RU2688765C1 - Method of metallized pellets production - Google Patents

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to ferrous metallurgy, particularly, to production of metallized pellets. Method involves preparation of charge by mixing of iron-ore materials with a solid reducing agent, formation of crude pellets, their loading onto the grate, treatment with gas-heat carrier with further cooling. Pellets are treated using in-series installed heating, metallization and cooling reactors and are carried out with a heat-transfer gas in counterflow at their movement in the heating and cooling reactor from top to bottom, and in the metallisation reactor from bottom to top. Heating of pellets in a heating reactor is carried out to temperature 800–850 °C mixture of gas coming from metallization reactor and natural gas combustion products at air flow rate coefficient α = 1.0–1.1. In metallization reactor heating is carried out to temperature of 1200–1400 °C mixture of gas coming from cooling reactor and additionally heated, and natural gas combustion products at air flow rate coefficient α = 0.4–0.5. Cooling is carried out with gas supplied from heating reactor and pre-cleaned from water and COusing calcined lime.EFFECT: invention is aimed at increasing efficiency, preventing secondary oxidation of metallized pellets and reducing heat power consumption.1 cl, 3 dwg

Description

The invention relates to the field of ferrous metallurgy, and in particular to methods for producing metallized pellets.

Known methods of metallization of iron ore pellets in shaft furnaces using hot reducing gas (Wiberg, Purofer, Armko, Midrex, etc.). The disadvantages of the described methods is their high cost associated with the need for pre-strengthening firing pellets, obtaining and heating a reducing gas, the use of sophisticated equipment, as well as a high level of energy consumption (Tulin N.А., Kudryavtsev BC, Pchelkin S.А., Werner D., Leselle, V., Muller, B., Papst, G., and Stefan, F., Development of Cokeless Metallurgy (Moscow: Metallurgy, 1987, 328 p.).

Similar disadvantages have methods of metallization (Copyright certificate No. 1468919, published 03/30/1989. Bull. No. 12; Copyright certificate No. 1677065, published 09/15/1991. Bull. No. 34), including the loading of burned pellets into retorts with a fixed layer, their recovery by gas in the process of heating, cooling and unloading.

Such deficiencies are devoid of methods for metallization of the coarse-ore pellets.

There is a method that includes the manufacture of coarse-angled pellets, their loading in a mixture with solid fuel in the grid-iron reactor and metallization. Heat for the implementation of the process is obtained by burning fuel in the charge layer with the organization of the movement of the combustion zone of the fuel towards the air blowing. The disadvantage of this method is low productivity, the need for high accuracy in selecting the intensity of air supply to the combustion site and its filtration rate to eliminate local overheating, sintering the charge and reduce the gas permeability of the layer (Kazakhstan, innovative patent No. 23799, published 03/15/2011. Bull. No. 3) .

There is a method of thermal metallization of coarse-angled pellets, including their production and heat treatment, which consists of drying operations on a grate-type drying unit, high-temperature calcination in a rotary hearth kiln in a reducing atmosphere and cooling in a rotary hearth cooler (RF patent №2489493, published 10.08.2013, Bulletin # 22). The main disadvantages of the method include high energy intensity, since the pellets are heated by supplying microwave energy, the possibility of secondary oxidation of the pellets, since they are cooled by filtration through a layer of atmospheric air pellets.

The closest to the technical nature of the invention is a method for producing metallized pellets on a conveyor machine, including mixing of coal materials, pelletizing, layer-by-layer laying on the grate of the conveyor machine, subsequent metallization and cooling (certificate of authorship No. 417473, published on 07/18/1974). The main disadvantages of the method are the low degree of metallization of the calcined pellets due to the high oxygen potential of the heat transfer gas, the difficulty of controlling the gas atmosphere and the organization of non-oxidative cooling. The prototype provides the possibility of obtaining pellets with a degree of metallization of 60%.

Metallization of the ore-coal pellets occurs at temperatures close to the temperature at which the charge softens. Such temperatures are achieved under the condition that a heat carrier gas is produced by burning natural gas at an air flow rate of α≈1.0-1.1. The design of the firing machine does not allow to achieve its complete sealing, therefore air leaks are possible. It also adversely affects the composition of the atmosphere, both during firing and during cooling. All this leads to the burning out of solid fuel, which requires additional introduction into the charge in excess of the stoichiometric iron required for complete reduction, as well as the secondary oxidation of reduced iron.

