EA029992B1 - Variable-diameter rotating furnace for processing of oxidized nickel ores - Google Patents

Abstract

The invention is related to non-ferrous metallurgy and can be used in processing of oxidized nickel ores to improve technical and economical indicators in traditional pyrometallurgical methods of ferronickel production. The objective of the invention is use of a variable-diameter rotating furnace for processing of oxidized nickel ores having a section widened by 20-35% in the ball formation zone, which leads to an increase in the heat-exchange surface, extension of time of material staying in this zone and reduction of heat stress of the furnace volume, which finally must result in improvement of quality of ferronickel balls. Said high-temperature zone having increased furnace drum diameter is lined using a lightweight heat-insulating material substrate layer under the main working lining layer, which decreases heat losses by the furnace body and reduces weight of the lining.

Description

The invention relates to non-ferrous metallurgy and can be used in the processing of oxidized nickel ores to improve technical and economic indicators in traditional pyrometallurgical methods for the production of ferronickel. The aim of the invention is the use of a rotary kiln with a variable diameter for the processing of oxidized nickel ores having an expansion of 20-35% in the zone of formation of chickens, which leads to an increase in heat exchange surface, an increase in the residence time of the material in this zone and a decrease in the thermal stress of the furnace volume and, ultimately in the end, should lead to an improvement in the quality of ferronickel crits. The lining of the specified high-temperature zone with a larger diameter of the furnace drum is performed using a lightweight insulating layer of the substrate under the main working layer, which allows to reduce heat loss by the furnace body and the weight of the lining.

029992 Β1

029992 Β1

029992

The technical field to which the invention relates.

The invention relates to non-ferrous metallurgy and can be used in the processing of oxidized nickel ores to improve technical and economic indicators in traditional pyrometallurgical methods for the production of ferronickel.

The level of technology

Known application of rotary kilns in various industries - cement, alumina and others (Diomidovsky DA Metallurgical furnaces of nonferrous metallurgy, M .: Metallurgy, 1970, p.544).

The main element of the furnace is a steel drum with a length of up to 240 m and a constant diameter of up to 6 m, lined with refractory products in temperature zones. To move the material to be baked, the drum has a slope of 4-6% of its length. The drum rotates at a speed of about 1 rpm from the electric drive through a reducer and an open gear transmission, which ends with a large crown gear mounted on the casing.

Since the weight of the drum is very significant (for example, when the length of the drum is 70 m, its weight, together with the lining, is about 400 tons), the supporting devices are a crucial node in the furnace design.

For the direct production of ferronickel from oxidized nickel ores, several processes are known. Melting in a blast furnace produces nickel-containing naturally alloyed cast iron with a relatively low melting point. It is possible to restore nickel and get its alloy with iron in an electric furnace. The critical process of low-temperature reduction of oxidized nickel ores with the formation of fine ferronickel crystals is known. The process of obtaining ferronickel nuclei in the slag phase, which is in a semi-molten state, is carried out in tube furnaces.

Crits (fine grains of ferronickel) are usually obtained in an inclined tubular furnace by heating a mixture of oxidized nickel ore with a reducing agent and subsequent magnetic separation. The tube furnace can be divided in length into three main zones: preheating (heating), reduction of oxides, and crying. The temperature in the heating zone is in the range from 3000 to 600 ° C. The temperature of the recovery zone rises from 6000 to 1100 ° C. The temperature of the zone of crisification reaches 12500-1350 ° С.

The process of cryogenesis is the limiting stage of all transformations of the initial charge in the firing process. The rate of formation of ferronickel krits is in the diffusion region. Technological techniques that can speed up this process, consisting in increasing the temperature in the zone of formation and / or reducing the viscosity of the liquid phase due to changes in the composition of the slag, are limited to ring formation processes and the formation of large material welds in a rotary kiln, which can lead to an emergency. In this case, the only way is to increase the residence time of the material in the zone of cryogenesis by increasing the furnace volume. In the case of increasing the length of the formation zone, it is more difficult to maintain the same temperature regime along its length, it may be necessary to install an additional burner, its fuel supply system and blast. In addition, increasing the length of the drum will require changes in supporting structures.

The most responsible and at the same time the most vulnerable part of the rotary kiln is its lining, the low resistance of which dramatically reduces the productivity of rotary kilns. In addition, the lining has significant heat loss.

There are single-layer (1 brick thick) methods of furnace lining, in which the refractory products used are selected according to their installation zones, taking into account changes in temperature conditions along the length of the furnace. There are also known options for lining, which are based on a combination of acidic and basic refractories, resulting in an increase in their service life (ed. St. 626335, 1977).

The difficulty of selecting refractories for rotary kilns is due to the extremely difficult working conditions of the furnace lining, especially in the zone of formation, where it is exposed to high flame temperatures (1450 ° C) and corrosive effects from liquid slags.

DISCLOSURE OF INVENTION

The problem to which the invention is directed is to increase the efficiency of the kiln production by increasing the length of time the material stays in the formation zone without increasing the kiln drum length and changing the kiln support structure, as well as reducing the heat loss from the kiln body.

The solution of the task is achieved by increasing the diameter of the furnace drum by 20-35% in the zone of formation of crystals with the simultaneous use in this area of a two-layer lining of lightweight refractory as a heat insulating substrate and magnesia refractories as a working layer.

