Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~55~L4
SHAFr~ FURU~ACE FOR THER~. P~OCE~SING OF
FINhl,Y DISPE~S~D ~lAT~IALS
The invention relates to metallurgical and chemical
technology, in particular, to shaft furnaces for therma~
treatment of finely dispersed materials.
r~he invention can be effectively used for drying and
calcining without access of air of powderg or pasty mate-
rials,auch as flotation concentrates and slimes, and for
driving off volatile and readily decomposing substancesl
such as mercury, sulfur and flotation reagents, in the me-
tallurgical and chemical industries.
Currently, powder-like materials are treated mostly
in multiple-hearth mechanically rabbled furnaces. ~hese
furnaces have several annu~ar hearths placed one above
another and enclosed in a metallic cylindrical casing lined
on the inside with a refractory material. The material is
moved from one hearth to another by rabbles attached to a
central cooled driving shaft. Modern furnaces have up to
16 hearths. The furnaces are heated by combustion gases and
burners provided additionally on some hearths. Gases are
drawn olf through a gas outlet in the top part of the fur-
nace.
r~his type of furnace is employed for drying and calci-
ning limestone, limestone s~imes and magnesite, and for
o~idizing roasting of sulfide materials. The furnace is
bulky, and mechanical rabbles inside the furnace complicate
its construction and sealing, which renders a multiple-
-hearth mechanical~y rabbled furnace practically unsuitab-
11~5S'~4
le for thermally treating of powdery and pasty materialswithout access of air.
Rotary kilns are widely employed for calcining or
roasting pasty materials. These kilns have a horizontally
arranged metallic casing lined on the inside with a refrac-
tory material. ~he heating arrangements of the rotary kiln
include a fire hood and a gas discharge end. ~lso provided
are devices for supplying fuel and discharging calcined
(roasted) material. Sea~ing devices at joints of rotating
and stationary parts of the kilns greatly complicate the
design thereof. ~hese kilns are used for sintering pasty
bauxite or nepheline materials and for oxidizing roasting
of sulfide materials. ~o effective sealing of rotary kilns is
practically possible, so that they are not employed for ther-
mal treatment without access of air of powder~ or pasty ma-
terials.
In addition, processing of powdery materials in rotary
ki~lns and multiple-hearth furnaces involves substantial
dusting, which adversely affects the good repair and service
life of units and component parts of the kilns and fux~aces.
~ aterials can also be treated in a protective atmosphere
in electrical resistor drum-type rotary kilns which are inten-
ded for treating non-caking and non-sticking loose materials.
~ hese kilns are suited for treating materials that give
off little dust, as then only it proves advantageouæ to circu-
late the costly inert gas.
However, electrical resistor-type rotary kilns cannot be
11~5544
used for thermal processing of f:LOtation concentrates which
are fine dusting materials. Another obstacle for treating
flotation concentrat~s is the attendant evolution of mois-
ture, of products from the pyrolysis of flotation reagents
and of sulfur.
~ inely dispersed dusting materials can also be treated
thermally in fluidized bed ~urnaces. '~hese furnaces comprise
a bottom through which hot air is supplied under pressure
to fluidize the material being treated. An important compo-
nent part of the ~urnace is the bottom which is a slab of
refractory concrete with many orifices that æe protected
against ingress o~ the materia~ by '1mushroom1'-shaped nozz-
les. The treated material is discharged from the fur~ace by
gravity through devices situated level with the fluidized
bed.
These furnaces are employed for oxidizingS reducing,
sulfidizing, chloridizing aud other kinds of roasting of
various concentrates and ores, for drying granula, pasty
and liqued materials.
However, these furnaces suffer from a considerable
entrainment of dust, the amount of which may attain 50 %
of the charge fed to the furnace. ~l~his complicates and rai-
ses the cost of dust cleaning system for collecting entrai-
ned particles. ~l~he recovered material requires re-roast~ng
in muffle furnaces and a subsequent individual treatment
for extraction of valuable components therefrom.
~ he devices for collecting entrained particles sub-
stantially complicate furnace design and raise the cost
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o~ furnace operation. '~o obviate this disadvantage, the
powder~ material is pelletized and subjected to a thermal
treatment in a shaft furnace.
There is widely known a sha~t furnace ~or thermal treat-
ment of pelletized materials in a stream o~ hot ~as. This
furnace consist~ of vertically arranged sections, each of
which is provided with pipes ~or supplying of hot gas and
pipes for exhausting o~ gaseous and v~pour substances. ~he
sha~t o~ the furnace expands towards the bottom. ~n essential
precondition o~ trouble-free operation o~ the furnace is the
charging of pelletized raw materials. ~his ensures the flow
of the heating agent through the bed of the material and the
continuous descent of the charge in the shaft by gravity.
