Double-machine regenerative steam-electricity double-drive small steam turbine thermodynamic system and control method

Abstract

The invention discloses a double-machine regenerative steam-electricity double-drive small turbine thermodynamic system and a control method, belongs to the technical field of power generation, and aims to solve the problem that steam extraction parameter reduction and system power balance maintenance cannot be both considered in the prior art. According to the system, the MCT is adopted to extract exhaust steam of the ultrahigh-pressure cylinder to drive the water feeding pump and the variable-frequency generator, and meanwhile, a low-superheat-degree steam source is provided for the multi-stage heater. When P is greater than Pmax, executing at least one of the following control strategies: (a) adjusting the opening degree of a steam inlet valve of the MCT; (b) the opening degree of an MCT steam exhaust valve is adjusted; (c) adjusting the opening degree of a heater bypass valve; the steam exhaust pressure of the MCT is kept stable through three-way closed-loop control, and safe and efficient operation is achieved by combining power compensation of the variable-frequency generator.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power generation, in particular to a regenerative system based on a steam turbine (MCT) in a double-reheat unit and a pressure control method. BACKGROUND

[0002] In the regenerative system of the existing coal-fired double-reheat steam turbine, the steam source of each heater comes from the multi-stage extraction of the steam turbine body (such as the super-high pressure cylinder, high pressure cylinder, and medium pressure cylinder). This design has the following defects:

[0003] 1. High superheat degree of regenerative extraction: the direct extraction from the steam turbine body results in high superheat degree of the regenerative extraction into the heater, and high steam superheat degree leads to decreased heat transfer efficiency;

[0004] 2. High equipment cost: high-temperature extraction requires the use of high-grade materials to manufacture the heater and pipeline, increasing the cost of the heater and pipeline;

[0005] 3. Poor system flexibility: fixed extraction parameters make it difficult to adapt to variable load conditions.

[0006] The existing technology cannot balance the need to reduce extraction parameters and maintain system power balance. SUMMARY

[0007] To solve the problem that the existing technology cannot balance the need to reduce extraction parameters and maintain system power balance, the present application provides a double-machine regenerative steam turbine thermal system and control method.

[0008] In one aspect of the present application, the double-machine regenerative steam turbine thermal system is provided, which includes a main steam turbine unit, a steam turbine 7, and a multi-stage heater 901-90n.

[0009] The main steam turbine unit: the super-high pressure cylinder 1, the high pressure cylinder 2, the medium pressure cylinder 3, the A low pressure cylinder 41, the B low pressure cylinder 42, and the generator 5 are coaxially arranged;

[0010] The steam turbine 7:

[0011] The steam inlet is connected to the exhaust pipe of the super-high pressure cylinder 1 and is adjusted by the MCT steam inlet valve 701;

[0012] The extraction port is connected to the front n-2 stage regenerative heater 901-90n-2;

[0013] The exhaust port is connected to the n-1 stage heater 90n-1, and the exhaust port is also connected to the final stage heater 90n through the MCT exhaust valve 702;

[0014] The coaxial driving feed water pump 6 and the variable frequency generator 8;

[0015] Final stage heater 90n: steam source from the middle pressure cylinder 3 exhaust, and set the heater bypass valve 90n01.

[0016] Preferably, the super-high pressure cylinder 1 steam inlet from the boiler main steam, exhaust connection boiler reheated cold end;

[0017] The high pressure cylinder 2 steam from the boiler primary reheated steam, exhaust connection boiler primary reheated cold end;

[0018] The middle pressure cylinder 3 steam from the boiler secondary reheated steam, exhaust connection A low pressure cylinder 41, B low pressure cylinder 42 and final stage heater 90n;

[0019] The exhaust of the A low pressure cylinder 41, B low pressure cylinder 42 is connected to the condenser.

[0020] Preferably, the steam extraction parameters of the dual drive small turbine 7 are adjusted by the super-high pressure cylinder 1 exhaust superheat degree, to reduce the steam superheat degree of the heater 901~90n-1.

[0021] Preferably, the variable frequency generator 8 dynamically compensates or absorbs power according to the power change of the dual drive small turbine 7, to balance the power demand of the feed water pump 6.

