FI83758B - FOERFARANDE MED VILKET SAMTIDIGT PRODUCERAS ELEMENTAERTSVAVEL UR H2S-HALTIGA OCH SO2-HALTIGA GASER. - Google Patents

Abstract

Various amount ratios are used in this continuous process, the total H2S-containing gas being partially oxidised in the presence of significant amounts of the SO2-containing gas in a 1st reaction zone at 800 - 1400 DEG C with an O2-containing gas, while the residual SO2-containing gas is partially reduced in the presence of a reducing gas in a 2nd zone at 1000 - 1500 DEG C and then the mixture from both zones with a now nearly stoichiometric H2S : SO2 ratio being reacted in a 3rd zone at 800 - 1300 DEG C without further direct heat addition to give sulphur, which is separated by condensation, and to give a gas mixture which can be processed further in a conventional Claus plant.

Description

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A process for the simultaneous production of elemental sulfur from H2S-containing and SO2-containing gases. - Förfarande med vilket samtidigt produceras elementärt-svavel ur H2S-haltiga och and SO2-haltiga gaser.

The invention relates to a continuous process for the simultaneous production of elemental sulfur from H2S-containing gases and 302-containing gases, in particular from crude gas and high-calorie SC> 2 gas obtained from flue gas desulphurisation.

It is technically normal to produce elemental sulfur on a large scale by the catalytic Claus reaction, but this requires a stoichiometric H2S: SO2 ratio and a large amount of dilute feed gases with limited moisture content.

In treatment plants to which a power plant is connected, both H2S-containing gases and also SO2-containing gases are generally available. The amount of sulfur compounds then depends on both the capacity of the plant and the raw materials to be processed, and varies accordingly without, however, achieving a stoichiometric H2S: SO2 ratio in the longer term. Concentrations are also many times too high, as the amount of H2S in the raw gas is more than 50 mol% and the amount of SO2 in the high calorific gas is more than 90 mol%.

It has therefore been proposed that the concentration of sulfur compounds be calculated in advance by direct thermal oxidation of H2S according to formula 2 H2S + 02 -> 2 S + 2 H2O or by thermal or catalytic reduction of SO2 according to formula

SO2 + 2 H2 -) S + 2 H2O

in accordance with.

2 83758 However, these balances do not correspond to the actual course. In either case, the equilibrium is about 60 to 70%, depending on the temperature, in which case a higher oxidized or reduced compound is always formed. Even if it were possible to continue the reactions to such an extent as to achieve the low concentrations of sulfur compounds required for the catalytic Claus reaction, these gases could be used in the Claus plant only to a limited extent due to the significant amounts of water formed at the same time due to high catalyst vapor activity losses. Thus, it has been found that when using commercial Claus catalysts, the loss of activity causes a reaction loss of about 20% within 3 months. Since, for thermal reasons, it is not possible to separate the water by condensation, all that remains is dilution with sulfur-free, inert gases, which is achieved, for example, by burning H2S with air instead of oxygen. However, this increases the device capacity and heat demand in an undesired way. Another very serious problem is the discoloration of the sulfur formed when the crude gas contains hydrocarbons, as is often the case. Investment costs and, especially in the case of downsizing, operating costs are also very high.

DE-OS 2346247 thus seeks to produce sulfur by reacting H 2 S directly with SC 2 without a catalyst, whereby part of the SC is obtained by oxidizing H 2 S and part is obtained by feeding another substance. Although the use of a SO2 concentration higher than stoichiometry is also suggested to be possible, only a procedure can be deduced from this publication for gases with an excess of H2S.

The residence time is also determined by the size of the H2S-POI feed chamber, without it being apparent that the low reaction rate of direct sulfur formation compared to e.g. oxidation could be taken into account.

The object of the present invention was therefore to find the most economical method possible for the simultaneous production of qualitatively sound elemental sulfur from H2S-containing and SO2-containing gases, the ratio and amounts of which can vary greatly, in which case the exhaust gas should be directly available in the catalytic Claus plant feed. as a gas.

