A method for calculating the influence quantity of heater end difference of a steam turbine regenerative system on heat rate

Abstract

This invention discloses a method for calculating the impact of heater terminal temperature difference in a steam turbine regenerative system on the heat rate. This method calculates the change in heat rate before and after changes in the upper and lower terminal temperature differences of the heaters, while keeping the upper and lower terminal temperature differences a single variable each time. The internal efficiency of the high-pressure and intermediate-pressure cylinders of the steam turbine is considered constant, and the change in relative internal efficiency is mainly caused by changes in the steam humidity of the low-pressure cylinder. This allows for the quantification of the impact of the terminal temperature difference on the heat rate. This invention fully considers the dynamic equilibrium process of steam turbine calculation under varying operating conditions, and the proposed method for calculating the impact of heater terminal temperature difference on the heat rate of the steam turbine regenerative system is more accurate than existing methods.

Description

[Technical Field]

[0001] This invention relates to the field of steam turbine technology, and specifically to a method for calculating the influence of the terminal temperature difference of a steam turbine regenerative system on the heat consumption rate. [Background Technology]

[0002] Thermal power units are major energy consumers in my country, and their energy conservation and emission reduction are of paramount importance to the country's energy strategy. The main focus of energy conservation in power plant steam turbine operation is the economic efficiency of the regenerative system, which is primarily reflected in the heater terminal temperature difference. The heater terminal temperature difference generally refers to the difference between the saturation temperature at the heater extraction pressure and the heater outlet water temperature. The heater terminal temperature difference is further divided into upper and lower terminal temperature differences. Upper terminal temperature difference = saturation temperature at the steam extraction pressure - water outlet temperature; lower terminal temperature difference = steam condensate temperature - water inlet temperature. Unless otherwise specified, it usually refers to the difference between the saturation temperature at the heater extraction pressure and the heater outlet water temperature.

[0003] Obviously, the smaller the terminal difference, the better the thermal economy. A deviation of the terminal difference from the design value will lead to a decrease in the economic efficiency of the turbine unit. The factors affecting the terminal difference are quite complex. It may be due to operational adjustments, instrument accuracy, or equipment reliability.

[0004] For the retrofitting of a steam turbine regenerative system, it is necessary to accurately calculate the energy-saving potential of each heater and conduct a technical and economic analysis in conjunction with the cost of each retrofitting scheme to inform the owner's investment decision. The energy-saving potential of the steam turbine regenerative system mainly refers to how much the terminal temperature difference of each heater deviates from the design value. Specific calculations require knowing the impact of each 1°C increase in the terminal temperature difference of the regenerative system heaters on the heat rate.

[0005] Currently, the methods for calculating the impact of heater terminal temperature difference in a steam turbine regenerative system on the heat rate are all based on the equivalent enthalpy drop method proposed by Lin Wanchao in his early work, and there are no other relatively mature calculation methods. The equivalent enthalpy drop method is not a dynamic equilibrium method; it only considers the changes in local steam extraction efficiency, and the calculated results deviate somewhat from the actual values. [Summary of the Invention]

[0006] This invention addresses the above-mentioned problems by proposing an algorithm for calculating the impact of heater terminal temperature difference in a turbine regenerative system on the heat rate. It fully considers the dynamic equilibrium process of turbine calculation under varying operating conditions, and the proposed method for calculating the impact of heater terminal temperature difference on the heat rate is more accurate than existing methods. Overcoming the shortcomings of existing algorithms, this calculation method is simpler and easier to understand, more adaptable to real-world situations, and has significant practical value.

[0007] Based on the variable operating characteristics of the steam turbine and the system energy balance method, the calculation method of the present invention provides another method for calculating the influence of the heater terminal difference of the steam turbine regenerative system on the heat rate. This calculation method calculates the change in heat rate before and after the change of the upper terminal difference of the heater and before and after the change of the lower terminal difference of the heater. While keeping the upper terminal difference or the lower terminal difference of the heater a single variable each time, the system efficiency is adjusted to remain constant to calculate the influence of heat rate.

