Furnace condition control method for blending combustion of high alkali metal coal in power station boiler

Abstract

A furnace condition control method for blending combustion of high alkali metal coal in a power station boiler comprises the steps of determining a blending combustion proportion limit value, determining a screen bottom flue gas temperature control limit value and determining a convection heating surface inlet flue gas temperature control limit value. According to the method, factors influencing the boiler condition in the blending combustion process of the high alkali metal coal are solidified, and certain quantitative standards are formed, so that a basis is provided for the blending combustion of the high alkali metal coal in the boiler. The control blending proportion of the high alkali metal power coal is determined through the blending index formed by the coal ash component variable factors, and the flue gas control temperature of the typical part of the boiler heating surface is corrected according to the blending proportion. And in the operation process, blending combustion is organized according to the controlled blending proportion, the flue gas temperature is controlled to operate in a safe area, and the furnace condition is kept stable. According to the method, the maximum potential of the blending combustion proportion of the high alkali metal power coal of boiler equipment can be exerted, and quantitative parameter control is implemented, so that high-proportion blending combustion of the high alkali metal power coal can be achieved, and the furnace condition can be kept relatively stable.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power production, and in particular relates to a furnace condition control method for a power station boiler blended with high-alkali metal coal. Background Art

[0002] Thermal power plants use boilers, steam turbines, generators and other process equipment to convert the chemical energy of coal into electrical energy to serve production and life. Fuel costs are the largest part of thermal power production, accounting for more than 60%. High-alkali metal coal has huge reserves in the eastern part of the Junggar Basin in Xinjiang, my country, and its price is significantly lower than that of general thermal coal. Increasing the blending ratio of high-alkali metal content thermal coal is the most important means for thermal power companies in Xinjiang and even surrounding provinces to reduce power generation costs and increase profits.

[0003] Due to the strong contamination of high-alkali thermal coal, deviations in boiler combustion control during the combustion process will lead to boiler coking, which will reduce output and affect production capacity tasks at the least; in serious cases, the furnace condition will deteriorate and the unit will be forced to shut down for treatment. In terms of furnace condition control, the existing conventional technology only controls by strengthening combustion adjustment and strengthening furnace condition tracking and observation. Once the furnace condition deteriorates, it can only be maintained by reducing the blending ratio or reducing the unit load, which seriously affects the increase in power generation costs. Summary of the invention

[0004] The purpose of the present invention is to provide a furnace condition control method for a power station boiler blended with high-alkali metal coal, so that the existing traditional coal-fired boiler can not only blend high-alkali metal thermal coal in a high proportion, but also maintain a stable furnace condition for a long period of time, thereby maximizing the benefits.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A method for controlling furnace conditions of a power station boiler blended with high-alkali metal coal comprises the following steps: S1. Determine the limit of the blending ratio: The following formula is used to set the thermal coal blending index. The blending index is the ratio of the sum of the percentage of alkaline oxides to the sum of the percentage of acidic oxides in the coal ash multiplied by the percentage of calcium oxide and then multiplied by 100. The blending index is less than or equal to 10 as the standard for limiting the blending ratio. Pc=(K2O+Na2O+MgO+CaO+Fe2O3) / (SiO2+Al2O3+Ti2O2)×CaO×100≤10 Where: Pc is the blending index of mixed coal; K2O, Na2O, MgO, CaO, Fe2O3, SiO2, Al2O3, and Ti2O2 are the mass percentages of each compound in the total amount of mixed coal ash respectively; S2. Determine the control limit of the flue gas temperature at the bottom of the screen: Take samples of the coal to be blended, mix them according to the blending ratio, and then conduct an ash melting point test. Based on the test results, revise the coefficient according to whether a soot blower is configured. T k = k1×FT Where: T k The temperature of the flue gas at the bottom of the screen is controlled, ℃; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; FT is the melting temperature of mixed coal ash, °C; S3. Determine the control limit of the flue gas temperature at the inlet of the convection heating surface: The design flue gas temperature of typical parts of the boiler heating surface is modified according to the mixed coal blending index, the gap between the convection tube screens, whether there is a soot blower, and the layout location. T k = T s ×(1-Pc / 100)×(1-5 / S)×k1×k2 Where: T k is the flue gas control temperature at the inlet of the convection heating surface, °C; T s is the design temperature of flue gas at the inlet of the convection heating surface, °C; Pc is the blending index of mixed coal; S is the middle gap of the convection tube panel, mm; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; K2 is the layout coefficient. If the horizontal flue is arranged behind the "ridge", the value is 1, and if it is arranged in front of the "ridge", the value is 1.01.

[0006] In order to further realize the present invention, the mass percentage of each compound in the mixed coal ash described in S1 is calculated according to the blending ratio of each coal type and the weighted average of the ash content.

[0007] Compared with the prior art, the present invention has the following beneficial effects: The present invention solidifies the factors that affect the boiler furnace condition during the process of blending and burning high-alkali metal coal, forms some quantitative standards, and provides a basis for blending and burning high-alkali coal in the boiler.

