Method for smelting reduction of Ni ore

Abstract: A method for smelting reduction of Ni ore comprises charging Ni ore and carbonaceous material into a converter type smelting reduction furnace (10) having bottom-blow tuyeres (22) and a top-blow lance (21), the smelting reduction furnace holding a molten metal (11), blowing oxygen gas from the top-blow lance and a stirring gas from the bottom-blow tuyeres into the furnace, and discharging slag so that a relation represented with a formula Vo > 0.4 Ws + 1.0 can be satisfied, Vo ( m³ per ton of molten metal ) being a specific volume of the smelting reduction furnace per ton of molten metal and Ws ( ton per ton of molten metal ) being a specific weight of slag per ton of molten metal.

Description: The present invention relates to a smelting reduction of Ni ore, and more particularly to a method for smelting reduction of Ni ore wherein a converter type smelting reduction furnace is used and a slopping due to slag produced in large quantities is prevented from taking place. Stainless steel has previously been manufactured by melting scrap and ferrochrome and ferronickel being ferro alloy or electrolytic nickel in an electric furnace. That is, Cr and Ni being main components of stainless steel has been obtained by melting ferro alloy having previously been reduced in an electric furnace. Against such prior art method, recently, attention is paid in terms of energy saving and a decrease of a manufacturing cost to a smelting reduction method wherein molten metal with high chromium content is obtained directly from Cr ore as a chromium source. Such a method id disclosed in for instance US-A-4 565 574. As far as Cr is concerned, it is tried to manufacture stainless steel by directly reducing Cr ore in a converter type smelting reduction furnace as described above. However, it is not tried to manufacture stainless steel by directly reducing Ni ore. The reason for this is that, since only about 2 to 3 % Ni is contained in Ni ore, a great amount of Ni ore has to be used for manufacturing stainless steel by directly reducing Ni ore, operations of the converter type furnace are regarded as difficult. In the case of manufacturing stainless steel of 8% Ni, for example, 3 to 4 tons of Ni ore per ton of stainless steel are used. Accordingly, during smelting reduction of Ni ore, there is a possibility of a break of operations, damages of equipment or a decrease of the yield of Ni due to occurrence of the slopping in connection with production of a great amount of slag. On the other hand, when the slag is many times discharged from a furnace to avoid the occurrence of the slopping, there is a possibility such that the yield of Ni decreases extremely as a result of an escape of molten metal during discharge of the slag and an efficiency in work lowers. The present invntion is made in view of the above-described situation and it is an object of the present invention to provide a method for smelting reduction of Ni ore wherein stability of operations is secured and the yield of Ni is not lowered by occurrence of a great amount of slag. To accomplish the above-mentioned object, the method for smelting reduction of Ni ore is provided, comprising: charging Ni ore and carbonaceous material into a converter type smelting reduction furnace having bottom-blow tuyeres and a top-blow lance, said smelting reduction furnace holding a molten metal; blowing oxygen gas from said top-blow lance and a stirring gas from said bottom-blow tuyeres into said furnace; and discharging slag so that a relation represented with a formula Vo > 0.4 Ws + 1.0 can be satisfied, Vo ( m³ per ton of molten metal ) being a specific volume of said smelting reduction furnace per ton of molten metal and Ws ( ton per ton of molten metal ) being a specific weight of slag per ton of molten metal. Preferred embodiments are given in the dependant claims. The above objects and other objects and advantages of the present invention will become apparent from detailed description which follows, taken in conjunction with the appended drawings. Fig.1 is a vertical sectional view illustrating a smelting reduction furnace of an example of the present invention; Fig.2 is a graphical representation indicating the relation between an amount of Ni ore charged into the smelting reduction furnace and a level of slag in the smelting reduction furnace; and Fig.3 is a graphical representation designating the relation between specific weight and specific volume of slag in the smelting reduction furnace. An example of the present invention will be described with specific reference to the appended drawings. Fig.1 is smelting reduction furnace 10 of the example. In the drawing, reference numeral 21 denotes a top-blow lance, 22 a bottom-blow tuyere, 11 molten metal, 12 a slag layer, 23 a hopper for charging Ni ore, carbonaceous material or flux as material into the smelting reduction furnace 10 and 24 