A method and system for calculating boiler flue gas acid dew point

Abstract

The present invention discloses a method and system for calculating the acid dew point of boiler flue gas, which belongs to the technical field of flue gas waste heat recovery. The method of the present invention includes: obtaining key data related to SO3 that affects the constant value and change law of flue gas acid dew point temperature; obtaining multiple theoretical flue gas acid dew points using multiple calculation methods under different calculation modes; obtaining historical data related to the target boiler and the flue gas acid dew point, and determining the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data; using the calculation mode and calculation method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among the multiple theoretical flue gas acid dew points as a calculation scheme for calculating the flue gas acid dew point of the boiler, and calculating the flue gas acid dew point of the boiler based on the calculation scheme. The present invention provides technical support for optimizing the structure of the original flue gas acid dew point temperature calculation mode and the selection of calculation formulas.

Description

Technical Field

[0001] The present invention relates to the technical field of flue gas waste heat recovery, and more particularly, to a method and system for calculating the acid dew point of boiler flue gas. Background Art

[0002] The calculation of flue gas acid dew point temperature is a basic professional technical issue in the research and application of low-temperature corrosion prevention and control of the rear heating surface and flue gas system of coal-fired boilers and flue gas waste heat recovery technology, and has always been the focus of boiler manufacturing and power design industries.

[0003] Before the 1980s, the method for determining the flue gas acid dew point temperature mainly followed the calculation formula in the Soviet Union's boiler unit thermal calculation standard; for the flue gas acid dew point temperature testing technology, some colleges and universities and scientific research institutions discussed the principles of dew point meters, and on this basis, they independently developed several acid dew point meters. Beijing Electric Power Pilot Plant, Zhejiang University, and Shanghai Power Generation Equipment Complete Design Institute have successively developed and manufactured different types of flue gas acid dew point meters and reported their testing results.

[0004] Since the 1980s, with the introduction of European and American power plant boiler design technology, major boiler factories have mainly adopted the ACET criteria developed by the American CE company when determining the allowable wall temperature of the air preheater; in the test of flue gas acid dew point temperature, in addition to some experimental research departments and universities such as Wangting Power Plant and Zhenjiang University of Technology continuing to develop self-made dew point meters, some power experimental research departments have also introduced Western LAND and other brands of dew point meters, but there are not many actual applications on coal-fired furnaces.

[0005] Since the 1990s until around 2005, the limestone-gypsum wet flue gas desulfurization technology has been widely promoted and applied in my country's thermal power plants. However, there is a great deal of controversy over whether to install GGH for wet flue gas dew point temperature assessment. In this context, domestic thermal power design and environmental protection departments have conducted extensive discussions on the feasibility of applying the existing foreign flue gas acid dew point temperature calculation method to verify the acid dew point temperature of wet flue gas. At this time, most of the published literature is a comparison of foreign flue gas acid dew point calculation formulas. In terms of basic theoretical research, Li Yan and others from Tsinghua University reported the test bench research results on the influence of flue gas components SO2, SO3 and H2O on flue gas dew point temperature; and in terms of flue gas acid dew point temperature test technology, the power industry generally believes that the success rate of direct test methods on coal-fired boilers is very low, and tends to adopt the "indirect" method of checking the acid dew point temperature by testing SO3.

[0006] Since 2005, with the research and application of energy-saving and emission-reduction technologies such as low-temperature economizers and low-temperature electrostatic precipitators, in order to determine the reasonable flue gas cooling depth, a new round of research and discussion on flue gas acid dew point temperature and its law of metal corrosion has been carried out in China. In terms of flue gas acid dew point temperature testing technology, practical experience shows that the current acid dew point meter (including LAND dew point meter) has a very poor effect on coal-fired boilers, and other testing methods must be sought; in addition to continuing to study the "indirect" method of checking the acid dew point temperature by testing SO3, there are also 1) "visual method" direct testing methods; 2) based on the concept of "limited corrosion", by testing the corrosion rate law of metal test pieces to determine a more practical acid dew point temperature and other methods.

[0007] As mentioned above, although a lot of research has been done on the determination of flue gas acid dew point temperature and its effect on metal corrosion, and the relevant literature covers multiple industries such as energy, petroleum, chemical industry, metallurgy, and environmental protection, there are still many difficulties that have not been well resolved to date. Summary of the invention

[0008] In view of the above problems, the present invention proposes a method for calculating the acid dew point of boiler flue gas, characterized in that the method comprises:

[0009] Carry out industrial tests on target boilers with different coal types and different operating conditions to obtain key data related to SO3 that affects the constant value and variation of flue gas acid dew point temperature;

[0010] Select multiple calculation methods under different calculation modes, calculate the target boiler based on the acid dew point calculation application criteria and the key data, and obtain multiple theoretical flue gas acid dew points using multiple calculation methods under different calculation modes;

[0011] Acquire historical data related to the flue gas acid dew point of the target boiler, and determine the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data;

[0012] The calculation mode and method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among multiple theoretical flue gas acid dew points are used as a calculation scheme for calculating the flue gas acid dew point of the boiler, and the flue gas acid dew point of the boiler is calculated based on the calculation scheme.

[0013] Optionally, when conducting industrial tests on different types of coal and under different operating conditions, a sampler with flow metering is used to collect samples, and the test washing liquid is a washing liquid with a color-changing agent. If the color of the washing liquid changes from the original light blue to pink, it is confirmed that SO3 has escaped. If SO3 has escaped, sampling is performed again.

[0014] Optionally, if there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until there is a theoretical flue gas acid dew point falling within the threshold range.

[0015] Optional, calculation schemes, including: original flue gas acid dew point temperature calculation scheme and net flue gas acid dew point temperature calculation scheme;

[0016] The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal;

[0017] The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method.

[0018] Optional, acid dew point calculation application criteria, including: acid dew point temperature calculation application criteria in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines.

[0019] In another aspect, the present invention further provides a system for calculating the acid dew point of boiler flue gas, comprising:

[0020] The data acquisition unit is used to obtain key data related to SO3 that affects the constant value and change law of flue gas acid dew point temperature after industrial testing of the target boiler with different coal types and different operating conditions;

[0021] A first calculation unit is used to select a plurality of calculation methods under different calculation modes, and calculate a plurality of theoretical flue gas acid dew points obtained by using a plurality of calculation methods under different calculation modes for a target boiler based on the acid dew point calculation application criteria and the key data;

[0022] A second calculation unit is used to obtain historical data related to the flue gas acid dew point of the target boiler, and determine a standard value and a threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data;

[0023] The output unit is used to use the calculation mode and calculation method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among multiple theoretical flue gas acid dew points as a calculation scheme for calculating the flue gas acid dew point of the boiler, and calculate the flue gas acid dew point of the boiler based on the calculation scheme.

[0024] Optionally, when conducting industrial tests on different types of coal and under different operating conditions, a sampler with flow metering is used to collect samples, and the test washing liquid is a washing liquid with a color-changing agent. If the color of the washing liquid changes from the original light blue to pink, it is confirmed that SO3 has escaped. If SO3 has escaped, sampling is performed again.

[0025] Optionally, if there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until there is a theoretical flue gas acid dew point falling within the threshold range.

[0026] Optional, calculation schemes, including: original flue gas acid dew point temperature calculation scheme and net flue gas acid dew point temperature calculation scheme;

[0027] The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal;

[0028] The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method.

