Steam Cracked Tar Depolymerization and Hydrogenation
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Solution Overview
Problem
Conventional steam cracking processes produce large amounts of tar, particularly when cracking heavier hydrocarbon feeds, which results in high-boiling, viscous, and less valuable products, and can foul equipment, limiting their economic value and compatibility with other streams.
Innovation Solution
A process involving the heating of steam cracked tar to depolymerize it, followed by hydrogenation using a catalyst to convert it into lower boiling molecules, and subsequent steam cracking in a furnace with both convection and radiant zones, minimizing the production of unwanted by-products and reducing tar asphaltenes, thereby creating a more valuable feedstock.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If heavier hydrocarbon feeds are cracked to improve economic value, then lower cost feedstocks can be processed, but large amounts of high-boiling viscous tar are produced which reduces economic value and can foul equipment
Solution Approach 1:
The patent converts the harmful tar byproduct into a beneficial feedstock by integrating a steam cracker within the vacuum tower. The tar, which would normally be discarded or require expensive treatment, is now fed to the integrated steam cracker to produce valuable light olefins and upgraded vacuum gas oil, transforming a waste stream into an economic asset.
Solution Approach 2:
The patent merges the steam cracking function directly into the vacuum tower by installing a steam cracker within the tower structure. This integration allows the vacuum tower to simultaneously perform vacuum distillation and steam cracking operations, enabling the direct conversion of tar produced in the vacuum tower into valuable products without requiring separate handling and processing facilities.
2Productivity
If steam cracked tar is produced to maintain product yield, then hydrocarbon conversion is achieved, but the tar becomes highly viscous and less compatible for mixing with paraffinic streams
Solution Approach 1:
Instead of treating tar as a problematic byproduct that requires stabilization or disposal, the patent converts it into a valuable feedstock for the integrated steam cracker. This transformation eliminates compatibility issues with paraffinic streams by completely reprocessing the tar into different product streams (light olefins and upgraded vacuum gas oil) that do not have mixing compatibility problems.
Solution Approach 2:
The patent fundamentally changes the parameters of the tar material by subjecting it to steam cracking conditions (high temperature, steam atmosphere). This converts the high-boiling, high-viscosity tar into lower molecular weight products with completely different physical and chemical properties, including lower viscosity and different compositional characteristics that are suitable for producing valuable chemicals rather than fuel blending components.
3Productivity
If tar is produced from cracking heavier feeds to maintain yield, then process throughput is maintained, but equipment fouling increases which reduces operational reliability
Solution Approach 1:
The patent converts the tar that would cause fouling into a feedstock for the integrated steam cracker. By continuously removing and reprocessing the tar rather than allowing it to accumulate or be stored, the system eliminates the fouling problem while maintaining high process throughput. The tar is immediately utilized as feed, preventing it from contacting and fouling downstream equipment.
Solution Approach 2:
The patent performs preliminary action by cracking the tar in-situ within the vacuum tower before the tar can cause fouling problems in downstream equipment. The integrated steam cracker is positioned to receive tar directly from the vacuum distillation section, converting it to lighter products before the tar has an opportunity to deposit on heat exchanger surfaces, valves, or other equipment where it would cause operational reliability issues.
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 process effectively converts steam cracked tar into lower boiling materials, increasing its value as a steam cracker feed, reducing fouling of hydrogenation catalysts, and producing a low sulfur vacuum tower bottoms stream with enhanced properties.
Implementation Method 1
a steam cracking furnace comprising a convection section and a radiant section
Implementation Method 2
Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules
Implementation Method 3
hydrogenation using a catalyst to convert it into lower boiling molecules
Implementation Method 4
hydrogenation of the depolymerized steam cracked tar with a hydrogenation catalyst
Data Source
AI summary
A process and apparatus are provided for steam cracking heavy feeds, including steam cracked tars. The invention heats a steam cracked tar feed to provide a depolymerized steam cracked tar containing lower boiling molecules than the steam cracked tar feed, hydrogenates the depolymerized steam cracked tar using a hydrogenating catalyst, e.g., a downward flow fixed bed hydrotreater, to provide a hydrogenated steam cracked tar. At least a portion of the hydrogenated steam cracked tar is steam cracked in a steam cracking furnace comprising a convection zone and a radiant zone.