Sulfuric acid production equipment and methods for sulfuric acid production.

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

Sulfuric acid manufacturing apparatus and sulfuric acid manufacturing method

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

[0002] Sulfuric acid (H ２ SO ４ ) 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 desulfurized waste liquid and regenerated sulfur from gas (coke oven gas: hereinafter referred to as "COG") generated during the process of producing coke used in steelmaking, and SOx-containing gas 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 (where 1≦x<3) and water-containing combustion gas are generated, and the combustion gas is cooled by a cooling means (waste heat boiler) and introduced into a reaction means (converter). In the reaction means (converter), sulfur oxides are oxidized with a catalyst to produce sulfur trioxide (SO ３ ) is produced, and the reaction gas is cooled in a dilute sulfuric acid production means (dilute sulfuric acid tower) to produce dilute sulfuric acid.

[0005] JP 2021-31305 A (Claim 1, paragraph 0062, etc.)

[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 to 1000°C, resulting in high-temperature combustion gas. The reaction in the converter is also exothermic, causing the gas temperature to rise. However, since the final product, a dilute sulfuric acid aqueous solution, is stored at room temperature, 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, sulfuric acid gas (H ２ SO ４ ), but when the temperature of the gas drops, it becomes an aqueous solution of sulfuric acid. Aqueous sulfuric acid is a strong acid and is highly corrosive to metals. To avoid this, if highly corrosion-resistant materials are used for the piping and equipment in the process, the equipment becomes expensive and the cost of producing dilute sulfuric acid increases. Conversely, if metals with low corrosion resistance are used for the piping, etc., the equipment becomes cheaper and the cost of producing dilute sulfuric acid decreases. However, in such cases, in order to avoid corrosion of the piping, etc., sulfuric acid gas (H ２ SO ４ In the waste heat boiler of this document, the temperature of the refrigerant must be adjusted so that the sulfuric acid gas (H ２ SO ４ Since the compressor is operated with a high-temperature, high-pressure refrigerant (water) that does not turn into a sulfuric acid solution, inexpensive metals with low corrosion resistance can be used, but expensive equipment with a special design and structure that can withstand high temperatures and high pressures is required.

[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.

[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 to be prepared at a higher temperature for the combustion gas cooling means, thereby enabling effective utilization 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 efficiently used 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] In this way, a part of the second coolant can also be used as a coolant for cooling the combustion gas.

[0019] The coolant return path includes a tank for storing the second coolant, and a pump for supplying 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 a 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 the catalytic reaction 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 and 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 the exhaust gas is absorbed into water to produce sulfurous acid, which is then oxidized and recovered as sulfuric acid. Since the exhaust gas contains approximately 10% oxygen, this oxygen can be used to oxidize the sulfuric acid, eliminating the need to add an oxidizing agent as in the past. This not only increases the recovery rate of sulfuric acid, but also reduces 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 utilization of exhaust heat. In addition, since the first refrigerant is heated to cool the combustion gas, a large 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 it 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] In this way, a part of the second coolant can also be used as a coolant 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 return means can be 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 in 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 leaking 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 the exhaust gas is absorbed into water to produce sulfurous acid, which is then oxidized and recovered as sulfuric acid. Since the exhaust gas contains approximately 10% oxygen, this oxygen can be used to oxidize the sulfuric acid, eliminating the need to add an oxidizing agent as in the past. This not only increases the recovery rate of sulfuric acid, but also reduces 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 the basic application> [1] A sulfuric acid manufacturing apparatus comprising: raw material supply means for supplying a raw material containing at least a sulfur content; combustion means for combusting the raw material to produce a combustion gas containing sulfur oxides; cooling means for cooling the combustion gas by heat exchange with a heated first refrigerant; reaction means for oxidizing the sulfur oxides using a catalyst to produce a reaction gas containing sulfur trioxide and water; heat exchange means for cooling the reaction gas by heat exchange with a second refrigerant; and 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, wherein the heat exchange means prepares the heated first refrigerant for the cooling means by heat exchange between the second refrigerant, the second refrigerant having been heated by heat exchange with the reaction gas, and the 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 sulfuric acid manufacturing apparatus according to [1], characterized in that the heat exchange means comprises: a cooler that cools the reaction gas by heat exchange with the second refrigerant; a refrigerant transfer path that transfers the second refrigerant heated by the heat exchange; a preheater that receives a first refrigerant, heats 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], characterized in that 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] The sulfuric acid manufacturing apparatus according to [8], further comprising: 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.

