In the field of high-temperature flue gas filtration, although organic fiber filter media are widely used, their temperature resistance limit is usually no more than 280℃. When the flue gas temperature exceeds 300℃, or even reaches above 500℃, organic fibers are no longer sufficient, making inorganic fibers and ceramic filter media the inevitable choice.
The common advantages of inorganic filter media lie in their excellent high-temperature resistance, good chemical stability, and dimensional stability. However, they also face their own limitations—high brittleness, difficult processing, poor thermal shock resistance, and high cost. Correctly understanding the characteristics of various inorganic filter media and making reasonable selections based on operating conditions is a key aspect of high-temperature dust removal system design.
I. Glass Fiber Filter Media
Glass fiber is one of the earliest inorganic fiber materials applied in high-temperature filtration, and its excellent cost-effectiveness has earned it an important position in industrial dust removal.
Medium-alkali glass fiber (C-glass) has a high sodium oxide content, exhibiting good acid resistance and some water resistance. Its long-term operating temperature is 260℃, and it is mainly used in acidic flue gas conditions in chemical and metallurgical industries. Alkali-free glass fiber (E-glass) has extremely low sodium oxide content, superior electrical properties and mechanical strength, and a long-term operating temperature up to 280℃, capable of withstanding instantaneous temperatures up to 350℃. High-silica glass fiber is a high-end variety of glass fiber, with its silica content increased to over 96% through acid leaching. It can operate continuously at temperatures up to 900℃, making it the glass fiber product with the best temperature resistance currently available.
The main advantages of glass fiber filter media are its low price, dimensional stability, and good corrosion resistance. It has the lowest cost among all high-temperature resistant filter media, making it suitable for large-scale industrial applications; it experiences almost no thermal shrinkage at high temperatures, maintaining its geometric shape over a long period; and it has good resistance to most acidic gases.
However, the limitations of glass fiber are also prominent. The biggest problem with glass fiber is its high brittleness; the fibers are prone to breakage when repeatedly bent, making it unsuitable for pulse-jet cleaning —the repeated impact of high-pressure airflow accelerates fiber breakage. Furthermore, the smooth surface of glass fibers results in poor dust adhesion, causing the filter cake to easily detach during cleaning, leading to a surge in instantaneous emission concentration. Therefore, glass fiber filter media is typically used in dust collectors with reverse-jet cleaning or as a reinforcing skeleton in composite filter media.
II. Basalt Fiber Filter Media
Basalt fiber is an inorganic fiber material made from natural basalt through high-temperature melting and drawing. In recent years, it has gained increasing attention in the field of high-temperature filtration.
Basalt fiber can operate at temperatures up to 300℃, with an extreme temperature reaching 860℃. As a natural mineral fiber, it is non-combustible, will not burn in a flame, and does not produce toxic fumes. Its acid and alkali resistance is superior to glass fiber, exhibiting good tolerance to most acid and alkali media, and it also has good water resistance and better stability in high-humidity flue gas environments.
The main advantages of basalt fiber lie in its natural mineral source, relatively environmentally friendly production process, abundant raw material resources, and alignment with sustainable development principles. Its temperature resistance is superior to glass fiber, and its price falls between glass fiber and ceramic fiber, offering good cost-effectiveness. Compared to glass fiber, basalt fiber exhibits better wear resistance, performing better under certain high-wear conditions.
Similar to glass fiber, basalt fiber also suffers from high brittleness, low elongation at break, and limited bending resistance, which restricts its mechanical life under pulse cleaning conditions. In European industrial practice, basalt fiber is often used in combination with organic fibers to balance temperature resistance and mechanical strength.
III. Ceramic Fiber Filter Media
Ceramic fiber is one of the inorganic filter media with the most outstanding temperature resistance, widely used in ultra-high temperature flue gas filtration and special operating conditions.
Quartz fiber, made from high-purity silica, can continuously operate at temperatures exceeding 1000℃, exhibiting excellent thermal shock resistance and an extremely low coefficient of thermal expansion. Silicon carbide fibers can operate at temperatures up to 1200℃, exhibiting excellent wear resistance and oxidation resistance, making them suitable for high-temperature and high-wear conditions. Alumina fibers can operate at temperatures above 1400℃, possessing extremely high melting points and chemical stability, but are more expensive. ABS fiber, developed by 3M, is a composite ceramic fiber with a continuous operating temperature up to 760℃, maintaining good temperature resistance while offering good flexibility and processability.
Ceramic filter media mainly come in two forms: fiber felt and sintered ceramic membranes. Fiber felt is a nonwoven felt made by needle-punching or bonding ceramic fibers, possessing high porosity and good air permeability, but with relatively limited filtration accuracy. Sintered ceramic membranes are porous membranes formed by sintering ceramic particles or fibers at high temperatures, possessing precise pore size distribution and extremely high filtration accuracy, enabling highly efficient capture of submicron-sized particles, with emission concentrations consistently below 1 mg/Nm³.
The core advantage of ceramic filter media lies in its superior temperature resistance and chemical stability, being virtually unaffected by acidic or alkaline media. However, its limitations are also quite prominent: poor thermal shock resistance, with drastic temperature changes potentially causing filter element cracking; difficult processing, making it hard to manufacture complex geometries; and high cost. In practical engineering, a gradient structure design is often adopted—using fiber felt as the matrix and coating the surface with a thin layer of ceramic membrane, ensuring both filtration accuracy and maintaining good thermal shock resistance.
Metal fiber filter media is an inorganic filter material that has seen rapid development in recent years, finding applications in specific fields due to its excellent mechanical properties and thermal shock resistance.
Stainless steel fibers mainly include grades such as 304, 316, and 310S, with operating temperatures reaching 450℃, 550℃, and 600℃ respectively. Iron-chromium-aluminum fibers can reach operating temperatures of up to 800℃, exhibiting excellent oxidation resistance and high-temperature strength. High-temperature alloy fibers such as Inconel and Hastelloy can reach operating temperatures above 1000℃, but are expensive and only used in special harsh conditions.
The core advantage of metal fiber filter media lies in its high mechanical strength, capable of withstanding repeated impacts from high-pressure pulse cleaning without easily being damaged. Its excellent thermal shock resistance allows it to maintain structural integrity even under drastic temperature changes, a quality unmatched by ceramic filter media. Metal fibers also possess good electrical conductivity, offering unique advantages in applications requiring anti-static properties.
However, metal fiber filter media also have significant limitations. Corrosion can still occur in strongly acidic or alkaline environments. The high density of metal fibers results in a significantly heavier filter cartridge of the same volume compared to other inorganic filter media, placing higher demands on the support structure. Furthermore, the high price of metal fibers limits their application in large-scale projects. In a coal gasification demonstration project in Germany, 310S stainless steel fiber filter cartridges achieved long-term stable operation at 450℃.
TrennTech, a leading supplier of high-temperature filter cartridges, has long been engaged in performance testing and application research of various inorganic filter materials. Their laboratory is equipped with a high-temperature hot-state filtration testing platform conforming to VDI 3926 standards, providing a scientific basis for filter media selection. Experience tells us that flue gas temperature, cleaning method, acid/alkali environment, and cost control are all factors that must be considered when selecting inorganic filter materials; currently, no single inorganic material can be suitable for all operating conditions. With the continuous advancement of industrial flue gas treatment technology, the performance boundaries of inorganic filter materials are constantly expanding, and new material combinations and structural designs will inevitably push high-temperature filtration technology to new heights.