In order to carry out the process of the process of crying, it is necessary to create the following technological conditions in the zone of formation of a rotary kiln: transfer the material to the semi-molten state and increase the height of the material flow layer. As it was established by the applicants, these conditions are achieved by an increase of 1 029992

the diameter of the furnace in the area of high temperatures by 20-35% relative to the diameter of the preheating zone and the recovery zone.

By increasing the diameter of the drum by 20-35% due to the creation of different conditions for the promotion of the material, the timing of all the processes occurring across the furnace zones (drying and heating, recovery and formation of crystals) is achieved, which ensures its continuous and uniform loading and thus the most efficient operation of the furnace unit .

The expansion of the furnace is less than 20% does not provide the necessary thickness of the layer of material. However, simultaneously with an increase in the diameter of the furnace, it is necessary to apply a lining with a heat-insulating layer to compensate for the increasing heat loss by the increased surface of the furnace body. To reduce heat loss in the zone of formation of crystals, a two-layer lining of lightweight refractories as a heat insulating substrate and magnesia refractories as a working layer is performed. This lining reduces heat loss without weighting the furnace and increasing the load on the supports. An increase in the furnace diameter of more than 35% is undesirable due to a significant increase in the mass of the unit. In this case, the increase in heat transfer surface is not compensated by the additional effect of the use of a 2-layer lining, and in an excessively large layer of material heat transfer deteriorates.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the hull and the distribution of the temperature zones of the rotary kiln to produce ferronickel crusts according to the invention;

FIG. 2 - the layout of the refractories in the area of the formation of crying according to the invention; FIG. 3 - photograph of the lining of the furnace.

The implementation of the invention

Hereinafter the invention will be described with reference to the above drawings.

The layout of the hull and the distribution of the temperature zones of the rotary kiln to produce ferronickel crusts according to the invention are shown in FIG. 1, and the layout of refractories of a double-layer lining in the zone of formation of crystals is shown in FIG. 2

FIG. 1 shows an oven 70 m long, rotating at a speed of 40-60 rev / h. The mixture, which is an iron ore, reducing solid fuel and flux, in certain proportions are mixed and loaded through the end into a rotary kiln. At the opposite end of the furnace there is a burner in which fuel is burned to heat the charge. The mixture as it moves in the furnace to the outlet is continuously heated by heating gases and various physical and chemical processes take place in it depending on the heating temperature. The relative distribution of temperature zones along the furnace in meters and percentages of the total furnace length is: a heating zone at a temperature of 300-600 ° С (20% of the furnace length), oxide reduction at a temperature of 600-1100 ° С (40% of the furnace length) and a zone cryogenesis at 1200-1400 ° С (20% of the furnace length). Clinker is discharged from the outlet of the furnace at 1250 ° C, and exhaust gases exit from the opposite end of the furnace.

The layout of refractories in the furnace of FIG. 1 (section A-A) is shown in FIG. 2. Layer (3) of a heat insulating substrate made of lightweight refractory material (heat insulating brick) is placed on a fireclay mortar (5) in a ring. The working layer (1.2) of magnesia refractories in the form of rib double-sided wedges is placed on top of the layer (3) of thermal insulation on the magnesian-ferruginous mortar (4). The use of such a lining design with a lightweight substrate provides a reduction in its weight and a higher total coefficient of thermal resistance of the lining layer.

Example.

In a pilot industrial furnace 0 0.6x8m, an expansion to oxidized nickel ore was made to burn up to 0.8 m over a 2-m long section, counting from the hot end of the furnace at a level from 1.5 to 3.5 m. The lining in this zone was done in 2 layers (Fig. 3): 1 - furnace shell, 2 - thermal insulating substrate layer, 3 - working layer, 4 - circling (styling device).

In the furnace, oxidized nickel ore was calcined (the amount of the calcined mixture was 280 kg, the humidity was 2.5%, the composition of the charge was 206 kg of ore, 36 kg of fluxes, 1.5 kg of the binder, 36.5 kg of carbon reducing agent)

The main results of the tests carried out in the traditional furnace and the furnace according to the invention are presented in the table.

Comparison of furnace performance

Indicator Comparison example Invention Example Housing temperature in the zone of crying 350 ° C 234 ° C The residual carbon content in ferronickel clinker 5.5% 0.8% Slag content in the creamer after magnetic separation five% one%

The decrease in the residual carbon content in the resulting ferronickel clinker and the slag content in the cris after magnetic separation indicates a more complete completion

- 2 029992

reduction processes and the separation of metal and slag in the reconstructed furnace. Such quality indicators were achieved by increasing the heat exchange surface and increasing the residence time of the calcined material in the reconstructed part of the furnace.

The decrease in the temperature of the furnace body in the zone of formation of crystals indicates the energy efficiency of the applied two-layer lining.

Claims (1)

CLAIM Rotary kiln for calcining oxidized nickel ores containing a lined steel drum, including a preheating zone, a reduction zone and a cresting area and located on support devices, characterized in that the diameter of the furnace drum in the cresting area is 20-35% larger than the diameter of the preheating zone and the zone of recovery, and the fact that in the zone of formation of lining is made of a two-layer of lightweight refractories as a heat insulating substrate and magnesia refractories in working layer.