CN112413570A

CN112413570A - Low-nitrogen burner for large and medium pulverized coal fired boiler under wide-load operation and use method

Info

Publication number: CN112413570A
Application number: CN202011523773.XA
Authority: CN
Inventors: 潘效军; 李乾军; 张长飞; 毕小龙; 严谨; 乔正辉
Original assignee: Nanjing Institute of Technology
Current assignee: Nanjing Institute of Technology
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2021-02-26

Abstract

The invention discloses a low-low nitrogen burner under a wide load condition of a large and medium pulverized coal boiler and a using method thereof.A primary air system which can meet the requirement that the inside of the cross section of a hearth at the position is always a high-concentration pulverized coal region and can stably burn without coking under any load/coal working condition is arranged at the middle position in the vertical direction of the hearth burner; in the operation of a low-load working condition, the concentration of the coal dust in the middle hearth space can be kept to be large enough to form an anoxic high-temperature combustion area, and a large amount of carbon monoxide is generated to fully inhibit the generation of thermal nitrogen oxides; and in the upper afterburning air area, the upper hearth becomes an oxygen-enriched relatively low-temperature combustion area by regulating and controlling the afterburning air quantity, and the temperature is lower than the temperature generated by thermal nitrogen oxide, so that high-concentration carbon monoxide is fully combusted. The method has obvious energy-saving and environment-friendly benefits when the large and medium boilers run under low load.

Description

Low-nitrogen burner for large and medium pulverized coal fired boiler under wide-load operation and use method

Technical Field

The invention belongs to the field of engineering thermophysics, and particularly relates to a low-nitrogen burner for a large and medium pulverized coal boiler under wide-load operation and a use method thereof.

Background

With the adjustment and gradual propulsion of energy structures in China, the electric energy generated by new energy technologies such as wind energy, solar energy and the like is gradually increased, the peak shaving amplitude of a boiler of a large-scale thermal power plant is increased, and low-load long-time operation becomes normalization. In order to meet the electric energy requirement in the peak or the time period of insufficient new energy, the boiler of the large and medium thermal power plant must be large enough to meet the peak regulation range of 25% -100%, and the rated evaporation capacity range is 670t/h (corresponding to the rated generated energy of 600 MW) -3000 t/h, so as to meet the power generation working condition of large-load operation. Under the conditions of meeting the environmental protection requirement and energy-saving operation, the regulation and control load of the boiler of the current large-scale thermal power plant is generally narrower. Because the furnace size is great, low-load economic operation often meets the problems that the combustion in the furnace is unstable, the oxygen content of the coal powder furnace is overlarge, the generation amount of nitrogen oxides is obviously increased, the environmental-friendly emission does not reach the standard or the ammonia injection amount is increased for reducing the nitrogen oxides. When the low-load and low-oxygen-content operation is carried out, the concentration of carbon monoxide generated in the furnace is generally overhigh, the concentration of carbon monoxide in the discharged flue gas is overhigh, and the utilization rate of coal-fired energy is reduced. Meanwhile, due to insufficient coal combustion, the temperature of the hearth can not reach the standard, the temperature of main steam of the superheater is too low, and the thermoelectric conversion efficiency of the steam turbine can be reduced accordingly.

Disclosure of Invention

The purpose of the invention is as follows: aiming at the large and medium pulverized coal boilers, the generation of nitrogen oxides is inhibited by increasing the concentration of pulverized coal in a middle main combustion area, and the high-concentration carbon monoxide is fully combusted under the condition of being lower than the generation temperature of thermal nitrogen by increasing the air quantity at the upper part of a hearth, so that the middle part of the hearth is in a high-temperature reducing atmosphere environment, the upper part of the hearth is in a relatively low-temperature oxidizing environment, and the purpose of fully inhibiting the generation of the thermal nitrogen oxides when the large and medium pulverized coal boilers stably and efficiently operate at low load is achieved.

The technical scheme is as follows: in order to achieve the purpose, the invention adopts the following technical scheme: a low-low nitrogen burner under the wide load operation of large-and-medium-sized pulverized coal fired boilers is characterized by comprising:

the primary air system is arranged in the middle of the vertical direction of the hearth combustor, meets the requirement of the position under any load or coal working condition, is always a high-concentration pulverized coal region in the cross section of the hearth and can stably combust without coking, and the high-concentration standard meets the requirement that the high-concentration pulverized coal region belongs to a main combustion region of a boiler;

the overfire air port of the secondary air distribution and supply of the hearth is formed by the upside of the primary air system on the hearth combustor, and the air supply quantity of the overfire air port is selected according to the following standard: when the upper limit of the air supply quantity meets the condition that excessive oxygen combustion does not occur in the space near the cross section area of the hearth at the position of the overfire air port, lifting adjustment is carried out according to the operating load requirement and the steam temperature change, and the central position of the flame is ensured to meet the steam temperature change requirement;

and the afterburning air system is arranged at the upper side of the vertical direction of the hearth combustor and at the upper side of the position of the overfire air port and used for injecting air to the inner space of the hearth cross section at the upper position.

