Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR COOLING A MATERIAL
The present invention relates to a method of and apparatus for cooling a
material, such as lime, which has been treated in a rotary tubular kiln, in a
s cooler associated with the kiln.
The present invention concentrates on intensifying the cooling of a material
treated in a rotary tubular kiln and discharged hot therefrom. A cooler used
in
rotary tubular kilns is a so-called sector cooler. It is a device located
outside
to the shell of the tubular kiln and formed of two cylinders positioned one
inside
the other, rotating together with the kiln. It is supported to the kiln shell
by
attaching it thereto at its inlet end and by way of sliding joint at its
discharge
end. The object of the cooler is to cool hot material coming from the kiln,
such
as burnt lime generated from lime mud, and to pre-heat combustion air
is entering the kiln, respectively. The outer and inner shells of the cooler
are joint
together by means of elongated plates arranged in the radial direction,
whereby the annular space formed between the shells may be divided into the
desired number of cooling sectors. At its inlet end the cooler is secured by
welding to the kiln shell via drop chutes. Through the drop chutes, hot
material
2o is led from the kiln to the inlet end of the cooler. The inlet end is
provided with
a conical part, receiving the material passing via the drop chutes. A
radiation
shield fixedly connected to a discharge hopper for cooled material surrounds
the cooler.
2s In sector coolers, the inlet end thereof is typically a conical and
relatively
elongated element. As the number of drop chutes (drop ducts) between the
kiln shell and the cooler is typically 8 - 10, the feed of the material to be
cooled to the conical part of the cooler is usually pulsating, whereby e.g.
hot
lime passes from the kiln directly, quickly and partially also unevenly to the
3o sector part, especially if the feed cone is very sharp. Not all of the
material
streams entering the sectors are equal, which also contributes to the back
flow
of material. In addition to that, a local heat load may be generated on a
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relatively short length at the forepart of the sector portion, which heat load
also
burdens the constructions.
Due to the above mentioned, especially if the material to be cooled is over-
s heated and has become tenacious, a further problem may have been the
accumulation of the material to be cooled in places where the major
temperature peaks prevail. This means that the foreparts of the sectors may
be clogged, which in part prevents the flow of the lime and further
contributes
to e.g. the back flow. Further, the feed cone creates at the forepart of the
io cooler a large space unused with respect to combustion air and the material
to
be cooled, which decreases the efficient heat transfer area and length of the
cooler and thus also the coefficient thereof. Mostly only in the lowermost
portion of the cone there is a single continuous lime bed with a relatively
small
contact surface with the cooling air. The surface layer of the lime bed
is efficiently isolates the lime inside the bed from air and prevents the
cooling of
the lime.
US publication A-4089641 describes a construction relating to satellite
coolers
of rotary tubular kilns, the purpose of which construction is to protect the
inner
2o wall of the cooler against the effect of hot material passing from the
kiln. A
deflector plate positioned inside the satellite cooler restricts the passage
of the
material so that material discharged from the kiln into the cooler during a
previous revolution forms a protective layer, onto which the hot material
discharging from the kiln impinges. According to said publication, this
prevents
2s rapid wear of the refractory lining when producing clinker in cement kilns.
On
the other hand, heat transfer from the protective layer to the environment,
i.e.
cooling of the material, takes place in principle during one revolution of the
kiln
only, until the satellite cooler together with the kiln again reaches its
lowermost
position. Heat transfer from the hot material discharging from the kiln to
3o combustion air is not specifically intensified.
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An object of this invention is to enhance the cooling of hot material passing
from the kiln in the coolers of rotary tubular kilns. Especially the object of
this
invention is to intensify heat transfer from hot material, such as lime, to
the
cooling airflow at the inlet end of the cooler as well as in the drop chutes
s between the kiln and the cooler. At the same time, an object of the
invention is
to reduce the heat load that the constructions of the cooler are subject to.
In order to effect these objects, the present invention relates to a method of
cooling a material, such as lime, treated in a rotary tubular kiln in a cooler
to associated with the kiln, which cooler comprises at least one chamber, to
the
inlet of which hot material treated in the kiln drops from the kiln via a
chute/chutes connecting the kiln and said chamber and forms in the
lowermost portion of said chamber a material bed, whereby material being at
the location of the chute drops onto a material layer formed of material that
is has earlier dropped out of the chute, and the material further flows
through the
chamber countercurrently in relation to the cooling gas flow and is discharged
from the outlet end of the chamber. A characteristic feature of the invention
is
that material is circulated at the inlet end of the cooling chamber and
returned
thereto so that at the location of the chute/chutes the material being
circulated
2o and the material being returned form a layer, onto which fresh hot material
dropping from the kiln continuously forms a new bed and is mixed with the
material being circulated and the material being returned. Further, the formed
material bed is preferably continuously divided to parts that are made to fall
through the cooling gas flow to form said material bed.
