CN111503625B

CN111503625B - Gap type exhaust preposed W-shaped flame pan with secondary air arranged on arch and air distribution method

Info

Publication number: CN111503625B
Application number: CN202010270574.6A
Authority: CN
Inventors: 杜贺; 李争起; 谭紫莹; 郑智巍; 曾令艳; 陈智超; 朱群益
Original assignee: Harbin Institute of Technology
Current assignee: Harbin Institute of Technology
Priority date: 2020-04-08
Filing date: 2020-04-08
Publication date: 2021-05-04
Anticipated expiration: 2040-04-08
Also published as: CN111503625A

Abstract

The invention relates to a gap type exhaust gas preposed W flame pot for arranging secondary air on an arch and an air distribution method, in particular to a coal-fired power station boiler, aiming at solving the problems of late ignition of coal dust airflow, unstable combustion and slag bonding of front and rear walls of the W flame pot, the invention also comprises two rows of double-cyclone-cylinder thick and thin coal dust burners, wherein each double-cyclone-cylinder thick and thin coal dust burner comprises an arch secondary air nozzle, two peripheral air nozzles, two thick and thin coal dust airflow nozzles and four gap type exhaust air nozzles; each dense coal powder airflow nozzle is arranged corresponding to two gap type exhaust nozzles, a peripheral air nozzle is arranged on the periphery of each dense coal powder airflow nozzle, and the secondary air nozzle on the arch, the two peripheral air nozzles, the two dense coal powder airflow nozzles and the four gap type exhaust nozzles are communicated with the lower hearth. The invention belongs to the technical field of boiler combustion.

Description

Gap type exhaust preposed W-shaped flame pan with secondary air arranged on arch and air distribution method

Technical Field

The invention relates to a coal-fired power plant boiler, in particular to a gap type exhaust gas preposed W-shaped flame boiler with secondary air arranged on an arch and an air distribution method, and belongs to the technical field of boiler combustion.

Background

China is the largest coal producing country and the largest coal consuming country in the world at present. From 2004 to 2006, the annual average composite growth rate of the coal yield in China reaches 10.3%, and the total coal yield in China in 2006 and the first half of 2007 is 23.8 hundred million tons and 10.82 hundred million tons respectively. At present, the coal consumption structure of China presents the characteristic of diversification, and 4 industries of electric power, metallurgy, chemical industry and building materials are main coal consumption industries for a long time. Coal consumption of four major industries accounts for about 70% of total consumption, wherein coal consumption (power coal) of the power industry accounts for more than 50% of the total consumption. However, with the improvement of the technological level, the utilization mode of coal resources in China is more and more exquisite, and the power coal for thermal power generation is generally poor coal with variable coal types and coal quality deviation. In order to burn the coal, in the nineties of the twentieth century, W flame boilers are gradually introduced from the northern Africa, Western Europe and other areas in China. 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. 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 can be widely applied quickly and becomes one of the main boiler types of thermal power generation. At present, 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 W flame boiler can be generally classified into four genres, i.e., an american Forst Wheeler (FW) W flame boiler, a bawei (B & W) W flame boiler, a korean figeba W flame boiler, and a stein W flame boiler, according to manufacturers. Among them, the forster wheeler type W flame boiler is most widely used, accounting for about 65% of the total market share. Compared with the other three W flame boilers, the FW type W flame boiler has the advantages that the lower hearth volume is small, the upper hearth volume is large, meanwhile, a special double-cyclone thick and thin pulverized coal burner is arranged, the arch part air rate is less than 30% of the total air rate of the boiler, and the arch part air rate can reach more than 50%. Long-term practical application shows that similar to other W flame boilers, FW type W flame boilers also have the common problem of high NOx emission, but besides, FW type W flame boilers have problems of late ignition of pulverized coal stream, unstable combustion, and slag formation on front and rear walls to different degrees. These problems are caused by the special burner structure and combustion organization of the FW type W flame boiler. Although the above problems can be alleviated to some extent by combustion adjustment, the above problems cannot be fundamentally solved because the combustion organization in the furnace is not fundamentally changed. Therefore, there is a need for new W-flame boilers and corresponding combustion methods and techniques.

