A system and control method for deep recovery and utilization of continuous drainage and steam

Abstract

The application discloses a kind of system machine control methods of deep recovery and utilization of continuous drainage steam exhaust, comprising: first flash tank;The first flash tank side is connected with boiler continuous blowdown flash tank, is connected with hot water heater above, the lower portion of the first flash tank is connected with second flash tank by electric valve, and the liquid level of the first flash tank and the second flash tank and the vacuum degree of the second flash tank are used for predictive control;The device combines the deep recovery of continuous drainage and steam exhaust together, and realizes full-automatic operation, integrates system parameters such as electric valve, water pump frequency, flow characteristics into the algorithm of system as fitting formula, judges the change trend of liquid level and vacuum degree in advance, adjusts in advance, ensures the accurate and stable operation of system, avoids the hysteresis of traditional PID regulation.

Description

Technical Field

[0001] This invention relates to the field of waste steam and waste heat recovery technology, and in particular to a system and control method for deep recovery and utilization of continuous wastewater steam. Background Technology

[0002] To ensure the safety and economic efficiency of the unit, power plants impose strict requirements on the cleanliness of steam. For this reason, boilers are equipped with blowdown devices and deaerator venting devices. Under normal circumstances, the blowdown rate of condensing power plants is 1% to 2%, and the blowdown rate of cogeneration power plants is 2% to 5%. The exhaust steam volume of the deaerator accounts for 4‰ of the inlet water volume. This part of the working fluid contains a large amount of heat energy, and at the same time, some demineralized water cannot be recovered along with the blowdown and exhaust steam discharge.

[0003] Currently, most waste heat recovery from exhaust steam and wastewater from high-pressure deaerators, both domestically and internationally, is carried out by power plants themselves through retrofitting and recovery. Waste heat recovery from exhaust steam of high-pressure deaerators can be mainly categorized as follows:

[0004] (1) Pressurized water is drawn in by a jet pump to heat domestic water through exhaust steam.

[0005] Since the user side has no requirements on the oxygen content of the steam, this scheme is feasible. However, for most thermal power plants, there are no such heat users, so this technology has great limitations in application.

[0006] (2) High-pressure steam is drawn in by a jet pump to supply exhaust steam for industrial extraction.

[0007] Using jet technology, high-pressure steam is forced through a supersonic nozzle to form a high-speed steam flow, drawing in and mixing with deaerator exhaust steam. This mixture is then diffused to form steam at the pressure required by the heat user. The ejector coefficient of the jet pump is the ratio of low-pressure steam to high-pressure steam, and it is related to the pressure and temperature of both high and low-pressure steam, as well as the pressure of the output steam. A higher ejector coefficient results in more low-pressure steam being drawn in, leading to better economic efficiency. Previously, cold reheat steam was used to eject deaerator exhaust steam through a pressure matching device for industrial steam extraction. However, due to a significant pressure difference between the cold reheat steam and the deaerator exhaust steam, it was found that the equipment could not extract deaerator exhaust steam under certain operating conditions, leading to excessive dissolved oxygen in the feedwater. This equipment has since been abandoned.

[0008] (3) Install a mixing heat exchanger to recover exhaust steam to the thermal system.

[0009] By adding a mixing heat exchanger to recover exhaust steam into the turbine thermal system, the main problem with this method is that the oxygen in the exhaust steam of the deaerator cannot be effectively vented, and some of it returns to the thermal system, increasing the burden on the deaerator.

[0010] The main methods for waste heat recovery from continuous drainage can be categorized as follows:

[0011] (1) Continuous drainage for heating water or turbine condensate

[0012] By adding a partition wall heat exchanger, the heat of the continuous drainage can be recovered and given to the heating water or turbine condensate. The cooled continuous drainage is then sent to the sewage treatment plant. This method can recover waste heat, but it cannot concentrate the sewage to reduce emissions.

[0013] (2) Concentration by continuous water distillation

[0014] Flash evaporation technology is used to recover part of the heat from the high-temperature wastewater to generate low-pressure steam, with the remainder being discharged. However, this method can only utilize a small portion of the highest-grade heat, and the amount of flash evaporation is very small, resulting in limited enrichment.

