EP2322675A1 - Procédé de fabrication d'un minerai fritté et machine à fritter - Google Patents

Procédé de fabrication d'un minerai fritté et machine à fritter Download PDF

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Publication number
EP2322675A1
EP2322675A1 EP08876783A EP08876783A EP2322675A1 EP 2322675 A1 EP2322675 A1 EP 2322675A1 EP 08876783 A EP08876783 A EP 08876783A EP 08876783 A EP08876783 A EP 08876783A EP 2322675 A1 EP2322675 A1 EP 2322675A1
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EP
European Patent Office
Prior art keywords
gaseous fuel
sintering
diluted
sintering bed
gas
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EP08876783A
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German (de)
English (en)
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EP2322675A4 (fr
EP2322675B1 (fr
Inventor
Nobuyuki Oyama
Katsuhiro Iwasaki
Hideki Kadoya
Yasuo Nagashima
Hiroshi Tako
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JFE Steel Corp
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JFE Steel Corp
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B19/00—Combinations of furnaces of kinds not covered by a single preceding main group
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
    • C22B1/205—Sintering; Agglomerating in sintering machines with movable grates regulation of the sintering process
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B1/00—Preliminary treatment of ores or scrap
    • C22B1/14—Agglomerating; Briquetting; Binding; Granulating
    • C22B1/16—Sintering; Agglomerating
    • C22B1/20—Sintering; Agglomerating in sintering machines with movable grates
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B21/00—Open or uncovered sintering apparatus; Other heat-treatment apparatus of like construction
    • F27B21/06—Endless-strand sintering machines

Definitions

  • the present invention relates to methods for producing a sintered ore used as a raw material for blast furnaces using a downdraft Dwight-Lloyd (DL) sintering machine and also relates to sintering machines used for such methods.
  • DL downdraft Dwight-Lloyd
  • Sintered ore serving as a main raw material for blast furnace iron making, is produced by steps shown in Fig. 1 .
  • the raw materials include iron ore fines, recovered fines in steel works, under-sieve fines of sintered ore, CaO-containing auxiliary raw materials such as limestone and dolomite, a granulation aid such as burnt lime, coke fines, and anthracite.
  • These raw materials are fed from hoppers 1 onto a conveyer in predetermined proportions.
  • the fed raw materials are mixed and granulated in, for example, a drum mixer 2 where an appropriate amount of water is added thereto, thus forming a sintering raw material in the form of quasi-particles having a mean size of 3.0 to 6.0 mm.
  • This sintering raw material is charged onto an endless moving sintering machine pallet 8 from surge hoppers 4 and 5 disposed above the sintering machine via a drum feeder 6 and a charging chute 7, thus forming a charged bed, also called a sintering bed.
  • the thickness (height) of the sintering bed is about 400 to 800 mm.
  • the carbonaceous material in the surface layer of the sintering bed is ignited by an ignition furnace 10 disposed above the sintering bed 9 and is sequentially combusted by air sucked downward through wind boxes 11 disposed under the pallet 8, when combustion heat is generated so that the sintering raw material is combusted and melted, thus forming a sinter cake.
  • the resultant sinter cake is then crushed and regularly sized and is recovered as a sintered ore product composed of agglomerates having a size of 5.0 mm or more.
  • the ignition furnace 10 ignites the surface layer of the sintering bed.
  • the carbonaceous material in the ignited sintering bed is successively combusted by air sucked downward from the upper layer to the lower layer of the sintering bed through the wind boxes, with the combustion zone gradually moving downward and frontward (downstream) as the pallet 8 moves.
  • moisture contained in the sintering raw material particles in the sintering bed is vaporized by heat generated by the combustion of the carbonaceous material and is sucked downward to form a wet zone where the moisture concentrates in the sintering raw material in the lower layer, where the temperature has yet to be increased.
  • the moisture concentration When the moisture concentration reaches or exceeds a certain level, the moisture fills voids between the raw material particles, which serve as channels for the suction gas, thus increasing the airflow resistance.
  • the airflow resistance is also increased by the melted portion, which is necessary for the sintering reaction occurring in the combustion zone.
  • the production capacity (t/hr) of a sintering machine is generally determined by the product of sinter productivity (t/hr ⁇ m 2 ) and the area of the sintering machine (m 2 ). That is, the production capacity of a sintering machine varies with, for example, the width and length of the sintering machine, the thickness of the charged bed (the thickness of the sintering bed), the bulk density of the sintering raw material, sintering (combustion) time, and yield. To increase the amount of sintered ore produced, for example, it is thought to be effective to improve the permeability (pressure loss) of the sintering bed to shorten the combustion time, or to increase the cold strength of sinter cake before crushing to improve the yield.
  • permeability pressure loss
  • Fig. 2 shows pressure loss and temperature distributions in a sintering bed having a height of 600 mm, where a combustion (flame) front propagating through the sintering bed is located at a position about 400 mm from the pallet (200 mm from the surface of the sintering bed) in the sintering bed.
  • a combustion (flame) front propagating through the sintering bed is located at a position about 400 mm from the pallet (200 mm from the surface of the sintering bed) in the sintering bed.
  • about 60% of the pressure loss distribution is in the wet zone, and about 40% is in the combustion and melting zone.
  • Fig. 3 shows temperature distributions in sintering beds for high production and low production of sintered ore.
  • the time during which the sintering raw material is maintained at a temperature of 1,200°C or more, where the particles of the sintering raw material start melting (hereinafter referred to as "high-temperature-zone holding time"), is denoted by t 1 for low production and is denoted by t 2 for high production, where productivity is given priority.
  • the high-temperature-zone holding time t 2 is shorter than the high-temperature-zone holding time t 1 for low production because the pallet traveling speed is increased.
  • the high-temperature-zone holding time becomes shorter, the cold strength of sintered ore is decreased because of insufficient firing, thus decreasing the yield.
  • Fig. 4(a) shows the sintering process of the sintering bed on the sintering machine pallet
  • Fig. 4(b) shows the temperature distribution (heat pattern) in the sintering bed during the sintering process
  • Fig. 4(c) shows the yield distribution of sinter cake.
  • the temperature of the sintering bed is less easily increased in the upper portion than in the lower layer, and the high-temperature-zone holding time is correspondingly shorter.
  • Patent Document 1 discloses a technique of ejecting a gaseous fuel onto a sintering bed after the ignition of the sintering bed.
  • a gaseous fuel which is not specified and is possibly propane gas (LPG) or natural gas (LNG)
  • LPG propane gas
  • LNG natural gas
  • the flammable gas is injected without reducing the amount of carbonaceous material, so that the sintering bed reaches a high temperature exceeding 1,380°C.
  • this technique does not provide a sufficient effect of improving cold strength and yield.
  • this technique is impractical and has yet to be put into practice because the ejection of the flammable gas immediately behind the ignition furnace poses a high risk of a fire in the space above the sintering bed due to combustion of the flammable gas.
  • Patent Document 2 also discloses a technique of adding a flammable gas to air sucked into the sintering bed after the ignition of the sintering bed. It discloses that the flammable gas is preferably supplied for about one to ten minutes after the ignition, although the sintered ore remains red-hot in the surface layer immediately after the ignition by the ignition furnace and, depending on the manner of supply, poses a high risk of a fire due to combustion of the flammable gas. In addition, although there is little specific description, the combustion of the flammable gas in the sinter zone, where sintering is completed, is ineffective and tends to decrease the productivity because the permeability is degraded by the temperature rise and thermal expansion due to the combustion gas. Thus, this technique has yet to be put into practice.
  • Patent Document 3 discloses a technique of injecting a mixture of air and coke oven gas immediately behind the ignition furnace through a hood disposed above the sintering bed of the sintering raw material to heat the sintering bed to high temperature. Again, this technique cannot achieve the effect of injecting coke oven gas since the combustion and melting zone in the sintering bed reaches a high temperature exceeding 1,380°C, and has yet to be put into practice because it poses a risk of a fire due to ignition of the flammable mixed gas in the space above the sintering bed.
  • Patent Document 4 discloses a method of simultaneously injecting a low-melting-point flux, a carbonaceous material, and a flammable gas immediately behind the ignition furnace. Again, this method poses a high risk of a fire in the space above the sintering bed because the flammable gas is injected into the surface while a fire remains therein and does not achieve a sufficient effect of injecting the flammable gas because the width of the sinter zone cannot be sufficiently increased (less than about 15 mm). Furthermore, the large amount of low-melting-point flux causes excessive melting in the upper layer and therefore blocks pores, serving as air channels, and degrades the permeability, thus decreasing the productivity. Accordingly, this technique has so far yet to be put into practice.
  • Control of the ultimate maximum temperature during combustion and the high-temperature-zone holding time is important because they determine the quality of sintered ore.
  • the method disclosed in Patent Document 1 is a technique for increasing the temperature of the upper portion of the sintering bed in the first half of the sintering process by combusting a gaseous fuel at the surface of the sintering bed.
  • This method has a problem in that it may cause a deficiency of air (oxygen) supporting the combustion due to the high concentration of gaseous fuel and may therefore result in insufficient combustion of the carbonaceous material (coke) in the sintering raw material, thus failing to improve the quality of sintered ore.
  • Patent Document 2 lacks specifics and has so far yet to be put into practice because it poses a high risk of a fire, depending on the manner of supply, and the combustion of a flammable gas in the sinter zone, where sintering is completed, is ineffective.
  • Patent Document 3 is a technique of injecting a mixture of air and coke oven gas immediately behind the ignition furnace through a hood disposed above the sintering bed of the sintering raw material to heat the sintering bed to high temperature.
  • the mixed gas is injected in the same coke proportion, a large amount of vitreous low-strength mineral is formed because the ultimate maximum temperature rises as the high-temperature holding time is extended, and consequently the effect of injecting the mixed gas cannot be achieved.
  • this technique has yet to be put into practice because it poses a risk of a fire due to ignition of the flammable mixed gas.
  • Patent Document 4 increases the combustion speed of a flammable gas and coke by mixing a low-melting-point flux and a carbonaceous material while increasing the amount of air (oxygen), although it has a problem in that the permeability for combustion air is decreased because the low-melting-point flux and the fines are injected together.
