Rotary Kilns the Psp Solution

7/30/2019 Rotary Kilns the Psp Solution

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ROTARY KILNS – THE PSP SOLUTION

Dipl.Ing. Marek Kratky

INTRODUCTION

PSP Engineering a.s. has supplied more than two hundred

rotary kilns for the pyro processing of cement clinker and

building materials. In fact PSP was one of the earliest kiln

manufacturers.

This tradition and our uninterrupted experience enable us to

continuously improve rotary kilns and its peripheral equipment

as well as the related procedures of design, manufacture,

erection, alignment and maintenance

We are not satisfied to be just an equipment manufacturer.

We rather wish to be involved in complete kiln solutions.

Especially, when it comes to reconstructions we like to

approach acceptable design limits, which will meet operating

requirements at best cost.

In designing rotary kilns we take into account information from

operation by monitoring, measuring and analyzing rotary kilns

during operation and stoppage. Individual constructional units

of standard or new design make the operation easy and

increasingly reliable.

Another source of information is our in-house manufacture

of all kiln components. Optimum balancing of design and

manufacture have resulted in reliable and still economical

kiln technology comprising tires, radial support rollers, axial

thrust rolls, their bearings, the kiln inlet and outlet seals and

the girth gear. Optimum materials are used and high quality

of shop work is ensured. The Czech Republic is a

renowned center of kiln technology.

The final source of knowledge stems from implementation of rotary kilns on site. Our experts provide supervision of

assembly and alignment. Check measurements and a rational sequence of adjustments to achieve the optimum final kiln

position are valuable PSP know how. Later on our kiln service assists to maintain this optimum position for the long-term

economy of this key unit of each cement factory.

This paper deals in detail with diagnostic activities. The design of important constructional units of the rotary kiln will

assist ou in understandin kiln dia nostics.



1. ROTARY KILN GEODETIC MEASUREMENT AND POSITIONING

1. 1. MEASUREMENT METHODS

Measurement and positioning of the rotary kiln is an activity aiming for the optimum position of all fixed and rotating

parts of the kiln including inlet chamber, drive, support rollers and kiln outlet – all viewed from a fixed axis inside thekiln shell.

In principle the fixed axis of a rotary

kiln is a line connecting the 3 points

A1, A2, A3 of a three-pier kiln. These

points are defined by the centers of

rotation. They are not accessible by

direct measurement. Support rollers

in wrong position continuously distort

the kiln shell during each revolution.

The aim of ideal positioning of the

rotary kiln is that the 3 points A1, A2

and A3 would be aligned to show on

a straight fixed axis, which is the

blue line in the left hand picture. In

operation the axes of the radial roller

shafts would be in parallel to the

fixed axis of the kiln.

1. 2. EVALUATION OF MEASUREMENTS The evaluation of our kiln measurement executed for a customer will result in the form of the three-dimensional picture

showing the x, y, z correction of alignment in mm required for each bearing of the support rollers. PSP calls it the

„Summary of radial roller realignment“.



1. 3. PRACTICAL CORRECTION OF RADIAL ROLLERS The customer shall undertake the corrections of the roller positions according to above summary during the

following kiln shut down. He shall lift the bearing housings by the z - values to the required levels. Then during the

kiln start up the roller bearings shall be shifted horizontally or slewed by the values of x and y. At the same time

the axial thrust of the bearings shall be monitored.

After realignment the ideal kiln position should be attained and the kiln fixed axis shall be a straight line parallel to

the axes of all radial rollers.

Such realignment can be done only if the shapes of

the supporting tire and the roller surface are cylindrical.

If the surface is conical or grooved, realignment of the

rollers will be carried out gradually and in steps until

the roller shafts are floating and the axial thrusts of the

bearings are approximately neutral.

Neutral axial thrust of a radial roller is attained, when a

V gap is formed between the flange of the shaft and

the front surface of the bearing seat as shown in the

left hand picture. In practice one of the seats often

slightly touches the flange and it is flushed with oil. 1. 4. RADIAL ROLLER REALIGNMENT

A. Correct radial roller inclination

When the axes of roller shafts and the kiln fixed axis are

misaligned, the surfaces of supporting tires and rollers will wear

out heavily.

