TECHNICAL FIELD

[0001] The present disclosure relates generally to a field of metallurgy. Particularly, but not exclusively, the disclosure relates to the method for dephosphorization of molten metal during a steelmaking process.
BACKGROUND
[0002] Background description includes information that may be useful in understanding the present subject matter. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed subject matter, or that any publication specifically or implicitly referenced is prior art.
[0003] Production of steel with extremely low phosphorous content has been a challenge to the steelmakers. In general, metals are found in impure states called ores, often oxidized and mixed with silicates and oxides of other metals. To extract iron from the ores, the ores are processed through a conversion process followed with a smelting process during which the iron ores are reduced and impure liquid iron is obtained which is also known as hot metal.
[0004] To separate impurities from the liquid iron, EAF (Electric Arc Furnaces) or EOF (Energy Optimizing Furnaces) or converters such as BOF (Basic Oxygen Furnaces) also known as LD converter in which oxygen gas is blown are used. In particular, to remove phosphorus dissolved in liquid iron or hot metal, BOF converters of various types, such as top blown, bottom blown or combined blown converters, are used.
[0005] Nowadays, during liquid iron refining processes, multi-phase flux/slag forming agents are introduced into the converters, such as BOF converters, to control the refining kinetics and the chemistry of the reactions of forming slag towards achieving lower phosphorous. Also, various studies have reported positive results on the addition of such slag forming agents after the start of the oxygen blow in the converters and then de-slagging of phosphorous rich slag within 6 -7 minutes. This process calls for the interruption in the oxygen blow and requires extra time for slag removal activity, which not only affects the cycle time but also poses a safety concern.
Prior Art References:
1. Wu Wei et al, Studies of effect of calcium ferrite pellets on dephosphorization of hot metal during pre-treatment in the BOS converter, Scanmet V, Lulea, 2016.
2. K. Ito and M Terasawa, Utilization of multiphase fluxes for the dephosphorization of hot metal, Steel Research International, 80, 10, 2009, p. 733-736.
3. Jiang Diao et al, Intl J of Min, Metal and Mater, V 22, No 3, 2015.
4. N Dogan et al, ISIJ, V49, 2009, 1474-82
5. C. Cicutti et al, Latin Am App Res, 32, 2002
6. R. J. Fruehan, The Making, Shaping and Treating of Steel, AISE Steel Foundation, PA, USA, 1998
[0006] Accordingly, there is a need for methods and systems that can overcome one or more limitations stated above or any other limitation associated with the conventional arts.
OBJECTS OF THE DISCLOSURE
[0007] Some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.
[0008] A general object of the present disclosure is to provide for effective dephosphorization of liquid iron or hot metal in BOF (Basic Oxygen Furnace) converter which would avoid the afore-mentioned limitations and complexities of dephosphorization of hot metal.
[0009] Another object of the present disclosure is to provide dephosphorization of hot metal which would favor effective dephosphorization of slag, without interrupting the process of oxygen blowing.
[0010] A further object of the present disclosure is to provide a method to develop an appropriate methodology for the production of low phosphorous (0.01%) steel at turndown in the convertor, such as Linz-Donawitz (LD) vessel, from relatively high phosphorous hot metal produced in a blast furnace.
[0011] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
SUMMARY
[0012] This summary is provided to introduce concepts related to a method for dephosphorization of hot metal during a steelmaking process. The concepts are further elaborated below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.
[0013] The present disclosure relates to a method for dephosphorization of a hot metal during a steelmaking process by two stage addition of calcium ferrite, a slag forming reagent. The steelmaking method includes adding an iron-bearing scrap in a vessel; firstly, adding initial batch of a calcium ferrite compound in the vessel; adding lime in the vessel; pouring the hot metal in the vessel; blowing oxygen into the said vessel using an oxygen lance forming slag; and secondly, adding another batch of calcium ferrite compound to the vessel after 9 to 10 minutes of the start of oxygen blowing, thereby forming slag with the added calcium ferrite composition charged into the vessel with required fluidity basicity.
[0014] In an aspect, the vessel is a Linz-Donawitz (LD) vessel or a basic oxygen furnace (BOF) converter.
[0015] In an aspect, the blowing of oxygen is carried out at supersonic speed through the oxygen lance to remove impurities such as Silicon, Phosphorus and Carbon form the hot metal.
