Apparatus for producing gas stream containing sulfur trioxide

Abstract

An apparatus for producing a gas stream comprising sulfur trioxide, the apparatus comprising: at least one converter stage for reacting a gas comprising sulfur dioxide and oxygen with oxygen to produce a gas stream comprising sulfur trioxide; the utility model relates to an apparatus for producing a sulfur trioxide-containing gas stream, comprising a first converter stage, a recirculation line for shunting a partial flow of the sulfur trioxide-containing gas stream as a recirculation flow and for recirculating the recirculation flow as part of a feed gas for the first converter stage, the apparatus comprising an ejector having an inlet for a power medium and an inlet for a suction medium, wherein the two inlets are arranged such that a sulfur dioxide-containing gas and added oxygen are introduced as a motive medium and the recycle stream is introduced as a suction medium. Compared with the prior art using a blower, the device using the ejector reduces the risk of leakage caused by sulfur trioxide, does not need cooling and reheating, reduces part equipment, and also reduces energy loss.

Description

TECHNICAL FIELD

[0001] The present utility model relates to a method for producing a sulfur trioxide containing gas stream and a corresponding apparatus, wherein a sulfur dioxide and oxygen containing gas is introduced into at least one converter stage to produce a sulfur trioxide containing gas stream in a heterogeneous catalysis, wherein a partial stream of the sulfur trioxide containing gas stream produced in the first converter stage or a subsequent converter stage is split off as a recycle stream and recycled as part of the feed gas of the first converter stage. BACKGROUND

[0002] Sulfuric acid is an inorganic acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is miscible with water. It is one of the most important chemicals and is therefore often used as an indicator of a nation's industrial strength. As a key substance in the chemical industry, it is most commonly used in fertilizer manufacture, but is also important in mineral processing, oil refining, waste water treatment, and chemical synthesis. In addition, it has a wide range of end applications, including in household acid drain cleaners, as the electrolyte in lead-acid batteries, in dehydrating compounds, and in various cleaning agents.

[0003] One of the main processes for producing sulfuric acid is the contact process, which includes the double absorption process as set out in detail in Ullmann's Encyclopaedia of Industrial Chemistry, 5th edition, volume A25, pages 635 to 700. Sulfur dioxide (SO2) is obtained by sulfur combustion or as off-gas from smelters. It is then converted into sulfur trioxide (SO3) in a typical four- or five-stage converter using vanadium pentoxide as a solid catalyst. The sulfur trioxide is produced and recovered after the contact stage of the converter and is transported to an intermediate absorber. Conversely, the sulfur trioxide can also be supplied to a final absorber after the final converter stage. In the final absorber, the sulfur trioxide containing gas is fed into concentrated sulfuric acid in a counter-current manner while being absorbed.

[0004] However, the conversion from sulfur dioxide to sulfur trioxide is one of the main steps in this industry, whereby the reaction in the converter stage takes place according to the following reaction:

[0005] 2 SO2(g) + O2(g) ⇌ 2 SO3(g): ΔH = -197 kJ·

[0006] From the given reaction parameters it is evident that the reaction is highly exothermic, which involves a high risk for so-called hot spots in the catalyst bed. Therein, the temperature locally increases, which in turn leads to even higher reaction rates and thus to even stronger local temperature increases. If the temperature locally exceeds a certain critical value, the catalyst is irreversibly damaged. This problem occurs especially in the first converter stage due to the too high level of sulfur dioxide during gas uptake, and the absence of sulfur trioxide in the gas stream, which would change the reaction rate in equilibrium.

[0007] Therefore, the most important measure is to divide the converter into separate stages, each stage being filled with catalyst. This allows the gas stream leaving one stage to be cooled before entering the next stage. Furthermore, measures such as different catalyst concentrations, catalyst types, bed sizes, etc. can influence the reaction in the individual stages in a way that avoids hot spots. However, in these converters the feed gas can only be applied with a maximum sulfur dioxide content of 11 to 13 volume percent to reliably avoid hot spots.

