Tail gas treatment system and method for sulfuric acid production equipment

Abstract

Improved systems and methods for treating off-gas in a sulfuric acid production plant are disclosed. A tail gas treatment system including a product stripper and a purge gas scrubber is employed. The arrangement of the invention provides an advantageous economical way to remove high levels of SO2 from the tail gas stream.

Description

Technical Field

[0001] The present invention relates to an improved tail gas treatment system and method of operation for a sulfuric acid production facility. Background Art

[0002] Sulfur dioxide is a commonly produced industrial chemical that is used as a reactant in various other chemical processes. It is produced as pure SO2 gas and / or liquefied SO2 for sale and as a gas mixture for use in downstream processes. The main industrial application of sulfur dioxide is the production of sulfuric acid, which is one of the most produced commodity chemicals in the world and is widely used in the chemical industry and commercial products.

[0003] Today, the contact process is the predominant process used commercially to produce sulfuric acid (developed by P. Phillips in 1831). Typically, this involves obtaining a supply of sulfur dioxide by burning a sulfur supply with ambient air and then oxidizing the sulfur dioxide with oxygen in the presence of a catalyst (typically vanadium oxide) that accelerates the reaction to produce sulfur trioxide. The reaction of sulfur dioxide to sulfur trioxide is reversible and exothermic, and it is important to properly control the temperature of the gas over the catalyst in order to achieve the desired conversion without damaging the catalyst and / or the contacting apparatus containing the catalyst.

[0004] The sulfur trioxide produced is then converted to sulfuric acid by absorption into a concentrated sulfuric acid solution, with subsequent addition of water to the now more concentrated acid to maintain the acid concentration. This indirect reaction of sulfur trioxide with water avoids the consequences of directly dissolving sulfur trioxide into water, which is a highly exothermic reaction. The absorption of sulfur trioxide is typically carried out in one or more absorption towers.

[0005] A distributor is used in the absorption tower to distribute the concentrated sulfuric acid solution to the top of the packed bed in the tower. The sulfur trioxide gas usually flows through the tower in a countercurrent manner to the solution, but it can also flow cocurrently. The concentrated sulfuric acid solution is used to absorb the flowing sulfur trioxide.

[0006] In WO 2008 / 052649, a process is disclosed for the continuous catalytic complete or partial oxidation of a starting gas containing 0.1 to 66% by volume of sulfur dioxide plus oxygen, wherein the catalyst is kept active by pseudo-isothermal process conditions with the introduction or removal of energy. The relevant device is for the continuous catalytic complete or partial oxidation of a starting gas containing sulfur dioxide and oxygen and is characterized in that at least one tube contact device is a vertical heat exchanger consisting of at least one double-walled tube, the inner tube of which, filled with the catalyst, forms a reaction tube, wherein heat is transferred in parallel around the reaction tube, and an absorber for separating off SO3 is installed downstream of the tube contact device. The reactivity of the catalyst is preset by mixing with an inert material. The method and the device are marketed under the trademark CORE TM and CORE-STM Commercially available.

[0007] Historically, commercial sulfur combustion, sulfuric acid plants have used ambient air as the source of oxygen required in the process. The use of ambient air is inexpensive and the conventional process operating with about 11-12 vol% SO2 entering the contacting device perfectly balances the O2:SO2 ratio required for high conversion and the maximum allowable temperature in the first catalyst bed. The disadvantage of using air is that each required oxygen molecule is also accompanied by about four inert gas molecules (mainly N2 and argon), which must also flow through the plant, so very large equipment is required to handle the entire gas stream. In order to improve efficiency and reduce emissions, commercial sulfuric acid plants using ambient air usually have a double contact, double absorption (DCDA) design. In a DCDA system, the process gas is subjected to two contact and absorption stages (i.e., a first catalytic conversion and a subsequent absorption step, followed by a second catalytic conversion and absorption step) in succession. Sulfur dioxide for this system can be produced by burning sulfur with ambient air in a single reactor, after which the produced reactor gas is cooled in a heat exchanger before being supplied to the contacting device. Due to the high proportion of inert gases in the incoming ambient air, most of the incoming air is discharged into the stack. As a result, even low concentrations of SO2 in the tail gas discharged to the stack can result in significant emissions when evaluated on a mass flow rate (kg / h) basis. Details regarding available and preferred conventional options for sulfuric acid production and contact processes are well known and can be found, for example, in "Handbook of Sulfuric Acid Manufacturing", Douglas Louie, ISBN 0-9738992-0-4, 2005, published by DKL Engineering, Inc., Ontario, Canada.

