What materials are hose filters suitable for?

Hose filters are suitable for a wide range of powdery and dusty bulk materials that are transported pneumatically. They are effective in handling minerals, chemicals, building materials and other dry bulk materials. Suitability depends on material properties such as particle size, temperature and moisture content. This article discusses the applications of bag filters, the importance of material selection and situations where they are not the best solution.

What are the most typical applications of bag filters in different industries?

Hose filters are best suited for pneumatic conveying systems to receiving tanks and silos at the end of the plant, where dry, powdery materials are handled. They effectively prevent dust emissions into the air when material is transferred under pressure or vacuum. In the construction industry they are used for handling cement, lime and gypsum, while in the chemical industry they are suitable for filtering pigments, polymers and various chemicals.

Silo filters are essential in situations where material is being filled or unloaded from a storage silo. Pneumatic transport causes variations in air pressure that require a robust structure. Typical applications include loading and unloading of tankers, filtration of target de-dusting lines and intermediate storage of processes.

The range of materials is wide. In the mineral industry, bag filters handle quartz, sand, bentonite and kaolin. In power generation, they are suitable for filtering fly ash, bottom ash and coke. Applications in the chemical industry include polyethylene, polypropylene, starch and various metal oxides such as CaO, MgO and zinc dust. In the construction industry, cement, lime and gypsum are processed.

Pneumatic conveying systems benefit from bag filters, especially because of their easy maintenance. When integrated as part of an overall solution, they ensure efficient dust removal and keep air quality in line with requirements. In applications where several different materials are handled in the same system, standard-size strainers offer flexibility and compatibility.

How does the choice of material for a bag filter affect its suitability?

The construction materials and filter fabrics of the bag filter determine the type of bulk materials the device is suitable for. Temperature, humidity, chemical aggressiveness and particle size are key factors guiding the choice of materials. The right material ensures effective filtration and long service life even in challenging conditions.

The filter cloth is the most critical component, as it is in direct contact with the material to be treated. Polyester fabrics are suitable for many general applications where temperatures are maintained below 130 degrees Celsius. For higher temperatures, special fibres such as aramides or glass fibre are required, which can withstand temperatures of up to 250°C.

The effect of humidity is an important factor in material selection. Hygroscopic materials, which absorb moisture, can cause clogging of the filter fabric and reduce filtration efficiency. In such situations, surface-treated fabrics are needed to repel moisture and prevent the material from sticking.

The aggressiveness of chemicals requires careful material selection. Acidic or alkaline materials can damage certain filter fabrics. For example, strong alkalis require polypropylene or other chemically resistant materials. Particle size affects the tightness requirements of the filter fabric. Fine particles require a denser fabric, while coarser materials allow a thinner structure, which improves airflow.

The choice of materials for structural components is equally important. Stainless steel is suitable for most industrial applications, offering good durability and ease of maintenance. In special situations, other alloys or surface treatments may be required. The choice of sealing materials will affect the ability of the equipment to withstand pressure variations and prevent leakage.

Which materials are not suitable for hose filters and why?

Hose filters are not suitable for handling very sticky, moist or hygroscopic materials, as these cause the filter fabric to become clogged and significantly reduce filtering efficiency. Also, very hot materials, which exceed the temperature resistance of filter fabrics, require alternative solutions. Awkward shaped or large pieces are not suitable for pneumatic transport and therefore not suitable for tubular filter applications.

Sticky materials tend to accumulate on the surface of the filter fabric, forming permanent deposits that cannot be removed by conventional cleaning methods. This reduces airflow and increases pressure drop, ultimately leading to a reduction in system efficiency. Moisture-containing materials cause similar problems, especially when moisture condenses on the surface of the filter cloth.

Hygroscopic materials, which absorb moisture from the air, easily become sticky and adhere to the filter fabric. Sugar and certain salts are typical examples of materials that require special arrangements or alternative filtration methods. In these situations, heated filters or completely different filtration technologies can be considered.

Extremely hot materials with temperatures above 250 degrees Celsius exceed the temperature resistance of most filter fabrics. Such applications require either cooling systems prior to filtration or special filters designed for high temperatures. Ceramic filters or metallic filter elements may be alternatives in these demanding conditions.

Wet or liquid materials are not suitable for bag filters designed to handle dry, powdery materials. The presence of liquid causes clogging of the filter fabric and can damage the structure. In such situations, wet filters or other separation methods are required.

The handling of explosive materials requires special safety arrangements. Although hose filters can be fitted with explosion protection, certain materials may require completely different approaches to minimise the risks. Anti-static filter cloths and earthing are essential, but not always sufficient for handling the most sensitive materials.

Alternative solutions to these challenging situations include cyclone filters, wet scrubbers, electrostatic precipitators or hybrid systems that combine several filtration technologies. Pre-treatment of the material, such as drying or cooling, can also extend the suitability of bag filters.