[0008] For converters capable of handling feed gases with higher sulfur dioxide contents, the so-called LUREC® (described in WO 2004 / 037719 Al) has been developed. This process uses the understanding of the reaction as an equilibrium reaction by recycling at least a part of the intermediate product stream or the final product stream containing sulfur trioxide back into the first contact stage. Thus, the contained sulfur trioxide influences the equilibrium between sulfur dioxide and sulfur trioxide in the reaction equation, so that the reaction rate for the preparation of sulfur trioxide is reduced. Thus, the reduced conversion also generates less energy, which prevents the formation of hot spots.

[0009] However, due to the pressure drop resulting from overcoming the flow resistance of the contact stage(s) of the converter, the recycled gas stream is characterized by a low gas pressure, which is usually between 90 kPa and 130 kPa. Therefore, the pressure of the partial gas stream has to be increased before the feed gas is circulated back to the initial contact stage to match the inlet conditions. As a result, the obtained feed gas must have a sufficient pressure to at least overcome the flow resistance of the first contact stage.

[0010] In conventional plants capable of handling increased sulfur dioxide contents, this is achieved by a hot gas blower. However, the hot sulfur trioxide-containing gas is highly corrosive and thus causes damage to sensitive parts of the blower, such as the fan or the seals. This damage will lead to a dangerous leakage of the corrosive gas over time, making the hot gas blower a high-maintenance device.

[0011] Thus, the part of the gas stream that is recirculated is usually cooled from a temperature between 420°C and 630°C to a temperature between 200°C and 250°C before passing through the hot gas blower. However, this temperature will result in a gas mixture that is so cold entering the first stage of the converter that no reaction will occur, at least if a certain recirculation rate is to be achieved. Therefore, the pressurized part of the gas stream is usually reheated to a temperature usually between 380°C and 420°C before being recirculated into the feed gas to ensure the necessary temperature of the feed gas for the catalytic converter ignition, which is about 400°C, although this partly mitigates the corrosion problem, the cooling and subsequent reheating stage requires additional heat exchangers. Furthermore, the heat exchangers cause a further pressure drop, which means that the hot gas blower has to be even more powerful. By avoiding the cooling and heating of the recirculation stream, the heat remains at a higher temperature level and can thus be utilized for e.g. higher pressure steam production or a reduction of the overall heat exchanger surface.

[0012] Furthermore, in order to feed a homogenous stream into the converter, to mix this circulating stream into a gas containing sulfur dioxide and oxygen, additional gas mixers are required. All these devices result in additional capital expenditure and operating expenditure. SUMMARY

[0013] It is therefore an object of the present invention to provide a method and a corresponding apparatus for producing a sulfur trioxide containing gas stream that more efficiently produces a homogeneous sulfur dioxide containing feed gas for the first converter stage.

[0014] In the method, a gas containing sulfur dioxide and oxygen is introduced into at least one converter stage to produce a sulfur trioxide containing gas stream in a heterogeneous catalysis. A part stream of the sulfur trioxide containing gas stream produced in the first converter stage or a subsequent converter stage is tapped off as a recirculation stream and is recirculated as part of the feed gas for the first converter stage.

[0015] According to the invention, the gas containing sulfur dioxide and oxygen is thereby introduced into an ejector as motive medium, so that the ejector sucks, accelerates and compresses the recirculation stream working as suction medium to produce a feed gas for the converter stage at a set pressure range.

[0016] The principle of the ejector is that the high pressure gas stream, i.e. the motive medium, enters the ejector via a nozzle. This enables the (static) pressure of the high pressure gas stream corresponding to the gas containing sulfur dioxide and oxygen to be converted into a higher dynamic pressure, so that the velocity of the gas containing sulfur dioxide and oxygen is increased.

