JPH03221704A - Combustion and burner - Google Patents

Abstract

PURPOSE:To suppress the quantity of the NOx generation without increasing the quantity of CO generation by making a cooling liquid flow in a cooling pipe installed in visible flame and extracting a specified quantity of heat that is generated in a gas burner, cooling part of the flame, and making the CO that is formed in the cooling section contact with the adjacent flame above the cooling section. CONSTITUTION:A U-shaped cooling pipe is installed above a unit burner 1 (the space in which visible flame is formed) and, as the cooling liquid is passed as in the arrow marks a, b, and c, flame 3' is formed with gas combustion. With this combustion of the combustion gas a flame cooling face Fc is formed in the section of the flame 3' which is in contact with the cooling pipe 5 and cooled and in the section of the flame 3' which is subject to radiation cooling by passing in the nearest distance to the cooling pipe 5 are formed, and the other sections form a normal flame Fn. The cooling of the flame by a cooling pipe consists of the extraction of sensible heat in the gap between the flame and the cooling pipe and the extraction of condensation heat of the steam in the gas formed in the combustion, and extraction of evaporation heat by reevaporation of the condensed steam in combination, and 2-4.5% of the heat generated in the visible flame is extracted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for combusting fuel gas, and particularly to a combustion method and apparatus improved to control the generation of NOx. be.

[Conventional technology]

Combustion devices that use gas as fuel are widely used in water heaters and space heaters, and improvements are being made to make them more compact and have higher loads.

On the other hand, from the standpoint of pollution prevention, it has become a social demand to suppress the occurrence of No-No-works.

However, there is a problem in gas combustion technology that it is difficult to achieve both compactness and high-load combustion equipment and reduction of N○χ.

As flE and low No. conversion burners, fully premixed burners such as Schwanck burners and secondary flame formation Bunsen burners with a primary combustion chamber are well known, but all of them have a combustion amount range. There are disadvantages such as the inability to obtain a wide range of air pressure, difficulty in controlling the primary air ratio, and the complicated structure and high manufacturing cost.

[Problem to be solved by the invention]

Known methods for suppressing the amount of NOx generated can be categorized in principle: a. flame cooling method; b.

These methods include the concentration combustion method, CO two-stage combustion method, d, exhaust gas recirculation, etc., but all of them require replacement or major modification of the burner to be applied to an existing combustion device, and are not economical.

Furthermore, although the flame cooling method described above is effective if it merely reduces the number of no-cuts, it is accompanied by the problem that the amount of CO generated increases by cooling the flame.

The present invention has been made in view of two circumstances: it does not require any modification to the main body of a conventional burner, and therefore does not adversely affect the combustion range, load performance, or combustion performance of the conventional burner. It is an object of the present invention to provide a combustion method and a combustion device capable of suppressing the amount of N○χ generated without causing any adverse effects or increasing the amount of CO generated.

[Means to solve the problem]

In order to achieve the above object, a combustion method according to the present invention includes: A method of burning fuel gas using a gas burner.

A cooling pipe is disposed within the visible flame formed by the gas burner, and a cooling liquid is passed through the cooling pipe to reduce the amount of heat generated by the gas burner by 2.
~4.5% of the heat is removed, and the above heat removal cools a part of the flame to suppress the generation of NOx, and the CO generated in the part where the flame has been cooled is removed from the adjacent area above the cooling part. It is characterized by complete combustion when exposed to flame.

Moreover, the combustion device according to the present invention is as follows.

In a combustion device having a flame forming surface constituted by a plurality of flame hole groups, a substantially horizontal cooling pipe is provided in a space where a flame is formed by the gas burner, and a cooling liquid is provided in the cooling pipe. It is characterized by comprising a means for distributing the.

[Effect]

According to the method of the present invention described above, a part of the flame is cooled, so
In the cooling section, the generation of NOx is suppressed and C
0 generation amount increases.

However, since the cooling part is located within the visible flame, the CO generated in this part rises and touches the surrounding flames, where it is completely combusted and becomes CO2.

In this way, N can be reduced without increasing the amount of C0 generated.
The amount of o and e generation is suppressed.

The amount of heat removed by the above cooling is 4.5% of the amount of heat generated.
If it exceeds 2%, there is a risk that water droplets will adhere to the cooling pipe and drip onto the burner, and if it is less than 2%, it will be difficult to control the flow rate of the cooling liquid, and if the refrigerant is water, bumping will occur. However, as mentioned above, the amount of heat removed should be 2 to 4 times the amount of heat generated.
．． By setting it to 5%, these difficulties can be overcome.

Further, according to the above-mentioned apparatus of the present invention, a cooling pipe is provided in the space where visible flame is formed, and a means for circulating a cooling liquid through the cooling pipe is provided. Heat can be easily removed.

Furthermore, since the flame forming surface of the burner is substantially horizontal and the cooling pipe is also substantially horizontal, heat can be efficiently removed even when the flames are arranged three-dimensionally.

