln,
both holes can be filled in first with grass, then
with
dirt. As long as the kiln is emitting
thick white smoke,
carbonization
is proceeding as planned. When blue
smoke is
spotted, too
much air is getting in at that spot and the hole
there, which
will be obvious, should be covered with grass
and dirt
until the blue smoke stops. As
carbonization progresses,
the height of
the pile will slowly collapse to about
one half the
original height. If white smoke slows
way down
or stops
emitting, air can be let in the pile by wiggling the
protruding
stakes. The rate of burning will depend
on the
amount of
moisture in the wood, the size of the wood, the
density of
the wood, and the amount of air allowed to pass
through the
kiln. About 40 stacked cubic feet of
wood will be
processed
each day. So a stack of wood five by
four by 10
feet would
take about five days to carbonize. When
carbonization
is complete,
allow the pit to cool off as long as there
is no smoke
coming from the pile, for at least one day.
When
extracting
charcoal, keep a water bucket nearby to douse any
live
embers. The charcoal should be allowed
to air out in a
place where
there is no fire hazard for at least 24 hours
before
storing it where it could cause damage if lit.
<MONTSERRATIAN
COAL PIT>
AFRICAN 3-PIPE MINI-CUSAB
02p05.gif (437x437)
(MODIFIED FROM THE 12-PIPE MINI CUSAB)
02p06.gif (540x540)
CONSTRUCTION
Tools
*
welding/cutting equipment, chisel, hammer
Materials
*
50 gallon drum
* cover from another 50 gallon
drum, or equivalent piece
of flat tin
*
3 pieces of threaded 2" pipe about 3" long
*
3 threaded caps for the pipes.
Method
Cut 3 holes
along the length of the barrel the same distance
away from
each other. Weld a piece of pipe to
each hole,
threaded end
facing away from drum. Cut out the top
of the
barrel,
leaving a 2 inch lip around the top edge.
OPERATION
To operate
the mini-CUSAB, unscrew the cap from the bottom
pipe and face
the pipes into the wind. Start a brisk
fire in
the bottom of
the drum. Begin to add wood about 3'
long or
shorter until
the kiln is about half full. Allow the
kiln to
burn until
red coals can be seen in the bottom of the kiln
through the
hole. Close off the bottom hole with
the cap and
open the
second one. Continue to add wood to the
kiln. Allow
it to burn
until red coals can be seen in the second hole.
Close this
hole and open the top and final hole.
Allow the
kiln to burn
until it is full of charcoal. Then
close the
final hole,
put the cover on and seal the kiln by putting
sand on top
of the cover around the edges. Be sure
that no
air is
getting into the kiln. Throughout the
burn, be sure
that thick
white smoke is coming from the kiln. If
the smoke
is blue that suggests
that too much air is in the kiln and
the charcoal
is being burnt up. The kiln can be
controlled by
shaking the
kiln, packing it tightly with wood and putting
the cover on
to reduce the quantity of air getting into it.
<AFRICAN
3-PIPE MINI-CUSAB>
<AFRICAN
12-PIPE MINI-CUSAB>
MONTSERRATIAN KILN (MODIFIED FROM COSTA
RICAN KILN)
02p08.gif (486x486)
02p09.gif (486x486)
CONSTRUCTION
Tools
*
hammer, chisel, tape
Material
*
50 gallon drum
*
cover from another 50 gallon drum, or equivalent piece
of flat tin.
Method
Cut a 6 inch
diameter round hole in the center of the bottom
of the drum.
Cut out the
top of the drum, leaving a 2 inch lip around the
edge.
OPERATION
Set drum
about 4 inches off the ground on some logs or rocks.
Load 32-33
inch long sticks vertically in the drum, leaving
an open
6-inch diameter column in the center.
Pack the sticks
so as to
leave as little air space as possible.
In the open
center column
put paper and dry sticks right into the top.
Light the
kiln by pushing a lit ball of paper underneath the
drum at the
open hole. As the kindling burns, add
more fuel,
dry at first
and greener wood later. When the top
outside of
the drum gets
too hot to touch, knock out the logs (stones)
from
underneath the drum so that it sits on the ground.
