Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
-2- ~25669~
l THIS INVENTION relates to combustible briquettes formed of
a mixture of sawdust or wood particles and a carbonaceous
material such as coal, coke, charcoal or coalchar.
The majority of briquettes produced at the present time
make use of a binder such as pitch or starch costing from
$350.00 - $900.00 per tonne. As a result of extensive
tests it has been found that by mixing the carbonaceous
material with sawdust and pressing the mixture into
briquettes at a suitable temperature and pressure it is
possible to produce a satisfactory briquette without the
use of a binder.
Thus in one form the invention resides in a method of
producing a combustible briquette which comprises mixing
sawdust or wood particles and a carbonaceous material such
as coal, coke, charcoal or coalchar, pressing the mixture
at a temperature and pressure sufficient to remove excess
moisture from the mixture, to substantially eliminate the
elasticity of the mixture, to substantially eliminate
springback and to bind the components of the mixture
together.
The invention will be better understood by reference to
the following description of investigations carried out
with mixtures of sawdust and coal.
Sawdust
The sawdust used was typical hardwood sawdust from kiln
dried wood or green sawdust dried as required. Its
moisture content was 13.5 percent although this was
adjusted by the addition of water for some tests. The
bulk density of the sawdust was 200 kilograms per cubic
metre (kg m ) when the container was loosely filled and
260 kg m 3 when the sawdust was lightly compacted by
--3--
~;6699
l vibration. Briquettes made from sawdust alone had a
density of 1080 kg m . The size analysis of the sawdust
was determined as:
Size Mass
5millimetre percent
+2.36 0.7
-2.36 1.4
-1.70 3.8
-1.18+1.70 9.3
-0.85+1.18 26.1
-0.60+0.85 58.6
+0.60
Coal
Coal from the Hebe seam in the Muja open cut in the Collie
field was partly dried and then ground for use. The
grinding was not to any particular degree of fineness and
for some tests the moisture content of the coal was
adjusted by the addition of water. Most of the testwork
was done with coal containing 11.8 percent moisture and
having the following size distribution:
Size Mass
micrometres percent
" +850 1.5
-850 +600 12.0
-600 +425 21.3
-425 +300 19.7
-300 45.5
The bulk density of coal lightly compacted by vibration
was 740 kg m 3.
4~ 5~
1 Equipment Used
Cylindrical briquettes were formed in two steel moulds
with diameters of 28.64 and 41.54mm respectively. The
maximum load that could be applied to the smaller mould
was 25 tons, equivalent to a pressure of 386 MPa (56000
psig). The maximum load that could be applied to the
large mould was 30 tons, equivalent to a pressure of 221
MPa (32000 psig).
Briquettes were formed individually in the mould by manual
application of hydraulic pressure. This mode of operation
allowed the elasticity of the briquette to manifest itself
in three ways:
i. by movement of the piston in the mould when the
applied pressure was released;
ii. by expansion of the dimensions of the briquette
as it was expelled from the mould;
iii. by an increase in the dimensions of the free-
standing briquette as the stresses induced by
the briquetting pressure was relieved over a few
hours.
The first and greatest of these elastic movements is
referred to as "springback" and was measured with a scale
and pointer fixed to the base plate of the mould and the
piston respectively. The second and third indications of
elasticity were measured with vernier calipers and are
much smaller than springback measurements.
The ba-tch method of producing single briquettes used in
this testwork does not parallel the industrial method of
continuous production of sawdust logs currently available
in the Australian market.
~Z~69~
1 E sticity of Briquetting Materials
Elasticity is a physical property of matter which allows
it to deform under pressure and return to its original
dimensions (more or less) when the deforming stress is
removed. However, elasticity values calculated for the
purpose of this specification were derived in particular
experimental conditions and should not be construed as
absolute values of the elasticity of the materials under
test.
The elasticity is presumed to cause planes of weakness in
the briquettes parallel to the ends of the cylindrical
shape. When the briquettes are stressed by being dropped
onto a cement floor from a height of about two metres,
they eventually fracture across such a plane. Similar
planes are evident in the commercial sawdust logs although
their frequency of occurrence along the length of a long
is presumably related to the stroke of the extrusion
mechanism as it compresses a slug of sawdust. The
commercial logs possessed a hard, surface sheen which
might be the result of heat generated by friction during
pressing.
