CN111737859B - Improved turbine unit variable-pressure operation consumption difference quantitative calculation model construction method - Google Patents

Abstract

A method for constructing an improved quantitative calculation model of the variable pressure operating loss of a steam turbine unit. The method uses the "circulation heat absorption amount" of 1kg unit steam, "effective enthalpy drop of the high-pressure cylinder" and "enthalpy rise of the feed water pump" as the main characteristic variables , and use the enthalpy drop correction coefficient and thermal system correction coefficient The "effective enthalpy drop of the high-pressure cylinder" and the "enthalpy rise of the feed water pump" were revised respectively, and a quantitative calculation model of the variable pressure operation consumption difference of the steam turbine unit based on the "relative comparison of unit heat rate" was constructed. The model has a simplified structure and only needs to collect a small number of temperature and pressure parameters that are easy to measure accurately during constant power and variable pressure operation of the steam turbine unit. It does not need to collect flow parameters that are relatively difficult to measure accurately. When the enthalpy drop correction coefficient and thermal system correction coefficient When segmented correction is adopted, the recurrence deviation of the unit heat rate of this model is ≤1 kJ/(kW.h), and it can accurately analyze the change of the unit heat rate when the inlet pressure amplitude of the steam turbine unit is ≥0.1MPa under constant power. quantity.

Description

An improved method for constructing a quantitative calculation model of variable pressure operation loss of steam turbine units

Technical field

The invention relates to a method for constructing a quantitative calculation model of the variable pressure operating loss of an improved steam turbine unit, and belongs to the technical field of steam turbine units.

Background technique

When the steam turbine unit is operating at constant power, the numerical correspondence between the inlet steam pressure and the heat rate of the unit under a given steam distribution method and valve opening sequence can be called the thermal economic characteristics of the constant power variable pressure operation of the steam turbine unit. In the AGC power grid dispatching mode with "unit power generation" as the tracking target, studying the thermal economic characteristics of variable pressure operation of the steam turbine unit will help reveal the heat rate of the unit under different initial pressures within the feasible valve position range of the steam turbine unit at constant power. The continuous changing trend shows the inherent laws of constant power and variable voltage operation of different types of steam turbine units.

Usually, when the steam turbine inlet pressure changes by 0.1MPa, the heat rate of the unit changes by about 2kJ/(kW.h).

The uncertainty of the high-accuracy test of large condensing steam turbines given in the American Society of Mechanical Engineers ASME PTC6-2004 "Steam Turbine Performance Test Procedure" is 0.3% respectively (Note: ASME PTC6 requires the same test conditions and repeats the test twice; if The two test results are considered acceptable if they are ≤0.3% of each other; otherwise, repeat a third time until the uncertainty is met). The heat rate of steam turbine units that have been put into production is roughly in the range of 7000~8000kJ/(kW.h). So, even if the performance test is completed according to the most stringent ASME performance test regulations, the uncertainty of the test results is about 21.0~24.0kJ/ (kW.h) range. Obviously, according to ASME PTC6, the test cannot accurately identify the impact of small changes in steam inlet pressure on the economic efficiency of the unit (such as 0.2Mpa, the adjustment accuracy that the current coordinated control system can achieve).

Conventional steam turbine unit constant sliding pressure test (also known as steam turbine unit optimal initial pressure optimization test or steam turbine unit operating mode optimization and adjustment test) is usually conducted according to ASME PTC6 regulations. However, there are often degradations in test instruments, test conditions, etc. Generally, a The working condition only arranges a single test instead of repeated testing under parallel working conditions, so naturally there is no concept of uncertainty. Therefore, objectively, it is difficult (or even impossible) to identify the difference in heat consumption at different inlet pressures using sliding pressure test methods.

Some test units have carried out targeted optimization of the inlet steam pressure based on the "valve point" effect of the steam turbine unit; however, if the valve overlap is set too large, the "valve point" bonus will be lost. Taking the pressure overlap as an example, it is generally believed that when the front valve opens to a pressure ratio of 0.85 to 0.90, it is more appropriate for the rear valve to open, that is, the pressure overlap ξp takes a value between 0.10 and 0.15. Assuming that the pressure overlap is 10%, the throttling loss at the two-valve point and the three-valve point will reach 30~80kJ/(kW.h), which almost exhausts the optimization potential of the constant sliding pressure test!

