Equipment for producing sulfuric acid

Abstract

The utility model relates to equipment for producing sulfuric acid. The equipment comprises at least one reactor for producing sulfur dioxide-containing gas with the quantity of a; a pre-converter 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; a recovery conduit for branching off a partial stream of the sulfur trioxide-containing gas stream and recovering it into the pre-converter or into the feed gas of the pre-converter; a pre-conversion absorber for absorbing the remaining portion of the sulfur trioxide-containing gas stream with sulfuric acid to produce a liquid sulfuric acid stream and a remaining sulfur dioxide-containing gas; and a conventional sulfuric acid plant comprising at least one contact stage of a main converter for reacting sulfur dioxide with oxygen to produce sulfur trioxide and at least one absorber for absorbing the produced sulfur trioxide in sulfuric acid, where the capacity of the amount of converted sulfur dioxide of the conventional sulfuric acid plant is lower than the amount a.

Description

TECHNICAL FIELD

[0001] The present utility model relates to a method for producing sulfuric acid and the corresponding equipment thereof, wherein at least one source produces a quantity of a sulfur dioxide containing gas a, wherein at least a part of the sulfur dioxide containing gas and added oxygen are introduced into a pre-converter stage as feed gas to produce a sulfur trioxide containing gas stream, wherein a part of the sulfur trioxide containing gas stream is branched off and directly recycled into the pre-converter stage or into the feed gas of the pre-converter stage, and the remaining part of the sulfur trioxide containing gas stream is passed through a pre-conversion absorber, wherein it is absorbed using sulfuric acid as an absorption medium to produce a liquid sulfuric acid stream and a remaining sulfur dioxide containing gas, wherein the remaining sulfur dioxide containing gas is passed through a conventional sulfuric acid plant, which comprises at least two contact stages of a main converter arranged in series to react the sulfur dioxide with oxygen to produce sulfur trioxide, and wherein the generated sulfur trioxide containing gas is fed to at least one absorber, wherein the produced sulfur trioxide is absorbed using sulfuric acid as an absorption medium to form sulfuric acid. BACKGROUND

[0002] Sulfuric acid production is usually realized using a double absorption process as explained in the Ullmann's Encyclopedia of Industrial Chemistry (5th edition, volume A25, pages 635-700). Sulfur dioxide (SO2) is obtained by sulfur combustion or as off-gas from metallurgical plants and then converted to sulfur trioxide (SO3) in a four or five stage converter, usually using a solid catalyst, e.g. vanadium pentoxide, as active ingredient. The produced sulfur trioxide is withdrawn after the contact stages of the converter and fed to an intermediate absorber. Alternatively, it can be supplied to a final absorber after the last converter stage. In the final absorber, the sulfur trioxide containing gas is supplied countercurrent to concentrated sulfuric acid and absorbed therein.

[0003] The reaction of SO2 to SO3 in the converter stages is exothermic and proceeds according to the following equation:

[0004]

[0005] This highly exothermic reaction leads to a temperature increase. In particular, so-called hot spots are formed, which are spatially limited areas where the catalyst is exposed to very high local temperatures leading to irreversible damage of the catalyst. This problem occurs in particular in the first converter stage, because here the incoming sulfur dioxide concentration is particularly high and no sulfur trioxide is yet present in the gas stream, which allows a high conversion from sulfur dioxide to sulfur trioxide to be achieved before equilibrium is reached. This high conversion is accompanied by a high enthalpy release, which can cause the temperature of the catalyst to exceed its stability limit depending on the initial SO2 content.

[0006] Therefore, the converter is divided into several stages, which offers some possibilities for controlling the energy return. Usually, a heat exchanger is provided between each stage in order to cool the gas leaving the converter stage before it is passed into the next stage. Furthermore, the catalyst concentration can be varied, so that the overall turnover rate can be controlled. However, all these measures are not sufficient to reliably avoid overheating at high sulfur dioxide concentrations. Therefore, usually feed gases with a maximum content of sulfur dioxide of between 11 and 13 vol% are applied in order to avoid excessively high temperatures in the converter stages.

[0007] However, gases containing sulfur dioxide, such as the above-mentioned sulfur combustion and metallurgical processes, usually have a higher sulfur dioxide content of between 18 and 50 vol%. Therefore, these gases have to be diluted before they are fed into a conventional sulfuric acid plant, which leads to a large gas volume and thus to a large size of all installations.

[0008] Therefore, so-called (described in WO 2004 / 037719 Al), which allows the processing of contact gases with a sulfur dioxide content of more than 13 vol%. Thereby, a partial gas stream comprising sulfur dioxide and sulfur trioxide is withdrawn from the product stream of the contact stage and recycled to the feed gas of the first contact stage. The increased proportion of sulfur trioxide influences the equilibrium between sulfur dioxide and sulfur trioxide shown in the above reaction equation, so that the conversion rate is reduced. This lower turnover also produces less energy, which prevents the catalyst from overheating.

