A control system for improving the motoring efficiency of a best small steam turbine during start-up

Abstract

This invention discloses a control system for improving the start-up efficiency of a BEST small steam turbine, including a BEST small steam turbine bypass valve control system and a control system for the difference between the actual back pressure and the set back pressure value of the BEST small steam turbine. This system can ensure the stable operation of the BEST small steam turbine.

Description

Technical Field

[0001] This invention belongs to the field of thermal control of BEST small steam turbines with small generators in ultra-supercritical double reheat coal-fired units, and relates to a control system for improving the start-up efficiency of BEST small steam turbines. Background Technology

[0002] In the thermal power sector, the experience and technology of BEST small steam turbine operation and commissioning are becoming increasingly sophisticated. During the cold start-up phase of the BEST small steam turbine, the control valve opening gradually increases while the bypass valve is fully open, and the speed rises to 1000 r / min. At this time, it is in a low-speed warm-up state, mainly to ensure that the various parts of the BEST small steam turbine expand evenly due to heat, and to prevent deformation and loosening of components such as cylinders, diaphragms, nozzles, shafts, impellers, steam seals, and shaft seals.

[0003] During the warm-up phase, because the bypass valve is fully open, the steam supply is large and the rotor mass-to-surface ratio is small while the cylinder mass-to-surface ratio is large. This causes the rotor expansion speed to be greater than the cylinder expansion speed, resulting in an increase in the differential expansion. This may even trigger the MEST protection, threatening the stable operation of the BEST small steam turbine and potentially causing an unplanned unit shutdown. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a control system for improving the start-up efficiency of the BEST small steam turbine, which can ensure the stable operation of the BEST small steam turbine.

[0005] To achieve the above objectives, the control system for improving the start-up efficiency of the BEST small steam turbine according to the present invention includes a BEST small steam turbine bypass valve control system and a control system for the difference between the actual back pressure and the set back pressure value of the BEST small steam turbine.

[0006] The BEST small turbine bypass valve control system includes the following terminals: BEST actual back pressure vs. back pressure setpoint difference input terminal; BEST final stage pressure ratio setpoint vs. actual pressure ratio difference input terminal; BEST small turbine start-up sequential control feedback terminal; No. 7 and No. 8 low-pressure heater cut-off feedback terminal; BEST bypass valve fully closed feedback terminal; bypass valve position control manual mode feedback terminal; No. 8 low-pressure heater cut-off feedback terminal; BEST small turbine trip feedback terminal; first two-way selector block; first NOT block; first AND block; RS trigger; second AND block; first OR block; second NOT block; small turbine shaft seal programmable control command 4 feedback terminal; B... The following components are included: EST small steam turbine sequential control step 8 feedback terminal, bypass valve quick-opening solenoid valve energized command feedback terminal, BEST small steam turbine bypass valve opening output module, first pulse block, second pulse block, third pulse block, first analog constant block, second analog constant block, third analog constant block, second OR block, second two-to-one switching block, third two-to-one switching block, first PID controller, first F(x) function block, BEST small steam turbine differential expansion input terminal, first subtraction block, greater than comparison block, second PID controller, limiting block, second F(x) function block and second subtraction block;

[0007] The BEST small steam turbine start-up sequential control feedback terminal is connected to the input terminal of the first AND block via the first NOT block, the low-pressure cut-off feedback terminals No. 7 and No. 8 are connected to the input terminal of the first AND block, and the output terminal of the first AND block is connected to the S terminal of the RS flip-flop.

[0008] The No. 8 low-pressure cut-off feedback terminal is connected to the input terminal of the second AND block via the second NOT block. The BEST bypass valve fully closed feedback terminal and the bypass valve position control manual mode feedback terminal are connected to the input terminal of the second AND block. The output terminal of the second AND block and the BEST small steam turbine trip feedback terminal are connected to the input terminal of the first OR block. The output terminal of the first OR block is connected to the R terminal of the RS trigger.

