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Design Equations For Venturi Scrubbers




Design Equations For Venturi Scrubbers 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
 
dl = (0.000585/vr)*sqrt(σ/ρl) + 0.0597*(µl /sqrt(σ/ρl))^0.45*(Ql/Qg)^1.5
where:
dl = mean droplet diameter, m
vr = relative velocity of gas to liquid, m/s = vg –vl ≈vg
Note: In most cases, the gas velocity is much higher than the liquid velocity and vr may be considered equal to vg
σ = liquid surface tension, N/m
ρl = liquid density, kg/m3
µl = liquid viscosity, Pa.s
Ql = volumetric flow rate of liquid, m3/s
Qg = volumetric flow rate of liquid, m3/s
 
Boll et. al Correlation
 
dl = (0.042 +0.00565*(1000*Ql / Qg)) / vr^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, m3/1000 m3
ψ = inertial impaction parameter, dimensionless
Note: R values between 0.936 m3/1000 m3 and 1.337 m3/1000 m3 provide optimum collection efficiency
ψ = C*dp^2*ρp*vt / (9*µg*dl)-----(2)
 
where:
C = Cunningham Slip correction factor, dimensionless
 
C = 1 + (0.000621*Tg / (dp*10^6))-----(3)
Tg = inlet gas absolute temperature, K
dp = particle diameter, m
ρp = particle density, kg/m3
vt = throat velocity, m/s
µg = gas viscosity, Pa.s
dl = 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 vt:
vt = ψ*9*µg*dl / (C*dp^2*ρp)-----(5)
 
Throat Length
 
lt = 369.561*R^0.293 / vt^1.127
where:
lt = throat length, m
R = liquid-to-gas ratio in L/m3 (to convert m3/1000 m3 to L/m3 multiply m3/1000 m3 with 0.001)
vt = throat velocity, m/s
 
Throat Area
 
At = Qg / vt
where:
At = throat area, m2
Qg = process gas flow rate, m3/s
vt = throat velocity, m/s
 
Pressure Drop in Venturi Scrubbers (Hesketh Equation)
 
ΔP = 0.532*vt^2*ρg*At^0.133*(0.56 + 16.6*(Ql/Qg) + 40.7*(Ql/Qg)^2)
where:
ΔP = Pressure drop, Pa
vt = throat velocity, m/s
ρg = gas density downstream of throat, kg/m3
At = throat area, m2
Ql = volumetric flow rate of liquid, m3/s
Qg = volumetric flow rate of gas, m3/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

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alfredopinillos
Feb 06 2014 09:41 AM

Good News! Thks.

Regards

Thanx a lot, Great Work

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sridharkintali
Feb 21 2014 11:14 PM

Thank You sir, The information you have provide in the blog is correct. We have use Venturi scrubber in our project for Uranium project for high pressure vessel.  Design is different but the concept is same. The hot vapour/air comes from vessel which contains inert gases which is above 160 oC  and sent to the Venturi for scrubber purpose. Here we reduce the pressure drop of vapor/air and also the temperature before venting with normal water at atmospheric temp. Here basic parameter like temperatue, Pressure, and PH of the coolent takes place.

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Shishir Vikash Singh
Mar 05 2014 03:02 AM

Dear Sir,

 

What will be the general collection efficiency range for the venturi scrubbers? Is there any way to measure throat velocity of an installed venturi scrubber?

 

Will be looking forward to your reply.

 

Regards

Shishir Vikash Singh

Dear Sir,

 

What will be the general collection efficiency range for the venturi scrubbers? Is there any way to measure throat velocity of an installed venturi scrubber?

 

Will be looking forward to your reply.

 

Regards

Shishir Vikash Singh

Shishir,

 

Generally for well designed scrubbers the collection efficiency is >98%. Collection efficiency depends on the following factors:

 

1. Higher the throat velocity, better the collection density. However, increasing the throat velocity beyond a certain value does not increase the collection efficiency. Studies show that that optimal gas velocity in the throat are from 70-90 m/s.

2. Higher the contaminant particle size greater will be the collection efficiency. For contaminant particles over 5 microns, the efficiency is >99%.

3. Increase in Liquid-to-gas Ratios ® increases the collection efficiency. The optimum 'R' values have been provided in the main blog article.

