EA039970B1 - METHOD FOR PRODUCING SULFUR AND SULFURIC ACID - Google Patents

Description

(57) The invention relates to a process plant including a Claus reaction furnace, a Claus gas cooler, a Claus conversion section, a Claus off-gas oxidizer, and a sulfuric acid production section, the Claus reaction furnace having an inlet and an outlet, and one or more spray nozzles for adding a recycled stream of concentrated sulfuric acid to the Claus reaction furnace in the form of droplets, the gas cooling device of the Claus plant has a gas inlet, a gas outlet and an outlet for elemental sulfur, the Claus conversion section has an inlet gas outlet, gas outlet and elemental sulfur outlet, the Claus off-gas oxidizer has a Claus off-gas inlet, a Claus off-gas oxidizer inlet, and a floor section has a gas inlet, a gas outlet, and a sulfuric acid outlet, and wherein the inlet of the Claus reaction furnace is configured to receive feed gas, sulfuric acid, and oxidant for the Claus reaction furnace, and the outlet of the Claus reaction furnace is made so that it communicates in flow with the inlet of the gas cooling device of the Claus plant, and the outlet of the gas cooler of the Claus plant is made so that it communicates in flow with the inlet of the Claus conversion section, and the inlet for the exhaust gas of the Claus plant of the device for oxidizing the off-gas of the Claus plant is made so that it communicates with the outlet of the specified section of the Claus conversion, the outlet for the process gas of the device for oxidizing the off-gas of the Claus plant is made so that it communicates with the flow with the inlet of the section obtained and the sulfuric acid outlet of the sulfuric acid production section is in fluid communication with the inlet of said Claus reaction furnace and associated process. Said method has the corresponding advantage that such a method prevents the undesired production of sulfuric acid and also reduces the volume of gas in the Claus process.

039970 B1

The present invention relates to a process for converting H2S into elemental sulfur and sulfuric acid, optionally with a controlled ratio between elemental sulfur and sulfuric acid.

H2S is a common by-product in many processes, including the hydrodesulfurization of refinery streams and the production of viscose. It is desirable to undergo H ₂ S conversion prior to release to the atmosphere, as H ₂ S is highly toxic, odorous, and a problem for the environment.

Refining processes, in addition to producing the well-known gas with a high concentration of H ₂ S, can often also produce a so-called sour water stripping gas, which contains H2S, H2O and NH ₃ in almost equal amounts.

Particularly in refineries, the process of choice for reducing H2S emissions is the Claus process, which has been known and optimized for more than 8 decades. The Claus process proceeds by sub-stoichiometric combustion of H2S to form SO2 in a Claus reaction furnace to provide feed gas for the Claus converter. The subsequent Claus process will convert H2S and SO2 to form elemental sulfur which can condense and be removed.

Typically, the removal efficiency for the Claus process is between 95 and 98%, which is not enough to meet environmental regulations. Therefore, it is common practice to provide off-gas treatment after the Claus process in order to obtain a reduction in sulfur emissions of more than 99%. The off-gas treatment is often a sulfuric acid plant, which introduces a requirement for handling sulfuric acid.

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

International application WO 2012/152919 A1 discloses a process for the production of sulfuric acid for Claus off-gas treatment, which describes the conversion of H2S to H2SO4 in the Claus off-gas.

The process steps are:

1) Substoichiometric oxidation;

2) Klaus conversion;

3) Oxidation of reduced sulfur compounds (H2S) in the off-gas of the Claus plant in an atmosphere with a high oxygen content at 400-700°C;

4) Catalytic oxidation of SO2 to SO ₃ ;

5) H ₂ SO ₄ condensation.

It is recognized that the H ₂ SO ₄ product is not always desirable and it is proposed to recycle the sulfuric acid to an upstream Claus reaction furnace or to the H2S oxidation stage as described above. However, sulfuric acid recycling is only thought of as a reduction in sulfuric acid emissions, and the consequences of H ₂ SO ₄ recycling in a WSA® or Claus process have not been assessed, i.e. it has not been taken into account that H ₂ SO ₄ recycling requires reducing the amount of O ₂ sent to the Claus reaction furnace, and the beneficial effect on the Claus process and the process of obtaining sulfuric acid is not realized. This is especially true when highly concentrated sulfuric acid from a sulfuric acid plant is recycled.

WO 2012/152919 A1 also acknowledges that auxiliary fuel may be required in both the Claus reaction furnace and the H2S oxidation step to achieve the desired operating temperature without understanding the beneficial effects of using feed gases as auxiliary fuel for the oxidation of H ₂ S during the production of sulfuric acid.

Therefore, the proposal to recycle H2SO4 to the Claus reaction furnace would not provide a workflow by itself, but would require additional process modifications.

The present invention provides a process for converting H2S to elemental sulfur with increased efficiency, in which the Claus process is combined with a process for producing sulfuric acid. In addition, mutual reinforcement of the optimal combination of these two processes is realized. According to this method, the sulfuric acid produced in the sulfuric acid production process of the Claus off-gas treatment is recycled to the Claus reaction furnace to decompose and produce elemental sulfur.

For the purposes of this application, the stoichiometric amount of oxygen must be determined with the assumption that the products obtained from N, H, C, S and O in the feed gas are N ₂ , H 2 O, CO 2 and SO 2 . If less than stoichiometric (also called substoichiometric) oxygen is present, this means that not all of the feedstock components are completely oxidized. For the Claus plant feed gas, this means that the substoichiometric combustion/reaction process gas will contain unreacted H2S, NH3 and hydrocarbons from the feed stream(s) and _H2 , CO, COS, SO2 and CS2 formed in the _O2 deficient environment .

For the purposes of this application, a fuel should be defined as a composition that, when oxidized with

- 1 039970 using O ₂ will form N2, H2O, CO2 and SO2 as reaction products and release a significant amount of energy during these reactions. A mixture of hydrocarbons (eg natural gas with CH ₄ and C ₂ H ₆ ) as well as H2S is a typical fuel gas, but fuel gas can also contain CO, NH3 and H ₂ .

For the purposes of this application, oxygen (O ₂ ) is understood to be an O 2 containing stream such as air, enriched air and pure oxygen, but which can also be an O ₂ containing process gas.

For the purposes of this application, the stoichiometric quantities of H2S and O2 of the Claus process, corrected for oxidation to compounds other than H2S and SO2, should be calculated based on the theoretical O demand based on the stoichiometry of the Claus process and the unrealized consumption of O2 due to partially oxidized products ( other than H2S and SO2).

For the purposes of this application, the unit of wt.%, should denote % wt./wt., and the unit of vol.% should denote % v/v.

For the purposes of this application, where gas phase concentrations are indicated, unless otherwise indicated, they are given as volume/volume concentration.

The input sulfur compounds are assumed to be oxidized according to the overall Claus reactions, with an average consumption of one O atom per S atom. The nitrogen atoms are assumed to require no O consumption. The hydrocarbon compounds are assumed to require the consumption of 2 O atoms per C atom. and % O atom for each H atom:

^•0,Klaus 2tIq T T ^-S

The oxygen consumption must be corrected due to incomplete oxidation according to the required oxygen consumption for fully oxidizing products to theoretical end products, eg COS + 3/2 O ₂ to CO ₂ and SO2. The partial oxidation products presented here are merely examples and should not be considered a complete list.

^ • O, incomplete 3 n _cos + 6n _C5 - ₂ + mr _co _ 1

Io ₂ , corrected ^- D (Ao, stoichiometric ^ O, incomplete.

^O ₂ , corrected 2 C^O, stoichiometric 71o, incomplete) '^total

The corrected oxygen consumption in the Claus process can in practice be estimated based on an analysis of the volumes and compositions of the streams entering and leaving the Claus section of the process plant, possibly in combination with the volumes and compositions of other streams.

In a broad aspect, the present invention relates to a method for producing sulfur from a source gas containing from 30, 40 or 50 to 99 vol.% or 100 vol. % H2S, and a recycled stream of sulfuric acid, including the stages:

a) supplying to a Claus reaction furnace operating at an elevated temperature, such as above 900° C., a Claus reaction furnace feed stream containing said feed gas, some recycled sulfuric acid and some oxygen, and optionally some fuel, with obtaining the source gas for the Claus converter, and the amount of oxygen is substoichiometric,

b) cooling said Claus converter feed gas to produce a cooled Claus converter feed gas and, if necessary, some elemental sulfur,

c) directing said cooled feed gas to the Claus converter to contact the Claus catalytically active material,

d) removing the Claus plant off-gas and elemental sulfur, if necessary by cooling the effluent from said Claus catalytic material,

e) sending a stream containing said Claus off-gas, oxygen and fuel as feed gas to a Claus off-gas oxidizer operating at a temperature above 900° C. and/or a catalytic oxidizer to produce a converter feed gas with a high content of SO ₂ ,

f) sending said feed gas to the SO2 converter to contact a material catalytically active in the oxidation of SO ₂ to SO ₃ to produce a high SO ₃ gas, and

g) converting said SO3 rich gas into concentrated sulfuric acid and SO3 depleted gas, either by absorbing SO3 in sulfuric acid or by hydrating SO ₃ , cooling and condensing the sulfuric acid,

- 2 039970 wherein said sulfuric acid recycle stream contains some of said concentrated sulfuric acid, and wherein said concentrated sulfuric acid contains from 90 to 98 wt.% or 98.5 wt.% H2SO ₄ , the corresponding advantage of such a process being that it has high conversion and thermal efficiency and prevents unwanted formation of sulfuric acid. The use of a Claus reaction furnace and a Claus off-gas oxidizer operating at a temperature above 900° C. has the effect of ensuring complete conversion of the components present, and this may, if necessary, require the presence of fuel in addition to the feed gas. In addition, homogeneous Claus reactions will occur in the Claus reaction furnace so that sulfur can be removed when the feed gas for the Claus converter is cooled. The feed stream to the Claus off-gas oxidizer may typically include H2S as fuel from the Claus off-gas and/or a separate stream containing H2S, a hydrocarbon or other fuel. In addition to the process steps mentioned, this method may include other steps such as heat exchange to change the temperature (or adjust the process streams by other means) to an appropriate range for the processes involved.

