Symmetrical combustion w-flame furnace with high burnout, low slagging, ultra-low nitrogen and anti-dust hopper overheating

Abstract

The application discloses a symmetric combustion W flame furnace with high burnout, low slagging, ultra-low nitrogen and anti-heat overburning of the ash bucket, which comprises two furnace arches, one row of main burners, one row of staged air nozzles, one row of pulverized coal reburning nozzles, one row of upper cold ash bucket air nozzles and one row of lower cold ash bucket air nozzles, which are symmetrically arranged on the left wall side and the right wall side of the lower hearth, thereby constructing a symmetric W type flame along the vertical section of the left wall, the right wall and the hearth outlet flue gas flow direction, strengthening the oxygen-poor atmosphere of the combustion early stage area of the lower part of the furnace arch and the deep air staging condition in the furnace, reducing the NOx in the furnace by using the fine pulverized coal in the exhaust gas as the reburning fuel, pushing the downward main pulverized coal flow to the furnace center side which is closer to the high temperature by the wall jet of the staged air, the dilute pulverized coal flue gas flow and the upper staged type cold ash bucket air, and simultaneously achieving the effects of shortening the main flame stroke and protecting the cold ash bucket wall surface; the furnace has the advantages of high efficient burnout, significant reduction of NOx emission and avoidance of heat overburning of the ash bucket.

Description

TECHNICAL FIELD

[0001] The present application relates to W flame furnace, especially to a symmetrical combustion W flame furnace with high burnout, low slagging, ultra-low nitrogen and anti-heat runaway of ash bucket. BACKGROUND

[0002] The W flame furnace developed for burning low-volatile pulverized coal such as anthracite has been widely promoted in China. However, a large number of operation performances show that the front and back wall leading W flame furnace using the existing mainstream technology generally has the problems of poor burnout, serious slagging, high NOx emission and asymmetric combustion. The asymmetric combustion is manifested as a large difference in the depth of the flame underflow on the front wall side and the back wall side, good combustion on one side and poor combustion on the other side; the temperature on the side with good combustion is significantly higher, the heat load is large, and the slagging is particularly serious, and a large number of local high-temperature zones promote the generation of thermal NOx; the temperature on the side with poor combustion is low, and the burnout effect is significantly poor, resulting in deterioration of the overall burnout effect of the W flame furnace. Therefore, asymmetric combustion has a great negative impact on the W flame furnace, and must be mitigated or completely eliminated.

[0003] The relevant research shows that the combustion asymmetry is due to the flow field deflection in the W flame furnace, and the root cause of the flow field deflection is that the two coal powder gas flows on the front wall side and the back wall side are guided by the asymmetric structure effect of the upper furnace (i.e. the arch angle and the furnace outlet located on the back wall side), and one side of the coal powder gas flow is easy to turn early and deviate to the other side of the coal powder gas flow upward, the flame travel is short, and under the pressure of the deflection and extrusion, the other side of the coal powder gas flow is deep, and then turns and intersects with the above-mentioned short gas flow to deviate upward, thereby forming a deflected flow field. In order to build symmetric combustion, and eliminate the flow field deflection inducement of the guiding effect of the asymmetric structure effect of the upper furnace from the root, the Chinese invention patent "Symmetric combustion W type flame boiler with side wall arranged arch combustion burner" (patent number ZL201710896667.8, authorized announcement date 2019.08.02, hereinafter referred to as "document one") proposes a left and right wall main symmetric combustion W flame technology of arranging the furnace arch, the arch combustion burner and the staged air on the side wall, and builds a W type flow field perpendicular to the flue gas flow direction of the furnace outlet, the two U type main gas flows on the left and right sides of the "first down and then up" have equal distances to the furnace outlet, and the guiding effect of the furnace outlet is symmetrically applied to the whole W type flow field, thereby eliminating the guiding effect of the asymmetric structure of the upper furnace on the two U type main gas flows on the front and back walls, and creating a symmetric W type flame along the furnace width direction on the longitudinal section of the furnace. Although "document one" solves the problem of combustion asymmetry and relieves the slagging in the lower furnace, it does not involve the improvement and strengthening of the arch dense and thin combustion and low NOx combustion, and still has problems of serious slagging in the arch near the throat and high NOx emission. Correspondingly, the Chinese invention patent "Low-nitrogen and high-efficiency burnout W flame boiler with side wall main symmetric combustion" (patent number ZL201810032042.1, authorized announcement date 2019.10.11, hereinafter referred to as "document two") is based on the side wall main symmetric combustion W flame furnace of "document one", and sets up left and right throat burnout air and front and back wall burnout air at the intersection of the upper and lower furnaces and the lower part of the front and back walls of the upper furnace respectively, in order to strengthen the air staging in the furnace and move the left and right arches near the throat to the middle part of the front and back walls. Although "document two" effectively solves the problem of slagging in the arch near the throat and reduces the NOx emission, the relevant research results show that it still has three problems: (i) in the face of the increasingly stringent emission requirements, its NOx emission is still high; (ii) the flue gas is arranged in the main flue gas upward region of the middle part of the front and back walls, on the one hand, this region is far away from the main combustion zone of the flue gas downward and has low oxygen concentration, on the other hand, the flue gas with relatively weak rigidity in the front and back walls is difficult to penetrate to the center of the furnace and mix well with the high temperature flue gas, and the flue gas burnout is difficult to guarantee; (iii) in order to achieve good burnout, the high arch air momentum is used to prolong the flame travel by adding the burnout air to strengthen the low NOx combustion by air staging, and the result is that the flame is shot to the lower part of the cold ash bucket, which leads to overheating of the cold ash bucket area and causes thermal fatigue problem. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a high burnout low slagging, ultra-low nitrogen and anti-ash bucket overheating symmetrical combustion W flame furnace which can realize efficient burnout, significantly reduce NOx emission and avoid ash bucket overheating.

