CN102156112B - Flue gas flow velocity measuring device and method - Google Patents

Flue gas flow velocity measuring device and method Download PDF

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CN102156112B
CN102156112B CN 201110054000 CN201110054000A CN102156112B CN 102156112 B CN102156112 B CN 102156112B CN 201110054000 CN201110054000 CN 201110054000 CN 201110054000 A CN201110054000 A CN 201110054000A CN 102156112 B CN102156112 B CN 102156112B
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light
flue gas
flue
flow velocity
kappa
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CN102156112A (en
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董凤忠
杨阳
倪志波
庞涛
张志荣
吴边
曾宗泳
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Anhui Institute of Optics and Fine Mechanics of CAS
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Abstract

The invention discloses a flue gas flow velocity measuring device and method. The flue gas flow velocity measuring device comprises two groups of light emitting systems and light receiving systems which are respectively arranged at two sides of a flue, wherein each light emitting system comprises an LED light source and a collimating lens located on an exiting light path of the LED light source; each light receiving system comprises a focusing lens and a photoelectric detector located on a transmittance light path of the focusing lens; light beams emitted by the LED light source are collimated to parallel light beams through the collimating lens and then to pass through the flue, then the parallel light beams are received by the focusing lens and sent to the photoelectric detector; and a digital display is connected outside the photoelectric detector through a data processing system. In the invention, a high frequency flash signal caused by temperature fluctuation can be measured, and a low frequency flash signal caused by smoke dust concentration fluctuation can also be processed at the same time; a light flash signal can be obtained under the condition that the turbulent flow of a flue refractive index is very weak (light velocity and flow meters can not be adopted); and the flue gas flow velocity measuring device has the characteristics of high measurement precision, non-interference, convenience for installation, broader application range and the like.

