Process and apparatus for producing sulfuric acid

Abstract

The invention relates to a method for producing sulfuric acid and a plant for carrying out the method. At least one source produces a quantity a of sulfur dioxide containing gas, so that at least a part of the sulfur dioxide containing gas and added oxygen gas is introduced as feed gas into a pre-converter stage to produce a sulfur trioxide containing gas stream. The quantity of inert gas added together with the oxygen gas is between 0 and 78 vol.%. A partial stream of the sulfur trioxide containing gas stream is branched off and recycled directly into the pre-converter stage or into the feed gas of the pre-converter stage. The remaining sulfur dioxide containing gas is passed through a conventional sulfuric acid plant which comprises at least one contact stage arranged in a main converter to react the sulfur dioxide with oxygen to produce sulfur trioxide. Therein, the generated sulfur trioxide containing gas is fed into at least one absorber, wherein the produced sulfur trioxide is absorbed using sulfuric acid as absorption medium to form sulfuric acid. The capacity of the conventional sulfuric acid plant for converting sulfur dioxide is lower than the quantity a.

Description

Technical Field

[0001] This invention relates to a method for producing sulfuric acid and a corresponding apparatus thereof, wherein at least one source produces a sulfur dioxide-containing gas in an amount of a, wherein at least a portion of the sulfur dioxide-containing gas and added oxygen are introduced as feed gas into a pre-converter stage to produce a sulfur trioxide-containing gas stream, wherein a portion of the sulfur trioxide-containing gas stream is branched off and directly recycled to the pre-converter stage or the feed gas of the pre-converter stage, while the remaining portion of the sulfur trioxide-containing gas stream passes through a pre-converter absorber, wherein it is absorbed using sulfuric acid as an absorbent medium to produce a liquid sulfuric acid stream and the remaining sulfur dioxide-containing gas, wherein the remaining sulfur dioxide-containing gas passes through a conventional sulfuric acid plant comprising at least two contact stages of a main converter arranged in series to react sulfur dioxide with oxygen to produce sulfur trioxide, and wherein the generated sulfur trioxide-containing gas is sent to at least one absorber, wherein the generated sulfur trioxide is absorbed using sulfuric acid as an absorbent medium to form sulfuric acid. Background Technology

[0002] Sulfuric acid production is typically achieved using a dual-absorption method, as explained in the Ullman Encyclopedia of Industrial Chemistry (5th edition, Vol. A25, pp. 635-700). Sulfur dioxide (SO2) is obtained through sulfur combustion or as waste gas from metallurgical equipment, and is then converted to sulfur trioxide (SO3) in a four- or five-stage converter, typically using a solid catalyst, such as vanadium pentoxide, as the active ingredient. The resulting sulfur trioxide is extracted after the contact stage of the converter and conveyed to an intermediate absorber. Alternatively, it can be supplied to a final absorber after the last converter stage. In the final absorber, sulfur trioxide-containing gas is countercurrently supplied to concentrated sulfuric acid and absorbed therein.

[0003] The reaction from SO2 to SO3 in the converter stage is exothermic and proceeds according to the following equation: 2 SO 2(g) + O 2(g) 2 SO 3(g) : Δ H = -197 kJ This highly exothermic reaction leads to a rise in temperature. In particular, so-called hot spots form, which are confined areas of space where the catalyst is exposed to very high local temperatures, leading to irreversible damage. This problem is especially pronounced in the first converter stage because the concentration of sulfur dioxide entering here is particularly high, and sulfur trioxide is not yet present in the gas stream. This allows the reaction from sulfur dioxide to sulfur trioxide to achieve a high conversion rate before reaching equilibrium. This high conversion rate is accompanied by a high enthalpy release, which, depending on the initial SO2 content, can cause the catalyst temperature to exceed its stability limit.

[0004] Therefore, the converter is divided into multiple stages, which provides some possibilities for controlling energy return. Typically, heat exchangers are installed between each stage to cool the gas leaving the converter stage before it enters the next stage. Furthermore, the catalyst concentration can be varied, thereby controlling the overall turnover rate. However, all these measures are insufficient to reliably prevent overheating at high sulfur dioxide concentrations. Therefore, feed gas with a maximum sulfur dioxide content between 11 and 13% by volume is typically used to avoid excessively high temperatures in the converter stages.

[0005] However, sulfur dioxide-containing gases produced by methods such as sulfur combustion and metallurgical processes typically have a higher sulfur dioxide content, ranging from 18% to 50% by volume. Therefore, these gases must be diluted before being fed into conventional sulfuric acid plants, resulting in large gas volumes and consequently, large-scale equipment.

[0006] Therefore, the so-called LUREC® (described in WO 2004 / 037719 A1) was developed, which allows the processing of contact gases with a sulfur dioxide content exceeding 13% by volume. This involves extracting a portion of the gas stream, including sulfur dioxide and sulfur trioxide, from the product stream of the contact stage and recycling it back to the feed gas of the first contact stage. The increased sulfur trioxide proportion affects the balance between sulfur dioxide and sulfur trioxide as shown in the reaction equation above, resulting in a lower conversion rate. This lower turnover also generates less energy, which prevents the catalyst from overheating.

