Subcritical steam turbine shaft seal electric heating system and control method

Abstract

The invention discloses a subcritical steam turbine shaft seal electric heating system and a control method, and relates to the technical field of steam turbine shaft seal systems, and the subcritical steam turbine shaft seal electric heating system comprises a steam turbine, a steam source, two steam supply pipelines and an electric heating assembly. The steam turbine has a high-pressure cylinder with a first front shaft seal and an intermediate-pressure cylinder with a second front shaft seal. The electric heating assembly comprises two heating cables, and the heating cables are spirally wound on the outer side walls of the corresponding steam supply pipelines in the extending directions of the corresponding steam supply pipelines. The heating cable is spirally wound on the outer side wall of the corresponding steam supply pipeline in the extending direction of the corresponding steam supply pipeline, so that contact between the heating cable and steam can be reduced, meanwhile, the heating area of the steam supply pipeline can be increased, the heating density of the heating cable is reduced, faults of the heating cable are reduced, and the service life of the heating cable is prolonged. And the heating effect on shaft seal steam is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of steam turbine gland sealing systems, and particularly to a subcritical steam turbine gland electrical heating system and a control method therefor. Background Art

[0002] In thermal power generation, when a steam turbine starts or stops in a hot state and operates at a low load, it is often necessary to supply gland steam to the steam turbine by means of external gas supply. When the steam turbine is in a hot state, the working temperature at the front gland of the high-pressure and intermediate-pressure cylinders of the steam turbine is relatively high. When the gland steam is significantly lower than the surface temperature of the steam turbine rotor in the gland section, the surface of the high-temperature steam turbine rotor will be rapidly cooled and plastic deformation will occur, which will further lead to problems such as shaft seizure and vibration. In a conventional gland electrical heater scheme, the gland electrical heating element is in direct contact with the gland steam, and the heating element is prone to failures such as insulation short circuit and overheating of the heating element, and it is not easy to repair, making it difficult to guarantee the heating effect on the gland steam. In addition, the conventional gland electrical heater scheme has problems such as complex system configuration, high operation difficulty, easy failure of the heating element, and high implementation cost, and the actual application effect is not good. Summary of the Invention

[0003] The main object of the present invention is to propose a subcritical steam turbine gland electrical heating system and a control method therefor, aiming to guarantee the heating effect on the gland steam.

[0004] To achieve the above object, the subcritical steam turbine gland electrical heating system proposed by the present invention includes:

[0005] A steam turbine having a high-pressure cylinder and an intermediate-pressure cylinder, the high-pressure cylinder having a first front gland, and the intermediate-pressure cylinder having a second front gland;

[0006] A steam steam source;

[0007] Two steam supply pipes, including a first steam supply pipe and a second steam supply pipe. The same ends of the first steam supply pipe and the second steam supply pipe are both connected to the steam steam source. The other end of the first steam supply pipe is connected to the first front gland, and the other end of the second steam supply pipe is connected to the second front gland; and,

[0008] An electrical heating assembly including two heating cables. The two heating cables are arranged corresponding to the two steam supply pipes, and the heating cable is spirally wound around the outer side wall of the corresponding steam supply pipe along the extending direction of the corresponding steam supply pipe.

[0009] In an embodiment, a spirally arranged installation groove is formed on the outer side wall of the steam supply pipe along the extending direction of the steam supply pipe, and the corresponding heating cable is arranged in the installation groove.

[0010] In one embodiment, fins are spirally wound around the outer sidewall of the steam supply pipe along the extending direction, and mounting grooves are formed between adjacent fins.

[0011] In one embodiment, a heat insulation layer is provided outside the steam supply pipe, and the heat insulation layer covers the heating cable.

[0012] In one embodiment, the steam source includes a first steam source and a second steam source, and both the first steam source and the second steam source are connected to any one of the steam supply pipes.

[0013] The present invention also provides a control method for a subcritical steam turbine shaft seal electric heating system, which is used for a subcritical steam turbine shaft seal electric heating system and includes:

[0014] A first steam supply step for supplying steam to the first front shaft seal;

[0015] A second steam supply step for supplying steam to the second front shaft seal;

[0016] A first steam stop step for stopping supplying steam to the first front shaft seal; and,

[0017] A second steam stop step for stopping supplying steam to the second front shaft seal;

[0018] The subcritical steam turbine shaft seal electric heating system includes:

[0019] A steam turbine having a high-pressure cylinder and an intermediate-pressure cylinder, the high-pressure cylinder having a first front shaft seal, and the intermediate-pressure cylinder having a second front shaft seal;

[0020] A steam source;

[0021] Two steam supply pipes, including a first steam supply pipe and a second steam supply pipe. The same ends of the first steam supply pipe and the second steam supply pipe are both connected to the steam source. The other end of the first steam supply pipe is connected to the first front shaft seal, and the other end of the second steam supply pipe is connected to the second front shaft seal; and,

[0022] An electric heating assembly including two heating cables. The two heating cables are arranged corresponding to the two steam supply pipes one by one, and the heating cables are spirally wound around the outer sidewalls of the corresponding steam supply pipes along the extending directions of the corresponding steam supply pipes.

