Blast furnace top exhaust gas treatment method and blast furnace auxiliary equipment

Abstract

To provide a method for treating furnace top exhaust gas of a blast furnace and a blast furnace ancillary facility, which can treat furnace top exhaust gas of the blast furnace even when treating furnace top exhaust gas of the blast furnace including cyanide in the reduction operation of the blast furnace and can properly perform the reduction operation of the blast furnace.SOLUTION: In a method for treating furnace top exhaust gas of a blast furnace at the time of the reduction operation of the blast furnace in which the height of the surface of the raw material layered bed of the blast furnace is reduced from the height of the upper end of a bosh, furnace top exhaust gas of the blast furnace is cooled and collected by a wet dust collector, dust collection water of the wet dust collector is subjected to a flocculation treatment to remove dust components and to cool, and then is supplied to the wet dust collector again to circulate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a blast furnace top exhaust gas treatment method and blast furnace auxiliary equipment during reduced-scale operation of a blast furnace in which the height of the surface of the raw material packed bed of the blast furnace is reduced below the height of the upper end of the morning glory. [Background technology]

[0002] In recent years, the lifespan of blast furnaces has been significantly extended due to advances in equipment and operation technologies, and many large blast furnaces have been in operation for more than 10 years. As the years of operation pass, the lining thickness of the lower shaft and the morning glory decreases. Therefore, it is necessary to repair the inner surface of the shaft and the morning glory. In this case, since repairs cannot be made if there is raw material in these areas, the raw material charging level in the blast furnace is lowered to a specified height and then the blowing is stopped. When starting up the blast furnace after the repairs inside the furnace are completed, the raw materials are filled again and started up. Also, when blowing down the blast furnace and disassembling and repairing it, one method is to remove all the contents of the furnace. In this case, the operation of lowering the raw material charging level in the blast furnace is also carried out.

[0003] This type of operation, in which the level of raw materials charged in a blast furnace is lowered when intermediate repairs are made to the furnace body or when the blast furnace is dismantled and repaired, is called reduced-scale operation. The basic method of reduced-scale operation is to stop charging raw materials from the top of the furnace, replace them with coke, and lower the level of the raw materials charged, usually to the tuyere level, while burning the coke with high-temperature air supplied from the tuyere.

[0004] As the length of the furnace decreases, the gas inside the furnace cannot be cooled by the raw materials, and the hot air blown in from the tuyere does not cool the gas, causing the temperature of the exhaust gas from the top of the blast furnace to rise. If the temperature of the exhaust gas from the top of the blast furnace is too high, it may cause damage to the top of the furnace equipment or exceed the expansion limit of the piping that connects the top of the furnace equipment to the gas holder that stores the exhaust gas from the top of the blast furnace. This raises the concern that it may cause a leak accident of the exhaust gas from the top of the blast furnace. If damage to the top of the blast furnace equipment or a leak from the expansion of the piping is confirmed, an unplanned shutdown is necessary to repair the equipment. In addition, if the equipment repair takes time and the shutdown time is long, it may cause a furnace cooling problem when the blast furnace is started up, in which the temperature of the molten iron in the furnace drops and it becomes impossible to remove it.

[0005] In response to this, a method of cooling the gas by spraying water from a sprinkler pipe installed at the top of the blast furnace has been used to suppress the temperature rise of the blast furnace top exhaust gas. For example, Patent Document 1 discloses a method of spraying water from a sprinkler pipe installed at the top of the furnace, setting the upper limit of the top exhaust gas temperature at 350°C, and performing reduced-scale operation. Patent Document 2 discloses a method of reducing the amount of hot air blown into the furnace and keeping the top exhaust gas temperature low by reducing the amount of blown air while increasing the amount of enriched oxygen. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2001-73014 A [Patent Document 2] Japanese Patent Application Publication No. 2-282408 Summary of the Invention [Problem to be solved by the invention]

[0007] However, during the cutback operation of the blast furnace, harmful cyanide compounds are generated in the lower part of the blast furnace. That is, although they are usually decomposed during the process of heat exchange with the charged raw materials, in the cutback operation, the gas in the furnace rises to the upper part of the furnace without being sufficiently cooled, so that cyanide is contained in the top exhaust gas of the blast furnace. If cyanide is contained in the top exhaust gas of the blast furnace, it is absorbed in the dust collection water of the wet dust collection, and when the dust collection water is discharged outside the system, there is a risk of violating the Water Pollution Prevention Law, which specifies the upper limit of the cyanide concentration. Therefore, the cooling of the top exhaust gas described in Patent Document 1 and Patent Document 2 alone could not sufficiently treat the dust collection water of the wet dust collection containing cyanide due to the cyanide in the top exhaust gas of the blast furnace.

