Claus Plant Retrofit Using Sulfuric Acid

Abstract

The present invention relates to a modification method for improving a sulfur reduction device, which device includes a Claus process device for producing elemental sulfur, the Claus process device includes a Claus reactor and one or more Claus conversion stages, each Claus conversion stage includes a conversion reactor and a device for condensing elemental sulfur, and a Claus tail gas oxidation device configured to receive Claus tail gas from the Claus process device and configured to provide oxidized Claus tail gas, the process modification includes: a. providing a tail gas treatment device for producing sulfuric acid to produce sulfuric acid, and, b. providing a device for transferring a certain amount or all of the sulfuric acid produced in the tail gas treatment device for producing sulfuric acid to the Claus reactor, characterized in that the molar number of sulfur in the transferred sulfuric acid is 3% or 5% to 15%, 20% or 25% relative to the molar number of elemental sulfur withdrawn from the Claus process device, the related benefits are that a higher sulfur reduction capacity and / or a higher degree of sulfur removal can be achieved, while producing elemental sulfur, which is a valuable product that can be processed with almost no safety restrictions compared to, for example, sulfuric acid, while avoiding excessive use of auxiliary fuels to compensate for the energy consumed by evaporation of sulfuric acid in the Claus reactor.

Description

Technical Field

[0001] The present invention relates to a modification method for improving sulfur removal, operating costs and H 2 One or more of the abilities of S to be converted into elemental sulfur and sulfuric acid. Background Art

[0002] H 2 S is a common by-product in many processes including hydrodesulfurization of refinery streams, natural gas processing, and viscose fiber production. 2 S is converted before being emitted into the atmosphere, because H 2 S is highly toxic, has an odor and poses environmental challenges.

[0003] In the oil refining process, in addition to the production of well-known high-concentration H 2 In addition to the S gas, so-called sour water stripping gas may also be produced, which contains approximately the same amount of H 2 S.H. 2 O and NH 3 .

[0004] Especially in refineries, it is used to reduce H 2 The process of choice for S has been the Claus process, which has been well known and optimized over the past eighty years. 2 Substoichiometric combustion of sulfur in a Claus reactor to produce SO 2 , thus providing the Claus converter feed gas. The subsequent Claus process will convert H 2 S and SO 2 Converted to form elemental sulfur, which can be condensed and removed.

[0005] Typically, the sulfur removal efficiency of the Claus process is 95% to 98%, which is not enough to meet environmental requirements. Therefore, it is common practice to perform tail gas treatment after the Claus process to reduce more than 99% of the sulfur. The tail gas treatment can be a sulfuric acid plant, which introduces the requirement for handling sulfuric acid.

[0006] It has been determined that existing Claus plants can be modified by adding a sulphuric acid plant to recycle the sulphuric acid to the Claus reactor where it can promote elemental sulphur formation, in addition to providing opportunities to optimise Claus reaction and Claus tail gas process plant size and operating costs.

[0007] In WO 2012 / 152919 A1, a sulfuric acid process for treating Claus tail gas is proposed, wherein H 2 S to H 2 SO 4 The steps of this method are:

[0008] 1. Substoichiometric oxidation

[0009] 2. Claus transformation

[0010] 3. In an oxygen-rich atmosphere at 400-700°C, the reduced sulfur species (H 2 S) Oxidation

[0011] 4.SO 2 Catalytic oxidation to SO 3

[0012] 5. Condensation of sulfuric acid

[0013] It has been recognized that H 2 SO 4 The product is not always desirable and it is advisable to recycle the sulfuric acid to an upstream Claus reactor as described above or to the H 2 However, the recycling of sulfuric acid is only considered as a reduction of sulfuric acid, and the H 2 SO 4 The consequences of recycling for wet sulfuric acid processes or Claus processes, i.e., failure to recognize H 2 SO 4 Recirculation requires reduction of O directed to the Claus reactor 2 The amount was not significantly reduced, and no favorable impact on the Claus process and sulfuric acid process was achieved.

[0014] WO 2012 / 152919 A1 also recognizes that in the Claus reactor and H 2 The sulfur oxidation step may require auxiliary fuel to obtain the required operating temperature, without realizing that the use of feed gas as H in the sulfuric acid process 2 Beneficial effects of S-oxidation of auxiliary fuels.

[0015] Therefore, H 2 SO 4 The proposal of recycling to the Claus reactor does not provide an executable process in itself but requires additional process modifications in terms of the physical layout of the plant / equipment and process control, availability and safety. Summary of the invention

[0016] According to the present invention, a method for converting H into a 2 A method for converting sulfur into elemental sulfur, wherein the Claus process is modified by adding an integrated sulfuric acid process. According to this method, sulfuric acid produced in the sulfuric acid process for treating Claus tail gas is recycled to the Claus reactor for decomposition and generation of elemental sulfur. DETAILED DESCRIPTION

[0017] For the purpose of this application, the products derived from N, H, C, S and O in the feed gas shall be assumed to be N 2 , H 2 O、CO 2 and SO 2 The stoichiometric amount of oxygen is defined in the case of a stoichiometric amount of oxygen. If less than the stoichiometric amount of oxygen is present (also called sub-stoichiometric), this means that not all feed components are completely oxidized. For a Claus gas feed, this means that after a sub-stoichiometric combustion / reaction, the process gas may contain unconverted H from the feed stream. 2 S. NH 3 and hydrocarbons as well as in O 2 H formed in an environment with insufficient 2 , CO, COS and CS 2 .

[0018] For the purpose of this application, a fuel shall be defined as a composition which, when 2 When oxidized, it forms N 2 , H 2 O、CO 2 and SO 2 As reaction products, a large amount of energy is released through the reaction. Hydrocarbons (such as natural gas, which contains CH 4 and C 2 H 6 ) and H 2 A mixture of S is a typical fuel gas, but the fuel gas may also contain CO, NH 3 and H 2 .

[0019] For the purpose of this application, oxygen (O 2 ) is understood to include O 2 The feed streams may include air, enriched air and pure oxygen, but may also include O 2 of process gas.

[0020] For the purpose of this application, a sulfuric acid stage is understood to be a section for treating sulfur (e.g. H 2 S. SO 2 , COS, CS 2 The sulfuric acid section can be used to oxidize sulfur substances into SO 2 The catalytic or thermal process is then followed by the SO 2 Oxidized to SO 3 The process is then condensed and hydrated by SO 3 Provide a condenser for sulfuric acid or absorb SO from sulfuric acid 3 An absorber for producing sulfuric acid is provided, but other devices for producing sulfuric acid are also known to the skilled person, such as H2 O 2 Scrubber.

[0021] For the purposes of this application, a device for sulfur oxidation is understood to be any device that receives reduced sulfur or elemental sulfur and converts it into SO 2 The process equipment for sulfur oxidation can be an incinerator, a catalytic device or a combination thereof.

[0022] For the purposes of this application, pressures indicated in the unit mbarg are to be understood as gauge pressures relative to atmospheric pressure.

[0023] For the purposes of this application, the term "providing" is used to cover not only the steps of adding physical equipment to the process equipment, but also the steps of providing missing elements or reconfiguring existing elements to create the described configuration.

[0024] The present invention relates to a modification method for improving a sulfur emission reduction device, the device comprising a Claus process device for producing elemental sulfur, the Claus process device comprising a Claus reactor and one or more Claus conversion stages, each Claus conversion stage comprising a conversion reactor and a device for condensing elemental sulfur, and a Claus tail gas oxidation device configured to receive Claus tail gas from the Claus process device and configured to provide oxidized Claus tail gas,

[0025] The process modification comprises the following steps:

[0026] a. Provide tail gas treatment equipment for the production of sulfuric acid to produce sulfuric acid, and

[0027] b. providing a device for transferring a certain amount or all of the sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid to the Claus reactor,

[0028] Characterized in that the molar amount of sulfur in the recycled sulfuric acid is from 3% or 5% to 15%, 20% or 25% relative to the molar amount of elemental sulfur withdrawn from the Claus process unit, with the associated benefit of being able to achieve higher sulfur reduction capabilities and / or higher levels of sulfur removal while producing elemental sulfur, a valuable product that can be handled with almost no safety restrictions compared to, for example, sulfuric acid, while avoiding excessive use of auxiliary fuels caused by the evaporation of sulfuric acid in the Claus reactor.

[0029] In another embodiment, the concentrated sulfuric acid contains 90% w / w to 98% w / w or 98.5% w / w H 2 SO 4 A related benefit is that this concentrated sulfuric acid is strong enough to provide the benefit of supplying oxygen to the Claus process while avoiding or reducing the need for auxiliary fuel for sulfuric acid vaporization.

[0030] In another embodiment, if the Claus process plant comprises more than two Claus conversion stages, the conversion method comprises the step of limiting the number of Claus conversion stages to two, the associated benefit of 2 Claus process stages being high conversion rates at low equipment cost and pressure loss.

[0031] In another embodiment, step (a) comprises providing a tail gas treatment device for producing sulfuric acid, the device comprising a catalytic SO 2 Converter, including SO 2 Oxidation to SO 3 A catalytically active material configured to receive the oxidized Claus tail gas and configured to provide SO to a sulfuric acid unit 2 The converter exhaust gas is configured to hydrate SO 3 by condensation or by absorption of SO in sulfuric acid 3 To produce concentrated sulfuric acid, SO 2 Oxidized to SO 3 The benefits of the sulfuric acid process are high sulfur removal efficiency while being cost effective and producing concentrated sulfuric acid provides higher thermal efficiency in the Claus reactor as less water must be evaporated. The condensation based process is superior to the absorption based process as the absorption based process requires water to be removed from the Claus process gas to ensure high concentration of sulfuric acid.

[0032] In a further embodiment, the transformation method also includes the step of providing a device for temporarily storing sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid, the device having a volume corresponding to the amount of sulfuric acid produced by the tail gas treatment equipment for producing sulfuric acid within 4 hours, 8 hours or 24 hours to 50 hours or 120 hours, wherein the device for storing sulfuric acid is configured to receive sulfuric acid from the tail gas treatment equipment for producing sulfuric acid and guide the sulfuric acid to the Claus reactor, and a related benefit of such a sulfuric acid tank is that in the event that the sulfuric acid nozzle must be replaced, the sulfur emission reduction equipment can be operated stably while maintaining a low equipment investment.

[0033] In another embodiment, a flow control device is provided that can be configured by the user to allow the outlet of the Claus tail gas oxidation unit to bypass the tail gas treatment equipment for producing sulfuric acid, with the associated benefit of allowing the sulfur reduction equipment to operate without releasing H2 in the event that the tail gas treatment equipment for producing sulfuric acid is shut down. 2 S.

[0034] In another embodiment, a device is provided for catalytically oxidizing at least a certain amount of the Claus process tail gas, and a related benefit is that the catalytic oxidation of the Claus process tail gas is more energy-efficient than the thermal incineration of the Claus process tail gas. This is because the catalytic oxidation can be carried out in the temperature range of 200-500°C, which can save a large amount of auxiliary fuel compared to the thermal incineration carried out at 850-1000°C.

[0035] In another embodiment, the catalytic oxidizer is configured to receive at least a certain amount of Claus process tail gas and is combined with one or more of an oxidant, a heated gas, a recycled process gas and a heat exchanger so that the temperature at the inlet of the catalytic oxidizer is greater than 200°C and the temperature at the outlet of the catalytic oxidizer is less than 500°C, with the associated benefit that this inlet temperature is suitable for catalytic oxidation and that this temperature can be obtained by mixing available gas streams with little or no addition of thermal energy.

[0036] In another embodiment, the Claus reactor is provided with one or more inlet nozzles configured to atomize the recirculating sulfuric acid to a droplet size distribution wherein 90% by mass of the droplets are smaller than 500 μm, with the associated benefit that such droplet size allows evaporation within the typical dimensions of a Claus reactor.

[0037] In another embodiment, the inlet nozzle is a pressure nozzle or a two-phase nozzle, with the associated benefit that this nozzle type is well suited for providing small droplets.

[0038] In another embodiment, the inlet nozzle is located a distance downstream of the gas inlet of the Claus reactor corresponding to a residence time of at least 1 second for the process gas, with the associated benefit of maintaining the flame temperature of the Claus reactor while also vaporizing sulfuric acid.

[0039] In another embodiment, the Claus reactor is enlarged to a certain volume to increase the residence time of the process gas by at least 1 second, with the associated benefit of extending the residence time to ensure complete evaporation of the sulfuric acid droplets.

[0040] In another embodiment, the Claus reactor is provided with means for impingement, such as a lattice wall or a bed of packing material, with the associated benefit of breaking up the droplets by impact to ensure that no liquid H is present in the Claus converter feed gas. 2 SO 4 .

[0041] In another embodiment, the Claus reactor is provided with means for increasing turbulence, such as vector walls, chokes, or inlets tangential to the Claus reactor, with the associated benefits of reducing residence time, temperature, and gas composition distribution in the Claus reactor.

[0042] In another embodiment, the control scheme for the amount of oxygen introduced into the Claus reactor is modified to depend on a feedforward control based on the amount and composition of the feedstock and sulfuric acid and based on the amount of H in the inlet stream of the final Claus conversion stage or the outlet stream of the final Claus conversion stage. 2 S and SO 2 A combination of ratio feedback control.

[0043] In another embodiment, the outlet of the Claus reactor is directed to absorb or convert SO 3 SO 3 protection device, where the SO 3 Removal of active SO 3 The protective material ensures long-term operation of the catalyst active in the Claus reaction, making it possible to ensure long-term operation of the Claus process plant if the sulfuric acid droplets in the gas phase are not completely evaporated and reduced.

