JPH08270931A - Combustion apparatus and method for pulverized coal - Google Patents

Abstract

PURPOSE: To provide a means for suppressing NOx to be evolved in the combustion of pulverized coal by a pulverized coal burner in an in-flame deoxidation system. CONSTITUTION: Light emitted from flames, which is viewed from a nozzle 3 for pulverized coal, is led by a condenser 1 through the interior of the nozzle 3 of a pulverized coal burner 100 in an in-flame deoxidation system, and an emission strength is detected by an emission analyzer 16 to calculate a flame temperature 41b or an air ratio 41a, thereby controlling an amount of pulverized coal, or a volume of air, which is fed to the burner, or a particle size of pulverized coal to be fed to the burner. Thus, by calculating a temperature of a reducing flame or an air ratio and controlling the operation of the burner, an amount of NOx to be discharged can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pulverized coal combustion apparatus and combustion method, and more particularly to a combustion apparatus suitable for application to a coal-fired boiler.

[0002]

2. Description of the Related Art A coal-fired boiler usually has a plurality of burners in the height direction of a furnace, and each stage has a plurality of burners. The burners at each stage are usually installed on the wall of the furnace or at the corners of a rectangular furnace. Then, the number of burner stages to be used or the number of burners at each stage is selected according to the load. An after-air port is often provided in the upper stage of the burner in the uppermost stage of the furnace to burn carbon monoxide that remains unburned in the burner.

Needless to say, when operating a pulverized coal combustion apparatus such as a coal-fired boiler, it is necessary to examine the state of the flame in detail and control the amount of pulverized coal and the amount of air. Therefore, conventionally, a flame is detected using a frame detector or a video camera, and feature quantities such as the position, brightness, and length of the flame are extracted by image processing to grasp the combustion state, or a spectroscopic analyzer is used. The flame is analyzed. Publications relating to these include JP-A-2-306017, JP-A-60-133217, and JP-A-60-133217.
JP-A-5-231642, JP-A-60-129524, JP-A-4
-184009, JP-A-2-208412, US Pat. No. 4435149, US Pat. No. 4528918, US Pat. No. 4934926 and the like. As a method for calculating the air ratio from the emission intensity of flame, C ₂ radical and CH
A method of calculating the air ratio from the emission intensity ratio of radicals is known.

General properties required for combustion of pulverized coal are that the amount of NOx produced is small and the amount of unburned matter is small. In order to improve these, various studies have been made on the burner structure and combustion method. One of them is to install an after-air port in the upper stage of the furnace to perform two-stage combustion, and the use of a flame denitration type burner is also one of them.
One. The in-flame denitration system uses a double structure of an internal reducing flame and an oxidizing flame formed around the flame, and NOx is reduced by using the oxygen-deficient reducing flame formed inside the flame, and the outer periphery is reduced. The unburned content is reduced by utilizing the oxidative flame of excess oxygen formed in the. Publications relating to the denitration system in flame include JP-A No. 62-276310 and JP-B 2-59361.
There is a bulletin, etc.

[0005]

Many of the conventional methods for examining the state of flame by optical means are to calculate the temperature of the flame or to calculate the air ratio based on the emission intensity of the flame surface. In a pulverized coal combustion device equipped with an internal flame denitration type burner, even if the amount of pulverized coal or the amount of air supplied to the burner is calculated by calculating the temperature or air ratio based on the emission intensity of the flame surface, It was found that the effect of reducing the NOx generation amount was very poor.

Therefore, an object of the present invention is to provide a pulverized coal combustion apparatus equipped with an effective means capable of reducing the NOx generation amount in the pulverized coal combustion apparatus equipped with a flame denitration type burner.

Another object of the present invention is to provide a combustion method for reducing the amount of NOx produced in a combustion method for pulverized coal by a burner of a flame denitration system.

[0008]

In the combustion of pulverized coal by a burner of a flame denitration system, the NOx concentration in the exhaust gas is greatly affected by the temperature of the reducing flame or the air ratio of the reducing flame, and particularly by the air ratio of the reducing flame. It was revealed that it is necessary to measure the air ratio of the reducing flame or the temperature of the reducing flame in order to control the burner so as to be significantly affected and suppress the generation of NOx. The present invention is based on this finding.

According to the present invention, in a pulverized coal combustion apparatus equipped with a pulverized coal burner for forming a flame having a reducing flame region with insufficient oxygen and an oxidizing flame region with excessive oxygen, the flame in the reducing flame region formed by the burner is used. Fine powder comprising means for controlling at least one of the amount of pulverized coal and air supplied to the burner or the particle size of the pulverized coal so that at least one of temperature and air ratio is set. It is in a charcoal combustion device.

In order to burn a pulverized coal to form a flame composed of an oxygen-deficient reducing flame region and an oxygen-excessive oxidizing flame region, the pulverized coal burner is a pulverized coal nozzle which is carried by air flow and ejected. It is desirable to provide a pulverized coal burner concentrically provided with at least one annular air nozzle on the outer periphery of the. By controlling the amount of pulverized coal or the amount of air supplied to the pulverized coal nozzle and air nozzle,
A reducing flame region and an oxidizing flame region can be formed in the flame formed by the burner.

Further, according to the present invention, pulverized coal is burned by a pulverized coal burner equipped with at least one air nozzle on the outer periphery of a pulverized coal nozzle for carrying and ejecting pulverized coal by air flow.
In a pulverized coal combustion method in which a reducing flame lacking oxygen is formed to completely burn pulverized coal near the burner, and an oxidizing flame with excess oxygen is formed on the outer periphery of the reducing flame, from the emission of the reducing flame. A pulverized coal combustion method is characterized in that one of the reducing flame temperature and the air ratio is obtained, and the pulverized coal and air supply conditions are controlled so that these values are set. .

