RU2822142C2 - Method of producing sulphur and sulphuric acid - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a process plant and a method of producing sulphur from feed gas. Method of producing sulphur consisting of 15 vol.%, 20 vol.%, 30 vol.%, 40 vol.% or 50-99 vol.% or 100 vol.% of H₂S, and a stream of sulphuric acid includes the following steps: g. providing a Claus reaction furnace feed stream containing said feed gas, an amount of sulphuric acid, an amount of oxygen and optionally an amount of fuel, where amount of oxygen is substoichiometric, h. direction of said Claus reaction furnace feed stream into Claus reaction furnace operating at high temperature, such as above 900 °C, providing feed gas for Claus converter, i. cooling said feed gas for the Claus converter to provide a cooled feed gas for the Claus converter and optionally removing elementary sulphur from the gas, j. direction of said cooled feed gas for Claus converter after optional pre-heating for contact with a substance catalytically active in Claus reaction, k. removing the residual Claus reaction gas and elemental sulphur, optionally by cooling the effluent, from said substance catalytically active in the Claus reaction, l. directing a flow containing said residual Claus reaction gas to treating the residual Claus reaction gas, where said sulphuric acid directed into said Claus reaction furnace is in the form of droplets with a droplet size distribution characterized by fact that 90% of the mass of the droplets have diameter below 500 mcm, 200 mcm or 100 mcm, with the accompanying advantage of such a method, which effectively converts all liquid H₂SO₄ into gaseous H₂SO₄, and then into SO₃ and, ultimately, into SO₂, which is well suited for the Claus process.

EFFECT: high efficiency of producing elementary sulphur.

12 cl, 3 dwg, 2 tbl

Description

The present invention relates to a process for converting H ₂ S into elemental sulfur and sulfuric acid, optionally at a specified ratio between elemental sulfur and sulfuric acid.

H ₂ S is a common by-product in many processes, including hydrodesulfurization of refinery streams and rayon production. It is advisable to convert H ₂ S before release to the atmosphere because H ₂ S is highly toxic, has an unpleasant odor and is hazardous to the environment.

Petroleum refining processes, in addition to producing the well-known highly concentrated H ₂ S gas, can often also produce so-called sour water stripper gas, which contains H ₂ S, H ₂ O and NH ₃ in approximately equal molar quantities.

In particular, in oil refineries, the Claus process, which has been known and optimized for more than 8 decades, was chosen as the process to reduce _H2S emissions. The Claus process occurs by substoichiometric combustion of H ₂ S to form SO ₂ in a Claus reaction furnace, providing the feed gas for the Claus converter. In subsequent stages of the Claus process, H ₂ S and SO ₂ are converted to form elemental sulfur, which can be condensed and removed.

Typically, the sulfur removal efficiency of the Claus process is 95% to 98%, which is not sufficient to meet environmental regulations. Therefore, it is common practice to treat residual gases from the Claus process to ensure sulfur reduction above 99%. Residual gas treatment is sometimes carried out in a sulfuric acid plant, which requires handling of sulfuric acid.

It has now been found that sulfuric acid can be recycled to the Claus reaction furnace, where it can promote sulfur formation and also provide opportunities for optimizing Claus process equipment size and operating costs.

WO 2012/152919 A1 presents a sulfuric acid method for treating Claus reaction tail gas, which describes the conversion of H ₂ S to H ₂ SO ₄ in the Claus reaction tail gas. The method steps are as follows:

1. Substoichiometric oxidation

2. Transformation according to the Klass reaction

3. Oxidation of reduced sulfur compounds (H ₂ S) in the residual gas of the Claus reaction in an oxygen-enriched atmosphere at 400-700°C

4. Catalytic oxidation of SO ₄ to SO ₃

5. Condensation of H ₂ SO ₄

It is recognized that the H ₂ SO ₄ product is not always desirable and it is proposed to recycle the sulfuric acid to the upstream Claus reaction step or to the H ₂ S oxidation step as described above. However, sulfuric acid recycling is considered simply as a reduction in sulfuric acid emissions, and the effects of H ₂ SO ₄ recycling on wet sulfuric acid or the Claus process have not been assessed, i.e. It is not recognized that recycling H ₂ SO ₄ makes it possible to reduce the amount of O ₂ (in the form of air, enriched air or pure oxygen) sent to the Claus reaction furnace, as well as realize the positive effect on the Claus reaction and sulfuric acid processes.

WO 2012/152919 A1 also discloses that auxiliary fuel may be required in both the Claus reaction furnace stage and the H ₂ S oxidation stage to obtain the desired operating temperature, without reference to realizing the beneficial effects of using feed gases as auxiliary fuel for oxygenation H ₂ S in the sulfuric acid process.

Thus, the proposal to recycle H ₂ SO ₄ into the Claus reaction furnace does not in itself provide a working method, but requires additional modifications to the method.

The present invention provides a process for converting H ₂ S to elemental sulfur with increased efficiency, which combines the Claus process with the sulfuric acid process. According to this method, sulfuric acid produced in the sulfuric acid Claus reaction tail gas process is recycled to the Claus reaction furnace to decompose and produce elemental sulfur.

For the purposes of the present invention, the stoichiometric amount of oxygen must be determined by assuming that the products derived from N, H, C, S and O in the feed gas are N ₂ , H ₂ O, CO ₂ and SO ₂ . If a lower than stoichiometric (also called substoichiometric) amount of oxygen is present, this means that not all components of the feed are fully oxidized. For Claus reaction feed gas, this means that the process gas after substoichiometric combustion/reaction may contain unreacted H ₂ S, NH ₃ and hydrocarbons from the feed stream(s), as well as H ₂ , CO, COS and CS ₂ formed in the environment with O ₂ deficiency.

For the purposes of this application, a fuel is defined as a substance whose composition upon oxidation of O ₂ produces N ₂ , H ₂ O, CO ₂ and SO ₂ as a reaction product and releases a significant amount of energy as a result of the reactions. A mixture of hydrocarbons (eg natural gas with CH ₄ and C ₂ H ₆ ) and H ₂ S is a typical fuel gas, but fuel gas may also contain CO, NH ₃ and H ₂ .

For the purposes of the present invention, oxygen (O ₂ ) refers to an O ₂ containing stream such as air, enriched air and pure oxygen, but may also be other O ₂ containing gas.

According to a broad aspect, the present invention relates to a process for producing sulfur from a feed gas consisting of 15%, 20%, 30 vol.%, 40 vol.% or 50% - 99 vol.% or 100 vol.% H ₂ S, and a stream sulfuric acid, including stages

a. providing a Claus reaction furnace feed stream containing said feed gas, an amount of sulfuric acid, an amount of oxygen, and optionally an amount of fuel, where the amount of oxygen is substoichiometric,

b. directing said Claus reaction furnace feed stream to a Claus reaction furnace operating at an elevated temperature, such as above 900°C, providing feed gas for the Claus converter

c. cooling said feed gas for the Claus converter, providing cooled feed gas for the Claus converter and optionally removing elemental sulfur from the gas

d. directing said cooled feed gas to the Claus converter, after optional preheating, into contact with a substance catalytically active in the Claus reaction,

e. removing residual Claus reaction gas and elemental sulfur, optionally by cooling the effluent, from said Claus reaction catalytically active substance,

f. directing a stream containing said residual Claus reaction gas to treat the residual Claus reaction gas,

wherein said sulfuric acid sent to said Claus reaction furnace is in the form of droplets with a droplet size distribution characterized in that 90% of the droplet mass has a diameter below 500 µm, 200 µm or 100 µm, with the concomitant advantage of such a process effectively converting all liquid H ₂ SO ₄ into gaseous H ₂ SO ₄ and then into SO ₃ and ultimately into SO ₂ , which is well suited to the Claus process.

According to another embodiment, at least an amount of sulfuric acid is directed into said Claus reaction furnace through at least one air nozzle, producing sulfuric acid and an atomizing medium, with the concomitant advantage of such a nozzle producing fine droplets suitable for rapid evaporation. Air nozzles are also known to one skilled in the art as "pneumatic atomizers" or "two-phase nozzles."

According to another embodiment, the atomizing medium is compressed air and the flow is between 25 Nm ³ air/ton acid or 50 Nm ³ air/ton acid l 200 Nm ³ air/ton acid or 500 Nm ³ air/ton acid, with the attendant advantage such a nozzle, operating at these parameters, with the formation of small droplets with a low flow rate of the atomizing medium.

In another embodiment, at least an amount of sulfuric acid is directed into said Claus reaction furnace through at least one hydraulic nozzle designed to produce fine droplets, with the attendant advantage of a hydraulic nozzle that is easy to operate, producing sufficiently fine droplets, without diluting the process gas any spray medium.

In another embodiment, the average residence time of the process gas in the Claus reaction furnace is less than 5 seconds, more preferably less than 2 seconds, with the corresponding advantage of such a reaction furnace being suitably sized while still allowing sufficient time for the sulfuric acid droplets to evaporate, as well as the necessary partial chemical conversion of H ₂ S and SO ₂ to elemental sulfur.

In another embodiment, the Claus reaction furnace includes one or more turbulence enhancers with the associated benefit of reducing residence time, temperature, and gas composition distribution in the Claus reaction furnace.

According to another embodiment, the Claus reaction furnace includes an impacting means, such as an impact wall or volume filled with inert material, with the corresponding advantage of breaking the droplets upon impact to ensure that there is no liquid H ₂ SO ₄ in the feed gas to the Claus converter.