[0008] An object of the present invention is to solve the above problems and to propose a blast furnace top exhaust gas treatment method and blast furnace ancillary equipment which can treat the blast furnace top exhaust gas containing cyanide even when treating the blast furnace top exhaust gas during reduced scale operation of the blast furnace and can properly perform reduced scale operation of the blast furnace. [Means for solving the problem]

[0009] The blast furnace top exhaust gas treatment method of the present invention was developed to solve the above-mentioned problems, and is a blast furnace top exhaust gas treatment method during reduced-scale operation in which the height of the surface of the raw material packed bed of the blast furnace is reduced below the height of the upper end of the morning glory portion, and is characterized in that the blast furnace top exhaust gas is cooled and dust collected by a wet dust collector, the dust collection water of the wet dust collector is subjected to a coagulation and sedimentation process to remove dust components and is cooled, and then supplied again to the wet dust collector for circulation.

[0010] In the blast furnace top exhaust gas treatment method according to the present invention configured as described above, (1) The collected water from the wet dust collector is cooled to a predetermined temperature or lower and then subjected to a coagulation and sedimentation treatment, and the treated water after the coagulation and sedimentation treatment is cooled to a predetermined temperature or lower and then supplied to the wet dust collector again for circulation. (2) cooling the collected water of the wet dust collector to a predetermined temperature or lower using a heat exchanger, and cooling the treated water after the coagulation and sedimentation treatment to a predetermined temperature or lower using a cooling tower; (3) The cooling pipe having the heat exchanger can be switched to a cooling pipe having a spare heat exchanger, and the cooling pipe having the heat exchanger can be cleaned by flowing cleaning water from the outlet side to the inlet side of the heat exchanger. (4) When subjecting the cooled dust-collected water to a coagulation and sedimentation treatment, a chemical for treating cyanide is added; is considered to be a more preferable solution.

[0011] The blast furnace auxiliary equipment of the present invention is an auxiliary equipment for a blast furnace used during reduced-scale operation in which the height of the surface of the raw material packed bed of the blast furnace is reduced below the height of the upper end of the morning glory portion, and includes a wet dust collector that cools the exhaust gas from the top of the blast furnace to collect dust water, equipment that cools the collected dust water of the wet dust collector to a predetermined temperature or lower, and equipment that cools the treated water to a predetermined temperature or lower after subjecting the collected dust water to a coagulation and sedimentation treatment to remove dust components, and is characterized in that the collected dust water of the wet dust collector is supplied again to the wet dust collector and circulated. Effect of the Invention

[0012] According to the blast furnace top exhaust gas treatment method and blast furnace ancillary equipment of the present invention, the blast furnace top exhaust gas is properly treated during reduced-scale operation of the blast furnace, thereby preventing equipment trouble and lowering the blast furnace raw material level to the target level without causing environmental trouble.

[0013] As a preferred example, the cooling pipe with the heat exchanger can be switched to a cooling pipe with a spare heat exchanger, and the cooling pipe with the heat exchanger can be provided with a backwash mechanism that allows washing water to flow from the outlet side to the inlet side of the heat exchanger to wash it. Blast furnace dust collection water contains about 10 g / L of dust, which can cause the heat exchanger to become clogged, but this backwash mechanism can prevent the heat exchanger from becoming unusable during the reduction in length period. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram for explaining one embodiment of a blast furnace auxiliary facility for implementing a blast furnace top exhaust gas treatment method of the present invention. [Diagram 2] FIG. 1 is a diagram showing a water passage when a normal heat exchanger is used in the blast furnace auxiliary equipment of the present invention. [Diagram 3] FIG. 1 is a diagram showing a water passage when a spare heat exchanger is used in the blast furnace auxiliary equipment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments of the present invention will be described in detail. Note that the following embodiments are merely examples of devices and methods for embodying the technical ideas of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical ideas of the present invention can be modified in various ways within the technical scope described in the claims.

