NL2008801C2

NL2008801C2 - A method for treating a sulfur-containing gas stream.

Info

Publication number: NL2008801C2
Application number: NL2008801A
Authority: NL
Inventors: Wei Wang; Xiping Song
Original assignee: Hofung Sulphur Technology Ltd
Priority date: 2011-05-11
Filing date: 2012-05-11
Publication date: 2013-05-28
Also published as: WO2012152919A1; NL2008801A; CN102198365B; CN102198365A

Abstract

The invention pertains to a method for treating a sulfur-containing gas stream, comprising the steps of (1) providing a gas stream comprising H2S and SO2 to a Claus reactor where it is contacted under reaction conditions with a catalyst, to form a product comprising elemental sulfur, water, and residual H2S and SO2, (2) contacting a tail gas from a Claus reactor which comprises H2S and SO2 with oxygen in an oxidation step under oxidising conditions to obtain a gas stream comprising SO2, (3) contacting the SO2-containing gas stream in an SO2 conversion step with a catalyst to form a gas stream comprising SO3, (4) contacting the gas stream comprising SO3 with water under hydration conditions to form sulfuric acid. The present invention provides a process in which a sulfur-containing gas stream is efficiently converted to elemental sulfur and, if so desired, sulfuric acid while the sulfur content of the flue gas is so low that direct provision to the atmosphere is possible, while at the same time efficient use is made of energy and resources.

Description

13031-Hs/id A method for treating a sulfur-containing gas stream

The present invention relates to a method for treating a sulfur-containing gas stream, in particular a gas stream containing H2S and/or S02.

5 While various processes for converting gas streams containing H2S and S02 are known in the art, it has been found that there is still need for improved processes. More in particular, it has been found that there is a need for a process which converts H2S and S02 in an efficient manner to high value products such 10 as elemental sulfur, while producing gas streams which do not require purification through processes such as solvent adsorption or caustic washing treatment, and which at the same time make efficient use of energy and resources through appropriate use of recycle streams.

15

That a caustic washing treatment can be dispensed with is particularly attractive due to the following: Normally, the caustic solvent is a Ca(OH)2 solution at a certain concentration, NaOH, or ammonia. The investment of the above 20 methods is big and the process is complicated, while the desulfurization efficiency is low. In industrial applications, the Ca (OH) 2 solution is made by several sequences, such as CaO grinding, manufacturing of a solution, multistage filtration and dilution. The calcium sulfite hyperoxidation needs air, 25 and the atomizing nozzle is easily plugged during operation. The NaOH solution is costly and the washing process discharges a large waste water stream.

The ammonia absorption process needs an oxidizing process to obtain (NH4)2 S04, and the tower circulation flow is very big, 30 causing the need for a large column diameter, and in order 2 to achieve (NH4) 2 SO4, it is necessary to blow large amounts of air into the column to oxidize the sulfite and hydrosulfite . This oxidizing reaction is very slow and meanwhile the ammonia can easily escape from the solvent.

The present invention provides a process in which a sulfur-containing gas stream is efficiently converted to elemental sulfur and, if so desired, sulfuric acid while the sulfur content of the flue gas is so low that direct provision 10 to the atmosphere is possible, while at the same time efficient use is made of energy and resources.

The present invention pertains to a method for treating a sulfur-containing gas stream, comprising the steps of 15 (1} providing a gas stream comprising H2S and S02 to a Claus reactor where it is contacted under reaction conditions with a catalyst, to form a product comprising elemental sulfur, water, and residual H2S and S02, (2) contacting a tail gas from a Claus reactor which 20 comprises H2S and S02 with oxygen in an oxidation step under oxidising conditions to obtain a gas stream comprising S02, (3) contacting the S02-containing gas stream in an S02 conversion step with a catalyst to form a gas stream comprising S03, 25 (4) contacting the gas stream comprising S03 with water under hydration conditions to form sulfuric acid.

It has been found that the integrated method according to the invention combined a high yield of elemental sulfur with 30 efficient removal of remaining sulfur compounds from the tail gas, and formation of sulfuric acid which can be recycled back into the process to form elemental sulfur, and/or be recovered separately. More specifically, it has been found that the process according to the invention can simultaneously fulfill both the highest sulfur recovery requirements and the lowest SO2 emission requirements known in the industry today. This is a unique feature of the process according to the invention.

5 Additional embodiments and advantages of the present invention will become clear from the further specification.

The process according to the invention starts out with a gas stream comprising H2S and S02, which is provided to a catalytic 10 Claus reactor.

The gas stream provided to the catalytic Claus reactor generally contains between 0.5 and 8 vol.% of H2S, in particular between 2.0 and 6 vol.% of H2S. The gas stream generally contains between 0.3 and 5 vol.% of S02, in 15 particular between 1.0 and 3 vol.% of S02.

The gas stream comprising H2S and S02 may be obtained in various manners, depending on the concentration of the H2S stream that is available .

