Method for the continuous sintering of mineral material and sintering equipment

Abstract

The invention relates to a method and equipment for the continuous sintering of mineral material in a sintering furnace (S). In the method, a material bed (2) is formed on a conveyor base (1), the material bed (2) is conveyed by the conveyor base (1) through the process zones (I-VII) of the sintering furnace that have different temperatures, the zones including at least one drying zone (I), at least one cooling zone (VII), and at least one other process zone (II, III, IV, V, VI) between the said drying zone and cooling zone, and gas is conducted through the conveyor base and the material bed (2), when the material bed travels through the process zones (I-VII), and gas is circulated in a circulation gas duct (3) from the last cooling zone (VII) to the drying zone (I). Part of the gas flow that is conducted to the drying zone (I) in the circulation gas duct (3) is removed as an exhaust gas flow (B) by the exhaust gas blower (5) of an exhaust gas duct (4). The volume flow of the exhaust gas flow (B) is regulated by regulating the blowing power of the blower (5) to control the temperature of the gas flow travelling through the material bed in the drying zone.

Claims

1. A method for the continuous sintering of mineral material in a sintering furnace, comprising forming a material bed on a conveyor base; conveying the material bed by the conveyor base through process zones of the sintering furnace that have different temperatures, the zones including at least one drying zone, at least one cooling zone, and at least one other process zone between the said drying zone and cooling zone; and conducting gas through the conveyor base and the material bed when the material bed travels through the process zones; circulating gas in a circulation gas duct from the last cooling zone to the drying zone, at least a portion of the circulation gas duct comprising an upper section above the material bed, where part of the gas flow that is conducted toward the drying zone in the upper section of the circulation gas duct is removed as an exhaust gas flow through an exhaust gas duct, and part of the gas flow that is conducted toward the drying zone in the upper section of the circulation gas duct is removed through a bypass channel that bypasses the drying zone, the bypass channel different than the exhaust gas duct; and selectively controlling the temperature and volume of the gas flow traveling through the circulation gas duct and through the material bed in the drying zone whereby said temperature is selectively controlled by varying the rotation speed of an exhaust gas blower in the exhaust gas duct while the volume of the gas flow in the circulation gas duct that is passed to the drying zone is selectively controlled by a regulating device of the bypass channel.

2. The method according to claim 1, wherein the exhaust gas duct connects to the circulation gas duct at a first location and the bypass channel connects to the circulation gas duct at a second location between the first location and the drying zone.

3. The method according to claim 1, wherein half of the volume flow of the circulation gas duct is removed as the exhaust gas flow.

4. The method according to claim 3, wherein dust particles are removed from the exhaust gas flow, and the purified exhaust gas flow is conducted into the atmosphere.

5. The method according to claim 1, wherein the exhaust gas flow is purified by a cleaning device.

6. Sintering equipment for the continuous sintering of mineral material arranged in a material bed, including a sintering furnace, comprising sequential process zones that have different temperature conditions, the zones including at least one drying zone, at least one cooling zone and at least one other process zone between the said drying zone and cooling zone; a conveyor base for conveying the material bed through the process zones, the conveyor base being gas permeable; at least one circulation gas duct, at least a portion of which is above the conveyor base, for conducting gas from at least one cooling zone to at least one drying zone and within an upper section of the circulation gas duct that is above the material bed; output gas channels, which are below the conveyor base, for conducting the gas that exits the process zone and is conducted through the material bed and the conveyor base; inlet gas channels, which are below the conveyor base, for conducting gas to the cooling zone; blowers, which are arranged in the output gas channels and the inlet gas channels to produce a gas flow, an exhaust gas duct connected to the circulation gas duct and which conducts gas from the last cooling zone to the drying zone, to remove part of the gas flow conducted in the upper section of the circulation gas duct, as an exhaust gas flow; a bypass channel that bypasses the drying zone, the bypass channel different than the exhaust gas duct, that removes a part of the gas flow that is conducted toward the drying zone in the upper section of the circulation gas duct; an exhaust gas blower, which is arranged in the exhaust gas duct to produce the exhaust gas flow; and a first regulating device associated with the exhaust gas duct and capable of selectively controlling the temperature of the gas flow that travels through the circulation gas duct by regulating the blowing power of the exhaust gas blower, and a second regulating device associated with the bypass channel and capable of regulating the volume of the gas flow in the circulation gas duct that is passed to the drying zone.

7. The equipment according to claim 6, where the exhaust gas duct connects to the circulation gas duct at a first location and the bypass channel connects to the circulation gas duct at a second location between the first location and the drying zone.

8. The equipment according to claim 7 wherein the cleaning device is a gas scrubber.

9. The equipment according to claim 6, including a cleaning device for purifying the exhaust gas flow.

10. The equipment according to claim 6, wherein at least one other process zone between the drying zone and the cooling zone comprises a heating zone for heating the dried material bed, a sintering zone for sintering the material, a balancing zone for balancing the temperature of the material bed, and cooling zones for gradually cooling the sintered material bed.

