JP2016047782A - Heat recovery method and heat recovery system for coagulation slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat recovery method and a heat recovery system for coagulation slag which can gain high quality coagulation slag by preventing vitrification of the coagulation slag.SOLUTION: When heat is collected from coagulation slag S in which molten slag M generated in a blast furnace is solidified, the heat is collected from the coagulation slag S after soaking the coagulation slag S at an appointed temperature and crystallizing a glass layer contained in the coagulation slag S.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat recovery method and a heat recovery system for solidified slag, and more particularly to a heat recovery method and a heat recovery system for solidified slag capable of obtaining a high-quality solidified slag by suppressing vitrification of the solidified slag. .

  Slag discharged in the steel manufacturing process is used as granulated sand or slag aggregate through granulation or slow cooling. As for the latter slag aggregate, the slag bone having a predetermined particle size distribution (for example, JIS A5011-1) is usually obtained by gradually cooling and solidifying the slag discharged into the dry pit, followed by crushing and sieving. The material is manufactured. Alternatively, as disclosed in Patent Document 1, the molten slag is solidified and formed so as to have a thickness of 10 mm to 30 mm using a casting machine provided with a metal moving mold, and is formed into a dense and high-strength plate shape. There is also a method for producing an aggregate by preparing a solidified slag and then similarly performing crushing treatment and sieving.

  On the other hand, in recent years, heat retention of slag has attracted attention as an energy-saving measure, and recovery and use of slag retention heat has been set as a goal in terms of slag utilization as well as the above-mentioned use of slag. The amount of heat of the molten slag has a size of about 0.5 GJ per ton of pig iron. If the heat of this slag can be recovered, a large energy saving effect can be expected.

  As a slag heat recovery method, for example, in Patent Document 2, molten slag is solidified and formed into a relatively thick shape using a caster, and the solidified slag is charged into a heat recovery device at a high temperature to recover heat. A method is disclosed. When the slag is solidified and formed into a thick wall, the surface area per unit volume of the slag is reduced, so that the solidified slag is easy to keep warm, the temperature drop of the solidified slag due to transportation etc. is suppressed, and it can be supplied to the heat recovery device at a high temperature. it can. Moreover, since it has thickness, since it is easy to hold | maintain in the state where the temperature of the solidification slag board thickness center is high, it becomes possible to supply to a heat recovery apparatus in the state which has high calorie | heat amount.

JP 2003-82606 A JP-A-57-182086

  However, when heat is recovered from the slag that has been rapidly solidified by the casting machine as described above, the cooling rate varies between the part that touches the mold and the part that does not touch the casting machine. The slag in the vicinity of the contact surface is vitrified by rapid cooling, thereby reducing the slag quality.

  Then, the objective of this invention is providing the heat recovery method and heat recovery system of the solidification slag which can suppress vitrification of the solidification slag and can obtain high quality solidification slag.

  As a result of intensive investigations on how to solve the above problems, the inventors crystallized the glass layer contained in the solidified slag by holding the solidified slag soaking at a predetermined temperature before recovering the heat of the solidified slag. It has been found that it is extremely effective to complete the present invention.

That is, the gist of the present invention is as follows.
(1) In recovering heat from the solidified slag obtained by solidifying the molten slag generated in the blast furnace, the solidified slag is crystallized after the glass layer contained in the solidified slag is crystallized by keeping the solidified slag soaked at a predetermined temperature. A method for recovering heat of solidified slag, wherein heat is recovered from the slag.

(2) The heat recovery method for solidified slag according to (1), wherein the soaking of the solidified slag is performed by heating the solidified slag.

(3) The heat recovery method for solidified slag according to (1) or (2), wherein the predetermined temperature is 900 ° C. or higher.

(4) The heat recovery method for solidified slag according to any one of (1) to (3), wherein the heat recovery from the solidified slag is performed after removing sulfur released from the solidified slag.

(5) The heat recovery method for solidified slag according to any one of (1) to (4), wherein heat recovery from the solidified slag is performed after the solidified slag is crushed.

(6) A casting machine having a mold for receiving molten slag generated in a blast furnace, casting the received molten slag into a plate shape, supplying heat recovery gas, and supplying the plate through the gas A molten slag heat recovery system comprising a heat recovery device that recovers heat of the solidified slag, and is included in the solidified slag by holding the solidified slag soaking at a predetermined temperature immediately below the casting machine. A heat recovery system for solidified slag, characterized in that a heat insulation tank for crystallizing the glass layer is provided.

