Dilute sulfuric acid production apparatus and dilute sulfuric acid production method

Abstract

A dilute sulfuric acid manufacturing apparatus (40) includes: a pipe (42) or the like that supplies a raw material containing at least a sulfur component, a nitrogen component, and 40 to 80% by weight or more of moisture; a PVSA 45d or the like that generates an oxygen-containing gas having an oxygen concentration of 22 to 40% by volume; a combustion furnace (51) that combusts the raw material using the oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx: here, 1 ≤ x < 3) and 10% by volume or more of moisture; a waste heat boiler (52) that cools the combustion gas; a converter (61) that oxidizes the sulfur oxides (SOx) using a catalyst to generate a reaction gas containing sulfur trioxide (SO3); and a dilute sulfuric acid tower (71) that cools the reaction gas to generate dilute sulfuric acid, and does not add water from at least the combustion furnace (51) up to the dilute sulfuric acid tower (71), and generates dilute sulfuric acid of less than 90% by weight using only the moisture of the raw material.

Description

TECHNICAL FIELD

[0001] The present application relates to a dilute sulfuric acid manufacturing apparatus and a dilute sulfuric acid manufacturing method. BACKGROUND

[0002] Sulfuric acid (H2SO4) is a strong acid, which is manufactured in a large amount and used in various fields. Sulfuric acid is roughly classified into industrial concentrated sulfuric acid, which shows a sulfuric acid concentration of 90% by weight or more, and industrial dilute sulfuric acid, which shows less than 90% by weight, and the properties thereof are different from each other. Among them, dilute sulfuric acid is strongly acidic, but unlike concentrated sulfuric acid, it has no oxidizing action, dehydrating action, on the other hand, it shows strong corrosiveness to metal materials and the like. Dilute sulfuric acid is used for various purposes such as industrial goods, medicines, pesticides, reagents, and the like.

[0003] In the production of sulfuric acid, it is necessary to use a raw material containing sulfur. As the raw material, desulfurization waste liquid from gas generated in the production process of coke used in iron making and the like (Coke Oven Gas: hereinafter referred to as "COG") and regenerated sulfur, a gas containing SOx discharged from a copper refining process, and the like are used.

[0004] In the past, as a method of producing sulfuric acid, for example, the method of Patent Literature 1 is known. In this document, it is described that (a) a carbon-containing fuel is burned to supply heat for forming sulfur dioxide from a sulfur-containing material, and an oxygen-rich gas (hereinafter referred to as an oxygen-containing gas) selected from pure oxygen and a mixed gas containing 30% by volume or more of oxygen is supplied to support the combustion of the fuel; (b) a mixed gas containing sulfur dioxide and a gas generated by combustion of the fuel is formed; (c) the mixed gas contains 30% by volume or more of carbon dioxide and more than 16% by volume of sulfur dioxide after drying; and the like.

[0005] In addition, although there is no description of the production of dilute sulfuric acid, a wet treatment system of desulfurization waste liquid is disclosed in Patent Literature 2. This system includes the following steps: the desulfurization waste liquid is supplied to a combustion device together with a fuel gas and air, combustion is performed at 1050 to 1100°C, and a treatment gas containing SO2 is generated; the treatment gas is cooled by heat exchange; the cooled treatment gas is supplied to a reaction device after passing through a denitration reactor to convert from SO2 to SO3; the treatment gas containing SO3 is passed through a condenser and an acid mist catcher to generate sulfuric acid; SO2 remaining in the exhaust gas from the acid mist catcher is treated with ammonia water in an exhaust gas treatment device, and ammonium sulfate is recovered. Air is supplied to the combustion device.

[0006] Also, although there is no description of the production of dilute sulfuric acid, in Patent Literature 3, a method is described in which, in a contact method of sulfuric acid production in which a gas obtained by burning sulfur is used as a raw material, an oxygen-enrichment device is assembled, and oxygen-enriched air is supplied to a sulfur combustion furnace and / or a converter.

[0007] Prior Art Documents

[0008] Patent Literature

[0009] Patent Literature 1: Japanese Patent No. 2519691 (claim 1, etc.)

[0010] Patent Literature 2: Chinese Patent CN110282606A

[0011] Patent Literature 3: Japanese Patent Application Laid-Open No. H1-160809 SUMMARY

[0012] PROBLEMS TO BE SOLVED BY THE INVENTION

[0013] The method of Patent Literature 1 includes a process of drying the mixed gas, and therefore aims at producing concentrated sulfuric acid having a high concentration of sulfuric acid rather than dilute sulfuric acid. Generally, in the production of dilute sulfuric acid, a method of diluting concentrated sulfuric acid with water after the production of concentrated sulfuric acid is employed, or a sulfuric acid production device with a special temperature adjustment machine capable of adjusting the condensation temperature (boiling point) of sulfuric acid is employed. In the method based on the former, in order to adjust the moisture concentration, the high-temperature combustion gas needs to be first cooled and dehumidified to a dehumidification tower at a temperature lower than 100°C or a drying tower using the dehydration action based on concentrated sulfuric acid, or the like. In addition, after such a dehumidification tower or drying tower, an instrument (heat exchanger, etc.) for reheating to 400 to 450°C, piping, a rotating machine, or the like are required. On the other hand, in the method based on the latter, a very expensive special temperature adjustment machine capable of adjusting the condensation temperature (boiling point) of sulfuric acid is required. Therefore, in such a method, there is a problem that the cost is consumed in the production of dilute sulfuric acid.

[0014] In addition, the sulfuric acid produced by the system described in Patent Literature 2 is high-concentration sulfuric acid having a concentration of 93% by weight, and dilute sulfuric acid having a concentration of 90% by weight or less is not produced. In this document, it is described that water is supplied to the washing tower at the rear stage of the combustion means and the front stage of the reaction means, but since the outlet temperature of the washing tower is the degree of the saturation water vapor temperature, water vapor is hardly generated, and therefore the water content in the combustion gas does not increase. Therefore, even if water is supplied to the washing tower, dilute sulfuric acid cannot be produced. Furthermore, in the system of Patent Literature 2, air is supplied to the combustion device, and the necessary structure at the rear stage of the combustion device is a purification device and a denitration reactor.

[0015] Patent Document 3 does not describe the production of dilute sulfuric acid. In addition, the oxygen enrichment device is used to increase the equilibrium conversion rate from SO2 to SO3 by increasing the relative concentration of O2 with respect to SO2, and there is no description of nitrogen oxides (NO x ).

[0016] The present application aims to provide a dilute sulfuric acid production device and a dilute sulfuric acid production method that can produce dilute sulfuric acid at low cost.

[0017] Means for solving the problem

[0018] The present inventors found that by using a raw material that contains a large amount of moisture in addition to sulfur components and nitrogen components as a raw material and combusting the raw material using an oxygen gas having a high oxygen concentration, it is possible to produce dilute sulfuric acid, and thus completed the present application.

[0019] The present application relates to a dilute sulfuric acid production device, characterized by comprising: a raw material supply means that supplies a raw material containing at least sulfur components, nitrogen components, and 40 to 80% by weight or more of moisture; an oxygen gas generation means that generates an oxygen gas having an oxygen concentration of 22 to 40% by volume; a combustion means that combusts the raw material using the oxygen gas to generate a combustion gas containing sulfur oxides (SOx: 1 ≤ x < 3 here) and 10% by volume or more of moisture; a cooling means that cools the combustion gas; a reaction means that oxidizes the sulfur oxides (SOx) using a catalyst to generate a reaction gas containing sulfur trioxide (SO3); and a dilute sulfuric acid generation means that cools the reaction gas to generate dilute sulfuric acid, and does not add water at least from the combustion means to the dilute sulfuric acid generation means, and generates dilute sulfuric acid of less than 90% by weight using only the moisture of the raw material.

[0020] In the present application, a raw material that contains a large amount of moisture in addition to sulfur components and nitrogen components is used as a raw material, and the raw material is combusted using an oxygen gas having a high oxygen concentration, and thus it is possible to produce sulfuric acid in a state containing a certain amount or more of moisture. Therefore, the produced sulfuric acid is dilute sulfuric acid, and it is not necessary to provide a dehumidification device or a drying device to produce sulfuric acid as in the past. Therefore, it is possible to reduce the cost of producing dilute sulfuric acid compared to the past.

[0021] In addition, in the present application, it is possible to produce dilute sulfuric acid of less than 90% by weight using only the moisture of the raw material without adding water from the combustion means to the dilute sulfuric acid generation means. In the present application, special devices such as a water supply device are not required, and thus it is possible to reduce the production cost of dilute sulfuric acid.

[0022] Further, in the present application, the raw material is combusted using an oxygen-containing gas having an oxygen concentration of 22 to 40 vol%. Here, generally, if the oxygen concentration at the time of combustion of the raw material is increased, or the combustion temperature is increased, nitrogen oxides (NOx) are easily generated. However, in the present application, by using an oxygen-containing gas having an oxygen concentration of 22 to 40 vol%, the amount of exhaust gas generated itself can be reduced (when the PVSA 45d is provided, the amount of exhaust gas is 10951 Nm 3 / h, and when the PVSA 45d is not provided, the amount of exhaust gas is 13207 Nm 3 / h). As a result, the amount of nitrogen oxides contained in the combustion gas does not increase, and instead, compared to the case where air (oxygen concentration 21 vol%) is used, the amount of NOx contained in the combustion gas is reduced (see below). Figure 4

[0023] In this case, by combusting the raw material using the above-described oxygen-containing gas having an oxygen concentration of 22 to 40 vol% generated by the above-described oxygen-containing gas generation means, the amount of nitrogen oxides of the combustion gas generated by the above-described combustion means is less than the amount of nitrogen oxides of the combustion gas generated when the raw material is combusted under the same conditions assuming that air having an oxygen concentration of 21 vol% is used.

[0024] Thus, by combusting the raw material using an oxygen-containing gas, compared to the case where the raw material is combusted using air as usual, the amount of nitrogen oxides contained in the combustion gas generated can be reduced.

[0025] Preferably, at least between the above-described combustion means and the above-described reaction means, there is no equipment for denitration.

[0026] In this case, the above-described combustion means preferably combusts the above-described raw material at 900 to 1100°C.

[0027] Compared to existing sulfuric acid production equipment, in the present application, because the oxygen concentration is high, the combustion-supporting agent (COG, etc.) required to maintain combustion can be further reduced, and the combustion cost can be reduced. Also, generally, if the oxygen concentration is increased, or the combustion temperature is increased, atmospheric pollutants such as nitrogen oxides (NOx) are easily generated, but in the present application, even if the raw material and the combustion-supporting agent are combusted at a high oxygen concentration, the amount of nitrogen oxides generated does not increase, so the environmental load can be reduced. Therefore, no or minimal equipment for removing nitrogen oxides is required, so the production cost of the dilute sulfuric acid can also be reduced.

[0028] In this case, the above-described combustion means preferably combusts the above-described raw material at 1050°C or less.