In order to detect at least one of the temperature and the air ratio of the reducing flame, it is desirable to illuminate the luminescence of the flame through the inside of the pulverized coal nozzle as seen from the nozzle. The field of view of the flame seen through the interior of the pulverized coal nozzle is a flame lacking oxygen, and the emission of the reducing flame can be captured by collecting the emission of the flame in this field.

In order to collect the light emission of the flame through the inside of the pulverized coal nozzle, it is desirable to provide a lighting device inside the pulverized coal nozzle or in the extension direction of the pulverized coal nozzle. In particular, it is desirable to provide a lighting device outside the bent portion of the pulverized coal nozzle in the direction of the central axis of the nozzle. It is better to provide the light collector outside the pulverized coal nozzle than to provide it inside because it is not affected by abrasion due to collision of the pulverized coal flow.
Further, it is advantageous to provide the daylighting device outside the bent portion of the pulverized coal nozzle in the direction of the central axis, because the daylighting device can be easily installed and the light collecting device does not have to have a cooling structure. Further, if a light collector is provided in the extension direction of the central axis of the pulverized coal nozzle, it is easy to collect the flame emission.

If the emission of the flame contained in the distance from the flame root portion toward the flame tip direction up to 3 times the pulverized coal nozzle diameter (D) is taken, the amount of pulverized coal supplied to the pulverized coal nozzle and the amount of air Even if the amount of the reducing flame fluctuates and the size of the reducing flame changes, the emission of the reducing flame can be collected without being affected by them. In order to more completely collect only the emission of the reducing flame, the distance is up to 3 times the pulverized coal nozzle diameter (D) from the flame root toward the flame tip and in the extension direction of the pulverized coal nozzle. It is to collect the light emission of the flame of the area.

At least one of the temperature and the air ratio of the flame in the central portion is calculated by collecting the light emission in the substantially central portion in the width direction of the flame, and based on this, the pulverized coal and air supplied to the pulverized coal burner are calculated. Even if the supply conditions are controlled, the effect of suppressing the generation of NOx is greater than that of detecting the light emission intensity on the flame surface and controlling the amount of pulverized coal or the amount of air.

In the burner of the denitrification type in the flame, in order to stabilize the flame, a flame holding ring composed of a trumpet ring whose diameter is expanded outward is provided at the tip of the pulverized coal nozzle. It is preferable to provide such a flame holding ring also in the combustion apparatus of the present invention.

The present invention is also applicable to an atomizer type pulverized coal nozzle that atomizes and ejects the pulverized coal by colliding a mixed flow of pulverized coal and water with an air flow.

Further, in the present invention, the emitted light of the oxidizing flame is sampled, the air ratio of the oxidizing flame is obtained from the emission intensity, and the amount of air supplied to the air nozzle is adjusted so that the air ratio of the oxidizing flame becomes 1 or almost 1. Providing means for controlling is preferred.

In a coal-fired boiler, a plurality of burners arranged horizontally in a furnace are often burned under similar conditions. Although pulverized coal and air are supplied to each burner in the same manner, the reducing flames often have different states. This is mainly due to the difference in the amount and particle size of the pulverized coal due to the difference in the shape and length of the piping system that supplies the pulverized coal. If there are variations in the state of the reducing flame of the burners at each stage, adverse effects such as combustion oscillation and increase in unburned content will also occur. The present invention does not cause such a problem because the burner is controlled by grasping the combustion state of the reducing flame from the temperature of the reducing flame or the air ratio of the reducing flame.

In the combustion of pulverized coal by the burner of the denitration system in the flame, the brightness of the oxidizing flame is higher than that of the reducing flame.
Therefore, when the light emission of the flame is detected from the outside of the flame, only the light emission in which the light emission of the oxidizing flame and the light emission of the reducing flame are superposed or the light emission of only the oxidizing flame can be detected. Therefore, the air ratio of the reducing flame cannot be known.

There is also a method of controlling combustion by obtaining the air ratio of the flame from the emission intensity ratio of C ₂ radicals and CH radicals contained in the emission of flame, but in pulverized coal combustion, radiation from the flame and solids is generated. Yes, solid-state radiation contains a continuous spectrum from the visible region to the infrared region, and C ₂
The emission of radicals and CH radicals is scattered and absorbed by the pulverized coal and soot particles contained in the flame, and is therefore unsuitable as a method for accurately measuring the emission intensity.

In a two-stage combustion type pulverized coal boiler in which an after-air port is arranged in the upper stage of the furnace to burn unburned matter generated in the burner part, a dimmer for illuminating flame emission is also provided in the after-air port. Then, it is desirable to collect the light emission inside the flame formed in this portion, calculate the air ratio inside the flame, and control the flow rate or swirl intensity of the air so that the air ratio becomes 1 or almost 1. .

[0023]

[Function] The emission of the reducing flame can be detected by collecting the light emission of the flame in the field of view seen from the inside of the pulverized coal nozzle of the burner of the denitration system in the flame through the pulverized coal nozzle. Further, since the emitted light of the flame that is collected does not include the emitted light of the flame from other pulverized coal burners in the vicinity, it is possible to collect the emitted light of the flame of the burner itself. With a burner that has a flame holding ring at the tip of the pulverized coal nozzle, the only flame that can be formed inside the flame holding ring is a reducing flame, so when you look at the flame from the viewpoint inside the pulverized coal nozzle toward the flame holding ring, The field of view becomes a reducing flame.

