JPS62158906A - Low nox combustion burner for coal and water slurry - Google Patents

Abstract

PURPOSE:To get a stable flame of CWM at the same time to improve an efficiency of combustion as well as to reduce NOX by a method wherein two preliminary combustion chambers are arranged in a coal and water slurry (CWM) burner. CONSTITUTION:CWM of fuel is injected from a nozzle 1 and turned into fine particles and then ignited at a primary combustion chamber 4 constituted by a block 7 of ceramics installed around an outer circumference of the nozzle 1. The fuel is ignited with secondary air within a cylindrical secondary preliminary combustion chamber 5 at downstream side and thereafter the fuel is completely ignited with ternary air within a combustion furnace. When the primary preliminary combustion chamber 2 is made of ceramic block 7 having a high thermal accumulation property instead of steel, resulting in that the heat is accumulated in the block during a preliminary heating operation and further the ignition of CWM is facilitated with this heat. With the installation of the secondary preliminary combustion chamber 5, a formation of the low air flame is facilitated and an effect of a low NOX combustion can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a low NOx combustion burner for coal-water slurry (hereinafter referred to as CWM).

[Background of the Invention] One of the problems in using coal is that it is not easy to handle the solid. For this reason, various technologies for converting coal into fluid fuel are being developed. Among them, coal slurry (hereinafter referred to as CWM), which is a mixture of atomized coal and water, has excellent economic efficiency. , is attracting worldwide attention.

CWM has great advantages in terms of low production and transportation costs and handling, but because the fuel contains a large amount of water, there is a risk that the combustion efficiency will be lower than that of conventional pulverized coal. CWM is sprayed into the combustion furnace in fine particles. For atomizing a relatively highly viscous fluid such as CWM, a two-fluid atomizer that causes a high-velocity atomizing medium to collide with a spraying medium is generally used. In a two-fluid atomizer, the faster the flow rate of the atomizing medium, the higher the atomization performance, and the speed of the CWM airflow ejected from the atomizer is.

The amount is about five times that of pulverized coal transported by air.

Additionally, atomized CWM requires a zone of moisture evaporation prior to its ignition. As the ejection speed is fast and water evaporation time is required, the ignition position of CWM tends to be lifted from the burner surface to the downstream side, and the flame temperature is also 100° to 200°.
It is known to be relatively low. Such a retreat of the ignition position requires suppression of bad NOx for combustion efficiency, flame stability, and suppression of nitrogen oxides (NOX), and is required to suppress NOx emissions at least as much as normal pulverized coal combustion.

NOx generated during combustion of various fuels including CWM is
Heat-generated Now is generated when nitrogen (N2) in the combustion air is oxidized at high temperature, and fuel-derived NO is generated when nitrogen (N) contained in the fuel is oxidized during combustion.
It is roughly divided into x.

Of these two types of NOx, the amount of thermally generated NOx strongly depends on the temperature of the combustion flame.

When the flame temperature is low as in CWM, the reaction between Nt and 02 is suppressed, and the amount generated is relatively small. On the other hand, fuel-derived NOx does not change much depending on the flame temperature, but rather depends on the N content in the fuel. ,. C
Coal, which is the combustible component of WM, has a temperature of 0.5 to 2.0% depending on the type of coal.
Contains 5% by weight of N. This is extremely high compared to 0% by weight for LNG and 0.1% by weight for heavy oil C. Therefore, the amount of fuel-originated NOx generated is large and accounts for most of the total amount of NOx generated. In the combustion of pulverized coal, the NO
It is known that it is essential to stably form a reducing region inside the flame in order to reduce x.

Coal releases reducing gases such as Ha and Go under air-deficient combustion conditions (low air ratio combustion conditions) and forms a reducing region. Under such a reduction region, the N content in the coal is released as compounds such as NH3 and HCN. These nitrogen compounds are immediately oxidized to NOx in the presence of a high concentration of O2, but have the effect of reducing NOx to N2 when the O2 concentration is low. Therefore, pulverized coal low NOx burners are designed to stably form a reduction region and a low O2 concentration region (denitrification region) by separating a large amount of combustion air and gradually mixing it. There is.

On the other hand, in C and WM, the time required for ignition is longer by the time taken to evaporate water, and since the flame is ejected at high speed when atomized, the flame tends to separate from the burner surface. That is, C.W.M.
Since combustion progresses in the downstream region where the mixture of air and air rapidly progresses, it is difficult to form a reducing region like in pulverized coal combustion, and NOx
It becomes difficult to control emissions. In addition, low ignitability is naturally a direct cause of a decrease in combustion rate, and furthermore, if the flame moves away from the burner, it will lead to an unstable combustion state that is prone to misfires.
There are also problems with the reliability of the combustion equipment.