[0029] Optional, acid dew point calculation application criteria, including: acid dew point temperature calculation application criteria in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention proposes a method for calculating the acid dew point of boiler flue gas, including: for a target boiler, industrial tests of different coal types and different working conditions are carried out to obtain key data related to SO3 that affect the constant value and change law of flue gas acid dew point temperature; select multiple calculation methods under different calculation modes, calculate the target boiler based on the acid dew point calculation application criteria and the key data, and use multiple theoretical flue gas acid dew points obtained by multiple calculation methods under different calculation modes; obtain historical data related to the flue gas acid dew point of the target boiler, and determine the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data; use the calculation mode and calculation method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among multiple theoretical flue gas acid dew points as a calculation scheme for calculating the flue gas acid dew point of the boiler, and calculate the flue gas acid dew point of the boiler based on the calculation scheme. The present invention proposes a new method for improving and perfecting the calculation of the acid dew point temperature of coal-fired flue gas, and provides technical support for optimizing the structure of the original flue gas acid dew point temperature calculation mode and the selection of calculation formulas. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the method of the present invention;

[0033] Figure 2 It is a structural diagram of the system of the present invention. DETAILED DESCRIPTION

[0034] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0035] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0036] Embodiment 1:

[0037] The present invention proposes a method for calculating the acid dew point of boiler flue gas, such as Figure 1 As shown, including:

[0038] Step 1: Carry out industrial tests on target boilers with different coal types and different operating conditions to obtain key data related to SO3 that affects the constant value and variation law of flue gas acid dew point temperature;

[0039] Step 2, selecting a plurality of calculation methods under different calculation modes, and calculating a target boiler based on the acid dew point calculation application criteria and the key data, and obtaining a plurality of theoretical flue gas acid dew points using a plurality of calculation methods under different calculation modes;

[0040] Step 3, obtaining historical data related to the flue gas acid dew point of the target boiler, and determining the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data;

[0041] Step 4: The calculation mode and method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among multiple theoretical flue gas acid dew points are used as a calculation scheme for calculating the flue gas acid dew point of the boiler, and the flue gas acid dew point of the boiler is calculated based on the calculation scheme.

[0042] Among them, when conducting industrial tests on different types of coal and different working conditions, a sampler with flow metering is used to collect samples, and the test washing liquid is a washing liquid with a color-changing agent. If the color of the washing liquid changes from the original light blue to pink, it is confirmed that SO3 has escaped. If SO3 has escaped, sampling is carried out again.

[0043] If there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until a theoretical flue gas acid dew point falls within the threshold range.

[0044] The calculation scheme includes: the original flue gas acid dew point temperature calculation scheme and the net flue gas acid dew point temperature calculation scheme;

[0045] The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal;

[0046] The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method.

[0047] Among them, the application criteria for acid dew point calculation include: application criteria for acid dew point temperature calculation in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines.

[0048] In the present invention, a perfect condensation control method is selected to carry out SO3 testing, including:

[0049] 1) In principle, it is consistent with the national standard GB / T21508 and the industry standard DL / T998;

[0050] 2) The sampling design is more perfect, consisting of a heated sampling gun + heated hose + fly ash filter + two-stage series serpentine glass tube (the final stage uses a reinforced type) collector / water bath + automatic sampler (including flow meter);

[0051] 3) The test process is equipped with a terminal detection mechanism. The washing liquid used for the test is a washing liquid with a color change indicator. It is required that the washing liquid in the second half of the last stage of the absorption tube should not change from light blue to pink during the flushing. If it changes color, it indicates that SO3 may escape and has not been absorbed. It will be treated as a waste sample. At this time, the sample is re-prepared by adjusting the flow rate of flue gas extraction (generally reducing it) and increasing the length of the absorption tube to ensure that the extracted sample is qualified. If there is still part that has not changed color during the previous flushing, the tester will increase the flue gas flow rate to increase the total amount of SO3 to ensure accuracy;

[0052] 4) In operation, the water bath temperature should be controlled reasonably. The water dew point should be calculated according to the smoke humidity, pressure, etc. for each test. The water bath temperature should be controlled to 5-10℃ above the water dew point, and the collector outlet should be kept warm to avoid condensation due to the smoke temperature being lower than the water dew point.

[0053] In the present invention, the calculation scheme includes: a calculation scheme for the acid dew point temperature of raw flue gas and a calculation scheme for the acid dew point temperature of net flue gas;

[0054] The following is a detailed description of the two calculation schemes mentioned above:

[0055] Calculation scheme for the acid dew point temperature of raw flue gas:

[0056] The original flue gas acid dew point temperature calculation scheme includes the following modes:

[0057] Acid dew point calculation model A based on coal quality analysis data;

[0058] The basic formula 1 (upper limit 1) of mode A is as follows:

[0059]

[0060] In formula (1):

[0061] n=α fly ·A sp (2)

[0062] In formula (2):

[0063] S SP The sulfur content of fuel is converted into

[0064] A SP is the fuel ash content,

[0065] t DT.0 is the pure water dew point temperature in flue gas, in °C; n is an index indicating the degree of influence of fly ash content on acid dew point; α fly is the fly ash share, for pulverized coal furnace α fly =0.8~0.9;

[0066] β is the excess air coefficient α at the furnace outlet F The relevant parameters are determined by the following formula:

[0067]

[0068]

[0069] Among them, Δα F =(α F-1)×100; B is the coefficient, when SO3≤5ppm, take b=40, when SO3≥5ppm, take b=52; f c The combustible component correction factor for the sulfur content in coal is generally 0.85 to 0.9; Δt DT.SCR It is the increase in acid dew point temperature of flue gas after passing through the SCR denitrification device, in ℃.

[0070] Mode A basic formula 2 (low lower limit) is as follows:

[0071]

[0072] In formula (5), K C is the comprehensive correction coefficient of the effect of fly ash alkalinity on SO3 conversion rate;

[0073] Acid dew point calculation model B based on flue gas composition:

[0074] Mode B basic formula 1, Mode B basic equation recommends the following equation as the calculation formula for the upper limit value 2 of the original flue gas acid dew point, as follows:

[0075]

[0076] In formula (6), SO3 is the SO3 component in the flue gas (according to the excess air coefficient at the calculation point), %; V a.wg The flue gas volume of 1kg coal completely burned (according to the excess air coefficient at the calculation point), Nm 3 / kg.

[0077] Mode B basic formula 2, the original flue gas acid dew point temperature calculation formula based on the flue gas composition, its general empirical formula structure is:

[0078] t DT =a+blg[SO3]+clg[H2O], ℃; (7)

[0079] or DT =a+blg[P SO3 ]+clg[P H2O ], ℃; (8)

[0080] In formulas (7) and (8), a, b, and c are constant coefficients in the empirical formulas.

[0081] Among them, for the original flue gas with SO3≥5ppm, the following equation is used as the acid dew point lower limit verification formula:

[0082] t DT =200+52lgSO3+40lgH2O,℃; (9)

[0083] In formula (9), SO3 is the SO3 component in the flue gas (according to the excess air coefficient at the calculation point), %; H2O is the water vapor component in the flue gas (according to the excess air coefficient at the calculation point), %.

[0084] The calculation methods for Mode A and Mode B include the following:

[0085] Water dew point temperature t DT.0 Calculation method:

[0086] Calculation formula 1 (standard formula) is as follows:

[0087]

[0088] In formula (10), P H2O is the partial pressure of water vapor in the original flue gas, and the excess air coefficient α is calculated according to the combustion system. / / or α n The calculation data is based on kPa;

[0089] Calculation formula 2 (calculation formula) is as follows:

[0090] t DT.0 =6.715+13.787lnP H2O +1.357[lnP H2O ] 2 ,℃;(11)

[0091] Among them, the comprehensive correction coefficient of fly ash alkalinity is 1 / K C ,as follows:

[0092] 1 / K C =(1 / K)+0.08 (12)

[0093] In formula (12):

[0094]

[0095] For lgR opt For the range of <1.9 (mainly corresponding to low sulfur coal), the following equation with better fitting degree is used:

[0096]

[0097] In formula (14),

[0098] In summary, the determination of SO3 composition in acid dew point calculation is calculated according to the following equation:

[0099]

[0100]

[0101] In formulas (16) and (17), K G is the gaseous proportion of SO3. In the calculation, K can be taken for the original flue gas. G =0.95; SO2 and It is the calculated value of SO2 composition and partial pressure when the coal ash alkalinity correction is not considered in the combustion calculation.

