Stepwise system and method for producing lime and hydrogen using by-product gypsum

Abstract

The present invention relates to a stepwise system and method for producing lime and hydrogen using by-product gypsum and the system includes: a lime production unit that reacts the by-product gypsum with a hydroxide of an alkali metal to produce lime and alkali metal sulfate, an electrolysis unit that electrolyzes the aqueous solution of the generated alkali metal sulfate to produce alkali metal hydroxide and hydrogen, and a circulation unit that provides the produced alkali metal hydroxide back to the lime production unit.

Description

STEPWISE SYSTEM AND METHOD FOR PRODUCING LIME AND HYDROGEN USING BY-PRODUCT GYPSUM

[0001] The present invention relates to a stepwise system and method for producing lime and hydrogen using by-product gypsum. More specifically, it involves the production of lime and alkali metal sulfates using by-product gypsum, the electrolysis of the aqueous solution of alkali metal sulfates to produce alkali metal hydroxides and hydrogen, and the reaction of the alkali metal hydroxides with by-product gypsum to repeat the aforementioned process in a step-by-step manner.

[0002] Lime substances such as slaked lime (Ca(OH)2) and quicklime (CaO) are one of the most consumed chemicals worldwide, and are used in various industries such as construction and civil engineering as well as ironmaking, steelmaking, papermaking, agriculture, food industry, and environmental, medical, and chemical industries. Hydrogen, in addition to its extensive existing applications in various fields such as chemistry, electricity, metals, ceramics, aerospace, military, optical fibers, lighting, and solar power generation, is increasingly in demand as a fuel for hydrogen fuel cells.

[0003] In the production of lime, a widely used method involves calcining (heating) limestone to decompose the main component, calcium carbonate, into calcium oxide and carbon dioxide, thereby producing quicklime. However, this method emits approximately 0.75 tons of carbon dioxide for every ton of lime produced and is recognized as a major global contributor to carbon emissions and subsequent climate change.

[0004] Meanwhile, by-product gypsum refers to the gypsum discharged as a by- product of industrial activities. For example, in the case of a phosphate fertilizer production plant, by-product phosphogypsum is generated as a by-product during the wet process of treating phosphate rock with sulfuric acid to produce phosphate fertilizers, and in the case of a thermal power plant, flue gas desulfurization gypsum is produced as a by-product during the process of removing sulfur from exhaust gases using lime.

[0005] The total amount of phosphogypsum and flue-gas desulfurization gypsum discharged annually from the above-described phosphate fertilizer production plants, thermal power plants, and other such facilities reaches to several million tons. However, only a part of this by-product gypsum is being recycled, with the majority remaining unused and stockpiled. Therefore, the development of technologies that can effectively utilize by-product gypsum is urgently needed.

[0006] Meanwhile, the aforementioned background technology includes technical information that the inventor possessed or acquired during the development process of the present invention and cannot necessarily be considered prior art that was publicly disclosed to the general public before the filing of this invention.

[0007] An object of the present invention is to provide a stepwise system and method for producing lime and hydrogen using by-product gypsum, which minimizes the carbon dioxide emissions associated with lime production.

[0008] In addition, another object of the present invention is to provide a stepwise system and method for producing lime and hydrogen using by-product gypsum, which effectively recycles gypsum discharged as a by-product of industrial activities.

[0009] The objects of the present invention are not limited to those mentioned above, and other objects not explicitly mentioned will be clearly understood by those skilled in the art from the description below.

[0010] As a technical means to achieve the mentioned technical objectives, one aspect of the present invention provides a stepwise system for producing lime and hydrogen using by-product gypsum. The system includes a lime generation unit that reacts by-product gypsum with alkali metal hydroxides to produce lime and alkali metal sulfates, an electrolysis unit that electrolyzes the solution of the generated alkali metal sulfates to produce alkali metal hydroxides and hydrogen, and a circulation unit that supplies the produced alkali metal hydroxides back to the lime generation unit.

[0011] According to one embodiment of the present invention, the stepwise system for producing lime and hydrogen using by-product gypsum may further include a sulfate separation unit that separates the alkali metal sulfate generated from the lime generating unit.

[0012] According to one embodiment of the present invention, the lime production unit may generate a slurry containing hydrated lime by reacting the by-product gypsum with a hydroxide of an alkali metal. The stepwise system for producing lime and hydrogen using by-product gypsum may further include a slaked lime separation unit for washing the produced slurry to separate the slaked lime, and a quicklime production unit for calcining the separated slaked lime to produce quicklime.

[0013] According to one embodiment of the present invention, the stepwise system for producing lime and hydrogen using by-product gypsum may further include a discharge unit that discharges at least one of the lime and the alkali metal sulfate generated from the lime generating unit.

[0014] According to one embodiment of the present invention, the electrolysis unit may include an anode part where current flows in from an external source, a cathode part where current flows out to an external source, a separation membrane that separates the anode and cathode parts, and a power supply unit that provides power to the anode and cathode parts. The anode part may include an anode and an anode electrolyte, and the cathode part may include a cathode and a cathode electrolyte. The separation membrane may include at least one of a cation exchange membrane that allows cations to pass through and an anion exchange membrane that allows anions to pass through.

[0015] According to one embodiment of the present invention, the circulation unit may include a concentration unit that concentrates the hydroxide of the alkali metal produced in the electrolysis unit.

[0016] According to one embodiment of the present invention, the circulation unit may include a measuring unit that measures the pH of a solution including the alkali metal hydroxide produced in the electrolysis unit.

[0017] According to one embodiment of the present invention, the by-product gypsum may include at least one of phosphogypsum including calcium sulfate and desulfurization gypsum including calcium sulfate.

[0018] According to one embodiment of the present invention, the alkali metal sulfate generated in the lime generating unit may include at least one of sodium sulfate and potassium sulfate.

[0019] According to one embodiment of the present invention, the alkali metal hydroxide produced in the electrolysis unit may include at least one of sodium hydroxide and potassium hydroxide.

[0020] As a technical means for achieving the above-mentioned technical objects, according to another aspect of the present invention, a stepwise method of producing lime and hydrogen using by-product gypsum includes: generating lime and an alkali metal sulfate by allowing by-product gypsum to react with an alkali metal hydroxide through a lime generating unit; producing an alkali metal hydroxide and hydrogen by electrolyzing an aqueous solution of the alkali metal sulfate through an electrolysis unit; and circulating and providing the alkali metal hydroxide to the lime generating unit through a circulation unit.

