Frantisek Cervinka, PSP-Engineering as., Czech Republic, evaluates the benefits possible
from restructuring rotary kilns in the light of present operational demands.
lntroduction
Kiln lines
per 24 hours which corresponds t o the absolute
reducing of RK dimensions with the comparable output.
The structures of the main junction points of the
kiln have been developed t o be more reliable and
durable with the present increase of rpm of the shell
from 0.8 up t o 4.2.
There is an increase of load caused by the lining
and deposits in the RK in lines with a high precalcination. If the burning zone of the classic dry RK
lined with magnesite with some deposits took up
approximately 35 - 45% of the kiln length, then
almost al1 the burning zone in the RK with a high
precalcination will be lined with rnagnesite and
deposits that take up approximately 70 - 80% of the
kiln length.
The majority of modern rotary kilns with L:D = 13
- 16 are seated on 3 supports, and sometimes there
are designs with seating on 2 supports with L:D = 11 14. 80th constructional designs must cope with the
problern of thermal deformation of the rotating
weightless axis of the shell that has an important
influence on the load of junction points in operation.
This phenomenon which will be explained in the next
section, unfortunately can be neither directly controlled nor measured with the kiln seated on 3 sup
ports, and so it is sometimes of limited use in
considering whether the old RK will conform with
new operating conditions.
At present there are approximately 2500 cement kiln
lines al1 over the world of various ages and conse-
Thermal deformation
quently different technical levels. These range from
wet process long kilns (RK) t o the latest lines incorporating preheaters, calciners and channels with their
own heating, with a high calcination rate of clinker
before it enters the rotary kiln (RK) plus effective
grate coolers with controlled cooling.
A certain portion of older lines has already been or
will be reconstructed in a short time for output t o be
increased and consumption t o be decreased. It ir necessary to solve the problem of whether the structure
and strength dimensioning of the old rotary kiln will
conform with new operating conditions.
With the technological development of clinker
burning, rotary kilns have undergone changes especially as far as the substantial reduction ratio L:D is
concerned, where L:D means the ratio of the length
io the shell internal diameter, from the value of 40
with the wet process upto 12 (10) - 16 with the dry
process of clinker production.'The specific output of
the kiln was increased from 0.5 t o more then 5 t/m3
The RK has its fixed axis determined by the radial
roller positions on the foundations with the deflection between supports caused by loading due t o
weight of the shell, lining, deposit and material.
The deflection between supports is small, usually 2
- 4 mm. In view of gravity the position of the fixed axis
remains unchanged during rotation with the preassembled cold kiln ideally manufactured. The deviation in the positioning of radial rollers on sorne of the
supports means unalterable change of reactions in
time to the foundation.
The term - weightless axis of the RK defines the
kiln axis in a weightless condition, fixed to the outside
supports. and it was established t o differentiate
between the distortion of the kiln caured by other
influences than those of weight. With the ideally
manufactured and assembled kiln without thermal
differences along the shell periphery. the weightlers
axis is a straight Iine.
During the RK operation the shell is not heated
The reconstruction of kiln lines in order t o increase
output and reduce consumption raises the question,
which is sometimes considered second-rate, as to
whether the ~tructureand strength dimensioning of
the old rotary kiln is capable of meeting new operating conditions.
It results from the evaluation of data of thermovision measurements of the shell surface temperatures of
kiln lines with a high specific output (over 3.5 t of clinker/m3 of the internal volume of the kiln per 24 hours),
and a cornparison with kilns with lower specific output.
When the specific output is increased, it is more probable that the thermal deformation of the longitudinal
axis of kiln, which is the main criterion for judgement
of the increased cyclic load of the main junction points
of the kiln and thus also of the extent of the reconstruction, will be increased.
This article deals with the process of strength evaluation of the rotary kiln structure, and presents an
interesting solution of the modification of the kiln
seated on three supports for a higher working load in
keeping the existing seating of supporting rings and
radial rollers by means of elastic seating of the central support. At the same time it describes the structure of the most exposed junction point of the rotary
kiln.
