JPS60225626A - Acidic gas removing apparatus - Google Patents

Abstract

PURPOSE:To attain to enhance the reliability of an acidic gas removing apparatus by detecting the life of an absorbent, by providing an acidic gas detector to the rear stage of the absorbent comprising potassium carbonate to detect that the absorbing efficiency of acidic gas reached a predetermined limit. CONSTITUTION:An acidic gas detector 3, wherein a silver conductive layer 7 is formed to a heat resistant insulating substrate 5, is arranged to the rear stage of an acidic absorber prepared by adhering potassium carbonate to the surface of the skeletal of ceramic foam and brought into contact with gas passing through the absorbent at 200-900 deg.C to make it possible to detect the life of the acidic gas detector on the basis of the change in the electric resistant value of said detector. This acidic gas removing apparatus can selectively remove acidic gas from gas having acidic gas such as HCl or SOx and tritium steam coexisting therein and can be utilized in tritium monitor for measuring the concn. of tritium contained in the exhaust gas from the incinerator of an atomic power plant.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to an acid gas removal device, and in particular to a device for removing acid gases, and in particular, a device for removing acid gases in which acid gases such as hydrogen chloride gas and sulfur oxides (SOx) coexist with tritium water vapor. This is a device that selectively removes acid gas from gas, and can be used as a tritium monitor to measure the concentration of tritium contained in the exhaust gas discharged from the incinerator of a nuclear power plant.

[Prior art and its drawbacks]

The emission level of radioactive substances such as tritium in exhaust gas discharged into the atmosphere from incinerators and the like in nuclear power plants is strictly regulated. Normally, most of the tritium contained in exhaust gas exists in the chemical form of aqueous tritium such as HTO or T20, so the tritium that is guided in a gaseous state through a heated sampling pipe is condensed and frozen using a condenser. , detect the tritium concentration using a liquid mintilator after melting. However, since trace amounts of acidic gases such as hydrogen chloride gas and sulfur oxides coexist in the incinerator exhaust gas, when these gases condense, water vapor (1-■20)
When it condenses with water-type tritium vapor (HTO, H2O), it may corrode the condenser or the detector, and even contaminate the condensed water.) It was lowering it. Conventionally, as a countermeasure against the causes of such troubles, the piping material has been changed to stainless steel material, titanium material, etc., or the surface has been lined or coated with a corrosion-resistant material. However, changing the material or lining or coating can have a significant impact on the gas collection performance of the device, or changing the material may be inappropriate in the case of nuclear equipment, so there are no effective solutions. It wasn't.

One possible effective measure to solve this problem is to selectively remove only the acid gas using an acid gas absorbent before it reaches the condenser. for that purpose,
It is desirable to reliably remove only acidic gas without collecting any chemical form of tritium.

In order to solve these problems, the present inventors have developed an acid gas removal method in which high-temperature exhaust gas is brought into contact with an absorbent whose main component is potassium carbonate, and the acid gas components are separated and accumulated in the absorbent as potassium salts. invented and proposed (patent application 1982-
186127).

Furthermore, in order to extend the life of the absorbent, the present inventors developed an acid gas removal device in which an absorbent mainly composed of potassium carbonate was attached to the surface of a heat-resistant integral bone channel having a plurality of through holes. Invented it.

However, because the concentration of acid gas in exhaust gas fluctuates, it is difficult to estimate the life of the absorbent from the amount of absorbent filled. The absorbent had to be replaced periodically. Therefore, the maintenance of the absorbent is troublesome and there are maintenance problems, and the amount of degraded absorbent that becomes low-level radioactive waste increases, resulting in an increase in running costs.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the prior art and provide an acidic gas removal device that can detect when the life of the absorbent, that is, when the acidic gas absorption efficiency has reached a predetermined limit. There is a particular thing.