[0044] The present invention relates to a method for implementing a method comprising 15 vol%, 30 vol%, 40 vol% or 50 vol% to 99 vol% or 100 vol% of H 2 A method for producing sulfur from a raw gas of S and a recycled sulfuric acid stream, the method may include one or more of the following steps:

[0045] a. providing a Claus reactor feed stream comprising said feed gas, an amount of recycled sulfuric acid, an amount of oxygen and optionally an amount of fuel, wherein the amount of oxygen is substoichiometric with respect to the Claus reaction;

[0046] b. directing the Claus reactor feed stream to a reactor operating at a high temperature, for example, above 900° C., to provide a Claus converter feed gas;

[0047] c. cooling the Claus converter feed gas and optionally removing elemental sulfur from the gas;

[0048] d. directing the cooled Claus converter feed gas to contact with a material having catalytic activity in the Claus reaction;

[0049] e. optionally removing Claus tail gas and elemental sulfur by cooling the effluent from the material catalytically active in the Claus reaction;

[0050] f. directing a stream comprising the Claus tail gas, oxygen and fuel as a feed gas to a Claus tail gas burner or a catalytic oxidation unit operating at a temperature above 900° C. to provide a SO-rich 2 The converter feed gas of

[0051] g. Cooling the SO-rich 2 The converter feed gas provides cooled SO2 Converter feed gas;

[0052] h. Guide the SO 2 The feed gas to the converter is SO 2 Oxidation to SO 3 contact with catalytically active materials to provide SO-rich 3 of gas;

[0053] i. By passing SO 3 Absorbed into sulfuric acid or SO 3 hydrate, the SO-rich 3 The gas is converted into concentrated sulfuric acid, and the sulfuric acid is cooled and condensed;

[0054] The recirculating sulfuric acid stream contains a certain amount of the concentrated sulfuric acid, and the associated benefits are that this method has a high conversion rate and thermal efficiency and avoids the formation of undesirable sulfuric acid. The use of a Claus reactor and a Claus tail gas burner operating at above 900°C has the effect of ensuring complete conversion of the components present, and optionally requires the presence of fuel in addition to the feed gas. In addition, a homogeneous Claus reaction occurs in the Claus reactor, so that elemental sulfur can be discharged when the Claus converter feed gas is cooled. The feed stream to the Claus tail gas burner can usually include H as a fuel from the Claus tail gas. 2 S and / or contain H 2 In addition to the process steps mentioned, the method may also include other steps, such as heat exchange for changing the temperature (or otherwise adjusting the process stream) to a range suitable for the process to occur. However, other aspects of the present disclosure may also involve other aspects of each step, as the present invention focuses on implementing this process and similar processes in existing process equipment through modification.

[0055] In another embodiment, the Claus reactor feed gas contains less than 0.1 vol% of non-elemental nitrogen, such as NH 3 , a related benefit is the avoidance of the formation of ammonia salts which could, for example, plug the Claus condenser.

[0056] In another embodiment, the feed stream to the Claus reactor contains less than 50%, 20%, 10%, or 1% elemental nitrogen, and the associated benefits are due to the reduction in N 2 The presence of provides a high temperature process in the Claus reactor and reduces the volume of process gas. This can be achieved by using pure O 2 Or oxygen-enriched air as the oxygen source.

[0057] In another embodiment, the H of the Claus converter feed gas is 2 S:SO 2Ratios below 4:1, 3:1 or 2:1 have the associated benefit that this feed gas provides a H-containing feed to the Claus tail gas burner. 2 The Claus exhaust gas of S, due to H 2 S oxidation releases a large amount of energy, thus minimizing the need to add fuel gas, while SO 2 No energy is released in the Claus tail gas incinerator.

[0058] In another embodiment, the H of the Claus converter gas is 2 S:SO 2 The ratio is less than 1.6:1, 1.8:1 or 2:1, with the associated benefit of having substantially no H 2 In a downstream sulfuric acid plant, this can be an advantage because SO 2 In the absence of SO 2 The conversion catalyst does not oxidize, so it can be catalyzed by H 2 S oxidation (containing H 2 S) and catalytic H 2 The combination of process gas recirculation near the S oxidation to preheat the Claus tail gas allows for tight control of H 2 The temperature on the S oxidation catalyst increases. 2 S concentration is unknown and / or varies, H 2 The risk of overheating the S-oxidation catalyst is high.

[0059] In another embodiment, the process further comprises the step of directing a quantity of additional feed gas to the Claus tail gas burner, with the associated benefit of providing additional sulfur and fuel for the sulfuric acid process. The additional feed gas may contain impurities (which may be incinerated prior to treatment in the sulfuric acid process), and / or hydrogen sulfide and other fuels that may contribute to sulfuric acid production and combustion in the Claus gas burner. If the additional feed gas contains a significant amount of inert gases or sulfur-free fuels, the process also has the advantage of avoiding an increase in the size of the Claus converter due to non-contributing streams. The additional feed gas may be from the same source as the feed gas, or from a different source.

[0060] In another embodiment, the additional feed gas contains more than 5 vol% of non-elemental nitrogen, such as ammonia, with the associated benefit of enabling non-elemental nitrogen components that are difficult to oxidize in the substoichiometric atmosphere of the Claus reactor to be directed to the Claus tail gas burner. 2 S. NH 3 and H 2 O (of which only H 2 S is expected, while NH 3This process may be particularly beneficial if the sour water stripper (SWS) gas is not produced in the Claus process because ammonia salts may cause plugging. Instead, this SWS gas can be directed to the sulfuric acid plant where the NH 3 is well known.

[0061] In another embodiment, the amount of sulfur in the additional feed gas is at least 1%, 2% or 5% of the total amount of elemental sulfur removed from the process, with the associated benefit that such feed gas can provide thermal energy while also aiding in sulfur reduction.

[0062] In another embodiment, the material catalytically active in the Claus reaction comprises an activated aluminum (III) oxide or titanium (IV) oxide, with the associated benefit that such material provides an efficient method for producing elemental sulfur.

[0063] In another embodiment, step (d) is carried out at a pressure of 200 mbarg to 700 mbarg, a temperature of 200° C. to 350° C. and a flow rate of 800 Nm 3 / h / m 3 Up to 3000Nm 3 / h / m 3 The reaction is carried out at a space velocity of 100 0.1 0.04 0.08 0.06 ...

[0064] In another embodiment, step (d) is carried out at a temperature of 100°C to 150°C and step (e) comprises the step of periodically heating the material catalytically active in the Claus reaction to allow the condensed elemental sulfur to be removed in the liquid or vapor phase, with the associated benefit that low temperatures are conducive to achieving SO 2 and H 2 The very high conversion of S to sulfur is due both to the favorable equilibrium at low temperatures and to shifting the equilibrium by removing the reaction products.

[0065] In another embodiment, the SO 2 Convert to SO 3 The catalytically active material comprises vanadium, with the associated benefit that such material provides an efficient process for producing sulfuric acid.

[0066] In another embodiment, step (h) is carried out at a pressure of 50 mbar g to 200 mbar g, a temperature of 380° C. to 520° C. and a flow rate of 800 Nm per catalyst bed. 3 / h / m 3 Up to 1500Nm 3 / h / m 3 The associated benefit of operating at a space velocity of 1.5 s is that such conditions are very effective for the SO 2Oxidation to form SO 3 In another embodiment, the amount of sulfur in the recycle stream of sulfuric acid is greater than 1%, 3% or 5% and less than 17%, 21% or 25% of the total amount of elemental sulfur removed from the process. The benefit of recycle above the lower limit is to provide the effect of reducing the volume of process gas, while recycle below the upper limit avoids the situation where additional fuel must be added to the Claus reactor, resulting in additional process volume and operating costs.

[0067] In another embodiment, the concentration of sulfuric acid is at least 80 w / w% or 90 w / w%. A related benefit is that this acid is obtained from H 2 SO 4 Released O 2 This provides additional oxidant to the Claus process while minimizing the amount of water that must be evaporated in the Claus reactor.

[0068] In another embodiment, the sulfuric acid in the recycle stream of sulfuric acid is atomized in the Claus reactor in a two-phase nozzle or a pressure nozzle using compressed air and wherein the residence time in the Claus reactor is at least 0.5 seconds, 1 second or 1.5 seconds, with the associated benefit that such residence time is sufficient for complete evaporation of the sulfuric acid droplets.

[0069] In another embodiment, the molar ratio H of the components introduced into the Claus reactor is 2 S:O 2 is at least 2.5, with the associated benefit that, due to the 2 SO 4 The contribution of thermal decomposition to H 2 S to SO 2 Substoichiometric partial conversion, adding the remaining O 2 Thus, the desired H of 2.0 is obtained in the Claus tail gas. 2 S:SO 2 Compare.

[0070] In another embodiment, an amount of the sulfuric acid is derived from a source other than the Claus tail gas processing unit, with the associated benefit of providing additional conversion of sulfuric acid to elemental sulfur.

[0071] In another embodiment, a certain amount of SWS gas contains 20-50% NH 3 , 20-50% H 2 S and at least 80% of the remainder is H 2 O, which is introduced as additional feedstock into one or more of the Claus reactors and the Claus tail gas treatment.

[0072] In another embodiment, a quantity of the gas in the process is cooled and directed to an upstream location to control the process temperature, with the associated benefit of enabling active control of the temperature of a highly exothermic process.

[0073] In another embodiment, one or more streams directed to the Claus reactor are preheated by heat exchange with a hot process stream, with the associated benefit of minimizing or avoiding the need for auxiliary fuel to achieve the desired temperature for vaporizing sulfuric acid and feedstock conversion.

[0074] In another embodiment, one or more streams directed to the Claus tail gas combustor are preheated by heat exchange with a hot process stream, with the associated benefit of minimizing or avoiding the effects of heat on the combustion and subsequent SO 2 Auxiliary fuel requirements for the desired temperature of oxidation.

[0075] In another embodiment, the SO is cooled by heat exchange (e.g., inter-bed heat exchange or an internally cooled catalytic reactor). 2 Oxidized to SO 3 Or H 2 At least one of the catalytically active materials for the oxidation of S to elemental sulfur and / or at least one product removed from one of the catalytically active materials has the associated benefit of being able to achieve active control of the temperature of a highly exothermic process by inter-bed heat exchange or an internally cooled catalytic reactor (e.g. a boiling water reactor) with a tubular or hot plate cooling circuit.

[0076] The present invention describes a modification of Claus with a sulfuric acid process that can efficiently produce the amount of sulfuric acid required by the process equipment, or even avoid the production of sulfuric acid and convert the excess sulfuric acid into elemental sulfur, which can be transported to other locations.

[0077] In order to achieve the maximum conversion rate to elemental sulfur, 1 / 3 of the H 2 S to SO 2 .

[0078] H 2 S+1.5 O 2 ->SO 2 +H 2 O(1)

[0079] By controlling the amount of oxygen in the Claus reactor, the H 2 S and SO 2 The oxygen is usually provided by atmospheric air, but can also be enriched air or even pure O 2 .

[0080] The oxygen added to the Claus reactor must also take into account the NH3 , CO, H 2 and the amount of hydrocarbons.

[0081] If the combustion temperature in the Claus reactor is below 1100°C, then for example NH 3 The conversion of the Claus converter may be incomplete. As a result, the Claus converter feed gas may form ammonia salts (e.g. (NH 4 ) 2 SO 4 and (NH 4 ) 2 S 2 O 3 ).

[0082] The partially oxidized Claus converter feed gas is then converted to elemental sulfur in the presence of a catalytically active material such as activated aluminum (III) oxide or titanium (IV) oxide, typically at temperatures above 200° C., by the following reaction:

[0083] 2H 2 S+SO 2 ->3 / 8 S 8 +2H 2 O(2)

[0084] Usually 3-4 Claus converters are operated in series to maximize the conversion rate, which increases the cost of the Claus equipment.

[0085] Temperature control in the Claus process is important to ensure that elemental sulphur formed in the catalytic converter remains in the gaseous state until condensed at the desired process location. A further limitation is related to the fact that, because the Claus process is exothermic, it is beneficial to operate at low temperatures.

[0086] An alternative to the above process is the so-called sub-dew point Claus process, in which the catalytically active material is operated at a temperature at which the elemental sulfur is not in the gas phase. Such a sub-dew point Claus process will require an appropriate scheme to remove the condensed elemental sulfur, for example by pulsing the temperature and purging the elemental sulfur with an inert gas.

[0087] Even with 3-4 Claus converters / condensers / reheaters in series, sulfur recovery cannot reach above about 98%, which is not enough to meet the requirements of most environmental regulations. Therefore, Claus plants are usually equipped with so-called Claus tail gas solutions, of which the above-mentioned sub-dew point process is an example. There are many tail gas processes with different characteristics. In order to achieve very high removal efficiencies, these Claus tail gas plants become complicated and the cost is close to that of the Claus plant itself.

[0088] The elemental sulfur produced is usually not directly used in the production of H2 S is used in equipment that removes sulfur from the waste stream, but elemental sulfur is easily transported to other locations and can be stored for long periods of time.

[0089] A common alternative to the Claus process is to convert H into H by the so-called wet sulfuric acid process, for example. 2 S is converted into sulfuric acid. The produced sulfuric acid can be used in other chemical processes of the plant. The wet sulfuric acid process can also constitute the tail gas purification of the Claus process plant. A similar dry sulfuric acid process can also be used in this connection.

[0090] The sulfuric acid process converts H 2 Oxidation of S to SO 2 , and will SO 2 Oxidation to SO 3 , then SO 3 The latter is achieved by reaction with water in the gas phase in the so-called wet sulfuric acid process or by absorption in concentrated sulfuric acid in the so-called contact process or dry process. In the presence of a catalytically active material, which usually contains vanadium, SO 2 Oxidized to SO 3 The reaction temperature during this period will be in the range of 400-500° C. Typically, the wet sulfuric acid process produces sulfuric acid with a concentration range of 92%-98%, while the dry sulfuric acid process can also produce sulfuric acid with a concentration exceeding 98%.

[0091] In addition, it is also attractive to collect hot high pressure steam in the range of 30 barg to 80 barg from the highly exothermic sulfuric acid process, whereas the Claus process can only provide steam at low pressure and in significantly smaller quantities. This high temperature / high pressure steam would allow efficient heat integration in the process, for example by preheating the process gas.

[0092] However, even if sulfuric acid were commercially traded, production of large quantities of sulfuric acid may not be attractive because transportation of sulfuric acid is complex and regulated.