In order to calculate the flame temperature or the air ratio from the emission of the flame, the emitted emission of the flame is guided to the emission analyzer. Then, the emission intensity is detected and the flame temperature is calculated. The calculated flame temperature is input to the air ratio calculator. In the air ratio calculator, equilibrium calculation is performed using the composition of the coal species and the reaction rate constant designated in advance, and a table of temperature and gas composition with respect to the air ratio, that is, an equilibrium gas composition table is created. The air ratio calculator refers to this equilibrium gas composition table to determine the air ratio with respect to temperature. The obtained temperature and air ratio are input to the combustion control means. The combustion control means includes means for controlling the flow rate of fuel, that is, pulverized coal or air, and the particle size of fuel.

In pulverized coal combustion, the NOx concentration of the reducing flame is determined by the air ratio of the reducing flame.
The concentration of is low. Also, the smaller the particle size of pulverized coal, the more NO
The x concentration can be kept low. From these relationships, in the combustion control means, N corresponding to the air ratio obtained from the air ratio calculator
The Ox concentration is obtained, and when this value is larger than the set value, a control signal is sent to the air flow rate adjusting means so as to reduce the flow rate of the combustion air. Also, a signal is sent to the particle size adjusting means so as to make the particle size finer.

In the emission analyzer, the emission of the reducing flame guided by the optical fiber from the pulverized coal nozzle is guided and divided into two beams, and the temperature of the reducing flame is determined from the emission intensity ratio of a specific wavelength by the two-wavelength analysis method. To detect. The air ratio calculator calculates the air ratio with respect to the temperature of the reducing flame with reference to the equilibrium gas composition table.
The detected flame temperature and air ratio are input to the pulverized coal amount calculator. The pulverized coal amount calculator refers to the values required to calculate the reaction of coal from the coal type database based on the elements and composition of the coal currently burning, the calorific value, the frequency factor of the coal reaction and the activation energy. In addition to the coal type information, the pulverized coal amount calculator obtains the flow rate of the pulverized coal from the pulverized coal flow rate measuring device and the value of the pulverized coal particle size from the particle size measuring device. The pulverized coal amount calculator uses this information to simulate the combustion process of the coal ejected from the burner. At this time, it is assumed that the reaction rate in the gas phase is infinite and the composition is in an equilibrium state. The gas phase gas composition is determined by referring to the equilibrium gas composition table. The combustion amount and burning rate of the fuel in the reducing flame and the composition of combustion gas and coal are calculated from the pulverized coal amount calculator, and the pulverized coal amount is estimated from the combustion amount and burning rate of coal. The amount of pulverized coal is calculated as a value obtained by dividing the combustion amount by the combustion rate.

As described above, the amount of pulverized coal is calculated from the result calculated by the pulverized coal amount calculator based on the temperature and air ratio of the reducing flame, the coal type database and the equilibrium gas composition table.

[0028]

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

FIG. 1 shows a pulverized coal burner 100 mounted on an inner wall 8 of a furnace of a boiler, which is provided with a light collector 1 for collecting the emission of flame, and further an emission analyzer 16 and a combustion control means 31.
1 shows an embodiment of a pulverized coal combustion apparatus of the present invention provided with. The combustion control means sends a control signal to the means for supplying pulverized coal and air to the pulverized coal burner. In this embodiment, the daylight collector 1 is provided on the nozzle wall outside the curved portion 23 of the pulverized coal nozzle 3, but the present invention is not limited to this.

A pulverized coal nozzle 3 located at the center of the pulverized coal burner 100 ejects a mixture 10 of pulverized coal and primary air into the furnace, and a secondary air nozzle 11 and a tertiary air nozzle arranged concentrically outside the pulverized coal nozzle. Secondary air 11a and tertiary air 12a are supplied from the air nozzle 12, respectively. The secondary air and the tertiary air are both swirled in the circumferential direction by swirl vanes 9 provided in each nozzle. A flame holding ring 5 is attached to the tip of the pulverized coal nozzle 3 to stabilize the flame. Further, an auxiliary combustion oil burner 4 is attached to a central portion inside the pulverized coal nozzle so as to penetrate the wall surface of the curved portion on the upstream side of the pulverized coal nozzle. On the outer wall surface of the bent portion of the pulverized coal nozzle, a small hole 65 for taking in the emission of flame to the daylight collector 1 is formed. The light collector collects the light emission of the flame in the field of view indicated by the chain line through the hole 65 described above. An optical fiber 21 is connected to the light collector 1,
The light emission detected by the light collector 1 is guided to the light emission analyzer 16 via the optical fiber 21.

Most of the pulverized coal particles supplied into the pulverized coal nozzle 3 collide with the nozzle wall surface at the curved portion 23 and flow downstream. When a daylight collector is provided in the pulverized coal nozzle, the daylight collector is easily damaged by collision of the pulverized coal particles, and even when the daylight collector is provided on the outer wall surface of the bent portion 23 of the pulverized coal nozzle, the portion of the hole 65 is There is a risk that pulverized coal particles will invade and damage the light collector due to wear. However, by providing a blowing port for the sealing air 64 in the vicinity of the lighting device and blowing the sealing air 64 into the pulverized coal nozzle, it is possible to prevent the pulverized coal particles from entering the lighting device side. A daylighter may be provided inside the auxiliary combustion oil burner 4 in the pulverized coal nozzle.

Inside the flame holding ring 5, a reducing flame 6 deficient in oxygen is formed by a mixture 10 of pulverized coal and primary air jetted into the furnace and secondary air. On the outside of the reducing flame 6, an oxygen-rich oxidizing flame 7 is formed by the air supplied from the tertiary air nozzle. From the secondary air nozzle and the tertiary air nozzle, in the case of a normal pulverized coal burner, about 40
Secondary air or tertiary air preheated to 0 ° C. is ejected, but just supplying pulverized coal and preheated air to the burner does not ignite because the temperature is low. Therefore, the auxiliary combustion oil burner 4
Is used for preheating the entire furnace and igniting pulverized coal at the start of combustion. Once the flame is formed by the combustion of the pulverized coal, the pulverized coal is heated by the radiant heat from the flame and the combustion continues, so that the auxiliary combustion oil burner becomes unnecessary.

