JPH0360765B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalytic process for converting sulfur dioxide to sulfur trioxide in the production of sulfuric acid.

Numerous methods have been developed for the production of sulfuric acid, nearly all of which involve oxidizing a sulfur-containing feedstock to produce a gaseous stream containing sulfur dioxide, and catalytically oxidizing the sulfur dioxide to produce sulfuric acid. It involves the basic process of converting sulfur oxide to sulfur trioxide and absorbing the sulfur trioxide in concentrated sulfuric acid to produce more concentrated sulfuric acid. The sulfur-containing feed stream for combustion may contain elemental sulfur, hydrogen sulfide, pyrite or other sulfides, or sludgeacid obtained from petroleum refining. Elemental sulfur is the preferred raw material for most large scale industrial equipment. The oxidation of sulfur dioxide to sulfur trioxide is usually carried out in the presence of vanadium or platinum type catalysts, although other catalytic materials known in the art may also be used where appropriate. The oxidation reaction of sulfur dioxide to sulfur trioxide is a highly exothermic reaction. Therefore, in order to avoid overheating of the catalyst, the reaction is usually carried out in several steps consisting of partial conversion with cooling of the gas stream, the cooling section being carried out between each step. The resulting sulfur trioxide is absorbed into concentrated sulfuric acid to produce more concentrated sulfuric acid.

As previously mentioned, vanadium or platinum containing catalysts are commonly used in the catalytic oxidation of sulfur dioxide to sulfur trioxide. Traditionally, in industrial sulfuric acid operations, these catalysts have been used in granular form, that is, as a plurality of separate particles of catalyst-containing material, and placed in a compressed bed for passage through which the sulfur dioxide-containing gas passes. It's arranged. The use of a bed of such catalyst-containing material allows the catalytic sulfur dioxide oxidation portion of the sulfuric acid production process to operate at superficial gas velocities in the range of about 80-100 ft. (24-30 m)/min. This was common practice, and this superficial gas velocity required a large converter so that the gas could not be transferred between the converter and other equipment located at or near the ground surface, such as a heat exchanger. A long pipeline is required to transport it. The construction costs for equipment for producing sulfuric acid are thereby relatively high. Therefore, significantly reducing the size of the processing equipment for a given capacity facility as well as reducing the site requirements for the facility typically results in reduced construction capital.

U.S. Patent No. 1 for the manufacture of honeycomb catalysts
No. 3554929 lists this species of vanadia.
It is mentioned that the use of the containing catalyst in the oxidation of sulfur dioxide can be envisaged (see column 7, lines 12 to 16). In this patent, it is proposed that the employment of such a catalyst would require no change in normal process conditions to result in a significant increase in the yield of sulfur trioxide, and thus the yield of sulfuric acid, for a given volume and capital of catalyst. It is not disclosed that it could be combined with special modifications. As far as is known, catalysts of this type have not previously been utilized in the oxidation of sulfur dioxide.

It is an object of the present invention to provide a process for the conversion of sulfur dioxide to sulfur trioxide in the production of sulfuric acid, which inter alia eliminates the conventional catalytic converter design and requires a considerable amount of pipework. ,
The overall capital cost of sulfuric acid production facilities can be reduced by eliminating struts, piping and other structural materials, and by reducing site requirements in terms of volume given to sulfuric acid production operations.

In its broader aspects, the invention comprises: by passing a gaseous stream containing sulfur dioxide and oxygen in contact with a solid oxidation catalyst at an elevated temperature;
A catalytic catalytic oxidation process for producing sulfur trioxide from sulfur dioxide is directed to convert at least a portion of the sulfur dioxide in a gaseous stream to sulfur trioxide. In this method, the catalyst has a large surface area, i.e., a honeycomb-shaped configuration;
The sulfur dioxide and oxygen containing gas stream is also contacted with the oxidation catalyst at a superficial gas velocity of at least about 500 ft. (152 m)/min. According to the present invention, this superficial gas velocity is about 500 to 3000 ft. (152 to 914 m)/
preferably in the range of about 1500 to 2500 ft. (457 to 762 m) per minute. These rates are at oxidation reaction conditions and therefore refer to actual ft. (m)/min. The present invention specifically describes a plant designed for the oxidation of sulfur dioxide to sulfur trioxide and the production of sulfuric acid by using unique oxidation catalyst structures and operating conditions for the chemical conversion, including, among others: This is based on the recognition that the capital cost is greatly reduced, yet it can be installed with satisfactory yields of sulfur trioxide and sulfuric acid. Thus, for example, by operating with superficial gas velocities of the above order in a catalytic converter for the present process, the dimensions of the converter, along with the length of other associated processing equipment, e.g. It becomes possible to reduce the