[0021] According to one embodiment of the present invention, the stepwise method of producing lime and hydrogen using by-product gypsum may include, after the generating of the lime and the alkali metal sulfate, separating the generated alkali metal sulfate.

[0022] According to one embodiment of the present invention, the generating of the lime and the alkali metal sulfate may include generating a slurry including slaked lime by allowing the by-product gypsum to react with the alkali metal hydroxide, and the stepwise method of producing lime and hydrogen using the by-product gypsum may further include, after the generating of the lime and the alkali metal sulfate, separating the slaked lime by washing the generated slurry; and generating quicklime by calcining the separated slaked lime.

[0023] According to one embodiment of the present invention, the stepwise method of producing lime and hydrogen using by-product gypsum may further include, after the generating of the lime and the alkali metal sulfate, discharging at least one of the generated lime and alkali metal sulfate.

[0024] According to one embodiment of the present invention, the circulating and providing of the alkali metal hydroxide to the lime generating unit may include concentrating the produced alkali metal hydroxide.

[0025] According to any one of the above-described means for achieving the above objects of the present invention, a stepwise system and method for producing lime and hydrogen using by-product gypsum may produce lime and an alkali metal sulfate by allowing by-product gypsum to react with an alkali metal hydroxide, and accordingly, are capable of producing lime without using the existing method using calcium carbonate, thereby exhibiting an effect of significantly reducing carbon dioxide generation and emissions during the lime production process. In addition, the system and the method enable the production of lime and an alkali metal sulfate by recycling by-product gypsum, which is a neglected by-product, thereby exhibiting an effect of enabling efficient resource utilization.

[0026] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum are capable of efficiently producing various useful products such as slaked lime, quicklime, the above-described slurry, hydrogen gas, solid alkali metal sulfates, sulfuric acid, and oxygen gas in an environmentally friendly manner, and the produced products have the advantage that they can be widely utilized in various technical fields as described above.

[0027] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum may produce a large amount of alkali metal hydroxide in the electrolysis unit and recycle it to the lime generating unit through the circulation unit, so there is the advantage of minimizing the input of additional raw materials and thereby establishing an efficient circulation structure.

[0028] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum may allow for the precise and easy adjustment of the pH of the aqueous solution of the alkali metal hydroxide provided to the lime production unit through the circulation unit. This ensures that the process of producing lime and alkali metal sulfate in the lime production unit can be carried out efficiently under optimal conditions.

[0029] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum may allow for the concentration of reactants to be easily controlled by adding water as a solvent in the reaction of producing lime and alkali metal sulfate in the lime production unit. This facilitates the easy mixing of different reactants and the easy separation of different products. Specifically, it allows for the easy separation of the produced alkali metal cations and sulfate ions (sulfate, SO42-), effectively preventing the formation of precipitates.

[0030] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum may have the advantages that the circulation system can be operated continuously and eco- friendly mass production of the above-described useful products is possible for the above-described reasons. In particular, since the raw materials needed for mass production are by-products of industrial activities such as by-product gypsum, there are also effects such as reducing production costs and recycling resources through recycling of by-products.

[0031] In addition, according to any one of the means for achieving the above objects of the present invention, the stepwise system and method for producing lime and hydrogen using by-product gypsum may minimize emissions of greenhouse gases such as carbon dioxide during the course of the process as described above, so there are advantages of contributing to carbon neutrality and climate change mitigation.

[0032] The effects that can be obtained from the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the description below.

[0033] FIG. 1 shows a diagram for explaining a stepwise system for producing lime and hydrogen using by-product gypsum according to one embodiment of the present invention.

[0034] FIG. 2 shows a flowchart explaining a stepwise method of producing lime and hydrogen utilizing by-product gypsum according to one embodiment of the present invention.

[0035] Hereinafter, with reference to the attached drawings, embodiments of the present invention will be described in detail so that those skilled in the art may easily implement the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. In order to clearly explain the present invention in the drawings, parts that are not related to the description are omitted, and similar parts are given similar reference numerals throughout the specification.

[0036] Throughout the specification, when a part is described as being “connected” to another part, this includes not only cases where they are “directly connected” but also cases where they are “indirectly connected” with another member or an element therebetween. In addition, when a part "includes" a certain component, this means that unless explicitly stated otherwise, it can include other components as well and is not limited to excluding other components. Furthermore, when a component is described in the singular form, it also includes the plural form unless explicitly stated otherwise.

[0037] The shapes, sizes, proportions, angles, numbers, and the like disclosed in the drawings for describing the embodiments of the present invention are illustrative and not restrictive, so the present invention is not limited to the details shown. Also, in describing the present invention, detailed descriptions of related known technologies may be omitted if it is determined that they could unnecessarily obscure the gist of the present invention.

[0038] In interpreting the components, they are understood to include tolerance ranges unless explicitly stated otherwise.

[0039] Although “first,” “second,” and the like are used to describe various elements, these elements are not limited by these terms. These terms are merely used to distinguish one element from another. Therefore, a first element mentioned below may also be a second element within the technical spirit of the present invention.

[0040] Each feature of the various embodiments of the present invention may be partially or fully coupled or combined with each other, and as can be fully understood by those skilled in the art, various technical interconnections and operations are possible, and each embodiment may be implemented independently of each other or may possibly be implemented together in an associated relationship.

[0041] Meanwhile, potential effects that may be expected from technical features of the present invention that are not specifically mentioned in the specification of the present invention are handled as if described in the present specification, and since the present embodiments are provided to completely explain the present invention to those with average knowledge in the art, the details illustrated in the drawings may be exaggerated compared to the actual implementation of the invention, and the detailed description of a configuration that is considered to unnecessarily obscure the gist of the present invention is omitted or briefly described.

[0042] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[0043] FIG. 1 shows a diagram for explaining a stepwise system for producing lime and hydrogen using by-product gypsum according to one embodiment of the present invention.

[0044] Referring to FIG. 1, a stepwise system 1000 for producing lime and hydrogen using by-product gypsum according to one embodiment of the present invention includes a lime generating unit 1100, an electrolysis unit 1600, and a circulation unit 1700 providing the produced alkali metal hydroxide to the lime generating unit 1100.

[0045] In addition, the stepwise system 1000 for producing lime and hydrogen using by-product gypsum according to one embodiment of the present invention may further include a sulfate separation unit 1200, a slaked lime separation unit 1300, a quicklime generating unit 1400, and a discharge unit 1500.

