Method for determining electric load supply guaranteeing capacity of thermal power generating unit according to meteorological conditions

Abstract

The invention discloses a method for determining the power load supply guarantee capacity of a thermal power generating unit according to meteorological conditions, and belongs to the technical field of thermal power generating unit thermal equipment performance state monitoring and diagnosis. Based on the energy mass principle, the combustion theory and the energy balance equation of the coal mill, the method systematically calculates the influence of meteorological condition change on the calorific value of the coal type, and analyzes the change of outlet wind powder temperature through the heat balance method of the coal mill to obtain the coal type calorific value. And further evaluating the ignition heat change after the pulverized coal airflow is fed into the boiler and judging the stable combustion characteristic of the pulverized coal airflow. Through calculation and evaluation of the key parameters, the power load supply guaranteeing capacity of the thermal power generating unit can be calculated according to change of meteorological conditions. According to the method, through accurate correlation calculation of meteorological conditions and coal type characteristics, the influence of meteorological changes on the power load supply guaranteeing capacity of the thermal power generating unit is determined, and particularly during extreme weather or power demand peak periods, stable operation of a power system can be ensured through quantitative analysis of the power load supply guaranteeing capacity of the thermal power generating unit.

Description

Technical Field

[0001] The present invention belongs to the technical field of performance status monitoring and diagnosis of thermal equipment in thermal power units, and particularly relates to a method for determining the power supply guarantee capacity of thermal power units according to meteorological conditions. Background Art

[0002] Although China is committed to promoting the development of new energy and renewable energy, considering the resource endowment and a large number of high-quality existing coal-fired power units, coal power will still play an important role in power security supply, large-scale carbon reduction, and supporting the development of new energy in the medium and long term. It is predicted that by 2060, the installed capacity of coal power will still need to be maintained at more than 400 million kilowatts to meet the energy and power supply guarantee requirements. Data from the China Electricity Council shows that in 2023, the national coal power installed capacity was 1.16 billion kilowatts, accounting for 39.9% of the total power installed capacity, and the power generation accounted for nearly 60%. However, in recent years, the coal power industry has shown a trend of improving flexibility and cleanliness.

[0003] In recent years, affected by various factors such as extreme weather and fuel supply, the power supply and demand situation in China has been complex and changeable, the power demand volatility has increased, but the trend of energy electrification has also been strengthening.

[0004] Currently, changes in extreme meteorological conditions, such as heavy rain, hail, heavy snow and other weather, usually block the transportation of thermal coal. In this case, the power supply guarantee capacity of thermal power units can generally be judged according to the amount of coal in the coal storage yard of the power plant. However, there is another situation that is not easy to determine. That is, heavy rain and heavy snow, and the change of weather temperature usually affects the change of coal volume and air volume temperature, and then affects the operation characteristics of the coal pulverizing system of the boiler. With the change of the temperature of the air-powder flow at the outlet of the boiler coal pulverizing system, it affects the ignition characteristics and stable combustion characteristics of the boiler. The increase of the ignition heat of the boiler, the rise of the ignition temperature and the deterioration of the stable combustion characteristics usually mean the risk of flameout and the loss of the power supply guarantee capacity of the unit. There are few studies and reports on the quantitative description and characterization of this situation.

[0005] Therefore, it is necessary to effectively clarify the power supply guarantee capacity of thermal power units according to the change of meteorological conditions, and then give reasonable decisions and basis for the power load dispatching of the power grid. It is necessary to study the calculation method for determining the power supply guarantee capacity of thermal power units according to meteorological conditions, which has important engineering practical significance for the quantitative and accurate evaluation of the power supply guarantee capacity of power plants.

[0006] Therefore, there is an urgent need for a new technical solution in the existing technology to solve this problem. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for determining the power supply capacity of a thermal power unit based on meteorological conditions, which is used to solve the problem that it is impossible to determine whether the power supply capacity of the thermal power unit will be affected when extreme meteorological conditions occur in the prior art.

[0008] The technical solution adopted by the present invention is to provide a method for determining the power supply capacity of a thermal power unit based on meteorological conditions, including the following steps:

[0009] Step 1: Calculate the change in the low calorific value of the coal type after the change in meteorological conditions;

[0010] Step 2: Determine the temperature of the pulverized coal-air mixture at the outlet of the coal mill through the heat balance equation of the coal mill;

[0011] Step 3: Determine the calculation equations for the ignition temperature and the change in heat of ignition through the principles of pulverized coal combustion and heat balance in the furnace;

[0012] Step 4: Dynamically evaluate the power supply capacity of the unit by calculating the pulverized coal ignition stability index and combining the change in heat of ignition and the test ignition temperature.

