JPS60131446A - Method for measuring dew point in furnace - Google Patents

Abstract

PURPOSE:To measure a dew point at the vicinity of a material surface in a furnace by passing an electromagnetic beam through a vicinity of the material in a furnace, and measuring the absorbing characteristic against water vapor. CONSTITUTION:A beam 5 is made incident into the furnace 1 from a window 3 through a filter 10, a beam splitter 7, a rotating sector 11 from a light source 4. The beam 5 passes through the vicinity of the surface of a material 9, then reflects by a reflecting mirror 6, returns through the same course and enters to a detector 8. Since the beam 5 indicating the absorbing characteristic against water vapor is used, the light quantity detected by the detector 8 depends on the water vapor quantity in the vicinity of the material surface in the furnace 1. The water vapor quantity can be measured by a ratio of the light quantity to that detected when a total reflection mirror surface 11' is positioned on the light passage by rotating the sector 11. If the water vapor quantity is known, the dew point can be obtained, and the dew point can be controlled.

Description

[Detailed description of the invention] (Industrial use fairness F) ±The invention is used in various processes of steel manufacturing.
The present invention relates to a method for measuring dew points in various high-temperature furnaces.

(prior art).

Control of the dew point inside the furnace is very important in the annealing process of various high-temperature furnaces used in steel manufacturing, especially in annealing furnaces such as electromagnetic steel decarburization annealing furnaces, stainless steel bright annealing furnaces, and continuous thin plate annealing furnaces.

For example, in electrical steel sheets, it has been revealed that the decarburization reaction between the steam in the furnace and the surface of the steel sheet influences the iron quasi-characteristics, and therefore it is extremely important to maintain the amount of water vapor. Furthermore, with stainless steel sheets, a small amount of water vapor in the furnace forms a thin oxide film on the surface of the steel sheet, which has a decisive effect on the surface quality and aesthetic appearance. Furthermore, surface oxidation caused by water vapor in thin sheets such as cold-rolled steel sheets has a great effect on the quality of subsequent plating treatments, such as zinc plating.

As described above, dew point control in a heat treatment furnace such as an annealing furnace process is very important, but the current dew point control is not sufficient. In other words, the dew point control of heat treatment furnaces that has been generally carried out in the past is, for example, as shown in the Japanese Patent Association's "3rd Edition Iron and Steel Handbook - Secondary Processing, Surface Treatment, Heat Treatment, Welding", page 561. A DeW Probe, which utilizes the moisture absorption saturation characteristics of , the dew point at one point in the furnace is measured and considered as the dew point of the entire furnace. However, it is doubtful whether the dew point value obtained in this way is representative of the entire dew point in the furnace, and therefore it is difficult to control the process or the quality of the materials in the furnace based on such information. It is easy to understand that it would be difficult to accurately control specific operations.

(Objective of the Invention) It is an object of the present invention to provide a method for measuring the truly necessary dew point in response to the current situation. In other words, the truly necessary dew point in the various processes described above is the dew point near the surface of the material heat-treated in the furnace, and the present invention measures the dew point by measuring the amount of water vapor near the surface that directly reacts with the material surface. This provides a method to do so.

(Construction and Effect of the Invention) The present invention detects that when an electromagnetic wave beam of a specific wavelength exhibiting absorption characteristics for water vapor propagates through space, the amount of the electromagnetic wave absorbed changes in response to changes in the dew point value. This method is used to measure the average dew point in the vicinity of the surface of a material that is stationary or moving in a furnace. The present invention will also be explained in detail below with reference to the drawings.

Fig. 1 shows the basic configuration of the present invention. Small holes are provided in both side walls 2 and 2' of a furnace 1, and electromagnetic wave transmitting windows 3 and 3' made of quartz glass or the like are installed to prevent the atmosphere inside the furnace from leaking. Seal. On the other hand, a light source 4 of an electromagnetic wave beam 5 having a wavelength exhibiting absorption characteristics for water vapor and a beam splitter 7 are located opposite the electromagnetic wave transmission window 3, and a detector 8 is further opposed to the beam splitter 7. will be established. Further, a reflecting mirror 6 is provided outside the other electromagnetic wave transmitting window 3'.

