JP2013087290A - Method for removing sulfur from desulfurization slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively recycle desulfurization slag as a CaO source in a pig iron making step or a steelmaking step, without any effect of sulfur contained therein, by efficiently removing sulfur contained in the desulfurization slag produced by a desulfurization treatment of molten iron.SOLUTION: The method for removing sulfur from the desulfurization slag comprises: a first step of exposing the sulfur-containing desulfurization slag produced by the desulfurization treatment of the molten iron to an atmosphere in which the temperature is within the range of 1,100-1,400°C and the CO/COratio is adjusted according to the form of a sulfur compound in the desulfurization slag, thereby transferring the sulfur as SOfrom the desulfurization slag into a gas phase; a second step of carrying out a desulfurization treatment of exhaust gas containing SOtransferred into the gas phase in the first step; and a third step of recycling the desulfurization slag in which the sulfur content is reduced by the first step as the 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 of steel products and the increasing demand for quality, hot metal desulfurization treatment is being carried out at each steel company as a preliminary refining of hot metal. 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. The hot metal desulfurization treatment is a treatment for removing sulfur in the hot metal in the hot metal stage before decarburization and refining in a converter.

  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. Moreover, the utilization efficiency of CaO as a desulfurization agent in the desulfurization treatment of hot metal 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. .

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

  For example, in Patent Document 1, 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 desulfurization slag emissions. Techniques to do this 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 as the number of recycling is repeated. 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 desulfurization in the atmosphere, as described later in this specification, only sulfur in CaS contained in the desulfurization slag can be removed to the gas phase side, such as CaSO ₃ and CaSO _4. There is a problem that sulfur existing in the desulfurized slag in the form of a sulfur compound 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 the CO / CO ₂ ratio of the atmosphere is in the form of the sulfur compound in the desulfurization slag. And a first step of removing sulfur in the desulfurized slag as SOx on the gas phase side of the atmosphere and SOx removed on the gas phase side in the first step. A second step of desulfurizing the exhaust gas, and a third step of recycling the desulfurized slag whose sulfur content has been reduced by the first step as a CaO source in the ironmaking step or the steelmaking step. And a method for removing sulfur from desulfurized slag.
(2) In the first step, the CO / CO ₂ ratio of the atmosphere is adjusted such that the desulfurization rate of the desulfurization slag is 80% or more. To remove sulfur in water.
(3) In the first step, the CO / CO ₂ ratio of the atmosphere is set such that the sulfur is removed as SOx when the sulfur in the desulfurized slag is a compound in the form of CaS, and the sulfur in the desulfurized slag is CaSO _3. And sulfur from the desulfurized slag according to (1) or (2) above, wherein the sulfur is changed to at least two ranges of the range removed as SOx in the case of a compound in the form of CaSO ₄ Removal method.
(4) The recycle 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, wherein (1) to (3) above The removal method of sulfur from the desulfurization slag of any one of Claims 1.
(5) The recycle destination of the desulfurization slag after the treatment in the third step is any one of hot metal desulfurization treatment, preliminary dephosphorization treatment, and decarburization refining treatment in the steelmaking refining step, 1) thru | or the removal method of sulfur from the desulfurization slag in any one of said (3).
(6) The removal of sulfur from the desulfurized slag according to any one of (1) to (5) above, wherein metallic iron is separated in advance from the desulfurized slag used in the first step. Method.

According to the present invention, when recycling the desulfurization slag generated in the hot metal desulfurization process to the steelmaking process or the steelmaking process, first, sulfur in the desulfurization slag is treated with the treatment atmosphere temperature and the CO / CO ₂ ratio of the treatment atmosphere. Since it is adjusted and removed to the gas phase side as SOx, and the slag with reduced sulfur content is recycled as a CaO source in the ironmaking process or steelmaking process, 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, it 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. 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.

  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 the desulfurized slag was present in the form of CaSO ₃ or CaSO _{4 in} addition to the conventionally considered compound form of CaS. This is presumably because CaS is oxidized into the atmosphere during the cooling / pulverization process, and CaSO ₃ and CaSO ₄ are generated.

