Sulfuric acid manufacturing apparatus and sulfuric acid manufacturing method

Abstract

The present invention is a sulfuric acid production apparatus provided with: a conduit 41 through which a starting material comprising at least a sulfur component is supplied; a conduit 45 through which a first cooling medium is introduced; a combustion furnace 51 in which the starting material is combusted to produce a combustion gas containing a sulfur oxide; a waste heat boiler 52 in which the combustion gas is cooled by the heat exchange with the temperature-risen first cooling medium; a converter 61 in which the sulfur oxide is oxidized with a catalyst to produce a reaction gas comprising sulfur trioxide and water; a cooling device 62 in which the reaction gas is cooled by the heat exchange with a second cooling medium; a dilute sulfuric acid column 71 in which sulfur trioxide and water contained in the cooled reaction gas are absorbed by an aqueous sulfuric acid solution to produce dilute sulfuric acid and from which an exhaust gas comprising sulfur dioxide and oxygen is discharged; and a heat exchange means 63 for preparing the temperature-risen first cooling medium and the cooled second cooling medium by the heat exchange between the temperature-risen second cooling medium and the first cooling medium and supplying either one of the temperature-risen first cooling medium or the cooled second cooling medium to the waste heat boiler 52.

Description

[Technical Field]

[0001] The present invention relates to an apparatus and a method for producing sulfuric acid. [Background technology]

[0002] Sulfuric acid (H2SO4) is a strong acid that is produced in large quantities and used in a variety of fields. Sulfuric acid can be broadly divided into industrial concentrated sulfuric acid, which is indicated by a sulfuric acid concentration of 90% by weight or more, and industrial dilute sulfuric acid, which is indicated by a sulfuric acid concentration of less than 90% by weight, and each has different properties. Of these, dilute sulfuric acid is a strong acid, but unlike concentrated sulfuric acid, it does not have the oxidizing or dehydrating properties, but it is highly corrosive to metal materials and other materials. Dilute sulfuric acid is used for a variety of purposes, including industrial supplies, pharmaceuticals, pesticides, and reagents.

[0003] The production of sulfuric acid requires raw materials containing sulfur, such as desulfurization waste liquid and recycled sulfur from gas (coke oven gas: hereafter referred to as "COG") generated during the process of producing coke used in steelmaking, and SOx-containing gases emitted from the copper refining process.

[0004] As a method capable of inexpensively producing dilute sulfuric acid, for example, the method described in Patent Document 1 is known. In this document, a raw material containing a large amount of water in addition to sulfur and nitrogen is used, and an oxygen-containing gas with a high oxygen concentration is introduced into a combustion means. In the combustion means (combustion furnace), the raw material is combusted to produce sulfur oxides (SO x Here, combustion gas containing 1≦x<3) and water is generated, cooled in a cooling means (waste heat boiler), and introduced into a reaction means (converter). In the reaction means (converter), sulfur oxides are oxidized using a catalyst to generate sulfur trioxide (SO3), and the reaction gas is cooled in a dilute sulfuric acid generation means (dilute sulfuric acid tower) to generate dilute sulfuric acid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2021-31305 A (Claim 1, paragraph 0062, etc.) Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, gas is transferred in the following order: combustion furnace, converter, and dilute sulfuric acid tower. The combustion furnace burns the raw material at 950-1000°C, resulting in high-temperature combustion gas. The reaction in the converter is also exothermic, causing the gas temperature to rise. However, the final product, a dilute sulfuric acid aqueous solution, is stored at room temperature, so a cooling means must be provided to cool the gas as needed during the process. In this document, a waste heat boiler is provided as such a cooling means, and the combustion gas is cooled by heat exchange between a refrigerant (water) and the combustion gas.

[0007] However, the gas contains sulfuric acid gas (H2SO4), which becomes a sulfuric acid solution when the gas temperature drops. Sulfuric acid solution is a strong acid and highly corrosive to metals. To avoid this, using highly corrosion-resistant materials for the piping and equipment in the process would increase the equipment cost and the cost of producing dilute sulfuric acid. Conversely, using metals with low corrosion resistance for the piping would reduce the equipment cost and lower the production cost of dilute sulfuric acid. However, in such cases, to avoid corrosion of the piping, it is necessary to adjust the refrigerant temperature when cooling the gas so that the sulfuric acid gas (H2SO4) does not become a sulfuric acid solution. The waste heat boiler described in this document operates with a high-temperature, high-pressure refrigerant (water) that does not convert the sulfuric acid gas (H2SO4) into a sulfuric acid solution. Therefore, although inexpensive, low-corrosion-resistant metals can be used, expensive equipment with a special design and structure is required to handle high temperatures and pressures.

[0008] On the other hand, this document does not particularly mention the waste heat generated when cooling the gas. In the production of dilute sulfuric acid, it is desirable to increase the heat recovery rate and effectively utilize the waste heat, obtain dilute sulfuric acid with a higher conversion rate, and reduce the amount of sulfur dioxide emitted into the atmosphere. Furthermore, the waste heat boiler in this document directly supplies low-temperature pure water to the boiler to cool the combustion gas, so the amount of steam generated from the waste heat boiler is reduced, and the amount of steam that can be effectively used is also reduced.

[0009] An object of the present invention is to provide an apparatus and a method for producing sulfuric acid which are capable of producing sulfuric acid at low cost, obtaining sulfuric acid with a higher recovery rate, reducing sulfur dioxide released into the atmosphere, and making effective use of exhaust heat. [Means for solving the problem]

[0010] The present inventors have discovered that by performing a plurality of predetermined heat exchanges using a predetermined refrigerant, sulfuric acid can be produced inexpensively, sulfuric acid can be obtained with a higher recovery rate, sulfur dioxide emitted into the atmosphere can be reduced, and waste heat can be effectively utilized, thereby completing the present invention.

[0011] a reaction means for catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a reaction gas cooling means for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery means for absorbing the sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to produce sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; and a heat exchange means for heat exchange between the first refrigerant and the second refrigerant, the second refrigerant having been heated by heat exchange with the reaction gas, to prepare a heated first refrigerant and a cooled second refrigerant, and to supply either the heated first refrigerant or the cooled second refrigerant to the combustion gas cooling means.

[0012] The present invention includes a combustion gas cooling means for cooling the combustion gas, a reaction gas cooling means for cooling the reaction gas, and a heat exchange means. In the heat exchange means, heat is exchanged between a second refrigerant whose temperature has been increased by heat exchange with the reaction gas and a first refrigerant. This allows the first refrigerant with an increased temperature for the combustion gas cooling means to be prepared, enabling effective use of exhaust heat. In addition, because the first refrigerant is heated to cool the combustion gas, a larger amount of steam is generated by cooling the combustion gas, which has the advantage of increasing the amount of steam that can be effectively used.

[0013] In addition, in the present invention, the combustion gas cooling means has the heated first refrigerant at a temperature equal to or higher than the acid dew point of the combustion gas, and the reaction gas cooling means has the second refrigerant at a temperature equal to or higher than the acid dew point of the reaction gas.

[0014] In this way, the combustion gas cooling means and the reaction gas cooling means use a refrigerant with a temperature equal to or higher than the acid dew point of the gas to be heat exchanged, so that the gas is not cooled to a temperature below the acid dew point by these means and becomes a highly corrosive aqueous sulfuric acid solution. Therefore, even relatively inexpensive metal piping can be used in the production of sulfuric acid, and sulfuric acid can be produced inexpensively.

[0015] Furthermore, in the present invention, the heat exchange means includes a refrigerant transfer path that transfers the heated second refrigerant, a preheater to which the first refrigerant is supplied and which heats the first refrigerant by heat exchange with the heated second refrigerant and supplies the first refrigerant to the combustion gas cooling means, and a refrigerant return path that returns the second refrigerant after heat exchange with the first refrigerant from the preheater to the reaction gas cooling means.

[0016] By configuring the heat exchange means in this manner, the first refrigerant can be heated while circulating the second refrigerant, and the second refrigerant can be used efficiently both to cool the reactive gas and to heat the first refrigerant.