In another embodiment, the feed stream for the Claus reaction furnace contains less than 0.1 wt.% non-elemental nitrogen, such as NH ₃ , with the corresponding advantage of preventing the formation of, for example, ammonia salts, which can clog the condenser(s) in the Claus process.

In another embodiment, the Claus reaction furnace feed stream contains less than 50%, 20%, 10% or 1 vol% N2, with the corresponding advantage of providing a high temperature process in the Claus reaction furnace and in a reduced volume of process gas due to the reduced presence of N2 . This can be achieved by using pure O ₂ or oxygen enriched air as the oxygen source.

In an alternative process, steps c) and d) are performed sequentially 2-5 times, with the corresponding advantage of allowing higher conversion in the process when multiple Claus steps are performed, as a result of the equilibrium being shifted towards product formation if sulfur is removed.

In an alternative process, step f) is carried out 2-5 times in succession at a temperature between 380 and 450° C., with intermediate cooling and usually also cooling between steps f) and g), with the corresponding advantage of shifting the equilibrium of the exothermic process towards product formation, thus enabling higher conversions in the process when multiple SO2 oxidation beds are operated at optimum temperature.

In another embodiment, the ratio of H ₂ S : SO2 in said Claus off-gas is greater than 2, preferably from 2.5 or 5 to 10 or 20, the corresponding advantage being that such a source gas provides an H2S-containing Claus off-gas for the Claus off-gas oxidizer.

Such a feed gas containing an increased amount of H2S minimizes the need to add fuel gas, since the oxidation of H2S releases a significant amount of energy, while SO2 does not release energy in the Claus off-gas oxidizer. This off-gas composition can be obtained if the ratio of H ₂ S : SO2 in the Claus converter feed gas is slightly above 2:1.

In another embodiment, the ratio of H ₂ S : SO2 in said off-gas from the Claus plant is less than 2, preferably from 0.05 or 0.1 to 1 or 1.8, the corresponding advantage being the presence of an essentially H ₂ S-free off-gas. gas installation Claus. In a downstream sulfuric acid plant, such a Claus off-gas substantially free of H2S can be advantageous since SO2 will not oxidize without a SO2 shift catalyst and thus it will be possible to preheat the Claus off-gas with a combination of H2S catalytic oxidation (controlled bypass of H2S containing feed gas) and process gas recirculation in the H2S catalytic oxidation zone so that temperature rise within the _H2S oxidation catalyst can be carefully controlled. With an unknown and/or varying concentration of H ₂ S in the off-gas of the Claus plant, the risk of overheating the H ₂ S oxidation catalyst is high. Such an off-gas composition can be obtained if the ratio of H ₂ S : SO ₂ in the Claus converter feed gas is slightly below 2:1.

In another embodiment, the method further includes the step of directing some additional feed gas to said Claus off-gas oxidizer, with the corresponding benefit of providing additional sulfur and fuel for the sulfuric acid production process. This additional feed gas may contain impurities that may be burned prior to treatment in the sulfuric acid production process and/or hydrogen sulfide and other fuels that may contribute to the production of sulfuric acid and combustion

- 3 039970 in the Claus off-gas oxidizer. If the additional source gas contains a large amount of inert gases or sulfur-free fuel, the method also has the advantage of preventing the Claus converter from growing in size due to the non-contributing flow. The additional feed gas may come from the same source as the feed gas, or it may come from a different source.

In another embodiment, said additional feed gas contains more than 5% by volume of non-elemental nitrogen, such as NH ₃ , with the corresponding advantage being that it allows for a process in which non-elemental nitrogen species that may be difficult to oxidize in a sub-stoichiometric reaction atmosphere Claus furnaces can be sent to the Claus off-gas oxidizer. Such a process can be particularly useful if the additional feed gas is a sour water stripper (SWS) gas containing H2S, NH ₃ and H2O, of which only H2S is desirable in the Claus process and NH ₃ is problematic in the Claus process. due to potential clogging with ammonia salt. Instead, such SWS gas can be sent to a sulfuric acid plant where NH ₃ is well known to be operated.

In another embodiment, the amount of sulfur in the additional feed gas is at least 1, 2, or 5 wt % of the total elemental sulfur removed from the process, the corresponding advantage of such a feed gas being that it is capable of providing thermal energy, and while also helping to reduce sulfur emissions.

In another embodiment, the material catalytically active in the Claus reaction contains activated alumina (III) or titanium (IV) oxide, and the corresponding advantage of such a material is that it provides an efficient process for obtaining elemental sulfur.

In another embodiment, step (c) is carried out at a pressure of 200 to 700 mbarg, a temperature of 200 to 350° C. and a space velocity of 800 to 3000 Nm ³ /h/m ³ , with the corresponding advantage of such conditions being that they are effective for obtaining elemental sulphur.

In another embodiment, step (c) is carried out at a temperature of from 100 to 150°C, and step (d) includes the step of periodically heating said material catalytically active in the Claus reaction to allow the removal of condensed elemental sulfur in the liquid or gas phase, and the corresponding The advantage of low temperature is that it is advantageous in achieving very high conversions of SO2 and H2S to elemental sulfur, both because of the low temperature and because the reaction product is removed, providing even better conditions for high conversion.

In another embodiment, said material catalytically active in the conversion of SO ₂ to SO ₃ contains vanadium, the corresponding advantage of such a material being that it provides an efficient process for producing sulfuric acid.

In another embodiment, said step (g) is carried out at a pressure of 50 to 200 mbarg, a temperature of 380 to 520° C. and a space velocity of 800 to 1500 Nm ³ /h/m ³ , based on the catalyst bed, with the corresponding the advantage of such conditions is that they are effective in oxidizing SO2 to form SO3.

In another embodiment, the amount of sulfur in the sulfuric acid recycle stream is greater than 1, 3, or 5 wt.% and less than 17, 21, or 25 wt.% of the total amount of elemental sulfur removed from the process. Recirculation above the lower limits has the advantage of having the effect of reducing the volume of the process gas, while recirculation that is less than the upper limits avoids the situation where it is necessary to add additional fuel to the Claus reaction furnace, which leads to excessive process volume and operating costs. . In particular, when the oxygen source in the Claus reaction furnace is oxygen-enriched air, a high ratio between sulfuric acid recycle and elemental sulfur removed, such as above 10%, is advantageous.

In another embodiment, the sulfuric acid in the sulfuric acid recycle stream is atomized in said Claus reaction furnace, either using dual-flow nozzles driven by compressed air, N2 or steam, or using hydraulic nozzles, and wherein the residence time in the Claus reaction furnace is from 1 .5 to 4 s, the corresponding advantage of such nozzles being that they atomize fine droplets and that the residence time is sufficient to completely evaporate the droplets of sulfuric acid.

In another embodiment, the molar ratio of H ₂ S:O ₂ in the combined streams sent to the Claus reaction furnace is at least 2.5, with the corresponding advantage of such a low oxygen feedstock being to allow substoichiometric partial conversion of H ₂ S to SO ₂ and from the contribution from thermal dissociation of H ₂ SO ₄ providing the remaining oxygen to obtain the desired H ₂ S:SO ₂ ratio of 2.0 in the Claus converter feed gas.

In another embodiment, the molar ratio of H ₂ S:O ₂ in the combined streams sent to the Claus reaction furnace, corrected for other oxygen consuming compounds, is

- 4 039970 feedstock and corrected for products of partial oxidation in the off-gas of the Claus plant, is greater than 2.1, 2.2 or 2.5, with the corresponding advantage being that the remaining required oxygen atoms are obtained from sulfuric acid, so that the amount of molecular oxygen fed into the process is reduced, and thus less inert nitrogen is provided compared to a full supply of oxygen from atmospheric air, with a corresponding reduction in process gas flow.

In another embodiment, some of the gas in the process is cooled as needed and directed to an upstream position to control the process temperature, with the corresponding advantage being the ability to actively control the temperature of highly exothermic processes. Refrigeration may not be required if the gas is already at a lower temperature than the upstream temperature.

In another embodiment, one or more of the streams directed to said Claus reaction furnace is preheated by heat exchange with the hot process stream, with the corresponding advantage of minimizing or avoiding the need for auxiliary fuel to achieve the desired temperature to vaporize the sulfuric acid and convert the feedstock. .

In another embodiment, one or more of the streams directed to said Claus off-gas oxidizer is preheated by heat exchange with the hot process stream, with the corresponding advantage of minimizing or avoiding the need for auxiliary fuel to reach the desired temperature for combustion and subsequent SO ₂ oxidation.

In another embodiment, said material catalytically active in the oxidation of SO2 to SO ₃ contains vanadium, the corresponding advantage being that such material has a high activity for the oxidation of SO2.