  • the present invention provides a method for producing sintered ore, comprising a charging step of charging a sintering raw material onto a pallet, an ignition step of igniting a carbonaceous material on a surface of the sintering bed, a diluted gaseous fuel producing step, and a combustion step of combusting the carbonaceous material in the sintering bed, thereby forming a sinter cake.
  • the charging step comprises charging a sintering raw material containing ore fines and a carbonaceous material onto a circulating pallet to form a sintering bed of the sintering raw material on the pallet.
  • the diluted gaseous fuel producing step comprises producing a diluted gaseous fuel having a concentration of a lower flammable limit concentration or less by supplying a gaseous fuel to air above the sintering bed to dilute the gaseous fuel.
  • the combustion step comprises combusting, in the sintering bed, the diluted gaseous fuel and the carbonaceous material contained in the sintering bed by sucking the diluted gaseous fuel and air into the sintering bed through a wind box disposed below the pallet, thereby forming a sinter cake.
  • the diluted gaseous fuel producing step preferably comprises producing a diluted gaseous fuel having a concentration of a lower flammable limit concentration or less by supplying a gaseous fuel to air above the sintering bed at a flow speed at which a blow-off occurs to dilute the gaseous.
  • the flow speed at which a blow-off occurs is preferably a speed exceeding the burning velocity of the gaseous fuel.
  • the diluted gaseous fuel producing step preferably comprises producing a diluted gaseous fuel having a concentration of a lower flammable limit concentration or less by ejecting a gaseous fuel into air above the sintering bed at a speed twice or more the burning velocity of the gaseous fuel to dilute the gaseous fuel. More preferably, the diluted gaseous fuel producing step comprises producing a diluted gaseous fuel having a concentration of a lower flammable limit concentration or less by ejecting a gaseous fuel into air above the sintering bed at a speed twice or more the turbulent burning velocity of the gaseous fuel to dilute the gaseous fuel.
  • methane gas has a laminar burning velocity of about 0.4 m/s and a turbulent burning velocity of about 4 m/s.
  • the diluted gaseous fuel producing step preferably comprises producing a diluted gaseous fuel having a concentration of a lower flammable limit concentration or less by ejecting a gaseous fuel into air above the sintering bed at a pressure of 300 mmAq to less than 40,000 mmAq with respect to an ambient pressure to dilute the gaseous fuel.
  • the diluted gaseous fuel producing step preferably comprises ejecting a gaseous fuel from an outlet having an opening diameter of less than 3 mm into air above the sintering bed. More preferably, the opening diameter is 0.5 to 1.5 mm.
  • the method for producing sintered ore preferably further comprises the step of:
  • the method for producing sintered ore preferably further comprises the step of adjusting the shape of a combustion and melting zone in the sintering bed by combusting the diluted gaseous fuel introduced from above the sintering bed.
  • the step of adjusting the shape of the combustion and melting zone preferably comprises adjusting the thickness of the combustion and melting zone in a height direction and/or the width of the combustion and melting zone in a movement direction of the pallet by combusting the diluted gaseous fuel introduced from above the sintering bed.
  • the method for producing sintered ore preferably further comprises the step of adjusting a position where the diluted gaseous fuel is introduced into the sintering bed.
  • the method for producing sintered ore preferably further comprises the step of adjusting the cold strength of sintered ore.
  • the combustion step of combusting the diluted gaseous fuel and the carbonaceous material in the sintering bed to form a sinter cake is preferably as follows:
  • the diluted gaseous fuel is preferably a flammable gas diluted to a concentration of 75% to 2% of the lower flammable limit concentration, more preferably, a flammable gas diluted to a concentration of 60% to 2% of the lower flammable limit concentration, and most preferably a flammable gas diluted to a concentration of 25% to 2% of the lower flammable limit concentration.
  • the gaseous fuel supplied to the sintering bed is preferably:
  • the present invention further provides a sintering machine comprising:
  • the gaseous fuel supply unit preferably ejects a gaseous fuel into air above the sintering bed so as to mix the gaseous fuel with air, thereby preparing a diluted gaseous fuel in a concentration at or below a lower flammable limit concentration.
  • the gaseous fuel supply unit is preferably as follows:
  • the gaseous fuel supply unit is preferably disposed as follows:
  • a diluted gaseous fuel in the operation of a downdraft sintering machine, can be supplied (introduced) to a sintering bed and combusted at a target position in the sintering bed by ejecting a gaseous fuel into air above the sintering bed so as to dilute and adjust it to a predetermined concentration.
  • the position where the diluted gaseous fuel is supplied and the ultimate maximum temperature and high-temperature-zone holding time during the combustion can be controlled to perform an operation that increases the sintered ore strength not only in the upper portion of the sintering bed, where the cold strength of sintered ore tends to be lower because of insufficient combustion, but also at any position in the middle and lower layers of the sintering bed.
  • the strength of sinter cake can be controlled at any position without degrading the permeability of the entire sintering bed, particularly by controlling the reaction in the combustion and melting zone, for example, controlling the thickness of the zone in the vertical direction and the width in the movement direction of the pallet, so that a sintered ore product with high cold strength can be produced in high yield with high productivity as a whole.
  • the sintering machine of the present invention such a sintering machine operation can be stably performed.
  • a method for producing sintered ore according to the present invention includes a charging step, an ignition step, a diluted gaseous fuel producing step, and a combustion step.
  • the charging step is a step of charging a sintering raw material containing ore fines and a carbonaceous material onto a circulating pallet to form a sintering bed of the sintering raw material on the pallet.
  • the ignition step is a step of igniting the carbonaceous material on a surface of the sintering bed using an ignition furnace.
  • the diluted gaseous fuel producing step is a step of preparing a diluted gaseous fuel in a concentration at or below a lower flammable limit concentration by supplying a gaseous fuel to air above the sintering bed so as to dilute the gaseous fuel.
  • the combustion step is a step of combusting the diluted gaseous fuel in the sintering bed by sucking the diluted gaseous fuel and air into the sintering bed by suction through a wind box disposed below the pallet while combusting the carbonaceous material in the sintering bed with the air sucked into the sintering bed to sinter the sintering raw material with combustion heat generated thereby, thus forming a sinter cake.
  • the present invention is characterized by the diluted gaseous fuel producing step and the combustion step.
  • the diluted gaseous fuel producing step is a step of preparing a diluted gaseous fuel in a concentration at or below a lower flammable limit concentration by ejecting a gaseous fuel at high speed into air above the sintering bed downstream of the ignition furnace in the movement direction of the pallet so as to mix the gaseous fuel with air before introducing the diluted gaseous fuel into the sintering bed.
  • a sintering machine of the present invention is characterized in that it includes a gaseous fuel supply unit for preparing the above diluted gaseous fuel.
  • the above gaseous fuel supply unit is preferably capable of controlling the amount of gaseous fuel supplied in the width direction of the pallet by, for example, flow control means provided on the gaseous fuel supply pipes or the nozzles.
  • the gaseous fuel supply unit is preferably cable of supplying more gaseous fuel near sidewalls in the width direction of the pallet because the gaseous fuel concentration tends to become lower near the sidewalls as the supplied gaseous fuel flows sideward or leaks outside under the influence of crosswinds.
  • the above gaseous fuel supply unit needs to dilute the gaseous fuel to a concentration at or below the lower flammable limit concentration thereof by ejecting the gaseous fuel into air above the sintering bed at high speed so as to mix the gaseous fuel with ambient air within a short period of time before introducing the diluted gaseous fuel into the sintering bed.
  • Tables 1A and 1B show the lower flammable limit concentrations, supply concentrations, etc. of typical gaseous fuels that can be used for the present invention.
  • it is safer to supply the gaseous fuel to the sintering raw material in a lower gas concentration as compared to the lower flammable limit concentration.
  • town gas which has a lower flammable limit concentration approximate to that of coke oven gas (C-gas)
  • C-gas coke oven gas
  • town gas contains no carbon monoxide (CO), which is hazardous to the human body, as its component, and also contains no hydrogen.
  • Tables 2A and 2B show the types of combustible components (hydrogen, CO, and methane) contained in the gaseous fuel and the lower and upper flammable limit concentrations, laminar and turbulent burning velocities, etc. of these components.
  • the gaseous fuel may be ejected at a high speed, namely, at least at or above the laminar burning velocity, preferably at or above the turbulent burning velocity.
  • the gaseous fuel is methane, which is the main combustible component of town gas
  • there is no risk of a flashback if the gaseous fuel is ejected at a speed exceeding 3.7 m/s.
  • Hydrogen has a higher turbulent burning velocity than CO and methane and must therefore be ejected at a correspondingly higher speed to ensure safety.
  • town gas which contains no hydrogen
  • C-gas which contains 59% by volume of hydrogen, in that the ejection speed can be lowered.
  • town gas is safe without the risk of gas poisoning because it contains no CO.
  • town gas has preferred properties for use as the gaseous fuel in view of ensuring safety.
  • C-gas can also be used as the gaseous fuel, although in that case it is necessary to increase the gas ejection speed and to take a measure against CO.
  • Table 2A Combustible component Molecular weight (M) Combustion heat (kcal/g) Theoretical mixture proportion (Fuel vol.%) Hydrogen 2.0 28.62 29.5 CO 28.0 2.406 29.5 Methane 16.0 11.93 9.47
  • Table 3 shows the evaluation results of methods for supplying a gaseous fuel for advantages and disadvantages.
  • direct injection refers to a method in which a gaseous fuel, such as town gas or C-gas, is diluted to a predetermined concentration by directly supplying (ejecting) it so as to draw ambient air therein and is sucked (introduced) into the sintering bed
  • premix injection refers to a method in which a gaseous fuel diluted to a predetermined concentration by mixing it with air in advance is supplied to the sintering bed and is sucked (introduced) into the sintering bed.
  • direct injection In direct injection, a flashback can be easily avoided by ejecting the gaseous fuel at or above the turbulent burning velocity described above; in premix injection, a flashback can be caused by a concentration deviation.
  • direct injection has a higher possibility of abnormal combustion than premix injection because a concentration variation occurs easily when the gaseous fuel is diluted by mixing it with ambient air. Nevertheless, direct injection with town gas is most advantageous when evaluated as a whole, including equipment costs.
