JP2004271537A - Method for measuring temperature of molten slag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus for measuring the temperature of a molten slag which can surely measure the liquid level temperature of the molten slag even in a furnace having a high smoke dust concentration. <P>SOLUTION: A method for measuring the temperature of the molten slag includes the steps of condensing a plurality of the radiant beams of light 8 having a wavelength region of 2-20 μm of the radiant beams of the light 8 radiated from the liquid level 5a of the molten slag 5 contained in the furnace, generating the output voltage having an amplitude in response to the intensity of the incident radiant beam of the light 8 from a pyroelectric element 28 by intermittently radiating the radiant beams of the light 8 to the pyroelectric element 28, and estimating the liquid level temperature of the molten slag 5 from this output voltage value and a Planck's radiation law. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a temperature measurement method capable of reliably measuring a liquid surface temperature of molten slag even in a furnace having a high dust concentration.

Conventionally, in order to measure the liquid surface temperature of the molten slag contained in the furnace, the intensity of near-infrared radiation having a wavelength of about 1 to 2 μm radiated from the liquid surface, or having a different wavelength 2 The temperature of the slag liquid surface 5a is estimated from the intensity ratio of the radiant light of more than kinds.
However, since the dust in the furnace has a diameter of about 1 to 2 μm and the same size as the wavelength of the near-infrared radiation, the dust concentration in the furnace is extremely high, for example, in a plasma ash melting furnace. In addition, the near-infrared radiation of the molten slag is scattered by dust. Therefore, the near-infrared radiation does not reach the window provided on the ceiling of the furnace, and the temperature of the slag liquid level cannot be estimated.
Therefore, in the plasma ash melting furnace, the temperature of the molten slag discharged from the slag port of the furnace is measured by a thermocouple or the like, and the furnace temperature is estimated based on the measured values. However, with this method, it is difficult to accurately estimate the liquid surface temperature of the molten slag.

  An object of the present invention is to solve the above problems and to provide a molten slag temperature measuring device capable of reliably measuring the liquid surface temperature of molten slag even in a furnace having a high dust concentration.

  The method for measuring the temperature of molten slag according to the present invention, in order to achieve the above object, of the radiation emitted from the liquid level of the molten slag contained in the furnace, the radiation in the mid-infrared range or far-infrared range. A method of generating an output voltage having an amplitude corresponding to the intensity of incident radiant light from a photoelectric element, and determining the liquid surface temperature of the molten slag from this output voltage value and Planck's radiation law. It is.

Here, there is a pyroelectric element as a photoelectric element that can be used in the mid-infrared region. The pyroelectric element outputs an AC signal synchronized with the intermittently incident radiation light, and the amplitude of the AC signal has a magnitude proportional to the amount of light. In this way, the true light intensity ratio is calculated by taking into account the dust in the furnace and the transmittance of the light collecting window provided on the furnace wall to the amplitude value of the output signal of each wavelength, and the melting slag is calculated from Planck's radiation law. Can be estimated.
Usually, the dust has a diameter of 1 to 2 μm, and the near-infrared radiation having a wavelength substantially equal to this diameter is scattered by the dust, and it is difficult to reach the furnace ceiling and the like. . For this reason, among the radiations emitted from the surface of the molten slag, the liquid surface temperature of the molten slag cannot be estimated by the radiation in the near infrared region.
However, according to the present invention, to use radiation in the middle infrared or far-infrared region of the wavelength range larger than the diameter of the dust, even if the dust concentration in the furnace is very high, than the diameter of the dust. Radiation light in the mid-infrared region or far-infrared region having a larger wavelength reaches the furnace wall without being scattered by dust, and the surface temperature of the molten slag can be reliably estimated. Further, since the temperature is directly measured using the radiation light of the molten slag, the temperature can be accurately measured, and the type of the radiation light may be two or more wavelengths. The pyroelectric element is a general-purpose element used for detecting a human body or the like, and is lower in cost than a far-infrared CCD element or the like, and does not require any additional equipment such as cooling.

