CN107013903B - Vertical pulverized coal boiler - Google Patents

Vertical pulverized coal boiler Download PDF

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Publication number
CN107013903B
CN107013903B CN201710425488.6A CN201710425488A CN107013903B CN 107013903 B CN107013903 B CN 107013903B CN 201710425488 A CN201710425488 A CN 201710425488A CN 107013903 B CN107013903 B CN 107013903B
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China
Prior art keywords
pulverized coal
hearth
secondary air
furnace
side walls
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CN107013903A (en
Inventor
吕清刚
朱建国
满承波
欧阳子区
刘敬樟
高鸣
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Institute of Engineering Thermophysics of CAS
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Institute of Engineering Thermophysics of CAS
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C7/00—Combustion apparatus characterised by arrangements for air supply
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C10/00—Fluidised bed combustion apparatus
    • F23C10/002—Fluidised bed combustion apparatus for pulverulent solid fuel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23C—METHODS OR APPARATUS FOR COMBUSTION USING FLUID FUEL OR SOLID FUEL SUSPENDED IN  A CARRIER GAS OR AIR 
    • F23C10/00—Fluidised bed combustion apparatus
    • F23C10/18—Details; Accessories
    • F23C10/20—Inlets for fluidisation air, e.g. grids; Bottoms
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
    • F23L—SUPPLYING AIR OR NON-COMBUSTIBLE LIQUIDS OR GASES TO COMBUSTION APPARATUS IN GENERAL ; VALVES OR DAMPERS SPECIALLY ADAPTED FOR CONTROLLING AIR SUPPLY OR DRAUGHT IN COMBUSTION APPARATUS; INDUCING DRAUGHT IN COMBUSTION APPARATUS; TOPS FOR CHIMNEYS OR VENTILATING SHAFTS; TERMINALS FOR FLUES
    • F23L9/00—Passages or apertures for delivering secondary air for completing combustion of fuel 
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E20/00—Combustion technologies with mitigation potential
    • Y02E20/34—Indirect CO2mitigation, i.e. by acting on non CO2directly related matters of the process, e.g. pre-heating or heat recovery

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)

Abstract

The invention provides a vertical pulverized coal boiler, comprising: the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the hearth; at least one pulverized coal burner comprising a main body and a burner outlet pipe extending from the main body, the main body being arranged at the lower part of the side wall of the furnace, the burner outlet pipe extending from the outer side of the lower part of the side wall of the furnace into the inner cavity of the furnace and being adapted to introduce a mixture of primary air and pulverized coal into the inner cavity of the furnace; and the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth. The secondary air distribution device comprises a plurality of secondary air distribution pipes distributed at the bottom of the hearth, and a plurality of air outlet holes are formed in the pipe wall of each air pipe. The mixture of primary air and coal dust is mixed with secondary air to form a wind-powder mixture which flows upwards in a plug flow integrally in the inner cavity of the hearth.

Description

Vertical pulverized coal boiler
Technical Field
The invention relates to the field of boilers, in particular to a vertical pulverized coal boiler.
Background
The structure taking coal as a main energy source in China is difficult to change in the long time in the future, the annual coal consumption in China reaches 15 hundred million tons, 8 hundred million tons of coal are used for coal-fired thermal power generation, and 7 hundred million tons of coal are used for a coal-fired industrial boiler. With the improvement of the emission standard of the atmospheric pollutants of the coal-fired boiler, the efficient clean combustion technology of the coal is a necessary requirement for future development.
In addition, in the traditional combustion mode, the difference between the injection speed of primary air and secondary air in a hearth and the average speed of the section of the hearth is large, a large backflow area exists in the hearth, high-temperature flue gas can be sucked in the backflow area to preheat coal dust, but the control of the backflow area is complex, agglomeration of coal dust particles easily occurs in the backflow area, if the structure of an in-furnace flow field is poor, the slagging tendency of the hearth is large, and the safe and stable operation of a boiler is influenced.
Traditional combustion modes include tangential firing using a direct flow burner and swirl firing using a swirl burner. In the traditional combustion mode, primary air carries pulverized coal and is sprayed into a hearth at the speed of 20-30m/s, and secondary air surrounds the primary air and is sprayed into the hearth at the speed of 30-40m/s, so that the combustion mode of wind-packed powder is formed. The pulverized coal is burned intensively in a specific area, the local combustion temperature is high, and the original NOx emission value of pulverized coal combustion is high. For pulverized coal fired boiler using anthracite, the original NOx emission value exceeds 800mg/m 3 The method comprises the steps of carrying out a first treatment on the surface of the For bituminous coal fired boilers, the original NOx emissions value is typically in excess of 400mg/m 3 Both significantly exceeding the relevant emission standards.