[0008] A method for calculating the influence of heater terminal temperature difference on heat rate in a steam turbine regenerative system includes the following steps:

[0009] 1. Collect the raw data required for the heat rate calculation method;

[0010] 2. First calculation of heater terminal temperature difference and heat rate of the unit's regenerative system;

[0011] 3. Calculate the temperature difference at the top of heater #i in the regenerative system. lower end difference Heaters #1, #2, and #3 are high-pressure heaters; heaters #5 and #6 are low-pressure heaters. The low-pressure cylinder efficiency η′ d Test heat rate HR;

[0012] 4. Iteratively calculate the test heat rate of the regenerating system after the change of the heater terminal difference by adjusting either the upper or lower difference of the heater and the condensate flow rate Q. When adjusting the parameters, keep the upper or lower difference of the heater a single variable each time, while keeping the efficiency of the system constant, and calculate the thermal efficiency after adjustment.

[0013] 5. Calculate the effect of the heater terminal temperature difference in the regenerative system on the heat consumption rate.

[0014] The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate, specifically step four, involves calculating the impact of the terminal temperature difference of the #1 high-pressure heater on the heat rate. The specific steps for the calculation are as follows:

[0015] (4.1.1) Changing the outlet water temperature of the #1 high-pressure heater causes a change in the temperature difference at the upper end of the #1 high-pressure heater. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will remain unchanged, but the calculated efficiency of the low-pressure cylinder will change.

[0016] (4.1.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0017] (4.1.3) Comparison With η′ d The difference, if With η′ dIf the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.1.2).

[0018] (4.1.4) Output the heat dissipation rate until the iteration ends. Calculate the effect of the temperature difference at the top of the #1 high-pressure heater on the heat rate.

[0019] The formula for calculating the effect of a 1°C change in the upper temperature difference of the #1 high-pressure heater on the heat consumption rate is as follows:

[0020]

[0021] The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate is described below, specifically for calculating the impact of the terminal temperature difference of the #5 low-pressure heater on the heat rate. The calculation method is the same as that for the upper end difference of the #1 high-pressure heater.

[0022] The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate is described above, specifically for calculating the impact of the terminal temperature difference of the #2 high-pressure heater on the heat rate. The specific steps for the calculation are as follows:

[0023] (4.2.1) Changing the outlet water temperature of the #2 high-pressure heater causes a change in the temperature difference at the upper end of the #2 high-pressure heater. If the change in condensate temperature of high-pressure heater #1 and the change in outlet water temperature of high-pressure heater #2 are the same, and other system parameters remain unchanged, then the efficiency of high-pressure cylinder, medium-pressure cylinder and other boundary conditions of the regenerative system will not change, but the calculated efficiency of low-pressure cylinder will change.

[0024] (4.2.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0025] (4.2.3) Comparison With η′ d The difference, if With η′ d If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.2.2).

[0026] (4.2.4) Output the heat dissipation rate until the iteration ends. Calculate the effect of the upper end difference of the #2 high-pressure heater on the heat rate.

[0027] The formula for calculating the effect of a 1°C change in the upper temperature difference of the #2 high-pressure heater on the heat consumption rate is as follows:

[0028]

[0029] The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate is described below, focusing on the impact of the terminal temperature difference between the #3 high-pressure heater and the #6 low-pressure heater on the heat rate. and The calculation method is the same as that for the upper end difference of the #2 high-pressure heater.

[0030] The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate is described below, focusing on the impact of the lower terminal temperature difference of the #1 high-pressure heater on the heat rate. The specific steps for the calculation are as follows:

[0031] (4.3.1) Changing the condensate temperature of high-pressure heater #1 causes a change in the temperature difference at the lower end of high-pressure heater #1. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will remain unchanged, but the calculated efficiency of the low-pressure cylinder will change.

[0032] (4.3.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0033] (4.3.3) Comparison With η′ d The difference, if With η′ d If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.3.2).

[0034] (4.3.4) The iteration ends, and the heat dissipation rate is output. Calculate the effect of the temperature difference at the lower end of the #1 high-pressure heater on the heat rate.