Cooling pipes do not have to be placed strictly horizontally.

It should be horizontal. The reason for this is that when drawing out the coolant (for example, water) from the cooling pipe, it is better to have a slight slope. This is because the slope allows the relative positions of the plurality of flames to change little by little, making it easier to accommodate various combustion conditions.

〔Example〕

Fig. S shows a conventional gas burner to which an embodiment of the present invention is applied, for comparison and reference; (A) is a front view, and (B) is a side view. .

Reference numeral 1 denotes a unit burner, which mixes fuel gas ejected from a nozzle 2 with air, blows it upward, and burns it to form a flame 3.

A large number of unit burners 1 are arranged in rows in the depth direction of the page,
The flame forming surface is aligned horizontally. Reference numeral 4 denotes a wire mesh for rectification provided near the flame formation surface.

The flame 3 is an inner flame light emitting part 3a as shown in the figure.

A visible flame consisting of a CO danger zone 3b, a maximum temperature zone 3c, and an outer flame emitting zone 3d, and an invisible flame 3e at its outer periphery.
It is formed by.

In the apparatus of this embodiment, a cooling pipe is arranged approximately horizontally within the visible flame.

FIG. 2 shows a cooling pipe 5 disposed above the unit burner 1 shown in FIG. 5 so as to penetrate through the visible flame, and its overall perspective view is as shown in FIG. 1. It is.

As shown in FIG. 1, the cooling pipe 5 of this example has a U-shaped tube shape, and one of its parallel parts is an outgoing pipe 5a.

The other is echo 5b.

Cooling fluid (cooling water in this example) is
Water is supplied as indicated by arrow a, and water is passed as indicated by arrows S and C.

In this example, the outgoing pipe 5a has a slight upward slope, and the reverberation pipe 5b has a slight downward slope.

As a result, the height H3 of the outgoing tube 5a appearing in FIG. 2(A) is slightly lower than the height H2 of the echo 5b.

In FIG. 2(B), the outgoing tube 5a and the echo 5b almost overlap.

Having a slope in this way is convenient for draining water, makes it difficult for air bubbles to flow into the pipe, and widens the range of combustion conditions that can be accommodated, as will be described in detail later.

In this example (see Figure 2), Width W of flame 3' = s o Distance between outgoing pipe M5a and echo 5b W2 = 40 mm Height of flame 3' H1 = 70 m++ Height of outgoing pipe 5a H3# return Height of pipe 5b H2# 30 m
It is.

An example of implementing the combustion method according to the present invention using an embodiment of the combustion apparatus according to the present invention configured as described above will be described next.

As shown in FIG. 1, in a combustion apparatus in which unit burners 1 are arranged in a row and a group of flame holes constituted by these unit burners constitutes a flame formation surface, the unit burners 1 are arranged above the unit burners 1 (that is, visible flame A U-shaped cooling pipe is installed in the space formed by the arrows a and b to supply cooling liquid (water in this example).

While circulating as shown in C, gas combustion is performed to create flame 3.
′ is formed.

When the fuel gas is combusted in this manner, the result is as shown in FIG. 3. That is, the part of the flame 3' that is cooled by touching the cooling pipe 5 and the part that passes within close range of the cooling pipe 5 and receives radiation cooling form the flame cooling surface Fc, and the other part (
The part not subjected to cooling) normally forms a flame Fn. Generally speaking, a cooling zone Fc' is formed around and above the cooling pipe 5.

The cooling of the flame by the cooling pipe described above is achieved by removing sensible heat through heat conduction between the flame and the cooling pipe, removing heat of condensation from water vapor in the combustion gas, and re-evaporating the condensed water vapor. This is done in combination with the removal of heat of evaporation, and heat is removed from the visible flame.

Due to the above heat removal, the temperature of the flame cooling surface Fc becomes lower, and NO
Generation of x is suppressed.

Due to the bluff body effect of the cooling pipe 5, an exhaust gas recirculation region (in FIG. 3, the gas flow is indicated by an arrow) is formed near the flame cooling surface Fc. Through this partial exhaust gas self-recirculation, the cooled unburned gas directly above the pipe and the hot combustion gas further above are mixed in sequence and burn while extending the residence time, further suppressing the amount of NOx generated. Ru.

However, when a portion of the flame is cooled as described above, although the cooling effect reduces the amount by more than 100%, the problem arises that the amount of CO generated increases due to the cooling. Therefore, there is no practical value unless this increase in the amount of C○ generation is prevented.

In this embodiment, C generated near the cooling pipe 5
○ flows into the aforementioned exhaust gas recirculation region (represented by many small arrows), flows in a spiral shape, and flows into the adjacent normal flame F.
When it comes into contact with n, it is combusted and becomes CO2.

FIG. 4 is a chart in which the horizontal axis shows the amount of heat removed and the vertical axis shows the Noχ reduction.

