RU2260624C2 - Method and apparatus for recirculation of iron-containing dust and slime at cast iron production process with use of coal and ore fines - Google Patents

Abstract

FIELD: recirculation of dust and slime obtained in metallurgical plants where cast iron is produced with use of non-coking coal and iron-ore fines.

SUBSTANCE: zinc component contained in dust and slime is extracted by evaporation in apparatus having feed hoppers, agitator, granulator, dryer, shaft furnace and hot screen. Said hoppers are designed for accumulating and feeding dust and slime after their dehumidification, drying and disintegration, binder and iron-ore fines to be further agitated in agitator. Granulator provides coagulation of mixed initial materials supplied from agitator for producing pellets of predetermined size to be dried in drier. Shaft furnace is coupled with melting-gas generation furnace through gas duct and it is designed for receiving pellets from drier and for evaporating zinc component contained in pellets. Hot closed screen sieves reduced iron pellets by large-size and small-size ones and selectively feeds sieved pellets to melting-gas generation furnace and to briquetting installation.

EFFECT: lowered cost of slime processing process, prevention of environment contamination.

11 cl, 3 dwg, 1 tbl

Description

FIELD OF THE INVENTION

The present invention relates to the recycling of dust and sludge obtained in metallurgical plants, in which the process of producing pig iron using non-coking coal and iron ore fines is carried out, and more particularly, to an improved device and method for recycling iron-containing dust and sludge, which allows to extract contained in dust and sludge the zinc (Zn) component by gasification and the iron (Fe) component in the form of molten iron by reduction, thereby reducing the cost of processing the sludge and not floating pollution.

State of the art

To date, in the art it has not been possible to create a process for the production of cast iron that would be superior to the blast furnace process in terms of energy efficiency or productivity. However, the blast furnace process is usually based on the use of coke obtained by treating special grades of coal as a carbon source, which is used as a fuel and a reducing agent, and also on the use of ore sinter obtained by sintering processes and serving as a source of iron.

In this regard, the existing blast furnace process is necessarily associated with equipment for pre-processing, such as plants for the production of coke and sinter. However, the construction of such plants require additional costs and these installations emit into the environment of large amounts of contaminants such as SO _X, NO _X and dust, which is contrary to internationally accepted more stringent requirements for the environment protection. In order to ensure compliance with these requirements, it is necessary to invest in large treatment facilities, which also leads to a significant increase in costs. In this regard, existing blast furnaces are gradually losing their competitiveness.

In this regard, in many countries of the world, active efforts are being made to create improved processes for the production of pig iron, which can eliminate the above-mentioned disadvantages of the blast furnace process. As one of the most well-known improved processes for the production of pig iron, which are currently under development, we can mention a coal-smelting and reduction process using directly non-coking coal as fuel and a reducing agent and iron ore fines, which account for about 80% world reserves of iron ore, as a source of iron.

A cast iron production system related to such a technology using a non-coking angle and iron ore fines is described in US Pat. No. 5,785,733, issued July 28, 1998.

As shown in FIG. 1, the entire cast iron production system comprises three fluidized-bed reduction furnaces, which include a pre-heating furnace 10, a preliminary reduction furnace 20 and a final reduction furnace 30, as well as a smelter-gas generator 40 with a semi-coke bed.

According to this document, the iron ore fines are continuously charged through the first ore duct 12 into the preheating furnace 10, where it is subjected to preheating with the reducing gas supplied through the third gas pipeline 21 during the formation of a fluidized or turbulent fluidized bed.

After that, the iron ore fines preheated in the preheating furnace 10 are discharged through the second ore duct 22 into the preliminary reduction furnace 20, where it is subjected to preliminary reduction with the reducing gas entering through the second gas pipeline 31 during the formation of a fluidized or turbulent fluidized bed. The pre-reduced iron ore fines are discharged through the third ore duct 32 into the final reduction furnace 30, where it is subjected to final reduction by the reducing gas supplied through the first gas pipeline 41, during the formation of a fluidized or turbulent fluidized bed. The finally restored iron ore fines are continuously discharged through the fourth ore box 42 for further processing.

