RU2368667C2 - Method of direct reduction of iron - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: charge is preliminarily separated for two fractions, distinguished by particles size, - with large particle size and fine-dispersed fraction, which is introduced into reactionary volume of plasma furnace with flow of reducing gas. Additionally fraction with large particle size is introduced in the opposite direction to the stream of effluent gas.

EFFECT: loss enhancement of charge owing to carry-over with effluent gas, energy intensity reduction of process ensured by reduction of charge in gas phase with simultaneous usage of thermal and chemical energy of effluent gas for partial preliminary restoration of charge fraction with large particle size, implementation of process in continuous operation.

3 cl, 1 ex

Description

The invention relates to non-coke metallurgy, in particular to methods and devices for direct reduction of iron group metals from dispersed (non-uniform in particle size) oxide raw materials by gaseous and dispersed reducing agents.

A known method of direct reduction of metals in a plasma-arc furnace with a molten bath (Tsvetkov Yu.V., Panfilov SA "Low-temperature plasma in the recovery process". M: Nauka, 1980, p.232). The furnace has a ceramic crucible and a plasmatron introduced into the working space of the furnace through its arch. The plasma arc burns directly on the melt located in the ceramic crucible. The introduction of the charge is carried out on top of the bathtub mirror. In the case of metal reduction, a plasma-forming gas is supplied to the furnace, which is a necessary chemical reagent, while the recovery process is accompanied by a large amount of both the furnace gas and the exhaust gas discharged through an opening in the roof. The disadvantage of this method is the entrainment with the exhaust gases of a significant portion of the feed mixture.

To eliminate this drawback, compacting and pelletizing of oxide fines is used (Kinetics of recovery and morphological evaluation of self-healing briquettes based on hematite and magnetite ores. J.Kh. Noldin et al. Steel No. 10, 2005), recovery in cyclone reactors (Dust utilization from steel production in arc steel-smelting furnaces. L.N. Kuznetsov, L.A. Volokhonsky. Electrometallurgy 2004, No. 9), the introduction of dispersed reagents into the melt through a gas jet (US Pat. RF No. 2226219).

In the known methods, the problem of restoring a mixture consisting of several fractions according to particle size has not been solved. Namely, either the fraction from large particles is completely restored, but the entrainment of the finely dispersed fraction is large, or the entire incoming finely dispersed fraction is restored, but large particles do not have time to melt and recover. At the same time, compacting and pelletizing dispersed materials is a complex and energy-intensive technological process. The use of various designs of cyclone devices significantly complicates the technological scheme and also leads to significant energy costs, since these devices are based on gas thermal enlargement of the dispersed mass (melting, coagulation, particle sticking).

In the known direct reduction method (US Pat. RF No. 2072639 from 1992), the finely dispersed part of the charge carried out by the plasma arc plasma exhaust gas is collected using a separately installed dust precipitation chamber, in the outlet pipe of which a fine filter equipped with filter elements made of composite heat-resistant materials is built-in , while the mixture is fed through a hole in the lid. The use of filters made of composite materials complicates and increases the cost of the process.

There is a method of direct reduction of iron from dispersed ore raw materials, which includes introducing a charge into the reaction volume of a plasma furnace, initiating a discharge, melting and reducing a charge, and discharging off-gas (Plasma-arc reduction furnaces in the structure of an energy metallurgical complex. A.V. Nikolayev, A. A. Nikolayev. Proceedings of the Fifth Steelmakers Congress. 1999). A plasma discharge burns between the surface of the bath and the hollow graphite electrode introduced through the arch of the furnace. The charge is introduced into the furnace directly into the arc discharge of the furnace through the internal cavity of the electrode. In this case, the charge is fed to the surface of the bath in the area of the electrical arc binding.

In this device, the charge leaving the channel of the electrode above the surface of the bath enters the zone of high-speed plasma flows, a significant part of the introduced charge does not reach the surface of the bath and is carried away from the furnace with exhaust gases.

The closest prototype of the present invention is a method for direct reduction of iron from dispersed ore raw materials, comprising introducing a charge into the reaction volume of a plasma furnace, exciting a plasma discharge, melting the charge and reducing iron, and discharging off-gas (RU 2040548). In the known method, after the appearance of the melt in the melting chamber, pulverized material is periodically introduced into it until the melting is completely completed. The exhaust gases, filtered through a layer of the charge, pre-heat and process the charge. The finely dispersed part contained in the charge is carried away by the exhaust gases.

The known method has the following disadvantages:

- the process of restoring raw materials to iron is carried out in the charge melt, which is inefficient and requires high energy costs;

- the process is cyclic;

- the exhaust gases contain dust particles that clog the inlets in the bunker with the charge.

The technical problem solved by the invention is to eliminate the disadvantages of the prototype, ensuring the continuity of the process, increasing the efficiency of the recovery process and more fully using the supplied dispersed raw materials.

The main technical result of the use of the invention is to significantly reduce the entrainment of the finely dispersed part of the charge with exhaust gases from the furnace and the process of recovery in the gas phase.

This result is achieved in that the mixture is preliminarily divided into two fractions differing in particle size, a finely dispersed fraction is introduced into the reaction volume together with a reducing gas stream, and a fraction with a large particle size is introduced towards the exhaust gas stream.