[0009] The DV terminal of the RS flip-flop is connected to the EN terminal of the first two-to-one switch block. The input terminal of the difference between the actual back pressure and the back pressure setting value of BEST and the input terminal of the difference between the final stage voltage ratio setting and the actual voltage ratio of BEST are connected to the input terminal of the first two-to-one switch block. The RV terminal of the RS flip-flop is connected to the EN terminal of the third two-to-one switch block and the EN terminal of the second two-to-one switch block.

[0010] The feedback terminal of the small turbine shaft seal program control command 4 is connected to the input terminal of the second OR block via the first pulse block; the feedback terminal of the BEST small turbine sequential control step 8 is connected to the input terminal of the second OR block via the second pulse block; the feedback terminal of the BEST small turbine trip is connected to the input terminal of the second OR block via the third pulse block; the feedback terminal of the bypass valve quick-opening solenoid valve energization command is connected to the input terminal of the second OR block; the output terminals of the first analog constant block, the second analog constant block, the third analog constant block, the second OR block, the second two-to-one switching block, and the third two-to-one switching block are respectively connected to the E terminal, H terminal, L terminal, TR terminal, TS terminal, Kp terminal, and Ti terminal of the first PID controller;

[0011] The output of the first PID controller is connected to the input of the second subtraction block via the first F(x) function block; the differential expansion input of the BEST small steam turbine is connected to the input of the first subtraction block and the input of the larger comparison block; the output of the first subtraction block and the output of the comparison block are connected to the input of the second PID controller; the output of the second PID controller is connected to the input of the second subtraction block via the limiting block and the second F(x) function block; and the output of the second subtraction block is connected to the BEST small steam turbine bypass valve opening output module.

[0012] During operation, the deviation value of the expansion difference is calculated in advance using the second F(x) function block, and the opening degree of the BEST small turbine bypass valve needs to be reduced accordingly.

[0013] When the differential pressure gradually increases, the BEST small steam turbine bypass valve reduces its opening, increasing the BEST small steam turbine warm-up time.

[0014] The BEST small steam turbine actual back pressure and back pressure setpoint difference control system includes a BEST exhaust pressure input terminal, a BEST delayed back pressure setpoint input terminal, a multiplication block, a BEST actual back pressure and back pressure setpoint difference output module, a third F(x) function block, an addition block, a fourth two-to-one switching block, and a third subtraction block.

[0015] The BEST small steam turbine expansion differential input terminal is connected to the input terminal of the adder block via the third F(x) function block; the BEST delay back pressure setpoint input terminal is connected to the input terminal of the adder block; the BEST exhaust pressure input terminal is connected to the input terminal of the fourth two-to-one switching block and the input terminal of the third subtraction block.

[0016] The feedback terminal of the bypass valve position control manual mode and the output terminal of the adder block are connected to the input terminal of the fourth two-to-one switching block. The output terminal of the fourth two-to-one switching block is connected to the input terminal of the third subtraction block. The output terminal of the third subtraction block is connected to the input terminal of the multiplication block. The output terminal of the multiplication block is connected to the output module of the difference between the actual back pressure and the back pressure setting value of BEST.

[0017] The present invention has the following beneficial effects:

[0018] The control system for improving start-up efficiency of the BEST small steam turbine described in this invention, during cold start-up of the BEST small steam turbine, when the speed reaches 1000 r / min and the bypass valve is fully open, effectively controls the increasing differential expansion by monitoring the differential expansion and controlling the opening of the bypass valve in advance. This prevents the rotor expansion speed from exceeding the cylinder expansion speed during warm-up when the bypass valve is fully open and the steam supply is increased, causing the differential expansion to increase and ultimately triggering the METS protection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the BEST small steam turbine before startup.

[0020] Figure 2 A schematic diagram showing the BEST small steam turbine reaching 1000 r / min after startup;

[0021] Figure 3 A schematic diagram showing the BEST small steam turbine reaching 2400 r / min after startup;

[0022] Figure 4 This is a schematic diagram of the original control system for the bypass valve of the BEST small steam turbine.

