1 reply to this topic

[Sarva]

Hi,

I am currently designing a wet scrubber to remove acid fumes. I am looking for guidance / correction on my design approach.

The scrubber will be connected to the vent of a 10000 liter HCl storage tank and is meant to operate during unloading of HCl from tanker to the storage. The duty conditions are as follows,

1) Gas (i.e. HCl fumes) flowrate = Rate of displacement of air from storage tank = unloading rate = 15000 L/hr
2) Concentration of HCl-water solution to be unloaded = 34% (w/w %)
3) Inlet gas temperature = 60 C (the ambient temperature does not exceed 45 C, but temp rise due to absorption and neutralisation is accounted by assuming higher temp. This is expected to make a safe design)

Particulate free water is planned to be used as the scrubbing liquid (provision for adding NaOH to improve absorption is also made).

I have started with the equilibrium data of HCl partial pressure (above different HCl liquid concentrations and temperatures) given in Perry's chem eng handbook. The approach followed in short is as follows,
1) Conversion of volumetric gas flowrate to molar gas flow (using ideal gas law)
2) Assuming counter current flow, stream concentrations at column top and bottom sections are set. It is assumed that inlet gas conc. is in equilbrm with outlet liquid conc. Max inlet liquid conc. of 10% (w/w) is used at the top while outlet gas conc. is assumed to be equilibrium conc. corresponding to 6% liquid @ 35 C (from Perry's data)
3) Then ratio of inert liquid to gas molar flowrates is determined (Li / Vi)
4) Based on this ratio, min. liquid flow (Li min) and design liquid flow (1.5 Li min) are obtained using relations given in Perry's.

I am getting a design flow of 93 L/hr for scrubbing water. It feels low for the duty. Could you advice if this result / approach is correct ? We have a recirculation pump of 5000 L/hr available for the scrubbing liquid. I plan to use this high flowrate to be on the safe side (efficiency is not important since it will be sparingly used). But when designing the column i'm not able to determine the flowrate at which flooding occurs. As of now the design consists of following,

Scrubber internal dia - 230 mm
Packing section height - 1 m
Packing sections - 2
Packing - Plastic pall rings (16 mm size)

For calculating HETP I am unable to find the mass transfer co-efficient. Please advice on where I can find such data and also how to determine flooding conditions?

Thanks a lot for your help!

[breizh]

Sarva,
Consider the search button ( top right) , you will find a lot of info about , absorbtion , HCL Fumes absorption , scrubber , HCL vapor pressure,....

Attached some info about flooding using Eckert and Lobo correlation .

Hope this helps

Breizh

Edited by breizh, 18 September 2012 - 11:26 PM.