Low-pressure cylinder switching system and low-pressure cylinder switching cooling flow online obtaining method

Abstract

The invention discloses a low-pressure cylinder switching system and a low-pressure cylinder switching cooling flow online obtaining method. A low-pressure cooling pipeline of the low-pressure cylinder switching system is not provided with a flowmeter, a thermocouple and a pressure transmitter. The online acquisition method comprises the following steps: step 1, carrying out a low-pressure heater full-switching test on a low-pressure cylinder according to ASME PTC6 regulations before cylinder switching and commissioning, and carrying out joint calculation to obtain steam flow at a steam inlet of the low-pressure cylinder; 2, the flow characteristic coefficient of a low-pressure through-flow part is obtained through calculation according to the steam flow at the steam inlet position of the low-pressure cylinder in the step 1 and the corresponding low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure steam exhaust pressure; and 3, during low-pressure cylinder switching operation, through the obtained flow characteristic coefficient of the low-pressure through-flow part, in combination with the low-pressure steam inlet temperature, the low-pressure steam inlet pressure and the low-pressure steam exhaust pressure which are measured during current collection, the steam flow at the steam inlet position of the low-pressure cylinder during current collection is obtained through calculation. While the technical requirements are met, the transformation and operation maintenance cost is low, and the economical efficiency is good.

Description

Technical Field

[0001] The invention relates to an operation control technology of an extraction steam heating steam turbine unit, in particular to a low-pressure cylinder cutting system of a medium-pressure exhaust steam heating unit, and an online acquisition method of a low-pressure cylinder cutting cooling flow based on the low-pressure cylinder cutting system. Background Art

[0002] In order to meet the technical requirements of thermal-electric decoupling and deep peak regulation, it is necessary to perform cylinder cutting heating transformation on the steam turbine units of the power plant, so that the steam turbine units can cut off the expansion work of the low-pressure cylinders at low loads to improve thermal efficiency and economy. After the low-pressure cylinder cutting of the steam turbine unit is completed, its operating status needs to be continuously monitored, which also includes continuous monitoring of the minimum steam inlet cooling flow rate to ensure the safe operation of the low-pressure cylinder. If the steam turbine unit is found to be operating abnormally or the parameters are out of the normal range during continuous monitoring, timely measures need to be taken to adjust and handle it.

[0003] Common low-pressure cylinder cutting systems for medium-pressure exhaust steam heating units are as follows: Figure 1 As shown:

[0004] The exhaust of the medium-pressure cylinder 1 is connected with a medium-pressure exhaust thermocouple 6, a medium-pressure exhaust pressure transmitter 7, a low-pressure cooling main line 3, a low-pressure cooling bypass line 4 and a heating pipeline 5; wherein the medium-pressure exhaust thermocouple 6 is used to measure the real-time steam temperature of the exhaust of the medium-pressure cylinder 1; the medium-pressure exhaust pressure transmitter 7 is used to measure the real-time steam pressure of the exhaust of the medium-pressure cylinder 1; the low-pressure cooling main line 3 and the low-pressure cooling bypass 4 are used to transport cooling steam to the low-pressure cylinder 2 under different working conditions;

[0005] A low-pressure steam inlet thermocouple 8, a low-pressure steam inlet pressure transmitter 9, a low-pressure cooling main line 3 and a low-pressure cooling bypass line 4 are connected to the steam inlet of the low-pressure cylinder 2; wherein the low-pressure steam inlet thermocouple 8 is used to measure the real-time steam temperature of the steam inlet of the low-pressure cylinder 2; the low-pressure steam inlet pressure transmitter 9 is used to measure the real-time steam pressure of the steam inlet of the low-pressure cylinder 2;

[0006] A low-pressure exhaust steam pressure transmitter 10 is connected to the exhaust of the low-pressure cylinder 2; the low-pressure exhaust steam pressure transmitter 10 is used to measure the real-time steam pressure of the exhaust steam of the low-pressure cylinder 2;

[0007] A main butterfly valve 11 is connected to the low-pressure cooling main line 3, and when the low-pressure cylinder cutting operation is in progress, the main butterfly valve 11 on the low-pressure cooling main line 3 is in a fully closed state, that is, when the low-pressure cylinder cutting operation is in progress, the cooling steam delivered to the low-pressure cylinder 2 flows through the low-pressure cooling bypass 4;

