A quantitative calculation method for the effect of changes in calorific value on the electrical output of peak-shaving units

Abstract

The present invention is applicable to the technical field of thermal equipment performance monitoring, and provides a quantitative calculation method for the effect of combustion calorific value changes on the electrical output of a peak-shaving unit, including the derivation of a main steam flow calculation equation, the derivation of a unit electrical output calculation method, and the steps of solving the change in unit electrical output. The present invention obtains the change in the main steam flow before and after the change in the low calorific value of coal based on the mass and energy conservation principle of the unit after the change in the low calorific value of coal, and then derives a quantitative calculation equation for the effect of the change in the main steam flow on the unit's power generation based on the thermodynamics and water vapor work conversion principle. The idea of ​​computational iteration is combined with the water vapor state equation and the variable operating condition equation of the turbine flow change to verify the accuracy of the main steam flow calculation, thereby achieving the purpose of quantitatively calculating the main steam flow and the unit's power generation of the peak-shaving unit after the change in the calorific value of coal. The technical problem that the current boiler cannot quantitatively calculate the electrical output of the peak-shaving unit based on the change in the calorific value of the fuel is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal equipment performance monitoring, and in particular relates to a method for quantitatively calculating the effect of combustion calorific value changes on the electrical output of a peak-shaving unit. Background Art

[0002] Currently, changes in coal-fired power unit load significantly impact steam turbine power generation. Peaking units, in particular, require precise control of their power output regulation capabilities and range. Grids often rely on the thermal characteristics of peaking units for real-time load scheduling. Furthermore, power generation companies also need to clearly understand the power output regulation characteristics of their peaking units, particularly thermal power units. Coal-fired power units, based on the power output regulation characteristics of their own peaking units, must provide power generation data to grid dispatchers for reference. Therefore, effectively understanding the output characteristics of peaking units is crucial for maximizing economic returns, both for grid dispatchers and for coal-fired power companies.

[0003] However, there is currently no accurate calculation method for the quantitative impact of changes in the low calorific value of fuel on the electrical output, and it is mainly determined by experience. In addition, although the variable operating condition thermal calculation method of the boiler and turbine of the coal-fired power unit can determine the impact of changes in the low calorific value of fuel on the electrical output of the unit. However, this method requires the structural parameters of the heating surfaces of each level of the boiler and turbine, and the amount of calculation is large, and the speed and real-time performance are poor. This method is complex to calculate and is often not easy for the operating personnel of the power plant to master quickly. Therefore, it is particularly urgent to seek a simple calculation method that can quickly analyze the quantitative impact of changes in the low calorific value of fuel on the electrical output of the peak-shaving unit. To this end, the present invention proposes a quantitative calculation method for the effect of changes in combustion calorific value on the electrical output of the peak-shaving unit. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for quantitatively calculating the effect of combustion calorific value changes on the electrical output of a peak-shaving unit, in order to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for quantitatively calculating the effect of combustion calorific value changes on the power output of a peak-shaving unit includes the following steps:

[0007] Step 1: Derivation of the main steam flow calculation equation: Using the principles of conservation of energy and mass, combined with differential thinking, a differential equation is constructed to show how the main steam flow changes with the calorific value of the fuel.

[0008] Step 2: Derivation of the unit power output calculation method: Using the energy equation of the steam turbine and combining it with differential thinking, a mathematical model is constructed to show how the calorific value changes affect the unit power output.

[0009] Step 3: Solve the change of unit power output: Consider the superheated steam as an ideal gas and verify the pressure through the ideal state equation of gas P and temperature t The correctness of the calculation is verified; the correctness of the main steam flow is verified by using the Flugel formula, and the changes in the verified main steam flow are used to calculate the changes in the group's power generation power.