[0008] To date, the use of highly enriched or pure oxygen has also been hampered by the cost of providing such oxygen, and the equipment would have to offset the cost of the oxygen with cost savings in the process. New and emerging technologies are now becoming available where oxygen or high purity oxygen is a byproduct from a process (e.g., water hydrolysis to produce green hydrogen), and this can provide a lower cost source of highly enriched or pure oxygen with the potential for economic integration for a variety of processes. One such example is described in published PCT application WO 2021 / 118599 (Application No. PCT / US 2019 / 066262).

[0009] Sulfuric acid plants and processes have recently been proposed in which sulphur combustion is carried out using pure oxygen and a submerged combustion process. In this process, highly enriched or pure oxygen is injected into a bath of molten sulphur. The energy released when the oxygen reacts with the sulphur is used to evaporate the sulphur from the bath. The evaporated sulphur is condensed in a downstream condenser to recover energy and return the condensed sulphur to the bath. An advantage of submerged combustion is that the temperature of the combustion products is limited to the boiling point of sulphur, which is about 450°C at a pressure of 0.5 barg. This technology is described in detail in a patent application entitled Sulfuric Acid Plant The invention is disclosed in detail in Canadian patent application CA 3021202 published on December 24, 2018. The design provides lower capital expenditure and improved energy recovery, and allows practical production capacity exceeding 10,000 mtpd. Submerged combustion does not require large gas recirculation in order to control the temperature, and involves minimal NOx formation due to the low operating temperature. However, the submerged combustion system is relatively complex because it involves the suppression of sulfur vapor at high temperatures and therefore material issues.

[0010] In Canadian patent application 3,141,027 published on February 15, 2022, improved systems and methods for producing sulfuric acid or for producing liquefied sulfur dioxide are disclosed. The system includes a reactor for burning sulfur into sulfur dioxide, a reactor gas heat exchanger, and a contact device and an absorption device combination or an absorption subsystem and a liquefaction device combination for producing sulfuric acid or liquid sulfur dioxide, respectively. By appropriately combining two recirculation loops, the first after the reactor gas heat exchanger and the second after the absorption device or liquefaction device, several advantages can be obtained. These include reducing instrument size, complexity, power consumption energy losses, and suppressing NOx formation.

[0011] In EP 1654052 and US 5019361, a process is described for removing SO2 from a gas stream using an aqueous absorption medium containing a water-soluble amine and subsequently regenerating the spent absorbent using low-pressure steam. The disadvantages of this process are the high steam consumption in the regeneration system and the need to remove impurities from the absorbent, which results in the formation of an effluent stream that must be treated.

[0012] There are many methods for removing SO2 from gas streams by absorbing SO2 in aqueous solutions containing reagents (e.g., sodium hydroxide, calcium hydroxide, ammonia or hydrogen peroxide) (e.g., as described in EP 0238811), which react with SO2 to form stable components with low SO2 vapor pressure. The disadvantages of these methods are that the use of reagents is directly related to the amount of SO2 that needs to be removed from the gas, and in many cases, aqueous or solid effluents are generated that must be further treated.

