DE2910945A1 - PROCEDURE FOR DETERMINING SO LOW 2 AND H LOW 2 S CONTENT IN AN EXHAUST FLUE - Google Patents

Description

Procedure for determining the SO, - and H _o S content

in an exhaust gas stream.

The invention relates to an improved method for determining the SO ₂ content and the H ^ S content and the ratio of these contents in an exhaust gas flow, which is intended to provide a possibility for better regulation of the composition of this exhaust gas flow.

The extraction of sulfur from an _{acidic gas containing H 9} S is based on the application of the GLAUS process, which takes place according to the following reaction equation

2 HS + SO ₂ 3 / nS _n + 2 H ₃ O

According to this process, a _{gas containing H 2} S, which is obtained from the desulphurisation of natural gas or the hydrogenation of petroleum products, is passed into a combustion zone in which some of the hydrogen sulphide is converted to sulfur and by air at an elevated temperature (about 1000 ° C) SO _{2 is} oxidized; then the stream emerging from the combustion zone, after the condensation of the sulfur contained in it, is passed into a zone for catalytic oxidation; several converters connected in series, which are kept at a temperature between 200 and 400 ° C, are used for this purpose. This converter may be followed by another converter, which operates at a temperature below the dew point of the sulfur and is periodically regenerated; the hydrogen sulfide contained in the exhaust gas stream is then converted into sulfur in this catalyst zone using the same CLAUS process

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oxidized.

_{The process parameters are optimal when the H 2} S / SO ₂ ratio measured at the output of the penultimate converter or at the input of any additional converter is equal to 2. Two methods are already known for measuring the content of SO _{2 and HoS.}

The measurement of the absorption in the ultraviolet during the Passage of this radiation through a cell produced by the gas flow is flowed through, then leads to satisfactory results if the flow cell at a Temperature can be operated below the dew point of the sulfur. Since this condition is in the removal zone, which is selected in the sulfur production, can only be adhered to with difficulty, deposits are formed on the windows of the Cell. In any case, the presence of sulfur flowers in the exhaust gas streams of sulfur production forms one Difficulty in applying the laws of absorption. For these reasons, one generally arises strong deviation from the baseline, and this method, although it allows the measurement result to be recognized immediately, becomes rare applied.

The checking of SO ₂ and H ₂ S by means of gas chromatography has been used on an industrial scale when the difficulties arising during sampling have been eliminated, especially the problems caused by pipes and valves. This procedure gives good results with no noticeable deviations. However, it takes about three minutes until the measurement result is available; this time is very significant compared to the gas throughput in the sulfur recovery

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system that runs through in about 20 seconds.

With the invention, the difficulties encountered in these two methods can be avoided; despite this the measurement result is instantaneous and deviations do not occur.

The method according to the invention for determining the SO ₂ and HS content in an exhaust gas stream provides the following method steps:

- A representative amount of gas is withdrawn from the gas flow;

this amount of gas is mixed with an amount of air which is constant and so large that it is sufficient _{under all circumstances to completely oxidize the amount of H 2 S contained in the amount of gas;}

the amount A of the SO ₂ content is measured using an interference spectrometric method;

- the amount of gas plus the amount of additional air is set with a selective oxidation catalyst brought into contact in a room, the temperature of which is at a value between 200 and 400 ° C is maintained;

the amount B of the SO ₂ content is measured using an interference spectrometric method;

- The amounts A and B of the SO ₂ content are compared with each other, the value C = BA of the H ₃ S content of the exhaust gas flow is formed.

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- ο -

The method of interference spectrometry is one of the results of the work at the Institut d'Optique de Paris and the Ecole Normale Superieure de l'Enseignement Technique de Cachan on the detection of low-intensity luminous fluxes using an interferometer system. These Work is reflected in the following French patents:

French patent 1 411 738 dated June 30, 1964, according to which the introduction of an interferometer with transverse doubling (French: interferometre a dedoublement transversal) in a conventional interference spectrometer an improvement in the light output while maintaining the level already achieved achieved resolution made possible.

