SU1747516A1 - Method of producing iron ore pellets - Google Patents

Abstract

Usage: the invention can be used in the production of fluxed iron ore pellets obtained by replacing bentonite in the pelletizing mixture with quicklime. SUBSTANCE: pellets are dried to 400 ° C and preheated on a grid and then calcined in a tubular rotary kiln and cooled. The duration of drying is adjusted depending on the content of quicklime in the charge, the content of active calcium and magnesium oxides in lime and the moisture content of raw pellets according to the formula: p (CaO + MD) / 15 - W, where g is the minimum drying time, min; M - the content of quicklime in the mixture, kg / t concentrate; CaO + MgO - content of active calcium and magnesium oxides in lime.,%; W is the moisture content of raw pellets. A reduction in the fines content in the pellets and an increase in productivity is achieved by ensuring the sustainability of the process throughout the production line. 1 tab. WITH

Description

The invention relates to ferrous metallurgy and can be used in the production of fluxed iron ore pellets obtained by replacing bentonite in a pelletizing mixture with superficial lime.

A known method of preparation of the charge for the production of fluxed iron ore pellets involves the introduction into the stream of wet iron ore concentrate fine quick lime and finely divided limestone, the consumption of which depends on the physicochemical properties of the components of the charge, mixing the charge and holding it until the lime is spent in the mixture. % followed by pelletizing, drying and high temperature calcination. In this case, lime obtained by roasting finely crushed limestone in a vortex flow of high-temperature gases can be used. According to a known method, the optimal composition of bessonite-free calcified iron ore charge for pelletizing, which corresponds to the highest strength characteristics of the pellets, is determined.

However, to obtain fired pellets with fines content, a certain mode of their thermal conversion is necessary. wherein the limiting is drying. For the most complete removal of moisture from the pellets without destroying them, the drying process must proceed for at least the minimum required time. At the same time, the drying temperature should not exceed the temperature of the pellet shock.

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The disadvantage of this method is that it does not provide for heat treatment conditions, in particular, drying lime pellets with bentonite, which ensure the integrity of the pellets and high process performance.

The closest in technical essence to the claimed method is the production of iron ore pellets, including their drying at 150-400 ° C for 4-8 minutes and preheating to 950-1100 ° C on a grid, firing in a tubular rotary kiln and cooling up to 90-120 ° С on the lattice.

The disadvantages of this method are that the specified drying time of the pellets is not optimal, despite the fact that the maximum drying temperature (400 ° C) does not exceed the shock temperature of the pellets with lime (400-470 ° C). The lime pellets partially contain external moisture and completely hydrated moisture, which, released in the preheating zone, destroys the pellets with the formation of fines. The presence of fines in the pellets leads to a deterioration of the gas-dynamic environment, which is especially noticeable when the pellets are cooled on the grid, the gas permeability of the layer decreases dramatically, the temperature of the cooled pellets increases, the specs appear. drying time is longer than the optimum unreasonably reduced production line performance

The purpose of the invention is to reduce the content of fines in the pellets and increase productivity by ensuring the stability of the heat treatment process throughout the production line.

The goal is achieved by the fact that in the known method of producing iron ore pellets, which include pelletizing concentrate and quicklime, drying the pellets at temperatures up to 400 ° C and preheating them on a grid, firing in a tubular rotary kiln and cooling on a grid, the drying time is adjusted to depending on the content of quicklime in the mixture, the content of active oxides of Sam Md in lime and the moisture content of raw pellets according to the formula

oo8

M (CaO + MDO) t UlJ15-W

where t is the minimum drying time, min;

M - consumption of quicklime in the charge, kg / t concentrate;

CaO + MDO — content of active calcium and magnesium oxides in lime (lime activity)%;

W is the moisture content of raw pellets,%. The given dependence is experimental and allows to determine the optimal (minimum

0 required) drying time of iron ore pellets with lime instead of bentonite. Regulation of the drying time of the pellets in accordance with the above dependence allows to have at the exit of the zone 5 pellets with completely removed external moisture and partially hydration, which, falling into the preheating zone, are not destroyed.

With a pellet drying time longer

0 the minimum required, determined by the proposed dependency, unreasonably decreases the performance of the technological line for fired pellets (drying the pellets has a limiting

5 effect on the entire heat treatment process. The drying time of the pellets and the plant capacity are inversely related

The deviation of the drying time of the pellets

0 on the value determined by the proposed dependence, downward leads to the fact that the pellets at the exit of the drying zone contain a significant amount of residual moisture, mainly hydrated In the zone

5, the pre-heating residual moisture begins to evaporate intensively when the pellets are heated. The destruction of the pellets occurs under the action of too much moisture differential and no vapor pressure over the section of the pellet. With an increase in the amount of residual moisture in the pellets after drying, the number of fine fractions in the finished product increases. The increased content of fines in the layer worsens

5 its gas permeability At the same time, the thermotechnological parameters also change. In a tube furnace, nastils are formed, rolling of the pellets deteriorates. When cooling pellets on the grid decreases

0 gas permeability of the layer, formed pellets of pellets, the temperature of the cooled pellets rises. All this violates the steady operation of the process line and sharply reduces its performance.

5 A method of producing iron ore pellets is implemented by dispensing fine quicklime of lime and finely divided limestone into the stream of wet iron ore concentrate. After dosing, the mixture is mixed in a mixer and kept on conveyors and in bins. The mixture thus prepared is pelleted in pelletizers, e.g. drum type, and the resulting raw pellets are heat treated. At the same time, the pellets are dried on a lattice at a temperature of up to 400 ° C and the duration of the drying is controlled depending on the content of quick lime in the charge, the content of active calcium and magnesium oxides in lime and the humidity of the raw pellets according to the formula

oo8

M (CaO + MgO) U.J15-W

where r is the minimum drying time, min;

M - quick lime consumption in the charge, kg / t concentrate:

CaO + MDO - content of active calcium and magnesium oxides in lime,%;

W is the moisture content of raw pellets,%. The dried pellets are pre-heated on a grid to 950-1100 ° C, and then burned in a tubular rotary kiln. Burned pellets are cooled on a lattice.

