Sulfuric acid production device and sulfuric acid production method

Abstract

The present invention relates to a sulfuric acid production device provided with: a line (41) for supplying a raw material containing at least a sulfur component; a conduit (45) into which the first refrigerant is introduced; a combustion furnace (51) that combusts the starting material and generates a combustion gas containing sulfur oxides; a waste heat boiler (52) that cools the combustion gas by heat exchange with the first refrigerant that has been heated; a converter (61) for generating a reaction gas containing sulfur trioxide and water by oxidizing the sulfur oxide with a catalyst; a cooler (62) that cools the reaction gas by heat exchange with the second refrigerant; a dilute sulfuric acid tower (71) for absorbing sulfur trioxide and water contained in the cooled reaction gas into the sulfuric acid aqueous solution to generate dilute sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; and a heat exchange means (63) for preparing a heated first refrigerant and a cooled second refrigerant by heat exchange between the heated second refrigerant and the first refrigerant, and supplying either the heated first refrigerant or the cooled second refrigerant to the waste heat boiler (52).

Description

Technical Field

[0001] The present invention relates to a sulfuric acid production device and a sulfuric acid production method. Background Art

[0002] Sulfuric acid (H2SO4) is a strong acid that is manufactured in large quantities and used in various fields. Sulfuric acid is roughly divided into industrial concentrated sulfuric acid with a sulfuric acid concentration of more than 90% by weight and industrial dilute sulfuric acid with a sulfuric acid concentration of less than 90% by weight, each with different properties. Among them, dilute sulfuric acid is strongly acidic, but unlike concentrated sulfuric acid, it has no oxidation or dehydration effect. On the other hand, it shows strong corrosiveness to metal materials and the like. Dilute sulfuric acid is used in various applications such as industrial products, medicines, pesticides, reagents, etc.

[0003] The production of sulfuric acid requires a raw material containing sulfur. As raw materials, desulfurized waste liquid and regenerated sulfur from the gas (coke oven gas (COG) hereinafter referred to as "COG") generated in the production process of coke used in steelmaking and the like, and gas containing SOx discharged from the copper refining process are used.

[0004] As a method capable of producing dilute sulfuric acid at low cost, for example, the method of Patent Document 1 is known. In this document, a raw material containing a large amount of water in addition to sulfur and nitrogen is used as a raw material, and an oxygen-containing gas with a high oxygen concentration is introduced into a combustion unit. In the combustion unit (combustion furnace), the raw material is burned to generate sulfur oxides (SO x :Here, 1≤x<3) and water combustion gas, the combustion gas is cooled by a cooling unit (waste heat boiler) and introduced into a reaction unit (converter). In the reaction unit (converter), sulfur oxides are oxidized by a catalyst to generate sulfur trioxide (SO3), and the reaction gas is cooled by a dilute sulfuric acid generating unit (dilute sulfuric acid tower) to generate dilute sulfuric acid.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-31305 (Claim 1, paragraph 0062, etc.) Summary of the invention

[0008] Problems to be solved by the invention

[0009] In Patent Document 1, the gas is transported in the order of a combustion furnace, a converter, and a dilute sulfuric acid tower. The raw material is burned at 950 to 1000°C in the combustion furnace, so the generated combustion gas is high temperature. The reaction in the converter is also an exothermic reaction, so the temperature of the gas rises. However, the dilute sulfuric acid aqueous solution as the final product is an aqueous solution stored at room temperature, so a cooling unit is required to cool the gas at any time during the process. In this document, a waste heat boiler is provided as such a cooling unit, and the combustion gas is cooled by heat exchange between a refrigerant (water) and the combustion gas.

[0010] However, although sulfuric acid is contained in the gas in the form of sulfuric acid gas (H2SO4), if the temperature of the gas drops, it becomes an aqueous sulfuric acid solution as an aqueous solution. Aqueous sulfuric acid solution is a strong acid and is highly corrosive to metals. If, in order to avoid this, the piping and equipment in the process are made of raw materials with high corrosion resistance, the equipment becomes expensive and the cost of manufacturing dilute sulfuric acid increases. On the contrary, if metals with low corrosion resistance are used for piping, etc., the equipment becomes cheap and the manufacturing cost of dilute sulfuric acid decreases. However, in such a case, in order to avoid corrosion of piping, etc., it is required to adjust the temperature of the refrigerant when cooling the gas so that the sulfuric acid gas (H2SO4) does not become an aqueous sulfuric acid solution. In the waste heat boiler of this document, since the sulfuric acid gas (H2SO4) is operated using a high-temperature and high-pressure refrigerant (water) that does not become an aqueous sulfuric acid solution, although cheap and low-corrosion-resistant metals can be used, in order to cope with high temperatures and high pressures, expensive equipment with a specially designed structure is required.

[0011] On the other hand, the document does not specifically mention the waste heat generated when cooling the gas. In the production of dilute sulfuric acid, it is desirable to improve the heat recovery rate, effectively utilize the waste heat, obtain dilute sulfuric acid at a higher conversion rate, and reduce the sulfur dioxide discharged into the atmosphere. In addition, the waste heat boiler of the document directly supplies low-temperature pure water into the boiler to cool the combustion gas, so the amount of steam generated from the waste heat boiler is reduced, and the amount of steam that can be effectively used is reduced.

[0012] The object of the present invention is to provide a sulfuric acid production device and a sulfuric acid production method, which can not only produce sulfuric acid at a low cost, but also obtain sulfuric acid at a higher recovery rate, reduce sulfur dioxide released into the atmosphere, and effectively utilize waste heat.

[0013] Means for solving problems

[0014] The present inventors have discovered that by performing a predetermined heat exchange using a predetermined refrigerant multiple times, sulfuric acid can be produced inexpensively and sulfuric acid can be obtained at a higher recovery rate to reduce sulfur dioxide discharged into the atmosphere, thereby effectively utilizing waste heat, thereby completing the present invention.

[0015] The present invention relates to a sulfuric acid manufacturing device, characterized in that it comprises: a raw material supply unit for supplying a raw material containing at least sulfur components; a combustion unit for burning the raw material to generate a combustion gas containing sulfur oxides; a refrigerant introduction unit for introducing a first refrigerant; a combustion gas cooling unit for cooling the combustion gas by heat exchange with the refrigerant; a reaction unit for oxidizing the sulfur oxides by using a catalyst to generate a reaction gas containing sulfur trioxide and water; a reaction gas cooling unit for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery unit for absorbing sulfur trioxide and water contained in the reaction gas after cooling into a sulfuric acid aqueous solution to generate sulfuric acid and discharging a discharge gas containing sulfur dioxide and oxygen; and a heat exchange unit for preparing the first refrigerant after heating and the second refrigerant after cooling by heat exchange between the second refrigerant heated by heat exchange with the reaction gas and the first refrigerant, and supplying any one of the first refrigerant after heating and the second refrigerant after cooling as the refrigerant to the combustion gas cooling unit.

[0016] In the present invention, a combustion gas cooling unit for cooling the combustion gas, a reaction gas cooling unit for cooling the reaction gas, and a heat exchange unit are provided. In the heat exchange unit, the second refrigerant heated by the heat exchange with the reaction gas is heat exchanged with the first refrigerant. Thus, the first refrigerant heated to be used in the combustion gas cooling unit is prepared, and waste heat can be effectively utilized. In addition, since the first refrigerant is heated to cool the combustion gas, the amount of steam generated by cooling the combustion gas increases, and as a result, there is an advantage that the amount of steam that can be effectively used increases.

[0017] In the present invention, in the combustion gas cooling unit, the temperature of the first refrigerant after the temperature increase is higher than the acid dew point of the combustion gas, and in the reaction gas cooling unit, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

[0018] Thus, in the combustion gas cooling unit and the reaction gas cooling unit, since a refrigerant having a temperature higher than the acid dew point of the target gas for heat exchange is used, the gas is not cooled to a temperature lower than the acid dew point by these units to form a highly corrosive sulfuric acid aqueous solution. Therefore, even relatively inexpensive metal pipes and the like can be used for the production of sulfuric acid, and sulfuric acid can be produced inexpensively.

[0019] In addition, in the present invention, the heat exchange unit comprises: a refrigerant conveying path for conveying the second refrigerant after the temperature increase; a preheater to which the first refrigerant is supplied, and the first refrigerant is heated by heat exchange with the second refrigerant after the temperature increase, and is supplied to the combustion gas cooling unit; and

[0020] The refrigerant return path returns the second refrigerant after heat exchange with the first refrigerant from the preheater to the reaction gas cooling unit.