[0005] The technical scheme adopted by the present application to solve the above technical problem is as follows: a high burnout low slagging, ultra-low nitrogen and anti-ash bucket overheating symmetrical combustion W flame furnace, comprising a hearth body enclosed by a left wall, a right wall, a front wall and a rear wall, wherein the hearth body is composed of a lower hearth and an upper hearth, the lower hearth is composed of a furnace arch part, a lower hearth main part and a cold ash bucket arranged in sequence from top to bottom, the furnace arch part comprises a left furnace arch and a right furnace arch symmetrically arranged on the left wall side and the right wall side, the lower hearth and the upper hearth are the same in size in the furnace depth direction, the size of the lower hearth main part in the furnace width direction is 1.8 to 2.2 times the size of the upper hearth, the upper part of a part of the rear wall enclosing the upper hearth is provided with a refractory angle and a hearth outlet in the horizontal direction, a row of main burners for feeding a downward main pulverized coal gas flow is arranged along the furnace depth direction at the left furnace arch and the right furnace arch, a row of staged air nozzles, a row of pulverized coal reburning nozzles and a row of upper cold ash bucket air nozzles are symmetrically arranged in sequence from top to bottom at the left wall and the right wall of the lower hearth main part, the staged air nozzles are used to feed downward inclined staged air to organize first layer air staged combustion, the pulverized coal reburning nozzles are used to feed a weak pulverized coal flue gas flow strengthened by flue gas recirculation to form a lean oxygen atmosphere, so that the fine pulverized coal in the flue gas of the rich-lean combustion is used as reburning fuel, the upper cold ash bucket air nozzles are used to feed upper staged type cold ash bucket air to the cold ash bucket to promote the combustion of coke from the upstream reburning zone and organize second layer air staged combustion, a row of lower cold ash bucket air nozzles is symmetrically arranged on the left wall and the right wall of the cold ash bucket, the lower cold ash bucket air nozzles are used to feed lower staged type cold ash bucket air to the cold ash bucket in a horizontal or downward inclined manner to adjust the flame downward penetration depth and protect the cold ash bucket from overheating; a row of burnout air nozzles is symmetrically arranged along the furnace depth direction at the left wall and the right wall at the junction of the lower hearth and the upper hearth, the burnout air nozzles are used to feed burnout air to the lower hearth in a downward inclined manner to organize third layer air staged combustion.

[0006] The row of main burners is located in the middle region of the two furnace arches.

[0007] The row of staged air nozzles is arranged at the middle upper region of the lower hearth main part.

[0008] The row of pulverized coal reburning nozzles is arranged at the middle lower region of the lower hearth main part.

[0009] The upper row of air injection ports is arranged near the ash hopper of the main furnace body.

[0010] The lower row of air injection ports is arranged at the upper region of the ash hopper.

[0011] The lean oxygen atmosphere enhanced by the flue gas recirculation has multiple input modes, wherein the first input mode is direct input through the row of coal powder reburning injection ports, the second input mode is direct mixing into the main coal powder gas stream through the row of main burners, the third input mode is input through the row of staged air injection ports, and the fourth input mode is a combination of any two or three of the above first, second, and third input modes.

[0012] The upper staged type ash hopper air and the lower staged type ash hopper air have three types of staging organization, the first type of staging organization is an upper air dominant mode in which the upper staged type ash hopper air is mainly used for enhancing staged combustion and the lower staged type ash hopper air is used for preventing the ash hopper from overheating, the second type of staging organization is a lower air dominant mode in which the lower staged type ash hopper air is mainly used for preventing the ash hopper from overheating and the upper staged type ash hopper air is used for enhancing staged combustion, and the third type of staging organization is an equal mode between the upper air dominant mode and the lower air dominant mode; when the upper air dominant mode is adopted, the volume ratio of the upper staged type ash hopper air in the total ash hopper air formed by the upper staged type ash hopper air and the lower staged type ash hopper air is 60-80%; when the lower air dominant mode is adopted, the volume ratio of the upper staged type ash hopper air to the lower staged type ash hopper air is 4:6; and when the equal mode is adopted, the volume ratio of the upper staged type ash hopper air to the lower staged type ash hopper air is 5:5.

[0013] Compared with the prior art, the application has the advantages that: by symmetrically arranging two arches, one row of main burners, one row of staged air nozzles, one row of pulverized coal reburning nozzles, one row of upper layer cold ash hopper air nozzles and one row of lower layer cold ash hopper air nozzles on the left wall and the right wall of the lower hearth, the multiple wall jets such as the staged air, the light pulverized coal flue gas flow, the upper layer staged type cold ash hopper air and the lower layer staged type cold ash hopper air which are fed step by step along the main flame downward are symmetrically arranged on the left wall side and the right wall side of the lower hearth, thereby constructing a symmetric W-shaped flame on the vertical section of the hearth along the left wall, the right wall and the flue gas flow direction of the hearth outlet, and the problems of poor burnout, serious slagging and high generation of thermal NOx caused by the asymmetric combustion of the prior art W-shaped flame furnace are solved; by reducing the secondary air of the main burner and additionally arranging the upper layer staged type cold ash hopper air and the lower layer staged type cold ash hopper air, the oxygen-poor atmosphere in the early combustion stage of the lower part of the arch and the deep air staging condition in the furnace are strengthened, so that the generation of fuel NOx and thermal NOx is simultaneously inhibited; the arrangement of the flue gas is abandoned, and instead, the fine pulverized coal in the flue gas is used as reburning fuel and is fed into the light pulverized coal flue gas flow composed of flue gas and fine pulverized coal in the middle and lower part of the left wall and the right wall of the lower hearth, that is, the pulverized coal reburning is used to reduce NOx by using the flue gas recirculation, which further reduces the NOx emission and avoids the problems of poor burnout, high NOx emission and serious slagging caused by the unreasonable arrangement of the flue gas in the prior art; the wall jets such as the staged air, the light pulverized coal flue gas flow and the upper layer staged type cold ash hopper air which are fed step by step push the downward main pulverized coal flow to the hearth center side which is closer to the high temperature, which is beneficial to the combustion of the main pulverized coal flow and the avoidance of slagging on the left wall and the right wall, and the arch underflow is strengthened, which is helpful to the ignition and combustion of the coal, and the upper layer staged type cold ash hopper air fed downstream of the reburning area is beneficial to the disturbance and combustion of the later coke, so as to improve the overall burnout effect of the boiler; in addition, by reducing the secondary air of the main burner, greatly lifting the position of the staged air, arranging the upper layer staged type cold ash hopper air and the lower layer staged type cold ash hopper air to form two layers of staged type cold ash hopper air, the main flame travel is shortened, the staged type cold ash hopper air is better to protect the cold ash hopper wall, and based on the promotion of coke combustion by the upper layer staged type cold ash hopper air and the interception of the downward main flame by the lower layer staged type cold ash hopper air, the burnout is considered and the cold ash hopper overheating is prevented, so that the application can realize efficient burnout, significantly reduce NOx emission and avoid cold ash hopper overheating. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a main view of the hearth structure and the combustion system arrangement of the symmetric combustion W-shaped flame furnace with high burnout, low slagging, ultra-low nitrogen and cold ash hopper overheating prevention of the application.

