An Improved Method of Calcining and Heating Argillaceous, Calcareous, and Metalliferous Substances, and any Mixture thereof, and in Apparatus therefor.
Year: 1887

page_text: Date of Application, 22nd Aug., 1887
Complete Specification Left, 22nd May, 1888
Complete Specification Accepted, 17th Aug., 1888
An Improved Method of Calcining and Heating Argillaceous,
Calcareous, and Metalliferous Substances, and any Mixture
thereof, and in Apparatus therefor.
BENJAMIN HOWARTH THWAITE of 37 Victoria Street Liverpool in the County of
Lancaster Civil Engineer do hereby declare the nature of this invention to be as
follows:-
My Invention is for improved method of calcining and heating argillaceous
calcareous and metalliferous substances and any mixture thereof.
My Invention when applied for the calcination of calcareous substances or for a
mixture of argillaceous and calcareous materials is as follows-
I utilise two distinct furnaces but so arranged with regard to each other, that the
operation can be carried on continuously, without the loss of their sensible heat—
acquired in the operation, and in such a way that a higher final temperature of
materials can be obtained in the revolving apparatus or furnace used.
I employ by preference gaseous or liquid fuel in the first furnace, or that in which
I drive off the uncombined water and any vapour volatilizable below 800° Fahr.
from the material to be treated. I use simple combustion without the aid of
recuperation because in the first furnace I do not require such a high temperature
of combustion, and as the materials are charged into the first furnace in a cold
condition, the temperature of the waste gases as they leave the first treatment furnace,
is very low, and only sufficient to enable a draught or aspiratory action to be
produced in the Chimney.
The material from the first furnace is transferred automatically by gravity or
mechanically, into the second furnace, or in such a way as to prevent the loss of its
sensible heat. In this second furnace the temperature of combustion is increased by
the use of air bighly heated by recuperation, accomplished by the restoration of the
sensible heat of the waste gases or the products of combustion-by this addition to
the thermal heat units set free by combustion, a temperature of a very highly
intense character is produced, sufficiently high indeed, to fuse the materials under
treatment.

page_text: When I employ rocking or revolving cylindrical furnaces of the type shewn in my
patent specification number 11402, 1885 and in my patent specification numbered 1972,
1886, inclined so that the materials gravitate from the higher to the lower end.
I construct the sides of the first treatment cylinder simply of wrought and cast iron.
I form longitudinal corrugations or special shaped internal shelve like or spiral
shaped projections of cast or wrought iron bolted or otherwise fixed to the shell.
I may in some instances line the first treating furnace with refractory material
but I usually prefer to confine myself to the use of a simple cast or wrought iron
lining.
In the second or finishing and high temperature furnace, I use a refractory basic
or siliceous lining of a character suitable for the material under treatment, for
instance, if the material to be treated is limestone I use a calcined magnesite or
limestone lining, the joints being made of anhydrous tar. I usually employ a perfectly
circular lining without shelves or other projections, the materials simply moving by
gravity along the lower invert or periphery of cylinder.
I prefer to make the second treating furnace of a greater diameter than the first
one so that the calcination and chemical action resulting therefrom is not affected
by too great a vibration of the particles or materials under treatment and, I may
make this cylinder cone shaped, the combustion end being the largest and in this one
the refractory linings are stepped down from the smallest internal diameter to the
largest at the combustion end.
In order to ensure a transmission or conveyance of the partially heated material as
it leaves the first treating furnace from the latter to the second or finishing furnace
I prefer to use a covered archimedean screw trough which works in conjunction and
may be actuated by a belt spur fixed on cylinder casing, and delivers the material into
an inclined chamber that deposits it into a sloping chamber from which it falls into
finishing cylinder.
I prefer in order to effect my invention more perfectly to employ or make use of
the system of recuperation shown in my patent specification number 1972, 1886, and
already referred to.
In this system the heated gases at the upper outlet end of furnace ascend into a
reversing valve from which they pass into one of two recuperator cylindrical vessels.
After the heated or waste gases of combustion have passed for a sufficient time to
ensure the transmission of their sensible heat to the checker brickwork, the current
or flow of the gases and air is reversed by the reversal of the valve, and the heated
gases are directed into the other vessel. The air to support combustion meanwhile
passing into the heated vessel or recuperator stove on its way to support combustion
of gaseous fuel in first treating furnace-and in connection with this system of
recuperation which I prefer to use to effect my invention I provide a duplicate
reversing valve for chimney and heated air, working simultaneously with the cold air
and gas valve and where a chimney draught is not available, I should force the air
through the air valve by means of a Roots blower or other description of fan.
In another modification of my invention as far as relates to the method of restoring
heat to the furnace or recuperator required to effect my invention I form a chamber
beneath the furnace which I divide into three horizontal divisions, these I construct
of rebated tiles-the joints I support by means of checker brick walls.
I lead the gaseous products of combustion into the upper one, of the three horizontal
chambers to the end thereof nearest the combustion chamber, and then by two ports
lead the products of combustion to the lowest of the three chambers.
The intermediate horizontal chamber I use for heating the air to support com-
bustion. The air enters through regulating valves and flows through the intermediate
recuperator chamber to the combustion chamber where it meets the gaseous fuel.
Instead of the archimedian screw arrangement for transferring the material from
one revolving furnace to the other I may connect them by a steep slope, midway
between the furnaces; I construct a midfeather wall with an opening beneath to allow
the movement of the material. I connect the Recuperator vessels connection, with
the first furnace, between the end thereof and the midfeather wall-so that the waste

