The risk of fire becomes increasingly significant as more waste heads into temporary storage. Infrared cameras can help control this risk, writes Peter Smorscek
Environmental concerns are pushing for an increasingly streamlined process of waste disposal, treatment, neutralization and recycling. In some regions, while waste treatment capacity is trying to catch up with an increasing demand, it has become necessary to store solid waste in waste bunkers before treatment. The potential for fires in storage areas is a key concern for plant operators.
Waste stored temporarily in bunkers is potentially flammable. Fires can result from self-combustion, heat development due to pressure, spontaneous chemical reactions between the waste materials, and build-up of methane gas. The need for fire prevention becomes even more acute for installations with a waste shredder: sparks formed during the shredding of metal and other solid parts can react with methane gas, resulting in an explosive cocktail scattering around the entire waste bunker.
Waste bunker fires can be hazardous not only for operators but also the environment. In addition to the fire and its emissions, the heavily contaminated water used in firefighting, which hampers the further processing of the waste, has to be disposed of as well. Furthermore, it is difficult to reach potential fire spots still dangerously smouldering somewhere in a large and deep bunker.
Preventing fires with infrared
Options for fire prevention and detection include laser-based scanning and infrared camera. In particular, infrared cameras are an excellent tool, provided they offer some basic features, namely the ability to:
• detect and clearly visualize nascent hot spots through smoke and dust
• measure and indicate temperature
• control pre-defined areas continually
• raise an alarm when a temperature threshold is passed.
Case study
Fire prevention systems are installed by specialized system integrators. One such leading integrator on the market is the technology company m.u.t GmbH, based near Hamburg, Germany. One of the areas that m.u.t. has specialized in is early fire detection for air and land transportation carriers and thermal treatment plants.
m.u.t. offers a complete solution including planning, installation, software, hardware and maintenance. It has installed more 40 infrared camera-based early fire detection systems in waste bunkers across Europe. ‘Preliminary planning is the hardest part of the job’, says Werner Hagedorn, Account Manager for the early fire detection products. ‘We have to define the best place to install the camera, divide the entire waste bunker in zones and ensure that the minimum surface area required for detecting hot spots (commonly 30 x 30 cm in Germany) is covered by the camera.’
FLIR Systems, an infrared camera manufacturer based in Sweden and the US, introduced its ThermoVision A40-M fix-mounted camera in 2002. Since then, m.u.t has integrated the camera into all its waste bunker installations and into ARTUS, its early fire detection software suite.
The A40 camera offers a spectral range of 7.5-13 mm, which allows monitoring through smoke and dust. One A40 camera, mounted on a pan stilt and placed in an appropriate protective housing, is able to inspect a surface of up to 2000 m2. The camera registers the surface temperature of the waste, comparing it to the maximum temperature defined by the waste bunker operator.
The m.u.t. engineers divide the bunker surface in zones depending on the size of the waste bunker. The camera checks every zone subsequently and its FireWire output provides temperature information and infrared imaging to the crane operator’s monitor screen in real-time. Operator can also steer the camera from their working place. Three alarm levels marked by visual as well as sound alarms warn the crane operator of substantial temperature differences on the waste surface in a particular zone. The waste is then mixed and turned, transferred to another zone, or carried directly to the oven for combustion.
Although every pixel of the infrared camera detector measures a temperature value, the m.u.t engineers have chosen a temperature measurement based on a 3 x 3 pixel grid. They considered 2 x 2 pixels as inadequate and unreliable: ‘3 x 3 pixel secures additional measurement accuracy and consequently a clearer image contrast, while excluding false alarms’, says Volker Meliss, Marketing Director at m.u.t.
‘The ThermoVision A40 does all the measurements’, says Hagedorn, ‘and its measurement accuracy and reliability are excellent. But above all, there is no need for a camera with a cooled detector for such applications as waste bunker inspections: the A40-M has an uncooled detector and needs virtually no specific maintenance.’
Peter Smorscek works at FLIR Systems, Belgium.
e-mail: Peter.Smorscek@flir.be