(7) The heat recovery system for solidified slag according to (6), wherein the heat retaining tank includes means for heating the solidified slag accommodated in the heat retaining tank.

(8) The heat recovery system for solidified slag according to (6) or (7), wherein the predetermined temperature is 900 ° C. or higher.

(9) The solidification according to any one of (6) to (8), further including a desulfurization device that removes a sulfur content released from the solidification slag between the heat retaining tank and the heat recovery device. Slag heat recovery system.

(10) The heat recovery system for solidified slag according to any one of (6) to (9), further including a crusher that crushes the solidified slag between the heat retaining tank and the heat recovery device.

  According to the present invention, the solidified slag is soaked at a predetermined temperature so that heat is recovered from the solidified slag after crystallization of the glass layer contained in the solidified slag. While obtaining high quality solidified slag, heat can be recovered from the solidified slag.

It is a figure showing a suitable example of a heat recovery system concerning the present invention. It is a figure which shows an example of the casting_mold | template used for casting of plate-shaped solidification slag. It is an isothermal transformation diagram regarding crystallization of blast furnace slag. It is a figure which shows the temperature distribution of the plate | board thickness direction of plate-shaped solidification slag. It is a figure which shows the slag temperature history on the isothermal transformation diagram at the time of heat-recovering from the solidification slag before crystallization. It is a figure which shows the diffusion behavior of sulfur dioxide at the time of performing differential thermal-thermogravimetric simultaneous measurement analysis with respect to the grinding | pulverization sample of solidification slag. It is a figure which shows the density | concentration of the sulfur content contained in the sample of solidification slag. It is a figure which shows the iron casting_mold | templates used for the Example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The heat recovery method for solidified slag according to the present invention supplies molten slag generated in a blast furnace to a mold and recovers heat from the solidified slag cast into a plate shape. Here, it is important to recover heat from the solidified slag after the solidified slag is maintained at a predetermined temperature so as to crystallize the glass layer contained in the solidified slag.

  FIG. 1 is a diagram showing a preferred example of a heat recovery system according to the present invention. This heat recovery system 1 has a mold 11 that receives molten slag M generated in a blast furnace, a caster 12 that solidifies the received molten slag M into a plate shape, and a direct downstream of the caster 12. A heat insulating tank 16 for keeping the solidified slag S soaked and crystallizing the glass layer contained in the solidified slag S, and a sulfur oxide contained in the solidified slag S provided in the heat insulating tank 16. (SOx) The desulfurization apparatus 17 which removes gas, the crusher 18 which crushes the solidification slag S discharged | emitted from the heat retention tank 16, and the heat recovery apparatus 19 which collect | recovers the heat | fever of the crushing solidification slag S 'are provided. Hereinafter, although the heat recovery method according to the present invention using this heat recovery system 1 will be described, it is not limited to this embodiment.

  First, molten slag M generated in a blast furnace is supplied to the mold 11 and cast into a plate shape to obtain a solidified slag S. As described above, a large amount of molten slag M is generated in the blast furnace. By recovering the sensible heat of the molten slag M, a very large energy saving effect can be expected. However, it is difficult to directly recover heat from the liquid molten slag M. Therefore, first, the molten slag M is supplied to the mold 11 to cast the solidified slag S.

  Here, the shape of the solidified slag is, for example, a plate shape, and the solidified slag S is “plate-shaped” means that the thickness direction is a direction corresponding to the depth direction of the mold used for solidification of the molten slag M. Therefore, it means that the plate thickness is smaller than the dimension in two directions perpendicular to each other in the thickness direction.

  Casting of the plate-shaped solidified slag S can be performed using the cast iron machine 12 illustrated in FIG. This casting machine 12 has a plurality of molds 11 that are continuously conveyed, and when molten slag M is supplied from the slag pan 14 to the mold 11 via the slag bar 15, it is conveyed by a conveyor, During this conveyance, the molten slag in the mold 11 is cooled and a plate-like solidified slag S is cast. The solidified slag S thus cast is recovered by dropping it from the mold 11 by dropping the mold 11 at the end of the casting machine 12 and dropping it into the ground or a container.

  The mold 11 from which the solidified slag S has been peeled is then returned to the supply position of the molten slag M and reversed again, receiving the molten slag M from the slag pan 14 again, and the solidified slag S is continuously cast. It will be. Thus, the plate-shaped solidified slag S can be continuously cast from the molten slag M. In addition, the said casting machine 12 can be changed suitably according to a use and the objective, and is not limited to the structure shown by FIG.