20

In a first embodiment, the gas stream comprising H2S and S02 is obtained through partial combustion of a gas stream containing H2S. The gas stream subjected to partial combustion may contain, e. g. , at least 15 vol.% of H2S. It is preferred, 25 however, for the gas stream to contain a relatively high concentration of H2S, e. g., at least 30 vol.%, more in particular at least 35 vol. %. The gas stream may contain up to 100 vol. % of H2S . In one embodiment the gas stream contains at least 55 vol. % of H2S, in particular at least 60 vol. % of 30 H2S. In another embodiment the gas stream contains between 15 and up to 55 vol. % of H2S.

In the combustion step the gas stream containing H2S is partially combusted to form a gas stream comprising H2S and S02. The combustion step is carried out in the presence of 4 oxygen, which can be provided using an oxygen-containing gas such as oxygen, air, or air to which additional oxygen has been added. Where necessary, fuel gas may be added to the combustion step to raise the temperature. The fuel gas for 5 the combustion step, if present, may be any kind of combustible gas, solid, or liquid.

The combustion temperature generally is in the range of 350-1400°C, preferably in the range of 1000-1350°C. During the combustion step, a burner is generally used, with or 10 without atomizing fluid. It is preferred for the burner to atomize air or steam. The use of a burner which atomizes steam is particularly preferred, because steam is the most efficient atomizing fluid, and is readily available in the majority of cases .

15 If so desired, the gas to be provided to the combustion step is preheated to a temperature of 80-400°C, in particular 80-220°C.

The gas resulting from the combustion reaction in the burner comprises H2S and S02. In general, the gas contains between 20 1 and 60 vol. % of H2S, in particular between 10 and 30 vol.% of H2S . In general, the gas contains between 0.5 and 30 vol.% of S02, in particular between 5 and 15 vol. % of S02. The molar ratio between H2S and S02 generally is between 4 :1 and 0.5:1, in particular between 3 :1 and 1.5:1, still more in particular 25 between 2.1:1 and 1.9:1.

Where the gas resulting from the combustion reaction has a relatively high concentration, e . g. , in the particular ranges indicated above, the H2S and the S02 will react in the combustion chamber, at the prevailing high temperature to form 30 elemental sulfur according to the following equilibrium reaction: 2H2S + S02 = 2H20 + 3S

In general after the above mentioned reaction the gas contains between 0.5 and 8 vol. % of H2S, in particular between 2.0 and # 6 vol. % of H2S . In general after the above mentioned reaction the gas contains between 0.3 and 5 vol. % of SO2, in particular between 1.0 and 3 vol. % of SO2.

After removing the elemental sulfur by a low temperature 5 condensing step this gas is suitable for further processing in the catalytic Claus reactor.

The composition of the gas from the combustion chamber (also sometimes indicated as combustion reactor or thermal reactor) is dependent on the composition of the gas provided to the 10 combustion step, on the combustion conditions, and on the amount of oxygen provided during the combustion step. It is within the scope of the skilled person to select the parameters in such a manner that a gas with a suitable composition is obtained.

15 The gas resulting from the combustion step may be provided directly to the Claus reactor, or may be subjected to intermediate processing steps such as heating up, cooling down, Heating up by of the gas to the required Claus reactor inlet temperature may be necessary by means of direct heating or 20 a heat exchanger. The heating medium can be steam, hot oil, hot gas, hot gas derived from fuel gas combustion with an oxygen containing gas stream, or an electric type heat exchanger using an electric power source.

It is preferred for the gas obtained from the combustion step 25 to be provided directly to the Claus reactor, whether or not after an intermediate cooling of heating step, with an intermediate cooling step being more often required.

In another embodiment, the starting gas stream comprising H2S 30 and SO2 is not derived from a partial combustion step as described above, but from other sources. In one embodiment, the starting gas stream containing H2S and SO2 is obtained by adding SO2 to a gas stream containing H2S in an amount of, say, 1-15 vol. %, in particular 1 to 8 vol. % . The amount of SO2 to 6 be added is governed by the desired composition of the gas to be provided to the catalytic Claus reactor, as has been discussed in more detail above. By adding SO2 to a H2S containing gas stream, the process according to the invention v5 is a suitable outlet for relatively lean H2S-containing gas streams. This is of particular interest, as the other currently available processes to treat these gases to form elemental sulfur are troublesome to operate, have low recovery efficiency, and have high investment costs. Further, they 10 often yield a sulfur product with low quality.

The S02 used in this embodiment can, e.g., be obtained by combustion of elemental sulfur with oxygen in a combustion chamber, and subsequent cooling in a heat exchanger, if this is required.

15

For gas streams containing an intermediate amount of H2S, e.g., in the range of 5-30 vol. %, more in particular 8-15 vol.%, a further approach may be followed. This gas has a H2S content which is less preferred for direct provision to the catalytic 20 Claus reactor. On the other hand, if this gas is subj ected to the partial combustion step as described above, the H2S concentration will be undesirably low. Further, this process is difficult to carry out through dependable methods.