The invention relates also to an apparatus for cooling a material treated in a
tubular kiln, which apparatus comprises at least two cylindrical shells
disposed .
one inside the other, surrounding the kiln and rotating together with the kiln
around the longitudinal axis of the kiln, which shells are mounted at the
3o discharge end of the kiln concentrically with the kiln, and between which
shells
an annular space is formed, said space communicating with the kiln via a
chute/chutes connecting the kiln and said space; hot material treated in the
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kiln drops from the kiln via said chutes into the inlet end of said annular
space
forming a bed of material in the lowermost portion of said space.
Characteristic features of the apparatuses are disclosed in the appended
claims.
s
In the present invention, material that is already somewhat cooled is
circulated
so that a protective .layer is provided that acts as insulant between the hot
material bed and the cooler at the inlet end of the cooler chamber or the
annular space in an area whereto the hottest material, such as lime, coming
io from the kiln, drops. This reduces the heat loads that the cooling elements
are
subject to.
According to the invention, intensifying the cooling is based on increasing
the
contact surface, i.e. the heat transfer surface between the cooling air and
the
is material to be cooled. FI-patent application 20000782 discloses a sector
cooler, in which the conical construction of the inlet end thereof has been
replaced with a cylinder, whereby the effect of the cooling air flow can cover
a
greater amount of material and the cooling is intensified. The present
invention may preferably be applied in connection with this kind of cooler
2o construction. When practicing the method according to the invention, the
cooling is further intensified by an increase in the heat transfer surface
between the material bed and the cooling combustion air, which increasing
heat transfer surface is a result of the accretion of said material bed due to
the
circulation and returning of the material to be cooled, such as lime. The heat
2s being transferred from the hot material during the cooling is most
appropriately
utilized to preheat the combustion air. As the volume of the feed cylinder is
larger than that of the feed cone used in older coolers, it can accommodate a
larger lime bed, in which circulating lime that is returned from the forepart
of
the cooling sectors and is already somewhat cooled is efficiently mixed with
3o the hot lime coming from the kiln, due to the rotating motion of the kiln.
As a
result of the mixing, the lime being fed to the cooling sector portion is
cooled
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so that sintering of the hot lime on the fiorepart walls of the sector portion
is
prevented.
In the material bed the surface layer cools down first. If only one continuous
s bed of material, which is not mixed, is provided in the cooler, the material
on
the surface thereof acts after cooling as an insulant and efficiently prevents
heat transfer from inside the bed to the ambient air. The cooling may be
further intensified according to a preferred embodiment of the invention by
means of increasing the contact surface between the hot material and the
to cooling air by dividing the material bed at the inlet end of the cooler to
multiple
sections. Thus, a greater part of the material to be cooled is taken into
contact
with the air. By decomposing at least part of the material bed into separate
particles to the cooling gas flow at the ascending or descending side of the
cooler, the cooling may be further intensified.
According to one embodiment, it is further possible to return at least part of
the material bed back into the kiln in the zone of the drop chutes, whereby
they are further "flushed" by the combustion air flowing through the chute and
being cooler than the material. This is effected by moving the material bed
2o upwards by applicable means during the rotation of the kiln, whereby
material
drops back into the kiln through the drop chutes at the uppermost position and
through the drop chutes facing downward further into the cooler.
The present invention is disclosed in more detail with reference to the
2s appended figures, of which
Fig. 1 illustrates a preferred apparatus for effecting the method according to
the invention. The Figure illustrates an elevation view of a tubular kiln
cooler
and a cross-section taken along line A - A;
Fig. 2 illustrates another preferred apparatus for effecting the method
3o according to the invention. The Figure illustrates an elevation view of a
tubular
kiln cooler and a cross-section taken along line A - A;
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Fig. 3 illustrates a third preferred apparatus for effecting the method
according
to the invention. The Figure illustrates the cooler in cross section seen from
the end of the kiln;
Fig. 4 illustrates a fourth preferred apparatus for effecting the method
s according to the invention. The Figure illustrates the cooler in cross
section
seen from the end of the kiln;
Fig. 5 illustrates a fifth preferred apparatus for effecting the method
according
to the invention. The Figure illustrates an elevation view of a tubular kiln
cooler
and a cross section according to line A - A; and
to Fig. 6 illustrates a sixth preferred apparatus for effecting the method
according
to the invention. The Figure illustrates the cooler in cross section seen from
the end of the kiln.
Fig. 1 is a cross-sectional view of the cooling end of a rotary tubular kiln,
via
is which cooling end the material treated in the kiln is discharged therefrom.
