Ultrasonics regulate dust suppression

London - The non-contacting ultrasonic equipment that is being used to initiate and switch off dust suppression systems at a Lafarge Aggregates site in Leicestershire is proving more reliable and accurate than other methods that have been tried.

The installation is at a rail loading station and at a key conveyor transfer point and it is vital that dust emissions are controlled as both the open-topped rail trucks and the long conveyors pass close to residential areas. Pulsar Process Measurement of Malvern supplied the ultrasonic equipment and it is controlling the application and use of the dust suppression chemicals better than the load sensors previously tried on the conveyor and the optical systems on the rail cars.

On the rail cars, Pulsar supplied a black-box control unit with a dB10 transducer providing a measurement range of up to 10 metres. As the stone is fed into the rail truck the ultrasonic unit is set to provide a relay signal once the car is full. This initiates the spray system and the stone is doused with the dust suppressant. The ultrasonic unit will not allow the stone to be sprayed until it sees a full level, and it also switches off the spray between rail trucks.

The conveyor application is slightly different. The “span” - the difference between the measurement with no stone present and with stone on the conveyor - is of the order of 50–100mm, so a dB3 transducer with a three-metre range has been fitted above the conveyor and controls a spray bar that coats the stone as it passes along the conveyor.