Static Two Stage Extractor Performance

[dipak2]

Dear All Freinds/Experts..

Hello!!!Everybody,

I have two Stage Extractor.Which has Internal Baffles,Static Mixture.Both Stage has two Comartments Organic Side and Water side.The Main function of the Extractor is to extract the Organic with the use of Solvent from the Waste Water.

Basically,I have Sp. Gravity ,Viscosity,Flow rates.I would like to Calculate its performance

How can i Do ? I have refered Trebyal,Mass Transfer.But it is not mentioned about Static Mixture,Baffled ( Mixture Settler) Design and Performance.

Pl. be highlight on this topic/any website/any Formulaes/any other Guidence

Thanks in Advance to all of you & hope for positive response.

 

[25362]

Try
Kirk-Othmer Encyclopedia of Chemical Technology (John Wiley & Sons)
Ullmann's Encyclopedia of Industrial Chemistry (VCH)
Perry's Chemical Engineering Manual (McGraw-Hill)

 

[dipak2]

Dear Freinds

I have gone through the Kirk Othmers book.But I would like to know about the design calculations of Static Mixture type Extractor(Horizontal Extractor with Internal static mixture which is driven by velocity of fluids produced by pump).Where I would also like to know about the Equilibrium Datas of Nitrobenzene ,Aniline.Because I want to extract Aniline from Waste Water with the use of Nitrobenzene.

Pl .be enlighten about the formulaes to fine equilibrium curve,Diameter of dispersion,Height of dispersion bend etc.

Thanks in advance to all of you.!!!!!

 

[dipak2]

Let us discuss !!!come on. I request to all of you!!!!

 

[sshep]

dipak2,

It sounds like you are describing a 3 component, 2 stage mixer-settler system. Your equilibrium process can only approach two stages regardless of the mixer performance. Two configurations are possible depending on solvent flow between stages: counter-current or cross-flow. Both cases are covered by Treybal if you have the equilibrium data.

If you are hurting for equilibrium data try:

http://www.dechema.de/detherm.html

There is one LLE data set with 17 lines- it will cost you just under $60.

You appear to be dealing with an existing process which means troubleshooting rather than design. You will need to calculate the expected performance of 2 theoretical stages for comparison to plant data. There is unlikely to be any problem with mass transfer at the mixer if mixer velocity is at design. Usually creating the dispersion is the easy part (if mixing energy is available) and you will get a distribution of droplets of which the "fog" tail often causes a problem- unfortunately I don't know where to direct you for dispersion distribution data.

The biggest performance problem for mixer-settlers is the settling step- presumably this is why you ask about dispersion diameter etc. I envision that water is probably the continuous phase (this is important to conceptualizing the process). Entrainment of solvent in the water phase is the most likely problem you will have, and alot of factors can play into this (temperature, solids, ph and other water quality, settling time, etc). Sampling should tell you the amount of entrainment, and additional observations (i.e. is the entrainment a fog?) and tests (settling tests) on the samples can clue you into potential mitigations.

Performance can be a pretty generic term when not defined mathematically. If you give some more info about your system and the problem then maybe you can get some better response.

best wishes,
sshep

 

[dipak2]

Now I elaborate about my Liquid Liquid Extraction
System as per Below ---I thanks for your reply in
Engineering Tips Forum.

Sir,

I have two stage Liquid Liquid Extraction System.Basic
function of the Extractor is to extract Aniline from
waste water with the use of Nitrobenzene.

The waste water contains around 4-5 % Aniline which is
extracted by this extractors to bring down Aniline up
to 0.01 % in Waste water.The limit of Nitrobenzene in
waste water is around 0.25 %.

This Extractor having Static Mixtures in both stage.It
is horizontal type extractors with Internal Baffles
inside.TWO Compartments in each stage---Organic &
Water.Operating Temp. is around 40 C.Density of N.B.
is around 1120 kg/m3,Waste Water is around 980
kg/m3,Aniline is around 1018 kg/m3.

Two stages are countercurrent,but the feeding to both
extractors is coccurently.That means---
1.Pure Nitrobenzene Solvent along with Water side
phase separated from 1st stage from Water side
Compartment enters cocurrently in 2nd stage.(Via pump)
2.From 2nd Stage Organic Side Compartments Organic
i.e.N.B.went to 1st extractor Cocurrenlty with Feed
flow of Waste water (via pump)
3.1st Stage Organic phase is extracted phase.
4.2nd Stage Water phase is the Final Effluent
Discharge.

There is interphase level in both stage.

I face problems of formation of Rag at the interphase
.
I face problems of Higher Aniline % in Effluent even
with stabilization of Interphase level.
I face problem of some time water carry over from
Extracted phase of 1st stage.
ALSO I FACE PROBLEM OF EMULSION IN ORGANIC PHASE IN BOTH EXTRACTOR (FIRST STAGE EXTRACTOR)

There is Level control valves on Interphase levels in
both stages.Two Level control valves in water side in
both stage.

Pl. be enligten to improve above performance or to
Calculate all the design datas i.e.Dispersion
bend,diameters,Extractor Efficiency etc.

If you need any clarity pl. feel free.

Thanking You,

Yours Sincerally,

 

[sshep]

Hey dipak2,

This seems to be the settling type problem situation that I would suspect. In order to verify that the aniline in your effluent water is due to poor settling, check what is the nitrobenzene concentration in the water effluent. A low nitrobenzene level means that the aniline is probably not from solvent carry-over, but rather from a LLE problem. If this is the case you can increase your solvent flow, or consider going to a cross flow configuration (use some lean solvent in both reactors rather than the present counter current design).

Rags are always a threat to settler performance, and provisions must be in place to draw these off and break externally if needed. Troubleshooting emulsion problems are usually addressed by a combination of process changes based on qualitative understanding (lower velocities, longer residence time), and bench testing of samples (settling and shake tests, heating or cooling, mitigating solids and other water quality issues, trying various additives, etc).

best wishes,
ssehp

 

[dipak2]

Thanks for your reply.

We have tried with increasing the inlet Solvent to Water feed ratio.Also we have tried with diffrent Interphase leveles i.e.by keeping higher Interphase levels in both extractor.But eventhough Emulsion at interphase observed in 1st stage.That means there is some time no clear cut interphase level eventhough Level trends on DCS panel seems normal of both extractor with both phase.But still Aniline % in effluent comes higher side.Before two month this type of problem started.till that time normal.

Pl. be enlighten.