Improvements in Rotary Furnaces.
Year: 1899

page_text: Date of Application, 23rd Jan., 1899-Accepted, 20th Jan., 1900
COMPLETE SPECIFICATION.
Improvements in Rotary Furnaces.
We, EDWARD HENRY HURRY, of Bethlehem, County of Northampton, State of
Pennsylvania, U.S.A., and HARRY JOHN SEAMAN, of Catasauqua, Lehigh County,
State of Pennsylvania, U.S.A., 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.:-
In the manufacture of l'ortland and other basic cements in rotary furnaces
lined with firebrick it is found that a rapid deterioration of the lining takes
place due to the fluxing action of the cement material on the lining. This
involves frequent renewals of the bricks forming the lining and a consequent
serious expense, due not only to the labor and material necessary for relining
the furnace, but also to the reduction of the operative time of the plant.
The rotary furnaces employed in this industry are cylinders built up of sheet
iron or steel and lined with firebrick. They are set at a slight incline and
given a slow axial rotation. At the higher end the raw cement materials are
introduced, in a powdered form or as a wet slurry.
A flame produced by petroleum, coal, or other suitable fuel is introduced at
the lower end, and the upper end being provided with a smoke stack, this flame
and the products of combustion are carried through the inclined furnace, render-
ing it intensely hot.
The combined effect of the rotation of the furnace and its inclination is to
cause the cement material to be slowly conveyed along the lower portion of the
cylindrical furnace, the flame of combustion passing along the furnace in the
contrary direction.
The cement material thus operated on consists largely of basic matter; for
instance in the case of Portland cement about 75 per cent. of the raw mixture
introduced is carbonate of lime, which is converted by the heat of the furnace
into caustic lime.
The composition of firebrick is usually almost entirely acid consisting almost
exclusively of silica and alumina. The basic cement material is brought into
moving contact with this acid lining, and both being raised to a high temperature
they serve to mutually flux each other for the reason that certain compounds
of silica and alumina with lime are more easily fusible than are the individual
materials.
In practice the effect of these properties is that the lining of the furnace is
rapidly fluxed away by the action of the cement material at the temperature
necessary for its calcination.
In order to avoid this deleterious action we proceed as follows:-
We apply a coating of common salt to the firebrick lining of the lower portion
of the furnace which is exposed to the fluxing action of the clinker (say the
lower fourth of its length) and heat the furnace so that this portion is at a high
temperature. Or the same result may be attained by heating the furnace first
and then applying a coating of common salt. We then introduce cement raw

page_text: material. The material thus introduced is raised to a temperature at or about
that of clinkering and in that condition is beaten or pressed down on to the
heated surface of the fire brick lining. This coating is made thick enough to
protect its junction with the firebrick. A thickness of two inches will usually
be found convenient.
The coating of cement clinker thus formed adheres with great tenacity to the
firebrick lining and forms a highly refractory layer of considerable mechanical
strength on the firebrick lining, of a nature to resist the action of the heated
basic material moving thereon.
Occasionally it happens that during the working of the furnace a portion of
this protective coating becomes dislodged leaving the firebrick exposed to the
fluxing action of the passing cement material. In this event we arrest the
rotation of the furnace when this unprotected portion of the firebrick is at the
lowest point; we then apply salt to the unprotected portion of the firebrick and
beat or press down thereon some of the hot cement material contained in the
furnace so as to renew the coating on the exposed place. We find that the
adherence of the cement material is increased by allowing the furnace to be
stationary for a time and to cool slightly before resuming working.
Instead of common salt other suitable fusible material may be used such as
potassium or calcium chloride.
By this method of procedure we provide a coating of cement material which
adheres to and protects the firebrick lining of the furnace.
The use of salt or other suitable fusible material increases the case with
which the protective coating is caused to adhere to the firebrick lining, but we
can also produce an adherent and protective coating without its use. In this
case we heat the firebrick lining to a high temperature before applying the
cement material and proceed in the same manner as is used when salt is
employed. Likewise we can repair any injured portion of the coating without
the use of salt by applying thereto hot cement material in the manner above
described.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, we declare that what
we claim is :-
'
First. The herein described method of coating the firebrick lining of a rotary
cement furnace with a refractory and adherent layer of cement material which
consists in first heating the firebrick lining to a high temperature (with or without
the use of salt or other suitable fusible material) and beating or pressing down
on it a layer of cement material substantially as described.
Second. A rotary cement furnace having a firebrick lining protected by an
adherent coating of cement material substantially as described.
Dated this 23rd day of January 1899.