Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B5/00—Making pig-iron in the blast furnace
  • C21B5/001—Injecting additional fuel or reducing agents
  • C21B5/003—Injection of pulverulent coal
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21B—MANUFACTURE OF IRON OR STEEL
  • C21B7/00—Blast furnaces
  • C21B7/16—Tuyéres
  • C21B7/163—Blowpipe assembly
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D3/00—Charging; Discharging; Manipulation of charge
  • F27D3/16—Introducing a fluid jet or current into the charge
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F27—FURNACES; KILNS; OVENS; RETORTS
  • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
  • F27D3/00—Charging; Discharging; Manipulation of charge
  • F27D3/16—Introducing a fluid jet or current into the charge
  • F27D2003/168—Introducing a fluid jet or current into the charge through a lance
  • F27D2003/169—Construction of the lance, e.g. lances for injecting particles

Definitions

• the present invention relates to a method for operating a blast furnace that includes injecting pulverized coal through a blast furnace tuyere to increase the combustion temperature, thereby improving productivity and reducing CO 2 emissions.
• Patent Literature 1 discloses that the combustion efficiency can be improved by using pulverized coal having a volatile matter content of 25 mass% or less at a pulverized coal ratio of 150 kg/t-pig iron or more, supplying the pulverized coal and oxygen to a lance for injecting a fuel through a tuyere, and increasing the oxygen concentration in the lance to 70% by volume or more.
• Patent Literature 1 it is also proposed in Patent Literature 1 that in the case of a single-tube lance a mixture of oxygen and pulverized coal is injected through the single-tube lance, and in the case of a double wall lance pulverized coal is injected through an inner tube of the double wall lance, and oxygen is injected through an outer tube of the double wall lance.
• the pulverized coal ratio is the mass of pulverized coal used per ton of pig iron.
• Patent Literature 2 discloses that a reaction between pulverized coal and oxygen is promoted by dispersing the pulverized coal utilizing asperities formed on an outer tube of a double wall lance.
• Patent Literature 3 discloses that in a double wall lance for injecting pulverized coal through an inner tube thereof and oxygen through an outer tube thereof the contact between pulverized coal and oxygen is improved by shortening the inner tube relative to the outer tube, that is, placing a pulverized coal injecting front end of the inner tube upstream from an oxygen injecting front end of the outer tube in the injecting direction.
• JP 2000 192119 A describing a blowing method of auxiliary fuel into a blast furnace by which the auxiliary fuel is blown into the blast furnace from an auxiliary fuel blowing tuyere. Further related art may also be found in CN 102 268 496 A .
• a gas flowing through an outer tube of a double wall lance also functions to cool the outer tube.
• an obstacle that interferes with the gas flow such as the asperities formed on the outer tube in Patent Literature 2
• a heat load is applied to a slow flow region, possibly causing wear damage, such as cracking or a melting loss.
• wear damage may induce backfire or clogging of a lance.
• An increase in the amount of pulverized coal inevitably causes a problem of abrasion of a raised portion due to pulverized coal injected through an inner tube.
• Patent Literature 3 Although shortening the front end of the inner tube of the double wall lance relative to the outer tube of the double wall lance as described in Patent Literature 3 may improve the contact between pulverized coal and oxygen, an oxygen flow suppresses the dispersion of pulverized coal, and the combustibility of pulverized coal is not sufficiently improved.
• the present invention has paid attention to these problems and aims to provide a blast furnace operation method for increasing the combustion temperature and thereby reducing CO 2 emissions.
• the method includes injecting pulverized coal together with a carrier gas through an inner tube of the double wall lance, injecting a combustion-supporting gas through an outer tube of the double wall lance, and forming notches in a injecting front end of the inner tube of the double wall lance, wherein the concentration of oxygen in a gas composed of the carrier gas and the combustion-supporting gas in the double wall lance is 35% by volume or more and less than 70% by volume.
• the notches circumferentially evenly spaced in the front end of the inner tube of the double wall lance improve the diffusion of pulverized coal and the combustion-supporting gas and further improve combustion efficiency
• Injecting part of oxygen for enrichment into a blast as a combustion-supporting gas through the outer tube of the double wall lance can prevent excess oxygen supply without disturbing the gas balance in the blast furnace.