[0016] <One embodiment of a blast furnace auxiliary facility for implementing the blast furnace top exhaust gas treatment method of the present invention> FIG. 1 is a schematic diagram for explaining one embodiment of a blast furnace auxiliary facility for carrying out the blast furnace top exhaust gas treatment method of the present invention. In the embodiment shown in FIG. 1, the blast furnace top exhaust gas (B gas) is collected by a dust catcher 2 (DC), and then cooled and collected by a wet dust collector 3 such as a Venturi scrubber (VS). The blast furnace top exhaust gas cooled and collected by the wet dust collector 3 is stored in a gas holder (not shown) via a septum valve 4 (SV) and a dry dust collector 5 such as a high-pressure electrostatic precipitator (EP). In addition, the energy recovery efficiency is improved by supplying the blast furnace top exhaust gas cooled and collected by the wet dust collector 3 to a top pressure turbine 6 (TRT). The above-mentioned configuration is the same as the configuration conventionally known as a blast furnace top gas energy recovery method.

[0017] The present invention, which relates to a blast furnace top exhaust gas treatment method and blast furnace ancillary equipment during reduced-scale operation, is characterized in that the top exhaust gas (B gas) of the blast furnace 1 is cooled and dust collected by a wet dust collector 3, and the dust collection water W1 from the wet dust collector 3 is subjected to coagulation and sedimentation treatment by a coagulation and sedimentation treatment facility 11 to remove dust components and to cool the water, and then is supplied again to the wet dust collector 3 as cooling water CW and circulated.

[0018] In the blast furnace top exhaust gas treatment method and blast furnace auxiliary equipment of the present invention, the coagulation and sedimentation treatment equipment 11 may have any configuration as long as the cyanide-containing dust collection water W1 can be subjected to coagulation and sedimentation treatment to remove dust components and cooled to produce cooling water CW. According to the present invention configured in this manner, even when treating the cyanide-containing dust collection water of the wet dust collection originating from the cyanide-containing blast furnace top exhaust gas during reduced-scale operation of the blast furnace, the cyanide-containing dust collection water can be treated, and the blast furnace can be properly operated at reduced scale.

[0019] Here, as a configuration for this purpose, as shown in the embodiment of FIG. 1, in the coagulation sedimentation treatment equipment 11, the dust collection water W1 of the wet dust collector 3 is cooled to a predetermined temperature or lower by the heat exchanger 12, and the dust collection water W2 cooled to a predetermined temperature or lower is stored in the wastewater pit 13. Next, the dust collection water W2 stored in the wastewater pit 13 is supplied to the trough 15 by the wastewater pump 14, and a chemical solution for cyanide treatment is supplied to the trough 15 from the CN treatment equipment 17. Next, the cyanide-treated dust collection water W3 supplied through the trough 15 is supplied to the coagulation sedimentation equipment 16 that separates dust such as a thickener by precipitating it into a slurry state, and is precipitated and separated. Next, the dust collection water W4 from which dust has been removed by the precipitating and separating equipment 16 is cooled by the cooling tower 18, and the cooled dust collection water W5 is stored in the treatment pond 19. Next, the dust-collected water W5 stored in the treatment pond 19 is supplied as cooling water CW to the wet dust collector 3 by the treatment water pump 20 and circulated. In order to smoothly store the cooled dust-collected water W5 in the treatment pond 19, a cold water pond (not shown) may be installed near the cooling tower 18, and the dust-collected water W5 may be stored in the treatment pond 19 after passing through the cold water pond.

[0020] <Suitable operating conditions for the furnace top exhaust gas treatment method of the present invention> When storing blast furnace top gas in a gas holder, it is desirable that the temperature at the outlet of EP5 does not exceed 60°C from the viewpoint of protecting the piping. In this regard, in reduced-scale operation in which the height of the surface of the raw material packed bed of the blast furnace is reduced below the height of the upper end of the morning glory, the gas inside the furnace is not sufficiently cooled by the charged raw materials, and the blast furnace top gas temperature becomes high, so cooling of the blast furnace top gas is necessary. To cool the blast furnace top gas, it is desirable to spray water from the top of the blast furnace to reduce the blast furnace top gas temperature to 350°C (preferably 330°C) or less.

[0021] The collected water W1 generated by the wet dust collector 3 such as VS is passed through a coagulation settling equipment 16 such as a thickener which condenses and settles dust into a slurry state, and is then supplied to the wet dust collector 3 again as cooling water CW. When the collected water W1 is recycled to the wet dust collector 3, it is desirable to provide a wastewater pit 13 and a treatment pond 19 upstream and downstream of the coagulation settling equipment 16 such as the thickener described above, respectively, as temporary storage facilities for the collected water W1.

