EP1989142A2

EP1989142A2 - Method of optimizing the operation of claus units

Info

Publication number: EP1989142A2
Application number: EP07731009A
Authority: EP
Inventors: Pierre Kaplan
Original assignee: Total France SA
Current assignee: TotalEnergies Marketing Services SA
Priority date: 2006-02-27
Filing date: 2007-02-19
Publication date: 2008-11-12
Also published as: FR2897860B1; FR2897860A1; ZA200806561B; WO2007096512A2; CN101389568A; WO2007096512A3; US20090226363A1; US7780942B2; EA200870298A1; CA2641424C; JP5259427B2; CN101389568B; JP2009528245A; CA2641424A1; EA016923B1

Abstract

The invention relates to a catalytic method for treating an H2S/SO2 mixture for producing liquid sulphur, said method comprising the following steps: a) at least one step of heating the mixture containing SO2 and ?2S to a temperature Tc; b) at least one step of catalytically reacting the heated mixture obtained in a) in the presence of at least one catalyst and at least one step of recovering the exiting mixture containing gaseous sulphur; and c) at least one step of converting the gaseous sulphur contained in the exiting mixture obtained at step b) into liquid sulphur, said method being characterized in that, between step b) and step c), the temperature Ts of said exiting mixture and the dew point Tr of the gaseous sulphur contained in said exiting mixture are measured and in that the heating temperature Tc of step a) is adjusted so that the temperature Ts is 5°C to 30°C above the dew point Tr.

Description

METHOD OF OPTIMIZING THE UNIT MARKET

CLAUS

The present invention relates to the oil and gas industries, and more particularly the liquid sulfur production units called CLAUS units.

Petroleum desulfurization converts sulfur-containing organic compounds into H2S hydrogen sulfide, whose toxicity and ignition hazards are well known. H2S is also a constituent of natural gas, and it acts as a poison that deactivates the industrial catalysts used in natural gas recovery processes. It is therefore essential to convert hydrogen sulphide into non-toxic elemental sulfur and also a useful raw material. Indeed, the sulfur produced is generally of good purity, and can be sold as such or in the form of sulfuric acid H2SO4.

Industrially, this conversion is carried out in a refinery using a process based on CLAUS technology. The recovery rates generally reached being about 95%, the fumes emitted by these installations contain most often significant quantities of acid gases, in particular H2S and SO2. This makes it necessary to treat these waste gases, with the aim of allowing them to be released to the atmosphere after incineration by respecting the increasingly stringent standards imposed by the legislation on air pollution, both in France and at European level. and global, where the trend is to set a 99.5% yield for final sulfur recovery. It is then easy to see that the complementary treatments of the tail gases, making it possible to reach these high yields, generate very considerable additional economic and energy costs, thus making it imperative to improve the recovery rates achieved by the CLAUS units.

The CLAUS process is generally a two-step process. A first combustion step is performed by burning a third of the H ₂ S in a first chamber equipped with a boiler. During this thermal step, one third of I 2 S 2 is partially oxidized to SO 2 by air and / or oxygen (I). This reaction (I) is complete and stops when all the oxygen is consumed. In a second step, the sulfur dioxide SO2 thus formed reacts with remaining H2S to form sulfur gas and water according to the so-called CLAUS reaction (II). This reaction is balanced and the equilibrium constant depends essentially on the temperature. The overall chemical reactions involved are as follows: H ₂ S + 3/2 O ₂ -> SO ₂ + H ₂ O (I)

2 H ₂ S + SO ₂ <-> 3 / n S _n + 2 H ₂ O (II)

At this point, the reaction stops and most of the sulfur gas is produced (about 70%). The reaction products are generally cooled in a condenser to recover, in liquid form, the elemental sulfur vapors that have formed in the combustion chamber and in the boiler.

The gaseous mixture containing H ₂ S and SO ₂ residual, in a molar ratio H ₂ S / SO ₂ equal to two, then undergoes a catalytic reaction of step (II). In practice, the unit generally comprises a series of catalytic reactors in series, each of them being associated with a gas heating system and a sulfur condenser.

The CLAUS reaction being exothermic, the conversion to sulfur is favored by low temperatures. It is necessary, nevertheless, to maintain the temperature of the catalytic reactor at a sufficient level, not only to promote the kinetics of the CLAUS reaction, but especially to prevent the appearance of liquid sulfur dew on the surface of the catalysts, which would cause their deactivation .