It has been found that these cases can be converted to a gas 25 stream containing H2S and S02 in the desired range by providing the H2S containing gas stream to a combustion chamber which also contains a suitable amount of elemental sulfur and oxygen. The elemental sulfur is converted to S02, which results in the formation of a gas stream with a relatively high concentration 30 of H2S and S02 . At the prevailing high temperature this results in the formation of elemental sulfur through the thermal Claus reaction, leaving a gas stream with a containing H2S and S02 in the ranges specified above. This stream is suitable for provision to the catalytic Claus reactor. An attractive 7 feature of this process is that the amount of sulfur added to the reactor is not very critical, as elemental sulfur will be consumed by the combustion and generated through the thermal Claus reaction. The amount of oxygen should be 5 resulted to ensure that the desired amount of SO2 is generated. The combustion step can be carried out as described above for the combustion of more concentrated H2S streams.

The gas stream comprising H2S and S02 that may, e.g., be 10 obtained through any of the processes described above is provided in step (1) of the process according to the invention to a Claus reactor where it is contacted under reaction conditions with a catalyst, to form a product comprising elemental sulfur, water, and residual H2S and S02, in accordance 15 with the following formula: 2H2S + S02 = 2H20 + 3S i

As indicated above, the starting gas stream generally comprises between 0.5 and 8 vol. % of H2S, in particular between 20 2.0 and 6 vol. % of H2S. The gas stream generally comprises between 0.3 and 5 vol. % of S02, in particular between 1.0 and 3 vol. % of S02 - The molar ratio between H2S and S02 generally is between 4 :1 and 0.5:1, in particular between 3 :1 and 1.5:1, still more in particular between 2.1:1 and 1.9:1.

25 The gas stream may also comprise one or more of the following components, e.g., water, e.g., in an amount of 10-30 wt. %.

In the Claus reactor the gas comprising H2S and S02 is contacted under reaction conditions with a catalyst, to form a gas 30 product comprising elemental sulfur, water, and a tail gas containing residual H2S and S02.

Claus reactors, catalysts, and reaction conditions are known in the art. Reaction conditions include, e.g., a temperature in the range of 200 to 350°C, in particular 220 to 300°C and 8 a pressure of, e . g. , 0.1 bar gauge to 3 bar gauge, in particular 0.3 bar gauge to 1.5 bar gauge, still more in particular 0.6 bar gauge to 0.8 bar gauge. Suitable catalysts include those known in the art such catalysts containing alumina and/or 5 titania.

The gas product comprising elemental sulfur, water, and a tail gas containing residual H2S and S02 is provided to a condenser to condense the elemental sulfur. The tail gas may if so desired be provided to a further Claus reactor followed by a further 10 condenser, which again may be followed by further reactor condensor sets. The number of Claus reactor / condenser assemblies used in the process according to the invention is not critical, it generally ranges from 2 to 4.

15 The tail gas from the final Claus reactor generally has to following composition: In general, the gas contains between 0.2 and 10 vol.% of H2S, in particular between 0.5 and 3 vol. % of H2S. In general, the gas contains between 0.1 and 5 vol.% of S02, in particular between 0.2 and 1.5 vol. % of S02. The 20 molar ratio between H2S and S02 generally is between 3:1 and 1 :1, more in particular between 2.1:1 and 1.5:1. The tail gas may contain COS, e.g. , in an amount of 0 to 0.2 vol. %, and/or CS2, in an amount of 0 to 0.2 vol. %.

25 The gas is provided to an oxidation step, where it is contacted with oxygen to convert the sulfur compounds to S02.

The main reactions are: 2H2S + 302 = 2S02 + 2H20 2COS + 302 = 2S02 + 2C02 30 CS2+ 302 = 2S02 +C02

If present, small amounts of elemental sulfur may also be converted to S02. It may be needed to add oxygen containing gas to the tail gas. This depends on the amount of oxygen 9 already present in the gas as it leaves the Claus reactor. Oxygen may or may not be present in this gas. Whether or not oxygen has to be added and if so how much also depends on the concentration of components that will react with oxygen, ,5 such as H2S, COS, CS2, vapor-phase elemental sulfur, but also CO and H2. It is within the scope of the skilled person to calculate the required amount of oxygen. After the addition, the oxygen content is generally in the range of 3-15 vol%. The oxygen may be provided as normal air, or other 10 oxygen-containing gases, such as air to which additional oxygen has been added. The reaction temperature in this step generally is 300-800°C, best between 400-700°C. Where necessary, fuel gas may be added to the oxidation step to raise the temperature. The fuel gas for the oxidation step, 15 if present, may be any kind of combustible gas, solid, or liquid.

The product from the oxidation step is a gas stream wherein at least 95% of the sulfur is present in the form of S02, more in particular at least 97% of the sulfur is present in the 20 form of S02, still more in particular at least 99%. More in particular, at least 99.9% of the sulfur is present in the form of S02 .