[0010] Furthermore, the specific process of step 1 is as follows:

[0011] When the boiler blowdown is neglected, the boiler energy balance equation is:

[0012] Equation 1: ;

[0013] Where: D gr is the superheated steam flow rate; h gr is the enthalpy of superheated steam; h fw is the boiler feed water enthalpy; D zr is the reheat steam flow rate; is the outlet enthalpy of reheat steam; is the reheat steam inlet enthalpy; B i Calculated fuel quantity for the boiler; The low calorific value of the coal quality for the boiler; is the boiler thermal efficiency;

[0014] By transforming Equation 1, the calculation equation for the main steam flow is obtained as follows:

[0015] Equation 2: ;

[0016] Let the heat absorption ratio of reheated steam and superheated steam remain unchanged at the same load, that is:

[0017] Equation 3: ;

[0018] Where: f is the heat absorption ratio of reheat steam, which can be determined based on the baseline operating condition or design operating condition;

[0019] Combined with Equation 3, Equation 2 is further transformed into:

[0020] Equation 4: ;

[0021] The calculated fuel quantity for the boiler is expressed as:

[0022] Equation 5: ;

[0023] Where:q 4 is the heat loss of solid unburned carbon in the boiler; B is the actual amount of fuel fed into the boiler;

[0024] Substituting Equation 5 into Equation 2, we obtain:

[0025] Equation 6: ;

[0026] When the fuel quantity and feed water temperature remain unchanged, the change in superheated steam flow rate in Equation 6 is expressed as:

[0027] Equation 7: ;

[0028] middle: θ py is the exhaust gas temperature; is the change in fuel calorific value; is the change in superheated steam flow rate;

[0029] in:

[0030] Equation 8: ;

[0031] Equation 9: ;

[0032] Equation 10: ;

[0033] Equation 11: ;

[0034] q 4 is represented by:

[0035] Equation 12: ;

[0036] Where: is the amount of unburned carbon in 1 kg of fuel; 33727 is the calorific value per kg of pure carbon;

[0037] therefore Expressed as:

[0038] Equation 13: ;

[0039] The calculation equation for boiler thermal efficiency is:

[0040] Equation 14: ;

[0041] Where: q 2 is the heat loss of boiler exhaust gas; q 3 is the heat loss of boiler chemical incomplete combustion; q 4 is the heat loss of solid unburned carbon in the boiler;q 5 is the heat loss from the boiler; q 6 is the physical heat loss of boiler ash;

[0042] The change in boiler thermal efficiency to boiler exhaust heat loss and solid incomplete combustion heat loss is expressed as:

[0043] Equation 15: ;

[0044] The exhaust heat loss of the boiler is expressed as:

[0045] Equation 16: ;

[0046] Where: V g is the total volume of flue gas; c gp is the constant pressure specific heat of the flue gas; t 0 is the ambient temperature;

[0047] Assuming that the change of coal lower calorific value does not affect the flue gas volume and the constant pressure specific heat of flue gas, the partial derivatives of Equation 16 are obtained respectively, and the partial derivatives of exhaust heat loss with respect to coal lower calorific value and exhaust heat loss with respect to exhaust temperature are obtained respectively:

[0048] Equation 17: ;

[0049] Equation 18: ;

[0050] The exhaust gas temperature of the boiler is expressed as:

[0051] Equation 19: ;

[0052] Where: a is the excess air coefficient, a e is the excess air coefficient at rated load; t e is the ambient temperature under rated load; t is the actual ambient temperature; is the rated steam load; is the boiler exhaust temperature at rated load;

[0053] In equation 7, the effect of the change in excess air coefficient is not considered, is represented as:

[0054] Equation 20: ;

[0055] By combining equations 1 to 18, we can obtain the change in the main steam flow rate due to the change in fuel calorific value:

[0056] Equation 21: ;

[0057] Equation 21 is the quantitative calculation equation for the effect of fuel calorific value changes on the main steam flow of the peak-shaving unit.

[0058] Furthermore, the specific process of step 2 is as follows:

[0059] The energy equation of the steam turbine generator is:

[0060] Equation 22: ;

[0061] Where: P el is the power generated by the steam turbine; is the ideal enthalpy drop of the steam turbine; is the average relative internal efficiency of the steam turbine; is the mechanical efficiency of the steam turbine; is the electrical efficiency of the steam turbine; Correction factor for main steam flow considering heat recovery;

[0062] Ignoring the effects of mechanical efficiency, electrical efficiency, and the correction coefficient of main steam flow, the change in turbine power is obtained by using the differential method:

[0063] Equation 23: ;

[0064] Where: is the change in power generated by the steam turbine generator set; Use step 1 to calculate; Take 1 / 50.

