JPS5948134B2 - Method for reducing NOx in combustion gas from a high-temperature furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reducing NOx in combustion gas from a high temperature furnace.

High-temperature furnaces, typified by glass melting furnaces, generally involve some kind of physical or chemical reaction in the furnace, and the concentration of NOx generated in the combustion gas of these furnaces is often high.

Therefore, from the viewpoint of preventing air pollution, it is desired to quickly establish technology for reducing NOx concentration in exhaust gas.

NOx released into the atmosphere with exhaust gas during fuel combustion
Two methods are being considered to reduce the amount: a method of suppressing the generation of NOx during fuel combustion in the furnace mouth body, and a method of separately removing NOx generated by fuel combustion.

The former method includes methods for suppressing NOx generation by suppressing the flame temperature itself, such as the two-stage combustion method and the exhaust gas circulation method, which have already been implemented in some boilers, but such technologies require high temperatures. The side bottom cannot be put to practical use in high-temperature reactors.

For example, in a glass melting furnace, if the furnace temperature, that is, the temperature of the flame, is lowered, defects such as bubbles and smudges will occur in the product glass, making it impossible to maintain the original functions of the high-temperature reactor.

Further, as the latter method for removing generated NOx, a dry denitrification method and a wet denitrification method are known.

The dry denitrification method uses a reduction catalyst such as iron oxide to reduce NH3,
There are two methods: one in which NOx is reduced using Co, etc., and one in which NOx is reduced in a non-catalytic manner using NH3, both of which are partially in practical use in boilers and the like.

However, the dry catalytic reduction method using a catalyst has the disadvantage that the denitration equipment including the catalyst is generally expensive, and it also costs a lot of money to maintain and operate. In some cases, the exhaust gas is generally dirty, so it has the disadvantage that in many cases it is unavoidable that the performance and life of the catalyst will be significantly reduced.

For example, the combustion gas from a glass melting furnace is in a state of so-called dirty gas, which contains NOx, SOx generated from sulfur in the fuel, scattered glass raw materials, and dust such as decomposed raw materials, which can cause clogging phenomena. No means or methods have been established to resolve the adverse effects on the catalyst.

In addition, the non-catalytic method using NHa has the drawback that although the effective application temperature is low, the range is extremely limited, and it is extremely difficult to perform such control using combustion gas from a high-temperature furnace, and it is not economical. Also inferior.

On the other hand, the wet denitrification method is a method in which NOx is oxidized to N02 and then absorbed into water or alkaline liquid. This method has drawbacks such as requiring a huge amount of wastewater treatment equipment for post-treatment of the treatment liquid that has absorbed □.

The present invention provides a method for effectively reducing NOx in exhaust gas from a high-temperature furnace, particularly a high-temperature reactor, using a very simple method.

That is, in the method of the present invention, the combustion gas from the high temperature furnace is heated to 1100°C.
While in the above temperature range, the hydrocarbon, its oxygen-containing derivative, or a substance containing these will not be incompletely combusted without introducing air or oxygen separately. By introducing it into the system within a quantitative range and bringing it into contact with the combustion gas, the NOx concentration in the combustion gas is reduced.

The exhaust gas targeted in the method of the present invention may essentially be from any so-called high-temperature furnace; for example, exhaust gas from a glass melting furnace, industrial kiln, or other reactor that requires a reaction temperature of 1100°C or higher is used. Applicable as appropriate.

The essence of the method of the present invention is to use hydrocarbons or their oxygen-containing derivatives as the treatment substance for NOx reduction.

As hydrocarbons, lower hydrocarbons such as methane, ethane, propane, and butane are preferably used for economical reasons, but as can be understood from the high processing temperature, they are essentially higher-grade hydrocarbons. Hydrocarbons such as hexane, octane, decane, benzene, and xylene can also be used as appropriate.

In addition, oxygen-containing derivatives of hydrocarbons have molecules such as carbon, hydrogen,
Essentially any compound consisting of oxygen may be used, and flammable oxygen-containing derivatives typified by alcohols such as methyl alcohol, ethyl alcohol, and propyl alcohol may be used as appropriate.

These NOx-reducing treatment substances may be used alone, in combination of two or more, or as a mixture with other components.

Examples of the mixture containing the NOx reduction treatment substance of the present invention include liquefied petroleum gas (L, P, G), kerosene,
There are heavy oil, city gas, etc., and any of these can be used very suitably.

There is no particular limit to the amount of these NOx reduction treatment substances added, and a small amount will have some effect.

Usually, it is used in an amount ranging from about equimolar amount to the amount of NOx generated to an amount that does not generate soot derived from these processing substances.

Specifically, it is determined depending on the amount of NOx generated, the amount of residual oxygen, etc.

When carrying out a catalytic reaction between these treated substances for NOx reduction and combustion gas, there is normally about 0.5 to 10% oxygen remaining in the system, so there is no need to separately introduce air or oxygen, but the furnace body The suction of air leaking into the combustion gas through the gaps between the supports is a phenomenon that is often seen in ordinary furnaces, and is of course not a problem.

