Note: Descriptions are shown in the official language in which they were submitted.
WO 9Ci239-~8 PCT/GB9~C100~4~
21 ~45~7
A P~RNAC~
TXIS I~VENTION relate~ to a furnace. It relates aiso to a
method of carrying out a reaction, ut~lizing the furnace.
According_ to a first aspect of the invention, there is
- pro~ided a furrace compr sing a furnace shell rotatable
5~ about a rotational axis, the furnace shell providing a
furnace chamber for holding a solid particulate reagent as
the furnace shell rotateQ; and at least two electrodes
exp~sed to t~e ~h~mher and being mounted in electrically
~sulated fashion therein, with the electrodes ~ein~ spaced
apart 30 that 301id particulate reagent in the furnace
~h~h~r can be heated up ~y direct r-sista~ce heating
thereo~, ut~lizing the electrodes.
The furn~ce shell will normally be cylindrical, and be
located substantial~y horizontally so that the rotational
axis extends substaneially horizontally.
The fu~nace i~ suieable for carrying out rea~tions whereby
a solid particulate reagent is reacted with a further
reagcnt at elevated temperature. The reactions may be
endothermic or exothermi~. Examples of e~dothermic
reacticns are nitriding o~ a titanium-contai~ing materiai
as the solid par~iculate reagent, such as a titaniferous
ore or slag, ~o convert titanium values therei~ to titanium
ni~ride; nitriding of a ~anad ium containing material; and
the carbiding of silicon-bearing mAterial. The solid
reagen~ is thus heated tO said elevated temperature, and is
supplied with heat ~or the endothermic reac~ion at said
W095/~39~8 2 ~ 7 pcTlGss~/owJo
eleva~ed temperat~re, 3y ~irect resls;ance heating .hereof
in the f~rnace chamber The furnace can also be used for
the regeneration of spent acti~ated carbon.
In other words, an electrlcal potential or ~oltage ~s
S applied to the material of the solid reagene w~ereby an
elect-ical c~rrer.t is passed by means of the electrodes,
through the material, thereby generating heat within the
material, to raise the temperature of the material to the
ele~ated temperature, to supply heat at that temperature
for the endother~c react~on (where app~icable~ and/or to
enhance the reacti~ity of the reactants. Thus, the
electrodes wil~ be o~ different polarity.
Thus, accor~ing to a secon~ aspect of the in~ention, there
is provided a method of carrying out a reacticn wh~ch
includes heating the solid reagent to the ele~ated
temperature in the ~urnace chamber of a furnace as
hereinbefore described.
The method may inc~ude introduc~ng a se~ond or further
reage~ into the ch~her, to react with the solid reagent.
The ~urther reagent may be a further solid reagent, but is
typically a gaseous reagent. The gaseous reagent can t~en
be passed over the solid reagent in the furnace chamber
and/or through ~t, eg by being introduced into ehe boetom
of a ~ed of the material in the cha~ber.
~y 'partlculate' is meant any desired particle shape and
size. Thus, the solid reagent particles can have an
irregular shape and fall with~n a predetermined ranse of
sizes, as would be the case when it comprises ore which has
keen mined and m lled. Instead, it can be of resular shape
3~ and size, eg in the form of a powder, granules, pellets,
briquettes, cr the ~i~e.
21 ~45~7
wo ~n3s4s Pcrl~ssloo~o
The e~evated temperature ac which the reaction ta~es place
may be 1000 - 1800C, preferably llO0 - 1600C and more
pre~erably 1200 - 1350C, and the Yoltage app~ied to the
material will be selected acc~rdingly, bearing i~ mind the
resistivity of the material.
Certain solid reagent materials to which it is contemplated
the method will in p~actice be applied, such as
titan~fer~us ores (eg ilmenites) or titaniferous slags,
which are to be reacted with gaseous nitrogen to ~itride
t~tanium values therein, can be relatively non-conducti~e
to electricity at am~ie~t temperatures. For such
materials, i~itial heati~g may be by other methods, such as
preheating the solid reagent by radiative, con~ectional
and/or thermal-conducti~e meehods, tO raise the tempera~ure
lS of the material from ambient temperature up to an
intermediate value at which ohmic- or direct-resistance
heating ~s effecti~e, after which the ohmic- or
d~ect-resistance heating can be employed further to raiqe
the temperat~re of the material up to its f~nal ~alue, and
to supply the heat needed for the endothermic reaction.
Such intermcdiate ~alue may be 700 - 1300C, preferably
700 - lOOO~C, eg 700 - aoooc.
I~ctead or in addition, ehe method may include the step of
mixing the solid reagent in particulate form with a
pa~ticula~e solid electrical conductor, to pro~ide a
mixture having increased electrical conducti~ity compare~
with that of the soli~ reagent. The mixt~re may be
compacted or consolidated, eg by pelletisins, extruding or
briquetting the mixture, ~urther to increase said
conduct~ity. Fo~ the mixing, the solid reagent and
electrical cond~ctor may be in finely di~ided ~orm, ha~ins
a particle size of at most 1000 ~m, eg S0 - 200~m, and the
consolidation, at leas~ in the case cf briquet~ing, may
be by subjecting the mixture to a pressure o~ at least ~ -
llMPa. Carbon may be employed as the electrical conductor,
wo ~sn39 18
2 1 ,3 ~i ~ ~ 7 PCT/GBss/oo~o
and has t~e advantase, ln the nitriding of
tita~um-cor~tainin~ sol_d reagents, of pro~iding a reducing
en~i-onment ~or the e~do;herm~c nieriding reaction. The
pelle~s or bri~uettes may be in the ~ize range 5 - ~Omm, eg
lO - 20mm.
When car~on is used as the electrica} conductor, i~ may
form 13 - 9G~ by mass of the mixture, eg 12 - 60~ thereof.
The carbon may be in the form of coal, anthracite, coke,
i~dustrial char, charcoal, graphite or the like, i~
par~ic~lar duff coal, which is readily obtainable and
- inexpensive.
The ohmic- or direct-resistance heating is thus applied eo
a moving bed of the solid reagent, eg a mo~i~g bed of said
pel~ets or briquettes, in the furnace cham~er as it rotates
so that any preferentia~ paths through the bed of material
along which electrical currents pass in response to the
applied ~oltage are continuously or interm~ttent~y
di~rupted, and so that more or le~s u~iform heating of the
particulate material i9 yLO.~O~ed.
The spacing between the electrodes may be lOO - lOOOmm,
typically se}ected on the basis of ehe loading cr proposed
loading o~ solid material in the furnace chamber, ie the
furnace chamber capacity, the resistivity of the solid
mater~al, and the required operacing ~olta~e. Such
spacings permlt operating voltages conveniently of
~oo - 200 V to be used, al~hough higher spacings of up to
1,5 - 3m or more, requi~ing ~oltages of ~0 - 5QO v or
more, ca~ in principle be feasible.
The power supply used may be AC or ~C.
In accordance with the method, the operating ~olta~e
between the eleccrodes may be altered from tsme tO tsme,
either manually or automatically by means of an autcmated
wogs/23s48 PCTIGB95/00440
~_ 5
control 5ystem, which may be elocl_onic, in response to
changes in the temperature of the solid reactant in the
interior of the fur~ace, ie in the furnace cham~er, which
temperature may be sense~ eg by suitably located
S thermocouples in the interior of the furnace. In this way,
the operating ~o'tage can be increased to increAse the
power supply to the fusnace and hence to increase the
temperature of the solid reagent, or said voltage can be
reduced to reduce the power supp}y and temperature. ~n one
embodiment thsee voltages may be employed, eg 60V, llOV and
220V, the lowermost Yoltage being used when the solid
reagent temperature exceeds a desired ~alue by more than a
- predetermined amount, the uppermo~t Yo~tage being used when
said reagent temperature falls shor~ of the desired ~alue
by more than a predetesmined amo~nt, and the intermediate
~oltage being u9ed w~en the reagent temperature is closer
to the desired ~alue tha~ said predetermined amounts.
