CN110440281B

CN110440281B - A equally divide formula secondary bellows for W flame boiler

Info

Publication number: CN110440281B
Application number: CN201910771110.0A
Authority: CN
Inventors: 李争起; 杜贺; 韩徽; 张鑫; 曾令艳; 陈智超
Original assignee: Harbin Institute of Technology
Current assignee: Harbin Institute of Technology
Priority date: 2019-08-20
Filing date: 2019-08-20
Publication date: 2020-10-27
Anticipated expiration: 2039-08-20
Also published as: CN110440281A

Abstract

The invention relates to a uniform distribution type secondary air box for a W flame boiler, which relates to a secondary air box and aims to solve the problems that the air quantity in the secondary air box of the existing W flame boiler is gradually reduced from two sides to the center to cause the air shortage in the middle of a hearth, thereby causing high CO emission and high carbon content of fly ash combustible substances; the invention relates to a power station boiler, which comprises an upper air box, a lower air box, an upper air box separation plate, a lower air box separation plate, two upper air box separation plates, two side arch air boxes, a plurality of ventilation openings, a small air channel and a plurality of lower air box separation plates.

Description

A equally divide formula secondary bellows for W flame boiler

Technical Field

The invention relates to a secondary air box, in particular to an equal-distribution type secondary air box for a W flame boiler.

Background

The W flame boiler is a power station boiler specially designed for burning low-volatile and difficult-to-burn coal. It has the advantages of high hearth temperature, long coal powder airflow combustion stroke and the like. China introduced W-flame boilers from the regions of North Africa and Western Europe since the nineties of the twentieth century. Because the resources of anthracite and lean coal in China are rich and the price is low compared with that of coal used for other power, the W flame boiler is quickly and widely applied and becomes one of the main boiler types of thermal power generation. By far, the number of W flame boilers built and constructed in China exceeds 130, the total installed capacity exceeds 41000MW, and accounts for 80% of the total reserved quantity of the world.

The air supply system of the W flame boiler consists of a primary air system and a secondary air system. The secondary air system mainly comprises a fan, an air preheater, a secondary air box, an air duct and the like. The secondary air is introduced by the fan, heated by the air preheater and then enters the secondary air box, and is distributed to secondary air nozzles of each group of burners by the secondary air box, so that necessary air is provided for the combustion of pulverized coal. Therefore, the structure of the secondary wind box is important for adjusting the secondary wind distribution of the W-flame boiler and the combustion condition in the boiler. As shown in figure 1, at present, the secondary wind boxes of the W flame boiler in the active service of the power plant are generally of an integrated structure, an upper wind box 1 and a lower wind box 13 are communicated with each other, after secondary wind enters the upper wind box 1 from two sides, one part of the secondary wind enters all levels of arch secondary wind nozzles of a burner through arch secondary wind nozzles 9, shown in figure 2, and the other part of the secondary wind enters the lower wind box 13, enters all levels of arch secondary wind boxes 14 through arch secondary wind doors 12, and is finally supplied to all levels of arch secondary wind nozzles, shown in figure 3. However, because the width of the furnace of the W flame boiler is large, the amount of secondary air entering the windbox gradually decreases from two sides to the center as shown in FIG. 4, which easily causes air shortage in the middle of the furnace, uneven temperature distribution, and finally results in high CO emission of the boiler and high carbon content of the combustible fly ash. Aiming at the problem, a common solution of the power plant is to increase the opening degree of a secondary air door in the middle of a hearth according to the operation experience. Although the method can reduce the problem of lack of air in the middle of the hearth to a certain extent, the control difficulty of secondary air is increased, and the reduction of the emission level of NOx is not facilitated. In addition, on the W flame boiler adopting the over fire air structure, a part of secondary air moves from arch to arch or to the hearth, the difficulty in regulating and controlling the secondary air is further increased, and the over fire air, the arch and the secondary air under the arch are easily distributed and disordered by adopting a mode of gradually opening large secondary air doors from two sides to the center, so that the problems of air shortage in the middle of the hearth, high CO emission caused by the air shortage, high carbon content of fly ash combustible materials and the like cannot be effectively solved. Therefore, in order to ensure the uniform distribution of the secondary air of each group of burners of the boiler, a new W flame boiler secondary air box needs to be developed.

Disclosure of Invention

The invention aims to solve the problems that the middle part of a hearth is short of air and further the CO emission is high and the carbon content of fly ash combustible is high due to the fact that the air quantity in the secondary air box of the existing W flame boiler is gradually reduced from two sides to the center, and further provides a uniform-distribution secondary air box for the W flame boiler.