[0015] Because the two types of waste heat recovery have different working fluids, it is difficult to determine the appropriate temperature range for heat exchange, making it difficult to combine the two. Furthermore, the traditional control method is based on PID regulation. For example, given a flash tank level value, when the incoming flow rate suddenly increases and the level exceeds the given value, the opening of the outlet regulating valve increases. When the level falls back below the set value, the opening of the outlet valve decreases again. This control method, which tracks the controlled parameter, will always have a certain degree of lag, bringing a certain degree of instability to the system. Summary of the Invention

[0016] The purpose of this invention is to address the shortcomings of existing technologies by proposing a system and control method for deep recovery and utilization of waste steam from continuous drainage. This system achieves deep concentration of continuous drainage through two flash evaporations, maximizes the energy utilization of waste steam through ejection, and simultaneously extracts heat from waste steam and continuous drainage to heat demineralized water.

[0017] To achieve the above objectives, the present invention adopts the following technical solution: a system for deep recovery and utilization of waste steam from continuous drainage, comprising:

[0018] First flash evaporator;

[0019] The first flash tank is connected to a continuous blowdown expansion tank of the boiler on one side and a hot water heater on the top. The bottom of the first flash tank is connected to the second flash tank through an electric valve. Predictive control is performed by the liquid levels of the first and second flash tanks and the vacuum degree of the second flash tank.

[0020] As a further description of the above technical solution: the first flash tank and the second flash tank are equipped with liquid level gauges.

[0021] As a further description of the above technical solution: the exhaust steam from the low-pressure deaerator enters the second flash tank through the temperature element, and after heat exchange and condensation, the exhaust steam from the low-pressure deaerator is output as condensate.

[0022] As a further description of the above technical solution: the boiler continuous blowdown expansion valve outputs continuous water to the first flash tank, and after enrichment, the primary steam is transported to the second flash tank for secondary enrichment.

[0023] As a further description of the above technical solution: the continuous drainage in the second flash tank is output to the exhaust steam heat exchanger and the concentrate heat exchanger through the continuous drainage output pump. The exhaust steam heat exchanger sends the heat-exchanged continuous drainage into the second flash tank for recirculation through temperature elements and pressure transmitters. After heat exchange, the concentrate heat exchanger sends the continuous drainage to the boiler periodic blowdown expansion tank.

[0024] As a further description of the above technical solution: the exhaust steam from the high-pressure deaerator enters the steam ejector through an electric valve, a temperature element, and a pressure transmitter. The steam ejector then transports the exhaust steam to the exhaust steam heat exchanger, where it is monitored again by the temperature element and pressure transmitter. The exhaust steam heat exchanger performs heat exchange, and the exhaust steam condensate is discharged after condensation.

[0025] As a further description of the above technical solution: the demineralized water is transported to the concentrate heat exchanger via a pressure transmitter and a demineralized water booster pump for heat exchange. A temperature element is provided between the demineralized water booster pump and the concentrate heat exchanger. The concentrate heat exchanger transports the demineralized water through the temperature element to the condenser for heat exchange with secondary steam, and then delivers it to the deaerator balance pipe. A pressure transmitter, a temperature element, and a flow transmitter are provided between the condenser and the deaerator balance pipe.

[0026] As a further description of the above technical solution: the liquid at the top of the second flash tank is transported to the condenser for heat exchange through a pressure transmitter and a temperature element, and discharged as unit condensate after passing through a flow transmitter. A vacuum pump is connected in parallel on the other side of the flow transmitter.

[0027] As a further description of the above technical solution: an electric valve connects the condensate outlet of the condenser to the steam ejector.

[0028] A control method for deep recovery and utilization of waste steam from continuous discharge water, the method being applicable to the system described in any one of the above technical solutions, comprising:

[0029] S1: Prediction function f1 can predict the change in the liquid level of the first flash tank in advance based on the change in the reading of the upstream connected drainage flow meter. Combined with the fluctuation of the upstream connected drainage to the calculation time of the first flash tank, the system can prepare in advance to deal with disturbances and maintain the liquid level of the first flash tank basically unchanged.

[0030] f1 is the liquid level prediction control function of the first flash tank, and the control value is the opening degree of the electric valve between the first flash tank and the second flash tank.

