A power plant hot standby auxiliary heating system and operation optimization method

Abstract

The invention relates to the technical field of coal-fired power plants, and provides a power plant hot standby auxiliary heating system and an operation optimization method. The power plant hot standby auxiliary heating system uses a first-level electric heater, a second-level electric heater and a third-level electric heater to provide the heat required for the hot standby of the power plant, without the need for auxiliary steam from adjacent machines and heat storage energy, so that the power plant can operate in a hot standby state at any time, and the system operation mode is more flexible; and the working states of the second-level electric heater inlet valve, the third-level electric heater inlet valve, the medium-pressure cylinder inlet valve, the low-pressure cylinder inlet valve, the second-level electric heater bypass valve, the third-level electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve can be switched to optimize the distribution of heat in different equipment, and on the premise of maintaining the power plant in a hot standby state, the energy consumption of maintaining the hot standby state is reduced, thereby improving the thermal economy of the unit.

Description

Technical Field

[0001] The invention relates to the technical field of coal-fired power plants, and in particular to a hot standby auxiliary heating system for a power plant and an operation optimization method. Background Art

[0002] With the continuous development of renewable energy, the proportion of renewable energy power generation is also increasing. However, due to the intermittent and unpredictable characteristics of renewable energy, in order to maintain the stability of the power grid, the peak load regulation tasks of coal-fired power plants are also increasing. Rapid load change and start-stop are effective methods for peak load regulation of coal-fired power plants. Some units are shut down due to the need for peak load regulation of the power grid and restarted within 24 hours. Generally, after the unit is shut down, due to heat dissipation, the temperature level of the unit continues to decrease. When it is restarted, it needs to be preheated again, resulting in an increase in the startup time and startup energy consumption of the unit. Therefore, how to maintain the power plant in a hot standby state and reduce the energy consumption of maintaining the hot standby state is an important aspect of reducing startup time and energy consumption. Summary of the invention

[0003] Therefore, the technical problem to be solved by the present invention is how to maintain a power plant in a hot standby state and reduce the energy consumption of maintaining the hot standby state, thereby providing a power plant hot standby auxiliary heating system and an operation optimization method.

[0004] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0005] A hot standby auxiliary heating system for a power plant comprises at least: a unit, wherein a first-stage electric heater, a second-stage electric heater and a third-stage electric heater are sequentially arranged between a steam-water separator and a high-pressure cylinder in the unit; a second-stage electric heater inlet valve is arranged on a pipeline between an outlet of the first-stage electric heater and an inlet of the second-stage electric heater, and a third-stage electric heater inlet valve is arranged on a pipeline between an outlet of the second-stage electric heater and an inlet of the third-stage electric heater; an intermediate-pressure cylinder inlet valve is arranged between the high-pressure cylinder and the intermediate-pressure cylinder in the unit, and a low-pressure cylinder inlet valve is arranged between the intermediate-pressure cylinder and the low-pressure cylinder in the unit; a second-stage electric heater bypass valve is arranged in parallel with the second-stage electric heater inlet valve and the second-stage electric heater; a third-stage electric heater bypass valve is arranged in parallel with the third-stage electric heater inlet valve and the third-stage electric heater; an intermediate-pressure cylinder bypass valve is arranged in parallel with the intermediate-pressure cylinder inlet valve and the intermediate-pressure cylinder; and a low-pressure cylinder bypass valve is arranged in parallel with the low-pressure cylinder inlet valve and the low-pressure cylinder.

[0006] Furthermore, the outlet of the first-stage electric heater is connected to the inlet of the low-pressure cylinder in the unit.

[0007] Furthermore, the outlet of the secondary electric heater bypass valve is connected to the inlet of the medium-pressure cylinder in the unit.

[0008] Furthermore, the unit includes a four-stage electric heater, a water-cooled wall, a steam-water separator, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a condensate pump, a low-pressure heater, a feedwater pump, a high-pressure heater, a feedwater valve, a water storage tank and a preheater; the outlet of the four-stage electric heater is connected to the inlet of the water-cooled wall, the outlet of the water-cooled wall is connected to the inlet of the steam-water mixture of the steam-water separator, the steam outlet of the steam-water separator is connected to the steam inlet of the first-stage electric heater; the high-pressure cylinder, the medium-pressure cylinder, the low-pressure cylinder and the generator are coaxially connected; the The outlet is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the condensate pump, the outlet of the condensate pump is connected to the inlet of the low-pressure heater, the outlet of the low-pressure heater is connected to the inlet of the feed water pump, the outlet of the feed water pump is connected to the inlet of the high-pressure heater, the outlet of the high-pressure heater is connected to the inlet of the feed water valve, the outlet of the feed water valve is connected to the inlet of the preheater, and the outlet of the preheater is connected to the inlet of the four-stage electric heater; the feed water outlet of the steam-water separator is connected to the inlet of the water storage tank.