[0016] In an aspect, the blowing of oxygen is carried out for 15 to 17 minutes.
[0017] In an aspect, the calcium ferrite compound has a composition, in approximate weight percentage, Calcium Oxide (CaO) 37.6%, Iron Oxide (Fe2O3) 51.2%, Silicon dioxide (SiO2) 4.6%, Aluminium Oxide (Al2O3) 1.28%, and Magnesium oxide (MgO) 2.86%.
[0018] In an aspect, the flow temperature of the calcium ferrite compound is 1330 °C.
[0019] In an aspect, the firstly adding the calcium ferrite compound in the vessel (102) is 0.75%-1.0625% of the weight of heat.
[0020] In an aspect, the secondly adding the calcium ferrite compound in the vessel (102) is 0.3%-0.4% of the weight of heat.
[0021] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.
[0022] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.
[0023] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The accompanying drawings, which are incorporated in and constitute a part of this disclosure, illustrate exemplary embodiments and, together with the description, serve to explain the disclosed principles. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the figures to reference like features and components. Some embodiments of system and/or methods in accordance with embodiments of the present subject matter are now described, by way of example only, and with reference to the accompanying figures, in which:
[0025] FIGS. 1A-1D illustrate various stages of a typical steel making process;
[0026] FIG. 2 illustrates a block diagram of a first experimental strategy of calcium ferrite addition in LD vessel during the making of the steel;
[0027] FIG. 3 illustrates a block diagram of a second experimental strategy of two-stage calcium ferrite addition in LD vessel during the making of the steel in accordance with some embodiments of the present disclosure;
[0028] FIG. 4 illustrates a graph showing slag evolution during a blow in LD vessel;
[0029] FIG. 5 illustrates a graph showing a trend of undissolved lime during a blow in LD vessel;
[0030] FIG. 6 illustrates a graph showing the removal of impurities present in hot metal during oxygen blow; and
[0031] FIG. 7 illustrates a method for dephosphorization of molten metal during a steelmaking process, according to an embodiment of the present disclosure.
[0032] It should be appreciated by those skilled in the art that any block diagrams herein represent conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in a computer-readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.
DETAILED DESCRIPTION
[0033] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.
[0034] While the disclosure is susceptible to various modifications and alternative forms, specific embodiment thereof has been shown by way of example in the drawings and will be described in detail below. It should be understood, however that it is not intended to limit the disclosure to the forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.
[0035] The terms “comprises”, “comprising”, “includes” or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that includes a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises… a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
[0036] Disclosed herein is a method for dephosphorization of molten metal during a steelmaking process. Typical stages of a steelmaking process in a Linz-Donawitz (LD) vessel 102 is shown in FIGS. 1A to 1D. In the first stage shown in FIG. 1A, iron-bearing scrap 104 and some lime (CaO) are added into the LD vessel 102. After addition of the iron-bearing scrap 104 and the lime (CaO), hot metal 106 or liquid iron is added in the LD vessel 102 (FIG. 1B). Then, in the next stage shown in FIG. 1C, a lance 108 is lowered and 99.5% pure oxygen gas is blown into a metal bath at supersonic speed (Mach no 2) to remove impurities such as Carbon (C), Phosphorus (P), and Silicon (Si) from the hot metal by oxidation. Typically, the oxygen is blown for 15 -17 min during the steel making process. On completion of the oxygen blowing process, the sample and temperature are taken and liquid steel is tapped in a ladle 110 for further processing, as shown in FIG. 1D.
[0037] In an aspect, the oxygen blowing process refines Carbon, Silicon, and Phosphorus, which are impurities in hot metal or liquid iron, by blowing oxygen at a very high flow rate through the lance 108 in the LD vessel 102. In an aspect, the LD vessel can be a basic oxygen furnace (BOF) converter.
[0038] During the oxygen blowing process, a series of reactions which takes place are reproduced below:
C + ½ O2(g) = CO(g)
CO(g) + ½ O2(g) = CO2(g)
Fe + ½ O2(g) = FeO
C + FeO = CO(g) + Fe
CO(g) + FeO = CO2(g) + Fe
Si + 2 FeO = SiO2 + 2 Fe
2 P + 5 FeO = P2O5 + 5 Fe
[0039] The solid reaction products such as SiO2, P2O5, and the like, which form by oxidation reactions are captured by the addition of freshly prepared lime (CaO) in the LD vessel 102. This, in turn, causes fluxing actions and forms liquid slag. The CaO, being a very high melting compound, does not melt in a steelmaking temperature, and dissolves gradually and forms slag.
