Steam Cracked Tar Cooling to Reduce Asphaltene Content
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Solution Overview
Problem
The production of steam cracked tar from hydrocarbon pyrolysis units, especially those using naphtha or heavier feeds, results in high amounts of asphaltenes and toluene insolubles, which increase viscosity and render the tar incompatible with fuel oils and carbon black production, requiring external additives or reducing cracking severity, thus affecting process efficiency and product quality.
Innovation Solution
A method involving cooling and recycling steam cracked tar within a separation vessel to reduce asphaltene and toluene insoluble content, utilizing transfer line heat exchangers and quenching processes to condense tar, thereby minimizing condensation reactions and reducing viscosity, allowing for the production of tar suitable for fuel blending or carbon black feedstock without external additives.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cracking severity is increased to improve olefin yield, then productivity increases, but asphaltene and toluene insoluble content in tar increases, worsening product quality
Solution Approach 1:
The patent applies preliminary action by rapidly quenching the pyrolysis effluent immediately after the cracking furnace to stop the thermal decomposition reactions. This rapid cooling prevents further formation of asphaltenes and toluene insolubles in the tar, allowing high cracking severity to be used for maximum olefin yield without compromising tar quality. The quenching action is performed before the tar can undergo additional condensation and polymerization reactions that would increase asphaltene content.
2Manufacturing precision
If external additives are used to reduce tar viscosity and improve compatibility, then product quality improves, but device complexity and processing steps increase
Solution Approach 1:
The patent converts the harmful effect of high-temperature cracking (which produces high asphaltene content) into a benefit by rapidly quenching the effluent. This stops the unwanted condensation reactions that form asphaltenes, thereby producing high-quality tar suitable for fuel blending and carbon black feedstock without requiring external additives or additional processing steps to reduce viscosity or improve compatibility.
3Manufacturing precision
If cracking severity is reduced to improve tar quality, then asphaltene content decreases, but olefin yield and process productivity decrease
Solution Approach 1:
The patent applies preliminary action by rapidly quenching the pyrolysis effluent immediately after the cracking furnace to stop the thermal decomposition reactions. This rapid cooling prevents further formation of asphaltenes and toluene insolubles in the tar, allowing high cracking severity to be used for maximum olefin yield without compromising tar quality. The quenching action is performed before the tar can undergo additional condensation and polymerization reactions that would increase asphaltene content.
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 method effectively reduces asphaltene and toluene insoluble content in steam cracked tar, improving its compatibility and marketability as a fuel blending stock or carbon black feedstock, while maintaining quench balance and reducing the need for external additives, thus enhancing the steam cracking process efficiency.
Implementation Method 1
cooling the effluent from the cracking furnace using a system of transfer line heat exchangers
Implementation Method 2
cool the effluent to a temperature at which tar formed during the pyrolysis process condenses
Implementation Method 3
a water quench tower in which the condensibles are removed
Data Source
AI summary
A method is disclosed for treating gaseous effluent from a hydrocarbon pyrolysis unit to provide steam cracked tar of reduced asphaltene and toluene insolubles content. The method is suitable for preparing reduced viscosity tar useful as a fuel blending stock, or feedstock for producing carbon black, while reducing or eliminating the need for externally sourced lighter aromatics additives to meet viscosity specifications. The method comprises drawing steam cracked tar from a separation vessel, e.g., a primary fractionator or tar knock-out drum, cooling the tar, and returning it to the separation vessel to effect lower overall tar temperatures within the separation vessel, in order to reduce viscosity increasing condensation reactions. An apparatus for carrying out the method is also provided.