[0029] Thus, in the combustion means, by making the combustion temperature 1050°C or less, the NOx concentration in the combustion gas can be reduced (as described below). Figure 15 ​As shown, as the temperature rises, the NOx concentration also rises, thus enabling processing without special equipment for denitration downstream.

[0030] Further, in the combustion means, the oxygen concentration of the oxygen-containing gas introduced from the oxygen-containing gas generation means is in the range of 22 to 30 vol%, and the oxygen concentration in the combustion gas generated by the combustion means is in the range of 2.0 to 7.0 vol%.

[0031] In the combustion means, by introducing the oxygen-containing gas under the above conditions to reduce the combustion exhaust gas amount, and controlling the oxygen concentration in the combustion exhaust gas, the SO3 conversion rate can be maintained at a value equivalent to the case of air (no oxygen enrichment) combustion. Thus, the SO3 conversion rate shown below in the combustion gas generated by the combustion means can also be made a low value in the range of, for example, 1.0 to 3.0%.

[0032] SO3 conversion rate = (SO3 / SOx) x 100

[0033] (Here, SO3 is the volume concentration of SO3 contained in the combustion gas, and SOx is the volume concentration of SOx contained in the combustion gas).

[0034] Thus, without affecting the acid dew point in the waste heat boiler downstream of the combustion furnace, processing can be performed equivalent to the case of air (no oxygen enrichment) supply.

[0035] Further, it is preferable to further have a gas removal means that removes unreacted sulfur dioxide in the dilute sulfuric acid generation means.

[0036] In this way, since unreacted sulfur dioxide is removed, it can be disposed of without being released into the environment.

[0037] In this case, in the gas removal means, it is preferable to cause the unreacted sulfur dioxide to react with ammonia to generate ammonium sulfite ((NH4)2SO3: imidogen), and to be recovered in the form of ammonium sulfate ((NH4)2SO4: thionyl) by oxidation.

[0038] In this way, unreacted sulfur dioxide can be caused to react with ammonia to generate ammonium sulfite, and then oxidized, thereby being recovered in the form of ammonium sulfate.

[0039] In this case, it is preferable that the ammonia be present in the case of absorbing sulfur dioxide with aqueous ammonia, and in the case of absorbing sulfur dioxide with ammonia contained in desulfurization waste liquid, the latter of which is recirculated as the raw material after reacting with the unreacted sulfur dioxide.

[0040] Thus, by using the desulfurization waste liquid as an ammonia source and recycling the desulfurization waste liquid after the reaction with sulfur dioxide as a raw material, the desulfurization waste liquid can be effectively utilized.

[0041] Further, the above combustion means preferably uses a combustion furnace having a checker brick with a partially opened interior.

[0042] The checker brick has a heat retaining effect when heated, and thus enables after-burning of unreacted raw material. In addition, in addition to reducing radiation to downstream instruments, the checker brick has a moderate opening, and thus enables good flow of the raw material, oxygen-containing gas, and combustion gas in the form of a rectifying effect. Thus, the combustion means can effectively perform combustion of the raw material.

[0043] Further, in the reaction means in which the above sulfur oxide (SOx) is oxidized by a catalyst to generate a reaction gas containing sulfur trioxide (SO3), the above catalyst is preferably vanadium pentoxide (V2O5), which has a denitration function.

[0044] Thus, by using vanadium pentoxide (V2O5) as the catalyst of the reaction means and having a denitration function, oxidation of the sulfur oxide and decomposition of the nitrogen component can be simultaneously performed.

[0045] In this case, in the case where a higher denitration rate is required, the above reaction means preferably further has a denitration catalyst containing titanium oxide (TiO2) as a catalytic aid in addition to the above catalyst.

[0046] In the conversion of the sulfur oxide, in the case where the concentration of the nitrogen component (e.g., undecomposed NH3, NO, NO2, and the like NOx) generated by combustion in the raw material is high and a high denitration rate is required, the conversion of the sulfur oxide is preferentially performed over the decomposition of the nitrogen component in vanadium pentoxide not containing a catalytic aid. Thus, by providing the above denitration catalyst containing a catalytic aid, the decomposition reaction of the nitrogen component is preferentially performed over the conversion of the sulfur oxide, and decomposition of the nitrogen component can be performed.

[0047] The above reaction means preferably has the above catalyst provided in a plurality of stages, performs the above oxidation of the above sulfur oxide using the above catalyst of the front stage of the plurality of stages, directly mixes the converted gas warmed by an exothermic reaction based on the above oxidation with atmospheric air drawn from the outside, and reduces the temperature thereof to a temperature suitable for catalytic reaction of the rear stage, thereby reducing the temperature of the above converted gas without a heat exchanger.

[0048] Thus, by cooling the converted gas in the front stage of the catalyst in the plurality of stages, the temperature of the rear stage can be lowered. Therefore, the reaction rate can be prevented from decreasing due to an increase in the temperature of the rear stage, and in addition, by directly introducing air from the outside, an effect of promoting the reaction by increasing the partial pressure of oxygen required in the conversion is obtained in addition to the cooling effect.

[0049] Further, by attracting air to supplement oxygen using the reaction means (converter) instead of the combustion means (combustion furnace) of the uppermost stream device, the air supply capacity of the combustion furnace and boiler of the upper stream device can be made smaller, and this is effective in the miniaturization of the combustion furnace / boiler and the reduction of combustion furnace combustion aids. In addition, according to the above-described configuration, since the cooling of the converted gas is also performed using the converter, a heat exchanger for cooling can be omitted.

[0050] Further, in the above-described reaction means, an indirect cooling means that indirectly cools the above-described converted gas using a heat exchanger can be used in combination with the above-described cooling based on the direct mixing of air.

[0051] Thus, in addition to the cooling by the direct mixing of air attracted from the outside, cooling is performed using the indirect cooling means, whereby the gas temperature of the rear stage of the catalyst can be effectively lowered to a temperature suitable for the catalytic reaction, and the increase in the gas amount can be suppressed by reducing the amount of air mixed.

[0052] In the above-described combustion means, it is preferable to supply the above-described oxygen-containing gas to the raw material of less than 5000 kJ / kg and to supply air to the raw material of 5000 kJ / kg or more for combustion.

[0053] Alternatively, in the above-described combustion means, the above-described oxygen-containing gas can be supplied to the raw material of less than 5000 kJ / kg for combustion, and in the case where the above-described raw material of less than 5000 kJ / kg is small, the oxygen-containing gas can also be supplied to the raw material of 5000 kJ / kg or more and combustion aids (COG, etc.).

[0054] In the case of the raw material of less than 5000 kJ / kg, combustion becomes unstable, and thus by supplying the oxygen-containing gas having a high oxygen concentration for combustion, the combustion can be stabilized. In the case of the raw material of 5000 kJ / kg or more, air can be easily used for combustion, and thus air can be supplied, and the oxygen-containing gas can also be supplied. That is, the oxygen-containing gas can be supplied to all of the raw material or a part of the raw material according to the supply ratio of the raw material.

[0055] Thus, by distributing the oxygen-containing gas according to the raw material, the combustion of the raw material can be effectively performed.

[0056] Further, in the above-described dilute sulfuric acid generation means, it is preferable to adjust the concentration of the dilute sulfuric acid by up and down control of the temperature of the circulating sulfuric acid aqueous solution.

[0057] In the dilute sulfuric acid generating means, by controlling the temperature of the circulating sulfuric acid aqueous solution up and down, the concentration of the generated dilute sulfuric acid can be adjusted, and thus, for example, when the water content in the desulfurization waste liquid is 50% by weight, by raising the temperature of the dilute sulfuric acid to about 80°C, dilute sulfuric acid that provides the value of about 70% by weight as a trading commodity can be generated.

[0058] Further, it is preferable to further provide a sulfuric acid concentration means that concentrates the concentration of the dilute sulfuric acid generated by the above-described dilute sulfuric acid generating means to 70 to 80% by weight.

[0059] In this way, by concentrating the concentration of the dilute sulfuric acid generated by the above-described dilute sulfuric acid generating means to 70 to 80% by weight, dilute sulfuric acid that provides a value of more than 70% as a trading commodity can be generated, and at the same time, dilute sulfuric acid that can cope with corrosion resistance of a product line composed of carbon steel of more than 70% (preferably about 75%) can be generated.

[0060] Further, in the above-described dilute sulfuric acid generating means, it is preferable to directly contact cool the above-described reaction gas using a part of the generated sulfuric acid aqueous solution, and not to have a device for indirectly cooling the above-described reaction gas.

[0061] In this way, in the dilute sulfuric acid generating means, by directly cooling the reaction gas using a part of the generated sulfuric acid aqueous solution, it is possible to eliminate the need for a special device for indirect cooling in the dilute sulfuric acid generating means.

[0062] Further, it is preferable that the above-described cooling means be a waste heat boiler having a boiler, and the waste heat boiler have:

[0063] a feed water means that supplies water to the above-described boiler; and

[0064] a heat exchange means that evaporates the above-described water using the above-described combustion gas to generate steam, and cools the above-described combustion gas by heat exchange.

[0065] In this case, it is preferable to further provide an outlet temperature adjusting means that includes a boiler bypass for fixing the outlet temperature of the above-described boiler against variation of the outlet temperature, and a regulating valve.

[0066] In this way, by making the cooling means a waste heat boiler and fixing the temperature at the outlet of the boiler, it is possible to prevent variation of the outlet temperature of the boiler due to variation of the raw material and fouling of the water tube of the boiler, and to supply the reactive gas at a fixed temperature to the reaction means.

[0067] Further, in the above dilute sulfuric acid production means, the concentration of the dilute sulfuric acid produced by the dilute sulfuric acid production means is adjusted by adjusting the water content of the raw material without adding water from the above combustion means to the dilute sulfuric acid production means.

[0068] Thus, by adjusting the water content of the raw material, the concentration of the dilute sulfuric acid can be adjusted without adding water.

[0069] The present application relates to a dilute sulfuric acid production method, characterized by comprising: a raw material supply step of supplying a raw material containing at least a sulfur component, a nitrogen component, and 40 to 80% by weight or more of moisture; an oxygen-containing gas production step of producing an oxygen-containing gas having an oxygen concentration of 22 to 40% by volume; a combustion step of combusting the raw material using the oxygen-containing gas to produce a combustion gas containing a sulfur oxide (SOx: 1≤x<3 here) and 10% by volume or more of moisture; a cooling step of cooling the combustion gas; a reaction step of oxidizing the sulfur oxide (SOx) using a catalyst to produce a reaction gas containing sulfur trioxide (SO3); and a dilute sulfuric acid production step of cooling the reaction gas to produce dilute sulfuric acid, without adding water from at least the combustion step to the dilute sulfuric acid production step, and producing dilute sulfuric acid of less than 90% by weight using only the moisture of the raw material.