[0093] The reactions that occur in the sulfuric acid process (dry and wet) are:

[0094] H 2 S+1.5 O 2 ->SO 2 +H 2 O(3)

[0095] SO 2 +0.5 O 2 ->SO 3 (4)

[0096] SO 3 +H 2 O->H 2 SO 4 (5)

[0097] The overall reaction of the Claus sulfuric acid process can be described as follows:

[0098] H 2 S+2 O 2 ->H 2 SO 4 (6)

[0099] As a common Claus tail gas modification solution, the wet sulfuric acid process provides a solution to meet environmental regulations at lower capital and operating costs than alternatives. Until now, the only disadvantage of the wet sulfuric acid process has been that the sulfuric acid product is not always desirable. With the new invention, the integrated Claus process with the addition of sulfuric acid process modification will eliminate this disadvantage while increasing the capacity of the Claus plant.

[0100] It has been recognized that retrofitting an existing Claus process by adding a wet sulfuric acid process can be advantageously performed by recycling all or substantially all of the sulfuric acid produced to the Claus reactor. The integration of the Claus / wet sulfuric acid process according to the present invention will eliminate the disadvantages of the inconvenient sulfuric acid product while reducing the equipment size of the Claus process and the wet sulfuric acid process.

[0101] The combustion of sulphuric acid is known from the regeneration of spent sulphuric acid in wet sulphuric acid plants, but has not yet been carried out in the reactor of the Claus process or under Claus process conditions.

[0102] When sulfuric acid is injected into the sulfuric acid evaporation zone, the following overall reactions occur:

[0103] H 2 SO 4 +3 H 2 S→2 S 2 +4 H 2 O(7)

[0104] To complete this overall reaction, the following reactions must be completed:

[0105] H 2 SO 4 (Liquid) → H 2 SO 4 (Gas)(8)

[0106] H 2 SO 4 (gas) → H 2 O(gas)+SO 3 (Gas)(9)

[0107] SO 3 (gas) → SO 2 (Gas) + 0.5 O2 (Gas)(10)

[0108] Reaction (8) is a common evaporation reaction in which the energy required to heat the liquid and evaporate the water and sulfuric acid is provided by the surrounding hot process gas. The effect of complete evaporation of the sulfuric acid is that the gaseous H 2 SO 4 The corrosiveness is much lower than that of liquid H 2 SO 4 Droplets.

[0109] Reaction (9) is an endothermic dissociation reaction that occurs almost instantaneously at temperatures above 600°C. At this point, some SO 3 Will start with H 2 S reacts to form SO 2 , H 2 O and elemental sulfur.

[0110] Reaction (10) is an endothermic decomposition reaction that is rapid at temperatures above 900°C. In an oxygen-rich atmosphere, chemical equilibrium prevents complete dissociation, but in a reducing atmosphere, O 2 Removal of products (by reacting with H 2 S reaction) will allow complete decomposition. At these elevated temperatures, H 2 S and O 2 The reaction was very fast.

[0111] Since the residence time in the sulfuric acid evaporation zone is typically 1-2 seconds, it must be ensured that reactions 8, 9, 10 and 1 are completed within this time. When the process gas is cooled (i.e. in the Claus waste heat boiler), the reaction rate drops sharply and further conversion will be negligible.

[0112] In the downstream Claus reactor, the process gas in contact with the catalyst contains O 2 and / or SO 3 This will result in catalyst deactivation due to a "sulfation" reaction in which catalytically active aluminum oxide or titanium oxide is converted to catalytically inactive aluminum sulfate or titanium sulfate, so that the formation of elemental sulfur in these reactors will be reduced, resulting in an increase in unconverted sulfur species going to the downstream tail gas sulfuric acid plant and increased emissions to the atmosphere.

[0113] In addition, SO in process gas 3 During passage through the sulfur condensing unit it may combine with water and condense, forming sulfuric acid in the elemental sulfur product, which can cause corrosion of process equipment.

[0114] To remove any unconverted SO from the sulfuric acid evaporation zone 3In order to avoid the risk of causing operational problems in the Claus converter and the elemental sulfur condenser, it is preferable to install a catalytic reactor between the outlet of the waste heat boiler and the first elemental sulfur condenser or the first Claus catalytic reactor. The catalyst can effectively pass through the H present in the exhaust gas of the reactor. 2 S and H 2 Will SO 3 Restore to harmless SO 2 and / or elemental sulfur.

[0115] If all the sulfuric acid produced in the Claus tail gas sulfuric acid process is directed to the Claus reactor, it is possible to operate the Claus process with H 2 The reduction of S takes advantage of the very high removal and thermal efficiency of the sulfuric acid plant, and the only product is elemental sulfur, which is easy to handle and transport.

[0116] In addition, by recycling sulfuric acid, H 2 SO 4 The decomposition releases O 2 , thereby reducing the amount of combustion oxidant added, and if the oxidant is atmospheric air, this has the benefit of greatly reducing the process volume, since atmospheric air contains close to 80% of inert N 2 , that is, per volume O 2 N has 4 volumes 2 .

[0117] Based on air as the oxygen carrier to the Claus reactor, the overall Claus reaction is:

[0118] 4H 2 S+2 O 2 +8 N 2 →2 S 2 +4 H 2 O+8 N 2 (11)

[0119] Similarly, based on H 2 SO 4 As O to the Claus reactor 2 carrier, the overall Claus reaction is:

[0120] 3 H 2 S+H 2 SO 4 →2 S 2 +4 H 2 O(12)

[0121] Comparing these two reactions, it is clear that H 2 SO 4 It's an excellent O 2carrier and has the (theoretical) potential to reduce the Claus tail gas volume flow by 67% compared to atmospheric air.

[0122] It may also be beneficial to bypass a certain amount of feed gas to the Claus tail gas burner, as the feed gas has heating value and can be used in the Claus tail gas burner, thus reducing the need to add auxiliary fuel. 3 The other contains NH 3 feed gas, which may be more favorable because the substoichiometric conditions in the reactor zone hinder the NH 3 The so-called sour water stripper (SWS) gas mainly contains similar amounts of NH 3 , H 2 S and H 2 O, is this type of NH 3 Example of raw gas.

[0123] In the Claus process for processing SWS gas, it is necessary to completely destroy NH in the Claus reactor. 3 Otherwise, ammonium salts will be formed, such as (NH 4 ) 2 SO 4 and (NH 4 ) 2 S 2 O 3 , and block the final elemental condenser. Special high intensity (two-stage) burners are able to thermally decompose NH 3 The high temperatures required, however, require accurate control of the acid gases in two separate streams.

[0124] However, the treatment of SWS gas in sulfuric acid plants is well known, as NH 3 Completely oxidized to N 2 and NO. Therefore, it may be necessary to configure an integrated Claus / sulfuric acid process with two thermal stages for converting the H 2 S and little or no NH 3 The first feedstock is directed to the Claus reactor, while the 3 The gas, for example SWS gas, is directed to the Claus tail gas incinerator. In this configuration, it may be necessary to design the sulfuric acid plant to include the use of NH 3 Selective Catalytic Reduction (SCR) NO x section.

[0125] When designing Claus burners and reactors, hydrocarbons (such as CH 4 and BTX) and NH 3The destruction of sulfur (if present) usually determines the operating temperature and residence time. The breakthrough of these species into the catalytic Claus section may cause catalyst fouling, deactivation and plugging of the elemental sulfur condenser, resulting in unplanned shutdowns.

[0126] Considering H 2 The reactions of S (reactions 1 and 2) are generally considered to be rapid and will not be the rate determining reactions.

[0127] As a rule of thumb, temperatures of 1000-1050°C are required to completely destroy hydrocarbons, taking into account the effects of slow mixing and temperature / composition gradients. Similarly, 1200-1250°C is required to ensure that NH 3 Correct destruction.

[0128] To achieve such high temperatures, especially in the case of feed gases with low calorific value, feed gas preheating, oxygen enrichment, acid gas staging and / or fuel gas co-firing may be required.

[0129] In refineries, for example, there is often concentrated acid gas (>80 vol% H 2 S) and NH 3 and H 2 S gas (sour water stripper (SWS) gas, containing 20-50% NH 3 , 20-50% H 2 S and the balance at least 80% is H 2 O, with similar contents), with the majority of the sulfur input being present in the acid gas. The reactor zone can then be configured to receive the full amount of SWS gas and combustion air and an amount of acid gas such that the reactor zone temperature is approximately 1200 to 1250°C and complete NH 3 Destruction, in which sulfuric acid, any atomized media and remaining acid gases are injected.

[0130] In natural gas processing equipment, the feed gas to the Claus plant will contain a lower concentration of H 2 S (typically < 60 vol%), and will contain hydrocarbons, which require temperatures above 1000-1050°C to ensure complete destruction of the hydrocarbons. In this case, the preferred option is most likely to direct the entire amount of acid gas into the reactor zone.

[0131] The integrated process may also benefit from the use of enriched air or substantially pure oxygen in the Claus reactor. The benefit of using enriched air is that the amount of inert nitrogen in the process gas is reduced, thereby reducing the volume of process gas and reducing the size of the equipment. The lack of dilution with nitrogen also has the effect of increasing the combustion temperature, which may be beneficial if there are impurities that need to be fully converted, especially because the amount of oxygen in the Claus reactor is substoichiometric. Since Claus catalysts are sensitive to the presence of impurities such as light hydrocarbons, it is often advantageous to operate the Claus reactor with enriched air to reach elevated temperatures in order to fully oxidize the impurities. This also has the additional benefit of being able to carry out an initial homogeneous non-catalyzed Claus conversion, which can be carried out at temperatures above 900°C.

[0132] However, from a thermal efficiency perspective, high combustion temperatures may be limited by the choice of construction materials in the Claus reactor and the downstream waste heat boiler. 2 S feed gas, oxygen enrichment will increase the process gas temperature above the design temperature of the material. However, H 2 SO 4 A combination of recirculation (cooling of the process gas by evaporation and acid decomposition) would make it possible to exploit the enriched oxygen in this arrangement.

[0133] The Claus tail gas burner will typically be run on atmospheric air, however, it may also be beneficial to direct the gas with a low concentration of sulfur species to the incinerator since complete combustion of the sulfur species releases significantly more energy than the partial oxidation that occurs in the Claus reactor.

[0134] As a result, it may be beneficial to include high concentrations of H 2 The feed gas containing S is directed to the Claus plant, while the feed gas with lower concentration and containing NH 3 The raw gas bypasses the Claus tail gas burner.

[0135] An example might be that the feed gas to the sulfur abatement plant is a highly concentrated H 2 S and a gas containing NH 3 Here, the sulfuric acid plant can be configured to receive the entire amount of SWS gas, thereby saving fuel in the Claus tail gas burner and eliminating the NH3 in the Claus plant and in the Claus reactor. 3 Operational issues related to incomplete destruction of

[0136] If the Claus tail gas burner receives only a limited amount of H 2 If the Claus tail gas is not saturated with S, the calorific value is too low to maintain stable combustion. In that case, auxiliary fuel needs to be added. This auxiliary fuel can be H 2S, SWS gas or hydrocarbon feed, but preferably using an amount of existing feed gas to an integrated Claus and sulphuric acid plant.

[0137] Integration between the Claus process and the sulfuric acid process has integration advantages. These include the possibility of reducing the volume flow in the Claus process by providing an oxidant in the form of sulfuric acid, which can replace the atmosphere. In addition, the use of the feed gas can be optimized, so that a feed gas containing fuels that contribute greatly to the production of elemental sulfur can be directed to the Claus process, while a feed gas that contributes greatly to heat energy and non-reactive products (such as CO) can be directed to the Claus process. 2 ) The contributing raw gas is directed to the sulfuric acid process. When the process is designed to recycle excessive amounts of sulfuric acid, additional fuel may be required to provide the heat required for evaporation and dissociation of the sulfuric acid.

[0138] In a preferred embodiment, the sulfuric acid produced in the Claus tail gas sulfuric acid plant is cooled and directed to an intermediate storage tank. In principle, the sulfuric acid storage tank can be omitted, since the Claus reactor is designed to accept the entire sulfuric acid product from the sulfuric acid plant. However, in order to ensure high reliability of the entire plant, the installation of the tank allows the Claus plant to be operated (for a short time) without sulfuric acid injection while the sulfuric acid plant is still in operation. This situation occurs during startup and shutdown and if maintenance of the sulfuric acid lance / nozzle is required. The tank also enables the sulfuric acid product to be removed if sulfuric acid is the desired product, and also allows the import of sulfuric acid from other sources.

[0139] In sulphuric acid production from 4 hours to 120 hours, 1-4 days of tank capacity is a good compromise between tank costs and the flexibility of a Claus + Claus tail gas sulphuric acid plant. Sulphuric acid production is typically around 0.1m 3 Sulfuric acid / ton of elemental sulfur.

[0140] In addition to the wet sulfuric acid process, other sulfur reduction plants can also produce sulfuric acid. The first example is the SNOX process, in which NO x The selective catalytic reduction of SO is combined with the wet sulfuric acid process. This layout is particularly suitable for SO 2 Less than 1 vol% in flue gas. Also relevant is H 2 O 2 Scrubbers, which are usually applied to SO 2 Small exhaust gas with low concentration, including SO 2 With H 2 O 2 Direct reaction to form H 2 SO 4In addition, a dry sulfuric acid process operating by absorption in sulfuric acid may be considered. Sulfuric acid is also produced as the feed gas enters the reactor and passes upward through an activated carbon bed where sulfur dioxide is converted to sulfuric acid by wet catalysis in the presence of oxygen and water. Sulfuric acid from all of these and other sources may also be beneficially fed directly to the Claus reactor.

[0141] However, as the sulfuric acid concentration decreases, the benefits of injecting sulfuric acid into the Claus reactor decrease, due to the additional energy required for water evaporation and the increased process gas flow rate caused by the increased amount of water in the sulfuric acid feed. 2 O 2 The sulfuric acid produced by the activated carbon process reaction is usually too low to be beneficially integrated into a Claus plant.

[0142] It may therefore be beneficial to further concentrate the sulphuric acid produced in the Claus tail gas sulphuric acid plant in an acid concentrator before recycling to the Claus reactor. The operation of such a concentrator plant will require energy to evaporate the water from the sulphuric acid, but a large part of this energy is then saved in the Claus reactor. The benefit is a lower reduction in process gas temperature in the sulphuric acid evaporation zone, and a reduction in process gas flow through the Claus plant and the Claus tail gas plant.

