FR2765808A1 - New apparatus for the vaporisation of sulphur for the subsequent formation of hydrogen sulphide - Google Patents

Abstract

A new apparatus for the vaporisation of sulphur which comprises an inner tube(22) and outer tube(21) which are coaxial, and a supply of liquid sulphur comprising a means (26) for spraying the sulphur in the up-stream section of the inner tube.The inner tube has a gas inlet(25) on the up-stream side and an exit for vapourised sulphur on the downstream side : the outer tube has an inlet (21a) for a hot gas mixture from (6) and an exit(21b) at the up-stream side of the inner tube communicating with the gas inlet (25).The inner and outer tubes are arranged so that the mixture circulates counter-currently in the annular section between the tubes (exchanging heat indirectly with the gas circulating in the inner tube) and co-currently with the vapourised sulphur in the inner tube. Also claimed, is the process for the synthesis of hydrogen sulphide.

Description

The present invention relates to a device for vaporization of sulfur and a process for the synthesis of hydrogen sulphide. Hydrogen sulfide does not store, it is useful to have a device that allows to produce on demand hydrogen sulfide in selected quantity.

The crystalline sulfur melts between 112 and 120 ° C, depending on the crystalline variety envisaged, towards 160 ° C this liquid becomes viscous exbân, a peak of 93,000 centipoises is obtained around 187-188 ° C, then it becomes fluid again towards 250 "C to boil to 444.6" C. In the hydrogen sulfide synthesis processes and especially in the process according to the invention, it is particularly advisable to handle the sulfur when it is not too much viscous that is to say in a temperature range of 112 or 120 "C to about 150" C.

The synthesis of hydrogen sulfide is obtained by conventional methods in which hydrogen is bubbled into liquid sulfur; this type of process is confronted with the problem of the viscosity of liquid sulfur. Another type of process involves a reaction between sulfur and hydrogen in a gas phase, in the presence or absence of a catalyst, this process requires close control of the temperature in the reactor. The temperature in the chamber where the synthesis takes place may increase excessively under the action of the heat released by the synthesis reaction - which is highly exothermic - or by the means set up for the reaction such as, for example , the use of a flame. It must also be controlled that the temperature does not decrease excessively, which would bring the sulfur into a temperature range where it is more viscous, which could also slow the speed of the reaction or stop it.

According to the disclosure of US Pat. No. 4,629,617, hydrogen and sulfur react in the gaseous state over a flame (650-1300 ° C), they are fed into this reactor by two separate conduits, the products of the reaction, and unreacted sulfur, are quenched to less than 400 ° C. This process is confronted with two problems of temperature control and the risk of increasing the viscosity of liquid sulfur. US 5173285 discloses the problems of temperature control in sulfur synthesis processes. In the embodiment described, the reducing gas is bubbled in liquid sulfur, the temperature in this vaporizer is controlled and kept constant by means of a heat exchanger, in this case a regular control of the temperature is necessary.

Other prior art disclosures suggest the use of a vaporizer to heat and saturate the sulfur with hydrogen sulfide prior to introduction into a reactor. But all these descriptions, either by the heating process or by the configuration of the vaporizer, note that the main problem encountered is the viscosity of sulfur. Too much viscosity can generate a deposit on the inner wall of the turns of the vaporizer which has the effect of obstructing them. This is the case, for example, of the implementation described in US Patent 4404180.

The present invention relates to a continuous process for the synthesis of hydrogen sulphide which comprises the use of a vaporizer of liquid sulfur in fine droplets, the advantages of which will be seen below, as well as a device for recycling hydrogen sulphide. product.

The sulfur to be treated is liquid, its minimum temperature is between 112 and 120 ° C depending on the melting point of the crystallized sulfur variety, its maximum temperature is about 150 ° C, preferably the temperature of the sulfur to be treated is about 130 to 140 ° C.

The present invention also relates to a vaporizer which will instantaneously pass the liquid sulfur into fine droplets.

