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Preventive Fire Protection in Tobacco Processing Source from: Tobacco Asia 07/03/2013  Since the first tobacco plants came to Europe about 500 years ago, smokers have been enjoying tobacco. The tobacco processing industry does not like the embers that occur in the processing of different tobacco products. The risk of fire in tobacco dust is, however, only natural. Tobacco is a natural product which can be contaminated with small stones and sand which might strike sparks in mills and pipes. Even fermentation and frictional heat can heat up the tobacco to glow temperatures. All drying processes are also classic fire origins. Tobacco production in Germany is subject to German Food Law regulations and inspections and therefore special demands are placed on providing suitable extinguishing systems.
The majority of the processing industry relies on efficient machines. For this reason, the likelihood that local operating personnel would notice the smell of glowing embers is drastically reduced. But when the smoke has already permeated the production process, you can often do nothing but clean the production hall and the machines. However, in those cases in which fire occurs, control units and electronic components can be affected and this might cause long production standstills and high losses. This is why a modern spark detection and extinguishing system is imperative in today's tobacco processing industry. The big global tobacco players have been relying on GreCon's experience in the planning and execution of spark extinguishing and diversion systems for many years. The following article shows the use of GreCon spark detection and extinguishing systems in different applications. 1) GreCon spark detection with water extinguishing Dust that occurs in the primary tobacco processing is not yet flavored or aromatized. This dust can therefore be easily extinguished with water without having to worry about it sticking to the filter because the tendency to stick to the filter depends considerably on the tobacco's content of sugar and starch. 2) GreCon spark detection with fire trap If dust is extracted which is clearly prone to conglutinate (reconstructed or homogenised tobacco), a fire trap can be used instead of a water extinguisher. Upon detection of sparks, the trap is activated and the pipe leading to the filter is closed within 200 milliseconds. Simultaneously, the production line is stopped and the fan shut off. The sparks and glowing particles caught by the trap have to be removed manually. The alarm can be reset only after having opened the trap to prevent an unintended restart of the production process without first checking the fire trap. This principle of detection and closure of the pipe is especially suitable for processes in which the risk of sparks is very low (e.g. cigarette completion). By design, the GreCon fire traps are close to gas proof and ensure that glowing embers (and unwanted particles) are prevented from continuing in the primary process. As an additional precautionary measure, the fire traps can be combined with gas extinguishers using either carbon dioxide, nitrogen or argon – depending on the environment. In order to contain the gas, the extinguishment is implemented in conjunction with fire traps or shut off gates. Upon its insertion, the inert gas is to remain in the area to be extinguished for a period of at least 15 minutes to ensure that further influx of oxygen will be blocked. During the 15-minute inertization phase, the ongoing production will be halted. The processes described above have a very low material throughput. In most cases, the pipe dimensions are only DN100 to DN350. 3) GreCon spark detection with diversion gate If tobacco transport pipes are monitored, an extinguishing or closure of the pipe is not reasonable because the conveyed material quantity is too large. A water extinguishing would cause a choking of the transport pipe. In case of a closure of the pipe, a large amount of tobacco would accumulate upstream of the fire trap that would lead to a high fire load. In this case, diversion gates can be used if they can be installed on the pressure side (not suitable for installation on suction side). Glowing particles are diverted from the process without interruption of the production. The diversion gate is reset to its normal position after five seconds. The glowing particles are transported to a reject bin where they can be safely extinguished without influence on the production process. Diversion gates are used for the production of homogenized tobacco (e.g. binder, wrapper, filler). For the production of tobacco paper, tobacco is ground by hammer mills to dust of a median between 63µm and 10µm. To increase the capacity of the hammer mill, the flow rate is increased by means of compressed air. The spark detection system is positioned in the transport pipe between hammer mill and separator cyclone. In case of an alarm, the diversion gate is activated within 200 milliseconds to divert the material flow to the reject bin. To avoid the production of dust, water is injected into the refuse pipe and the extinguished material transported to the reject bin. If the material flow is diverted over a long period, it is recommended to stop the mill to check it. The period until hammer mill shut-off is adjustable by the operator. 4) Spark detection in hot areas In tobacco drying areas and the cooling conveyor and during flavoring there are high temperature processes. Hot areas exceeding 80° C are defined as "high temperature application". In these areas, spark detectors with fiber optic cables, facing the processed material, are used. Thus, the detector electronics can be installed in areas of low temperature. A reliable detection by means of fiber optic cables is feasible in temperatures of up to 360° C. 5) Areas of high material throughput In tobacco bale processing or pneumatic tobacco conveying processes, glowing embers may be buried by several layers of tobacco. It is recommended to use special detectors in these areas. FM 1/8-PM detectors achieve the highest sensitivity in the emission spectrum of burning tobacco and were developed specifically for the tobacco industry. In areas where high-pressure blowers increase the material throughput, the GreCon detectors are installed by means of welded mounting adapters which guarantee a secure fitting of the sensors in these transport environments. 6) Areas with light ingress Several processes in the tobacco industry are conducted via open systems where light ingress is likely to occur, such as conveyors, feeding hoppers and vibrating conveyors. In these cases, spark detectors (DLD) which are insensitive to daylight and detect a heat signature in the far infrared spectrum can be used. Due to the IR filters being used, these DLD detectors are not as sensitive as standard detectors. DLD detectors are the #1 choice on the clean air side of filters, where they reliably detect small glowing particles indicating a fire in the dust collector. 7) Areas with sticky materials The use of sticky materials in cigarette production (e.g. side-seam adhesive, filter adhesive, shellac, glycol, liquorice) may cause unwanted accumulations within the exhaust pipes. To prevent these unwanted accumulations from "blinding" (i.e. clogging) the sensors, they can be equipped with air purge adapters. A permanent air flow prevents the accumulation of material in the area of the sensor optics. The consumption of compressed air can be minimised by means of fine dosing valves. 8) Additional dangers in extraction systems Most of the extraction systems are subject to only few inspections. Maintenance in areas of fine dust deposits is mandatory. This dust represents an increased fire load in filters and cyclones. Therefore, all filters should be equipped with thermo sensors and a clean air monitoring system. Separator cyclones should, at least, have an outgoing air monitoring system. With these measures, fire can be indicated very quickly. Measurements in a filter system with clean air monitoring revealed a delay time of 20 seconds between release of the fire and detection. For ATEX zones, sensors and extinguishing devices of 1, 2 or 3 D categories and fire traps and diversion gates of 2 or 3 D categories are available. Enditem Related Updates |