Disclosure of Invention

The invention aims to solve the problems of late ignition of pulverized coal airflow, unstable combustion and slag bonding of front and rear walls of a W-flame boiler, and further provides a gap type exhaust preposed W-flame boiler with secondary air arranged on an arch and an air distribution method.

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

the first scheme is as follows: the double-cyclone-cylinder thick and thin pulverized coal burner comprises an upper furnace chamber, a lower furnace chamber, a front furnace arch and a rear furnace arch, wherein the upper furnace chamber, the front furnace arch, the lower furnace chamber and the rear furnace arch form a furnace body; four slit type exhaust nozzles on the double-cyclone barrel thick and thin pulverized coal burner are arranged side by side along the width direction of a hearth, an upper arch secondary air nozzle of the double-cyclone barrel thick and thin pulverized coal burner is arranged opposite to the four slit type exhaust nozzles, two thick pulverized coal airflow nozzles are arranged between the upper arch secondary air nozzle and the four slit type exhaust nozzles along the depth direction of the hearth, each thick pulverized coal airflow nozzle is arranged corresponding to the two slit type exhaust nozzles, a peripheral air nozzle is arranged on the periphery of each thick pulverized coal airflow nozzle, and the upper arch secondary air nozzle, the two peripheral air nozzles, the two thick pulverized coal airflow nozzles and the four slit type exhaust nozzles are communicated with a lower hearth.

Scheme II: the air distribution method of the exhaust gas rear W flame boiler arranged on the secondary air nozzles on the arch comprises the following steps:

it comprises the following steps: an arch secondary air nozzle is additionally arranged at the arch part of the W flame boiler, when the boiler runs at full load, the arch secondary air rate is about 20 percent of the total air rate of the boiler, and the air speed is about 20 m/s; and a plurality of groups of gap type ventilation air nozzles are arranged between the concentrated coal powder nozzles and the central side of the hearth, the primary air accounts for 25 percent of the total air rate of the furnace, the ventilation air rate accounts for about 50 percent of the total air rate of the primary air, and the air speed is about 20 m/s.

Compared with the prior art, the invention has the following beneficial effects:

1. the arrangement mode of exhaust gas and dense pulverized coal airflow nozzles is optimized, and the exhaust gas and the dense pulverized coal airflow are arranged on the fire facing side, so that ignition and stable combustion of the pulverized coal airflow are facilitated.

As shown in fig. 1 and 3, each double-cyclone thick-thin pulverized coal burner of the conventional FW-type W-flame boiler includes two thick-pulverized coal airflows and two exhaust gas nozzles. Wherein the exhaust gas nozzle is arranged at the side near the center of the hearth, and the dense coal airflow nozzle 9 is arranged at the side near the wall of the front wall and the rear wall of the lower hearth 2. The thick and thin pulverized coal airflow nozzles are arranged on the same straight line along the width direction of the hearth, and the thin pulverized coal airflow is arranged between the thick pulverized coal airflow and the high-temperature region of the hearth along the depth direction of the hearth. Only light pulverized coal airflow can directly reach the high-temperature area of the hearth under the arrangement mode of the nozzles and is heated by the high-temperature area. Due to the obstruction of the light coal dust airflow, the high-temperature backflow area cannot directly heat the thick coal dust airflow, so that the temperature rise speed is low, and the ignition and stable combustion of the coal dust airflow are not facilitated.

As shown in fig. 2 and 4, the W-flame boiler of the present invention employs the slit type exhaust gas nozzles 6, and the slit type exhaust gas nozzles 6 are still arranged between the rich coal airflow nozzles 9 and the high temperature zone of the furnace in the depth direction of the furnace, but are staggered with the rich coal airflow nozzles 9 in the width direction of the furnace. Compared with the traditional FW type W flame boiler, the thick coal powder airflow and the thin coal powder airflow are both directly arranged in the high-temperature backflow area of the boiler and are directly heated by the backflow area, so that the temperature rise speed of the coal powder airflow is accelerated, and the ignition and stable combustion of the coal powder airflow are facilitated.