In this way, in CWM combustion, the retraction of the ignition position has a negative effect on the combustion characteristics, and the key to developing a CWM burner is to improve the ignition performance of CWM and to bring the ignition position as close to the burner as possible.

As a method of pulling the ignition position closer, a method of introducing combustion air as a swirling flow is known. For example, as in the pulverized coal burner shown in Japanese Patent Application Laid-Open No. 59-208305, the position of the tertiary air nozzle is separated from the fuel nozzle,
There is also a burner that injects tertiary air as an intense swirling flow. When fuel is ejected at a flow velocity equal to that of air, such as in pulverized coal, it is effective to introduce combustion air as a strongly swirling flow.

However, when fuel is injected from the fuel nozzle at a high speed of 3 to 5 times or more than the combustion air flow rate, as in CWM, if flame stabilization is attempted only by the swirling force of the air, the optimum swirling strength range will be very limited. The area is narrow, making it difficult to operate the burner. Furthermore, in a two-fluid atomizer, if the flow velocity of the atomizing medium is lowered to reduce the ejection velocity to Cw, atomization of CWM is inhibited and a good CWM combustion flame cannot be obtained.

That is, as the CWM atomized particle size increases, the heat transfer characteristics of the particles deteriorate, resulting in a decrease in ignitability.

Burner device! It is. This device consists of a burner gun equipped with a burner tube that sprays fuel at its tip, a primary swirler surrounding the burner gun for supplying swirling primary air, and air supplied from the primary swirler. A primary burner metal that mixes and burns the primary air and the fuel sprayed from the burner tip, and a secondary burner metal that surrounds the tip side of the primary burner metal with a predetermined gap. , a secondary swirler for supplying swirling secondary air provided in a gap between this secondary burner metal and the primary burner metal, and tertiary air provided around the tip side of the secondary burner metal. It is equipped with a tertiary air nozzle for supply, and the total length of the primary burna metal is not more than twice the diameter of the primary swirler, and the inner peripheral ring at the tip of the primary burna metal has a diameter of the primary swirler. forming a horizontal cylindrical portion having a shorter length than the primary burner metal, and forming a conical portion extending outward at an angle of 30 degrees to 60 degrees on the outer periphery of the tip of the primary burner metal; The present invention is characterized in that the inner circumferential surface of the leading end of the secondary burner metal is formed to have a substantially similar divergence angle to the outer circumferential surface of the primary burner metal.

This device is highly effective for burners with good ignitability such as oil fuel, but does not provide good combustibility for fuels with low ignitability such as CWM. First, if you install the primary air nozzle around the outer periphery of the fuel nozzle and try to burn the fuel in the primary burner metal installed around it,
Since the negative pressure region formed by the high-speed jet of fuel is eliminated by the primary air, there is no entrainment of secondary air into the ignition region formed by the primary burna metal, and ignitability is inhibited. In other words, ignition and flame stabilization can be achieved by forming a large and stable circulating flow around the fuel flow.If a structure is adopted in which the tip of the barrel is directed outward to suppress the initial mixing of secondary air and fuel, as in CWM, In the case of fuel with low ignitability,
The flame becomes easier to separate from the burner surface. In this way, C.W.M.
#fI requires a new burner aimed at improving ignition performance.

[Purpose of the invention]

As mentioned above, in CWM combustion, C is ejected at high speed.
Improving the ignitability of WM is a major technical challenge.
The purpose of the present invention is to obtain a stable CWM flame while at the same time
It is possible to improve the combustion rate and reduce NOx.

[Summary of the invention]

That is, one of the four features of the present invention is a fuel nozzle that atomizes slurry fuel and jets it out, and a fuel jetted from the fuel nozzle that is provided concentrically with the fuel nozzle and is formed in an annular shape that widens toward the end. a primary preliminary combustion chamber for burning;
An annular secondary air nozzle is installed on the outer periphery of the primary equipment combustion chamber and blows out combustion air as a swirling flow, and an annular secondary air nozzle is installed in front of the primary pre-combustion chamber by an outer cylinder of the secondary air nozzle. The present invention is a low NOx combustion burner for coal/water slurry consisting of a secondary pre-combustion chamber formed in