[0009] Furthermore, the outlet of the water storage tank is connected to the drain inlet of the condenser, and a drain bypass valve is arranged on the pipeline between the two.

[0010] Furthermore, the outlet of the water storage tank is connected to the inlet of the preheater, and a circulating water valve and a circulating water pump are arranged on the pipeline between the two.

[0011] A method for optimizing the operation of a hot standby auxiliary heating system of a power plant, comprising the hot standby auxiliary heating system of the power plant described above, wherein the method for optimizing the operation is as follows: when the temperatures of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder are lower than 150°C: close the secondary electric heater inlet valve, the tertiary electric heater inlet valve, the medium-pressure cylinder inlet valve and the low-pressure cylinder inlet valve; open the secondary electric heater bypass valve, the tertiary electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve, so that the drain water of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder is sent to the condenser in the unit.

[0012] Furthermore, when the temperature of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder is higher than 150°C: the optimization algorithm is used to optimize the operation strategy of the system, and the optimization goal is:

[0013] min(f)=min(P1+P2+P3);

[0014] The constraints are:

[0015] r b1 +r1=1;

[0016] r b2 +r2=1;

[0017] r b3 +r3=1;

[0018] r b4 +r4=1;

[0019] 10℃ <T s -T w <50℃;

[0020] T wh >300℃;

[0021] T wm >200℃;

[0022] T wl >100℃;

[0023] Where: P1 is the electric power of the first-stage electric heater; P2 is the electric power of the second-stage electric heater; P3 is the electric power of the third-stage electric heater; r1 is the valve position signal of the inlet valve of the second-stage electric heater; r b1 is the valve position signal of the bypass valve of the secondary electric heater; r2 is the valve position signal of the inlet valve of the tertiary electric heater; r b2 is the valve position signal of the bypass valve of the three-stage electric heater; r3 is the valve position signal of the inlet valve of the medium pressure cylinder; r b3 is the valve position signal of the bypass valve of the medium pressure cylinder; r4 is the valve position signal of the inlet valve of the low pressure cylinder; r b4 is the valve position signal of the low-pressure cylinder bypass valve; T s is the inlet steam temperature of the high pressure cylinder, medium pressure cylinder and low pressure cylinder, T w is the metal temperature of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder; T wh is the metal temperature of the high pressure cylinder; T wm is the metal temperature of the medium pressure cylinder; T wl is the metal temperature of the low-pressure cylinder.

[0024] Furthermore, when the outlet steam quality of the high-pressure cylinder is lower than 0.8, the inlet valve of the intermediate-pressure cylinder is closed; when the outlet steam quality of the intermediate-pressure cylinder is lower than 0.8, the inlet valve of the low-pressure cylinder is closed.

[0025] Further, when the valve position signal of the second-stage electric heater inlet valve is less than 0.2, the second-stage electric heater inlet valve is closed and the second-stage electric heater bypass valve is opened; when the valve position signal of the third-stage electric heater inlet valve is less than 0.2, the third-stage electric heater inlet valve is closed and the third-stage electric heater bypass valve is opened; when the valve position signal of the intermediate pressure cylinder inlet valve is less than 0.2, the intermediate pressure cylinder inlet valve is closed and the intermediate pressure cylinder bypass valve is opened; when the valve position signal of the low pressure cylinder inlet valve is less than 0.2, the low pressure cylinder inlet valve is closed and the low pressure cylinder bypass valve is opened.

[0026] The technical solution of the present invention has the following advantages:

[0027] The power plant hot standby auxiliary heating system provided by the present invention uses a first-level electric heater, a second-level electric heater and a third-level electric heater to provide the heat required for the hot standby of the power plant, without the need for auxiliary steam from adjacent machines and heat storage energy, so that the power plant can operate in a hot standby state at any time, and the system operation mode is more flexible; and the working states of the second-level electric heater inlet valve, the third-level electric heater inlet valve, the medium-pressure cylinder inlet valve, the low-pressure cylinder inlet valve, the second-level electric heater bypass valve, the third-level electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve can be switched to optimize the distribution of heat in different equipment, and on the premise of maintaining the power plant in a hot standby state, the energy consumption of maintaining the hot standby state is reduced, thereby improving the thermal economy of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 Schematic diagram of a hot standby auxiliary heating system for a power plant in an embodiment of the present invention.

