JP2013189688A - Method for removing sulfur from desulfurization slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove sulfur contained in desulfurization slag, in order to utilize the desulfurization slag produced in the desulfurizing treatment of molten iron in a recycling manner.SOLUTION: This method for removing sulfur from desulfurization slag includes: a first step of heating the desulfurization slag in an atmosphere where an atmospheric temperature is in the range of 1,100 to 1,400°C and CO/COratio in the atmosphere is adjusted so that oxygen gas partial pressure (P) defined in formula (1): P=(P/P)×[1/exp(-ΔG/R×T)] lies in the range of 10to 10atm, and removing the sulfur in the desulfurization slag to the gas phase side of the atmosphere as SOx; a second step of applying a desulfurization treatment to exhaust gas containing the SOx removed to the gas phase side in the first process; and a third step of recycling the desulfurization slag in which the sulfur content is reduced by the first step as a CaO source in the pig iron making step or a steelmaking step.

Description

  The present invention removes sulfur contained in this desulfurization slag from the desulfurization slag containing CaO as a main component generated by the desulfurization treatment of hot metal, and the desulfurization slag having a reduced sulfur content is produced in a steelmaking process or a steelmaking process. The present invention relates to a method for removing sulfur from desulfurized slag to enable effective use as a CaO source.

  In response to the improvement in material properties and quality requirements of steel products, hot metal desulfurization treatment is performed in steel companies as a pretreatment for hot metal before decarburization and refining in converters. In this desulfurization treatment, the sulfur in the hot metal generally becomes a sulfide form by adding a flux (desulfurization agent) mainly composed of CaO and stirring the flux and the hot metal into slag. Has been removed. Slag generated by this desulfurization treatment is called desulfurization slag.

  The amount of desulfurization slag generated increases as the desulfurization treatment ratio to hot metal increases. However, this desulfurized slag contains sulfur, and if desulfurized slag is reused in an environment where water is present, sulfur (yellow water) may elute and adversely affect the environment. The reality is that there are significant restrictions on the conversion. In hot metal desulfurization treatment, the utilization efficiency of CaO as a desulfurization agent is at most several percent, and most of the CaO used in the desulfurization treatment is discharged outside the steelworks as desulfurization slag without being used. Yes.

  In order to solve these problems, the following techniques have been proposed.

  For example, Patent Document 1 discloses that high-temperature desulfurization slag generated by hot metal desulfurization treatment is recycled at a high temperature and used for new hot metal desulfurization treatment, thereby increasing the utilization efficiency of CaO and reducing the amount of desulfurization slag discharged. Techniques for reducing are disclosed.

  In Patent Document 2, sulfur containing slag is immersed in a solvent, carbon dioxide is blown into the solvent, and the solvent is adjusted to pH 4 to 10, so that sulfur contained in the slag is extracted into the solvent. Techniques for reducing the sulfur content are disclosed.

Patent Document 3 discloses a technique in which desulfurized slag is heated to 1100 to 1400 ° C. in the atmosphere to remove sulfur contained in the desulfurized slag as sulfurous acid gas (SO ₂ ).

JP 2004-244706 A JP 2011-93761 A Japanese Patent Laid-Open No. 7-10616

  However, the above prior art has the following problems.

  That is, in Patent Document 1, sulfur is contained in desulfurized slag that is recycled at a high temperature, and the sulfur concentration in the desulfurized slag increases and the desulfurization ability decreases by repeated recycling. There are limitations. Further, although the amount of desulfurized slag generated is reduced, it is finally necessary to treat the desulfurized slag.

  Patent Document 2 is a wet process, and in the case of a wet process, not only chemicals necessary for the process are expensive, but also a large-scale processing facility is required, and both the equipment cost and the operation cost are expensive.

Since Patent Document 3 is a sulfur removal treatment in the atmosphere, as will be described later in this specification, only sulfur in CaS contained in the desulfurization slag can be removed to the gas phase side, and CaSO ₃ and CaSO ₃ can be removed. There is a problem that sulfur existing in the desulfurized slag in the form of a sulfur compound such as ₄ cannot be removed.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to efficiently remove sulfur contained in the desulfurization slag generated in the desulfurization treatment of the hot metal, thereby making the steelmaking process and the steelmaking process effective. An object of the present invention is to provide a method for removing sulfur from desulfurized slag, in which desulfurized slag having a reduced sulfur concentration can be effectively recycled as a CaO source without being affected by sulfur.