[0009] However, this method cannot be implemented in existing so-called brown field sulfuric acid plants without extensive and expensive modifications to process the occurring high-temperature and high-pressure gas streams. In the case of metallurgical processes producing a higher amount of sulfur dioxide due to a decrease in ore quality or in the case of increasing the capacity of the plant by burning more sulfur, the capacity c of such an existing plant cannot exceed the originally designed amount of sulfur dioxide a. Utility model content

[0010] Therefore, it is the object of the present utility model to provide a method for producing sulfuric acid and a corresponding plant, which allows the operation of a conventional sulfuric acid plant with a capacity c in combination with a source of a gas containing sulfur dioxide generated in an amount exceeding the capacity of the plant for converting sulfur dioxide.

[0011] This object is solved by a method. In this method a conventional plant having a capacity c is combined with at least one source producing a quantity a of a sulfur dioxide containing gas. At least a part of the sulfur dioxide containing gas and added oxygen gas is introduced as feed gas into a first pre-converter stage of a pre-converter to produce a sulfur trioxide containing gas stream. The added oxygen gas stream can be added at any location, but in each case it comprises an amount of inert gas and / or impurities in the range between 80 vol.% and 0.0001 vol.%.

[0012] After the first pre-converter stage or other subsequent pre-converter stage of the pre-converter, a part stream of the sulfur trioxide containing outlet gas stream is branched off and directly recycled into the feed gas of the first pre-converter stage or the pre-converter stage, while the remaining part of the sulfur trioxide containing gas stream is passed through the downstream stages of the pre-converter and then through a pre-conversion absorber or directly into the pre-conversion absorber. Therein, the gas is absorbed as sulfuric acid as absorption medium to produce a liquid sulfuric acid stream and a remaining sulfur dioxide containing gas of quantity a or less.

[0013] The remaining sulfur dioxide containing gas of quantity a or less is then 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 fed to at least one absorber, and wherein the generated sulfur trioxide is absorbed as sulfuric acid as absorption medium to form sulfuric acid.

[0014] Thereby, no modification of the existing plant is required, but the capacity can be increased. Thus, the basic idea of the present invention is to interact with the addition of oxygen having a concentration significantly higher than the oxygen concentration in air. Thereby, the volume flow through the conventional plant can be significantly reduced. At the same time, the combination of the pre-converter with the recycling of sulfur trioxide ensures that the sulfur dioxide load of the first stage of the converter in the conventional plant does not exceed the specific maximum sulfur dioxide concentration which can be handled in the converter.

[0015] It is also important in this context that the addition of relatively pure oxygen also results in the desired gas volume reduction for the pre-converter, which relieves components such as heat exchangers and blowers. However, these lower gas volumes will typically result in higher temperatures in the sulfur dioxide converter stage, since an equal amount of sulfur dioxide in a lower total gas volume of the feed gas corresponds to a higher concentration, which shifts the reaction equilibrium towards sulfur trioxide. Furthermore, an equal amount of released reaction heat will result in a higher gas temperature if the volume is lower. Therefore, the pre-converter according to the present invention has the function of recycling part of the sulfur trioxide containing gas stream to the first pre-converter stage or the feed gas of this first pre-converter stage, thereby allowing the temperature to remain within the working range of the catalyst, which is typically 370 to 440 °C. At the same time, it reduces the remaining sulfur dioxide concentration to a level suitable for downstream conventional sulfuric acid plants, although its capacity to convert sulfur dioxide is lower than the amount a generated by at least one source.

[0016] To make this effect partially significant, the added oxygen is introduced at a concentration between 90 and 99 vol.% and / or the concentration of sulfur dioxide in the sulfur dioxide containing gas is at least 14 vol.%, particularly preferably between 18 and 65 vol.% before mixing the streams. In other words, the amount of inert gas added with the oxygen is between 0 and 78 vol.% in the oxygen feed stream, preferably between 0 and 50 vol.%. Thus, in the case of a constant volumetric flow of sulfur dioxide containing gas and oxygen, the ratio of sulfur dioxide to oxygen entering the pre-converter stage is between 0.14 and 2.95, preferably between 0.18 and 1.3, most preferably between 0.45 and 0.6.

[0017] While a higher purity of oxygen further reduces the gas volume, oxygen with a concentration between 95 and 99.5 vol.% is an easily available and inexpensive source of oxygen. This applies in particular to technical purity oxygen, i.e. oxygen grade 2.5 (99.5 vol.%). Thus, the problems typically associated with the use of lower grade oxygen, such as technical purity oxygen and below, i.e. the need to remove the impurities contained therein by means of a waste stream in a subsequent stage, are mitigated. While the impurities in the purification stream and the high sulfur dioxide content would typically result in costs that are too high to comply with today's ecological standards, the processing by a conventional sulfuric acid plant eliminates the need for separate cleaning of the purification stream.