Französiches Patent 72.02754 from 27/01/1972, according to which the simplification of the structure of interferometric resulted in a greater operating reliability of the appliance in the analysis of a '"wavelength to another.

French patent 73.04040 dated February 6, 1973, according to which the installation of a correlation grating means the production of Correlations of spectra or derived spectra made possible.

French additional patent 75.04264 dated February 11, 1975, according to which birefringent mirrors instead of the previously provided mirrors Elements, e.g. Wollaston prisms were provided, which results in a considerable simplification of the assembly while at the same time being more compact in construction and retention the performance already achieved.

French additional patent 75.04247 of 02/11/75, according to which the use of birefringent elements the

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Realization of a two-beam interference spectrometer enabled absorption problems to be treated.

French additional patent 77.02902 dated February 2, 1977, in which a device is described which, using birefringent components, enabled _{an investigation by correlation comparison of gas spectra, such as the SO 0 spectrum.}

In the inventive method for determining SO ₂ ^- and H ₂ S ~ content in an exhaust stream consisting of any measurement process for measuring the amount of SO ₂ for a -GeIIaItS interferenzspektrometrischen process in that

- A stream of ultraviolet radiation in the wavelength range between 280 and 310 nm is emitted;

- This radiation current is guided on a limited optical path through a room in which the to investigating exhaust is located;

- this radiation is then passed through a two-beam interferometer, in which, after passing through a fixed polarizer, an optical path length difference e. ^ n (product of the strength of a crystalline substance and the amount <£ η of the birefringence of this crystalline substance) is brought about, being the difference in path

Is the periodicity of the absorption bands of SO _2;

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- The radiation is then passed through an analyzer which rotates at a suitable frequency f;

- which modulated in this way at the frequency 2f Luminous flux is captured and converted into an electrical current, which is detected synchronously and provides a signal indicative of the SO ^ content of the exhaust gas.

According to a first embodiment of the invention, the Amount of the luminous flux of the ultraviolet radiation measured after this for the measurement of the amount B has covered the same optical path as for the measurement of the amount A.

According to a preferred way of practicing this procedure, the amounts belonging to amounts A and B are then informed Ultraviolet radiation fluxes a complementary partial coverage such that for the measurement of B three times of the luminous flux of the luminous flux intended for the measurement of A.

In a second embodiment, the amount of Ultraviolet radiation flux measured after passing through an optical path used to measure A was three times as long as when measuring B.

Among the different process variants, a method is preferred which is based on the fact that the two for Determination of A and of B required ultraviolet radiation currents can be derived from one and the same radiation source and on one and the same receiver

be collected, the two ultraviolet radiation currents corresponding bundles perpendicular to each other and at 45 opposite the axis of the crystalline Are polarized substance, which causes the path length difference.

In the various processes, the amount of gas contained hydrogen sulfide completely burned by the said amount of gas during a constant long time between 1 and 15 see in a selective Oxidation catalyst at constant, between 200 and 400 ° C temperature is maintained; such a catalyst consists of an aluminum or silicon oxide support the one with a mixture of iron and / or vanadium and / or nickel and / or cobalt and / or calcium and / or zinc is soaked.

When the method is used, the molar ratio of H ₂ S to SO _{2 is kept} at a target value in a gas stream used to feed a CLAUS process; In this application, the instantaneous value of _{the ratio H 2 SZSO 2 is determined} from the instantaneous values of the quantities A and B, whereupon a signal is emitted which represents a measure of the difference between the instantaneous value determined in this way and the setpoint, and this signal becomes a control mechanism fed, which returns the instantaneous value of the ratio to the setpoint.