According to another embodiment, said treatment of the Claus reaction tail gas comprises the steps

g. directing a stream containing said Claus reaction residual gas, oxygen and fuel as feed gas into a Claus reaction residual gas combustion chamber operating at a temperature above 900° C. or an oxidation catalyst providing feed gas for the SO ₂ converter,

h. directing said feed gas to the SO ₂ converter into contact with a substance catalytically active in the oxidation of SO ₂ to SO ₃ , providing a gas enriched in SO ₃ ,

i. converting said _SO3 -rich gas into concentrated sulfuric acid, either by absorption of _SO3 by sulfuric acid or by hydration of _SO3 , cooling and condensation of the sulfuric acid,

j. recycling at least a portion of the resulting sulfuric acid to a Claus reaction furnace,

with the attendant advantage of such a process having high conversion and thermal efficiency and avoiding the unwanted formation of sulfuric acid. The use of a Claus reaction furnace and a Claus reaction tail gas combustor operating at temperatures above 900° C. ensures complete conversion of the components present, and this may not necessarily require the presence of fuel in addition to the feed gas. In addition, homogeneous Claus reactions will take place in the Claus reaction furnace, so that sulfur can be removed while cooling the feed gas for the Claus converter. The stream fed to the Claus tail gas combustor may typically include H ₂ S as a Claus tail gas fuel, and/or a separate stream containing H ₂ S, a hydrocarbon, or other fuel. In addition to the mentioned method steps, the method may include additional steps, such as heat exchange to change the temperature (or otherwise condition the process streams) to a range appropriate to the processes occurring.

According to another embodiment, the Claus reaction furnace feed gas contains less than 0.1 vol.% non-elemental nitrogen, such as NH ₃ , with the concomitant advantage of preventing the formation of, for example, ammonium salts that could plug the Claus condenser(s).

In another embodiment, the Claus reaction furnace feed stream contains less than 50%, 20%, 10%, or 1% elemental nitrogen with the attendant advantage of providing a high temperature process in the Claus reaction furnace and a reduced volume of process gas due to the reduced presence of N ₂ avoiding at the same time, excessive temperatures are lower downstream, since the evaporation of sulfuric acid cools the process gas. This can be achieved by using pure _O2 or oxygen enriched air as an oxygen source.

In an alternative process, steps d and e are performed 2-5 times sequentially, which has the advantage of providing higher conversion in the process.

In another embodiment, the H ₂ S:SO ₂ ratio of said Claus converter feed gas is less than 4:1, 3:1 or 2:1, with the concomitant advantage of such feed gas providing a residual Claus reaction gas containing H ₂ S to the chamber combustion of the Claus reaction tail gas, minimizing the need to add fuel gas since the oxidation of H ₂ S releases a significant amount of energy, whereas SO ₂ releases no energy in the Claus reaction tail gas combustion chamber.

In another embodiment, the H ₂ S:SO ₂ ratio of said Claus converter gas is less than 1.6:1, 1.8:1, or 2:1, with the concomitant benefit of having a substantially H ₂ S-free Claus reaction tail gas. In a downstream sulfuric acid plant this may be advantageous since the _SO2 will not be oxidized without a _SO2 conversion catalyst and thus the tail gas of the Claus reaction can be preheated with a combination of _SO2 catalytic oxidation (controlled feed gas bypass containing H ₂ S) and process gas recirculation around the H ₂ S oxidation catalytic process so that the temperature rise across the H ₂ S oxidation catalyst can be precisely controlled. With an unknown and/or varying concentration of _H2S in the tail gas of the Claus reaction, there is a high risk of overheating of the _H2S oxidation catalyst.

According to another embodiment, the method further includes the step of directing an amount of additional feed gas to said Claus reaction residual gas combustion chamber with the attendant advantage of providing additional sulfur and fuel for the sulfuric acid process. The additional feed gas may contain impurities that may be burned prior to treatment by the sulfuric acid process, and/or hydrogen sulfide and other fuels that may contribute to the production of sulfuric acid and combustion of the residual Claus reaction gas in the combustion chamber. If the additional feed gas contains a large amount of inert gases or sulfur-free fuel, the method also has the advantage of avoiding the increase in size of the Claus converter due to the secondary stream. The additional feed gas may come from the same source as the feed gas or from a different source.

According to another embodiment, said additional feed gas contains more than 5 vol.% non-elemental nitrogen, such as ammonia, with the concomitant advantage of providing a process in which components of non-elemental nitrogen that may be difficult to oxidize in the substoichiometric atmosphere of a Claus reaction furnace can be directed into the combustion chamber of the residual gas of the Claus reaction. This process may be particularly advantageous if the additional feed gas is sour water stripper (SWS) gas containing 10 vol%-50 vol% H ₂ S, 10 vol%-50 vol% NH ₃ and 10 vol%-50 vol% NH 3 H ₂ O - where in the Claus process only H ₂ S is desired and NH ₃ is problematic in the Claus process due to potential plugging with ammonium salts. Instead, such SWS gas can be sent to a sulfuric acid plant, where NH ₃ works well due to the excess oxygen that prevails there.

In another embodiment, the amount of sulfur in the additional feed gas is at least 1%, 2% or 5% of the total elemental sulfur removed from the process, with the concomitant advantage of such feed gas being able to provide thermal energy as well as contribute in reducing sulfur.

In another embodiment, the Claus catalytically active substance comprises activated aluminum (III) oxide or titanium (IV) oxide, with the concomitant benefit of such a substance providing an efficient elemental sulfur production process.

According to another embodiment, step (d) is carried out at a pressure of 200 mbarg. up to 700 mbarg, temperatures from 200°C to 350°C and flow rates from 800 Nm ³ /h/m ³ to 3000 Nm ³ /h/m ³ , with the concomitant advantage of such conditions being effective for the production of elemental sulfur.

According to another embodiment, step (d) is carried out at a temperature of from 100°C to 150°C, and step (e) includes the step of periodically heating the specified substance, catalytically active in the Claus reaction, to ensure the removal of condensed elemental sulfur into the liquid or gas phase, with the concomitant advantage of low temperature being favorable for achieving very high conversions of SO ₂ and H ₂ S to elemental sulfur, both due to the low temperature and the removal of the reaction product, providing even better conditions for high.

According to another embodiment, said substance catalytically active in converting SO ₂ to SO ₃ contains vanadium, with the concomitant advantage of such a substance providing an efficient method for producing sulfuric acid.

According to another embodiment, said step (h) of oxidation of SO ₂ to SO ₃ is carried out at a pressure of 50 mbarg to 200 mbarg, a temperature of 370° C. to 530° C. and a space velocity of 800 Nm ³ /h/m ³ to 1500 Nm ³ /h/m ³ , per catalyst bed, with the concomitant advantage of conditions that are effective in oxidizing SO ₂ to form SO ₃ .

In another embodiment, the amount of sulfur in the sulfuric acid stream is greater than 1%, 3%, or 5% and less than 17%, 21%, or 25% of the total elemental sulfur removed from the process. Recirculation above the lower limits has the advantage of having the effect of reducing the volume of process gas, while recirculation below the upper limits avoids the situation where additional fuel must be added to the Claus reaction furnace, resulting in additional process volume and operating costs.

In another embodiment, the sulfuric acid in the sulfuric acid stream is atomized in said Claus reaction furnace using air nozzles (powered by compressed air or other compressed gas such as steam or nitrogen) or hydraulic nozzles (also known as pressure nozzles), and wherein the residence time in the Claus reaction furnace is at least 0.5 seconds, 1 second or 1.5 seconds, with the associated advantage of such a residence time being sufficient for complete evaporation of the sulfuric acid droplets.

According to another embodiment, the molar ratio of H ₂ S:O ₂ components sent to the Claus reaction furnace is at least 2.5, with the concomitant advantage of such low oxygen content providing substoichiometric partial conversion of H ₂ S to SO ₂ by contribution of thermal dissociation of H ₂ SO ₄ by adding the remaining O ₂ to obtain the desired H ₂ S:SO ₂ ratio of 2.0 in the feed gas for the Claus converter.

In another embodiment, the amount of gas in the process is cooled and directed upstream to control the process temperature, allowing active temperature control of highly exothermic processes.

In another embodiment, one or more streams directed to said Claus reaction furnace are preheated by heat exchange with the hot process stream, thereby minimizing or avoiding auxiliary fuel requirements to achieve the desired temperature for sulfuric acid vaporization and feed conversion.

In another embodiment, one or more streams directed to said Claus reaction tail gas combustion chamber is preheated by heat exchange with the hot process stream with the corresponding advantage of minimizing or eliminating the requirement of auxiliary fuel to achieve the desired combustion temperature and subsequent SO ₂ oxidation.

According to another embodiment, at least one of said catalytically active substances for the oxidation of SO ₂ to SO ₃ or H ₂ S to elemental sulfur and/or at least one product withdrawn from one of said catalytically active substances is cooled by heat exchange, such as an interlayer heat exchange or internally cooled catalytic reactor, with the concomitant advantage of allowing the temperature of highly exothermic processes to be actively controlled by an interlayer heat exchange or internally cooled catalytic reactor, such as a boiling water reactor having a tubular or plate cooling loop.

