JP2021031305A - Diluted sulfuric acid production device and diluted sulfuric acid production method - Google Patents

Abstract

To provide a diluted sulfuric acid production device and a diluted sulfuric acid production method capable of inexpensively producing diluted sulfuric acid.SOLUTION: A diluted acid production device 40 comprises: a conduit line 41a or the like feeding raw material at least comprising a sulfur component, a nitrogen component and moisture of 40 to 80 mass% or more; PVSA45d or the like generating an oxygen-containing gas having an oxygen concentration of 25 to 40 vol.%; a burning furnace 51 burning the raw material with the oxygen-containing gas to generate a sulfur oxide (SOx: 1≤x<3) and moisture of 10 mass% or more; a heat exhaust boiler 52 cooling the burning gas; a converter 61 oxidizing the sulfur oxide (SOx) with a catalyst to generate a reaction gas comprising sulfur trioxide (SO3); and a diluted acid tower 71 cooling the reaction gas to generate diluted acid.SELECTED DRAWING: Figure 1

Description

The present invention relates to a dilute sulfuric acid producing apparatus and a dilute sulfuric acid producing method.

Sulfuric acid (H ₂ SO ₄ ) is a strong acid that is produced in large quantities and used in various fields. Sulfuric acid is roughly classified into industrial concentrated sulfuric acid having a sulfuric acid concentration of 90% by mass or more and industrial dilute sulfuric acid having a sulfuric acid concentration of less than 90% by mass, each of which has different properties. Of these, dilute sulfuric acid is strongly acidic, but unlike concentrated sulfuric acid, it does not have oxidative or dehydrating effects, but it is highly corrosive to metal materials and others. Dilute sulfuric acid is used in various applications such as industrial products, pharmaceuticals, pesticides, and reagents.

Raw materials containing sulfur are required for the production of sulfuric acid. As raw materials, desulfurization waste liquid and regenerated sulfur from gas (COG) generated in the process of producing coke used for iron making and the like, SOx-containing gas discharged from the copper refining process, and the like are used.

Conventionally, as a method for producing sulfuric acid, for example, the method of Patent Document 1 is known. In this document, it is selected from (a) a mixed gas that burns a carbon-containing fuel to supply heat for forming sulfur dioxide from a sulfur-containing material, and also contains pure oxygen and 30% by volume or more of oxygen. To support the combustion of the fuel by supplying an oxygen-enriched gas, (b) to form a mixed gas containing sulfur dioxide and the gas generated from the combustion of the fuel, (c) to dry the mixed gas, and the like. It is described that the mixed gas contains 30% by volume or more of carbon dioxide and 16% by volume of sulfur dioxide after drying.

Patent No. 2519691 (Claim 1 etc.)

Since the method of Patent Document 1 includes a step of drying the mixed gas, it is an object of producing concentrated sulfuric acid having a high sulfuric acid concentration instead of dilute sulfuric acid. Generally, for the production of dilute sulfuric acid, a method of producing concentrated sulfuric acid and then diluting it with water, or a sulfuric acid production apparatus equipped with a special temperature controller capable of adjusting the sulfuric acid condensation temperature (boiling point) is adopted. The former method requires equipment such as a dehumidifying tower that temporarily cools and dehumidifies the high-temperature combustion gas to less than 100 ° C. and a drying tower that utilizes the dehydration action of concentrated sulfuric acid in order to adjust the water concentration. Further, following such a dehumidifying tower and a drying tower, equipment (heat exchanger, etc.), piping, rotating machine, etc. for reheating to 400 to 450 ° C. are required. On the other hand, the latter method requires a very expensive special temperature controller capable of adjusting the sulfuric acid condensation temperature (boiling point). Therefore, such a method has a problem that the production of dilute sulfuric acid is costly.

An object of the present invention is to provide a dilute sulfuric acid production apparatus and a dilute sulfuric acid production method capable of producing dilute sulfuric acid at low cost.

The present inventors have found that dilute sulfuric acid can be produced by using a raw material containing a large amount of water in addition to sulfur and nitrogen as a raw material and burning the raw material with an oxygen-containing gas having a high oxygen concentration. Completed the invention.

The present invention comprises a raw material supply means for supplying a raw material containing at least sulfur content, nitrogen content, and water content of 40 to 80% by mass or more, and an oxygen-containing gas that produces an oxygen-containing gas having an oxygen concentration of 25 to 40% by volume. A gas generating means and a combustion means for burning the raw material with the oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx: here, 1 ≦ x <3) and 10% by mass or more of water. , A cooling means for cooling the combustion gas, _{a reaction means for oxidizing the sulfur oxide (SOx) with a catalyst to generate a reaction gas containing sulfur trioxide (SO 3} ), and a rare reaction means for cooling the reaction gas. A dilute sulfuric acid producing apparatus comprising: a dilute sulfuric acid producing means for producing sulfuric acid.

In the present invention, as a raw material, a material containing a large amount of water in addition to sulfur and nitrogen is used, and by burning the raw material with an oxygen-containing gas having a high oxygen concentration, sulfuric acid is produced in a state of containing a certain amount of water or more. Manufacture. Therefore, the sulfuric acid to be produced becomes dilute sulfuric acid, and it is not necessary to provide a dehumidifying facility or a drying facility to produce sulfuric acid as in the conventional case. Therefore, the cost for producing dilute sulfuric acid can be reduced as compared with the conventional case.