The pulverized coal jetted into the furnace by the pulverized coal nozzle 3 rapidly rises in temperature due to radiation from the flame. The reaction of coal includes a thermal decomposition reaction in which volatile matters in coal are released in the form of H ₂ and CO, and carbon on the surface of coal particles is oxidized by oxygen in the air and released in the form of CO or CO _2. Surface reaction. The rate of volatile matter released in the thermal decomposition reaction is determined by the rate of temperature increase and the particle size of coal. The faster the rate of temperature increase and the smaller the particle size, the higher the rate of volatile matter release. Temperature rising rate is 10 ⁴ to 10 ⁵ K in pulverized coal combustion
The value of / s. The temperature rising rate of particles with a particle size of 20 μm is 9
At 00 K / s, it takes about 20 ms for 80% of the volatile matter to undergo thermal decomposition. The surface reaction of coal is determined by the surface area of the coal, the temperature of the surface and the oxygen partial pressure. The larger the surface area, the higher the temperature and the higher the oxygen partial pressure, the faster the surface reaction rate.

Comparing the rates of the thermal decomposition reaction and the surface reaction, the thermal decomposition rate is overwhelmingly faster. When the temperature of the coal is raised, a thermal decomposition reaction first occurs and volatile matter is released, while the carbon on the surface of the coal is oxidized by the surface reaction. Volatile components are mainly released as CO, CO ₂ , H ₂ and H ₂ O, and flammable gases CO and H ₂ are burned in the gas phase if O ₂ is present in the surroundings to form CO ₂ and H ₂ O, respectively. Become. Ignition of pulverized coal occurs when the gas released as volatile components burns in the gas phase, the flame moves to the surface of the pulverized coal particles, and combustion continues. Although the thermal decomposition reaction and the surface reaction proceed at the same time, the thermal decomposition reaction ends earlier and all the volatile matter is released, and then the surface reaction proceeds from the surface of the coal toward the inside. Due to the above-described coal combustion process, the pulverized coal immediately after being ejected from the pulverized coal nozzle 3 is heated by the radiation of the flame, and most of the volatile components are released near the burner. At this time, the nitrogen contained in the coal is released in the form of HCN and NH ₃ . HCN and NH ₃
If the ambient is an oxidizing atmosphere, it reacts with O ₂ to become NOx, and if it is a reducing atmosphere, it is converted to N ₂ by char.
Most of NOx which is a problem in the combustion of pulverized coal is fuel NOx generated by oxidizing nitrogen contained in coal. Therefore, if a place where volatile matter is released is reduced atmosphere, NOx is generated.
Generation of x can be suppressed. The more volatiles are released in the reducing atmosphere, the less nitrogen is left in the coal,
Ox generation amount is reduced. Inadequate emission of volatiles,
When coal containing a large amount of nitrogen burns in an oxidizing atmosphere, the nitrogen remaining in the coal is directly oxidized and released as NOx, so the NOx concentration increases. The larger the surface area of coal, the faster the release rate of volatile matter. Therefore, if the particle size of coal is made smaller and the release rate of volatile matter is increased so that most of the nitrogen in the coal is released in the reducing atmosphere, NO
Generation of x can be suppressed. In the pulverized coal burner, the fuel NOx can be suppressed by increasing the reduction area or making the particle size fine.

An index representing an oxidizing atmosphere or a reducing atmosphere is represented by a gas phase air ratio. The gas-phase air ratio is defined as the ratio of the theoretical amount of oxygen required to completely burn the combustible components released from coal. When the air ratio in the gas phase is greater than 1, almost all the combustible components released from coal burn, but the supplied oxygen is not completely consumed but a part thereof remains, so that an oxidizing atmosphere occurs. On the other hand, when the air ratio in the gas phase is less than 1, the combustible components released from the coal remain unburned and the oxygen is almost lost, resulting in a reducing atmosphere. Fuel NOx can be suppressed by reducing the air ratio in the region where volatile matter is released to be less than 1 to create a reducing atmosphere.

FIG. 2 shows the relationship between the NOx concentration and the air ratio in the flame, that is, the air ratio in the gas phase. An example is given of the case where three types of coal, A coal, B coal, and C coal are used. The NOx concentration becomes lower as the gas-phase air ratio becomes smaller. When the air ratio in the gas phase is 1 or less, the effect of coal type is unlikely to occur. In particular, if the air ratio of the gas phase is 0.9 or less, the NOx concentration is determined only by the value of the air ratio of the gas phase regardless of the coal type. Therefore, it is preferable to set the upper limit of the air ratio in the gas phase of the reducing flame to 0.9 so that the NOx concentration can be suppressed to a low value regardless of the type of coal.

Most of the combustible gas contained in the volatile matter released in the vicinity of the burner is burned by oxygen contained in the primary air and the secondary air, but since the coal is burned with insufficient air, a reducing flame is formed near the burner. To be done. In the reducing flame, the oxygen partial pressure is close to 0, so that the surface reaction by oxygen hardly occurs and the surface reaction by CO ₂ or H ₂ O occurs. When the tertiary air is supplied from the tertiary air nozzle to the outside of the reducing flame by turbulent flow mixing, the flame in the mixed portion becomes an oxidizing atmosphere, and the combustion proceeds due to the surface reaction with the volatile components left unburned.