-
WORLD CEMENT January2000
83
in an uniform way, which is
especially caused by irregular
deposit production or i t s
falling off. Distortion does
not occur if the temperature
Figure l . Disroiiion of the rotary kiln.
of the shell changes only in
the direction of the kiln axis.
The weightless axis is distorted by the temperature difference along the shell periphery
(always measured in one circumscribed circle perpendicular to the
RK longitudinal axis), especially, if
it occurs in the sarne direction on
the major or even on the whole
length of the kiln. Then, the socalled 'banana distortion' occurs,
see Figure 1.
The spatial distortion of the
weightless rotating axis that is
alterable in time occurs in practice, and it cannot be evaluated
figure 2. Cvclic reaction on the foundatfon.
without using the thermovision
device that rneasures the surface
it is always necessary t o evaluate
temperature of the shell or withrelevant mechanical conditions
out subsequent calculation.
and the leve1 of the structure
The cyclic reactions on the
design of the main junction
foundations and al1 evaluated
points.
values are changed during the
A standard reconstruction
rotation of such thermally distortshould have:
ed weightless axes. The rotating
component of the reaction Q2,
0 full supporting rings of a recthe intensity of which is alterable
tangular-shape, seated on sufin time according t o the value of
ficiently
solid supporting
the thermal distortion of the
segments of the shell, with
weightless axis is added t o the
free support plates.
constant static vertical reaction
0 reliabie radial rollers with the
Q,on the foundation (see Figure
possibility to regulate the neu2).
tral axial tension, easily
The resulting influence of disequipped with a system of
tortion of the fixed and weightcooling, measuring and temless axes on the RK is described in
perature regulation.
following sections.
O hydraulic axial roller for the
controlled axial movement of
Scope of reconstruction
the kiln.
The reconstruction of the kiln line
0 inlet and outlet end of the kiln
aimed a t the increase of output in
designed for high heat load.
clinker that is to be up to 1.5-2
0 effective, reliable inlet and
times higher than the original
outlet sealing of the kiln of a
output using the up-to-date techsimple design.
nology of burning with high pre0 cooling of the kiln sheil.
calcination of the clinker a t the RK
inlet, is what will be presented.
It is clear that there is no general rule on how t o design modifications for the RK. They depend
especially on the initiai condition.
whether, for exarnpie some part
of a long kiln or the existing kiln
with suitable ratio L:D seated on 3
supports will be used.
If the RK is t o meet the
demanding operation conditions,
It stands to reason that the drive
must be reconstructed so that it
meets the requirement for the RK
revolutions t o be increased. It is
customary t o use an asynchronous
motor controlled with the frequency converter.
If the dimensions of the RK and
data of loads are known, it is possible t o start the strength evaluation. Then it can be asked, why it
is necessary to check the
strength e.g. the RK with the
ratio L:D=14,5, of the up-todate design, when it worked
for 15 years without serious
Droblems in the line fitted
with the classic cyclone pre
heater and grate cooler,
when the data of loads had not
been changed too much? 'Just'
the length of the burning zone
with the heavier magnesite lining
and also the deposit will be
extended, the rate of filling of the
kiln remains approximately the
same.
The next section explains why
the strength check is necessary.
Check of strength rotary kiln on 3 supports
As the first step of the calculation
the so called nominal values of
the results are evaluated on the
basis of the load data. The nominal condition means that the
fixed as well as the weightless
axes are straight, which is an ideal
condition that never occurs in
operation. The evaluated values
are nameiy reaction on the supports, longitudinal tension in the
shell and i t s deflection, bending
and contacting stress in the supporting ring and i t s ovality, relative ovality and transversal
tension a t supporting segmentr
dependent on the size of diametricai clearance between the sheli
and supporting ring, suitability of
radial and axial roller sizes
designed for the stated load. The
results mostly meet the generally
certified and pubiished criteria for
the strength evaluation of the RK
under nominal conditions.
The distortion of the RK axis
always occurs in operation which
then causes a substantial difference of evaluated values from the
nominal condition.
