System Integration & Control Systems Design


Rockwell Automation’s high-­pressure mist fire suppression

November 2014 System Integration & Control Systems Design

The Rockwell Automation installations of automation instrumentation for controlling conveyor belt speed and sequencing can include a fire suppression system in the form of a Fogtec high-pressure water mist solution, designed to suppress underground fires caused by conveyor belt friction.

The system discharges a fine mist at 100 bar through directionally oriented nozzles installed on the conveyor belt structure. These nozzles are typically installed on the head and tail pulleys and idlers, where belt friction produced by a jammed pulley creates the most likely source of combustion. Sensor arrays, including smoke and temperature monitors, are rigged as process inputs to Rockwell Automation Allen-Bradley PLC modules that trigger the mist system and halt the conveyor upon detection of any environmental abnormality.

A high-pressure mist system provides numerous advantages over traditional sprinkler systems and gas alternatives in an underground mine environment. A water-based system is favourable in an underground setting, because it poses no inhalation danger to mine workers. With high-pressure water mist utilising about one tenth of the water requirements of conventional sprinklers (about 10 litres per minute versus 100 litres per minute), it eliminates the possibility of an underground flood caused by fire suppression, and places less demands on a mines’ sump pump networks. The fine mist also provides a superior ability to absorb heat from flames, lowering ambient air temperatures and providing air rinsing potential.

The system consists of stainless steel piping, Fogtec mist nozzles and automation instrumentation, a high-pressure water pump and a water storage tank with built-in straining and filtration facilities for the removal of suspended solids. The tank is designed to spray, in the event of interrupted replenishing, for at least five minutes.

The level of the water tank, as well as the pressure and flow of the pipe circuit, is also monitored by the PLC, which executes daily flushing maintenance to ensure dust does not collect on the nozzle perforations.

In South Africa, the main application of Fogtec is in fire suppression in underground conveyor installations, while in Europe, safety legislation dictates that such technology is utilised as fire suppression in transportation tunnels, which comprises Fogtec’s primary application in that region.

For more information contact JH Slabbert, Rockwell Automation, +27 (0)11 998 1000, raza_ssb@ra.rockwell.com, www.rockwellautomation.co.za



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