阅读说明：本技术 基于锅炉设计角度的防结渣方法 (Anti-slagging method based on boiler design angle ) 是由 刘彦鹏 高智溥 金安 赵天亮 于兴宝 丁浩植 段婕 李军强 于 2020-04-10 设计创作，主要内容包括：本发明涉及一种基于锅炉设计角度的防结渣方法,包括：选用能降低燃烧器区域温度水平,使炉内热负荷均匀并能保证煤粉在炉膛上部有足够的停留时间燃尽的各个炉膛热力参数,采用正方形或趋于正方形的大切角炉膛,选用合适的燃烧器型式和喷口布置方式,减小燃烧器假想切圆直径、燃烧器单只一次风喷口热功率及一、二次风动量比,使炉内有良好的空气动力工况,防止带粉气流偏斜冲墙。本发明提高了锅炉运行的安全性及可靠性。(The invention relates to a boiler design angle-based anti-slagging method, which comprises the following steps: the method selects thermal parameters of each hearth which can reduce the temperature level of a burner region, enable the thermal load in the furnace to be uniform and can ensure that pulverized coal is burnt out in enough residence time at the upper part of the hearth, adopts a square or large-tangential-angle hearth which tends to be square, selects a proper burner type and a proper nozzle arrangement mode, reduces the diameter of an imaginary tangent circle of the burner, the thermal power of a single primary air nozzle of the burner and the ratio of primary air momentum to secondary air momentum, enables the furnace to have good aerodynamic working condition, and prevents the pulverized coal-carrying airflow from obliquely rushing towards the wall. The invention improves the safety and reliability of the boiler operation.)

1. A slag preventing method based on a boiler design angle is characterized by comprising the following steps:

the method selects thermal parameters of each hearth which can reduce the temperature level of a burner region, enable the thermal load in the furnace to be uniform and can ensure that pulverized coal is burnt out in enough residence time at the upper part of the hearth, adopts a square or large-tangential-angle hearth which tends to be square, selects a proper burner type and a proper nozzle arrangement mode, reduces the diameter of an imaginary tangent circle of the burner, the thermal power of a single primary air nozzle of the burner and the ratio of primary air momentum to secondary air momentum, enables the furnace to have good aerodynamic working condition, and prevents the pulverized coal-carrying airflow from obliquely rushing towards the wall.

2. The boiler design angle-based slagging prevention method according to claim 1, specifically comprising:

for a boiler with high slag bonding property for designing coal types, a lower furnace section heat load, a combustor area wall heat load, a burnout area volume heat load and a furnace volume heat load are selected during boiler design;

selecting the heat load of the hearth volume according to the combustion condition of the pulverized coal in the furnace and the cooling condition of the flue gas, preventing slag bonding of a water-cooled wall and a screen area by selecting the heat load of the hearth volume with smaller size, expanding the application range of the fuel, increasing the residence time of the fuel in the furnace and being beneficial to complete combustion of the fuel;

expanding the actual tangent circle diameter to seven and eight times of the imaginary tangent circle diameter for the multi-layer arranged burner;

the burners are divided into two groups, and a distance delta H is reserved between the two groups, so that airflow flows from a fire-facing surface of jet flow at the outlet of the burner to a back-fire surface through the distance, the negative pressure at the position is reduced, the pressure difference at two sides of the jet flow is sharply reduced, and the deviation of the jet flow in the middle of the burner is reduced;

the upper group and the lower group of the burners are grouped to form relatively independent aerodynamic fields respectively, the diameters of actual tangent circles are correspondingly reduced after the burners are grouped, and the wall surface heat load of a burner region and the volume heat load of the burner region are reduced;

the height-width ratio of each group of grouped burners is set to be 3.5-5.0, the relative space distance delta H/b between the two groups of burners is more than 2, so that the airflow entering delta H from the fire-facing surface is larger than the airflow sucked by the upper jet flow and the lower jet flow, and part of the gas can enter the back fire surface from the fire-facing surface, thereby reducing the negative pressure of the back fire surface and avoiding wall sticking and slag bonding caused by serious deviation of the jet flow.