[0007] However, this method cannot be implemented in existing so-called brown field sulfuric acid plants without requiring extensive and costly modifications to handle the resulting high-temperature and high-pressure gas flows. In cases where metallurgical processes generate more sulfur dioxide due to deteriorating ore quality, or where plant capacity is increased by burning more sulfur, the capacity (c) of such existing plants cannot exceed their originally designed sulfur dioxide production (a). Summary of the Invention

[0008] Therefore, the object of the present invention is to provide a method for producing sulfuric acid and a corresponding apparatus thereof, which allows a conventional sulfuric acid plant with a capacity of c to be operated in combination with a source that generates sulfur dioxide-containing gas in an amount exceeding the capacity of the plant that converts sulfur dioxide.

[0009] This objective is achieved by a method having the features of claim 1. In this method, a conventional apparatus having a capacity of c is combined with at least one source of a sulfur dioxide-containing gas producing an amount of a. At least a portion of the sulfur dioxide-containing gas and added oxygen are introduced as feed gas into a first pre-converter stage of the pre-converter to produce a sulfur trioxide-containing gas stream. The added oxygen stream can be added at any location, but in each case it includes an amount of inert gas and / or impurities ranging from 80 vol% to 0.0001 vol%.

[0010] Following the first preconverter stage or other subsequent preconverter stages, a portion of the sulfur trioxide-containing outlet gas stream is branched off and directly recycled back into the feed gas of the first preconverter stage or preconverter stage, while the remaining portion of the sulfur trioxide-containing gas stream passes through a downstream stage of the preconverter and then through a preconversion absorber or directly into the preconversion absorber. There, the gas is absorbed by sulfuric acid as the absorption medium to produce a liquid sulfuric acid stream and a residual sulfur dioxide-containing gas in an amount of a or less.

[0011] Then, the remaining sulfur dioxide-containing gas, in an amount of a or less, is passed through a conventional sulfuric acid plant comprising at least two contact stages of a main converter arranged in series to react the sulfur dioxide with oxygen to produce sulfur trioxide, wherein the generated sulfur trioxide-containing gas is sent to at least one absorber, and wherein the generated sulfur trioxide is absorbed by sulfuric acid, which serves as the absorbent medium, to form sulfuric acid.

[0012] Therefore, no modifications to existing equipment are required, but capacity can be increased. The basic concept of this invention is the interaction with oxygen addition at a concentration significantly higher than that in the air. Consequently, the volumetric flow rate through conventional equipment can be greatly reduced. Simultaneously, the combination of the pre-converter and sulfur trioxide recirculation ensures that the sulfur dioxide load in the first stage of the converter in conventional equipment does not exceed the specific maximum sulfur dioxide concentration that can be handled in the converter.

[0013] Importantly, the addition of relatively pure oxygen also results in a desired reduction in gas volume for the preconverter, easing the burden on components such as heat exchangers and blowers. However, these lower gas volumes typically lead to higher temperatures in the sulfur dioxide converter stage because an equal amount of sulfur dioxide in the lower total gas volume of the feed gas corresponds to a higher concentration, which shifts the reaction equilibrium towards sulfur trioxide. Furthermore, a lower volume results in an equal amount of released heat of reaction leading to higher gas temperatures. Therefore, the preconverter according to the invention has the function of recovering a portion of the sulfur trioxide-containing gas stream to the first preconverter stage or the feed gas of that first preconverter stage, thereby allowing the temperature to be maintained within the catalyst's typically operating range of 370°C to 440°C. Simultaneously, it reduces the remaining sulfur dioxide concentration to a level suitable for downstream conventional sulfuric acid plants, although its sulfur dioxide conversion capacity is lower than the amount generated by at least one source.

[0014] To make this effect partially significant, before mixing these streams, oxygen is introduced at a concentration between 90 and 99 vol% and / or sulfur dioxide concentration in the sulfur dioxide-containing gas is at least 14 vol%, particularly preferably between 18 and 65 vol%. In other words, the amount of inert gas added with the oxygen is between 0 and 78 vol%, preferably between 0 and 50 vol%, in the oxygen feed stream. Therefore, with a constant volumetric flow rate of sulfur dioxide-containing gas and oxygen, the sulfur dioxide to oxygen ratio entering the pre-converter stage is between 0.14 and 2.95, preferably between 0.18 and 1.3, and most preferably between 0.45 and 0.6.

[0015] While higher purity oxygen further reduces gas volume, oxygen with a concentration between 95 and 99.5% by volume is an readily available and inexpensive source. This is particularly true for technical purity oxygen, i.e., oxygen grade 2.5 (99.5% by volume). Therefore, the problems typically associated with using lower grades of oxygen, such as technical purity oxygen and below, namely the need to remove impurities contained within the oxygen stream through subsequent stages, are mitigated. Although impurities and high concentrations of sulfur dioxide in the purified stream often make compliance with current ecological standards prohibitively expensive, treatment with conventional sulfuric acid equipment eliminates the need for separate cleaning of the purified stream.