page_text: gases are drawn from the first furnace, and do not interfere with the action of
combustion in the second furnace.
By the use of my Invention, I obtain two zones of initial temperature of combustion
by which calcination is rendered more effective-and in the instance of heating a
mixture of argillaceous and calcareous material such as Portland cement Slurry, the
moisture is driven off in the first treating cylinder, and becomes partially calcined
and highly heated prior to its transference to second or finishing treating furnace, so
that in the second furnace a far higher range of temperature can be obtained,
sufficient to effect the thorough calcination of the material, necessary to expel the
combined water and carbondioxide, which has not been so successfully done in
ordinary revolving furnaces up to the present time. The wear and tear of the
Duplex Revolving furnace arrangement is less, because the two cylindrical revolving
furnaces are kept at a more equable temperature from end to end.

page_text: Calcareous, and
ада
αναν π
Metalliferous Substances, and any Mixture
thereof, and in Apparatus therefor.
BENJAMIN HOWARTH THWAITE of 37 Victoria Street Liverpool in the County of
Lancaster Civil Engineer do hereby declare the nature of this invention and in
what manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
My Invention relates to improvements in Methods of calcining and heating
argillaceous calcareous and metalliferous substances and in any mixture thereof and
in apparatus therefor.
Before referring to the four sheets of drawings that accompany and are intended to
form part of this Specification I wish it to be distinctly understood that I do not wish
to be confined to the exact details shewn therein as these may be considerably modified
without departing from the nature of my said Invention.
Referring to Sheet 1 of drawings, Figure 1 is a longitudinal section through two
inclined revolving furnaces, working in combination, and shewing elevation of one
recuperator vessel.
Figure 2 is a general plan of this arrangement.
Referring to figures I and 2-The first treating revolving furnace a is inclined
from the horizontal. The Portland cement materials in the form, technically known as
slurry, compressed into balls or nodules of the size of a chestnut, in a machine suitable for
the purpose, is partially dried by the waste heat from first treating furnace, by being
placed over flues through which the said waste heat flows in its way to the chimney
the nodules or balls of slurry are fed into a pit c, having an inclined plane d down
which the raw materials gravitate into the interior of revolving furnace-the latter
being formed preferably of wrought iron-without any lining of refractory character,
except for the treatment of materials requiring higher ranges of temperature.
The material in gravitating through the furnace has its hygroscopic or sensible
moisture driven from it and is heated up to the temperature of from 300° to 700° Fahr.,
it finally falls into. a chamber, from which by means of an archimedian screw conveyor,
it is removed into the second or finishing furnace y, in which the materials are sub-
jected to a higher range of temperature, in the instance of cement slurry the
anhydrous or dried balls are in their slow and comparatively quiet gravitation through
the cylinders converted into hard clinker the materials being in their fusion chemically
rearranged, with the expulsion of the combined water and carbondioxide; the clinkered