[0017] The coolant return line may also supply a portion of the second coolant to the combustion gas cooling means.

[0018] By doing so, a part of the second refrigerant can also be used as a refrigerant for cooling the combustion gas.

[0019] The coolant return path includes a tank that stores the second coolant, and a pump that supplies the second coolant to the reaction gas cooling means.

[0020] The second refrigerant is preferably an organic refrigerant that is liquid at least within the range of -20°C to 350°C.

[0021] If a substance that is solid at room temperature, such as a molten salt, is used as a refrigerant, it will solidify at room temperature and lose its function as a refrigerant. However, an organic refrigerant that is liquid at least within the range of −20°C to 350°C will not solidify in the heat exchange means, and therefore can stably continue heat exchange with the reaction gas.

[0022] Preferably, the first refrigerant is water and the second refrigerant is a mixture of diphenyl and diphenyl oxide.

[0023] The heat exchange means is preferably a fire tube type. The combustion gas cooling means is preferably a water tube type that is applied to combustion gas containing dust, but if the combustion gas does not contain dust, the refrigerant return path can be adapted to a fire tube type by supplying a portion of the second refrigerant to the combustion gas cooling means and using the portion of the second refrigerant as a refrigerant for cooling the combustion gas.

[0024] By using an inexpensive fire tube type heat exchanger, the cost of sulfuric acid production can be reduced. On the other hand, with regard to the combustion gas cooling means, the combustion gas transferred from the combustion means may contain adhesive dust, and if the dust adheres to the inside of the downstream means, there is a risk of blockage. In the case of a water tube boiler, dust adheres to the outer surface of the tubes through which water flows, so blockage of the tubes does not occur. In addition, dust adhering to the outer surface of the tubes can be easily removed, for example, by soot blowing.

[0025] Furthermore, the sulfuric acid manufacturing apparatus of the present invention preferably includes a means for negative pressure operation.

[0026] By operating under negative pressure, oxygen from the atmosphere is attracted to the reaction means without the need for special equipment. The oxygen thus attracted promotes catalytic reactions within the reaction means, resulting in a high cumulative conversion rate of over 98.9%. Furthermore, by operating under negative pressure, it is possible to prevent hot, harmful gases from leaking into the atmosphere.

[0027] In this case, it is preferable to further comprise a hot air introducing means for introducing hot air into the reaction means, and a purge flow path capable of purging reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means.

[0028] By introducing hot air into the reaction means, it is possible to preheat the reaction means before the equipment is put into operation. By preheating to the reaction temperature in advance, the start-up time can be shortened, and it can be reduced to more than half the time. The introduction of hot air is also effective for purging the reaction means during maintenance. Due to the negative pressure operation, the hot air is drawn into the reaction means, making it difficult for the hot air to drift inside the reaction means. Localized generation of sulfuric acid liquid or molten catalyst deposits inside the reaction means is avoided.

[0029] In addition, when hot air is introduced into the reaction means in an apparatus that is operated under pressure rather than under negative pressure, the hot air flows unevenly, making it difficult to purge the entire reaction means uniformly. Areas in the reaction means that the hot air does not reach are created locally, resulting in the local formation of sulfuric acid liquid and solidified catalyst melt. To operate the apparatus normally, the complicated process of discharging these substances outside the system, sieving and separating them, and then refilling only the normal catalyst is required.

[0030] Therefore, by carrying out negative pressure operation and introducing hot air into the reaction means, it becomes possible to restart the equipment after hot air purging without the need for work such as screening and sorting of the catalyst.

[0031] It is preferable that the exhaust gas purification plant further comprises a sulfur dioxide recovery means for recovering sulfur dioxide contained in the exhaust gas.

[0032] In this way, sulfur dioxide contained in the exhaust gas is recovered, so that the sulfur dioxide can be removed without being released into the environment.

[0033] In this case, it is preferable that the sulfur dioxide recovery means absorbs sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizes the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

[0034] In this way, sulfur dioxide in exhaust gas is absorbed into water to produce sulfurous acid, which is then oxidized and recovered as sulfuric acid. Since exhaust gas contains about 10% oxygen, this oxygen can be used to oxidize it to sulfuric acid, eliminating the need to add an oxidizing agent as in the past. In addition to increasing the recovery rate of sulfuric acid, it is also possible to reduce the amount of sulfur dioxide released into the atmosphere.

[0035] a reaction step of catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a reaction gas cooling step of cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery step of absorbing the sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to produce sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; and a heat exchange step of heat exchange between the first refrigerant and the second refrigerant, the second refrigerant having been heated by heat exchange with the reaction gas, to prepare a heated first refrigerant and a cooled second refrigerant, and supplying either the heated first refrigerant or the cooled second refrigerant to the combustion gas cooling step.

[0036] The present invention includes a cooling step for cooling the combustion gas and a heat exchange step for cooling the reaction gas. In the heat exchange step, heat is exchanged between a second refrigerant whose temperature has been increased by heat exchange with the reaction gas and a first refrigerant. This allows the first refrigerant with an increased temperature for the cooling step to be prepared, allowing for effective use of exhaust heat. In addition, since the first refrigerant is heated to cool the combustion gas, a larger amount of steam is generated by cooling the combustion gas, which has the advantage of increasing the amount of steam that can be effectively used.

[0037] Furthermore, it is preferable that in the combustion gas cooling process, the heated first refrigerant is at a temperature equal to or higher than the acid dew point of the combustion gas, and that in the reaction gas cooling process, the second refrigerant is at a temperature equal to or higher than the acid dew point of the reaction gas.

[0038] In this way, since the cooling process and heat exchange process use a refrigerant whose temperature is equal to or higher than the acid dew point of the gas to be heat exchanged, the gas is not cooled to a temperature below the acid dew point by these steps, and a highly corrosive sulfuric acid solution is not formed. Therefore, even relatively inexpensive metal piping can be used to produce sulfuric acid, allowing sulfuric acid to be produced inexpensively.

[0039] The heat exchange process includes a process of cooling the reaction gas by heat exchange with the second refrigerant, a transfer process of transferring the heated second refrigerant, a preheating process of heating the first refrigerant in the preheater by heat exchange with the heated second refrigerant and supplying the first refrigerant to the combustion gas cooling process, and a refrigerant return process of returning the second refrigerant after heat exchange with the first refrigerant and using it for heat exchange with the reaction gas.

[0040] By providing such a heat exchange process, the first refrigerant can be heated while circulating the second refrigerant, and the second refrigerant can be used efficiently both to cool the reactive gas and to heat the first refrigerant.

[0041] The refrigerant returning step may also supply a portion of the second refrigerant to the combustion gas cooling means.

[0042] By doing so, a part of the second refrigerant can also be used as a refrigerant for cooling the combustion gas.

[0043] The coolant returning step includes a step of storing the second coolant and a step of supplying the second coolant to the reaction gas cooling step.

[0044] As the second refrigerant, it is preferable to use an organic refrigerant that is liquid at least within the range of -20°C to 350°C.

[0045] If a substance that is solid at room temperature, such as a molten salt, is used as a refrigerant, it will solidify at room temperature and lose its function as a refrigerant. However, an organic refrigerant that is liquid at least within the range of −20°C to 350°C will not solidify in the heat exchange means, and therefore can stably continue heat exchange with the reaction gas.

[0046] It is preferable to use water as the first refrigerant and a mixture of diphenyl and diphenyl oxide as the second refrigerant.

[0047] The heat exchange means is preferably a fire tube type. The combustion gas cooling means is preferably a water tube type that is applied to combustion gas containing dust, but if the combustion gas does not contain dust, the refrigerant transfer and refrigerant return means can be adapted to a fire tube type by supplying a portion of the second refrigerant to the combustion gas cooling means and using a portion of the second refrigerant as a refrigerant for cooling the combustion gas.

[0048] Combustion gas transported from the combustion process may contain adhesive dust, which may cause blockages if it adheres to the inside of the downstream process. In the case of a water-tube boiler, the dust adheres to the outer surface of the tubes through which the water flows, so the dust can be easily removed by soot blowing.