Some test units have also proposed using local energy consumption analysis methods to compare unit heat consumption rates under different test conditions; however, their local consumption difference analysis methods often look at the impact of changes in a single characteristic parameter on the unit heat consumption rate in isolation, ignoring each parameter. Coupling with each other; the theoretical basis of this method is insufficient, and there must be a large deviation between the analysis results and the actual situation.

To sum up, existing test methods are limited by accuracy and are difficult to accurately analyze the thermal economic characteristics of constant-power variable-voltage operation of steam turbine units.

According to the principle of steam turbine, from the perspective of energy balance, during the constant power and variable pressure operation of the steam turbine unit, if the work gain of the high-pressure cylinder (that is, the work gain of the main steam), medium/low pressure cylinder of 1kg steam can be measured, The relative changes in the thermal economy of the unit can be determined by the work gain (that is, the work gain of the reheated steam) and the cycle heat absorption gain. As mentioned before, whether to solve the work done by the main steam in the high-pressure cylinder or the work done by the reheated steam in the medium/low-pressure cylinder or the heat absorbed by the cycle, it is necessary to measure hundreds of steam and water including flow rate. The parameters to be tested are not only complex, but the measurement accuracy is difficult to guarantee.

Professor Cai Yinian of Xi'an Jiaotong University explained in the book "Steam Turbine" (Xi'an Jiaotong University, 1986 edition) a method based on "effective enthalpy drop of high-pressure cylinder" and "circulation heat absorption" to quantitatively analyze the differences between different steam distribution modes and operating modes. The thermal efficiency difference method; the theoretical mechanism of this method is clear and the implementation process is simple. CN102998122B discloses a global optimization method for the best initial pressure of a steam turbine unit based on multiple factors. The invention is based on the steam turbine principle method and is based on the two main variables of "effective enthalpy drop of high-pressure cylinder" and "circulation heat absorption". , introducing the third main variable of "feed water enthalpy", a quantitative model of variable pressure operation consumption difference of steam turbine units is proposed, and applied to the analysis and comparison of thermal economic characteristics of constant power variable pressure operation of the same steam turbine unit. The model is detailed as follows:

Let h ₀ , h ₁ , Δh, Δτ, H, Q, η and HR be the main steam enthalpy, high-pressure cylinder exhaust steam enthalpy, high-pressure cylinder effective enthalpy drop, feed water enthalpy rise, unit steam useful work, Cycle heat absorption, cycle efficiency and unit heat consumption rate; h′ ₀ , h′ ₁ , Δh′, Δτ′, H′, Q′, η′, HR′ are the main steam enthalpy and high pressure after changing working conditions, respectively. Cylinder exhaust steam enthalpy, high-pressure cylinder effective enthalpy drop, feed water enthalpy rise, unit steam useful work, cycle heat absorption, cycle efficiency and unit heat rate; δ(Δh), δ(Δτ), δ(Δq) are variables respectively. The effective enthalpy drop gain, feed water enthalpy rise gain and cycle heat absorption gain of the high-pressure cylinder before and after working conditions; α is the reheat coefficient; Δη is the change in cycle efficiency before and after changing working conditions.