[0013] The change in the low calorific value of the coal type in Step 1 is expressed as:

[0014]

[0015] In the formula: Q 2 ar.net is the low calorific value of the coal after the change in moisture, kJ / kg; Q 1 ar.net is the low calorific value of the original coal type before the change in moisture, kJ / kg; M 1 ar is the moisture content of the original coal type before the change in moisture, %; M 2 ar is the moisture content in the coal after the change in moisture, %; r is the latent heat of vaporization, taken as 2510 kJ / kg;

[0016] Among them, k is the proportionality coefficient for converting the coal quality components:

[0017]

[0018] The heat balance equation of the coal mill in Step 2 is that the input heat of the coal mill is equal to the output heat, that is

[0019] Q gz +Q j +Q lf +Q r =Q zf +Q z +Q jr +Q 5

[0020] Wherein, Q gz is the physical heat of the desiccant, i.e., the heat brought into the boiler by the air, kJ / kg; Q j is the heat converted from mechanical energy during the grinding process of the coal mill, kJ / kg; Q lf is the heat brought in by the air leakage of the coal mill, kJ / kg; Q r is the heat brought in by the fuel entering the coal mill, kJ / kg; Q zf is the heat consumed by the evaporation of moisture in the coal mill, kJ / kg; Q z is the heat carried out of the system by the lean gas, kJ / kg; Q jr is the heat consumed for heating the fuel, kJ / kg; Q 5 is the heat lost due to the heat dissipation of the coal mill, kJ / kg.

[0021] The physical heat Q of the desiccant gz is expressed as:

[0022] Q gz = g 1 c gz t In

[0023] Wherein: g 1 is the air-coal ratio of the coal mill, kg / kg; t In is the temperature of the air entering the coal mill, °C; c gz is the specific heat capacity of the air entering the coal mill, which is determined by interpolation through the temperature t of the air entering the coal mill In , kJ / (kg·°C);

[0024] Among them, the temperature t of the air entering the coal mill In is:

[0025]

[0026] Wherein: r 1 is the primary air rate recommended according to the combustion conditions; t 一次风 is the primary hot air temperature at the outlet of the air preheater, °C; t 二次风 is the secondary hot air temperature at the outlet of the air preheater, °C;

[0027] Among them, the air-coal ratio g of the coal mill 1 is expressed as:

[0028]

[0029] Wherein: α″ is the excess air coefficient at the furnace outlet; K lf is the air leakage coefficient of the coal mill, taking an empirical value. For the medium-speed coal mill pulverizing system, take 0.2; V0 is the theoretical air volume, determined according to the coal type, m 3 / kg;

[0030] The theoretical air volume V 0 is expressed as:

[0031]

[0032] The primary air rate r 1 is expressed as:

[0033]

[0034] In the formula: V 一 is the total primary air volume, t / h; V 二 is the total secondary air volume, t / h;

[0035] The excess air coefficient α″ is expressed as:

[0036]

[0037] In the formula: O 2 is the operating oxygen content at the boiler furnace outlet, %; ψ is the burnout coefficient of the boiler pulverized coal;

[0038] The burnout coefficient ψ of the boiler pulverized coal is expressed as:

[0039]

[0040] In the formula: C fh is the carbon content in fly ash, taking the experimental value, %; A ar is the ash content as received of the fuel, taking the coal type test value, %; a fh is the fly ash fraction, taking the value 0.95; C ar is the carbon content as received of the fuel, taking the test value, %.

[0041] The heat Q converted from mechanical energy during the grinding process of the coal mill j is expressed as:

[0042] Q j = 3.6K j E

[0043] In the formula: K j is the energy conversion coefficient during the grinding process of the coal mill. For medium-speed coal mills, K j = 0.6; E is the unit power consumption of the coal mill, kW·h / t;

[0044] Among them, the unit power consumption E of the coal mill is expressed as:

[0045]

[0046] Where: P M is the electric power consumed by the coal mill, kW; B M is the amount of coal milled by the coal mill, t / h;

[0047] The heat Q brought in by the air leakage of the coal mill lf is expressed as:

[0048] Q lf = K lf g 1 c lk t lk

[0049] Where: t lk is the cold air temperature leaking into the coal mill, generally taking the ambient temperature of 30°C; c lk is the specific heat capacity of air at t lk in kJ / (kg·°C);

[0050] The heat Q brought in by the fuel entering the coal mill r is expressed as:

[0051] Q r = c p，ar t r

[0052] Where: t r is the temperature of the fuel when it enters the coal mill system, taking the actual ambient temperature, °C; c p，ar is the specific heat capacity at constant pressure of the fuel as received, kJ / (kg·°C);

[0053] Among them, the specific heat capacity at constant pressure c p，ar of the fuel as received is expressed as:

[0054]

[0055] Where: c dr is the specific heat capacity of the fuel on a dry basis, interpolated and calculated based on the ambient temperature, kJ / (kg·°C).

[0056] The heat Q consumed by the evaporation of moisture in the coal mill zf is expressed as:

[0057] Q zf = ΔM[4.187(100 - t r ) + 2261 - 1.884(100 - t Out )]

[0058] Where: ΔM is the moisture evaporated per kilogram of raw coal during the drying process in the coal mill, kg / kg; 4.187 and 1.884 are the specific heat capacities of water and water vapor respectively, kJ / (kg·°C); 2261 is the latent heat of vaporization under the negative pressure condition of the coal mill, kJ / kg; t Out is the temperature of the drying agent at the outlet of the coal pulverizing system. For the positive pressure direct blow coal pulverizing system, t Out is equal to the temperature of the air - powder mixture at the outlet of the coal mill, °C;

[0059] Among them, the moisture ΔM evaporated per kilogram of raw coal during the drying process in the coal mill is:

[0060]

[0061] Where: M mf is the moisture content of the pulverized coal at the outlet of the coal mill, determined by chemical analysis, %.