Continue
to add fuel
as the burned wood falling down permits.
After an hour
or so a load of wood is put in with some sticks
protruding
slightly above the top of the drum lay the lid on
top.
This will slow down the burning rate.
At about hourly
intervals
wood can be added for the next 3-6 hours.
If the
fire
threatens to go out, take the lid off.
A more extreme
measure would
be to tilt the drum for a short time.
Set it on
a small stick
or rock to let more air in the bottom.
Load
brands from a
former burn last. To slow down the
burning at
any time,
shake the drum to settle the wood down.
This
reduces the
air spaces between wood pieces. When
smoke turns
from mostly
white to mostly blue, and (by inspection under
the lid) all
the wood has apparently carbonized on the outside
of the
pieces, seal the kiln by putting fine, clean
(no sticks,
leaves, etc.) sand around the base and around the
edge of the
lid. Make sure no air can get in or
smoke get
out.
Let the kiln cool down overnight before unloading
charcoal the
following day.
<MONTSERRATIAN
KILN>
<COSTA
RICAN KILN>
TONGAN KILN
02p12.gif (486x486)
CONSTRUCTION
Tools
*
chisel, tape, hammer
Materials
*
50 gallon drum
Method
Cut out an
8" strip down the length of the drum.
Keep the
piece cut out
to be used as a cover.
OPERATION
Firing
Lay the kiln
on its side with the opening facing toward the
wind.
Prop the kiln with a stone so that the
bottom edge of
the opening
is about 3" from the ground. Start
a fire in the
kiln (with
twigs, etc.) across its full length.
Add dry
sticks.
Be prepared to turn the kiln into the wind
at all
times in
order to maintain an even and vigorous fire.
First Loading
When there is
a good, strong and even fire going, add more
wood slowly,
the small pieces first to ensure that the fire
maintains its
vigorous state. Stop adding wood when
its level
comes up to
just above the bottom edge of the opening.
Leave
sufficient
time for the wood to burn into embers, then roll
the kiln back
by removing the stone that is propping it in
preparation
for the second loading. Brands, which
are the
partly burned
wood from previous burns, can be loaded into
the kiln when
the fire is burning vigorously or at any stage
after the
first loading.
Second
Loading
Prop the kiln
so that the bottom edge of the opening is now
about 6"
- 8" from the ground. This will
help to block air
from the
charcoal already formed during the first loading.
Add more
wood, making sure that even burning and strength of
the fire are
maintained. Stop adding wood when its
level
comes above
the bottom edge of the opening. Leave
sufficient
time for the
wood to burn into embers, then roll the kiln
back in
preparation for the third loading.
Third Loading
At this stage
the opening should be about 12" - 16" from the
ground.
Add the larger wood, making sure that even
burning
and strength
of the fire are maintained. Stop adding
wood
when the
level comes up to the top edge of the opening.
Allow
the wood to
burn into embers.
Final Loading
Rotate the
kiln so that the opening is pointing straight up.
Add wood,
making sure that even burning and strength of the
fire are
maintained. When the kiln is filled
with wood, allow
sufficient
time for burning into embers.
Sealing Off
When all wood
from the final loading has carbonized, take the
cut-out piece
obtained during the construction of the kiln
and cover the
opening with it. Roll the kiln over so
that the
sealed
opening lies flat on the ground. Using
gloves, hold
the cover in
place while rolling the kiln. Seal the
bottom
edges with
sand to make the kiln airtight. Leave
sufficient
time for the
kiln to cool off, usually about 4-5 hours,
before taking
out the charcoal.
<TONGAN
KILN>
NEW HAMPSHIRE (BLACK ROCK)
KILN
02p17.gif (600x600)
CONSTRUCTION
Tools
*
welding/cutting equipment, tape, straight edge
Materials
*
Two sheets of 1/8" or 3/16" plate steel 61' x 101'
*
24 lineal feet of 4" galvanized pipe
*
Four 4" galvanized pipe elbows (optional)
*
40 inches of 1/2" reinforcing rod (5 handles)
*
40 lineal feet of 2" angle iron
*
eight pieces of tin seven inches square or eight paint
can lids.
Method
For the kiln
body, cut one steel sheet in half lengthwise.