According to another aspect, the present invention relates to a process plant comprising a Claus reaction furnace, a Claus recovery boiler, a Claus conversion section, a Claus reaction residual gas combustion chamber, and a sulfuric acid section, where the Claus reaction furnace has a furnace inlet, an acid nozzle inlet and an outlet, a recovery The Claus boiler has a gas inlet, a gas outlet and an elemental sulfur outlet, the Claus conversion section has a gas inlet, a gas outlet and an elemental sulfur outlet, the Claus reaction tail gas combustion chamber has an inlet and an outlet, and the sulfuric acid section has an inlet. for gas, a gas outlet and a sulfuric acid outlet, and wherein the Claus reaction furnace inlet is configured to receive feed gas and oxidant, and the Claus reaction furnace outlet is configured for liquid communication with the Claus recovery boiler inlet, where the Claus recovery boiler outlet is configured for liquid communication with an input of the Claus conversion section, and wherein the input of a Claus reaction residual gas combustion chamber is configured for liquid communication with an output of said Claus conversion section output for gas, wherein the output of the Claus reaction residual gas combustion chamber is configured for liquid communication with an input of a sulfuric acid section different further in that the sulfuric acid outlet of the sulfuric acid section is in fluid communication with the acid nozzle inlet of said Claus reaction furnace, with the attendant advantage of such a process avoiding unwanted production of sulfuric acid as well as reducing the volume of process gas.

According to another embodiment, the process unit further comprises a sulfur storage tank having a volume corresponding to the amount of sulfuric acid withdrawn from the sulfuric acid outlet of the sulfuric acid section in 1 day to 4 days, with the concomitant advantage of separating the Claus process and the sulfuric acid process, providing stabilized operation of the process unit

The present invention describes a combination of the Claus process and the sulfuric acid process that can efficiently produce the amount of sulfuric acid needed for a process plant, or even avoid the production of sulfuric acid and convert excess sulfuric acid into elemental sulfur that can be transported to other locations.

For maximum conversion to elemental sulfur, 1/3 of H ₂ S should be converted to SO ₂ .

The stoichiometric ratio between H ₂ S and SO ₂ is controlled by controlling the amount of oxygen in the Claus reaction furnace. Oxygen is usually supplied with atmospheric air, but can also be air enriched with O ₂ or even pure O ₂ .

The addition of oxygen to the Claus reaction furnace must also take into account the amount of NH ₃ , CO, H ₂ and hydrocarbons in the feed streams.

If the combustion temperature in the Claus reaction furnace is less than 1100°C, the conversion of, for example, NH ₃ may be incomplete. The consequence of this will be that the feed gas to the Claus converter has the potential to form ammonia salts such as (NH ₄ ) ₂ SO ₄ and (NH ₄ ) ₂ S ₂ O ₃ which can plug the Claus condenser.

The partially oxidized Claus converter feed gas is then converted to elemental sulfur by the following reactions at temperatures typically above 200° C. in the presence of a catalytically active substance such as activated alumina (III) or titanium (IV) oxide.

Often 3-4 Claus converters are operated in series to maximize conversion, which increases the cost of a Claus installation.

Temperature control in the Claus process is important to ensure that the elemental sulfur produced in the catalyst remains gaseous so that it condenses only at the desired position in the process. Another limitation stems from the fact that since the Claus process is exothermic, it is advantageous to operate at low temperatures.

An alternative to the above process is the so-called sub-dew point Claus process, in which the catalytically active substance is operated at temperatures at which elemental sulfur is not in the gas phase. For such a Claus process at temperatures below the dew point, an appropriate condensed sulfur removal circuit will be required, i.e. pulsing the temperature and purging elemental sulfur with an inert gas.

Even with 3-4 Claus converters/capacitors/superheaters connected in series, it is impossible to achieve sulfur recovery greater than -98%, which is not enough to meet most environmental regulations. Therefore, a Claus plant is usually equipped with a so-called residual gas Claus reaction plant, one example of which is the sub-dew point process mentioned above. There are many residual gas processes with different characteristics. To achieve very high removal efficiencies, these residual gas Claus reaction plants become more complex and approach the same cost as the Claus plant itself.

The resulting elemental sulfur generally has no direct use in plants producing waste streams containing H ₂ S, but elemental sulfur is easily transported to other sites and stored for long periods of time.

A common alternative to the Claus process is to convert _H2S to sulfuric acid, i.e. the so-called wet sulfuric acid process. The resulting sulfuric acid can be used in other chemical processes in the plant. The wet sulfuric acid process can also be a purification of residual gases from a Claus process plant. A similar process using dry sulfuric acid may also have application in this regard.

Sulfuric acid processes oxidize _H2S to _SO2 , typically in a Claus reaction tail gas combustion chamber, and _SO2 to _SO3 , and then hydrate _SO3 to sulfuric acid, or by reaction with water in the gas phase in what is called wet sulfuric acid. process, or by absorption in concentrated sulfuric acid in the so-called contact process or dry process. The reaction temperature for the oxidation of SO ₂ to SO ₃ will be in the range of 370-530°C in the presence of a catalytically active substance, usually including vanadium. Typically, wet sulfuric acid processes produce sulfuric acid concentrations in the range of 92%-98%, while dry sulfuric acid processes can also produce sulfuric acid concentrations above 98%.

Additionally, it may also be attractive to collect high pressure steam in the range of 30 barg. up to 80 barg from highly exothermic processes with sulfuric acid, whereas the Claus process will only produce lower pressure steam.

However, producing large quantities of sulfuric acid may be less attractive, even if the sulfuric acid is sold commercially, since transporting sulfuric acid is complex and regulated.

The reactions occurring in the sulfuric acid process (dry and wet) are

The general reaction of the sulfuric acid process can be described according to

The wet sulfuric acid process as a conventional tail gas solution for the Claus reaction provides a solution that meets environmental regulations at lower capital and operating costs than alternatives. The only drawback of the wet sulfuric acid process so far has been the production of sulfuric acid, which is not always desirable.

It has now become clear that combining the Claus process and the sulfuric acid process can also be accomplished by recycling all or substantially all of the sulfuric acid produced to the Claus reaction furnace. With the new invention, the integrated Claus/wet sulfuric acid process eliminates the disadvantage associated with the inconvenient sulfuric acid product and at the same time reduces the plant size of both the Claus process and the wet sulfuric acid process.

Combustion of sulfuric acid is known for the regeneration of spent sulfuric acid in a wet sulfuric acid process plant, but has not been used in practice in a Claus process reaction furnace or under Claus process conditions.

Although sulfuric acid injection into a wet sulfuric acid process plant and a Claus plant have similarities, the purpose and conditions are significantly different. In a wet sulfuric acid process plant _, the main purpose of waste sulfuric acid injection is to burn the tarry compounds present in the acid, while = _H2SO4 and _SO3 are not relevant since downstream processes will convert the sulfur compounds to _{H2SO 4} , which is the final product.

In the Claus process, the sulfuric acid from the downstream sulfuric acid plant is free of resins, and the purpose of the recycled acid injection is to ensure complete destruction of _H2SO4 and _SO3 before the process gas leaves the reaction room _. furnace, so that elemental sulfur is the only product. H ₂ SO ₄ /SO ₃ leaving the reaction furnace can cause catalyst deactivation and/or sulfuric acid condensation and corrosion of process equipment.

In the sulfuric acid process for waste acid regeneration, the atmosphere is oxidizing and the waste sulfuric acid typically constitutes more than 80% of the total sulfur input, whereas the Claus reaction furnace of the present invention operates with a reducing atmosphere and the sulfuric acid flow is typically <10% of the total sulfur input, although up to 25% is possible in special circumstances. Another difference is that the partial oxidation of H ₂ S is an exothermic process, releasing heat, whereas the combustion of sulfuric acid in spent acid regeneration is an endothermic process requiring an auxiliary fuel.

The spent acid recovery furnace residence time is typically 2-5 seconds to ensure complete destruction of the tar compounds, while the Claus reaction furnace is typically designed for a residence time of 1-2 seconds to ensure destruction of hydrocarbon gases and NH ₃ present in the feed gas.

When sulfuric acid is introduced into a Claus reaction furnace, the following general reaction occurs

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

Reaction (8) is a conventional evaporation reaction in which the energy required to heat the liquid and evaporate the water and sulfuric acid is provided by the hot ambient process gas. The effect of complete evaporation of sulfuric acid is that _{gaseous H2SO4} is much less aggressive than droplets _of liquid _H2SO4 , and gaseous _{H2SO4 is} much more reactive.

Reaction (9) is an endothermic dissociation reaction that occurs almost instantly at temperatures above 600°C. At this point in time, some SO ₃ will begin to react with H ₂ S to form SO ₂ , H ₂ O and sulfur.

Reaction (10) is an endothermic decomposition reaction that occurs rapidly at temperatures above 900°C. In oxygenated atmospheres, chemical equilibrium prevents complete dissociation, but in reducing atmospheres, removal of the O ₂ product (by reaction with H ₂ S) allows complete decomposition. The reaction between H ₂ S and O ₂ occurs very quickly at these elevated temperatures. The S atom in SO ₃ formed by reaction 9 is in the +6 oxidation state and is a highly reactive oxidizing agent, capable of oxidizing not only H ₂ S, but also hydrocarbons (including BTX = benzene, toluene and xylene) and NH ₃ . Hydrocarbons and NH ₃ are commonly present in feed streams and it is important that these compounds are destroyed in the reaction furnace as they can cause catalyst deactivation, fouling and plugging of downstream Claus catalytic conversion stages and sulfur condensers.

Compared to NH ₃ and hydrocarbons, H ₂ S has the highest affinity for O ₂ , and since the O ₂ supply is substoichiometric, there is no O ₂ left to oxidize hydrocarbons and NH ₃ according to conventional oxidation reactions 11 and 12:

Reaction 11 is representative of all types of hydrocarbons since they basically follow the same general oxidation mechanisms, that is, C and H are converted to CO ₂ and H ₂ O.