The discharge end of a rotary tubular kiln 1 is supported in a way known per
se by means of a support ring (not shown) to the supporting rolls as the kiln
rotates around its longitudinal axis L. The material to be thermally treated,
2o such as lime mud, is transferred as known per se through the kiln and
heated
and decomposed in the kiln by means of flue gases and heat radiation to burnt
lime and carbon dioxide. The thermally treated material is discharged via the
outlet 5 of the kiln, which outlet communicates with the cooler 2.
2s The cooler 2 comprises two cylindrical shells 6 and 7 located one inside
the
other, which shells are mounted at the discharge end of the kiln 1 concentri-
cally with the kiln, surround the kiln and rotate together with the kiln. An
an-
nular space 5 is formed between them. The inner cylindrical shell 6 is
fastened
at one end to the kiln via drop chutes (drop ducts) 3. Via the drop chutes the
3o inlet opening 11 of the annular space 8 of the cooler communicates with the
discharge opening 5 of the kiln for leading the hot material from the kiln
into
the cooler 2. Multiple drop chutes 3 are provided around the circumference of
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the kiln. The shells 6 and 7 are fastened together by means of longitudinal in-
termediate walls 16 that divide the annular space to cooling sectors.
The annular space 8 is arranged to have at least two separate parts so that
s each cylindrical shell 6 and 7 comprises at least two cylinders fastened to
each other and positioned in the direction of the longitudinal axis L of the
kiln
consecutively. The inner shell 6 comprises consecutive cylindrical parts,
cylin-
ders 6a and 6b, and the outer shell 7 comprises consecutive cylinders 7a and
7b.
Due to the construction of the shells in two parts, the cooler may be divided
in
the longitudinal direction into two separate parts. The cooler part, through
which the material to be treated flows first, is later referred to as "pre-
cooler"
12 and the part, wherefrom the material exits the kiln and is passed to the
is process is later referred to as "secondary cooler" 13.
The pre-cooler 12 comprising cylinders 6a and 7a is located at the inlet end
of
the cooler 2 and receives the hot material coming from the drop chutes, which
material forms a bed 26 on the inner surface of the outer cylinder 7a. The
inlet
2o end of the cylinder 6a is supported to the kiln 1 via these drop chutes 3.
The
discharge end of the pre-cooler 12 is supported at the joint 20 of the pre-
cooler and the secondary cooler by means of a light slide joint 22 known per
se to the inlet end of the secondary cooler, which allows for the necessary
radial and axial motion. The cylinders 6a and 7a extend at the joint 20 to a
2s sufficient extent inside the annular space 13 formed by the cylinders 6b
and
7b for forming a slide joint between the pre-cooler and the secondary cooler
13. The inlet end of the inner cylinder 6b of the secondary cooler is fastened
by means of elements 24 and the discharge end by means of elements 25 to
the shell of the kiln 1.
At the inlet end of the pre-cooler 12 - surrounding the drop chutes 3 - there
is
no feed cone, but both the outer shell 7a and the inner shell 6a are
cylindrical
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along the whole of their length, whereby a "feed cylinder" is provided at the
drop chutes. In the zone of the feed cylinder there are no intermediate walls
16 connecting the shells 6 and 7.
s The transfer of the material to be cooled inside the cooler from the bed of
material 26 is effected by feeding devices known per se, such as feed flights
19 which may be located on any wall of the cooler space. The transfer may be
effected by separate members as well, said members being arranged inside
the cooler space. On the outer circumference of the cooler 2 there is provided
to a feeding spiral 14 which introduces the material possibly passed through
from the joint 20 of the pre-cooler and secondary cooler back to the process.
The cooled material is discharged from the secondary cooler 13 through an
opening 21 to a discharge hopper (not shown). Cooling air enters the coolers
is 2 through the outlet 21 and flows countercurrently with respect to the
material
and ultimately flows via the drop chutes 3 into the kiln 1 as combustion air.
In the apparatus according to Fig. 1, the circulation and returning of the
mate-
rial according to the invention is effected by means of troughs 4 of an appro-
2o priate size, which are welded at the inlet end of the pre-cooler and which
cir-
culate and at the same time cool and also mix the desired amount of the ma-
terial to be cooled with the hot lime stream coming from the kiln in the lower-
most portion of the feed cylinder.
2s In the solution according to Fig. 2, lightening openings 27 (Fig. 1) at the
fore-
part of the intermediate walls 16 of the pre-cooler, on the outer
circumference,
are omitted and an appropriate laminarelement 9 is fastened e.g. by. welding
at the forepart of the intermediate wall. The laminar element 9 has to be such
that a plane surface 9a is formed at the end of the intermediate wall, which
3o plane surface restricts the feed of material to be cooled between the
cooling
sectors, whereby material is returned into the feed cylinder, below the hot
material coming from the kiln through the drop chute 3. In this way, a desired
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filling degree and more efficient internal circulation are effected in the
feed
cylinder of the pre-cooler.