More specifically, the invention relates to a sulfur vaporization device characterized in that it comprises an inner duct (22) and an outer duct (21), substantially coaxial, a liquid sulfur supply means comprising at least means (26) for spraying the sulfur in the upstream portion of the inner conduit, the inner conduit (22) including at least one upstream gas inlet (25) and one gas outlet, including the sulfur, part-side downstream, the external duct having at least one inlet (21a) of a hot gas mixture on the downstream side of the inner duct, connected to a means (6) for supplying the gas mixture and at least one outlet (21b) the upstream portion of the inner duct in communication with the gas inlet (25) of the inner duct, the inner and outer ducts being arranged in such a way that said mixture circulates counter-current to the direction of circulation of the sulfur in the annular part included between the conduit internal and external duct, heat exchange indirectly with the gas flowing in the inner duct and circulates cocurrently with vaporized sulfur in the inner duct.

Among the advantages provided by the present invention will be noted: 1) the elimination of the risk of a sudden increase in the viscosity of sulfur
by saturating the liquid sulfur with recycled hydrogen sulphide, the
gas mixture obtained after the passage of sulfur in the nozzle of
vaporization is a gaseous mixture of sulfur, hydrogen and sulphide
hydrogen; 2) the absence of a risk of sudden increase in temperature at
inside the vaporizer: it is maintained at a temperature above
350 ° C and preferably between about 360 and 410 ° C by a
equilibrium: the gaseous mixture of hydrogen and hydrogen sulphide provides
from heat to the system while sulfur, when it goes from the liquid state
in the gaseous state, as well as the outlet effluent of the vaporizer absorb the
heat. The temperature is kept constant by the exchanges of
heat quoted above and ordered upstream by an oven.

It is furthermore avoided by dilution of the hydrogenation charge with hydrogen sulphide to overheat the catalyst.

According to a feature of the device, the liquid sulfur supply means is a conduit (23) substantially coaxial with the inner and outer conduits, which opens below the inlet of the inner conduit.

According to a first variant of the device, the output of the external duct and the inlet of the internal duct may communicate by an external transfer loop (8).

According to a second variant of the device, the inlet of the internal duct can communicate directly with the outlet of the external duct, said inlet and said outlet being annular.

According to a feature of the device, the outlet of the inner conduit is connected to a hydrogen sulfide synthesis reactor. The inlet of the so-called hot gas mixture into the external conduit is connected to at least one heating means, for example an oven, of the gas mixture consisting of a part of the synthesized hydrogen sulphide and hydrogen.

The invention also relates to a process for the synthesis of hydrogen sulphide in a catalytic reaction zone from which an effluent containing hydrogen sulphide is recovered, characterized in that a portion of the effluent is removed, mixed with hydrogen, the mixture is heated to a suitable temperature and pressure and introduced into the vaporizer, liquid sulfur is sprayed upstream of the inner conduit, the mixture is circulated in the outer conduit (21) against flow of the sulfur flow direction and said mixture is introduced into the inner pipe (22) so as to vaporize the pulverized sulfur and to maintain the gas mixture obtained containing the steam sulfur vaporizer said effluent at a temperature sufficient for the catalytic synthesis of hydrogen sulfide, by indirect heat exchange with the mixture circulating in the outer conduit.

The invention will be better understood in view of the following figures schematically illustrating the invention, among which: - Figure 1 shows the vaporizer according to the invention - Figure 2 shows the implementation of the method of synthesis device
hydrogen sulfide comprising the vaporizer according to the invention.

In the following description, numbers 1 to 15 refer to the diagram of the device (Figure 2) and numbers 21 to 25 refer to the details of the vaporizer (Figure 1).

In FIG. 1, the numbers 21 to 25 refer to duct parts where heat transfers are required which are necessary in the device according to the invention. The zone (21) corresponds to the end of the duct (6), the zones (22) and (25) are parts of the duct (11), the zone (23) is the end of the duct (9).