In another embodiment, the condensation of sulfuric acid according to step (g) is carried out in a condenser where the cooling medium and the high SO ₃ gas are separated by glass, the corresponding advantage being that the condensation of sulfuric acid is carried out in equipment which is stable to the effects of corrosion. The glass may in particular be borosilicate glass. The glass can either be in the form of horizontal glass tubes containing a cooling medium or vertical glass tubes containing a high SO ₃ gas and condensed sulfuric acid. The cooling medium may preferably be a process gas intended for a process operating at an elevated temperature and thus benefiting from the production of a preheated process gas, such as Claus off-gas sent to a Claus off-gas oxidizer, or oxidant sent to one or both of the Claus furnaces or to the off-gas oxidizer of the Claus plant.

In another embodiment, at least one of said catalytically active materials for the oxidation of SO2 to SO ₃ or H2S to elemental sulfur and/or at least one product withdrawn from one of said catalytically active materials is cooled by heat exchange, such as interlayer heat exchange or an internally cooled catalytic reactor, the corresponding advantage being the ability to actively control the temperature of highly exothermic processes by means of interlayer heat exchange or an internally cooled catalytic reactor such as a boiling water reactor having a tubular or thermoplate cooling loop.

In another embodiment, the amount of sulfuric acid recycled is chosen such that the temperature in the Claus reaction furnace is between 800, 900 or 1000 to 1300°C, 1400 or 1500°C without the addition of auxiliary fuel to the Claus reaction furnace, the corresponding advantage being that that this temperature range is sufficient to oxidize impurities in the feedstock under sub-stoichiometric conditions, while being low enough to avoid excessive material costs. The amount of recycled sulfuric acid can be controlled either in the control loop depending on the measured temperature, or in the flow chart in accordance with the calculated material and heat balance.

Another aspect of the present invention relates to a process plant including a Claus reaction furnace, a Claus gas cooler, a Claus conversion section, a Claus off-gas oxidizer, and a sulfuric acid production section, the Claus reaction furnace having an inlet and an outlet, and one or more spray nozzles for adding a recycled stream of concentrated sulfuric acid to the Claus reaction furnace in the form of droplets, the gas cooling device of the Claus plant has a gas inlet, a gas outlet and an outlet for elemental sulfur, the Claus conversion section has an inlet gas outlet, gas outlet and elemental sulfur outlet, off-gas oxidizer installed

- 5 039970 ki Claus has an off-gas inlet, an oxidizer inlet for the Claus off-gas and, if necessary, an inlet for additional feedstock and a process gas outlet, and the sulfuric acid section has a gas inlet, an outlet for gas and an outlet for sulfuric acid, and wherein the inlet of the Claus reaction furnace is made to receive the source gas, sulfuric acid, fuel and oxidizer for the Claus reaction furnace, and the outlet of the Claus reaction furnace is made so that it communicates downstream with the inlet of the device for gas cooling of the Claus plant, and the outlet of the device for gas cooling of the Claus plant is made so that it communicates downstream with the inlet of the Claus conversion section, and moreover, the inlet for the off-gas of the Claus plant of the device for oxidizing the off-gas of the Claus plant in is configured to be in fluid communication with the outlet of said Claus conversion section, the process gas outlet of the Claus plant off-gas oxidizer is configured to be in fluid communication with the inlet of the sulfuric acid production section, and the sulfuric acid outlet of the production section sulfuric acid is in fluid communication with the inlet of said Claus reaction furnace, the corresponding advantage of such a process being the avoidance of undesired production of sulfuric acid as well as the reduction of the process gas volume.

In a preferred embodiment of the process plant, the Claus plant's off-gas oxidizer additionally has a fuel inlet.

In a preferred embodiment of the process plant, the Claus off-gas oxidizer further has an inlet and an outlet for additional feedstock.

In another embodiment, said sulfuric acid production section includes a sulfur dioxide oxidation reactor having an inlet and an outlet, and a sulfuric acid condenser having a process side having a process gas inlet, a process gas outlet, and a sulfuric acid outlet, and a coolant side having a coolant inlet and a coolant outlet, and wherein the sulfuric acid condenser is optionally configured to preheat at least one of two substances, the oxidizer for the Claus reaction furnace and the oxidizer for the off-gas of the plant Claus by directing the sulfuric acid condenser into the inlet on the side of the cooling medium and by withdrawing sulfuric acid from the outlet on the side of the cooling medium of this condenser, and the corresponding advantage of such technological plant is that it has high energy efficiency and high efficiency in removing sulfur from the process gas.

In another embodiment, the process unit further comprises at least one heat exchanger having a hot side of the heat exchanger and a cold side of the heat exchanger, configured so that on the cold side of the heat exchanger, one of said feed gas, sulfuric acid, and oxidant is preheated before to the said device for oxidizing the off-gas of the Claus plant, and so that the hot side of the heat exchanger is designed to cool the hot process stream, the corresponding advantage being to increase the energy efficiency of the process plant. The heat exchanger can either be a gas/gas heat exchanger or use a steam circuit or other heat exchange medium.

In another embodiment, the hot process stream is taken from the group consisting of a Claus off-gas oxidizer outlet stream, a Claus reaction furnace outlet stream, and a sulfur dioxide oxidation reactor outlet stream, with the corresponding benefit of energy efficiency.

In another embodiment, said one or more spray nozzles are dual flow spray nozzles or hydraulic spray nozzles, the corresponding advantage being that the sulfuric acid droplets are small and thus evaporate quickly and completely.

In another embodiment, the process plant further includes an SO ₃ reduction device having an inlet and an outlet configured such that the inlet of the SO ₃ reduction device is in fluid communication with the outlet of the Claus reaction furnace, and that the outlet of the SO 3 reduction device ₃ is in fluid communication with the inlet of the Claus conversion section, the corresponding advantage being that such arrangement effectively prevents sulfuric acid, SO ₃ or O 2 from being directed to contact with the catalytically active material in the Claus conversion section. The SO ₃ reduction device may preferably be a catalytically active material containing, for example, one or more of vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), copper (Cu), zinc (Zn ), nickel (Ni), molybdenum (Mo), tungsten (W), antimony (Sb), titanium (Ti) and bismuth (Bi) deposited on one or more compounds of aluminum (AI), titanium (Ti), silicon

- 6 039970 (Si), diatomaceous earth, zirconium (Zr), magnesium (Md) and cordierite. The SO3 reduction device may be located in a separate reactor, a separate reactor bed, or as a layer of catalytically active material on top of the Claus catalytically active material.

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

For maximum conversion to elemental sulfur, 1/3 H2S must be converted to SO2.

H ₂ S + 1.5 O ₂ -\u003e SO ₂ + H ₂ O

The stoichiometric ratio between H2S and SO2 is controlled by adjusting the amount of oxygen in the Claus reaction furnace. Oxygen is usually supplied by atmospheric air, but can also be oxygen 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, then, for example, the conversion of NH ₃ may not be complete. The consequence of this will be the feed gas for the Claus converter, which has the potential to form ammonia salts such as (NH4)2SO4 and (NH4)2S2O ₃ , which can plug the Claus plant's 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 material such as activated alumina (III) or titanium (IV) oxide.

2H ₂ S + SO ₂ -> 3/8 S ₈ + 2H ₂ O

Often 3-4 Claus converters work in series to maximize the conversion, which will increase the cost of installing Claus.

Temperature control in the Claus process is important to ensure that the elemental sulfur generated in the catalytic converter remains gaseous so that it condenses only at the desired location in the process. Because the Claus reaction is exothermic, another limitation comes from the fact that because 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 material is catalytically active at temperatures where elemental sulfur is not in the gas phase. Such a Claus process below the dew point would require an appropriate scheme to remove the condensed sulfur, for example by temperature fluctuation and purge of elemental sulfur with an inert gas.

Even with 3-4 Claus converters/condensers/heaters operating in series, it is not possible to achieve sulfur recovery of more than ~98%, which is insufficient to meet most environmental regulations. Therefore, a Claus plant is usually equipped with a so-called Claus off-gas process solution, where the aforementioned sub-dew point process is an example. There are numerous ways to work with off-gas, with different characteristics. In order to achieve very high removal efficiencies, these Claus off-gas units 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 an H ₂ S waste stream, but elemental sulfur is easily transported to other locations and stored for long periods of time.

A common alternative to the Claus process is the conversion of H2S to sulfuric acid, for example by the so-called wet catalysis sulfuric acid process (WSA® process). The resulting sulfuric acid can be used in other chemical processes in the plant. The WSA® process can also be an off-gas treatment of a Claus process plant. A similar dry process for the production of sulfuric acid may also find use in this connection.

Sulfuric acid processes oxidize H2S to SO ₂ and SO ₂ to SO ₃ and then add water to SO ₃ to produce sulfuric acid, either by reacting with water in the gas phase in the so-called wet catalysis sulfuric acid process (WSA® process). ), or by absorption in concentrated sulfuric acid in the so-called contact method or dry method. The reaction temperature during the oxidation of SO2 to SO3 will be in the range of 400-500°C, in the presence of a catalytically active material, usually containing vanadium. Typically, wet catalyzed sulfuric acid processes produce sulfuric acid having a concentration in the range of 9298%, while dry sulfuric acid processes can also produce sulfuric acid having a concentration in excess of 98%.

In addition, it can also be attractive to collect high pressure steam in the range of 30

- 7 039970 up to 80 barg from highly exothermic sulfuric acid processes, while the Claus process will only produce steam at a lower pressure and in much smaller quantities.

The production of large quantities of sulfuric acid, however, may be less attractive, even if the sulfuric acid is sold commercially, because the transportation of sulfuric acid is complex and regulated.

