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Recently we are facing topping unit furnace inlet becomes lower than expected. The normal temperature is 215-220 degree centigrade. But now we are getting only 200-205 degree centigrade. What are the probable reasons behind this? And what measures should be taken to overcome the problem?
 
Answers
12/02/2010 A: Marcello Ferrara, ITW SrL, mferrara@itw.it
Fouling due to ashpaltene/paraffin precipitation is a well recognized cause of the problem. Our Online Cleaning technology will allow to perform the cleaning of the entire Unit is as low as 24 hours on a oil-to-oil basis. This means, you can recover furnace inlet temperature immediately and solving your problem without any mechanical cleaning.
11/02/2010 A: Berthold Otzisk, Kurita Europe GmbH, Berthold.Otzisk@kurita.eu
It is possible, that asphaltene precipitation after electrical desalting is the reason for the observed temperature decrease. Some crude oil blends have high asphaltene precipitation tendencies. The flocculation of asphaltenes in paraffinic oils is known to be irreversible. It is better to avoid destabilization of asphaltenes by using special antifoulants. Typical dosing rates are in the 3-6 ppm range. If mechanical cleaning is not possible without shutdown of the crude unit, the usage of antifoulants is a cost-effective solution.
09/02/2010 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Assuming that your crude rate has not increased and your crude slate has not changed, then the decrease is most likely due to fouling. Once fouling has started it is very difficult to stop. Most likely you will need to figure out which exchanger(s) has fouled and take it off line to have it mechanically cleaned.
There are various causes of fouling - low asphaltene stability, solids, vaporization leading to deposition of water soluble solids or asphaltenes. Preventing vaporization and keeping exchanger tube velocity high to prevent foulant from sticking to tubes will help. In some cases, tube inserts can be useful. To prevent shell side fouling use fouling resistant designs like helical or em baffle exchangers.
In some cases vendor supplied antifoulants can be successful, but they are usually very expensive. Good exchanger design and a regular cleaning program are the best ways to minimize the impact of fouling.
09/02/2010 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
It would be worthwhile to check burners are not fouled. if the burners are fouled due to pipescale, corrosion products, polymerised liquid hydrocarbons, and / or ammonium chloride salts sometimes found in fuel gas networks and the fuel gas flow may be constructed this can cause loss of furnace efficiency.
A visual inspection of the burners would be recommended. This is especially a problem with low NOx or ultra low NOX burners as the orifices are much smaller and hence these burners are more prone to fouling due to solids and liquid contaminants in the fuel gas network. If this is indeed the problem, or part of the problem, a regular burner cleaning program may be needed however a better solution would be a permanent high efficciency fuel gas filter or LG coalescer. This would normally be installed just before the furnace. Pall Corp has provided sever hundred fuel gas coalescers to refiers and petrochemical plants to prevent burner fouling and the process fine tuning and maintenance issues this can cause.
08/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
It sounds like fouling of the exchangers, probably on the crude side. Fouling can be tracked over time if there are adequate flow and temperature readings available on a regular basis. The heat transfer rate for each service can be calculated, compared with design, and watched over time. Some services can be taken off line for cleaning between unit shutdowns. Otherwise, tracking the calculated results can be one factor in planning the next turnaround, when all exchangers can be cleaned.
Fouling can go hand in hand with corrosion. Make sure the desalter is performing well. Inspect for corrosion in the exchangers at every opportunity.
08/02/2010 A: Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
there are a lot of reasons for that happening:
product yield change (producing more low temperature product)
Pumparound flowrates changes
Generally it could be a sign of heat exchanger fouling, for that, you need to evaluate each exchanger to determine the fouling factor, of course you should be doing that from the beginning to see how this fouling factor is increasing.