[0023] In one embodiment, the first steam supply step includes:

[0024] Measuring the pressure of the steam entering the high-pressure cylinder;

[0025] When the pressure of the steam entering the high-pressure cylinder is less than a first preset pressure, controlling the steam source to supply steam to the first front shaft seal;

[0026] Measure the temperature of the steam from the steam source.

[0027] When the temperature of the steam from the steam source is lower than the first preset temperature, start the heating cable on the first steam supply pipe to heat the steam flowing through the first steam supply pipe.

[0028] In one embodiment, the second steam supply step includes:

[0029] Measure the pressure of the steam entering the intermediate pressure cylinder.

[0030] When the pressure of the steam entering the intermediate pressure cylinder is less than the second preset pressure, control the steam source to supply steam to the second front shaft seal.

[0031] Measure the temperature of the steam from the steam source.

[0032] When the temperature of the steam from the steam source is lower than the second preset temperature, start the heating cable on the second steam supply pipe to heat the steam flowing through the second steam supply pipe.

[0033] In one embodiment, the first steam cut-off step includes:

[0034] When the steam source supplies steam to the first front shaft seal, measure the pressure of the steam entering the high pressure cylinder.

[0035] When the pressure of the steam entering the high pressure cylinder is higher than the third preset pressure and lasts for the first preset duration, control the steam source to stop supplying steam to the first front shaft seal and stop the heating wire on the first steam supply pipe.

[0036] When the pressure of the steam entering the high pressure cylinder is lower than the third preset pressure, measure the temperature of the steam from the steam source.

[0037] When the temperature of the steam from the steam source is higher than the third preset temperature and lasts for the first preset duration, stop the heating wire on the first steam supply pipe.

[0038] In one embodiment, the second steam cut-off step includes:

[0039] When the steam source supplies steam to the second front shaft seal, measure the pressure of the steam entering the intermediate pressure cylinder.

[0040] When the pressure of the steam entering the intermediate pressure cylinder is higher than the fourth preset pressure and lasts for the second preset duration, control the steam source to stop supplying steam to the second front shaft seal and stop the heating wire on the second steam supply pipe.

[0041] When the pressure of the steam inlet to the intermediate pressure cylinder is lower than the third preset pressure, measure the steam temperature of the steam source.

[0042] When the steam temperature of the steam source is higher than the third preset temperature and lasts for the second preset duration, stop the operation of the heating wire on the second steam supply pipe.

[0043] In the technical solution of the present invention, after the steam source supplies steam, part of the steam can seal the first front shaft seal through the first steam supply pipe, and another part of the steam can seal the second front shaft seal through the second steam supply pipe; in addition, by spirally winding the heating cable around the outer side wall of the corresponding steam supply pipe along the extension direction of the corresponding steam supply pipe, the contact between the heating cable and the steam can be reduced, and at the same time, the heating area of the steam supply pipe can be increased, the heating density of the heating cable is reduced, the faults of the heating cable are reduced, and the heating effect of the shaft seal steam is ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on the structures shown in these drawings without creative efforts.

[0045] Figure 1 FIG. is a schematic structural diagram of an embodiment of a subcritical steam turbine shaft seal electric heating system provided by the present invention;

[0046] Figure 2 For Figure 1 Partial enlarged view of the middle steam supply pipe;

[0047] Figure 3 FIG. is a schematic flow diagram of the first steam supply step;

[0048] Figure 4 FIG. is a schematic flow diagram of the second steam supply step;

[0049] Figure 5 FIG. is a schematic flow diagram of the first gas stop step;

[0050] Figure 6 FIG. is a schematic flow diagram of the second gas stop step;

[0051] Figure 7 FIG. is a schematic diagram of the heating power of the cylinder to be measured.

[0052] Explanation of the reference numerals in the drawings:

[0053] 1. Steam turbine; 11. High-pressure cylinder; 111. First front shaft seal; 112. High-pressure cylinder inlet steam pressure measuring point; 113. High-pressure inner cylinder front section metal temperature measuring point; 12. Intermediate-pressure cylinder; 121. Second front shaft seal; 122. Intermediate-pressure cylinder inlet steam pressure measuring point; 123. Intermediate-pressure inner cylinder front section metal temperature measuring point; 13. Low-pressure cylinder; 14. Coupling; 2. Steam source; 21. First steam source; 211. Main steam source steam temperature measuring point; 22. Second steam source; 221. Auxiliary steam supply shaft seal regulating valve; 3. Steam supply pipeline; 31. First steam supply pipeline; 311. High-pressure cylinder front steam seal steam temperature measuring point; 32. Second steam supply pipeline; 321. Intermediate-pressure cylinder front steam seal steam temperature measuring point; 33. Installation groove; 34. Fins; 35. Thermal insulation layer; 351. Thermal insulation reflective film; 4. Electric heating component; 41. Heating cable; 42. Heating control module; 5. Connecting pipe; 51. Low-pressure cylinder rear shaft seal spray desuperheater; 52. High-pressure cylinder rear shaft seal spray desuperheater; 53. Shaft seal supply air pressure detector; 54. Steam seal overflow regulating valve; 55. Steam turbine extraction pipeline No. 8; 6. Shaft seal supply air pipe; 61. Main steam supply shaft seal regulating valve; 62. Main steam supply shaft seal regulating valve; 63. Shaft seal steam pressure measuring point.

