A boiler at a chemical the plant produces 37 t/h (tonnes per hour) of process steam and operates 24/7 all year round. The boiler has two motor-driven forced draft fans to provide the furnace air flow. Until recently, the two 220 kW 440 V motors were run at their nominal speed of 1750 rpm and the air flow was controlled by means of mechanical dampers. On average, the dampers were operated at only 30% open, resulting in significant energy waste. Annual electricity consumption by the two fan motors was 2176 MWh.

To save energy, the company decided to replace the dampers with AC drives, which would control the air flow by adjusting the speed of the fan motors. Based on application knowledge, they were recommended the use of two ABB Low Voltage industrial drives as the optimal solution.

Massive reduction in energy consumption

By installing ABB industrial drives to control the fan speed according to the needs of the process rather than dampers. The fan motor speed is adjusted to generate the pressure needed to deliver the desired air flow. For the same flow of 535 m3/min, the fans run at around 760 rpm.

Lower maintenance costs

In addition to energy savings, the VSDs have improved the operating life of the motors. Running at lower speeds has reduced vibration and wear, helping to cut maintenance costs. Lower speeds also mean quieter operation, with the sound pressure level (SPL) reduced from 94 to 78 dB(A).

By using drives incorporating DTC (direct torque control), allows accurate control of both motor speed and torque without the need for pulse encoder feedback from the motor shaft. It provides precise and consistent control of the furnace air flow and combustion process.

Benefits

–     Energy consumption of fan motors reduced by 85% from 2176 to 317 MWh per year

–     Motor lifetime improved

–     Reduced vibration and mechanical wear due to lower motor speed, so maintenance costs decreased

–     Sound pressure level reduced by 16 dB(A)

–     Precise and consistent control of the air flow and therefore of the combustion process

–     System redundancy achieved by leaving mechanical dampers in place (set fully open)

Download application notes here

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