page_text: cement falls into a depositing chamber hat the lower end of the second revolving
furnace, and by means of an inclined floor it is transferred or gravitates to a pit
from which it can be elevated to an upper floor or into a grinding mill.
The combustion arrangement is as follows, the gaseous fuel enters into the base of
combustion chamber i, the valve j is provided, for providing air for ignition-the air
to support combustion flows from an upper tube k, supplied from one or other of two
recuperator vessels l, combustion occurs, the flame flowing through an opening m into
furnace, through which it traverses, the products of combustion thereof flowing
through a valve n, through which they are directed through one of the recuperators 1,
for a period sufficiently to raise their contained and open brickwork, to a condition of
high temperature-the products of combustion are then by the valve being reversed,
directed into the other recuperator.
The flow of air to support combustion being simultaneously reversed and directed
through the highly heated brickwork-in traversing which, the air becomes elevated
to a high temperature, and adds pro-rata to the temperature resulting from com-
bustion, the air flows to support combustion by means of the pipes m. The flow
of the chimney gases is regulated simultaneously by the valvo n. The products
of combustion after flowing through recuperator vessels enter the combustion
chamber o-of first treating furnace where its, remaining heat is utilised in the
preliminary heating of the slurry balls-if the heat is not sufficiently adequate for
the purpose of first treating furnace, an additional supply of gaseous fuel may be
provided by means of the conduit p. The additional heat would be undoubtedly
necessary when the slurry drying flues b are considerably extensive in area or length.
Figures 3. 4. 5 and 6. sheet 2 of drawings shew another modification of my Invention
more particularly adapted for treating a mixture of calcareous and argillaceous
materials such as that constituting Portland cement slurry.
Figure 3 is a Longitudinal Section taken through second treating furnace, and an
elevation of first treating furnace.
Figure 4 is cross section through two of the second treating furnaces working in
combination with a centrally fixed first treating furnace.
Figure 5 is a half plan of arrangement shewing in sectional plan the recuperator
chamber of second treating furnace and a plan in section through the first treating
furnace.
Figure 6 shews a section of second treating furnace with recuperator chambers.
In this instance the nodules of cement Slurry or other material, are fed by a revolving
feed g, provided with a differential mechanical arrangement, by which they are
delivered into the interior of first treating furnace r, through which they gravitate and
fall into a depositing well at the lower end of furnace provided with shoots s, by
which the dried materials are fed into the hoppers & or other suitable receptacle of the
second treating furnaces u. In passing through the latter the materials become
vitrified or thoroughly calcined, and in the instance of Portland cement slurry nodules
or balls they are converted into clinker.
The combustion arrangements are as follows-
The gaseous fuel enters the second treating furnaces through the valve w, and
enters the combustion chamber when it is met by the air flowing from recuperators
at y, the combustion here ensues, the flame flowing upward and through the opening z-
into second treating furnace u, after flowing through the second furnace u it passes
down the port 2 into horizontal flue chambers z in recuperators, flowing through to the
front or initial combustion end of furnace and descending by ports 4 into a series of
lower flue chambers 5 escaping therefrom by means of the flue 6, from which they
flow to a central vertical conduit 7-by which the products of combustion are delivered
into a first treating furnace; when the sensible heat they possess is inadequate for
the purpose it is supplemented by an additional supply of gaseous fuel supplied by
conduits S.
-
The products of combustion after leaving the first treating furnace r may be led
into slurry drying flues.