Before changing working conditions:

After changing working conditions:

The effective enthalpy drop gain of the high-pressure cylinder after changing working conditions relative to that before working conditions:

δ(Δh)=(h′ ₀ -h′ ₁ )-(h ₀ -h ₁ )=Δh ₀ -Δh ₁ (5)

The cycle heat absorption gain after changing working conditions relative to before working conditions:

δ(Δq)=(h′ ₀ -h ₀ )-α·(h′1-h ₁ )=Δh ₀ -α·Δh ₁ (6)

The gain of feed water enthalpy rise after changing working conditions relative to before working conditions:

δ(Δτ)=Δτ′-Δτ (7)

Although the theoretical mechanism of this model is relatively clear, CN102998122B discloses a multi-factor global optimization method for the optimal initial pressure of a steam turbine unit. In equation (2), the "effective enthalpy drop gain of the high-pressure cylinder δ (Δh)" and " "Feed water enthalpy rise gain δ (Δτ)" directly replaces the high-pressure cylinder work gain (main steam work gain) and medium/low-pressure cylinder work gain (reheat steam work gain) of 1kg steam, that is, " The coefficients of "effective enthalpy drop gain δ (Δh)" of the high-pressure cylinder and "feed water enthalpy rise gain δ (Δτ)" are both "1". Attached Figures 1 and 2 show the quantitative calculation model of the original steam turbine unit's variable pressure operation loss for supercritical N600 nozzle steam distribution machine type A and supercritical N600 overload steam supply machine type B under 480MW load. Reproduction effect of thermal economic characteristics of pressure operation. In the figure, the coefficients of "high-pressure cylinder effective enthalpy drop gain δ (Δh)" and "feed water enthalpy rise gain δ (Δτ)" are both "1", and the numerical mechanism is insufficient; although the model heat rate is consistent with the simulated heat rate The trends of the two rates are similar, but there is a certain deviation and the effect is not ideal.

Obviously, elucidating the numerical mechanisms of "high-pressure cylinder effective enthalpy drop gain δ (Δh)" and "feed water enthalpy rise gain δ (Δτ)" will help improve the original consumption difference model. Figures 3 and 4 show the main steam power gain, reheat steam power gain, and high-pressure cylinder effectiveness of the supercritical N600 nozzle steam distribution machine type A and the supercritical N600 overload steam supply machine type B under a load of 480MW. The changing trend of enthalpy drop gain and steam pump enthalpy rise gain with steam inlet pressure. It can be seen from the figure that the effective enthalpy drop gain of the high-pressure cylinder and the work gain of the main steam are in the same direction, with a high degree of similarity; the enthalpy rise gain of the steam pump and the work gain of the reheated steam are in an inverse relationship, and they also have a certain degree of similarity. similarity. After a large number of simulation studies, the similarities in the trends of "effective enthalpy drop gain of high-pressure cylinder and main steam work gain" and "steam pump enthalpy rise gain and reheat steam work gain" are common rules for various types of steam turbine units. At the same time, compared with solving the work amount of 1kg steam, to solve the effective enthalpy drop of the high-pressure cylinder or the enthalpy rise of the steam pump for 1kg steam, you only need to know the inlet and outlet pressure and temperature parameters of the high-pressure cylinder or the inlet and outlet pressure and temperature parameters of the feed water pump, etc. With a small number of parameters, test accuracy is also guaranteed. Therefore, the easy-to-measure high-pressure cylinder effective enthalpy drop gain δ (Δh) and the feed water enthalpy rise gain δ (Δτ) are used to numerically represent the difficult-to-measure main steam power gain and reheat steam power gain. Numerical mechanism of quantitative calculation model of running loss difference.

Contents of the invention

The purpose of the present invention is to propose an improved method for constructing a quantitative calculation model of the variable pressure operation consumption difference of a steam turbine unit in view of the disadvantages of existing test methods that it is difficult to accurately identify the thermal economic characteristics of constant power variable pressure operation of steam turbine units.

The technical solution to realize the present invention is as follows, a method for constructing a quantitative calculation model of the variable pressure operation consumption difference of an improved steam turbine unit. The method is based on the correlation analysis of the intrinsic mechanism of the thermal economic characteristics of variable pressure operation and the characteristic variables. "Circulation heat absorption", "high-pressure cylinder effective enthalpy drop" and "feed water pump enthalpy rise" are used as characteristic variables, and the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are used to calculate the "high-pressure cylinder effective enthalpy drop" and "feed water pump enthalpy rise" respectively. "Water pump enthalpy rise" is corrected to obtain a quantitative calculation model of steam turbine unit variable pressure operation consumption difference based on "relative comparison of unit heat rate":