[0021] By configuring the heat exchange unit in this manner, the temperature of the first refrigerant can be raised while the second refrigerant circulates, and the second refrigerant can be effectively used for both cooling the reactive gas and raising the temperature of the first refrigerant.

[0022] The refrigerant return path may further supply a part of the second refrigerant to the combustion gas cooling unit.

[0023] Thereby, a part of the second refrigerant can also be used as a refrigerant for cooling the combustion gas.

[0024] The refrigerant return path includes a tank storing the second refrigerant and a pump supplying the second refrigerant to the reaction gas cooling unit.

[0025] The second refrigerant is preferably an organic refrigerant that is liquid at least in the range of -20°C to 350°C.

[0026] When a substance that is solid at room temperature, such as molten salt, is used as a refrigerant, it solidifies at room temperature and loses its function as a refrigerant. An organic refrigerant that is liquid at least in the range of -20°C to 350°C will not solidify in the heat exchange unit, so heat exchange with the reaction gas can be stably continued.

[0027] Preferably, the first refrigerant is water, and the second refrigerant is a mixture of biphenyl and biphenyl ether.

[0028] The heat exchange unit is preferably a smoke tube type. In addition, the combustion gas cooling unit is preferably a water tube type suitable for combustion gas containing dust, but if the combustion gas does not contain dust, a part of the second refrigerant is supplied to the combustion gas cooling unit and a part of the second refrigerant is used as a refrigerant for cooling the combustion gas, so that the refrigerant return path can be suitable for a smoke tube type.

[0029] By making the heat exchange unit into an inexpensive smoke tube type, the cost of sulfuric acid production can be reduced. On the other hand, regarding the combustion gas cooling unit, sometimes the combustion gas transported from the combustion unit contains adhesive dust, so if the dust adheres to the inside of the unit on the downstream side, a blockage failure may occur. In the case of a water tube boiler, the dust adheres to the outer surface of the tube where water flows, so the tube will not be blocked. In addition, the dust attached to the outer surface of the tube can also be easily removed by, for example, soot blowing.

[0030] Furthermore, the sulfuric acid production apparatus of the present invention preferably includes means for negative pressure operation.

[0031] By performing negative pressure operation, oxygen in the atmosphere is attracted to the reaction unit even without installing special equipment. The oxygen attracted in this way promotes the catalytic reaction in the reaction unit, so the cumulative conversion rate reaches a high value of more than 98.9%. In addition, by performing negative pressure operation, it is also possible to prevent hot and harmful gases from flowing into the atmosphere.

[0032] In this case, it is preferable to further include: a hot air introduction unit for introducing hot air into the reaction unit; and a purge flow path for purging the reaction gas remaining in the reaction unit upstream of the sulfuric acid recovery unit.

[0033] By introducing hot air into the reaction unit, the reaction unit can be preheated before the equipment is put into operation. By preheating to the reaction temperature in advance, the operation start-up time can be shortened to less than half the time. The introduction of hot air is also effectively used for purging the reaction unit during maintenance. Due to negative pressure operation, the hot air is sucked into the reaction unit, and it is difficult to produce a biased flow of hot air inside the reaction unit. In the reaction unit, the local generation of sulfuric acid liquid and catalyst melt adhesion is avoided.

[0034] It should be noted that when hot air is introduced into the reaction unit in a device that is operated under pressure rather than under negative pressure, the hot air is biased, so it is difficult to evenly purge the entire area in the reaction unit. Areas that the hot air does not reach are locally generated in the reaction unit, and sulfuric acid liquid and catalyst melt adhesions are locally generated. In order to make the device operate normally, it is necessary to discharge them outside the system for screening and differentiation, and only refill the normal catalyst, which is a complicated operation.

[0035] Therefore, by performing negative pressure operation and introducing hot air into the reaction unit, the equipment can be operated again after the hot air purge without the need for work such as catalyst sorting.

[0036] It is preferable to further include a sulfur dioxide recovery unit for recovering sulfur dioxide contained in the exhaust gas.

[0037] In this way, sulfur dioxide contained in the exhaust gas is recovered, so that the harm of sulfur dioxide can be eliminated without releasing it into the environment.

[0038] In this case, it is preferred that the sulfur dioxide recovery unit absorbs the sulfur dioxide contained in the exhaust gas into water to generate sulfurous acid, and oxidizes the sulfurous acid with oxygen contained in the exhaust gas to generate sulfuric acid.

[0039] In this way, sulfur dioxide in the exhaust gas can be absorbed into water to generate sulfurous acid, which can then be oxidized and recovered as sulfuric acid. Since the exhaust gas contains about 10% oxygen, this oxygen can be used to oxidize sulfuric acid, and there is no need to add an oxidant as in the past. In addition to improving the recovery rate of sulfuric acid, it is also possible to reduce the sulfur dioxide released into the atmosphere.

[0040] The present invention relates to a method for producing sulfuric acid, characterized in that it comprises: a raw material supplying step for supplying a raw material containing at least a sulfur component; a combustion step for burning the raw material to generate a combustion gas containing sulfur oxides; a refrigerant introducing step for introducing a first refrigerant; a combustion gas cooling step for cooling the combustion gas by heat exchange with the refrigerant; a reaction step for oxidizing the sulfur oxides by using a catalyst to generate a reaction gas containing sulfur trioxide and water; a reaction gas cooling step for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery step for absorbing sulfur trioxide and water contained in the reaction gas after cooling into a sulfuric acid aqueous solution to generate sulfuric acid and discharging a discharge gas containing sulfur dioxide and oxygen; and a heat exchange step for preparing the first refrigerant after heating and the second refrigerant after cooling by heat exchange between the second refrigerant heated by heat exchange with the reaction gas and the first refrigerant, and supplying any one of the first refrigerant after heating and the second refrigerant after cooling as the refrigerant to the combustion gas cooling step.

[0041] The present invention includes a cooling step for cooling the combustion gas and a heat exchange step for cooling the reaction gas. The heat exchange step performs heat exchange between the second refrigerant heated by heat exchange with the reaction gas and the first refrigerant. Thus, the first refrigerant heated to be used in the cooling step is prepared, and waste heat can be effectively utilized. In addition, since the first refrigerant is heated to cool the combustion gas, the amount of steam generated by cooling the combustion gas increases, and as a result, there is an advantage that the amount of steam that can be effectively used increases.

[0042] In addition, preferably, in the combustion gas cooling step, the temperature of the heated first refrigerant is higher than the acid dew point of the combustion gas, and in the reaction gas cooling step, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

[0043] Thus, in the cooling process and the heat exchange process, since a refrigerant having a temperature higher than the acid dew point of the target gas for heat exchange is used, the gas is not cooled to a temperature lower than the acid dew point in these processes to form a highly corrosive sulfuric acid aqueous solution. Therefore, even relatively cheap metal pipes and the like can be used for the production of sulfuric acid, and sulfuric acid can be produced cheaply.

[0044] The heat exchange process includes: a process of cooling the reaction gas by heat exchange with the second refrigerant; a transport process of transporting the heated second refrigerant; a preheating process of heating the first refrigerant in the preheater by heat exchange with the heated second refrigerant and supplying it to the combustion gas cooling process; and a refrigerant return process of returning the second refrigerant after heat exchange with the first refrigerant for heat exchange with the reaction gas.

[0045] By providing the heat exchange step in this manner, the temperature of the first refrigerant can be raised while the second refrigerant is circulated, and the second refrigerant can be effectively used for both cooling the reactive gas and raising the temperature of the first refrigerant.

[0046] The refrigerant returning step may further supply a part of the second refrigerant to the combustion gas cooling unit.

[0047] Thereby, a part of the second refrigerant can also be used as a refrigerant for cooling the combustion gas.

[0048] The refrigerant returning step includes: a step of storing the second refrigerant; and a step of supplying the second refrigerant to the reaction gas cooling step.

[0049] As the second refrigerant, it is preferable to use an organic refrigerant that is liquid at least in the range of -20°C to 350°C.

[0050] When a substance that is solid at room temperature, such as molten salt, is used as a refrigerant, it solidifies at room temperature and loses its function as a refrigerant. An organic refrigerant that is liquid at least in the range of -20°C to 350°C will not solidify in the heat exchange unit, so heat exchange with the reaction gas can be stably continued.

[0051] It is preferable to use water as the first refrigerant and to use a mixture of biphenyl and biphenyl ether as the second refrigerant.