Therefore, the second step of
the calculation is the evaluation of
the extreme condition when the
distortion of the kiin is so big that
some of the supporting rings fail
to touch the rollers. Usually the
simulated distortion of the kiln
shell is considered only in one
plane into the banana shape from
the certain temperature drop
given by the difference between
the upper and lower temperature
1 Rotarv kiln
4.4 x 64 m
Vertical reaction on the
couple of rollers (kN)
Basic bending
Stress SR (MPa)
Relative ovality of SR
according to Nies (96)
Contad pressure (Hertz)
between SR and RR (MPa)
I
3000 tpd
355U4325
22%
4936ü.2
22%
O.1 5N0.188
22%
4191462
10%
0.32110.363
13%
3848/5393
52%
53.4n4.9
52%
O.167M.237
52%
436516
23%
0.343íO.456
42%
Relative ovality of shell at
the cleatance 2 mrn (%)
SR - supporfing ring, RR - radial roller
shell with the defined
temperature). lnserting
the input file of temperature data of the
shell into the strength
calculation of the RK,
t h e relevant values
corresponding to the
present operating condition can be subsequently evaluated. The
calculating program
evaluates the resulting
spatial distortion of
I
Foundation 1
1500 tpd
Foundation 2
15Wtpd
3wO tpd
1
42675961
40%
47.3/66.2
40%
O. 14UO.199
40%
428/506
18%
0.292/0.386
32%
5043/8430
98%
55.9/93.6
98%
O.16W0.283
98%
466602
41%
0.332/0.484
65%
. . . . ....... .... -
I-wv
I
---._.
--v.c.
d....-I
*
LBmlliPmUnlllm
l
Foundation 3
1500 tpd
3299/4218
28%
45.W58.6
28%
0.143/0,183
28%
403/457
13%
0.320/0.368
15%
1
3000 tpd
319115030
52%
44.3h9.6
52%
O.1 3810.21O
52%
3971498
24%
0.312/0.451
41%
.
ones.
There is a problem
that the size of the
thermal distortion of
the weightless axis can
not be monitored geo
metrically w i t h the
kiln seated o n 3 sup
ports as the kiln fitr
closely to al1 supporir
as a result of gravity.
Only the extreme condition c a n be monitored when some of
SR iiipporririg rmq, RR - radiairolier
tains approximately a constant
reaction when the rotary kiln axis
is distorted.
The correct function of the
seating i s conditioned by t h e
roller adjustment in the initial
position parallel t o the kiln axis at
the neutral axial tension which is
possible thanks t o the frame structure. The central lubrication station lubricates the sliding surfaces
regularly. In case the pressure
drop occurs in the system during a
long operation, the frame is fitted
w i t h the pumping station
equipped with the high-pressure
pump and pressure switch t o
maintain the pressure constant. It
was not necessarv t o refill the
oil during longer tests, the
tightness of the system is 100%.
In Table 2 the results of the
strength calculation of the
rotary kiln, 4.4 m dia. x 64 m,
after reconstruction to the output of 3000 tpd are compared.
The first figure represents the
expected operating condition
(maximal vaiues) without the
elaStiC support (ES), the second
dia x 57 rn
one when the elastic support
was used, the lower figure states the value
drop in %.
In Figure 5 the courses of the longitudinal
tension on the shell of
the expected operating
condition without and
with the elastic support
are illustrated.
As it was described
the free thermal distortion of the weightless
I
I axis is prevented by the
kiln seating o n 3 supF i y m 5 Comes of the longitudinal bending fension of rhe shell aker
retunilruttion without arid with elastic support
ports in spite of the fact
The nitrogen accumulator prousers d o not pay great attention
duces the necessary pressure of oil
to this phenomenon that, in such
in the hydraulics corresponding to
a fatal way, influences the reliathe nominal reaction. In distortbility and service life of al1 juncing the rotary kiln, the roller pertion points o f t h e rotary kiln
pendicular t o the kiln axis turns in
including the lining.
a reverse way by means of which
The passive solution is t o build
an approximately constant reacthe evaluation program for the
tion is maintained and simultanetalculation of the thermal distorously t h e possible clearance
tion of the weightless axis of the
between the roller and the ring is
kiln from the thermovision measuring device into a control comeliminated. The lift and intensity
o f the reaction.damping can be
puter in a control room that
would draw the operator's attenchanged by the accumulator size
and the nitrogen amount. Afier
tion e.g. t o the dangerous kiln
distortion in t w o levels of values.
long-lasting tests it was verified
After evaluating the situation
that the elastic support meets the
fundamental function ¡.e. mainduring a longer mechanical overloadina.
t
h
e
o
D
e
r
a
t
o
r
can
~.
intervene in the operation e.g.
to decrease the output temporarily.