[0102] The supporting calculation methods for coal quality characteristics include the following:

[0103] Correction factor for coal ash basicity (According to the standard formula of domestic test data), the calculation formula is as follows

[0104]

[0105] Among them, A b =0.239α fly A SP (7CaO+3.5MgO+Fe2O3)(19)

[0106] The correction factor φ of coal ash alkalinity (calibration formula) is as follows:

[0107]

[0108] in,

[0109] The total sulfur / coal ash composition factor U is used as the basic parameter, as follows:

[0110] U=f(∑CaO、S ar , A ar )

[0111] ∑CaO=CaO+1.39MgO (22)

[0112] SO3 conversion rate K SO3 , the formula is as follows:

[0113] K SO3 =K F ×Δα F m (twenty one)

[0114] The coefficient K for smoke, lean coal, and pulverized coal furnaces F The values ​​of and m are shown in Table 1:

[0115] Table 1

[0116]

[0117] Among them, Δα Fis the excess air coefficient parameter; Δα F =100(α F -1); K G It is the gaseous proportion of SO3 in the original flue gas, which can usually be taken as 0.95.

[0118] SO3 conversion rate K for lignite and pulverized coal furnace F ×100% is determined by the following empirical equation:

[0119] U=0.35~0.55, K F ×100%=exp[-3.045+5.88U];

[0120] U=0.5~1.1, K F ×100%=exp[-1.059+2.326U];

[0121] U=1~1.5, K F ×100%=exp[-0.1+1.35U];

[0122] Among them, the calculation method used for the supporting data used for comparison and calculation with the test data in the calculation process is as follows:

[0123] The total amount of dry basis SO3 in the flue gas is calculated as follows:

[0124]

[0125] In formula (22), SO2 is the standard excess air coefficient α of the combustion system. n Calculated wet basis data.

[0126] Estimation method of the increase in acid dew point temperature of original flue gas after SCR denitrification:

[0127] The increase of acid dew point temperature Δt after flue gas passes through SCR denitrification device DT.SCR , determined by the following formula:

[0128]

[0129] In formula (23), K SO3 K is the SO3 conversion rate of flue gas at the inlet of the SCR denitrification device, calculated by volume ppm, or 0.8 times the mass ratio; SO3.SCR is the SO3 conversion rate of flue gas increased in the SCR denitrification device, generally taken as ≤1%; b is the empirical coefficient, when SO3≤5ppm, b=40, when SO3≥5ppm, b=52.

[0130] Correction scheme for the calculation method of acid dew point of original flue gas by cooling / dust removal:

[0131] The revised opinions on the acid dew point temperature ADTc under the original flue gas cooling conditions are as follows:

[0132] When the flue gas temperature drops, the change in acid dew point temperature can be estimated as follows:

[0133]

[0134] In formula (24), a, b, n, M, and N are coefficients, and M and N are taken according to Table 2;

[0135] Table 2

[0136]

[0137] When the flue gas temperature decreases, the result calculated by the above formula is a negative value, indicating that the acid dew point temperature decreases as the flue gas temperature decreases.

[0138] The revised opinions on the acid dew point temperature ADTc of the original flue gas dust removal working condition are as follows:

[0139] The change in the acid dew point temperature of the flue gas at the outlet of the electrostatic precipitator can be estimated by the following formula:

[0140]

[0141] In formula (25), t DT,1 is the acid dew point of the flue gas at the dust collector inlet, ℃; SO 3,1 、SO 3,2 is the SO3 concentration of the flue gas at the inlet and outlet of the dust collector; a, b, n are coefficients; Δt DT,jc It is the change of acid dew point caused by flue gas dust settling.

[0142] The present invention uses the Taylor data table as a reference for evaluating the acid dew point change rate of the original flue gas cooling condition; according to the different water vapor partial pressures, a detailed fitting formula is proposed, and its verification result is basically consistent with the data table.

[0143] The present invention proposes a correction calculation formula for the change in flue gas acid dew point due to flue gas temperature change; after the initial acid dew point of the flue gas and the cooling range are known, the recommended formula can be used to calculate the change in the acid dew point during the flue gas cooling process and the acid dew point temperature corresponding to the final flue gas temperature, and the safety of the flue gas cooling depth can be evaluated accordingly.

[0144] The calculation example of the present invention shows that under the flue gas cooling condition, the flue gas temperature of high-sulfur coal is allowed to be reduced to 90-95°C, and the initial dew point of the original flue gas should not exceed 110°C; the flue gas temperature of low-sulfur coal is allowed to be reduced to 80-85°C, and the initial dew point of the original flue gas should not exceed 100°C.

[0145] In the present invention, the adsorption effect of fly ash on SO3 in flue gas will extend to the downstream of the electrostatic precipitator. If the possible SO3 removal efficiency factor of the electrostatic precipitator is taken into account, when determining the flue gas cooling depth of the heat exchanger set downstream of the electrostatic precipitator, a lower acid dew point temperature value is allowed under the same original flue gas SO3 concentration conditions.

[0146] Calculation method of net flue gas acid dew point temperature:

[0147] Calculation of the upper limit of the acid dew point temperature of clean flue gas (SO3≤10ppm):

[0148] The preferred "acid dew point temperature calculation formula for converting coal quality benchmark to flue gas composition benchmark" in the present invention is:

[0149] The following formula is used as the standard value for calculating the net flue gas acid dew point temperature:

[0150]

[0151] In formula (26), SO3 is the volume concentration of SO3 in the clean flue gas, %; β is the coefficient, which is determined according to the original flue gas calculation method, usually β = 121; Φ is the flue gas alkalinity correction coefficient, which is determined according to the original flue gas calculation method; V a.wg is the actual wet flue gas volume per kg of coal, Nm 3 / kg, calculated and determined according to the desulfurization tower outlet conditions.

[0152] In the present invention, the upper limit check value is determined according to the universal curve diagram.

[0153] The lower limit of the acid dew point temperature of clean flue gas (SO3≤10ppm) is as follows:

[0154] In the present invention, the lower limit calibration value is determined according to the Taylor curve;

[0155] If the acid dew point determined by the Taylor curve is less than 60℃, use 60℃.

[0156] Calculation of net flue gas composition and partial pressure:

[0157] Calculation of SO3 concentration in net flue gas, including:

[0158] In the present invention, Estimate the basic value, and then estimate the SO3 concentration (dry basis) in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. The SO3 removal efficiency of the absorber is usually 60% to 95%, with the higher value for low-sulfur coal and the lower limit for high-sulfur coal.

[0159] The main calculation steps are as follows:

[0160] The calculation formula for SO3 concentration (dry basis) in the original flue gas at the desulfurization tower inlet is as follows:

[0161]

[0162] In formula (27), SO′2 is the SO2 concentration in the FGD inlet flue gas, mg / Nm d 3 ; is the proportion of SO3 in the FGD inlet flue gas converted to SO3, which is 1.5%, that is,

[0163] The SO3 concentration (dry basis) in the net flue gas at the outlet of the desulfurization tower is calculated as follows:

[0164]

[0165]

[0166] In formula (28) and (29) is the desulfurization efficiency of the desulfurization tower, which is 0.96-0.98 for high-sulfur coal and 0.95 for low-sulfur coal;

[0167] is the SO3 conversion rate in the flue gas at the outlet of the desulfurization tower. According to the experimental data of Jiulong Power Plant, 2% can be taken in the preliminary calculation, that is, Estimate the basic value, and then estimate the SO3 concentration (dry basis) in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. The SO3 removal efficiency of the absorber is usually 60% to 95%, with the higher value for low-sulfur coal and the lower limit for high-sulfur coal.