In addition, in the traditional combustion mode, the difference between the jet speed of primary air and secondary air in the hearth and the average speed of air flow on the cross section of the hearth is larger, a larger backflow area exists in the hearth, high-temperature flue gas can be sucked in the backflow area, coal dust is preheated, the control of the backflow area is complex, coal dust particle agglomeration easily occurs in the backflow area, if the structure of an in-furnace flow field is poor, the slagging tendency of the hearth is large, and the safe and stable operation of a boiler is influenced.
In addition, in the tangential firing mode or the cyclone firing mode of the pulverized coal, because the pulverized coal is burned intensively and releases heat, the pulverized coal combustion temperature exceeds the ash fusion point, the pulverized coal combustion is easy to form slag bonding, and part of slag is adhered to the water-cooled wall of the hearth to influence the heat transfer performance of the boiler. During operation of the boiler, part of the slag needs to be discharged from the bottom of the furnace, thus reducing the boiler efficiency.
Disclosure of Invention
In order to overcome at least one aspect of the above-mentioned prior art drawbacks, the present invention proposes a vertical pulverized coal boiler capable of achieving uniform and efficient combustion of pulverized coal, low nitrogen oxide emission, and avoiding accumulation of pulverized coal particles in the inner cavity of a furnace.
According to an aspect of the present invention, there is provided a vertical pulverized coal boiler including:
the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the side walls;
at least one pulverized coal burner comprising a main body disposed at a lower portion of the sidewall of the furnace and a burner outlet pipe extending from the main body into the furnace cavity from an outer side of the lower portion of the sidewall of the furnace and adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity; and
the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth,
the secondary air distribution device comprises a plurality of secondary air distribution pipes distributed at the bottom of the hearth, and a plurality of air outlet holes are formed in the pipe wall of each secondary air distribution pipe; and
the mixture of the primary air and the pulverized coal is mixed with the secondary air to form a wind-powder mixture which flows upwards in a plug flow overall manner in the inner cavity of the hearth.
According to an exemplary embodiment of the present invention, a hood is disposed in the air outlet hole of the secondary air distribution pipe.
According to another exemplary embodiment of the present invention, the lower portion of the sidewall of the furnace is an inverted cone portion with a cross section gradually increasing from bottom to top.
According to another exemplary embodiment of the invention, the furnace comprises four side walls, wherein two opposite side walls are inclined inwardly at their lower portions, and the other two opposite side walls remain vertical in the vertical direction.
According to another exemplary embodiment of the invention, the furnace comprises four side walls, the middle and lower parts of which remain vertical, and the cross section of the side walls of the furnace is substantially rectangular and the area remains unchanged, said middle and lower parts having a height of 20 to 40% of the total height of the side walls, respectively.
According to another exemplary embodiment of the present invention, the pulverized coal burner is provided on a lower portion of the two sidewalls of which lower portions are inwardly inclined and/or on a lower portion of the two sidewalls of which the vertical is maintained.
According to another exemplary embodiment of the present invention, the at least one pulverized coal burner comprises two or four groups of burners, which are respectively arranged on two opposite side walls in case of comprising two groups of pulverized coal burners, and which are respectively arranged at four corners of a cross section of the furnace in case of comprising four groups of pulverized coal burners, each group of pulverized coal burners comprising the same number of pulverized coal burners greater than or equal to 1.
According to another exemplary embodiment of the present invention, the vertical pulverized coal boiler further includes: and the at least one layer of tertiary air nozzle is suitable for introducing tertiary air into the hearth and is arranged on the side wall of the hearth in a layered manner, and one layer of nozzle in the at least one layer of tertiary air nozzle is arranged on the lower part of the side wall of the hearth.
According to another exemplary embodiment of the present invention, the secondary air distribution device is provided at the bottom of the furnace to be distributed over the entire cross section of the bottom of the furnace.
According to another exemplary embodiment of the present invention, the center-to-center distance between the hoods on the secondary air distribution duct and the interval between the ducts is not more than 300mm.
