Plasma Method - The Process of Direct Steel Production

[Peyman 16150]

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THE MAIN CHARACTERISTICS

 

OF THE INSTALLATION FOR DIRECT STEEL PRODUCTION WHILE USING LOW-TEMPERATURE PLASMA (IDSP-125) WITH ANNUAL STEEL OUTPUT 125000 TONNES PER YEAR

 

 

SYSTEMS AND PARTS LIST

 

IDSP-125 includes the following units, systems, and parts:

- Metallurgical assembly for direct steel production

- Charge materials yard

- Continuous steel teeming department

- Department of metal processing out of furnace

- Department for repairing and testing plasma generators

- Gas-supply system

- Water-supply system

- Power-supply system

- Gas cleaning installation

- Automated, control, and alarm systems

- Control desk for the metallurgical set

- Equipment for utilizing metallurgical slag, heat, water, and gas

- Auxiliary departments

- Office buildings

 

 

METALLURGICAL ASSEMBLY FOR DIRECT STEEL PRODUCTION

 

It is an independent process that operates with IDSP power-supply systems, and includes the following sets and equipment:

- Plasma-metallurgical reactor

- Gas-supply system for MADSP

- Water-supply system for MADSP

- Power-supply system for MADSP

- System for charging iron ore raw material

- MADSP control desk

- Teeming department

- Automated, control, and alarm systems

- Gas cleaning

 

 

PLASMA-METALLURGICAL REACTOR

 

Means of processing iron ore raw material into the final product – steel. It includes the following assemblies and settings:

- Shaft

- Secondary reduction chamber

- Charge material feeding

- Electric-arc plasma equipment

 

 

 

 

 

 

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PROCESS OF DIRECT STEEL PRODUCTION

The process is realized in the assembly which consists of shaft furnace and secondary reduction chamber. There is a countercurrent flow of iron ore materials and reducing gases in the shaft furnace. Iron ore materials are charged into the upper part of shaft furnace and move upwards. There are electric-arc plasma generators in the lower part of shaft furnace. Reducing gas that is heated in electric-arc plasma generators moves upwards. The use of plasma generators helps to obtain reducing gas with average mass temperature 2500-3000 K. Being introduced into iron ore material layer, reducing gas heats it intensively, melts, and partially reduces. Oxide melt and reduced metal flow through the special channels into secondary reduction chamber. Secondary reduction chamber is a tank where oxide melt is treated by splashing with high temperature reducing gases. The gas is heated in electric-arc plasma generators that are placed in the walls of the chamber. Such treatment of oxide melt by the splashing provides almost complete iron reduction. Liquid metal and slag are tapped from the secondary reduction chamber through the runner opening. Metals that have been melted this way correspond the analysis of widespread brand steel, i.e. [C] = 0.01÷0.9%. = 0.007÷0.03%, [Mn], [Cr], [Ni] and other alloy elements where [P] depends on ore feedstock. There are small quantities of dissolved gases: [H]=0.001÷0.0034%, [N]=0.004÷0.0104%, [O]=0.008÷0.04%.

TECHNICAL INDICES OF THE PROCESS

Electric-arc plasma generators that are used in metallurgical assembly are uniform. All of them set in shaft and reducing bath have the same design and the same butt-joints. Electric-arc plasma generator serves to generate high-enthalpy flow of reducing plasma when direct current is used as a power source of electric-arc. The principle of plasma generator operation is to convert electric energy into heat energy by Joule gas heating where gas blows electric arc. Plasma-forming gas (CH4 – 70% vol., O2 – 30% vol.) is ionized and changed into plasma state in electric-arc column and nearby. It can absorb large amount of heat given off by arc. Gas in plasma state has much higher enthalpy than in ordinary combustion processes. Changing the power (led to plasma generator) and flow rate of plasma-forming gas provides the parameters of high-enthalpy gas flow that correspond technical regulations of this process.