[0168] Δα GGH is the air leakage coefficient of GGH (based on the smoke volume at the GGH inlet), and for the rotary GGH, Δα is taken GGH =0.03, take Δα for tube-box GGH GGH =0.00~0.0005.

[0169] The calculation formula for the water vapor partial pressure in the clean flue gas is as follows:

[0170] It is known that the water vapor content in the clean flue gas is H2O N , then the water vapor partial pressure in the clean flue gas is:

[0171]

[0172] In formula (30), P g ——absolute pressure of clean flue gas, kPa or at;

[0173] in:

[0174]

[0175] Among them, ΔP fgd is the flue gas negative pressure (gauge pressure) in the desulfurization tower, kPa or at; P a is the ambient atmospheric pressure, usually P a =101.3kPa or 1at.

[0176] Calculation of SO3 partial pressure in net flue gas, including:

[0177] Determined based on wet gaseous conditions, including:

[0178] The SO3" share in the net flue gas is calculated as follows:

[0179]

[0180] SO3"(ppm)(wet basis) = 0.28SO3"(dry basis), ppm(33)

[0181] SO3" partial pressure in clean flue gas The calculation formula is as follows:

[0182]

[0183] or

[0184] in, ——The gaseous fraction of SO3 in the clean flue gas is taken as 0.45, 0.5 and 0.75 respectively when the superheat is +5℃, +(10~30)℃ and +40℃, or it can be taken according to the relationship diagram of the gaseous fraction of SO2 in the clean flue gas and the superheat.

[0185] The calculation formula for the partial pressure of sulfuric acid vapor in the clean flue gas is as follows:

[0186]

[0187] In summary:

[0188] The acid dew point temperature of clean flue gas is lower than that of original flue gas; if GGH can heat the clean flue gas to above 72℃~80℃, it is possible to make the metal wall temperature higher than the acid dew point temperature.

[0189] When GGH heats the clean flue gas to above 72°C, that is, the superheat of the clean flue gas is above +26°C, the gaseous portion of SO3 is more than 50%. Theoretically, this part of SO3 no longer constitutes a corrosion source, and the aerosol SO3 part basically avoids the corrosion zone because the wall temperature is higher than the flue gas acid dew point. In fact, whether local corrosion of the flue metal wall can be avoided at this time is largely related to whether the flue gas carries mechanical water droplets and other conditions, which depends on the grade and operation of the demister.

[0190] Considering the uneven heating temperature of flue and chimney inner wall by GGH, and the possibility that the clean flue gas after heating still contains a small amount of gypsum slurry, fine mist acid liquid and even acid water droplets, anti-corrosion measures are still required for the low temperature area of ​​GGH and the inner wall of GGH outlet flue and chimney. However, its anti-corrosion level is allowed to be lower than that of "wet chimney" without GGH.

[0191] The following details the application criteria for calculating the flue gas acid dew point temperature:

[0192] The application criteria of acid dew point temperature calculation in thermal power plant design include the following:

[0193] Original flue gas temperature criteria to avoid low temperature corrosion:

[0194] In order to avoid or reduce low temperature corrosion, the original flue gas temperature t g.0 or metal wall temperature t m.0 It should be determined according to the following principles, including:

[0195] 1) The flue gas temperature t in the tail flue g.0 or metal wall temperature t m.0 :

[0196] 2) Should be higher than the acid dew point temperature ADT inst or ADT c , and leave a temperature margin of not less than 5℃, otherwise anti-corrosion measures should be taken;

[0197] 3) The acid dew point calculation temperature ADTc is determined according to the calculation method 3.1;

[0198] 4) For the outlet flue of the electrostatic precipitator, the acid dew point calculation temperature ADT c Determined according to the above-mentioned “Correction of the calculation method of acid dew point of original flue gas due to cooling / dust removal”.

[0199] Application criteria for air / air heat exchangers:

[0200] 1) Acid dew point calculation temperature ADT c Determined according to the above-mentioned “Calculation method of acid dew point temperature of raw flue gas”;

[0201] 2) Cold end smoke temperature θ G: It should be higher than the acid dew point temperature ADT and leave a temperature margin of not less than 5℃, or according to the acid dew point temperature ADT of limited corrosion rate lim The allowable average wall temperature ACET, whichever is lower, can be used;

[0202] When the inlet air temperature is given, the lower limit of the exhaust temperature determined by ACET is:

[0203] θ G ≥2×ACET-t AH.I ℃

[0204] 3) Cold end temperature t AH.I :It is advisable to follow the acid dew point temperature ADT with limited corrosion rate lim The permissible average wall temperature ACET is determined;

[0205] When the exhaust gas temperature is given, the lower limit of the inlet air temperature determined by ACET is:

[0206] t AH.I ≥2×ACET-θ G ℃

[0207] For low calorific value bituminous coal and lignite with CaO+MgO≥Fe2O3 in ash, when using the curve of the relationship between the average cold end temperature ACET and the sulfur content of the coal, the sulfur content should be converted into the equivalent sulfur content Seq according to the following formula, that is:

[0208]

[0209] Wherein, Qgr,ar is the received basis high calorific value of coal, kJ / kg.

[0210] For other rotary air preheater products, the required inlet air temperature or exhaust gas temperature lower limit should be calculated based on the cold end wall temperature allowed by the manufacturer.

[0211] Application criteria for the air / water heat exchanger (low temperature economizer) in the tail duct downstream of the air preheater:

[0212] 1) Cold end wall temperature t m.0 :It is advisable to follow the acid dew point temperature ADT with limited corrosion rate lim to determine;

[0213] 2) Cold end smoke temperature t g.0 : is the cold end wall temperature t m.0 Increase heat transfer temperature difference.

[0214] Application criteria for electrostatic precipitator inlet ducts:

[0215] When a low-temperature economizer is set, the acid dew point calculation temperature ADT cDetermined by the above-mentioned "correction of the original flue gas acid dew point calculation method by cooling / dust removal".

[0216] 1.5 Net flue gas temperature to avoid low temperature corrosion of tail flue

[0217] In order to avoid or reduce low temperature corrosion of the tail flue after wet desulfurization, the net flue gas temperature tg. C Or metal wall temperature tm .C It should be determined according to the following principles:

[0218] 1) Acid dew point calculation temperature ADT c Determined by "Calculation method of net flue gas acid dew point temperature"

[0219] 2) It should be higher than the calculated value of the acid dew point temperature ADTc of the clean flue gas and leave a temperature margin of 5 to 10°C, otherwise anti-corrosion measures should be taken according to the level of highly corrosive flue gas.

[0220] When GGH heats the clean flue gas to above 70℃, that is, the superheat of the clean flue gas is above +20℃, the gaseous portion of SO3 is more than 50%. Theoretically, this part of SO3 no longer constitutes a corrosion source, and the aerosol SO3 part basically avoids the corrosion zone because the wall temperature is higher than the flue gas acid dew point. In fact, whether local corrosion of the flue metal wall can be avoided at this time is largely related to whether the flue gas carries mechanical water droplets and other conditions, which depends on the grade and operation of the demister.

[0221] The present invention takes into account the uneven heating temperature of the flue and chimney inner wall by GGH, and the possibility that the clean flue gas after heating still contains a small amount of gypsum slurry, fine mist acid liquid and even acid water droplets, so anti-corrosion measures should still be taken for the low temperature area of ​​GGH and the flue and chimney inner wall of GGH outlet. However, its anti-corrosion level is allowed to be lower than that of the "wet chimney" without GGH.

[0222] For chimneys made of non-steel inner tubes, the present invention should also pay attention to verifying the static pressure distribution inside the smoke exhaust pipe; if the static pressure exceeds the standard and the mechanical water content exceeds the standard, simply heating the flue gas to above 70°C is not enough to prevent the inner wall of the smoke exhaust pipe from being corroded by wet flue gas.