Technical Field

The invention belongs to the technical field of safe operation of thermal power plants, and particularly relates to a boiler design angle-based anti-slagging method.

Background

The slagging is mainly formed by that molten or partially molten particles carried in flue gas collide on a furnace wall, a water-cooled wall or a pipe to be cooled and solidified, the slagging is mainly in the form of viscous or molten precipitates, and coking is mainly on a radiation heating surface.

In recent years, in order to save fuel cost, many power plants in China burn a large amount of low-quality coal, especially high-sulfur and high-alkali coal, so that the phenomenon of boiler slagging is aggravated, and severe slagging can have adverse effects on the safety and the economical efficiency of boiler operation. Therefore, there is a need for a method of preventing slagging from the perspective of boiler design.

Disclosure of Invention

The invention aims to provide a slag preventing method based on a boiler design angle so as to guarantee the safety of boiler operation.

The invention provides a boiler design angle-based anti-slagging method, which comprises the following steps:

the method selects thermal parameters of each hearth which can reduce the temperature level of a burner region, enable the thermal load in the furnace to be uniform and can ensure that pulverized coal is burnt out in enough residence time at the upper part of the hearth, adopts a square or large-tangential-angle hearth which tends to be square, selects a proper burner type and a proper nozzle arrangement mode, reduces the diameter of an imaginary tangent circle of the burner, the thermal power of a single primary air nozzle of the burner and the ratio of primary air momentum to secondary air momentum, enables the furnace to have good aerodynamic working condition, and prevents the pulverized coal-carrying airflow from obliquely rushing towards the wall.

Further, the method specifically comprises:

for a boiler with high slag bonding property for designing coal types, a lower furnace section heat load, a combustor area wall heat load, a burnout area volume heat load and a furnace volume heat load are selected during boiler design;

selecting the heat load of the hearth volume according to the combustion condition of the pulverized coal in the furnace and the cooling condition of the flue gas, preventing slag bonding of a water-cooled wall and a screen area by selecting the heat load of the hearth volume with smaller size, expanding the application range of the fuel, increasing the residence time of the fuel in the furnace and being beneficial to complete combustion of the fuel;

expanding the actual tangent circle diameter to seven and eight times of the imaginary tangent circle diameter for the multi-layer arranged burner;

the burners are divided into two groups, and a distance delta H is reserved between the two groups, so that airflow flows from a fire-facing surface of jet flow at the outlet of the burner to a back-fire surface through the distance, the negative pressure at the position is reduced, the pressure difference at two sides of the jet flow is sharply reduced, and the deviation of the jet flow in the middle of the burner is reduced;

the upper group and the lower group of the burners are grouped to form relatively independent aerodynamic fields respectively, the diameters of actual tangent circles are correspondingly reduced after the burners are grouped, and the wall surface heat load of a burner region and the volume heat load of the burner region are reduced;

the height-width ratio of each group of grouped burners is set to be 3.5-5.0, the relative space distance delta H/b between the two groups of burners is more than 2, so that the airflow entering delta H from the fire-facing surface is larger than the airflow sucked by the upper jet flow and the lower jet flow, and part of the gas can enter the back fire surface from the fire-facing surface, thereby reducing the negative pressure of the back fire surface and avoiding wall sticking and slag bonding caused by serious deviation of the jet flow.

By means of the scheme, the safety and the reliability of boiler operation are improved through the anti-slagging method based on the design angle of the boiler.

The foregoing is a summary of the present invention, and in order to provide a clear understanding of the technical means of the present invention and to be implemented in accordance with the present specification, the following is a detailed description of the preferred embodiments of the present invention.