[Key points of the invention]

In order to achieve the above object, this invention brings exhaust gas into contact with an absorbent containing potassium carbonate as a main component at high temperature, and selectively separates and accumulates only the acidic gas in the exhaust gas as potassium salt in the absorbent. In an acidic gas removal device, an acidic gas detector is installed downstream of the absorbent to detect when the acidic gas absorption efficiency of the absorbent has reached a predetermined limit. The acid gas detector is made by adhering a conductive metal mainly composed of silver to a part of a heat-resistant insulating substrate.
It is designed to detect an increase in the resistance value of the conductive metal layer due to the reaction between the conductive metal and the acidic gas by contacting the conductive metal layer at a temperature of .degree.

The method of neutralizing and removing acidic gas in gas using an alkaline absorbent containing potassium carbonate as its main component is, for example, when the acidic gas components are hydrogen chloride and sulfuric acid mist.
It uses the following reactions.

K2 Co3+ 2 HC1→2 K C1+H20+
C02... (1) K2 Co3+ H2804 → 2 S 04 + H20+ C02... (2) Most of the acidic gas in the exhaust gas is hydrogen chloride, and as a result, according to the above reaction formula (1), the amount of 2CO3 Most of it is consumed.

Furthermore, according to the experiments conducted by the present inventors, the reaction temperature was set at 200°C.
By setting the above value, a high reaction efficiency with acidic gas, that is, removal efficiency can be obtained. This is thought to be because silver, which is an insulator, gradually changes to silver chloride, which is an insulator, according to the following reaction formula (3), and the conductive layer decreases.

2Ag +2HCt→2Ag C1+ H2...
・・・・・・・・・(3) Because the detector is heated to a high temperature, the reaction is rapid, and because the volume of the conductive metal in the detector is small, the resistance changes extremely sensitively to hydrogen chloride gas. shows.

In addition, the reaction temperature was set at 200°C to 900°C.
When the detector is used at temperatures below 00°C, there are problems such as adsorption of water-type tritium and an increase in the resistance of the detector due to the formation of silver oxide or silver carbonate.On the other hand, when the detector is used at temperatures above 900°C In this case, since the temperature is just below the melting point of silver (978° C.), the reactivity of the conductive metal made of silver with impurities increases, causing problems in terms of long-term stability.

[Embodiments of the invention]

Embodiments of the acid gas removal apparatus according to the present invention will be described below with reference to the drawings.

Figure 1 shows a sampling system for removing tritium contained in exhaust gas. On the sampling pipe 1, an acid gas absorbent 2, an acid gas detector 3 and a condenser 4 are installed. Next, the preparation of the absorbent 2 will be described.

The absorbent was prepared by attaching potassium carbonate to the surface of the skeleton of a ceramic foam made of copillite, and the specific preparation method was as follows.

Express potassium carbonate powder 70 dried at 300℃ for 10 hours
Y,! : Reagent-R ethyl alcohol 150 ii
i+ and colloidal silica1. Of is mixed in a ball mill for about 5 hours to prepare a slurry in which fine potassium carbonate is dispersed. After mixing, the slurry was taken out to a beaker and stirred, then immersed in a ceramic foam slurry with a hole diameter of 13 mesh that had been previously dried in the atmosphere for 3 hours, pulled up, and the excess slurry was separated with compressed air. A layer of potassium carbonate is then deposited on the skeletal surface of the ceramic foam by drying at 150° C. for 1 hour. After repeating the impregnating and drying operation to make the adhesion amount of potassium carbonate about 50% of the weight of the ceramic foam, in order to increase the adhesion strength of potassium carbonate, the above-mentioned potassium carbonate was added to the mixed solution of colloidal silica 2Or and ethyl alcohol 802. Soak the foam and separate excess liquid. Next, this was dried at 150°C for 1 hour and then at 50°C for 1 hour.
Heat treatment at 00°C for 1 hour.

Next, the structure of the acidic gas detector will be explained with reference to FIGS. 2 and 3.

