DK201800057A1

DK201800057A1 - Sulfuric acid Claus thermal stage for sulfuric acid injection into a Claus process

Info

Publication number: DK201800057A1
Application number: DKPA201800057A
Authority: DK
Inventors: Thellefsen Morten
Original assignee: Haldor Topsøe A/S
Priority date: 2018-02-08
Filing date: 2018-02-08
Publication date: 2019-09-18

Abstract

The present invention relates to a sulfuric acid Claus thermal stage comprising a burner system and a reaction furnace, wherein liquid or gaseous sulfuric acid is injected into the reaction furnace.

Description

Title: Sulfuric acid Claus thermal stage for sulfuric acid injection into a Claus process

The Claus process is a well-established technology for conversion of H2S in a gas comprising H2S into elemental sulfur, Sx, where X is an integer between 2 and 8. At high temperature (> 600 °C), X is 2, whereas X is 6-8 at lower temperature (< 400 °C)

The industrial Claus process consist of a thermal stage and one or more catalytic stages to complete the Claus reaction:

H2S + SO2 θ 3/X Sx + 2 H2O (1)

The elemental sulfur is withdrawn on several positions in the Claus process by means of cooling and condensation of liquid sulfur.

A typical Claus plant layout consists of a burner system, a refractory lined reaction furnace, a waste heat boiler and a number of catalytic stages comprising a catalytic reactor, a sulfur condenser and a process gas reheater. The Claus plant layout and chemistry is well described in the literature.

Due to chemical equilibrium limitations of the Claus reaction (1), it is normally not possible to comply with environmental emission legislation without adding a so-called Claus tail gas plant downstream the Claus process. Numerous technologies are available for these Claus tail gas plants, each possessing their own advantages and disadvantages.

One such Claus tail gas plant is the SCOT process in which all sulfur containing gas molecules in the Claus tail gas (SO2, COS, CS2 and S8) are converted into H2S, captured in an absorption liquid, released from the liquid in a regenerator and returned to the frontend of the Claus plant as a concentrated H2S gas.

DK 2018 00057 A1

Another Claus tail gas plant is the CANSOLV process in which all sulfur containing gas molecules in the Claus tail gas (H2S, COS, CS2 and S8) are converted into SO2, captured in an absorption liquid, released from the liquid in a regenerator and returned to the frontend of the Claus plant as a concentrated SO2 gas.

Recycling of the H2S and SO2 to the frontend of the Claus plant ensures that elemental sulfur is the only product from the Claus plant.

A recent invention describes a sulfuric acid plant as a Claus tail gas plant, converting all sulfur containing gas molecules (H2S, SO2, COS, CS2 and S8) in the Claus tail gas into sulfuric acid, H2SO4, and return the sulfuric acid to the front end of the Claus plant. H2SO4 has proved to be a very efficient O2 carrier for the (partial) oxidation of H2S to SO2 and thus the size of the Claus plant can be significantly reduced if air (with 79 vol% N2) can be replaced with H2SO4. This combination of Claus and sulfuric acid process is described more thoroughly in PCT/EP2017/080721 and DK201700691.

This invention describes methods for adding sulfuric acid to the thermal stage of the Claus plant, where the sulfuric acid is either produced in the Claus tail gas plant or in an external sulfuric acid plant.

In this text, sulfuric acid is to be understood as a mixture of H2SO4 and H2O in any proportion. Typically, sulfuric acid is associated with a given concentration, i.e. 90 %w/w H2SO4, which means than there is up to 10 %w/w H2O in the mixture.

The burner system and reaction furnace of the presented invention can in principle receive a sulfuric acid stream with any concentration of H2SO4, but as the H2O does not have any beneficial role in the desired chemistry, reduces process gas temperature by evaporation and furthermore dilutes the process gas, it is desired to operate with as high H2SO4 concentration as possible. It is preferred to add sulfuric acid to the thermal Claus stage with a concentration of H2SO4 of no less than 80 %w/w and preferably higher than 90 %w/w H2SO4.

DK 2018 00057 A1

Fuming sulfuric acid, also called oleum, is H2SO4 with dissolved SO3 (i.e. no free water) and can also be used as feed as the dilution effect and evaporation duty is minimal. However, the cost of oleum is much higher than sulfuric acid and that will limit the practical use of oleum for this invention.