[0016] In a preferred embodiment, oxygen for the pre-converter stage is added to at least one source for generating sulfur dioxide-containing gas. This allows the method of the invention to be implemented with minimal structural changes, since the generation of sulfur dioxide requires the addition of oxygen-containing gas and therefore mechanisms for adding oxygen to the source already exist. Furthermore, a smaller blower can be used to introduce the oxygen-containing gas into the source for generating sulfur dioxide-containing gas, as a smaller volume of gas is sufficient to provide adequate oxygen compared to air, which contains, for example, only about 20% by volume. Additionally, all downstream components can then be designed to be smaller.

[0017] More preferably, at least one source for the feed gas containing sulfur dioxide is the combustion of elemental sulfur with oxygen. An elemental sulfur burner can generate a particularly concentrated and high-purity sulfur dioxide gas, with a concentration up to 66% by volume. In the sense of this invention, the combustion of elemental sulfur with oxygen encompasses all catalytic and non-catalytic methods in which sulfur and oxygen react to produce sulfur dioxide, regardless of whether flame formation occurs.

[0018] Alternatively or additionally, exhaust gas from metallurgical processes (as mentioned at the beginning) may be used as at least one source for feed gas containing sulfur dioxide.

[0019] According to a preferred embodiment, the oxygen introduced during the combustion of elemental sulfur described above is introduced into a gas stream having an oxygen content of at least 25% by volume, preferably more than 95% by volume. This also has a positive impact on improving combustion efficiency.

[0020] Further preferably, at least a portion of the sulfur dioxide-containing feed gas is cooled to a temperature between 350°C and 450°C, preferably between 380°C and 430°C, and most preferably between 390°C and 410°C before entering the pre-converter. This avoids excessively high temperatures in the pre-converter stage, and the heat contained in at least a portion of the sulfur dioxide-containing feed gas can be used to (pre)heat other process streams, such as water for steam generation or oxygen for the pre-converter stage.

[0021] According to another embodiment, the portion of the sulfur trioxide-containing gas stream branching off from the sulfur trioxide-containing gas stream generated in the pre-converter stage accounts for 10% to 80% of the volume of the sulfur trioxide-containing gas stream, preferably 12% to 50%. This ensures that the feed gas used in the pre-converter stage contains a sufficient concentration of sulfur trioxide.

[0022] Accordingly, the remaining portion of the sulfur trioxide-containing gas stream fed into the pre-conversion absorber may account for 90 to 20% by volume, preferably between 50 and 88% by volume, of the sulfur trioxide-containing gas stream.

[0023] The preferred fractionation depends on the sulfur trioxide content after contact, which in turn depends on the number of contact stages. The more contact stages used, the higher the sulfur trioxide content, and the less the required balance change in the recovered stream can be achieved.

[0024] According to another embodiment, the sulfur dioxide-containing gas is branched off before being introduced into the pre-converter stage and directly fed into the conventional sulfuric acid plant. Therefore, at least a portion of the sulfur dioxide-containing gas used in the pre-converter stage is less than 100% by volume of the sulfur dioxide-containing gas generated from at least one source, preferably between 12% and 90% of the sulfur dioxide-containing gas generated from at least one source. Typically, the sulfur dioxide-containing feed gas is branched off before the addition of oxygen for the converter stage. The advantage of partially bypassing the pre-converter is that it fully utilizes the capacity of existing equipment. Furthermore, the sulfur dioxide load can be distributed between the pre-converter stage and the conventional sulfuric acid plant to, for example, allow for responses to variations in sulfur dioxide concentration.

[0025] In another embodiment, a separate sulfur trioxide-containing gas stream branches off downstream of the contact stage of the main converter in a conventional sulfuric acid plant and is directly recycled into the feed gas of the pre-converter or the first pre-converter stage. This not only creates redundancy for the recycling of a portion of the sulfur trioxide-containing gas stream at the pre-converter stage, but also allows for better control over the sulfur trioxide content fed into the pre-converter stage as part of the feed gas.

[0026] In addition, residual sulfur dioxide stream from the final absorber of conventional equipment can be mixed in at any point before the pre-converter to increase total turnover.

[0027] In a further modification, at least one absorber in the pre-conversion absorber and the conventional sulfuric acid plant has a common pump tank for the sulfuric acid used as the absorption medium. Therefore, the existing pump tank in the conventional sulfuric acid plant can be utilized, which reduces the cost of retrofitting existing equipment and further provides the opportunity for centralized further processing of the generated sulfuric acid.

[0028] In a particularly preferred embodiment, a portion of the sulfur trioxide-containing gas stream is mixed into the feed gas for the pre-converter stage via a gas injector. Thus, the sulfur dioxide-containing gas and added oxygen are introduced as a driving medium into the driving medium inlet of the injector, causing it to be drawn in and accelerated as a recovery stream in the intake medium inlet to generate the feed gas flowing through the exhaust outlet for the converter stage.