[0049] In the present invention, negative pressure operation is preferably performed, but pressurized operation may also be performed.

[0050] By operating under negative pressure, oxygen from the atmosphere is drawn into the reaction process without the need for special equipment. The oxygen thus drawn promotes catalytic reactions within the reaction process, resulting in a high cumulative conversion rate of over 99%. Furthermore, by operating under negative pressure, it is possible to prevent hot, harmful gases from escaping into the atmosphere.

[0051] It is preferable that the method further comprises a sulfur dioxide recovery step of recovering sulfur dioxide contained in the exhaust gas.

[0052] In this way, sulfur dioxide contained in the exhaust gas is recovered, so that the sulfur dioxide can be removed without being released into the environment.

[0053] In this case, the sulfur dioxide recovery step preferably includes absorbing sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizing the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

[0054] In this way, sulfur dioxide in exhaust gas is absorbed into water to produce sulfurous acid, which is then oxidized and recovered as sulfuric acid. Since exhaust gas contains about 10% oxygen, this oxygen can be used to oxidize it to sulfuric acid, eliminating the need to add an oxidizing agent as in the past. In addition to increasing the recovery rate of sulfuric acid, it is also possible to reduce the amount of sulfur dioxide released into the atmosphere.

[0055] The present invention is a maintenance method characterized by introducing hot air from the hot air introduction means into the reaction means while operating under negative pressure, purging the reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means, and introducing the resulting purge gas into the sulfur dioxide recovery means.

[0056] In an apparatus operating under pressure, when hot air is introduced into the reaction means, the hot air flows unevenly, making it difficult to purge the entire area of ​​the reaction means evenly. Areas where the hot air does not reach are created locally within the reaction means, resulting in the local formation of sulfuric acid liquid and solidified catalyst melt. To operate the apparatus normally, the complicated process of discharging these substances outside the system, separating them by sieving, and then refilling only the normal catalyst is required.

[0057] During maintenance, hot air is introduced into the reaction means while operating under negative pressure to purge the reaction gas remaining in the reaction means, thereby preventing the generation of acid dew point by cooling the purge gas using the retained heat.

[0058] <Invention of basic application> [1] A raw material supply means for supplying a raw material containing at least a sulfur content; a combustion means for combusting the raw material to generate a combustion gas containing sulfur oxides; a cooling means for cooling the combustion gas by heat exchange with a first refrigerant having a raised temperature; a reaction means for catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a heat exchange means for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery means for absorbing sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to generate sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen, The heat exchange means prepares the heated first refrigerant for the cooling means by heat exchange between a second refrigerant whose temperature has been increased by heat exchange with the reaction gas and a first refrigerant.

[0059] [2] The sulfuric acid manufacturing apparatus according to [1], characterized in that the cooling means has the heated first refrigerant at a temperature equal to or higher than the acid dew point of the combustion gas, and the heat exchange means has the second refrigerant at a temperature equal to or higher than the acid dew point of the reaction gas.

[0060] [3] The heat exchange means is a cooler that cools the reaction gas by heat exchange with the second refrigerant; a refrigerant transfer path for transferring the second refrigerant whose temperature has been increased by the heat exchange; The sulfuric acid manufacturing apparatus according to [1], further comprising: a preheater that receives a first refrigerant, raises the temperature of the first refrigerant by heat exchange with the heated second refrigerant, and supplies the first refrigerant to the cooling means; and a refrigerant return path that returns the second refrigerant after heat exchange with the first refrigerant from the preheater to the cooler.

[0061] [4] The sulfuric acid manufacturing apparatus described in [2], characterized in that the refrigerant return path includes a tank for storing the second refrigerant and a pump for driving the second refrigerant to the cooler.

[0062] [5] The sulfuric acid manufacturing apparatus according to [1], wherein the second refrigerant is an organic refrigerant that is liquid at least within the range of -20°C to 350°C.

[0063] [6] The sulfuric acid manufacturing apparatus according to [1], wherein the first refrigerant is water, and the second refrigerant is a mixture of diphenyl and diphenyl oxide.

[0064] [7] The sulfuric acid manufacturing apparatus according to [1], characterized in that the heat exchange means is of a smoke tube type.

[0065] [8] The sulfuric acid manufacturing apparatus according to [1], further comprising a means for negative pressure operation.

[0066] [9] a hot air introducing means for introducing hot air into the reaction means; a purge flow path capable of purging reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means; The sulfuric acid manufacturing apparatus according to [8], further comprising:

[0067]

[10] The sulfuric acid manufacturing apparatus according to [1], further comprising a sulfur dioxide recovery means for recovering sulfur dioxide contained in the exhaust gas.

[0068]

[11] The sulfur dioxide recovery means absorbs sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizes the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

[10] The sulfuric acid manufacturing apparatus according to

[10] .

[0069]

[12] A raw material supply means for supplying a raw material containing at least a sulfur content; a combustion means for combusting the raw material to generate a combustion gas containing sulfur oxides; a cooling means for cooling the combustion gas by heat exchange with a first refrigerant having a raised temperature; a reaction means for catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a heat exchange means for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery means for absorbing sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to generate sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen, the heat exchange means prepares the heated first refrigerant for the cooling step by heat exchange between a second refrigerant heated by heat exchange with the reaction gas and a first refrigerant.

[0070]

[13] The method for producing sulfuric acid according to

[12] , wherein in the cooling step, the heated first refrigerant is at a temperature equal to or higher than the acid dew point of the combustion gas, and in the heat exchange step, the second refrigerant is at a temperature equal to or higher than the acid dew point of the reaction gas.

[0071]

[14] The heat exchange step cooling the reaction gas by heat exchange with the second refrigerant; transferring the second refrigerant whose temperature has been increased by the heat exchange; a step of increasing the temperature of the first refrigerant by heat exchange with the heated second refrigerant and supplying the first refrigerant to the cooling step; and returning the second refrigerant after heat exchange with the first refrigerant to use it for heat exchange with the reaction gas.

[0072]

[15] The sulfuric acid manufacturing method according to

[14] , characterized in that the refrigerant return path includes a step of storing the second refrigerant and a step of driving the second refrigerant to the cooler.

[0073]

[16] The method for producing sulfuric acid according to

[12] , wherein an organic refrigerant that is liquid at least within the range of -20°C to 350°C is used as the second refrigerant.

[0074]

[17] The method for producing sulfuric acid according to

[12] , wherein water is used as the first refrigerant and a mixture of diphenyl and diphenyl oxide is used as the second refrigerant.

[0075]

[18] The method for producing sulfuric acid according to

[12] , characterized in that the heat exchange step is carried out using a smoke tube system.

[0076]

[19] The method for producing sulfuric acid according to

[12] , characterized in that negative pressure operation is carried out.

[0077]

[20] The method for producing sulfuric acid according to

[12] , further comprising a sulfur dioxide recovery step of recovering sulfur dioxide contained in the exhaust gas.