[0065] Furthermore, the specific process of step 3 is as follows:

[0066] Considering superheated steam as an ideal gas, Pv The relationship with steam temperature and steam pressure is as follows:

[0067] Equation 24: ;

[0068] Where: θ is the boiler main steam temperature; P is the main steam pressure of the boiler; v is the specific volume of the boiler main steam;

[0069] When the fuel calorific value changes, first select a , calculate ; Select another one , calculate ,in accordance with P 1 andt 1Find v 1. P 1. t 1 and v Substitute 1 into equation 24. If the two equations are equal, the choice is correct. After completing the pressure and temperature calibration, the new P 1 and t 1 Calculated by the steam equation h 1, and calculate , The differentiation of is in the form of difference:

[0070] Equation 25: ;

[0071] In: Subscript 0 indicates the initial value; subscript 1 indicates the parameter after the working condition changes;

[0072] Substitute into equation 21 to calculate ,when D gr After calculation, find , and substitute into the following equation:

[0073] Equation 26: ;

[0074] If Equation 26 is satisfied, then the chosen and and calculated That's correct; then the change in fuel calorific value is calculated using Equation 23: The impact on the change of power generation of peak-shaving units, namely .

[0075] Compared with the prior art, the present invention has the following beneficial effects:

[0076] The method proposed in the present invention effectively solves the problem that the main steam flow, main steam pressure and temperature cannot be accurately and quantitatively calculated due to changes in the low calorific value of boiler fuel. The calculation method is simple, accurate and scientific, and can achieve the purpose of accurately calculating and diagnosing the changes in the main steam flow and main steam parameters of coal-fired power units caused by changes in the low calorific value of fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] Figure 1 Flowchart of the present invention.

[0078] Figure 2 This is a schematic diagram of the algorithm of the present invention. DETAILED DESCRIPTION

[0079] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0080] The specific implementation of the present invention is described in detail below with reference to specific embodiments.

[0081] One embodiment of the present invention provides a method for quantitatively calculating the effect of combustion calorific value changes on the power output of a peak-shaving unit, based on the following concepts:

[0082] 1) On the one hand, changes in the fuel's lower heating value directly cause changes in steam flow. On the other hand, changes in the fuel's lower heating value cause changes in the furnace's combustion conditions, which in turn lead to changes in heat loss from incomplete combustion of solids and flue gas temperature. These changes also cause changes in boiler thermal efficiency, thus leading to changes in the main steam flow. Furthermore, changes in the fuel's lower heating value also cause changes in the main steam pressure and temperature, which, if the main steam valve opening remains unchanged, will cause changes in the boiler's main steam flow.

[0083] 2) To simplify the calculation, the impact of changes in the fuel's lower heating value on the mill's operating conditions is not considered. Consequently, the impact of parameters such as the mill outlet air-pulverized mixture temperature on the main steam flow rate is also not considered. Furthermore, the heat absorption ratio of reheated steam and superheated steam at the same load is assumed to remain constant, allowing the calculation of the main and reheated steam flows to be separated.

[0084] Based on the above concept, the present invention obtains the functional relationship of the main steam flow rate change according to the energy conservation equation after the change of the lower calorific value of the boiler fuel, and further proposes the principle followed by the implementation of the technical solution of the present invention in combination with the differential theory, namely:

[0085] 1) Changes in the lower calorific value of boiler fuel will cause incomplete combustion heat loss and changes in boiler exhaust temperature, which in turn will cause changes in boiler thermal efficiency;

[0086] 2) Changes in the lower calorific value of boiler fuel will cause changes in the main steam pressure and temperature. If the main steam valve opening of the turbine remains unchanged, this will affect the change in the main steam flow rate.

