JPS6116884B2 - - Google Patents

Description

[Detailed description of the invention]

This invention deals with NOx generated when combustion is used as fuel.
This relates to a combustion method that reduces NOx emissions by reducing and denitrating NOx in the combustion region where hydrocarbons are present. Methods for reducing NOx in combustion exhaust gas from boilers, etc. can be roughly divided into: (a) Reduction by combustion improvement, (b) In-furnace high-temperature denitrification using ammonia injection, etc., (c) Dry catalytic denitrification method, (d) Methods such as wet absorption treatment. have been proposed, but none of these methods is satisfactory in terms of economy, reliability, etc. According to the above classification, the present invention falls under the category of (a) combustion improvement, and relates to a simple and effective low NOx combustion method, which is superior to conventional combustion methods in terms of economy and reliability. It shows that. In combustion devices such as large boilers, fuel and air for combustion are supplied from a large number of burners in order to burn a large amount of fuel, but in general, combustion devices such as large boilers are supplied with fuel and air. Depending on the installation position of the burner, it is roughly divided into the following two types. The first is a tangential ring furnace in which the burners are attached to the corners of a rectangular furnace. Due to the physical constraints of installing a burner in one section, the fuel supply section and the air supply section are usually separated vertically. The second type is a front combustion furnace in which a burner is attached to the back of a rectangular flame. The present invention provides a method of low NOx combustion in a front-burning furnace. Conventionally, front combustion furnaces have a structure in which combustion air is supplied to each burner around a fuel supply pipe in order to maintain good combustibility in each burner. . As a result, the combustion of the oil droplets injected into the furnace occurs rapidly during the mixing process with the surrounding combustion air, forming a so-called independent flame, making it easy to achieve good combustion in terms of combustibility. has been achieved. By the way, in the conventional combustion method that forms independent flames, the combustion area becomes high temperature, so NOx
In addition to the relatively large amount of NOx produced, NOx emissions once produced are emitted outside the furnace without being decomposed, so the NOx emission concentration tends to be high. Therefore, conventionally, in order to reduce NOx, the main focus was to suppress the generation of NOx in the furnace.
The main methods used have been to suppress the combustion temperature using exhaust gas recirculation methods, two-stage combustion methods, low NOx burners, etc. Two of the inventors of the present invention first introduced combustion gas containing a high concentration of NOx into the combustion region of hydrocarbon fuel, thereby removing most of the NOx (approximately 95%) from _N2.
An invention that enables denitrification to make it harmless (Unexamined Japanese Patent Publication No.
No. 52-101663 invention) was completed, but the principle of NOx decomposition by passing the hydrocarbon fuel through the combustion region described in the above-mentioned earlier invention of the present inventors was further applied to the NOx decomposition method of several tens to several hundred ppm, which is found in boilers, etc. They continued their intensive research to apply this method to NOx decomposition, and finally arrived at the present invention. Here, the combustion region means the inside of the flame where unburned hydrocarbon components exist. The reaction mechanism of NOx decomposition due to passage of hydrocarbon fuel into the combustion region is expressed as follows. NOx + HC → HCN, NH ₃ + ... [] HCN, NH ₃ + OX → NOx + ... [] HCN, NH ₃ + NOx → N ₂ + ... [] Here, HC is an intermediate product of the combustion process of fuel oil Activated hydrocarbons such as CH ₃ and OX represent oxidizing agents such as O ₂ and OH. In other words, when NOx combines with activated hydrocarbons HC while passing through the combustion zone, HCN and
They become N compounds such as NH ₃ , and they are [], []
As a result of the _competing reactions shown in
becomes harmless. Therefore, the reaction
The more NOx progresses, the more NOx is decomposed and the NOx concentration becomes lower. Conversely, in order to reduce NOx, the combustion gas containing NOx should be passed through the combustion region where hydrocarbons are present again. Incidentally, specific reactions of reactions [] to [] include the following. NO+CH ₃ →HCN+H ₂ O []′ HCN+O ₂ →NO+CHO []′ HCN+NO→N ₂ +CHO []′ Note that CO and H ₂ as unburned components that are not hydrocarbons
In this case, NOx does not decompose, and since there are no hydrocarbons outside the combustion zone, there is no decomposition of NOx. Focusing on this point, the inventors have developed
Conventional low-temperature technology that suppresses NOx generation itself
Completely different from the idea of NOx combustion method, NOx is reduced by promoting the decomposition of NOx in the combustion area of the furnace.