[0078]

[21] The sulfur dioxide production method according to

[20] , wherein the sulfur dioxide recovery step comprises absorbing sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizing the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

[0079]

[22] A maintenance method for the sulfuric acid manufacturing apparatus according to

[10] above, A maintenance method characterized by introducing hot air from the hot air introduction means into the reaction means while operating under negative pressure, purging reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means, and introducing the resulting purge gas into the sulfur dioxide recovery means. [Effects of the Invention]

[0080] According to the present invention, it is possible to provide an apparatus and a method for producing sulfuric acid that are capable of producing sulfuric acid at low cost, obtaining sulfuric acid with a higher recovery rate, reducing sulfur dioxide released into the atmosphere, and making effective use of exhaust heat. [Brief explanation of the drawings]

[0081] [Figure 1] 1 is a schematic diagram showing an upstream process of a dilute sulfuric acid manufacturing apparatus, which is one type of sulfuric acid manufacturing apparatus of the present invention. [Figure 2] 1 is a schematic diagram showing a downstream process of a dilute sulfuric acid manufacturing apparatus, which is one type of sulfuric acid manufacturing apparatus of the present invention. [Figure 3] FIG. 2 is a schematic diagram showing the internal structure of a combustion means (combustion furnace). [Figure 4] FIG. 4 is a schematic diagram showing a hot air introduction means. [Figure 5] FIG. 2 is a schematic diagram showing the internal structure of a converter. [Figure 6] FIG. 1 is a cross-sectional view of a water tube boiler. [Figure 7] FIG. 1 is a graph showing the relationship between the SO3 concentration and water vapor concentration in gas and the estimated sulfuric acid dew point. [Figure 8] 1 is a nomogram of the equilibrium conversion rate of SO2 to SO3. [Figure 9] FIG. 10 is a schematic diagram showing an upstream process of a dilute sulfuric acid manufacturing apparatus according to a second embodiment. [Figure 10] FIG. 10 is a schematic diagram showing a downstream process of a dilute sulfuric acid manufacturing apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0082] Hereinafter, the configuration of an embodiment of the present invention will be described. The present invention can be implemented with appropriate modifications within the scope of the present invention. In the following embodiment, the production of dilute sulfuric acid, which is a type of sulfuric acid of the present invention, is described, but the present invention is not limited thereto and can also be applied to the production of concentrated sulfuric acid, for example.

[0083] 1. Dilute sulfuric acid manufacturing apparatus and method (first embodiment) Hereinafter, an apparatus and method for producing dilute sulfuric acid according to one embodiment (first embodiment) of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the upstream process of a dilute sulfuric acid production apparatus 40, and shows an embodiment in which an oxygen-containing gas is supplied to a raw material (here, desulfurization waste liquid and molten sulfur). Note that the sulfur concentration can be adjusted by adding molten sulfur to the hydrogen sulfide raw material, and thus, for example, the sulfuric acid concentration can be increased, and the present invention can also be used to produce concentrated sulfuric acid.

[0084] 2 is a schematic diagram showing the downstream process of a dilute sulfuric acid manufacturing apparatus 40. Note that "sulfuric acid" in the present invention means sulfuric acid with no limitations on sulfuric acid concentration, and specifically includes, for example, dilute sulfuric acid and concentrated sulfuric acid. Here, "dilute sulfuric acid" means an aqueous sulfuric acid solution with a sulfuric acid concentration of less than 90% by weight, and includes "dilute sulfuric acid" (sulfuric acid content 60 to 80% by weight) and "purified dilute sulfuric acid" (sulfuric acid content 27 to 50% by weight) specified in JIS K1321.

[0085] As shown in FIG. 1, the dilute sulfuric acid manufacturing apparatus 40 of this embodiment includes a means for supplying a raw material. The raw material in this embodiment contains at least a sulfur component and is composed of molten sulfur and desulfurization waste liquid in this embodiment, but the raw material is not limited to these. The raw material may further include refined COG or the like as a combustion improver. The raw material supply means is a means for supplying these raw materials to a combustion furnace 51. The dilute sulfuric acid manufacturing apparatus 40 of this embodiment includes a pipeline 41 for supplying molten sulfur as the raw material. The molten sulfur is sulfur recovered from an oil refinery or the like that has been made into a molten state. The raw material is supplied into the combustion furnace 51 via a pump (not shown) installed in the pipeline 41.

[0086] The dilute sulfuric acid production apparatus 40 also includes a pipeline 42 for supplying the desulfurization waste liquid, which is the raw material. The desulfurization waste liquid is waste liquid from a desulfurization facility installed to remove soot, organic matter, sulfur compounds, and the like from exhaust gas (crude COG) emitted from a coke oven facility or the like. Desulfurization waste liquid generally contains components such as free sulfur, free NH3, NHClSCN, (NH4)2SO3, and HO. Of these, water (HO) often accounts for 50% by weight or more of the total desulfurization waste liquid, although not specifically specified. The pipeline 42 is connected to a combustion furnace 51, into which the desulfurization waste liquid is also supplied as a raw material.

[0087] Pipes 41 and 42 correspond to the raw material supply means of the present invention, and these means realize the raw material supply step. Of the raw materials (molten sulfur, desulfurization waste liquid) supplied to combustion furnace 51 by these means, the desulfurization waste liquid contains, in addition to elemental sulfur, sulfur components such as (NH4)2S2O3 (10 to 40 wt%), nitrogen components such as NH3 (5 to 25 wt%), and moisture (40 to 80 wt%). When there are multiple types of raw materials (for example, in this embodiment, two types, molten sulfur and desulfurization waste liquid), as in the present embodiment, the moisture content is defined as the combined amount of moisture in each raw material and the combustion improver.

[0088] The dilute sulfuric acid manufacturing apparatus 40 is also provided with a pipe 43 for supplying air. A pipe 44 for supplying oxygen gas is connected to the pipe 43. For example, an oxygen gas generator (e.g., a PVSA (vacuum pressure swing adsorption) type: not shown) may be provided to supply high-concentration oxygen from the oxygen gas generator. The oxygen gas generator is a device that uses an adsorbent such as zeolite to adsorb and remove nitrogen from the air under pressure, thereby efficiently obtaining high-purity oxygen. The oxygen gas generator is capable of generating oxygen with a purity of 90% by volume or more. This oxygen is mixed with the air in the pipe 43 and supplied into the combustion furnace 51 as air with a high oxygen concentration. A PSA (pressure swing adsorption) type oxygen generator may also be used. Alternatively, oxygen may be supplied by branching off from an existing oxygen gas pipe.

[0089] The oxygen gas generator, pipelines 43 and 44 can be referred to as oxygen-containing gas generating means. The oxygen-containing gas supplied to the combustion furnace 51 by these means is adjusted to an oxygen concentration of 21 to 40% by volume, preferably 21 to 30% by volume, and more preferably 25 to 30% by volume.

[0090] The combustion furnace 51 (combustion means) performs a combustion step in which raw materials are combusted with an oxygen-containing gas to generate combustion gas containing sulfur oxides (SOx). FIG. 3 is a schematic diagram showing the internal structure of the combustion furnace 51. As shown in the figure, a supply port 51a through which raw materials and an oxygen-containing gas are supplied is provided upstream of the combustion furnace 51. The raw materials are combusted inside the furnace, and combustion gas is discharged from a downstream discharge port 51b. In this embodiment, molten sulfur is supplied from the supply port 51a in the upper part of the figure, desulfurization waste liquid is supplied from the supply port 51a in the middle part, and air is supplied from the supply port 51a in the lower part. In addition to the embodiment in which raw materials are supplied from separate supply ports for each type of raw material, as in this embodiment, the raw materials may be supplied to the combustion furnace 51 in a state in which some or all of the raw materials are mixed in advance.

[0091] On the raw material supply side of the combustion furnace 51, there is a water evaporation zone, where the combustion of molten sulfur and refined COG and the evaporation of water in the desulfurization waste liquid mainly take place. Behind this zone is the combustible combustion zone, where the combustibles in the desulfurization waste liquid are burned. A boundary is formed between these zones. Lattice bricks 51c are provided between the combustible combustion zone and the discharge port 51b. The lattice bricks 51c are cubic heat-resistant bricks arranged in a lattice pattern, with some of them open. The open area ratio of the lattice bricks 51c is preferably around 50%. The lattice bricks 51c are often provided in multiple stages.

[0092] The oxygen concentration of the oxygen-containing gas introduced into the combustion furnace 51 is in the range of 21 to 40% by volume, preferably 21 to 30% by volume, the oxygen concentration in the combustion gas generated in the combustion furnace 51 is in the range of 2.0 to 7.0% by volume, and it is more preferable that the SO3 conversion rate in the combustion gas generated in the combustion furnace 51 is in the range of 1.0 to 3.0%. The SO3 conversion rate is expressed by the following formula. SO3 conversion rate = (SO3 / SO x ) x 100 (Here, SO3 is the volume concentration of SO3 contained in the combustion gas, SO x is the volume concentration of SOx contained in the combustion gas).

