Rotary Kiln Drive Motors

A rotary kiln is a very long, slightly inclined steel cylinder lined with refractory brick; raw material enters at one end, travels to the other as the kiln turns and is fired on the way. The job of the drive motor is to rotate this huge cylinder at a few revolutions per minute, and below one revolution when required. Manufacturer catalogues start small calcining kilns at a 22 kW main motor; on cement kilns the main drive reaches several hundred kW and on the largest lines two 950 kW motors; every large kiln also has an auxiliary drive independent of the main motor.

DRG Motor is a manufacturer, supplier and seller of electric motors. We do not sell the kiln, the refractory, the girth gear, the pinion, the main or auxiliary gearbox, the clutch, the brake unit or the inverter; we supply only the squirrel-cage three-phase motor at the head of each of these drives. The kiln drive motor always sits outside the kiln: beside the girth gear, a few metres from the hot shell, on its own base. Our models are on the Buy Electric Motors Online page.

Types of rotary kiln: cement, lime, calcining and dryer drum

Cylinders that look alike do different work, and that difference drives motor selection. What the kiln fires, how long and thick it is, its refractory load and its speed range all change the motor power directly.

Cement and lime kilns

A cement kiln burns raw meal into clinker; a preheater tower stands in front of it and a clinker cooler behind it. A lime kiln turns limestone into quicklime and is usually built with a vertical preheater. In both, the shell is lined with thick refractory, the load is heavy and the start is hard. The other motors of a cement line are covered in motor selection in cement plants; here only the rotation drive of the kiln is discussed.

Calcining kilns and the dryer drum

Smaller kilns are used to calcine dolomite, kaolin, magnesite and bauxite; activated carbon regeneration and waste incineration also belong here. A dryer drum looks like a kiln from outside but runs at low temperature, mostly without refractory and at a higher speed. Its motor power is therefore usually lower than that of a kiln of the same diameter; industrial dryers are the topic of a separate sub-page.

Main drive: motor, gearbox, pinion and girth gear

A large girth gear is fixed to the kiln shell. The main motor turns the main gearbox, the gearbox turns the pinion and the pinion turns the girth gear. Small and medium kilns use a single drive; large cement kilns use a twin drive with one pinion on each side of the girth gear, and the two motors are controlled together to share the load evenly.

Chain, friction and direct drives

A drive handbook considers chain-and-sprocket and direct shaft drives suitable for small kilns up to about 55 kW; heavier kilns need a girth gear. Small kilns may also use a friction drive in which two of the support rollers are turned by a motor with a gearbox. Some small lime and incineration kilns use a hydraulic drive, where the electric motor turns a hydraulic pump rather than the kiln.

Speed range and inverter

Catalogues give kiln speed as a range rather than a single figure, such as 0.21–2.1 rpm or 0.41–4.07 rpm. This range comes from driving the main motor with a frequency converter; the catalogues name inverter-duty 4-pole motor types. A self-ventilated motor receives less air as its speed drops. If the kiln will turn at its lowest speed under full torque for long periods, this is discussed before ordering and a larger frame is chosen if needed. The drive itself is not our product.

Auxiliary and emergency drive: why the kiln must not stop

When a hot kiln stops, the top of the shell cools quickly while the bottom stays on hot material; the cylinder can bend under its own weight and the refractory cracks. A separate auxiliary motor therefore keeps the kiln turning slowly when the main supply is lost. In the maker’s table the auxiliary drive motors are standard 4 and 6-pole motors from 4 kW to 132 kW.

Slow turning during maintenance

While refractory is being laid or the shell aligned, the kiln has to turn very slowly and stop at a chosen angle. A drive document gives 5.5–15 kW and a kiln speed of 0.1–0.5 rpm for this task; the auxiliary drive is disengaged from the main train by a clutch and holds the kiln in place through a self-locking worm gearbox. In an emergency the auxiliary motor is often fed from a generator line; it must be checked in advance that the generator can handle its starting current.