According to another exemplary embodiment of the present invention, the plurality of secondary air distribution pipes are parallel to each other and traverse the side wall near the bottom of the furnace chamber so that both ends thereof are located outside the furnace chamber, and one end of the secondary air distribution pipe is in fluid communication with the secondary air main pipe, and the other end is provided with a detachable plug.
According to another exemplary embodiment of the present invention, the jet momentum of the secondary air is less than or equal to the jet momentum of the mixture of the primary air and the pulverized coal.
According to another exemplary embodiment of the present invention, the injection momentum of the secondary air is between 70% and 90% of the injection momentum of the mixture of the primary air and the pulverized coal.
According to another exemplary embodiment of the present invention, the pulverized coal burner is a pulverized coal preheating burner to preheat a mixture of primary air and pulverized coal to 850 ℃ or more.
According to another aspect of the present invention, there is provided a pulverized coal combustion method for a vertical pulverized coal boiler, the pulverized coal boiler including: the hearth comprises a hearth, wherein the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the side walls; at least one pulverized coal burner comprising a main body disposed at a lower portion of the sidewall of the furnace and a burner outlet pipe extending from the main body into the furnace cavity from an outer side of the lower portion of the sidewall of the furnace and adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity; and a secondary air distribution device, the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth, wherein the secondary air distribution device comprises a plurality of secondary air distribution pipes distributed in the bottom of the hearth, and a plurality of air outlet holes are formed in the pipe wall of each secondary air distribution pipe, and the method comprises the following steps:
introducing a mixture of primary air and pulverized coal into the inner cavity of the hearth from the lower part of the side wall of the hearth through at least one pulverized coal burner,
and introducing secondary air into the inner cavity of the hearth from the bottom of the hearth through a secondary air distribution device, so that the mixture of the primary air and the pulverized coal is mixed with the secondary air in the inner cavity of the hearth to form an air-powder mixture which flows upwards in a plug flow integrally, and the air-powder mixture is combusted in the inner cavity of the hearth at the uniform temperature.
According to an exemplary embodiment of the present invention, the mixture of the primary air and the pulverized coal is preheated to 850 ℃ or more by a pulverized coal burner.
According to another exemplary embodiment of the present invention, the injection momentum of the secondary air is between 70% and 90% of the injection momentum of the mixture of the primary air and the pulverized coal.
According to another exemplary embodiment of the present invention, the secondary air is air or a mixture of air and flue gas.
In each embodiment of the vertical pulverized coal boiler according to the embodiment of the invention, the secondary air is provided by adopting the air distribution pipes arranged on the whole cross section of the bottom of the hearth, the air supply is uniform, entrainment and backflow hardly occur, and the speed difference of each part on the cross section of the hearth is small, so that the dispersed air-powder mixture integrally flows upwards, and the conventional air-powder combustion mode is changed. Therefore, the invention realizes the overall upward thrust flow of the wind-powder mixture in the whole hearth space, no reflux area appears in the hearth, the accumulation of coal powder particles in the hearth is avoided, and the running stability of the system is improved.
Drawings
The invention may be best understood from the following detailed description of various embodiments of the invention when read in connection with the accompanying drawings, wherein:
fig. 1 is a schematic view of a furnace of a vertical pulverized coal boiler according to an exemplary embodiment of the present invention.
Fig. 2 is a view showing a bottom of a furnace of the vertical pulverized coal boiler of fig. 1.
Fig. 3 is a plan view of a bottom portion of a furnace of a vertical pulverized coal boiler according to another exemplary embodiment of the present invention.
Fig. 4 is a cross-sectional view of a cloth air duct according to an exemplary embodiment of the present invention.
Detailed Description
The technical scheme of the invention is further specifically described below through examples and with reference to the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of embodiments of the present invention with reference to the accompanying drawings is intended to illustrate the general inventive concept and should not be taken as limiting the invention.
Furthermore, in the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments disclosed herein. It may be evident, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown in the drawings in order to simplify the drawings.
