CFD Simulation of Diesel Hydrotreaters Under Periodic Operation Mode

Middle distillate hydrotreating is the most important refining process for the production of ultra-low-sulfur diesel, in which sulfur content is required to be less than 15 wppm. Hydrotreating is usually conducted in trickle bed hydrotreaters under steady-state operation with constant gas and liquid flows and constant temperature and pressure. Under this operation mode, mass and heat transfers are important factors affecting the operation and performance of hydrotreaters.

In recent years, periodic (non-steady-state) operation has generated growing interest in view of the resulting performance enhancements (increased conversion and selectivity). The central attribute of periodic operation is control of the trickle bed reactor in a transient mode by periodically changing the gas and/or liquid flows, leading to non-steady-state fluid hydrodynamics, nonlinear performance of chemical reactions, and enhanced heat and mass transfers. Although studies have been conducted using some selected chemical reactors, none has been published so far investigating the impacts or enhancements associated with periodic operation of petroleum hydrotreating reactors. Computational fluid dynamics (CFD) simulation provides an efficient approach for performing such studies qualitatively.

This paper will discuss CFD simulation results on periodic operation of middle distillate hydrotreaters. As the first step, the flow dynamics (without reactions) under commercial hydrotreating conditions are simulated by periodically changing the gas and/or liquid flow (base-pulse strategy, slow versus fast modulation), pressure, and other operating conditions. The details of the CFD model and simulation results will be provided in the extended abstract and in the presentation.