Sequential Thermal Cracking Process for Coke Reduction
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Solution Overview
Problem
Current thermal cracking processes for hydrocarbon feedstocks result in high coke formation and require severe downstream upgrading, leading to inefficient production of middle distillates and potential agglomeration of asphaltenes.
Innovation Solution
A sequential thermal cracking process in a cascade of cracking units with increasing temperatures, where the hydrocarbon feedstock is heated to specific temperatures in each unit to prevent coke precursor formation, with short residence times and fractionation steps to maintain asphaltenes in solution, reducing coke formation and enhancing middle distillate production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If severe thermal cracking conditions are applied to convert heavy hydrocarbons to middle distillates, then conversion efficiency improves, but coke formation increases and asphaltenes may agglomerate
Solution Approach 1:
The cracking process is divided into multiple sequential stages with progressively increasing temperatures. The first stage operates at moderate temperatures to perform mild cracking, while subsequent stages operate at higher temperatures for more severe cracking. This segmentation allows the process to achieve high overall conversion efficiency while controlling coke formation at each individual stage, as no single stage experiences excessively severe conditions that would lead to rapid coking.
Solution Approach 2:
The first cracking stage performs preliminary cracking of the heavy feedstock at moderate temperatures before the material enters subsequent high-temperature stages. This preliminary action breaks down some of the heavy molecules early, preventing them from undergoing excessive cracking and coking in later stages, thereby reducing overall coke formation while still achieving the desired conversion to middle distillates.
2Productivity
If longer residence times are used to enhance cracking conversion, then middle distillate yield improves, but coke formation increases
Solution Approach 1:
The total residence time is distributed across multiple cracking stages rather than using one long residence time in a single stage. Each stage has a relatively short residence time that is optimized for its specific temperature level, achieving cumulative conversion without the excessive coke formation that would result from a single prolonged exposure to high temperatures.
Solution Approach 2:
The temperature parameter is changed progressively across stages while residence time is kept relatively short in each stage. This parameter change strategy allows the process to achieve high conversion through the cumulative effect of multiple moderate cracking events rather than one severe cracking event, thereby maximizing middle distillate yield while minimizing coke formation.
3Productivity
If higher cracking temperatures are applied to increase conversion rate, then productivity improves, but asphaltene agglomeration and coke formation increase
Solution Approach 1:
The high temperature cracking is segmented into multiple stages rather than applied in a single high-temperature zone. This allows asphaltenes to be gradually transformed through successive milder heating zones, maintaining their stability and preventing agglomeration, while still achieving high overall conversion rates through the cumulative effect of all stages.
Solution Approach 2:
Temperature is changed progressively across stages rather than applied abruptly at high levels. This gradual parameter change allows asphaltenes to adapt and transform smoothly, preventing the sudden thermal shock that would cause agglomeration, while still achieving the desired high conversion rate through the cumulative thermal treatment.
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
The process effectively reduces coke formation and increases the yield of useful middle distillates by maintaining asphaltenes in solution and controlling temperature and residence times, resulting in lower coke yields and reduced hydrogen requirements for further upgrading.
Implementation Method 1
heating said hydrocarbon feedstock in said furnace to a cracking temperature T1
Implementation Method 2
thermally cracked in the cascade of cracking units
Implementation Method 3
separating the product stream from said first cracking unit into a light fraction and a heavy fraction
Data Source
AI summary
A sequential cracking process for the thermal cracking of a hydrocarbon feedstock in a cascade of cracking units wherein said hydrocarbon feedstock is heated in a furnace to a predetermined maximum temperature and thermally cracked in the cascade of cracking, such that the formation of coke is reduced.