Steam Effluent Exchanger Layout for Low-Emission Hydrocarbon Cracking
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Solution Overview
Problem
Existing hydrocarbon cracking systems face challenges in achieving high efficiency and reducing emissions, particularly due to the limitations of the convection section in superheating high pressure steam, which can lead to condensation issues in downstream turbines and reduced radiant section efficiency.
Innovation Solution
The system superheats high pressure steam outside the convection section using waste heat from the cracked effluent gas, employing one or more steam effluent exchangers to generate and further superheat steam, minimizing the convection section's non-process duty and optimizing radiant section efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the convection section is used to superheat high pressure steam, then steam superheating is achieved, but radiant section efficiency is reduced and convection section capacity is insufficient
Solution Approach 1:
The patent extracts the steam superheating function from the convection section and relocates it to a separate waste heat recovery system. The convection section is relieved of the non-process duty of steam superheating, allowing it to focus on process heating duties. A separate waste heat recovery system using cracked effluent gas is introduced to perform the steam superheating function, thereby resolving the contradiction between steam superheating and radiant section efficiency.
2Temperature
If the convection section capacity is increased to handle steam superheating, then steam superheating is achieved, but fuel consumption increases and CO2 emissions increase
Solution Approach 1:
The patent converts the waste heat in the cracked effluent gas, which would otherwise be discarded, into a useful resource for steam superheating. By utilizing the thermal energy contained in the hot effluent gas through waste heat recovery exchangers, the system achieves steam superheating without requiring additional fuel combustion in the convection section, thereby eliminating the associated fuel consumption and CO2 emissions.
3Loss of energy
If waste heat from cracked effluent gas is used to superheat steam, then fuel consumption is reduced, but steam superheating efficiency may be insufficient
Solution Approach 1:
The patent segments the steam superheating process into multiple stages using a series of waste heat recovery exchangers arranged in the effluent gas flow path. This includes feed effluent exchangers, transfer line exchangers, and steam effluent exchangers, each contributing to different aspects of steam heating and superheating. This segmented approach allows efficient extraction of waste heat at different temperature levels, ensuring adequate steam superheating efficiency while maximizing fuel savings.
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 enhances radiant section efficiency while maintaining sufficient convection section capacity, reduces fuel consumption, and decreases CO2 emissions by utilizing waste heat effectively, preventing condensation in downstream turbines.
Implementation Method 1
a steam effluent exchanger arranged to receive a high pressure steam flow and to generate superheated high pressure steam therefrom using waste heat from the cracked effluent gas
Implementation Method 2
a transfer line exchanger arranged to receive a boiler water flow and to generate at least partly vaporized boiler water therefrom using waste heat from the cracked effluent gas
Data Source
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AI summary
A low-emission hydrocarbon cracking system for converting a hydrocarbon feedstock into cracked effluent gas is disclosed. The low-emission hydrocarbon cracking system can include a cracking furnace having a convection section heated by flue gas and configured to perform process and non-process heating operations, and a radiant section within which the hydrocarbon feedstock can be cracked by high temperature heating. The low-emission hydrocarbon cracking system may minimize the non-process duty of the cracking furnace convection section to ensure that sufficient convection section duty capacity is available even if flue gas output is reduced through use of a high efficiency radiant section. The non-process duty of the convection section may be minimized in some cases by superheating high pressure steam partly or completely outside of the convection section of the cracking furnace, such as by using one or more steam effluent exchangers that utilize waste heat from the cracked effluent gas. In an embodiment, a heat exchanger and cracking furnace arrangement comprises a transfer line exchanger (TLE) positioned in a cracked effluent gas flow path from a (fired) steam cracking furnace and a steam effluent exchanger positioned in the cracked effluent gas flow path in series with the transfer line exchanger, wherein the transfer line exchanger comprises a boiler water input and an at least partly vaporized boiler water output, the transfer line exchanger configured to at least partly vaporize the boiler water using waste heat from the cracked effluent gas; and wherein the steam effluent exchanger comprises a high pressure steam input and a superheated high pressure steam output, the steam effluent exchanger configured to generate the superheated high pressure steam using waste heat from the cracked effluent gas.