[0008] A cooling steam regulating valve 12 is connected to the low-pressure cooling bypass 4, and a pre-metering thermocouple 13, a pre-metering pressure transmitter 14 and a flowmeter 15 are connected to the low-pressure cooling bypass 4 downstream of the cooling steam regulating valve 12; wherein, the cooling steam regulating valve 12 is used to adjust the cooling steam flow entering the low-pressure cylinder 2; the flowmeter 15 needs to form temperature measuring points and pressure measuring points before and after according to the working characteristics, so the pre-metering thermocouple 13 and the pre-metering pressure transmitter 14 cooperate with the low-pressure steam inlet thermocouple 8 and the low-pressure steam inlet pressure transmitter 9 at the steam inlet of the low-pressure cylinder 2 to enable the flowmeter 15 to measure the cooling steam flow.

[0009] In the low-pressure cylinder cutting system of the above-mentioned medium-pressure exhaust steam heating unit, the flow meter on the low-pressure cooling bypass continuously monitors the minimum steam inlet cooling flow rate to ensure the safe operation of the low-pressure cylinder.

[0010] However, in the low-pressure cylinder cutting system of the above-mentioned medium-pressure exhaust steam heating unit, not only is it necessary to add a pre-metering thermocouple and a pre-metering pressure transmitter to match the flow meter on the low-pressure cooling bypass, but also, due to the working characteristics of the flow meter, it is required to form a straight pipe section of at least 5 times the DN length before the installation position and a straight pipe section of at least 2 times the DN length after the installation position, otherwise there will be a large error in the measurement result. In this way, the above-mentioned low-pressure cylinder cutting cooling flow monitoring technology is not conducive to the compactness and flexibility of the structure of the steam turbine unit in the field modification. In addition, the price of the flow meter is relatively expensive, and it needs to be regularly dismantled for inspection and installation after inspection after service, which increases the cost of cylinder cutting modification. Summary of the invention

[0011] The technical purpose of the present invention is to provide a low-pressure cylinder cutting system with a compact and flexible structure that is conducive to on-site transformation of steam turbine units and reduces transformation and maintenance costs, as well as an online acquisition method for the low-pressure cylinder cutting cooling flow based on the low-pressure cylinder cutting system, in view of the particularity of the cylinder cutting transformation of the above-mentioned medium-pressure exhaust steam heating unit and the shortcomings of the existing technology.

[0012] The technical purpose of the present invention is achieved through the following technical solution: a low-pressure cylinder cutting system, comprising a medium-pressure cylinder and a low-pressure cylinder;

[0013] The exhaust of the medium-pressure cylinder is connected with a medium-pressure exhaust thermocouple, a medium-pressure exhaust pressure transmitter, a low-pressure cooling main line, a low-pressure cooling bypass and a heating pipeline;

[0014] The steam inlet of the low-pressure cylinder is connected with a low-pressure steam inlet thermocouple, a low-pressure steam inlet pressure transmitter, a low-pressure cooling main line and a low-pressure cooling bypass, and the steam exhaust of the low-pressure cylinder is connected with a low-pressure exhaust pressure transmitter;

[0015] The low-pressure cooling main line is connected with a main butterfly valve, and during low-pressure cylinder cutting operation, the main butterfly valve on the low-pressure cooling main line is in a fully closed state;

[0016] The low-pressure cooling bypass is connected with a cooling steam regulating valve, and there is no flow meter, pre-metering thermocouple, and pre-metering pressure transmitter on the low-pressure cooling bypass.

[0017] The low-pressure cylinder cutting system is used to cut cylinders and supply heat to the medium-pressure exhaust steam heating unit when the load is low.

[0018] An online acquisition method for the low-pressure cylinder cutting cooling flow of the above-mentioned low-pressure cylinder cutting system, the online acquisition method comprises the following process steps:

[0019] Step 1. In the unit performance assessment or supervision test before the low-pressure cylinder cutting operation, a full cutting test of the low-pressure heater on the low-pressure cylinder is carried out, and the current low-pressure inlet steam temperature is measured by the low-pressure inlet steam thermocouple, the current low-pressure inlet steam pressure is measured by the low-pressure inlet steam pressure transmitter, and the current low-pressure exhaust steam pressure is measured by the low-pressure exhaust steam pressure transmitter, and the steam flow at the low-pressure cylinder steam inlet is obtained by joint calculation;

