Online cleaning method for header system steam turbine

Abstract

The invention discloses an on-line cleaning method for a header system steam turbine, which belongs to the technical field of header system steam turbines, and comprises the following steps: setting temperature and pressure measuring points between the left and right sides of an electric main steam valve for steam admission of a unit and between the left and right sides of an automatic main steam valve, and setting a temperature measuring point on upper half metal of a regulating stage of a high-pressure and medium-pressure inner cylinder of the unit; closely monitoring related parameters of the unit through the temperature and pressure measuring points after the unit is stopped; and heating a steam inlet pipeline of the unit, and starting online cleaning when the steam inlet temperature of the unit is higher than the saturation temperature under the corresponding steam inlet pressure, low-superheat-degree steam is formed and the steam inlet temperature is higher than the upper half metal temperature of the regulating stage of the high-medium-pressure inner cylinder of the unit. The steam inlet temperature of the steam turbine is adjusted to be slightly higher than the corresponding saturation temperature of the steam turbine, low-superheat-degree steam is formed, in the low-rotating-speed acting process of a unit, salt scales on the blades are scoured, the salt scales accumulated on the blades are dissolved in the scoured steam, and therefore the purpose of online cleaning is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of main pipe steam turbines, and in particular to an online cleaning method for main pipe steam turbines. Background Art

[0002] The steam turbine unit of the thermal power department is equipped with three steam turbine generator sets (two 135MW direct air-cooled condensing units and one 30MW back-pressure unit), and all the units use the main pipe steam supply method. During operation, it was found that the #2 steam turbine (135MW direct air-cooled condensing unit) had insufficient load capacity under pure condensing conditions, and the situation became more and more serious over time. After analysis, it was determined that it might be caused by scaling in the flow part of the unit.

[0003] There are two mature technical solutions for dealing with scaling of the flow passage of steam turbines. One is to open the cylinder for cleaning. This method is more thorough and effective, but has the disadvantages of long unit shutdown time, high cost, and high technical difficulty. It is not suitable for the current high-load production situation of the branch company. The other is to cool and reduce the pressure of the steam turbine for online cleaning (using the working principle of wet steam dissolving sodium salt). This method costs less, takes less time, and has good results, but has the disadvantage that it is easier to implement for unit-type units. For mother pipe control units, it is impossible to adjust the steam inlet temperature and pressure of a single unit under normal production conditions, which is not feasible. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention provides an online cleaning method for a main pipe steam turbine, the method comprising:

[0005] S1: Set temperature and pressure measuring points between the left and right sides of the unit's steam inlet electric main steam valve and the left and right sides of the automatic main steam valve, and set a temperature measuring point on the upper metal of the unit's high and medium pressure inner cylinder regulating stage;

[0006] S2: After the unit is shut down, closely monitor the relevant parameters of the unit through the temperature and pressure measuring points;

[0007] S3: Warm up the steam inlet pipes of the unit. When the steam inlet temperature of the unit is higher than the saturation temperature at the corresponding steam inlet pressure, low superheated steam is formed, and the steam inlet temperature is higher than the upper metal temperature of the high and medium pressure inner cylinder regulating stage of the unit, the conditions for online cleaning are met;

[0008] S4: Start online cleaning.

[0009] Furthermore, in S3, when the inlet steam temperature is 50°C higher than the upper metal temperature of the high and medium pressure inner cylinder regulating stage of the unit, the conditions for online cleaning are met.

[0010] Furthermore, in S3, the operation of warming up the steam inlet pipe of the unit specifically includes:

[0011] Two bypass pipelines are set between the main steam main pipe and the unit steam inlet electric isolation door, and two bypass valves are set on each bypass pipeline; steam traps are set on the pipelines on the left and right sides of the unit steam inlet electric main steam door respectively;

[0012] The steam inlet flow rate is controlled by four bypass valves and two steam traps, thereby controlling the temperature rise rate of the steam inlet pipeline.

