DE2918084B2 - Device for determining the extinctions of components of an exhaust gas mixture - Google Patents

Description

40

The invention relates to a device for determining the extinctions of various gases and possibly. Components of an exhaust gas mixture consisting of smoke particles according to the preamble of claim 1.

In all known devices of this type (DE-AS 21 30 331, DE-OS 22 13 456, DE-AS 25 21 934) must the extinction coefficients of the individual components must be known in order to derive the coefficients of the To determine linear combination. The determination of the wavelength dependence of the extinctions of each However, components is a very complex process. Also, it is difficult during the Measure the dust density or gas concentration «to keep constant. Finally, for the coefficient determination a simultaneous measurement can be carried out at all measurement wavelengths.

The object of the invention is now to provide a device by the preamble of claim 1 bo with the genus marked without prior knowledge of the specific extinction coefficients of the components, the coefficients of the linear combination can be determined in a simple manner can. t> 5

To solve this problem, the features of claim 1 are provided.

The invention is based on the knowledge that only when changing the specific extinction coefficient of the absorbing components a clear, converging adjustment of the coefficients of the linear combination it is possible that, on the other hand, when the coefficients change, the linear combination no clear and correct solution of the linear combination for all concentrations of the absorbing components results

It is particularly advantageous if one of the components is insulated with the device according to the invention is examined, that is, the concentration of the remaining components is zero

In the case of unknown and therefore arbitrarily set specific extinction coefficients of those components, whose concentration is zero leads to the change in the specific extinction coefficient one absorbent component, unknown in terms of its concentration and extinction, becomes one Approximation of the output of the first computing circuit to the extinction of the one with regard to its concentration and absorbance of unknown component and the absorbance of zero for the remaining components.

With known and correctly set specific extinction coefficients of all components except for one leads to a change in the specific extinction coefficients of the one in terms of their concentration and extinction of unknown component to approximate the output of the first arithmetic circuit to the extinction of the one component whose concentration and extinction are unknown and the known absorbances of the remaining components.

The device according to the invention is particularly preferably used when determining the coefficients of the linear combination of the components of an exhaust gas mixture consisting of two gases and smoke. The gases are in particular SO ₂ and NO ₂ .

With the device according to the invention, in particular, the not negligible wavelength dependency can also be achieved determine the extinction of the smoke in a simple way.

Since the determination of the coefficients of the linear combination depends on the concentration of the component, whose specific extinction coefficients are changed does not matter, fluctuations in the play Concentration of the gas in question or the dust or smoke that is blown up during the Measurement does not matter and does not falsify the measurement result.

The device according to the invention can be used directly on an exhaust chimney, however the absorbances of all components but one must be known. That is why it is preferred that, for example, a dust sample is taken from the chimney and placed in a test chamber is swirled around to which the device according to the invention is connected.

The coefficients of the linear combination determined with the device according to the invention can be used in one Read-only memory can be stored and used during the ongoing measurement.

With the device according to the invention, a zero adjustment can easily be carried out by it is determined whether at the end of a calibration process carried out by changing the switching elements, by deliberately induced changes in the respective component, the specific extinction coefficient of which is changed, that of the first

Calculation circuit determined the value of the extinction of the remaining known with regard to their concentration Components is still affected.

By the embodiment according to claim 2, it is possible to use the second computing circuit with several Devices to determine the extinction apply, in which they each for the time of determining the Coefficients of the linear combination is connected to the first arithmetic circuit. After the investigation the coefficients can be stored in a read-only memory and then represent the further operation of the device is continuously available.

In the simplest case, the switching elements are for changing the specific extinction coefficient Potentiometer at the input of the second computing circuit.

Further developments of the invention are the subject of the subclaims.

The invention is described below, for example, with reference to the drawing, the figure of which is a schematic block-like representation of a device for determining the extinctions of two gases and Shows smoke particles existing components of an exhaust gas mixture.