When mixtures of sawdust and coal in mass ratios 1:1 and
1:2 are briquetted, the volume of sawdust is much greater
than the volume of the coal. Sawdust itself can be formed
into a firm briquette but Collie coal by itself does not
yield a competent briquette. As well, the coarser coal
particules tend to fracture under high pressure. Hence,
in briquetting these mixtures of sawdust and coal, it may
be considered that the sawdust functions as the binder and
the elastic properties of the mixture are more associated
with the sawdust than with the coal.
~2~699
1 Springback
Springback measurements were made as indicated above by
measuring ~he movement of the piston in the mould when the
pressure was released. It is expressed as a percentage of
the height of the compressed cylindrical briquette. Most
tests were made in duplicate and, generally, average
results are reported even though replicate measurements
may have differed by 2-4 percent. Hence, the
interpretation of the results is qualified because of the
lack of precision in the technique.
Effect of Particle Size of Sawdust
The sawdust as received, containing about 12-13 percent of
moisture, was screened on square mesh laboratory screens
of aperture 600 and 300 micrometres.
Measurements of springback for the three resultant size
fractions were made at different pressures as indicated
below and other values are included for comparison.
TABLE 1
Springback of Sized Fractions of Sawdust Etc.
Pressure MPa 77 154 232 309 286
Size of Sawdust Springback
micrometres ........................
~600 20.0 20.8 19.2 19.4 18.0
-600 +300 25.2 23.2 22~8 22.8 23.2
-300 22.9 22.8 22.0 21.6 21.~
As received 19.6 20.7 20.0 19.7 19.2
Pine Sawd~lst 22.6 22.5 23.4 22.4 22.6
Coal 16.8 19.3 18.9 19.4 19.0
_7_ 12~69~
1 The interpretation of these values is that the briquetting
components have similar springback characteristics which
are not destroyed by the pressures appl.ied. There does
not appear to be any benefit in sizing the sawdust to a
particular size.
Effect of Moisture Content and Heatin~
The sawdust being used was hardwood sawdust with 12-13
percent of moisture. A quantity of sawdust with
sufficient added water to raise the moisture content to 25
percent was left in a sealed plastic bag f~r about 18
hours to equilibrate. Portions of this wet sawdust were
dried to different levels of moisture content and spring-
back measurements were made for an applied pressure of
386MPa. Other portions of sawdust were completely dried
at 110 C or heated to 200 C and 300 C before similar
springback measurements were made. The results are shown
in Table 2.
TABLE 2
Effect of Moisture Conten'c or Heating on Springback
Treated Sawdust Springback
percent
Moisture -
25.0 percent 59.1
18.7 percent 25.8
15.5 percent 23.2
12.0 percent 19.3
5.7 percent 19.0
0.0 percent 2~.1
Heated to -
200C 22.9
300C 33.6
-8- ~2~669~
1 These results indicate that springback is least with a
mo;sture content in the sawdust in the range of 6-12
percent. Certainly, sawdust with moisture contents in the
range 20-25 percent yields weak briquettes.
Expansion After Moulding
As they were expelled from the mould, briquettes expanded
in both height and diameter. For sawdust (12-13 percent
moisture) pressed at 386MPa, the expansion immediately
after expulsion was about 5 10 percent in height and less
than 1 percent in diameter. As the briquettes aged they
expanded more, about 15 percent in height and less than 1
percent in diameter. This expansion was less when
briquettes were pressed at 221MPa.
The expansions described above were presumably associated
with the elastic recovery of the sawdust (12-13 percent
moisture) from the stresses induced by the briquetting
pressure. For dry and wet (25 percent moisture)
briquettes, some of the dimensional changes were
associated with gain or loss of moisture. There is an
obvious need for the briquetted material to have a
moisture content which is stable with respect to ambient
conditions or to be protected from changes in its moisture
content.
Total Expansion of Briquettes
The briquettes made with sawdust containing different
levels of moisture (see Table 2) were observed over a
period of six days. A briquette has its maximum specific
gravity and minimum dimensions under pressure (386MPa) in
the mould. The dimensions increase immediately on
expulsion from the mould so that -the specific gravity
decreases. The dimensions increase again as the briquette
g lZ~S~9~
l ages and the final specific gravity is affected by these
dimensional changes and any changes in moisture content.
