A simple plug-flow model was developed to study the deactivation mechanisms of hydroprocessing catalysts in atmospheric residue desulfurization (ARDS) units. The three stages of catalyst deactivationsat the start of the run, middle of the run, and end of the runsare considered. The catalyst deactivation is mainly due to metal and coke deposition. The model parameters considered are the unit temperature, fluid velocity, reaction rate constant, catalyst combination, catalyst bed length, and feed concentration of sulfur, metals, and asphaltenes. The simulated results compared very well with our laboratory data for a long catalyst life test operated under constanttemperature mode. The model is further applied to a parametric study that examines the effects of space velocity, unit temperature, and maximum metal capacity on the performance of catalyst systems. A constant-sulfur-mode simulation is also given.

A hydroprocessing multicatalyst deactivation and reactor performance model was originally developed to predict the life and performance of atmospheric residue hydroprocessing catalysts in a pilot-plant long-life test. The model has been subsequently applied to predict catalyst and reactor behavior in an accelerated life test using Boscan crude oil as the feedstock. Simulations from the original model did not compare well with accelerated test run data. Because Boscan crude oil has very high metal and asphaltene contents, mass balance terms that emphasized noncatalytic hydrothermal reactions in the model were needed, especially when catalysts were severely deactivated. Excellent comparisons were obtained after including hydrothermal reaction terms to refine the model. The model was then used to simulate the Boscan crude oil hydroprocessing in constantsulfur-mode operations, and it was found that it would be more beneficial to operate the atmospheric residue desulfurization unit at a lower initial temperature.

SUMMARYIn this paper a control algorithm that minimizes the auxiliary energy consumption in a typical solar cooling system while maintaining appropriate comfortable conditions in the cooled enclosure is devised. A dynamic mathematical model for a lithium bromide-water absorption chiller is developed to be used for deriving the optimal control algorithm. Finally, the results of simulation of the optimal control algorithm indicate that a net reduction of more than 30% in auxiliary energy is possible.

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