[0008] The present invention determines the controlled blending ratio of high-alkali metal thermal coal through the blending index composed of the variable factors of coal ash composition, and then corrects the flue gas control temperature of the typical parts of the boiler heating surface according to the blending ratio. During operation, the blending is organized according to the controlled blending ratio and the flue gas temperature is controlled to operate in a safe area to maintain stable furnace conditions.

[0009] The present invention can maximize the potential of the blending ratio of high-alkali metal thermal coal in boiler equipment and implement quantitative parameter control to achieve both high-proportion blending of high-alkali metal thermal coal and relatively stable furnace conditions. It is the optimal choice for maximizing the cost-effectiveness of thermal power generation. DETAILED DESCRIPTION

[0010] The present invention will be further described below in conjunction with specific implementation modes.

[0011] A method for controlling furnace conditions of a power station boiler blended with high-alkali metal coal comprises the following steps: S1. Determine the limit of the blending ratio: The following formula is used to set the thermal coal blending index. The blending index is the ratio of the sum of the percentage of alkaline oxides to the sum of the percentage of acidic oxides in the coal ash multiplied by the percentage of calcium oxide and then multiplied by 100. The blending index is less than or equal to 10 as the standard for limiting the blending ratio. Pc=(K2O+Na2O+MgO+CaO+Fe2O3) / (SiO2+Al2O3+Ti2O2)×CaO×100≤10 Where: Pc is the blending index of mixed coal; K2O, Na2O, MgO, CaO, Fe2O3, SiO2, Al2O3, and Ti2O2 are the mass percentages of each compound in the total amount of mixed coal ash respectively; The mass percentage of each compound in the mixed coal ash is calculated according to the blending ratio of each coal type and the weighted average of the ash content; S2. Determine the control limit of the flue gas temperature at the bottom of the screen: Take samples of the coal to be blended, mix them according to the blending ratio, and then conduct an ash melting point test. Based on the test results, revise the coefficient according to whether a soot blower is configured. T k = k1×FT Where: T k The temperature of the flue gas at the bottom of the screen is controlled, ℃; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; FT is the melting temperature of mixed coal ash, °C; S3. Determine the control limit of the flue gas temperature at the inlet of the convection heating surface: The design flue gas temperature of typical parts of the boiler heating surface is modified according to the mixed coal blending index, the gap between the convection tube screens, whether there is a soot blower, and the layout location. T k = T s ×(1-Pc / 100)×(1-5 / S)×k1×k2 Where: T k is the flue gas control temperature at the inlet of the convection heating surface, °C; T s is the design temperature of flue gas at the inlet of the convection heating surface, °C; Pc is the blending index of mixed coal; S is the middle gap of the convection tube panel, mm; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; K2 is the layout coefficient. If the horizontal flue is arranged behind the "ridge", the value is 1, and if it is arranged in front of the "ridge", the value is 1.01.

[0012] Experimental Example 1: There is a certain type of high-alkali metal thermal coal that has an obvious price advantage per unit calorific value, and a power plant is planning to organize blending.

[0013] First, the ash composition of the coal types that the power plant has burned and the high-alkali metal thermal coal that is planned to be burned should be comprehensively determined. The relevant data are as follows: According to the coal ash composition data, according to the standard of Pc=(K2O+Na2O+MgO+CaO+Fe2O3) / (SiO2+Al2O3+Ti2O2)×CaO×100≤10, the blending index of the proposed high-alkali coal is equal to 27.8, which is much greater than 10 and cannot be burned purely. According to the mixing conditions, the mixed material method of separate bunker loading is adopted: 25% A coal plus 25% C coal plus 50% D coal blending index is equal to 10.95, which is greater than the standard 10 and does not meet the blending conditions. 25% B coal plus 25% C coal plus 50% D coal blending index is equal to 7.92, the blending ratio meets the standard conditions, and it is determined to organize the blending according to this ratio.

[0014] Determination of screen bottom control temperature: Mixed coal sampling is carried out according to the proportion of B coal, C coal and D coal determined above. The test ash melting temperature is 1190℃, and the screen bottom temperature is 1249.5℃ after correction according to Tk = k1×FT.

[0015] Determination of the control limit of the flue gas temperature at the inlet of the convection heating surface: According to the formula T k = T s × (1-Pc / 100) × (1-5 / S) × k1 × k2, calculate the control temperature of the heating surface in a typical area as follows: Experimental Example 2: A new high-alkali metal thermal coal E has a price advantage per unit calorific value over coal D, and it is planned to be mixed and burned in three boilers equipped with double inlet and double outlet mills. The relevant data of coal ash composition determination are as follows: According to the coal ash composition data, according to the standard of Pc=(K2O+Na2O+MgO+CaO+Fe2O3) / (SiO2+Al2O3+Ti2O2)×CaO×100≤10, the blending index of the proposed high-alkali coal E is equal to 27.2, which is much greater than 10 and cannot be burned purely. The blending indexes corresponding to the pure coal types A, B, and C are 3.24, 2.03, and 8.72 respectively. The blending index of the C coal type is close to 10. When determining the blending scheme of the E coal type, the blending with the C coal type is not considered. According to the mixing conditions, the bin-loading blending method is adopted: the blending index of 34% B coal plus 66% E coal is equal to 11.88, which is greater than the standard 10, and does not meet the blending conditions, excluding the possibility of blending E coal at a ratio of 66%. The blending index of 50% A coal plus 50% E coal is equal to 9.47. The blending ratio meets the standard conditions. It can be determined that while maintaining the blending ratio of 50% E coal, A coal and B coal are burned in four ratios of 50% and 0%, 33% and 17%, 17% and 33%, and 0% and 50%.