[0062] The heat Q carried out by the exhausted air system z is expressed as:

[0063] Q z =(1 + K lf )g 1 c 2 t Out

[0064] Where: c 2 is the specific heat capacity of the drying agent at temperature t Out , kJ / (kg·°C);

[0065] The heat Q consumed by the heating fuel jr is expressed as:

[0066]

[0067] The heat Q lost due to heat dissipation in the coal pulverizing system 5 is expressed as:

[0068]

[0069] Where: Q 5 z is the total heat loss of the coal pulverizing system. For the medium - speed coal mill positive pressure cold primary air fan direct blow coal pulverizing system, it is selected according to the coal type and the type of coal mill, ×10 3 kJ / h.

[0070] The temperature t of the air - powder mixture at the outlet of the coal mill out is:

[0071]

[0072] In step 3, the changes in ignition temperature and heat of ignition are based on the dynamic heat balance equation in the boiler furnace:

[0073]

[0074] In the formula: ρ is the density of the mixture of high-temperature flue gas, pulverized coal and ash, kg / m 3 ; c p is the specific heat capacity at constant pressure of the flue gas, kJ / (m 3 ·°C); T is the temperature of the combustion products, K; τ is the time, s; Q f is the heat generated by the combustion reaction, kJ / (m 3 ·s); Q s is the heat dissipated from the container to the surrounding environment, kJ / (m 3 ·s);

[0075] The heat Q f generated by the combustion of the combustible mixture in the boiler furnace is expressed as:

[0076] Q f = k 0 c f n c a m e -E / RT Q d

[0077] In the formula: k 0 is the frequency factor; is the fuel concentration of the combustible mixture, mol / m 3 ; c a is the oxygen concentration, mol / m 3 ; E is the activation energy of the coal type, kJ / mol; R is the universal gas constant; Q d is the calorific value of the fuel, kJ / mol;

[0078] The heat Q s dissipated from the high-temperature combustion products in the furnace to the surrounding environment is expressed as:

[0079]

[0080] In the formula: α is the heat dissipation coefficient, kJ / (m 2 ·°C·s); S is the surface area in the furnace, m 2 ; T 0 is the initial temperature of the primary air pulverized coal stream, K;

[0081] The ignition temperature T c is determined according to the following conditions:

[0082] Q f = Q s

[0083]

[0084] That is:

[0085]

[0086] Converted to:

[0087]

[0088] Solving the above equation and omitting the impossible + sign values, the ignition temperature T c Is expressed as:

[0089]

[0090] When the ignition temperature T in the boiler furnace c Is determined, the heat of ignition Q zh Is expressed as:

[0091]

[0092] In the formula: V 1 Is the primary air volume, m 3 / kg (under standard conditions); c k Is the specific heat capacity of air, determined according to the temperature (T 0C +T C ) / 2, kJ / (m 3 ·℃); c r g Is the specific heat capacity on a dry basis, determined according to the temperature (T 0C +T C ) / 2, kJ / (kg·℃); c q Is the specific heat capacity of water vapor, kJ / (m 3 ·℃), taking 1.884 kJ / (kg·℃).

[0093] The ignition stability index R in step 4 described above w The calculation method is expressed as:

[0094]

[0095] In the formula: R w Is the ignition and stable combustion index of the boiler; T 1max Is the temperature corresponding to the maximum weight loss rate, taking the experimental value, ℃; W 1max Is the maximum weight loss rate, taking the experimental value, mg / min;

[0096] The criteria for judging the power supply capacity of a thermal power unit are as follows:

[0097]

[0098] If the thermal power unit simultaneously meets the above three conditions, it is determined that the power supply capacity of the thermal power unit decreases or is lost.

[0099] The principle of a method for determining the power supply capacity of a thermal power unit according to meteorological conditions in the present invention:

[0100] 1. After the thermal power unit experiences extreme meteorological conditions such as heavy rain, heavy snow, hail, etc., the moisture content of the coal type changes. A typical change is an increase in moisture, which will affect the net calorific value of the coal quality. Actually, it is necessary to correct the coal type. And the change in the calorific value of the coal type has a great influence on the stable combustion characteristics of the boiler;

[0101] 2. As the moisture content of the coal type increases, the temperature of the drying agent at the outlet terminal of the coal pulverizing system changes. Actually, it is the initial temperature of the primary air pulverized coal flow that changes, resulting in a decrease in the temperature of the pulverized coal flow entering the boiler, and then affecting the ignition and combustion performance of the fuel;

[0102] 3. By calculating the initial temperature of the primary air pulverized coal flow, the heat of ignition and the ignition temperature of the pulverized coal flow are further determined. As long as the heat of ignition increases and the ignition temperature is higher than the normal experimental value and the stable combustion index is difficult to reach, it can be determined the power supply capacity of the thermal power unit.