[0023] Figure 5 Schematic diagram of the new control system for the bypass valve of the BEST small steam turbine;

[0024] Figure 6 A schematic diagram of the original control system for the difference between the actual back pressure and the set back pressure value of the BEST small steam turbine;

[0025] Figure 7 A schematic diagram of the new control system for the difference between the actual back pressure and the set back pressure value of the BEST small steam turbine.

[0026] Among them, B001 is the input terminal for the difference between the actual back pressure and the back pressure setpoint in BEST; B002 is the input terminal for the difference between the final stage pressure ratio setpoint and the actual pressure ratio in BEST; B003 is the feedback terminal for the start-up sequential control of the small steam turbine in BEST; B004 is the feedback terminal for the removal of the No. 7 and No. 8 low-pressure heaters; B005 is the feedback terminal for the full closure of the BEST bypass valve; B006 is the feedback terminal for the manual mode of the bypass valve position control; B007 is the feedback terminal for the removal of the No. 8 low-pressure heater; B008 is the feedback terminal for the tripping of the small steam turbine in BEST; and B009... B010 is the first AND block, B011 is the first NOT block, B012 is the RS trigger, B013 is the second AND block, B014 is the first OR block, B015 is the second NOT block, B016 is the feedback terminal for the 4th step of the small turbine shaft seal program control command, B017 is the feedback terminal for the 8th step of the BEST small turbine sequential control, B018 is the feedback terminal for the energized command of the bypass valve quick-opening solenoid valve, B019 is the BEST small turbine bypass valve opening output module, B020 is the first pulse block, B02... B021 is the second pulse block, B022 is the third pulse block, B023 is the first analog constant block, B024 is the second analog constant block, B025 is the third analog constant block, B026 is the second OR block, B027 is the second 2-to-1 switching block, B028 is the third 2-to-1 switching block, B029 is the first PID controller, B030 is the first F(x) function block, B031 is the BEST small turbine expansion differential input terminal, B032 is the first subtraction block, and B033 is the greater than comparison block. B034 is the second PID controller, B035 is the limiting block, B036 is the second F(x) function block, B037 is the second subtraction block, D001 is the BEST exhaust pressure input terminal, D002 is the BEST delay back pressure setpoint input terminal, D003 is the multiplication block, D004 is the output module for the difference between the actual back pressure and the back pressure setpoint of BEST, D005 is the third F(x) function block, D006 is the addition block, D007 is the fourth two-to-one switching block, and D008 is the third subtraction block. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0028] The accompanying drawings show structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not drawn to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0029] Figure 1 This is a schematic diagram of the BEST small steam turbine before startup.

[0030] 1) Figure 1 The operating conditions before starting the BEST small steam turbine;

[0031] 2) Line 1 represents the speed of the BEST small steam turbine, line 2 represents the differential pressure of the BEST small steam turbine, line 3 represents the feedback of the opening of the BEST small steam turbine's steam supply regulating valve, line 4 represents the steam supply temperature of the BEST small steam turbine's shaft seal, line 5 represents the pressure of the BEST small steam turbine's shaft seal header, line 6 represents the feedback of the opening of the BEST small steam turbine's bypass valve, and line 7 represents the exhaust pressure of the BEST small steam turbine.

[0032] 3) At 16:45:07, line 1 indicates the BEST small steam turbine's speed is 104.9 r / min, line 2 indicates the BEST small steam turbine's differential expansion is 0 mm, line 3 indicates the BEST small steam turbine's steam supply regulating valve opening is 0.01%, line 4 indicates the BEST small steam turbine's shaft seal steam supply temperature is 28.91℃, line 5 indicates the BEST small steam turbine's shaft seal header pressure is -0.07 kPa, line 6 indicates the BEST small steam turbine's bypass valve opening is 0%, and line 7 indicates the BEST small steam turbine's exhaust pressure is 0 MPa.

[0033] 4) At 16:45:07, it indicates that the BEST small steam turbine is in the turning state at 104.9 r / min, the steam supply regulating valve is not open, and the expansion difference is in normal condition.

[0034] 5) During the period from 16:45:07 to 18:23:57, the BEST small steam turbine was in a turning state at 104.9 r / min. The opening of the steam supply regulating valve of the BEST small steam turbine gradually increased, and the expansion difference gradually increased accordingly.

