Cracked Naphtha Desulfurization via Fractionation and Heat Integration
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Solution Overview
Problem
Current desulfurization processes for catalytically cracked gasoline are energy-intensive and costly, leading to a significant drop in octane number due to olefin saturation, and require extensive fractionation and high-pressure steam for distillation, which is expensive and inefficient.
Innovation Solution
A process that fractionates cracked naphtha into light and heavy fractions using a distillation column with an intermediate reboiler, where the intermediate naphtha fraction is heated by a lower-temperature heat source and recycled back into the column, reducing energy consumption and operating costs by utilizing internal process streams for heat integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional hydrodesulfurization is applied to catalytic cracking gasoline, then sulfur content is reduced, but octane number drops substantially due to olefin saturation
Solution Approach 1:
The catalytic cracking gasoline is divided into two fractions based on boiling point: a light fraction (C5-C6) and a heavy fraction (C7+). The heavy fraction, which contains the majority of sulfur compounds, is selectively hydrodesulfurized, while the light fraction rich in olefins is preserved to maintain octane number.
Solution Approach 2:
Different treatment conditions are applied to different fractions of the gasoline. The heavy fraction undergoes hydrodesulfurization under specific conditions optimized for sulfur removal, while the light fraction is left largely untreated to preserve its high-octane olefin content.
2Manufacturing precision
If the whole feed is desulfurized by hydrodesulfurization, then sulfur content is reduced, but very large volumes of feed must be treated under severe temperature and pressure conditions, leading to substantial investment
Solution Approach 1:
The heavy fraction containing the bulk of sulfur compounds (approximately 80-90% of total sulfur) is extracted from the whole gasoline feed through distillation. Only this concentrated sulfur-bearing fraction is then subjected to hydrodesulfurization, significantly reducing the volume of feed requiring severe treatment conditions.
Solution Approach 2:
Instead of treating the entire gasoline feed with hydrodesulfurization, only the necessary heavy fraction is treated. This partial action achieves the required overall sulfur reduction (to below 10 ppm) while minimizing energy consumption and equipment investment.
3Manufacturing precision
If fractionation into multiple cuts is performed before hydrotreating, then desulfurization efficiency is improved, but the process becomes complex and must be repeated every time gasoline composition changes
Solution Approach 1:
The gasoline is segmented into only two fractions (light and heavy) based on boiling point, rather than dividing into multiple cuts. This simplified segmentation is sufficient to achieve effective desulfurization while avoiding the complexity of analyzing and treating numerous individual fractions.
4Quantity of substance
If distillation column is operated with bottom reboiler using high pressure steam or fuel, then fractionation is achieved, but energy consumption is very high and operating cost is expensive
Solution Approach 1:
The distillation column is integrated with the hydrodesulfurization unit, combining two previously separate processes. The bottom reboiler of the distillation column uses the hot effluent from the hydrodesulfurization reactor as a heat source, merging the thermal needs of both units and eliminating the need for separate high-pressure steam heating.
Solution Approach 2:
The hydrodesulfurization unit provides its own heat to the distillation column through the bottom reboiler. The hot effluent from hydrodesulfurization, which would otherwise require cooling, is used to generate the reboiling duty, making the system self-sufficient and reducing external energy requirements.
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 lowers energy consumption and operating costs by using internal heat sources, maintaining higher octane numbers and achieving effective desulfurization while minimizing the need for high-pressure steam, thus improving the overall energy efficacy of the desulfurization process.
Implementation Method 1
fractionating the cracked naphtha into a light naphtha fraction and a heavy naphtha fraction which is removed as bottoms from the distillation column
Implementation Method 2
heating said intermediate naphtha fraction at a lower temperature than the bottom reboiler, with an intermediate reboiler supplied with a heat source having a temperature lower than the bottom reboiler
Implementation Method 3
feeding the heavy naphtha fraction and hydrogen to a hydrodesulfurization unit containing a hydrodesulfurization catalyst to produce a desulfurized heavy naphtha effluent
Implementation Method 4
feeding the cracked naphtha to a distillation column comprising a bottom reboiler; fractionating said cracked naphtha into a light naphtha fraction and a heavy naphtha fraction
Data Source
AI summary
A process for desulfurizing a cracked naphtha containing organic sulfur compounds:a) feeding the cracked naphtha to a distillation column comprising a bottom reboiler;b) fractionating said cracked naphtha into a light naphtha fraction and a heavy naphtha fraction which is removed as bottoms from the distillation column;c) feeding the heavy naphtha fraction and hydrogen to a hydrodesulfurization unit containing a hydrodesulfurization catalyst to produce a desulfurized heavy naphtha effluent.The process further includes providing heat to the distillation column by an intermediate reboiler powered with a heat source having a temperature lower than that one of the bottom reboiler.