Power station boiler desuperheating water temperature adjusting system and control method thereof

Abstract

The invention discloses a power station boiler desuperheating water temperature adjusting system and a control method thereof.The power station boiler desuperheating water temperature adjusting system comprises a main desuperheating water pipeline, a preheating bypass water inlet pipeline, a furnace top small chamber and a preheating bypass water outlet pipeline, the main desuperheating water pipeline is connected with a main water supply pipeline and a desuperheater, and one end of the preheating bypass water inlet pipeline is connected with the main desuperheating water pipeline in a converged mode; the other end of the preheating pipeline is connected with one end of the preheating bypass water outlet pipeline, the other end of the preheating bypass water outlet pipeline is connected with the main desuperheating water pipeline in a converging mode, and waste heat of the furnace top small chamber provides heat to adjust the temperature of desuperheating water. The desuperheating water bypass system is additionally arranged, waste heat of the boiler is used for preheating desuperheating water, a desuperheater can be protected from being damaged due to frequent cold and hot fatigue, the service life of equipment is prolonged, and the controller dynamically adjusts the opening degree of a preheating bypass valve according to the temperature, pressure and flow parameter feedback of reheated steam, so that the temperature of the desuperheating water is stabilized at a set value.

Description

Technical Field

[0001] The invention belongs to the technical field of desuperheating water regulation, and in particular relates to a desuperheating water temperature regulation system for a power station boiler and a control method thereof. Background Art

[0002] At present, large-scale power station boilers mainly use two measures to adjust the steam temperature: water spray cooling and swing burners. Among them, water spray cooling is widely used in the steam temperature regulation of power station boilers due to its simple component structure, large temperature adjustment range, high adjustment sensitivity and easy automation. The reheater cooling water is generally pumped out by a high-pressure feed water pump. Before the cooling water is put into use, the cooling water is stored in the pipeline for a long time to form liquid water. During the commissioning process, the water spray cooler is subjected to the thermal cycle working state of rapid cooling and rapid heating of the water spray, which is easy to cause thermal fatigue fracture of the water spray cooler, posing a safety hazard to the safe and stable operation of the unit. Therefore, it is necessary to set up a power station boiler cooling water temperature regulation system to increase the commissioning temperature of the cooling water. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention aims to provide a power station boiler desuperheating water temperature regulating system and a control method thereof.

[0004] The specific technical solutions are as follows: A power station boiler desuperheating water temperature regulating system comprises a main desuperheating water pipeline, a preheating bypass water inlet pipeline, a furnace top chamber and a preheating bypass water outlet pipeline, wherein the main desuperheating water pipeline is connected to a main water supply pipeline and a desuperheater, one end of the preheating bypass water inlet pipeline is connected to the main desuperheating water pipeline, and the other end is connected to one end of a preheating pipeline in the furnace top chamber, the other end of the preheating pipeline is connected to one end of a preheating bypass water outlet pipeline, and the other end of the preheating bypass water outlet pipeline is connected to the main desuperheating water pipeline, waste heat of the furnace top chamber provides heat to regulate the desuperheating water temperature, and improves the commissioning temperature of the desuperheating water, and the desuperheater is connected to a power station boiler requiring temperature regulation.

[0005] Furthermore, a first stop valve and a first regulating valve are provided on the preheating bypass water inlet pipeline, and a second stop valve is provided on the preheating bypass water outlet pipeline.

[0006] Furthermore, a first temperature sensor and a first pressure sensor are provided on the preheating bypass water outlet pipe.

[0007] Furthermore, a second regulating valve, a third stop valve and a fourth stop valve are provided on the main desuperheating water pipeline. The third stop valve is located between the main water supply pipeline and the preheating bypass water inlet pipeline, the fourth stop valve is located between the desuperheater and the preheating bypass water outlet pipeline, and the second regulating valve is located between the preheating bypass water inlet pipeline and the preheating bypass water outlet pipeline.

[0008] Furthermore, a second temperature sensor and a second pressure sensor are provided on the main desuperheating water pipeline. The second temperature sensor is located between the main water supply pipeline and the preheating bypass water inlet pipeline, and the second pressure sensor is located between the desuperheater and the preheating bypass water outlet pipeline.