The technical result of the proposed solution is to prevent the secondary oxidation of metallized pellets and reduce heat and power costs.

This technical result is achieved by the fact that in a known method of producing metallized pellets, including preparation of the charge by mixing iron ore materials with a solid carbonaceous reducing agent, forming raw pellets, loading them onto a grate and processing with coolant gas, followed by cooling, the pellets are processed with using successively installed reactors for heating, metallization and cooling and carry out gas-coolant in counter-current e when moving them in the heating and cooling reactor from top to bottom, and in the metallization reactor from bottom to top, the pellets in the heating reactor are heated to a temperature of 800-850 ° C with a mixture of gas coming from the metallization reactor and natural gas combustion products at a flow rate air α = 1.0-1.1, and in the metallization reactor, heating is conducted to a temperature of 1200-1400 ° C with a mixture of gas coming from the cooling reactor additionally heated, and natural gas combustion products with an air flow coefficient α = 0.4-0 , 5, and cooling Ved gas coming from the heating rector pre-cleaned of water and CO ₂ using calcined lime in the purification reactor.

The most common characteristic that reflects the intensity of the flow of mass-heat exchange processes during processing is the rate of gas filtration through the layer of pellets. An increase in the filtration rate leads to an increase in the heating rate of the pellets and a reduction in the firing time. In turn, the filtration rate is a function of the layer height and with the increase in the latter, there is an increase in gas-dynamic resistance, which causes a decrease in the filtration rate, an increase in energy consumption per process. Separation of the roasting process into heating and metallization and its implementation in the heating and metallization reactors allowed, at a constant filtration rate and total roasting time, to increase the height of the pellet layer and thereby increase the overall plant capacity.

Based on laboratory experiments, it was found that heating raw pellets to temperatures of 800–850 ° C with α = 1.0–1.1 does not lead to carbon burnout, and metallization with air flow coefficient α = 0.4–0.5 takes place without secondary oxidation. The final metallization temperature of the pellets is 1200-1400 ° C. To achieve it, the heat-transfer gas consisting of a mixture of gas coming from the cooling reactor and natural gas combustion products with an air flow rate α = 0.4-0.5 should be heated to higher temperatures. This is achieved by additional heating of the gas from the cooling reactor.

Figure 1 shows a schematic diagram of an installation for implementing a method for producing metallized pellets.

The method is carried out at an installation consisting of successively installed reactors for heating (1), metallization (2) and cooling (3), in which grates (5) are placed, as well as a gas purification reactor (4). The heating and metallization reactors are connected by a tunnel to move the grates in the lower part, and the metallization and cooling in the upper part. The movement of grates with pellets in the heating and cooling reactors is carried out from top to bottom, and in the metallization reactor - from bottom to top.

Raw ore-coal pellets are loaded onto the grate (5) and placed in the upper part of the heating reactor (1). The grates move from top to bottom, and as they descend, the pellets are heated and heated to a temperature of 800-850 ° C. Heating is carried out by the heat-transfer gas obtained by mixing the gas leaving the metallization reactor (2) with the combustion products of natural gas with α = 1-1.1. At the bottom of the grate goes into the metallization reactor and moves upwards. In the process of moving, the pellets are further heated to a temperature of 1200-1400 ° C and iron is reduced. Heating is carried out with a mixture of gas leaving the cooling reactor (3), preheated in the plasma torch, and the combustion products of natural gas at α = 0.4-0.5. The grate with recovered pellets is transferred to the cooling reactor (3), where the metallized pellets are cooled, as it is lowered from top to bottom, to a temperature of 60-80 ° C. The gas cooler is obtained by passing the gas leaving the heating reactor through a cleaning reactor (4) filled with pieces of calcined lime. The movement of gas in the purification reactor is carried out from the bottom up. In the process of gas interaction with lime, it is purified from water and carbon dioxide due to the formation of calcium carbonate and hydrated lime and cooled to a temperature of 40-50 ° C. Periodically, the lower part in the form of CaCO ₃ and Ca (OH) ₂ is removed, and the burnt lime (CaO) is loaded from above

The method was carried out in laboratory conditions using the process simulation method.

