JP2012158781A - Method for melting cold iron source by combined arc melting furnace and combined arc melting furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for melting a cold iron source by a combined arc melting furnace for the cold iron source which can effectively utilize exhaust gas generated in a combined arc melting furnace for pre-heating of the cold iron source without causing oxidation of the cold iron source, can reform the exhaust gas and reduce the electric power consumption rate, when melting the cold iron source in the combined arc melting furnace, and to provide the combined arc melting furnace.SOLUTION: In the method for melting the cold iron source using the combined arc melting furnace comprising a melting chamber and a shaft-type pre-heating chamber which is vertically provided on the upper part thereof and communicates to the melting chamber, the cold iron source successively lowers inside of a pre-heating chamber, is pre-heated by using a high temperature exhaust gas generated in a combined arc melting furnace to arc melt and is continuously introduced into the melting chamber, where an ammonia gas is blown into the pre-heating chamber under conditions wherein the cold iron source is present striding over the pre-heating chamber and the upper part in the melting chamber.

Description

  The present invention relates to a method for melting a cold iron source such as iron scrap or directly reduced iron using a combined arc melting furnace having a shaft-type preheating chamber, and to the combined arc melting furnace.

  Conventionally, cold iron sources such as iron scrap are heated and melted using various arc furnaces, refined, and then regenerated as molten steel. However, since a large amount of electric power is required to melt the cold iron source by the arc furnace, in recent years, the cold iron source is generated by the high-temperature exhaust gas generated from the melting chamber of the arc furnace for the purpose of reducing the power consumption. There has been proposed a new method of melting while preheating.

  As a typical example, Patent Document 1 proposes a composite arc melting furnace including a melting chamber and a shaft-type preheating chamber for introducing exhaust gas generated in the melting chamber. In the operation of this combined arc melting furnace, the iron scrap to be charged exists between the preheating chamber and the melting chamber, and the iron scrap is heated and melted by arc heat in the melting chamber. This is a method for melting iron scrap, characterized in that molten steel is discharged when at least one heat of molten metal has accumulated.

  Moreover, in patent document 2, in using the exhaust gas generated from the composite arc melting furnace, an oxygen-containing gas is supplied to the preheating chamber to burn the unburned gas, and the iron scrap is preheated using the combustion heat. And the method of reducing the electric power consumption unit which melt | dissolves iron scrap is disclosed.

JP-A-10-292990 Japanese Patent Laid-Open No. 10-310814

However, the method disclosed in Patent Document 1 has a problem in terms of effective use of exhaust gas because the exhaust gas generated in the melting chamber is discharged without being burned. Further, in the method disclosed in Patent Document 2, the cold iron source is oxidized by the O ₂ gas supplied to the preheating shaft portion. As a result, the yield is reduced, or the work of reducing FeO generated by the oxidation with coke or the like is performed. Is required, and there is a problem that the power consumption rate is reduced.

  The present invention is a technology developed in view of the above-described circumstances of the prior art, and the object of the present invention is to provide a composite arc melting furnace in the melting of a cold iron source in a composite arc melting furnace. Cold iron source by combined arc melting furnace of cold iron source, which can effectively use the generated exhaust gas for preheating the cold iron source without causing oxidation of the cold iron source and reduce the power intensity The present invention is to propose a melting method and a combined arc melting furnace.

  In order to achieve the object, in the present invention, instead of introducing the oxygen-containing gas as proposed in Patent Document 2, by introducing ammonia gas, the ammonia gas and the unburned gas component in the exhaust gas We propose a method that uses the heat generated at this time to preheat the cold iron source and an arc melting furnace for that purpose.

It is known that ammonia gas reacts with carbon monoxide and is reformed into various hydrocarbons, methanol, dimethyl ether, and the like. An example of the chemical reaction formula is shown in the following formula (1).
2NH ₃ + CO → CH ₄ + H ₂ O + N ₂ (1)

The standard enthalpy change per mole of NH _{3 in the} formula (1) is −13.6 kcal / mol—NH ₃ , and this reaction is an exothermic reaction.

  That is, the present invention uses a complex arc melting furnace comprising a melting chamber and a shaft-type preheating chamber that stands upright and communicates with the melting chamber to dissolve a cold iron source that descends sequentially in the preheating chamber. In the method for melting a cold iron source using a composite arc melting furnace that is preheated using high-temperature exhaust gas generated in the chamber and is subsequently guided to the melting chamber and melted in the arc, the cold iron source includes a preheating chamber and A melting method using a combined arc melting furnace of a cold iron source is proposed, in which ammonia gas is blown into the preheating chamber under a condition that extends over the upper portion of the melting chamber.