In the oxidation of sulfur dioxide, monolithic catalysts are used in the present invention, which combine the catalytically active metal component with a solid support having a relatively high geometric or void surface area and a relatively low resistance to gas flow. It is placed on the body. Most of the cross section of the catalyst structure is open for gas flow therethrough. Furthermore, this structure, unlike compressed beds of individual particles, has a relatively low resistance to gas flow and therefore exhibits low pressure drop performance. Characteristically, this catalyst structure has a plurality of relatively large gas flow passages, which can be used to obtain the desired low pressure drop.
As long as it is not essentially unidirectional, it suffices if it is approximately unidirectional.

This shape of the catalyst support is clearly exemplified by a monolithic or honeycomb support. These carriers have a plurality of channels extending through the monolithic structure, and these channels are open to fluid flow, so that these channels are connected from one inlet to another outlet. It will not become blocked or sealed against the flow. This channel is very large compared to the size of any surface pores, and the fluid passing through this channel does not experience an excessive pressure drop. Preferably, the flow path is essentially straight from its fluid inlet to its fluid outlet. The open area of a cross-section essentially perpendicular to the direction of gas flow through the structure of the catalyst may be about 50-60% or more of such total cross-sectional area. This open area is approximately 70-90% of the cross-sectional area of the catalyst structure.
It is preferable that This structure has a cross section
It is possible to have at least about 50 or more gas inlet openings for flow channels and a corresponding number of gas flow channels per in ² (6.45 cm ² ). The number of such channels may be less than about 400, or up to about 350 or slightly more ^per in ² of cross-section. This structure has a cross section in ²
It is preferred to have about 100 to 300 gas inlets and channels per (6.45 cm ² ). The major cross-sectional dimensions of the individual channels in the structure may be at least about 0.5 mm.

As used herein, the term "monolithic catalyst" refers to a catalyst of the present invention consisting of a type having a substantial cross-section of a framework support structure;
This is to be distinguished from pellet-type catalysts, which are normally arranged as compacted beds in particle-to-particle contact that meander from one interstitial space to another in response to a passing gas flow. be. The cross-sectional area of the catalyst according to the invention need not be a single piece forming a monolith, but rather a plurality of monolithic sections deployed in parallel relationship with cross-sectional dimensions appropriate to the dimensions of the converter used. It may be of any size, larger, and forming an essentially monolithic structure.

The flow paths of monolithic carriers are typically thin-walled channels with a relatively large geometric surface area. These channels can have one or more of a variety of cross-sectional shapes and dimensions. These channels are therefore
For example, it may consist of a trapezoidal, rectangular, square, sinusoidal, hexagonal, oval, circular or other shaped cross-sectional shape, so that the cross-section of the support has a repeating pattern, i.e. a honeycomb, a wave or a lattice. This indicates a pattern that can be expressed as a morphological structure. The walls of the chamber channels are generally of a thickness necessary to obtain a strong unitary body, and most have a thickness of about 0.5
In the range of 25 mils (approximately 0.013 mm to 0.635 mm). Metal structures are preferred; most have a thickness of about 0.5 to 25 mils.
0.635 mm), whereas ceramic structures typically have a thickness of about 5 to 25 mils (0.13 mm).
The thickness is between 0.635mm and 0.635mm.

Although the carrier may have ceramic properties in nature, it is preferably made of metal, preferably one or more metals or alloys. Such metal structures should be able to withstand oxidizing atmospheres and temperatures, including the conversion of sulfur dioxide to sulfur trioxide.
The degree (order) of such a temperature is about 1300〓
(up to 704℃). Accordingly, the metallic support can be prepared from heat resistant, base metal alloys, especially those in which iron is a substantial or major component. Various nickel-containing alloys, such as stainless steel, are among those that can be used. The surface of the metal carrier is exposed to very high temperatures, e.g. at least about 1000°C.
to improve the corrosion resistance of the alloy by forming an oxide layer on the surface of the support.
In this case, the oxide layer is of greater thickness and surface area than would be obtained by room temperature oxidation. Oxidation or establishment of a broadly developed surface on the alloy support by high temperature oxidation can enhance the adhesion of the refractory oxide support and the contact-promoting metal component to the support. In general, suitable metal-based substrates have properties such as stability under process operating conditions, the ability to form strong bonds with the applied catalytic material, and ease of manufacturing shaped bodies.