[0070] In the present application, a raw material containing a large amount of moisture in addition to a sulfur component and a nitrogen component is used, and the raw material is combusted using an oxygen-containing gas having a high oxygen concentration, whereby sulfuric acid can be produced in a state containing a certain amount or more of moisture. Therefore, the produced sulfuric acid is dilute sulfuric acid, and it is not necessary to provide a dehumidifying device or a drying device as in the past to produce sulfuric acid. Therefore, the cost of producing dilute sulfuric acid can be reduced compared to the past. Further, in the present application, dilute sulfuric acid of less than 90% by weight can be produced using only the moisture of the raw material without adding water from the raw material supply step to the dilute sulfuric acid production step. Therefore, special devices such as a water supply device are not necessary, and the production cost of dilute sulfuric acid can be reduced.

[0071] Further, in the present application, since the raw material is combusted using an oxygen-containing gas having an oxygen concentration of 22 to 40% by volume, the amount of NOx contained in the combustion gas can be reduced compared to the case where air is used. By using such an oxygen-containing gas having a high oxygen concentration, the amount of exhaust gas itself produced can also be reduced.

[0072] In this case, by combusting the raw material using the oxygen-containing gas having an oxygen concentration of 22 to 40% by volume produced by the above oxygen-containing gas production step, the amount of nitrogen oxides in the combustion gas produced by the combustion step is less than the amount of nitrogen oxides in the combustion gas produced when the raw material is combusted under the same conditions assuming that air having an oxygen concentration of 21% by volume is used.

[0073] Thus, by using an oxygen-containing gas to combust the raw material, the amount of nitrogen oxides contained in the combustion gas generated can be reduced compared to the case where air is used to combust the raw material as usual.

[0074] Preferably, at least between the above combustion step and the above reaction step, there is no equipment for denitration.

[0075] In this case, the above combustion step preferably combusts the above raw material at 900 to 1100°C.

[0076] In the present application, since the oxygen concentration is high, the raw material and the combustion-supporting agent (COG, etc.) required to maintain combustion can be further reduced, and the combustion cost can be reduced. Also, generally, if the oxygen concentration is increased or the combustion temperature is increased, atmospheric pollutants such as nitrogen oxides (NOx) are easily generated, but in the present application, even if the raw material is combusted at a high oxygen concentration, the amount of nitrogen oxides generated is small, and thus the environmental load can be reduced. Therefore, no or minimal equipment for removing nitrogen oxides is required, and thus the manufacturing cost of dilute sulfuric acid can also be reduced.

[0077] Thus, the above combustion step preferably combusts the above raw material at a temperature of 1050°C or lower.

[0078] Thus, in the combustion step, by reducing the combustion temperature to 1050°C or lower, the NOx concentration in the combustion gas can be reduced, and thus special equipment for denitration can not be required downstream.

[0079] Further, in the above combustion step, the oxygen concentration of the above oxygen-containing gas introduced from the above oxygen-containing gas generation step is in the range of 22 to 30 vol%, and the oxygen concentration in the above combustion gas generated by the above combustion step is in the range of 2.0 to 7.0 vol%.

[0080] In the combustion step, by introducing the oxygen-containing gas under the above conditions to reduce the amount of combustion exhaust gas, and by controlling the oxygen concentration in the combustion exhaust gas, the SO3 conversion rate can be maintained at a value equivalent to that in the case where there is no oxygen enrichment. Therefore, the SO3 conversion rate in the combustion gas generated by the combustion step can also be made a low value, such as in the range of 1.0 to 3.0%.

[0081] Thus, the acid dew point in the waste heat boiler downstream of the combustion furnace can be treated without affecting the acid dew point, and can be treated equivalent to the case of air (no oxygen enrichment) combustion.

[0082] Further, it is preferable to further have a gas removal step that removes unreacted sulfur dioxide in the above dilute sulfuric acid generation step.

[0083] Thus, since the unreacted sulfur dioxide is removed, it is not released into the environment and can be eliminated.

[0084] In this case, in the gas removal step, the unreacted sulfur dioxide is preferably reacted with ammonia to produce ammonium sulfite ((NH4)2SO3: imido), which is recovered by oxidation in the form of ammonium sulfate ((NH4)2SO4: sulfamate).

[0085] Thus, the unreacted sulfur dioxide is reacted with ammonia to produce ammonium sulfite, and then oxidation is performed to recover it in the form of ammonium sulfate.

[0086] In this case, it is preferable that the ammonia is present in a case where sulfur dioxide is absorbed using aqueous ammonia and a case where sulfur dioxide is absorbed using ammonia contained in desulfurization waste liquid, and the latter desulfurization waste liquid is recirculated as the raw material after being reacted with the unreacted sulfur dioxide.

[0087] Thus, by using the desulfurization waste liquid as the ammonia source and recirculating the desulfurization waste liquid after being reacted with sulfur dioxide as the raw material, the desulfurization waste liquid can be effectively utilized.

[0088] Further, the combustion step preferably uses a combustion furnace having a checker brick with a portion of the inside opened.

[0089] Thus, since the checker brick has a heat retaining effect when heated, it is possible to perform after-combustion of the uncombusted raw material. In addition, since the checker brick has a moderate opening, it makes the flow of the raw material, the oxygen-containing gas, and the combustion gas good in the form of a rectifying effect, in addition to reducing radiation to the downstream instrument. Thus, the combustion of the raw material can be effectively performed using the combustion means.

[0090] Further, in the reaction step, the catalyst is preferably vanadium pentoxide (V2O5), which has a denitration function.

[0091] Thus, by making the catalyst of the reaction step vanadium pentoxide (V2O5) and having a denitration function, it is possible to simultaneously perform oxidation of the sulfur oxide and decomposition of the nitrogen component.

[0092] In this case, in a case where a higher denitration rate is required, the reaction step preferably further has a denitration catalyst containing titanium oxide (TiO2) as a catalytic aid in addition to the catalyst.

[0093] In the conversion of sulfur oxides, in the case where the concentration of nitrogen components (e.g., undecomposed NH3, NO, NO2, etc., NOx) generated by combustion in the raw material is relatively high, the conversion of sulfur oxides is preferentially performed in vanadium pentoxide that does not contain a catalytic aid, rather than the decomposition of nitrogen components. Therefore, by providing the above-described denitration catalyst containing a catalytic aid, the decomposition reaction of nitrogen components is preferentially performed over the conversion of sulfur oxides, and the decomposition of nitrogen components can be performed.

[0094] The above-described reaction process preferably has the above-described catalysts provided in a plurality of stages, performs the above-described oxidation of the sulfur oxides using the above-described catalysts in the front stage of the plurality of stages, directly mixes the conversion gas, which is warmed by an exothermic reaction based on the oxidation, with the atmosphere drawn from the outside, and lowers it to a temperature suitable for catalytic reaction in the rear stage, thereby lowering the temperature of the conversion gas without a heat exchanger.

[0095] Thus, by cooling the conversion gas in the front stage of the catalysts in the plurality of stages, the temperature of the rear stage can be lowered. Therefore, the decrease in the reaction rate due to the increase in the temperature of the rear stage can be prevented. In addition, by directly introducing air from the outside, in addition to the cooling effect, the insufficient amount of oxygen required for the conversion can also be supplied. Furthermore, by performing oxygen supplementation using the reaction process (converter) rather than the combustion process (combustion furnace) of the most upstream equipment, the ventilation capacity of the combustion furnace and the boiler of the upstream equipment can be suppressed to be smaller, and this is effective in the miniaturization of the combustion furnace / boiler and the reduction of the combustion aid. In addition, according to the above-described configuration, the heat exchanger of the converter can be omitted.

[0096] In addition, in the above-described reaction process, an indirect cooling process in which the above-described conversion gas is indirectly cooled using a heat exchanger can be combined with the above-described cooling by direct mixing with the atmosphere.

[0097] Thus, in addition to the cooling by direct mixing with the atmosphere drawn from the outside, the indirect cooling process is also used for cooling, whereby the gas temperature of the rear stage of the catalyst can be effectively lowered to a temperature suitable for catalytic reaction, and the increase in the gas amount can be suppressed by reducing the amount of mixing of the atmosphere.

[0098] In the above-described combustion process, it is preferable to supply the above-described oxygen-containing gas for combustion to the raw material of less than 5000 kJ / kg, and to supply air for combustion to the raw material of 5000 kJ / kg or more.

[0099] Alternatively, in the above-described combustion process, the above-described oxygen-containing gas can be supplied for combustion to the raw material of less than 5000 kJ / kg, and in the case where the raw material of less than 5000 kJ / kg is small, the oxygen-containing gas can also be supplied for combustion to the raw material of 5000 kJ / kg or more and the combustion aid (COG, etc.).

[0100] When the raw material is less than 5000 kJ / kg, combustion becomes unstable, and thus combustion is stabilized by supplying an oxygen gas having a high oxygen concentration. When the raw material is 5000 kJ / kg or more, the raw material can be easily combusted using air, and thus air or an oxygen gas can be supplied. That is, an oxygen gas can be supplied to all or part of the raw material according to the supply ratio of the raw material.

[0101] Thus, by supplying an oxygen gas to the raw material, combustion of the raw material can be efficiently performed.

[0102] Further, in the dilute sulfuric acid production step, the concentration of the dilute sulfuric acid is preferably adjusted by up-and-down control of the temperature of the circulating aqueous sulfuric acid solution.

[0103] In the dilute sulfuric acid production step, the concentration of the produced dilute sulfuric acid can be adjusted by up-and-down control of the temperature of the circulating aqueous sulfuric acid solution, and thus, for example, when the water content in the desulfurization waste liquid is 50% by weight, by increasing the temperature of the dilute sulfuric acid to about 80°C, dilute sulfuric acid having a value that can be provided as a commercial product of about 70% by weight can be produced.

[0104] Further, it is preferable to further include a sulfuric acid concentration step of concentrating the concentration of the dilute sulfuric acid produced in the above-described dilute sulfuric acid production step to 70 to 80% by weight.

[0105] Thus, by concentrating the concentration of the dilute sulfuric acid produced in the above-described dilute sulfuric acid production step to 70 to 80% by weight, dilute sulfuric acid having a value of 70% or more that can be provided as a commercial product can be produced, and at the same time, dilute sulfuric acid having a value of 70% or more (preferably about 75%) that can cope with corrosion resistance of a product line composed of carbon steel can be produced.

[0106] Further, in the dilute sulfuric acid production step, it is preferable to directly contact cool the above-described reaction gas using the produced aqueous sulfuric acid solution, and not to have a device for indirectly cooling the above-described reaction gas.

[0107] Thus, in the dilute sulfuric acid production step, by directly cooling the reaction gas using a part of the produced aqueous sulfuric acid solution, it is not necessary to have a special device for indirect cooling in this dilute sulfuric acid production step.

[0108] Further, it is preferable that the above-described cooling step use a waste heat boiler having a boiler, and the waste heat boiler includes:

[0109] a feed water step of supplying water to the above-described boiler; and

[0110] a heat exchange step of evaporating the above-described water using the above-described combustion gas to generate steam, and cooling the above-described combustion gas by heat exchange.

[0111] In this case, it is preferable to further include an outlet temperature adjustment process including a bypass around the boiler for fixing the outlet temperature of the boiler against variations in the outlet temperature, and a regulating valve.

