JPS62298613A - Method and device for removing soot in exhaust gas - Google Patents

Abstract

PURPOSE:To remove soot contained in an exhaust gas simply and efficiently by introducing said exhaust gas containing soot into an atmosphere in which at least oxygen and/or water exists and carrying out electric discharge in this atmosphere. CONSTITUTION:When removing soot contained in an exhaust gas, the exhaust gas containing the soot is introduced into an atmosphere in which at least oxygen and/or water exists and electric discharge is carried out in this atmosphere, thereby, removing the soot contained in the exhaust gas. As for the means of electric discharge, the quantity of discharge is controlled based on the detected result of the quantity of the soot, and a pulse corona discharge is employed. For example, a combustion device 1 is formed by stretching a nichrome wire 3 on the axial line of a cylinder part 2, and a high frequency current is allowed to flow in the nichrome wire 3, to generate silent discharge over the whole tube length. Thereby, the soot in the exhaust gas can be removed simply and efficiently.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method and device for removing soot from exhaust gas such as diesel engine exhaust gas.

[Problems to be solved by the prior art and the invention today]
The soot contained in the exhaust gas from diesel engines is a major source of air pollution, but because the particle size of this soot is small, it remains suspended in the atmosphere for a long time and is absorbed into the body through breathing, etc. Moreover, these soots are also contaminated with various harmful substances, which is extremely problematic from a health perspective.Therefore, there is a strong demand for efficient removal of soot from exhaust gases. There is. However, conventionally known methods for removing this soot include filtration using a ceramic filter or electrostatic precipitator; Not only is soot easy to re-disperse, soot has a seemingly very low specific gravity, so the equipment itself has to be large in order to continuously collect large amounts of soot. It is not only difficult to install it in moving vehicles such as cars and passenger cars, but also the disadvantage is that it frequently requires troublesome and tedious maintenance work other than replacing filters and removing collected soot. There are some problems.

[Means for Solving the Problems] In view of the above-mentioned circumstances, the present invention was devised for the purpose of providing a method and device for removing soot from exhaust gas that can eliminate these drawbacks. hand,
It removes soot by burning it,
As a means for achieving this, the first invention is characterized in that the exhaust gas containing soot is subjected to electrical discharge in the presence of at least oxygen and/or water to burn and remove the soot. Further, the second invention is characterized in that a discharge means is provided in the flow path of the exhaust gas containing at least oxygen and/or water along with soot.

According to the present invention, with this configuration, soot can be removed efficiently, almost no maintenance is required, and the device itself can be made lightweight and compact.

As the discharge means used in the present invention, discharge methods such as silent discharge and corona discharge can be adopted, and in corona discharge, there are further methods such as alternating current corona discharge, negative pulse corona discharge, and positive pulse corona discharge. can be further adopted. Furthermore, if the discharge screen of the discharge means is configured to detect the amount of soot and be controlled in accordance with the detection result, higher efficiency can be achieved.

[Experimental Example 1] A wire cylinder type discharge reactor was used as shown in Fig. 1, and the discharge method was silent discharge t1! A combustion device 1 made of toshite soot was formed. Here, the cylinder part 2 is made of brass with an inner diameter of 32mm and a length of 000ffII11, and a nichrome wire 3 with a diameter of 0.5mm is attached to the cylinder part 2.
A high-frequency current is applied to the nichrome wire 3 to generate a silent discharge over approximately the entire length of the pipe.

Furthermore, Fig. 2 shows a flow sheet for this experiment, which shows that city gas is combusted at a low air ratio, and secondary air with an oxygen concentration of 1 to 5% is blown into the combustion apparatus. i! 1 and measure the soot concentration. Figure 3 shows the change in soot 4 degrees due to discharge, and according to this,
The soot concentration when not discharging was about 450 mg/Nm3, but it was observed that the soot concentration was reduced to almost zero by discharging, which shows how effective the present invention is. Almost the same results were obtained when the discharge method was corona discharge.

Note that the reaction temperature in this experiment was 80° C., and the flow rate of exhaust gas to the cylinder part 2 was 2 L/+nin.

The soot concentration was measured by capturing scattered light with an intensity corresponding to the soot number concentration by laser irradiation using a lens and a photomultiplier, and displaying this as a voltage value (mV). Furthermore, it has been experimentally determined in advance that the 41 measurement results are linearly proportional to the soot concentration by performing comparative calibration with the filter weight method.

[Experimental Example 2] In Experimental Example 1, the significant reduction in soot concentration due to discharge was
? 1I11, but we next examine how they are affected by the gas combustion components.

Here, soot is collected in advance on a glass filter,
This was subjected to corona discharge in the combustion device 5 shown in FIG. 4, and the state of combustion of soot by the supplied gas components was examined. Here, the combustion device 5 is constructed by using an electrode plate 7 and a discharge plate 8 formed of brass plates in a closed container 6 in which a supply gas flow L1 and an outflow L1, which will be described later, are formed. A glass filter 9 that had collected the soot was placed on the plate 7, and a silent discharge was generated under the flow of the supplied gas. The reaction temperature was 80° C., the amount of gas supplied was IQ/min, and the discharge voltage was 23 kV.

The supply gas was argon-based, with run 1 being argon only, run 2 being 1% oxygen/argon, run 3 being 2% water/argon, and run 4 being 2% water/1% oxygen/argon. Four types of gas.

