Patent ID: 12241790

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be further described below with reference to the accompanying drawing and embodiments:

1. Composition of an Image Detector

With a common color industrial camera as an example, a flame image detector is formed by arranging a dual-narrow-band pass color filter in front of a camera sensor in combination with a long lens rod. Two central wavelengths λRand λGof the dual-narrow-band pass color filter are located near peaks of spectral response curves of R and G channels of the industrial camera respectively, and a half bandwidth is less than 20 nm, so as to cooperate with the camera to obtain an approximate monochromatic flame image with a high signal-to-noise ratio.

2. Arrangement Forms of Image Detectors and a Spectrometer

As shown inFIG.1, four image detectors200-1,200-2,200-3and200-4are arranged at observation holes on the same layer of a furnace, the image detectors200-1,200-2,200-3and200-4are perpendicular to an external facade of the furnace and penetrates a certain distance inside a water-cooled wall to obtain a better field of view. The four image detectors200-1,200-2,200-3and200-4are connected to a gigabit network switch via gigabit network cables, and then communicate with a computer300equipped with control software via the gigabit network switch. The fiber optic spectrometer100is bundled together with any one of the image detectors200-1,200-2,200-3and200-4, and communicates with the computer300via a USB data line400, and a collimating lens500is disposed at the front end of an optical fiber600, and perpendicular to the external facade of the furnace.

3. Reconstruction of a Cross-Section Temperature Field

1) The image detectors and the spectrometer respectively acquire flame radiation images and spectra inside the furnace synchronously.

2) A ratio ελG/ελRof emissivities of a flame at wavelengths of λGand λRis calculated according to analysis on the flame radiation spectra.

3) According to the size of the furnace, a cross-section of the furnace is divided into m space medium units and n wall units; if a furnace wall is a gray emission, absorption and diffuse reflection surface, the emissivity of the furnace wall is ε, and it is assumed that ε=0.9.

Since a biquadrate relation is formed between the radiation intensity and the temperature, and the furnace wall is covered with a water-cooled wall, the temperature of the wall is obviously lower than the flame temperature, so the radiation of the furnace wall is not considered, and only the flame radiation reflected by the furnace wall is considered.

4) A flame monochromatic radiation intensity received by each pixel unit of the image detector may be expressed by Equation (1):

Iλ(O,s)=∫0lw[1π⁢e-∫lβ⁡(l′)⁢dl′⁢κλ(l)⁢n2]⁢Ib⁢λ(T,v)⁢dl+∫S[∫0lw1π⁢e-∫lβ⁡(l′)⁢dl′⁢κλ(v)⁢n2⁢Rds(v,l,s)⁢dl+4π⁢e-∫lwβ⁡(l′)⁢dl′⁢κλ(v)⁢n2⁢Rds(v,w,s)]⁢Ib⁢λ(T,v)⁢ds(1)

where, I and I′ represent paths of radiation transmission of the space medium units, Iwrepresents a path of radiation transmission of the wall unit, and w represents the wall unit; v and v′ represent the space medium units; s represents a whole space medium area; σ is a Stefan-Boltzmann constant, 5.67×10−8, W/(m2·K4); a parameter in the shape of Rds(a, b, s) is called DRESOR number and represents a product of 4π and the share of energy emitted from a volume element centred on point a scattered by a unit volume centred on point b within a unit solid angle with s as a center line; k and n are a medium absorption coefficient and a refractive index; β=σ+κ is an attenuation coefficient, and σ is a medium scattering coefficient; ε is a wall emissivity; and Ibλis a monochromatic blackbody radiation intensity, W/m3·sr. According to the Planck's Blackbody radiation law:

Ib⁢λ(T)=1π⁢C1λ5⁢exp⁡(-C2λ⁢T)(2)

Equation (1) is discretized to obtain:

Iλ(i)=∑j=1mRd,gIλ(j→i)⁢4⁢κj⁢1π⁢C1λ5⁢exp⁡(-C2λ⁢Tg,j)))⁢Δ⁢Sg,j=∑j=1mAIλ(i,j)⁢Ib⁢λ(j),i=1,…,p(3)

where, Rd,gI(j→i) represents the share of radiation from each unit in the furnace to each pixel unit of the image detector; Tg,jis the temperature of the space medium unit; ΔSg,jis a space medium area element; and AIλ(i,j)=Rd,gIλ(j→i)4κjis a radiation intensity imaging coefficient; and for a R channel of the image detector, Equation (3) is matrixed to obtain:

IλR=AIλR(κλR,σλR)⁢Ib⁢λR(T)(4)

5) In the process of calculation, it is first assumed that the absorption coefficient and the scattering coefficient κλRand σνRof the R channel at the corresponding wavelength λRare uniformly distributed. In this case, a coefficient matrix