  • the above gaseous fuel supply unit needs to dilute the gaseous fuel to a concentration at or below the lower flammable limit concentration thereof by ejecting the gaseous fuel into air above the sintering bed at high speed so as to mix the gaseous fuel with ambient air within a short period of time before introducing the diluted gaseous fuel into the sintering bed. The reason will be described below.
  • Fig. 7 shows diagrams illustrating an experiment for examining the effect of the position where the gaseous fuel is supplied on sinter cake.
  • sinter cake was charged into a sinter pot having an inner diameter of 300 mm and a height of 400 mm, and a nozzle was embedded to a depth of 90 mm from the top in the center of the sinter cake.
  • a 100% methane gas was injected in a concentration of 1% by volume based on the volume of air, and the methane gas concentration of the sinter cake was measured in the circumferential direction and the depth direction.
  • the measurement results are shown in Table 4.
  • Fig. 7(a) sinter cake was charged into a sinter pot having an inner diameter of 300 mm and a height of 400 mm, and a nozzle was embedded to a depth of 90 mm from the top in the center of the sinter cake.
  • a 100% methane gas was injected in a concentration of 1% by volume based on the volume of air, and the
  • a methane gas concentration of 10.23% or more could not be measured.
  • the gaseous fuel is preferably ejected at high speed from the outlets, such as slits or nozzles, provided in the gaseous fuel supply pipes of the gaseous fuel supply unit in view of avoiding a flashback. That is, in the sintering operation of the present invention, the gaseous fuel, which is diluted to a concentration at or below the lower flammable limit concentration before being sucked and introduced into the surface layer of the sintering bed, is supplied from above the sintering bed while the sinter pallet carries an ignition source, that is, a sintering bed in which the combustion and melting zone is to be formed or is being formed.
  • an ignition source that is, a sintering bed in which the combustion and melting zone is to be formed or is being formed.
  • the gaseous fuel is preferably ejected at a speed twice or more the burning velocity of the gaseous fuel, more preferably twice or more the turbulent burning velocity of the gaseous fuel, so that no flashback occurs in the event of ignition of the gaseous fuel.
  • methane gas has a laminar burning velocity of about 0.4 m/s and a turbulent burning velocity of about 4 m/s.
  • outlets having opening diameters of 1, 2, and 3 mm were formed in 25A pipes.
  • LNG gas was supplied to the pipes so as to be ejected from the outlets and was ignited using an ignition source. Subsequently, the ejection speed at which a blow-off occurred when the ignition source was separated was measured.
  • the above ejection speed was controlled by changing the header pressure of the LNG gas.
  • the gaseous fuel could be prevented from burning at the outlets by ejecting the gaseous fuel at a supersonic speed with the header pressure of the LNG gas raised to 2,000 mmH 2 O, although the gaseous fuel burned in the downstream low-speed region, which is called lifting, and the fire could not be reliably blown off.
  • the gaseous fuel can be prevented from burning at the outlets simply by ejecting the gaseous fuel at or above the burning velocity, it cannot be prevented from burning in the downstream low-speed region (lifting). In the present invention, therefore, the gaseous fuel is ejected from the outlets at or above the speed at which a blow-off occurs to prevent lifting.
  • the gaseous fuel is preferably ejected at high speed from gas outlets having an opening diameter of less than 3 mm, for example, at a speed of 70 m/s or more if the opening diameter is equivalent to 1 mm, at a speed of 100 m/s or more if the opening diameter is equivalent to 1.5 mm, and at a speed of 130 m/s or more if the opening diameter is 2 mm.
  • the opening diameter preferably falls within the range of 0.5 to 1.5 mm. If the opening diameter falls below 0.5 mm, such openings are difficult to form in pipes and are also easily clogged with, for example, dust contained in the gas. On the other hand, if the opening diameter exceeds 1.5 mm, a relatively high ejection speed is required to cause a blow-off; a lower ejection speed is preferred to ensure safety.
  • outlets are specified in terms of the diameter of circular outlets in the above description, the outlets may have any other shape having the same opening area, such as oval outlets or elongated outlets (slits).
  • the ejection speed of the gaseous fuel varies not only with the opening diameter, but also with the supply pressure of the gaseous fuel, it may be controlled on the basis of the relationship between the pressure and flow speed (ejection speed) of the nozzles forming the openings to attain an ejection speed at which a blow-off occurs.
  • a blow-off can be caused by ejecting the gas at a speed of 70 m/s for a nozzle pressure of 300 mmH 2 O. If LNG gas is ejected from orifices having an opening diameter of 1.5 mm, a blow-off can be caused by ejecting the gas at a speed of 100 m/s for a nozzle pressure of 700 mmH 2 O.
  • the pressure of the gaseous fuel ejected from the nozzles, openings, or slits is preferably 300 mmAq to less than 40,000 mmAq with respect to the ambient pressure.
  • the fuel can be uniformly supplied despite their large pipe length by applying one or a combination of the following techniques:
  • any of the following methods can be employed:
  • the above gaseous fuel supply unit preferably ejects the gaseous fuel at a height of 300 mm or more above the surface of the sintering bed.
  • Fig. 12 shows the measurement results of spreads of methane gas (concentration: 100%) ejected vertically downward from two types of nozzles having nozzle diameters of 2 mm and 1 mm at flow speeds varying in the range of 20 to 300 m/s.
  • Fig. 12 shows spreads of methane gas at positions 0.2 m, 0.4 m, 0.6 m, and 0.8 m from the tips of the nozzles. As shown in Fig.
  • the gaseous fuel is more smoothly mixed and diluted with ambient air as the nozzle diameter becomes smaller and the ejection speed of the gaseous fuel becomes higher, and particularly, the effect of facilitating dilution by increasing the speed is increased at a distance from the tips of the nozzles of 0.4 m.
  • the gaseous fuel is preferably supplied to air at a height of 300 mm or more above the surface of the sintering bed.
  • the gaseous fuel is more smoothly mixed and diluted with ambient air as the ejection speed of the gaseous fuel becomes higher.
  • some ignition source might ignite the gaseous fuel supplied from the gaseous fuel supply unit to cause a flashback, thus leading to explosion and combustion in the gaseous fuel supply unit or the gaseous fuel supply pipes.
  • the gaseous fuel is preferably ejected at a speed twice or more the burning velocity of the gaseous fuel used, more preferably twice or more the turbulent burning velocity of the gaseous fuel.
  • methane gas has a laminar burning velocity of about 0.4 m/s and a turbulent burning velocity of about 4 m/s.
  • the gaseous fuel supplied from the gaseous fuel supply unit to air above the sintering bed is diluted and sucked through the wind boxes disposed below the pallet.
  • the supplied gaseous fuel may flow sideward when blown by a crosswind laterally with respect to the movement direction of the pallet, particularly, as the wind speed becomes higher.
  • Fig. 13 shows the results of an analysis of the influence of crosswinds on the concentration distribution of the gaseous fuel at wind speeds of 2 m/s and 5 m/s.
  • Fig. 14(a) which shows the results of the case where the 2 m high partitions were disposed, revealed that the partitions did not provide a sufficient effect because a swirling occurred inside the partitions and dissipated the gaseous fuel at a wind speed of 5 m/s.
  • Fig. 14(a) which shows the results of the case where the 2 m high partitions were disposed, revealed that the partitions did not provide a sufficient effect because a swirling occurred inside the partitions and dissipated the gaseous fuel at a wind speed of 5 m/s.
  • the present inventors further studied the reduction of the influence of crosswinds by providing a hood above the gaseous fuel supply unit. As a result, it was found that a hood provides a greater effect as a measure against crosswinds than partitions.
  • This hood is preferably configured to have an opening or appropriate permeability (void rate) in the center of the top portion so that air can be taken in through that portion. This allows air to be mixed with the gaseous fuel ejected from the gaseous fuel supply pipes to prepare a diluted gaseous fuel inside the hood.
  • void rate opening or appropriate permeability
  • the above seals are preferably heat-resistant, highly flexible or deformable, and are nonabrasive to the surface of the sintering bed.
  • FIG. 17 shows a gaseous fuel supply unit used for calculation and a hood disposed thereabove.
  • the pallet width of the sintering machine was 5 m.
  • Gas injection pipes for ejecting a gaseous fuel were arranged in parallel with the movement direction of the pallet at intervals of 600 mm at a height of 500 mm above the sintering bed (sintering bed), straightening vanes were disposed on and above the gas injection pipes, and the food was disposed thereabove.
  • An opening having a width of 1,000 mm (the void rates for calculation were 100% and 80%) was provided in the center of the top portion.
  • fences for attenuating crosswinds having a permeability of 30% were provided above the side of the hood.
  • the permeability at the bottom end of the hood was set to 20% on the assumption that chain curtains were provided.
  • Fig. 18 shows the analytical results of the concentration distribution of the gaseous fuel. These results demonstrate that the concentration distribution of the gaseous fuel is improved if the top portions of the sidewalls of the hood are inclined so as to narrow the top portion of the hood, that the difference between the case where the void rate of the opening is 100% and the case where the void rate of the opening is 80% is small, and that swirling is inhibited by the straightening vanes.
  • Fig. 19 shows the analytical results of pressure distribution, demonstrating that the pressure loss due to the inclined top portion of the hood is small and that swirling is inhibited by the straightening vanes.
  • Fig. 20 shows the analytical results of gas flow velocity distribution, demonstrating that a drift is caused by an inflow of air if the bottom end of the hood is permeable.
  • Fig. 21 shows a vector diagram of the gas flow velocity, demonstrating that swirling is inhibited by the inclined top portion of the hood and the straightening vanes.
  • Fig. 22 shows an example in which a hood having an opening in the top portion thereof is disposed above the gas supply unit, fences for preventing swirling having a permeability of 30% are disposed thereabove, chain curtains (wire-plate seals) for preventing intrusion of crosswinds through the gaps between the hood and the pallet are suspended from the bottom end of the hood, and straightening vanes are disposed on the gas injection pipes located at both ends.
  • Fig. 23 a modification of Fig.
  • Fig. 22 above shows an example in which straightening vanes are disposed along the gaseous fuel supply pipes in the hood.