[0013] In a process for producing sulfuric acid using pure oxygen, a small portion of the gas must be continuously removed (purged) from the process because otherwise the inert gases (primarily argon and nitrogen) entering the process with the pure oxygen stream would accumulate to unacceptable levels. Therefore, there remains a desire to continually improve plant design to reduce undesirable components (e.g., SO2) from the purge gas stream before it is discharged into the atmosphere. The present invention addresses this need and provides other benefits as disclosed below. Summary of the invention

[0014] An improved system and related method for treating tail gas in a sulfuric acid plant are disclosed. Specifically, the tail gas treatment system of the present invention is used in a sulfuric acid production plant, which includes: a pure oxygen supplier; a combustion reactor, which is used to burn sulfur into sulfur dioxide using oxygen from the pure oxygen supplier; a reactor gas heat exchanger, which is fluidly connected to the combustion reactor for cooling the combustion reactor outlet gas; a contact device, which is fluidly connected to the reactor gas heat exchanger for converting sulfur dioxide into sulfur trioxide; an absorption device, which is fluidly connected to the contact device for absorbing sulfur trioxide into sulfuric acid to form concentrated sulfuric acid; the tail gas treatment system; and an exhaust chimney, which is fluidly connected to the tail gas treatment system, wherein the absorption device includes an outlet fluidly connected to both the combustion reactor and the tail gas treatment system. The tail gas treatment system includes:

[0015] A product stripper, the product stripper comprising:

[0016] Stripping tower;

[0017] a liquid inlet for concentrated (i.e. >93%) sulphuric acid containing dissolved sulphur dioxide from the absorber;

[0018] a stripping gas inlet for a stripping gas containing oxygen;

[0019] an outlet for sulfuric acid partially stripped of sulfur dioxide; and

[0020] an outlet for a stripping gas comprising sulfur dioxide partially stripped from sulfuric acid;

[0021] as well as

[0022] A purge gas scrubber, the purge gas scrubber comprising:

[0023] Absorption tower;

[0024] an inlet for partially stripped sulfuric acid of sulfur dioxide from the product stripper;

[0025] a purge gas inlet for a purge gas obtained from a gas outlet of the absorber;

[0026] an outlet for sulfuric acid containing dissolved sulfur dioxide from the purge gas;

[0027] An outlet for purge gas comprising purge gas partially stripped of sulphur dioxide.

[0028] In the tail gas treatment system, the oxygen-containing stripper gas may be pure oxygen from a pure oxygen supplier. In addition, the tail gas treatment system may include a heat exchanger for cooling the sulfuric acid from the product stripper that is partially stripped of sulfur dioxide.

[0029] In the tail gas treatment system, the outlet for sulfuric acid from the purge gas scrubber can be fluidly connected to the sulfuric acid inlet in the absorption device. Alternatively, the outlet for sulfuric acid from the purge gas scrubber can be fluidly connected to the liquid inlet of the product stripper. In addition, the outlet for stripping gas from the product stripper can be fluidly connected to the combustion reactor or the contacting device. Still further, the tail gas treatment system can include a liquid ring compressor for increasing the operating pressure of the purge gas scrubber.

[0030] In certain embodiments, the operating pressure of the purge gas scrubber may be greater than the operating pressure of the product stripper.

[0031] In certain embodiments, the tail gas treatment system may desirably additionally include a tail gas reactor comprising activated carbon, a catalyst, or an absorbent for removing additional sulfur dioxide from the purge gas obtained from the purge gas outlet of the purge gas scrubber.

[0032] The present invention also includes a sulfuric acid production device, which includes the tail gas treatment system of the present invention described above. Such sulfuric acid production equipment includes: a pure oxygen supplier; a combustion reactor, which is used to burn sulfur into sulfur dioxide using oxygen from the pure oxygen supplier; a reactor gas heat exchanger, which is fluidly connected to the combustion reactor for cooling the combustion reactor outlet gas; a contact device, which is fluidly connected to the reactor gas heat exchanger for converting sulfur dioxide into sulfur trioxide; an absorption device, which is fluidly connected to the contact device for absorbing sulfur trioxide into sulfuric acid to form concentrated sulfuric acid; the aforementioned tail gas treatment system; and an exhaust chimney, which is fluidly connected to the tail gas treatment system, wherein the absorption device includes an outlet fluidly connected to both the combustion reactor and the tail gas treatment system.

[0033] The related method of the present invention is used to remove sulfur dioxide from the purge gas in the sulfuric acid production plant described above. Specifically, the method of the present invention comprises:

[0034] The exhaust gas treatment system described above is used as the exhaust gas treatment system in the device.