[0054] The realization of the object, functional features and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed implementation manners

[0055] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] It should be noted that if there are directional indications (such as up, down, left, right, front, back...) involved in the embodiments of the present invention, the directional indications are only used to explain the relative position relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0057] In addition, if the embodiments of the present invention involve descriptions such as "first" and "second", the descriptions of "first", "second", etc. are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, if "and / or" or "and / or" appears throughout the text, its meaning includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0058] In thermal power generation, when the steam turbine starts and stops in a hot state and operates at low load, it is often necessary to supply shaft seal steam to the steam turbine by means of external air supply. When the steam turbine is in a hot state, the working temperature at the front steam seals of the high and intermediate pressure cylinders of the steam turbine is relatively high. The working temperature at the front steam seals of the high and intermediate pressure cylinders of the steam turbine is relatively high (under rated conditions, the working temperature of the front shaft seal of the high pressure cylinder is about 480 °C, and the working temperature of the front shaft seal of the intermediate pressure cylinder is about 510 °C), and the steam seal clearance is small. Once cold steam enters, problems such as shaft seizure and vibration are more likely to occur. That is, when the shaft seal steam is significantly lower than the surface temperature of the steam turbine rotor in the shaft seal section, it will cause the surface of the high-temperature steam turbine rotor to be rapidly cooled and produce plastic deformation, which will further lead to problems such as shaft seizure and vibration. In the conventional shaft seal electric heater scheme, the shaft seal electric heating element is in direct contact with the shaft seal steam, and the heating element is prone to failures such as insulation short circuit and overheating of the heating element, and it is not easy to repair, making it difficult to ensure the heating effect on the shaft seal steam.

[0059] The present invention proposes a subcritical steam turbine shaft seal electric heating system.

[0060] Please refer to Figure 1 and Figure 2, in an embodiment of the present invention, the subcritical steam turbine shaft seal electric heating system includes a steam turbine 1, a steam source 2, two steam supply pipelines 3, and an electric heating component 4. The steam turbine 1 has a high-pressure cylinder 11 and an intermediate-pressure cylinder 12. The high-pressure cylinder 11 has a first front shaft seal 111, and the intermediate-pressure cylinder 12 has a second front shaft seal 121. The two steam supply pipelines 3 include a first steam supply pipeline 313 and a second steam supply pipeline 323. The same ends of the first steam supply pipeline 313 and the second steam supply pipeline 323 are both connected to the steam source 2. The other end of the first steam supply pipeline 313 is connected to the first front shaft seal 111, and the other end of the second steam supply pipeline 323 is connected to the second front shaft seal 121. The electric heating component 4 includes two heating cables 41. The two heating cables 41 are arranged corresponding to the two steam supply pipelines 3 one by one. The heating cable 41 is spirally wound around the outer sidewall of the corresponding steam supply pipeline 3 along the extension direction of the corresponding steam supply pipeline 3.

[0061] In the technical solution of the present invention, after the steam source 2 supplies steam, part of the steam can seal the first front shaft seal 111 through the first steam supply pipeline 313, and the other part of the steam can seal the second front shaft seal 121 through the second steam supply pipeline 323. In addition, by spirally winding the heating cable 41 around the outer sidewall of the corresponding steam supply pipeline 3 along the extension direction of the corresponding steam supply pipeline 3, the contact between the heating cable 41 and the steam can be reduced, and at the same time, the heating area of the steam supply pipeline 3 can be increased, the heating density of the heating cable 41 can be reduced, the faults of the heating cable 41 can be reduced, and the heating effect on the shaft seal steam can be guaranteed.

[0062] The first front shaft seal 111 is the front shaft seal of the high-pressure cylinder 11, and the second front shaft seal 121 is the front shaft seal of the intermediate-pressure cylinder 12. The heating cable 41 is a high-temperature-resistant heating cable. Specifically, the heating cable adopts a high-temperature-resistant mineral-insulated heating cable, and the maximum heating temperature can reach 600 °C. The heating cable is of a two-core type, and the heating cable is configured with one in use and one in reserve, and is laid outside the corresponding steam supply pipeline 3, which is convenient for maintenance and improves the reliability of the equipment. After supplying steam to the first front shaft seal 111, the sealing of the front shaft seal can be improved. After supplying steam to the second front shaft seal 121, the sealing of the rear shaft seal can be improved.

[0063] Please refer to Figure 1 and Figure 2 , the electric heating component 4 further includes a heating control module 42. The heating control module 42 is electrically connected to the heating cable 41. Through the heating control module 42, the heating power of the heating cable 41 can be controlled.

[0064] A spiral installation groove 33 is formed on the outer side wall of the steam supply pipe 3 along the extension direction of the steam supply pipe 3, and the corresponding heating cable 41 is arranged in the installation groove 33. By providing the installation groove 33, the contact area between the heating cable 41 and the steam supply pipe 3 can be increased, so as to increase the heat transfer area, improve the heat transfer efficiency, and enhance the heating effect on the steam supply pipe 3.

[0065] Fins 34 are spirally wound around the outer side wall of the steam supply pipe 3 along the extension direction, and the installation groove 33 is formed between adjacent fins 34. By providing the fins 34, the formation of the installation groove 33 can be realized.

