Hearth Furnace Iron Nugget Sulfur Control
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Solution Overview
Problem
Conventional direct reduction processes for producing metallic iron nuggets result in high sulfur content, making them undesirable for steelmaking processes due to increased energy consumption and refractory wear from additives like MgO, which raise slag melting temperatures.
Innovation Solution
A method involving multiple layers of a reducible iron mixture with a hearth layer of carbonaceous material, including non-coking coal, and a coarse carbonaceous overlayer to control sulfur levels and improve productivity, where the reducible mixture is heated to form metallic iron nuggets and slag, with additives like fluorspar to manage sulfur content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional direct reduction processes are used to produce metallic iron nuggets, then production efficiency is maintained, but sulfur content increases to unacceptable levels
Solution Approach 1:
The reduction process is divided into multiple zones within the hearth furnace: a preheating zone, a reduction zone, and a fusion zone. This segmentation allows different temperature and chemical conditions in each zone to optimize both sulfur removal and production efficiency simultaneously
Solution Approach 2:
Different regions of the hearth are provided with distinct functional characteristics - the preheating zone prepares the charge, the reduction zone removes sulfur through controlled atmosphere, and the fusion zone completes metallization. This local differentiation enables simultaneous optimization of sulfur content and productivity
2Manufacturing precision
If additives like MgO are used to manage sulfur content, then sulfur removal is achieved, but slag melting temperature increases and refractory wear increases
Solution Approach 1:
Sulfur is extracted from the iron charge through the reducing atmosphere in the hearth furnace, allowing sulfur removal without adding MgO or other fluxes that would raise slag melting temperature and cause refractory wear
Solution Approach 2:
A reducing atmosphere acts as an intermediary medium to remove sulfur from the iron charge through chemical reduction, avoiding the need for MgO additives and their associated negative effects on slag properties and refractory life
3Manufacturing precision
If additives are used to control sulfur, then sulfur content decreases, but energy consumption increases
Solution Approach 1:
The system uses its own reducing atmosphere, generated from the charge materials and hearth environment, to remove sulfur from the iron. This self-service approach eliminates the need for additional energy-intensive flux addition and processing steps
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 method effectively reduces sulfur content in metallic iron nuggets to less than 0.05%, minimizing micro-nugget formation and energy consumption, while maintaining high productivity and reducing refractory wear.
Implementation Method 1
direct reduction of iron oxide (e.g., iron ores or iron oxide pellets) employs the use of a reducing gas (e.g., reformed natural gas) to reduce the iron oxide and obtain DRI
Implementation Method 2
heating beneficiated iron ores to below the melting point of iron, below 1200° C. (2372° F.), either by gas-based processes or coal-based processes
Data Source
AI summary
A method and system for producing metallic iron nuggets may include providing multiple layers of agglomerates, such as briquettes, balls and extrusions, of a reducible mixture of reducing material (such as carbonaceous material) and of a reducible iron bearing material (such as iron oxide) on a hearth material layer (such as carbonaceous material) and providing a coarse overlayer of carbonaceous material over at least some of the agglomerates. Heating the agglomerates of reducible mixture to 1425° C. or 1400° C. or 1375° C. results in formation of an intermediate product of one or more metallic iron nuggets, which may have a sulfur content of less than 0.03%, and slag, which may have less than 5% mass MgO, which may have a ratio of percent by weight sulfur in the slag over percent by weight sulfur in the metallic nuggets of at least about 12 or at least about 15.