The gas stream generally contains between 0.1 and 5 vol. % of S02, in particular between 0.3 and 3 vol. % of S02. The gas 25 stream may further contain other components, e.g. , water, generally in an amount of 10-30 vol. %, nitrogen, e.g., in an amount of 50-7 0 vol. %, C02, e . g . , in an amount of 1-40 vol. % , NOx, e.g., in an amount of 0 to 1000 ppm, and oxygen, e.g., in an amount of 2-8 vol. %.

30 The H2S content preferably is very low, e.g., in the range of 0-20 ppm, in particular 0-10 ppm. CO and hydrogen may, e.g., be present in an amount of 0-3000 ppm, in particular 0-1000 ppm, more in particular 0-600 ppm for each compound. The gas may also contain minor amounts of COS and CS2, e.g.

10 for each compound in an amount of 0-20 ppm, in particular 0-10 ppm.

The S02-containing gas stream is provided to a reactor where 5: the S02 is converted at least in part to S03. The oxidation reaction is generally carried out in the presence of a catalyst, which can be any SO2/SO3 conversion catalysts for, such as vanadium based catalyst (vanadic oxide and its carrier), or platinum based catalyst.

10

The S02 to S03 conversion is an exothermic reaction, and it is necessary to cool the process gas gradually in the heat exchanger. The best option for the cooling medium is air (but it can also be considered to use oil, water or steam). In 15 one embodiment, the cooling air from the S02 to S03 conversion unit is returned in whole or in part to one or more of the combustion step, the oxidation step, or other section as oxygen supply.

In the effluent from the S02 to SO3 conversion step generally 20 at least 95 % of the sulfur is present in the form of SO3, in particular at least 97 %, more in particular at least 99%.

The effluent from the S03 formation step is hydrated and cooled by contacting it with water to form sulfuric acid. The 25 concentration of sulfuric acid in the resulting product is 10-98 wt.%, preferably 50 to 90 wt.%, more preferably 75 to 85 wt.%. The temperature generally is 30-300°C, preferably 200 to 250°C.

The sulfuric acid may sometimes contain trace amounts of 30 sulfinic acid, formed as a result of the presence of trace S02. If present, the sulfinic acid is present in an amount of 0.01 to 0.5 wt.%, calculated on sulfuric acid.

11

The tail gas from the hydration step has a very low S02 content. For example, the amount of SO2 in the tail gas or flue gas is in the range of 0 to 1 mol. % more specifically in the range of 0 to 0.5 mol.%. It is possible to obtain values in the ..5 range of 0 to 0.2 mol. %, or even lower, e. g. , in the range of 0 to 0.1 mol.%, or below 0.05 mol.%, or even below 0.01 mol. %.

The H2S content of the tail gas from the hydration unit preferably is very low, e.g., in the range of 0-20 ppm, in .10 particular 0-10 ppm, or even in the range of 0-5 ppm. The content of COS and CS2, if present at all is preferably also very low, e . g. , in an amount of 0-2 0 ppm, in particular 0-10 ppm for each compound. The same goes for the S03 content, which, if present is preferably in the range of 0 to 20 ppm, 15 in particular 0 to 10 ppm. CO and hydrogen may, e.g., be present in an amount of 0-3000 ppm, in particular 0-1000 ppm, more in particular 0-600 ppm for each compound.

The tail gas can be sent to the downstream unit for further treatment and released to the atmosphere. It is a particular 20 feature of the invention that the tail gas may in some embodiments be directly released into the atmosphere as it may meet all presently known environmental requirements.

The sulfuric acid and, if present, sulfinic acid can be 25 discharged directly. It should be noted that the sulfuric acid has a purity which is sufficiently high for it to be used as starting material in other processes.

The sulfuric acid may also be recycled in whole or in part.

E.g. it can be returned back to the H2S combustion step 30 described above, if present. It can also be provided to a step where S02 is manufactured by combustion of elemental sulfur, e.g., in the case where gases with a low H2S content are processed.

At a high temperature of 1000-1350°C, the sulfuric acid can 12 react with H2S in the acid gas to obtain S02 and elemental sulfur, in accordance with the following formula:

H2S04 = S02 + 0.502 + H20 H2S + H2S04 = S + S02 + 2H20 J

The trace amount of sulfinic acid, if present, will decompose in the combustion step to S02, which can react with H2S in the acid gas to obtain elemental sulfur.

10 A particular feature of the present invention is that it allows reuse of various gas streams.

In a first embodiment, the oxygen-containing hot gas withdrawn from the hydration unit is provided in whole or in part to one or more of the combustion step, if present, 15 the oxidation unit, the S02 conversion unit, or a unit where elemental sulfur is combusted to form S02, if present.

In a second embodiment cooling air from the S02 to S03 conversion unit is returned in whole or in part to one or more of the combustion step, the oxidation step or other 20 section as oxygen supply. Alternatively cooling can be achieved by raising valuable steam and/or heating boiler feed water and/or heating hot oil for general use in the plant or other facilities.