According to the drawing, an optical measuring device 12 is arranged on a chimney 13, which by two diametrically opposite openings of the chimney 13 sends a parallel bundle of light 18 which through e inen the retroreflector 14 arranged on the other side of the chimney is reflected back to the measuring device 12, where a suitably filtered photoreceiver receives the received signal at three different wavelengths determines if SO2, NO2 and smoke are measured these wavelengths are 313, 436 and 546 nm, respectively. In detail, the structure of the optical Measuring device with the subsequent electronic exit stages in DE-PS 25 21 934 described.

The optical measuring device 12 supplies the total extinction signals A 1, A ₂ and A i determined at the three measurement wavelengths to a first arithmetic circuit 11 . This arithmetic circuit 11 calculates from the three Gesamtextinktionswerten and six supplied by a read only memory 15 constant k \, O _2, Ar _3, fo, λ-5, and kt three for the concentrations of SO2, NO2 or smoke characteristic output signals E (SO ₂ ), E (NO2) and E (R). These can be displayed on numerical display instruments 19, 20 or 21, for example.

For the sake of simplicity, the three characteristics characteristic of the concentration are calculated Initial values under the following conditions:

1. The dependence of the extinction £ (NO ₂ ) and E (R) on the NO2 or smoke concentration \ tt linear.

_{2. Only the exhaust gas components SO 2} , NO ₂ and smoke absorb at wavelengths 313, 436 and 546 nm.

Furthermore, the output instruments 19, 20 and 21 do not immediately show the concentrations Q (SO2), C ₂ (NO2) or C ₃ (smoke), but rather absorbances, which are defined as follows:

(1) gives the extinction caused by SO ₂ only on the 313 nm line.

Zi (SO ₂ ) - / :,

/ ■ C

(1)

where E _{u is} the specific kxtincon of component j at wavelength i, I is the length of the total measurement path covered and C ₇ - is the concentration of component j.

£ (NO ₂ ) = E ₂₂ - I ■ C ₂ .

This indicates the extinction caused by NO ₂ on the line 436 nm.

E (R) = E ₃₃ - / - C ₃

This is the absorbance caused by the smoke on the 546 nm line

In practice, however, these extinctions are a measure of the three concentrations because of the linear relationship with Ci, C ₂ and C _{3 and the constant factors.} The three display devices 19, 20, 21 are expediently calibrated directly in concentrations. It can be shown that the three output values displayed by the measuring instruments 19, 20, 21 with the total absorbances A; at the three wavelengths are related as follows:

£ (S0 ₂ ) = Λ, + A-, ■ / I ₂ + As · A ₃
£ (NO ₂ ) = A ₃ * A ₂ + k, ■ A ₃

E (H) = A ₅ ■

The coefficients A :, of the measured three total absorbances A \ to A3 are functions of the specific smoke absorbance coefficients En and En. The specific extinction coefficients must be known in the conventional devices and used as constants.

For the example described, the following relationships result for the coefficients Αί to h:

(10)

(11)

A, - E \ 2 - E \ 3 E22 - E ₂₃ E22 - E _{23 E.} ? 22- £ 23 E22
1 -E ₂₃

E "- Ey

According to the drawing, only the specific smoke extinction coefficients En, £ 23 can be set on a potentiometer 22 or 23. The set voltages are fed to a second computing circuit 16 via an analog / digital converter 24, 25 in each case. The second arithmetic circuit 16 calculates coefficients iti to kf » from equations (7) to (11), the horizontal line being intended to express that the six coefficients can be varied by adjusting the potentiometers 22, 23.

In the first arithmetic circuit 11 the coefficients k \ to A ^ are combined with the total extinctions A], A ₂ and Ai according to equations (4), (5) and (6), so that the measuring instruments 19, 20 and

21 corresponding output values £ (SO ₂ ), £ (NO ₂ ) or. E (R) appear.

Now the optical measuring device 12 is installed in a test chimney in which a smoke sample (dust sample) filtered out of the smoke of the actual measuring chimney 13 is swirled around. The gases SOj and NO ₂ are not present in the test chimney, so that if the constants k \ to Jt _{6 were} chosen correctly, the instruments 19, 20 would have to show zero.