For a better understanding of the invention, a non-limiting embodiment of the invention is described below described with reference to the drawings, which show the following:

1 measuring arrangement for interference spectrometry;

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2 shows a diagram for a first system for determining the SCU and EUS content of a gas stream;

3 shows a diagram of a covering device with screens;

4 shows a diagram of a second system for determining the SCu and H ^ S content of a gas stream;

FIG. 5 is a diagram of a system for determining the SC 1 and the H ₂ S content of a gas stream according to FIG. 4 with a single radiation source and a single receiver; FIG.

Fig. 6 Basic structure of a control system for a sulfur recovery system .

A source 1 for ultraviolet radiation has an exit window I ¹ which points in the direction of an axis XX ¹ , which is at the same time the axis of an interference spectrometer.

The ultraviolet radiation, which is limited to the area between 280 and 310 nm, penetrates one after the other:

- a quartz optic 2 with a focal length of 200 mm,

- a closed room 3, in which the gas to be examined is located,

- a fixed polarizer 4,

a filter 5 for ultraviolet radiation

- A birefringent plate 6 of thickness 3 and with the

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Birefringence coefficient Δη. The plate from parallel Quartz cut to the axis of symmetry of the crystal consists of a wedge and a counter-wedge of the same type Dimension with which the total thickness of the plate can be adjusted to an amount of about 3 mm in this way can that

where Ά * Ο is the periodicity of the absorption bands of the product in question, in the present case of SO ₂ ,

- an analyzer rotating at a frequency f of 10 Hz 7,

- a lens 8 with a focal length of 100 mm,

- an aperture 9,

a photomultiplier 10, e.g. of the 1P28 type.

You can work with any photoelectric receiver that is sensitive to the area in question, especially with photovoltaic cells.

Fig. 2 shows schematically the structure of a system for determining the content of SO ₂ and H ₂ S in a gas stream, using the differential interferometric measuring method.

A quantity of gas is conveyed from a sampling point 11 through a line 12 into a measuring cell 13. To the Line 12 is connected to a nozzle 14 with a compressed air source (not shown) and associated control devices; through the nozzle a constant air flow

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amount introduced.

The cell 13 for measuring the amount A is connected via a line 15 to an oxidation furnace 16, the in turn is connected to a second measuring cell 18 via a line 17. The second cell 18 for the measurement d he size B is connected via a line 19 to a vacuum chamber, not shown, which is in a Desulfurization plant or opens into a chimney.

Each of the two measuring cells 13 and 18 has two opposing windows, 20, 21 in cell 13 and 22, 23 in cell 18. Aligned with the common axis of these opposing windows is a source 1 or I ^{1 in each cell} arranged for ultraviolet radiation and, on the other hand, a measuring device 24 and 24 ', as shown in FIG. 2; elements 4 to 10 are also provided.

Each measuring device 24 or 24 ″ is connected via an electrical conductor to a device 25 for processing electrical signals; the device calculates an error signal from the signals supplied by each receiver, which has the value zero if the ratio between H ₂ S and SO _{2 reaches} its optimum value.

Two devices, which are shown in FIGS. 3 and 4, enable the luminous flux values of the ultraviolet radiation to be changed by purely optical means. When such devices are used, the signals emanating from receivers 24 and 24 'are the same when the ratio of H ₂ S to SO ₂ has reached its optimum value; the processing device 25 then compares the two signals and determines an error signal by

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times subtraction.

Fig. 3 shows a device, the two aperture openings 27 and 23 with contiguous contours, the same dimensions and fixed in the same plane Plate 29 are attached, assigns a right-angled aperture 30, which is cut into a flat plate 31 which is parallel to the plane of the two diaphragms and is parallel to the straight line by longitudinal movement can move that connects the centers of the two aperture openings.

3 shows that the movable diaphragm 30 releases partial areas from the diaphragms 27 and 28, the sum of their area sizes is constant. By moving the diaphragm 30, the size of the partial area 27 'can therefore be reduced to a third set the size of the partial area 28 '.