[0066] A heat insulation layer 35 is provided outside the steam supply pipe 3, and the heat insulation layer 35 covers the heating cable 41. By providing the heat insulation layer 35, the heat generated by the heating cable 41 can be conducted to the steam supply pipe 3 as much as possible.

[0067] Multiple layers of heat insulation and reflection films 351 are arranged in the heat insulation layer 35. By arranging the multiple layers of heat insulation and reflection films 351, the heat insulation effect of the heat insulation layer 35 can be further improved.

[0068] The steam source 2 includes a first steam source 212 and a second steam source 222, and both the first steam source 212 and the second steam source 222 are connected to any one of the steam supply pipes 3. By providing the first steam source 212 and the second steam source 222, the first steam source 212 and the second steam source 222 can be switched according to needs to ensure the gas supply of the steam source 2.

[0069] Please refer to Figure 1 and Figure 2 , the first front shaft seal 111 and the second front shaft seal 121 are connected by a coupling 14, the rear shaft seal of the intermediate pressure cylinder 12 is connected to the front shaft seal of the low pressure cylinder 13, a connecting pipe 5 is connected between the rear shaft seal of the low pressure cylinder 13 and the rear shaft seal of the high pressure cylinder 11, one end of the steam supply pipe 3 is communicated with the connecting pipe 5, and a low pressure cylinder 13 rear shaft seal spray desuperheater, a high pressure cylinder 11 rear shaft seal spray desuperheater and a shaft seal gas supply pressure detector 53 are arranged on the connecting pipe 5. The high pressure rear shaft seal spray desuperheater and the low pressure rear shaft seal spray desuperheater are provided to prevent overheating caused by too high external steam temperature of the shaft seal; through the shaft seal gas supply pressure detector 53, the gas supply pressure of the steam source 2 can be detected.

[0070] The connecting pipe 5 is also connected with a gland steam overflow regulating valve 54, and the outlet of the gland steam overflow regulating valve 54 is used to connect to the extraction pipeline of the eighth stage of the steam turbine 1. When the steam turbine 1 operates with load, steam enters the steam turbine 1. The front parts of the high-pressure cylinder 11, the intermediate-pressure cylinder 12, and the low-pressure cylinder 13 are all under positive pressure, and only the exhaust port of the low-pressure cylinder 13 is under negative pressure. Steam leaks out from the front shaft seal of the high-pressure cylinder 11, the rear shaft seal of the high-pressure cylinder 11, and the front shaft seal of the intermediate-pressure cylinder 12, and is collected through the shaft seal pipeline and sent to the rear shaft seal of the low-pressure cylinder on the negative pressure side. The excess steam is then connected to the extraction pipeline of the eighth stage of the steam turbine 1 through the gland steam overflow regulating valve 54, and the shaft seal system realizes self-sealing. At this time, there is no risk of cold steam entering the shaft seal.

[0071] A high-pressure cylinder 11 front gland steam temperature measuring point is provided at one end of the first steam supply pipeline 313 close to the first front shaft seal 111. Through the high-pressure cylinder 11 front gland steam temperature measuring point, the temperature of the steam at the outlet of the first steam supply pipeline 313 can be measured; a middle-pressure cylinder 12 front gland steam temperature measuring point is provided at one end of the second steam supply pipeline 323 close to the second front shaft seal 121. Through the middle-pressure cylinder 12 front gland steam temperature measuring point, the temperature of the steam at the outlet of the second steam supply pipeline 323 can be measured.

[0072] A high-pressure cylinder 11 inlet steam pressure measuring point is provided on the high-pressure cylinder 11. Through the high-pressure cylinder 11 inlet steam pressure measuring point, the inlet steam pressure of the high-pressure cylinder 11 can be measured. A high-pressure inner cylinder front section metal temperature measuring point 113 is provided on the high-pressure cylinder 11. Through the high-pressure inner cylinder front section metal temperature measuring point 113, the metal temperature of the front section of the high-pressure inner cylinder can be detected.

[0073] Please refer to Figure 1 and Figure 2 , a middle-pressure cylinder 12 inlet steam pressure measuring point is provided on the middle-pressure cylinder 12. Through the middle-pressure cylinder 12 inlet steam pressure measuring point, the inlet steam pressure of the middle-pressure cylinder 12 can be measured. A middle-pressure inner cylinder front section metal temperature measuring point 123 is provided on the middle-pressure cylinder 12. Through the middle-pressure inner cylinder front section metal temperature measuring point 123, the metal temperature of the front section of the middle-pressure inner cylinder can be detected.

[0074] The first steam source 212 is the main steam source, the second steam source 222 is the auxiliary steam source, and the temperature of the first steam source is higher than that of the second steam source.

[0075] The connecting pipe 5 is connected with a shaft seal air supply pipe 6. A main steam supply to shaft seal regulating valve 6261 is connected between the outlet of the first steam source 212 and the shaft seal air supply pipe 6. Through the main steam supply to shaft seal regulating valve 6261, the on-off of the air supply of the first steam source 212 can be controlled. A first steam source 2 steam temperature measuring point is provided between the first steam source 212 and the main steam supply to shaft seal regulating valve 6261, and the temperature of the steam of the main steam source can be detected.