 

Based on the equation given in the blog article, you need the inputs to calculate the throat velocity. I am not sure if you can make theoretical calculations for throat velocity of an installed venturi scrubber. It might definitely be possible to measure the actual throat velocity by providing some measurement instrument. However, I do not have much idea of any such on-line measurement. Maybe, the supplier of the complete venturi scrubber package would be able to provide some guidance.

 

Hope this helps.

 

Regards,

Ankur

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Shishir Vikash Singh
Mar 05 2014 10:10 PM

The information which you shared was really helpful. Thanks a lot

 

Regards

Shishir

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Arif Shahzad
Feb 23 2015 04:47 AM

Thanks sir for the valuable information, however please guide me a bit further as I am designing a venturi scrubber for removal of particulate matter (218 mg/m3) from air at 1.6 m3/s.

 

I have assumed "Vr" (Liquid-Gas relative velocity) to be same as "Vt" (Throat velocity), am I right in making this assumption?

Droplet size is dependent upon "Vr", while suited "Vt" depends upon droplet size (dl), so I have used iterative approach to converge at

"Vr" or "Vt" = 86 m/s

"dl" = 0.82 micrometer

throat length is calculated to be 2.5 meters, isn't it on higher side a bit?

 

I have taken "R = 1.2 m3/1000m3", "k = 0.15", "PM removal efficiency = 0.98 (fraction)"

Also I haven't yet included the factor of vaporization losses of injected water due to high air temperature.

 

I would be grateful if you can take a look at the excel spreadsheet in which I am doing these calculations.

 

Regards,

Arif

Dear Sir,

     Thanks for valuable information ragarding scrubber.

     I want to design the ventury scrubber for biomass gasifier.Can you please send me some data sheets/pdf for that?

 

     Thanking You.

 

email:rajeshpawar910@gmail.com

Dear Sir,

     Thanks for valuable information ragarding scrubber.

     I want to design the ventury scrubber for biomass gasifier.Can you please send me some data sheets/pdf for that?

 

     Thanking You.

 

email:rajeshpawar910@gmail.com

Your question is not clear. Which datasheets / pdf do you want?

 

Regards,

Ankur.

Dear Sir,

I am doing my BE project in Ventury scrubber design.As i am from Mechanical background,i have very less info.about this.So if you have previously done excel sheet/pdf of ventury scrubber design then that is very helpfull for me and that gives exact direction to my project work.

My project topic is "Design of Ventury scrubber for 1Mw biomass gasifier plant."

 

Yours faithfully

Rajesh Pawar

Dear Sir,

I am doing my BE project in Ventury scrubber design.As i am from Mechanical background,i have very less info.about this.So if you have previously done excel sheet/pdf of ventury scrubber design then that is very helpfull for me and that gives exact direction to my project work.

My project topic is "Design of Ventury scrubber for 1Mw biomass gasifier plant."

 

Yours faithfully

Rajesh Pawar

Rajesh,

 

The article is good enough to generate your own excel spreadsheet. Do that and I can review your work and point out any corrections if required. Please do not expect a ready-made spreadsheet.

 

Regards,

Ankur.

hi sir,
i noticed that the design was based on dry gas,the process i am working on produce a humid air(12%) how can i do the calculation taking account on that .
i would also to know how to calculate all venturi dimension(Lconv,Ldiv,angles..)
Thank you.

Dear Sir,

 

      Firstly thanks for all data provided by you for Ventury Scrubber.I need your help for designing of Tray Scrubber for tar removal from product gas outlet of biomass gasifier.

     So this is my humble request to you if you have any pdf/lietrature regarding plate/tray scrubber please send me.

 

Thanking You

Rajesh Pawar

Dear sir, I need help finding the converging and diverging angles of the throat of a venturi scrubber and also the diameter of the nozzle and the inlet and outlet diameter of a Venturi scrubber. so far I have the Vt Qw Qg Lt At Ld from using Calvert's model Thank you, Kofi Kwakyi

Dear Sir,

 

Thank you for bringing this discussion.

 

First, I would like to know under which operational conditions these equations are a decent fit since most are correlations.

 

These equations are a good approach for particulates, but they do not describe absorption of volatiles or high solubility gases.

Are there any good references on this matter?

 

Venturi Scrubbers are sometimes used to absorb gases such as CO2 or SO3 for instance, but there is lack of literature on venturis as absorbers.

 

It is known that venturis have limited efficiency to absorb gases, but they are used for such in several cases - surprisingly with few output control as they lack proper understanding and dimensioning.

 

Cheers!

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