In the sulfuric acid industry, the addition of sulfuric acid to a thermal combustor is wellknown, e.g. in the regeneration of spent sulfuric acid from alkylation processes and for treatment of diluted and/or polluted sulfuric acid from other processes. Typically, the sulfuric acid is atomized into the combustion chamber as a cloud of fine droplets. The droplets evaporate, the sulfuric acid dissociates into SO3 and H2O and, if the temperature is sufficiently high, decomposes to SO2, ¹X O2 and H2O. In a later stage the reaction scheme is reversed, such that a concentrated H2SO4 without pollutants can be withdrawn from an absorption or condensation step.

The conditions in the thermal combustor in a sulfuric acid plant differ compared to the conditions in the Claus thermal stage by the following:

1. The thermal combustor in the sulfuric acid plant operates under super-stoichiometric conditions, which means that there is a surplus of O2 in the process gas after the thermal stage. This also means that in a sulfuric acid plant accurate O2 addition is not crucial as long as there is a surplus.

2. The thermal stage in the Claus process operates under sub-stoichiometric conditions, which means that the O2 addition from the H2SO4 and the combustion air must be adjusted such that the desired 2:1 H2S to SO2 ratio can be established in the reaction furnace (see reaction 1).

3. In the sulfuric acid plant, it is not important to which extent the added H2SO4 is decomposed in the thermal combustor as it will be reformed in a later stage of the sulfuric acid plant. In the Claus plant, however, it is important that there are few or no traces of SO3 leaving the reaction furnace as the SO3 can cause plant corrosion and deactivate the Claus reaction catalyst. Therefore, it is desirable

DK 2018 00057 A1 that the addition of the sulfuric acid is carried out in an efficient way.

The thermal stage of a Claus plant comprises a burner system in which the gas comprising H2S is mixed with an O2 rich stream and optionally a fuel gas or another H2S containing gas (e.g. Sour Water Stripper gas, SWS) in a flame, where H2S and hydrocarbons present are at least partially combusted, increasing the process gas temperature to typically 1,000 - 1,400 °C, with local flame temperatures well above these temperatures.

The flame extends into the Claus reaction furnace, which is a refractory lined chamber, wherein the gases from the flame are allowed to react at the high temperature. Usually the reaction furnace is designed for 1-2 seconds of residence time. The reaction furnace outlet is connected to a waste heat boiler wherein the process gas is cooled by indirect heat transfer to boiling water, producing medium to high pressure steam. A simple fire tube boiler is the preferred design.

The flame zone is defined as the distance, in the reaction furnace, from the burner tip to the end of the flame. The reaction furnace extends from the burner tip(s) at the burner wall to the inlet of the waste heat boiler, i.e. the entire refractory lined chamber.

Inside the reaction furnace there can be installed checker walls, choke rings and/ or vector walls in order to enhance gas mixing to achieve uniform temperature distribution and gas composition.

The injection of liquid sulfuric acid into a Claus thermal stage can be carried out in numerous ways, depending on the design of the burner system and the reaction furnace.

In one embodiment of the invention liquid sulfuric acid is introduced into the reaction furnace by means of atomization, in which the liquid is sprayed into the reaction furnace as a cloud or mist, containing small droplets of sulfuric acid. The evaporation time

DK 2018 00057 A1 of the droplets is very much dependent of the droplet diameter and therefore a small droplet size is preferred. This is easiest accomplished in a so-called two-fluid nozzle, also called pneumatic nozzle, in which an atomization media is used to “cut” the liquid acid into fine droplets. Compressed air, steam and N2 are the well proven atomization medias, but the feed gas to the Claus thermal stage could also be used, provided the pressure is sufficiently high. Using compressed air, the flow of combustion air to the burner system must be reduced by the flow of compressed air and that could affect the flame stability. That issue is not relevant for steam and N2 atomization, but these streams will dilute the process gas.

Using a gas comprising H2S as carrier gas for the sulfuric acid atomization, it is likely that H2S and H2SO4 will react in the liquid phase, forming solid elemental sulfur before the mixture is injected into the reaction furnace. That may cause nozzle plugging unless the nozzle is designed for liquid slurries.