[0030] 1. Four-stage electric heater; 2. Water-cooled wall; 3. Steam-water separator; 4. First-stage electric heater; 5. Second-stage electric heater bypass valve; 6. Second-stage electric heater inlet valve; 7. Second-stage electric heater; 8. Third-stage electric heater bypass valve; 9. Third-stage electric heater inlet valve; 10. Third-stage electric heater; 11. High-pressure cylinder; 12. Medium-pressure cylinder inlet valve; 13. Medium-pressure cylinder bypass valve; 14. Medium-pressure cylinder; 15. Low-pressure cylinder inlet valve; 16. Low-pressure cylinder bypass valve; 17. Low-pressure cylinder; 18. Generator; 19. Condenser; 20. Condensate pump; 21. Low-pressure heater; 22. Feed water pump; 23. High-pressure heater; 24. Drain bypass valve; 25. Feed water valve; 26. Circulating water pump; 27. Circulating water valve; 28. Water storage tank; 29. ​​Preheater. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0033] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Figure 1 Schematic diagram of a hot standby auxiliary heating system for a power plant in an embodiment of the present invention. Figure 1As shown, this embodiment provides a hot standby auxiliary heating system for a power plant, which at least includes: a unit, wherein a first-stage electric heater 4, a second-stage electric heater 7 and a third-stage electric heater 10 are sequentially arranged between a steam-water separator 3 and a high-pressure cylinder 11 in the unit; a second-stage electric heater inlet valve 6 is arranged on the pipeline between the outlet of the first-stage electric heater 4 and the inlet of the second-stage electric heater 7, and a third-stage electric heater inlet valve 9 is arranged on the pipeline between the outlet of the second-stage electric heater 7 and the inlet of the third-stage electric heater 10; a high-pressure cylinder 11 in the unit and a medium-pressure cylinder 14 are connected to each other. A medium-pressure cylinder inlet valve 12 is arranged between the medium-pressure cylinder 14 and the low-pressure cylinder 17 in the unit, and a low-pressure cylinder inlet valve 15 is arranged between the medium-pressure cylinder 14 and the low-pressure cylinder 17 in the unit; a secondary electric heater bypass valve 5 is arranged in parallel with the secondary electric heater inlet valve 6 and the secondary electric heater 7; a tertiary electric heater bypass valve 8 is arranged in parallel with the tertiary electric heater inlet valve 9 and the tertiary electric heater 10; a medium-pressure cylinder bypass valve 13 is arranged in parallel with the medium-pressure cylinder inlet valve 12 and the medium-pressure cylinder 14; a low-pressure cylinder bypass valve 16 is arranged in parallel with the low-pressure cylinder inlet valve 15 and the low-pressure cylinder 17.

[0036] The power plant hot standby auxiliary heating system provided in this embodiment uses a first-level electric heater, a second-level electric heater and a third-level electric heater to provide the heat required for the hot standby of the power plant, without the need for auxiliary steam from adjacent machines and heat storage energy, so that the power plant can operate in a hot standby state at any time, and the system operation mode is more flexible; and the working states of the second-level electric heater inlet valve, the third-level electric heater inlet valve, the medium-pressure cylinder inlet valve, the low-pressure cylinder inlet valve, the second-level electric heater bypass valve, the third-level electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve can be switched to optimize the distribution of heat among different equipment, and on the premise of maintaining the power plant in a hot standby state, the energy consumption of maintaining the hot standby state can be reduced, thereby improving the thermal economy of the unit.

[0037] Among them, the outlet of the first-stage electric heater 4 is connected to the inlet of the low-pressure cylinder 17 in the unit.

[0038] The outlet of the secondary electric heater bypass valve 5 is connected to the inlet of the medium-pressure cylinder 14 in the unit.

