[0001 ] The present application relates generally to heating blast air before providing the blast air to a blast furnace and, more specifically, to heating the blast air beyond its normal temperature.

BACKGROUND

[0002] The purpose of a blast furnace is to chemically reduce and physically convert iron oxides into liquid iron. The blast furnace is a huge furnace and features a conical steel stack lined with refractory brick and copper and/or cast-iron cooling elements. In operation, raw materials, such as iron ore pellets, sinter and/or lump ore, coke and fluxing materials, are charged into the top of the blast furnace and preheated air and oxygen is blown into the bottom of the blast furnace together with injected fuels. The raw materials require 6 to 8 hours to descend to the bottom of the blast furnace, by which point, the raw materials have become final products of liquid slag and liquid iron. In some cases, these liquid products are drained from the furnace at regular intervals, while, in other cases, the liquids are continuously drained from the furnace. The heated air that was blown into the bottom of the blast furnace ascends to the top of the blast furnace in six to eight seconds, all the while going through numerous chemical reactions.

[0003] Hot blast stoves heat air and discharge the heated air (known as hot blast air) to the blast furnace at about 900 to 1 ,300°C. In the blast furnace, the hot blast air and added oxygen burns the coke and injected fuels. The products of such burning include heat, gases (CO and H2), char and ash. These combustion products reduce iron oxide to molten pig iron. Gangue minerals from ore and ash from coal and coke combine with fluxes to form molten slag.

BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Reference will now be made, by way of example, to the accompanying drawings which show example implementations; and in which: [0005] FIG. 1 illustrates a typical arrangement for a blast furnace including a hot blast main;

[0006] FIG. 2 illustrates, in plan view, a typical air mixer in relation to the hot blast main of FIG. 1 ;

[0007] FIG. 3 illustrates, in A-A section view, the typical air mixer of FIG. 2 in relation to the hot blast main of FIG. 1 , including B-B arrows;

[0008] FIG. 4 illustrates, in B-B arrow view, the typical air mixer of FIG. 3 in relation to the hot blast main of FIG. 1 ;

[0009] FIG. 5 illustrates, in a right-front perspective view, a hot blast main including an air mixer retrofitted with a plasma torch according to an aspect of the present application;

[0010] FIG. 6 illustrates, in a cut-away perspective view, the combination incomplete air mixer with plasma torches and hot blast main of FIG. 5;

[001 1 ] FIG. 7 illustrates, in a cut-away perspective view, a plasma torch in a mixing finger of the air mixer of FIG. 5 with an air shroud and a protective refractory tube added;

[0012] FIG. 8 illustrates, in a schematic cross-sectional view, a plasma torch and an associated tuyere;

[0013] FIG. 9 illustrates, in section view, a plasma torch installed in conjunction with a water cooling member in accordance with aspects of the present application;

[0014] FIG. 10 illustrates, in a section view, a mixing chamber adapted with a plasma torch in a mixer air inlet;

[0015] FIG. 1 1 illustrates, in elevation view, the adapted mixing chamber of FIG.

10;

[0016] FIG. 12 illustrates, in a section view, a mixing pot adapted with a plasma torch in a mixer air inlet;

[0017] FIG. 13 illustrates, in elevation view, the adapted mixing pot of FIG. 12; [0018] FIG. 14 illustrates, in section view, a line mixer adapted with a plasma torch in an air inlet; and

[0019] FIG. 15 illustrates a table summarizing effects of increasing blast air temperature using plasma energy.

DETAILED DESCRI PTION

[0020] According to an aspect of the present disclosure, there is provided a method of operating a blast furnace system, the blast furnace system including a hot blast main through which hot blast air passes from at least one stove to a blast furnace and the hot blast main having an air inlet designated for hot blast air temperature control. The method includes reducing an amount of carbon dioxide emitted by the blast furnace system. The reducing being accomplished by heating, by a jet of plasma heated gas from a plasma torch mounted in the mixer air inlet, air passing from the mixer air inlet into the hot blast main to mix with the hot blast air. Heat transferred to a hot blast main refractory material is reduced by providing a shroud of cooling air surrounding the jet of plasma heated gas exiting the plasma torch, controlling temperature for the hot blast main refractory material associated with the hot blast main.