• Fig. 1 is an overall view of a blast furnace to which a blast furnace operation method according to the present embodiment is applied.
• a tuyere 3 of a blast furnace 1 is coupled to a blow pipe 2 for blowing hot air, and a lance 4 is inserted in the blow pipe 2.
• a combustion space called a raceway 5 is disposed over a coke layer in front of the tuyere 3 in a hot air blowing direction. Combustion and gasification of a reducing material occur mainly in this combustion space.
• Fig. 2 illustrates the combustion state when only pulverized coal 6 is injected as a solid reducing material through the lance 4.
• the pulverized coal 6 is injected from the lance 4 into the raceway 5 through the tuyere 3.
• the volatile matter and fixed carbon of the pulverized coal 6 burn together with coke 7.
• an aggregate of carbon and ash which is generally called char, is discharged from the raceway as unburned char 8.
• the hot air velocity in front of the tuyere 3 in the hot air blowing direction is approximately 200 m/sec.
• An oxygen zone extends approximately 0.3 to 0.5 m from a front end of the lance 4 into the raceway 5.
• Fig. 3 illustrates the combustion mechanism in the case that only the pulverized coal (PC in the figure) 6 is injected into the blow pipe 2 through the lance 4.
• Particles of the pulverized coal 6 injected into the raceway 5 through the tuyere 3 are heated through radiative heat transfer from flames in the raceway 5.
• the temperature of the particles increases rapidly through radiative heat transfer and conductive heat transfer.
• the particles start to decompose at a temperature of 300°C or more.
• the volatile matter of the particles ignites and forms a flame.
• the combustion temperature reaches a temperature in the range of 1400°C to 1700°C.
• the char 8 remains. Since the char 8 is mainly composed of fixed carbon, a combustion reaction is accompanied by a carbon dissolution reaction, such as a solution-loss reaction or a hydrogen gas shift reaction.
• a combustion experiment was performed with a combustion experimental apparatus illustrated in Fig. 5 .
• Imitating the interior of a blast furnace an experiment furnace 11 is filled with coke, and the interior of a raceway 15 can be observed through an observation window.
• a lance 14 is inserted in a blow pipe 12.
• a hot air blown from an air-heating furnace to the blast furnace a hot air produced by a combustion burner 13 can be blasted into the experiment furnace 11 at a predetermined blast rate.
• the oxygen enrichment level of the blast air can be controlled with the blow pipe 12.
• One or both of pulverized coal and oxygen can be injected into the blow pipe 12 through the lance 14.
• An exhaust gas from the experiment furnace 11 is separated into an exhaust gas and dust in a separator 16 called cyclone.
• the exhaust gas is sent to an exhaust gas treatment system, such as an auxiliary combustion furnace.
• the dust is collected in a collecting box 17.
• the pulverized coal is composed of fixed carbon (FC) 71.4%, volatile matter (VM) 19.5%, and ash 9.1%.
• the blast conditions include a blast temperature of 1200°C, a flow rate of 300 Nm 3 /hr, a blast velocity of 130 m/sec at a front end of the tuyere, and an oxygen enrichment of 6% (an oxygen concentration of 27.0%, an enrichment of 6.0% relative to an oxygen concentration of 21% in air).
• the lance 14 was a double wall lance
• pulverized coal was injected through an inner tube of the double wall lance
• oxygen was injected as a combustion-supporting gas through an outer tube of the double wall lance.
• Pulverized coal was carried by a carrier gas.
• the carrier gas for pulverized coal was nitrogen.
• the solid-gas ratio of pulverized coal to a carrier gas for carrying pulverized coal ranges from 10 to 25 kg/Nm 3 in the case that a powder, that is, pulverized coal is carried by a small amount of gas (high concentration transport) or 5 to 10 kg/Nm 3 in the case that pulverized coal is carried by a large amount of gas (low concentration transport).
• the carrier gas may also be air.
• An experiment was conducted with a focus on variations in pulverized coal flow at a pulverized coal ratio in the range of 100 to 180 kg/t.
• oxygen was injected as a combustion-supporting gas, part of oxygen for enrichment was included in the blast so as not to change the total amount of oxygen blown into the furnace.
• the combustion-supporting gas may also be an oxygen-enriched air.