[0009] Furthermore, the heat exchange area of ​​the preheating pipeline in the furnace top chamber is not less than 3 times the heat exchange area of ​​the main desuperheating water pipeline.

[0010] A control method for a power station boiler desuperheating water temperature regulating system, comprising the following steps: 1) When the temperature of the cooling water measured by the second temperature sensor is lower than the set temperature, the third stop valve, the first stop valve and the first regulating valve are opened to allow the cooling water flowing out of the main water supply pipe to flow to the preheating bypass water inlet pipe and enter the preheating pipeline in the furnace top chamber; 2) The temperature-time curve of the preheating and cooling water in the furnace top chamber is obtained from the operating experience, and the time required for the cooling water to be preheated to the set temperature is determined according to the set temperature; 3) When the high-temperature reheat steam of the power plant boiler exceeds the set temperature or the average change rate of the reheat steam exceeds the set rate, the temperature can be adjusted by cooling water. When the first temperature sensor measures that the cooling water has reached the preset temperature, the second stop valve and the fourth stop valve are opened to allow the heated cooling water to enter the desuperheater and then be put into use in the reheater of the power plant boiler.

[0011] Furthermore, the calculation formula for the amount of desuperheating water used in the reheater is: w =M s ×C s ×(T1-T2) / C w / (T w2 -T w1 ), where M w is the desuperheating water flow rate, t / h; T w1 is the initial temperature of the cooling water, °C; T w2 is the temperature of the desuperheating water after preheating, ℃; T1 is the initial temperature of the reheated steam, ℃; T2 is the set temperature of the reheated steam, ℃; M s is the reheat steam flow rate, t / h, C s is the specific heat capacity of reheat steam, J / (kg·℃); C w is the specific heat capacity of desuperheated water, J / (kg·℃).

[0012] The beneficial effects of the present invention are: 1) Simple structure, no need to change the desuperheater structure, reliable operation.

[0013] 2) Utilize the waste heat from the boiler top chamber to reduce the energy consumption required for re-gasification of cooling water directly into the desuperheater.

[0014] 3) The present invention increases the temperature of the desuperheated water when it is put into use, thereby eliminating the potential safety hazard caused by fatigue of the desuperheater. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the desuperheating water temperature regulating system of the present invention; Figure 2 This is a flow chart of a method for controlling a desuperheating water temperature regulating system of a thermal power unit provided in an embodiment of the present invention; Figure 3 This is a curve showing the change of the medium temperature of the cooling water pipeline in the furnace top chamber over time in the embodiment of the present invention.

[0016] In the figure: 1. main cooling water pipeline; 11. main water supply pipeline; 12. desuperheater; 13. second regulating valve; 14. third stop valve; 15. fourth stop valve; 16. second temperature sensor; 17. second pressure sensor; 2. preheating bypass water inlet pipeline; 21. first stop valve; 22. first regulating valve; 3. furnace top chamber; 4. preheating bypass water outlet pipeline; 41. second stop valve; 42. first temperature sensor; 43. first pressure sensor. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with the accompanying drawings and embodiments of the specification. However, the description of the following embodiments can only be used to help understand the present invention. It should be pointed out that for ordinary personnel in this technical field, the present invention can be modified in several ways without departing from the principle of the present invention. These improvements and modifications also fall within the scope of protection of the present invention.