  • Fig. 24 shows an example in which the top portion of the hood in Fig. 23 above is open and straightening vanes are disposed instead. It is preferable to appropriately change the intervals at which the above straightening vanes are arranged.
  • Fig. 25 shows an example in which the top portion of the hood in Fig. 24 is completely open and only straightening vanes are disposed in the top portion
  • Fig. 26 shows an example in which straightening vanes and baffle plates for facilitating the mixing of the gaseous fuel are used in combination in the hood. All the hoods shown above have the effect of reducing the influence of crosswinds.
  • the gaseous fuel is preferably used as a diluted gaseous fuel by diluting it so that the concentration of the combustible component contained in the flammable gas is 75% or less of the lower flammable limit concentration, more preferably 60% or less of the lower flammable limit concentration, and further preferably 25% or less of the lower flammable limit concentration, at normal temperature in air.
  • the flammable gas diluted to a concentration of 75% or less of the lower flammable limit concentration or less is used for the following two reasons:
  • the gaseous fuel must be diluted to such an extent as not to cause insufficient combustion due to a deficiency of air (oxygen) required for combustion of all carbonaceous material in the sintering raw material (solid and gaseous fuels).
  • the concentration of the diluted gaseous fuel is preferably 2% or more of the lower flammable limit concentration. If the concentration falls below 2%, the heat generated by combustion is insufficient to improve the strength and yield of sintered ore.
  • the concentration of the diluted gaseous fuel is preferably adjusted depending on the amount of carbonaceous material (solid fuel). Furthermore, the diluted gaseous fuel can be combusted at a particular position in the sintering bed by adjusting the concentration thereof.
  • the diluted gaseous fuel is preferably supplied (introduced) to the sintering bed after the ignition of the carbonaceous material in the sintering bed.
  • the diluted gaseous fuel is preferably supplied to the sintering bed after the sintering raw material in the upper portion of the sintering bed is fired to form a layer of sinter cake.
  • the diluted gaseous fuel can be supplied at any position before burn-through as long as a layer of sinter cake has been formed on the surface of the sintering bed.
  • Other reasons for supplying the diluted gaseous fuel after the formation of a layer of sinter cake are as follows:
  • the diluted gaseous fuel is preferably supplied after the thickness of the combustion and melting zone reaches at least 15 mm or more, preferably 20 mm or more, and more preferably 30 mm or more. If the thickness of the combustion and melting zone falls below 15 mm, the thickness of the combustion and melting zone cannot be increased because the combustion of the gaseous fuel has an insufficient effect under the cooling effect of the air and diluted gaseous fuel sucked through the sintering bed (sinter cake).
  • the thickness of the combustion and melting zone increases significantly so that the high-temperature-zone holding time can be extended, thus providing a sintered ore with high cold strength.
  • the thickness of the combustion and melting zone can be examined using, for example, a vertical cylindrical test pot with a transparent quartz window. This test pot is effective means for determining the position where the diluted gaseous fuel is supplied.
  • the diluted gaseous fuel is preferably introduced into the sintering bed at a position where the combustion front has propagated below the surface and the combustion and melting zone has propagated 100 mm or more, more preferably 200 mm or more, downward from the surface, that is, to the middle or lower layer region.
  • the diluted gaseous fuel is preferably supplied so that it passes, without burning, through the sinter cake region (sintering bed) generated in the surface layer of the sintering bed and burns after the combustion front propagates 50 mm or more from the surface.
  • the reason is that the adverse effect of cooling due to air sucked through the sintering bed can be reduced at a position where the combustion front has propagated 100 mm or more downward from the surface so that the thickness of the combustion and melting zone can be increased. Furthermore, the effect of cooling due to air can be substantially eliminated at a position where the combustion front has propagated 200 mm or more downward from the surface so that the thickness of the combustion and melting zone can be increased to 30 mm or more.
  • the diluted gaseous fuel is more preferably supplied near the sidewalls on both sides of the pallet in the width direction thereof, where the yield is lower.
  • the diluted gaseous fuel generation unit is preferably disposed at a position about 5 m or more downstream of the ignition furnace for a sintering machine having a gaseous fuel supply capacity of 1,000 to 5,000 m 3 (standard)/h, a production capacity of about 15,000 t/day, and a length of 90 m, although the position depends on the size of the sintering machine.
  • the diluted gaseous fuel is preferably supplied (introduced into the sintering bed) at any one or more positions downstream of the ignition furnace in the movement direction of the pallet between a position where the combustion front has propagated below the surface after the formation of sinter cake (for example, a position 100 mm or more, preferably about 200 mm or more, below the surface where the combustion of the gaseous fuel occurs) and a burn-through position.
  • the introduction of the diluted gaseous fuel into the sintering bed also means that reheating of the resultant sinter cake is facilitated. That is, the diluted gaseous fuel, which is more reactive than the solid fuel, is supplied to a portion where the cold strength of sintered ore tends to be lower because of insufficient heat due to a short high-temperature-zone holding time, to supplement the combustion heat in that portion with insufficient heat, thus playing a role in regeneration and broadening of the combustion and melting zone.
  • the diluted gaseous fuel is preferably supplied from above the sintering bed after the ignition so that at least a portion of the diluted gaseous fuel introduced into the sintering bed reaches the combustion and melting zone while remaining unburned, thus burning at a position where the combustion heat should be supplemented.
  • the reason is that it is more effective to spread the effect of supplying the diluted gaseous fuel, that is, introducing it into the sintering bed, beyond the upper portion of the sintering bed to the central portion in the thickness direction, namely, the combustion and melting zone.
  • the gaseous fuel is supplied to the upper layer of the sintering bed, which tends to have insufficient heat (insufficient high-temperature-zone holding time)
  • sufficient combustion heat can be supplied to improve the quality of sinter cake in that portion.
  • the effect of supplying the diluted gaseous fuel is spread to the middle and lower layers, the result is equivalent to the formation of a recombustion and remelting zone by the diluted gaseous fuel above the original combustion and melting zone formed by the carbonaceous material, thus broadening the combustion and melting zone in the vertical direction.
  • the high-temperature-zone holding time can be extended without raising the ultimate maximum temperature so that sufficient sintering can be achieved without decreasing the movement speed of the pallet. This improves the quality (cold strength) of sinter cake in the entire sintering bed and therefore improves the quality (cold strength) and productivity of sintered ore products.
  • a first characteristic of the present invention lies in that the position where the diluted gaseous fuel is supplied is determined in view of where to apply the effect of supplying the diluted gaseous fuel in the sintering bed.
  • a second characteristic lies in to which levels to control the ultimate maximum temperature and the high-temperature-zone holding time in the sintering bed depending on the amount of solid fuel with the calorific value remaining constant while supplying the fuel.
  • the position of the combustion and melting zone changes as shown in Fig. 4(a) while the combustion (flame) front propagates gradually downward and frontward (downstream) as the pallet is moved.
  • the thermal history of the sintering bed during the sintering process differs between the upper, middle, and lower layers, and the high-temperature-zone holding time (time during which the temperature is about 1,200°C or more) differs significantly between the upper to lower layers.
  • the yields of sintered ore at different positions in the pallet have the distribution shown in Fig. 4(c) . Specifically, the yield is lower in the surface layer (upper layer) and is higher in the middle and lower layers.
  • the combustion and melting zone is broadened, for example, across the thickness in the vertical direction and the width in the movement direction of the pallet, thus leading to an improvement in the quality of sintered ore products.
  • the high-temperature-zone holding time can also be controlled in the middle and lower layers, where the yield is higher, so that the yield can be further improved.
  • the supply (introduction) of the diluted gaseous fuel to the sintering bed in the present invention is intended to control the cold strength of sintered ore products as a whole. That is, the original object of supplying the diluted gaseous fuel is to improve the cold strength of sinter cake and therefore the cold strength of sintered ore, particularly, to achieve a cold strength (shutter index SI) of sintered ore of about 75% to 85%, preferably 80% or more, and more preferably 90% or more, by controlling the position where the gaseous fuel is supplied, the high-temperature-zone holding time, which is the time during which the sintering raw material remains in the combustion and melting zone, and the ultimate maximum temperature.
  • a cold strength (shutter index SI) of sintered ore of about 75% to 85%, preferably 80% or more, and more preferably 90% or more
  • This strength level can be achieved at low cost in the present invention by adjusting, particularly, the concentration, amount, position, and range where the diluted gaseous fuel is supplied, preferably taking into account the amount of carbonaceous material in the sintering raw material (with the calorific value supplied remaining constant). Improving the cold strength of sintered ore may involve increased airflow resistance and therefore decreased productivity.
  • the present invention solves that problem by controlling the ultimate maximum temperature and the high-temperature-zone holding time while improving the cold strength of sintered ore.
  • the cold strength, SI, of a sintered ore produced by an actual sintering machine is 10% to 15% higher than the value obtained by a pot test.
  • the position where the diluted gaseous fuel is introduced into the sintering bed in the movement direction of the pallet is controlled on the basis of the intended cold strength of sintered ore in any region between the sinter cake formed in the sintering bed and the wet zone.
  • the scale (size), number, positions (distances from the ignition furnace), and gas concentration of gaseous fuel supply units are adjusted, preferably depending on the amount of carbonaceous material (solid fuel) in the sintering raw material, not only to control the size of the combustion and melting zone (the thickness in the vertical direction and the width in the movement direction of the pallet), but also to control the high temperature reached and the high-temperature-zone holding time, thereby controlling the strength of the sinter cake formed in the sintering bed.
  • the gaseous fuel supplied to the sintering bed is preferably one of blast furnace gas, coke oven gas, a mixture of blast furnace gas and coke oven gas, town gas, natural gas, methane gas, ethane gas, propane gas, butane gas, and a mixture thereof.
  • One of these gaseous fuels, all of which contain a combustible component, is ejected into air at high speed so as to be mixed and diluted with air and is supplied (introduced) to the sintering bed as a diluted gaseous fuel in a concentration of about 75% or less of the lower flammable limit concentration.
  • vapors of liquid fuels having an ignition temperature in vapor phase higher than the temperature of the surface layer of the sintering bed can also be used as the gaseous fuel supplied to the sintering bed, including alcohols, ethers, petroleum oils, and other hydrocarbon compounds.