One of the factors that determines the size of the reducing flame inside the flame is the swirl strength of the tertiary air. The swirl strength of the tertiary air can be adjusted by swirl vanes. When the swirl strength of the tertiary air is increased, the mixing of oxygen into the central reducing flame is delayed due to the centrifugal force, and the reducing flame extends in the downstream direction. When the swirl strength is further increased, oxygen in the tertiary air is hardly supplied to the reducing flame, and a large amount of unburned carbon is produced. Fuel NOx can be suppressed to a low level by increasing the swirl strength of the tertiary air and increasing the area of the reducing flame.
The swirl number is an index for determining the swirl strength, and the swirl number is defined by the ratio of the momentum of the fluid in the circumferential direction to the value obtained by adding the pressure difference to the momentum in the axial direction. The swirl number is about 0.
It is better to set it to a value between 2 and 0.4. When using two-stage combustion together, the tertiary air has an air ratio of 0.7-
It is supplied by adjusting the flow rate so that it becomes 0.9.

The detailed structure of the emission analyzer is shown in FIG. In FIG. 3, the structure of the pulverized coal burner is simplified and shown. In the emission analyzer 16, the emission from the reducing flame is split into two by the spectroscopic prism 55. Divided emission passing any two wavelengths i.e. wavelengths lambda ₁ of the filter 50a and the wavelength lambda ₂ of the filter 50b. The flame temperature can be calculated from the ratio of the emission intensities of arbitrary two wavelengths by the formula (1).

LogT = a log (Iλ ₁ / Iλ ₂ ) + b (1) Here, Iλ ₁ and Iλ ₂ are light emission intensities of arbitrary two wavelengths, respectively.
T is an absolute temperature, and a and b are constants. The wavelengths λ ₁ and λ ₂ are
An arbitrary wavelength can be selected as long as it has a value different from the wavelengths of the absorption bands of OH, C ₂ , and CH contained in the emission of flame. Emission intensity Iλ of each wavelength for a blackbody radiation furnace of known temperature
₁ and Iλ ₂ are measured, and absolute temperature T and emission intensity ratio Iλ ₁ / I
If λ ₂ is plotted on a logarithmic paper, it becomes a straight line. The value of a can be found from the slope of this straight line, and the value of b can be found from the cut edge. If the values of the constants a and b are obtained as described above, the temperature of the flame can be detected from the light emission of an arbitrary flame using the same optical system. One of the two beams divided above is passed through a filter 50a that passes only the emission of wavelength λ ₁ , and the other is passed through a filter 50b that passes only the wavelength λ _2, and the emission of the reducing flame 6 is changed to wavelengths λ ₁ and λ _2. Only the luminescence of is extracted. The light emitted through the filter is converted into an electric signal by the optoelectronic device tube 51,
The voltage is boosted by the amplifier 52. The ratio of the boosted voltage corresponds to the ratio of emission intensity Iλ ₁ / Iλ ₂ , and the calculator 53 performs the above calculation from the values of these voltages to the air ratio calculator 15 using the reducing flame temperature 41b as an electric signal. Output. The air ratio calculator 15 changes the reducing flame temperature 41b to the reducing flame air ratio 41a.
To calculate. In the combustion of pulverized coal burner, the mixing speed due to turbulent flow is slower than the progress of chemical reaction, and the diffusion is rate-determining. In the case of diffusion control, the composition of the gas phase is close to the equilibrium composition. If the vapor phase is in equilibrium, temperature and gas composition are determined only by the air ratio of the vapor phase. From this, the air ratio calculator 15
Then, the equilibrium calculation is carried out in advance for various kinds of gas-phase air ratios for the coal species to be used, and the relationship between the gas-phase air ratio, temperature and gas composition is prepared as an equilibrium gas composition table. The air ratio calculator 15 refers to the equilibrium gas composition table based on the temperature 41b of the reducing flame obtained from the emission analyzer 16 to determine the temperature 41b.
The air ratio 41a corresponding to is calculated. Table 1 shows an example of the equilibrium gas composition table.

[0041]

[Table 1]

The calculated gas-phase air ratio 41a corresponds to the reducing flame 6
This is the air ratio of the gas phase of
The amount of Ox generated can be controlled. In the reducing atmosphere, the NOx concentration is determined by the value of the air ratio in the gas phase, so by controlling the supply amount of secondary air, the air ratio in the gas phase of the reducing flame 6 can be changed to control the amount of NOx. Further, since the NOx concentration can be lowered by making the pulverized coal particle size fine, the pulverized coal particle size may be made fine instead of reducing the flow rate of the secondary air.

The amount of pulverized coal can be known from the detected reducing flame temperature 41b and the gas phase air ratio 41a. The operation of the pulverized coal amount calculator will be described with reference to FIG. Arrows in FIG. 4 indicate data input destinations and output destinations. The pulverized coal amount calculator has a reaction model for evaluating the reaction of coal inside. For the air ratio and temperature, use the values obtained using an emission analyzer. From the coal type database, the reaction rate constants for the thermal decomposition and surface reaction of the coal used, the elemental composition of the coal, and the calorific value are determined. The residence time of the fuel in the reducing flame, that is, the pulverized coal, is obtained by dividing the length of the reducing flame by the fuel supply flow rate. First, the reaction rate constant of coal is calculated from the values of frequency factor, activation energy and temperature,
If the residence time is added to this, the combustion amount of the fuel can be obtained. On the other hand, the reaction model using the composition and heat generation amount of the fuel, the temperature of the primary air, the reaction rate constant previously obtained and the residence time of the fuel, and the air ratio 41a of the reducing flame 6 obtained from the air ratio calculator 15. The burning rate can be obtained by.

The calculation procedure of the reaction model is shown in FIG. This reaction model uses two assumptions: the gas composition is in equilibrium and the gas and coal particle temperatures are equal. The reaction model calculates changes in the composition and temperature of combustion gas and coal over time when the composition and temperature of coal and combustion gas and the air ratio are given as initial conditions. Can also be calculated.

