JP5515364B2 - Hot metal pretreatment method and system - Google Patents

Description

  The present invention relates to a hot metal pretreatment method and system in which powdered iron oxide is blown into a hot metal in a processing vessel together with a carrier gas to perform dephosphorization and desiliconization, and in particular, hot metal pretreatment for recycling dust generated during hot metal pretreatment. It relates to a method and a system.

  In recent years, in the steelmaking process, in order to reduce the load of converter blowing and minimize the total cost of steelmaking, hot metal pretreatment is performed to remove phosphorus and silicon contained in the hot metal before oxygen blowing in the converter. Yes. There are various hot metal pretreatment methods depending on the processing container to be used (for example, a kneading wheel, a hot metal ladle, a converter, etc.).

  Among these, the hot metal dephosphorization process, in which the oxidizing agent is injected into the hot metal held in the kneading car, has the advantages of higher oxidant reaction efficiency and lower processing cost than the processing using the converter. Have. In this injection type hot metal dephosphorization system, powdered iron oxide formed by pulverizing sintered ore is used as an oxidizing agent. The powdered iron oxide stored in the hopper is blown by the carrier gas and blown into the hot metal in the kneading vehicle from the blowing lance.

  Dust is generated when the oxidant is injected into the hot metal in the chaotic vehicle. After the exhaust gas containing dust is cooled by the cooling device, the dust in the exhaust gas is recovered by the dust collector. A bag filter that collects fine dust mixed in exhaust gas by passing a cloth or the like is used for the dust collector. The dust collected by the bag filter is blown again into the hot metal in the kneading vehicle for reuse.

  As a technique for reusing dust collection dust, Patent Document 1 discloses that dust generated when hot metal is desulfurized in a lime-based desulfurization facility is recovered, and the recovered lime-based dust is classified into fine dust and coarse dust using a classifier. Dust collection dust reclassified by classifying into fine dust, blowing fine dust into the hot metal in the kneading car using a lance and desulfurizing, and adding coarse dust to the hot metal in the kneading car by the top method. A method of use is disclosed.

JP-A-6-220514

  However, when dust was actually collected by the bag filter and again blown into the molten iron in the kneading vehicle, there was a problem that the amount of dust collected when the exhaust gas was sucked was reduced. This was caused by dust collecting clogging in the cooling device. A decrease in the amount of dust collected causes equipment damage due to the flame ejection. Even if the cooling device was periodically cleaned in order to prevent a decrease in the amount of collected air, the clogging of dust accumulated only after a few days, and the amount of collected air decreased again. Only regular cleaning with a lot of time and effort has made it a mess.

  Accordingly, an object of the present invention is to provide a hot metal preliminary treatment method and apparatus capable of preventing the dust collection air volume from decreasing even when dust generated from a processing container such as a kneading vehicle is recycled.

In order to solve the above-described problems, an aspect of the present invention provides a hot metal preliminary treatment method in which powdered iron oxide is blown together with a carrier gas into hot metal in a processing container, and exhaust gas generated from the processing container is cooled by a cooling device. the dust in the cooled exhaust gas recovered by the dust collector, the collected dust collecting dust, iron oxide hopper for storing a powdered iron oxide obtained by pulverizing a solid oxygen source, the oxidation and the dust collecting device Directly supplied to the iron oxide hopper via a dust collection line connected to the iron hopper, and the powdered iron oxide and the dust collection dust mixed in the iron oxide hopper are contained in the processing container. only write blown into molten iron, a hot metal pre-treatment methods for recycling the dust generated at the time of hot metal pre-treatment.

Another aspect of the present invention is a hot metal preliminary treatment system in which powdered iron oxide is blown into a hot metal in a processing vessel including a kneading vehicle together with a carrier gas, a cooling device for cooling the exhaust gas generated from the processing vessel, and cooling A dust collector that collects dust in the exhaust gas; an iron oxide hopper that stores powdered iron oxide obtained by pulverizing a solid oxygen source; and the dust collector that is connected to the dust collector and the iron oxide hopper. A dust collection line for supplying the collected dust collected by the apparatus directly to the iron oxide hopper, and the powdered iron oxide and the dust collected mixed in the iron oxide hopper in the processing vessel. A hot metal pretreatment system for recycling dust generated during hot metal pretreatment.

