Ethane Cracker Furnace Fuel Switching for Lower CO2 Emissions
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Solution Overview
Problem
Existing ethane steam cracking processes produce significant CO2 emissions due to the combustion of methane-rich tail gas used as fuel for furnace burners, necessitating a reduction in CO2 output.
Innovation Solution
Separate the tail gas into a hydrogen-rich stream and a methane-rich stream, using the hydrogen-rich stream as fuel for the furnace burners, and optimize the system by preheating combustion air and adjusting heat recovery processes to compensate for reduced fire duty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If methane-rich tail gas is burned as fuel for furnace burners, then furnace fuel demand is satisfied, but CO2 emissions increase significantly
Solution Approach 1:
The tail gas stream is separated into two distinct streams: a hydrogen-enriched stream and a methane-enriched stream. This segmentation allows the hydrogen-rich portion to be used as fuel for furnace burners, producing minimal CO2, while the methane-rich portion is handled separately, thus resolving the contradiction between satisfying fuel demand and reducing CO2 emissions.
Solution Approach 2:
The hydrogen component is extracted from the methane-rich tail gas and isolated as a separate hydrogen-enriched stream. This extracted hydrogen stream is then used as the primary fuel source for furnace burners, eliminating the CO2-generating combustion of methane while maintaining adequate fuel supply for furnace operation.
2Object-generated harmful factors
If tail gas is separated into hydrogen-enriched and methane-enriched streams, then CO2 emissions are reduced, but system complexity increases
Solution Approach 1:
The separation of tail gas into hydrogen-enriched and methane-enriched streams is achieved by exploiting differences in physical properties (parameters) of the gases, such as condensation temperatures or adsorption characteristics. By changing these parameters, the mixture separates into distinct streams that can be differently routed for fuel use, reducing CO2 emissions without requiring overly complex equipment.
3Object-generated harmful factors
If hydrogen-enriched stream is used as fuel, then CO2 emissions decrease, but furnace heat output may be insufficient
Solution Approach 1:
The system maintains continuous and adequate fuel supply to furnace burners by using the hydrogen-enriched stream as the primary fuel source. The continuous availability of this low-CO2 fuel ensures that the furnace operates at required capacity levels without interruption, maintaining both reduced emissions and sufficient heat output for cracking operations.
Solution Approach 2:
The combustion characteristics of the fuel are optimized by using hydrogen-enriched gas, which has different combustion parameters (higher flame speed, different adiabatic flame temperature) compared to methane. These parameter changes allow the furnace to achieve required heat output levels through adjusted burner design or operating conditions, compensating for the lower energy density of hydrogen while maintaining low CO2 emissions.
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
Reduces CO2 emissions by over 50% while maintaining system functionality, achieving a hydrogen-rich fuel stream with greater than 90% hydrogen content and optimizing furnace operation.
Implementation Method 1
expanding the H2-enriched stream in an expander to produce an expanded H2-enriched stream
Implementation Method 2
separating the tail gas stream into the hydrocarbon-enriched stream and the H2-enriched stream comprises cooling the tail gas stream using heat exchange against the expanded H2-enriched stream
Implementation Method 3
burning the combustion mixture in the furnace burners
Implementation Method 4
preheating the combustion air using heat from flue gas in the convection section before the combustion air is mixed with the fuel stream
Data Source
AI summary
Low carbon dioxide-emitting processes and systems for steam cracking hydrocarbons to produce products such as ethylene are described. The processes and systems involve cracking the feed in a furnace that is configured to burn a hydrogen-rich fuel, which produces less carbon dioxide than methane, which is typically used as fuel for such furnaces. The hydrogen-rich stream can be isolated and recycled from the cracker tail gas.