[0031] f1=f(p)=4.0339ln(p)-14.371

[0032] p=ρgL t0106

[0033]

[0034]

[0035] Where p—pressure before the electric valve; ρ—continuous drainage density; L0—design liquid level of the first flash tank; Q0—design continuous drainage flow rate; ν—incoming continuous drainage velocity; s—length of the pipeline from the continuous sewage expansion tank to the first flash tank; r—radius of the first flash tank; Q s —Flow rate entering the upstream continuous sewage discharge expansion tank; Q—Instantaneous flow rate entering the first flash tank;

[0036] S2: The increase in flow rate of the first flash tank is equal to the increase in flow rate of the second flash tank. Therefore, the outlet pump of the second flash tank needs to discharge the increased flow rate. Thus, the initial calculation of the pump frequency is:

[0037]

[0038] Since the circulating concentrate pipeline uses a self-operated electric valve, an increase in pump frequency will lead to an increase in the circulating pipeline flow rate. Based on experimental data of the self-operated pressure regulating valve and pipeline characteristics, the relationship between the circulating pipeline flow rate and the pump flow rate is derived as follows:

[0039]

[0040]

[0041] f2 is the liquid level prediction control function of the second flash tank, and the control value is the frequency of the continuous output pump.

[0042] Wherein, Q0—design continuous drainage flow rate; Q—instantaneous flow rate entering the first flash tank; q—flow rate per revolution of the continuous drainage pump; n—rated speed of the continuous drainage pump; f0—pump frequency when the design continuous drainage flow rate Q0 is stable during commissioning; Q 21 —Initial calculation of f 21 The corresponding water pump flow rate; Q x —Flow rate in the circulation pipeline;

[0043] S3: The negative pressure control of the second flash tank is mainly driven by the ejection of the steam ejector, that is, the exhaust of the high-pressure deaerator. According to the operating characteristics of the high-pressure deaerator, the fluctuation of the exhaust pressure is mainly due to the fluctuation of the deaerator inlet water volume. Therefore, based on the relationship between the high-pressure deaerator inlet water volume and exhaust pressure, the relationship between exhaust pressure and ejection ratio, and the relationship between ejection ratio and valve opening, the air extraction volume can be adjusted in advance to maintain the pressure stability of the second flash tank.

[0044] f3 is the pressure control function for the second flash tank, outputting the opening degree of the electric valve between the condenser and the steam ejector:

[0045] f3 = 7.4302δ 3 -8.8455δ 3 +5.8077δ-1.0291

[0046]

[0047]

[0048] Wherein, δ—steam ejector ejection ratio; p f —High-pressure deaerator exhaust pressure; Q s —Water intake of a single deaerator.

[0049] The above technical solution has the following advantages or beneficial effects:

[0050] 1. It combines the deep recovery of continuous drainage and exhaust steam and achieves fully automated operation. The system parameters such as electric valve, water pump frequency, and flow characteristics are converted into fitting formulas and integrated into the system algorithm. It can predict the changing trends of liquid level and vacuum in advance and make early adjustments to ensure the accurate and stable operation of the system, avoiding the lag of traditional PID regulation. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the connection structure of a system and control method for deep recovery and utilization of waste steam from continuous drainage proposed in this invention.

[0052] Legend:

[0053] 1. First flash tank; 2. Second flash tank; 3. Continuous exhaust pump; 4. Waste steam heat exchanger; 5. Concentrate heat exchanger; 6. Steam ejector; 7. Demineralized water booster pump; 8. Condenser; 9. Vacuum pump. Detailed Implementation

[0054] 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 only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0055] Reference Figure 1 The present invention provides an embodiment of a system for deep recovery and utilization of waste steam from continuous drainage, comprising: a first flash tank 1; the first flash tank 1 is connected to a boiler continuous blowdown expansion tank on one side and a hot water heater on the top; the lower part of the first flash tank 1 is connected to a second flash tank 2 via an electric valve; and the system is controlled by predictive control based on the liquid levels of the first flash tank 1 and the second flash tank 2 and the vacuum degree of the second flash tank 2.

[0056] In this embodiment, by connecting the first flash tank 1 and the second flash tank 2, the internal drain water can be further heated and concentrated. By monitoring the temperature and pressure changes during the input and output of the first flash tank 1, the degree of concentration can be monitored. Based on the current liquid level values ​​of the first flash tank 1 and the second flash tank 2, combined with the output curve of the electric valve at the output end, the liquid level can be adjusted in advance.

[0057] Specifically, the first flash tank 1 and the second flash tank 2 are equipped with level gauges, which can control the heating and concentration of the first flash tank 1 and the second flash tank 2.

[0058] The exhaust steam from the low-pressure deaerator enters the second flash tank 2 after passing through a temperature element. After heat exchange and condensation, the exhaust steam is discharged into the boiler periodic blowdown expansion tank after passing through another temperature element.