Detailed Description

The following examples are given to further illustrate the embodiments of the present invention. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

The embodiment provides a slag preventing method based on a boiler design angle, which comprises the following steps:

the method selects thermal parameters of each hearth which can reduce the temperature level of a burner region, enable the thermal load in the furnace to be uniform and can ensure that pulverized coal is burnt out in enough residence time at the upper part of the hearth, adopts a square or large-tangential-angle hearth which tends to be square, selects a proper burner type and a proper nozzle arrangement mode, reduces the diameter of an imaginary tangent circle of the burner, the thermal power of a single primary air nozzle of the burner and the ratio of primary air momentum to secondary air momentum, enables the furnace to have good aerodynamic working condition, and prevents the pulverized coal-carrying airflow from obliquely rushing towards the wall.

By the method for preventing coking by mixing and burning the inferior coal in the boiler, the safety and the reliability of the operation of the boiler can be improved.

The method specifically comprises the following steps:

for a boiler with high slag bonding property for designing coal types, a lower furnace section heat load, a combustor area wall heat load, a burnout area volume heat load and a furnace volume heat load are selected during boiler design;

selecting the heat load of the hearth volume according to the combustion condition of the pulverized coal in the furnace and the cooling condition of the flue gas, preventing slag bonding of a water-cooled wall and a screen area by selecting the heat load of the hearth volume with smaller size, expanding the application range of the fuel, increasing the residence time of the fuel in the furnace and being beneficial to complete combustion of the fuel;

expanding the actual tangent circle diameter to seven and eight times of the imaginary tangent circle diameter for the multi-layer arranged burner;

the burners are divided into two groups, and a distance delta H is reserved between the two groups, so that airflow flows from a fire-facing surface of jet flow at the outlet of the burner to a back-fire surface through the distance, the negative pressure at the position is reduced, the pressure difference at two sides of the jet flow is sharply reduced, and the deviation of the jet flow in the middle of the burner is reduced;

the upper group and the lower group of the burners are grouped to form relatively independent aerodynamic fields respectively, the diameters of actual tangent circles are correspondingly reduced after the burners are grouped, and the wall surface heat load of a burner region and the volume heat load of the burner region are reduced;

the height-width ratio of each group of grouped burners is set to be 3.5-5.0, the relative space distance delta H/b between the two groups of burners is more than 2, so that the airflow entering delta H from the fire-facing surface is larger than the airflow sucked by the upper jet flow and the lower jet flow, and part of the gas can enter the back fire surface from the fire-facing surface, thereby reducing the negative pressure of the back fire surface and avoiding wall sticking and slag bonding caused by serious deviation of the jet flow.

The present invention is described in further detail below.

1. Boiler boundary geometry and burner placement

The large-capacity boiler furnace is surrounded by membrane water-cooled walls and steam tube banks. The structural size of the hearth is measured according to the central line of the water-cooling or steam-cooling wall pipe.

The characteristic dimensions are illustrated below:

h, the height of the hearth, the distance from a slag discharge throat at the bottom of the hearth to the central line of a ceiling pipe of the hearth, unit, m;

w is the width of the hearth, the distance between the central lines of the water wall tubes on the left side wall and the right side wall, unit and m;

d, the depth of a hearth, the distance between the central lines of the front and rear wall water wall tubes, unit and m;

h1, height of burnout zone, which is vertical distance (screen type heating surface is generally not lower than the tip of the flame folding angle too much), unit, m, from the center line of the primary air coal powder nozzle of the burner at the uppermost layer (for example, a matched silo type pulverizing system, and the exhaust gas nozzle is above the primary air nozzle at the uppermost layer, and is the exhaust gas nozzle at the uppermost layer) to the tip of the flame folding angle (if a straight section is present, the upper folding point is obtained);

h 2-the vertical distance between the pulverized coal nozzle (or exhaust gas nozzle) of the uppermost burner and the pulverized coal nozzle of the lowermost burner, the height of the burner region, bits, m;

h3 vertical distance, unit, m, between the central line of the pulverized coal nozzle of the lowermost burner and the upper break point of the cold ash bucket;

h 4-the distance from the tip of the flare angle (if there is a straight section, i.e., the upper break point) vertically upward to the centerline of the ceiling tube, in m;

h5, the height of the cold ash bucket, namely the height from the slag discharge port to the upper break point, unit, m of the cold ash bucket;

dl-depth of the dog-ear angle, unit, m;

d 2-the throat depth of slag discharge, unit, m;

α -flare angle downtilt;

beta-included angle between slope of ash cooling bucket and horizontal plane.