The following values were noted:
TABLE 3
Changes in Briquette Parameters with Time (a~
Moisture Content Specific Gravity Total Expansion (b~
Initial Final Initial (c) Final
... percent.............................. .... percent
25.0 11.1 0~84 0.62 109.~
lO18.7 11.7 1.07 0.89 55.7
15.5 11.3 1.11 0.97 47.2
12.0 10.5 1.16 0.99 43.3
5.7 9.2 1.20 0.94 46.5
0.0 8.8 1.18 0.81 61.0
(a) Six days between making briquettes and final measure-
ment.
(b) Based on increases in the height of the briquette
expressed as a percentage of the minimum height under
pressure.
(c) This is the specific gravity immediately after
expulsion from the mould. Specific gravities in the
mould under 386MPa varied over the much narrower
range of 1.48-1.52.
These data show that dimensional changes in sawdust
briquettes are least when the moisture content is 10-12
percent and stable and this may be the optimum level for
briquetting. ~ high specific gravity is associated with
high compressive strength in a briquette but none of these
briquettes was sufficiently strongly bonded under pressure
~` ~25~6g~3
--1 0--
1 to retain the specific gravity of 1.48-1~52 developed in
the mould. The decreases in specific gravity after
expulsion from the mould and as the briquettes age
indicate a weakening of the inter-particle bond and a loss
of strength in the briquettes. Commercial sawdust logs
had retained specific gravities of 1.2 and moisture
contents of 8-9 percent even after prolonged exposure.
Sawdust-Coal Mixtures
As indicated above, the properties of sawdust-coal
briquettes might be expected to be similar to those of
sawdust briquettes because the major value component is
sawdust and coal is also elastic in the briquetting
conditions employed. Some briquettes were made with
mixtures of sawdust and coal with various moisture
contents. The briquetting details are shown in Table 4
and the properties of the briquettes are shown in Table 5
with corresponding item numbers to assist interpretation
(see below).
This data confirms that sawdust-coal briquettes behave
similarly to sawdust briquettes with respect to elasticity
as defined in this report. There does not appear to be
any significant difference between mass ratios of 1:1 and
1:2 (sawdust:coal) but dry sawdust and dry coal (dry =
less than 5% by weight moisture) appear to yield weaker
briquettes judged on appearance and specific gravity
measurements.
TABLE 4
sriquetting Mixtures of Sawdust and Coal
.25~69~
l ItemMoisture Content Mass Ratio Pressure
Sawdust Coal Sawdust : Coal
.~.percent................................ MPa
1 13.1 20.2 1:1 3~36
2 13.1 12.3 1:1 386
3 13.1 12.3 1.1 386
~ 13.1 12.3 1:2 386
13.1 12.3 1:2 386
6 13.1 12.3 1:1 221
7 13.1 12.3 1:1 221
8 13.1 12.3 1:2 221
9 13.1 12.3 1:2 221
13.1 6.1 1:2 221
11 0.0 0.0 1:2 221
TABLE 5
Properties of Sawdust-Coal Briquettes
Item Specific Gravity Expansion - percent (a)
Under After In On After
Pressure Expulsion Mould Expulsion 24 Hours
1 1.48 1.13 20.4 28.0 37.7
2 1.48 1.18 18.8 24.5 33.8
3 1.48 1.17 21.0 25.0 35.7
4 1.48 1.17 18.5 24.1 34.1
1.46 1.18 20.0 21.8 31.1
6 - 1.14
7 - 1.13 no results available
8 - 1.13
9 - 1.12
- 1.10
11 - 1~05
-12- ~25~6~
1 (a) This expansion refers to increases in the height
of the briquette expressed as a percentage of the
minimum height under pressure. These increases are
additive in the three stages of pressure release
(springback), expulsion from the mould and aging.
Conclusions
The testwork has shown that the elasticity of the
materials increases the dimensions of sawdust-coal
briquettes from the moment that -the moulding pressure is
released until the briquettes stabilise on free-standing.
