How long can a Refinery Heater be operated above design duty in case skin temperatures are within range and heater tubes design life is completed. Can decoking of such a heater result in any tubes problem i.e bulging, sagging or rupture?
Answers
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19/01/2018
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Ashutosh Garg, Furnace Improvements Inc, agarg@heatflux.com
You can operate a refinery heater above design duty for short term only. There are a number of parameters that are involved in heater operation. Skin temperature measurement is only a point measurement and is no assurance that whole tube length or all the tubes are being heated uniformly. You may also get draft limited or O2 limited after a certain over capacity. Flame impingement is a common issue when you overfire your heater.
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27/08/2014
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Rupali Sahu, KBR, rupali.sahu@kbr.com
The furnace tube design temperature takes into consideration a certain margin above the calculated maximum tube skin temperature. accordingly the tube thickness is decided.
Hence as long as skin temperature of tubes and other vital operating parameters are within normal limits as specified by API datasheet of the heater, it can be operated. However care should be taken that all instruments are working accurate.
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07/05/2013
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Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
regular decoking of tubes is essential but preferably using a reliable stud pigging company of which there are 14 worldwide. Some less experienced ones can score the tube bore which is disastrous.
Another issue is to ensure the external surfaces are also cleaned back to bare metal as otherwise you create a "bi metalic striip" effect i.e. it has a different heat transfer points - "hot spotting" which will make the tube distort, that said you must also ensure the increase in heat doesnt cause the refractory to disintegrate such that the fragments fall off and cover or deflect the burners and creatre a flame imbalance i.e. over heating one set of tubes more than the others....which too can lead to tube distorition.. If its cleaning you need we can help or advise the companies in your area.
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29/04/2013
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Jayaraj Jayam, Chennai Petroleum Corporation Limited, njayaraj@gmail.com
Though heater tubes are designed for a particular life span, it doesn't mean life of the tubes become over by the end of the design running hours. Heater tubes can be used as long as tubes are healthy. It means skin temperatures under control, no hot spot (need not be only glowing spot, can be black spot also), no bulging or sagging.
If the heater is provided with velocity steam in case of handling heavy oil (atmospheric column bottom) maintain it properly to break the boundary layer so that coke accumulation can be reduced or the time between two decoking can be extended.
Possibility for tube failure during decoking is higher compare with normal operation. This is due to the severe condition the tubes are exposed to during decoking. Care should be taken when to call off decoking by regular sampling of decoking effluent for CO2& CO. However effect of decoking on tubes are common to all tubes. When it is at its end of life, decoking should be done more cautiously but be ready for any eventuality.
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