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Reply To: Velocity water x feedrate

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Mike Kimbrell

Yes, with high enough velocity from hydrocarbons additional velocity media does not change the film thickness or heat transfer coefficient so that the additional velocity media is not necessary for the heater tubes. The Bechtel distillate recycle technology takes advantage of this and requires a lower velocity media rate to prevent heater fouling.

I am aware of a case where a Coker was operating at much higher than design rates and the velocity steam was removed to reduce the pressure drop through the heater. In this case, the velocity in the transfer line from the heater to the coke drums was high enough that coke formation was still uniform around the circumference of the pipe.

I am also aware of another Coker that reduced velocity media to reduce pressure drop through the heater; however, the velocity in the transfer line was low enough to allow the liquid to settle and coke which resulted in excessive coking in the transfer line. This transfer line coking raised the pressure in the heater coil and increased the heater fouling rate.

For a low recycle ratio Coker operating near the design rate for the unit, I would always have some velocity media in the heater coils.

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