[0018] In a preferred embodiment, oxygen for the pre-reformer stage is added to at least one source for generating a sulfur dioxide containing gas. This allows to implement the method of the present utility model with minimal structural changes, as the generation of sulfur dioxide requires the addition of an oxygen containing gas and thus already the mechanism for adding oxygen to the source is present. Furthermore, a smaller blower can be used to introduce the oxygen containing gas into the source for generating a sulfur dioxide containing gas, as a smaller volume of gas is sufficient to provide sufficient oxygen compared to, for example, air which comprises only about 20 vol.-% of oxygen. Furthermore, all downstream components can then also be designed smaller.

[0019] It is further preferred that the at least one source for a sulfur dioxide containing feed gas is the combustion of elemental sulfur with oxygen. A particularly dense and high purity sulfur dioxide containing gas can be generated by elemental sulfur burners, which have a concentration of up to 66 vol.-%. In the sense of the present utility model, the combustion of elemental sulfur with oxygen covers all catalytic and non-catalytic methods, in which sulfur and oxygen react to form sulfur dioxide, whether or not a flame formation occurs.

[0020] Alternatively or additionally, the off-gas of a metallurgical process, as mentioned at the outset, can be used as the at least one source for a sulfur dioxide containing feed gas.

[0021] According to a preferred embodiment, the oxygen introduced in the above-mentioned combustion of elemental sulfur is introduced into a gas stream having at least 25 vol.-%, preferably more than 95 vol.-%, of oxygen. This also has a positive influence on the increase in combustion efficiency.

[0022] It is further preferred that 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, most preferably between 390°C and 410°C, before entering the pre-reformer. This way, excessively high temperatures in the pre-reformer stage can be avoided 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, for example water for generating steam or oxygen for the pre-reformer stage.

[0023] According to another embodiment, the portion of the sulfur trioxide containing gas stream branched off from the sulfur trioxide containing gas stream generated in the pre-reformer stage amounts to between 10 and 80 vol.-%, preferably between 12 and 50 vol.-%, of the sulfur trioxide containing gas stream. Thus, it is ensured that there is a sufficient concentration of sulfur trioxide in the feed gas for the pre-reformer stage.

[0024] Correspondingly, the remaining portion of the sulfur trioxide containing gas stream fed into the pre-reformer absorber can amount to between 90 and 20 vol.-%, preferably between 50 and 88 vol.-%, of the sulfur trioxide containing gas stream.

[0025] The preferred split fraction depends on the content of sulfur trioxide after the contact, which depends on the number of contact stages. The more contact stages that are used, the higher the sulfur trioxide content, and the less of the desired equilibrium shifted recovery stream that can be achieved.

[0026] According to another embodiment, the sulfur dioxide containing gas is branched off before being introduced into the pre-converter stage and directly into the conventional sulfuric acid plant. Thus, at least a fraction of the sulfur dioxide containing gas used in the pre-converter stage is less than 100 vol% of the sulfur dioxide containing gas produced by the at least one source, preferably the amount is between 12 and 90% of the sulfur dioxide containing gas generated in the at least one source. Typically, the sulfur dioxide containing feed gas is branched off before the oxygen used for the converter stage is added. The advantage of partially bypassing the pre-converter is to make full use of the capacity of the existing plant. Furthermore, the sulfur dioxide load can be distributed between the pre-converter stage and the conventional sulfuric acid plant in order to, for example, allow for variations in the sulfur dioxide concentration.

[0027] In another embodiment, a further sulfur trioxide containing gas stream is branched off downstream of the contact stage of the main converter in the conventional sulfuric acid plant and directly recycled into the feed gas of the pre-converter or the first pre-converter stage. This not only creates a redundancy for the recycling of a fraction of the sulfur trioxide containing gas stream at the pre-converter stage, but also allows for a better control of the sulfur trioxide content that is fed into the pre-converter stage as part of the feed gas.

[0028] Furthermore, the remaining sulfur dioxide stream from the final absorber of the conventional plant can be mixed in at any point before the pre-converter to increase the overall turnover.

[0029] In a further modification, the pre-conversion absorber and at least one absorber of the conventional sulfuric acid plant have a common pump tank for sulfuric acid used as absorption medium. Thus, the already existing pump tank in the conventional sulfuric acid plant can be utilized, which reduces the cost of retrofitting the existing plant and further provides the opportunity to centralize the further processing of the generated sulfuric acid.