Q=(h ₀ -h _f )-α(h _r -h ₁ );

H=nQ

δ(Δh)=Δh′-Δh=(h′ ₀ -h′ ₁ )-(h ₀ -h ₁ )

δ(Δτ)=Δτ′-Δτ

H′=H+βδ(Δh)-γ(Δτ)

Q′=(h′ ₀ -h′ _f )-α(h′ _r -h′ ₁ )

ΔHR=HR′-HR

In the formula, h ₀ is the main steam enthalpy before changing working conditions, h ₁ is the high-pressure cylinder exhaust steam enthalpy before changing working conditions, Δh is the effective enthalpy drop of high-pressure cylinder before changing working conditions, Δτ is the water supply before changing working conditions. Enthalpy rise, H is the useful work per unit steam before changing working conditions, Q is the cycle heat absorption before changing working conditions, h _f is the final feed water enthalpy before changing working conditions, h _r is the reheated steam before changing working conditions Enthalpy and eta are the cycle efficiency before changing working conditions, HR is the unit heat rate before changing working conditions; h′ ₀ is the main steam enthalpy after changing working conditions, h′ ₁ is the high-pressure cylinder exhaust steam after changing working conditions Enthalpy, Δh′ is the effective enthalpy drop of the high-pressure cylinder after changing working conditions, Δτ′ is the enthalpy rise of feed water after changing working conditions, H′ is the useful work per unit steam after changing working conditions, Q′ is the cycle after changing working conditions Heat absorption, h′ _f is the final feed water enthalpy after changing working conditions, h′ _r is the reheat steam enthalpy after changing working conditions, η′ is the cycle efficiency after changing working conditions, HR′ is the Unit heat consumption rate; δ (Δh) is the effective enthalpy drop gain of the high-pressure cylinder before and after changing working conditions; δ (Δτ) is the feed water enthalpy rise gain before and after changing working conditions; α is the reheat coefficient, β is the enthalpy down correction coefficient; γ is the correction coefficient of the thermal system; ΔHR is the amplitude of the heat rate of the unit before and after changing working conditions.

The enthalpy drop correction coefficient β and thermal system correction coefficient γ can be corrected and calculated based on the unit design parameters or test parameters using professional steam turbine simulation software or the EXCEL self-programmed thermal calculation program that complies with ASME PTC6A-1982 calculation examples.

For steam turbine units that adopt the "multi-step" opening method, the valve point should be used as the dividing point to perform segmented correction calculations on the enthalpy drop correction coefficient β and the thermal system correction coefficient γ to reduce the unit heat rate recurrence deviation of the model. . Among them, the nozzle steam supply model A can be divided into three stages according to valve points: "four valve points - three valve points", "three valve points - two valve points" and "two valve throttling"; the overload steam supply model B. It can be divided into two stages according to valve points: "Admission steam valve fully open - Admission valve fully closed and main control valve fully open" and "Main control valve throttling".

The working principle of the present invention is that after extensive simulation research, the similarities in the trends of "high-pressure cylinder effective enthalpy drop gain and main steam work gain" and "steam pump enthalpy rise gain and reheat steam work gain" are various types General rules for steam turbine units. The present invention proposes to use the easily measurable effective enthalpy drop gain δ (Δh) of the high-pressure cylinder and the feed water enthalpy rise gain δ (Δτ) to numerically represent the hard-to-measure main steam work gain and reheat steam work gain, and then solve Relative changes in unit thermal economy.