Description

Flue gas flow rate measuring instrument and measuring method
Technical field
The present invention relates to the pipe flow speed field of measuring technique, be specifically related to a kind of flue gas flow rate measuring instrument and measuring method.
Background technology
Particle has very serious harm to every field such as human health, commercial production, ecologic environments.And to control, administer pollution, and must carry out the on-line continuous monitoring to the pollutant emission of industrial enterprise, particle concentration and the total emission volumn that discharges carried out Measurement accuracy.In the fume emission monitoring instrument, the instrument of measuring smoke gas flow speed and particle concentration is a lot, wherein adopting the measurement of optical flare method is a kind of monitoring method with advantage, and it has adopted the optical flare technology of non-intervention type to measure simultaneously flue gas flow rate and particle concentration.Because its non-invasi, reduced maintaining time, increased serviceable life, and can be in very extreme situation, use in the environment such as explosive, high temperature, compare with the light decay subtraction, also have simple in structure, the advantage of stable performance.
U.S. OSI(Optical Scientific Inc.) be the producer of external unique production optics flow sensor (OFS), American National Environmental Protection Administration approved is with the technical standard of OFS as fluid-velocity survey, and the optics velocimeter of its production has been widely used in the monitoring of factory's gas pollutant discharging.This optics velocimeter adopts the structure of single light source, double detector, and the Receiver aperture diameter is a centimetre magnitude, the about 2cm of two hole centre distances.According to existing theoretical, the characteristic frequency of the optical flare that measures equals the ratio of flue gas flow rate and receiver lens diameter.Suppose flue gas flow rate at 10m/s, then move the characteristic frequency of the flicker that causes 10 by particle 3About Hz, uniformity of temperature profile in smoke gas flow, in the very weak situation of refractive index fluctuation, the OFS velocimeter is measured less than flow velocity.Because two receiver lenss distance is too near, can not utilize that frequency is lower, the scale dependent flue gas concentration of large (suitable with the diameter of the flue) optical flare that rises and falls and cause.
On the measuring method based on particle Extinction Characteristic optical flare that stochastic distribution causes, many the units such as domestic Tsing-Hua University, Zhejiang University, Shanghai University of Science and Technology have all carried out the research of similar work, but also there is larger defective in actual applications in their work, its reason mainly contains three: 1) when too many through the particle of light beam, the optical flare signal very a little less than, can not measure when namely dust concentration is too high; 2) few in order to make through the particle of light beam, must adopt laser beam measuring, and the noise of laser is in standard deviation that the 0.01(relative light intensity rises and falls) about, so dust concentration can not measure the optical flare signal when low.3) in principle, the method has a fatal weakness: flicker is consistent to the characteristic frequency that is had by the flicker of particle stochastic distribution with refractive index (temperature), and is all relevant with the ratio of beam diameter with flow velocity.Therefore unlikely refractive index is glimmered therefrom deducted, and can not get accurately dust concentration, is a kind of method that lacks of prospects.
Summary of the invention
The purpose of this invention is to provide a kind of flue gas flow rate measuring instrument and measuring method, simple crosscorrelation when propagating in flue gas based on two-beam and the design of optical flare effect, actual conditions according to smoke gas flow, can in a big way, change two distances that receive between pupil, increase the ability of processing the low frequency optical flare signal that rises and falls because of dust concentration, the flow velocity of surveying is the arithmetic mean on the light path, is easy to accurately calculate discharge capacity.
Technical scheme of the present invention is as follows:
A kind of flue gas flow rate measuring instrument, it is characterized in that: include light emission system and optical receiver system that two components are located at the flue both sides, wherein light emission system includes led light source and the collimation lens that is positioned on the led light source emitting light path, optical receiver system includes condenser lens and the photodetector that is positioned on the condenser lens transmitted light path, the light beam that described led light source sends passes flue after the collimation lens collimation is for parallel beam, receive and send into photodetector by condenser lens again; Described photodetector is by the external digital indicator of data handling system.
A kind of flue gas flow rate measuring method, it is characterized in that: it specifically may further comprise the steps: in the both sides of flue two groups of light emission systems and optical receiver system are installed respectively, wherein light emission system includes led light source and the collimation lens that is positioned on the led light source emitting light path, optical receiver system includes condenser lens and the photodetector that is positioned on the condenser lens transmitted light path, photodetector is by the external digital indicator of data handling system, the light beam that led light source sends passes flue after the collimation lens collimation is for parallel beam, receive and send into photodetector by condenser lens again, photodetector is transformed into electric signal with the light signal of sending into, then be sent to data handling system and carry out filtering, the time-variable data of logarithm light intensity is processed and is obtained in detection and amplification, calculate at last the flow velocity of flue gas in flue and the particle concentration in the flue gas, and send the flow velocity of flue gas and the particle concentration information in the flue gas to digital indicator and show.
Described flue gas flow rate measuring instrument is characterized in that: described led light source is driven by constant current source.
Described flue gas flow rate measuring instrument is characterized in that: the front end of described condenser lens is equipped with dust cover.
The present invention has used the split-type structural of two light sources, double detector, can change according to the actual conditions of flue two distances that receive between pupil in a big way.
The present invention has increased the ability of processing the low frequency optical flare that causes because of the dust concentration fluctuating, can measure the optical flare signal in the very faint situation of uniformity of temperature profile, refractive index fluctuation.
The present invention adopts large-power light-emitting diodes, and the small-bore transmits and receives, and is smoothly little to the flash signal aperture, thereby increased the reliability of measuring flow velocity when flash signal is weak.
The simple crosscorrelation expression formula that receives two ways of optical signals is
(1)
In the formula, K 0Be the space wave number in the flue, v (z) be flow velocity,
Figure 2011100540006100002DEST_PATH_IMAGE006
Be the mean distance between two light beams,
Figure 2011100540006100002DEST_PATH_IMAGE008
For time delay, L are that beam Propagation distance, k are the light wave numbers, transmit and receive the aperture and use respectively
Figure DEST_PATH_IMAGE010
With
Figure DEST_PATH_IMAGE012
Expression,
Figure DEST_PATH_IMAGE014
,
Figure DEST_PATH_IMAGE016
Respectively zeroth order and single order Bessel function,
Figure DEST_PATH_IMAGE018
It is the spectrum of refractive index imaginary part.Utilize the cross correlation function curve, be easy to calculate flow velocity, for example for maximum cross correlation, satisfy condition time delay
Figure DEST_PATH_IMAGE020
(2)
Can calculate mean flow rate thus.By the weights function that formula (1) is derived, the flow velocity that is easy to prove measurement is the arithmetic mean on the light path, therefore than the discharge capacity of the easier calculating flue gas of OFS velocimeter.
Experience shows: logarithm light intensity fluctuation standard deviation
Figure DEST_PATH_IMAGE022
With particle mean concentration m 0Satisfy relation