  FIG. 2 is a view showing an example of a mold 11 used for casting the plate-shaped solidified slag S. As shown in FIG. The shape inside the mold 11 is not particularly limited as long as a plate-shaped solidified slag S is obtained. The molten slag M supplied to the mold 11 is uniformly cooled in the mold to become a plate-shaped solidified slag S having a thickness t.

The thickness t of the solidified slag S is preferably 5 mm or more and 30 mm or less. Here, when the thickness t is 5 mm or more, when the molten slag M is cast into a plate shape, the variation in the cooling rate and the temperature drop during the conveyance are suppressed, and as a result, the solidified slag supplied to the heat recovery device 19. Variation in the temperature of S can be suppressed. In addition, by setting the thickness t to 30 mm or less, a decrease in the cooling rate when casting the molten slag M is suppressed, and the generation of bubbles in the solidified slag S is suppressed and the porosity is suppressed and the strength is high. Solidified slag can be obtained.
In this way, by controlling the slag solidification thickness to 5 mm or more and 30 mm or less, when supplying the solidification slag to the heat recovery device, the slag can be supplied in a state where the temperature variation is small at high temperature and the strength is high. A reduction in the heat recovery rate and the pressure of the heat recovery gas when recovering heat from the solidified slag S, that is, variations in pressure loss can be suppressed.

  When the casting of the solidified slag S is repeatedly performed using the continuously conveyed mold 11, the temperature of the mold 11 gradually increases, and when the temperature exceeds a certain temperature, the molten slag M becomes difficult to be cooled. In addition, the strength of the mold 11 itself may decrease, or the slag and the mold 11 may be seized and the solidified slag S may not be peeled off. Therefore, in order to prevent an excessive temperature rise of the mold 11, it is preferable to cool the mold 11 by washing the mold 11 with water when the solidified slag S is discharged, for example.

  Next, the plate-like solidified slag S cast by the casting machine 12 is charged into the heat retaining tank 16 and kept soaked at a predetermined temperature to crystallize the glass layer contained in the solidified slag S. As described above, in the present invention, it is important to recover heat from the solidified slag S after the solidified slag S is soaked at a predetermined temperature to crystallize the glass layer contained in the solidified slag S. Therefore, the solidified slag S is once charged in the heat insulation tank 16 and is kept soaked at a predetermined temperature at which the glass layer contained in the solidified slag S crystallizes.

  FIG. 3 is an isothermal transformation (Time-Temperature-Transformation, TTT) diagram (Yoshiaki KASHIWAYA, Toshiki NAKAUCHI, Khanh Son PHAM, Seitarou AKIYAMA and Kuniyoshi ISHII, ISIJ Internatinal, Vol. 47 (2007), No. 1, see pp. 44-52). From this figure, it can be seen that the glass layer contained in the solidified slag S is crystallized if it is kept soaked at a specific temperature below the melting point, specifically, at a temperature of about 900 ° C. or higher. Therefore, the temperature at which the solidified slag S is kept soaked in the heat insulating tank 16 is preferably 900 ° C. or higher. Here, when the molten slag M solidifies, the portion that comes into contact with the mold 11 is vitrified, and thus the above temperature refers to the surface temperature of the solidified slag.

  FIG. 4 is a view showing a temperature distribution in the plate thickness direction of the plate-like solidified slag S. As shown in FIG. As shown in this figure, the solidified slag S has a high temperature region of 1000 ° C. or more at the center in the thickness direction. Therefore, the glass layer contained in the solidified slag S can be crystallized by the heat held by the solidified slag S itself by maintaining the temperature in the heat retaining tank 16 immediately after solidification. However, if the heat recovery of the solidified slag S is started before the crystallization by such slag self-contained heat is completed, the slag temperature falls below the crystallization limit line expected from the TTT diagram, and the solidified slag S There is a concern that the glass layer remains in S.

FIG. 5 is a diagram showing a slag temperature history on a TTT diagram when heat is recovered from the solidified slag S before crystallization, and the solidified slag S having a plate thickness of 25 mm and a temperature of 1000 ° C. has a diameter of 5 m, Height: Temporal change in slag surface temperature when heat recovery was performed at a gas flow rate of 100,000 Nm ³ / h while charging / discharging into a packed bed as a heat recovery device of 5 m at a processing pitch of 60 t / h The calculation result is shown. As is apparent from this figure, the temperature of the solidified slag S surface during heat recovery is reduced to near the lower limit of the crystallization temperature in the TTT diagram.

