Air-Heater Drive Gearbox.

Rotary air heaters recover heat from the boiler's outgoing flue gas and transfer it to the incoming combustion air, improving boiler efficiency and reducing fuel consumption. The air-heater drive gearbox provides the high torque and low rotational speed required to continuously turn the large air-heater rotor through its drive pinion and peripheral gear.

The gearbox must maintain reliable continuous rotation under high thermal loading, seal drag and variable operating resistance, while providing sufficient torque to restart or keep the rotor moving during abnormal conditions and prevent heat distortion, seal damage or localised overheating.

MEA has worked with CS Energy for more than 30 years to refurbish and upgrade rotary air-heater drive gearboxes at Callide Power Station. These specialised gearboxes incorporate an internal switching gear mechanism, making accurate assembly, alignment and adjustment critical to reliable operation.

During refurbishment, MEA completes a full strip-down, cleaning and inspection of the gearbox and replaces the complete switch-shaft assembly, including the switch shaft, switching arms and bronze wear shoes. In recent years, CS Energy's engineering team has also engaged MEA to manufacture and replace the complete splined switching gear assembly, input gear and first intermediate gear as part of a broader reliability upgrade.

Replacement gears and shafts are precision-machined and finish-ground to achieve the required tooth geometry, spline fit, concentricity and surface finish, with splined switching components nitrided after machining to improve surface hardness, wear resistance and fatigue life. During reassembly, critical settings such as shaft alignment, gear backlash, bearing condition, end float and contact patterns are checked to ensure correct load distribution and smooth operation.

As the air-heater gearboxes operate continuously, their reliability is essential to maintaining boiler availability. Each refurbishment is therefore completed under controlled inspection and assembly procedures within MEA's Clean Fitting Room, followed by functional testing and final quality verification before the gearbox is returned to service.