[0039] The unit includes a four-stage electric heater 1, a water-cooled wall 2, a steam-water separator 3, a high-pressure cylinder 11, a medium-pressure cylinder 14, a low-pressure cylinder 17, a generator 18, a condenser 19, a condensate pump 20, a low-pressure heater 21, a feed water pump 22, a high-pressure heater 23, a feed water valve 25, a water storage tank 28 and a preheater 29; the outlet of the four-stage electric heater 1 is connected to the inlet of the water-cooled wall 2, the outlet of the water-cooled wall 2 is connected to the inlet of the steam-water mixture of the steam-water separator 3, and the steam outlet of the steam-water separator 3 is connected to the steam inlet of the first-stage electric heater 4; the high-pressure cylinder 11, the medium-pressure cylinder 14, the low-pressure cylinder 17 and the generator 18 are connected together. The outlet of the low-pressure cylinder 17 is connected to the inlet of the condenser 19, the outlet of the condenser 19 is connected to the inlet of the condensate pump 20, the outlet of the condensate pump 20 is connected to the inlet of the low-pressure heater 21, the outlet of the low-pressure heater 21 is connected to the inlet of the feed water pump 22, the outlet of the feed water pump 22 is connected to the inlet of the high-pressure heater 23, the outlet of the high-pressure heater 23 is connected to the inlet of the feed water valve 25, the outlet of the feed water valve 25 is connected to the inlet of the preheater 29, and the outlet of the preheater 29 is connected to the inlet of the four-stage electric heater 1; the feed water outlet of the steam-water separator 3 is connected to the inlet of the water storage tank 28.

[0040] The outlet of the water storage tank 28 is connected to the drain inlet of the condenser 19, and a drain bypass valve 24 is provided on the pipeline between the two.

[0041] The outlet of the water storage tank 28 is connected to the inlet of the preheater 29, and a circulating water valve 27 and a circulating water pump 26 are provided on the pipeline between the two.

[0042] Specifically, Figure 1 The hot standby auxiliary heating system of the power plant includes a four-stage electric heater 1, a water-cooled wall 2, a steam-water separator 3, a first-stage electric heater 4, a second-stage electric heater bypass valve 5, a second-stage electric heater inlet valve 6, a second-stage electric heater 7, a third-stage electric heater bypass valve 8, a third-stage electric heater inlet valve 9, a third-stage electric heater 10, a high-pressure cylinder 11, a medium-pressure cylinder inlet valve 12, a medium-pressure cylinder bypass valve 13, a medium-pressure cylinder 14, a low-pressure cylinder inlet valve 15, a low-pressure cylinder bypass valve 16, a low-pressure cylinder 17, a generator 18, a condenser 19, a condensate pump 20, a low-pressure heater 21, a feed water pump 22, a high-pressure heater 23, a drain bypass valve 24, a feed water valve 25, a circulating water pump 26, a circulating water valve 27, a water storage tank 28, and a preheater 29.

[0043] The outlet of the four-stage electric heater 1 is connected to the inlet of the water-cooled wall 2, the outlet of the water-cooled wall 2 is connected to the inlet of the steam-water mixture of the steam-water separator 3, the steam outlet of the steam-water separator 3 is connected to the steam inlet of the first-stage electric heater 4, the steam outlet of the first-stage electric heater 4 is connected to the inlet of the second-stage electric heater 7 through the second-stage electric heater inlet valve 6, the outlet of the second-stage electric heater 7 is connected to the inlet of the third-stage electric heater 10 through the third-stage electric heater inlet valve 9, the outlet of the third-stage electric heater 10 is connected to the inlet of the high-pressure cylinder 11, and the outlet of the high-pressure cylinder 11 is connected to the medium-pressure cylinder inlet valve 12 through the medium-pressure cylinder inlet valve 13. The outlet of the medium-pressure cylinder 14 is connected to the inlet of the low-pressure cylinder 17 through the low-pressure cylinder inlet valve 15, the outlet of the low-pressure cylinder 17 is connected to the inlet of the condenser 19, the outlet of the condenser 19 is connected to the inlet of the condensate pump 20, the outlet of the condensate pump 20 is connected to the inlet of the low-pressure heater 21, the outlet of the low-pressure heater 21 is connected to the inlet of the feed water pump 22, the outlet of the feed water pump 22 is connected to the inlet of the high-pressure heater 23, the outlet of the high-pressure heater 23 is connected to the inlet of the feed water valve 25, and the outlet of the feed water valve 25 is connected to the inlet of the four-stage electric heater 1.