[0020] Step 2. Calculate the flow characteristic coefficient of the low-pressure flow part based on the steam flow at the low-pressure cylinder steam inlet under the low-pressure heater full cut test on the low-pressure cylinder, and the corresponding low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure exhaust pressure;

[0021] Step 3. During low-pressure cylinder cutting operation, the current low-pressure steam inlet temperature is measured by a low-pressure steam inlet thermocouple, the current low-pressure steam inlet pressure is measured by a low-pressure steam inlet pressure transmitter, and the current low-pressure exhaust pressure is measured by a low-pressure steam exhaust pressure transmitter. The steam flow rate of the low-pressure cylinder steam inlet at the current time of collection during low-pressure cylinder cutting operation is calculated by combining the obtained low-pressure flow part flow characteristic coefficient with the current low-pressure steam inlet temperature, low-pressure steam inlet pressure, and low-pressure exhaust pressure.

[0022] In step 1, the steam flow at the low-pressure cylinder inlet is calculated by combining the low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure exhaust pressure, which is carried out according to the PTC6 procedure in the ASME performance test standard.

[0023] In step 2, the flow characteristic coefficient of the low-pressure flow portion satisfies the following relationship:

[0024]

[0025] Where:

[0026] f is the flow characteristic coefficient of the low-pressure flow part;

[0027] G0 is the steam flow rate at the steam inlet of the low-pressure cylinder under the full cut-off test of the low-pressure heater on the low-pressure cylinder, in t / h;

[0028] P0 is the low-pressure steam inlet pressure measured by the low-pressure steam inlet pressure transmitter under the full cut-off test of the low-pressure heater on the low-pressure cylinder, in MPa;

[0029] P K0 It is the low-pressure exhaust steam pressure measured by the low-pressure exhaust steam pressure transmitter under the low-pressure heater full cut test on the low-pressure cylinder, in MPa;

[0030] T0 is the low-pressure inlet steam temperature measured by the low-pressure exhaust steam inlet thermocouple under the full cut test of the low-pressure heater on the low-pressure cylinder, in K.

[0031] In step 3, the steam flow at the low-pressure cylinder steam inlet during low-pressure cylinder cutting operation is calculated by combining the obtained low-pressure flow characteristic coefficient with the low-pressure steam inlet temperature, low-pressure steam inlet pressure, and low-pressure exhaust pressure, and satisfies the following relationship:

[0032]

[0033] Where:

[0034] G1 is the steam flow rate at the low-pressure cylinder steam inlet during low-pressure cylinder cutting operation at the time of current collection, in t / h;

[0035] f is the flow characteristic coefficient of the low-pressure flow part;

[0036] P 01 It is the low-pressure steam inlet pressure transmitter during low-pressure cylinder cutting operation. It is the low-pressure steam inlet pressure measured during the current collection, in MPa.

[0037] P K1 It is the low-pressure exhaust steam pressure transmitter during low-pressure cylinder cutting operation. It measures the low-pressure exhaust steam pressure during the current collection, in MPa.

[0038] T 01 It is the low-pressure exhaust steam inlet thermocouple during low-pressure cylinder cutting operation. It is the low-pressure steam inlet temperature measured during the current collection, in K.

[0039] The beneficial technical effect of the present invention is: the above-mentioned technical measures are aimed at the technical particularities of the cylinder cutting transformation of the above-mentioned medium-pressure exhaust steam heating unit. The flow meter originally used to monitor the low-pressure cylinder cutting cooling flow on the low-pressure cooling bypass is removed in the low-pressure cylinder cutting system, as well as the pre-metering thermocouple and pre-metering pressure transmitter that cooperate with the original flow meter. In this way, when the medium-pressure exhaust steam heating unit is subjected to on-site cylinder cutting transformation, there is no need to consider the installation technical requirements of the flow meter, which is conducive to carrying out compact and flexible cylinder cutting transformation according to local conditions based on the on-site environment, with strong operability and greatly reducing the transformation and maintenance costs.

[0040] Based on the above-mentioned low-pressure cylinder cutting system, the cooling flow monitoring of the low-pressure cylinder cutting is changed to an online calculation with good flexibility and high accuracy. That is, the calculation results of the real-time low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure exhaust pressure under the formal operating conditions are corrected based on the flow characteristic coefficient of the low-pressure flow part obtained under the test working condition, so as to obtain a high-accuracy low-pressure cooling flow. This can be achieved on the basis of the original temperature measuring point and pressure measuring point hardware, without the need to add additional related hardware for cooling flow monitoring. While meeting the technical requirements, the transformation and operation and maintenance costs are low and the economy is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a structural schematic diagram of the existing low-pressure cylinder cutting system of the medium-pressure exhaust steam heating unit.

