Coker Bb Case Study

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On 1/7, the Alky started to only process FCCU BB and no longer process Coker BB. Alkylation chemistry, neither likes contaminants nor diluents. Contaminants are direct acid consumers. The more contaminants in the feed, the more often the unit will be at an acid constraint. Diluents do not react in alkylation chemistry, but they take up space and decrease the effective area for isobutane and olefin to contact. With less contact, side reactions like polymerization are more likely to occur; polymerization reactions are a direct acid consumer. Comparing the FCCU and Coker BB, Coker BB contains far more contaminants and diluents than FCCU BB (see Table 2, pg.4). By lowering the amount of contaminants and diluents, acid consumption reduced 0.2…show more content…
By leaving the acid and olefin in contact with no isobutane, polymerization occurred which increased acid consumption. After the shutdown, processing off-spec material also contributed to an increased acid consumption (see Figure 2, pg.4). Because of long residence times between the contactors and settlers, it will take time for the acid consumption to reduce to pre-shutdown levels. Acid spend strength has been higher than required for this period (see Figure 4, pg.5). Process Support recommends lowering the amount of fresh acid consumed to get closer to the spend target. Noticeably, there is very little reduction in acid strength from A train to B train. This indicates that there is not much additional reaction happening between the two. Process Support will contact Stratco to determine what could be causing this phenomenon. In general, the unit consumes more acid than required (91 target spend strength vs. 89 technical target spend strength) because controlling the series acid flow is a manual operation (see Figure 4, pg.5). During the turnaround, instrumentation will be installed to better control acid spend strength to the lower target (see Figure 5,
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