On
each half mark
three perpendicular lines across the width so
that the
length is quartered. Each section
should be two and
one half feet
wide. Along each marked line cut three
slots
which
represent about one half the total line length.
This is
to weaken the
sheet to facilitate bending along the line.
Cut
a cardboard
model of an angle of 135 degrees. Bend
each sheet along
the lines so
that each bend fits the cardboard model.
A temporary
jig can be
made to hold the sheet during bending.
After
bending, weld the two pieces together to make an octagonal
shape.
Weld the bending slots so that they are air
tight.
Reinforce all the way around the bottom by
welding on
angle iron.
Weld angle
iron right around the top so that it acts as reinforcement
and a cup to
hold sand and support the cover. At
the bottom
center of each section, firmly weld an eight inch
square piece
of sheet steel. Cut a hole through each
of these
and the body
so that the holes are centered in the reinforcing
plates.
These eight holes should be slightly larger
than
the outside
diameters of the pipe elbows to allow for easy
insertion of
the pipes, but small enough to hold the flue
pipes
vertically without further support.
From the
second sheet, cut the cover so it has a conical
shape, fits
inside the top angle iron and has an eight inch
diameter hole
at the top. The eight triangles that
make up
the cover are
measured on the sheet with bases of 30 inches
and sides of
38 inches. To minimize expensive
cutting, two or
three
adjacent sections can be cut out as one piece.
In this
case the slot
method can be used to bend on the lines between
sections.
Before
welding the sections together, present them in place
with the
bases of triangles resting on the top angle iron of
the body and
the tops resting on some makeshift support in
the
center. Since it is difficult to cut
and bend precisely
this is the
chance to custom fit the cover to the body.
Any
overlaps of
one section over another can be marked to guide
final
cutting. When all sections fit, they
are welded together.
Then an eight
inch diameter hole is cut in the top
center of the
cover. An eight inch diameter chimney,
eight
inches tall
is welded around the hole. Then a cap
is made to
fit over the
chimney. Sides of the cap should
extend down to
the
cover. A two inch high collar is welded
around the bottom
of the
chimney to hold the sand that seals off the bottom of
the cap when
it is on the chimney. Using 1/2 inch
reinforcing
rod, handles
are welded on top of the chimney cap and on the
cover.
Four handles are spaced on the cover for two
persons
to put it on
and take it off.
Four flue
pipes about six feet long are made from four inch
pipe.
If elbows are available, they are threaded
or welded
onto the
bottom end. If elbows are not
available, a six inch
long piece
from the bottom end can be cut off at 45 [degrees], rotated,
and welded
into a 90 [degrees] bend.
OPERATION
Loading the
Kiln
Cut wood to a
length approximately equal to the height of the
kiln (3 feet
in our case). Prepare the core about
which the
wood will be
stacked by tying three sticks together at one
end to make a
tripod. Place the tripod in the exact
center of
the
kiln. Crumpled paper, dry sticks, and
twigs are piled
between the
tripod legs. The wood to be made into
charcoal is
carefully
leaned vertically against the tripod and is piled
equally
around all sides. The longer pieces of
wood should be
placed near
the center.
Larger
diameter sticks should be packed about a quarter of
the way from
the center to the outside. Stick
diameter should
be limited to
6 inches. Larger pieces can be split
lengthwise.
Continue to
pack the kiln until there is no open space
between the
wood and the kiln. Short chunks and
brands should
be placed on
top and used to fill empty spaces. If desired
the kiln can
be set on its side until the pile is half completed,
then
carefully let down over the pile. Make
sure the
tripod is in
the center of the kiln.
Firing the
Kiln
Put the cover
on but leave the cap off. Pour about 1
pint of
kerosene through
the hole in the cover. Make sure that
the
kerosene goes
down to the fuel in the tripod. Light
the kiln
through the
top hole. Add small pieces of dry
sticks if
necessary to
maintain the early fire.
Allow the
kiln to burn for about 20-30 minutes.
Lightly cover
the bottom of
the kiln with sand to seal it with the ground.
Sand or dirt
should be fine and free of sticks, leaves, and
rocks.
