We are facing frequent fouling in our falling film evaporators because of tar content in our feed. Currently we down our plant once in 3 months for cleaning these evaporators. Can anyone suggest the best method in reducing this fouling?? how about tube inserts ?? or do we have any advance technology in heat transfer for reducing fouling??
I know twisted tubes can reduce fouling but can we use for falling film evaporator??
Answers
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24/08/2012
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S Banik, Centre for High Technology, sbdr@rediffmail.com
It appears, based on the discussion by others, Wiped film evaporator or short path distillation would be most suitable. We have distilled refinery vacuum residue in a short-path distiller without any fouling problem.
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02/06/2011
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Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
First things first - You need a cleaning method that will remove the fouling, quicker, safer and faster than your traditional water jetting or chemicals. Call us we have 12 alternative cleaning methods you can choose from. You may be interested to know that we are developing an On-Line Falling Film Evaporator Cleaning System in the near future.
Re: The future - You really need to answer the questions posed by Alan of Jacobs i.e. is the 'tar' part of an oil liquid being evaporated or is 'tar' a contaminant and also to advise on the fouling viscosity, characteristics, thickness, location etc. Digital images and a short 10 second video clip of someone scraping at the deposit is always a great help.
With this we will be able to establish whether Keith of B and B Consulting has a point in respect of appropriate design type
'PTFE' inserts in principal are an option however be aware that the ability to clean can be reduced as Water Jetting can shred or lift the inserts out. A remote / robotic cleaning technology is therefore advised (Non man entry) to eliminate the risk and fatigue out of manual water jetting. See case studies at Tube Tech International Ltd.
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01/06/2011
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Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Question = What is being or becoming evaporated in the Falling Film Evaporators ?
Is the 'tar' part of an oil liquid being evaporated or is 'tar' a contaminant ?
Question = Are the distributor devices for liquids at the top the bundle appropriate for the service in terms of flow splitting among tubes and in getting the entire tube perimeter wetted near top of tube?
Question = Is the top tube sheet truly level ?
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01/06/2011
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keith bowers, B and B Consulting, kebowers47@gmail.com
A falling film evaporator is not appropriate type for a feed with fouling residue. You MAY be able to decrease fouling by reducing the hot side temperature--increasing the 'wash liquid' at the lower end of the tubes (I am presuming that is where fouling is.)
If fouling starts at top of tubes--all is lost--the sticky residue will continue to foul unless you use 'PTFE' inserts.
Depending on the amount of residue in the feed, it may be much better to use 'dead-end' kettle re-boiler type exchanger--similar to those used in EDC/VCM plants to remove 'high boilers' from the recirculating EDC. The only way out is as a vapor, leaving the heavies behind.
Each of the two exchangers are designed for easy clean-out periodically.
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