CA1325880C

CA1325880C - Process for simultaneous production of sulfur from h_s-containing gases and so -containing gases

Info

Publication number: CA1325880C
Application number: CA000554553A
Authority: CA
Inventors: Rainer Lell; Kuldip Sud
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1986-12-16
Filing date: 1987-12-16
Publication date: 1994-01-11
Anticipated expiration: 2011-01-11
Also published as: DE3775908D1; EP0271654A3; EP0271654A2; ATE71339T1; FI875465A; FI83758B; FI83758C; DE3642858A1; FI875465A0; EP0271654B1

Abstract

ABSTRACT

The invention relates to a continuous production process in which elementary sulphur is obtained simultaneously from H2S-gases as well as from SO2-gases in various quantity ratios. In the presence of considerable quantities of the SO2-gas, all of the H2S-gas is partially being oxidized with a O2-gas in a 1st reaction zone at 800 - 1400°C, whereas the balance of the SO2-gas is partially being reduced in a 2nd zone at 1000 - 1500°C in the presence of a reducing gas. Subsequently the mixture from both zones, which has now an almost stoichiometric H2S:SO2 ratio, is being converted to sulphur in a 3rd zone at 800 -1300°C without any additional, direct heat supply. The sulphur is separated by way of condensation and the remaining gas mixture is further processed in a conventional Claus installation.

Description

1 132588~

The invention relates to a contlnuous production proces~ to simultaneously obtaln elementary sulphur from H2S-gases and from S02-gases, especlally from sour gas and from S02-rich gas derived from the desulphurlzatlon of flue gas.

To obtain elementary sulphur by means of a catalytlc Claus reactlon 18 standard lndustrlal practice but requlres, however, a stolchlometrlc H2S : S02 ratlo and greatly dlluted feed gases with a limited moisture content.

In refining plants with ad~oinlng power station, H2S-gases as well a~ -S02-gases are generally availabIe. The quantity of the sulphur compounds depends on the capacity of the plants as well as on the processed raw materials and, therefore, fluctuates widely without ever reaching the stoichiometric H2S : S02 ratio over a prolonged period of time. Furthermore, the concentrations, which reach over 50 molar % of H2S in sour gas and more than 90 molar ~ of S02 in rich gas are by far too high.

:, . ~ .

.

It was therefore suggested to first of all lower the concentration of sulphuric compounds by way of tirect thermal oxidation of the ~2S
according eo 2 ~2S ~ 2 ~ 2 S + 2 ~2 or by the thermal or catalytic reduction of the S02 according to 2 + 2 ~2 f S + 2 ~2~

~owever, ehese eauations do not correspond to the actual course of react$on. Depending on the temperature, the equilibrium in both cases 19 somewhere bet~een 60 - 70Z which always results in a greaeer oxidized or reduced compound. Even lf it were possible to continue with the reactions to éhe extent of attaining the low concentration of sulphuric compounds required for the catalytic Claus reaction, these gases could only conditionally be introduced to the Claus installation i~ view of the quantities of water which will si~uleaneously form and on account of ehe increased steam content which will result in considerable activity losses of the catalyst. It has been established that the activity 1088 over a three-month period will result in a decrease of conversion of approximately 20Z if customary Claus catalygtq are used. Since a water separation by way of conden3ation i3 not feagible also for reason3 of heat economy, the only other alternative i5 the diluting with sulphur-frQe, inert gases which la achieved, e.g. by combu~tlng the ~2S with air instead of oxygen. ~owever, thi3 procedure result3 in an undesirable increase in the capacity of the apparatuses as well as in the heat supply. Another very aggravating problem is the discolouration of the sulphur that has been for~ed. This will occur i ehe 80ur gag, which is generally pre3en~, contalns hydrocarbons. Furthermore~ the lnvestment costs and, especially wlth respect to reduction~ the , ;, ~ 3 ~ 1325880 operating costs are very high.

Specification DE-OS 2346247 attempts, therefore, to obtain sulphur by way of a direct non-catalytic conversion of the H2S
with SO2, in which the SO2 is made available partly through H2S
oxidation and partly through foreign supply. Although it is insinuated that the application should also be possible in gases with an overstoichiometric SO2 content, the aforementioned specification refers only to a procedure involving gases with a H2S excess.

The specification states further that the retention time is determined by the dimensions of the H2S combustion chamber.
However, it is not clear how the rate of reaction of the direct sulphur formation which is lower in comparison to oxidation, could be taken into consideration.