Thus, it is necessary that the set temperature imposed on the inlet of the catalytic reactor, noted Tc in the present invention, be adjusted so that the outlet temperature of the catalytic reactor, denoted Ts, is greater than the dew point temperature. sulfur at the outlet of said reactor, denoted Tr in the present invention. This applies in fact to each of the catalytic reactors that the CLAUS unit can count. The adjustment of Tc is done in an empirical manner known to those skilled in the art, so that Ts takes the desired value.

However, the dew point of sulfur is unknown because it depends, among other things, on the composition of the gas, which changes as it goes along. This is why one generally proceeds to a temperature adjustment Tc to a much higher level, to have a margin of safety as to the temperature of appearance of this dew point. The set temperature is thus generally adjusted so that the temperature Ts has several tens of degrees Celsius more than the expected temperature Tr at the exit of this same reactor. This technique has the major disadvantage of being disadvantageous from an economic and environmental point of view because, since the operation of the unit is not optimized, the conversion rate to sulfur is not satisfactory enough, which results in waste gases charged with acid gases (more particularly with H2S and SO2) requiring a greater complementary treatment.

Several methods and methods have been proposed to go further in sulfur recovery levels, but none have addressed the problem of working closer to the dew point. Only the refiners know the technique of carrying out a sampling campaign for the different gases at the CLAUS unit and performing a material balance to deduce the temperature of the dew point. The disadvantage of such a technique is that it requires a team of specialists, and that the measurement is only punctual. Thus, there is a need in the art for a more accurate, in situ and continuous determination of the sulfur dewpoint to reduce the gap (Ts-Tr) between the catalytic reactor outlet temperature and the temperature of the reactor. dew sulfur.

The Applicant proposes to provide a technical solution to operate near the dew point by its continuous measurement, to optimize the reactor temperatures and thus increase the efficiency of the CLAUS unit. To this end, the invention provides a catalytic process for treating a mixture of HbS and SO2 to produce liquid sulfur, said process comprising the following steps: a) at least one step of heating at a temperature Tc of the mixture containing SO2 and I2S, b) at least one step of catalytic reaction of the heated mixture obtained in a) in the presence of at least one catalyst and at least one step of recovering the output mixture containing sulfur gas, c) at least one step of transforming the sulfur gas contained in the exit mixture obtained in step b) into liquid sulfur, said process being characterized in that, between step b) and step c), the temperatures Ts of said mixture of output and sulfur dew tr gaseous content in said output mixture is measured, and in that the heating temperature Tc of step a) is adjusted so that the temperature Ts is greater than that of dew Tr from 5 ° C to 30 ^° C. To this end, the invention also relates to a device for carrying out the method according to the invention, characterized in that it makes it possible to measure the dew point temperature of sulfur.

The invention has several advantages, including optimizing the operation of the CLAUS unit and reducing the amount of untreated residual sulfur species, in particular H2S and SO2. Thus, the size of the additional waste gas treatment units is also optimized, resulting in additional energy and cost savings. In addition, the invention is not only applicable to new units, but also to pre-existing units, which can significantly reduce the operating costs of maintenance of the latter.

Advantageously, the heating temperature Tc of step a) is adjusted so that said temperature Ts is greater than that of dew Tr from 5 ⁰ C to 20 ⁰ C, and more advantageously from 5 ° C to 10 ⁰ C .

According to the invention, this process is such that it is carried out in at least one CLAUS catalytic unit reactor, and preferably in at least two CLAUS catalytic reactor units.

According to another characteristic of the invention, the device for implementing the method according to the invention comprises a calorimetric or magnetic probe. The invention will be better understood on reading the detailed description of various embodiments with reference to the attached figure which schematically represents a CLAUS unit comprising a thermal stage (Eo) and three catalytic stages (E ₁ , E ₂ , E ₃ ). serial. The first stage of combustion of IΗ2S takes place in a first chamber equipped with a boiler 1. During this thermal stage, a third of IΗ2S is partially oxidized to SO2 by air and / or oxygen. Sulfur dioxide SO2 thus formed reacts with remaining H2S to form gaseous sulfur and water according to the so-called CLAUS (II) reaction. The combustion products are cooled in a condenser 2 to recover, in liquid form, sulfur vapors element which formed in the combustion chamber and in the boiler by line 9.