[0143] If a sulfuric acid condenser is used, it is also possible to reduce the H 2 O concentration to increase the sulfuric acid concentration. Claus tail gas usually contains 25-30 vol% H 2 O, reducing the concentration will not only increase the sulfuric acid concentration, but also significantly reduce the process gas flow in the sulfuric acid plant. However, the cost of reducing the water concentration in the process gas is very high, because the process gas temperature should be reduced to below 50-60 ° C to condense most of the water, and the water will be condensed by elemental sulfur, H 2 S. SO 2 and / or H 2 SO 4 contamination and therefore requires further treatment.

[0144] Integration of the two processes also enables a process in which operation of the Claus process can be carried out at low conversions (eg 90% or 95%), since it may be cheaper to carry out additional conversion in the sulfuric acid process than to add additional Claus converter stages.

[0145] The standard Claus plant layout requires that the H in the feed gas 2 S>50vol% can achieve thermal self-sustaining in the Claus reactor. 2 S concentrations, feed gas preheating and a so-called split configuration are required. It is rare to see Claus plants processing feed gases with less than 10-20 vol% H 2On the other hand, the sulfuric acid process is very effective in treating these so-called H-depleted 2 S gas, thereby producing concentrated sulfuric acid. The sulfuric acid product is highly concentrated in terms of sulfur and oxygen.

[0146] Treatment of H deficiency 2 Sulfuric acid plant and treatment of H2S (and / or other sulphur compounds) gas 2 A combination of a Claus plant producing S gas and receiving acid from a sulphuric acid plant would be an advantageous arrangement since the feed streams to the Claus plant and the sulphuric acid plant are optimized in terms of conversion efficiency, thermal efficiency and plant size / cost.

[0147] The Claus process can also be modified by adding sulfuric acid to optimize feed handling. The advantages of the sulfuric acid process, especially the wet sulfuric acid process, are that it is very suitable for contaminated feeds, including SWS gas containing ammonia as discussed above, "dirty sulfur" containing organic impurities and moderate inorganic impurities, dilute H 2 S. SO 2 and other dilute streams containing sulfur compounds, including flue gas from combustors and FCC gas. Similarly, H-rich 2 The S gas, which has to be diluted before being processed in the wet sulphuric acid plant, can be used directly in the Claus process.

[0148] A Claus plant may include a thermal step and 1 to 3 catalytic steps, wherein H 2 S and SO 2 The reaction forms elemental sulfur, which is discharged in 1-4 condensers. The sulfur recovery requirements determine the number of catalytic steps required. As a rule of thumb, the cumulative sulfur recovery efficiency after the thermal step is 60-75%, after the first catalytic step is 85-88%, after the second catalytic step is 94-97%, and after the third catalytic step is 97-98%. Sulfur recoveries exceeding 98% usually require a so-called Claus tail gas treatment plant TGTP, of which more than a dozen technologies are available, depending on the sulfur recovery requirements and the cost of the technology.

[0149] If a Claus unit needs to be modified or upgraded to increase sulfur recovery, capacity and / or reduce emissions, the desired sulfur recovery will largely determine the technology of choice. For sulfur recoveries of 99.9% and above, amine-based TGTP is typically selected, where all sulfur-containing species are first reacted with H 2 The reaction is reduced to H 2 S, H 2 The S is captured in the amine solution and released in the stripping unit as concentrated H 2 The S gas is returned to the Claus reactor. This technology is characterized by high capital cost and high operating cost.

[0150] Another option is to install a sulfuric acid plant as a TGTP. It has recently been determined that this configuration can benefit from recycling the captured sulfur to the Claus reactor in the form of concentrated sulfuric acid. This technology features increased capacity of the Claus plant and reduced capital and operating costs.

[0151] Another important factor in selecting a TGTP is availability, that is, a process trip (i.e., a safe shutdown due to out-of-range operating conditions) of the TGTP does not necessarily lead to a shutdown of the Claus plant, which would result in the shutdown of upstream plants, such as the hydrotreater for fuel desulfurization. Such a shutdown of the hydrotreater would be very expensive for the refinery and therefore undesirable.

[0152] Retrofitting or upgrading a Claus plant with a sulfuric acid plant as TGTP and sulfuric acid recycle will involve at least some of the following process improvements:

[0153] - dismantling of process equipment related to the Claus process downstream of the sulfur condenser after the second catalytic Claus converter,

[0154] - Evaluation of the Claus burner and reactor design, including positioning of the sulfuric acid nozzles without affecting the main flame, possible installation of droplet impaction devices (e.g., lattice walls) in the Claus reactor, etc.

[0155] - Update the tripping system and control system of Claus equipment

[0156] - Design and installation of new sulphuric acid plants and sulphuric acid storage tanks or integration of existing sulphuric acid plants.

[0157] -Design and installation of sulfuric acid feed system for Claus reactor, such as atomizing nozzles, pumps and monitoring of acid feed system.

[0158] - Evaluation of the reuse of existing tail gas flares and chimneys

[0159] - Evaluate the impact of total equipment utilization

[0160] The preferred Claus plant layout for the conversion of a TGTP with a sulphuric acid plant is a layout with 2 catalytic stages, the sulphur recovery of such a Claus plant is in the range of 94-97%, while the 3-6% of the sulphur introduced into the sulphuric acid plant is effectively converted into concentrated sulphuric acid which can be recycled to the thermal stage of the Claus plant.

[0161] Having 3 catalytic Claus stages will have a high cost impact on the Claus plant but only a small impact on the size of the sulfuric acid plant and from an operational perspective, the additional pressure loss of the 3rd stage and the additional complexity of the Claus plant do not provide a net advantage for the Claus + sulfuric acid TGTP combination.

[0162] If the entire sulfuric acid production in the sulfuric acid TGTP is recycled to the thermal stage of the Claus plant, then having only one catalytic stage would be non-optimal in most cases, since this would require adding 12-15% sulfur in the form of sulfuric acid to the Claus reactor, which could make it difficult to operate the thermal stage at optimal temperature. However, if rich air and / or fuel gas is used in the combustion of the hot Claus stage, such an arrangement would be possible.

[0163] About H 2 Environmental regulations for H2 emissions are very strict. Therefore, Claus plants include a tail gas incinerator, which converts the unconverted H 2 S to SO 2 Depending on local environmental regulations, tail gas treatment equipment can also be installed to remove SO from the tail gas before it is introduced into the chimney. 2 . Tail gas incinerators are typically designed to process Claus tail gas with a composition based on the TGTP inlet, allowing the TGTP plant to bypass the Claus plant, i.e. the design heating value of the tail gas feed may be higher than normal operation. To minimize gas consumption, the operating temperature is typically 900°C, which will ensure that the chimney emissions comply with environmental regulations. The residence time is typically 1 second. Other incinerators may use, for example, lower temperatures (e.g. 800°C) and / or longer residence times (up to 10 seconds), and a case-by-case assessment is required to evaluate whether the incinerator can be reused. Reusing an incinerator will significantly reduce the cost of the renovation project.

[0164] In the treatment of H 2 , H 2 S, COS, S 8 and CS 2 In wet sulfuric acid plants for gas, the incinerator is usually operated at 1000°C with a residence time of 1 second to ensure complete conversion of sulfur compounds to SO 2 At first glance, the increase in temperature and residence time would suggest that a replacement tail gas incinerator is required.

[0165] However, an assessment of whether an existing incinerator can be used will include many considerations, including the thermal stability, volumetric capacity and residence time of the material.

[0166] Normally, the temperature increase from 900°C to 1000°C is not critical for the relevant building materials, since refractory materials are highly heat resistant.

[0167] The increase in volume requirement due to the increased amount of auxiliary fuel to reach 1000°C is only secondary to the volume capacity or residence time. 2The possibility of recovering heat energy from the oxidation will reduce the need for auxiliary fuels. Finally, a detailed analysis of the integrated process showed that the total process gas flow rate could be reduced due to the reduced need for combustion air in the Claus reactor. It was therefore recognized that the tail gas incinerator could often be reused in a Claus process plant operated with recycle from the sulfuric acid tail gas treatment plant.

[0168] In summary, for a large part of the feed stream to the Claus plant, acid recirculation to reduce the Claus tail gas flow, the use of preheated Claus tail gas and combustion air will allow the reuse of existing incinerators after retrofitting the Claus plant with a sulfuric acid plant (see Figure 2 ).

[0169] In the Claus tail gas incinerator, all sulfur compounds are oxidized to SO 2 , while several percent of SO 2 will be further oxidized to SO 3 Since the calorific value of the Claus tail gas is too low to maintain a stable flame, fuel gas needs to be added. The fuel gas is usually hydrocarbon-based (e.g. natural gas), but can also be the feed gas to an upstream Claus plant, e.g. containing H 2 S gas and also contains NH 3 The so-called sour water stripping gas. Using the sour water stripping gas as fuel will produce NO x , the NO x It can be effectively removed in the SCR reactor, which can be located in the SO 2 Upstream of the converter. NH for SCR reaction 3 It can be provided from external storage equipment or obtained from sour water stripping gas.

[0170] Since Claus tail gas does not contain O 2 , so O must be added 2 , usually added in atmospheric form.

[0171] The exhaust gas from the Claus incinerator is then cooled in one or two steps to a temperature of 370-450°C, which is the SO 2 Typical inlet temperature of the converter, in SO 2 In the converter, SO 2 By 2 The reaction catalyzes the conversion into SO 3 .

[0172] It may be necessary to 2 O is added in the form of atmospheric air upstream of the converter. 2 , because existing tail gas incinerators are usually designed to use low excess O in the exhaust gas 2Therefore, adding SO 2 Oxidized to SO 3 The additional air required may not be feasible because it would increase fuel consumption and reduce residence time in the incinerator.

[0173] On SO 2 In the converter, 1-3 catalyst layers are installed with integrated cooling, usually by heat exchangers located below each layer to remove the heat of reaction and control the inlet temperature of the next catalyst layer. These inter-bed heat exchangers usually use high-pressure steam as the cooling medium, but high-pressure water, molten heat transfer salts, process gases and air can also be used. SO 2 The oxidation catalyst is vanadium based. SO 2 SO in converter 2 Conversion efficiencies are typically greater than 99%, ensuring greater than 99.9% of the total sulfur is removed from the feed gas.

[0174] Will SO 2 The converter off-gas is cooled and directed to a sulfuric acid condenser where the gas is further cooled, SO 3 With H 2 O reacts to form H 2 SO 4 and condenses in the form of concentrated sulfuric acid with a concentration of 90-98% w / w. The hot concentrated sulfuric acid is taken from the condenser, cooled in a recirculation loop and pumped to a storage tank. From there it can be recycled to the Claus plant and injected into the Claus reactor for evaporation, decomposition and formation of elemental sulfur.

[0175] The cooled gas leaving the sulphuric acid condenser is substantially free of sulphuric acid and may be directed to a chimney, which may typically be an existing chimney.

[0176] The cooling medium in the sulfuric acid condenser is atmospheric air, which receives heat indirectly from the process gas by heat exchange through glass walls (usually tubes). The cooling air can be inside or outside the tubes and will leave the condenser at a temperature of 180°C to 270°C. A portion of the hot air can be used as combustion air in the incinerator and / or in the SO 2 converter upstream to provide for SO 2 Oxidized O 2 .

[0177] If it is concluded that the existing incinerator cannot for some reason be used with the standard sulfuric acid plant layout just described (see Figure 2 ), then a semi-catalytic sulfuric acid plant layout can be used (see Figure 3 ).

[0178] In another layout of the semi-catalytic sulfuric acid plant, the Claus tail gas can be optionally preheated and split upstream of the existing incinerator: a portion is directed to the incinerator for the treatment of sulfur compounds (and H 2 and CO) for thermal destruction, while another part bypasses the incinerator and mixes with the hot incinerator exhaust gases. With this arrangement, there are no problems in obtaining the required temperature and residence time in the incinerator and, in fact, the fuel gas consumption is significantly reduced compared to normal operation when the incinerator treats the entire Claus tail gas.

[0179] The 900-1000°C exhaust gas from the incinerator is mixed with the preheated Claus tail gas to produce H 2 S.S 8 , COS, CS 2 , CO and H 2 The semi-oxidized process gas is of a lower concentration and higher temperature due to dilution with hot incinerator exhaust gas. The mixing temperature is usually in the range of 400-750 °C and at this temperature, H 2 S and CS 2 The residual COS, CO and H 2 Catalytic oxidation will be required, so this semi-oxidized process gas must be cooled to the optimum oxidation catalyst temperature.Gas cooling can be performed using, for example, a waste heat boiler to generate steam, a steam superheater, a gas / gas heat exchanger or any other heat exchanger alone or in combination.

[0180] H 2 , COS, CS 2 The catalytic oxidation of CO is carried out using catalysts doped with noble metals, which must be resistant to sulfur compounds. Such catalysts are described, for example, in EP 2878358 and generally contain V, Ti and Pd.

[0181] The temperature increase in the catalytic oxidation reactor will preferably bring the process gas temperature to the downstream SO 2 Converter and SO 2 The desired value of at the oxidation catalyst inlet is usually in the range of 370-450° C. The temperature rise in the catalytic oxidation reactor can be controlled by the fraction of the Claus tail gas bypassing the incinerator and / or the degree of heat removal in the heat exchanger between the incinerator outlet and the catalytic oxidation reactor inlet.

[0182] On SO 2 In the converter, one or more catalyst layers are installed to ensure the required SO 2 To SO 3 oxidation, so that the emission target can be achieved. 2The oxidation reaction is exothermic and reversible, so heat must be removed to achieve SO 2 Optimal thermodynamic conditions for the conversion. Typically, heat is removed in heat exchangers installed between the catalyst layers using steam generators, steam superheaters and / or gas / gas heat exchangers, while ensuring that the cooling medium always remains above the dew point temperature of the sulfuric acid in the process gas.

[0183] Incinerators, catalytic oxidation reactors and SO 2 Converter consumption O 2 , and this O 2 As atmospheric or O-rich 2 The air is supplied to the incinerator and / or added at a point between the incinerator outlet and the catalytic reactor inlet. In order to reduce fuel consumption in the incinerator and reduce heat exchanger costs, as much necessary air as possible is added immediately upstream of the catalytic oxidation reactor. In principle, this air can be added between the catalytic oxidation reactor and the SO 2 divided between the converters, but the increased equipment complexity due to two air control systems is likely to outweigh the benefit of a slightly lower process gas flow through the catalytic oxidation reactor.