To save ore material, ore-coal briquettes were investigated. Previously, ore (62.6% Fe) and coal (81% C) were used to prepare the charge. The amount of coal in the charge was taken at the rate of 0.8; 1.0 and 1.2 of the amount of carbon stoichiometrically necessary for complete reduction of iron, suggesting that during the reduction of iron, carbon is oxidized to monoxide. As a result, the amount of coal in the charge per 100 g of ore was 18.5; 23.15 and 27.78, respectively.

Briquettes were pressed from the batch: briquette diameter - 20 mm; pressing pressure - 1000 kg / cm ² ; briquette weight 23.7 g, 24.63 g, 25.56 g, depending on the amount of carbon introduced.

The restoration of the briquettes was carried out on a flow thermogravimetric installation. The purpose of the experiments is to determine the efficiency of the metallization process in the atmosphere corresponding to α≈1.0-1.1 and α≈0.4-0.5. The test briquettes were placed in a closed alundum reactor equipped with gas supply and gas exhaust tubes. The reactor was suspended from an electronic scale connected to a computer and lowered into the furnace. Heating and isothermal exposure at a furnace temperature of 1100 ° C was carried out in a stream of reaction gas. Argon, CO ₂ and CO were used as the latter. A TP703 regulator with a platinum-platinum thermocouple was used to measure and stabilize the furnace temperature. The current temperature was recorded in the file every minute simultaneously with the reading of the electronic scales.

Before the start of the experiment, the supply of the corresponding gas was turned on. Gas consumption was 0.7 l / min. After the scales were settled, their readings were reset to zero, the furnace was turned on, and the change in weight of the reactor with the sample was recorded every minute. The experiment ended upon reaching a weight loss rate of 0.1 g / min.

Three series of experiments were carried out. In the first series, roasting was carried out in a neutral atmosphere (Ar). In the second series, carbon dioxide was used as the reaction gas. In the third series, heating to a temperature of 800 ° C was carried out in a CO ₂ atmosphere, and further calcination was carried out in a CO atmosphere.

Figure 2 shows thermograms of calcination of ore-coal briquettes with a solid reducing agent (coal) content: a) 0.8, b) 1.0, c) 1.2 from the stoichiometrically necessary (dependence of weight loss (ΔР) and furnace temperature on roasting time) ) in argon (Ar), CO ₂ and CO. The weight loss of the briquette was determined by the formula:

where, P _beg , P _τ - the initial and current weight of the sample, respectively.

Figure 2 shows the thermograms of calcination of ore-coal briquettes with the content of solid reducing agent 0.8, 1.0 and 1.2 stoichiometrically necessary for complete reduction of iron to metal in argon (a), CO ₂ (b) and CO (c).

Figure 3 shows a thermogram of the calcination of the ore-coal briquettes in argon, CO ₂ and CO with the coal content: a) 0.8, b) 1.0, c) 1.2 of the stoichiometric required.

According to experimental data, heating to temperatures of 800-850 ° C occurs approximately equally, regardless of the furnace atmosphere. With further heating, the metallization in an atmosphere of neutral gas or CO, which corresponds to α = 0.5, passes by 94-98%, in an atmosphere of CO ₂ - it is much lower, besides, the effect of secondary oxidation is seen - a decrease in weight loss.

Claims (1)

The method of obtaining metallized pellets, including the preparation of the mixture by mixing iron ore materials with a solid reducing agent, forming raw pellets, loading them onto the grate, processing with heat-transfer gas followed by cooling, characterized in that the processing of pellets is carried out using sequentially installed reactors for heating, metallization and cooling and conduct gas-coolant in countercurrent when moving them in the reactor heating and cooling from top to bottom, and in the reactor met Allowing from the bottom up, while heating the pellets in the heating reactor lead to a temperature of 800-850 ° C with a mixture of gas coming from the metallization reactor and natural gas combustion products with an air flow coefficient α = 1.0-1.1, and in the metallization reactor heating is carried out to a temperature of 1200-1400 ° C with a mixture of gas coming from the cooling reactor and additionally heated, and natural gas combustion products with an air flow rate α = 0.4-0.5, and cooling is carried out with gas coming from the heating rector and previously purified from water and CO ₂ using burnt lime.

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