[0052] The heat exchange unit is preferably a smoke tube type. In addition, the combustion gas cooling unit is preferably a water tube type suitable for combustion gas containing dust, but if the combustion gas does not contain dust, a part of the second refrigerant is supplied to the combustion gas cooling unit and a part of the second refrigerant is used as a refrigerant for cooling the combustion gas, so that the refrigerant transport and refrigerant return units can be applied to the smoke tube type.

[0053] Sometimes the combustion gas delivered from the combustion process contains adherent dust, so if it adheres to the inside of the downstream process, it may cause clogging. In the case of a water tube boiler, the dust adheres to the outer surface of the tube where water flows, so the dust can be easily removed by soot blowing.

[0054] In the present invention, negative pressure operation is preferably performed, but pressurized operation may be performed in some cases.

[0055] By performing negative pressure operation, oxygen in the atmosphere is attracted to the reaction process even without installing special equipment. The oxygen attracted in this way promotes the catalytic reaction in the reaction process, so the cumulative conversion rate reaches a high value of more than 99%. In addition, by performing negative pressure operation, it is also possible to prevent hot and harmful gases from flowing into the atmosphere.

[0056] It is preferable to further include a sulfur dioxide recovery step of recovering sulfur dioxide contained in the exhaust gas.

[0057] In this way, sulfur dioxide contained in the exhaust gas is recovered, so that the harm of sulfur dioxide can be eliminated without releasing it into the environment.

[0058] In this case, it is preferred that the sulfur dioxide recovery step absorbs the sulfur dioxide contained in the exhaust gas into water to generate sulfurous acid, and oxidizes the sulfurous acid with oxygen contained in the exhaust gas to generate sulfuric acid.

[0059] In this way, sulfur dioxide in the exhaust gas can be absorbed into water to generate sulfurous acid, which can then be oxidized and recovered as sulfuric acid. Since the exhaust gas contains about 10% oxygen, this oxygen can be used to oxidize sulfuric acid, and there is no need to add an oxidant as in the past. In addition to improving the recovery rate of sulfuric acid, it is also possible to reduce the sulfur dioxide released into the atmosphere.

[0060] The present invention also relates to a maintenance method, characterized in that, while performing negative pressure operation, hot air is introduced from the hot air introduction unit to the reaction unit, the reaction gas remaining in the reaction unit is purged upstream of the sulfuric acid recovery unit, and the obtained purge gas is introduced into the sulfur dioxide recovery unit.

[0061] In a device that is operated under pressure, when hot air is introduced into a reaction unit, the hot air is biased, making it difficult to evenly purge the entire area in the reaction unit. Areas that are not reached by the hot air are locally generated in the reaction unit, and sulfuric acid liquid and catalyst melt adhesions are locally generated. In order to operate the device normally, it is necessary to discharge them outside the system for screening and separation, and then refill only the normal catalyst, which is a complicated operation.

[0062] During maintenance, hot air is introduced into the reaction unit while performing negative pressure operation to purge the reaction gas remaining in the reaction unit, thereby preventing acid dew point generation by cooling the purge gas based on latent heat.

[0063] <Inventions of the Basic Application>

[0064] [1] A sulfuric acid production device, the sulfuric acid production device comprising:

[0065] A raw material supply unit supplies a raw material containing at least sulfur;

[0066] A combustion unit that burns the raw material to generate a combustion gas containing sulfur oxides;

[0067] a cooling unit for cooling the combustion gas by heat exchange with the first refrigerant having a raised temperature;

[0068] A reaction unit, which oxidizes the sulfur oxides using a catalyst to generate a reaction gas containing sulfur trioxide and water;

[0069] a heat exchange unit for cooling the reaction gas by heat exchange with a second refrigerant;

[0070] a sulfuric acid recovery unit that absorbs sulfur trioxide and water contained in the cooled reaction gas into a sulfuric acid aqueous solution to generate sulfuric acid and discharges exhaust gas containing sulfur dioxide and oxygen,

[0071] The sulfuric acid production device is characterized in that

[0072] The heat exchange unit prepares the first refrigerant after the temperature is increased for use in the cooling unit by heat exchange between the second refrigerant whose temperature is increased by heat exchange with the reaction gas and the first refrigerant.

[0073] [2] The sulfuric acid production apparatus as described in [1] is characterized in that in the cooling unit, the temperature of the first refrigerant after the temperature increase is higher than the acid dew point of the combustion gas, and in the heat exchange unit, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

[0074] [3] The sulfuric acid production apparatus according to [1], wherein the heat exchange unit comprises:

[0075] a cooler for cooling the reaction gas by heat exchange with the second refrigerant;

[0076] a refrigerant transport path for transporting the second refrigerant heated by the heat exchange;

[0077] a preheater supplied with a first refrigerant, which heats up the first refrigerant by heat exchange with the second refrigerant whose temperature has been raised, and supplies the first refrigerant to the cooling unit; and

[0078] The refrigerant return path returns the second refrigerant after heat exchange with the first refrigerant from the preheater to the cooler.

[0079] [4] The sulfuric acid production apparatus according to [2], wherein the refrigerant return path comprises: a tank storing the second refrigerant; and a pump driving the second refrigerant to the cooler.

[0080] [5] The sulfuric acid production apparatus according to [1], wherein the second refrigerant is an organic refrigerant that is liquid at least in the range of -20°C to 350°C.

[0081] [6] The sulfuric acid production apparatus according to [1], wherein the first refrigerant is water and the second refrigerant is a mixture of biphenyl and biphenyl ether.

[0082] [7] The sulfuric acid production apparatus described in [1] is characterized in that the above-mentioned heat exchange unit is a smoke tube type.

[0083] [8] The sulfuric acid production apparatus according to [1], further comprising a unit for negative pressure operation.

[0084] [9] The sulfuric acid production apparatus according to [8], further comprising:

[0085] A hot air introduction unit for introducing hot air into the reaction unit; and

[0086] The purge flow path can purge the reaction gas remaining in the reaction unit upstream of the sulfuric acid recovery unit.

[0087]

[10] The sulfuric acid production apparatus according to [1] is characterized by further comprising a sulfur dioxide recovery unit that recovers sulfur dioxide contained in the exhaust gas.

[0088]

[11] The sulfuric acid production apparatus according to

[10] , wherein the sulfur dioxide recovery unit absorbs the sulfur dioxide contained in the exhaust gas into water to generate sulfurous acid, and oxidizes the sulfurous acid using oxygen contained in the exhaust gas to generate sulfuric acid.

[0089]

[12] A method for producing sulfuric acid, comprising:

[0090] A raw material supply unit supplies a raw material containing at least sulfur;

[0091] A combustion unit that burns the raw material to generate a combustion gas containing sulfur oxides;

[0092] a cooling unit for cooling the combustion gas by heat exchange with the first refrigerant having a raised temperature;

[0093] A reaction unit, which oxidizes the sulfur oxides using a catalyst to generate a reaction gas containing sulfur trioxide and water;

[0094] a heat exchange unit for cooling the reaction gas by heat exchange with a second refrigerant;

[0095] a sulfuric acid recovery unit that absorbs sulfur trioxide and water contained in the cooled reaction gas into a sulfuric acid aqueous solution to generate sulfuric acid and discharges exhaust gas containing sulfur dioxide and oxygen,

[0096] The method for producing sulfuric acid is characterized in that:

[0097] The heat exchange unit prepares the first refrigerant after the temperature is increased for use in the cooling step by heat exchange between the second refrigerant whose temperature is increased by heat exchange with the reaction gas and the first refrigerant.

[0098]

[13] The method for producing sulfuric acid as described in

[12] is characterized in that in the cooling step, the temperature of the first refrigerant after the temperature increase is higher than the acid dew point of the combustion gas, and in the heat exchange step, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

[0099]

[14] The method for producing sulfuric acid according to

[12] , wherein the heat exchange step comprises:

[0100] The step of cooling the reaction gas by heat exchange with the second refrigerant;

[0101] a step of conveying the second refrigerant heated by the heat exchange;

[0102] A step of raising the temperature of the first refrigerant by heat exchange with the second refrigerant having a raised temperature, and supplying the first refrigerant to the cooling step; and

[0103] The second refrigerant after exchanging heat with the first refrigerant is returned to be used for heat exchange with the reaction gas.

[0104]

[15] The sulfuric acid production method as described in

[14] is characterized in that the above-mentioned refrigerant return path includes: a step of storing the above-mentioned second refrigerant; and a step of driving the above-mentioned second refrigerant to the above-mentioned cooler.

[0105]

[16] The method for producing sulfuric acid as described in

[12] is characterized in that an organic refrigerant that is liquid at least in the range of -20°C to 350°C is used as the above-mentioned second refrigerant.