Further, another feature of the present invention is a fuel nozzle for atomizing slurry fuel and ejecting the atomized fuel, and a fuel nozzle provided concentrically with the fuel nozzle and formed in an annular shape that widens toward the end. a primary pre-combustion chamber that burns fuel ejected from a fuel nozzle; an annular secondary air nozzle that is installed on the outer periphery of the primary pre-combustion chamber and ejects combustion air as a swirling flow;
Secondary pre-combustion chamber A secondary pre-combustion chamber is formed in an annular shape by the outer cylinder of a secondary air nozzle in front of the secondary pre-combustion chamber, and a ring-shaped tertiary combustion chamber is installed on the outer circumference of the secondary air nozzle and ejects combustion air as a swirling flow. Low N for coal/water slurry consisting of air nozzle
Located in Ox combustion burner.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. 1 is a fuel nozzle that atomizes coal-water slurry fuel and ejects it; 4 is a primary preliminary combustion chamber arranged concentrically with the fuel nozzle 1 and formed in an annular shape that widens from the tip of the fuel nozzle 1; , 2 is an annular secondary air nozzle that is installed on the outer periphery of the primary pre-combustion chamber 4 and ejects combustion air as a swirling flow. It also serves as the outer peripheral surface of chamber 4.

Further, the inner cylinder of this secondary air nozzle is formed to be shorter than its outer cylinder in the fuel injection direction. Reference numeral 5 denotes a secondary pre-combustion chamber formed by the outer cylinder of the secondary air nozzle 2 in front of the primary pre-combustion chamber 4 . 3 is an annular secondary air nozzle that is installed on the outer periphery of the secondary pre-combustion chamber 5 and blows out combustion air as a swirling flow; It also serves as a tube. 6 is a swirling flow generator provided at the inlet of each nozzle 2.3;
The air ejected from the nozzles 2 and 3 is ejected as a swirling flow. 7 indicates a block portion of the primary preliminary combustion chamber, and 9 indicates a combustion furnace.

In the above configuration, the fuel CWM is atomized by the fuel nozzle 1 to have an average particle size of about 50 to 100 μm, and is ejected. The atomized CWM is ignited in a conical primary pre-combustion chamber 4 installed around the outer periphery of the fuel nozzle, and then ignited in a cylindrical secondary pre-combustion chamber provided downstream of the primary pre-combustion chamber 4. After being combusted with secondary air in the chamber 5, it is completely combusted with tertiary air in the combustion furnace. What is the ejection speed of CWM?

In order to promote atomization, the flow rate is usually set at a high speed of 3 to 5 times or more than the combustion air flow rate. Therefore, the static pressure around the outer circumference of the CWM jet becomes negative pressure, and part of the secondary air flows into the primary pre-combustion chamber 4.
Some of the secondary air that gets caught up in the C
Used for ignition of WM.

The remaining secondary air that is not used for ignition is mixed with the CWM in the secondary pre-combustion chamber 5 and used to form a flame, before the CWM is mixed with the tertiary air. Secondary air nozzle 2
The air outlet of 3 forms the secondary pre-combustion chamber 5.
It is installed inside the air outlet of the secondary air nozzle 3. 2
The proportion of secondary air drawn into the primary pre-combustion chamber 4, and 2
The rate of consumption in the secondary pre-combustion chamber 5 is controlled by the swirling strength of the secondary air, and for stable flame formation,
Appropriate turning strength is selected. The secondary air is CW like this
The air flow rate is set to be lower than the air flow rate required for complete combustibility of the CWM.

1st child a#! The material of the block 7 constituting the I-grilling chamber 4 is as follows:
Although it is possible to use steel, it is also possible to use heat-resistant ceramic.

This is effective considering the heat storage properties of bricks and their longevity due to burnout. Typically, a CWM combustion device is preheated with gas or liquid fuel until the combustion furnace reaches a temperature sufficient to form a CWM flame.

Therefore, if the block 7 is made of a material with high heat storage properties,
During preheating, heat is stored in it and the ignition of the CWM is facilitated by this heat. Furthermore, if a heating element such as a ceramic heater is made of the material of block 7, the CWM jet can be heated by the heating element, and ignition can be controlled by the amount of heat generated. If the material of the block 7 is selected from the viewpoint of heat storage or heat generation in this way, the ignition performance at the start of CWM injection is improved. Once a stable flame is formed, the block 7 is heated by heat transfer from the flame, so the CW
The problem of ignitability of M becomes smaller.

In addition to supplying heat for ignition, if a primary pre-combustion chamber 4 as shown in FIG. 12 is installed, CWM ejected at high speed is mixed with secondary air in the secondary pre-combustion chamber 5 Since the flow velocity is attenuated before the air is mixed, the residence time during air mixing becomes longer, which is effective in bringing the ignition position closer to the burner surface. That is, flame formation within the secondary pre-combustion chamber 5 becomes easier.