[0035] 6) During the period from 18:23:57 to 21:23:57, the BEST small steam turbine was in a turning state at 104.9 r / min. The opening of the BEST small steam turbine steam supply regulating valve had decreased and maintained this opening state, and the expansion difference gradually tended to stabilize.

[0036] 7) During the period from 21:23:57 to 00:23:57, the BEST small steam turbine starts up, the opening of the BEST small steam turbine steam supply regulating valve gradually increases, the opening of the BEST small steam turbine bypass valve gradually reaches the fully open state, and the expansion difference begins to increase.

[0037] See Figure 2 A schematic diagram of the BEST small steam turbine reaching 1000 r / min after startup;

[0038] 1) Figure 2 The main demonstration showed the operating conditions of the BEST small steam turbine after startup, reaching 1000 r / min.

[0039] 2) Line 1 represents the speed of the BEST small steam turbine, line 2 represents the differential pressure of the BEST small steam turbine, line 3 represents the feedback of the opening of the BEST small steam turbine's steam supply regulating valve, line 4 represents the steam supply temperature of the BEST small steam turbine's shaft seal, line 5 represents the pressure of the BEST small steam turbine's shaft seal header, line 6 represents the feedback of the opening of the BEST small steam turbine's bypass valve, and line 7 represents the exhaust pressure of the BEST small steam turbine.

[0040] 3) At 16:45:07, line 1 indicates the BEST small steam turbine's speed is 1000.14 r / min; line 2 indicates the BEST small steam turbine's differential expansion is 1.38 mm; line 3 indicates the feedback of the BEST small steam turbine's steam supply regulating valve opening is 4.83%; line 4 indicates the BEST small steam turbine's shaft seal steam supply temperature is 156.55℃; line 5 indicates the BEST small steam turbine's shaft seal header pressure is -0.72 kPa; line 6 indicates the BEST small steam turbine's bypass valve opening is 99.78%; and line 7 indicates the BEST small steam turbine's exhaust pressure is 0 MPa.

[0041] 4) At this point, the BEST miniature steam turbine has successfully started and reached 1000 r / min, entering the warm-up phase. The BEST miniature steam turbine maintains a certain speed, and the steam passing through it causes the rotor and cylinder to expand evenly due to heat. The rotor, which had slightly bent after shutdown, slowly straightens. Simultaneously, the warm-up process allows the cylinder to expand fully, preventing excessively rapid rotor expansion that could increase differential expansion between the rotor and cylinder, causing friction between the rotor and stationary parts and resulting in turbine vibration. The warm-up process also ensures that the internal metal temperature of the rotor's central bore is above the brittle transition temperature.

[0042] 5) The differential expansion of a BEST small steam turbine is the change in the axial relative position of the cylinder block and the rotor at a certain cross-section. It is the difference in axial expansion between the rotor and the cylinder block, and is called the relative expansion difference between the rotor and the cylinder block. The differential expansion of a BEST small steam turbine is mainly affected by three factors: first, the difference in thermal expansion displacement between the rotor and the cylinder block; second, the displacement of the rotor shortening caused by centrifugal force when the rotor rotates; and third, the axial displacement of the rotor at the thrust bearing.

[0043] The theoretical formula for calculating the difference in expansion is:

[0044] Z = Za-Zb+Zc-Zd

[0045] Where Z is the differential expansion, Za is the rotor thermal expansion, Zb is the rotor deformation due to centrifugal force, Zc is the rotor axial displacement, and Zd is the cylinder thermal expansion.

[0046] 6) During the warm-up phase, the BEST small steam turbine's steam supply regulating valve has gradually closed, while the BEST small steam turbine's bypass valve is fully open, allowing a large amount of steam to flow into the rotor and cylinder. Because the rotor has a smaller surface area ratio and the cylinder has a larger surface area ratio, the thermal expansion rates of the rotor and cylinder are no longer consistent, and the expansion difference begins to gradually increase, approaching the trip value, which seriously threatens the start-up of the BEST small steam turbine.

