A method for reducing slagging and fouling of high-temperature heating surfaces of boilers

Abstract

The present invention discloses a method for reducing slagging and fouling of high-temperature heating surfaces of boilers, which comprises the following steps: 1. Defining the position of the flue gas window at the furnace outlet; 2. Obtaining the basic coal quality parameters of the coal sample, including V daf , S t,ar , A d %, ST, coal ash component values (Fe2O3, CaO, MgO, Na2O, K2O), Cl ar ; 3. Determining the flue gas temperature at the furnace outlet according to the coal quality parameters of the steam coal; 4. Determining the flue gas temperature at the bottom of the platen according to the coal quality parameters of the steam coal. The method of the present invention is simple and fast, and is obtained through a large number of evaluations, researches and calculations on the matching of boiler design, fuel characteristics and boiler operation results. It has high engineering application value and can guide the design, operation optimization of pulverized coal boilers and the blending of fuels fed into the furnace. It can reduce the slagging and fouling of the platen superheater and the high-temperature heating surfaces of the horizontal flue, and improve the safety of boiler operation.

Description

Technical Field

[0001] The present invention relates to the technical field of the design and operation of pulverized coal fired boilers in power plants, and specifically relates to a method for reducing slagging and fouling of high-temperature heating surfaces of boilers, which is applicable to pulverized coal fired boilers with a П-shaped furnace layout using tangential combustion or wall-firing methods for burning anthracite, lean coal, bituminous coal, long-flame coal, and lignite. Background Art

[0002] When designing a boiler, the bottom platen gas temperature and the furnace outlet gas temperature are one of the key indicators in thermal calculations, which are related to the layout of boiler heating surfaces and furnace combustion. Reasonable bottom platen gas temperature and furnace outlet gas temperature should meet the boiler safety and economic indicators, which can not only ensure the reliability of the radiant heating surface operation, but also make the distribution of boiler radiant heat transfer and convective heat transfer conform to the economic principle. For pulverized coal fired boilers in power plants, if the bottom platen gas temperature and the furnace outlet gas temperature are too high, it will lead to serious slagging of the platen superheater and severe ash accumulation on the heating surfaces in the horizontal flue, affecting the safe and stable operation of the boiler. If the bottom platen gas temperature and the furnace outlet gas temperature are designed too low, it will increase the area of the heating surface, resulting in an increase in boiler cost. Currently, there is no relevant document clearly stipulating the selection principle of the bottom platen gas temperature of the boiler, and only the "DL / T / 831—2022 Guide for the Selection of Furnace Types of Large-Capacity Pulverized Coal Combustion Boilers" clearly stipulates the selection principle of the furnace outlet gas temperature. Specifically as follows:

[0003] Determination of the position of the furnace outlet smoke window (section):

[0004] (1) For boilers with a П-shaped layout, the furnace outlet smoke window (section) is generally specified in the imaginary plane formed by vertically extending upward from the tip of the re-entrant angle at the rear wall of the furnace until the ceiling tubes. The average clear distance between the platen plates of the platen heating surface arranged within the above imaginary plane (i.e., on the furnace side) should be greater than or equal to 457 mm; if it is less than 457 mm, then this platen area should be excluded from the effective volume of the furnace. For example, if the average clear distance of the platen (generally called the rear platen) arranged in front of the above imaginary plane is less than 457 mm, then at this time the furnace outlet smoke window should be moved to the front of this platen area.

[0005] If the average clear distance between the platen plates of the platen heating surface behind the above imaginary plane is greater than or equal to 457 mm, at this time the furnace outlet smoke window can be moved backward along the flue gas flow direction to the section where the average transverse clear distance between the tubes is less than 457 mm, but the farthest distance shall not exceed the section formed by the upward extension of the center line of the water-cooled wall tubes at the rear wall of the furnace.

[0006] Determination principle of the furnace outlet gas temperature:

[0007] The designed calculated gas temperature θ of the furnace outlet smoke window under the BMCR condition f 〃 should preferably be determined according to the coal ash deformation temperature, θ f〃≤(DT - 100)°C; however, if the difference between the ash softening temperature and the deformation temperature of the coal ash (ST - DT) ≤ 50°C, then θ should be taken. f 〃≤(ST - 150)°C.