Iron ore fines, finally restored in the furnace 30 of the final reduction and unloaded through the fourth ore duct 42, is fed to the briquetting unit 50, where it is formed from metallized briquettes of hot briquetting (HBI - Hot Briquetted Iron). HBI briquettes are fed via the briquette conveying line 51 to a melting gas generator 40, where they are melted in a semicoke layer, turning into molten iron or molten metal. After that, the liquid metal is discharged from the smelter-gas generator 40.

Each of the first to fourth ore baskets, i.e. duct 12, 22, 32 and 42 is equipped with hot gas impermeable valves 13, 23, 33 and 43, which perform opening and closing operations in order to regulate the flow of iron ore fines, so that the flow of iron ore fines can be interrupted if necessary.

Large pieces of non-coking coal are continuously fed through an opening in the upper part of the smelter-gas generator 40 to form a semi-coke layer of a certain thickness in the furnace. When oxygen is injected into the semicoke layer through a plurality of tuyeres located in the lower part of the smelting gas generator furnace 40, the semicoke burns in the semicoke layers.

The gas that is obtained through the combustion of the semicoke and which becomes the reducing gas in the fluidized bed rises through the semicoke coke in order to be discharged from the smelter-gas generator 40. The exhausted reducing gas passes sequentially through the first, second and third gas pipelines 41, 31 and 21 to power each of the three fluidized-bed reduction furnaces 10, 20, and 30, after which he leaves the process through the fourth gas pipeline 11.

At the same time, the process of producing cast iron using non-coking coal and iron ore fines leads to the formation of a large amount of dust and sludge, which is dried and then blown into the smelter-gas generator 40 or preheating furnace 10 without further processing. However, since the dust / sludge consists of extremely small particles (the maximum particle size does not exceed about a few tenths of a micron), it / it “pops up” immediately after loading the final reduction furnace 30, which uses iron ore fines from particles with relatively large sizes ( generally about 10 mm) than dust / sludge particle sizes. As a result, this process exhibits a low actual recovery rate and is thus ineffective.

In addition, if the dust / sludge contains a large amount of zinc component, then the zinc component evaporates in the smelting gas generator furnace 40 at a high temperature of about 1000 ° C. or more. The evaporated zinc component is re-oxidized and condensed in the form of ZnO in a preheating furnace 10, which has a relatively low temperature of about 600-700 ° C. Condensed ZnO adheres to the walls of the furnace, growing on them and thus creating serious interference with the operation.

The present invention is aimed at solving the above problems associated with existing technical solutions, and therefore, the aim of the present invention is to provide a device and method for recycling iron dust and sludge in the production of cast iron using non-coking coal and iron ore fines, which allows to increase the recovery rate, while avoiding sticking condensed zinc component on the walls of the furnace and thus increasing productivity.

Disclosure of invention

According to one aspect of the present invention, to achieve these objectives, there is provided a device for recirculating iron dust and sludge into a cast iron production system using non-coking coal and iron ore fines, including three fluidized bed reduction furnaces, including a pre-heating furnace, a preliminary reduction furnace and a final furnace recovery, as well as a smelter and gas generator with a layer of semi-coke and briquette installation, and the recirculation device It contains: a lot of consumables for raw materials intended for storage of dust / sludge (which is subjected to dehydration, drying and crushing), binder and iron ore fines and for the delivery of these materials in specified quantities; an agitator designed for mixing and mixing a certain amount of dust / sludge, binder and iron ore fines, issued from consumables for raw materials; a granulator intended for enlarging the mixture of starting materials leaving the mixer to pellets of certain sizes; a dryer for drying pellets coming from the granulator; a shaft furnace connected to the smelter and gas generator furnace through a fifth gas pipeline and designed to receive pellets from the dryer and to vaporize the zinc component (Zn) contained in the pellets with reducing gas, the shaft furnace including a sixth gas pipeline located in its upper part and designed to exhaust the exhaust gas containing the vaporized zinc component, and a screw feeder designed to issue the recovered iron pellets that are recovered restore nym gas; and a hot closed screen intended for sorting the reduced iron pellets given out by a screw feeder into large and small pellets depending on their size and having fifth and sixth ore boxes intended for selectively feeding sorted pellets to a smelter and gas generator and briquetting unit.