To postpone such liquid phase reaction to the reaction furnace, a special concentric nozzle can be used. In the center of the nozzle either the sulfuric acid or the gas comprising H2S flows. This central nozzle is surrounded by a narrow slit with a “separation fluid”, which can be air, steam and any other composition that is considered unreactive. Outside this separation slit is the outer slit in which the gas comprising H2S or sulfuric acid flows. With the introduction of the separation fluid, any reactions on the nozzle tip are avoided.

In another embodiment of the invention, a so-called pressure nozzle, also called hydraulic nozzle, may be used for the atomization, in which it is the pressure of the liquid that provides the energy and velocity for “cutting” the acid into droplets. The principle is very simple, but the average droplet size is larger than for the two-fluid nozzles and the turn down capabilities are not as good as for the two-fluid nozzles either. This means that longer residence time in the reaction furnace is required to ensure complete droplet evaporation. The advantage of the pressure nozzle is that the process gas is not diluted by any atomization media.

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For addition of liquid sulfuric acid into the reaction furnace, so-called rotating discs can be used to atomize the liquid feed in a further embodiment of the invention. In this embodiment it has to be considered that relatively large droplets are formed, requiring high residence time in the reaction furnace for complete evaporation. Furthermore, the high corrosiveness of the sulfuric acid will decrease the lifetime of the rotating disc.

In a further embodiment, another method of adding sulfuric acid to the Claus thermal stage is to inject the sulfuric acid as a jet and let the liquid impinge on a hot surface, which will provide the energy for evaporation of the acid. This surface could e.g. be the wall of the reaction furnace, an internal wall or any other internal surface in the reaction furnace, such as a packed bed. Ceramics with high temperature stability and chemical resistance could be materials for such surfaces. This principle is used in rotary kilns, where the rotating refractory wall of the kiln provides surface and residence time for evaporation.

Although the addition of sulfuric acid into the Claus thermal stage is simplest when the acid is in liquid form, there could be situations in which the cooling effect of the sulfuric acid evaporation and decomposition is too high to sustain a stable flame. In that situation it is possible to evaporate the sulfuric acid in an external plant or unit, thus providing a hot gas containing SO3 + H2O or even SO2 + ¹X O2 + H2O if the temperature is sufficiently high. This can be accomplished in e.g. a packed bed of ceramics in which downward flowing acid is contacted with an upward flowing hot gas, which will contain substantial amounts of acid vapor when it leaves the packed bed and enters into the Claus thermal stage. The hot gas can be air, O2, N2, feed gas or process gas as long as it contains the energy to evaporate the acid.

If more energy is required, a combustor can be used to generate heat and the combustor off gas is then added to the Claus reaction furnace, either as “combustion air” or simply as a side stream.

The position of the addition of the (liquid) sulfuric acid is of great importance as the sulfuric acid is an O2 carrier with significantly different thermodynamic properties than the

DK 2018 00057 A1 usual combustion air (or enriched air, i.e. air with a O2 concentration > 21 vol%).

The overall Claus reaction in the thermal stage in which H2SO4 is the O2 carrier is

H2SO4(g) + 3 H2S + 104 kJ/mole 2 S2 + 4 H2O (2)

The overall Claus reaction in the thermal stage in which atmospheric air is the O2 carrier is (including the presence of inert N2)

H2S + 1½ O2 + 7½ N2 1½ S2 + 3 H2O + 7½ N2 + 471 kJ/mole (3)

The two overall reactions very clearly show the difference between the two O2 carriers: the reaction using air (3) releases a substantial amount of energy, whereas the use of H2SO4 (2) requires energy for the reaction to proceed. On the other hand, atmospheric air addition also implies N2 addition and thus process gas dilution, whereas no process gas dilution with N2 takes place with H2SO4 addition. The two reactions also show that H2SO4 cannot be the only O2 carrier as some air or enriched air is needed to provide a high temperature in the Claus thermal stage via reaction (3).

In a special layout with gas comprising H2S in high concentration and O2 enrichment, there is a risk of overheating the reaction furnace and here H2SO4 addition will reduce the temperature such that the benefit of O2 enrichment can be achieved without exceeding material design temperature or requiring exotic materials and special designs to withstand the high temperature.