[0059] After the low-pressure deaerator exhaust steam enters the second flash tank 2 for heating and enrichment, and the exhaust steam temperature reaches 80℃, it is discharged as exhaust steam condensate from the low-pressure deaerator. The second flash tank 2 is a negative pressure chamber with an evaporation temperature of less than 100℃, which causes the exhaust steam to condense.

[0060] After heat exchange with the continuous wastewater in the concentrated water heat exchanger 5, the wastewater is discharged into the boiler periodic blowdown expansion tank after passing through the temperature element.

[0061] The continuous blowdown expansion valve of the boiler outputs continuous wastewater to the first flash tank 1. After enrichment, the primary steam is sent to the second flash tank 2 for secondary enrichment. The continuous wastewater in the second flash tank 2 is output to the exhaust steam heat exchanger 4 and the concentrate heat exchanger 5 through the continuous blowdown output pump 3. The exhaust steam heat exchanger 4 sends the heat-exchanged continuous wastewater to the second flash tank 2 for recirculation through temperature elements and pressure transmitters. After heat exchange in the concentrate heat exchanger 5, the continuous wastewater is sent to the boiler periodic blowdown expansion tank.

[0062] The continuous blowdown expansion tank of the boiler sequentially transports the continuous wastewater to the first flash tank 1 and the second flash tank 2 for secondary enrichment. After enrichment, it is transported to the concentrate heat exchanger 5 through the continuous blowdown output pump 3. After heat exchange with the demineralized water, it is monitored by the temperature element and, after reaching the predetermined temperature, is transported to the boiler periodic blowdown expansion tank. The exhaust steam heat exchanger 4 transports the heat-exchanged continuous wastewater to the second flash tank 2 through the temperature element and pressure transmitter, and recovers the heat of the exhaust steam after the ejector into the second flash tank 2.

[0063] The wastewater flows into the first flash tank 1 for initial enrichment at 157.5℃, then into the second flash tank 2 for secondary enrichment at 110℃. After enrichment, a portion of the wastewater is sent to the exhaust steam heat exchanger 4 for heat exchange and then returned to the second flash tank 2. The other portion of the wastewater is sent to the concentrate heat exchanger 5 when the temperature drops to 81℃ to exchange heat with the demineralized water again. When the temperature drops to 50℃, it is sent to the boiler periodic blowdown expansion tank.

[0064] The exhaust steam from the high-pressure deaerator enters the steam ejector 6 through an electric valve, temperature element, and pressure transmitter. The steam ejector 6 then delivers the exhaust steam heat exchanger 4, where it is monitored again by the temperature element and pressure transmitter. The exhaust steam heat exchanger 4 performs heat exchange, and the exhaust steam condensate is discharged after condensation.

[0065] The liquid from the top of the second flash tank 2 is delivered to the condenser 8 for heat exchange via a pressure transmitter and a temperature element. After passing through a flow transmitter, it is discharged as unit condensate. A vacuum pump 9 is connected in parallel on the other side of the flow transmitter.

[0066] In this embodiment, the exhaust steam from the high-pressure deaerator enters the steam ejector 6 at 158°C and 0.587 MPa. After being supplied with a certain pressure, it is delivered to the exhaust steam heat exchanger 4 for heat exchange, and then the exhaust steam condensate is output at 80°C.

[0067] The demineralized water is delivered to the concentrate heat exchanger 5 via a pressure transmitter and a demineralized water booster pump 7 for heat exchange. A temperature element is installed between the demineralized water booster pump 7 and the concentrate heat exchanger 5. The concentrate heat exchanger 5 delivers the demineralized water through the temperature element to the condenser 8 for heat exchange with the secondary steam, and then delivers it to the deaerator balance pipe. A pressure transmitter, a temperature element, and a flow transmitter are installed between the condenser 8 and the deaerator balance pipe.

[0068] In this embodiment, the demineralized water enters the concentrate heat exchanger 5 at a dew point temperature of 33.5°C, and after heat exchange, it is heated to 44°C before entering the condenser 8. After heat exchange again, it is heated to 73°C before being discharged into the deaerator balance pipe.

[0069] An electric valve connects the condenser 8 and the steam ejector 6. The system controls the pressure of the second flash tank 2 by detecting the inlet pressure of the steam ejector 6, calculating the ejection ratio and the opening degree of the electric valve.