The beneficial effect of the present invention is that the structure of the quantitative calculation model of the variable pressure operation consumption of the improved steam turbine unit is simplified, and only a small amount of temperature and pressure parameters that are easy to be accurately measured in the constant power variable pressure operation of the steam turbine unit are collected, and there is no need to collect relative parameters. Flow parameters that are difficult to accurately measure; when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are modified step by step, the unit heat rate recurrence deviation of this model is ≤1kJ/(kW.h), and the steam turbine unit can be accurately analyzed. The change in the heat rate of the unit when the inlet pressure amplitude changes ≥0.1MPa under power; after a large number of simulations, the model can reproduce various capacity levels, parameter levels, steam distribution methods and different conditions with high accuracy. The thermal economic characteristics of the steam turbine unit with a thermal system structure at constant power and variable pressure operation; and the enthalpy drop correction coefficient β and the thermal system correction coefficient γ have excellent inheritance for the thermal economic characteristics of the steam turbine unit at constant power and variable pressure operation, and can be determined according to the unit design Parameters or test parameters are calibrated and calculated using professional steam turbine simulation software or the EXCEL self-programming thermal calculation program that complies with ASME PTC6A-1982 calculation examples, and are directly transplanted into field tests. In practical applications, this model can be combined with the constant power global variable voltage dynamic test of the steam turbine unit, or with the constant sliding pressure optimization steady state test of the steam turbine unit following the "ASME PTC6-2004 Steam Turbine Performance Test Procedure". It can significantly improve the accuracy of solving the heat consumption rate of the field test unit.

Description of the drawings

Figure 1 shows the reproduction effect of the improved quantitative calculation model of variable pressure operation consumption difference of the steam turbine unit on the thermal economic characteristics of variable pressure operation of nozzle steam turbine type A under a load of 480MW (both the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are taken value "1");

Figure 2 shows the reproduction effect of the improved quantitative calculation model of variable pressure operation consumption difference of the steam turbine unit on the thermal economic characteristics of variable pressure operation of nozzle steam turbine type A under a load of 480MW (both the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are taken value "1");

Figure 3 shows the changing trend of main steam power gain, reheat steam power gain, high-pressure cylinder effective enthalpy drop gain and steam pump enthalpy rise gain with the inlet pressure of nozzle steam distribution machine type A under 480MW load;

Figure 4 shows the changing trend of the main steam power gain, reheat steam power gain, high-pressure cylinder effective enthalpy drop gain and steam pump enthalpy rise gain with the inlet steam pressure of overload steam admission model B under 480MW load;

Figure 5 shows when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ do not adopt segmented correction, the improved steam turbine unit variable pressure operation consumption difference quantitative calculation model is thermally economical for the nozzle steam distribution machine type A under the 480MW load of variable pressure operation. Reproduction effect of characteristics;

Figure 6 shows the thermal economic characteristics of the improved steam turbine unit variable pressure operation consumption difference quantitative calculation model for the nozzle steam distribution machine type A under a load of 480MW when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are modified step by step. The recurrence effect;

Figure 7 shows the thermal economy of the improved steam turbine unit variable pressure operation difference quantitative calculation model for overload steam admission unit type B under variable pressure operation under 480MW load when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ do not adopt segmented correction. Reproduction effect of characteristics;

Figure 8 shows the thermal economic characteristics of the improved steam turbine unit variable pressure operation consumption difference quantitative calculation model for overload steam admission unit type B under variable pressure operation under 480MW load when the enthalpy drop correction coefficient β and thermal system correction coefficient γ are modified step by step. the recurrence effect.

Detailed ways

The specific implementation of the present invention is shown in the figure. The technical solution in the embodiment of the present invention will be clearly and completely described below with reference to Figures 5-8 in the embodiment of the present invention.

The units in this embodiment are supercritical N600 nozzle steam distribution machine type A and supercritical N600 overload steam supply machine type B. Among them, model A is a four-valve nozzle steam distribution unit (the valve opening sequence is GV1/2 synchronization→GV3→GV4), and model B is an overload steam admission throttle steam distribution unit (the valve opening sequence is main regulating valve→admission steam valve), the rated parameters of both types of models are 660MW/24.2MPa/566℃/566℃. Figure 5-8 shows the reproduction effect of the improved steam turbine unit’s quantitative calculation model of variable pressure operation loss on the thermal economic characteristics of variable pressure operation of models A and B under a load of 480MW.