[0030] In a particularly preferred embodiment, the fraction of the sulfur trioxide containing gas stream is mixed into the feed gas for the pre-converter stage by means of a gas eductor. Thus, the sulfur dioxide containing gas and the added oxygen are introduced as motive medium into the motive medium inlet of the eductor, such that they draw in and accelerate the recycle stream as suction medium in the suction medium inlet to produce the feed gas that flows through the discharge outlet for the converter stage.

[0031] In contrast to this solution, it is common to use hot gas blowers to increase the pressure of the branched-off and recovered partial stream of the sulfur trioxide containing gas stream in the preconverter stage or in the feed gas to the preconverter stage. However, the fans and seals of these blowers are prone to wear due to the contact with the hot and highly corrosive sulfur trioxide containing gas stream. In addition to the described pressurization, a homogenously mixed feed gas is also obtained, which renders additional gas mixers superfluous and reduces the chance of local overtemperatures, i.e. hot spots, in the preconverter stage.

[0032] It is further considered that the ejector has no sensitive components, such as fans or necessary seals in hot gas blowers, and that the recovered partial stream neither needs to be actively heated nor cooled.

[0033] The pressure of the feed gas leaving the ejector is preferably between 130 kPa and 150 kPa to ensure sufficient pressure within the system.

[0034] The utility model also relates to a kind of equipment, especially the equipment for executing the method as described above, which comprises: at least one reactor for generating sulfur dioxide containing gas of amount a;Preconverter for reacting feed gas comprising at least a part of sulfur dioxide containing gas and added oxygen to generate sulfur trioxide containing gas stream;Recycle pipeline for branching off partial stream of sulfur trioxide containing gas stream and recycling it to preconverter or feed gas of preconverter;Preconversion absorber for absorbing remaining part of sulfur trioxide containing gas using sulfuric acid to generate liquid sulfuric acid stream and remaining sulfur dioxide containing gas;And conventional sulfuric acid equipment, it includes at least one contact stage of main converter for reacting sulfur dioxide with oxygen to generate sulfur trioxide and at least one absorber for absorbing generated sulfur trioxide in sulfuric acid, wherein the capacity of conventional sulfuric acid equipment for converting sulfur dioxide is lower than amount a.Such equipment for generating sulfuric acid includes at least one source for generating sulfur dioxide containing gas of amount a.In addition, it includes preconverter with at least one preconverter stage, for reacting feed gas comprising at least a part of sulfur dioxide containing gas and added oxygen to generate sulfur trioxide containing gas stream.Thereby, the size of pipeline for adding oxygen and preconverter and related devices, such as heat exchanger, fan etc. is designed so that the oxygen concentration in this gas stream is at least 11.6% by volume.

[0035] In this case, the equipment also includes pipeline for branching off partial stream of sulfur trioxide containing gas stream and recycling it to first preconverter stage or feed gas of first preconverter stage.Downstream of preconverter, absorber is also provided for absorbing remaining part of sulfur trioxide containing gas using sulfuric acid to generate liquid sulfuric acid stream and remaining sulfur dioxide containing gas.After that, conventional sulfuric acid equipment with capacity c is provided.

[0036] The conventional sulphuric acid plant comprises at least two contact stages of a series arrangement of primary converters for reacting sulphur dioxide with oxygen to produce sulphur trioxide and at least one absorber for absorbing the produced sulphur trioxide in sulphuric acid, and the capacity of which to convert sulphur dioxide is below the amount a.

[0037] The plant has all the advantages of the method described before which can be performed in such a plant. All preferred embodiments apply to the preferred design of such a plant as well.

[0038] As described above, it is preferred that the at least one source for producing a sulphur dioxide containing feed gas comprises an elemental sulphur burner. It is preferred that the line into which oxygen is introduced into the burner is designed such that the amount of introduced oxygen is at least 22 vol.%. In one embodiment, the plant comprises an elemental sulphur burner combined with a fire tube boiler to produce superheated steam using the heat generated in the burner.

[0039] Alternatively, as at least one source for a sulphur dioxide containing gas a roaster, e.g. a fluidized bed reactor for roasting sulphidic ores, or a smelting furnace can be used which is configured to provide a sulphur dioxide containing off-gas.

[0040] In particular, these sources have in common that the amount a of the generated sulphur dioxide containing gas easily exceeds the capacity of a conventional sulphuric acid plant to convert sulphur dioxide in a continuous process.

[0041] In one embodiment, the plant comprises at least one heat exchanger configured to cool at least a part of the sulphur dioxide containing gas to a temperature between 380°C and 430°C, preferably to a temperature between 390°C and 410°C, before entering the pre-converter stage. Additionally or alternatively, a heat exchanger can be provided which is configured to cool the remaining sulphur dioxide containing gas to a temperature between 250°C and 180°C.