In this case, it is preferable that the combustion means burns the raw material at 900 to 1100 ° C.

In a conventional sulfuric acid production plant, the combustion temperature is as high as 1100 ° C. or higher, but in the present invention, since the oxygen concentration is high, the combustion temperature can be lowered and the combustion cost can be reduced. In general, when the oxygen concentration is high or the combustion temperature is high, air pollutants such as nitrogen oxides (NOx) are likely to be generated, but in the present invention, they are generated even if the raw materials are burned at a high oxygen concentration and a low temperature. The amount of nitrogen oxides produced is relatively small, which makes it possible to reduce the environmental load. Therefore, since the equipment for removing nitrogen oxides is unnecessary or minimal, the production cost of dilute sulfuric acid can be reduced.

Further, it is preferable to further provide a gas removing means for removing unreacted sulfur dioxide in the dilute sulfuric acid producing means.

In this way, since unreacted sulfur dioxide is removed, nitrogen dioxide can be detoxified without being released into the environment.

In this case, the gas removing means reacts the unreacted sulfur dioxide with ammonia to produce ammonium sulfite (NH ₄ HSO ₃ : ammonium sulfate), and recovers it as _{ammonium sulfate (NH 4} HSO _{4) by oxidation.} Is preferable.

In this way, unreacted sulfur dioxide can be reacted with ammonia to produce ammonium sulfate, which can be subsequently oxidized and recovered as ammonium sulfate.

Furthermore, it is preferable that the combustion means employs a combustion furnace having a partially open grid-like brick inside.

Since bricks have a long-term heat retention effect when heated, unreacted raw materials can be post-combusted. Further, since the lattice brick has an appropriate opening, this can improve the flow of the raw material, the oxygen-containing gas, and the combustion gas as a rectifying effect. Therefore, the raw material can be efficiently burned by the combustion means.

Further, in the reaction means, it is preferable that the catalyst is vanadium pentoxide (V ₂ O ₅ ) and also has a denitration function.

As described above, the catalyst of the reaction means is vanadium pentoxide (V ₂ O ₅ ), and by also having a denitration function, the sulfur oxide can be oxidized and the nitrogen component can be decomposed at the same time.

In this case, it is preferable that the reaction means further includes a denitration catalyst containing _{titanium oxide (TiO 2} ) and / or vanadyl sulfate (VOSO _{4) as an auxiliary catalyst in addition to the catalyst.}

During the conversion of sulfur oxides, _{if the concentration of nitrogen (for example, NOx such as undecomposed NH 3} , NO, NO ₂ ) generated by combustion in the raw material is relatively high, vanadium pentoxide without a cocatalyst is used. In, the conversion of sulfur oxides takes precedence over the decomposition of nitrogen components. Therefore, by providing the denitration catalyst containing the co-catalyst as described above, the decomposition of nitrogen can be promoted by giving priority to the reaction of decomposition of nitrogen rather than the conversion of sulfur oxide.

The reaction means includes the catalyst installed in a plurality of stages, and the atmosphere attracted from the outside to the converted gas whose temperature is raised by the exothermic reaction between the sulfur oxide and the oxygen by the catalyst in the previous stage among the plurality of stages. It is preferable to mix them directly and lower the temperature to a temperature suitable for the catalytic reaction in the subsequent stage.

In this way, by cooling the converted gas in the front stage of the plurality of stages of catalyst, the temperature can be lowered in the rear stage. Therefore, it is possible to prevent a decrease in the reaction rate due to an increase in temperature in the subsequent stage. In addition to the cooling effect, by taking in air directly from the outside, it is possible to supply the shortage of oxygen required for conversion.

The combustion means preferably supplies the oxygen-containing gas to a raw material of less than 5000 kJ / kg for combustion, and supplies air to a raw material of 5000 kJ / kg or more for combustion.

If the raw material is less than 5000 kJ / kg, the combustion becomes unstable. Therefore, the combustion can be stabilized by supplying an oxygen-containing gas having a high oxygen concentration to the combustion. In the case of a raw material of 5000 kJ / kg or more, it is easily burned by air without supplying an oxygen-containing gas. By distributing the oxygen-containing gas for each raw material in this way, the raw material can be efficiently burned.

The present invention comprises a raw material supply step of supplying a raw material containing at least sulfur content, nitrogen content, and water content of 40 to 80% by mass or more, and an oxygen content that produces an oxygen-containing gas having an oxygen concentration of 25 to 40% by volume. A gas generation step and a combustion step of burning the raw material with the oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx: here, 1 ≦ x <3) and 10% by mass or more of water. , A cooling step of cooling the combustion gas, a reaction step of oxidizing the sulfur oxide (SOx) with a catalyst _{to generate a reaction gas containing sulfur trioxide (SO 3} ), and a rare process of cooling the reaction gas. It is a method for producing dilute sulfuric acid, which comprises a dilute sulfuric acid producing step for producing sulfuric acid.