The metal-supported catalyst can have a number of suitable shapes, including corrugated and coiled shapes to form a structure with a plurality of parallel-extending tubes or cells. Examples of metal-based catalyst shapes and methods for their preparation are disclosed in US Pat. No. 3,891,575 and US Pat. No. 4,098,722. In choosing the appropriate geometry for this type of metal-supported catalyst, there are competing advantages: minimizing the diameter of the flow path to maximize the effective catalyst surface, and minimizing the pressure drop across the catalyst. A balance should be struck between maximizing the diameter of the flow path and minimizing it. Advantages of metal-supported catalysts include, in addition to the high gas velocities mentioned herein in practice, resistance to mechanical and thermal shock, high surface area-to-volume ratios, and the ability to rapidly bring the catalyst up to operating temperature during start-up. High thermal conductivity and low thermal mass that cause heating, particulate matter transferred into the gas stream,
Examples include resistance to clogging by dust and the like, and high porosity resulting in a low pressure drop across the catalyst.

The catalyst of the present invention contains trace amounts of one or more catalytically active metal components that enhance the oxidation of sulfur dioxide to sulfur trioxide, and has a large geometric surface area. deposited on a carrier. The catalytically active metal component is preferably supported by a relatively porous refractory metal oxide, such as alumina, silica, magnesia, diatomaceous earth, or a combination of these materials, such as magnesia-alumina. Typically, this carrier has a molecular weight of about 10% as determined by the BTE method.
The total surface area includes an area of pores ranging from less than 20 m ² /g, often less than about 1 m ² /g. In comparison, porous refractory oxide supports for catalytically active metals should have a total surface area of at least about 50 m ² /g, and for example up to about 350 to 400 m ² /g. be. These supports may be a minor portion of the total catalyst, ie, about 1 to 35% by weight, alternatively about 5 to 25% by weight.

The catalytically active metal component of the catalyst may be one of many materials suitable for promoting the oxidation of sulfur dioxide to sulfur trioxide. These promoters generally contain metals in elemental or compounded form, and the promoters are a minor portion of the catalyst;
It is sufficient to promote oxidation. Among the known promoters, noble metals, especially platinum, constitute a minor portion, up to about 1% by weight of the catalyst, and usually at least about 0.1%. Vanadia-containing catalysts were often even more preferred. Catalysts of this type may then contain trace amounts of vanadium, ie about 1 to 10%, or often about 5 to 10%, of vanadium. Vanadium-containing catalysts may also contain small amounts of alkali metals such as potassium.

In the catalytic oxidation method for sulfuric acid production,
A sulfur dioxide-containing feed stream obtained from the combustion of sulfur is used as a source of sulfur dioxide in the catalytic conversion process. The total sulfur dioxide-containing feed gas contains sufficient molecular oxygen-containing gas, such as air or oxygen-enriched air, to effect essentially complete oxidation of sulfur dioxide to sulfur trioxide. The feed gas is passed through one or more typically adiabatic catalytic conversion zones containing multiple catalyst beds or stages. At least a portion of the sulfur dioxide passing through each catalyst stage is oxidized to sulfur trioxide, and the thermal energy generated by the catalytic conversion of sulfur dioxide to sulfur trioxide is then recovered at various points in the conversion system. It is possible to do so. The effluent from the conversion zone is passed through the absorption zone;
In this absorption zone, sulfur trioxide in the effluent is absorbed by contact with concentrated sulfuric acid, increasing the concentration of sulfuric acid.