[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 method for producing sulfuric acid, comprising: raw material supply means for supplying a raw material containing at least a sulfur content; combustion means for burning the raw material to produce a combustion gas containing sulfur oxides; cooling means for cooling the combustion gas by heat exchange with a heated first refrigerant; reaction means for catalytically oxidizing the sulfur oxides to produce a reaction gas containing sulfur trioxide and water; heat exchange means for cooling the reaction gas by heat exchange with a second refrigerant; and 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, wherein the heat exchange means prepares the heated first refrigerant for the cooling step by heat exchange between the second refrigerant, the temperature of which has been increased by heat exchange with the reaction gas, and the first refrigerant.

[0070]

[13] The method for producing sulfuric acid according to

[12] , wherein in the 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 heat exchange step, the second refrigerant has a temperature equal to or higher than the acid dew point of the reaction gas.

[0071]

[14] The method for producing sulfuric acid according to

[12] , wherein the heat exchange step comprises: a step of cooling the reaction gas by heat exchange with the second refrigerant; a step of transporting the second refrigerant heated by the heat exchange; a step of heating the first refrigerant by heat exchange with the heated second refrigerant and supplying the first refrigerant to the cooling step; and a step of returning the second refrigerant after heat exchange with the first refrigerant and using 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] , characterized in that an organic refrigerant that is liquid at least within a 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 by a smoke tube method.

[0076]

[19] The method for producing sulfuric acid according to

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

[0077]

[20] The sulfuric acid manufacturing method 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 described in

[10] above, characterized in that hot air is introduced from the hot air introduction means to the reaction means while operating under negative pressure, reaction gas remaining in the reaction means is purged upstream of the sulfuric acid recovery means, and the obtained purge gas is introduced into the sulfur dioxide recovery means.

[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.

[0081] FIG. 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; FIG. 2 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; FIG. 3 is a schematic diagram showing the internal structure of a combustion means (combustion furnace); FIG. 4 is a schematic diagram showing a hot air introduction means; FIG. 5 is a schematic diagram showing the internal structure of a converter; ３ 1 is a graph showing the relationship between the concentration of sulfuric acid, the water vapor concentration, and the estimated sulfuric acid dew point. ２ →SO ３ 1 is a nomogram of equilibrium conversion. 2 is a schematic diagram showing an upstream process of a dilute sulfuric acid manufacturing apparatus according to a second embodiment. 3 is a schematic diagram showing a downstream process of a dilute sulfuric acid manufacturing apparatus according to a second embodiment.

[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. Apparatus and method for producing dilute sulfuric acid (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 producing 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 the present invention can also be used to produce concentrated sulfuric acid by increasing the sulfuric acid concentration, for example.

[0084] 2 is a schematic diagram showing downstream processes of the 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 of 60 to 80% by weight) and "purified dilute sulfuric acid" (sulfuric acid content of 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 the 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) provided in the pipeline 41.

[0086] The dilute sulfuric acid manufacturing 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 for the purpose of removing soot, organic matter, sulfur compounds, etc. from exhaust gas (crude COG) discharged from a coke oven facility or the like. In general, the desulfurization waste liquid contains free sulfur, free NH ３ , N.H. ４ SCN, (NH ４ ) ２ S ２ O ３ , H２ O and other components. ２ Although not particularly specified, the content of the desulfurization waste liquid is often 50% by weight or more of the total desulfurization waste liquid. The pipe 42 is connected to a combustion furnace 51, and the desulfurization waste liquid is also supplied to the combustion furnace 51 as a raw material.

[0087] The pipelines 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 and desulfurization waste liquid) supplied to the combustion furnace 51 by these means, the desulfurization waste liquid contains, in addition to elemental sulfur, (NH ４ ) ２ S ２ O ３ Sulfur content (10 to 40% by weight) such as NH ３ The raw material contains nitrogen (5 to 25% by weight) such as sulfur dioxide and desulfurization waste liquid, and moisture (40 to 80% by weight). When there are multiple types of raw materials (for example, two types in this embodiment, molten sulfur and desulfurization waste liquid), the moisture content is defined as the combined amount of moisture in each raw material and the combustion improver.