[0021 ] According to another aspect of the present disclosure, there is provided a modified air mixer. The modified air mixer includes an air inlet including a refractory material, a plasma torch mounted in the air inlet and adapted to heat, using a jet of plasma heated gas, air passing through the air inlet to mix with hot air from a hot blast main and a shroud gas inlet assembly to provide a shroud of cooling air surrounding the jet of plasma heated gas, thereby reducing heat transferred to the refractory material.

[0022] According to a further aspect of the present disclosure, there is provided a method of adapting a mixer, the mixer including an air inlet including a refractory material. The method includes mounting a plasma torch to the air inlet to allow for heating, by a jet of plasma heated gas from the plasma torch, of air passing from the cold air inlet to mix with hot blast air and mounting, in association with the plasma torch, a shroud gas inlet assembly to provide an air shroud of cooling air surrounding the plasma, thereby reducing heat transferred to the refractory material. [0023] Other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific implementations of the disclosure in conjunction with the accompanying figures.

[0024] FIG. 1 illustrates a blast furnace system 100 including a blast furnace 102, a plurality of hot stoves 104 and a refractory-material-lined ductwork system. The blast furnace 102 includes tuyeres 106. The refractory-material-lined ductwork system may be seen to include a hot blast main 108.

[0025] In operation, the hot stoves 104 heat cold air. The heated blast air (now, hot blast air, typically 900-1300°C) is transported through the hot blast main 108 to the tuyeres 106. Upon entering the blast furnace 102, via the tuyeres 106, the hot blast air combusts with coke and injected fuel to smelt iron ore, pellets and sinter into molten pig iron and slag.

[0026] The hot stoves 104 are regenerative heat exchangers and are understood to be unable to supply hot blast air to the blast furnace 102 at a consistent temperature. At the start of a stove air heating cycle, the temperature of air exiting a selected hot stove 104 is at its maximum value. Unfortunately, with time, the temperature drops due to loss of thermal energy from refractory checker bricks inside the hot stove 104.

[0027] FIG. 2 illustrates, in plan view, a known air mixer 200 in relation to the hot blast main 108. The air mixer 200 includes a mixing air inlet 202 and a plurality of mixing fingers 204. FIG. 2 illustrates one of the mixing fingers 204 being fed directly from the mixing air inlet 202. FIG. 2 also illustrates one of the mixing fingers 204 being fed via a distributer 206. FIG. 3 illustrates, in A-A section view, the air mixer 200 of FIG. 2 in relation to the hot blast main 108, including B-B arrows. FIG. 4 illustrates, in B-B arrow view, the air mixer 200 of FIG. 2 in relation to the hot blast main 108.

[0028] To provide a consistent temperature to the blast furnace 102, the air mixer 200 may be used to add further mixing air (at ~100-300°C) to the hot blast air exiting the hot stove 104 into the hot blast main 108. This is often done as the hot stove 104 is put into service at the end of its heating cycle. The mixing air is mixed, within the hot blast main 108, with the hot blast air to produce mixed blast air. The mixed blast air has a selected setpoint temperature that is less than the temperature of the hot blast air before mixing. The rate of flow of mixing air being added to the hot blast air through the air mixer 200 may be gradually reduced, using an air valve (not shown), throughout the stove blast cycle. The gradual reduction may be seen to achieve a consistent temperature for the mixed blast air entering the blast furnace 102. Once the air valve servicing the air mixer 200 is closed, the hot stove 104 may be removed from the blast cycle and returned to a heating cycle. During the heating cycle, the refractory checker bricks within the hot stove 104 are reheated by combusting blast furnace gas, often supplemented with natural gas and/or oxygen. A new hot stove 104 may then be brought into service. Responsively, the mixing air may again be added, at the air mixer 200, to control the temperature of the mixed blast air to achieve the setpoint.

[0029] Since mixing the mixing air with the hot blast air results in mixed blast air having a temperature lower than the temperature of the hot blast air, it may be considered that this version of the blast furnace smelting process has a built-in inefficiency. The blast furnace smelting process runs smoothly when the mixed blast air is supplied at a consistent temperature, but the efficiency of the blast furnace smelting process is limited by a maximum consistent mixed blast air temperature achievable utilizing the air mixer 200.