feed pipe for feeding stirring gas to the bottom-blow tuyere 22. A method for manufacturing molten metal containing a predetermined amount of Ni by the use of the smelting reduction furnace constituted as described above will be described. Initially, molten metal of iron is charged into the smelting reduction furnace. Subsequently, carbonaceous material is charged into the smelting reduction furnace. Then, after oxygen has been blown into the smelting reduction furnace and a temperature of the molten metal has been raised upto about 1500 °C, Ni ore begins to be charged into the smelting reduction furnace 10. In the case of repeatedly carrying out operations, the molten metal is made up for by the molten metal containing Ni which has previously been charged. The stirring gas begins to be blown from the bottom-blow tuyeres 22 into the smelting reduction furnace 10 from the moment when the molten metal has been charged into the smelting reduction furnace 10 with a flow of the stirring gas so that the tuyeres 22 cannot be blocked. Blow of said stirring gas is increased if necessary. Charged Ni ore is reduced by C in the molten metal. Heat energy for smelting Ni ore is supplied by combustion of the carbonaceous material in its reaction with oxygen, that is, by reaction C→ CO, CO → CO₂. A content of oxides of Fe and Ni contained in Ni ore generally used is about 30%. The other 70% consists of SiO₂, MgO, crystallization water and other slag components. A content of Ni in Ni ore is about 2 to 3 %. Slag produced by both of Ni ore and carbonaceous material forms slag during smelting reduction of Ni ore. Weight of slag accounts for about 80% of weight of Ni ore. Accordingly, when molten metal containing 8 wt.% Ni is manufactured, 2 to 3 tons of slag per ton of the molten metal are produced although the amount of produced slag per ton of the molten metal varies dependent on the content of Ni in Ni ore and a predetermined content of Ni in molten iron. Since a bulk density of slag during the smelting reduction is about 1.5, the volume of slag can be about 15 times larger than that of the molten metal. In consequence, a break of operations and damages of equipment can be produced by a slopping of the slag and this prevents the operations from being stably carried out and decreases the yield of Ni. Moreover, it can greatly decrease the yield of Ni due to an outflow of the molten metal during discharge of slag to increase the number of discharges of the slag during the smelting reduction of Ni ore in order to prevent the slopping from being produced due to the great amount of slag. A problem of a volume of the smelting reduction furnace and a time of discharge of slag is posed to secure the stability of operations and to increase the yield of Ni. Accordingly, tests were conducted to find the relation between an amount of Ni ore charged into the smelting reduction furnace and a level of slag therein for the purpose of finding an appropriate time of the discharge of slag, the amount of Ni ore to be charged into the smelting reduction furnace and the volume of the smelting reduction furnace. A result of the tests is shown in Fig.2. In Fig.2, a graph is of a straight line when the amount of charged Ni ore is 4 t or more. It is thought that this is because a volume of gas contained in slag is large when the volume of slag is small. Fig.3 is a graphical representation indicating the relation between a specific weight Ws and a specific volume Vs of the slag which was obtained by analyzing a data in Fig.2. Ws is a specific weight of slag per ton of molten metal and Vs is a specific volume of smelting reduction furnace per ton of slag. Hereinafter, the units of V and W are the same as those mentioned above. From a graph in Fig.3, the relation between the specific gravity Ws and specific volume Vs of slag can be represented with a formula Vs = 0.4 Ws + 0.85 in a portion of a staight line where Ws is 1 or more. By adding the specific volume of molten metal of 0.15 to this formula, a specific volume Vsm of the slag and molten metal held in the smelting reduction furnace is represented with the following formula: Vsm = 0.4 Ws + 1.0 (1) A constant of the formula (1) is determined so that units in both sides of the fomula can be the same. An actual operation satisfies Ws >1 . The volume of the smelting reduction furnace and the time for the discharge of slag will be studied below relative to said formula (1). When the specific volume of the smelting reduction furnace 10 is Vo, the following condition is indispensable to prevent the smelting reduction furnace from being unstably operated due to the slopping of the slag: Vsm < Vo (2) This condition can be represented as follows by putting the formula (1) into the formula (2): Vo > 0.4 Ws + 1.0 (3) Further, the formula (2) can be converted to the following formula: Vsm = αVo (4) In the formula (4), α is 0 < α < 1 . When α is near 1, the operation can