Next, a thermodynamic study was performed. As a result, if CaS, the desulfurization slag becomes SOx sulfur in gas in CaS by oxidizing in the atmosphere, it is possible to remove the sulfur in the desulfurization slag into the gas phase side, CaSO ₃ It has been found that CaSO ₄ cannot be removed to the gas phase side as SOx even when oxidized in the atmosphere. That is, it has been found that in order to remove CaSO ₃ and CaSO ₄ in the desulfurized slag as SOx into the gas phase, it is necessary to lower the equilibrium oxygen potential of the reaction atmosphere and dissociate SOx.

The present inventors conducted an experimental investigation to confirm the validity of the above-described thermodynamic examination. The experiment was performed by inserting a slag sample into the heating furnace and adjusting the CO / CO ₂ ratio in order to control the oxygen potential in the heating furnace. As a result, it was confirmed that by adjusting the CO / CO ₂ ratio in the heating furnace, sulfur in the desulfurized slag can be removed even in the form of CaS, or in the form of CaSO ₃ or CaSO ₄ . Regarding the desulfurized slag that was investigated this time, when removing sulfur in the form of CaS to the gas phase, the CO / CO ₂ ratio was made less than 0.01, while sulfur in the form of CaSO ₃ or CaSO _4. In the gas phase, the CO / CO ₂ ratio is 0.1 or more, so that 80% or more of the sulfur mass contained in the desulfurization slag can be removed, that is, the sulfur is removed at a desulfurization rate of 80% or more. It was found that it can be removed in the gas phase.

In addition, an experimental investigation was also conducted in the case where CaS, CaSO ₃ and CaSO ₄ were mixed in the desulfurized slag. When these sulfur compounds are mixed, the CO / CO ₂ ratio cannot be determined unconditionally. However, when sulfur compounds are mixed as a result of various investigations, first, sulfur present in the form of CaS is removed by setting the CO / CO ₂ ratio of the atmosphere to less than 0.01, and then the CO / CO _{2 of the} atmosphere is removed. It is possible to remove sulfur in two stages by changing the CO / CO ₂ ratio of the atmosphere to two levels during the sulfur removal process by removing the sulfur present in the form of CaSO ₃ or CaSO ₄ by increasing the ratio to 0.1 or more. It was confirmed that. In this case, sulfur existing in the form of CaSO ₃ or CaSO ₄ may be removed first, and then sulfur existing in the form of CaS may be removed. However, even if they are mixed, if most of the sulfur present in the desulfurized slag is in the form of CaS, the CO / CO ₂ ratio of the atmosphere is set to less than 0.01 without performing two-stage sulfur removal. Even in one-stage treatment, a desulfurization rate of 80% or more can be obtained.

In addition, in the desulfurization slag described in this specification (see the examples described later), the CO / CO ₂ ratio for removing sulfur to the gas phase became the above threshold, but the CaS in the desulfurization slag, When the abundance ratio of each sulfur compound of CaSO ₃ and CaSO ₄ is greatly different from the range of desulfurization slag shown in the examples, the CO / CO ₂ ratio is adjusted to an appropriate range while checking the sulfur concentration in the slag after treatment. Adjust it. If qualitatively high existence ratio of CaS can lower the CO / CO ₂ ratio, when the existence ratio of CaSO ₃ and CaSO ₄ higher can be coped with by increasing the CO / CO ₂ ratio This is confirmed by a separate experiment.

  Furthermore, as a result of conducting an experimental investigation on the atmospheric temperature during the treatment, it was found that a range of 1100 to 1400 ° C. is suitable for removing sulfur from the desulfurized slag. Below 1100 ° C., the desulfurization rate was slightly low due to the slow removal reaction rate of sulfur. On the other hand, at a processing temperature higher than 1400 ° C., although the desulfurization rate did not change so much, damage to the refractory in the processing container was greatly increased, and the cost was increased.

