Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FUEL BRIQUETTES AND PROCESS FOR MAKING SAME
The invention relates to a process for the production of fuel
briquettes, especially for heating purposes, wherein a non-caking carbon
carrier of small grain size, preferably petrol coke, is mixed with a pitch
containing binder material to form a starting mixture, which mixture is
subsequently compressed to briquette blanks and subjected to a heat
treatment for solidification of the briquette blanks and production of the
fuel briquettes.
Coke of sandy consistency, preferably petrol coke, is generally
used for the manufacture of such fuel briquettes, whereby the coke used has
a grain size range of .05 to 2 mm and is preferably selected from a narrower
grain size band within that range. The carbon carrier of sandy consistency
may also be or contain non-caking coal. The invention further relates to
fuel briquettes manufactured by the above process. Fuel briquettes for the
above identified applications must conform to certain physical
requirements. The fuel briquettes m~st be of sufficient solidity for
transport and combustion and should neither burn too violently nor merely
smolder. These characteristics may be controlled through an adjustment of
the compression force used in forming the briquette blanks.
In a prior art process known from German Published Application
~E 37 27 464, of which the present invention is an improvement, briquette
blanks which are sufficiently free of caking coal are used and a binder
aided briquette forming process is employed. Any admixed caking coal of
fine grain is present in such a small amount that it has no influence on the
binder aided briquette forming. The heat treatment is carried out in a
rotary kiln, a lower part of which is filled sufficiently high with coke of
sandy consistency to provide that the heat treatment takes place in a coke
submersion bed. This process has proved to be advantageous. Particularly,
the fuel briquettes manufactured by such a process comply with all
requirements to be met during combustion. However, with respect to their
longevity before combustion, fuel briquettes manufactured in accordance with
35 '~this prior art process may be much improved. The mechanical stability of
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such fuel briquettes decreases over time during storage, and in some cases
decreases so far as to become unacceptable. This decrease may be explained
by air diffusing into the fuel briquettes and water penetrating into the
fuel briquettes, especially during outside storage, which leads to a
reduction in the binding forces of the petrol coke structure in the fuel
briquettes.
The present invention provides a process for the manufacture of
fuel briquettes which do not only meet all requirements during combustion,
but are also characterized by excellent long term storage properties and
substantially retain their solidity especially during transport and outside
storage.
This is achieved in a process in accordance with the invention,
wherein a pitch containing a binder, which includes a mixture of pitch and
caking coal and has a temperature between 100 and 200 C, is admixed with a
non-caking carbon carrier at a mixing temperature within the same
temperature range as the binder temperature, the resulting starting mixture
is compressed to fuel briquette blanks starting at the mixing temperature,
and the briquette blanks are subjected to a solidifing heat treatment. It
is understood that the pressing of the briquette blanks is preferably
carried out at a briquette forming temperature which is lower than the
mixing temperature. The briquette forming temperature is, for example,
about 50 C lower than the mixing temperature. The solidifying heat
treatment may be carried out with a final temperature of over 400 or even
over 450 C. In a process in accordance with the invention, the briquette
forming process, which is used for the production of the briquette blanks,
is a binder aided briquette forming process which is generally used in the
manufacture of mineral coal briquettes. Therefore, the technology-of known
binder aided briquette forming processes may be employed. In general,
commonly known briquette presses and briquette forming pressures may be
employed.
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It is an unexpected result that, when the mentioned binder aided
briquette forming process is used and the mentioned parameters are employed,
the resulting fuel briquettes comply with all above-mentioned requirements
even with respect to their long term properties. This is especially
apparent, when a binder mixture is used which is a pitch/coal alloy. A
pitch/coal alloy in accordance with the invention occurs, if the pitch and
the caking coal are, 60 to speak, dissolved in each other so that a complete
integration of the two components into a new binder material has taken
place. This may be readily achieved especially when coal of sufficiently
fine grain is used. In the fuel briquettes, the pitch/coal alloy is
substantially unaffected by air and humidity diffusing into the fuel
briquettes. The alloy is very reactive. The reactivity of the alloy is
comparable to the reactivity of the compressed materials in the fuel
briquettes.
Several variants of the briquette manufacturing process in
accordance with the invention are within the scope of the invention.
Especially good results are achieved if the non-caking carbon carrier,
especially coke of sandy consistency, and the binder mixture, have the same
temperature during admixture and if the admixture is carried out at a
preferred temperature of about 160 C.