[0015] Figure 2 It is a main view of the hearth structure and the combustion system arrangement of the symmetric combustion W-shaped flame furnace with high burnout, low slagging, ultra-low nitrogen and cold ash hopper overheating prevention of the application. Figure 1 It is a side view of the hearth structure and the combustion system arrangement of the symmetric combustion W-shaped flame furnace with high burnout, low slagging, ultra-low nitrogen and cold ash hopper overheating prevention of the application.

[0016] Figure 3 Figure 1 is a schematic diagram of the furnace structure, combustion system and furnace skew flow field of a prior art front and back wall dominated W-flame furnace using mainstream technology;

[0017] Figure 4 Figure 2 is a front view of the furnace structure and combustion system arrangement of a prior art low-nitrogen high-efficiency burnout W-flame furnace with side wall dominated symmetric combustion disclosed in "Document Two";

[0018] Figure 5 Figure 3 is a schematic diagram of the furnace structure, combustion system and furnace skew flow field of the W-flame furnace shown in Figure 2; Figure 4 Figure 4 is an A-direction side view of the furnace structure and combustion system shown in Figure 3. DETAILED DESCRIPTION

[0019] The application will be further described in detail below with reference to the embodiments shown in the accompanying drawings.

[0020] Example One: As shown in Figure 1, the furnace structure, combustion system and furnace skew flow field of a prior art front and back wall dominated W-flame furnace using mainstream technology are shown. Figure 1 and Figure 2As shown, a symmetrical combustion W-flame furnace with high burnout, low slagging, ultra-low nitrogen and anti-heat damage to the hopper includes a hearth body wrapped by a left wall 1, a right wall 2, a front wall 3 and a rear wall 4, the hearth body is composed of a lower hearth 5 and an upper hearth 6, the lower hearth 5 is composed of a furnace arch part, a lower hearth main part 7 and a cold ash hopper 8 arranged in sequence from top to bottom, the furnace arch part includes left and right furnace arches 5a and 5b symmetrically arranged on the left and right wall sides, the lower hearth 5 and the upper hearth 6 have the same size in the furnace depth direction, the size of the lower hearth main part 7 in the furnace width direction is 1.8 to 2.2 times that of the upper hearth 6, the upper part of the rear wall 4 wrapping the upper hearth 6 is provided with a refractory angle 9 and a hearth outlet 10 in the horizontal direction, a row of main burners 11 for feeding the downwardly injected main pulverized coal gas flow 15 into the lower hearth 5 is arranged along the furnace depth direction at the left and right furnace arches 5a and 5b, a row of staged air injection ports 12, a row of pulverized coal reburning injection ports 17 and a row of upper cold ash hopper air injection ports 19 are symmetrically arranged in sequence from top to bottom at the left and right walls 1 and 2 of the lower hearth main part 7, the row of staged air injection ports 12 are all used for feeding the downwardly injected staged air 16 into the lower hearth main part 7, so as to organize the first layer of air staged combustion, the row of pulverized coal reburning injection ports 17 are all used for feeding the light pulverized coal flue gas flow 18 with the strengthened lean oxygen atmosphere by the flue gas recirculation into the lower hearth main part 7, so as to use the fine pulverized coal in the dense and light combustion flue gas as reburning fuel, the row of upper cold ash hopper air injection ports 19 are all used for feeding the upper staged type cold ash hopper air 20 into the cold ash hopper 8, so as to promote the coke combustion from the upstream reburning zone, and organize the second layer of air staged combustion, a row of lower cold ash hopper air injection ports 21 are symmetrically arranged on the left and right walls 1 and 2 of the cold ash hopper 8, the row of lower cold ash hopper air injection ports 21 are all used for feeding the lower staged type cold ash hopper air 22 into the cold ash hopper 8 in the horizontal or downwardly inclined manner, so as to adjust the flame downwash depth and protect the cold ash hopper 8 from overheating; a row of burnout air injection ports 13 are symmetrically arranged along the furnace depth direction at the left and right walls 1 and 2 at the junction of the lower hearth 5 and the upper hearth 6, the row of burnout air injection ports 13 are all used for feeding the downwardly injected burnout air 14 into the lower hearth 5, so as to organize the third layer of air staged combustion.

[0021] In this embodiment, the row of main burners 11 is located in the middle region of the two furnace arches 5a and 5b.

[0022] In this embodiment, the row of staged air injection ports 12 is arranged at the middle upper region of the lower hearth main part 7.

[0023] In this embodiment, the row of pulverized coal reburning injection ports 17 is arranged at the middle lower region of the lower hearth main part 7.

[0024] In this embodiment, the row of upper cold ash hopper air injection ports 19 is arranged at the cold ash hopper 8 close to the lower hearth main part 7.

[0025] In this embodiment, a row of lower-level cold ash hopper air nozzles 21 are arranged in the upper part of the cold ash hopper 8.