Therefore, the ob~ect of this invention was to find a possibly economical method to simultaneously produce qualitatively acceptable elementary sulphur from H2S-gases and from S02-gases where the ratio to each other as well as the quantity would be subject to great fluctuations and where it should be possible to use waste gas directly as supply gas for a catalytic Claus lnstallation.

This task has been accomplished by the invented method as mentioned at the outset and according to which a) all of the H2S-gas is being subjected to partial combustion, in the presence of a 2 -gas, preferably air, at a H2S : 2 molar ratio of less than 2 : 1, and in the presence of a portion of the 132~880 S02-gas at 8 ~Zs: S02 molar ratio of re than 4 : l. This process takes place ln the frontal area of a 1st reaction zone at temperatures ~n the 800-1400C range and thus results in a reaction mi~ture of elementary sulphur with a ~2S and S02 quantity at a molar ratio of 2 : l up to l : lO;

b) the balance of the S02-ga~ 19 converted into elementary sulphur in a 2nd reaction zone by way of reaction ~ith a reducing gas at temperature~ in the 1000 - 1500C range and into a reaction mixture containing ~2S and S02 at a molar ratio of 2 : 1 to 10 : 1;

c) the ~i~ture of the reaction flow~ originating from stages a) and b), as formed in the rear area of the 1st reaction zone, is converted into elementary ~ulphur at a temperature in the 800 - 1300C range in a ~ub-~equene 3rd reaction zone without requlri~g a further direct heat supply. The wagte gas at a ~2S : SO2 molar ratio of approximately 2 : l contains maximum approximately 20 Z of ~2S and less than approximately 65 molar Z of ~2;

d) the waste gas from stage c) 1~ being con~erted into addi-tional elementary sulphur in a mult~-~tage Claug lnstallatiOn ln the customary manner ~ubsequent to partial cooling, heat recovery and sulphur condensation.

The invented method is applied mainly in refining plants with an ad~oining power station for the purpose of reprocesslng simultaneously the sour gas from the refining plant and the S02-rich gaR derived from the desulphuri2ation of the flue gas. However, the process is equally suitable for gas flows of other provenances.

All of the H2S gas is fed into the oxidation zone whereas the S02-gas is being dlvided, i.e. preferably quantitatively controlled, between the oxidation and the reduction zones. The quantity of H2S to be oxidized to S02 will only be as much as is required for flame 6tabillty. This quantity increases only when proces6ing 8ases with a great surplus of H2S. Depending on the S02 quantity to be processed, a larger or lesser portion is being reduced to sulphur and H2S. The only limitation is the quantity of water (generally less than approximately 65 molar ~) that i8 being tolerated by the subsequent catalytic Claus ln6tallatlon. It would be po66ible to exceed said water content if H2 were used as reducing gas. It could be counterscted by using a methane and/or C0-reducing gas.

In addition, a 02-gas, e6pecially air, is being fed into the oxidation zone. The quantity of 2 correspond~ to the quantity of H2S which i6 to be oxidized to S02. H2, C0 and/or low hydrocarbons such a6 methane, ethane, etc. may be u6ed a6 reducing gas. Gas mixtures which contain methane, H2 and C0 and which are frequently available at low cost in refining plants can be used without detrimental effects.

With respect to heat economy, it has proven especially successful to combine to a certain degree the production of the reducing gas and 13258~0 the heat requlred for the S02 reduction. In thls case, the heating gas, whlch consists mostly of methane, is being dlvided into 3 partial streams at a ratio of about (20 to 50) : (79 to 30) : (1 to 20) with the total equalling 100, i.e. preferably 35 : 50 : 15. The 1st stream i6 being combusted understoichiometrically with air, preferably with ~
equalling approximately 0.6 - 0.95 or most preferably if ~ equals about 0.7. The hot combustion gases ranging between 1700 - 1900C, depending on the heat losses, are being mixed with the 2nd stream and ~ubsequently fed into the actual reduction zone. The 3rd stream, after possibly being indirectly preheated, e.g. to 150C, will be fed into the reduction zone together with the S02-rich gas. The reducing gas made available in the above-described manner contains methane, hydrogen and carbon monoxide as reducing components and ranges in temperature from 1350 - 1550 C, depending on heat 1088. For example it can be composed as follows:
CH4 20.0 molar %
N2 50-9 molar %
C2 6.8 molar %

2 8.7 molar %
C0 2.9 molar H20 10.7 molar ~

In order to effect further sa~ings ln energy, the S02-gas, which is to be fed into the 2nd zone, can be divlded into two partial streams at a ratio of sllghtly more than 2 : 1, i.e. preferably after belng preheated by indirect heat exchange , e.g. to 450C. The larger stream is being llreduced in the actual reduction zone by means of the reducing gas obtalned in the above-descrlbed manner at a resulting mixing temperature 132~880 of about 1200C. ThQ remainder of the S02 part~al stream is fed into ehe react~on ~ixture obtained fro~ the reduction zone prior to combining the reaction mixture ~ith the ~;Yture from the oxidation zone which, in view of a m~ing temperature in excess of 900C a~d an already adequate retention time, leads to the formation of elementary sulphur. A checker wall advantageously separates the actual reduction zone from the preceding c bustion zone and, provlded one e~ists, from the subsequent ..
sulphur forming zone.

