Liquid Feed Gas Cracker Tar Control via Quench
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Solution Overview
Problem
Conventional steam cracking systems lack flexibility to process liquid hydrocarbon feedstocks that produce high amounts of tar, leading to equipment fouling and operational challenges, particularly when dealing with heavier feeds like kerosene and gas oils, which result in costly shutdowns and environmental concerns due to stable emulsions formed with water quenching.
Innovation Solution
A process and apparatus that extend the range of feedstocks for gas cracker systems to include liquid hydrocarbons by incorporating a primary transfer line exchanger, direct quench injection, a tar knockout system, and a tar solvation system, which separates and manages tar effectively, using a quench tower and flash separator to control tar buildup and produce clean quench water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional steam cracking systems process liquid hydrocarbon feedstocks containing non-volatile components, then feedstock flexibility is improved, but equipment fouling increases and operational reliability deteriorates
Solution Approach 1:
The flash separator is positioned upstream of the cracker to remove non-volatile components from liquid feedstocks before they enter the cracking system. This preliminary separation action prevents coke formation in the convection section and tar production in downstream equipment, thereby maintaining operational reliability while enabling processing of diverse liquid feedstocks
Solution Approach 2:
The system segments the feedstock processing into distinct stages: flash separation of non-volatile components, cracking of vaporized feedstock, and separate handling of tar produced from cracked effluent. This segmentation allows each component to be treated appropriately, preventing fouling while maintaining feedstock flexibility
2Speed
If water quenching is used to cool cracked effluent, then cooling efficiency is improved, but stable emulsion formation increases causing downstream fouling
Solution Approach 1:
The tar knockout system extracts tar from the cracked effluent stream before water quenching occurs. By removing tar upstream, the subsequent water quenching process no longer produces stable emulsions, eliminating downstream fouling while maintaining efficient cooling
3Use of energy by moving object
If transfer line exchangers are used to recover energy from effluent, then energy recovery is improved, but tar deposition increases causing fouling
Solution Approach 1:
The tar knockout system performs preliminary removal of tar from the effluent stream before it reaches the transfer line exchangers. This preliminary action prevents tar deposition in the exchangers, allowing continuous energy recovery operation without fouling
Solution Approach 2:
The tar knockout system extracts and removes tar from the effluent stream, separating it before the effluent enters the transfer line exchangers. This extraction prevents the harmful interaction between tar and exchanger surfaces, maintaining energy recovery efficiency
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
Enables the production of olefin products from liquid feedstocks that yield up to 15 wt% tar, reducing fouling and operational issues, allowing for continuous operation and minimizing capital investment by avoiding the need for costly primary fractionators and maintaining environmentally acceptable disposal of quench water.
Implementation Method 1
a flash separator to separate non-volatile components from the vaporized feedstock
Implementation Method 2
cooling of the effluent from the cracking furnace is normally achieved using a system of transfer line heat exchangers
Implementation Method 3
the process gas is further cooled by direct contact with quench water
Implementation Method 4
the bottoms of the quench tower feed a quench drum, which functions as a three-phase separator
Implementation Method 5
a light hydrocarbon phase that floats on water and tar, which sinks in water, as the bottom phase
Implementation Method 6
Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules
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 a primary transfer line exchanger to quench the process effluent comprising olefins, separating in a first separation vessel a cracked product and a first byproduct stream comprising tar from the quenched effluent, directing the separated cracked product to a 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 carrying out such process is also provided.