[0070] The technical solution of the present invention also includes an embodiment of a control method for deep recovery and utilization of waste steam from continuous drainage, the method being applicable to the system of any of the above technical solutions.

[0071] Includes: S1: Prediction function f1, which can predict the change in the liquid level of the first flash tank 1 in advance based on the change in the reading of the upstream connected drainage flow meter, and combine the fluctuation of the upstream connected drainage to the calculation time of the first flash tank 1, so that the system can prepare to deal with the disturbance in advance and maintain the liquid level of the first flash tank 1 basically unchanged.

[0072] f1 is the liquid level prediction control function of the first flash tank. The control value is the opening degree of the electric valve between the first flash tank 1 and the second flash tank 2. This electric valve is the liquid outlet regulating valve.

[0073] f1=f(p)=4.0339ln(p)-14.371 (1-1)

[0074]

[0075]

[0076]

[0077] Where p—pressure before the electric valve; ρ—continuous drainage density; L0—design liquid level of the first flash tank; Q0—design continuous drainage flow rate; ν—incoming continuous drainage velocity; s—length of the pipeline from the continuous sewage expansion tank to the first flash tank; r—radius of the first flash tank; Q s —Flow rate entering the upstream continuous sewage discharge expansion tank; Q—Instantaneous flow rate entering the first flash tank;

[0078] In Equation 1-1, based on the valve flow regulation curve of the electric valve at the output end of the first flash tank 1, and combined with the relationship between the opening degree of the electric valve and the pressure before the valve, the instantaneous flow rate entering the first flash tank 1 and the inflow discharge velocity are obtained by monitoring with a liquid level gauge. The value of the instantaneous flow rate entering the first flash tank 1 is verified by Equation 1-4. Based on the flow rate before the continuous blowdown expansion tank of the upstream boiler and the thermodynamic characteristics of the continuous blowdown expansion tank, the value is obtained by fitting the theoretical calculation and the monitored data.

[0079] S2: The increase in flow rate of the first flash tank 1 is equal to the increase in flow rate of the second flash tank 2. Therefore, the outlet pump of the second flash tank 2 needs to discharge the increased flow rate. Thus, the initial calculation of the pump frequency is:

[0080]

[0081] Since the circulating concentrate pipeline uses a self-operated electric valve, an increase in pump frequency will lead to an increase in the circulating pipeline flow rate. Based on experimental data of the self-operated pressure regulating valve and pipeline characteristics, the relationship between the circulating pipeline flow rate and the pump flow rate is derived as follows:

[0082]

[0083]

[0084] f2 is the liquid level prediction control function of the second flash tank 2, and the control value is the frequency of the continuous output pump 3.

[0085] Where, Q0—design continuous drainage flow rate; Q—instantaneous flow rate entering the first flash tank; q—flow rate per revolution of the continuous drainage pump; n—rated speed of the continuous drainage pump; f0—frequency of the pump when the design continuous drainage flow rate Q0 is stable during commissioning; Q 21 —Initial calculation of f 21 The corresponding water pump flow rate; Q x —Flow rate in the circulation pipeline;

[0086] By monitoring the liquid level of the second flash tank 2 to maintain the stability of the system loop, and through monitoring by temperature elements and pressure transmitters, the flow rate increase of the second flash tank 2 is obtained by monitoring the flow rate increase of the first flash tank 1. Based on the single-rotation flow rate and frequency of the continuous discharge pump 3 at the output end of the second flash tank 2, the flow rate of the circulation pipeline is calculated. The liquid level prediction calculation formula of the second flash tank 2 is obtained by calculating with the flow rate of the continuous discharge pump 3.

[0087] S3: The negative pressure control of the second flash tank 2 is mainly driven by the ejection of the steam ejector 6, that is, the exhaust of the high-pressure deaerator. According to the operating characteristics of the high-pressure deaerator, the fluctuation of the exhaust pressure is mainly due to the fluctuation of the deaerator inlet water volume. Therefore, based on the relationship between the high-pressure deaerator inlet water volume and exhaust pressure, the relationship between exhaust pressure and ejection ratio, and the relationship between ejection ratio and valve opening, the air extraction volume can be adjusted in advance to maintain the pressure stability of the second flash tank 2.

[0088] f3 is the pressure control function for the second flash tank 2, outputting the opening degree of the electric valve between the condenser 8 and the steam ejector 6. This electric valve is a suction regulating valve.