  • Table 6 shows types and properties of liquid fuels that can be used in the present invention.
  • Such a vaporized liquid fuel is effective in broadening the marginal temperature range of the combustion and melting zone at the injection position because it has a higher ignition temperature than the gaseous fuels described above and therefore burns in a deeper region of the sintering bed at a higher temperature than the surface layer of the sintering bed.
  • a vaporized liquid fuel having an ignition temperature close to 500°C is highly effective. If a vaporized liquid fuel is used, the gas supply pipes are preferably maintained at a temperature of not less than the boiling point of the liquid fuel and less than the ignition temperature thereof so that the vaporized fuel does not reliquefy.
  • Waste oil for example, is not preferred for use in the present invention because it sometimes contains an easily flammable component or a component having a low ignition temperature. If a liquid fuel, such as waste oil, containing a component having a low ignition temperature or flashpoint is vaporized in advance and is supplied to the sintering raw material bed, the effect, intended by the present invention, of extending the high-temperature holding time by combusting the gaseous fuel near the combustion zone of the sintering raw material bed cannot be achieved because the liquid fuel burns in the space above the surface layer of the mix bed or near the surface layer of the mix bed before reaching the combustion zone in the mix bed.
  • the above gaseous fuels those having a CO content of 50 ppm by mass or less are preferably used. This is because CO gas is hazardous to the human body and might cause a man-made disaster if the gaseous fuel supplied to the sintering bed leaks from the machine without all being introduced into the sintering bed. Specifically, the use of town gas 13A or propane gas is more preferable in view of safety and cost.
  • sintered ore is produced by the method of the present invention using a sintering machine including a circulating pallet, a mix supply unit for charging a sintering raw material containing ore fines and a carbonaceous material onto the pallet to form a sintering bed, an ignition furnace for igniting the carbonaceous material in the sintering raw material, a wind box disposed below the pallet, and a gaseous fuel supply unit, disposed downstream of the ignition furnace, for introducing a gaseous fuel into the sintering bed by supplying the gaseous fuel to air above the sintering bed so as to dilute the gaseous fuel to a concentration at or below a lower flammable limit concentration.
  • the gaseous fuel supply unit of the sintering machine of the present invention is preferably disposed so as to straddle both sidewalls of the pallet along the width direction of the sintering machine.
  • the gaseous fuel supply unit includes a plurality of, preferably three to fifteen, gaseous fuel supply pipes disposed in a direction parallel or perpendicular to the movement direction of the pallet.
  • each pipe has a plurality of slits, outlets, or nozzles for supplying the gaseous fuel to air at high speed.
  • At least one gaseous fuel supply unit is disposed at any position downstream of the ignition furnace in the movement direction of the pallet in the process in which the combustion and melting zone propagates through the sintering bed.
  • the gaseous fuel is preferably supplied to the sintering bed after the ignition of the carbonaceous material in the sintering bed. That is, at least one unit is disposed at any position downstream of the ignition furnace where the combustion front has propagated below the surface, and the size, positions, and number of units are determined in view of adjusting the target cold strength of sintered ore products.
  • the gaseous fuel supply unit is preferably disposed at low-yield portions near both sidewalls.
  • the gaseous fuel used is preferably a flammable gas diluted to a concentration of 75% to 2% of the lower flammable limit concentration, 60% to 2% of the lower flammable limit concentration, or 25% to 2% of the lower flammable limit concentration.
  • Fig. 27 shows an embodiment of the apparatus for producing sintered ore according to the present invention, although the present invention is not limited to this exemplary embodiment.
  • a single gaseous fuel supply unit 12 for ejecting a gaseous fuel, such as a mixture of blast furnace gas and coke oven gas (M-gas), into air above a sintering bed downstream of an ignition furnace 10 in the movement direction of a pallet so as to dilute the gaseous fuel to the intended concentration.
  • a gaseous fuel such as a mixture of blast furnace gas and coke oven gas (M-gas
  • the gaseous fuel supply unit 12 includes a plurality of gaseous fuel supply pipes 12a disposed along the width direction of the pallet and a plurality of nozzles 12b, for ejecting the gaseous fuel into air at high speed, disposed on the pipes downward and along the width direction of the pallet so as to cover the sintering bed above the sidewalls (not shown).
  • the M-gas supplied from the gaseous fuel supply unit 12 is mixed with ambient air as a diluted gaseous fuel and is then introduced from above the sintering bed into the deep portion (lower layer) of the sintering bed through the sinter cake formed in the surface layer by means of suction through wind boxes (not shown) below the pallet 8.
  • the gaseous fuel supply unit 12 preferably has the nozzles 12a concentrated near both sidewalls of the pallet to supply more gaseous fuel there, particularly for improving the yield on both sides of the pallet (regions with a yield of 60% in Fig. 4(c) ).
  • gaseous fuel supplied from the gaseous fuel supply unit 12 examples include blast furnace gas (B-gas), coke oven gas (C-gas), a mixture of blast furnace gas and coke oven gas (M-gas), town gas, natural gas (LNG), methane gas, ethane gas, propane gas, butane gas, and mixtures thereof.
  • B-gas blast furnace gas
  • C-gas coke oven gas
  • M-gas mixture of blast furnace gas and coke oven gas
  • LNG natural gas
  • methane gas methane gas
  • propane gas propane gas
  • butane gas propane gas
  • Table 7 shows the lower flammable limit concentrations of various gaseous fuels for use in the present invention and the upper injection limit concentrations (75%, 60%, and 25% of the lower flammable limit concentrations) of those gaseous fuels.
  • propane gas has a lower flammable limit concentration of 2.2% by volume. Accordingly, the upper limit gas concentration at a dilution of 75% is 1.7% by volume, the upper limit gas concentration at a dilution of 60% is 1.3% by volume, and the gas concentration at a dilution of 25% is 0.6% by volume.
  • the preferred ranges are as follows, where the lower limit of the diluted gas concentration, that is, the lower limit concentration of propane gas at which the effect of supplying the gaseous fuel appears, is 0.05% by volume:
  • C-gas has a lower flammable limit concentration of 5.0% by volume. Accordingly, the upper limit gas concentration at a dilution of 75% is 3.8% by volume, the upper limit gas concentration at a dilution of 60% is 3.0% by volume, and the gas concentration at a dilution of 25% is 1.3% by volume.
  • the preferred ranges are as follows, where the lower limit concentration of C-gas at which the effect of supplying the gaseous fuel appears is 0.24% by volume:
  • LNG gas has a lower flammable limit concentration of 4.8% by volume. Accordingly, the upper limit gas concentration at a dilution of 75% is 3.6% by volume, the upper limit gas concentration at a dilution of 60% is 2.9% by volume, and the gas concentration at a dilution of 25% is 1.2% by volume.
  • the preferred ranges are as follows, where the lower limit concentration of LNG gas at which the effect of supplying the gaseous fuel appears is 0.1% by volume:
  • blast furnace gas has a lower flammable limit concentration of 40.0% by volume.
  • the upper limit gas concentration at a dilution of 75% is 30.0% by volume
  • the upper limit gas concentration at a dilution of 60% is 24.0% by volume
  • the gas concentration at a dilution of 25% is 10.0% by volume.
  • the preferred ranges are as follows, where the lower limit concentration of blast furnace gas at which the effect of supplying the gaseous fuel appears is 0.24% by volume:
  • Table 8 shows the amounts and calorific values of hydrogen, CO, methane, ethane, and propane contained in C-gas, LNG, and B-gas as combustible components.
  • Table 7 Type of gas Lower flammable limit concentration, % to air (Lower explosion limit) Upper injection limit concentration, % to air (75%) Upper injection limit concentration, % to air (60%) Upper injection limit concentration, % to air (25%) Ignition temperature In air (°C) Propane 2.2 1.7 1.3 0.4 528 to 588 Hydrogen 4.0 3.0 2.4 0.8 580 to 590 Methane 5.0 3.8 3.0 0.9 650 to 750 CO gas 12.5 9.4 7.5 2.3 658 to 674 Coke oven gas 5.0 3.8 3.0 0.9 About 630 LNG 4.8 3.6 2.9 0.9 About 680 Blast furnace gas 40.0 30.0 24.0 7.5 About 680
  • Table 8 Type of gas Hydrogen (vol%) Nitrogen (vol%) CO (vol%) CO 2 (vol%) Methane (vol%)
  • This experiment is a sinter pot test conducted using a vertical cylindrical test pot (150 mm in diameter by 400 mm, in height) with a transparent quartz window, using a mixture of blast furnace gas and coke oven gas (M-gas) as the gaseous fuel used, and using the same sintering raw material as that used in the sinter plants of the applicant company, that is, the sintering raw material shown in Table 9, at a constant downdraft pressure of 11.8 kPa.
  • the concentration of the combustible component of the M-gas was varied in the range of 0.5% to 15% by volume by dilution with air.
  • the M-gas used in this experiment had a lower flammable limit concentration of 12% by volume.
  • Table 9 Mix species Proportion (mass%) Robe River 9.6 Yandi 23.8 Carajas 42.6 Limestone 16.6 Silica 2.7 Coke fines 4.7
  • Fig. 28 shows combustion and melting zones observed on video through the transparent quartz window of the test pot, particularly showing the conditions of the combustion zones descending as the combustion fronts propagated.
  • a gaseous fuel containing 15% by volume of M-gas which exceeds the lower flammable limit concentration (12% by volume)
  • the gaseous fuel started burning promptly at the surface of the sintering bed and did not reach the lower layer of the sintering bed, thus providing no injection effect.
  • Figs. 29(a) to 29(d) summarize the results of the above sinter pot test.
  • the injection of the properly diluted M-gas into the mix sintering bed according to the present invention slightly improved the yield ( Fig. 29(a) ) and increased the sinter productivity ( Fig. 29(b) ) despite little change in sintering time.
  • the shutter index (SI) serving as a control measure of cold strength, which greatly affects the operational performance of a blast furnace, was improved by not less than 10% ( Fig. 29(c) ), and the reduction-degradation index (RDI) was improved by 8% ( Fig. 29(d) ).
  • a diluted flammable gas is used as the gaseous fuel introduced into the sintering bed.
