Improvements in Rotative Furnaces or Kilns for Roasting, Calcining, or otherwise Treating Granular or Pulverulent Materials such as Cement and Ores.
Year: 1888

page_text: Improvements in Rotative Furnaces or Kilns for Roasting, Calcining,
or otherwise Treating Granular or Pulverulent Materials such
as Cement and Ores.
I FREDERICK SIEMENS of No. 12 Queen Annes Gate Westminster in the County of
Middlesex 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 a construction of rotative furnaces or kilns, preferably
heated by gaseous fuel. Such furnaces were described in Sir William Siemens's
Patents No. 189268 157509 307771 364272 407573 4375, 37147 51507 and 3792*1 in
which the furnace chamber consisted of a horizontal cylindrical or spheroidal chamber
made to revolve slowly upon its horizontal axis, the gaseous fuel from the gas pro-
ducer and the heated air supply being made to enter through ports at the one end of
such cylinder and the resulting flame after sweeping round the furnace chamber
being caused to escape either at the other end of the chamber or through other ports
at the same end of the chamber where the gas and air entered.
By the rotative motion of the furnace chamber the material contained therein is
made to turn over continuously so as to offer fresh portions thereof to the action of
the flame and by placing the charging shoot at a higher level than the outlet for
materials treated, or by placing the axis of the furnace on an incline the material fed
in at the higher end is at the same time made to travel slowly towards the lower end
from which it can be continuously discharged.
In constructing such furnaces according to my present invention, I make the
revolving furnace chamber of a larger diameter at the end where the combustible
gases and air enter than at the other end where the material to be treated enters,
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page_text: whereby I, in the first place, obtain a greatly increased sectional area for the expansion
of the flames and combustion gases at the end where the combustion takes place,
while the sectional area at the opposite end is kept comparatively small, and secondly
if the chamber be made conical, I obtain the requisite inclination on the lower side of
the furnace chamber for effecting the longitudinal travel of the material while the
axis of the chamber remains in a horizontal position.
The form of the revolving furnace chamber and the arrangement of the gas pro-
ducer and regenerators, when such are employed, may be variously modified; thus
the furnace chamber may be made uniformly conical throughout its length, or the
combustion end only may be made conical and the other end cylindrical or only
slightly conical or the combustion end may be made cylindrical of large diameter and
the other end either conical or cylindrical of smaller diameter.
The heating of the furnace chamber may be effected either by means of an arrange-
ment of gas producer and a set of four regenerators with reversing action for heating
the gas and air supply in the well known manner, or there may be only two
regenerators for heating the air supply alone or again the regenerators may be
arranged in the known manner for continuous action, the outflowing gases passing
in one direction while the inflowing gases pass in the contrary direction in adjacent
channels.
In all the above cases the flames and combustion gases may be made to flow from
the combustion end to the opposite end whence they pass to the regenerators, but by
preference I arrange the regenerators, and ports so that the flames after passing from
one set of ports at the combustion end to a certain distance along the combustion
chamber, are caused to sweep round and return to a port or set of ports at the
same end.
It will be evident that although it is preferable in many cases to work the above
described rotative furnaces by means of gaseous fuel and regenerators an ordinary
grate fire might be used as the source of heat in combination with my improved
construction of rotative chamber.
The accompanying drawings shew an arrangement of my before described furnace
or kiln in which the combustion chamber is of a uniformly conical form and is heated
by gases from a gas producer combined with two regenerators for heating the air
supply.
Figs. 1 and 1ª shew a longitudinal section.
Fig. 1 shewing the heating apparatus and front part of the rotative furnace
chamber while Fig. 1 shews the continuation thereof to the charging end; Fig. 2
shews a cross section on line X X Fig. 1.
The furnace chamber A is of considerably greater diameter at the combustion end
than at the opposite end where the material to be operated upon enters through a
shoot B by this means the flames resulting from the combustion of gas entering
through the ports C, and the air entering alternately by the ports D or D¹, have free
room to expand and thus the advantage of heating by radiated heat from the flames
without extensive contact therewith of the material to be treated is obtained.
At the same time, although the axis of the furnace chamber is maintained horizontal
so that the flames can pass more or less centrally along the same without materially
coming in contact with its sides or the material thereon, the bottom of the chamber
obtains a sufficient inclination to cause the material to travel slowly forward as it is
turned over by the rotation of the chamber, the latter action being promoted by
providing longitudinal ribs or projections in the chamber as shown in Specification
No. 1892 of /68 and 1575 of /69.
The rotation may be effected in any convenient manner, such as by a toothed ring
fixed at any point of the outer surface of the chamber and gearing with a worn on
a shaft driven by a motor engine, or rotary motion may be imparted to the wheels
that support the chamber so as to carry this round by frictional contact.
The gas producer E is of known form with grate at F and feeding hopper at G
the gases given off being caused to pass to the rising flue H leading to the port C