[0184] Another implication of supplying oxygen to the Claus tail gas is to ensure that the resulting mixture of Claus tail gas (comprising combustible gases), burner exhaust gases and air (comprising oxygen) does not form an explosive mixture with the attendant risk of causing uncontrolled oxidation (explosion) in the plant. This can be achieved by ensuring that the concentration of combustibles is safely below the so-called lower flammability level LFL, or O 2 This is achieved by keeping the concentration below the so-called limiting oxygen concentration LOC. Keeping the mixture below the LFL requires the addition of large amounts of process gas from the burner and / or oxygen-containing 2 The Claus tail gas is diluted with a gas (usually air). Keeping the mixture below the LOC requires 2 The addition of O is well controlled so that it does not exceed the safe value. This solution usually requires the addition of O in one or more stages. 2 of gas.

[0185] The choice of strategy is best made with knowledge of the composition of the Claus tail gas and the degree of combustible fluctuations (which are likely to be in the tail gas). Upsets in the upstream Claus equipment may result in increased concentrations of combustibles, such as H 2 S will increase the calorific value of the gas and therefore the energy released in the process, thereby increasing the temperature of the process gas. Care must be taken to design the equipment to be robust enough so that it can withstand a given temperature increase. This is particularly true for equipment used to oxidize H 2 S.H. 2 , CO, CS 2 , CO and S xThe layout of a semi-catalytic sulphuric acid plant is robust to such fluctuations, since a large part of the combustible gases are oxidized in the hot gases before the process gas cooling in the burners and waste heat boilers.

[0186] Leave SO 2 Converter SO 3 The gas contains almost no S 8 , H 2 S, COS, CS 2 , H 2 and CO. SO 3 The H in the process gas 2 O combines to form H 2 SO 4 steam, which is then condensed into concentrated sulfuric acid in an indirectly cooled sulfuric acid condenser. 2 SO 4 The concentration range is 90-98.5% w / w, depending on the H content in the process gas. 2 O and SO 3 Claus tail gas usually has a high H 2 O concentration (>20 vol% H 2 O), so 90-94% w / w H 2 SO 4 is the expected acid concentration. Concentrated sulfuric acid is taken out from the sulfuric acid condenser, cooled and sent to the Claus reactor or sulfuric acid storage tank.

[0187] Cooling SO 3 The gas contains almost no SO 3 and H 2 SO 4 , so it can be directed to the chimney. In some cases, it may be necessary to remove SO 2 and additional units for acid mist, such as SO 2 Scrubbers and wet electrostatic filters.

[0188] Atmospheric air is usually used as the cooling medium in the sulfuric acid condenser, while the SO 3 Most of the heat recovered from gas cooling and acid condensation is used in the sulphuric acid plant, for example as heated combustion and oxidation air and for preheating boiler feed water or Claus tail gas.

[0189] If the operating conditions are out of range and the SO is shut down safely 2 If the incinerator and, therefore, the Claus plant are kept in operation, the process gas upstream of the catalytic oxidation reactor can be bypassed to the chimney if the restrictions on (temporary) emissions allow this.

[0190] An alternative to the semi-catalytic sulfuric acid plant layout is the fully catalytic sulfuric acid plant layout. In such a layout, the existing incinerator is only used when the WSA plant is not in operation, i.e. the sulfuric acid plant can be built without shutting down the Claus plant until the necessary connection is required. Under normal operation, the incinerator can be operated on standby with minimal fuel gas consumption, thus saving fuel compared to normal operation in the Claus process (with TGTP) layout, in which the Claus tail gas is fully introduced into the incinerator for heating to 800-900°C.

[0191] In most cases, a fully catalytic Claus sulfuric acid plant will be able to operate without consumption of fuel gas, as the H2 in the Claus tail gas is converted to sulphuric acid at 200°C to 500°C. 2 , CO, H 2 S, COS, CS 2 and S 8 Catalytic oxidation to H 2 O、CO 2 and SO 2 And SO 2 Oxidized to SO 3 The contributor to the Claus calorific value is H 2 S.H. 2 and CO. If these calorific values ​​become too low, it is possible to direct a small portion of the feed gas to the Claus plant to the Claus tail gas and increase the calorific value in this way. Another way to increase the calorific value of the Claus tail gas is to deliberately reduce the conversion of the Claus plant. This can be done, for example, by increasing the H 2 S / SO 2 ratio and / or operating the Claus catalytic reactor at a non-optimal temperature (usually increasing the inlet temperature).

[0192] Although generally high enough for a Claus sulphuric acid plant, the calorific value of the Claus tail gas is still considered low, thus requiring a very high thermal efficiency of the sulphuric acid plant layout, i.e., the thermal efficiency of the Claus tail gas is very high. 2 , CO, H 2 S, COS, CS 2 ) oxidation, SO 2 Oxidation and SO 3 A considerable part of the heat released by the conversion to concentrated sulfuric acid must be used to heat the Claus tail gas and the air required for the oxidation reaction.

[0193] The Claus tail gas and optionally the pit vent gas are preheated with excess heat from the sulfuric acid plant, preferably in the form of high pressure steam or hot cooling air. 2Therefore, in order for the oxidation reaction to proceed, O must be supplied to the tail gas. 2 Preferably, atmospheric air is used as O 2 carrier, but rich in O 2 Air and / or recirculated process gas is also an option.

[0194] Adding air to the Claus tail gas is not an easy task as explosive mixtures may form and this risk must be minimized / eliminated. 2 and H 2 The content of S is relevant for the formation of explosive mixtures, since the lower flammability limit (LFL) of these compounds at room temperature of ~4 vol% is reduced to ~1.8-3.2 vol% when the Claus tail gas is heated to 200°C. As a rule of thumb, the concentration of combustibles should not exceed 25% of the LFL, i.e., H2O2 after mixing with air. 2 and H 2 The sum of the concentrations of S must not exceed 0.5-0.8 vol%. In some industries, operation at concentrations not exceeding 50% of the LFL is permitted. This dilution results in a large amount of air addition, which increases the process gas flow and thus makes all parts of the sulfuric acid plant larger. In addition, the energy balance will be impaired because a large amount of air addition will require a lot of energy for heating and may require the addition of fuel. Another option would be to dilute the Claus tail gas with recycled process gas from a point downstream of the catalytic oxidation reactor. This option effectively dilutes the process gas below the LFL limit while limiting the volume increase of the process gas to a small part of the plant compared to dilution of the entire plant with atmospheric air.

[0195] Another more energy-efficient method is to convert O 2 Added to Claus tail gas in stages, so that O 2 The concentration can always be kept below the so-called limiting oxygen concentration LOC. Below this O 2 concentration, the mixed gas will be non-flammable, independent of the concentration of combustibles. By using staged addition of oxygen, the oxidation reaction of the reducing species in the Claus tail gas can be carried out with minimal addition of oxygen, minimizing the size of the equipment and eliminating the need for external energy supplies such as fuel addition and (electric) heaters. This method also has the advantage of simple control, as only the amount of oxygen-containing gas needs to be controlled, so that operation below LOC can always be achieved. Dilution with gas to stay below LFL will depend on the concentration of combustibles, which can fluctuate over time or may shift, rapidly increasing the concentration of combustibles.

[0196] For optimal operation of the catalytic oxidation step, the operating temperature must also be strictly controlled so that the inlet temperature is above the ignition temperature of the catalyst and the outlet temperature is below the maximum design temperature of the catalyst (e.g. to avoid mechanical damage or chemical sintering). In order to control these temperatures, recirculation of the already converted process gas can be used. In principle, the temperature can also be controlled by air dilution, but the addition of air is also limited by the flammability limits. In addition, recirculation is preferred over simple dilution because dilution increases the process gas flow in all process equipment, while recirculation of process gas limits the increase in process gas flow to a limited number of process equipment.

[0197] Preheated Claus tail gas and sulfur pit exhaust gas can be mixed with preheated atmospheric air to make O 2 The concentration is below the limiting oxygen concentration limit and is then directed to the first catalytic oxidation reactor. The catalyst is characterized by being free of precious metals and thus only partially oxidizes the combustible compounds in the process gas. The catalyst converts H 2 Oxidation of S to SO 2 and H 2 O and CS 2 Oxidized to COS and SO 2 , while COS, CO and H 2 The advantage of this catalyst is that its ignition temperature is significantly lower than that of oxidation catalysts based on precious metals (see EP 2878358). The heat released in the first oxidation reactor raises the process gas temperature to a level above the ignition temperature of the second oxidation catalyst, which converts all reducing substances (mainly COS, CO and H) into 2 ) is completely converted to SO 2 , H 2 O and CO 2 It may be necessary to supply additional O before the second oxidation reactor. 2 , which can be done in stages to convert O 2 The concentration is kept below the LOC value, or the combustible concentration is kept below 25%-50% of the LFL by dilution. 2 In the case of high S concentrations, the heat released in the first oxidation reactor may result in an outlet temperature that is too high to be suitable for the inlet of the second oxidation reactor, so it may be necessary to install a heat exchanger between the first and second oxidation reactors.

[0198] In order to control the outlet temperature of the second catalytic reactor, preferably a process gas recirculation loop is applied, which loop can be equipped with a temperature control device (heat exchanger), making it possible to simultaneously control the temperature at the inlet of the second oxidation reactor.

[0199] Downstream of the second oxidation reactor, all sulfur-containing species are SO 2 form, of which perhaps a few percent may be converted into SO 3 The SO is then optionally adjusted by passing the process gas through a heat exchanger and adding preheated air. 2 The temperature of the gas and the 2 concentration, thus in SO 2 The desired temperature and O2 are achieved at the inlet of the converter. 2 / SO 2 ratio. It is also possible to adjust the process gas temperature by preheating the air temperature, thus eliminating the need for heat exchangers on the process gas stream - the optimization of such a layout will depend on the concentration of combustibles in the Claus tail gas and the air added to the upstream catalytic reactor. If air preheating involves heat exchange with partially or fully converted process gas, it must be ensured that the air temperature is above the dew point temperature of the sulfuric acid in the process gas. Otherwise, sulfuric acid will condense on the heat exchanger surfaces, leading to corrosion and possible damage to the heat exchanger material.

[0200] On SO 2 In the converter, SO is converted to CO with the aid of a vanadium-based catalyst installed in one or more catalyst layers with heat exchangers installed between the layers. 2 Oxidized to SO 3 The desired conversion efficiency determines the number of catalyst layers, but typically 1-3 layers are required. 2 Converter SO 3 The gas is conveyed to the sulfuric acid condenser, where the process gas is indirectly cooled by the atmosphere, the sulfuric acid is condensed and removed, and the clean process gas is directed to the chimney. The hot cooling air from the sulfuric acid condenser is used as O 2 source, thereby utilizing the heat taken out in the condenser of the sulphuric acid plant.

[0201] The sulfuric acid is cooled and may be pumped to a sulfuric acid storage tank from which it is pumped to the Claus reactor to be decomposed and reformed into elemental sulfur in the Claus plant.

[0202] An alternative to the two-stage catalytic oxidation reactor with staged air addition, mixing and heat exchange between the reactors is a cooled reactor in which both catalysts are located in a cooled reactor and internal cooling ensures that the catalysts operate within their minimum and maximum allowable temperature ranges.

[0203] If it is difficult to stay below LFL and / or LOC in this cooled reactor, one option is to use two reactors in series and cool at least one of them. The first catalytic reactor is best suited for cooling because the exotherm is usually the highest and fluctuations in heating value usually come from H 2 S, H 2S will be oxidized in the first catalytic reactor, thus reducing the risk of catalyst overheating.

[0204] Since the calorific value of the Claus tail gas is relatively low, conservation of the reaction energy released within the sulphuric acid plant is crucial, and therefore the optimum combination of air staged addition, air dilution, process gas recirculation and heat exchanger location will depend on the exact amount of combustibles in the Claus tail gas. In addition, any deviations in the calorific value of the Claus tail gas must be taken into account, since such deviations will change the temperature and oxygen distribution in the sulphuric acid plant. It is possible that a design that is non-optimal for a normal Claus tail gas composition may be preferred in order to still be able to operate the sulphuric acid plant safely if the calorific value suddenly increases (e.g. due to a change in the feed gas composition to the Claus plant or poor oxygen control in the Claus plant). Such a design will usually involve a larger recirculation of process gas than is necessary, since this is an effective way to suppress the temperature increase in the catalytic oxidation reactor.

[0205] When the Claus tail gas incinerator is decoupled from the fully catalytic sulfuric acid plant, a start-up heater will be required to heat the process gas TGTP plant feed to the required temperature of 200-400°C, i.e. the minimum ignition temperature of the Claus tail gas on different catalysts. The heater can be a fired heater, a heat exchanger with a heat medium from an external source, or an electric heater. The location of the start-up heater is preferably upstream of the second catalytic oxidation reactor, but it can also be upstream of the first catalytic oxidation reactor or in the process gas recirculation loop.

[0206] Independently of the layout of the sulfuric acid TGTP, the operation of the Claus reactor will be identical and must ensure safe and reliable operation of the Claus plant with or without sulfur addition and during startup and shutdown.

[0207] The control system of the Claus burner must be updated to reduce the inflow of combustion air when sulfuric acid is injected. Usually, the combustion air flow control is a feedforward system that controls most of the air flow and adjusts a small amount of air flow to obtain the desired H2 in the Claus tail gas. 2 S and SO 2 The feedback system will remain unchanged, but the feedforward system must be updated to reflect the new feed flow. Given a given feed flow composition and flow rate, the ratio of the compounds in a given feed flow to O 2 Calculate the chemical reaction between 2 Then the O of each feed stream 2 The demands are added together and the sum is sent as a signal to the feed forward combustion air controller to adjust the combustion air flow to the calculated value. The general equation for calculating the combustion air flow is

[0208] G 空气 =∑Ki ·G i

[0209] G 空气 The necessary oxidation reaction is carried out in the Claus reactor, that is, hydrocarbons and NH 3 The complete oxidation of H 2 The combustion air flow rate required for the staged conversion of S. i is the flow rate of the individual feed streams entering the Claus reactor, including the H 2 S feed flow, pit exhaust gas, H 2 S gas or H 2 SO 4 Liquid recycle streams, fuel gas, and any H 2 SO 4 Atomized fluid of liquid. These flows are measured by instruments and the values ​​are transmitted to the equipment control system for further processing. i The values ​​are the air requirement factors; that is, how much combustion air is required to oxidize one unit of feed stream i. These factors depend on the composition of the feed stream, and if the feed gas composition varies, either the design composition or the analytical composition can be used. For most feed streams, K i The K value will be positive, while for a sulfuric acid stream and optional atomizing air, the K value will be negative. i Examples of calculation of values ​​are given in Examples 1-3.