[0106]

[17] The method for producing sulfuric acid as described in

[12] is characterized in that water is used as the above-mentioned first refrigerant, and a mixture of biphenyl and diphenyl ether is used as the above-mentioned second refrigerant.

[0107]

[18] The method for producing sulfuric acid as described in

[12] is characterized in that the above-mentioned heat exchange step is carried out by a smoke tube type.

[0108]

[19] The method for producing sulfuric acid according to

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

[0109]

[20] The method for producing sulfuric acid according to

[12] is characterized by further comprising a sulfur dioxide recovery step for recovering sulfur dioxide contained in the exhaust gas.

[0110]

[21] The method for producing sulfuric acid as described in

[20] , wherein, in the sulfur dioxide recovery step, sulfur dioxide contained in the exhaust gas is absorbed into water to generate sulfurous acid, and the sulfurous acid is oxidized by oxygen contained in the exhaust gas to generate sulfuric acid.

[0111]

[22] A maintenance method, which is the maintenance method for the sulfuric acid production device described in

[10] above, characterized in that:

[0112] While performing negative pressure operation, hot air is introduced from the hot air introduction unit to the reaction unit, reaction gas remaining in the reaction unit is purged upstream of the sulfuric acid recovery unit, and the obtained purge gas is introduced into the sulfur dioxide recovery unit.

[0113] Effects of the Invention

[0114] According to the present invention, a sulfuric acid production apparatus and a sulfuric acid production method can be provided, which can produce sulfuric acid at a low cost, obtain sulfuric acid at a higher recovery rate, reduce sulfur dioxide released into the atmosphere, and effectively utilize waste heat. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] Figure 1 This is a schematic diagram showing an upstream process of a dilute sulfuric acid production apparatus which is one type of sulfuric acid production apparatus of the present invention.

[0116] Figure 2 This is a schematic diagram showing a downstream process of a dilute sulfuric acid production apparatus which is one type of sulfuric acid production apparatus of the present invention.

[0117] Figure 3It is a schematic diagram showing the internal structure of the combustion unit (combustion furnace).

[0118] Figure 4 : is a schematic diagram showing the hot air introduction unit.

[0119] Figure 5 is a schematic diagram showing the internal structure of the converter.

[0120] Figure 6 It is a cross-sectional view of a water tube boiler.

[0121] Figure 7 It is a graph showing the relationship between the SO 3 concentration in the gas, the water vapor concentration, and the estimated value of the sulfuric acid dew point.

[0122] Figure 8 This is a calculation chart for the equilibrium conversion rate of SO2→SO3.

[0123] Fig. 9 It is a schematic diagram showing the upstream process of the dilute sulfuric acid production apparatus according to the second embodiment.

[0124] Fig.10 It is a schematic diagram which shows the downstream process of the dilute sulfuric acid production apparatus of 2nd Embodiment. DETAILED DESCRIPTION

[0125] The following describes the structure of the embodiments of the present invention. The present invention can be implemented by changing appropriately within the scope of not changing its main points. It should be noted that, in the following embodiments, the manufacture of dilute sulfuric acid as a kind of sulfuric acid of the present invention is described, but the present invention is not limited thereto, and for example, can also be applied to the manufacture of concentrated sulfuric acid.

[0126] 1. Apparatus and method for producing dilute sulfuric acid (first embodiment)

[0127] Hereinafter, an apparatus for producing dilute sulfuric acid and a method for producing dilute sulfuric acid according to one embodiment (first embodiment) of the present invention will be described with reference to the drawings. Figure 1 Schematic diagram showing the upstream process of the dilute sulfuric acid manufacturing device 40, showing an embodiment of supplying oxygen-containing gas to the raw material (here, desulfurization waste liquid / molten sulfur). It should be noted that by adding molten sulfur to the hydrogen sulfide raw material, the sulfur concentration can be adjusted, and thus, for example, by increasing the sulfuric acid concentration, the present invention can also be used in the production of concentrated sulfuric acid.

[0128] Figure 2Schematic diagram showing the downstream process of the dilute sulfuric acid manufacturing device 40. It should be noted that the "sulfuric acid" of the present invention refers to sulfuric acid with no limitation on sulfuric acid concentration, specifically, for example, including dilute sulfuric acid and concentrated sulfuric acid. Here, "dilute sulfuric acid" refers to a sulfuric acid aqueous solution with a sulfuric acid concentration of less than 90% by weight, including "dilute sulfuric acid (thin sulfuric acid)" (sulfuric acid content 60 to 80% by weight) and "purified dilute sulfuric acid" (sulfuric acid content 27 to 50% by weight) specified in JIS K1321.

[0129] like Figure 1 As shown, the dilute sulfuric acid manufacturing device 40 of the present embodiment includes a unit for supplying raw materials. The raw materials of the present embodiment contain at least sulfur components, and in the present embodiment, they are composed of molten sulfur and desulfurization waste liquid, but are not limited to this as raw materials. In addition, the raw materials may also include refined COG as a combustion aid, etc. The raw material supply unit is a unit that supplies these raw materials to the combustion furnace 51. The dilute sulfuric acid manufacturing device 40 of the present embodiment is equipped with a pipeline 41 for supplying molten sulfur as a raw material. Molten sulfur is a material obtained by making sulfur recovered from an oil refinery, etc. into a molten state. The raw materials are supplied to the combustion furnace 51 via a pump (not shown) arranged midway in the pipeline 41.

[0130] In addition, the dilute sulfuric acid manufacturing device 40 is equipped with a pipeline 42 for supplying desulfurized waste liquid as a raw material. Desulfurized waste liquid is waste liquid from a desulfurization device installed to remove coal dust, organic matter, sulfur-containing compounds, etc. in the exhaust gas (crude COG) discharged from a coke oven device, etc. Usually, the desulfurized waste liquid contains components such as free sulfur, free NH3, NH4SCN, (NH4)2S2O3, and H2O. Among them, water (H2O) is not particularly limited, but in most cases it accounts for more than 50% by weight of the entire desulfurized waste liquid. The pipeline 42 is connected to the combustion furnace 51, and the desulfurized waste liquid is also supplied to the combustion furnace 51 as a raw material.

[0131] Pipeline 41 and pipeline 42 are equivalent to the raw material supply unit of the present invention, and the raw material supply process is realized by these units. The desulfurization waste liquid in the raw material (molten sulfur, desulfurization waste liquid) supplied to the combustion furnace 51 by them contains, in addition to sulfur, sulfur components such as (NH4)2S2O3 (10 to 40 weight%), nitrogen components such as NH3 (5 to 25 weight%), and water (40 to 80 weight%). As in the present embodiment, when there are multiple raw materials (for example, molten sulfur and desulfurization waste liquid in the present embodiment), the water content is defined as the amount of water mixed in each raw material and the combustion aid.

[0132] In addition, a pipe 43 for supplying air is provided in the dilute sulfuric acid manufacturing device 40. A pipe 44 for supplying oxygen is connected to the pipe 43. For example, an oxygen generator (for example, PVSA (vacuum type pressure swing adsorption method) method: not shown) can be provided, and high-concentration oxygen is supplied from the oxygen generator. The oxygen generator is a device that uses an adsorbent such as zeolite to adsorb and remove nitrogen in the air under pressure to effectively obtain high-purity oxygen. The oxygen generator can produce oxygen with a purity of more than 90% by volume. The oxygen is mixed with the air in the pipe 43 and supplied to the combustion furnace 51 as air with a high oxygen concentration. As the oxygen generator, the PSA method (pressure swing adsorption method) can be used. In addition, as an alternative, oxygen can also be supplied by branching the existing oxygen pipe.

[0133] The oxygen generator, the pipeline 43, and the pipeline 44 are referred to as oxygen-containing gas generating means, and the oxygen-containing gas supplied to the combustion furnace 51 through these means is adjusted to an oxygen concentration of 21 to 40 volume %, preferably 21 to 30 volume %, and more preferably 25 to 30 volume %.

[0134] The combustion furnace 51 (combustion means) performs a combustion step of combusting a raw material with an oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx). Figure 3 : is a schematic diagram showing the internal structure of the combustion furnace 51. As shown in the figure, a supply port 51a for supplying raw materials and oxygen-containing gas is provided upstream of the combustion furnace 51, the raw materials are burned inside, and the combustion gas is discharged from the exhaust port 51b downstream. In the present embodiment, molten sulfur is supplied from the supply port 51a in the upper section of the figure, desulfurization waste liquid is supplied from the supply port 51a in the middle section, and air is supplied from the supply port 51a in the lower section. It should be noted that, in addition to the method of supplying raw materials from separate supply ports according to the type of raw materials as in the present embodiment, part or all of the raw materials can also be mixed in advance and the raw materials can be supplied to the combustion furnace 51 in this state.