  As a method for recycling desulfurized slag whose sulfur content has been reduced by such treatment, it is used as a CaO source (slagging agent) in the iron ore sintering process, and then used as a raw material in the hot metal production process in a blast furnace. In addition to the method used, it can be used directly as a CaO-based iron making agent in the hot metal production process in the blast furnace, or as a CaO-based flux in the preliminary dephosphorization treatment or desulfurization treatment of the blast furnace hot metal, or A suitable example is a method of using it as a slag-forming agent in a decarburizing and refining process of hot metal in a furnace. Even if it is a process other than this, 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 treatment of the present invention, it is also effective from the viewpoint of resource saving to use the desulfurized slag generated in the hot metal desulfurization treatment again for the desulfurization treatment of hot metal. It is. In other words, until the sulfur concentration in the desulfurization slag is increased by recycling and the effect as a desulfurization agent is lost, recycling to the hot metal desulfurization treatment process is performed, and the sulfur concentration in the desulfurization slag becomes high and the effect as a desulfurization agent is lost. At some 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 becomes iron oxide after the sulfur removal treatment. 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.

  The exhaust gas containing SOx removed to the gas phase side is subjected to desulfurization treatment to prevent the SOx in the exhaust gas from being released into 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 employed. For the flue gas desulfurization method, an optimum method may be selected by comprehensively considering the flow rate of exhaust gas generated by the sulfur removal treatment, the treatment of by-products, the processing cost, the equipment cost, and the like.

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

As described above, according to the present invention, when recycling the desulfurization slag generated in the hot metal desulfurization process to the ironmaking process or the steelmaking process, the processing temperature is set to an optimum range, and the sulfur compound in the desulfurization slag is used. Since the sulfur removal treatment is applied to the desulfurization slag by controlling the CO / CO ₂ ratio of the treatment atmosphere according to the form, the sulfur in the desulfurization slag can be removed to the gas phase as gaseous SOx, and the sulfur content is low Effective utilization of desulfurized slag as a CaO source is realized. 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, the blast furnace hot metal accommodated in the topped car is subjected to desiliconization treatment and preliminary dephosphorization treatment, and then the blast furnace hot metal is transferred to the hot metal ladle and the blast furnace in the hot metal ladle. The hot metal is desulfurized by a mechanical stirring desulfurization device, the blast furnace hot metal after this desulfurization treatment is charged into the converter, and decarburization refining is performed in the converter, thus producing molten steel from the blast furnace hot metal. The present invention was applied in the 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, and 0.002 by adding a CaO source as a desulfurization agent in the hot metal desulfurization step and stirring. Desulfurized to mass%. The test which applies this invention with respect to the desulfurization slag generated 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 remove sulfur from the desulfurized slag. Regarding the form of the sulfur compound in the desulfurized slag, a sample was taken from the desulfurized slag before the treatment, and the abundance ratio was confirmed using an X-ray diffractometer. The temperature in the furnace atmosphere was controlled by adjusting the output of the heating burner, and the CO / CO ₂ ratio was controlled in the furnace atmosphere by changing the gas conditions of the burner. 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.

In the inventive examples 1 to 4, since the form of the sulfur compound in the desulfurized slag was mainly CaS, the desulfurization rate of 80% or more at the treatment temperature of 1100 to 1400 ° C. was achieved only by reducing the CO / CO ₂ ratio. Could get.

  On the other hand, in Comparative Example 1 and Comparative Example 3, the form of the sulfur compound in the desulfurized slag was mainly CaS as in Examples 1-4 of the present invention, but the processing temperatures were 1000 ° C and 1500 ° C, respectively, and the scope of the present invention. It was outside. As a result, in Comparative Example 1, the desulfurization rate was less than 80% due to a decrease in the desulfurization rate due to the low temperature, and in Comparative Example 3, the desulfurization rate was 80% or more, but the refractory in the furnace was melted. .

