Scrubber Aerodynamic Conditions
Calvert & Yung high-energy venturi wet scrubber model
Hydraulic & Pressure Drop Results
Calvert pressure drop, submicron cut-point, and fan power
Worked Mathematical & Calvert Pressure Derivations
Throat velocity, droplet momentum acceleration, and cut-point evaluated live
Per Calvert (1970) and EPA Air Pollution Control Engineering, the static pressure drop across a venturi scrubber is primarily caused by accelerating the stationary liquid droplets up to high gas throat velocity:
1. Gas Throat Velocity (v_t): For volumetric gas flow Q = 15,000 ACFM (250 cfs) through throat area A_t = 1.25 sq ft:
2. Flue Gas Density (ρ_g): At temperature 180°F (355.4 K):
3. Calvert Static Pressure Drop (ΔP): With L/G = 10.0 Gal/1000 ACFM and droplet acceleration friction factor f = 0.35:
4. Aerodynamic Cut-Point Diameter (d₅₀): Calculated from inertial impaction parameter K_p = 0.50 and Sauter droplet d₃₂ = 74.2 μm:
5. Induced Draft Fan Brake Horsepower: With fan efficiency η = 0.65:
5 Fatal Traps in Venturi Scrubber Engineering
EPA Control Techniques, ACGIH Industrial Ventilation, and Chemical Plant Guidelines
Venturi scrubbers are the most energy-intensive particulate devices in industry, commonly demanding 25 to 60 inches of water gauge (ΔP = 6 to 15 kPa). Installing a standard industrial fan rated for only 15 to 20 in. w.g. causes severe aerodynamic fan stall. The scrubber chokes gas flow, backing up poisonous combustion fumes and acid gas into production furnaces and boilers. Always verify fan test curves for high static head capability.
Operating at throat velocities beyond 350 ft/s (110 m/s) with abrasive fly ash or metallurgical dust creates violent sonic sandblasting. Abrasive particles accelerated by the high-velocity gas jet scour through 316L stainless steel throat damper plates and rubber linings in weeks. Restrict throat velocities to between 180 and 280 ft/s, using silicon carbide or ceramic brick linings in abrasive applications.
Using recirculated scrubbing slurry with high suspended solids (TSS > 5%) in standard hollow-cone spray nozzles inevitably leads to nozzle clogs. If liquid flow to one side of the throat is blocked, hot uncooled gas (300°C+) impinges directly on dry walls, vaporizing protective liquid films, warping metal throat dampers, and melting downstream FRP/polypropylene piping. Always employ wide-orifice tangential nozzles with low-flow interlocks.
A venturi scrubber merely conditions particulate by impaction into water droplets; it does NOT remove them from the gas stream. That duty falls on the downstream cyclonic separator. If the separator is undersized or gas velocity exceeds 15 ft/s (4.5 m/s) through the mist eliminator chevrons, liquid droplets re-entrain into the clean gas, carrying dirty acid slurry out the exhaust stack ("raining" on surrounding plant property).
The boundary where hot incoming dusty gas first contacts liquid spray creates a rapid evaporation zone. Dissolved salts (calcium sulfate, carbonates) precipitate out rapidly at this wet-dry interface, forming hard, rock-like scale ridges. Over time, scale buildup chokes the throat area, increasing system pressure drop exponentially and driving the ID fan into overload. Wetted-wall approach weirs are required to wash the transition line continuously.