[0029] In contrast to this solution, hot gas blowers are typically used to increase the pressure of a portion of the feed gas stream containing sulfur trioxide that branches off and is recovered to the pre-converter stage or pre-converter stage. However, the fans and seals of these blowers are prone to wear due to contact with the hot and highly corrosive sulfur trioxide-containing gas stream. In addition to the pressurization described, a uniformly mixed feed gas is obtained, which makes an additional gas mixer redundant and reduces the chance of localized overheating (i.e., hot spots) in the pre-converter stage.

[0030] Furthermore, considering that the injector has no sensitive components, such as the fan in a hot air blower or the necessary seals, the recovered portion of the flow does not require active heating or cooling.

[0031] The pressure of the feed gas leaving the injector is preferably between 130 kPa and 150 kPa to ensure sufficient pressure within the system.

[0032] The present invention also relates to the apparatus according to claim 13, and particularly to an apparatus for performing the method according to claims 1 to 12. Such an apparatus for producing sulfuric acid comprises at least one source for producing a sulfur dioxide-containing gas in an amount of a. Furthermore, it includes a pre-converter having at least one pre-converter stage for reacting a feed gas comprising at least a portion of the sulfur dioxide-containing gas and added oxygen to produce a sulfur trioxide-containing gas stream. Thus, the piping for adding oxygen and the pre-converter and related devices, such as heat exchangers, fans, etc., are sized such that the oxygen concentration in the gas stream is at least 11.6% by volume.

[0033] In this configuration, the equipment also includes a line for branching off a portion of the sulfur trioxide-containing gas stream and recovering it into the first pre-converter stage or the feed gas of the first pre-converter stage. Downstream of the pre-converter, an absorber is provided for absorbing the remainder of the sulfur trioxide-containing gas stream with sulfuric acid to produce a liquid sulfuric acid stream and the remaining sulfur dioxide-containing gas. A conventional sulfuric acid unit with a capacity of c is then installed.

[0034] The conventional sulfuric acid plant includes at least two contact stages of a main converter arranged in series for reacting sulfur dioxide with oxygen to produce sulfur trioxide, and at least one absorber for absorbing the sulfur trioxide produced in sulfuric acid, and its capacity for converting the amount of sulfur dioxide is less than a.

[0035] This device possesses all the advantages of the methods previously described that can be performed in such a device. All preferred embodiments also apply to the preferred design of such a device.

[0036] As described above, preferably, at least one source for generating the feed gas containing sulfur dioxide includes an elemental sulfur burner. Preferably, the pipeline for introducing oxygen into the burner is designed such that the amount of oxygen introduced is at least 22% by volume. In one embodiment, the device includes an elemental sulfur burner combined with a fire-tube boiler to utilize the heat generated in the burner to produce superheated steam.

[0037] Alternatively, a roasting furnace, such as a fluidized bed reactor for roasting sulfide ores, or a smelting furnace, can be used as at least one source for the sulfur dioxide-containing gas, and these furnaces are configured to provide the sulfur dioxide-containing exhaust gas.

[0038] In particular, these sources have in common that the amount of sulfur dioxide-containing gas generated easily exceeds the capacity of conventional sulfuric acid equipment to convert sulfur dioxide in a continuous process.

[0039] In one embodiment, the device includes at least one heat exchanger configured to cool at least a portion of the sulfur dioxide-containing gas to a temperature between 380°C and 430°C, preferably between 390°C and 410°C, before it enters the pre-converter stage. Alternatively or additionally, a heat exchanger may be provided configured to cool the remaining sulfur dioxide-containing gas to a temperature between 250°C and 180°C.

[0040] In another embodiment, the device includes a gas ejector for mixing a portion of the sulfur trioxide-containing gas stream with the feed gas from the pre-converter stage and simultaneously regulating the pressure of the feed gas for the pre-converter. The ejector is thus configured such that sulfur dioxide-containing gas, typically at a pressure of 130 to 150 kPa, and added oxygen are introduced as driving gases through the ejector nozzle. This results in acceleration, creating a low-pressure region around the nozzle tip. The lower pressure causes a portion of the recovered sulfur trioxide-containing gas stream to be drawn into the ejector as a suction medium, where the gases are subsequently mixed, and a feed gas with a set pressure typically between 130 and 150 kPa is generated in the ejector's diffuser.

[0041] In another embodiment, a pipeline, or conduit, is provided, configured to branch off an additional sulfur trioxide-containing gas stream downstream of at least one of the at least two contact stages of the main converter in a conventional sulfuric acid plant, and to directly recover said additional stream into the pre-converter stage or the feed gas of the pre-converter stage. Preferably, the additional sulfur trioxide-containing gas stream operates as the intake medium in the aforementioned gas ejector.

