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Baghouse Filter Bags: Structure, Types of Materials, Working Principle, Cleaning of Bags, Calculation

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Baghouse filter bags are the primary components of dust collection systems. It is through them that industrial gas is purified from contaminants.
Baghouse socks have found applications in various industrial sectors, including:
  • Cement silos.
  • Asphalt and concrete plants.
  • Mineral mining.
  • Laser cutting.
  • Agriculture.
  • Wood processing.
  • Food production.
  • Pharmaceuticals.
  • Chemical industry.
  • Casting and metallization.
  • Rubber.
  • Plastics.
Bags for dust collection systems ensure a maximum level of purification, up to 99.9%, from various types of pollutants.

Baghouse Filter Bags Structure

Bags for the baghouse have a relatively simple structure. They consist of filtration material and a frame.

The frame is essential to expand the bag, increase its volume and working area, and prevent the collapse of the fabric. Depending on the frame type, the air purifying elements come in two variations — round and flat. The conventional round-framed filter is used in productions with high pollutant loads and productivity. However, flat-framed bags are increasingly being ordered for production as they take up less space in the filtration system, consequently reducing the overall size of the installation.

However, the filtration fabric, whether woven or non-woven, forms the basis of baghouse filter socks. The selected substance determines the substances the system will handle, the efficiency of purification, its speed, and various other performance indicators.

Working Principle

Dusty gas passes through the fabric, and particles are captured on the threads and fibers. The greater the fiber density, the more effectively pollutants will be trapped. Clean air exits either outside or inside to preserve warmth.

The precoating process for baghouse bags involves applying a thin layer of a special substance to the surface of the components before the unit begins operation. This coating can enhance adhesion to pollutants, reduce clogging, and increase air purification efficiency. Pre-coating can be particularly beneficial in situations where particles have specific chemical properties or when treating air with a high concentration of heavy or sticky particles.
Industrial Filtration System Schematic
Industrial Filtration System Schematic

Cleaning of Bags

To clean baghouse filter bags of accumulated contaminants, initiate the regeneration process. Several regeneration systems are available, including pulse-jet cleaning (pneumatic cleaning), vibration cleaning, and mechanical (manual) cleaning.
  • Pulse jet cleaning or pneumatic cleaning is one of the most effective types of regeneration. A strong stream of air from the outside enters inside, causing them to expand, and contaminants settle in the hopper.
  • Vibration cleaning involves mechanically shaking the sock. Reciprocating movements occur within the bags themselves, not as a result of the housing's vibration.
• Mechanical cleaning (also known as manual cleaning) occurs through a shaking mechanism (a special handle) that is manually operated.
The choice of cleaning method depends on production volumes, area, speed, etc.

Types of Materials

Filter materials come in various types, each with its own characteristics and suitability for specific applications. Here are some common types:

Woven Components:
  • Fiberglass elements are durable and resistant to high temperatures, making them suitable for applications involving hot gases and aggressive chemical environments.
  • Polyester elements offer good chemical resistance and are effective in capturing fine particles, making them suitable for general industrial applications.

Non-Woven Components:
  • Felted fabrics are non-woven materials made by mechanically bonding or needling fibers together. They provide good particle retention and are commonly used in applications with moderate temperature conditions.
  • Needle felt bags are created by interlocking fibers through a needling process. They offer high efficiency in particle capture and are often used in high-temperature applications.
  • Acrylic elements are recognized for their excellent resistance to acids and alkalis. They are suitable for applications where chemical resistance is crucial.
Filter fabrics
Filter fabrics
Composite Materials:
  • PTFE-coated (polytetrafluoroethylene) components offer excellent chemical resistance and withstand extreme temperatures. They are often used in industries dealing with corrosive gases and high-temperature processes.
  • P84 components are crafted from a polyimide substance and are known for their thermal stability at elevated temperatures. They are commonly used in applications involving incineration or metal smelting.
Blended Materials:
  • Polyphenylene Sulfide (PPS): PPS baghouse bags are a blend of synthetic fibers, offering good chemical resistance and stability at high temperatures. They are suitable for applications in industries such as power generation. Polypropylene baghouse bags are known for their durability and resistance to various environmental conditions.

The choice of baghouse filter material depends on factors such as the temperature of the gases, chemical composition, particle size, and the specific requirements of the industrial process. Each type has its advantages and limitations, making it important to select the most appropriate products for the given application.

How to Choose the Material?

As mentioned, the efficiency and performance of gas cleaning, as well as the overall functionality of the collector, depend directly on the fabric of the baghouse sock. When selecting fabric, it is important to consider numerous parameters:
Manufacturers always tailor their products based on specific requirements. The production of air purifying elements is approached individually, considering the particular task at hand.

Pleated Filters

Pleated baghouse filters feature a pleated structure, wherein the media is folded to enhance the surface area. Cartridge air purifiers are compact and typically consist of a cylindrical shape with flat or conical side surfaces.

The pleated structure reduces pressure drop, potentially leading to energy savings in the overall air purification system.

Furthermore, the pleated structure enables a higher dust-holding capacity, signifying that the bags accumulate and retain a larger volume of dust before requiring replacement. This characteristic leads to less frequent changes of air purifying elements, reducing maintenance costs and downtime.
Filter fabrics
Filter fabrics

Calculation

Calculating bag parameters involves several steps and factors to determine optimal settings for a specific system. Here is a general set of steps:

1. Defining Requirements:
Determine the volume of gas passing through the system per unit of time (Q) generated by your process.

2. Identifying Dust Characteristics:
Examine the characteristics of pollutants, such as particle size, concentration, and physicochemical properties.

3. Choosing Component Type:
Determine the type of filtration products to use, such as bags or cartridges. This decision may depend on the characteristics of your process and dust collection requirements.

4. Calculating Filtration Area:
Use the air volume and dust concentration parameters to determine the required filtration area. This can be calculated using the formula: Area = (Q * C) / (V * η), where Q is the air volume, C is the dust concentration, V is the air velocity, and η is the efficiency.

5. Determining Pressure Drop Resistance:
Calculate the pressure drop resistance across the filter. This is a crucial parameter for selecting the fan and determining the energy consumption of the system.

6. Selecting Material:
Select the suitable material based on the characteristics of the contaminants and the requirements of the process.

7. Choosing Regeneration Type:
If using a regenerable system, select the appropriate regeneration method: pulse-jet cleaning, vibration cleaning, mechanical cleaning, etc.

8. Consulting with Professionals:
For complex systems and processes, it is always recommended to consult with engineers or experts in the field of air purification.

The number of bags in a baghouse filter depends on the air volume, dust concentration, required filtration efficiency, and system characteristics. Manufacturer recommendations and specific system parameters are crucial for determining the optimal number of bags.

Each of these steps requires a detailed analysis and may vary depending on the specific conditions of your process.
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We always make extremely precise calculations and provide assistance in choosing the optimal cleaning systems, which usually takes 1 to 2 days.
Head of Engineering,
Vladimir Nikulin
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