Ingtead,eg 3~0V ~an be used for start-up, whereafter two
~oltages such as llOV and 200V may be used, the lower
2C ~olta~e being used when ~he reagent temperature is above
the dcs~red temperature and the higher voltage bei~g used
when the reagent temperature is below the desired
ten~erature .
Whe~ the particulate solid electrical conductor which is
mixed with the solid reagent i9 carbonaceous~ eg du~f coal,
the heating of the solid reagent to operating temperaeure
can giYe rise ~o the production of a com~usti~le off-gas in
the interior of the ~urnace, containing carbon monox~de,
vaporized ~olatile coal constituents or the like. The
method may include the step of burning this of~ gas tO
provide the heat used ~or preheating the solid reagent, as
descsibed above, although elect~ical or any othe~ suitable
heat~ng may ~aturally be used instead.
When the ~urnace is operated with a nitro~en atmosphere, as
mentioned a~cve, a~d a carbonaceous particulate solid
wos~/23948
2 1 36 1 ~ ~ 7 PcTiGBs~o~
electrical conductc~ _s use~, mixed with a solid reagent
contai~ing titanium ~alues, suitable concrol of the
reaction environment ln the furnace can permlt not only the
ni~ ing cf the titan um values, but, instead or i-.
add7tion, the carbiding, c~rbonitriding or
oxycarbon7tr~ding thereof, which permits the production, as
desired, of titanium ~tride, titanium ~arbide and/or
titanium carbonitride. It will further be appreciated
that, although the description of the prosent in~ention
emphasizes the nitrlding of titanium, it may easily, in
ana~o~ous f~9hion, be applied to reactions in~ol~i~g other
solid reagenrs, eg ~or the nitriding, car~iding or
car~onitridi~g thereof, such as irl the production of
sillcon c~rbide by reacting a solid rea~ent comprisin~
15 Qilicon with a 801id car~on-conta~ning reductant in an
inert en~ironment in the ~urnace. Bearing in mind that the
carbonaceous particulate material such as duff coal can
have the functions, for a tita~7um-co~taining solid
reagent, of both increaging electrical conductivity of the
2Q solid reagent and of pro~id~ng of~-gas for preheating, an
exces~ thereof ig preferably used oYer the stoichiometric
requirement for red~cing all the citanium (as the ox~de) ln
the solid reagent, con~eniently double said stoichiometr7c
requiremenr of carbonaceous material is uscd.
surprisingly, the Applicant has foun~ that, in the case
where the solid reagent is vanadium-bearing maeerial,
tita~ium-bearing materia~, or silicon-bearing mater~al, the
increased conducti~ity of the solid ~eagent (whether or noe
it is with any partic~late co~duct~r to raise ts
3 0 conducti~iey) achieved by preheating the solid reagent, is
related to the rate of heating the solid reagent, a~d is
related t5 the rate at which a~y carbonaceo~s material
mixed wlth the solid reage~t is de~olatalized. It is
acccrdi~gly desirable to preheat as quickly as po~sible, eg
at least 20C/min, prefera~ly at least 80C/min.
wog~/23948 2 1 & ~ ~ i PCT/GB95iOo440
The method may be car_iea out batchwise, whe_eby a charge
of solid reagent is charged into the furnace chambe~ and
heated to cause the required react1on to take place, before
being discharged and replaced by a succeeding charge; or it
may be continuous, a stream of solid reagent passing
continuously thrcugh the furnace, where it is subjected to
required reaction.
The furnace may thus be constructed tO cause or permit
passage therethrou5h of ~oth the solid reagent and the
gaseous reagent, to permit the ~ontinuous operation, and
may have an interior which is sealed off from t~e
atmosphere. The furnace 9hell may comprlse an outer ski~
or wall, lined with ~ suitably inert shock-resistant
electronically non-conductive and thermally i~sulating
refractory lining, e~ a calcium silicate ant~or an
a-alumina linlng; and the spaci~g of the e7ectrodes, which
may b~ of copper, silicon carbide or prefera~ly of
graphite, may be as deccribed above. The electrode
material wi}l be selected according to the operating
temperatures and conditions. Thus, at lower operating
temperatures, copper electrodes can be used, while at
higher temperature5, graphite electrodes can be used.
While the furnace may in principle have any suitable
construction, such as a v~bratory table ~ocated i~ its
fuxnace chamber, to convey the solid reagent through its
i~terior, eg from an inlet to its furnace chamber to an
outlet therefrom for continuous operation, the fur~ace is
conveniently such that rota~ion of the furnace shell causes
pas~age of solid reagent ehrough or along i~s c~mher The
~us~ace will naturally include suitable d~ive means for
drtving the shell to rotate.
The furnace or kiln may be provided with an zlternating
current (AC) or d~rec~ current IDC) power supp}y to the
electrodes, via o~e or more suitable 61ip-rings mounted on
the furnace. Similarly, the furnace may have a slip-ring
wos~39~8 7 PCTIGBsSl~440
arra~gement connected e~ to one or more thermocouples
arranged in the f~rnace chamber, fcr monitoring the
temFerature in the chamber. The e~ectrodes may th~s be
arranged ir. sne c- more pairs in the interior of ~he
s furnace so that ~~ey are located at suitable location3 and
spaci~gs whereby the passage of an electrical current
between the electrode~ o~ e~ch pair in response to
application thereCo of a sufficient electrical potential
is promoted, and the passage of electrical current between
electrodes of different paixs is diQcouraged.
_The potentlal difference between the electro~es of a pair,
- measured through the sol~d reagent, is proportional to the
distance ~etween the electrodes, so that the distance
between the electrodes of a pair i8 in principle l~mited
only by the voltage supply a~ail~ble; howe~er, the ~oltage
i 9 also a function of the nature and resistivity of the
solid reagent. Excessi~e ~oltages can cause difficulties
related to unwa~ted electrical dischar~es ~etween the
elect~ode8 across ehe-surface o~ the solid r~agent, along
the surface of ~he insulating refractory lining of the
furnace cr through the refractory ~ ining to the exterior ~f
~he furnace.
According to one embcdiment of the in~ention, each of the
electrodes may be of annular fcrm and extend
c rcumferentially along an inner surface o the furnace
shell while protruding radially inward}y therefrcm, with
the electrodes bein5 spaced axially or longit~inAl}y
apart.
Howe~er, the in~ention also contemplates the pro~ision of
a plurality of pairs of the electrodes in the furnace, the
electrodes of each pair being spaced ~rom one another a~
the pairs of electrodes being arranged and located in the
~nterior of the furnace so that elect~ical discharge3 will
take place only between the elec~rodes of said pairs, and
wo9~/~948 ~ r, '-'7
2 1 ~ ~ 5 ~ ~ P~IGB9S/00440
g
no- between electr~des o_ dif~erer.t pairs; and so ;hat a
-elatively long rotary furnace can be used with relatlvely
small spacings between the electrodes of each pair, thereby
permltting reiatively low voltage9 (eg 100 - ~SoV) to be
s used. Thus, for example, the pairs o~ electrodes may be
spaced lonqltudinally from one a~other.