[0022] Preferably, it further comprises a controller, the controller 11 real-time acquisition of the dual drive small turbine 7 exhaust pressure P, and control at least one of the following adjustment mode:

[0023] (a) adjusting the MCT inlet valve 701 opening;

[0024] (b) adjusting the MCT exhaust valve 702 opening;

[0025] (c) adjusting the heater bypass valve 90n01 opening;

[0026] To maintain the dual drive small turbine 7 exhaust pressure P≤ preset upper limit value Pmax.

[0027] Another aspect of the present application, a dual machine regenerative steam dual drive small turbine thermal system control method, the method comprising the following steps:

[0028] Step 1, real-time monitoring of the dual drive small turbine 7 exhaust pressure P;

[0029] Step 2, when P>Pmax, at least one of the following control strategy:

[0030] (a) reducing the MCT inlet valve 701 opening, reducing the steam flow into the dual drive small turbine 7;

[0031] (b) Increase the opening of the MCT exhaust valve 702 to divert part of the steam from the dual-drive small steam turbine 7 to the final heater 90n, reducing the amount of steam entering the n-1th stage heater 90n-1 to lower the exhaust pressure P;

[0032] (c) Decreasing the opening of the heater bypass valve 90n01 to lower the feedwater inlet temperature of the n-1 stage heater 90n-1 to reduce its saturation pressure requirement, thereby changing the inlet steam pressure of the n-1 stage heater 90n-1, that is, reducing the exhaust steam pressure P;

[0033] Step 3: Real-time monitoring of the output power of the steam-electric dual-drive small steam turbine 7 ;

[0034] Step 4: Controller 11 and the power required by water pump 6 Calculate real-time power difference ;

[0035] Step 5: The variable frequency generator 8 generates power according to the real-time power difference. Switch working mode:

[0036] when When the frequency conversion generator 8 switches to the power generation mode, the steam-electric dual-drive small steam turbine 7 drives the water feed pump 6 to work, and at the same time, the excess energy is fed back to the power grid through the frequency conversion generator 8;

[0037] when When the frequency conversion generator 8 switches to the electric mode, the frequency conversion generator 8 absorbs electric energy from the power grid to supplement the power for the steam-electric dual-drive small steam turbine 7, so that the steam-electric dual-drive small steam turbine 7 drives the water feed pump 6 to work stably.

[0038] Preferably, the exhaust steam pressure P in step 1 is measured in real time by a pressure sensor.

[0039] Preferably, the output power of step 3 Measured in real time by shaft torque sensor or electrical power transmitter.

[0040] Preferably, the water pump 6 requires power It is the preset power value to maintain the stable operation of the water supply pump 6.

[0041] Beneficial effects of the present invention:

[0042] 1. Energy efficiency improvement: Utilize the low superheated steam from the ultra-high pressure cylinder exhaust to supply the heat recovery system to improve heat transfer efficiency;

[0043] 2. Cost reduction: heaters and pipes can be made of low-grade heat-resistant materials;

[0044] 3. Flexible regulation: three-way pressure control method adapts to load fluctuation, ensuring safe operation;

[0045] 4. Power balance: variable frequency generator automatically compensates for MCT power variation, maintaining stable feed water pump output. BRIEF DESCRIPTION OF DRAWINGS

[0046] Fig. 1 is a structural diagram of the double-machine regenerative steam and electricity dual-drive small steam turbine thermal system according to the present application;

[0047] Fig. 2 is a control method principle block diagram. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0050] The present application will be further described below with reference to the accompanying drawings and specific embodiments, but is not limited by the present application.

[0051] The steam and electricity dual-drive small steam turbine according to the present application uses super-high pressure exhaust steam for steam admission, the main shaft is connected with the feed water pump and the variable frequency generator, and simultaneously provides steam extraction for the regenerative heater, effectively utilizes the superheat degree of the steam, reduces the cost of the heater and the corresponding pipeline, and improves the circulating efficiency of the steam turbine regenerative cycle. Meanwhile, three control methods of steam admission valve control, exhaust back pressure control and heater bypass control for the steam and electricity dual-drive small steam turbine are proposed, providing control guidance for equipment operation.

