Do Not Let the Ignition Source Take the Initiative
Modern spark detection and extinguishment systems are imperative as preventive fire protection systems. Basic precondition for danger potentials are combustible raw materials which are processed to small pieces.
Today‘s industrial productions are characterized by the fact that all parameters involved in the production process are precisely known and can be influenced at any time and in a controlled way so that the products can be continuously produced in a defined quality and quantity. Moreover, global competition requires an uninterrupted operation of the production plants to achieve the necessary economics.
Unscheduled events and their consequences are therefore to be excluded in any case. Such events include – first and foremost – fire and explosions that, besides property and personal damage, cause expensive production interruptions.
Permanently existing potential
Basic precondition for such danger potentials are combustible raw materials which are processed to small pieces, such as chips or dust in the wood based panel industry. Especially in filters and silos, these materials form an explosive atmosphere in connection with oxygen in the air, which is merely “missing“ an appropriate ignition source to cause a damaging fire or explosion.
As machine tools or dryers cannot be prevented from generating sparks or glowing embers, which are transported via pneumatic or mechanical conveying systems to downstream plant areas that are at risk of explosion, the potential for “unscheduled events“ exists permanently.
Extinguish before you get burned
The only possibility is to prevent a meeting of the three elements in a safe and controlled way. As an explosive atmosphere is not to be expected in the exhaust and transport ducts themselves, it would seem to be the thing to do is to nip impending fires and explosions in the bud by means of spark extinguishing systems.
GreCon from Alfeld, Germany, has continuously developed the basic principle of spark detection and extinguishment to a hightech fire protection system. Ignition sources are reliably detected by infrared spark detectors and extinguished by one or several downstream extinguishing nozzles in pneumatic and mechanical conveying systems or drop chutes before they reach filters and silos. The extinguishing nozzles, which are installed approximately four to seven meters downstream of the spark detectors, depending on the conveying velocity, generate a fine water spray within a split second which fills the entire cross section of the duct. When engineered properly, the ignition sources fly into the water spray and go out. The extinguishing valve closes immediately afterwards. The required water pressure of at least six bar is usually produced by pressure increasing units.
The amount of water used per extinguishment is so low that downstream plant areas and processes are not impaired. In 99 percent of all cases, extinguishment takes place without machinery shut-down and thus without interruption of the running production. The extraction and production systems will only be shut down if spark flight is registered for a longer time period or if a large number of sparks is detected within a short time.
Optimal detectors for any medium
The material flow is preferably monitored in the darkness of closed ducts and chutes. In such environments, the sensitivity of the infrared spark detectors, which are flush-mounted in the duct wall like the extinguishing nozzles, is the highest. According to the company, even small ignition sources, which pass the detectors at an average speed of 25 m/s, are reliably detected.
Besides these ideal installation situations, there are numerous “more demanding“ ambient conditions that are to be met by modified or new concepts and technical solutions to make spark detection possible also in these areas. Due to experiences of many years, GreCon is familiar with any requirements that might occur and has developed appropriate system components. Also areas with high process temperatures, as occur in drying processes, can be reliably monitored. For this, GreCon uses spark detectors, the electronics of which are protected against process temperatures of up to 600 °C by means of light polyps.
For the monitoring of open conveyors or other conveying systems where light ingress cannot be prevented special daylight spark detectors are part of the product range. These detectors ignore the infrared spectrum occurring in daylight or artificial light, which allows a reliable detection of relevant ignition sources nevertheless. Especially in drop chutes with dense material flows, an infrared light sensor that is installed on the chute wall is not sufficient. Therefore, the company developed a linear light polyp (LLQ) which is installed directly in the material flow and with which the optical detection of ignition sources can be substantially improved.
Thermal detectors, which trigger an alarm in case of temperature rises which are typical of fire, as well as conflagration gas detectors which also detect glowing embers that are located deeply in the material, complete the range of detectors developed by GreCon.
A short way to success
For plant areas in which the required “extinguishing distance“ cannot be realized or only realized by construction measures, the German-based provider has developed a new ultrahigh-speed extinguishment (UHS). This extinguishing device is based on a special high-speed solenoid valve and one or several full-cone nozzles. Thanks to a significant reduction of the reaction time from spark detection until the complete spreading of the water spray, the length of the required “extinguishing distance“ can be reduced to up to two meters.
For applications in which water extinguishment is impossible or not reasonable, GreCon developed special fire traps and diversion gates which interrupt or divert the material flow and thus reliably prevent ignition source and explosive atmosphere from meeting.
The engineering of a spark extinguishing system always starts with a detailed risk analysis to determine the most suitable system components for the protection of the customer‘s production plant, the German specialist assures.
User-friendly “blackbox“
The core of each spark extinguishing system is the processor-controlled control console. It collects all information from the individual spark extinguishing zones of a plant, which is the basis for all automatic measures and always available to the operator for evaluation. The events that are stored in the database exactly to the millisecond serve, above all, the purpose to visualize the alarm frequency in form of statistics and to supply information to identify the causes. The systematic structure of the software guarantees that extensions and changes of the spark extinguishing system can be easily implemented in an existing control console.
According to GreCon, the control console can be operated in an easy and intuitive way by means of a touch and slide display, known from modern mobile phones. Information can be selected and called up directly from the current screen content (touch). Details can be zoomed in by spreading fingers, without having to manoeuver through complicated and time-consuming menus. A big advantage is the possibility to represent complete flowsheets by zooming and shifting (slide). The patent-protected touch screen display can be easily retrofitted in all control consoles from the model 2003.
Graphic: GreCon
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