The feed gas supplied to the catalytic oxidation system generally comprises a small amount of sulfur dioxide, ie, about 3 to 20 volume percent, preferably about 8 to 12 volume percent, on a dry basis. The molecular oxygen content of this gas is also often in minute proportions, e.g. about 0.5 mole per mole of sulfur dioxide, and there is no excess oxygen used based on the complete conversion of sulfur dioxide to sulfur trioxide. Preferably present. The largest and principal component of this gas is inert or relatively inert substances, especially nitrogen contained in the air, which is used as a source of oxygen in the oxidation of sulfur to sulfur dioxide. The sulfur dioxide stream from the sulfur combustion process contains water vapor, which is largely removed before the sulfur dioxide is used in the catalytic conversion process to avoid the formation of sulfuric acid mist.

For example, a sulfur dioxide-containing gas stream can be conveniently dried in a drying tower arrangement in which the feed is contacted with concentrated sulfuric acid from, for example, a sulfur trioxide absorption zone.

The dry, dilute sulfur dioxide-containing stream comprises the feedstock for the first catalytic stage in the conversion zone and typically contains a stoichiometric excess of oxygen.
Prior to contacting the dilute sulfur dioxide gas with the first stage catalyst, the temperature of the gas is adjusted to be slightly higher than the starting temperature for the catalytic oxidation of sulfur dioxide to sulfur trioxide. This adjustment involves cooling or heating treatment with a gas source. The onset temperature for catalytic oxidation of sulfur dioxide can be varied depending on the catalytic gas composition and catalyst. Vanadium pentoxide catalysts, for example, can oxidize most sulfur dioxide-containing process gases over a temperature range of about 400°C.
It can be activated at temperatures between 450°C and 450°C. However, certain catalysts and contact gases can be used at lower temperatures. Furthermore, this starting temperature can vary from one catalytic zone to another in a multistage converter. The catalytic oxidation onset temperature typically ranges from about 380°C to 470°C, and the catalytic gas flow supplied to each catalytic stage within the conversion zone typically has an inlet temperature approximately equal to or slightly above the catalytic oxidation onset temperature. Heated to temperature or cooled (if necessary). When converting a gas containing sulfur dioxide to sulfur oxide, a large amount of heat is released in the first catalyst flow path, in which a major portion (e.g. more than 50%) of the sulfur dioxide in the feed stream fed to this catalyst is released. ) can be converted. Thus, the sulfur dioxide gas stream entering the converter at approximately 420°C, while traversing the first catalyst structure,
It will be exothermically heated to over 600°C. Exothermic heat is also generated in other catalyst stages throughout the conversion zone, but to a lesser extent. The heat produced by the exothermic catalytic oxidation of sulfur dioxide to sulfur trioxide in the conversion zone can be removed from the gas stream by indirect heat exchange in a heat exchanger, such as a self-contained heat exchanger.
This indirect heat exchange relationship between the gaseous stream containing the first catalyst stage effluent and the heat exchange medium brings the gaseous stream to a temperature corresponding to or slightly above the oxidation onset temperature for the second catalyst stage in the conversion zone. and this temperature is, for example, between 400°C and 460°C, especially when using a vanadium pentoxide catalyst, about
Preferably, the temperature is 420°C to 440°C.

In the second catalytic stage, sulfur dioxide is further converted to sulfur trioxide as follows. That is, after the second catalytic stage, about 50 to 80 volume percent of the total sulfur dioxide fed to the conversion zone has been oxidized to sulfur trioxide. If the conversion rates of sulfur dioxide to sulfur trioxide in the first catalytic stage and the second catalytic stage are considered to be equal, the conversion rate per catalytic stage is about 30 to 60% by volume for each stage. Second
The effluent from the catalyst stage is continuously fed through at least one additional catalyst stage within the conversion zone to provide substantially complete conversion of sulfur dioxide to sulfur trioxide. If desired, a portion of the sulfur dioxide or oxygen fed to the process may be added to one or more second or subsequent catalyst stages. A portion of the exothermic energy produced in such additional catalyst stages can be recovered by cooling the effluent from each stage in an indirect heat exchanger to a temperature suitable for subsequent catalyst stages. Any suitable refrigerant, such as water, steam or other gases, may be utilized to recover heat within the self-contained heat exchange device.