[0044] The secondary electric heater bypass valve 5 is connected in parallel with the secondary electric heater inlet valve 6 and the secondary electric heater 7, the tertiary electric heater bypass valve 8 is connected in parallel with the tertiary electric heater inlet valve 9 and the tertiary electric heater 10, the medium-pressure cylinder bypass valve 13 is connected in parallel with the medium-pressure cylinder inlet valve 12 and the medium-pressure cylinder 14, the low-pressure cylinder bypass valve 16 is connected in parallel with the low-pressure cylinder inlet valve 15 and the low-pressure cylinder 17, the outlet of the first-stage electric heater 4 is also connected to the inlet of the low-pressure cylinder 17, and the outlet of the secondary electric heater 7 is also connected to the inlet of the medium-pressure cylinder 14.

[0045] The water supply outlet of the steam-water separator 3 is connected to the inlet of the water storage tank 28. The outlet of the water storage tank 28 is divided into two branches. One branch is connected to the drain inlet of the condenser 19 through the drain bypass valve 24; the other branch is connected to the inlet of the preheater 29 through the circulating water valve 27 and the circulating water pump 26 in turn, and the branch merges with the outlet of the water supply valve 25 at the inlet of the preheater 29.

[0046] Another embodiment also provides an operation optimization method for a hot standby auxiliary heating system of a power plant, including the above-mentioned hot standby auxiliary heating system of a power plant, and the operation optimization method is as follows: when the temperature of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder is lower than 150°C: close the secondary electric heater inlet valve, the tertiary electric heater inlet valve, the medium-pressure cylinder inlet valve and the low-pressure cylinder inlet valve; open the secondary electric heater bypass valve, the tertiary electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve to allow the drain from the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder to be sent to the condenser in the unit.

[0047] Among them, when the temperature of the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder is higher than 150°C: the optimization algorithm is used to optimize the operation strategy of the system, and the optimization goal is:

[0048] min(f)=min(P1+P2+P3);

[0049] The constraints are:

[0050] r b1 +r1=1;

[0051] r b2 +r2=1;

[0052] r b3 +r3=1;

[0053] r b4 +r4=1;

[0054] 10℃ <T s -T w <50℃;

[0055] T wh >300℃;

[0056] T wm >200℃;

[0057] T wl >100℃;

[0058] Where: P1 is the electric power of the first-stage electric heater; P2 is the electric power of the second-stage electric heater; P3 is the electric power of the third-stage electric heater; r1 is the valve position signal of the inlet valve of the second-stage electric heater; r b1 is the valve position signal of the bypass valve of the secondary electric heater; r2 is the valve position signal of the inlet valve of the tertiary electric heater; r b2 is the valve position signal of the bypass valve of the three-stage electric heater; r3 is the valve position signal of the inlet valve of the medium pressure cylinder; r b3 is the valve position signal of the bypass valve of the medium pressure cylinder; r4 is the valve position signal of the inlet valve of the low pressure cylinder; r b4 is the valve position signal of the low-pressure cylinder bypass valve; T s is the inlet steam temperature of the high pressure cylinder, medium pressure cylinder and low pressure cylinder, T w is the metal temperature of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder; T wh is the metal temperature of the high pressure cylinder; T wm is the metal temperature of the medium pressure cylinder; T wl is the metal temperature of the low-pressure cylinder.

[0059] Among them, when the outlet steam dryness of the high-pressure cylinder is lower than 0.8, the inlet valve of the intermediate-pressure cylinder is closed; when the outlet steam dryness of the intermediate-pressure cylinder is lower than 0.8, the inlet valve of the low-pressure cylinder is closed.

[0060] Among them, when the valve position signal of the second-stage electric heater inlet valve is less than 0.2, the second-stage electric heater inlet valve is closed and the second-stage electric heater bypass valve is opened; when the valve position signal of the third-stage electric heater inlet valve is less than 0.2, the third-stage electric heater inlet valve is closed and the third-stage electric heater bypass valve is opened; when the valve position signal of the intermediate pressure cylinder inlet valve is less than 0.2, the intermediate pressure cylinder inlet valve is closed and the intermediate pressure cylinder bypass valve is opened; when the valve position signal of the low pressure cylinder inlet valve is less than 0.2, the low pressure cylinder inlet valve is closed and the low pressure cylinder bypass valve is opened.