In the Claus thermal stage, it is not uncommon to have staged combustion, such that 2 or more reaction zones exist, each with different stoichiometry. For example, in combustion of feed gases containing NH3 and/or heavy hydrocarbons/BTX(Benzene, Toluene, Xylene), it is common to have a first stage in which a relatively large fraction of the O2 is added, providing a stage with very high temperature and possibly O2 surplus. In

DK 2018 00057 A1 the second stage, gas comprising H2S without NH3 is added, optionally together with the rest of the O2, to obtain the desired 2:1 H2S:SO2 ratio in the process gas leaving the reaction furnace.

Such requirements for high temperature zones must be specially considered when adding sulfuric acid to the Claus thermal stage as the cooling effect of the sulfuric acid evaporation, dissociation and decomposition can be considerable.

In an embodiment of the invention, the Claus burner layout is a single flame in which a gas comprising H2S is combusted with addition of combustion air. The main burner will be located in the center of the burner wall. Sulfuric acid nozzles will be positioned on the burner wall such that they encircle the central flame and the acid can be sprayed into the reaction furnace without affecting the flame significantly.

The nozzles can be sloped a bit towards the flame to ensure that the cloud gets into intimate contact with the hot flame, but without quenching the flame. Depending on the sulfuric acid flow, 2-4 nozzles are typically distributed on the burner wall along the circle.

In a further embodiment, the sulfuric acid nozzles can be located on the reaction furnace wall, close to the burner end. The nozzles then spray in the acid perpendicular to the general process gas direction and that can enhance the residence time for the acid droplets, ensuring evaporation at a shorter process gas path distance. The nozzles can either inject the acid directly towards the center of the reaction furnace (i.e. directly towards the central flame) or in a tangential manner, providing a swirl of acid cloud around the flame and thus ensuring that the flame is not quenched by direct acid injection.

In yet a further embodiment of the invention for Claus plants utilizing O2 enrichment, the burner system typically comprises a number of small burners located in a ring on

DK 2018 00057 A1 the burner wall. In that case the acid nozzle could be a large central nozzle or a number of smaller nozzles positioned in a ring with smaller diameter than the burner ring. With such a setup, the flame will not be quenched by the acid injection.

In an embodiment of the invention, another way to ensure that the flame is not quenched by the acid injection is to inject the acid somewhere downstream the flame zone. The injection points could be both in front and behind any physical obstacles in the reaction furnace, positioned to provide extra turbulence for enhanced process gas mixing. These obstacles are typically choke rings, checker walls, vector walls or similar structures that change the gas path. Such enhanced turbulence will also help in mixing the sulfuric acid with the process gas, ensuring fast droplet evaporation and reaction. The drawback of this layout may be that the time for droplet evaporation is too short and thus the reaction furnace must be extended to provide sufficient residence time for evaporation of sulfuric acid and associated reaction (3).

Figures:

Figure 1 shows a typical Claus thermal stage with the addition of sulfuric acid through two-fluid atomization nozzles.

Air or slightly enriched air (2) and gas comprising H2S (4) are combusted in a flame (10), the flame extends from the center of the burner wall. Normally the gas comprising H2S is injected via a central nozzle (11) and air through an outer annulus and typically with some swirl motion.

The sulfuric acid (6) is injected via atomization nozzles (7), which are of the two-fluid type. The atomization media (8) is typically compressed air, but could also be steam, N2 or a fraction of the gas comprising H2S (4). The atomization pressure of the atomization media preferably has a pressure above 1.2 Bar absolute pressure. The nozzles (7) are distributed on a circle surrounding the flame, normally 2-4 nozzles are installed. Sometimes the nozzles are evenly distributed on the circle, but most often there is a

DK 2018 00057 A1 tendency towards having the nozzles concentrated in the upper part of the burner wall. This is in order to give the droplets a longer vertical residence time, i.e. it will take longer time for the largest droplets to reach the bottom of the reaction furnace.

The acid cloud (12) from the nozzles are slightly sloped towards the flame, such that the cloud gets in intimate contact with the hot flame (10) but without quenching the flame.

Inside the refractory lined reaction furnace (16), one or more physical obstructions (14) are typically placed to provide turbulence and enhance mixing of the process gas. Connected to the outlet of the reaction furnace, a waste heat boiler (18) is positioned to cool the process gas to lower temperatures needed for catalytic conversion of H2S and SO2 into sulfur.

Figure 2 shows a Claus thermal stage with O2 enrichment and a central addition of sulfuric acid.

