JPS5813906A - Combustion method for generating low nitrogen oxide exhaust - Google Patents

Abstract

PURPOSE:To reduce the quantity of exhaust NOX by injecting and adding Ca compound having catalytic effect together with secondary fuel to the following stream of flame produced by primary combustion in a combustion chamber such as a boiler or the like, thereby enhancing the velocity of the reducing reaction of the NOX. CONSTITUTION:A plurality of burners 6 are disposed at the lower part of a combustion chamber 5 in a boiler 4 for injecting primary fuel and air which is suppressed at the ratio of the primary fuel to the air to less than 1 into the chamber 5 for primary combustion. An intermediate air hole 7 is disposed above the uppermost stage burner 6a of the burners 6 for suitably supplying air to preferably react for reducing NOX to N2, and a secondary burner 8 is provided at the part corresponding to the following stream of the primary combustion flame above the hole 7 to inject only secondary fuel. A catalyst injection hole 9 is formed in parallel with the burner 8 to inject Ca compound, thereby accelerating the reaction of the NOX with the intermediate product in the secondary combustion by the catalytic operation of the Ca compound.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel low nitrogen oxide combustion method in boilers and the like, and in particular, in order to reduce nitrogen oxides (hereinafter abbreviated as NOx), A secondary fuel is added in the wake of the flame, and the pyrolysis intermediate products (CO, CHX) of this secondary fuel are added.

In a low nitrogen oxide combustion method in which NO is reduced with C9NH The present invention relates to a low nitrogen oxide combustion method that can reduce NOx generation as much as possible.

Generally, in boilers etc., exhaust gas circulation combustion method,
Steam injection methods, staged combustion methods, etc. are known.

By the way, among the above methods, the staged combustion method has the advantage of having a high NO 2 reduction effect and requiring no operating costs, and is a method that is widely adopted in large boilers. To explain this method based on Fig. 1, the air ratio between the fuel from the plurality of burners 2 provided at the bottom of the combustion chamber 1 of a boiler, etc. is suppressed to 1 or less (0.8 to 0.9). The mixture with combustion air is injected and is subjected to secondary combustion. Co, C, CHX, etc., which are unburned components generated at this time, coexist with NOx, and move up in the combustion chamber 1 to the wake of the flame while reducing NOx to N2. Thereafter, the unburned matter is completely combusted in secondary combustion by combustion air supplied from a secondary combustion air port (over air port) 3 provided above the combustion chamber 1.

However, in such a 'combustion method, No.
4 In order to perform the N2 reduction reaction sufficiently, it is necessary to make the distance between the burner 2 and the secondary combustion air hole 3 sufficiently long, and therefore the height of the combustion chamber 1 or the boiler must be increased. In addition, there was a problem that the amount of NO generated could not be sufficiently reduced.

Therefore, as shown in Figure 2, it is used as surplus air.

Before supplying air for secondary combustion, secondary fuel is injected and supplied from the secondary burner 2a to the wake of the secondary combustion flame, and thermal decomposition intermediate products (CO, C, etc.) of this fuel are injected and supplied from the secondary burner 2a.

CHx, etc.) (Does not burn immediately due to lack of oxygen)
Combustion methods have also been adopted that reduce and decompose NO through the reducing action of NO. However, even in this case, there are limits to the NO reduction reaction and it is often not possible to completely meet the demands for lower NO. Also, a certain distance -e2 must be maintained between the secondary burner 2a and the secondary combustion air hole 3.

The present invention has been devised to effectively solve the above-mentioned problems, and its purpose is to provide a catalyst along with secondary fuel in the wake of the flame generated by primary combustion. A Ca compound that has an effect is added by injection, and this C
A low nitrogen oxide combustion method that promotes the reductive decomposition reaction of NOx through the catalytic action of a compound, thereby reducing NOx emissions as much as possible and promoting the downsizing of combustion equipment such as boilers. It is on offer.

