1. Working Conditions to Confirm Before Selection
Filter bag selection starts with the process data, not with the fabric. Confirm the handling air volume, inlet dust concentration, particle size and stickiness, gas temperature and dew point, moisture and oil content, and the cleaning method (pulse jet, mechanical shaking or reverse air). These values determine the temperature class, fabric weight and surface treatment, and they also set the allowable air-to-cloth ratio.
2. Filter Media and Temperature Limits
- Polyester needle felt: the common choice for ambient-temperature duty, with a continuous limit around 130 degrees Celsius and good abrasion resistance.
- Membrane media: a micro-porous film is laminated to the base fabric so dust does not embed in the depth of the media, which suits fine and sticky dust.
- Anti-static media: conductive fibres are woven in for coal or aluminium dust, and the bag must be reliably earthed to the tube sheet.
- High-temperature media: used where gas temperature exceeds the limit of ambient media; check both short-term peaks and acid dew point corrosion.
3. Setting the Air-to-Cloth Ratio
The air-to-cloth ratio drives bag life. For ambient duty with coarse dust and effective cleaning, 1.0 to 1.2 m/min is workable; for fine, sticky or moist dust, reduce to 0.6 to 0.8 m/min. A high ratio forces dust into the media, cleaning becomes incomplete, pressure drop keeps rising and dust penetration risk increases.
4. Criteria for Replacement Timing
Do not replace bags on running hours alone. Use differential pressure as the primary indicator and confirm it with visual inspection. If pressure drop after cleaning keeps rising beyond the allowable value, the media is blinded or blocked. If visible dust appears at the stack, or pressure drop suddenly falls, a bag may be torn or dislodged. During shutdown, check the area around the bag mouth opposite the blowpipe and the bag bottom where it touches the cage, and decide whether the cause is mechanical wear, gas scour or chemical attack.
5. Field Measures to Extend Service Life
Keep the inlet temperature above the dew point with a margin to avoid condensation; hold cleaning pressure steady and avoid over-long pulse duration; pre-coat or run at low load at start-up to reduce the initial dust shock; and check cage welds, burrs and coating whenever bags are replaced, since a damaged cage will wear out new bags quickly.
6. Self-Check List After Bag Installation
Do not start up immediately after installation. Confirm that every snap ring is fully seated in the tube sheet hole, that each bag is centred under its blowpipe, that bags hang vertically without twisting, and that venturis are in place. A torch inspection from the clean-air side quickly reveals loose bags or bags resting on the hopper.
During initial operation, run at low load and log the pressure drop trend. A rapid rise indicates blinding or an excessive air-to-cloth ratio; a persistently low pressure drop together with visible dust at the stack points to a torn bag or a leaking bag seat.
7. Matching Different Cleaning Methods
Pulse jet cleaning uses a short compressed-air pulse that induces secondary air, giving strong cleaning on line but demanding good flex resistance from the media. Mechanical shaking is simple and suits small units, but cleaning is uneven and the lower part of the bag tends to collect dust. Reverse air is gentle and suits low-stickiness dust, though the cleaning cycle is longer.
- Pulse jet: keep pulse pressure stable and align blowpipes with bag centres to avoid off-centre wear.
- Mechanical shaking: control amplitude and frequency to limit chafing between bag and cage.
- Reverse air: verify reverse flow and damper sealing, otherwise pressure drop creeps up.
References
- GB/T 6719-2009 Technical requirements for bag filters
- GB 16297-1996 Integrated emission standard of air pollutants
- GB/T 16845-2017 Dust collector — Terminology
- HJ 2020-2012 Technical specification for bag filter engineering
