(101b) Understanding Vapor-Liquid Equilibrium in Bitumen Derived Heavy Gas Oil Hydrotreater

Primary upgrading of bitumen (coking or hydroconversion) yields three distillate streams: naphtha, light gas oil (LGO), and heavy gas oil (HGO). These three materials have to undergo hydrotreating to remove most of the sulfur, nitrogen, and metals before they are blended into synthetic crude oil (SCO). The hydrotreating reactors used in these hydrotreating processes are operated under vapor-liquid equilibrium (VLE), with both vapor and liquid phases containing oil and hydrogen. Different operating conditions (temperature, pressure, gas/oil ratio, etc.) result in different flow dynamics and operating regimes in the hydrotreating reactors, and therefore differences in process performance and efficiency. It is always desirable to operate these hydrotreaters in ideal operating regimes (trickle flow, plug flow, fully wetted catalysts, etc.) that achieve optimal reactor performance. This is especially important in processing the HGO stream process since the HGO hydrotreater accounts for about 30% of the total capital and operating cost in a bitumen upgrader.

In order to describe the flow dynamics precisely and to predict operating regimes in the hydrotreating reactors under typical commercial operating conditions, it is essential to understand the VLE behaviors and to conduct VLE calculations correctly. In this study VLE experiments (flash experiments) were conducted in a continuous-flow unit over a wide range of operating conditions commonly employed during HGO hydrotreating. The feedstocks used in the experiments were HGOs derived from Canadian bitumen. It was found that, although HGO hydrotreating is conducted at relatively high pressure and the feedstock is less volatile than naphtha or LGO substantial amounts of the HGO feed are still vaporized at relatively high reaction temperatures. These losses to vapor phase need to be accounted for during reactor modeling, simulation, and design. In order to perform flash calculations accurately to predict VLE in the hydrotreater under any operating conditions, the experimental data were used to evaluate the interaction coefficients between hydrogen and hydrocarbon pseudo-components in the equation of state used for the flash calculations. The interaction coefficients were correlated with the boiling point of the pseudo-components and the aromatics content in the feedstock. Detailed results and discussion will be presented.