[0026] In this embodiment, by symmetrically arranging two furnace arches 5a and 5b, a row of main burners 11, a row of staged air nozzles 12, a row of pulverized coal reburning nozzles 17, a row of upper-layer cold ash hopper air nozzles 19, and a row of lower-layer cold ash hopper air nozzles 21 on the left wall 1 and right wall 2 of the lower furnace 5, multiple wall jets, including staged air 16, light pulverized coal flue gas 18, upper-layer staged cold ash hopper air 20, and lower-layer staged cold ash hopper air 22, which are fed down step by step along the main flame, are symmetrically arranged on the left wall 1 and right wall 2 sides of the lower furnace 5. This constructs a symmetrical W-shaped flame along the longitudinal section of the furnace perpendicular to the flue gas flow direction of the left wall 1, right wall 2, and furnace outlet 10. This invention addresses the problems of poor burnout, severe slagging, and high thermal NOx generation caused by asymmetrical combustion in existing mainstream W-flame furnaces with front and rear walls. It achieves this by reducing the secondary air supply to the first row of main burners 11 while simultaneously adding two layers of graded cold ash hopper air: an upper-level graded cold ash hopper air supply 20 and a lower-level graded cold ash hopper air supply 22. This strengthens the oxygen-deficient atmosphere in the pre-combustion zone below the furnace arch 5a and enhances the deep air grading conditions within the furnace, thereby simultaneously suppressing the generation of both fuel-type and thermal NOx. Furthermore, it abandons the use of exhaust gas and instead utilizes fine pulverized coal from the exhaust gas as reburning fuel, introducing a light pulverized coal flue gas mixture composed of flue gas and fine pulverized coal into the lower middle regions of the left wall 1 and right wall 2 of the lower furnace 5. Airflow 18 utilizes pulverized coal reburning enhanced by flue gas recirculation to reduce NOx, further reducing NOx emissions while avoiding problems such as poor burnout, high NOx emissions, and severe slagging caused by unreasonable exhaust gas arrangement in existing mainstream technologies. The progressively introduced staged airflow 16, the light pulverized coal flue gas flow 18, and the upper-level staged cold ash hopper airflow 20—these wall jets push the downward main pulverized coal flow 15 downwards towards the furnace center, closer to the high temperature. This is beneficial for the combustion of the main pulverized coal flow 15 and for preventing slagging on the left wall 1 and right wall 2. Simultaneously, the under-arch recirculation is enhanced, aiding coal ignition and combustion. Furthermore, the upper-level staged cold ash hopper airflow 20, introduced downstream of the reburning zone, further contributes to... The later stage of coke combustion is beneficial, thus helping to improve the overall burnout effect of the boiler. In addition, by reducing the secondary air volume of the main burner 11, significantly raising the position of the staged air 16, and setting up a staged cold ash hopper formed by the upper staged cold ash hopper air 20 and the lower staged cold ash hopper air 22, the main flame stroke is shortened while the staged cold ash hopper air better protects the wall of the cold ash hopper 8. Based on the effect of the upper staged cold ash hopper air 20 promoting coke combustion and the lower staged cold ash hopper air 22 intercepting the downward main flame, the cold ash hopper 8 is prevented from overheating while ensuring burnout. Thus, the present invention can achieve efficient burnout, significantly reduce NOx emissions, and avoid overheating of the cold ash hopper.

[0027] Embodiment two: this embodiment is basically the same as embodiment one, the difference is that in this embodiment, the lean coal dust flue gas stream 18 with the oxygen-lean atmosphere strengthened by flue gas recirculation has multiple feeding modes, the first feeding mode is direct feeding through a row of coal dust reburning injection ports 17, the second feeding mode is direct mixing into the main coal dust gas stream 15 through a row of main burners 11, the third feeding mode is feeding through a row of staged air injection ports 12, and the fourth feeding mode is a combination of any two or three of the first, second and third feeding modes.

[0028] In this embodiment, the coupling of coal dust reburning and flue gas recirculation in the W-flame furnace for low-nitrogen combustion can have three organization modes according to the principle of NOx emission reduction and the influence degree on the combustion condition and burnout in the furnace. The first mode is that the flue gas recirculation is directly mixed into the main coal dust gas stream 15 through a row of main burners 11, thereby further strengthening the oxygen-lean atmosphere in the pre-combustion stage under the arch to inhibit the generation of fuel-type NOx, and because the amount of NOx generated in the pre-combustion stage is significantly reduced, it helps to alleviate the pressure of coal dust reburning reduction of NOx in the reburning zone, this mode has the best low-nitrogen effect but is not conducive to ignition and stable combustion when the coal quality is poor; the second mode is that the flue gas recirculation is fed through a row of staged air injection ports 12, and the recirculated flue gas is mixed with the staged air 16 in the main combustion zone and the ignited main coal dust gas stream 15, aiming to reduce the oxygen concentration in the main combustion zone, inhibit the main combustion intensity and reduce the combustion temperature to reduce the generation of thermal-type NOx, and because the amount of NOx generated in the main combustion stage is reduced, it also helps to alleviate the pressure of reburning reduction of NOx, this mode has good low-nitrogen effect when the furnace temperature is high at high load but may affect the burnout; the third mode is that the flue gas recirculation carries fine coal dust and is fed into the reburning zone through a row of coal dust reburning injection ports 17, that is, the lean coal dust flue gas stream 18 with the oxygen-lean atmosphere strengthened by flue gas recirculation is used to strengthen the coal dust reburning reduction of NOx, this mode does not affect the upstream combustion and is beneficial to the overall combustion performance of the boiler, but because the upstream NOx is not reduced as in the first two modes, the demand for coal dust reburning reduction of NOx is higher. It should be noted that the above three organization modes can be used alone or in combination, and in actual application, the appropriate organization mode of coupling of flue gas recirculation and coal dust reburning for low-nitrogen combustion should be selected according to the coal type, burnout and NOx emission reduction demand.

[0029] Embodiment three: this embodiment is basically the same as embodiment one, the difference is that in this embodiment, the upper and lower layer classified type of cold ash hopper wind 20 and 22 have three kinds of classified organization ways, the first kind of classified organization way is the upper wind leading mode that the upper layer classified type of cold ash hopper wind 20 is mainly used for strengthening classified combustion and the lower layer classified type of cold ash hopper wind 22 is used for preventing the cold ash hopper 8 from overheating, the second kind of classified organization way is the lower wind leading mode that the upper layer classified type of cold ash hopper wind 20 is used for strengthening classified combustion and the lower layer classified type of cold ash hopper wind 22 is mainly used for preventing the cold ash hopper 8 from overheating, the third kind of classified organization way is the equal mode between the upper wind leading mode and the lower wind leading mode; when the upper wind leading mode is adopted, the volume ratio of the upper layer classified type of cold ash hopper wind 20 in the total cold ash hopper 8 wind formed by the upper and lower layer classified type of cold ash hopper wind 20 and 22 is 60-80%; when the lower wind leading mode is adopted, the volume ratio of the upper and lower layer classified type of cold ash hopper wind 20 and 22 is 4:6; when the equal mode is adopted, the volume ratio of the upper and lower layer classified type of cold ash hopper wind 20 and 22 is 5:5.

