Gas Cracker Tar Removal for Liquid Feedstock Processing
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Solution Overview
Problem
Conventional steam cracking systems lack flexibility to process liquid hydrocarbon feedstocks that produce high levels of tar, leading to equipment fouling and operational challenges, particularly when dealing with feedstocks like crude oil and contaminated naphthas, which result in inefficient energy recovery and environmentally difficult quench water disposal.
Innovation Solution
A process and apparatus that extend the range of feedstocks in gas cracker systems to include liquids by incorporating a tar knockout system, flash separator, and tar solvation system, allowing for the separation and removal of tar from the quench fluid, using a combination of steam and aromatic solvents to manage tar production and prevent fouling, and enabling the use of liquid feedstocks that yield up to 15 wt% tar.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional steam cracking systems process liquid hydrocarbon feedstocks with high tar yields, then feedstock flexibility is improved, but equipment fouling increases
Solution Approach 1:
The patent extracts and removes tar from the process stream using a tar knockout drum and tar solvation system. The tar solvation system uses aromatic solvents to selectively dissolve and separate tar from quench water, preventing tar from fouling downstream equipment while allowing the cracker to process high-tar liquid feedstocks
Solution Approach 2:
The patent introduces aromatic solvents as an intermediary substance between the tar-containing quench water and the downstream equipment. The aromatic solvent acts as a mediator that binds to tar, forming a separable phase that can be easily removed, thus protecting equipment from direct contact with tar
2Adaptability or versatility
If liquid feedstocks with high non-volatile components are processed in conventional pyrolysis furnaces, then feedstock versatility is improved, but coke deposition in the convection section increases
Solution Approach 1:
The patent performs preliminary separation of non-volatile components from the liquid feedstock before the feed enters the convection section of the pyrolysis furnace. A flash separator removes heavy ends and non-volatile materials upstream, preventing these components from reaching the convection section where they would otherwise deposit as coke
Solution Approach 2:
The patent segments the feedstock processing into distinct stages: preliminary flashing to remove non-volatiles, then controlled vaporization in the radiant section. This segmentation ensures that only volatile components enter the convection section, preventing coke deposition while maintaining the ability to process diverse liquid feedstocks
3Use of energy by moving object
If transfer line exchangers are used for energy recovery in high-tar cracking processes, then energy efficiency is improved, but TLE fouling increases
Solution Approach 1:
The patent extracts and removes tar from the process stream before it reaches the transfer line exchangers. By using a tar knockout drum and tar solvation system upstream of the TLEs, the patent prevents tar from entering and fouling the heat exchange surfaces, maintaining energy recovery efficiency
Solution Approach 2:
The patent performs preliminary tar removal actions before the effluent enters the transfer line exchangers. The tar solvation system operates upstream to dissolve and separate tar, protecting the TLEs from fouling while allowing them to continue functioning for energy recovery
4Speed
If quench water is used for cooling cracked effluent, then cooling efficiency is improved, but quench water disposal becomes environmentally problematic
Solution Approach 1:
The patent converts the harmful tar-contaminated quench water into a beneficial separated stream. By using a tar solvation system with aromatic solvents, the patent selectively extracts tar from the quench water, producing cleaned quench water that can be environmentally disposed of or reused, while the tar-laden solvent phase is separately handled
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 solution enables the efficient cracking of liquid hydrocarbon feedstocks with high tar yields, reducing equipment fouling, improving energy recovery, and facilitating environmentally acceptable quench water disposal, thereby enhancing the operational flexibility and economic viability of gas cracker systems.
Implementation Method 1
a flash separator to separate non-volatile components from liquid feedstocks
Implementation Method 2
Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules
Implementation Method 3
primary, secondary, and even tertiary transfer line exchangers (TLEs) are utilized to recover energy through the generation of high pressure and medium pressure steam
Implementation Method 4
The process gas is normally then fed to a quench tower wherein the process gas is further cooled by direct contact with quench water
Implementation Method 5
separating in a separation vessel a cracked product and a first byproduct stream comprising tar from the quenched effluent
Implementation Method 6
Aromatic solvents may be used in a tar solvation system to remove tar from the quench fluid
Data Source
AI summary
In a system for thermal cracking gaseous feedstocks, the system including a gas cracker for producing an effluent comprising olefins, at least one transfer line exchanger for the recovery of process energy from the effluent and a water quench tower system, a process for extending the range of system feedstocks to include liquid feedstocks that yield tar is provided. The process includes the steps of injecting a first quench fluid downstream of the at least one transfer line exchanger to quench the process effluent comprising olefins, separating in a separation vessel a cracked product and a first byproduct stream comprising tar from the quenched effluent, directing the separated cracked product to the water quench tower system and quenching the separated cracked product with a second quench fluid to produce a cracked gas effluent for recovery and a second byproduct stream comprising tar. An apparatus for cracking a liquid hydrocarbon feedstock that yield tar is also provided.