[0042] Further developments, advantages, and possible applications can also be derived from the following description of exemplary embodiments and the accompanying drawings. All features described and / or illustrated are derived from the subject matter of the invention itself or any combination thereof, regardless of whether they are included in the claims or their references. Attached Figure Description

[0043] In the attached diagram: Figure 1 schematically illustrates a conventional sulfuric acid equipment. Figure 2 A first embodiment of a source for generating sulfur dioxide-containing gas, as described in the invention, is connected to a conventional sulfuric acid plant via a pre-converter. Figure 3 A second embodiment of the invention is schematically illustrated, which includes a pre-converter having two converter stages. Figure 4 A third embodiment of the invention is illustrated schematically, which includes a bypass line for a gas containing sulfur dioxide. Figure 5 The fourth embodiment of the invention is illustrated schematically, comprising two sources for generating a gas containing sulfur dioxide. Figure 6 A schematic diagram showing a detailed view of a pre-converter stage including an injector according to a third embodiment of the present invention is shown. Detailed Implementation

[0044] Figure 1 illustrates a conventional sulfuric acid plant according to the prior art. However, the present invention is not limited to this specific plant, but can be applied to any type of sulfuric acid plant including a converter with at least one contact stage and at least one absorber. In this plant, a sulfur dioxide-containing gas stream is introduced into a main converter 20, which includes four contact stages 21' to 21'''' arranged in series to react sulfur dioxide with oxygen to produce sulfur trioxide. Between each contact stage 21' to 21'''', a heat exchanger (not shown) is provided to cool the sulfur trioxide-containing gas stream obtained from the corresponding contact stage to a sufficiently low temperature to avoid excessively high temperatures in subsequent contact stages 21'' to 21'''' and / or absorbers 30, 30'.

[0045] The sulfur trioxide-containing gas obtained from contact stage 21''' is then extracted through pipe 24 and fed into intermediate absorber 30. Preferred concentrated sulfuric acid with a concentration between 93% and 99.5% is supplied to intermediate absorber 30 via pipe 31 through pump tank 34, preferably countercurrent to the sulfur trioxide-containing gas. The remaining sulfur dioxide-containing gas obtained is extracted through pipe 32 and supplied through pipe 32 to any of contact stages 21'' to 21''', preferably the last contact stage, while the resulting sulfuric acid is recycled back to pump tank 34. From there, the sulfuric acid product stream is extracted through pipe 35 for further processing. To improve absorption, sulfur trioxide from at least one subsequent contact stage 21'' to 21''' is fed into final absorber 30'.

[0046] Preferably, all absorbers 30 and 30' have a common pump tank for supplying sulfuric acid. The heat exchangers are typically configured such that the concentrated sulfuric acid supplied to absorbers 30 and 30' is at substantially the same temperature, preferably between 60°C and 230°C, and more preferably 80 ± 5°C. This ensures optimal conditions for sulfur trioxide absorption in a simple manner.

[0047] The remaining exhaust gas passes through a gas cleaning section (not shown) via pipe 36 to remove any remaining sulfur dioxide and / or other impurities, while the sulfuric acid formed in the final absorber 30' is recycled to the pump tank 34 via pipe 33'.

[0048] It should be noted that the conventional sulfuric acid plant 20 may also have a configuration different from the 3+1 arrangement of the contact stages 21' to 21'''' shown in the main converter. For example, a 3+2 arrangement of the contact stages is possible. Furthermore, the number and arrangement of the absorbers 30 and 30' may vary. Moreover, the sulfur trioxide-containing gas stream can be branched off at any location and recycled back to the converter stage, preferably the first converter stage 21', as described in WO 2004 / 037719 A1.

[0049] Any conventional sulfuric acid equipment has a specific capacity c. Since any increase in the amount a results in the supply of even larger volumes of sulfur dioxide-containing feed gas to the conventional sulfuric acid equipment 20, it is easy to exceed the amount a of sulfur dioxide-containing gas.

[0050] Typically, sulfur-containing materials, such as elemental sulfur in the case of an elemental sulfur burner or sulfur-containing ore in the case of a pyrometallurgical reactor, are introduced into the reactor, where they undergo conversion with oxygen. One possible oxygen source is dry air obtained from the drying tower of a downstream sulfuric acid plant. However, the amount of sulfur converted is the determining factor for the amount of sulfur dioxide produced, which is why the amount of sulfur converted must be controlled so that amount a is not exceeded. Moreover, for the reasons stated above, namely to avoid catalyst hotspot damage, not only amount a must be controlled, but also the concentration of sulfur dioxide must be controlled.

[0051] In contrast to these limiting factors, the present invention provides the possibility of increasing the capacity of existing equipment. A sulfur dioxide-containing gas is generated by at least one source 10 and, together with added oxygen, is fed as a feed gas through pipes 14, 42, and 43 into a pre-converter 40, which includes at least one pre-converter stage, i.e., at least a first pre-converter stage 40'.

[0052] In principle, the added oxygen stream can be added at any location. In this embodiment, conduit 41 is configured to add the added oxygen stream to the sulfur dioxide-containing gas, wherein the total amount of inert gases and / or impurities in the added oxygen stream is in the range of 0 to 78% by volume. This means that the oxygen is added at a high concentration, preferably at least 25% by volume. Preferably, conduit 41 is arranged such that oxygen for the pre-converter is added after the generated sulfur dioxide-containing gas has been cooled to a temperature between 350°C and 430°C by a heat exchanger (not shown). Therefore, the volume of the generated feed gas is lower compared to using air containing only about 20% by volume of oxygen. Therefore, the capacity of the conventional sulfuric acid plant 20 in terms of the maximum processable gas volume is not exceeded.