[0047] See Figure 3 A schematic diagram of the BEST small steam turbine reaching 2400 r / min after startup;

[0048] 1) Figure 3 The main demonstration showed the operating conditions of the BEST small steam turbine reaching 2400 r / min after startup;

[0049] 2) Line 1 represents the speed of the BEST small steam turbine, line 2 represents the differential pressure of the BEST small steam turbine, line 3 represents the feedback of the opening of the BEST small steam turbine's steam supply regulating valve, line 4 represents the steam supply temperature of the BEST small steam turbine's shaft seal, line 5 represents the pressure of the BEST small steam turbine's shaft seal header, line 6 represents the feedback of the opening of the BEST small steam turbine's bypass valve, and line 7 represents the exhaust pressure of the BEST small steam turbine.

[0050] 3) At 16:45:07, line 1 shows the BEST small steam turbine's speed at 2441.11 r / min; line 2 shows the BEST small steam turbine's differential expansion at 1.61 mm; line 3 shows the feedback of the BEST small steam turbine's steam supply regulating valve opening at 5.18%; line 4 shows the BEST small steam turbine's shaft seal steam supply temperature at 155.9℃; line 5 shows the BEST small steam turbine's shaft seal header pressure at -0.71 kPa; line 6 shows the feedback of the BEST small steam turbine's bypass valve opening at 99.75%; and line 7 shows the BEST small steam turbine's exhaust pressure at 0 MPa.

[0051] 4) At this point, the BEST small steam turbine has successfully started and completed the warm-up process at 1000 r / min, with the speed rising above 2400 r / min. The No. 7 low-pressure heater has been activated, and the primary low-temperature reheat steam inlet valve has been opened. Simultaneously, the exhaust steam switching is complete. Through this stage, it can be observed that although the BEST small steam turbine has completed its warm-up, the differential expansion has not improved. The rotor's thermal expansion rate is still greater than the cylinder block's expansion rate and is approaching the trip value, potentially triggering the METS protection at any time and causing a non-shutdown of the unit.

[0052] refer to Figure 4 In the existing BEST small steam turbine bypass valve control system, after the BEST small steam turbine starts and reaches 1000 r / min, it is in a warm-up state with the bypass valve fully open. The steam passing through the fully open bypass valve has an excessive impact on the expansion rate of the rotor and cylinder, leading to increased differential expansion. To address this issue, adjustments are needed. Figure 4 The original control system of the bypass valve of the BEST small steam turbine has been optimized to avoid the problem that the bypass valve is in a fully open state when the BEST small steam turbine is in the warm-up state, which would lead to an increase in steam flow and a gradual increase in differential expansion.

[0053] refer to Figure 5Based on this, the present invention designs a new control system for the BEST small steam turbine bypass valve, including: B001, input terminal for the difference between BEST actual back pressure and back pressure set value; B002, input terminal for the difference between BEST final stage pressure ratio set value and actual pressure ratio; B003, BEST small steam turbine start-up sequential control feedback terminal; B004, feedback terminal for the cut-off of No. 7 and No. 8 low-pressure heaters; B005, BEST bypass valve fully closed feedback terminal; B006, bypass valve position control manual mode feedback terminal; B007, No. 8 low-pressure heater cut-off feedback terminal; B008, BEST small steam turbine trip feedback terminal; B009, first two-way switching block; B010, first NOT block; B011, first AND block; B012, RS trigger; B013, second AND block; B014, first OR block; second NOT block; B015, small turbine shaft seal program control command 4 feedback terminal; B016, BEST... Feedback terminal B017 for step 8 of small steam turbine sequential control, feedback terminal B018 for energized command of bypass valve quick-opening solenoid valve, B019 for BEST small steam turbine bypass valve opening output module, first pulse block B020, second pulse block B021, third pulse block B022, first analog constant block B023, second analog constant block B024, third analog constant block B025, second OR block B026, second 2-to-1 switching block B027, third 2-to-1 switching block B028, first PID controller B029, first F(x) function block B030, BEST small steam turbine expansion difference input terminal B031, first subtraction block B032, greater than comparison block B033, second PID controller B034, limiting block B035, second F(x) function block B036 and second subtraction block B037;

[0054] The BEST small steam turbine start-up sequential control feedback terminal B003 is connected to the input terminal of the first NOT block B010 and the first AND block B011. The low-pressure cut-off feedback terminals B004 (No. 7 and No. 8) are connected to the input terminal of the first AND block B011. The output terminal of the first AND block B011 is connected to the S terminal of the RS flip-flop B012.