The gist of the present invention for solving the above problems is as follows.
[1] The desulfurization slag containing sulfur generated in the desulfurization treatment of hot metal has an atmospheric temperature in the range of 1100 to 1400 ° C. and an oxygen gas partial pressure defined by the following formula (1) of 10 ^{−3. 10-9} heated in atm atmosphere CO / CO ₂ ratio of the atmosphere so that the range is adjusted, the first step of removing the sulfur in the desulfurization slag into the gas phase side of the atmosphere as SOx A second step of desulfurizing the exhaust gas containing SOx removed on the gas phase side in the first step, and a desulfurization slag having a reduced sulfur content in the first step, a steelmaking step or a steelmaking And a third step of recycling as a CaO source in the step. A method for removing sulfur from desulfurized slag.
P _O2 = (P _CO2 / P _CO ) ² × [1 / exp (−ΔG / R × T)] (1)
However, in the equation (1), P _O2 is the atmospheric oxygen gas partial pressure (atm), P _CO2 is the atmospheric CO ₂ gas partial pressure (atm), and P _CO is the atmospheric CO gas partial pressure (atm). , R is a gas constant (= 8.314 J / (mol · K)), ΔG is a free energy (J / mol), and is defined by the following formula (2): (1) and (2) T in the equation is the ambient temperature (K).
ΔG = −565160 + 172.03 × T (2)
[2] From the desulfurization slag according to the above [1], the recycling destination of the desulfurization slag after the treatment in the third step is an iron ore sintering step or a hot metal production step in a blast furnace To remove sulfur in water.
[3] The above-mentioned [1], wherein the desulfurization slag after the treatment in the third step is recycled to any one of hot metal desulfurization treatment, dephosphorization treatment, and decarburization refining in the steelmaking refining step. A method for removing sulfur from the desulfurized slag as described in 1.
[4] The removal of sulfur from the desulfurized slag according to any one of [1] to [3] above, wherein metallic iron is separated in advance from the desulfurized slag used in the first step. Method.

According to the present invention, when the desulfurization slag generated in the hot metal desulfurization process is recycled to the steelmaking process or the steelmaking process, the desulfurization slag is in the range of 1100 to 1400 ° C. and the above formula (1) In the desulfurized slag by heating in an atmosphere in which the CO / CO ₂ ratio of the atmosphere is adjusted so that the oxygen gas partial pressure (P _O2 ) defined in the formula is in the range of 10 ⁻³ to 10 ⁻⁹ atm. Sulfur is removed to the gas phase side as SOx, and desulfurized slag with reduced sulfur content is recycled as a CaO source in the ironmaking process or steelmaking process, so most of the sulfur contained in the desulfurized slag is removed to the gas phase side. In the iron making process and the steel making process, desulfurized slag can be reused as a CaO source without being affected by sulfur.

In recycling to the ironmaking process, the amount of blast furnace slag generated increases due to the iron ore sintering process or recycling to the blast furnace, but the blast furnace slag should be used as a cement admixture in the form of fine powder. As a result, the CaO content in the blast furnace slag causes a pozzolanic reaction similar to that of the cement and develops the strength of the cement. Conventionally, the CaO content of the cement raw material has been manufactured by calcining calcium carbonate (CaCO ₃ ), and this calcining requires not only thermal energy but also generates CO ₂ gas. When mixed into a blast furnace slag cement (referred to as “blast furnace cement”), the firing energy and the amount of CO ₂ gas generated can be reduced according to the mixing ratio of blast furnace slag fine powder / ordinary Portland cement. Moreover, in recycling to a steelmaking process, the amount of quicklime (CaO) used can be reduced by recycling slag as a CaO source, and the generated amount of steelmaking slag can be greatly reduced. At the same time, by recycling the desulfurized slag to the iron making process and the steel making process, it becomes possible to effectively use the iron content in the desulfurized slag as an iron resource.

It is a figure which shows the relationship between the oxygen gas partial pressure of the atmosphere defined by (1) Formula, and the desulfurization rate obtained from the test in the range whose atmospheric temperature is 1100-1400 degreeC.

  Hereinafter, the present invention will be described in detail.

The inventors of the present invention used CaO alone, or hot metal using CaO—CaF ₂ or CaO—Al ₂ O ₃ obtained by adding CaF ₂ or Al ₂ O ₃ to CaO as a CaO hatching accelerator. When the desulfurization slag generated in the desulfurization treatment is recycled as a CaO source in the steelmaking process or the steelmaking process, a method for removing sulfur from the desulfurization slag before recycling is examined.