2. The secondary air ratio of the boiler above the arch and below the arch is changed, the staged combustion level in the boiler is enhanced, and the NOx emission level is favorably reduced.

As shown in fig. 1: d, E layers and F layers of secondary air nozzles under an arch are sequentially arranged on the front wall and the rear wall of a lower hearth of the traditional FW type W flame boiler from top to bottom, and the arch part of the boiler is only provided with peripheral air as a cooling position. In the actual operation process of the boiler, the downdraft rate of the arch is about 70% of the total air rate entering the boiler, and the air rate of the arch part is less than 30%. Most of secondary air is intensively supplied into a hearth under the arch, and the pulverized coal is combusted in an oxygen-enriched environment. The N element in the coal powder and the N2 in the air fully react with the oxygen in the air, so the air classification level in the furnace is low, and the generation of fuel type NOx is not inhibited.

As shown in figure 2, a plurality of arch-up secondary air nozzles 7 are additionally arranged on a front arch and a rear arch of the boiler, and the arch-up secondary air nozzles 7 are arranged close to the front wall side and the rear wall side of a hearth on the boiler. The secondary air with the air rate of about 20 percent moves from the arch to the arch, and the air rate under the arch is reduced to 50 percent of the air rate of the furnace. The pulverized coal airflow is uniformly supplied in the downward flushing process after being sprayed into the hearth, so that the pulverized coal airflow is in a proper low-chemical equivalence ratio condition in each combustion stage, the pulverized coal combustion is guaranteed, the efficiency is improved, the staged combustion level in the furnace is enhanced, the generation of NOx is inhibited, and the NOx discharge amount of the boiler is reduced.

3. Can effectively prevent the top of the front wall and the top of the rear wall of the lower hearth of the boiler from slagging.

As shown in fig. 1 and 3, each double cyclone thick-thin pulverized coal burner of the conventional FW-type W-flame boiler includes two thick-thin pulverized coals and two exhaust gas nozzles. Wherein the exhaust gas nozzle is arranged at the side near the center of the hearth, and the dense coal powder airflow is arranged at the side near the wall of the front wall and the rear wall of the lower hearth. Because the boiler arch part is only provided with peripheral air except thick and thin pulverized coal airflow, the secondary air rate of the arch part is less than 5 percent of the total air rate of the boiler. The experimental measurement shows that the oxygen concentration of the near-wall sides of the top parts of the front wall and the rear wall of the hearth is about 7%, the atmosphere has strong reducibility, the ash melting point of the coal powder under the reducing atmosphere is low, and the ash in the coal powder is easy to be heated to a molten state and is attached to the combustion preventing belt of the front wall and the rear wall to cause slagging.

As shown in figures 2 and 4, the invention arranges the secondary air nozzles 7 on the front wall and the rear wall of the arch part of the boiler near the wall, and the more 20 percent of the total air rate entering the boiler is fed into the hearth by the secondary air nozzles. The secondary air is sprayed into the arch to greatly enhance the oxidability of the atmosphere on the near wall side of the front and rear walls, and the oxygen concentration can be increased to more than 15%. The melting point of ash in the coal powder is higher in the oxygen-enriched environment, and the ash in the coal powder airflow is not easy to heat to a molten state, so that the slagging phenomenon is effectively prevented.

In addition, for the traditional FW W flame boiler, the concentrated coal dust airflow is arranged close to the front wall and the rear wall of the lower hearth of the boiler, other airflow barriers do not exist between the concentrated coal dust airflow and the front wall and the rear wall, and the slag formation of the front wall and the rear wall is easily caused due to the fact that molten coal dust particles flush the combustion control belt.

