Aspen hydrocracking

Rigorous models for stand-alone units also can provide significant benefits. Previously, we reported benefits of US 3,000 per day (US 0.15 per barrel) for the initial optimizer on the hydrocracking complex these benefits were in addition to those provided by model-predictive DMC control. For RWO, a revised model based on Aspen Hydrocracker (AHYC) was developed. It includes a catalyst deactivation block, which enhances maintenance turnaround planning by predicting future catalyst activity, product yields and product properties for a variety of assumed feeds and specified operating conditions. This information also is used to impose constraints on present-day operation. 

We are pleased to thank the following people for their contributions to RWO and to the development of Aspen FCC or Aspen Hydrocracker John Adams, John Ayala, Darin Campbell, Steve Dziuk, Fernando Garcia-Duaite, Steve Hendon, Nigel Johnson, Ajay Lakshmanan, Jiurm-shyan Liou, Skip Paules, Rosalyn Preston, and Charles Sandmann. 

Several of the commercial simulation programs offer preconfigured complex column rigorous models for petroleum fractionation. These models include charge heaters, several side strippers, and one or two pump-around loops. These fractionation column models can be used to model refinery distillation operations such as crude oil distillation, vacuum distillation of atmospheric residue oil, fluidized catalytic cracking (FCC) process main columns, and hydrocracker or coker main columns. Aspen Plus also has a shortcut fractionation model, SCFrac, which can be used to configure fractionation columns in the same way that shortcut distillation models are used to initialize multicomponent rigorous distillation models. 

The cahbration process for the FCC is square . This implies that there are no user adjustable tuning factors unlike the Aspen HYSYS Reformer or Hydrocracking models. In other words, the number of tuning parameters equals the number of available measurements and the calibration is a much simpler root-finding exercise. In general, the calibration process is quick and converges within 20 iterations. If there is difficulty during calibration, it is mostly likely due to inconsistent product measurements. 

Because of heat effects of the reactions, the calculated reactor temperature profiles from previous steps would show deviations from actual plant data. We tune the global activity factors again to ensure that the deviations of reactor temperature predictions are within tolerance. We repeat the calibration of reactor temperature profiles and mass yields ofhquid products several times until the errors of model predictions are within the acceptable tolerance. These back-and-forth procedures compose the first phase shown in Figure 6.13 which is a generalized guideline of initial calibration for the Aspen HYSYS Petroleum Refining HCR model. This follows because reactor temjjerature profiles and major liquid product yields are always crucial considerations for any hydrocracker. 

Aspen Plus Hydrocracker User s Guide, AspenTech, Burlington, MA (2006). 

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