These dimensional changes are aggravated by changes in the
moisture content of the briquettes until equilibrim with
ambient conditions is attained. In the cirucmstances of
this testwor~, the dimensional changes due to both causes
were minimised when the moisture contents of the sawdust
and coal were each about 10-12 percent. It is probable
that the moisture content of the sawdust is more critical
than that of the coal because the sawdust is the major
volume component of the mixutre. The particle size of the
sawdust does not appear to be a significant factor.
Attempts were made to moderate the elasticity of the
sawdust by heating it in air to 200 C and 300 C as a
literature reference suggested that 270c was an approp-
riate temperature. These attempts were unsuccessful. The
elasticity of the materials did not appear to be affected
by the pressures attained (386MPa) in the briquetting
press.
Commercially produced sawdust logs appear to have a stable
moisture content of 8-9 percent and a stable specific
gravity of 1.20-1.23. Although they are segmented
longitudinally, the logs have a hard surface sheen which
may be induced by the commercial process - it was not
-13- ~ 2 5 ~6~
1 achieved in the circumstances of the testwork now
reported.
The main conclusion is that the least dimensional changes
occur in sawdust-coal briquettes when the moisture
contents of the sawdust and coal are each about 10-12
percent. As dimensional changes are minimised, the
briquettes should be close to maximum strength although
this will also be affected by the briquetting pre~sure.
The investigations and tests, described above establishes
that satisfactorily strong briquettes could be made with
mix~res of sawdust and Collie coal were compacted under a
pressure of 220 megapascals.
Mixtures of sawdust and coal in mass ratios of in the
range of 1:1 to 1:6 yielded firm briquettes with the
potential to withstand reasonable handling stresses.
However, the briquettes were not considered firm enough
for handling and tranport in commercial application.
The results of additional tests described below establish
that it is possible to produce a superior briquet-te with
the introduction of greater pressure and heat, improving
the handling capability of the briquette to a commercially
acceptable level.
The aforementioned investigations established that a 1 1
mix of coal and sawdust, with a moisture content of 12-14%
when compacted under a pressure of 368 MPa, produced a
stronger briquette.
Further tests described below were carried out to
determine what factors would enable the elasticity of the
briquetting mix-ture to be controlled, to so avoid the
briquettes expanding~ and developing lateral cracks when
-14- ~ 2 5 ~ 6 9~
l expelled from the mould, which in turn would render the
briquettes unacceptable for commercial use.
Three head samples of sawdust and coal mix were prepared.
Each bag contained approximately 5 kilograms of sawdust
and coal mixed on a mass ratio of 1:1.
The moisture contents marked on the samples were 25%, 12%
and 3% respectively.
Three separate sets of trials were conducted.
The first series of trials used a manually operated 100
tonne press.
A high tensile steel mould and piston were manufactured
for the trials to facilitate the manufacture of the
briquettes.
The external size of the mould was 150mm height x 149mm
diameter, and the internal size was 150mm height x 82mm
diameter, giving the mould wall a thickness of 33.5mm.
The piston measure 79mm height x 82mm diameter.
To allow moisture to escape during compaction, holes were
drilled vertically down the piston from face to face. The
six holes were drilled to 4mm in diameter at 60 pitch
circule diame-ter, each at 60 points of the piston face.
A seventh hole was drilled down the centre of the piston.
An Industrial welding blow torch was used to heat the
mould. A hole was drilled into the side of the mould to
insert a thermometer which measured the heat of the mould,
approximately 8.5mm from the internal face of the mould.
125~ 3
1 A Second and Third series of Trials were conducted using
the same equipment, with a foot operated mechanical 150
tonne press~
Vernier Calipers were used to measure the respective
heights of briquettes during the trials.
Varying quantities of mixtures were pressed in the mould
in order to determine the ideal pressure per square inch
required to destroy elasticity of the mixture.
25% Moisture Content
In the First and Second series of Trials, it was
established that the mix of 25% moisture content was
unsatisfactory as moisture could not be expelled due to
lack of breathing space for the moisture to escape.
A mixture of 25% moisture content slowly extruded under
certain pressures and temperature~,) it is envisaged that
the final product would still be neutralised without
springback, and contain the ideal Gross Specific Energy,
Speci.fic Gravity, Moisture Level and ~sh Content.
A fifth series of Trials, proved that 25% moisture mix
could produce very satisfactory briquettes and these
Trials are discussed later.
12% Moisture Content
.