The temperature of the combustion gas when brought into contact with the treatment substance for NOx reduction of the present invention needs to be 1100° C. or higher, and if it is lower than this, there is practically no effect of reducing the NOx concentration.

As long as the temperature is 1100° C. or higher, there is no particular upper limit, and the effect is exhibited over a wide range.

Generally, the temperature is particularly preferably about 1200 to 1500°C.

An appropriate contact point is selected from the combustion section of the furnace to the flue section.

For example, in an industrial kiln, between the combustion chamber and the flue outlet, or in a furnace equipped with a heat recovery device, the inside of the heat recovery device
In a glass melting furnace, an appropriate location is selected near the port at the end of the melting tank, inside the heat storage chamber, inside the heat exchanger chamber, or between the flue section.

The contact between the NOx reduction treatment substance and the combustion gas is similar to that in a normal gas phase chemical reaction, and it is desirable to have as large a contact area as possible and to maintain a good mixing state. There is no need for similar, NO
It is sufficient to simply provide nozzles for introducing the x-reducing treatment substance into predetermined locations.

In this way, it has become possible to efficiently reduce NOx in exhaust gas from a high-temperature furnace very easily and inexpensively.

Below, experimental results in a glass melting furnace will be shown as examples.

FIG. 1 is a schematic diagram of a small glass melting tank furnace with a capacity of 750 kg used in the experiment.

This furnace consists of a glass melting section 1, a heat storage chamber 2 with an internal cross section of 1 m x 1 m and a height of about 2.7 m, which has a structure similar to that of a large glass melting tank furnace (however, in experiments, the combustion gas was always directed in a fixed direction). The secondary air is not heated in this part.

), and a flue part 3, and 1 and 2 are connected by a blowing part 4.

In the glass melting section 1, there is molten glass 5 in the lower part, and in the combustion 6 in the upper part, heavy oil A is sprayed from the burner 7 provided at the end of the melting tank 1, and secondary air is introduced from around the burner. burns and keeps the furnace at a high temperature.

The inside of the heat storage chamber 2 is made of checkered bricks 8 as shown in the figure.
It is loaded with.

Therefore, the heavy oil ejected from the burner at the end of the melting tank is burned in the combustion chamber, and the combustion gas passes through the blowout 4 from the melting tank, enters the heat storage chamber 2, passes through the gap between the checker bricks 8, and passes through the flue. Although not shown in the figure, it is discharged into the atmosphere from the flue outlet 9 by an exhaust fan.

Treatment substances for NOx reduction were supplied from the following 10 to 14 positions.

That is, the blowout area 10 at the end of the melting tank, the ceiling 11 of the heat storage chamber.
Upper tier 12 of the part where checker bricks are piled up in the heat storage room,
It was introduced into the combustion gas from the middle stage 13 and the lower stage 14.

Combustion gas (or untreated exhaust gas) to which no treated substances are fed and treated exhaust gas when treated substances are fed are sampled near the flue outlet 15, and are analyzed using a continuous NOx analyzer, and By continuous type 02 analyzer, N
The Ox,02 concentration was measured.

The experiments described in the afternoon were conducted after the furnace was in a steady state, but the temperature of the furnace and therefore the regenerator was relatively low, and the NOx concentration in the combustion gas was relatively low, and the NOx concentration in the combustion gas was relatively high. This was done twice in total.

Table 1 shows an outline of the furnace operation conditions at this time, and the temperature measurement positions were near the treatment material inlet parts 10 to 13, the flue outlet of the heat storage chamber, and the vicinity of the exhaust gas sampling position 15.

The initial contact temperature between the processing material and combustion gas becomes lower as the processing material feeding point becomes processing material supply position 10, 11, 12, 13, and 14 in the order of processing material supply position 10, 11, 12, 13, and 14 in FIG. It means it's smaller.

Example 1 Processing materials were Citrus, P, Go, city gas (4500Kc
The composition published in al/rr+F is expressed in Vol and % as CO5, HH246, CH422, CmHn5.
When injecting CO210022, N210),
If the amount of feed was too large, soot was generated in the exhaust gas after treatment, but when it was thought that no soot would be generated, zero in the exhaust gas after treatment.
□Table 2 shows the relationship between the NOx concentration in the untreated and treated exhaust gas and the inlet point when the concentration is 1%, and the NOx concentration in the untreated exhaust gas is 320 ppm. there were.

These experiments were conducted under the first operation conditions shown in Table 1, and the NOx concentration in the flue gas after treatment decreased at all inlet points. It can be seen that the higher the entrance temperature, the greater the reduction rate.

Example 2 Under the second operation conditions shown in Table 1, when city gas was fed as a treatment substance, the amount of feed and NO in the exhaust gas
The relationship between the X and O□ concentrations is shown in FIGS. 2 and 3.