The technical scheme adopted by the invention for solving the problems is as follows:

the air box comprises an upper air box, a lower air box, a plurality of secondary air nozzles on an arch, a plurality of lower air box partition plates, a plurality of secondary air nozzles under the arch and a plurality of secondary air doors under the arch, and further comprises upper and lower air box partition plates, two upper air box partition plates, two side air doors and a plurality of small air channels; an upper air box is arranged above a lower air box, upper and lower air box partition plates are arranged between the upper air box and the lower air box, two upper air box partition plates are oppositely arranged on the inner side wall of the upper air box and divide the upper air box into a main arch part air box and two side arch part air boxes through the two upper air box partition plates, each side arch part air box is provided with a side air door, a plurality of arch-up secondary air nozzles are arranged on the side wall of the upper air box, a plurality of lower air box partition plates are arranged on the inner side wall of the lower air box in parallel side by side and divide the lower air box into a plurality of arch-down secondary air boxes, a plurality of vent holes are processed on the upper and lower air box partition plates below each side arch part air box, a small air channel is correspondingly arranged below each vent hole, and the top end of each small air channel is, the bottom end of each small air duct is correspondingly provided with an under-arch secondary air door which is respectively communicated with an under-arch secondary air nozzle, each under-arch secondary air nozzle is arranged on the side wall of the lower air box, and each small air duct is arranged at the upper part of the under-arch secondary air chamber.

The invention has the beneficial effects that:

1. in the application, high-temperature secondary air heated by an air preheater enters the air box through the main air channels on two sides of the secondary air box and then is uniformly divided into three strands by the side air door 5 to respectively enter the three arch air chambers. One part of secondary air in the arch part air chamber is supplied to the hearth through an arch-up secondary air nozzle 9, the other part of secondary air is uniformly supplied to each arch-down secondary air chamber 14 of the lower air box along the width direction of the hearth through a vent 8 and a small air duct 10 on an air box partition plate, and finally distributed to each arch-down secondary air nozzle to be supplied to the hearth.

2. The secondary air box is equally divided into a plurality of groups of independent air supply units along the width direction of the hearth, so that the secondary air can be uniformly distributed into the air chambers of the burners after entering from the two sides of the air box, and the problem of air shortage in the middle of the hearth is effectively avoided.

The wind pressure and the wind speed of a secondary air nozzle of a combustor in the 1 st group at the inlet of the wind box are greatly improved.

As shown in FIG. 1, the upper and lower windboxes of the conventional W-flame boiler are communicated with each other, and the overfire air is supplied from the air duct inlets at both sides of the windbox and then diffused into the whole windbox. Because the sectional area of the air box is about 3 times of the sectional area of the air channel inlet, the air pressure of secondary air supplied into the air box is rapidly reduced, the air speeds of the secondary air nozzles above and below the arch of the 1 st burner at the inlets at two sides of the air box are lower, and the air quantity is less.

The upper and lower bellows partitions 7 of the present invention integrally divide the secondary bellows into an upper bellows 1 and a lower bellows 2, as shown in FIG. 5. Wherein, the upper air box 1 is divided into a main arch air chamber 3 and two side arch air chambers 4 by two upper air box clapboards 2. Under the blocking of the partition board, the secondary air is supplied by the air channel and then enters into three relatively narrow arch air chambers of the upper air box 1, and enters into the lower air box 2 through the ventilation opening 8 and the small air channel 10. Because the sectional area of the air duct inlets at the two sides of the air box is the same as the total sectional area of the air chamber inlet of the arch part, the on-way resistance is small, and the air pressure is still kept at a high level after secondary air is supplied. The air pressure at the secondary air nozzles above and below the arch of the first group of burners at the inlets at two sides of the air box is obviously improved and the air quantity is larger than that before modification.

Secondly, the middle part of the air box has a high-pressure air belt which is equivalent to the air inlet, and the central air quantity of the hearth is obviously increased.

As shown in FIG. 4, the secondary wind box of the conventional W-flame boiler supplies wind into the furnace along the width direction of the furnace according to the wind pressure gradient. Because the width of the hearth is large, along with the increase of the air supply distance, the on-way resistance is increased, and a large amount of secondary air flows from the inlet of the air box to the upper secondary air nozzle and the lower secondary air nozzle along the way in the central flow process step by step, so that the secondary air pressure is reduced rapidly. Along the width of the furnace, only two high-pressure zones are present at the inlets on both sides of the windbox. When the secondary air reaches the center of the hearth, the air pressure is reduced to a lower level. Through resistance calculation, the air quantity of secondary air nozzles at the upper arch part and the lower arch part of the middle part of the hearth is less than 10 percent of the total secondary air quantity, and pulverized coal airflow is combusted in a fuel-rich and low-oxygen environment to generate a large amount of CO which is not beneficial to the burnout of pulverized coal.