  That is, it can be seen that when heat is recovered from the solidified slag S immediately after solidification, there is a risk that the glass layer remains in the solidified slag S. Therefore, in the present invention, the glass contained in the solidified slag S is charged by charging the solidified slag S immediately after solidification into the heat insulating tank 16 and holding it at a predetermined temperature at which the glass layer can be crystallized in the heat insulating tank 16. The layer is crystallized and heat is recovered from the solidified slag S after the crystallization of the glass layer is complete. As a result, the heat of the solidified slag S can be recovered without degrading the quality of the solidified slag S.

  The heat insulation tank 16 that holds the solidified slag S soaked is not particularly limited as long as the solidified slag S can be kept soaked at a temperature at which the glass layer can be crystallized. For example, it can be comprised with the structure enclosed with the heat insulation wall, such as a refractory brick, the slag conveyance pot using the heat resistant steel which has sufficient thickness for heat retention.

  The soaking time of the solidified slag S is set to an appropriate time according to the temperature at which the soaking is maintained. As is apparent from FIG. 3, when the soaking temperature is 950 ° C., for example, it can be seen that about 50 seconds is sufficient for the soaking time.

  Further, it is preferable that the soaking of the solidified slag S is performed by heating the solidified slag S. Thereby, a glass layer can be crystallized in a short time. Such heating of the solidified slag S can be performed by providing heating means such as a hot air generator or a radiant tube burner in the heat insulating tank 16.

Furthermore, it is preferable that the heat recovery from the solidified slag S is performed after the sulfur component released from the solidified slag S is removed. FIG. 6 shows a simultaneous differential thermo-thermogravimetric measurement (TG-DTA) using a pulverized sample of a blast furnace slag (molten slag M) solidified to a thickness of 25 mm by a cast iron 12. The results are shown. As is apparent from this figure, it can be seen that a large amount of sulfur dioxide (SO ₂ ) gas, which is a sulfur component, is generated at a temperature of 900 ° C. or higher. That is, it can be seen that in the temperature range of 900 ° C. or higher necessary for crystallizing the glass layer contained in the solidified slag S, the sulfur content is simultaneously released from the solidified slag S.

  FIG. 7 shows the result of measuring the concentration of sulfur contained in the above-mentioned 25 mm thick solidified slag sample, and the sample is not crushed but remains at the full thickness at 1000 ° C. for 5 minutes, 10 minutes and 20 minutes. It shows the concentration of residual sulfur after being kept isothermal for 1 minute. From this figure, it can be seen that approximately 0.3% of the sulfur content is reduced by isothermal holding in the sulfur emission temperature range. It can also be seen that the effect of increasing the holding time is small. This is presumed to be because the sulfur content in the slag is combined with oxygen in the outside air and gasified, so only the surface of the solidified slag S in contact with the outside air and the sulfur content in the vicinity of the surface contribute to the emission. The

The high-temperature heat recovery gas G obtained in the heat recovery device 19 is supplied to a heat exchange facility such as a boiler. Therefore, if sulfur content is mixed in the heat recovery gas as SO _x , corrosion of heat exchanger components may be accelerated. When the heat exchanger components are corroded, air leakage occurs and heat utilization efficiency decreases. Since heat exchangers are generally designed on the premise of long-term use, if the corrosion frequency of parts is high, maintenance costs are high, and the equipment becomes unfit for investment.

  Therefore, by removing in advance the sulfur content released from the solidified slag S before recovering heat from the solidified slag S, corrosion of the components of the heat exchanger described above can be prevented. For example, as shown in FIG. 1, the sulfur content released from the solidified slag S can be removed by providing a desulfurization device 17 on the outlet side of the heat insulating tank 16.

  Subsequently, the solidified slag S is preferably introduced into the crusher 18 and crushed, and heat is recovered from the crushed solidified slag S ′. Thereby, the surface area of the solidification slag S increases, and the heat recovery from the solidification slag S can be performed efficiently.