According to one aspect of the present invention, there is provided a vertical pulverized coal boiler including: a furnace 1 comprising side walls 11 at the periphery thereof, a furnace bottom 12 below the side walls, a furnace cavity 13 enclosed by the side walls and the furnace bottom, wherein the side walls comprise a side wall lower portion 111 accounting for 20 to 40% of the total height thereof; at least one pulverized coal burner 5 comprising a main body 52 and a burner outlet pipe 51 extending from the main body 52, the main body 52 being arranged at the lower furnace sidewall portion 111, the burner outlet pipe 51 extending from outside the lower furnace sidewall portion 111 into the furnace cavity 13 and being adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity 13; and the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth, wherein the secondary air distribution device comprises a plurality of secondary air distribution pipes 2 distributed in the bottom of the hearth, and a plurality of air outlet holes 21 are formed in the pipe wall of each secondary air distribution pipe. In an exemplary embodiment of the invention, the cloth duct 2 occupies substantially the entire cross section of the bottom of the furnace. Since the secondary air is supplied from the substantially entire cross section of the bottom of the furnace, the speed difference is small at all parts of the cross section of the furnace, and therefore, the primary air and the pulverized coal mixture and the secondary air form a dispersed air-powder mixture without entrainment and backflow, and therefore, the air-powder mixture flows upwards in a plug flow, thereby changing the conventional air-bag powder combustion mode.
In an exemplary embodiment according to the present invention, the secondary air distribution duct 2 includes a set of secondary air ducts 2 and a total air duct 20 in fluid communication with a plurality of secondary air ducts, the secondary air ducts 20 may be parallel to each other, and air caps (not shown) may be provided in the air outlet holes 21 of the secondary air ducts 2, the center distance between the air caps and the interval between the air ducts being not more than 300mm, and the secondary air distribution means is provided at the bottom of the furnace so as to be distributed over the entire cross section of the bottom of the furnace so that the secondary air is uniformly fed into the inner cavity of the furnace from almost the entire cross section of the bottom of the furnace. In one example, the plurality of overgrate air distribution pipes 2 are parallel to each other across the side wall 11 near the bottom of the furnace so that both ends are located outside the furnace, one end of the overgrate air distribution pipes being in fluid communication with the overgrate air main 20 and the other end being provided with a removable plug 22.
Because the plurality of secondary air distribution pipes 2 and the air outlet holes 21 thereon extend over the entire cross section of the bottom of the furnace, in one example, the number of the air outlet holes 21 may be hundreds, and thus, regardless of whether one or several preheating burners 5 are provided, a plurality of air outlet holes 21 are present near the outlet pipe of the burner, instead of just a conventional once-through burner or a cyclone burner, only a considerable number of secondary air passages are arranged around the primary air passages of the burner arranged on the side wall of the furnace. In the conventional burner, it is generally necessary to arrange the secondary air duct closely around the primary air duct because only the wind thus blown out from the secondary air duct can tightly surround the mixture of the primary air and the pulverized coal, so that the pulverized coal is not easily diffused, thereby more facilitating ignition of the pulverized coal in a local area by means of high temperature inside the boiler. However, in the embodiment according to the present invention, the provision of the plurality of air outlet holes 21, the number of which is much larger than the number of the burner outlet pipes 51, in the vicinity of one burner outlet pipe enables the secondary air to be more uniformly injected at the bottom of the furnace and to be more easily uniformly mixed with the mixture of the primary air and the pulverized coal, instead of being tightly enclosed. It should be noted that the number of the secondary air distribution pipes 2 and the air outlet holes 21 thereon and the number of the burners 5 may vary according to the actual needs and the area of the cross section of the bottom of the furnace, and the secondary air distribution pipes 2 may not be parallel to each other, such as a star-shaped arrangement.
In an exemplary embodiment according to the present invention, as shown in fig. 1, the sidewall 11 of the furnace 1 includes a sidewall lower portion 111 having a height of 20% -40% of the total height of the sidewall, and the sidewall lower portion 111 is an inverted cone portion having a cross section that gradually increases from bottom to top. Specifically, in one example, as shown in fig. 2, the side walls include four pieces of side walls SF1, SF2, SF3, and SF4, wherein two opposite pieces of side walls SF1 and SF3 are inclined inwardly at lower portions thereof to be reverse tapered, and the other two opposite pieces of side walls SF2 and SF4 remain vertical in a vertical direction. The pulverized coal burner 5 is disposed on the lower portion of the two side walls SF1 and SF3 inclined inward at the lower portion and/or on the lower portion of the two side walls SF2 and SF4 kept vertical, wherein the number of burners disposed on each side wall may be one or more.