Therefore, it is desirable to make the primary pre-combustion chamber 4 as large as possible in order to attenuate the CWM flow velocity, but if it is made too large, there is a risk that CWM particles will adhere to the inner wall in addition to the deviation of the jet flow as described later. It becomes expensive, and it is required to design it to an appropriate size. In addition, the primary preliminary combustion chamber 4
The opening angle 2 is.

In order to prevent adhesion of CWM particles, it is preferable to set the injection angle to be larger than the injection angle of the CWM fuel nozzle 1.

The secondary pre-combustion chamber 5 is formed by an annular inner cylinder of tertiary air 3 and is installed downstream of the primary pre-combustion chamber 4 . As already mentioned, this secondary pre-combustion chamber 5 is used to combust the CWM with secondary air. As mentioned above, the formation of a reduction region obtained by a low air ratio flame is important for low NOx combustion. The installation of the secondary pre-combustion chamber 5 facilitates the formation of this low-air flame, and furthermore, the secondary and tertiary
Next, clarify the action of air. Since the tertiary air outlet is downstream from the secondary pre-combustion chamber 5, mixing of tertiary air and CWM near the burner is suppressed, and if a low air ratio flame is formed, it can be stored for a relatively long time. easy.

In addition, since the flow of secondary air is prevented from spreading to the outer periphery by the inner wall of the secondary pre-combustion chamber 5 (i.e., the inner cylinder of the tertiary air nozzle 3), mixing with CWM is promoted and the air flow is reduced. The formation of a specific flame becomes easier. Also, tertiary air or secondary
The material of the next air nozzle is usually steel, but like block 7, in order to promote low air ratio combustion,
It is also effective to configure the inner wall with a heat-resistant ceramic with high heat storage ability or a heating element such as a ceramic heater.

As described above, according to the burner of FIG. 1, the ignitability of CWM is improved, so it becomes easier to obtain a stable flame and the combustibility is improved. In addition, it becomes easier to form a low air ratio flame, and at the same time, the mixing of tertiary air is slowed down.
The burner shown in Figure 1 can have a large reduction area.
It is effective in suppressing NOx emissions. If you add more, 3
Slowing the mixing of air has the disadvantage that the flame becomes longer, that is, the combustion apparatus becomes larger. For this purpose, it is important to eject the tertiary air as a swirling flow. When the swirling flow is ejected, the inside of the swirling flow becomes a negative pressure, so that a flow in the opposite direction from downstream toward the burner surface is formed in the flame trailing stream. As a result, tertiary air and C
Mixing with WM is promoted and flame lengthening is prevented.

At the burner surface, the CWM ejected in a flow close to a straight flow and the air ejected as a swirling flow have different flow directions, so mixing is suppressed. The circulation created by the flow facilitates air mixing.

FIG. 3 shows another embodiment. In this embodiment, the shape of the primary pre-combustion chamber 4 is different from that in FIG. The cylindrical part after enlargement is longer.

If the primary pre-combustion chamber 4 is shaped like this, the effect of the primary pre-combustion chamber 4 will be increased, but if the central axis of the combustion chamber and the central axis of the fuel nozzle 1 are not aligned well, the secondary air will be The amount of entrainment is uneven, and the CWM jet tends to deviate from the center, so care must be taken when manufacturing and assembling burner parts.

In the burner shown in Fig. 3, in addition to the shape of the primary pre-combustion chamber 4, a deflector plate 8 is provided at the outlet of the 3rd air, making the mixing of the tertiary air even slower than in the burner shown in Fig. 1. is being done. Installing such a deflecting plate 8 means that
Of course, this is also possible with the burner shown in FIG. 1, and is effective in improving the effect of low NOx combustion. Such modification of the air injection nozzle is required when changing the capacity of the burner, that is, the combustion amount of the burner. As the capacity increases, the overall burner diameter becomes larger, so mixing of tertiary air becomes slower even without using means such as the baffle plate 8. However, as the capacity decreases, the burner diameter becomes smaller, so two , the mixing of tertiary air becomes faster, and it is necessary to devise ways to clarify the role of each air.

Regarding the shape of the block 7 constituting the primary pre-combustion chamber, depending on the capacity of the burner, in addition to what is shown in Figures 1 and 3, for example, a deflector plate similar to the tertiary air nozzle in Figure 3 may be attached. At the same time, by increasing the ejection speed or swirl strength of the secondary air, a negative pressure region is formed inside the baffle plate, thereby increasing the amount of secondary air drawn into the primary pre-combustion chamber 4. . Furthermore, the primary preliminary combustion chamber 4
Modifications such as installing flame-holding plates of various shapes to form a rapid contracted flow on the inner periphery of the outlet are also possible.