The secondary air on the arch of the invention is sprayed into the hearth and then rapidly diffuses, so that an air curtain can be formed between the concentrated pulverized coal airflow and the front wall and the rear wall of the lower hearth to separate the concentrated pulverized coal airflow from the front wall and the rear wall, the concentration of the pulverized coal on the near wall side of the front wall and the rear wall is reduced to about 20% of the original concentration, the washing effect of ash in the pulverized coal on the combustion control zone is weakened, and the slag bonding of the front wall and the rear wall of the boiler can be further prevented. .

Drawings

Fig. 1 is a schematic cross-sectional flow field diagram of a conventional FW-type W-flame boiler.

FIG. 2 is a schematic cross-sectional flow field of the W flame boiler of the present invention.

FIG. 3 is a schematic view of the direction A in FIG. 1

Fig. 4 is a schematic view of fig. 2 from direction B.

Detailed Description

The first embodiment is as follows: the embodiment is described by combining fig. 2 and fig. 4, the gap type exhaust gas front-mounted W flame boiler with secondary air on the arch is arranged in the embodiment, the gap type exhaust gas front-mounted W flame boiler comprises an upper hearth 1, a lower hearth 2, a front furnace arch 3 and a rear furnace arch 4, the upper hearth 1, the front furnace arch 3, the lower hearth 2 and the rear furnace arch 4 form a boiler body, and the gap type exhaust gas front-mounted W flame boiler is characterized in that: the double-cyclone-cylinder thick-thin pulverized coal burner also comprises two rows of double-cyclone-cylinder thick-thin pulverized coal burners 5, wherein each row of double-cyclone-cylinder thick-thin pulverized coal burners 5 comprises a plurality of double-cyclone-cylinder thick-thin pulverized coal burners 5, the double-cyclone-cylinder thick-thin pulverized coal burners 5 are symmetrically arranged on the front furnace arch 3 and the rear furnace arch 4 in a straight line shape, and each double-cyclone-cylinder thick-thin pulverized coal burner 5 comprises an arch secondary air nozzle 7, two peripheral air nozzles 8, two thick-coal airflow nozzles 9 and four slit type exhaust air nozzles 6; four slit type exhaust nozzles 6 on the double-cyclone-barrel thick and thin coal powder burner 5 are arranged side by side along the width direction of a hearth, an upper arch secondary air nozzle 7 of the double-cyclone-barrel thick and thin coal powder burner 5 is arranged opposite to the four slit type exhaust nozzles 6, two thick coal powder airflow nozzles 9 are arranged between the upper arch secondary air nozzle 7 and the four slit type exhaust nozzles 6 along the depth direction of the hearth, each thick coal powder airflow nozzle 9 is arranged corresponding to the two slit type exhaust nozzles 6, a peripheral air nozzle 8 is arranged on the periphery of each thick coal powder airflow nozzle 9, and the upper arch secondary air nozzle 7, the two peripheral air nozzles 8, the two thick coal powder airflow nozzles 9 and the four slit type exhaust nozzles 6 are all communicated with the lower hearth 2.

The second embodiment is as follows: in the present embodiment, the cross section of the slit type exhaust gas nozzles 6 is rectangular, and the sum of the cross sections of the four slit type exhaust gas nozzles 6 of each double cyclone duct pulverized coal burner 5 is equal to the cross section of a single exhaust gas duct.

Other components and connections are the same as in the first embodiment.

The third concrete implementation mode: the present embodiment is described with reference to fig. 4, and the four slit type exhaust air nozzles 6 of the present embodiment are arranged in parallel near the center plane of the furnace 2, the secondary air nozzles 7 on the upper arch of the front arch 3 are arranged near the front wall of the lower furnace 2, and the secondary air nozzles 7 on the upper arch of the rear arch 4 are arranged near the rear wall of the lower furnace 2.

Other components and connections are the same as in the first embodiment.

The fourth concrete implementation mode: the present embodiment is described with reference to fig. 2, in the present embodiment, each rich coal airflow nozzle 9 of the double-cyclone-cylinder rich-lean coal burner 5 along the width direction of the furnace is arranged between two parallel slit type exhaust nozzles 6, and the distance between the two parallel slit type exhaust nozzles 6 is greater than the outer diameter of the rich coal airflow nozzle 9

Other compositions and connection relations are the same as those of the third embodiment.

