JPH0526082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion method for reducing nitrogen oxide emissions, and more particularly to a method capable of reducing nitrogen oxide emissions when burning gaseous fuel.

Among gaseous fuels, for example, a considerable amount of natural gas reserves have been confirmed around the world, and the situation is such that a considerable amount of supply and demand for commercial boilers as a clean fuel will be secured in the future.

Natural gas can certainly be said to be a cleaner fuel compared to heavy oil and coal. For example, regarding nitrogen oxides (hereinafter referred to as NOx), which are said to be the main cause of air pollution, fuel contains almost no organic nitrogen, so the NOx generated is limited to so-called thermal NOx.

Therefore, the concentration of NOx emitted from gas fuel combustion devices, such as natural gas-fired boilers, has now been suppressed to an extremely low concentration compared to other oil- and coal-fired boilers. However, considering the increasingly serious air pollution problem, the development of more advanced low NOx combustion technology is desired.

Here, most of the NOx in gas-fired boilers is
Since it is limited to thermal NOx, the exhaust gas mixing method is the most effective NOx suppression technology, and it has been confirmed that combining this with the two-stage combustion method has a significant NOx reduction effect. However, the exhaust gas mixing method has drawbacks in terms of ignitability and flame stability, and the two-stage combustion method generates a lot of soot and dust.
Both methods have limitations in their implementation, and although both are extremely effective NOx reduction technologies, the reality is that it is no longer possible to significantly reduce NOx using these methods.

In view of the above-mentioned problems, it is an object of the present invention to provide a combustion method that can improve ignitability and flame stability, reduce the generation of soot and dust, and achieve a significant reduction in NOx.

In short, the present invention provides a combustion method in which nitrogen oxides in a main burner flame are reduced in the gas phase by products in a sub-burner flame formed by combustion under a low oxygen partial pressure. A partition member is provided which is arranged alternately on a virtual circumference in a plane, and has a cylindrical primary air passage opening coaxially within the circle and at the center, and partitions the main burner nozzle and the sub burner nozzle, and the main burner nozzle is In the secondary air passage, the auxiliary burner nozzle is located in the low oxygen-containing gas, the main burner flame is upstream of the burner device, and the main burner flame and the auxiliary burner flame are controlled downstream of the main burner flame by controlling the supply amount of the low-oxygen gas. This is a combustion method for reducing nitrogen oxides, which is characterized by selecting a location where nitrogen oxides are mixed and performing gas phase reduction.

Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a burner device for carrying out the method according to the invention. In the figure, 1 is the inner cylinder, 2
is a partition member, which alternately partitions adjacent small burners among a plurality of small burners (8 pieces) arranged on a virtual circle in one plane as shown in FIGS. 3 and 4,
The main burner 70, which mainly bears the heat load, and the NOx
and an auxiliary burner 80 for gas phase reduction. As a result, a primary air passage 20 is formed in the inner cylinder 1, and a partition member 2 is formed inside the inner cylinder 1.
A secondary air passage 30 is provided inside the partition member 2 and the outer cylinder 60.
A low oxygen-containing gas passage 50 is formed between the two. In the case of Fig. 2, the low oxygen-containing gas passage 5
0 are formed independently so as to surround each sub-burner 80, and the outermost periphery of the burner body is used as a tertiary air passage 40. In addition, the code|symbol 10 is an impeller.

The method according to the present invention will be explained below, focusing on the burner device shown in FIG.

In FIGS. 3 and 4, first, the primary air passage 2
Primary air A ₁ is supplied into the furnace from 0, and the flame F ₁ of the main burner 70 placed in the secondary air 30 formed around it is surrounded by secondary air A ₂ and injected. . Furthermore, since these main burner flames F ₁ are formed by injection toward the burner central axis 5, they burn at a high O ₂ partial pressure in the presence of primary air A ₁ and secondary air A ₂ and bear the heat load of the burner device. . Therefore, the main burner flame F burns at a relatively high temperature and has high ignitability and flame stability, and therefore, by controlling these main burners 70, the load of the entire burner device can be easily adjusted. Note that the symbol G in the figure indicates a combustion exhaust gas supplied as a low oxygen-containing gas.

Next, FIG. 4 shows the combustion state of the auxiliary burner.