[0042] Figure 2 It is a structural schematic diagram of the present invention.

[0043] The meaning of the codes in the figure are: 1—medium-pressure cylinder; 2—low-pressure cylinder; 3—low-pressure cooling main line; 4—low-pressure cooling bypass; 5—heating pipeline; 6—medium-pressure exhaust steam thermocouple; 7—medium-pressure exhaust steam pressure transmitter; 8—low-pressure inlet steam thermocouple; 9—low-pressure inlet steam pressure transmitter; 10—low-pressure exhaust steam pressure transmitter; 11—main butterfly valve; 12—cooling steam regulating valve; 13—thermocouple before metering; 14—pressure transmitter before metering; 15—flow meter. DETAILED DESCRIPTION

[0044] The present invention relates to an operation control technology for an extraction steam heating steam turbine unit, specifically a low-pressure cylinder cutting system for a medium-pressure exhaust steam heating unit, and an online acquisition method for the low-pressure cylinder cutting cooling flow based on the low-pressure cylinder cutting system. Figure 2 The technical solution of the present invention is explained clearly and in detail.

[0045] It should be noted that the drawings of the present invention are schematic, and unnecessary details have been simplified to clarify the technical purpose of the present invention, so as to avoid blurring the technical solution of the present invention that contributes to the prior art. In addition, the expressions "approximately", "substantially" and the like regarding quantity or matching relationship in the following text mean that reasonable assembly errors and processing errors in the industry are allowed to exist, and do not literally express absolute quantities or matching relationships.

[0046] The low-pressure cylinder cutting system of the present invention is to cut cylinders and heat the medium-pressure exhaust steam heating unit when it is put into operation at low load. Figure 2 As shown, the low-pressure cylinder cutting system of the present invention comprises a medium-pressure cylinder 1 and a low-pressure cylinder 2.

[0047] Specifically, the exhaust of the medium-pressure cylinder 1 (or the medium-pressure exhaust pipeline) is connected with a medium-pressure exhaust thermocouple 6, a medium-pressure exhaust pressure transmitter 7, a low-pressure cooling main line 3, a low-pressure cooling bypass 4 and a heating pipeline 5. Among them, the low-pressure cooling main line 3, the low-pressure cooling bypass 4 and the heating pipeline 5 are located downstream of the medium-pressure exhaust thermocouple 6 and the medium-pressure exhaust pressure transmitter 7. The medium-pressure exhaust thermocouple 6 is used to measure the real-time steam temperature of the exhaust of the medium-pressure cylinder 1. The medium-pressure exhaust pressure transmitter 7 is used to measure the real-time steam pressure of the exhaust of the medium-pressure cylinder 1. The low-pressure cooling main line 3 and the low-pressure cooling bypass 4 are used to transport cooling steam to the low-pressure cylinder 2 under different working conditions, that is, in the non-cylinder cutting operation state, the low-pressure cooling main line 3 is used to transport cooling steam to the low-pressure cylinder 2; in the cylinder cutting operation state, the low-pressure cooling bypass 4 is used to transport cooling steam to the low-pressure cylinder 2.

[0048] A low-pressure steam inlet thermocouple 8, a low-pressure steam inlet pressure transmitter 9, a low-pressure cooling main line 3 and a low-pressure cooling bypass 4 are connected to the steam inlet of the low-pressure cylinder 2 (or the low-pressure steam inlet pipeline). The low-pressure cooling main line 3 and the low-pressure cooling bypass 4 are located upstream of the low-pressure steam inlet thermocouple 8 and the low-pressure steam inlet pressure transmitter 9. The low-pressure steam inlet thermocouple 8 is used to measure the real-time steam temperature of the low-pressure cylinder 2 steam inlet. The low-pressure steam inlet pressure transmitter 9 is used to measure the real-time steam pressure of the low-pressure cylinder 2 steam inlet.

[0049] A low-pressure exhaust steam pressure transmitter 10 is connected to the exhaust of the low-pressure cylinder 2 (or the low-pressure exhaust steam pipeline). The low-pressure exhaust steam pressure transmitter 10 is used to measure the real-time steam pressure of the low-pressure cylinder 2 exhaust steam.