In the present invention, as a raw material, a material containing a large amount of water in addition to sulfur and nitrogen is used, and by burning the raw material with an oxygen-containing gas having a high oxygen concentration, sulfuric acid is produced in a state of containing a certain amount of water or more. Manufacture. Therefore, the sulfuric acid to be produced becomes dilute sulfuric acid, and it is not necessary to provide a dehumidifying facility or a drying facility to produce sulfuric acid as in the conventional case. Therefore, the cost for producing dilute sulfuric acid can be reduced as compared with the conventional case.

In this case, it is preferable that the combustion step burns the raw material at 900 to 1100 ° C.

In the present invention, since the oxygen concentration is high, the combustion temperature can be lowered and the combustion cost can be reduced. In general, when the oxygen concentration is high or the combustion temperature is high, air pollutants such as nitrogen oxides (NOx) are likely to be generated, but in the present invention, they are generated even if the raw materials are burned at a high oxygen concentration and a low temperature. Since the amount of nitrogen oxides produced is small, it is possible to reduce the environmental load. Therefore, since the equipment for removing nitrogen oxides is unnecessary or minimal, the production cost of dilute sulfuric acid can be reduced.

Further, it is preferable to further include a gas removing step of removing unreacted sulfur dioxide in the dilute sulfuric acid producing step.

In this way, since unreacted sulfur dioxide is removed, nitrogen dioxide can be detoxified without being released into the environment.

In this case, in the gas removal step, the unreacted sulfur dioxide is reacted with ammonia to produce ammonium sulfite (NH ₄ HSO ₃ : ammonium sulfate), which is then recovered as _{ammonium sulfate (NH 4} HSO _{4) by oxidation.} Is preferable.

In this way, unreacted sulfur dioxide can be reacted with ammonia to produce ammonium sulfate, which can be subsequently oxidized and recovered as ammonium sulfate.

Furthermore, in the combustion step, it is preferable to employ a combustion furnace provided with a partially open grid-like brick inside.

As described above, since the brick has a heat retention effect for a long time when heated, the unburned raw material can be post-combusted. Further, since the lattice brick has an appropriate opening, this can improve the flow of the raw material, the oxygen-containing gas, and the combustion gas as a rectifying effect. Therefore, the raw material can be efficiently burned by the combustion means.

Further, in the reaction step, it is preferable that the catalyst is vanadium pentoxide (V ₂ O ₅ ) and also has a denitration function.

As described above, the catalyst of the reaction step is vanadium pentoxide (V ₂ O ₅ ), and by also having the denitration function, the sulfur oxide can be oxidized and the nitrogen component can be decomposed at the same time.

In this case, it is preferable that the reaction step further includes a denitration catalyst containing _{titanium oxide (TiO 2} ) and / or vanadyl sulfate (VOSO _{4) as an auxiliary catalyst in addition to the catalyst.}

During the conversion of sulfur oxides, _{if the concentration of nitrogen (for example, NOx such as undecomposed NH 3} , NO, NO ₂ ) generated by combustion in the raw material is relatively high, vanadium pentoxide without a cocatalyst is used. In, the conversion of sulfur oxides takes precedence over the decomposition of nitrogen components. Therefore, by providing the denitration catalyst containing the co-catalyst as described above, the decomposition of nitrogen can be promoted by giving priority to the reaction of decomposition of nitrogen rather than the conversion of sulfur oxide.

The reaction step includes the catalyst installed in a plurality of stages, and the atmosphere attracted from the outside is introduced into the converted gas whose temperature is raised by the exothermic reaction between the sulfur oxide and the oxygen by the catalyst in the previous stage among the plurality of stages. It is preferable to mix them directly and lower the temperature to a temperature suitable for the catalytic reaction in the subsequent stage.

In this way, by cooling the converted gas in the front stage of the plurality of stages of catalyst, the temperature can be lowered in the rear stage. Therefore, it is possible to prevent a decrease in the reaction rate due to an increase in temperature in the subsequent stage. In addition to the cooling effect, by taking in air directly from the outside, it is possible to supply the shortage of oxygen required for conversion.

In the combustion step, it is preferable that the oxygen-containing gas is supplied to a raw material of less than 5000 kJ / kg for combustion, and air is supplied to a raw material of 5000 kJ / kg or more for combustion.

If the raw material is less than 5000 kJ / kg, the combustion becomes unstable. Therefore, the combustion can be stabilized by supplying an oxygen-containing gas having a high oxygen concentration to the combustion. In the case of a raw material of 5000 kJ / kg or more, it is easily burned by air without supplying an oxygen-containing gas. By distributing the oxygen-containing gas for each raw material in this way, the raw material can be efficiently burned.

According to the present invention, it is possible to provide a dilute sulfuric acid production apparatus and a dilute sulfuric acid production method capable of producing dilute sulfuric acid at low cost.

It is a schematic diagram which shows the upstream process of the dilute sulfuric acid production apparatus of this invention. It is a schematic diagram which shows the downstream process of the dilute sulfuric acid production apparatus of this invention. It is a schematic diagram which shows the internal structure of the combustion means (combustion furnace) of this invention. It is a graph which shows the result of the simulation of the combustion furnace 51. It is a schematic diagram which shows the internal structure of a converter 61. It is a schematic diagram which shows the internal structure of another embodiment of the combustion means (combustion furnace) of this invention.