The reactions that occur during the production of sulfuric acid (dry method and wet catalysis) are

H ₂ S + 1.5O ₂ -> SO2 + H2O

SO ₂ + 0.5 O2 -> SO3

SO ₃ + H ₂ O -> H2SO4

The overall reaction of the sulfuric acid production process can be described in accordance with H ₂ S + 2 O ₂ -> H ₂ SO ₄

The WSA® process, as a conventional Claus off-gas solution, provides a solution that meets environmental regulations at lower capital and operating costs than alternatives. So far, the only drawback of the WSA® process has been the product in the form of sulfuric acid, which is not always desirable. With the new invention, the integrated Claus + WSA® process will eliminate this drawback and at the same time reduce the plant size of both the Claus process and the WSA® process.

It has now become clear that the combination of the Claus process and the sulfuric acid production process can also be accomplished by recycling all or substantially all of the sulfuric acid produced to the Claus reaction furnace. The combustion of sulfuric acid is known from the recovery of spent sulfuric acid in a wet catalysis sulfuric acid plant, but has not been practiced in the Claus reaction furnace, ie in the combustion chamber of the Claus process. As a result of the combustion/decomposition of sulfuric acid at elevated temperature, the following reaction occurs:

H ₂ SO ₄ ^ H ₂ O + SO2 + Y2 0 ₂

Sulfuric acid will not decompose until it has evaporated and heated to >600°C. To allow sufficient time for the droplets to evaporate, it is recommended to design the combustor with a residence time of at least 2 s, while conventional Claus reaction furnaces with gas phase only reactions are usually designed for a residence time of 1 s.

The atomizing medium is preferably compressed air, since oxygen will also be supplied to the process gas. An alternative is pressure nozzles or hydraulic nozzles.

If all the sulfuric acid produced in the sulfuric acid process downstream of the Claus process is sent to the Claus reaction furnace, it is possible to carry out the Claus process in which the reduction of H ₂ S emissions utilizes very high removal efficiency as well as the thermal efficiency of the sulfuric acid plant. acids, but in which the product is sulfur, which is easy to handle and transport.

In addition, when sulfuric acid is recycled, the decomposition of H ₂ SO ₄ releases O ₂ , so that the amount of added oxidant for combustion will be reduced, which, if the oxidant is atmospheric air, has the advantage of a significant reduction in process volume, since atmospheric air contains almost 80% inert N ₂ ie 4 volumes of N ₂ per volume of O2.

The overall Claus reaction based on air as O ₂ carrier for the Claus reaction furnace is

H ₂ S + 2 O ₂ + 8 N ₂ ^ 2 S ₂ + 4 H ₂ O + 8 N ₂

Similarly, the overall Claus reaction based on H ₂ SO ₄ as the oxygen carrier for the Claus reaction furnace is

H ₂ S + H ₂ SO ₄ ^ 2 S ₂ + 4 H ₂ O

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 Claus off-gas volumetric flow rate by 67% compared to atmospheric air.

The above reaction is based on 100 wt.% H ₂ SO ₄ , which for practical reasons cannot be obtained in the production of sulfuric acid from the off-gas of the Claus plant, which is characterized by a very high concentration of H ₂ O (20-35 vol.%). H ₂ SO ₄ is hygroscopic and will absorb water from the gas phase. As a consequence, in the sulfuric acid plant for the off-gas of the Claus plant, a weak, for example 45 wt.%, H2SO4, 45 wt.% H2SO4

- 8 039970 corresponds to a molar ratio of H2SO4:H2O of 1:6.7, since the remaining 55 wt.% is H2O, and thus the reaction with H2SO4 as oxygen carrier turns into the following:

H ₂ S + H2SO4 + 6.7 H ₂ O 2 S ₂ + 10.7 H ₂ O

One can define α, the ratio of inert process gas to elemental sulfur, as:

K _ number of moles of inert process gas number of moles s ₂

For the overall Claus reaction, using atmospheric air as the oxygen carrier, α is 6, and using 100 wt.% H2SO4 as the oxygen carrier, α is 2, i.e. significantly less than the inert process gas (primarily N2 and H2O ) is formed when H2SO4 is used as an oxygen carrier.

When using 45 wt.% H2SO4, added at the thermal stage of the Claus installation, the value of α becomes equal to 5.35 - a value close to using atmospheric air.

In the WSA® process, sulfuric acid concentrations >90 wt% H2SO4 can easily be obtained without a dedicated sulfuric acid concentration column, even at the high H ₂ O concentrations found in the Claus off-gas. At 95 wt.% H2SO4, the value of α becomes equal to 2.15, that is, close to the theoretical minimum and much better than for 45 wt.% H2SO4.

Another important aspect of adding sulfuric acid to the thermal stage of the Claus plant is the energy balance, since the thermal stage requires a minimum temperature of about 900-1000°C to ensure the destruction of impurities such as CH4 in the feed gas. The overall Claus reaction using atmospheric air as the oxygen source is exothermic and thus contributes to high operating temperatures. Sulfuric acid, however, requires energy to vaporize the H2SO4 and H2O, and the Claus reaction itself is endothermic, that is, effectively cooling the thermal step. In addition to diluting the Claus process gas, the additional water in sulfuric acid also further cools the thermal stage and thus limits the amount of sulfuric acid that can be added. Alternatively, fuel gas must be added to the system to supply thermal energy, increasing the process gas flow in the Claus plant and the cost of operation.

The preferred H ₂ SO ₄ recycle stream is determined by the amount of sulfur fed to the downstream Claus off-gas oxidizer, i.e., the sum of sulfur in the off-gas and other WSA feed streams, and the sulfur recovery in the WSA. Because the sulfur recovery in a WSA unit will typically be above 90%, most of the sulfur in the feedstock will be recycled to the Claus furnace.

The increased flow of H2SO4 to the Claus reaction furnace will reduce the combustion air requirement and hence the output of the process gas stream from the Claus reaction furnace to the point where additional fuel is needed to maintain the desired temperature in the reaction furnace.

Therefore, optimal sulfur recovery in the Claus plant, the total amount of sulfur in the off-gas and bypass gas in the WSA, occurs when the temperature in the Claus reaction furnace can be maintained in the preferred range between 800 and 1400°C without the need to supply heat with a fuel gas or take measures to cool the reaction furnace.

It may also be advantageous to pass some feed gas through the bypass line to the Claus off-gas oxidizer because the feed gas has a high heating value that can be used in the Claus off-gas oxidizer and thus reduce the need for adding auxiliary fuel. This can be even more advantageous if there are two sources of feed gas, such as one feed gas containing no NH3 and another feed gas containing NH3, since substoichiometric conditions in the Claus reaction furnace prevent complete oxidation of NH3. The so-called sour water stripper gases (SWS) are an example of such an NH3-containing feed gas.

In Claus processes for SWS gas treatment, complete decomposition of NH3 in the Claus reaction furnace is critical, otherwise ammonia salts such as (NH ₄ ) ₂ SO ₄ and (NH ₄ ) ₂ S ₂ O ₃ will form and clog the final condenser sulfur. Dedicated high intensity (two-stage) burners are capable of reaching the high temperatures needed to thermally destroy NH3, but require precise oxygen control in two separate streams.

However, it is well known that the SWS gas is treated in a sulfuric acid plant because the complete oxidation of NH3 to N2 and NO is achieved with an excess of oxygen. Therefore, it may be desirable to configure an integrated Claus + sulfuric acid process with two combustion chambers to route a first feedstock containing H ₂ S and a small amount of co

- 9 039970 no or no NH ₃ into the Claus reaction furnace, while at the same time directing a gas containing NH ₃ , such as SWS gas, to the Claus off-gas oxidizer. In such a configuration, it may be desirable to design the sulfuric acid plant to include a selective catalytic reduction (SCR) NO _x section.

An integrated process according to the present disclosure may also benefit from the use of oxygen-enriched air, or substantially pure oxygen, in the Claus reaction furnace. The use of oxygen-enriched air has the advantage of reducing the amount of inert nitrogen in the process gas and thus reducing the volume of the process gas and hence the plant size. The lack of dilution with nitrogen also results in an increase in the combustion temperature, which can be advantageous if impurities are present that need complete conversion, especially since the amount of oxygen in the Claus reaction furnace is substoichiometric. Because the Claus catalyst is sensitive to the presence of impurities, such as light hydrocarbons, it can often be advantageous to operate the Claus reaction furnace with oxygen enriched air to achieve an elevated temperature to completely oxidize the impurities. This also has the additional advantage of allowing an initial homogeneous non-catalytic Claus conversion that can take place at temperatures above 900°C.

However, in terms of thermal efficiency, the high combustion temperature may be limited by the choice of materials of construction in the Claus reaction furnace and the downstream waste heat boiler. For feed gases with a high concentration of H2S, oxygen enrichment can raise the process gas temperature above the design temperatures for the materials. However, the combination with H2SO4 recirculation (which cools the process gas by evaporating and decomposing the acid) will make it possible to use enriched O2 in such a process flow.

The Claus off-gas oxidizer will typically operate with ambient air, and in addition, it may also be beneficial to feed gases with a low concentration of sulfur compounds into this Claus off-gas oxidizer, as the complete combustion of sulfur compounds releases significantly more energy than the partial oxidation that occurs in the Claus reaction furnace.

As a consequence, it may be advantageous to direct feed gases containing high concentrations of H2S to the Claus plant while bypassing less concentrated feed gases as well as feed gases containing NH ₃ to the Claus off-gas oxidizer.