V-effective volume of furnace, m³；

F_CCross-sectional area of furnace space in burner zone, m²；

F_C＝W×D；

F_BBurner zone wall area, m²；

FB＝2(W+D)(h2+3)

Where 3 is the hypothetical increase in burner zone height over h2, m;

V_mvolume of burnout zone of furnace hearth, m³；

V_m＝W×D×h1。

Wherein, the volume occupied by the furnace chamber flame folding angle does not need to be deducted.

2. Characteristic parameters of pulverized coal combustion furnace

(1) Rated boiler output, BRL (BoilerRated load)

Under the conditions of rated steam parameters and feed water temperature, the boiler output thermal power (MW) matched with the TRL (turbo rated load) working condition of the turbo generator set is also commonly expressed by the main steam flow (t/h) under the working condition, so the rated evaporation capacity of the boiler is also realized. The main steam flow of the TRL working condition is the same as the main steam flow of the Maximum Continuous output TMCR (turbine Maximum Continuous output rating) working condition of the steam turbine generator unit. The BRL working condition is in a load region with the highest boiler thermal efficiency, and is usually a boiler thermal efficiency guarantee working condition.

(2) Maximum Continuous boiler output, BMCR (DoilerMaximum Continuous rating)

The maximum continuous output thermal power (MW) of a boiler specified for matching with the design flow working condition of a steam turbine set is also conventionally expressed by the main steam flow (t/h) under the working condition, and BMCR is a design guarantee value of the boiler. Under this condition, the hearth should not have a severe or high slagging tendency.

Boiler input thermal power, P, MW:

P＝B(1-L_UBC/100)×Q_net.ar

in the formula:

designing coal consumption in kg/s under the working condition of B-BMCR;

L_UBCheat loss from unburned carbon in BMCR operation,％；

Q_net.ardesigning the low calorific value of the fire coal, MJ/kg.

(3) Heat release intensity of furnace volume, q_V，kW/m³

The heat release intensity of the hearth volume is the ratio of the boiler input heat power to the effective hearth volume, namely:

q_V＝(P/V)×10³

the heat release intensity of the furnace volume basically reflects the residence time of fuel and combustion products in the furnace under the conditions of flow field and temperature field in the furnace. Under the condition of given P, q_VThe smaller the furnace chamber volume, the longer the residence time, the more beneficial the coal powder is to burn out, and the less the possibility of slag bonding in the furnace chamber.

(4) Intensity of heat release of hearth section, q_F，MW/m²

The heat release intensity of the furnace section is the ratio of the input heat power of the boiler to the cross-sectional area of the burner zone

q_F＝(P/F_C)

The heat release intensity of the hearth section reflects the average flow velocity of combustion products on the horizontal section of the hearth.

Under the condition of given P, q_FThe smaller the cross-sectional mean flow velocity, the lower the turbulence pulsation and mixing conditions of the gas-powder flow may be, which may affect the combustion strength and ignition stability, but the longer the residence time in the high temperature zone, which is also beneficial to reduce the slag bonding and high temperature corrosion on the surface of the water wall.

(5) Heat release strength of burner zone wall, q_B，MW/m²

The heat release intensity of the wall surface of the burner area is the ratio of the boiler input heat power to the area of the wall surface of the burner area, namely:

qB＝(P/F_B)

the heat release intensity of the wall surface of the burner zone can reflect the flame temperature level of the combustion center in the furnace to a certain extent. q. q.s_BThe smaller, the lower the temperature level of the zone; the relatively larger burner region space and lower temperature levels are beneficial in mitigating the tendency of the walls in that region to slag.