Based on the new idea of reducing NOx, we have invented a low NOx combustion method that is achieved by separating fuel and combustion air from separate ports and injecting them into the furnace. In other words, in conventional burners, combustion air is supplied at high speed surrounding the fuel oil as described above, so the combustion of the fuel is completed within each independent flame, and the combustion gas containing NOx generated there is distributed to other flames. However, in the combustion method of the present invention, fuel and combustion air are separated from separate ports. Since the input fuel is inevitably mixed well with the combustion gas generated on the upstream side, it comes into contact with the combustion air and combusts. This means that most of the NOx that is produced is naturally reduced and denitrated. By repeatedly undergoing such denitrification reactions, the low NOx combustion method of the present invention easily achieves significantly low NOx combustion. The present invention provides a front combustion section having a plurality of burners, in which fuel and combustion air are separated from separate ports and supplied into the furnace, and is better than a flame holding burner using at least one ordinary burner. This is a low NOx combustion method that maintains a flame, and uses a fuel combustion device consisting of a single or multiple blocks, each block having multiple fuel supply ports and individual two-stage combustion air. This is a low NOx combustion device in which the ports are spaced separately and each block is equipped with at least one flame holding burner upstream of the fuel supply port.
NOx and hydrocarbons mix well, promoting NOx reduction, achieving low NOx levels, and because it is equipped with a flame-holding burner, combustion instability does not occur. The minimum number of flame-holding burners required to maintain stable combustion may be installed at appropriate locations. Next, the present invention will be explained with reference to the drawings. FIG. 1 shows a schematic diagram of an embodiment of the apparatus used in the present invention. In FIG. 1, 1 is a normal boiler for power generation or steam generation, including a furnace 1a, heat exchangers 1b and 1c. , an air preparator 2, and a chimney 3.
The fuel is introduced into the furnace through fuel supply ports 4a, 4b, and 4c having fuel injection pipes attached to the ends of the fuel supply line 4 for denitrification combustion, and is mixed with the previously combusted combustion gas. A major feature of the fuel supply port here is that it simply has a fuel injection function and does not have a combustion air supply function. Hereinafter, the fuel supply ports 4a, 4b, 4c and the group of individual two-stage combustion air ports 5a, 5b, 5c will be referred to as a denitrification combustion burner. A portion of the combustion air is supplied along with the fuel from the flame-holding burner, but
Most of the air ports 5a, 5b, 5c for individual two-stage combustion are passed through the air supply line 5 for individual two-stage combustion.
The fuel is supplied into the furnace from the fuel supply ports 4a, 4.
It mixes with the fuel supplied from b and 4c to continue combustion. Reference numeral 8 denotes a flame stabilizing burner installed to stabilize combustion in the furnace, and there is a flame stabilizing burner fuel supply line 6 and a flame stabilizing burner combustion air supply line 6 to maintain combustion in the flame. Fuel (flame holding fuel) and air are supplied from lines 7, respectively. In conventional burners where air is supplied around the fuel supply pipe, the flame is stabilized in each individual burner, but in the front combustion furnace of the present invention, the flame is formed only after the fuel and combustion gas are mixed. The ignition position becomes unstable, and in order to maintain good combustibility in each burner, each burner has a structure in which combustion air is supplied around the fuel supply pipe. In order to reduce NOx by promoting the decomposition of NOx in the combustion area of the furnace, the present invention separates fuel and combustion air from separate boats and injects them into the furnace. After mixing with the side combustion gas, a flame is formed and the desulfurization reaction is caused to occur repeatedly. The effect of this has been confirmed by the examples described later, but at the same time, in the front-burning furnace of the present invention, if there is no flame stabilizing burner, the combustion in the furnace will become unstable, and the fuel and air will be separated. The method of the present invention that supplies Therefore, a flame-holding burner as a heat source for flame formation and a source of fuel gas generation is an essential requirement of the present invention. Note that 9 is an air port for the TSC, which will be described later.
Used in one embodiment of the present invention. According to the method of the present invention, a certain amount of NOx is generated in the flame holding burner 8, but some NOx is decomposed during the combustion process in which fuel is blown into the combustion gas from the fuel supply port 4a, and further NOx is generated in the flame holding burner 8. Active combustion during the mixing process with stage combustion air causes a NOx reduction reaction and reduces the amount of NOx. The combustion gas produced in this way is further regenerated by a combustion reaction in a mixing region with fuel from port 4b and air from port 5b in a later stage.
NOx is reduced or denitrated. By repeating this process further in the later stages, the denitrification reaction progresses and the NOx emission concentration becomes significantly lower. Next, the present invention will be explained with reference to Examples. Example 1 Experiments were conducted using a small reactor. . The combustion furnace is a horizontal cylindrical furnace with an inner diameter of 1 m and a length of 3.65 m. Burners are installed in four stages on the side wall of the furnace, with the first stage being a flame-holding burner and the second to fourth stage burners for denitrification. It was used as a combustion burner. On the downstream side of each of the fuel supply ports of the second to fourth stages, individual two-stage combustion air supply ports are provided in the same manner as shown in FIG. As fuel,
Using three types of fuel oil: C heavy oil containing 0.149% nitrogen, kerosene with pyridine added to contain 0.1% nitrogen, and kerosene, the amount of fuel burned was 40 kg/h and 60 kg/h.
The experiment was conducted in two cases of Kg/h, and the amount of fuel supplied to each fuel port was kept uniform. The experimental results are shown in Table 1.