[0018] like Figure 1As shown, a power station boiler desuperheating water temperature regulating system comprises a main desuperheating water pipeline 1, a preheating bypass water inlet pipeline 2, a furnace top chamber 3 and a preheating bypass water outlet pipeline 4. The main desuperheating water pipeline 1 is connected to a main water supply pipeline 11 and a desuperheater 12. One end of the preheating bypass water inlet pipeline 2 is connected to the main desuperheating water pipeline 1, and the other end is connected to one end of a preheating pipeline in the furnace top chamber 3. The other end of the preheating pipeline is connected to one end of a preheating bypass water outlet pipeline 4. The other end of the preheating bypass water outlet pipeline 4 is connected to the main desuperheating water pipeline 1. The waste heat of the furnace top chamber 3 provides heat to adjust the desuperheating water temperature. The preheating bypass water inlet pipeline 2 is provided with a preheating bypass water outlet pipeline 4. There are a first stop valve 21 and a first regulating valve 22, a second stop valve 41, a first temperature sensor 42 and a first pressure sensor 43 are arranged on the preheating bypass outlet pipe 4, a second regulating valve 13, a third stop valve 14, a fourth stop valve 15, a second temperature sensor 16 and a second pressure sensor 17 are arranged on the main desuperheating water pipe 1, the third stop valve 14 and the second temperature sensor 16 are located between the main water supply pipe 11 and the preheating bypass inlet pipe 2, the fourth stop valve 15 and the second pressure sensor 17 are located between the desuperheater 12 and the preheating bypass outlet pipe 4, and the desuperheater 12 is connected to the power station boiler that needs temperature regulation. The heat exchange area of ​​the preheating pipeline in the furnace top chamber 3 is not less than 3 times the heat exchange area of ​​the main desuperheating water pipe 1.

[0019] Taking the desuperheater temperature control system as an example, the length of the main desuperheating water pipeline 1 is 150m, the length of the preheating pipeline in the furnace top chamber 3 is 450m, the pipeline adopts a serpentine pipe layout, and the diameters of the main desuperheating water pipeline 1 and the preheating pipeline are φ168×28mm.

[0020] Example 1

[0021] like Figure 2 As shown, the power plant boiler desuperheating water temperature control system of the present invention is used for a thermal power unit, and a first desuperheater (DS1) before the low temperature reheater (LRH) and a second desuperheater (DS2) before the high temperature reheater (HRH) are respectively provided with a Figure 1 The desuperheating water temperature control system shown in the figure adopts a controller (PLC) to control the valves in the control system. The desuperheating water temperature control system is arranged at both the primary desuperheater and the secondary desuperheater. On the one hand, it can better protect the desuperheater and prevent the desuperheater from thermal fatigue and cracks. On the other hand, by using the low temperature reheater (LRH) as a feedforward quantity, the temperature control system at the primary desuperheater can be started in advance, which can control the reheat steam temperature of the power station boiler more quickly.