Moreover, in one embodiment, a finely dispersed fraction is introduced in the center of the furnace, and a fraction with a large particle size is introduced along its periphery, in another embodiment, vice versa.

Terms and definitions used

Plasma discharge - a discharge excited in a gas by one of the known methods, for example using a plasma torch.

Plasma furnace - a device containing means for forming a plasma discharge and a crucible with a processed material, the heating, melting and chemical-thermal treatment of which is carried out using a plasma discharge.

Oxide raw materials - ores, concentrates and industrial substances based on metal oxides.

A mixture is a mixture consisting of oxide raw materials, alloying and refining additives and, in some cases, a solid reducing agent.

The fine fraction of the charge is a charge with particle sizes not exceeding (300-400) microns.

A fraction with a large particle size is a charge with particles exceeding 400 microns.

The method is implemented as follows. First, the charge is divided into two fractions - finely dispersed and with a large particle size; by conventional techniques, a plasma discharge is excited in the reaction volume of the plasma furnace, into which a finely dispersed fraction of the charge is supplied together with the flow of reducing gas. The gas leaving after interaction with the finely dispersed fraction acquires a high temperature in the plasma discharge and retains, to a large extent, reducing properties. A fraction with large particles, which are heated by this gas and partially reduced, is supplied to meet the flow of this gas, carrying particles of a finely dispersed charge reduced to metal. Continuing towards the flow of exhaust gas, large particles of the mixture fall into the reaction volume of the furnace, where they are finally restored.

Since large particles of the charge can be reduced only in the liquid phase, preheating and their partial recovery ensures the melting and complete restoration of this part of the charge in the reaction volume.

At least two variants of a particular method are possible. In one embodiment, a finely divided fraction and reducing gas are supplied along the central axis of the furnace, for example, along the axial cavity of the central electrode, exhaust gas is directed to the upper part of the furnace reaction chamber at its periphery, and a fraction with a large particle size is introduced through nozzles in the side wall or in the discharge cap chamber towards the flow of exhaust gas.

In another embodiment, a finely divided fraction with a reducing gas is introduced at the periphery of the reaction chamber, and the exhaust gases are directed upward along the axis of the furnace, for example, along the axial cavity of the central electrode, and a fraction with a large particle size is introduced towards it.

In any case, the flow of the fraction of large particles directed towards the flow of exhaust gases carries with it the finely dispersed fraction of the charge in reverse movement to the reaction volume of the furnace and the metal collector and prevents its entrainment. The mixture and reducing gas are supplied continuously, the finished metal can also be discharged continuously.

An example of the method

Fine fraction with a particle size of the mixture of 400 microns or less.

Coarse fraction with particle sizes from 400 microns to 5 mm.

Arc voltage - 90-100 V.

Arc current - 600 A.

Gas consumption 45 l / min at a flow rate of 60 g / min.

The gas flow rate is (1-3) m / s.

The duration of the heat - 42 minutes

Metal yield - 1170 g.

The calculation of the gas flow rate necessary for the removal of falling particles of raw materials can be performed on the basis of the laws of aerodynamics (G. Ebert. A brief guide to physics. Fizmatgiz, Moscow, 1963, pp. 168-170). As is known, a force f acts on a body blown by a gas stream, the magnitude of which at low flow velocities and small Reynolds numbers is

f = 6πηυα,

where η is the viscosity of the gas,

υ is the gas flow rate,

α is the radius of the particle (we take the shape of the particles spheroidal),

π = 3.14.

From the condition that gravity exceeds the force of the upward gas flow acting on the particle, for the iron oxide particles after the transformations we obtain the relation for the particle size of the charge α, at which they cannot be carried away by the gas flow at a given speed υ

2α> 10 ^-3 υ ^1/2

Here υ is expressed in [cm / s], α - in [cm].

From the above relation it follows that for the exhaust gases to carry particles with a size of 2α = 400 μm (minimum for large particles), the oncoming gas flow velocity of at least 16 m / s is required, which is significantly higher than the flow velocity in experimental melting.

Thus, the present invention allows:

- significantly reduce the loss of the mixture due to ablation with exhaust gases;

- reduce the energy intensity of the process due to the recovery of the charge in the gas phase while using the thermal and chemical energy of the exhaust gas for partial preliminary recovery of the charge fraction with large particles;

- lead the process in continuous mode.

The invention can be used at the enterprises of metallurgy and mechanical engineering for the direct production of metal from dispersed oxide raw materials using gaseous and dispersed reducing agents.

The possibility of realizing all the effects accompanying the method of introducing the charge into the plasma furnace proposed in the present invention was first established by us and has not been published anywhere.

Claims (3)

1. A method of direct reduction of iron from dispersed ore raw materials, including introducing a charge into the reaction volume of a plasma furnace, exciting a plasma discharge, melting the charge and reducing iron, discharging the exhaust gas, characterized in that the charge is previously divided into two fractions - with a large particle size and fine fraction, which is introduced into the reaction volume of the furnace together with a stream of reducing gas, and a fraction with a large particle size is introduced towards the flow of exhaust gas. 2. The method according to claim 1, characterized in that the finely dispersed fraction is introduced in the center of the plasma furnace, and the fraction with a large particle size is introduced along its periphery. 3. The method according to claim 1, characterized in that the fraction with a large particle size is introduced in the center of the plasma furnace, and the finely divided fraction is introduced along its periphery.