Ultrasonic Sensors Ensure Wood Supply in Combined Heat and Power Plants

Wood can provide cozy warmth—and not only in fireplaces at home. Combined heat and power plants fueled by wood waste generate electricity and heat for the surrounding industrial area. Ultrasonic sensors ensure that the fuel material is always in the right place.

The wood fuel material is delivered on trucks and transported on a conveyor belt to the silo, which is filled with this material. At the bottom of the silo, worm conveyors transport the wood waste to the adjacent burning chamber. To ensure continuous plant operation, the fill level of the silo is monitored and filling is automatically controlled. Ultrasonic measurement is the best choice for this process because the sensor functionality is not affected by adverse conditions like wood chip dust.

The 6.5 m high silo has a rectangular base. In order to fill it evenly, the end of the conveyor belt pivots between three positions. Significant quantities of dust are created during filling. The moisture contained in the wood evaporates and creates an atmosphere with very high humidity levels. Most surfaces in the silo are covered with sticky, moist wood dust. The silo is equipped with three F260 ultrasonic sensors, which have a 10 m detection range. These sensors cover the entire filling material surface and send signals for conveyor belt control.

To ensure continuous power plant operation, there must always be enough wood fuel in the silo. The fuel should be evenly distributed so that the worm conveyors have material to move at all times. The control system ensures that fuel is supplied at the correct time and that it is evenly distributed.

Three synchronized ultrasonic sensors provide full fill level surface coverage for the entire silo. Measurement parameters like the beam angle are set so material accumulations on the silo wall have no influence on the measurement. Through accurate parameterization, you can also minimize other interference factors such as the rotating worm conveyors or flying pieces of wood. The solution averages ten measured values to ensure a smooth, consistent output.

1. Truck
The fuel material is delivered on trucks.

2. Conveyor belt
A conveyor belt transports the material into silo.

3. Silo/sensors
Three ultrasonic sensors cover the entire surface of the filling material and send signals for conveyor belt control.

4. Worm conveyors
At the bottom of the silo, worm conveyors transport the wood waste to the adjacent burning chamber.

5. Burning chamber
In the burning chamber, the fuel material is burned.

Ultrasonic sensor functionality is not affected by dust particles or the high humidity levels. Because the sensors detect the fill level from the top, no large deposits can build up on the ultrasonic transducer. Accumulations of wood dust, which are unavoidable in this application, do not influence the measurement. The temperature and color of the material also have no effect. Because the sensors are noncontact and are not sensitive to external conditions, they require no maintenance.

• Reliable fill level control 
• Even filling
• Easy adjustment using SONPROG parameterization software
• Large functional reserve (10 m detection range)
• Maintenance-free operation