Sea sand seals well, but accelerates
oxidation of the
steel due to
the salt. Keep the sand from entering
or blocking
draft and
flue holes. Examine the flue pipes to
make sure
that they are
not clogged with tar. Hold the elbows
of the
pipes over
the flame coming from the cap hole to warm them.
(This helps
with getting a good draft.) Quickly put the pipes
in every
other hole. If smoke leaks from other
parts of the
kiln, these
places should be sealed with clean sand.
When all
the pipes are
in place it is time to put on the cap and seal
around its
edges with sand. The flue pipes should
now be putting
off white smoke,
feebly at first but getting stronger.
If a pipe
stops or does not start drawing it should be
removed,
cleared, warmed up, and replaced in the kiln.
Care of Kiln
While Coaling
During the
early stages, if smoke stops coming through the
pipes or
stays very feeble, take the cap off for a short time
and allow the
fire to flame up through the caphole, adding
more dry
sticks if necessary. Kilns that are lit
in the
afternoon can
be left overnight but must be slowed down by
almost
closing the open holes with the pieces of tin (paint
can lids work
well).
When all the
wood in one section of the kiln is turned into
charcoal, the
coals glow red at that hole and the adjacent
pipes only
send off thin, blue smoke. To assure an
even burn
throughout
the kiln, pipes can be shifted to holes with
glowing coals
until the original flue pipe holes show glowing
coals.
As each section shows glowing coals, remove
the pipes
and close the
holes with tin, and cover them with sand.
If
allowed to
burn too hot, the kiln sides will warp permanently,
making
chimney placement difficult. And the
steel will
oxidize
faster, reducing kiln life. After red
coals have
shown at all
holes, remove all pipes and seal all holes with
steel or tin
covers backed by clean, fine sand. This
may be
eight to 12
hours after lighting, depending on the moisture
content of
the wood. Make sure after you seal that
there is
no smoke
escaping from anywhere. Leave about
12-24 hours for
cooling
before opening. If the kiln still feels
warm it
should not be
opened. If a slower burn is desired for
a
heavier, more
solid product, only two pipes on opposite sides
of the kiln
can be used, and all vents should be nearly
closed with
tin. In this mode, the burn will take
at least 15
hours.
Care of Kiln
Between Charges
To protect
welded joints, handle the kiln with care.
Do not
let the kiln
stand for long periods on its side. Let
the kiln
down from its
side gently. To protect from oxidation
when not
in use, set
the kiln up on three rocks spaced evenly around
the edges to
keep it off of the moist ground.
<NEW
HAMPSHIRE KILN>
JAMAICAN 2-DRUM RETORT WITH TAR
CONDENSER
02p20.gif (600x600)
CONSTRUCTION
Tools
*
welding/cutting equipment, pipe wrench, shovel
Materials
*
1 - 2" pipe, 2 feet long, threaded at one end
*
1 - 2" pipe, 10 feet long, threaded at both ends
*
1 - 2" pipe, 3 feet long, threaded at one end
*
1 - 2" pipe T
*
1 - 2" pipe collar
*
1 - 3/16" sheet steel 36" x 36" for door, tabs, and
wedges
*
1 - 3' x 6' of tin sheeting
*
2 - 50 gallon drums
*
15 linear feet of angle iron
*
7 linear feet of 1/2" reinforcing rod
*
50 - 6" cement blocks
*
5 bags of cement
*
sand
*
gravel
*
soil
*
reinforcing mesh, 6' x 6'
Method
Remove both
the top and bottom from one drum.
Remove only the
top from the
other drum. Weld these two drums
together,
leaving the
closed end to the outside. Put the
least damaged
end of the
drum without top or bottom toward the outside.
Weld the
threaded collar into the top of the closed end.
Weld angle
iron to the front, middle, and rear of the chamber
bottom for
support (see sketch). Weld the
reinforcing rod
around the
outside front of the chamber just behind the drum
lip.
Weld 5 or 6
slotted tabs to the outside of the reinforcing
ring so they
protrude beyond the front of the chamber.
Space
them
equidistant around the circumference.
Cut slots in the
appropriate
places in the steel door so the tabs can pass
through when
the door is on the chamber.
Make wedges
to drop through the slots in the tabs.