Hereinafter, the configuration of the embodiment of the present invention will be described. The present invention can be carried out with appropriate modifications without changing the gist thereof.

1. 1. Dilute Sulfuric Acid Production Equipment and Dilute Sulfuric Acid Production Method Hereinafter, the dilute sulfuric acid production equipment and the dilute sulfuric acid production method according to one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a schematic view showing an upstream process of the dilute sulfuric acid producing apparatus 40, and FIG. 2 is a schematic diagram showing a downstream process of the dilute sulfuric acid producing apparatus 40. The "dilute sulfuric acid" of the present invention means an aqueous sulfuric acid solution having a sulfuric acid concentration of less than 90% by mass, and is defined by JIS K1321 as "thin sulfuric acid" (sulfuric acid content 60 to 80% by mass) or "purified dilute sulfuric acid". (Sulfuric acid content 27 to 50% by mass).

The dilute sulfuric acid production apparatus 40 of the present embodiment includes means for supplying a raw material. The raw material of the present embodiment comprises molten sulfur, desulfurization waste liquid, and purified COG as an auxiliary combustion material. The raw material supply means is a means for supplying these raw materials to the combustion furnace 51. The dilute sulfuric acid production apparatus 40 of the present embodiment includes a pipeline 41a for supplying a raw material containing molten sulfur as a raw material. Molten sulfur is sulfur recovered from refineries and the like in a molten state. A pump 41b is connected to the pipeline 41a, whereby the raw material is transferred to the pipeline 41c and supplied into the combustion furnace 51.

Further, the dilute sulfuric acid production apparatus 40 includes a pipeline 42 for supplying a desulfurization waste liquid which is a raw material. The desulfurization waste liquid is waste liquid from the desulfurization equipment installed for the purpose of removing soot, organic substances, sulfur compounds and the like in the exhaust gas (crude COG) discharged from the coke oven equipment and the like. Generally, the desulfurization waste liquid contains components such as _{free sulfur, free NH 3} , NH ₄ SCN, (NH ₄ ) ₂ S ₂ O ₃ , and H _{2 O.} The Among water (H 2 _O) is not particularly defined, but it is often a least 50 mass% of the total desulfurization effluent. The pipeline 42 communicates with the combustion furnace 51, and the desulfurization waste liquid is also supplied into the combustion furnace 51 as a raw material.

Further, the dilute sulfuric acid production apparatus 40 includes a pipeline 43 for supplying purified COG as an auxiliary combustion material. Refined COG is a gas generated in the process of producing coke used for iron making and the like. In general, purified COG _{contains components such as H 2} , N ₂ , O ₂ , CO, CO ₂ , CH ₄ , C ₂ H ₆ , and trace amounts of sulfur compounds. The pipeline 43 also communicates with the combustion furnace 51, and the refined COG is also supplied into the combustion furnace 51 as an auxiliary combustion material.

The pipeline 41a, the pump 41b, the pipeline 41c, the pipeline 42, and the pipeline 43 correspond to the raw material supply means of the present invention, and the raw material supply process is realized by these means. The raw materials (molten sulfur, desulfurization waste liquid, purified COG) supplied to the combustion furnace 51 by these are sulfur content (10 to 40% by mass) such as _{(NH 4} ) ₂ S ₂ O ₃ and nitrogen content such as _{NH 3.} It contains (5 to 20% by mass) and water (40 to 80% by mass). When there are a plurality of types of raw materials (three types of molten sulfur, desulfurization waste liquid, and purified COG) as in the present embodiment, the water content is defined as a value calculated in a state where each raw material is mixed.

A pipe line 44a for supplying compressed air, which is a spray medium, is connected to the pipe line 41c and the pipe line 42. A steam heater 44b is provided in the pipeline 44a, and heated air is supplied to the pipeline 41c to perform fine spraying to improve the combustion efficiency of these raw materials. Further, the dilute sulfuric acid production apparatus 40 is provided with a pipeline 45a for supplying air. The air supplied from the conduit 45a is transferred to the conduit 45c via the blower 45b.

An oxygen gas generator (PVSA45d) is provided in the pipeline 45c, and a high concentration of oxygen is supplied from the PVSA45d. PVSA45d is a device that efficiently obtains high-purity oxygen by adsorbing and removing nitrogen in the air under pressure using an adsorbent such as zeolite. PVSA45d is capable of generating oxygen with a purity of 90-93% by mass. This oxygen is mixed with the air in the pipeline 45a and supplied into the combustion furnace 51 as air having a high oxygen concentration. The PSA method may be used as the oxygen gas generator 45d. Alternatively, oxygen may be supplied by branching from the existing oxygen gas pipe.

The pipe line 44a, the steam heater 44b, the pipe line 41c, the pipe line 45a, the blower 45b, the pipe line 45c, and the PVSA 45d correspond to the oxygen-containing gas generating means of the present invention, and the oxygen-containing gas generating step is realized by these means. To do. The oxygen-containing gas supplied to the combustion furnace 51 by these means has an oxygen concentration of 25 to 40% by volume.