[0135] There is a water evaporation zone on the raw material supply side of the combustion furnace 51, where the combustion of molten sulfur and refined COG, and the evaporation of water in the desulfurization waste liquid are mainly carried out. Its downstream is the combustible combustion zone, where the combustibles in the desulfurization waste liquid are burned. They form a boundary. A lattice brick 51c is provided between the combustible combustion zone and the discharge port 51b. In the lattice brick 51c, cubic heat-resistant bricks are arranged in a lattice shape and a part of them is made into an open state. The opening rate of the lattice brick 51c is preferably about 50%. In most cases, the lattice brick 51c is provided in multiple stages.

[0136] In the combustion furnace 51, the oxygen concentration of the oxygen-containing gas introduced is more preferably in the range of 21 to 40 volume %, preferably 21 to 30 volume %, the oxygen concentration in the combustion gas generated by the combustion furnace 51 is in the range of 2.0 to 7.0 volume %, 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.

[0137] SO3 conversion rate = (SO3 / SO x )×100

[0138] (Here, SO3 is the volume concentration of SO3 contained in the above combustion gas, SO x is the volume concentration of SOx contained in the above combustion gas. )

[0139] The lattice bricks 51c provided downstream of the combustible combustion zone can, in addition to reducing radiation to downstream instruments, also perform the following functions. Even if the mixing state of air and combustibles in the combustible combustion zone is poor, the lattice bricks 51c physically promote the remixing of air and combustibles in a manner that does not cause the deflection phenomenon (blowing and pulling phenomenon) in the combustibles in an unburned state, and have the function of promoting the recombustion based on the latent heat of the bricks. For this purpose, it is preferred to provide multiple sections of lattice bricks 51c. In addition, the openings of each section of the multiple sections of lattice bricks 51c are arranged in a staggered manner. As a result, dust in the gas adheres to, grows on, and falls off the brick surface, so it is preferred to provide multiple sections of lattice bricks 51c at the bottom that do not have openings and accumulate the fallen dust.

[0140] The combustion temperature at which the raw material is combusted in the combustion furnace 51 is preferably in the range of 900 to 1100° C. The upper limit of the combustion temperature is preferably 1050° C. or lower. For the purpose of reducing the amount of NOx in the combustion gas, the combustion temperature is preferably low, for example, preferably 1025° C. or lower, and further preferably 1000° C. or lower.

[0141] In the combustion furnace 51, the raw material is burned with an oxygen-containing gas having an oxygen concentration of 21 to 40% by volume, so that the amount of NOx contained in the generated combustion gas can be reduced compared to the case where the raw material is burned under the same conditions using ordinary air (oxygen concentration is less than 21% by volume). For example, the amount of NOx contained in the combustion gas when the raw material is burned with an oxygen-containing gas having an oxygen concentration of 21 to 40% by volume is referred to as NOx. (rich) The amount of NOx contained in the combustion gas when the same raw material is burned under the same conditions using air with an oxygen concentration of less than 21% by volume is defined as NOx (air) When the NOx reduction rate represented by the following formula is 50 to 95%,

[0142] NOx reduction rate: NOx(rich) / NOx (air) ×100(%)

[0143] The NOx reduction rate tends to decrease as the oxygen concentration increases, and may be approximately 80% when the oxygen concentration is 25% by volume, and may be approximately 60% when the oxygen concentration is 30% by volume.

[0144] like Figure 1 As shown, the combustion gas generated in the combustion furnace 51 is sent to the waste heat boiler 52 (Waste Heat Boiler: WHB) (combustion gas cooling unit). In addition, water is supplied from the pipeline 45 (refrigerant introduction unit), and the water is introduced into the waste heat boiler 52 through the feed water preheater 63b described later. The waste heat boiler 52 performs a combustion gas cooling process: that is, water (water in this embodiment) heated as a refrigerant is supplied to the boiler, and the water generates steam by evaporation of the combustion gas, and the combustion gas is cooled by heat exchange with the water. It should be noted that in this embodiment, the "first refrigerant" of the present invention corresponds to the water introduced into the waste heat boiler 52 from the pipeline 45, that is, "boiler feed water", and the "first refrigerant after heating" corresponds to "boiler water". The combustion gas is cooled to a temperature not lower than the acid dew point (220°C), and the boiler pressure at this time is about 3MPa. In the waste heat boiler 52, the combustion gas is cooled to 420-360°C, preferably about 375°C. It should be noted that, in Patent Document 1, the temperature of the combustion gas is cooled to 380 to 460° C., preferably about 420° C., but in the present embodiment, the combustion gas is cooled to a lower temperature.

[0145] Here, refer to Figure 7 The acid dew point will be described. Figure 7 The relationship between the acid dew point of sulfuric acid (vertical axis) and the SO3 concentration (horizontal axis) contained in the combustion gas is shown in a graph for each amount of water (water vapor concentration) contained in the combustion gas. The acid dew point is determined by the SO3 concentration, water vapor concentration, pressure, etc. in the combustion gas. If the acid dew point is lower than the acid dew point, the solution containing condensed sulfuric acid will cause severe corrosion (acid dew point corrosion) inside the equipment. In order to avoid acid dew point corrosion, the combustion gas needs to be kept at a temperature above the acid dew point. Figure 7 The curve diagram shows that, at the same water vapor concentration, the higher the SO 3 concentration in the combustion gas, the higher the acid dew point; at the same SO 3 concentration, the higher the water vapor concentration, the higher the acid dew point.

[0146] Here, as shown in the simulation described later, the combustion gas generated in the combustion furnace 51 and introduced into the waste heat boiler 52 contains 0.2 to 0.3 volume % (i.e., 2000 to 3000 ppm) of SO3 and about 25 volume % of H2O. The composition of the combustion gas is shown by hollow circles in Figure 7, the dew point of sulfuric acid is about 190° C. That is, the acid dew point of the combustion gas in the waste heat boiler 52 is 190° C., and the temperature of the combustion gas in the waste heat boiler 52 needs to be maintained above the acid dew point, preferably above 190° C.

[0147] The waste heat boiler 52 is provided with a boiler in which the combustion gas is cooled. The waste heat boiler 52 is provided with: a refrigerant supply unit (refrigerant supply process) for supplying a predetermined refrigerant (in this embodiment, boiler feed water) into the above-mentioned boiler; a combustion gas cooling unit (combustion gas cooling process) for evaporating the refrigerant from the refrigerant supply unit by using the combustion gas to generate steam, and cooling the combustion gas by heat exchange; and a water vapor discharge unit (water vapor discharge process). Here, in the waste heat boiler 52, as described above, the combustion gas needs to be above the acid dew point, for example, more than 190°C, so the temperature of the boiler water as the refrigerant also needs to be more than 190°C. The refrigerant and the refrigerant supply unit (refrigerant supply process) used here will be described in detail later.

[0148] As the combustion gas cooling means, there are smoke tube type and water tube type, but considering the removal of dust adhering to the boiler, the water tube type is preferably used. Figure 6 As shown in the figure, the waste heat boiler 52 includes: a boiler body 52a defining the outer shape of the boiler; a drum 52b provided on the upper portion of the boiler body 52a; a boiler tube 52c provided inside the boiler body 52a; and a soot blower 52d provided inside the boiler body 52a.

[0149] The combustion gas generated in the combustion furnace 51 is introduced into the boiler body 52a from the opening on one end side (the left side in the figure) of the openings provided at both ends of the boiler body 52a, and is discharged from the opening on the other end side (the right side in the figure). Boiler water and water vapor as refrigerant are stored in the drum 52b. An inlet (opening with a downward arrow) for introducing the refrigerant and an outlet (opening with an upward arrow) for discharging the refrigerant are provided on the upper surface of the drum 52b. Boiler feed water from the feed water preheater 63b described later is introduced into the drum 52b from the refrigerant inlet, and the evaporated water vapor in the drum 52b is discharged to the outside from the refrigerant outlet.

[0150] The interior of the boiler tube 52c is composed of a hollow tube, which is composed of a longitudinal tube arranged in the longitudinal direction relative to the boiler body 52a and a transverse tube arranged in the transverse direction. The longitudinal tube is arranged at the lower part of the drum 52b and communicates with the inside of the drum 52b, and the transverse tube connects the lower parts of the longitudinal tubes to each other. With such a structure, the boiler water of the drum 52b circulates in the boiler tube 52c and returns to the drum 52b again. The combustion gas passing through the outside of the boiler tube 52a contacts the boiler tube 52c and is cooled by heat exchange.