25 The present invention provides a process wherein H2S containing gas streams can efficiently be converted to elemental sulfur and sulfuric acid, which are both suitable for further processing as desired. Due to the integration of the various process steps optimum use may be made of the various 30 recycle possibilities . Further, a particular advantage of the present invention is that not only elemental sulfur can be recovered after treating, but the tail gas is also able to meet emission requirements. The air from the heat exchanger 13 mentioned above can be the source of oxygen, so reaction heat can be recovered and resources recycled.

The process according to the invention makes it possible to achieve an overall achievable sulfur recovery figure of 99.99 5 %, and this is particularly attractive in combination with the low S02 emissions. The process according to the invention can simultaneously fulfill both the highest sulfur recovery requirements and the lowest SO?, emission requirements known in the industry today. This is a unique feature of the process 10 according to the invention.

The process according to the invention dispenses with the need to use caustic washing processes, which lead to loss of elemental sulfur which put additional loads on the downstream 15 unit. The sulfur content in the discharged gas from this invented process is very low, achieving higher sulfur recovery efficiency. The process in this invention is easy to operate, effectively purifies the acid gas and adopts a simplified acid gas treating process scheme, reducing operating costs and 20 difficulties and making it suitable for use in many different applications .

Examples 25 The following examples illustrate the process of this invention, but the invention is not limited thereto or thereby.

In Example 1, reference is made to Figure 1, which illustrates the invention, without limitation. In this figure, the signs 30 have the following meaning: 11 is the combustion reactor, followed by a cooling step 12, which is e.g. a condensor 21, 22 are Claus reactors 31 and 32 are sulfur condensors, where elemental sulfur is 14 removed from the gas stream 4 is the oxidation chamber where sulfur compounds are reacted with oxygen to form S02 5 is the S02 converter, where S02 is converted into S03 5 6 is the hydration unit where S03 is reacted with water to form sulfuric acid and optionally trace amounts of sulfinic acid

Example 1 10 With reference to figure 1: Acid gas G comprising H2S with a temperature of about 40°C is provided to a combustion reactor 11 together with oxygen containing gas provided through a line from the condenser 6 (air, pure oxygen, or other oxygen-containing gas) (and if necessary additional 15 air through feeds not shown) . In combustion reactor 11 vapor phase elemental sulfur is obtained and a gas mixture containing H2S and S02. The gas mixture is provided to a condenser/cooler 12, where the elemental sulfur is removed (arrow SI) . The gas mixture containing H2S and S02 is provided 20 to Claus reactor 21, where H2S and S02 react to form elemental sulfur. The effluent from the Claus reactor is provided to a condenser 31, where elemental sulfur is removed. The Claus tail gas from which the elemental sulfur is removed is provided to a second Claus reactor 22, which is followed by 25 a second condenser 32 . Further Claus reactors/condensers may be present. The effluent from the last condenser is combined with hot air from the hydration unit 6 are preheated to 350°C and then thermally incinerated in the oxidation chamber 4 to convert sulfur compounds into S02 under a temperature 30 between 300-800°C. The gas containing S02 is mixed with the hot air from 11 and enters the S02 convertor 5 to obtain S03. The required quantity of air is calculated by measuring the flue gas flow and the 02 and S02 contents in the incinerator flue gas to get the theoretical air demand. The actual air 15 demand is 12% higher than the theoretical air demand. The convertor catalyst is a vanadium based catalyst (such as vanadic oxide), and the reaction is carried out at a space velocity of 3000 h"1. The temperature is, e.g., 500°C.

;5

The S03 containing gas from convertor 5 enters hydration unit 6, also indicated as condenser. The cooling medium is oxygen enriched air 10, entering through line A. The cooling medium enters the condenser to cool the S03 containing gas and heated 10 air 1 is emitted through line B. The S03 containing gas is cooled to about 100°C, meanwhile sulfuric acid and, if formed, trace amounts of sulfinic acid are obtained in the bottom of the condenser 6, and withdrawn through line SA. The sulfuric acid and, where present, sulfinic acid may be returned in whole 15 or in part to the combustion step 1 through return line SA2 to be converted into elemental sulfur. The sulfuric acid and, where present, sulf inic acid also be removed from the system for further uses through removal line SAl.

20 The tail gas (or flue gas) stream from condenser 6 contains hardly any sulfur compounds, and may be emitted to the atmosphere through line 0 or otherwise processed further.

The equipment to be used in this case, such as incinerator, 25 Claus reactor, and thermal stage, are all general equipment widely known and used by the technical people and operators in this field.