[0046] The stepwise system 1000 for producing lime and hydrogen according to the present invention is a system for producing lime and hydrogen using by-product gypsum as a raw material, characterized in that a by-product generated from the electrolysis unit 1600 producing hydrogen is circulated and provided to the lime generating unit 1100 producing lime to recycle the by-product.

[0047] Hereinafter, each component of the stepwise system 1000 for producing lime and hydrogen will be described in detail.

[0048] The lime generating unit 1100 is a component that generates lime and an alkali metal sulfate using by-product gypsum as a raw material, and it may be connected to the circulation unit 1700 and the sulfate separation unit 1200.

[0049] The lime generating unit 1100 may be provided with at least one inlet through which raw materials are input. For example, there can be a gypsum inlet for feeding by-product gypsum and a hydroxide inlet for feeding the hydroxide of an alkali metal.

[0050] In this case, the hydroxide inlet may consist of a first hydroxide inlet through which the alkali metal hydroxide supplied from the circulation unit (1700) is fed, and a second hydroxide inlet through which an external alkali metal hydroxide is fed. In some embodiments, the lime production unit (1100) can also be equipped with a water inlet through which water is fed.

[0051] The lime generating unit 1100 may include a stirring unit for promoting the reaction between by-product gypsum and an alkali metal hydroxide.

[0052] In addition, a lower end portion of the lime generating unit 1100 may be provided with an outlet through which by-products including lime and an alkali metal sulfate formed by the reaction of by-product gypsum and an alkali metal hydroxide may be discharged. The outlet may be connected to the sulfate separation unit 1200.

[0053] The sulfate separation unit 1200 is configured to separate an alkali metal sulfate from by-products discharged from the lime generating unit 1100.

[0054] The sulfate separation unit 1200 may separate the alkali metal sulfate from the by-products provided from the lime generating unit 1100 and provide the same to the electrolysis unit 1600 and provide lime to the slaked lime separation unit 1300. At this time, the alkali metal sulfate provided to the electrolysis unit 1600 may be present in a state of being ionized into an alkali metal cation and a sulfate ion.

[0055] Hereinafter, the configuration of the sulfate separation unit 1200 will be described in more detail.

[0056] The sulfate separation unit (1200) may include a solid-liquid separation unit that separates most of the liquid material from the solid material. For example, the sulfate separation unit (1200) may be equipped with a settling tank for precipitation as the solid-liquid separation unit. The aforementioned by-products produced in the lime production unit (1100) are fed into the settling tank, and after a certain amount of time, due to Earth's gravity, the supernatant, which is an aqueous solution of an alkali metal sulfate as the liquid material, is positioned at the top of the settling tank, while the precipitate, which is a mixture of the solid material and residual liquid material in the form of a slurry, is positioned at the bottom of the settling tank.

[0057] At this time, the slurry collectively refers to a mixture composed of lime, an alkali metal sulfate, and various impurities generated in the lime generating unit 1100, and the fluidity of the slurry may vary depending on the size and proportion of solid particles contained in the slurry.

[0058] In addition, the sulfate separation unit 1200 may include a drying device that produces a solid alkali metal sulfate by drying the aqueous solution of alkali metal sulfate.

[0059] Accordingly, the alkali metal sulfate in an aqueous solution separated through the sulfate separation unit 1200 may be provided to the electrolysis unit 1600, and the alkali metal sulfate in a solid state dried through the drying device may be discharged through a separate salt outlet in the form of a by-product.

[0060] Meanwhile, as described above, a slurry remaining after most of the alkali metal sulfate is separated may be treated through the slaked lime separation unit 1300 and the discharge unit 1500, which will be described later.

[0061] The sulfate separation unit 1200 may be provided with a slurry outlet through which the above-described residual slurry may be discharged. The slurry outlet may be connected to the slaked lime separation unit 1300 and the discharge unit 1500, respectively.

[0062] The slaked lime separation unit 1300 is configured to wash the slurry provided from the sulfate separation unit 1200 to separate the slaked lime contained in the slurry.

[0063] The slaked lime separation unit 1300 may include a washing unit that performs the above-described washing process. In addition, the slaked lime separation unit 1300 may include a drying unit that dries the slaked lime that has been completely washed.

[0064] The slaked lime separation unit 1300 may discharge dried slaked lime to the outside through a first slaked lime discharge outlet. In addition, the slaked lime separation unit 1300 may provide dried slaked lime to the quicklime generating unit 1400 through a second slaked lime outlet.

[0065] The quicklime generating unit 1400 produces quicklime by calcining slaked lime at a predetermined calcination temperature. A detailed description of this will be provided later.

[0066] The quicklime generating unit 1400 discharges the produced quicklime to the outside through a quicklime outlet.

[0067] Meanwhile, the discharge unit 1500 is configured to discharge the slurry provided from the sulfate separation unit 1200 to the outside through a mixture outlet without any additional processing.

[0068] Hereinafter, the electrolysis unit 1600, which receives the alkali metal sulfate in an aqueous solution phase from the sulfate separation unit 1200, will be described in detail.

[0069] The electrolysis unit 1600 electrolyzes the provided aqueous solution of alkali metal sulfate to produce an alkali metal hydroxide and hydrogen.

[0070] The electrolysis unit 1600 may include an anode part 1610, a cathode part 1620, a separation membrane 1630, and a power supply unit 1640.

[0071] The anode part (1610) serves as the electrode that receives current from the outside and includes an anode electrolyte solution (1612) and an anode (1611) contained therein. The anode electrolyte solution (1612) may have a water inlet through which water is supplied from an external source. Preferably, the water inlet may be provided at the bottom of the anode electrolyte solution (1612).

[0072] The anode electrolyte solution 1612 contains water and sulfate ions provided from the sulfate separation unit 1200. The anode (1611) includes an anode material that has high electrical conductivity, and it is preferable that the anode material consists of elements or compounds that provide a higher standard electrode potential for the anode reaction compared to the cathode reaction. For example, materials such as titanium, platinum, lead dioxide, graphite, and nickel may be used as the anode material.

[0073] In the anode part (1610), sulfuric acid is produced, and the generated sulfuric acid can be supplied to the outside. To facilitate this, the anode part (1610) can include a sulfuric acid outlet connected to the external environment near the anode (1611). Additionally, oxygen is generated in the anode part (1610), and an oxygen capture device can be installed near the anode (1611) to collect the generated oxygen.

[0074] The cathode part 1620, which is an electrode unit that transmits a current to the outside, includes a cathode electrolyte solution 1622 and a cathode 1621 immersed therein. The cathode electrolyte solution 1622 may be provided with a water inlet through which water is supplied from the outside. Preferably, the water inlet may be provided at a lower portion of the cathode electrolyte solution 1622.