According to another aspect of the invention, to achieve these goals, there is provided a method for recycling iron dust and sludge into a pig iron production process using non-coking coal and iron ore fines, including three fluidized-bed reduction furnaces, including a pre-heating furnace, a preliminary reduction furnace and a final reduction furnace, as well as a smelter and gas generator with a layer of semi-coke and a briquette installation. The recirculation method comprises the following stages: mixing in the mixer certain quantities of dust / sludge, binder and iron ore fines, issued from consumables for raw materials; enlargement of the mixture of starting materials leaving the mixer in the granulator to pellets of certain sizes; drying the pellets in the dryer, loading the dried pellets into the shaft furnace, evaporating the zinc component contained in the loaded pellets using reducing gas coming from the smelting gas generator through the fifth gas pipeline, discharging the zinc component with the exhaust gas, and discharging the restored shaft furnace with a screw feeder reducing gas of iron pellets; and sorting in a hot closed screen issued by the screw feeder of the restored iron pellets into large and small (disintegrated) pellets for selective feeding into each of the smelter and gas generator and briquetting unit.

Brief Description of the Drawings

Figure 1 schematically shows the entire process for the production of cast iron using non-coking coal and iron ore fines;

figure 2 schematically shows the design of a device for recirculating iron dust and slag in the process of iron production using non-coking coal and iron ore fines;

figure 3 illustrates the equilibrium diagram between Zn (G) and ZnO (S), calculated using thermochemistry in an atmosphere of a reducing gas.

The best embodiments of the invention

The following detailed description will present a preferred embodiment of the invention with reference to the accompanying drawings.

As shown in FIG. 2, the inventive recirculation device 1 processes (returns to the process) sludge / dust that is generated during the production of cast iron. For this, the recirculation device removes the zinc component that is contained in the sludge / dust by evaporating it with reducing gas, and loads the sludge / dust from the reduced iron into the smelter-gas generator 40. The device 1 contains consumables 110a, 110b and 110c for the source materials, a mixer 100, a granulator 90, a dryer 80, a shaft furnace 70, and a hot indoor screen 60.

That is, the feed hoppers 110a, 110b, and 110c for the feed materials contain a dust / slurry mixture, a binder, and iron ore fines of 1 mm or less. Before loading into the feed hopper (110), the sludge is mixed with iron dust after dehydration, drying and crushing. Accordingly, feeders (not shown) are installed in the lower parts of the supply bins 110a, 110b and 110c for supplying / discharging a mixture of dust / sludge, binder and iron ore fines in specified (set) quantities. After dispensing from the feed hoppers 110a, 110b, and 110c, the feed materials are fed by means of a vehicle, such as a conveyor belt (not shown), into the mixer 100 for feeding to the next steps.

The mixer 100 mixes and mixes in a certain ratio a mixture of dust / sludge, binder and iron ore fines, issued from the supply hoppers 110A, 110b and 110C in the specified quantities. This mixing ratio varies with the Fe content of the dust / sludge mixture.

Granulator 90 receives a mixture of starting materials containing dust / sludge, binder and iron ore fines mixed in a mixer 100, and enlarges this mixture, turning it into pellets of certain sizes.

Preferably, the pellets produced by the granulator 90 are about 30 mm or less, depending on the reaction rate in the shaft furnace 70.

After receiving the pellets from the granulator 90, the dryer 80 heats and dries the pellets in order to remove moisture that enters while the granulator is enlarging the mixture of the starting materials and converting it into pellets of a certain size.

After drying in the dryer 80, the pellets are loaded into a shaft furnace 70 connected to a smelter and gas generator 40 through a fifth gas pipeline 44 to produce reducing gas therefrom. In the shaft furnace 70, the zinc component is vaporized and the iron component is reduced by means of reducing gas supplied through the fifth gas pipeline 44. A screw feeder 72 is installed in the lower part of the shaft furnace 70, which is used to discharge the reduced iron pellets from the shaft furnace 70.

