Colour during reboiler change over 2

[sgoel]

We have a kerosene rerun column. This column is separating heavy kerosene from desired cut required for N Paraffin manufacture. Reboiler for this column is a hot oil heated shall and tube reboiler with hot oil on tube side.

We face repetitive problem of fouling on shall side. We have provided one more reboiler for preventing shutdown required for cleaning.

The problem is during changeover of reboilers [From fouled to clean], bottoms product colour gets degraded badly, resulting in product downgradation. This continues for two to three days and normalises later on.

Has anyone else faced similar problem? What could be the possible causes and remedies for such a problem so that bottoms product colour does not go bad during changeover.

 

[rsvs3248]

Hi,
During change over ,residence time may exceed the design limit leading to decomposition of one of the components. Decomposition will result in carbon formation that may change the color .

 

[25362]

Some thoughts: How do you clean your fouled exchanger ? Do you use any particular chemical that may remain in the cleaned unit and somehow react with the hevy kero fraction when the reboiler is brought again in commission ?

 

[sgoel]

Dear 25362

Thanks a lot! We simply hydrojet the exchenger, no chemical cleaning is done.

thanks again

 

[sshep]

My theory is that high tube wall temps cause your problem, which occures when clean heat transfer surfaces are brought on line. Within a few days the resistance builds up as a result of the very same degredation that causes color. If it is possible to reduce the hot oil temperature for a few days after switch over your problem may be reduced.