The height and number of feed elements (feed flat bars 9) located on the outer
s circumference of the feed cylinder of the pre-cooler and at the forepart of
the
sectors, as well as the inclination of the elements in relation to each other,
are
determined so that preferably an appropriate filling degree and internal
circulation are effected in the feed cylinder of the pre-cooler.
io The reference numerals of Fig. 2 - 6 are the same as in Fig. 1, where
appropriate.
In the solutions according to Figures 3 and 4, the ends of drop chutes 3 going
into the pre-cooler are covered with a plate 10 (Fig. 3) or with plain bars 18
is (Fig. 4). Thus, a pocket-like space 28 is formed at the end of each drop
chute,
which space prevents the material from dropping directly into the feed
cylinder
of the pre-cooler. In this way, the contacting heat surface between the
material
being treated and the cooling air is increased to some extent.
2o Fig. 5 further illustrates an apparatus for effecting the invention. The
drop
chutes 3 in connection with the feed end of the pre-cooler 12 are extended in-
side the feed cylinder so that the extensions 22 of the chutes extend ade-
quately to the lime bed 26. The chutes are extended in a single-side method
so that the trailing side 23 (in the rotational direction of the kiln the
latter side
2s of the chute) of each chute 3 is shorter, whereby e.g. the flowing of the
cooling
air (shown by arrow in the Fig.) into the kiln is not prevented. So the
leading
side 22 of the drop chute (in the-rotation direction of the kiln the anterior
side)
forms a feed plane (a feed flight), by means of which, if required, a
circulation
of desired volume for the material being cooled is effected at the feed end of
3o the cooler and a feed of desired volume is effected in the sector part
formed
by the intermediate walls 16, from which sector part some of the material re-
turns back into the feed cylinder. Additionally, part of the bed may be
divided
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into separate particles into the cooling gas flow inside the cooler. This is
ef
fected so that when the kiln rotates, the side of the drop chute 3 that acts
as
the feed plane (extension 22) scoops along material to be cooled, and as the
drop chutes travel upwards under the effect of the rotational motion of the
kiln
s to a position more inclined than the angle of repose of the material, the
mate-
rial will flow downwards onto the outer shell of the feed cylinder, partly in
form
of separate particles being mixed with air. The leading edge of the drop chute
has to extend into the feed cylinder to such a distance that the feed plane
formed thereof can efficiently remove and lift the material bed.
to
The extensions of the drop chutes serve also to prevent uncontrolled return of
lime via the drop chutes into the kiln onto the burner pipe.
The whole internal circulation of the material may be divided into several
parts
is of bed in a controlled way also by means of a "regulation edge" on the
trailing
side of the drop chute 3. The regulation edge is part 29 on the trailing side
23
of the drop chute that extends into the annular space 8. By means of the
regulation edge 29, part of the material circulation may be returned back to
the
cooling air flow in the drop chutes and at the same time back into the kiln,
2o wherefrom it again drops back into the cooler. By means of the regulation
edge 29, part of the material circulation may be divided into separate
particles
into the cooling gas flow also in the descending zone of the pre-cooler 12,
wherein the drop chutes rotate downwards. In this way, the contacting heat
surface between the material and the cooling air may be increased in a con-
es trolled way. Further, material, e.g. lime, that has been cooled during the
cir-
culation, forms a protective bed-type layer in the bottom part of the feed
cylin-
der, which layer protects the constructions against hot material entering di-
rectly from the kiln.
3o Fig. 6 illustrates a solution, in which the drop chutes also extend into
the feed
cylinder, but so that an appropriate distance is left between the end of the
drop chute 3 and the outer shell 7 of the feed cylinder, which distance is es-
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sentially longer than in the apparatus of Fig. 5. Thus, the drop chutes do not
extend to the material bed.
Plate- or bucket-like lifting elements 30 are attached (e.g. by welding)
radially
s in the longitudinal direction to the inner surface 7a of the feed cylinder,
be-
tween the drop chutes 3, the shape and height of which elements 30 is
adapted so that they move the material bed located in the bottom part of the
feed cylinder upwards in the ascending part of the cooler in form of parts of
material bed 26a, from which ascending part the parts partly drop down divid-
to ing into separate particles both into the cooling gas flow and partly also
onto
the drop chute located lower. In this way, a circulation of the material being
cooled is effected in the zone of the feed cylinder, in principle similar to
that of
Fig. 5.
is The application of the invention is not restricted to a cooler construction
de-
scribed in the above, but the invention may as well be applied in connection
with other cooling device constructions, in which the essential characteristic
features of the invention may be effected.