In the absence of free _O2, the general concept is that _SO2 plays an important role in oxidation since the S atom in _SO2 is in the +4 oxidation state and is thus a strong oxidizing agent. As described in Sulfur magazine no 375, March-April issue 2018, (“Combustion challenges in the reaction furnace”), the following general reactions are responsible for the oxidation of _CH4 : (reactions are scaled for ease of review)

Summarizing reactions 13-16, the overall reaction is

which is similar to reaction 11, which is the oxidation of CH ₄ by free O2.

Reaction 14 is a reaction in which _SO2 oxidizes the S atoms in _CS2 from the -2 oxidation state to +0 in _S2 , while the S atom in _SO2 is reduced from the +4 oxidation state to 0.

Reaction 15 is the normal Claus reaction that is already occurring, and reaction 16 is the very rapid oxidation of H ₂ S to free O ₂ . Thus, reactions 13 and 14 will determine the degree and rate of hydrocarbon destruction.

Since SO ₃ is not present in a regular Claus reaction furnace, the above analysis did not take into account the presence of this compound. Since the S atom in SO ₃ is in the +6 oxidation state, the oxidation power is higher than that of SO ₂ and therefore the oxidation of S atoms in a CS ₂ molecule is expected to occur at a higher rate at the same temperature or at the same rate, but at a lower temperature.

The general reaction between SO ₃ and CS ₂ is assumed to be:

The rule of thumb for traditional Claus processes is that at least 1000-1050°C is required in a Claus reaction furnace to fully oxidize hydrocarbons within a residence time of 1-2, but in the presence of SO ₃ it is expected that hydrocarbons can be oxidized as early as 900°C .

To destroy NH ₃ the normal oxidation reaction is described in Reaction 12, but since there is no free O ₂ in the reaction furnace, SO ₂ plays an important role as an oxidizing agent. Oxidation of NH ₃ without O ₂ also involves the oxidizing abilities of SO ₂ , as described in reaction 19:

Summing up reactions 19 and 20, the overall reaction is:

Reaction 20 is a very rapid oxidation of _H2S by free _O2 , and thus the decomposition of _NH3 is limited by the overall rate of reaction 19.

Similar to the decomposition of hydrocarbons, the S atom in SO ₃ is in the +6 oxidation state, whereas the S atom in SO ₂ is in the +4 oxidation state, and thus SO ₃ is a stronger oxidizing agent. It is expected that the decomposition of NH ₃ will occur at a higher rate in the presence of SO ₃ , which will either allow the reaction to be completed in less time at a constant temperature in the reaction furnace, or at a lower temperature with the same residence time.

The total reaction of the decomposition of NH ₃ under the influence of SO ₃ is assumed to be as follows:

The rule of thumb is that to ensure complete decomposition of NH ₃ in 1-2 seconds, a reaction furnace temperature of 1200-1250°C is required. The presence of SO ₃ as an oxidizing agent can, by analogy with the oxidation of hydrocarbons, reduce the temperature of this reaction by 50-200°C.

Since the residence time in the Claus reaction oven is usually 1-2 seconds, it is necessary to ensure that reactions 8, 9, 10 and 1, as well as the decomposition of impurities, are completed within this time, and that reaction 2 has reached chemical equilibrium. When the process gas is cooled, the reaction rates decrease sharply and further conversion in the gas phase will be insignificant.

The presence of O ₂ and/or SO ₃ in the process gas contacting the catalyst in downstream Claus reactors will result in catalyst deactivation due to a "sulfation" reaction in which the catalytically active aluminum oxide or titanium oxide is converted to the catalytically inactive aluminum sulfate or sulfate titanium and therefore sulfur production in these reactors will be reduced, leading to an increase in the amount of unreacted sulfur compounds in the tail gas of the downstream sulfuric acid plant and to increased emissions to the atmosphere.

In addition, SO ₃ in the process gas can, when passing through sulfur condensation units, combine with water, condense and form sulfuric acid in the elemental sulfur product, which can lead to corrosion of process equipment and unwanted contamination of the sulfur product.

While reactions 9 and 10 can be considered very fast, the rate-determining step may be reaction 8, i.e. evaporation of sulfuric acid. It is obvious that liquid sulfuric acid with a maximum boiling point of ~ 340°C cannot be in equilibrium in a reaction furnace at a temperature of 1000°C, but the evaporation rate is limited by heat and mass transfer between the surface of the liquid and the process gas, and therefore the temporary existence of sulfuric droplets is possible acids. A detailed mathematical analysis of droplet evaporation, including convective heat and mass transfer, radiative heat transfer, and sulfuric acid thermodynamics, shows that the time for complete droplet evaporation depends on temperature and the square of the initial droplet diameter.

The time for complete evaporation can range from 0.2 seconds for a droplet with an initial diameter of 200 μm and up to 2 seconds for a droplet with an initial diameter of 700 μm. Thus, to ensure that all droplets evaporate and react in the reaction furnace, the size distribution of the droplets from the sulfuric acid injection nozzle(s) is of great importance.

Thus, the choice of sulfuric acid atomization nozzle is an important factor in achieving successful operation of a Claus plant - there are many types of atomization nozzle, some of which can produce fine droplets of sulfuric acid, and some of which cannot.

So-called air nozzles (also known as pneumatic or two-fluid nozzles) typically produce tiny droplets. These nozzles use kinetic energy to atomize sulfuric acid into small enough droplets so that the compressed air mixes with the liquid at the tip of the nozzle. Instead of air, low pressure steam, oxygen, _N2 and other gaseous liquids can be used. When properly selected for nozzle size and operating pressure, these nozzles provide a size distribution suitable for rapid droplet evaporation.

Hydraulic spray nozzles use the pressure of a liquid (such as sulfuric acid) to provide the energy to atomize the liquid, and with proper pressure selection and nozzle design, these nozzles can also produce fine droplets. In general, droplet size decreases with increasing pressure, decreasing flow rate, and increasing spray angle. The advantage of a hydraulic nozzle is lower operating costs since no compressed air is consumed. However, the performance and dynamic range of these nozzles are not as good as forced air nozzles.

The performance of spray nozzles is typically measured using water as the liquid and air as the spray medium (for pneumatic nozzles only). Size accumulation is measured and characterized by one-dimensional parameters such as VMD, SMD, DV _0.9 , etc. The relevance of the characteristics depends on the application.

VMD is volumetric mean diameter, which means that 50% of the droplet volume/mass is larger than a given diameter.

SMD is the so-called Sauter mean diameter, defined as the diameter that has the same volume-to-surface ratio as the total volume of the droplets to the total surface area of the droplets.

D _0.9 - diameter at which 90% of the total volume/mass of droplets is smaller.

D _max is the maximum diameter found in the size distribution.

For evaporation purposes, D _0.9 and D _max are the most important nozzle dimensions.

These values, however, do not provide complete information about the size distribution, where the distribution of the largest droplets is particularly important for the present invention.

The actual droplet sizes for a liquid with properties other than water at room temperature can only be approximately estimated from the liquid properties such as viscosity, surface tension, and density. Density has little effect on droplet size, while increasing viscosity and surface tension lead to larger droplet sizes. Sulfuric acid has a higher viscosity and lower surface tension compared to water, and the extent to which the complex interactions of the two opposing effects cancel each other must be determined experimentally or through detailed modeling.

After some time in use, the nozzles will eventually wear out due to acid and/or air (particle) erosion and sulfuric acid corrosion. Worn nozzles will produce a less uniform spray pattern and the size distribution will shift towards larger droplets, so it is important to ensure that the nozzles are in good condition, i.e. by visual inspection or observation of pressure differences between the fluid and, in the case of an air nozzle, the gas to the nozzle. Additionally, if the acid injection system is properly designed, it will be possible to insulate the acid injection tubes and remove them from the reaction furnace while maintaining the operation of the Claus unit.

With proper selection and operation of the sulfuric acid spray nozzle, complete evaporation of the droplets and complete conversion of SO ₃ and O ₂ can be achieved in less than 1-2 seconds, which is the normal residence time for a Claus reaction furnace.

However, various means exist to ensure that large droplets formed at the nozzle tip do not result in excessive droplets and H ₂ SO ₄ /SO ₃ exiting the reaction furnace.

One design option is to provide a large reaction furnace chamber so that the residence time of the process gas is long, but this can be expensive.

Turbulence in the reaction furnace chamber can be increased by retarding or redirecting the flow, i.e. through the use of throttle rings, vector walls, tangential inlets, etc., which will provide a narrower droplet residence time distribution, reducing the likelihood of a droplet residence time being much less than average.

Likewise, the presence of an impactor, such as an impact wall, grid wall or compacted volume or inert material compartment, can reduce the number of large droplets that, due to their high inertia, will not be able to follow the flow lines of gas vented near the obstruction. Instead, large droplets will move further, collide with the obstacle, and evaporate from the surface of the obstacle. This impactor is typically strong enough and not a load-bearing structure to avoid stability problems due to wear of the structural material.

To avoid sulfation of Claus catalysts, a substance catalytically active in the conversion of SO ₃ to SO ₂ , including, for example, one or more compounds of V, Mn, Fe, Co, Cu, Zn, Ni, Mo, W, Sb, Ti and Bi, supported on one or more compounds of Al, Ti, Si, diatomaceous earth, Zr, Mg and cordierite, may also be located downstream of the Claus reaction furnace. Such material may be in the form of catalyst granules or structured catalysts such as monoliths.