Preferably, the primary air system includes the first primary air inlet of connecting furnace combustor middle part position furnace wall, the second primary air inlet of connecting furnace combustor bottommost position furnace wall, be used for buggy volume to switch first blast gate and second blast gate of adjusting, be used for carrying the first wind channel and the second primary air channel and the first main pipeline of wind, first coal pulverizer of buggy, first primary air inlet and second primary air inlet are located the downside of burn-out air inlet, wherein:

the first primary air port, the first air valve, the first primary air channel, the first primary air main pipeline and the first coal mill are sequentially connected into a through coal powder conveying passage;

the second primary air port, the second air valve, the second primary air channel, the first primary air main pipeline and the first coal mill are sequentially connected to form a through coal powder conveying passage.

Preferably, the after-combustion air system comprises an after-combustion air port which is arranged on two parallel side walls of the hearth and is right opposite, an after-combustion air valve for air quantity adjustment and an after-combustion air pipeline for conveying air, wherein the after-combustion air port is positioned on the upper side of the after-combustion air port, the after-combustion air port is connected to the after-combustion air pipeline through the after-combustion air valve, and the after-combustion air pipeline is connected with the after-combustion air pipeline correspondingly connected with the after-combustion air port.

Preferably, the rated load evaporation capacity of the large and medium-sized pulverized coal fired boiler is 670 t/h-3000 t/h.

A use method of a low-nitrogen burner under wide-load operation of a large and medium-sized pulverized coal fired boiler is characterized by comprising the following steps:

in the low-load working condition operation process of the large and medium pulverized coal fired boiler, opening a first air valve and closing a second air valve, wherein the first coal mill only conveys pulverized coal for a first primary air port;

in the high-load working condition operation process of the large and medium-sized pulverized coal fired boiler, opening a second air valve and closing a first air valve, wherein the first coal mill only conveys pulverized coal for a second primary air port;

in the afterburning air area, the air quantity of the afterburning air port and the air quantity of the over-fired air port sprayed into the hearth are regulated and controlled by regulating and controlling the opening of an afterburning air valve.

Has the advantages that: the invention has the following remarkable beneficial effects:

the low-low nitrogen burner under the wide-load operation of the boiler of the thermal power plant and the use method thereof can realize the obvious low-low nitrogen combustion effect in the low-load operation process in the process of reforming the existing or designing a newly-built large and medium-sized pulverized coal fired boiler: during low-load operation, coal dust with enough concentration can be kept in a hearth space corresponding to the middle position of the hearth combustor in the vertical direction, the reducing atmosphere in the area is kept, and the generated sufficient carbon monoxide can inhibit the formation of nitrogen oxides to the maximum extent; in upper portion afterburning wind region, through regulation and control air quantity, guarantee that the oxygen after regulation and control on the one hand fully burns with carbon monoxide, on the other hand guarantees simultaneously that the temperature is less than nitrogen oxide's formation temperature in this region, finally realizes: the middle area of the hearth combustor is an oxygen-deficient high-temperature combustion area, the high temperature means that the actual operation temperature is higher than the temperature generated by nitrogen oxides, the air supplementing area at the upper part of the hearth combustor is an oxygen-enriched relatively low-temperature combustion area, and the relatively low temperature means that the actual operation temperature is lower than the temperature generated by the nitrogen oxides. The invention can be used for the design and the transformation of the low-load stable non-coking combustion of the large and medium boiler burner, has the advantages of improving the utilization rate of fire coal and reducing the generation amount of nitrogen oxides in the boiler, and reduces the risk of coking in the boiler by complementarily regulating and controlling air distribution at the middle part and the upper part of the hearth.