[0035] obtaining a purge gas from the gas outlet of the absorber, and

[0036] removing sulfur dioxide from the purge gas in the purge gas scrubber using sulfuric acid obtained from the product stripper that is partially stripped of sulfur dioxide;

[0037] Wherein the sulphur dioxide concentration in the purge gas obtained from the gas outlet of the absorption device is greater than at least 5% by volume.

[0038] In certain embodiments, the sulfur dioxide concentration in the purge gas obtained from the gas outlet of the absorption device may be greater than or equal to 10% by volume. For example, in an exemplary embodiment, the sulfur dioxide concentration in the purge gas obtained from the gas outlet of the absorption device is about 20% by volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic diagram of a sulfuric acid plant including the tail gas treatment system of the present invention.

[0040] Figure 2 It shows Figure 1 A schematic diagram showing more details of the various components of the exhaust gas treatment system and their interconnections.

[0041] Figure 3 It shows Figure 1 Schematic diagram of more details of the tail gas reactor in the tail gas treatment system. DETAILED DESCRIPTION

[0042] Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising", etc. should be interpreted in an open, inclusive sense. The words "a / an", etc. should be deemed to mean at least one and not limited to only one.

[0043] The term "pure oxygen" should be taken to mean a concentration equal to or exceeding 90% by volume of oxygen.

[0044] As used herein, "concentrated sulfuric acid" refers to sulfuric acid having a concentration exceeding 93% by weight.

[0045] The term "tail gas" refers to all or part of the gas leaving the absorption unit in a sulphuric acid plant, which is discharged to the atmosphere via a chimney.

[0046] The term "purge gas" refers to that portion of the gas leaving the absorption unit which has to be removed from the gas recycle stream in a sulphuric acid plant using pure oxygen in order to maintain a constant inert gas concentration in the process.

[0047] The term "inert gas" refers to gases other than O2, SO2 and SO3 which may be present in the gas stream in a sulfuric acid plant.

[0048] Trademark CORE-S TM It refers to the molten salt cooled tubular reactor of the technology disclosed in the above-mentioned WO 2008 / 052649.

[0049] CORE-SO2 for the production of sulfuric acid from sulfur and pure oxygen TM The process requires a small amount of purge gas to continuously remove inert gases contained in the incoming pure oxygen from the recycle gas. This gas stream is very small compared to the tail gas discharged to the stack of the DCDA plant and contains a much higher concentration (>5 vol%) of residual SO2, which must be removed before the gas can be safely discharged into the atmosphere.

[0050] In the present invention, sulfur dioxide gas in the purge gas stream is absorbed into concentrated sulfuric acid. Conventionally, concentrated sulfuric acid is not considered a suitable absorbent for removing SO2 from a tail gas stream due to the low solubility of SO2 in concentrated sulfuric acid. This low solubility limits the practical removal of SO2 from the gas stream to about 400 ppmv. Therefore, sulfuric acid cannot be used in a tail gas treatment system for gas from a conventional DCDA process because the gas leaving the secondary absorption system is already well below this value.

[0051] However, in the CORE-SO2 process, the volume of purge gas that must be treated is small and contains a high (>5 vol%) concentration of SO2, and therefore the purge gas scrubber can be designed to achieve high removal rates despite the use of liquids with low SO2 solubility. Advantageously, the CORE-SO2 process already includes a product stripper in which dissolved sulfur dioxide is removed from the concentrated sulfuric acid product. Therefore, purge gas scrubbing can be accomplished with minimal additional instrumentation and using liquid streams already present in the process.

[0052] In a preferred embodiment, the purge gas may be compressed to 1-10 barg to enhance absorption of sulfur dioxide in sulfuric acid. The dissolved sulfur dioxide is recovered by returning the sulfur dioxide-rich acid to an absorption device (e.g., a column) or to a product stripper in the plant, although an absorption device (e.g., a column) is preferred.