The gaseous waste mixture, containing 12 S and the unreacted SO 2, undergoes several stages of catalytic reaction (II). A catalytic first stage section (Ei) comprises heating the gas

CLAUS by a heater 3, the actual catalytic conversion in a reactor 4, the cooling and condensation of sulfur in a condenser 5. This step also participates most often in the hydrolysis of COS and CS2, undesirable compounds formed upstream. This is made possible by operating the reactor at a sufficiently high temperature to promote hydrolysis at the expense of poorer sulfur conversion at this stage. Two additional catalytic steps (E2, E3) respectively comprising heating by 3 'and 3 "heaters, conversion on catalyst in 4' and 4" reactors, and condensation of sulfur by 5 'and 5 "condensers, complete the device, thus allowing to continue the CLAUS reaction.

The sulfur is recovered in the liquid state by condensation after each reaction step by the lines 8, 8 'and 8 "corresponding to the reactors 4, 4' and 4". In the case shown in the figure, the invention is implemented in at least one of the reactors 4, 4 'or 4 ".The method according to the invention is such that it is implemented in one, two or three The recovered sulfur can be stored either in liquid form in tanks maintained at 140 ° C. or in solid form in a tank 6. As for all the residual sulfur components leaving via a line 7 after passing through the condenser 5 ", these are either directed to a waste gas treatment unit, or converted to SO2 before their discharge to the atmosphere.

The essential characteristic of the process according to the invention is that it measures the temperature Ts of the output mixture of a catalytic reactor implementing step b) and the dew point temperature Tr of the sulfur gas contained in said output mixture, and the heating temperature Tc is adjusted so that the temperature Ts is greater than that of dew Tr, from 5 ° C. to 30 ^° C., and advantageously from 5 ° C. to 20 ^° C., and more advantageously by 5 ° C. at 10 ^° C. According to the invention, this process is such that it is implemented in at least one catalytic reactor of the CLAUS unit.

According to another modality, the process according to the invention is such that it is implemented in at least two catalytic reactors of the CLAUS unit. In this case, it is generally more interesting to adjust the temperature Tc of the last two reactors. Indeed, as indicated above, the first catalytic reactor generally operates at a sufficiently high temperature to promote the hydrolysis of compounds such as COS and CS2. Nevertheless, the present invention does not exclude an embodiment according to which the process is such that it is used in all the catalytic reactors of the CLAUS unit.

The invention also relates to a device for carrying out the catalytic process according to any one of the preceding claims, intended to treat a mixture of H2S and SO2 to produce liquid sulfur, said device comprising the following means: at least heating means at a temperature Tc of the mixture containing SO2 and IΗ2S; at least one means for catalytically reacting the heated mixture obtained at the outlet of the heating means in the presence of at least one catalyst and at least one means for recovering an exit mixture containing sulfur gas; at least one means for transforming the sulfur gas contained in the liquid sulfur output mixture, said device being characterized in that it makes it possible to measure the dew point temperature of the sulfur.

According to a first embodiment, said device comprises a calorimetric probe. According to a second embodiment, said device comprises a magnetic probe.

A typical method of dew point measurement is to cool an appropriate surface until dew occurs, to detect the time of dew, then to measure the temperature corresponding to the moment of the first dew. appearance of the dew deposit. Different devices, manual or automatic, measure the dew point temperature. They can use a calorimetric, magnetic, optical or capacitive detection to follow the dew on this surface. Patent EP 542 582 describes certain embodiments of such a probe for measuring the dew point. Advantageously, the dew-point measuring device according to the method of the invention is a calorimetric or magnetic probe for measuring the dew point.

EXAMPLES

The following examples illustrate the invention and its advantages without, however, limiting its scope.

It operates on a sulfur unit as shown in the attached figure, composed of three catalytic stages (E ₁ , E ₂ , E ₃ ). The catalyst used is TiO 2 titanium oxide. The inflow is 100

T / day of acid gas, having the following molar composition: Hydrocarbons = 1% - H ₂ S = 87% - CO ₂ = 8.7% - H ₂ O = 3.3%. Thus, the inflow into sulfur is 81.5 T / d.

The setpoint temperature for the ^1st catalytic stage is set so that the outlet temperature of the first reactor 4 be equal to 31O ⁰ C.

To demonstrate the particular advantages of the improved process of the invention, the dew point temperature is measured at the outlet of the 4 'and / or 4 "catalytic reactor (s), and the temperature (s) are adjusted. (s) Setpoint heaters 3 'and / or 3 ".

The condenser 2 is set at 170 ° C while the condensers 5, 5 'and 5 "are set at 135 ° C.