If the Claus off-gas oxidizer receives only the Claus off-gas containing only a limited amount of H2S, the calorific value is too low to maintain stable combustion. In this situation, the addition of auxiliary fuel is required. This auxiliary fuel can be either H2S, SWS gas, or hydrocarbon feedstock, but preferably some of the existing feed gas is used for the integrated Claus plant and sulfuric acid production.

The integration between the Claus process and the sulfuric acid process provides the benefits of integration. These include the ability to reduce volume flow in the Claus process by providing an oxidant in the form of sulfuric acid that can replace atmospheric air. In addition, feed gas utilization can be optimized so that fuel containing feed gases that contribute significantly to sulfur production can be sent to the Claus process, while feed gases that contribute thermal energy and do not react products, such as CO2, can be directed to the process of obtaining sulfuric acid. If the process is designed to recycle too much sulfuric acid, additional fuel may be required to provide the heat needed to vaporize and dissociate the sulfuric acid. Plant size may even benefit from increased acid recycle since the size of the WSA® plant does not increase significantly with the amount of acid produced, while the size of the Claus plant and the WSA® plant decrease with decreasing inert gas flow.

The integration of these two processes also provides a way in which the Claus process is operated at a low conversion, such as 90 or 95%, because compared to adding an additional Claus converter stage, it may be cheaper to carry out the additional conversion in the sulfuric acid process.

In addition to the WSA® process, sulfuric acid can also be produced in other processes to reduce sulfur emissions. The first example is the SNOX process, in which NOx selective catalytic reduction is integrated with WSA®, a process flow that is particularly favorable for off-gases with SO2 content of less than 1 vol.%.

The standard Claus setup requires >50 vol% H2S in the feed gas (excluding oxidizer gas) to be thermally self-sufficient in a Claus reaction furnace. At lower con

- 10 039970 H2S centration requires feed gas preheating and a so-called split flow configuration. Claus plants handling feed gases containing < 10-20 vol% H2S are rare. Sulfuric acid processes, on the other hand, treat these so-called H2S-poor gases very efficiently, producing concentrated sulfuric acid. The sulfuric acid product will be highly concentrated in sulfur and oxygen.

A combination of a sulfuric acid plant to treat low H ₂ S gas (and/or other sulfur compounds) in combination with a Claus plant that treats high H ₂ S gas and receives acid from the sulfuric acid plant would be a useful arrangement because the feed streams to both the Claus plant and the sulfuric acid plant are optimal in terms of conversion efficiency, thermal efficiency and plant size/cost.

The interaction between the Claus process and sulfuric acid production processes can also be used to optimize feedstock processing. Sulfuric acid processes, and in particular the WSA® process, have the advantage that they are well suited to contaminated feedstocks, including SWS gases containing ammonia as discussed above, dirty sulfur containing organic impurities and moderate amounts of inorganic impurities diluted streams of H ₂ S, SO2 and other sulfur compounds, including flue gases from burners and fluid catalytic cracking (FCC) gas. Similarly, gases with a high H2S content, including off-gases from CS2 processes that need to be diluted prior to WSA® treatment, can be sent directly to the Claus process instead. Also, other high sulfur process streams, such as effluent streams from coal gasification or natural gas refining, may be sent to one or both stages of the integrated Claus/WSA® process.

figures

Fig. 1 shows an integrated Claus + sulfuric acid process with a single combustion chamber.

Fig. 2 shows the prior art Claus+sulfuric acid sequential process.

Fig. 3 shows an integrated Claus + sulfuric acid production process with sulfuric acid combustion in a Claus reaction furnace according to the present disclosure.

In FIG. 1 shows an integrated Claus + sulfuric acid process with a single combustion chamber. The H2S-rich feed gas 2 is combined with the SO2-rich gas 36 and fed as feed gas of the Claus plant 4 to the reactor 8, which, especially if the SO2-rich gas 36 contains O ₂ , can contain optionally available material catalytically active in the oxidation of H2S, to convert O ₂ and H2S into SO2 and H ₂ O (10) to form an O _2- free Claus plant feed gas. The _O2- free Claus feed gas is sent to contact the Claus catalytically active material 12 (i.e., the Claus catalyst) in the same or a different reactor to produce a Claus product 14. The Claus product 14 is sent to a sulfur condensation unit 16 to produce condensed sulfur 18 and wet Claus off-gas 20. The wet Claus off-gas 20 may optionally be further reacted in the presence of additional material catalytically active in the Claus process, followed by further condensation of the sulfur in one to four additional process steps. Claus (not shown here) to produce the final wet off-gas of the Claus plant. The aqueous phase 24 may optionally be separated from the wet Claus off-gas 20 in a separator 22 to produce a dried Claus off-gas 26. An amount of dried Claus off-gas containing H2S 28, optionally together with some sulfuric acid 60, is sent into the combustor 32 to produce a high SO2 process gas 34 which is separated into a recycle process gas containing SO2 36 and a SO2 converter feed gas 38. Some of the dried Claus off-gas containing H2S 26 can be sent as recycled dried off-gas from the Claus 30 plant to suppress temperature rise in the reactors by diluting the exothermic reaction mixture. The source gas for the SO2 converter 38 is sent to the SO2 converter 40 containing one or more layers or layers of catalytically active material 42, 44, 46, if necessary with interlayer cooling, from which gas 48 with a high content of SO3 is removed. Because this high SO3 gas contains water, SO3 can add water to form H ₂ SO ₄ . H ₂ SO ₄ condenses as concentrated sulfuric acid 52 in sulfuric acid condenser 50. If the amount of water is insufficient to completely hydrate SO3, it may be preferable to add steam at an upstream location. From the sulfuric acid condenser 50, a substantially pure gas 62 may be removed and _sent to a series of stacks ₆₄ . through line 36 to the Claus reaction catalyst 12 to form

- 11 039970 elemental sulfur, while if sulfuric acid is required in an adjacent process, then all sulfuric acid can be removed through line 54. An acid cooling system (not shown) is located between the outlet of the sulfuric acid condenser and the separation into two streams of acid 54 and 56.

In a variation of the process, the conversion and condensation of sulfuric acid can be carried out in two steps, where the remaining SO2 is oxidized, water added and condensed, with the corresponding advantage of providing increased sulfur removal.

In another variation, the SO2 converter feed gas 38 can be dried so that the high SO3 48 gas contains little or no water. In this case, the sulfuric acid condenser 50 can be replaced by an absorber in which SO3 can be absorbed into sulfuric acid to produce concentrated sulfuric acid by a dry sulfuric acid production process.

Alternatively, some elemental sulfur may also be transferred to combustor 32, which will have the effect of introducing SO2 into the sulfuric acid process without introducing water, which may be useful if it is desired to increase the concentration of SO3, which may be useful in a dry process. sulfuric acid.

Alternatively, some of the H2S rich feed gas 2 can also be divided into the amount sent to the Claus reactor 8 and the amount sent to combustion chamber 32 for oxidation.

In another embodiment, some fuel gas is sent to the combustion chamber 32 to be able to maintain a stable flame and a temperature high enough to completely oxidize the reduced compounds such as H ₂ S, CO, H ₂ , COS present in the final off-gas of the Claus plant 26 .

In FIG. 2 shows a process for producing sulfur and sulfuric acid in accordance with the prior art. In this case, the source gas 2 with a high content of H2S is sent to the Claus process, from which the off-gas of the Claus plant 26 is sent to the sulfuric acid production process. The H2S rich feed gas 2 is sent to a Claus reaction furnace 66 converting some H ₂ S to SO ₂ to form a Claus converter feed gas 4 having a ratio between H2S and SO2 close to 2:1. This Claus converter gas 4 is sent to a converter 8 containing Claus catalytic material 12 to produce a Claus process product 14. The Claus process product 14 is sent to a sulfur condensation unit 16 to produce condensed sulfur 18 and Claus plant off-gas 20. The wet off-gas of a Claus plant 20 is typically further reacted in the presence of additional Claus catalytic material, followed by additional sulfur condensation in one to four additional Claus process steps (not shown here) to produce the final wet off-gas Claus settings. The aqueous phase 24 may optionally be separated from the wet Claus off-gas 20 in a separator 22 to produce a dried Claus off-gas 26, which is sent to combustion chamber 32 to produce feed gas for SO ₂ converter 34. Feed gas for SO2 converter 34 is sent into an SO2 converter 40 containing one or more layers (layers) of catalytically active material 42, 44, 46, if necessary with interlayer cooling, from which a gas 48 with a high SO3 content is removed. Because this high SO3 gas contains water, this SO3 can add water to form H ₂ SO ₄ . H ₂ SO ₄ is condensed as concentrated sulfuric acid 52 in a sulfuric acid condenser 50. From the sulfuric acid condenser 50, a substantially pure gas 62 can be removed and sent to a series of stacks 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 may be directed into combustion chamber 32. Oxygen is also supplied, typically by air, to provide oxygen both for the combustion reactions in the combustion chamber 32, but also as the oxygen needed to oxidize the SO2 in the SO2 converter. To reduce fuel consumption, SO2 oxidation oxygen can be added between the combustion chamber outlet 32 and the SO2 converter inlet 40.