[0042] In another embodiment, the plant comprises a gas ejector for mixing a part of the stream of the sulphur trioxide containing gas stream with the feed gas of the pre-converter stage and simultaneously adjusting the pressure of the feed gas for the pre-converter. Thereby, the ejector is configured such that the sulphur dioxide containing gas, which usually has a pressure of 130 to 150 kPa, and the added oxygen gas as motive gas pass through the ejector nozzle into the ejector. This results in an acceleration such that a low pressure area is formed around the end of the nozzle. The lower pressure results in that a part of the stream of the recovered sulphur trioxide containing gas stream is sucked into the ejector as a suction medium, whereafter the gases are mixed and a feed gas having a set pressure of usually between 130 kPa and 150 kPa is generated in the diffuser of the ejector.

[0043] In another embodiment, a line, i.e. a pipe, is provided which is configured to branch off an additional sulphur trioxide containing gas stream downstream of at least one of the at least two contact stages of the main converter in a conventional sulphuric acid plant and to directly recycle said additional stream to the pre-converter stage or to the feed gas of the pre-converter stage. Preferably, the additional sulphur trioxide containing gas stream works as a suction medium in the above-mentioned gas ejector.

[0044] Further developments, advantages and possible applications can also be derived from the following description of exemplary embodiments and the attached drawings. All described and / or illustrated features result from the subject matter of the application itself or any combination thereof, independently of whether they are contained in the claims or not or in which relation they are cited. BRIEF DESCRIPTION OF DRAWINGS

[0045] In the drawings:

[0046] Figure 1 schematically showing a conventional sulphuric acid plant,

[0047] Figure 2 schematically showing a first embodiment of a source for generating sulphur dioxide containing gas coupled with a conventional sulphuric acid plant by a pre-converter according to the present application,

[0048] Figure 3 schematically showing a second embodiment of the present application comprising a pre-converter with two converter stages,

[0049] Figure 4 schematically showing a third embodiment of the present application comprising a bypass line for sulphur dioxide containing gas,

[0050] Figure 5 schematically showing a fourth embodiment of the present application comprising two sources for generating sulphur dioxide containing gas,

[0051] Figure 6 schematically showing a detail view of a pre-converter stage according to the third embodiment of the present application comprising an ejector. DETAILED DESCRIPTION

[0052] Figure 1A conventional sulphuric acid plant according to the prior art is shown. However, the present utility model is not limited to this particular plant, but can be applied to any type of sulphuric acid plant comprising a converter with at least one contact stage and at least one absorber. In which, a sulphur dioxide containing gas stream is introduced into a main converter 20 comprising four contact stages 21'to 21 " of the main converter arranged in series for reacting the sulphur dioxide with oxygen to produce sulphur trioxide. Between each contact stage 21'to 21 " an unshown heat exchanger is provided for cooling the sulphur trioxide containing gas stream obtained from the respective contact stage to a sufficiently low temperature to avoid excessive temperatures in the subsequent contact stages 21 " to 21 " " and / or absorbers 30, 30'.

[0053] The sulphur trioxide containing gas obtained from the contact stage 21 "'is then withdrawn through a conduit 24 and fed into an intermediate absorber 30. Concentrated sulphuric acid of a concentration preferably between 93% and 99.5% is supplied through a conduit 31 of a pump tank 34 to the intermediate absorber 30 as absorption medium for the sulphur trioxide produced, preferably countercurrent to the sulphur trioxide containing gas. The remaining sulphur dioxide containing gas obtained is withdrawn through a conduit 32 and supplied through a conduit 32 to any one of the contact stages 21'to 21 " ', preferably the last one, while the formed sulphuric acid is recycled into the pump tank 34. From there, a sulphuric acid product stream is withdrawn through a conduit 35 for further processing. For improving the absorption, sulphur trioxide from at least one subsequent contact stage 21 " to 21 "'is fed into a final absorber 30 '.

[0054] It is preferred that all absorbers 30 and 30'have a common pump tank for supplying the sulphuric acid. The heat exchangers are generally positioned such that the concentrated sulphuric acid supplied to the absorbers 30, 30'has substantially the same temperature, i.e. a temperature preferably between 60°C and 230°C, preferably 80 + / - 5°C. In this way, optimal conditions for absorbing the sulphur trioxide can be ensured in a simple manner.

[0055] The remaining tail gas is subjected to a gas cleaning section (not shown) through a conduit 36 to remove any remaining sulphur dioxide and / or other impurities, while the sulphuric acid formed in the final absorber 30'is recycled through a conduit 33'into the pump tank 34.

[0056] It is noted that the conventional sulphuric acid plant 20 can also have a different setup than the shown 3+1 arrangement of contact stages 21'to 21 " " of the main converter. For example, a 3+2 arrangement of contact stages is possible. Furthermore, the number and arrangement of absorbers 30 and 30'can vary. Also, the sulphur trioxide containing gas stream can be branched off at any location and recycled to a converter stage, preferably the first converter stage 21 ', as described in WO 2004 / 037719 Al.