[0093] The provision of lattice bricks 51c downstream of the combustible combustion zone not only reduces radiation to downstream equipment, but also fulfills the following functions. Even if an imperfection occurs in the mixing of air and combustibles in the combustible combustion zone, the lattice bricks 51c physically promote remixing of the air and combustibles, preventing unburned combustibles from blowing through. This promotes recombustion using the heat retained by the bricks. For this purpose, it is preferable to install multiple tiers of lattice bricks 51c. Furthermore, the openings of each tier of the lattice bricks 51c are arranged in a staggered pattern. This allows dust in the gas to adhere to and grow on the brick surfaces before falling. Therefore, it is preferable to install multiple tiers of lattice bricks 51c without openings at the bottom to accumulate the falling dust.

[0094] The combustion temperature at which the raw material is combusted in the combustion furnace 51 is preferably within a range of 900 to 1100°C. The upper limit of the combustion temperature is preferably 1050°C or less. For the purpose of reducing the amount of NOx in the combustion gas, the combustion temperature is preferably low, for example, 1025°C or less, and more preferably 1000°C or less.

[0095] In the combustion furnace 51, the raw materials are combusted with an oxygen-containing gas of 21 to 40% by volume, so the amount of NOx contained in the generated combustion gas can be reduced compared to when the raw materials are combusted under the same conditions using normal air (oxygen concentration less than 21% by volume). For example, the amount of NOx contained in the combustion gas when the raw materials are combusted with an oxygen-containing gas of an oxygen concentration of 21 to 40% by volume is calculated as follows: (rich) The amount of NOx contained in the combustion gas when the same raw material is combusted under the same conditions using air with an oxygen concentration of less than 21% by volume is calculated as NOx (air) When this is done, the NOx reduction rate shown by the following formula can be set to 50 to 95%. NOx reduction rate: NOx (rich) / NOx (air) ×100(%) The NOx reduction rate tends to decrease as the oxygen concentration increases, and can be approximately 80% when the oxygen concentration is 25% by volume, and approximately 60% when the oxygen concentration is 30% by volume.

[0096] As shown in FIG. 1 , combustion gas generated in a combustion furnace 51 is transferred to a waste heat boiler (WHB) 52 (combustion gas cooling means). Water is supplied from a pipe 45 (refrigerant introduction means), and this water passes through a feedwater preheater 63b (described later) before being introduced into the waste heat boiler 52. In the waste heat boiler 52, heated water (water in this embodiment) is supplied as a refrigerant into the boiler. The water evaporates with the combustion gas to generate steam, and a combustion gas cooling process is performed in which the combustion gas is cooled by heat exchange with the water. In this embodiment, the “first refrigerant” of the present invention corresponds to the water introduced into the waste heat boiler 52 from the pipe 45, i.e., “boiler feedwater,” and the “heated first refrigerant” corresponds to “boiler water.” The combustion gas is cooled to a temperature not lower than the acid dew point (220°C), and the boiler pressure in this case is approximately 3 MPa. In the waste heat boiler 52, the combustion gas is cooled to 420 to 360°C, preferably to about 375°C. Note that Patent Document 1 states that the temperature of the combustion gas is cooled to 380 to 460°C, preferably to about 420°C, but in this embodiment, the combustion gas is cooled to a lower temperature.

[0097] Here, we will explain acid dew point with reference to Figure 7. Figure 7 shows the relationship between the acid dew point of sulfuric acid (vertical axis) and the SO3 concentration in combustion gas (horizontal axis) for each amount of water (water vapor concentration) contained in the combustion gas. The acid dew point is determined by the SO3 concentration, water vapor concentration, pressure, etc. in the combustion gas. If the temperature is below the acid dew point, the condensed solution containing sulfuric acid will cause severe corrosion inside the equipment (acid dew point corrosion). To avoid acid dew point corrosion, the combustion gas must be maintained at a temperature above the acid dew point. The graph in Figure 7 shows that, for the same water vapor concentration, the higher the SO3 concentration in the combustion gas, the higher the acid dew point, and that, for the same SO3 concentration, the higher the water vapor concentration, the higher the acid dew point.

[0098] As shown in a simulation described later, the combustion gas generated in the combustion furnace 51 and introduced into the waste heat boiler 52 contains 0.2 to 0.3 volume % (i.e., 2000 to 3000 ppm) of SO3 and approximately 25 volume % of HO. The composition of this combustion gas is shown by the open circles in Figure 7, and the sulfuric acid dew point is approximately 190°C. In other words, the acid dew point of the combustion gas in the waste heat boiler 52 is 190°C, and it is necessary to maintain the temperature of the combustion gas in the waste heat boiler 52 at or above the acid dew point, preferably above 190°C.

[0099] The waste heat boiler 52 includes a boiler in which the combustion gas is cooled. The waste heat boiler 52 includes a refrigerant supply means (refrigerant supply step) that supplies a predetermined refrigerant (boiler feedwater in this embodiment) into the boiler, a combustion gas cooling means (combustion gas cooling step) that evaporates the refrigerant from the refrigerant supply means with the combustion gas to generate steam and cool the combustion gas through heat exchange, and a water vapor discharge means (water vapor discharge step). As described above, in the waste heat boiler 52, the combustion gas needs to be kept at or above the acid dew point, for example, above 190°C, and therefore the temperature of the boiler water, which serves as the refrigerant, also needs to be above 190°C. The refrigerant used here and the refrigerant supply means (refrigerant supply step) will be described in detail later.

[0100] Examples of combustion gas cooling means include fire tube and water tube types, but considering the removal of dust adhering to the inside of the boiler, it is preferable to use a water tube type boiler. A water tube boiler will be described with reference to Fig. 6. As shown in the figure, the waste heat boiler 52 includes a boiler body 52a that defines the outer shape of the boiler, a boiler drum 52b provided on top of the boiler body 52a, boiler tubes 52c provided inside the boiler body 52a, and a soot blower 52d provided inside the boiler body 52a.

[0101] The combustion gas generated in the combustion furnace 51 is introduced into the boiler body 52a through one of the openings provided at both ends of the boiler body 52a (the left side in the figure) and discharged from the opening at the other end (the right side in the figure). Boiler water and steam serving as refrigerants are stored in the boiler drum 52b. The top surface of the boiler drum 52b is provided with an inlet (opening with a downward arrow) for introducing the refrigerant and an outlet (opening with an upward arrow) for discharging the refrigerant. Boiler feedwater from a feedwater preheater 63b (described later) is introduced into the boiler drum 52b through the refrigerant inlet, and evaporated steam inside the boiler drum 52b is discharged to the outside through the refrigerant outlet.

[0102] The boiler tubes 52c are hollow pipes, and are composed of vertical tubes arranged vertically relative to the boiler body 52a and horizontal tubes arranged horizontally. The vertical tubes are arranged below the boiler drum 52b and communicate with the inside of the boiler drum 52b, and the horizontal tubes communicate with each other at the bottom of the vertical tubes. With this configuration, the boiler water in the boiler drum 52b circulates within the boiler tubes 52c and returns to the boiler drum 52b. The combustion gas passing outside the boiler tubes 52a comes into contact with the boiler tubes 52c and is cooled by heat exchange.

[0103] The soot blower 52d is a cylindrical component provided within the boiler body 52a, and is capable of blowing air into the interior of the tube. The soot blower 52d has multiple openings that communicate with the interior, and the air introduced into the interior of the tube is ejected from the openings. The soot blower 52d is also rotatable. Combustion gas contains adhesive dust, which adheres to the outer surface of the boiler tube 52c. However, the air ejected from the soot blower 52d blows away the dust, cleaning the outer surface of the boiler tube 52c. Furthermore, the rotation of the soot blower 52d itself allows cleaning of a wide area of ​​the outer surface of the boiler tube 52c.

[0104] The combustion gas cooled by the waste heat boiler 52 is introduced into the converter 61 (reaction means) via a dust collector 55. The dust collector 55 is a means for removing dust contained in the combustion gas. A hot air introduction means X1 is preferably provided midway along the pipeline from the dust collector 55 to the converter 61. As shown in FIG. 4, the hot air introduction means X1 is equipped with a hot air stove 101 and a hot air stove fan 102, and COG is introduced into the hot air stove 101. The hot air stove 101 is a means for burning the COG to generate high-temperature heated gas. The hot air stove fan 102 is equipped with a blower fan and is a means for sending out the heated gas generated in the hot air stove 101 as hot air. By introducing hot air at 300 to 400°C into the converter 61 from the hot air introduction means X1, the converter 61 can be preheated or subjected to maintenance purging.

