MXPA97006926A - Procedure and device for the treatment of a gas containing hydrogenosulfurate and sulfur dioxide, which takes a stiff employment stage of the solvent recicl - Google Patents

Abstract

The present invention discloses a process and a device for treating a gas containing sulfur hydrogen and sulfur dioxide, which is intended to reduce appreciably the sulfur vapor emissions in the treated gases, the process is characterized in that they are contacted in a gas-liquid contactor reactor (2), gas with a solvent (5) and a gas (20) is recovered which is sent to a second reactor (102) where it is brought into contact with a solvent ( 105), said solvent is cooled by the appropriate means (190), which allows a part of sulfur to be separated from the solvent. This de-saturated sulfur solvent is used to make contact with the gas (20) coming from the first reactor (2). The gas (120) exiting the second reactor is very poor in sulfur vapor. At least one of the reactors contains a catalyst. The invention has application in the purification of the effluents of the Cla units

Description

PROCEDURE AND DEVICE FOR THE TREATMENT OF ÜN GAS CONTAINING SULFURATED HYDROGEN AND SULFUR DIOXIDE, WHICH TAKES A STAGE OF EMPLOYMENT OF SULFUR FROM THE SOLVENT RECYCLING Field of the Invention The subject of the present invention is a method and a device for treating a gaseous effluent from a Claus unit or a gas containing sulfur hydrogen and sulfur dioxide. It especially refers to the treatment of effluents from Claus units that come from hydrodesulfurization and catalytic thermofraction units. It also refers to the purification treatment of natural gas.

