Conveyors in mines and quarries for heavy material handling are an important logistics management asset on the site, delivering the raw or product material from the mine excavation right through to shipping.
They are also one of the highest maintenance costs items with frequent (e.g. shift) inspections of drive bearings, idler rollers, conveyor belts and tracking, chute blockages, spillage and so on. Conveyor belts can span from 1 up to 4 metres in width and travel up to speeds of 5-6 m/s, and can cost in the vicinity of $1M to replace for a 1-2 km conveyor length.
A fire (e.g. 09-21-2015-Swanton fire ) on a conveyor system can start from multiple sources, including the material being transported itself, right through to overheated components such as drive or idler bearings, or smouldering dusts leading to spontaneous combustion situations.
Traditional fire detection on and around mine and process plant conveyors has been difficult to achieve using conventional point heat detectors and aspirating CO gas detectors. This is mainly due to the conveyors’ long length and variable physical orientation (e.g. slopes, corners, enclosed or open structure), high speed of the belt dispersing any gases, harsh operating environment, and prohibitive costs for the supply, installation, and maintenance of effective conventional fire detection systems on this scale. The result has been inadequately performing conveyor fire detection systems, and in most cases no fire detection at all.
This overheated bearing can damage the conveyor belt via gouging and become a fire ignition hazard.
In fact, it has reached a temperature of over 180ºC, which is well above the ignition temperatures of many dusts including coal.
A fire detection system that can address these conveyor operating conditions would greatly increase fire safety for the protection of people, fixed assets, and minimise disruptions to plant production.
Case Study Fire Detection – Coal Conveyor
This is an example of using a DTS system for fire detection in and around a coal conveyor. It has one sensor cable going out along one side of the conveyor and returning along the other side. Alternatively, one sensor cable can run under the conveyor and one above under the tunnel roof depending on your installation. This provides full fire detection coverage around the conveyor structure area.
One end of each of the two fibre cores of the cable is connected to the DTS, and the other ends are terminated with a connector signalling the end of the cable run to the DTS.
The DTS unit is installed outside the potential hazardous area, with only the fibre optic cable inside the hazardous zone.
Distributed Temperature Sensing (DTS) technology using a resettable linear heat detector on a single fibre optic core has been successfully tested and deployed on underground and surface conveyor systems.
The DTS system’s capabilities have been proven to exceed conventional point or linear (copper wire based) heat detectors, or aspirating CO gas detectors. The ruggedized fibre optic based system has the capacity to detect fires quickly and localise the source to within 0.5 metres. This precision is unaffected by wind and other environmental effects, because not only convective, but also conductive and radiant (infrared) heat is measured by the system.
Advanced Photonics Australia integrated DTS
Our fibre optic cable Distributed Temperature Sensing (DTS), provides an integrated fire detection alarm & monitoring system as shown in the diagram for mining & heavy materials handling conveyor systems.
Summary of Features
- Accredited for fire detection (flame resistance 750°C for 2 hours, IEC 60331).
- Ruggedised “stainless steel cable sheath” for any harsh
- Doesn’t propagate the flame along the cable (IEC60332-3).
- Provides the exact location of the fire to remote monitoring control rooms.
- Provides early warning of heat before a flame occurs.
- Can be installed in hazardous areas (zone 0 and zone 20).
- Is immune to EMI (electromagnetic interference).
- Requires no maintenance.
- The fibre cable is the sensor, no other cabling or field interface devices required.