Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
This invention relates generally to an improved
method of cooling hot agglomerates of the type used for fuel in
industrial application and processes such as, for example, the
production of iron and steel, and in foundries.
More specifically the invention relates to a method
of producing and cooli~g hot agglomerates in a continuous
coking operation so that the resulting product will not oxidize
with the atmosphere and provide a product of lower chemical
reactivity with respect to CO2 so as to render the produced
product more attractive to industrial use. The method of the
invention utilizes a countercurrent furnace into which a strea.
of cool CO2 rich gas is injected. The cool CO2 gas does not
react with the agglomerates being discharged because at the
discharge end the products are sufficiently cool so the cooling
stream of CO2 gas provides a final cooling sta~e wherein the
fuel products can be handled without significant reoxidation.
Metallurgical coke is an essential material in an
industrial society; it is indispensable for ironmaking opera-
tions in blast furnaces--the most i.mportant source of iron for
steel production. It is also utilized in selected steel.~akin3
processes and in the foundry industry.
Conventional coke is produced primarily in so-called
"by-product coke ovens" where a blend of various coals is
introduced and subjected to distillation to re~ove the volatile
constituents from the coal. The end product is a porous m3ss
that must be cooled to prevent burning durin~ stora3e under
atmospheric conditions. The principal method to accomplish
this is by quenchin~ with water, althou~h dry quenchin~ methods
have recently been intrGduced as well.
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These techniques suffer from the following
disadvantages:
a) There is significant pollution associated with
quenching operations, particularly with the most commonly
practiced technique of water quenching.
b) The heat released in cooling operations is not
recoverable and represents a significant fraction of the heat
losses in cokemaking operations.
c) Such cooling operations cause thermal shock
which in turn leads to product degradation, thereby increasing
operating costs in ironmaking and in steelmaking.
d) Normally, the methods used for cooling permit
moisture pickup in the product and this must be removed in
subsequent operations, thus a~ain increasing thermal
inefficiencies.
However, interest in coke coolin~ technology need not
be limited to conventional cokemaking applications. In recent
years, the general scarcity of good quality coking coals, plus
the attendant price, and increases experienced by the industry
have caused much interest in the so-called "formed cok~"
technology which does not require quality cokin3 coals as raw
materials. These new processes reportedly operate with
low-rank coals but provide a uniform metallur~ical coke that
can replace the conventional product in most industrial
applications. Unfortunately, formed coke technolo~y suffers
from the same problems associated with conventional cokemakin~
applications, i.e., coolin~ of the final product. In addition,
it has been found that formed coke tends to be ~ore reactive
with respect to CO2 than conventional coke and this leads to
lower productivity in blast furnaces.
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It is a general object of the present invention to
provide an improved method to cool coke which avoids the
above-stated problems.
Yet another object of the present invention is to
provide an improved metho~ for co,oling coke products which not
only eliminates the drawbacks of conventional cooling methods
but can also reduce the chemical reactivities in the coke
product.
SUMMARY OF THE INVENTION
According to the invention, there is provided a
method of producing and cooling hot agglomerates of the type
used for fuel to prevent oxidization of the agglomerates upon
contact with atmosphere and to regenerate process gas, wherein
a fuel material, such as coking coal or a mixture of fine coal,
char, and non-coking agglomerates, is continuously moved
therethrough to process gases which serve to preheat the
material to form char, and then continue to heat the material
to devolatilize the coal and form coke agglomerates of plastic
consistency, characterized by the steps of:
(a) introducing CO2 rich gas into the formed
agglomerates at a cooling stage in their
production where the agglomerates are at a
temperature in the range of 100 to ~00F.,
(b) heating the C~2 ga~ in the cooling stage
to a temperature to initiate the reaction
C~2 + C ~ 2 CO to cause unreacted carbon in
the hot agglomerate to react and elevate the
agglomerates to a final carbonization
temperature not exceeding 2350F,
(c) moving the gas to a heat-hardening and carbon-
ization zone wherein the temperature of the
a~lo~erates does not exceed 2000F,
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(d) introducing oxidizing gases into the agglomer-
ates in the heat hardening and carbonization
zone,
(e) continuing the heating of the gas for a duration
to cause the reaction CO ~ l/2 2 C ~ CO2
and to maintain the temperature of the
agglomerate in the zone of step (c) in a range
of 1200F to 2000F.,
(f) collecting the CO2 gas produced by step (e), and
(g) re-introducing the CO2 gas as cooling gas into
the process accordin3 to step (a).
Preferably, there is included the further step of:
continuing the reaction of step (b) until a tempera-
ture is reached where the reaction becomes
exothermic.