First, in the process of cooling and pulverizing desulfurized slag in the steelworks, a sample was taken from the desulfurized slag, and the compound form of sulfur in the desulfurized slag was investigated using X-ray diffraction. As a result, it was confirmed that sulfur was present in the desulfurized slag in the form of CaSO ₃ or CaSO _{4 in} addition to the conventionally considered compound form of CaS. This is considered that CaS is oxidized in the air in the course of the desulfurization slag cooling / pulverization process, and CaSO ₃ and CaSO ₄ are generated.

Next, the present inventors conducted experiments and thermodynamic studies on the conditions under which sulfur can be removed from any sulfur compound of CaS, CaSO ₃ , and CaSO _{4 in} the desulfurized slag to the gas phase side. . In the experiment, the slag sample was heated by charging the slag sample in the heating furnace and controlling the oxygen potential in the heating furnace by adjusting the CO / CO ₂ ratio of the atmosphere in the heating furnace.

As a result, any sulfur compound of CaS, CaSO ₃ , and CaSO ₄ can be obtained by adjusting the oxygen gas partial pressure of the atmosphere determined from the CO / CO ₂ ratio of the atmosphere in the heating furnace and the ambient temperature within a certain predetermined range. It was also found that sulfur can be removed from slag. Specifically, it was found that a desulfurization rate of 80% or more can be obtained by controlling the oxygen gas partial pressure defined by the following formula (1) within a range of 10 ⁻³ to 10 ⁻⁹ atm.

P _O2 = (P _CO2 / P _CO ) ² × [1 / exp (−ΔG / R × T)] (1)
However, in the equation (1), P _O2 is the atmospheric oxygen gas partial pressure (atm), P _CO2 is the atmospheric CO ₂ gas partial pressure (atm), and P _CO is the atmospheric CO gas partial pressure (atm). , R is a gas constant (= 8.314 J / (mol · K)), ΔG is a free energy (J / mol), and is defined by the following formula (2): (1) and (2) T in the equation is the ambient temperature (K).

ΔG = −565160 + 172.03 × T (2)
In heating in the atmosphere (partial pressure of oxygen gas = 0.2), sulfur in CaS contained in the desulfurized slag becomes gaseous SOx, but sulfur in CaSO ₃ contained in the desulfurized slag or in CaSO ₄ It was confirmed that sulfur cannot be removed to the gas phase side as SOx.

  As for the atmospheric temperature at this time, it was found from the experimental results and thermodynamic examination that it is necessary to set the atmospheric temperature in the heating furnace to 1100 ° C. or higher in order to obtain a desulfurization rate of 80% or higher. . The upper limit of the atmospheric temperature is not particularly limited from the viewpoint of the removal reaction of sulfur to the gas phase side, but if it is heat-treated at a too high temperature, it will cause damage to the furnace refractory and increase in heating energy costs. It turned out that it is preferable to set it as 1400 degrees C or less.

  As a method for recycling desulfurized slag whose sulfur content has been reduced by such heat treatment (also referred to as “sulfur removal treatment”), it is used as a CaO source (slagging agent) in the iron ore sintering process, and then the blast furnace In addition to the method used as a charging raw material in the hot metal production process in Japan, the method used directly as a CaO-based iron making agent in the hot metal production process in the blast furnace, or the dephosphorization treatment performed on the blast furnace hot metal as a preliminary treatment Suitable examples include a method of using it as a CaO-based flux in desulfurization and a method of using it as a fossilizing agent in a decarburization and refining process of hot metal in a converter. Even if it is processes other than these, as long as it is the process which uses the quicklime of the iron making process and steelmaking process in an ironworks, it can be used as a substitute for quicklime. Although the total amount of desulfurized slag generated may be subjected to the sulfur removal treatment of the present invention, it is from a resource-saving viewpoint that the desulfurized slag generated in the hot metal desulfurization treatment is used again for the hot metal desulfurization treatment. Is also effective. In other words, until the sulfur concentration in the desulfurization slag becomes high due to recycling and the utility as a desulfurization agent ceases, the sulfur concentration in the desulfurization slag becomes high and the utility as a desulfurization agent is lost. At this point, it is preferable to apply the present invention.

  Moreover, the desulfurization slag used for the sulfur removal treatment of the present invention often contains metallic iron, and a part of this metallic iron is oxidized to iron oxide after undergoing the sulfur removal treatment of the present invention. . When slag containing iron oxide is recycled to the iron making process or the steel making process, the iron oxide can be reduced to become an iron resource, but the reduction energy of iron oxide is required. Therefore, it is preferable to remove metallic iron from the desulfurized slag before being subjected to the sulfur removal treatment of the present invention. For separation of metallic iron, an appropriate process may be selected according to the shape and processing amount of slag, such as separation using magnetic force or centrifugal airflow separation using the difference in specific gravity between iron and slag.