[0052] Specific embodiment one: the present embodiment will be described below with reference to the accompanying drawings. Figs. 1-2 The double-machine regenerative steam and electricity dual-drive small steam turbine thermal system according to the present embodiment includes a main steam turbine unit, a steam and electricity dual-drive small steam turbine 7 and multi-stage heaters 901~90n.

[0053] The main steam turbine unit: ultra-high pressure cylinder 1, high pressure cylinder 2, medium pressure cylinder 3, A low pressure cylinder 41, B low pressure cylinder 42 and generator 5 are coaxially arranged; the steam inlet of the ultra-high pressure cylinder 1 is from the main steam of the boiler, and the exhaust steam is connected to the cold end of the boiler reheater; the steam inlet of the high pressure cylinder 2 is from the primary reheated steam of the boiler, and the exhaust steam is connected to the cold end of the primary reheated boiler; the steam inlet of the medium pressure cylinder 3 is from the secondary reheated steam of the boiler, and the exhaust steam is connected to the A low pressure cylinder 41, B low pressure cylinder 42 and the last stage heater 90n respectively; the exhaust steam of the A low pressure cylinder 41 and B low pressure cylinder 42 is connected to the condenser.

[0054] MCT 7:

[0055] The steam inlet is connected to the exhaust pipe of the ultra-high pressure cylinder 1, and is adjusted through the MCT inlet valve 701;

[0056] The steam extraction port is connected to the front n-2 stage regenerative heater 901~90n-2;

[0057] The exhaust port is connected to the n-1 stage heater 90n-1; the exhaust port is also connected to the last stage heater 90n through the MCT exhaust valve 702;

[0058] The coaxial driving feed water pump 6 and the variable frequency generator 8; the MCT 7, the feed water pump 6 and the variable frequency generator 8 are coaxially arranged.

[0059] The last stage heater 90n: the steam source is from the exhaust steam of the medium pressure cylinder 3, and the heater bypass valve 90n01 is arranged.

[0060] The steam extraction parameter of the MCT 7 is adjusted by the superheat degree of the exhaust steam of the ultra-high pressure cylinder 1, so as to reduce the steam superheat degree of the heater 901~90n-1. The steam source of each stage heater of the present application is not directly taken from the high pressure cylinder with high superheat degree of the main steam turbine, the front n-2 stage regenerative heater 901~90n-2 is taken from the MCT 7, and the last stage heater 90n is taken from the medium pressure cylinder 3, which effectively reduces the steam superheat degree.

[0061] The variable frequency generator 8 dynamically compensates or absorbs power according to the power change of the MCT 7, so as to balance the power demand of the feed water pump 6. The power of the feed water pump 6 is kept constant, and the operation is stable.

[0062] It also includes a controller, the controller 11 collects the exhaust steam pressure P of the MCT 7 in real time, and controls at least one of the following adjustment modes:

[0063] (a) adjusting the opening degree of the MCT inlet valve 701;

[0064] (b) adjusting the opening degree of the MCT exhaust valve 702;

[0065] (c) adjusting the opening degree of the heater bypass valve 90n01;

[0066] To maintain the exhaust pressure P of the steam turbine 7 ≤ preset upper limit value Pmax.

[0067] The system of the present application acquires the exhaust pressure P of the steam turbine 7 in real time as a control target, and ensures that the exhaust pressure P is not higher than the preset upper limit value Pmax through control measures.