[0087] 3) When the lower heating value of the boiler fuel changes, the main steam flow rate and main steam parameters change simultaneously, and the relationship between them is coupled, which increases the technical difficulty of solving the equations. Therefore, the superheated steam is treated as an ideal gas and the superheated steam equation is discretized. The parameters are first verified through an estimation-then-calibration method. Secondly, the calculated value of the main steam flow rate is verified according to the steam turbine Flügel formula.

[0088] 4) After the lower calorific value of the boiler fuel changes, the main steam flow rate changes slightly due to the use of differential theory. Therefore, the changes in boiler heat loss and ash physical heat loss are ignored. In addition, the change in heat loss due to incomplete combustion of gas is ignored.

[0089] 5) The rate of change of the lower calorific value of boiler fuel relative to the main steam enthalpy value can be calculated by using the idea of ​​difference instead of differentiation, which can simplify the calculation steps.

[0090] like Figure 1 and Figure 2 As shown, the method specifically includes the following steps:

[0091] Step 1. Derivation of the main steam flow calculation equation: Using the principles of conservation of energy and mass, combined with differential thinking, construct a differential equation for the main steam flow rate changing with the calorific value of the fuel; the details are as follows:

[0092] When the boiler blowdown is neglected, the boiler energy balance equation is:

[0093] Equation 1: ;

[0094] Where: D gr is the superheated steam flow rate, kg / s; h gr is the superheated steam enthalpy, kJ / kg; h fw is the boiler feed water enthalpy, kJ / kg; D zr is the reheat steam flow rate, kg / s; is the outlet enthalpy of reheat steam, kJ / kg; is the reheat steam inlet enthalpy, kJ / kg; B i is the calculated fuel quantity of the boiler, kg / s; is the low calorific value of boiler coal, kJ / kg; is the boiler thermal efficiency, %;

[0095] The calculation equation for the main steam flow rate obtained by transforming equation 1 is:

[0096] Equation 2: ;

[0097] The heat absorption ratio of reheated steam and superheated steam under the same load can be kept unchanged, that is:

[0098] Equation 3: ;

[0099] Where: f is the heat absorption ratio of reheat steam, which can be determined based on the baseline operating condition or design operating condition;

[0100] Combined with Equation 3, Equation 2 can be further transformed into:

[0101] Equation 4: ;

[0102] Under the same load, as long as the air-coal ratio, pulverizing system, and combustion system remain unchanged, the carbon content of the generated fly ash and slag can be considered unchanged. The calculated fuel quantity of the boiler can be expressed as:

[0103] Equation 5: ;

[0104] Where: q 4 is the heat loss of solid unburned carbon in the boiler, %; B is the actual amount of fuel fed into the boiler, kg / s,

[0105] Substituting Equation 5 into Equation 2, we get:

[0106] Equation 6: ;

[0107] In Equation 6, as the calorific value of the fuel changes, the boiler q 4. The main steam pressure and temperature will change, causing h gr The change of will eventually cause the change of the main steam flow entering the boiler. Therefore, when the fuel amount and feed water temperature remain unchanged, the change of superheated steam flow in equation 6 can be expressed as:

[0108] Equation 7: ;

[0109] Where: θ py is the exhaust gas temperature, °C; is the change in fuel calorific value; is the change in superheated steam flow rate;

[0110] in,

[0111] Equation 8: ;

[0112] Equation 9: ;

[0113] Equation 10: ;

[0114] Equation 11: ;

[0115] Next, we discuss the calculation of the second term of the differential in Equation 7, where q 4 can be expressed as:

[0116] Equation 12: ;

[0117] Where: is the amount of unburned carbon in 1 kg of fuel, m³ / kg; 33727 is the calorific value per kilogram of pure carbon, kJ / kg,

[0118] therefore, It can be expressed as:

[0119] Equation 13: ;

[0120] The calculation equation for boiler thermal efficiency is:

[0121] Equation 14: ;

[0122] Where: q 2 is the heat loss of boiler exhaust gas, %; q 3 is the heat loss of boiler chemical incomplete combustion, %; q 4 is the heat loss of solid unburned carbon in the boiler, %; q 5 is the heat loss of boiler, %; q 6 is the physical heat loss of boiler ash, %. For large-capacity boilers, it can be considered as chemical incomplete combustion heat loss. q 3 and boiler heat loss q The change of 5 is small, so the impact on the main steam flow is not considered here.