The quantitative calculation model of the variable pressure operating loss of the improved steam turbine unit in this embodiment includes the following steps:

Step 1: The technical solution implemented by the present invention is as follows: an improved variable pressure operation consumption difference quantitative calculation model of the steam turbine unit. The method is based on the correlation analysis of the intrinsic mechanism of the thermal economic characteristics of variable pressure operation and the characteristic variables. 1kg unit steam The "circulation heat absorption", "high-pressure cylinder effective enthalpy drop" and "feed water pump enthalpy rise" are used as the main characteristic variables, and the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are used to respectively adjust the "high-pressure cylinder effective enthalpy drop" and The "feed water pump enthalpy rise" is corrected, and a quantitative calculation model of the steam turbine unit's variable pressure operation consumption difference based on "relative comparison of unit heat rate" is constructed.

Let h ₀ , h ₁ , Δh, Δτ, H, Q, h _f , h _r , eta, and HR be the main steam enthalpy, high-pressure cylinder exhaust steam enthalpy, high-pressure cylinder effective enthalpy drop, and feed water enthalpy rise before changing working conditions, respectively. , unit steam useful work, cycle heat absorption, final feed water enthalpy, reheat steam enthalpy, cycle efficiency and unit heat rate; h′ ₀ , h′ ₁ , Δh′, Δτ′, H′, Q′, h′ _f , h′ _r , η′, and HR′ are respectively the main steam enthalpy, high-pressure cylinder exhaust steam enthalpy, high-pressure cylinder effective enthalpy drop, feed water enthalpy rise, unit steam useful work, cycle heat absorption, and final feed water after changing working conditions. Enthalpy, reheat steam enthalpy, cycle efficiency and unit heat rate; δ(Δh) and δ(Δτ) are the effective enthalpy drop gain and feed water enthalpy rise gain of the high-pressure cylinder before and after changing working conditions respectively; α, β, γ are the reheat coefficient, enthalpy drop correction coefficient and thermal system correction coefficient respectively; ΔHR is the amplitude of the heat rate of the unit before and after changing operating conditions.

Q＝(h ₀ -h _f )-α·(h _r -h ₁ ) (2)

H＝η·Q (3)

δ(Δh)=Δh′-Δh=(h′ ₀ -h′ ₁ )-(h ₀ -h ₁ ) (4)

δ(Δτ)=Δτ′-Δτ (5)

H′＝H+β·δ(Δh)-γ·δ(Δτ) (6)

Q′=(h′ ₀ -h′ _f )-α·(h′ _r -h′ ₁ ) (7)

ΔHR＝HR′-HR (10)

Step 2: Complete the constant-power variable-voltage operation simulation calculation of the case unit (model A and model B); extract some characteristic parameters in the simulation conditions, substitute them into the improved steam turbine unit variable-voltage operation consumption difference quantitative calculation model, correct and Calculate the enthalpy drop correction coefficient β and the thermal system correction coefficient γ. The simulation calculation is carried out based on the unit design parameters or test parameters. It can either use professional simulation software for steam turbine units or use the EXCEL self-programming thermal calculation program that complies with ASME PTC6A-1982 calculation examples. For steam turbine units that adopt the "multi-step" opening method, the valve point should be used as the dividing point to perform segmented correction calculations on the enthalpy drop correction coefficient β and the thermal system correction coefficient γ to reduce the unit heat rate recurrence deviation of the model. . Among them, the nozzle steam supply model A can be divided into three stages according to valve points: "four valve points - three valve points", "three valve points - two valve points" and "two valve throttling"; the overload steam supply model B. It can be divided into two stages according to valve points: "Admission steam valve fully open - Admission valve fully closed and main control valve fully open" and "Main control valve throttling".

When the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are not modified step by step, the reproduction effect of the model is shown in Figure 5 and Figure 7; when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are modified step by step, the model The reproduction effect is shown in Figures 6 and 8; it has been observed that when the enthalpy drop correction coefficient β and the thermal system correction coefficient γ are modified in sections, the reproduction deviation of the unit heat rate of the model is ≤1kJ/(kW.h).