[0112] Thus, by making the cooling process a waste heat boiler and fixing the temperature at the outlet of the boiler, it is possible to prevent variations in the outlet temperature of the boiler due to variations in the raw material and fouling of the boiler water tubes, and to supply the reactive gas at a fixed temperature to the reaction process.

[0113] In addition, in the dilute sulfuric acid production process, it is preferable to adjust the concentration of the dilute sulfuric acid produced by the dilute sulfuric acid production process by adjusting the water content of the raw material without adding water from the combustion process to the dilute sulfuric acid production process.

[0114] Thus, by adjusting the water content of the raw material, it is possible to adjust the concentration of the dilute sulfuric acid without adding water.

[0115] Effects of the Invention

[0116] According to the present application, it is possible to provide a dilute sulfuric acid production device and a dilute sulfuric acid production method that can produce dilute sulfuric acid at low cost. BRIEF DESCRIPTION OF DRAWINGS

[0117] Figure 1 is a schematic diagram showing the upstream side process of the dilute sulfuric acid production device of the present application.

[0118] Figure 2 is a schematic diagram showing the downstream side process of the dilute sulfuric acid production device of the present application.

[0119] Figure 3 is a schematic diagram showing the internal structure of the combustion means (combustion furnace) of the present application.

[0120] Figure 4 is a graph showing the simulation results of the combustion furnace 51.

[0121] Figure 5 is a schematic diagram showing the internal structure of the converter 61.

[0122] Figure 6 is a schematic diagram showing the internal structure of the combustion means (combustion furnace) of the embodiment of the present application.

[0123] Figure 7 is a system diagram of the equipment used in the example.

[0124] Figure 8 is a graph showing the results of the example.

[0125] Figure 9 is a graph showing the results of the example.

[0126] Figure 10 is a graph showing the results of the examples.

[0127] Figure 11 is a graph showing the results of the examples.

[0128] Figure 12 is a graph showing the results of the examples.

[0129] Figure 13 is a graph showing the results of the examples.

[0130] Figure 14 is a graph showing the results of the examples.

[0131] Figure 15 is a graph showing the results of the examples.

[0132] Figure 16 is a graph showing the results of the examples.

[0133] Figure 17 is a graph showing the results of the examples.

[0134] Figure 18 is a graph showing the results of the examples.

[0135] Figure 19 is a graph showing the corrosiveness of carbon steel with respect to sulfuric acid. DETAILED DESCRIPTION

[0136] The following describes the configuration of the embodiments of the present application. The present application can be suitably modified and implemented within the scope of the gist thereof.

[0137] 1. Dilute sulfuric acid manufacturing apparatus and dilute sulfuric acid manufacturing method

[0138] The following describes Figures 1 to 3 A dilute sulfuric acid manufacturing apparatus and a dilute sulfuric acid manufacturing method according to one embodiment of the present application are described. Figure 1 is a schematic view showing the upstream-side process of the dilute sulfuric acid manufacturing apparatus 40, Figure 1 is a schematic view showing the case where an oxygen-containing gas is supplied to the raw material (here, desulfurization waste liquid / molten sulfur). There are cases where an oxygen-containing gas is supplied and cases where air is supplied when refining COG.

[0139] Figure 2 is a schematic view showing the downstream-side process of the dilute sulfuric acid manufacturing apparatus 40. Note that the "dilute sulfuric acid" of the present application refers to an aqueous sulfuric acid solution having a sulfuric acid concentration of less than 90% by weight, including "dilute sulfuric acid (thin sulfuric acid)" (sulfuric acid amount 60 to 80% by weight) and "refined dilute sulfuric acid" (sulfuric acid amount 27 to 50% by weight) defined in JIS K1321.

[0140] As Figure 1 shown, the dilute sulfuric acid manufacturing apparatus 40 of the present embodiment includes means for supplying raw materials. The raw materials of the present embodiment include molten sulfur, desulfurization waste liquid, and refined COG as a combustion improver. The raw material supply means is means for supplying these raw materials into the combustion furnace 51. The dilute sulfuric acid manufacturing apparatus 40 of the present embodiment is provided with a pipe 41a that supplies molten sulfur as a raw material. The molten sulfur is a material obtained by bringing sulfur recovered from oil refineries and the like into a molten state. A pump 41b is connected to the pipe 41a, whereby the raw material is transported to a pipe 41c and supplied into the combustion furnace 51.

[0141] In addition, the dilute sulfuric acid manufacturing apparatus 40 is provided with a pipe 42 that supplies desulfurization waste liquid as a raw material. The desulfurization waste liquid is a waste liquid from a desulfurization device provided to remove coal dust, organic matter, sulfur-containing compounds, and the like from exhaust gas (crude COG) discharged from coke oven facilities and the like. Generally, the desulfurization waste liquid contains components such as free sulfur, free NH3, NH4SCN, (NH4)2S2O3, H2O, and the like. Among these, the water (H2O) is not particularly limited, but accounts for 50% by weight or more of the entire desulfurization waste liquid in many cases. The pipe 42 is in communication with the combustion furnace 51, and the desulfurization waste liquid is also supplied as a raw material into the combustion furnace 51.

[0142] Further, the dilute sulfuric acid manufacturing apparatus 40 is provided with a pipe 43 that supplies refined COG as a combustion improver. The refined COG is a gas generated in the process of manufacturing coke used in ironmaking and the like. Generally, the refined COG contains components such as H2, N2, O2, CO, CO2, CH4, C2H6, a small amount of sulfur-containing compounds, and the like. The pipe 43 is also in communication with the combustion furnace 51, and the refined COG is also supplied as a combustion improver into the combustion furnace 51.

[0143] The pipe 41a, the pump 41b, the pipe 41c, the pipe 42, and the pipe 43 correspond to the raw material and combustion improver supply means of the present invention, and the combustible raw material supply process is achieved by these means. Of the raw materials (molten sulfur, desulfurization waste liquid) supplied into the combustion furnace 51 by them, the desulfurization waste liquid contains, in addition to elemental sulfur, sulfur components such as (NH4)2S2O3 (10 to 40% by weight), nitrogen components such as NH3 (5 to 25% by weight), and moisture (40 to 80% by weight). In the case where, as in the present embodiment, there are a plurality of raw materials (for example, two in the present embodiment, molten sulfur and desulfurization waste liquid), the content of moisture is defined as the amount of mixing the moisture in each of the raw materials and the combustion improver.

[0144] A pipe 44a for supplying compressed air as a spray medium is connected to the pipe 41c and the pipe 42. A steam heater 44b is provided in the pipe 44a, and heated air is supplied to the pipe 41c, and micro-spray atomization for improving the combustion efficiency of the raw materials is performed. In addition, a pipe 45a for supplying air is provided in the dilute sulfuric acid production apparatus 40. The air supplied from the pipe 45a is delivered to a pipe 45c by a blower 45b.

[0145] Figure 1 In the pipe 45c, an oxygen generation device (PVSA 45d: vacuum-type pressure swing adsorption method) is provided, and high-concentration oxygen is supplied from the PVSA 45d. The PVSA 45d is a device that uses an adsorbent such as zeolite to adsorb and remove nitrogen from air under pressure, and efficiently obtains high-purity oxygen. The PVSA 45d can generate oxygen having a purity of 90 vol% or more. The oxygen is mixed with the air of the pipe 45a, and is supplied into the combustion furnace 51 as air having a high oxygen concentration. As the oxygen generation device 45d, a PSA method (pressure swing adsorption method) can be used. In addition, as an alternative, oxygen can be supplied by branching from an existing oxygen piping. Here, a pipe 45e is used for supplying oxygen-containing gas to the desulfurization waste liquid, and a pipe 45f is used for supplying oxygen-containing gas to the molten sulfur.

[0146] The pipe 45a, the blower 45b, the PVSA 45d, the pipe 45c, the pipe 45e, and the pipe 45f correspond to the oxygen-containing gas generation means of the present application, and the oxygen-containing gas generation step is achieved by these means. There is also a case where air is used instead of oxygen-containing gas in the pipe 45c, and this is shown by a dotted line. The oxygen-containing gas supplied to the combustion furnace 51 by them is adjusted to an oxygen concentration of 22 to 40 vol%, preferably 22 to 30 vol%, and more preferably 25 to 30 vol%.

[0147] The combustion furnace 51 (combustion means) performs a combustion step of combusting the raw materials with the oxygen-containing gas to generate combustion gas containing sulfur oxides (SOx) and 10 vol% or more of moisture. Figure 3 is a schematic view showing the internal structure of the combustion furnace 51. As shown in the drawing, a supply port 51a for supplying raw materials and oxygen-containing gas is provided at the upstream of the combustion furnace 51, and the raw materials are combusted inside, and combustion gas is discharged from a discharge port 51b at the downstream. In the present embodiment, molten sulfur is supplied from the supply port 51a at the upper stage, desulfurization waste liquid is supplied from the supply port 51a at the middle stage, and refined COG is supplied from the supply port 51a at the lower stage. Note that, in addition to the method of supplying raw materials from separate supply ports according to the kind of the raw materials as in the present embodiment, a part or all of the raw materials can be mixed in advance and the raw materials can be supplied to the combustion furnace 51 in this state.

[0148] The water evaporation zone is provided on the raw material supply side of the combustion furnace 51, and combustion of molten sulfur and refined COG and evaporation of water in the desulfurization waste liquid are mainly performed in this zone. Downstream of the water evaporation zone is the combustible combustion zone, in which combustibles in the desulfurization waste liquid are combusted. The water evaporation zone and the combustible combustion zone form a boundary. A checkered brick 51c is provided between the combustible combustion zone and the exhaust port 51b. In the checkered brick 51c, cubic heat-resistant bricks are arranged in a checkered pattern, and a portion of the checkered pattern is in an open state. The open ratio of the checkered brick 51c is preferably about 50%. The checkered brick 51c is often provided in multiple stages.

[0149] In the combustion furnace 51, more preferably, the oxygen concentration of the introduced oxygen-containing gas is in the range of 22 to 40 vol%, and preferably in the range of 22 to 30 vol%, the oxygen concentration in the combustion gas generated by the combustion furnace 51 is in the range of 2.0 to 7.0 vol%, and the SO3 conversion rate in the combustion gas generated by the combustion furnace 51 is in the range of 1.0 to 3.0%. The SO3 conversion rate is represented by the following formula.

[0150] SO3 conversion rate = (SO3 / SOx) x 100

[0151] (Here, SO3 is the volume concentration of SO3 contained in the above-mentioned combustion gas, and SOx is the volume concentration of SOx contained in the above-mentioned combustion gas).

[0152] By providing the checkered brick 51c downstream of the combustible combustion zone, in addition to reducing radiation to downstream instruments, the following functions can also be exhibited. Even if the mixing state of air and combustibles in the combustible combustion zone is insufficient, the checkered brick 51c physically promotes the re-mixing of air and combustibles in such a manner that the combustibles do not experience the blow-through phenomenon in the unburned state, and has the function of promoting the re-combustion of the heat retained by the bricks. For this purpose, it is preferable to provide the checkered brick 51c in multiple stages. In addition, the open portions of the stages of the checkered brick 51c are arranged in a staggered manner with respect to each other. Due to this, dust in the gas adheres and grows on the surface of the bricks and falls, and therefore it is preferable to provide the checkered brick 51c in the lowermost stage without an open portion, which accumulates and falls the dust.

