Side Stream Withdrawal for HPNA Reduction in Hydrocracking
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Solution Overview
Problem
Hydrocracking processes face challenges with the accumulation of heavy polycyclic aromatic compounds (HPNA) in the recycle loop, which poison catalysts and disrupt operations, while existing methods to reduce these compounds often result in yield losses and high costs.
Innovation Solution
A process involving a side stream withdrawal above the supply plate in a fractionation column, with partial recycling and optional stripping, effectively reduces HPNA concentration and improves yield by recycling unconverted hydrocarbons, thereby minimizing the introduction of refractory HPNA into the hydrocracker.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If unconverted feed is recycled to increase hydrocracking conversion, then conversion rate is improved, but polycyclic aromatic compounds accumulate and poison the catalyst
Solution Approach 1:
The patent extracts and removes polycyclic aromatic compounds from the recycle loop through a side stream withdrawal system positioned above the supply plate in the fractionation column. This selective removal prevents catalyst poisoning while maintaining the beneficial recycle of unconverted feed, thus resolving the contradiction between improving conversion rate and maintaining catalyst activity.
2Object-affected harmful factors
If heavy fraction is withdrawn and recycled to reduce HPNA concentration, then HPNA accumulation is reduced, but yield losses and hydrogen costs increase
Solution Approach 1:
The patent applies local quality by positioning the side stream withdrawal at a specific location (above the supply plate) where the concentration of polycyclic aromatic compounds is highest. This localized removal targets HPNA compounds specifically without unnecessarily removing valuable unconverted hydrocarbons, thus reducing HPNA accumulation while minimizing yield losses compared to bulk heavy fraction withdrawal.
3Reliability
If stripping is applied to reduce HPNA in recycled fraction, then catalyst poisoning is reduced, but energy consumption and operational complexity increase
Solution Approach 1:
The patent implements preliminary action by removing polycyclic aromatic compounds through fractionation before the recycled fraction re-enters the hydrocracker. The side stream withdrawal positioned above the supply plate performs this separation in advance, preventing HPNA accumulation and catalyst poisoning without requiring additional stripping equipment or complex post-treatment systems.
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 concentration of HPNA with 6 or more aromatic rings, enhancing catalytic activity and cycle time while maintaining or improving the yield of upgradeable products, thus overcoming the limitations of prior art methods.
Implementation Method 1
a step for fractionation of said effluent, which separates at least one distillate and a residue
Implementation Method 2
the bottom of the fractionation column (residue) is stripped as a counter-current in a stripping column
Implementation Method 3
their reduction via a hydrogenation
Data Source
AI summary
The invention concerns a process and a facility for reducing the concentration of heavy polycyclic aromatic compounds (HPNA) in the recycle loop of hydrocracking units, which comprises a fractionation column.In accordance with this process, a portion of the stream present at the level of at least one plate located between the plate for supplying hydrocracked effluent and the plate for withdrawing the distillate fraction which is the heaviest is withdrawn from the fractionation column and at least a portion of said withdrawn stream is recycled to the column directly or after optional liquid separation, and optionally a portion of said withdrawn stream is recycled to the hydrocracking step directly or after optional gas separation.