Pyrolysis Effluent Quenching via Tar Recycle
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Pyrolysis processes face challenges with fouling due to reactive free radicals in pyrolysis effluents, leading to coke deposition in transfer line exchangers, which reduces heat transfer efficiency and requires frequent decoking.
Innovation Solution
A process and system where pyrolysis effluents are quenched using a quench medium comprising a portion of the tar stream, which is recycled and potentially hydroprocessed, to inhibit fouling by maintaining the quench medium in a liquid phase and reducing coke deposition, thereby extending the life of heat exchangers and improving heat recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If indirect heat exchanger quenching is used to rapidly cool pyrolysis effluent and recover energy, then heat recovery efficiency is improved, but coke deposition on inner surfaces occurs and heat transfer efficiency decreases
Solution Approach 1:
The patent introduces an injection medium (steam, water, or quench oil) as an intermediary substance between the pyrolysis effluent and the heat exchanger surfaces. This intermediary absorbs reactive free radicals from the effluent through chemical reactions, preventing them from reaching and polymerizing on the heat exchanger inner surfaces. The injection medium thus mediates the interaction between effluent and equipment, eliminating the harmful effect while preserving the beneficial heat recovery function.
Solution Approach 2:
The patent applies preliminary action by injecting the quench medium into the pyrolysis effluent before it contacts the heat exchanger surfaces. This pre-treatment step occurs in the quench section upstream of the heat exchanger, where reactive species are neutralized in advance. By performing this protective action beforehand, the effluent is prepared in a state that will not cause coke deposition during subsequent heat exchange operations.
2Manufacturing precision
If quenching is performed to stop unselective cracking reactions, then product selectivity is improved, but reactive free radicals cause fouling and equipment degradation
Solution Approach 1:
The patent converts the harmful reactive free radicals into beneficial effects by introducing an injection medium that reacts with these radicals. The radicals that would otherwise cause fouling are instead consumed in controlled reactions with the injection medium (steam, water, or quench oil), producing stable products. This transforms the harmful fouling mechanism into a beneficial protective reaction that cleanses the effluent while maintaining product selectivity.
Solution Approach 2:
The injection medium serves as a mediator between the reactive effluent and the equipment. It provides a controlled chemical environment where radicals can be safely neutralized through reactions with the injection medium, preventing uncontrolled polymerization on surfaces. This intermediary approach allows the system to tolerate the presence of reactive species without suffering their harmful effects.
3Speed
If transfer line exchanger is used for rapid quenching, then cooling speed is improved, but coke accumulation rapidly reduces heat transfer efficiency
Solution Approach 1:
The patent implements preliminary action by injecting the quench medium into the pyrolysis effluent before it enters the transfer line exchanger. This pre-quenching step occurs in the injection section upstream of the exchanger, where reactive species are neutralized in advance. By preparing the effluent beforehand, the subsequent heat exchange process can proceed at high speed without the risk of coke deposition, maintaining both cooling speed and heat transfer efficiency throughout operation.
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 solution effectively reduces fouling, extends the operational life of heat exchangers, and enhances heat recovery by maintaining the quench medium in a liquid phase, allowing for longer heat exchanger lengths and increased heat transfer efficiency.
Implementation Method 1
The primary purpose of the transfer line exchanger is to rapidly quench the pyrolysis effluent to stop the unselective cracking reactions
Implementation Method 2
Pyrolysis processes, e.g., steam cracking, convert saturated hydrocarbons to higher-value products
Data Source
AI summary
Processes and systems for quenching an effluent. In certain embodiments, the process can include contacting a pyrolysis effluent and a first quench medium to produce a first quenched effluent. A bottoms stream that can include tar and an overhead stream that can include ethylene and propylene can be obtained from the first quenched effluent. The first quench medium can include a first portion of the bottoms stream that can include a first portion of the tar. In certain embodiments, the process can also include hydroprocessing a second portion of the bottoms stream that can include a second portion of the tar to produce a hydroprocessed product. A hydroprocessed bottoms stream can be obtained from the hydroprocessed product. In certain embodiments, the process can also include contacting at least a portion of the hydroprocessed bottoms stream and the first portion of the bottoms stream to produce the first quench medium.