As shown in FIG. 8, after the present invention is adopted, the secondary air in the middle of the furnace is supplied separately from the main arch plenum 3. Due to the obstruction of the upper air box partition plate 2, the air pressure attenuation of secondary air in the air chamber flowing process is slow. The main arch plenum 3 and the side arch plenum 4 are connected in parallel. After secondary air is supplied into the air box from the air channels at two sides, the secondary air is uniformly divided into three strands under the regulation of the side air doors 5 and respectively enters the main arch air chamber 3 and the two side arch air chambers 4. Because no air volume is lost in the process that the secondary air flows from the two ends of the main arch air chamber 3 to the center, the secondary air pressure is only slightly reduced under the influence of on-way resistance. Therefore, the wind pressure of the secondary air nozzles on the arches at the two sides of the main arch part wind chamber 3 and the wind pressure of the corresponding secondary air nozzles under the arches are basically consistent with the wind pressure of the secondary air nozzles under the arches of the 1 st group of burners at the inlets at the two sides of the wind box, and 4 high-pressure belts appear along the width direction of the hearth. The air quantity in the middle of the hearth is remarkably increased to about 30 percent through resistance calculation.

And the gradient difference of the wind pressure in each arch part wind chamber is obviously reduced, and the secondary wind distribution is more uniform along the width direction of the hearth.

As shown in FIG. 4, the air supply distance between the inlet high pressure zones at both sides and the central low pressure zone of the secondary windbox of the conventional W-flame boiler is half of the total width of the windbox. After the invention is adopted, the upper and lower air boxes are separated by the partition plate, the on-way resistance of the secondary air flowing in the upper air box is reduced, and the air supply lengths of the main arch part air box 3 and the side arch part air box 4 are both shortened to one third of the length of the original air box, as shown in figure 8. Through resistance calculation, the gradient difference of wind pressure between the two sides of the main arch part air chamber 3 and the center is reduced to 30% of the original gradient difference of wind pressure, and the gradient difference of wind pressure in the two side arch part air chambers 4 is reduced to 60% of the original gradient difference of wind pressure; the secondary air nozzles under the arch are equal to the secondary air nozzles on the corresponding arch in air pressure, and the uniformity of secondary air distribution along the width direction of the hearth is obviously improved. Each arch partThe secondary air in the air chamber is uniformly distributed to the secondary air nozzles 11 under each arch through the air vents 8 and the small air ducts 10 and finally supplied to each combustor, so that the current situation that the secondary air quantity of the W flame boiler is gradually reduced from two sides to the center along the width direction of the hearth and the current situation that the secondary air quantity is gradually reduced from two sides to the center of the W flame boiler are effectively changed, and the secondary air quantity in the middle of the hearth is O₂The concentration is improved, the CO concentration is reduced, the complete combustion of pulverized coal airflow is promoted, and the carbon content and the O content of the fly ash combustible at the outlet of a hearth are reduced₂And (4) concentration.

2. The structure of the traditional secondary air box is not changed, only the interior of the traditional air box is modified, and the air supply capacity of the secondary air box is basically not influenced; in addition, the invention does not need to change an air supply system outside the air box, and has low manufacturing cost and strong applicability.

Drawings

FIG. 1 is a sectional view of a secondary windbox of a conventional W-flame boiler.

Fig. 2 is a sectional view taken along the line a in fig. 1.

Fig. 3 is a sectional view taken along line B of fig. 1.

FIG. 4 is a schematic diagram of the distribution head of the flow field in the secondary windbox of the prior W-flame boiler.

Fig. 5 is a schematic structural diagram of the present invention.

Fig. 6 is a cross-sectional view taken along line C of fig. 5.

Fig. 7 is a cross-sectional view taken along line D of fig. 5.

FIG. 8 is a schematic view of the flow field distribution head in the secondary windbox of the present invention.