This object is achieved by the method already mentioned according to the invention in that a) at the front of the reaction zone 1 at a temperature of 800 to 1400 ° C partially all the H2S-containing gas is combusted in a molar ratio H2S: C> 2 of less than H2S-containing gas, preferably in the presence of air 2: 1, and a portion of the SC> 2-containing gas with a molar ratio of H2S: SC> 2 greater than 4: 1, resulting in a reaction mixture of elemental sulfur with a molar ratio of H2S to SC> 2 of 2: 1 to 1:10; b) the remaining SC> 2 -containing gas is converted in reaction zone 2 into a reaction mixture containing elemental sulfur and H2S and SC> 2 in a molar ratio of 2: 1 to 10: 1 by reacting it with a reducing gas at temperatures between 1000 and 1500 ° C; c) The mixture of reaction streams from steps a) and b) formed at the rear of reaction zone 1 is reacted as elemental sulfur in the next reaction zone 3 without further direct heat supply at a temperature between 800 and 1300 ° C, with a molar ratio of H 2 S: SO 2 of about 2: 1 up to about 20 mole percent H 2 S and less than about 65 mole percent H 2 O; d) The exhaust gas obtained from step c), after partial cooling and heat recovery and condensation of sulfur, is reacted in a known manner in the Claus plant as an additional batch of elemental sulfur.

The process according to the invention can best be used in refineries involving a power plant for the simultaneous further processing of high-calorie SO2 gas from the refinery's raw gas and flue gas desulphurisation, but it is also suitable for gas streams of other origins.

The H2S-containing gas is introduced entirely into the oxidation zone, while the SC> 2 -containing gas is divided between the oxidation and reduction zones, preferably in a controlled amount, however, only as much of the H2S is oxidized to SC1 as required by the flame stability. This amount only increases when refining gases with a large excess of H2S. Depending on the amount of SO2 to be processed in each case, a more or less large proportion is reduced to sulfur and glass, the only limitation being the amount of water tolerated by the subsequent catalytic Claus plant (generally less than about 65 mol%). This amount of water can be exceeded when using hydrogen as the reducing gas. The opposite direction can be effected by using a methane and / or CO-containing reducing gas.

In addition, O 2 -containing gas, in particular air, is introduced into the oxidation zone, the amount of C> 2 corresponding to the amount of H2S to be oxidized to SC2. Useful reducing gases are H2, CO and / or lower hydrocarbons such as methane, ethane, etc. Gas mixtures containing methane, hydrogen and CO can be used without disadvantages and are often advantageously used in treatment plants. # It has proved particularly advantageous from a thermal point of view to combine a certain amount of reducing gas. and the heat required to reduce SC> 2. In this case, the heating gas consisting essentially of methane is divided into three substreams in a ratio of about (20-50) :( 79-30) :( 1-20), the sum being 100, preferably in a ratio of about 35:50:15. 1. the partial stream is combusted with air non-stoichiometrically, preferably with a λ of about 0.6 to 0.95, particularly preferably λ of about 0.7, and after heat loss of about 1700 to 1900 ° C the hot combustion gases are mixed 2.

5 83758 with partial flow and is led to the actual reduction zone. 3. The partial stream is introduced, possibly after being indirectly preheated, e.g. to about 150 ° C, together with high-calorie SO 2 gas to the reduction zone. The reducing gas obtained in this way contains methane, hydrogen and carbon monoxide as reducing components and has a temperature of 1350 to 1550 ° C, depending on the temperature losses. For example, its composition may be as follows: CH4 20.0 mol% N2 50.9 mol% CO2 6.8 mol% H2 8.7 mol% CO 2.9 mol% H2O 10.7 mol%

Further energy savings can be achieved by dividing the SO 2 -containing gas introduced into zone 2 into two partial streams in a ratio of 2: 1, preferably after it has been preheated by indirect heat exchange, e.g. to 450 ° C. The larger partial stream is reduced in the actual reduction zone at a mixture temperature of about 1200 ° C with the reduction gas obtained as described above. The remainder of the SO 2 substream is then introduced into the reaction mixture from the reduction zone before being combined with the mixture from the oxidation zone, which, given the mixture temperature above 900 ° C, already leads to the formation of elemental sulfur when the residence time is long enough. It is preferred that the mixing walls separate the actual reduction zone from the preceding combustion zone and, if present, from the next sulfur formation zone.

The gas mixture formed in the reduction zone, whether or not followed by a sulfur-forming zone, is mixed with the gas of the oxidation zone at the rear of this zone and then passed to the 3rd reaction zone, the actual sulfur-forming zone. Good mixing of the gases is ensured by separating this zone 3 from the preceding zone by means of a vertical lattice-shaped or perforated mixing wall with a pressure difference of about 3 to 10 mbar.

Although under conditions deviating from the stoichiometric ratios, no significant reaction of H2S with SC> 2 is allowed to occur in the oxidation zone, and only small amounts of sulfur are generated in the reduction zone, sulfur formation is concentrated in this zone 3. Separating the state in which sulfur is formed in this case achieves the following advantages: 1. individual residence time and the resulting optimal approach to thermodynamic equilibrium 2. formation of very pure sulfur because the hydrocarbons present in both the heating gas and the raw gas are burned almost completely, or due to the individual residence time the carbon formed reacts with the reaction components to form COS and CS2, so that no soot can be formed at all.

