| name | baghouse-filter |
| description | Baghouse filter design — pulse-jet/shaker/reverse-air cleaning, air-to-cloth ratio, pressure drop, filter media selection, cake filtration, emission limits, NFPA 654, EPA Method 5. |
| metadata | {"priority":7,"promptSignals":{"phrases":["baghouse filter","fabric filter","pulse jet baghouse","air to cloth ratio","bag filter design","dust collector baghouse"],"minScore":3}} |
Baghouse Filter Design — Complete Skill
Operating Principles
Mechanism: dirty gas passes through fabric filter bags; particulate builds up as filter cake on bag exterior (outside-in) or interior (inside-out depending on type)
Cleaning: periodic removal of cake to maintain acceptable pressure drop
Particle collection mechanisms:
- Inertial impaction: >1 μm particles; dominant for coarse dust
- Interception: medium particles (0.1–1 μm) contact fiber
- Diffusion (Brownian motion): < 0.1 μm particles; diffuse to fiber
- Electrostatic attraction: for electrostatically charged particles
Cleaning Types
| Type | Mechanism | A/C ratio [m/min] | Pressure drop [Pa] |
|---|
| Pulse-jet (online) | Compressed air pulse; bag flexes; cake falls | 1.5–5.0 | 1000–2500 |
| Shaker (offline) | Mechanical shaking; bag oscillates | 0.5–1.5 | 500–1500 |
| Reverse-air (offline) | Gentle air reversal; collapse bag | 0.5–1.0 | 500–1500 |
Pulse-jet: most common; can clean while operating (online); short cleaning pulse (100 ms at 6–7 bar)
Shaker/reverse-air: offline cleaning; compartmentalized design; gentler on fabric
Air-to-Cloth (A/C) Ratio Design
Definition:
A/C = Q_gas / A_fabric [m/min or ft/min]
Q_gas = actual gas flow rate at filter conditions [m³/min]
A_fabric = total active filtering area [m²]
Guideline (pulse-jet):
| Dust type | A/C ratio [m/min] |
|---|
| Cement, limestone | 2.5–4.0 |
| Coal ash, fly ash | 1.5–2.5 |
| Fine chemical dust | 1.0–2.0 |
| Silica, quartz | 1.5–3.0 |
| Carbon black | 0.8–1.5 |
Lower A/C: lower velocity through fabric → better particle capture; lower pressure drop; more fabric required
Pressure Drop (Kozeny-Carman for Cake)
Total ΔP:
ΔP_total = ΔP_fabric + ΔP_cake [Pa]
Fabric ΔP:
ΔP_fabric = K_f × μ × V_f [Pa; K_f = fabric resistance coefficient [m⁻¹]; μ = viscosity [Pa·s]; V_f = filtration velocity = A/C ratio [m/s]]
K_f = 10⁸–10¹⁰ m⁻¹ (clean fabric); increases with blinding (particle embedding)
Cake ΔP (Kozeny-Carman):
ΔP_cake = α_cake × μ × c × V_f × t [Pa]
α_cake = specific cake resistance [m/kg]; c = dust concentration [kg/m³]; t = time since last cleaning [s]
α_cake = 10⁸–10¹² m/kg (depends on particle size and shape)
Combined ΔP model (Rubow):
ΔP = SE × V_f + K₂ × c × V_f² × t [SE = fabric residual resistance; K₂ = cake specific resistance]
Target ΔP: 1000–2500 Pa for pulse-jet; trigger cleaning at 2000–2500 Pa; clean-to 1000 Pa
Filter Bag Sizing
Required fabric area:
A = Q / (A/C) [m²; Q in m³/min; A/C in m/min]
Number of bags:
N_bags = A / (π × d × L) [d = bag diameter; L = bag length; typical d = 100–300 mm; L = 2–8 m]
Housing:
Height: L_bag + cleaning section + hopper ≈ L_bag + 2–3 m
Width/length: determined by number of bags and row spacing (600–900 mm between bags)
Filter Media Selection
Common materials:
| Medium | Max T [°C] | Chemical resistance | Best for |
|---|
| Polyester (PET) | 135 | Acid resistant; not alkali | General industrial |
| Polypropylene (PP) | 95 | Acid + alkali resistant | Chemical dust |
| Fiberglass | 260 | Fair; not HF | Hot flue gas, cement kiln |
| PTFE membrane | 260 | Excellent (all chemicals) | Fine dust; high efficiency |
| Nomex (aramid) | 200 | Moderate; good | High-T industrial |
| P84 (polyimide) | 240 | Very good | High-T, sub-micron |
PTFE membrane:
Applied to base fabric; extremely smooth; particle release >99%; very low ΔP_cake
Required for: sub-micron particles; highly toxic dust; high-efficiency requirement
Weight (fabric weight):
400–600 g/m² for industrial dust; higher weight → more durable but higher ΔP_fabric
Emission and Efficiency
Collection efficiency:
η = 1 - C_outlet / C_inlet [typical: 99.5–99.99%]
HEPA-grade filter: η ≥ 99.97% at 0.3 μm (not achievable by baghouse for all particle sizes)
Emission limit (USA, PM₁₀):
EPA NESHAP: 0.005–0.02 kg PM / kg product (source-specific)
EPA Method 5: stack test; isokinetic sampling to measure outlet concentration [mg/Nm³]
EU directive (IED): PM < 5–20 mg/Nm³ for most industrial sources; 50 mg/Nm³ for some
Fire and Explosion Safety (NFPA 654)
Dust explosion risk:
K_st = maximum rate of pressure rise × volume^(1/3) [bar·m/s]
K_st > 200 → St 2 (violent explosion); K_st > 300 → St 3 (very violent)
Mitigation for explosive dust (baghouse):
- Explosion venting: rupture disk or explosion vent on housing; V_vent = A_s / (K_st × P_max^0.5) × C₁ (per NFPA 68)
- Suppression system: detects pressure rise → discharges suppressant (Na₂CO₃, NaHCO₃)
- Isolation: rotary valve or fast-acting gate on inlet duct
- Grounding and bonding: prevent electrostatic discharge ignition
Interlock: high-ΔP alarm → shutdown; high-T alarm → shutdown; ATEX zone 22 (dust) classification for interior
Standards
| Standard | Scope |
|---|
| NFPA 654 | Fire/explosion protection for dust-producing operations |
| NFPA 68 | Deflagration venting |
| EPA Method 5 | Stack sampling for PM |
| ISO 11057 | Fabric filter test methods |
| EN 15609 | Fabric filter design and installation |
Output
Provide: cleaning type (pulse-jet/shaker/reverse-air), A/C ratio [m/min], total fabric area [m²], number of bags (d × L [mm × m]), filter media type and temperature rating [°C], operating ΔP [Pa] (design and cleaning trigger), outlet emission concentration [mg/Nm³] vs. regulatory limit, dust explosion Kst class (if applicable) and mitigation strategy (venting/suppression), electrical grounding requirement, and applicable standard (NFPA 654, NFPA 68, EPA Method 5).
