Among chips and other wood-based fuels, there will always be a varying number of foreign objects no matter how well and carefully the processing processes are designed. In just over ten years and with X-ray scanning of tens of millions of cubic meters of wood chips, we have seen a wide range of foreign objects that have been introduced at various stages of the production chain. Here are some examples of foreign objects which have been introduced from different processing steps:
- Harvester head cutting chains
- Rocks, sand and soil from stockpiles
- Chipper blades
- Crushed stone, asphalt and concrete from the terminal
- Saw blades and other parts of equipment
- Bottom shovels, shovels and tools from trucks
- Metal fasteners and remnants of previous freight from train carriages
- Support irons, scrapers and dam plates from the plant’s own process equipment
In addition to the above mentioned, foreign objects of unknown origin have been found, which cannot be explained with logic as to where and how they have strayed into the fuel.
Plants are typically prepared for foreign objects with magnets and screens to avoid some of the problems. However, practice has shown that these are not always enough. With the Inray Seeker X-ray scanner, quality management can be taken to a new level. The scanner recognizes foreign objects and classifies them according to their density in real time. The following is an example case where the removal of foreign objects is automated.
Case example
The challenge for our customer was the stones and metals entering the process with the sawdust, which caused equipment breakdowns and sparks in the hammer mills, which in turn resulted in automatic fire extinguishing and additional production shutdowns. The original solution for the plant was a traditional disc screen and a magnet to divert oversized pieces and some of the magnetic metals out of the process. Despite these measures, not all stones and metals could be removed but problems remained, thus an Inray Seeker X-ray scanner was installed at the facility.
Picture Inray Seeker installed in a hopper between conveyors
The scanner was installed in the falling current between the two conveyors before the screen and the magnet. The scanner detects rocks and metals above 0.5 cubic centimeters, and alerts the plant control system if the size of the foreign object exceeds 1 cubic centimeter. After the alarm, the plant automation stops the first conveyor and changes the direction of the second conveyor, so that the debris containing the foreign body can be removed from the process in a controlled manner. The operation takes less than ten seconds, after which the process continues normally. Inray Seeker also stores X-ray images in a database that can be viewed from the interface and utilized for quality feedback to suppliers. With the installation of the system, the usability of the plant has improved and operating costs have decreased.
Video Falling current as measuring point
Image User interface where measurement data and X-ray images can be viewed on a load-by-load basis