Rotary Kiln Main Motor And Torque Data

INSTRUCTION MANUAL

Motors for rotary kilns

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Kilns with gear rim transmission

VIGERSLEV ALLÉ 77 - 2500 VALBY - DENMARK ! 2040 AVENUE C - PA 18017-2188 BETHLEHEM – USA ! CAPITAL TOWERS 180. KODAMBAKKAM HIGH ROAD, NUNGAMBAKKAM,- CHENNAI 600 034 - INDIA

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List of contents: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Page:

Mode of operation .................................................................................... 4 Output........................................................................................................ 4 Speed control............................................................................................ 5 Starting conditions.................................................................................... 6 Damping of torsional vibrations, dual drives .......................................... 8 Reverse rotation when the kiln is stopped ............................................. 9 Barring of kiln.......................................................................................... 10 Inclination of motor shaft ....................................................................... 10 Direction of rotation................................................................................ 10

Edited by: Approved by:

KelH N-PB

Translated by: MGN code:

Pages:

T600

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Appendices: Page: Appendix 1. Power and torque requirements.............................................. 11 Appendix 2. Definition of heavy and easy start........................................... 13 Appendix 3. PWM Vector Control Diagram................................................. 15

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1. Mode of operation The present instruction manual is concerned with the situations which, according to the experience of FLS, are the most likely to occur. An exhaustive enumeration of all conceivable situations which may occur during the erection, operation, maintenance of the plant, machine, equipment cannot be provided.

Consequently, if a situation should arise, the occurrence of which is not foreseen in the instruction manual, and which the operator is/or feels unable to handle, we would recommend that FLS is contacted without undue delay for advice on appropriate action.

The motor(s)/drive(s) must be sized and engineered for continuous operation corresponding to duty type S1 according to IEC 34-1, i.e. 24-hour operation for prolonged periods. (Approx. 8000 h/year).

2. Output The motor and drive output at nominal speed, n nom , and maximum speed nmax and the speed range are specified in the order. From minimum speed, n min , to nominal speed, n nom , the motor must yield a constant torque. From nominal speed, n nom , to maximum speed, n max, the motor must work with constant power, see Appendix 1. In case of dual drive the difference in power consumption between the two motors must be less than 5%.

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3. Speed control Irrespective of load torque variations, the speed control must be stable over the entire speed range. A kiln speed expressed in rpm or sec. per revolution is the mean value of the kiln speed during one revolution of the kiln. Independent of the selected type of motor drive system, the kiln speed must be adjusted and maintained with the accuracy described in sub-section 3.1.

3.1 The following requirements apply to AC drive systems with frequency converters (VFD) only:

3.1.1 The kiln speed must be maintained within a relative accuracy of ±1% within one complete kiln revolution.

This requirement must be met over the entire speed range without any adjustment of the reference equipment (potentiometer, current signal or similar) irrespective of load torque and temperature variations and with a variation of ±10% of the rated supply voltage.

3.1.2 The speed reference equipment must be designed so that the actual kiln speed can be controlled and instrument readings can be taken with an accuracy of 1% of the kiln reference speed within the speed range from Nnom to Nmax. In the speed range from 0.1·nmax to n nom the speed must be controlled with an accuracy of 5% at 0.1·n max dropping to 1% of the kiln reference speed at nnom .

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4. Starting conditions 4.1 Motor and converter equipment must be able to yield the maximum initial torque as specified in the order (normally 200-250 % of full-load torque) from 0 to 0.1·n max during the entire starting period, see Appendix 1. The maximum initial torque must be yielded even under adverse working conditions, under which the starting period may become the time (including acceleration time) it takes to O turn the kiln through 120 at the lowest working speed 0.1·n nom . See example of “heavy start” at a load torque of 200-250% of full-load torque, Appendix 2.

4.2 Concerning the requirement to the time for turning the kiln at the mentioned low speeds, the accuracy will be sufficient if the requirement specifies that the drive must be capable of yielding the starting torque (“heavy start”) for 60 seconds at least once per hour reckoned from cold condition.

4.3 In order not to overstrain the mechanical transmission between motor and kiln, the motor torque must at no time exceed the initial torque as specified in the order, normally 200 or 250 % of full-load torque.