[0153] Figure 6is a schematic view of an embodiment example of a means for supplying an oxygen-containing gas to the combustion furnace 51. As described in the figure, the combustion furnace at the supply port 51a of the raw material in which sulfur is burned is provided with a means for supplying an oxygen-containing gas from the line 45f, and the combustion furnace at the supply port 51a of the desulfurization waste liquid is provided with a means for supplying an oxygen-containing gas from the line 45e. In the path in which the refined COG is supplied to the combustion furnace 51, as shown in (b) in the figure, the combustion furnace at the supply port 51a of the refined COG is provided with a means for supplying an oxygen-containing gas from the line 45c. Generally, since the heat release amount of the desulfurization waste liquid is as low as less than 5000 kJ / kg, it is not easy to burn, but by supplying an oxygen-containing gas containing 22 to 40 vol% of oxygen to the combustion furnace, combustion can be promoted. On the other hand, for a raw material such as molten sulfur, which has a high heat release amount, only air can be supplied. Similarly, for the refined COG, only air can be supplied. It is preferable that the combustion control be performed independently for each of the two.

[0154] As the combustion temperature at which the raw material is burned in the combustion furnace 51, it is preferable to be in the range of 900 to 1100°C. The upper limit of the combustion temperature is preferably 1050°C or lower. In order to reduce the amount of NOx in the combustion gas, it is preferable that the combustion temperature be low, for example, 1025°C or lower, and further 100°C or lower. This is because, as will be described later, if the combustion temperature is increased, the NOx concentration increases. Figure 15

[0155] In the combustion furnace 51, the raw material is burned using an oxygen-containing gas having 22 to 40 vol% of oxygen, and thus, compared to a case in which the raw material is burned under the same conditions using normal air (oxygen concentration 21 vol%), it is possible to reduce the amount of NOx contained in the generated combustion gas. For example, the amount of NOx contained in the combustion gas when the raw material is burned using an oxygen-containing gas having an oxygen concentration of 22 to 40 vol% is set to NOx (rich) , and the amount of NOx contained in the combustion gas when the same raw material is burned under the same conditions using air having an oxygen concentration of 21 vol% is set to NOx (air) , it is possible to make the NOx reduction rate represented by the following equation 50 to 95%.

[0156] NOx reduction rate: NOx (rich) / NOx (air) x 100 (%)

[0157] Regarding the NOx reduction rate, it tends to decrease as the oxygen concentration increases, and it can be about 80% at an oxygen concentration of 25 vol%, and about 60% at an oxygen concentration of 30 vol%.

[0158] ​The combustion gas generated in the combustion furnace 51 is sent to a waste heat boiler 52 (Waste Heat Boiler: WHB) (cooling means). The waste heat boiler (1) 52 performs a cooling process of feeding water adjusted with a chemical to the boiler, evaporating the water with the combustion gas to generate steam, and cooling the combustion gas by heat exchange. The combustion gas is thereby cooled to a temperature of 380 to 460°C, and preferably about 420°C.

[0159] The waste heat boiler (1) 52 includes a boiler that cools the combustion gas. The waste heat boiler (1) 52 includes a water feeding means (water feeding process) that feeds water to the above-mentioned boiler, and a heat exchange means (heat exchange process) that evaporates the water from the water feeding means with the combustion gas to generate steam and cools the combustion gas by heat exchange. Further, the waste heat boiler (1) 52 of the present embodiment includes an outlet temperature adjusting means (outlet temperature adjusting process) that adjusts the outlet temperature of the converter 61 in the boiler to a temperature required for generating the reaction gas by the converter 61, and a constant temperature means (constant temperature process) that includes a boiler bypass and a regulating valve for fixing the outlet temperature against a variation in the outlet temperature of the boiler. The outlet temperature adjusting means includes a bypass pipe of the boiler and a bypass gas amount adjusting valve, and adjusts the amount of the high-temperature bypass gas to obtain the combustion gas of a prescribed temperature by mixing with the low-temperature gas at the outlet of the boiler. Note that the waste heat boiler (1) 52 can also include a recirculation means (recirculation process) that recovers the steam generated by the heat exchange means and reuses it as the water of the water feeding means.

[0160] The combustion gas cooled by the waste heat boiler (1) 52 is introduced into the converter 61 (reaction means). The combustion gas cooled by the waste heat boiler (1) 52 contains a small amount of nitrogen components (e.g., undecomposed NH3, NO, NO2, and the like, NOx). The converter 61 performs the following reaction using a catalyst provided in a plurality of stages (three stages in the drawing): oxidation of sulfur dioxide (SO2) in the combustion gas with oxygen to generate a reaction gas containing sulfur trioxide (SO3) (reaction process). In more detail, the converter 61 efficiently converts sulfur dioxide into sulfur trioxide (SO3) by the following method: oxidation (exothermic reaction) of sulfur oxides (SOx) with oxygen using a catalyst of a front stage of the plurality of stages, directly mixing the post-conversion gas warmed by the oxidation with atmospheric air drawn from the outside to lower it to a temperature suitable for catalytic reaction of a rear stage.

[0161] Figure 5Fig. 6 is a schematic diagram showing the internal structure of the converter 61, and (a) is a side view, (b) is a cross-sectional view of A-A' of (a), and (c) is an enlarged view of the dotted circle in (b). As shown in the figure, the converter 61 is provided with a main air pipe 61a through which atmospheric air is introduced, a branch air pipe 61b branched from the main air pipe 61a inside the device, and an air port 61d through which air is sent from the branch air pipe 61b into the device.

[0162] As the catalyst, a known catalyst used in the production of sulfuric acid can be used, and for example, vanadium pentoxide (V2O5) or the like can be given. Vanadium pentoxide has a denitration function, and NH3 and NOx are reacted and decomposed into nitrogen (N2) and water (H2O). Therefore, the production of sulfur trioxide and the decomposition of nitrogen components (NH3 and NOx) can be simultaneously performed using the present catalyst. At this time, in order to be used for denitration, NH3 can be injected. Since 60 to 80% of sulfur dioxide (SO2) is oxidized in the first stage of the converter 61, the temperature of the gas after the reaction is 500 to 600°C, and preferably about 540°C. In the second and third stages of the converter 61, the remaining sulfur dioxide (SO2) is oxidized to sulfur trioxide (SO3), but the inlet temperature of either stage is preferably 410 to 440°C, and the atmospheric air is directly mixed with the outlet gas of the previous stage to adjust the temperature.

[0163] Note that a denitration catalyst can be provided on the upstream side of the first stage of the converter 61 (the inflow side of the combustion gas from the waste heat boiler (1) 52), and as the denitration catalyst, a substance in which a catalytic aid is mixed in vanadium pentoxide can be used. As the catalytic aid, titanium oxide (TiO2) or the like, or a mixture thereof can be given. At the time of conversion of sulfur oxides, by providing the above-described denitration catalyst containing a catalytic aid, the decomposition reaction of nitrogen components is preferentially performed over the conversion of sulfur oxides, and the nitrogen components are decomposed. Thereafter, in the latter stage of the denitration catalyst, vanadium pentoxide not containing a catalytic aid can be used to effectively perform the conversion of sulfur oxides in a state not easily affected by nitrogen components.

[0164] In addition, the converter 61 can also use an indirect cooling means (not shown) for indirectly cooling the converted gas by heat exchange in combination with direct cooling. "Indirect cooling" is different from the case where the converted gas is directly cooled by mixing the atmospheric air drawn from the outside with the converted gas, and for example, refers to cooling in a case where a refrigerant does not directly contact the converted gas downstream of the first stage. The indirect cooling means is a device that implements a process (indirect cooling process) for performing indirect cooling. As the indirect cooling means, from the aspect of preventing the acid dew point of the heat transfer surface, a heat exchanger, a boiler, or the like using a vapor on the low temperature side is preferable.

[0165] The reaction gas generated by the converter 61 is sent to a waste heat boiler (2) 62 to be cooled. The waste heat boiler (2) 62 can use the same device as the waste heat boiler (1) 52 described above. The reaction gas is cooled to about 280 to 300°C by the waste heat boiler (2) 62, which is a temperature that avoids the sulfuric acid dew point of about 250°C. Note that the waste heat boiler (2) 62 is recommended to be provided from the viewpoint of energy efficient use, but is not an essential device in the present application and can be provided arbitrarily.

[0166] Next, as shown in FIG. 2, the reaction gas cooled by the waste heat boiler (2) 62 is sent to the bottom of a dilute sulfuric acid tower 71 (dilute sulfuric acid generation means) that performs a dilute sulfuric acid generation process. The dilute sulfuric acid tower 71 is a device that generates product dilute sulfuric acid by absorbing H2O and SO3 in the reaction gas into a circulating sulfuric acid aqueous solution (dilute sulfuric acid), and is also called an absorption tower. A packing is filled into the inside of the dilute sulfuric acid tower 71, and the sulfuric acid aqueous solution is sprayed from the upper portion of the tower toward the packing, and H2O and SO3 are absorbed by the sulfuric acid aqueous solution while the reaction gas passes between the packing. Figure 2 The sulfuric acid aqueous solution in which SO3 is absorbed is sent to a tank 73 (dilute sulfuric acid generation means), and after being cooled by a heat exchanger 74 (dilute sulfuric acid generation means) using cooling water from a cooling tower not shown, is stored as a final product in a tank 75. In the tank 75, the temperature of the sulfuric acid aqueous solution is reduced to about 50 to 60°C.

[0167] In addition, the sulfuric acid concentration of the sulfuric acid aqueous solution stored in the tank 75 as a final product is in the range of 50 to 70% by weight in many cases depending on the raw material that contains sulfuric acid components, nitrogen components, and 40 to 80% by weight or more of moisture. In the present embodiment, in order to provide value as a transaction commodity to the dilute sulfuric acid as a final product, the sulfuric acid concentration can also be increased to 70% by weight or more. The heat exchanger 74 (temperature control means) of the present embodiment can control the temperature of the circulating sulfuric acid aqueous solution from the dilute sulfuric acid tower 71 up and down. Also, in order to increase the sulfuric acid concentration of the final product, the degree of cooling in the heat exchanger 74 is reduced, and the temperature of the sulfuric acid aqueous solution sprayed from the upper portion of the dilute sulfuric acid tower 71 is increased from about 50 to 60°C to about 80 to 100°C, and preferably to about 80°C. Thus, the entrained water content in the outlet gas of the dilute sulfuric acid tower 71 is increased, and the sulfuric acid concentration of the sulfuric acid aqueous solution stored in the tank 75 can be increased to 70% by weight or more. In addition, the temperature of the sulfuric acid aqueous solution in the tank 75 is inevitably increased to 80 to 100°C.