[0030] In overview, it is proposed herein to heat, using plasma torches, some or all of the mixing air to a high temperature and then mix the heated mixing air with the hot blast air exiting the hot stoves 104. The resulting mixed blast air that enters the blast furnace 102 through the tuyeres 106 would have a temperature that is higher than the hot blast air.

[0031 ] FIG. 5 illustrates, in a perspective view, a modified air mixer 500 in relation to the hot blast main 108. The modified air mixer 500 includes a mixing air inlet 502 and a plurality of mixing fingers 504.

[0032] In accordance with aspects of the present application, the modified air mixer 500 differs from the air mixer 200 of FIG. 2 in that the modified air mixer 500 includes a plurality of plasma torches 508A, 508B, 508C, 508D (individually or collectively 508).

[0033] Plasma torches are electric arc gas heaters that produce a high temperature, ionized and conductive gas to achieve direct heat transfer from an arc. It has been found that the Marc 1 1 H torch marketed by Westinghouse Plasma Corporation of Mt. Pleasant, Pennsylvania is suitable for use for the plurality of plasma torches 508.

[0034] As illustrated in FIG. 5, the plasma torches 508 are inserted into the mixing fingers 504 that are fed via a distributer 506.

[0035] It is conventional to add, by way of the air mixer 200, relatively cold mixing air to the hot blast air exiting the hot stoves 104.

[0036] Conveniently, it is proposed herein to add, by way of the hot blast air mixer 500, heated mixing air to the hot blast air exiting the hot stoves 104.

[0037] One result of the proposed heated mixing air addition is that the temperature of the mixed blast air supplied to the blast furnace 102 is equal to or greater than the temperature of hot blast air that initially exits the hot stove 104 during the blast air heating cycle, when the refractory checker bricks within the hot stove 104 are at their hottest. This is opposite to the conventional method to maintain a consistent mixed blast air temperature entering the blast furnace 102 through the addition of cooler mixing air. The conventional method may also be known as "downward temperature trimming." This approach, proposed herein, that involves providing heated air to the hot blast main 108 may be shown to increase the temperature of the mixed blast air so that the mixed blast air has a temperature that exceeds the thermal capabilities of the hot stoves 104. Use of the approach proposed herein may be shown to lead to reduced coke consumption, increased blast furnace productivity and reduced CO2 emissions, in that more efficient use is made of available energy.

[0038] As illustrated in FIG. 5, the modified air mixer 500 includes the cold air inlet 502 arranged to feed plural mixing fingers 504 via the distributer 506. The hot blast main 108, to which the modified air mixer 500 is connected, is illustrated as having multiple apertures for connection with the plural mixing fingers 504 of the modified air mixer 500. Each aperture is associated with a flanged inlet 516. The plasma torch associated with reference number 508A is associated with the one mixing finger that is associated with reference number 504. The additional plasma torches 508B, 508C, 508D are associated with further mixing fingers that are not associated with specific reference numbers.

[0039] As best reviewed in FIG. 6, the hot blast main 108 is illustrated as having an outer shell 514, which may be formed of steel, and a refractory material 510. Each of the plurality of apertures in the outer shell 514 of the hot blast main 108 is associated with a channel through the flanged inlet 516 and through the refractory material 510 to an interior of the hot blast main 108. Notably, operation of each plasma torch 508 may be seen to increase a likelihood of overheating of the refractory material 510 and/or the outer shell 514 of the hot blast main 108, which would likely lead to damage to the refractory material 510 and/or the outer shell 514 of the hot blast main 108.

[0040] It is proposed herein to mitigate any overheating of the refractory material 510 and/or the outer shell 514 of the hot blast main 108 by providing an air shroud. To that end, the plasma torch 508A is illustrated as connecting to the aperture in the hot blast main 108 via a shroud gas inlet assembly 614. A non-diatomic gas may be added to the shroud air used in the air shroud. Example non-diatomic gases include H ₂ 0 and CO2. It may be shown that non-diatomic gases act to absorb some of the radiant energy emitted from the plasma jet. In this way, it may be shown that non- diatomic gases enhance the ability of the shroud air to reduce heating of refractory material 510 due to radiant heat transfer.