[0210] The composition of the feed stream may vary over time, may deviate slightly from the design value, and the flow measurement may be incorrect. Therefore, the feedforward signal may also be incorrect. To compensate for these (small) deviations, the feedback signal is compensated by fine-tuning the combustion air addition. Typically, the H content of the Claus tail gas is measured. 2 S / SO 2 The ratio analyzer will provide a feedback signal. If the ratio is too high, add slightly more combustion air.

[0211] The acid injection nozzles are usually positioned in such a way that the sulfuric acid is atomized into the Claus reactor without affecting the flame and the flame stability. An example might be three nozzles located on the burner wall at the periphery of the flame with the nozzle tips pointing slightly towards the center of the furnace chamber. A swirling motion of the atomized acid can also be provided, making the mixing of the acid droplets and the combustion gases more efficient.

[0212] Complete evaporation and decomposition of H in a Claus reactor 2 SO 4The atomization of sulfuric acid is therefore important, and since the droplet evaporation rate depends on the square of the droplet diameter, the atomizing nozzle must be able to provide droplets as small as possible, preferably less than 500 μm in diameter. Some hydraulic nozzles operating at high pressure will provide such small droplets, while pneumatic nozzles are usually able to provide droplets small enough for rapid evaporation. The nozzle is usually defined by a diameter D 0.9 The value characterizes that 90% of the droplets accounting for the total mass (or volume) have a smaller diameter.

[0213] If large droplets are expected, impact surfaces can be installed in the furnace chamber. Such an impact surface can be, for example, a vector wall or a lattice wall, where the gas flow undergoes a sudden change in flow direction and large droplets, due to their high inertia, will not be able to change direction and will therefore impact with the surface, from which they will evaporate rapidly. In principle, the acid injection nozzles can be directed towards the refractory walls of the Claus reactor, as the hot refractory walls will also provide a diversion of the process gas and heat, allowing the impinging droplets to evaporate rapidly. Beds of packed material (e.g. Rasching rings) can also serve as impact surfaces for large droplets.

[0214] The droplet size from the atomizing nozzles can change over time as the nozzle tip wears due to clogging, erosion and corrosion. If care is not taken, the droplets can become so large that they do not fully evaporate in the Claus reactor, leading to the associated risk of sulfuric acid corrosion in the downstream Claus unit and deactivation of the Claus catalyst in the Claus reactor.

[0215] The condition of the nozzle can be monitored by observation through a sight glass, by removing the nozzle from the Claus reactor and inspecting it, and by continuously monitoring the operating parameters of the nozzle. Each nozzle is preferably equipped with flow and pressure monitors for the sulfuric acid side and the atomizing medium side. Each fluid side will have a characteristic interdependence between flow and pressure (drop), and if this characteristic value changes over time, this may be caused by changes in the nozzle geometry. For example, corrosion of the nozzle will result in a greater flow at the same pressure compared to a new nozzle.

[0216] By continuously monitoring these characteristic parameters and calculating a characteristic value for the nozzle, for example setting high and low alarms on the value, poorly performing nozzles can be detected and replaced before any damage occurs. Preferably, the nozzles are designed so that they can be isolated and withdrawn during operation of the Claus plant.

[0217] TripsIt may be necessary to stop the injection of sulfuric acid into the Claus reactor, for example due to a failure of the acid tank acid pump, a failure of the sulfuric acid flow controller, or a loss of atomizing liquid. In this case, the tripping system of the Claus unit must be updated to handle such an event, allowing the acid nozzle to be tripped while keeping the Claus unit running. If acid injection is stopped, the feedforward combustion air control will compensate for the lack of oxygen by increasing the air flow, allowing the Claus unit to resume normal operation.

[0218] During operation, the atomizing nozzles and the nozzles are cooled by the atomizing air flow and especially the sulfuric acid flow. As the acid flow stops, much of the cooling is lost and the nozzle temperature will increase. The nozzle material will be able to withstand the Claus reactor operating temperatures, but any acid trapped in the nozzle will become hot. The corrosion rate will increase significantly and boiling of the sulfuric acid may also occur. To avoid this, the acid lines can be flushed with a gaseous flushing medium to remove liquid acid from the nozzles. This minimizes acid corrosion while providing some additional cooling to the nozzles and avoiding the entry of Claus reactor process gas into the nozzles. Flushing will continue as long as the acid flow stops. The flushing medium is typically N 2 As an alternative, air can be used as the flushing medium, but this also adds O to the Claus reactor. 2 If the purge gas stream is not instrumented, there is a risk of disturbing the combustion air control. Stopping the sulfuric acid injection will also cause the temperature in the Claus reactor to increase, but the temperature increase will not be a problem in most cases because the refractory walls will be able to withstand the higher temperatures and the higher temperatures will not have a negative effect on the Claus reactor chemistry.

[0219] In the event of an acid jet trip, the atomizing medium will continue to flow, thereby cooling the nozzle and preventing process gas from entering the nozzle.

[0220] Brief description of the drawings:

[0221] Figure 1 The known Claus layout and tail gas treatment plant (TGTP) are depicted.

[0222] Figure 2 Depicted is a Claus layout with sulfuric acid TGTP and recycle of the acid to the Claus reactor.

[0223] Figure 3 A Claus layout is depicted with recycle of part of the catalytic sulfuric acid TGTP and the acid to the Claus reactor.

[0224] Figure 4A Claus layout is depicted with pure catalytic sulfuric acid TGTP and recycle of the acid to the Claus reactor.

[0225] Figure 5 Depicted is the control system for adding combustion air to a Claus burner.

[0226] exist Figure 1 The well-known Claus layout with a tail gas treatment plant (TGTP) is shown. The Claus plant receives a gas containing H 2 The feed gas (2) containing H2S is burned in the Claus reactor (6) together with the atmosphere or oxygen-enriched air (4). 2 The so-called pit off-gas (72) of S is directed to the Claus reactor (6). In case of low sulfur recovery requirements, the pit off-gas can be sent to the incinerator (42). In the Claus reactor, H 2 S is partially oxidized to SO 2 and forms sulfur. Any NH 3 and / or hydrocarbons are decomposed into N 2 and H 2 O and CO 2 and H 2 O. The temperature of the Claus reactor is typically 1,000-1,400°C with a residence time of 1-2 seconds. The Claus reactor gases are typically cooled to around 300°C in a waste heat boiler located at the furnace outlet, and the offgas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser offgas (12) is reheated in a heat exchanger (14) or by an in-line burner, and the reheated process gas (16) enters the first Claus reactor (18) which is filled with a catalyst comprising activated alumina or titania to convert H 2 S and SO 2 The reaction produces elemental sulfur. The reactor offgas (20) is directed to another sulfur condenser (22) where the elemental sulfur is condensed and discharged to a sulfur pit (66) via line 62. The process gas (24) then passes through a further catalytic Claus stage via a process gas reheater (26) connected by lines 28 and 32, a Claus reactor (30) and a sulfur condenser (34). The condensed sulfur is discharged to a sulfur pit (66) via line 64.

[0227] After the Claus reactor (30) and the sulfur condenser (34), the sulfur recovery is about 94-97%, depending on the local requirements for sulfur recovery (blow-off), an additional sulfur recovery unit is installed. This process is often called a Claus tail gas treatment plant (TGTP) (38), and there are several types of TGTPs. They can be another Claus reactor followed by a sulfur condenser, it can be a so-called sub-dew point reactor, a reactor for converting H 2 Catalytic systems for the selective oxidation of sulfur to elemental sulfur or amine-based H 2 S scrubbing unit, which captures H in the Claus tail gas (36) 2 S and returns it to the Claus reactor (6). Such plants allow high sulfur recovery rates, but the cost is as high as the cost of the Claus plant itself, depending on the complexity and efficiency of the TGTP.

[0228] Downstream of the TGTP, the exhaust gas 40 is directed to an incinerator (42) which thermally oxidizes all sulfur compounds into SO 2 After cooling in a waste heat boiler (usually part of the incinerator), the incinerator exhaust gas (48) is sent to a chimney (50). The Claus plant tail gas flow has a low calorific value and does not contain oxygen, so fuel (44) and combustion air (46) are required for incinerator operation.

[0229] If the TGTP unit fails, the tail gas can bypass the TGTP via line 52 and be directed to the incinerator (42), thereby allowing the Claus plant to continue operating.

[0230] All liquid sulfur from the sulfur condensers (10, 22, 34) is collected in a sulfur pit (66) through lines (60, 62, 64). The pit is vented / flushed with atmospheric air (70) to drive off H dissolved in the sulfur. 2 S. The sulfur pit exhaust gas (72) contains a small amount of H 2 S, which can be directed to the Claus reactor (6) or the incinerator (42). The combined stream of liquid sulfur is discharged in line 68.

[0231] exist Figure 2 In the present invention, the wet sulfuric acid plant is a TGTP Claus, characterized in that at least a portion of the produced sulfuric acid is recycled to the Claus reactor. The Claus plant receives a stream containing H 2 S feed gas (2), which is burned in the Claus reactor (6) with atmospheric air or oxygen-enriched air (4). In the Claus reactor, H 2 S is partially oxidized to SO 2 and form sulfur. Any NH in the feed gas 3 and / or hydrocarbons are decomposed into N 2 and H 2 O and CO2 and H 2 O. The temperature of the Claus reactor is typically 1,000-1,400°C with a residence time of 1-2 seconds. The Claus reactor gases are typically cooled to about 300°C in a waste heat boiler located just at the furnace outlet, and the offgas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser offgas (12) is reheated in a heat exchanger (14) or by an in-line burner, and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to convert H 2 S and SO 2 The reaction forms elemental sulfur. The reactor off-gas (20) is directed to another sulfur condenser (22) in which the elemental sulfur is condensed and discharged to a sulfur pit (66) via line 62. The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), a Claus reactor (30) and a sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged to a sulfur pit (66) via line 64. The Claus tail gas (36) is heated in a heat exchanger (37), which preferably uses excess heat (usually in the form of high-pressure steam) from a sulfuric acid plant. The heated Claus tail gas (39) is directed to an incinerator (42) where it is mixed with hot air (100), fuel (44) and pit exhaust gas (72) from a downstream sulfuric acid plant. The pit exhaust gas (72) can also be directed to a Claus reactor (6). The temperature and residence time in the incinerator are high enough to allow complete conversion of all sulfur-containing species to SO 2 , a few percent of SO 2 is further oxidized to SO 3 The incinerator exhaust gas is cooled in a waste heat boiler (which is usually an integral part of the incinerator) and directed through lines 74, 76 and 78 to a heat exchanger (80) for further cooling to SO 2 The desired temperature at the inlet of the converter (84). 2 In the converter, 1-3 layers of SO containing vanadium oxide are installed 2The oxidizing catalyst is separated by heat exchangers to remove the heat of reaction. The converted and cooled process gas (86) is directed to a sulfuric acid condenser (88) where the sulfuric acid is condensed, concentrated and separated from the process gas, exits through line 104 at the bottom of the condenser, and is cooled and pumped to a sulfuric acid storage tank (106). The clean process gas (90) is directed to a chimney (50). The sulfuric acid condenser (88) uses indirect air cooling, where cold cooling air enters the top via line 92 and hot air exits at the bottom via line 94. At least a portion of the hot air can be further heated in a heat exchanger (80) and the further heated air is directed to the incinerator via line 100, and a portion of the further heated air (98) is added to the incinerator exhaust gas (76) to ensure that there is enough oxygen available for SO 2 SO in converter (84) 2 Oxidation. Further heated air (98) may also be added to the process gas (82) downstream of the heat exchanger (80), with the associated benefit of reducing the size of the heat exchanger.

[0232] If SO 2 Should the converter (84) or the sulfuric acid condenser (88) fail for unknown reasons, the incinerator exhaust gas (74) can be directed to the stack via line 102, thereby keeping the Claus plant operational, which will ensure a 94-97% sulfur reduction during the failure.

[0233] Sulfuric acid from the sulphuric acid storage tank (106) is pumped and directed to the Claus reactor (6) via line 108. The sulphuric acid is atomized into the furnace via hydraulic nozzles or preferably via pneumatic (two fluid) nozzles.

[0234] Figure 3 A sulphuric acid plant is shown as a TGTP Claus, in which part of the sulphur compounds in the Claus tail gas ( 36 ) are catalytically oxidized.

[0235] Claus equipment receives H 2 S feed gas (2), which is burned in the Claus reactor (6) with atmospheric air or oxygen-enriched air (4). In the Claus reactor, H 2 S is partially oxidized to SO 2 and form sulfur. Any NH in the feed gas 3 and / or hydrocarbons are decomposed into N 2 and H 2 O and CO 2 and H 2O. The temperature of the Claus reactor is typically 1,000-1,400°C with a residence time of 1-2 seconds. The Claus reactor gases are typically cooled to about 300°C in a waste heat boiler located just at the furnace outlet, and the offgas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser offgas (12) is reheated in a heat exchanger (14) or by an in-line burner, and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to convert H 2 S and SO 2 The reaction forms elemental sulfur. The reactor offgas (20) is directed to another sulfur condenser (22) where the elemental sulfur is condensed and discharged to a sulfur pit (66) via line 62. The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), a Claus reactor (30) and a sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged to a sulfur pit (66) via line 64.