  As a result of investigating the cause of clogging of recycle dust in the cooling device, the concentration of low melting point substances in the recycle dust is high. It was presumed that, while trapping, it adhered to and deposited on the element, which caused an increase in the pressure loss of the cooling device, which in turn led to a decrease in the amount of dust collected. Conventionally, the recycled dust has been blown into the processing container alone immediately before the end of the processing. It is considered that low melting point substances are concentrated in the system by repeated recycling.

  Next, the relationship between the accumulated amount of recycled dust and the pressure loss of the cooling device was compared between the pretreatment system B with a small amount of dust recycling and the pretreatment system A with a large amount of dust recycling. As a result, even if the cumulative amount of recycled dust used in the preliminary equipment system B reaches the same level as the cumulative amount used in the preliminary processing system A that caused an increase in pressure loss, an increase in pressure loss in the preliminary processing system B was observed. There wasn't. From this, it was found that even if the final input low-melting-point substance is equivalent, an increase in the pressure loss of the cooling device can be prevented by blowing in small amounts.

  According to the present invention, the recycled dust is not blown into the processing container at a stretch immediately before the end of the hot metal preliminary treatment, but once mixed with the iron oxide hopper and blown into the processing container with the recycled dust dispersed in the iron oxide, Recycled dust can be blown into the processing container little by little. For this reason, an increase in the pressure loss of the cooling device can be prevented, and as a result, a decrease in the amount of collected air can be prevented.

1 is an overall view of a hot metal pretreatment system according to an embodiment of the present invention. Comparison diagram of connection status of dust collection line ((a) in the figure shows a conventional example, and (b) in the figure shows an example of the present invention) Configuration diagram of cooling device Graph showing the pressure loss of each device of the cooling device Comparison chart of gas cooler pressure loss in hot metal pretreatment system A and system B Graph showing the relationship between the differential pressure of the gas cooler and the amount of dust collected

  Hereinafter, an embodiment of a hot metal pretreatment system of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an overall view of a hot metal pretreatment system. In steelmaking plants, a torpedo type hot metal dephosphorization process is carried out in order to minimize the refining costs in the steelmaking process. Powdered iron oxide 3 as a dephosphorizing agent is injected into the hot metal 2 in the kneading wheel 1 from the tip of the immersion lance 4 together with a carrier gas. The iron oxide 3 is mixed with a refining agent such as quick lime and calcium carbonate.

  Powdered iron oxide 3 is produced by pulverizing sintered ore. The sintered ore produced in the sintering plant is put into the truck hopper 7 by the dump truck 6. The powder is pulverized by a roller mill 8 which is a sintered ore pulverizer. The pulverized iron oxide powder is aired and stored in the iron oxide hopper 9 in the sinter ore pulverization room. The iron oxide hopper 9 is also charged with a refining agent such as quick lime and calcium carbonate conveyed by a lorry 10.

  Solid oxygen sources other than sintered ore include iron ore, mill scale (oxide film that is generated and adhered by reacting with oxygen in the air when heated to a high temperature in the manufacturing process of steel), hot metal reserve Dust generated in a process other than the treatment process (for example, a iron making process) can be used.

  The powdered iron oxide 3 stored in the iron oxide hopper 9 is aired to the kneading vehicle 1 together with the carrier gas by the blowing dispenser 11. The exhaust gas generated from the chaotic vehicle 1 is sucked by the exhaust fan 12. Dust contained in the exhaust gas is collected by a bag filter 13 as a dust collector. The exhaust gas is cooled by the cooling device before reaching the bag filter 13. The cooling device includes a heat accumulator 14 that stores heat of exhaust gas, a gas cooler 15 having an element that exchanges heat with the exhaust gas, and a U-shaped tube 16 that releases heat of the exhaust gas to the atmosphere (see FIG. 3). The gas cooler 15 is provided with a soot blower for removing dust adhering to the element.