In the melting method of the cold iron source by the combined arc melting furnace,
(1) In the preheating chamber, a reaction between ammonia gas and exhaust gas generated from the melting chamber is guided to reform unburned components of the exhaust gas, and heat generated during this reaction is converted into cold iron in the preheating chamber. To preheat the source,
(2) The ammonia gas is blown from an ammonia gas introduction port provided at one or a plurality of locations in a region from the position of the molten metal surface in the melting chamber of the preheating chamber to the upper end position of the deposition layer of the cold iron source in the upper portion of the preheating chamber. (3) The amount of ammonia gas blown is 5 to 25% of the amount of exhaust gas generated from the dissolution chamber,
Is a more preferable solution.

  Further, in the present invention, a melting chamber provided with an arc electrode for arc melting of a cold iron source, and a cold iron that is installed above and is connected to the melting chamber and is charged and filled. A shaft type preheating chamber that preheats the source, and one or a plurality of ammonia gas inlets are provided in the region from the position of the molten metal surface in the melting chamber of the preheating chamber to the top end position of the cold iron source deposition layer in the upper portion of the preheating chamber A composite arc melting furnace is provided.

According to the present invention configured as described above, when producing a molten steel by arc melting of a cold iron source, ammonia (NH ₃ ) gas is added to the exhaust gas (unburned gas) generated when the cold iron source is melted. The reaction heat generated during the reaction can be used to preheat the cold iron source, so that the cold iron source is not oxidized and the heat energy of the exhaust gas is used effectively. can do.
Moreover, according to the present invention, it is possible to provide a composite arc melting furnace that is effective in reducing the power consumption.

It is a schematic sectional drawing which shows one Embodiment of the composite arc melting furnace of this invention. It is a schematic sectional drawing which shows the composite arc melting furnace used for the Example of this invention.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a longitudinal section showing an example of a combined arc melting furnace used in the present invention.

  As shown in the figure, the composite arc melting furnace 1 used in the present invention comprises a melting chamber 2 and a shaft-type preheating chamber 3 standing upward from a part of the upper portion thereof, and the inside thereof is lined with a refractory. ing. The melting chamber 2 has a furnace bottom electrode 6 at the bottom, and has the shaft-shaped preheating chamber 3 and the water-cooled furnace wall 4 communicating with the melting chamber 2 at the top. A furnace lid 5 is provided so as to cover the opening. The furnace lid 5 has a water-cooling structure that can be opened and closed, and a graphite upper electrode 7 disposed so as to penetrate the furnace lid 5 is provided in the melting chamber 2 so as to be vertically movable. The upper electrode 7 and the furnace bottom electrode 6 are energized by a direct current power source (not shown) through a cold iron source in the furnace so that an arc 19 can be generated therebetween. It has become.

  Above the preheating chamber 3, a bottom-opening type supply bucket 13 suspended from the traveling carriage 24 is provided, and from this supply bucket 13, an openable and closable supply port provided at the top of the preheating chamber 3 A cold iron source (for example, iron scrap) 15 is charged into the preheating chamber 3 through 20.

  The cold iron source 15 charged in the preheating chamber 3 is preheated while descending sequentially with time, and eventually reaches the melting chamber 2 and is then melted by the heat of the arc 19 generated from the upper electrode 7. When the cold iron source 15 is melted, high-temperature exhaust gas (unburned gas) is generated in the melting chamber 2. The exhaust gas is sucked into the duct 21 through the preheating chamber 3 by a blower or a dust collector (not shown) provided upstream of the duct 21 provided above the preheating chamber 3. The cold iron source 15 is preheated by the high temperature exhaust gas. The preheated cold iron source 15 in the preheating chamber 3 falls freely according to the speed of melting in the melting chamber 2 and moves sequentially or intermittently into the melting chamber 2 sequentially.

  As described above, the present invention is a method in which ammonia gas is blown into the preheating chamber 3 while the high-temperature exhaust gas generated in the melting chamber 2 is sucked into the duct 21 through the preheating chamber 3. As a result, in the present invention, ammonia gas and unburned gas (such as CO) in the exhaust gas rising in the preheating chamber 3 cause a reaction as expressed by the above formula (1), and the reaction causes a hydrocarbon system. It is characterized in that gas is generated and the reaction heat generated at this time is used for preheating the cold iron source 15 in the preheating chamber 3.

