Oxygen Mixing Nozzles at Duct Bends for Uniform Combustion
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Solution Overview
Problem
In oxygen combustion boilers, achieving uniform mixing of oxygen with circulating exhaust gas is challenging due to the low diffusivity of CO2 and temperature differences, leading to nonuniform combustion and furnace temperatures.
Innovation Solution
An oxygen mixer comprising a preheater, a combustion gas duct with bends, and oxygen injection nozzles arranged at upstream bends closest to the preheater, with injection ports on the downstream surface of the nozzles to ensure uniform mixing of oxygen with the circulating exhaust gas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If oxygen is injected into circulating exhaust gas to achieve oxygen combustion, then CO2 concentration in exhaust gas increases, but uniform mixing is difficult due to low diffusivity of CO2 and temperature differences
Solution Approach 1:
The oxygen injection system is divided into multiple injection nozzles arranged at different positions (upstream bend and downstream bend) along the combustion gas duct. This segmentation allows oxygen to be injected at multiple locations, creating multiple mixing zones that collectively achieve uniform distribution throughout the exhaust gas stream, overcoming the low diffusivity of CO2.
Solution Approach 2:
The injection nozzles are strategically positioned at bent sections of the combustion gas duct where the gas flow follows a curved path. This curvature creates enhanced mixing through centrifugal effects and flow separation, promoting better integration of oxygen with the exhaust gas compared to straight duct configurations.
2Productivity
If oxygen injection nozzles are placed upstream of the boiler furnace, then mixing distance is reduced, but uniform mixing is achieved through optimized nozzle positioning at bends
Solution Approach 1:
Oxygen is injected at the upstream bend of the combustion gas duct, initiating the mixing process early in the gas flow path. This preliminary action ensures that oxygen and exhaust gas begin mixing before reaching the boiler furnace, allowing sufficient time for diffusion and convection to achieve uniform composition by the time the mixed gas enters the combustion zone.
Solution Approach 2:
The injection nozzles are positioned specifically at the upstream bend where flow characteristics (velocity, pressure, turbulence) are most favorable for mixing. This localized positioning exploits the specific hydrodynamic conditions at the bend to maximize mixing efficiency without requiring extended duct length throughout the entire system.
3Stability of the object's composition
If multiple oxygen injection nozzles are arranged at bends, then mixing is improved, but device complexity increases
Solution Approach 1:
The bent sections of the combustion gas duct serve dual functions: they guide the gas flow toward the boiler furnace and simultaneously act as mixing zones where oxygen injection occurs. This multi-functionality reduces the need for additional dedicated mixing components, achieving improved mixing without proportionally increasing device complexity.
Solution Approach 2:
The oxygen injection system is merged with the existing combustion gas duct structure by positioning nozzles at the duct's bends. This integration combines the flow guidance function of the bends with the oxygen injection function, achieving effective mixing while utilizing the existing duct geometry rather than adding separate mixing chambers or complex injection systems.
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 oxygen mixer ensures uniform mixing of oxygen with the circulating exhaust gas, optimizing the length of the combustion gas duct and achieving uniform combustion in the boiler furnace.
Implementation Method 1
a preheater for heating circulating exhaust gas
Implementation Method 2
uniform mixing of the oxygen with the circulating exhaust gas is difficult to attain particularly due to a small diffusion coefficient of CO 2
Implementation Method 3
the pulverized coal is burned with mixed gas which is a mixture of oxygen with the circulating exhaust gas
Implementation Method 4
combustion of coal with oxygen having a concentration of nearly 100%
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
In an oxygen mixer for an oxygen combustion boiler, circulating exhaust gas 8a heated in a rotary preheater 11a is mixed with oxygen. Resultant mixed gas 4 is guided to a boiler furnace 1 through a combustion gas duct 3 having bends 21a, 21b and 21c. At the bend 21a closest to the rotary preheater 11a in the combustion gas duct 3, an oxygen injection nozzle 23 is arranged to have a plurality of injection ports 26 for injection of oxygen 22 into circulating exhaust gas 8a.