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We are planning for revamp in naphtha hydrotreater feed / effluent exchanger system. Could anyone guide us on the minimum hot end approach can be taken to design the system. At present we are having hot end approach at 60 degC. Can we add another shell to decrease the hot end approach as we are facing severe constraints in the hydrotreater furnace?
 
Answers
02/03/2015 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
Can you tell me if this is a vertical Texas Tower that you intend to design/install?
28/02/2015 A: Satish Angadi, Haldor topsoe, satish.angadi@gmail.com
If your naphtha is straightrun (no cracked/coker naphtha), involve Alfalaval/Packinox... you can have very very low approach in their plate type heat exchanger.
28/02/2015 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
More tips: (1) Provide a bypass on the feed side to use when the exchangers are cleaner than represented by the fouling factor. (2) Design the exchanger arrangement to have the same pressure drop as before. This may require piping revisions at the existing stack and/or changing individual exchangers from 4-pass to 2-pass by modifying baffles in channel heads.
28/02/2015 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The limiting factor should be as follows: Of the total heat input to the feed stream, at least 15% should be provided by the furnace at any time during the run. Less than that will result in problems maintaining a stable reactor inlet temperature.
28/02/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
You will need to consider the other impacts when deciding if you can add more preheat. The extra pressure drop may lower reactor pressure a little and could impact hydrogen circulation. You will need to consider if you can live with any runlength impacts these have. Also the effluent will get cooler, so you will need to think about ammonium chloride formation risk. If you have a water wash, the location may need to be moved due the changes in heat balance. Some of these impacts could be minimized by retubing the other feed/effluent bundles to reduce DP.
27/02/2015 A: Marcello Ferrara, ITW SrL, mferrara@itwtechnologies.com
If you are facing a severe constraints in the furnace, you can use ITW Online Cleaning for cleaning in 24 hours on a oil-to-oil basis the entire preheat train.
This will allow you to immediately recover furnace inlet temperature and reduce furnace firing.
Please contact me privately for more informations.