JP2005077355A - Apparatus and method for measuring mercury concentration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for measuring mercury concentration allowing high-precision measurement even when organic substances are contained in a sample gas. <P>SOLUTION: The apparatus includes a sample gas introduction channel which introduces the sample gas into a measurement cell which measures the mercury concentration in the sample gas by atomic absorption analysis and a reference gas introduction channel which introduces a reference gas obtained by removing mercury from the sample gas. The reference gas introduction channel has a structure provided with a honeycomb structure having, on its surface, a metal constituting amalgam through contact with mercury. Gold is used as the metal constituting amalgam. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a mercury concentration measuring apparatus using atomic absorption spectrometry and a mercury concentration measuring method.

  Mercury may be contained in the exhaust gas from incineration facilities such as waste incineration plants due to the fact that substances containing mercury such as dry cells are mixed into municipal waste. In addition to exhaust gas from incineration facilities, since mercury is a harmful substance, it is required to detect the concentration of mercury contained in gases such as the atmosphere and the amount of mercury contained in liquid or solid samples. Sometimes.

  As an apparatus for measuring such mercury concentration, a mercury concentration measuring apparatus using atomic absorption spectrometry is used. Such a mercury concentration measuring device detects the amount of light absorbed at a specific wavelength by irradiating light to a sample gas introduced into a measurement cell (if the sample is liquid or solid, the gas that vaporizes this sample), The concentration of mercury contained in the sample gas is obtained (for example, see Patent Document 1).

  For example, as shown in FIG. 6, the mercury concentration measuring apparatus makes light emitted from a light source 2 containing a large amount of light in the ultraviolet region, such as a mercury lamp, enter a measurement cell 1 and transmit the transmitted light to a phototube or the like. Light is received by the light receiver 3 and output to the computing means 16 as an electrical signal.

  Further, the measurement cell 1 is provided with a temperature sensor and a pressure sensor, and the outputs of these sensors are input to the temperature detection means 14 and the pressure detection means 15 and converted into temperature information and pressure information. , Input to the arithmetic means 16. The computing means 16 can correct the measured mercury concentration based on such information.

  On the other hand, the sample gas 10 is introduced into the measurement cell 1 by the suction pump 9 provided on the exhaust side of the measurement cell 1, but before being introduced into the measurement cell 1, a compound such as a chloride is reduced by the reducing means 4. Mercury present in this state is reduced to atomic mercury.

  Between the reducing means 4 and the measurement cell 1, the transport path of the sample gas 10 is once branched into two and then joined again, and either of them is provided by an electromagnetic valve 8 provided at the joining point. One route is selected.

  One of the two paths transports the sample gas 10 after the reduction treatment to the measurement cell 1 as it is (sample gas introduction path 5), and the other path is the mercury removing means 7 provided in the path. Thus, mercury in the sample gas 10 is removed and transported to the measurement cell 1 (reference gas introduction path 6).

  As shown in FIG. 7, the mercury removing means 7 is filled with a catalyst 12 made of ceramic pellets having a noble metal supported on the surface, and the atomic mercury contained in the sample gas 10 passing through the inside. Is absorbed by amalgamating with the noble metal on the surface of the catalyst 12. Hereinafter, the sample gas that has passed through the mercury removing means 7 will be referred to as a reference gas 11.

  In the above configuration, the mercury concentration measuring device obtains the mercury concentration in the sample gas 10 according to the following procedure.

First, the reference gas 11 that has passed through the mercury removing means 7 is introduced into the measuring cell 1, and the light intensity at a specific wavelength, for example, 254 nm, which is the absorption wavelength of atomic mercury, is measured. Next, the electromagnetic valve is switched to introduce the sample gas 10 into the measurement cell 1, and the light intensity of the specific wavelength is measured. At this time, the difference between the two light intensities becomes the light absorption amount of the substance removed from the sample gas 10 by the mercury removing means 7. Therefore, the mercury concentration in the sample gas 10 can be obtained from this absorbance based on the known relationship between the absorbance at a specific wavelength and the mercury concentration.
Japanese Patent Application No. 2002-168773

  However, when the sample gas 10 contains an organic substance, the catalyst 12 used in the above configuration attaches not only mercury but also an organic substance to the surface. As a result, the reference gas 11 obtained will be described later in detail, but the content of organic matter is smaller than the amount of organic matter that is originally contained. In general, an organic substance has a broad light absorption characteristic over a wide wavelength range, and absorbs light having an absorption wavelength of atomic mercury. For this reason, the light absorption obtained by the conventional mercury concentration measuring apparatus is the sum of the light absorption of mercury and the light absorption of the reduced organic matter. Accordingly, the mercury concentration obtained from the light absorption amount includes an error corresponding to the light absorption amount of the organic matter adsorbed on the catalyst 12.