[0055] The No. 8 low-pressure cut-off feedback terminal B007 is connected to the input terminal of the second NOT block B015 and the second AND block B013. The BEST bypass valve fully closed feedback terminal B005 and the bypass valve position control manual mode feedback terminal B006 are connected to the input terminal of the second AND block B013. The output terminal of the second AND block B013 and the BEST small steam turbine trip feedback terminal B008 are connected to the input terminal of the first OR block B014. The output terminal of the first OR block B014 is connected to the R terminal of the RS trigger B012.

[0056] The DV terminal of RS flip-flop B012 is connected to the EN terminal of the first two-to-one switch block B009. The input terminal B001, which is the difference between the actual back pressure and the back pressure setting value of BEST, and the input terminal B002, which is the difference between the final stage voltage ratio setting and the actual voltage ratio of BEST, are connected to the input terminals of the first two-to-one switch block B009. The RV terminal of RS flip-flop B012 is connected to the EN terminal of the third two-to-one switch block B028 and the EN terminal of the second two-to-one switch block B027.

[0057] The feedback terminal B016 of the small turbine shaft seal program control command 4 is connected to the input terminal of the second OR block B026 via the first pulse block B020. The feedback terminal B017 of the BEST small turbine sequential control step 8 is connected to the input terminal of the second OR block B026 via the second pulse block B021. The trip feedback terminal B008 of the BEST small turbine is connected to the input terminal of the second OR block B026 via the third pulse block B022. The feedback terminal B018 of the bypass valve quick-opening solenoid valve energization command is connected to the input terminal of the second OR block B026. The output terminals of the first analog constant block B023, the second analog constant block B024, the third analog constant block B025, the second OR block B026, the second two-to-one switching block B027, and the third two-to-one switching block B028 are respectively connected to the E terminal, H terminal, L terminal, TR terminal, TS terminal, Kp terminal, and Ti terminal of the first PID controller B029.

[0058] The output of the first PID controller B029 is connected to the input of the second subtraction block B037 via the first F(x) function block B030; the BEST small turbine expansion differential input B031 is connected to the input of the first subtraction block B032 and the input of the larger comparison block B033; the output of the first subtraction block B032 and the output of the comparison block are connected to the input of the second PID controller B034; the output of the second PID controller B034 is connected to the input of the second subtraction block B037 via the limiting block B035 and the second F(x) function block B036; and the output of the second subtraction block B037 is connected to the BEST small turbine bypass valve opening output module B019.

[0059] During operation, the deviation value of the expansion difference is calculated in advance using the second F(x) function block B036, and the opening degree of the bypass valve that needs to be reduced is calculated accordingly. Then, the opening degree of the bypass valve corresponding to the expansion difference is calculated using the first F(x) function block B030. The two are subtracted using the second subtraction block B037, and the opening degree of the bypass valve of the BEST small steam turbine is controlled by the calculation result.

[0060] With this invention, when the BEST small steam turbine is in the warm-up state, if the expansion difference gradually increases, the BEST small steam turbine bypass valve will appropriately reduce its opening through the expansion difference monitoring device, thereby increasing the warm-up time of the BEST small steam turbine, reducing the impact of steam on the expansion rate of the rotor and cylinder, and preventing the expansion difference from increasing further.

[0061] refer to Figure 6 After the BEST small steam turbine starts and reaches 1000 r / min, it is in a warm-up state with the bypass valve fully open. The steam passing through the fully open bypass valve has an excessive impact on the expansion speed of the rotor and cylinder, leading to an increased differential expansion. To address this issue, it is necessary to... Figure 6 The original control system was optimized to avoid the problem of increased steam flow and gradually increasing differential pressure when the BEST small steam turbine is in the warm-up state, as the bypass valve is fully open.