Example 1: In a first step, only the set temperature of the second reactor 4 'is adjusted so as to vary the margin between the outlet temperature of the second reactor and the dew temperature measured at its outlet. The set temperature for the heater of the last reactor 4 "is fixed, so that the margin (Ts3-Tr3) is equal to 60 ^° C. Table 1 groups together the results obtained.

Table 1

The above example shows that the smaller the margin between the outlet temperature of the second reactor 4 'and the measured dew point temperature, the greater the overall efficiency achieved. This results in the reduction of SO2 emissions and the residual load to be treated in the tail gas unit.

Thus, an adjustment of the second heater 3 'at 244 ° C. corresponds to a dew point margin of 60 ^° C. at the outlet of the second reactor. A different setting with a margin of 5 ° C, for example, relative to the dew point would lead to setting the temperature of the second heater to 190 ^° C and reduce SO2 emissions by 31, 1% by an overall efficiency of 98. , 4%. The residual charge to be processed in the tail gas unit is reduced from 1.94 T / d to 1.34 T / d.

Example 2

In this example, it is the set temperature of the third reactor 4 "which is adjusted so as to vary the margin between the outlet temperature of this reactor and the measured dew point temperature. reactor is fixed, so that the margin (Ts2-Tr2) is equal to 60 ^° C.

Table 2 groups the results obtained.

Table 2

More importantly, as the gap (Ts3-Tr3) decreases, the overall efficiency achieved is greater. Thus, a setting of the third heater at 227 ^° C. corresponds to a dew point margin of 60 ° C. at the outlet of this same reactor, whereas a different adjustment with a margin of 5 ° C., for example, with respect to Dew point would set the temperature of the third heater (3 ") at 179 ° C and reduce SO2 emissions by 44.5% by an overall efficiency of 98.7%. Tail gas unit is reduced from 1.94 T / d to 1.08 T / d.

Example 3

In this example, both the set temperature of the second and the third reactor are adjusted so as to vary the margin between the outlet temperature of these reactors and the measured dew point temperature. Table 3 groups the results obtained.

Table 3

The example above shows that the optimization of the heating temperatures of the last two catalytic stages, leads to a significantly improved overall efficiency. Thus, an adjustment of the heaters of the last two reactors 4 'and 4 ", with a margin of 5 ⁰ C for example, compared to the dew point reduces the SO2 emissions by 59.2% by an overall efficiency of 99% The residual charge to be treated in the tail gas unit is reduced to 0.79 T / d.

Claims

1) A catalytic process for treating a mixture of HbS and SO2 to produce liquid sulfur, said process comprising the following steps: a) at least one step of heating at a temperature Tc of the mixture containing SO2 and I2S, b) at least one step of catalytic reaction of the heated mixture obtained in a) in the presence of at least one catalyst and at least one step of recovering the output mixture containing sulfur gas, c) at least one. a step of transforming the sulfur gas contained in the exit mixture obtained in step b) into liquid sulfur, said process being characterized in that, between step b) and step c), the temperatures Ts of said mixture output and dew point of the sulfur gas contained in said output mixture are measured, and in that the heating temperature Tc of step a) is adjusted so that the temperature Ts is greater than that of dew Tr from 5 ° C to 30 ^° C.

2) Process according to claim 1, characterized in that the heating temperature Tc of step a) is adjusted so that said temperature Ts is greater than that of dew Tr from 5 ⁰ C to 20 ° C.

3) Process according to any one of the preceding claims, characterized in that the heating temperature Tc of step a) is adjusted so that said temperature Ts is greater than that of dew Tr of 5 ⁰ C to 10 ⁰ C.

4) Process according to any one of the preceding claims, as it is implemented in at least one CLAUS catalytic unit reactor.

5) Process according to any one of the preceding claims, as it is implemented in at least two CLAUS catalytic unit reactors. 6) Device for carrying out the catalytic process according to any one of the preceding claims, for treating a mixture of HaS and SO2 to produce liquid sulfur, said device comprising the following means: at least one heating means at a temperature Tc of the mixture containing SO2 and IΗ2S; at least one means for catalytically reacting the heated mixture obtained at the outlet of the heating means in the presence of at least one catalyst and at least one means for recovering an exit mixture containing sulfur gas; at least one means for transforming the sulfur gas contained in the liquid sulfur output mixture, said device being characterized in that it makes it possible to measure the dew point temperature of the sulfur.

7) Device according to claim 6, characterized in that it comprises a calorimetric probe.

8) Device according to claim 6, characterized in that it comprises a magnetic probe.