[0022] In reduced-scale operation, the temperature of the cooling water CW circulated and supplied to the wet dust collector 3 is desirably 40°C or less (preferably 30°C). If the temperature of the circulated cooling water CW exceeds 40°C, the temperature at the outlet of EP5 exceeds 60°C, and there is a risk of damage to the expansion of the piping connecting EP5 to the gas holder that stores the top exhaust gas of the blast furnace 1. In addition, the higher the amount of circulated cooling water CW supplied to the wet dust collector 3, the greater the cooling effect of the top exhaust gas of the blast furnace 1, but this is limited by the discharge speed of the dust collector water W1 from the wet dust collector 3. The amount of circulated cooling water CW supplied to the wet dust collector 3 is desirably 700t / hr or more.

[0023] In order to keep the temperature of the cooling water CW circulated to the wet dust collector 3 at 40° C. or less, for example, the water temperature of the treatment pond 19 provided downstream of the condensation and sedimentation equipment 16 such as a thickener must be kept at 40° C. or less. In order to lower the water temperature of the treatment pond 19, it is desirable to install a cooling tower 18 between the condensation and sedimentation equipment 16 such as a thickener and the treatment pond 19. A heat exchanger may be installed instead of the cooling tower 18 to lower the water temperature of the treatment pond 19. If an attempt is made to lower the water temperature by newly supplying cooling water to the treatment pond 19, the amount of circulating water will increase, and treated water will overflow from the wastewater pit 13, the treatment pond 19, or the condensation and sedimentation equipment 16 such as a thickener.

[0024] The water temperature of the dust-collected water W2 in the wastewater pit 13 provided upstream of the condensation and settling equipment 16 such as a thickener is desirably 65°C or less (preferably 60°C). If the water temperature of the dust-collected water W2 in the wastewater pit 13 exceeds 65°C, the water temperature of the dust-collected water W5 in the treatment tank 19 will exceed 40°C even if a cooling tower 18 is installed between the condensation and settling equipment 16 such as a thickener and the treatment tank 19. For this reason, the water temperature of the cooling water CW supplied to the wet dust collector 3 exceeds 40°C, and the temperature of the outlet side of the EP5 exceeds 65°C, so that there is a risk of damage to the expansion of the piping connecting the EP5 to the gas holder that stores the top exhaust gas of the blast furnace 1.

[0025] To keep the water temperature of the wastewater pit 13 provided upstream of the coagulation and settling equipment 16 such as a thickener at 65°C or less, the dust collection water W1 of a wet dust collector 3 such as a VS is cooled, for example, by a plate-type heat exchanger 12. By bringing a pipe containing the dust collection water W1 of the wet dust collector 3 into contact with a pipe containing cooling water (indirect water) for cooling the tuyere, stave, and hearth of the blast furnace 1, for example, via the heat exchanger 12, the temperature of the dust collection water W1 of the wet dust collector 3 is reduced to 65°C or less.

[0026] Since the dust collecting water W1 of the wet dust collector 3 contains dust, when cooling it with the heat exchanger 12, clogging of the piping occurs frequently. The dust concentration in the blast furnace dust collecting water is in the range of about 6 to 10 g / L. Therefore, as shown in FIG. 2, it is preferable that the heat exchanger 12 is composed of a first heat exchanger 12-1 and a second heat exchanger 12-2, and the piping having the first heat exchanger 12-1 is structured so as to be switchable to the piping having the spare second heat exchanger 12-2. The differential pressure before and after the first heat exchanger 12-1 is measured, and when the differential pressure becomes equal to or greater than a reference value, the piping having the first heat exchanger 12-1 is switched to the piping having the spare second heat exchanger 12-2. An upper limit may be set on the usage period of the first heat exchanger 12-1, and the piping having the first heat exchanger 12-1 may be switched to the piping having the spare second heat exchanger 12-2.

[0027] Furthermore, when switching from the piping having the first heat exchanger 12-1 normally used to the piping having the second heat exchanger 12-2 as a spare, it is preferable to backwash the first heat exchanger 12-1 as shown in Fig. 3. Specifically, it is preferable to have a structure that can introduce cleaning water from the downstream side to the upstream side of the first heat exchanger 12-1 normally used to remove clogging in the piping of the heat exchanger portion.