[0075] The cathode electrolyte solution 1622 contains water and alkali metal cations provided from the sulfate separation unit 1200. The cathode (1621) includes a cathode material with high electrical conductivity, and it is desirable for the cathode material to consist of elements or compounds that create a lower standard electrode potential for the cathode reaction compared to the anode reaction. For example, materials such as nickel, steel, copper, titanium, graphite, platinum, and silver may be used as the cathode material.

[0076] An alkali metal hydroxide is generated in the cathode part 1620, and the generated alkali metal hydroxide may be provided to the circulation unit 1700. To this end, the cathode part 1620 may include an alkali metal hydroxide outlet connected to the circulation unit 1700 near the cathode 1621.

[0077] In addition, hydrogen is generated in the cathode part 1620, and a hydrogen collection device for collecting the generated hydrogen may be provided near the cathode 1621.

[0078] The power supply unit 1640, which is a component inducing electrolysis by supplying power to the anode 1611 and the cathode 1621, may be configured as a direct current (DC) power supply.

[0079] Specifically, the power supply unit 1640 causes a current in a circuit to flow from the cathode 1621 to the anode 1611 as direct current and allows electrons to move in the opposite direction, that is, from the anode 1611 to the cathode 1621.

[0080] The separation membrane 1630, which is a membrane that separates the anode part 1610 and the cathode part 1620, may include a cation exchange membrane (CEM) and an anion exchange membrane (AEM).

[0081] The CEM and the AEM according to one embodiment of the present invention may be disposed within the separation membrane 1630 to block an internal passage of the separation membrane 1630 connecting the cathode part 1620 and the anode part 1610. The CEM and the AEM may be provided to be spaced apart from each other within the separation membrane 1630, with the CEM being provided near the cathode part 1620 and the AEM being provided near the anode part 1610. A sulfate inlet through which the alkali metal sulfate generated in the lime generating unit 1100 is supplied may be provided between the CEM and the AEM. Preferably, as shown in FIG. 1, the sulfate inlet may be provided at a lower portion of the separation membrane 1630.

[0082] Meanwhile, cations such as alkali metal cations may pass through the CEM according to one embodiment of the present invention, and other ions may be blocked so that they may not pass through.

[0083] In addition, anions such as sulfate ions may pass through the AEM according to one embodiment of the present invention, and other ions may be blocked so that they may not pass through.

[0084] In some embodiments, the separation membrane 1630 of the present invention may be configured as a single membrane. For example, a bipolar membrane may be used as the separation membrane 1630. Accordingly, alkali metal cations and sulfate ions may move freely toward the cathode 1621 and the anode 1611, respectively, and the dissociation of water molecules into hydrogen ions and hydroxide ions (OH-) may also be promoted.

[0085] Hereinafter, the anode electrolyte and the cathode electrolyte that are present in the above-described anode electrolyte solution 1612 and cathode electrolyte solution 1622, respectively, will be described in detail.

[0086] As the anode electrolyte is an electrolyte that acts as an ion in the anode electrolyte solution 1612, an anion may move toward the anode 1611 and, when necessary, it may be oxidized by providing electrons to the anode 1611. Alternatively, some of the neutral atoms constituting the anode 1611 may be oxidized to become cations and included in the anode electrolyte. The anode electrolyte according to one embodiment of the present invention may include hydrogen ions, hydroxide ions, and sulfate ions.

[0087] As the cathode electrolyte is an electrolyte that acts as an ion in the cathode electrolyte solution 1622, a cation may move toward the cathode 1621 and, when necessary, it may be reduced by receiving electrons from the cathode 1621. Alternatively, some of the neutral atoms constituting the cathode 1621 may be reduced to anions and included in the cathode electrolyte. The cathode electrolyte according to one embodiment of the present invention may include hydrogen ions, hydroxide ions, and alkali metal cations.

[0088] When selective movement of specific ions becomes possible through the above-described separation membrane 1630, current may be generated through the movement of the ions between the anode 1611 and the cathode 1621 so that electrolysis may proceed, and since unnecessary crossing of substances that should not occur between the anode electrolyte solution 1612 and the cathode electrolyte solution 1622 may be blocked, an anode reaction and a cathode reaction may not mix with each other.

[0089] Details of each chemical reaction that occurs in the anode part 1610 and the cathode part 1620 of the present invention will be described later.

[0090] Hereinafter, the circulation unit 1700 will be described in detail.

[0091] The circulation unit 1700 recovers the alkali metal hydroxide produced in the electrolysis unit 1600 and circulates and provides it as a reactant for a reaction producing lime and alkali metal sulfate in the lime generating unit 1100, and thus is a component forming a circulation structure of the stepwise system 1000 for producing lime and hydrogen using by-product gypsum.

[0092] The circulation unit 1700 may be provided with a first base inlet through which an alkali metal hydroxide is introduced from the cathode electrolyte solution 1622. In addition, the circulation unit 1700 may be further provided with a second base inlet through which an alkali metal hydroxide is introduced from the outside. In some embodiments, the above-described first base inlet and second base inlet may be provided in the concentration unit 1710, which will be described later.

[0093] The circulation unit 1700 may include a concentration unit 1710 that concentrates the alkali metal hydroxide produced in the electrolysis unit 1600 and a measuring unit 1720 that measures the pH of an aqueous solution.

[0094] The concentration unit 1710 is a device that concentrates an alkali metal hydroxide so that the alkali metal hydroxide provided to the lime generating unit 1100 may have a pH sufficient to react with by-product gypsum.

[0095] The measuring unit 1720 is a device that measures the pH of a solution containing an alkali metal hydroxide passing through the circulation unit 1700, and the degree of the above-described concentration may be determined according to the measurement result.

[0096] The detailed type and shape of the pH measuring equipment are not limited as long as the initial pH value of the aqueous solution of alkali metal hydroxide produced in the electrolysis unit 1600 may be measured. For example, the measuring unit 1720 may be provided with a pH-meter having electrodes, and a glass electrode, a hydrogen electrode, a quinhydrone electrode, an antimony electrode, and the like may be used as the above-mentioned electrodes.

[0097] Finally, the circulation unit 1700 may circulate and provide the alkali metal hydroxide that has been concentrated as described above to the lime generating unit 1100 through a base outlet.

[0098] FIG. 2 shows a flowchart explaining a stepwise method of producing lime and hydrogen utilizing by-product gypsum according to one embodiment of the present invention.