[Table] The conventional combustion method in the table was carried out as a comparative example of the present invention, and combustion air was not flowed from the individual two-stage combustion air ports, but the fuel injection pipe was used as in the conventional burner. Combustion air was supplied surrounding the Regarding the NOx emission rate, the NOx emission concentration is expressed as 100 when 40 kg/h of C heavy oil is burned using the conventional combustion method. On the other hand, in the combustion method of the present invention, the second to fourth stage
In the denitrification combustion burner section up to the stage, only the atomized fuel is supplied from the fuel supply port, and the combustion air is supplied from the separate two-stage combustion air port. However, using only a denitrification combustion burner that separates fuel and air may cause combustion instability.
Only the first stage uses a conventional burner that simultaneously supplies fuel and air, and is used as a flame-holding burner. It is desirable to keep the number of conventional flame holding burners to a minimum from the viewpoint of NOx suppression. Comparing the combustion method of the present invention and the conventional combustion method, in the present invention, the NOx emission rate is reduced to about ⅓ for both fuels, and the NOx reduction rate is 68% on average. Furthermore, the emissions of unburned components represented by CO remain almost unchanged. From the above, it was confirmed that the combustion method of the present invention, in which fuel and combustion air are separated from separate ports and supplied into the furnace, can significantly reduce NOx. Furthermore, since the low NOx effect is almost the same regardless of whether fuel is used, such as heavy oil, kerosene, or pyridine-added kerosene, the present invention applies not only to all liquid fuels containing hydrocarbon components, but also to gaseous fuels such as LNG and LPG. It is also applicable to Furthermore, the present invention is not limited to a single front-fired boiler with a burner attached to one side of the boiler, but can also be applied to a plurality of opposite-fired blocks attached to both sides without any problems. Ru. In such a front combustion furnace consisting of a single block or a plurality of blocks, each block has a plurality of fuel supply ports and individual two-stage combustion air ports spaced separately, and each block has at least one It is sufficient to provide a flame holding burner upstream of the fuel supply port. Example 2 In Example 1, only fuel was supplied from the fuel supply port of the denitrification burner section, and combustion air was supplied to two separate
A typical example of the present invention is shown in which the entire amount is supplied from the stage combustion air port. The low NOx combustion method of the present invention can be achieved not only when no combustion air is supplied from the fuel supply port of the denitrification combustion burner section, but also when a portion of combustion air is supplied from the fuel supply port. Shown in Figure 2. The horizontal axis in Figure 2 is EB% (referred to as individual two-stage combustion air bias rate), and EB% is
80 means that 80% of the amount of air supplied for combustion of fuel for the denitrification burner is supplied from the individual two-stage combustion air port as air for individual two-stage combustion, and the remaining
This means that 20% of the fuel is supplied from the fuel supply port surrounding the fuel injection pipe. In other words, in the combustion method of the present invention (Figure 2), a typical example of A is EB = 100
%, conventional combustion method (Figure 2), B is EB = 0%
becomes. As a result of experiments with different EB%, if EB is 50% or more, low NOx is achieved, which is close to the typical example of the combustion method of the present invention.
It was confirmed that it is effective. In addition, when the present invention is combined with the two-stage combustion method TSC (a method in which part of the combustion air is branched and introduced into the furnace from a higher stage than the uppermost stage burner as shown in Fig. 1), As shown in Figure 2, it can be seen that the present invention is effective.Therefore, the low NOx combustion method of the present invention, which aims to reduce NOx by separating fuel and combustion air, This is not limited to complete separation of combustion air, but can also be achieved when approximately 50% of the combustion air is supplied from around the fuel injection pipe. In Figure 2, curve 10 is TSC=0%, 11
is for TSC=25%. Example 3 FIG. 2 shows that the NOx emission concentration can be further reduced by combining the already developed two-stage combustion method (TSC) with the present invention. Example 3 shows an improved example of the two-stage combustion method and the combined combustion of the present invention.