The method according to the present invention will be specifically explained in detail below.

First, as shown in FIGS. 3 to 4, in the lower part of the combustion chamber 5 in the boiler 4 used to carry out the method according to the present invention, the air ratio between the primary fuel and the secondary fuel is 1. below(
0.8 to 0.9) into the combustion chamber 5 and a plurality of main burners 6 for secondary combustion.
is located.

An intermediate air hole 7 is arranged above the uppermost burner 6a of the main burner 6 to supply air as appropriate to maintain optimal reaction conditions for the NOx-+N2 reduction reaction carried out above.

A secondary burner 8 for injecting only secondary fuel into the combustion chamber 5 is provided in the upper part of the intermediate air hole 7 and in the wake of the flame of the secondary combustion. Intermediate products (CO,
C, CHxt, NHX, etc.).

In this secondary burner 8, for example, CaO,
A catalyst injection hole 9 is formed for injecting a Ca compound (catalyst material) which is a feature of the present invention such as CaCO3,
The catalytic action of this Ca compound causes a reaction between NO and secondary fuel intermediate products (C, Co, CHx, etc.) (NOx
(reductive decomposition reaction).

Note that when injecting the secondary fuel, a Ca compound may be mixed into the secondary fuel, and this and the secondary fuel may be injected at the same time.

Further, in an upper part spaced apart from the secondary burner 8 by a predetermined distance, a secondary combustion chamber is provided as surplus air to completely burn the secondary fuel injected from the secondary burner 8 and its thermal decomposition intermediate products. A secondary combustion air port (over air port) 10 is provided to supply air for secondary combustion, and is configured so that the air can be completely combusted and then discharged to the outside of the system.

Note that a boiler for carrying out the method according to the present invention may be configured as shown in FIG.

That is, without providing the secondary burner 8 and intermediate air hole 7 that were provided in the boiler, fuel and Ca
(In this case, the air ratio is naturally suppressed to 1 or less), and the unburned matter that is often generated due to incomplete combustion is transferred to a secondary combustion engine installed above the main burner 11. It may be configured so that the secondary combustion air (excess air) from the air hole 10 is used to cause complete combustion.

The method according to the present invention is carried out in the boiler configured as described above.

First, a mixture of primary fuel and air whose air ratio to the secondary fuel is suppressed to 1 or less is injected from the main burner 6 into the combustion chamber 5, and is subjected to secondary combustion.

At this time, since the air ratio is suppressed to 1 or less, incomplete combustion generates unburned matter having a reducing effect such as Co and C, and NOx. This unburned content and NOx will rise in the combustion chamber 5 together with the flame generated in the primary combustion, and an appropriate amount of air is supplied into this flame from the intermediate air hole 7, and the intermediate air hole The reaction conditions for the NOx reduction reaction performed above No. 7 are optimized.

By the time the flame reaches the intermediate air hole 7, the i9 NOx has been reduced to some extent by the unburned matter.

The flame of the primary combustion that has passed through this intermediate air hole 7 rises further, and then the flame of this primary combustion
A secondary fuel and a catalytic material consisting of a Ca compound are added by injection into the wake of the catalytic converter. This injected secondary fuel is thermally decomposed into reducing intermediate products (CCo, CHx, NHx, etc.), and these products rise in the combustion chamber 5 together with the catalyst material and NOx rising downward. I will do it.

In this ascending process, intermediate products or unburned components of the same components react with No, reducing and decomposing NO.

At this time, the Ca compound acts selectively on the reductive decomposition reaction as a catalyst and accelerates the reaction rate, so N
The amount of Ox will decrease rapidly.

After the above reduction reaction is almost completed, secondary combustion air is further supplied as excess air from the secondary combustion air hole 10 into the exhaust gas that is rising in the combustion chamber 5. secondary combustion of intermediate products and unburned matter. The combustible material is completely burned by this secondary combustion, and the exhaust gas is then discharged to the outside of the system via the exhaust gas system 12.