  In carrying out the sulfur removal treatment, the exhaust gas containing SOx removed to the gas phase side is subjected to desulfurization treatment (smoke desulfurization treatment) to prevent the emission of SOx in the exhaust gas to the atmosphere. As the flue gas desulfurization treatment method, various methods such as a lime gypsum method, a magnesium hydroxide method, and a dry activated coke method which are generally widely used can be adopted. For the flue gas desulfurization treatment method, an optimum method may be selected by comprehensively judging the flow rate of exhaust gas generated by the sulfur removal treatment, the treatment of by-products, treatment costs, equipment costs, and the like.

The reaction vessel for performing the sulfur removal treatment may be any reactor as long as it can heat the desulfurization slag and control the atmosphere in the reaction vessel, and specifically includes a rotary kiln, RHF, fluidized bed, and the like. It is done. Further, if the heating method is an LPG burner or an LNG burner, the CO / CO ₂ ratio can also be adjusted.

As described above, according to the present invention, when the desulfurized slag generated in the hot metal desulfurization process is recycled to the steelmaking process or the steelmaking process, the desulfurized slag has an ambient temperature in the range of 1100 to 1400 ° C, and Since heating is performed in an atmosphere in which the CO / CO ₂ ratio of the atmosphere is adjusted so that the oxygen gas partial pressure (P _O2 ) defined by the above formula (1) is in the range of 10 ⁻³ to 10 ⁻⁹ atm. Thus, sulfur in the desulfurized slag can be removed to the gas phase as gaseous SOx, and it is realized that desulfurized slag with a low sulfur content is effectively used as a CaO source. Thereby, the generation amount of desulfurization slag itself can be reduced and the processing cost of the desulfurization slag can be reduced, and risks such as yellow water generation when the desulfurization slag is effectively used outside the steelworks can be avoided. .

  The blast furnace hot metal discharged from the blast furnace is received by a topped car, and the blast furnace hot metal contained in the topped car is subjected to desiliconization treatment and dephosphorization treatment as a preliminary treatment, and then the blast furnace hot metal is transferred to the hot metal ladle. The blast furnace hot metal was desulfurized by a mechanical stirring type desulfurization device, the blast furnace hot metal after this desulfurization treatment was charged into the converter, and decarburization refining was performed in the converter, thus melting the molten steel from the blast furnace hot metal. The present invention was applied in the steelmaking-steelmaking process. Table 1 shows examples of chemical components of the blast furnace hot metal and the molten steel produced from the blast furnace tapping to the end of converter decarburization refining.

  As shown in Table 1, the blast furnace hot metal before the desulfurization treatment contains about 0.03% by mass of sulfur. By adding a CaO source as a desulfurization agent in the hot metal desulfurization step and stirring the blast furnace hot metal, Is desulfurized to 0.002 mass%. The test which applies this invention with respect to the desulfurization slag generate | occur | produced at this time was done. Table 2 shows representative compositions of desulfurized slag.

50 tons of desulfurized slag was charged into a rotary kiln equipped with a heating burner, and the desulfurized slag was heated by the burner to perform sulfur removal treatment from the desulfurized slag. The temperature of the furnace atmosphere was controlled by adjusting the output of the heating burner, and the CO / CO ₂ ratio of the furnace atmosphere was controlled by changing the gas conditions of the burner. Specifically, a gas sample is taken from the furnace, the CO / CO ₂ ratio of the furnace atmosphere is obtained by quantitative analysis of the collected gas sample, and the burner gas is set so that the CO / CO ₂ ratio becomes a target value. The composition of the furnace atmosphere was adjusted by changing the conditions. A flue gas desulfurization facility was provided on the exhaust gas side to detoxify SOx in the exhaust gas.

  Table 3 shows test conditions and test results. FIG. 1 shows the relationship between the oxygen gas partial pressure and the desulfurization rate in the atmosphere defined by the equation (1), which was obtained from a test in which the ambient temperature is in the range of 1100 to 1400 ° C.

In Inventive Examples 1 to 16, the temperature of the atmosphere is 1100 to 1400 ° C., and the oxygen gas partial pressure (P _O2 ) of the atmosphere is controlled in the range of 10 ⁻³ to 10 ⁻⁹ atm, which is 80% or more. Desulfurization rate could be obtained. Here, the desulfurization rate is a numerical value indicating the difference between the sulfur concentration in the desulfurized slag before the heat treatment and the sulfur concentration in the desulfurized slag after the heat treatment as a percentage with respect to the sulfur concentration in the desulfurized slag before the heat treatment. is there.