The active solution i s to
install the elastic seating of radial rollers on the central sumort
..
(see Figure 4) maintaining the
constant reaction on al1 foundations with a smaller distortion
that is described in the following chapter.
Figure 4 Elastic iupport on rhe rotary kiln, 3 4 m
Elastic seating of
the radial roller
Since 1995, t h e elastic
hydraulic support has
been tested o n a
rotary kiln, 3.4 m dia. x
57 m. I t s structure is
quite simple. The sliding
plates with the lateral
guide are installed
under the bearing bodies of rollers. Each bearing rests o n the
hydraulic roller and
they are always interconnected o n one side.
I
Fglure ba (metj 5cheme ot the dischdrge end with cooling
Figure 6b Derail of the tivv-part diicharge segments
Discharge end of the rotary
kiln
that the load o f ali the main junction points of the rotary kiln is
increased in comparison with the
nominal condition. The load is
changed cyclically during the kiin
rotation. in extreme cases from
zero to maximum vaiue.
Conclusion
The connection of the evaiuation
of the distortion o f the weightless
kiln axis from the thermovision
measuring device with the eiastic
seating on the central support
contributes t o the increase of service life and reliabiiity of the operation o f new or reconstructed
rotary kilns seated o n 3 supports.
it can be used with the solid sheiis
of kiins with the ratio L:D = 12 - 16
where a smali thermai distortion
causes a great increase of supporting reactions and thus ali load values o f main junction points of the
rotary kiln.
If it is n o t certain whether the
central support dimensioning wili
meet the case after the kiln reconstruction t o the higher capacity
whether it will not be necessary t o
exchange the supporting segment
with the supporting ring and radial rollers for bigger ones; there is
quite a cheap and efficient design
of the structure fitted w i t h the
eiastic support.
With the rotary kiin the discharge
segments, made of the expensive
Cr-Ni material t h a t must be
exchanged f o r new ones after
approximately 10 - 20% is burnt,
are t h e parts that rnust be
exchanged most often.
Figure 6 illustrates a design of
the discharge end w i t h two-part
segments determined f o r the
rotary kiin w i t h a higher thermal
ioad.
The upper parts are fixed
onto the radial end flange made
of Cr-Ni material by means of
pins, the iower parts are fixed
radially t o t h e k i i n rheii by
screws. They are cooled by air
that enters through the outer
jacketing into the area of the
lower and upper segments where
it turns and it i s exhausted
through the inner jacketing. To
increase the efficiency o f cooling,
both castings are fitted w i t h ribs
inside.
The usual shaped bricks are
used t o line the discharge end.
The exchange o f the upper segm e n t i s easy and fast, b o t h
halves can be easily removed by
cutting them apart where the
surface is worn. The assembly of
30 - 36 upper segments the
weight o f which i s 25 - 40 kg
(according t o the diameter of the
kiin f r o m 3.2 t o 5 m) and fixing
by pins is aiso easy and fast. The
perfect locking of slots between
t h e segments prevents the false
air from penetrating into the
kiin hood and simultaneousiy the
material getting into the atmosphere even before the service
iife o f the upper segments is
over.
The basic piate of the end segrnent is made of the material of
the yieid point in cornpression a t
temperatures of 450 C of which is
approximateiy 200 MPa.
The structures of 15 lines were
modernised w i t h the aim o f
attaining maximum service iife.
.The minimum guaranteed service
iife of the upper segments is 1
year and for the lower ones, it is
3 years.
Enquiry no: 13