The reaction model requires, as parameters, the rate constant of the thermal decomposition reaction and surface reaction of coal, the calorific value of coal, the average particle size of coal, and the like. The initial conditions and parameters are input to the reaction model, and the combustion rate of coal is calculated assuming that the residence time obtained from the size of the reducing flame and the flow velocity of the fuel has elapsed. The composition of coal is roughly divided into volatile matter, fixed carbon and ash, and the release rate of each is calculated from the rate constant of thermal decomposition and the rate constant of surface reaction. First, the initial temperature
The rate constants of thermal decomposition and surface reaction rate at the (primary air temperature) are calculated, and this is multiplied by a time step to obtain the amount of each chemical species released into the gas phase within the time step. The mass on the solid side is reduced by the same mass as the species released into the gas phase.
The reaction model has an air ratio in the gas phase and a gas composition corresponding thereto as an equilibrium gas composition table. The gas-phase air ratio is calculated from the composition of the combustible gas released into the gas phase by thermal decomposition and surface reaction, and the gas composition corresponding to the air ratio is determined from the equilibrium gas composition table. On the other hand, the difference between the enthalpy of the gas composition before the reaction and the enthalpy of the equilibrium composition is calculated, and the temperature of the gas is raised by the amount of heat corresponding to this enthalpy difference.
Replace the initial gas and coal composition and temperature with new values,
The time step Δt is added to the time, and the calculation is repeated from the reaction rate constant until the time t becomes equal to the residence time. By the above calculation, the composition and temperature of gas and coal at any time can be calculated. Moreover, the burning rate of coal at an arbitrary time can be calculated from the change in coal composition.

The amount of fuel burned in the reducing flame and the burning rate can be found by the calculation of the reaction model, and the amount of fuel supplied can be found by dividing the burning amount by the burning rate. The amount of fuel is a value estimated from the light emission of a burning flame, and does not include measurement error by a measuring instrument or time delay.

The raw material coal 20, after being crushed by the crusher 19, is supplied to the burner via the flow rate control valve 29a, the flow rate measuring device 38a, and the particle size measuring device 34. The particle size of the crushed coal leaving the crusher 19 can be adjusted by a rotary classifier (not shown) provided in the crusher, and the larger the rotational speed of the rotary classifier, the finer the particle size. Combustion air 30 is supplied to the burner through a blower 39, an air preheater 40, a flow rate adjusting valve 29b, and a flow rate measuring device 38b.

The temperature 41b and the gas-phase air ratio 41a calculated by the emission analyzer 16 and the air ratio calculator 15 are converted into electric signals and input to the combustion control means 31 and the pulverized coal amount calculator 33. In the pulverized coal amount calculator 33, the gas phase air ratio is 4
The amount of pulverized coal is estimated from 1a, temperature 41b, and coal type information 42, converted into an electric signal 36, and sent to the combustion control means 31. The broken line in FIG. 1 indicates the flow of signals. The coal type information 42 includes frequency factors of thermal decomposition and surface reaction, activation energy, elemental composition of coal, calorific value, etc., and a value corresponding to the designated coal type 43 is read from the coal type database 35. In the combustion control means 31, the supply amounts of fuel and air are input from the flow rate measuring devices 38a and 38b, respectively. The particle size of the pulverized coal is input from the particle size measuring device 34. Furthermore, the combustion control means 31 includes a gas phase air ratio 41a and a temperature 41 of the reducing flame.
The electric signal 36 of b and the amount of pulverized coal is input. The combustion control means 31 calculates an appropriate fuel and air supply amount and pulverized coal particle size based on these information, and controls the pulverized coal amount control means 48, the air amount control means 49, and the particle size control means 28. Send signals and control them.

When the air ratio of the gas phase of the reducing flame is larger than the set value, the combustion control means 31 sends a signal to the particle size control means 28 so as to make the particle size fine, and the particle size control means 28 causes the crusher 19 to move. Control signal 17 to increase the rotation speed of the rotation classifier
Give out. When the difference between the calculated gas-phase air ratio 41a and the set value is large and the value of the gas-phase air ratio cannot be returned to the set value by changing the particle size, the air ratio can be controlled by changing the air flow rate. It is valid.

The pulverized coal amount obtained by the pulverized coal amount calculator 33 is more accurate than the value detected by the flow rate measuring device 38a and does not include a delay due to the mounting position of the flow rate system. Therefore, this pulverized coal amount can be used as a more accurate indicator of the fuel supply amount. The pulverized coal amount instruction value 44 for the load command value is compared with the pulverized coal amount estimated by the pulverized coal amount calculator 33. If the two values are different, the pulverized coal amount calculated by the pulverized coal amount calculator 33 is the fine powder. A signal is sent to the pulverized coal amount control means 48 so as to approach the coal amount instruction value 44, and the flow rate adjusting valve 29a is adjusted.

According to this embodiment, the amount of fuel and air supplied and the particle size of pulverized coal can be controlled so that the NOx discharged from the burner is minimized. In addition, the amount of pulverized coal can be estimated with high accuracy, and heat management and control of the boiler can be performed more accurately.

FIG. 6 shows an example of calculating the air ratio in a pulverized coal boiler having an after-air port by collecting the light emission of the flame generated by the after-air port. Figure 6
Then, the control system of the flame 14 generated by the pulverized coal burner is omitted. Figure 7 shows an enlarged view of the after-airport.
Shown in A plurality of after-air ports 70 are horizontally arranged and installed on one side of the furnace or on the opposite wall surface. The primary air 71 is ejected from the center of the after-air port 70, and the secondary air 72 is ejected from the outside of the after-air port 70 in a concentric manner with swirling. The swirl strength of the secondary air 72 can be adjusted by the swirl vanes 75. The air supplied from the after-air port mixes with carbon monoxide contained in the combustion exhaust gas of the burner to form a flame 77 due to the combustion of CO. A light collector 60 is provided from the outside of the wind box 74 of the after-air port in the primary air pipe 76, and the emission of the flame 77 due to the combustion of CO is guided to the emission analyzer 16 by the optical fiber 22. The emission analyzer 16 calculates the temperature 61b of the flame 77. The temperature 61b is input to the air ratio calculator 15 to calculate the air ratio 61a. Air ratio 61a of flame 77 calculated as above
Is less than 1, the air flow rate in the after-air port is increased, and when the air ratio is greater than 1, it is decreased in reverse.
By operating, the air ratio at the after-air port can always be kept close to 1.

