Cool-Wall Combustion Device with Recirculation
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Solution Overview
Problem
Current combustion technologies in industrial boilers and furnaces with 'cold' walls struggle to achieve low NOx emissions due to high temperature fluctuations and the inability to maintain self-ignition conditions, leading to inefficient combustion and increased NOx production.
Innovation Solution
A combustion device with a porous matrix injection system that heats recirculated combustion products above the self-ignition temperature, using a combination of primary and secondary reactant pipes to achieve stable, highly diluted combustion without a primary combustion zone, thereby reducing NOx emissions across varying power ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If flameless combustion with internal recirculation is used in high-temperature enclosures, then NOx emissions are drastically reduced, but the technology cannot be applied in cold-wall combustion chambers where auto-ignition temperature cannot be reached
Solution Approach 1:
The combustion chamber is divided into two distinct zones: a hot combustion zone where fuel and oxidizer mix and burn, and a cold-wall zone where combustion products are recirculated. This segmentation allows the hot zone to maintain auto-ignition conditions while the cold walls remain below 125°C, resolving the contradiction between flameless combustion requirements and cold-wall applicability.
Solution Approach 2:
A recirculation system acts as an intermediary between the combustion zone and the cold walls. It extracts hot combustion products, cools them through heat exchange, and recirculates them to dilute the reactant mixture, enabling low-NOx combustion in cold-wall chambers without direct contact between hot flames and cold walls.
2Reliability
If staged combustion with a hot flame root is used to stabilize combustion in cold-wall chambers, then combustion stability is achieved, but temperature peaks and long residence times cause high NOx emissions
Solution Approach 1:
The system dynamically adjusts the recirculation rate of combustion products to maintain stable combustion across varying power levels. By controlling the amount of hot gas recirculated to the burner, the system maintains auto-ignition conditions without creating excessive temperature peaks, thereby achieving both stability and low NOx emissions.
Solution Approach 2:
The system changes the temperature and composition parameters of the recirculated gas to optimize combustion. By controlling the recirculation temperature and ratio, the system maintains combustion stability while limiting peak temperatures to below NOx formation thresholds, eliminating the need for stabilization devices.
3Object-generated harmful factors
If existing combustion technologies are used to meet current emission limit values at rated power, then NOx emissions are controlled at design conditions, but compliance cannot be maintained across the entire power variation range especially at low power settings
Solution Approach 1:
The system incorporates feedback control through the recirculation mechanism, where combustion products are continuously monitored and recirculated in proportion to maintain optimal combustion conditions. This feedback loop ensures that even at low power settings, the recirculation rate adjusts to maintain auto-ignition and limit NOx formation, achieving compliance across the entire power range.
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
The solution enables stable, low NOx emissions across the entire power variation range, eliminating the need for stabilization devices and reducing thermal stresses on equipment, while maintaining efficient combustion performance.
Implementation Method 1
the combustion of the first reactant allowing to heat the recirculated combustion products in contact with the cold walls of the combustion chamber
Implementation Method 2
heats recirculated combustion products above the self-ignition temperature
Implementation Method 3
This combustion is based on the intense dilution of the oxidizer and fuel jets through internal recirculation of combustion products
Implementation Method 4
Flameless oxidation is self-sustaining through the auto-ignition of a ternary mixture of oxidizer, fuel, and exhaust gases. For auto-ignition to occur, the temperature in the mixing zone must be more than 300°C higher than the auto-ignition temperature of the fuel in question
Data Source
Figure 1~2
Figure 3~4
AI summary
The device (10) for burning reagents in a so-called cool-wall (610) combustion chamber (605), which means to say one having a wall temperature supporting a thermal charge of less than 125 comprises: - at least one inlet pipe (105) for admitting a first reagent to the combustion chamber, - at least one primary pipe (110) for letting the second reagent into the combustion chamber separate from the inlet pipe for the first reagent, and - at least one secondary pipe (115, 215) for admitting a mixture of reagents into the combustion chamber having a means of injection (120, 220, 320, 420) of a stream of mixture of reagent directed toward the stream of the first reagent that has entered the chamber, the mixture coming from the secondary pipe leading to combustion to heat up: - the stream of first reagent leaving at least one first reagent inlet pipe, - the second reagent coming from the primary pipe, and - the products of combustion recirculated into the chamber to dilute the incoming reagents, to a temperature higher than a self-ignition temperature of at least one dilute reagent.