Background of the Prior Art The prior art is especially illustrated by patent application FR-A-2 411 802. The Claus process is widely used to recover elemental sulfur from gaseous charges containing hydrogen sulphide (H2S). However, even after several catalytic stages, fumes emitted by the installations of Claus-type units comprise not insignificant quantities of acid gases. Because of this, it is necessary to treat these effluents (the bottom or bottom gases) of the Claus units to eliminate most of the toxic compounds in a way that the anti-pollution standards are respected. These standards have become increasingly and more severe and it is necessary to permanently improve the existing technology. It is already known, for example, the recovery, from one unit of Claus, of approximately 95% by weight of the sulfur present; a treatment of this effluent from the Claus unit (by a Clauspol unit for example) makes it possible, for example, to obtain 99.8% by weight of the sulfur recovered, from the reaction: 2 H2S + S02 * > 3 S + 2 H20 which uses a reaction medium consisting of an organic solvent and a catalyst comprising an alkaline or alkaline earth salt of an organic acid. The reaction is carried out countercurrent in a reactor-contactor and its temperature is controlled by the passage of the solvent that has been transferred to the lower end of the reactor by a circulation pump, in a heat exchanger, in such a way that the rate is favored. elevated sulfur conversion, avoiding the formation of solid sulfur at all. Sulfur is thus recovered under the liquid form. The procedure, although very functional, is limited by different restrictions: the thermodynamic equilibrium of the reaction is such that the reaction is never complete. The hydrogen sulphide and the sulfur dioxide remain in equilibrium with the sulfur and water formed. Typically, the amount of sulfur present in the unreacted H2S and S02 which is recovered in the reaction effluent (from Clauspol) corresponds to approximately 0.1% of the total sulfur of the initial charge of the Claus unit. An improved conversion can be contemplated at a lower operating temperature but this temperature must be maintained above the sulfur freezing point (approximately 120 ° C), otherwise the reactor would be obstructed by the solid sulfur; the presence of liquid sulfur not separated in the reactor-contactor, which is entrained in the solvent and the circulating catalyst, and which is recycled to the reactor-contactor. In effect, all liquid sulfur droplets not separated from the solvent and the presence of liquid sulfur irremediably involve the presence of gaseous sulfur in the effluent, due to the vapor tension of the sulfur. For example, the amount of sulfur not recovered attributable to its vapor tension is about 0.1% by weight of the sulfur of the initial charge. The object of the invention is to remedy the drawbacks of the prior art. Another object of the invention is to satisfy the strictest standards of the fight against atmospheric pollution for sulfur compounds. Another object is to be able to modify the existing facilities by placing a Claus unit and an effluent treatment unit of said unit (the Clauspol unit) at a very low cost. It has been found that appreciably eliminating all the sulfur vapor in the effluents of the gas treatment units and, for example, the final effluents or the tail of the Claus units., it could recover up to 99.9% of the total sulfur and thus minimize the amount of sulfur expelled into the atmosphere due to gas incineration. More precisely, the invention relates to a process for treating a gas containing sulfur hydrogen and sulfur dioxide in which the gas is brought into contact in at least one gas-liquid reactor-contactor at a suitable temperature. with an organic solvent containing a catalyst and a gaseous effluent which contains substantially no more hydrogen sulfide and sulfur dioxide but containing sulfur in the form of steam is recovered, the process is characterized in that the gaseous effluent from the reactor-contactor is contacted with the same organic solvent or with another organic solvent at a temperature lower than that of the solidification temperature of the sulfur (95 ° C for example) in a reactor-cooler. It has been observed that by contacting an organic solvent partially depleted in sulfur with a gaseous charge whose part of H2S and S02 has been removed, very good results are obtained. In a more detailed manner, the invention relates to a process for treating a gas containing sulfur hydrogen and sulfur dioxide in which the gas is brought into contact in a first contact and gas-liquid reaction zone at a suitable temperature. (3) with at least one organic solvent and an effluent containing water and sulfur vapor is recovered separately, the process is characterized in that the gaseous effluent is introduced into a second contact zone, contacting, under the appropriate conditions, with at least one recycled organic solvent poor in sulfur, a purified gas which essentially contains no sulfur vapor and said sulfur-rich solvent is recovered separately, at least a part of said sulfur-rich solvent is taken, advantageously at most 50% of the flow rate, said part of the solvent is cooled so that a suspension of sulfur crystals in the solvent is obtained, the sulfur crystals are separated of the solvent and said part of the cooled, sulfur-poor solvent is recycled, at least in part, to the second contact zone, the process is characterized in that at least one of the two contact zones contains at least one catalyst. According to a characteristic of the invention, the remaining part of the organic solvent rich in sulfur coming from the second contact zone can be recycled to the second contact zone and more precisely towards its upper part after having been cooled eventually. According to another characteristic of the process, the part of the solvent destined to be sulfur-depleted can be cooled by an indirect exchange of heat or by mixing with a suitable amount of water or by a combination of these media at a temperature generally lower than the temperature sulfur melting and preferably at a temperature between 40 and 110 ° C. The amount of water advantageously introduced is such that a solvent / water mixture of 30 to 70% by weight of water is obtained. The sulfur depletion operation consists in taking at least a part of the organic solvent rich in sulfur, which corresponds in general to at most 50% of the outflow from the second contact zone and preferably from 2 to 10% of the flow rate of the sulfur. the liquid phase, cooling it to a temperature such that a suspension of sulfur crystals is obtained in the solvent saturated in sulfur at said cooling temperature. After separation of the sulfur crystals, the sulfur-poor solvent with respect to that present in the second reactor-contactor, can be reheated to the temperature of this second reactor-contactor before being introduced there. According to a characteristic of the method, at least in part a monophasic solution of said organic solvent can be transferred from the lower part of the first contact zone, it can be cooled so that at least a part of the exposed heat of reaction is removed and can be recycled to the first contact zone. Advantageously, the temperature of the second contact zone may be lower than the temperature of the first, preferably 15 to 20 ° C.

