Spark extinguishing systems detect initial ignition in suction and conveying systems and produce an instant water curtain via automatic extinguishing feature in order to smother smoldering particles. These systems are recommended for use in areas where combustible materials are pneumatically transported and where there is a high risk of fires or dust explosions due to sparking or smoldering particles. As a rule, the extinguishing process occurs without interrupting operations.
A fully automatic spark extinguishing system consists of spark detectors, a control panel and an automatic extinguishing unit. Sparks travelling through the duct of the conveying system are instantly identified by the infrared spark detectors mounted flush to the wall of the duct. The spark detector sends a signal to the control panel which then triggers the solenoid valve of the automatic extinguishing unit, while simultaneously activating an audible alarm. The extinguishing water is released after milliseconds and injected into the duct via the strategically placed and patented flat spray nozzles creating a wall of water covering the entire cross section. The glowing particles are conveyed into the water spray curtain. Immediately afterwards the solenoid valve closes automatically. The complete detection and extinguishing process normally operates during production in order to eliminate expensive downtimes. Depending on the amount of potential ignition sources it is also possible to have the conveying machine automatically shut down.
The highly advanced Minimax infrared detectors are engineered for the immediate identification of sparks in industrial environments. The detector is flush mounted with the inside wall of the duct and responds to the infrared radiation generated by passing sources of heat, i.e., sparks or glowing embers. The detector continuously checks the correct function of its electronics. An additional spark test detector system is available to monitor visibility. Any faults identified are automatically relayed to the control panel notifying plant personnel. In areas where high ambient temperatures are expected, flexible temperature resistant fibre optic cables are used to thermally separate the electronic components of the spark detector from these hot areas. For conveyor systems which are not completely enclosed, e.g., conveyor belts, special spark detectors insensitive to daylight can be installed.
Automatic extinguishing unit
Upon receipt of a signal from the spark detector, the control panel activates the quick acting solenoid valve of the automatic extinguishing unit releasing a minimized quantity of extinguishing water. The water is injected by means of the unique fl at spray nozzles engineered for the conditions in conveying systems. It creates a water spray which covers the entire cross section of the duct. Conventional nozzles, though, can only fill the cross section completely with the help of turbulences in the duct. This requires a certain length of duct. In the installation this means longer necessary distances between the position of nozzles and downstream equipment to be protected. Distances, which are not available very often. In ducts without power venting only gravity is the driving force and, consequently, no turbulences occur. In such chutes, the spray pattern of conventional nozzles will completely fill the section of the duct only if more than one nozzle is installed, whereas with the Minimax flat spray pattern nozzle one nozzle will be sufficient in most cases. In Minimax systems, the flow detector is not installed at the water supply, but rather at the automatic extinguishing unit. This allows plant personnel to identify problem zones easily. The stainless steel material and the flush construction of the Minimax flat spray nozzle increase its durability against plugging and abrasion even in the most severe environments. The ball valve as part of the valve unit can also be monitored electronically to ensure that it is always in the correct operating position.
The Minimax pressure booster system, consisting of a centrifugal pump and a diaphragm pressure vessel, is the most cost effective and efficient means of increasing the water supply pressure if the minimum pressure required cannot be provided by an existing sprinkler system or a service water supply. The diaphragm pressure vessel supplies water with sufficient pressure immediately upon activation of the automatic extinguishing unit. The centrifugal pump automatically supplies the pressure vessel if the water pressure drops below a specified value. Even in the unlikely event of pump failure, several extinguishing impulses from the diaphragm pressure vessel are possible. Optionally, a monitoring device is available to detect a broken membrane inside the diaphragm pressure vessel.
As a rule the coal is stored outside at a dump without protection against humidity and damp. Coal bunkers on the other hand offer the option of dry-storing the fuel. Frequently both storage options are found at a fossil fuel power station.
Spontaneous ignition of coal
Potentially explosive atmospheres in coal bunkers due to coal dust
In order to provide fire protection for coal storage areas, extinguishing monitors are used, which combat fires from a safe distance and cool facilities at risk of ignition as a preventative measure. Depending on the version, the monitor can be aligned with the target either manually by remote control. Besides this a hydrant system is recommended for outside. Thermal cameras are used for monitoring which make the build-up of heat in coal dumps visible. In the coal bunker on the other hand gas emission detectors are used which react to escaping carbon monoxide in the event of fire.
Filter systems are used whenever the production process generates fumes, or when dusts are released through abrasion. Fine dusts occur for example, when milling or cutting plastics or when processing other materials.
Highly flammable dust in the filter bags
Carbon dioxide extinguishing systems are ideal for protecting filter housings against fires. In the case of metal extraction, however, the Oxeo extinguishing system using the argon extinguishing agent is the right choice to preclude interactions of the extinguishing agent with combustible metal. A fire detection system will trigger the extinguishing system.
During the entire production process, the raw materials, auxiliaries and consumables are transported to the next processing stations through enclosed or open conveyor belt systems.
Overheated roller bearings
Sparks generated during maintenance or welding works
Spontaneous combustion of the material to be conveyed
Deluge systems are ideal for protecting conveyor belts against fire, as the rapid spreading of fire requires immediate and large-scale activation or extinguishing across the entire protected area. Minifog ProCon water mist extinguishing systems are an efficient alternative for the direct protection of conveyor belt systems. A significant advantage is that this system uses considerably less extinguishing water compared to deluge systems. Detection of fires and triggering of the extinguishing system is via a fire detection system equipped with UniVario flame detectors and multisensor fire gas detectors.
The areas where flammable materials are pneumatically extracted or transported presentan increased risk of fire. This particularly applies to the material mix in the extraction and conveyor systems.
Sparks, hot particles or glowing embers in the processing machinery that penetrate into the conveyor systems
Function-monitored spark detectors respond reliably and immediately to the infrared radiation of passing ignition sources. They transmit a signal to the fire detection system, which consequently activates the solenoid valve of the automatic extinguishing systems within milliseconds. The extinguishing water is released through self-closing nozzles into the conveyor flow. The glowing particles fly into the water mist formed by the extinguishing nozzle and are thus extinguished. Immediately afterwards, the solenoid valve closes automatically.