Baghouse Filter Guide: Working Principles, Types, and Efficiency Factors

Author: Michael Klepik, Chief Executive Officer

Bags gradually clog and require periodic cleansing. The pollutants accumulating on the fabric increase resistance, making filtration less effective. Therefore, regeneration is a necessary procedure. With timely cleaning, the system operates smoothly without pressure drops, maintaining a high filtration level.

Automatic methods are generally the simplest and most effective. How does a baghouse filter work with a pulse jet system?

In the clean air chamber, pneumatic tubes connected to diaphragm valves of the pneumatic system are located at the top. The valves are installed on receivers that supply compressed air for the pneumatic pulse.

Air is pumped into the receivers by a compressor. Periodically, the valve activates, air enters the pneumatic tube, and then is distributed through nozzles along the bag.

The bag shakes, and the pores between the fabric fibers are blown out. Pollutants fall into the collection hopper.

Pulse jet cleaning system is the most efficient automatic method. In addition to shaking off contaminants from the walls, it restores the original sizes of the openings between the fabric fibers.

Waste from the collection hopper is removed in the following ways:

• By opening a manual dust slide gate;
• Using a mechanical “double dump” valve;
• Through an automatic “rotary airlock” valve.

In standard configurations, devices are equipped with manual slide gates for waste removal.

To use a baghouse filter working with pulse jet cleaning, a pneumatic system operating at sufficient pressure to fill the receiver is required. This method allows for a constant level of purification without the need to stop for maintenance.

Let’s look at how a baghouse works with a shaker cleaning system. Vibration is created by an electric drive. There is no need to temporarily stop the aspiration process. The equipment continues to operate as usual.

The shaking mechanism is integrated into the unit during its manufacturing. Subsequently, the equipment with a shaker mechanism operates automatically without the need for personnel intervention.

Dusty bags are shaken periodically using vibration. A vibrating plate with a shaker is installed in the center of the equipment housing.

The frequency and duration of the shaking are set by a controller mounted on the equipment housing. The duration and interval between shakes are programmable, with previous settings retained even after a power outage.

The vibratory motor shakes the rack to which the bags are attached. Accumulated waste falls into the hopper or another waste disposal system and is then removed, making room for new dust.

For filtering large volumes of gas-air mixtures, reverse airflow cleaning is often used. How does a baghouse work with a reverse air system? The filtered medium is fed from the bottom into a wide and long bag, where particles fall due to gravity. According to a set schedule, the direct gas supply is turned off, and a fan creates a counterflow, driving the accumulated contaminants into a waste receiver. The advantages of this technology are its simplicity and high efficiency, as well as an almost continuous operating mode.

Since aerodynamic compression of the fabric bag occurs when the ventilation is reversed, the fabric walls are reinforced with spacer rings. The rings prevent the bag from collapsing completely, significantly enhancing the purification efficiency of equipment.

When choosing a regeneration method, the type of fabric, apparatus design, emissions characteristics, technological process, and other factors are important.

The main properties of the gas stream that affect the efficiency include filtration velocity, dispersion and concentration of contaminants.

Accurate quantitative and qualitative assessment of these factors allows for more informed decisions to improve contaminant filtration levels.

How does a baghouse system work depending on changes in filtration velocity? It has been established that as the filtration velocity increases, the degree of airborne particle extraction decreases. As the airflow velocity exceeds the optimal level, the displacement of particles from their deposition sites and their carryover by the gas stream intensifies.

To improve the degree of cleaning, it is advisable to maintain the specified filtration velocity by thoroughly eliminating harmful air leaks in the system, which significantly reduce the efficiency of particulate removal.

Industrial aspiration typically deals with polydisperse particles. The baghouse working principle ensures high efficiency in capturing particles with various degrees of dispersion. According to the main rule of filtration, particles of the same size fraction that make up the dust layer will not pass through it.

The decline in purification efficiency with increasing dispersion is explained by the fact that as particle sizes decrease, the hydraulic resistance of the apparatus increases. Consequently, the number of dynamic breakthroughs in the dust layer, as well as the actual flow rate of gases in the dust-free pores of the filter material or in the cracks forming in the layer, also increases.

When filtering aerosols with vastly different dispersions but identical hydraulic resistance, the degree of particulate removal is roughly the same and, with proper operation, exceeds 99% even for the most highly dispersed dusts (with particle sizes of 1 micron and less).

As the concentration of aerosol entering the fabric increases, the pollutant capture efficiency improves (particularly in the range up to 0.2 g/m³) because less time is required to form or restore a continuous dust layer.

A baghouse filter operation with higher pollutants concentrations and increased efficiency typically results in a higher residual dust load. When filtering highly concentrated pollutants, the operation involves higher hydraulic resistance or more frequent regeneration of the bags. In both cases, as is known, particulate removal effectiveness decreases.

When filtering gases with very low incoming dust concentrations, the process of forming and restoring a continuous dust layer is so slow that using conventional filter materials sometimes does not achieve the required level of
cleanliness.
In such cases, the following measures can be recommended:

• Use a thick, dense material (such as felt) with a large specific surface area of fibers, good dust-holding capacity, and high dust separation capability even in an unladen state.
• Perform regeneration of the filtration system as infrequently as possible, experimentally determining the optimal frequency for each specific case.
• Sometimes it is advisable to use material with an artificial dust layer. This layer can be created by pre-dusting the filter material.

When considering gas purification solutions, it is essential to ask: in what industry do baghouses work best? They are highly effective in a variety of industries due to their ability to efficiently capture and remove fine particulate matter from exhaust gases. Here are some key industries where devices are particularly beneficial:

• Control emissions from kilns, clinker coolers, and mills, ensuring compliance with environmental regulations and improving air quality.
• In foundries, steel mills, and other metal processing facilities, capture pollutants from smelting, casting, and grinding operations, protecting workers and reducing emissions.
• Woodworking shops and lumber mills capture sawdust and wood chips from cutting, sanding, and milling operations, ensuring a safer and cleaner work environment.
• In pharmaceutical manufacturing, the working of baghouse is essential for controlling particulate matter from tablet pressing, coating, and packaging processes, thereby maintaining product quality and worker safety.
• Control emissions from grain handling, milling, and food packaging operations, preventing contamination and maintaining product quality.
• In these industries, capture pollutants from crushing, grinding, and conveying operations, protecting equipment and ensuring regulatory compliance.

If you have any questions about how baghouses work, please contact us. Our specialists will provide detailed answers and help make the air cleaner!