[0017] As a result, the velocity is highest around the tip of the nozzle, which is why a low pressure area is created, because this high gas velocity entrains gas from the adjacent sub-areas. The created low pressure sucks the recirculation flow via the suction medium inlet of the ejector, also called suction leg. Thereby, the recirculation flow is accelerated and compressed. Then, both gas flows travel through the so-called diffuser section of the ejector, where the flows are mixed to form a homogeneous feed gas for the first converter stage. Due to the diverging geometry of the diffuser section, the gas velocity decreases and a set pressure is obtained, which is between the initial pressure of the sulfur dioxide and oxygen containing gas and the initial pressure of the recirculation flow.

[0018] In comparison to conventionally used hot gas blowers, the simple and robust design of the ejector does not have sensitive moving parts, such as a fan, or seals which are sensitive to corrosion. Therefore, the risk of leaks caused by sulfur trioxide is reduced and no cooling and reheating is necessary.

[0019] Furthermore, a homogeneous feed gas for the first converter stage is created without additional mixing devices, despite the differences in pressure, temperature and chemical composition between the sulfur dioxide and oxygen containing gas and the recirculation flow.

[0020] It is preferred that the feed gas leaving the ejector has a pressure range of 110 kPa to 160 kPa. This pressure range corresponds to a pressure which is sufficient to overcome the flow resistance of at least one converter stage. Depending on the number of converter stages, the pressure is set towards the lower or upper limit of the above mentioned range. The pressure range can be adjusted by the inlet pressure of the motive medium.

[0021] In another or complementary embodiment, the pressure difference between the suction medium inlet and the discharge outlet is between 5 kPa and 30 kPa. This pressure range is particularly preferred for a constant flow of the recirculation flow and a complete mixture in the ejector.

[0022] In another embodiment, the concentration of sulfur dioxide in the sulfur dioxide containing feed gas is at least 14 volume percent, preferably 18 to 66 volume percent, whereby the overall plant production capacity can be increased.

[0023] It is further preferred that the recirculation flow is neither actively heated nor cooled. As mentioned above, the sensitivity of the ejector is lower than conventional hot gas blowers due to the absence of components which are particularly sensitive to the sulfur trioxide containing hot gas flow. Therefore, the gas flow does not need to be cooled and subsequently reheated, which improves the energy balance of the process.

[0024] This embodiment also corresponds to the best possible utilization of the heat of reaction in the recirculation stream in terms of efficiency, given that no active heat transfer to another medium with losses occurs. In particular, a feed gas can be obtained which has a temperature higher than the minimum operating temperature of at least one converter stage, although the temperature of the sulfur dioxide and oxygen containing gas is relatively low. This in turn allows a better utilization of the heat content of the gas stream elsewhere in the process. For example, the heat of reaction from the initial generation of sulfur dioxide used in the process can be used to a greater extent, for example in a fire tube boiler, to generate superheated steam.

[0025] Alternatively, the at least one heat exchanger can be preset to actively heat or cool the recirculation stream. This allows an exact control of the temperature of the recirculation stream.

[0026] In another embodiment, the pressure of the sulfur dioxide and oxygen containing gas is used as a control variable for the pressure of the feed gas. As described above, the pressure of the feed gas leaving the ejector depends on the pressure of the motive medium as well as the suction medium. Given that there is inevitably a device for adjusting the pressure of the sulfur dioxide and oxygen containing gas, such as a blower, to deliver the gas stream, the pressure of the sulfur dioxide and oxygen containing gas can thus be adjusted. However, the pressure of the gas stream working as motive medium directly influences the suction on the circulation stream as well as the outlet pressure of the mixed feed gas. Therefore, the pressure of the sulfur dioxide and oxygen containing gas can be used as a control variable for the pressure of the feed gas. In this case, a pressure of 120 kPa to 200 kPa is particularly preferred for the gas stream when entering the ejector as motive medium.

[0027] To cover a wider range of operating conditions, an array of different sizes of ejectors can be used. These ejectors are arranged in series, in parallel or a combination of series and parallel.