[0041 ] It is also proposed herein to mitigate any overheating of the refractory material 510 and/or the outer shell 514 of the hot blast main 108 by providing a zoned refractory construction using refractory or ceramic materials designated for ultrahigh temperature service close to the plasma torch flame location. The zoned refractory construction may be realized as a physical shroud passing through each flanged inlet 516 of the hot blast main 108 and through the refractory material 510 to protect the refractory material 510 from exceeding its service temperature limit. Notably, the physical shroud material may be distinct from the refractory material 510 of the hot blast main 108. As illustrated in FIG. 6, the physical shroud may include two pieces, namely, an inlet refractory tube 612A, to protect the flanged inlet 516, and a host refractory tube 612B, to protect the refractory material 510 of the hot blast main 108. Alternately, the physical shroud may be formed as a single refractory tube.

[0042] FIG. 7 illustrates, in a cut-away perspective view, the plasma torch 508A in operation in a mixing finger of the modified air mixer 500 of FIG. 5. In operation, the plasma torch 508A produces a jet 722 of plasma heated gas.

[0043] Also in operation, the shroud gas inlet assembly 614 provides a shroud 720 of cooler air with or without added non-diatomic gas around the jet 722 of plasma heated gas to, thereby, protect the refractory shroud 612A 612B, the refractory material 510 and/or the outer shell 514 of the hot blast main 108.

[0044] A disclosure of an example of the shroud gas inlet assembly 614 may be found in US Patent no. 7,095,283, in which FIG. 8 originally appears.

[0045] FIG. 8 illustrates, a schematic cross-sectional view, a plasma torch 40 positioned adjacent to an inlet 42 of a tuyere 44. The tuyere 44 is mounted in the wall of a reactor vessel 10 and defines a chamber 46. The chamber 46 can have a cylindrical or frustoconical shape. The plasma torch 40 includes a nozzle 48 that is configured to direct a jet of plasma heated gas in an axial direction (in this example, the jet of plasma heated gas is directed along a central axis 50 of the chamber 46). The chamber 46 can have a circular cross-section in a plane perpendicular to the central axis 50. The plasma jet can have a temperature in a range extending, for example, from 5,000-8,000° C. A shroud gas inlet assembly 52 is configured to deliver cooler gas (i.e., a shroud gas) to surrounds the plasma heated gas (plasma jet) and shields the plasma jet from the chamber walls. The shroud gas inlet assembly 52 can be positioned adjacent to the tuyere inlet. The tuyere chamber 46 can be lined with a refractory material 54 and can be cooled by a fluid, potentially with a water jacket or a tubular cooling coil, not shown in this view, which can be embedded within the walls of the tuyere 44. In other embodiments, the chamber could be in a water-cooled coil or a copper block with cooling channels, which are not lined with a refractory material. The cold gas streams can be directed in a way such that the plasma jet remains focused in axial direction, with the shroud gases flowing between the plasma jet and the chamber wall.

[0046] FIG. 9 illustrates, in section view, a plasma torch 908 installed in the flanged inlet 516 of the hot blast main 108 in conjunction with an air-cooled refractory sleeve 902 and/or a water-cooled sleeve 904 in accordance with aspects of the present application. It is proposed herein to use refractory sleeves and cooling air and/or water channels to protect the refractory material 510 and the outer shell 514 of the hot blast main 108.

[0047] As discussed in conjunction with FIG. 7, the jet of plasma heated gas generated by the plasma torch 908 may be surrounded by an air shroud created using a shroud gas inlet assembly 922 defining shroud gas inlets. The air shroud may be created as cooling air passes through the shroud gas inlet assembly 922 and interposes the plasma jet and the air-cooled refractory sleeve 902. As referenced hereinbefore, a non-diatomic gas, such as H ₂ 0 (steam), may be added to the cooling air to absorb some radiant heat from the plasma jet to reduce heat transferred to refractory material 910.

[0048] As will be understood by a person of skill in the art, the air mixer 200 of FIG. 2 is not the only known way mixing air may be mixed with hot blast air from the hot stoves 104. FIGS. 10-16 illustrate other known air mixers adapted, according to aspects of the present application, to heat the blast air beyond its normal temperature.