[0053] A close examination of the sulfur dioxide concentration that can be handled in the sulfuric acid plant 20 reveals the crucial role of the pre-converter 40: In the pre-converter stage 40', a sulfur trioxide-containing gas stream is generated and extracted through pipe 44. To prevent excessively high temperatures in the pre-converter stage 40', a portion of the sulfur trioxide-containing gas stream is branched off and recovered into the feed gas of the pre-converter stage 40' via recovery pipe 45. Alternatively, this portion can be directly recovered into the pre-converter stage 40'. The portion of the sulfur trioxide-containing gas stream constitutes 7% to 90% of the total sulfur trioxide-containing gas stream by volume. Therefore, the reaction equilibrium is shifted, resulting in a reduced reaction rate for sulfur trioxide production and less heat generation in the pre-converter stage 40'. Of course, additional pre-converter stages can be provided. However, the simplest arrangement is a single-stage pre-converter.

[0054] To increase the pressure of a portion of the sulfur trioxide-containing gas stream, preferably to a pressure between 110 kPa and 160 kPa, a hot gas blower 47 is provided. However, for such a hot gas blower, it is necessary that the portion of the sulfur trioxide-containing gas stream be cooled to a temperature between 250°C and 300°C by a heat exchanger 46 before passing through the hot gas blower 47, and then reheated to a temperature between 380°C and 450°C by a heat exchanger 46'.

[0055] The remaining sulfur trioxide-containing gas stream, i.e., the portion that is not branched off and recovered, is supplied to the pre-conversion absorber 50 via pipe 51. Before entering the pre-conversion absorber 50, the remaining sulfur trioxide-containing gas stream is cooled to a temperature between 150°C and 250°C via heat exchanger 52. In the pre-conversion absorber 50, concentrated sulfuric acid is introduced from a pump tank via pipe 53 as the absorption medium to produce a liquid sulfuric acid stream and a quantity of a or less of the remaining sulfur dioxide-containing gas. Thus, the pre-converter is able to reduce the sulfur dioxide concentration entering the conventional sulfuric acid plant 20 to a concentration that the plant can handle.

[0056] The second embodiment of the present invention is in Figure 3 As shown in the image. (and) Figure 2 Compared to the illustrated embodiment, conduit 12 is configured to add oxygen for the feed gas, particularly in the form of oxygen-containing gas with an oxygen content of 50% to 95% by volume or technically pure oxygen, to reactor 10. Therefore, a separate conduit 41 is not required to introduce the desired oxygen.

[0057] If reactor 10 is designed for roasting sulfur-containing gases, for example, it can be constructed as a fluidized bed, which means that the amount of oxygen in the fluidized gas is increased. In a more preferred embodiment, sulfur is burned in reactor 10. In the sense of this invention, the term "burning" covers any reaction of sulfur with oxygen, whether or not a flame occurs. In particular, it covers lances, nozzles, spray pipes, and all other possibilities for introducing molten sulfur droplets into a high-temperature furnace.

[0058] Furthermore, the preconverter 40 preferably includes a first preconverter stage 40', and optionally also includes an additional second preconverter stage 40'', to increase the total sulfur dioxide conversion rate in the preconverter 40. The first sulfur trioxide-containing gas stream obtained from the first preconverter stage 40' is fed into the second preconverter stage via a conduit 48, which may include a heat exchanger (not shown) to reduce the temperature of the first sulfur trioxide-containing gas stream from 650°C to a temperature between 400°C and 450°C, thereby preventing excessively high temperatures in the second preconverter stage 40''. Although the second preconverter stage 40'' can ensure a higher overall turnover rate, the design with only one preconverter stage 40' has the advantages of being very simple and cost-effective.

[0059] In this embodiment, a portion of the sulfur trioxide-containing gas stream obtained from the second pre-converter stage 40'' is recovered via recovery pipe 45 into the feed gas for the first pre-converter stage 40' in the same manner as described above. Alternatively, a portion of the sulfur trioxide-containing gas stream can be extracted and recovered from pipe 48.

[0060] Furthermore, a portion of the sulfur trioxide-containing gas stream obtained from the contact stages 21' to 21'''' of the main converter 21 of a conventional sulfuric acid plant 20 can be recovered into the first pre-converter stage 40' or the feed gas of the pre-converter 40. This has the advantage of recovering the gas stream that still contains a considerable amount of residual sulfur dioxide.

[0061] Particularly preferred is that pump tank 34 serves as a common storage tank for concentrated sulfuric acid used as the absorption medium in both the pre-conversion absorber 50 and the absorbers 30, 30' of the conventional sulfuric acid plant 20. Thus, concentrated sulfuric acid can be supplied to the pre-conversion absorber 50, and the resulting liquid sulfuric acid stream can be returned to pump tank 34 via pipe 54. Therefore, centralized sulfuric acid supply and further processing of the sulfuric acid product stream are achieved with only minor modifications to the existing structure.