The state of soot on the glass filter was observed after two hours. The results are shown in FIG. According to this, run 2,
A decrease in soot is observed in Runs 3 and 4, and it can be seen that it is particularly remarkable in Run 4.

Although this is qualitative, it is clear that at least either oxygen or water must be present in order for soot to burn in an electric discharge, and in particular, soot combustion can occur even in the absence of oxygen if water is present. It can also be noted that the presence of both water and oxygen is optimal.

[Experimental Example 3] Next, in the above example, it was found that electric discharge in the presence of at least one of water and oxygen is effective for soot combustion.
Here, we will observe this quantitatively. The reaction conditions are the same as in Experimental Example 2.

Here, approximately 10 m was added to the glass filter used in Experimental Example 2.
g of soot was collected and accurately weighed, and after discharging the supplied gas components for a predetermined time under the conditions of runs 1 to 6, the amount of remaining soot was measured, and the results are shown in Table 1.

Table 1 From the results in this table, it can be observed that, as in Experimental Example 2, the combustion of soot is promoted by discharge when at least either oxygen or water is present, but especially when there is water. It can be seen that the soot combustion is promoted compared to the case where only oxygen is supplied, and the soot combustion is remarkable in Runs 4 and 5, in which both were supplied. And it turns out that this becomes more pronounced as the amount of water and oxygen increases.

[Experimental Example 4] Next, flammability depending on temperature will be observed. The experimental conditions were as follows: the supplied gas components were the same as in Run 4 of Experimental Example 3, and the combustion temperature was varied. Table 2 shows the results.

Table 2 From the results in this table, it can be concluded that the higher the reaction temperature is, the more effective it is, and that depending on the selection of equipment and conditions, it is possible to cause instantaneous combustion of soot.

[Experimental Example 5] Next, the effects of the present invention will be confirmed using actual exhaust gas from a diesel engine. The soot combustion device used here is the same as that used in Experimental Example 1 (however, the length of part of the cylinder is 500 mm).
+n+n), and the amount of soot is 80mg/
~ m1, exhaust gas with oxygen concentration 5%, carbon dioxide concentration 8%, nitrogen chloride concentration 50 ppm, water concentration 10%, 2Q/
Supply at a flow rate of +++in. And at 30kV, 10
A pulsed corona discharge with a frequency of 0 Hz was discharged to cause a continuous reaction at a reaction temperature of 80° C., and changes in soot concentration were measured. As a result, the soot concentration was 55 mg/Nm.
', and a reduction in soot of 25 mg/Nm' was observed, which proves that the present invention is also effective for diesel engine exhaust gas.

And in this one, by increasing the pulse energy (that is, increasing the voltage frequency), which is +30 II z, the
An increase of 5 mg/Nm' was observed. this is,
It can be inferred that this is due to the fact that the pulsed corona discharge can create a stronger electrolytic atmosphere by applying a high frequency voltage, which improves the volumetric efficiency in the combustion chamber. From this, it is possible to detect the amount of soot, control the amount of discharge by pulse energy based on this, and perform soot combustion in an appropriate state that corresponds to the soot rat. This is convenient because wasteful discharge can be avoided and efficient soot combustion can be performed.

[Operation and Effect] Considering the above, it was confirmed that soot is burned and consumed by discharging in the presence of oxygen and water, but in the presence of oxygen, oxygen receives discharge energy and becomes oxygen It dissociates into radicals, which react with soot to oxidize the soot. Also, in the presence of water, water similarly receives discharge energy and dissociates into 014 radicals.
It is inferred that this attacks the soot and oxidizes it. When water and oxygen coexist, )-I, O+ e →○r■・+H・+e○, +)i
-→OH・10・2F Engineering・+O・→oI (・10M It can be inferred that the generation of ○H radicals (OH・) is further promoted by the formula, and this results in a significant reduction in the amount of soot. This can be confirmed by the fact that the higher the temperature or the higher the discharge energy, the more likely the generation of ○H radicals, the more pronounced this becomes.

Therefore, in the present invention, soot can be burned by extremely simple means of discharging soot in the presence of at least water or oxygen, and soot can be removed from exhaust gas. It can be made lightweight and compact, and because it oxidizes and burns soot, it does not require the troublesome maintenance that conventional traps require.

[Brief explanation of the drawing]

The drawings show an embodiment of the method and device for removing soot from exhaust gas according to the present invention, and FIG. 1 is a side view of a wire cylinder one-type soot combustion device, and FIG. Figure 3 is a measurement result diagram showing changes in soot concentration, Figure 4 is a schematic sectional view of the soot combustion device on the other side, and Figure 5 is a photographic diagram showing the 1Hll'l results of Experimental Example 2. It is. In the figure, 1 is a soot combustion device, 2 is a part of a cylinder, and 3 is a nichrome wire.

Claims (1)

[Claims] 1) Soot-containing exhaust gas is treated with at least oxygen and/or
Alternatively, a method for removing soot from exhaust gas, characterized in that soot is burned and removed by discharging in the presence of water. 2) An apparatus for removing soot from exhaust gas, characterized in that a discharge means is provided in a flow path of exhaust gas containing at least oxygen and/or water along with soot. 3) The device for removing soot from exhaust gas according to claim 2, wherein the discharge means is configured to control the amount of discharge based on the detection result by the soot amount detection means. . 4) The apparatus for removing soot from exhaust gas according to claim 2, wherein the discharge means is a pulse corona discharge.