RU2075066C1 - Process of determination of concentration of gases in gas mixture and gear for its implementation - Google Patents

Abstract

FIELD: gas analysis. SUBSTANCE: invention can be used for analysis of such gases as CO₂•SO₂NO and so on in gas mixture formed as result of burning of fuel in industrial plants, boilers of thermal power stations, boiler plants, etc. Process is carried out by reception of optical radiation passed through gas mixture with measurement and reference channels which number corresponds to number of sought-for gases in gas mixture. Spatial positions of optical inputs of measurement and reference channels for each sought-for gas is fixed during radiation reception in first time interval, then spatial positions of measurement and reference channels are so changed that optical inlet of measurement channel occupies spatial position of optical input of reference channel and vice versa. Then optical radiation passed through gas mixture during second measurement time interval is received and concentration of sought-for gas is determined by output signals of measurement and reference channels received during two time intervals. Spatial positions of optical inputs of measurement and reference channels are changed by attachment of photoelectric receivers of each channel to disc set on shaft of motor by their displacement through angular distance equal to 180 deg relative to each other. EFFECT: improved reliability of process and gear. 2 cl, 2 dwg

Description

The invention relates to techniques for gas analysis and can be used to determine the content of gases such as CO ₂ , SO ₂ , NO, etc. in a gas mixture resulting from the combustion of fuel in industrial plants, boilers of thermal power plants, boiler houses, etc.

 Currently, to determine the gas content in gas mixtures, a method is widely used based on passing optical radiation through a gas mixture, receiving optical radiation transmitted through the gas mixture at the absorption frequency of the optical radiation by the desired gas, and determining the concentration of the desired gas from the intensity of the received radiation using the Baire law (e.g. US Pat. No. 4,126,396, CL 356,434, and also cited below). To implement this method in the chimneys perform windows that are transparent to optical radiation in a wide frequency range. During operation, these windows are quickly contaminated, covered with soot and, as a result, lose their transparency. This leads to errors, for the elimination of which calibration is used in the pauses between radiation receptions in the measuring channels. Calibration of measurements is known for a reference gas placed in a tube installed in a chimney so that the input and output windows of the tube are not contaminated along the path of the optical radiation through the tube. These tubes are either periodically introduced into the volume of the gas mixture in the chimneys (US Pat. Nos. 4,247,2205, Cl. 356,438), or are installed permanently (US Pat. No. 4,583,859, Cl. 356,438). The device described in US Pat. No. 4,583,859 also uses window cleaning of the measurement channel by air flow. The main elements of the devices are a light source, an optically connected photoelectric receiver of the measuring channel, a photoelectric receiver of the calibration channel and a signal processing unit connected to the outputs of the photoelectric receivers. The disadvantage of these devices is associated with the complexity of using both movable and stationary calibration tubes in chimneys of large diameters.

 There is also a method of determining the concentration of gases in a gas mixture, including transmitting optical radiation through a gas mixture, simultaneously receiving optical radiation transmitted through the gas mixture by a photoelectric receiver of the measuring channel in the absorption frequency band of the desired gas and a photoelectric receiver of the reference channel in the frequency band that does not coincide with the absorption band of the desired gas, and determining the content of the desired gas from the output signals of the measuring and reference channels (German patent N 3512861, l. G 01 N 21/27).

 A device for implementing this method does not contain elements placed in the volume of the test gas. Its main elements are a light source, optically coupled photodetectors of at least one measuring and one reference channel, the outputs of which are connected to a ratiometric circuit. The photoelectric receiver of each channel contains a filter, a photodetector and an amplifier rigidly connected to it, and the number of channels is determined by the number of gases sought.

 The disadvantage of this method and device is the influence of uneven window contamination on the measurement result, since the filter and photodetector of the measuring channel and the filter and photodetector of the reference channel are spatially separated from each other.

 The technical problem solved by the invention is the development of such a method, which would eliminate the effect of window contamination on the measurement results when processing signals from the measuring and reference channels.