A sixth gas line 71 is connected between the upper part of the shaft furnace 70 and the scrubber 120, wherein cold water is used in the scrubber 120 to flush the exhaust gas and condense the zinc component vaporized by the hot reducing gas. The clean exhaust gas purified from the zinc component in the scrubber 120 is discharged out through the exhaust pipe 121 and the afterburning pipe. A cyclone-type zinc removal bath 130 is installed underneath the scrubber 120 and connected to it via a lower channel 122 to discharge a high zinc sludge obtained from zinc-containing dust / sludge.

A hot closed screen 60, located between the shaft furnace 70 and the melter gas generator furnace 40, sorts the reduced iron pellets from the screw feeder 72 of the furnace 70 into small and large pellets depending on their size, and sends them respectively to the melter gas generator furnace 40 and briquette unit 50 for the fifth and sixth ore boxes 61 and 62. Preferably, the reduced iron pellets entering the hot closed screen 60 are sorted according to a reference particle size equal to CB about 5-10 mm, in accordance with the current reduction process in a fluidized bed, which uses a blend having a particle size of about 8 mm or less.

In addition, the hot enclosed screen 60 may be connected to an inert gas line 69 for supplying an inert gas, such as Ar or N ₂ gas, to maintain a hot inert atmosphere, thereby preventing the pellets from cooling and re-oxidizing.

Accordingly, when sorting the reduced iron particles coming from the shaft furnace 70 into large and small (decayed) pellets, the reference particle size is set to 8 mm, the reduced iron pellets are sorted into large pellets with a size of about 8 mm or more and small (decayed) ) pellets with a size of approximately 8 mm or less in a hot enclosed space. Pellets, classified on the screen 60 as large, are loaded into a melting and gas generating furnace 40 through a sixth ore box 62 connected to the transport line 51 under the briquetting unit 50; on the other hand, the pellets classified as small on the screen 60 are loaded into the briquetting unit 50 via the fifth ore box 61 connected to the fourth ore box 42 above the briquetting unit 50, where small (broken up) pellets are briquetted into large ones. Large briquetted pellets are loaded into a smelter-gas generator 40.

The following detailed description will present the operating procedure and the effect that the invention provides with the device shown above.

Iron dust / sludge generated during the production of cast iron using non-coking coal and iron ore fines is subjected to dehydration, drying and crushing. Then, the pre-treated slurry / dust mixture is stored in a feed hopper, while the binder and iron ore fines are stored in separate feed hoppers. The sludge / dust mixture, binder and iron ore fines are discharged in a predetermined quantity from the feed hoppers 110a, 110b and 110c into the mixer 100, in which the sludge / dust mixture, binder and iron ore fines are mixed in the required proportions to obtain a mixture of source materials, after whereby the mixture of raw materials is fed into a granulator 90.

In granulator 90, pellets with a grain size of 30 mm or less are obtained from a mixture of starting materials. The obtained pellets are loaded into a dryer 80, where residual moisture is removed, and the dried pellets are loaded into a shaft furnace 70.

Then, after the pellets from the mixture of starting materials are completely loaded from the granulator 90 into the furnace 70, through the fifth gas pipeline 44, one end connected to the upper part of the melting gas generator furnace 40, and the other end connected to the lower part of the furnace 70, into the furnace 70 supply reducing gas.

The result is the evaporation and removal of the zinc component from the pellets under the influence of reducing gas entering through the lower part of the furnace 70, as a result of which the zinc component is discharged with the exhaust gas through the sixth gas pipeline 71. On the other hand, the iron component remaining in the pellets while in furnace 70 is reduced to iron oxide (FeO) or to metallic iron.

Preferably, in the shaft furnace 70, an internal pressure of about 4 bar or less is maintained at an internal temperature of about 800 to 1100 ° C. during the production of pig iron using non-coking coal and iron ore fines.