[0057] Any conventional sulphuric acid plant has a specific capacity c, which is easily exceeded by the amount a of sulphur dioxide containing gas, since any increased amount a leads to the supply of even larger volumes of sulphur dioxide containing feed gas to the conventional sulphuric acid plant 20.

[0058] Generally, sulphur containing material, for example elemental sulphur in the case of an elemental sulphur burner or sulphur containing ore in the case of a pyrometallurgical reactor, is introduced into the reactor, where it is converted with oxygen. One possible source of oxygen is dry air obtained from the drying tower of a downstream sulphuric acid plant. However, the amount of converted sulphur is a determining factor for the amount of sulphur dioxide produced, which is why the amount of converted sulphur must be controlled so that the amount a is not exceeded. Moreover, due to the said reasons, i.e. to avoid catalyst destroying hot spots, not only the amount a must be controlled, but also the concentration of sulphur dioxide.

[0059] In contrast to these limiting factors, the utility model provides the possibility to increase the capacity of existing plants. The sulphur dioxide containing gas is produced by at least one source 10 and together with the added oxygen as feed gas through the pipes 14, 42 and 43 to the pre-converter 40, which comprises at least one pre-converter stage, i.e. at least a first pre-converter stage 40'.

[0060] In principle, the added oxygen stream can be added at any location. In the present embodiment, the pipe 41 is configured to add the added oxygen stream to the sulphur dioxide containing gas, wherein the total amount of inert gas and / or impurities of the added oxygen stream is in the range of 0 to 78 vol.%. This means that the oxygen is added in a high concentration of preferably at least 25 vol.%. Preferably, the pipe 41 is arranged such that the oxygen for the pre-converter is added after the produced sulphur dioxide containing gas is cooled down to a temperature between 350°C and 430°C by a not shown heat exchanger. Thus, the volume of the generated feed gas is lower compared to a dilution with air containing only about 20 vol.% of oxygen. Therefore, the capacity of the conventional sulphuric acid plant 20 in terms of maximum processable gas volume is not exceeded.

[0061] The pre-reformer 40 plays an important role in view of the sulphur dioxide concentration that can be handled in the sulphuric acid plant 20: in the pre-reformer stage 40', a gas stream containing sulphur trioxide is generated, which is withdrawn through the conduit 44. In order to avoid excessively high temperatures in the pre-reformer stage 40', a part stream of the gas stream containing sulphur trioxide is branched off and recycled through the recycling conduit 45 to the feed gas in the pre-reformer stage 40'. Alternatively, the part stream can be recycled directly into the pre-reformer stage 40'. The part stream of the gas stream containing sulphur trioxide amounts to a volume fraction of 7% to 90% of the gas stream containing sulphur trioxide. As a result, the reaction equilibrium is shifted, so that the reaction rate of the sulphur trioxide generation is reduced and less heat is generated in the pre-reformer stage 40'. Of course, a further pre-reformer stage can be provided. However, the simplest arrangement is a pre-reformer with only one stage.

[0062] In order to increase the gas pressure of the part stream of the gas stream containing sulphur trioxide and preferably to increase it to a pressure of between 110 kPa and 160 kPa, a hot gas blower 47 is provided. However, for such a hot gas blower it is required that the part stream of the gas stream containing sulphur trioxide has to be cooled to a temperature of between 250°C and 300°C through the heat exchanger 46 before passing through the hot gas blower 47 and subsequently reheated to a temperature of between 380°C and 450°C through the heat exchanger 46'.

[0063] The remaining gas stream containing sulphur trioxide, i.e. the component which is not branched off and recycled, is supplied through the conduit 51 to the pre-reforming absorber 50. The remaining gas stream containing sulphur trioxide is cooled to a temperature of between 150°C and 250°C through the heat exchanger 52 before entering the pre-reforming absorber 50. In the pre-reforming absorber 50, concentrated sulphuric acid is introduced as an absorption medium from a pump tank through the conduit 53 in order to generate a liquid sulphuric acid stream and a remaining gas containing sulphur dioxide in an amount a or less. Thereby, the pre-reformer is able to reduce the sulphur dioxide concentration entering the conventional sulphuric acid plant 20 to a concentration which can be handled by the plant.

[0064] A second embodiment of the present utility model is shown in Figure 3 compared to the embodiment shown in Figure 2 The conduit 12 is configured to add oxygen for the feed gas, in particular in the form of an oxygen-containing gas with an oxygen content of 50% by volume to 95% by volume or technical pure oxygen, into the reactor 10. Therefore, a separate conduit 41 for the introduction of the required oxygen is not required.

