CN104280355A - Detection device and detection method of ammonia gas and sulfur dioxide gas concentration - Google Patents

Abstract

The invention relates to a detection device and a detection method of ammonia gas and sulfur dioxide gas concentration. The device consists of an ultraviolet light source, a collimate lens, a runner, a gas absorption pool, a convergent lens, an ultraviolet optical fiber, a spectrograph and a computer. By adopting the detection device and the detection method, the problem that the FFT characteristic frequency peak values of the absorption spectrum of two gases interfere with each other can be solved. The detection device and the detection method have the advantages of not needing measurement on a gas absorption cross section and being simple in calculation, high in response speed and the like, the temperature and pressure do not need to correct the absorption cross section, the cost is low, and the stability is good.

Description

The pick-up unit of ammonia and concentration of SO 2 gas and detection method

Technical field

The present invention relates to pick-up unit and the detection method of gas concentration detection, particularly a kind of ammonia and concentration of SO 2 gas.

Background technology

Along with China's expanding economy, the consumption of electric power and coal is increasing, and thermal power generation can produce a large amount of oxides of nitrogen and sulphuric dioxide, works the mischief to environment, is therefore one of emphasis of national energy-saving and emission-reduction.General to coal-burning power plant's oxides of nitrogen reduction of discharging SCR (SCR) gas denitrifying technology.Wherein for the NH of denitration ₃escape is one of key index of this process control.For ammonia (NH ₃) detection of concentration, compared to traditional electrochemical method, optical method has noncontact, quick and sensitivity high, be widely used in the monitoring and measurement of industrial process and the continuous on-line monitoring etc. of industrial gas emission, as non-dispersion infrared analytic approach, Differential Optical Absorption Spectroscopy, tunable diode laser absorption spectroscopy method etc.A diode laser can only measure a kind of gas, and to detect multiple gases simultaneously, need to increase number of lasers, cost is high, is also difficult to integrated.Non-dispersion infrared analytic approach and Differential Optical Absorption Spectroscopy can be used for the measurement of multicomponent gas.

In first technology one, utilize non-dispersion infrared commercial measurement gas concentration, see " patent: non-dispersion infrared polycomponent flue gas analyzer [P] .2011 ".This device contains an optically filtering wheel, the infrared light of broadband (1 ~ 10 μm) is divided into multiple wave band by the multiple narrow band pass filters in filter wheel, the absorption of the corresponding a kind of gas of each wave band, infrared light is received by infrared eye through multiple reflectance cell, the treated concentration calculating various gas.The use of multiple reflectance cell adds absorption light path, improves precision, but the prerequisite that this technology uses is that each component gas absorbs without juxtaposition, and stability does not have Differential Optical Absorption Spectroscopy good.

In first technology two, utilize absorption cross section measure gas concentrations, see " patent: the portable unit and measuring method [P] .2008 that simultaneously monitor sulphuric dioxide and nitric oxide gas concentration ".This method is according to SO ₂with the absorption peak different characteristic of NO gas at two wave band places, measure SO ₂with NO gas concentration, SO ₂have obvious absorption peak at 200nm and 300nm wave band, and NO gas do not have absorption peak at 300nm wave band place.Concrete enforcement: first utilize 300nm wave band SO ₂the absorption line of gas calculates SO ₂gas concentration, then selects 200nm wave band and SO ₂there is an absorption peak (226nm) of the NO gas of overlapping absorbance, utilize the SO that the measurement of 300nm wave band obtains ₂the absorption line at concentration and 226nm place calculates NO gas concentration.This technology can be used for measuring SO ₂and NH ₃the concentration of mixed gas, but the absorption cross section needing measurement gas, and absorption cross section can change with factors such as temperature, pressures, accurately measuring needs the correction it being done to temperature and pressure, and computation process is complicated.

In first technology three, use Fourier transform measure gas concentrations, see " document: the application [J] of Fourier transform in difference absorption spectrum technical gas concentration calculates. spectroscopy and spectral analysis, 2008,28 (12): 2830-2834 ".This technology is to SO ₂, NO, NO ₂do Fourier transform etc. the absorption spectrum with characteristic quasi-periodicity, utilize the amplitude of characteristic frequency and the linear thus concentration of inverting gas of gas concentration.But when two kinds of gases are when absorption characteristic quasi-periodicity of the same band is identical or close, influencing each other of two kinds of gases will be very serious, the non-absolute periodic of absorption line due to two kinds of gases, the absorption of one side also can have contribution to the FFT peak value of the opposing party, the peak value at direct utilization FFT characteristic frequency place carrys out Simultaneous Inversion two kinds of gas concentrations by producing larger error, particularly at high SO ₂under gas concentration (5000 ~ 10000ppm), cannot accurately measure 200 ~ 230nm wave band and SO ₂the low NH having overlapping to absorb ₃the concentration (0 ~ 20ppm) of gas.