Accordi~g to another embodiment of the invention, one of
the electrode5 ('the firYt electrode') may extend cenerally
a~ong the rotational axis, with a plurality o~ the other
elecerodes ('the second electrodes~) being pro~ided, the
second electrode5 protrudins from and exten~in~ along an
inner sur~ace Oc the furnace shell in a longit~in~l
direct~on, and bei~ spaced circumferentially from cn-
another. The central electrode will thus be of a
particular po~ariey, wi~h the second electrode5 being of
opposite polarity, to pro~ide for current ~lows ~etween the
ceneral electrode and those- second peripheral electrodes
which are at any time submerged by the particulate material
in the furnace, the ~urnace bein5 operated with a bed of
particulate material therein of sufficient depth to be i~
contact with the central electrode.
In yet a further emko~tment, a plurality o~ the e~ectrodes,
arran~ed in pairs, eg th~ee pairs, and protruding from and
extendin5 along an inner surface of the furnace 3hell in
~he longie~J~in~l direction, may be provided, with the p~irs
bei~g circumferentially spaced from one another, and the
electrodes of each pair being spaced circumfe-entiaily from
each other by a spacing which is less than the spaci~g
between adjacent pairs. In this case, a~ wi~h the
electrodes discussed abo~e, the electrodes may stand proud
of the surface of .he lining. They can then also a~t as
lifters for lifting particulate material in the kiln as it
rotates, thereby assisting in keepin~ the part~c~late
mate_ial con~i~uously i~ motion and ~iyin~ it, to disrupt
the paths of electrical currents ~lowing therethroush.
W~ 9~123948 2 j ~ ~ 5 ~ 7 pcTlGBssloo44o
In a still further embodiment, the electrodes may be of
non-annular for~., and protrude from an inner surface of the
~urnace shell, with the one electrode ~ t~e first
electrode'~ being spaced lo~gitudinally from the other
electrode t~ehe second elect.ode~). A p}urality of che
'~rst elec~rodes, circumferentially aligned and spaced
apart circumferer.tially, and ~eing of the same polarity, as
well as a plurality of the second e}ectrodes,
circumferentially alisned and spaced apart
~0 circumferent'ally, and being of the same polarity, may ~e
provided. Thus, the first electrodes will ~e in the form
of a group, while the second e}ectrodes will also be in the
form of a group, ~ith the groups being spaced axially or
longitudinally and the electrodes of one group being of
1~ differe~.t polarity to ehose in the other groups. The
electrodes of the f irst group may be aligned with those in
the second sroup, in the longit~ n~ direction. If
desired, a further group of the first electrodes, spaced
axially or lon~it~in~l~y from the group of second
eiectrodes ~o that the group of second electrodes is
located ~etween the two groups of first electrodes, may be
pro~ided.
The Appl~cant has found, that in certain cases, the
resistiYity of the soli~ reagent decreases as the
temperature of the solid reagent increases with heating
thereof andlor as the sclid reagent reacts progressively
wieh the gaseous reagent (thereby progressively cha~ging
the composition of the solid reagent) so that, after such
heating and/or reactis~, a relatively lower voltage i9
required to ~aintain a consiseent current flow in the sol~d
reagent.
T~us the method may ~nclude the step of pass~ ng the solid
reagent through a series of successive furnace chambers or
reaction zones, each cham~er o~ zone including said at
~5 least two electrodes. The spacing ~etween the electrodes
wo 95l2394~ ~ 1 8 ~ 7 PCr/GB9510044n
11
in each succeedi~g zone-may ther. be greater than tha~ of
the precedt~g zone. The method may in this case, in
partlcular, inc~ude pas9ing the so~id reagent through the
zones so that ~t forms a separate bed in each zone, with
5 the beds bei~g electrically isolate~ from each other.
Thus, the material dams up in each segment, so that a~
lea~t some parametexs can be controlled separately in each
segment, eg temperature, re~idence time, and applied
~oltage.
In this way, by selecting zo~es of appropriate size or
length for a partic~lar solid reage~t and a particular
gaseous reagent, substantially the same voltage may be u~ed
for each pair of electrodes in each of the zones, despite
~ariations of the spacing between the el~ctrode~ in the
'~ different zones. In part~cular, in the ca~e of three
zones, a sing~e three-phase source of pcwcr can be used
with ane sa~d phase supplying power to each of said zones.
Thus, the furnace may inc}ude a ~eco~d sub~ta~tially
horizontal cylindrical fu~nace s~ell rotatab~e abaut the
rotational axis and spaced axially or longitudinally from
the other or first furnace shell, the second furnace shell
pro~iding a second fur~ace chamber or reaction zone which
ig in cor~un~cat~on with the first fur~ace ~hamh~r or
reaction zone and through which solid pa~ticulate react~nt
from the f~r3t cha~ber can pass in the longitu~in~l
direction, and wlth said at lea~t two electrodes also being
proYided in the second furnace cham~er. ~f desired, at
least one further similar horizont~l cylindrical furnace
shell may be provided adjacent the second furnace shell, to
provide t~e succcsai~e reaction zones.
The ~irst and second cham~ers may ha~e the same or
dif f erent diameters. For example, the second rh~her may
have a greater diameter than the ~irst ~h~mher.
WO 9~/23948 , I r; ~ L, ~3
C 1 ~ Lt ~ ) / PCTtGB951~0440
12
Additi~nally o- in~tead, the f irs_ and second '~rnace
shells may be of :~e same cr differe~t len~th, and the
spac~ng between the electrodes of the first furnace shell
may be the same of ~ifferent to that of the electrode~ of
S the second furnace shell.
In other words, the furnace can thus be segme~ted,
comp.is~ng a series o~ ax~ally spaced portions ~r segments,
each containing a pair of the eiectrodes. Each ~egmene may
be of a different diameter from the adjacent p~rtion or
segment. ~hus, the ~urnace may comprise a plurality of
such segments increasin~ progresB~vely in diameter from one
_ portion to the next, the portion of smallest diameter being
at thc upstream end of the furnace relative to the
d~rection of solid reagent flow.
Instead, the ~urnace may comprise a plural~ty of successive
sesments of the same or generally similar diameter, each
successive ~egment being longer, in a downstream direction,
than the se~-.c--t precedlng it, and the distance between the
electrode9 of each succe~sive segment being
corres~on~in~ly greater. This construction ta~es advantage
of the find~ng ~y t~e Appl~cant, referrcd to above, that
the resistivity of the solid reage~t, and hence the voltage
re$uired to cause passage 2f a current of a giv-n Yalue
through a ~iven mass or volume of the solid reagent,
decreases as the temperature af the solid reagent is
i~creased and~or as the solid reagent progressL~ely
undergoes reaction wit~ the gaseous re~gent.
For example, the fur~ace may comprise three successive
segments, each ha~in~ first a~d second e}ectrodes, in which
the distance between the electrodes in successi~e segments
is 650-7~0mm, aso-gsomm and 1050-1250mm respectively, the
inner diamete~ of the furnace chamber being 500mm.
w09~l2~948
PC'r/GB95100~40
- ` - 21 ~5~37
~he inner su_faCe c~ the '~ g of the furnace is
preferably smo~th and both non-porous and electrical~y
lns~lating, so ~hat impre~nation thereof or coating thereof
by solid reagent ~nd particularly by any particulate solid
S conductor ~dded eo said reagent is discouraged. As
mentioned abo~e, a-alumina ~uch ns castable a-alumina, has
been found to be suitable for this purpose.
Preferably the furnace hag its interior closed of~ from the
atmo~pher~ and/or is operable at a~o~e a~ospheric pre~sure
to permit maintenance of a ccntrolled atmosphere thesein.
