Annular Kiln Air Feeding to Prevent High-Density Anode Cracks
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Solution Overview
Problem
High-density anodes in the production of primary aluminum for fused-salt electrolysis often crack due to high heating gradients, which cannot be effectively managed in open annular kilns, leading to inefficiencies and the need for less productive covered kilns.
Innovation Solution
Introducing a secondary air feeding device into the heating zone of the annular kiln allows for selective control of the heating gradient, enabling reduced gradients and complete combustion, thus preventing cracks and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high heating gradient (>14° K/h) is applied during heating phase, then productivity is improved, but crack formation increases leading to reduced manufacturing precision
Solution Approach 1:
The heating zone is segmented into multiple zones with different heating gradients. The first heating zone has a lower heating gradient to prevent crack formation, while the second heating zone has a higher heating gradient to increase productivity. This spatial segmentation allows simultaneous optimization of both manufacturing precision and productivity.
Solution Approach 2:
Different regions of the heating zone are assigned different thermal characteristics. The region near the firing zone receives lower heating gradient to protect against cracking, while regions farther away receive higher heating gradients. This local differentiation of thermal quality enables crack-free production without sacrificing overall productivity.
2Manufacturing precision
If lower heating gradient is applied to prevent crack formation, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
The heating process is divided into sequential stages with different heating gradients. The first stage uses lower gradient for crack prevention, followed by a second stage with higher gradient for productivity enhancement. This temporal and spatial segmentation resolves the contradiction between precision and productivity.
Solution Approach 2:
The heating gradient is made dynamic rather than static. It varies along the length of the heating zone and can be adjusted during operation. This dynamic control allows the system to maintain low gradients where cracks form and high gradients where productivity is needed, simultaneously achieving both objectives.
3Manufacturing precision
If air-fuel ratio in firing zone is altered to reduce heating gradient, then crack formation is reduced, but combustion efficiency decreases
Solution Approach 1:
The thermal control is segmented into different zones. The firing zone maintains its optimal air-fuel ratio for high combustion efficiency, while the heating zone uses separate air feeding to control the heating gradient. This spatial separation of control functions allows independent optimization of both combustion efficiency and crack prevention.
Solution Approach 2:
A secondary air feeding device acts as an intermediary between the firing zone and the anodes. It introduces additional air into the heating zone to reduce the heating gradient without affecting the air-fuel ratio in the firing zone. This intermediary mechanism enables independent control of heating gradient and combustion efficiency.
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 enables the production of high-density anodes with reduced crack formation and lower emissions, while maintaining productivity comparable to low-density anode production, and reducing energy consumption.
Implementation Method 1
secondary air is fed into the heating zone, upstream of the exhaust device, by means of a secondary air feeding device
Implementation Method 2
complete combustion of the pitch can be achieved even in the case of high-density anodes
Implementation Method 3
chambers being formed as heat exchangers and being used to receive anodes
Implementation Method 4
raw anodes are heated or pre-heated in the heating zone before being heated in the burning or firing zone
Implementation Method 5
primary air being introduced into the cooling zone by means of an air feeding device for the passage of air through the kiln unit
Data Source
AI summary
The invention relates to a method and to an air feeding device for producing anodes in an annular kiln (10), comprising at least one kiln unit (“fire”) (11) having a heating zone (13), a firing zone (14), and a cooling zone (15), each having a plurality of kiln chambers (12) which are interconnected by heating channels (17), are formed as heat exchangers and are used to receive anodes, in said method primary air being introduced into the cooling zone by means of a primary air feeding device (21) for the passage of air through the kiln unit and, once it has passed through the firing zone, being discharged from the heating zone as flue gas by means of an exhaust device (22), wherein secondary air is fed into the heating zone in the direction of the primary air flow, upstream of the exhaust device, by means of a secondary air feeding device (24).