[0030] In this embodiment, the upper wind leading mode needs to adopt large upper cold ash hopper wind nozzle 19 and high nozzle wind speed in order to give consideration to the roles of coke combustion and lifting the downward main flame, and is suitable for W flame furnace with large lower hearth 5 and cold ash hopper 8 and short and small upper hearth 6, the lower wind leading mode is suitable for W flame furnace with small lower hearth 5 and cold ash hopper 8 and tall and thin upper hearth 6, and the equal mode is suitable for W flame furnace with moderate space of lower hearth 5 and cold ash hopper 8. In actual application, according to the hearth structure characteristics and the designed main flame downward depth, the three kinds of classified organization ways are reasonably selected in order to give consideration to coke combustion and prevent the cold ash hopper 8 from overheating.

[0031] In order to verify the performance of the symmetrical combustion W flame furnace with high burnout, low slagging, ultra-low nitrogen and ash hopper overheating prevention of the present application, the symmetrical combustion W flame furnace with high burnout, low slagging, ultra-low nitrogen and ash hopper overheating prevention of the present application is compared with two existing W flame furnaces, wherein the hearth structure, combustion system and furnace inner deflection flow field of the existing front and back wall leading W flame furnace of the mainstream technology are shown in Figure 3 , the main view of the hearth structure and combustion system arrangement of the existing side wall leading symmetrical combustion low-nitrogen high-efficiency burnout W flame furnace disclosed in "Document two" is shown in Figure 4 , the A-direction side view of the hearth structure and combustion system of the existing side wall leading symmetrical combustion low-nitrogen high-efficiency burnout W flame furnace disclosed in "Document two" is shown in Figure 4 , and the B-direction side view of the hearth structure and combustion system of the existing side wall leading symmetrical combustion low-nitrogen high-efficiency burnout W flame furnace disclosed in "Document two" is shown in Figure 5 .

[0032] The existing front and back wall leading W flame furnace of the mainstream technology (such as Figure 3The front and rear arches 1' and 2' are symmetrically arranged along the furnace center line 1-1' and the main burners 3' are arranged in rows on the front and rear arches 1' and 2' for the front and rear wall sides to give the main pulverized coal gas streams 12a' and 12b'. The exhaust gas injection ports 4' are symmetrically arranged on the front and rear arches 1' and 2' and close to the intersection of the lower furnace 8' and the upper furnace 9' (referred to as the throat) for the dense and thin combustion of the exhaust gas (also referred to as the thin pulverized coal gas stream). The primary air 13a' and 13b' is symmetrically introduced from the lower part of the front wall 5' and the rear wall 6' respectively. According to the design concept, the front and rear wall side main pulverized coal gas streams 12a' and 12b' and the primary air 13a' and 13b' should be mixed in the upper part of the cold ash bucket 7' and then turned up to form two symmetric U-shaped flames that converge in the center of the furnace to form a symmetric W-shaped flow field. However, as described in the background, due to the guiding effect of the asymmetric structure of the upper furnace and the closer distance between the main pulverized coal gas stream 12b' under the rear arch 2' and the furnace outlet 11', the main pulverized coal gas stream 12b' under the rear arch 2' is more likely to turn up early and has a short travel distance, resulting in a skewed flow field 14' with a longer front and a shorter rear and a whole flow field skewed to the front wall side. Under the action of the skewed flow field 14', a small and strong recirculation zone is formed in the lower part of the rear arch 2', while the recirculation zone in the lower part of the front arch 1' is skewed and weak. The strong recirculation zone on the rear wall side entrains the high-temperature flue gas in the center of the furnace to heat the main pulverized coal gas stream 12b' on this side, and the main pulverized coal gas stream 12b' itself tends to flow downward to the high-temperature center of the furnace due to the skewed flow field, thereby resulting in good combustion and high temperature on the rear wall side, which generates more local high-temperature zones that promote the formation of thermal NOx and aggravates the slagging on this side of the furnace wall. On the contrary, the weak recirculation zone on the front wall side has little effect on promoting the main pulverized coal gas stream 12a' on this side, and the main pulverized coal gas stream 12a' on the front wall side mainly flows downward in the low-temperature region near the front wall due to the suppression of the skewed upward flow, thereby resulting in poor combustion on the front wall side and ultimately leading to poor burnout of the boiler. Thus, the asymmetric combustion in the furnace corresponding to the skewed flow field 14' is characterized by a weak front and a strong rear, and at the same time, the high-temperature and strong recirculation flue gas flowing to the burner region collides with the exhaust gas jet of the exhaust gas injection port 4' on this side, and the exhaust gas is relatively weak, which leads to two problems, one is that the fine coal powder carried by the exhaust gas burns in the high-temperature and oxygen-rich atmosphere to generate a large amount of fuel-type NOx, and the other is that the fine coal powder particles carried by the exhaust gas are softened and precipitated in the arch region around the exhaust gas injection port 4' due to the impact of the strong recirculation flue gas, resulting in serious slagging in the arch region near the throat. Thus, the front and rear wall leading W-flame furnace of the existing mainstream technology has the problems of severe asymmetric combustion, poor burnout, high NOx emission and serious slagging as described in the background.

