Hydrocracking Process with Vacuum Distillation to Control Polycyclic Aromatic Buildup
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Solution Overview
Problem
The hydrocracking process faces challenges with the buildup of polycyclic aromatic (PCA) hydrocarbons in the heavy oil recycle stream, leading to catalyst deactivation, reduced conversion yields, and equipment fouling.
Innovation Solution
The process integrates hydrocracking with vacuum distillation and solvent deasphalting, where a portion of the heavy oil recycle stream is distilled to separate PCA hydrocarbons, and the resulting streams are processed to reduce PCA concentrations, with the deasphalted paraffinic oil being recycled back to the hydrocracker reactor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher severity hydrocracker reactor conditions are used to achieve desired high conversion, then conversion yield is improved, but polycyclic aromatic hydrocarbon buildup increases causing catalyst deactivation and equipment fouling
Solution Approach 1:
The patent extracts and removes polycyclic aromatic hydrocarbons from the heavy oil recycle stream using a bleed stream that is discarded or sent to a coker unit, preventing their accumulation and harmful effects while maintaining high conversion conditions in the hydrocracker
Solution Approach 2:
The patent discards the bleed stream containing accumulated polycyclic aromatic hydrocarbons to a coker unit or flare, eliminating the harmful substances while recovering any remaining valuable components through the coking process
2Productivity
If heavy oil recycle rate is increased to achieve desired conversion of heavy feedstock, then conversion is improved, but polycyclic aromatic hydrocarbon accumulation worsens
Solution Approach 1:
The patent implements a feedback control mechanism where a portion of the heavy oil recycle stream is bled off and removed based on polycyclic aromatic hydrocarbon concentration measurements, preventing accumulation while allowing the majority of the stream to be recycled for maintaining high conversion
3Object-generated harmful factors
If a bleed stream is discarded to remove polycyclic aromatic hydrocarbons, then polycyclic aromatic hydrocarbon buildup is reduced, but valuable lower boiling hydrocarbons are lost
Solution Approach 1:
Instead of simply discarding the bleed stream, the patent sends it to a coker unit where valuable lower boiling hydrocarbons are recovered through thermal cracking and separation processes, while polycyclic aromatic hydrocarbons are removed as coke or gas products
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces the buildup of PCA hydrocarbons in the heavy oil recycle stream, maintaining acceptable concentrations and enhancing overall conversion yields while preventing equipment fouling.
Implementation Method 1
a second portion of the heavy oil recycle stream is passed to a vacuum distillation unit (also referred to herein as a 'VDU' or a 'vacuum tower') where the second portion is distilled into at least a light vacuum gas oil stream
Implementation Method 2
the second portion of the heavy oil recycle stream is distilled into at least a light vacuum gas oil streams, a heavier vacuum gas oil stream, a slop oil or slop wax stream
Implementation Method 3
the slop oil/wax stream and the vacuum resid stream are passed from the VDU to a solvent deasphalting unit wherein asphaltenes and heavy polycyclic aromatic hydrocarbons are separated from said streams
Data Source
Figure 1
AI summary
An integrated hydrocracking, vacuum distillation and solvent deasphalting process that provides for controlling the amount of polycyclic aromatic hydrocarbons in a heavy oil recycle stream by separating a portion of the heavy oil recycle stream into various fractions in a vacuum distillation unit, and processing the various fractions in a manner, including solvent deasphalting, that allows for the control of the polycyclic aromatic hydrocarbons in the heavy oil recycle stream.