[0053] In further embodiments, the entire sulfuric acid production process can be carried out at high pressure. For the CORE-SO2 process, operation at high pressure (e.g., between 1-10 bar gauge) can be economically achieved because pure oxygen can be supplied at high pressure relatively easily and there is no need to recover the very small amount of energy contained in the small purge gas stream. It will be apparent to those skilled in the art that this not only reduces the instrument size in the CORE-SO2 process, but also eliminates the need for a purge gas compressor upstream of the purge gas scrubber.

[0054] Advantages of the present invention include requiring minimal additional equipment, using absorbent already present in the process (ie, sulfuric acid), and requiring only a small amount of additional energy (eg, to operate pumps and compressors) since regeneration of the absorbent is also accomplished in equipment already present in the process.

[0055] An exemplary embodiment of the exhaust gas treatment system of the present invention is Figures 1 to 3 Shown in. Figure 1 A schematic diagram of a complete sulfuric acid plant including the tail gas treatment system of the present invention is shown. (Specifically, Figure 1 The device in is similar to the one in CA3141027 mentioned above Figure 2 a, but incorporating the exhaust gas treatment system of the present invention.

[0056] Figure 1 A schematic diagram of a portion of a sulfuric acid production plant using pure oxygen (>90%) in the sulfur combustion is shown. Here, the sulfuric acid production plant 1 includes a combustion reactor 5 for combusting sulfur into sulfur dioxide, a reactor gas heat exchanger 6 for cooling the outlet gas from the combustion reactor 5, a contact device 7 for converting SO2 into SO3, and an absorption device 8 for absorbing SO3 into a lower concentration sulfuric acid supply. Downstream of the absorption device 8 is a purge gas scrubber 10 and a tail gas reactor 20, followed by a chimney 11 for exhausting gases from the system. A product stripper 50 is also present in the system 1, as shown. In this embodiment, the tail gas treatment system includes the product stripper 50, the purge gas scrubber 10 and the tail gas reactor 20, which are interconnected with the rest of the plant 1, as shown.

[0057] In the sulfuric acid production plant 1, sulfur 12 and pure oxygen 14 (e.g. 99.5%) are supplied to the combustion reactor 5 at inlets 5A and 5B, respectively, and react together to form SO2. Reactor outlet gas containing this SO2 is obtained at outlet 5C of the combustion reactor 5 and is led to inlet 6A of a reactor gas heat exchanger 6, in which these gases are cooled. The cooled reactor gas is then led from the reactor gas heat exchanger outlet 6B to the inlet 7A of the contact device 7. In the contact device 7, the SO2 in the cooled reactor gas is converted into SO3, after which the gas from the contact device 7 is led from outlet 7B to the absorption device 8 (at Figure 2 8A of the contactor (shown as a tower in FIG. 1 ). In the absorber 8, SO3 is absorbed into the weaker sulfuric acid solution to produce the desired higher concentration sulfuric acid product. The higher concentration sulfuric acid is removed at outlet 8B, and the remaining unabsorbed gas from the contactor is removed at outlet 8C and then directed to the purge gas scrubber 10.

[0058] Likewise Figure 1 As shown and as discussed in detail in the aforementioned CA3141027, the gases from both the first recirculation loop 30 and the second recirculation loop 40 are used to dilute and cool the combustion gases in the combustion reactor 5. The first recirculation loop 30 connects the outlet 6B of the reactor gas heat exchanger 6 to the recirculation inlet 5D of the reactor 5, and thus recirculates a portion of the cooled reactor gas from the reactor gas heat exchanger 6, while the second recirculation loop 40 also connects the outlet 8C of the absorption device to the recirculation inlet 5D of the combustion reactor 5, and thus recirculates a portion of the unabsorbed contact device gas from the absorption device 8. The two recirculation loops include pumps 31 and 41, respectively, and in principle any type of pump can be considered for such use, including blowers, fans or ejectors. However, due to the larger pressure difference that the pump 41 must handle in the second recirculation loop 40, the pump 41 may need to have a more advanced design than the pump 31 in the first recirculation loop 30.

[0059] As mentioned above, the tail gas treatment system in the figure of the present invention includes a product stripper 50, a purge gas scrubber 10 and an optional tail gas reactor 20, which are appropriately interconnected with the rest of the equipment 1. The tail gas treatment system removes SO2 from a small flow of purge gas and then discharges it to the chimney 11.

