For many refiners, the hydrocracking unit is a key component in refinery optimization. Proper selection of catalysts for this unit is critical but not often straightforward.
For hydrocracking units where the most important product is gasoline, catalyst selection decisions are complicated by hydrogen utilization issues. The traditional logic for selecting hydrocracking catalysts based on activity, stability, yield pattern and cost may not provide an optimum solution if the decision-maker’s view is confined only to the hydrocracking unit. If the optimization calculations are based only on this unit, yield improvements achieved through volume swell could incorrectly influence the decisions.
Most hydrocracking units which produce maximum naphtha product slates, operate in conjunction with a reforming unit. UOP has found it very useful to consider the combined reformer/hydrocracking unit performance when designing hydrocracking catalyst configurations for these refiners. The results of this type of optimization are interesting and sometimes surprising.
Our analysis has shown that judgements must include consideration of hydrocracking unit yields and product quality plus reformer severity. If heavy naphtha aromatics saturation increases in the hydrocracking unit, required severity and resulting yields from the reforming unit are impacted. To some extent, hydrogen is being added to this fraction in one unit and the severity in the reformer must be increased to remove the added hydrogen.
Relative to the base case, saturation of the heavy naphtha shows significant negative impacts on octane barrels for cases where the there was no gain in heavy naphtha yield or where the gain in heavy naphtha was offset by decreases in light naphtha. A positive result is seen only when the gain in heavy naphtha is offset by butane and lighter losses.
Optimization for all aspects of refining is becoming more and more critical. As an important component in the overall optimization, catalyst selection for hydrocracking units will achieve the highest value for the refiner if the reformer/hydrocracking complex is taken into consideration as a whole. So, delivering this broad-scope optimized solution requires both catalyst and process expertise.
by Don Ackelson, Catalysts and Advanced Materials