They
tighten the
door on the chamber. From the tin
sheeting,
fashion a
curved drawer to fit inside the chamber.
Folding
over the
front edge twice provides a handle to pull the
drawer out.
Excavate a
trench (or build a cement block or rock wall to
form a
"trench") 1 foot deep, 1 foot wide, and several feet
longer than
the retort length (2 to 4 drums can be welded
together to
form the chamber). Set the retort over
the trench
with about 4
inches of the trench protruding from the rear of
the
retort. Using cement blocks, build a
wall around both
sides and the
rear to a level halfway up on the chamber.
Continue the
rear wall to above the chamber. Form,
reinforce,
and pour an
arched roof over the retort, leaving about two
inches space
between it and the chamber. Location of
the rear
wall should
leave 4 inches clearance to the back of the
chamber.
Above this space in the center of the roof
leave a 4
inch hole for
a smoke outlet. There should be a hole
in the
rear wall to
allow the 10 feet piece of pipe to pass through
to the
threaded collar. At the other end of
the long pipe,
the middle of
the T is threaded. Then the short pipe
is
threaded to
the bottom and the eight feet piece is threaded
to the top,
sticking straight up in the air. A
simple tripod
tied with
wire can be used to support the weight of this tar
condenser
near the end with the T. The long pipe
coming from
the retort
should slope downwardn toward the T. A
bucket is
placed
directly under the vertical pipes of the T to collect
the condensed
water and tars.
OPERATION
Wood to be
carbonized is loaded into the retort chamber
leaving as
little void space as possible. Once
loaded, the
door is put
on the front of the retort and secured and
tightened by
wedges inserted in the tab slots.
A vigorous,
but not all-out fire is built for the entire
length of the
fire box under the retort. This fire is
maintained
for five or
six hours until the smoke coming from the
vertical pipe
diminishes to almost nothing. Fuel can
be any
scrap wood
having no better use.
Let the
retort cool overnight before taking off the door and
extracting
the charcoal. Then allow the charcoal
24 hours to
air out in a
place where if it ignites, it will not be a
hazard.
<JAMAICAN
2-DRUM RETORT WITH TAR CONDENSER>
02p20.gif (600x600)
JAMAICAN 2-DRUM RETORT WITH GAS
PORTS
02p22.gif (600x600)
CONSTRUCTION
Tools
*
welding/cutting equipment, shovel
Materials
*
Same as retort with the tar condenser, except substitute
two four-inch lengths of 2" pipe
for the three
pieces of 2" pipe.
Method
Same as
retort with tar condenser except threaded collar at
rear of
chamber, and all connected pipes.
Substitute
two pipes welded to the bottom of the chamber as
gas ports.
The bottom ends of the pipes should angle
toward
the rear of
the chamber at about 45 [degrees]. Each
pipe should be
located in
the front third of each drum. The
drawer should
have holes
punched in it at the locations of the gas ports to
facilitate
passage of the gases.
OPERATION
Same as the
retort with tar condenser, except the addition of
fuel under
the retort can stop after the gas ports are flaming
(after 2-1/2
to 3 hours). Once fueling is stopped,
an old
piece of tin
can be placed across the fire box opening to
keep cool
breezes from blowing the flames out, and to hold
heat under
the front end of the retort.
<JAMAICAN
2-DRUM RETORT WITH GAS PORTS>
APPENDIX II
RELATIVE EFFICIENCY TESTING PROCEDURES FOR
CHARCOAL KILNS
In order to
compare different designs of kilns, all variables
other than
kiln design that might affect efficiency such as fuel
species,
moisture content and size; operator and operating sequence
and schedule;
and weather are to be held as nearly consistent
as possible.
The testing
procedure is:
1.
Take a representative sample of the wood
going into the kiln
to determine moisture content (MC).
One inch thick disks
should be cut from different diameters
and from the middle
portions of the sticks.
Approximately five samples per ton
of wood should be adequate. (10-15 per
standard cord.)
2.
Each disk should be labeled (with magic
marker) to identify
the test and disk number.
3.
Weigh the disks immediately and record the
weights opposite
the identification.
Weigh to the nearest one-tenth ounce.