Previous tests have established that an ideal moisture
level was 12-14%, and because of the success of trials
with the prepared sample of 12% moisture level, it was
decided to attempt only one test with the 3% moisture
level mi~ due to the economic disadvantage of drying the
mixture to such a level for commercial production.
-16- ~2566~
1 The elasticity of 1:1 mixture of sawdust and coal is
directly related to the pressure applied for compaction,
and the moisture level of the mix, both during compaction
and at completion of compaction.
The application of heat to the moulding process not only
appears to extract the lignin content of the sawdust and
so assist in the binding of the two materials, but also
accelerates the removal of excess moisture from the mix by
driving off steam.
The process of driving out moisture from the sawdust as
steam appears to also release compounds from the sawdust
such as lignins which act to bind the particles together.
Test results indicate that a variation of moisture level
of the mixture, heat, compaction pressure, and duration of
compaction pressure; directly cause a change in the hard-
ness of the briquette and its Gross Specific Energy.
At particular pressures and heats with compaction sustain-
ed for a period of time, the elasticity of the mixture
appears to neutralise completely, producing a hard
shelled, very dense and compact briquette, without any
springback.
Springback
Springback has been isolated and can be removed, as ex-
plained under Elasticity.
~yg~ n~y ~ ~awau~ ~n~ $ ~g ~
~l~s~icity 9 the coalJsawdust mixture, and in turn
e~fects the springback percentage of the ~riquette
produced, is directly c~ntrolled by the moisture level of
the mix, heat and pressure to neutralise the elasticity,
-17- ~ 6~
1 and duration of pressure of moulding to stabilise the
mixture in its new briquetted form.
To avoid the use of costly abnormally high compaction
pressure, a duration of compaction for a certain given
period of -time at particular pressures achieves the same
result.
Expansion After Moulding
Expansion of briquettes after moulding occurred in certain
Trials.
The expansion can be attributed to any one of the follow-
ing:-
(a) Too much moisture still locked in mix.
(b) Too little moisture.
(c) Too low a compaction pressure.
~d) Not long enough period of compaction pressure.
(e) Not enough heat.
(f) Too much heat.
Total Expansion of Briquettes
Those briquettes which were considered successfully manu-
factured had very little or not expansion after one, two
and three days following manufacture. Even after a period
of ten months there was no measurable expansion.
The Specific Gravity of the similar sized briquettes
compares favourably with each other when tested one, two,
Z5 three and ten days after manufac-ture.
~25~
-18-
l Gross Ener~y Values
Collie Coal as mined may contain 24-28 percent moisture
and 3-8 percent ash~ The Gross Specific Energy of that
coal would be approximately 19.9 Mgj/kilogram.
Coal with a moisture content of 12.5 percent would have a
Gross Energy Value of about 24.75 Mgj/kilogram.
To achieve its optimum Gross Energy Value of some 29.g
Mgj/kilogram, Collie Coal would have to be passed through
the expensive process of drying to achieve nil moisture
level and ash free state.
A commerclal plant as envisaged for production of the
briquettes, would need to dry economically the
sawdust/coal mixture to about 12 percent moisture, before
manufacture of the briquette.
Briquettes produced would have Gross Energy Values of
between 23-24 Mgj/kilogram and an ash content of some 2
percent.
Much of the further drying process of the mix is carried
out during the briquettes' manufacture, by the process of
heat and pressure to produce a briquette containing a
moisture level of some 5 percent.
It can be recognised that the moisture level of the
briquette at time of expulsion from the mould, is critical
as to the elasticity of the mixture, and so effects
spring~ack.
In the Third and Fourth Series of manufacturing Trials,
selected mould temperatures and compaction pressures were
shown to remove elasticity and springback.
-19- ~25~j~,9~
l It was also discovered that the greater the volume of
material to be moulded, the greater the period of time the
compaction pressure was required, to neutralise
elasticity.
In the q'hird series of Trials, a mass of 180z of material
at 25% moisture level, compressed in the mould for a
period of ten minutes with pressure on the piston main
tained at 100 Tonne.
The briquette demonstrated grea-t elasticity and spring-
back, and finally broke into several pieces.
When a mass of 70z of material at 12% moisture level was
compressed in the mould for twenty minutes, at a commence-
ment heat of 170 C and conclusion heat of 110 C, the
briquette had no elasticity and no springback.