In fact, however, the instruments 19, 20 show a certain amount due to the cross-sensitivity Rash, especially because the extinction of the smoke depends on the wavelength. In particular the experiment shows that the spectral course of the extinction in smoke samples from different chimneys is different.

In the arrangement on the test chimney, the potentiometers 22, 23 are now adjusted until the measuring instruments 19, 20 indicate the value zero. This is achieved in just a few adjustment steps that take place one after the other. The coefficients Jti to fo now have the correct value and can be written into the read-only memory 15 via the line 17.

The first computing circuit 11 with the read-only memory 15 and the optical measuring device 12 is now installed on the actual measuring chimney 13, the coefficients k 1 to k t, once determined in the preliminary test, being constantly available. After the connections with the read-only memory 15 and the first arithmetic circuit 11 have been broken, the second arithmetic circuit 16 can be used for calibrating another device.

If in the actual measuring chimney with fluctuations in the wavelength dependence of the smoke must be expected, the test measurement can be repeated from time to time, for example by removing dust collected from the smoke and used with the apparatus described to correct the Jt ^ values.

One could also use a closed balancing control loop create, in which the analog output voltage of the first arithmetic circuit 11 as the actual value is used. In the same way, a purely digital control loop could also be set up analogously by the digital output variables of the first computing circuit 11 are used as the actual value.

The device described can also be used alone on the measuring chimney if the concentration of the smoke and the gases of interest can be determined with sufficient accuracy in another way. The unknown extinction coefficients E, j are then also changed here until the known extinctions or concentrations are displayed. Furthermore, the device can also be used to adjust the coefficients in analysis devices to determine the concentration of liquid or solid substances. In this case, the measuring section is not a chimney but z. B. a cuvette.

The functional units shown in the drawing that are additionally required for the coefficient adjustment 16, 22, 23, 24, 25 or the corresponding functional units in closed balancing control loops can be permanently arranged in the optical measuring device, in particular the first and second Computing circuit 11, 16 be combined in one functional unit.

Instead of the coefficients E /, the ratios of E, j of one and the same material components can also be changed. The equation coefficients k are calculated accordingly in the above example with three material components as follows:

(12)

A ₄ = -

A ₅ = -

£ 23 £ 22 E? J E _n £ j2 £ 33 En En £ 23
£, 3 £ 22
£, 2 Ε » £ 23 £ 22 E ₂₂
£ 33 £ 33 £ 32 £ 23 £ 23 £ 22
£ 33 £ 32 £ 23 £ 22 £ 33 £ 23
i £ 33 £ 23
£ 32 £ 22 £ 33 £ 23

(13)

(14)

(15)

(16)

It should be noted that often only the ratios of the extinction coefficients Ey of a material component are determined as pure numbers, not their absolute values with a physical dimension. It is therefore advisable to set an extinction coefficient of each substance component equal to 1.

When using multipliers, the range of values of the extinction coefficients Ey can be adapted to the ratios of the two measured substance components.

1 sheet of drawings

Claims (3)

Patent claims: 1. Device for determining the extinctions of various gases and possibly smoke particles existing components of an exhaust gas mixture with a) a device for measuring the total optical absorbance of the exhaust gas mixture a number of wavelengths corresponding to the number of components, b) a first arithmetic circuit to determine the Extinctions of the individual components based on one of the Lambert-Beer law derived, the absorbances as a linear combination of the total absorbance representing system of equations, characterized by c) a second computing circuit (16) for determining the coefficients (k ") of the linear combination from the specific extinction coefficient (Ey) of the components and for supplying the first computing circuit (II) with the determined coefficient of the linear combination, and d) Switching elements (22, 23) for changing the specific extinction coefficient (Ey) of one of the components used in the second arithmetic circuit (16). 2. Apparatus according to claim 1, characterized in that the second computing circuit (16) has detachable plug connections are connected to the first computing circuit (11). 3. Apparatus according to claim 1 or 2, characterized in that the switching elements are potentiometers (22,23) are.