4.
Record the weight of all the wood going
into the kiln.
5.
Carbonize the wood.
6.
After carbonization, record the weight of
all marketable
charcoal.
7.
Record the weight of all uncarbonized
brands.
8.
Weigh and record the weight of (or
estimate) the fines below
one inch cube size (use of a sieve with
one-inch holes would
facilitate the particle size separation).
9.
Record person hours to tend the kiln.
10.
If desired, extract a representative sample
of about two
pounds of charcoal for proximate
analysis.
11.
Back in the test center, put moisture
content samples in
oven at 220 degrees F (105 degrees C) and
intermittently
weigh and dry until no further weight
loss is shown. Record
the oven-dry weight.
Be certain not to lose any pieces of
bark or wood.
12.
To calculate kiln efficiency on a green
weight of wood
basis (EG):
Weight of marketable charcoal
EG = -----------------------------
(100)
Green weight of wood
or on an oven-dry weight of wood basis
(ED), which eliminates
most of the variability in efficiency due
to moisture
content:
Weight of marketable charcoal
ED = -----------------------------
(100)
Oven-dry weight of wood
Oven-dry weight of wood = 1 minus wood MC
(green basis) in
decimal form
times green weight
of wood.
Wood MC (green basis) = Original sample
green weight minus
Sample oven dry
weight
Original sample
green weight
MC sample weights can be totaled for
green weight and for
dry weight to arrive at the average MC.
Results might
seem low, but calculated this way, the maximum
efficiency
can only reach slightly more than 30 percent.
An efficiency
based on net heat values (ENHV) can also be calculated
using the
following assumptions:
*
Oven dry wood gives 8,500 Btu's per pound.
*
Moisture requires 1,200 Btu's per pound for evaporation.
*
Charcoal gives 12,500 Btu's per pound and the formula:
Pounds of marketable charcoal x 12,500
ENHV =
-----------------------------------------------------------
(Pounds of oven-dry wood x 8,500) minus
(pounds of moisture
times 1,200)
Pounds of
moisture = wood MC (green basis) in decimal form
times green weight of
wood.
Pounds of
oven-dry wood = 1 minus MC (green basis) in decimal form
times green weight
of wood.
In practice
it is not necessary to consider the charcoal MC
unless water
has been used to quench hot spots. The
same procedure
is used for
calculating wood or charcoal MC.
Charcoal is
weighed and
dried in a container, and tare weight is subtracted.
If possible,
kilns should be tested on a cement slab to reduce
the detrimental
effect of ground moisture.
APPENDIX III
CHARCOAL KILN TEST DATA
SHEET
DATE:
KILN TYPE:
OPERATOR(S):
MODIFICATIONS:
TEST
NUMBER: PERSON HOURS
NEEDED:
MOISTURE CONTENT (MC)
SAMPLES
IDENT.
DIAM.
FRESH WEIGHT OVEN-DRY
WEIGHT MC
(FW)
(DW)
(GREEN BASIS)
COMMENTS ON THE BURN
(TIMES, ADJUSTMENTS, TEMPERATURES,
PROBLEMS, ETC.)
WEIGHTS
RAW
MATERIAL MARKETABLE
UNCARBONIZED
CHARCOAL
(RM)
CHARCOAL (AC)
BRANDS (UC) FINES (CF)
APPENDIX IV
SPECIES OF WOOD COMMONLY USED IN
CHARCOAL PRODUCTION
Green Moisture
Content (percent
Local
Name
Botanical Name
green basis)
French
cusha Prosopsis juliflora
39
Logwood
Haematoxylon campechianum
45
Locust
Hymenaea courbaril
38
Cusha
Acacia spp. (mostly
tortuosa) 32
Red wood
Cocolobis diversifolia
--
Bread
--
and cheese
Pithecellobium unguis - cate
--
Wild
tamarind Leucaena leucocephala
39
Fiddlewood
Cetharexylum fructicosum
--
White
birch Eugenia spp.