The fifth concrete implementation mode: the present embodiment is described with reference to fig. 2 and 4, and the gap type exhaust gas front-mounted W-flame boiler and the air distribution method of the present embodiment, in which the secondary air is arranged on the arch, includes the following steps:

an arch secondary air nozzle 7 is additionally arranged at the arch part of the W flame boiler, when the boiler runs at full load, the arch secondary air rate is about 20 percent of the total air rate of the boiler, and the air speed is about 20 m/s; and a plurality of groups of gap type ventilation air nozzles 6 are arranged between the dense coal powder nozzles 9 and the central side of the hearth, the primary air accounts for 25 percent of the total air rate of the furnace, the ventilation air rate accounts for about 50 percent of the total air rate of the primary air, and the air speed is about 20 m/s.

The sixth specific implementation mode: this embodiment will be described with reference to fig. 2 and 4, and is described below

And a peripheral air nozzle 8 is arranged outside each concentrated coal powder nozzle 9, the peripheral air rate accounts for 5 percent of the total air rate of the furnace, and the air speed is about 10 m/s.

Other components and connection relationships are the same as those in the fifth embodiment.

The seventh embodiment: the present embodiment will be described with reference to fig. 2 and 4, in which the boiler crown air rate and the crown air rate each account for 50% of the total air rate of the furnace.

Example (b):

the invention is applied to a 600MW FW W flame boiler produced by Foster Whileler, USA, and 18 groups of double-cyclone-barrel shade-separation pulverized coal burners are symmetrically arranged in front and rear arches of the boiler. After the invention is adopted, 18 groups of arch secondary air nozzles with the length of 600mm and the width of 150mm are additionally arranged at the arch part of the boiler, and about 25 percent of secondary air is supplied to a hearth through the nozzles. Two exhaust nozzles of the original burner are split into 4 gap type exhaust nozzles which are fed into the hearth from the side close to the center of the hearth. Each slit type exhaust gas nozzle is 300mm long and 100mm wide. Through test measurement, the secondary air speed on the arch is about 20m/s, and the exhaust air speed is about 23 m/s.

Before the invention is adopted, secondary air is only supplied by the peripheral air nozzles of the arch part of the boiler, the air rate is about 10 percent, and the NOx emission amount of the hearth outlet under the full load working condition is about 1350mg/m³The ignition and stable combustion capacity of the pulverized coal airflow is poor under the low-load working condition or when low-volatile coal is used, and fire extinguishing accidents of a boiler can be caused under the 300MW load working condition, so that huge economic loss is caused. In addition, the front wall and the rear wall have serious slagging phenomena, and the furnace is required to be stopped for ash removal for many times every year.

After the invention is adopted, the secondary air rate of the arch part and the secondary air rate under the arch are both about 50 percent, and the NOx emission at the outlet of the furnace chamber under the full load working condition is reduced to 700mg/m³The ignition and stable combustion capability of the pulverized coal airflow is obviously improved and adjusted by combustionTests show that the pulverized coal airflow can still stably ignite and burn when burning inferior coal. The slagging phenomenon of the front wall and the rear wall of the hearth basically disappears, and all the burners can be normally put into operation.