[0088] The dilute sulfuric acid production 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 (pressure swing adsorption) system (not shown) may be provided to supply high-concentration oxygen from the oxygen gas generator. The oxygen gas generator uses an adsorbent such as zeolite to adsorb and remove nitrogen from air under pressure, 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 to the combustion furnace 51 as oxygen-enriched air. A PSA (pressure swing adsorption) system may also be used as the oxygen gas generator. 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 the raw materials and 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 section of the figure, desulfurization waste liquid is supplied from the supply port 51a in the middle section, and air is supplied from the supply port 51a in the lower section. 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 are mainly carried out. Behind this zone is the combustible combustion zone, where combustibles in the desulfurization waste liquid are burned. A boundary is formed between these zones. Grid-like bricks 51c are provided between the combustible combustion zone and the discharge port 51b. The lattice-like bricks 51c are cubic heat-resistant bricks arranged in a lattice pattern, with some of the bricks open. The open area ratio of the lattice-like bricks 51c is preferably around 50%. The lattice-like bricks 51c are often provided in multiple stages.

[0092] The combustion furnace 51 is configured such that the oxygen concentration of the oxygen-containing gas introduced therein is within a 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 within a range of 2.0 to 7.0% by volume, and the SO in the combustion gas generated in the combustion furnace 51 is ３ It is more preferable that the conversion rate is within the range of 1.0 to 3.0%. ３ The conversion rate is expressed by the following formula: SO ３ Conversion rate = (SO ３ / SO ｘ ) × 100 (where SO ３ is the SO contained in the combustion gas ３ volume concentration of 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 can reduce radiation to downstream equipment and also fulfill the following functions. Even if an imperfection occurs in the mixing state of the air and combustibles in the combustible combustion zone, the lattice bricks 51c physically promote remixing of the air and combustibles, preventing the combustibles from blowing through unburned. The lattice bricks 51c promote recombustion using the heat retained by the bricks. For this purpose, it is preferable to provide 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 provide 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 material is 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 material is 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 material is combusted with an oxygen-containing gas of 21 to 40% by volume can be calculated by the following formula: （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 the NOx reduction rate is 50 to 95%, the NOx reduction rate shown by the following formula can be achieved. （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 through 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. 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 through 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. Although Patent Document 1 states that the temperature of the combustion gas is cooled to 380 to 460° C., preferably to about 420° C., in this embodiment, the combustion gas is cooled to a lower temperature.

[0097] Here, the acid dew point will be explained with reference to Fig. 7. Fig. 7 shows the acid dew point of sulfuric acid (vertical axis) and the SO contained in combustion gas. ３ The relationship between the concentration (horizontal axis) and the amount of water (water vapor concentration) contained in the combustion gas is shown in the graph. ３ The temperature is determined by the concentration of sulfuric acid, water vapor concentration, pressure, etc., and if the temperature is below the acid dew point, the solution containing condensed sulfuric acid will cause severe corrosion inside the equipment (acid dew point corrosion). In order to avoid acid dew point corrosion, it is necessary to maintain the temperature of the combustion gas above the acid dew point. The graph in Figure 7 shows that at the same water vapor concentration, the SO ３ The higher the concentration, the higher the acid dew point. ３ It has been shown that 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 about 25% by volume of H ２ The composition of this combustion gas is shown by the open circles in Fig. 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 combustion gas is cooled. The waste heat boiler 52 includes a refrigerant supplying means (refrigerant supplying 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 supplying means with the combustion gas to generate steam and cool the combustion gas through heat exchange, and a water vapor discharging means (water vapor discharging step). As described above, the waste heat boiler 52 requires the combustion gas to be heated to a temperature above the acid dew point, e.g., above 190°C, and therefore the temperature of the boiler water, which serves as the refrigerant, must also be above 190°C. The refrigerant used here and the refrigerant supplying means (refrigerant supplying step) will be described in detail later.

[0100] The combustion gas cooling means may be a fire tube type or a water tube type, but considering the removal of dust adhering to the inside of the boiler, a water tube type boiler is preferably used. 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 the 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] 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 other opening (the right side in the figure). A boiler drum 52b stores boiler water and steam as refrigerants. The top surface of the boiler drum 52b is provided with an inlet (opening indicated by a downward arrow) for introducing the refrigerant and an outlet (opening indicated by 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 in 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 includes 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 also 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 from the hot air introduction means X1 into the converter 61, the converter 61 can be preheated or subjected to maintenance purging.