Detailed Description

The first embodiment is as follows: the present embodiment is described with reference to fig. 5 to 7, and the present embodiment describes a uniform distribution type secondary air box for a W flame boiler, which includes an upper air box 1, a lower air box 13, a plurality of secondary air nozzles 9 on an arch, a plurality of lower air box partitions, a plurality of secondary air nozzles 11 under the arch, a plurality of secondary air doors 12 under the arch, an upper and a lower air box partition 7, two upper air box partitions 2, two side air doors 5, and a plurality of small air ducts 10; an upper air box 1 is arranged above a lower air box 13, an upper air box separating plate 7 and a lower air box separating plate 7 are arranged between the upper air box 1 and the lower air box 13, two upper air box separating plates 2 are oppositely arranged on the inner side wall of the upper air box 1 and divide the upper air box 1 into a main arch part air box 3 and two side arch part air boxes 4 through the two upper air box separating plates 2, each side arch part air box 4 is provided with a side air door 5, a plurality of arch part secondary air nozzles 9 are arranged on the side wall of the upper air box 1, a plurality of lower air box separating plates are arranged on the inner side wall of the lower air box 13 in parallel side by side and divide the lower air box 13 into a plurality of arch part secondary air boxes 14, a plurality of vent holes 8 are processed on the upper air box separating plate 7 below each side arch part air box 4, a plurality of vent holes 8 are processed on the upper air, the top end of each small air duct 10 is fixedly connected with the bottom ends of the upper and lower air box partition plates 7, the bottom end of each small air duct 10 is correspondingly provided with an under-arch secondary air door 12, each under-arch secondary air door 12 is respectively communicated with an under-arch secondary air nozzle 11, each under-arch secondary air nozzle 11 is installed on the side wall of the lower air box 13, and each small air duct 10 is arranged at the upper part of an under-arch secondary air chamber 14.

The second embodiment is as follows: referring to fig. 5 and 6, the present embodiment will be described, which further includes four wind measuring devices 6, one wind measuring device 6 is respectively disposed on both sides of the main arch portion wind chamber 3, one wind measuring device 6 is disposed on each side arch portion wind chamber 4 near the side air door 5, and the wind volume in each arch portion wind chamber is determined according to the trisection principle: namely, the air volume in the three air supply units is always kept consistent by adjusting the opening degree of the side air door 5. The other methods are the same as those in the first embodiment.

The third concrete implementation mode: referring to fig. 1 to 2, the present embodiment will be described, in which an upper windbox partition 2 includes a straight plate and a bent plate, one end of the straight plate is fixedly connected to one end of the bent plate, and the other end of the straight plate and the other end of the bent plate are fixedly connected to an inner sidewall of an upper windbox 1. The other methods are the same as those in the first embodiment.

The fourth concrete implementation mode: referring to fig. 5, the present embodiment, which is a uniform-distribution type secondary air box for a W-flame boiler, is described, in which two side arch plenums 4 are symmetrically disposed at both sides of a main arch plenum 3. The other methods are the same as those in the first embodiment.

Example (b):

the invention is applied to a 300MW FW W flame boiler produced by Foster Whileler company in America in a certain power plant, 12 groups of double-cyclone-barrel shade-separation pulverized coal burners are symmetrically arranged in the front arch and the rear arch of the boiler. After the invention is adopted, an air box clapboard is additionally arranged at the position 2307mm away from the top of the air box in the secondary air box of the boiler, and the whole secondary air box is divided into an upper air box and a lower air box. Wherein the upper air box is divided into a main arch air chamber and two side arch air chambers by two upper air box clapboards. And a group of side air doors and actuators are arranged at the inlet of each side arch part air chamber. Air quantity measuring devices are arranged at inlets at two ends of the main arch portion air chamber and the side arch portion air chamber. In the actual operation of the boiler, the openings of two side air doors are both 50%, the air quantity in each arch air chamber is about 30% of the total secondary air quantity, and the air is supplied to 4 groups of burners respectively. 12 rectangular ventilation openings with the length of 1150mm and the width of 420mm are arranged on the partition plate between the upper air box and the lower air box. The bottom of the clapboard is provided with 12 rectangular small air ducts which are in one-to-one correspondence with 12 secondary air chambers under the arch in the lower air box. The inlet of the small air duct is connected with the ventilation opening, and the outlet extends to the top of the secondary air chamber under the arch. After entering the air box from two sides, the secondary air is divided into three arch air chambers, and then is uniformly distributed to 12 arch secondary air chambers to supply air for each combustor.