[0103] Through the above design scheme, the present invention can bring the following beneficial effects:

[0104] 1. Based on the principles of energy quality and combustion, the present invention calculates the influence on the net calorific value of the coal type after the moisture increases according to meteorological conditions, and then considers the influence on the stable combustion characteristics of the boiler;

[0105] 2. According to the energy balance equation of the coal mill, the initial temperature of the primary air powder flow at the outlet of the coal mill can be calculated. The initial temperature of the primary air powder flow at the outlet of the coal mill can be determined by iterative calculation, and then the influence on the ignition and combustion performance of the fuel is considered;

[0106] 3. Through the principles of combustion and the law of conservation of energy, the ignition temperature and the heat of ignition after the change of meteorological conditions are calculated;

[0107] 4. For the fuel ignition stability index, if the calculated heat of ignition is greater than zero, the stable combustion index is difficult to reach, and at the same time the calculated ignition temperature is higher than the normal experimental value, it can be determined that the power supply capacity of the thermal power unit decreases or is lost;

[0108] 5. The method of the present invention combines the analytic hierarchy process and the entropy weight method, which not only overcomes the strong objectivity of the entropy weight method but also introduces subjective judgment, making the final weight calculation more comprehensive and accurate. Description of the Drawings

[0109] Figure 1 Schematic diagram of ignition in the furnace of a thermal power unit boiler for a method of determining the power supply capacity of a thermal power unit based on meteorological conditions according to the present invention;

[0110] Figure 2 Schematic diagram of the principle of determining the power supply capacity of a thermal power unit based on meteorological conditions for a method of determining the power supply capacity of a thermal power unit based on meteorological conditions according to the present invention;

[0111] Figure 3 Schematic diagram of the algorithm flow for determining the power supply capacity of a thermal power unit based on meteorological conditions for a method of determining the power supply capacity of a thermal power unit based on meteorological conditions according to the present invention. Detailed implementation manners

[0112] The present invention will be further described below in conjunction with the accompanying drawings and detailed implementation manners:

[0113] Refer to Figures 1 to 3 , a method of determining the power supply capacity of a thermal power unit based on meteorological conditions according to the present invention includes the following contents:

[0114] (1) Influence of meteorological condition changes on the calorific value of coal types

[0115] Based on the changes in meteorological conditions, which are mainly reflected in the changes in ambient temperature and coal moisture content caused by rain and snow weather. When the coal in the coal yard experiences changes in rain and snow weather, the moisture content in the coal increases, resulting in a change in the lower calorific value of the coal. Therefore, the change in the lower calorific value of the coal type caused by the increase in the moisture content of the coal type can be expressed as:

[0116]

[0117] In the formula: Q 2 ar.net is the lower calorific value of the coal after the moisture change, kJ / kg; Q 1 ar.net is the lower calorific value of the coal type before the moisture change, kJ / kg; M 1 ar is the moisture content of the coal type before the moisture change, %; M 2 ar is the moisture content in the coal after the moisture change, %; k is the proportionality coefficient for coal quality component conversion; r is the latent heat of vaporization, taking 2510 kJ / kg.

[0118] The proportionality coefficient k for coal quality component conversion is:

[0119]

[0120] (2) Calculating the outlet air-powder temperature of the coal mill by the heat balance method

[0121] With the changes in the moisture content of coal and the ambient temperature, when the air flow rate entering the boiler remains unchanged, it will cause the temperature of the air-powder mixture at the outlet of the coal mill to change, and ultimately lead to the temperature change of the pulverized coal and air entering the boiler burner, thereby affecting the stability of the combustion conditions in the furnace. Regarding the coal mill as an open thermal system, based on the energy balance equation that the input heat of the coal mill is equal to the output heat, it can be expressed as:

[0122] Q gz +Q j +Q lf +Q r =Q zf +Q z +Q jr +Q 5 (3)

[0123] In the formula, Q gz is the physical heat of the desiccant, that is, the heat brought into the boiler by air, kJ / kg; Q j is the heat converted from mechanical energy during the grinding process of the coal mill, kJ / kg; Q lf is the heat brought in by the air leakage of the coal mill, kJ / kg; Q r is the heat brought in by the fuel entering the coal mill, kJ / kg; Q zf is the heat consumed by evaporating moisture in the coal mill, kJ / kg; Q z is the heat carried out of the system by the exhausted gas, kJ / kg; Q jr is the heat consumed for heating the fuel, kJ / kg; Q 5 is the heat lost due to the heat dissipation of the coal mill, kJ / kg.

[0124] a. Heat input to the coal mill:

[0125] Among them, the calculation equation of the physical heat Q gz of the desiccant can be expressed as:

[0126] Q gz =g 1 c gz t In (4)

[0127] In the formula: g 1 is the air-coal ratio of the coal mill, which refers to how many kilograms of coal correspond to each kilogram of air volume in the coal mill. For existing large-scale coal pulverizing systems, the air-coal ratio is usually set as a function of the boiler load, kg / kg; t In is the temperature of the air entering the coal mill. This temperature is usually the mixed temperature of the cold air and hot air entering the coal mill and should be calculated and determined based on the proportion and temperature of the cold and hot air, ℃; c gz is the specific heat capacity of the air entering the coal mill, which can be obtained through the temperature t of the air entering the coal millIn It is determined by the interpolation method, kJ / (kg·℃).

[0128] The temperature t of the air entering the coal mill In is:

[0129]

[0130] In the formula: r 1 is the primary air ratio recommended according to the combustion conditions. For an operating boiler, this value is the ratio of the primary air volume to the total air volume; t 一次风 is the primary air temperature, which is the primary hot air temperature at the outlet of the air preheater, ℃; t 二次风 is the secondary air temperature, which is the secondary hot air temperature at the outlet of the air preheater, ℃.