[0076] Please refer toFigure 1 and Figure 2 A supplementary steam supply regulating valve for gland sealing 221 is connected between the outlet of the second steam source 222 and the gland sealing steam supply pipe 6. By means of the supplementary steam supply regulating valve for gland sealing 221, the on-off of the air supply of the second steam source 222 can be controlled. A steam temperature measuring point for the supplementary steam source 2 is arranged between the second steam source 222 and the supplementary steam supply regulating valve for gland sealing 221, and the temperature of the steam of the supplementary steam source can be detected.

[0077] A gland sealing steam pressure measuring point 63 is arranged on the gland sealing steam supply pipe 6. By means of the gland sealing steam pressure measuring point 63, the air supply pressure of the steam source 2 can be detected.

[0078] The length of the steam supply pipe 3 is about 10 - 15 m, and the pipe specification is φ168x6 - φ219x8. The steam supply pipe 3 can be an alloy with a specific heat capacity of not less than 0.46 kJ / kg·°C, which can increase the heat capacity of the steam supply pipe 3. When the temperature of the externally supplied steam is relatively low and heating is required, during the start-up and temperature rise process of the heating cable (about 20 seconds), the steam can be reversely heated by the heat stored in the metal wall of the steam supply pipe 3 (heated to 20°C lower than the wall temperature), thus solving the problem that the start-up and temperature rise process of the heating cable is relatively slow and avoiding the cold steam entering the front gland seals of the high-pressure cylinder 11 and the intermediate-pressure cylinder 12 in a short time. In addition, for different working conditions, the size and material of the steam supply pipe 3 can also be adaptively set so that the heat stored in the metal wall of the steam supply pipe 3 reversely heats the steam, thus solving the problem that the start-up and temperature rise process of the heating cable is relatively slow.

[0079] The solution of the present invention aims at the current situation that the risk of cold steam entering the front gland seals of the high-pressure and intermediate-pressure cylinders is relatively high during the hot start-up, shutdown and operation of a subcritical steam turbine. By adopting this solution, the risk of gland sealing cold steam can be effectively reduced at a relatively low cost.

[0080] It can also be applied to supercritical and ultra-supercritical units of subcritical and above. Through the solution of the present invention, gland sealing steam can be provided during the operation of supercritical and ultra-supercritical units of subcritical and above.

[0081] The system configuration of the conventional shaft seal electric heater is relatively complex, and a series of valves and instruments are required for operation and control, resulting in high costs. In addition, the system has a slow response speed, frequent electric heater failures, and when it is necessary to switch to external steam supply during load mutations, the startup speed of the shaft seal heater cannot keep up, making it easy to introduce cold steam. In this solution, by setting up heating cables, the rapid heating of the steam supply pipeline is ensured. At the same time, the size of the steam supply pipeline 3 is set so that during the startup and heating process of the heating cables, the heat accumulated by the metal of the steam supply pipeline 3 wall is used to heat the steam in the reverse direction, reducing the problem of cold steam introduction. By arranging the heating cables, the heating power per unit area of the heating cables is reduced, the overheating of the heating cables is reduced, and the damage to the heating cables is reduced.

[0082] The external heating cable is used to indirectly heat the shaft seal steam. Compared with the conventional method of adding an electric heater, it can avoid the problems of insulation short circuit and electric leakage that are prone to occur when steam directly contacts the heating element, and can also prevent the problem of overheating and damage of the heating element caused by excessive heating power per unit area.

[0083] The present invention also proposes a control method for the shaft seal electric heating system of a subcritical steam turbine. This control method for the shaft seal electric heating system of a subcritical steam turbine is used for the shaft seal electric heating system of a subcritical steam turbine. The specific structure of this shaft seal electric heating system of a subcritical steam turbine refers to the above-mentioned embodiments. Since this control method for the shaft seal electric heating system of a subcritical steam turbine adopts all the technical solutions of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments, which will not be elaborated here one by one. Among them, the control method for the shaft seal electric heating system of a subcritical steam turbine includes:

[0084] The first steam supply step is used to supply steam to the first front shaft seal 111;

[0085] The second steam supply step is used to supply steam to the second front shaft seal 121;

[0086] The first steam cut-off step is to stop supplying steam to the first front shaft seal 111; and,

[0087] The second steam cut-off step is to stop supplying steam to the second front shaft seal 121.

[0088] Through the first steam supply step, sealing steam can be provided to the first front shaft seal 111, and through the second steam supply step, sealing steam can be provided to the second front shaft seal 121.

[0089] The first steam supply step includes:

[0090] S11: Measuring the pressure of the steam entering the high-pressure cylinder 11;

[0091] S12: When the pressure of the steam admitted to the high-pressure cylinder 11 is less than the first preset pressure, control the steam source 2 to supply steam to the first front shaft seal 111.

[0092] S13: Measure the temperature of the steam from the steam source 2.

[0093] S14: When the temperature of the steam from the steam source 2 is lower than the first preset temperature, start the heating cable 41 on the first steam supply pipe 313 to heat the steam flowing through the first steam supply pipe 313.

