Wet Scrubber Gas Absorption & NTU Sizing Calculator

Determine Number of Transfer Units (NTU), packed bed depth (Z), liquid-to-gas ratio (L/G), and pressure drop for chemical packed tower absorption scrubbers.

Gas Stream & Pollutant

Exhaust Gas Flow (ACFM):

Gas Pollutant:

Inlet Concentration (ppmv):

Target Outlet (ppmv):

Scrubber Column & Hydraulics

Column Diameter (ft):

Liquid-to-Gas Ratio L/G (GPM/kCFM):

Absorption Mass Transfer Sizing

Required Packed Bed Depth (Z)

-- ft

-- meters packed packing

Transfer Units (NTU)

-- NTU

--% removal

Recirculating Liquid

-- GPM

-- GPM/1000 CFM

Superficial Gas Velocity: -- FPM

Height of Transfer Unit (HTU): -- ft

Bed Pressure Drop: -- in. w.g.

Chemical packed scrubbers require superficial gas velocities between 300 to 450 FPM to prevent column flooding while maintaining uniform liquid wetting.

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Frequently Asked Questions

What is the Number of Transfer Units (NTU) in wet scrubber design?

The Number of Transfer Units (NTU) is a dimensionless measure of the difficulty of a mass transfer separation task. For lean dilute gas absorption with an irreversible chemical reaction, NTU is the natural logarithm of the ratio of inlet to outlet pollutant concentration: NTU = ln(Cin / Cout).

What is the Height of a Transfer Unit (HTU)?

HTU represents the physical depth of packing (in feet or meters) required to achieve one transfer unit of separation. Highly soluble acid gases like HCl have low HTUs (1.5 to 2.0 ft), whereas less reactive gases like H2S have larger HTUs (3.0 to 4.0 ft).

What causes packed column flooding in wet scrubbers?

Flooding occurs when upward gas velocity is so high that the aerodynamic upward drag halts the downward gravitational drainage of the scrubbing liquid. Liquid accumulates in the packing voids, causing static pressure drop to spike dramatically and blowing scrubbing solution out the exhaust stack.