11. The equipment according to claim 6, wherein the material to be sintered consists of pelletized mineral material.

12. The equipment according to claim 6 where the inlet gas channels open into the cooling zone from beneath the conveyor base.

13. The method of claim 1 including the step of introducing cooling gas into the last cooling zone from below and through the material bed.

Description

LIST OF FIGURES

(1) In the following, the invention is described in detail by means of an exemplary embodiment and with reference to the appended drawing, wherein the FIGURE presents schematically an embodiment of the sintering equipment, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) FIG. 1 shows the sintering equipment for the continuous sintering of mineral material, such as ferro-chromium.

(3) The equipment includes a strand sintering furnace S, which comprises a number of sequential process zones I-VII, different temperature conditions prevailing in each one of them when the sintering furnace is running.

(4) The zones include a drying zone I, where the temperature is about 500 C. and where the material is dried, that is, water is removed from the material; a heating zone II for heating the dried material, where the temperature of the material is increased to about 1150 C.; a sintering zone III, where the temperature is about 1350 C. and where the material is sintered; and a balancing zone IV. After the balancing zone IV, there are three sequential cooling zones V, VI, VI, where the sintered material is gradually cooled, so that when leaving the furnace, its temperature is about 400 C.

(5) The belt conveyor 1, which conveys the material bed 2 through the zones mentioned above, is a perforated steel belt, where the perforation allows the gas to pass through. The invention, however, is also useful in connection with a sintering furnace of the so-called moving grate type.

(6) The mineral material to be sintered can be, for example, in a pelletized or some other granular form.

(7) The sintering furnace S functions so that fresh material is fed so as to form a material bed 2 with a thickness of several dozens of centimeters, on top of a steel belt 1 at the forward end of the furnace S (left in the FIGURE). The belt conveyor 1 travels as an endless loop around a creasing roll 25 and a drive roll 24. Above the belt conveyor 8, there are three overhead circulation gas ducts 3, 6, 7, which conduct gas from the cooling zones V, VI, VII to the drying, heating, and sintering zones I, II, III on top of the material bed. Each circulation gas duct 6 and 7 contains a burner (not shown) for heating the gas. Lower exhaust gas ducts 8, 9, 10 that are below the belt conveyor 1 conduct, enhanced by blowers 14, 15, 16, the gas which is conducted through the material bed 2 and the belt conveyor 1, away from the drying, heating, and sintering zones I, II, III. Lower inlet gas channels 11, 12, 13 conduct gas from below the belt conveyor 1 to the cooling zones V, VI, and VII. The movement of gas in the inlet gas channels 11, 12, and 13 is caused by blowers 17, 18, and 19, respectively.

(8) The equipment further includes a by-pass channel 20, through which gas can be conducted from the circulation gas duct 3, which conducts the gas from the last cooling zone VII to the drying zone I, past the material bed 2 and into the exhaust gas duct 8 of the drying zone. The volume flow of the by-pass gas flow is regulated in the by-pass gas channel 20 by adjusting the control valve 21.

(9) The equipment further includes an exhaust gas duct 4, which is connected to the circulation gas duct 3 that conducts gas from the last cooling zone VII to the drying zone I, so that part of the gas flow that is conducted in the circulation gas duct 3 can be removed as an exhaust gas flow B. An exhaust gas blower 5 produces an exhaust gas flow in the exhaust gas duct 4, and a regulating device 22 can regulate the blowing power of the exhaust gas blower 5. By regulating the blowing power, the volume flow of the exhaust gas flow B is regulated to control the gas flow travelling through the material bed in the drying zone and, through that, the temperature of the drying gas that is conducted through the material bed in the drying zone. The blowing power is regulated by regulating the rotation speed of the driving motor M of the exhaust gas blower 5 by a VSD unit (VSD=Variable Speed Drive).

(10) The equipment also includes a cleaning device 23, such as a gas scrubber, to purify the exhaust gas flow B before it is conducted into the atmosphere.

(11) When using the sintering equipment, the volume flow of the gas flow that is conducted through the material bed 2 in the drying zone I is regulated by conducting part of the gas flow of the circulation gas duct 3 as a by-pass flow A past the material bed, and the volume flow of the by-pass gas flow A is set at an essentially standard volume. At the same time, part of the gas flow that is conducted in the circulation gas duct 3 to the drying zone I is removed as the exhaust gas flow B through the exhaust gas duct 4, and the volume flow of the exhaust gas flow B is regulated to control the temperature of the gas flow travelling through the material bed in the drying zone.

(12) The invention is not limited to the application examples described above only, but many modifications are possible within the inventive idea defined by the claims.