be unstable due to the slopping of slag and, conversely, when α is near 0 , the volume of the smelting reduction furnace becomes too large although the slopping does not affect the operation. This is not economical and makes it difficult to carry out an effective operation. In terms of the above-described, α is desired to be within the following range: 0.8 < α < 0.95 (5) This condition can be converted to the following formula by putting the formulas (1) and (4) into the formula (5): 0.8 Vo< 0.4 Ws + 1.0 < 0.95 Vo (6) From the formulas (3) or (6), the time for discharge of slag is determined with regard to the specific gravity Ws of the slag so that the slopping of the slag cannot occur. Further, when an allowable specific gravity Ws of produced slag is determined on the basis of a predetermined amount of molten metal of Ni and Ni component contained in the molten metal so that any slopping cannot be produced before the discahrge of slag, the specific volume Vo of the smelting reduction furnace can be found. Since the relation between an amount Wn of Ni ore charged into the furnace and said Ws is easily known by the amount of material charged into the furnace and Ni component contained in Ni ore, the time for discharge of slag can be determined to avoid unstable operations of the furnace and the decrease of the yield of Ni in connection with the occurrence of the slopping. According to the present invention, since the relation between the amount of slag and the amount of Ni ore charged into the smelting reduction furnace is found, a time for discharge of slag or molten metal can be determined so that any slopping cannot occur and, moreover, when an amount of molten metal to be manufactured and a content of Ni are determined, a favorable volume of the smelting reduction furnace can be found. Example A specific example in case Ni ore is smelted in a smelting reduction furnace of 5 tons capacity with a content volume of 10 m³ will be described. An amount of produced slag accounts for 80 % of the amount of Ni ore charged into the furnace as described above. When the amount of Ni ore charged into the furnace before the discharge of slag is 13 t/ch and molten metal is 10 t/ch, Vsm = 0.4 x 2.0 + 1.0 = 1.80 is obtained by putting Ws=10/5=2.0 into the formula (1). In connection with α = Vsm/Vo = 1.8/2 = 0.90 , the following formyula is obtained: 0.8 <α =0.90 < 0.95 In this way, the above-mentioned formula (5) is satisfied. Accordingly, in this case, if slag is dischraged when the amount of Ni ore charged into the furnace reaches 13 t, the slopping of slag can be avoided.

Claims: A method for smelting reduction of Ni ore, comprising: charging Ni ore and carbonaceous material into a converter type smelting reduction furnace (10) having bottom-blow tuyeres (22) and a top-blow lance (21), said smelting reduction furnace holding a molten metal (11); and blowing oxygen gas from said top-blow lance and a stirring gas from said bottom-blow tuyeres into said furnace; characterized by discharging slag so that a relation represented with a formula Vo > 0.4 Ws + 1.0 can be satisfied, Vo ( m³ per ton of molten metal ) being a specific volume of said smelting reduction furnace per ton of molten metal and Ws ( ton per ton of molten metal ) being a specific weight of slag per ton of molten metal. The method of claim 1, characterized in that said discharging slag includes discharging slag so that a relation represented with a formula 0.4 Ws + 1.0 < Vo < ( 0.4 Ws + 1.0 ) / 0.8 can be satisfied, Vo ( m³ per ton of molten metal ) being a specific volume of said smelting reduction furnace per ton of molten metal and Ws ( ton per ton of molten metal ) being a specific weight of slag per ton of molten metal. The method of claim 1, characterized in that said discharging slag includes discharging slag so that a relation represented with a formula ( 0.4 Ws + 1.0 ) / 0.95 < Vo < ( 0.4 Ws + 1.0 )/0.8 is satisfied, Vo ( m³ per ton of molten metal ) being a specific volume of said smelting reduction furnace per ton of molten metal and Ws ( ton per ton of molten metal ) being a specific weight of slag per ton of molten metal.

Inventors: IWASAKI KATSHUHIRO C O PATENT, KAWAKAMI MASAHIRO C O PATENT L, TAKAOKA TOSHIO C O PATENT LICE, TAKI CHIHIRO C O PATENT LICENS, TANABE HARUYOSHI C O PATENT LI, IWASAKI, KATSHUHIRO, C/O PATENT & LICENSE DEP., KAWAKAMI, MASAHIRO, C/O PATENT & LICENSE DEP., TAKAOKA, TOSHIO, C/O PATENT & LICENSE DEP., TAKI, CHIHIRO, C/O PATENT & LICENSE DEP., TANABE, HARUYOSHI, C/O PATENT & LICENSE DEPARTMENT, Iwasaki, Katshuhiro, c/o Patent &amp; License Dep., Kawakami, Masahiro, c/o Patent &amp; License Dep., Takaoka, Toshio, c/o Patent &amp; License Dep., Taki, Chihiro, c/o Patent &amp; License Dep., Tanabe, Haruyoshi, c/o Patent &amp; License Department
Applicants: NIPPON KOKAN KK, NKK CORPORATION
Application year: 1990
Main classification: C21B13
IPC codes: C22B23, C22C33, C21B13, C21B5