It is very advantageous to use the same organic solvent in the first and second contact zones. In this case, a solvent line can be connected between the recycling means of the single-phase solution that comes from the first reactor whose temperature has been reduced, and the inlet of the heat exchanger that cools at least a part of the sulfur-rich solvent. This line serves as a complementary line of the solvent for the second reactor-contactor. It has been found that it has been preferable to introduce the catalyst into the first reactor-contactor. This eliminates most of the sulfur present in the form of H2S and S02 and contained in the gas to be treated, the second reactor does not ensure a finishing treatment with the reduced dimensions of the apparatus. As it is very evident, it can be introduced only in the second reactor-contactor, or even in both. The method according to the invention can be put into operation according to two variants, in vertical reactors. According to a first variant, the contacting of the gas and the organic solvent in the first contact zone and that of the gaseous effluent and of the organic solvent in the second countercurrent contact zone, the supply of the gas in which a Gaseous effluent is obtained in the upper part of the contact zones as well as the organic solvent feed. According to a second preferred variant, the contacting of the gas and the organic solvent in the first contact zone and that of the gaseous effluent and the organic solvent in the second countercurrent contact zone, the supply of the gas or the Gaseous effluent is made in the lower part of the contact zones, and the organic solvent supply in the upper part of the contact zones. Very obviously, the procedure can also be put into horizontal reactors-contactors. The invention also relates to a device for treating a gas containing hydrogen sulfide and sulfur dioxide. Usually, it comprises a first gas-liquid reactor-contactor (2), supply means (3) for the gas to be treated and means (5) for feeding the organic solvent, means for recovering (25) the sulfur and means (20) outlet of a gaseous effluent containing sulfur in the form of vapor, the device is characterized in that it carries a second reactor-contactor (102) connected to the output means of the gaseous effluent, feed means (105) of a organic solvent poor in sulfur connected to the second reactor-contactor, recovery means (120) of a purified or sulfur-free gaseous effluent, connected to the second reactor-contactor, transfer means (104) of a liquid phase containing the organic solvent and the sulfur, connected to the second reactor-contactor, at least one means of sulfur depletion of at least a part of the liquid phase connected to the means for transferring the liquid phases, comprising at least one cooling means (190) of said phase connected to a separation means (118) of the solid sulfur that supplies a solid phase (125) of sulfur to a first end and a liquid phase (121) poor in sulfur to a second end , the second end is connected to the means (105) for feeding the solvent poor in sulfur, the device is further characterized in that at least one of the contactor-reactors contains a catalyst. According to a feature of the device, when only a part of the liquid phase containing the organic solvent and sulfur, which comes from the second reactor-contactor is cooled to remove the sulfur, a line connected to the means of transfer of said liquid phase may be connected to the feed means of the sulfur-poor solvent of the second reactor-contactor to recycle the remaining part of the liquid phase there. It may be advantageous to combine the first reactor-contactor and the second reactor-contactor in the same room. But these two contactor-reactors can be dissociated. This is especially the case where the second reactor-contactor comprises a mixer-contactor of the venturi-scrubber type associated with a separator of the purified gaseous effluent., of the liquid phase whose transfer line is connected to the sulfur depletion medium. The organic solvent can be cooled in different ways: according to a first variant, if the organic solvent is miscible in water, it can be cooled by the heat exchange in a heat exchanger, before being mixed with the gaseous effluent to be purified, by a supply equipment of complementary water at a temperature lower than that of the organic solvent whose heat of vaporization during contact with the gaseous effluent will allow to reduce the temperature of the mixture, or by a combination of the two previous stages. Preferably, it will be cooled by injection with water. according to a second variant, if the organic solvent is not miscible with water, it can be cooled in the same way as those according to the first variant. Preferably, it will be cooled by a heat exchanger. The different types of solvents can be the following: in the category of insoluble solvents, there are hydrocarbons with a boiling point above 250 ° C and preferably dodecane, tridecane, naphtha with boiling points between 225 and 335 ° C - in the category of solvents soluble in water with a boiling point above 200 ° C, there are polyols of 2 to 15 carbon atoms, and preferably glycerol, thiodiglycol, cyclohexane dimethylethanol, acid esters from 5 to 15 carbon atoms and more particularly trimethylpentane monoisobutyrate and dimethyl adipate, glycol ethers of 5 to 15 carbon atoms and advantageously butoxytriglycol, ethoxytriglycol, diethylene glycol butyl ether, ethylene glycol phenyl ether , monobenzyl ether of terpinyl ethylene glycol, ethylene glycol butyl phenyl ether, diethylene glycol, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylene glycol, tetraethylene glycol dimethyl ether, n-butyl propylene ether, dipropylene ether -butyl, tripropylene n-butyl ether, tripropylene n-butyl ether, and polyethylene glycols of molecular masses 200, 300 , 400 or 600. The catalysts and solvents generally used are those described, for example, in patents FR 2 115 721 (US 3796796), FR 2 122 674 and FR 2 138 371 (US 3832454) incorporated by reference. More particularly, alkali salts of organic acids such as benzoic acid and salicylic acid can be used as catalysts. The invention will be better understood in view of the following figures, which illustrate schematically a device according to the prior art (figure 1) and two variants of the device among which: Figure 2 shows two disconnected contactor-reactors, and Figure 3 shows the two contactor-reactors in the same enclosure.

