A method and system for predicting coal contamination characteristics of a thermal power plant

Abstract

The present application belongs to the technical field of coal-fired power generation, and discloses a method for predicting the coal contamination characteristics of a thermal power plant. S1 obtains the volume of flue gas generated by complete combustion of raw coal; S2 burns the weighed raw coal, respectively records the flame temperature, gas-phase potassium concentration and gas-phase sodium concentration in the combustion process, and calculates the average temperature, gas-phase sodium release amount and gas-phase potassium release amount in the combustion process; S3 collects the ash after combustion and weighs the mass of the ash, respectively detects the ash melting point and the mass proportion of sodium oxide and potassium oxide in the ash; S4 calculates the release rate of alkali metal and uses the release rate of alkali metal to solve the solid-phase contamination index, calculates the gas-phase contamination index and sums it with the solid-phase contamination index to obtain the total contamination index, that is, to realize the prediction of the contamination characteristics. Through the present application, the problem that the contamination characteristics cannot be obtained according to the gaseous alkali metal released by coal combustion is solved.

Description

Technical Field

[0001] This invention belongs to the technical field of coal-fired power generation, and more specifically, relates to a method and system for predicting the fouling characteristics of coal in thermal power plants. Background Technology

[0002] High-temperature sintering ash buildup occurs on the heating surfaces of screen-type and convection-type superheaters and reheaters in coal-fired power plants. The fundamental reason is that gaseous alkali metal compounds such as sodium and potassium, produced during combustion, condense on the tube walls of the superheaters and reheaters at slightly lower temperatures, forming a thin white ash layer. This ash then adheres to fly ash and continues to thicken, further contributing to the buildup. Severe fouling and slagging are more likely to occur in high-temperature superheaters and reheaters when burning Zhundong coal or blended with high-alkali fuels such as biomass. This results in a decrease in outlet air temperature and an increase in outlet flue gas temperature, leading to higher boiler exhaust temperatures and reduced unit economics. Therefore, accurately predicting the fouling characteristics of coal in power plants is crucial for taking better measures to prevent severe slagging, which is of great significance for further improving the economics of coal-fired power generating units.

[0003] The national standard GB / T 39836-2021, "Determination Method of Slagging Index of Coal Combustion," implemented in 2021, specifies the determination method, test apparatus, test instruments and methods, data processing and calculation methods for the slagging index of coal combustion. This standard primarily involves conducting pulverized coal combustion tests in a one-dimensional furnace. Through ash sampling and analysis, static monitoring indicators such as softening temperature, silica-alumina ratio, alkali-acid ratio, and silica ratio are obtained. Then, the slagging characteristics of coal combustion are classified into slight slagging, moderate slagging, and severe slagging using the coal ash probe slagging discrimination index, the comprehensive coal ash slagging discrimination index, and the coal ash clustering slagging discrimination index. Existing methods for judging coal slagging characteristics require pilot-scale testing equipment such as one-dimensional combustion test furnaces to analyze the morphology and composition of collected sediments. These methods do not consider the influence of actual combustion process temperature and component release, and are not applicable to the slagging determination of high-alkali coal. As mentioned earlier, the fundamental cause of high-temperature sintering ash buildup on the heating surfaces of superheaters and reheaters is the gaseous alkali metal compounds produced during combustion. Therefore, it is necessary to propose a method for predicting fouling characteristics based on the detection of gaseous alkali metals released during coal combustion. Summary of the Invention

[0004] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method and system for predicting the fouling characteristics of coal combustion in thermal power plants, solving the problem of predicting fouling characteristics based on the gaseous alkali metals released during actual combustion.

[0005] To achieve the above objectives, according to one aspect of the present invention, a method for predicting the fouling characteristics of coal in thermal power plants is provided, the method comprising the following steps:

[0006] S1 performs industrial and elemental analysis on the raw coal used in thermal power plants to obtain the element content of the raw coal; and uses the element content to obtain the volume of flue gas produced by the complete combustion of the raw coal.