Advantageously, the total sulfur dioxide conversion in the multi-stage conversion zone is at least about 90% by volume. for example. The conversion ranges from about 92 to 99.8% by volume of the total sulfur dioxide introduced into the conversion zone.
In single absorption type operations, essentially no sulfur trioxide is removed from the process gas stream between each catalyst stage. Rather, the sulfur trioxide-rich gaseous effluent from the final stage within the conversion zone is
It is preferably cooled by indirect heat exchange with the first stage feed stream of dilute sulfur dioxide and fed to an absorption zone where the sulfur trioxide is absorbed from the process gas stream by concentrated liquid sulfuric acid. Sulfur trioxide can also be removed from the reaction mixture by absorption in sulfuric acid between stages, for example in the well-known double absorption process. The conversion zone effluent is cooled to a temperature suitable for feeding the sulfur trioxide containing effluent to the sulfur trioxide absorption zone. Generally, such suitable temperatures range from about 120°C to 320°C.

The absorption zone can be configured to include any absorption device that functions to perform gas-liquid contact scraping. A number of commercially available absorption devices are capable of providing satisfactory service to either the intermediate or final absorption zone. Packed bed, countercurrent absorption devices using spherical or ring packing are
spray unit, disk and donuts,
Guided flow, ventilated co-current flow, bubble bell plate columns, perforated plate columns or similar devices are commonly used as well. Typically, the sulfur trioxide-containing process gas is introduced at the bottom of the absorber and rises countercurrently to the stream of scrubbing liquid that is introduced at the top of the device. The scrubbing liquid used in the absorber is typically a sulfuric acid solution containing at least about 98% by weight sulfuric acid. An enriched sulfuric acid solution, i.e., a strong acid product, is produced in the absorber and can be removed as product or recycled through the sulfur dioxide feed gas and oxygen-containing feed gas drying system. .

The gaseous effluent from the sulfur trioxide absorption zone may be passed through a mist eliminator to remove any carryover sulfuric acid and is then discharged from the sulfur trioxide absorption zone. Such a discharge stream consists primarily of nitrogen and also contains small amounts of oxygen. This is because an excess amount of oxygen is generally used in the oxidation system for complete conversion of sulfur dioxide to sulfur trioxide. The amount of sulfur dioxide in the effluent has very important implications as to whether it can be discharged into the atmosphere or whether such disposal should be prohibited from a pollution or economic point of view. To avoid emissions into the atmosphere, the exhaust gas from the sulfur trioxide absorber is reheated and passed through a further catalytic conversion zone, and then passed through a second absorption zone with the effluent being discharged to the atmosphere. Let it be absorbed in the room.

In accordance with the present invention, the above-described multistage catalytic oxidation process comprises combining a sulfur dioxide-containing feed gas stream with an oxidation catalyst in a conversion zone at a superficial gas velocity of at least about 500 ft.
(approximately 152 m)/min, preferably approximately 500 to 3000 ft. (approx.
152 to 914 m)/min, most preferably about 1500 to 914 m)/min.
At a speed within the range of 2500 ft. (approximately 457 to 762 m)/minute,
It operates by passing through contact.
For purposes of this invention, the superficial gas velocity is
as the volumetric flow rate of the gas stream passing through the conversion zone, e.g. ft. ³ (m ² )/min, divided by the cross-sectional area of the conversion zone across the flow of the gas flow expressed as, for example, ft ² (m ² )/min. It can be limited and determined by expressing it as . Therefore, for example about
A gas flow rate of 240,000 ft ³ (6797
m ³ )/min will have a superficial gas velocity of about 2125 ft./min (about 648 ft./min).

Referring to the accompanying drawings, an oxygen-containing gas, such as atmospheric air, preferably previously dried, typically by scrubbing with concentrated sulfuric acid, is transported by line 10 to line 14. A feed stream consisting of a sulfur-containing material, for example elemental sulfur, is fed into the combustion furnace 12. The oxygen and sulfur-containing gases become a mixture in furnace 12 and the mixture is maintained at a temperature of about 1000-1200°C, thereby causing the oxygen to react with the sulfur from line 14 to form sulfur dioxide. This sulfur dioxide is removed from the furnace 12 as a sulfur dioxide-containing stream in line 16. Also, this sulfur dioxide-containing stream is approximately
having a temperature in the range of 800-1200°C, usually above about 1000°C, and with excess oxygen about 8-14% by volume.
Contains sulfur dioxide.

