Electric Arc DRI Melting With Soft Slag and High Carburizing
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Solution Overview
Problem
Existing methods for producing hot metal from lower quality DRI in an electric arc furnace face challenges such as low power density, dense and non-foamy slag characteristics, poor mixing of carbon materials, and inefficient carburizing, leading to increased operating costs and reduced productivity.
Innovation Solution
A method and system that includes injecting oxygen into the slag layer without penetrating the molten iron, using lumpy carbonaceous materials, and optionally injecting combustible gases to maintain a soft and sparse slag, enhancing energy transfer and mixing, with features like electromagnetic stirring to achieve high power density and carburizing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional EAF is used to melt low grade DRI, then the furnace area is reduced, but the slag becomes dense and non-foamy which obstructs electric arc and reduces energy efficiency
Solution Approach 1:
The patent changes the physical and chemical parameters of the slag by controlling FeO content (5-20%) and basicity (1.5-2.5), transforming it from dense and non-foamy to soft and sparse, which allows the electric arc to penetrate effectively while maintaining compact furnace dimensions
Solution Approach 2:
The patent introduces fluxes as intermediary substances that modify the slag properties. By adding specific fluxes to control FeO and basicity, the slag acts as a mediator that enables effective heat transfer and arc penetration without requiring large furnace area
2Reliability
If oxygen is injected to oxidize FeO in slag, then the FeO content increases which improves arc penetration, but the carbon content in hot metal decreases due to oxidation
Solution Approach 1:
The patent employs feedback control by monitoring and adjusting oxygen injection rates, carbonaceous material addition, and FeO/B basicity ratios dynamically during the melting process to maintain optimal FeO content (5-20%) while preserving carbon content (2.5-4.5%) in the hot metal
Solution Approach 2:
The patent carefully controls the oxidation process by adjusting oxygen injection parameters and FeO content to a specific range (5-20%), preventing excessive oxidation that would lose carbon, while still achieving sufficient arc penetration
3Loss of substance
If carbonaceous material is added to enhance carburizing, then the carbon content increases, but the mixing efficiency decreases due to poor stirring in conventional EAF
Solution Approach 1:
The patent introduces electromagnetic stirring as a mechanical vibration mechanism that agitates the molten metal and slag, significantly improving mixing efficiency and carbon distribution without requiring additional mechanical stirrers
Solution Approach 2:
The patent uses gas injection (oxygen and combustible gases) to create fluid flow and stirring effects in the molten metal, enhancing carbon distribution and mixing efficiency through pneumatic action
4Use of energy by moving object
If SAF is used to melt DRI, then the Joule heating mechanism is utilized, but the power density is low (less than 300 kw/m2) compared to conventional EAF (higher than 2000 kw/m2)
Solution Approach 1:
The patent replaces the indirect Joule heating mechanism of SAF with direct electric arc heating, substituting the thermal conduction-based heating with electromagnetic arc heating that delivers much higher power density (600-2000 kw/m2) directly to the molten metal
Solution Approach 2:
The patent changes the heating mechanism from low-power-density Joule heating through thick slag layer to high-power-density electric arc heating, achieving power densities over 600 kw/m2 by optimizing slag properties to allow arc penetration
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 approach allows for efficient energy transfer to molten iron with power input over 600 KW/m2, maintaining low FeO content in slag and high carbon content in the product, thereby improving energy efficiency and productivity while reducing operating costs.
Implementation Method 1
charging the DRI to the DRI melting furnace through a chute; forming a slag layer comprising slag and forming a layer of molten iron below the slag layer
Implementation Method 2
The blast furnace (BF)—basic oxygen furnace (BOF) process route has been the most predominant method globally for producing crude steel
Implementation Method 3
injecting the oxygen into the slag layer not penetrating the slag or reaching the molten iron from the at least one oxygen injection nozzle
Implementation Method 4
charging lumpy carbonaceous material fed along with the DRI
Implementation Method 5
with features like electromagnetic stirring to achieve high power density and carburizing efficiency
Data Source
AI summary
According to embodiments, disclosed is a method and system to maintain the soft and sparse slag characteristic favorable for an electric arc to efficiently transfer the energy to molten iron with the power input per furnace area higher than 600 KW/m2 while keeping FeO amount less than 5% in the slag and carbon amount higher than 2.5% in the product hot metal at a DRI melting furnace.