  In addition, according to such a series of reaction, since the said reforming reaction using the exhaust gas sensible heat of the high temperature (about 400-1000 degreeC) generate | occur | produced in the melting chamber 2 occurs, unburned gas is made effective. Not only can it be used, but the cold iron source 15 in the preheating chamber 3 can be efficiently preheated without being oxidized. And since the cold iron source 15 preheated in this way is melted in the melting chamber 2, the reduction of the power consumption is achieved simultaneously with the efficient preheating and melting of the cold iron source 15. can do.

In the preheating chamber 3, in addition to the reaction shown in the above equation (1), the reaction between the hydrocarbon gas generated by this reaction and CO ₂ in the exhaust gas (the following equation (2)), and the exhaust gas sensible heat of ammonia gas The utilized thermal decomposition reaction (the following formula (3)) occurs, the amount of CO and H _{2 in} the exhaust gas increases, and the exhaust gas can be reformed.
CH ₄ + CO ₂ → 2CO + 2H ₂ (2)
2NH ₃ → N ₂ + 3H ₂ (3)

  Ammonia gas is blown from an ammonia gas inlet 25 provided on the side wall of the preheating chamber 3. The ammonia inlet 25 is provided at one or a plurality of locations in the circumferential direction and the longitudinal direction of the side wall in the region from the molten metal surface position in the melting chamber 2 to the top position of the deposition layer of the cold iron source 15 in the preheating chamber 3. . That is, the reaction between the exhaust gas generated from the melting chamber 2 and the ammonia gas can be reliably performed at each position level, and by providing the ammonia introduction ports 25 at a plurality of positions, the cooling in the preheating chamber 3 can be performed. This is because the heat of reaction can be effectively used for preheating the cold iron source 15 without the temperature of the iron source 15 being biased.

  The furnace lid 5 of the melting chamber 2 is provided with an oxygen blowing lance 8 and a charcoal blowing lance 9 so as to penetrate the furnace lid 5, and the oxygen blowing lance 8 assists the melting of the cold iron source 15. On the other hand, an auxiliary heat source such as coke, char, coal, charcoal, graphite, biomass charcoal powder, or a mixture of these from the charcoal blowing lance 9 via air, nitrogen, etc. Is blown. As a result, the generated exhaust gas always contains an unburned component (CO gas).

  In addition, the furnace bottom portion of the melting chamber 2 on the side opposite to the preheating chamber 3 is closed by a door 22 and has a steel outlet 11 filled with stuffed sand or mud agent on the inner side thereof, Further, the side wall portion is provided with an outlet 12 which is closed by a door 23 and is filled with stuffed sand or mud agent.

  A burner 10 is attached to the furnace lid 5 at a position corresponding to the upper portion of the steel outlet 11, and fossil fuel or biomass fuel such as heavy oil, kerosene, pulverized coal, propane gas, natural gas, etc. By burning in the melting chamber 2 with air, oxygen, or oxygen-enriched air, the temperature of the molten steel to be output can be raised.

Hereinafter, a procedure for melting the cold iron source in the DC arc furnace 1 will be described.
First, the cold iron source 15 is charged into the preheating chamber 3 from the supply bucket 13. The charged cold iron source 15 passes through the preheating chamber 3 and is first charged into the melting chamber 2 and then gradually filled into the preheating chamber 3. In order to uniformly charge the cold iron source 15 into the melting chamber 2, the cold iron source 15 is placed in the melting chamber 2 on the side opposite to the side directly connected to the preheating chamber 3 with the furnace lid 5 opened. It can also be charged. In addition, hot metal may be charged into the melting chamber 2 when the cold iron source 15 is charged, and according to this, the amount of power used can be significantly reduced by the heat of the hot metal. The hot metal is charged into the melting chamber 2 with a ladle for supply (not shown) or hot metal (not shown) connected to the melting chamber 2.

  Next, while feeding a direct current between the furnace bottom electrode 6 and the upper electrode 7 in the melting chamber 2, the upper electrode 7 was moved up and down, and was inserted between the furnace bottom electrode 6 and the upper electrode 7 or charged. An arc 19 is generated between the cold iron source 15 and the upper electrode 7, and the cold iron source 15 is melted by the heat of the arc 19. At this time, it is preferable to generate the molten slag 18 by melting the flux. This is because the molten metal 17 can be kept warm by the molten slag 18. In addition, when there is too much production amount of the molten slag 18, you may discharge the molten slag 18 from the spout 12 during operation.