Summary of the invention

The object of the invention is to solve the above-mentioned deficiency in first technology, the absorption line of ammonia and sulfur dioxide gas is utilized to have the feature of quasi periodic rule, there is provided pick-up unit and the detection method of a kind of ammonia and concentration of SO 2 gas, the problem that the FFT characteristic frequency place peak value solving two kinds of gas absorption spectrum lines disturbs mutually.Without the need to measurement gas absorption cross section, calculate simple, can at high SO ₂accurately low NH is measured under gas concentration (5000 ~ 10000ppm) ₃gas concentration (0 ~ 20ppm).

Technical solution of the present invention is as follows:

A pick-up unit for ammonia and concentration of SO 2 gas, its feature is that this device is made up of ultraviolet source, collimation lens, runner, gas absorption cell, convergent lens, UV fiber, spectrometer and computing machine; The ultraviolet light sent along described ultraviolet source is nitrogen reference air chamber on described collimation lens, runner or ammonia reference air chamber, gas absorption cell, convergent lens, UV fiber successively, the output terminal of this UV fiber connects the receiving end of spectrometer, the input end of the output terminate computer of this spectrometer;

The ammonia concentration of described ammonia reference air chamber is 1000ppm ~ 2000ppm;

Described ultraviolet source is xenon lamp, deuterium lamp or halogen tungsten lamp, and the optical band of transmitting covers 185 ~ 400nm;

Utilize the pick-up unit of above-mentioned ammonia and concentration of SO 2 gas to detect the method for ammonia and concentration of SO 2 gas, its feature is that the method comprises the steps:

Step one, demarcation:

1) nitrogen is filled with at described gas absorption cell, described nitrogen reference air chamber is placed in light path by runner, ultraviolet source described in startup and computing machine, ultraviolet source sends ultraviolet light and after collimation lens, becomes directional light by nitrogen-rich gas reference air chamber, incide gas absorption cell, be coupled into through convergent lens focusing the receiving end that UV fiber is input to described spectrometer from the light of gas absorption cell outgoing, the computing machine described in data-signal input that spectrometer exports, computing machine obtains background light intensity I by software collection ₀(λ);

2) be filled with at described gas absorption cell the sulfur dioxide gas that concentration is 1000ppm, described ammonia reference air chamber is placed in light path by runner, ultraviolet source sends ultraviolet light and after collimation lens, becomes directional light by high concentration ammonia reference air chamber, incide gas absorption cell, be coupled into through convergent lens focusing the receiving end that UV fiber is input to described spectrometer from the light of gas absorption cell outgoing, the computing machine described in data-signal input that spectrometer exports, computing machine obtains the light intensity I after gas absorption by software collection ₁(λ);

3) computing machine carries out computing to data-signal, chooses the spectroscopic data of 195 ~ 225nm, according to Beer-Lambert law: I ₁(λ)=I ₀(λ) exp (-σ (λ) CL), σ (λ) is absorption cross section, and C is gas concentration, and L is absorption length, degree of being absorbed wherein i represents gas composition; Because object to be measured mostly is the potpourri of mixed gas and particle, so there is the impact of the absorption of water vapor, the response of CCD, Mie scattering, Rayleigh scattering factor, thus absorbance log is divided into and becomes D ' soon ₁(λ) He slowly D is become " ₁(λ) two parts:

D ₁(λ)＝D′ ₁(λ)+D″ ₁(λ)

$D_1^{\′}\left(\mathrm{\λ}\right)=L\underset{i}{\mathrm{\Σ}}{\mathrm{\σ}}_i^{\′}\left(\mathrm{\λ}\right)C_i,$

$D_1^{\′\′}\left(\mathrm{\λ}\right)=\underset{i}{\mathrm{\Σ}}[{\mathrm{\σ}}_{\mathrm{ib}}\left(\mathrm{\λ}\right)C_i+{\mathrm{\ϵ}}_R\left(\mathrm{\λ}\right)+{\mathrm{\ϵ}}_M\left(\mathrm{\λ}\right)]L,$

Wherein ε _r, ε _mrepresent rayleigh scattering coefficient and Mie scattering coefficient respectively, σ ' _iwith the fast-changing narrow-band absorption cross section of wavelength, σ _ibit is the wide band absorption cross section slowly changed with wavelength; To the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₁(λ) carry out five rank fitting of a polynomials, obtain fitting coefficient a ₁, b ₁, c ₁, d ₁, e ₁, f ₁, absorbance log change part is slowly expressed as:

D″ ₁(λ)＝a ₁λ ⁵+b ₁λ ⁴+c ₁λ ³+d ₁λ ²+e ₁λ+f ₁，

Difference Absorption degree D ' ₁(λ)=D ₁(λ)-D " ₁(λ), to the Difference Absorption degree D ' with quasi periodic rule ₁(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas

4) repeat step 2), 3), difference be described gas absorption cell be filled with successively concentration be 1500,2000,2500,3000,3500,4000,4500, the sulfur dioxide gas of 5000ppm, obtain the characteristic peaks of sulfur dioxide gas respectively

5) by the characteristic peaks of least square method to sulfur dioxide gas with the gas concentration of sulphuric dioxide carry out linear fit, obtain fitting coefficient m ₁, n ₁,

6) repeat step 2), 3), difference be described gas absorption cell be filled with concentration be respectively 2,4,6,8,10,12,14,16,18, the ammonia of 20ppm and the sulfur dioxide mixture gas of 1000ppm, by the characteristic peaks of least square method to ammonia with ammonia concentration carry out linear fit, obtain fitting coefficient m ₂, n ₂, described ammonia concentration

7) repeat step 6), difference be the concentration of sulphuric dioxide change 1500 successively into, 2000,2500,3000,3500,4000,4500,5000ppm, obtain the characteristic peaks of the ammonia under different sulfur dioxide concentration with ammonia concentration linear fit formula, described fitting coefficient m ₂with sulfur dioxide concentration approximate cubic function relation, obtains fitting coefficient p by cubic fit ₁, p ₂, p ₃, p ₄, described fitting coefficient n ₂with sulfur dioxide concentration linear approximate relationship, obtains coefficient q by linear fit ₁, q ₂, described fitting coefficient

Step 2, measurement:

1) repeat 2 in step one), 3), difference is filled with ammonia to be measured and sulfur dioxide mixture gas at described gas absorption cell, obtains the light intensity I after reference gas chamber ammonia, ammonia to be measured and sulfur dioxide mixture gas absorb ₂(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₂(λ), D ₂(λ)=D' ₂(λ)+D " ₂(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₂(λ) five rank fitting of a polynomials are carried out, D " ₂(λ)=a ₂λ ⁵+ b ₂λ ⁴+ c ₂λ ³+ d ₂λ ²+ e ₂λ+f ₂, obtain fitting coefficient a ₂, b ₂, c ₂, d ₂, e ₂, f ₂, Difference Absorption degree D' ₂(λ)=D ₂(λ)-D " ₂(λ), to the Difference Absorption degree D' with quasi periodic rule ₂(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas to be measured concentration of SO 2 gas is calculated by following formula

$C_{S{O}_2}=m_1{F}_{{\mathrm{SO}}_2}+n_1;$

2) 1 in step 2 is repeated), difference is: runner rotates 180 °, is switched to nitrogen reference air chamber, obtains the light intensity I after ammonia to be measured and sulfur dioxide mixture gas absorption ₃(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₃(λ), D ₃(λ)=D ' ₃(λ)+D " ₃(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₃(λ) five rank fitting of a polynomials are carried out, D " ₃(λ)=a ₃λ ⁵+ b ₃λ ⁴+ c ₃λ ³+ d ₃λ ²+ e ₃λ+f ₃, obtain fitting coefficient a ₃, b ₃, c ₃, d ₃, e ₃, f ₃, Difference Absorption degree D ' ₃(λ)=D ₃(λ)-D " ₃(λ), to the Difference Absorption degree D ' with quasi periodic rule ₃(λ) carry out Fourier transform, obtain the characteristic peaks of ammonia gas the concentration of ammonia is calculated by following formula

$C_{{\mathrm{NH}}_3}=m_2{F}_{{\mathrm{NH}}_3}+n_2.$

Technique effect of the present invention is as follows:

The present invention utilizes Fourier transformation method, add high concentration ammonia reference air chamber and nitrogen reference air chamber, and the switching both being realized by runner, with compared with first technology three, solve fourier transform method and can not measure two kinds of identical or close gases of absorption characteristic quasi-periodicity, overcome SO ₂and NH ₃the problem that the FFT characteristic frequency place peak value of two kinds of gas absorption spectrum lines disturbs mutually, can measure SO simultaneously ₂and NH ₃the concentration of gas, compared in first technology two Differential Optical Absorption Spectroscopy used, the present invention has without the need to measurement gas absorption cross section, calculates the advantages such as simple, fast response time, and without the need to revising absorption cross section with temperature and pressure, therefore cost is low, good stability.