[0035] The formula for calculating the effect of a 1°C change in the lower end temperature difference of the #1 high-pressure heater on the heat consumption rate is as follows:

[0036]

[0037] The calculation method for the influence of the heater terminal temperature difference of the turbine regenerative system on the heat rate is as follows: The influence of the lower terminal temperature difference of heaters #1, #2, #3, #5, and #6 on the heat rate is calculated. The calculation method is the same as that for the lower end difference of the #1 high-pressure heater.

[0038] Preferably, all the original data for calculating the upper and lower differences of the heater in the regenerative system and the heat consumption rate are obtained using experimental measurement points, resulting in high calculation accuracy.

[0039] Preferably, each calculation changes a single variable to ensure that the heater terminal temperature difference and turbine internal efficiency of other regenerative systems remain constant. This is a dynamic equilibrium process with high accuracy.

[0040] The calculation principle involved in this invention is simple and easy to understand, and has strong practical value and operability. The calculation method fully considers the dynamic balance process of turbine variable operating conditions calculation, and the proposed calculation method for the influence of the heater terminal difference of the turbine regenerating system on the heat consumption rate is more accurate than the existing methods. [Attached Image Description]

[0041] Figure 1 This is a flowchart of the iterative method for the influence of the upper end difference of the #1 high-pressure heater on the heat consumption rate in this invention;

[0042] Figure 2 This is a flowchart of the iterative method for the influence of the upper end difference of the #2 high-pressure heater on the heat consumption rate in this invention;

[0043] Figure 3 This is a flowchart of the iterative method for the influence of the lower end difference of the #1 high-pressure heater on the heat consumption rate of the present invention.

Detailed Implementation Methods

[0044] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0045] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0046] To facilitate a detailed explanation of the calculation methods involved in this invention and to aid in better understanding, the following description uses a domestically produced supercritical, single-shaft, three-cylinder, four-exhaust, dual-backpressure, condensing steam turbine with a feedwater reheat system consisting of 3 high-pressure heaters + 1 deaerator + 4 low-pressure heaters, and equipped with a steam-driven feedwater pump as an example.

[0047] This invention provides a method for calculating the influence of heater terminal temperature difference on heat rate in a steam turbine regenerative system, comprising the following specific steps:

[0048] (1) Collect the raw data required for heat loss calculation methods:

[0049]

[0050]

[0051]

[0052] (2) Calculate the temperature difference at the top of heater #i in the regenerative system. lower end difference Heaters #1, #2, and #3 are high-pressure heaters; heaters #5 and #6 are low-pressure heaters. The low-pressure cylinder efficiency η′ d Test heat rate HR;

[0053]

[0054]

[0055] (3) Change in the upper end difference of #1 high-pressure heater With the system efficiency remaining constant, calculate the corrected heat rate.

[0056] (4) By changing the outlet water temperature of the #1 high-pressure heater, the temperature difference at the upper end of the #1 high-pressure heater is changed. Pick Calculate the corrected heat rate The method is as follows:

[0057] 4.1) Change the outlet water temperature of #1 high-pressure heater to 276.18℃, thereby changing the temperature difference at the upper end of #1 high-pressure heater. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will remain unchanged, but the calculated efficiency of the low-pressure cylinder will change.

[0058] 4.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0059] 4.3) Comparison With η′ d The difference, if With η′ d If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, then redesign the condensate flow rate Q and return to step 4.2);

[0060] 4.4) The iteration ends, the condensate flow rate Q is 1287.94 t / h, and the output heat rate is... Given a heat rate of 7973.88 kJ / kWh, calculate the effect of the temperature difference at the upper end of the #1 high-pressure heater on the heat rate.

[0061]

[0062] Investigating the effect of the upper end difference of the #5 low-pressure heater on the heat rate. The calculation method is the same as the calculation method for the upper end difference of the #1 high-pressure heater.

[0063] #2 High-pressure heater upper end temperature difference change With the system efficiency remaining constant, calculate the corrected heat rate.

