JP2010126774A - Method for manufacturing sintered ore - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing sintered ore with which in the case of using at least a part of exhausted gas in a sintering machine by circulating and even in the case of lowering oxygen concentration in the exhausted gas, the lowering of combustion speed of carbonaceous material in a charged layer is prevented and the manufacturing rate is improved with maintenance and the quality of the sintered ore can be improved. <P>SOLUTION: The charged layer is formed on a pallet 2 by charging sintering raw material on the pallet 2 circulatingly moved, and when the charged layer is sintered by using the sintering machine 1 for manufacturing the sintered ore by sintering this charged layer; this method for manufacturing the sintered ore is performed as the followings, that gaseous fuel is supplied from the top part into the upstream side of the charged layer and also, at least a part of the exhaust gas generated, when the exhaust gas generated in the sintering machine 1 and/or the manufactured sintered ore, are cooled, is circulated and injected from the upper part to the downstream side of the charged layer. It is desirable that the gaseous fuel supplied into the charged layer is diluted to the lower limit or lower of combustion. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a sintered ore that agglomerates a powdery raw material using a downward suction type Dwytroid (DL) sintering machine, and produces a raw material suitable for a smelting process. The present invention relates to a method for producing sintered ore in which a part of exhaust gas is circulated and used when sintering raw materials.

  Sintered ore, which is the main raw material for the blast furnace smelting method, is generally composed of iron ore powder, recovered iron mill powder, sintered ore sieving powder, CaO-containing raw materials such as limestone and dolomite, granulation aids such as quick lime, and powder coke Using a charcoal material (solid fuel) such as anthracite or an anthracite as a raw material, a Dwytroid (DL) sintering machine (hereinafter simply referred to as “sintering machine”) which is an endless moving bed type grate-type sintering machine. Manufactured. The raw material of the sintered ore is mixed while adding an appropriate amount of water using a drum mixer or the like, and then granulated to form a sintered raw material that is a pseudo particle having an average diameter of 3.0 to 6.0 mm. The formed sintering raw material is dried and then charged onto an endless moving pallet of a sintering machine to form a charging layer called a sintering bed. The thickness (height) of the charging layer is about 400 to 800 mm. Thereafter, the carbon material in the charging layer is ignited by an ignition furnace installed above the charging layer. By sucking the air in the charging layer downward through the wind box arranged under the pallet, the carbonaceous material in the charging layer burns sequentially, and the combustion gradually becomes lower as the pallet moves. Go forward and forward. Due to the combustion heat generated at this time, the sintered raw material is burned and melted to produce a sintered cake. Thereafter, the obtained sintered cake is cooled by a cooler after crushing, sized, and recovered as a product sintered ore composed of agglomerates having a predetermined particle size (for example, 5.0 mm or more).

At this time, the air that has passed through the charging layer is removed by the dust collector, and then sucked by the exhaust fan to become exhaust gas and discharged out of the system. In general, this exhaust gas contains a small amount of harmful gases such as SO _x and NO _x in addition to N ₂ , O ₂ , CO ₂ and CO. Furthermore, although fine dust generated from the charging layer is removed when passing through the dust collector, it is not perfect. Therefore, the exhaust gas from the sintering machine needs to be treated by an exhaust gas treatment process. In addition, there is a similar problem with the exhaust gas when the cooler is cooled. In order to reduce the load of exhaust gas treatment, a technique is known in which at least a part of exhaust gas from a sintering machine is circulated and reused (see, for example, Patent Document 1). By using exhaust gas in a circulating manner, it is possible to reduce the amount of harmful gas and dust discharged outside the sintering system, and to reduce the total amount of exhaust gas and to treat the exhaust gas at low cost. Become. In the technique described in Patent Document 1, the exhaust gas in the ignition furnace region is circulated in the center of the sintering machine in the longitudinal direction, and the exhaust gas in the rear of the sintering machine in the longitudinal direction is circulated in the front of the sintering machine. Specifically, an operation is performed in which exhaust gas at the rear of the sintering machine is collected and circulated to the front.
Japanese Patent Laid-Open No. 5-43951

  However, since the circulating exhaust gas has a low oxygen concentration, there is a problem that the combustion rate of carbonaceous materials such as powdered coke in the charging layer is lowered. On the other hand, in patent document 1, the oxygen concentration in exhaust gas is prescribed | regulated as 18% or more. For this purpose, the exhaust gas circulation rate needs to be a predetermined value or less, and the effect of reducing the total amount of exhaust gas is not sufficient.