[0033] To address the problems of severely asymmetrical combustion, poor burnout, high NOx emissions, and severe slagging in existing mainstream W-flame furnaces dominated by the front and rear walls, the existing technology of low-NOx, high-efficiency burnout W-flame furnaces with side-wall dominated symmetrical combustion (i.e., "Document Two" mentioned in the background technology, such as...) Figure 4 and Figure 5 As shown, the two protruding furnace arches 3 (i.e., left furnace arch 3a" and right furnace arch 3b") of the lower furnace 1” are respectively arranged on the left wall 4” side and the right wall 5” side. In this way, the longitudinal section of the furnace where the two symmetrical main pulverized coal airflows 16” of the main burners 11” of the left and right furnace arches are located is perpendicular to the flue gas flow direction of the furnace outlet 10”. The distances from the two symmetrical downward pulverized coal airflows 16” to the furnace outlet 10” are equal. The asymmetric structural effect of the upper furnace 2” (i.e., the flame deflector angle 9” and the furnace outlet 10” being located on the rear wall 7”) acts symmetrically on the two U-shaped torches on the left and right walls, fundamentally eliminating the main cause of flow field deviation in "Document 1" that is "guided by the asymmetric structural effect of the upper furnace + the main pulverized coal airflow 12b' on the rear wall side is closer to the upper furnace outlet 11' and rises earlier". Figure 3 This results in a symmetrical W-shaped flame 18” forming on the longitudinal section of the furnace along the furnace width, which improves the combustion of the main pulverized coal airflow 16” on both the left and right walls and significantly reduces local high-temperature zones. This is beneficial for improving burnout, reducing NOx emissions, and controlling slagging in the main combustion zone of the lower furnace 1”. In terms of strengthening the air classification in the furnace to reduce NOx emissions, "Document Two" sets up classification air nozzles 12” on the lower part of the left wall 4” and right wall 5” of the lower furnace 1”, and a burnout air nozzle 13” at the intersection of the lower furnace 1” and the upper furnace 2” (called the throat) to introduce classification air 17” and throat burnout air 20” respectively. Since classification air 17” is close to the downward main pulverized coal airflow 16” and throat burnout air 20” is close to the upward flue gas in the upper furnace 2”, a better mixing effect can be achieved, which helps to achieve efficient and low-NOx combustion. To (i) reduce the tendency of the W-shaped flame 18” perpendicular to the furnace depth profile to tilt towards the rear wall 7” due to the guiding effect of the furnace outlet 10”, (ii) avoid severe slagging in the near throat area caused by the exhaust gas arrangement, and (iii) further enhance air classification, "Document Two" arranges exhaust gas nozzles 14” in the middle of the front and rear walls of the lower furnace 1” and wall burnout air nozzles 15” in the lower part of the front and rear walls of the upper furnace 2” to counteract the intake exhaust gas 19” and wall burnout air 21”. Figure 5). Although the hedging effect of the weak gas 19" and the wall part burnout wind 21" can effectively reduce the inclination of the W-shaped flame 18" to the rear wall 7", the weak gas 19" and the wall part burnout wind 21" cannot be well mixed with the main flame and the upward main flue gas flow due to the small amount of wind and the far distance from the main flame and the upward main flue gas flow in the central area of the furnace depth direction, resulting in poor burnout of fine coal powder carried by the weak gas 19", low utilization of the wall part burnout wind 21", and affecting the low NOx combustion effect and burnout. In addition, due to the significant strengthening of air staging in "Document Two", the oxygen-poor atmosphere in the lower hearth 1" is strengthened, the combustion is delayed, and the downward flame travels deep into the middle and lower part of the cold ash bucket 8". In the case of strong assistance of the staged air 17" for coke combustion, the cold ash bucket 8" has overheating and thermal fatigue problems. It can be seen that "Document Two" has better solved the problems of asymmetric combustion and slagging, but still has high NOx emission, poor weak gas burnout effect, and causes cold ash bucket overheating problem in actual application.

[0034] The high-burnout low-slagging, ultra-low-nitrogen and anti-ash-bucket-overheating symmetrical combustion W-flame furnace of the present application Figure 1 and Figure 2 ), compared with the above-mentioned existing mainstream technology of front and rear wall leading W-flame furnace and "Document Two" of side wall leading symmetrical combustion low-nitrogen high-efficiency burnout W-flame furnace, on the basis of still adopting side wall leading W-flame to build symmetrical combustion, with the help of greatly moving up the side wall staged air, canceling the original arch part weak gas (or front and rear wall weak gas) and setting up side wall light coal powder flue gas flow to organize flue gas recirculation and coal powder reburning, introducing staged type cold ash bucket wind to strengthen air staging and protect cold ash bucket, etc., the problems of "Document Two" of side wall leading symmetrical combustion low-nitrogen high-efficiency burnout W-flame furnace are solved, that is, "high NOx emission, poor weak gas burnout and cold ash bucket overheating". In addition to the conventional construction of symmetrical combustion, the following will be described from four aspects of ultra-low NOx generation, strengthening burnout, reducing slagging and preventing cold ash bucket overheating:

[0035] 1) Ultra-low NOx generation. Firstly, the present invention still adopts the side wall dominated W-flame to construct symmetrical combustion, which has good combustion stability and significantly reduces local high temperature zone, thus controlling the thermal NOx generation; secondly, compared with the two-stage staged combustion constructed by the staged air 17" and the overfire air 20" in "Document Two", the present invention further reduces the secondary air of the main burner 11 and additionally sets the upper layer cold ash hopper nozzle 19 and the lower layer cold ash hopper nozzle 21 at the corner and the middle-upper part of the cold ash hopper 8, respectively, to construct the three-stage staged combustion formed by the staged air 16, the upper layer staged type cold ash hopper air 20 and the lower layer staged type cold ash hopper air 22, which on the one hand significantly strengthens the oxygen-poor atmosphere in the early stage of combustion under the furnace arch to greatly inhibit the fuel NOx generation, and on the other hand, by strengthening the deep air staging condition in the furnace, the combustion intensity in the main combustion zone is inhibited, thus further inhibiting the thermal NOx generation; thirdly, the main pulverized coal gas flow 15 mixes with the staged air 16 in the main combustion zone, and after intense combustion, enters the fine pulverized coal reburning zone corresponding to the pulverized coal reburning nozzle 17, and the dilute pulverized coal flue gas flow 18 using the reducing property of the pulverized coal particles in the upper stream main flame reduces the NOx generated in the upstream main flame into N2, thus further reducing the NOx emission in the furnace, although the residual coke in the downstream mixes and burns with the two layers of cold ash hopper air, i.e. the upper layer staged type cold ash hopper air 20 and the lower layer staged type cold ash hopper air 22, and the overfire air 14, but there is little new thermal NOx generation due to the small combustion share and low temperature; finally, the "Document Two" has the flue gas 19" which is injected into the high temperature zone in the lower part of the lower furnace 1" through the flue gas nozzle 14" and the front wall 6" and the back wall 7", and the dilute pulverized coal concentration and high oxygen environment are conducive to the generation of fuel NOx, while the present invention cancels the flue gas setting and instead introduces the dilute pulverized coal flue gas flow 18 into the pulverized coal reburning nozzle 17, which not only avoids the fuel NOx generation caused by the combustion of the flue gas 19" in "Document Two", but also uses the fine pulverized coal in the dilute pulverized coal flue gas flow 18 to reburn and reduce NOx. Therefore, the W-flame furnace in the present invention achieves ultra-low NOx combustion effect through (i) constructing symmetrical combustion to reduce local high temperature zone, (ii) further reducing the air supply of the main burner 11 to significantly strengthen the oxygen-poor atmosphere under the arch, (iii) adding the two layers of cold ash hopper air, i.e. the upper layer staged type cold ash hopper air 20 and the lower layer staged type cold ash hopper air 22, to strengthen air staging, (iv) introducing the dilute pulverized coal flue gas flow 18 into the pulverized coal reburning nozzle 17 to reburn and reduce NOx, and (v) no fuel NOx generated by the combustion of the aforementioned flue gas.

[0036] 2) Strengthen the burnout. First, the side wall of the invention is built to dominate the symmetrical combustion, avoiding the poor burnout problem caused by the unsymmetrical combustion of the existing mainstream technology W-flame furnace dominated by the front and back walls. Second, in the long flame path from the main combustion zone (only staged air 17" for combustion support) to the burnout zone (throat burnout air 20" for combustion support), there is no other combustion-supporting air input, and the flame turns up and burns weakly, resulting in poor burnout. The invention, on the one hand, gradually inputs staged air 16, light coal powder flue gas stream 18, upper layer staged type cold ash hopper air 20 and lower layer staged type cold ash hopper air 22 along the downward flame, which strengthens the lateral pushing effect of the left and right wall jets on the main coal powder gas stream 15 and makes it slightly closer to the high-temperature furnace center line 1-1 side, at the same time, this change reduces the space between the downward main coal powder gas stream 15 and the furnace center line 1-1, and further strengthens the backflow area under the arch. These two changes are helpful to the burnout of the main coal powder gas stream, on the other hand, with the upward movement of the staged air 16, the main combustion zone moves upward first, and then in the downstream, it goes through the re-burning reduction, combustion support and strong disturbance and mixing of the air and powder brought by the light coal powder flue gas stream 18, the upper layer staged type cold ash hopper air 20 and the lower layer staged type cold ash hopper air 22, which also strengthens the burnout effect of the main coal powder gas stream. Finally, as mentioned earlier, the flue gas 19" and the wall burnout air 21" arranged in the front and back walls of "Document Two" cannot mix well with the downward main flame and upward main flue gas stream due to their small air volume / weak rigidity and far distance from the center area of the furnace depth direction, resulting in poor burnout of the fine coal powder carried by the flue gas 19", low utilization of the wall burnout air 21" and poor burnout of the residual coke in the upper furnace 2". In comparison, the invention does not have such flue gas and wall burnout air settings, only burnout air 14 is arranged in the left and right walls at the throat, and the flue gas is changed into light coal powder flue gas stream 18 from the lower part of the left and right walls of the lower furnace 5 as coal powder re-burning input, so there is no problem such as poor burnout of flue gas 19" and poor burnout of coke in the upper furnace 2" in "Document Two". In summary, the invention has obvious effect in strengthening the burnout compared with the existing technology.

[0037] 3) Reduce slagging. First, the side wall of the invention is dominated by symmetrical combustion with good combustion stability and uniform heat load distribution on the left and right walls, avoiding the high-temperature strong slagging environment on the side with good combustion in the existing mainstream technology of front and back wall dominated W flame furnace; Second, as mentioned earlier, the existing mainstream technology of front and back wall dominated W flame furnace causes severe slagging in the arch near the throat area due to the arrangement of the exhaust gas nozzle 4' near the throat, and the front and back wall of "Document Two" is also prone to slagging in the high-temperature wall surface area around the exhaust gas nozzle 14' near the front and back wall of the lower hearth 1" due to its small wind volume / weak rigidity and far distance from the center area of the furnace depth direction. The invention completely gives up the above two exhaust gas arrangement methods and instead changes the exhaust gas into a dilute coal powder flue gas stream 18 and feeds it into the left and right walls of the lower hearth 5 as a coal powder reburning, which is close to the continuously decaying downward main coal powder gas stream 15 and easy to mix and react, so the invention has no problem of slagging in the arch near the throat and the high-temperature area of the front and back wall caused by the exhaust gas. Finally, the invention feeds the staged air 16, the dilute coal powder flue gas stream 18, the upper layered type cold ash hopper air 20 and the lower layered type cold ash hopper air 22 into the left and right walls along the flame downward, and under the transverse pushing action of these jets, the distance between the downward main coal powder gas stream 15 and the left and right walls increases, and these jets also have a certain protective effect on the wall surface of the left and right walls and the cold ash hopper 8, which avoids the slagging of the left and right walls and the cold ash hopper 8. In summary, the invention is more effective than the existing technology in controlling the slagging in the furnace.