The sulfur vaporization device or vaporizer (7) according to the invention, illustrated schematically in FIG. 1, comprises three coaxial ducts: an internal sulfur supply duct (23), an intermediate duct (25, 22) and a external duct (21) for supplying the mixture of hydrogen and hydrogen sulphide. The end section of the outer conduit (21) includes the intermediate conduit (22) where the sulfur is dispersed into fine droplets; the gaseous mixture of hydrogen and hydrogen sulphide thus transfers part of its heat to the effluent which circulates in the intermediate duct (22) (the sulfur dispersed in fine droplets instantly passes into the gaseous state; this gaseous effluent thus contains sulfur, hydrogen and hydrogen sulphide). In this zone of the vaporizer, the three internal, intermediate and external ducts coexist.

The outer conduit (21) is connected to the intermediate conduit (25, 22) by means of a loop (8). In order to minimize heat loss, the length of this loop will be as small as possible. Thus the mixture of hydrogen and hydrogen sulphide circulates in a coaxial duct (25) external to the sulfur supply duct (23) in the same direction as the sulfur, this allows, by a transfer of heat, the maintenance sulfur in the non-viscous liquid state. The sulfur feed line terminates in a vaporization means (26), which is preferably a spray nozzle whose opening is about 1 to 10 mm and preferably about 4 to 7 mm.

After the vaporization, the mixture of sulfur, hydrogen and hydrogen sulfide circulates in the conduit (22), this effluent is heated by the mixture of hydrogen and recycled hydrogen sulphide from a furnace (5). ), which circulates in the duct (21) against the flow direction of the vaporized sulfur. The effluent of the conduit (22) is heated to a temperature above 350 ° C which is the reaction temperature of the reaction.

The effluent leaving the vaporizer has a sulfur content of between 4 and 20% by volume of the mixture, a hydrogen content of approximately 5 to 30% by volume of the mixture and a hydrogen sulphide content of approximately 50 and 91% by volume of the mixture, preferably between 70 and 80%.

In the device for synthesizing hydrogen sulfide according to the invention (FIG. 2), the liquid sulfur is brought via a conduit (9) into the vaporizer. As has been seen in the detailed description of the vaporizer, this sulfur is heated by a gaseous mixture of hydrogen sulphide and hydrogen flowing in an intermediate coaxial duct (25); it is then vaporized by a spraying means. The sulfur gas passes into the mixture of hydrogen sulphide and hydrogen, this effluent is heated by the arrival of the mixture of hydrogen and hydrogen sulphide circulating in countercurrent in an outer coaxial conduit (21). It is then sent to a reactor (4) where the synthesis of hydrogen sulphide takes place.

The diameter of the outer duct (21) may be of the order of twice that of the intermediate duct (22). Similarly, the diameter of the intermediate duct (25) may be of the order of twice that of the inner duct (23).

According to a particular embodiment of the invention, it is possible to place a heat exchanger (10) between the vaporizer and the reactor. In this exchanger,
The effluent that leaves the vaporizer in a conduit (11) is reheated by the mixture of hydrogen and hydrogen sulfide leaving the furnace via a conduit (6) and circulates in a coaxial conduit outside the conduit (11). ).

Hydrogen sulfide synthesis can be achieved by any of the known catalytic processes. The catalysts commonly employed contain at least one metal of groups Vb, Vlb, VIII or the rare earth series of the periodic table of elements, published in "Handbook of chemistry and physics, 45th edition", preferably these catalysts contain at least a metal selected from the group consisting of cobalt, molybdenum, iron, chromium, vanadium, thorium, nickel, tungsten, palladium, platinum, uranium. The catalyst support is often alumina, silica or a mixture of silica-alumina. Preferably, the alumina will be used.