In FIG. 3 shows an integrated Claus+sulfuric acid process with sulfuric acid combustion in a Claus reaction furnace 66 according to the present disclosure. The H2S rich feed gas 2, sulfuric acid 52, the oxygen rich gas 72, optionally the fuel containing gas 68 and optionally the second H2S and NH3 rich feed gas 70 are sent to the Claus reaction furnace 66 and the combustion product as the O ₂ free feed gas for the Claus converter 4 is sent to the converter 8. Between the outlet of the Claus reaction furnace 66 and the inlet of the Claus converter 8 a recovery boiler (not shown) is usually installed to reduce the temperature to the optimum operating temperature for the Claus catalyst, at necessary, also with the removal of elemental sulfur formed in the Claus reaction furnace 66. The O2-free feed gas for the Claus converter 4 is sent to contact with the catalytically active in the Claus reaction material 12, obtaining the product of the Claus 14 process. The product of the Claus 14 process is sent to the sulfur condensation unit 16, getting condensed

- 12 039970 sulfur 18 and off-gas from the Claus 20 plant.

The Claus off-gas 20 may optionally be further reacted in the presence of additional Claus catalytic material, followed by additional sulfur condensation in one to four additional Claus process steps (not shown here) to produce the final Claus off-gas. Some of the final Claus off-gas containing H ₂ S 20 is sent to the Claus off-gas oxidizer 32 to produce feed gas for the SO2 converter 34. To oxidize the compounds in the Claus off-gas, gas 72 is sent to combustion chamber 32 with a high content of O ₂ .

The SO2 converter feed gas is typically cooled in a waste heat boiler (not shown) to provide the optimum temperature for the first catalyst bed 42 in the SO2 converter 40. The SO2 converter feed gas 34 is sent to the SO2 converter 40 containing one or more catalytic beds/beds. active material 42, 44, 46, optionally with interlayer cooling, from which the high SO3 gas 48 is removed. Since this high SO3 gas contains water, SO3 can add water to form H ₂ SO ₄ . H ₂ SO ₄ condenses as concentrated sulfuric acid 52 in sulfuric acid condenser 50. If the amount of water is insufficient to completely hydrate SO3, it may be preferable to add steam at a location upstream of sulfuric acid condenser 50. From sulfuric acid condenser 50 substantially pure gas 62 may be removed and sent to a series of stacks 64. Typically, all of the sulfuric acid 52 is recycled to the Claus reaction furnace 66, but if desired, some sulfuric acid may be withdrawn for other process uses.

In another embodiment, the conversion and condensation of sulfuric acid can be carried out in two stages, where the remaining SO2 from the first stage is further oxidized, water is added and condensed, with the corresponding advantage of providing increased sulfur removal.

In another embodiment, additional SO2 conversion can be achieved by placing the off-gas treatment plant downstream of the sulfuric acid production process. Numerous solutions exist for these off-gases, with alkaline scrubbers, if necessary in combination with suspended solids filters, being the most common type. Scrubbers using H ₂ O ₂ or NH3 are preferred because the effluents from these scrubbers are 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 , that is, by eliminating the waste stream.

In another embodiment, the SO2 converter feed gas 34 can be dried such that the high SO3 gas 48 contains little or no water. In this case, the sulfuric acid condenser 50 can be replaced by an absorber in which SO3 can be absorbed into sulfuric acid to produce concentrated sulfuric acid using a dry sulfuric acid process.

In another embodiment, some elemental sulfur may also be transferred to combustor 32, which will have the effect of providing SO2 for the sulfuric acid process without introducing water, which may be useful if it is desired to increase the concentration of SO3, which may be useful in a dry process. obtaining sulfuric acid.

In another embodiment, some fuel gas 68 is sent to the Claus 32 off-gas oxidizer to provide a temperature high enough to completely oxidize all of the reduced compounds in the Claus 20 off-gas.

In another embodiment, some of the H2S rich feed gas 2 can also be divided by the amount sent to the Claus combustor (i.e., the Claus reaction furnace) 66 and the amount sent to the Claus off-gas oxidizer 32. This will reduce the need to add fuel gas to the Claus 32 off-gas oxidiser.

In another embodiment, the entire second feedstock containing NH3 and H2S 70 is sent to the Claus off-gas oxidizer 32, eliminating the risk of NH3 salt formation in the sulfur condensation units (i.e., Claus condensers) 16. In this embodiment, there will be a NO ^x 33 reduction system is installed between the outlet of the Claus 32 off-gas oxidizer and the inlet of the SO2 converter 40. Typically, a so-called SCR (Selective Catalytic Reaction) reactor will be used, requiring the addition of NH3 for this reaction to proceed SCR. The NH3 addition may be from an external source or may be a small second feed stream containing NH3 and H2S, 70 which is then bypassed to the Claus off-gas oxidizer.

In another embodiment, a catalytic reactor 35 may be installed to oxidize remaining impurities such as hydrocarbons, CO, COS, CS ₂ , S and H ₂ S.

In another embodiment, part of the Claus 20 off-gas is bypassed

- 13 039970 of the Claus off-gas oxidizer 32 and combine with the hot off-gas 34 from the Claus off-gas oxidizer at the gas mixing point immediately downstream of the Claus off-gas oxidizer. This reduces the amount of fuel gas 68 required by the Claus off-gas oxidizer to maintain a sufficiently high temperature. The combined off-gas from the Claus off-gas oxidiser and the bypassed off-gas from the Claus must have a mixed gas temperature in excess of 400° C. to ensure homogeneous (i.e., in gas phase) oxidation of H ₂ S. To ensure complete oxidation "difficult" compounds such as COS and CO, an optional oxidation catalyst 35 can be installed between the gas mixing point and the inlet to the SO2 converter 40. To ensure optimum temperature control of the oxidation catalyst, between the gas mixing point and the inlet to the oxidation catalyst a waste heat boiler or any other heat exchanger can be installed. The oxidation catalyst typically contains a noble metal such as platinum (Pt) or palladium (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.

Examples 1 -3.

Three examples were explored by process simulations for typical Claus process feedstocks that include hydrocarbons, without being directly related to the present invention.

The feed gas (2) is a high H2S gas from a refinery and has the following composition:

Feed gas consumption : 1593 Nm ³ /h

H ₂ S concentration: 91.6% vol.

H ₂ O concentration: 3.7% vol.

H ₂ concentration: 1.9% vol.

CO ₂ concentration: 2.8% vol.

Example 1 refers to a process as shown in FIG. 1, in which it is desirable to convert 70% H2S to elemental sulfur and the remaining 30% to sulfuric acid. This example would require only one combustion chamber and the volume of gas processed in the Claus section would be 67% of the volume of gas processed in the sulfuric acid section.

Example 2 refers to a process as shown in FIG. 1, in which it is desirable to convert 100% H ₂ S to elemental sulfur by recycling all of the produced sulfuric acid. This example will also require only one combustion chamber. Since more sulfur must be produced, the flows around the catalyst section and the Claus condenser were increased, while the flow to the sulfuric acid process was slightly reduced.

Example 3 relates to the prior art method as shown in FIG. 2, in which it is desirable to convert 70% of the H ₂ S to elemental sulfur and the remaining 30% to sulfuric acid. Such a process can be done with a single Claus process step, but would require a Claus reaction furnace as well as a Claus off-gas oxidizer. Compared to example 1, the process gas flow through the single pass process is lower in the Claus section and is similar in the sulfuric acid section. The cost of the larger Claus reactor and sulfur condenser is small compared to the cost of the Claus reaction furnace and waste heat boiler as in the prior art.

It is clear from the above examples that the integration of the Claus process and the WSA® process offers the potential for significant savings in equipment costs. This integration can avoid the need for a combustion chamber, and furthermore, the number of Claus process steps can also be reduced.

Examples 4-7.

Four other examples were analyzed for the method shown in FIG. 3 compared to the prior art method as shown in FIG. 2.

These examples are based on the following source gases:

High H2S feed gas (stream 2 in FIGS. 2 and 3):

Total gas consumption : 8190nm ³ /h

H ₂ S concentration: 94% vol.

H ₂ O concentration: 6 % vol.

High H2S gas is typical of refineries and will also

- 14 039970 hold various amounts of light hydrocarbons.

High H2S and NH3 feed gas (stream 70 in FIGS. 2 and 3):

Total gas consumption : 3669 ^Nm3 /h

H ₂ S concentration: 28% vol.

NH ₃ concentration: 45% vol.

H ₂ O concentration: 27% vol.

These streams containing H2S and NH3 are typically off-gases from so-called acid water strippers and are referred to as SWS gases. They may also contain varying amounts of light hydrocarbons.

The fuel gas is a mixture of light hydrocarbons (mainly CH ₄ ) with a lower calorific value of 12,200 kcal/Nm ³ .

Feed streams, combustion air and off-gas from the Claus plant are preheated as far as possible by using the heat released from the combined Claus + sulfuric acid processes.

In these examples, the Claus process is operating at 94-95% sulfur recovery from the feedstock, ie, it could be a well-performing Claus plant having only 2 catalytic stages.

Example 4 Sequential Claus + Sulfuric Acid Process According to the Prior Art

In Example 4, all feed streams are treated in a Claus process to produce a stream of 11.7 t/h of elemental sulfur and a Claus plant off-gas containing ~5% of S in the feed gases. In the Claus off-gas oxidizer, the sulfur compounds present in the off-gas of the Claus plant are oxidized, and fuel gas is provided to maintain the combustion chamber temperature at 1000° C., so that all the reduced compounds such as CO, COS, H ₂ , H ₂ S Sx and CS2 are completely oxidized to CO ₂ , H ₂ O and SO2.

Getting concentrated sulfuric acid is 2.4 t/h, in terms of 100 wt.% H ₂ SO ₄ .