Should a powdery or a pasty material be charged, the heating
agent can no longer filter through the bed. ~he material
will then stick to ~urnace walls and so block ducts for gas
flow.
~ here is also known a plant ~or thermal treatment o~
loose materials, comprising a vertical casing with heat ex-
change heating and cooling surfaces situated vertically and
s~mmetrically relative to the vertical axis o~ the casing.
~he heat exchange surfaces are formed with bundles of hori-
zontal tubes connected to collector boxes. In the heating zone,
the tubes are heated by combustion gases.~ In the tubes o~ the
cooling zone circulateSwater~ ~he casing o~ the plant and the
tubes are oscillated by a vibrator~ The casing is provided
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on the inside in the material heating zone with louvered
grates to ensure a uniform removal of vapours. The louvered
grates are formed wi-th two groups of plates equidistant from
the vertical axis of the casing. The clear cross section
of these plates is suited to the variation in the moisture
con~ent and the parameters of ~he thermal treatment.
'l'he material is supplied from the top throug~ a char-
ging hopper mounted atop the casing. The material descends
by gravity and under the action of vibratory forces contact-
ing the external surfaces of pipes. r~his heats the materia~
and so vaporizes the moisture contained therein. The vapour
is directed toward the walls of the casing, flows through
the louvered grates into the vapour conduits which exhaust
it to the atmosphere. '~he dried material passes through the
cooling zone and is discharged by a feeder.
An essential precondition for a trouble-free perfor-
mance of this device iB the provision of a vibrator and
of vibrating heat exchange surfaces placed inside the bed
of the material. ~his impairs the reliabi~ity of the fur-
nace, complicates its operation and repair. ~he material,
which is pasty, is liable to stick to the heat exchange sur-
faces located inside the furnace. This destabilizes the ther-
mal conditions inside the ~urnace, and, therefore, affects
the quality of finished product.
It should be noted that ores extracted at present are
characterized by an increase in the proportion of lean poly-
metallic ores which require beneficiation. ~he resultant
concentrates are pasty and moist powdery materials, the furt-
11~5544
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her treatment of which necessarily involves their thermal
processing (drying, roasting, calcining).
However, known furnaces fail to provide efficient
ther~al treatment without access of air of these finely
dispersed materials, and this has given rise to a need for
substantially improving the designs of known furnaces or
developing new types of furnaces for the purpose.
Serious problems are encountered in the processing of
an ever increasing amount of pasty and moist powdery materi-
alæ, the thermal treatment of which requires additional in-
vestments for collecting dust, for moving the materia~ inside
a furnace, for rotating a kiln or for pelleti~ing these fi-
nely dispersed materials.
l`he invention is aimed at enhancing the reliability of
a shaft furnace for thermal treatment of finely dispersed
materials and improving the quality of the product.
This aim is attained in a sha t furnace for thermal
treatment of finely dispersed~matexials, comprising a heated
casing of rect~ngular cross section, atop which is mounted
a charging hopper, pipes for eXhausting process gases being
situated in the top part of the casing, with ~wo groups of
plates equidistant irom the vertical axis of the casing
being arranged inside the internal ca~ity thereof, wherein,
according to the invention, the plates are in parallel
space relationship with the vertical axis of the casing,
have different lengths increasing in the direction from the
vertical axis toward the narrower wall and forming passa-
ges therebetween and the narrow Wall of the casing, so as
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to channel process tases toward the exhaust pipes.
To make the passages for the flow of gases
extend longer toward the e~haust pipes for drawing off
process gases and thus to enhance the removal of gases ~rom
a treated ~aterial prior to their discharge from the furnace,
the bottom ends of the plates situated near the periphery
of the casing are bent in the direction of the vertical axis
of the casing at an angle of 10 to 50 relative to the verti-
cal part thereof~
To make the furnace more compact, the bottom part of
the nar~ow walls thereof is preferably bent inwards toward
the vertical axis of the casing, and in parallel space rela-
tionship with the bent ends of the plates.
To avoid the hanging o~ material~ and to ensure norma
~herm~ conditions inside the furnace, it is advisable
to have the width of the narrow walls equal to 8 to 10
times that of the wide walls of the furnace.
Such furnace construction makes it possible to subject
to thermal treatment, effected without access of air and
without a protective atmosphere, non-pelle~ized powdery or
pasty materials, to improve operating reliability of the fur-
nace and to ensure higher quality of the product being treat-
ed. ~he provision of different-in-length plates arranged in-
side the furnace in parallel relationship with one another
and with the vertical axis of the casing, is intended as a
means to control the amount of material entering the furnace,
which is governed by the dista~ce between the two plates
nearest the vertical axi~ of the casing , and to ensure an
~S54~
unimpeded flow of the treated material from the point of
charging -to the point of discharge of the product.