Detailed description of the invention According to figure 1, a vertical reactor-contactor (2) receives via a feed line (3) in its lower part, a gas containing H2S and S02. This reactor comprises a column (2) containing an infill bed of Intalox chairs, for example, which has the property of retaining the sodium salts formed at the time of the reaction. An organic solvent containing a soluble catalyst fed by a line (1) and coming from a recycling line (4) in the lower part of the reactor-contactor (2), is introduced by a line (5) at the top of this reactor in such a way that the contact of the gas to be treated and of the solvent is carried out countercurrently. The solvent of line (4) is cooled by a heat exchanger (19) whose temperature is controlled and regulated by a measuring system (30) associated with a valve (31) located on a hot water introduction line (32) at 80 ° C. This water is evacuated by a line (32a). The purified gas is decanted or removed from the reactor by a line (20) in the upper part of the reactor while the sulfur formed decant towards the bottom of the reactor and is extracted by a line (25). According to Figure 2 illustrating an embodiment of the device according to the invention, this carries two separate vertical contactor-reactors, the first of which is in accordance with the description of figure 1 with the same references. The line (20) that recovers the gaseous effluent from the first reactor-contactor (2), feeds a second reactor-contactor (102) in its lower part. This reactor (102) carries a filling bed (102a) which may or may not be identical to that of the first reactor. The catalyst carried by the line (101) and the organic solvent are introduced by lines (104), (104a) and (105) in the upper part of the second reactor-contactor which thus performs a gas-liquid contact in countercurrent in the stuffing A part, 2 to 10%, for example, of the solvent containing the sulfur and the catalyst stripped by the line (104) is cooled to 60-70 ° C by an indirect heat exchanger (190) by means of the line (116). ), which produces the crystallization of sulfur and the impoverishment in sulfur of the solvent. Heat exchange is performed by injecting water (132) and evacuating (132a) onto a line (121) above an exchanger (121a). The sulfur in suspension is sent to a hydrocyclone (118) where the solvent is separated from the sulfur. In the upper part of the hydrocyclone, a line (121) on which another heat exchanger (121a) is possibly located, intended to reheat the sulfur-poor solvent, is connected to the line (104a), possibly cooled on its return, and its content is recycled by line (105) above the filling (102a). A cooling control valve (131) connected to the exchanger (190) is associated with a temperature control (130) connected to a temperature probe which is placed upstream of the exchanger (121a) on the line (121). At the bottom of the hydrocyclone (118), sulfur is recovered by a line (125) which is mixed with that which comes from the first reactor-contactor (2) and which is melted or incorporated there before being carried over the line (25). ). The finally purified gas is recovered in the upper part of the second reactor-contactor by a line (120). When the organic solvent and the catalyst are the same in the two reactors, a line (5a) connected to the line (5) of the first reactor-contactor allows to make a complement of the solvent and the catalyst in the second, introducing it at the entrance of the reactor. exchanger (190). As is evident, when the solvents in the reactors are different, this line (5a) is suppressed and the sulfur coming from the hydrocyclone (118) is produced and incorporated separately by the line (125). According to Figure 3, a vertical reactor-contactor composed of two reaction ss (2 and 102) and contact, according to the first and second reactor-contactors of Figure 2 is used, except that: the first reactor-contactor does not contain the catalyst, but the feed line (1) of the catalyst in the solvent line (4), the partly free gas of H2S and S02 (20) is introduced directly into the lower part of the second stage (102) by the intermediation of the chimney or pipe (20) which in addition to the solvent, the catalyst and the sulfur by the line (104) to be depleted in part of the sulfur by the exchanger (190) and the hydrocyclone (118).

The following examples illustrate the invention: Example 1 according to the prior art (figure 1).