In another exemplary embodiment according to the present invention, the cross-sectional area of the furnace may remain unchanged. In one example, as shown in fig. 4, the furnace comprises four side walls SF1', SF2', SF3', and SF4', the middle and lower portions of which remain vertical and have a substantially rectangular cross section with a constant area, wherein the middle and lower portions respectively account for 20% to 40% of the total height of the side walls of the furnace. It is to be understood that the embodiment shown in fig. 4 only shows a preferred embodiment of the invention, and that the furnace cross-section of the invention is not limited to the cross-section shown in fig. 4, and that the furnace cross-section may be circular, rectangular, other polygonal, etc. In case of comprising two sets of pulverized coal burners, the two sets of burners are arranged on opposite two side walls, e.g. on SFl 'and SF3' or on SF2 'and SF4', respectively. In the case of four groups of pulverized coal burners, which are arranged at four corners of the cross section of the furnace, respectively, each group of pulverized coal burners includes the same number of pulverized coal burners greater than or equal to 1, as shown in fig. 4.
In an exemplary embodiment according to the present invention, the vertical pulverized coal boiler further comprises at least one layer of tertiary air nozzles 6 adapted to introduce tertiary air into the furnace and arranged in layers on the side walls 11 of the furnace, one layer of the at least one layer of tertiary air nozzles 6 being arranged on the lower part 111 of the side walls 11 of the furnace, combustion of pulverized coal being maintained by the tertiary air fed into the interior of the furnace and the cross-sectional velocity of the furnace being maintained at not less than 2.0m/s. In the embodiment shown in fig. 2, one layer of the at least one layer of tertiary air jets 6 is arranged on the lower inwardly inclined side walls SF1 and SF 3.
In an exemplary embodiment according to the present invention, the injection momentum of the secondary air is less than or equal to the injection momentum of the mixture of the primary air and the pulverized coal. Further, the jet momentum of the secondary air is 70% to 90% of the jet momentum of the mixture of the primary air and the pulverized coal. The mixing of the secondary air and the mixture of the primary air and the pulverized coal is facilitated by making the injection momentum of the secondary air slightly smaller than that of the mixture of the primary air and the pulverized coal, so that the combustion is facilitated more, and the secondary air reaches the upper part of the hearth earlier than the mixture of the primary air and the pulverized coal. In the process that the mixture of primary air and pulverized coal and secondary air flow upwards from the lower space of the inner cavity of the hearth, partial combustion reaction occurs, heat released by pulverized coal combustion is transferred to water-cooled walls around the bottom of the hearth, and along with the increase of the height of the hearth and the expansion of the sectional area of the hearth, the combustion of pulverized coal is maintained by means of tertiary air supplied into the hearth, and the section speed of the hearth is kept to be not lower than 2.0m/s.
In one embodiment according to the invention, the pulverized coal burner adopts a circulating fluidized bed preheating burner, pulverized coal carried by primary air can be preheated to 800-850 ℃ or even higher in the circulating fluidized bed preheating burner, the pulverized coal is ignited in the burner, and the preheated pulverized coal is quickly mixed with secondary air after being introduced into a hearth and is stably combusted. At this time, primary air and pulverized coal which are introduced into a hearth through a pulverized coal burner are precisely high-temperature powdery fuel formed after the pulverized coal is partially combusted and high-temperature gas containing a large amount of combustible components. However, as for ignition of the pulverized coal, it is understood by those skilled in the art that, instead of preheating the burner or the like to bring the pulverized coal into the furnace to the ignition temperature, plasma ignition or other treatment of the pulverized coal to lower the ignition point may be employed.
When the boiler is in operation, a mixture of primary air and coal dust is introduced into the hearth cavity 13 from the lower side wall part 111 through the coal dust burner 5, secondary air is introduced into the hearth from the bottom of the hearth through the secondary air outlet 21, and tertiary air is introduced into the hearth through the tertiary air nozzle. Because the secondary air is evenly supplied to the inner cavity of the hearth and matched with reasonable jet momentum of the primary air and the secondary air, the mixture of the primary air and the pulverized coal is mixed with the secondary air strongly and evenly, entrainment and backflow hardly occur, and the speed difference of each part on the cross section of the hearth is small, the dispersed air-powder mixture integrally flows upwards, namely the air-powder mixture flows upwards in a flat pushing way, so that the conventional air-powder combustion mode is changed. The air-powder mixture fills the inner cavity of the hearth, the combustion mode of the pulverized coal is full-field space combustion in the hearth, and the staged combustion and the uniform temperature control of the pulverized coal are realized in the full-field space of the hearth by combining the air distribution control of tertiary air.