[0028] According to another embodiment, further sulfur trioxide containing gas streams from subsequent converter stages are also recirculated into the ejector or mixed separately to form the feed gas for the first converter stage. Thus, a better control of the amount of sulfur trioxide recirculated as part of the feed gas for the first converter stage is achieved.

[0029] Preferably, the partial streams of sulfur trioxide containing gas streams add up to a volume percentage of 15% to 80% of the sulfur trioxide containing gas stream generated in the first or subsequent converter stage. It is particularly preferred that the recirculation of the partial stream(s) is carried out such that the resulting feed gas has a sulfur trioxide content of between 2 and 50 volume percent.

[0030] According to another embodiment, a further gas stream is also fed to the ejector to form the feed gas for the first converter stage. The excellent mixing properties of the ejector are utilized to better control the amount of sulfur trioxide for the first converter stage or the temperature of the feed gas.

[0031] According to one of the most preferred embodiments, the first conversion stage takes place in a pre-converter, which is characterized by having at least one pre-converter stage. A part of the sulfur trioxide containing stream from this first stage is recycled into the feed of the first converter stage to limit the reaction by shifting the equilibrium. Naturally, the mixing of the sulfur trioxide containing stream and the feed gas for the first pre-converter stage takes place in the ejector according to the present application.

[0032] The remaining part of the sulfur trioxide containing gas stream, i.e. the part of the sulfur trioxide containing gas stream that is not recycled, is fed to further conversion stages in the pre-converter and / or the main converter.

[0033] Furthermore, a subsequent pre-converter absorber between the pre-converter and the main converter can be provided for sulfuric acid absorption to form sulfuric acid. In the subsequent pre-converter absorber, the remaining part of the sulfur trioxide containing gas stream is absorbed using sulfuric acid as the absorption medium, so that at least part of the sulfur trioxide is processed into sulfuric acid at an early process stage, i.e. before entering the conventional sulfuric acid plant.

[0034] The conventional sulfuric acid plant comprises at least two contact stages of the main converter, which are arranged in series to react the sulfur dioxide with oxygen to produce sulfur trioxide. The produced sulfur trioxide containing gas is fed to at least one further absorber, in which the produced sulfur trioxide is absorbed using sulfuric acid as the absorption medium. The production capacity c of such a sulfuric acid plant is limited by the total gas volume V that can be processed in the plant and the amount a of sulfur dioxide that can be reacted in the main converter. By using a pre-converter with a recycle stream of sulfur trioxide, the amount of sulfur dioxide that can be processed can be increased. Furthermore, this arrangement allows to control the reaction with an increased amount of oxygen, preferably an oxygen concentration of 75 to 100 volume percent in the added gas stream. Compared to the traditional control reaction with air, the proportion of inert gas is significantly reduced, which means that the volume flow can be significantly reduced. Thus, the range of limiting factors for the gas volume V and the amount a of sulfur dioxide is greatly widened.

[0035] This arrangement is particularly useful if the production capacity c of the conventional plant has to be increased due to an increased demand or due to the need to treat more sulfur dioxide. An increased demand can be considered in particular if the source of the sulfur dioxide is the combustion of elemental sulfur with oxygen. This can easily be scaled up by additional burners in parallel, where the term "burner" covers all kinds of reactions between sulfur and oxygen, irrespective of whether a flame occurs or not. On the other hand, the amount of sulfur dioxide produced in a smelting process can increase due to a decrease in ore quality. This allows the conventional sulfuric acid plant with a production capacity c for converted sulfur dioxide to be operated in combination with the above-mentioned source of a sulfur dioxide containing gas which produces an amount a of sulfur dioxide which exceeds the production capacity c of the plant.