- The furnace axis may be tilted at an angle cf a~out 1-3,
preferab~y about 2 to the horizontal, the downstream end
being the lower end, to assist in passage of solid material
through the o~her.
The furnace may be provided w~th longic~t~inAlly spaced
annular isolating pastitions fos e~ectrically isolating
sol~d reagent in one segment fro~ that in an adiacent
s~ c.-t. The partitions will be of a refractory a~d
preferably insulating material. The furnace may, further,
be pro~ide~ with lifting mem~ers or bars which, as the
furnace rotates, cause 50l? d material to be li~ted and
transferred pr2gre9sively from one segment to an adjacent
~egment.
The ~urnace may include feed a~d extraction means ~or
2S feeding and extracting soli~ reagent and wa~te product
therefrom, as well a~ gas feed means and gas ext_action
means for feeding gas into and withdrawins ? t from the
chamber respecti~ely.
T~e gas ~eed means may include a plurality of gas per~eable
distributors in the furnace shell, the distri~utors bein~
circumferentially spaced from one another; gas delivery
means for deliverin~ ga5 to the outsides of the
os~n3s48 2 ~ 7 PCTIGB9~/0~0
14 -_
distributors, with the gas passin5 t~-oush the dist-iburors
~nto the furnace chamber; and gas flow control means
operable, during rotation of the furnace, to deliver gas
only to those distributors which are at or near eheir
S lowermost position so that, in use, inflowing gas passes
large}y thrcu5h a charge of solid particulate reagent in
the furnace cham~er.
The in~ention will now be described, by way of example,
with reference to the following Exampies and with reference
to the accompanyi~g diagrammatic drawings, in which:
FIGURE 1 show~ a schematic sectional side elevat~on of
a furnace i~ a~cordance with a f lr5t e~bo~; ment of the
present in~ention; --
FIGURE 2 shows a view, similar to Figure ~, of a
furnace accordi~g to a second em~odiment of the invention;FI~URE 3 shows a plot of power input agai~st time for
activated car~on used in a batch-type method according to
the present ~n~ention carried out in the fur~ace of Figure
l; .
2~ FIG~RE ~ show~ a plot of re~istance-~gain~t time for
the activated carbon whose power input is plotted in Figure
3;
FIGURE S shows a ploe of resistance agains~
temperature for the acti~ated carbon whose power input is
plotted in Fisure 3;
FIG~E 6 Qhows a plot, similar to Figure 3, for a
mixture of ilmenlte and duf f coal;
FIGUR~ 7 shows a plot similar ~o Figure 4 fo~ the
mixture of ~igure 6;
F~GC2E 8 shows a p}ot similar to Fig~re S for the
mix~ure of Figure 6;
FIGURE 9 shows a pl~t similar to Figure 4 for a
mixture of titanirerous slag and duff coal;
FIG~RE 10 shows a p~ot similar eo Figure S for the
3s mixture of Figure 9;
wo 95~g48 ~ i 8 4 5 ~ 7 PCI'IGB95100~40
r IGUR~ ;1 shows a piot simi~ar ~o Figure 3 for the
m~xture of Figure 9;
FIGUR~ 12 shows a ~iew, simllar to Figures 1 and 2, of
a ~urnace according to a third embodiment of the in~ention;
FI~U~E 13 shows a view, similar to Figures 1 and 2 of
furnace in accordance with a fourth e~o~ nt of the
in~ention;
FIGURE 14 show9 a view, simil~r to Figures 1 and 2, of
a furnace in accordance with a f~fth em~odiment of the
i~ention;
FIGURE lS shows a view, similar to F~gures 1 and 2, of
a furnace in accordance with a six~h embo~im~nt of the
in~ention;
FTGURE 16 ~hows a view, similar to Figures 1 ant 2, of
a furnace in accordance with a sevcnth embodiment of the
inve~tion , with some detail omitted for clarity;
FIGURE 17 shows a seCtiohal ~iew through A-A in Figure
16, with some detail omitted for clarity;
FIG~R~ la shows a sectional view through B-~ in Figure
16, wlth some ~etail omitted for clarity;
FIGURE 1~ ~howq a sectional ~icw through C-C ~n Figure
16, with some detail omitted for clarity; and
FIG~RE 20 shows, schematically, a representation of a
power contrcl syseem for controlling power to two
successi~e portions of a furnace according to the
invention.
ln the drawings, the same or similar parts are indicated
w-th the same reference numerals.
Referring to Figure 1 a ro~ary batch-operation furnace in
accordance wit~ a fi~st embo~im~nt of the present
inventton, and suitable for pilo~ scale batch operation, is
designated ~y reference numeral 10. The ~urnace has a
ho~low-cylindrical outer mild steel wall 12, close~ off ~y
annular mild steel end plates 14 and 16 at opposite ends
thereof. The central opening of the end plate 14 forms an
woss/23948
~ 1 8 ~ PCTI~B9S~OO~O
16
inlet eo the f~rnace ehambe- or interlor and opens into
g2s iniet passage 1~ wlth an extenslon 20- The end plate
i6 h~s an annular hinged door 22 provided with a spigot 23
throu~h which the furnace is loaded, discharged and sampled
and which, thus, ~rms a samplin~ port into the interior of
the furnace and a gas outlet therefor.
The wa~l 12 and end platc~ ~4, 16 are lined on their ~nner
surfaces ~y a lining 24 of electrically insulating calcium
silicate kricks, whlch lining 24 is, in turn, inter~zlly
lined ~y a lining 26 of electrically insulating refractory
-br~ks, a layer of ceramic fibre paper at 27 being pro~ide~
~ between the lini~gs 12 and 24. The l1ning 26 hag a
cylindrical part on which is pro~ided a cylindrical
internal lining 28, also of electrically insulating
refractory brlcks, at opposite ends of which are mou~ted,
on the lining 26, a pair of annular ~Yi~lly or
ionsit~ n~lly spaced c~rcumferentially exten~ing graphite
electrodes ~0 and 32, ~e a first electrode 30 and a second
electrode 32. The i~ner p~riphe~ies of the electrodes 30,
32 stand radially inwardly proud of the inner ~urface of
the lining 28. Two castable ~-alumina retorts, each 500mm
in lensth and shown, schematically at 34, define a further
non-porous inner llning which abuts the linin~ 28. The
retorts 34 are recessed by about 10-lSmm from ~he in~er
per~pheri-s of the elec~rodes 30, 32. The ioin between the
retorts 34 is sealed wi~h refractory concrete (not shown~.
The electrodes 30, 32 are spaced ~par~ ~y lOOOmm and are
connectet to a single-phase AC power supply.
The extension 2C t S pro~ided, on its outer surfa~e, with a
plurality of siip rings 36, some of which are connected to
~arious thermocouples (not shown) in the furnace by
electrical leads (not shown~, and two of which are
connected respectiYely to the electrodes 30, 32 by
electrical leads (also not shown).
woss/239~ 8 4 ~ 8 7 pcTtGss
' 17
Operation of the furnace o~ Figure 1 will now ~e described
by way of illustrative non-lim~t~n~ example, with reference
to the following Examples.
~XZ~h~PT.~ 1
A 20 kg batch of solid material was prepared by mixsng
together a solid part~culate ilmenite reagent with ~
part~culate solid electrical conductor in the form of duff
coal, there bei~g a58 g of duff coalJkg reagent, amounting
to about double the amount of duff coal re~uired to provide
sufficient carbon to reduce all the tttanium and iron (as
- the oxides~ in the ilmenite. ~he i~menite had the
- compositson given in the Table hereunder. By 'particulate
ilmenite' is meant ilmenite as mined and milled, ant having
irregular shaped partlcles of di~ferent 3izes.
