CRUDE DISTILLATION UNIT (CDU)

Crude Distillation Unit (CDU) operates with the basic principle of separation based on boiling point of the constituent components. CDU column produces LPG, naphtha, kerosene, and diesel by 50-60% the volume of feed, whereas the other products of 40-50% by volume of atmospheric residue feed.

Atmospheric residue at the old refinery, which does not have a Vacuum Distillation Unit / VDU, usually only used as a fuel oil which is its very low value or sold to other refineries for further dioleh on the VDU. Whereas in a modern refinery, the atmospheric residue is sent as feed Vacuum Distillation Unit or as a feed Residuel Catalytic Cracking (after some in-treating in Atmospheric Residue Hydro Demetalization unit to eliminate the metal content of atmospheric residue).

Process Variable Crude Distillation Unit

Some process variables that affect the CDU operation are as follows:

1. Flash Zone Temperature

The higher flash zone temperature, the more the yield of product produced, and conversely the less yield bottom-CDU. But flash temperatue zone should not be too high because it can result in thermal decomposition / cracking bait. Temperature of thermal decomposition / cracking depends on type of bait. In general, temperatures of thermal decomposition / cracking of crude is around 370 ° C (385 ° C mentioned UOP). Flash zone temperature is regulated indirectly, ie by setting the Combined Outlet Temperature / COT-fired heater.

2. Top Column Temperature CDU

CDU column top temperature is set to restore some of naphtha which has been condensed as reflux back to the top column of the CDU. If flash zone temperature is raised, then the reflux rate should be raised to keep the temperature fixed top. Temperature is one of the top column naphtha endpoint directions. To obtain endpoint products of lower overhead then the top temperature should be lowered by increasing the number of top reflux.

3. Top Column Pressure CDU

Although the column top pressure never varied, but the small changes in the top column pressure will produce large changes in temperature at a fixed feed composition. If the column top pressure can not be kept fixed and CDU operations rely solely on quality control of products simply by setting tray temperatures / temperature draw off, then the product composition will change significantly. Pressure swing very often will make the CDU operation becomes unstable. To maintain the stability of the column top pressure mounted temperature controller that in-cascade with top reflux flow.

4. Steam Stripping

The amount of stripping steam (superheated) is inserted into the bottom of each side cut product steam stripper used to remove dissolved in the product lighter, which will determine the flash point products. Stripping steam can also be inserted into the bottom / bottom column reboiler with the CDU as a replacement for similar functions, ie removing the existing light fraction in the column bottom product CDU.