[0060] like Figure 1 As shown Figure 2, the product stripper 50 comprises a stripping column 501, a liquid inlet 502 for concentrated (i.e., >93%) sulfuric acid containing dissolved sulfur dioxide (shown for this example as 2000 ppm dissolved SO2) from the absorption unit 8, a stripping gas inlet 503 for an oxygen-containing stripping gas (here pure oxygen supply 14), an outlet 504 for sulfuric acid 52 partially stripped of sulfur dioxide (shown for this example as 20 ppm dissolved SO2), and an outlet 505 for stripping gas 51 containing sulfur dioxide partially stripped from the sulfuric acid. In the product stripper 50, the stripping column 501 also serves as a stripping column for product acid from the plant.

[0061] The purge gas scrubber 10 comprises an absorption tower 101, an inlet 102 for sulfuric acid 52 partially stripped of sulfur dioxide from the product stripper 50, a purge gas inlet 103 for the purge gas 400 obtained from the gas outlet 8C of the absorption device 8, an outlet 104 for sulfuric acid 54 containing dissolved sulfur dioxide from the purge gas 400 (shown as 4500 ppm dissolved SO2 for this example), and an outlet 105 for the purge gas 53 containing the purge gas partially stripped of sulfur dioxide (shown as <1000 ppm SO2 for this example).

[0062] Figure 3 It shows Figure 1 Schematic diagram of more details of the tail gas reactor 20 in the tail gas treatment system of FIG. The tail gas reactor 20 includes a reactor tower 70 containing activated carbon and an outlet 201 for exhaust gas (shown as <100 ppm SO2 for this example) to the chimney 11.

[0063] Although the above description discloses the general arrangement and operation of some embodiments of the present invention, it will be appreciated by ordinary technicians that some details may need to be modified according to different situations and equipment. However, it is expected that ordinary technicians will be able to easily make such modifications based on the disclosed guiding teaching content.

[0064] The present invention addresses the situation where, after the absorption unit, the residual gas stream in the plant still contains significant amounts of sulfur dioxide, which is preferably recycled to the contacting unit for conversion to SO3, and also contains inert gases which need to be purged to avoid continued accumulation in a "closed loop" system. Although secondary tail gas treatment may still be required to obtain an exhaust gas low enough in SO2 for release to the atmosphere, the present method represents a lower cost and more elegant way of removing the majority of the residual SO2 from the purge stream.

[0065] The present invention adopts a new method of using product acid as a washing or spraying liquid provided to a purge gas scrubber and using pure oxygen instead of air as a gas provided to the bottom of a product stripper. The product acid, which initially strips most of the dissolved sulfur dioxide, is used to absorb sulfur dioxide in the purge gas scrubber, thereby reducing the residual sulfur dioxide concentration in the purge gas stream to a range of 400-2000ppm. However, in some cases, the concentration is still too high to be discharged without further treatment. The acid is treated by directing the acid loaded with sulfur dioxide in the purge gas scrubber back to an absorber or product stripper to release the absorbed sulfur dioxide back into the main process stream. The product stripper in the present invention uses pure oxygen to strip dissolved sulfur dioxide (typically about 2000ppm to about 20ppm) from the product acid. Then, the gas leaving the product stripper is oxygen rich in sulfur dioxide and can be used as one of the oxygen sources in the combustion reactor of the device.

[0066] As mentioned, the tail gas stream loaded with 400-2000ppm sulfur dioxide may require further treatment before it can be discharged into the atmosphere. The use of a tail gas reactor containing activated carbon or other low temperature catalyst is an economical way to achieve low SO2 emissions. The activated carbon or low temperature catalyst converts SO2 into SO3 and / or H2SO4 within the pores of the material, which is periodically removed as dilute (<20wt%) sulfuric acid by flushing the material with water. Dilute sulfuric acid can be added to the absorption tower as a diluent, and therefore no effluent is produced.