In the Fourth Trials, smaller quantities of mix were
moulded to attempt less moulding time.
lO~oz mixture was pressed at l~100 Tonne for twenty
seconds and left in the mould for three minutes without
constant pressure being reappliedO When expelled from the
mould, the briquette contained too much elasticity, and
crazed laterally.
Very successful manufacturing results of the Third and
Fourth series of Trials, were achieved when a series of
40z of mixutres at 12% moisture level were compressed at a
maintained pressure of 120 tonnes for a period of three
and a half minutes and a commencement mould temperature of
195 C and conclusion mould temperature between 170 C and
180C
'~25~
-20-
1 The Fifth series of Trials was designed to prove or dis-
prove the briquettability of a mix containing a moisture
level of 25%.
The first of the Trials "T17" used 4OZ of mix at 25
moisture content. The moisture escape holes blocked up,
and when the briquette was expelled from the mould, the
moisture content caused springback in the top section of
the briquette. Cores of the mix were extruded from the
moisture escape holes.
Trial "T20", used 4OZ of 25% moisture mix, compacted at a
pressure of 12 Tonnes for a period of eight minutes, at a
mould commencement temperature of 170C and mould temper-
ature of 136C at completion.
The briquette showed no signs of springback after
twenty-four hours following manufacture, prior to being
pulped up for laboratory analysis.
Trial "T23", was designed to prove the duration of time of
pressure under compaction was relative to the quantity of
mix to be briquetted.
Allowing two minutes of compaction time for loz of mixture
at 25% moisture level; 6 oz of mix was compacted at 120
Tonnes pressure for a period of twelve minutes, at a mould
commencment temperature of 170 C and mould temper ature of
110C at completion.
No springback was recorded and the briquette was submitted
for laboratory analysis.
Trial "T24" was a repeat of Trial "T20", although the
mould completion temperature had dropped to 113C compared
to 136 C in Trial "T20".
-21- 12~
1 No springback was recorded, and the briquette has been
kept.
Comparing the successfully manufactured briquettes in the
Third, Fourth and Fifth Trials, the following conculsions
can be drawn.
Moisture Level and Temperature Relativity
The moisture level of the mix determines at what pressure
and temperature the mix needs to be manufactured, to
destroy elasticity and springback.
3% Mositure Level
A moisture ~ontent of 3% will produce a briquette at 120
Tonnes pressure held for 3-5 minutes, at a temperature of
170C at commencement of moulding, (see Trial 19).
A temperature of 120 C is not adequate for a 3% moisture
mix and results in the briquette developing lateral
cracks, (see Trial 22).
12% Moisture Level
Trial 18 produced a good briquette when 4OZ of 12~
moisture mix was compacted under 120 Tonne for a period of
3-5 minutes at a mould commencement temperature of 170C.
Trial 21 demonstrated that a mould commencement temper-
ature of 120C was not satisfactory and the briquette
produced, developed lateral cracks caused by springback.
25% Moisture Level
-22- 1256~9~
l Trials 20, 23 and 24, proved that good briquettes can be
produced from a mix containing 25% moisture, so long as a
long enough period of time is given to expell the moisture
content and so avoid springback.
The mix must be briquetted at a temperature of some 150C
to 170 C, and a compaction pressure of 12 Tonnes ,'32,480
p.s.i.) must be maintained for a period of two minutes per
loz of mix.
Pressure
The optimum compaction pressure required to briquette a
mixture of 1:1 sawdust and coal by mass (appears to be of
the order of 12 Tonnes, (32,480 p.s.i.~.
Temperature
l'he temperature of the mould should be in excess of 120C
and preferable no greater than 195 C although temperatures
of up to 285 C may be required with coalchar.
Duration of Compaction Relative To Moisture Level
For mixtures containing a moisture content of between
three and twelve percent, some fifty and sixty seconds
should be allowed per loz of material.
For a 25% moisture content, 100 to 120 seconds should be
allowed for every loz of material.
By compacting the mixture in accordance with the criteria
discussed above it is possible to produce briquettes
having a distinct surface sheen which contributes to the
water resistance and hardness of the briquettes.
