Steam Cracking Fractionation Scheme to Limit Furnace Coking
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Solution Overview
Problem
Heavier hydrocarbons pose challenges in steam cracking due to high final boiling points, impurities, difficult vaporization, and coking, leading to energy waste and reduced ethylene yield, necessitating improved process and system designs.
Innovation Solution
A process involving multiple separations and steam cracking stages to manage hydrocarbon fractions, including flash separations, fractional distillations, and controlled vaporization to minimize coking and enhance ethylene yield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If multi-stage flash method is used to vaporize heavier hydrocarbons, then vaporization is achieved, but non-volatile components are enriched in the liquid phase causing coking in the convection zone
Solution Approach 1:
The vaporization process is divided into multiple stages with intermediate separation. The first stage produces a vapor phase and liquid phase, the second stage further separates the vapor phase into lighter and heavier fractions. This segmentation prevents non-volatile components from concentrating in the liquid phase that enters the convection zone, thereby preventing coking while achieving complete vaporization.
Solution Approach 2:
The invention extracts and removes non-volatile components through the multi-stage flash separation process. By separating the vapor phase from the liquid phase in the first stage, and further separating the vapor phase into lighter and heavier fractions in the second stage, the non-volatile components are effectively removed from the stream that enters the convection zone, preventing coking.
2Productivity
If first-stage flash vapor phase with high potential aromatic content is directly steam cracked, then cracking is achieved, but energy is wasted and ethylene yield is reduced
Solution Approach 1:
The vapor phase from the first stage is segmented into two fractions in the second stage: a lighter fraction and a heavier fraction. The lighter fraction with high potential aromatic content is separated and not directly steam cracked, while the heavier fraction is steam cracked. This segmentation allows selective cracking of appropriate fractions, improving ethylene yield and reducing energy waste.
Solution Approach 2:
The invention extracts and separates the lighter fraction with high potential aromatic content from the vapor phase in the second stage. This extracted lighter fraction is then not subjected to steam cracking, while the heavier fraction is cracked. This extraction prevents energy waste and reduces ethylene yield loss by avoiding unnecessary cracking of aromatic-rich fractions.
3Productivity
If first-stage flash vapor phase is directly steam cracked, then cracking is achieved, but non-volatile components are carried over causing coking in the radiant zone
Solution Approach 1:
The vapor phase is segmented into lighter and heavier fractions in the second stage. The heavier fraction, which contains fewer non-volatile components, is selected for steam cracking in the radiant zone. This segmentation reduces the load of non-volatile components on the cracking process, maintaining cracking efficiency while preventing coking in the radiant zone.
Solution Approach 2:
The invention extracts and removes non-volatile components through the multi-stage flash separation. The lighter fraction with higher non-volatile content is extracted and separated from the stream that enters the radiant zone. This extraction prevents non-volatile components from causing coking in the radiant zone while maintaining effective cracking of the heavier fraction.
4Productivity
If heavier hydrocarbons are directly steam cracked, then ethylene production is achieved, but coking occurs reducing furnace operation duration
Solution Approach 1:
The heavier hydrocarbon feed is segmented into multiple fractions through multi-stage flash separation and fractional distillation. The separated fractions are then steam cracked in the radiant zone. This segmentation prevents coking by distributing the cracking load across different fractions with different coking tendencies, thereby extending furnace operation duration while maintaining ethylene production.
Solution Approach 2:
The invention performs preliminary separation and fractionation of the heavier hydrocarbon feed before steam cracking. Through multi-stage flash separation and fractional distillation, the feed is pre-separated into lighter and heavier fractions, and the lighter fraction is removed. This preliminary action reduces the coking potential of the feedstock entering the radiant zone, extending furnace operation duration while maintaining ethylene production.
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 process achieves high ethylene yield, reduces energy consumption, and extends cracking furnace operation by preventing coking and optimizing component utilization.
Implementation Method 1
subjecting a heavier hydrocarbon to a first separation to obtain a first vapour stream and a first liquid stream
Implementation Method 2
subjecting the first vapour stream to a second separation to obtain at least a third lighter fraction, a first intermediate fraction and a third heavier fraction
Implementation Method 3
subjecting the second vapour stream to steam cracking to obtain a cracked product comprising the olefin
Implementation Method 4
introducing at least a portion of the third heavier fraction into the first liquid stream to obtain a first modified liquid stream
Data Source
AI summary
A process for producing olefins by steam cracking of a heavier hydrocarbon includes the steps of: subjecting a heavier hydrocarbon to a first separation to obtain a first vapour stream and a first liquid stream, partially condensing (second separation) the first vapour stream to obtain a condensate (third heavier fraction), introducing at least a portion of the third heavier fraction into the first liquid stream to obtain a first modified liquid stream, subjecting the first modified liquid stream to a third separation to obtain a second vapour stream and a second liquid stream, and carrying out steam cracking on the second vapour stream to obtain a cracked gas effluent containing the olefins. This process inhibits the coking of the convection zone, and provide a high utilization rate of heavier hydrocarbon (crude oil) and a high ethylene yield.