[0022] like Figure 2 The operation of the system shown is as follows: 1) The curve of the medium temperature in the furnace top chamber 3 changing with the preheating time is obtained through experiments, such as Figure 3As shown, it should be noted that the preheating temperature is set according to the temperature of the desuperheating water in different boilers. In this embodiment, preheating the desuperheating water to 284°C does not constitute a recommended value for the preheating temperature; 2) When the temperature of the cooling water measured by the second temperature sensor 16 is lower than the set temperature (set to 220°C in this embodiment), the third stop valve 14, the first stop valve 21 and the first regulating valve 22 are opened in sequence, so that the cooling water flowing out of the main water supply pipe 11 flows to the preheating bypass water inlet pipe 2 and enters the preheating pipeline in the furnace top chamber 3. The stop valve controls the opening and closing of the pipeline, and the regulating valve regulates the flow of the medium. The opening of the third stop valve 14 and the first stop valve 21 is 100%. The control measure of the first regulating valve 22 is: slowly control the opening of the regulating valve to 10%, and then gradually control the opening to 50%, so as to avoid the rapid opening of the valve causing a sudden change in the flow rate of the medium in the pipeline, and to prevent the occurrence of pipeline water hammer, air hammer and other phenomena; 3) Close the second regulating valve 13 and the third stop valve 14, so that in the initial stage of the desuperheating water, only the preheated desuperheating water in the preheating pipeline in the furnace top chamber 3 enters the desuperheater 12, thereby protecting the desuperheater 12 and the reheater from being affected by the excessively low desuperheating water temperature and causing thermal fatigue. The desuperheating water preheating setting temperature can be higher than the original desuperheating water temperature, which can better protect the reheater and the desuperheater 12. At the same time, the higher desuperheating water temperature also increases the desuperheating water consumption and improves the evaporation capacity of the unit; 4) When the reheated steam in the power plant boiler exceeds the set temperature (480°C in this embodiment) by 5°C or the average change rate of the reheated steam exceeds the set rate (set to 1°C / min in this embodiment), the temperature can be adjusted by cooling water. When the first temperature sensor 42 measures that the cooling water reaches the preset temperature, the second stop valve 41 and the fourth stop valve 15 are opened to allow the heated cooling water to enter the desuperheater 12. The second stop valve 41 is controlled as follows: the opening is slowly controlled to 10%, and then gradually opened to 100%, to avoid rapid opening of the valve resulting in a sudden change in the flow rate of the medium in the pipeline, and to prevent pipeline water hammer, air hammer and other phenomena; 5) When the cooling water measured by the second temperature sensor 16 reaches the set temperature (220°C in this embodiment), the second stop valve 41 and the first stop valve 21 are closed, and the first regulating valve 22 is closed after a delay of 2 seconds, and then the second regulating valve 13 and the third stop valve 14 are opened, and the valve openings are controlled to be 100% and 50% respectively; 6) When the temperature of the reheated steam in the power plant boiler returns to the set temperature (480° C. in this embodiment), the second regulating valve 13 and the fourth stop valve 15 in step 5) are closed in sequence, and the use of the desuperheating water is stopped; 7) The cooling water temperature control system before the low-temperature reheater LRH and the cooling water temperature control system between the low-temperature reheater LRH and the high-temperature reheater HRH are operated according to steps 2)-7), and the low-temperature reheater LRH inlet temperature is introduced as the feedforward quantity. From operating experience, it can be known that when the low-temperature reheater inlet temperature exceeds the corresponding temperature under its load by 5°C, the cooling water temperature control system at the secondary desuperheater is opened to adjust the cooling water temperature, and the valve of the control system at the primary desuperheater is opened and closed to control the low-temperature reheater inlet temperature, and combined with the cooling water temperature at the secondary desuperheater, the outlet temperature of the high-temperature reheater is controlled.

[0023] In step 7), the PLC controls the valves of the regulating system to control the direction of the boiler cooling water; the operating experience refers to recording the load, time and temperature data of the equipment during operation, and drawing the load-temperature curve with the above data, that is, the main steam, high-temperature reheat steam and low-temperature reheat steam temperatures under different loads. In this embodiment, the low-temperature reheater inlet corresponding to a load of 50% is 350°C; 8) Determine the amount of desuperheating water based on the temperature difference between the desuperheating water temperature and the reheated steam temperature. The calculation formula is: M w =M s ×C s ×(T1-T2) / C w / (T w2 -T w1 ), where M w is the desuperheating water flow rate, t / h; T w1 is the initial temperature of the cooling water, °C; T w2 is the temperature of the desuperheating water after preheating, ℃; T1 is the initial temperature of the reheated steam, ℃; T2 is the set temperature of the reheated steam, ℃; M s is the reheat steam flow rate, t / h, C s is the specific heat capacity of reheat steam, J / (kg·℃); C w is the specific heat capacity of the desuperheating water, J / (kg·℃). The smaller the temperature difference between the desuperheating water and the reheated steam, the more desuperheating water is used. Preferably, in this embodiment, the desuperheating water preheating temperature can be set to 300℃, so that there is a smaller temperature difference with the low-temperature reheat outlet temperature (about 480℃), so as to better protect the reheater desuperheater and prevent it from being frequently subjected to sudden cooling and heating and causing thermal fatigue and cracking. It can be understood that the increase in the desuperheating water temperature requires the use of more desuperheating water to achieve the preset cooling effect and restore the reheated steam temperature to the set temperature.