If all of the sulfuric acid produced in the sulfuric acid production process downstream of the Claus process is sent to the Claus reaction furnace, the Claus process can be used, which takes advantage of the very high removal efficiency as well as the thermal efficiency of the sulfuric acid plant to reduce _H2S emissions , but whose only product is sulfur, which is easy to handle and transport.

In addition, when recirculating sulfuric acid, O ₂ is released during the decomposition of H ₂ SO ₄ , so the amount of combustion oxidizer added will be reduced, which, if the oxidizer is atmospheric air, allows a sharp reduction in the volume of the process, since atmospheric air contains about 80% inert N ₂ , i.e. 4 volumes of N ₂ per volume of O ₂ .

The general reaction based on the use of air as an _O2 carrier for a Claus reaction furnace is as follows:

Likewise, the general Claus reaction based on _H2SO4 as _{the O2} carrier for the Claus reaction furnace is as follows:

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

It may also be useful to redirect some of the feed gas to the Claus reaction tail gas combustor since the feed gas has a heating value that can be used in the Claus reaction tail gas combustor and thus reduce the need to add auxiliary fuel. This may be even more advantageous if there are two feed gas sources, such as one feed gas containing no NH ₃ and another feed gas containing NH ₃ , since the substoichiometric conditions in the Claus reaction furnace prevent complete oxidation of the NH ₃ . So-called sour water stripper (SWS) column gases are an example of such NH ₃ -containing feed gas.

In Claus processes for treating SWS gas, complete destruction of NH ₃ in the Claus reaction furnace is critical, otherwise ammonia salts such as (NH ₄ ) ₂ SO ₄ and (NN ₄ ) ₂ S ₂ O ₃ are formed, which plug the final condenser sulfur. Special high-intensity (two-stage) burners are capable of achieving the high temperatures required for thermal destruction of NH ₃ but require precise control of the oxygen in two separate streams.

However, the treatment of SWS gas in a sulfuric acid plant is well known, since complete oxidation of NH ₃ to N ₂ and NO is achieved by excess oxygen at temperatures above 1000°C. Thus, it may be desirable to configure an integrated Claus/sulfuric acid process with two combustion chambers to send a first feed containing H ₂ S and little or no NH ₃ to the Claus reaction furnace, wherein a gas containing NH ₃ such as SWS gas is sent to the combustion chamber of the residual gas of the Claus reaction. In such a configuration, it may be desirable to design the sulfuric acid plant to include a selective catalytic reduction (SCR) section for NO _x with NH ₃ in the presence of a vanadium-based catalyst.

The integrated process of the present invention may also benefit from the use of oxygen-enriched air or substantially pure oxygen in a Claus reaction furnace. The advantage of using oxygen-enriched air is to reduce the amount of inert nitrogen in the process gas and thus reduce the volume of process gas and thus reduce the size of the plant. The lack of nitrogen dilution also results in higher combustion temperatures, which can be beneficial if impurities are present that require complete conversion, especially since the amount of oxygen in the Claus reaction furnace is substoichiometric. Since the Claus catalyst is sensitive to impurities such as light hydrocarbons, it may often be advantageous to operate the Claus reaction furnace with oxygen-enriched air to achieve elevated temperatures to completely oxidize the impurities. This also has the added benefit of allowing initial homogeneous non-catalytic Claus conversion, which can occur at temperatures above 900°C.

However, from a thermal efficiency point of view, the high combustion temperature may be limited by the choice of materials of construction in the Claus reaction furnace and subsequent recovery boiler. For feed gases with high H ₂ S concentrations, oxygen enrichment may cause the process gas temperature to rise above the design temperature of the materials. However, the combination of H ₂ SO ₄ recirculation (which cools the process gas through evaporation and acid decomposition) makes it possible to use enriched O ₂ in such a scheme.

The Claus tail gas combustor will typically operate with ambient air, and it may also be advantageous to direct gases with low concentrations of sulfur compounds into the Claus tail gas combustor to completely burn the sulfur compounds, releasing significantly more energy than partial oxidation occurring in a Claus reaction furnace.

As a consequence, it may be advantageous to route feed gases containing high concentrations (eg greater than 50 vol.%) of H ₂ S to the Claus unit, diverting feed gases with lower concentrations, as well as feed gases containing NH ₃ , into the residual combustion chamber. Claus reaction gas.

If the residual Claus reaction gas combustor receives only residual Claus reaction gas containing only a limited amount of H ₂ S, the heating value is too low to maintain stable combustion. In this situation, the addition of auxiliary fuel is required. This auxiliary fuel may be H ₂ S, SWS gas or hydrocarbon feedstock, but it is preferable to use the amount of existing feed gas for the integrated Claus and sulfuric acid plant.

Integration of the Claus process and the sulfuric acid process provides integration benefits. These include the possibility of reducing the volumetric flow rate in the Claus process by supplying an oxidizing agent in the form of sulfuric acid, which can replace atmospheric air. In addition, the use of feed gas can be optimized such that feed gases containing fuels that contribute significantly to sulfur production can be sent to the Claus process, while feed gases containing thermal energy and non-reactive products such as CO ₂ , can be sent to the sulfuric acid process. If the process is designed to recycle too much sulfuric acid, additional fuel may be required to provide the heat needed to evaporate and dissociate the sulfuric acid.

Integrating the two processes also allows for a process to be implemented in which the Claus process is operated at a low conversion, such as 90% or 95%, since it may be cheaper to carry out additional conversion in the sulfuric acid process compared to adding an additional Claus converter stage.

In an integrated process in which sulfuric acid from the sulfuric acid process is recycled to the thermal stage of the Claus plant, an intermediate sulfuric acid storage tank may be advantageously located between the sulfuric acid outlet of the sulfuric acid plant and the sulfuric acid input to the Claus reaction furnace. Such a reservoir would allow more reliable and safe control of the acid input into the Claus reaction furnace, so that bias periods could be operated without acid input. For example, when starting and stopping an integrated process, it will be advantageous to operate without the introduction of sulfuric acid. Additionally, if the acid injection pipes require maintenance, the integrated process can operate without stopping the sulfuric acid production process.

The reservoir will also allow sulfuric acid product to be diverted should it become a demanded product, as well as allow sulfuric acid to be imported from other sources. The reservoir can also act as a buffer separating the Claus process from the sulfuric acid production process (sulfuric acid process), which ensures the stability of the entire system.

Tank capacity to produce sulfuric acid in 1-4 days is a good compromise between tank cost and the flexibility of an integrated Claus and sulfuric acid process.

For reliable operation of an industrial installation, a "shutdown system" is typically used to detect and handle unexpected shutdowns ("outages"). For an integrated Claus and sulfuric acid process, an outage may occur in either of the two processes, and it is important that the process is tolerant of such outages so that the consequences are minimized.

It may be necessary to stop the sulfuric acid supply to the Claus reaction furnace due to failure of the acid pump in the sulfuric acid tank, failure of the sulfuric acid flow regulator, and loss of atomizing fluid. In such a situation, it is necessary to update the Claus unit shutdown system to deal with such incidents, allowing the acid injection nozzles to be turned off while keeping the Claus unit operating. In the event of a loss of acid supply, the combustion air control system of the Claus reaction furnace compensates for the lack of oxygen by increasing the air flow, thereby returning the Claus unit to normal operation.

During operation, the sulfuric acid atomization pipes and nozzles are cooled by the atomization air flow and especially by the sulfuric acid flow. When the acid flow stops, the cooling largely disappears and the pipe temperature rises. The pipe material can withstand the operating temperature of the reaction furnace, but any acid entering the pipe will be heated. The corrosion rate will increase significantly and boiling of the sulfuric acid may also occur. To avoid this situation, the acid lines can be flushed with a gaseous flushing medium to remove liquid acid from the pipe so that acid corrosion is minimized, the pipe is provided with some additional cooling, and Claus reaction furnace process gas is avoided from entering the pipe. Flushing will continue until the acid flow is stopped. The flushing medium is typically an N ₂ stream, which is already available and used in Claus units, and is an inert gas that will not interfere with the chemistry in the reaction furnace. Alternatively, air can be used as the scrubbing medium, but this will add _O2 to the Claus reaction furnace and there is a risk of interfering with the combustion air control if the scrubbing stream is not equipped with a flow meter. Stopping the supply of sulfuric acid will also raise the temperature in the reaction furnace, but the increase in temperature will not be a problem in most cases since the refractory walls will be able to withstand the higher temperature and the higher temperature will not adversely affect the reaction chemistry in the Claus furnace.

When the acid injection shutdown is triggered, the atomizing medium of the air nozzles will continue to flow so that the pipe is cooled and the process gas is prevented from entering the pipe. Once the acid flow is turned off, stagnant acid will remain in the acid line of the pipe, and without the cooling provided by the acid flow, the temperature of the acid will increase and thus the rate of acid corrosion will also increase. To avoid corrosion of the acid line after the acid flow is turned off, the acid line is flushed with N ₂ or air to clear the acid from the line. This flushing will be performed on both pneumatic and hydraulic nozzles and will continue indefinitely to prevent process gas from entering the nozzles.

In addition to the wet sulfuric acid production process, sulfuric acid can also be produced in other sulfur reduction processes, and this sulfuric acid can also be sent to the Claus reaction furnace according to similar principles, especially if the resulting sulfuric acid is at least 90%.

A typical Claus setup requires >50 vol% H ₂ S in the feed gas to be thermally self-sustaining in the Claus reaction furnace. At lower H ₂ S concentrations, preheating of the feed gas is required and a so-called split-flow configuration is required. Claus plants that process feed gases containing H ₂ S < 10-20 vol.% are rare. On the other hand, sulfuric acid processes treat these so-called _H2S -depleted gases very efficiently, producing concentrated sulfuric acid. The sulfuric acid product will have a high concentration of sulfur and oxygen.