The furnace lo was preheated ~y charg$ng it with 4 kg of
granular act~vated carbon and by app}ying a potentlal of
380 V between the electrodes 30 and 32. The carbon was
heated under nitrogen and reached 1~00C in 12 hours,
heat~ng being monitored to keep it at this temperature by
means o~ a reduced potential for a further 5 hours to heat
up the furnace lin~ng to cause it to reach a steady state
as re~asds temperature. The ~sln was rotated at 1 rpm.
Figure 3 is a plot of power input against time for the
furnace preheating, showing that power supply decreased
after 1 hour. ~igures 4 and 5 respectively show the change
of electrical resistance of the acti~ated car~on against
time and against temperature of said carbon. In this
regard it should be ~oted that, naturally, if desiret,
electrical preheating by mea~s of heating e~ementq embedded
in the furnace ~ining or any other s~itable pretreating can
be used instead.
After the kiln was preheated rotation wa~ stopped and the
carbon was extracted under nitrogen, the 20 kg charge of
ilmenite/duff coal then being l~aded into the furnace under
W0 95n3948
2 1 ~ 4 5 ~, 7 PCI/GB9SiW4~0
18
nitrogen. Roeation o~ the furnace was restarted
immediate}y after this loading and the temperature of the
~harge rose rapidly to a~out ~50C. A potential of 220V
was app~ied as ~oon as rotation restarted, to heat the
charge to 1300C, with the potential being reduced whenever
power input exceeded 22 kW. The operating temperature of
1300C was reached after 1 hour and was maintained for a
further 3 hour~ by select~vely altering the ~oltage of the
potential applied to the electrode~ 30, 32 to appropriate
Yalues to keep as clo9e to 1300~C as po9~ible. The
interior of the furnace was ed with nitrogen 50 th~t the
charge was maintaincd under ~itrogen atmosphere, and so
that the titanium sn the charge became fully nitr~ded.
M~ m power input was nct allowed to exceed ~2 kW and
temperature was not aliowed to exceed 1300C to guard
against thermal shock to the furnace lining a~d three input
potentials were used a~ter 1300C had been reached, namely
60 V, 110 ~ and 220 V. Power input for heatins the charge
is plotted i~ Figure 6 a5ain~t time; re~ista~ce of the
rharge i- plotted in Figure 7 against eime; ~d re~istance
of the charge is plotted in Figure 5 agai~t temperature of
the charge.
.
Riln r~tatlon was kept at 1 rpm and the nitrogen feed rate
was 2,19 ~gJhr, nitrogen eed being continuous, the
nitrogen feed amounting to 3 times the stoich~ometric
requirement to nitride the titanium in the charse. After 3
ho~rs of nitrogen feed the power supply was cut off and the
fur~ace was allowed to cool naturally with constant
rotati~n at 1 rpm w$th the charge under nitrogen. The
charge was removed when the temperature ~o~c~ to under
400~C. In the nitrided charge ~35~ of the titanium was
found to ha~e been converted to non-stoichiometric titanium
nitride.
wo 95/239-18
2 ~ ~ 4 5 ~ 7 PCr/GBgS~O~
lg
Similar results were o~tained whe~ Example 1 was repeated
using the charge mixtur~ in the form of ~i) pellets of a
10mm ~iame~er, co~taining 2~ ~y mass bentonite binder,
although lt was found that a substantial proportion of the
pellets had disin~egrated by the end of the test;
br~quettes having a size of 45mm x 20mm x 20mm; and (iiil
larger and smaller particles than the pellet~ and
briquettes.
~y~yPr.~ 2
Example 1 was repeated using an 20 kg charge w~ich was a
mixture of titan~fercus slag a~tai~ed from ~ish~eld Steel
and Vanadium COL~ tiOn ~Proprietary~ Limited mixed with
tuff coal i~ a proportion Of 350 g ~oal/kg slag. This was
double the stoichiometric amount of coal rec~uired
completely to reduce the titanium ~as the oxide) i~ the
slag. The charge wa~ pelleelzed using 2~ by mass bentonite
binder, into 10mm diameter pe~lets.
r
The compos~tion of this slag, ~nd that of the ilme~ite u-~ed
~or Example 1, are set forth ~n the following Table:
TA~E
Chem~cal Comro3itlons of Titaniferous Sl~g and
Ilmenite
Constituent Titaniferous ~lme~ite
Slag (mass ~)
~mass % )
T~ 30.5 48.8
2~ SlO. 20.7~ 1.3
MqO 14.10 1.0
CaO 16.8 0.04
Al.l 13.65 0.7
Cr.Ol 0.1g co.o~
FeO ~.15 47.0
v2~ 1.05 0.12
MnO ~.6g 0.82
~1 ~4~37
woss/23948 PCT/GBs~/o~o
The TiO~ in ~he glag was prese~t pr~n~ipally as fassaite
[Ca~T~,Mg,Al)tSi,A~)2O6J~ and perc~skite [CaT~03~, and to a
lesser exee~t as pseudobrookite [Fe2O3TiO2 and ulvospi~el
~Fe2TiO4] .
The charge was heated to 1300C as soon as possible, power
inpu~ being restricted to 20 kW to resist si~tering the
charge, and u~ing a potential of 380 V. The operatins
te~perature of 1300C was reached after ~,~ hours an~ was
maintained thereafter ~or 3 hours by electrically applying
~oten~ials o~ 230 V or 110 V, as re~ui~ed. The nitrogen
~ flow rate du_ing the 3 hour reaction period was 0,4 kg/hr,
wh~ch amounted to 4 times the stoichiometric re~uirement to
nitr~de the titanium in the charge.
A co~version of ~92~ of the tita~ium in the charge to
no~-stoichiometric titan~um nitride was achieved. Figure 9
~hows a plot o~ resistance of the charge against time;
F~gure 10 shows a plot of resistance of the~ charge against
the temperature thereof; ~d Figure 11 showæ power supply
to the fur~ace plotted aga~nst time.
~MPLE 3
A meta~ oxide-carbon mixture was prepzred by mixing l5,6 kg
~23 with 4.2 kg pitch coke (consisting o~ 82,5~ fixed
carbon and lS,~% volatiles) ~nd 0,4 ~g stabilised polymer
emulsion plus starch ~inder.
The mixture was formed into pellets, ha~ing a diamerer of
approximately 10mm, on a disk pelletiser and cured. ~he
expected chemical reac~ion was
V23 ~ 3C + ~2 = 2vN ~ 3Co.
The furnaoe 10 was pre-heated and loaded w~th the cured
pellets as i~ Example 1. The ~harge was hea~ed to 1350C
in S hour~ and maintained at 1350c for 2 hours. Power
W09~/23948 PCTtGB9~loO~n
21
~,,
input was restrict~d ;o ~2 ~W to pre~ent 'ocalised
sintering of the charge- The potential difference settingS
applied across the electrodes 30, 32, in order to ensure
sufficient power input, were limited to 60, ~1~, 220 and
; 380 ~. The kiln was rotated at 1 rpm during t~e re~ction,
and ~ nitrosen flow rate of 2,19 kg~h was maintained during
the procedure.
After reactio~ had been compl~ted, the furn~ce was al~owed
to cocl under nitrogen- The char~e was unloaded at am~ient
temperature to pre~ent ~e-oxidation of the vanadium
- c~rb~nitride produ~t. The product, whic~ was hard and
~ dense and h~d a volume about one half of the orisinal
vo~ume, co~tained co~tains 77, 2~ ~anadium, 2, 7~ carbon,
17,6~ ni~rogen and 2,6~ oxygen.