Figure DEST_PATH_IMAGE024
(3)
Therefore, providing calibration coefficient with weight method
Figure DEST_PATH_IMAGE026
After, be easy to obtain mean concentration m 0
Beneficial effect of the present invention:
(1), the present invention take through the LED of high frequency modulated as light source, light arrives optical receiver system after flue is propagated, the arrival photodetector carries out opto-electronic conversion after being focused lens focus, and electric signal enters data processing equipment after signal processing circuit, and measuring accuracy is high.
(2), the present invention has used the split-type structural of two light sources, double detector, based on the space correlation yardstick of the flue dust optical flare characteristics much larger than refractive index flicker scale dependent, can in a big way in, change according to the actual conditions of flue the distances between two reception pupils.
(3), the present invention not only can measure the high frequency flicker that is caused by temperature fluctuation, can also be according to the needs of industry spot, the low frequency optical flare signal that causes that processing rises and falls because of dust concentration, in the time of can measuring uniformity of temperature profile, there is particle concentration to change the flicker that causes in the very faint situation of refractive index fluctuation.
(4), the measured flow velocity of the present invention, be the arithmetic mean on the light path, easier calculating for smoke discharge amount, and measurement result is more accurate.
(5), the present invention adopts large-power light-emitting diodes, the small-bore transmits and receives, and is little to the flash signal decay, thereby increased the reliability of weak flash signal time institute velocity measurement.
Description of drawings
Fig. 1 is the structural representation of light emission system of the present invention.
Fig. 2 is the structural representation of optical receiver system of the present invention, and wherein the figure (a) and (b) are respectively the structural drawing of the optical receiver system under two different angles.
Fig. 3 is structure principle chart of the present invention.
Fig. 4 is data processor surface chart of the present invention.
Embodiment
Referring to Fig. 1,2,3, a kind of flue gas flow rate measuring instrument, include two components and be located at light emission system and the optical receiver system of flue both sides, wherein light emission system includes led light source 2 and the collimation lens 3 that is positioned on led light source 2 emitting light paths, optical receiver system includes condenser lens 5 and the photodetector 6 that is positioned on condenser lens 5 transmitted light paths, the light beam that led light source 2 sends passes flue after collimation lens 3 collimations are for parallel beam, receive and send into photodetector by condenser lens 5 again; Photodetector is by the external digital indicator 9 of data handling system.
Led light source 2 is driven by constant current source 1; The front end of condenser lens 5 is equipped with dust cover 4.
A kind of flue gas flow rate measuring method, specifically may further comprise the steps: in the both sides of flue two groups of light emission systems and optical receiver system are installed respectively, wherein light emission system includes led light source and the collimation lens that is positioned on the led light source emitting light path, optical receiver system includes condenser lens and the photodetector that is positioned on the condenser lens transmitted light path, photodetector is by the external digital indicator of data handling system, the light beam that led light source sends passes flue after the collimation lens collimation is for parallel beam, receive and send into photodetector by condenser lens again, photodetector is transformed into electric signal with the light signal of sending into, then be sent to data handling system and carry out filtering, the time-variable data of logarithm light intensity is processed and is obtained in detection and amplification, calculate at last the flow velocity of flue gas in flue and the particle concentration in the flue gas, and send the flow velocity of flue gas and the particle concentration information in the flue gas to digital indicator and show.
The present invention is further illustrated below in conjunction with accompanying drawing:
Led light source 2 is driven by constant current source 1, and light intensity can be regulated by potentiometer.Light beam has passed through the preliminary collimation of collimation lens 3 before entering flue, led light source 2 is adjustable to the distance between the collimation lens 3.Whole led light source has the advantages such as stabilized intensity, volume is little, quality is light, can be directly installed on the flue outer wall by flange.
Light beam enters optical receiver system through flue is laggard, focuses on the photodetector 6 through being focused lens 5 behind the dustproof window 4, and the useful detection area of photodetector 6 is 5*5mm 2, the spot diameter after the focusing is 1.5mm.7 pairs of signals of circuit board carry out preposition amplification and bandpass filtering, and the filter center frequency is consistent with modulating frequency.8 pairs of flash signals of circuit board are processed, and comprise detection, filtering and amplification, guarantee only signal to be amplified, and ground unrest is not affected substantially, have improved signal to noise ratio (S/N ratio).Can be directly show at the digital indicator 9 of receiving system tail end through the electric signal of circuit board 8, so that regulate in real time led light source intensity, avoid occuring saturated, can utilize 16 capture cards to gather to computing machine simultaneously, carry out that real-time data are processed and calculating.In the data handling procedure, can adopt two kinds of patterns of single step collection and continuous acquisition, and can regulate as required at any time sample frequency, mean time, level and smooth point, interpolation point and average time, with real-time being presented on the screen of the result of calculation of flue gas flow rate and particle concentration, increased the dirigibility that data are processed.
During experiment, two led light sources are installed in a side of flue, and both lines are parallel with the flow of flue gas direction.Optical receiver system lays respectively at the right opposite of two light sources.Behind the light signal process flue that the led light source of path one end sends, the detection system that enters the other end.Because through collimation, its light beam can not enter another detection system except its opposite to light source.
Concrete measuring principle is as follows:
The double light path correlation flue gas flow rate and the measuring concentration of granules in certain system that utilize the present invention to propose are divided into real part and imaginary part two parts with refractive index, derive as can be known according to theory, and particle concentration changes the light intensity fluctuation related function that causes and can be expressed as:
Figure 844448DEST_PATH_IMAGE002
Figure 951469DEST_PATH_IMAGE004
(1)
In the formula, K 0Be the space wave number in the flue, v (z) be flow velocity,
Figure 668889DEST_PATH_IMAGE006
Be the mean distance between two light beams,
Figure 251049DEST_PATH_IMAGE008
For time delay, L are that beam Propagation distance, k are the light wave numbers, transmit and receive the aperture and use respectively
Figure 3105DEST_PATH_IMAGE010
With
Figure 12518DEST_PATH_IMAGE012
Expression,
Figure 217234DEST_PATH_IMAGE014
,
Figure 603085DEST_PATH_IMAGE016
Respectively zeroth order and single order Bessel function,
Figure 399527DEST_PATH_IMAGE018
It is the spectrum of refractive index imaginary part.Utilize the cross correlation function curve, be easy to calculate flow velocity, for example for maximum cross correlation, satisfy condition time delay
Figure 330574DEST_PATH_IMAGE020
(2)
Can calculate mean flow rate thus.By the weights function that formula (1) is derived, the flow velocity that is easy to prove measurement is the arithmetic mean on the light path, therefore than the discharge capacity of the easier calculating flue gas of OFS velocimeter.
Experience shows: logarithm light intensity fluctuation standard deviation
Figure 271854DEST_PATH_IMAGE022
With particle mean concentration m 0Satisfy relation
Figure 946549DEST_PATH_IMAGE024
(3)
Therefore, providing calibration coefficient with weight method
Figure 656885DEST_PATH_IMAGE026
After, be easy to obtain mean concentration m 0