[0007] S2 Weigh an appropriate amount of raw coal and record its mass. Burn the weighed raw coal and record the changes in flame temperature, gaseous potassium concentration and gaseous sodium concentration over time during the combustion process. Calculate the average temperature, gaseous sodium release and gaseous potassium release during the combustion process.

[0008] S3 collects the ash residue after combustion and weighs the ash residue, and detects the ash melting point and the mass ratio of sodium oxide and potassium oxide in the ash residue respectively.

[0009] S4 calculates the release rate of alkali metals and uses the release rate of alkali metals to solve the solid phase contamination index. It then calculates the gas phase contamination index and sums it with the solid phase contamination index to obtain the total contamination index, thus realizing the prediction of contamination characteristics.

[0010] More preferably, in step S2, the average temperature during the combustion process is determined according to the following formula:

[0011]

[0012] Where T is the average temperature during combustion, t0 is the initial moment of stable combustion, t1 is the moment of burnout, T(t) is the change in flame temperature over time during combustion, and t is time.

[0013] More preferably, in step S2, the amount of gaseous potassium released during the combustion process is determined according to the following formula:

[0014]

[0015] Among them, C K t is the amount of gaseous potassium released, t0 is the initial moment of stable combustion, t1 is the moment of burnout, K(t) is the change of gaseous potassium concentration over time, and t is time.

[0016] More preferably, in step S2, the amount of gaseous sodium released during the combustion process is determined according to the following formula:

[0017]

[0018] Among them, C Na t is the amount of sodium released in the gas phase, t0 is the initial moment of stable combustion, t1 is the moment of burnout, Na(t) is the change of sodium concentration in the gas phase over time, and t is time.

[0019] More preferably, in step S4, the release rate of the alkali metal is determined according to the following formula:

[0020]

[0021] Where φ is the alkali metal release rate, and C Na It is the amount of sodium released in the gas phase, C K V is the amount of gaseous potassium released, V is the volume of flue gas produced by the complete combustion of raw coal, m2 is the mass of burnt ash, Na2O is the mass percentage of sodium oxide in the ash residue, and K2O is the mass percentage of potassium oxide in the ash residue.

[0022] More preferably, in step S4, the solid phase contamination index is determined according to the following formula:

[0023] R s =(1-φ)(Na2O+K2O)

[0024] Among them, R s φ is the solid fouling index, φ is the alkali metal release rate, Na2O is the mass percentage of sodium oxide in the ash, and K2O is the mass percentage of potassium oxide in the ash.

[0025] More preferably, in step S4, the gas phase contamination index is determined according to the following formula:

[0026]

[0027] Among them, R g It is the gaseous fouling index, C Na It is the amount of sodium released in the gas phase, C K This represents the amount of potassium released in the gas phase, V is the volume of flue gas produced by the complete combustion of raw coal, m2 is the mass of burnt ash, and T / T. ash This is a correction factor for the gas phase fouling index.

[0028] More preferably, in step S1, the element content includes the respective content percentages of C, H, O, and N of the coal type, as well as total moisture (M), volatile matter (V), fixed carbon (FC), and ash (A).

[0029] According to another aspect of the present invention, a system for predicting the contamination characteristics of coal-fired power plants is provided, as described above, along with a method for predicting the contamination characteristics of coal-fired power plants.

[0030] According to another aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements a method for predicting the coal-fired pollution characteristics of a thermal power plant as described above.

[0031] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0032] 1. The method of the present invention couples multiple factors. Compared with the existing methods for contamination characteristics that have special requirements for combustion equipment, the present invention has no special requirements for combustion equipment, is universal, easy to operate, and has high testing efficiency.

[0033] 2. This invention eliminates the need for an ash-making process, thus avoiding systematic errors caused by the release of alkali metals during high-temperature ash-making when predicting the contamination characteristics based on ash composition;

[0034] 3. This invention not only considers the influence of alkali metal elements in coal ash on contamination, but also the influence of gaseous alkali metals in the actual combustion process on contamination. Based on the correction of flame temperature and alkali metal release rate, it highlights the decisive role of gaseous alkali metals in contamination. Attached Figure Description

[0035] Figure 1 This is a flowchart of a method for predicting the coal-fired pollution characteristics of thermal power plants, constructed according to a preferred embodiment of the present invention.