As long as inclination is not correct, the tire gets worn out as

well and finally it can be conical and its surface gets worn out

even faster. Wrong inclination and axial thrust are the reason

for the damage shown in the right hand picture.

While kiln support rollers may be slewed during operation, any vertical adjustment requires a ki ln stop as the

bearings must be lifted and shimmed. Some users do not regard a 1 mm vertical adjustment of the roller inclination

as worthwhile and they try to overcome a small gap between tire and roller by horizontal roller adjustment (slewing).

However, non-parallelism of the axes of rollers and kiln result in additional axial thrust and surface wear.

Here is an example of a measurement of axial thrust of a roller:

Vertical reaction on a pair of rollers of 1400 mm diameter correctly inclined be Q = 2806 kN. If one bearing is slewed

out of its neutral position by only 0.5 mm (non-parallelism of 0.032%), axial thrust results in A1 = 53 kN i.e. 1.9% Q.

With a pair of rollers 2 *A1 amounts to 106 kN i.e. 3.6% Q. If there is a 3 mm shift (non-parallelism of 0.193%) A1

will reach 320 kN i.e. 11.4% of Q.



With a kiln inclination of 3% the axial

component Qa of the force of the kiln

weight Q is Qa = 0.03*Q. If the

actual position of all pairs of rollers

deviates by approximately 0.5 mm

from their neutral parallel position,

then axial upward thrust of the rollers

will about balance (3.6% 3.0%) the

downhill thrust of the kiln. In this

optimum position greasing of the

roller surfaces would reduce the

thrust to let the kiln travel downhill.

The balancing thrust could be

generated by one roller only slewed

by 3 mm. In this case the axial thrust

of the bearing reaches 4.7% of the

kiln weight Q.

Correct roller realignment is important. For balanced thrust a roller is slewed horizontally or lifted upwards slightly

during operation. Precise roller inclination parallel to the kiln axis is indispensable.

For rotary kilns in good mechanical condition PSP aims at an accuracy of 0.02% of the distance between roller axis

and kiln axis.

1. 5. CONCLUSION PSP measured kilns of all levels of mechanical condition, some of them

perfect, some even catastrophic. It is without saying that the correct

alignment of a rotary kiln at the beginning and at periodical inspections will

protect all parts of the kiln against wear. In fact, regular realignment in

combination with lubrication will render spare parts unnecessary for normal

operation.

With correct alignment the wear of the roller and tire surfaces may be less

than 1 mm for 10 years of operation. The upper left hand side picture gives

an example.

Quite often PSP has encountered roller positions, which generate

counteracting thrusts. Mostly, it is with kilns without or with just a fixed axial

thrust roller.

A support roller, which is set for axial thrust, will at the same time be

exposed to increased wear. This wear will reduce the roller diameter at its

ends so that its surface will become more and more convex so that more

and more slewing of this roller will be required for the same thrust. In the

end the wear may have resulted in such a convex roller surface that the

concave tire will be locked and no axial floating of the kiln will be possible.

PSP has seen roller diameter wear of over 10 mm during 1 year of

operation and many pittings and caves had developed on the surface of the

tire of the right hand picture.

The repair of such damage is complicated. Most worn t ires, rollers and

bearings need replacement. The replaced part may partially be renovated

by machining in a shop.





2. 4. EVALUATION OF MEASUREMENTS The distances measured between the laser and the

surface line on the shell are evaluated by a

proprietary program. In a first step the program

designs the shell periphery shown in the right hand

picture in blue. Then the program interpolates the

red periphery representing the original idealcylindrical shape of the shell. Its radius, center C,

offsets X and Y as well as distance R from center C

of the rotation are determined at the same t ime.

Connecting the red centers C of all shell sections

determine the position of the kiln axis. I ts spatial

distortion indicates permanent deformation. The

picture below gives an idea of the typical distortion

of the weightless axis.