Accompanying drawing explanation

Fig. 1 is the structured flowchart of the pick-up unit of ammonia of the present invention and concentration of SO 2 gas;

Fig. 2 is the absorption cross section of sulfur dioxide gas of the present invention at 183 ~ 227nm wave band;

Fig. 3 is the absorption cross section of ammonia of the present invention at 170 ~ 230nm wave band;

Fig. 4 is the FFT amplitude figure of ammonia of the present invention and sulfur dioxide mixture gas;

Fig. 5 is the measurement procedure figure of the method for the invention.

Embodiment

Below in conjunction with example and accompanying drawing, the present invention is further described, but be not limited thereto.

Embodiment one

Refer to Fig. 1, Fig. 1 is the structured flowchart of the pick-up unit of ammonia of the present invention and concentration of SO 2 gas, as seen from the figure, the pick-up unit of ammonia of the present invention and concentration of SO 2 gas is made up of ultraviolet source 1, collimation lens 2, runner 3, nitrogen reference air chamber 301, ammonia reference air chamber 302, gas absorption cell 4, convergent lens 5, UV fiber 6, spectrometer 7 and computing machine 8; The ultraviolet light that ultraviolet source 1 sends becomes directional light by the reference air chamber on runner 3 through collimation lens 2 and is incident to gas absorption cell 4, light output from gas absorption cell outgoing is coupled into UV fiber 6 by convergent lens 5, UV fiber 6 connects the receiving end of spectrometer 7, data-signal is transferred to computing machine 8 by spectrometer 7, computing machine 8 pairs of data-signals process, and are finally inversed by gas concentration.

The step of present embodiment is as follows:

Step one, demarcation:

1) nitrogen is filled with at described gas absorption cell 4, described nitrogen reference air chamber 301 is placed in light path by runner 3, ultraviolet source 1 described in startup and computing machine 8, ultraviolet source 1 sends ultraviolet light and after collimation lens 2, becomes directional light by nitrogen-rich gas reference air chamber 301, incide gas absorption cell 4, be coupled into through convergent lens 5 focusing the receiving end that UV fiber 6 is input to described spectrometer 7 from the light of gas absorption cell 4 outgoing, the computing machine 8 described in data-signal input that spectrometer 7 exports, computing machine 8 obtains background light intensity I by software collection ₀(λ);

2) be filled with at described gas absorption cell 4 sulfur dioxide gas that concentration is 1000ppm, described ammonia reference air chamber 302 is placed in light path by runner 3, ultraviolet source 1 sends ultraviolet light and after collimation lens 2, becomes directional light by high concentration ammonia reference air chamber 302, incide gas absorption cell 4, be coupled into through convergent lens 5 focusing the receiving end that UV fiber 6 is input to described spectrometer 7 from the light of gas absorption cell 4 outgoing, the computing machine 8 described in data-signal input that spectrometer 7 exports, computing machine 8 obtains the light intensity I after gas absorption by software collection ₁(λ);

3) computing machine 8 pairs of data-signals carry out computing, choose the spectroscopic data of 195 ~ 225nm, according to Beer-Lambert law: I ₁(λ)=I ₀(λ) exp (-σ (λ) CL), σ (λ) is absorption cross section, and C is gas concentration, and L is absorption length, degree of being absorbed wherein i represents gas composition; Because object to be measured mostly is the potpourri of mixed gas and particle, so there is the impact of the absorption of water vapor, the response of CCD, Mie scattering, Rayleigh scattering factor, thus absorbance log is divided into and becomes D ' soon ₁(λ) He slowly D is become " ₁(λ) two parts:

D ₁(λ)＝D′ ₁(λ)+D″ ₁(λ)

$D_1^{\′}\left(\mathrm{\λ}\right)=L\underset{i}{\mathrm{\Σ}}{\mathrm{\σ}}_i^{\′}\left(\mathrm{\λ}\right)C_i,$

$D_1^{\′\′}\left(\mathrm{\λ}\right)=\underset{i}{\mathrm{\Σ}}[{\mathrm{\σ}}_{\mathrm{ib}}\left(\mathrm{\λ}\right)C_i+{\mathrm{\ϵ}}_R\left(\mathrm{\λ}\right)+{\mathrm{\ϵ}}_M\left(\mathrm{\λ}\right)]L,$

Wherein ε _r, ε _mrepresent rayleigh scattering coefficient and Mie scattering coefficient respectively, σ ' _iwith the fast-changing narrow-band absorption cross section of wavelength, σ _ibit is the wide band absorption cross section slowly changed with wavelength; To the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₁(λ) carry out five rank fitting of a polynomials, obtain fitting coefficient a ₁, b ₁, c ₁, d ₁, e ₁, f ₁, absorbance log change part is slowly expressed as:

D″ ₁(λ)＝a ₁λ ⁵+b ₁λ ⁴+c ₁λ ³+d ₁λ ²+e ₁λ+f ₁，

Difference Absorption degree D ' ₁(λ)=D ₁(λ)-D " ₁(λ), to the Difference Absorption degree D ' with quasi periodic rule ₁(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas

4) repeat step 2), 3), difference be described gas absorption cell 4 be filled with successively concentration be 1500,2000,2500,3000,3500,4000,4500, the sulfur dioxide gas of 5000ppm, obtain the characteristic peaks of sulfur dioxide gas respectively

5) by the characteristic peaks of least square method to sulfur dioxide gas with the gas concentration of sulphuric dioxide carry out linear fit, obtain fitting coefficient m ₁, n ₁,

6) repeat step 2), 3), difference be described gas absorption cell 4 be filled with successively concentration be respectively 2,4,6,8,10,12,14,16,18, the ammonia of 20ppm and the sulfur dioxide mixture gas of 1000ppm, by the characteristic peaks of least square method to ammonia with ammonia concentration carry out linear fit, obtain fitting coefficient m ₂, n ₂, $C_{{\mathrm{NH}}_3}=m_2{F}_{{\mathrm{NH}}_3}+n_2;$

7) repeat step 6), difference be the concentration of sulphuric dioxide change 1500 successively into, 2000,2500,3000,3500,4000,4500,5000ppm, under obtaining different sulfur dioxide concentration, the characteristic peaks of ammonia with ammonia concentration linear fit formula, m ₂with sulfur dioxide concentration meet cubic function relation, obtain fitting coefficient p by cubic fit ₁, p ₂, p ₃, p ₄, n ₂with sulfur dioxide concentration meet linear relationship, obtain coefficient q by linear fit ₁, q ₂,

Step 2, measurement: refer to Fig. 5, Fig. 5 is the measurement procedure figure of the method for the invention.

1) repeat 2 in step one), 3), difference is filled with ammonia to be measured and sulfur dioxide mixture gas at described gas absorption cell 4, obtains the light intensity I after reference gas chamber ammonia, ammonia to be measured and sulfur dioxide mixture gas absorb ₂(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₂(λ), D ₂(λ)=D' ₂(λ)+D " ₂(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₂(λ) five rank fitting of a polynomials are carried out, D " ₂(λ)=a ₂λ ⁵+ b ₂λ ⁴+ c ₂λ ³+ d ₂λ ²+ e ₂λ+f ₂, obtain fitting coefficient a ₂, b ₂, c ₂, d ₂, e ₂, f ₂, Difference Absorption degree D' ₂(λ)=D ₂(λ)-D " ₂(λ), to the Difference Absorption degree D' with quasi periodic rule ₂(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas to be measured concentration of SO 2 gas is calculated by following formula

$C_{S{O}_2}=m_1{F}_{{\mathrm{SO}}_2}+n_1;$

2) 1 in step 2 is repeated), difference is: runner rotates 180 °, is switched to nitrogen reference air chamber 301, obtains the light intensity I after ammonia to be measured and sulfur dioxide mixture gas absorption ₃(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₃(λ), D ₃(λ)=D ' ₃(λ)+D " ₃(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₃(λ) five rank fitting of a polynomials are carried out, D " ₃(λ)=a ₃λ ⁵+ b ₃λ ⁴+ c ₃λ ³+ d ₃λ ²+ e ₃λ+f ₃, obtain fitting coefficient a ₃, b ₃, c ₃, d ₃, e ₃, f ₃, Difference Absorption degree D ' ₃(λ)=D ₃(λ)-D " ₃(λ), to the Difference Absorption degree D ' with quasi periodic rule ₃(λ) carry out Fourier transform, obtain the characteristic peaks of ammonia gas the concentration of ammonia is calculated by following formula

$C_{{\mathrm{NH}}_3}=m_2{F}_{{\mathrm{NH}}_3}+n_2.$

The principle that pick-up unit of the present invention is measured ammonia and sulfur dioxide concentration is as follows:

Composition graphs 2,3,4 illustrates principle of work of the present invention, after the ultraviolet light that ultraviolet source sends is absorbed by ammonia and sulfur dioxide mixture gas, occur that shock absorption is composed at 195 ~ 225nm wave band, this absorbs generation jointly due to ammonia and sulphuric dioxide, interval between this wave band sulphuric dioxide two absorption peak is about 1.6 ~ 1.8nm, and the interval between ammonia two absorption peak is about 3.6 ~ 3.8nm.Therefore we can be absorbed by the periodic oscillation of ultraviolet light wave band near 200nm and do Fast Fourier Transform (FFT) (FFT) to its characteristic absorption spectrum data, because the cycle of two kinds of gas absorption spectrum lines is different, there will be different characteristic peaks, as shown in Figure 4.And when a kind of gas concentration is fixing time, the characteristic peaks of another gas FFT and gas concentration are good linear relationship.