Click to see current electric motor prices and order nowSEE PRICES →

Rotary kiln motor kW: catalogue values

A) Motor power given in manufacturer catalogues by kiln size and duty:

Taken together, the catalogues show roughly 22–1900 kW for the main drive (two motors combined on the largest kiln), 4–132 kW for the auxiliary drive and 5.5–15 kW for the maintenance drive. Two kilns of the same diameter may need different power: length, refractory thickness, filling ratio and speed range decide together; capacity in t/day alone is not enough for a power calculation.

B) Overlap with the DRG range: main drives between 22 and 315 kW, that is calcining kilns, all the lime kilns listed and cement kilns up to Ø4.0×60 m, are covered by our cast iron frames. All auxiliary and maintenance drives fall within this range too. Main drives above 355 kW, medium-voltage motors and older kiln drives with DC motors are outside our range.

Worked example: Ø2.5×50 m calcining kiln

Take the kiln listed at 0.21–2.1 rpm and 55 kW. Its match in our range is DRG-250M-4: 55 kW, 1485 rpm, 97.6 A at 400 V, rated torque 353.7 Nm. We computed the figures with python:

Multiply 353.7 Nm by 707 and you land on the kiln’s top-speed torque demand; in other words the motor power on this kiln is selected at the limit, and the margin for drive losses is sought on the gearbox side. The lowest speed corresponds to 5 Hz: if the motor runs at this frequency for long periods, its cooling is assessed separately. Ratios can be tried in our gearbox output speed calculator; for a side-by-side view of start-up options open star-delta and starting methods.

Other motors around the kiln and the hot environment

Shell cooling fans blow air onto the zone where the refractory overheats; in one installation two 45 kW axial fans deliver 130,000 m³ of air per hour each. The burner primary air fan, the exhaust (induced draught) fan, coal feed screws and cooler fans are also on the kiln line; on large cement lines the exhaust fan is medium-voltage, while on small kilns its power is set from application data. For motor protection on fans handling hot gas, see High Temperature Fan Motors.

A motor close to the hot shell

Even though the motor stays outside the kiln, the girth gear and riding ring area receives radiation from the hot shell. Our catalogue data apply to −15 °C to +40 °C ambient and altitudes up to 1000 m; if the drive area exceeds this, the motor position, a heat shield or ventilation is arranged with the machine builder and the ambient temperature is stated with the order. Our insulation class is F; special high-temperature motors are not in our range. The brake holding the kiln at standstill is on the gearbox or drive side; brake motors are not in our range.

Rotary kiln drives with DRG motors

Options spanning the inching unit up to the main motor of a large lime kiln:

Almost all main drive motors in the catalogues are 4-pole; a few auxiliary drives carry 6-pole (1000 rpm) units, and a replacement should match that. The motors are foot-mounted B3 on the gearbox base. No fit is promised before shaft diameter and key, shaft height and foot holes have been compared with the old motor; on a twin-drive kiln both motors must be the same model.

Live price table

Current prices of the models that match main, auxiliary and fan drives come from the shop:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate).

Motors in this power range

• DRG-160L-4 – 15 kW – 1465 rpm – 160L cast iron
• DRG-180L-4 – 22 kW – 1470 rpm – 180L cast iron
• DRG-225M-4 – 45 kW – 1485 rpm – 225M cast iron
• DRG-250M-4 – 55 kW – 1485 rpm – 250M cast iron
• DRG-355L-4 – 315 kW – 1490 rpm – 355L cast iron

Click to see current prices and order these motors nowSEE PRICES →

Kiln drive motors and quotations: the Buy Electric Motors Online page lists every model suited to main and auxiliary kiln drives. Write the kiln diameter and length, its speed range and a photo of the motor nameplate to our WhatsApp line, or call +90 (542) 666 11 11; we will assess the main and auxiliary motor together.

Frequently asked questions

Why is a rotary kiln motor driven by an inverter?

Kiln speed sets the firing time, and operators adjust it to the raw material and temperature. The inverter provides that adjustment and a smooth start of the heavy cylinder.

How much smaller is the auxiliary drive motor?

In the catalogues the auxiliary motor is roughly one tenth to one fifth of the main motor; the value in the kiln builder’s table is what counts.

Where can I see rotary kiln motor prices?

Live prices of the models matching kiln drive ratings are in the table on this page.

Reach us: +90 (542) 666 11 11 · info@drgmotor.com · contact.