Cracking Furnace Heat Recovery via Transfer Line Exchanger
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Solution Overview
Problem
Conventional cracking furnace systems face challenges in reducing fuel consumption and CO2 emissions due to limited heat recovery capabilities, leading to increased product degradation and fouling issues in the transfer line exchanger.
Innovation Solution
A three-step preheating process is implemented, where the hydrocarbon feedstock is preheated by hot flue gases in a first high temperature coil, followed by waste heat from cracked gas in a transfer line exchanger, and further preheated by hot flue gases in a second high temperature coil before entering the radiant section, optimizing the logarithmic mean temperature difference and reducing energy supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If firebox efficiency is significantly increased to reduce fuel consumption, then fuel consumption and CO2 emission are reduced, but the heat available for feedstock preheating in the convection section is reduced
Solution Approach 1:
The feedstock is preheated in the cooling section by the transfer line exchanger before entering the radiant section. This preliminary preheating action allows the system to operate with higher firebox efficiency since less heat is needed in the convection section, thereby reducing overall fuel consumption while still achieving the required feedstock temperature for pyrolysis
Solution Approach 2:
The system changes the preheating temperature parameters by preheating the feedstock to a higher temperature in the cooling section (using waste heat from cracked gas) before it enters the radiant section. This parameter change enables the convection section to operate with reduced heat duty, allowing higher firebox efficiency and lower fuel consumption
2Loss of energy
If feedstock is preheated in the cooling section using waste heat of cracked gas, then firebox efficiency is increased and fuel gas is reduced, but the logarithmic mean temperature difference is reduced which may slow down the freezing of reaction equilibria
Solution Approach 1:
The feedstock undergoes preliminary preheating in the cooling section by the transfer line exchanger, which increases the logarithmic mean temperature difference in the radiant section. This preliminary action ensures that the feedstock enters the radiant section at an optimized temperature, allowing rapid freezing of reaction equilibria and high productivity while maintaining low fuel gas consumption
Solution Approach 2:
The system uses a composite preheating approach combining convection section heating and cooling section preheating. This composite approach optimizes the temperature profile of the feedstock, ensuring both energy efficiency (low fuel gas) and process effectiveness (rapid equilibrium freezing) are achieved simultaneously
3Temperature
If conventional heat recovery scheme is used in the convection section, then feedstock can be preheated, but the firebox efficiency cannot be significantly increased and fuel consumption remains high
Solution Approach 1:
The system implements preliminary preheating of feedstock in the cooling section by the transfer line exchanger before the feedstock enters the radiant section. This preliminary action shifts the heat recovery function to the cooling section, enabling the convection section to operate with lower heat duty and allowing significantly higher firebox efficiency, thereby reducing fuel consumption while maintaining adequate feedstock preheating
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 minimizes product degradation, maintains low energy needs, and reduces CO2 emissions while enhancing firebox efficiency, allowing for up to 20% fuel savings and improved yield by accelerating the freezing of reaction equilibria.
Implementation Method 1
the feedstock is preheated by the transfer line exchanger before entry into the radiant section
Implementation Method 2
preheating hydrocarbon feedstock by hot flue gasses of the cracking furnace system, for example in one of the plurality of convection banks in the convection section
Implementation Method 3
at least one radiant coil in a firebox, in which the feedstock-dilution steam mixture from the convection section is converted into product and by-product components at high temperature by pyrolysis
Implementation Method 4
at least one quench exchanger, for example a transfer line exchanger, configured to quickly quench the product or cracked gas leaving the radiant section in order to stop pyrolysis side reactions
Data Source
AI summary
Cracking furnace system for converting a hydrocarbon feedstock into cracked gas comprising a convection section, a radiant section and a cooling section, wherein the convection section includes a plurality of convection banks, including a first high temperature coil, configured to receive and preheat hydrocarbon feedstock, wherein the radiant section includes a firebox comprising at least one radiant coil configured to heat up the feedstock to a temperature allowing a pyrolysis reaction, wherein the cooling section includes at least one transfer line exchanger.