In one aspect of the method for measuring the temperature of molten slag according to the present invention, the dust has a diameter of 1 to 2 μm, and a plurality of radiations emitted from the surface of the molten slag have a wavelength range of 2 to 20 μm. It is infrared radiation.
The wavelength of the radiation emitted from the molten slag is larger than the diameter of the dust filling the furnace, and the radiation is not significantly affected by the scattering of the dust, so the liquid surface temperature of the molten slag can be reliably estimated. can do.

  According to the present invention, the liquid surface temperature of the molten slag can be accurately and inexpensively estimated even in a furnace having a high dust concentration.

Hereinafter, a measuring device used in a method for measuring the temperature of molten slag according to an embodiment of the present invention will be described in detail with reference to the drawings.
The present invention detects far-infrared light of a plurality of wavelengths, corrects the light intensity of each wavelength from the wavelength dependence of the transmittance of the far-infrared light with respect to dust, and then uses the Planck's radiation law to determine the liquid of the molten slag. This is a method of measuring the surface temperature. In addition, in order to remove the effects of dust, the dust transmittance and emissivity of the radiant light according to the operating conditions of the main ash alone, mixed ash, and no ash input are calibrated using a personal computer, In order to remove the influence of the attenuation of the transmitted light, the intensity ratio of the intensity ranges of a plurality of wavelength ranges is obtained.
FIG. 1 is a schematic view showing a temperature measuring device for the molten slag and a plasma arc melting furnace provided with the temperature measuring device.

A main electrode 2 and a bottom electrode 3 are disposed along the vertical direction at the center of the inside of the plasma arc melting furnace 1 (hereinafter, also simply referred to as a melting furnace). 5 are accommodated. A plasma arc 7 is emitted from the lower end of the main electrode 2 toward the furnace bottom electrode 3, and radiation 8 is emitted upward from a liquid level 5 a of the molten slag 5. As shown in FIG. 2, the wavelength of the radiated light 8 is often about 2 μm when there is no scattering, and is about 5 to 10 μm when scattering is considered.
Further, on the ceiling 10 of the melting furnace 1, a temperature measuring device 15 that collects the radiant light 8 through a light collecting window 11 and estimates the liquid surface temperature of the molten slag 5 using the collected light is provided. ing.

The light collecting window 11 is made of ZnSe and is configured to be slidable in the horizontal direction. Therefore, when the light collecting window 11 becomes dirty, it can be easily replaced. Therefore, the dirt on the light collecting window 11 may be removed by wiping instead of the sliding method. Although not shown, the window holder 16 is cooled by cooling water, and the inside of the furnace of the condenser window 11 is purged with N ₂ gas.
A condenser lens 20 made of ZnSe is disposed above the condenser window 11 and can collect the radiated light 8 from the condenser window 11. A light chopper 22 is provided above the condenser lens 20. It is arranged. The light chopper 22 is attached to a DC motor (reduction gear) 25 connected to a DC power supply 24, and can be freely rotated by the DC motor 25.

  A pyroelectric element (also referred to as a pyroelectric element) 28 is provided above the light chopper 22, and is connected to a personal computer 30 and a control device via an amplifier 29. Here, when the pyroelectric element 28 is irradiated with the radiated light 8 in the far-infrared region, the temperature rises, the polarization value changes, and an amount of electric charge proportional to the intensity of the radiated light 8 is released. After the charge amount is amplified, it can be sent to the personal computer 30. However, since the pyroelectric element 28 has a property called so-called saturation, which does not react when the stationary light, which is light having a certain intensity, is applied for a certain time or more, the radiant light 8 is intermittently blocked by the light chopper 22. It is necessary to irradiate the pyroelectric element 28 in an intermittent state. FIG. 1 shows the temperature measuring device 15 in the case where the number of pyroelectric elements 28 is one. However, the present invention is not limited to this, and two or more pyroelectric elements 28 are provided. May be applied.