[0061] During operation: When the power plant is in hot standby mode, the first-stage electric heater 4, circulating water pump 26, circulating water valve 27, fourth-stage electric heater 1 and drain bypass valve 24 are turned on, and the fourth-stage electric heater 1 is used to heat the feed water, thereby increasing the temperature and pressure of the entire steam-water system. The outlet of the water-cooled wall 2 is a steam-water mixture, which is separated into liquid water and steam after passing through the steam-water separator 3. The steam enters the first-stage electric heater 4 and is heated to superheated steam, thereby preventing saturated steam from entering the high-pressure cylinder 11, the medium-pressure cylinder 14 and the low-pressure cylinder 17 and causing thermal shock. The liquid water separated by the steam-water separator 3 enters the water storage tank 28. As the water storage capacity of the water storage tank 28 increases, the excess water working medium is sent to the condenser 19, and part of the water working medium is sent back to the preheater 29 through the circulating water pump 26, thereby forming a water working medium circulation of the preheater 29, the four-stage electric heater 1, the water-cooled wall 2, the steam-water separator 3, the water storage tank 28, the circulating water valve 27 and the circulating water pump 26.

[0062] When the temperature of the high pressure cylinder 11, the medium pressure cylinder 14 and the low pressure cylinder 17 is lower than 150°C, the secondary electric heater inlet valve 6, the tertiary electric heater inlet valve 9, the medium pressure cylinder inlet valve 12 and the low pressure cylinder inlet valve 15 are closed, and the secondary electric heater bypass valve 5, the tertiary electric heater bypass valve 8, the medium pressure cylinder bypass valve 13 and the low pressure cylinder bypass valve 16 are opened. The water from the high pressure cylinder 11, the medium pressure cylinder 14 and the low pressure cylinder 17 is sent to the condenser 19. This is because if the temperature of the high pressure cylinder 11, the medium pressure cylinder 14 and the low pressure cylinder 17 is low, the temperature will be significantly reduced after the steam enters the cylinder, and even the steam condensation state will occur. At this time, if it is sent to the next stage cylinder, even if it is mixed with high temperature steam, the preheating effect on the next stage cylinder is poor, so the condensed steam is sent to the condenser 19.

[0063] When the temperature of the high-pressure cylinder 11, the medium-pressure cylinder 14 and the low-pressure cylinder 17 is higher than 150°C, the steam after heat release from the cylinder still has a certain preheating capacity. The optimization algorithm is used to optimize the operation strategy of the system. The optimization goal is that the total electric power efficiency of the first-stage electric heater, the second-stage electric heater and the third-stage electric heater is the lowest during the hot standby process of the power plant. The mathematical expression is:

[0064] min(f)=min(P1+P2+P3);

[0065] Wherein: P1 is the electric power of the first-stage electric heater 4; P2 is the electric power of the second-stage electric heater 7; P3 is the electric power of the third-stage electric heater 10.

[0066] In the process of preheating with electric heaters, there are multiple valve signals that need to be optimized. If each valve signal is used as an optimization variable, the number of optimization variables will increase significantly, thereby increasing the complexity of the calculation. Generally, when the valve of the main branch is closed, the bypass valve is opened accordingly. Therefore, the sum of the valve signal of the main branch valve and the valve signal of the bypass valve is set to 1, which can reduce the number of variables to be optimized and conform to the actual operation mode of the valve. In addition, the temperature of the steam entering the cylinder must be within a reasonable range. If the temperature is too high, it will cause thermal shock to the cylinder and the rotor. If the temperature is too low, the preheating effect of the cylinder is poor. Therefore, in the hot standby process of the power plant, the mathematical expression of the constraint condition is:

[0067] r b1 +r1=1;

[0068] r b2 +r2=1;

[0069] r b3 +r3=1;

[0070] r b4 +r4=1;

[0071] 10℃ <T s -T w <50℃;

[0072] T wh >300℃;

[0073] T wm >200℃;

[0074] T wl >100℃;

[0075] Where: r1 is the valve position signal of the inlet valve 6 of the secondary electric heater; r b1 is the valve position signal of the bypass valve 5 of the secondary electric heater; r2 is the valve position signal of the inlet valve 9 of the tertiary electric heater; r b2 is the valve position signal of the bypass valve 8 of the three-stage electric heater; r3 is the valve position signal of the inlet valve 12 of the medium pressure cylinder; r b3 is the valve position signal of the bypass valve 13 of the medium pressure cylinder; r4 is the valve position signal of the inlet valve 15 of the low pressure cylinder; r b4 is the valve position signal of the low-pressure cylinder bypass valve 16; Ts is the inlet steam temperature of the high pressure cylinder 11, the medium pressure cylinder 14 and the low pressure cylinder 17; T w is the metal temperature of the high pressure cylinder 11, the medium pressure cylinder 14 and the low pressure cylinder 17; T wh is the metal temperature of the high pressure cylinder 11; T wm is the metal temperature of the medium pressure cylinder 14; T wl is the metal temperature of the low-pressure cylinder 17.