The gas mixture formed in the reduction zone, either with or without a subsequent sulphur- forming zone, ig being combined with the gas mixture from the oxidation zone in the rear area of the latter zone a~d is then subsequently fed into a 3rt reaction zone. In order to ensure a thorough ~lxing of the gases, the 3rd zone i9 separated from the preceding zones preferably by a vertical laetice--shaped or honeycombed checker wall with a dlfferential pressure of approximately 3 - lO mbar.

Whereas in the oxidation zone, under conditiong which deviate from stolchlometrlc rat~os, a conversion of ~zS and SO2 to sulphur worth mentioning is not accomplished and, whereas only small qua~tities of sulphur are being formed in the reduction zone, the production of sulphur, therefore, concentrates on zone 3. Due to the physical separation of the sulphur formation, the following advantages are realized:
1. indl~idual retention time and con~equently an optimum approximation to the thermodynamic equilibrium;
2. Production of a 3ulphur of great purity due to the fact that the hydrocarbons, which are contain~d in the heatlng gag ag well as ln the ., 1 sour gas, are combusted almost completely and/or that the resulting carbon reacts with the reaction components to COS and CS2 owinq to the indi~idual retention time, thus preventing soot from forming.

The temperature in the zones should preferably be as follows:
zone 1 900 - 1250C; zone 2 1150 to 1300C; zone 3 900 - 1200 C.
In order to reach these temperatures, it ~ay be necessary to burn a hydrocarbon heating gas geparately in Zone 2 andlor to add same to the sour gas in Zone 1. In additlon, the S02-gag, the reduction gas, the sour gas andtor the combuqtion air can be heated by way of indirect heat e~change prior to being fed into the respective zones. In view of the puriey of the sulphur which formg already ln zone 2, it is preferable to . . , conduct at least a-portion of the heat indirectly to zone 2. This measure is a posslbility especially If methane is-available as reducing gas. Any economical low hydrocarbon mi~ture 3ay be used as heating gas. Depending on the construction of the burner, lt is possible in princlple to use a liquid fuel. Since none of the three reaction zones has a catalyst, it is not necessary to make any special demands on the heatlng gas with respect to caealyst poi~on. ~n principle, a catalytic reduction would be e~pediene only if such catalygt would tolerate temperaeures of 800 - 1500C.
For practical reasons, the cemperature of the 1st and 2nd zone is appropriately in the upper ran8e of the gpecified temperature interval.
Thus the formation of COS and CS2 is advantageouglr reduced and, secondly, the temperature in zone 3 can be retained within the in~erval wiehout burning additlonal heaeing gag. In view of the fact that the sulphur forming reaction 19 ~lightly endothermic, ehe temperature of the 3rd zone is re~pectively gomewhat lower than that of ehe precediny zones.

_ 9 _ The tivisios of the S0 -gas flow, as descr~bed above, and the e~tent ofthe oxidat~on and reduction reactions are decisive for the composition of the waste gas in the 3rd zone. In order to render further processing in a catalytic Claus installation possible without the recovery of a possible surplus component, the H2S : S02 ratio should be approximately Z or, to be more preclse, H25 + ( COS . a ~ + ( 2 C52 b ) =2 a and b can ln this case be either the same or may differ; however, they represent the degree of conversion of COS and/or CS2 in the 3ubsequent Claus installatian. I~ addition, the ~2S concentration i9 to be l~;ted to about 20 molar ~ ma~i~um. S~nce the equilibrium of the sulphur-forming react~on ig somewhere between 60 - 70Z, depending on the tenperature, a continuous, partlal and premature removal of the sulphur ls a possibility. ~owever, this measure i~ llmdted to special ind~vidual cases for rea30ns of heat economy.

Normally, the entlre sulphur, as for~ed in zoneg 1 to 3, ls ~eparaeed after the 3rd reacti.on zone subsequent to cooling the g?S m~xture below the condensat~on temperature o~ gulphur while at the same time recovering the heat, e.g. in the form of steam. By subjecting the gas from which the s~ulphur has ~een removed in the above described-manner to a catalytic Claus installation and, if necessary, by slightly reheating the ~as, further 5ul~hur i5. beino o~ta~ned.

