Note: Descriptions are shown in the official language in which they were submitted.
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HOE 79/H 01g
The present invention relates to a process for the
production ~f calcium carbide by reacting coke with lime
in the presence of oxygen inside an oxygen-thermal furnace,
also termed carbothermal furnace, the coke coming from a
hearth furnace.
It has been described that calcium carbide can be
made by a process, known as the oxygen-thermal process
(cf. Chemie-Ingenieur-TechnLk 28 (1956), pages 4 - 5~,
wherein coke is burnt together with high percentage
oxygen to provide the energy necessary for carbide
formation at the very high temperat~res of about 2000
to 2500 C. Needless to say, technical difficulties had
to be overcome prior to operation of oxygen-thermal
furnaces with a production capacity of 100 metric tons
of carbide per day, with the use of lumpy coal coke. For
lack of commercial attractiveness, the oxygen-thermal
production of carbide has however been replaced by an
electrothermal process, and it has been suggested that
lignite coke should be used therein. It has been practically
impossible however for the coal coke or anthracite quantities
to be replaced by lignite coke to an extent of more than
66 percen~ (cf. Braunkohle 11 (1956), 361). For reasons
of cost, the use OL formed lignite coke in mode~n carbide
furnaces has, however, been stopped. On the other hand,
it has not been possible heretofore to operate an electro-
thermal carbide furnace exclusively with the use of ~ine coke.
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Despite the fact that its co~mercial attractiveness
is not fully satisfactory, the oxygen-thermal process
has recen~ly regained interest as a potential alternative
to the electrothermal production of calcium carbide.
The present invention now unexpectedly provides
a process for the oxygen-thermal production of calcium
carbide, in which use can be made of coal coke or
anthracite or a mixture thereof with lignite coke
or of lignite coke alone, the latter being an especially
inexpensive carbon carrier in the form of fine coke, the
process permitting the oxygen~thermal production of
calcium carbide to be improved.
The present invention relates more particularly to
a process for the production of calcium carbide by reacting
coke with lime in the presence of oxygen inside an oxygen-
thermal furnace, which comprises: subjecting coal to a
coking reaction inside a hearth furnace at temperatures
for the issuing gas of at least 750 C, preferably w~thin
the range 1100 to 1500 C; directly introducing the re-
sulting coke with an inherent temperature of at least500 C into the oxygen-thermal furnace; admixing the
coke ~ith lime and oxygen, and producing calcium oxide
therefrom.
The term "introduction of coke" into the oxygen-
thermal furnace or process as used in accordance withthis invention should be interpreted in a broad sense,
i. e. so as to comprise the direct introduction of coke
into the reactor and also the introduction of coke into
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an apparatus unit arranged ahead of the oxygen-thermal
furnace, between hearth furnace and oxygen-thermal
furnace, wherein it is mixed with the other component
forming the furnace burden, more especially with lime
which is thereby heated. In other words, critical~ty
just resides in the direct or indirect introduction
of the total heat of the coke into the oxygen-thermal
furnace.
The term "coal" as used herein denotes all car-
bonaceous materials which are commonly employed in
a hearth furnace, e. g. mineral coal, brown coal (lignite),
petroleum coke. Coke produced inside the hearth furnace
is always introduced into the oxygen-thermal furnace.
The use of brown coal has been found to have highly
beneficial effects. With respect thereto, it is pre-
ferable ~or brown coal to be dried with counterpressure
steam so as to contain less than about 25 weight%,more
preferably less than about 15 weight%, of water. It is
also preferable for brown coal to be used in the form
of particles with a size o~ less than 20 mm, more pre-
ferably less than 6 mm and most preferably less than
~ mm. Needless to say,however, it is also possible to
use lumpy, e. g. formed coal with a size of up to
150 mm. In any case, care should be taken to ensure
that the coke coming from the hearth furnace has a
maximum particle size which does not ~nterfere with its
use in an oxygen-thermal furnace. The present process
even permits advantageous use to be made of fine particula~e
coke.
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The carbonaceous starting material is subjected to
cokinE inside the hearth furnace, in customary manner.
The issuing gas should have a te~perature higher than
calcination temperature, i. e. higher than 900 C, and
the coke which is taken from the hearth furnace should
preferably be at calcination temperature, i. e. at more
than 500 C. Coke materials made as described herein
are normally free from water and contain 0.5 to 20.0
weight% oi volatile matter together with 3 to 12 weight%
of ash. The content of C-fix may be as high as 65 to 90
weight% or even higher.
A further feature of the present invention provides
for waste heat originating from the hearth furnace and
oxygen-thermal furnace, respectively, to be used at least
partially, preferably completely, for the generation of
steam. To this end, the invention provides for the waste-
heat boiler to have an after-combustion unit associated
with it, in which combustible matter forming part of the
waste gas is burnt. By optimum use of waste gas heat, it
is possible to provide the heat energy necessary for
drying brown coal, the entire electric power for operation
of the plant, and the energy necessary for oxygen production.
In other words, a preferred feature oi this invention pro-
vides for generated steam to be partially used for the
production oi oxygen and partially ior drying the coal
for use in the hearth furnace.
Coke which is produced in, and taken from, the
hearth iurnace is directly employed in the carbide
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furnace process. This compares favorably with those prior
art processes which are carried out ~ith customary coke
material. More particularly, the present process permits
the amount of energy which is necessary for heating coke
to be considerably reduced and the expenses which are
normally incurred by the step of cooling coke to be
avoided. The coke coming from the hearth furnace is
introduced in customary manner, e. g. via a lock or by
means of a carrier gas or under the action of gravity,
into the oxygen-thermal furnace which is incidentally
operated in customary manner. The resulting calcium
carbide has properties corresponding to those of
electrothermally made carbide and can be put to
customary uses, just as the crude furnace gas. Energy
in excess, for example, can be used for converting the
crude furnace gas to synthetic gas.