In FIG. 2, reference numeral 5 denotes an insulating substrate made of alumina. Inside this insulating substrate 5, a heater made of a W metal thin film is printed and embedded, and the surface of the terminal 6 is plated with Au. There is. Further, a silver conductor layer 7 shown with hatching is formed on the insulating substrate 5, and its detection portion 8 is formed in a W-shape. In order to form this silver conductor layer 7, a silver thin film having a thickness of 1 μm is deposited on the insulating substrate 5, and then a strip-shaped silver conductor layer having a width of 1 mm is formed by photo-etching.

Terminals 9, 9 for resistance measurement are provided at the ends of the silver conductor layer 7, and the silver conductor layer 7 is heated by passing a current through a W heater.

FIG. 3 shows the configuration of a sensor that utilizes the resistance change of an extremely thin silver wire, and is an example in which an extremely thin chain line is used and heating is performed by direct energization of the silver wire. In the figure, reference numeral 11 indicates an insulating tube, and this insulating tube 1 has two through holes, through which an ultrafine silver wire 1 is passed.
2 is inserted through the insulating tube 11 and protrudes from the tip of the insulating tube 11.
3 is formed, while lead terminals 1.4 and 4 are formed from the rear end.
14 is derived.

In addition, a heat-resistant inorganic adhesive +5, i5 is attached to the part where the silver wire 12 protrudes from the insulating tube 11.
The silver wire is fixed and the gas is sealed. In this embodiment, the detection section is heated by directly applying electricity to the silver wire 13 and utilizing Joule heat generation.

The relationship between the acidic gas absorption efficiency of the absorbent and the resistance value of the detector in the acidic gas detector configured as described above can be measured using the test apparatus shown in FIG. 4.

In the test apparatus shown in FIG. 4, an absorbent 20 is filled into a quartz reaction tube 21 and set on a honeycomb-shaped perforated plate fixed at the center of an electric furnace 22. The acid gas detector 24 is provided downstream of the absorbent 20.

A honeycomb-shaped perforated plate 5 is fixed to the upper part of the absorbent 20,
Furthermore, a vaporizer filled with glass beads 26 is provided above it. This vaporizer is heated by an electric furnace n, and the temperatures of the absorbent 20, the glass beads 26 and the detector are measured by thermocouples 27, 28 and '29, respectively. As a test gas, a dilute aqueous hydrochloric acid solution 30 of a predetermined concentration was passed through a vaporizer using a liquid metering pump 31 to vaporize it, and this was diluted with air from a dry air cylinder 32 to obtain a test gas containing hydrogen chloride gas and water vapor.

The performance test conditions are shown in the table below.

After the test gas passes through the absorbent Δ, it passes through the acid gas detector 24 and is cooled by the cooler 33, and the hydrogen chloride gas contained in the test gas is condensed together with water vapor and stored in the test tube 34. There is. In addition, cooling water cooled by a refrigerator 35 is circulated in the cooler 33, and the reaction tube on the test gas outlet side is heated to -100°C by a mantle heater 36.
The water vapor is heated to an even higher temperature, preventing condensation of water vapor.

Pass the test gas through the absorbent layer and test tube 34 every hour.
The condensed water produced in the water is collected, the chloride ion concentration therein is determined by ion chromatography, and the hydrogen chloride removal efficiency of the absorbent can be calculated using the following formula.

Further, the resistance value of the acidic gas detector U can be measured using the digital multimeter 37 at any time.

When the relationship between the acid gas absorption efficiency of the absorbent and the change in the resistance value of the detector over time is investigated using such a test device, the results shown in FIG. 5 are obtained. In FIG. 5, the curve (a) shows the change over time in the absorption efficiency of the absorbent, the curve (b) shows the change over time in the resistance value of the silver thin film of the detector shown in FIG. → indicates the change over time in the resistance value of the silver wire of the detector shown in FIG.

As is clear from this figure, about 250 hours after the start of the test, the absorbent exhibits a constant absorption efficiency of 999% or more, but after 250 hours, the absorption efficiency decreases rapidly. Corresponding to the change in absorption efficiency of this absorbent over time, approximately 25
The resistance value of the detector (curve end, ...), which showed a constant value equivalent to the initial value until 0 hours, suddenly increased as the absorption efficiency of the absorbent decreased, and it was considered that the absorbent was reaching its end of life. When the absorption efficiency reached 90%, there is a resistance change of several orders of magnitude.

