Pre-Quenching Oil Cracking for Steam Cracker Tar Reduction
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Solution Overview
Problem
Conventional steam cracking systems face challenges in processing hydrocarbon feeds containing non-volatile components, such as resids and crude oils, which lead to coke deposition and tar formation, limiting their flexibility and efficiency, especially when these feeds are contaminated with heavy crude oil or non-volatile components.
Innovation Solution
A quench header apparatus and process that utilizes pre-quenching oil, specifically the bottoms from a vapor/liquid separator, to crack hydrocarbonaceous feeds, allowing for substantial cracking of crackable components before the primary quenching, thereby reducing tar formation and coke deposition by introducing a pre-quenching oil containing C5+ components and a quenching oil in a controlled manner within the quench header.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional steam cracking systems process heavy feedstocks containing non-volatile components, then feedstock flexibility is improved, but coke deposition and tar formation increase
Solution Approach 1:
The patent applies preliminary action by introducing pre-quenching oil into the effluent stream before the main quenching step. This pre-quenching oil contains crackable components that are cracked in advance to generate free radicals which then attack and prevent tar formation from the heavy feedstock components. The premature cracking action occurs in the transition zone between the radiant and convection sections, before the effluent would normally proceed to standard quenching equipment where tar would form.
Solution Approach 2:
The pre-quenching oil acts as an intermediary substance between the heavy feedstock and the quenching system. Its crackable components serve as a mediator that generates free radicals to chemically interfere with the tar formation process. The pre-quenching oil bridges the gap between processing heavy feeds and preventing harmful tar deposition, allowing the system to handle diverse feedstocks without fouling downstream equipment.
2Object-generated harmful factors
If pre-quenching oil containing crackable components is introduced, then tar formation is reduced, but process complexity increases
Solution Approach 1:
The pre-quenching oil injection system serves multiple functions simultaneously: it cools the effluent stream (quenching), generates free radicals through cracking of its components, and these free radicals then prevent tar formation. By introducing a single substance that performs multiple roles, the patent avoids the need for separate systems for cooling and tar prevention, thereby limiting the increase in process complexity despite the additional functionality.
Solution Approach 2:
The patent changes the chemical composition parameter of the quenching system by introducing pre-quenching oil with specific crackable components. This parameter change enables the quenching medium to actively participate in preventing tar formation through free radical generation, rather than merely serving as a cooling agent. The controlled introduction of this substance with specific properties allows tar reduction without requiring complex additional equipment.
3Loss of substance
If bottoms from vapor/liquid separator are used as pre-quenching oil, then resource utilization is improved, but cracking control becomes more difficult
Solution Approach 1:
The bottoms from the vapor/liquid separator contain crackable components that inherently possess the chemical properties needed for pre-quenching. By utilizing these bottoms as the pre-quenching oil, the system makes the waste stream serve its own useful function - the crackable components in the bottoms automatically provide the free radical generation capability required for tar prevention. This self-service approach converts a waste product into a functional reagent, improving resource utilization while the inherent properties of the bottoms simplify rather than complicate cracking control.
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 enables the effective utilization of bottoms from a vapor/liquid separator as a pre-quenching oil, allowing for at least 50% cracking of crackable components, reducing tar formation, and managing coke deposition, thereby improving the processing of heavy feeds and reducing equipment fouling.
Implementation Method 1
Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules. The resulting products including olefins leave the pyrolysis furnace for further downstream processing, including quenching.
Implementation Method 2
The formation of tar after the pyrolysis effluent leaves the steam cracking furnace can be minimized by rapidly reducing the temperature of the effluent exiting the pyrolysis unit to a level at which the tar-forming reactions are greatly slowed. This cooling, achieved in one or more steps and using one or more methods, is referred to as quenching.
Data Source
AI summary
An apparatus and process are provided for cracking hydrocarbons. Hot, cracked effluent is removed to a quench header where it is pre-quenched with an oil containing crackable components, e.g., 1000° F.+ (538° C.+) boiling range bottoms taken from a vapor/liquid separator, cracking the bottoms to more valuable products, e.g., steam crack naphtha. The overhead of the separator is fed to a cracker, and then quenched with a quenching oil.