[0076] If the steam entering the cylinder condenses into unsaturated steam, its effect of preheating the cylinder becomes poor, so it is no longer sent to the next-level cylinder. Therefore, if the outlet steam dryness of the high-pressure cylinder 11 is lower than 0.8, the intermediate-pressure cylinder inlet valve 12 is closed; if the outlet steam dryness of the intermediate-pressure cylinder 14 is lower than 0.8, the low-pressure cylinder inlet valve 15 is closed.

[0077] Moreover, due to the nonlinear characteristics of the valve, when the valve signal is small, the flow rate of the working fluid passing through is low, and the control effect of the valve will also deteriorate. At this time, the valve is directly closed, and the corresponding bypass valve is opened to allow the working fluid to flow normally. For example, when the valve position signal of the secondary electric heater inlet valve 6, the tertiary electric heater inlet valve 9, the medium-pressure cylinder inlet valve 12, and the low-pressure cylinder inlet valve 15 is less than 0.2, the corresponding valve should be closed, and the corresponding bypass valves, the secondary electric heater bypass valve 5, the tertiary electric heater bypass valve 8, the medium-pressure cylinder bypass valve 13, and the low-pressure cylinder bypass valve 16, should be opened.

[0078] In summary, the power plant hot standby auxiliary heating system in the present application can enable the power plant to operate in a hot standby state at any time by using electric heaters at each stage without the need for adjacent machine auxiliary steam or heat storage systems. Therefore, the system operation mode is more flexible, and by optimizing the distribution of heat from electric heaters at each stage to different equipment, the total energy consumption of electric heaters at each stage can be reduced, which can reduce the energy consumption of hot standby in the power plant and improve the thermal economy of the unit.

[0079] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A hot standby auxiliary heating system for a power plant, characterized in that: At least: A unit, wherein a first-stage electric heater, a second-stage electric heater and a third-stage electric heater are sequentially arranged between a steam-water separator and a high-pressure cylinder in the unit; a second-stage electric heater inlet valve is arranged on a pipeline between an outlet of the first-stage electric heater and an inlet of the second-stage electric heater, and a third-stage electric heater inlet valve is arranged on a pipeline between an outlet of the second-stage electric heater and an inlet of the third-stage electric heater; an intermediate-pressure cylinder inlet valve is arranged between the high-pressure cylinder and the intermediate-pressure cylinder in the unit, and a low-pressure cylinder inlet valve is arranged between the intermediate-pressure cylinder and the low-pressure cylinder in the unit; A secondary electric heater bypass valve is arranged in parallel with the secondary electric heater inlet valve and the secondary electric heater; A three-stage electric heater bypass valve is arranged in parallel with the three-stage electric heater inlet valve and the three-stage electric heater; A medium-pressure cylinder bypass valve is arranged in parallel with the medium-pressure cylinder inlet valve and the medium-pressure cylinder; A low-pressure cylinder bypass valve is arranged in parallel with the low-pressure cylinder inlet valve and the low-pressure cylinder; The outlet of the primary electric heater is connected to the inlet of the low-pressure cylinder in the unit; The outlet of the secondary electric heater bypass valve is connected to the inlet of the medium pressure cylinder in the unit; The unit includes a four-stage electric heater, a water-cooled wall, a steam-water separator, a high-pressure cylinder, a medium-pressure cylinder, a low-pressure cylinder, a generator, a condenser, a condensate pump, a low-pressure heater, a feedwater pump, a high-pressure heater, a feedwater valve, a water storage tank and a preheater; The outlet of the four-stage electric heater is connected to the inlet of the water-cooled wall, the outlet of the water-cooled wall is connected to the inlet of the steam-water mixture of the steam-water separator, and the steam outlet of the steam-water separator is connected to the steam inlet of the first-stage electric heater; The high-pressure cylinder, the medium-pressure cylinder, the low-pressure cylinder and the generator are coaxially connected; The outlet of the low-pressure cylinder is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the condensate pump, the outlet of the condensate pump is connected to the inlet of the low-pressure heater, the outlet of the low-pressure heater is connected to the inlet of the feedwater pump, the outlet of the feedwater pump is connected to the inlet of the high-pressure heater, the outlet of the high-pressure heater is connected to the inlet of the feedwater valve, the outlet of the feedwater valve is connected to the inlet of the preheater, and the outlet of the preheater is connected to the inlet of the four-stage electric heater; The water supply outlet of the steam-water separator is connected to the inlet of the water storage tank.