[0068] The method based on the above system includes the following steps:

[0069] Step 1, real-time monitoring of the exhaust pressure P of the steam turbine 7;

[0070] Step 2, when P > Pmax, at least one of the following control strategies is executed:

[0071] (a) reducing the opening of the MCT inlet valve 701 to reduce the steam flow into the steam turbine 7; this strategy changes the flow into the steam turbine 7 by adjusting the opening of the valve, and according to the principle of self-balancing of heater heat and pressure, the inlet pressure of the heater 90n-1, i.e. the exhaust pressure P, is changed;

[0072] (b) increasing the opening of the MCT exhaust valve 702 to divert part of the steam of the steam turbine 7 to the final heater 90n, reducing the amount of steam entering the n-1 stage heater 90n-1, so as to reduce the exhaust pressure P; this strategy changes the flow into the heater 90n by adjusting the opening of the valve, and after the exhaust flow is diverted, the flow into the heater 90n-1 is reduced accordingly, according to the principle of self-balancing of heater heat and pressure, the inlet pressure of the heater 90n-1, i.e. the exhaust pressure P, is changed;

[0073] (c) reducing the opening of the heater bypass valve 90n01 to reduce the feedwater inlet temperature of the n-1 stage heater 90n-1, so as to reduce its saturation pressure requirement, thereby changing the inlet pressure of the n-1 stage heater 90n-1, i.e. reducing the exhaust pressure P; this strategy changes the feedwater inlet temperature of the heater 90n-1 by adjusting the opening of the valve, and according to the principle of self-balancing of heater heat and pressure, the inlet pressure of the heater 90n-1, i.e. the exhaust pressure P, is changed;

[0074] Step 3, real-time monitoring of the output power of the steam turbine 7 ;

[0075] Step 4, the controller 11 calculates the real-time power difference and the demand power of the feedwater pump 6 ; ;

[0076] Step 5, the variable frequency generator 8 switches the working mode according to the real-time power difference ;

[0077] When , the frequency converter generator 8 switches to the power generation mode, the steam-electric dual drive small turbine 7 drives the feed water pump 6 to work, and the excess energy is fed back to the power grid through the frequency converter generator 8 (consumes the excess power);

[0078] When , the frequency converter generator 8 switches to the power generation mode, the steam-electric dual drive small turbine 7 drives the feed water pump 6 to work, and the excess energy is fed back to the power grid through the frequency converter generator 8 (consumes the excess power);

[0079] The exhaust steam pressure P of step 1 is measured in real time by a pressure sensor.

[0080] The output power of step 3 is measured in real time by a shaft torque sensor or an electrical power transmitter. The demand power of the feed water pump 6 is a preset power value for maintaining the stable work of the feed water pump 6.

[0081] The present application also provides a fault protection. When the steam-electric dual drive small turbine 7 fails and the output power is 0, the frequency converter generator 8 switches to the full-power electric mode to drive the feed water pump 6.

[0082] The frequency converter generator 8 of the present application is a "power buffer" that ensures the constant energy input of the feed water pump 6. The frequency converter generator 8 can switch between the electric mode and the power generation mode in milliseconds to quickly compensate for the power fluctuation. The excess power of the MCT is converted into electrical energy (rather than throttling loss), and the overall efficiency of the system is improved.

[0083] Although the present application is described herein with reference to particular embodiments, it is to be understood that these examples are merely illustrative of the principles and applications of the present application. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and that other arrangements can be devised without departing from the spirit and scope of the present application as defined by the appended claims. It is to be understood that the features of the dependent claims can be combined with those of the parent application in the manner set forth in the description. It is also to be understood that the features described in connection with one embodiment can be used in conjunction with other embodiments.

Claims

1. Dual-unit heat recovery steam-electric dual-drive small steam turbine thermal system, characterized by: It includes a main steam turbine unit, a steam-electric dual-drive small steam turbine (7) and a multi-stage heater (901) to (90n); Main steam turbine unit: ultra-high pressure cylinder (1), high pressure cylinder (2), medium pressure cylinder (3), low pressure cylinder A (41), low pressure cylinder B (42) and generator (5) are coaxially arranged; Small steam turbine with dual steam and electric drive (7): The steam inlet is connected to the exhaust pipe of the ultra-high pressure cylinder (1) and is regulated by the MCT steam inlet valve (701); The steam extraction port is connected to the front n-2 stage regenerative heaters (901) to (90n-2); The exhaust port is connected to the n-1 stage heater (90n-1); the exhaust port is also connected to the final stage heater 90n through the MCT exhaust valve (702); Coaxially driving a water feed pump (6) and a variable frequency generator (8); Final stage heater (90n): The steam source comes from the exhaust steam of the medium pressure cylinder (3), and a heater bypass valve (90n01) is provided.