[0036] Figure 2 The graphs are curves showing the changes in temperature, gaseous sodium concentration, and gaseous potassium concentration over time during a uniform and stable combustion process constructed according to a preferred embodiment of the present invention. (a) is a curve showing the change in temperature over time during combustion, (b) is a curve showing the change in gaseous sodium concentration over time during combustion, and (c) is a curve showing the change in gaseous potassium concentration over time during combustion. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0038] An invention of a method for predicting the fouling characteristics of coal in thermal power plants includes the following steps:

[0039] S1 coal quality analysis and flue gas calculation: Obtain industrial and elemental analysis results for the coal type, acquire the coal sample mass by weighing, and calculate the flue gas volume V produced by complete coal combustion; specifically:

[0040] (1) Take a certain amount of raw coal and obtain the content ratio of C, H, O and N of the coal type, as well as the total moisture M, volatile matter V, fixed carbon FC and ash A through industrial analysis and elemental analysis.

[0041] (2) Take another certain amount of raw coal, grind it into coal powder, dry it, weigh the coal powder to be used and record it.

[0042] (3) Based on the obtained data, calculate the flue gas volume V produced by the complete combustion of the coal sample. The calculation method of the flue gas volume V is based on the boiler thermal calculation in conventional literature, which will not be repeated here.

[0043] S2 Combustion Detection: Temperature and gaseous alkali metal concentration are monitored during combustion until combustion is complete. The average temperature T and the amount of sodium released in the gaseous phase C during combustion are calculated. Na With gas phase potassium release C K Collect coal dust and ash; specifically:

[0044] (1) Place the weighed coal powder into the combustion equipment to make the coal powder burn evenly and stably. Record the initial time t0 when the combustion is stable and the time t1 when the combustion is exhausted. Detect the changes in flame temperature T(t), gaseous potassium concentration K(t), and gaseous sodium concentration Na(t) during the combustion process.

[0045] (2) Calculate the average temperature T and the amount of sodium released in the gas phase during the combustion process using the following formula. Na With gas phase potassium release C K :

[0046]

[0047]

[0048]

[0049] After the burning is finished, collect the ashes.

[0050] S3 Ash Analysis: Based on the data obtained in step S1, the ash mass m2 is weighed, the ash is analyzed, the mass ratio of Na2O and K2O in the ash residue is obtained, and the ash melting point T is measured. ash ;Specifically:

[0051] (1) Collect the residual ash after combustion, weigh it to obtain the mass m2 of the burnt ash, and detect the mass ratio of sodium oxide and potassium oxide in the ash, which are recorded as Na2O and K2O respectively.

[0052] (2) Take another portion of the burnt ash sample and measure the ash melting point T of the ash sample. ash .

[0053] S4 Alkali Metal Release Rate and Contamination Index Calculation: Based on the results obtained from steps S1 to S3, the alkali metal release rate is calculated; specifically:

[0054] (1) The amount of gaseous alkali metals released is calculated by multiplying the sum of the gaseous potassium release concentration and the gaseous sodium release concentration by the flue gas volume. The amount of solid alkali metals is calculated by multiplying the sum of potassium oxide and sodium oxide in the ash by the mass of the burnt ash. The sum of the amount of gaseous alkali metals released and the amount of solid alkali metals is the total alkali metal content in the coal.