In addition, among coals, C
In a burner for burning WM, it is also possible to modify the burner to have a structure in which all the combustion air is input as secondary air without installing a tertiary air nozzle. However, in this case as well, the IUI of the secondary combustion chamber is valid, and in this case, the secondary combustion chamber is constituted by the outer cylinder of the entire burner.

FIG. 4 shows the results of burning CWM using the burner shown in FIG. 1. The figure shows a comparison of the results obtained when CWM was burned using the low NOx burner for pulverized coal shown in JP-A No. 59-208305, and a CWM jet nozzle was installed instead of the pulverized coal nozzle. I have included it for this purpose. The fuel nozzle used was the same for both burners. The horizontal axis of the figure shows the proportion of unburned matter contained in the combustion ash collected at the outlet of the combustion furnace, and the smaller this value, the higher the combustion rate.

The vertical axis shows the concentration of NOx measured at the combustion furnace outlet.
2. Shows the value converted to the concentration standard. Generally, as the unburned content in the ash increases, the amount of N remaining in the ash increases.
Ox degree becomes lower. Therefore, a burner that reduces unburned content in the ash and also reduces NOx is most desirable, and has good combustion characteristics. The CWM used consisted of 63% Pacific coal and 37% water by weight. In the figure, the marks indicate the results when a low NOx burner for pulverized coal was used. Pulverized coal has better ignitability than CWM,
Even if the combustion air and fuel are mixed for a relatively long time,
With the burner No. 9-208305, it is possible to obtain high combustibility and at the same time reduce NOx. On the other hand, when CWM is burned using a pulverized coal burner,
The figure shows that it is difficult to achieve both NOx reduction and high efficiency combustion at the same time. The 0 mark indicates the result of combustion in the burner shown in FIG. Compared to the results of combustion using a conventional pulverized coal burner, the burner shown in Figure 1 allows CWM to be combusted in areas where the amount of unburned matter in the ash is small, and this burner is effective in improving the combustion rate. Recognize. Furthermore, it can be seen that the amount of NOx emissions can be reduced while maintaining a high combustion rate. This adjustment of the NOx emission amount is performed by the flow rate distribution of the secondary and tertiary air and the selection of the swirl strength of each air. From the results shown in FIG. 4, it can be seen that the burner according to the present invention is effective for CWM combustion.

〔Effect of the invention〕

As described above, according to the present invention, by installing two pre-combustion chambers in the CWM burner, it is possible to improve the CWM firing capacity, and at the same time, it is easy to form a stable low air ratio flame. It is possible to improve the combustion rate of CWM and reduce the amount of NOx emissions.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a burner which is an embodiment of the present invention;
Figure 2 is a perspective view of the swirl flow generator shown in Figure 1;
The figure is a longitudinal sectional view showing another embodiment of the burner of the invention, and FIG. 4 is a diagram showing the combustion characteristics of the burner of the invention. 1...Fuel nozzle, 2...Secondary air nozzle, 3...
・Tertiary air nozzle, 4...-Tsuko# combustion chamber, 5...
Secondary pre-combustion chamber, 6... swirl flow generator.

Claims (1)

[Scope of Claims] 1. A fuel nozzle for atomizing and ejecting slurry-like fuel, and 1 for burning the fuel ejected from the fuel nozzle, which is provided concentrically with the fuel nozzle and is formed in an annular shape that widens toward the end. a secondary pre-combustion chamber; an annular secondary air nozzle that is installed on the outer periphery of the primary pre-combustion chamber and ejects combustion air as a swirling flow; and a secondary air nozzle located in front of the primary pre-combustion chamber. A low NOx combustion burner for coal/water slurry, characterized by comprising a secondary pre-combustion chamber formed in an annular shape by an outer cylinder. 2. A fuel nozzle that atomizes and ejects slurry-like fuel; and a primary preliminary combustion chamber that burns the fuel ejected from the fuel nozzle, which is provided concentrically with the fuel nozzle and is formed in an annular shape that widens toward the end. , an annular secondary air nozzle that is installed on the outer periphery of the primary pre-combustion chamber and ejects combustion air as a swirling flow; A method for coal/water slurry characterized by comprising a secondary pre-combustion chamber formed therein, and an annular tertiary air nozzle that is installed on the outer periphery of the secondary air nozzle and ejects combustion air as a swirling flow. Low NOx combustion burner.