  Therefore, if the exhaust gas circulation rate is increased and the load of the process for treating harmful gases and dusts discharged during the sinter production process is sufficiently reduced, the circulating exhaust gas has a low oxygen concentration. The burning rate of the carbonaceous material in the bed is lowered, and the production rate is lowered. Furthermore, when exhaust gas is supplied to the downstream side of the sintering machine, the cooling rate of the charged layer (sintered cake) after firing decreases due to the sensible heat of the exhaust gas, so the production rate also decreases. It is difficult to solve such a problem of a decrease in production rate by using conventional techniques.

  Therefore, the object of the present invention is to solve such problems of the prior art, and when circulating and using at least a part of the exhaust gas from the sintering machine, even if the oxygen concentration in the exhaust gas decreases, An object of the present invention is to provide a method for producing a sintered ore that can prevent a reduction in the burning rate of the carbonaceous material, maintain and improve the production rate, and improve the quality of the sintered ore.

The features of the present invention for solving such problems are as follows.
(1) Using a sintering machine that charges a sintering raw material on a circulating pallet to form a charging layer on the pallet, sinters the charging layer to produce a sintered ore,
When sintering the charging layer, supplying gaseous fuel to the upstream side of the charging layer from above,
The exhaust gas generated in the sintering machine and / or the exhaust gas generated when the produced sintered ore is cooled is circulated and blown into the downstream side of the charging layer from above. A method for producing sintered ore.
(2) The method for producing a sintered ore according to (1), wherein the gaseous fuel supplied to the charging layer is diluted to a lower combustion limit concentration or less.

  According to the present invention, by exhaustively using the exhaust gas from the sintering machine, it is possible to reduce the load of the exhaust gas treatment process, and at the same time, it is possible to suppress or extend the decrease in the high temperature region holding time of the charging layer. For this reason, it is possible to maintain and improve the quality such as the production rate, yield, and cold strength in the production of sintered ore while suppressing the exhaust gas emission.

  In the operation of the sintering machine, when the exhaust gas is circulated, the inventors of the present invention have reduced the oxygen concentration in the exhaust gas, the combustion rate of carbonaceous materials such as coke breeze is reduced, and the temperature in the charging layer is reduced. In addition, studies were made on the problem that the cooling rate was delayed due to the sensible heat of the exhaust gas and the production rate was lowered. And in this invention, said problem was solved by supplying gaseous fuel to the charging layer of the upstream (front stage of the whole sintering machine) near the ignition furnace of a sintering machine.

  For example, by supplying city gas as a gaseous fuel at a lower combustion limit concentration of 4.8% by volume or less to the downstream side of the sintering furnace ignition furnace (before the entire sintering machine), the combustion / melting zone inside the charging layer The width (high temperature range holding time) can be extended. As a result, even if exhaust gas circulation is performed on the rear side, the sinter properties and the production rate are not deteriorated. Furthermore, the sinter properties can be further improved by reducing the coke mixing ratio in order to adjust the combustion / melting zone temperature inside the sintering bed to an appropriate 1200 to 1400 ° C.

  According to the study by the present inventors, even if the temperature in the charging layer becomes too high during sintering, vitreous is formed, the strength of the sintered ore is reduced, and the yield is reduced. Therefore, in order to keep the quality of the sintered ore good, the temperature in the charging layer does not increase to a high temperature exceeding 1400 ° C., and the temperature in the charging layer is in the range of 1200 to 1400 ° C. It is preferable to sinter for a longer time. Therefore, when the combustibility of the carbonaceous material added to the sintered raw material by the gaseous fuel is improved, the time that is maintained in the high temperature range is increased and the production rate is improved, but the maximum temperature in the charging layer exceeds 1400 ° C. If so, it is preferable to adjust the amount of carbonaceous material according to the amount of gaseous fuel supplied, because the strength of the sintered ore produced is reduced.

  The effect in the case of supplying gaseous fuel to a charging layer is demonstrated using FIG. FIG. 3 is an example in which the temperature distribution in the thickness direction in the charging layer is measured, and the charging layer height direction position indicates a position in the height direction where the lower end of the charging layer is zero. The broken line in the figure shows the case where normal air is used and 5.0 mass% of powder coke is added as a carbonaceous material. The solid line in the figure shows the case where the amount of carbonaceous material added is 4.6 mass% and liquefied natural gas (LNG) is mixed with 0.4% by volume of air. It turns out that the area | region hold | maintained between 1200-1400 degreeC becomes long by supplying LNG.