[0040] In the present disclosure, calcium ferrite is proposed as a dephosphorizing compound. Such compound has the following properties:
• Composition: CaO-37.6%, Fe2O3 – 51.2%, SiO2-4.6%, Al2O3-1.28%, MgO-2.86%
• Size = 10 – 40 mm,
• Flow Temp of Ca-ferrite = 1330 °C (determined by high temp heating microscopy)
[0041] Because of its low melting temperature, calcium ferrite liquefies quickly, unlike CaO, and provides basic and fluid slag readily and aids in phosphorus removal.
[0042] In a strategy shown in FIG. 2, calcium ferrite was added after two minutes of the start of oxygen blow (202). However, no slag was removed at 6-7 minutes of blow start as done elsewhere in the refining process, rather slag-off was carried out at the end of processing following the regular practice of the steel plant.
[0043] In an aspect of the present disclosure, calcium ferrite is used as a dephosphorizing compound. As shown in FIG. 3, two-stage addition strategy was followed in which first batch (302) of ca-ferrite was added before addition of hot metal and start of oxygen blow, while the second batch (304) was added at 9-10 minutes of start of oxygen blow, i.e., mid-way of the oxygen blow.
[0044] The reasoning behind the selection of the addition of calcium ferrite, before the addition of hot metal and start of oxygen blow, is that overall mass transfer co-efficient of Phosphorus in slag and metal phase reported being 0.0047 to 0.0240 cm/s respectively at 1350 °C. Thus, to facilitate phosphorus removal, the presence of basic and fluid slag beforehand is essential. This is accomplished by the addition of the calcium ferrite after addition of the scarp 104, and before hot metal 106 pouring in the LD vessel 102. Such addition of the slag forming/fluxing agent can enhance mass transfer co-efficient and kinetics of phosphorus removal at the beginning of the steelmaking process.
[0045] Further, the reasoning behind the selection of the addition of calcium ferrite, 9-10 minutes after the start of oxygen blow, is that in LD vessel, several physio-chemical reactions take place. Blowing oxygen in the liquid iron bath at a very high speed through oxygen lance 108 along with the addition of lime causes several exothermic reactions. Formation of slag and change in its composition may be noted from FIG. 4, while FIG. 5 shows un-dissolved lime content as the blow progresses. It is clear from FIG. 6 that lime dissolution suffers in the mid part of the blow and un-dissolved lime content increases significantly. At the mid part of the blow, the kinetics of Carbon removal is very high and FeO content of slag decreases significantly, which in effect lowers dissolution of lime and fluidity of slag. At this point, the slag becomes dry and phosphorous holding capacity of slag decreases and it reverts into the metal (FIG. 6). Addition of calcium ferrite at this point provides liquid slag and thus prevents phosphorous reversion. This can only be verified by taking a sample in the mid part of the oxygen blow, which is very difficult in absence of sub-lance and has not been done here. However, analysis of final steel and slag samples have revealed improved dephosphorization in the second strategy as compared to the first strategy. The results have been compared and are provided in the following Table 1.
Conventional Process As Per FIG. 2 As per Embodiments of disclosure Fig. 3
Count Count Count
Avg Hot Metal Si 0.67 454 0.66 16 0.549 35
Avg Hot Metal P 0.166 454 0.195 16 0.178 35
Avg Turndown P 0.0162 454 0.014 15 0.011 29
%Dephosphorisation Avg. 90.27% Range
72-97.7 % Avg. 92.8% Range 85.6-
97.0% Avg. 93.80% Range 86.2%-98%
Table 1: Comparative results of regular and experimented strategies
[0046] From the above-presented Table 1, it can be gathered that the embodiments as per Fig. 3 is more beneficial to produce steel with dephosphorization ranging from 86.2 to 98 %.
[0047] Therefore, the present disclosure herein proposes a two-stage calcium ferrite addition in LD vessel during the steel manufacturing process for production of low phosphorous (0.01%) steel.
[0048] FIG. 7 illustrates a method 700 for dephosphorization of hot metal during a steelmaking process by two stage addition of calcium ferrite, according to an embodiment of the present disclosure. The order in which the method 700 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any appropriate order to carry out the method 700 or an alternative method. Additionally, individual blocks may be deleted from the method 700 without departing from the scope of the subject matter described herein.