[0099] Referring to FIG. 2, a stepwise method of producing lime and hydrogen using by-product gypsum according to one embodiment of the present invention includes: generating lime and an alkali metal sulfate by allowing by-product gypsum to react with an alkali metal hydroxide through a lime generating unit 1100 (S1000); producing an alkali metal hydroxide and hydrogen by electrolyzing an aqueous solution of the alkali metal sulfate through an electrolysis unit 1600 (S2000); and circulating and providing the alkali metal hydroxide to the lime generating unit 1100 through a circulation unit 1700 (S3000).

[0100] Gypsum is a material containing calcium sulfate, and its main ingredient is CaSO4·2H2O. As described above, by-product gypsum discharged as a by-product of industrial activities may include, for example, at least one of phosphogypsum including calcium sulfate and desulfurization gypsum including calcium sulfate.

[0101] An alkali metal hydroxide is a base composed of an alkali metal cation and a hydroxide ion and may preferably be present in an ionized state in the form of an aqueous solution.

[0102] An alkali metal hydroxide that reacts with the above-described by-product gypsum may include, for example, at least one of sodium hydroxide and potassium hydroxide.

[0103] Lime is a material containing at least one of the above-described slaked lime and quicklime, and the lime generated in the lime generating unit 1100 according to one embodiment of the present invention may preferably be composed of slaked lime. As described above, slaked lime is composed of calcium hydroxide, and quicklime is composed of calcium oxide.

[0104] An alkali metal sulfate is a salt composed of an alkali metal cation and a sulfate ion, and it may preferably be present in an ionized state in the form of an aqueous solution.

[0105] The alkali metal sulfate produced in the lime generating unit 1100 according to one embodiment of the present invention may include, for example, at least one of sodium sulfate and potassium sulfate.

[0106] A reaction generating of lime and an alkali metal sulfate in the lime generating unit 1100 according to one embodiment of the present invention may be expressed, for example, as [Chemical Reaction 1] below.

[0107] [Chemical Reaction 1]

[0108] Ca compound + xMeOH → Ca(OH)2+ xMe++SO42-+ 2H2O

[0109] Where, the Ca compound may include CaSO4·2H2O contained in by-product gypsum and various Ca compounds. Me refers to an alkali metal such as sodium and potassium, and x may have a value ranging from 1.5 to 1.9.

[0110] As expressed through [Chemical Reaction 1], when the above-described by- product gypsum and sodium hydroxide react in the lime generating unit 1100 according to one embodiment of the present invention, sodium sulfate may be generated, and when the above-described by-product gypsum and potassium hydroxide react, potassium sulfate may be produced.

[0111] In the lime and alkali metal sulfate production reaction in the lime generating unit 1100 according to one embodiment of the present invention, water may be added as a solvent in addition to the reactants of [Chemical Reaction 1]. As a result, the concentrations of the reactants of [Chemical Reaction 1] may be easily adjusted, different reactants may be easily mixed, and different products may be easily separated from each other. In particular, the generated alkali metal cations and sulfate ions may be easily separated from each other, so that there is an effect of preventing sediment formation.

[0112] At this time, the specific mixing sequence of the by-product gypsum, alkali metal hydroxide, and water is not limited as long as the above-described chemical reaction may occur. For example, after an alkali metal hydroxide and water are mixed to form an aqueous solution of an alkali metal hydroxide at an appropriate concentration, the aqueous solution may be mixed with the by-product gypsum, so that the above-described chemical reaction may occur. Alternatively, an alkali metal hydroxide and water may each be mixed with by-product gypsum, so that the chemical reaction may occur.

[0113] Preferably, after an alkali metal hydroxide and water are mixed to form an aqueous solution of an alkali metal hydroxide at an appropriate concentration, the aqueous solution may be mixed with by-product gypsum at an appropriate ratio, so that the above-described chemical reaction may occur. For example, for 100 g of by-product gypsum, 270 mL to 320 mL of an aqueous alkali metal hydroxide solution may be mixed.

[0114] The generating of lime and an alkali metal sulfate by allowing by-product gypsum to react with an alkali metal hydroxide through a lime generating unit 1100 (S1000) according to one embodiment of the present invention may be performed at room temperature and last for at least 5 to 30 minutes. In addition, as illustrated in FIG. 1, mixing reactants may be further promoted by a stirring process for sufficient chemical reaction. At this time, stirring may be performed for at least 5 to 10 minutes, and the specific stirring method is not limited as long as mixing reactants may be promoted. For example, as the stirring method, various stirring methods may be used, such as mechanical stirring, magnetic stirring, manual stirring, vibrational stirring, and ultrasonic stirring.

[0115] As described above, in the lime generating unit 1100 according to one embodiment of the present invention, by-product gypsum reacts with an alkali metal hydroxide to produce lime and an alkali metal sulfate, and accordingly, lime can be produced without using the existing method using calcium carbonate, so that there is an effect of significantly reducing carbon dioxide generation and emissions during the lime production process. In addition, lime and an alkali metal sulfate are produced by recycling by-product gypsum, which is an abandoned by-product, so that there is an effect of enabling efficient resource recycling.

[0116] In addition, the stepwise method of producing lime and hydrogen using by- product gypsum according to one embodiment of the present invention may further include, after the generating of lime and an alkali metal sulfate (S1000), separating the produced alkali metal sulfate.

[0117] The separating of the alkali metal sulfate according to one embodiment of the present invention is for separating a large amount of alkali metal sulfate from a mixture of the lime, alkali metal sulfate, and various impurities generated in the lime generating unit 1100, and the specific method of separating the mixture is not limited as long as most of the aqueous substances may be physically separated from the solid substances. For example, methods such as sedimentation, centrifugation, and filtration may be used as a separation method.

[0118] Impurities contained in the above-described mixture may include solid ingredients such as sulfur trioxide and sodium oxide, depending on the type of by- product gypsum introduced to the above-described chemical reaction. In addition, as the lime produced by the above-described chemical reaction absorbs some of the carbon dioxide in the air, further solid ingredients such as calcium carbonate may be present. The total amount of these impurities may be 10% by weight or less based on the total amount of all solid ingredients including lime.

[0119] The aqueous solution of the alkali metal sulfate separated in the separating of the alkali metal sulfate may be provided to the electrolysis unit 1600 as described above, or the alkali metal sulfate may be produced as a solid alkali metal sulfate. The produced solid alkali metal sulfate may be used in various ways. For example, when the alkali metal is potassium, solid potassium sulfate produced by drying according to the above-described method can be easily used as a fertilizer.