[0236] The Claus tail gas (36) is heated in a heat exchanger (37), preferably using excess energy from the sulfuric acid plant, preferably in the form of high-pressure steam. Downstream of the heat exchanger (37), the Claus tail gas is divided into two parts: one part (41) is directed to the incinerator (42) and one part is directed via line 43 to a location immediately downstream of the incinerator (42). The incinerator (42) receives oxygen from the hot air (128) from the sulfuric acid plant, fuel (44) and optionally pit exhaust gas (72) from the sulfur pit (66), and all sulfur compounds are oxidized to SO 2 The hot process gas (45) from the incinerator is mixed with a bypass portion of the Claus tail gas to form a mixed process gas (110) which will contain a certain content of combustible Claus tail gas compounds, such as H 2 S, COS, CS 2 , H 2 , S 8 and CO. The mixed process gas is cooled in one or two steps by a waste heat boiler (112) and / or a gas / air heat exchanger (116) to reach the desired inlet temperature of the catalytic oxidation reactor (120), typically 300°C to 400°C. The catalyst in (120) is a catalyst that converts all Claus tail gas compounds (e.g. H 2 S, COS, CS 2 , H 2 , S 8 and CO) to SO 2 , H 2 O and CO 2The oxidized process gas (122) is then directed to the SO 2 Converter (84) in which SO 2 Oxidized to SO 3 An air / gas heat exchanger (116) may also be located downstream of the catalytic reactor (120), depending on the exact composition of the Claus tail gas (36).

[0237] SO 2 The converter (84) includes 1 to 3 for SO 2 The catalyst layers for oxidation are provided, wherein coolers are installed between the layers to remove the released reaction heat. The converted and cooled process gas (86) is directed to the sulfuric acid condenser (88), in which the concentrated sulfuric acid is removed via the pipeline 104 and directed to the sulfuric acid storage tank (106), and the clean process gas (90) is directed to the chimney (50). The cooling air for the indirectly cooled sulfuric acid condenser (88) is supplied via the pipeline 92, and the hot cooling air is removed via the pipeline 94. Optionally, at least a portion of the hot cooling air is further heated in the gas / air heat exchanger 116, and the further heated cooling air (126) is directed to the incinerator via the pipeline 128, and a portion of the air can be directed to the catalytic oxidation reactor (120) and the SO via the pipeline 130. 2 The location between the converter inlet (124) is SO 2 SO in converter (84) 2 Oxidation provides sufficient oxygen. Further heated air (130) may also be added upstream of the catalytic oxidation reactor (120).

[0238] Sulfuric acid from the sulphuric acid storage tank (106) is pumped and directed to the Claus reactor (6) via line 108. The sulphuric acid is atomized into the furnace via hydraulic nozzles or preferably via pneumatic (two fluid) nozzles.

[0239] On SO 2 In the event of failure of the converter (84) and the sulfuric acid condenser (88), the oxidized Claus tail gas (122) can be directed to the stack (50) for a limited time, thereby keeping the Claus plant operational.

[0240] Figure 4 A sulphuric acid TGTP Claus is shown, where the Claus tail gas is 100% catalytically treated.

[0241] Claus equipment receives H 2 S feed gas (2), which is burned in the Claus reactor (6) with atmospheric air or oxygen-enriched air (4). In the Claus reactor, H 2 S is partially oxidized to SO 2and form sulfur. Any NH in the feed gas 3 and / or hydrocarbons are decomposed into N 2 and H 2 O and CO 2 and H 2 O. The temperature of the Claus reactor is typically 1,000-1,400°C with a residence time of 1-2 seconds. The Claus reactor gases are typically cooled to about 300°C in a waste heat boiler located just at the furnace outlet, and the offgas (8) is optionally directed to a sulfur condenser (10) where elemental sulfur is condensed and discharged to a sulfur pit (66) via line 60. The condenser offgas (12) is reheated in a heat exchanger (14) or by an in-line burner, and the reheated process gas (16) enters a first Claus reactor (18) filled with a catalyst comprising activated alumina or titania to convert H 2 S and SO 2 The reaction forms elemental sulfur. The reactor offgas (20) is directed to another sulfur condenser (22) where the elemental sulfur is condensed and discharged to a sulfur pit (66) via line 62. The process gas (24) then passes through another catalytic Claus stage via a process gas reheater (26), a Claus reactor (30) and a sulfur condenser (34) connected by lines 28 and 32. The condensed sulfur is discharged to a sulfur pit (66) via line 64.

[0242] The Claus tail gas (36) from the Claus plant is heated in a heat exchanger (37) using excess heat from the sulfuric acid plant. The heated Claus tail gas (39) is mixed with the pit exhaust gas (72) and hot air (166) and optionally a certain amount of recycled process gas (162). The mixed process gas (134) is conducted to a first catalytic reactor (136), in which a partial exothermic oxidation, in particular H 2 S and CS 2 , but some compounds in the mixed process gas are not oxidized. The partially converted process gas (138) is then optionally cooled in a heat exchanger (not shown), mixed with recycled process gas (160) and / or optionally a certain amount of hot air (168) to produce partially converted process gas (140) and directed to a second catalytic reactor (142), wherein all combustible compounds (especially H 2 , CO and COS) are completely oxidized to CO 2 , H 2 O and SO 2 The reactor offgas (144) is then divided into a recycle portion (154) and a portion (146) which is directed to a process gas cooler (148) and further to the SO 2The recycle portion (154) is optionally cooled in a heat exchanger 156 and the cooled recycle gas (158) is directed via line 160 to a location upstream of the second catalytic reactor (142) and optionally via line 162 to a location upstream of the first catalytic reactor (136). The process gas recycle blower will overcome the pressure differential of the process gas, the recycle stream and the control damper (not shown). The purpose of recirculating the oxidized process gas is to moderate the temperatures in the first catalytic reactor (136) and the second catalytic reactor (142). 2 Converted process gas from any stage in the converter (84) may also be used as recycle gas to optimize the temperature of the catalytic converter.

[0243] Optionally, the cooled converted process gas (150) from the process gas cooler (148) is mixed with hot air to allow the SO 2 The process gas (152) from the converter is of suitable temperature and contains sufficient oxygen for SO 2 The process gas (152) is then directed to the SO 2 Converter (84) in which SO 2 Oxidized to SO 3 . The converter comprises 1-3 catalyst layers, wherein coolers are installed between the layers to remove the heat of reaction. The converted and cooled process gas (86) is directed to the sulfuric acid condenser (88), wherein the concentrated sulfuric acid is taken out via pipeline 104 and directed to the sulfuric acid storage tank (106), and the clean process gas (90) is directed to the chimney (50). Cooling air for the indirectly cooled sulfuric acid condenser (88) is supplied via pipeline 92, and the hot cooling air is taken out via pipeline 94. A portion of the hot cooling air can be supplied to one or more locations in the sulfuric acid plant: via a pipeline to the upstream of the first catalytic reactor (136), via a pipeline to between the outlet of the first catalytic reactor (136) and the inlet of the second catalytic reactor (142), and / or via pipeline 174 to the SO 2 The entire hot air (168) stream or either of the streams (164, 170) may be further heated in a heat exchanger, such as for SO 2 The hot air from the reformer is shown as being further heated in heat exchanger 172 before being mixed with process gas 150, which may be achieved by heat exchange with superheated steam or hot process gas.

[0244] Sulfuric acid from the sulphuric acid storage tank (106) is pumped and directed to the Claus reactor (6) via line 108. The sulphuric acid is atomized into the furnace via hydraulic nozzles or preferably via pneumatic (two fluid) nozzles.

[0245] In the event of a malfunction of the sulfuric acid plant, the heated Claus tail gas (39) can be diverted to the hot incinerator (42) via line 131. Fuel (44) and combustion air (46) are supplied to ensure calorific value and oxygen for complete oxidation of the combustible substances in the Claus tail gas. The exhaust gas from the incinerator is cooled in an integrated waste heat boiler and directed via line 48 to a chimney (50).

[0246] Since the process gas temperature is not high enough to start H 2 The catalytic oxidation of S, therefore requires a startup heater (not shown) to start the sulfuric acid plant, and is preferably placed immediately upstream of the second catalytic reactor (142). The heater can be an electric heater, a fuel gas fired heater or receive a heating medium from other process equipment.

[0247] Figure 5 The configuration of the Claus reactor and the associated control scheme are shown. The Claus reactor (6) receives the following feed streams: one or more feed gases, including H 2 S (2), fuel gas (3), sulfuric acid (108) and optionally an atomizing medium (109), which is usually compressed air but can also be, for example, N 2 and steam. Each pipeline is equipped with a flow measurement device FI, which provides information about the flow to the calculation unit (1). The output of the calculation unit is the air demand, which is sent to the flow controller FIC on the combustion air pipeline (4). The combustion air flow is mainly controlled by the air demand calculated by the calculation unit (1) and to a lesser extent by measuring the H in the Claus tail gas. 2 S / SO 2 Ratio (e.g. Figure 1 The Claus tail gas (36) in the reactor is regulated.

[0248] Example

[0249] Example 1: Combustion air calculation.

[0250] Example 1.1: Calculation of combustion air demand for fuel gas

[0251] The flow of combustion air into the Claus reactor is usually controlled by measuring the flow rates of the other feed gases and, using their composition, calculating the air requirement per unit of feed gas flow. The total air requirement is calculated by adding the air requirements for each feed stream:

[0252] G 空气 =∑K i ·G i

[0253] K iis the air demand coefficient, the unit air flow per feed flow i; G i is the flow rate of feed stream i. The unit can be freely selected according to the nature of the feed stream, but care should be taken to ensure that each air demand (K i ··G i For airflow, the typical flow unit is Nm 3 / h, kg / h and kmol / h. For liquid flow, the most common is m 3 / h and kg / h.

[0254] Air demand factor K i Calculated from the composition of the feed stream. For a 100 vol% CH 4 The air requirement for the feed flow can be calculated from the following chemical reaction:

[0255] CH 4 +2O 2 →CO 2 +2H 2 O

[0256] Each CH 4 The molecule needs 2 oxygen molecules to be fully converted into CO 2 , so O 2 The demand factor K will be 2Nm per 3 O 2 / Nm 3 CH 4 . 1Nm 3 Defined as 1m at 0℃ and 1atm 3 gas, corresponding to 44.6 mol.

[0257] K can also be calculated by dividing the O 2 The mole fraction is calculated as per Nm 3 CH 4 Nm 3 Air. For dry air, O 2 The mole fraction of is 0.21, so K is 2 / 0.21=9.52Nm 3 Air / Nm 3 CH 4 .

[0258] If the CH 4 The concentration of O is only 80%. 2 The demand is only 80%, so the K value will become 9.52*0.80=7.62Nm 3 Air / Nm 3 Fuel gas.

[0259] If the fuel gas contains more than one oxygen-demanding compound (e.g. C 2 H 6 ), the air requirement for each compound is simply added to the total oxygen demand.

[0260] Example 1.2: H 2 Calculation of the demand for combustion air by S gas

[0261] Conversion of H in the feed gas 2 S of O 2 The requirement is based on the consideration that a complete H 2 S oxidation, but hope H 2 S and SO 2 The ratio is calculated in the range of 2-4.

[0262] H 2 S and SO 2 The ratio R is defined as:

[0263]

[0264] In the equation, n is the number of moles and α is the H 2 S to SO 2 On the right side of the equation, n H2S is the H in the feed gas 2 The number of moles of S.

[0265] H 2 The chemical reaction of S oxidation is

[0266] H 2 S+3 / 2O 2 →SO 2 +H 2 O

[0267] Use stoichiometry and rearrange the equation for R, O 2 The demand becomes

[0268]

[0269] where n H2S is the H in the feed gas 2 The number of moles of S, nO 2 is to obtain a given H in the converted gas 2 S and SO 2 Ratio R required O 2 Mole number. Considering the H in the feed gas 2 S concentration, yH in combustion air 2 S (mole fraction) and O 2 ,YO 2 (Mole fraction) Air demand G 空气becomes:

[0270]

[0271] K ag is the acid gas air demand factor (Nm 3 Air / Nm 3 Acid gas), G ag is the acid gas flow rate (Nm 3 / h).

[0272] Example 1.3 Calculation of the demand for sulfuric acid for combustion air.

[0273] Sulfuric acid decomposes into SO according to the overall reaction 2 , H 2 O and O 2 :

[0274] H 2 SO 4 →SO 2 +H 2 O+1 / 2O 2

[0275] Sulfuric acid directly provides O to the reaction system 2 , and also indirectly provide SO 2 , SO 2 No need to pass H 2 Oxidation of S (see Example 2). Using the same principles as described in Example 2, O 2 The requirements become:

[0276]

[0277] R is H as defined in Example 2 2 S and SO 2 Ratio, nH 2 SO 4 is the H in the sulfuric acid feed 2 SO 4 The minus sign indicates the addition of H 2 SO 4 Less O is needed 2 .

[0278] The flow rate of sulfuric acid is usually expressed in mass flow, which is based on the sulfuric acid concentration Csa (kg H 2 SO 4 / kg acid), the air demand is calculated as follows

[0279]

[0280] Msa is the mass flow rate of sulfuric acid (kg / h), Csa is the H 2SO 4 Weight fraction, YO 2 O in the combustion air 2 Molar vapor fraction, R is the H in the process gas 2 S and SO 2 proportion.

[0281] Most often, sulfuric acid is atomized into the Claus reactor via a two-fluid nozzle using compressed air as the atomizing medium. In this case, the atomizing gas flow also leads to a reduction in the combustion air requirement:

[0282]

[0283] If you use N 2 Or steam is used as the atomizing medium, the air demand coefficient will be 0.

[0284] Example 2-6: Combination of Claus process and sulfuric acid process

[0285] and Figure 1 Compared with the prior art process shown, Figure 2 The process shown analyzes five additional examples.

[0286] These examples are based on the following feed gases:

[0287] Rich in H 2 S raw gas ( Figure 1 and Figure 2 Feed gas 2):

[0288] Total gas flow: 8190Nm 3 / h

[0289] H 2 S concentration: 94 vol%

[0290] H 2 O concentration: 6 vol%

[0291] Rich in H 2 The S gas is typical of a refinery and will also contain varying amounts of light hydrocarbons.

[0292] Rich in H 2 S and NH 3 The raw gas (SWS gas, contained in the fuel (44), such as Figure 2-4 shown):

[0293] Total gas flow: 3669Nm 3 / h

[0294] H 2 S concentration: 28 vol%

[0295] NH 3 Concentration: 45 vol%

[0296] H 2 O concentration: 27 vol%

[0297] These include H 2 S and NH 3 The streams are usually the off-gas from a so-called sour water stripper and are considered SWS gases. They may also contain varying amounts of light hydrocarbons.