[0168]

[0169] ​On the other hand, since the temperature of the circulating aqueous sulfuric acid solution is raised by the heat exchanger 74, corrosion becomes a problem. When the temperature of the aqueous sulfuric acid solution is raised, the corrosion increases. Therefore, if the temperature of the circulating aqueous sulfuric acid solution is raised, in the contact portions of the aqueous sulfuric acid solution such as the dilute sulfuric acid column 71, the heat exchanger 74, the tank 73, the tank 75, the piping, and the like, expensive materials (for example, lead, Hastelloy B2, Teflon (registered trademark) lining, and the like) having high corrosion resistance to sulfuric acid are required to be used. This results in an increase in the equipment cost.

[0170] Therefore, in the present embodiment, an aqueous sulfuric acid concentration device (sulfuric acid concentration means) for concentrating the aqueous sulfuric acid solution stored in the tank 75 can also be provided. The aqueous sulfuric acid concentration device can concentrate and increase the concentration of sulfuric acid contained in the aqueous sulfuric acid solution (sulfuric acid concentration step). As the aqueous sulfuric acid concentration device, a device that evaporates and concentrates water contained in the aqueous sulfuric acid solution by heating or the like can be given. By having such an aqueous sulfuric acid concentration device, the low-concentration aqueous sulfuric acid solution of 50 to 70% by weight in the tank 75 can be made into a high-concentration aqueous sulfuric acid solution of 70% by weight or more in the aqueous sulfuric acid concentration device. Thus, if the aqueous sulfuric acid solution of 50 to 70% by weight is obtained in the tank 75 without raising the temperature of the aqueous sulfuric acid solution circulating in the dilute sulfuric acid column 71, the heat exchanger 74, and the like, an aqueous sulfuric acid solution having a marketable concentration of 70% by weight or more can be obtained in the aqueous sulfuric acid concentration device. Therefore, in the equipment such as the dilute sulfuric acid column 71 and the heat exchanger 74, expensive materials having high corrosion resistance to sulfuric acid are not required to be used, or even if they are used, only a small scale (capacity) is required, so that the equipment can be made low in cost.

[0171] In addition, carbon steel is used in various product lines, but it has weak resistance to sulfuric acid corrosion, so it has a problem that corrosion occurs immediately if it contacts high-concentration and high-temperature sulfuric acid. Figure 19 is a graph showing the corrosion resistance of carbon steel (SS400 material) to sulfuric acid. The horizontal axis indicates the concentration of sulfuric acid (wt%), and the vertical axis indicates the corrosion rate. As shown in the graph, in the vicinity of 70 to 80% by weight of the concentration of sulfuric acid, the corrosion of carbon steel is reduced, and the corrosion rate is significantly reduced by lowering the temperature. That is, in any of the above methods, by lowering the temperature of the product sulfuric acid having a concentration of 70 to 80% by weight, carbon steel can be used.

[0172] A gas containing sulfuric acid mist, unreacted SO2, and the like is discharged from the top portion of the dilute sulfuric acid column 71. The discharged gas is recovered by a wet-type electric dust collector 76 or a mist eliminator, and is transported to the tank 73 as an aqueous sulfuric acid solution to be reused, and the remainder is transported to a decontamination column 81a (gas removal means) in which a gas removal step is performed.

[0173] The exhaust gas from the wet electric dust collector 76 or the mist eliminator is delivered to the bottom of the decontamination tower 81a and contacted with ammonia water introduced from the bottom. Unreacted SO2 in the exhaust gas reacts with ammonia to form ammonium sulfite ((NH4)2SO3: imido). The waste liquid containing ammonium sulfite is mostly recycled to the decontamination tower 81a by the pump 82, and a part thereof is air-oxidized by the oxidizing gas from the blower 83 by an in-line mixer or the like, and delivered to the tank 85 as ammonium sulfate ((NH4)2SO4: sulfamate) by the gas-liquid separator 84. The gas and the entrained mist from the decontamination tower 81a are cleaned by the circulating liquid of the decontamination tower 81b based on the pump 86, and the gas is exhausted from the decontamination tower 81b. The exhaust gas after decontamination does not contain SO2, but only N2, O2, CO2, and NOx within the limit value.

[0174] Note that, as the absorption neutralizer for unreacted sulfur dioxide (SO2) gas treatment (flue gas desulfurization), the desulfurization waste liquid can also be used to cause ammonia contained in the desulfurization waste liquid to react with sulfur dioxide. In this case, the desulfurization waste liquid after SO2 absorption is removed from the line 89 and returned to the line 42 ("desulfurization waste liquid return" in the figure), whereby the desulfurization waste liquid can be recycled as a raw material. Thus, the desulfurization waste liquid can be effectively utilized.

[0175] The exhaust gas is drawn / boosted by the blower 87 and exhausted to the atmosphere via the smoke stack 88. The blower 87 has a function of making all of the devices of the present dilute sulfuric acid manufacturing apparatus 40 negative pressure. Thus, temperature increase and emission of harmful gas to the atmosphere can be prevented. In addition, the blower 87 has a function of inducing air in the atmosphere without providing a special device in the converter 61. Dilute sulfuric acid manufacturing and exhaust gas treatment are performed as described above.

[0176] In the dilute sulfuric acid manufacturing apparatus and the dilute sulfuric acid manufacturing method of the present embodiment, dilute sulfuric acid having a concentration of less than 90% by weight can be produced using only moisture contained in raw materials without adding water (including water vapor) to the combustion gas, the reaction gas, and the aqueous sulfuric acid solution generated at least from the combustion means (combustion furnace 51) to the dilute sulfuric acid tower 71 (dilute sulfuric acid generation means). Thus, a water supply device required for dilute sulfuric acid manufacturing is not needed, and the cost of dilute sulfuric acid manufacturing can be reduced.

[0177] 2. Simulation

[0178] (1) Simulation of the entire dilute sulfuric acid manufacturing apparatus

[0179] For Figure 1 , Figure 2dilute sulfuric acid manufacturing apparatus 40, based on the set values shown in Table 1, using an electrolyte simulation program "OLI Flowsheet: ESP" (OLI systems, Inc.), a general-purpose process simulation program PRO / II (Honeywell International, Inc.), and a calculation software, ASPEN PLUS (ASPEN Technology, Inc.), simulation was performed. TM (AVEVA, Inc.), and a calculation software, ASPEN PLUS (ASPEN Technology, Inc.), simulation was performed.

[0180] For each of the apparatuses in the figure, the set values for the mass balance used the values of the following table.

[0181] [Table 1]

[0182]

[0183] For the raw materials, desulfurization waste liquid and COG, the set values for the components used the values of the following table.

[0184] [Table 2]

[0185]

[0186] [Table 3]

[0187]

[0188] The results of the above simulation are shown in the following table. The values surrounded by a diamond in the "Item" row of the table indicate the temperature, components, and the like at the position of the item, and the results are shown in the row below. Figure 1 , Figure 2

[0189] From the results, the concentration of the final dilute sulfuric acid was 67.4% by weight (Item 22). In addition, the same simulation was performed for the dilute sulfuric acid manufacturing apparatus 40 in which the oxygen concentration of the air introduced into the combustion furnace 51 was the same as the atmosphere, without the PVSA 45d. As a result, with respect to the combustion exhaust gas discharged from the combustion furnace 51 (Item 6) and the exhaust gas discharged to the stack 88 (Item 31), in the case with the PVSA 45d, 7829 Nm 3 / h (the following table) and 10951 Nm 3 / h (the following table), respectively. On the other hand, in the case without the PVSA 45d, the above items were 10365 Nm 3 / h and 13207 Nm 3 / h, respectively. From this, it was found that by using the PVSA 45d as in the present application, the oxygen concentration of the oxygen-containing gas was made as high as 25% by volume, and the amount of exhaust gas could be reduced by about 25%. As a result, for example, in the case of the reformer 61, the necessary amount of catalyst was calculated under the condition that the space velocity SV (unit, 1 / hr), which is the reciprocal of the time during which the gas contacts the catalyst layer per unit time, was substantially constant, and therefore, by reducing the amount of gas by 25%, the necessary amount of catalyst could be reduced by 25%.​

[0190] [Table 4]

[0191]

[0192] [Table 5]

[0193]

[0194] (2) Simulation of the combustion furnace 51

[0195] For the combustion furnace 51 of Figure 3 , a simulation was performed using a chemical reaction simulation software "CHEMKIN" (ANSYS Inc.). The conditions were as described below.

[0196] <Calculation conditions>

[0197] • The liquid substance was replaced with a gas.

[0198] • For the chemical species containing S, N2was replaced as an inert substance.

[0199] • The combustion furnace was in a plug flow state.

[0200] • The heat release associated with combustion was not taken into account.

[0201] • Analysis was performed for the cases with and without PVSA.

[0202] The composition at the inlet of the combustion furnace 51 was set to the values of the following table.

[0203] [Table 6]

[0204]

[0205] For the above composition, the input values for the simulation were set to the following values.

[0206] [Table 7]

[0207] [H2] kmol / h 0.2 [N2] kmol / h 208.0 O2 kmol / h 72.4 [CAT] kmol / h 0.1 CO2 kmol / h 0.0 H2O kmol / h 142.6 [CAT] kmol / h 32.3 Total kmol / h 455.7

[0208] The calculation conditions for the combustion furnace 51 were set to the following values.

[0209] [Table 8]

[0210]

[0211] The results of the simulation (graph) are shown in Figure 4The amount of NO generated at the outlet of the furnace without PVSA was taken as 1, and compared with the case with PVSA. As shown by NO in the figure, it was found that the amount of NOx generated was less in the case with PVSA. It was found that in the case without PVSA, NOx was generated at the inlet side of the combustion furnace due to the combustion of COG gas (CH4, H2, CO). As a reason for the decrease in the amount of NOx generated in the case with PVSA, it was presumed that the reason was that the generation of NOx from COG gas was suppressed in the case with PVSA.

[0212] Example

[0213] The present application will be specifically described below based on examples. However, they do not limit the purpose of the present application. The present examples were implemented mainly for the purpose of confirming the combustion characteristics of the raw material based on the oxygen-containing gas as the main part of the present patent, and experiments were performed using actual equipment with respect to the constitution of the raw material supply means, the oxygen-containing gas generation means, and the combustion means of the present application. Note that in the following examples, the correspondence with the terms of the present application is as shown below.

[0214] (Terms of the present application: terms in the examples)

[0215] • Raw material (desulfurization waste liquid): combustion liquid

[0216] • COG: COG (also written as coke oven gas)

[0217] • Oxygen-containing gas: oxygen-enriched air

[0218] • Combustion gas: exhaust gas (also written as combustion exhaust gas, etc.)

[0219] • Combustion means: furnace (also written as cylindrical furnace, combustion furnace, etc.)

[0220] • Molten sulfur is not used in the raw material.

[0221] 1. Outline of experiments in the experimental furnace

[0222] Combustion experiments were performed using a cylindrical furnace.

[0223] (1) System diagram

[0224] The system diagram of the equipment used in the present test is shown in Figure 7 .

[0225] (2) Raw material specifications

[0226] The specifications of the combustion liquid and COG are as shown below.

