JPH0245793Y2 - - Google Patents

Description

[Detailed explanation of the idea]

(Field to which it belongs) This invention relates to a sample gas collection conduit that leads sample gas containing low concentration ammonia (NH ₃ ) gas to an NH ₃ gas analyzer. In particular, there is no loss due to chemical changes of NH ₃ within the conduit, and NH ₃
This invention relates to a device that enables accurate measurement of gas concentration using an analyzer. (Prior art) With the recent demand for a clean air environment, ammonia catalytic reduction type denitrification equipment has been introduced in order to reduce NOx in so-called flue gas emitted from chimneys. It became necessary to measure the leak ammonia leaking from the machine. Exhaust gas often contains sulfur oxides, and in exhaust gas from bad oil or coal, there is a high concentration of sulfur oxides (SOx) represented by sulfur dioxide gas (for example, the concentration is over 1,000 ppm). There is a need to accurately measure low concentrations of ammonia (for example, concentrations of several ppm). When there is such a high concentration of sulfur dioxide gas (SO ₂ ) in the exhaust gas, it is common to use sulfuric anhydride (SO ₃ )
The concentration is also high, ranging from several ppm to several tens of ppm. If the SO ₃ concentration is high, the NH ₃ to be measured will undergo a chemical reaction with SO ₃ during the sampling process from the sampling point to the analyzer, precipitating acidic ammonium sulfate or ammonium sulfate, which may lead to incorrect NH ₃ analysis. become unable. for that,
The structure of the sampling conduit requires considerable technical consideration. However, the task of collecting this type of sample gas is a completely new technical field.
There is no such thing in the prior art. barely,
Since NH ₃ gas has the property of dissolving well in water,
It is known that it is necessary to maintain the water at a high temperature of 100°C or higher to prevent condensation of water in the conduit, but the problem that this invention is trying to solve is that low concentration of NH ₃ in the presence of high concentration of SOx The structure of the sampling conduit required for accurate component analysis of gas containing gas was unknown. (Summary of the idea) In order to solve the above problem, this idea is based on the facts derived from the results of several experiments.
Consists of either SUS304, nickel tube, or glass material tube whose main component is silicon dioxide.
The main idea is to have a structure in which the temperature is heated to 300°C or higher using a heater covered with an electrical insulator, such as a sheath heater. (Structure of the invention) The structure of the invention will be described in detail with reference to drawings. FIG. 1 shows a configuration in which the sample gas sampling conduit of the present invention is used in a flue gas component analysis system. The exhaust gas 1 contains a high concentration of SOx and a low concentration of _NH3 . A probe 3 inserted into the flue penetrating the flue wall 2 takes a sample of the flue gas and directs it to a sample gas sampling conduit 4 . Depending on the distance to which the gas is to be guided, several sample gas sampling conduits may be connected to obtain a considerable length. A special connecting device 5 is used in this case. 6 is a power supply line for the heater. The sample gas is transferred to the NH ₃ analyzer main body 1 through a sampling conduit connected with a connecting device.
It leads to 0. FIG. 2 is a schematic diagram showing the detailed structure of the sample gas sampling conduit 4. As shown in FIG. The central part has been omitted. A conduit 41 runs through the center. along with the sheath heater 4
2, and there are U-shaped or hook-shaped bent portions 43 at the connecting portions at both ends of the conduit 41. A terminal portion 44 of the sheath heater is connected to a conductor 46 through a connection point 45 with an electric wire, and is connected to a power source through a cable 47 and a connector 48. Although the conduit 41 is sometimes called a sampling conduit, there is no particular risk of confusion with the sample gas sampling conduit 4. The sheath heater 42 not only increases the temperature of the conduit 41 to prevent water from condensing within the tube, but also maintains the temperature of the conduit at a predetermined value and maintains the composition of the sample gas introduced into the tube unchanged. The conduit is covered with a heat insulating material 50 such as glass wool, and further covered with a waterproof material 51 to make it durable for outdoor use. A thermocouple 52 is attached to the conduit 41, and the thermoelectromotive force generated by the thermocouple is guided to the connector 54 via the compensation conductor 53, and a temperature measurement signal of the conduit is obtained, which can be used for current control (temperature control) of the sheath heater. It is said that Now, it is necessary to carefully consider the material used for the conduit and its temperature. The inventors obtained new data for determining materials and temperatures based on several experimental results. Next, we will describe the gist of the experiment. According to preliminary experiments, it is known that in order to measure low-concentration NH ₃ in a sample gas containing high-concentration SOx without loss, it is necessary to maintain the gas temperature at 350°C or higher. If the temperature of the conduit is 350℃,
Since it is not possible to use organic materials such as Teflon, possible targets include stainless steel, titanium, and nickel, which are considered relatively chemically stable. The sample gas will be led to the NH ₃ analyzer via a 4 m long tube made of each material, and actual exhaust gas containing about 10 ppm SO ₃ will be sucked into the tube from the inlet of each tube (point A). While injecting NH ₃ gas at a predetermined concentration from the branch port near the pipe inlet (point B), and when injecting NH 3 gas at a predetermined concentration from the branch port near the pipe exit (point C
Point) That is, the value displayed by the NH ₃ analyzer was measured when NH ₃ gas of a predetermined concentration was introduced near the main body inlet of the NH ₃ analyzer. The result is (collected)
Conduit made of nickel, titanium, and stainless steel
The cases of SUS316 and stainless steel 304 are shown in Tables 1, 2, 3, and 4, respectively. The temperature was 350°C in both cases. If there is no difference between the introduction of NH ₃ at point B and point C, it can be determined that there is no loss of NH ₃ within the conduit. The results show that nickel and stainless steel SUS304 are suitable. However, considering its long lifespan in terms of its ability to withstand SOx, stainless steel SUS304 is judged to be superior to nickel, but even nickel can last several years if maintained at high temperatures (over 300°C). The reason Tatin and stainless steel SUS316 are unpalatable is that they have a catalytic action that promotes the precipitation of ammonium sulfate and acidic ammonium sulfate. Next, we attempted an experiment by varying the temperature of the sampling conduit made of SUS304 stainless steel pipe and sucking in actual exhaust gas. Figure 3 shows a record of the output of the NH ₃ analyzer.