Acid gas feed composition for this example 30

Component kmol/h _ kg/h moll wt%_ I : 30.7913 ~lo7f ~:;o52 23.5A n 19.6443 .......COB i 073491 ; 2 0 . Cï -! 7 Ï 0.21'! 0.3 ' _'_ ................^ I 0>55p-7 9.4 A:;; "0.411 n____0.17 82 : 16 ; _ 1 O. S -2 5 4 | 14.7119 0.409 9 0.27 60 ___üz___, _JL^ijÖ66~ 2.213? " 0.817F * o70415 ( _____ co. _i_8 8_.0374 ' 387 3.644 5 J ?7.44CS 72.6824 ___67 ,jj,4 5 I' 1.837 4 J_. 2 600 H?0 j _0J_7 0?9 14.20^8 0.6082 0.7681 | ! 'IV,, _ U . 53"5~ 8.60Öf~ 0.^4118 . n7l614 __6__ _ SLzI'133 15.8483 0.404^ 0.2974 ___c-H3_l^liT7_ 11,42.79 ï. 3482 J~ 1.4528 ^ | Hip ___-...:.9905 ~"l73.4 505 2.2 911__, 3^2 545 1 CV *.OH____ 0.1 504 " 4.8112 0.1161 0.090 3__ (____Total 1 1 30.5287 | 5329.5526 100.0000^ ] 100.DQ0ÏÏ~ "

Process gas from condenser 12 provided to the Claus reactor 22 ;; Component 1 kmol/h_ kg/h mol% wt% L_ H-D _ 5.6876““rT9373793 ; 2.8609 2.8541 ~ __" i 2 90624 : 2.3111 6 4.3400 j [_COG 2.3872 j 143.2335 1.2008 2.1140 ; ' "" ~ 0.64 45 48.9820 : 0.3242 ~ 0.7229 ; : 5 6 0.1892 o 36.3168 0.0951 0.5360 ;

Ss J 0.3353 85.8240 0.1686 3.2 667 ! CO ; 18.1062 506.9736 9.1074 7.4 824 , H2 4.2022 8.404 4 2.1137 1 0.124 0 ' C02 8 6.7689 3817.8327 43.6448 56.3469 i : N2 26.8241 751 .0734 713.4925 j 11.0850 ?

Ar. ; 0.28 61 c 11.4 4 40 0.1439 0.1689 ~ lHaO 48.7811 878,0589 24.5369 12.9592

Total ; 198.8070 6775.5850 100.0000 7 100.00 0 0 I'

Claus tail gas, provided to oxidation unit4

Component kmol/h kg/h mol%__wt% H.2S 0.8542 29.0411 0.4400 0.4996 SÖ2 ...........™ 0.4243 27.1520 j 0.2186 0.4671 j; —og82 353.6IO0" I 0.0506 6.08 36 —^ ; 0>0330 2.5061 "I 0 • 0Ï:TÖ ' 1 0.0431 — j 0.0014': |__ 0.~2736 ; 0.0007 0.0047 7 _ 0“ g"0_n 3 . 1184 _0 ._0_04 3_ _ ccT~— ‘ i sTïoei ' 506.97V. | 9\_327^ |^8-7221 j 17 i' H2Q ;] 4.2022 75,6396 [ 2.1648 1.301_3__ C02 8 9.6695 3945.4558 ’ -16.1991 1 67.8787

Nr ~ 26.8241 " ~ ~751.0734....... ï/ . 1 7 8 ‘ . 2~ 9217~ ~

Ar 0.2861 /11.4440 0.1474 0.1966 H2 53.6100 i 107.2199 1 27.6173 1.8446 " Total ~ 194.1173 ; 5812.5075 [100.0000 100.0000

Fuel gas to oxidation unit 4

Component | kmol/h kg/h mol%_ wt% T CO 0.5271 1 14.7595 12.7710 i 14.4331 : H2 ~ T......1.0192 U..................2.0384__24.6923 1.9933 C02 1: 1.5583 68.5641 37.7535 67.0477 02 0.0004 " 0.0136__0.0103 0.01 33 ;

! N2 ' 0.0235 ;r 0.6587 ~ 0.5700 0.6441 J

CH4 0......9816 15.7060 23.782 6 15.358 6 I

f C2H6 0.0169 r 0.5078 0.4101 0.4965 f ___ 0.0004 ’ ~0.0136 0.0103 0.0133 _Total ~ 4,1275 ' ~102.2616 |;; 100.0000 100.0000 ~ 5 Combust ion ....air to oxidation unit 4

Component kmol/h kg/h mol% wt% C02 " 0.0312 ~| ÏT3728 0.0298 1 6.0454 r~ 02 21.7881 ! 697.2176 20.8206 23.0645 N2 " Hl.2108 " 2273.9864 77.6077 75.2253 - Ar ' 079672 38.6880 0.9243 1.2798