The tertiary air for pulverized coal combustion is added along the height of the hearth in multiple layers, the reducing atmosphere is arranged below the top layer nozzle of the tertiary air, and fuel nitrogen released in pulverized coal combustion is converted into multidirectional nitrogen. Because the concentrated combustion area does not exist in the pulverized coal combustion, the highest temperature level of the pulverized coal combustion is low, and thermal NOx is basically not generated in the pulverized coal combustion. Thus, the original emission level of NOx is much lower than conventional pulverized coal combustion technology.
In addition, as the hearth is internally provided with a horizontal plug flow which integrally flows upwards, the section speed of the hearth is controlled not to be too low, pulverized coal is not lost, the uniform temperature is controlled, and the worry that the powder deposition and slag discharge at the bottom of the hearth fall into an air chamber is not needed, so that a blast cap is not needed, secondary air is directly provided through small holes on an air distribution pipe, and the small holes on the air distribution pipe are basically uniformly arranged at the moment, and the distance is not more than 300mm.
In addition, the invention also provides a pulverized coal combustion method, which adopts the vertical pulverized coal burner, and the pulverized coal boiler comprises the following steps: the hearth comprises a hearth, wherein the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the side walls; at least one pulverized coal burner comprising a main body disposed at a lower portion of the sidewall of the furnace and a burner outlet pipe extending from the main body into the furnace cavity from an outer side of the lower portion of the sidewall of the furnace and adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity; and a secondary air distribution device, the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth, wherein the secondary air distribution device comprises a plurality of secondary air distribution pipes distributed in the bottom of the hearth, and a plurality of air outlet holes are formed in the pipe wall of each secondary air distribution pipe, and the method comprises the following steps: introducing a mixture of primary air and pulverized coal into the hearth cavity from the lower part of the side wall of the hearth through at least one pulverized coal burner, and introducing secondary air into the hearth cavity from the bottom of the hearth through a secondary air distribution device, so that the mixture of the primary air and the pulverized coal and the secondary air are mixed in the hearth cavity to form an air-pulverized coal mixture flowing upwards in a plug flow integrally so as to burn at the same temperature in the hearth cavity
On the basis of the vertical pulverized coal boiler according to the embodiment of the present invention, several experiments were performed to exemplarily better illustrate the technical effects of the boiler according to the present invention, and the specific experiments are as follows:
test 1
On the basis of the vertical pulverized coal boiler provided by the embodiment of the invention, the fuel is bituminous coal powder, the granularity of the pulverized coal is below 200 mu m, the secondary air is the mixed gas of preheated air and flue gas recirculation, the oxygen content is 15%, and the temperature is 150 ℃; the tertiary air is preheated air, and the air temperature is 150 ℃; the combustion efficiency of the bituminous coal powder is 99.2%, the original NOx emission value is 120mg/Nm3, the original NOx emission value is obviously reduced, and the high-efficiency low-nitrogen combustion of the bituminous coal is realized.
Test 2
On the basis of the vertical pulverized coal boiler provided by the embodiment of the invention, the fuel is semicoke powder with very low volatile matters, and a circulating fluidized bed type preheating burner is adopted to spray a mixture of the semicoke powder preheated to 850 ℃ and primary air into a hearth; the temperature of the secondary air is 200 ℃; the apparent velocity of the coke powder air flow in the hearth is 3.0m/s, and the combustion temperature of the hearth is 1100 ℃; along the height direction of the hearth, two layers of tertiary air are arranged. The test result shows that the combustion efficiency of semicoke is 96.5%, the original emission level of NOx is 50mg/Nm3, the original emission value of NOx is obviously reduced, and the high-efficiency low-nitrogen combustion of low-volatile flame-retardant fuel is realized.
Therefore, in the vertical pulverized coal boiler according to the embodiment of the invention, the secondary air is provided by the air distribution pipe arranged on the whole cross section of the bottom of the hearth, the air supply is uniform, entrainment and backflow hardly occur, and the speed difference of each part on the cross section of the hearth is small, so that the dispersed air-powder mixture integrally flows upwards, and the conventional air-powder combustion mode is changed. Therefore, the invention realizes the overall upward thrust flow of the wind-powder mixture in the whole hearth space, no reflux area appears in the hearth, the accumulation of coal powder particles in the hearth is avoided, and the running stability of the system is improved.
