JPH026018B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for accurately analyzing NH ₃ in a gas in which SO ₃ coexists. In conventional methods for analyzing ammonia in exhaust gas, when the SO ₃ component coexists, ammonium sulfate compounds are produced from these two components, so it is difficult to accurately analyze ammonia as described below. Conventional methods for analyzing _NH3 in exhaust gas have been established in the Japanese Industrial Standards (JIS K 0099-1969), and
The method used is to collect NH ₃ using the NH ₃ sampling device shown in the figure and analyze it as ammonium ions using the neutralization titration method or the indophenol method. According to the JIS method, when collecting sample gas, in order to prevent moisture from condensing in the sampling tube, the distance between the sample gas sampling tube and the sample gas sampling tube and the absorption bottle must be 120 mm.
NH ₃ in the sample gas is collected by heating the sample gas to a temperature above ℃ and passing the sample gas through an absorption bottle using a boric acid solution (0.5%) as an absorption liquid at a rate of 1 to 2 min. Even if SO ₃ coexists in the exhaust gas at this time, there is no problem with the analysis of NH ₃ captured in the absorption liquid. However, the following points became clear from the results of NH ₃ analysis in exhaust gas using the conventional method (JIS method) shown in Figure 2. (1) The ammonia concentration obtained from the analysis results was 10 to 20 ppm lower than the ammonia concentration in the exhaust gas calculated from the amount of ammonia gas added. (2) After absorption of the sample gas, a white deposit was observed on the inner wall of the sample gas sampling tube, and analysis of this deposit revealed that it was a mixture of ammonium hydrogen sulfate (NH ₄ HSO ₄ ) and ammonium sulfate. These results show that while the sample gas temperature drops to 120°C in the sample gas sampling device, about 10 ppm is lost in the exhaust gas.
Contained SO ₃ and added NH ₃ react to form ammonium hydrogen sulfate (liquid or solid) or ammonium sulfate through the reaction of NH ₃ +H ₂ O + SO ₃ →NH ₄ HSO ₄ NH ₄ HSO ₄ +NH ₃ →(NH ₄ ) ₂ SO ₄ It was assumed that this solid had adhered to the inner wall of the sample gas sampling tube. In other words, JIS K 0099 states that the sample gas sampling tube and the space between the sample gas sampling tube and the absorption bottle must be heated to 120°C or higher.
However, this is not sufficient for the above-mentioned gases in which SO ₃ is present. Therefore, when the heating of the sampling tube was increased and the gas temperature at the outlet of the sampling tube reached the temperature above the formation temperature of ammonium hydrogen sulfate (250°C or higher) shown in Figure 3, the HN ₃ salt no longer adhered to the inner wall of the sampling tube. However, in this case, not only did the temperature of the absorption liquid rise, making it necessary to cool the absorption bottle, but also the ammonia concentration in the flue gas calculated from the amount of ammonia gas added, although not as high as in Figure 2, could be obtained from the analytical results. The ammonia concentration was
It showed a value lower than ppm to 10ppm. This is presumed to be because the above-mentioned reaction occurred in the absorption liquid, producing mist (liquid particles of 10 μm or less) and fume (solid particles of 1 μm or less), which were difficult to capture in the absorption bottle and escaped. As described above, since the conventional method (JIS K 0099) has the drawbacks (1) to (3) shown above, it is not possible to accurately measure the NH ₃ concentration in exhaust gas in which SO ₃ coexists. The present invention eliminates the above-mentioned drawbacks of the JISK0099NH ₃ analytical method and provides an analytical method that meets its objectives.
More specifically, the NH ₃ analysis method of the present invention can be applied even when SO ₃ , halogens (Cl, Bvr), etc., and moisture are present in the exhaust gas, or when the exhaust gas temperature is 250°C or higher. be. The present invention attaches and collects liquid or solid (mist and fume) generated from NH ₃ and sulfuric acid.
This is an NH ₃ analysis method, in which liquid or solid ammonia salt is collected using a filtered tube, and the gaseous ammonia salt is collected.
The feature is that it absorbs and collects NH ₃ . That is, the present invention sequentially collects at least a portion of the gas (hereinafter referred to as sample gas) from a gas containing ammonia and sulfur trioxide (SO ₃ ) through a sampling tube,
A method for analyzing ammonia by guiding the mist/fume to a filtered mist/fume trapping section and an absorption bottle, capturing the ammonia content in the trapping section and the absorption bottle, and maintaining the temperature of the collection tube at 250 ° C. or higher,
The method for analyzing ammonia is characterized in that the trapping section is cooled to a temperature at which all solid or liquid products from the ammonia and SO ₃ are produced. Specifically, the cooling of the trapping section is performed until the total amount of ammonia and SO ₃ produces ammonium hydrogen sulfate or ammonium sulfate, and the total amount of ammonia and SO ₃ is the total amount of reaction equivalents. means. In other words, the NH ₃ /SO ₃ concentration ratio in the exhaust gas is 2.0.
If this is the case, NH ₃ exists in a gas state downstream from the trapping section, and can be collected by an absorption bottle. In addition, the NH ₃ /SO ₃ concentration ratio in exhaust gas is