According to this embodiment, C at the after-airport
It is possible to keep the air ratio at the time of O combustion at 1 and operate with high efficiency while keeping the oxygen concentration in unburned coal and combustion exhaust gas to a minimum. Moreover, since the calculated air ratio does not include a delay due to gas analysis or the like, it is possible to easily cope with a rapid load change.

In each of the above examples, the secondary air nozzle and the tertiary air nozzle are provided around the pulverized coal nozzle, the flame holding ring is provided at the tip of the pulverized coal nozzle, and the mixture of pulverized coal and primary air goes straight. A combustion device having a pulverized coal burner having a structure in which a secondary flow and a tertiary air are ejected in a swirl flow has been described, but the present invention is not limited to this. If an oxidizing flame is formed around the reducing flame,
The burner may have any structure. For example, it may have a structure in which one or two air nozzles are stacked with a pulverized coal nozzle interposed therebetween, or may be one in which secondary air or tertiary air is swirled by a cyclone without using swirling blades.

Further, an example in which the air ratio of the reducing flame is calculated to suppress NOx generation has been described. However, since the air ratio and the temperature have a correlation, the amount of pulverized coal or the amount of air is determined based on the temperature of the reducing flame. It is also possible to control.

In the combustion of pulverized coal, it is also possible to detect the air ratio of the oxidizing flame in order to reduce the unburned content and adjust the amount of air ejected from the air nozzle so that the air ratio becomes 1. is important. In a pulverized coal boiler, there is a dormant burner.Therefore, a lighting device installed in the burner is used to collect the flame emission of the oxidizing flame, calculate the air ratio, and control the air volume of the air nozzle. To do is extremely effective. It is desirable that the air ratio of the oxidizing flame be 1 or more.

[0057]

INDUSTRIAL APPLICABILITY In the combustion of pulverized coal by the pulverized coal burner of the in-flame deoxidizing method, the temperature or the air ratio of the reducing flame formed inside the flame is calculated to supply the amount of pulverized coal or air or the grains of pulverized coal. By controlling the diameter, the generation of NOx can be minimized.

Further, by obtaining the air ratio from the emission intensity of the flame from the after air port and controlling the air amount, the effect of reducing the unburned content can be further enhanced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a pulverized coal combustion apparatus showing an embodiment of the present invention.

FIG. 2 is a correlation diagram between a gas-phase air ratio and NOx concentration.

FIG. 3 is a schematic configuration diagram of an emission analyzer.

FIG. 4 is an explanatory diagram showing a method of calculating the amount of pulverized coal by a pulverized coal amount calculator.

FIG. 5 is a diagram showing a calculation procedure of a reaction model.

FIG. 6 is a schematic view of a combustion device including a pulverized coal boiler having an after-air port and a unit for calculating an air ratio of a flame formed at the after-air port portion.

FIG. 7 is an enlarged view of an after-airport portion.

[Explanation of symbols]

1 ... Dimmer, 3 ... Pulverized coal nozzle, 5 ... Flame retaining ring, 6 ...
Reduction flame, 7 ... Oxidizing flame, 9 ... Swirl blade, 10 ... Mixture of pulverized coal and primary air, 11 ... Secondary air nozzle, 12 ... Tertiary air nozzle, 15 ... Air ratio calculator, 16 ... Emission analyzer, 2
1 ... Optical fiber, 31 ... Combustion control means, 41a ... Air ratio of reducing flame, 41b ... Temperature of reducing flame, 70 ... After air port, 100 ... Pulverized coal burner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Taniguchi 7-1, 1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Hiroshi Okazaki 1-chome, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Company Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Shigeki Morita 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Kure Factory

Claims (16)