Next, the present invention will be described in more detail with reference to an example in which the temperature measuring device 15 having the above configuration is provided in a demonstration furnace.
[Overview of temperature measurement device]
First, the configuration of the temperature measuring device 15 will be described. The measuring device 15 used in the present embodiment has a configuration as shown in FIG. 1, and has three pyroelectric devices having band-pass filters having wavelength ranges of 2 to 20 μm, 5 to 20 μm, and 7 to 20 μm. An element 28 is provided. The pyroelectric element 28 is a ferroelectric crystal whose dielectric constant changes depending on the temperature, and has a maximum sensitivity of 1000 V / W. The condenser lens 20 is a convex lens, and the radiated light 8 forms an image on the light receiving surface of the pyroelectric element 28 by the condenser lens 20, making it difficult to detect other light.

[Configuration of optical system]
As shown in FIG. 3, radiation light 8 in the far infrared region is emitted from the liquid surface 5 a of the molten slag 5, and the radiation light 8 is condensed on the pyroelectric element 28 via the condenser lens 20. Is done. Since the diameter of the focal lens 20 is φ50 mm and the focal length is f = 50 mm, when the distance a from the focal lens 20 to the liquid surface 5 a of the molten slag 5 is about 1500 mm, the focal lens 20 is focused. An image is formed when the distance b from the optical element 28 is 51.7 mm calculated by the following (Equation 1).

However, since the slag surface may be lowered, b is set to 52 to 53 [mm].
Further, since the diameter of the light receiving surface of the pyroelectric element 28 is dp = 2 [mm], the area of the slag surface 5a incident on the pyroelectric element 28 is:
ds = dp · a / b = 2 × 1500/53 = 56.6 ≒ 57 [mm]
The solid angles of the focal lens 20 as viewed from the slug surface 5a are as follows.
ω = 2π (1-cos θ) = 2π [1-cos (0.0167)]
= 8.8 × 10 ^-4 [srad]
θ = arctan (25/1500)
= 0.0167 [rad]

[Radiation energy of slag surface]
The radiation energy per unit wavelength radiated from the unit area of the slag surface 5a is calculated from the following (Equation 2).

Here, ε · τ is emissivity × transmittance, h is Planck's constant, k is Boltzmann's constant, C is the speed of light, and ν is the frequency of the radiated light.
(Eλ / C) when ε · τ = 1 is as shown in the graph of FIG.

  Assuming that the sensitivity wavelength range of the pyroelectric element 28 is 2 to 20 μm, 5 to 20 μm, and 7 to 20 μm, at 1800 [k], the radiation energy radiated from the slag surface 5 a is expressed by the following (Equation 3) to (Equation 5). )become that way.

[Attenuation of radiation intensity by dust]
Σ · n = 3.5 [m ⁻¹ ] based on the measurement results of the light scattering characteristics of the dust by the He—Ne laser in the demonstration furnace. Here, σ is the dust scattering cross section, and n is the dust density.
The rate at which the radiated light 8 emitted from the slag surface 5a attenuates before reaching the measurement light condensing window 11 is:
η = exp (−σ · n · L) = exp (−3.5 × 15) = 5.2 × 10 ³
Here, L is the distance from the slag surface 5a to the light collection window 11, and is assumed to be substantially equal to a in FIG.