  Gaseous fuel has an ignition temperature lower than that of powdered coke, and can be burned at an upper part (near the surface layer part) than the position where the coke in the charging layer burns. Thus, it is considered that the high temperature range retention time can be extended without increasing the maximum temperature reached in the charging layer.

As the gaseous fuel, it is preferable to use a combustible gas diluted to a combustion lower limit concentration or less. By using the diluted combustible gas, it is possible to adjust combustion at a predetermined region position in the charging layer without abnormal combustion near the sintering bed. As the gaseous fuel, it is preferable to use a combustible gas diluted to a concentration of 3/4 or less of the lower limit concentration of combustion. More preferred is a combustible gas diluted to a concentration of 3/5 or less of the lower combustion limit concentration, and still more preferred is a combustible gas diluted to a concentration of 1/5 or lower of the lower combustion limit concentration. In this case, the lower limit is preferably 1/50 or more. The reason why it is preferable to use a combustible gas diluted to 3/4 or less of the lower combustion limit concentration is the following two points.
(A) Since the supply of the gaseous fuel to the upper part of the charging layer sometimes causes explosive combustion, at least at room temperature, even if there is a fire type, it is not burned.
(B) Even if it reaches the electrostatic precipitator on the downstream side of the sintering machine without being burned completely on the sintering machine (in the charging layer), It is performed under the condition that there is no possibility of burning under discharge, that is, under the condition of 3/4 or less of the lower limit concentration of combustion.
On the other hand, if the concentration is 1/50 or more of the lower combustion limit concentration, there is an effect of extending the time during which the inside of the charging layer is maintained in the high temperature range. The lower limit concentration of combustion is the lower limit value of the concentration to be ignited and burned, 40% by volume for blast furnace gas, 5% by volume for coke oven gas, 2.2% by volume for propane gas, and 4.8% for natural gas. %, Methane gas is 4.9% by volume.

  Therefore, by adjusting the concentration of the gaseous fuel in the above range according to the amount of carbonaceous material (solid fuel), it can be burned at an appropriate position in the charging layer, and the inside of the charging layer becomes a high temperature range. The holding time can be extended. Specifically, blast furnace gas, coke oven gas, blast furnace / coke oven mixed gas, propane gas, natural gas, liquefied natural gas (LNG), methane gas, or the like can be used as the gaseous fuel.

  As described above, by injecting diluted gaseous fuel, the thickness of the combustion / melting zone formed in the charging layer can be increased. In the present invention, the thickness of the combustion / melting zone in the charging layer is preferably at least 15 mm, more preferably, in order to adjust the maximum reached temperature of the charging layer to 1400 ° C. or less and adjust the high temperature region holding time. The diluted gas fuel is supplied under conditions of 20 mm or more, more preferably 30 mm or more. In normal operation (operation without diluting fuel supply), the upper layer of the charging layer has a thinner combustion / melt zone than the middle and lower layers, and a thicker combustion / melt zone in the upper layer. In the present invention, diluted gas fuel is supplied in the sintering front portion (C region described later) as described later. Under conditions where the temperature distribution in the upper part of the combustion / melting zone is gentle upward (in general, the wider the combustion / melting zone width), the position where the diluted gas fuel ignites and starts to generate heat. Therefore, the coke ignites and moves away from the level at which heat is generated by combustion, and the combustion / melting zone expansion effect by dilute gas fuel injection is increased.

  In the present invention, gaseous fuel is supplied from the upper part of the charging layer of the sintering machine to the front part (upstream side of the charging layer on the pallet) from the raw material charging side to the discharge side, and the rear part (on the pallet). The circulating exhaust gas is supplied to the downstream side of the charging layer. An embodiment of the present invention will be described with reference to FIG.

