baghouse (baghouse)

A baghouse is the standard industrial dust collector used at recycling plants, foundries, cement works, and most other facilities that generate fine particulate matter. The baghouse is a sealed chamber containing dozens or hundreds of cylindrical fabric filter bags (or pleated cartridge filters) suspended vertically. Process air laden with dust is drawn through the chamber walls into the bag exteriors; the dust accumulates as a cake on the bag surface while clean air passes through the fabric and exits through the top of the chamber to atmosphere via an induced-draft fan.

Cleaning mechanism: Dust accumulating on the bag surface progressively increases the pressure drop across the filter. To maintain steady airflow, the dust cake must be periodically dislodged. Pulse-jet baghouses (the dominant modern design) inject a high-pressure burst of compressed air (typically 6-7 bar, lasting 100-200 milliseconds) into the bag interior every few minutes, briefly reversing airflow and flexing the bag to shed the dust cake into a collection hopper below. The pulse cycle is controlled to clean only a few bags at a time, so the baghouse continues to filter air through the remaining clean bags without interrupting the process.

Performance and design parameters: A well-designed pulse-jet baghouse achieves outlet dust concentration of 5-20 milligrams per normal cubic metre, well below the typical Indian SPCB limit of 50 mg/Nm3 for industrial sources. Filter bags are sized by 'air-to-cloth ratio' — typically 1.0-2.0 cubic metres of airflow per minute per square metre of filter area for difficult dust, allowing 2.0-3.5 for easier dust. Bags are typically polyester or PTFE fabric with a service life of 18-36 months under continuous duty. Capital cost for a 50,000 Nm3/h baghouse including induced-draft fan, control system, and ducting is Rs 35-80 lakh INR; annual filter-bag replacement adds Rs 4-10 lakh.

Trade-offs and failure modes: Baghouses cannot handle moist or sticky dust without pre-treatment, because moisture cakes the bags and blinds the filter surface. Cold inlet gas can produce condensation; very hot gas (above 250 degC) requires high-temperature fabric (Nomex, P84, fibreglass with PTFE membrane) and increases bag cost. Combustible dust (aluminium fines, magnesium, certain plastic and biomass dusts) demands antistatic bag fabric and spark-detection systems to prevent baghouse fires — a major safety concern in shredder-line dust collection. Routine maintenance focuses on detecting bag failure early, because a single failed bag dramatically raises outlet emissions and triggers stack-monitoring violations.