[0123] The change in boiler thermal efficiency to boiler exhaust heat loss and solid incomplete combustion heat loss can be expressed as:

[0124] Equation 15: ;

[0125] The exhaust heat loss of the boiler can be expressed as:

[0126] Equation 16: ;

[0127] Where: V g is the total volume of flue gas, m³ / kg; c gp is the constant pressure specific heat of flue gas, ；t 0 is the ambient temperature, °C;

[0128] Therefore, assuming that the change of the lower calorific value of coal does not affect the flue gas volume and the constant pressure specific heat of the flue gas, the partial derivatives of Equation 16 can be obtained respectively, and the partial derivatives of the exhaust heat loss with respect to the lower calorific value of coal and the exhaust heat loss with respect to the exhaust temperature are:

[0129] Equation 17: ;

[0130] Equation 18: ;

[0131] The exhaust gas temperature of the boiler can be expressed as:

[0132] Equation 19: ;

[0133] Where: a is the excess air coefficient; a e is the excess air coefficient at rated load; t e is the ambient temperature under rated load; t is the actual ambient temperature, °C; is the rated steam load, kg / s; Boiler exhaust gas temperature at rated load, °C;

[0134] In equation 7, the effect of the change in excess air coefficient is not considered, can be expressed as:

[0135] Equation 20: ;

[0136] By combining equations 1 to 18, we can obtain the change in the main steam flow rate due to the change in fuel calorific value:

[0137] Equation 21: ;

[0138] Equation 21 is the quantitative calculation equation for the effect of fuel calorific value change on the main steam flow of the peak-shaving unit;

[0139] Step 2: Derivation of the unit power output calculation method: Using the turbine energy equation and combining differential thinking, a mathematical model is constructed to show how calorific value changes affect unit power output. The details are as follows:

[0140] The energy equation of the steam turbine generator is:

[0141] Equation 22: ;

[0142] Where: P el is the power generated by the steam turbine, kW; is the ideal enthalpy drop of the steam turbine, kJ / kg; is the average relative internal efficiency of the steam turbine; is the mechanical efficiency of the steam turbine; is the electrical efficiency of the steam turbine; It is the correction factor for the main steam flow considering the heat recovery.

[0143] When the lower heating value of coal changes, as long as the impact on the main steam flow is not significant, the flow is diverted to the various heat extraction ports of the steam turbine, and the impact on the ideal enthalpy drop of the turbine and its changes can be ignored. If the effects of changes in mechanical efficiency, electrical efficiency, and the correction coefficient of the main steam flow are not considered, the change in turbine power can be obtained by using the differential method:

[0144] Equation 23: ;

[0145] Where: is the change in power generated by the steam turbine generator set; You can use step 1 to calculate; It can be roughly taken as 1 / 50.

[0146] Step 3: Solve the change of unit power output: Consider the superheated steam as an ideal gas and verify the pressure through the ideal state equation of gas P and temperature t The correctness of the main steam flow is verified by using the Flugel formula, and the changes in the main steam flow after verification are used to calculate the changes in the group's power generation power; the details are as follows:

[0147] Considering superheated steam as an ideal gas, Pv It is approximately linearly related to steam temperature and steam pressure, that is:

[0148] Equation 24: ;

[0149] in: θ is the main steam temperature of the boiler, °C; P is the main steam pressure of the boiler, MPa; v is the specific volume of the boiler main steam, m³ / kg;

[0150] When the fuel calorific value changes, you can first estimate a , calculate ; Estimate another , calculate ,in accordance with P 1 and t 1Find v 1. P 1. t 1 and v Substitute 1 into equation 24. If the two equations are equal, it can be proved to be correct. After completing the pressure and temperature calibration, the new P 1 and t 1 Calculated by the steam equation h 1, and calculated from this , The differentiation of is in the form of difference:

[0151] Equation 25: ;

[0152] Where: subscript 0 represents the initial value or reference value; subscript 1 represents the parameter after the working condition changes;

[0153] Substitute into equation 21 to calculate ,when D gr After calculation, find Should comply with:

[0154] Equation 26: ;

[0155] Where: subscript 0 represents the initial value or reference value; subscript 1 represents the parameter after the working condition changes;

[0156] If the above equations are satisfied, then the estimated and and calculated Absolutely correct. So far, the fuel calorific value has changed The calculation of the quantitative impact on steam flow, pressure and temperature is completed;

[0157] Then the fuel calorific value change is calculated by Equation 23 The impact on the change of power generation of peak-shaving units, namely .