2. The power plant hot standby auxiliary heating system according to claim 1, characterized in that: The outlet of the water storage tank is communicated with the drain inlet of the condenser, and a drain bypass valve is arranged on the pipeline between the two.

3. The power plant hot standby auxiliary heating system according to claim 1, characterized in that: The outlet of the water storage tank is connected to the inlet of the preheater, and a circulating water valve and a circulating water pump are arranged on the pipeline between the two.

4. A method for optimizing the operation of a hot standby auxiliary heating system of a power plant, characterized in that: The power plant hot standby auxiliary heating system comprising any one of claims 1 to 3, and the operation optimization method is as follows: When the temperature of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder is lower than 150°C: Close the second-stage electric heater inlet valve, the third-stage electric heater inlet valve, the medium-pressure cylinder inlet valve and the low-pressure cylinder inlet valve; Open the secondary electric heater bypass valve, the tertiary electric heater bypass valve, the medium-pressure cylinder bypass valve and the low-pressure cylinder bypass valve to allow the drain water from the high-pressure cylinder, the medium-pressure cylinder and the low-pressure cylinder to be sent to the condenser in the unit.

5. The operation optimization method of the power plant hot standby auxiliary heating system according to claim 4 is characterized in that: When the temperature of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder is higher than 150°C: The optimization algorithm is used to optimize the system's operation strategy, and the optimization goal is: my( f )=min( P 1+ P 2+ P 3); The constraints are: r b1 + r 1=1； r b2 + r 2=1； r b3 + r 3=1； r b4 + r 4=1； 10℃< T s - T w <50℃； T wh >300℃； T wm >200℃； T wl >100℃； in: P 1 is the electric power of the first-stage electric heater; P 2 is the electric power of the secondary electric heater; P 3 is the electric power of the three-stage electric heater; r 1 is the valve position signal of the inlet valve of the secondary electric heater; r b1 It is the valve position signal of the bypass valve of the secondary electric heater; r 2 is the valve position signal of the inlet valve of the three-stage electric heater; r b2 It is the valve position signal of the bypass valve of the three-stage electric heater; r 3 is the valve position signal of the inlet valve of the medium pressure cylinder; r b3 It is the valve position signal of the bypass valve of the medium pressure cylinder; r 4 is the valve position signal of the low-pressure cylinder inlet valve; r b4 It is the valve position signal of the low-pressure cylinder bypass valve; T s is the inlet steam temperature of the high pressure cylinder, medium pressure cylinder and low pressure cylinder, T w is the metal temperature of the high-pressure cylinder, medium-pressure cylinder and low-pressure cylinder; T wh is the metal temperature of the high pressure cylinder; T wm is the metal temperature of the medium pressure cylinder; T wl is the metal temperature of the low-pressure cylinder.

6. The operation optimization method of the power plant hot standby auxiliary heating system according to claim 5, characterized in that: When the outlet steam dryness of the high-pressure cylinder is lower than 0.8, the inlet valve of the medium-pressure cylinder is closed; When the outlet steam dryness of the intermediate pressure cylinder is lower than 0.8, the low pressure cylinder inlet valve is closed.

7. The operation optimization method of the power plant hot standby auxiliary heating system according to claim 5, characterized in that: When the valve position signal of the secondary electric heater inlet valve is less than 0.2, the secondary electric heater inlet valve is closed and the secondary electric heater bypass valve is opened; When the valve position signal of the inlet valve of the three-stage electric heater is less than 0.2, the inlet valve of the three-stage electric heater is closed and the bypass valve of the three-stage electric heater is opened; When the valve position signal of the intermediate pressure cylinder inlet valve is less than 0.2, the intermediate pressure cylinder inlet valve is closed and the intermediate pressure cylinder bypass valve is opened; When the valve position signal of the low-pressure cylinder inlet valve is less than 0.2, the low-pressure cylinder inlet valve is closed and the low-pressure cylinder bypass valve is opened.

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