On the other hand, in Comparative Examples 1 to 7, the atmospheric temperature was 1100 to 1400 ° C., but the oxygen gas partial pressure (P _O2 ) of the atmosphere was outside the scope of the present invention, and the desulfurization rate was below 80%.

In Comparative Example 8, although the oxygen gas partial pressure (P _O2 ) in the atmosphere was within the range of the present invention, the desulfurization rate was low because the ambient temperature was low. On the other hand, in Comparative Example 9, the oxygen gas partial pressure (P _O2 ) in the atmosphere was within the range of the present invention and the desulfurization rate was high, but refractory refractory damage was observed due to the high atmospheric temperature.

  The desulfurization slag after the sulfur removal treatment of Invention Examples 1 to 16 was used as a CaO source for a slagging agent in the iron ore sintering step, and the produced sintered ore was charged into a blast furnace as an iron source, Produced no problems. In addition, blast furnace slag cement was manufactured using the blast furnace slag that was recycled, but it satisfied the quality standard of JIS A 6206 “Blast furnace slag fine powder for concrete” and JIS R 5211 “Blast furnace cement” The strength and other properties are the same as in the past, and there are no problems.

  Moreover, although the desulfurization slag after the sulfur removal treatment of Invention Examples 1 to 16 was used as a CaO source in hot metal desulfurization treatment, dephosphorization treatment, and decarburization refining in the steelmaking process, refining can be performed without any problem. did it.

Furthermore, even if the metallic iron is removed from the desulfurization slag by magnetic separation in advance and the sulfur removal treatment is performed, the desulfurization rate satisfies 80% or more if the temperature of the atmosphere and the CO / CO ₂ ratio are appropriate. In addition, the metal iron removed in advance could be utilized as iron resources without consuming reducing energy in the iron making process or the steel making process.

  On the other hand, when the desulfurization slag generated in the hot metal desulfurization process is recycled as it is as a CaO source of sintered ore without performing the sulfur removal process of the present invention, the SOx concentration in the exhaust gas during sintering exceeds the regulation value. Therefore, the operation could not be realized without installing flue gas desulfurization treatment in the sintering equipment. In addition, when the desulfurized slag was recycled to the blast furnace as it was without performing the sulfur removal treatment of the present invention, the sulfur concentration of the blast furnace slag increased, and the production conditions for the blast furnace slag cement could not be satisfied. Furthermore, if the desulfurized slag is recycled without being subjected to the sulfur removal treatment of the present invention as it is as a source of CaO in the dephosphorization treatment or decarburization refining of the steelmaking process, the sulfur concentration of the hot metal or molten steel will increase, causing an operation hindrance. In addition, when recycled as a CaO source for the desulfurization treatment of hot metal, it was possible to recycle up to a certain amount, but it was impossible to recycle the entire amount of desulfurized slag generated in the steelworks.

Claims (4)

The desulfurization slag containing sulfur generated in the hot metal desulfurization treatment has an atmospheric temperature in the range of 1100 to 1400 ° C. and an oxygen gas partial pressure defined by the following formula (1) of 10 ⁻³ to 10 ^−. Heating in an atmosphere in which the CO / CO ₂ ratio of the atmosphere is adjusted to be in the range of ⁹ atm, and removing sulfur in the desulfurized slag as SOx to the gas phase side of the atmosphere;
A second step of desulfurizing the exhaust gas containing SOx removed on the gas phase side in the first step;
A third step of recycling the desulfurized slag having a reduced sulfur content in the first step as a CaO source in the iron making step or the steel making step;
A method for removing sulfur from desulfurized slag, comprising:

However, in the equation (1), P _O2 is the atmospheric oxygen gas partial pressure (atm), P _CO2 is the atmospheric CO ₂ gas partial pressure (atm), and P _CO is the atmospheric CO gas partial pressure (atm). , R is a gas constant (= 8.314 J / (mol · K)), ΔG is a free energy (J / mol), and is defined by the following formula (2): (1) and (2) T in the equation is the ambient temperature (K).
ΔG = −565160 + 172.03 × T (2)   The removal destination of sulfur from the desulfurization slag according to claim 1, wherein a recycling destination of the desulfurization slag after the treatment in the third step is an iron ore sintering step or a hot metal production step in a blast furnace. Method.   2. The desulfurization according to claim 1, wherein a recycling destination of the desulfurization slag after the treatment in the third step is any one of hot metal desulfurization treatment, dephosphorization treatment, and decarburization refining in the steelmaking refining step. How to remove sulfur from slag.   The method for removing sulfur from desulfurized slag according to any one of claims 1 to 3, wherein metallic iron is separated in advance from the desulfurized slag used in the first step.

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