The amount of heat removed is expressed as a percentage of the rated amount of heat generated by the gas burner.

The N○χ reduction rate is expressed as a percentage compared to the amount of N○χ generated in the conventional example (FIG. 5).

In this example, a peak of the reduction rate is observed around 4% of the amount of heat removed.

The amount of heat removed is obtained by multiplying the temperature difference ΔT between the inflow temperature and the outflow temperature of the cooling water by the flow rate, but when removing 4% heat, the combination of flow rate and temperature difference can be changed in various ways.

In FIG. 4, the solid line curve is for a temperature difference ΔT=6°C, and the broken line curve is for a temperature difference ΔT=50°C.

In this example, specifically, when ΔT=6°C, the inlet water temperature is 17°C, and the water outlet is 23°C. Further, when ΔT=50°C, the inlet water temperature is 17°C, and the water outlet temperature is 67°C.

Although there are some differences in the NOx reduction effect as the temperature difference ΔT changes, the best results were obtained in all cases when the amount of heat removed was around 4%.

According to experiments conducted by the present inventors, when the specifications of the gas burner and the composition of the calorific gas change, the amount of heat removed to obtain the best results also changes, but it is generally within the range of 2 to 4.5%.

Furthermore, it is not preferable for the amount of heat removed to deviate from this range for the following reasons.

In order to reduce the amount of heat removed, specifically, the diameter of the cooling pipe is made smaller and the flow rate of the coolant is reduced, but since there is a limit to making the diameter smaller, the amount of heat removed is as small as less than 2%. To obtain this, the flow rate of the coolant must be considerably reduced. As a practical matter, reducing the flow rate makes flow control difficult. Therefore, if the flow rate control is inappropriate, there is a risk that the coolant will cause bumping.

Moreover, when the amount of heat removed is made larger than 4.5%, water condensed on the outer circumferential surface of the cooling pipe drips. This water is disadvantageous because it contains nitrogen compounds similar to nitric acid and corrodes the burner. For these reasons, the amount of heat removed is 2 to 4.5
% is appropriate. The diameter of the cooling pipe may be appropriately set so as to obtain the above-mentioned amount of heat removal.

(See Figure 2) Cooling pipe 5a relative to flame height Hl
Although the height of the flame does not need to be strictly regulated, according to experiments conducted by the present inventors, it is advantageous to set the height of the cooling pipe to 0.4 or more of the flame height Hl.

However, the flame height Hl changes depending on the load on the gas combustion device. Therefore, it is not possible to obtain the optimum cooling pipe height under all load conditions.

The cooling pipe 5 of this embodiment has a slope and its height changes steplessly including H2 + H3, so the best condition can be obtained somewhere in the cooling pipe under all load conditions. . As a result, even if the load state changes, the NOx reduction rate remains approximately constant within the range where the cooling pipe is inside the visible flame.

〔Effect of the invention〕

As explained above, according to the combustion method according to the present invention,
There is no need to modify the burner main body, and therefore there is no risk of adversely affecting the burner combustion range or load performance, and the amount of NO generation can be suppressed without increasing the amount of C○ generated.

Furthermore, since the combustion apparatus of the present invention is equipped with a substantially horizontal cooling pipe provided in a space where a visible flame is formed, and means for causing a cooling liquid to flow through the cooling pipe, the above-mentioned The invented method can be easily and reliably implemented.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a combustion apparatus according to the present invention. FIG. 2(A) is a front view of the above embodiment, and FIG. 2(B) is a side view of the same. FIG. 3 is an explanatory diagram of a combustion state in one example in which the combustion method according to the present invention is implemented using the combustion apparatus of the above embodiment. FIG. 4 is a chart for explaining the effects of the above embodiment. FIG. 5 shows a conventional combustion device, with FIG. 5(A) being a front view and FIG. 5(B) being a side view. Engineering...unit burner, 2...nozzle, 3,3'...
Flame, 3a... Inner flame light emitting part, 3b... CO danger area,
3C... Maximum temperature range, 3d... Outer flame emitting zone, 3e...
・・Invisible flame, 4 ・Wire mesh, 5・・Cooling pipe, 5a
... Outgoing pipe of cooling pipe, 5b... Rebellion of cooling pipe.

Claims (1)

[Claims] 1. A method of burning fuel gas with a gas burner, comprising: arranging a cooling pipe within a visible flame formed by the gas burner, and flowing a cooling liquid through the cooling pipe; 2 of the amount of heat generated by the gas burner
~4.5% of the heat is removed, and the above heat removal cools a part of the flame to suppress the generation of NOx, and the CO generated in the part where the flame has been cooled is removed from the adjacent area above the cooling part. A combustion method characterized by combustion by contact with flame. 2. In a combustion device having a flame forming surface constituted by a plurality of flame hole groups, a substantially horizontal cooling pipe provided in the space where a visible flame is formed by the gas burner; A combustion device characterized by comprising: means for circulating a cooling liquid.