[0105] The combustion gas cooled by the waste heat boiler 52 contains trace amounts of nitrogen (e.g., undecomposed NH3, NO, NO2, etc.). x The converter 61 uses catalysts installed in multiple stages (three stages in the figure) to react and oxidize sulfur dioxide (SO2) in the combustion gas with oxygen to generate a reaction gas containing sulfur trioxide (SO3) (reaction step). More specifically, the converter 61 uses catalysts installed in the previous stages to convert sulfur dioxide (SO3) into sulfur trioxide (SO4). x The converted gas, which is heated by oxidation (exothermic reaction) of sulfur dioxide with oxygen, is directly mixed with air drawn in from the outside, lowering the temperature to a level suitable for the subsequent catalytic reaction, thereby highly efficiently converting sulfur dioxide to sulfur trioxide (SO3).

[0106] 5 is a schematic diagram showing the internal structure of converter 61, where (a) is a side view, (b) is a cross-sectional view taken along the line A-A' in (a), and (c) is an enlarged view of the area circled by the dashed line in (b). As shown in this figure, converter 61 is equipped with a main air pipe 61a that takes in atmospheric air, a branch air pipe 61b that branches off from main air pipe 61a inside the chamber, and an air port 61d that sends air into the chamber from branch air pipe 61b.

[0107] As the catalyst, a known catalyst used in the production of sulfuric acid can be used, such as vanadium pentoxide (V2O5). Vanadium pentoxide has a denitrification function, and it converts NH3 and NO x This catalyst reacts with sulfur trioxide and decomposes it into nitrogen (N2) and water (H2O). x ) can be decomposed simultaneously. At this time, NH3 may be injected for denitration.

[0108] The temperature of the combustion gas introduced into the converter 61 is approximately 370°C. In the first stage of the converter 61, approximately 55% of the sulfur dioxide (SO2) contained in the combustion gas introduced into the converter 61 is oxidized and converted to SO3, and the gas temperature after the reaction reaches approximately 500°C. The remaining sulfur dioxide (SO2) is oxidized to sulfur trioxide (SO3) in the second and third stages of the converter 61. The inlet temperature of the second stage is approximately 410°C, and the gas temperature after the reaction is approximately 480°C. Due to air mixing, approximately 95% of the SO2 contained in the combustion gas introduced into the converter 61 is converted to SO3. The inlet temperature of the third stage is approximately 390°C. Due to air mixing, approximately 98.9% of the SO2 contained in the combustion gas introduced into the converter 61 is converted to SO3. The gas temperature after the reaction in the third stage is limited to 410°C. In this way, even if the temperature of the combustion gas introduced into the converter 61 is low at around 370°C, by introducing air into the converter 61, 98.9% of the SO2 contained in the combustion gas can be converted to SO3, and SO3 can be produced at a high conversion rate.

[0109] In addition, a denitration catalyst may be placed upstream of the first stage of the converter 61 (on the inflow side of the combustion gas from the waste heat boiler 52), and the denitration catalyst may be a mixture of vanadium pentoxide and a promoter.

[0110] The reaction gas generated in the converter 61 is transferred to a cooler 62 (reaction gas cooling means) and cooled. As shown in a simulation described later, the reaction gas generated in the converter 61 and transferred to the cooler 62 contains 5 to 6% by volume (i.e., 5×104 ~6×10 4 The reaction gas contains approximately 15% by volume of sulfuric acid (ppm) and approximately 15% by volume of H2O. The composition of this reaction gas is shown by the open squares in Figure 7, and the sulfuric acid dew point is approximately 240°C. In other words, the acid dew point of the reaction gas introduced into the cooler 62 is approximately 240°C, and the cooler 62 must maintain the temperature of the reaction gas at or above the acid dew point, preferably at or above 250°C.

[0111] The cooler 62 cools the reaction gas by heat exchange with a second refrigerant. A fire-tube type is preferably used as the cooler 62. A fire-tube heat exchanger is a heat exchanger in which the reaction gas flows inside a thin tube and a refrigerant circulates around the outside of the tube. A fire-tube heat exchanger is preferably used as the cooler 62 because it is less expensive and has higher cooling efficiency than a water-tube boiler such as the waste heat boiler 52, but the cooler 62 may be of another type, such as a water-tube type.

[0112] The second refrigerant is an organic refrigerant that is liquid in the temperature range of -20°C to 350°C. Examples of organic refrigerants include Dowtherm (registered trademark) A, which is a mixture of diphenyl and diphenyl oxide (diphenyl ether), as well as NeoSK-OIL 1400, NeoSK-OIL 1300, NeoSK-OIL 330, NeoSK-OIL 360, NeoSK-OIL L400, and KSK-OIL 260. Of these, the organic refrigerant suitable for use in the liquid phase in this case is preferably "NeoSK-OIL 1400," which is widely used and has excellent heat resistance.

[0113] The reaction gas has a high temperature of about 410°C at the outlet of the converter 61, but is cooled in the cooler 62 to a temperature of about 270 to 320°C, which is above the acid dew point of about 250°C. In this case, the refrigerant pressure of the cooler 62 is about 0.1 MPa. A purge pipe X2 (purge flow path) is preferably provided in the path that transfers the reaction gas cooled in the cooler 62 downstream.

[0114] The heat exchange means 63 includes a feedwater preheater 63b, a heat medium tank 63c, a heat medium circulation pump 63d, a refrigerant transfer line 63e, and a refrigerant return line 63h. The refrigerant transfer line 63e transfers the second refrigerant, which has been heated to about 320°C by heat exchange with the reaction gas, from the cooler 62 to the feedwater preheater 63b.

[0115] A multi-tube heat exchanger can be used as feedwater preheater 63b. A first refrigerant (boiler feedwater) at approximately 105°C is introduced into feedwater preheater 63b from the outside via refrigerant introduction path 63f. The second refrigerant, whose temperature has been raised to approximately 320°C in cooler 62, undergoes heat exchange with the first refrigerant in feedwater preheater 63b. As a result, the first refrigerant is heated to approximately 220°C, and the second refrigerant is heated to approximately 270°C. The first refrigerant, whose temperature has been raised to approximately 220°C by heat exchange, is supplied to waste heat boiler 52 via refrigerant supply path 63g. This increases the amount of first refrigerant (water vapor) recovered in waste heat boiler 52. Refrigerant introduction path 63f, feedwater preheater 63b, and refrigerant supply path 63g correspond to refrigerant supply means for the combustion gas cooling means (waste heat boiler 52).

[0116] The refrigerant return path 63h returns the second refrigerant after heat exchange with the first refrigerant (boiler feed water) from the feed water preheater 63b to the cooler 62. The refrigerant return path 63h includes a heat medium tank 63c that stores the second refrigerant and is capable of releasing a small amount of mixed inert gas into the atmosphere, and a heat medium circulating pump 63d that drives the second refrigerant to the cooler 62. In this way, the reaction gas is cooled by heat exchange between the reaction gas and the second refrigerant in the cooler 62 (heat exchange process). Furthermore, the first refrigerant is heated by heat exchange between the heated second refrigerant and the first refrigerant (boiler feed water), and the heated first refrigerant can be obtained for the combustion gas cooling means (exhaust heat boiler 52).