The process of this invention also provides for
the coke coming from the hearth furnace ~ be introduced
into the reactor of the carbothermal furnace via one or
~o more heat-insulated feed pipes which are down pipes, for
example, the escape of gas through the feed pipes being
avoided by pressure equalization inside the reactor. In
accordance with this invention, it is particularly ad-
vantageous for hot hearth furnace coke to be mixed at
least with a portion of lime, the coke and lime being
incidentally used in the form of particles approximately
identical in size, and for the resulting mixture to be in-
troduced into the reactor of the carbothermal furnace. It
~s gen~r~lly good practice to admix the hot coke with
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a quantity of lime, which is thereby preheated,
sufficient for the resulting lime/coke-mixture to
assume a temperature of about 600 C or less, ahead
of the reactor. In other words, as a result of the
lime componen~ having a portion of the heat absorbed
~erein, the mixture is at a temperature lower than
the very hot coke and therefore relatively easy to
handle technically in the absence of adverse effects.
Despite this, the entire heat is admitted to the reactor
inside which temperature peaks are not liable to occur.
This is highly desirable inasmuch as a regular temperature
gradient is established therein which makes it possible
for the reaction to follow a regular course.
A further feature of this invention provides for
the hot coke or hot lime/coke-mixture to be injected
at least partially into the reactor of the carbothermal
furnace, with the use of an inert gas, or preferably
with C0-containing furnace off-gas. In all those cases
; in which material coming from the hearth furnace is in-
jected into the oxygen-thermal furnace, it is possible
for the two furnaces to be positioned side by side~ i. e.
it is then not absolutely necessary for the latter furnace
to have the hearth furnace mounted thereabove.
Beneficial effects of th~ present process reside
in the possib~ity of operating a carbide furnace ex-
clusively with the use of lignite coke, and of pro-
ducing carbide ~y the oxygen-thermal process with
the use just of fine coke. As a result, this process
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has been considerably improved as to energy balance and
commercial attractiveness. Contributed to this has the
possibility that limy ash constituents, if any, of the
coal can also be transformed to calcium carbide.
The process of the present invention will now be
described with reference to the accompanying drawing
showing a diagrammatic and exemplary embodiment. Need-
less to say, the invention which admits of various modi-
fications without departing from its scope, is naturally
not limited to the specific embodimen~ shown.
With reference to the drawings:
Brown coal ground to particles with a size of up
to 10 mm is dried in an apparatus unit 1 so as to establish
a water content of 14 weight% with the use of counter-
pressure steam coming from a turbine 2. Vaporous matterand condensate~ respectively, obtained during drying is
removed. Next~ the dry coal is introduced into hearth
furnace 3 and subjected to coking therein in contact
with air, at a temperature of 1400 C, for example, in
the gas chamber. Off-gas coming from the gas chamber is
introduced into waste-heat boiler 4 and used for generating
superheated high pressure steam which is delivered to
turbine 2. Power transformed to mechanical energy in the
turbine 2 is used for low temperature decomposition of air
in apparatus unit 5, i. e. for the production of oxygen
needed in oxygen-thermal carbide furnace 6 and for the
generation of electrical power in generator 8. Coke of
900 C which is taken ~rom hearth furnace 3 is introduced
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into the reactor with the use of an injector, for example,
and a carrier gas, which is of~-gas coming from the
carbide furnace. The reactor is also fed with lime and
oxygen coming from unit 5. Off-gas of about 600 C from
carbide furnace 6 is freed from dust in a cyclone 7 and
used for heating boiler feed water, a portion of the off-
gas being used as a carrier gas for hearth furnace coke~
Carbide is taken ~rom carbide furnace 6. Inasmuch as the
crude furnace gas contains about 87 volume% CO and about
12 volume% H2, it is good practice for this gas to be
converted to synthetic gas with the excess of energy
aforesaid.
The following Examples illustrate the invention
which is, however, not limited thereto:
EXAMPLE 1: (Comparative Example)
28 tons/h of lignite coke, 15 tons/h of lime
(CaO-content = 94 weight%~ and 17 300 m3/h (S.T.P.)
of oxygen were introduced into an oxygen-thermal furnace
and reacted therein to give 13 tons/h of calcium carbide
(carbide content = 80 weight%). 43 000 m3/h (S.T.P.) of
crude ~as which had a temperature of about 600 C was
recovered from the carbide furnace.
EXAMPLE 2: (Process of invention)
The procedure was as in Example 1 but the coke
was left uncooled and introduced, while hot, into the
reactor. 139 tons/h of crude brown coal (water content
= 60 weight%) was treated to obtain 65 tons/h of dry
coal (particle size = up to 10 mm; water content =
7~
14 weight~o). As a result of the coke being introduced
while hot, it was possible to reduce the quantity of
coke to 23 tons/h. Downstream of the hearth furnace,
it had a temperature of about 900 C. The coke was
mixed with 7.5 tons/h of lime, which was used in the
form of particles with a size of up to 5 rnm, and the
resulting hot mixture (about 600 C) was introduced
into the reactor for reaction therein with the balance
quanti~y of llme and -- as a result of the coke being in-
troduced while hot -- with a quantity of oxygen reduced
to 13 400 m3/h (S.T.P.)~
EXAMPLE 3: (Process of invention)
The procedure was as in Example 2 but the coke
(23 tons/h) which had a temperature of about 900 C
downstream of the hearth furnace was used with that tempe-
rature in the oxygen-thermal process. It was mixed with
15 tons/h of lime and the resulting hot mixture (about
400 C) was introduced into the reactor and reacted with
oxygen therein.
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