What is a good starting superficial gas velocity for random packing?

Start around 1.5–3.0 m/s and verify flooding margin using an F-factor or vendor capacity curve.

How is packing height estimated here?

Using HTU–NTU with NTU = −ln(1 − η) and a user-specified HTU. Use vendor or pilot data for final HTU values.

How is pressure drop calculated?

An Ergun-style correlation for gas through a packed bed. Wet operation typically increases ΔP; confirm with vendor charts.

How do I reduce pressure drop?

Increase column diameter (lower superficial velocity), use larger or structured packing, or optimize liquid distribution.

Scrubber Design & Sizing Calculator | GrowMechanical

Scrubber Design & Sizing Calculator

Empowering Process, Mechanical & Chemical Engineers

https://www.growmechanical.com

Gas Flow (Normal)

Nm³/h

Basis: 0°C & 101.325 kPa

Liquid Flow

m³/h

Target Removal η

Used for NTU via HTU–NTU

Gas Temp (operating)

°C

Gas Pressure (abs)

kPa

Design v_s

m/s

Typical 1.5–3.0 m/s for random packing

Gas Density ρ_G

kg/m³

Gas Viscosity μ_G

mPa·s

Enter mPa·s (1 mPa·s = 0.001 Pa·s)

Liquid Density ρ_L

kg/m³

Surface Tension σ

mN/m

For F-factor guideline

Packing Size d_p

e.g., 1" random ≈ 0.025 m

Void Fraction ε

–

Bed Height (initial)

Used to compute ΔP

HTU (gas-phase)

Typical 0.6–1.5 m (packing/solvent)

F-factor Limit

(Pa)^0.5

Operate ≤ 70–80% of limit

Gravity g

m/s²

Results (SI)

Actual Gas Flow (Q)

–

Liquid Flow (Q_L)

–

Mass L/G (kg/kg)

–

Column Diameter (D)

–

Superficial v_s

–

Gas Reynolds (Re)

–

ΔP per meter

–

Bed ΔP (for H_guess)

–

Pump TDH (est.)

–

NTU (from η)

–

Packing Height (HTU×NTU)

–

F-factor (utilization)

–

Notes: Q (actual) via ideal gas (T,P). ΔP from Ergun-style gas flow in packed bed. Height = HTU × NTU where NTU ≈ −ln(1−η). TDH ≈ static (H) + ΔP/ρ_Lg (excludes piping losses).

🔰 Beginner Guide — How to use this scrubber calculator

Step 1 Enter your gas flow at normal conditions (Nm³/h). Set actual T (°C) and P (kPa). The tool converts to actual m³/s.

Step 2 Provide liquid flow (m³/h), fluid densities, and gas viscosity. If unsure, keep water at 1000 kg/m³.

Step 3 Choose a design superficial velocity (1.5–3.0 m/s is a common start). The calculator sizes the column diameter.

Step 4 Select packing size and void fraction. For 1″ random packing, d_p≈0.025 m, ε≈0.90.

Step 5 Set target removal efficiency (η). Height is computed as HTU × NTU with NTU=−ln(1−η).

Step 6 Check F-factor utilization < 80% of the limit to avoid flooding.

Tip: If F-factor utilization is high, reduce v_s, choose larger column diameter, or pick packing with higher capacity.

🎯 Accuracy & Design Notes — Assumptions, limits & when to refine

Flow conversion: Ideal-gas basis from Nm³/h → actual m³/s. For high-pressure or heavy gases, use real-gas (Z-factor) for tighter accuracy.
Pressure drop: Ergun-style correlation assumes dry gas through packing. Wet pressure drop is typically higher; confirm with vendor curves.
HTU values: The default HTU is a placeholder. Use pilot data or vendor guidance for the solvent/packing system to set realistic HTU.
L/G: Computed as mass ratio (kg/kg). Real designs balance mass transfer, hydraulics, and solvent economics—tune against process targets.
TDH: We estimate static head (≈ height) + ΔP/ρg and add a small margin. Include piping, fittings, and elevation losses in detailed design.
Safety margins: Keep operation at ~70–80% of the F-factor limit for stable operation and to account for fouling/foaming.
Scale-up: Before procurement, reconcile with vendor datasheets for packing type/size, liquid distributors, and demister selection.

🧪 Advanced — HTU–NTU, mass transfer & flooding checks

NTU from removal: For a dilute component with linear driving force, NTU ≈ −ln(1−η). For non-linear isotherms or rich/lean ends, integrate stage-wise or use rate-based simulation.
HTU sources: Estimate from literature/vendor data as a function of L/G, packing type, fluid properties. For structured packing, HTU often decreases with liquid load to a minimum, then rises.
Flooding/capacity: A Leva-type capacity model or vendor charts can predict v_s,max. Operate at 70–80% of capacity. (Ask us if you want an auto-selector for v_s from % of flooding.)
Wet pressure drop: Add a correction for liquid holdup. Vendor correlations (e.g., for Pall rings/IMTP/structured packing) are recommended for final numbers.
Mass transfer enhancement: Lower surface tension increases wetting; surfactants change hydrodynamics. Re-validate HTU if σ deviates strongly from water.
Demister selection: Check gas outlet velocity to size a mesh pad or vane pack; target < design mist carryover. Pressure drop across demister is additional.

❓ FAQ — Short answers engineers actually need

What’s a good starting v_s? 1.5–3.0 m/s for random packing; structured packings can allow slightly higher for the same flood margin.
How do I reduce ΔP? Increase column diameter (lower v_s), choose larger packing size (↑ε, ↑d_p), or switch to structured packing.
Does η=99% explode height? Yes—NTU rises sharply as η→1. Balance removal spec with solvent rate and packing selection.
Do I need Z-factor? If P is high (>~300 kPa) or gas is non-ideal, yes—update Q conversion and density accordingly.

🔗 Related Tools & Internal Links (GrowMechanical)

These internal links strengthen topic clusters for SEO and help users move from sizing to hydraulics and equipment selection.

Results (SI)

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