Next, using the detector shown in Figure 2, the temperature of the detector was changed from 100℃ to 900℃, and the relationship between the absorption efficiency of the absorbent and the change in resistance value of the detector over time was investigated, as shown in Figure 6. It will be as shown. In Figure 6, curve (a) shows the change in absorption efficiency of the absorbent over time, and curves (0) (d) (e) (he) (g)
The detector temperatures are 300℃, 200℃, and 450℃, respectively.
It shows the change in resistance value of the detector over time under example test conditions of 100°C, 900°C, and 100°C. As can be seen from Figure 6, under the condition that the detector temperature is between 200°C and 900°C (curve m (mouth 1 (=) (e) (he)), the change in the resistance value of the detector over time is It corresponds well to the change in absorption efficiency over time. However, when the detector temperature is 100 tll:
In the case of (curve (L)), even though hydrogen chloride has not broken through, the resistance value of the detector gradually increases and does not correspond well to the change in absorption efficiency over time.

When the cause of this was considered, it was found that at temperatures below 200°C, carbon dioxide and oxygen gas coexisting in the exhaust gas produce silver carbonate, silver oxide, etc., and the use of buttons with good electrical conductivity decreases. Furthermore, if the temperature exceeds 900° C. and approaches the melting point of silver (978° C.), silver may soften or react with various impurities contained in exhaust gas, which is undesirable from the viewpoint of long-term stability.

〔Effect of the invention〕

As described above, according to the present invention, an acid gas detector made of a conductive metal containing silver as a main component is installed downstream of the absorbent, and the gas that has passed through the absorbent at a temperature of 200°C to 900°C is It is now possible to determine the lifespan of the absorbent by contacting it with the absorbent and detecting the change in the electrical resistance value of the detector, which enables long-term use of the absorbent and improves the reliability of the acid gas removal equipment. It is possible to achieve improvements such as reducing the amount of used absorbent to be disposed of as radioactive waste.

[Brief explanation of the drawing]

Figure 1 is a system diagram showing the arrangement of the absorbent, acid gas detector, and condenser. Figure 2 is a vertical cross-sectional view of a thin film type acid gas detector. Figure 3 is an ultra-fine wire type acid gas detector. Figure 4 is a schematic diagram showing the acid gas detector performance test equipment, Figure 5 is a side view showing the acid gas detector temperature.
A diagram showing the relationship between the absorption efficiency of the absorbent and the resistance value of the acidic gas detector when heated to ℃. Figure 6 shows the relationship between the absorption efficiency of the absorbent and the acidity when the operating temperature of the acidic gas detector is changed. 0 is a diagram showing the relationship between resistance values of gas detectors. 1... Sampling pipe line, 2... Acidic gas absorbent,
3...Acidic gas detector, 4...Condenser, 5...Insulating substrate, 7...Silver conductor layer Patent applicant Fuji Electric Research Institute Co., Ltd. Fuji Electric Manufacturing Co., Ltd. 2 fetus count 3 figures

Claims (1)

[Scope of Claims] 1. In an acid gas removal device that brings exhaust gas into contact with an absorbent containing potassium carbonate as a main component at high temperature, the acid gas in the exhaust gas is separated and accumulated in the absorbent as potassium salt. An acid gas removal device characterized in that an acid gas detector is installed downstream of the absorbent to detect when the acid gas absorption efficiency of the absorbent reaches a predetermined limit. 2. In the acidic gas removal device according to claim 1, the acidic gas detector is formed by adhering a conductive metal mainly composed of silver to a part of a heat-resistant insulating substrate. An acid gas removal device characterized by: 3. The acidic gas removal device according to claim 2, wherein the acidic gas detector is brought into contact with exhaust gas at a temperature of 200°C to 900°C.