(6) Volumetric heat release intensity of burnout zone, q_m，kW/m³

The volume heat release intensity of the burnout zone is the ratio of the boiler input thermal power to the volume of the hearth of the burnout zone, namely:

q_m＝(P/V_m)×10³

the volume heat release intensity of the burnout area basically reflects the shortest possible retention time of the pulverized coal sprayed from the nozzle at the uppermost layer in the furnace. q. q.s_mThe smaller the coal powder stays in the hearth for the longer the coal powder stays in the hearth, the more the burnout of the coal powder jet flow of the layer can be ensured, the lower the local smoke temperature at the inlet of the screen area is facilitated, and the higher the pollution and slagging tendency of the hearth is reduced.

3. Correlation and value of hearth characteristic parameters

For a newly designed boiler, if the slag bonding property of the designed coal is strong, a lower hearth section heat load q is selected during the design of the boiler_FBurner zone wall surface thermal load q_BVolumetric heat load q in burnout zone_mAnd furnace volume heat load q_V。

q_FThe heat release strength of combustion on the unit section of the burner area is shown, and the heat release strength influences the slagging tendency of the water wall of the burner area and the ignition stability of pulverized coal. q. q.s_FLarge value, high temperature level in burner region, small furnace section, crowded flame, easy adherence of pulverized coal airflow to wash water-cooled wall, high possibility of slag bonding, obvious effect in boiler below 100MW, and good effect on boiler above 100MW_FThe increasing trend of (a) is gradually gentle. Medium and small capacity boilers, q_FThe value is relatively large and is generally not q_FUsed as the check slagging index. For boilers with more than 100MW, because the ratio of the radiant heating surface of the hearth to the volume of the hearth is reduced along with the increase of the capacity of the boiler, the large-capacity boiler always has higher temperature level of the hearth, and in addition, the thickness of the effective radiant layer of the flame in the boiler is increased, the blackness of the flame is increased, the heat transfer is enhanced, the temperature level in the boiler is promoted to be higher, and the possibility of slag bonding is higher. For a newly designed boiler with strong coal slag bonding, the lower limit in table 1 can be selected.

TABLE 1 furnace section Heat load q_F(MW/m²) Recommended value

Surface notes that ① takes the lower limit for lignite and easy-to-slag coal, ② takes the upper limit for natural gas, ③ open-type and semi-open-type liquid slag-off furnace q_F＝(2.9～4.65)MW/m²④ total q in multi-layer arrangement of burners_FHigher than in the single layer arrangement.

Burner zone wall heat load q_B. Representing the temperature level and heat transfer characteristics of the burner region in the furnace, q_BIs an important parameter for preventing slag bonding and ensuring the ignition and complete combustion of the pulverized coal, if the slag bonding is a main contradiction, the q should be reduced firstly_BThe value is obtained.

Combustor area volumetric heat load q_BVPhysical significance of (1) and q_B. The same is true. When designing a coal-fired boiler with high slag bonding property, q is_BAnd q is_BVThe lower limit in table 2 should be selected. The burner region, e.g. covered with a partial refractory band, pair q_BAnd q is_BVThe value will increase, calculating q_BAnd q is_BVThe influence of the contamination coefficient of the guard burning zone must be considered.

TABLE 2 q_BAnd q is_BVRecommended value

Volumetric heat load q of furnace_VThe heat release of the fuel per hour, expressed in terms of unit volume of the furnace, which reflects the residence time of the fuel in the furnace, also directly affects the temperature level in the furnace. q. q.s_VThe value principal show is selected according to the combustion (burnout) condition of pulverized coal in the furnace and the cooling condition of flue gas, q_VThe value is selected to be higher, the volume of the hearth is reduced, and the temperature level of the whole hearth is improved. Choose to useSmaller q_VThe value can not only prevent the water wall and the screen area from slagging, but also enlarge the application range of the fuel, increase the residence time of the fuel in the furnace and be beneficial to the complete combustion of the fuel. For q_FA certain furnace chamber, selected q_VThe value of the flame vertical height h1 from the central line of the primary air (or tertiary air) nozzle at the top to the lower edge of the platen superheater can meet the requirement of pulverized coal burnout.