[0105] The combustion gas cooled by the waste heat boiler 52 contains a small amount of nitrogen (e.g., undecomposed NH ３ No, no. ２ Such as NO ｘ The converter 61 converts sulfur dioxide (SO ) in the combustion gas into sulfur dioxide (SO ) by using catalysts installed in multiple stages (three stages in the figure). ２ ) reacts with oxygen to oxidize it, producing sulfur trioxide (SO ３ In more detail, the converter 61 converts sulfur oxides (SO ) produced by a catalyst in a previous stage of the multiple stages into a reaction gas (reaction step). ｘ The converted gas, which is heated by oxidation (exothermic reaction) of sulfur dioxide with oxygen, is directly mixed with air drawn from the outside to lower the temperature to a level suitable for the subsequent catalytic reaction. This method allows for the highly efficient conversion of sulfur dioxide to sulfur trioxide (SO ). ３ ) to

[0106] 5 is a schematic diagram showing the internal structure of the converter 61. (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 broken line in (b). As shown in this figure, the converter 61 is equipped with a main air pipe 61a for taking in atmospheric air, a branch air pipe 61b branching off from the main air pipe 61a inside the converter, and an air port 61d for sending air from the branch air pipe 61b into the converter.

[0107] As the catalyst, a known catalyst used in the production of sulfuric acid can be used, for example, vanadium pentoxide (V ２ O ５ Vanadium pentoxide has a denitrifying function and can remove NH ３ and NO ｘ and react with nitrogen (N ２ ) and water (H ２ Therefore, this catalyst produces sulfur trioxide and nitrogen (NH ３ and NO ｘ ) can be decomposed simultaneously. ３ may be injected.

[0108] The temperature of the combustion gas introduced into the converter 61 is about 370° C. In the first stage of the converter 61, sulfur dioxide (SO ) contained in the combustion gas introduced into the converter 61 is converted into sulfur dioxide (SO ). ２ ) undergoes oxidation reaction to produce SO ３ The gas temperature after the reaction reaches nearly 500°C. The remaining sulfur dioxide (SO ２ ) to sulfur trioxide (SO ３ The inlet temperature of the second stage is about 410°C, and the gas temperature after the reaction is about 480°C. SO 2 contained in the combustion gas introduced into the converter 61 due to air mixing is ２ Approximately 95% of the ３ The inlet temperature of the third stage is about 390°C. Due to air mixing, SO contained in the combustion gas introduced into the converter 61 is converted into ２ Approximately 98.9% of the ３ 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 as low as about 370°C, the SO contained in the combustion gas can be reduced by introducing air into the converter 61. ２ 98.9% of the SO ３ can be converted to SO with high conversion. ３ can be generated.

[0109] Incidentally, a denitration catalyst may be disposed on the upstream side of the first stage of the converter 61 (the inflow side of the combustion gas from the exhaust heat boiler 52). As the denitration catalyst, a mixture of vanadium pentoxide and a promoter can be used.

[0110] The reaction gas generated in the converter 61 is transferred to a cooler 62 (reaction gas cooling means) and cooled. Here, as shown in the 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., 5×10 ４ to 6×10 ４ ppm) of SO ３ and about 15% by volume of H ２ O. The composition of this reaction gas is shown by white squares in FIG. 7, and the sulfuric acid dew point is about 240°C. That is, the acid dew point of the reaction gas introduced into the cooler 62 is about 240°C, and it is necessary to maintain the temperature of the reaction gas in the cooler 62 above the above acid dew point, preferably 250°C or higher.

[0111] The cooler 62 cools the reaction gas by heat exchange with a second refrigerant. As the cooler 62, it is preferable to use a smoke tube type. A smoke tube heat exchanger is a heat exchanger in which the reaction gas flows inside thin tubes and the refrigerant circulates outside the tubes. A smoke tube heat exchanger is preferably used as the cooler 62 because it is inexpensive and has high cooling efficiency compared to a water tube boiler such as the exhaust heat boiler 52, but other types such as a water tube type may be used as the cooler 62.

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

[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 for transferring the reaction gas cooled in the cooler 62 downstream.

[0114] The heat exchange means 63 includes a feed water 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 feed water preheater 63b.

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

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

[0117] The reaction gas cooled by the cooler 62 is transferred to the bottom of a dilute sulfuric acid tower 71 (sulfuric acid recovery means) which performs a dilute sulfuric acid recovery step, as shown in FIG. ２ O and SO ３ The dilute sulfuric acid tower 71 is an apparatus for absorbing H 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 H ２ O and SO ３ is absorbed in the sulfuric acid solution. ３ The sulfuric acid aqueous solution that has absorbed the sulfuric acid is transferred to a dilute sulfuric acid tank 73 and cooled by a heat exchanger 74 with cooling water from a cooling tower (not shown).