~IL25669~
Supplementary Disclosure
1 It is also recognized that in ]ceeping within the
intendment of the presen-t invention, other cellulosic
materials other than sawdust may be used in the formation
of briquettes as is presently disclosed. Such other
cellulosic mal:erials may include, but are not limited to,
such materials as wood particles, lea~ materials, plant
material, barl; particles, coconut shell par-ticles, or rice
husks.
Thus a further object of the present invention
is to provide a method of producing a combustible
briquette hav:ng the desired properties of hardness and
resistance to crumbling, using cellulosic materials other
than sawdust :Ln combination with a carbonaceous material
such as coke, coal, charcoal, coalchar, or peat.
Yet another object of the present invention now
realized is the production of a smokeless briquette and
the reduction of the high ash and sulpher levels çontained
in some carbonaceous materials. Such smokeless capability
is made possible by the addition of a cellulose material
to the carbonaceous material. It is now realized the high
ash and sul-fur levels contained in ordinary carbonaceous
briquettes may be reduced proportionally in accordance
with the ratio of sawdust or cellulose particles to
- 24 - ~5~9~
1 carbonaceous material contained in the briquette feed
mixture of the presen-t invention.
It is further recognized that briquettes formed
in the manner presently disclosed are not to be limited
to the combinat.ion of a cellulosic material and a single
carbonaceous material selected from the group consisting
of coal coke charcoal coalchar or peat. Such invention
also comprises a briquette consisting of the combination
of cellulosic materials and any combination of carbonaceous
materials such as those :isted above.
As previously d:sclosed the preferred method
of producing combustible hriquettes of -the present
invention comprises mixing cellu;osic materials and one
or more carbonaceous materials such as coal coke charcoal
coal char or peat together in a mass ratio of between
one part sawdust to one to six parts coal or carbonaceous
material and pressing the mixture at a -temperature between
about 120C to 285C and a pressure sufficient to remove
excess moisture from the mixture. Such pressure required
has generally been found to be between 150 MPa and 650MPa
and when carried out with the above temperatures binds the
components of the mixture together and subs-tantially reduces
springback to produce a satisfactory briquette. Using
soft lignite or sub-bituminous coal as the carbonaceous
material an especially preferred temperature range has
. .
~25~69~
- 25 -
1 been found to be be-tween 150C and 195C.
However, for harder carbonaceous materials, such
as the harder bituminous and anthracite coals, and chars,
it has been found higher temperatures of up to 285C to
320C result in a more desirable hardness and enhanced
resistance to springback for briquettes manufactured from
such materials.
In addition, it has been found that for the
harder coals such as anthracite and bituminous, greater
compaction times are required than are required for the
softer sub-bituminous and lignite coals.
! For example, for a mixture containing between
3 and 12% moisture content, and a preferred compaction
pressure of between 150MPa and 650MPa for brlquetting a
mixture of 1:1 sawdust to coal by mass, a compaction time
of about 50 to 60 seconds is required to produce a
satisfactory sub-bituminous coal-based briquette.
However, experimentation with briquettes
fabricated from carbonaceous mixtures of hard coals or
chars and/or washeries' tailings indicates longer periods
of pressing are required than are necessary for softer
carbonaceous materials. While satisfactory briquettes
can be produced with compaction times of 50 to 60 seconds,
briquettes fabricated from harder coals require a
~2~
- 26 -
1 proportional increase in the pressures, temperatures, and
press time applied to reach the same static weight strength
and water resistance of briquettes formed from softer
sub-bituminous coals. However, the maximum -temperature
is generally limited to approximately 320C, as too high
a temperature during the briquette process can induce
explosion of the briquette during either formation or
upon expulsion of the briquette from -the briquette mould.
. Briquette static weight strength tests and
burning tests demonstrate briquettes can be produced
with:
- 1700% increased strength over convent:ional
briquettes using starch binders
- capacity to withstand temperatures in excess
of 1200C without disintegration duri.ng
burning, when burnt under load to simulate
briquettes being burnt in retorts.
It should be understood, of course, that the
foregoing Supplementary Disclosure and origi.nal disclosure
relate only to preferred embodiments of the present
invention, and it will be apparent to one skilled in the
art tha-t various changes and modifications may be made
therein without departing from the spirit and scope of
the invention as set out in both the original and
Supplementary Claims.
1:`