Drawings

FIG. 1 is a schematic view of a large and medium sized pulverized coal boiler (with an evaporation capacity of 670 t/h-3000 t/h) according to the present invention;

FIG. 2 is a schematic view of a low-nitrogen burner of a large and medium sized pulverized coal fired boiler according to the present invention;

FIG. 3 is a schematic diagram of a coal powder four-corner conveying system and an air secondary air conveying system of a large and medium boiler according to the present invention;

FIG. 4 is a schematic view showing the correspondence between the primary tuyere of a large and medium sized pulverized coal boiler and the serial number of a pulverized coal supplying pulverizer of the present invention;

FIG. 5 is a schematic view of the positions of the primary tuyere, the secondary tuyere, the over-fire tuyere and the after-fire tuyere of the large and medium pulverized coal fired boiler according to the present invention;

in the figure: 2-primary air system; 21-first primary tuyere; 211-a second primary tuyere; 22-a first primary air duct; 221-a second primary air duct; 23-a first air valve; 231-a second air valve; 24-a first coal mill; 25-a first primary air main pipeline; 3-a post combustion air system; 31-a post-combustion tuyere; 32-afterburning air valve; 33-afterburning air duct.

Detailed Description

The present invention will be further described with reference to the accompanying drawings.

The invention discloses a low-low nitrogen burner under a wide-load operation condition of a large and medium pulverized coal boiler, which corresponds to the rated load evaporation capacity of the large and medium pulverized coal boiler of 670 t/h-3000 t/h and comprises the following components: the primary air system 2 is arranged in the middle of the furnace combustor in the vertical direction, the primary air system 2 can meet the requirement that the inside of the cross section of the furnace at the position is always a high-concentration pulverized coal region and can stably burn without coking under any load or any coal working condition, and the high-concentration size standard meets the requirement that the high-concentration pulverized coal region belongs to the main combustion region of a boiler.

The primary air system 2 comprises a first primary air port 21 connected with the furnace wall at the middle position of the furnace combustor, a second primary air port 211 connected with the furnace wall at the bottommost position of the furnace combustor, a first air valve 23 and a second air valve 231 for switching and adjusting the coal dust amount, a first primary air duct 22 and a second primary air duct 221 for conveying coal dust, a first primary air main pipeline 25 and a first coal mill 24;

sequentially connecting a first primary air port 21, a first air valve 23, a first primary air duct 22, a first primary air main pipeline 25 and a first coal pulverizer 24 into a through coal powder conveying passage;

and the second primary air port 211, the second air valve 231, the second primary air channel 221, the first primary air main pipeline 25 and the first coal pulverizer 24 are sequentially connected into a through coal powder conveying passage.

The operation and installation criteria of the first damper 23 and the second damper 231 are: the switching adjustment of the coal powder quantity conveyed to the first primary tuyere 21 and the second primary tuyere 211 by the first coal mill 24 through the coal powder conveying passage is satisfied.

The upper portion in the primary air inlet on the furnace combustor sets up the after-combustion air inlet, constitutes the secondary that sends into furnace and joins in marriage the air supply, and the primary air inlet includes first primary air inlet 21 and second primary air inlet 211, and the air supply volume size selection standard that the air supply was joined in marriage to the secondary is: under the condition that the upper limit of the air supply amount meets the requirement of the over-fire air port, and the oxygen excess combustion does not occur in the space near the cross section area of the hearth, the lifting adjustment can be carried out according to the operating load requirement and the steam temperature change, and the central position of the flame is ensured to meet the steam temperature change requirement. The over-fire air inlet is correspondingly provided with an over-fire air pipeline.

The afterburning air system 3 capable of injecting air to the inner space of the cross section of the hearth at the upper part of the vertical direction of the hearth combustor and the upper part of the position of the overfire air port is arranged, the afterburning air system 3 comprises a plurality of just-opposite afterburning air ports 31 arranged on two parallel side walls of the hearth, an afterburning air valve 32 used for air quantity adjustment and an afterburning air pipeline 33 connected with the overfire air pipeline and used for conveying air, wherein the afterburning air port 31 is positioned at the upper part of the position of the overfire air port, and the afterburning air port 31 is connected with the afterburning air pipeline 33 through the afterburning air valve 32.

In an embodiment of the invention, the low-nitrogen burner for the large and medium-sized pulverized coal fired boiler under the wide-load operation further comprises a secondary air port, and the primary air port of the primary air system 2 further comprises other primary air ports.

The primary air port, the secondary air port and the over-fire air port of the primary air system 2 are all arranged on four hearth corners of a hearth, the after-fire air ports 31 are symmetrically arranged on the upper portions of the left side wall and the right side wall of the hearth, the over-fire air ports are all positioned on the upper sides of the primary air port and the secondary air port, the after-fire air ports 31 are all positioned on the upper sides of the primary air port, the secondary air port and the over-fire air port, and the centers of the bottommost primary air ports on the four hearth corners are positioned.