[0062] The third embodiment of the present invention is in Figure 4 As shown in the diagram, only a portion of the generated sulfur dioxide-containing gas is supplied to the pre-converter 40 via pipes 42 and 43. The remaining portion branches off upstream of the pre-converter via pipe 19. Preferably, pipe 19 is configured such that the branched-off sulfur dioxide-containing gas constitutes between 13% and 90% of the total sulfur dioxide-containing gas volume. Subsequently, the branched-off gas is mixed with the remaining sulfur dioxide-containing gas extracted from the pre-conversion absorber 50 via pipe 55 and supplied to the conventional sulfuric acid plant 20 via pipe 56. In this case, the sulfur dioxide concentration in pipe 56 is less than 14% of the volume required for conventional plant operation.

[0063] As an alternative, the generated sulfur dioxide-containing gas is conveyed from reactor 10 through pipe 14 via water-tube boiler 18. Regardless of this design, an additional heat exchanger 49 can be provided to cool at least a portion of the sulfur dioxide-containing gas in pipe 42. This allows for better control of the temperature of the feed gas to pre-converter 40, especially in the event of volume changes in the sulfur dioxide-containing gas branching off through pipe 19.

[0064] Further embodiments are in Figure 6 As shown in the image. (For example, regarding...) Figure 2In embodiments of the invention, the main blower 17 can operate at less than full capacity, for example, only at 66%. The idle capacity can be used to supply oxygen-containing gas, such as air or technically pure oxygen, to another reactor 11 via pipe 13'. Preferably, the other reactor 11 is an elemental oxygen burner.

[0065] Sulfur-containing materials, such as elemental sulfur in the case of an elemental sulfur burner, or sulfide ores, such as in the case of a pyrometallurgical reactor, are introduced into reactor 11 via pipe 12'. Similar to source 10, additional sulfur dioxide-containing gas generated in reactor 11 is fed into another fire-tube boiler 18' via pipe 14'. Then, additional sulfur dioxide-containing gas is added to the sulfur dioxide-containing gas branching off from pipe 19'. Alternatively, additional sulfur dioxide-containing gas may also be mixed into at least a portion of the sulfur dioxide-containing gas as part of the feed gas for pre-converter 40 (not shown).

[0066] In this example, the total amount of sulfur-containing material fed into reactors 10 and 11 can be increased by up to 37% compared to the prior art described above.

[0067] Figure 6 A more detailed view of the pre-converter 40 is provided. In it, a gas injector 49 is provided, configured to mix a portion of the sulfur trioxide-containing gas stream recovered via the recovery conduit 45 with at least a portion of the sulfur dioxide-containing gas supplied via conduit 42 and added oxygen. In other words, the sulfur dioxide-containing gas and added oxygen are introduced as a driving medium, causing them to be drawn in and accelerated by the recovered stream, which operates as a draw-in medium in conduit 45, to generate feed gas flowing through the discharge outlet for the converter stage within a set pressure range. Therefore, the two streams are perfectly mixed, eliminating the need for additional mixing elements. Furthermore, no blower, fan, or similar device is required in the recovery conduit 45. This also eliminates the need to cool the stream to a temperature at which such a blower could be used. Reheating is also no longer necessary. Simultaneously, the pressure of the feed gas supplied to at least one (first) pre-converter stage 40' of the pre-converter 40 is regulated.

[0068] Therefore, sulfur dioxide-containing gas with a pressure of 130 kPa to 160 kPa and added oxygen enter injector 49. The lower pressure causes a portion of the recovered sulfur trioxide-containing gas stream to be drawn into injector 49 as a suction medium, thereby generating a feed gas with a set pressure typically between 130 kPa and 150 kPa. This modification can be used in any previous embodiment.