The combustion furnace 51 (combustion means) performs a combustion step of burning a raw material with an oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx) and 10% by mass or more of water. FIG. 3 is a schematic view showing the internal structure of the combustion furnace 51. As shown in this figure, on the left side of the combustion furnace 51, a supply port 51a for supplying the raw material and the oxygen-containing gas is provided, and the raw material is burned inside and the combustion gas is discharged from the discharge port 51b on the right side. It is discharged. In the present embodiment, molten sulfur is supplied from the upper supply port 51a in the figure, desulfurization waste liquid is supplied from the lower supply port 51a, and purified COG is supplied from a supply port (not shown). In addition to the mode in which the raw materials are supplied from different supply ports for each type of raw materials as in the present embodiment, the raw materials may be supplied to the combustion furnace 51 in a state where a part or all of the raw materials are mixed in advance.

There is a water evaporation region on the raw material supply side of the combustion furnace 51, where the water in the desulfurization waste liquid mainly evaporates. The right side is the combustible material combustion area, and the combustible material in the desulfurization waste liquid, which is a combustible material, burns. There is a boundary between them. A grid-like brick 51c is provided between the combustible material combustion area and the discharge port 51b. The lattice-shaped brick 51c is formed by arranging cubic heat-resistant bricks in a lattice pattern and partially opening the bricks. The aperture ratio of the lattice brick 51c is preferably around 50%. The lattice brick 51c is often provided in a plurality of stages.

The oxygen-containing gas of the present invention contains 25 to 40% by volume of oxygen, but if it is burned in the atmosphere (21% by volume oxygen), the oxygen concentration in the wet gas-based combustion air in the boundary region will be. It drops to the level of 10% by volume. Therefore, in this case, in order to completely burn the combustible material (raw material), it is necessary to keep the temperature at 1000 ° C. or higher, preferably 1100 ° C.

On the other hand, in the present invention, it is an oxygen-containing gas (tomi-oxygen air) containing 25 to 40% by volume of oxygen. Therefore, although the oxygen concentration in the wet gas-based combustion air in the boundary region drops to the level of 20% by volume, the combustion state of the raw material in the normal atmosphere can be maintained. Therefore, in the present invention, complete combustion can be achieved in the combustion furnace 51 at a relatively low temperature of 1000 ° C. or lower, preferably around 950 to 1000 ° C.

By providing the grid-like brick 51c provided in the wake of the combustible material combustion region, the following functions can be exhibited. The lattice brick 51c is physically combined with air so that the combustible material does not cause a blow-by phenomenon in the unburned state even if there is a defect in the mixed state of the air and the combustible material in the combustible material combustion region. It has the function of promoting remixing with combustibles and promoting reburning due to the heat possessed by the bricks. For this purpose, it is preferable to install a plurality of stages of latticed bricks 51c. Further, the openings of the plurality of stages of the grid-like bricks 51c are arranged in a staggered manner. As a result, the dust in the gas adheres to and grows on the brick surface and falls. Therefore, it is preferable to install a plurality of stages of grid-like bricks 51c that accumulate the falling dust without providing an opening at the lowermost portion.

FIG. 6 is a schematic view of another embodiment of the means for supplying the oxygen-containing gas to the combustion furnace 51. Among the raw materials to be burned, the burner of the sulfur supply port 51a is provided with a means for supplying air from the pipeline 45e, and the burner of the desulfurization waste liquid supply port 51a is provided with a means for supplying oxygen-containing gas from the pipeline 45e. .. Since the calorific value of the desulfurization waste liquid is as low as less than 5000 kJ / kg, it is difficult to burn, but combustion is promoted by supplying an oxygen-containing gas containing 25 to 40% by volume of oxygen to the burner. On the other hand, it is only necessary to supply air to a raw material having a high calorific value such as molten sulfur. It is preferable that both are independently controlled for combustion.

The combustion gas generated in the combustion furnace 51 is transferred to a waste heat boiler 52 (Waste Heat Boiler: WHB) (cooling means). The exhaust heat boiler 52 supplies pure water into the boiler, evaporates with the combustion gas to generate steam, and performs a cooling step of cooling the combustion gas by heat exchange. As a result, the temperature of the combustion gas is cooled to 380 to 460 ° C, preferably about 420 ° C.

The combustion gas cooled by the exhaust heat boiler 52 is introduced into the converter 61 (reaction means). The combustion gas cooled by the exhaust heat boiler 52 contains a small amount of nitrogen (for example, undecomposed NH ₃ and NOx such as NO and NO _2). The converter 61 is a reaction gas containing _{sulfur trioxide (SO 3} ), which is oxidized by reacting _{sulfur dioxide (SO 2} ) in the combustion gas with oxygen by a catalyst installed in a plurality of stages (three stages in the figure). Perform a reaction step to produce. More specifically, the converter 61 directly mixes the atmosphere attracted from the outside with the converted gas whose temperature rises due to the exothermic reaction of sulfur oxide (SOx) and oxygen by the catalyst of the previous stage among the plurality of stages. A reaction gas containing _{sulfur trioxide (SO 3} ) is produced by a method of lowering the temperature to a temperature suitable for the catalytic reaction in the subsequent stage.