[0151] The soot blower 52d is a cylindrical member provided in the boiler body 52a, and air is blown into the inside of the tube. The soot blower 52d is provided with a plurality of openings connected to the inside, and the air introduced into the inside of the tube is ejected from the openings. In addition, the soot blower 52d can rotate. The combustion gas contains adhesive dust, and the dust adheres to the outer surface of the boiler tube 52c, but the dust can be blown away by the air ejected from the soot blower 52d to clean the outer surface of the boiler tube 52c. In addition, by rotating the soot blower 52d itself, a large range of the outer surface of the boiler tube 52c can be cleaned.

[0152] The combustion gas cooled in the waste heat boiler 52 is introduced into the converter 61 (reaction unit) via the dust collector 55. The dust collector 55 is a unit for removing dust contained in the combustion gas. It is preferred to provide a hot air introduction unit X1 in the middle of the pipeline from the dust collector 55 to the converter 61. Figure 4 As shown, the hot air introduction unit X1 includes a hot air stove 101 and a hot air stove fan 102, and COG is introduced into the hot air stove 101. The hot air stove 101 is a unit that burns COG to generate high-temperature heated gas. In addition, the hot air stove fan 102 includes a blast fan, and is a unit that sends the heated gas generated in the hot air stove 101 as hot air. By introducing hot air of 300 to 400° C. from the hot air introduction unit X1 into the converter 61, the converter 61 can be preheated or maintained by purging.

[0153] The combustion gas cooled in the waste heat boiler 52 contains a small amount of nitrogen (such as undecomposed NH3, NO, NO2, etc.). x The converter 61 uses a catalyst disposed in a plurality of stages (three stages in the figure) to perform the following reaction: sulfur dioxide (SO2) in the combustion gas is oxidized by reacting with oxygen to generate a reaction gas containing sulfur trioxide (SO3) (reaction process). More specifically, the converter 61 efficiently converts sulfur dioxide into sulfur trioxide (SO3) by using a catalyst disposed in a front stage among the plurality of stages to convert sulfur oxides (SO x ) is oxidized with oxygen (exothermic reaction), and the converted gas whose temperature is increased by the oxidation is directly mixed with the atmosphere sucked in from the outside to reduce its temperature to a temperature suitable for the subsequent catalytic reaction.

[0154] Figure 5 Schematic diagram showing the internal structure of the converter 61, (a) is a side view, (b) is a cross-sectional view of (a) along the line A-A', and (c) is an enlarged view of the dotted circle of (b). As shown in the figure, the converter 61 includes a main air pipe 61a for introducing atmospheric air, a branch air pipe 61b branching from the main air pipe 61a in the converter, and an air port 61d for delivering air from the branch air pipe 61b into the converter.

[0155] As the catalyst, a known catalyst used in the production of sulfuric acid can be used, for example, vanadium pentoxide (V2O5) etc. Vanadium pentoxide has a denitrification function, which degrades NH3 and NO. x The reaction decomposes into nitrogen (N2) and water (H2O). Therefore, the catalyst can be used to simultaneously generate sulfur trioxide and nitrogen components (NH3 and NO x ) decomposition. At this time, NH3 can be injected for denitrification.

[0156] The temperature of the combustion gas introduced into the converter 61 is about 370°C. In the first section of the converter 61, about 55% of the sulfur dioxide (SO2) contained in the combustion gas introduced into the converter 61 undergoes an oxidation reaction and is converted into SO3, and the temperature of the gas after the reaction is close to 500°C. In the second and third sections of the converter 61, the remaining sulfur dioxide (SO2) is oxidized to sulfur trioxide (SO3). The inlet temperature of the second section is about 410°C, and the temperature of the gas after the reaction is about 480°C. Due to the mixing of air, about 95% of the SO2 contained in the combustion gas introduced into the converter 61 is converted into SO3. The inlet temperature of the third section is about 390°C. Due to the mixing of air, about 98.9% of the SO2 contained in the combustion gas introduced into the converter 61 is converted into SO3. The temperature of the gas after the reaction in the third section stops at 410°C. Thus, even if the temperature of the combustion gas introduced into the reformer 61 is as low as about 370° C., by introducing air into the reformer 61, 98.9% of SO 2 contained in the combustion gas can be converted into SO 3, and SO 3 can be generated at a high conversion rate.

[0157] It should be noted that a denitration catalyst may be disposed on the upstream side of the first stage of the converter 61 (the side into which the combustion gas from the waste heat boiler 52 flows). As the denitration catalyst, a mixture of vanadium pentoxide and a catalyst promoter may be used.

[0158] The reaction gas generated in the reformer 61 is sent to the cooler 62 (reaction gas cooling unit) for cooling. Here, as shown in the simulation described later, the reaction gas generated in the reformer 61 and sent to the cooler 62 contains 5 to 6 volume % (i.e., 5×10 4 ~6×10 4 ppm) of SO3 and about 15 volume % of H2O. The composition of the reaction gas is shown in FIG. Figure 7 , the dew point of sulfuric acid is about 240° C. That is, the acid dew point of the reaction gas introduced into the cooler 62 is about 240° C., and the temperature of the reaction gas in the cooler 62 needs to be maintained at or above the acid dew point, preferably at or above 250° C.

[0159] The cooler 62 cools the reaction gas by heat exchange with the second refrigerant. As the cooler 62, a smoke tube type is preferably used. The smoke tube type heat exchanger is a heat exchanger in which the reaction gas flows inside a narrow tube and the refrigerant circulates outside the tube. Compared with a water tube boiler such as the waste heat boiler 52, the smoke tube type heat exchanger is preferably used as the cooler 62 because it is cheap and has high cooling efficiency. However, as the cooler 62, other types such as a water tube type may also be used.

[0160] As the second refrigerant, an organic refrigerant that is liquid in the temperature range of -20°C to 350°C is used. Examples of the organic refrigerant include Dowtherm (Dowtherm: registered trademark) A, which is a mixture of biphenyl and biphenyl ether (diphenyl ether), NeoSK-OIL 1400, NeoSK-OIL 1300, NeoSK-OIL 330, NeoSK-OIL 360, NeoSK-OIL L400, and KSK-OIL 260. Among them, as an organic refrigerant suitable for this liquid phase use, "NeoSK-OIL 1400" which is generally widely used and has excellent heat resistance is preferred.

[0161] The outlet temperature of the reaction gas at the converter 61 is a high temperature of about 410°C, and is cooled by the cooler 62 to about 270 to 320°C, which is a temperature exceeding the acid dew point of about 250°C. The refrigerant pressure of the cooler 62 in this case is about 0.1 MPa. It is preferred to provide a purge pipe X2 (purge flow path) in the path for conveying the reaction gas cooled by the cooler 62 to the downstream.

[0162] The heat exchange unit 63 includes a feed water preheater 63b, a heat medium tank 63c, a heat medium circulation pump 63d, a refrigerant delivery path 63e, and a refrigerant return path 63h. The refrigerant delivery pipe 63e delivers the second refrigerant, which has been heated to about 320°C by heat exchange with the reaction gas, from the cooler 62 to the feed water preheater 63b.

[0163] As the feed water preheater 63b, a multi-tube heat exchanger can be used. In the feed water preheater 63b, the first refrigerant (boiler feed water) of about 105°C is introduced from the outside via the refrigerant inlet path 63f. The second refrigerant heated to about 320°C in the cooler 62 exchanges heat with the first refrigerant in the feed water preheater 63b. As a result, the first refrigerant becomes about 220°C and the second refrigerant becomes about 270°C. The first refrigerant heated to about 220°C by heat exchange is supplied to the waste heat boiler 52 via the refrigerant supply path 63g. As a result, the recovery amount of the first refrigerant (water vapor) in the waste heat boiler 52 can be increased. It should be noted that the refrigerant inlet path 63f, the feed water preheater 63b and the refrigerant supply path 63g are equivalent to the refrigerant supply unit for the combustion gas cooling unit (waste heat boiler 52).

[0164] The refrigerant return path 63h returns the second refrigerant after heat exchange with the first refrigerant (boiler feed water) from the feed water preheater 63b to the cooler 62. The refrigerant return path 63h includes: a heat medium tank 63c that stores the second refrigerant and can release a small amount of inert gas mixed into the atmosphere; and a heat medium circulation pump 63d that drives the second refrigerant to the cooler 62.