4.4 The working speed range for the motor must be 0.1·n max to n max. The drive system must be thermally designed according to this speed range and to the requirements specified in subsections 4.1 and 4.2.

4.5 Start of the kiln is normally taking place with the charge of material (inside the kiln) positioned at the angle of repose, (i.e. side-heavy position).

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This means that the start is normally considered as a “heavy start”, see Appendix 2. In order to be considered an “easy start”, the charge of material inside the kiln must be in neutral position, see Appendix 2.

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5. Damping of torsional vibrations, dual drives The two motors (with gears) are connected to the kiln through elastic couplings (torsion shafts). The drive can thus be considered forming a three-mass oscillation system. Such systems have two natural oscillation modes with corresponding frequencies, see Figs. 1 and 2. The oscillations can be excited by any small mechanical irregularity and grow excessively if not damped.

Mode 1: The motors are oscillating in opposite phase. One runs up in speed, while the other slows down and vice versa. The motors thus alternate to pull the kiln, which maintains a constant speed. In this mode the mechanical damping is practically zero and electrical damping is thus a must. The frequency is low, usually between 1-3 Hz. See Fig. 1. Fig. 1. Mode 1 oscillations.

Mode 2: The motors are oscillating in phase and opposite to the kiln. That is, when the motors speed up, the kiln slows down and vice versa. This mode seldom causes problems due to a certain mechanical damping and the normal kiln speed control. The frequency is higher than in mode 1, usually between 2-5 Hz. See Fig. 2. Fig. 2. Mode 2 oscillations.

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The motor/control system must be designed to dampen these oscillations. That can be provided by a sloping torque relative to the speed characteristics of each motor corresponding to constant voltage/frequency. A normal way, however, has been to design the control system with a fast inner loop maintaining a constant current (= constant torque) of each motor and then adjust the current reference values by tacho signals, thus actively dampening oscillations. It must be stressed that it is necessary to control each current reference individually to provide damping of Mode 1. A simple way is to let each motor have its own speed control and use a common speed reference. Should there be a slight difference in torque between the two drives a correction is added to the slave reference as shown on Appendix 3. This system will dampen both modes, provided that the torque equalizing loop is much slower than the mode 1 frequency.

6. Reverse rotation when the kiln is stopped The barring device is equipped with a releasable backstop with centrifugal brake which prevents that the kiln motor is driven in the opposite direction of rotation by the charge in the kiln immediately after the power supply is switched off. This releasable backstop with centrifugal brake in the barring device means that if the kiln is reversed to neutral position, i.e. with the charge at the bottom, this is done with a controlled slow reversal speed, not exceeding the main motor speed.

However, the motor must therefore be tested at an overspeed of 1.2·nmax. This ensures that the motor is safe regarding mechanical design.

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7. Barring of kiln The rotary kiln can be barred for a prolonged period at reduced speed (approximately 2 - 5% of n max) by means of a separate motor and barring gear unit. Since the kiln motor is mechanically connected during barring, but electrically unloaded, the motor bearings must be designed taking this mode of operation in consideration.

8. Inclination of motor shaft The motor, in particular the bearings, must be designed so that the motor can be mounted with an inclination of the motor shaft, normally between 2 and 3 degrees. The inclination related to horizontal level and whether the shaft extension is placed highest or lowest is specified in the order.

9. Direction of rotation The direction of rotation of the motor is specified in the order. (The motor may be driven in the reverse direction - refer section 6.)

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Appendix 1. Power and torque requirements

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Appendix 2. Definition of heavy and easy start

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Nomenclature for PWM Vector Control Diagram

Parameter

nM1 nM2 Tref,M1 Tref,M2 Tact,M1 Tact,M2

Explanation Common reference speed master/follower motor [rpm.] Motor speed master [rpm.] Motor speed follower [rpm.] Torque reference master [Nm] Torque reference follower [Nm] Actual torque master [Nm] Actual torque follower [Nm]

UM1 UM2 fs1 fs2 Is,M1 Is,M2

Stator voltage master [V] Stator voltage follower [V] Stator frequency master [Hz] Stator frequency follower [Hz] Stator current master [A] Stator current follower [A]

nref,M1

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Appendix 3. PWM Vector Control Diagram

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