[0055] (2) The alkali metal release rate is the ratio of the mass of gaseous alkali metals to the total alkali metals in the coal sample. The alkali metal release rate φ is calculated according to the following formula:

[0056]

[0057] (3) Calculate the gaseous fouling index R according to the following formula. g With solid fouling index R s :

[0058]

[0059] R s =(1-φ)(Na2O+K2O)

[0060] In the formula, m1 represents the mass of pulverized coal fed into the combustion equipment, and φ represents the alkali metal release rate calculated in step S4. (T / T) ash The correction factor for the gas phase fouling index is 1-φ, which is used because in actual boilers, higher flame temperatures make it easier for ash produced during combustion to melt, thus exacerbating slagging. The solid phase correction factor is used because the solid phase has a smaller impact on fouling than the gas phase. Gas phase fouling index R g With solid fouling index R s All are dimensionless quantities.

[0061] (4) Calculate the total pollution index using the following formula:

[0062] R = R g +R s

[0063] The pollution characteristics of coal are predicted based on the magnitude of the total pollution index. The higher the total pollution index, the stronger the predicted pollution characteristics of the coal.

[0064] The present invention will be further described below with reference to specific embodiments.

[0065] Taking Zhundong coal as an example, the method for predicting the pollution characteristics of coal in thermal power plants includes the following steps:

[0066] S1 Analysis: Coal Quality and Flue Gas Calculation. The raw coal sample was ground into pulverized coal in a coal mill. A certain amount of the pulverized coal was then used for industrial and elemental analysis (on an as-received basis) according to relevant standards. The contents of C, H, O, N, and S, as well as the percentages of total moisture (M), volatile matter (V), fixed carbon (FC), and ash (A) for this coal type were obtained, in %. The results are shown in Table 1.

[0067] Table 1

[0068]

[0069] Take another portion of coal powder, sieve it to below 200μm using a coal powder sieve, weigh the coal sample to be used as m1 = 55mg, and record the results accordingly.

[0070] Based on the data obtained in step S1, the dry air volume V required for the complete combustion of 1 kg of pulverized coal under standard operating conditions (equivalent ratio of 1) is first calculated using the following formula. 0 :

[0071] V 0 =0.0889(C+0.375S)+0.265H-0.0333O (1)

[0072] Where C, S, H, and O represent the percentages of carbon, sulfur, hydrogen, and oxygen in the coal obtained in step S1. Substituting the data from Table 1 into formula (4), we obtain the volumetric dry air required for the complete combustion of 1 kg of Zhundong coal, V. 0 =5.88m 3 / kg. Then, using the following formulas, calculate the volumes of nitrogen, carbon dioxide, and water vapor in the flue gas produced by burning 1 kg of coal under standard operating conditions (equivalent ratio of 1):

[0073]

[0074] Substituting the data from Table 1 into formula (5), we obtain the volume of nitrogen in the flue gas produced by burning 1 kg of Zhundong coal under standard operating conditions (equivalent ratio of 1). carbon dioxide volume With water vapor volume In actual combustion processes, the amount of air used for combustion often exceeds the amount required for the combustion reaction. Therefore, an excess air coefficient needs to be introduced to correct for the volume of dry flue gas and water vapor.

[0075]

[0076] In the formula, V gy For dry flue gas volume, Let be the volume of water vapor, and α be the excess air coefficient. In the combustion device of step S2, α = 3. Substituting the calculated data into formula (6), the dry flue gas volume V is calculated. gy =17.60mg 3 / kg, water vapor volume Calculate the total volume of flue gas produced by the complete combustion of 1 kg of coal using the following formula:

[0077]