  • the degree of dilution will now be described.
  • Table 10 shows the lower and upper flammable limit concentrations of blast furnace gas, coke oven gas, a mixture thereof (M-gas), propane, methane, and natural gas. For example, if a gas having such a flammable limit concentration flows toward a ventilator without burning in the sintering bed, it can explode or burn, for example, in an electrostatic precipitator.
  • the present inventors conducted, by trial and error, numerous experiments using gaseous fuels diluted to concentrations that pose no such risk, that is, concentrations at or below the lower flammable limit, for introduction into the sintering bed, and to ensure higher safety, using diluted gaseous fuels in concentrations of 75% or less of the lower flammable limit concentration. As a result, it was confirmed that no problem arose.
  • the lower flammable limit of the concentration range where blast furnace gas burns in air at normal temperature is 40% by volume. In other words, it does not burn in a concentration below 40% by volume.
  • the upper flammable limit is 71% by volume. This means that a blast furnace gas in a concentration above 71% by volume does not burn because of the excessive concentration.
  • Table 10 (vol%) Type of gas Lower flammable limit Upper flammable limit Blast furnace gas 40.0 71 Coke oven gas 5.0 22 Mixed gas (M-gas) 12.0 42 Propane 2.2 9.35 Methane 4.9 15.0 Natural gas 4.8 13.5
  • Fig. 30 shows an example of the method for determining the flammable limits of blast furnace gas.
  • the proportions of the combustible components (flammable gases) and others (inert gases) contained in blast furnace gas in the graph are as follows, where they are discussed on the basis of the combination of H 2 and CO 2 and the combination of CO and N 2 :
  • the flammable limit has temperature dependence. According to "Nenryo Binran (Handbook of Fuels)" (edited by the Fuel Society of Japan), as the effect of temperature, heat dissipation speed becomes lower at a higher temperature, so that the intersection of heat generation and dissipation speed curves becomes deeper, thus broadening the explosion range (combustion range) laterally.
  • the flammable limit has temperature dependence
  • "Nenryo Binran (Handbook of Fuels)" (edited by the Fuel Society of Japan) shows the example in Table 11 as the effect of temperature on the combustion range of methane gas. This can be used to draw a graph of the temperature dependence of the lower flammable limit concentration, as shown in Fig. 31 , where the black circles indicate the example of methane gas in Table 11.
  • Fig. 32 shows the relationship between temperature and the combustible component (combustion gas) concentration of the gaseous fuel in air at normal temperature.
  • the flammable limit can be determined as described above, the flammable limit has temperature dependence.
  • the lower flammable limit (corresponding to the combustion gas concentration in the graph), which is about 40% by volume at normal temperature, changes to 26% to 27% by volume in the range around 200°C and to several percents in the range around 1,000°C, and the gaseous fuel burns even in a concentration below 1% by volume in the range around 1,200°C.
  • the concentration (combustible component content) of the gaseous fuel supplied to the sintering bed is lower than the lower flammable limit at normal temperature and that the position where the gaseous fuel is combusted in the sintering bed in the thickness direction thereof can be controlled with increased flexibility only if the concentration of the diluted gas is adjusted to an appropriate range.
  • the combustion of the gaseous fuel has such temperature dependence and, for example, the combustion range becomes broader at a higher ambient temperature, and that a gaseous fuel in a concentration as shown in the preferred examples of the present invention burns well in the temperature field around the combustion and melting zone of the sintering machine but does not burn in a temperature field around 200°C, such as in an electrostatic precipitator disposed downstream of the sintering machine.
  • the diluted gaseous fuel supplied to the sintering bed of the sintering raw material is sucked through the wind boxes disposed below the pallet and is combusted in the high-temperature combustion and melting zone formed by combustion of the solid fuel (coke fines) in the sintering bed. Accordingly, the amount of coke fines in the sintering raw material can be adjusted (reduced) if the diluted gaseous fuel is supplied while controlling, for example, the concentration and amount of diluted gaseous fuel supplied with the calorific value supplied to the sintering bed remaining constant.
  • the concentration adjustment of the diluted gaseous fuel means to control the combustion of the gaseous fuel so that the combustion of the gaseous fuel occurs at the intended position (concentration region) in the sintering bed.
  • the combustion and melting zone in the sintering bed in the conventional art is a zone where only the solid fuel (coke fines) is combusted
  • the combustion and melting zone in the sintering bed in the present invention is a zone where the coke fines are combusted together with the gaseous fuel.
  • the supply conditions including the concentration and amount of diluted gaseous fuel supplied, are appropriately changed in relation to coke fines taking into account the presence of coke fines as part of the fuel, the ultimate maximum temperature and/or the high-temperature-zone holding time can be appropriately controlled for improved strength of sinter cake.
  • Another reason for using the diluted gaseous fuel in the method of the present invention is to control the strength and yield of sinter cake by controlling the form of the combustion and melting zone described above.
  • the diluted gaseous fuel plays an effective role in controlling how long the sinter cake is maintained in the high-temperature region (combustion and melting region) and what temperature is reached.
  • the use of the diluted gaseous fuel means to control the high-temperature-zone holding time in the sintering raw material so that it becomes longer and the ultimate maximum temperature so that it becomes moderately high.
  • Such control also means to use a gaseous fuel diluted and adjusted depending on the amount of solid fuel (amount of coke fines) in the sintering raw material so that the amount of combustion-supporting gas (air or oxygen) in the combustion atmosphere is not excessive or insufficient.
  • the amount of combustion-supporting gas (oxygen) matching the amount of solid fuel and flammable gas is not supplied because the flammable gas is injected irrespective of the amount of solid fuel in the sintering raw material and without adjusting the concentration of the flammable gas, and this results in insufficient combustion or, conversely, partial excessive combustion, thus causing variations in strength. That is, the present invention avoids that problem by the dilution and concentration adjustment of the gaseous fuel.
  • FIG. 33 shows the experimental results of a comparison between a sintering method of the present invention using several types of gaseous fuels diluted to a concentration at or below the lower flammable limit concentration and a conventional sintering method without injection of a gaseous fuel.
  • a conventional sintering method without injection of a gaseous fuel 5% by mass of coke fines were added.
  • the diluted gaseous fuel was injected in an amount equivalent to 0.8% by mass of coke fines, and accordingly 4.2% by mass of coke fines were added so that the total calorific value remained constant.
  • the shutter index, the product yield, and the productivity were improved in any of the examples using a diluted gaseous fuel.
  • the reason why the shutter index, the product yield, etc. were improved in the examples using a diluted gaseous fuel is that the combustion and melting zone was broadened, as shown in the combustion conditions, and accordingly the high-temperature-zone holding time was extended.
  • Fig. 34 shows graphs showing the effect of the injection gas concentration in the case where propane gas was used as the gaseous fuel, showing the relationships between the concentration of the diluted gaseous fuel and (a) the shutter index, (b) the yield, (c) the sintering time, and (d) the productivity.
  • the effect of improving the shutter index appears at 0.05% by volume, and the effect of improving the yield appears similarly.
  • propane gas a noticeable effect appears at 0.1% by volume or more, preferably 0.2% by volume.
  • the effect of C-gas appears at 0.24% by volume, preferably 0.5% by volume or more, and a noticeable improvement effect appears at 1.0% by volume or more.
  • the amount of propane gas added is at least 0.05% by volume or more, preferably 0.1% by volume or more, and more preferably 0.2% by volume or more.
  • the amount of C-gas added is at least 0.24% by volume or more, preferably 0.5% by volume or more, and more preferably 1.0% by volume or more, and the upper limit is 75% of the lower flammable limit.
  • propane gas the effect is almost saturated at 0.4% by volume, which is equivalent to 25% of the lower flammable limit.
  • RDI cold strength and reduction-degradation index
  • the prevent inventors conducted an experiment in which a propane gas diluted with exhaust gas from a sintering machine cooler was injected into a sintering bed of sintering raw material in a vertical cylindrical test pot with a transparent quartz window from above the pot.
  • the sintering raw material used in this experiment was a common sintering raw material used by the applicant company, and the suction pressure was maintained at 1,200 mmAq.
  • propane gases diluted to concentrations of 0.5% and 2.5% by volume were injected. In terms of the calorific value supplied, 0.5% by volume of propane injected is substantially equivalent to 1% by mass of coke fines.
  • Fig. 37 shows photographs showing the forms of combustion zones observed when propane gas was injected in this experiment.
  • the propane gas diluted to 2.5% by volume which is close to the lower flammable limit concentration (theoretical value, with respect to air), burned above the mix sintering bed immediately after the injection and did not enter the sintering bed, thus providing no gaseous fuel supply effect.
  • the propane gas diluted to a concentration of 0.5% by volume with respect to air entered the sintering bed without burning above the sintering bed and burned at high speed in the sintering bed.
  • the width (thickness) of the combustion zone in the vertical direction for sintering in air was about 70 mm
  • the width of the combustion zone for injection of the diluted propane gas was 150 mm, that is, not less than two times higher. This means that the high-temperature-zone holding time was extended.
  • the present inventors conducted a sinter pot experiment using a coke oven gas (C-gas) diluted to 2% as the gaseous fuel, where the diluted gaseous fuel was injected between positions 100 and 200 mm from the surface of the sintering bed, between positions 200 and 300 mm from the surface of the sintering bed, and between positions 300 and 400 mm from the surface of the sintering bed.
  • C-gas coke oven gas
  • the injection between positions 100 and 200 mm from the surface of the sintering bed, shown along the horizontal axis in Fig. 38 refers to an example in which the diluted gaseous fuel was injected and combusted during the period of time after the combustion and melting zone, looking bright (white) in the diagram, reaching a position 100 mm from the surface of the sintering bed, when the supply of the diluted gaseous fuel from above the test pot was started, until the combustion and melting zone reached a position 200 mm from the surface of the sintering bed.
  • the observation results of the propagation process of the combustion and melting zone (the combustion and melting zone looks bright (white) in the diagram) in this case are shown along the vertical axis.