Before the invention is adopted, along the width direction of the hearth, the secondary air pressure in the secondary air nozzles of the 1 st group of burners at the inlets at the two sides of the air box is highest and is about 12 KPa. The CO content of the region at a position 1m close to the water wall is about 350 ppm; along with the flowing of secondary air from two sides of the air box to the center, the secondary air pressure is rapidly reduced, when the secondary air reaches the position of a secondary air nozzle on the arch of the 6 th combustor in the center of the hearth, the secondary air pressure is reduced to 3KPa, and the CO content at the corresponding position is up to 1200 ppm. The secondary air volume of 5 th to 8 th burners at the middle parts of the front and rear walls is arched up and arched down, the sum of the secondary air volume only accounts for 9.3 percent of the total secondary air volume, and the air volume of the O at the outlet of the hearth₂The content is about 5.6 percent, and the carbon content of the fly ash combustible is about 5.89 percent.

The secondary air pressure at the position of the secondary air nozzles on the first arches at the two sides of the front wall and the rear wall of the rear hearth is increased to 14KPa, and two air chambers of the main arch part are adoptedThe secondary air pressure at the position of the secondary air nozzle on the arch of the 5 th and 8 th burners on the side reaches 12KPa, and the secondary air quantity on the arch and under the arch of the four burners is increased to 31.5 percent of the total secondary air quantity. Along the width direction of the hearth, the wind pressure of the secondary air nozzles above and below the arch of each combustor is above 8KPa, the CO content at the position 1m away from the water cooling wall in the hearth is about 500ppm, and the outlet O of the hearth₂The content is reduced to 3.8%, and the carbon content of the fly ash combustible is reduced to 4.28%.

The total secondary air volume of the boiler before the adoption of the invention is 1047.832t/h, the total secondary air volume after the adoption of the invention is 1022.313t/h, the total secondary air volume after the modification of the air box is basically unchanged, and the air supply capacity of the boiler is not influenced. In addition, the modification cost of the air box is low, the modification period is only about 1 month, and the applicability is strong.

Claims

1. The utility model provides a divide equally formula secondary bellows for W flame boiler, it includes upper portion bellows (1), lower part bellows (13), two upper portion bellows baffles (2), a plurality of arch up overgrate air spout (9), a plurality of lower part bellows baffles, a plurality of arch under overgrate air spout (11) and a plurality of arch under overgrate air door (12), its characterized in that: the air box also comprises an upper air box partition plate, a lower air box partition plate (7), two side air doors (5), four air measuring devices (6) and a plurality of small air channels (10); an upper air box (1) is arranged above a lower air box (13), upper and lower air box separation plates (7) are arranged between the upper air box (1) and the lower air box (13), two upper air box separation plates (2) are oppositely arranged on the inner side wall of the upper air box (1) and divide the upper air box (1) into a main arch part air box (3) and two side arch part air boxes (4) through the two upper air box separation plates (2), each side arch part air box (4) is provided with a side air door (5), a plurality of arch part secondary air nozzles (9) are arranged on the side wall of the upper air box (1), a plurality of lower air box separation plates are arranged on the inner side wall of the lower air box (13) in parallel side by side and divide the lower air box (13) into a plurality of arch part secondary air boxes (14), a plurality of ventilation openings (8) are processed on the upper and lower air box separation plates (7), a plurality of ventilation openings (8) are processed on an upper air box separation plate (7) and a lower air box separation plate (7) below a main arch portion air chamber (3), a small air duct (10) is correspondingly arranged below each ventilation opening (8), the top end of each small air duct (10) is fixedly connected with the bottom ends of the upper air box separation plate and the lower air box separation plate (7), an arch lower secondary air door (12) is correspondingly arranged at the bottom end of each small air duct (10), each arch lower secondary air door (12) is respectively communicated with an arch lower secondary air nozzle (11), each arch lower secondary air nozzle (11) is installed on the side wall of a lower air box (13), each small air duct (10) is arranged on the upper portion of each arch lower secondary air chamber (14), air measuring devices (6) are respectively arranged on two sides of the main arch portion air chamber (3), and an air measuring device (6) is arranged on each side arch portion air chamber.

2. The equal-sharing secondary windbox for a W-flame boiler according to claim 1, wherein: the upper portion bellows baffle (2) include straight board and bent plate, the one end of straight board and the one end fixed connection of bent plate, the other end of straight board and the other end of bent plate all with upper portion bellows (1) inside wall fixed connection.

3. The equal-sharing secondary windbox for a W-flame boiler according to claim 1, wherein: the two side arch air chambers (4) are symmetrically arranged at two sides of the main arch air chamber (3).