[0118] From the top of the dilute sulfuric acid tower 71, sulfuric acid mist and unreacted SO ２ This exhaust gas is discharged into a wet electrostatic precipitator 76 or a mist eliminator, where sulfuric acid mist is recovered and transferred to a tank 73 for reuse as an aqueous sulfuric acid solution, but the remainder is transferred to a sulfite tower 81 (sulfur dioxide recovery means) for producing sulfurous acid.

[0119] The exhaust gas transferred to the sulfite tower 81 contains about 200 ppm (dry content) of SO ２ , about 10% (dry content) O ２ The remainder is CO ２ and N ２ In the sulfite tower 81, water (industrial water) is converted into SO ２ It is used as an absorbent to ２ SO ３) is generated (sulfur dioxide recovery process). This sulfurous acid is oxidized to sulfuric acid by oxygen contained in the exhaust gas. The purge gas of the converter 61, which is required during maintenance of the dilute sulfuric acid tower 71 and the wet electrostatic precipitator 76, is led out from a purge pipe X2 provided downstream of the cooler 62 and introduced into a pipe for direct transfer to the sulfurous acid 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, it is possible to prevent acid dew-point corrosion caused by the purge gas. Furthermore, by introducing the purge gas for maintenance into the sulfurous acid tower 81, the SO contained in the purge gas can be reduced. ２ This also has the effect of removing gas.

[0120] The exhaust gas from the top of the sulfurous acid tower 81 is sucked / pressurized by an induced draft fan 87 and discharged into the atmosphere via a chimney 88. ２ is absorbed and recovered as sulfuric acid, reducing the amount of SO released into the atmosphere. ２ Emissions are significantly reduced, and can be kept below the exhaust gas control value of approximately 50 ppm. 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. Negative pressure operation by the induced draft fan 87 induces gas, preventing high-temperature, harmful gas from escaping into the atmosphere. In addition, the converter 61 also has the function of induced 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 a second refrigerant whose temperature has been increased by heat exchange with the reaction gas and the first refrigerant. 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 Regarding the dilute sulfuric acid manufacturing apparatus 40 shown in FIGS. 1 and 2, the SO ２ →SO ３ A calculation simulation was carried out based on the equilibrium conversion nomogram 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]

[0126] As shown in the table above, the SO ３ The concentration is 0.26% by volume, H ２ The O concentration was 24.86% by volume. From this, it can be seen from the graph in Figure 7 that the acid dew point of the combustion gas was 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] The amount of air introduced into the second and third stage catalysts was 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, the SO ２ →SO ３ Simulations using a nomograph for equilibrium conversion showed that combustion gases could be converted at a high cumulative conversion rate of 98.9% up to 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]

[0132] As shown in the table above, the reaction gas SO ３ The concentration is 5.4% by volume, H ２ The O concentration was 15.1% by volume. From this, it can be seen from the graph in FIG. 7 that the acid dew point of the reaction gas was around 240°C.

[0133] In the similar actual operation data, the SO in the exhaust gas at the outlet of the wet electrostatic precipitator 76 ２ The gas concentration value has decreased to about 200 ppm. ２ →SO ３ The conversion rate obtained from the equilibrium conversion nomogram was 98.9%. ３ +H ２ O → H ２ SO ４ ) The conversion rate is multiplied to achieve a conversion rate of 99.7% or more. As a result of calculation simulation, the values ​​shown in the table below were obtained.

[0134]

[0135] By performing a calculation simulation of the first stage catalytic reaction at a low temperature of 370°C in this case, 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 in the case of a temperature of 370°C: a Amount of heat recovered by the cooler 62 in the case of a low temperature of 370°C: b Difference in the amount of heat recovered by the waste heat boiler 52: c Difference in the amount of heat recovered loss by the cooler 62: d Difference in heat recovery between the low temperature case and the high temperature case = {1 - (a + b - c - d) / (a ​​+ b)} × 100 ≈ 13 Formula (1) From the above, a 13% heat recovery benefit is obtained in the case of a low temperature of 370°C compared to the case of a high temperature of 410°C.

[0138] 3. Second embodiment Next, a dilute sulfuric acid manufacturing apparatus and a dilute sulfuric acid manufacturing method according to another embodiment (second embodiment) of the present invention will be described. Figure 9 is a schematic diagram showing the upstream process of the dilute sulfuric acid manufacturing apparatus of this embodiment, and Figure 10 is a schematic diagram showing the downstream process of the dilute sulfuric acid manufacturing apparatus of this embodiment. The same devices as in the first embodiment are assigned 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, generated by the air introduced through the duct 43.

[0140] Furthermore, in this embodiment, the structure of the heat exchanger 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, which 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 manner, 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.

[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)

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