The total recovery of sulfur and sulfuric acid is > 99.9% of the S in the feedstock, even with stringent environmental regulations.

Example 5 Recycle H ₂ SO ₄ to a Claus Reaction Furnace

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

The total elemental sulfur product stream is now equal to S in the feed streams, which corresponds to 107% of the base case, such as described in example 4.

The temperature in the Claus reaction furnace decreases by ~200°C due to evaporation and decomposition of H ₂ SO ₄ , but this temperature is still well above the minimum for complete burnout of hydrocarbons and NH3. No fuel gas is required in the Claus reaction furnace.

Because H2SO4 is an excellent O2 carrier, combustion air requirements are reduced and thus process gas volume is reduced as inert N ₂ flow is reduced. In total, the process gas flow from the Claus reaction furnace is reduced to 94% of the base flow, and the process gas flow from the Claus off-gas oxidizer is reduced to 93% due to this reduction in N2 flow. Since less process gas needs to be heated to 1000°C in the Claus off-gas oxidizer, the fuel gas consumption is only 92% of the base case.

The benefit from H2SO4 recycling was surprisingly high, as not only did the Claus plant's sulfur production increase by 7%, but at the same time the process gas volume decreased by 6-7%. This corresponds to an ~15% increase in Claus plant capacity, assuming that the process gas flow rate is 100% of the base case.

Example 6 Recirculation of H2SO4 to a Claus Reaction Furnace and Bypass SWS Gas to the Claus Off-Gas Oxidizer

In this example, fuel gas consumption in the Claus off-gas oxidizer was minimized by passing a portion of the SWS gas through a bypass line to the Claus off-gas oxidizer. SWS gas has a high calorific value and can easily act as a fuel gas. A feed gas with a high H ₂ S concentration could also be used, but since SWS gas can be problematic in the Claus process and does not pose problems in the WSA® process, bypassing the SWS gas has greater advantages than bypassing the H2S gas. As for the process gas, there will also be a decrease in gas volume because the NH3 in the SWS gas will increase the process gas volume in the Claus process due to the oxygen (air) requirement to burn the NH3 to N2 and H2O.

- 15 039970

The amount of recycle gas SWS is controlled so that 1000° C. is reached in the Claus off-gas oxidizer, ensuring complete burn-off of the reduced compounds from the Claus off-gas, such as H2S, COS, CO, H2, S _x and CS2.

Because the fuel gas in the Claus off-gas oxidizer now contains H2S, H2SO4 production will increase, now accounting for ~13% of S in the feed streams. This large amount of recycled sulfuric acid leads to a significant decrease in the temperature of the Claus reaction furnace.

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

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

The sulfuric acid plant will also be smaller, as the process gas consumption is only 90% of that of the base case. This is surprising as the H2SO4 production more than doubled compared to the baseline, but this is mainly due to the large reduction in off-gas flow from the Claus plant.

Most notably, the reduction in fuel gas consumption, now only 16% of the base case, contributes to significantly lower operating costs of the integrated Claus + sulfuric acid process.

Example 7 Recirculation of H2SO4 and complete SWS gas bypass to the Claus off-gas oxidiser

This example focuses on the complete elimination of the SWS gas from the Claus plant, ensuring that the formation of ammonia salt in the sulfur condensers is not possible, and thus the risk of failure of the Claus plant is reduced.

The flow of process gas from the Claus reaction furnace is 69% of the base case, but slightly higher compared to example 6, where only part of the SWS gas is bypassed. The increase in process gas flow is due to the need to add fuel gas to the Claus reaction furnace to maintain a high operating temperature.

The production of H2SO4 in the WSA® plant in this case increased to 17% of the S in the feed gases, and the recirculation of all production in this case quickly reduces the temperature of the Claus reaction furnace to the point that fuel gas is required. The process gas from the Claus off-gas oxidizer increased to 107% of the base case due to the increased sulfur feed 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 to be less optimal than example 6, ie there is an optimal H2SO4 recycle ratio that depends on the actual flow rates and feed gas compositions. Bypassing even more feed gas through the bypass will increase the production of sulfuric acid, which will further cool the Claus reaction furnace, again requiring more fuel gas and hence the Claus plant off-gas flow will increase.

For the feed gas compositions and flow rates described above, the optimal value in terms of plant size and fuel flow is between 13 and 17% of the H2SO4 recycle stream of the S feed stream in the feed streams.

Typically, the optimum feed gas bypass flow is close to the point at which the Claus reaction furnace is operating at the minimum allowable temperature, i.e. feed can be passed through the bypass to produce more sulfuric acid as long as the Claus reaction furnace temperature will not reach the limit for thermal destruction of hydrocarbons and sulfuric acid. Increasing the bypass feed ratio will reduce the fuel gas requirement in the Claus off-gas oxidizer, but will increase the fuel gas flow in the Claus reaction furnace to a much greater extent, since the fuel gas in the Claus reaction furnace must vaporize and decompose sulfuric acid and heat the process gas, while the Claus off-gas oxidizer only needs to heat the process gas.

For a feed gas containing, for example, 50% vol. H2S, the optimal H2SO4 recycle stream is ~7% of the S feed in the feed stream. The acid gas bypass to the Claus off-gas oxidizer is only 2% because the relatively low concentration of H ₂ S results in a low temperature in the Claus reaction furnace, and thus the sulfuric acid will rapidly lower the temperature and require the addition of fuel.

- 16 039970 gas into the Claus reaction furnace. The use of O2-enriched air in the Claus reaction furnace will allow for a greater H2SO4 recycle stream.

Example 8 Recycle H2SO4, bypass SWS gas to Claus off-gas oxidizer and use O2-enriched air

To increase the capacity of the Claus plant, a well-known retrofit option is to install special burners that can operate with enriched air containing > 21 vol.% O ₂ , the generally accepted quality of O ₂ is 93-99 vol.% O ₂ .

In this example, enriched air containing 80% O ₂ by volume is used in the Claus process, while ambient air is used in the sulfuric acid process.

The effect of the enriched air is to significantly reduce the process gas flow from the Claus reaction furnace, mainly due to the reduced amount of N2 associated with the O ₂ consumption. Also, the lower process gas flow allows the Claus reaction furnace to operate without adding fuel, since less inert gas needs to be heated.

Since the process gas flow from the Claus reaction furnace is then reduced to 38% of the base case, the supply of Claus off-gas to the Claus off-gas oxidizer is also significantly reduced. The process gas leaving the Claus off-gas oxidiser is only 56% of the base case, which is relatively higher than the Claus flow due to the large amount of SWS gas bypassed to the WSA®.

With this process flow 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 H2SO4 from the sulfuric acid process.

Example 9 Effect of H ₂ SO ₄ Concentration in Recycled Sulfuric Acid on Claus Plant Operation

In this example, the effect of sulfuric acid concentration is demonstrated by comparison with concentrated sulfuric acid containing 45% H2SO4.

The conditions in the example correspond to the conditions of example 6, that is, a part of the SWS gas is bypassed to the Claus off-gas oxidizer to reduce fuel gas consumption. However, since the Claus plant receives less concentrated sulfuric acid, more energy in the form of SWS gas is required to vaporize H2SO4 and H ₂ O in the Claus combustion chamber. A higher flow rate of SWS gas results in a higher combustion air flow rate and therefore a higher process gas flow rate. In addition to this, the water in the sulfuric acid stream also greatly increases the flow rate of the process gas; this water is about. 15% of the total process gas flow (in example 6, the water from the acid stream is only ~2% of the total process gas flow).

The higher process gas flow rate from the Claus plant requires additional energy to be supplied to the Claus off-gas oxidizer, and since the SWS gas flow is limited due to consumption in the Claus reaction furnace, a significant fuel gas flow is required to maintain a high temperature.

Comparing the data in Table 2, it can be seen that the combined effect of the Claus gas and the Claus off-gas is significantly reduced in Example 9 compared to the highly concentrated sulfuric acid recycle in Example 6.

The amount of added energy needed for a Claus reaction furnace producing less concentrated sulfuric acid can be reduced if the amount of acid recycled is reduced, but this would require increased efficiency of the Claus process, which could mean an additional Claus conversion step.

In conclusion, Examples 4-9 demonstrate that the integration of the Claus process with the WSA® process or other sulfuric acid process enables process-related cost optimization. This may include reduced Claus process volume and reduced pilot fuel. In particular, if the concentration of recycled sulfuric acid is above 60%, 80% or 90%, then the integrated process is highly efficient.