Preferably the CO2 gas is introduced into the
agglomerates at a zone of the furnace where the
agglomerates have a temperature of 600F. Preferably
there is included the still further step of:
processing said gas through drying, preheating and
incipient carbonization zones of the furnace at a
rate which will enrich the gas in hydrogen according
to the reaction (3) ~2 + CO ~ ~2 2
be seen that, in subsequent stages of the gas phase
composition accordin3 to the method of the invention,
several reactions occur. ~hese are:
(l) CO2 + C ~ 2C~
(2) CO + l/2 32~ 2
(3) H20 + CO----~H2 + C~2
AS a result, the gas becomes pro~essively enriched in
H2 and CO until the tempe~ature drops sufficiently to reverse
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such reactions with the eventual precipitation of carbon black
and moisture pickup. However, since the uncarbonized fuel
consists primarily of chars and coal fractions with significant
volatile content, such volatiles are incorporated into the gas
stream. The final gas compositi4n of the gas at the exit point
will then consist of coal volatiles, C02, plus varying amounts
of hydrogen and CO depending on the gas temperature. It is
expected that the entrained carbon black particles would be
removed in conventional dust control systems; they are valuable
for reuse during fuel agglomeration, both to achieve higher
agglomerate densities resulting in hi~her product strength and
also because of their low impurity levels. The gas would also
be cooled by heat exchange for steam or power generation and to
permit recycling into the vessel.
DESCRIPTION OF THE DRAWING
The invention will now be described in detail, with
reference, by way of example, to the accompanying diagrammatic
drawing which is a schematic view of a vertical shaft furnace
and associated gas and solid flow diagram.
DESCRIPTION OF T~E INV~NTION
In the method of the invention a~glomerates are
cooled so that the resulting product will not react (oxidize)
with the atmosphere, while concurrently providing a product of
lower chemical reactivity with respect to C~2 so as to render
such product more attractive for industrial use.
The method is utilized in a countercurrent vessel
which can be either vertically or horizontally arranged and
depicted as a vertical shaft furnace 10 into which process gas
flows upwardly countercurrent to the pro3ressive downward
movement of the fuel material.
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According to the invention, a stream of CO2 rich gas
comprising approximately 0.4-2% 2; 60-70~ N2; 15-25~ CO2;
5-10% CO is injected via pipes 11 at a temperature
approximately 200-300F into a mass of uncarbonized fuel
agglomerates comprising fine coa~, char and noncoking coal
which has been charged into the furnace at the top thereof.
The cool CO2 gas does not react with the a3glomerates being
discharged because at the discharge end such products are
sufficiently cool already; at this point the cooling stream of
CO2 simply provides a final cooling stage so that the fuel
products can be handled without significant reoxidation.
As the CO2 enters the cooling section of the vessel
it becomes heated due to heat exchange between the warm fuel
and the gas. At temperatures of several hundred degrees F,
however, the gas reacts with the carbon-rich fuel according to
the following reaction:
(1) CO2 + C ~ 2 CO.
Since the reaction becomes exothermic at high temperatures,
both the gas and the solids will show a steep but transient
temperature increase. Such a sta3e provides the necessary heat
for the final induration step in carbonization. At the same
time, since the chemical reaction shifts toward the right at
higher temperatures, the gas becomes CO rich an~ CO2 poor.
This prevents further CO2 conversion while providing a
relatively stable temperature regime during final carboniza-
tion. An important feature at this sta~e is that the chemical
reaction occurs preferentially at those sites where there is an
excess of free energy, i.e., at those points that are respon-
sible for the hi3h chemical reactivity of the fuel a~31Omer-
ates. Therefore, the initial reaction of CO2 with carbon not
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only provides the heat for temperature induration but alsoremoves much of the excess reactivity in the product.
As the gas stream progresses inside the vessel it
transfers heat to the solids that move countercurrently. To
provide sufficient heat so as to maintain carbonization as well
as to raise the temperature to the carbonization range
(1290-1830~F), it becomes necessary to oxidize the gas by
injecting air, oxygen, or similar gases (such as blast furnace
top gases) via pipes 14 containing sufficient oxidating
constitutes. The chemical reaction is: !
(2) CO + 1/2 2 ~ CO2;
which again permits reaction 1 to take place. Because these
two reactions are strongly exothermic the result is sufficient
heat being released into the solid phase, thus increasing the
temperature to the point of incipient carbonization and beyond.
In subsequent stages, the gas phase composition is
regulated by reactions 1 and 2, plus reaction of:
(8) H2O + CO ~ H2 + C2;
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which tends to enrich the gas in hydrogen. The water, of
course, derives from moisture elimination near the feed end of
the vessel.
As a result of these reactions, the gas becomes
progressively enriched in H2 and CO until the temperature
drops sufficiently to reverse such reactions with the eventual
precipitation of carbon black and moisture pickup. However,
since the uncarbonized fuel consists primarily of chars and
coal fractions with significant volatile content, such vola-
tiles are incorporated into the gas stream. The final gascomposition of the gas at the exit point will then consist of
coal volatiles, C02, plus varying amounts of hydrogen and CO,
depending on the gas temperature. The entrained carbon black
particles will be removed in conventional dust control systems
and reuse during fuel agglomeration, both to achieve higher
agglomerate densities (leading to higher product strength) and
also because of their low impurity levels. The gas would also
be cooled by heat exchange for steam or power generation, and
to permit recycling into the vessel.