The necessity of these conditions is explained by the fact that at an internal temperature below 800 ° C, the reaction rate remains low, and at an internal temperature above 1100 ° C, adhesion easily occurs. Figure 3 shows the equilibrium diagram between Zn (gaseous) and ZnO (solid), thermodynamically calculated for a reducing gas atmosphere containing 65 wt.% CO, 5 wt.% CO ₂ , 25 wt.% H ₂ and 2 wt.% H ₂ O at a gas overpressure of about 3 bar.

The exhaust gas from the furnace 70 is fed through a sixth gas line 71 to a water-cooled scrubber 120, in which the gaseous zinc component of the exhaust gas condenses to form Zn or ZnO under the influence of cooling water, which is injected into the scrubber 120. The condensed zinc component is discharged in the form sludge through a lower channel 122 into a cyclone-type zinc removal bath 130. When passing through the zinc removal bath 130, the sludge is concentrated and converted to a high zinc sludge.

While the exhaust gas is discharged from the shaft furnace 70 through a sixth gas line 71, the pellets remaining in the furnace 70 contain oxidized iron (mainly Fe ₃ O ₃ ), which is usually reduced to almost molten iron.

The recovered pellets are discharged by means of a screw feeder 72 mounted in the lower part of the reduction furnace 70 for feeding to a hot closed screen 60, which sorts the pellets into large and small (decayed), based on the reference particle size.

Of the recovered iron pellets sorted by screen 60, large pellets are sent directly to the smelter 40 through a sixth ore duct 62 connected to the molded iron line 51 because they cannot fly away (“washed out”) due to their size exceeding the reference particle size. On the other hand, in order to prevent leaching, small (disintegrated) pellets are fed into the fifth ore box 61 connected to the fourth ore box 42 so that they are briquetted in the briquette installation and then loaded into the smelter 40 through line 51 of the molded gland.

From a mixture consisting of the components listed in Table 1, pellets of approximately 10 to 30 mm in size were obtained. The pellets were dried and subjected to reduction in a reducing gas (65 wt.% CO, 5 wt.% CO ₂ , 25 wt.% H ₂ and 2 wt.% H ₂ O) at a temperature of about 900 ° C and at a gas overpressure of about 3 bar for about 1 hour. As a result, the degree of reduction of the iron component was at least 90%, and the degree of removal of Zn was at least 80%, thus providing the indicated effects of the invention.

Table 1
The chemical composition of the mixture obtained by mixing iron-containing sludge, dust and inorganic binder Total Fe C CaO SiO ₂ Zn Content% 32,4 18.6 9.2 5.9 1.9

Industrial applicability

As described above with respect to the non-coking coal and iron ore fines production process, the present invention provides pellets from a raw material mixture consisting of sludge / dust (dehydrated, dried and crushed in the previous process), binder and iron ore fines, such so as to remove the zinc component in the sludge / dust by evaporating it from the sludge / dust with a reducing gas, and then remove the iron remaining in the sludge / dust th component in the form of molten metal by reduction and load sludge / dust into the melter gasifier, thus enhancing the recovery ratio of the iron component in the apparatus for the production of pig iron, with simultaneous prevention of adhesion of the zinc component on the furnace wall condensed deposits to ensure process stability. In addition, it is also possible to increase productivity due to the fact that iron ore fines are mixed with sludge / dust.

Although preferred embodiments of the present invention are described for purposes of illustration, it will be apparent to those skilled in the art that various modifications, additions, and substitutions can be made without departing from the scope and spirit of the invention set forth in the appended claims.

Claims (11)