[0036] The utility model also relates to a kind of equipment. This equipment includes at least one converter stage, for the gas containing sulfur dioxide and oxygen is reacted to produce the gas stream containing sulfur trioxide. In addition, it is characterized by the recirculation pipeline for the partial flow of the gas stream containing sulfur trioxide is shunted and is recycled to the first converter stage. In order to mix the recirculation stream with the gas containing sulfur dioxide and oxygen, ejector is preset.The ejector is characterized by having the inlet for motive medium and the inlet for suction medium, wherein two inlets are arranged so that the gas containing sulfur dioxide and oxygen is introduced as motive medium, and the recirculation stream is introduced as suction medium.

[0037] As the source of sulfur dioxide, the equipment can include at least one elemental sulfur combustion device for producing a sulfur dioxide containing gas as a reactant to produce sulfur trioxide. In this context, the term "combustion unit" covers all catalytic and non-catalytic processes for reacting sulfur and oxygen to sulfur dioxide, irrespective of whether a flame is formed or not. In particular, a sulfur lance, a lance and any other kind of furnace are disclosed in this wording, in which droplets of molten sulfur are converted.

[0038] It is particularly preferred that the combustion unit is designed so that it works with relatively pure oxygen, for example in an amount of less than 20 volume percent of inert gas. In particular, the oxygen content is between 85 and 99 volume percent. This allows to reduce the gas volume through all downstream reaction stages.

[0039] It is further preferred that the recirculation pipeline does not have a heat exchanger directly combined with the basic idea of the utility model, i.e. the mixing of the gas stream containing sulfur trioxide with the primary feed gas containing sulfur dioxide and oxygen is carried out using an ejector. By eliminating the conventional blower, there is no longer a need to adjust the temperature of the recirculation stream to the temperature range of the blower. In addition to reducing the component equipment, this also has the advantage of reducing energy losses.

[0040] According to another embodiment, the first converter stage is carried out in a pre-converter, which has a subsequent pre-converter absorber, in which the remaining portion of the sulfur trioxide-containing gas stream, which is not recycled, is fed to an absorption section using sulfuric acid as absorption medium to form sulfuric acid. Therein, the sulfur trioxide contained in the gas stream is absorbed in the sulfuric acid, forming a remaining sulfur dioxide-containing gas stream, which is used for further processing. The sulfuric acid withdrawn from the pre-converter absorber is supplied to a pump tank, which in a particularly preferred embodiment also acts as a reservoir for the sulfuric acid to be fed to the pre-converter absorber as absorption medium.

[0041] In this respect, it is particularly preferred that the plant comprises a conventional sulfuric acid plant with a production capacity c arranged downstream, which plant is characterized by having a main converter with at least two main converter stages arranged in series, which main converter stages are capable of processing a quantity a of sulfur dioxide, and furthermore, it contains at least one further absorber for absorbing the sulfur trioxide produced in the sulfuric acid. In this embodiment, the remaining sulfur dioxide-containing gas stream is fed to the main converter, so that even if the raw feed gas has a very high quantity a of sulfur dioxide, this main converter is capable of processing the gas stream. Thus, the combination of the pre-converter with the recycling of the sulfur trioxide via the ejector is particularly advantageous for increasing the production capacity c of an existing conventional sulfuric acid plant.

[0042] In this case, it is preferred that the conventional plant and the pre-converter are connected to each other. One possibility can be a common pump tank shared by all absorbers of the conventional plant and the absorber of the pre-converter. Additionally or alternatively, a sulfur trioxide stream can be recycled from any stage of the main converter back into the pre-converter.

[0043] According to another embodiment, the ejector sucks and accelerates the recycling stream as a sucked medium through an inlet for the sucked medium to generate a feed gas stream flowing through a discharge outlet of the at least one converter stage at a set pressure range.

[0044] According to another embodiment, the pressure difference between the inlet for the sucked medium and the discharge outlet is between 1 kPa and 30 kPa.

[0045] According to another embodiment, the recycling stream is not actively cooled and / or not heated and thus designed to minimize the pressure drop.

[0046] According to another embodiment, the plant comprises at least two ejectors used in an array.

[0047] Furthermore, the plant according to the invention can show every design related to the embodiments of the method described previously and the advantages described previously for the method, and vice versa.

