Multi-Stage Catalytic Combustion for Submarine Methanol Burners
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Solution Overview
Problem
Submarines with fuel cell drives face challenges in achieving lower combustion temperatures and precise oxygen dosing in flame burners, leading to high temperatures, gas leaks, and non-water-soluble exhaust components, which are problematic for military submarines.
Innovation Solution
A multi-stage catalytic combustion method where a sub-stoichiometric fuel-oxygen mixture is processed through multiple catalytic converters, with each stage adjusting oxygen supply based on temperature and product gas conditions to maintain low operating temperatures and precise oxygen control, ensuring minimal non-soluble components in exhaust gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a slight excess of oxygen is used in the flame burner to contain soluble exhaust gas, then the exhaust gas becomes soluble in seawater, but the combustion temperature rises above 2500°C
Solution Approach 1:
The combustion process is divided into multiple stages with separate catalysts. The first catalyst performs partial oxidation of fuel with limited oxygen, and subsequent catalysts complete the combustion. This segmentation allows precise control of oxygen addition at each stage, maintaining exhaust gas solubility while avoiding excessive temperature rise that would occur with single-stage combustion using slight oxygen excess.
Solution Approach 2:
The invention changes the parameter of oxygen concentration dynamically during the combustion process. By adding oxygen in controlled amounts at different stages rather than using a constant slight excess, the system maintains exhaust gas solubility (requiring near-stoichiometric ratio) while preventing temperature from rising above 2500°C through staged oxygen introduction.
2Reliability
If a movable igniter design is used to remove the igniter after flame ignition, then the igniter can be removed from the combustion chamber, but the construction volume increases and gas leak risks arise
Solution Approach 1:
The igniter function is extracted and separated from the combustion chamber. The igniter is positioned externally and delivers ignition energy through a sealed interface without being permanently installed inside the combustion chamber. This eliminates the need for complex movable mechanisms while maintaining reliability by removing the igniter from the high-temperature environment after ignition.
Solution Approach 2:
A sealed interface or intermediary structure is introduced between the igniter and combustion chamber, allowing ignition energy transfer while maintaining gas-tight sealing. This intermediary solution provides a reliable sealed connection without requiring complex movable parts or dynamic seals in the high-temperature zone.
3Difficulty of detecting and measuring
If optical flame monitoring is used instead of thermocouples due to high temperatures, then flame monitoring is possible, but additional methanol must be added to generate sufficient ionization potential
Solution Approach 1:
The optical flame monitoring system provides real-time feedback on flame presence and characteristics. This feedback enables precise control of the combustion process, allowing the system to detect flame establishment and adjust fuel and oxygen addition accordingly, thereby reducing the need for additional methanol that would otherwise be required to maintain ionization potential for monitoring.
4Measurement precision
If oxygen addition control is based on outlet oxygen measurement, then oxygen dosage can be controlled, but control dead time exceeds thirty seconds causing exhaust gas composition fluctuations
Solution Approach 1:
Oxygen is added in predetermined controlled amounts at multiple stages before the exhaust gas reaches the measurement point. The first catalyst receives a controlled substoichiometric mixture, and subsequent catalysts receive additional controlled oxygen. This preliminary staged addition prevents the need for long-delay feedback control, maintaining stable exhaust gas composition with minimal dead time.
Solution Approach 2:
The control system replaces long-delay mechanical/f feedback loops with a staged chemical control approach. Instead of measuring outlet oxygen and waiting thirty seconds to adjust inlet oxygen, the system pre-distributes oxygen addition across multiple catalyst stages, achieving precise control without time delays.
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 method achieves combustion at significantly lower temperatures, precise oxygen dosing, and reduced non-soluble exhaust components, enhancing safety and stealth by minimizing detectable gas bubbles in seawater.
Implementation Method 1
The fuel-oxygen mixture is burned in the presence of the catalyst, i.e. oxidation of combustible gas components takes place
Implementation Method 2
oxidation of combustible gas components takes place
Implementation Method 3
the exothermic oxidation reaction in the individual catalysts heats the individual catalysts to a temperature level
Data Source
Figure 1
AI summary
In a method for the combustion of a fuel-oxygen mixture, which is intended in particular for the combustion of a methanol-oxygen mixture in a submarine, a substoichiometric fuel-oxygen mixture is fed to a first catalyst (2a) and catalytically combusted in the catalyst (2a), the excess fuel being converted into a product gas which is fed to at least one further catalyst (2a, 2c, 2d, 2e, 2f), where it is combusted with the addition of oxygen.