Dear All,

Many of you involved in engineering and design of wet scrubbing systems are already familiar with “Venturi Scrubbers”.

Venturi Scrubbers are primarily designed to control fine particulate matter (PM) from gaseous streams. Before releasing waste gases that contain PM to the atmosphere, these gases are treated using venturi scrubbers to remove PM. Generally the effective range of PM removal is from 10 microns to 2.5 microns. They are also capable of some incidental control of “Volatile Organic Compounds”, which, however is not their primary function. They can also be used for capturing high solubility gases which have good solubility with the sprayed liquid.

Venturi scrubbers have high efficiencies when capturing PM in the range of 0.5-5 micron.

Venturi scrubbers have following typical industrial applications:

a. Boiler waste gases utilizing coal, oil, biomass and liquid waste

b. Metal Processing – Iron & Steel, Aluminum

c. Wood, Pulp & Paper Industry

d. Chemical Industries

e. Municipal Solid Waste Incinerators

For a detailed description on venturi scrubbers refer the Wikipedia link below:

http://en.wikipedia....enturi_scrubber

Today’s blog entry relates to some design equations for evaluating liquid droplet diameter, collection efficiency, throat velocity, throat diameter, throat length and pressure drop for venturi scrubbers:

**Liquid Mean Droplet Size or Sauter Mean Diameter**

*Nukiyama & Tanasawa Correlation*d

_{l}= (0.000585/v

_{r})*sqrt(σ/ρ

_{l}) + 0.0597*(µ

_{l}/sqrt(σ/ρ

_{l}))^0.45*(Q

_{l}/Q

_{g})^1.5

where:

d

_{l}= mean droplet diameter, m

v

_{r}= relative velocity of gas to liquid, m/s = v

_{g}–v

_{l}≈v

_{g}

**Note**: In most cases, the gas velocity is much higher than the liquid velocity and v

_{r}may be considered equal to v

_{g}

σ = liquid surface tension, N/m

ρ

_{l}= liquid density, kg/m

^{3}

µ

_{l}= liquid viscosity, Pa.s

Q

_{l}= volumetric flow rate of liquid, m

^{3}/s

Q

_{g}= volumetric flow rate of liquid, m

^{3}/s

*Boll et. al Correlation*d

_{l}= (0.042 +0.00565*(1000*Q

_{l}/ Q

_{g})) / v

_{r}^1.602

**Collection Efficiency**

η = 1 – e^(-k*R*sqrt(ψ))----(1)

where:

η = collection efficiency of the venture scrubber, fraction

k = correlation coefficient whose value depends on system geometry and operating conditions (typically 0.1-0.2)

R = liquid-to-gas ratio, m

^{3}/1000 m

^{3}

ψ = inertial impaction parameter, dimensionless

**Note**: R values between 0.936 m

^{3}/1000 m

^{3}and 1.337 m

^{3}/1000 m

^{3}provide optimum collection efficiency

ψ = C*d

_{p}^2*ρ

_{p}*v

_{t}/ (9*µ

_{g}*d

_{l})-----(2)

where:

C = Cunningham Slip correction factor, dimensionless

C = 1 + (0.000621*Tg / (d

_{p}*10^6))-----(3)

T

_{g}= inlet gas absolute temperature, K

d

_{p}= particle diameter, m

ρ

_{p}= particle density, kg/m

^{3}

v

_{t}= throat velocity, m/s

µ

_{g}= gas viscosity, Pa.s

d

_{l}= liquid mean droplet diameter, m

Normally collection efficiency is an input, so re-writing equation (1) in terms of ψ:

ψ = (ln(1-η) /(k*R))^2-----(4)

Since we want to know the throat velocity, re-writing equation (2) in terms of v

_{t}:

v

_{t}= ψ*9*µ

_{g}*d

_{l}/ (C*d

_{p}^2*ρ

_{p})-----(5)

**Throat Length**

l

_{t}= 369.561*R^0.293 / v

_{t}^1.127

where:

l

_{t}= throat length, m

R = liquid-to-gas ratio in L/m

^{3}(to convert m

^{3}/1000 m

^{3}to L/m

^{3}multiply m

^{3}/1000 m

^{3}with 0.001)

v

_{t}= throat velocity, m/s

**Throat Area**

A

_{t}= Q

_{g}/ v

_{t}

where:

A

_{t}= throat area, m

^{2}

Q

_{g}= process gas flow rate, m

^{3}/s

v

_{t}= throat velocity, m/s

**Pressure Drop in Venturi Scrubbers (Hesketh Equation)**

ΔP = 0.532*v

_{t}^2*ρ

_{g}*A

_{t}^0.133*(0.56 + 16.6*(Q

_{l}/Q

_{g}) + 40.7*(Q

_{l}/Q

_{g})^2)

where:

ΔP = Pressure drop, Pa

v

_{t}= throat velocity, m/s

ρ

_{g}= gas density downstream of throat, kg/m

^{3}

A

_{t}= throat area, m

^{2}

Q

_{l}= volumetric flow rate of liquid, m

^{3}/s

Q

_{g}= volumetric flow rate of gas, m

^{3}/s

Hope the readers of this blog entry have now some idea about the design equations related to venturi scrubbers. Please note that the liquid-to-gas ratios are basically ratios and any set of volumetric flow rate units may be used as long as they are consistent for both liquid and gas.

The entire blog entry has been a compilation from various resources related to Venturi scrubbers. However the following resources can be referenced from the links provided below:

http://web2.clarkson... Dev_120408.pdf

http://tean.teikoz.g...ations/12_3.pdf

http://books.google....bber Pa&f=false

I will try my best to provide answers to any questions raised. All these equations are programmable in an excel spreadsheet.

Regards,

Ankur.

really great article.means alot to me.Thanks Sir