Ideally, the process equipment should be disassembled for internal inspection of the bed — pay particular attention to the distribution plate and tubes at the bottom of the reactor and the inlet of the cyclone. Next, look at the air locks on the first bed and at the recycle compressor discharge and inlet of the second bed. You'll also want to inspect the product line connecting to the receiver feeding the second fluid-bed reactor. Look for solids buildup; take samples for scanning with an electron microscope.
Dirk Willard, senior process engineer
Ambitech Engineering, Joliet, Ill.
The atmospheric tower (Figure 1) of our crude distillation unit performs adequately but we'd like to improve its efficiency and capacity as well as eliminate a few nagging problems. We've run a few experiments to justify simulation runs. Gamma scans have shown flooding in the sieve trays at and above stage 8 in the heavy gas oil (HGO) section of the column when we tried to increase crude feed. We also see some channeling in the structured packing in the light gas oil. In addition, we're concerned about whether the type-304 stainless steel used for the structured packing in the naphtha pump-around and elsewhere is adequate now that we've increased the ratio of heavy to sweet crude; samples in that section show higher H2S concentration than ever before. We have caustic injection quills downstream of the desalters to neutralize HCl but we're worried about downstream sodium. Other problems include a slightly higher pressure between the outlet of the air condenser and the vent discharge to the sour gas knockout drum. Occasionally, we're seeing dry trays between stages 13 and 20. Also, the control valve for the HGO steam stripper sometimes runs 100% open, restricting tower throughput. What should we include in future analyses and what do you recommend to improve tower performance?
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