[0067] Concentrated sulfuric acid is not usually considered for tail gas treatment because sulfur dioxide does not dissolve in sulfuric acid in large quantities. In addition, the demand for removing dissolved sulfur dioxide from product acid is usually not necessary in conventional DCDA sulfur combustion acid production equipment because acid does not contact with gas streams with high sulfur dioxide concentrations, and acid is simply cooled before entering the reservoir. However, in the present invention, the gas flowing to the purge gas scrubber has both high sulfur dioxide concentration (e.g., >5vol%) and small volume flow. This causes enough sulfur dioxide to dissolve in the acid so that the purge gas treatment system can be operated under moderate sulfuric acid flow. Using the acid from the product stripper utilizes instruments already needed in the process and reduces the cost of the equipment. In addition, in theory, the system can operate without any acid entering the reservoir (that is, the operation of the system does not require the acid entering the reservoir).

[0068] The use of pure oxygen instead of air is also generally not considered because air is low cost and can be easily added back into the conventional DCDA process.

[0069] The purge gas scrubber (and therefore the absorber) can be operated at a higher pressure than the product stripper. This may be advantageous because when operating at high pressure, more SO2 dissolves into the acid, and the required volume of acid required is reduced. In addition, a higher SO2 partial pressure increases the rate at which SO2 dissolves into the acid, and thus reduces the required height of the tower. Finally, a higher pressure reduces the volume of the purge gas, and thus reduces the diameter of the required purge gas scrubber. This is not generally considered in prior art equipment because pressurizing the gas stream to the purge gas scrubber consumes energy, and the volume of gas that needs to be processed in a typical sulfuric acid plant tail gas application is very large, and the energy required is very expensive.

[0070] The compression of the purge gas can advantageously be carried out in a liquid ring compressor using sulfuric acid or water as the sealing liquid to produce a liquid ring. This method has the advantage that the turbulent mixing of liquid and gas within the compressor already removes a portion of the SO2 from the gas. In addition, it also completes the compression at low temperatures, which improves the removal of SO2 in the scrubber and prevents corrosion of the instrumentation. The excess sealing liquid used in the compressor can simply be directed to the absorption tower for recycling the dissolved SO2 and therefore no effluent is produced.

[0071] It is known that cooling the sulfuric acid before it enters the purge gas scrubber facilitates absorption. In the present application, this can be done more economically because the acid delivered as a product must be cooled to prevent corrosion in the storage tank and no additional instrumentation needs to be installed.

[0072] Although the present invention requires an additional purge gas scrubber, it is a more advantageous and economical way to remove high levels of SO2 from the tail gas stream (which needs to be vented to control inert levels in a typical "closed loop" system) and return them to the process. Otherwise, a more substantial conventional tail gas treatment system would be required (e.g., a regenerative scrubber using amines or a chemical scrubber using caustic, lime, etc.). In order to avoid these expensive amine-based systems or chemical scrubbers that will consume large amounts of energy or chemicals and produce additional effluent, the present invention recovers most of the SO2 in an efficient manner and generally does not require an additional tail gas treatment system, or a simplified tail gas reactor system of the present invention can be used.

[0073] All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications, and non-patent publications mentioned in this specification are incorporated herein by reference in their entirety.

[0074] Although particular elements, embodiments, and applications of the present invention have been shown and described, it will of course be understood that the present invention is not limited thereto, since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are considered to be within the purview and scope of the appended claims.