S 70

20002010202020302040205020602070

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2 3 4 56

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+Y

Y = -20,6

R = 28,5

+XX = 19,6

CRC

Accurate values of permanent deformation of the

kiln axis will be found only under ideal conditions i.e.

at the start up of a kiln, when there is no coating so

that the temperatures of each shell section will be

equal.

Permanent deformation of most shell sections can

be found quite accurately. Only close to the supports

the results are distorted, i.e. the deformation

measured is less than the real one.

Accuracy of measured values is good ( 1 mm) as

long as the spacing along the periphery is regular.

The number of sections measured along the kiln

length depends on the expected distortion of the

shell. A more detailed measurement of selected

sections of the shell where bigger distortions are

expected can be added. By this way small local

bulges will be identified.



2. 5. CONCLUSION

To prevent rotary kiln deformation means to prevent heat distortion of its axis. Nowadays, short kilns with a high

degree of pre-calcining are used. The heat load of these kilns is increased and instability of operation is higher.

The present trend of burning waste and of harmful

substances contained in the gas after combustion is of

great influence on the deformation. The left hand picture

shows a temperature map of the shell of a short kiln.

Temperature differences over the shell circumference cause

distortion of the weightless axis. In case temperature difference

is big or if it spreads along the length of the kiln, i.e. in case of a

drive failure, then the distortion of the weightless axis turns into

the shape of a “banana”. The right hand picture shows a

maximum of the kiln load resting on the outside piers.

PSP Engineering a.s. has developed a flexible support of the rotary kiln,

which provides a semi-constant load during the entire kiln revolution. The

support roller rests on a sliding frame held in constant load position by

hydraulic cylinders.

After 5 years of operation of a kiln equipped with this flexible frame not the

slightest shell deformation was detected.

The following chapter deals with the system in more detail.

If the deformed kiln is bent up at its center, its axis is bent downwards owing to the kiln weight itself, vertical support by

the central support drops and the load on the outside supports is proportionally increased. At the same time thelongitudinal stress on the shell is increased. If the axis distortion at the central support is big, vertical support becomes

nil and the supporting tire will not contact its rollers any more.

Analogically if the deformed kiln is bent down, its axis is bent upwards owing to the kiln weight itself, vertical support of

the central pier increases and at the same time the longitudinal stress on the shell increases. This is critical for the

operation.

Extreme distortion of the rotating kiln axis at the central support can cause an eccentricity of 30 – 50 mm, which mean

that acceptable stress values of the shell will be exceeded. This is the cause of permanent deformations. Eye checking

will not detect, if the supporting tire is lifted from the roller. Only measurement of the deflection of the shaft of the

respective roller will indicate an active support.

Shell segments will cause permanent distortion, if the faces of the segments are not perpendicular to the kiln axis. An

uneven gap between segments connected by welding will also cause distortion.

If peaks of the longitudinal stress occur in areas of the shell of high temperature, transversal stress exceeding the yield

point of steel will permanently deform not only the cyl indrical shell but also the rotating axis.

It should be noted that flexible deformations, which affect the refractory lining, occur before permanent plastic

deformations of the kiln shell section will occur.

The described dynamics refer to only statically indefinite kilns with 3 or more supports.

For a 2-support kiln with a distorted axis the vertical supports during one revolution remain constant and the shell

stress reaches still same nominal values.

This is an apparent disadvantage of 3-support kilns especially short ones the L/D ratio of which ranges from 13 to

15 and tires are relatively close to each other.

If the central support of these kilns was flexible – adjusted so that during one revolution of the rotary kiln it would

transmit constant load corresponding to the vertical nominal reaction, reactions on outside supports and longitudinal

stress on the shell would be constant equal to nominal load of the kiln i.e. identically with the 2-support rotary kiln.



3. FLEXIBLE ROTARY KILNS

3. 1. FLEXIBLE FRAME

The roller bearing housings of the central pier are connected to a sliding

frame, which is held in position by hydraulic cylinders. If the kiln axis is

distorted, the sliding frame moves laterally in a horizontal plane

perpendicular to the kiln axis. For easy motion the sliding frame is

lubricated.

The hydraulic cylinders are connected to high-capacity accumulators.