page_text: Between the upper recuperator chambers 3 and the lower ones 5 there are the air
heating flue chambers g.
The air flowing through the latter abstracts a great part of the heat from the
products of combustion. The air enters the valves 10 and flows through to the
combustion chamber z.
Figures 7 and 8 on sheet 3 of drawings and figures 9 10 11 and 12 of sheet 4
of drawings show another modification of my Invention, in this arrangement the
first and second treating revolving furnaces, are placed side by side and inclined in
opposite directions, the furnaces may be placed on the same level or floor, the materials
being hoisted as they leave the first treating furnace into the second one-or they may
be placed at different levels as shown in other modifications, so that the materials may
gravitate from the first to the second furnace or furnaces.
In the arrangement shewn in figures 7 and 8, on sheet 3 of drawings, and figures 9
10 11 and 12 on sheet 4 of drawings, the first and second treating furnaces are placed,
side by side on the same level.
The products of combustion from second treating furnaces 11, are led into the first
treating furnace 12, the direction of flow of gases being controlled by the valve 13 of
flue or conduit 14, by which the gases flow from first to second furnaces-The
connecting flues 14 may be placed overhead as shewn in figure 9-or underground
as shewn in figures 7 and 8.
The form of the ring 15 forming the joint between the furnace cylinder and brick-
work chambers at each end is such, as to allow for the longitudinal and circumferential
movement of the cylinder without breaking the joint.
The cylinders may be revolved by worm or spur gearing as found most desirable.
The friction rollers and roller path rings are made so as to be easily renewable and
adjusted to wear.
When treating purely calcareous material such as carbonate of lime, I prefer, to
support combustion, the use of oxygen prepared by the Brin or any other process.
By the use of my Invention I obtain two zones of initial temperature of combustion,
by which calcination is rendered more effective, and in the instance of heating a
mixture of argillaceous and calcareous materials such as Portland Cement Slurry-the
moisture is driven off in the first treating cylinder and becomes partially calcined and
highly heated prior to its transference to second or finishing treating furnace, so that
in the second furnace a higher range of temperature, can be obtained sufficient to effect
the thorough calcination of the material or that necessary to expel the combined water
and carbondioxide and effect complete chemical rearrangement which has not been so
successfully done in the ordinary revolving furnace up to the present.
The wear and tear of my arrangement of plant which I term the Duplex revolving
furnace plant arrangement, is less, because the two cylindrical.revolving furnaces are
kept at a more equable temperature from end to end.
The economy in fuel with my arrangement is very considerable because not only
is perfect combustion attainable, but because the waste heat from second furnace or
from its recuperators is utilised for heating the material in first furnace.
When I am treating metalliferous substances, I prefer to increase the number of
frictional or bearing rollers and I chill the periphery or contact surface of these
rollers.
I do not confine myself to the use of gaseous or liquid fuel as 1 may convert the
combustion chamber into an ordinary open firebar furnace with natural or forced
draught.
Having now particularly described and ascertained the nature of my said Inven-
tion, and in what manner the same may be performed, I declare that what I
claim is
1. The combination of a first treating revolving furnace working simultaneously and
continuously with one or more second treating and higher temperature revolving

page_text: 2. The method of utilising the waste heat from the second treating furnace or
furnaces for the treatment or heating of materials gravitating through first treating
furnace.
3. The continuous recuperator arrangement shewn in figures 3 4 5 and 6.
4. The alternate recuperative arrangement shewn in figures 1 and 2 in its application
to revolving furnaces, substantially as herein shewn and described.
5. I claim the method of preliminary heating, to drive off the moisture in one
inclined revolving furnace, and completing calcination in a second revolving furnace
continuously and without the loss of the whole of the sensible heat of the materials as
they leave the first treating furnace and are transferred to the second one.