5A and 5B are schematic views showing the internal structure of the converter 61. FIG. 5A is a side sectional view, FIG. 5B is a sectional view taken along the line AA'of FIG. It is an enlarged view in the broken line circle. As shown in this figure, the converter 61 sends out air from the main air pipe 61a that takes in atmospheric air, the branch air pipe 61b that branches from the main air pipe 61a in the vessel, and the branch air pipe 61b into the vessel. It is provided with an air port 61c and the like.

As the catalyst, a known catalyst used for producing sulfuric acid can be used, and examples thereof include vanadium pentoxide (V ₂ O ₅ ). Vanadium pentoxide has a denitration function _{and reacts NH 3} with NOx to decompose it into nitrogen (N ₂ ) and water (H _{2 O).} Therefore, it is possible to perform the generation of sulfur trioxide by the present catalyst, the nitrogen partial decomposition of (NH ₃ and NOx) simultaneously. _{Since 60 to 80% of sulfur dioxide (SO 2} ) undergoes an oxidation reaction in the first stage of the converter 61, the gas temperature after the reaction is about 500 to 600 ° C, preferably about 540 ° C. _{The remaining sulfur dioxide (SO 2} ) is oxidized to sulfur trioxide (SO ₃ ) in the second and third stages of the converter 61, and the inlet temperature of either stage is preferably around 420 ° C. Therefore, the temperature is controlled by directly mixing the atmosphere with the outlet gas in the previous stage.

A denitration catalyst may be arranged on the upstream side of the first stage of the converter 61 (the inflow side of the combustion gas from the exhaust heat boiler 52), and as the denitration catalyst, vanadium pentoxide is mixed with an auxiliary catalyst. Can be used. Examples of the co-catalyst include titanium oxide (TiO ₂ ), vanadyl sulfate (VOSO ₄ ), or a mixture thereof. When converting sulfur oxides, by providing a denitration catalyst containing the above-mentioned co-catalyst, the reaction of nitrogen decomposition takes precedence over the conversion of sulfur oxides, and the nitrogen content proceeds. It is disassembled. Then, in the subsequent stage of the denitration catalyst, the sulfur oxide can be efficiently converted in a state where it is not easily affected by the nitrogen content by vanadium pentoxide containing no co-catalyst.

The reaction gas generated by the converter 61 is transferred to the exhaust heat boiler 62 and cooled. As the exhaust heat boiler 62, the same device as the exhaust heat boiler 52 described above can be used. In the exhaust heat boiler 62, the reaction gas is cooled to about 300 ° C., which is a temperature avoiding the sulfuric acid dew point, which is about 250 ° C. The exhaust heat boiler 62 is recommended to be installed from the viewpoint of effective use of energy, but it is not an essential device in the present invention and can be installed arbitrarily.

Next, as shown in FIG. 2, the reaction gas cooled by the exhaust heat boiler 62 is transferred to the bottom of the dilute sulfuric acid column 71 (dilute sulfuric acid producing means) that performs the dilute sulfuric acid producing step. The dilute sulfuric acid tower 71 is _{a device that absorbs H 2} O and SO ₃ in the reaction gas into a circulating sulfuric acid aqueous solution (H ₂ SO ₄ ) to generate dilute sulfuric acid for the product, and is also called an absorption tower. The inside of the dilute sulfuric acid column 71 is filled with a filler, and the sulfuric acid aqueous solution is sprayed toward the filler from the upper part of the column, and when the reaction gas passes between the fillers, it comes into contact with the sulfuric acid aqueous solution. ₂ O and SO ₃ are absorbed in the sulfuric acid aqueous solution.

The _{aqueous sulfuric acid solution that has absorbed SO 3} is transferred to the tank 73, cooled by CWS (Cooling Water Supply) and CWR (Cooling Water Return) in the heat exchanger 74 with cooling water from a cooling tower (not shown), and then cooled. It is stored in the tank 75 as a final product. In the tank 75, the temperature of the aqueous sulfuric acid solution has dropped to about 60 ° C.

_{Gas containing sulfuric acid mist, unreacted SO 2, and the} like is discharged from the top of the dilute sulfuric acid column 71. In this exhaust gas, the sulfuric acid mist recovered by the electrostatic precipitator 76 is transferred to the tank 73 and reused as an aqueous sulfuric acid solution, but the rest is transferred to the abatement tower 81a (gas removing means) for performing the gas removing step. Will be done.

The exhaust gas from the electrostatic precipitator 76 is transferred to the bottom of the abatement tower 81a and comes into contact with the ammonia water also introduced from the bottom of the tower. _{SO 2} in the exhaust gas reacts with ammonia to produce ammonium sulfite (NH ₄ HSO ₃ : Ammonium Sulfate). Most of the waste liquid containing ammonium sulfate is circulated and returned to the abatement tower 81a by the pump 82, and a part of the waste liquid is air-oxidized by the oxidizing air from the blower 83 through an in-line mixer or the like, and is passed through the gas-liquid separator 84. It is transferred to the tank 85 as ammonium sulfate (NH ₄ HSO _4). The gas from the abatement tower 81a and the accompanying mist are washed with the circulating fluid of the abatement tower 81b by the pump 86, and the gas is discharged from the abatement tower 81b. The exhaust gas after detoxification does not contain _{SO 2, but only N 2} , O ₂ , CO ₂ and NOx within the regulation value.