[0094] When the pressure of the steam admitted to the high-pressure cylinder 11 is less than the first preset pressure and the first front shaft seal 111 needs external steam supply, and when the temperature of the steam from the steam source 2 is lower than the preset temperature, there is a risk of cold steam entering the front shaft seal of the high-pressure cylinder 11. Then, automatically turn on the heating cable 41 on the first steam supply pipe 313 to heat the steam flowing through the first steam supply pipe 313, preventing cold air from entering the steam turbine 1 and ensuring that the temperature of the supplied steam matches the temperature of each shaft seal. The step of the steam source supplying steam to the first front shaft seal can be actively controlled or, when the conditions are met, the steam from the steam source is automatically supplied to the first front shaft seal.

[0095] The first preset pressure is 0.2 MPa, and the value of the first preset temperature is 90 °C lower than the temperature inside the high-pressure inner cylinder.

[0096] The second steam supply step includes:

[0097] S21: Measure the pressure of the steam admitted to the intermediate-pressure cylinder 12.

[0098] S22: When the pressure of the steam admitted to the intermediate-pressure cylinder 12 is less than the second preset pressure, control the steam source 2 to supply steam to the second front shaft seal 121.

[0099] S23: Measure the temperature of the steam from the steam source 2.

[0100] S24: When the temperature of the steam from the steam source 2 is lower than the second preset temperature, start the heating cable 41 on the second steam supply pipe 323 to heat the steam flowing through the second steam supply pipe 323.

[0101] When the pressure of the steam admitted to the intermediate-pressure cylinder 12 is less than the second preset pressure, the second front shaft seal 121 needs to be externally supplied with steam. When the steam temperature of the steam source 2 is lower than the preset temperature, there is a risk of cold steam entering the front shaft seal of the intermediate-pressure cylinder 12. Then, the heating cable 41 on the second steam supply pipe 323 is automatically turned on to heat the steam flowing through the second steam supply pipe 323, preventing cold air from entering the steam turbine 1 and ensuring that the temperature of the supplied steam matches the temperature of each shaft seal. The second preset pressure is 0.2 MPa, and the value of the first preset temperature is 90 °C lower than the temperature of the intermediate-pressure inner cylinder. The internal temperature of the high-pressure cylinder 11 and the intermediate-pressure cylinder 12 during normal operation is 500 °C.

[0102] The first steam cut-off step includes:

[0103] S31: When the steam source 2 supplies steam to the first front shaft seal 111, measure the pressure of the steam admitted to the high-pressure cylinder 11;

[0104] S32: When the pressure of the steam admitted to the high-pressure cylinder 11 is higher than the third preset pressure and lasts for the first preset duration, control the steam source 2 to stop supplying steam to the first front shaft seal 111 and stop the heating wire on the first steam supply pipe 313;

[0105] S33: When the pressure of the steam admitted to the high-pressure cylinder 11 is lower than the third preset pressure, measure the steam temperature of the steam source 2;

[0106] S34: When the steam temperature of the steam source 2 is higher than the third preset temperature and lasts for the first preset duration, stop the heating wire on the first steam supply pipe 313.

[0107] When the pressure of the steam admitted to the high-pressure cylinder 11 is higher than the third preset pressure, it indicates that the front shaft seal of the high-pressure cylinder 11 does not require external steam supply. Thus, control the steam source 2 to stop supplying steam to the first front shaft seal 111 and stop the heating wire on the first steam supply pipe 313.

[0108] When the pressure of the steam admitted to the high-pressure cylinder 11 is lower than the third preset pressure and the steam temperature of the steam source 2 is higher than the third preset temperature, it indicates that the shaft seal steam source temperature is relatively high. Thus, stop the heating wire on the first steam supply pipe 313 to directly send the steam into the front shaft seal of the high-pressure cylinder 11.

[0109] The third preset pressure is 0.3 MPa, and the value of the third preset temperature is 30 °C lower than the metal temperature of the high-pressure inner cylinder. The first preset duration is 1 minute.

[0110] The second steam cut-off step includes:

[0111] S41: When the steam source 2 supplies steam to the second front shaft seal 121, measure the inlet steam pressure of the intermediate pressure cylinder 12;

[0112] S42: When the inlet steam pressure of the intermediate pressure cylinder 12 is higher than the fourth preset pressure and lasts for the second preset duration, control the steam source 2 to stop supplying steam to the second front shaft seal 121, and stop the heating wire on the second steam supply pipe 323 from operating;

[0113] S43: When the inlet steam pressure of the intermediate pressure cylinder 12 is lower than the third preset pressure, measure the steam temperature of the steam source 2;

[0114] S44: When the steam temperature of the steam source 2 is higher than the third preset temperature and lasts for the second preset duration, stop the heating wire on the second steam supply pipe 323 from operating.

[0115] When the inlet steam pressure of the intermediate pressure cylinder 12 is higher than the fourth preset pressure, it indicates that the front shaft seal of the intermediate pressure cylinder 12 does not require external steam supply. Thus, control the steam source 2 to stop supplying steam to the second front shaft seal 121, and stop the heating wire on the second steam supply pipe 323 from operating.

[0116] When the inlet steam pressure of the intermediate pressure cylinder 12 is lower than the fourth preset pressure and the steam temperature of the steam source 2 is higher than the fourth preset temperature, it indicates that the temperature of the shaft seal steam source is relatively high. Thus, stop the heating wire on the second steam supply pipe 323 from operating to directly send the steam into the front shaft seal of the intermediate pressure cylinder 12.