[0008] Through the statistical analysis of a large number of boiler design data, according to the above principles, for the tangential combustion or wall - type combustion Π - shaped furnace layout of pulverized coal power boilers, part of the furnace outlet position is at the imaginary section formed by vertically extending upward from the tip of the retarding angle of the rear wall of the furnace to the ceiling tubes, and part is at the section formed by the upward extension of the center line of the water - cooled wall tubes on the rear wall of the furnace. The flue gas temperature deviation at these two positions can reach more than 100 degrees. According to this selection principle, it may lead to inappropriate selection of the flue gas temperature at the furnace outlet of some boilers, and serious slagging and fouling problems of the platen superheater and the heating surface in the horizontal flue also occur during the actual operation of some boilers. Summary of the Invention

[0009] In order to overcome the shortcomings of the above - mentioned existing technologies, the present invention provides a method for reducing slagging and fouling of high - temperature heating surfaces of boilers, which is applicable to pulverized coal power boilers with tangential combustion or wall - type combustion Π - shaped furnace layouts burning anthracite, lean coal, bituminous coal, long - flame coal, and lignite.

[0010] The present invention is implemented by the following technical solutions:

[0011] A method for reducing slagging and fouling of high - temperature heating surfaces of boilers includes the following steps:

[0012] The first step: For tangential or wall - type combustion boilers with a Π - shaped furnace layout, uniformly stipulate that the furnace outlet smoke window is the imaginary section formed by the upward extension of the center line of the water - cooled wall tubes on the rear wall of the furnace to the ceiling tubes and the horizontal flue.

[0013] The second step: Obtain the dry ash - free basis volatile matter V daf , %; total sulfur S t,ar , %; dry - basis ash content A d , %; ash softening temperature ST, °C; ash composition values, %; and chlorine Cl ar , % in the coal; the ash composition values include Fe2O3, CaO, MgO, Na2O, and K2O.

[0014] The third step: Determine whether the coal sample is a conventional coal type.

[0015] The fourth step: For conventional coal types, determine the upper limit value of the flue gas temperature t F at the furnace outlet and the upper limit value of the screen bottom flue gas temperature t P under the BMCR operating condition according to the preset principle; so that when the boiler is operating, the flue gas temperature t F at the furnace outlet and the screen bottom flue gas temperature t PDo not exceed the recommended upper limit value.

[0016] A further improvement of the present invention lies in that the method is applicable to pulverized coal-fired power boilers with a Π-shaped furnace layout for tangential combustion or wall-firing of anthracite, lean coal, bituminous coal, long-flame coal, or lignite.

[0017] A further improvement of the present invention lies in that in the third step, it is determined whether any of the following conditions exist for the coal quality parameters; if none of the following conditions exist, the coal sample is a conventional coal type; if any of the following conditions occur, the coal sample is an unconventional coal type: (1) S t,ar > 2.5%, (2) A d > 45%, (3) Na2O > 5%, (4) K2O in coal ash > 5%, (5) Na2O + K2O > 6%, (6) Fe2O3 > 20%, (7) the sum B of the contents of basic oxides in coal ash > 35%, B = CaO + MgO + Fe2O3 + K2O + Na2O, (8) Cl in coal ar > 0.2%.

[0018] A further improvement of the present invention lies in that in the fourth step, the determination method for the upper limit value of the flue gas temperature at the furnace outlet under the BMCR condition: F When Na2O in the coal ash ≤ 3% and K2O ≤ 4%, the flue gas temperature t at the furnace outlet under the BMCR condition is determined according to the following principles:

[0019] F :

[0020] ① When ST ≤ 1100 °C, t F ≤ 960 °C;

[0021] ② When 1100 °C < ST ≤ 1150 °C, t F ≤ 0.2 × ST + 740 °C;

[0022] ③ When 1150 °C < ST ≤ 1350 °C, t F ≤ 0.1 × ST + 855 °C;

[0023] ④ When 1350 °C < ST ≤ 1450 °C, t F ≤ 0.3 × ST + 585 °C;

[0024] ⑤ When ST > 1450 °C, t F < 1020 °C.