The exhaust gas is sucked / boosted by the blower 87 and discharged into the atmosphere through the chimney 88. The blower 87 has a function of creating a negative pressure for all of the individual devices of the dilute sulfuric acid production device 40. This prevents harmful gases from flowing out to the atmosphere due to their high temperature. Further, the converter 61 also has a function of attracting air in the atmosphere without providing any special equipment. As described above, dilute sulfuric acid production and exhaust gas treatment are performed.

2. Simulation (1) Simulation of the entire dilute sulfuric acid production equipment For the dilute sulfuric acid production equipment 40 shown in FIGS. 1 and 2, an electrolyte simulator “OLI Flowsheet: ESP” (OLI systems) and a general-purpose process simulator are used based on the set values shown in Table 1. Simulation was performed using PRO / II ^TM (AVEVA) and calculation software.

For each device in the figure, the values in the table below were used as the setting values for material balance.

For the desulfurized waste liquid and COG of the raw materials, the values in the table below were used as the set values of the components.

The results of the above simulation are shown in the table below. The "item" row of the table shows the numerical values surrounded by diamonds in FIGS. 1 and 2, and the rows below it show the results such as temperature and component at the position of the item.

From this result, it was found that the final concentration of dilute sulfuric acid was 58.0% by mass (item 22). Further, the same simulation was performed for the dilute sulfuric acid production apparatus 40 having no PVSA45d and having the same oxygen concentration in the air introduced into the combustion furnace 51 as the atmosphere. As a result, the exhaust gas (item 6) discharged from the combustion furnace 51, the converter inlet gas (item 12), and the exhaust gas (item 31) discharged to the chimney 88 are 10105 Nm ³ /, respectively, when PVSA45d is present. It was h (table below), 10105 Nm ³ / h (table below), and 11095 Nm ³ / h (table below). On the other hand, the items are, if there is no PVSA45d were respectively 17350Nm ³ / h and 17350Nm ³ / h and 17861Nm ³ / h. From this, it was found that the amount of exhaust gas can be reduced by about 40% by increasing the oxygen concentration of the oxygen-containing gas to 33% by volume by PVSA45d as in the present invention. As a result, for example, in the case of the converter 61, the required amount of catalyst is calculated under almost constant conditions, that is, the inverse of the time that the gas contacts the catalyst layer per unit time, that is, the space velocity SV (unit, 1 / hr). Therefore, the required amount of catalyst can be reduced by 42% by reducing the amount of gas by 42%.

(2) Simulation of Combustion Furnace 51 The combustion furnace 51 of FIG. 3 was simulated using the chemical reaction simulation software “CHEMKIN” (ANSYS). The conditions are as follows.
<Calculation conditions>
-Replace all liquid substances with gas.
-For chemical species containing S, replace with _{N 2 as an inert substance.}
・ Plug flow flow inside the combustion furnace.
・ The heat generated by combustion is not considered.
-Perform the analysis with and without PVSA.

The values in the table below were set for the components at the inlet of the combustion furnace 51.

For the above components, the following numerical values were set as the input values for the simulation.

The following numerical values were set as the calculation conditions for the combustion furnace 51.

The result (graph) of the simulation is shown in FIG. The NO production amount at the furnace outlet in the case without PVSA was set to 1, and the case was compared with the case with PVSA. As shown by NO in this figure, it can be seen that the amount of NOx produced is smaller in the case with PVSA. In the case without PVSA, it was found that NOx was generated by the combustion of _{CH 4} , H _{2, and CO on the combustion furnace inlet side.} It is presumed that the reason why the amount of NOx produced is lower with PVSA is that in the case with PVSA, there is almost no inflow of flammable gas from the COG gas line.

40 Dilute sulfuric acid production equipment, 41a pipeline (raw material supply means), 41b pump (raw material supply means), 41c pipeline (raw material supply means), 42 pipeline (raw material supply means), 43 pipeline (raw material supply means), 44a pipeline (oxygen-containing gas generating means), 44b steam heater (oxygen-containing gas generating means), 45a pipeline (oxygen-containing gas generating means), 45b blower (oxygen-containing gas generating means), 45c pipeline ( Oxygen-containing gas generating means), 45d PVSA (oxygen-containing gas generating means), 45e pipeline, 51 combustion furnace (combustion means), 51a supply port, 51b discharge port, 51c lattice brick, 52 exhaust heat boiler (cooling means) , 61 converter (reaction means), 61a main air pipe, 61b branch air pipe, 61c air port, 62 exhaust heat boiler, 71 dilute sulfuric acid tower (dilute sulfuric acid producing means), 73 tanks, 74 heat exchangers, 75 tanks, 76 Electrostatic collector, 81a abatement tower (gas removal means), 81b abatement tower (gas removal means), 82 pump, 83 blower, 84 gas-liquid separator, 85 tank, 86 pump, 87 blower, 88 chimney

Claims (18)