  As shown in FIG. 1, the dust collected by the bag filter 13 is temporarily stored in a dust collection dust hopper 17. The dust collection dust hopper 17 and the iron oxide hopper 9 are connected by a dust collection dust mixing line 18, and the dust collection dust once stored in the dust collection dust hopper 17 is sent to the iron oxide hopper 9. The recycled dust charged into the iron oxide hopper 9 is mixed with the powdered iron oxide 3.

  FIG. 2 shows a comparison of the connection status of the dust collection line 18 between the present invention and the conventional example. As shown in FIG. 2 (a), in the conventional hot metal pretreatment system, the dust collection line 18 is connected to the downstream side of the iron oxide hopper 9. And when blowing dust collection dust into the kneading wheel 1, the blowing dispenser 11 which blows in powdered iron oxide 3 was stopped, and it was blowing at a stretch just before the completion of hot metal pretreatment. On the other hand, as shown in FIG. 2 (b), in the hot metal preliminary processing system of the present invention, the dust collection dust mixing line 18 is connected to the upstream side of the iron oxide hopper 9. Then, dust collection dust is once put into the iron oxide hopper 9 and blown into the kneading vehicle 1 in a state where the recycle dust is dispersed in the powdered iron oxide 3. For this reason, dust collection dust can be blown into the chaotic vehicle 1 little by little.

If dust collecting dust can be blown into the chaotic vehicle 1 little by little as in the present invention, it is possible to prevent a reduction in the amount of dust collecting air. The correlations between “injecting dust collection dust into the chaotic vehicle little by little” and “decreasing the amount of dust collection air” are as follows (1) to (3).
It is.

(1) The cause of the decrease in the amount of collected dust is the pressure loss of the gas cooler.
FIG. 4 shows a range in which the pressure loss of the cooling device that caused a decrease in the amount of dust collected is measured. By measuring the pressure at the regenerator inlet, gas cooler inlet, U-shaped tube inlet, and U-shaped tube outlet (differential pressure from the atmospheric pressure), pressure loss at the regenerator 14, gas cooler 15, and U-shaped tube 16 is evaluated. did. As a result, it was found that the pressure loss in the gas cooler 15 was maximized as shown in FIG. In order to prevent a reduction in the amount of collected air, it is necessary to avoid pressure loss in the gas cooler 15. The pressure loss can be suppressed to a low level by preventing the adhesion and accumulation of dust on the elements of the gas cooler 15.

(2) Origin of clogging of gas cooler Next, components of deposits adhering to the elements of the gas cooler 15 were analyzed. As a result of the analysis, FeO, Zn, and the like, which are low melting point substances, are detected, and these are likely to cause clogging.

  Presumably, low melting point substances are deposited in the exhaust gas cooling process and are attached to the element while trapping surrounding dust particles on the gas cooler inlet side where the passage is fine and cooled at a low temperature of 300 ° C. It is done.

  Recycled dust is conventionally blown alone into a kneading vehicle immediately before the hot metal pretreatment is completed, and it is considered that low melting point substances are concentrated in the system by repeated recycling.

(3) Countermeasure The upper part of FIG. 5 shows a comparison of gas cooler pressure loss conditions in the hot metal pretreatment systems A and B. In the system B gas cooler, no significant pressure loss is observed, which is consistent with the fact that the reduction in the amount of dust collected in system B is not a problem. Table 1 shows a comparison between the systems A and B for items that appear to be caused by clogging of the gas cooler.

  As a factor that makes system B difficult to clog, it can be considered that a soot blower is installed and clogging can be removed automatically and periodically. In addition, the amount of dust recycled in system B is less than half that of system A, and the blowing speed of system B is a low value of about 100 to 150 kg / min at maximum with respect to 250 kg / min of system A. In addition, the low melting point concentration in the dust is low due to the low recycling rate.