This method Main Basis is Beer-Lambert law:

I(λ)＝I ₀(λ)exp(-σ(λ)CL)

Wherein I ₀(λ) be background light intensity, I (λ) is the light intensity after gas absorption, and σ (λ) is absorption cross section, and C is gas concentration, and L is absorption length.

Because object to be measured mostly is the potpourri of mixed gas and particle, so there is the impact of the absorption of water vapor, the factor such as response, Mie scattering, Rayleigh scattering of CCD, thus absorption cross section is divided into two parts, and one is with wavelength fast-changing narrow-band absorption cross section σ ' _i, two is the wide band absorption cross section σ slowly changed with wavelength _ib, σ _i=σ ' _i+ σ _ib, so do following correction to above formula:

$I\left(\mathrm{\λ}\right)=I_0\left(\mathrm{\λ}\right)\exp \left\{\underset{i}{\mathrm{\Σ}}\right[(-{\mathrm{\σ}}_i\left(\mathrm{\λ}\right)C_i)+{\mathrm{\ϵ}}_R\left(\mathrm{\λ}\right)+{\mathrm{\ϵ}}_M\left(\mathrm{\λ}\right)]L)$

Above formula can be reduced to:

$I\left(\mathrm{\λ}\right)=I_0^{\′}\left(\mathrm{\λ}\right)\exp [\underset{i}{\mathrm{\Σ}}-{\mathrm{\σ}}_i^{\′}\left(\mathrm{\λ}\right)C_{i}L]$

Wherein $I_0^{\′}\left(\mathrm{\λ}\right)=I_0\exp \left\{\underset{i}{\mathrm{\Σ}}\right[(-{\mathrm{\σ}}_{\mathrm{ib}}\left(\mathrm{\λ}\right)C_i)+{\mathrm{\ϵ}}_R\left(\mathrm{\λ}\right)+{\mathrm{\ϵ}}_M\left(\mathrm{\λ}\right)]L)$

I ₀' (λ) represent the slow change part of absorption spectrum with wavelength, ε _r, ε _mrepresent rayleigh scattering coefficient and Mie scattering coefficient respectively.Definition Difference Absorption degree:

$D^{\′}\left(\mathrm{\λ}\right)=\ln (I_0^{\′}\left(\mathrm{\λ}\right)/I\left(\mathrm{\λ}\right))=L\underset{i}{\mathrm{\Σ}}{\mathrm{\σ}}_i\left(\mathrm{\λ}\right)C_i$

Illogical mixed gas to be measured, the Difference Absorption degree after high concentration ammonia is:

$D_1^{\′}\left(\mathrm{\λ}\right)={\mathrm{L\σ}}_{\mathrm{NH}3}\left(\mathrm{\λ}\right)C_{\mathrm{NH}3}^H$

The Difference Absorption degree passed into after ammonia to be measured and sulfur dioxide mixture gas is:

$\begin{array}{c}{D}_2^{\′}\left(\mathrm{\λ}\right)=L[{\mathrm{\σ}}_{\mathrm{NH}3}\left(\mathrm{\λ}\right)C_{\mathrm{NH}3}^H+{\mathrm{\σ}}_{\mathrm{NH}3}\left(\mathrm{\λ}\right)C_{\mathrm{NH}3}^L+{\mathrm{\σ}}_{\mathrm{SO}2}\left(\mathrm{\λ}\right)C_{\mathrm{SO}2}]\\ =L[{\mathrm{\σ}}_{\mathrm{NH}3}\left(\mathrm{\λ}\right)(C_{\mathrm{NH}3}^H+C_{\mathrm{NH}3}^L)+{\mathrm{\σ}}_{\mathrm{SO}2}\left(\mathrm{\λ}\right)C_{\mathrm{SO}2}]\end{array}$

Wherein, σ _nH3, σ _sO2be respectively the absorption cross section of ammonia and sulphuric dioxide, c _sO2be respectively reference air chamber high concentration ammonia, low concentration ammonia to be measured and concentration of SO 2 gas to be measured.Because ammonia reference air chamber is equipped with the ammonia (1000 ~ 2000ppm) of high concentration, and ammonia concentration to be measured lower (0 ~ 20ppm), namely so ammonia concentration to be measured can be ignored, obtain the Difference Absorption degree of sulphuric dioxide:

D _SO2'(λ)＝D ₂'(λ)-D ₁'(λ)＝σ _SO2(λ)C _SO2

According to the FFT characteristic peaks of sulfur dioxide gas under fixing ammonia concentration and the linear and fitting calibrating formula drawn of concentration of SO 2 gas calculate the concentration of sulphuric dioxide, wherein for SO to be measured ₂gas concentration, for sulfur dioxide gas FFT characteristic peaks, m ₁, n ₁be respectively slope and intercept that matching obtains.Switch nitrogen reference air chamber 301, i.e. known concentration of SO 2 gas, under fixing concentration of SO 2 gas the FFT characteristic peaks of ammonia and the concentration of ammonia linear, fitting formula is wherein for NH to be measured ₃gas concentration, for ammonia FFT characteristic peaks, m ₂, n ₂be respectively slope and intercept that matching obtains; The slope m finding the FFT characteristic peaks of ammonia and the linear relation of ammonia concentration is calculated by mass data ₂cubic function relation is met with sulfur dioxide concentration intercept n ₂linear relationship is met with sulfur dioxide concentration wherein p ₁, p ₂, p ₃, p ₄, q ₁, q ₂for fitting coefficient.Namely by demarcating, when obtaining concentration of SO 2 gas, the slope m of ammonia linear formula can just be calculated ₂with intercept n ₂, then can according to calibration formula according to the characteristic peaks of ammonia calculate the concentration of ammonia.

Claims (4)

1. a pick-up unit for ammonia and concentration of SO 2 gas, is characterized in that this device is made up of ultraviolet source (1), collimation lens (2), runner (3), gas absorption cell (4), convergent lens (5), UV fiber (6), spectrometer (7) and computing machine (8); The ultraviolet light sent along described ultraviolet source (1) is nitrogen reference air chamber (301) on described collimation lens (2), runner (3) or ammonia reference air chamber (302), gas absorption cell (4), convergent lens (5), UV fiber (6) successively, the output terminal of this UV fiber (6) connects the receiving end of spectrometer (7), the input end of the output terminate computer (8) of this spectrometer (7).

2. the pick-up unit of ammonia according to claim 1 and concentration of SO 2 gas, is characterized in that the ammonia concentration of described ammonia reference air chamber (302) is 1000ppm ~ 2000ppm.

3. the pick-up unit of ammonia according to claim 1 and concentration of SO 2 gas, is characterized in that described ultraviolet source (1) is xenon lamp, deuterium lamp or halogen tungsten lamp, and the optical band of transmitting covers 185 ~ 400nm.

4. utilize the pick-up unit of the ammonia described in claim 1 and concentration of SO 2 gas to detect the method for ammonia and concentration of SO 2 gas, it is characterized in that the method comprises the steps:

Step one, demarcation:

1) nitrogen is filled with at described gas absorption cell (4), described nitrogen reference air chamber (301) is placed in light path by runner (3), ultraviolet source (1) described in startup and computing machine (8), ultraviolet source (1) sends ultraviolet light and after collimation lens (2), becomes directional light by nitrogen-rich gas reference air chamber (301), incide gas absorption cell (4), be coupled into through convergent lens (5) focusing the receiving end that UV fiber (6) is input to described spectrometer (7) from the light of gas absorption cell (4) outgoing, the computing machine (8) described in data-signal input that spectrometer (7) exports, computing machine (8) obtains background light intensity I by software collection ₀(λ),

2) be filled with at described gas absorption cell (4) sulfur dioxide gas that concentration is 1000ppm, described ammonia reference air chamber (302) is placed in light path by runner (3), ultraviolet source (1) sends ultraviolet light and after collimation lens (2), becomes directional light by high concentration ammonia reference air chamber (302), incide gas absorption cell (4), be coupled into through convergent lens (5) focusing the receiving end that UV fiber (6) is input to described spectrometer (7) from the light of gas absorption cell (4) outgoing, the computing machine (8) described in data-signal input that spectrometer (7) exports, computing machine (8) obtains the light intensity I after gas absorption by software collection ₁(λ),

3) computing machine (8) carries out computing to data-signal, chooses the spectroscopic data of 195 ~ 225nm, according to Beer-Lambert law: I ₁(λ)=I ₀(λ) exp (-σ (λ) CL), σ (λ) is absorption cross section, and C is gas concentration, and L is absorption length, degree of being absorbed wherein i represents gas composition; Because object to be measured mostly is the potpourri of mixed gas and particle, so there is the impact of the absorption of water vapor, the response of CCD, Mie scattering, Rayleigh scattering factor, thus absorbance log is divided into and becomes D ' soon ₁(λ) He slowly D is become " ₁(λ) two parts:

D ₁(λ)＝D′ ₁(λ)+D″ ₁(λ)

Wherein ε _r, ε _mrepresent rayleigh scattering coefficient and Mie scattering coefficient respectively, σ ' _iwith the fast-changing narrow-band absorption cross section of wavelength, σ _ibit is the wide band absorption cross section slowly changed with wavelength; To the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₁(λ) carry out five rank fitting of a polynomials, obtain fitting coefficient a ₁, b ₁, c ₁, d ₁, e ₁, f ₁, absorbance log change part is slowly expressed as:

D″ ₁(λ)＝a ₁λ ⁵+b ₁λ ⁴+c ₁λ ³+d ₁λ ²+e ₁λ+f ₁，

Difference Absorption degree D ' ₁(λ)=D ₁(λ)-D " ₁(λ), to the Difference Absorption degree D ' with quasi periodic rule ₁(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas

4) repeat step 2), 3), difference be described gas absorption cell (4) be filled with successively concentration be 1500,2000,2500,3000,3500,4000,4500, the sulfur dioxide gas of 5000ppm, obtain the characteristic peaks of sulfur dioxide gas respectively

5) by the characteristic peaks of least square method to sulfur dioxide gas with the gas concentration of sulphuric dioxide carry out matching, obtain fitting coefficient m ₁, n ₁,

6) repeat step 2), 3), difference be described gas absorption cell (4) be filled with concentration be respectively 2,4,6,8,10,12,14,16,18, the ammonia of 20ppm and the sulfur dioxide mixture gas of 1000ppm, by the characteristic peaks of least square method to ammonia with ammonia concentration carry out linear fit, obtain fitting coefficient m ₂, n ₂, described ammonia concentration

7) repeat step 6), difference be the concentration of sulphuric dioxide change 1500 successively into, 2000,2500,3000,3500,4000,4500,5000ppm, obtain the characteristic peaks of the ammonia under different sulfur dioxide concentration with ammonia concentration fitting formula, described fitting coefficient m ₂with sulfur dioxide concentration approximate cubic function relation, obtains fitting coefficient p by cubic fit ₁, p ₂, p ₃, p ₄, described fitting coefficient n ₂with sulfur dioxide concentration linear approximate relationship, obtains coefficient q by matching ₁, q ₂, described fitting coefficient

Step 2, measurement:

1) repeat 2 in step one), 3), difference is filled with ammonia to be measured and sulfur dioxide mixture gas at described gas absorption cell (4), obtains the light intensity I after reference gas chamber ammonia, ammonia to be measured and sulfur dioxide mixture gas absorb ₂(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₂(λ), D ₂(λ)=D ' ₂(λ)+D " ₂(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₂(λ) five rank fitting of a polynomials are carried out, D " ₂(λ)=a ₂λ ⁵+ b ₂λ ⁴+ c ₂λ ³+ d ₂λ ²+ e ₂λ+f ₂, obtain fitting coefficient a ₂, b ₂, c ₂, d ₂, e ₂, f ₂, Difference Absorption degree D ' ₂(λ)=D ₂(λ)-D " ₂(λ), to the Difference Absorption degree D ' with quasi periodic rule ₂(λ) carry out Fourier transform, obtain the characteristic peaks of sulfur dioxide gas to be measured concentration of SO 2 gas is calculated by following formula

2) 1 in step 2 is repeated), difference is: runner rotates 180 °, is switched to nitrogen reference air chamber (301), obtains the light intensity I after ammonia to be measured and sulfur dioxide mixture gas absorption ₃(λ), computing machine carries out computing to the data-signal that spectrometer transmits, and obtains the absorbance log D absorbed through nitrogen reference air chamber and ammonia, sulfur dioxide mixture gas that wavelength is 195 ~ 225nm ₃(λ), D ₃(λ)=D ' ₃(λ)+D " ₃(λ), to the absorbance log D that the spectroscopic data by 195 ~ 225nm calculates ₃(λ) five rank fitting of a polynomials are carried out, D " ₃(λ)=a ₃λ ⁵+ b ₃λ ⁴+ c ₃λ ³+ d ₃λ ²+ e ₃λ+f ₃, obtain fitting coefficient a ₃, b ₃, c ₃, d ₃, e ₃, f ₃, Difference Absorption degree D ' ₃(λ)=D ₃(λ)-D " ₃(λ), to the Difference Absorption degree D ' with quasi periodic rule ₃(λ) carry out Fourier transform, obtain the characteristic peaks of ammonia gas the concentration of ammonia is calculated by following formula