  Thereafter, the crushed solidified slag S ′ is introduced into the heat recovery device 19, and the heat recovery gas G is supplied into the device 19 to recover the heat of the solidified slag S ′. The apparatus configuration of the heat recovery apparatus 19 is not particularly limited, and for example, a countercurrent packed bed system composed of a slag filling tank, a slag charging apparatus, a slag discharge apparatus, and a blower can be used. After the solidified slag S ′ is charged from the upper part of the heat recovery device 19 to form a packed layer of the solidified slag S ′, the heat recovery gas G is supplied from the lower part of the device 19 to exchange heat in the packed bed. Then, the heat of the solidified slag S ′ is recovered, and the heated heat recovery gas G is discharged from the heat recovery device 19. In the present invention, the heat of slag means sensible heat.

  Here, as the heat recovery gas G, room temperature gas such as air, combustion exhaust gas discharged from a hot stove, or the like can be used.

  Thus, it is possible to recover heat from the solidified slag while suppressing the vitrification of the solidified slag to obtain a high-quality solidified slag.

(Invention example)
Examples of the present invention will be described below.
First, molten slag obtained by melting using a high-frequency melting furnace is poured into an iron mold (inner dimensions: 120 × 120 mm) shown in FIG. 8 and solidified to a thickness of 25 mm. When the temperature of the solidified slag measured by (1) reached 1000 ° C., the mold was inverted and the solidified slag was taken out. Next, the solidified slag taken out was charged into a heat insulating tank (250 mm × 250 mm × 50 mm) constituted by a heat insulating material (castable), and kept soaked for 10 minutes, and then the solidified slag was crushed by a crusher. Thereafter, the crushed solidified slag was introduced into a heat recovery apparatus to perform heat recovery.

(Comparative example)
Heat recovery was performed in the same manner as in the inventive examples. However, the solidified slag was supplied to the crusher without charging the heat insulation tank. Other conditions are the same as those of the invention examples.

  After heat recovery, the sample was crushed with a hammer, and the average value of the thickness of the glass layer adhering to the solidified slag was measured. As a result, the glass layer did not remain for the inventive example, whereas the glass layer remained for the comparative example, and the average thickness was 1.5 mm. As described above, by maintaining the soaked solid slag before heat recovery, the glass layer contained in the solidified slag can be crystallized to improve the slag quality.

  According to the present invention, the solidified slag is soaked at a predetermined temperature so that the glass layer contained in the solidified slag is crystallized, and then heat is recovered from the solidified slag. Since heat recovery can be performed while obtaining solidified slag of quality, it is useful in the steel industry.

DESCRIPTION OF SYMBOLS 1 Heat recovery system 11 Mold 12 Casting machine 14 Slag pan 15 Slag pot 16 Thermal insulation tank 17 Desulfurization apparatus 18 Crusher 19 Heat recovery apparatus M Molten slag S, S 'Solidification slag G Heat recovery gas

Claims (10)

In recovering heat from the solidified slag that solidifies the molten slag generated in the blast furnace,
A method for recovering heat of solidified slag, characterized in that the solidified slag is maintained at a predetermined temperature so as to crystallize a glass layer contained in the solidified slag, and then heat is recovered from the solidified slag.   The heat recovery method for solidified slag according to claim 1, wherein the soaking of the solidified slag is performed by heating the solidified slag.   The heat recovery method for solidified slag according to claim 1 or 2, wherein the predetermined temperature is 900 ° C or higher.   The heat recovery method of the solidification slag as described in any one of Claims 1-3 performed after removing the sulfur content discharge | released from the said solidification slag.   The heat recovery method of the solidified slag according to any one of claims 1 to 4, wherein the heat recovery from the solidified slag is performed after the solidified slag is crushed. A casting machine having a mold for receiving molten slag generated in a blast furnace, casting the received molten slag into a plate shape, supplying heat recovery gas, and the plate-like solidified slag through the gas; In a heat recovery system for molten slag, comprising a heat recovery device that recovers the heat of
A heat recovery system for solidified slag, characterized in that a heat retention tank is provided immediately below the casting machine to keep the solidified slag soaked at a predetermined temperature to crystallize the glass layer contained in the solidified slag. .   The said heat retention tank is a heat recovery system of the solidification slag of Claim 6 which has a means to heat the solidification slag accommodated in the said heat retention tank.   The heat recovery system for solidified slag according to claim 6 or 7, wherein the predetermined temperature is 900 ° C or higher.   The heat recovery system for solidified slag according to any one of claims 6 to 8, further comprising a desulfurization device that removes a sulfur content released from the solidified slag between the heat retaining tank and the heat recovery device.   The heat recovery system of the solidification slag as described in any one of Claims 6-9 further provided with the crusher which crushes the said solidification slag between the said heat retention tank and the said heat recovery apparatus.

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