[0016] Determination of screen bottom control temperature: Mixed coal sampling is carried out according to the above-determined blending index corresponding to 9.47 with a ratio of 50% for A coal and E coal respectively. The test ash melting temperature is 1206℃, and the screen bottom temperature is 1266.3℃ after correction according to Tk = k1×FT.

[0017] Determination of the control limit of the flue gas temperature at the inlet of the convection heating surface: According to the formula T k = T s × (1-Pc / 100) × (1-5 / S) × k1 × k2, calculate the control temperature of the heating surface in a typical area as follows: Higher than imports Furnace outlet High re-entry Low re-entry Lower than the entrance <![CDATA[Design temperature T s > 1094 982 975 875 799 Blending index Pc 7.92 7.92 7.92 7.92 7.92 Tube screen gap S 526.5 357 294.8 57.3 63.5 <![CDATA[External strengthening coefficient K1]]> 1.05 1.05 1.05 1.05 1.05 <![CDATA[Arrangement form factor K2]]> 1.01 1.01 1.01 1 1 <![CDATA[Control temperature T k > 1040.3 929.6 920.2 759.2 699.7 Experimental Example 3: The newly purchased high-alkali metal thermal coal E with a lower calorific value unit price can only meet the 27% blending amount. In order to maintain a low coal cost for power generation, it is necessary to blend multiple coal types with high-alkali metal thermal coal D in a boiler equipped with five coal mills. The relevant data of the measurement are as follows: Since the pure coal blending indexes of high-alkali coals D and E are 27.8 and 27.2 respectively, and the data are similar, it can be determined that the highest blending ratio after considering the mixing conditions is 50%. According to the maximum proportion of E coal, i.e. 25%, the blending index of 50%A+25%D+25%E blending method is 9.88, and the blending index of 50%B+25%D+25%E blending method is 8.51, which meets the blending requirements, and the above two methods can be selected for blending.

[0018] Determination of screen bottom control temperature: Select coal A with lower ash melting point among coal A and B and mix them with coal D and E in a ratio of 50%:25%:25%. The test ash melting temperature is 1184℃, and the screen bottom temperature is 1243.2℃ after correction according to Tk = k1×FT.

[0019] Determination of the control limit of the flue gas temperature at the inlet of the convection heating surface: According to the formula T k = T s × (1-Pc / 100) × (1-5 / S) × k1 × k2, calculate the control temperature of the heating surface in a typical area as follows: In the actual production process, the blending ratio of strong coking coal is controlled according to the coal blending index of the furnace being lower than 10. During operation, the flue gas temperature parameters of each part of the boiler are adjusted to operate within a safe range below the limit to maintain stable furnace conditions. The method of the present invention has been verified on 10 boilers of three types, namely, ultra-high pressure, subcritical and supercritical, with different capacities ranging from 435t / h to 1208t / h, and achieved good results.

Claims

1. A method for controlling furnace conditions of a power station boiler burning high-alkali metal coal, characterized in that The steps include: S1. Determine the limit of the blending ratio: The thermal coal blending index is set using the following formula: Pc=(K2O+Na2O+MgO+CaO+Fe2O3) / (SiO2+Al2O3+Ti2O2)×CaO×100≤10 Where: Pc is the blending index of mixed coal; K2O, Na2O, MgO, CaO, Fe2O3, SiO2, Al2O3, and Ti2O2 are the mass percentages of each compound in the total amount of mixed coal ash respectively; S2. Determine the control limit of the flue gas temperature at the bottom of the screen: T k = k1×FT Where: T k The temperature of the flue gas at the bottom of the screen is controlled, ℃; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; FT is the melting temperature of mixed coal ash, °C; S3. Determine the control limit of the flue gas temperature at the inlet of the convection heating surface: T k = T s ×(1-Pc / 100)×(1-5 / S)×k1×k2 Where: T k is the flue gas control temperature at the inlet of the convection heating surface, °C; T s is the design temperature of flue gas at the inlet of the convection heating surface, °C; Pc is the blending index of mixed coal; S is the middle gap of the convection tube panel, mm; K1 is the external enhancement coefficient, which is 1 in the area without soot blowers and 1.05 in the area with soot blowers; K2 is the layout coefficient. If the horizontal flue is arranged behind the "ridge", the value is 1, and if it is arranged in front of the "ridge", the value is 1.

01.

2. The furnace condition control method for a power station boiler burning high-alkali metal coal as claimed in claim 1, characterized in that: The mass percentage of each compound in the mixed coal ash described in S1 is calculated according to the blending ratio of each coal type and the weighted average of the ash content.

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