[0120] Meanwhile, in the generating of lime and alkali metal sulfate (S1000), a slurry containing slaked lime may be generated, and thereafter, a process of separating the slaked lime by washing the generated slurry and a process of generating quicklime by calcining the separated slaked lime may be performed.

[0121] At this time, the specific method of washing the slurry is not limited as long as it does not seriously dissolve the slaked lime chemically. For example, as a washing method, there is a method of adding a large amount of water to a slurry containing slaked lime and washing the slurry by stirring it, and through this, solid ingredients containing slaked lime may be separated and recovered, and other alkali metal sulfates, impurities, and the like may be removed together with a large amount of water.

[0122] The slurry obtained after completing the above-described washing process may be dried and finally produced into slaked lime. In addition to the above- described uses, the produced slaked lime may also be used as a raw material for producing quicklime.

[0123] A calcining reaction for producing quicklime by calcining slaked lime may be expressed, for example, as [Chemical Reaction 2] below.

[0124] [Chemical Reaction 2]

[0125] Ca(OH)2→ CaO + H2O

[0126] The process of generating of quicklime by calcining the slaked lime through the quicklime generating unit 1400 according to one embodiment of the present invention may be performed at a calcining temperature of 500 °C to 700 °C, and the total amount of quicklime may be 90% by weight or more based on the total amount of all finally recovered solid materials.

[0127] The method of heating slaked lime to the above-described calcining temperature is not limited as long as an appropriate temperature may be maintained for a predetermined time. For example, various methods such as rotary kiln calcination, shaft kiln calcination, fluidized bed calcination, and flash calcination may be used.

[0128] The produced quicklime may be used in various fields as described above. For example, as a main ingredient in cement and mortar, it may be used as a key raw material in the manufacture of building materials. In addition, it is widely used in flue gas desulfurization, and it may be applied and utilized in various industrial fields such as agriculture, fisheries, the food industry, the papermaking industry, and the environmental industry with the purpose of adjusting pH, such as neutralizing acidic environments. For example, quicklime may be used as a soil conditioner, and it may improve the growth environment for crops by neutralizing acidic soil.

[0129] The stepwise method of producing lime and hydrogen using by-product gypsum according one embodiment of the present invention may further include, after the generating of the lime and the alkali metal sulfate (S1000), discharging at least one of the generated lime and alkali metal sulfate. For example, after the generating of the lime and alkali metal sulfate (S1000), the slurry with most of the liquid substances separated and removed through the separating of the alkali metal sulfate may be discharged to the outside.

[0130] The discharged slurry may include slaked lime, an alkali metal sulfate, and impurities, and it may be effectively used as a fertilizer, soil conditioner, or the like without any further purification or processing. In some cases, in order to produce fertilizers, soil conditioners, and the like under specific conditions, the proportions of slaked lime and an alkali metal sulfate may be adjusted in accordance with the conditions, and further additives may be added.

[0131] As described above, when producing fertilizers, soil conditioners, and the like using the slurry according to one embodiment of the present invention, there may be several advantages. For example, when a calcareous soil conditioner prepared based on the above-described device and method is used, the physical and chemical properties of the soil may be improved. Specifically, by using a calcareous soil conditioner, the pH of the soil may be adjusted, such as neutralizing acidified soil, the structure of the soil may be improved, plants may easily absorb, nutrients from the soil, the growth of beneficial microorganisms in the soil may be promoted, and the adsorption of heavy metals into the soil and living organisms may be suppressed. In addition, the fertility of the soil may be improved, and diseases that may occur in the soil may be prevented. In addition to the above- described advantages, the soil improvement efficiency is the same or higher than that of existing product groups, and greenhouse gas emissions during the soil conditioner production process may be reduced, so there is an advantageous effect in responding to environmental problems.

[0132] Hereinafter, the producing of an alkali metal hydroxide and hydrogen by electrolyzing an aqueous solution of the alkali metal sulfate through the above- described electrolysis unit 1600 (S2000) according to one embodiment of the present invention will be described in detail.

[0133] The alkali metal sulfate produced in the lime generating unit 1100 according to one embodiment of the present invention may be injected between the CEM and the AEM in the separation membrane 1630. The injected alkali metal sulfate may be present in a state of being ionized into an alkali metal cation and a sulfate ion. As a result, the alkali metal cation may pass through the CEM and move to the cathode electrolyte solution 1622, and the sulfate ion may pass through the AEM and move to the anode electrolyte solution 1612. As a result, the ionization of water is promoted, so that electrolysis may be activated.

[0134] The ionization reaction of water may be expressed as [Chemical Reaction 3] below.

[0135] [Chemical Reaction 3]

[0136] H2O→ H++OH-

[0137] An alkali metal hydroxide may be produced in the cathode part 1620 according to one embodiment of the present invention. Specifically, cations of an alkali metal in the cathode electrolyte solution 1622 may move toward the cathode 1621. As a result, the cations of the alkali metal may be distributed near the cathode 1621 in a concentrated manner, and the hydroxide ions in the cathode electrolyte solution 1622 may form an alkali metal hydroxide together with the cations of the alkali metal, so that the alkali metal hydroxide is produced in a large quantity especially near the cathode 1621. The produced alkali metal hydroxide may be recovered in the circulating and providing of the alkali metal hydroxide to the lime generating unit 1100 through a circulation unit 1700 (S3000), which will be described later.

[0138] The alkali metal hydroxide generated in the electrolysis unit 1600 according to one embodiment of the present invention may include, for example, at least one of sodium hydroxide and potassium hydroxide.

[0139] Specifically, when an aqueous solution of sodium sulfate is electrolyzed in the electrolysis unit 1600 according to one embodiment of the present invention, sodium hydroxide may be produced, and when an aqueous solution of potassium sulfate is electrolyzed, potassium hydroxide may be produced.

[0140] In addition, hydrogen may be produced in the cathode part 1620 according to one embodiment of the present invention. Specifically, hydrogen ions in the cathode electrolyte solution 1622 may move toward the cathode 1621. As a result, some of the hydrogen ions distributed near the cathode 1621 in a concentrated manner may receive electrons from the cathode 1621 and may be reduced to form hydrogen gas, thereby producing hydrogen at the cathode 1621.

[0141] The hydrogen production reaction may be expressed as [Chemical Reaction 4] below.