1 5 13XAMpt .~ 4
A metal oxide-car~on mixture was prepared by mixing 9,6 kg
SiO2 with 10,4 kg of carbon (precipitated from a coal
~olutio~ by e~aporati~g the sol~e~t).
Bri~ueetes ha~lng a size of 40mm x 23mm x 12mm were
prepared from the ~ix~ure by compressing at lS00 psi a~d
curing at 230C. The expected reaction is given by the
equation
SiO2 + 3C = SiC + 2CO
The fu~nace 10 was pre-heated and loaded with the ~ure~
briquettes as fcr ~xample i. The charge was hea~ed to
lS~O~C o~er a period of 8 hours and maintained at 1500C
for 9 hours. Power input was restricted to 25 kW to
prevent localised sinter~ng of the charge. The potaneial
dif_erence se~tings applied over the electrodes 30, 32, in
order tO ensure su~ficient power i~pUt, were limited to 60,
110, 220 a~d 380 volts. The kiln was rotated at 1 rpm
du~ing the reaction, whi~e an argon flow-raee of 10 ~/min
was maintained.
2F (~4L~7
WOg~l23948 PCT~GB95100440
22 -~
After the reaction, the furnace was allowed to cool to
600C unde_ argon. The charge was unloaded and cured at
600~C for lC hours to remove any excess carbon. After
curl~g the p~oduct was found to consist of lOO~ SiC.
EXAMPLE 5
~luted carbon from a gold extraction process, and having a
moi~ture conter,t of 42~, was loaded into the preheated
furnace (800C) u~der nitrogen. Rotation was started
immediately a~ter loading, and ~ol~age was applied across
the bed o~ wet carbon- Typical voltages throughout the
regeneration p.rocess ranged from 3B0~-60V as the
resisti~ity of the carbon changed. Steam was emitted in
the first fi~ e m~nutes of the process ~efore regeneration
as such commenced. The residence time of the carbon in the
furnace was 20 minutes ~t a temperature of 720OC. This
facilitated the dr.ving off of the organics from the porous
car~on thereby reactivatln5 it and preparing the carbon for
deli~ery to the adsorption 9ection of the gcld extraction
plant.
The organics thae are dri~en off the carbon during
regeneration come from rea~ents added upstream of the
elution process. These oxga~ics wastefully occupy sites on
the car~on that ext~acred gold should occupy duri~g
adsorption, rendering the adsorption process i~ef~icient.
When the residence time o~ 20 minutes has been co~pleted
the car~on w~s discharged ir.to a quench tank of water where
lt was cooled, and then pumped ~ack to the adsorption
sectlon. Quenching the carbon inhi~itc oxidizins thereof
a~d pro~ides rapid cooling.
~eferring to Figure 2, a furnace in accordance with a
second em~odiment of the in~entior. is also generally
designated 10. The fur~ce 10 of Figure 2 is, in co~.rast
2i~4j&7
wo9sl23s48 PCT/CB95/0~40
~, 23
to that of Figure ', ineended for continuous operation and
is also opera~le by means of an AC power supply.
Accordingly, the en~ of the feed passage lB remote from the
wall 12 is fed by a soiids feed chute 38 which i9 supplied
by a worm feeder 40 fo~ extracting feed pellets from a
pellet ~upply hopper 42. The hopper 42 is in ~urn fed from
a pe}let drying hopper 44 by a rotary star feeder 46.
The central opening of the end p7ate 16 forms an outlet for
the furnace lO and is pro~ided with ~ hood 43 sealed to an
ou~let passage 50 protruding from said central opening by
a circumferenti~lly extending bear~ng seal 52. The hood 48
has an off-gas outlet du~ ~4 extending to a com~ustion
chamber (descri~ed hereunder~. The hood 48 also has a
sigh~ glass 56, a solid9 discharge de~ice 58 and an
l~ adjustable chute 60. The chute 60, when the furnace is in
steady-state operation, allows the flow issuing from the
furnace via solids d~scharge device 5B temporarily to be
~ncreased, when desired.
The duct 54 extends to a combustion ch~or 62 enclosing
the upstream end of the passage 18, which cha~ber is sealed
to said passage lB by a~nular bearing se~ls 64. The
chamber 62 has a pi}ot burner 56 and an outlet-p~o~ided
with an extraction fan 5~ and a flow control slide valYe
7~. A gas duct 72 leads from the fan 68 to the drying
hopper 44.
In Figure 2, the slip rings 36 o~ Figure 1 are omitted and
repiaced by elect-ode connection boxes 74. The h~nged door
22 and spigot 23 of F~ gure ' are also omit~ed from Figure
2.
3C A particu~ar fea~ure of the fur~a~e lO of Figure 2 is that
i~ compr~ses two axially aligned portions or segments,
namely an upstrea~ portion 76 Oc re7atively reduced
2~ ~sg7
f ~ :
woss/23s48 PCTtGBg~100440
24
-
diameter and a downst-eam portion 78 of relatively
increased diameter. Each portion 76, 78 has a pair of
~raphite elec~~odes 3~, 3~ Ypaced apart by S~Omm, and each
portion 76, 78 is o~ broad~y simila~ construction eo the
S furnace lO of ~igure l.
In eaeh portion 76, 78, the lnner surface of the lining 26,
upstream of the first electrote 30 and downstream of the
second eleetrode 32, is provided with a plurality of
axially extending c~r~um~e~entially spaced extractor ~ars
or ri~s ~0, standing radially inwardly proud o~ the inner
-surface of the linir,g 26, for keeping solids ~n the fusnace
~ l~ in motlcn as it rotates and for assisting in mo~ing the
solids axially throug~ the furnace.
The connection boxes 74 are arranged in f our rings arou~d
i5 the furnace shell lZ, each ring comprising four equally
circumfe~entially 6p~ced boxes 14 mounted on the shell 12.
Each box is ro~ected ~y an electrically insulated
elect~ical lcad ~2 leading to the associated electrode 30
or 32 as the case may be. The boxes serve to connect the
electrodes 30, 32 by means of slip rings ~ro~ shown) to an
AC power supply (not shown~.
An eiec~rical preheater 84 is shown enclosing the
~ownstream portion of the passage 18.
A feature of the ~urnace lO of Figure 2 is that the
~ncrease ir. diamerer from the portion 76 to the portion 76,
which is in the form of a step in diameter at 86, promotes
electrical ~solation of the electrode 32 o~ the portion 76
from the electro~e 30 of the portion 78, by causing a brea~
or di~conti~uity, in use, between solids in the por~ion 76
and solids i~ the portion ~8, so that there are separate
beds of so~ids ir. the portions 76, ~8, which beds do not
merge into each other. ~n other words, ~here is a ~mmj
effec~ in each portion or ~egment, so that each port~on ca~
21 845~7
woss/23s~8
Pc~/Gs9~/0~40
be operated and controlled, eg as regards applied ~oltagee
and residence times, substantially independently of each
other.
The operation of the furnace iO of Figure 2 will be
essentially similar to that of the ~urnace of Figure l, but
on a continuous rather than a batch basis. Thus,
optionally, after preheating the furnace lO using granular
acti~ated car~on fed throu5h the furnace under nitroger.
while applying a suitable ~ol~age untll the interior of the
furnace is at a steady state temperature of 1300C, feed of
-a pelleted rea~tion mixture, similar to those of Examples
~ l or 2, can be started.