When using pure O2 or a highly concentrated O2 stream it is common practice to use many smaller burners (11), positioned in a circle on the burner wall. The sulfuric acid can then be injected from the center of the burner wall. In this figure, the atomization nozzle (7) is of the pressure type, i.e. it is the pressure of the acid that atomizes the acid to form the cloud (12). In order to improve turn down capabilities there could be a number of smaller nozzles, still positioned close to the center of the burner wall. These nozzles can also be sloped towards the flames.

Turbulence providers (14) and waste heat boiler (18) positioned at the outlet of the reaction furnace are as described in figure 1.

Figure 3 shows a Claus thermal stage in which there are two feed streams to the Claus plant: a normal gas comprising H2S (4), highly concentrated in H2S, and a so

DK 2018 00057 A1 called sour water stripper(SWS) gas (3), which besides a high H2S concentration also has a high concentration of NH3. To thermally destroy the NH3, which otherwise cause operational issues with plugging of downstream equipment, the flame temperature (10) is typically above 1,300-1,350 °C. A high intensity high temperature flame (10) is established by feeding all SWS gas (3), a fraction of the gas comprising H2S (4) and the combustion air/enriched air (2) to the burner (11), providing a flame (10) with relatively high O2/combustible ratio and thus higher degree of H2S oxidation , higher flame temperature and efficient NH3 destruction. Downstream the flame zone, the remaining gas comprising H2S (4) is added, such that the overall 2:1 H2S to SO2 stoichiometry ratio is obtained. Also downstream the high temperature flame zone, the sulfuric acid (6) is injected, using two-fluid nozzles (7) with pressurized air (8) as atomization media. Alternatively, any gas stream with sufficient pressure and available flow can be used as atomization media. The nozzles can point towards the flame, straight out or away from the zone.

The gas comprising H2S and sulfuric acid are injected close to the physical obstructions (14), such that the turbulence of these obstructions can enhance the mixing quality. Addition both upstream and downstream the obstructions will result in an increase in mixing quality. If so-called choke rings are used, the gas comprising H2S and/or sulfuric acid can be injected via holes in the choke ring.

If the mixing is slow and the evaporation time of the acid droplets is relatively high, i.e.

> 1 second, it may be necessary to extend the length of the reaction furnace (16), such that all necessary reactions are complete when the process gas reaches the inlet to the WHB (18).

In Figure 4 a thermal Claus stage with multiple sulfuric acid injection positions is shown. The layout is in many ways similar to figure 1, but the sulfuric acid injection is staged. A fraction of the sulfuric acid (6) is injected at the burner wall around the flame (10) while the rest of the sulfuric acid (6) is injected close to the internal obstruction (14). This setup ensures an enhanced flame temperature control, such that any risk of flame (10) quenching can be minimized while ensuring a high (average) sulfuric acid

DK 2018 00057 A1 residence time in the reaction furnace (16), reducing the need for extending the length of the reaction furnace.

Figure 5 shows a configuration of the Claus thermal stage in which the sulfuric acid is vaporized prior to injection into the reaction furnace (16).

Sulfuric acid (6) is atomized into an evaporation chamber (13) via a pressure nozzle (7), forming a cloud of sulfuric acid droplets (12). The energy for evaporation of the sulfuric acid can be supplied with a stream of air/enriched air (8), which then must be preheated in an upstream process step. Sulfuric acid vapor and cooled air/enriched air is leaving the evaporation chamber via line 15 and injected into the reaction furnace (16). Using air and enriched air as the evaporation media (8) the O2 in stream 15 is used as combustion air for the substoichiometric combustion of gas comprising H2S (2) and optionally SWS gas (4). The sulfuric acid vapor and carrier gas injection can be staged if required for the chemical reactions in the flame (10) to proceed to completion.

If the energy for sulfuric acid evaporation cannot be supplied via the hot air alone (8), it may be necessary to burn a support fuel (5) in the evaporation chamber (13). Depending on the temperature, the sulfuric acid can evaporate to H2SO4 vapor (low temperature), dissociate to SO3 and H2O (medium temperature) or even decompose to SO2, O2 and H2S (high temperature).

The advantage of this layout is an uncomplicated revamp of an existing plant, but the layout is more complex than the liquid injection shown in Figures 1-4.