Fig. 2 shows the results when the material was introduced from the relatively high-temperature melting tank and the ceiling of the heat storage chamber, and Fig. 3 shows the results when the material was introduced from the upper, middle, and lower stages of the relatively low-temperature heat storage chamber.

In both figures, the NOx and O□ concentrations in exhaust gas decrease as the amount of city gas fed increases, and the effect of city gas on reducing NOx in exhaust gas is clear.

Also, for the same amount of feed, the one in Fig. 3 has a higher NOx, 0
2. The amount of decrease in concentration is large.

Example 3 Under the second furnace operation conditions shown in Table 1, when P and G are fed as treatment substances, the relationship between the amount of feed and the NOx, 0□ concentration in the exhaust gas is calculated. It is shown in Figure 4.

At this time as well, it can be fed from any position, P, G,
NOx in the exhaust gas increases with the increase in the amount of NOx fed into the exhaust gas.

Although the 0□ concentration has decreased, it can be seen that at the same feed rate, the higher the feed point temperature is, the greater the decrease in the NOx concentration is.

When feeding from the melting tank with the highest feeding point temperature, NOx
The concentration has been reduced from about 750 ppm to 200 ppm.

Example 4 Under the second furnace operation conditions shown in Table 1, ethyl alcohol was used as the treatment substance and was fed through a special burner equipped with a water cooling device.

The measurement results are shown in Table-3.

According to these results, it can be seen that ethyl alcohol is also effective in reducing NOx concentration.

Example 5 (Comparative Example) Tables 4 and 5 show the results when CO and NH3 were introduced as treatment substances under the first furnace operation conditions shown in Table 1.

1 According to these results, NH3,
When CO is introduced, the NOx concentration increases even though the 02 concentration in the exhaust gas after treatment decreases, indicating that it is not a treated substance for NOx reduction.

Table 4 also shows that for comparison, L, P, and G were fed from the melting tank, and the 0□ concentration in the exhaust gas after treatment was set to the same value as when CO was fed. NOx in exhaust gas after treatment
Concentrations are decreasing.

Since it was confirmed that the temperature near the feeding point increased due to the feeding of these treated substances, it is clear that the fed treated substances were combusted.

However, with N 2 H3 and CO, no NOx reduction effect was observed at all, and it can be seen that the combination of the treatment substance of the present invention and the treatment temperature exhibits a remarkable effect.

Example 6 The same procedure as in Example 6 was carried out under the conditions shown in Table 6 except that kerosene was used instead of ethyl alcohol. The results are shown in Table 6.

This experiment was conducted in a glass melting furnace and a heat storage chamber attached to it, but compared to ordinary high-temperature reactors, no special refractories were used, and the molten glass was already in another furnace. Since the molten glass cullet is simply put into the furnace in advance and no raw material dust is scattered, there are no special conditions required, and it is easy to understand that these results can be applied to high-temperature reactors in general. It will be.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the small glass melting tank furnace used in the experiment, and Figure 2 shows the city gas flow when city gas is used as the processing substance and the feeding point is inside the melting tank and at the ceiling of the regenerator. Figure 3 is a diagram showing the relationship between the amount of NOx and O□ concentration changes in exhaust gas. ,P.G.
FIG. 2 is a diagram showing the relationship between the feed amount and the change in NOX and 02 concentration in the exhaust gas when using the same. 1... Melting furnace, 2... Heat storage chamber, 3...
...Flue section, 4...Blowout section, 5...
- Molten glass, 6... Combustion chamber, 7...
Burner, 8... Brick, 9... Flue outlet, 10, 11.12.13.14... Processing substance supply position, 10... Near the blowout at the end of the melting tank, 11... Near the ceiling of the heat storage chamber, 15...
- Exhaust gas sampling location (near the flue exit).

Claims (1)

[Claims] 1. While the combustion gas from the high-temperature furnace is in a temperature range of 1100° C. or higher, the hydrocarbons, oxygen-containing derivatives thereof, or substances containing these are carbonized without separately introducing air or oxygen. Hydrogen, its oxygen-containing derivatives, or substances containing them are introduced into the system within a quantitative range that does not cause incomplete combustion,
A method for reducing NOx in combustion gas from a high-temperature furnace, the method comprising bringing the combustion gas into contact with the combustion gas. 2. The method according to claim 1, wherein the high temperature furnace is an industrial kiln. 3. In the case of a furnace having a heat recovery device between the combustion chamber and the flue outlet or a heat recovery device, a patent claim that introduces hydrocarbons, oxygen-containing derivatives thereof, or substances containing these into the device and contacts the combustion gas. The method described in Scope No. 2. 4. The method according to claim 1, wherein the high temperature furnace is a glass melting furnace. 5. A patent claim in which hydrocarbons, oxygen-containing derivatives thereof, or substances containing these are introduced into the vicinity of the boat at the end of the melting tank, inside the heat storage chamber, inside the heat exchanger chamber, or in the flue section and brought into contact with combustion gas. The method described in Scope No. 4.