[0117] As shown in FIG. 2, the reaction gas cooled in the cooler 62 is transferred to the bottom of a dilute sulfuric acid tower 71 (sulfuric acid recovery means) that performs a dilute sulfuric acid recovery step. The dilute sulfuric acid tower 71 is a device that absorbs H2O and SO3 in the reaction gas into a circulating aqueous sulfuric acid solution (dilute sulfuric acid) to produce dilute sulfuric acid as a product, and is also called an absorption tower. The dilute sulfuric acid tower 71 is filled with packings, and the aqueous sulfuric acid solution is sprayed onto the packings from the top of the tower. When the reaction gas passes between the packings, it comes into contact with the aqueous sulfuric acid solution, and the H2O and SO3 are absorbed into the aqueous sulfuric acid solution. The aqueous sulfuric acid solution that has absorbed the SO3 is transferred to a dilute sulfuric acid tank 73 and cooled by a heat exchanger 74 with cooling water from a cooling water tower (not shown).

[0118] Gas containing sulfuric acid mist and unreacted SO2 is discharged from the top of the dilute sulfuric acid tower 71. The sulfuric acid mist from this exhaust gas is recovered by a wet electrostatic precipitator 76 or a mist eliminator and transferred to a tank 73 where it is reused as an aqueous sulfuric acid solution, but the remainder is transferred to a sulfite tower 81 (sulfur dioxide recovery means) which produces sulfurous acid.

[0119] The exhaust gas transferred to the sulfite tower 81 contains approximately 200 ppm (dry content) of SO2, approximately 10% (dry content) of O2, and the remainder being CO2 and N2. In the sulfite tower 81, water (industrial water) is used as an SO2 absorbent to produce sulfurous acid (H2SO3) (sulfur dioxide recovery process). This sulfurous acid is oxidized to sulfuric acid by oxygen contained in the exhaust gas. The purge gas from the converter 61, required for maintenance of the dilute sulfuric acid tower 71 and the wet electrostatic precipitator 76, is extracted from a purge line X2 downstream of the cooler 62 and introduced into a line directly transferred to the sulfite tower 81. The temperature of the maintenance purge gas from the converter 61 decreases over time, causing acid dew-point corrosion. Therefore, by heating the purge gas in the cooler 62 using the heat of the second refrigerant, acid dew-point corrosion caused by the purge gas can be prevented. Furthermore, by introducing purge gas for maintenance into the sulfite tower 81, it is possible to obtain the effect of removing SO2 gas contained in the purge gas.

[0120] The exhaust gas from the top of the sulfur dioxide tower 81 is sucked in and pressurized by the induced draft fan 87 and discharged into the atmosphere via the chimney 88. Because SO2 is absorbed in the sulfur dioxide tower 81 and recovered as sulfuric acid, the amount of SO2 emitted into the atmosphere is significantly reduced, reaching an exhaust gas control value of approximately 50 ppm or less. The induced draft fan 87 has the function of creating negative pressure in all of the individual devices of the dilute sulfuric acid production system 40 located upstream of it. The negative pressure operation of the induced draft fan 87 induces gas, preventing hot, harmful gas from escaping into the atmosphere. The converter 61 also has the function of suctioning air without the need for special equipment. Dilute sulfuric acid production and exhaust gas treatment are carried out in this manner.

[0121] The dilute sulfuric acid manufacturing apparatus and method of this embodiment include a combustion gas cooling means for cooling the combustion gas, a reaction gas cooling means for cooling the reaction gas, and a heat exchange means. In the heat exchange means, heat is exchanged between the first refrigerant and a second refrigerant whose temperature has been increased by heat exchange with the reaction gas. This allows the first refrigerant to be heated for the combustion gas cooling means, making it possible to effectively utilize exhaust heat.

[0122] During normal operation, the cooler cools the reaction gas through heat exchange and recovers cooling heat to preheat the waste heat boiler. Furthermore, during maintenance purging, the cooler prevents the purge gas from being cooled by the retained heat, thereby contributing to the prevention of corrosion downstream.

[0123] 2. Simulation A calculation simulation was carried out for the dilute sulfuric acid manufacturing plant 40 shown in Figs. 1 and 2 based on the nomogram of the SO2 → SO3 equilibrium conversion rate shown in Fig. 8 and similar actual operating data.

[0124] The gas composition of the combustion gas between the combustion furnace 51 and the dust collector 55 was calculated and simulated, and the values ​​shown in the table below were obtained.

[0125] [Table 1]

[0126] As shown in the table above, the SO3 concentration of the combustion gas is 0.26% by volume, and the H2O concentration is 24.86% by volume. From this, and based on the graph in Figure 7, it can be seen that the acid dew point of the combustion gas is around 190°C.

[0127] The temperatures and conversion rates at each stage of the converter 61 were calculated and simulated, resulting in the values ​​shown in the table below.

[0128] [Table 2] The amount of air introduced into the second and third stage catalysts is 4900 Nm 3 / Hr.

[0129] As shown in the table above, even if the temperature of the combustion gas introduced into the first-stage catalyst is as low as 370°C, calculation simulation using the SO2 → SO3 equilibrium conversion nomogram in Figure 8 shows that the combustion gas can be converted at a high cumulative conversion rate of 98.9% by the time it reaches the third-stage catalyst.

[0130] The gas composition of the reaction gas between the converter 61 and the cooler 62 was calculated and simulated, and the values ​​shown in the table below were obtained.

[0131] [Table 3]

[0132] As shown in the table above, the SO3 concentration of the reaction gas is 5.4% by volume, and the H2O concentration is 15.1% by volume. From this, and based on the graph in Figure 7, it can be seen that the acid dew point of the reaction gas is around 240°C.

[0133] In the data from similar actual operation, the SO2 gas concentration value in the exhaust gas at the outlet of the wet electrostatic precipitator 76 has dropped to approximately 200 ppm. The conversion rate of 98.9% obtained from the SO2 → SO3 equilibrium conversion rate nomogram is multiplied by the conversion rate of the gas phase reaction (SO3 + H2O → H2SO4), resulting in a conversion rate of over 99.7%. The results of a calculation simulation were as shown in the table below.

[0134] [Table 4]

[0135] By performing a calculation simulation of the first stage catalytic reaction at a low temperature of 370°C compared to the conventional high temperature of 410°C, the following benefits of effective utilization of exhaust heat recovery can be obtained.

[0136] As shown in Table 2, the inlet temperature of the first stage catalyst was 410°C, and the outlet temperature of the third stage catalyst was 420°C.

[0137] The total exhaust gas volume shown in Table 3 is 13,700 Nm 3 / Hr. Amount of heat recovered by the waste heat boiler 52 at a temperature of 370°C: a Heat recovery amount of cooler 62 in the case of low temperature 370℃: b Difference in heat recovery amount in the waste heat boiler 52: c Difference in heat recovery loss in cooler 62: d Difference in heat recovery between the low temperature case and the high temperature case = {1-(a+bcd) / (a+b)}×100 ≒ 13 Equation (1) From the above, the low temperature case of 370°C provides a 13% heat recovery advantage over the high temperature case of 410°C.

[0138] 3. Second embodiment Next, an apparatus and method for producing dilute sulfuric acid according to another embodiment (second embodiment) of the present invention will be described. Fig. 9 is a schematic diagram showing the upstream process of the apparatus for producing dilute sulfuric acid of this embodiment, and Fig. 10 is a schematic diagram showing the downstream process of the apparatus for producing dilute sulfuric acid of this embodiment. The same devices as those in the first embodiment are given the same reference numerals, and their description will be omitted below.

[0139] In this embodiment, a vertical fire-tube waste heat boiler 91 is used instead of the water-tube waste heat boiler 52. That is, this boiler is arranged so that the combustion gas supply port and outlet are perpendicular to the ground (i.e., parallel to the direction of gravity). This configuration allows dust that does not clog the waste heat boiler 91 to fall downward and be easily discharged from the waste heat boiler 91. In this embodiment, no induced draft fan 87 is provided, and gas is transported downstream by the pressure from the upstream side caused by the pushing of air introduced through the duct 43.

[0140] Furthermore, in this embodiment, the structure of the heat exchange means 100 is different from that of the first embodiment. In this embodiment, a pipe 63i is provided in the discharge flow of the heat medium circulating pump 63d that drives the second refrigerant to the cooler 62, branching from the pipe that introduces the second refrigerant to the cooler 62 and introducing the second refrigerant into the waste heat boiler 91. The waste heat boiler 91 cools the combustion gas using the second refrigerant. In this way, the waste heat boiler 91 is cooled using the second refrigerant that cools the cooler 63. The second refrigerant introduced into the waste heat boiler 91 cools the combustion gas, and is then introduced into the heat medium cooler (steam generator) 102. The second refrigerant cooled in the heat medium cooler (steam generator) 102 is returned to the refrigerant tank 63c.

