FLIR Systems discusses the use of thermal imaging to prevent coal self-combustion.
Gone are the days when thermal imaging was prohibitively expensive. The cost of the technology has fallen exponentially with its take-up, yet at the same time cameras have become even smarter and easier to use. Indeed, the scope of thermal imaging is now way beyond the defence and law enforcement sectors where is was first commercially applied. Its applications span industry, offering distinct advantages over other monitoring technologies.
Manufacturing economies have resulted in the dramatic fall in the cost of radiometric detectors. In turn, this has made the technology easily affordable by anyone whose job can benefit from the ability to either detect a heat source, such as a person, or to examine the thermal profile of a scene or system for signs of hotspots.
Indeed, it is the flexible application of the technology that enhances its cost efficiency. The same device can be used to see through smoke to spot fire casualties or scan the industrial environment to identify systems or components that are operating at abnormally high temperatures. And with every application added to the list, return on investment is even quicker.
Self-combustionOf particular relevance to the mining industry is the technology’s ability to monitor stored material that has the potential to self-combust. Coal starts to oxidise when exposed to air and this causes a rise in temperature. Initially this is slightly above ambient temperature, but if left unchecked it can rise to above 400?C, causing the coal to burst into flame.
During the pre-combustion oxidisation process, the coal can also produce large amounts of methane and carbon monoxide gases. These toxic and explosive gases can make it even more difficult for fire fighters to control any subsequent fire so early detection of any temperature rise is vital.
Thermal imaging acts as an early warning system by spotting any abnormal rise in temperature before any fire breaks out. A fixed mounted camera can be used economically to constantly survey an indoor or outdoor area day and night, in rain or snow and through fog and smoke. Not only does it provide an early warning of potential fire, it pinpoints its source too.
These benefits are prompting the wide adoption of thermal imaging to ensure the safe handling of coal. The Dangjin coal-fired power complex (DGFPC) in South Korea is one example. To transport coal to its boilers, a belt conveyor of several kilometres in length is used. It is especially important that the coal’s temperature is continually monitored during transportation, as movement increases its potential for spontaneous combustion.
The Danglin coal-fired power complex in South Korea uses thermal imaging to monitor the temperature of coal on the belt conveyor that transports the fuel to its boilers.
To protect assets and personnel and ensure continued productivity, DGFPC installed several fixed mounted thermal imaging cameras. These devices not only detect the slightest rise in temperature and automatically trigger an alarm, but also activate an automatic sprinkler system. This is possible because the type of camera the plant’s management chose has multiple I/O ports.
One of the cameras is installed in the coal store, recording the temperature of the material as it enters the conveyor system. As the coal is transported to the boilers, at a speed of 4 m/sec, several additional cameras check its temperature in transit. All are connected to a TCP/IP network using a standard ethernet cable. And through the network the thermal data is shared with a programmable logic controller, which immediately stops the conveyor belt and activates the sprinklers when the camera triggers the alarm.
Coal pile storage
A similar system is used by the Nástup Mines Co-operation in Tusimice, Czech Republic, to continually and automatically monitor a coal pile that occupies a site, approximately 800 x 200 m in size. For the purpose, the five cameras are mounted on steel masts at strategic locations around the site. The thermal data they collect is transmitted via 3 km of fibre-optic cable to the control room.
The cameras are configured to generate a direct alarm output to an operator, if the pre-determined temperature threshold is exceeded. An acoustic alarm and display on the control room monitor concurrently draws the operator’s attention to the location of the potential spontaneous fire.
The ability to monitor the entire piles of coal rather than rely on spot measurement was also the reason why the Dutch bulk handling company, OBA, also opted for fixed mounted thermal imaging. The company operates two terminals in the port of Amsterdam for handling a variety of commodities including biomass and coal.
Temperature certificationSeveral European countries also impose additional requirements for the transportation of coal. A multilateral agreement makes it mandatory for the temperature of a coal load – before, during and after the loading process – to be below 60?C. Accordingly every shipload of coal that leaves the terminal to Germany, for example, needs to carry a valid temperature monitoring certificate.
The company used to outsource this job which added costs to the operation but, thanks to its investment in thermal imaging, OBA can now perform that task itself, adding value to the service it provides.
The technology is now used to visualise the entire stretch of conveyor belts from coal store to ship, a distance of around 900 m. This allows coal temperature to be monitored up to the last moment before loading. The thermal video images are sent over IP to a central control room where they are continuously monitored. A proprietary software system provides a colour-coded visual guide: green indicates a safe temperature; amber, rising temperature; and red, danger of self-combustion.
OBA uses handheld imaging cameras to regularly determine the temperature of its coal storage piles.
OBA also uses handheld thermal imaging cameras to regularly determine the temperature of its coal storage piles. They also give site engineers greater intelligence in the event of an amber warning from the control room. The fixed cameras determine the location of the potential problem and handheld versions provide the means for further investigation. And as thermal imaging is a non-contact technology, it allows the job to be done without compromising personal safety.
Written by FLIR Systems. Edited by Jonathan Rowland
Read the article online at: https://www.worldcoal.com/handling/30092014/world-coal-using-thermal-imaging-to-prevent-self-combustion-coal1374/