After the furnace bottom electrode 6 and the upper electrode 7 are energized, when the oxygen blowing lance 8 and the carbonaceous material blowing lance 9 can be inserted into the melting chamber 2, oxygen is supplied from the oxygen blowing lance 8, and a cold iron source is supplied. It is preferable that carbon material is blown into the molten slag 18 as an auxiliary heat source from the carbon material blowing lance 9 while assisting the melting of 15. The amount of oxygen blown is preferably 15 Nm ³ or more per ton of the molten metal 17 staying in the melting chamber 2 between the start of melting and the tapping. This is because when the amount of oxygen blown is less than 15 Nm ³ per ton of molten metal, the effect of reducing the power intensity by melting the cold iron source and the oxidation reaction of the carbonaceous material described later is small.

  The carbon material dissolved in the molten metal 17 or the carbon material suspended in the molten slag 18 reacts with oxygen blown from the oxygen blowing lance 8 to be decarburized to become CO gas, and its reaction heat is an auxiliary heat source. This will contribute to the reduction of power consumption. Further, the molten slag 18 is expanded by forming with the CO gas as the reaction product, so that the tip of the upper electrode 7 is buried in the molten slag 18. Therefore, the arc 19 generated from the upper electrode 7 is wrapped by the molten slag 18, so that the heat receiving efficiency of the arc 19 is increased and the preheating efficiency of the cold iron source 15 can be improved.

  The addition of the carbon material by the carbon material blowing lance 9 is determined according to the amount of oxygen blown from the oxygen blowing lance 8, and is preferably equal to or more than the chemical equivalent of the blown oxygen. This is because if the carbon content of the carbon material is smaller than the oxygen gas to be blown, the molten metal 17 is excessively oxidized or the carbon concentration is lowered.

  A large amount of high-temperature exhaust gas generated when the cold iron source 15 is melted as described above is supplied to the preheating chamber 3 and then blown from the ammonia gas inlet 25 provided on the side wall of the preheating chamber 3. The cold iron source 15 in the preheating chamber 3 is efficiently preheated by the heat generated at the same time as it is reformed by reacting with gas to various hydrocarbons, oxygenated compounds such as methanol.

The composition of exhaust gas generated from the melting chamber _{2, CO: 2~8%, CO} 2: 5~15%, O 2: 1~15%, N 2: 50~80%, H 2 O: 0~ _5%, H 2: 0 to 3%.

  The amount of ammonia gas blown into the preheating chamber 3 is about 5 to 25%, preferably 8 to 18%, of the flow rate of the exhaust gas generated from the melting chamber 2. This is because when the amount of ammonia gas blown is less than 5% of the exhaust gas flow rate, the amount of ammonia gas is insufficient with respect to the amount of exhaust gas, and the reforming reaction does not occur sufficiently. Is excessive and is released unreacted, resulting in odor problems.

  Further, since the cold iron source 15 in the preheating chamber 3 falls and freely falls into the melting chamber 2 in accordance with the amount of the cold iron source 15 in the melting chamber 2, this decrease is reduced by the supply bucket 13. Is supplemented by sequentially charging the cold iron source 15 into the preheating chamber 3. The charging of the cold iron source 15 into the preheating chamber 3 is continuous or intermittent so that the cold iron source 15 can be maintained (continuously) across the preheating chamber 3 and the melting chamber 2. To do. At that time, it is preferable that the cold iron source 15 remains in the preheating chamber 3 and the melting chamber 2 at 50 mass% or more of the amount of the hot water discharged at one time. This is because the high-temperature exhaust gas generated from the melting chamber 2 is efficiently used for preheating the cold iron source 15.

  Although the case where the arc furnace 1 is a direct current type has been described above, the present invention can be applied without any problem even when an alternating current type arc furnace is used.

  In this example, the DC capacity of the furnace having a melting capacity of 180 tons comprising the melting chamber 2 (furnace diameter 7.2 m, height 4 m) and the preheating chamber 3 (width 3 m, length 5 m, height 7 m) shown in FIG. In the combined arc melting furnace 1, first, about 70 tons of normal-temperature iron scrap 15 is charged into the preheating chamber 3, and then 70 tons of normal-temperature iron scrap 15 is charged into the melting chamber 2 with a diameter of 30 The arc melting of iron scrap in the melting chamber 2 was started by generating an arc 19 having a maximum power source capacity of 750 V and 130 KA using the inch upper graphite electrode 7. During melting operation of the iron scrap 15, ammonia gas is blown from the ammonia gas inlet 25 provided on the side wall of the preheating chamber 3 under the conditions shown in Table 1, and the lower end inlet of the preheating chamber 3 (before the reforming reaction with ammonia gas) and the preheating chamber The gas composition of the exhaust gas was measured at the upper exhaust duct 21 inlet position (after the reforming reaction with ammonia gas), and the exhaust gas temperature was measured at the exhaust duct 21 inlet. The ammonia gas inlets 25 were provided at three locations: A: the position of the molten metal in the melting chamber, C: the upper end position of the cold iron source in the upper part of the preheating chamber, and B: the intermediate position between A and C.