[0158] In the embodiment of the present invention, the computer software program of the present invention is compiled based on automatic control and computer processing technology, which is a technology familiar to those skilled in the art.

[0159] Example 1: A case study of the quantitative calculation method for the effect of fuel quantity changes on the power output of a peak-shaving unit is presented. The operating data of a 330MW unit is used as the basic data, as shown in Table 1:

[0160] Table 1 Coal-fired power unit data (rated operating conditions)

[0161]

[0162] (a) Estimate the change in main steam pressure Δp and main steam temperature Δt. The main steam pressure and temperature after the change are:

[0163] ;

[0164] ;

[0165] Equation 24 is used to verify the accuracy of the estimated pressure and temperature changes, given by and Calculate the specific heat capacity of superheated steam using the water vapor state equation =0.0179661m 3 / kg, and the change rate of main steam enthalpy with the lower calorific value of coal is calculated as follows:

[0166] ;

[0167] This shows that the estimated main steam pressure and temperature are basically correct. and The corresponding enthalpy value h gr1 , calculate the rate of change of main steam enthalpy with fuel calorific value.

[0168] ;

[0169] Further calculation :

[0170] ;

[0171] (b) Substitute into equation 21 and calculate :

[0172] Establishing changes in coal calorific value is 500 kJ / kg, so the change of main steam flow is:

[0173] ;

[0174] After being calculated and determined, the new main steam flow rate can be obtained as follows:

[0175] ;

[0176] Equation 26 is used to verify the correctness of the main steam flow calculation results:

[0177] ;

[0178] ;

[0179] If the calculation result of the main steam flow is within the allowable range of engineering error, it means that the calculation result is correct, and the calculation result is output.

[0180] Using Equation 23, the effect of main steam flow rate changes on turbine power changes can be determined as:

[0181] ;

[0182] Right now kW.