[0131] Among them, for medium-speed coal mills, the air-to-coal ratio g of the coal mill 1 can be expressed as:

[0132]

[0133] In the formula: α″ is the excess air coefficient at the furnace outlet; K lf is the air leakage coefficient of the coal mill, and an empirical value can be taken. For the medium-speed coal mill pulverizing system, 0.2 can be taken; V 0 is the theoretical air volume, which can be determined according to the coal type, m 3 / kg.

[0134] The theoretical air volume can be calculated according to the coal type after the moisture change. The calculation equation is:

[0135]

[0136] For an operating boiler, the primary air ratio is:

[0137]

[0138] In the formula: V 一 is the total primary air volume, usually the sum of the measured primary air volumes of two air preheaters, t / h; V 二 is the total secondary air volume, usually the sum of the measured secondary air volumes of two air preheaters, t / h.

[0139] The excess air coefficient of the boiler can be expressed as:

[0140]

[0141] In the formula: O 2is the operating oxygen content at the boiler furnace outlet, usually taking the operating oxygen content after the economizer, %, and the operating oxygen content after the air preheater cannot be taken. This is mainly to exclude the influence of air preheater air leakage on the oxygen content. ψ is the burnout coefficient of the boiler pulverized coal, mainly considering the correction of the unburned pulverized coal to the boiler operating excess air coefficient. For a fixed boiler load, approximate substitution calculation can be carried out based on the carbon content in fly ash.

[0142] The burnout coefficient ψ of the boiler pulverized coal can be expressed as:

[0143]

[0144] In the formula: C fh is the carbon content in fly ash, and the experimental value can be taken, %; A ar is the ash content as received by the fuel, and the coal type test value can be taken, %; a fh is the fly ash fraction, with a value of 0.95; C ar is the carbon content as received by the fuel, and the test value can be taken, %.

[0145] The heat Q converted from mechanical energy during the grinding process of the coal mill j can be expressed as:

[0146] Q j = 3.6K j E (11)

[0147] In the formula: K j is the energy conversion coefficient during the grinding process of the coal mill. For medium-speed coal mills, K j = 0.6; E is the unit power consumption of the coal mill, kW·h / t.

[0148] The unit power consumption of the coal mill can be expressed as:

[0149]

[0150] In the formula: P M is the electric power consumed by the coal mill, kW; B M is the coal quantity ground by the coal mill, t / h.

[0151] The heat Q brought in by the air leakage of the coal mill lf can be expressed as:

[0152] Q lf = K lf g 1 c lk t lk (13)

[0153] In the formula: t lk is the cold air temperature leaking into the coal mill, generally taking the ambient temperature of 30°C; c lk is the air at tlk Specific heat capacity at this time, kJ / (kg·°C).

[0154] After the moisture in the coal and the ambient temperature change, the heat Q brought in by the fuel entering the coal mill r can be expressed as:

[0155] Q r = c p，ar t r (14)

[0156] In the formula: t r is the temperature when the fuel enters the coal mill system, and the actual ambient temperature can be taken, °C; c p，ar is the specific heat capacity at constant pressure of the fuel as received, kJ / (kg·°C).

[0157] The specific heat capacity at constant pressure of the fuel as received can be expressed as:

[0158]

[0159] In the formula: c dr is the specific heat capacity of the dry basis of the fuel, which can be calculated by interpolation based on the ambient temperature, kJ / (kg·°C).

[0160] b. Heat output from the coal mill:

[0161] The heat Q consumed for evaporating moisture in the coal mill zf can be expressed as:

[0162] Q zf = ΔM[4.187(100 - t r ) + 2261 - 1.884(100 - t Out )] (16)

[0163] In the formula: ΔM is the moisture evaporated per kilogram of raw coal during the drying process in the coal mill, kg / kg; 4.187 and 1.884 are the specific heat capacities of water and water vapor respectively, kJ / (kg·°C); 2261 is the latent heat of vaporization under the negative pressure condition of the coal mill, kJ / kg; t Out is the temperature of the drying agent at the outlet of the coal preparation system. For a positive pressure direct - blow coal preparation system, t Out is equal to the outlet temperature of the pulverized coal - air mixture in the coal mill, °C.

[0164] The moisture ΔM evaporated per kilogram of raw coal during the drying process in the coal mill is:

[0165]

[0166] In the formula: M mf is the moisture content of the pulverized coal at the outlet of the coal mill, which can be determined by chemical analysis, %.

[0167] Exhaust gas takes away the heat Q of the system z It can be expressed as:

[0168] Q z =(1+K lf ) 1 c 2 t Out (18)

[0169] Where: c 2 t Out Specific heat capacity of the desiccant at temperature, kJ / (kg·℃).

[0170] Heat consumed by heating fuel Q jr It can be expressed as:

[0171]

[0172] Heat lost by the milling system Q 5 for:

[0173]

[0174] Where: Q 5 z is the total heat loss of the pulverizing system. For the medium-speed coal mill positive pressure cooling primary fan direct blowing pulverizing system, it can be selected according to Table 1 and based on the coal type and coal mill type, ×10 3 kJ / h.