[0142] [Chemical Reaction 4]

[0143] 2H++2e-→H2(g)

[0144] The produced hydrogen gas may be recovered in part or whole by a collection device, and it may be widely used in various technical fields as described above.

[0145] Meanwhile, sulfuric acid may be produced in the anode part 1610 according to one embodiment of the present invention. Specifically, sulfate ions in the anode electrolyte solution 1612 may move toward the anode 1611. As a result, sulfate ions may be distributed near the anode 1611 in a concentrated manner, and hydrogen ions in the anode electrolyte solution 1612 may form sulfuric acid together with the sulfate ions, so that sulfuric acid is produced in a large quantity especially near the anode 1611.

[0146] The produced sulfuric acid may be supplied externally and used effectively in various fields. For example, it may be used as a major chemical substance in a wide range of technological fields such as fertilizer production, petroleum refining, chemical synthesis, metal processing, wastewater treatment, disinfection, battery manufacturing, textile manufacturing, papermaking, and the pharmaceutical industry.

[0147] In addition, oxygen may be produced in the anode part 1610 according to one embodiment of the present invention. Specifically, hydroxide ions in the anode electrolyte solution 1612 may move toward the anode 1611. As a result, some of the hydroxide ions distributed near the anode 1611 in a concentrated manner may provide electrons to the anode 1611 and may be oxidized to form oxygen gas, so that oxygen is produced at the anode 1611.

[0148] The oxygen production reaction may be expressed as [Chemical Reaction 5] below.

[0149] [Chemical Reaction 5]

[0150] 2OH-→2H++O2(g)+4e-

[0151] The produced oxygen gas may be recovered in part or whole by a collection device, and it may be widely used in various technical fields.

[0152] In the electrolysis unit according to another embodiment of the present invention, instead of the above-described alkali metal sulfate, another electrolyte containing an alkali metal, such as sodium chloride, may be provided. Accordingly, the electrolyte may be present in a state of being ionized into a cation of the alkali metal and other anions, and cations of the alkali metal may pass through the CEM and move to the cathode electrolyte solution, and the other anions may pass through the AEM to the anode electrolyte solution.

[0153] For example, when sodium chloride is provided, sodium chloride may be present in a state of being ionized into a sodium cation and a chloride anion, and the sodium cations may pass through the CEM and move to the cathode electrolyte solution, and the chloride ions may pass through the AEM and move to the anode electrolyte solution.

[0154] In this case, in the anode part according to another embodiment of the present invention, instead of the above-described sulfuric acid, an acid composed of a hydrogen ion and another anion may be produced. For example, when sodium chloride is provided, hydrochloric acid composed of a hydrogen ion and a chloride ion may be produced in the anode electrolyte solution. The produced hydrochloric acid may be provided externally and used effectively in various fields.

[0155] As described above, except that the type of anion and the type of acid containing the anion are different, even when another electrolyte containing an alkali metal is provided, electrolysis may be carried out in the same or similar manner as when the above-described alkali metal sulfate is provided, and accordingly, useful products may be produced.

[0156] Hereinafter, the circulating and providing of the alkali metal hydroxide produced through the electrolysis unit 1600 to the lime generating unit 1100 (S3000) will be described in detail.

[0157] The circulating and providing of the alkali metal hydroxide produced through the electrolysis unit 1600 to the lime generating unit 1100 (S3000) according to one embodiment of the present invention may further include concentrating the alkali metal hydroxide produced through the electrolysis unit 1600.

[0158] For example, in order for the lime and alkali metal sulfate generation reaction to occur smoothly in the lime generating unit 1100 according to one embodiment of the present invention, the pH value of the reaction environment is preferably 10 or higher. Accordingly, in the concentrating of the alkali metal hydroxide above-described, when the pH value of the aqueous solution of the alkali metal hydroxide prepared in the electrolysis unit 1600 fails to satisfy the above condition, an additional alkali metal hydroxide may be further mixed into the aqueous solution, so that the aqueous solution of the alkali metal hydroxide to be provided to the lime generating unit 1100 is concentrated.

[0159] At this time, the form of the alkali metal hydroxide that is further mixed is not limited as long as the aqueous solution of the alkali metal hydroxide may be concentrated. For example, it may be in the form of a high-concentration aqueous solution or a solid crystal form, and the specific form of the crystal may also be selected from various forms such as powder and pellets.

[0160] As described above, through the concentrating of the alkali metal hydroxide of the present invention, an aqueous solution of the alkali metal hydroxide of at appropriate concentration may be provided to the lime generating unit 1100, so that the lime and alkali metal sulfate generation process in the lime generating unit 1100 may be efficiently carried out under sufficient supply of the raw materials and in an optimal pH environment.

[0161] The circulating and providing of the alkali metal hydroxide produced through the electrolysis unit 1600 to the lime generating unit 1100 (S3000) according to one embodiment of the present invention may further include measuring the pH of a solution including the alkali metal hydroxide produced in the electrolysis unit 1600.

[0162] As described above, in order for the lime and alkali metal sulfate generation reaction to occur smoothly in the lime generating unit 1100 according to one embodiment of the present invention, the pH value of the reaction environment is preferably 10 or higher, and when the pH value of the aqueous solution of the alkali metal hydroxide prepared in the electrolysis unit 1600 fails to satisfy this condition, the pH value of the aqueous solution may need to be adjusted in the circulating and providing of the alkali metal hydroxide produced through the electrolysis unit 1600 to the lime generating unit 1100 (S3000).

[0163] At this time, the pH value before pH adjustment and the pH value after pH adjustment may be measured through the above-described pH measurement, thereby making it possible to easily control the pH of the alkali metal hydroxide. Accordingly, the aqueous solution of alkali metal hydroxide may be adjusted to have an appropriate pH with a minimum of additional raw materials, and the lime and alkali metal sulfate generation process in the lime generating unit 1100 may be efficiently carried out in an optimal pH environment.

[0164] In addition, in the above-described circulating and providing (S3000), the above-described concentration of the alkali metal hydroxide and the above- described pH measurement may be performed together, and as a result, the above- described effects may be comprehensively exhibited, for example, the aqueous solution of the alkali metal hydroxide provided to the lime generating unit 1100 may be easily and precisely adjusted to have an optimal pH, and the lime and alkali metal sulfate generation process in the lime generating unit 1100 may be efficiently carried out under optimal conditions.

[0165] Through the above-described circulating and providing (S3000), the alkali metal hydroxide recovered from the electrolysis unit 1600 may be provided to the lime generating unit 1100 through appropriate processing as needed, so that a circulation structure of the stepwise system 1000 for producing lime and hydrogen using by-product gypsum may be completed.