Table 1

Process calculations for the Claus + WSA® flow chart as shown in FIG. 1

Example 1 Example 2 Example 3 Sulfur production 70% 100% 70% _{H2SO4 production} thirty% 0% thirty % Recirculation of H ₂ SO ₄ to the combustion chamber 0% 0% Process gas to the Claus reactor 6300 nm ³ /h 4400 nm ³ /h 9700 nm ³ /h Waste gas from the Claus plant 11450 nm ³ /h 6800 nm ³ /h 9200 nm ³ /h Process gas to SO ₂ converter 4400 nm ³ /h 3000 nm ³ /h 9600 nm ³ /h

- 17 039970

table 2

Process calculations for the Claus + WSA® flow chart as shown in FIG. 3

Example 4 Example 5 Example 6 Example 7 Example 8 Example 9 The content of O ₂ in the air for the Claus burner 21% 21% 21% 21% 75% 21% Sulfur production 100% 107% 107% 107% 107% 107% H2SO4 production 6% No No No No No _{H2SO4 recycling} 0% 6% 13% 17% 13% 9% _{H2SO4 concentration} 93% 93% 93% 93% 93% 45% Gaseous acid feed to the Claus process 100% 100 % 100 % 100 % 100 % 100 % Supply of SWS gas to the Claus process 100% 100% 33% 0% 19% 79% Process gas outlet for Claus reaction furnace 100% 94% 65% 69% 38% 97% Process gas outlet for the Claus off-gas oxidizer 100% 93% 90% 107% 56% 97% Fuel gas consumption 100% 92% 16 % 41% 0% 79%

CLAIM

Claims (33)

1. A method for producing sulfur from a source gas containing from 30 to 100 vol.% H ₂ S and a recycled stream of sulfuric acid, including the steps: a) supplying a Claus reaction furnace operating at an elevated temperature with a Claus reaction furnace feed stream containing said feed gas, some recycled sulfuric acid and some oxygen to form a Claus converter feed gas, the amount of oxygen being sub-stoichiometric, b) cooling said Claus converter feed gas to produce a cooled Claus converter feed gas, c) directing said cooled feed gas to the Claus converter to contact the Claus catalytically active material, d) removal of Claus plant off-gas and elemental sulphur, e) sending a stream containing said Claus off-gas, oxygen and fuel as feed gas to a Claus off-gas oxidizer operating at a temperature above 900° C. and/or a catalytic oxidizer to produce a converter feed gas SO2 f) sending said feed gas to the SO2 converter to contact a material catalytically active in the oxidation of SO2 to SO ₃ to produce a gas with a high SO ₃ content,u g) converting said SO ₃ rich gas into concentrated sulfuric acid and SO ₃ depleted gas, either by absorbing SO ₃ in sulfuric acid or by hydrating SO 3 , cooling and condensing sulfuric acid, said sulfuric acid recycle stream containing a quantity of said concentrated sulfuric acid, and wherein said concentrated sulfuric acid contains from 90 to 98.5% by weight of H2SO4. 2. The method of claim 1, wherein the feed gas contains 30 to 99% vol or 99% or 50 to 99% vol or 40 to 100% vol or 50 to 100% H2S. 3. Process according to claim 1, wherein said concentrated sulfuric acid contains 90 to 98 wt% H2SO4. 4. The method of claim 1, wherein in step a) the Claus reaction furnace feed stream is sent to a Claus reaction furnace operating at 800 to 1500°C. 5. The method of claim 1, wherein in step a) said Claus reaction furnace feedstock stream further comprises some fuel. 6. The method according to claim 1, wherein in step b) an additional amount of elemental sulfur is cooled. 7. Process according to claim 1, wherein in step d) the effluent from said Claus catalytically active material is further cooled. 8. A process according to one of claims 1 to 7, wherein the feed stream for the Claus reaction furnace contains less than 0.1 wt% non-elemental nitrogen, such as NH ₃ . 9. A process according to one of claims 1 to 8, wherein the feed stream for the Claus reaction furnace further comprises less than 50%, 20%, 10%, or 1% N2 by volume. 10. Process according to one of claims 1 to 9, wherein the H ₂ S:SO ₂ ratio in said off-gas from the Claus plant is less than 2, preferably from 0.05 or 0.1 to 1 or 1.8. 11. Process according to one of claims 1 to 9, wherein the ratio of H ₂ S:SO ₂ in said off-gas of the Claus plant is greater than 2, preferably from 2.5 or 5 to 10 or 20. 12. The method according to one of claims 1 to 11, further comprising the step of directing some co - 18 039970 supply of additional source gas to the specified device for oxidizing the off-gas of the Claus plant. 13. A process according to one of claims 1 to 12, wherein said additional feed gas contains more than 5% non-elemental nitrogen such as NH3. 14. The method according to claim 12 or 13, wherein the amount of sulfur in the additional source gas is at least 1, 2 or 5 wt.% of the total amount of elemental sulfur removed from the process. 15. Process according to one of claims 1 to 14, wherein the material catalytically active in the Claus reaction comprises activated alumina (III) or titanium (IV) oxide. 16. The method according to one of claims 1 to 15, wherein the amount of sulfur in the sulfuric acid recycle stream is greater than 1, 3, or 5 wt.% and less than 17, 21, or 25 wt.% of the total amount of elemental sulfur removed from the process. 17. The method according to one of claims 1 to 16, wherein the recycled stream of sulfuric acid is atomized in said Claus reaction furnace, either using dual-flow nozzles driven by compressed air, N ₂ or steam, or using hydraulic nozzles, and wherein the residence time in the Claus reaction furnace is from 1.5 to 4 s. 18. Process according to one of claims 1 to 17, wherein the H ₂ S:O ₂ molar ratio of the combined streams sent to the Claus reaction furnace is greater than 2.5. 19. The method according to one of claims 1 to 18, wherein the H ₂ S:O ₂ molar ratio of the combined streams directed to the Claus reaction furnace, corrected for other oxygen-consuming compounds in the feedstock and corrected for products of incomplete oxidation in exhaust gas of the Claus plant is greater than 2.1, 2.2 or 2.5. 20. A process according to one of claims 1 to 19, wherein some of the gas in the process is cooled if necessary and directed to an upstream position to control the temperature of the process. 21. A process according to one of claims 1 to 20, wherein one or more streams directed to said Claus reaction furnace are preheated by heat exchange with the hot process stream. 22. A process according to one of claims 1 to 21, wherein one or more streams directed to said Claus off-gas oxidizer are preheated by heat exchange with the hot process stream. 23. A process according to one of claims 1 to 22, wherein said material catalytically active in the oxidation of SO2 to SO3 contains vanadium. 24. Method according to one of claims 1 to 23, wherein the condensation of sulfuric acid according to step (g) is carried out in a condenser, the cooling medium and the gas with a high SO3 content being separated by glass. 25. The method according to one of claims 1 to 24, wherein the amount of recycled sulfuric acid is chosen so that the temperature in the Claus reaction furnace is from 800, 900 or 1000 to 1300 ° C, 1400 or 1500 ° C without adding an auxiliary to the Claus reaction furnace fuel. 26. A process plant including a Claus reaction furnace, a Claus gas cooler, a Claus conversion section, a Claus off-gas oxidizer, and a sulfuric acid production section, the Claus reaction furnace having an inlet and an outlet, and one or more spray nozzles. nozzles designed to add a recycled stream of concentrated sulfuric acid to the Claus reaction furnace in the form of drops, the gas cooling device of the Claus plant has a gas inlet, a gas outlet and an outlet for elemental sulfur, the Claus conversion section has a gas inlet, gas outlet and elemental sulfur outlet, the Claus off-gas oxidizer has a Claus off-gas inlet, a Claus off-gas oxidizer inlet, and the sulfuric acid production section has there is a gas inlet, a gas outlet, and a sulfuric acid outlet, and wherein the inlet of the Claus reaction furnace is configured to receive feed gas, sulfuric acid, and oxidant for the Claus reaction furnace, and the outlet of the Claus reaction furnace is configured such that which is in flow communication with the inlet of the Claus gas cooler, wherein the outlet of the Claus gas cooler is configured to be in flow communication with the inlet of the Claus conversion section, and wherein the off-gas inlet of the Claus unit of the off-gas oxidizer of the Claus plant is configured to be in flow communication with the outlet of said Claus conversion section, the process gas outlet of the Claus plant off-gas oxidizer is configured to be in fluid communication with the inlet of the sulfuric acid production section, and the outlet The sulfuric acid inlet of the sulfuric acid production section is in fluid communication with an inlet of said Claus reaction furnace. 27. Process plant according to claim 26, wherein the Claus plant off-gas oxidizer further has a fuel inlet. - 19 039970 28. Process plant according to claim 26, wherein the Claus off-gas oxidizer further has an inlet and an outlet for additional feedstock. 29. Process plant according to one of claims 26 to 28, wherein said sulfuric acid production section includes a sulfur dioxide oxidation reactor having an inlet and an outlet, and a sulfuric acid condenser having a process side having a process gas inlet, an outlet a process gas outlet and a sulfuric acid outlet, and a coolant side having a coolant inlet and a coolant outlet, and wherein the sulfuric acid condenser is configured to preheat at least one of two - an oxidizer for a Claus reaction furnace and an oxidizer for the exhaust gas of the Claus plant by leading the sulfuric acid condenser refrigerant side inlet to the inlet and withdrawing the sulfuric acid condenser refrigerant side from the outlet. 30. The process plant according to one of claims 26-29, further comprising at least one heat exchanger having a hot side of the heat exchanger and a cold side of the heat exchanger, made for preheating on the cold side of the heat exchanger of one of the above - source gas, sulfuric acid and oxidizer before directing to said Claus reaction furnace, and such that the hot side of the heat exchanger is configured to cool the hot process stream. 31. The process plant of claim 30, wherein the hot process stream is taken from the group consisting of a Claus plant off-gas oxidizer outlet stream, a Claus reaction furnace outlet stream, and a sulfur dioxide oxidation reactor outlet stream. 32. Process plant according to one of claims 26 to 31, wherein said one or more spray nozzles are dual flow spray nozzles or hydraulic spray nozzles. 33. Process plant according to one of claims 26 to 32, further comprising an SO ₃ reduction device having an inlet and an outlet configured such that the inlet of the SO ₃ reduction device is in fluid communication with the outlet of the Claus reaction furnace, and so that the outlet of the SO ₃ reduction device is in fluid communication with the inlet of the Claus conversion section.