[0069] List of reference numerals

[0070] 10 Reactors

[0071] 11 Reactors

[0072] 12-16 Pipeline

[0073] 17 Main blower

[0074] 18' and 18' fire-tube boilers

[0075] 19, 19' pipes

[0076] 20. Conventional sulfuric acid equipment

[0077] 21. Main Converter

[0078] 21'-21'''' Contact level

[0079] 22-25 Pipeline

[0080] 30 Intermediate Absorber

[0081] 30' Final Absorber

[0082] 31-33'' Pipeline

[0083] 34 Pump tank

[0084] Pipes 35 and 36

[0085] 40 Pre-converter

[0086] 40', 40'' Pre-converter stage

[0087] Pipes 41-44

[0088] 45 Recycling Pipeline

[0089] 46' heat exchanger

[0090] 47 Hot air blower

[0091] 48 pipes

[0092] 49 Injectors

[0093] 50 Pre-conversion absorber

[0094] 51 Pipeline

[0095] 52 Heat Exchanger

[0096] 53-56 Pipelines

Claims

1. A method for producing sulfuric acid, wherein, At least one source generates a sulfur dioxide-containing gas of amount a, wherein at least a portion of the sulfur dioxide-containing gas and added oxygen are introduced as feed gas into a pre-converter stage to generate a sulfur trioxide-containing gas stream, wherein the amount of inert gas added together with oxygen is between 0 and 78% by volume, wherein a portion of the sulfur trioxide-containing gas stream is branched off and directly recycled to the pre-converter stage or the feed gas of the pre-converter stage, wherein the remaining unrecovered sulfur dioxide-containing gas is passed through a conventional sulfuric acid plant, the conventional sulfuric acid plant including at least one contact stage arranged in a main converter to react sulfur dioxide with oxygen to generate sulfur trioxide, and wherein the generated sulfur trioxide-containing gas is fed into at least one absorber, wherein the generated sulfur trioxide is absorbed using sulfuric acid as an absorbent medium to form sulfuric acid, wherein the capacity of the conventional sulfuric acid plant to convert sulfur dioxide is less than amount a.

2. The method according to claim 1, characterized in that, Oxygen for the preconverter stage is introduced at a concentration between 22% and 100% by volume, and / or the concentration of sulfur dioxide in the sulfur dioxide-containing gas is at least 13% by volume.

3. The method according to claim 1 or 2, characterized in that, Oxygen for the pre-converter stage is added to at least one source for generating a gas containing sulfur dioxide.

4. The method according to any one of the preceding claims, characterized in that, The at least one source used for the feed gas containing sulfur dioxide is the reaction of elemental sulfur with oxygen.

5. The method according to claim 4, characterized in that, The oxygen in the reaction that introduces elemental sulfur is introduced into a gas stream having at least 22% by volume oxygen.

6. The method according to any one of the preceding claims, characterized in that, At least a portion of the sulfur dioxide-containing feed gas is cooled to a temperature such that the gas entering the catalyst bed has a technically feasible catalyst inlet temperature, between 350°C and 450°C, before entering the pre-converter stage.

7. The method according to any one of the preceding claims, characterized in that, The portion of the branched sulfur trioxide-containing gas stream accounts for between 7% and 90% of the total volume of the sulfur trioxide-containing gas stream.

8. The method according to any one of the preceding claims, characterized in that, The feed gas containing sulfur dioxide is branched off before being introduced into the pre-converter stage and then directly fed into the conventional sulfuric acid plant.

9. The method according to claim 8, characterized in that, The volume fraction of the feed gas containing sulfur dioxide branched off is used to adjust the sulfur dioxide content of conventional downstream acid equipment.

10. The method according to any one of the preceding claims, characterized in that, The remainder of the sulfur trioxide-containing gas stream from the preconverter stage passes through the preconverter absorber.

11. The method according to claim 10, characterized in that, The sulfur trioxide-containing gas is branched out before being introduced into the pre-conversion absorber and then directly fed into the conventional sulfuric acid equipment.

12. The method according to any one of the preceding claims, characterized in that, The additional sulfur trioxide-containing gas stream is branched off downstream of at least one of the at least two contact stages in a conventional sulfuric acid plant and directly recycled to the pre-converter stage or the feed gas of the pre-converter stage.

13. The method according to any one of the preceding claims, characterized in that, The pre-conversion absorber and at least one absorber in the conventional sulfuric acid plant have a common pump tank for the sulfuric acid used as the absorption medium.

14. The method according to any one of the preceding claims, characterized in that, A portion of the sulfur trioxide-containing gas stream is mixed into the feed gas for the pre-converter stage via a gas injector, thereby simultaneously regulating the pressure of the feed gas for the pre-converter stage.

15. An apparatus for producing sulfuric acid, particularly an apparatus for performing the method according to any one of claims 1 to 14, comprising: At least one reactor (10) for producing a sulfur dioxide-containing gas in an amount of a. A pre-converter (40) for reacting a feed gas comprising at least a portion of a sulfur dioxide-containing gas and added oxygen to produce a sulfur trioxide-containing gas stream; a recovery conduit (45) for branching off a portion of the sulfur trioxide-containing gas stream and recovering it to the pre-converter (40) or the feed gas of the pre-converter (40); a pre-conversion absorber (50) for absorbing the remainder of the sulfur trioxide-containing gas stream with sulfuric acid to produce a liquid sulfuric acid stream and the remaining sulfur dioxide-containing gas; and a conventional sulfuric acid plant (20) comprising at least one contact stage (21) of a main converter for reacting sulfur dioxide with oxygen to produce sulfur trioxide and at least one absorber (30, 30') for absorbing the produced sulfur trioxide in sulfuric acid, wherein the capacity of the conventional sulfuric acid plant (20) to convert the amount of sulfur dioxide is less than amount a.

16. The apparatus for producing sulfuric acid according to claim 15, characterized in that, The at least one reactor (10) used to generate feed gas containing sulfur dioxide includes an elemental sulfur burner.

17. The apparatus for producing sulfuric acid according to claim 15 or 16, characterized in that, The apparatus for producing sulfuric acid includes a gas injector (49) for mixing a portion of the sulfur trioxide-containing gas stream with the feed gas of the preconverter (40) and simultaneously regulating the pressure of the feed gas for the preconverter (40).

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