Claims

1. A power station boiler desuperheating water temperature control system, characterized in that: The invention comprises a main cooling water pipeline (1), a preheating bypass water inlet pipeline (2), a furnace top chamber (3) and a preheating bypass water outlet pipeline (4); the main cooling water pipeline (1) is connected to a main water supply pipeline (11) and a desuperheater (12); one end of the preheating bypass water inlet pipeline (2) is connected to the main cooling water pipeline (1), and the other end is connected to one end of a preheating pipeline in the furnace top chamber (3); the other end of the preheating pipeline is connected to one end of a preheating bypass water outlet pipeline (4); the other end of the preheating bypass water outlet pipeline (4) is connected to the main cooling water pipeline (1); waste heat in the furnace top chamber (3) provides heat to adjust the cooling water temperature, thereby increasing the commissioning temperature of the cooling water; the desuperheater (12) is connected to a power station boiler that needs temperature adjustment.

2. A power station boiler desuperheating water temperature control system as claimed in claim 1, characterized in that: A first stop valve (21) and a first regulating valve (22) are provided on the preheating bypass water inlet pipeline (2), and a second stop valve (41) is provided on the preheating bypass water outlet pipeline (4).

3. A power station boiler desuperheating water temperature control system as claimed in claim 2, characterized in that: A first temperature sensor (42) and a first pressure sensor (43) are provided on the preheating bypass water outlet pipe (4).

4. A power station boiler desuperheating water temperature control system as claimed in claim 3, characterized in that: A second regulating valve (13), a third stop valve (14) and a fourth stop valve (15) are provided on the main desuperheating water pipeline (1); the third stop valve (14) is located between the main water supply pipeline (11) and the preheating bypass water inlet pipeline (2); the fourth stop valve (15) is located between the desuperheater (12) and the preheating bypass water outlet pipeline (4); and the second regulating valve (13) is located between the preheating bypass water inlet pipeline (2) and the preheating bypass water outlet pipeline (4).

5. A power station boiler desuperheating water temperature control system as claimed in claim 4, characterized in that: The main desuperheating water pipeline (1) is also provided with a second temperature sensor (16) and a second pressure sensor (17); the second temperature sensor (16) is located between the main water supply pipeline (11) and the preheating bypass water inlet pipeline (2); and the second pressure sensor (17) is located between the desuperheater (12) and the preheating bypass water outlet pipeline (4).

6. A power station boiler desuperheating water temperature control system as claimed in claim 5, characterized in that: The heat exchange area of ​​the preheating pipeline in the furnace top chamber (3) is not less than 3 times the heat exchange area of ​​the main desuperheating water pipeline (1).

7. A control method for a power station boiler desuperheating water temperature regulating system as claimed in claim 6, characterized in that: The steps include: 1) when the temperature of the cooling water measured by the second temperature sensor (16) is lower than the set temperature, the third stop valve (14), the first stop valve (21) and the first regulating valve (22) are opened, so that the cooling water flowing out of the main water supply pipe (11) flows to the preheating bypass water inlet pipe (2) and enters the preheating pipeline in the furnace top chamber (3); 2) Obtain the temperature-time curve of the preheating and desuperheating water in the furnace top chamber (3) based on operating experience, and determine the time required for preheating the desuperheating water to the set temperature according to the set temperature; 3) When the high-temperature reheated steam of the power station boiler exceeds a set temperature or the average rate of change of the reheated steam exceeds a set rate, the temperature can be adjusted by using desuperheating water. When the first temperature sensor (42) measures that the desuperheating water has reached a preset temperature, the second stop valve (41) and the fourth stop valve (15) are opened to allow the desuperheated water after the temperature increase to enter the desuperheater (12) and then be used in the reheater of the power station boiler.

8. A control method for a power station boiler desuperheating water temperature regulating system as claimed in claim 7, characterized in that: The calculation formula for the amount of desuperheating water used in the reheater is: M w =M s ×C s ×(T1-T2) / C w / (T w2 -T w1 ), where M w is the desuperheating water flow rate, t / h; T w1 is the initial temperature of the cooling water, °C; T w2 is the temperature of the desuperheating water after preheating, ℃; T1 is the initial temperature of the reheated steam, ℃; T2 is the set temperature of the reheated steam, ℃; M s is the reheat steam flow rate, t / h, C s is the specific heat capacity of reheat steam, J / (kg·℃); C w is the specific heat capacity of desuperheated water, J / (kg·℃).

Images