Furthermore, the invention breaks through the wind powder-wrapping mode of the conventional burner, so that the combustion temperature of the pulverized coal in the whole hearth space is uniformly distributed, and the highest temperature of pulverized coal combustion is stabilized, so that the uniform temperature combustion can be realized, the current situations of concentrated combustion and concentrated heat release of the conventional combustion mode can be changed, the concentrated high temperature area in the furnace in the conventional pulverized coal combustion mode is eliminated, and thermal NOx is not generated.
Furthermore, because the uniform temperature combustion is realized in the inner cavity of the hearth, the highest temperature in the furnace is lower than the ash fusion point by the uniform temperature combustion of the pulverized coal, slag bonding is avoided, and fly ash generated by the combustion of the pulverized coal enters the tail part along with the flue gas, so that slag discharge is not needed in the operation of the boiler, the thermal efficiency of the boiler is high, and the system is simple to operate.
Furthermore, the pulverized coal is combusted at the uniform temperature, so that the temperature of the hearth is uniformly distributed, the average temperature in the furnace is higher than that of the conventional combustion mode, the radiation heat transfer capacity in the furnace is enhanced, the volume of the boiler can be reduced, and the manufacturing cost of the boiler is saved.
Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims (15)

1. A vertical pulverized coal fired boiler comprising:
the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the side walls;
at least one pulverized coal burner comprising a main body disposed at a lower portion of the sidewall of the furnace and a burner outlet pipe extending from the main body into the furnace cavity from an outer side of the lower portion of the sidewall of the furnace and adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity; and
the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth,
the secondary air distribution device comprises a plurality of secondary air distribution pipes distributed at the bottom of the hearth, and a plurality of air outlet holes are formed in the pipe wall of each secondary air distribution pipe; and
the method comprises the steps of mixing a mixture of primary air and pulverized coal with secondary air to form a wind-powder mixture which flows upwards in a plug flow overall manner in a cavity of a hearth;
the secondary air distribution device is arranged at the bottom of the hearth and distributed on the whole cross section of the bottom of the hearth; the jet momentum of the secondary air is smaller than or equal to the jet momentum of the mixture of the primary air and the pulverized coal; and a hood is arranged in the air outlet of the secondary air distribution pipe.
2. The vertical pulverized coal boiler as set forth in claim 1, wherein the lower portion of the sidewall of the furnace is an inverted cone portion having a cross section that gradually increases from bottom to top.
3. The vertical pulverized coal boiler as claimed in claim 2, wherein the furnace comprises four side walls, wherein two opposite side walls are inclined inwardly at lower portions thereof, and the other two opposite side walls remain vertical in a vertical direction.
4. The vertical pulverized coal boiler as claimed in claim 1, wherein the furnace comprises four side walls, the middle and lower parts of which are kept vertical, and the cross section of the middle and lower parts of the side walls of the furnace is substantially rectangular and the area is kept constant, the height of the middle and lower parts respectively accounting for 20 to 40% of the total height of the side walls.
5. A vertical pulverized coal boiler according to claim 3, wherein the pulverized coal burner is arranged on the lower part of the two side walls which are inclined inwards in the lower part and/or on the lower part of the two side walls which are kept vertical.
6. The vertical pulverized coal boiler according to claim 4, wherein the at least one pulverized coal burner comprises two or four groups of burners, which are respectively arranged on two opposite side walls in case of comprising two groups of pulverized coal burners, and which are respectively arranged at four corners of a cross section of a furnace in case of comprising four groups of pulverized coal burners, each group of pulverized coal burners comprising the same number of pulverized coal burners greater than or equal to 1.
7. The vertical pulverized coal boiler according to claim 2 or 4, further comprising: and the at least one layer of tertiary air nozzle is suitable for introducing tertiary air into the hearth and is arranged on the side wall of the hearth in a layered manner, and one layer of nozzle in the at least one layer of tertiary air nozzle is arranged on the lower part of the side wall of the hearth.
8. The vertical pulverized coal boiler according to claim 1, wherein a center-to-center distance between hoods on the secondary air distribution pipes and a distance between the pipes are not more than 300mm.
