Steam Cracking Heavy Hydrocarbon Feedstocks with Variable Dilution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional steam cracking systems face challenges in processing heavy hydrocarbon feedstocks containing non-volatile components, leading to coke deposition and fouling in the furnace and transfer line exchangers, due to the inability to maintain a consistent vapor-to-liquid ratio and excessive film temperatures.
Innovation Solution
A process involving heating heavy hydrocarbon feedstocks, mixing with a fluid to form a mixture stream, flashing to separate vapor and liquid phases, and cracking the vapor phase in a pyrolysis furnace, while using a transfer line exchanger for quenching, with the amount of fluid varied based on operating parameters to control temperature and pressure, and superheating steam to prevent coking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If heavy hydrocarbon feedstocks containing non-volatile components are processed in conventional steam cracking systems, then the feedstock can be cracked into olefins, but coke deposition and fouling occur in the furnace and transfer line exchangers
Solution Approach 1:
The feedstock is preheated and partially vaporized in the convection section before entering the radiant section, and dilution steam is added in advance to control the vaporization process and prevent excessive film temperatures that lead to coking
Solution Approach 2:
The process controls the degree of vaporization and film temperature through parameter adjustments, maintaining conditions that prevent coke formation while still enabling efficient cracking of heavy feedstocks into olefins
2Productivity
If the feedstock is fully vaporized in the convection section, then cracking efficiency improves, but non-volatile components lay down as coke in the convection section
Solution Approach 1:
The feedstock undergoes preliminary heating and partial vaporization in the convection section, with dilution steam added to control the vaporization extent, preparing the feed for efficient cracking in the radiant section without allowing complete vaporization that would cause coking
Solution Approach 2:
Different sections of the furnace have different functions: the convection section performs partial vaporization and heating, while the radiant section completes the cracking process, with each section optimized for its specific purpose to prevent coke deposition
3Power
If transfer line exchangers are used for quenching, then steam can be generated to drive turbines, but rapid coking occurs in the radiant section and fouling in the exchangers when processing heavy feeds
Solution Approach 1:
The process controls the effluent temperature and composition before it enters the transfer line exchangers by adjusting cracking conditions and dilution steam addition, ensuring that the effluent is suitable for quenching without causing rapid coking or fouling in the exchangers
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 effectively reduces coke formation and fouling by maintaining a controlled vapor-to-liquid ratio and film temperature, allowing for efficient processing of heavy hydrocarbon feedstocks and optimizing steam superheating for energy efficiency.
Implementation Method 1
Pyrolysis involves heating the feedstock sufficiently to cause thermal decomposition of the larger molecules
Implementation Method 2
This cooling, which may be achieved in one or more steps and using one or more methods, is referred to as quenching
Implementation Method 3
flashing the mixture stream to form a vapor phase and a liquid phase
Data Source
AI summary
A process for cracking heavy hydrocarbon comprising heating the heavy hydrocarbon feedstock, mixing the heavy hydrocarbon feedstock with a fluid and/or a primary dilution steam stream to form a mixture, flashing the mixture to form a vapor phase and a liquid phase, separating and cracking the vapor phase, and cooling the product effluent in a transfer line exchanger, wherein the amount of the fluid and/or the primary dilution steam stream mixed with the heavy hydrocarbon feedstock is varied in accordance with at least one selected operating parameter of the process, such as the temperature of the flash stream before entering the flash/separator vessel.