[0175] Table 1 Total heat loss Q of direct-blowing powder making system 5 z

[0176]

[0177] Combining equations (2) to (19), we can get the temperature t of the air-powder mixture at the coal mill outlet: out for:

[0179] (3) Heat changes of pulverized coal airflow entering the boiler

[0180] According to the theory of natural ignition of heat in the boiler furnace, ignoring the change of coal powder concentration in the furnace, the dynamic heat balance equation in the boiler furnace can be expressed as:

[0181]

[0182] Where: ρ is the density of the mixture of high temperature flue gas, coal powder and ash, kg / m 3 ;cp is the specific heat capacity at constant pressure of the flue gas, kJ / (m 3 ·°C); T is the temperature of the combustion products, K; τ is the time, s; Q f is the heat generated by the combustion reaction, kJ / (m 3 ·s); Q s is the heat dissipated from the container to the surrounding environment, kJ / (m 3 ·s).

[0183] The heat Q generated by the combustion of the combustible mixture in the boiler furnace f can be expressed as:

[0184] Q f = k 0 c f n c a m e -E / RT Q d (23)

[0185] In the formula: k 0 is the frequency factor; is the fuel concentration of the combustible mixture, mol / m 3 ; c a is the oxygen concentration, mol / m 3 ; E is the activation energy of the coal type, kJ / mol; R is the universal gas constant; Q d is the calorific value of the fuel, kJ / mol.

[0186] The heat Q dissipated from the high-temperature combustion products in the furnace to the surrounding environment s can be expressed as:

[0187]

[0188] In the formula: α is the heat dissipation coefficient, kJ / (m 2 ·°C·s); S is the surface area in the furnace, m 2 ; T 0 is the initial temperature of the primary air pulverized coal stream, K.

[0189] As Figure 1 shown, the tangent point C is an equilibrium point. From Figure 1 it can be seen that Q f > Q s , and dT > 0. At this time, the flue gas temperature in the boiler furnace is continuously increasing, reaching the self-ignition combustion state. The tangent point C is the critical ignition point, and the corresponding T c is called the ignition temperature. The self-ignition temperature can be determined according to the following conditions:

[0190] Q f = Q s(25)

[0191]

[0192] That is, the following equation holds:

[0193]

[0194] By combining Equation (21) - Equation (25), the following calculation equation can be obtained:

[0195]

[0196] By solving Equation (29) and omitting the impossible + sign values, the following can be obtained:

[0197]

[0198] When the ignition temperature in the boiler furnace is determined, the heat of ignition Q zh can be expressed as:

[0199]

[0200] Where: V 1 is the primary air volume, m 3 / kg (under standard conditions); c k is the specific heat capacity of air, determined according to the temperature (T 0C +T C ), kJ / (m 3 ·℃); c r g is the specific heat capacity on a dry basis, determined according to the temperature (T 0C +T C ), kJ / (kg·℃); c q is the specific heat capacity of water vapor, kJ / (m 3 ·℃), and 1.884 kJ / (kg·℃) can be taken.

[0201] (4) Judgment of the stable combustion characteristics of pulverized coal flow

[0202] The ignition and stable combustion performance index is represented by the fuel ignition stability index R w and can be calculated according to the following empirical equation:

[0203]

[0204] Where: R w is the ignition and stable combustion index of the boiler; T 1max is the temperature corresponding to the maximum weight loss rate, and the experimental value can be taken, ℃; W 1max is the maximum weight loss rate, and the experimental value can be taken, mg / min.

[0205] Table 2 Discrimination Criteria for Ignition and Stable Combustion Characteristics

[0206] <![CDATA[R w > less than 4.0 4.0-4.65 4.65-5.0 5.0-5.7 greater than 5.7 level extremely difficult difficult medium easy extremely easy

[0207] The discrimination criteria for the power supply guarantee capacity of thermal power units are as follows:

[0208]

[0209] If a thermal power unit simultaneously meets the three conditions in Equation (33), it can be determined that the power supply guarantee capacity of the thermal power unit has decreased or been lost.

[0210] The computer software program of the present invention is compiled based on automation control and computer processing technologies, which are familiar technologies to those skilled in the art.

[0211] Calculation example: Taking the open coal yard of a certain power plant as an example, the data collected according to the coal quality and unit operation are shown in Table 3. Now, a calculation and diagnosis case is described based on the method for determining the power supply guarantee capacity of thermal power units according to the changes in meteorological conditions.

[0212] Table 3 Data Collected on Coal Quality and Unit Operation

[0213]

[0214]

[0215] (1) Calculation link for the influence of meteorological condition changes on the calorific value of coal types

[0216] The proportionality coefficient k for coal quality component conversion is:

[0217]

[0218] The change amount of the low calorific value of coal types caused by the increase in the moisture content of coal types can be expressed as:

[0219]

[0220] (2) Calculation link for the outlet air-powder temperature of the coal mill by the heat balance method

[0221] The burnout coefficient ψ of boiler pulverized coal can be expressed as:

[0222]

[0223] The excess air coefficient of the boiler can be expressed as:

[0224]

[0225] For an operating boiler, the primary air rate is:

[0226]

[0227] The theoretical air volume can be calculated based on the coal type after moisture change, and the calculation equation is:

[0228]

[0229] For medium-speed coal mills, the air-to-coal ratio of the coal mill can be expressed as:

[0230]

[0231] The temperature of the air entering the coal mill is:

[0232]

[0233] c gz is the specific heat capacity of the air entering the coal mill, which is determined by using the interpolation method through the temperature t of the air entering the coal mill: 1 Adopt the interpolation method to determine:

[0234]

[0235] E is the unit power consumption of the coal mill:

[0236]