9. The vertical pulverized coal fired boiler according to claim 1, wherein the plurality of secondary air distribution pipes are parallel to each other and transversely penetrate through the side wall near the bottom of the furnace so that both ends of the secondary air distribution pipes are positioned outside the furnace, one end of each secondary air distribution pipe is in fluid communication with the secondary air main pipe, and the other end of each secondary air distribution pipe is provided with a detachable plug.
10. The vertical pulverized coal boiler according to claim 1, wherein the injection momentum of the secondary air is between 70% and 90% of the injection momentum of the mixture of primary air and pulverized coal.
11. The vertical pulverized coal boiler according to claim 1, wherein the pulverized coal burner is a pulverized coal preheating burner to preheat a mixture of primary air and pulverized coal to 850 ℃ or more.
12. A pulverized coal combustion method for a vertical pulverized coal boiler, the pulverized coal boiler comprising: the hearth comprises a hearth, wherein the hearth comprises side walls positioned at the periphery of the hearth, a hearth bottom positioned below the side walls, and a hearth cavity formed by surrounding the side walls and the hearth bottom, wherein the side walls comprise lower parts of the side walls accounting for 20-40% of the total height of the side walls; at least one pulverized coal burner comprising a main body disposed at a lower portion of the sidewall of the furnace and a burner outlet pipe extending from the main body into the furnace cavity from an outer side of the lower portion of the sidewall of the furnace and adapted to introduce a mixture of primary air and pulverized coal into the furnace cavity; and a secondary air distribution device, the secondary air distribution device is arranged in the bottom of the hearth and is suitable for introducing secondary air into the inner cavity of the hearth, the secondary air distribution device is arranged at the bottom of the hearth so as to be distributed on the whole cross section of the bottom of the hearth, wherein the secondary air distribution device comprises a plurality of secondary air distribution pipes distributed at the bottom of the hearth, a plurality of air outlet holes are formed in the pipe wall of each secondary air distribution pipe, and an air cap is arranged in the air outlet hole of each secondary air distribution pipe, and the method comprises the following steps:
introducing a mixture of primary air and pulverized coal into the inner cavity of the hearth from the lower part of the side wall of the hearth through at least one pulverized coal burner,
and introducing secondary air into the inner cavity of the furnace from the bottom of the furnace through a secondary air distribution device, so that the mixture of the primary air and the pulverized coal is mixed with the secondary air in the inner cavity of the furnace to form an air-powder mixture which flows upwards in a plug flow integrally so as to burn in the inner cavity of the furnace at the uniform temperature, and the injection momentum of the secondary air is smaller than or equal to that of the mixture of the primary air and the pulverized coal.
13. The method of claim 12, wherein,
the mixture of primary air and pulverized coal is preheated to 850 ℃ or above by a pulverized coal burner.
14. The method of claim 13, wherein,
the jet momentum of the secondary air is between 70% and 90% of the jet momentum of the mixture of the primary air and the pulverized coal.
15. The pulverized coal combustion method as claimed in claim 13, wherein,
the secondary air is air or mixed gas of air and flue gas.
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CN1082164A (en) * 1993-06-30 1994-02-16 清华大学 Burner for heating powdered coal on fluidized bed by precombustion
CN102235675A (en) * 2011-08-23 2011-11-09 无锡太湖锅炉有限公司 Open air distribution plate for circulating fluidized bed garbage incineration boiler
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CN104061569A (en) * 2014-07-10 2014-09-24 国家电网公司 W-shaped flame boiler combustion and pulverization system
CN106051744A (en) * 2016-06-30 2016-10-26 哈尔滨工业大学 W-shaped flame direct-current burner pulverized coal composite furnace with fluidized bed

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1082164A (en) * 1993-06-30 1994-02-16 清华大学 Burner for heating powdered coal on fluidized bed by precombustion
CN102235675A (en) * 2011-08-23 2011-11-09 无锡太湖锅炉有限公司 Open air distribution plate for circulating fluidized bed garbage incineration boiler
CN103604117A (en) * 2013-11-04 2014-02-26 武汉和信益科技有限公司 Multi-grade high-efficiency low-nitrogen combustion method and multi-grade high-efficiency low-nitrogen combustion system for circulating fluidized bed boiler
CN104061569A (en) * 2014-07-10 2014-09-24 国家电网公司 W-shaped flame boiler combustion and pulverization system
CN106051744A (en) * 2016-06-30 2016-10-26 哈尔滨工业大学 W-shaped flame direct-current burner pulverized coal composite furnace with fluidized bed

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