[0223] Acid Dew Point Temperature (ADT) lim Method for determining:

[0224] Guidelines for the use of graphical representations:

[0225] 1) The low-temperature corrosion of the boiler tail heating surface can be divided into two corrosion peaks. The first peak appears at a temperature several tens of degrees below the acid dew point, and the second peak appears near the water dew point. There is a valley with a low corrosion rate between the two peaks, which can be located as the acid dew point temperature ADT with a limited corrosion rate. limdistrict;

[0226] 2) The difference Δt between the wall temperature t0 of the first corrosion rate peak area and the acid dew point temperature ADT is related to the acid dew point temperature ADT. The higher the acid dew point, the larger the difference, and the lower the acid dew point, the smaller the difference.

[0227] Application criteria for the relationship between low temperature corrosion rate and wall temperature of the boiler tail heating surface:

[0228] Experiments show that a corrosion peak appears near the acid dew point temperature; and there is a low corrosion rate temperature zone between the wall temperature of the corrosion peak and the water dew point temperature. Although this temperature zone is several dozen degrees lower than the acid dew point temperature, the corrosion rate is very low, so the working life of the heated surface can be very long.

[0229] Evaluation index: A judgment index of 0.1-0.15 mm / a as the allowable corrosion rate is formulated for low-temperature corrosion of the heating surface at the rear of the boiler;

[0230] Typical relationships between the peak corrosion rate and wall temperature include the following:

[0231] Observations on tubular air preheaters show that when burning fuels with a high sulfur content, the area where corrosion is greatest is not on the cold side, but in the higher temperature area where the wall temperature is close to the acid dew point temperature;

[0232] Observation of the economizer shows that when burning suburban coal, the wall thickness at the outlet of the pipe with higher water temperature (120°C) decreased by 1.5mm after two years of operation, but the wall thickness at the outlet of the pipe with lower water temperature (110-112°C) remained unchanged;

[0233] Observations on heating economizers show that when lean coal is used, the reduction in tube diameter is 0.6-0.7 mm / a in areas where the water temperature is below 60°C, while the reduction in tube diameter is 0.0-0.2 mm / a in the outlet area where the water temperature is higher (75-106°C);

[0234] Controlling the limited corrosion rate acid dew point temperature ADT lim Reference Guidelines

[0235] 1) In order to eliminate severe corrosion, the wall temperature range of 105-138°C must be avoided;

[0236] 2) From the perspective of allowable corrosion rate index, the flue gas acid dew point temperature is divided into "acid dew point temperature ADT c " and "the temperature ADT at which there is no risk of corrosion (i.e., limited corrosion rate) lim These two different concepts:

[0237] For various fuels, the "lower limit temperature without corrosion risk" is close to 20°C above the water dew point temperature (corresponding to the water vapor partial pressure in the flue gas);

[0238] The "upper limit temperature without risk of corrosion" is determined by tests;

[0239] 3) The "acid dew point temperature" and "temperature without corrosion risk" of a certain type of coal are shown in Table 3:

[0240] For domestic fuel use, the guidelines are as follows:

[0241] (1) “Lower temperature without corrosion risk” ADT lim.l It can be used according to the water dew point temperature +20℃;

[0242] (2) “Upper limit temperature without corrosion risk” ADT lim.u For general bituminous coal, the temperature can be 80-90℃.

[0243] The present invention determines a calculation scheme for the acid dew point, and provides a reference basis for formulating an application criterion for calculating the acid dew point temperature of flue gas.

[0244] Embodiment 2:

[0245] The present invention also provides a system 200 for calculating the acid dew point of boiler flue gas, such as Figure 2 As shown, including:

[0246] The data acquisition unit 201 is used to obtain key data related to SO3 that affects the constant value and change law of flue gas acid dew point temperature after industrial testing of different coal types and different operating conditions on the target boiler;

[0247] The first calculation unit 202 is used to select a plurality of calculation methods under different calculation modes, and calculate a plurality of theoretical flue gas acid dew points obtained by using a plurality of calculation methods under different calculation modes for a target boiler based on the acid dew point calculation application criteria and the key data;

[0248] The second calculation unit 203 is used to obtain historical data related to the flue gas acid dew point of the target boiler, and determine the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data;

[0249] The output unit 204 is used to use the calculation mode and calculation method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among multiple theoretical flue gas acid dew points as a calculation scheme for calculating the flue gas acid dew point of the boiler, and calculate the flue gas acid dew point of the boiler based on the calculation scheme.

[0250] Among them, when conducting industrial tests on different types of coal and different working conditions, a sampler with flow metering is used to collect samples, and the test washing liquid is a washing liquid with a color-changing agent. If the color of the washing liquid changes from the original light blue to pink, it is confirmed that SO3 has escaped. If SO3 has escaped, sampling is carried out again.

[0251] If there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until a theoretical flue gas acid dew point falls within the threshold range.

[0252] The calculation scheme includes: the original flue gas acid dew point temperature calculation scheme and the net flue gas acid dew point temperature calculation scheme;

[0253] The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal;

[0254] The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method.

[0255] Among them, the application criteria for acid dew point calculation include: application criteria for acid dew point temperature calculation in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines.

[0256] The present invention proposes a new method for improving and perfecting the calculation of the acid dew point temperature of coal-fired flue gas, and provides technical support for optimizing the structure of the original flue gas acid dew point temperature calculation model and the selection of the calculation formula.

[0257] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes. The schemes in the embodiments of the present invention may be implemented in various computer languages, for example, object-oriented programming language Java and literal scripting language JavaScript, etc.