  FIG. 1 is a schematic configuration diagram showing an example of a sintering machine. In FIG. 1, reference numeral 1 denotes a sintering machine body, which includes an endless moving floor pallet (hereinafter referred to as “pallet”) 2 and a wind box 3. The powdery sintered raw material charged into the pallet 2 from the sintering raw material charging device 4 is ignited in the ignition furnace 5 and then supplied from the upper gaseous fuel supply hood 6 and the exhaust gas blowing hood 7. As well as being subjected to the action of the sucked air, the exhaust gas coming out of the sintering raw material layer (charging layer) is sucked and exhausted downward by the lower windbox 3, and the sintering is completed and exhausted. Is done. The gaseous fuel may be supplied by any method as long as it is supplied into the hood. However, it is possible to directly blow the gaseous fuel into the hood or to blow a gas previously mixed with air into the hood. In FIG. 1, the gaseous fuel is supplied into the hood by a separate system from the air. Here, as shown in FIG. 1, the pallet 2 is shown in order from the raw material charging side to the discharge side, A: raw material charging region, B: ignition region, C: sintering front, D: sintering rear Divide into C is a region where air and gaseous fuel are supplied from the top, D is a region from the rearmost end of the region of C to the discharge portion, and a region where circulating exhaust gas is supplied to at least a part from the top Is included. 11 is an exhaust gas supply blower, 12 is an exhaust gas flow rate adjusting valve, 13 is a dust collector, 14 is an exhaust fan, and 15 is a chimney. As the circulating exhaust gas, in addition to the main exhaust gas of the sintering machine, a cooler exhaust gas generated from a cooler for cooling the produced sintered ore can be used.

  In order to improve the productivity of sintered ore, gaseous fuel is supplied. The gaseous fuel is supplied to the area C: sintering front part, and air is supplied from the air line 8 to the gaseous fuel. Gaseous fuel is supplied from the line 9 to the gaseous fuel supply hood 7, mixed at a predetermined ratio, and blown into the charging layer. The C region is preferably 70% or less of the front portion with respect to a region (C + D region) obtained by subtracting the ignition region (B region) from the firing effective great area (B, C, D region). . This is because if it exceeds 70%, the quality (strength, reactivity) of the sintered ore fired in the lower layer portion of the charging layer may be deteriorated. In general, about 20 to 50% is more preferable. The sintering speed is improved according to the amount of gaseous fuel diluted at the front part of the sintering machine, and the lowering of the sintered surface in the sintering raw material becomes faster. In addition, since the ignition temperature of gaseous fuel is lower than that of charcoal (powder coke), it burns in the upper part of the charging layer than the charcoal burns, and does not increase the maximum temperature and maintains the high temperature range holding time. Can be extended.

  On the other hand, the ratio of the D region is set to 30% or more in the rear portion with respect to the C + D region, and the circulating exhaust gas is blown from the circulating exhaust gas line 10 into at least a part of the D region. As the circulating exhaust gas, a part of the exhaust gas sucked from the B, C and D regions mixed at a predetermined ratio is circulated and used. The amount of the circulating exhaust gas used is the B region (ignition region), the C region, The amount of exhaust gas is a predetermined ratio (hereinafter referred to as “exhaust gas circulation rate”) with respect to the total amount of exhaust gas exhausted from the D region. In addition, the gas suck | inhaled as circulating exhaust gas is good also from only any 1 or 2 area | regions of BD area | region. The B region has a relatively high residual oxygen concentration in the exhaust gas, the D region has a relatively high exhaust gas temperature, and the C region is in the middle, so it can be selected in accordance with the operating conditions.

  As shown in FIG. 1, a gaseous fuel blowing device for supplying gaseous fuel having a gaseous fuel supply hood on the upstream side of the sintering machine, and an exhaust gas circulation for supplying exhaust gas having an exhaust gas blowing hood on the downstream side of the sintering machine By using a sintering machine equipped with an apparatus, the present invention can be suitably implemented. At the gaseous fuel injection position, a thermocouple or ignition detection sensor is provided. When ignition occurs, the supply of gaseous fuel is stopped by the interlock function, and the inside of the gaseous fuel supply hood is purged with nitrogen gas quickly. It is preferable to provide a function capable of restarting the fuel injection operation.

A production test of the sintered ore was performed using a downward suction type Dwytroid sintering machine similar to that shown in FIG. The length of the used sintering machine is 90 m from the ignition furnace to the discharge section, and the width is 5 m. A gas fuel supply hood having a length (pallet movement direction) of 30 m and a size covering the entire machine width is provided at a position about 10 m behind the ignition furnace of the sintering machine, and a 10 m interval is provided downstream thereof. A circulating exhaust gas blowing hood with a length (pallet moving direction) of 40 m and a size that covers the entire machine width is provided, and gaseous fuel is blown upstream of the charging layer and circulating exhaust gas is injected downstream of the charging layer. No. 1 shown in Table 1. The sintered ore was manufactured on the conditions of 1-3. When circulating exhaust gas was blown, a part of the exhaust gas was circulated using an exhaust gas blowing hood. The details of the exhaust gas blowing hood are shown in FIG. In this embodiment, five hoods are continuously installed in the machine length direction, and in FIG. 1, the entire five hoods are represented as one hood. In FIG. 2, the pallet moves from left to right toward the paper surface, and an exhaust gas blowing pipe 20 is installed on the upper part of the exhaust gas blowing hood 7. 21 is a sintering main exhaust gas blowing line, and 22 is a sintering cooler exhaust gas blowing line. Reference numeral 23 denotes a charging layer. Sintered main exhaust gas was 200 ° C., and 6750 Nm ³ / h × 80 exhaust gases were supplied from each exhaust gas blowing pipe 20.