[0062] refer to Figure 7 Based on this, the new control system for the difference between the actual back pressure and the set back pressure value of the BEST small steam turbine described in this invention includes a BEST exhaust pressure input terminal D001, a BEST delayed back pressure set value input terminal D002, a multiplication block D003, a BEST actual back pressure and back pressure set value difference output module D004, a third F(x) function block D005, an addition block D006, a fourth two-to-one switching block D007, and a third subtraction block D008.

[0063] The BEST small steam turbine expansion differential input terminal B031 is connected to the input terminal of the adder block D006 via the third F(x) function block D005; the BEST delay back pressure setpoint input terminal D002 is connected to the input terminal of the adder block D006; the BEST exhaust pressure input terminal D001 is connected to the input terminal of the fourth two-to-one switching block D007 and the input terminal of the third subtraction block D008.

[0064] The bypass valve position control manual mode feedback terminal B006 and the output terminal of the adder D006 are connected to the input terminal of the fourth two-to-one switcher D007. The output terminal of the fourth two-to-one switcher D007 is connected to the input terminal of the third subtraction block D008. The output terminal of the third subtraction block D008 is connected to the input terminal of the multiplication block D003. The output terminal of the multiplication block D003 is connected to the output module D004, which is the difference between the actual back pressure and the back pressure set value of BEST.

[0065] According to this invention, when the BEST small steam turbine is in the warm-up state, if the expansion difference gradually increases, the bypass valve will appropriately reduce its opening by means of the expansion difference monitoring device, thereby increasing the warm-up time of the BEST small steam turbine, so as to reduce the influence of steam on the expansion rate of the rotor and cylinder and prevent the expansion difference from increasing further.