Example 1

In this example a Claus plant designed for 1000 tons/day of sulfur production receives a feed stream of gas comprising H2S and a sulfuric acid feed stream. In the present case the sulfuric acid feed stream is the product stream of the Claus tail gas plant, but

DK 2018 00057 A1 could just as well originate from another sulfuric acid plant not related to the Claus plant.

The gas comprising H2S has the following flow and composition:

40,600 Nm³/h vol% H2S, 22 vol% CO2, 6 vol% H2O and minor amounts of BTX, CH4 and COS

The sulfuric acid feed has the following flow and composition:

6,114 kg/h %w/w H2SO4, 2 %w/w H2O

611 Nm³/h compressed air is used to atomize the sulfuric acid in two-fluid nozzles

The combustion air flow is 57,200 Nm³/h, the air is preheated to 490 °C

The sulfur content in the sulfuric acid feed account for 4.7 % of the total sulfur production and the O2 supplied via the H2SO4 and atomization air account for 19 % of the total O2 demand, significantly reducing the volume of N2 dilution gas introduced into the Claus plant via the combustion air.

In the Claus reaction furnace 20 % of the H2S conversion is associated with the reaction with H2SO4 (reaction 2), while the remaining 80 % of the H2S conversion is associated with the normal Claus reaction (reaction 3). The total H2S conversion in the Claus reaction furnace is 70%, the remaining H2S conversion is taking place in the downstream catalytic section and Claus tail gas plant.

The normal reaction path from H2S to S2 via partial H2S oxidation and Claus reaction

DK 2018 00057 A1 will result in a process gas temperature around 1,180 °C. The addition of H2SO4 with associated evaporation and reaction with H2S will result in a process gas temperature decrease of ~115 °C, i.e. after completion of the chemical reactions the Claus furnace outlet temperature will be around 1,065 °C.

Due to the relatively low temperature drop caused by sulfuric acid addition, the sulfuric acid nozzles could be installed as shown in Figure 1, i.e. located in a circle around the central flame. 4-6 nozzles will be required to atomize the sulfuric acid feed.

Example 2

In this example, the same 1000 tons/day Claus plant receives a feed of gas comprising H2S with the composition as described in example 1. The flow is 38,370 Nm³/h.

To boost capacity, the plant uses pure O2 for the combustion, the pure O2 is not preheated. The flow is 9,200 Nm³/h, the O2 concentration is 100 vol%.

The sulfuric acid feed flow is 11,000 kg/h, the sulfur content in the H2SO4 accounts for

8.5 % of the total sulfur production. The sulfuric acid composition is 98%w/w H2SO4 and 2 %w/w H2O. The O2 introduced via sulfuric acid and atomization air accounts for 36 % of the total O2 introduced into the Claus plant. In this example, the addition of H2SO4 will not reduce the overall process gas flow since pure O2 is used and thus there is no N2 associated with that stream. The benefit of the H2SO4 addition is a reduction in operating cost as H2SO4 is a cheaper O2 carrier than pure O2 and besides the H2SO4 will cool the process gas temperature to such a degree that the refractory lining in the reaction furnace and the downstream waste heat boiler does not experience temperatures above their design limits or can be designed with lower design temperatures and thus material selection will allow for cheaper constructions.

DK 2018 00057 A1

The chemical reactions not associated with the sulfuric acid addition will result in a process gas temperature above 1,350 °C, which is very suited for e.g. thermal destruction of NH3 and BTX if present in the gas comprising H2S.

The cooling effect of the sulfuric acid addition, evaporation and associated reactions is around 350 °C, reducing the Claus reaction furnace outlet temperature to around 1,000 °C, which is an appropriate temperature for the downstream waste heat boiler.

The atomization nozzles can be located in the center of the burner wall as shown in

Figure 2, but also outside a central flame as shown in Figure 1. The latter will to some extent protect the refractory lining from excessive temperatures in the pure O2 flame.

If the gas comprising H2S contains large concentrations of NH3 and/or BTX, the layout in Figure 3 will allow a sufficient residence time at high temperature to destroy the NH3 15 and BTX, while protecting the waste heat boiler from excessive temperatures.

To better control the process gas temperature it may be more beneficial to use a layout as shown in Figure 4, where sulfuric acid is injected in two stages. That will also make it easier to distribute the many nozzles needed for the atomization of the sulfuric acid.