AIλR
is a known parameter, and a monochromatic blackbody radiation intensity distribution IbλR(T) can be calculated by using the regularization algorithm. The base principle is to find one IbλR(T) to minimize the following Equation:

R⁡(IλR,α)=IλR-AIλR(κλR,σλR)⁢Ib⁢λR(T)2+α⁢DIb⁢λR(T)2(5)

where a is a regularization parameter, and D is a regularization matrix. When Equation (5) is minimized, a solution of Equation (4) is:

Ib⁢λR(T)=(AIλRT(κλR,σλR)⁢AIλR(κλR,σλR)+α⁢DT⁢D)-1⁢AIλRT(κλR,σλR)⁢IλR=BIλR(κλR,σλR)⁢IλR(6)

where

BIλR
is a cross-section temperature field reconstruction matrix of the R channel.

For a G channel, the solution of Equation (4) can be written as:

Ib⁢λG(T)=BIλG(κλG,σλG)⁢IλG=BIλR(κλR,σλR)·ελGελR·IλG(7)

where

BIλG
is a cross-section temperature field reconstruction matrix of the G channel, and ελG/ελRis an emissivity ratio obtained by spectrum analysis.

6) The temperatures in Equations (6) and (7) can be calculated by the following Equation:

T=-C2λ/ln⁡(Ib⁢λ⁢λ5C1)(8)

in the process of calculation, the absorption coefficient and the scattering coefficient κλRand σλRare updated by using the Newton iteration algorithm, temperature distributions reconstructed by the radiation intensities IλRand IλGacquired by the image detector in the R and G channels are calculated respectively, and the two temperature distributions after being averaged are substituted into Equation (5) until the residual is minimized, so as to obtain a temperature field under an assumption of uniform κλRand σλR.

7) σλRis a known parameter, and Equation (4) can be amended to:

IλR=AIλR′(σλR)⁢κλR⁢Ib⁢λR(T)(9)

where,

AIλR′
is a new coefficient matrix that does not contain κλR·κλRIbλ(T) is calculated by using the regularization algorithm, and then the temperature distribution T calculated by Equation (8) is substituted into κλRIbλ(T) so as to obtain a distribution of the absorption coefficient κλR.

4. Implementation of Real-Time Visual Monitoring for Cross-Section Temperature Fields and Radiation Characteristics of Boiler Furnaces by Combining Radiation Images and Spectra in a Boil Site

In this embodiment, the real-time visual monitoring of cross-section temperature distribution and radiation characteristics of boiler furnaces by combining radiation images and spectra is performed at three heights above a burner layer of a 600 MW tangentially fired boiler in a coal-fired power plant somewhere, and a field detection experiment is schematically shown inFIG.2.FIG.2shows the furnace size of each layer and the positions of the four image detectors, shaded areas indicate actual cross-section of the furnace, and the fiber optic spectrometer is bundled together with the image detector #1.

Typical flame radiation images acquired by the image detectors under five operating conditions (330 MW at the first layer, 330 MW at the second layer, and 330 MW, 500 MW and 550 MW at the third layer) are shown inFIG.3, where exposure time is marked. It can be seen that when a load is 330 MW, there is no significant difference in the brightness of flame images acquired by the same image detector at the 1st to 3rd layers, but the exposure time decreases with the decrease of the height of the detection layer. This is due to that the detection layer at a lower position is closer to a burner region, and the flame radiation is stronger. In order to avoid image saturation, acquisition software of the image detectors moderately reduces the exposure time of an acquired image, so that the flame image has a high signal-to-noise ratio while it is unsaturated. In the third layer of field detection, with the increase of the boiler load, the exposure time of flame image acquisition also decreases. After the image detectors are subjected to blackbody furnace radiation calibration, acquired flame images can be converted into radiation intensity images.

The flame radiation spectrum acquired by the fiber optic spectrometer is shown inFIG.4. The emissivity ratios obtained by spectrum analysis under five operating conditions are 0.9153 (1-330 MW), 0.9341 (2-330 MW), 0.8801 (3-330 MW), 0.8845 (3-500 MW) and 0.9032 (3-550 MW) respectively.

A flame radiation intensity corresponding to a horizontal position in each typical flame image inFIG.3, after being interpolated by pixels from right to left to 100 pixel units, is used for reconstruction calculation so as to obtain cross-section temperature field and absorption coefficient distributions inside the furnace under four operating conditions as shown inFIGS.5and6, and a cross-section grid resolution is 10×10. InFIG.7, with an operating condition 3-330 MW as an example, a comparison between a calculated value and an initial value of a boundary radiation intensity is given according to the pixel units after interpolation (4 image detectors×100 pixel units). It can be seen that the reconstructed boundary radiation intensity is relatively smooth in comparison with an initial radiation intensity, but the two are basically consistent, which indicates that the reconstructed results of the cross-section temperature field and the space medium radiation parameters are very reliable.