[0050] A main butterfly valve 11 is connected to the low-pressure cooling main line 3, and when the low-pressure cylinder cutting operation is in progress, the main butterfly valve 11 on the low-pressure cooling main line 3 is in a fully closed state, that is, when the low-pressure cylinder cutting operation is in progress, the cooling steam delivered to the low-pressure cylinder 2 flows through the low-pressure cooling bypass 4.

[0051] A cooling steam regulating valve 12 is connected to the low-pressure cooling bypass 4. The cooling steam regulating valve 12 is used to regulate the cooling steam flow entering the low-pressure cylinder 2. There is no connection of a pre-metering thermocouple, a pre-metering pressure transmitter, and a flow meter on the low-pressure cooling bypass 4 downstream of the cooling steam regulating valve 12. In other words, Figure 1 The existing low-pressure cylinder cutting system shown in the figure, the modification of the low-pressure cylinder cutting system of the present invention is to remove the pre-metering thermocouple 13, the pre-metering pressure transmitter 14 and the flow meter 15 on the low-pressure cooling bypass 4, so there is no need to consider their purchase and subsequent maintenance costs, and there is no need to consider their modification and installation technical requirements.

[0052] For the low-pressure cylinder cutting system with the above structural characteristics, according to the low-pressure cylinder's own flow that meets the flow stage group characteristics when the low-pressure heating extraction steam is cut off, the low-pressure flow rheological operating parameters can be analyzed using the Flugel formula. Specifically, in order to achieve continuous and accurate monitoring of the low-pressure cylinder cutting cooling flow, a low-pressure heater full-cut test condition is added on the low-pressure cylinder during the unit performance assessment or supervision test. Through the existing temperature and pressure measuring points at the low-pressure steam inlet and low-pressure exhaust, a set of relatively accurate low-pressure steam inlet pressure, low-pressure steam inlet temperature, and low-pressure exhaust pressure are obtained. The corresponding steam flow at the low-pressure cylinder steam inlet at this time is obtained through comprehensive calculation of the performance test data, and then the low-pressure flow characteristic coefficient f at this time is further calculated; when the heating cylinder cutting operation is in progress, the low-pressure heater on the low-pressure cylinder is fully cut off, and through the existing temperature and pressure measuring points at the low-pressure steam inlet and low-pressure exhaust, the low-pressure steam inlet pressure 1, low-pressure steam inlet temperature and low-pressure exhaust pressure are obtained. The corresponding relatively accurate low-pressure steam inlet steam flow at this time can be calculated online through the Flügel formula, thereby realizing the online calculation and acquisition of the low-pressure cylinder cutting cooling flow (relevant computer programming needs to be input into the turbine control system), without relying on the hardware investment of flow monitoring.

[0053] Based on this, the present invention provides a method for online obtaining the low-pressure cylinder cutting cooling flow rate of the low-pressure cylinder cutting system, which includes the following process steps:

[0054] Step 1. In the unit performance assessment or supervision test before the low-pressure cylinder cut-off operation, carry out the low-pressure heater full cut-off test on the low-pressure cylinder;

[0055] In this test, the current low-pressure steam inlet temperature T0 is measured by the low-pressure steam inlet thermocouple 8, the current low-pressure steam inlet pressure P0 is measured by the low-pressure steam inlet pressure transmitter 9, and the current low-pressure steam exhaust pressure P is measured by the low-pressure steam exhaust pressure transmitter 10. K0 , the measured low-pressure steam inlet temperature T0, low-pressure steam inlet pressure P0 and low-pressure exhaust pressure P K0 Carry out joint calculation according to the PTC6 procedure in the ASME performance test standard to obtain the steam flow G0 at the steam inlet of the low-pressure cylinder;

[0056] Step 2. Take the steam flow rate G0 at the steam inlet of the low-pressure cylinder under the full cut test of the low-pressure heater on the low-pressure cylinder, and the corresponding low-pressure steam inlet temperature T0, low-pressure steam inlet pressure P0 and low-pressure exhaust pressure P K0 , calculate and obtain the flow characteristic coefficient f of the low-pressure flow part;

[0057] The calculation of the flow characteristic coefficient f of the low-pressure flow part satisfies the following relationship:

[0058]

[0059] Where:

[0060] f is the flow characteristic coefficient of the low-pressure flow part;

[0061] G0 is the steam flow rate at the steam inlet of the low-pressure cylinder under the full cut-off test of the low-pressure heater on the low-pressure cylinder, in t / h;

[0062] P0 is the low-pressure steam inlet pressure measured by the low-pressure steam inlet pressure transmitter under the full cut-off test of the low-pressure heater on the low-pressure cylinder, in MPa;

[0063] P K0 It is the low-pressure exhaust steam pressure measured by the low-pressure exhaust steam pressure transmitter under the low-pressure heater full cut test on the low-pressure cylinder, in MPa;

[0064] T0 is the low-pressure inlet steam temperature measured by the low-pressure exhaust steam inlet thermocouple under the low-pressure heater full cut test on the low-pressure cylinder, in K;

[0065] Step 3: During low-pressure cylinder cutting operation, the current low-pressure steam inlet temperature T is measured using the low-pressure steam inlet thermocouple 8. 01 , the low-pressure steam inlet pressure transmitter 9 measures the current low-pressure steam inlet pressure P 01 , the low-pressure exhaust steam pressure transmitter 10 measures the current low-pressure exhaust steam pressure P K1 , through the obtained low-pressure flow characteristic coefficient f, combined with the current low-pressure steam inlet temperature T 01 , low pressure steam inlet pressure P 01 , low pressure exhaust steam pressure P K1 Calculate and obtain the steam flow G1 of the low-pressure cylinder steam inlet at the current time of collection when the low-pressure cylinder cut operation is in progress;

[0066] By using the obtained low-pressure flow characteristic coefficient f, combined with the current low-pressure steam inlet temperature T 01 , low pressure steam inlet pressure P 01 , low pressure exhaust steam pressure P K1 The steam flow calculation at the low-pressure cylinder steam inlet satisfies the following relationship:

[0067]

[0068] Where:

[0069] G1 is the steam flow rate at the low-pressure cylinder steam inlet during low-pressure cylinder cutting operation at the time of current collection, in t / h;

[0070] f is the flow characteristic coefficient of the low-pressure flow part;

[0071] P 01 It is the low-pressure steam inlet pressure transmitter during low-pressure cylinder cutting operation. It is the low-pressure steam inlet pressure measured during the current collection, in MPa.

[0072] P K1It is the low-pressure exhaust steam pressure transmitter during low-pressure cylinder cutting operation. It measures the low-pressure exhaust steam pressure during the current collection, in MPa.

[0073] T 01 It is the low-pressure exhaust steam inlet thermocouple during low-pressure cylinder cutting operation. It is the low-pressure steam inlet temperature measured during the current collection, in K.

[0074] In the above step 2, when the low pressure exhaust steam pressure P K When it is low and close to 0, it can be simplified as follows:

[0075]

[0076] In the above step 3, when the low pressure exhaust steam pressure P K When it is low and close to 0, it can be simplified as follows:

[0077]

[0078] The above specific technical solutions are only used to illustrate the present invention rather than to limit it.

[0079] Although the present invention is described in detail with reference to the above specific technical solutions, those skilled in the art should understand that they can still modify the above specific technical solutions or replace some of the technical features therein by equivalents. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the present invention.

Claims

1. A low-pressure cylinder cutting system, comprising a medium-pressure cylinder (1) and a low-pressure cylinder (2); The exhaust port of the medium-pressure cylinder (1) is connected to a medium-pressure exhaust thermocouple (6), a medium-pressure exhaust pressure transmitter (7), a low-pressure cooling main line (3), a low-pressure cooling bypass (4) and a heating pipeline (5); The steam inlet of the low-pressure cylinder (2) is connected to a low-pressure steam inlet thermocouple (8), a low-pressure steam inlet pressure transmitter (9), a low-pressure cooling main line (3) and a low-pressure cooling bypass line (4), and the steam exhaust of the low-pressure cylinder (2) is connected to a low-pressure exhaust steam pressure transmitter (10); The low-pressure cooling main line (3) is connected to a main butterfly valve (11), and during low-pressure cylinder cutting operation, the main butterfly valve (11) on the low-pressure cooling main line (3) is in a fully closed state; Features: The low-pressure cooling bypass (4) is connected to a cooling steam regulating valve (12), and the low-pressure cooling bypass (4) is free of a flow meter, a pre-metering thermocouple, and a pre-metering pressure transmitter.