[0013] Furthermore, in S4, during online flushing, the steam inlet flow is controlled to be a small flow steam through four bypass valves and two steam traps, and the unit is flushed and cleaned at a low speed.

[0014] Furthermore, the low speed is 600 rpm and the acceleration rate is 200 r / min.

[0015] The technical solution provided by the embodiment of the present invention has the following beneficial effects: in the present invention, temperature and pressure measuring points are set between the left and right sides of the unit's steam inlet electric main steam valve and the left and right sides of the automatic main steam valve, and a temperature measuring point is set on the upper metal of the high- and medium-pressure inner cylinder regulating stage of the unit. When the unit's steam inlet temperature is higher than the saturation temperature at the corresponding steam inlet pressure and the steam inlet temperature is higher than the upper metal temperature of the high- and medium-pressure inner cylinder regulating stage of the unit, online cleaning is performed. The characteristic that the lower the temperature, the greater the solubility of sodium salts and silicates in superheated steam under constant pressure is mainly utilized. The steam inlet temperature of the turbine is adjusted to be slightly higher than its corresponding saturation temperature to form low superheated steam. In the process of the unit working at low speed, the salt scale on the blades is flushed. The characteristic of its high solubility is utilized to dissolve the salt scale accumulated on the blades in the flushing steam and be carried out of the system by the working steam, thereby achieving the purpose of dissolving the salt scale and cleaning the unit online. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 The present invention provides a schematic flow chart of an online cleaning method for a mother pipe steam turbine.

[0018] Figure numerals: 1-temperature and pressure measuring point; 2-temperature measuring point; 3-bypass valve; 4-drain valve. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Embodiment 1

[0022] A method for online cleaning of a main pipe steam turbine comprises the following steps:

[0023] Step (101): temperature and pressure measuring points 1 are set between the left and right sides of the unit's steam inlet electric main steam valve and the left and right sides of the automatic main steam valve, and temperature measuring point 2 is set on the upper metal of the unit's high and medium pressure inner cylinder regulating stage.

[0024] Step (102): After the unit is shut down, the temperature and pressure of the unit are monitored by the temperature sensor and pressure sensor at the temperature and pressure measuring point 1, and the temperature sensor at the temperature measuring point 2.

[0025] Step (103): The steam inlet pipeline of the unit is heated. During the heating, the electric isolation door from the main steam main pipe to the unit steam inlet pipeline shall not be used. Instead, two bypass pipelines should be set between the main steam main pipe and the unit steam inlet electric isolation door. Two bypass valves 3 are set on each bypass pipeline; steam traps 4 are respectively set on the pipelines behind the left and right sides of the unit steam inlet electric main steam valve. The steam inlet flow rate is controlled by four bypass valves and two steam traps, so that the steam flow rate is a small flow rate, thereby controlling the temperature rise rate of the steam inlet pipeline.

[0026] When the unit's steam inlet temperature is slightly higher than the saturation temperature at the corresponding steam inlet pressure, forming low superheated steam, and the steam inlet temperature is 50°C higher than the upper metal temperature of the unit's high and medium pressure inner cylinder regulating stage, the cleaning conditions are met.

[0027] Step (104): Calculate the maximum steam inlet flow rate and maximum flushing speed that can be reached by the unit's steam inlet bypass. Considering the safety and applicability of the unit, select a lower cleaning speed. Use four bypass valves and two steam traps to control the steam inlet flow rate to a small flow rate of steam, and perform low-speed flushing cleaning on the unit. In this embodiment, the speed is 600 rpm and the acceleration rate is 200 r / min.

[0028] It is worth mentioning that the present invention mainly utilizes the characteristic that sodium salts and silicates have greater solubility as the temperature becomes lower when the pressure in superheated steam is constant, and adjusts the steam inlet temperature of the turbine to be slightly higher than its corresponding saturation temperature to form low superheated steam. In the process of the unit working at a low speed, the salt scale on the blades is flushed, and the high solubility characteristic is utilized to dissolve the salt scale accumulated on the blades in the flushing steam and is carried out of the system by the working steam, thereby achieving the purpose of dissolving the salt scale and cleaning the unit online.

