(44b) Experiences in Maximizing Performance of ULSD Units

ABSTRACT Refiners in the US and Europe, as well as many other countries, have been producing ULSD for at least 4 years. While some problems were encountered in the transition to ULSD, the vast majority of these new ULSD units and unit revamps have performed as well as, or better than, expected. As these units reach the end of their first cycles, it's worthwhile to review their operating experiences and investigate opportunities to further optimize performance. One area of significant progress in the interim is in understanding the chemistry of hydroprocessing for ULSD. It turns out that there are more significant differences in the desulfuri-zation chemistry for these units than can be accurately understood by using average bed temperature and basic kinetics. What is needed is a look inside the reactor in order to develop a better understanding of the discrete reactions taking place. Albemarle has developed a methodology and a model to accomplish just that. This technology, designated STAX®, predicts the required catalyst functionality for each section of the reactor based on key parameters for the particular ULSD unit. The result is a catalyst system design which delivers maximum performance within the capabilities and constraints of the unit and the objectives of the refiner. In this paper we review development of the concepts and methodology behind STAX® technology. Commercial experience, where the STAX® design techniques have been successfully applied, will also be discussed.