In Invention Examples 5 to 11, since the sulfur compound in the desulfurized slag was a mixture of CaS, CaSO ₃ and CaSO ₄ , first, the CO / CO ₂ ratio in the furnace atmosphere was lowered to remove CaS. Thereafter, removal of CaSO ₃ and CaSO ₄ was attempted by increasing the CO / CO ₂ ratio in the furnace atmosphere. As a result, in all cases, the desulfurization rate was 80% or more.

On the other hand, in Comparative Example 2 and Comparative Example 4, the sulfur compound in the desulfurized slag is a mixture of CaS, CaSO ₃ , and CaSO _4. First, the CO / CO ₂ ratio in the furnace atmosphere is lowered, and then the CO / CO ₂ is reduced. _{2 The} ratio was increased, but the processing temperatures were 1000 ° C. and 1500 ° C., respectively, outside the scope of the present invention. As a result, in Comparative Example 2 where the treatment temperature was 1000 ° C., the desulfurization rate was less than 80%, and in Comparative Example 4 where the treatment temperature was 1500 ° C., the refractory was melted.

In Comparative Example 5 and Comparative Example 6, the form of the sulfur compound in the desulfurized slag was mainly CaS, but the test was conducted with a slightly higher CO / CO ₂ ratio in the treatment atmosphere. In this case, sulfur could not be removed sufficiently, and the desulfurization rate was less than 80%. Further, Comparative Examples 7 and 8 in the form of sulfur compounds in desulfurization slag CaS, CaSO _3, although there was a mixture of CaSO _4, was tested slightly lower CO / CO ₂ ratio of the treatment atmosphere . In this case, the desulfurization rate was similarly less than 80%.

  The desulfurization slag after the sulfur removal treatment of Invention Examples 1 to 11 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 11 was used as a CaO source for hot metal desulfurization treatment, preliminary dephosphorization treatment, and decarburization refining treatment in the steelmaking process, the refining operation can be performed without any problem. Could be done.

Furthermore, even after removing metallic iron from the desulfurization slag by magnetic separation in advance and performing the sulfur removal treatment, 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 treatment is recycled as it is as a CaO source of sintered ore without performing the sulfur removal treatment of the present invention, the SOx concentration in the exhaust gas during sintering exceeds the regulation value. For this reason, the operation could not be completed unless the flue gas desulfurization treatment was installed in the sintering facility. 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 as a CaO source for the preliminary dephosphorization process or decarburization refining process of the steelmaking process without performing the sulfur removal process of the present invention, the sulfur concentration of the hot metal or the molten steel increases and operation is inhibited. Caused. When the hot metal desulfurization treatment was recycled as a CaO source, it was possible to recycle up to a certain amount, but it was impossible to recycle the entire amount of desulfurization slag generated in the steelworks.

Claims (6)

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 the CO / CO ₂ ratio of the atmosphere is adjusted according to the form of the sulfur compound in the desulfurization slag A first step of exposing to the atmosphere 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: The removal of sulfur from the desulfurized slag according to claim 1, wherein the CO / CO ₂ ratio of the atmosphere is adjusted so that the desulfurization rate of the desulfurized slag is 80% or more in the first step. Method. In the first step, the CO / CO ₂ ratio of the atmosphere is set such that the sulfur is removed as SOx when sulfur in the desulfurized slag is a compound in the form of CaS, and the sulfur in the desulfurized slag is CaSO ₃ and CaSO _4. The method for removing sulfur from the desulfurized slag according to claim 1 or 2, wherein the range is changed to at least two ranges of the range of removal as SOx in the case of a compound of the form.   The recycle 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, according to any one of claims 1 to 3. A method for removing sulfur from the desulfurized slag as described.   The recycling destination of the desulfurization slag after the treatment in the third step is any one of hot metal desulfurization treatment, preliminary dephosphorization treatment, and decarburization refining treatment in the steelmaking refining step. Item 4. The method for removing sulfur from the desulfurized slag according to any one of Items 3 to 4.   The method for removing sulfur from desulfurized slag according to any one of claims 1 to 5, wherein metallic iron is separated in advance from the desulfurized slag used in the first step.