[0237] The constant-pressure specific heat capacity of the fuel as-received basis can be expressed as:

[0238]

[0239] The moisture evaporated per kilogram of raw coal during the drying process in the coal mill is:

[0240]

[0241] The heat loss Q of the coal pulverizing system 5 is:

[0242]

[0243] Assume t out is 40°C, c 2 is 1.0126 kJ / (kg·°C), and t is calculated through Equation (21) as: out is:

[0244]

[0245] Assume t out is 36°C, c 2 is 1.01244 kJ / (kg·°C), and t is calculated through Equation (21) as: out is:

[0246]

[0247] (3) Calculation link for the heat of ignition change of pulverized coal air flow entering the boiler

[0248] The ignition temperature is:

[0249]

[0250] c r g is the specific heat capacity on a dry basis, based on the temperature (T 0C +T C ) / 2:

[0251] c r g = 1.46 kJ / (kg·°C)

[0252] The heat of ignition is:

[0253]

[0254] (4) Judging link for the stable combustion characteristics of pulverized coal air flow

[0255] The ignition and stable combustion performance index is represented by the fuel ignition stability index R w and can be calculated according to the following empirical equation:

[0256]

[0257] According to Table 2, the criterion for judging the ignition and stable combustion characteristics is 4.0 < R w < 4.65, so the ignition and stable combustion grade is difficult.

[0258]

[0259] Since the three conditions in equation (33) are satisfied, it can be determined that the power supply capacity of the thermal power unit has decreased.

[0260] The implementation modes of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for determining the power load supply capacity of a thermal power unit based on meteorological conditions, characterized in that: The following steps are involved: Step 1: Calculate the change in the lower heating value of coal types after the meteorological conditions change; Step 2: Determine the temperature of the air-powder mixture at the coal mill outlet through the coal mill heat balance equation; Step 3: Determine the calculation equations for ignition temperature and ignition heat change through the combustion principle of coal powder in the furnace and the principle of heat balance; Step 4: Dynamically evaluate the unit's power load supply capability by calculating the pulverized coal ignition stability index and combining the ignition thermal changes and test ignition temperature.

2. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 1, characterized in that: The change in the lower calorific value of the coal in step 1 is expressed as: Where: Q 2 ar.net is the lower calorific value of coal after moisture content changes, kJ / kg; Q 1 ar.net is the lower calorific value of the coal before moisture changes, kJ / kg; M 1 ar is the moisture content of the coal before moisture change, %; M 2 ar is the moisture content in coal after moisture change, %; r is the latent heat of vaporization, taken as 2510 kJ / kg; Among them, k is the proportional coefficient of coal quality composition conversion:

3. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 1, characterized in that: The heat balance equation of the coal mill in step 2 is that the heat input of the coal mill is equal to the heat output, that is, Q gz +Q j +Q lf +Q r =Q zf +Q z +Q jr +Q5 In the formula, Q gz is the physical heat of the desiccant, that is, the heat brought into the boiler by the air, kJ / kg; Q j Q is the heat converted from mechanical energy during the coal mill grinding process, kJ / kg; lf is the heat brought into the coal mill by air leakage, kJ / kg; Q r is the heat brought into the coal mill by the fuel, kJ / kg; Q zf is the heat consumed by evaporating water in the coal mill, kJ / kg; Q z The heat carried out of the system by the exhaust gas, kJ / kg; Q jr is the heat consumed in heating the fuel, kJ / kg; Q5 is the heat lost in the heat dissipation of the coal mill, kJ / kg.

4. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 3 is characterized in that: The physical heat Q of the desiccant gz It is expressed as: Q gz =g1c gz t In Where: g1 is the air-coal ratio of the coal mill, kg / kg; t In is the temperature of the air entering the coal mill, ℃; c gz is the specific heat capacity of the air entering the coal mill, and the temperature of the air entering the coal mill is t In Determined by interpolation method, kJ / (kg·℃); Among them, the temperature of the air entering the coal mill is t In for: Where: r1 is the primary air rate recommended according to combustion conditions; t 一次风 is the primary hot air temperature at the outlet of the air preheater, °C; t 二次风 is the secondary hot air temperature at the outlet of the air preheater, °C; Among them, the air-coal ratio g1 of the coal mill is expressed as: Where: α″ is the excess air coefficient at the furnace outlet; K lf V is the air leakage coefficient of the coal mill, which is an empirical value. For the medium-speed coal mill pulverizing system, it is 0.2; 0 is the theoretical air volume, determined according to the type of coal, m 3 / kg; Theoretical air volume V 0 It is expressed as: The primary wind rate r1 is expressed as: Where: V 一 is the total air volume of primary air, t / h; V 二 is the total secondary air volume, t / h; The excess air coefficient α″ is expressed as: Where: O2 is the operating oxygen content at the boiler furnace outlet, %; ψ is the burnout coefficient of boiler coal powder; The burnout coefficient ψ of boiler coal powder is expressed as: Where: C fh is the carbon content of fly ash, taking the experimental value, %; A ar The basic ash content of the fuel is taken from the coal test value, %; a fh is the fly ash proportion, which is 0.95; C ar It is the as-received carbon content of the fuel, taken as the assay value, %.

5. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 3 is characterized in that: The heat Q converted from mechanical energy during the coal mill grinding process j It is expressed as: Q j =3.6K j E Where: K j is the energy conversion coefficient in the coal mill grinding process. For medium-speed coal mill, K j =0.6; E is the unit power consumption of coal mill, kW·h / t; Among them, the unit power consumption E of the coal mill is expressed as: Where: P M is the electrical power consumed by the coal mill, kW; B M is the amount of coal ground by the coal mill, t / h; The heat Q brought into the coal mill by air leakage lf It is expressed as: Q lf =K lf g1c lk t lk Where: t lk The temperature of the cold air leaking into the coal mill is generally taken as the ambient temperature of 30℃; c lk For air at t lk Specific heat capacity at , kJ / (kg·℃); The heat Q brought by the fuel entering the coal mill r It is expressed as: Q r =c p，ar t r Where: t r is the temperature of the fuel when it enters the coal mill system, taking the actual ambient temperature, ℃; c p，ar is the specific heat capacity of the fuel at constant pressure, kJ / (kg·℃); The fuel receives the specific heat capacity of the base pressure c p，ar It is expressed as: Where: c dr is the dry basis specific heat capacity of the fuel, calculated by interpolation based on the ambient temperature, kJ / (kg·℃).

6. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 3 is characterized in that: The heat consumed by evaporating water in the coal mill Q zf It is expressed as: Q zf =ΔM[4.187(100-t r )+2261-1.884(100-t Out )] Where: ΔM is the amount of water evaporated from each kilogram of raw coal during the drying process of the coal mill, kg / kg; 4.187 and 1.884 are the specific heat capacities of water and water vapor, kJ / (kg·℃); 2261 is the latent heat of vaporization under negative pressure conditions of the coal mill, kJ / kg; t Out is the temperature of the desiccant at the outlet of the powder making system. For the positive pressure direct blowing powder making system, t Out Equal to the temperature of the air-powder mixture at the outlet of the coal mill, °C; Among them, the amount of water evaporated per kilogram of raw coal during the drying process of the coal mill is: Where: M mf It is the moisture content of pulverized coal at the outlet of pulverizer, determined by chemical analysis, %.

7. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 3, characterized in that: The exhaust gas takes out the heat Q of the system z It is expressed as: Q z =(1+K lf )g1c2t Out Where: c2 is t Out Specific heat capacity of the desiccant at temperature, kJ / (kg·℃); The heat consumed by the heating fuel is Q jr It is expressed as: The heat Q5 lost by the powder making system is expressed as: Where: Q5 z is the total heat loss of the pulverizing system. For the medium-speed coal mill positive pressure cooling primary fan direct blowing pulverizing system, select according to the type of coal and coal mill type, ×10 3 kJ / h.

8. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 3 is characterized in that: The temperature of the air-powder mixture at the coal mill outlet is t out for:

9. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 1, characterized in that: The ignition temperature and ignition heat changes in step 3 are based on the dynamic heat balance equation in the boiler furnace: Where: ρ is the density of the mixture of high temperature flue gas, coal powder and ash, kg / m 3 ;c p is the specific heat capacity of flue gas at constant pressure, kJ / (m 3 ·℃); T is the temperature of the combustion products, K; τ is the time, s; Q f is the heat generated by the combustion reaction, kJ / (m 3 ·s); Q s is the amount of heat dissipated from the container to the surrounding environment, kJ / (m 3 s); The heat generated by the combustion of the combustible mixture in the boiler furnace Q f It is expressed as: Q f =k0c f n c a m e -E / RT Q d Where: k0 is the frequency factor; is the fuel concentration of the combustible mixture, mol / m 3 ;c a is the oxygen concentration, mol / m 3 ; E is the activation energy of the coal, kJ / mol; R is the universal gas constant; Q d is the calorific value of the fuel, kJ / mol; The amount of heat Q dissipated by the high-temperature combustion products in the furnace to the surrounding environment s It is expressed as: Where: α is the heat dissipation coefficient, kJ / (m 2 ·℃·s); S is the surface area of ​​the furnace, m 2 ; T0 is the initial temperature of the primary coal powder airflow, K; Ignition temperature T c Determined based on the following conditions: Q f =Q s Right now: Convert to: Solve the above equation, ignite the ignition temperature T after igniting the impossible + value. c It is expressed as: When the ignition temperature in the boiler furnace is T c After confirming, the hot Q zh It is expressed as: Where: V1 is the primary air volume, m 3 / kg (under standard conditions); c k is the specific heat capacity of air, according to the temperature (T 0C +T C ) / 2, kJ / (m 3 ℃); c r g is the specific heat capacity on a dry basis, depending on the temperature (T 0C +T C ) / 2, kJ / (kg·℃); c q is the specific heat capacity of water vapor, kJ / (m 3 ·℃), take 1.884kJ / (kg·℃).

10. The method for determining the power load supply capacity of a thermal power unit according to meteorological conditions according to claim 1, characterized in that: The ignition stability index R in step 4 w The calculation method is expressed as: Where: R w is the ignition and stable combustion index of the boiler; T 1max is the temperature corresponding to the maximum weight loss rate, taking the experimental value, ℃; W 1max is the maximum weight loss rate, taking the experimental value, mg / min; The criteria for judging the power load supply capacity of thermal power units are as follows: If a thermal power unit meets the above three conditions at the same time, it is determined that the thermal power unit's ability to ensure power load supply is reduced or lost.

Images