[0141] The water that has cooled the second refrigerant in the refrigerant transfer path 63e becomes high-temperature steam and is introduced into the steam drum 101. The steam from the steam drum is introduced into the heat medium drum 102 and is used to cool the second refrigerant. This steam is returned to the steam drum 101, and a portion of it is purged to the outside through the pipe 46. [Explanation of symbols]

[0142] 40 Dilute sulfuric acid manufacturing apparatus, 41 Pipe line (raw material supply means), 42 Pipe line (raw material supply means), 43 Pipe line, 44 Pipe line, 45 Pipe line (refrigerant introduction means), 46 Pipe line, 51 Combustion furnace (combustion means), 51a Supply port, 51b Discharge port, 51c Lattice brick, 52 Waste heat boiler (combustion gas cooling means), 52a Boiler body, 52b Boiler drum, 52c Boiler tube, 52d Soot blower, 55 Dust collector, 61 Converter (reaction means), 62 Cooler (reaction gas cooling means), 63 Heat exchange means, 63b Feedwater preheater, 63c Heat medium tank, 63d Heat medium circulation pump, 63e Refrigerant transfer path, 63f Refrigerant introduction path, 63g Refrigerant supply path, 63h Refrigerant return path, 63i Pipe line, 71 Dilute sulfuric acid tower (sulfuric acid recovery means), 73 tank, 74 heat exchanger, 76 wet electrostatic precipitator, 81 sulfite tower (sulfur dioxide recovery means), 87 induced draft fan, 88 chimney, 91 waste heat boiler (combustion gas cooling means), 100 heat exchange means, 101 steam drum, 102 heat medium cooler (steam generator)

Claims

1. a raw material supply means for supplying a raw material containing at least a sulfur content; a combustion means for combusting the raw material to generate a combustion gas containing sulfur oxides; a refrigerant introducing means for introducing a first refrigerant; a combustion gas cooling means for cooling the combustion gas by heat exchange with a refrigerant; a reaction means for catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a reaction gas cooling means for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery means for absorbing sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to generate sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; a heat exchange means for preparing a heated first refrigerant and a cooled second refrigerant by heat exchange between a second refrigerant heated by heat exchange with the reaction gas and the first refrigerant, and supplying either the heated first refrigerant or the cooled second refrigerant to the combustion gas cooling means.

2. 2. The sulfuric acid manufacturing apparatus according to claim 1, wherein the combustion gas cooling means has the heated first refrigerant at a temperature equal to or higher than the acid dew point of the combustion gas, and the reaction gas cooling means has the second refrigerant at a temperature equal to or higher than the acid dew point of the reaction gas.

3. The heat exchange means is a refrigerant transfer path for transferring the heated second refrigerant; a preheater to which the first refrigerant is supplied, which heats the first refrigerant by heat exchange with the heated second refrigerant, and supplies the first refrigerant to the combustion gas cooling means; 2. The sulfuric acid manufacturing apparatus according to claim 1, further comprising: a refrigerant return line for returning the second refrigerant after heat exchange with the first refrigerant from the preheater to the reaction gas cooling means.

4. 4. The sulfuric acid manufacturing apparatus according to claim 3, wherein the refrigerant return line supplies a part of the second refrigerant to the combustion gas cooling means.

5. 4. The sulfuric acid manufacturing apparatus according to claim 3, wherein the refrigerant return path comprises a tank for storing the second refrigerant, and a pump for supplying the second refrigerant to the reaction gas cooling means.

6. 2. The sulfuric acid manufacturing apparatus according to claim 1, wherein the second refrigerant is an organic refrigerant that is liquid at least within a range of −20° C. to 350° C.

7. 2. The sulfuric acid manufacturing apparatus according to claim 1, wherein the first refrigerant is water, and the second refrigerant is a mixture of diphenyl and diphenyl oxide.

8. 2. The sulfuric acid manufacturing apparatus according to claim 1, wherein the heat exchange means is of a smoke tube type.

9. 2. The sulfuric acid manufacturing apparatus according to claim 1, further comprising a means for negative pressure operation.

10. hot air introducing means for introducing hot air into the reaction means; 10. The sulfuric acid manufacturing apparatus according to claim 9, further comprising: a purge passage capable of purging reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means.

11. 11. The sulfuric acid manufacturing apparatus according to claim 10, further comprising a sulfur dioxide recovery means for recovering sulfur dioxide contained in the exhaust gas.

12. 12. The sulfuric acid manufacturing apparatus according to claim 11, wherein the sulfur dioxide recovery means absorbs sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizes the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

13. a raw material supplying step of supplying a raw material containing at least a sulfur content; a combustion step of combusting the raw material to produce combustion gas containing sulfur oxides; a refrigerant introducing step of introducing a first refrigerant; a combustion gas cooling step of cooling the combustion gas by heat exchange with a refrigerant; a reaction step of catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; a reaction gas cooling step of cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery step of absorbing sulfur trioxide and water contained in the cooled reaction gas into an aqueous sulfuric acid solution to generate sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; a heat exchange step of preparing the heated first refrigerant and the cooled second refrigerant by heat exchange between the first refrigerant and a second refrigerant that has been heated by heat exchange with the reaction gas, and supplying either the heated first refrigerant or the cooled second refrigerant to the combustion gas cooling step as the refrigerant.

14. 14. The method for producing sulfuric acid according to claim 13, wherein in the combustion gas cooling step, the heated first refrigerant has a temperature equal to or higher than the acid dew point of the combustion gas, and in the reaction gas cooling step, the second refrigerant has a temperature equal to or higher than the acid dew point of the reaction gas.

15. The heat exchange step includes: a refrigerant transfer step of transferring the heated second refrigerant; a preheating step of raising the temperature of the first refrigerant by heat exchange with the heated second refrigerant and supplying the first refrigerant to the combustion gas cooling step; 14. The method for producing sulfuric acid according to claim 13, further comprising a refrigerant returning step of returning the second refrigerant after heat exchange with the first refrigerant and using the second refrigerant for heat exchange with the reaction gas.

16. 16. The method for producing sulfuric acid according to claim 15, wherein the refrigerant returning step supplies a part of the second refrigerant to the combustion gas cooling step.

17. 16. The method for producing sulfuric acid according to claim 15, wherein the refrigerant returning step comprises: a step of storing the second refrigerant; and a step of supplying the second refrigerant to the reaction gas cooling step.

18. 14. The method for producing sulfuric acid according to claim 13, wherein an organic refrigerant that is liquid at least within a range of −20° C. to 350° C. is used as the second refrigerant.

19. 14. The method for producing sulfuric acid according to claim 13, wherein water is used as the first refrigerant and a mixture of diphenyl and diphenyl oxide is used as the second refrigerant.

20. 14. The method for producing sulfuric acid according to claim 13, wherein the heat exchange step is carried out by a smoke tube method.

21. 14. The method for producing sulfuric acid according to claim 13, wherein negative pressure operation is performed.

22. 14. The method for producing sulfuric acid according to claim 13, further comprising a sulfur dioxide recovery step of recovering sulfur dioxide contained in the exhaust gas.

23. 23. The method for producing sulfuric acid according to claim 22, wherein the sulfur dioxide recovery step comprises absorbing sulfur dioxide contained in the exhaust gas into water to produce sulfurous acid, and oxidizing the sulfurous acid with oxygen contained in the exhaust gas to produce sulfuric acid.

24. The maintenance method for a sulfuric acid manufacturing apparatus according to claim 11, A maintenance method characterized by introducing hot air from the hot air introduction means into the reaction means while operating under negative pressure, purging reaction gas remaining in the reaction means upstream of the sulfuric acid recovery means, and introducing the resulting purge gas into the sulfur dioxide recovery means.

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