[0025] A further improvement of the present invention lies in that in the fourth step, the determination method for the upper limit value of the flue gas temperature t at the furnace outlet under the BMCR condition: When Na2O in the coal ash > 3% or K2O > 4%, the flue gas temperature t at the furnace outlet under the BMCR condition F ≤ 960 °C.​​

[0026] A further improvement of the present invention lies in that, in the fourth step, the bottom screen gas temperature t under BMCR conditions P Determination method of the upper limit value:

[0027] When Na2O ≤ 3% and K2O ≤ 4% in the coal ash, the bottom screen gas temperature t under BMCR conditions is determined according to the following principles P :

[0028] ① When ST ≤ 1150 °C, t P ≤ 1280 °C;

[0029] ② When 1150 < ST ≤ 1250 °C, t P ≤ 0.1×ST + 1165 °C;

[0030] ③ When 1250 °C < ST ≤ 1350 °C, t P = 0.2×ST + 1040 °C;

[0031] ④ When 1350 °C < ST ≤ 1450 °C, t P = 0.4×ST + 770 °C;

[0032] ⑤ When 1450 °C < ST, t P < 1370 °C.

[0033] A further improvement of the present invention lies in that, in the fourth step, the determination method of the upper limit value of the bottom screen gas temperature t under BMCR conditions: when Na2O > 3% or K2O > 4% in the coal ash, the bottom screen gas temperature t under BMCR conditions P ≤ 1280 °C. P ≤ 1280 °C.

[0034] A further improvement of the present invention lies in that, in the fourth step, for a newly designed boiler, it is required during design that the t of the flue gas temperature at the furnace outlet F and the bottom screen gas temperature t P do not exceed the recommended upper limit value; for an already designed boiler, when the t of the flue gas temperature at the furnace outlet obtained according to the coal quality fed into the furnace F and the bottom screen gas temperature t P do not exceed the design value, the safe combustion of the boiler can be ensured; otherwise, attention should be paid to the possible problems of increased slagging and fouling of the boiler, and it is necessary to replace the coal fed into the furnace if necessary.

[0035] The present invention has at least the following beneficial technical effects:

[0036] The present invention relates to the technical fields of power station pulverized coal boiler design and operation, and specifically relates to a method for reducing slagging and fouling of high-temperature heating surfaces of boilers, which is applicable to power station pulverized coal boilers with a П-shaped furnace layout in tangential combustion or wall combustion modes burning anthracite, lean coal, bituminous coal, long-flame coal, or lignite.

[0037] The advantages of the present invention are as follows: ① The position of the furnace outlet is defined, and the selection principle of the flue gas temperature at this position is specified. Under this principle, the lower the softening temperature ST of the coal ash of non-special coal samples, the lower the required flue gas temperature at the furnace outlet, which is beneficial to alleviating slagging and fouling of the high-temperature heating surfaces in the horizontal flue. ② The design of the screen bottom flue gas temperature is clearly specified. According to the principle of the present invention, slagging of the platen superheater can be alleviated. ③ Coordinating the control of the screen bottom flue gas temperature and the furnace outlet flue gas temperature is beneficial to alleviating slagging and fouling of the high-temperature heating surfaces and improving the operating safety of the boiler. ④ It is clearly specified that this invention method can be adopted for conventional coal types, and special consideration is required for special coal types. ⑤ The present invention is obtained through a large number of evaluations, studies, and calculations on the matching of boiler design, fuel characteristics, and boiler operation results, and has high engineering application value. It can guide the design, operation optimization of pulverized coal boilers, and the blending of fuels entering the furnace, and improve the operating safety of the boiler. Specific embodiments

[0038] Exemplary embodiments of the present disclosure will be described in more detail below. Although the exemplary embodiments of the present disclosure are shown, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0039] Example 1: Selection of screen bottom flue gas temperature and furnace outlet flue gas temperature for low ash-melting point slagging coal types

[0040] First step: For tangentially or wall-fired boilers with a П-shaped furnace layout, it is uniformly specified that the furnace outlet flue gas window (cross-section) is the imaginary cross-section formed by the center line of the rear wall water-cooled tubes of the furnace extending upward to the ceiling tubes and the horizontal flue.

[0041] Second step: Obtain the dry ash-free basis volatile matter V daf (%), received basis total sulfur S t,ar (%), dry basis ash content A d (%), coal ash softening temperature ST (°C), coal ash component values (Fe2O3, CaO, MgO, Na2O, K2O, %), chlorine Cl in coal ar (%);

[0042] Third step: Determine whether the coal sample is a conventional coal type. Determine whether any of the following coal quality parameters exist; if none of the following situations exist, the coal sample is a conventional coal type; if any of the following situations occur, the coal sample is an unconventional coal type, and the selection of the screen bottom flue gas temperature and the furnace outlet temperature is not within the scope of the method of the present invention. (1) St,ar > 2.5%, (2) A d > 45%, (3) Na2O > 5%, (4) ash K2O > 5%, (5) Na2O + K2O > 6%, (6) Fe2O3 > 20%, (7) sum of basic oxide content in ash B > 35%, B = CaO + MgO + Fe2O3 + K2O + Na2O, (8) Cl in coal ar > 0.2%.