The above is a detailed introduction to the quantitative calculation model of the variable pressure operating loss of an improved steam turbine unit provided by the present invention. In this embodiment, specific examples are used to illustrate the principle and implementation of the present invention. The description of the above embodiments It is only used to help understand the method and its core idea of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of the claims of the present invention.

Claims (2)

1. The method is characterized in that the method takes the 'circulating heat absorption capacity', 'effective enthalpy drop of a high-pressure cylinder' and 'enthalpy rise of a feed pump' of 1kg unit steam as characteristic variables, and corrects the 'effective enthalpy drop of the high-pressure cylinder' and the 'enthalpy rise of the feed pump' by adopting an enthalpy drop correction coefficient beta and a thermodynamic system correction coefficient gamma respectively to obtain a turbine unit variable-pressure operation difference quantitative calculation model based on 'unit heat rate relative comparison':

Q＝(h ₀ -h _f )-α(h _r -h ₁ )；

H＝ηQ

δ(Δh)＝Δh′-Δh＝(h′ ₀ -h′ ₁ )-(h ₀ -h ₁ )

δ(Δτ)＝Δτ′-Δτ

H′＝H+βδ(Δh)-γ(Δτ)

Q′＝(h′ ₀ -h′ _f )-α(h′ _r -h′ ₁ )

ΔHR＝HR′-HR

in the formula, h ₀ Is the enthalpy of main steam before changing working condition, h ₁ The method is characterized in that the exhaust enthalpy of the high-pressure cylinder before the working condition is changed, Δh is the effective enthalpy drop of the high-pressure cylinder before the working condition, Δτ is the feed water enthalpy rise before the working condition, H is the unit steam useful work before the working condition, Q is the circulating heat absorption quantity before the working condition, and H _f For final feed enthalpy before changing working condition, h _r The enthalpy of reheat steam before the variable working condition, eta is the circulation efficiency before the variable working condition, and HR is the heat consumption rate of the unit before the variable working condition; h's' ₀ Is the enthalpy of main steam after working condition change, h' ₁ The method is characterized in that the method comprises the steps of taking the exhaust enthalpy of a high-pressure cylinder after the working condition, delta H ' as the effective enthalpy drop of the high-pressure cylinder after the working condition, delta tau ' as the feed water enthalpy rise after the working condition, H ' as the useful work of unit steam after the working condition, Q ' as the circulating heat absorption quantity after the working condition and H ' _f Is the final feed enthalpy after changing working conditions, h' _r The enthalpy of the reheat steam after the working condition is changed, eta 'is the circulation efficiency after the working condition is changed, and HR' is the heat consumption rate of the unit after the working condition is changed; delta (delta h) is the effective enthalpy drop gain of the high-pressure cylinder before and after the variable working condition; delta (delta tau) is the enthalpy rise gain of the feedwater before and after the variable working condition; alpha is a reheat coefficient, and beta is an enthalpy drop correction coefficient; gamma is a thermodynamic system correction coefficient; ΔHR is the amplitude of the heat rate of the unit before and after the variable working condition;

for a steam turbine set adopting a multi-step sequence opening mode, taking a valve point as a demarcation point, carrying out sectional correction and accounting on enthalpy drop correction coefficient beta and thermodynamic system correction coefficient gamma so as to improve the unit heat rate change analysis precision of a model; the nozzle gas distribution type A can be divided into three sections of four valve points, three valve points, two valve points and two valve throttling according to valve points in sequence; the overload steam supplementing machine type B can be divided into two sections of 'full opening of a steam supplementing valve-full closing of the steam supplementing valve and full opening of a main regulating valve' and 'throttling of the main regulating valve' according to valve points in sequence.

2. The method for constructing the quantitative calculation model of the variable-pressure operation consumption difference of the improved turbine unit according to claim 1, wherein the enthalpy drop correction coefficient beta and the thermodynamic system correction coefficient gamma are corrected and calculated by adopting turbine unit professional simulation software or EXCEL self-programming thermodynamic calculation program conforming to ASME PTC6A-1982 calculation example according to unit design parameters or test parameters.