In order to prevent slag bonding in the screen area, h1 is about 1.35 (furnace width + furnace depth)/2 for a 200MW boiler which uses anthracite and hot air to supply powder with tertiary air; the 300MW and 600MW boilers hl of the drying agent powder feeding direct-blowing system for bituminous coal are (1.2-1.4) (furnace width + furnace depth)/2. The h1 values selected for the boiler design are shown in Table 3. For the design coal with strong slag bonding property and the heat load q of the furnace volume_vSelected according to the recommended lower limit in table 4.

TABLE 3 h1 values selected for boiler design

TABLE 4 furnace volumetric Heat load q_V(MW/m³) Recommended value

4. Selecting smaller burner imaginary tangent circle diameter

The central line of each angle burner nozzle of the tangential firing pulverized coal boiler is tangent to the geometric center in the furnace with the diameter d_jxIs an imaginary tangent circle of the tangentially fired pulverized coal boiler. Many characteristics of the power field in the boiler depend on the size and the caps of the imaginary tangent circle. When the boiler is actually operated, a strong air ring diameter or an actual tangent circle diameter d is formed in the boiler_yIs much larger than the diameter d of the imaginary circle of tangency_jx。d_yDiameter d of the imaginary circle of tangency in the normal wind speed range_jxIs obviously increased mainly due to the primary and secondary air jetsThe deflection of the stream, the main causes of the jet deflection are:

1) the jet entrains the differential pressure formed by the air flow on both sides to cause the jet to deflect. The long and narrow direct-current combustors are arranged at four corners at a certain angle, an included angle alpha 1 between each long and narrow direct-current combustor and the front wall is an included angle alpha 2 between each long and narrow direct-current combustor and the side wall, high-temperature flue gas on two sides is continuously sucked after jet flow is sprayed out, and negative pressure and supplementary air flow are formed because the flue gas on the two sides is sucked and carried away by the jet flow. Because of the general condition of alpha 1> alpha 2, the free space near the front wall is large, the air supplement condition is good, the air supplement flow resistance is small, and the pressure is higher; on the side wall, due to the small angle alpha 2 and the poor air supply condition, the pressure difference delta p acting on two side faces of the jet flow is formed when the pressure is low, so that the jet flow deflects. Typically, the burners are located at four corners of the furnace, α 1+ α 2 ═ 90 °, and the relevant data indicates that the jet differential pressure increases only sharply at α 2<30 °. When alpha 2 is greater than 30 degrees, the differential pressure between two sides of jet flow is not large (when the jet flow speed is 25 m/s, delta p is less than 7 Pa).

2) For example, when the impact velocity of the jet flow at the adjacent angle is 15 m/s, the impact dynamic pressure at the temperature in the furnace reaches 22.5-23.5 Pa, which is several times of the differential pressure formed by unequal included angles at two sides of the jet flow, so that the impact of the air flow at the adjacent angle on the jet flow action point has a great influence on the deflection track of the jet flow_yThe larger. Although the jet flow deflection is not large due to the difference of air supply conditions caused by different included angles, the imaginary tangent circle is enlarged as a result, the intersection point of the airflow of the adjacent angles is moved forward, and the diameter of the actual tangent circle is increased more under the combined action of the two factors.

3) Influence of the direct-flow burner structure on the jet deflection. The main influencing parameter is the height-width ratio of the direct-current combustor, and the high-width ratio indicates that the combustor is thin and high and has poor deflection resistance.

Expansion is typically three or four times for single layer combustors; for the multilayer burner, the flow rate is increased due to the fact that the airflow at the upper layer is continuously sucked to the lower layer, so that the diameter of the vortex is increased. The estimation calculation is typically performed using the following empirical formula:

in the formula: z is the number of layers of the burner; b is the burner nozzle width; k is the test constant, varying with the Z value, see Table 5.