The mixture containing hydrogen sulphide, sulfur and a quantity of hydrogen at least equal to the stoichiometric quantity necessary for the conversion of all the sulfur contained in said gas mixture to hydrogen sulphide is introduced via line (11) into the reactor (4). This reactor contains a hydrogenation catalyst at a temperature of at least 350 ° C. under pressure and space velocity conditions enabling at least partial conversion of the sulfur gas contained in said mixture to hydrogen sulphide. a duct (12) is cooled by a heat exchanger (3), where it transfers part of its heat to heat the recycle mixture and is then conveyed via a duct (13) to a heat exchanger (14) where it is cooled to room temperature A pipe (15) ensures the evacuation of this effluent The hydrogen sulphide fraction intended to be recycled is returned to the circuit via a pipe (1) After being compressed by a compressor ( 30) and enriched with hydrogen introduced via a pipe (2), this gas is heated by the heat exchanger (3), then by an oven (5) to reach an inlet temperature in the vaporizer which is such that the n In fine droplets, all the vapors pass completely and instantly into gaseous sulfur. The line (6) allows the transport of said gas from the oven (5) to the vaporizer (7), preferably a heat exchanger (10) is placed between the vaporizer and the reactor.

According to a variant of the vaporizer illustrated in Figure 2, the outer conduit (21) surrounding the inner conduit (intermediate) (22) can communicate directly therewith. The annular outlet of the fluid flowing in the external duct against the current of the flow direction of the sulfur, is contiguous with the annular inlet of the same fluid flowing cocurrently in the inner duct. The liquid sulfur feed duct, of smaller diameter, is generally coaxial with the other two ducts and the liquid sulfur spraying nozzle is generally located immediately after the entry of the gaseous fluid into the internal duct so that the temperature of the liquid sulfur is substantially unchanged.

Example
The invention has been realized for a small installation whose production is 10,000 kg of hydrogen sulfide per day, but the invention can very well be adapted to other dimensions.

The vaporizer used in this example is that schematically illustrated in Figure 1. It has the following characteristics: the gases flow countercurrently over a distance L1 equal to 8 m. The gases of the external duct yield on the path L1 of the heat to the internal duct so that these gases pass from 405 "C, at the entrance of the duct (6) in the vaporizer (7) to 384" C to the gas inlet in the loop (8). The gases then circulate at co-current over a distance L2 equal to 23 cm. The gases of the intermediate duct (25) are at a temperature of 340 ° C. at the point where this duct (25) encloses the sulfur supply duct (23). The gaseous effluent composed of sulfur and hydrogen and hydrogen sulfide exits the vaporizer at the temperature of 356 ° C. In this particular embodiment, the diameter of the sulfur adduction duct is 3.8 cm, the duct of the mixture of sulfur, hydrogen and hydrogen sulphide after evaporation of about 7.6 cm and the duct of arrival of hydrogen and hydrogen sulfide fresh about 15.2 cm.

The process for the synthesis of hydrogen sulphide using the vaporization device according to the invention has been tested with a conventional catalytic conversion process; the catalyst used is the catalyst described and used in the examples of US Pat. No. 4,144,680, the spatial space velocity is 2,000 h -1, the other operating conditions of the embodiment are the following: (the flow rates are given under the temperature conditions and example pressures)

<tb><SEP> Pressure <SEP> (Bar) <SEP> Temperature <SEP> Flow
<tb><SEP> OC <SEP> (Kmol / h)
<tb> Reactor
<tb><SEP> -entere <SEP> 10.9 <SEP> 356 <SEP> 119.01
<tb><SEP> -output <SEP> 10.4 <SEP> 465 <SEP> 106.69
<tb> A <SEP> aspiration <SEP> 9 <SEP> 45 <SEP> 93.05
<tb> of
<tb> compressor
<Tb>
The flow rates, temperatures and pressures of the reagents of the synthesis are recorded in the following table:

<tb><SEP> Pressure <SEP> (Bar) <SEP> Temperature <SEP> Flow
<tb><SEP> OC <SEP> (Kmol / h)
<tb> Sulfur <SEP> 0 <SEP> 130 <SEP> 12.32
<tb> Hydrogen <SEP> 12.5 <SEP> 40 <SEP> 27.90
<tb> Sulfide
<tb> hydrogen <SEP> 11.8 <SEP> 59 <SEP> 91.17
<tb> recycled
<Tb>
In order for all the sulfur to react in the reactor, hydrogen is circulated in excess with respect to the sulfur. In this example, the flow rate of sulfur is 12.32 Kmol / h, so 12.32 Kmol / h of hydrogen sulfide, measured in moles of sulfur atoms (S1), is produced. According to this embodiment, 91.17 kmol / h of hydrogen sulphide is maintained in the recycling circuit.