[0227] [Table 9]

[0228] Combustion liquid (desulfurization waste liquid)

[0229] Temperature Normal temperature Composition (wt. %) S 3.2 NH3 0.4 NH4SCN 28 (NH4)2S2O3 7.9 (NH4)2SO4 10.3 H2O 50.2 Total 100

[0230] [Table 10]

[0231] COG

[0232] Temperature 30℃ Composition (dry vol. %) H2 52.7 N2 8.3 O2 0.5 CO 8.6 CO2 3.1 CH4 24.3 C2H6 2.4 Total 100

[0233] (3) Main instrument specifications

[0234] The main instruments are as described below.

[0235] [Table 11]

[0236] No. Instrument name 1 Combustion furnace 2 Combustion liquid burner 3 COG burner (preheating, combustion supporting sub burner) 4 Combustion liquid pump 5 Combustion liquid tank

[0237] (4) Regarding exhaust gas analysis

[0238] The exhaust gas analysis items are shown in the table below.

[0239] [Table 12]

[0240] Object of measurement Analytical instrument / method NOx Continuous analysis O2 Continuous analysis CO Continuous analysis [CAT] Neutralization titration SO2 Neutralization titration SO3 Neutralization titration

[0241] (5) Experimental outline

[0242] The operating conditions for each experiment are as described below.

[0243] The experiments described in the examples are cases where the oxygen concentration in the oxygen-containing gas was changed, and the comparative examples are cases where air was supplied. Note that the oxygen concentration in the table below indicates the oxygen concentration in the primary combustion air, and the exhaust gas temperature indicates the target value.

[0244] [Table 13]

[0245]

[0246] 1) Preheating operation

[0247] Preheating was performed by COG-only operation at the time of cold start.

[0248] 2) This experiment

[0249] According to the above "(5) Experimental outline", combustion experiments were performed by changing the operating conditions. Specifically, after confirming that the furnace was sufficiently preheated by COG-only operation, the combustion liquid was slowly supplied, and for the molten sulfur planned for the actual machine, COG was supplied in an amount that generated the corresponding heat. After setting the operating conditions, the exhaust gas composition was measured using an automatic analyzer and gas sampling / neutralization titration analysis.

[0250] 2. Experimental results

[0251] (1) Experimental results at a glance

[0252] The experimental results are shown in Table 14. It should be noted that, despite complete combustion of the raw materials, the oxygen concentration in the exhaust gas did not match the calculated value in this experiment. Assuming air leakage due to furnace aging, the combustion air volume was corrected to ensure the measured oxygen concentration in the exhaust gas was consistent with the input oxygen, and the experimental results were then compiled. Additionally, Figures 8 to 14 The temperature distribution inside the furnace is shown in the figure.

[0253] (2) Summary of experimental results

[0254] The experimental results are summarized below. It should be noted that the combustion exhaust gas temperature was calculated using... Figures 8 to 14 Furnace temperature No. 3.

[0255] [Table 14]

[0256] (a) Experimental results showed no oxygen enrichment (O2 = 21%).

[0257]

[0258] (b) Experimental results: oxygen-rich (O2 = 25%)

[0259]

[0260] (c) Experimental results: oxygen-rich (O2 = 30%)

[0261]

[0262] Note: NOx concentration (converted from O2 = 12%) represents the ratio of the measured value to the environmental limit value.

[0263] (3) Results of ammonia analysis of exhaust gas

[0264] The analytical value was confirmed to be below the titration limit of quantitation, and the ammonia concentration was below 1 ppm (below the detection limit). Furthermore, the exhaust gas temperature condition was confirmed to be 900°C, which is considered the most stringent condition for ammonia combustion.

[0265] 3. Evaluation of Results

[0266] (1) NO x Evaluation of generation quantity

[0267] The NOx concentrations in the exhaust gas are shown in Tables 14(a), (b), and (c) above. Figure 15 As shown, the higher the exhaust gas temperature, the higher the NO content. x The higher the value, the more confirmed NO is in every result. x It is well below the environmental limit value.

[0268] Based on the reduction of NOx levels in oxygen-enriched environments ( Figure 16 )

[0269] • At 1000°C, 950°C, a decrease in the amount of NOx generation due to oxygen enrichment was observed. This result is also consistent with the simulation.

[0270] It is presumed that this is based on a decrease in COG due to oxygen enrichment.

[0271] • At 900°C, the original amount of NOx generation is small, and no significant difference due to oxygen concentration was observed.

[0272] (2) Evaluation of SO3 conversion rate

[0273] Conversion of SO2 to SO3 is generally demonstrated using the following oxidation reaction formula (exothermic) and chemical equilibrium formula.

[0274] [Equation 1]

[0275]

[0276]

[0277]

[0278] Kp: Chemical equilibrium constant

[0279] pX: Partial pressure of each component X

[0280] These formulas indicate the following 2 points.

[0281] 1) The higher the temperature, the smaller the SO3 / SO2 ratio

[0282] 2) The higher the oxygen concentration, the larger the SO3 / SO2 ratio

[0283] First, it was observed that the higher the exhaust gas temperature, the more the SO3 conversion rate tends to decrease, and this was explained using the above-described 1 formula. On the other hand, the experimental results were collated using the oxygen concentration of the exhaust gas regardless of the oxygen enrichment rate, and the result obtained was Figure 17 According to this graph, the higher the oxygen concentration of the exhaust gas, the higher the SO3 conversion rate, and this was explained using the above-described 2 formula.

[0284] From the experimental results, it can be considered that the temperature and oxygen concentration of the exhaust gas in the post-stage region of the combustion furnace have an influence on the SO3 conversion rate compared to the oxygen partial pressure in the combustion zone. That is, the oxygen enrichment rate does not have an influence on the SO3 conversion rate, and the temperature and oxygen concentration of the exhaust gas at the furnace outlet have an influence on the SO3 conversion rate. It was thus confirmed that it is appropriate to evaluate the SO3 conversion rate not only using the combustion zone but also using the exhaust gas at the furnace outlet.

[0285] Note that the SO3 conversion rate is represented by the following formula.

[0286] SO3 conversion rate = (SO3 / SOx) x 100

[0287] (Here, SO3 is the volume concentration of SO3 contained in the above exhaust gas, and SOx is the volume concentration of SOx contained in the above exhaust gas).

[0288] Regarding the above chemical equilibrium constant (Kp), Bodenstein and Pohl's formula was presented, and the experimental results were evaluated using the formula. With regard to the partial pressure of each gas component obtained in the experiment, it was found that by correcting the exhaust gas temperature of the above 3 formulas, the measured value was approximately consistent with the value obtained from the 3 formulas. Figure 18 The measured value around the oxygen concentration of 6% and the equilibrium curve of the 3 formulas are shown in the middle.

[0289] (3) Evaluation of ammonia

[0290] Ammonia was not detected in the exhaust gas, and complete combustion of the desulfurization waste liquid was confirmed, and the ammonia concentration was lower than the environmental limit value.

[0291] 4. Summary

[0292] 1) Reduction of the amount of combustion exhaust gas based on oxygen enrichment

[0293] The effect of reducing the amount of exhaust gas based on oxygen enrichment was also confirmed in the experiment.

[0294] 2) Reduction of the amount of NOx based on oxygen enrichment

[0295] In oxygen-enriched combustion, the NOx concentration was a low value that satisfied the environmental limit value.

[0296] At 1000°C and 950°C, a reduction in the amount of NOx generated based on oxygen enrichment was observed. This result was also consistent with the simulation.

[0297] 3) Ammonia concentration

[0298] In oxygen-enriched combustion, the ammonia concentration was confirmed to be a low value that satisfied the environmental limit value.

[0299] 4) SO3 conversion rate based on oxygen enrichment

[0300] It was confirmed that oxygen enrichment had no effect on the SO3 conversion rate in the exhaust gas at the furnace outlet. The effect of the oxygen concentration in the exhaust gas on the conversion rate to SO3 was confirmed.

[0301] By adjusting the oxygen concentration in the exhaust gas, it is possible to reduce the exhaust gas flow rate by oxygen enrichment, and to make the SO3 conversion rate equivalent to that in air combustion.

[0302] The relationship between the oxygen enrichment and the exhaust gas amount (Wet) at an exhaust gas temperature of 950°C is shown in Table 15. As shown in this table, it was confirmed that the more the oxygen enrichment rate was increased, the more the exhaust gas amount could be reduced. In an actual apparatus, it was predicted that the exhaust gas flow could be reduced by about 30%.

[0303] [Table 15]

[0304] Reduction effect of exhaust gas amount due to oxygen enrichment

[0305]

[0306] Explanation of symbols

[0307] 40 dilute sulfuric acid manufacturing apparatus, 41a pipe (raw material supply means), 41b pump (raw material supply means), 41c pipe (raw material supply means), 42 pipe (raw material supply means), 43 pipe (raw material supply means), 44a pipe (oxygen-containing gas generation means), 44b steam heater (oxygen-containing gas generation means), 45a pipe (oxygen-containing gas generation means), 45b blower (oxygen-containing gas generation means), 45c pipe (oxygen-containing gas generation means), 45d PVSA (oxygen-containing gas generation means), 45e pipe, 51 combustion furnace (combustion means), 51a supply port, 51b exhaust port, 51c checkered brick, 52 exhaust heat boiler (1) (cooling means), 61 converter (reaction means), 61a main air pipe, 61b branch air pipe, 61c air port, 62 exhaust heat boiler (2), 71 dilute sulfuric acid tower (dilute sulfuric acid generation means), 73 tank (dilute sulfuric acid generation means), 74 heat exchanger (dilute sulfuric acid generation means), 75 tank, 76 wet-type electric dust collector, 81a decontamination tower (gas removal means), 81b decontamination tower (gas removal means), 82 pump, 83 blower, 84 gas-liquid separator, 85 tank, 86 pump, 87 blower, 88 smoke stack

Claims

1. A dilute sulfuric acid manufacturing apparatus, characterized in that, It includes: A raw material supply means that supplies a raw material containing at least a sulfur component, a nitrogen component, and 40 to 80% or more of moisture by weight; An oxygen-containing gas generation means that generates an oxygen-containing gas having an oxygen concentration of 22 to 40% by volume; combustion means for combusting the raw material with the oxygen-containing gas to generate a combustion gas containing sulfur oxides and 10% by volume or more of moisture, the sulfur oxides being SO x and 1 < x < 3. A cooling means that cools the combustion gas; The reaction means, using a catalyst, oxidize the sulfur oxide SO x oxidation, generating a reaction gas comprising sulfur trioxide SO3; and A dilute sulfuric acid generation means that cools the reaction gas to generate dilute sulfuric acid, The dilute sulfuric acid having a concentration of less than 90% by weight is generated using only the moisture of the raw material without adding water from the combustion means to the dilute sulfuric acid generation means.

2. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein The combustion gas generated by the combustion means has a smaller amount of nitrogen oxides than the combustion gas generated when the raw material is combusted under the same conditions using air having an oxygen concentration of 21% by volume.

3. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein There is no device for denitration between the combustion means and the reaction means.

4. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein The combustion means combusts the raw material at 900 to 1100°C.

