On-line determination of pulverised coal mass flow using an ultrasonic technique

The performance of pulverized coal-fired boilers in power stations can be improved by adjusting combustion conditions to minimize losses due to incomplete combustion and excess air. This can be achieved by balancing the burners and then adjusting excess air to minimize losses. Balancing burners under a range of boiler conditions requires on-line measurement of pulverized coal mass flow to individual burners. An ultrasonic technique to meet this need is described. The technique is noninvasive and has no moving parts. It was used to determine air velocity to within 0.35 m/s over the range 10 to 30 m/s. Calibration against beta-ray transmission using glass microspheres in a large-scale laboratory recirculating rig showed that mass loading could be determined to within 5% relative over the range 0.1 to 1.0 mg/cm³ at constant velocity and 8% relative over a wide range of velocities