Claims (10)

1-sulfur vaporization device characterized in that it comprises an inner conduit (22) and an outer conduit (21), substantially coaxial, a liquid sulfur supply means comprising at least one means (26) for spraying the sulfur in the upstream portion of the inner pipe, the inner pipe (22) comprising at least one gas inlet (25) on the upstream side and an outlet of a gas, including sulfur, on the downstream side, the outer pipe having at least an inlet (21a) of a hot gas mixture on the downstream side of the inner pipe, connected to a means (6) for supplying the gas mixture and at least one outlet (21b) on the upstream side of the inner pipe, communicating with the gas inlet (25) of the inner duct, the inner and outer ducts being arranged in such a way that said mixture circulates counter-current to the direction of circulation of the sulfur in the annular portion between the internal duct and the duct external, exchange of the indirectly with the gas circulating in the internal duct and circulates cocurrently with vaporized sulfur in the inner duct. 2- Device according to claim 1, wherein the liquid sulfur supply means is a duct (23) substantially coaxial with the inner and outer ducts, which opens below the inlet of the inner duct. 3- Device according to one of claims 1 and 2, wherein the outlet of the outer conduit and the inlet of the inner conduit communicate by an outer transfer loop. 4- Device according to one of claims 1 and 2 wherein the inlet of the inner conduit and the outlet of the outer conduit are annular. 5-Device according to one of claims 1 to 4, having the output of the inner conduit connected to a hydrogen sulfide synthesis reactor, wherein the inlet of the hot gas mixture in the outer conduit is connected to at least one means (5) for heating the gas mixture consisting of a part of the synthesized hydrogen sulphide and hydrogen. 6- Process for the synthesis of hydrogen sulphide in a reaction zone  catalyst from which an effluent containing hydrogen is recovered.  sulfide, characterized in that a part of the effluent is removed, it is  mixed with hydrogen, the mixture is heated to a temperature and  appropriate pressure and introduced into the vaporizer according to one of the  1 to 5, liquid sulfur is sprayed upstream of the duct.  internally, the mixture is circulated in the outer conduit (21) against  current flow direction of sulfur and introduced said mixture in the  internal duct (22) so as to vaporize the pulverized sulfur and to maintain the  obtained gas mixture containing the sulfur vapor called effluent of  vaporizer at a temperature sufficient for catalytic synthesis  of hydrogen sulphide, by indirect heat exchange with the mixture  circulating in the external conduit. 7. Process for the synthesis of hydrogen sulphide according to claim 6,  characterized in that the amounts of liquid sulfur, hydrogen and  hydrogen sulphide introduced into the vaporizer are chosen from  the vaporizer effluent contains, by volume, approximately 4 to 20% of  sulfur, 5 to 30% hydrogen and 50 to 91% hydrogen sulfide. 8- Process for the synthesis of hydrogen sulphide according to one of the claims  7 and 8, wherein the effluent of the vaporizer containing a quantity  of hydrogen at least equal to the stoichiometric quantity required for  transformation of all the sulfur contained in said effluent into  hydrogen sulphide is introduced into the reaction zone containing a  hydrogenation catalyst at a temperature of at least 350 ° C in  pressure conditions and hourly volume velocity allowing the  at least partial transformation of the sulfur gas contained in said  hydrogen sulfide mixture. 9- Method according to one of claims 7 to 8, wherein the outgoing effluent  of the reaction zone is cooled and then divided into two parts, one of which  is recovered and the other after compression and enrichment  hydrogen is used as gaseous cooling mixture in at  at least one of the steps of cooling the effluent of said zone. 10- Process according to claim 9, wherein the gaseous mixture of  cooling containing hydrogen and outgoing hydrogen sulfide  of the cooling zone is sent into an oven before its  introduction into the vaporizer, the mixture is heated to a temperature  enough that, in the vaporizer, the sulfur in fine droplets  passes, when in contact with said mixture, completely and very quickly  in the gaseous state.