page_text: through the passage formed between the firebrick arches E' and E2 and the space
between the underside of these arches and the incandescent fuel, whereby the hydro-
carbon gases are heated for the purpose described in the Specification to Patent
No. 9103 of /84. On each side of the gas producer is situated a regenerator I l' for
alternately taking up the heat from the products of combustion and imparting the
same to the air supply, for which purpose they communicate at top respectively by
flues J. J with the ports D. D' and at the bottom through a reversing valve K of
known construction alternately with the outer air and with a chimney flue O.
By placing the gas producer close to the combustion end of the furnace chamber
as shewn, the combustible gas arrives with its full heat in the furnace chamber, and
by placing the regenerators close against each side of the producer, not only is loss
of heat by radiation from the side walls of the latter prevented, but a portion of the
intense heat of the combustion gases passing through the one or other renerator is
transmitted through the side walls so as to raise the temperature in the producer to a
corresponding extent.
As before stated, the arrangement of a second set of regenerators for heating the
gas supply may also be adopted, in which case the four regenerators would be
arranged immediately in front of the combustion chamber, while the gas producer
would be placed further back, and in that case the gas could be brought to the
reversing valve comparitively cold.
Or again, as before stated, the arrangement of continuous curren onerators may
be used.
As the combustible gas enters through the port Cand the heated air say through
the port D, the resulting flame will shoot forward with gradually diminishing velocity
in the furnace chamber until a point is reached where its progress is arrested by the
draught in the contrary direction exercised by the chimney through the port D',
which will then cause the flames to sweep round and return through the port Di
passing through regenerator I¹ and thence to the chimney.
When burning ground cement material, it is found that until this has been acted
upon to certain degree by the heat it is apt to give off a considerable quantity of fine
dust, which, if allowed to be carried by the draught into the regenerators, would be
liable to choke these in course of time and interfere with their action.
In order to prevent this, the extent to which the flame passes along the furnace
chamber is so regulated that the cement travelling forward from the inlet end will
have attained the degree of heat at which the production of dust ceases before it is
brought under the influence of the return draught.
In order to prevent as much as possible the passage of such dust into the
regenerators, I place the charging end of the chamber in communication with a
chimney by a flue M provided with a damper, so that, if required, by opening this to
a certain extent a slight draught in that direction will be produced in the part of the
chamber beyond the point to which the flame extends, whereby the dust produced
in that part of the chamber will be carried backward, to be deposited into a pocket
such as L.
The burnt cement or other material is delivered into the space N, whence it is
removed in any convenient manner.
As before stated, the furnace chamber may be constructed of various different forms,
such for example as that shown in dotted lines.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
(1) Constructing furnaces or kilns with revolving furnace chambers that are of a
larger diameter at the end where the flame enters than at the opposite end where the
materials to be acted upon are charged, substantially as herein described.
(2) In furnaces or kilns for calcining roasting or otherwise treating granular or
pulverulent materials the combination of a revolving furnace chamber A made of

page_text: larger diameter at the combustion end than at the charging end with a gas producer E
communicating with the furnace chamber by a port and two regenerators I. I' for
heating the air supply situated closely on each side of the gas producer and com-
municating with the furnace chamber by ports D. D'; arranged and operating
substantially as herein described with reference to the accompanying drawing.
(3) In combination with a roasting or calcining furnace or kiln such as is referred
to in the preceding claims, the use of a chimney flue at the supply end of the furnace
chamber for preventing dust from being carried into the regenerators, substantially as
herein described.