In contrast to the above described prior art process taught in
DE 37 27 464, wherein the solidifying heat treatment must be carried out in
a rotary kiln, in accordance with the present invention, the heat treatment
may also be effected in a different manner, for example, on a moving grate
which passes through an appropriate oven or an appropriate heat chamber and
is loaded with a single layer or multiple layers of briquette blanks.
However, in a preferred embodiment of the process in accordance with the
invention, the blanks are subjected to the solidifying heat treatment in a
rotary kiln. A very careful heat treatment and a high final rigidity of the
briquettes may be achieved, if the rotary kiln has a mineral bed of fine
grain minerals. According to a preferred embodiment of the present
invention, which is of special interest, briquette blanks which have a
35\~,higher specific weight than a shooting weight of the fine grain minerals,
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are produced by selecting an appropriate mixing ratio of the components in
the starting mixture and an appropriate degree of compression of the
starting mixture during the forming of the briquette blanks, and are fed to
a heated rotary kiln for the solidifying heat treatment, which kiln is
filled with fine grain minerals to such a height that the heat treatment of
the blanks is effected in a mineral submersion bed. The fine grain minerals
preferably have a temperature of about 500 to 530 C at least towards the
exit end of the rotary kiln. In order to prevent the blanks from contacting
each other in the kiln and to prevent their abrasion, the kiln is preferably
filled with a volume of minerals which is larger than twice the volume of
the voids within a loose briquette blank filling of the kiln. For the
remainder of the process in accordance with the invention, recourse to the
technology disclosed in DE 37 27 464 may be had. Accordingly, the briquette
blanks may be formed in a pellet forming apparatus, which yields spherical
pellets, or in a briquette forming press. The use of the latter is
preferred, since the specific weight of the briquette blanks may be
controlled through an adjuatment of the briquetting force of the press. The
briquette blanks are fed into the kiln through an entry end thereof together
with a flow of minerals for the submersion bed. Both the produced fuel
briquettes and the heated minerals leave the kiln at an exit end thereof.
The length of the heat treatment of the blanks and thus their speed of
passing through the kiln is adjusted to provide a sufficient solidification
of the blanks. The heated minerals which exit the rotary kiln together with
the heat treated fuel briquettes are separated and transported to the entry
end of the rotary kiln for recycling. Thus, the heat energy stored ln the
minerals may be reused for heating the briquette blanks in the kiln. The
briquettes whlch exit the kiln are preferably cooled to about 50 C on a
cooling conveyor. It is an advantage of the rotary kiln heat treatment,
that volatile components which evaporate from the briquette blanks during
the heat treatment may be combusted in the kiln. The resulting combustion
heat may be used to retain the kiln at the required temperature and to make
the heat treatment substantially independent of additional heat sources.
Thus, the one or more burners which are preferably provided at the entry end
of the kiln may be only required ~or the start o the heat treatment process
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and for special situations. The fine grain minerals are preferably sand,
foamed perlite or vermiculite or fine grain petrol coke if the atmosphere in
the oven prevents combustion of the latter. If petrol coke is used, the
heated fine grain coke exiting the kiln may be recycled into the kiln or
used as part of the starting mixture. In any event, it should be asserted
that the temperature at the beginning of the heat treatment is sufficiently
high to force highly volatile components from the briquette blanks. The gas
exiting the briquette blanks generally prevents oxidation of the materials
in the kiln.
To optimize the process in accordance with the invention, it is
preferred to employ a binder mixture which, with respect to the starting
mixture from which the blanks are pressed, contains at least 7~ per weight
of pitch as crude oil or coal pitch, especially electrode pitch, and at
least 12~ per weight of fine grain caking coal. The binder mixture
preferably contains 7 to 12~ per weight of pitch and 12 to 14~ per weight of
fine grain caking coal. Preferably, petrol coke or another non-caking
carbon carrier is used, which has a grsin size below 2 mm with at least 60
below .5 mm.
It is within the scope of the invention to add small sized lime
stone to the starting mixture as combustion inhibitor. Accordingly, the
invention provides for a starting mixture which contains petrol coke, 3 to
6~ per weight of lime stone and the binder mixture. It is preferred to use
petrol coke of a grain size below 2 mm with at least 60~ per weight below .5
mm, and lime stone with a grain size below .5 mm.
The fuel briquettes manufactured by a process in accordance with
the invention, are characterized by their long term storage properties and
their behavior during combustion in a furnace. The fuel briquettes
manufactured bya process in accordance with the invention may also be
employed as carbon carriers during the manufacture of cast iron in a cupola
furnace.
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