[Claims] 1. A pulverized coal combustion apparatus equipped with a pulverized coal burner that forms a flame having a reducing flame region having an oxygen deficiency and an oxidizing flame region having an oxygen excess, and a flame temperature of a reducing flame region formed by the burner, Combustion of pulverized coal provided with means for controlling at least one of the amount of pulverized coal and air supplied to the burner or the particle size of the pulverized coal so that at least one of the air ratios becomes a set condition. apparatus. 2. A combustion apparatus comprising a pulverized coal burner concentrically provided with at least one annular air nozzle on the outer periphery of a pulverized coal nozzle for conveying and ejecting pulverized coal by air flow. Pulverized coal supplied to the pulverized coal burner such that the emission of flame in the field of view seen from the nozzle is sampled through the interior and at least one of the flame temperature and the air ratio calculated from the emission is in a set condition. A pulverized coal combustion apparatus comprising means for controlling air supply conditions. 3. The pulverized coal combustion apparatus according to claim 2, wherein a light collector for collecting the light emission of the oxygen-deficient flame is provided outside the curved portion of the pulverized coal nozzle in the direction of the central axis of the pulverized coal nozzle. . 4. The pulverized coal combustion apparatus according to claim 2 or 3, further comprising means for calculating an air ratio based on the flame temperature calculated from the emission intensity of the collected flame. 5. A pulverized coal burner having at least one annular air nozzle which is concentrically provided on the outer periphery of a pulverized coal nozzle for conveying and ejecting pulverized coal by air, and the pulverized coal is completely burned by the burner. In the combustion device configured to form a flame having an oxygen-deficient reducing flame region and an oxygen-excessive oxidizing flame region, from the flame root portion in the flame formed by the pulverized coal burner toward the flame tip direction. Pulverized coal nozzle diameter (D) 3
The supply conditions of pulverized coal and air to be supplied to the pulverized coal burner are controlled so that at least one of the flame temperature and the air ratio obtained by collecting the light emission of the flame included in the distance up to twice becomes the set condition. A pulverized coal combustion apparatus characterized by comprising means. 6. The inside of the flame included in a region extending in the pulverized coal nozzle extension direction at a distance of up to 3 times the pulverized coal nozzle diameter (D) from the flame root portion toward the flame tip direction. From light emission to flame temperature and air ratio of at least 1
The pulverized coal combustion apparatus is provided with a means for calculating the two and controlling the supply conditions of the pulverized coal and air to be supplied to the pulverized coal burner so that these become the set conditions. 7. A pulverized coal burner having at least one annular air nozzle concentrically on the outer periphery of a pulverized coal nozzle for carrying and ejecting the pulverized coal by air flow, and oxygen is provided for complete combustion of the pulverized coal. In a combustion device configured to form a flame having an insufficient reducing flame and an oxygen-excessive oxidizing flame, the temperature of the flame formed by the pulverized coal burner is measured by collecting light emission inside the flame in substantially the center of the flame. And at least one of the air ratios, and means for controlling the supply conditions of the pulverized coal and the air to be supplied to the pulverized coal burner so that these are set conditions. apparatus. 8. A pulverized coal burner concentrically provided with at least one annular air nozzle on the outer periphery of a pulverized coal nozzle for conveying and ejecting pulverized coal by air is arranged in at least one stage in the height direction of the furnace. A combustion device in which a plurality of pulverized coal burners are arranged in each stage, and a flame having an oxygen-deficient reducing flame and an oxygen-excessive oxidizing flame is formed in order to completely burn the pulverized coal by each burner. In, all of the pulverized coal burner is provided with a dimmer that illuminates the light emission of the flame in the field of view seen from the inside of the pulverized coal nozzle, and at least one of the flame temperature and the air ratio is calculated from the emission of the flame lit by the dimmer. And a means for controlling the supply conditions of the pulverized coal and air to be supplied to each burner so that the calculated value is the same for all of the pulverized coal burners of the respective stages and the set conditions are satisfied. A pulverized coal combustion device characterized in that 9. The atomizer type nozzle according to claim 2, wherein said pulverized coal nozzle atomizes and ejects pulverized coal by colliding an air flow with a mixed flow of pulverized coal and water. A pulverized coal combustion device characterized by: 10. A pulverized coal burner concentrically provided with at least one annular air nozzle on the outer periphery of a pulverized coal nozzle for conveying and ejecting pulverized coal by air is arranged in at least one stage in the height direction of the furnace. A plurality of pulverized coal burners are arranged in each stage, and in order to completely burn the pulverized coal by each burner, a flame having an oxygen-deficient reducing flame and an oxygen-excessive oxidizing flame is formed. In the combustion device having an after-air port in the upper stage of the pulverized coal burner, the pulverized coal burner is provided with a dimmer that illuminates the emission of the flame in the field of view seen from inside the pulverized coal nozzle, and the flame lit by the dimmer At least 1 of flame temperature and air ratio
And a means for controlling the supply conditions of the pulverized coal and air to be supplied to each burner so that the obtained value is the same as that of the pulverized coal burner of each stage and has the set condition. Then, the air ratio is calculated by collecting the light emission inside the flame formed by the air ejected from the after-air port and the unburned components in the furnace, and the air ratio is set to approximately 1 to the after-air port. A pulverized coal combustion apparatus comprising: means for controlling at least one of an amount of supplied air and an amount of swirling air. 11. The emission analysis means for analyzing the luminescence of the flame lit by the illuminator, the flame temperature, the air ratio, and the coal species database calculated from the luminescence of the flame according to any one of claims 2 to 10. And a means for calculating the amount of pulverized coal supplied from the equilibrium gas composition table. 12. The pulverized coal burner according to claim 2, further comprising a pulverized coal burner having a flame-holding ring whose diameter increases outward at the tip of the pulverized coal nozzle. Characterized pulverized coal combustion device. 13. The air ratio according to claim 2, wherein the air ratio is detected from the emission intensity of an oxygen-excessive flame formed by the pulverized coal burner, and the air ratio is approximately 1.
The pulverized coal combustion apparatus is provided with a means for controlling the amount of air supplied to the air nozzle. 14. A pulverized coal burner is burned by a pulverized coal burner concentrically provided with at least one air nozzle on the outer periphery of a pulverized coal nozzle for conveying and ejecting the pulverized coal by air, and the pulverized coal is provided in the vicinity of the burner. In a pulverized coal combustion method in which an oxygen-deficient reducing flame is formed for complete combustion of the reducing flame, and an oxygen-excessive oxidizing flame is formed on the outer periphery of the reducing flame. A method for combusting pulverized coal, characterized in that at least one of the air ratios is obtained, and the conditions for supplying pulverized coal and air supplied to the burner are controlled so that these values become set conditions. . 15. The method according to claim 14, wherein at least one of the flame temperature and the air ratio is calculated from the emission intensity obtained by collecting the emission of the flame in the field of view seen from the inside of the pulverized coal nozzle through the inside of the nozzle. The pulverized coal combustion method is characterized in that the conditions for supplying pulverized coal and air are controlled so that the above condition is set. 16. The pulverized coal combustion according to claim 14 or 15, wherein the conditions for supplying pulverized coal and air are controlled so that the upper limit of the air ratio of the oxygen-deficient flame does not exceed 0.9. Method.