[0065] If the reactor 10 is designed for the combustion of sulfur-containing gases, for example it can be constructed as a fluidized bed, this means that the amount of oxygen in the fluidizing gas is increased. In a more preferred embodiment, sulfur is burned in the reactor 10. In the sense of the present invention, the term "burning" encompasses any reaction of sulfur with oxygen, whether or not a flame occurs. In particular, it encompasses the possibility of lance, nozzle, lances and all other possibilities of introducing molten sulfur droplets into a high-temperature furnace.

[0066] Furthermore, the pre-converter 40 preferably comprises a first pre-converter stage 40' and optionally also a second additional pre-converter stage 40" to increase the overall sulfur dioxide conversion in the pre-converter 40. The first sulfur trioxide-containing gas stream obtained from the first pre-converter stage 40' is fed via a pipe 48 into the second pre-converter stage, which pipe can comprise 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 avoiding excessively high temperatures in the second pre-converter stage 40". Although the second pre-converter stage 40" can ensure a higher overall turnover, the design with only one pre-converter stage 40' has the advantage of a very simple and cost-effective design.

[0067] In the present embodiment, a partial stream of the sulfur trioxide-containing gas stream obtained from the second pre-converter stage 40" is recycled via a recycling pipe 45 to the feed gas for the first pre-converter stage 40' in the same way as described above. Alternatively, a partial stream of the sulfur trioxide-containing gas stream can be withdrawn from the pipe 48 and recycled.

[0068] Furthermore, a partial stream of the sulfur trioxide-containing gas stream obtained from the contact stages 21' to 21'" of the main converter 21 of the conventional sulfuric acid plant 20 can be recycled to the feed gas of the first pre-converter stage 40' or the pre-converter 40. This has the advantage that a gas stream is recycled which still contains a considerable amount of residual sulfur dioxide.

[0069] It is particularly preferred that the pump tank 34 constitutes a common reservoir for the concentrated sulfuric acid used as absorption medium in the pre-conversion absorber 50 as well as in 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 generated liquid sulfuric acid stream is returned via a pipe 54 to the pump tank 34. Thus, a centralized supply of sulfuric acid as well as a further processing of the sulfuric acid product stream is achieved with only a small amount of adjustments to the existing structure.

[0070] A third embodiment of the present invention is in Figure 4In this case, only a part of the generated sulfur dioxide containing gas is supplied to the preroaster 40 through the pipes 42 and 43. The remaining amount is branched off upstream of the preroaster through the pipe 19. Preferably, the pipe 19 is configured such that the branched-off sulfur dioxide containing gas amounts to between 13% and 90% of the volume of the sulfur dioxide containing gas. Subsequently, the branched-off gas is mixed with the remaining sulfur dioxide containing gas drawn from the preroaster absorber 50 through the pipe 55 and supplied to the conventional sulfuric acid plant 20 through the pipe 56. In this case, the sulfur dioxide concentration in the pipe 56 is below 14% by volume for the operation of the conventional plant.

[0071] As one of the other options, the generated sulfur dioxide containing gas is conveyed from the reactor 10 through the water tube boiler 18 through the pipe 14. Regardless of this design, a further heat exchanger 49 can be provided for cooling at least a part of the sulfur dioxide containing gas in the pipe 42. This allows a better control of the temperature of the feed gas of the preroaster 40, in particular in case of a volume variation of the branched-off sulfur dioxide containing gas through the pipe 19.

[0072] A further embodiment is shown in Figure 6 As described with respect to Figure 2 In the embodiment of the utility model, the main blower 17 can be operated at less than full capacity, for example only at 66%. The idle capacity can be used to supply the additional reactor 11 with an oxygen containing gas, for example air or technical oxygen, through the pipe 13'. Preferably, the additional reactor 11 is an elemental sulfur burner.

[0073] The sulfur containing material, for example elemental sulfur in case of an elemental sulfur burner or sulfidic ore in case of a pyrometallurgical reactor, is introduced into the reactor 11 through the pipe 12'. Similar to the source 10, the additional sulfur dioxide containing gas generated in the reactor 11 is fed through the pipe 14' into the additional water tube boiler 18'. The additional sulfur dioxide containing gas is then added to the branched-off sulfur dioxide containing gas in the pipe 19 through the pipe 19'. Alternatively, the additional sulfur dioxide containing gas can also be mixed into at least a part of the sulfur dioxide containing gas as part of the feed gas for the preroaster 40 (not shown).

[0074] In the present example, the total amount of sulfur containing material fed into the reactors 10 and 11 can be increased by up to 37% compared to the prior art described above.