The characteristics are the following: Load: gas from the tail or bottom of the Claus unit, flow: 12302 Nm3 / h. Reactor temperature: 125 ° C. Filling: Intalox ceramic chairs, specific surface area: 250 m2 / m3 Solvent: Polyethylene glycol M = 400, flow: 500 m3 / h. Catalyst: sodium salicylate at a concentration of 100 millimoles per kg of solvent. Recycled solvent (lines 4 and 5). - Flow: 500 m3 / h. - Temperature: 123 ° C. Flow of sulfur produced (line 25): 315 kg / h.

The compositions of the inlet and outlet gas of the unit are in table I given below: labia i Inlet gas Outlet gas (line 3) (line 20)% volume% volume H2S 1,234 0,126 S02 0,617 0,063 C02 4,000 4,072 COS 0,015 0,009 CS2 0,015 0,009 S¿ 0,140 0,031 N2 60,000 61,079 H20 34,000 34,612 sum of the 2,036 0,247 oans • sulfur Sv = sulfur vapor + vesicular sulfur The yield of the sulfur compounds in the reactor is equal to: (% compounds sulfur- -% compounds sulfur-) xl00 two input two output% sulfur compounds input = (2.036 - 0.247) xl00 = 88% 2.036 Claus's unit has a 94% yield The performance of the unit set of Claus + finishing unit is equal to: 94 + (6 x 88) = 99.28 100 Example 2 according to the invention (figure 2).

The filler, the organic solvent, the catalyst and the filler are those of example 1. The operating conditions of the first reactor-contactor (2) are those of example 1. The relative conditions of the second reactor-contactor (102) are the following: Temperature: 110 ° C. Flow rate of solvent and sulfur (line 104): 500 m3 / h. Flow rate of the cooled solvent (line 116): 50 m3 / h. Cooled solvent temperature: 65 ° C. Recycled solvent temperature (line 105): 108 ° C. Sulfur collected (line 25): 344.3 kg / h.

The compositions of the inlet gas (line 3) and the outlet of the unit are given in the following table II: Table p Sy = sulfur vapor + sulfur vesic -1-ar The yield of the compounds in the reactor is equal to: (% compounds sulfur- -% compounds sulfur-) xl00 two input two output% sulfur compounds input = (2.032 - 0.090) xl00 = 95.57% 2.032 Claus's unit has a performance of 94% The performance of the unit set of Claus + finishing unit is equal to: 94 + (6x95.57) = 99.73 100 Example III according to the invention (figure 3) A vertical reactor-contactor composed of 2 stages successively traversed by the gas to be treated is used: - Lower stage (2) The conditions are similar to those of the reactor of example 1; the conditions of the gas flow and the composition of the gas to be treated are the same. In compensation, the catalyst is not used at this stage.

Upper stage (102) The operating conditions are strictly the same as those of reactor (102) of example 2. All the catalyst is introduced by line (101). The input (line 3) and output (line 120) composition of the unit is given in Table III.

Table III Sv = sulfur vapor + vesicular sulfur The yield of the compounds in the reactor is equal to: (% compounds sulfur- -% compounds sulfur-) xlOO two input two output% sulfur compounds input = (2.036 - 0.1165) xl00 = 94.27% 2.036 Claus's unit has a performance of 94% The performance of the unit set of Claus + the finishing unit is equal to: 94 + (6x94.27) = 99.65 100 It is noted that in relation to this date the best method known by the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, property is claimed as contained in the following

Claims (18)

1. A method of treating a gas containing sulfur hydrogen and sulfur dioxide, in which gas (3) is brought into contact with at least one solvent in a first contact and reaction zone of the gas liquid at a suitable temperature. organic and an effluent containing water and sulfur and sulfur vapor is recovered separately, the process is characterized in that the gaseous effluent is introduced into a second contact zone, under the appropriate conditions, with at least one recycled organic solvent poor in sulfur; a purified gas which does not substantially contain sulfur vapor and said sulfur-rich solvent is recovered separately, at least a portion of the sulfur-rich solvent is taken or extracted, advantageously when much 50% of the flow is cooled said part of the solvent so that a suspension of sulfur crystals in the solvent is obtained, the sulfur crystals are separated and said part of the cooled, sulfur-poor solvent is recycled at least in part to the second contact zone, the process is further characterized because at least one of the two contact zones contains at least one catalyst.

2. The process according to claim 1, characterized in that the remaining part of the sulfur-rich solvent is recycled towards the top in the contact zone.