• the present inventors found the following in this experiment.
• a combustion-supporting gas that is, oxygen
• the combustion temperature is increased by increasing the oxygen concentration in an operation at a low pulverized coal ratio of less than 150 kg/t even if the pulverized coal has a volatile matter content of 25 mass% or less.
• the combustion temperature is not increased by increasing the oxygen concentration.
• the pulverized coal ratio is 150 kg/t or more, the combustion temperature levels off at an oxygen concentration of approximately 35% by volume.
• pulverized coal injected through the inner tube of the double wall lance localizes (or is concentrated) in the center of a blast flow and rarely or does not come into contact with oxygen injected through the outer tube of the double wall lance.
• the present invention is the same as the related art in that pulverized coal is injected through an inner tube of a double wall lance and a combustion-supporting gas, for example, oxygen is injected through an outer tube of the double wall lance.
• notches formed in a injecting front end of an inner tube of a double wall lance can improve the diffusion of pulverized coal and a combustion-supporting gas and thereby promote contact between the pulverized coal and the combustion-supporting gas and increase the combustion temperature.
• the combustion temperature also levels off at an oxygen concentration of 70% by volume or more in the lance.
• an oxygen concentration of more than 70% by volume does not contribute to high combustion efficiency and results in an increased specific oxygen consumption.
• the notches formed in the inner tube of the double wall lance have no wear damage trouble.
• pulverized coal in an operation at a high pulverized coal ratio of 170 kg/t or more, pulverized coal is highly concentrated in the center of the pulverized coal flow. Since oxygen is injected through the outer tube of the double wall lance, pulverized coal concentrated in the center of the pulverized coal flow does not come into contact with oxygen, and such unburned pulverized coal injected into the furnace interferes with aeration in the blast furnace. Even if the amount of oxygen blown is increased to promote contact with oxygen, when the amount of oxygen blown exceeds a certain threshold, as illustrated in Fig. 6(c) , the pulverized coal flow is further concentrated in the center of the surrounding oxygen flow. Thus, the contact with oxygen is not substantially promoted, and the combustion temperature levels off as described later.
• Fig. 7 illustrates the details of a injecting front end of the double wall lance 4 according to the present embodiment.
• Fig. 7(a) is a longitudinal sectional view
• Fig. 7(b) is a cross-sectional view taken along the line A-A in Fig. 7(a) .
• notches 23 are formed in a injecting front end of an inner tube 21 of the double wall lance 4. Pulverized coal 6 and a combustion-supporting gas oxygen 9 diffuse through the notches 23. This allows efficient contact between the pulverized coal 6 and the oxygen 9 and increases the combustion temperature.
• notches 23 When the inner tube 21 has an inner diameter of approximately 16 mm, four notches 23 each having an approximately 5 mm x 5 mm square cross section are circumferentially evenly spaced in the inner tube 21 at intervals of 90 degrees.
• An outer tube 22 is a straight tube.
• the shape of the notches 23 is not limited to the shape described above and may be triangular or U-shaped as described below. The number of the notches 23 is also not limited to four.
• the pulverized coal 6 and the combustion-supporting gas oxygen 9 can diffuse through the notches 23 formed in the injecting front end of the inner tube 21 of the double wall lance 4 and come into contact with each other, thereby increasing the combustion temperature.
• pulverized coal 6 is concentrated in a central portion of a combustion-supporting gas oxygen 9. This results in poor contact between the pulverized coal 6 and the oxygen 9, and the combustion temperature levels off.
• the notches 23 formed in the inner tube 21 of the double wall lance 4 have no wear damage trouble.
• Fig. 9 shows the combustion temperature represented by the combustion rate under the conditions that the pulverized coal ratio is 150 kg/t, the volatile matter of the pulverized coal is 25 mass% or less, the blast conditions are fixed, the oxygen enrichment ratio is fixed, and the injecting front end of the inner tube 21 of the double wall lance 4 has the notches 23 or no notch.
• pulverized coal is injected through the inner tube of the double wall lance 4, and a combustion-supporting gas oxygen is injected through the outer tube of the double wall lance 4.
• the combustion temperature levels off when the concentration of oxygen in a gas composed of the carrier gas and the combustion-supporting gas in the lance is 70% by volume or more, and the combustion temperature is not increased at an oxygen concentration of more than 70% by volume.