Pellets are fed from hopper 44 by feeder 46 to hopper 42
and thence they are fed by feeder 40 ~ia chute 38 into
passage l~. In passage 13 they are heated by the
elec~rical heater ~4. As the pellets pass through the
rotati~g p~rt~ons 76 ~d 78 they are heated by electrical
currents flowing throu~h the pellets between the elec~rodes
30, 32 of each portion 76, 78. Suitable potentials (eg
~D Examples 1 and 2) are applied to the electrodes 30, 32 to
maintain pellet temperature at l300C and nitrogen at a
su~eable stoichiome_ric rate (see Examples 1 and 2~ is fed
into the furnace along duct 20. The pellet ~eed rate is
selected su~h that the Fellets have a residence time of 3
hours in the furnace at l3000r
Off-gas from the pellets in the furnace is ducted along
duct s4 by f an 68 to combustion chamber 62 where it ~s
ignited by pi~ot burner 66. Heat frcm the burning off-gas
asslsts ~ n prehea~ing ;he pellets before they enter ehe
furnace lO, and combustion ga~ from the chamber 62 is fed
along duct 72 by fan 68 to hopper 44 where it dries the
pellets.
2 i ~8$5~87
~r
wo gSI23948
PCT/GB9~/OO~n
26
Product is extracted from hood 48 via dischar~e device 58
and can be sampled by means of the adiustable samp7ing
chute 60. The reaction in the furnace can be monitored
vicuaily by means of the sight glass 56, and the
; temperature ~t ~arious places in the furnace ca~ ~e
monitored by means of suitably located thermocouples ~not
shown). The connection boxes 74 are used to feed current
via the leads e2 to the electrodes 30, 32 as required, and
are u~ed to receive inputs from the thermocoupies and to
tr~nsmit them to external monitoring devi~es (not shown).
A parti~ular feature of the ~nvention, as demonstrated with
reference to the Figures, is that constant motion of the
solids ~harge in the furnace continually disrupts the paths
of electrical discharses between the electrodes 30 and 32,
new discharge paths c~ntinually being established. Local
o~erheating of the charge ~s a~oided ~as could take place
in a fixed bed) ~nd miYi~ of the charge promotes an e~e~
te~perature thereof.
~eferring now to Figure 12, reference numeral 100 generally
indic~tes a third em~odiment of a rotary continuous
operation furnace in accorda~ce with the present in~ention.
The furnace lOo generally resembles the furnace lO of
Figure 2.
The furnace 100 differs from the furnaoe lO of Figure 2 in
that it lacks the solids feed chute 3~ and, i~stead, the
worm feeder 40 feeds feed material direct~y into the
furnace. Further, ins~ead of the off-gas outlet duct 54
and the combustion chamber 6~, the hood 48 of the furnace
100 is provided with a burn-off burner 102. In this
embodiment of the invent_on the solids discharge device 5~
feeds direc~ly into a sealed storage hopper 104 wh-ch ~s
provided with a wor~ extractor 106 for discharging solid
material. If desired, the storage hopper 104 can be
provided with a sui~ahle gas inlet (not shown) , eg i~ it
. 2 1 ~537
WO9S/23948 PCT/G895/oo~o
27
-
is required to conrrol the atmosphere in t~e hopper. The
entire assembly from the wor~ feeder 40 to the worm
extractor 106 is more or less gas tight.
The furnace lO0 differs, further, from the fu~nace lO of
~igure 2 ~ n that it comprises three axially aligned
portions or segments namely a first se~ment 110, a second
segment 112 and a third segment 114, segment 110 being
upstream of segment 112, and segment 112 being up~tream of
segment 114. The se~ments 110, 112 and 114 all ha~e an
inter~al diameter of 500mm but d~ffer in length. In
additio~, the distance ~etween the electrodes 30, 32 of ehe
first segment is 700mm, that between the electrodes 30, 32
of the second se~m-nt is 910mm, and that between the
electrodes 30, 32 of the third segment is 1120mm.
The first, second and third segments llO, 112, 114 are
separated from one another by annular partit~ons, or
orifice rings, of electrically insulatin~ refractory ~ricks
116. The furnace 100 is further pro~ided with lifti~g bars
~not shown) ad~acent the or~fice rings 116 for transferring
solid material l;B from one segment to the next as the
fur~ace 100 rotates, through the central opening of the
assoclated par~ition 11~. The entire furnace is inclined
a~ an angle of 2 to the horizontal to fac~litate the
passage of the solid materlal 118 through the furnace lOo,
whose downstream end is its lower end. The orifice rings
116 ser~e electrically to isolate the solid material llB in
one adjacer~t segment from solid material lla in the other
ad~acent segment. The electrodes 30, 32 of the separate
~egments llO, 112, 114 are connected via the connec~ior.
boxes 74 by electrical connectors (not shown~ to a single
rhree-pha9e source of electrical power, one phase beins
connected to eac~ of the segme~ts.
The construction of the furnace 100 ta~es advanta~e Oc the
fact that the resisti~iry o. the solid material 11~
21 84~
.~
wo~/23948
PCl'JGB95tO044~
2~
prepared according tO the method of Example 1 descri~ed
above, reduces as th^ material is heated and as reaceion of
the c~tanium and iron in the material proceeds so that
although the distan~e between the electro~es 30, 32 of the
third segment 114 is greater than that between the
electrodes 30, 32 of the second segment 112, the same
~oltage ca~ be usea to achieve the same current flow in
both segments. The same holds for the segments 112 and
110 .
~0 Referring to Figure 13, reference numera} 200 generally
-indicates a iourth embodiment of a rotary
~ continuous-operation furnace in accordance with the present
in~ention. The furnace 200 generally resembles the furnace
10 of Figure 2.
la The fur~ace 200 di~fers from the furnace 10 of Figure 2 in
tha~ che combustion chamber 6~ of the furnace 10 is a~sen~
in the furnac~ 200, the off-~as outlet duct ~4 se~ing
simply ~o ~ent the of~-gasses. In ~his embo~ nt of the
invention, the electrical pre-heater 84 alone serves to
preheat the feed pel~ets and in}et gas. The furnace 200,
~urther, includes thermocouples 202, 204 projecting,
respecti~ely, ~nto the interior of the portions 76,-7~. In
this e~bodiment of the inYention, there are three hoppers
44 (of which only one is shown in the drawing~ each of
5 - 8 ~on capacity for holding pellets or particulate
materials. The hopper 42 is a 2 ton supp~y hopper. ~he
o~erall length of the portio~s 76, 7~ ls 2/2m.
Referring now tc F~re 14, reference numeral 300 generally
indicates a fifth em~odiment of a rotary continuous
operation furna~e in accor~ance with the in~entior,. T~e
furnace 300 general}y resembles the furnace lo of Figure 2.
21 845~
W095l23948
pcTlGBs5loo44
29
The furnace 300 dir~rs frcm the furnace lQ of Fisure 2
only in that the port~cns or segments 76, 78 are of the
same diameter so ~ha. the step 86 in diameter ~s absent.
The capacity of the hoppers 42,44 and the overall lengths
of the portions 76, 78 are substantially the same as those
of t~e furnace 200 of Figure 13.
Referring to Figure 1~, reference numeral 400 generally
indicates a sixth embodiment o~ a furnace in accordance
with the invention. Again, the furnace 400 rcsembles the
-furnace 10 of Figure 2.
The furnace 400 d~ffers from the furnace 10 of Figure 2 in
th~t it includes a further portion 402, in addition to the
portions 76, 78. The portion 402 has a larger diameter
than the portion 78 with a further step in diame~er at 86
~etween the portions 7B, 4~2. This step also ser~es to
promote electrical isolation of the electrode 32 of the
portion 78 from the electrode 30 of the pcrtion 402, as
described abo~e, by a ~reak in continuity betwcen solids i~
the portion 1~ and solids in the portion 402.