[Radiation energy incident on the pyroelectric element]
If the emissivity ε of the molten slag 5 is 0.1 and the total transmittance τ of the condenser window 11 and the focusing lens 20 is 0.1, then ε · τ = 0.01.
The area of the region indicated by ds in FIG. 3 is S = π · (ds / 2) ²
= Π · (57 × 10 ^3/2 ) ² = 2.6 × 10 ^-3 [m ^-2 ]
Therefore, the radiant energy incident on the pyroelectric element 28 is as follows for each wavelength range: e2-20 = ω / 2π · E2-20 · S · ε · τ · η
= 8.8 × 10 ^-4 /2π×1.42×10 ⁶ × 2.64 × 10 ^-3
× 0.01 × 2.75 × 10 ⁻⁵ = 1.4 × 10 ⁻⁷ [W]
e5-20 = ω / 2π · E5-20 · S · ε · τ · η
= 8.8 × 10 ^-4 /2π×1.42×10 ⁵ × 2.64 × 10 ^-3
× 0.01 × 2.75 × 10 ⁻⁵ = 2.6 × 10 ⁻⁸ [W]
e7-20 = ω / 2π · E7-20 · S · ε · τ · η
= 8.8 × 10 ^-4 /2π×2.56×10 ⁵ × 2.64 × 10 ^-3
× 0.01 × 2.75 × 10 ⁻⁵ = 1.1 × 10 ⁻⁸ [W]

[Output power of pyroelectric element]
The sensitivity of the pyroelectric element 28 is
ρ2-20 = ρ2-20 · e2-20 = 1500 × 1.4 × 10 ⁻⁷ = 2.1 × 10 ⁻⁴ [V]
ρ5-20 = ρ5-20〜e5-20 = 1500 × 2.6 × 10 ^-8 = 3.9 × 10 ^-5 [V]
ρ7-20 = ρ7-20〜e7-20 = 1500 × 1.4 × 10 ⁻⁸ = 1.4 × 10 ⁻⁵ [V]
Therefore, the measuring device requires 10 ³ to 10 ⁴ times of amplifier.

[Estimation of slag temperature]
Next, the intensity ratio of radiant energy is determined from Planck's radiation law.

FIG. 5 shows the values of E5-7 / E2-5 and E7-20 / E2-5 at each temperature.
The values of ε and τ in each wavelength range are separately obtained from the measured value by the thermocouple and the output value of the pyroelectric element 28 during the trial run of the actual device. Since the pyroelectric element outputs are V2-20, V5-20, and V7-20, they are as follows.
V2 ~ 5 ∝ε2 ・ τ2 ・ E2〜5
V5-7 ∝ε5 ・ τ5 ・ E5〜7
V7-20 ∝ε7 ・ τ7 ・ E7-20
Therefore, the following equation is derived.

  When the pyroelectric element outputs are obtained as V'2 to 5, V'5 to 7, and V'7 to 20, the corrected spectral intensity ratio is as follows.

  Using these spectral intensity ratios, the temperature of the slag liquid level 5a can be obtained from FIG.

It is a sectional view showing the melting furnace provided with the temperature measuring device concerning the present invention. It is a graph which shows the relationship between the wavelength and intensity | strength of radiant light in the case where there is scattering by dust. It is the schematic which shows the state which condenses radiation light. It is a graph which shows the relationship between the wavelength of radiation light, and radiation energy. 4 is a graph showing a relationship between a temperature and a radiation spectrum intensity ratio.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Plasma arc melting furnace 2 Main electrode 3 Furnace bottom electrode 5 Melting slag 7 Plasma arc 8 Radiation light 10 Ceiling 11 Condensing window 15 Temperature measuring device 16 Window holder 20 Condensing lens 22 Light chopper 24 DC power supply 25 DC motor 28 Focus Element 29 Amplifier 30 PC

Claims (4)

  Among the radiated light emitted from the liquid surface of the molten slag contained in the furnace, the radiated light having a wavelength range of 2 to 20 μm is focused on the photoelectric element, and the output voltage according to the intensity of the incident radiated light Is generated from a photoelectric element, and the liquid surface temperature of the molten slag is determined from the corrected spectrum intensity ratio obtained from the output voltage value and Planck's radiation law.   The method for measuring the temperature of a molten slag according to claim 1, wherein the liquid surface temperature of the molten slag is determined by using radiation light of two or more different wavelengths.   The method for measuring the temperature of molten slag according to claim 1, wherein the diameter of the dust present in the furnace is 1 to 2 μm.   The method for measuring the temperature of molten slag according to claim 1, wherein the photoelectric element is a pyroelectric element.

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