[0048] Further developments, advantages and possible applications can also be derived from the following description of exemplary embodiments and the drawings. All features described and / or shown in the subject matter of the present application itself or in any combination are, irrespective of their combination in the claims, possible solutions to the problem. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 : shows schematically an apparatus for producing a stream containing sulfur trioxide with an ejector of the present application,

[0050] Figure 2 : shows a detail view of an ejector according to the present application,

[0051] Figure 3 : shows schematically an apparatus for producing a stream containing sulfur trioxide with a hot gas blower as known in the prior art, and

[0052] Figure 4 : shows schematically a combination of an apparatus for converting sulfur trioxide with a conventional sulfuric acid plant. DETAILED DESCRIPTION

[0053] Figure 1 The basic principle of the present application is shown. A gas containing sulfur dioxide and oxygen is reacted in a converter 10 to produce a stream containing sulfur trioxide.

[0054] The gas containing sulfur dioxide and oxygen is produced in at least one not shown source and is then fed into the converter 10, which can be designed as a pre-converter or as a main converter. In any case, it is characterized by having at least one converter stage 11, wherein the main converter usually has 4 to 8 converter stages. In any case, these converter stages are filled with a solid catalyst, wherein the reaction takes place heterogeneously catalytic.

[0055] The produced stream containing sulfur trioxide is discharged from the converter 10 via a pipe 14. From said pipe 14, a pipe 15 branches off for recycling a partial stream of the stream containing sulfur trioxide as a recycle stream. The remaining stream of the gas containing sulfur trioxide, i.e. the gas stream not recycled, is passed via a pipe 18.

[0056] The recycle stream in the pipe 15 is mixed with the gas containing sulfur dioxide and oxygen from the pipe 12, so that a mixed feed gas is produced, which is conveyed via a pipe 13 into the converter 10. In order to mix the streams from the pipes 12 and 15 and at the same time to adjust the pressure of the resulting mixed feed gas in the pipe 13, a pre-set ejector 20 sucks the recycle stream.

[0057] The basic principle of the ejector 20 is described in Figure 2 .

[0058] The injector 20 comprises an inlet 21 for the motive medium, from which a nozzle 22 extends. The inlet 21 is arranged such that the sulphur dioxide and oxygen containing gas, which is transported via the conduit 12, is introduced as motive medium. By passing through the converging nozzle 22, the sulphur dioxide and oxygen containing gas, which has an initial pressure between 90 kPa and 170 kPa, is accelerated. The increased gas velocity entrains gas from the surrounding non-flowing area. Thereby, a low pressure area 23 is created. In this low pressure area or upstream, an inlet for the suction medium 24 can be pre-set. In the present application, this inlet for the suction medium 24 is connected to the conduit 15, through which the sulphur trioxide containing recycle stream is sucked.

[0059] The two gas streams of motive and suction medium are subsequently mixed in the diverging diffuser 25 of the injector 20, thereby forming a homogeneous feed gas. Preferably, the injector 20 is configured to produce a feed gas via the conduit 13 into the converter 10, which feed gas preferably has a pressure between 140 kPa and 160 kPa. For a pre-converter setup, this pressure can be significantly lower, as the total pressure drop of a pre-converter is much lower than for a conventional plant.

[0060] Relatively, Figure 3 A system of conventional design is shown, which utilizes a hot gas blower 16 for transporting the recycle stream in conduit 15 back into the mixing with the sulphur dioxide and oxygen containing gas. However, the use of this blower is limited to a certain temperature range of the recycle gas stream to prevent damage caused by corrosion from hot sulphur trioxide.

[0061] To avoid excessive wear on sensitive components of the hot blower 16, the recycle stream leaving the converter at a temperature between 600 °C and 640 °C is cooled. This cooling to a temperature range of typically 250 °C - 300 °C is performed in a heat exchanger 17, after which the recycle gas stream typically has to be reheated to a temperature to ensure sufficient mixing of the sulphur dioxide and oxygen containing gas and to meet the necessary inlet temperature of the converter of between 380 °C - 420 °C. Furthermore, in most cases, only a homogeneous mixing can be achieved with additional mixing devices 18 when the two streams meet.