[0166] The stepwise system for producing lime and hydrogen using by-product gypsum and the method of producing the same of the present invention produce lime and alkali metal sulfate by allowing by-product gypsum to react with metal hydroxide, and accordingly, are capable of producing lime without using the existing method using calcium carbonate, thereby exhibiting an effect of significantly reducing carbon dioxide generation and emissions during the lime production process. In addition, the system and the method enable the production of lime and alkali metal sulfate by recycling by-product gypsum, which is an abandoned by-product, thereby exhibiting an effect of enabling efficient resource recycling.

[0167] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention are capable of efficiently producing various useful products such as slaked lime, quicklime, the above-described slurry, hydrogen gas, solid alkali metal sulfates, sulfuric acid, and oxygen gas in an environmentally friendly manner, and the produced products have the advantage that they can be widely utilized in various technical fields as described above.

[0168] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention produce a large amount of alkali metal hydroxide in the electrolysis unit and recycle it to the lime generating unit through the circulation unit, so there is the advantage of minimizing the input of additional raw materials and thereby establishing an efficient circulation structure.

[0169] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention are capable of easily and precisely adjusting an aqueous solution of alkali metal hydroxide provided to the lime generating unit through the circulation unit to have an optimal pH and have the advantage that the lime and alkali metal sulfate generation process in the lime generating unit can be carried out efficiently under optimal conditions.

[0170] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention have the advantages of easily adjusting the concentrations of reactants by adding water as a solvent in the reaction for producing lime and alkali metal sulfate in the lime generating unit, mixing different reactants easily, and separating different products easily from each other. In particular, the generated alkali metal cations and sulfate ions can be easily separated from each other, so there is an effect of preventing sediment formation.

[0171] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention have the advantages that the circulation system can be operated continuously and eco- friendly mass production of the above-described useful products is possible for the above-described reasons. In particular, since the raw materials needed for mass production are by-products of industrial activities such as by-product gypsum, there are also effects such as reducing production costs and recycling resources through recycling of by-products.

[0172] In addition, the stepwise system for producing lime and hydrogen using by- product gypsum and the method of producing the same of the present invention minimize emissions of greenhouse gases such as carbon dioxide during the course of the process as described above, so there are advantages of contributing to carbon neutrality and climate change mitigation.

[0173] The description of the present invention above is for illustrative purposes, and those skilled in the relevant technical field will understand that the technical spirit or essential features of the present invention can be easily modified into other specific forms without altering them. Therefore, the embodiments described above should be understood as being illustrative in all respects and not restrictive. For example, each component described in a standalone form may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

[0174] The scope of the present invention is defined by the claims that will be made later, rather than the detailed description provided above. Any modifications or alterations derived from the meaning and scope of the claims and their equivalents should be interpreted as being included within the scope of the present invention.

[0175] The present invention can be applied to various industries where lime is used. For example, it can be applied to construction and civil engineering industries and steelmaking, chemical, and pharmaceutical industries.

Claims

1.A stepwise system for producing lime and hydrogen using by-product gypsum, comprising:a lime generation unit that reacts by-product gypsum with alkali metal hydroxides to produce lime and alkali metal sulfates;an electrolysis unit that electrolyzes the solution of the generated alkali metal sulfates to produce alkali metal hydroxides and hydrogen; anda circulation unit that supplies the produced alkali metal hydroxides back to the lime generation unit.2.The system of claim 1, further comprising a sulfate separation unit that separates the alkali metal sulfate generated from the lime generating unit.3.The system of claim 1, wherein the lime production unit generates a slurry including a slaked lime by reacting the by-product gypsum with a hydroxide of an alkali metal, andthe stepwise system for producing lime and hydrogen using by-product gypsum further includes:a slaked lime separation unit for washing the produced slurry to separate the slaked lime; anda quicklime production unit for calcining the separated hydrated lime to produce quicklime.4.The system of claim 1, further comprising a discharge unit that discharges at least one of the lime and the alkali metal sulfate generated in the lime generating unit.5.The system of claim 1, wherein the electrolysis unit includes:an anode part where current flows in from an external source;a cathode part where current flows out to an external source;a separation membrane that separates the anode part and cathode part; anda power supply unit that provides power to the anode part and cathode part,wherein the anode part may include an anode and an anode electrolyte,the cathode part may include a cathode and a cathode electrolyte, andthe separation membrane may include at least one of a cation exchange membrane that allows cations to pass through and an anion exchange membrane that allows anions to pass through.6.The system of claim 1, wherein the circulation unit includes a concentration unit that concentrates the alkali metal hydroxide produced in the electrolysis unit.7.The system of claim 1, wherein the circulation unit includes a measuring unit that measures the pH of a solution including the alkali metal hydroxide produced in the electrolysis unit.8.The system of claim 1, wherein the by-product gypsum includes at least one of phosphogypsum including calcium sulfate and desulfurization gypsum including calcium sulfate.9.The system of claim 1, wherein the alkali metal sulfate generated in the lime generating unit includes at least one of sodium sulfate and potassium sulfate.10.The system of claim 1, wherein the alkali metal hydroxide produced in the electrolysis unit includes at least one of sodium hydroxide and potassium hydroxide.11.A stepwise method of producing lime and hydrogen using by-product gypsum, comprising:generating lime and an alkali metal sulfate by allowing by-product gypsum to react with an alkali metal hydroxide through a lime generating unit;producing an alkali metal hydroxide and hydrogen by electrolyzing an aqueous solution of the alkali metal sulfate through an electrolysis unit; andcirculating and providing the alkali metal hydroxide to the lime generating unit through a circulation unit.12.The method of claim 11, further comprising, after the generating of the lime and the alkali metal sulfate, separating the generated alkali metal sulfate.13.The method of claim 11, wherein the generating of the lime and the alkali metal sulfate includes generating a slurry including slaked lime by allowing the by- product gypsum to react with the alkali metal hydroxide, andthe stepwise method of producing lime and hydrogen using by-product gypsum further includes:after the generating of the lime and the alkali metal sulfate, separating the slaked lime by washing the generated slurry; and generating quicklime by calcining the separated slaked lime.14.The method of claim 11, further comprising, after the generating of the lime and the alkali metal sulfate,discharging at least one of the generated lime and alkali metal sulfate.15.The method of claim 11, wherein the circulating and providing of the alkali metal hydroxide to the lime generating unit includes concentrating the produced alkali metal hydroxide.

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