Скачать или смотреть Vertical Roller Coal Bowl Mill Gearbox And Motor Alignment of Thermal Power Plant Alstom HP 1003

https://cementl.com/ Check out the installation process of our ZJTL series vertical roller mill coal pulverizer for rotary kiln and power plant combustion. The title includes alstom is only for increase some exposure, thank you for understanding.

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The bowl mill consists of a grinding table (bowl) rotated by a drive shaft connected to a heavy-duty gearbox. Above the table, grinding rollers apply hydraulic pressure to crush the coal, while hot primary air enters the mill to dry and carry pulverized fuel toward the classifier. The gearbox provides speed reduction and torque multiplication, typically reducing motor speed from 1000–1500 rpm down to 25–40 rpm for the bowl. The gearbox is usually a planetary or worm gear design, rated for outputs of 500–1000 kW depending on unit size.

The electric motor is mounted close to the mill, connected by a rigid or flexible coupling to the gearbox input shaft. For large bowl mills in 500–800 MW thermal units, drive motors may range from 800 kW to 1250 kW. The motor operates at medium voltage (6.6 kV or 11 kV), with squirrel-cage induction design being the most common.

Alignment procedure is essential during installation and periodic maintenance. Misalignment between motor and gearbox leads to high vibration, bearing overload, and premature coupling failure. The alignment process involves several steps:

Base Preparation – Foundations are leveled with precision shims or epoxy grout. Anchor bolts are tightened to specified torque.

Rough Alignment – The motor is positioned to align roughly with the gearbox input flange.

Dial Gauge or Laser Alignment – Modern plants use laser alignment tools to measure angular and parallel misalignment. Tolerances are usually within ±0.05 mm for parallel and ±0.05 mm/100 mm for angular deviation.

Coupling Check – Flexible couplings are inspected for wear and properly lubricated if required.

Hot Alignment Compensation – Because motors and gearboxes expand under operating temperatures, alignment targets are adjusted for thermal growth.

Once aligned, the assembly is test-run at no load to confirm vibration levels within acceptable limits, usually below 4.5 mm/s RMS. The gearbox oil circulation system is checked for pressure (1.5–2.5 bar) and temperature (65–75°C). Bearing temperatures are monitored to remain below 90°C during continuous operation.

The gearbox itself requires regular inspection. Gear teeth are exposed to high contact stress, and oil quality must be maintained with ISO VG 320–460 grade lubricants. Oil particle counts and wear metal analysis help detect early gear or bearing degradation. Alignment issues can accelerate wear, so stable motor-gearbox geometry extends component life.

For the grinding process, stable drive performance ensures the bowl rotates smoothly at design speed. This keeps coal bed thickness uniform and supports consistent fineness from the classifier. If alignment drifts, vibration is transmitted to the grinding table and rollers, reducing grinding efficiency and increasing maintenance needs.

During outages, utilities often combine gearbox overhaul with alignment verification. This includes replacing seals, bearings, and sometimes the high-speed pinion shaft. Coupling hubs are checked for runout, and soft foot on motor bases is corrected. In larger plants, laser trackers are used to measure shaft positions relative to design coordinates.

Motor and gearbox alignment also ties into plant safety. Misalignment can cause unexpected trips of the pulverizer, leading to sudden load changes on the boiler. Stable alignment, along with proper lubrication and cooling, ensures that the mill can meet fuel demand smoothly during load ramps and transient operation.

In summary, the vertical roller coal bowl mill gearbox and motor alignment is not only a mechanical maintenance task but a key factor in fuel grinding performance.

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