[0258] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0259] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0260] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0261] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0262] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for calculating the acid dew point of boiler flue gas, characterized in that: The method comprises: Carry out industrial tests on target boilers with different coal types and different operating conditions to obtain key data related to SO3 that affects the constant value and variation of flue gas acid dew point temperature; Select multiple calculation methods under different calculation modes, calculate the target boiler based on the acid dew point calculation application criteria and the key data, and obtain multiple theoretical flue gas acid dew points using multiple calculation methods under different calculation modes; Acquire historical data related to the flue gas acid dew point of the target boiler, and determine the standard value and threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data; The calculation mode and method corresponding to the theoretical flue gas acid dew point that falls within the threshold range and is closest to the standard value among the multiple theoretical flue gas acid dew points are used as a calculation scheme for calculating the flue gas acid dew point of the boiler, and the flue gas acid dew point of the boiler is calculated based on the calculation scheme; If there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until a theoretical flue gas acid dew point falls within the threshold range; The calculation scheme includes: a calculation scheme for the acid dew point temperature of raw flue gas and a calculation scheme for the acid dew point temperature of net flue gas; The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal; The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method; The acid dew point calculation application criteria include: application criteria for acid dew point temperature calculation in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines for Among them, the original flue gas acid dew point temperature calculation scheme includes: The original flue gas acid dew point temperature calculation scheme includes the following modes: Acid dew point calculation model A based on coal quality analysis data; The basic formula 1 of mode A, and the upper limit value 1, are as follows: In formula (1): n=a fly ·A sp (2) In formula (2): S SP The sulfur content of fuel is converted into A SP is the fuel ash content, Among them, t DT.0 is the pure water dew point temperature in flue gas, in °C; n is an index indicating the degree of influence of fly ash content on acid dew point; α fly is the fly ash share, for pulverized coal furnace α fly =0.8~0.9; β is the excess air coefficient α at the furnace outlet F The relevant parameters are determined by the following formula: Among them, Δα F =(α F -1)×100; B is the coefficient, when SO3≤5ppm, take b=40, when SO3≥5ppm, take b=52; f c The combustible component correction factor for the sulfur content in coal is generally 0.85 to 0.9; Δt DT.SCR is the increase in acid dew point temperature of flue gas after passing through the SCR denitrification device, in °C; The basic formula 2 of Mode A and the lower limit are as follows: In formula (5), K C is the comprehensive correction coefficient of the effect of fly ash alkalinity on SO3 conversion rate; Acid dew point calculation model B based on flue gas composition: Mode B basic formula 1, Mode B basic equation recommends the following equation as the calculation formula for the upper limit value 2 of the original flue gas acid dew point, as follows: In formula (6), SO3 is the SO3 component in the flue gas, calculated according to the excess air coefficient at the calculation point, %; V a.wg The flue gas volume of 1kg coal completely burned is calculated according to the excess air coefficient at the calculation point, Nm 3 / kg; Mode B basic formula 2, the original flue gas acid dew point temperature calculation formula based on the flue gas composition, its general empirical formula structure is: t DT =a+blg[SO3]+clg[H2O],℃; (7) or DT =a+blg[P SO3 ]+clg[P H2O ], ℃; (8) In formulas (7) and (8), a, b, and c are constant coefficients in the empirical formulas; Among them, for the original flue gas with SO3≥5ppm, the following equation is used as the acid dew point lower limit verification formula: t DT =200+52lgSO3+40lg H2O,℃; (9) In formula (9), the calculation is performed according to the excess air coefficient at the calculation point, SO3 is the SO3 component in the flue gas, %; the calculation is performed according to the excess air coefficient at the calculation point, H2O is the water vapor component in the flue gas, %; The calculation methods for Mode A and Mode B include the following: Water dew point temperature t DT.0 Calculation method: The calculation formula 1 and the standard formula are as follows: In formula (10), P H2O is the partial pressure of water vapor in the original flue gas, and the excess air coefficient α / / or α n The calculation data is based on kPa; Calculation formula 2 and calculation formula are as follows: t DT.0 =6.715+13.787ln P H2O +1.357[ln P H2O ] 2 ,℃; (11) Among them, the comprehensive correction coefficient of fly ash alkalinity is 1 / K C ,as follows: 1 / K C =(1 / K)+0.08 (12) In formula (12): For lgR opt The range of <1.9 corresponds to low sulfur coal, and the following equation with better fitting degree is used: In formula (14), In summary, the determination of SO3 composition in acid dew point calculation is calculated according to the following equation: In formulas (16) and (17), K G is the gaseous proportion of SO3. In the calculation, K can be taken for the original flue gas. G =0.95; SO2 and It is the calculated value of SO2 composition and partial pressure when the coal ash alkalinity correction is not considered in the combustion calculation; The supporting calculation methods for coal quality characteristics include the following: According to the standard calculation of domestic test data, the coal ash alkalinity correction factor The calculation formula is as follows: Among them, A b =0.239α fly A SP (7CaO+3.5MgO+Fe2O3) (19) The correction coefficient φ of coal ash alkalinity and the verification formula are as follows: in, The total sulfur / coal ash composition factor U is used as the basic parameter, as follows: U=f(∑CaO、S ar 、A ar ) ∑CaO=CaO+1.39MgO (22) SO3 conversion rate K SO3 , the formula is as follows: K SO3 =K F ×Δα F m (21) The coefficient K for smoke, lean coal and pulverized coal furnaces F And the value of m is as follows: When the coal type is low sulfur coal, S ar ≤1.00,K F is 0.15, m is 0.86; When the coal type is medium sulfur coal, S ar =1.01~2.0, K F is 0.11, m is 0.86; When the coal type is high sulfur coal, S ar =2.01~3.0,K F is 0.137, m is 0.86; Among them, Δα F is the excess air coefficient parameter; Δα F =100(α F -1); K G It is the gaseous proportion of SO3 in the original flue gas, which can usually be taken as 0.95; SO3 conversion rate K for lignite and pulverized coal furnace F ×100% is determined by the following empirical equation: U=0.35~0.55, K F ×100%=exp[-3.045+5.88U]; U=0.5~1.1, K F ×100%=exp[-1.059+2.326U]; U=1~1.5, K F ×100%=exp[-0.1+1.35U]; Among them, the calculation method used for the supporting data used for comparison and calculation with the test data in the calculation process is as follows: The total amount of dry basis SO3 in the flue gas is calculated as follows: In formula (22), SO2 is the standard excess air coefficient α of the combustion system. n Calculated wet basis data; Estimation method of the increase in acid dew point temperature of original flue gas after SCR denitrification: The increase of acid dew point temperature Δt after flue gas passes through SCR denitrification device DT.SCR , determined by the following formula: In formula (23), K SO3 K is the SO3 conversion rate of flue gas at the inlet of the SCR denitrification device, calculated by volume ppm, or 0.8 times the mass ratio; SO3.SCR is the SO3 conversion rate of flue gas in the SCR denitrification device, generally taken as ≤1%; b is the empirical coefficient, when SO3≤5ppm, take b=40, when SO3≥5ppm, take b=52; Correction scheme for the calculation method of acid dew point of original flue gas by cooling / dust removal: The revised opinions on the acid dew point temperature ADTc under the original flue gas cooling conditions are as follows: When the flue gas temperature drops, the change in acid dew point temperature can be estimated as follows: In formula (24), a, b, n, M, and N are coefficients, and M and N are taken as follows; Before the dust collector, the M value of high-sulfur coal is 0.0111 and the N value is 0.9195, while the M value of low-sulfur coal is 0.0125 and the N value is 0.9304; When the smoke temperature decreases, the result calculated by the above formula is a negative value, indicating that the acid dew point temperature decreases as the smoke temperature decreases; The revised opinions on the acid dew point temperature ADTc of the original flue gas dust removal working condition are as follows: The change in the acid dew point temperature of the flue gas at the outlet of the electrostatic precipitator can be estimated by the following formula: In formula (25), t DT,1 is the acid dew point of the flue gas at the dust collector inlet, ℃; SO 3,1 、SO 3,2 is the SO3 concentration of the flue gas at the inlet and outlet of the dust collector; a, b, n are coefficients; Δt DT,jc is the change in acid dew point caused by dust fall in flue gas; The Taylor data table is used as a reference for evaluating the acid dew point change rate of the original flue gas cooling condition; according to the different water vapor partial pressures, a detailed fitting formula is proposed, and its verification results are consistent with the data table; Among them, the calculation method of net flue gas acid dew point temperature is as follows: Calculation of the upper limit of the acid dew point temperature for clean flue gas SO3≤10ppm: The preferred acid dew point temperature calculation formula for converting coal quality standards to flue gas composition standards; The following formula is used as the standard value for calculating the net flue gas acid dew point temperature: In formula (26), SO3 is the volume concentration of SO3 in the clean flue gas, %; β is the coefficient, which is determined according to the original flue gas calculation method, usually β = 121; Φ is the flue gas alkalinity correction coefficient, which is determined according to the original flue gas calculation method; V a.wg is the actual wet flue gas volume per kg of coal, Nm 3 / kg, calculated and determined according to the desulfurization tower outlet conditions; Determine the upper limit check value according to the general curve chart; The lower limit of the acid dew point temperature for clean flue gas SO3≤10ppm is as follows: Determine the lower limit calibration value according to the Taylor curve; If the acid dew point determined by the Taylor curve is less than 60°C, use 60°C; Calculation of net flue gas composition and partial pressure: Calculation of SO3 concentration in net flue gas, including: according to Estimate the basic value, and then estimate the SO3 concentration in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. On a dry basis, the SO3 removal efficiency of the absorber is usually 60% to 95%. For low-sulfur coal, the higher value is taken, and for high-sulfur coal, the lower limit is taken; The main calculation steps are as follows: The SO3 concentration in the raw flue gas at the desulfurization tower inlet, dry basis, is calculated as follows: In formula (27), SO'2 is the SO2 concentration in the FGD inlet flue gas, mg / Nm d 3 ; is the proportion of SO3 in the FGD inlet flue gas converted to SO3, which is 1.5%, that is, The SO3 concentration in the net flue gas at the outlet of the desulfurization tower, dry basis, is calculated as follows: In formula (28) and (29) is the desulfurization efficiency of the desulfurization tower, which is 0.96-0.98 for high-sulfur coal and 0.95 for low-sulfur coal; is the SO3 conversion rate in the flue gas at the outlet of the desulfurization tower. According to the experimental data of Jiulong Power Plant, 2% can be taken in the preliminary calculation, that is, Estimate the basic value, and then estimate the SO3 concentration in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. On a dry basis, the SO3 removal efficiency of the absorber is usually 60% to 95%. For low-sulfur coal, the higher value is taken, and for high-sulfur coal, the lower limit is taken; Δα GGH is the air leakage coefficient of GGH, and for rotary GGH, Δα is taken GGH =0.03, take Δα for tube-box GGH GGH =0.00~0.0005; The calculation formula for the water vapor partial pressure in the clean flue gas is as follows: It is known that the water vapor fraction in the clean flue gas is H2O″, then the water vapor partial pressure in the clean flue gas is: kPa or at; (30) In formula (30), P g ——absolute pressure of clean flue gas, kPa or at; in: Among them, ΔP fgd is the flue gas negative pressure in the desulfurization tower, gauge pressure, kPa or at; P a is the ambient atmospheric pressure, usually P a =101.3 kPa or 1 at; Calculation of SO3 partial pressure in net flue gas, including: Determined according to wet gaseous conditions, including: The SO3" share in the net flue gas is calculated as follows: SO″3 (ppm) wet basis = 0.28SO″3, ppm (33) SO3 pressure in clean flue gas The calculation formula is as follows: in, ——The gaseous fraction of SO3 in the clean flue gas is taken as 0.45, 0.5 and 0.75 respectively when the superheat is +5℃, +10~30℃ and +40℃, or it can be taken according to the relationship diagram of the gaseous fraction of SO2 in the clean flue gas and the superheat; The calculation formula for the partial pressure of sulfuric acid vapor in the clean flue gas is as follows:

2. The method according to claim 1, characterized in that When conducting industrial tests on different types of coal and different working conditions, a sampler with flow meter is used to collect samples, and the test washing liquid is a washing liquid with a color-changing agent. If the color of the washing liquid changes from the original light blue to pink, it is confirmed that SO3 has escaped. If SO3 has escaped, sampling is carried out again.

3. A system for calculating the acid dew point of boiler flue gas, characterized in that: The system comprises: The data acquisition unit is used to obtain key data related to SO3 that affects the constant value and change law of flue gas acid dew point temperature after industrial testing of the target boiler with different coal types and different operating conditions; A first calculation unit is used to select a plurality of calculation methods under different calculation modes, and calculate a plurality of theoretical flue gas acid dew points obtained by using a plurality of calculation methods under different calculation modes for a target boiler based on the acid dew point calculation application criteria and the key data; A second calculation unit is used to obtain historical data related to the flue gas acid dew point of the target boiler, and determine a standard value and a threshold value of the flue gas acid dew point of the target boiler under normal conditions based on the historical data; an output unit, for taking a calculation mode and a calculation method corresponding to a theoretical flue gas acid dew point that falls within a threshold range and is closest to a standard value among a plurality of theoretical flue gas acid dew points as a calculation scheme for calculating the flue gas acid dew point of the boiler, and calculating the flue gas acid dew point of the boiler based on the calculation scheme; If there is no theoretical flue gas acid dew point falling within the threshold range, the fixed value used in the calculation method is corrected and the calculation is performed again until a theoretical flue gas acid dew point falls within the threshold range; The calculation scheme includes: a calculation scheme for the acid dew point temperature of raw flue gas and a calculation scheme for the acid dew point temperature of net flue gas; The original flue gas acid dew point temperature calculation scheme includes: the original flue gas acid dew point temperature calculation method, the original flue gas acid dew point temperature increase estimation method after SCR denitration and the original flue gas acid dew point temperature correction scheme for cooling / dust removal; The net flue gas acid dew point temperature calculation scheme includes: a net flue gas acid dew point temperature calculation method and a net flue gas composition and partial pressure calculation method; The acid dew point calculation application criteria include: application criteria for acid dew point temperature calculation in thermal power plant design, finite corrosion rate acid dew point temperature ADT lim Criteria for determining and controlling the rate-limited corrosion acid dew point temperature (ADT) lim guidelines for Among them, the original flue gas acid dew point temperature calculation scheme includes: The original flue gas acid dew point temperature calculation scheme includes the following modes: Acid dew point calculation model A based on coal quality analysis data; The basic formula 1 of mode A, and the upper limit value 1, are as follows: In formula (1): n=a fly ·A sp (2) In formula (2): S SP The sulfur content of fuel is converted into A SP is the fuel ash content, Among them, t DT.0 is the pure water dew point temperature in flue gas, in °C; n is an index indicating the degree of influence of fly ash content on acid dew point; α fly is the fly ash share, for pulverized coal furnace α fly =0.8~0.9; β is the excess air coefficient α at the furnace outlet F The relevant parameters are determined by the following formula: Among them, Δα F =(α F -1)×100; B is the coefficient, when SO3≤5ppm, take b=40, when SO3≥5ppm, take b=52; f c The combustible component correction factor for the sulfur content in coal is generally 0.85 to 0.9; Δt DT.SCR is the increase in acid dew point temperature of flue gas after passing through the SCR denitrification device, in °C; The basic formula 2 of Mode A, and the lower limit, are as follows: In formula (5), K C is the comprehensive correction coefficient of the effect of fly ash alkalinity on SO3 conversion rate; Acid dew point calculation model B based on flue gas composition: Mode B basic formula 1, Mode B basic equation recommends the following equation as the calculation formula for the upper limit value 2 of the original flue gas acid dew point, as follows: In formula (6), SO3 is the SO3 component in the flue gas, calculated according to the excess air coefficient at the calculation point, %; V a.wg The flue gas volume of 1kg coal completely burned is calculated according to the excess air coefficient at the calculation point, Nm 3 / kg; Mode B basic formula 2, the original flue gas acid dew point temperature calculation formula based on the flue gas composition, its general empirical formula structure is: t DT =a+blg[SO3]+clg[H2O],℃; (7) or DT =a+blg[P SO3 ]+clg[P H2O ], ℃; (8) In formulas (7) and (8), a, b, and c are constant coefficients in the empirical formulas; Among them, for the original flue gas with SO3≥5ppm, the following equation is used as the acid dew point lower limit verification formula: t DT =200+52lg SO3+40lg H2O,℃; (9) In formula (9), the calculation is performed according to the excess air coefficient at the calculation point, SO3 is the SO3 component in the flue gas, %; the calculation is performed according to the excess air coefficient at the calculation point, H2O is the water vapor component in the flue gas, %; The calculation methods for Mode A and Mode B include the following: Water dew point temperature t DT.0 Calculation method: The calculation formula 1 and the standard formula are as follows: In formula (10), P H2O is the partial pressure of water vapor in the original flue gas, and the excess air coefficient α is calculated according to the combustion system. / / or α n The calculation data is based on kPa; Calculation formula 2 and calculation formula are as follows: t DT.0 =6.715+13.787ln P H2O +1.357[ln P H2O ] 2 ,℃; (11) Among them, the comprehensive correction coefficient of fly ash alkalinity is 1 / K C ,as follows: 1 / K C =(1 / K)+0.08 (12) In formula (12): For lgR opt The range of <1.9 corresponds to low sulfur coal, and the following equation with better fitting degree is used: In summary, the determination of SO3 composition in acid dew point calculation is calculated according to the following equation: In formulas (16) and (17), K G is the gaseous proportion of SO3. In the calculation, K can be taken for the original flue gas. G =0.95; SO2 and It is the calculated value of SO2 composition and partial pressure when the coal ash alkalinity correction is not considered in the combustion calculation; The supporting calculation methods for coal quality characteristics include the following: According to the standard calculation of domestic test data, the coal ash alkalinity correction factor The calculation formula is as follows: Among them, A b =0.239α fly A SP (7CaO+3.5MgO+Fe2O3) (19) The correction coefficient φ of coal ash alkalinity and the verification formula are as follows: in, The total sulfur / coal ash composition factor U is used as the basic parameter, as follows: U=f(∑CaO、S ar 、A ar ) ∑CaO=CaO+1.39MgO (22) SO3 conversion rate K SO3 , the formula is as follows: K SO3 =K F ×Δα F m (21) The coefficient K for smoke, lean coal and pulverized coal furnaces F And the value of m is as follows: When the coal type is low sulfur coal, S ar ≤1.00,K