  The present invention has been proposed in view of the above-described conventional circumstances, and a mercury concentration measuring apparatus and a mercury concentration measuring method capable of performing highly accurate measurement even when an organic substance is contained in a sample gas. The purpose is to provide.

  In order to achieve the above object, the present invention employs the following means.

  The mercury concentration measuring apparatus of the present invention includes a sample gas introduction path for introducing a sample gas to a measurement cell for measuring the mercury concentration in the sample gas by atomic absorption spectrometry, and a reference gas obtained by removing mercury from the sample gas. A reference gas introduction path is introduced.

  In addition, the reference gas introduction path is provided with a honeycomb structure having a metal constituting the amalgam on the surface by direct contact with mercury for purification of the reference gas.

  According to the above configuration, it is possible to measure the light absorption amount of the reference gas and the light absorption amount of the sample gas from which only mercury is removed without removing organic substances from the sample gas.

  For this reason, it is possible to detect the amount of absorption of mercury contained in the sample gas, that is, the concentration of mercury with high accuracy from the difference between both amounts of absorption.

  The metal constituting the mercury and the amalgam is preferably gold. This is because mercury can be absorbed efficiently.

  In another aspect, the present invention can provide a mercury concentration measurement method comprising the above-described procedure.

  According to the present invention, the reference gas is purified by efficiently removing only mercury in the sample gas by providing the honeycomb structure having the metal constituting the amalgam on the surface by direct contact of the sample gas with mercury. Can do. For this reason, it is possible to obtain the mercury absorption amount with high accuracy from the difference between the transmitted light amount of the reference gas and the transmitted light amount of the sample gas.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic functional block diagram of a mercury concentration measuring apparatus to which the present invention is applied.

  The mercury concentration measuring apparatus of the present embodiment is the same as the configuration of the conventional mercury concentration measuring apparatus except that a honeycomb-like mercury removing means 13 is provided instead of the conventional mercury removing means 7. The measurement procedure is the same as that of the prior art except that the reference gas is purified by the honeycomb-like mercury removing means 13.

  As shown in FIG. 2, the honeycomb-like mercury removing means 13 houses a honeycomb structure 22 inside a housing 21. The honeycomb structure 22 has a structure in which a large number of through-holes in the axial direction are gathered, and the sample gas 10 entering from the introduction port 23 passes through the inside of the honeycomb structure 22 and is discharged from the discharge port 24. It has become so.

  FIG. 3 is a sectional view of the honeycomb structure 22 (AA section in FIG. 2). In the example shown in FIG. 3, a substrate having a honeycomb structure is formed by stacking a plurality of layers on a concentric circle with members on which corrugated plates 27 are arranged on the outer surface of a plate material 26.

  As shown in the cross-sectional view of FIG. 4, the surface of the plate material 26 and the corrugated plate 27 is washed by a coating process (process of fixing the surface by baking after being immersed in a gel body and coating the surface). As a result, a wash coat layer 28 such as a solid oxide or carbon fiber is formed, and a large number of gold particles 29 are dispersed and supported on the surface of the wash coat layer 28 by a process similar to the wash coat process.

  The material of the plate material 26 and the corrugated plate 27 that are the base material of the honeycomb structure 22 may be any material that can withstand the firing performed in the above-described washcoat treatment, and for example, a metal such as stainless steel or ceramics is used. be able to.

  The casing 21 may be made of any material, but is preferably a resin such as polypropylene that does not form atomic mercury and amalgam. In this way, even if the mercury removal capability of the honeycomb-like mercury removing means 13 is lowered due to long-term use, the material of the casing 21 does not change due to amalgamation. The mercury removal capability can be restored simply by exchanging 22.

  When the sample gas 10 is passed through the honeycomb structure 22 as described above, the atomic mercury contained in the sample gas 10 comes into contact with the gold particles 29 dispersedly supported on the surface of the honeycomb structure 22 to form an alloy. To make up amalgam. For this reason, atomic mercury is removed from the sample gas 10.

  On the other hand, organic substances contained in the sample gas 10 are not removed from the sample gas 10.

  As a specific example showing that the organic matter is not removed, FIG. 5A shows a case where a sample gas (containing no mercury) is allowed to pass through the honeycomb-like mercury removing means 13 of the present invention. Indicates the amount of transmitted light. As a comparative example, the amount of transmitted light of the conventional mercury removing means 7 is shown in FIG.

  In FIG. 5, the measurement cell 1 includes a gas not containing an organic substance, a gas containing an organic substance, and an organic substance that has passed through the honeycomb-like mercury removing unit 13 (or the mercury removing unit 7) as time passes. Gas is introduced in order.

  The honeycomb-shaped mercury removing means 13 uses a cylindrical honeycomb structure 22 having a diameter of 30 mm × a length of 50 mm and a cell density of 600 cells / square inch. An alumina washcoat layer 28 is formed on the surface of the honeycomb structure 22, and gold particles are dispersed and supported on the washcoat layer 28.