[0117] The fourth preset pressure is 0.3 MP, the value of the fourth preset temperature is 30 °C lower than the metal temperature of the intermediate pressure inner cylinder. The second preset duration is 1 minute.

[0118] The supply pressure of the steam source is the shaft seal supply pressure, the flow rate of the first steam supply pipe 313 is the shaft seal steam flow rate of the high-pressure front shaft seal, and the flow rate of the second steam supply pipe 323 is the shaft seal steam flow rate of the intermediate pressure front shaft seal.

[0119] The heating power of the heating cable 41 on the steam supply pipe 3 depends on the shaft seal steam flow rate to be heated and the heating steam temperature difference. The traditional method is to adjust the heating electric power through PID feedback based on the difference between the downstream steam temperature heated by electricity and the set temperature. However, due to the certain hysteresis of heat transfer, this results in large fluctuations and frequent adjustments of the electric heating power, which easily leads to overheating of the electric heating and is not conducive to the normal operation of the system.

[0120] In this application, for the designed steam turbine 1, the designed value of the required sealing steam quantity for the front shaft seals of the high- and intermediate-pressure cylinders 12 can be calculated based on the shaft seal clearance, the number of shaft seal teeth stages, and the pressure difference before and after the shaft seal teeth of the steam turbine 1. Generally, the steam quantity of the front shaft seals of the high- and intermediate-pressure cylinders 12 is mainly related to the pressure difference on both sides of the shaft seal. When the pressure in the high- and intermediate-pressure inner cylinders of the steam turbine 1 is at its lowest (-95 kPa), the required sealing steam flow rate is the largest.

[0121] The power of the heating cables for the front shaft seals of the high- and intermediate-pressure cylinders 12 is proportional to the shaft seal steam flow rate and the temperature difference to be heated. Based on the measured value of the shaft seal steam pressure P3, the inlet steam pressure P1 of the high-pressure cylinder 11, and the inlet steam pressure P2 of the intermediate-pressure cylinder 12, calculate the ratios of the steam flow rates of the front shaft seals of the high-pressure cylinder 11 and the intermediate-pressure cylinder 12 to the designed value respectively; and in combination with the shaft seal steam supply temperature T7 and the differences between the target temperatures T1 and T2 of the front shaft seals of the high- and intermediate-pressure cylinders 12, calculate the powers of the heating cables for the front shaft seals of the high- and intermediate-pressure cylinders 12 respectively; then after a 10-second delay (considering the heat transfer time), based on the differences between the shaft seal steam temperatures T3 and T4 after the heating cables and the target temperatures T1 and T2, make fine-tuning corrections to the heating power within a range of 20%, which can prevent large fluctuations and overheating of the heating power. The control method is shown in Figure 5 and Figure 6 . Where C1 is the specific heat capacity of the shaft seal steam, which is determined based on the average value of the operating parameter range of the shaft seal steam and is approximately 2.1 kJ / (kg·°C)

[0122] The calculation steps for the heating power of the corresponding cylinder to be measured are as follows (the cylinder to be measured can be the high-pressure cylinder 11 or the low-pressure cylinder 13):

[0123] S51: First, calculate the correction value K1 of the actual flow rate Q1 of the front shaft seal of the cylinder to be measured relative to the designed flow rate Q based on the shaft seal supply pressure P3 and the steam pressure P inside the cylinder to be measured;

[0124] S52: Calculate the actual flow rate Q1 = K1 * Q;

[0125] S53: Based on the temperature T2 of the steam source 2 (shaft seal supply) and the metal temperature T1 of the inner wall of the cylinder to be measured, calculate the temperature difference that the steam needs to be raised, T3 = T1 - T2;

[0126] S54: The power S1 to be set for the heating cable = Q1 * T3 * C1;

[0127] S55: Based on the difference between the temperature T4 measured by the temperature measuring point of the front shaft seal of the cylinder to be measured and the metal temperature T1 inside the cylinder to be measured, after a 10-second delay, repeat the above steps to correct the power of the heating cable.

[0128] The heating cable automatically controls the start and stop and the power of the heating cable according to the steam inlet pressure of the high and medium pressure cylinders 12 of the steam turbine 1 and the steam temperature in front of the shaft seal steam regulating valve. When the steam inlet pressure of the high and medium pressure cylinders 12 is lower than the set value and if the steam temperature of the steam source is lower than the set value (compared with the metal temperature of the high and medium pressure cylinders), the heating cable is started; when the steam inlet pressure of the high and medium pressure cylinders 12 is greater than the set value and lasts for 1 minute, or the steam temperature in front of the shaft seal steam regulating valve is greater than the set value (compared with the metal temperature of the cylinder) and lasts for 1 minute, the heating cable is shut down. This can prevent the heating cable from being frequently started and stopped to cause malfunctions when the operating conditions change or the parameters fluctuate.

[0129] This solution makes full use of the existing measuring points of the unit, does not require the configuration of additional valves, does not increase the resistance of the shaft seal steam pipeline, has little impact on the existing system, is low cost, does not require additional land, and is easy to repair and maintain. Furthermore, the system automatically controls the start and stop of the heating cable and the electrical power according to relevant operating parameters, improves the unit's automation rate and response speed, and reduces the probability of misoperation by operation and maintenance personnel.