In zone 1 the temperature is best 900 - 1250 ° C, in zone 2 1150 - 1300 ° C and in zone 3 900 - 1200 ° C. In order to achieve these temperatures, it may be necessary to burn the hydrocarbonaceous heating gas separately in zone 2 and / or to mix it with the raw gas in zone 1. In view of the purity of the sulfur already generated in zone 2, at least part of the heat is introduced indirectly into this zone. This measure is particularly relevant when methane is used as the reducing gas. Any low cost mixture of lower hydrocarbons can be used as the heating gas. By designing the bulb appropriately, it is in principle also possible to use liquid fuel. Since none of these three reaction zones contain a catalyst, no special requirements have been imposed on the heating gas with regard to possible catalyst poisons. Temperatures of 800 to 1500 ° C.

The temperature in zones 1 and 2 is suitably at the top of the given temperature range. Firstly, the formation of COS and CS2 is advantageously reduced in this way and secondly, the temperature in zone 3 can be kept within this interval without burning further heating gas. Since the sulfur formation reaction is slightly endothermic, the temperature in zone 3 is correspondingly slightly lower than in the preceding zones.

The distribution of the SC> 2 -containing gas stream described above and the extent of the oxidation and reduction reactions are crucial for the composition of the Zone 3 exhaust gases. In order for any additional components to be further processed in the Claus plant without recovery, the molar ratio H2S: SO2 should be about 2, more specifically H2S + (COS. A) + (2 CS2.8) ------------- ----------------- = 2 SO 2 where a and 8 may be the same and different and denote the reaction rate of COS or CS 2 in the next Claus plant. In addition, the H2S concentration is limited to a maximum of about 20 mol%. Since the equilibrium of the sulfur formation reaction, depending on the temperature, is about 60-70%, continuous, partial, prior desulphurisation would also be possible, which, however, is limited to individual cases for thermal reasons, especially when storage is possible.

8 83758

Normally, all the sulfur formed in zones 1-3 is separated after the 3rd reaction zone by cooling the gas mixture below the condensation temperature of the sulfur while simultaneously recovering the heat, e.g. as water vapor. The sulfur from which the sulfur has thus been removed is, after a possible slight reheating, more sulfur is obtained in a conventional catalytic Claus plant.

Surprisingly, it was found that, contrary to previous knowledge, H2S can be partially oxidized without any problems by spatially separating it from the sulfur formation zone even in the presence of large amounts of SC> 2, which can be multiples of hydrogen sulfide. The process according to the invention is not bound to any lowest H 2 S: SC> 2 molar ratio, and the process is even particularly suitable for the further treatment of gases with an excess of SO 2. The sulfur produced is very pure because, according to the invention, impurities due to incompletely burned hydrocarbons can be largely prevented.

The invention will be explained below by means of examples and with reference to the accompanying schematic drawing, but not limited to the conditions given by way of example.

Example 1: (use of natural gas as a reducing gas)

23.9 kmol / h of high-calorie SC> 2 gas (8) with a SC> 2 content of 95.27 mol% preheated to 450 ° C is introduced into the oxidation zone (1) and a H2S burner which it can also consist of a system of several individual bulbs, 137.9 kmol / h of raw gas (7) with an H2S content of 89.20 mol% and 233.2 kmol / h of air. At the same time, the remaining 21.4 kmol / h of preheated SC> 2 gas (9) and 10.79 kmol / h of reduction gas (10) having a composition of 97.5 mol% CH4, 0.9% C2H6.0 are fed to the reduction zone (2). .3% C3H0, 0.9% N2 and 0.4% CO2, and 4.38 kmol / h of heating gas (12) and 29.64 kmol / h of combustion air (11) through the heating gas burner, whereby the heating gas is burned non-stoichiometrically and the heating gas has the same li 5 83758 composition as a reducing gas11a.

Partial reduction of SO 2 in zone 2 takes place at a temperature of about 1250 ° C to give a mixture with a H 2 S: SO 2 ratio of 1.9: 1 and containing 9.1% of fumed sulfur (S 2). At the same time, due to the partial oxidation of H2S, a hot, sulfur-containing mixture with an H2S: SO2 ratio of 1.96: 1 is formed in the vicinity of the zone 1 bulb. Both mixtures are mixed at the back of zone 1 and passed through a mixing wall (5) to zone (3), where a further reaction to sulfur takes place with a delay of about one second. The temperature settles to about 1040 ° C. The mixture (4) leaving the reaction zone (3) is cooled to 240 ° C while generating 5 bar of steam and the condensed sulfur is separated off in the usual manner. 2800 kg / h of sulfur with a purity of 99.9% are obtained. The remaining gas mixture contains 7.4% H 2 S, 3.8% SC 2, 0.2% COS + CS 2 and 31% H 2 O and, after being indirectly heated to 260 ° in a known manner To C, it is reacted in an catalytic Claus plant with an additional batch of elemental sulfur.