[0043] The coal quality data of this low ash-melting point slagging coal sample are as follows: dry ash-free basis volatile matter V daf = 36.07%, received basis total sulfur S t,ar = 0.71%, dry basis ash A d = 23.15%, ash softening temperature ST = 1160 °C, Fe2O3 = 14.14%, CaO = 17.04%, MgO = 1.68%, Na2O = 0.58%, K2O = 1.26%, B = CaO + MgO + Fe2O3 + K2O + Na2O = 34.70%, Cl in coal ar = 0.01%; it is a conventional coal sample.

[0044] Step 4: For conventional coal types, determine the upper limit value of the flue gas temperature at the furnace outlet t under BMCR conditions and the upper limit value of the screen bottom flue gas temperature t F according to the following principles; P upper limit value;

[0045] Method for determining the upper limit value of the flue gas temperature at the furnace outlet t under BMCR conditions: F

[0046] (1) When Na2O ≤ 3% and K2O ≤ 4% in the coal ash, determine the flue gas temperature t at the furnace outlet under BMCR conditions according to the following principles F :

[0047] ① When ST ≤ 1100 °C, t F ≤ 960 °C

[0048] ② When 1100 °C < ST ≤ 1150 °C, t F ≤ 0.2 × ST + 740 °C

[0049] ③ When 1150 °C < ST ≤ 1350 °C, t F ≤ 0.1 × ST + 855 °C

[0050] ④ When 1350 °C < ST ≤ 1450 °C, t F ≤ 0.3 × ST + 585 °C

[0051] ⑤ When ST > 1450 °C, t F < 1020 °C​

[0052] (2) When Na2O > 3% or K2O > 4% in coal ash, the flue gas temperature t at the furnace outlet under BMCR condition F ≤ 960 °C

[0053] The bottom screen flue gas temperature t under BMCR condition P Determination method of the upper limit value:

[0054] (1) When Na2O ≤ 3% and K2O ≤ 4% in coal ash, the bottom screen flue gas temperature t under BMCR condition is determined according to the following principles P :

[0055] ① When ST ≤ 1150 °C, t P ≤ 1280 °C

[0056] ② When 1150 °C < ST ≤ 1250 °C, t P ≤ 0.1 × ST + 1165 °C

[0057] ③ When 1250 °C < ST ≤ 1350 °C, t P ≤ 0.2 × ST + 1040 °C

[0058] ④ When 1350 °C < ST ≤ 1450 °C, t P = 0.4 × ST + 770 °C

[0059] ⑤ When 1450 °C < ST, t P < 1370 °C

[0060] (2) When Na2O > 3% or K2O > 4% in coal ash, the flue gas temperature t at the furnace outlet under BMCR condition P ≤ 1280 °C

[0061] When Na2O ≤ 3% and K2O ≤ 4% in the low ash fusion temperature slagging coal sample of this time

[0062] and 1150 ≤ ST = 1160 °C ≤ 1350 °C, then the flue gas temperature at the furnace outlet under BMCR condition

[0063] t F ≤ 0.1 × ST + 855 °C = 0.1 × 1160 + 855 °C = 971 °C.

[0064] and 1150 °C < ST = 1160 °C ≤ 1250 °C, the bottom screen flue gas temperature under BMCR condition

[0065] t P ≤ 0.1 × ST + 1165 °C = 0.1 × 1160 + 1165 °C = 1281 °C

[0066] That is, the flue gas temperature t at the furnace outlet under BMCR conditionF ≤971 °C, the bottom panel flue gas temperature t P ≤1281 °C.

[0067] Example 2: Selection of the bottom panel flue gas temperature and the furnace outlet flue gas temperature for medium-high ash fusion point and medium slagging coal types

[0068] Step 1: For tangentially fired or wall-fired boilers with a Π-shaped furnace layout, it is uniformly stipulated that the furnace outlet flue gas window (cross-section) is the imaginary cross-section formed by extending the center line of the water-cooled wall tubes on the rear wall of the furnace upward to the ceiling tubes and the horizontal flue.

