COMPARING SIMPLE CHARCOAL PRODUCTION TECHNOLOGIES

Posted by Oliver Walker on

  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