[0165] In this way, the reaction gas is cooled by heat exchange between the reaction gas and the second refrigerant in the cooler 62 (heat exchange step). In addition, the temperature of the first refrigerant (boiler feed water) is increased by heat exchange between the heated second refrigerant and the first refrigerant, and the heated first refrigerant for the combustion gas cooling unit (waste heat boiler 52) can be obtained.

[0166] like Figure 2 As shown, the reaction gas cooled by the cooler 62 is transported to the bottom of the dilute sulfuric acid tower 71 (sulfuric acid recovery unit) for performing the dilute sulfuric acid recovery process. The dilute sulfuric acid tower 71 is a device for absorbing H2O and SO3 in the reaction gas into a circulating sulfuric acid aqueous solution (dilute sulfuric acid) to generate dilute sulfuric acid as a product, and is also called an absorption tower. The dilute sulfuric acid tower 71 is filled with fillers, and the sulfuric acid aqueous solution is sprayed onto the fillers from the top of the tower. When the reaction gas passes through the fillers, it contacts the sulfuric acid aqueous solution, whereby H2O and SO3 are absorbed into the sulfuric acid aqueous solution. The sulfuric acid aqueous solution that absorbs SO3 is transported to the dilute sulfuric acid tank 73, and is cooled by cooling water from a cooling water tower (not shown) through a heat exchanger 74.

[0167] Gas containing sulfuric acid mist, unreacted SO2, etc. is discharged from the top of the dilute sulfuric acid tower 71. The exhaust gas is used to recover sulfuric acid mist using a wet electrostatic precipitator 76 or a mist eliminator, and is transported to a tank 73 to be reused as a sulfuric acid aqueous solution, and the residue is transported to a sulfite tower 81 (sulfur dioxide recovery unit) for generating sulfurous acid.

[0168] The exhaust gas transported to the sulfite tower 81 contains about 200 ppm (dry content) of SO2, about 10% (dry content) of O2, and the remainder is CO2 and N2. In the sulfite tower 81, water (industrial water) is used as an SO2 absorbent to generate sulfurous acid (H2SO3) (sulfur dioxide recovery process). The sulfurous acid is oxidized into sulfuric acid by the oxygen contained in the exhaust gas. It should be noted that the purge gas of the converter 61 required for the maintenance of the dilute sulfuric acid tower 71 and the wet electrostatic precipitator 76 is led out from the purge pipe X2 arranged downstream of the cooler 62 and introduced into the pipe directly transported to the sulfite tower 81. The maintenance purge gas from the converter 61 causes acid dew point corrosion as the temperature decreases over time. Therefore, by using the heat of the second refrigerant to heat the purge gas in the cooler 62, the effect of preventing acid dew point corrosion caused by the purge gas can be obtained. In addition, by introducing the purge gas for maintenance into the sulfite tower 81, it is also possible to obtain an effect of being able to remove the SO 2 gas contained in the purge gas.

[0169] The exhaust gas from the top of the sulfite tower 81 is sucked / pressurized by the induced draft fan 87 and discharged into the atmosphere through the chimney 88. Since SO2 is absorbed in the sulfite tower 81 and recovered as sulfuric acid, the amount of SO2 discharged into the atmosphere is greatly reduced and can be about 50ppm or less, which is the exhaust gas management value. The induced draft fan 87 has the function of making all the devices of the dilute sulfuric acid manufacturing device 40 arranged on its upstream side negative pressure. By using the negative pressure operation of the induced draft fan 87 to suck the gas, the high-temperature and harmful gas is prevented from flowing into the atmosphere. In addition, in the converter 61, there is no special equipment, but it also has the function of sucking the atmosphere. In this way, dilute sulfuric acid is manufactured and the exhaust gas is treated.

[0170] The dilute sulfuric acid manufacturing apparatus and the dilute sulfuric acid manufacturing method of the present embodiment are provided with a combustion gas cooling unit for cooling the combustion gas, a reaction gas cooling unit for cooling the reaction gas, and a heat exchange unit. In the heat exchange unit, the second refrigerant heated by heat exchange with the reaction gas is heat exchanged with the first refrigerant. Thus, the first refrigerant after the temperature is raised is prepared for the combustion gas cooling unit, and waste heat can be effectively utilized.

[0171] The cooler cools the reaction gas by heat exchange during normal operation, and plays a cooling heat recovery effect for preheating the waste heat boiler. In addition, during maintenance purge, it can also help prevent corrosion on the downstream side by preventing the purge gas from being cooled by latent heat.

[0172] 2. Simulation

[0173] for Figure 1 , Figure 2 The dilute sulfuric acid production device 40 is based on Figure 8The calculation chart of SO2→SO3 equilibrium conversion rate is used for calculation simulation based on similar actual operation data.

[0174] The gas composition of the combustion gas between the combustion furnace 51 and the dust collector 55 was calculated and simulated, and the results were the numerical values ​​shown in the following table.

[0175] [Table 1]

[0176]

[0177] As shown in the table above, the SO3 concentration of the combustion gas is 0.26% by volume, and the H2O concentration is 24.86% by volume. Figure 7 According to the graph, the acid dew point of the combustion gas is around 190°C.

[0178] The temperature and conversion rate in each stage of the converter 61 were simulated and the results were the numerical values ​​shown in the table below.

[0179] [Table 2]

[0180]

[0181] The amount of air sucked and added to the second and third stage catalysts is 4900 Nm 3 / Hr.

[0182] As shown in the table above, even if the temperature of the combustion gas introduced into the first stage catalyst is as low as 370°C, Figure 8 The calculation simulation of the calculation chart of the SO2→SO3 equilibrium conversion rate also makes it possible to convert the combustion gas at a high conversion rate of 98.9% of the cumulative conversion rate until the third stage catalyst.

[0183] The gas composition of the reaction gas between the reformer 61 and the cooler 62 was calculated and simulated, and the results were the numerical values ​​shown in the following table.

[0184] [Table 3]

[0185]

[0186] As shown in the table above, the SO3 concentration of the reaction gas is 5.4% by volume and the H2O concentration is 15.1% by volume. Figure 7 The acid dew point of the reaction gas is around 240°C.

[0187] In similar actual operation data, the SO2 gas concentration value in the exhaust gas at the outlet of the wet electrostatic precipitator 76 is reduced to about 200ppm. The conversion rate of 98.9% obtained in the calculation chart of the SO2→SO3 equilibrium conversion rate is multiplied by the gas phase reaction (SO3+H2O→H2SO4) conversion rate to obtain a conversion rate of more than 99.7%. The results of the calculation simulation are the values ​​shown in the table below.

[0188] [Table 4]

[0189]

[0190] For the first stage catalytic reaction, the following advantages of effective utilization of waste heat recovery can be obtained through calculation simulation of the low temperature of 370°C this time and the high temperature of 410°C in the past.

[0191] The inlet temperature of the first stage catalyst shown in Table 2 was 410°C, and the outlet temperature of the third stage catalyst was 420°C.

[0192] The total exhaust gas volume shown in Table 3 is 13700Nm 3 / Hr.

[0193] · Heat recovery from waste heat boiler 52 at 370°C: a

[0194] · Heat recovery of cooler 62 at low temperature of 370℃: b

[0195] · Heat recovery difference in waste heat boiler 52: c

[0196] ·Differential heat loss in cooler 62: d

[0197] The difference in heat recovery between low temperature and high temperature conditions = {1-(a+bcd) / (a+b)}×100≒13··Formula (1)

[0198] Thus, at the low temperature, 370°C, a 13% heat recovery advantage is obtained compared to the high temperature, 410°C.

[0199] 3. Second Implementation Method

[0200] Next, a dilute sulfuric acid production apparatus and a dilute sulfuric acid production method according to another embodiment (second embodiment) of the present invention will be described. Fig. 9 Schematic diagram showing the upstream process of the dilute sulfuric acid production apparatus according to the present embodiment. Fig.10 Schematic diagram showing the downstream process of the dilute sulfuric acid production apparatus of the present embodiment. The same reference numerals are given to the same apparatuses as those in the first embodiment, and the description thereof will be omitted below.

[0201] In this embodiment, first, a vertical smoke tube type waste heat boiler 91 is used instead of the water tube type waste heat boiler 52. That is, the boiler is arranged vertically (i.e., in a direction parallel to the direction of gravity) relative to the ground from the supply port to the outlet of the combustion gas. As a result, the dust that is not blocked in the waste heat boiler 91 falls downward and is easily discharged from the waste heat boiler 91. In this embodiment, the induced draft fan 87 is not provided, and the gas is transported to the downstream side by the pressure from the upstream side by the air introduced from the pipeline 43.