There are 9 plasma generators in the assembly: 4 follow shaft perimeter, 5 follow the perimeter of secondary reducing chamber. Taking into account the conditions of plasma generator operating and technical data that should be provided, line structure has been chosen as an appropriate plasma generator design that is supposed to be with cylindrical vaporized (cooled) cored electrodes, gas vortex and magnetic regulation of arc column. Such structure of electric-arc plasma generators is widely used in industrial processes for equipment setting in multi-tonnage processes in metallurgy and chemical industry. E.g., Huls (Germany), Du Pont (USA), Hoehst (Germany), SKF (Sweden) use it. In this case, power of a single plasma generator goes up to 10 MW at the temperature of plasma flow 1500-2000K. Plasma generators of line structure with cylindrical cored electrodes have been used in pilot-plant installation of direct steel production at a metallurgical plant in Dnipropetrovsk. Such plasma generator design for this process has been chosen because of its structural simplicity, quite high thermal efficiency for gas heating, and available resources.

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There are 9 plasma generators in plasma-metallurgical reactor: 4 in the shaft, and 5 in the secondary reduction chamber. Modes of plasma generator operation in the shaft and secondary reduction chamber are different. An assembly with annual steel output 125000 t/y consumes 150.000.000nm³ of gas per year, i.e. 428571nm³ per 24 hours (for 350 working days), i.e. 17857 nm³/h. Gas distribution in plasma-metallurgical reactor is the following: 5000nm³/h in the shaft, 6250 nm³/h in the secondary reduction chamber; 6650 nm³/h for cold gas to decrease the temperature of gas mixture.

The rate for plasma-forming gas that goes through 1 plasma generator is 1250 nm³/h, i.e. 0.347 nm³/s.

If the density (ρ) of plasma-forming gas is 0.720 kg/ nm³, weight expenditure / consumption is 0.2498≈0.25 kg/s.

Plasma generators in reactor’s shaft are to provide the temperature of plasma current - 3300K; in reducing bath provided temperature of plasma current is supposed to be 2300K. According to thermo-dynamical data of plasma-forming gas, there should be the following power supply

∆h1= 7.328 kW/g/s

in order to obtain gas temperature 3300K.

For temperature 2300K, there should be ∆h1= 4.755 kW/g/s.

 

Thus, power needed for plasma-forming gas led to shaft plasma generator is

N1= G∆h2=250 g/s 7.328 kW/g/s=1832 kW.

Power needed for plasma-forming gas supplied to secondary reducing chamber is

N2= G∆h2=250 g/s 4.755 kW/g/s=1189 kW.

 

Having put plasma generators into operation, we define thermal efficiency as 0.7.

 

In this case, power of a single plasma generator in the shaft is

N1= 2617 kW. N1=2650 kW is accepted.

Power of a single plasma generator in secondary reducing chamber is

N2=1698 kW. N2=1750 kW is accepted.

Total power of shaft plasma generators is

Nsh=2650 kW, i.e. for 4 =10600 kW

 

Total power of plasma generators set in secondary reducing chamber is

Nrc=1750 kW, i.e. for 5=8750 kW

Total power for plasma generators set in plasma-metallurgical reactor is

Nr=106000 + 8750 = 19350 kW

 

The number and power of plasma generators needed for power supply system in terms of IDSP-125 depend on sources of direct current. Therefore, these parameters can be regulated.

 

 

SPECIFIC POWER IMPUTS PER 1 TONNE OF STEEL

- Consumption of iron ore pellets is 1.546 t

- Consumption of reducing gas mixture is 1200m³

- The amount of produced slag is 0.106 t

- The amount of furnace top gas is 1200m³

- Power imputs needed for melting and reduction is 750-800kW/h

 

During this process plasma-forming gas can be substituted by products obtained from gasificated coal.

 

 

ANNUAL CONSUMPTION

 

- Consumption of iron ore pellets is 193250 t

- Consumption of reducing gas mixture is 150 000 000 m³

- The amount of produced slag is 13250 t

- The amount of furnace top gas is 150 000 000 m³

- Power imputs needed for melting and reduction is 100 000 000 kW/h

 

For making project calculations, information concerning parameter values should be further specified.

 

 

 

 

[Peyman 16150]

 

 

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