[0028] The dust collection water W2 is supplied from the wastewater pit 13 to a condensation and settling equipment 16 such as a thickener through a trough 15 using a wastewater pump 14. A chemical for treating cyanide may be fed from a CN treatment equipment 17 to the above-mentioned trough 15. As a method for treating cyanide using a chemical, for example, the method for treating cyanide-containing water disclosed in JP-A-2013-56328 can be used. Note that in the present invention, the treatment of cyanide using a chemical is not an essential configuration but is a preferred embodiment. In the present invention, the treatment of cyanide is achieved by cooling and dust-treating the dust collection water W1 from the wet dust collector 3, and then circulating it again to the wet dust collector 3 as cooling water CW, thereby preventing it from being discharged out of the system. EXAMPLES

[0029] Internal volume 5000m 3In preparation for a long-term blasting shutdown, a reduced-scale operation was carried out at the blast furnace, in which the raw material charging level was lowered from the normal level. During the reduced-scale operation, the exhaust gas from the top of the blast furnace was cooled and dust-collected by a VS (wet dust collector), and the dust-collected water from the VS was cooled to 55°C using a heat exchanger and then stored in a wastewater pit. The amount of cooling water for the VS was 800t / hr. The dust-collected water was pumped up from the wastewater pit and introduced into a thickener via a trough, where the dust was removed in the form of a slurry. The supernatant liquid from the thickener after precipitation and coagulation was pumped up and cooled using a cooling tower, then passed through a cold water pond and stored in a treatment pond. The water temperature in the treatment pond was 30°C. The liquid was pumped up from the treatment pond and used as cooling water for the VS. The cyanide concentration in the wastewater after dust collection rose to 400ppm, compared to the Water Pollution Prevention Act regulation value of 1ppm and the Agreement regulation value of 0.3ppm for cyanide compounds. As a result of the above, the height of the top surface of the packed bed of raw materials in the furnace directly above the tuyere was reduced to 1 m below the top end of the blast furnace morning glory, making it possible to shut down the blowing. [Explanation of symbols]

[0030] 1 blast furnace 2 Dust Catcher (DC) 3 Wet type dust collector (VS) 4 Septum valve (SV) 5. Dry dust collector (EP) 6 Top pressure turbine (TRT) 11 Coagulation and sedimentation treatment equipment 12 Heat exchanger 12-1 First heat exchanger 12-2 Second heat exchanger 13 Sewage Pit 14 Sewage Pump 15 Trough 16 Coagulation and sedimentation equipment (thickener) 17 CN processing equipment 18 Cooling Tower 19 Water Treatment Pond 20 Treated water pump

Claims

1. A method for treating exhaust gas from the top of a blast furnace during reduced-scale operation in which the height of the surface of the raw material packed bed of the blast furnace is reduced below the height of the upper end of the morning glory, the method comprising: cooling and collecting dust from the top of the blast furnace using a wet dust collector; cooling the collected water from the wet dust collector to a predetermined temperature or lower using a heat exchanger, and then subjecting it to a coagulation and sedimentation process to remove dust components; and cooling the treated water after the coagulation and sedimentation process to a predetermined temperature or lower using a cooling tower, and then supplying it again to the wet dust collector for circulation.

2. 2. The method for treating exhaust gas from the top of a blast furnace according to claim 1, characterized in that the cooling pipe having the heat exchanger can be switched to a cooling pipe having a spare heat exchanger, and in the cooling pipe having the heat exchanger, cleaning water can be flowed from the outlet side to the inlet side of the heat exchanger to clean it.

3. 2. The method for treating exhaust gas from the top of a blast furnace according to claim 1, wherein an agent for treating cyanide is added when the cooled dust-collected water is subjected to a coagulation and sedimentation treatment.

4. A blast furnace ancillary equipment for carrying out the blast furnace top exhaust gas treatment method described in any one of claims 1 to 3, comprising: a wet dust collector for cooling the blast furnace top exhaust gas to produce collected dust water; equipment for cooling the collected dust water from the wet dust collector to a predetermined temperature or lower; and equipment for subjecting the collected dust water to a coagulation and sedimentation treatment to remove dust components, and then cooling the treated water after the coagulation and sedimentation treatment to a predetermined temperature or lower, characterized in that the collected dust water from the wet dust collector is supplied again to the wet dust collector and circulated.

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