[0029] Embodiment 2

[0030] A method for online cleaning of a main pipe steam turbine comprises the following steps:

[0031] Step (201): At 10:00 on May 6, the #2 steam turbine was shut down. Before flushing at 17:00 on May 8, the #2 steam turbine steam inlet electric main steam valve (left and right) was fully opened. The steam inlet pipeline parameters were ( Figure 1 Measuring point 1 and 2 in the unit): 0MPa, 264.2℃; upper metal temperature of the high and medium pressure inner cylinder regulating stage of the unit ( Figure 1 The measuring point 3) is 297.7℃.

[0032] Step (202): From 17:40 on May 8 to 18:23 on May 8, the #2 steam turbine automatic main steam valve front steam pipe was warmed up using the bypass valve from the #1 and #2 main steam main pipes at the 18-meter level to the #2 steam turbine steam inlet electric valve, as well as the drain valves of the left and right rear pipelines of the unit's steam inlet electric main steam valve; at 18:23:58, the main steam pressure before the automatic main steam valve was 10.8 MPa, the main steam temperature was 348.125°C, the steam inlet pipe warming was completed, and the conditions for online flushing were met; (10.8 MPa corresponds to a saturation temperature of 317°C, and the steam superheat is 31°C at this time).

[0033] Step (203): May 8, 18:23:58; Online cleaning of #2 steam turbine begins, setting the target speed to 600 rpm and the acceleration rate to 200 r / min, and starting online cleaning.

[0034] Step (204): At 18:45:35 on May 8, the cleaning was completed. At this time, the main steam pressure was 12.496 MPa; the main steam temperature was 400°C, and the speed of the #2 turbine was 600 rpm; (12.496 MPa corresponds to a saturation temperature of 328°C).

[0035] Step (205): At 23:12:25 on May 8, the #2 steam turbine was loaded to 143MW in pure condensing conditions, which was nearly 30MW higher than the maximum load of 114MW in pure condensing conditions before flushing.

[0036] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for online cleaning of a main pipe steam turbine, characterized in that: The method comprises: S1: Set temperature and pressure measuring points between the left and right sides of the unit's steam inlet electric main steam valve and the left and right sides of the automatic main steam valve, and set a temperature measuring point on the upper metal of the unit's high and medium pressure inner cylinder regulating stage; S2: After the unit is shut down, closely monitor the relevant parameters of the unit through the temperature and pressure measuring points; S3: Warm up the steam inlet pipes of the unit. When the steam inlet temperature of the unit is higher than the saturation temperature at the corresponding steam inlet pressure, low superheated steam is formed, and the steam inlet temperature is higher than the upper metal temperature of the high and medium pressure inner cylinder regulating stage of the unit, the conditions for online cleaning are met; S4: Start online cleaning.

2. The method for online cleaning of a main pipe steam turbine according to claim 1, characterized in that: In S3, when the steam inlet temperature (low superheated steam) is 50°C higher than the upper metal temperature of the high and medium pressure inner cylinder regulating stage of the unit, the conditions for online cleaning are met.

3. The method for online cleaning of a main pipe steam turbine according to claim 1, characterized in that: In S3, the specific operation of warming up the steam inlet pipe of the unit includes: Two bypass pipelines are set between the main steam main pipe and the unit steam inlet electric isolation door, and two bypass valves are set on each bypass pipeline; steam traps are set on the pipelines on the left and right sides of the unit steam inlet electric main steam door respectively; The steam inlet flow rate is controlled by four bypass valves and two steam traps, thereby controlling the temperature rise rate of the steam inlet pipeline.

4. The method for online cleaning of a main pipe steam turbine according to claim 3, characterized in that: In S4, during online flushing, the steam inlet flow is controlled to be a small flow steam through four bypass valves and two steam traps, and the unit is flushed and cleaned at a low speed.

5. The method for online cleaning of a main pipe steam turbine according to claim 4, characterized in that: The low speed is 600 rpm and the acceleration rate is 200 r / min.

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