2. The dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 1 is characterized in that: The inlet steam of the ultra-high pressure cylinder (1) comes from the main steam of the boiler, and the exhaust steam is connected to the reheat cold end of the boiler; The steam inlet of the high-pressure cylinder (2) comes from the boiler's primary reheat steam, and the exhaust steam is connected to the boiler's primary reheat cold end; The steam inlet of the intermediate pressure cylinder (3) comes from the secondary reheat steam of the boiler, and the exhaust steam is connected to the low pressure cylinder A (41), the low pressure cylinder B (42) and the final stage heater (90n) respectively; The exhaust steam of the A low-pressure cylinder (41) and the B low-pressure cylinder (42) is connected to a condenser.

3. The dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 2 is characterized in that: The steam extraction parameters of the steam-electric dual-drive small steam turbine (7) are adjusted by the superheat of the exhaust steam from the ultra-high pressure cylinder (1) to reduce the superheat of the steam in the heaters (901) to (90n-1).

4. The dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 1 is characterized in that: The variable frequency generator (8) dynamically compensates or absorbs power according to the power change of the steam-electric dual-drive small steam turbine (7) to balance the power demand of the water feed pump (6).

5. The dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 1 is characterized in that: It also includes a controller, wherein the controller (11) collects the exhaust pressure P of the steam-electric dual-drive small steam turbine (7) in real time and controls at least one of the following adjustment modes: (a) Adjust the opening of the MCT steam inlet valve (701); (b) adjusting the opening of the MCT exhaust valve (702); (c) Adjust the opening of the heater bypass valve (90n01); To maintain the exhaust pressure P of the steam-electric dual-drive small steam turbine (7) ≤ the preset upper limit value Pmax.

6. A control method for a dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system, characterized in that: The method comprises the following steps: Step 1: Real-time monitoring of the exhaust pressure P of the steam-electric dual-drive small steam turbine (7); Step 2: When P>Pmax, execute at least one of the following control strategies: (a) reducing the opening of the MCT steam inlet valve (701) to reduce the steam flow rate entering the steam-electric dual-drive small steam turbine (7); (b) increasing the opening of the MCT exhaust valve (702) to divert part of the steam from the steam-electric dual-drive small turbine (7) to the final stage heater 90n, thereby reducing the amount of steam entering the n-1 stage heater 90n-1 and lowering the exhaust pressure P; (c) reducing the opening of the heater bypass valve (90n01) to lower the feedwater inlet temperature of the n-1 stage heater (90n-1) to reduce its saturation pressure requirement, thereby changing the inlet steam pressure of the n-1 stage heater (90n-1), that is, reducing the exhaust steam pressure P; Step 3: Real-time monitoring of the output power of the steam-electric dual-drive small steam turbine (7) ; Step 4: Controller (11) and the power requirement of the water supply pump (6) Calculate real-time power difference ; Step 5: The variable frequency generator (8) generates a current according to the real-time power difference. Switch working mode: when When the frequency conversion generator (8) switches to the power generation mode, the steam-electric dual-drive small steam turbine (7) drives the water feed pump (6) to work, and at the same time, the excess energy is fed back to the power grid through the frequency conversion generator (8); when When the frequency conversion generator (8) switches to the electric mode, the frequency conversion generator (8) absorbs electric energy from the power grid to supplement the power of the steam-electric dual-drive small steam turbine (7), so that the steam-electric dual-drive small steam turbine (7) drives the feed water pump (6) to work stably.

7. The control method of the dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 6 is characterized in that: The exhaust steam pressure P of step 1 is measured in real time by a pressure sensor.

8. The control method of the dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 6 is characterized in that: Output power of step 3 Measured in real time by shaft torque sensor or electrical power transmitter.

9. The control method of the dual-engine heat recovery steam-electric dual-drive small steam turbine thermal system according to claim 6, characterized in that: Power requirement of water supply pump (6) It is the preset power value for maintaining the stable operation of the water supply pump (6).

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