Example 2: (use of hydrogen as a reducing gas)

Proceed as in Example 1, but without preheating the high-calorie SC> 2 gas. Zone (1) is charged with 137.9 kmol / h of crude gas (89.2% H2S), 233.2 kmol / h of oxidizing air and 23.9 kmol / h of high calorific SC> 2 gas and a mixture is formed at 1000 ° C with H2S : The SC> 2 ratio is 1.9: 1. At the same time, 21.4 kmol / h of high calorific SC> 2 gas and 42.1 kmol / h of hydrogen are charged to zone (2) and converted at 1320 ° C by partial reduction to a mixture with a 2: 1 H2S: SC> 2 ratio. and a sulfur content (S2) of 11.6%.

After stirring, a further reaction to sulfur occurs in zone 3 at 1150 ° C with a one second delay. Upon cooling to 240 ° C, 2800 kg / h of sulfur with a purity of 99.9% are released.

83758 The remaining gas mixture, consisting of 7.6% H 2 S, 3.85% SO 2, 0.1% COS + CS 2 and 32.7% H 2 O, is worked up as in Example 1.

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Claims (9)

1. A continuous process whereby elemental sulfur is produced from H2S-containing gases and SO2-containing gases, characterized in that a) in the front part of a first reaction zone, a total H2S-containing gas is subjected to the presence of a 02 "containing gas, preferably air, in the molar ratio H2S: 02 less than 2: 1, and in the presence of a portion of the SO2-containing gas, in the molar ratio H2S: SO2 more than 4: 1, a partial combustion at a temperature of 800 - 1400 ° C, whereby a reaction mixture of elemental sulfur with an H 2 S and SO 2 amount in the molar ratio 2: - 1:10 is obtained; b) the remainder of the SO2-containing gas is transferred in a second reaction zone by reaction with a reducing gas at a temperature of 1000 - 1500 ° C to a reaction mixture containing elemental sulfur and H2S and SO2 in the molar ratio 2: 1 -10: 1, c) the mixture of the reaction streams formed from steps a) and b) formed in the rear of the first reaction zone was reacted in a connecting third reaction zone without further direct heat supply at a temperature between 800 - 1300 ° G. v11 'ment of sulfur, whereby the exhaust gas at a mole ratio H2S: SOP of approx. 2: 1 contains a maximum of approx. D) the exhaust gas c) obtained from the stage, after partial cooling during recovery of heat and sulfur condensation, is further converted into elemental sulfur as is known in a Claus plant. Process according to Claim 1, characterized in that the rear part of the first reaction zone is joined by a nozzle to the second reaction zone and by a vertical stand, cross-like or inclined mixing wall, down to a pressure difference of approx. 3 - 10 mbar, joined to the third reaction zone. 83758 3. A process according to any one of claims 1 to 2, characterized in that, for controlling the temperature in step a), a hydrocarbon-containing gas is simultaneously combusted. 4. A process according to any one of claims 1 to 3 wherein the control of the temperature of step n), the SO₂-containing gas is heated prior to reaction with the reducing gas directly by combustion of a hydrocarbon-containing gas. 5. A process according to any one of claims 1 to 4, characterized in that the SC₂-containing gas and / or the S₂-containing gas and / or the reduction gas and / or the ( introduction to the respective steps through indirect external heat supply. 6. A method according to any one of claims 1 to 5 of claim 1. c- t e c k n a t of the fact that, as reducing gas, pure whiteness, soil, carbon monoxide or an I 2 -f CH 2 - and / or CO-containing gas are used. 7. A process according to any one of claims 1 to 6, characterized in that the reducing gas is cured by under-stockometric combustion of 20 - 50 # substantially methane-based heating gas with air and mixing of the combustion gases with the remaining 80 - 50 percent of this heating gas. 8. A process according to any one of claims 1 to 7 characterized in that, of the SC 2 -containing gas to be initiated in the second reaction zone, only about two-thirds of the reduction is subjected and the remainder is added to the reaction mixture from this reaction zone, before it is mixed with the mixture from the first reaction zone to form elemental sulfur. 16 83758 9. A process according to any one of claims 1 to 10, characterized in that the temperature in step a) is 900 -1250 ° C, in the stage "b) 1150 - 1300 ° C and in step c) 900 - 1200 ° G.