Multistage Hydroprocessing Configuration for High Conversion
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Solution Overview
Problem
Current hydroprocessing methods for heavy hydrocarbon materials boiling in the vacuum gas oil range face challenges in achieving high selectivity and conversion efficiency while maintaining low capital investment, particularly in upgrading external distillates and managing recycle liquids, which often result in higher costs and complications.
Innovation Solution
A multistage hydroprocessing configuration involving a once-through liquid unit with two reactors, a high-pressure separator, and split feed injection, operating at lower pressures and optimized reaction zones to minimize overcracking and catalyst volume, allowing for high conversion and selectivity of distillates without separate fractionation zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multistage recycle is used to achieve high conversion and selectivity, then liquid yield and flexibility are improved, but capital investment and operational complexity increase significantly
Solution Approach 1:
The process divides the hydroprocessing into two distinct reaction zones: a first reactor for hydrotreating VGO at high pressure, and a second reactor for hydrocracking the bottoms fraction at lower pressure. This segmentation allows each reactor to be optimized for its specific function, achieving high conversion and selectivity without requiring complex multistage recycle systems
Solution Approach 2:
The process extracts the distillate fraction overhead from the first reactor and directs it to a distillate upgrader, preventing it from entering the second reactor. This extraction of the valuable distillate stream early in the process eliminates overcracking and allows the second reactor to focus on converting bottoms to additional distillates, achieving high overall yield without complex recycle operations
2Device complexity
If single stage once through design is used to reduce capital cost, then equipment investment is reduced, but conversion efficiency and selectivity are limited
Solution Approach 1:
The process uses two separate reactors in series, with the first dedicated to hydrotreating and the second to hydrocracking. This segmentation enables high conversion efficiency comparable to multistage systems while maintaining simpler equipment requirements and lower capital investment than true multistage recycle units
Solution Approach 2:
Each reactor operates under locally optimized conditions: the first reactor operates at high pressure (1500-3000 psig) for effective hydrotreating, while the second reactor operates at lower pressure (500-2000 psig) for efficient hydrocracking. This local optimization of operating conditions maximizes conversion efficiency in each zone while keeping overall system complexity low
3Productivity
If high pressure is maintained throughout the process to ensure effective hydrotreating, then hydrotreating efficiency is improved, but overcracking of distillates increases and hydrogen consumption rises
Solution Approach 1:
The process applies high pressure locally only in the first reactor where hydrotreating is required, and reduces pressure in the second reactor where hydrocracking occurs. This localized pressure optimization ensures effective hydrotreating while minimizing overcracking and hydrogen consumption in the downstream hydrocracking section
Solution Approach 2:
By extracting the distillate fraction overhead from the first reactor and directing it to a distillate upgrader, the process removes these lighter fractions before they can undergo unwanted overcracking reactions in the second reactor, thereby reducing hydrogen consumption and improving distillate selectivity
4Adaptability or versatility
If separate fractionation zones are used to upgrade external distillates, then upgrading capability is improved, but process complexity and equipment requirements increase
Solution Approach 1:
The process merges the upgrading of external distillates with the hydrocracking of VGO bottoms by feeding both streams to the second reactor. This integration allows simultaneous upgrading of multiple feedstocks in a single reactor, eliminating the need for separate fractionation zones and reducing overall process complexity
Solution Approach 2:
The second reactor serves multiple functions: it hydrocracks the bottoms from the first reactor, upgrades external distillate feeds, and produces additional middle distillate products. This multi-functionality achieves versatile upgrading capability without requiring separate dedicated units for each function
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 configuration achieves high conversion and selectivity comparable to multistage recycle units at lower capital costs, minimizing overcracking and hydrogen consumption, and effectively upgrades external distillates, producing high yields of middle distillates with reduced equipment needs and operational complexity.
Implementation Method 1
passing the effluent of step (b), following pressure reduction, to a very hot separator maintained at high pressure, where it is separated into an overhead fraction and a bottoms fraction
Implementation Method 2
contacting it with hydroprocessing catalyst, thereby creating a hydroprocessed effluent
Implementation Method 3
combining the upgraded effluent of step (d) with the second hydroprocessed effluent of step (e), the combined stream then entering a hot separator maintained at high pressure, in which the combined stream is separated into an overhead fraction and a bottoms fraction
Data Source
AI summary
In the refining of crude oil, hydroprocessing units such as hydrotreaters and hydrocrackers are used to remove impurities such as sulfur, nitrogen, and metals from the crude oil. They are also used to convert the feed into valuable products such as naphtha, jet fuel, kerosene and diesel. The current invention provides very high to total conversion of heavy oils to products in a single high-pressure loop, using multiple reaction stages. A hot high pressure separator is located between the first and second reaction stages. Overhead from the separator is treated in a distillate upgrader, which may operate in co-current or countercurrent mode.