Safe separation of quartz fine dust
The sensitivity regarding fine quartz dusts has grown considerably in the mineral processing industry in recent years. Against the backdrop of continuously stricter standards and limits, the requirements for filtration efficiency and safety are also growing. The Herding® Sinter-Plate Filter combines incomparably high filtration efficiency with outstanding wear resistance.
The generation of particulate emissions containing silica in various process steps of the mineral processing industry can hardly be avoided. Basically, such high-emission processes should be separated from other workplaces as far as possible. However, in the rather rough environment of mineral processing, this is rarely possible and in most cases hardly economically feasible. Therefore it requires individually designed filter systems for the dust extraction. This includes an efficient dust collection directly at the point of emission, often in combination with measures to minimize open cross sections at dust-generating machines or transfer points of conveying systems.
The standardization bodies in the national and international context have harmonized the limit values for quartz fine dust emissions. The aim is to sustainably minimize potential personal exposure to respirable crystalline silica in the workplace.
The fineness of the mineral dusts to be separated, in combination with their abrasive properties, places high demands on the filter technology. Conventional systems working with cartridge or bag filter media based on deep bed filtration can prove inefficient. The fine fraction irreversibly penetrates into flexible, woven or needle-felt filter media and clogs them, leading to increasing pressure drop and in consequence to instable and insufficient air flow. The abrasive nature of the mineral particles also wears out quickly such filter media. This can result in dust breakthroughs which are possibly leading to production losses. Therefore it is essential to appropriately evaluate existing filter systems and compare them objectively to filter systems that operate on the basis of surface filtration.
Pure surface filtration
Contrary to conventional filter systems based on depth filtration, the patented Herding® Sinter-Plate Filter enables pure surface filtration. This property, and thus no affinity for the penetration of fine particles, is achieved by a coating with PTFE as a filter-active layer that is homogeneously embedded in the surface of the PE rigid body. This combination of an absolutely robust sintered structure and the homogeneously embedded coating with PTFE makes the Sinter-Plate Filter so effective. Abrasive mineral substances such as quartz dust get separated consequently reliably without damaging the filter-active layer.
The resistant filter medium is also not subject to the risk of permanent flexing of other filter media, which occurs particularly with high mechanical stresses from alternating pressure loads. Filtration-related wear is thus reduced to a minimum and the filter-active layer remains intact over the entire life cycle and, as experience has shown, undamaged.
The described properties of pure surface filtration in combination with energy-optimized compressed air pulse cleaning result in an almost constant differential pressure behavior of the filter and thus constant operating conditions over the entire life cycle of the filter systems. The extraction thus remains stable and safe with service lives of up to 15 years and more.
Independent verification of suitability for air recirculation
Measurements by independent institutes on Herding® filter systems have tested the A dust fraction according to DIN EN 481. According to this, the manufacturer’s filter systems with the rigid Sinter-Plate Filter have clean gas concentrations for fine quartz dust of less than 0.005 mg/m³. This confirms that Herding® filter systems with the integrated Herding® Sinter-Plate Filter can also be used for air recirculation in application with exposure to fine quartz dust.
The possible recirculation mode and heat recovery by recirculation of the filtered exhaust air make an important contribution to increasing efficiency and saving energy. In addition, retrofit solutions from Herding offer the attractive possibility of upgrading existing systems to an up-to-date level and thus optimizing work and process safety.
Author:Dipl.-Ing. Jörg-Armin Schulz, CSO/CMO, Herding GmbH Filtertechnik
Features of Herding® Sinter-Plate Filter
• Pure surface filtration
• Constant operating conditions and flow rates
• Low maintenance costs due to rigid filter medium
• Wear-resistant filter element with a service life > 15 years even with abrasive dust
• Low space requirement due to compact, customized system design
• Highest availability and fast amortization
• Energy-efficient recirculation operation possible even with respirable quartz fine dust
• Extremely low guaranteed clean gas values << 0,1 mg/m³
Quartz fine dust ...
... is usually referred to as “fine quartz dust content” and is the PM4 fraction of the total dust spectrum or the A fraction of the total spectrum. Quartz fine dust is listed in the EU Cancer Directive because the airborne, alveolar fraction poses a significant silicosis and cancer risk. The size of these alveolar particles is described as having an aerodynamic diameter of less than 10 µm.