.
Referring to Figu~es 16 - lg, reference numeral sOC
genera~ly indicates a seventh embo~i~ent of a continuous
o?erat~on rotary furnace in accordance with the present
in~ention.
The furnace 500 also has a hollow cylindrical outer mild
2S steel wall 12, whic~. is ii~ed on its inner surface with z
linir~g of insulating tiles ~52 which lining is, in turn,
interna~ly lined by a layer of refractory concrete 504.
The furnace 500 is DC operable.
Eighty four generally elongate porous or permeable plugs or
3C distributors ~06 of porous refractor~ material, eg silicon
carbi~e, each ha~ing a generally square cross-section, and
arranged in seven groups of twelve distributors 506 each,
project inwardly form the wall 12. The distributors of
each group are arranged in an annular fashion and are
circumferentially spaced from each other as can be seen, in
particular, in Figure 18, and are aligned axially. The
groups are axially spaced from each other as can be seen,
in particular, in Figure 16. Each distributor 506 is
embedded in linings 502, 504 with an inwardly directed
face thereof flush with the inner surface of the refractory
concrete lining 504.
Each distributor 506 is connected to a nitrogen inlet
manifold 508, which is mounted to the furnace wall 12 and
thus with the rotation of the furnace. Each manifold 508
has nitrogen inlet conduits 510 so that the axially aligned
distributors 506 of each group are served by a single or
common manifold 508. The manifolds 508 are in turn
connected to a ring manifold 509 mounted to the wall 12.
The ring manifold 509 slidingly abuts a stationary annular
manifold component 511 so that the ring manifold 509 moves
relative to the manifold component 511 as the wall 12
rotates. A conduit 513, connected to a nitrogen source
(not shown) leads through the manifold component 511 at a
low level. Thus, as one of the manifolds 508 comes into
register with the conduit 513, nitrogen thus flows along
that manifold, thereby to inject nitrogen sequentially only
into those distributors 506 which are at their lowermost
position during rotation of the furnace, so that the
nitrogen passes into solid reagent material located at the
bottom of the furnace chamber.
The furnace 500 includes riding rings 512. Unlike the
furnaces 10, 100, 200, 300 and 400, the furnace 500 has
twelve non-annular or elongate electrodes, arranged in
three axially spaced groups 515, 517, 519 each comprising
four electrodes. The electrodes of each group project
radially inwardly and are spaced circumferentially from one
w~ y~ 4 5 ~ 7 ~ "~
31
~otr.er at angies cf gO~. Each eiecc~ode has a generally
squ~re c_oss-section.
Figure 19 shows the four elec~rodes 514, 516, 518, 520 of
the group 5i7 of electrodes. The sroup 515 cf electrodes,
of which only two S~1, 522 can ~e seer. in Figure 16, is
positioned ~ear to the inlet end of the furnace S00 and the
group 519 cf which also only two electroàes 526, 528 can be
seen in Figure 16, is positioned near to the outlet end of
the furnace. The third group 517 of electrodes 514, 516,
518, 520 (Figure l9~ ~ 5 posirioned near to the middle of
the furnace S00. The electrode~ in each group are aligned
circumferentially while the e}ectrodes of the three groups
are aligned in ~he longitudinal dlrection.
Each electrode has an i~er e~d which stands ~nwardly
lS radi~lly proud of the refractory c~nc~ete lining, as can be
seen in Figures 16 and 18, ~nd each is mounted in a
mo~nting bracket 529
Each electrode comprises tWO parts engaged with one another
spigot and socket fashion. 3y way of illustration, the
~0 electrode 518 con~ists of an outer part 518.1 and an inner
part 51~.2, the outer part 518.1 haYing a spigot portion
525 which is enga5ed, ~y a friction ~it, with a socker
por~ion SZ7 in the inner part 51~.2. Thus, ~s the inner
part 518.2 is abraded away during use, the outer part 519.1
is pushed progressive7y i~wardly until ~t eYentually
replaces the inne_ part 518.2 and a further outer part
51~.1 is inserted behind i.. In this way the electrodes of
the furnace 500 are continuous}y replaced.
As msntioned hereir~efore, the furnace 500 is powered ~y a
DC electrical supply. Thus, the group 517 o electrodes is
maintai~ed at a negati~e polarity, while the ~roups 515,
51~ cf eiectrodes are maintained at positi~e polarity so
that ourre~t flow is towards the ceneral group 517. The
~ ~,
wossl239~8 32 PCTIGss5/~o
pocential difference ~etween the gro~p 517 ~nd the groups
515, 519 wil' ~epend on the material with which the 'urnace
500 has been chargec and the process taking place and, _n
the case of nitriding ilmenlte in order to recover titanium
will typically ~e 350-~oO vol~s.
The f~rnace 5~0, furthert includes a feed chuee 522 which
is supplied by a worm feeder, or feed scroll, 40 for
extracting pel}ets frcm a pellet supply hopper 44. A lower
porticn 524 o~ the hopper 44 which is circular cylindr~cal
~0 ~n shape is surrounde~ by a cylin~rical shell 528 of
- rèfractory concrete in a mi~d steel casins 529. The shell
528 has walls 531 and upper and lower inwardly directed
annular portions S33, 535 between which extend eight
cylindrical silicon car~ide electrodes 530 in a
circumferentially spaced symmetrical arra~seme~t. The
shell S28 and electrodes 530 act as a shaft-type pre-heater
for ~he ~ater~al in the lower portlon 524 of the hopper 44,
and, in use, 9er~es to pre-heat the materi~l passing
through t~e lower port~on 524 to a temperature of about
800C. The off-gasec from the furnace can, opt~onally, ~e
dire~ted to atmosphere in a counter current direction to
the material ~n the feed scroll 40, vla the walls of the
feed scroll 40 to ensure sustained pre-heating af-the
material fed into the furnace.
.
The furnace 500, further, has an outlet 530 leading to a
coo}er 532 provided with a worm screw 533, a water sprayer
535 and a sump 537. The worm scr~w 533 feeds ccoled
product into a discharge chute 534 pro~ided with a screw
conveyor 535 which L~",oves the material when i~ has reac~ed
a temperaeure below 200C.
Referri~g to Figure 20, a control sys~em 600 for the
~urnaces operates primar~ly on ~eedback 602 from the
chermocouple readings in the furnace, which prov~ted
measured values 604. Set values 606 for power and
w095/239~8 ~ 5 ~ ~ PCT/Gs
- 33
tempe~ature are supplied to a control lnstrument 608, whic:~
rece~es also the measured value 604. The contrcl
~nstr~ment 608 is connected to two thyristor dri~es 610 i~
ser~es, each drivins a separate f~rnace segmen~.
Naturally, a 5reater ~umber of the drlves will be pr~vided
if there are a greater num~e- of individually dr~ven
fur~ace segments. The thyristors are driven by independent
~ransformers 6~2, delta connected on the secondary side of
each transformer. The thyristors 610 are connected to the
furnaces by means of transformers 614.
-The furnaces 10, lOO, 200, ~Oo, 400 and 500 will naturally
include suitable dri~e means for dri~ing the furnace shells
to roeate. The dri~e mea~s may include an AC elect ic
motor and reduction-gear box with ~ariable speed dri~e,
togerher with, for smaller furnases, ~ chain and sprocker
mechanism for drlving the casing to rotate, or, for larger
f~rnaces, spur gears or driv~n support rollers for driving
the sheli or casi~g to rotate.
,~ ~