With this arrangement of the plates, passges are form-
ed between the plates and the narrow wall of the casing,
which promote selective removal of vapour and ga~eous
substances given off during the proces~ing of material.
Different vapours and gases pass through different passages
toward the e~haust pipes.
The inve~tion will IlOW be described, by way of example
only, with reference to the accompa~ying drawings, in which:
FIG. 1 illustrates a shaft furnace for thexmal treat-
ment o~ finely dispersed materials with two pairs of p~ates
(isometric projection), according to the invention;
~ IG. 2 (a, b) shows a shaft furnace for thermal treatment
of finely dispersed materials with one pair of plates (ver-
tical section through the furnace casing vertical axis),
according to the invention;
FI~. 3 (a, b) represents schematically a shaft furnace
for thermal treatment of finely dispersed materials with
groups of plates and a narrowed bottom part of the casing
(vertical section through the furnace casing axis) 9 accord~
ing to the invention.
Referring now to the above drawings and to FIG. 1 in
particular, there is shown therein a furnace for thermal
-treatment of finely dispersed materials, which comprises a
casing 1 (~IG. 1) of rectangular cross section and a detach-
able top cover 2 formed with a refractory concrete 20 to 30
~14554~
mm thick. `Nide walls 3 of -the casing 1 are provided with
grooves 4 which accommodate resistor heaters (omitted on
the drawing). '~wo groups of plates 5, 6 parallel to a ver-
tical axis 7 and equidistant ~rom this axis 7 are situated
transversally in the top part o~ the internal space of the
casing 1 between the heated v~ide walls 3. ~he number o~
the plates 5, 6 in each of the groups depends on the pro-
perties of the material being treated and the thermal pro-
cessing (drying, roasting, calcining) conditions.
The plates 5, 6 have di~erent lengths increasing in
the direction from the vertical axis 7 to the narrow wall
8 of the casing 1. The two nearest the vertical axis 7
short plates 5 are rigidl~ secured to narrow walls 9 of a
hopper 10 for charging materials, which is sealed into the
cover 2. ~he remaining plates 6 are detachable, secured to
~he cover 2 and carry holes 11 in the top part. Illhe plates
5, 6, and ~he narrow wall & of thq c~ing 1 ~orm passages
12 for the flow of vapour and ~aseous substances toward
exhaust pipes 13, which are provided in the narrow wall 8
of the casing 1. ~he bottom ends of the narrow walls 8 and
the wide walls 3 form a discharge port 14 of the furnace.
The ratio of the width of the narrow wall 8 to the
width o~ the wide wall 3 of the casing 1 approximates 1:8
to 10, so as to keep the width o~ the furnace within optimum
limits. An increase in this ratio reduces the furnace width,
so impedillg the descent of the material inside the casing
1, which then tends to hang and overheat. A decrease in the
value of the above ratio results in a deterioration of the
~1 ~554~
- 10 _
thermal conditions inside the furnace.
A ~urnace for therrnal -treatment of finely dispersed
material may be designed with a single plate 5 (FIG. 2,
a, b) in each of the groups. ~hese plate~ 5 are rigidly se-
cured to the narrow walls g of the char~ing hopper 10 and
are situated parallelly to the vertical axis 7 inside the
ca~ing 1. ~he narrow walls 8 of the casing 1 actually serve
as the second long plates. The space 12 between the plates 5
and the narrow wall 8 of the casing 1, which is free of a
material being treated, is the passage 12 through which
flow the vapour and gaseous subs-ta~ces evolving from the
material being treated toward e~haust pipes 13.
A furnace according to the invention may contain three
plates 5, 6 and 15 (FIG. 3, a, b).
This embodiment of a furnace for thermal treatment of
finely disperssd material enhances the removal of gaseous
substances from the material being treated. In this case,
bottom ends 16 of the extreme plates 15 situated on the
periphery near the narrow wall 8 of the casing 1, are bent
at a~ angle of 10 to 50 relative to the vertical axis 7
of the casing 1. Bottom ends 17 of the narrow walls 8 of
the casing 1 are bent through a same angle. ~hiæ resu~ts
in additional passages 18 for the flow of ga~eous substan-
ces toward the exhaust pipes 13 be~ween the extreme pla-
tes 15 and the narrow wall 8 of the casing 1~ through which
is exhausted the re~ainder of vapour or gaseous ~ubstances
given off by a material being treated prior to the dischæ -
ge thereof through the port 14 of the fu~nace.