[Table] Table 2 shows a comparative example of exhaust gas properties with and without exhaust gas recirculation under the conditions of TSC = 25% and EB = 100%. C heavy oil and pyridine-added kerosene were used as fuel. Exhaust gas recirculation GM _B
(GM _B % = Recirculated exhaust gas amount Nm ³ / Combustion air amount N
^m3 Therefore, all exhaust gas was fed to the fuel supply port. By implementing GM _B , NOx in C heavy oil can be reduced.
Emission rate reduced by 2%, CO reduced by 15ppm, _O2 reduced by 0.4
%is decreasing. With pyridine-added kerosene, NOx remained unchanged, but CO decreased by 45 ppm and O ₂ decreased by 0.5%. In this way, implementing GM _B not only makes it possible to reduce NOx, but also reduces CO and
_O2 operation is possible. Example 4 The low NOx combustion of the present invention can be further improved by optimizing the distribution of combustion air introduced into the furnace. The first method of distributing combustion air is
This will be explained using figures. The amount of fuel supplied to 6, 4a, 4b, and 4c is set to 10 kg/h, respectively, and 7,
The total amount of combustion air supplied to 5a, 5b, and 5c is 75% of the total air amount, and the second stage combustion air 9 is the total amount of air.
25% (TSC%), and GM _B was kept at 25% of the total air volume. Of the four burners, the lower two burners are called the front burners and the two upper burners are called the rear burners.The air ratio determined by the amount of fuel in the front stage (6+4a) and the amount of combustion air in the front stage (7+5a) is is defined as the average air ratio λ. FIG. 3 shows an embodiment in which the low NOx combustion method of the present invention is further improved by changing the supply distribution of combustion air.
We operated at a low O _{2 level} as much as possible under conditions that did not emit much unburned components such as CO. When the combustion air is uniformly distributed to each burner section, λ is 0.80 to 0.87
(λ = total air ratio λ _T ×0.75). Figure 3 shows λ _T = 1.06 to 1.16, EB = 100%, TSC = 25%,
This shows the measurement results at GM _B = 25%. According to the experimental results, compared to the case where air is uniformly distributed, when a slightly larger amount of combustion air is distributed to the front stage, the NOx emission rate is lower, and as indicated by the subscript, low O ₂ operation is possible. It's summery. It can be said that a more desirable range of λ is 0.9 to 1.4 (λ). This example uses four burners, but even when the number of burners is different and the amount of fuel supplied is not uniform for each burner, the amount of air in the front stage is larger than the amount of air in the rear stage. The NOx emission concentration is lower in the case of carbon fiber. In Figure 3, 12 is pyridine-added kerosene, 13
is a curve showing the relationship between the average air ratio λ of each front stage burner and NOx emission rate (%) when C heavy oil is used, and 14 is a straight line of uniform air distribution, fλ
indicates the optimum range of λ, and the numbers attached to curves 12 and 13 indicate O ₂ %, respectively. The effects of the present invention are summarized as follows, and it can be seen that the present invention exhibits significantly superior effects compared to conventional methods. (a) In a fuel combustion device having a plurality of burners, fuel and combustion air are separated from separate ports and supplied into the furnace, and the flame is held by at least one flame holding burner. In the combustion method of the present invention, the NOx generated in the furnace repeatedly passes through the combustion zone having denitrification ability, so that combustion with significantly low NOx can be easily achieved. Furthermore, combustion instability does not occur due to the function of the flame-holding burner. (b) Even if approximately 50% or more of the combustion air is supplied as individual two-stage combustion air, and the rest of the combustion air is supplied from around the fuel injection pipe, low NOx performance almost equivalent to (b) can be achieved. maintained. (c) Low NOx such as two-stage combustion method and exhaust gas recirculation method
The effects of the present invention can also be obtained when the combustion method and the present invention are combined. In particular, by implementing exhaust gas recirculation surrounding the fuel injection pipe, low
Low NOx, low CO, and low O ₂ are achieved at the same time, and the effect is significant. (d) By distributing more combustion air to the front burner section, preferably by setting the average air ratio of the front burner section to 0.9 to 1.4, low NOx can be achieved.
oxidation and lower O ₂ are further promoted.

[Brief explanation of the drawing]

FIG. 1 shows a schematic diagram of one embodiment of the apparatus used in the present invention. Figure 2 is a comparison diagram of NOx emission rates between the combustion method of the present invention and the conventional combustion method. FIG. 3 shows the results of an experiment investigating the appropriate range of combustion air distribution for more effective implementation of the present invention. 1... Boiler main body, 4... Fuel supply line for denitrification burner, 4a, 4b, 4c... Fuel supply port, 5
...Complete supply line for individual two-stage combustion, 5a, 5b,
5c...Individual two-stage combustion air port, 8...Flame holding burner, 9...Two-stage combustion air supply line.

Claims (1)

[Claims] 1. In a front combustion furnace having a plurality of burners, fuel and combustion air are separated from separate boats and supplied into the furnace, and at least one flame stabilizing burner is used to maintain the flame. If we adopt a two-stage combustion method in which the combustion air is kept at = 0.9 to 1.4. A low NOx combustion method. 2. The low NOx combustion method according to claim 1, wherein approximately 50% or more of the combustion air is supplied separately from separate boats, and the remainder of the combustion air is supplied from around the fuel injection pipe.