Claims

1. Arrange and encircle leading type W flame pot of gap formula exhaust gas of overfire air, it includes furnace (1), lower furnace (2), preceding stove arch (3) and back stove arch (4), goes up furnace (1), preceding stove arch (3), lower furnace (2) and back stove arch (4) and constitutes the furnace body, its characterized in that: the double-cyclone-barrel thick and thin pulverized coal burner system is characterized by further comprising two rows of double-cyclone-barrel thick and thin pulverized coal burners (5), wherein each row of double-cyclone-barrel thick and thin pulverized coal burners (5) comprises a plurality of double-cyclone-barrel thick and thin pulverized coal burners (5), the double-cyclone-barrel thick and thin pulverized coal burners (5) are symmetrically arranged on the front furnace arch (3) and the rear furnace arch (4) in a straight line shape, and each double-cyclone-barrel thick and thin pulverized coal burner (5) comprises an arch secondary air nozzle (7), two peripheral air nozzles (8), two thick and thin pulverized coal airflow nozzles (9) and four slit type exhaust air nozzles (6); four slit type exhaust air nozzles (6) on the double-cyclone-barrel thick and thin pulverized coal burner (5) are arranged side by side along the width direction of a hearth, an upper arch secondary air nozzle (7) of the double-cyclone-barrel thick and thin pulverized coal burner (5) is arranged opposite to the four slit type exhaust air nozzles (6), two thick pulverized coal airflow nozzles (9) are arranged between the upper arch secondary air nozzle (7) and the four slit type exhaust air nozzles (6) along the depth direction of the hearth, each thick pulverized coal airflow nozzle (9) is arranged corresponding to the two slit type exhaust air nozzles (6), a perimeter air nozzle (8) is arranged on the periphery of each thick pulverized coal airflow nozzle (9), the upper arch secondary air nozzle (7), the two perimeter air nozzles (8), the two thick pulverized coal airflow nozzles (9) and the four slit type exhaust air nozzles (6) are communicated with the lower hearth (2).

2. The gap type exhaust gas front-mounted W flame pan with the secondary air arranged on the arch according to claim 1, is characterized in that: the cross section of the slit type exhaust gas nozzle (6) is rectangular, and the sum of the cross sections of the four slit type exhaust gas nozzles (6) on each double-cyclone-cylinder thick-thin pulverized coal burner (5) is equal to the cross section of a single exhaust gas pipeline.

3. The gap type exhaust gas front-mounted W flame pan with the secondary air arranged on the arch according to claim 1, is characterized in that: the four gap type exhaust air nozzles (6) are arranged in parallel near the central plane of the hearth (2), the secondary air nozzles (7) on the upper arch of the front furnace arch (3) are arranged near the front wall of the lower hearth (2), and the secondary air nozzles (7) on the upper arch of the rear furnace arch (4) are arranged near the rear wall of the lower hearth (2).

4. The gap type exhaust gas front-mounted W flame pan with the secondary air arranged on the arch according to claim 3, is characterized in that: each dense coal airflow nozzle (9) on the double-cyclone-cylinder dense and thin coal powder burner (5) along the width direction of the hearth is arranged between two parallel-arranged slit type exhaust nozzles (6), and the distance between the two parallel-arranged slit type exhaust nozzles (6) is larger than the outer diameter of the dense coal airflow nozzle (9).

5. The air distribution method of the gap type exhaust gas front-mounted W flame pot for arranging the secondary air on the arch according to any one of claims 1 to 4, characterized in that: it comprises the following steps:

an arch secondary air nozzle (7) is additionally arranged at the arch part of the W flame boiler, when the boiler runs at full load, the arch secondary air rate is 20 percent of the total air rate entering the boiler, and the air speed is 20 m/s; a plurality of groups of gap type ventilation air nozzles (6) are arranged between the dense coal powder nozzles (9) and the central side of the hearth, the primary air accounts for 25 percent of the total air rate of the furnace, the ventilation air rate accounts for 50 percent of the total air rate of the primary air, and the wind speed is 20 m/s.

6. The air distribution method of the gap type exhaust gas front type W flame pan with the secondary air arranged on the arch according to claim 5, characterized in that: and a peripheral air nozzle (8) is arranged outside each concentrated coal powder nozzle (9), the peripheral air rate accounts for 5% of the total air rate of the furnace, and the air speed is 10 m/s.

7. The air distribution method of the gap type exhaust gas front type W flame pan with the secondary air arranged on the arch according to claim 6, characterized in that: the air-up rate and the air-down rate of the boiler respectively account for 50 percent of the total air rate of the boiler.