The Residuum Hydrotreating Process
Purpose:
Upgrading heavy oil fractions (residuum) from crude oil by:
Reducing sulfur content: This is crucial to meet environmental regulations for low-sulfur fuel oil (LSFO) and cleaner transportation fuels.
Removing metals: Protects downstream catalysts in other refinery processes.
Saturating aromatics: Improves stability and reduces emissions.
Reducing nitrogen compounds: Improves combustion and reduces emissions.
Feedstock:
Residuum, the heaviest fraction remaining after other distillation processes in the refinery. It contains high concentrations of sulfur, metals, and complex organic molecules.
Key Steps:
Feedstock Preparation:
The residuum is preheated and mixed with hydrogen gas.
Reactor:
The mixture enters a series of fixed-bed reactors containing a combination of catalysts:
Hydrodemetallization (HDM) catalysts: Remove metals like nickel and vanadium that can deactivate downstream catalysts.
Transition catalysts: Further protect downstream catalysts from metal deactivation.
Hydrodesulfurization (HDS) catalysts: The workhorses, responsible for converting sulfur and nitrogen compounds to hydrogen sulfide and ammonia, respectively.
Under high temperatures (around 300-370°C) and moderate to high pressures (around 30-130 bar), the catalysts promote various reactions:
Hydrogenation of sulfur compounds to hydrogen sulfide.
Hydrogenation of nitrogen compounds to ammonia.
Partial saturation of aromatic rings.
Conversion of some asphaltenes (complex organic molecules) into lighter hydrocarbons.
Separation:
The product stream leaving the reactor is cooled and sent to separators:
Hydrogen gas is separated and recycled back to the process.
Liquid hydrocarbons (treated residuum) are separated from water and gas byproducts.
Further Processing:
The treated residuum may undergo additional processes like:
Fractionation to separate various hydrocarbon fractions based on boiling points.
Resid fluid catalytic cracking (RFCC) for further conversion into lighter fuels like gasoline and diesel.
Benefits:
Produces cleaner fuel oil with lower sulfur content, meeting environmental regulations.
Enables processing of heavier oil fractions, maximizing refinery output.
Improves stability and reduces emissions of treated products.
Additional Points:
Residuum hydrotreating is a complex process requiring specialized catalysts and high operating pressures.
The specific catalyst configuration and operating conditions can be adjusted depending on the desired product properties and feedstock characteristics.
This process often plays a crucial role in integrated refinery configurations where residuum is further converted into valuable transportation fuels.
Here are some resources for further exploration:
Hydrotreating | Resid hydrotreating: https://www.topsoe.com/processes/hydrotreating/resid-hydrotreating
Modeling and Simulation of Reaction and Fractionation Systems for the Industrial Residue Hydrotreating Process: https://www.mdpi.com/2227-9717/8/1/32