H2Q ’ i 0.64 64 11.634 8 0.617 7 1 ~ 0.3849 I

Total" | 104.64 66~ 3022.8 996 100.0000 100,0000 f

Flue gas from oxidation unit 4, provided to S02 converter 5

Component kmol/h kg/h mol%__wt%

Ih2S~I 0.0000 0.0000__0.0000 U 0.0000 S02 ~ 1.5425 ' 98/720 0 0.5248 1 .0428 : ” cos " o.oooo o.oooo 0.0000 0.0000 / }' CS2 0.0000 0.0Q00 0.0000___0.0000 j" CO 0.9053 25.348 4 0.3080 0.2678 p :H2 'p 0.1261 0.2522 0.0429 0.0027 I C02 110.1312 4845.7728 37.4678 _51.18 6~7 18 02 1 7.3484 1 238.1472 ; 2.5000 2.483« N2 110.’ 3085.9631 17.5442 32.6398 4 '_^ Ar ~ «Ti0(7 | 51.2250___ 0.4357 0.5411_| H20 r 63-2459 | 112C.4262 :: ll.l767 11.8353

Total,. |_ 2 93.9358 1 9466.8549 100.0000 j 100.0000_

Process gas from the S02 corr~' i ror 5 _ irovi" ~ 1 1 o hydration unit .6

Component kme L/h kg/h mol% wt% i H2S.................................................. 0 0 00 0 0.0000 0.0000 ' 0.0000 S°2 0.0 617 3.4-480 0.0210 0.0417 " "~S07 1.4808 —8~ ,}64^r ' Q.5051 I 1.2514 COS " 0.0000 0.0000 0.0000 i ö.'oooo '............CS2............... 0~. 0000_ 0.0000 F 0.0000 öj~“ 0.0000 i CO 0.9053 25.3484 " 0.3088 0.2678 ____0.1261_ 0.2522 ” [ 0.0430 j 0.0027 C02 110.1 'l" ~ 4845.7728 37.5624 ]_ 51.1867 02 ~ 6. = 0'U1 ' 211.454 4, ; 2.2538 7 2.2336 N2 ~TTÖT355R 3089.9631 37.6390 2 32,6398

Ar " 1.2806^ """'.51.2250 0.4368 ; 0.5411 3; ^120 62.2459 1120.4262 21.2302 Jj 11.8353 j3 : Total | 293.1954 9466.8549 1 00.0000 100.00ÖÖ~1|i <J ......... .......'.........

Tail gas from hydration unit6

Component kmol/h kg/h mol% wt% ; H2S "“O.OOOO ; 0.0000 0.0000 0.0000 SO~2 0.0106 ï 0.6784 J 0.0037 __ 0.0074 r S03 = 0.0005 ' 0.04000.0002 0.0004 j cos ~ ö.'oooo ; o.oooo o.oooq o.oooo V" cs2 ...... o.o o o o T 0.0000 0.0000 0.0000 j CO ; 0.9053 I 25.3484 0.3148 0.2765 I H2 0.1261 0.2522 0.04380.0028 j C02 ; 110.1312~~4845.7728 ~~3~8.2932 52.8652 j 02 : 6.6080 1 10 5.7272 2,2976 1.1534 i N2 110.3558I 3089.9631 38.3713 33.7101 r Ar 1.2806 51.2250 0.4453 0.5588 ~; “ _H2Ö 58.1819 r: 1047.2742 20.2301 :1.4253

Total 287.6000 9166.2813 100.0000 100.0000; 19

In the process of this Example, the acid feed gas flow is 5333.25kg/h. After a series of process treatments, the S02 5 content in the tail gas of the hydration unit is less than 106mg/Nm3, which makes it suitable for direct emission to the atmosphere. The process of this example shows a sulfur recovery yield of more than 99.9%, specifically 99.96%, with an SO2 content in the hydration unit tail gas of 0.0037 mol.%.

10

Example 2

In this example, the treatment of an acid gas with a H2S content of 1-8 mol. % will be described in more detail. It should be 15 noted that the description in this example is applicable in combination with the entire description above.

Acid gas with a H2S content of 1-8 mol. % and a temperature of about 40 °C is mixed with a S02 containing gas such that in the mixture the molar ratio between H2S and S02 is between 20 3 : 1 and 0.5 : 1, more particular between 2.1 :1 and 1.9 : 1. In most cases the S02 containing gas is not available in adequate quantity and composition. Therefore the gas is generated by the combustion of elemental sulfur, as produced in the downstream Claus reactors and sulfur condensers or a 25 sulfur species containing gas. For the combustion of sulfur an oxygen containing gas, pure oxygen, air enriched with oxygen or normal air can be used. The combustion of sulfur takes place in a suitable burner and combustion chamber with or without an atomizing fluid and may be assisted by co- firing 30 fuel gas, any kind of combustible gas , solid or liquid. The combustion temperature in the combustion chamber is generally in the range of 700 - 1500 °C, preferably in the range of 1000-1300 °C. The S02 containing gas is cooled in a heat exchanger by means of a suitable cooling fluid such as steam, 20 water, oil or air. Preferably a fire-tube waste heat boiler type heat exchanger is used whereby steam is produced from boiler feed water generally at a pressure in the range of 15-50 Bar(g) , more particular in the range of 25-45 Bar(g) . The 5 temperature of the S02 containing gas from the heat exchanger is adjusted such that after mixing with the H2S containing acid gas the required inlet temperature of the Claus reactor is obtained which generally is in the range of 180-260 °C, in particular in the range of 210-240 °C. After the cooling step 10 a heat exchanger may be included to slightly heat up the S02 containing gas in order to obtain a more precise inlet temperature of the Claus reactor. This heat exchanger can be provided with a heating fluid such as steam, hot water or hot oil, or the heater can be of the electric type. The mixture 15 of H2S containing acid gas and the S02 containing gas is introduced into the catalytic Claus reactor and further processed according to the invention as described in Example 1. If so desired, sulfuric acid can be recycled to the S02 generation step and decomposed.