Therefore, an electromagnetic wave beam 5 (for example, an infrared beam) is emitted from the light source 4, and the electromagnetic wave beam is transmitted from the electromagnetic wave transmission window 3 very close to the surface 9' of the material 9 where an interfacial reaction occurs with the water vapor in the furnace interior 1'. It is propagated, reflected by a reflection mirror 6 provided outside the electromagnetic wave transmission window 3', passed through the furnace 1' again, taken out from the furnace through the electromagnetic wave transmission window 3, reflected by the beam splitter 7, and sent to the detector 8. lead to. Since the electromagnetic wave intensity detected by the detector 8 changes in accordance with the dew point in the furnace, that is, in accordance with the amount of moisture in the furnace, the dew point can be measured. In this case, if the electromagnetic wave beam 5 is made to pass through the material 9 in the furnace in its width direction,
Since the average value of the dew point in the very vicinity of the material 9 is measured, it becomes possible to perform process control and material control that are completely different from conventional dew point control. Furthermore, since the electromagnetic beam can be detected at high speed, the dew point can be measured continuously even when the material 9 is running at high speed inside the furnace 1'.

Here, the measurement principle of the present invention will be explained.

Now, if the intensity at the propagation distance 2 of the wavelength λ that exhibits absorption characteristics for water vapor is I (Z), then Lambert-
The following equation, well known as Lambert-Beer's law, holds true.

12(Z) =I2(0) exp' (-tx・n6
Z) ・=(11 In formula (1), I, (0') is Z
= 0, that is, the incident intensity is reduced to zero. In addition, n is the number of moles of water vapor per unit volume of the space through which the beam propagates, and α is the absorption coefficient for water vapor at wavelength λ. In FIG. 1, the incident light travels back and forth over one width l and is detected, so the propagation distance is L=2#. Therefore, by substituting Z=L into equation (11) and rearranging, the following equation holds true.

Taking the logarithm of both sides of equation (2) and rearranging it, in equation (3), the right side and α are constants, so the detection intensity I
The number of moles of water vapor, n, can be determined from the ratio of λ(L) and the incident intensity rλ(0).

By the way, the furnace space in Figure 1 is an open system, and steam is constantly supplied from the outside, so that the ratio with other components in the furnace is almost maintained.
It is assumed that the pressure inside the furnace is maintained at approximately 1 atm. At this time,
The partial pressure of steam in the furnace Pw, the furnace volume as ■, the number of moles of steam as N,
And when the furnace atmosphere temperature is T (K), Pw-V=N-R-T (4) holds true. Here R is an expectation constant. In equation (4), the number n of water vapor moles per unit volume is expressed as n=N/■, so the water vapor partial pressure Pw is given by the following equation.

Pw=n -R-T...-(51 In other words, the in-furnace water vapor partial pressure Pw can be determined from equation (5) if n is measured by equation (3) and the in-furnace ambient temperature T is obtained.On the other hand, , as shown in Fig. 2, there is a certain relational expression between the saturated water vapor pressure Pw and the corresponding dew point tw ('C), so if Pw is calculated by equation (5), the dew point tw becomes Obtained from Figure 2.

The above is the principle of the present invention. An example of a configuration embodying this principle is shown in FIG. In FIG. 3, an electromagnetic wave beam from a light source ± passes through a filter 1 that passes only the wavelength λ that exhibits absorption characteristics for water vapor, and then reaches a beam splinter 1, where there is a total absorption surface. When the sector 11 rotates and the window portion ↓Top' comes to the optical path of the electromagnetic beam l, the beam Σ propagates in the path and is reflected by the reflection mirror 6 provided on the furnace side wall Y to return to its original state. The beam returns along its optical path, is reflected by the beam splinter 7, and enters the detector 8. Let this detection signal be I+. Also sector 1
When the total reflection mirror 11'' of No. 1 is in the optical path, the beam 5 is totally reflected there, reflected by the beam splitter 7, and similarly enters the detector 8. This detection signal is designated as 12. Furthermore, the total absorption surface 11 ” is in the optical path, the signal reflected and detected here is regarded as the zero base and is designated as I3.

Each detection signal can be written as follows.

1 + =k + lλ(0) exp (-αn'Z
.