  On the other hand, the conventional mercury removing means 7 uses a glass tube filled with a catalyst 12 in which a noble metal is supported on the surface of a pellet made of cylindrical alumina having a diameter of 3 mm and a length of 3.5 mm. .

  Although quantitative values cannot be specified on the surfaces of both mercury removing means, there is sufficient gold (noble metal) to purify the reference gas 11 (remove atomic mercury from the sample gas). ing.

  The gas flow rate of the sample gas was 300 ml / min, and paradichlorobenzene was mixed as an organic substance.

  5A and 5B, there is no difference between the time region 31 in which a gas not containing an organic material is introduced and the time region 32 in which a gas containing an organic material is introduced, and a gas containing an organic material is introduced. When this is done, it can be confirmed that the amount of transmitted light is reduced by the absorption of the organic matter.

  On the other hand, in the time region 33 in which the gas passed through the honeycomb-shaped mercury removing means 13 of the present invention and the conventional mercury removing means 7 is introduced, both show different results. That is, the sample gas that has passed through the conventional mercury removing means 7 shows the same amount of light transmission as when the sample gas containing no organic matter in the time domain 31 was introduced because the organic matter in the sample gas was removed. The sample gas that has passed through the honeycomb-shaped mercury removing means 13 of the present invention once shows the same light transmission amount as the sample gas not containing organic matter, and then the same light as when the gas containing organic matter in the time region 32 was introduced immediately. The amount of transmission.

  From the decrease A of the light transmission amount in the time region 33, it can be understood that the organic matter is not removed when the honeycomb-like mercury removing means 13 is used.

  As described above, by passing the sample gas 10 through the honeycomb-shaped mercury removing means 13, the reference gas 11 from which only atomic mercury has been removed can be purified without removing the organic matter in the sample gas 10. It becomes possible.

  Therefore, the amount of transmitted light of the sample gas 10 introduced into the measurement cell 1 and the amount of transmitted light of the reference gas 11 are individually measured by switching the electromagnetic valve 8, and from this difference, the amount of absorption of the sample gas 10 is obtained, The amount of atomic mercury contained in the sample gas 10 can be obtained with high accuracy. At this time, by shortening the switching cycle of the solenoid valve 8 (several seconds to several tens of seconds), it is possible to measure mercury concentration closer to real time.

  The configuration of the honeycomb-like mercury removing means shown in the above embodiment shows a specific example, and does not limit the technical scope of the present invention. For example, instead of gold, mercury, such as silver, copper, tin, zinc, lead, sodium, potassium, and cadmium, and a metal constituting amalgam may be supported. Further, the shape thereof may be any shape as long as it has a honeycomb structure and a metal constituting the amalgam exists on the surface thereof, and can be appropriately changed within a range having the effect of the present invention. is there.

1 is a schematic functional block diagram of a mercury concentration measuring apparatus to which the present invention is applied. Sectional drawing of the honeycomb-like mercury removal means of this invention. Sectional drawing of the honeycomb structure of this invention. Sectional drawing of the honeycomb structure of this invention. Explanatory drawing which shows the difference of the adsorption power of the organic substance in the honeycomb-like mercury removal means of this invention, and the conventional mercury removal means. Schematic functional block diagram of a conventional mercury concentration measuring device. Sectional drawing of the conventional mercury removal means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement cell 2 Light source 3 Light receiver 5 Sample gas introduction path 6 Reference gas introduction path 7 Mercury removal means 8 Electromagnetic valve 10 Sample gas 11 Reference gas 13 Honeycomb-like mercury removal means 22 Honeycomb structure

Claims (4)

In a mercury concentration measurement device that measures the mercury concentration in a sample gas by atomic absorption spectrometry,
A sample gas introduction path for introducing the sample gas into a measurement cell for performing absorption analysis;
A reference gas introduction path for introducing a reference gas obtained by removing mercury from the sample gas into the measurement cell;
Provided in the reference gas introduction path, a honeycomb structure carrying a metal constituting the amalgam by direct contact with mercury;
A mercury concentration measuring device characterized by comprising: The mercury concentration measuring apparatus according to claim 1, wherein the metal constituting the amalgam is gold. In the mercury concentration measurement method that measures the mercury concentration in the sample gas by atomic absorption spectrometry,
A step of purifying the reference gas by passing the sample gas through a honeycomb structure supporting a metal constituting the amalgam by direct contact with mercury;
Performing an absorption analysis of the reference gas;
Performing an absorption analysis of the sample gas;
Calculating a difference between an absorption analysis result of the reference gas and an absorption analysis result of the sample gas;
A method for measuring mercury concentration, comprising: The mercury concentration measuring method according to claim 3, wherein the metal constituting the amalgam is gold.

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