After removal from the furnace 12, the gas stream in line 16 is passed through a heat exchanger 18 in which the gas is cooled to a temperature suitable for catalytic oxidation of sulfur dioxide to sulfur trioxide. Ru. The heat exchanger or boiler 18 may employ a heat exchange medium, such as water, which is introduced by conduit 17 and is passed through it in indirect heat exchange relationship with the gas stream. The steam produced leaves the heat exchanger 18 via line 19.

The heat extracted from the thermal sulfur dioxide-containing gas stream can be used, for example, to generate water vapor for use in the method or in the production of energy. The cooling gas exiting heat exchanger 18 has a temperature within the range of approximately 400°C to 550°C.

The sulfur dioxide-containing gas stream is then fed into the first monolithic catalyst stage at a high superficial velocity, i.e. about 200
It was introduced with a measured ft. (approximately 610 measured m)/minute.
The catalytic materials in the first and subsequent catalytic stages are deposited on the surface of the channels of the monolithic support and are preferably bound to a refractory oxide support such as activated alumina or magnesia-alumina. These catalyst stages are followed by a heat exchange section in which the gas stream from the nearest preceding catalyst is cooled prior to its introduction into the subsequent catalyst or other equipment.
Preferably, the installed heat exchanger has approximately the same diameter as the preceding catalytic stage. The illustrated apparatus is designed and operated so that only partial conversion of sulfur dioxide to sulfur trioxide occurs in each stage to minimize excessive temperature increases due to the exothermic nature of the reaction. This is because, among other things, the heat generated can cause deterioration of the catalyst and equipment.

The heat from the catalytic stage 22, the partially reacted gases, is cooled in a heat exchanger or boiler 24 by indirect contact with water, which is again taken in by line 23, to produce water vapor, which is removed by line 25. exit the exchanger. A cooled process gas having a temperature sufficient to initiate and maintain the oxidation of sulfur dioxide to sulfur trioxide is transferred to the second stage monolithic catalyst 2.
6, where additional amounts of sulfur dioxide in the gas stream are converted to sulfur trioxide.

The outflow gas from the second catalyst stage 26 is gas-to-gas;
It is cooled by indirect heat exchange in indirect heat exchanger 28. Temperature less than about 200℃, typically about 100-200℃
The resulting cooling gas having a temperature in the range of
9 to an intermediate absorption column (not shown), such as a packed gas-scrubbing column, where the reaction gas is in countercurrent to the flow of concentrated liquid acid. Sulfur trioxide in the gaseous stream fed to the column is absorbed into the fed sulfuric acid, with the consequent production of more concentrated sulfuric acid, which is diluted and partially recycled. Alternatively, it may be sent to a product utilization stage.

The remaining, unabsorbed gas stream from the intermediate absorber is substantially free of sulfur trioxide, but contains a small percentage, eg, about 0.1 to 1%, of unconverted sulfur dioxide. This gas stream is fed by line 30 to heat exchanger 28 where it is used as a cooling medium, so that the medium is fed from line 32 to converter 40 at a temperature in the range of approximately 400-500°C. heated to a temperature of Converter 40 includes two additional stages 41 of the sulfur dioxide oxidation catalyst of the present invention.
and 42 in series, thereby converting substantially all of the contained sulfur dioxide into sulfur trioxide. Each subsequent catalyst stage within converter 40 is an indirect heat exchanger for cooling the process gas stream. Following the third catalytic stage 41 is a steam superheater and following the fourth catalytic stage 42 is an economizer 44. The effluent gas leaving the converter 40 by line 45 is routed to a final absorption column (not shown) where the effluent gas is treated with a countercurrent of concentrated liquid sulfuric acid which absorbs substantially all the sulfur trioxide contained in the gas stream. come into contact with the current. The residual gas stream from the final absorber is substantially free of sulfur dioxide and can therefore be discharged to the atmosphere.

As will be apparent to those skilled in the art, the above description of one embodiment of the process for producing sulfuric acid is simplified for purposes of clarity and, therefore, many variations may be made in view of the economics of the process. It is possible to do this. For example, it is possible to use appropriate process gas streams for heat exchange in various parts of the process, rather than utilizing separate heat exchange media to maximize heat transfer within the plant. . It is also possible to combine the heat exchange functions of one or more separate heat exchangers and utilize various types of heat exchangers, such as gas-to-gas, boiler-type and economizer-type heat exchangers. be able to. Furthermore,
Although the sulfuric acid production process has been carried out in "dual absorption" type equipment, i.e. in which sulfur trioxide is removed from the process gas in both intermediate and final absorption, the present invention Also, "single absorption" type devices, i.e.
It can also be applied to devices in which sulfur trioxide is removed from the process gas stream only after leaving the last catalytic stage.