[0049] At block 702, the method 700 includes adding an iron-bearing scrap in a vessel.
[0050] At block 704, the method 700 includes firstly adding a calcium ferrite compound in the vessel.
[0051] At block 706, the method 700 includes adding lime in the vessel.
[0052] At block 708, the method 700 includes pouring the hot metal in the vessel.
[0053] At block 710, the method 700 includes blowing oxygen into the said vessel using an oxygen lance forming slag.
[0054] At block 712, the method 700 includes secondly adding calcium ferrite compound to the vessel after 9 to 10 minutes of the start of oxygen blowing, thereby forming slag with the added calcium ferrite composition charged into the vessel.
[0055] In an aspect, the calcium ferrite compound has a composition, in weight percentage, Calcium Oxide (CaO) 35-38%, Iron Oxide (Fe2O3) 50-52%, Silicon dioxide (SiO2) 4-6%, Aluminium Oxide (Al2O3) 1-2%, and Magnesium oxide (MgO) 2-4%.
Equivalents:
[0056] A description of an embodiment with several components in communication with each other does not imply that all such components are required. On the contrary, a variety of optional components are described to illustrate the wide variety of possible embodiments of the invention. When a single device or article is described herein, it will be apparent that more than one device/article (whether or not they cooperate) may be used in place of a single device/article. Similarly, where more than one device or article is described herein (whether or not they cooperate), it will be apparent that a single device/article may be used in place of the more than one device or article or a different number of devices/articles may be used instead of the shown number of devices or programs. The functionality and/or the features of a device may be alternatively embodied by one or more other devices which are not explicitly described as having such functionality/features. Thus, other embodiments of the invention need not include the device itself.
[0057] The specification has described a method for dephosphorization of hot metal during steelmaking process. The illustrated steps are set out to explain the exemplary embodiments shown, and it should be anticipated that ongoing technological development will change the manner in which particular functions are performed. These examples are presented herein for purposes of illustration, and not limitation. Further, the boundaries of the functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternative boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. Alternatives (including equivalents, extensions, variations, deviations, etc., of those described herein) will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Such alternatives fall within the scope and spirit of the disclosed embodiments. Also, the words “comprising,” “having,” “containing,” and “including,” and other similar forms are intended to be equivalent in meaning and be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items, or meant to be limited to only the listed item or items. It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
[0058] Finally, the language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based here on. Accordingly, the embodiments of the present invention are intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims.

Claims:

1.A method for dephosphorization of a hot metal (106) during a steelmaking process by two stage addition of calcium ferrite, the method comprising:
adding an iron-bearing scrap (104) in a vessel (102);
firstly adding a calcium ferrite compound in the vessel (102);
adding lime in the vessel (102);
pouring the hot metal (106) in the vessel (102);
blowing oxygen into the said vessel (102) using an oxygen lance (108) forming slag; and
secondly adding the calcium ferrite compound to the vessel after 9 to 10 minutes of the start of oxygen blowing, thereby forming slag with the added calcium ferrite composition charged into the vessel (102).
2. The method as claimed in claim 1, wherein the vessel (102) is a Linz-Donawitz (LD) vessel or a basic oxygen furnace (BOF) converter.
3. The method as claimed in claim 1, wherein the blowing of oxygen is carried out at supersonic speed through the oxygen lance (108) to remove impurities including Silicon, Phosphorus and Carbon form the hot metal.
4. The method as claimed in claim 1, wherein the blowing of oxygen is carried out for 15 to 17 minutes.
5. The method as claimed in claim 1, wherein the calcium ferrite compound has a composition, in weight percentage, Calcium Oxide (CaO) 35-38%, Iron Oxide (Fe2O3) 50-52%, Silicon dioxide (SiO2) 4-6%, Aluminium Oxide (Al2O3) 1-2%, and Magnesium oxide (MgO) 2-4%.
6. The method as claimed in claim 1, wherein the flow temperature of the calcium ferrite compound is 1330 °C.
7. The method as claimed in claim 1, wherein the firstly adding the calcium ferrite compound in the vessel (102) is 0.75%-1.0625% of the weight of heat.
8. The method as claimed in claim 1, wherein the secondly adding the calcium ferrite compound in the vessel (102) is 0.3%-0.4% of the weight of heat. ,