The combination of a sulfuric acid plant for treating depleted _H2S gas (and/or other sulfur compounds) in combination with a Claus plant for treating high _H2S gas and receiving acid from the sulfuric acid plant would be an advantageous plant because the feed streams of both the Claus plant and and for a sulfuric acid plant are optimal in terms of conversion efficiency, thermal efficiency and plant size/cost.

A combination of the Claus process and the sulfuric acid process can also be used to optimize feedstock processing. Sulfuric acid processes and in particular the wet sulfuric acid process have the advantage that they are well suited to dirty feedstocks including SWS gases containing ammonia as discussed above, "dirty sulfur" containing organic impurities and moderate amounts of inorganic impurities, dilute H streams ₂ S, SO ₂ and other sulfur compounds, including burner flue gases and FCC gas. Similarly, gases with high hydrogen sulfide content, which must be diluted before being processed in a wet sulfuric acid process plant, can instead be sent directly to the Claus process.

Brief description of drawings

In FIG. 1 shows a sequential Claus + sulfuric acid process according to the prior art.

In fig. 2 shows an integrated Claus + sulfuric acid process with the introduction of sulfuric acid into a Claus reaction furnace according to the present invention

In FIG. 1 shows a method for producing sulfur and sulfuric acid according to the prior art. In this case, feed gas 2 enriched in H ₂ S is sent to the Claus process, from which the residual gas 26 is sent to the sulfuric acid process. Feed gas 2, enriched in H ₂ S, is sent to a Claus reaction furnace 66, which converts an amount of H ₂ S into SO ₂ to form a feed gas for a Claus converter 4 having a ratio of H ₂ S to SO ₂ close to 2:1. The feed gas for the Claus converter 4 is sent to a converter 8 containing a substance catalytically active in the Claus reaction 12, providing the Claus reaction product 14. The Claus reaction product 14 is sent to a sulfur condensation unit 16, providing condensed sulfur 18 and residual Claus reaction gas 20. Wet the Claus reaction tail gas 20 is typically further reacted in the presence of a Claus catalytically active substance, followed by further condensation of sulfur, in one to four additional Claus steps (not shown), to provide a final wet Claus reaction tail gas. The aqueous phase 24 may optionally be separated from the wet Claus reaction tail gas 20 in a separator 22, providing dried Claus reaction tail gas 26, which is sent to the Claus reaction tail gas combustor 32, providing feed gas 34 for the SO ₂ converter. The feed gas 34 for the SO converter is cooled and sent to the SO ₂ converter 40 containing one or more beads (layers) of the catalytically active substance 42, 44, 46, optionally with cooling between the layers, from which the SO ₃ -enriched gas 48 is removed. Since SO ₃ -rich gas contains water, SO ₃ can hydrate to form H ₂ SO ₄ . H ₂ SO ₄ is condensed as concentrated sulfuric acid 52 in sulfuric acid condenser 50. From sulfuric acid condenser 50, substantially pure gas 62 can be withdrawn and directed to outlet 64.

To maintain a stable flame and a temperature high enough to completely oxidize H ₂ S, CO, CS ₂ , COS and H _2, fuel gas can be sent to the Claus reaction tail gas combustion chamber 32. Oxygen is also supplied, usually by air, and preferably hot air from the sulfuric acid condenser (50) to supply oxygen both for the combustion reactions in the Claus reaction tail gas combustion chamber 32 and to supply the oxygen required for the oxidation of SO ₂ in the SO ₂ converter. To reduce fuel consumption, oxygen for SO ₂ oxidation can be added between the outlet of the Claus reaction residual gas combustion chamber 32 and the inlet of the SO ₂ converter 40.

In FIG. 2 shows an integrated Claus/sulfuric acid process with sulfuric acid introduced into a Claus reaction furnace 66 according to the present invention. Feed gas 2 enriched in H ₂ S, sulfuric acid 56 and oxygen enriched gas 72, and optionally a gas containing fuel, and optionally a second feed gas, for example containing a low concentration of H ₂ S and possibly NH ₃ is sent to the Claus reaction furnace 66, and the combustion product is sent as an O ₂ -free feed gas for the Claus converter 4 to the converter 8. Between the outlet of the Claus reaction furnace 66 and the inlet of the Claus converter 8, a recovery boiler and optionally a sulfur condensation unit (not shown) typically are typically set to reduce the temperature to the optimum operating temperature for the Claus catalyst, optionally also removing the elemental sulfur generated in the Claus reaction furnace 66. The O ₂ -free feed gas for the Claus converter 4 is sent to contact with an additional substance catalytically active in converting SO ₃ to SO ₂ 10 (containing, for example, one or more compounds of V, Mn, Fe, Co, Cu, Zn, Ni, Mo, W, Sb, Ti and Bi, supported on one or more compounds of Al, Ti, Si, diatomaceous earth , Zr, Mg and cordierite), and a substance catalytically active in the Claus reaction 12, containing, for example, aluminum oxide or titanium oxide, providing the Claus reaction product 14. The Claus reaction product 14 is sent to a sulfur condensation unit 16, providing condensed sulfur 18 and Claus Reaction Tail Gas 20. The Claus Reaction Tail Gas 20 may optionally be further reacted in the presence of additional catalytically active material in a Claus process, followed by condensation of sulfur, in one to four additional Claus steps (not shown here), to provide a final residual gas Klaus' reactions. The final Claus reaction tail gas containing H ₂ S 20 is sent to the Claus reaction tail gas combustor 32 to produce SO ₂ condenser feed gas 34. In order to allow the compounds in the Claus reaction tail gas to be oxidized, the O ₂ -rich gas 72 sent to the combustion chamber of the residual gas of the Claus reaction 32.

The SO2 converter feed gas 34 is typically cooled in a recovery boiler (not shown) to provide an optimum temperature for the first catalyst bed 42 in the SO ₂ converter 40. The SO ₂ converter feed gas 34 is sent to an SO ₂ converter 40 containing one or more beds. layers of catalytically active substance 42, 44, 46, optionally with cooling between the layers, from which gas 48 rich in SO ₃ is removed. Since SO ₃ -rich gas contains water, SO ₃ can hydrate to form H ₂ SO ₄ . H ₂ SO ₄ is condensed as concentrated sulfuric acid 52 in a sulfuric acid condenser 50 . If the amount of water is insufficient to completely hydrate the SO ₃ , it may be preferable to add steam at a position upstream of the sulfuric acid condenser 50. Substantially pure gas 62 may be withdrawn from the sulfuric acid condenser 50 and sent to riser 64. Typically, all of the sulfuric acid 56 is recycled to the Claus reaction furnace 66, but an optional amount of sulfuric acid may be withdrawn for other process purposes. For this purpose, an intermediate sulfuric acid tank (54) can be located between the sulfuric acid outlet of the sulfuric acid condenser 50 and the Claus reaction furnace 66, which can act as a buffer, disconnecting the Claus process from the operation of the sulfuric acid process, which ensures the stability of the entire system.

An optional catalytic reactor 35 for oxidizing remaining impurities such as hydrocarbons, CO, COS, CS ₂ , S, H ₂ and H ₂ S is also shown in FIG. 2.

According to another embodiment, the entire amount of secondary feedstock containing NH ₃ and H ₂ S 70 is sent to the residual gas combustion chamber of the Claus reaction 32, eliminating the risk of formation of NH ₃ salts in the Claus condensers 16. According to this embodiment, a NO _X recovery system can be installed 33, located between the outlet of the residual gas combustion chamber of the Claus reaction 32 and the inlet of the SO ₂ converter 40. Typically, a so-called SCR (selective catalytic reaction) catalytic reactor is used, requiring the addition of NH ₃ for the SCR reaction to occur. The addition of NH ₃ may come from an external source or may be a small stream of second feed containing NH ₃ and H ₂ S 70, which is then passed through the Claus reaction tail gas combustor.

According to a selected embodiment, the conversion and condensation of sulfuric acid can be carried out in two stages, where the remaining SO ₂ from the first stage undergoes further oxidation, hydration and condensation with the concomitant advantage of providing increased sulfur removal.

According to this embodiment, additional SO ₂ conversion can be achieved by installing a residual gas purification unit from the sulfuric acid process. There are many such solutions for residual gases, the most common of which are alkaline scrubbers, which are not necessarily combined with mist filters. Scrubbers using H ₂ O ₂ or NH ₃ are preferred since the effluent from these scrubbers is H ₂ SO ₄ and (NH ₄ ) ₂ SO ₄ respectively, both of which can be recycled to the Claus reaction furnace for thermal destruction , i.e. disposal of the waste stream.

In another embodiment, the SO ₂ converter feed gas 34 may be dried such that the SO ₃ -rich gas 48 contains little or no water. In this case, the condenser 50 can be replaced by an absorber in which SO ₃ can be absorbed with sulfuric acid to produce concentrated sulfuric acid through the dry sulfuric acid process.

According to another embodiment, an amount of elemental sulfur can also be transferred to the Claus reaction tail gas combustion chamber 32, which will have the effect of supplying SO ₂ to the sulfuric acid production process without introducing water, which can be useful if it is desired to increase the SO ₃ concentration, which can be useful in the dry sulfuric acid process.

In another embodiment, an amount of fuel gas 68 is directed to the residual Claus reaction gas combustion chamber 32 to provide a sufficiently high temperature to completely oxidize all reduced compounds in the residual Claus reaction gas 20.