  • the injection between positions 200 and 300 mm from the surface of the sintering bed refers to an example in which the diluted gaseous fuel was supplied and combusted during the period of time after the combustion and melting zone reaching a position 200 mm from the surface of the sintering bed until it reached a position 300 mm from the surface of the sintering bed
  • the injection between positions 300 and 400 mm from the surface of the sintering bed refers to an example in which the diluted gaseous fuel was supplied and combusted during the period of time after the combustion and melting zone reaching a position 300 mm from the surface of the sintering bed until it reached a position 400 mm from the surface of the sintering bed.
  • the thickness of the combustion and melting zone in the case where the diluted gaseous fuel was supplied while the combustion and melting zone was located in the region between positions 100 and 200 mm from the surface of the sintering bed was only slightly larger than in the conventional method.
  • the thickness of the combustion and melting zone in the case where the diluted gaseous fuel was supplied while the combustion and melting zone was located in the region between positions 200 and 300 mm from the surface of the sintering bed was noticeably larger than in the conventional method.
  • the diluted gaseous fuel is preferably injected into a portion where the combustion and melting zone is located in the region below a position 200 mm from the surface of the sintering bed.
  • the gaseous fuel does not have to be supplied to the region above a position 200 mm from the surface of the sintering bed because if the gaseous fuel is supplied to the region below a position 200 mm from the surface of the sintering bed, the shutter index of sintered ore in that region can be significantly improved, so that the yield of sintered ore products can be improved as a whole.
  • the cost of the gaseous fuel can also be reduced.
  • Fig. 39 schematically shows the combustion conditions of the upper layer above a position 200 mm from the surface of the charged layer and the middle and lower layers below a position 200 mm from the surface of the sintering bed.
  • Arrows A shown in the diagram indicate the direction in which sintering proceeds (fuel direction)
  • Fig. 39(a) shows the positions where coke fines and the gaseous fuel burned in the upper layer (less than 200 mm).
  • the temperature pattern shown to the right of the diagram is obtained because the combustion zone formed by the coke fine fuel is originally narrow in the upper portion of the sintering bed and is close to the point of combustion of the gaseous fuel combusted in the combustion zone.
  • the combustion zone of coke fines solid fuel
  • the temperature range where the gaseous fuel burns thereabove is shown as an unhatched portion.
  • the high-temperature-zone holding times (equivalent to about 1,200°C), denoted by T 1 and T 2 in the diagram, are short because the coke and the gaseous fuel burn concurrently (both burn in proximity to each other) in the upper portion of the sintering bed. That is, the coke combustion zone, shown as the hatched portion, is only slightly broadened.
  • Fig. 39(b) shows the case where the gaseous fuel was supplied to the middle and lower layers.
  • the combustion zone is broadened with increasing temperature in the sintering bed as the combustion zone propagates from top to bottom so that the gaseous fuel burns at a farther position than in the case in Fig. 39(a) .
  • the temperature distribution shown in the right of Fig. 39(b) is obtained. That is, the combined temperature distribution curve shows a broad temperature distribution because the point of combustion of the gaseous fuel is remote from the point of combustion of the solid fuel (coke), shown by hatching.
  • the high-temperature-zone holding time based on the combustion of the solid fuel and the gaseous fuel denoted by T 3 and T 4 , is extended so that the resultant sintered ore has improved shutter index.
  • the ignition temperature of the gaseous fuel for controlling (extending) the high-temperature-zone holding time is preferably 400°C to 800°C, more preferably 500°C to 700°C. The reason is that if the ignition temperature falls below 400°C, it is only possible to broaden the low-temperature range distribution, rather than the high-temperature range, and if the ignition temperature exceeds 800°C, the effect of extending the high-temperature-zone holding time is small because the high-temperature-zone holding time is excessively close to that due to the combustion of the solid fuel and only results in a rise in ultimate maximum temperature.
  • Fig. 40 shows the measurement results of the temperature profile of a test pot during sintering, where the example shown to the left is a conventional sintering method using coke fines alone, and the example shown to the right is a method using a diluted town gas (LNG).
  • LNG diluted town gas
  • the coke fines burned at the lower end of the combustion zone, LNG burned in the portion thereabove, and a region where the temperature was slightly lower was present between the position where the coke fines burned (the lower end of the combustion zone) and the position where the LNG burned (the portion above the melting zone). If LNG is combusted so that the region where the temperature is slightly lower reaches a temperature of 1,200°C or more, the region where the temperature is 1,200°C or more is extensively distributed while the maximum temperature is lowered due to the reduced amount of coke fines used. As a result, the high-temperature-zone holding time is extended.
  • Fig. 41 summarizes the temperature histories during the sintering based on the above thermoviewer results.
  • the area of the region where the temperature was 1,200°C or more could be increased to about twice that in the case where sintering was performed using coke fines alone without the maximum temperature exceeding 1,400°C, preferably 1,380°C.
  • two peaks were observed in the temperature pattern: the first peak (peak closer to the upper layer of the mix bed) is due to the combustion of LNG injected into the portion above the coke combustion zone, and the second peak (peak closer to the lower layer of the mix bed) is due to the combustion of coke. It is assumed that the temperature pattern resulted from the combination of the temperature variations due to their combustion.
  • the ultimate maximum temperature due to the combustion of coke was controlled by combusting the coke and the injected town gas at different positions in combination (second peak), and the region therebetween was maintained at 1,200°C or more by the subsequent combustion of LNG (first peak), so that the high-temperature-retained region where the temperature was 1,200°C or more, forming the combustion and melting zone effective in forming sintered ore, was significantly broadened.
  • the high-temperature-zone holding time in the combustion and melting zone was continuously extended, thus significantly improving the strength of sintered ore products.
  • FIG. 42 schematically shows temperature distributions in sintering beds during sintering, illustrating a sintering method according to the present invention in which a diluted C-gas is injected and the amount of coke is correspondingly reduced, where a temperature distribution obtained by adding 5% by mass of solid fuel (coke fines), which corresponds to a conventional sintering method, serves as a reference.
  • curve a indicates the relationship between in-bed temperature and time for the conventional sintering method in which sintering is performed by adding 5% by mass of coke.
  • the high-temperature-zone holding time is extended by increasing the amount of coke fines added. For example, as indicated by the curve for the case where 10% by mass of coke fines are added, namely, broken line b, the high-temperature-zone holding time is increased from (0-A) to (0'-B) if the amount of coke is increased. At the same time, however, the ultimate maximum temperature rises from about 1,300°C to about 1,400°C, and therefore a sintered ore having low RDI and high strength cannot be achieved.
  • the sinter operation process according to the method of the present invention in which a diluted C-gas is injected while reducing the amount of coke fines to 4.2% by mass, can limit the ultimate maximum temperature to 1,380°C while increasing the high-temperature-zone holding time to (0-C), thus sufficiently achieving the initial object, that is, the production of a sintered ore having low RDI and high strength that is not achieved by a conventional method.
  • conventional sintering methods are operating methods focusing on either the high-temperature-zone holding time or the maximum temperature control.
  • the method of the present invention is an operating method for adjusting the high-temperature-zone holding time by injecting a diluted gaseous fuel while adjusting the ultimate maximum temperature (to 1,205°C to 1,380°C) by adjusting the amount of coke fines used (for example, to 4.2% by mass).
  • Curve d in Fig. 40 indicating an example in which the amount of solid fuel used is simply reduced to 4.2% by mass, has a low ultimate maximum temperature and a short high-temperature-zone holding time.
  • Fig. 43 shows the combustion conditions of an example of a conventional sintering method using 5% by mass of coke fines and an example according to the present invention using 4.2% by mass of coke fines in combination with injection of a C-gas diluted to a concentration of 2.0% by volume.
  • a combustion condition exceeding 1,400°C occurred in the conventional method.
  • a C-gas in a concentration of 2% by volume was injected while reducing the amount of coke fines used to 4.2% by mass, it was found that the high-temperature-zone holding time could be extended while limiting the ultimate maximum temperature to 1,380°C or less without forming a 1,400°C region.
  • Fig. 44 shows changes over time in (a) the temperature in the sintering bed, (b) the temperature of exhaust gas, (c) the volume of air passed, and (d) the composition of exhaust gas due to injection of a diluted propane gas with the calorific value supplied remaining constant.
  • the temperature in the sintering bed was measured in the above test pot using a thermocouple inserted to a position 400 mm below the surface of the sintering bed (sintering bed thickness: 600 mm) at two positions in the circumferential direction of the test pot, namely, the center and a position 5 mm from the wall.
  • Fig. 45 shows changes over time in (a) the temperature in the sintering bed and (b) the temperature of exhaust gas in the case where a diluted propane gas was injected (0.5% by volume) in contrast with changes over time in (a') the temperature in the sintering bed and (b') the temperature of exhaust gas in the case where the amount of coke was increased (10% by mass).
  • the high-temperature-zone holding time that is, the time during which the temperature was 1,200°C or more, was substantially equivalent to that in the case where the propane gas diluted to a concentration of 0.5% by volume was injected, although the ultimate maximum temperature exceeded 1,380°C.
  • the increase in the amount of coke fines significantly increased the CO 2 concentration of the exhaust gas, namely, from 20% to 25% by volume, and also increased the CO concentration, demonstrating that the contribution of coke fines to combustion was decreased.
  • Test No. 1 serving as the current base conditions, 5% by mass of coke was added to a sintering raw material.
  • Test No. 2 the amount of coke fines was decreased by 1% by mass, namely, to 4% by mass, and 0.5% by volume of propane gas was injected instead so that the calorific value supplied remained constant.
  • Test No. 3 10% by mass of coke fines were added.
  • Test No. 4 high-temperature gas at 450°C was injected for the purpose of verifying the difference from a heat-retaining furnace (Japanese Unexamined Patent Application Publication No. 60-155626 ).
  • Fig. 46 summarizes the results of various property tests in these tests.
  • the injection of the diluted propane gas slightly extended the sintering time but improved the yield, the shutter index (SI), and the productivity and also significantly improved the reduction-degradation index (RDI) and the reducibility index (RI).
  • RDI reduction-degradation index
  • RI reducibility index
  • the gas burns in the sintering bed to broaden the combustion zone in the bed, and a broad combustion zone is formed by the synergy between combustion heat from the coke in the sintering raw material and combustion heat from the diluted propane gas.
  • the high-temperature-zone holding time can be extended without excessively raising the ultimate maximum temperature.