Surprisingly, lt was d~scovered that contrar7 to prevlou~ knowledge, the partial oxidatio~ of the ~2S, when physically geparated from the j~ ~ `J `

j,~7 132~880 sulphur-forming zone, can be csrried out without any difficultles even in the presence of large quantities of S02 which may be many time~ thst of the H2S. The invented method is not limited to a minimum rstio of H2S : S02. It is especially suited for the reprocessing of gases with an S2 surplu~. The sulphur thus produced is of great purity due to the fact that impurities caused by hydrocarbons which have not been completely combusted are to a large extent prevented by the featur2s of novelty of the invention.

132~

The in~en~ion will be explained below by way of e~amples and by referring to the atrached sche~atic drawing but, however, without limiting it to the conditions given in the e~ample.

Example l:(use of natural gas as reducing gas) 23.9 I~molth of S02 rich gas (8) with a S02 content of 95.27 molar ~, preheated to 450C, is fea into the oxidation zone (1), as well as 137.9 kmol/h of sour gas (7) with a H2S content of 89.20 molar ~ and 2~3.2 kmal/h of air ~61 via t~e ~_5 hurner which may consist of a system comprised of several indi~idual burners. At the same time, the reduction zone (2) 1~ being fed with the remaining Z1.4 kmollh of preheated S02 rich gas (9) and with 10.79Dlol/h of a reducing gas (10) with 97 5 molar Z of C~4,0.9% of C2~6, 0.3% of C3~8, 0~9~ of 2 f C2 as well 85 with 4.38 kmol/h of heati~g gas (12) ant 29.64 kmol/h of combustion air (11) via a heating gaq burner. rhe heating ga~, having the same compo-~ition as the reducing gas,is burned understoichiometr~c311y.

A partlal retuc~ion of the SO2 take3 place in zone 2 at a temperature of approximately 1250 C, thus resulting in a nLLxture with a ~2S : S02 ratio of 1.9 : 1 and a vaporous sulphur (S2) content of 9.1Z. At the same time a hot sulphur-containing mixture of approximately 1000C and with a ~2S
: 52 ratio of 1.96 : 1 is formed hy way of partial ~25 oxidation in zone 1 in tne vicinity-of tn~-burn~r. BQth liiixturas are t~n mixed in the rear area of zone 1 and fed into zone (3) via the checker ~all (5). During a retention time of a~proximately 1 second, a further conversiOn to sulphur takes -lZ -place in zone 3. The temperature sets itself to a~out 1040 C. The m~xture(4) leaving reaction zone (3) is then be~ng cooled to 240C by way of 5 bar-steam production, and the condensing sulphur is separated in the usual manner. The yleld ~8 2800 kg/h of sulphur with a 99.9% purity. After being indirectly heated to 260C, the rema;~ing gas mixture containing 7.4Z of ~2S, 3.8% of S02, 0.2% of COS and CS2, as ~ell as 31% of a2o i9 converted into further elementary sulphur in the customary manner in a catalyt~c Claus installation.

Example Z: (use of hydrogen as reducing gas) The procedure is si3ilar to example 1 except for the preheating of the S2 rich gas. Zone (1) is fed with 137.9 kmol/h of sour gas (89.2Z of S~, 233~2 kmol/h of the oxidation air as well a3 23.9 kmol/h of S02 rich gas, thus produc~ng at a temperature of 1000C a m~Yture with a H2S : 52 ratio of 1.9 : 1. At the same time zone (2) i9 fed with 21.4 kmol/h of S02 rich gas and 42.1 kmol/h of hydrogeu and converted by means of partial reduction at 13Z0 C into a m~xtur~ ~ith a a2s : S02 ratio of 2 : 1 and a sulphur content (S2) of 11.6Z.

Subsequent to mixing, a further conversion to sulphur takes place in zone 3 ae 1150 C and a retention tlme or 1 second. By cooling to 240 C, 2800 kg/h of sulphur of 99.9Z i~ separ3ted. The remaining gaq mixture containing 7.6Z of ~2S, 3.~5% of S02, O.lZ of COS and CS2 and 32-72 of a2o i5 further processed as de~cribed in Example 1.