The fuel injection port of the auxiliary burner 80 is connected to the main burner 7 described above.
In contrast to the fuel injection ports 0, each of the fuel injection ports opens radially with respect to the burner axis 5, that is, each opens outward. Further, the injection speed of the exhaust gas G is set to a value higher than the fuel injection speed from the auxiliary burner 80 and/or each combustion air injection speed. The fuel injected from the auxiliary burner 80 in this manner is included in the high-speed exhaust gas flow and injected into the furnace. In other words, the ignition time is delayed under low O ₂ partial pressure, and since it is surrounded by gas injected at high speed, the flame F ₂ from the auxiliary burner 80 is formed downstream of the main burner flame F ₁ described above. That will happen. Therefore, reducing radicals such as NH ₂ and CN generated under low oxygen partial pressure are present in the reducing flame, and the sub-burner flame F ₂ containing these reducing radicals is located downstream of the main burner flame. It will be merged and mixed. The main burner flame F is formed on the upstream side and at a high temperature and therefore contains a considerable amount of NOx, but these NOx are reduced to harmless N ₂ by the products in the auxiliary burner flame.
An example of this is as follows.

NO+・NH ₂ →N+H ₂ O ......(1) NO+CN→N ₂ +CO ...(2) Note that the air supply amount for the burner device as a whole is slightly insufficient, that is, the air ratio is set to 1 or less and the method described above is used. It will be more effective if two-stage combustion is carried out together with this. However, as mentioned above, the two-stage combustion method tends to increase the amount of soot and dust generated, but if used in combination with this method, such a situation will not occur. That is, since the excess fuel area is diluted with inert gas such as exhaust gas, the following values y and z become smaller when the spatial distance is x.

y = δP / δX (P: O ₂ partial pressure) z = δT / δX (T: gas temperature) Under conditions where the values y and z shown by the above formula are small, the formation of vapor phase precipitated carbon is suppressed. This is known to reduce the amount of soot and dust generated.

Furthermore, since the CO ₂ high concentration region is secured in advance by the injection of the inert gas G, the reaction shown in the following equation 3 tends to react in a leftward direction at high temperatures, and from this point as well, the amount of soot and dust generated can be reduced.

2CO→CO ₂ +C (solid) ...(3) This CO also helps in the gas phase reduction of NOx as shown in the following equation 4.

NO+CO→1/2N ₂ +CO ₂ ...(4) Although the above explanation has been made using the burner device shown in FIG. 1, the burner device shown in FIG. The same can be done.

Figure 5 shows the results of a comparative experiment between the method according to the present invention (diagram B) and the conventional method (diagram A), and the method according to the present invention is larger at all air ratios. This shows that it is possible to achieve a NOx reduction rate.

By implementing this invention, it is possible to achieve a high NOx reduction rate while maintaining good ignition flame stability.

Furthermore, as can be seen from FIG. 1, since the distance between the burners can be reduced, the overall shape of the burner device can be made compact.

Further, by using the two-stage combustion method in combination, the NOx reduction rate can be further increased, and in this case, the generation of soot and dust, which is a side effect of the two-stage combustion method, can be significantly reduced.

[Brief explanation of drawings]

1 and 2 are front views of a burner device for carrying out the method according to the present invention, FIG. 3 is a cross-sectional view taken along the - line in FIG. 1, and FIG. Figure 5 shows the burner zone air ratio and
FIG. 3 is a diagram showing the relationship with NOx concentration. 5...Burner axis center, 70...Main burner, 80...
...Auxiliary burner, A ₁ ...Primary air, A ₂ ...Secondary air,
F ₁ ... Main burner flame, F ₂ ... Sub-burner flame, G
...Combustion exhaust gas.

Claims (1)

[Claims] 1. A combustion method in which nitrogen oxides in a main burner flame are reduced in the gas phase by products in a sub-burner flame formed by combustion under a low oxygen partial pressure, in which a plurality of main burner nozzles and a plurality of sub-burner nozzles are Partition members are provided which are arranged alternately on a virtual circumference in one plane, have cylindrical primary air passages opening coaxially within the circle and at the center, and partition the main burner nozzle and the sub burner nozzle. The burner nozzle is located in the secondary air passage.
The secondary burner nozzle is located in a low oxygen-containing gas,
Nitrogen is characterized in that the upstream side of the burner device is the main burner flame, and the position where the main burner flame and auxiliary burner flame mix is selected by controlling the supply amount of low oxygen-containing gas on the downstream side to perform gas phase reduction. Combustion method to reduce oxides. 2. The combustion method for reducing nitrogen oxides according to claim 1, characterized in that the amount of air supplied to the burner device as a whole is controlled so that the air ratio is 1 or less. 3. Claim 1 or 2, characterized in that the injection speed of the low oxygen-containing gas in the direction of the burner axis is controlled to be higher than the fuel injection speed and the combustion air injection speed of the auxiliary burner. A combustion method that reduces nitrogen oxides.