Claims

1. A control system for improving the start-up efficiency of a BEST small steam turbine, characterized in that, This includes the BEST small steam turbine bypass valve control system and the BEST small steam turbine actual back pressure and back pressure setpoint difference control system. The BEST small turbine bypass valve control system includes the following input terminals: BEST actual back pressure vs. back pressure setpoint difference (B001), BEST final stage pressure ratio setpoint vs. actual pressure ratio difference (B002), BEST small turbine start-up sequential control feedback terminal (B003), No. 7 and No. 8 low-pressure heater cut-off feedback terminal (B004), BEST bypass valve fully closed feedback terminal (B005), bypass valve position control manual mode feedback terminal (B006), No. 8 low-pressure heater cut-off feedback terminal (B007), BEST small turbine trip feedback terminal (B008), first two-way switching block (B009), first NOT block (B010), first AND block (B011), RS trigger (B012), second AND block (B013), first OR block (B014), second NOT block (B015), small turbine shaft seal program control command 4 feedback terminal (B016), and BEST small turbine sequential control step 8 feedback terminal. (B017), bypass valve quick-opening solenoid valve live command feedback terminal (B018), BEST small steam turbine bypass valve opening output module (B019), first pulse block (B020), second pulse block (B021), third pulse block (B022), first analog constant block (B023), second analog constant block (B024), third analog constant block (B025), second OR block (B026), second two-to-one switching block (B027), third two-to-one switching block (B028), first PID controller (B029), first F(x) function block (B030), BEST small steam turbine expansion difference input terminal (B031), first subtraction block (B032), greater than comparison block (B033), second PID controller (B034), limiting block (B035), second F(x) function block (B036) and second subtraction block (B037); The BEST small steam turbine start-up sequential control feedback terminal (B003) is connected to the input terminal of the first AND block (B011) via the first NOT block (B010), the No. 7 and No. 8 low-pressure cut-off feedback terminals (B004) are connected to the input terminal of the first AND block (B011), and the output terminal of the first AND block (B011) is connected to the S terminal of the RS flip-flop (B012). The No. 8 low-pressure cut-off feedback terminal (B007) is connected to the input terminal of the second AND block (B013) via the second NOT block (B015). The BEST bypass valve fully closed feedback terminal (B005) and the bypass valve position control manual mode feedback terminal (B006) are connected to the input terminal of the second AND block (B013). The output terminal of the second AND block (B013) and the BEST small steam turbine trip feedback terminal (B008) are connected to the input terminal of the first OR block (B014). The output terminal of the first OR block (B014) is connected to the R terminal of the RS trigger (B012). The DV terminal of the RS flip-flop (B012) is connected to the EN terminal of the first two-to-one switch block (B009). The input terminal (B001) of the difference between the actual back pressure and the back pressure setting value of BEST and the input terminal (B002) of the difference between the final stage voltage ratio setting and the actual voltage ratio of BEST are connected to the input terminal of the first two-to-one switch block (B009). The RV terminal of the RS flip-flop (B012) is connected to the EN terminal of the third two-to-one switch block (B028) and the EN terminal of the second two-to-one switch block (B027). The feedback terminal (B016) of the small turbine shaft seal program control command 4 is connected to the input terminal of the second OR block (B026) via the first pulse block (B020). The feedback terminal (B017) of the 8th step of the BEST small turbine sequential control is connected to the input terminal of the second OR block (B026) via the second pulse block (B021). The trip feedback terminal (B008) of the BEST small turbine is connected to the input terminal of the second OR block (B026) via the third pulse block (B022). The bypass valve quick-opening solenoid valve energized command feedback terminal... (B018) is connected to the input terminal of the second OR block (B026). The output terminals of the first analog constant block (B023), the second analog constant block (B024), the third analog constant block (B025), the second OR block (B026), the second 2-to-1 switch block (B027), and the third 2-to-1 switch block (B028) are respectively connected to the E terminal, H terminal, L terminal, TR terminal, TS terminal, Kp terminal, and Ti terminal of the first PID controller (B029). The output of the first PID controller (B029) is connected to the input of the second subtraction block (B037) via the first F(x) function block (B030); the differential expansion input of the BEST small steam turbine (B031) is connected to the input of the first subtraction block (B032) and the input of the larger comparison block (B033); the output of the first subtraction block (B032) and the output of the larger comparison block (B033) are connected to the input of the second PID controller (B034); the output of the second PID controller (B034) is connected to the input of the second subtraction block (B037) via the limiting block (B035) and the second F(x) function block (B036); and the output of the second subtraction block (B037) is connected to the BEST small steam turbine bypass valve opening output module (B019). The BEST small steam turbine actual back pressure and back pressure setpoint difference control system includes the BEST exhaust pressure input terminal (D001), the BEST delayed back pressure setpoint input terminal (D002), the multiplication block (D003), the BEST actual back pressure and back pressure setpoint difference output module (D004), the third F(x) function block (D005), the addition block (D006), the fourth two-to-one switching block (D007), and the third subtraction block (D008). The BEST small steam turbine expansion differential input terminal (B031) is connected to the input terminal of the adder block (D006) via the third F(x) function block (D005); the BEST delay back pressure setpoint input terminal (D002) is connected to the input terminal of the adder block (D006); the BEST exhaust pressure input terminal (D001) is connected to the input terminal of the fourth two-to-one switching block (D007) and the input terminal of the third subtraction block (D008); The output terminals of the bypass valve position control manual mode feedback terminal (B006) and the adder block (D006) are connected to the input terminal of the fourth two-to-one switch block (D007). The output terminal of the fourth two-to-one switch block (D007) is connected to the input terminal of the third subtraction block (D008). The output terminal of the third subtraction block (D008) is connected to the input terminal of the multiplication block (D003). The output terminal of the multiplication block (D003) is connected to the output module (D004) for the difference between the actual back pressure and the back pressure set value of BEST. During operation, the deviation value of the expansion difference is calculated in advance using the second F(x) function block (B036), which corresponds to the opening degree of the BEST small turbine bypass valve that needs to be reduced. Then, the opening degree of the bypass valve corresponding to the expansion difference is calculated using the first F(x) function block (B030). The two are subtracted using the second subtraction block (B037), and the opening degree of the BEST small turbine bypass valve is controlled by the calculation result.

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