  The lower part of FIG. 5 shows a comparison between the amount of accumulated recycled dust used after regular cleaning and the gas cooler pressure loss situation. Even if the cumulative amount of recycled dust used reached the same level P as the value that caused an increase in pressure loss in system A, no increase in pressure loss was observed in system B. From this, it is considered that even if the final input low melting point substance is the same, pressure loss can be prevented to some extent by blowing small amounts. Further, it is considered that pressure loss can be further prevented by periodically cleaning before accumulation of recycled dust.

  In order to detoxify low melting point substances, (1) separation from dust, (2) discontinuation of dust recycling, (3) reduction in the concentration of low melting point substances in dust, (4) reduction of consumption per use (at once (5) removing before deposition, etc. can be considered. Considering the generation amount of 1300 t / month, the possibility of realizing (1) to (3) is not clear due to the problem of waste disposal. On the other hand, from the consideration shown in FIG. 5, clogging can be reduced by dispersing and blowing recycled dust immediately before the end of processing as in the prior art. Furthermore, it seems that the rise in pressure loss can be sufficiently avoided by installing soot blowers and removing minute clogs at an early stage.

  FIG. 6 shows the relationship between the differential pressure of the gas cooler and the dust collection air volume. As mentioned above, a strong correlation is observed. From this, it is possible to know the degree of gas cooler clogging and the amount of dust collection air flow on-time by monitoring the differential pressure before and after the gas cooler, rather than monitoring the amount of dust collection air flow with extremely large fluctuations. Become. By setting a threshold for differential pressure and sounding an alarm when the pressure exceeds a certain value, it is possible to take equipment burnout prevention measures such as clogging prevention measures such as prohibiting the use of recycled dust, emergency soot blower activation, and periodic cleaning timing adjustment. .

1 ... Chaotic car (processing container)
2 ... Hot metal 3 ... Iron oxide 4 ... Lance 9 ... Iron oxide hopper 12 ... Exhaust fan 13 ... Bag filter (dust collector)
15 ... Gas cooler (cooling device)
17 ... Dust collection dust hopper 18 ... Dust collection dust mixing line

Claims (5)

In the hot metal preliminary treatment method in which powdered iron oxide is blown into the hot metal in the processing vessel together with the carrier gas,
The exhaust gas generated from the treatment container is cooled with a cooling device, and dust in the cooled exhaust gas is recovered with a dust collector,
Collected dust collection dust is collected in an iron oxide hopper that stores powdered iron oxide obtained by pulverizing a solid oxygen source , via a dust collection dust mixing line connected to the dust collector and the iron oxide hopper. Supplying directly to the iron oxide hopper ,
The saw write blown into molten pig iron in the iron oxide mixed with the powder-like iron oxide and the dust collected in the hopper the processing vessel, molten iron pretreatment method of recycling the dust generated during hot metal pretreatment. The cooling device is a gas cooler having an element that exchanges heat with exhaust gas,
The hot metal preliminary treatment method according to claim 1, wherein the element of the gas cooler is periodically cleaned. The cooling device is a gas cooler having an element that exchanges heat with exhaust gas,
The hot metal pretreatment method according to claim 1, wherein a pressure loss of the gas cooler is measured. In the hot metal pretreatment system in which powdered iron oxide is blown into the hot metal in the processing vessel including the kneading vehicle together with the carrier gas,
A cooling device for cooling the exhaust gas generated from the processing vessel;
A dust collector for collecting dust in the cooled exhaust gas;
An iron oxide hopper for storing powdered iron oxide obtained by pulverizing a solid oxygen source;
A dust collection line connected to the dust collector and the iron oxide hopper, and supplying dust collection dust collected by the dust collector directly to the iron oxide hopper;
A hot metal pretreatment system comprising: a lance for blowing the powdered iron oxide and the dust collection dust mixed in the iron oxide hopper into the hot metal in the processing container, and recycling dust generated during the hot metal pretreatment. The cooling device is a gas cooler having an element that exchanges heat with exhaust gas,
The hot metal pretreatment system according to claim 4, wherein the gas cooler is provided with a soot blower for removing dust adhering to the element.

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