Claims

1. A tail gas treatment system for a sulfuric acid production plant, the sulfuric acid production plant comprising: A pure oxygen supplier; a combustion reactor for burning sulfur into sulfur dioxide using oxygen from the pure oxygen supplier; a reactor gas heat exchanger, the reactor gas heat exchanger fluidly connected to the combustion reactor for cooling the combustion reactor outlet gas; a contact device, the contact device fluidly connected to the reactor gas heat exchanger for converting sulfur dioxide into sulfur trioxide; an absorption device, the absorption device fluidly connected to the contact device for absorbing sulfur trioxide into sulfuric acid to form concentrated sulfuric acid; the tail gas treatment system; and an exhaust chimney, the exhaust chimney being fluidly connected to the tail gas treatment system, wherein the absorption device comprises an outlet fluidly connected to both the combustion reactor and the tail gas treatment system, characterized in that the tail gas treatment system comprises: A product stripper, the product stripper comprising: Stripping tower; a liquid inlet for concentrated sulfuric acid containing dissolved sulfur dioxide from the absorption unit; a stripping gas inlet for a stripping gas containing oxygen; an outlet for sulfuric acid partially stripped of sulfur dioxide; and an outlet for a stripping gas comprising sulfur dioxide partially stripped from sulfuric acid; and A purge gas scrubber, the purge gas scrubber comprising: Absorption tower; an inlet for partially stripped sulfuric acid of sulfur dioxide from the product stripper; a purge gas inlet for a purge gas obtained from a gas outlet of the absorber; an outlet for sulfuric acid containing dissolved sulfur dioxide from the purge gas; An outlet for purge gas comprising purge gas partially stripped of sulphur dioxide.

2. The exhaust gas treatment system according to claim 1, wherein: The oxygen-containing stripper gas is pure oxygen from the pure oxygen supplier.

3. The tail gas treatment system of claim 1, comprising a heat exchanger for cooling the sulfuric acid from the product stripper that is partially stripped of sulfur dioxide.

4. The exhaust gas treatment system according to claim 1, wherein: The outlet for sulfuric acid from the purge gas scrubber is fluidly connected to the sulfuric acid inlet in the absorption unit.

5. The exhaust gas treatment system according to claim 1, wherein: The outlet for sulfuric acid from the purge gas scrubber is fluidly connected to the liquid inlet of the product stripper.

6. The exhaust gas treatment system according to claim 1, wherein: An outlet for stripping gas from the product stripper is fluidly connected to the combustion reactor or to the contacting device.

7. The tail gas treatment system of claim 1, comprising a liquid ring compressor for increasing the operating pressure of the purge gas scrubber.

8. The tail gas treatment system of claim 1, further comprising a tail gas reactor comprising activated carbon for removing sulfur dioxide from the purge gas obtained from the purge gas outlet of the purge gas scrubber.

9. A sulfuric acid production plant, comprising: Pure oxygen supplier; a combustion reactor for combusting sulfur into sulfur dioxide using oxygen from the pure oxygen supplier; a reactor gas heat exchanger fluidly connected to the combustion reactor for cooling the combustion reactor outlet gas; a contacting device fluidly connected to the reactor gas heat exchanger for converting sulfur dioxide to sulfur trioxide; an absorption device fluidly connected to the contacting device for absorbing sulfur trioxide into sulfuric acid to form concentrated sulfuric acid; The exhaust gas treatment system according to claim 1; and an exhaust chimney fluidly connected to the exhaust treatment system, Wherein the absorption device includes an outlet fluidly connected to both the combustion reactor and the tail gas treatment system.

10. A method for removing sulfur dioxide from a purge gas in a sulfuric acid production plant, the sulfuric acid production plant comprising a pure oxygen supplier, a reactor for burning sulfur into sulfur dioxide using oxygen from the pure oxygen supplier, a reactor gas heat exchanger for cooling the reactor outlet gas, a contact device for converting sulfur dioxide into sulfur trioxide, an absorption device for absorbing sulfur trioxide into sulfuric acid to form concentrated sulfuric acid, a tail gas treatment system, and an exhaust stack, wherein the tail gas treatment system is located between the absorption device and the exhaust stack, the method comprising: Using the exhaust gas treatment system as claimed in claim 1 as the exhaust gas treatment system in the device; obtaining a purge gas from a gas outlet of the absorber; as well as removing sulfur dioxide from the purge gas in the purge gas scrubber using sulfuric acid obtained from the product stripper that is partially stripped of sulfur dioxide; Wherein the sulphur dioxide concentration in the purge gas obtained from the gas outlet of the absorption device is greater than at least 5% by volume.

11. The method of claim 10, wherein: The sulphur dioxide concentration in the purge gas obtained from the gas outlet of the absorption device is greater than or equal to 10% by volume.

12. The method of claim 10, wherein: The operating pressure of the purge gas scrubber is greater than the operating pressure of the product stripper.

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