The treatment of dust particles, SO2, and NXO in industrial flue gas has led to the application of dust removal filter materials, and the "ultra-low emission" transformation of various industries has promoted the rapid development of dust removal filter materials. As dust removal filter materials and dust removal technologies have flourished, various industrial dust removal filter materials and dust removal equipment have been updated and iterated, gradually moving towards digitalization, automation, dataization, and intelligence.

In 2023, the national ambient air quality will maintain a long-term positive trend. The average concentration of fine particulate matter (PM2.5) in cities at or above the prefecture level is 30 micrograms per cubic meter, which is nearly 3 micrograms per cubic meter better than the annual target. The proportion of good days nationwide is 85.5%, and after deducting the days with abnormal dust exceeding the standard, it is 86.8%, which is 0.6 percentage points better than the annual target.

As the requirements of national air control become more and more stringent, and emission requirements enter the "single digit" era, the basic performance and functions of filter materials have quietly changed. In terms of traditional filter materials and dust removal equipment structures, a variety of new materials and new application technologies have evolved. This article will give a comprehensive introduction to the current development status of industrial dust removal filter materials and discuss new development directions that have begun and will emerge in the future.

Dust removal principle and basic requirements for filter materials

1 Basic principle of dust removal

The main principle of dust removal is to achieve gas-solid separation or gas-liquid separation through a series of physical/chemical effects. Some dust collectors with special functions can also achieve gas-gas separation or gas-solid-liquid three-phase separation. Dust removal filter material is the core component of dust removal work and the key material for dust collectors to ensure good operation. The performance of the filter material directly determines the dust removal effect.

The main principles are as follows:

(1) Physical interception: The gaps between the filter cloth fibers or the gaps between the dust adsorbed on the filter cloth surface will separate the dust larger than the gap diameter.

(2) Inertial collision: When the dust-laden gas passes through the filter cloth, the larger dust particles collide with the fibers due to inertia and are captured.

(3) Adhesion: When fine dust particles flow around with the airflow, if the radius of the dust is greater than the distance from the center of the dust to the edge of the filter cloth, the dust is adhered to the filter cloth and captured.

(4) Diffusion: For extremely fine dust particles, Brownian motion increases the chance of contact with the filter cloth, so that the dust is captured.

(5) Electrostatic effect: Dust particles collide with each other to generate static electricity. If the dust and the filter cloth have opposite charges, the dust is adsorbed on the filter cloth, achieving dust capture and improving dust removal efficiency.

(6) Gravity: When the air flow speed suddenly decreases or the air flow changes direction, larger dust particles are separated from the gas under the action of gravity and inertia, and the dust removal effect is achieved through sedimentation.

2 Basic performance of dust removal

The effect of dust collector operation is mainly judged by comparing the basic performance indicators of dust removal and filtration. In general, the basic performance of dust collector filtration includes the following aspects:

(1) Filtration performance: large dust holding capacity, and a certain permanent dust holding capacity can be retained after cleaning to maintain a high filtration efficiency. Good air permeability, small pressure loss, and smooth airflow.

(2) Physical durability: good wrinkle resistance, wear resistance, heat resistance, and corrosion resistance, high mechanical strength, and ensures the stability of filter materials in harsh environments. Stable size and not easy to deform.

(3) Cleaning characteristics: low hygroscopicity, good peeling property, easy to clean, ensuring that dust does not easily adhere to the surface of the filter material, and easy to clean.

(4) Economic practicality: long service life and reduced replacement frequency. Low cost, reasonable price, and economic benefits.

Industrial dust removal types

There are many types of industrial dust removal, which can be mainly divided into two categories: dry and wet.

Dry dust collectors, such as bag dust collectors, cartridge dust collectors, desulfurization dust collectors, cyclone dust collectors, electrostatic dust collectors, etc., mainly separate particulate matter from gas through filtration, inertia, electrostatic dust removal, etc., are suitable for different scenarios and needs.

Wet dust collector: such as wet cyclone dust collector, wet electrostatic precipitator, wet scrubber, etc., use water film or liquid spray to mix the particulate matter in the gas with water to achieve the purpose of dust removal, and are often used to deal with high temperature, high humidity, viscous, and easy-to-adhere dust. In addition, there are some special types of dust collectors, such as activated carbon adsorption dust collectors, which are mainly used to deal with organic pollutants.

At present, the most common dust removal technologies are bag dust removal or electric/bag composite dust removal. Bag dust removal mainly uses woven or non-woven methods to make fibers into felt filter materials, and finally forms dust filter bags through the bag-making process. The dust filter bags are installed in bag dust collectors. Through the filtering effect of the filter bags, the dust particles in the flue gas are removed to achieve the dust removal effect.

Recycling and reuse of filter materials

With the increasing awareness of environmental protection and the demand for resource recycling, the recycling and reuse of filter materials has become increasingly important. The recycling and reuse of filter materials is an important part of environmental protection and resource recycling, which not only helps to reduce environmental pollution but also saves resources and reduces production costs. There are various ways to recycle and reuse dust removal filter materials, which can be summarized into the following categories:

1 Cleaning and utilization

Primary cycle: dust removal and cleaning of high-resistance filter bags. For high-resistance failure caused by condensation, oil sticking, sticking, etc. of filter bags, they can be cleaned and reused after confirming that other performance is acceptable.

2 Material reuse

Secondary cycle: reuse of old filter bag filter cloth. For filter bag failure caused by local mechanical damage or structural damage, it can be cleaned, cut, and sewn for reuse to achieve secondary recycling.

3 Fiber extraction

Primary recycling: reuse of old filter bag fibers. The filter bag performance has degraded and cannot be reused, but the fiber material has not been abnormal or damaged. It can be washed and broken up as reused fiber to achieve primary recycling.

4 Material extraction

Secondary recycling: high-quality resin recycling and reuse. The fiber performance has degraded and cannot be used directly, or the composite fiber filter material cannot be directly reused. It can be purified by chemical methods and then remade to form new recycling materials to achieve secondary recycling.

5 Thermal energy recovery

Energy utilization: incineration to recover energy. If the filter bag material structure is destroyed or the material molecules have lost their utilization value and cannot be reused, or the filter bags are of low value and not worth recycling, they can be incinerated to recover heat energy.

Outlook

Industrial dust removal filter materials in my country are developing rapidly. Industrial dust removal products and filter materials for different industries are gradually developing towards intelligence, specialization, functionality, and energy saving. The main specific manifestations are as follows:

(1) After long-term development, the fiber material selection, fabric structure, filtration method, etc. of filter materials have basically taken shape, and the industry has basically formed an application consensus and a stable production process.

(2) The "ultra-low emission" requirement promotes the advancement of filter material technology, and new filter material designs and new filter material processes continue to emerge; composite and special functional filter materials and products are becoming more mature and popular, and the technology is constantly updated and iterated.

(3) Integrated, functional, digital, and intelligent control systems, machine applications are constantly being demonstrated, which is a new research and development direction for filter materials.

(4) The recycling and reuse of waste filter materials have been put on the agenda and have begun to take shape, and there is still a long way to go for resource utilization and harmless treatment.

(5) Energy saving and carbon reduction, high efficiency and low resistance, intelligent monitoring, ultra-high temperature, and ultrafiltration materials will become the future development direction of filter materials.