[0064] By changing the outlet water temperature of the #2 high-pressure heater, the temperature difference at the upper end of the #2 high-pressure heater is altered. Simultaneously, the condensate temperature of the #1 high-pressure heater changes. Pick Calculate the corrected heat rate The method is as follows:

[0065] 7.1) Change the outlet water temperature of the #2 high-pressure heater to 250.27℃, thereby changing the temperature difference at the upper end of the #2 high-pressure heater. At the same time, if the condensate temperature of the #1 high-pressure heater is changed by 254.83℃, and other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder, as well as other boundary conditions of the regenerative system, will not change, but the calculated efficiency of the low-pressure cylinder will change.

[0066] 7.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0067] 7.3) Comparison With η′ d The difference, if With η′ d If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, then redesign the condensate flow rate Q and return to step 7.2).

[0068] 7.4) The iteration ends, the condensate flow rate Q is 1287.46 t / h, and the output heat rate is... Given a heat rate of 7972.11 kJ / kWh, calculate the effect of the temperature difference at the upper end of the #2 high-pressure heater on the heat rate.

[0069]

[0070] The effect of the temperature difference between the upper ends of the #3 high-pressure heater and the #6 low-pressure heater on the heat rate was investigated. and The calculation method is the same as the calculation method for the upper end difference of the #2 high-pressure heater.

[0071] #1 Change in the lower end temperature difference of the high-pressure heater With the system efficiency remaining constant, calculate the corrected heat rate.

[0072] The temperature difference at the lower end of the #1 high-pressure heater is changed by altering the condensate temperature of the #1 high-pressure heater. Calculate the corrected heat rate The method is as follows:

[0073] 10.1) Change the condensate temperature of high-pressure heater #1 to 256.83℃, thereby changing the temperature difference at the lower end of high-pressure heater #1. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will remain unchanged, but the calculated efficiency of the low-pressure cylinder will change.

[0074] 10.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q.

[0075] 10.3) Comparison With η′ d The difference, if With η′ d If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. if With η′ d If the difference is greater than 0.001%, then redesign the condensate flow rate Q and return to step 10.2).

[0076] 10.4) The iteration ends, the condensate flow rate Q is 1287.23 t / h, and the output heat rate is... Given a heat rate of 7971.39 kJ / kWh, calculate the effect of the temperature difference at the lower end of the #1 high-pressure heater on the heat rate.

[0077]

[0078] Investigate the influence of the difference in the lower end of other heaters on the heat rate. The calculation method is the same as the calculation method for the lower end difference of the #1 high-pressure heater.

[0079] All raw data for calculating the upper and lower temperature differences of the regenerative system heaters and the heat rate were obtained from experimental measurement points, resulting in high calculation accuracy. Each calculation modifies a single variable while maintaining constant temperature differences in other regenerative system heaters and turbine internal efficiency, representing a dynamic equilibrium process with high accuracy. The calculation results for the impact of a 1°C increase in temperature difference on the heat rate are as follows:

[0080]

[0081]

[0082] The calculation method involved in this invention mainly describes the impact of the heater terminal temperature difference in a regenerative system on the heat rate. For ease of description and understanding, the calculation method is presented as follows: Figures 1 to 3 The process is illustrated below. Regardless of changes in the thermal power unit's thermal system, calculations can be performed using the methods described in this invention. Therefore, the embodiments of this invention do not constitute a limitation of the invention.