  LNG (liquefied natural gas) was used as the gaseous fuel. The blowing concentration of the gaseous fuel is a concentration with respect to the total amount of suction air, and is a concentration in the gaseous fuel supply hood. The lower combustion limit concentration of LNG was 4.8% by volume, and blowing was performed so as to be 0.8% by volume in the gaseous fuel supply hood. Moreover, the amount of coke blended is the ratio of the powder coke used as a charcoal material, and is expressed as an external number with respect to the total amount of sintered raw materials (iron ore, secondary raw materials, ores). In addition, although LNG liquefies natural gas and stores and conveys it, it used it after vaporizing in implementation of this invention.

  In Table 1, no. No. 1 is a case of a conventional method in which circulating exhaust gas is blown and gaseous fuel is not blown. No. 2 is a case where only circulating exhaust gas is blown into the charging layer downstream side and gaseous fuel is not blown. 3 is an example of the present invention, which is a case where an operation is performed in which gaseous fuel is injected upstream of the charging layer and circulating exhaust gas is injected downstream of the charging layer. In each case, the production rate, product yield, product strength, product reduction rate, and product reduced powdering rate of the manufactured sintered ore were measured. The results are also shown in Table 1.

  According to Table 1, no. No. 2 decreases the production rate. As shown in FIG. 3, the decreased production rate was recovered by performing gaseous fuel injection and exhaust gas circulation, and the product yield, product strength, and product reduction rate were improved. Furthermore, the amount of coke added could be reduced more than calculated from the calorific value of the gaseous fuel. Compared to the case without dilution gas fuel injection, in the case of the present invention, the sintering combustion / melting zone expands to the upper layer side than before (because combustion heat generation of the dilution gas fuel occurs before coke), and dilution gas fuel As the air is heated, it is supplied to the coke combustion zone in a state where the temperature of the air is high. Therefore, even if the coke blending amount is reduced beyond the amount calculated from the calorific value, the temperature required for the combustion / melting zone A level of 1200 to 1400 ° C. can be secured. The calorific value of the amount of coke that can be reduced corresponds to about twice the calorific value of the diluted gaseous fuel used. That is, the total energy consumption of the process can be reduced, and the carbon dioxide generation amount and the coke blending amount can be greatly reduced. Furthermore, since the coke basic unit was originally in excess of heat more than necessary in the lower layer portion of the charging layer, the reactivity of the product sintered ore could be improved by reducing the amount of coke.

The schematic block diagram of the sintering machine which shows one Embodiment of this invention. Schematic of the exhaust gas blowing hood. The graph which shows the comparison of the temperature change in a charging layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sintering machine main body 2 Pallet 3 Wind box 4 Sintering raw material charging device 5 Ignition furnace 6 Gas fuel supply hood 7 Exhaust gas injection hood 8 Air line 9 Gas fuel line 10 Circulating exhaust gas line 11 Exhaust gas supply blower 12 Exhaust gas flow adjustment valve 13 Dust Collector 14 Ventilator 15 Chimney 20 Exhaust Blow Pipe 21 Sintered Main Exhaust Blow Line 22 Sinter Cooler Exhaust Blow Line 23 Charged Layer A Raw Material Charge Area B Ignition Area C Sintering Front D Sintered Rear

Claims (2)

Using a sintering machine that charges a sintered raw material on a pallet that circulates to form a charging layer on the pallet, sinters the charging layer to produce a sintered ore,
When sintering the charging layer, supplying gaseous fuel to the upstream side of the charging layer from above,
The exhaust gas generated in the sintering machine and / or the exhaust gas generated when the produced sintered ore is cooled is circulated and blown into the downstream side of the charging layer from above. A method for producing sintered ore.   The method for producing a sintered ore according to claim 1, wherein the gaseous fuel supplied to the charging layer is diluted to a lower combustion limit concentration or less.

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