Claims

Claims

1. Sulfuric acid Claus thermal stage comprising a burner system and a reaction furnace, the burner system is adapted to mix a gas comprising H2S with a gas comprising O2 and optionally a fuel gas or a further gas comprising H2S in a flame, the reaction furnace is adapted to add an amount of sulfuric acid in the vicinity of the flame
2. Sulfuric acid Claus thermal stage according to claim 1 adapted to operate at a temperature at the outlet of the reaction furnace of between 1000°C - 1400 °C
3. Sulfuric acid Claus thermal stage according to claim 1 and 2, in which the sulfuric acid is a liquid and has a concentration of H2SO4 above 80 %w/w, preferably above 90% w/w.
4. Sulfuric acid Claus thermal stage according to any of the preceding claims, comprising at least one nozzle for atomization of liquid sulfuric acid into the reaction furnace.
5. Sulfuric acid Claus thermal stage according to claim 4, wherein the at least one nozzle is a two-fluid nozzle.
6. Sulfuric acid Claus thermal stage according to claim 5, wherein the two-fluid nozzle is concentric, comprising a central atomizer outlet for the first fluid, a surrounding slit adapted for injection of a separation fluid around the central atomizer and an outer slit adapted for the second fluid.
7. Sulfuric acid Claus thermal stage according to claim 4, wherein the at least one nozzle is a pressure nozzle.
8. Sulfuric acid Claus thermal stage according to claim 1,2 or 3, comprising at least one rotating disc atomizer for atomization of liquid sulfuric acid into the reaction furnace.

DK 2018 00057 A1
9. Sulfuric acid Claus thermal stage according to claim 1,2 or 3, comprising evaporation surface means in the reaction furnace and means for injecting liquid sulfuric acid as a jet into the reaction furnace adapted to impinge on and evaporate from the evaporation surface means.
10. Sulfuric acid Claus thermal stage according to any of the preceding claims, comprising atomizing means adapted to atomization of liquid sulfuric acid into the reaction furnace with a geometric volume mean droplet diameter below 500 μm, preferably below 300 μm, or more preferably below 150 μm.
11. Sulfuric acid Claus thermal stage according to any of the preceding claims, further comprising means to enhance gas mixing to achieve uniform temperature distribution and gas composition in the reaction furnace.
12. Sulfuric acid Claus thermal stage according to claim 11, wherein the means to enhance gas mixing comprises at least one checker wall.
13. Sulfuric acid Claus thermal stage according to claim 11 or 12, wherein the means to enhance gas mixing comprises at least one choke ring.
14. Sulfuric acid Claus thermal stage according to claim 11, 12 or 13, wherein the means to enhance gas mixing comprises at least one vector wall.
15. Sulfuric acid Claus thermal stage according to any of the preceding claims, wherein liquid sulfuric acid is atomized into the reaction furnace in two or more positions around a burner arranged centrally on a burner wall in the reaction furnace.
16. Sulfuric acid Claus thermal stage according to any of the claims 1-14, wherein liquid sulfuric acid is atomized into the reaction furnace in a central position of the burner wall and a plurality of burners are arranged around the central position.

DK 2018 00057 A1
17. Sulfuric acid Claus thermal stage according to any of the claims 1-14, wherein liquid sulfuric acid is atomized into the reaction furnace in one or more downstream positions relative to one or more burners in the burner system.
18. Sulfuric acid Claus thermal stage according to any of the claims 1-14, wherein liquid sulfuric acid is atomized into the reaction furnace in one or more positions downstreamthe flame zoneof a burner arranged on the burner wall.
19. A process for conversion of sulfuric acid and H2S in a Claus thermal stage comprising the steps of reacting a gas comprising H2S, a gas comprising O2, a sulfuric acid stream and optionally a fuel gas or a further H2S containing gas in a flame and reaction furnace, forming an amount of elemental sulfur providing a Claus reaction furnace off gas with few or no traces of sulfuric acid or SO3, directing the Claus reaction furnace off gas to a waste heat boiler, cooling the off gas and optionally condensing a part of the elemental sulfur providing a Claus converter feed gas and an optionally withdrawing an amount of condensed sulfur, directing the Claus converter feed gas to contact a catalyst active in the Claus reaction providing a converted Claus gas, cooling said converted Claus gas, withdrawing an amount of condensed sulfur and a desulfurized converted Claus gas.