[0078] Substituting the result into formula (7), the total volume of flue gas V produced by the complete combustion of 1 kg of coal is calculated. y V y =18.36m 3 / kg. V y Multiplying the mass of the coal sample (m1) by the total volume of flue gas produced by the combustion test (V = 0.00101 m³) yields the total volume of flue gas. 3 Combustion detection was performed using a Hencken flat-flame burner. Ethylene was used as fuel, and air as the oxidant. The ethylene flow rate was 0.8 L / min, and the air flow rate was 30 L / min. Multiple small, diffused flames formed a planar flame above the burner, providing heat to the lumpy coal sample for combustion. Weighed coal powder was moved to the center of the Hencken flat-flame burner via an electric displacement platform, ensuring uniform and stable combustion. The vertical height of the coal sample from the planar flame was 1 cm. After combustion stabilized, combustion detection began, with the initial stabilization time recorded as t0 = 5 s. An AvaSpec-2048-USB2 spectrometer, connected to a collimating lens and optical fiber, collected the spectral signal of the coal sample's combustion flame. The wavelength range was 300-800 nm, with a data acquisition interval of 1 s, until the combustion process ended. The burnout time was recorded as t1 = 601 s. To facilitate data processing, the collected spectral data underwent noise reduction and smoothing. According to NIST database data, the characteristic spectral lines of the main alkali metal atoms are sodium (Na) (589.598 nm) and potassium (K) (766.490 nm, 769.896 nm). Flame autoemission spectroscopy was used to obtain the temperature, gaseous sodium concentration, and gaseous potassium concentration changes over time during the combustion detection process, until the combustion process ended. The curves are shown below. Figure 2 As shown, calculate the average temperature T (°C) and the amount of sodium released in the gas phase C according to the following formulas. Na (mg / m 3 ), gas phase potassium release C K (mg / m 3 ):

[0079]

[0080]

[0081]

[0082] In the formula, K(t) represents the change in gaseous potassium concentration over time, and Na(t) represents the change in gaseous sodium concentration over time. Calculations yield: T = 1030℃, C... Na =4218.66mg / m 3 C K =68.86mg / m 3 .

[0083] S3 Combustion Ash Analysis. The mass of the combustion ash was weighed using an electronic balance, obtaining a mass m2 = 4.46 mg. After grinding the combustion ash, a portion of the ash was placed in an X-ray powder fluorescence spectrometer for X-ray powder fluorescence diffraction (XRF) analysis. The mass percentages of sodium oxide and potassium oxide in the ash were obtained, specifically Na2O = 3.87% and K2O = 0.51%. Another portion of the combustion ash sample was taken, and the ash melting point (deformation temperature) T was measured. ash =1246℃.

[0084] S4 Alkali Metal Release Rate Calculation. Based on the calculation results from steps S1 to S3, the alkali metal release rate φ is calculated according to the following formula:

[0085]

[0086] In the formula, the numerator represents the total amount of gaseous alkali metals released during combustion, and the denominator represents the sum of the total amount of gaseous alkali metals and the total amount of alkali metals in the burnt ash. The units of both the numerator and denominator are mg, and the release rate φ is a dimensionless quantity. The role of the alkali metal release rate is to correct the slagging index. Substituting the above calculated data into formula (8), we obtain the alkali metal release rate φ of Zhundong coal as 0.9569.

[0087] Calculate the vapor fouling index R using the following formulas. g With solid fouling index R s :

[0088]

[0089] R s =(1-φ)(Na2O+K2O) (10)

[0090] T / T ash This is a correction factor for the gas phase fouling index, taking into account that in actual boilers, higher flame temperatures make it easier for the ash produced during combustion to become molten, thus exacerbating slagging. Gas phase fouling index R g A higher solids fouling index (R0) indicates a higher amount of gaseous alkali metals released during combustion, and thus a stronger fouling characteristic. sThe higher the value, the higher the solid alkali metal content in the combustible ash of that coal type, and the stronger its fouling characteristics. Since the total amount of alkali metals in coal is constant, there is a certain competition between the solid and gaseous phases, but their effects on fouling differ. The solid phase has a smaller impact on fouling than the gaseous phase. Therefore, 1-φ is introduced as the solid fouling index R. s The correction factor. Gas phase contamination index R g With solid fouling index R s All are dimensionless quantities. Substitute the data and apply R... g With R s All values ​​are converted to percentages to obtain the vapor phase fouling index R. g =0.8034 and solid fouling index R s =0.1889. The total contamination index is the sum of the two, i.e.

[0091] R = R g +R s (11)

[0092] The pollution characteristics of coal are predicted based on the total pollution index. Substituting the data, we get R = 0.9923. The higher the total pollution index, the stronger the predicted pollution characteristics of the coal.