1. A device for recirculating iron-containing dust and sludge into a system for the production of cast iron using non-coking coal and iron ore fines, including three fluidized-bed reduction furnaces, including a pre-heating furnace, a preliminary reduction furnace and a final reduction furnace, as well as a smelter and gas generator with a layer of semicoke and a briquetting unit, the recirculation device comprising a plurality of feed bins for raw materials intended for specifically for storing dust / sludge subjected to dehydration, drying and crushing, binder and iron ore fines and for dispensing these materials in specified amounts, an agitator designed to mix and mix a certain amount of dust / sludge, binder and iron ore fines discharged from consumables for starting materials, a granulator intended for enlarging the mixture of starting materials leaving the mixer to pellets of certain sizes, a dryer for drying the pellets, supplied x from a granulator, a shaft furnace connected to a melting and gas generating furnace through a fifth gas pipeline and designed to receive pellets from the dryer and to vaporize the zinc component contained in the pellets with reducing gas, the shaft furnace including a sixth gas pipeline located in its upper part and designed to exhaust the exhaust gas containing the vaporized zinc component, and a screw feeder, designed to issue reduced iron pellets, which are restored reducing gas, and a hot closed screen designed for sorting the recovered iron pellets given out by a screw feeder into large and small decayed pellets, depending on their size, and having fifth and sixth ore boxes intended for selectively feeding sorted pellets to a smelter and gas-generating furnace and briquetting unit . 2. The iron dust and sludge recirculation device according to claim 1, which also contains a scrubber connected to the sixth gas pipeline and designed to inject water to condense the zinc component in the exhaust gas, a discharge pipe connected to the scrubber and designed to discharge clean exhaust gas, purified from the zinc component, to the afterburning pipe, and a zinc removal bath connected to the lower part of the scrubber by means of the lower channel and intended for condensation of high-content sludge zinc zinc. 3. The device for recycling iron-containing dust and sludge according to claim 1, which also contains an inert gas line for supplying inert gas to a hot closed screen in order to maintain a hot inert atmosphere there to prevent cooling and re-oxidation of the pellets. 4. A method for recycling iron-containing dust and sludge into the cast iron production using non-coking coal and iron ore fines, including three fluidized-bed reduction furnaces, including a pre-heating furnace, a preliminary reduction furnace, and a final reduction furnace, as well as a gas-melting furnace with a layer of semi-coke and a briquetting unit, the recirculation method comprising the following steps: mixing certain amounts of dust / sludge in a mixer, binder o and iron ore fines discharged from feed hoppers for raw materials, enlarging the mixture of raw materials leaving the mixer in the granulator to pellets of certain sizes, drying the pellets in a dryer, loading the dried pellets into a shaft furnace, evaporating the zinc component contained in the loaded pellets using reducing gas entering through the fifth gas pipeline from the smelter and gas generator furnace, the removal of the zinc component with the exhaust gas and the delivery of the shaft furnace by the screw feeder are restored reduced iron pellets from the reducing gas, and sorting in a hot closed screen, the reduced iron pellets issued by the screw feeder into large and small pellets for selective feeding into each of the smelting and gas generating furnaces and briquetting plants. 5. The method of recycling iron dust and sludge according to claim 4, in which the pellets obtained in the granulator have a reference size of about 30 mm, depending on the reaction rate in the shaft furnace. 6. The method for recycling iron dust and sludge according to claim 4, which also comprises the steps of supplying exhaust gas through a sixth gas pipeline connected to the shaft furnace to the scrubber, injecting cooling water into the scrubber to remove the zinc component from the exhaust gas by concentrating and discharging the exhaust gas purified from the zinc component through the afterburner and condensation of the sludge discharged from the scrubber in a cyclone-type zinc bath to a high zinc sludge to recover zinc component. 7. The method for recycling iron dust and sludge according to claim 4, in which the internal pressure of about 4 bar or less and the internal temperature of about 800 - 1100 ° C are maintained in a shaft furnace. 8. The method of recycling iron-containing dust and sludge according to claim 4, wherein an inert gas is supplied to the hot closed screen to maintain a hot inert atmosphere to prevent cooling and re-oxidation of the pellets. 9. The method for recycling iron dust and sludge according to claim 4, in which the hot closed screen has a reference particle size of about 5 to 10 mm, in order to sort the pellets into small and large pellets in relation to the recovery process in the fluidized bed. 10. The method for recycling iron-containing dust and sludge according to claim 9, in which large pellets sorted on a screen are loaded into a melting and gas-generating furnace through a sixth ore box connected to the feed line of hot briquettes under the briquetting installation. 11. The method for recycling iron dust and sludge according to claim 9, in which small disintegrated pellets sorted on a screen are loaded into a briquetting unit through a fifth ore box connected to a fourth ore box above the briquetting unit, briquetted in this unit, and then loaded into melting gas generator furnace.

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