Steam Stripping Cat Cracker Feed
A side-stream product drawn from a crude tower is only half fractionated. Refluxing below the drawoff tray controls the product end point. Front-end fractionation takes place in the side-stream stripper.
A typical stripper configuration is shown in Figure 1—4. Steam enters the bottom of the stripper and reduces the hydrocarbon partial pressure. The product partially vaporizes to reestablish vapor-liquid equilibrium. The heat for this vaporization comes from the product itself, not from the stripping steam.
On many crude units, steam stripping of naphtha, kerosene, and furnace oil appears adequate. On the other hand, stripping of FCCU feed is frequently poor. Figure 1-5 shows the effect of stripping. Hydrocarbons boiling below 500°F belong in naphtha reformer feed or kerosene, not in the FCCU charge.
Obtain a sample of FCCU feed produced at the crude unit. Run an ASTM atmospheric distillation. Ask the lab technician to stop the distillation at 680°F; this avoids thermal cracking. If more than a few percent is distilled off below 500°F, examine the operation of the FCCU feed stripper.
Categories: Process Troubleshooting | Tags: Steam Stripping | Leave a comment