20

Example 3

In this example, the treatment of an acid gas with a H2S content of 8-25 mol. % will be described in more detail. It should 25 be noted that the description in this example is applicable in combination with the entire description above.

A variation to the above principle which is suitable for acid gas with a H2S content between approximately 8 and 15% is as 30 follows:

The acid gas with a H2S content of 8-15 mol. % is introduced in the combustion chamber of the S02 generation step. The S02 containing gas is produced as described above . The temperature in the combustion chamber is maintained in the desired range 21 by co-firing fuel gas, any kind of combustible gas, solid or liquid. The combustion chamber has adequate dimensions to allow for the combustion of the elemental sulfur and/or a sulfur species containing gas, the mixing with the acid gas 5 containing H2S, and the equilibrium reaction between H2S and S02 according to the formula : 2H2S + S02=2H20+3S . The cooling of the gas takes place in a heat exchanger as described above followed by a sulfur condenser whereby sulfur is condensed and separated from the gas stream. The resulting gas stream 10 contains H2S in the range of 0.5- 8 mol. % and S02 in the range of 0.2-5 mol % suitable for treatment in a Claus reactor. The gas is heated up to the required inlet temperature of the Claus reactor as described above and further processed according to the invention.

15 If so desired sulfuric acid can be recycled to the S02 generation step and decomposed.

Although the above explanations offer a general introduction and more detailed descriptions about the use of the invented 20 process, modifications and improvements to the basis of the invented process which are obvious to experts in the field. Therefore, any such modifications and/or improvements that do not deviate from the spirit of this invention shall all be considered as part of the invention and within the scope 25 for protection.

Claims

A method for treating a sulfur-containing gas stream, comprising the steps of (1) supplying a gas stream comprising H 2 S and SO 2 to a Claus reactor where it is contacted with a catalyst under reaction conditions to produce a product forming elemental sulfur, water and residual H 2 S and SO 2, (2) contacting the gas from a Claus reactor comprising H 2 S and SO 2 with oxygen in an oxidation step under oxidizing conditions to obtain a gas stream comprising SO 2, (3) contacting the SO2-containing gas stream in a 502 conversion step with a catalyst to form a 503-comprising gas stream, (4) contacting the SO3-containing gas stream with water under hydration conditions to form sulfuric acid, wherein the gas stream comprising H 2 S and SO 2 used in step (1) is obtained by subjecting a gas stream comprising H 2 S to a combustion step, under v arrangement of a gas stream comprising H 2 S and SO 2, and wherein the sulfuric acid and any sulfinic acid contained therein is at least partially recycled to the combustion step, or wherein the gas stream comprising H 2 S and SO 2 used in step 25 (1) is obtained by adding SO 2 to a gas stream containing H2S, wherein the SO2 is optionally formed by burning elemental sulfur, and wherein the sulfuric acid and any sulphienic acid present therein is at least partially recycled to the SO2-30 formation step, or wherein the gas stream comprising H2S and SO2 used in step (1) is obtained by supplying a gas stream consisting of H 2 S to a combustion chamber which also comprises elemental sulfur which is converted into SO 2, and wherein the sulfuric acid and any sulphienic acid present therein is at least partially recycled to the SO 2 formation step.

2. Method according to claim 1, wherein the off-gas from the hydration step 4 is discharged into the atmosphere.

3. A method according to any one of the preceding claims, wherein oxygen-containing hot gas from the hydration unit in step (4) is wholly or partly recycled to one or more of the combustion step, if present, the oxidation step, the SO 2 conversion unit or a unit wherein elemental sulfur is burned to form SO 2, if present.

4. A method according to any one of the preceding claims, wherein cooling air from the SO 2 conversion step is wholly or partly recycled to one or more of the combustion step, if present, the oxidation step, or as an oxygen source to another step.

A method according to any one of the preceding claims, wherein the off-gas from a first Claus reactor is fed in step (1) to a second Claus reactor, the off-gas of which is optionally fed to a further Claus reactor, while the off-gas from the last Claus reactor is fed to the oxidation step (2}.

The method according to claim 6, wherein a total of at least two Claus reactors are used, in particular 2-4 Claus reactors.