[0183] The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention. These should also be regarded as the scope of protection of the present invention. These will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. A quantitative calculation method for the effect of combustion calorific value change on the power output of a peak load unit, characterized in that: The following steps are involved: Step 1: Derivation of the main steam flow calculation equation: Using the energy and mass conservation principles and combining differential thinking, a differential equation for the main steam flow changing with the fuel calorific value is constructed; Step 2: Derivation of the calculation method of the unit's electrical output: Using the energy equation of the steam turbine and combining the differential idea, a mathematical model of the impact of calorific value changes on the unit's electrical output changes is constructed; Step 3: Solve the change of unit power output: treat superheated steam as an ideal gas and verify the pressure through the ideal state equation of gas P and temperature t The correctness of the main steam flow is verified by using the Flugel formula, and the changes in the verified main steam flow are used to calculate the changes in the power generation of the computer group; The specific process of step 1 is as follows: When boiler blowdown is neglected, the energy balance equation of the boiler yields: Equation 1: ; Where: D gr is the superheated steam flow rate; h gr is the enthalpy of superheated steam; h fw is the boiler feed water enthalpy; D zr is the reheat steam flow rate; is the outlet enthalpy of reheat steam; is the reheat steam inlet enthalpy; B i Calculate fuel quantity for boiler; The low calorific value of the coal quality for the boiler; is the boiler thermal efficiency; After transforming equation 1, the calculation equation for the main steam flow is obtained as follows: Equation 2: ; Let the heat absorption ratio of reheat steam and superheat steam remain unchanged under the same load, that is: Equation 3: ; Where: f is the heat absorption ratio of reheat steam; Combined with equation 3, equation 2 is further transformed into: Equation 4: ; The calculated fuel quantity for the boiler is expressed as: Equation 5: ; Where: q 4 is the heat loss of boiler solid unburned carbon; B is the amount of fuel actually fed into the boiler; Substituting equation 5 into equation 2, we obtain: Equation 6: ; When the fuel quantity and feed water temperature remain unchanged, the change in superheated steam flow rate in equation 6 is expressed as: Equation 7: ; Where: θ py is the exhaust gas temperature; is the change in fuel calorific value; is the change in superheated steam flow rate; in: Equation 8: ; Equation 9: ; Equation 10: ; Equation 11: ; q 4 is expressed as: Equation 12: ; Where: is the amount of unburned carbon in 1 kg of fuel; 33727 is the calorific value per kg of pure carbon; therefore It is expressed as: Equation 13: ; The calculation equation for boiler thermal efficiency is: Equation 14: ; Where: q 2 is the heat loss of boiler exhaust gas; q 3 is the heat loss of boiler chemical incomplete combustion; q 4 is the heat loss of boiler solid unburned carbon; q 5 is the heat loss of boiler heat dissipation; q 6 is the physical heat loss of boiler ash; The change of boiler thermal efficiency to boiler exhaust heat loss and solid incomplete combustion heat loss is expressed as: Equation 15: ; The exhaust heat loss of the boiler is expressed as: Equation 16: ; Where: V g is the total volume of flue gas; c gp is the constant pressure specific heat of flue gas; t 0 is the ambient temperature; Assuming that the change of coal low calorific value does not affect the flue gas volume and the constant pressure specific heat of flue gas, the partial derivatives of equation 16 are obtained respectively, and the partial derivatives of flue gas heat loss to coal low calorific value and flue gas heat loss to flue gas temperature are obtained respectively: Equation 17: ; Equation 18: ; The exhaust gas temperature of the boiler is expressed as: Equation 19: ; Where: a is the excess air coefficient, a e is the excess air coefficient under rated load; t e is the ambient temperature under rated load; t is the actual ambient temperature; is the rated steam load; is the boiler exhaust temperature at rated load; In equation 7, the effect of the change in excess air coefficient is not considered, is represented as: Equation 20: ; By combining equations 1 to 18, we can obtain the change in the main steam flow rate due to the change in fuel calorific value: Equation 21: ; Equation 21 is the quantitative calculation equation for the effect of fuel calorific value change on the main steam flow of the peak-shaving unit; The specific process of step 2 is as follows: The energy equation of the steam turbine generator is: Equation 22: ; Where: P el is the power generated by the steam turbine; is the ideal enthalpy drop of the steam turbine; is the average relative internal efficiency of the steam turbine; is the mechanical efficiency of the steam turbine; is the electrical efficiency of the steam turbine; Correction factor for main steam flow considering heat recovery; Ignoring the influence of the change in mechanical efficiency, electrical efficiency and the correction coefficient of the main steam flow, the change in turbine power is obtained by using the differential idea: Equation 23: ; Where: is the change in power generated by the steam turbine generator set; Use step 1 to calculate; Take 1 / 50; The specific process of step 3 is as follows: The superheated steam is considered as an ideal gas, so Pv The relationship with steam temperature and steam pressure is as follows: Equation 24: ; Where: θ is the main steam temperature of the boiler; P is the main steam pressure of the boiler; v is the specific volume of the boiler main steam; When the fuel calorific value changes, first select , calculate ; Select one more , calculate ,in accordance with P 1 and Find v 1. P 1. and v Substitute 1 into equation 24. If the two equations are equal, the choice is correct. After completing the pressure and temperature calibration, the new P 1 and Calculated by the steam equation h 1, and calculate , The differentiation of is in the form of difference: Equation 25: ; In the formula: subscript 0 represents the initial value; subscript 1 represents the parameter after the working condition changes; Substituting into equation 21, we can get ,when After calculating, find , and substitute it into the following equation: Equation 26: ; If equation 26 is satisfied, then it is proved that the chosen and and calculated That's correct; then the change in fuel calorific value is calculated by equation 23 The impact on the change of power generation of the peak-shaving unit, that is, .

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