The device outlined in Fig. 3 is to be used so that the fixed panels 27 and 28 with the windows 21 and 23 of the measuring cells 13 and 18 are aligned.

This arrangement enables, among other things, a zero value setting regardless of the type of that contained in the cells Gas as well as a number of settings that may become necessary in the course of the measurement.

Fig. 4 shows the scheme of a system, as it is also in 2, and like reference numerals indicate like components.

According to Fig. 4, the optical travel distances of the ultraviolet rays are shown in the measuring shafts 13 and 18 in a ratio of 3: 1 to one another, while in the system according to FIG. 2 the same

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optical routes were provided.

The arrangement provided according to FIG. 4 leads to output signals at the output of the receiver devices 24 and 24 ″ which are of equal magnitude when the ratio between H ₂ S and SO ₂ has assumed the optimum value.

5 shows schematically a further system for determining the content of SO ₂ and H ₂ S in a gas stream; here the optical paths of the radiation in the gas to be examined are brought to a certain ratio to one another.

A sampling point 11 that supplies a quantity of gas is connected to a measuring cell 13 via a line 12. In the line 12 opens a nozzle 14, which is not with a Drawn compressed air source and is connected to a regulator, also not shown, which has a constant Air volume supplies.

The measuring cell 13 is connected via a line 15 to an oxidation furnace 16, which in turn is connected via a line 17 is connected to a second measuring cell 18. This second measuring cell 18 is via a line 19 with a not shown vacuum chamber in connection, which is in a desulfurization system or in a chimney flows out.

According to Figure 5, cells 13 and 18 are so close to each other arranged that their windows 20 and 22 illuminated by one and the same ultraviolet radiation source 1 will.

The radiation reaches the entry windows 20 and 22 of the cells 13 and 18 after it has passed through a covering device 3 '.

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29109A5

"* 1/ -

has set that is open to each of the two windows 20 and 22 alternately.

The optical path in cell 13 (measured variable A) is free times that in cell 18 (measured variable B).

The two luminous fluxes of ultraviolet radiation created in this way are transmitted through the fixed polarizers 4 'and 4 "polarized perpendicular to each other and at 45 relative to the axis of the crystalline matter, which causes the difference in optical path length.

The ultraviolet radiation emanating from cells 13 and 18 penetrates the individual elements one after the other a device 24 which determines the content of SC> 2 in an exhaust gas stream according to the method described above.

Such a device in which

- the optical paths in cells 13 and 18 are in a ratio of 3: 1,

- a single source of ultraviolet radiation and one only measuring device is used,

has a particularly high level of operational reliability because all deviations from the radiation source and the Measuring device originate in the subtraction of the measured variables from one another to be carried out to determine the error signal fall out.

Fig. 6 indicates very schematically a plant for sulfur production.

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A furnace 31 is followed by three converters 32, 33 and 34, in which the CLAÜS process takes place. After the furnace and after each converter is a cooler 35, 36, 37 and 38 for recovering the sulfur and cooling the exhaust gases.

The exhaust gas emerging from the cooler 38 is fed into a system 39 for processing end gas from the CLAUS ovens arranged, for example, a system according to the method described in French patents 2,180,473 and 2,224 described procedure works.

Between the cooler 38 and the system 39 there is a sampling point 11 which opens into a line 12 to which a nozzle 14 connected to a compressed air source leads. The line 12 opens into a device 40 for determining the SO ₂ and H ₂ S content, as is described in FIGS. 2, 4 or 5.

The signal emitted by such a device and forwarded via the electrical conductor 26 arrives into a control unit 41 for controlling the additional air for the furnace 31 and regulates the amount of incoming air there.

When metering SO2 using the interference spectrometry method there is no deviation because, according to the measuring principle, it is insensitive to variations is the permeability of the measuring cell window. One can therefore have a very good control of the sulfur recovery plants and in particular the final ones described in French patents 2,180,473 and 2,224,196 Make desulphurisation plants.