[0083] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A method for calculating the influence of heater terminal temperature difference in a steam turbine regenerative system on the heat rate, comprising the following steps: (1) Collect raw data of the unit's thermal balance system; (2) First calculation of heater terminal temperature difference and heat consumption rate of the unit's regenerative system; (3) Calculate the temperature difference at the top of heater #i in the regenerative system Lower end difference i=1, 2, 3, 5, 6, #1, 2, 3 are high-pressure heaters, #5, 6 are low-pressure heaters, and the low-pressure cylinder efficiency is... Test heat rate HR; (4) Adjust either the upper or lower difference of the heater and the condensate flow rate Q to perform iterative calculations and calculate the test heat rate after the change of the heater difference of the regenerating system. When adjusting the parameters, keep the upper or lower difference of the heater a single variable each time, while adjusting the efficiency of the system to remain unchanged, and calculate the thermal efficiency after adjustment. Calculate the influence of the heater terminal temperature difference of the regenerative system on the heat rate. In step (4), the influence of the terminal temperature difference of the #1 high-pressure heater on the heat rate is calculated. The specific steps for the calculation are as follows: (4.1.1) Change the outlet water temperature of the #1 high-pressure heater to change the temperature difference at the upper end of the #1 high-pressure heater. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will not change, but the calculated efficiency of the low-pressure cylinder will change. (4.1.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q. ; (4.1.3) Comparison and The difference, if and If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. ;if and If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.1.2). (4.1.4) Output the heat dissipation rate until the iteration ends. Calculate the effect of the temperature difference at the upper end of the #1 high-pressure heater on the heat consumption rate. The formula for calculating the effect of a 1°C change in the upper temperature difference of the #1 high-pressure heater on the heat consumption rate is as follows: ; The influence of the upper end difference of the #2 high-pressure heater on the heat rate was investigated. The specific steps for the calculation are as follows: (4.2.1) Changing the outlet water temperature of the #2 high-pressure heater causes a change in the temperature difference at the upper end of the #2 high-pressure heater. If the change in condensate temperature of high-pressure heater #1 and the change in outlet water temperature of high-pressure heater #2 are the same, and other system parameters remain unchanged, then the efficiency of high-pressure cylinder, medium-pressure cylinder and other boundary conditions of regenerative system will not change, but the calculated efficiency of low-pressure cylinder will change. (4.2.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q. ; (4.2.3) Comparison and The difference, if and If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. ;if and If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.2.2). (4.2.4) Output the heat dissipation rate until the iteration ends. Calculate the effect of the temperature difference at the upper end of the #2 high-pressure heater on the heat consumption rate. The formula for calculating the effect of a 1°C change in the upper temperature difference of the #2 high-pressure heater on the heat consumption rate is as follows: .

2. The method for calculating the influence of the heater terminal temperature difference on the heat rate of the turbine regenerative system according to claim 1, characterized in that, The method for calculating the impact of the heater terminal temperature difference in the turbine regenerative system on the heat rate is described below, specifically for calculating the impact of the terminal temperature difference of the #5 low-pressure heater on the heat rate. The calculation method is the same as that for the upper end difference of the #1 high-pressure heater.

3. The method for calculating the influence of the heater terminal temperature difference on the heat rate of the turbine regenerative system according to claim 1, characterized in that, The effect of the difference in the upper end pressure of the #3 high-pressure heater and the #6 low-pressure heater on the heat rate was investigated. and The calculation method is the same as that for the upper end difference of the #2 high-pressure heater.

4. The method for calculating the influence of the heater terminal temperature difference on the heat rate of the turbine regenerative system according to claim 1, characterized in that, The influence of the lower end temperature difference of the #1 high-pressure heater on the heat rate was investigated. The specific steps for the calculation are as follows: (4.3.1) Changing the condensate temperature of the #1 high-pressure heater causes a change in the differential pressure at the lower end of the #1 high-pressure heater. If other system parameters remain unchanged, the efficiency of the high-pressure cylinder and the medium-pressure cylinder will not change, but the calculated efficiency of the low-pressure cylinder will change. (4.3.2) Calculate the low-pressure cylinder efficiency by adjusting the condensate flow rate Q. ; (4.3.3) Comparison and The difference, if and If the difference is less than or equal to 0.001%, then the corrected heat rate will be output. ;if and If the difference is greater than 0.001%, the condensate flow rate Q is redesigned and the process returns to step (4.3.2). (4.3.4) The iteration ends, and the heat dissipation rate is output. Calculate the effect of the temperature difference at the lower end of the #1 high-pressure heater on the heat rate. .

5. The method for calculating the influence of the heater terminal temperature difference on the heat rate of the turbine regenerative system according to claim 4, characterized in that, The formula for calculating the effect of a 1°C change in the lower end temperature difference of the #1 high-pressure heater on the heat consumption rate is as follows: .

6. The method for calculating the influence of the heater terminal temperature difference on the heat rate of the turbine regenerative system according to claim 5, characterized in that, The influence of the lower end difference of heaters #2, #3, #5 and #6 on the heat rate was investigated. For i=2, 3, 5, 6, the calculation method is the same as that for the lower end difference of the #1 high-pressure heater.

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