Electric Furnace Oxygen Lance & Oxygen Supply Technology | Oxygen-Combustion, Coherent Jet & EBT Applications

Electric Furnace Oxygen Lance & Oxygen Supply Technology | Oxygen-Combustion, Coherent Jet & EBT Applications

1. What is the importance of oxygen in electric arc furnaces?

The heat of chemical reaction accounts for a considerable proportion of the energy input of an electric arc furnace, reaching 20%-30%; especially after the use of molten iron, the proportion of chemical heat reaches 40%-50%, which is a characteristic of modern electric arc furnace steelmaking processes. Oxygen technology is a concentrated embodiment of modern high technology, and the combination of power supply and oxygen supply is an important means for electric arc furnaces to improve production speed and save energy and reduce consumption.

2. What is the theoretical calorific value of each element in the molten pool oxidized to 1 kg under oxygen blowing conditions?

The theoretical calorific values of each element in the molten pool oxidized to 1 kg under oxygen blowing conditions are shown in the table below:

Element | Product | Heat of Reaction | Relative Cost ① (Reference Value)

kJ/kg | Kw·h/kg

Al | Al₂O₃ | 30.995 | 8.61 | 3.7

Si | SiO₂ | 32.157 | 8.93 | 3.2

Mn | MnO | 6.992 | 1.94 | 6.0

Fe | FeO | 4.775 | 1.33 | 1.8

C | CO | 9.159 | 2.54 | 0.5～0.6

C | CO₂ | 32.761 | 9.10 | 0.3～0.6

①Assume the electricity price per kWh is 1.

3. What is an electric arc furnace (EAF) door lance mechanical device?

Oxygen blowing in electric arc furnace (EAF) steelmaking is one of the important methods for enhancing EAF smelting. The most common method is to insert a steel pipe into the molten pool to blow oxygen. To fully utilize the chemical energy within the furnace, the oxygen consumption per ton of steel has gradually increased in recent years. Simultaneously, considering the poor working conditions, safety risks, and unstable efficiency of manual oxygen blowing, EAF door lance mechanical devices have been developed. Examples include the consumable oxygen lance device developed by BSE in Germany, and the water-cooled oxygen lance devices developed by Fuchs in Germany, Berry in the United States, and Combustion in the United States.

Because consumable oxygen lances consume a large number of oxygen pipes, they are rarely installed in newly built EAFs. The function of the door lance device is to blow oxygen to aid melting and refining, and to blow carbon powder into the molten pool to create foamy slag.

The overall benefits of using an EAF door lance are: improved oxygen blowing efficiency, shortening smelting time by 5-15 minutes; saving 80%-90% of oxygen pipes, reducing costs per ton of steel by 15-30 yuan; improving workers' working conditions, and replacing 90% of manual oxygen blowing.

4. What are the components of an electric arc furnace door lance device?

The door lance device consists of a water-cooled oxygen lance and a door lance. The mechanical system comprises a boom rotation system, a lance body rotation system, a lance body swing system, and a lifting system. The oxygen lance mounted on the door lance device assists melting during the melting period and decarburizes and refines during the oxidation period. The carbon lance mounted on the door lance device is mainly used for creating foamy slag.

5. What is a consumable electric arc furnace door carbon-oxygen lance?

Currently, electric arc furnace door lances are mostly water-cooled. Because water-cooled oxygen lances also have certain drawbacks, Baden Steel has researched and applied a consumable electric arc furnace door lance, which has the function of injecting lime and carbon powder to create foamy slag.

Compared to water-cooled oxygen lances, its advantages are a higher operational safety factor, a larger blowing angle, and the ability to directly cut scrap steel. Its disadvantages are the high cost of the oxygen blowing pipe and the inability to continuously blow oxygen.

6. What is Oxygen-Fuel Assisted Melting Technology?

As electric arc furnace (EAF) steelmaking both domestically and internationally develops towards larger scale and ultra-high power, manufacturers of large and ultra-high power EAFs have researched various smelting methods and adopted different enhanced smelting technologies and equipment to improve production efficiency and reduce power consumption. The power consumption of EAF smelting largely depends on the melting period, i.e., the speed at which the scrap steel melts. The thermal characteristics of EAF steelmaking during the steel melting process result in three cold zones within the furnace, especially pronounced when using high-power or ultra-high-power power supplies. Statistics show that power consumption during the melting period accounts for 70% of the total power consumption in the entire smelting cycle. Therefore, auxiliary energy-assisted melting technology has been widely introduced both domestically and internationally to eliminate the three cold zones, shorten smelting time, and achieve the goal of improving EAF production efficiency and reducing power consumption. It has been reported that in the 1980s, 50% of EAFs in Europe and 80% in Japan used oxy-fuel assisted melting for steelmaking. In the 1990s, almost 100% of newly commissioned large electric arc furnaces abroad adopted this technology, typically using natural gas and light diesel oil as fuel. In China, coal-to-oil fluxing technology was developed in the 1980s, achieving significant results in electric arc furnaces under 30 tons. However, due to the low calorific value of coal, this technology is not suitable for large electric arc furnaces, especially those requiring high efficiency and fast operation, such as high-power and ultra-high-power furnaces. Therefore, currently, oil or natural gas is mainly used as fluxing fuel in China.

7. What are the oxy-fuel fluxing fuels?

The fuels used in burners are classified into three categories: solid, liquid, and gaseous. Among liquid fuels, light diesel oil is currently preferred due to its ease of use, cleanliness, and simple equipment maintenance, making it the preferred auxiliary fuel. Natural gas is the main gaseous fuel, but its use is limited in my country due to limited resources; coal gas and other gaseous fuels are not used due to their low calorific value and large exhaust volume. my country has developed coal-oxygen technology for solid fuels based on its resource conditions, but the thermal efficiency of the injection is low, the investment is large, and the preparation, storage, transportation, and removal and separation of sulfur and ash residues from the combustion products are quite complicated.