[0038] 4) Preventing the cold ash bucket from overheating. Compared with "Document Two", the present application shortens the downward flame stroke and controls the near-wall area smoke temperature of the cold ash bucket 8 by three measures to prevent the cold ash bucket from overheating: first, to strengthen the air staging in the furnace, the upper staging type cold ash bucket air 20 and the lower staging type cold ash bucket air 22 are added and the secondary air volume of the main burner 11 is reduced, which essentially reduces the dome air momentum and shortens the downward stroke of the main pulverized coal gas flow 15, and the interception effect of the staging air 16 moved upward to organize the pulverized coal reburning on the downward flame is strengthened, so that the downward stroke of the main pulverized coal gas flow 15 is shortened; second, as described above, under the transverse pushing action of the multiple jets of the staging air 16, the dilute pulverized coal flue gas flow 18, the upper staging type cold ash bucket air 20 and the lower staging type cold ash bucket air 22, the main pulverized coal gas flow 15 gradually moves away from the left and right walls downward, so that the high-temperature flame in the cold ash bucket 8 is far away from the left and right side walls, which helps to prevent the cold ash bucket wall from overheating; finally, the present application adopts a unique upper and lower two-layer staging type cold ash bucket air setting, the downward upper staging type cold ash bucket air 20 mainly plays a role in strengthening air staging and promoting coke combustion, and the horizontal or slightly downward lower staging type cold ash bucket air 22 aims to intercept the downward main flame to avoid it from falling too deep, at the same time, under the suppression of the downward main flame, part of the air in the upper staging type cold ash bucket air 20 and the lower staging type cold ash bucket air 22 adheres to the left and right walls of the cold ash bucket 8 to form a layer of strong air film, thereby effectively protecting the cold ash bucket wall and preventing it from overheating.

[0039] In summary, the symmetrical combustion W-flame furnace of the present application with high burnout, low slagging, ultra-low nitrogen and ash bucket overheating prevention can realize efficient burnout, significantly reduce NOx emissions, and avoid cold ash bucket overheating, and comprehensively solve the problems of asymmetric combustion, efficient burnout, significantly reduced NOx emissions, control of lower furnace slagging and prevention of ash bucket overheating caused by deep downward flame in the prior art W-flame furnace.

Claims

1. A symmetrical combustion W-flame furnace with high burnout, low slagging, ultra-low nitrogen and anti-dust hopper overheating, comprising a hearth body enclosed by a left wall, a right wall, a front wall and a rear wall, the hearth body is composed of a lower hearth and an upper hearth, the lower hearth is composed of a furnace arch part, a lower hearth main part and a cold ash hopper arranged in sequence from top to bottom, the furnace arch part comprises a left furnace arch and a right furnace arch symmetrically arranged on the left wall side and the right wall side, the lower hearth and the upper hearth are the same in the furnace depth direction, the size of the lower hearth main part in the furnace width direction is 1.8 to 2.2 times of the upper hearth, the upper part of the rear wall enclosing the upper hearth is provided with a refractory angle and a hearth outlet in the horizontal direction, characterized in that The left arch and the right arch are provided with a row of main burners for feeding a downwardly-inclined main pulverized coal jet, and a row of staged air nozzles, a row of pulverized coal reburning nozzles and a row of upper cold ash bucket air nozzles are symmetrically arranged on the left wall and the right wall of the lower hearth body part in sequence from top to bottom, the staged air nozzles are used for feeding a downwardly-inclined staged air to organize the first layer of air staged combustion, the row of pulverized coal reburning nozzles are used for feeding a weak pulverized coal flue gas which is strengthened by flue gas recirculation to form a lean oxygen atmosphere, so as to use the fine pulverized coal in the flue gas of the dense-lean combustion as reburning fuel, and the upper cold ash bucket air nozzles are used for feeding an upper staged cold ash bucket air to the cold ash bucket to promote the coke combustion from the upstream reburning zone to organize the second layer of air staged combustion, and a row of lower cold ash bucket air nozzles are symmetrically arranged on the left wall and the right wall of the cold ash bucket, which are used for feeding a lower staged cold ash bucket air to the cold ash bucket in a horizontal or downwardly-inclined manner to adjust the flame underflush depth and protect the cold ash bucket from overheating; A row of burnout air nozzles are symmetrically arranged on the left wall and the right wall along the furnace depth direction at the intersection of the lower hearth and the upper hearth, which are used for feeding a downwardly-inclined burnout air to the lower hearth to organize the third layer of air staged combustion; The upper staged cold ash bucket air and the lower staged cold ash bucket air have three kinds of staged organization modes, the first kind of staged organization mode is an upper air dominant mode in which the upper staged cold ash bucket air is mainly used to strengthen the staged combustion and the lower staged cold ash bucket air is used to prevent the cold ash bucket from overheating, the second kind of staged organization mode is a lower air dominant mode in which the lower staged cold ash bucket air is mainly used to prevent the cold ash bucket from overheating and the upper staged cold ash bucket air is used to strengthen the staged combustion, and the third kind of staged organization mode is an equal mode between the upper air dominant mode and the lower air dominant mode, when the upper air dominant mode is adopted, the volume ratio of the upper staged cold ash bucket air in the total cold ash bucket air formed by the upper staged cold ash bucket air and the lower staged cold ash bucket air is 60-80%, when the lower air dominant mode is adopted, the volume ratio of the upper staged cold ash bucket air to the lower staged cold ash bucket air is 4:6, and when the equal mode is adopted, the volume ratio of the upper staged cold ash bucket air to the lower staged cold ash bucket air is 5:

5.

2. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The row of main burners is located in the middle region of the two arches.

3. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The row of staged air nozzles is arranged at the middle upper region of the lower hearth body part.

4. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The row of pulverized coal reburning nozzles is arranged at the middle lower region of the lower hearth body part.

5. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The row of upper cold ash bucket air nozzles is arranged near the cold ash bucket of the lower hearth body part.

6. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The row of lower cold ash bucket air nozzles is arranged at the middle upper region of the cold ash bucket.

7. The symmetrically fired W-flame furnace with high burnout, low slagging, ultra-low NOx and anti-overheating of hopper according to claim 1, characterized in that The lean coal powder flue gas stream with flue gas recirculation enhanced lean oxygen atmosphere has multiple feeding modes, wherein the first feeding mode is direct feeding through the one-row coal powder reburning nozzle, the second feeding mode is direct mixing into the main coal powder gas stream through the one-row main burner, the third feeding mode is feeding through the one-row staged air nozzle, and the fourth feeding mode is a combination of any two or three of the above first, second and third feeding modes.

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