[0062] Figure 4A further embodiment according to the present utility model is shown. Therein, the source for producing the amount a of sulfur dioxide containing gas is a sulfur burner unit 31 arranged upstream of the first converter stage 11. Therein, the sulfur dioxide containing gas is produced in the sulfur burner unit 31, wherein this unit is preferably an elemental sulfur burner. The sulfur containing substance is introduced into the reactor 31 via a pipe 32. The at least required oxygen for forming the sulfur dioxide is introduced into the reactor 31 via a pipe 33 and is conveyed by means of a blower 34 of sufficient size. It is preferred that the oxygen is already added in a high concentration, which is preferably higher than 90 volume percent. Alternatively, a smelting process can replace the sulfur burner unit as a source for the required sulfur dioxide.

[0063] In any case, the produced sulfur dioxide containing gas stream is discharged from the reactor 31 via a pipe 35. In a not shown way, the energy efficiency of the plant can be improved by cooling the hot sulfur dioxide stream to a temperature between 200°C and 420°C and using the obtained energy, for example by using a fire tube boiler.

[0064] Oxygen can be added to the sulfur dioxide containing gas via a pipe 36 to form a sulfur dioxide and oxygen containing gas. However, this is not mandatory if the sulfur burner unit is operated under excess oxygen.

[0065] In any case, the sulfur dioxide and oxygen containing gas stream enters the ejector 20 via a pipe 12 as motive gas, where it is mixed with the recirculation stream from pipe 15, as described with respect to Figure 1 .

[0066] The resulting feed gas is fed into the first converter stage 11 provided in a pre-converter 10', which can have only this first converter stage 11 and several stages. Therein, the remaining part of the sulfur trioxide containing gas, which is not recirculated, is passed through a pre-converter absorber 40 via a pipe 18. Optionally, a not shown heat exchanger for cooling the remaining sulfur trioxide containing part is provided before the pre-converter absorber 40 for further energy utilization.

[0067] In the pre-converter absorber 40, concentrated sulfuric acid is introduced as absorption medium from a pump tank (not shown) via a pipe 41 to produce a liquid sulfuric acid stream and a remaining sulfur dioxide containing gas. The liquid sulfuric acid stream is drawn off and recirculated to the pump tank, the remaining sulfur dioxide containing gas is passed via a pipe 43 to a conventional sulfuric acid plant 50 having a production capacity c of converted sulfur dioxide.

[0068] This conventional sulphuric acid plant 50 comprises a plurality of converter stages arranged in series to react the sulphur dioxide with oxygen to produce sulphur trioxide. The sulphur trioxide containing gas obtained from the converters is sent to at least one absorber, wherein it is common arrangement to use two absorbers, commonly referred to as an intermediate absorber and a final absorber, for the arrangement of the product gas streams of the different converter stages. Independently of the specific embodiment, concentrated sulphuric acid, preferably having a concentration of 93% - 99.5%, will be supplied as the absorption medium to the intermediate absorber in generally countercurrent fashion to the sulphur trioxide containing gas to produce sulphuric acid.