[0130] The operation of the heating cable is controlled by the existing temperature and pressure measuring points. There is no need to configure a separate steam electric heating device, nor is there any need to configure additional valves or flow measuring instruments. Instead, a low-cost, small-footprint heating cable is used to wrap around the outside of the pipeline for indirect heating. This solves many practical problems such as short circuits and overheating caused by contact between electric heaters and steam, complex systems, increased pipeline resistance, and high costs, and is more practical.

[0131] The above description is only an exemplary embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the technical concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A subcritical steam turbine shaft seal electric heating system, characterized in that, Comprising: A steam turbine having a high-pressure cylinder and an intermediate-pressure cylinder, the high-pressure cylinder having a first front shaft seal and the intermediate-pressure cylinder having a second front shaft seal; A steam source; Two steam supply pipes, including a first steam supply pipe and a second steam supply pipe, one end of the first steam supply pipe and the second steam supply pipe are both connected to the steam source, the other end of the first steam supply pipe is connected to the first front shaft seal, and the other end of the second steam supply pipe is connected to the second front shaft seal; and An electric heating assembly including two heating cables, the two heating cables are arranged corresponding to the two steam supply pipes one by one, and the heating cable is spirally wound around the outer side wall of the corresponding steam supply pipe along the extending direction of the corresponding steam supply pipe.

2. The subcritical steam turbine shaft seal electric heating system according to claim 1, wherein A spiral installation groove is formed on the outer side wall of the steam supply pipe along the extending direction of the steam supply pipe, and the corresponding heating cable is arranged in the installation groove.

3. The subcritical steam turbine shaft seal electric heating system according to claim 2, characterized in that, Fins are spirally wound around the outer side wall of the steam supply pipe along the extending direction, and an installation groove is formed between adjacent fins.

4. The subcritical steam turbine shaft seal electric heating system according to claim 2, characterized in that, A heat insulation layer is arranged outside the steam supply pipe, and the heat insulation layer covers the heating cable.

5. The subcritical steam turbine shaft seal electric heating system according to claim 2, wherein, The steam source includes a first steam source and a second steam source, and the first steam source and the second steam source are both connected to any one of the steam supply pipes.

6. A control method for a subcritical steam turbine shaft seal electric heating system, which is used for the subcritical steam turbine shaft seal electric heating system according to any one of claims 1 to 5, characterized in that, Comprising: A first steam supply step for supplying steam to the first front shaft seal; A second steam supply step for supplying steam to the second front shaft seal; A first steam stop step for stopping supplying steam to the first front shaft seal; and A second steam stop step for stopping supplying steam to the second front shaft seal.

7. The control method of the subcritical steam turbine shaft seal electric heating system according to claim 6, characterized in that, The first steam supply step includes: Measuring the pressure of the steam entering the high-pressure cylinder; When the pressure of the steam entering the high-pressure cylinder is less than a first preset pressure, controlling the steam source to supply steam to the first front shaft seal; Measuring the temperature of the steam of the steam source; When the temperature of the steam of the steam source is lower than a first preset temperature, starting the heating cable on the first steam supply pipe to heat the steam flowing through the first steam supply pipe.

8. The control method of the subcritical steam turbine shaft seal electric heating system according to claim 6, characterized in that, The second steam supply step includes: Measuring the pressure of the steam entering the intermediate-pressure cylinder; When the pressure of the steam entering the intermediate-pressure cylinder is less than a second preset pressure, controlling the steam source to supply steam to the second front shaft seal; Measuring the temperature of the steam of the steam source; When the temperature of the steam of the steam source is lower than a second preset temperature, starting the heating cable on the second steam supply pipe to heat the steam flowing through the second steam supply pipe.

9. The control method of the subcritical steam turbine shaft seal electric heating system according to claim 6, characterized in that, The first steam stop step includes: When the steam source supplies steam to the first front shaft seal, measuring the pressure of the steam entering the high-pressure cylinder; When the pressure of the steam entering the high-pressure cylinder is higher than a third preset pressure and continues for a first preset duration, controlling the steam source to stop supplying steam to the first front shaft seal and stopping the operation of the heating wire on the first steam supply pipe; When the pressure of the steam entering the high-pressure cylinder is lower than the third preset pressure, measuring the temperature of the steam of the steam source; When the temperature of the steam of the steam source is higher than the third preset temperature and continues for a first preset duration, stopping the operation of the heating wire on the first steam supply pipe.

10. The control method of the subcritical steam turbine shaft seal electric heating system according to claim 6, characterized in that, The second steam stop step includes: When the steam source supplies steam to the second front shaft seal, measure the pressure of the steam entering the intermediate pressure cylinder; When the pressure of the steam entering the intermediate pressure cylinder is higher than the fourth preset pressure and lasts for the second preset duration, control the steam source to stop supplying steam to the second front shaft seal and stop the heating wire on the second steam supply pipeline from operating; When the pressure of the steam entering the intermediate pressure cylinder is lower than the third preset pressure, measure the steam temperature of the steam source; When the steam temperature of the steam source is higher than the third preset temperature and lasts for the second preset duration, stop the heating wire on the second steam supply pipeline from operating.

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