In the boiler system shown in FIG. 5, the uppermost burner 11a of the main burner 11 plays the role of the secondary burner 8 of the boiler system shown in FIG.

Therefore, a part of the fuel (secondary fuel) injected from the uppermost stage burner 11a is thermally decomposed to produce an intermediate product, and this intermediate product and the unused material often generated due to incomplete combustion are thermally decomposed. Together with the fuel, NO is reduced and decomposed. At this time, as described above, the Ca compound acts as a catalyst, thereby accelerating the rate of the reduction reaction and promoting the reduction reaction of NOx.

As mentioned above, since we added a catalyst that promotes the reduction reaction of NOx, the NOx generated by secondary combustion
can be reductively decomposed with high efficiency in a short time.

Therefore, it is possible to obtain a NOx reduction effect greater than that of conventional methods, and also to reduce NOx.
The distance required to reductively decompose x, that is, the distance between the secondary burner 8 and the secondary combustion air hole 1o! 3 (in FIG. 5, the interval table between the uppermost burner 1.1a of the main burner 11 and the secondary combustion air hole 1o) can be shortened,
The height of the combustion chamber 5 or boiler 4 can be reduced.

In short, the method according to the present invention can exhibit the following excellent effects.

(1) Injecting and adding a Ca compound with catalytic action, NO
Since the reaction rate of the reduction reaction of x is increased, NOx can be reduced and decomposed in a short time, and the amount of NOx discharged can be reduced as much as possible.

(2) Therefore, since the time and distance required for reducing and decomposing NO (2) can be shortened, the height of the combustion chamber or the height of the boiler can be reduced.

(3) It is possible to eliminate the need for a denitrification device using ammonia provided in the exhaust gas system, or to reduce the amount of ammonia used as much as possible, thereby significantly reducing the cost required for denitrification.

(4) The method according to the present invention can be implemented without making major changes to existing equipment.

[Brief explanation of the drawing]

Figure 1 is a schematic side view of a boiler that uses a conventional low nitrogen oxide combustion method, Figure 2 is a schematic side view of a boiler that uses another conventional nitrogen oxide reduction method, and Figure 3 is a schematic side view of a boiler that uses a conventional low nitrogen oxide combustion method. FIG. 4 is a schematic side view showing a boiler in which the method according to the invention has been implemented, FIG. 4 is a schematic front view thereof, and FIG. 5 is a schematic side view showing a boiler in which another method according to the invention has been implemented. In the figure, 5 is a combustion chamber, 6, 11 is a main burner, 8 is a secondary burner, 9 is a catalyst injection hole, 10 is an air hole for secondary combustion, and 11 is a top burner. Patent Applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Representative Patent Attorney Nobuo Kinutani/Niyu

Claims (2)

[Claims] (1) Most of the fuel is primarily combusted in a combustion chamber such as a boiler, the remaining fuel is injected into the wake of the flame formed by the secondary combustion, and the secondary fuel is thermally decomposed. reducing the nitrogen oxides in the secondary combustion flame with the intermediate product;
In a low nitrogen oxide combustion method in which excess air is supplied downstream to achieve complete combustion, Ca
A low nitrogen oxide combustion method comprising injecting a compound to promote the reductive decomposition reaction of the nitrogen oxides by the catalytic action of the Ca compound. (2) Most of the fuel is primary-combusted in the combustion chamber of a boiler, etc., and nitrogen oxides in the secondary combustion flame are reduced with the unburned content of the secondary combustion, and surplus air is supplied to its wake. In a low nitrogen oxide combustion method in which complete combustion is achieved, a Ca compound is mixed with the fuel in the uppermost burner or injected alone at approximately the same position as the fuel to enhance the catalytic action of the Ca compound. A low nitrogen oxide combustion method characterized by promoting the reductive decomposition reaction of the nitrogen oxides.