Two-Stage Thermal Cracking Process for Coke Yield Reduction
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Solution Overview
Problem
The Delayed Coking process in petroleum refineries generates excessive petroleum coke, leading to challenges in handling, storage, and marketing, with existing methods relying on additives and catalysts that increase costs and potentially render products unusable due to ash content, and existing processes fail to effectively reduce coke yield beyond a certain limit.
Innovation Solution
A novel two-stage thermal cracking process with a multistage separation system, where the second stage operates under vacuum conditions, preventing heavier molecules from participating in coke formation reactions, thereby reducing overall coke yield without the use of external additives or catalysts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional delayed coking process is used to convert petroleum residue, then gaseous and liquid products are obtained, but excessive petroleum coke is generated leading to handling and storage problems
Solution Approach 1:
The coking process is divided into two distinct stages: a first thermal cracking stage at lower severity followed by a second thermal cracking stage at higher severity. This segmentation allows lighter products to be removed after the first stage, preventing them from participating in excessive cracking reactions that would otherwise generate additional coke in a single-stage process.
Solution Approach 2:
Lighter product streams are extracted and removed from the reaction mixture after the first thermal cracking stage. By taking out these lighter products before the second cracking stage, the process prevents their further conversion into coke, thereby reducing overall coke yield while maintaining productive conversion of the heavy residue feed.
2Loss of substance
If additives like free radical inhibitors or catalysts are used to reduce coke yield, then lighter product yields improve, but product usability deteriorates due to ash content and additional costs
Solution Approach 1:
The process uses controlled thermal cracking conditions and multistage separation to achieve coke reduction inherently, without requiring external additives or catalysts. The system serves itself by using temperature control and residence time management to direct reaction pathways toward lighter products while minimizing coke formation, eliminating the need for substances that would introduce ash contamination.
3Productivity
If feed throughput to delayed coking unit is increased, then processing capacity improves, but coke bed height increases requiring more drums and storage space
Solution Approach 1:
The two-stage cracking process segments the conversion of heavy residue into multiple controlled reactions. The first stage produces a mixture containing both intermediate and lighter products, which are then separated. This allows higher feed throughput to be processed while the lighter products are removed before second stage cracking, reducing the volume of coke generated per unit of feed processed.
Solution Approach 2:
Lighter product fractions are extracted after the first cracking stage and before the second stage. This extraction removes material that would otherwise continue cracking to form additional coke, enabling higher overall feed throughput while limiting coke bed height growth through reduced coke yield per barrel of feed.
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 achieves a significant reduction in coke yield by approximately 7 wt%, improving refinery margins and maximizing diesel production, while avoiding the costs and drawbacks associated with using additives and catalysts.
Implementation Method 1
passing the hot feed at desired temperature and pressure to the pre-cracking reactor, wherein the hot feed undergoes mild thermal cracking reactions
Implementation Method 2
separating first portion of the bottom fraction in a second separator column operating in vacuum conditions to obtain top product and heavier product
Implementation Method 3
heating the secondary hydrocarbon feedstock in a furnace to obtain hot feed at a desired inlet temperature
Implementation Method 4
passing the hot hydrocarbon stream from the furnace to a preheated coke drum... passing the product vapors exiting the coke drum
Data Source
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AI summary
The present invention relates to Delayed Coking of heavy petroleum residue producing petroleum coke and lighter hydrocarbon products. The invented process utilizes a pre-cracking reactor for mild thermal cracking of the feedstock and intermediate multistage separation system before being subjected to higher severity thermal cracking in delayed coking process, resulting in reduction in overall coke yield.