[0202] In addition, in the present embodiment, the structure of the heat exchange unit 100 is different from that in the first embodiment. In the present embodiment, in the discharge flow of the heat medium circulation pump 63d that drives the second refrigerant to the cooler 62, there is provided a pipe 63i that branches from the pipe that introduces the second refrigerant into the cooler 62 and introduces the second refrigerant into the waste heat boiler 91. And, in the waste heat boiler 91, the second refrigerant is used to cool the combustion gas. In this way, the waste heat boiler 91 is cooled using the second refrigerant that cools the cooler 63. After cooling the combustion gas, the second refrigerant introduced into the waste heat boiler 91 is introduced into the heat medium cooler (steam generator) 102. The second refrigerant cooled by the heat medium cooler (steam generator) 102 is returned to the refrigerant tank 63c.

[0203] The water that cools the second refrigerant in the refrigerant transport path 63e becomes high-temperature steam and is introduced into the drum 101. The steam in the drum is introduced into the heat medium cylinder 102 and used to cool the second refrigerant. The steam is sent back to the drum 101 again, and a part of it is purged to the outside through the pipe 46.

[0204] Description of Reference Numerals

[0205] 40 dilute sulfuric acid manufacturing device, 41 pipeline (raw material supply unit), 42 pipeline (raw material supply unit), 43 pipeline, 44 pipeline, 45 pipeline (refrigerant introduction unit), 46 pipeline, 51 combustion furnace (combustion unit), 51a supply port, 51b discharge port, 51c checker brick, 52 waste heat boiler (combustion gas cooling unit), 52a boiler body, 52b drum, 52c boiler tube, 52d soot blower, 55 dust collector, 61 converter (reaction unit), 62 cooler (reaction gas cooling unit), 63 heat exchange unit, 63 b feed water preheater, 63c heat carrier tank, 63d heat carrier circulation pump, 63e refrigerant transport path, 63f refrigerant introduction path, 63g refrigerant supply path, 63h refrigerant return path, 63i pipeline, 71 dilute sulfuric acid tower (sulfuric acid recovery unit), 73 tank, 74 heat exchanger, 76 wet electric precipitator, 81 sulfite tower (sulfur dioxide recovery unit), 87 induced draft fan, 88 chimney, 91 waste heat boiler (combustion gas cooling unit), 100 heat exchange unit, 101 steam drum, 102 heat carrier cooler (steam generator).

Claims

1. A sulfuric acid production device, characterized in that: It has: A raw material supply unit supplies a raw material containing at least sulfur; a combustion unit for burning the raw material to generate a combustion gas containing sulfur oxides; A refrigerant introduction unit for introducing a first refrigerant; a combustion gas cooling unit for cooling the combustion gas by heat exchange with a refrigerant; A reaction unit, which oxidizes the sulfur oxides using a catalyst to generate a reaction gas containing sulfur trioxide and water; a reaction gas cooling unit for cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery unit that absorbs sulfur trioxide and water contained in the cooled reaction gas into a sulfuric acid aqueous solution to generate sulfuric acid and discharges an exhaust gas containing sulfur dioxide and oxygen; and The heat exchange unit prepares the heated first refrigerant and the cooled second refrigerant by heat exchange between the second refrigerant whose temperature is heated by heat exchange with the reaction gas and the first refrigerant, and supplies either the heated first refrigerant or the cooled second refrigerant as the refrigerant to the combustion gas cooling unit.

2. The sulfuric acid production device according to claim 1, characterized in that In the combustion gas cooling unit, the temperature of the first refrigerant after the temperature increase is higher than the acid dew point of the combustion gas, and in the reaction gas cooling unit, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

3. The sulfuric acid production device according to claim 1, characterized in that The heat exchange unit comprises: A refrigerant transport path for transporting the second refrigerant after the temperature is increased; a preheater supplied with the first refrigerant, raising the temperature of the first refrigerant by heat exchange with the second refrigerant having the raised temperature, and supplying the first refrigerant to the combustion gas cooling unit; and The refrigerant return path returns the second refrigerant after heat exchange with the first refrigerant from the preheater to the reaction gas cooling unit.

4. The sulfuric acid production device according to claim 3, characterized in that The refrigerant return path supplies a part of the second refrigerant to the combustion gas cooling unit.

5. The sulfuric acid production device according to claim 3, characterized in that: The refrigerant return path includes a tank storing the second refrigerant and a pump supplying the second refrigerant to the reaction gas cooling unit.

6. The sulfuric acid production device according to claim 1, characterized in that The second refrigerant is an organic refrigerant that is liquid at least in the range of -20°C to 350°C.

7. The sulfuric acid production device according to claim 1, characterized in that The first refrigerant is water, and the second refrigerant is a mixture of biphenyl and biphenyl ether.

8. The sulfuric acid production device according to claim 1, characterized in that The heat exchange unit is of smoke tube type.

9. The sulfuric acid production device according to claim 1, characterized in that It also has a unit for negative pressure operation.

10. The sulfuric acid production device according to claim 9, characterized in that Also available: A hot air introduction unit for introducing hot air into the reaction unit; and The purge flow path can purge the reaction gas remaining in the reaction unit upstream of the sulfuric acid recovery unit.

11. The sulfuric acid production device according to claim 1, characterized in that: The device further includes a sulfur dioxide recovery unit for recovering sulfur dioxide contained in the exhaust gas.

12. The sulfuric acid production apparatus according to claim 11, wherein: The sulfur dioxide recovery unit absorbs sulfur dioxide contained in the exhaust gas into water to generate sulfurous acid, and oxidizes the sulfurous acid using oxygen contained in the exhaust gas to generate sulfuric acid.

13. A method for producing sulfuric acid, characterized in that: It has: A raw material supplying step of supplying a raw material containing at least a sulfur component; A combustion step of burning the raw material to generate a combustion gas containing sulfur oxides; A refrigerant introducing step of introducing a first refrigerant; a combustion gas cooling step of cooling the combustion gas by heat exchange with a refrigerant; A reaction step of oxidizing the sulfur oxides using a catalyst to generate a reaction gas containing sulfur trioxide and water; a reaction gas cooling step of cooling the reaction gas by heat exchange with a second refrigerant; a sulfuric acid recovery step of absorbing sulfur trioxide and water contained in the cooled reaction gas into a sulfuric acid aqueous solution to generate sulfuric acid, and discharging an exhaust gas containing sulfur dioxide and oxygen; and The heat exchange process prepares the heated first refrigerant and the cooled second refrigerant by heat exchanging the second refrigerant whose temperature is heated by heat exchange with the reaction gas with the first refrigerant, and supplies either the heated first refrigerant or the cooled second refrigerant as the refrigerant to the combustion gas process.

14. The method for producing sulfuric acid according to claim 13, wherein: In the combustion gas cooling step, the temperature of the first refrigerant after the temperature increase is higher than the acid dew point of the combustion gas, and in the reaction gas cooling step, the temperature of the second refrigerant is higher than the acid dew point of the reaction gas.

15. The method for producing sulfuric acid according to claim 13, wherein: The heat exchange process comprises: A refrigerant conveying step of conveying the second refrigerant after the temperature is increased; a preheating step of raising the temperature of the first refrigerant by heat exchange with the second refrigerant having a raised temperature, and supplying the first refrigerant to the combustion gas cooling step; and The refrigerant returning step returns the second refrigerant after exchanging heat with the first refrigerant to exchange heat with the reaction gas.

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

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

18. The method for producing sulfuric acid according to claim 13, wherein: As the second refrigerant, an organic refrigerant that is liquid at least in the range of -20°C to 350°C is used.

19. The method for producing sulfuric acid according to claim 13, wherein: Water is used as the first refrigerant, and a mixture of biphenyl and biphenyl ether is used as the second refrigerant.

20. The method for producing sulfuric acid according to claim 13, wherein: The heat exchange process is carried out in a smoke tube type.

21. The method for producing sulfuric acid according to claim 13, wherein: Perform negative pressure operation.

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

23. The method for producing sulfuric acid according to claim 22, wherein: In the sulfur dioxide recovery step, sulfur dioxide contained in the exhaust gas is absorbed in water to generate sulfurous acid, and the sulfurous acid is oxidized by oxygen contained in the exhaust gas to generate sulfuric acid.

24. A maintenance method, which is the maintenance method of the sulfuric acid production device according to claim 11, characterized in that: While performing negative pressure operation, hot air is introduced from the hot air introduction unit to the reaction unit, reaction gas remaining in the reaction unit is purged upstream of the sulfuric acid recovery unit, and the obtained purge gas is introduced into the sulfur dioxide recovery unit.

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