Claims (1)

1. flue gas flow rate measuring method, it is characterized in that: it specifically may further comprise the steps: in the both sides of flue two groups of light emission systems and optical receiver system are installed respectively, wherein light emission system includes led light source and the collimation lens that is positioned on the led light source emitting light path, optical receiver system includes condenser lens and the photodetector that is positioned on the condenser lens transmitted light path, photodetector is by the external digital indicator of data handling system, the light beam that led light source sends passes flue after the collimation lens collimation is for parallel beam, receive and send into photodetector by condenser lens again, photodetector is transformed into electric signal with the light signal of sending into, then be sent to data handling system and carry out filtering, the time-variable data of logarithm light intensity is processed and is obtained in detection and amplification, calculate at last the flow velocity of flue gas in flue and the particle concentration in the flue gas, and send the flow velocity of flue gas and the particle concentration information in the flue gas to digital indicator and show; Refractive index is divided into real part and imaginary part two parts, derives as can be known according to theory, particle concentration changes the light intensity fluctuation related function that causes and can be expressed as:
C ( ρ , τ ) = 4 π 2 k 2 ∫ 0 ∞ d κ 0 ∫ 0 L dz S nl ( κ 0 ) cos 2 [ κ 0 2 ( L - z ) 2 kL ] J 0 [ κ 0 ( ρ - v ( z ) τ )
× [ 2 J 1 ( D r κ 0 z / 2 L ) D r κ 0 z / 2 L ] 2 [ 2 J 1 ( D t κ 0 ( L - z ) / 2 L ) D t κ 0 ( L - z ) / 2 L ] 2 - - - ( 1 )
In the formula, K 0Be the space wave number in the flue, v (z) is that flow velocity, ρ are the mean distance between two light beams, and τ is that time delay, L are that beam Propagation distance, k are the light wave numbers, transmit and receive the aperture and use respectively D tAnd D rExpression, J 0, J 1Respectively zeroth order and single order Bessel function, S Nl(κ 0) be the spectrum of refractive index imaginary part, utilize the cross correlation function curve, calculate flow velocity, for maximum cross correlation, satisfy condition time delay
ρ - v ( z ) ‾ × τ p = 0 - - - ( 2 )
Can calculate mean flow rate thus; By the weights function that formula (1) is derived, prove that the flow velocity of measuring is the arithmetic mean on the light path, therefore than the discharge capacity of the easier calculating flue gas of OFS velocimeter;
Experience shows: logarithm light intensity fluctuation standard deviation β IWith particle mean concentration m 0Satisfy relation
β I＝α·m 0 (3)
Therefore, after providing calibration coefficient α with weight method, obtain mean concentration m 0
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