A raw material supply means for supplying a raw material containing at least sulfur content, nitrogen content, and water content of 40 to 80% by mass or more.
An oxygen-containing gas generating means for generating an oxygen-containing gas having an oxygen concentration of 25 to 40% by volume,
A combustion means for burning the raw material with the oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx: here, 1 ≦ x <3) and 10% by mass or more of water.
A cooling means for cooling the combustion gas and
A reaction means for generating a reaction gas containing _{sulfur trioxide (SO 3} ) by oxidizing the sulfur oxide (SOx) with a catalyst.
A dilute sulfuric acid producing apparatus comprising: a dilute sulfuric acid producing means for cooling the reaction gas to produce dilute sulfuric acid. The dilute sulfuric acid production apparatus according to claim 1, wherein the combustion means burns the raw material at 900 to 1100 ° C. The dilute sulfuric acid producing apparatus according to claim 1, further comprising a gas removing means for removing unreacted sulfur dioxide in the dilute sulfuric acid producing means. The gas removing means is characterized by reacting the unreacted sulfur dioxide with ammonia to produce ammonium sulfite (NH ₄ HSO ₃ : ammonium sulfate) and recovering it as _{ammonium sulfate (NH 4} HSO _{4) by oxidation.} The dilute sulfuric acid production apparatus according to claim 1. The dilute sulfuric acid production apparatus according to claim 1, wherein the combustion means is a combustion furnace provided with a partially open grid-like brick inside. The dilute sulfuric acid production apparatus according to claim 1, wherein the reaction means is vanadium pentoxide (V ₂ O _{5) as the catalyst and also has a denitration function.} The dilute sulfuric acid production apparatus according to claim 6, _{wherein the reaction means further comprises a denitration catalyst containing titanium oxide (TiO 2} ) and / or vanadyl sulfate (VOSO ₄ ) as an auxiliary catalyst in addition to the catalyst. .. The reaction means includes the catalyst installed in a plurality of stages, and the atmosphere attracted from the outside to the converted gas whose temperature is raised by the exothermic reaction between the sulfur oxide and the oxygen by the catalyst in the previous stage among the plurality of stages. The dilute sulfuric acid production apparatus according to claim 1, wherein the dilute sulfuric acid production apparatus is characterized by directly mixing and lowering the temperature to a temperature suitable for the catalytic reaction in the subsequent stage. The dilute sulfuric acid according to claim 1, wherein the combustion means supplies the oxygen-containing gas to a raw material of less than 5000 kJ / kg for combustion, and supplies air to a raw material of 5000 kJ / kg or more for combustion. Manufacturing equipment. A raw material supply process for supplying a raw material containing at least sulfur content, nitrogen content, and water content of 40 to 80% by mass or more.
An oxygen-containing gas generation step that produces an oxygen-containing gas having an oxygen concentration of 25 to 40% by volume,
A combustion step of burning the raw material with the oxygen-containing gas to generate a combustion gas containing sulfur oxides (SOx: here, 1 ≦ x <3) and 10% by mass or more of water.
A cooling process for cooling the combustion gas and
A reaction step of oxidizing the sulfur oxide (SOx) with a catalyst to generate a reaction gas containing _{sulfur trioxide (SO 3), and}
A method for producing dilute sulfuric acid, which comprises a dilute sulfuric acid producing step of cooling the reaction gas to produce dilute sulfuric acid. The dilute sulfuric acid production method according to claim 10, wherein the combustion step burns the raw material at 900 to 1100 ° C. The method for producing dilute sulfuric acid according to claim 10, further comprising a gas removing step for removing unreacted sulfur dioxide in the dilute sulfuric acid producing step. The gas removal step is characterized in that unreacted sulfur dioxide is reacted with ammonia to produce ammonium sulfite (NH ₄ HSO ₃ : ammonium sulfate) and recovered as _{ammonium sulfate (NH 4} HSO _{4) by oxidation.} The method for producing dilute sulfuric acid according to claim 10. The dilute sulfuric acid production method according to claim 10, wherein the combustion step uses a combustion furnace provided with a partially open grid-like brick inside. The dilute sulfuric acid production method according to claim 10, wherein in the reaction step, the catalyst is vanadium pentoxide (V ₂ O _{5) and also has a denitration function.} The method for producing dilute sulfuric acid according to claim 15, _{wherein the reaction step further comprises a denitration catalyst containing titanium oxide (TiO 2} ) and / or vanadyl sulfate (VOSO ₄ ) as an auxiliary catalyst in addition to the catalyst. .. The reaction step includes the catalyst installed in a plurality of stages, and the atmosphere attracted from the outside is introduced into the converted gas whose temperature is raised by the exothermic reaction between the sulfur oxide and the oxygen by the catalyst in the previous stage among the plurality of stages. The method for producing dilute sulfuric acid according to claim 10, wherein the dilute sulfuric acid is directly mixed and lowered to a temperature suitable for the catalytic reaction in the subsequent stage. The dilute sulfuric acid according to claim 10, wherein the combustion step supplies the oxygen-containing gas to a raw material of less than 5000 kJ / kg for combustion, and supplies air to a raw material of 5000 kJ / kg or more for combustion. Production method.