N концентрация искомого газа;

выходные сигналы измерительного и опорного каналов в первый интервал времени соответственно;

выходные сигналы измерительного и опорного каналов во второй интервал времени соответственно;
A калибровочный коэффициент;
s эффективное сечение поглощения искомого газа;
L длина слоя газовой смеси.To this end, a method for determining the concentration of gases in a gas mixture, including transmitting optical radiation through the gas mixture, simultaneously receiving the optical radiation transmitted through the gas mixture by the photoelectric receiver of the measuring channel in the absorption frequency band of the target gas and the photoelectric receiver of the reference channel in the frequency band that does not coincide with the frequency band absorption of the desired gas, and determination of the concentration of the desired gas from the output signals of the measuring and reference channels in accordance with retention is carried out in two time intervals, while the reception of optical radiation in the first time interval fixes the spatial position of the photoelectric receivers of the measuring and reference channels, the reception of optical radiation in the second time interval is carried out by mutually replacing the spatial position of the photoelectric receivers of the measuring and reference channels, and the concentration of the desired gas is determined by the formula

N is the concentration of the desired gas;

output signals of the measuring and reference channels in the first time interval, respectively;

output signals of the measuring and reference channels in the second time interval, respectively;
A calibration factor;
s effective absorption cross section of the desired gas;
L is the length of the gas mixture layer.

This method can be implemented using a device containing, as is known by German application N 3512861, a light source, optically coupled photoelectric detectors, at least one measuring and one reference channel and an information processing unit, wherein the photoelectric receiver of each channel includes filter rigidly connected to the photodetector and amplifier. In accordance with the invention, the filter and its corresponding photodetector of the measuring channel and the filter and its corresponding photodetector of the reference channel are mounted on a disk mounted on the motor shaft at an angular distance of 180 ^° from each other, while the information processing unit comprises an analog-to-digital converter connected in series and microprocessor, the engine is equipped with a control unit, which is connected through an microprocessor to an angle sensor, and the input of an analog-to-digital converter is connected to the outputs of the channels cut switch, the control input of which is connected to the microprocessor.

 Figure 1 shows a diagram of a device for determining the concentration of one of the desired gas in the gas mixture; figure 2 program of operation of this device.

The light source 1 is optically coupled to the photoelectric detector 2 of the measuring channel and the photoelectric receiver 3 of the reference channel through windows 4 transparent to the optical radiation, mounted in the walls of the chimney 5 of the industrial installation. The photoelectric receiver 2 of the measuring channel contains a filter 6 in the absorption band of the desired gas, a photodetector 7 and an amplifier 8. The photoelectric receiver 3 of the reference channel contains a filter 9, in the passband of which there is no absorption band of the desired gas, the photodetector 10 and amplifier 11. The filter and the corresponding him photodetector of each channel mounted on the disk 12 at an angular distance from each other equal to 180 ^o . The disk 12 is mounted on the shaft of an engine 13 provided with a control unit 14. The outputs of the amplifiers 8 and 11 are connected to the inputs of the switch 15, the output of which is connected to the input of the signal processing unit 16. The signal processing unit 16 has at the input an analog-to-digital converter ADC 17 and a microprocessor 18; the latter contains ALU 19, random access memory RAM 20, read-only memory ROM 21 and input / output ports PVV 22. Through port 22, the angle sensor 23 is connected to the motor control unit 14, the output of port 22 is also connected to the control input of the switch 15.

To determine the concentration of several gases in a gas mixture, the number of pairs consisting of a measuring and reference channels corresponds to the number of gases whose concentration is to be measured. In this case, the filters and the corresponding photodetectors of the measuring and reference channels of all pairs of channels are fixed on one disk so that the filter and the corresponding photodetector of the measuring and reference channels of each pair are offset from each other at an angular distance of 180 ^o .

The program of operation of the device is set by the microprocessor 18, in the ROM of which the calibration data of the measuring and reference channels are also entered: the intensities I _o and O _{c of the} optical radiation of the light source 1 in the passband of the filters of the reference and measuring channels of each channel pair and the calibration coefficients β _o and β _{c of the} reference and measuring channels, depending on attenuation of radiation by filters, sensitivity of photodetectors, amplification and conversion factors.

 On the presented device, the method is implemented as follows.

In the first measuring time interval, which corresponds to a certain spatial position of the optical inputs of the measuring and reference channels, i.e. filters 6, 9 and photodetectors 7, 10, the signals ¹ U _c = I _c α are received at the input of the ADC 17 through the switch 15 from the output of the amplifiers 8, 11 $\genfrac{}{}{0ex}{}{\text{c}}{\text{m}}$ β _c exp (-NsL) (α $\genfrac{}{}{0ex}{}{\text{c}}{\text{m}}$ attenuation of radiation due to the contamination of the windows 4 in the area corresponding to the spatial position of the optical input of the measuring channel) and ^I U _o = I _o α $\genfrac{}{}{0ex}{}{\text{o}}{\text{m}}$ β _o (α $\genfrac{}{}{0ex}{}{\text{o}}{\text{m}}$ - attenuation of radiation due to the contamination of the windows 4 in the area corresponding to the spatial position of the optical input of the reference channel). In the ADC 17, these signals are converted to digital and fed into RAM 20.

