Solvent Deasphalting Process for Steam Cracked Tar Upgrading
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Solution Overview
Problem
Steam cracked tar, a byproduct of pyrolysis, is difficult to utilize efficiently due to its incompatibility with other refinery products, primarily due to high asphaltene content, leading to disposal issues as it cannot be easily blended with fuel oils like Bunker C fuel oil, especially with tightening emission regulations.
Innovation Solution
A solvent deasphalting process using selected fluids such as butanes, light virgin naphtha, or fuel natural gas to separate asphaltenes from tar, producing a deasphalted tar fraction that is compatible with fuel oils, and integrating this process with pyrolysis furnaces to recycle solvents and enhance light olefin production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If steam cracked tar is blended with fuel oils, then disposal is simplified, but incompatibility due to high asphaltene content causes precipitation and operational problems
Solution Approach 1:
The patent applies extraction by contacting steam cracked tar with a deasphalting solvent (such as pentane, hexane, or heptane) to separate and remove asphaltenes from the tar. This extraction process produces a deasphalted tar fraction with reduced asphaltene content that is compatible with fuel oil blending, while the extracted asphaltenes are removed as a separate phase.
Solution Approach 2:
The patent changes the chemical composition parameter of the steam cracked tar by reducing its asphaltene content through deasphalting. This parameter change transforms the tar from an incompatible state (high asphaltene content) to a compatible state (low asphaltene content), enabling successful blending with fuel oils without precipitation issues.
2Object-generated harmful factors
If conversion of pyrolysis feed is limited to avoid SCT production, then asphaltene-related problems are reduced, but production of valuable light olefins is also reduced
Solution Approach 1:
The patent converts the harmful effect of high asphaltene content in steam cracked tar into a benefit by using the deasphalting process to remove asphaltenes. This allows the tar to be transformed from a problematic waste product into a valuable feedstock that can be reused in pyrolysis furnaces or blended with fuel oils, thereby maintaining high conversion rates for light olefin production while eliminating asphaltene-related problems.
Solution Approach 2:
The patent discards the harmful asphaltenes through deasphalting while recovering and reusing the deasphalted tar fraction as a valuable feedstock. This recovery process enables the tar to be cycled back into the pyrolysis process or utilized as fuel oil blendstock, maintaining productivity while removing the harmful components.
3Ease of operation
If SCT is diluted with stocks that do not contain asphaltenes, then blending compatibility is improved, but economic value is reduced due to use of high-value products
Solution Approach 1:
The patent introduces a deasphalting solvent as an intermediary substance that temporarily interacts with the steam cracked tar to remove asphaltenes. The solvent itself is not consumed in the process and can be recovered and reused. This intermediary approach enables compatibility improvement without requiring the dilution of valuable fuel stocks, as the solvent acts as a temporary tool rather than a permanent diluent.
4Ease of operation
If deasphalting process is implemented, then tar compatibility with fuel oils is improved, but process complexity increases
Solution Approach 1:
The patent segments the complex tar processing problem into distinct operational units: a deasphalting contactor where solvent and tar are mixed to separate asphaltenes, a settling or separation unit to divide the mixture into deasphalted tar and asphaltene-rich phases, and optional solvent recovery equipment. This segmentation allows each unit to perform a specific function, making the overall process more manageable and easier to operate despite the added complexity.
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 upgrades tar fractions, making them compatible with fuel oils and providing a valuable feedstock for pyrolysis furnaces, thereby increasing the efficiency of tar utilization and reducing disposal challenges.
Implementation Method 1
contacting a composition comprising tar and a solvent in a solvent deasphalter to produce a mixture comprising a first fraction comprising solvent and at least a portion of the tar that is relatively soluble in said solvent, and a second fraction comprising heavy tar that is relatively insoluble in said solvent
Data Source
AI summary
A feedstream comprising tar is fed to a solvent deasphalter wherein it is contacted with a deasphalting solvent or fluid to produce a composition comprising a mixture or slurry of solvent containing a soluble portion of the tar, and a heavy tar fraction comprising the insoluble portion of the tar. These fractions may be separated in the deasphalter apparatus, such as by gravity settling wherein the heavy tar fraction is taken off as bottoms, and the solvent-soluble fraction taken as overflow or overheads with the solvent. The overflow or overheads is sent to a solvent recovery unit, such as a distillation apparatus, wherein solvent is recovered as overheads and a deasphalted tar fraction is taken off as a sidestream or bottoms. The solvent or a portion thereof, recovered as overheads, may be then be recycled to the solvent deasphalter, or in a preferred embodiment, at least a portion of the solvent is steam cracked to produce a product comprising light olefins.