[0075] Figure 6A more detailed view of the pre-converter 40 is provided. Therein, a gas ejector 49 is provided which is configured to mix a part of the flow of the sulfur trioxide containing gas stream recovered through the recovery conduit 45 with at least a part of the sulfur dioxide containing gas and added oxygen supplied through conduit 42. In other words, the sulfur dioxide containing gas and added oxygen are introduced as motive medium such that it sucks in and accelerates the recovery stream working as suction medium in conduit 45 to generate a feed gas flowing through the discharge outlet for the converter stage in a set pressure range. Thus, the two streams are perfectly mixed without the need for additional mixing elements. Furthermore, no blower, fan or similar is needed in the recovery conduit 45. This also eliminates the need to cool the stream to a temperature at which such a blower can be used. Re-heating is no longer necessary either. At the same time, the pressure of the feed gas supplied to the at least one (first) pre-converter stage 40' of the pre-converter 40 is regulated.

[0076] Thus, the sulfur dioxide containing gas and added oxygen having a pressure of 130 kPa to 160 kPa enters the ejector 49. The lower pressure results in the part of the flow of the sulfur trioxide containing gas stream recovered being sucked into the ejector 49 as suction medium, thereby generating the feed gas having a set pressure typically between 130 kPa to 150 kPa. This modification can be used in any of the previous embodiments.

[0077] List of reference signs

[0078] 10 reactor

[0079] 11 reactor

[0080] 12-16 conduit

[0081] 17 main blower

[0082] 18, 18' fire tube boiler

[0083] 19, 19' conduit

[0084] 20 conventional sulfuric acid plant

[0085] 21 main converter

[0086] 21 '-21 " contact stage

[0087] 22-25 conduit

[0088] 30 intermediate absorber

[0089] 30' final absorber

[0090] 31-33" conduit

[0091] 34 pump tank

[0092] 35, 36 conduits

[0093] 40 pre-reformer

[0094] 40', 40" pre-reformer stage

[0095] 41-44 conduits

[0096] 45 recycle conduit

[0097] 46, 46' heat exchanger

[0098] 47 hot gas blower

[0099] 48 conduit

[0100] 49 ejector

[0101] 50 pre-reforming absorber

[0102] 51 conduit

[0103] 52 heat exchanger

[0104] 53-56 conduits

Claims

1. An apparatus for producing sulfuric acid, characterized by, The plant for producing sulfuric acid comprises at least one reactor (10) for producing a quantity a of a sulfur dioxide containing gas; a pre-converter (40) for reacting a feed gas comprising at least a part of the sulfur dioxide containing gas and added oxygen to produce a sulfur trioxide containing gas stream; a recycling conduit (45) for branching off a partial stream of the sulfur trioxide containing gas stream and recycling it into the pre-converter (40) or the feed gas of the pre-converter (40); a pre-conversion absorber (50) for absorbing the remaining part of the sulfur trioxide containing gas stream using sulfuric acid to produce a liquid sulfuric acid stream and a 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 for absorbing the produced sulfur trioxide in sulfuric acid, wherein the capacity of the conventional sulfuric acid plant (20) for converting sulfur dioxide is lower than the quantity a.

2. The apparatus for producing sulfuric acid according to claim 1, characterized by, The at least one reactor (10) for producing a sulfur dioxide containing feed gas comprises an elemental sulfur burner.

3. The apparatus for producing sulfuric acid according to claim 1 or 2, characterized by, The plant for producing sulfuric acid comprises a gas injector (49) for mixing the partial stream of the sulfur trioxide containing gas stream with the feed gas of the pre-converter (40) and simultaneously adjusting the pressure of the feed gas for the pre-converter (40).

4. The apparatus for producing sulfuric acid according to claim 1, characterized by, The oxygen for the pre-converter (40) is added to the at least one reactor (10) for producing a sulfur dioxide containing gas.

5. The apparatus for producing sulfuric acid according to claim 1, characterized by, The sulfur dioxide containing feed gas is branched off before being introduced into the pre-converter (40) and directly passed into the conventional sulfuric acid plant (20).

6. The apparatus for producing sulfuric acid according to claim 5, characterized by, A volume fraction of the branched off sulfur dioxide containing feed gas is used to adjust the sulfur dioxide content of the conventional sulfuric acid plant (20).

7. The apparatus for producing sulfuric acid according to claim 1, characterized by, The remaining part of the sulfur trioxide containing gas stream of the pre-converter (40) is passed through the pre-conversion absorber (50).

8. The apparatus for producing sulfuric acid according to claim 7, characterized by, The sulfur trioxide containing gas is branched off before being introduced into the pre-conversion absorber (50) and directly passed into the conventional sulfuric acid plant (20).

9. The apparatus for producing sulfuric acid according to claim 1, characterized by, A further sulfur trioxide containing gas stream is branched off downstream of at least one of the at least two contact stages of the conventional sulfuric acid plant (20) and directly recycled into the pre-converter (40) or the feed gas of the pre-converter (40).

10. The apparatus for producing sulfuric acid according to claim 1, characterized by, The pre-conversion absorber (50) and the at least one absorber of the conventional sulfuric acid plant (20) have a common pump tank for sulfuric acid used as absorption medium.

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