In this example, immediately after energization, quick lime and fluorite were added into the melting chamber, oxygen was blown from the oxygen blowing lance 8 at 6000 Nm ³ / hr, and coke was blown from the carbonaceous material blowing lance 9 at 80 kg / min. The quicklime and fluorite were heated to form molten slag 18 and then formed by blowing oxygen and coke, and the tip of upper electrode 7 was buried in molten slag 18. The voltage at this time was set to 550V. In the arc melting of iron scrap, the oxygen blowing rate was 30 Nm ³ / t and the coke blowing rate was 30 kg / t.

The results of the present invention are shown in Table 1 together with a comparative example (no introduction of ammonia gas).
The temperature of the ammonia gas inlet 25 when the ammonia gas was blown was 800 to 1300 ° C. for A, 500 to 800 ° C. for B, and 300 to 500 ° C. for C. Blowing amount of ammonia gas, the invention examples 1 to 5, 38 Nm ³ / min reasonable 7% of the exhaust gas flow rate, the invention example 6, was 57 nm ³ / min is equivalent to 15%.

  From the results of Table 1, in Invention Examples 1 to 6, by introducing ammonia gas into the preheating chamber and reacting with the exhaust gas to perform reforming, iron scrap in the preheating chamber can be preheated efficiently. It was confirmed that the power consumption can be reduced. Among these, in particular, in Invention Example 6, the ammonia gas was blown from three locations A to C, so that the exhaust gas temperature was 200 ° C. higher than the comparative example in which the ammonia gas was not blown, The power consumption can be reduced by 40 kWh / ts or more.

  The technology according to the present invention is useful as a method of effectively using a cold iron source such as iron scrap and direct reduced iron by the exemplified composite arc melting furnace, but the idea is applied to other melting furnaces that generate exhaust gas. It is possible to do.

DESCRIPTION OF SYMBOLS 1 Arc furnace 2 Melting room 3 Preheating room 4 Furnace wall 5 Furnace lid 6 Furnace bottom electrode 7 Upper electrode 8 Oxygen blowing lance 9 Carbon material blowing lance 10 Burner 11 Outlet 12 Outlet 13 Supply bucket 15 Cold iron source 17 Molten metal 18 Molten slag 19 Arc 20 Supply port 21 Duct 22 Door 23 Door 24 Traveling carriage 25 Ammonia gas introduction port

Claims (5)

High-temperature exhaust gas generated in the melting chamber by a combined arc melting furnace composed of a melting chamber and a shaft-type preheating chamber standing on the upper side thereof and communicating with the melting chamber. In the melting method of the cold iron source using the composite arc melting furnace, which is preheated with the use of, and subsequently led to the melting chamber and arc melting.
A melting method using a combined arc melting furnace for a cold iron source, wherein ammonia gas is blown into the preheating chamber in a state in which the cold iron source exists across the preheating chamber and the upper part of the melting chamber.   In the preheating chamber, a reforming reaction between the ammonia gas and the exhaust gas generated from the melting chamber is guided to reform unburned components of the exhaust gas, and heat generated during the reaction is supplied to a cold iron source in the preheating chamber. The melting method by the composite arc melting furnace of the cold iron source of Claim 1 characterized by using for the preheating of this.   The ammonia gas is blown from one or a plurality of ammonia gas inlets in a region from the position of the molten metal surface in the melting chamber of the preheating chamber to the upper end position of the cold iron source deposition layer in the upper portion of the preheating chamber. The melting method by the composite arc melting furnace of the cold iron source of Claim 1 or 2.   The melting amount of the cold iron source according to any one of claims 1 to 3, wherein the ammonia gas is blown in an amount of 5 to 25% of the amount of exhaust gas generated from the melting chamber. Method. A melting chamber provided with an arc electrode for arc melting of a cold iron source, and a shaft type which is installed above the melting chamber and communicates with the melting chamber and preheats the charged and filled cold iron source It is composed of a preheating chamber, and is provided with one or a plurality of ammonia gas inlets in a region from the position of the molten metal surface in the melting chamber of the preheating chamber to the upper end position of the deposited layer of the cold iron source in the upper portion of the preheating chamber. Combined arc melting furnace.

Images