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[Table] In the figure, the horizontal scale indicates time, and the vertical axis indicates NH ₃ concentration (ppm). A large change in the concentration output of the NH ₃ analyzer can be seen around the time when the temperature is changed.
When the temperature is raised, there is a temporary increase in output due to the release of adsorbed gas, and when the temperature is lowered, there is a temporary decrease in output due to gas adsorption. The important point is that there is a change depending on temperature between 250°C and 300°C, and the output at 250°C shows a low value, and the output value is almost stable above 300°C. As a result, there is no loss of NH ₃ due to precipitation of acidic ammonium sulfate or ammonium sulfate on the inner wall of the conduit at temperatures above 300℃.
It was found that an equilibrium state of NH ₃ was maintained, and it became clear that it was necessary to maintain the conduit at a temperature of at least 300°C or higher. Usually, according to data obtained in the laboratory, about 10 ppm of SO ₃ and several
Although it is known that precipitation of acidic ammonium sulfate or ammonium sulfate occurs only at temperatures below about 200°C in a mixed gas of ppm NH ₃ , the precipitation temperature in actual exhaust gas is about 100°C higher. . The cause is
This is thought to be because the actual exhaust gas is a multi-component mixed gas and also contains dust (generally containing heavy metals, etc.), which increases the precipitation temperature. Furthermore, using stainless steel pipe SUS304 as a conduit, the temperature of the conduit was varied, and the response speed of the analysis system was tested using actual exhaust gas, and the results shown in Table 5 were obtained.

[Table] Here too, the response time is delayed at a temperature of 250°C, and the response time is particularly long at the time of falling (when the amount of NH ₃ decreases). It can be determined that in order to keep the response time within about 2 minutes (to meet the practical requirements of the measurement system), it is necessary to set the temperature of the conduit to 300° C. or higher. Finally, as a supplementary measure, use a tube made of a glass material whose main component is silicon dioxide, such as quartz glass, hard glass, or Pyrex glass, and keep the temperature at 350℃.
The same experiment was conducted with stainless steel SUS304. As the results are summarized in Table 6, no loss of NH ₃ was found even in this type of material, and it was confirmed that the 90% response characteristic rose at 300°C and fell within 2 minutes and 0 seconds. In the examples of this specification, a sheath heater was used to heat the conduit, but this was because it was suitable as an experimental material. It is clear that the heater is not limited to the sheath heater as long as care is taken to prevent electrical leakage.

[Table] (Effects) As mentioned above, in this invention, the conduit is used as a sample gas collection conduit to accurately measure the NH ₃ concentration in a system that handles gas containing high concentration SOx and low concentration NH ₃ . A stainless steel tube (SUS304), a nickel tube, or a glass tube whose main component is silicon dioxide is used as the material, and a heater such as a sheath heater whose outside is covered with an electrical insulator is placed along the tube. Because the temperature of the tube was heated to over 300°C, the NH ₃ output was not reduced compared to other materials, making it possible to create a chemically stable and fast-responsive measurement system.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of a flue gas analysis system in which the sample gas sampling conduit of the present invention is used;
The figure is a schematic diagram showing the structure of the sample gas sampling conduit of the present invention, and Figure 3 is a diagram showing the experimental results for determining the appropriate temperature of the sampling conduit, and a record showing the change in NH ₃ output depending on temperature. It's a chat. 3 is a sampling probe, 4 is a sample gas sampling conduit, 1
0 indicates the analyzer body, 41 indicates a conduit, and 42 indicates a heater.

Claims (1)

[Scope of utility model registration request] Gas is collected using a probe installed in a system that handles gases containing high concentration SOx and low concentration _NH3 ,
The sample gas sampling conduit 4 is equipped with a considerably long conduit 41 that leads the sampled gas to an NH ₃ gas analyzer, and the conduit 41 is made of stainless steel pipe SUS304,
The conduit 4 is composed of either a nickel tube or a glass tube mainly composed of silicon dioxide.
1. A sample gas sampling conduit, characterized in that an insulated heater 42 for heating the sample gas to 300° C. or higher is provided along the conduit.