• the concentration of oxygen in the gas composed of the carrier gas and the combustion-supporting gas in the lance is 70% by volume or more, the combustion efficiency is not improved at a pulverized coal ratio of 170 kg/t or more, although the specific oxygen consumption increases.
• the concentration of oxygen in the gas composed of the carrier gas and the combustion-supporting gas is 35% by volume or more and less than 70% by volume, preferably 40% by volume or more and 65% by volume or less, more preferably 45% by volume or more and 60% by volume or less, at a pulverized coal ratio of 150 kg/t or more and less than 170 kg/t or a pulverized coal ratio of 170 kg/t.
• the upper limit of the pulverized coal ratio is 300 kg/t or less, preferably 250 kg/t or less.
• the shape of the notches 23 in the inner tube 21 viewed in the radial direction may be tetragonal as illustrated in Fig. 11(a) , triangular as illustrated in Fig. 11(b) , or U-shaped as illustrated in Fig. 11(c) .
• the size of the notches 23 is represented by the opening width of the notches 23 and the depth of the notches 23 from the opening to the bottom thereof.
• the angle ⁇ made by the center of the front end and the center of the lower end of each of the notches 23, more specifically the angle ⁇ of a line segment between the center of the opening and the center of the bottom of each of the notches 23 with respect to a chord of the opening preferably ranges from 30 to 90 degrees.
• Fig. 14 illustrates the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal as a function of the notch width.
• the notch width was represented by the ratio of the total width of the notches to the internal circumference of the inner tube.
• the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal were represented by ratios based on the case of the inner tube having no notch.
• the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal increased with increasing notch width.
• the dispersion width of the pulverized coal began to decrease at a certain notch width.
• the ratio of the total width of the notches to the circumference of the inner tube is preferably more than 0 and 0.5 or less, more preferably 0.05 or more and 0.3 or less, still more preferably 0.1 or more and 0.2 or less.
• Fig. 15 illustrates the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal as a function of the notch depth.
• the notch depth was represented by the depth itself.
• the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal was represented by ratios based on the case of the inner tube having no notch.
• the contact area between oxygen and pulverized coal and the dispersion width of the pulverized coal increased with increasing notch depth.
• the dispersion width of the pulverized coal began to decrease at a certain notch depth.
• the lance is a stainless steel pipe, for example.
• a lance is sometimes surrounded by a water jacket and is cooled with water, a front end of the lance cannot be surrounded by the water jacket.
• a front end of an outer tube of a double wall lance that cannot be cooled with water is likely to change its shape with heat.
• a pulverized coal flow may be changed and hit a tuyere, thereby causing damage to the tuyere.
• a bent outer tube of a double wall lance may block a gap between the outer tube and an inner tube of the lance.
• a blockage in the outer tube may result in a melting loss of the outer tube of the double wall lance or may cause damage to a blow pipe. Deformation or wear damage of a lance makes it difficult to achieve the desired combustion temperature and decrease the specific consumption of a reducing material.
• the outer tube of the double wall lance was a steel pipe called 20A schedule 5S.
• the inner tube of the double wall lance was a steel pipe called 15A schedule 90.
• the lance surface temperature was measured while changing the total flow velocity of oxygen and nitrogen injected through the outer tube.
• the terms "15A” and “20A” refer to the nominal outer diameter of a steel pipe according to JIS G 3459.
• 15A denotes an outer diameter of 21.7 mm
• 20A denotes an outer diameter of 27.2 mm.
• the term “schedule” is the nominal thickness of a steel pipe according to JIS G 3459.
• 20A schedule 5S denotes a thickness of 1.65 mm
• 15A schedule 90 denotes a thickness of 3.70 mm.
• plain steel may also be used.
• the outer diameter of a steel pipe is specified in JIS G 3452
• the thickness of the steel pipe is specified in JIS G 3454.
• the lance surface temperature decreases in inverse proportion to the flow velocity of a gas injected through the outer tube of the double wall lance.
• a double wall lance surface temperature of more than 880°C results in creep deformation and a bending of the double wall lance.
• the outlet flow velocity in the outer tube of the double wall lance is 20 m/sec or more.