[0069] Step 2: Obtain the dry ash-free basis volatile matter V daf (%), the total sulfur S t,ar on the as-received basis (%), the dry basis ash content A d (%), the ash softening temperature ST (°C), the ash composition values (Fe2O3, CaO, MgO, Na2O, K2O, %), the chlorine Cl in the coal ar (%);

[0070] Step 3: Determine whether the coal sample is a conventional coal type. Determine whether any of the following coal quality parameters exist; if none of the following situations exist, then the coal sample is a conventional coal type; if any of the following situations occur, then the coal sample is an unconventional coal type, and the selection of the bottom panel flue gas temperature and the furnace outlet temperature is not within the scope of the method of the present invention. (1) S t,ar > 2.5%, (2) A d > 45%, (3) Na2O > 5%, (4) K2O in the ash > 5%, (5) Na2O + K2O > 6%, (6) Fe2O3 > 20%, (7) the sum of the basic oxide contents in the ash B > 35%, B = CaO + MgO + Fe2O3 + K2O + Na2O, (8) Cl in the coal ar > 0.2%.

[0071] The coal quality data of this medium-high ash fusion point and medium slagging coal sample are as follows: the dry ash-free basis volatile matter V daf = 33.36%, the total sulfur S t,ar on the as-received basis = 1.17%, the dry basis ash content A d = 12.11%, the ash softening temperature ST = 1310 °C, Fe2O3 = 6.22%, CaO = 10.69%, MgO = 1.38%, Na2O = 1.73%, K2O = 2.32%, B = CaO + MgO + Fe2O3 + K2O + Na2O = 22.34%, the chlorine Cl in the coal ar = 0.02%; it is a conventional coal sample.

[0072] Step 4: For conventional coal types, determine the furnace outlet flue gas temperature t under the BMCR condition according to the following principle FUpper limit value and the bottom screen flue gas temperature t P Upper limit value;

[0073] t of the furnace outlet flue gas temperature under BMCR condition F Determination method of the upper limit value:

[0074] (1) When Na2O ≤ 3% and K2O ≤ 4% in the coal ash, determine the furnace outlet flue gas temperature t under BMCR condition according to the following principles F :

[0075] ① When ST ≤ 1100°C, t F ≤ 960°C

[0076] ② When 1100°C < ST ≤ 1150°C, t F ≤ 0.2×ST + 740°C

[0077] ③ When 1150°C < ST ≤ 1350°C, t F ≤ 0.1×ST + 855°C

[0078] ④ When 1350°C < ST ≤ 1450°C, t F ≤ 0.3×ST + 585°C

[0079] ⑤ When ST > 1450°C, t F < 1020°C

[0080] (2) When Na2O > 3% or K2O > 4% in the coal ash, the furnace outlet flue gas temperature t under BMCR condition F ≤ 960°C

[0081] Bottom screen flue gas temperature t under BMCR condition P Determination method of the upper limit value:

[0082] (1) When Na2O ≤ 3% and K2O ≤ 4% in the coal ash, determine the bottom screen flue gas temperature t under BMCR condition according to the following principles P :

[0083] ① When ST ≤ 1150°C, t P ≤ 1280°C

[0084] ② When 1150 < ST ≤ 1250°C, t P ≤ 0.1×ST + 1165°C

[0085] ③ When 1250°C < ST ≤ 1350°C, t P = 0.2×ST + 1040°C

[0086] ④ When 1350°C < ST ≤ 1450°C, t P = 0.4×ST + 770°C

[0087] ⑤1450 °C < ST, t P <1370 °C

[0088] (2) When Na2O > 3% or K2O > 4% in the coal ash, the flue gas temperature t at the furnace outlet under BMCR conditions P ≤ 1280 °C

[0089] When Na2O ≤ 3% and K2O ≤ 4% in this low ash-melting point slagging coal sample

[0090] And 1150 ≤ ST = 1310 °C ≤ 1350 °C, then the flue gas temperature at the furnace outlet under BMCR conditions

[0091] t F ≤ 0.1 × ST + 855 °C = 0.1 × 1310 + 855 °C ≤ 986 °C.

[0092] And 1250 °C < ST = 1310 °C ≤ 1350 °C, the flue gas temperature at the bottom of the screen under BMCR conditions

[0093] t P ≤ 0.2 × ST + 1040 °C = 0.2 × 1310 + 1040 °C = 1302 °C

[0094] That is, the flue gas temperature t at the furnace outlet under BMCR conditions F ≤ 986 °C, and the flue gas temperature t at the bottom of the screen P ≤ 1302 °C.