TABLE 5 test constants K

In the hot state, the actual tangent diameter d of the hot state for the multi-layer burner_yrIs a function of parameters such as the number of layers of the combustor, the width of the nozzle, the diameter of an imaginary tangent circle of the combustor, the momentum ratio of primary air to secondary air, the distance between the nozzles, the total height-width ratio of the combustor and the like. The hot pulverized coal airflow is ignited and combusted in the furnace, the temperature is raised, the volume of the flue gas is expanded, the viscosity of hot flue gas is higher, the attenuation of the hot tangential speed is faster than that of the cold state, the rotation degree of the airflow in the furnace is weaker than that of the cold state, the amount of the flue gas is increased from a lower-layer nozzle to an upper-layer nozzle, the flow is increased, and the diameter of a vortex is correspondingly increased. Therefore, the real actual tangent circle of the thermal state in the thermal state actual cutting hearth is a core of the inverted cone-shaped vortex, namely the vortex has a large upper part and a small lower part, and the diameter of the vortex is continuously increased, so that the diameter of the imaginary tangent circle of the lower secondary air can be slightly larger than the diameter of the imaginary tangent circle of the upper secondary air and the imaginary tangent circle of the middle secondary air when some boilers are designed.

In order to prevent the high-temperature flue gas carrying pulverized coal from deflecting and wall-impacting to cause slag bonding. The excessive tangent circle can increase the included angle difference of two sides of the outlet of the burner, the 'adsorption effect' of the jet flow at the outlet is intensified, and the possibility of flame deflection is high. In practice, a smaller burner imaginary tangent circle diameter d is preferably used for the coal with stronger slag bonding property. The two-side angle clamping difference Δ α may be expressed such that Δ α is 4 to 6 ° (a burner is disposed at a four-corner position). Certainly, the value d cannot be too small, the difference of the fullness degree of the hearth is prevented, the high-temperature flame set is arranged in the middle of the hearth, the temperature level around the hearth is low, and the ignition and stable combustion are not facilitated.

When the width-depth ratio of the hearth section is larger (W/D)>1.12), to ensure △ α ═ 4 to 6 °, the burner imaginary circle diameter d may be set to_yrThe design is a big and small circle (i.e. double circle) arrangement mode with one pair of angles being larger and the other pair of angles being smaller.

5. Burner grouping and spacing

The burners are divided into two groups, a certain distance is reserved between the two groups, airflow can flow from the fire-facing surface of the jet flow at the outlet of the burner to the back fire surface through the distance, so that negative pressure therein is reduced, the pressure difference at two sides of the jet flow is rapidly reduced, and the deviation of the jet flow in the middle of the burner is reduced (for the burner with a higher aspect ratio, the jet flow which is most prone to deflection is in the middle of the burner), the upper group and the lower group of burners can form relatively independent aerodynamic fields after grouping, the distance △ H can play a role in balancing the pressure difference at two sides of the wind-facing surface and the back wind surface of the airflow, the actual tangential diameter can be correspondingly reduced after grouping, and the thermal load q of the wall surface of the burner area can be reduced after_BAnd combustor area volumetric heat load q_BV。

Experience proves that: if the height-width ratio of each group of burners is 3.5-5.0 after grouping and the relative space distance delta H/b between the two groups of burners is more than 2, the air flow entering delta H from the fire-facing surface is larger than the air flow sucked by the upper jet flow and the lower jet flow, and part of air can enter the back fire surface from the fire-facing surface, so that the negative pressure of the back fire surface is reduced, and the phenomenon that the jet flows deviate seriously to cause wall sticking and slag bonding is avoided.