[0049] FIG. 10 illustrates, in a section view, a mixing chamber design 1000 for the air mixer. A plurality of these mixing chambers 1000 may be installed in a blast furnace system like the blast furnace system 100 of FIG. 1 . Indeed, of these mixing chambers 1000 may be installed at the outlet of each hot stove 104. The mixing chamber 1000 has a hot blast air input 1004 and a pair of mixing air inlets 1005A, 1005B (individually or collectively 1005). Typically, hot blast air, received at the hot blast input 1004, and mixing air, received at mixing air inlets 1005, mix in a column 1002 prior to entering a hot blast main 1008, analogous to the hot blast main 108 of FIG. 1 . [0050] According to aspects of the present application, plasma torches 1006A, 1006B (individually or collectively 1006) may be installed corresponding to each of the mixing air inlets 1005. As discussed hereinbefore, the plasma torches 1006 may be used to heat the mixing air before the mixing air mixes with the air exiting the hot stoves 104, thereby generating mixed blast air with a temperature greater than the hot stoves 104 typically generate.

[0051 ] In a manner consistent with the way the refractory material and steel of the hot blast main 108 are protected as illustrated in FIG. 7, the refractory material and steel of the mixing chamber 1000 may be protected by a refractory shroud. The refractory shroud may be cooled using air or water. Furthermore, in operation, the refractory material and the steel of the mixing chamber 1000 may be protected by an air shroud generated through the use of a shroud gas inlet assembly.

[0052] FIG. 1 1 illustrates, in elevation view, the adapted mixing chamber 1000 of FIG. 10. It should be clear that the plasma torches 1006 in FIGS. 10 and 1 1 may, alternatively, be positioned at the bottom of the mixing chamber 1000 such that the plasma jet from each of the plasma torches 1006 projects vertically upwards into the column 1002, rather than projecting horizontally. It is expected that vertically projecting plasma jets will have advantages over horizontally projecting plasma jets at least in terms of a reduction of refractory overheating challenges.

[0053] FIG. 12 illustrates, in a section view, a mixing pot design 1200 for the air mixer. The mixing pot 1200 is located downstream from the hot stoves 104 between the closest stove among the plurality of stoves 104 and a bustle pipe of the blast furnace complex. The "closest stove" is the stove closest to the blast furnace. In most blast furnace facilities, it is likely that the stoves are organized in a row and, accordingly, there will be a stove that is measurably closest to the blast furnace. In China, a square configuration of stoves can be used. In such a configuration, the stove that is physically closest to the blast furnace may not, necessarily, be the stove located furthest downstream, toward the blast furnace, among the plurality of stoves.

[0054] In operation, hot blast air exits the stoves 104 and flows along a hot blast main 1204 into a central chamber 1202 of the mixing pot 1200. Mixing air is injected from the bottom into the mixing pot 1200. The cooling air and the hot blast air mix in the central chamber and exit the mixing pot 1200, via a mixed air outlet 1208, to flow into the tuyeres 106. Use of the mixing pot 1200 is similar to use of the mixing chamber 1000. One of the distinctions is that there is only single mixing pot 1200, in contrast to a mixing chamber 1000 associated with each hot stove 104.

[0055] According to aspects of the present application, plasma torches 1206A, 1206B (individually or collectively 1206) may be installed at the mixing air inlet. As discussed hereinbefore, the plasma torches 1206 may be used to heat the mixing air before the mixing air mixes with the air exiting the hot stoves 104, thereby generating mixed blast air with a temperature greater than the hot stoves 104 typically generate.

[0056] In a manner consistent with the way the refractory material and the steel of the hot blast main 108 are protected as illustrated in FIG. 7, the refractory material and the steel of the mixing pot 1200 may be protected by a refractory shroud. The refractory shroud may be cooled using air or water. Furthermore, in operation, the refractory material and the steel of the mixing pot 1200 may be protected by an air shroud generated through the use of a shroud gas inlet assembly.

[0057] FIG. 13 illustrates, in elevation view, the adapted mixing pot 1200 of FIG. 12.