[0298] Gas is a mixture of light hydrocarbons (mainly CH 4 ), with a lower calorific value of 12,200 kcal / Nm 3 .

[0299] The feed stream, combustion air and Claus tail gas are preheated using heat generated by the Claus + sulfuric acid combined process.

[0300] In these examples, the Claus process recovers 94-95% of the sulfur from the feed, ie, a well-functioning Claus plant with only 2 catalytic stages is possible.

[0301] Example 2: Sequential Claus + sulfuric acid process according to prior art

[0302] In Example 2, all feed streams are treated in the Claus process, providing a stream of 11.7 t / h elemental sulfur and a Claus tail gas, which contains about 5% sulfur in the feed gas. In the Claus tail gas burner, the sulfur species present in the Claus tail gas are oxidized, and a fuel gas is provided to maintain a burner temperature of 1,000°C so that all reducing species, such as CO, COS, H 2 , H 2 S, SX and CS 2 , is completely oxidized to CO 2 , H 2 O and SO 2 .

[0303] The output of concentrated sulfuric acid is 2.4t / h, based on 100% w / w H 2 SO 4 calculate.

[0304] The total recovery of sulfur and sulfuric acid is greater than 99.9% of the sulfur in the feed, complying with even stringent environmental regulations.

[0305] Example 3: H 2 SO 4 Recycle to the Claus reactor.

[0306] In this embodiment, H 2 SO 4The entire acid production of the sulfuric acid process is not required as a product and is recycled to the Claus reactor. 2 SO 4 The recycle amount corresponds to about 6% of the total sulfur in the feed stream.

[0307] The total elemental sulfur product flow rate is now equal to the S in the feed stream, which is 107% of the base case described in Example 3.

[0308] Due to H 2 SO 4 The temperature in the Claus reactor drops by about 200°C due to the evaporation and decomposition of the hydrocarbons and NH 3 The lowest temperature for complete combustion. No fuel gas is required in the Claus reactor.

[0309] Due to H 2 SO 4 It is an excellent O 2 carrier, the combustion air demand is reduced, so with the inert N 2 The reduction in flow rate reduces the amount of process gas. In general, due to the 2 The reduction in flow rates reduces process gas flow from the Claus reactor to 94% of base flow, while process gas flow from the Claus tail gas burner is reduced to 93%. Since less process gas needs to be heated to 1000°C in the Claus tail gas burner, fuel gas consumption is only 92% of the base case.

[0310] It has been found that recycled H 2 SO 4 The benefits are surprisingly high, since not only does the sulfur formation capacity of the Claus plant increase by 7%, but at the same time the process gas volume is reduced by 6-7%. This corresponds to an increase in the Claus plant capacity of approximately 15%, provided that the process gas flow rate is 100% of the base case.

[0311] Example 4: H 2 SO 4 Recirculate to the Claus reactor, and the SWS gas bypasses the Claus tail gas burner.

[0312] In this embodiment, by bypassing a portion of the SWS gas to the Claus tail gas burner, the fuel gas consumption in the Claus tail gas burner has been minimized. SWS gas has a high calorific value and is easily used as a fuel gas. Concentrated H 2 S feed gas, but since SWS gas may cause problems in the Claus process but not in the WSA process, bypass SWS gas is more effective than bypass H 2 SWS gas has greater benefits. For process gas, the gas volume will also be reduced because the NH 3Increased process gas volume in the Claus process due to NH 3 Burning to N 2 and H 2 O requires oxygen (air).

[0313] Adjust the SWS gas recirculation volume to make the Claus tail gas burner reach 1,000℃ to ensure that the reducing substances in the Claus tail gas, such as H 2 S, COS, CO, H 2 , SX and CS 2 Completely burnt out.

[0314] NH 3 The combustion will mainly form N 2 , but a small amount of NO may also be formed X Depending on the concentration, it may be necessary to reduce NO X SCR catalyst. SCR catalyst needs NH 3 To restore NO X , which can be obtained from NH 3 Supplied from storage or obtained from SWS gas.

[0315] Since the fuel gas in the Claus tail gas burner now contains H 2 S, H 2 SO 4 The production of sulfur will increase, now accounting for about 13% of the sulfur in the feed stream. The large amount of sulfuric acid recycle leads to a significant reduction in Claus reactor temperature.

[0316] By appropriate preheating of the feed stream, sufficiently high temperatures can still be achieved in the Claus reactor without the need for auxiliary fuel.

[0317] The impact on the scale of the Claus process is huge: the process gas volume is reduced to 65% of the base case, still producing 107% of elemental sulfur. This process gas volume reduction can be used to increase the capacity of existing equipment or significantly reduce the cost of new equipment.

[0318] Since the process gas flow is only 90% of the base case flow, the sulfuric acid plant will be smaller. This is surprising because the H 2 SO 4 Production has more than doubled, but this is mainly due to a significant reduction in Claus tail gas flow.

[0319] Most notable is the reduction in fuel gas consumption, which is now only 16% of the base case flow rate, helping to significantly reduce operating costs for the integrated Claus + sulfuric acid process.

[0320] Example 5: H 2 SO 4Recirculation and SWS gas completely bypasses the Claus tail gas burner

[0321] This example focuses on completely eliminating SWS gas entering the Claus plant, ensuring that ammonia salts cannot form in the sulphur condenser, thereby reducing the risk of Claus plant failure.

[0322] The process gas flow from the Claus reactor is 69% of the base case, but slightly higher than in Example 3 where only a portion of the SWS gas is bypassed. The increase in process gas flow is due to the need to add fuel gas to the Claus reactor to maintain a higher operating temperature.

[0323] WSA device H 2 SO 4 Production has now increased to 17% of the S in the feed gas, at which point recirculation of the entire production quenches the Claus reactor temperature to the point where fuel gas is required. Due to the increased sulfur feed to the sulfuric acid plant, process gas from the Claus tail gas burner has increased to 107% of the base case.

[0324] Even though the Claus reactor requires fuel gas, the total flow of fuel gas is only 41% of the base case.

[0325] From the perspective of equipment scale and operating cost, this embodiment seems to be not as optimal as Embodiment 3, that is, there is an optimal H 2 SO 4 Recycle ratio, which depends on the actual feed gas flow and composition. Bypassing more feed gas will lead to increased sulfuric acid production, which will make the Claus reactor more quenched, which in turn will require more fuel gas, so the Claus tail gas flow will increase.

[0326] For the above feed gas composition and flow rate, the best choice with respect to plant size and fuel consumption is H 2 SO 4 The recycle rate is between 13% and 17% of Sfeed in the feed stream.

[0327] Generally speaking, the optimum feed gas bypass is close to the point where the Claus reactor is operating at the minimum allowable temperature, i.e., feed can be bypassed to produce more sulfuric acid until the Claus reactor temperature reaches the thermal destruction limit of hydrocarbons and sulfuric acid. Increasing the feed bypass ratio will reduce the fuel gas demand in the Claus tail gas burner, but will greatly increase the fuel gas consumption in the Claus reactor because the fuel gas in the Claus reactor needs to vaporize and decompose the sulfuric acid and heat the process gas, while in the Claus tail gas burner, only the process gas needs to be heated.

[0328] For raw gas, for example, 50 vol% H 2 S, best H 2 SO 4The recycle rate is ~7% of the S feed in the feed stream. Due to the relatively low H 2 The S concentration results in a lower temperature in the Claus reactor, so sulfuric acid will quickly reduce the temperature, requiring the addition of fuel gas to the Claus reactor. Using oxygen-enriched air in the Claus reactor will allow for higher H 2 SO 4 Recirculation flow.

[0329] Example 6: H 2 SO 4 The recirculation bypasses the SWS gas to the Claus tail gas burner and uses oxygen-enriched air.

[0330] To increase the capacity of a Claus plant, a known modification option is to install special burners that can handle gas containing > 21 vol% O 2 Oxygen-enriched air, commonly known as O 2 The quality is 93-99vol%O 2 .

[0331] In this example, a Claus process containing 80 vol% O 2 oxygen-enriched air is used in the sulfuric acid process, while atmospheric air is used in the sulfuric acid process.

[0332] The effect of oxygen-enriched air is a significant reduction in the process gas flow rate out of the Claus reactor, mainly due to the 2 Traffic-related N 2 In addition, lower process gas flows allow the Claus reactor to operate without adding fuel, as less inert gas needs to be heated.

[0333] Since the process gas flow from the Claus reactor is now reduced to only 38% of the base case, the Claus tail gas feed to the Claus tail gas burner is also significantly reduced. The process gas to the Claus tail gas burner is only 56% of the base case, which is higher than the Claus unit flow due to the large amount of SWS gas bypass to the WSA unit.

[0334] Using this layout, even in the sulfuric acid process, 2 SO 4 At such high recycle flows it is also possible to operate without fuel gas in both the Claus and the sulphuric acid processes.

[0335] Examples 2-6 are summarized in Table 2, which shows the potential for increased sulfur production, reduced fuel gas consumption and possible plant size reduction by a thoughtful modification of a Claus process plant by incorporating a sulfuric acid process. It is further seen that when more sulfuric acid is recycled, fuel gas consumption decreases.

[0336] Table 2

[0337]

Claims

1. A method for modifying a sulfur emission reduction device, the device comprising a Claus process device for producing elemental sulfur, the Claus process device comprising a Claus reactor and one or more Claus conversion stages, each Claus conversion stage comprising a conversion reactor and a device for condensing elemental sulfur, and a Claus tail gas oxidation device configured to receive Claus tail gas from the Claus process device and configured to provide oxidized Claus tail gas, The transformation method comprises the following steps: a. Provide tail gas treatment equipment for the production of sulfuric acid to produce sulfuric acid, and b. providing a device for transferring all sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid to the Claus reactor, Characterized in that the molar number of sulfur in the transferred sulfuric acid is 3% to 17% relative to the molar number of elemental sulfur taken out from the Claus process equipment.

2. The conversion method according to claim 1, further comprising the step of limiting the number of Claus conversion stages to two if the Claus process plant comprises more than two Claus conversion stages.

3. The transformation method according to claim 1 or 2, wherein step (a) includes providing a tail gas treatment device for producing sulfuric acid, the device comprising a catalytic SO2 converter, the converter containing a material having catalytic activity for the oxidation of SO2 to SO3, and configured to receive the oxidized Claus tail gas and to provide a SO2 converter exhaust gas; a sulfuric acid unit, which is configured to receive the SO2 converter exhaust gas and produce concentrated sulfuric acid by condensation of hydrated SO3 or by absorption of SO3 in sulfuric acid.

4. The transformation method according to claim 1 or 2, further comprising the step of providing a device for temporarily storing sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid, wherein the device for temporarily storing sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid has a volume corresponding to the amount of sulfuric acid produced by the tail gas treatment equipment for producing sulfuric acid within 4 hours to 120 hours, wherein the device for storing sulfuric acid is configured to receive sulfuric acid from the tail gas treatment equipment for producing sulfuric acid and guide the sulfuric acid to the Claus reactor.

5. The modification method according to claim 1 or 2, comprising the step of providing a flow control device, which is configured by a user to allow the outlet from the Claus tail gas oxidation unit to bypass the tail gas treatment equipment for producing sulfuric acid.

6. The conversion method according to claim 1 or 2, comprising the step of providing a device for catalytically oxidizing at least a certain amount of the Claus tail gas.

7. The conversion method according to claim 6, wherein the device for catalytic oxidation is configured to receive at least a certain amount of Claus tail gas and combine it with one or more of an oxidant, a heating gas, a recirculated process gas and a heat exchanger so that the inlet temperature of the catalytic oxidation device is higher than 200°C and the outlet temperature of the catalytic oxidation device is lower than 500°C.

8. The conversion method according to claim 1 or 2, wherein the Claus reactor is provided with one or more inlet nozzles configured for atomizing the amount of sulfuric acid into a droplet size distribution wherein 90% by mass of the droplets have a diameter of less than 500 μm.

9. The reconstruction method according to claim 8, wherein the inlet nozzle is a pressure nozzle or a two-phase nozzle.

10. The retrofitting method of claim 8, wherein the inlet nozzle is located at a distance downstream of the gas inlet of the Claus reactor corresponding to a residence time of at least 1 second for the process gas.

11. The conversion method according to claim 1 or 2, wherein the volume of the Claus reactor is extended so that the residence time of the process gas is increased by at least 1 second.

12. The reconstruction method according to claim 1 or 2, wherein the Claus reactor is provided with a device for impingement.

13. The reconstruction method according to claim 1 or 2, wherein the Claus reactor is provided with a device for enhancing turbulence.

14. A process according to claim 1 or 2, wherein the control scheme for the amount of oxygen introduced into the Claus reactor is modified to depend on a combination of a feedforward control based on the amount and composition of the feedstock and sulfuric acid and a feedback control based on the ratio of H2S to SO2 in the inlet stream of the final Claus conversion stage or in the outlet stream of the final Claus conversion stage.

15. The reforming method according to claim 1 or 2, wherein the outlet of the Claus reactor is guided to a SO3 protection device to absorb or convert SO3 to provide a Claus reactor outlet gas free of SO3.

16. The transformation method according to claim 1 or 2, wherein the concentrated sulfuric acid contains 90% w / w to 98.5% w / w H2SO4.

17. The reforming method of claim 12, wherein the means for impacting is a grid wall or a bed of packing material.

18. The process of claim 13, wherein the means for turbulence enhancement is a vector wall, a choke ring or an inlet tangential to the Claus reactor.

19. The transformation method according to claim 4, wherein the device for temporarily storing sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid has a volume corresponding to the amount of sulfuric acid produced by the tail gas treatment equipment for producing sulfuric acid within 8 hours to 50 hours.

20. The transformation method according to claim 4, wherein the device for temporarily storing sulfuric acid produced in the tail gas treatment equipment for producing sulfuric acid has a volume corresponding to the amount of sulfuric acid produced by the tail gas treatment equipment for producing sulfuric acid within 24 hours to 120 hours.

21. The transformation process according to claim 16, wherein the concentrated sulfuric acid contains 90% w / w to 98% w / w H2SO4.

22. The process of claim 1, wherein the molar amount of sulfur in the transferred sulfuric acid is between 5% and 17% relative to the molar amount of elemental sulfur removed from the Claus process unit.

Images