Annular Shaft Kiln Upper Shaft Diameter Reduction
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Solution Overview
Problem
Annular shaft furnaces of the Beckenbach type have high pollutant concentrations, particularly CO, in their exhaust gases, which exceed current emission limits, and suffer from material segregation and oversized refractory volumes leading to inefficiencies and increased investment costs.
Innovation Solution
The upper shaft is designed with a reduced inner diameter, increasing gas velocity for improved exhaust gas mixing and burnout, and features a feed chute with a matching reduced diameter to minimize segregation, along with an annular channel for exhaust gas extraction and a coolable metal support structure to prevent build-up, eliminating the need for an upper inner cylinder and allowing operational cleaning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the upper shaft has a standard inside diameter, then the gas velocity is insufficient for proper exhaust gas mixing, but reducing the diameter increases gas velocity and improves mixing
Solution Approach 1:
The patent applies parameter changes by reducing the inside diameter of the upper shaft to increase gas velocity. This geometric parameter modification directly addresses the insufficient mixing problem while maintaining structural feasibility through the stepped design that transitions from the narrower upper shaft to the wider main shaft.
2Object-affected harmful factors
If exhaust gases are discharged directly without treatment, then the system is simple, but pollutant emissions exceed legal limits
Solution Approach 1:
The patent converts the harmful exhaust gases into a beneficial resource by using them as combustion air for the burners. The exhaust gases are redirected through a combustion air blower and injection system into the combustion zone, where they serve as oxygen supply for burning residual CO and hydrocarbons, thereby reducing emissions while simplifying the overall system compared to conventional abatement technologies.
Solution Approach 2:
The patent employs strong oxidation by introducing the exhaust gases containing oxygen into the combustion zone where they participate in combustion reactions. This accelerated oxidation process effectively burns off CO and hydrocarbon components in the exhaust gases, converting them into less harmful substances and meeting emission requirements.
3Reliability
If an upper inner cylinder is installed in the upper shaft, then exhaust gas extraction is improved, but the refractory volume and investment costs increase
Solution Approach 1:
The patent extracts the upper inner cylinder component from the system entirely. Instead of using a separate inner cylinder structure, the invention achieves effective exhaust gas extraction through the reduced diameter of the upper shaft itself, combined with the optimized gas flow patterns created by the stepped geometry and the exhaust gas recirculation system.
Solution Approach 2:
The patent applies multi-functionality by using the upper shaft structure itself to perform multiple functions: it serves as both the structural support and the exhaust gas extraction channel. The reduced diameter of the upper shaft simultaneously achieves flow velocity control and exhaust gas extraction, eliminating the need for a separate upper inner cylinder.
4Stability of the object's composition
If the feed chute has a large diameter, then charging is simple, but material segregation occurs
Solution Approach 1:
The patent applies parameter changes by optimizing the diameter of the feed chute to match the reduced diameter of the upper shaft. This geometric parameter modification prevents material segregation by ensuring uniform flow characteristics, while the overall charging operation remains efficient due to the streamlined design.
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 design significantly reduces pollutant emissions, simplifies charging, reduces refractory volume, and lowers investment costs while maintaining high-quality fired goods, with improved convective heat transfer and minimal pressure loss impact.
Implementation Method 1
The reduction in the inner diameter of the upper shaft, which can be characterized geometrically in that the clear cross-sectional area of the upper shaft is preferably a maximum of 70% of the clear cross-sectional area of the main shaft, ensures a correspondingly increased gas velocity in the upper shaft
Implementation Method 2
Most of the exhaust gases flowing through the preheating zone of the upper shaft are extracted from the annular shaft furnace by an induced draft fan at the upper edge of the preheating zone and blown into the environment as furnace exhaust gases
Implementation Method 3
Combustion in the burners of the upper burner level is strongly sub-stoichiometric, so that the combustion gas exiting the upper combustion chambers contains a high concentration of CO and - if fuels containing hydrocarbons such as natural gas or oil are used - H2
Implementation Method 4
the fired material enters the cooling zone of the main shaft, where it is cooled down by countercurrent cooling air
Data Source
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AI summary
The invention relates to an annular shaft kiln for calcining granular material (G), in particular for calcining limestone or dolomite, comprising an upper shaft (20, 20') for preheating the granular material (G) and a main shaft (10, 10') arranged thereunder, with an axially arranged inner cylinder (30) for calcining and subsequently cooling the granular material. The annular shaft kiln according to the invention is characterized in that the upper shaft (20, 20') has a reduced inside diameter in comparison with the main shaft (10, 10').