If it is 1.0 or less, the entire amount of NH ₃ is captured in the trapping section as ammonium hydrogen sulfate. The above mist/fume trap with filter is
Gas fibers specified by the Japanese Industrial Standards (JIS-Z-8808) method for measuring dust concentration in exhaust gas,
A dust collector using a filter paper made of silica fiber, fluororesin, membrane, etc., a dust collector using a duct tube made of glass fiber, silica fiber, etc., or a combination of the above dust collector with a spiral tube, etc. Preferably, a spiral tube with a filter is used, and the filter is preferably a membrane filter. Next, the conventional NH ₃ analysis method and gas sampling device will be explained in detail. FIG. 1 is a schematic diagram of an exhaust gas sampling device used in a conventional NH ₃ analysis method. FIG. 2 is a diagram showing the results of NH ₃ analysis in exhaust gas according to the conventional method, and the solid line and dotted line are measured values and set values, respectively. FIG. 3 is a diagram showing conditions for producing ammonium hydrogen sulfate. In Fig. 1, 1 is a sample gas sampling tube, 2 is a filter material, 3 is a heat insulating material, 4 is an absorption bottle, 5 is a gas drying tower, 6 is a flow rate adjustment pot, 7 is a suction pump, 8
is a thermometer, 9 is a pressure gauge, 10 is a wet gas meter (1 rotation 1 to 5), 11 is a three-way pot, 12 is a bypass cleaning bottle, 13 is a heater, 14 is a flow meter, 15 is an ammonia gas cylinder, 16 is a smoke It is a road. In FIG. 1, exhaust gas flows through the flue 16 in the direction indicated by the arrow in the figure. The flow rate of the calculated amount of NH ₃ gas was adjusted using the flow meter 14, and the ammonia concentration in the exhaust gas was set to five conditions: 5, 15, 31, 51, and 58 ppm. Other compositions of this gas are shown in the table below. Gas composition NOx O ₂ CO ₂ SO ₂ SO ₃ N ₂ 120ppm 4% 12% 200ppm Approx. 10ppm Balance dry gas standard H ₂ O Approx. 12% Wet gas standard Set the sample gas sampling setup as shown in Figure 1 for each condition. , Heater 1 to heat the sample gas sampling tube 1 and the space between the sample gas sampling tube 1 and the absorption bottle 4 to 120℃ or higher.
Heat at 3 and then 1 to 2/min with vacuum pump 7.
The sample gas is passed through the absorption bottle 4 at a speed of NH ₃
Collect gas. If the heating between the sample gas sampling tube 1 and the sample gas sampling tube 1 to the absorption bottle 4 is slightly higher than 120°C, it will not be sufficient, and some of the NH ₃ contained in the sample gas will form ammonium hydrogen sulfate and ammonium sulfate in the piping. It was attached as. Therefore, when we analyzed the NH ₃ collected in the absorption bottle 4, we found that the ammonia concentration obtained from the analysis results was higher than the ammonia concentration in the exhaust gas calculated from the amount of ammonia gas added, as shown in Figure 2. The value was several ppm lower. Thus, it can be seen that the JIS method cannot accurately measure the ammonia gas concentration when SO ₃ coexists. As can be seen from Figure 3, this phenomenon corresponds to the fact that at temperatures below 180°C, NH ₃ reacts with SO ₃ to produce ammonium salts. Hereinafter, embodiments of the present invention will be described in detail. FIG. 4 is a schematic diagram of an NH ₃ sample gas sampling device according to the present invention, and FIG. 5 is a schematic diagram of a spiral tube with a membrane filter. In Fig. 4, 1 is a sample gas sampling tube, 2 is a heater, 3 is a spiral tube with a membrane filter, 4 is an absorption bottle, 5 is glass wool, 6 is a mercury manometer, 7 is a bypass, 8 is a vacuum pump,
9 is an oil mist remover, 10 is a thermometer, 11 is a pressure gauge, 12 is a gas meter, 13 is a flue, 14 is a flow meter, and 15 is an ammonia gas cylinder. In FIG. 5, 3a is a spiral tube, 5b is a sliding fitting and coil spring stopper, and 3c is a membrane filter (30φ). In FIG. 4, exhaust gas flows through the flue 13 in the direction indicated by the arrow in the figure. The flow rate of the calculated amount of NH ₃ gas was adjusted using a flow meter, and the ammonia concentration in the exhaust gas was varied from 5.7 to 75 ppm. 4th for each measurement
Set up the sample gas sampling device as shown in the figure, keep the sample gas sampling tube 1 at 250°C or higher (above the production temperature of ammonium hydrogen sulfate), and use the vacuum pump 8 to
The exhaust gas is introduced into the spiral tube 3 with a membrane filter at a rate of 4/min, and part of the NH ₃ is converted into an ammonium salt, and the NH ₃ gas is collected in the absorption bottle 4. The adhesion of the ammonium salt produced was investigated. The sample gas at 360°C was added so that the SO ₃ concentration was 10 ppm and the ammonia concentration was 50 ppm, and the sample gas was passed through a spiral tube with a membrane filter (6 mm φ total length 2.8 m) at a speed of 2 to 4 min. The temperature is set to 180℃ or less, and the ammonium salt generated at this time is attached to the inner wall of the tube.
Analysis of NH ₃ confirmed that 16 to 18 ppm of NH ₃ was attached. This is because ammonia is SO ₃
This shows that it was completely deposited as ammonium hydrogen sulfate or ammonium sulfate.
The collector for the ammonium salt produced at this time may be one that can cool the sample gas and sufficiently collect the ammonium salt dust; however, a spiral tube or a porous film-like membrane filter with a high porosity ( For example, a combination of "Millipore Membrane Filter" manufactured by Toyo Kagaku Sangyo Co., Ltd.) is convenient.
The results are shown in Table-1.