~1~55~9~
A slope of less than 10 of the plate~ 15 and the
narrow walls 8 results in a greater height of the furnace
~nd makes it bulkier, whereas a ~lope in e~cess of 50 leads
to an accumulation o~ a material being treated at the bends
of the plates 15 and so hinders the discharge thereof.
A furnace for thermal tre~tment of finely dispersed
material operates in the manner below.
A finely dispersed material is fed from the charging
hopper 10 (FIG. 1), sealed into the detachable cover 2,
inside the space formed bg the short plates 5 ne~rest the
vertical axis 7 of the casing 1 and descends by gravity.
The material then enters the space formed with the next
pair of the plates 6 and fills this space. ~ext, the mate-
rial moves toward the narrow wall 8 o~ the casing 1 and
fills only the bottom part of the casing 1 , descending
in the process toward the discharge port 14 of the furnace.
~ he temperature of the heated walls is maintained at a
level higher than the boiling point of a vapour ox a gase-
ous substance given off by a material being treated. The
temperature is controlled through the agency o~ resistor
hea~ers (omitted on the drawing) set in the grooves 4 of
the wall 3 o~ the casing 1. ~he vapour and the gaseous sub-
stances evolving from the heated material build a pressure
along the waLls ~ and 8 of the casing 1 and the plates 5,6.
Th~ prevents the material from sticking to the walls ~, 8
and to the plates 5, 6 and facilitates the descent thereof
by gravity toward the discharge port 14 of the ~urnace.
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~ he vapo~r and the gaseous substances given of~ by
the material being treated ri~e through the passages 12
into the top part of the casing 1, pass through the holes
11 of the plates 6 toward -the pipes 13 and are exhausted
under pressure into a condenser or to the atmosphere. The
pressure built up by the vapour and the gaseous substances
from below and the column of the material being treated,
which fills the casing 1 from the hopper 10 to the dischar-
ge port 14, prevents an ingres~ of air into the furnace
during its operation.
If a furnace for thermal treatment o~ a f`inely disper-
sed material is built as shown on ~IG. 2, the ma-terial
being treated, once it fills the space between the p~ates
5, enters directly the casing 1 of the fu~nace. '~he height
~o which ~he casing 1 is filled or the wi~th of the passage
12 formed with the plates 5 and the narrow wall 8 depend on
the physical properties (moisture content, fineness, angle
of repose) of the material being treated and on drying pa-
rameters.
~ his furnace is simple in manufacture and operation
and is employed for thermally processing materials of high
moisture contents, such as pastes and s~spensionsr
In a furn~ce for thermal treatment of finely dispersed
material with three plates in each group, once a material
being treated fills the space enclosed by the extreme plates
15 (FIG. ~), it enters the space formed with the bottom ends
16 of the plates 15. Next, the material fil~s the bottom
part of the casing 1 formed with the bottom part 17 of the
1~ ~554
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narrow walls 8 of the casing 1, bent at an angle 10 to 50
relative to the vertical axis 7, and descends towards the
discharge port 14 of the furnace. In the process, an addi-
tio~al amount of the remaining gaseous substances is remo-
ved from the material being discha~ged, this improving the
quality thereof.
~ furnace for thermal treatment of finely dispersed
material has been tested industrially for treating molybde-
num and tungsten products.
~ he drying of a pasty molybdenum semiproducts of a
total content of moisture and of flotation oils o~ 30% in
a furnace with a single pair of plates at the temperature
of the wide walls of 450C yielded a finished product with
a total content of moisture and of ~lotation oils of 5%.
A powdery tungsten concentrate with 7.09 % sulfur in
the form of pyrite was subjected to a thermal treatment at
the temperature of 800C to remove pyrite sulfur in a fur-
nace containing a group of plates, wherein the narrow walls
of the furnace casing, the ends of the plates and the bot-
tom part of the casing walls were bent relative to the ver-
tical. As the roasted concentrate contained 0.65 % sulfur,
this represented a substantial improvement of the quality
thereof.
~ he industrial experiments of a shaft furnace for ther-
mal treatment of ~inely dispersed materials, according to
the inventio~, have indicated its wide range of applicabili-
t~, as the furnace ca~ handle materials of different size,
ranging in composition from granular masses to pastes. The
11 45544
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furnace is characterized bg a hi~h specific throughput ca-
pacity, a lesser consumption of electric power as compared
to other furnaces for similar application, a considerably
improved quality of fini.shed product, an amerability to me-
chanization and automatior. of operations which a thermal
treatment of a material involves, a simplicity of both ma-
nufacture and operation of the furnace.