[0058] FIG. 14 illustrates, in section view, a line mixer 1400. In typical operation, mixing air enters the line mixer 1400 via a mixing air input and is directed

circumferentially around a hot blast flow.

[0059] According to aspects of the present application, plasma torches 1406A, 1406B (individually or collectively 1406) may be installed corresponding to each of the mixing air inlets. As discussed hereinbefore, the plasma torches 1406 may be used to heat mixing air before the mixing air mixes with the air exiting the hot stoves 104, thereby generating mixed blast air with a temperature greater than the hot stoves 104 typically generate.

[0060] Conveniently, aspects of the present application may be seen to lead to a general increase in hot blast temperature that will allow an increase in the rate of addition of relatively low cost injected fuel due to the greater amount of energy contained in the mixed hot blast air. [0061 ] In aspects of the present application the temperature of mixed hot blast air delivered to the blast furnace 102 is increased in a well controlled manner.

[0062] In overview, aspects of the present application allow for optimization of energy produced from the hot blast stoves 104 by adjustments to the addition of cooling air for temperature control. Additionally, the blast furnace 102 can operate closer to a maximum temperature limit of existing refractory systems. Furthermore, electrical energy is used as a supplementary source of energy for heating the air and can reduce the blast furnace's carbon consumption and, hence, CO2 emissions in an efficient way.

[0063] FIG. 15 illustrates a table 1500 comparing aspects of five cases (a base case a four alternatives) of temperature in the blast furnace 102 ("blast

temperature"). As can be seen from a review of the table 1500, responsive to increasing the blast temperature, various operational parameters also change. One example operational parameter is the amount of coke consumed by the blast furnace 102 to produce a tonne (t) of hot metal (HM). This amount is called a "coke rate." The coke rate is typically expressed in kg/t HM. From the table 1500, it can be observed that the coke rate decreases responsive to increasing blast temperature.

[0064] Another example operational parameter is Pulverized Coal Injection (PCI). Pulverized coal is typically injected at the tuyere level. From the table 1500, it can be observed that PCI, expressed in kg/t HM, increases responsive to increasing blast temperature. As will be understood, in assorted designs of blast furnaces, other fuels are injected at the tuyere level, including natural gas. Notably, PCI and natural gas may be available at a lower cost than coke. There are other less commonly injected fuels include: coke oven gas; heavy oil; coal tar derivatives, such as kerosene; waste (motor) oil; plastics; and biomass.

[0065] With coke rate decreasing and PCI increasing, responsive to higher temperatures, it may be considered worthwhile to consider an operational parameter representative of a combination of these two operational parameters. A "fuel rate" operational parameter is presented to achieve such a combination. From the table 1500, it can be observed that the fuel rate, expressed in kg/t HM, decreases responsive to increasing blast temperature. A corresponding reduction in CO2 emissions occurs as the fuel rate decreases, since coke and PCI (or other injected fuels) represent the largest carbon input to the blast furnace process.

[0066] A further notable operational parameter is electricity consumption, expressed in kilowatt hours per tonne of hot metal (kWh/t HM). From the table 1500, it can be observed that electricity consumption increases responsive to increasing blast temperature.

[0067] In review, responsive to heating the hot blast air beyond its normal temperature, coke usage may be reduced and more pulverized coal or natural gas may be injected. The resulting fuel rate decreases with increased hot blast air temperature. This may be seen to lead to greater productivity and reduced CO2 emissions, especially if the electricity provided to the blast furnace is obtained from a renewable (i.e., non-C02 producing) power source.

[0068] By heating the hot blast exiting the stoves beyond its normal temperature, the blast furnace process may also be seen to become more efficient. The efficiency may be measured in terms of operational expenditure savings, which may be observed because of reduced coke consumption and a reduction in a volume of blast air required (see "Specific Blast Volume" in table 1500). Specific Blast Volume is a measure of blast air used per tonne of iron produced. Furthermore, there may be an increase in production (tonnes of hot metal produced) from the furnace through implementation of aspects of the present application.

[0069] The above-described implementations of the present application are intended to be examples only. Alterations, modifications and variations may be effected to the particular implementations by those skilled in the art without departing from the scope of the application, which is defined by the claims appended hereto.