2. According to claim 1, the low-pressure cylinder cutting system, Features: The low-pressure cylinder cutting system is used to cut cylinders and supply heat to the medium-pressure exhaust steam heating unit when the load is low.

3. A method for online acquisition of low-pressure cylinder cutting cooling flow of the low-pressure cylinder cutting system according to claim 1 or 2, It is characterized in that The online acquisition method comprises the following process steps: Step 1. In the unit performance assessment or supervision test before the low-pressure cylinder cutting operation, a full cutting test of the low-pressure heater on the low-pressure cylinder is carried out, and the current low-pressure inlet steam temperature is measured by the low-pressure inlet steam thermocouple, the current low-pressure inlet steam pressure is measured by the low-pressure inlet steam pressure transmitter, and the current low-pressure exhaust steam pressure is measured by the low-pressure exhaust steam pressure transmitter, and the steam flow at the low-pressure cylinder steam inlet is obtained by joint calculation; Step 2. Calculate the flow characteristic coefficient of the low-pressure flow part based on the steam flow at the low-pressure cylinder steam inlet under the low-pressure heater full cut test on the low-pressure cylinder, and the corresponding low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure exhaust pressure; Step 3. During low-pressure cylinder cutting operation, the current low-pressure steam inlet temperature is measured by a low-pressure steam inlet thermocouple, the current low-pressure steam inlet pressure is measured by a low-pressure steam inlet pressure transmitter, and the current low-pressure exhaust pressure is measured by a low-pressure steam exhaust pressure transmitter. The steam flow rate of the low-pressure cylinder steam inlet at the current time of collection during low-pressure cylinder cutting operation is calculated by combining the obtained low-pressure flow part flow characteristic coefficient with the current low-pressure steam inlet temperature, low-pressure steam inlet pressure, and low-pressure exhaust pressure.

4. According to the method for online acquisition of low-pressure cylinder cutting cooling flow rate in claim 3, Features: In step 1, the steam flow at the low-pressure cylinder inlet is calculated by combining the low-pressure steam inlet temperature, low-pressure steam inlet pressure and low-pressure exhaust pressure, which is carried out according to the PTC6 procedure in the ASME performance test standard.

5. According to the method for online acquisition of low-pressure cylinder cutting cooling flow rate in claim 3, Features: In step 2, the flow characteristic coefficient of the low-pressure flow portion satisfies the following relationship: Where: f is the flow characteristic coefficient of the low-pressure flow part; G 0 It is the steam flow rate at the steam inlet of the low-pressure cylinder under the full cut-off test of the low-pressure heater on the low-pressure cylinder, in t / h; P 0 It is the low-pressure steam inlet pressure measured by the low-pressure steam inlet pressure transmitter under the low-pressure heater full cut test on the low-pressure cylinder, in MPa; P K0 It is the low-pressure exhaust steam pressure measured by the low-pressure exhaust steam pressure transmitter under the low-pressure heater full cut test on the low-pressure cylinder, in MPa; T 0 It is the low-pressure inlet steam temperature measured by the low-pressure exhaust inlet thermocouple under the full-cut test of the low-pressure heater on the low-pressure cylinder, the unit is K.

6. According to the method for online acquisition of low-pressure cylinder cutting cooling flow rate in claim 1, Features: In step 3, the steam flow at the low-pressure cylinder steam inlet during low-pressure cylinder cutting operation is calculated by combining the obtained low-pressure flow characteristic coefficient with the low-pressure steam inlet temperature, low-pressure steam inlet pressure, and low-pressure exhaust pressure, and satisfies the following relationship: Where: G 1 It is the steam flow rate at the steam inlet of the low-pressure cylinder during low-pressure cylinder cutting operation at the time of current collection, in t / h; f is the flow characteristic coefficient of the low-pressure flow part; P 01 It is the low-pressure steam inlet pressure transmitter during low-pressure cylinder cutting operation. It is the low-pressure steam inlet pressure measured during the current collection, in MPa. P K1 It is the low-pressure exhaust steam pressure transmitter during low-pressure cylinder cutting operation. It measures the low-pressure exhaust steam pressure during the current collection, in MPa. T 01 It is the low-pressure exhaust steam inlet thermocouple during low-pressure cylinder cutting operation. It is the low-pressure steam inlet temperature measured during the current collection, in K.

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