[0069] Reference signs

[0070] 10 converter

[0071] 10' pre-converter

[0072] 11, 11' converter stage

[0073] 12 to 15 pipe

[0074] 16 hot gas blower

[0075] 17, 17' heat exchanger

[0076] 18 pipe

[0077] 19 mixing device

[0078] 20 ejector

[0079] 21 inlet for motive medium

[0080] 22 nozzle

[0081] 23 low pressure area

[0082] 24 inlet for suction medium

[0083] 25 diffuser

[0084] 31 sulphur combustion unit

[0085] 32, 33 pipe

[0086] 34 blower

[0087] 35, 36 pipe

[0088] 40 pre-converter absorber

[0089] 41 to 43 pipe

[0090] 50 conventional sulphuric acid plant

Claims

1. An apparatus for producing a stream of sulfur trioxide containing gas, the apparatus comprising: at least one first converter stage (11) for reacting a gas containing sulfur dioxide and oxygen with oxygen to produce a gas stream containing sulfur trioxide; a recirculation conduit (15) for diverting a partial stream of the gas stream containing sulfur trioxide as a recirculation stream and for recirculating the recirculation stream as part of the feed gas to the first converter stage (11), characterized in that the apparatus comprises an ejector (20) having an inlet (21) for a motive medium and an inlet (24) for a suction medium, wherein the inlet for a motive medium and the inlet for a suction medium are arranged such that a sulfur dioxide containing gas and added oxygen are introduced as motive medium and the recirculation stream is introduced as suction medium.

2. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 1, characterized in that, The apparatus comprises at least one elemental sulfur combustion unit (31) for producing a sulfur dioxide containing feed gas.

3. The apparatus for producing a gas stream containing sulfur trioxide according to claim 1 or 2, characterized in that, There is no heat exchanger pre-set for the recirculation stream via the recirculation conduit (15).

4. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 1 or 2, characterized in that, The first converter stage (11) is carried out in a pre-converter (10') having a subsequent pre-converter absorber (40) in which the remainder of the sulfur trioxide containing gas stream not recirculated is sent to an absorption section with sulfuric acid to form sulfuric acid.

5. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 1 or 2, characterized in that, The apparatus comprises a conventional sulfuric acid apparatus (50) arranged downstream for processing a sulfur dioxide containing gas stream obtained from at least one absorber, wherein the conventional sulfuric acid apparatus comprises at least two further converter stages of main converters arranged in series to react sulfur dioxide with oxygen to produce sulfur trioxide and at least one further absorber for absorbing the produced sulfur trioxide in sulfuric acid.

6. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 1 or 2, characterized in that, The ejector (20) suctions and accelerates the recirculation stream as suction medium through the inlet for a suction medium (24) to produce a feed gas flowing at a set pressure range through a discharge outlet of the at least one first converter stage (11).

7. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 6, characterized in that, The pressure difference between the inlet for a suction medium and the discharge outlet is between 1 kPa and 30 kPa.

8. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 3, characterized in that, The recirculation stream is not actively cooled and / or not actively heated and thus designed for minimal pressure drop.

9. The apparatus for producing a stream of sulfur trioxide containing gas according to claim 1 or 2, characterized in that, The apparatus comprises at least two ejectors (20) used in an array. The apparatus comprises at least one elemental sulfur combustion unit (31) for producing a sulfur dioxide containing feed gas. There is no heat exchanger pre-set for the recirculation stream via the recirculation conduit (15). The first converter stage (11) is carried out in a pre-converter (10') having a subsequent pre-converter absorber (40) in which the remainder of the sulfur trioxide containing gas stream not recirculated is sent to an absorption section with sulfuric acid to form sulfuric acid. The apparatus comprises a conventional sulfuric acid apparatus (50) arranged downstream for processing a sulfur dioxide containing gas stream obtained from at least one absorber, wherein the conventional sulfuric acid apparatus comprises at least two further converter stages of main converters arranged in series to react sulfur dioxide with oxygen to produce sulfur trioxide and at least one further absorber for absorbing the produced sulfur trioxide in sulfuric acid. The ejector (20) suctions and accelerates the recirculation stream as suction medium through the inlet for a suction medium (24) to produce a feed gas flowing at a set pressure range through a discharge outlet of the at least one first converter stage (11). The pressure difference between the inlet for a suction medium and the discharge outlet is between 1 kPa and 30 kPa. The recirculation stream is not actively cooled and / or not actively heated and thus designed for minimal pressure drop. The apparatus comprises at least two ejectors (20) used in an array.

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