Venturi scrubbers are high-energy air pollution control devices used to remove particulate matter and hazardous gases from industrial exhaust streams. Designing an effective system requires precise calculations to balance collection efficiency against the energy costs of pressure drop. Fundamentals of Venturi Scrubber Design
A Venturi scrubber consists of three main sections: a converging section, a throat, and a diverging section. The process gas accelerates in the converging section, reaches maximum velocity in the throat where it contacts the scrubbing liquid, and سپس decelerates in the diverging section to recover static pressure.
The core of the design process focuses on determining the throat velocity and the liquid-to-gas (L/G) ratio. High throat velocities increase the relative velocity between the gas and liquid droplets, which enhances particle collection through inertial impaction. However, this also significantly increases the pressure drop across the system. Key Calculation Parameters
To build an accurate design spreadsheet, several critical variables must be accounted for:
Gas Flow Rate (Q_g): Usually measured in Actual Cubic Feet per Minute (ACFM).
Gas Density and Viscosity: These vary with temperature and pressure and affect the Reynolds number. venturi scrubber design calculation xls upd
Liquid Flow Rate (Q_l): The volume of scrubbing liquid injected.
Liquid-to-Gas Ratio (L/G): Typically expressed in gallons per 1,000 cubic feet of gas.
Throat Velocity (V_t): The speed of the gas at the narrowest point of the Venturi. Pressure Drop Equations The pressure drop ( ΔPcap delta cap P
) is the most important factor in determining the operating cost of the scrubber. The most common correlation used in design calculations is the Johnstone equation or the Calvert modification.
The Calvert equation for pressure drop is often expressed as: ΔPcap delta cap P is in inches of water column. Vtcap V sub t is throat velocity in feet per second. is in gallons per 1,000 ACFM. Collection Efficiency Calculation The collection efficiency ( Work & Finance
) is calculated based on the particle size distribution of the dust. Since scrubbers are more efficient at capturing larger particles, designers use the "cut diameter" ( d50d sub 50 ) method. The d50d sub 50
represents the particle size that is collected with 50% efficiency. The correlation typically follows the formula: Stkcap S t k
is the Stokes number, a dimensionless parameter representing the ratio of the stopping distance of a particle to the characteristic dimension of the obstacle (the liquid droplet). Structuring the XLS Tool
A modern "upd" (updated) Excel tool for Venturi design should be structured into clear input and output modules:
Input Module: Enter gas temperature, pressure, moisture content, and particle size distribution. tawa) Festive home decoration (rangoli
Physical Properties: Use built-in lookup tables for gas density and viscosity based on the inputs.
Sizing Module: Calculate the required throat area based on a target velocity.
Performance Module: Link the L/G ratio to the pressure drop and calculate the resulting collection efficiency for each particle size fraction.
Fan Power Requirements: Calculate the brake horsepower (BHP) required for the system fan based on the calculated ΔPcap delta cap P and fan efficiency. Maintenance and Optimization
Even a perfectly designed Venturi scrubber requires regular monitoring. Key performance indicators (KPIs) to track in your spreadsheet include the pressure drop stability and the liquid nozzle pressure. An updated design tool should also account for "evaporative cooling" effects if the inlet gas is significantly hotter than the scrubbing liquid, as this affects the actual gas volume inside the throat.
[ \eta = 1 - \exp\left(-k \cdot \fracLG \cdot \sqrt\frac\Delta P\mu_g\right) ]
Where k is the empirical constant. The UPD spreadsheet allows users to fit k based on dust type (fly ash: k≈0.15, silica: k≈0.22, oil-fired soot: k≈0.09).