According to this embodiment, the amount of H ₂ S-rich feed gas 2 can also be divided into an amount sent to the Claus reaction combustion chamber 66 and an amount sent to the Claus reaction residual gas combustion chamber 32. This will reduce the need to supplement fuel gas into the chamber combustion of the residual gas of the Claus reaction 32.

In another embodiment, a portion of the residual Claus reaction gas 20 is diverted from the residual Claus reaction gas combustor 32 and combined with the hot exhaust gas 34 from the Claus reaction residual gas combustor at a gas mixing point immediately downstream of the residual Claus reaction gas combustor. This reduces the amount of fuel gas 68 required by the Claus reaction residual gas combustor to maintain a sufficiently high temperature. The combined exhaust gas of the Claus reaction residual gas combustor and the withdrawn Claus reaction residual gas must have a gas mixture temperature above 400°C to ensure homogeneous (i.e. gas phase) oxidation of H ₂ S. To ensure complete oxidation of “difficult” compounds, such as COS and CO, an additional oxidation catalyst 35 can be installed between the gas mixing point and the inlet of the SO ₂ 40 converter. To ensure optimal control of the temperature of the oxidation catalyst, a heat boiler or any other heat exchanger can be installed between the gas mixing point and the inlet of the oxidation catalyst . The oxidation catalyst typically contains a noble metal such as Pt or Pd.

In another embodiment, the oxygen containing gas 72 may be pure oxygen or atmospheric air enriched with oxygen such that it contains less than 50%, 20%, 10% or even 1% N ₂ +Ar.

Example 1

The evaporation of sulfuric acid droplets was analyzed numerically using a detailed mathematical model including

1. Heat transfer to the drop due to convective heat exchange.

2. Heat transfer to the droplet by heat exchange by radiation from gas molecules and hot refractory walls in the reaction furnace.

3. Mass transfer between the drop and the process gas

4. Detailed thermodynamics of sulfuric acid/water mixtures.

It is assumed that the spray nozzle is of the pneumatic type, the initial droplet speed is about 50 m/s, and the process gas flow speed is about 10 m/s.

The simulation results for three different reaction furnace temperatures are shown in FIG. 3. Droplets of sulfuric acid (93% w/w H ₂ SO ₄ ) enter the hot reaction furnace at low temperature and initially grow by absorbing water from the surrounding process gas. When the droplet is heated, mostly water evaporates until the sulfuric acid concentration reaches approximately 98.5% w/w, which is the concentration of the azeotrope. From this point on, the concentration and temperature of the drop do not change until the drop completely evaporates.

It is clear from the results that the initial droplet size is important for the safe and long-term operation of the Claus unit, especially if the residence time in the reaction furnace is to be set at 1-2 seconds. Droplets with an initial diameter of more than 500 microns do not completely evaporate within 1 second at a temperature of 1000°C. As can be seen, the temperature effect is indeed present, but the influence of the initial droplet diameter is much stronger.

Example 2

Spraying sulfuric acid requires careful selection of nozzle type and nozzle operating mode. There are a variety of nozzles on the market with different characteristics in terms of fluid volume, pressure, type, etc., ranging from very fine atomizers with low output to large nozzles with very high output, depending on the application.

For evaporation purposes, a small size distribution is desirable, and for this purpose, air nozzle (air, two-phase) and hydraulic (pressure) nozzles are preferred, the former producing smaller droplets, but at the "cost" of consuming the atomizing fluid, which is usually compressed air.

Based on the data given in Tables 18-18 and 18-19 in Perry's Chemical Engineers Handbook, ^4th edition (McGraw-Hill 1963), the value of D _0.9 was calculated and shown in Table 1. D _0.9 determines the diameter, where 90% of the total mass (or volume) of the droplets have a smaller diameter. The data is based on water as a liquid and air, in the case of an air nozzle, at room temperature.

As can be seen from the table, the air nozzle produces tiny droplets. The hydraulic nozzle also produces small droplets, but up to 500 microns in size. Nozzle #2 and #3 differ only in fluid pressure, and it can be seen that higher fluid pressure results in smaller droplets. Although producing small droplets, hydraulic nozzles may be a worse choice if the residence time in the reaction oven is only 1 second, but with a residence time of 2 seconds the nozzles will work fine. In fig. Figure 3 shows the evaporation time of sulfuric acid droplets. For hydraulic nozzles, consideration should be given to installing an impact wall or similar material in the reaction furnace so that most of the largest droplets impinge on the wall and evaporate within the reaction furnace.

To document the effect of combining the Claus process and the sulfuric acid process, four additional examples of the process shown in FIG. 2, compared with the prior art process as shown in FIG. 1.

These examples are based on the following feed gases:

Feed gas enriched with H ₂ S (stream 2 in Fig. 1 and 2):

Total gas flow: 8190 Nm ³ /h

H ₂ S concentration: 94 vol.%

H ₂ O concentration: 6 vol.%

Gas enriched in _H2S is typical of oil refineries and will also contain varying amounts of light hydrocarbons.

Feed gas enriched with H ₂ S and NH ₃ (stream 70 in Fig. 1 and 2):

Total gas flow: 3669 Nm ³ /h

H ₂ S concentration: 28 vol.%

NH ₃ concentration: 45 vol.%

H ₂ O concentration: 27 vol.%

These streams, containing H ₂ S and NH ₃ , are typically off-gases from so-called sour water strippers and are considered SWS gases. They may also contain varying amounts of light hydrocarbons.

Fuel gas is a mixture of light hydrocarbons (mainly CH ₄ ) with a lower calorific value of 12,200 kcal/Nm3.

The feed streams, combustion air and Claus reaction tail gas are preheated as much as possible by utilizing the heat generated in the combined Claus + sulfuric acid process.

In these examples, the Claus process operates at 94-95% sulfur recovery from the feed, i.e. may represent a well-functioning Claus unit with only two catalytic stages.

Example 3

Sequential Claus + sulfuric acid process according to prior art.

In Example 3, all feed streams were treated in the Claus process, providing a stream of 11.7 t/h of elemental sulfur and a tail Claus reaction gas containing ~5% S in the feed gases. In the Claus reaction residual gas combustion chamber, the sulfur compounds present in the Claus reaction residual gas are oxidized, and fuel gas is supplied to maintain the combustion chamber temperature at 1000°C, so that all compounds such as CO, COS, _H2 , _H2S are reduced , S _X and CS ₂ are completely oxidized to CO ₂ , H ₂ O and SO ₂ .

The production of concentrated sulfuric acid is 2.4 t/h based on 100% w/w. _{H2SO4 .}

The total recovery of sulfur and sulfuric acid is >99.9% sulfur in the raw material, which meets the most stringent environmental standards.

Example 4

Recycle H ₂ SO ₄ into the Claus reaction furnace.

In this example, H ₂ SO ₄ is not the desired product and all of the acid produced from the sulfuric acid process is recycled to the Claus reaction furnace. The amount of H ₂ SO ₄ recycled corresponds to approximately 6% of the total amount of S in the feed streams.

The total elemental sulfur product stream is now equal to S in the feed streams, corresponding to 107% of the base case as described in Example 3.

The temperature in the Claus reaction furnace is reduced by ~200°C due to the evaporation and decomposition of H ₂ SO ₄ , but the temperature is still well above the minimum temperature for complete combustion of hydrocarbons and NH ₃ Fuel gas is not required in the Claus reaction furnace.

Since H ₂ SO ₄ is an excellent O ₂ carrier, the combustion air requirement is reduced and, therefore, the volume of process gas is reduced as the inert N ₂ flow is reduced. Overall, the process gas flow at the exit of the Claus reaction furnace is reduced to 94% of the base flow, and the process gas flow at the exit of the Claus reaction residual gas combustor is reduced to 93% due to this reduction in N ₂ flow. Since less process gas needs to be heated to 1000°C in the Claus reaction tail gas combustor, fuel gas consumption is only 92% of the base case.

The benefit from H ₂ SO ₄ recycling was unexpectedly high, since the sulfur production capacity of the Claus plant not only increased by 7%, but at the same time the volume of process gas decreased by 6-7%. This corresponds to an increase in the productivity of the Claus plant of approximately 15%, assuming that the process gas flow rate is 100% of the base case.

Example 5

Recycle H ₂ SO ₄ into the Claus reaction furnace and exhaust SWS gas into the combustion chamber of the residual gas of the Claus reaction.

In this example, fuel gas consumption in the Claus reaction tail gas combustor was minimized by passing a portion of the SWS gas into the Claus reaction tail gas combustor. SWS gas has a high calorific value and can easily act as a fuel gas. Concentrated H ₂ S feed gas could also be used, but since SWS gas can be problematic in the Claus process and is not problematic in the wet sulfuric acid process, venting SWS gas has more advantages than venting H ₂ S gas. Regarding process gas, the gas volume will also decrease because the NH3 in the SWS gas will increase the process gas volume in the Claus process due to the need for oxygen (air) to burn _NH3 into _N2 and _H2O .

The amount of recirculated SWS gas is adjusted so that the Claus tail gas combustion chamber reaches a temperature of 1000°C to ensure complete combustion of the reduced Claus tail gas compounds such as H ₂ S, COS, CO, H ₂ , S _X and CS ₂ .

Since the fuel gas in the Claus reaction tail gas combustor now contains H ₂ S, H ₂ SO ₄ production will increase, now accounting for ~13% S in the feed streams. This large amount of sulfuric acid recirculation results in a significant reduction in the temperature of the Claus reaction furnace.