The overfire air ports are communicated with the after-combustion air ports 31 through the after-combustion air valves 32, the after-combustion air pipelines 33 and the overfire air pipelines, and the air quantity proportion and the air quantity rate entering each after-combustion air port 31 and each overfire air port are divided by adjusting the opening degree of the after-combustion air valves 32 during work.

Aiming at each hearth corner, at least one secondary air port is arranged between any two primary air ports, the number of the secondary air ports on the four hearth corners is equal, the secondary air ports on each hearth corner are counted from the bottommost part of the hearth to the uppermost part of the hearth, and the secondary air ports with the same serial number are positioned on the same horizontal plane; the primary air ports on the four hearth corners are equal in number, the primary air ports on each hearth corner are counted from the bottommost part of the hearth to the uppermost part of the hearth respectively, and the primary air ports with the same serial number on the four hearth corners are located on the same horizontal plane.

Aiming at any one of the four hearth corners, a primary air port positioned at the bottommost part of the hearth is a second primary air port 211, a primary air port positioned in the middle position of the primary air port positioned at the bottommost part of the hearth and the primary air port positioned at the uppermost part of the hearth is a first primary air port 21, wherein two other primary air ports are arranged between the second primary air port 211 and the first primary air port 21 at equal intervals on each hearth corner; three other primary tuyeres are provided at equal intervals between the first primary tuyere 21 and the uppermost primary tuyere.

Aiming at any one of the four hearth corners, the first primary air opening 21 and the second primary air opening 211 are communicated through a first air valve 23, a first primary air duct 22, a second primary air duct 221 and a second air valve 231. First primary air inlet 21 and second primary air inlet 211 at arbitrary furnace angle are connected through the wind valve and the wind channel of the same pipe diameter respectively, and the wind channel is after gathering through the bifurcated pipe tee bend, is linked together with first coal pulverizer 24 through first primary air trunk line 25, and like this, four coal conveying pipeline are drawn forth altogether through first primary air trunk line 25 to first primary air inlet 21 and the second primary air inlet 211 of the co-altitude of conveying buggy to four furnace angles respectively to first coal pulverizer 24: by switching the air valve switch, the first coal mill 24 conveys and burns pulverized coal for the first primary air port 21 under the condition of low load, and the second air valve 231 is switched off; at high load the first mill 24 delivers pulverized coal to the second primary tuyere 211 and burns, while the first air flap 23 is opened.

In an embodiment of the invention, the primary air ports on each hearth corner are counted from the bottommost part of the hearth to the uppermost part of the hearth, except the first primary air port 21 and the second primary air port 211, other primary air ports with the same serial number on the four hearth corners are respectively communicated with the corresponding primary air channels, the corresponding primary air channels are converged again and are connected to an independent coal mill through a primary air main pipeline, and the primary air channels correspond to the counting from bottom to top and are respectively a second coal mill, a third coal mill, a fourth coal mill, a fifth coal mill, a sixth coal mill and a seventh coal mill.

In another embodiment of the invention, two other primary air ports are arranged between the first primary air port 21 and the second primary air port 211 at each hearth corner, the other primary air ports positioned between the first primary air port 21 and the second primary air port 211 at the four hearth corners are communicated with the corresponding primary air channels, and the corresponding primary air channels are converged and then connected to the same coal pulverizer through a primary air main pipeline.

The invention discloses a use method of a low-low nitrogen burner under a wide-load operation condition of a large and medium pulverized coal boiler, which comprises the following steps:

in the operation process of the large and medium pulverized coal boiler under the low-load working condition, the first air valve 23 is opened, the second air valve 231 is closed, the first coal mill 24 only conveys pulverized coal for the first primary air port 21, the pulverized coal concentration corresponding to the middle position of the vertical direction of the hearth combustor can keep enough pulverized coal concentration (the standard of the pulverized coal concentration is to keep the area to be reducing atmosphere, and enough carbon monoxide generated can inhibit the formation of nitrogen oxides to the maximum extent), and the main combustion area in the middle of the hearth combustor is an oxygen-deficient high-temperature combustion area (the 'high temperature' means that the actual operation temperature is equal to or higher than the temperature range generated by thermal nitrogen oxides);

in the high-load working condition operation process of the large and medium-sized pulverized coal boiler, the second air valve 231 is opened, the first air valve 23 is closed, and the first coal mill 24 only conveys pulverized coal for the second primary air port 211;

in the upper afterburning air area, the air quantity of the afterburning air port 31 and the over-fire air port sprayed into the hearth is regulated and controlled by regulating and controlling the opening degree of an afterburning air valve 32, and the upper afterburning air area of the hearth combustor is an oxygen-enriched relatively low-temperature combustion area (the relatively low temperature refers to the temperature of actual operation lower than the temperature generated by thermal nitrogen oxides), wherein the air quantity is regulated and controlled to meet the standard of ensuring that the regulated and controlled oxygen and carbon monoxide are fully combusted, and meanwhile, the temperature in the area is lower than the generation temperature of the nitrogen oxides.