There is usually one accumulator dedicated to each pair of bearing

housings on each side of the central station. The accumulators maintain

constant pressure in the hydraulic system and provide thereby a semi-

constant load on the pier.

Controlled by measuring and regulating elements for automatic operation a

pump supplies oil to the accumulators.

The flexible frame prevents rotary kiln shell distortion and increases the

service life of the lining, prevents overloading of supporting tires and radial

rollers. It also reduces wear of surfaces, increases reliability of the radial

rollers seat and rotary kiln itself, and reduces r isk of the forced kiln

stoppage even in case the rotary kiln axis is extremely distorted.

Besides the abovementioned mechanical and operating advantages, there is a strong possibility of investment

cost reduction of approximately 15% with a new 3-support rotary kiln equipped with the flexible frame.

In case the flexible frame is installed, there is a constant load during one revolution. So compared with the classic

three-support kiln, the supports of the rotary kiln that is equipped with the flexible frame can be designed for lower

loads while the coefficient of safety is higher.

We see the greatest cost savings at the central roller station. Another advantage is that all three supports of the

kiln, the L/D ratio of which does not exceed 15, can be identical, which means further reduction of manufacturing

and investment cost as well as cost for spare parts.

The flexible frame is also very often used for reconstructions of

existing rotary kilns the axis of which is distorted. As the supports are

overloaded, the kiln does not work properly, radial rollers are jammed,

the shell is deformed and cracked.

This equipment is mostly used for reconstructions of rotary kilns when

the customer wishes to increase the kiln line capacity and shorten the

kiln. As the kiln is shortened, the vertical nominal reaction on piers and

shell stress change after the planetary cooler is disassembled.

At present three flexible frames supplied by PSP Engineering a.s. are in operation, next year two more frames will

be implemented in optimizing operation of existing rotary kilns and one1 frame as part of a new kiln line IKN-PSP.



The drive of the rotary kiln consists of the girth gear

which is fixed to the kiln shell by means of flexible

tangential plates, pinion unit, pin coupling, main

gearbox, asynchronous motor with fluent regulation of

the revolutions, auxiliary drive with electric motor and

diesel engine and grease-spraying lubrication unit.

3. 2. SUPPORTS OF ROTARY KILN

Support segments of the rotary kiln shell such as supporting rings, complete seating of

radial rollers are manufactured and assembled in our manufacturing facilities. Forged

supporting ring is seated on free support plates that keep an optimum diameter

clearance. This so called floating seating of the supporting ring provides perfect ring

positioning on the radial roller and high resistance and long service life of the lining at the

base. The kiln shell is bent of steel of a high yield point at temperatures of 400o

C and itis machined.

Radial rollers of a full forged design are seated in sliding

pans positioned in ball supports cooled with water. This

means that the pin fits well in the bearing pan. Regulating

housings allowing the radial roller adjustment in operation

are part of the roller seating.

For axial motion of the rotary kiln to be continuous, a hydraulic axial roller is positioned

on the 1

st

base (at the drive). As stated in point 1 the greatest benefit of the hydraulicaxial roller is that radial rollers are kept parallel to the kiln axis, which considerably

decreases wear of circulation surfaces of supporting rings and radial rollers. Operation

of the hydraulic axial roller is completely automatic.

3.3. INLET END OF THE ROTARY KILN Inlet end of the rotary kiln consists of the conical part with heat resistant castings

and throat with blades lifting the material that fell through. The large throat catches a

great portion of the material in case the kiln is overdosed from the preheater.

Double lamellas sealing prevents the false air suction to the kiln even if the inlet end

run-out is big. The material that fell through is discharged via the hopper mounted in

the bottom part.

3. 4. DISCHARGE END OF THE ROTARY KILN The discharge end of kiln consists of the piece of the

shell with the heat resistant castings which are fixed on

the carriers, double cooling shell. The intensive cooling is

provided by the all-circumferential nozzle, which is

connected to the air piping and increases the lifetime and

reliability of the discharge end. The replaceable Cr-Nicastings are covered by the lining which prevents these

a ainst overheatin .

3. 5. DRIVE OF THE ROTARY KILN

Rotary Kilns the Psp Solution

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