Example. The proposed method was tested under pilot industrial and industrial conditions. Fine dispersed lime and, if necessary, finely divided limestone were injected into the stream of wet iron ore concentrate on the conveyor, the flow rate of which was determined by conveyor weights. After dosing, the mixture was stirred in a four-section rotary mixer and kept. Exposure of the charge was carried out as it stayed on the conveyor conveyors and in the feed bins, the filling level of which is maintained at 50-70%. In this case, the exposure time of the charge before pelletization was 20–30 min. After aging, the charge was pelleted in a drum pelletizer. The moisture content of the raw pellets was adjusted by injecting water into the pelletizer through nozzles. The raw pellets were thermally treated: on the grate with a layer thickness of 156-160 mm, pellets were dried and preheated; strengthening calcination was carried out in a tubular rotary kiln. The burned pellets were cooled on a lattice in a ring cooler. Drying of the pellets was carried out at a temperature of up to 400 ° C. The drying time was regulated according to the reduced dependence of an experimental nature. The temperature in the preheating zone was 1000-1100 ° C.

During the tests, the components of the charge were characterized by the following indicators: concentrate: Fe 62.56 - 62.82%; SI02 - 10.96-11.13%; CaO + MDO - 0.75-0.78%; humidity 10.0-10.32%, class content 53 microns 94.9-95.8%; specific surface 170-190 m / kg; known to: CaO + MDO 52.4-53.5%; SI02 - 2.4-2.7%; specific surface area 480-520 m / kg; lime: a / CaO + MgO 85.0%; SIO 4.2% CaOact hectare 67.5%; activity coefficient 0.93; quenching speed 2 min.

CaO + MDO 89.6%; SI02 4.7%; Caoact 80.1%; activity coefficient 0.96; quenching speed 1 min. 30s:

CaO + MdO 87.0%; SI02 4.3%: CaOact 71.3%; activity coefficient 0.96; hydration rate 1 min 30 s.

The test results of the proposed method for the production of iron ore pellets are presented in the table. In pp

1 ... 7.10.13.16,19,22 and 25 the data corresponding to the production of pellets with lime and for the duration of drying, regulated by the proposed dependency, is given. If the actual drying time of the pellets deviates to a lower level of up to 0.6% of the optimal value (see p. 16), the fines content in the calcined pellets is 1.4-2.6%, which does not exceed the value established by the technical conditions for the production of pellets. with bentonite on the processing line - 3% (for comparison, data on the production of pellets with bentonite are given in paragraphs 28 and 29). The deviation of the drying time of the pellets from the optimum in the direction of increase (see paragraph

2.5 ... 11.14,17,20,23 and 26) by 2.49-9.34% does not actually change the content of fines in the finished product. However, this reduces the line capacity by 2.7-9.0%. Drying the pellets over time is less than optimal by 3.74-7.29% (see pp 3,6,9.12.15,18,21,24 and 27} although it allows you to first increase the performance of the line for burnt pellets by 3.9-7.8%, but the fines content in the finished product is high due to the destruction of pellets on the grate and is 4.8-6.1%. With the increased fines content in the pellets, formation of walling in the tube furnace and specs was observed in the cooler, which caused private stops of the entire process line and disrupted the process of heat treatment of the pellets on it (as a result this reduced the capacity of the line by 5-15%.) The temperature of the pellets behind the cooler increased to 18Q-240UC against 90-120 ° С at the optimum mode

Pellets with lime, obtained by the proposed method, compared with bentonite pellets have greater basicity (depending on the amount of lime injected, their basicity is higher by 0.046-0.126 units of mod.) And the content of reduced iron in it is higher by 0.5%. The strength properties of heat-treated pellets were high in all cases and were 242-320 kg / approx.

The method provides production of similar non-bentonite pellets with lime with a fines content of 1.4-2.6%, which does not exceed the value established by the technical conditions for the production of pellets on a production line. The method provides a steady process of heat treatment of the pellets on the production line, eliminates the formation of walling in the furnace and spekoy in the cooler. In this case, the maximum possible production line performance is achieved. The temperature of the pellets behind the cooler remains at the required level and does not exceed 90-120 ° C

Claims (1)

Invention Formula Method for the production of iron ore pellets, which includes pelletizing of con0 five centering and burnt lime, drying the pellets at temperatures up to 400 ° C and preheating them on a grate, firing in a tubular rotary kiln and cooling on the grate, characterized in that, in order to reduce the fines content in the pellets and increase productivity by ensuring stable flow the process of heat treatment throughout the process line, the duration of drying is adjusted depending on the content of burnt lime in the charge, the content of active calcium and magnesium oxides in lime and the moisture of raw eyes yshey by the following formula g 0,3 oh o8 M (CaO + MDO) 15 -W where T is the minimum drying time, min; M - the content of quicklime in the charge, kg / t concentrate; Cao + MDO is the content of active calcium and magnesium oxides in lime. %; W is the moisture content of raw pellets,%; 0.3 - coefficient, min kg / t. Note: for comparison, information is given on pellets of current production with bentonite (columns 5 and 6 contain data on bentonite) at the base (design) productivity of the technological line grate - tube furnace - cooler, while in the bentonite contained SiO, 5.9-62 , CaO + MgO 5.1-5.9; specific surface 680 mg / kg