Claims

1. A continuous production method to simultaneously obtain elementary sulphur from H2S-gases as well as from SO2-gases is characterized in that (a) all of the H2S-gas is being subjected to partial combustion, and in the presence of an O2-gas at a H2S: O2 molar ratio of less than 2:1, and in the presence of a portion of the SO2-gas at a H2S:SO2 molar ratio of more than 4:1, and that the process takes place in the frontal area of a 1st reaction zone at temperatures in the 800 - 1400°C
range and thus results in a reaction mixture of elementary sulphur with a H2S and SO2 quantity at a molar ratio of 2:1 up to 1:10;
(b) the balance of the SO2-gas is converted into elementary sulphur in a 2nd reaction zone by way of reaction with a reducing gas at temperatures in the 1000 - 1500°C range and into a reaction mixture containing H2S and SO2 at a molar ratio of 2:1 to 10:1;
(c) the mixture of the reaction flows originating from stages a) and b), as formed in the rear area of the 1st reaction zone, is converted at a temperature in the 800 - 1300°C range in a subsequent 3rd reaction zone without requiring a further direct heat supply into elementary sulphur and into a waste gas with a H2S : SO2 molar ratio of approximately 2:1 and containing no more than approximately 20 molar % of H2S and less than approximately 65 molar % of H2O;
(d) the waste gas from stage (c) is being converted into additional elementary sulphur in a multi-stage Claus installation in the customary manner subsequent to partial cooling, heat recovery and sulphur condensation.

2. A method as set forth in Claim 1, wherein the rear portion of the 1st reaction zone is connected to the 2nd reaction zone by means of a connecting piece and to the 3rd reaction zone by way of a vertical, latticed or honeycombed checker wall with a differential pressure of approximately 3 - 10 mbar.

3. A method as set forth in Claim 1, wherein hydrocarbon gas is burned simultaneously in order to set the temperature for stage (a).

4. A method as set forth in Claim 2, wherein hydrocarbon gas is burned simultaneously in order to set the temperature for stage (a).

5. A method as set forth in Claim 1, wherein the SO2-gas is heated directly by combusting a hydrocarbon gas prior to reacting with the reducing gas in order to set the temperature for stage (b).

6. A method as set forth in Claims 2,3 or 4, wherein the SO2-gas is heated directly by combusting a hydrocarbon gas prior to reacting with the reducing gas in order to set the temperature for stage (b).

7. A method as set forth in Claim 1, where, in addition, at least one of the SO2-gas, the H2-gas, the reducing gas and the O2-gas is heated by an indirect external heat supply prior to being introduced to the respective stage.

8. A method as set forth in any one of Claims 2, 3, 4 or 5 where, in addition, at least one of the SO2-gas, the H2S-gas, the reducing gas and the O2-gas is heated by an indirect external heat supply prior to being introduced to the respective stage.

9. A method as set forth in Claim 1, wherein pure hydrogen, natural gas, carbonmonoxide or a gas containing H2, CH4 and/or CO is used as reducing gas.

10. A method as set forth in any one of Claims 2, 3, 4, 5 or 7,, wherein pure hydrogen, natural gas, carbon monoxide or a gas containing at least one of H2, CH4 and CO is used as reducing gas.

11. A method as set forth in Claim 9, wherein the reducing gas is formed by the understoichiometric combustion with air of 20 - 50% of the heating gas consisting for the most part of methane and by mixing the flue gases with the remaining 80 - 50% of said heating gas.

12. A method as set forth in Claim 1, wherein only a little more than two thirdsof the SO2-gas to be introduced to the 2nd reaction zone is subjected to reduction and the remainder is added to the reaction mixture originating from reaction zone while elementary sulphur is being formed.

13. A method as set forth in any one of Claims 2, 3, 4, 5, 7, 9 or 11, wherein only a minor amount more than two thirds of the SO2-gas to be introduced to the 2nd reaction zone is subjected to reduction and the remainder is added to the reaction mixture originating from the reduction zone prior to being combined with the mixture from the first reaction zone while elementary sulphur is being formed.

14. A method as set forth in anyone of Claims 1, 2, 3, 4, 5, 7, 9,11 or 12, wherein the temperature in the various stages is as follows: stage (a) 900 -1250°C; stage (b) 1150 - 1300°C; stage (c) 900 - 1200°C.

15. The method as set forth in any one of Claims 1, 2, 3, 4, 5, 7, 9, 11 or 12, wherein the O2-gas is air.

16. The method as set forth in Claim 6, wherein the O2-gas is air.

17. The method as set forth in Claim 8, wherein the O2-gas is air.

18. The method as set forth in Claim 10, wherein the O2-gas is air.

19. The method as set forth in Claim 13, wherein the O2-gas is air.

20. The method as set forth in Claim 14, wherein the O2-gas is air.