15t Electric Arc Furnaces Smelting Process in Ferrous Foundries

15t electric arc furnaces is a small to medium-sized furnace, commonly used in modern steel production to produce special steels, alloy steels, or as a supplement to large integrated steel enterprises. It is mainly used for short-process steelmaking of ferrous metals, and its raw materials can be 100% scrap steel, or a combination of scrap steel and molten iron (pig iron), or scrap steel and sponge iron (DRI).

The steelmaking electric furnace melts scrap steel using electrical energy, utilizing the electric arc formed between the charged material and electrodes for heating. These EAFs typically use 10-35kV voltage and are equipped with a water-cooling system to ensure safe operation.

15t Electric Arc Furnaces Smelting Process in Ferrous Foundries

The entire smelting process of the EAF smelting furnaces is a systematic engineering project that uses electric energy to heat raw materials such as scrap steel and/or pig iron, and through physicochemical reactions, to smelt steel with qualified composition and temperature. It is mainly divided into the following stages:

I: Preparation & Charging

1. Furnace Lining Preparation: Inspect and repair the refractory materials (usually magnesia-carbon bricks) of the furnace wall and bottom. Ensure the taphole is tightly sealed.

2. Batching Calculation: Based on the target steel composition, calculate the required proportions of scrap steel, pig iron, alloys, and slag-forming materials (lime, fluorite, etc.). A 15-ton EAF requires high batching accuracy.

3. Charging:

• Top Charging (Mainstream): Unscrew the furnace lid and use a crane to hoist the material basket to the top of the smelting furnaces, pouring the raw materials into the furnace in one go or in stages. To protect the furnace bottom and accelerate melting, light, thin materials are typically loaded at the bottom, heavy scrap steel in the middle, and pig iron or carbonizer at the top.

• Side Charging: A few furnace types use a charging machine through the furnace door.

II. Melting Period

• Arc Ignition: Lower the electrodes (usually three graphite electrodes) to the material surface, and apply electricity to generate a high-temperature electric arc (reaching over 3000℃), directly heating the furnace charge.

• Assisted Melting Operation: Oxygen blowing is a key technology. Operators blow oxygen into the unmelted solid charge through oxygen lances at the furnace door, utilizing the exothermic oxidation of iron to accelerate melting, while simultaneously cutting large pieces of scrap steel.

• Slag Formation & Covering: As the metal melts, slag-forming agents such as lime and fluorite are added to form molten slag that covers the molten steel, stabilizing the electric arc, preventing gas absorption, and facilitating early dephosphorization.

• Objective: To melt all solid charge into a homogeneous molten steel. This stage consumes the most electricity, approximately 60-70% of the total power consumption.

III: Oxidation Refining Stage 

After the steel is completely melted, oxidation refining begins. The main tasks are dephosphorization, decarburization, degassing (hydrogen and nitrogen), and removal of inclusions.

1. Sampling & Analysis: Steel and slag samples are taken for rapid analysis to determine the current composition.

2. Enhanced Dephosphorization: Lime is added again to adjust the basicity, and high-phosphorus slag is removed through slag removal or skimming operations.

3. Decarburization & Boiling: Oxygen is blown into the depths of the molten pool, where carbon is oxidized to generate CO bubbles, causing the molten pool to boil violently. This helps remove gases and inclusions from the steel and homogenizes the composition and temperature of the molten steel. Final carbon control is crucial, requiring precise timing of stopping oxygen blowing based on the steel grade requirements.

IV: Reduction Refining Period (Pre-tapping Treatment) 

After the oxidation phase, once the phosphorus and carbon content of the molten steel meets the requirements, it enters the reduction period (modern electric arc furnaces often use methods such as "tapping degassing and alloying" to simplify and replace the traditional reduction period).

1. Tapping: 

• Traditional processes remove oxide slag and add reducing slag materials (calcium carbide, ferrosilicon powder, etc.) for diffusion deoxidation and desulfurization. Modern 15t electric arc furnaces more commonly use "tapping process alloying":

• Alloys (ferromanganese, ferrosilicon, ferrochrome, etc.) and refining slag materials are pre-added to the tapping ladle.

• The steelmaking electric furnace is tilted, and molten steel is poured into the ladle, completing pre-deoxidation, alloying, and preliminary slag washing refining during the tapping process. This improves alloy yield and shortens furnace time.

2. Ladle Refining (Optional but Strongly Recommended): 

• For high-quality steel grades, the molten steel needs to be transferred to a ladle refining furnace (LF furnace) after tapping for:

• Electric Arc Heating (Precise Temperature Control)

• Bottom-blown Argon Stirring (Using homogenized composition and temperature, promoting inclusion flotation)

• White Slag Refining (Deep Deoxidation and Desulfurization)

• Composition Fine-tuning

V: Tapping & Casting

1. After the molten steel reaches the target composition and temperature (usually 80-120℃ higher than the melting point), the taphole is opened, and the molten steel is poured into the ladle.

2. The ladle is transported to the casting area for continuous casting or ingot casting to produce steel billets or ingots.

Technical Features of 15-Ton Electric Arc Furnace Smelting

1. High-Power/Ultra-High-Power Power Supply: 

Equipped with a high-capacity transformer, shortening melting time and increasing productivity.

2. Oxygen-Combustion Nozzle Assistance: 

Burners are installed on the furnace wall, burning natural gas or kerosene for auxiliary heating in the initial melting stage, saving electricity and increasing efficiency. 

3. Enhanced Oxygen Technology: 

In addition to the furnace door lance, supersonic cluster oxygen lances are commonly used, resulting in higher decarburization efficiency and significant energy savings.

4. Eccentric Bottom Tapping (EBT): 

Modern 15-ton EAF are almost all designed with EBT. The tap hole is located eccentrically at the furnace bottom, achieving slag-free tapping, creating favorable conditions for subsequent refining. The furnace body can also be operated with both steel and slag remaining, facilitating rapid melting of the next heat.

5. Automation & Intelligent Control:

• Automatic Electrode Adjustment System: Maintains arc stability, reduces short circuits, and saves energy and electrode consumption.

• Process Computer Control: Optimizes power curves and calculates alloy composition based on models.

6. Environmental Protection Facilities:

• Direct Dust Collection Through the Fourth Hole (Primary Dust Collection): Flue gas generated during smelting is directly drawn to the dust collection system through the fourth hole in the furnace cover.

• Enclosed Hood or Roof Hood Dust Collection (Secondary Dust Collection): Collects dust emitted during charging and tapping.

• Noise Control: Employs enclosed workshops and soundproof enclosures.

Technical & Economic Indicators of a 15t Steelmaking Electric Furnace (Reference Values)

• Smelting Cycle: Approximately 60-90 minutes

• Electricity Consumption: 320-420 kWh/ton of steel

• Electrode Consumption: 1.2-2.0 kg/ton of steel

• Oxygen Consumption: 25-40 Nm³/ton of steel

Today, the 15t electric arc furnaces has evolved into a "high-efficiency production unit" centered on efficient melting, rapid decarburization, energy conservation, and environmental protection, closely integrated with ladle refining. The core objective of the EAF smelting furnaces is to produce qualified molten steel in the shortest possible time, at the lowest cost and energy consumption, for use in subsequent processes.