[Table] Next, a simulated gas at the outlet gas of the economizer of a heavy oil-fired boiler equipped with a dry denitrification device in which NH ₃ gas and SO ₃ gas coexist was adjusted to the composition shown in the table below, and the sample gas shown in Figure 4 was collected. Set up the device and set the temperature of sample gas sampling tube 2 to 250℃ (the generation temperature of ammonium hydrogen sulfate).
That's all. Simulated exhaust gas composition NOx O ₂ SO ₂ SO ₃ CO ₂ N ₂ 120ppm 4% 200ppm 10ppm 12% Balance dry gas standard NH ₃ 6-75ppm H ₂ O Approx. 12% Wet gas standard Sample gas at a rate of 2-4/min NH ₃ and
SO ₃ is forced to react to produce ammonium hydrogen sulfate and ammonium sulfate. As in the previous example, under the conditions of SO ₃ 10ppm and NH ₃ 50ppm, the table -
As shown in Figure 1, the gaseous NH ₃ concentration captured in the absorption bottle is about 30 ppm. Therefore, if we look at the conditions for producing ammonium hydrogen sulfate in Figure 3, when NH ₃ is 30 ppm and SO ₃ is 1 ppm, the production temperature of ammonium hydrogen sulfate is approximately 203°C.
If it is cooled to 180℃, the gaseous SO ₃ concentration will be almost zero, and the entire amount of SO ₃ coexisting with NH ₃ will generate ammonium salts, so 180℃ can be said to be the temperature at which the entire amount is formed. . The generated mist and fume-like ammonium salt were collected in the spiral tube 3 with a membrane filter, and NH ₃ in the gas state was collected in the absorption bottle 4. Next, transfer the membrane filter to a beaker,
Thoroughly clean the inside of the spiral tube and filter holder, and add the cleaning solution to the beaker. Pour 50 ml of N/50 sulfuric acid solution into a beaker and heat to dissolve ammonium salts attached to the membrane filter and extract all NH ₃ . After distilling the main extract and absorption liquid, the distilled NH ₃ was measured by neutralization titration, and solid (fume-like) and gaseous NH 3 were measured.
The NH ₃ concentration was determined separately. The results are shown in FIG. As described above, it can be seen that according to the present invention, the NH ₃ concentration can be measured extremely accurately even if SO ₃ coexists in the exhaust gas.

[Brief explanation of drawings]

1 to 3 are explanatory diagrams of the conventional method, and FIGS. 4 to 6 are explanatory diagrams of the present invention. In Fig. 4, 1... collection tube, 3... spiral tube with membrane filter, 4... absorption bottle.

Claims (1)

[Claims] 1. At least a part of the gas containing ammonia and sulfur trioxide (SO ₃ ) (hereinafter referred to as sample gas) is sequentially introduced into the sampling tube, the mist/fume trapping section with a filter, and the absorption bottle, and In the method of collecting ammonia in a trapping section and an absorption bottle and analyzing ammonia, the temperature of the collection tube is maintained at 250 ° C. or higher, and the trapping section is
A method for analyzing ammonia, which comprises cooling to a temperature at which all solid or liquid products from the ammonia and SO ₃ are produced.