Since the response interval of such a control practically

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table is zero, better control and optimization of the working conditions of plants for reconditioning of exhaust gases reach when these systems are fed with exhaust gases in which sudden and strong Changes in gas volume and composition occur, as is the case with hydrocarbon refineries.

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Claims (8)

Patent claims: 1.) Method for determining the SO ~ and H _o S content in an exhaust gas stream, characterized by the following process steps: - A representative amount of gas is taken from the exhaust gas flow; this amount of gas is mixed with an amount of air which is constant and so large that it is sufficient _{under all circumstances to completely oxidize the amount of H 2 S contained in the amount of gas;} the amount A of the SO ₂ content is measured using an interference spectrometric method; - The amount of gas plus the amount of additional air is combined with a selective oxidation catalyst Brought into contact with the room, the temperature of which is kept at a value between 200 and 400 ° C; the amount B of the SO ₂ content is measured using an interference spectrometric method; - The amounts A and B of the SO ^ content are compared with each other, the value C = BA of the H ₃ S content of the exhaust gas flow is formed. 909840 / 06TQ 2. The method according to claim 1, characterized in that each measuring process for determining the amount of the SCU " Content according to an interference spectrometric method is that a stream of ultraviolet radiation in the wavelength range between 280 and 310 nm is emitted; - this radiant flux on a limited optical Path is passed through a space in which the exhaust gas to be examined is located; - this radiation then through a two-beam interferometer is conducted, in which, after passing through a fixed polarizer, an optical Path length difference e.-Δη (product of the strength of the crystalline substance and the amount Δη of the birefringence of this crystalline substance) is attached, where the difference in path e.4n =
where-6S * is the periodicity of the absorption bands of the the radiation is then passed through an analyzer which is operated at a suitable frequency f circulates; the luminous flux modulated in this way with the frequency 2f is captured and converted into an electric current which is detected synchronously and _{provides a signal indicative of the S0 2} content of the exhaust gas. 3. The method according to claim 2, characterized in that the amount of the luminous flux of the ultraviolet radiation 909840/0670 is measured after this for measuring the amount B has traveled the same optical path as for the measurement of the amount A. 4. The method according to claim 3, characterized in that the luminous fluxes of ultraviolet radiation intended for the measurement of the amounts A and B are complementary Experienced partial abbreviation in such a way that for the measurement of B three times the luminous flux of that for the measurement The luminous flux provided by A. 5. The method according to claim 2, characterized in that the amount of the luminous flux of the ultraviolet radiation after this luminous flux for the measurement of A is three times the length of the optical path in the Compared to the distance for the measurement of B. 6. The method according to any one of claims 3 to 5, characterized in that that the two luminous fluxes used for the measurement of A and B are ultraviolet radiation of emanate from a single light source and be received by a single receiver, and that the two Beams of ultraviolet rays perpendicular to each other and at 45 ° opposite the axis of the crystalline The substance is polarized, which causes the difference in the optical path length. 7. The method according to claim 1, characterized in that the complete combustion of the gas contained in the 908840/067!) tenen H ^ S is preceded by making the said Amount of gas during a constant period of time between 1 and 15 seconds in contact with a selective oxidation catalyst holds, which is at a temperature lying between 200 and 400 ° C, and that for such a catalyst a support made of aluminum or silicon oxide with iron and / or vanadium and / or Nickel and / or cobalt and / or calcium and / or zinc is impregnated. 8. Application of the method according to claim 1 for maintaining a desired value of the molar ratio of H ^ S and SO ₂ in a feed gas stream for a CLAUS process, in which application the instantaneous value of the ratio HS / SOo is determined from the instantaneous values of the amounts A and B. , a signal is emitted which represents a measure of the difference between the instantaneous value determined in the above-mentioned manner and the nominal value, and this signal is fed to a control mechanism which is able to return the instantaneous value of the ratio to the nominal value. 909840/0670