With proper preheating of the feed stream, it is still possible to achieve a sufficiently high temperature in a Claus reaction furnace without the need for auxiliary fuel.

The impact on the size of the Claus process is significant: process gas volume is reduced to 65% of the base case, while still producing 107% of elemental sulfur. This reduction in process gas volume can be used to either increase the performance of an existing plant or significantly reduce the costs of a new plant.

In addition, the sulfuric acid plant will be smaller, since the process gas flow is only 90% of the base case flow. This is surprising since H ₂ SO ₄ production more than doubled compared to the base case, but this is mainly due to a large reduction in the residual gas flow of the Claus reaction.

What is most remarkable is the reduction in fuel gas consumption, which is now only 16% of the base case, contributing to a significant reduction in operating costs for the integrated Claus+ sulfuric acid process.

Example 6

Recycle H ₂ SO ₄ and complete removal of SWS gas into the combustion chamber of the residual gas of the Claus reaction

This example focuses on the complete elimination of SWS gas in the Claus unit, which ensures that ammonia salts cannot form in the sulfur condensers and thus reduces the risk of Claus unit failure.

The process gas flow rate at the outlet of the Claus reaction furnace is 69% of the base case, but slightly higher compared to example 5, where only part of the SWS gas is removed. The increase in process gas consumption is due to the need to add fuel gas to the Claus reaction furnace to maintain a high operating temperature.

The production of H ₂ SO ₄ from the wet sulfuric acid process plant has now increased to 17% of the sulfur content of the feed gases, recirculation of all production now quenches the Claus reaction furnace temperature to the point where fuel gas is required. Process gas from the residual gas combustion chamber of the Claus reaction increased to 107% of the base case due to an increase in the supply of sulfur to the sulfuric acid plant.

Even if the Claus reaction furnace requires fuel gas, the total fuel gas consumption is only 41% of the base case.

In terms of plant size and operating costs, this example seems less optimal than example 5, i.e. There is an optimal H ₂ SO ₄ recycle ratio that depends on the actual feed gas flows and compositions. Removing even more feed gas will result in increased sulfuric acid production, which will further extinguish the Claus reaction furnace, again requiring more fuel gas, and therefore the Claus reaction tail gas flow will increase.

For the above-described compositions and raw material flows, the optimal one from the point of view of installation size and fuel consumption is the H ₂ SO ₄ recirculation flow in the range from 13% to 17% of the S supply in the raw material flows.

In general, the optimal feed gas supply removal is close to the point at which the Claus reaction furnace is operating at the minimum permissible temperature, i.e. the stock of feedstock can be diverted to produce more sulfuric acid until the Claus reaction temperature reaches the limit for thermal degradation of hydrocarbons and sulfuric acid. Increasing the feed stock withdrawal ratio will reduce the fuel gas requirement in the Claus reaction residual gas combustion chamber, but will increase the fuel gas consumption in the Claus reaction furnace by a much larger factor because fuel gas is required in the Claus reaction chamber to evaporate and decompose the sulfuric acid and heat the process gas , whereas in the residual gas combustion chamber of the Claus reaction only heating of the process gas is required.

For a feed gas supply of, for example, 50 vol.% H ₂ S, the optimal H ₂ SO ₄ recycle flow is ~7% of the S feed in the feed stream. The removal of acid gas into the residual Claus gas combustion chamber is only 2%, since the relatively low concentration of H ₂ S results in a low temperature in the Claus reaction furnace, and thus sulfuric acid quickly reduces the temperature and requires the addition of fuel gas to the Claus reaction furnace . The use of O ₂ -rich air in the Claus reaction furnace will increase the H ₂ SO ₄ recirculation flow.

Example 7

Recycle H ₂ SO ₄ , vent SWS gas into the Claus reaction residual gas combustion chamber and use O ₂ -enriched air.

To increase the productivity of the Claus installation, a design option is known that consists in installing special burners capable of operating with enriched air with an O ₂ content of >21 vol.%; the usual quality of O ₂ is 93-99 vol.% O ₂ .

In this example, enriched air with an _O2 content of 80 vol.% is used, as in the Claus process, while the sulfuric acid process uses atmospheric air.

The effect of enriched air is to significantly reduce the process gas flow leaving the Claus reaction furnace, mainly due to the reduction in the amount of N ₂ associated with the O ₂ stream. In addition, lower process gas consumption allows the Claus reaction furnace to be operated without adding fuel, since less inert gas needs to be heated.

Since the process gas flow rate at the outlet of the Claus reaction furnace is now reduced to only 38% of the base case, the supply of residual Claus reaction gas to the residual Claus reaction gas combustion chamber is also significantly reduced. The process gas flow rate from the residual gas combustion chamber of the Claus reaction is only 56% of the base case, which is relatively higher than the flow rate of the Claus unit due to the large amount of SWS gas exhaust to the wet sulfuric acid process unit.

With this design it is possible to operate without fuel gas in both the Claus process and the sulfuric acid process, even with such a high recycle flow of H ₂ SO ₄ from the sulfuric acid process.

Claims (23)

1. A method for producing sulfur from feed gas containing 15 vol. %, 20 vol. %, 30 vol. %, 40 vol. % or 50-99 vol. % or 100 vol. % H ₂ S, and a stream of sulfuric acid, including the stages: a. providing a Claus reaction furnace feed stream containing said feed gas, an amount of sulfuric acid, an amount of oxygen, and optionally an amount of fuel, where the amount of oxygen is substoichiometric, b. directing said Claus reaction furnace feed stream to a Claus reaction furnace operating at an elevated temperature, such as above 900°C, providing feed gas for the Claus converter, c. cooling said feed gas for the Claus converter, providing cooled feed gas for the Claus converter and optionally removing elemental sulfur from the gas, d. directing said cooled feed gas to the Claus converter, after optional preheating, into contact with a substance catalytically active in the Claus reaction, e. removing residual Claus reaction gas and elemental sulfur, optionally by cooling the effluent, from said Claus reaction catalytically active substance, f. directing a stream containing said residual Claus reaction gas to treat the residual Claus reaction gas, characterized in that said sulfuric acid sent to said Claus reaction furnace is in the form of droplets with a droplet size distribution characterized in that 90% of the droplet mass has a diameter below 500 μm, 200 μm or 100 μm. 2. The method of claim 1, wherein at least an amount of sulfuric acid is directed into said Claus reaction furnace through at least one air nozzle to produce sulfuric acid and atomizing medium. 3. The method according to claim 2, in which the atomizing medium is compressed air and the flow is from 25 Nm ³ air/ton of acid or from 50 to 200 Nm ³ air/ton of acid or 500 Nm ³ air/ton of acid. 4. The method of claim 1, wherein at least an amount of sulfuric acid is directed into said Claus reaction furnace by means of at least one hydraulic nozzle. 5. The method according to claim 1, where the average residence time of the process gas in the Claus reaction furnace is less than 5 seconds, more preferably less than 2 seconds. 6. The method according to claim 1, wherein the Claus reaction furnace contains a turbulence amplifier. 7. The method according to claim 1, wherein the Claus reaction furnace contains an impacting agent. 8. The method according to claim 1, wherein said treatment of the residual gas of the Claus reaction includes the steps of: g. directing a stream containing said Claus reaction residual gas, oxygen and fuel as feed gas into a Claus reaction residual gas combustion chamber operating at a temperature above 900° C. or an oxidation catalyst providing feed gas for the SO ₂ converter, h. directing said feed gas to the SO ₂ converter into contact with a substance catalytically active in the oxidation of SO ₂ to SO ₃ , providing a gas enriched in SO ₃ , i. converting said SO ₃ -rich gas into concentrated sulfuric acid, either by absorbing SO ₃ with sulfuric acid or by hydrating SO ₃ , cooling and condensing the sulfuric acid, j. recycling at least a portion of the resulting sulfuric acid into a Claus reaction furnace. 9. The method of claim 1, wherein the amount of sulfuric acid comes from a source other than treatment of the Claus reaction tail gas. 10. The method of claim 1, wherein the amount of sulfur in the sulfuric acid stream 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. 11. A process plant comprising a Claus reaction furnace, a Claus recovery boiler, a Claus conversion section, a Claus reaction residual gas combustion chamber and a sulfuric acid section, where the Claus reaction furnace has an inlet to the furnace, an acid nozzle inlet and outlet, a Claus recovery boiler has an inlet for gas, an outlet for gas and an outlet for elemental sulfur, the Claus conversion section has a gas inlet, an outlet for gas and an outlet for elemental sulfur, the Claus reaction residual gas combustion chamber has an inlet and an outlet, and the sulfuric acid section has an inlet for gas, an outlet for gas and an outlet for sulfuric acid, and wherein the Claus reaction furnace inlet is configured to receive feed gas and oxidant, and the Claus reaction furnace outlet is configured for liquid communication with the Claus recovery boiler inlet, where the Claus recovery boiler outlet is configured for liquid communication with the conversion section inlet a Claus reaction gas combustion chamber, and wherein the inlet of the Claus reaction residual gas combustor is configured in fluid communication with an output of said Claus conversion section outlet for gas, wherein the outlet of the Claus reaction residual gas combustion chamber is configured in fluid communication with an inlet of the sulfuric acid section, characterized further in that the output for sulfuric acid, the sulfuric acid section is in fluid communication with the acid nozzle inlet of said Claus reaction furnace. 12. The process plant of claim 11, further comprising a sulfur storage tank having a volume corresponding to the amount of sulfuric acid withdrawn from the sulfuric acid outlet of the sulfuric acid section in 1 to 4 days.