[0095] Although the present invention has been described in detail above with general descriptions and specific embodiments, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A method for reducing slagging and fouling of high-temperature heating surfaces of boilers, characterized in that, It includes the following steps: Step 1: For tangentially fired or wall-fired boilers with a Π-shaped furnace layout, the flue gas window at the furnace outlet is uniformly defined as the imaginary section formed by the centerline of the water-cooled wall tubes on the rear wall of the furnace extending upward to the ceiling tubes and the horizontal flue. Step 2: Obtain the dry ash-free basis volatile matter V of the coal sample daf , %; Total sulfur S on as-received basis t,ar , %; Dry basis ash content A d , %; Coal ash softening temperature ST, °C; Coal ash component values, %; and chlorine Cl in coal ar , %; Coal ash component values include Fe2O3, CaO, MgO, Na2O, and K2O; Step 3: Determine whether the coal sample is a conventional coal type; determine whether any of the following conditions exist for the coal quality parameters; if none of the following conditions exist, the coal sample is a conventional coal type; if any of the following conditions occur, the coal sample is an unconventional coal type: (1) S t,ar > 2.5%, (2) A d > 45%, (3) Na2O > 5%, (4) K2O in coal ash > 5%, (5) Na2O + K2O > 6%, (6) Fe2O3 > 20%, (7) the sum of basic oxide contents in coal ash B > 35%, B = CaO + MgO + Fe2O3 + K2O + Na2O, (8) Cl in coal ar > 0.2%; Step 4: For conventional coal types, determine the upper limit value of the flue gas temperature at the furnace outlet, t, and the upper limit value of the flue gas temperature at the bottom of the platen F under the BMCR condition according to the preset principle; so that during the operation of the boiler, the flue gas temperature at the furnace outlet, t, P and the flue gas temperature at the bottom of the platen, t, F do not exceed the recommended upper limit values. P ​ The flue gas temperature t at the furnace outlet under the BMCR condition F Determination method for the upper limit value: When Na2O ≤ 3% and K2O ≤ 4% in coal ash, determine the flue gas temperature t at the furnace outlet under BMCR conditions according to the following principles F : ①ST ≤ 1100 °C, t F ≤ 960 °C; ②1100 °C < ST ≤ 1150 °C, t F ≤ 0.2 × ST + 740 °C; ③1150 °C < ST ≤ 1350 °C, t F ≤ 0.1 × ST + 855 °C; ④1350℃ < ST ≤ 1450℃, t F ≤ 0.3×ST + 585℃; ⑤ST > 1450 °C, t F <1020 °C; The flue gas temperature t at the furnace outlet under BMCR condition F Determination method of the upper limit value: When Na2O > 3% or K2O > 4% in the coal ash, the flue gas temperature t at the furnace outlet under BMCR condition F ≤ 960 °C; Screen bottom flue gas temperature t under BMCR condition P Determination method of upper limit value: When Na2O ≤ 3% and K2O ≤ 4% in coal ash, the bottom platen gas temperature t under BMCR conditions is determined according to the following principles P : ①ST ≤ 1150 °C, t P ≤ 1280 °C; ② 1150 < ST ≤ 1250 °C, t P ≤ 0.1 × ST + 1165 °C; ③1250℃ < ST ≤ 1350℃, t P = 0.2 × ST + 1040℃; ④1350℃ < ST ≤ 1450℃, t P = 0.4 × ST + 770℃; ⑤ 1450℃ <ST, t P < 1370℃; Screen bottom flue gas temperature t under BMCR condition P Determination method of upper limit value: When Na2O > 3% or K2O > 4% in coal ash, the screen bottom flue gas temperature t under BMCR condition P ≤ 1280 °C.

2. A method for reducing slagging and fouling of high-temperature heating surfaces of a boiler according to claim 1, characterized in that, This method is applicable to pulverized coal-fired power station boilers with a Π-shaped furnace layout in tangential combustion or wall-firing mode, burning anthracite, lean coal, bituminous coal, long-flame coal, or lignite.

3. A method for reducing slagging and fouling of high-temperature heating surfaces of a boiler according to claim 1, characterized in that, In the fourth step, for the newly designed boiler, the flue gas temperature t at the furnace outlet is required to be F and the flue gas temperature t at the bottom of the platen P not exceed the recommended upper limit value; for the existing designed boiler, when the flue gas temperature t at the furnace outlet obtained according to the coal quality fed into the furnace F and the flue gas temperature t at the bottom of the platen P do not exceed the design value, the safe combustion of the boiler can be ensured.