Then, according to the signal from the microprocessor 18, the switch 15 disconnects the output of the amplifiers 8 from the input of the ADC 17 and the engine 13 is turned on. The disk 12 is rotated and after turning it 180 ^° by the signal from the angle sensor 23, the engine 13 is turned off. As a result, the optical input of the measuring channel occupies the spatial position of the optical input of the reference channel and vice versa.

т.е. выходной сигнал измерительного канала ²U_c пропорционален ослаблению излучения из-за загрязненности окон 4, соответствующему пространственному положению оптического входа опорного канала α $\genfrac{}{}{0ex}{}{\text{o}}{\text{м}}$ в предыдущий измерительный интервал времени, а выходной сигнал опорного канала ²U_o пропорционален α $\genfrac{}{}{0ex}{}{\text{c}}{\text{м}}$ , соответствующему пространственному положению оптического входа измерительного канала в предыдущий измерительный интервал времени. После преобразования сигналов ²U_c, ²U_o в цифровую форму данные заносятся в ОЗУ 20.The second measuring time interval begins with the signal from the microprocessor 18 to the control input of the switch 15. At the input of the ADC 17 receives signals

those. the output signal of the measuring channel ² U _{c is} proportional to the attenuation of radiation due to the contamination of the windows 4 corresponding to the spatial position of the optical input of the reference channel α $\genfrac{}{}{0ex}{}{\text{o}}{\text{m}}$ in the previous measuring time interval, and the output signal of the reference channel ² U _{o is} proportional to α $\genfrac{}{}{0ex}{}{\text{c}}{\text{m}}$ corresponding to the spatial position of the optical input of the measuring channel in the previous measuring time interval. After converting the signals ² U _c , ² U _o into digital form, the data is entered in RAM 20.

концентрация N искомого газа равна

где

калибровочный коэффициент устройства.ALU 19 performs the operation of calculating the concentration of the desired gas according to the information entered in RAM 20 and ROM 21, using the Baire law: since

the concentration N of the desired gas is equal to

Where

calibration factor of the device.

 Thus, the introduction of a known method for determining the concentration of gas in a gas mixture, based on the use of two receiving channels (measuring and reference), the additional operation of receiving transmitted through the gas mixture of optical radiation with the mutual replacement of the spatial position of the optical inputs of the measuring and reference channel allows you to eliminate the effect of pollution windows on the measurement results by processing the output signals of the measuring and reference channels.

Claims (2)

1. A method for determining the concentration of gases in a gas mixture, including transmitting optical radiation through the gas mixture, simultaneously receiving the optical radiation transmitted through the gas mixture by the photoelectric receiver of the measuring channel in the absorption frequency band of the desired gas and the photoelectric receiver of the reference source in the frequency band that does not coincide with the frequency band absorption of the desired gas, and determining the concentration of the desired gas from the output signals of the measuring and reference channels, characterized in that optical radiation that has come through the gas mixture is carried out in two time intervals, while receiving at the first time interval, the spatial position of the photoelectric receivers of the measuring and reference channels is fixed, reception at the second time interval is carried out when the spatial position of the photoelectric receivers of the measuring and reference channels is mutually replaced, and the concentration the desired gas is determined by the formula

where N is the concentration of the desired gas;
¹ U _c , ¹ U _{o the} output signals of the measuring and reference channels in the first time interval, respectively;
² U _c , ² U _{o the} output signals of the measuring and reference channels in the second time interval, respectively;
A calibration factor;
S is the effective absorption cross section of the gas sought
L is the length of the gas mixture layer. 2. A device for determining the concentration of gases in a gas mixture containing a light source, optically coupled photoelectric detectors of at least one measuring and one reference channel, each of which includes a filter, a photodetector and amplifier rigidly connected to it, and an information processing unit, characterized in that the filter and the corresponding photodetector of the measuring channel and the filter and the corresponding photodetector of the reference channel are mounted on an angular distance mounted on the disk of the motor shaft uu from each other of 180 ^o, with the information processing unit comprises a series-connected analog-to-digital converter and a microprocessor, the motor provided with a control unit which, via a microprocessor coupled to the angle sensor and the output of analog-to-digital converter coupled to the outputs of the measuring and reference amplifiers channels through the switch, the control input of which is connected to the microprocessor.

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