Once-through burners for bituminous coal-fired boilers are generally not grouped because:

1) the section of the hearth is close to a square shape, and a large cutting angle (the inclined edge is about 2000-2200mm) is adopted, so that the hearth is actually formed into an octagonal hearth, the 'air supplementing condition' at the two sides of the jet flow at the outlet of the nozzle is greatly improved, and the jet flow deflection caused by the pressure difference at the two sides of the jet flow entrainment is avoided.

2) The cross section from the primary air inlet nozzle pipeline to the secondary air outlet nozzle pipeline is properly reduced, and the air flow is contracted and accelerated. The secondary air inlet pipeline is provided with a guide plate, so that the secondary air outlet airflow is uniformly distributed, and the secondary air airflow does not deviate from the design direction. The vertical ribbed plate is also arranged at the straight section of the inlet of the primary air pulverized coal pipeline, so that the vortex generated when the pulverized coal air mixture flows through the elbow can be eliminated. The primary air nozzle outlet and the secondary air nozzle outlet are both provided with a plurality of horizontal and vertical partition plates, so that the non-uniformity of the air speed of the nozzle outlet section and the non-uniformity of the coal powder concentration distribution can be improved, and the good guiding effect on the outlet jet flow can be realized.

3) Because of adopting the direct-fired pulverizing system, if a 600MW boiler is provided with 6 medium-speed coal mills, only 5 boilers are needed to be put into operation when the maximum continuous output of the boiler is output, and one coal powder is reserved, namely, one layer of coal powder nozzle is always in the cut-off working condition. Likewise, a 300MW boiler has 5 medium speed mills, and 3 of them can be put into operation with full load, allowing two of them to be on standby. That is, two layers of pulverized coal nozzles are always in the stopping working condition, such as stopping the uppermost layer or the lowermost layer of pulverized coal nozzles, which is equivalent to reducing the height-to-width ratio of the whole group of burners; if the coal dust nozzle in the middle is cut off, the grouping effect is achieved.

4) The net spacing between the primary air nozzle and the secondary air nozzle is small, the periphery of the primary air nozzle is also provided with perimeter air of about 45m/s, and the mutual 'leading belt' action of the whole group of jet flow is strong.

6. Suitable primary and secondary air arrangement

Generally speaking, the primary wind speed W1 mainly ensures that the pulverized coal is stably ignited and is equivalent to the flame propagation speed, and simultaneously, the W1 is prevented from being too low, so that the pulverized coal pipeline is blocked; the secondary air speed W2 is mainly used for ensuring the diffusion mixed combustion of the air-powder airflow and the burnout of coke. One of the main reasons for the deflection of the primary air jet is that the inertia force F swept by the upstream adjacent angle is determined by the comprehensive momentum formed by mixing the upstream first, second and third air (for the powder making system of the exhaust gas powder conveying, no third air exists). Since the tertiary air is far from the primary air, the value of F is actually the combined momentum of the upstream primary air and the upstream secondary air. And the secondary wind amount is much larger than the primary wind amount.

The F value plays a main role in secondary wind momentum, and when the section of the hearth is fixed, the secondary wind momentum can be properly reduced and the primary wind momentum can be properly increased as long as the secondary wind range is enough to meet the combustion requirement. (without affecting the fire) the deflection of the primary wind jet will be improved. The value ranges of the primary and secondary air momentum ratios w2m2/w1m1 are shown in Table 6.

TABLE 6 Primary and secondary pneumatic M ratio value ranges

In a word, for the newly designed boiler, the main measure for preventing slagging is to select each hearth thermal parameter which can reduce the temperature level of the burner region, make the heat load in the boiler uniform and can ensure that the pulverized coal has enough residence time on the upper part of the hearth to burn out, adopt the square or large tangential angle hearth tending to the square, select the proper burner type and nozzle arrangement mode, reduce the assumed tangent circle diameter of the burner, the momentum ratio of primary air and secondary air, the thermal power of the single primary air nozzle of the burner, make the boiler have good aerodynamic working condition, prevent the pulverized coal-carrying airflow from obliquely rushing towards the wall.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.