8. What factors determine the efficiency of the burner?

Electric furnaces generate heat to smelt steel by igniting an arc at the electrodes. The steel material melts slowly from the center of the electrode outwards, resulting in significant heat loss and a long smelting time. The oxygen lance, also known as the oxygen burner, is placed on the furnace wall in the cold zone of the electric furnace. It relies on a proper match between the burner and the electric arc power supply to achieve balanced melting of the scrap steel. The efficiency of the burner depends on:

(1) The temperature of the scrap steel and the heating area. If the temperature of the scrap steel is high and the heating area is large in the initial stage of melting, the burner efficiency can reach 80%;

(2) Determining the appropriate oxygen-oil ratio at different stages. When the scrap steel is close to being completely melted, the amount of oil in the burner should be reduced. In addition to oil, the fuel used in the burner can also be natural gas or pulverized coal. Oxygen burners are also used to preheat scrap steel in flues, but environmental protection should be considered.

9. What is a CoherentJet oxygen lance for electric arc furnaces?

CoherentJet oxygen lance technology is a new type of oxygen injection technology that solves the shortcomings of traditional supersonic oxygen lances, such as short injection distance, low impact force, and low oxygen utilization. It mainly utilizes a protective envelope formed by the combustion of the medium to protect the main oxygen flow. The outlet Mach number of a CoherentJet oxygen lance can reach approximately 2.0, and the jet distance in technical condition can reach 1.2–2.1 m. It can be directly installed on the furnace wall to achieve functions such as fluxing and decarburization.

10. What are the main benefits of applying a CoherentJet oxygen lance to an electric arc furnace?

The main benefits of applying a CoherentJet oxygen lance to an electric arc furnace are:

(1) It has multiple functions such as oxygen blowing, combustion, and secondary combustion, and achieves centralized automatic control, thereby reducing the facility costs and process costs of setting up and operating each system separately. (2) Due to the combustion function, scrap steel can be preheated and melted, thereby reducing energy consumption (at least 20 kW·h per ton of steel).

(3) Due to its strong impact and stirring capabilities, the utilization rate of oxygen and injected charcoal powder is improved, thus reducing the consumption of oxygen and charcoal powder.

(4) Due to the secondary combustion function, the furnace temperature is increased by fully utilizing CO combustion in the furnace, thereby reducing energy consumption.

(5) Due to reduced splashing, the iron content in the slag is reduced, the metal recovery rate is increased, and the maintenance cost of the furnace body is reduced.

11. How to control the operation of the cluster oxygen lance?

The cluster oxygen lance cuts and melts scrap steel more quickly, and can blow oxygen into the molten pool more effectively, greatly improving the oxygen utilization rate. First, open the auxiliary oxygen system, then open the compressed air system after a certain delay, and then open the fuel oil (or gas) system after another certain delay, while simultaneously supplying the main oxygen. When shutting down, the fuel oil and main oxygen should be shut down first, and then the compressed air and auxiliary oxygen should be shut down sequentially. Automatic alarm processing is implemented to prevent serious safety accidents caused by the oil pressure exceeding the compressed air pressure. 12. What is the metallurgical principle of secondary combustion? Secondary combustion can be divided into the following processes:

2[C] + {O2} = 2{CO}

Where C comes from carbon powder, fuel, pig iron, or molten steel, and O2 comes from oxygen, air, slag, or molten steel.

2[C] + {O2} = 2{CO}

Where O2 theoretically comes from the aforementioned dedicated oxygen source for secondary combustion, but in practice there is no strict source restriction, and the two processes occur simultaneously.

13. What is the secondary combustion rate?

The index for evaluating the degree of reaction is called the secondary combustion rate, expressed by the following formula:

PCR = %CO2 / (%CO + %CO2) × 100% (4.3) Where PCR is the secondary combustion rate; %CO and %CO2 are the volume percentages of CO and CO2 in the combustion products, respectively.

14. What is an EBT oxygen lance?

Modern electric arc furnaces all adopt eccentric bottom tapping (EBT) technology to achieve slag-free steelmaking. This not only reduces the amount of slag during tapping but also shortens the smelting cycle and minimizes the temperature drop at tapping. However, it also makes the EBT zone one of the cold zones in the UHP-EAF system, resulting in slower scrap melting and a significant difference in molten pool composition compared to the central area.

To address the EBT cold zone issue, an EBT oxygen lance can be installed above the eccentric furnace side to blow oxygen into this zone for enhanced melting. The EBT oxygen lance promotes scrap melting in this zone and, after the molten pool appears, increases the molten pool temperature, homogenizes the molten pool composition, and facilitates CO re-combustion.

In practical applications, the use of an EBT oxygen lance completely solves the problems of scrap in the EBT zone not melting before tapping and the inability to open the taphole. Simultaneously, the temperature and composition difference between the EBT zone and the furnace door area at tapping is only 0.5% to 1.0%.

The impact force of the EBT oxygen lance needs to be considered in its design. Because the molten pool in the EBT zone is shallow, the penetration depth of the oxygen jet from the EBT oxygen lance is designed not to exceed 2/3 of the molten pool depth, and should also avoid the taphole area. Considering the attenuation of the oxygen jet, a telescopic drive EBT oxygen lance is used, and the lance position is adjusted according to the smelting conditions.