-αn'L)+Ib...(6)I2=k
211(0)e to p-txn'Z o) +Ib・=(
7)-13=Ib (8) Here, k+ and 2 are coefficients including the reflectance of the mirror and the geometric coefficient of the optical system, and are constants. n' is the optical path distance between the rotating sector and the beam splinter L and the detector 8, Ib
is the detection noise value including ambient background light. (6)-(8)
From the formula, CI+-13)/(I2-13) is created. From formula (9), however, k = 2/ + = (constant), that is, by formula 00, the number of moles of water vapor per unit volume in the road n becomes a circle. In this configuration, it is of course important that the beam Σ propagate near the material surface. Next, examples of the present invention will be shown.

(Example) In the configuration shown in FIG. 3, a halogen bulb was used as the light source, and as the filter 10, an interference filter of λ-1, 39 μm, 1 half-width Δλ=O, 15 μm was used.

The beam was propagated at a distance of 10++n+ from the surface of the material with a beam diameter of 3φ. A germanium (Ge') element was used as the detector 8. The furnace atmosphere temperature is approximately 700
It is ℃. By changing the dew point in the furnace, a signal <1'+-13)/(I2, I3') corresponding to equation (9) is detected, and based on this data, equation 00) is calculated. As shown in the figure, a relational expression between electrical output and dew point was obtained. The vertical axis shows nW mo
l/Nm3 and output voltage OUT (V) are taken,
The latter is Vsig/VI? Proportional to EF (terminal output voltage).

In this example, a halogen lamp was used as the light source, but other light bulbs such as xenon lamps and tungsten lamps, thermal radiation sources such as blackbody furnaces, semiconductor lasers, and CO
Tunable lasers such as 2 lasers can be used.

Furthermore, since a wavelength band in the microwave region that exhibits absorption characteristics for water vapor can be used, a microwave generation source such as a Gunn diode can also be used.

(Effects of the Invention) As explained above, the present invention can detect changes in the state of water vapor near the surface of road objects such as steel plates, and measure the dew point value based on the changes as an average value. This method is much more accurate than the conventional method of measuring at a single point to represent the inner path, and therefore has great effects, such as being able to use measured values for process control or quality control of objects in the furnace. .

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the measurement principle of the present invention, Figure 2 is a graph showing the relationship between saturated vapor pressure and dew point, Figure 3 is an explanatory diagram showing an example of the method of the present invention, and Figure 4 is the method of the present invention. 2 is a graph showing the relationship between output voltage and dew point in FIG. 1: Furnace, 1': Inside the furnace, 2. 2'F side wall, 3.3
′: Electromagnetic wave transmission window, 4: Light source, 5: Electromagnetic wave beam 4
, 6; Reflection mirror, 7: Beam subsoter, 8:
Detector, 9: Material, 9': Surface, 10: Filter, 11: Rotating sector, 11': Transmission window portion, 1
1: Total reflection mirror, 11: Total absorption surface. Applicant Nippon Steel Corporation Patent Attorney Minoru Aoyagi Procedural amendment (voluntary) 1. Indication of the case Patent Application No. 240678 filed in 1982. 2. Name of the invention Method for measuring dew point in a furnace 3. Amendments to be made Relationship with the case Patent applicant address 2-6-3 Otemachi, Chiyoda-ku, Tokyo Name (6
65) Nippon Steel Corporation Representative Takeshi 1) Yutaka 4, Agent 101

Claims (1)

[Scope of Claims] +11 An in-furnace dew point measuring method characterized by passing an electromagnetic wave beam near an in-furnace object and measuring the dew point near the object's surface based on the absorption characteristics of electromagnetic waves for water vapor in the furnace. (2) An electromagnetic wave beam with a wavelength that has absorption characteristics for water vapor in the reactor and an electromagnetic wave beam that does not have absorption characteristics are passed near the surface of the object in the reactor, and An in-furnace dew point measuring method characterized by measuring dew point. (3) As a source of electromagnetic wave beam, a halogen lamp,
Claims 1 or 2, characterized in that an infrared generating bulb such as a xenon lamp, a wavelength tunable infrared semiconductor laser, an infrared generating laser such as a CO2 laser, or a microwave generator such as a Gunn diode is used. Furnace dew point measurement method described in section. (4) The in-furnace dew point measuring method according to claim 1 or 2, characterized in that the average dew point near the surface of the object in the direction perpendicular to the traveling direction of the object traveling in the furnace is measured. Φ. (5) The in-furnace dew point measuring method according to claim 1 or 2, characterized in that the electromagnetic wave beam source and the receiver are set on a side wall of the furnace or outside the furnace.