3. The process according to claim 1 or 2, characterized in that said part of the solvent destined to be depleted in sulfur is cooled by an indirect heat exchange.

4. The process according to claims 1 to 3, characterized in that said part of the solvent intended to be depleted is cooled, by mixing with a suitable amount of water and preferably with an amount such that a mixture of solvent-water is obtained which contains 30 to 70% by weight of water.

5. The process according to one of claims 1 to 4, characterized in that said part of the solvent is cooled to a temperature below the melting temperature of the sulfur and preferably at a temperature comprised between 40 and 110 ° C.

6. The method according to one of claims 1 to 5, characterized in that at least in part a monophasic solution of said organic solvent is removed from the lower part of the first contact zone, cooling it so that at least a part of the reaction heat exposed during recycling in the first contact zone.

7. The method according to one of claims 1 to 6, characterized in that the temperature of the second contact zone is lower than the temperature of the first.

8. The process according to one of claims 1 to 7, characterized in that the organic solvent of the first contact zone and the organic solvent of the second contact zone are the same solvent.

9. The process according to one of claims 1 to 8, characterized in that the first contact zone contains the catalyst.

10. The process according to one of claims 1 to 9, characterized in that the gas and the organic solvent are brought into contact in the first contact zone and that of the gaseous effluent and the organic solvent in the second countercurrent contact zone. , the gas or gaseous effluent is fed into the lower part of the contact zones, and the organic solvent is fed into the upper part of the contact zones.

11. The process according to one of claims 1 to 10, characterized in that the gas and the organic solvent are brought into contact in the first contact zone and that of the gaseous effluent and the organic solvent in the second contact zone in streams. in the same flow direction, the supply of the gas or the gaseous effluent is carried out in the upper part of the contact zones as well as the supply of the organic solvent.

12. The device for treating a gas containing sulfurized hydrogen and sulfur dioxide, comprising a first reactor-contactor (2) of liquid gas, means (3) for feeding the gas to be treated and means (5) for feeding of the organic solvent, recovery means (25) of the sulfur and means (20) of exit of a gaseous effluent containing sulfur in the form of steam, the device is characterized in that it carries a second reactor-contactor (102) connected to the the gaseous effluent outlet means, feed means (105) of a sulfur-poor organic solvent, connected to the second reactor-contactor, recovery means (120) of a sulfur-free gaseous effluent, connected to the second reactor-contactor, transfer means (104) of a liquid phase containing the organic solvent and the sulfur, connected to the second reactor-contactor, at least one means of sulfur depletion of at least one part of the liquid phase with ected to the transfer means of the liquid phase, comprising at least one means (190) of cooling of said phase, connected to a separation means (118) of the solid sulfur that supplies a solid phase (125) of the sulfur to a first end and a liquid phase (121) poor in sulfur to a second end, the second end is connected to the sulfur-poor solvent feed means (105), the device is further characterized in that at least one of the contactors-reactors It contains a catalyst.

13. The device according to claim 12, characterized in that a line (104a) connected to the transfer means (104) of the liquid phase, containing the organic solvent and sulfur, is connected to the means (105) for feeding the solvent organic poor in sulfur.

14. The device according to one of claims 12 to 13, characterized in that the cooling means is chosen from the group consisting of a heat exchanger, a water complement and a combination of the two.

15. The device according to one of claims 12 to 14, characterized in that the first reactor-contactor (2) carries on one side of the lower end a means (4) for transferring a single-phase solution, means (19) for controlling the the temperature of the solution, associated with a heat exchanger and connected to the transfer medium of the solution and recycling means (5) of the single-phase solution cooled in the first reactor-contactor.

16. The device according to one of claims 12 to 15, characterized in that the first reactor-contactor (2) and the second reactor-contactor (102) are contained in the same enclosure.

17. The device according to claim (12), characterized in that the second reactor-contactor comprises a mixer-contactor of the venturi-scrubber type associated with a separator of the purified gaseous effluent, of the liquid phase.

18. The device according to one of claims 12 to 17, characterized in that a line (5a) is connected between the recycling means (5) in the first reactor-contactor of the single-phase solution coming from the first reactor-contactor, which has been cooled and the cooling medium inlet (190) of the liquid phase.