[0093] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting the pollution characteristics of coal combustion in thermal power plants, characterized in that, The method includes the following steps: S1 For the raw coal used in thermal power plants, industrial and elemental analysis is performed to obtain the element content in the raw coal; the volume of flue gas produced by the complete combustion of the raw coal is obtained using the element content. S2 Weigh an appropriate amount of raw coal and record its mass. Burn the weighed raw coal and record the changes in flame temperature, gaseous potassium concentration and gaseous sodium concentration over time during the combustion process. Calculate the average temperature, gaseous sodium release and gaseous potassium release during the combustion process. S3 collects the ash residue after combustion and weighs the ash residue, and detects the ash melting point and the mass ratio of sodium oxide and potassium oxide in the ash residue respectively. S4 calculates the release rate of alkali metals and uses the release rate of alkali metals to solve the solid phase fouling index. It then calculates the gas phase fouling index and sums it with the solid phase fouling index to obtain the total fouling index, thus realizing the prediction of fouling characteristics. In step S4, the solid phase contamination index is determined according to the following formula: Among them, R s It is the solid phase fouling index. Na2O is the alkali metal release rate, Na2O is the mass percentage of sodium oxide in the ash residue, and K2O is the mass percentage of potassium oxide in the ash residue. In step S4, the gas phase contamination index is determined according to the following formula: Among them, R g It is the gaseous fouling index, C Na It is the amount of sodium released in the gas phase, C K V is the amount of potassium released in the gaseous phase, and V is the volume of flue gas produced by the complete combustion of raw coal. m 2 represents the mass of the ashes, T ash The ash melting temperature is T / T ash This is a correction factor for the gas phase fouling index.

2. The method for predicting the pollution characteristics of coal combustion in thermal power plants as described in claim 1, characterized in that, In step S2, the average temperature during the combustion process is determined according to the following formula: Where T is the average temperature during combustion, t0 is the initial moment of stable combustion, t1 is the moment of burnout, T(t) is the change in flame temperature over time during combustion, and t is time.

3. A method for predicting the pollution characteristics of coal combustion in thermal power plants as described in claim 1 or 2, characterized in that, In step S2, the amount of gaseous potassium released during the combustion process is determined according to the following formula: Among them, C K t is the amount of gaseous potassium released, t0 is the initial moment of stable combustion, t1 is the moment of burnout, K(t) is the change of gaseous potassium concentration over time, and t is time.

4. The method for predicting the pollution characteristics of coal combustion in thermal power plants as described in claim 3, characterized in that, In step S2, the amount of gaseous sodium released during the combustion process is determined according to the following formula: Among them, C Na t is the amount of sodium released in the gas phase, t0 is the initial moment of stable combustion, t1 is the moment of burnout, Na(t) is the change of sodium concentration in the gas phase over time, and t is time.

5. The method for predicting the pollution characteristics of coal combustion in thermal power plants as described in claim 4, characterized in that, In step S4, the release rate of the alkali metal is determined according to the following formula: in, It is the alkali metal release rate, C Na It is the amount of sodium released in the gas phase, C K V is the amount of gaseous potassium released, V is the volume of flue gas produced by the complete combustion of raw coal, m2 is the mass of burnt ash, Na2O is the mass percentage of sodium oxide in the ash residue, and K2O is the mass percentage of potassium oxide in the ash residue.

6. The method for predicting the pollution characteristics of coal combustion in thermal power plants as described in claim 1, characterized in that, In step S1, the elemental content includes the respective percentages of C, H, O, and N in the coal type, as well as total moisture (M), volatile matter (V), fixed carbon (FC), and ash (A).

7. A system for predicting the fouling characteristics of coal-fired power plants, characterized in that, The system includes a processor for executing a method for predicting the fouling characteristics of coal-fired power plants as described in any one of claims 1-6.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements a method for predicting the coal contamination characteristics of a thermal power plant as described in any one of claims 1-6.

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