--
Black
birch Myrcia citrifolia
--
Spanish
oak Inga laurina
--
Snake
wood Ormosia monosperma
--
White
beech Symplocos
martinicensis --
Black
beech Ilex
sideroxyloides --
Manjack
Cordia sulcata
--
Cinnamon
Pimenta racemosa
--
Rainfall
Gliricidia sepium
44
Tamarind
Tamarindus indica
40
Casuarina
Casuarina equisetifolia
40
Neem
Azadirachta indica
44
Sesbania
(grandi) Sesbania grandiflora
61
BIBLIOGRAPHY
Agarwal,
Bina. The Woodfuel Problem and the Diffusion of Rural
Innovations.
Report by University of Sussex Science Policy
Research Unit To U.K.
Tropical Products Institute, 1980, 186
pp.
Baldwin,
Henry I. The New Hampshire Charcoal
Kiln. New Hampshire
Forestry Recreation Commission, 1958,
84pp. Illus.
Bulai, S.,
and Richolson, J.M. Fabrication and Use
of a Tongan
Charcoal Kiln.
Department of Forestry, Fiji. 10 pp. Illus.
Earl, D.E.
Charcoal - An Andre Mayer Fellowship Report. Rome:
Food and Agriculture Organization, 1974,
98 pp. Illus.
Earl, D.E.,
and Earl, A. Charcoal Making for
Small-Scale Enterprises:
An Illustrated Training Manual.
Geneva:
International
Labour Office, 1975, 26 pp. Illus.
Food and
Agricultural Organization. "Simple
Technologies for Charcoal
Making."
Rome: FAO Paper 41, 1983,
154 pp. Illus.
Government of
Montserrat. Preliminary Data of the
1980 Commonwealth
Caribbean Population Census, Part I:
Household and
Housing Information, 1980, 26 pp.
Instituto
Tecnologico De Costa Rica. Como Hacer
Carbon Vegetal
Usando un Estanon.
Serie Informativa Tecnologia Apropiada
No. 5. 9 pp. Illus.
Jamaica
Scientific Research Council. Make
Charcoal the Easy Way.
22 pp. Illus.
Lejeune, J.M.
The Development of Forest Energy Resources:
Ghana.
FAO GHA/74/013 Field Document No. 32,
1983, 48 pp. Illus.
Little,
E.C.S. "Mini-CUSAB Kiln for Rapid
Small-Scale Manufacture
of Charcoal from Scrub, Coconut Wood, and
Coconut Shells,"
Appropriate Technology Vol. 5 No. 1, May
1978, pp. 12-14.
Paddon, A.R.,
and Harker, A.P. The Production of Charcoal in a
Portable Metal Kiln. London:
Tropical Products Institute
Report G119, 1979, 29 pp. Illus.
Richolson,
J.M., and Alston, A.S. Part I:
Production With Simple
Steel Drum Kilns.
Department of Forestry, Fiji. 24 pp.
Illus.
Roos, Werner,
and Roos, Ursula. Survey of Simple Kiln
Systems
and Recommendations for the Selection of
Kilns. German Appropriate
Technology Exchange Report, 1979, 49 pp.
Illus.
USDA Forest
Service. Charcoal Production Marketing,
and Use.
Forest Products Laboratory Report No.
2213, 1961, 137 pp.
Illus.
Volunteers in
Technical Assistance (VITA). Making
Charcoal: The
Retort Method.
Arlington, Virginia:
Volunteers in Technical
Assistance (VITA), 1981, 29 pp. Illus.
Wartluft,
J.L. "Forecasting Charcoal and Woodfuel Demands and the
Level of Kiln Operation and Natural
Forest Acreage Needed to
Satisfy Demand." Memo to CDB, VITA,
and GOM, 1983.
ABOUT VITA
Volunteers in
Technical Assistance (VITA) is a private, non-profit,
international
development organization. VITA makes
available to
individuals and groups in developing countries a
variety of
information and technical resources aimed at fostering
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sufficiency--needs assessment and program development
support;
by-mail and on-site consulting services;
information
systems training; and management of long-term
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projects. VITA promotes the application
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food
processing, renewable energy applications, water supply
and
sanitation, housing and construction, and small business
development.
VITA's activities are facilitated by the
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involvement
of VITA Volunteer technical experts from around
the world and
by its documentation center containing specialized
technical
material of interest to people in developing
countries.
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