F is 0.15, m is 0.86; When the coal type is medium sulfur coal, S ar =1.01~2.0, K F is 0.11, m is 0.86; When the coal type is high sulfur coal, S ar =2.01~3.0, K F is 0.137, m is 0.86; Among them, Δα F is the excess air coefficient parameter; Δα F =100(α F -1); K G It is the gaseous proportion of SO3 in the original flue gas, which can usually be taken as 0.95; SO3 conversion rate K for lignite and pulverized coal furnace F ×100% is determined by the following empirical equation: U=0.35~0.55, K F ×100%=exp[-3.045+5.88U]; U=0.5~1.1, K F ×100%=exp[-1.059+2.326U]; U=1~1.5, K F ×100%=exp[-0.1+1.35U]; Among them, the calculation method used for the supporting data used for comparison and calculation with the test data in the calculation process is as follows: The total amount of dry basis SO3 in the flue gas is calculated as follows: In formula (22), SO2 is the standard excess air coefficient α of the combustion system. n Calculated wet basis data; Estimation method of the increase in acid dew point temperature of original flue gas after SCR denitrification: The increase of acid dew point temperature Δt after flue gas passes through SCR denitrification device DT.SCR , determined by the following formula: In formula (23), K SO3 K is the SO3 conversion rate of flue gas at the inlet of the SCR denitrification device, calculated by volume ppm, or 0.8 times the mass ratio; SO3.SCR is the SO3 conversion rate of flue gas in the SCR denitrification device, generally taken as ≤1%; b is the empirical coefficient, when SO3≤5ppm, take b=40, when SO3≥5ppm, take b=52; Correction scheme for the calculation method of acid dew point of original flue gas by cooling / dust removal: The revised opinions on the acid dew point temperature ADTc under the original flue gas cooling conditions are as follows: When the flue gas temperature drops, the change in acid dew point temperature can be estimated as follows: In formula (24), a, b, n, M, and N are coefficients, and M and N are taken as follows; Before the dust collector, the M value of high-sulfur coal is 0.0111 and the N value is 0.9195, while the M value of low-sulfur coal is 0.0125 and the N value is 0.9304; When the smoke temperature decreases, the result calculated by the above formula is a negative value, indicating that the acid dew point temperature decreases as the smoke temperature decreases; The revised opinions on the acid dew point temperature ADTc of the original flue gas dust removal working condition are as follows: The change in the acid dew point temperature of the flue gas at the outlet of the electrostatic precipitator can be estimated by the following formula: In formula (25), t DT,1 is the acid dew point of the flue gas at the dust collector inlet, ℃; SO 3,1 、SO 3,2 is the SO3 concentration of the flue gas at the inlet and outlet of the dust collector; a, b, n are coefficients; Δt DT,jc is the change in acid dew point caused by dust fall in flue gas; The Taylor data table is used as a reference for evaluating the acid dew point change rate of the original flue gas cooling condition; according to the different water vapor partial pressures, a detailed fitting formula is proposed, and its verification results are consistent with the data table; Among them, the calculation method of net flue gas acid dew point temperature is as follows: Calculation of the upper limit of the acid dew point temperature for clean flue gas SO3≤10ppm: The preferred acid dew point temperature calculation formula for converting coal quality standards to flue gas composition standards; The following formula is used as the standard value for calculating the net flue gas acid dew point temperature: In formula (26), SO3 is the volume concentration of SO3 in the clean flue gas, %; β is the coefficient, which is determined according to the original flue gas calculation method, usually β = 121; Φ is the flue gas alkalinity correction coefficient, which is determined according to the original flue gas calculation method; V a.wg is the actual wet flue gas volume per kg of coal, Nm 3 / kg, calculated and determined according to the desulfurization tower outlet conditions; Determine the upper limit check value according to the general curve chart; The lower limit of the acid dew point temperature for clean flue gas SO3≤10ppm is as follows: Determine the lower limit calibration value according to the Taylor curve; If the acid dew point determined by the Taylor curve is less than 60°C, use 60°C; Calculation of net flue gas composition and partial pressure: Calculation of SO3 concentration in net flue gas, including: according to Estimate the basic value, and then estimate the SO3 concentration in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. On a dry basis, the SO3 removal efficiency of the absorber is usually 60% to 95%. For low-sulfur coal, the higher value is taken, and for high-sulfur coal, the lower limit is taken; The main calculation steps are as follows: The SO3 concentration in the raw flue gas at the desulfurization tower inlet, dry basis, is calculated as follows: In formula (27), SO'2 is the SO2 concentration in the FGD inlet flue gas, mg / Nm d 3 ; is the proportion of SO3 in the FGD inlet flue gas converted to SO3, which is 1.5%, that is, The SO3 concentration in the net flue gas at the outlet of the desulfurization tower, dry basis, is calculated as follows: In formula (28) and (29) is the desulfurization efficiency of the desulfurization tower, which is 0.96-0.98 for high-sulfur coal and 0.95 for low-sulfur coal; is the SO3 conversion rate in the flue gas at the outlet of the desulfurization tower. According to the experimental data of Jiulong Power Plant, 2% can be taken in the preliminary calculation, that is, Estimate the basic value, and then estimate the SO3 concentration in the net flue gas at the outlet of the desulfurization tower according to the different SO3 removal efficiencies of the absorber. On a dry basis, the SO3 removal efficiency of the absorber is usually 60% to 95%. For low-sulfur coal, the higher value is taken, and for high-sulfur coal, the lower limit is taken; Δα GGH is the air leakage coefficient of GGH, and for rotary GGH, Δα is taken GGH =0.03, take Δα for tube-box GGH GGH =0.00~0.0005; The calculation formula for the water vapor partial pressure in the clean flue gas is as follows: It is known that the water vapor fraction in the clean flue gas is H2O″, then the water vapor partial pressure in the clean flue gas is: kPa or at; (30) In formula (30), P g ——absolute pressure of clean flue gas, kPa or at; in: Among them, ΔP fgd is the flue gas negative pressure in the desulfurization tower, gauge pressure, kPa or at; P a is the ambient atmospheric pressure, usually P a =101.3 kPa or 1 at; Calculation of SO3 partial pressure in net flue gas, including: Determined according to wet gaseous conditions, including: The SO″3 share in the net flue gas is calculated as follows: SO″3 (ppm) wet basis = 0.28SO″3, ppm (33) SO3 pressure in clean flue gas The calculation formula is as follows: in, ——The gaseous fraction of SO3 in the clean flue gas is taken as 0.45, 0.5 and 0.75 respectively when the superheat is +5℃, +10~30℃ and +40℃, or it can be taken according to the relationship diagram of the gaseous fraction of SO2 in the clean flue gas and the superheat; The calculation formula for the partial pressure of sulfuric acid vapor in the clean flue gas is as follows:

4. The system according to claim 3, characterized in that The different types of coal and During industrial testing under different working conditions, a sampler with flow meter is used to collect samples. And the test lotion is a lotion with a color-changing agent. If the color of the lotion changes from the original light blue to pink, It is confirmed that SO3 has escaped. If SO3 has escaped, sampling will be carried out again.

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