  • the present inventors examined the effect of the injection of a diluted gaseous fuel on the reducibility, cold strength, etc. of sintered ore products in contrast with conventional methods (5% by mass of coke, 10% by mass of coke, and hot air injection).
  • the measured items were the ore phase composition (which affects the cold strength and the reducibility), the apparent specific gravity (which affects the cold strength), and the distribution of pores with diameters of 0.5 mm or less (which affects the reducibility) of sintered ore products.
  • Fig. 47 shows the examination results of the ore phase compositions of the sintered ore products determined by powder X-ray diffractometry. This graph shows that calcium ferrite formed stably when the solid fuel and the diluted propane gas were used in combination with the calorific value supplied remaining constant (4% by mass of coke and 0.5% by volume of propane), which contributes to improved reducibility and increased cold strength.
  • Fig. 48 shows the measurement results of variations in the apparent specific gravity of the sintered ore products with and without injection of propane gas
  • Fig. 47 shows the measurement results of variations in the distribution of pores with diameters of 0.5 mm or less measured using a mercury intrusion porosimeter with and without injection of propane gas.
  • Fig. 46 shows that the injection of the propane gas increased the apparent specific gravity. This is because the injection of the propane gas caused the granulated particles to be externally heated to facilitate melt flow, thus decreasing the porosity for pores with diameters of 0.5 mm or more. This result contributes to improved cold strength.
  • Fig. 49 shows that the injection of the diluted propane gas with the calorific value supplied remaining constant increased the distribution of pores with diameters of 0.5 mm or less. This is because the heat source in the sintering raw material particles was reduced so that more ore-derived fine pores with diameters of 500 ⁇ m or less, which affect the reducibility, remained. This allows production of a sintered ore with high reducibility.
  • Fig. 50 schematically shows sintering behaviors in (a) the case where coke is used alone and (b) the case where coke is used in combination with a diluted gaseous fuel.
  • the quasi-particles are internally heated by combustion of coke fines in the conventional sintering method using coke alone
  • the quasi-particles are also externally heated by combustion of the gaseous fuel in the method using coke and the gaseous fuel in combination according to the present invention. This allows more fine pores in the ore to remain so that the reducibility index (RI) can be made relatively high despite low RDI.
  • Fig. 51 schematically shows variations in the pore distribution of sintered ore in the case where a diluted gaseous fuel is injected. As shown in this graph, it is effective in improving the productivity of sintered ore to reduce the number of pores having diameters of 0.5 to 5 mm, which affect the yield and the cold strength, by facilitating integration thereof, and to increase the proportion of pores having diameters of 5 mm or more, which affect the permeability. In addition, to improve the reducibility of sintered ore, it is preferable to form a porous structure in which more fine pores having diameters of 0.5 mm or less, mainly present in iron ore, remain. In this regard, according to the present invention, a sintered ore having a porous structure closer to the ideal porous structure can be achieved by injecting a diluted gaseous fuel.
  • Fig. 52 shows the results of a test for determining a critical coke proportion at which the desired cold strength can be maintained.
  • the critical coke proportion is defined as the amount of coke added in which the shutter index (SI) is equivalent to the maximum value (73%) obtained without using a diluted propane gas.
  • SI shutter index
  • 73%) the maximum value obtained without using a diluted propane gas.
  • the coke proportion at which the same cold strength as the current cold strength (shutter index of 73%) could be achieved was decreased from 5% by mass to 3% by mass (about 20 kg/t), as shown in Fig. 50(a) .
  • the coke proportion at which a yield of 74% and a productivity of 1.86 t/hr ⁇ m 2 were achieved were decreased from 5% by mass to 3.5% by mass.
  • the present invention provides the effect of broadening the function of the combustion and melting zone in the sintering bed by supplying a gaseous fuel appropriately diluted depending on the amount of carbonaceous material contained to an appropriate position while the combustion and melting zone propagates from the surface layer to the lower layer of the sintering bed as the pallet moves, thereby improving the quality of sintered ore and the productivity.
  • a sinter pot test of a sintering raw material containing 5% by mass of carbonaceous material (coke) using the test pot shown in Fig. 28 was carried out using coke oven gases (C-gases) diluted to 1 to 2.5% by volume as gaseous fuels, where the other conditions were the same as the experimental conditions described above (paragraph 0099).
  • C-gases coke oven gases
  • the results are shown in Fig. 51 .
  • a sinter pot test of a sintering raw material containing 5% by mass of carbonaceous material (coke) was carried out using propane gases diluted to 0.02 to 0.5% by volume as diluted gaseous fuels, where the other conditions were the same as those of Example 1.
  • the results are shown in Fig. 52 .
  • As shown in the diagram it was found that if a propane gas diluted according to the method of the present invention is used, increasing the concentration of propane gas significantly increases the width (thickness) of the combustion zone and also improves the yield, the productivity, and the cold strength (SI).
  • sintering pot tests (Nos. 2 to 7) using the test pot shown in Fig. 28 were carried out by injecting coke oven gases (C-gases) diluted to two levels, namely, 1.0% by volume and 2.0% by volume (with respect to air), with cooler exhaust gas from above the pot into sintering beds of sintering raw varietiess whose coke fine contents were at two varying levels, namely, 4.9% by mass and 4.8% by mass (excluded from the total).
  • C-gases coke oven gases
  • sintering raw substances whose coke fine contents were at two varying levels, namely, 4.9% by mass and 4.8% by mass (excluded from the total).
  • a sintering pot test (No. 1) in which the coke fine content was 5.0% by mass (excluded from the total) and no diluted gas was injected was similarly carried out.
  • the total thickness of the sintering raw material charged into the test pot was 600 mm, the sintering raw varietiess containing coke fines were deposited in the upper layer extending 400 mm from the surface of the sintering bed, and return ore was deposited in the lower layer extending 200 mm therebelow.
  • the above diluted C-gases were introduced into the sintering bed when the combustion and melting zone was located between positions 100 and 200 mm from the surface of the sintering bed, between positions 200 and 300 mm from the surface of the sintering bed, and between positions 300 and 400 mm from the surface of the sintering bed at a suction pressure of 1,200 mmAq (pressure difference: 1,000 mmAq).
  • the injection between positions 200 and 300 mm from the surface of the sintering bed is equivalent to an example in which a sinter operation is carried out using a 13.3 m long gaseous fuel supply unit disposed between positions 26.6 and 39.9 m from the origin of movement of the pallet
  • the injection between positions 300 and 400 mm from the surface of the sintering bed is equivalent to an example in which a sinter operation is carried out using a 13.3 m long gaseous fuel supply unit disposed between positions 39.9 and 53.2 m from the origin of the movement of the pallet.
  • Table 15 shows the results of the above sintering pot tests. According to these results, the invention examples in which the gaseous fuel was injected, namely, Nos. 2 to 7, had improved cold strengths (SI strengths) of sintered ore and yields as compared to the comparative example in which no gaseous fuel was injected, namely, No. 1, and particularly, the improvement was significant in Nos. 3, 4, 6, and 7, in which the gaseous fuel was injected into the middle or lower layer of the sintering bed. In addition, it was found that the productivity is highest if the amount of coke is 4.9% by mass and the C-gas concentration is 1% by volume.
  • the method for producing sintered ore according to the present invention was applied to a DL sintering machine with a daily production of 20,000 tons.
  • the DL sintering machine used had a length of 90 m from an ignition furnace to a discharge section, and a gaseous fuel supply unit was disposed at a position about 30 m behind the ignition furnace of the sintering machine.
  • This gaseous fuel supply unit included nine gaseous fuel supply pipes having a length of 15 m (in the movement direction of the pallet) and arranged in parallel along the movement direction of the pallet at a height of 500 mm above the sintering bed.
  • Each pipe had 149 nozzles, for ejecting a gaseous fuel downward, arranged at intervals of 100 mm (1,341 nozzles in total).
  • town gas was ejected from the nozzles into air at high speed so as to be supplied to the sintering bed as a diluted gaseous fuel having a town gas concentration of 0.8% by volume.
  • the total thickness of the sintering bed was 600 mm (where a sintering raw material containing 4.2% by mass of coke fines was deposited in the upper layer extending 400 mm from the surface of the sintering bed).
  • the position where the gaseous fuel was supplied is equivalent to the position where the combustion and melting zone is located between positions 200 and 300 mm from the surface of the sintering bed.
  • the diluted gaseous fuel, supplied as described above, was sucked and introduced into the sintering bed by suction negative pressure control of wind boxes located below the pallet of the sintering machine and was combusted through the sintering bed in the combustion and melting zone present at the position described above.
  • the amount of C-gas used was 3,000 m 3 (standard state)/hr.
  • the sintered ore yielded by the operation of the actual sintering machine had, as a whole, a tumbler index (TI) about 3% higher than that of a normal operation, a reduction-degradation index (RDI) about 3% higher than that of a normal operation, and a reducibility index (RI) about 4% higher than that of a normal operation.
  • the productivity was increased by 0.03 t/hr ⁇ m 2 .
  • the technique of the present invention is useful as a technique for producing a sintered ore used as a raw material for steelmaking, particularly for blast furnaces, although it can also be used as a technique for agglomerating other types of ores.

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WO2018151024A1 (fr) * 2017-02-16 2018-08-23 Ｊｆｅスチール株式会社 Procédé de fabrication de minerai fritté
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CN109526305B (zh) * 2018-11-21 2021-05-04 广东海洋大学 一种水稻耐盐碱性种质筛选用实验台
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AU2008360794A1 (en) 2010-02-25
KR101387811B1 (ko) 2014-04-21
CN102131941B (zh) 2013-07-17
BRPI0823086A2 (pt) 2016-11-08
TW201009090A (en) 2010-03-01
EP2322675A4 (fr) 2016-07-27
AU2008360794B8 (en) 2013-03-28
CN102131941A (zh) 2011-07-20
WO2010021065A1 (fr) 2010-02-25
EP2322675B1 (fr) 2018-03-07
JP4735682B2 (ja) 2011-07-27
TWI409339B (zh) 2013-09-21
AU2008360794B2 (en) 2013-03-07
JP2010047801A (ja) 2010-03-04

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