An ore chute may be defined as “an inclined passage, from 3 to 4 ft (approx. 1 m) square, for the transfer of ore to a lower level, car, conveyor, etc. It may be constructed through waste fills.”1
Blocked Chute Detectors also known as plugged chute detectors are the devices which are basically employed to identify material blockages in process ore chutes. In many equipments and processes, the materials have the tendency to get solidified and cause blockage in the chute. “In some cases the material blockage can be dangerous, e.g. spillage of hot or corrosive material, etc. and it is therefore critical to detect the blockage before it actually occurs.”2
Hence, the basic job of these detectors is to identify the material deposits on the process chutes and give an immediate warning signal as soon as the safe operating limit of the equipment gets crossed. The process is then brought to a halt for cleaning of deposits. The clearance of blockage requires the equipment to be stopped which results in longer process downtimes.
A typical point level chute detector basically employs gamma ray absorption for its working. The detection system mainly consists of a source emitting gamma radiations and an apt gamma sensor located on the opposite sides. When the material starts accumulating, the intensity of gamma ray absorption increases which causes a decrease in the amount of gamma rays received by the detector. The detector, in turn, sends out an output signal depending upon the level of blockage created.
This is a non contact type of measurement which remains uninfluenced by high pressure and temperature conditions, presence of dirt and dust and other factors like differences in viscosity or refractive indices etc. Unlike contact type measurement systems, these systems are free from maintenance, wear and corrosion problems. These blocked chute gamma detectors are available in two major types which are: “Detector with Remote mounting transmitter electronics or Detector with integrated processing electronics.”3
One of the popular blocked chute detector designs is flush-mounted Sensor which can effectively indicate the existence of material blockage through the chutes. “Since they are flush mounted through a chute wall, nothing protrudes into the chute to interfere with or to obstruct material flow. Rugged sensor design makes these systems ideal for coal (pulveriser and transfer chutes), wood chips, ores and powders.”4
Another type is microwave blocked chute detector which can be designed to work with longer distances around 100 metres. Since the microwave radiations have the ability to penetrate, their performance does not get affected by sensor coatings or deposits etc. Owing to this, these devices are considered ideal to work in dusty applications.