• the double wall lance has no deformation or bending.
• An outlet flow velocity of more than 120 m/sec in the outer tube of the double wall lance is not practical in terms of the operating cost of the equipment.
• 120 m/sec is the upper limit of the outlet flow velocity in the outer tube of the double wall lance.
• the outlet flow velocity may be 20 m/sec or more, if necessary.
• the pulverized coal may have an average particle size in the range of 10 to 100 ⁇ m. Considering combustibility as well as supply from the lance and supply to the lance, the pulverized coal preferably has an average particle size in the range of 20 to 50 ⁇ m. Although pulverized coal having an average particle size of less than 20 ⁇ m has high combustibility, the lance is often clogged during transport of the pulverized coal (pneumatic transport). Pulverized coal having an average particle size of more than 50 ⁇ m may have low combustibility.
• Pulverized coal injected through the inner tube of the double wall lance may be coal having a volatile matter content of 25 mass% or less or anthracite coal, which can be used as a solid reducing material.
• Anthracite coal has a volatile matter content in the range of 3 to 5 mass%.
• pulverized coal used in the present invention is referred to as pulverized coal having a volatile matter content of 3 mass% or more and 25 mass% or less, including anthracite coal.
• a solid reducing material to be injected mainly contains pulverized coal and may also contain a waste plastic, refuse-derived fuel (RDF), organic resource (biomass), scrap wood, and/or CDQ coke dust.
• CDQ coke dust is coke breeze collected by a coke dry quenching (CDQ) apparatus.
• CDQ coke dust is coke breeze collected by a coke dry quenching (CDQ) apparatus.
• CDQ coke dry quenching
• the ratio of pulverized coal to all the solid reducing material is preferably 80 mass% or more.
• the heat of reaction of pulverized coal is different from the heat of reaction of a waste plastic, refuse-derived fuel (RDF), organic resource (biomass), scrap wood, or CDQ coke dust.
• the calorific value of a combustion reaction of a waste plastic, refuse-derived fuel (RDF), organic resource (biomass), or scrap wood is lower than the calorific value of a combustion reaction of pulverized coal.
• RDF refuse-derived fuel
• biomass organic resource
• scrap wood is lower than the calorific value of a combustion reaction of pulverized coal.
• injecting a large amount of the auxiliary material results in low substitution efficiency for the solid reducing material charged through the top of the furnace.
• CDQ coke dust has a high calorific value
• CDQ coke dust contains no volatile matter, is difficult to ignite, and has low substitution efficiency.
• pulverized coal preferably accounts for 80 mass% or more.
• a waste plastic, refuse-derived fuel (RDF), organic resource (biomass), or scrap wood may be used in the form of small grains having a size of 6 mm or less, preferably 3 mm or less, in combination with pulverized coal.
• CDQ coke dust may be directly used.
• the auxiliary material may be mixed with pulverized coal carried by a carrier gas.
• the auxiliary material may be mixed with pulverized coal in advance.
• the method includes injecting pulverized coal through an inner tube 21 of the double wall lance 4, injecting oxygen (a combustion-supporting gas) through an outer tube 22 of the double wall lance 4, and forming notches 23 in a injecting front end of the inner tube 21 of the double wall lance 4, wherein the concentration of oxygen in a gas composed of a carrier gas for carrying the pulverized coal and the combustion-supporting gas is 35% by volume or more.

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• 2012
  • 2012-03-01 TW TW101106750A patent/TWI487791B/zh active
  • 2012-03-01 WO PCT/JP2012/055893 patent/WO2013094230A1/ja active Application Filing
  • 2012-03-01 AU AU2012355194A patent/AU2012355194B2/en active Active
  • 2012-03-01 EP EP12860851.0A patent/EP2796566B2/en active Active
  • 2012-03-01 EP EP18181898.0A patent/EP3421618B1/en active Active
  • 2012-03-01 KR KR1020147019598A patent/KR101629123B1/ko active Active
  • 2012-03-01 CN CN201280063993.6A patent/CN104024440B/zh active Active
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  • 2012-03-01 BR BR112014015336-1A patent/BR112014015336B1/pt active IP Right Grant
  • 2012-03-01 EP EP23184934.0A patent/EP4283233A1/en active Pending

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