The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention and these are intended to be within the scope of the invention.

Claims

1. A low-low nitrogen burner under the wide load operation of large-and-medium-sized pulverized coal fired boilers is characterized by comprising:

the primary air system (2) is arranged in the middle of the vertical direction of the hearth combustor, meets the requirements of the position under any load or coal working condition, is always a high-concentration pulverized coal region in the cross section of the hearth and can stably combust without coking, and the high-concentration standard meets the requirement that the high-concentration pulverized coal region belongs to a main combustion region of a boiler;

the upper side of the primary air system (2) on the hearth combustor is provided with an over-fire air port for secondary air distribution and supply, the air supply quantity of the over-fire air port is selected according to the following standard: when the upper limit of the air supply quantity meets the condition that excessive oxygen combustion does not occur in the space near the cross section area of the hearth at the position of the overfire air port, lifting adjustment is carried out according to the operating load requirement and the steam temperature change, and the central position of the flame is ensured to meet the steam temperature change requirement;

and the afterburning air system (3) is arranged at the upper side of the vertical direction upper part of the hearth combustor and at the position of the over-fire air inlet and used for injecting air to the inner space of the hearth cross section at the upper part.

2. The low-nitrogen burner for the wide-load operation of the large and medium-sized pulverized coal boiler according to claim 1, wherein the primary air system (2) comprises a first primary air port (21) connected to the furnace wall at the middle position of the furnace burner, a second primary air port (211) connected to the furnace wall at the bottommost position of the furnace burner, a first air valve (23) and a second air valve (231) for switching and adjusting the amount of pulverized coal, a first primary air duct (22) and a second primary air duct (221) and a first primary air duct (25) for conveying pulverized coal, and a first coal pulverizer (24), wherein the first primary air port (21) and the second primary air port (211) are located at the lower side of the burnout air port,

the first primary air port (21), the first air valve (23), the first primary air duct (22), the first primary air main pipeline (25) and the first coal pulverizer (24) are sequentially connected into a through coal powder conveying passage;

the second primary air port (211), the second air valve (231), the second primary air duct (221), the first primary air main pipeline (25) and the first coal pulverizer (24) are sequentially connected to form a through coal powder conveying passage.

3. The low-nitrogen burner for the large and medium-sized pulverized coal boiler under the wide-load operation according to claim 1, wherein the after-combustion air system (3) comprises opposite after-combustion air ports (31) arranged on two parallel side walls of the hearth, an after-combustion air valve (32) used for air quantity adjustment and an after-combustion air pipeline (33) used for conveying air, the after-combustion air ports (31) are positioned on the upper side of the after-combustion air ports, wherein the after-combustion air ports (31) are connected to the after-combustion air pipeline (33) through the after-combustion air valve (32), and the after-combustion air pipeline (33) is connected with the after-combustion air pipeline correspondingly connected with the after-combustion air ports.

4. The low-low nitrogen burner for the large and medium-sized pulverized coal fired boiler under the wide-load operation according to claim 1, wherein the rated load evaporation capacity of the large and medium-sized pulverized coal fired boiler is 670 t/h-3000 t/h.

5. A use method of a low-nitrogen burner under wide-load operation of a large and medium-sized pulverized coal fired boiler is characterized by comprising the following steps:

in the operation process of the large and medium pulverized coal boiler under the low-load working condition, the first air valve (23) is opened and the second air valve (231) is closed, and the first coal mill (24) only conveys pulverized coal for the first primary air port (21);

in the high-load working condition operation process of the large and medium-sized pulverized coal boiler, the second air valve (231) is opened, the first air valve (23) is closed, and the first coal mill (24) only conveys pulverized coal for the second primary air port (211);

in the afterburning air area, the air quantity of the afterburning air port (31) and the overfire air port sprayed into the hearth is regulated and controlled by regulating and controlling the opening degree of an afterburning air valve (32).