As mentioned earlier, an important feature of the present invention is that the method for producing sulfur trioxide from sulfur dioxide
This means that it is carried out at high superficial gas velocities, such as 500 to 3000 ft. (approximately 152 to 914 m)/min. The accompanying drawings show embodiments of a catalytic converter configuration that allows such flow rates to be achieved without substantial adverse effects, such as significant pressure drops. Although catalytic converters are shown in the drawings as arranged so that the gas flow through them is normally horizontal, these converters can also be used in other gas flow directions, such as vertically downwards, It should be appreciated that orientations such as vertically upwards may also be possible.

As previously mentioned, the use of the catalyst of the present invention with a gas stream having a superficial velocity of at least about 500 ft./min can significantly reduce the capital cost of a sulfuric acid production facility compared to conventional facilities. can be reduced to
These savings are achieved by, among other things, reducing the dimensions of the contact converter and simplifying its construction, reducing the number of conduits, and reducing the overall area required to accommodate the equipment.
For example, in a sulfuric acid production facility designed to produce approximately 1000 tons/day of sulfuric acid from a 10% sulfur dioxide feed gas stream, the flow of sulfur dioxide-containing gas through the converter is approximately 128,500 ACFM (approx.
3640cm ² /min.). Using a converter containing the catalyst of the present invention typically requires about 1130 ft ³ (about 32 m ³ ) of catalyst material. Therefore, if the superficial velocity of the gas stream passing through the converter is approximately
If the speed is 835 ft./min, a converter diameter of approximately 14 ft. (approximately 4.27 m) is sufficient.
However, if the superficial velocity increases to about 2000 ft./min, the diameter of the catalytic converter increases to about 7 ft./min.
(approximately 2.13m). This relatively small diameter allows factory fabrication of the converter to be carried out and allows the use of a converter with approximately the same diameter as the associated gas cooling equipment, thereby making it possible to use this process equipment. This results in significant economy in terms of conduits required for connection.

Although the invention has been described with respect to particular embodiments thereof, it will be understood that many modifications may be made without departing from the spirit and scope of the invention.

[Brief explanation of drawings]

The figure is a schematic process flow diagram showing the reaction section of an embodiment of the process of the invention for the production of sulfuric acid, and the figure shows an upright cross-section of the cylindrical apparatus. 10, 14, 16, 17, 19, 23, 25,
29, 30, 32, 45...pipeline, 12...combustion furnace,
18, 24... Heat exchanger (or boiler), 22
...first catalyst stage, 26...second catalyst stage, 28...indirect heat exchanger, 40...converter, 41...third catalyst stage,
42... Fourth catalyst stage, 43... Steam superheater, 44
...economizer.

Claims (1)

[Claims] 1. In the production of sulfuric acid, a gaseous stream containing sulfur dioxide and oxygen is passed in contact with a solid sulfur dioxide oxidation catalyst at a high enough temperature to oxidize sulfur dioxide to sulfur trioxide, thereby converting at least 30% by volume of the sulfur dioxide in the gaseous stream to sulfur trioxide in at least one stage of the oxidation step, and wherein the total conversion in said oxidation step is at least 90% by volume. In the catalytic oxidation process for producing oxidation, the gas stream is in contact with the oxidation catalyst in the at least one stage of the oxidation step, and the superficial gas velocity is at least
500 measured ft./min, and the catalyst is monolithic and has an open cross-sectional area of at least 50%, and the catalyst has a cross-sectional area of 1 square inch (6.45 cm ² ). hit at least
A method characterized in that it has 50 gas channels. 2. The method according to claim 1, wherein the number of gas channels is 100 to 300 per square inch (6.45 cm ² ) of cross-sectional area. 3. The method according to claim 1 or 2, wherein the catalyst comprises a metal carrier. 4 The superficial gas velocity is 1500 to 2500 ft. (approximately 457 ft.
762 m)/min. 5. The method of claim 4, wherein the catalyst comprises a metal carrier. 6. The method according to claim 5, wherein the metal carrier is stainless steel.