5. The dilute sulfuric acid manufacturing apparatus as claimed in claim 4, wherein The combustion means combusts the raw material at 1050°C or lower.

6. The dilute sulfuric acid production apparatus according to claim 1, wherein In the combustion means, The oxygen concentration of the oxygen-containing gas introduced from the oxygen-containing gas generation means is in a range of 22 to 30% by volume, The oxygen concentration in the combustion gas generated by the combustion means is in a range of 2.0 to 7.0% by volume.

7. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein It further has a gas removal means that removes unreacted sulfur dioxide in the dilute sulfuric acid generation means.

8. The dilute sulfuric acid manufacturing apparatus as claimed in claim 7, wherein In the gas removal means, the unreacted sulfur dioxide is reacted with ammonia to generate ammonium sulfite (NH4)2SO3, which is recovered in the form of ammonium sulfate (NH4)2SO4 by oxidation.

9. The dilute sulfuric acid manufacturing apparatus as claimed in claim 8, wherein The ammonia is present in a case where sulfur dioxide is absorbed using aqueous ammonia and a case where sulfur dioxide is absorbed using ammonia contained in desulfurization waste liquid, at least a part of which is recirculated as the raw material after being reacted with the unreacted sulfur dioxide.

10. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein The combustion means is a combustion furnace having a lattice brick with a part of the inside opened.

11. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein In the reaction means, the catalyst is vanadium pentoxide V2O5, which has a denitration function.

12. The dilute sulfuric acid manufacturing apparatus as claimed in claim 11, wherein The reaction means further has a denitration catalyst containing titanium oxide TiO2 as a catalytic aid in addition to the catalyst.

13. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein The reaction means has the catalyst provided in a plurality of stages, performs the oxidation of the sulfur oxides using the catalyst in the front stage of the plurality of stages, directly mixes the converted gas, which is warmed by an exothermic reaction based on the oxidation, with the atmosphere drawn from the outside to lower it to a temperature suitable for the catalytic reaction of the rear stage, thereby lowering the temperature of the converted gas without a heat exchanger.

14. The dilute sulfuric acid manufacturing apparatus as claimed in claim 13, wherein In the reaction means, an indirect cooling means that indirectly cools the converted gas using a heat exchanger is combined with the direct mixing based on the atmosphere.

15. The dilute sulfuric acid manufacturing apparatus as claimed in claim 1, wherein In the combustion means, the oxygen-containing gas is supplied to the raw material of less than 5000 kJ / kg to be combusted, and in the case of supplying the raw material of 5000 kJ / kg or more and a combustion supporting agent, air is supplied to the combustion supporting agent to be combusted.

16. The dilute sulfuric acid producing apparatus as claimed in claim 1, wherein In the combustion means, the oxygen-containing gas is supplied to the raw material of less than 5000 kJ / kg to be combusted, and in the case of supplying the raw material of less than 5000 kJ / kg, even if the raw material of 5000 kJ / kg or more and a combustion supporting agent are supplied, the oxygen-containing gas is supplied to be combusted.

17. The dilute sulfuric acid producing apparatus as claimed in claim 1, wherein In the dilute sulfuric acid generating means, the concentration of the dilute sulfuric acid is adjusted by up and down control of the temperature of the aqueous sulfuric acid solution.

18. The dilute sulfuric acid producing apparatus as claimed in claim 1, wherein Further, the sulfuric acid concentration means is provided to concentrate the concentration of the dilute sulfuric acid generated by the dilute sulfuric acid generating means to 70 to 80% by weight.

19. The dilute sulfuric acid producing apparatus as claimed in claim 1, wherein In the dilute sulfuric acid generating means, the generated aqueous sulfuric acid solution is directly contacted with the reaction gas to cool the reaction gas, and there is no equipment for indirectly cooling the reaction gas.

20. The dilute sulfuric acid manufacturing apparatus according to claim 1, wherein The cooling means is a waste heat boiler having a boiler, and the waste heat boiler has: a water supply means for supplying water to the boiler; and a heat exchange means for evaporating the water by the combustion gas to generate steam, and for cooling the combustion gas by heat exchange.

21. The dilute sulfuric acid manufacturing apparatus as claimed in claim 20, wherein The waste heat boiler further has an outlet temperature adjusting means including a boiler bypass for fixing the outlet temperature of the boiler against variation of the outlet temperature, and a regulating valve.

22. The dilute sulfuric acid producing apparatus as claimed in claim 1, wherein In the dilute sulfuric acid generating means, the concentration of the dilute sulfuric acid generated by the dilute sulfuric acid generating means is adjusted by adjusting the water content of the raw material without adding water from the combustion means to the dilute sulfuric acid generating means.

23. A method for producing dilute sulfuric acid, characterized by, It includes the following steps: a raw material supply step of supplying a raw material containing at least a sulfur component, a nitrogen component, and 40 to 80% by weight or more of moisture; an oxygen-containing gas generating step of generating an oxygen-containing gas having an oxygen concentration of 22 to 40% by volume; a combustion step of combusting the raw material with the oxygen-containing gas to produce a combustion gas containing sulfur oxides and 10% by volume or more of moisture, the sulfur oxides being SO x and 1≤x<3. a cooling step of cooling the combustion gas; In the reaction step, the sulfur oxides SOx are oxidized by means of a catalyst to form a reaction gas comprising sulfur trioxide SO3. x oxidized to form a reaction gas comprising sulfur trioxide SO3. a dilute sulfuric acid generating step of cooling the reaction gas to generate dilute sulfuric acid, less than 90% by weight of dilute sulfuric acid is generated using only the moisture of the raw material without adding water from at least the combustion step to the dilute sulfuric acid generating step.

24. The method for producing dilute sulfuric acid according to claim 23, wherein The amount of nitrogen oxides in the combustion gas generated by the combustion step is less than the amount of nitrogen oxides in the combustion gas generated when the raw material is combusted under the same conditions using air having an oxygen concentration of 21% by volume, by combusting the raw material using the oxygen-containing gas having an oxygen concentration of 22 to 40% by volume generated by the oxygen-containing gas generating step.

25. The method for producing dilute sulfuric acid according to claim 23, wherein There is no equipment for denitration between at least the combustion step and the reaction step.

26. The method for producing dilute sulfuric acid according to claim 23, wherein The combustion step combusts the raw material at 900 to 1100°C.

27. The method for producing dilute sulfuric acid according to claim 26, wherein The combustion step combusts the raw material at a temperature of 1050°C or less.

28. The dilute sulfuric acid manufacturing method according to claim 23, wherein In the combustion step, The oxygen concentration of the oxygen-containing gas introduced from the oxygen-containing gas generation step is in the range of 22 to 30 vol%, The oxygen concentration in the combustion gas generated by the combustion step is in the range of 2.0 to 7.0 vol%.

29. The method of producing dilute sulfuric acid according to Claim 23, wherein It further has a gas removal step for removing unreacted sulfur dioxide in the dilute sulfuric acid generation step.

30. The method for producing dilute sulfuric acid according to Claim 29, wherein In the gas removal step, the unreacted sulfur dioxide is reacted with ammonia to generate ammonium sulfite (NH4)2SO3, which is recovered in the form of ammonium sulfate (NH4)2SO4 by oxidation.

31. The method of producing dilute sulfuric acid according to Claim 30, wherein The ammonia is present in cases where sulfur dioxide is absorbed using aqueous ammonia and cases where sulfur dioxide is absorbed using ammonia contained in desulfurization waste liquid, and the latter desulfurization waste liquid is recirculated as the raw material after being reacted with the unreacted sulfur dioxide.

32. The method of producing dilute sulfuric acid according to Claim 23, wherein The combustion step uses a combustion furnace having a lattice brick with a part of the inside opened.

33. The method of producing dilute sulfuric acid according to Claim 23, wherein In the reaction step, the catalyst is vanadium pentoxide V2O5, which has a denitration function.

34. The method of producing dilute sulfuric acid according to claim 33, wherein The reaction step further has a denitration catalyst containing titanium oxide TiO2 as a catalytic aid in addition to the catalyst.

35. The method of producing dilute sulfuric acid according to Claim 23, wherein The reaction step has the catalyst provided in multiple stages, the oxidation of the sulfur oxides is performed using the catalyst in the first stage of the multiple stages, the converted gas, which is warmed by an exothermic reaction based on the oxidation, is directly mixed with the atmosphere drawn from the outside to lower it to a temperature suitable for catalytic reaction in the latter stages, and thus the temperature of the converted gas is lowered without a heat exchanger.

36. The method of producing dilute sulfuric acid according to claim 35, wherein In the reaction step, an indirect cooling step in which the converted gas is indirectly cooled using a heat exchanger is combined with the direct mixing with the atmosphere.

37. The method of producing dilute sulfuric acid according to Claim 23, wherein In the combustion step, the oxygen-containing gas is supplied to a raw material of less than 5000 kJ / kg for combustion, and in the case of supplying a raw material of 5000 kJ / kg or more and a combustion supporting agent, air is supplied to the combustion supporting agent for combustion.

38. The method of producing dilute sulfuric acid according to Claim 23, wherein In the combustion step, the oxygen-containing gas is supplied to a raw material of less than 5000 kJ / kg for combustion, and in the case of supplying a raw material of less than 5000 kJ / kg, even a raw material of 5000 kJ / kg or more and a combustion supporting agent, the oxygen-containing gas is supplied for combustion.

39. The method of producing dilute sulfuric acid according to Claim 23, wherein In the dilute sulfuric acid generation step, the concentration of the dilute sulfuric acid is adjusted by up-and-down control of the temperature of the aqueous sulfuric acid solution.

40. The method for producing dilute sulfuric acid according to Claim 23, wherein It further has a sulfuric acid concentration step for concentrating the concentration of the dilute sulfuric acid generated by the dilute sulfuric acid generation step to 70 to 80 wt%.

41. The method of producing dilute sulfuric acid according to Claim 23, wherein In the dilute sulfuric acid generation step, the generated aqueous sulfuric acid solution is used for direct contact cooling of the reaction gas, and there is no equipment for indirect cooling of the reaction gas.

42. The dilute sulfuric acid production method according to claim 23, wherein The cooling step uses a waste heat boiler having a boiler, and the waste heat boiler has: a feed water step for supplying water to the boiler; and a heat exchange step for evaporating the water using the combustion gas to generate steam and cooling the combustion gas by heat exchange. The cooling step uses a waste heat boiler having a boiler, and the waste heat boiler has: a feed water step for supplying water to the boiler; and a heat exchange step for evaporating the water using the combustion gas to generate steam and cooling the combustion gas by heat exchange.

43. The method of producing dilute sulfuric acid according to claim 42, wherein The waste heat boiler further has an outlet temperature adjusting step including a boiler bypass for fixing an outlet temperature of the boiler against variation of the outlet temperature, and a regulating valve.

44. The method of producing dilute sulfuric acid according to Claim 23, wherein In the dilute sulfuric acid production step, the concentration of the dilute sulfuric acid produced by the dilute sulfuric acid production step is adjusted without adding water from the combustion step up to the dilute sulfuric acid production step by adjusting the water content of the raw material.

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