[0089] f3 = 7.4302δ 3 -8.8455δ 3 +5.8077δ-1.0291 (3-1)

[0090]

[0091]

[0092] Wherein, δ—steam ejector ejection ratio; p f —High-pressure deaerator exhaust pressure; Q s —Water intake of a single deaerator.

[0093] Pressure transmitters are installed at the input and output ends of the second flash tank 2 to monitor the pressure of exhaust steam from the high-pressure deaerator entering the second flash tank 2. The pressure control calculation formula for the second flash tank 2 is obtained by monitoring the water inlet flow of a single deaerator and the ejection ratio of the steam ejector 6 connected to the output end of the second flash tank 2, and then pre-adjusted based on the monitored pressure data.

[0094] The system has three main control parameters: first, the liquid level of the first flash tank 1; the stability of the liquid level directly affects the amount of primary concentration and the continuous operation of the system. The liquid level of the first flash tank 1 is affected by the inflow discharge rate, the primary steam flow rate, and the electric valve at the outlet of the first flash tank 1. Second, the liquid level of the second flash tank 2; the stability of the liquid level in the second flash tank 2 is crucial to the success of the entire system. The liquid level in the second flash tank 2 is affected by the outlet valve of the first flash tank 1 and the frequency of the discharge pump. Third, the vacuum level of the second flash tank 2; the vacuum level of the second flash tank 2 is a key indicator for ensuring the concentration rate of the system. Specifically, the vacuum level of the second flash tank 2 is related to the electric valve at the steam ejector 6 and the vacuum pump 9.

[0095] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for deep recovery and utilization of waste steam from continuous drainage, characterized in that, include: First flash evaporator (1); The first flash tank (1) is connected to the boiler continuous blowdown expansion tank on one side and a hot water heater is connected above it. The first flash tank (1) is connected to the second flash tank (2) below through an electric valve. Predictive control is performed by the liquid levels of the first flash tank (1) and the second flash tank (2) and the vacuum degree of the second flash tank (2). The first flash tank (1) and the second flash tank (2) are equipped with level gauges; The exhaust steam from the low-pressure deaerator enters the second flash tank (2) through the temperature element. After heat exchange and condensation, the exhaust steam from the low-pressure deaerator is output as condensate. The boiler continuously blows out the wastewater from the expansion tank and sends it to the first flash tank (1). After enrichment, the primary steam is sent to the second flash tank (2) for secondary enrichment. The wastewater in the second flash tank (2) is output to the exhaust steam heat exchanger (4) and the concentrate heat exchanger (5) through the continuous discharge pump (3). The exhaust steam heat exchanger (4) sends the wastewater after heat exchange into the second flash tank (2) for recirculation through temperature elements and pressure transmitters. The concentrate heat exchanger (5) sends the wastewater to the boiler periodic blowdown expansion tank after heat exchange. The exhaust steam from the high-pressure deaerator enters the steam ejector (6) through an electric valve, temperature element and pressure transmitter, and is then transported to the exhaust steam heat exchanger (4) through the steam ejector (6). The exhaust steam is monitored again by the temperature element and pressure transmitter. The exhaust steam heat exchanger (4) performs heat exchange and discharges the exhaust steam condensate after condensation. The demineralized water is transported to the concentrated water heat exchanger (5) via a pressure transmitter and a demineralized water booster pump (7) for heat exchange. A temperature element is provided between the demineralized water booster pump (7) and the concentrated water heat exchanger (5). The concentrated water heat exchanger (5) transports the demineralized water through the temperature element to the condenser (8) for heat exchange with the secondary steam and then to the deaerator balance pipe. A pressure transmitter, a temperature element and a flow transmitter are provided between the condenser (8) and the deaerator balance pipe.

2. The system for deep recovery and utilization of waste steam from continuous drainage as described in claim 1, characterized in that: The liquid is transported to the condenser (8) for heat exchange through the pressure transmitter and temperature element at the top of the second flash tank (2). After passing through the flow transmitter, it is discharged as unit condensate. A vacuum pump (9) is connected in parallel on the other side of the flow transmitter.

3. The system for deep recovery and utilization of waste steam from continuous drainage as described in claim 1, characterized in that: The condensate outlet of the condenser (8) is connected to the steam ejector (6) by an electric valve.

4. A control method for deep recovery and utilization of waste steam from continuous discharge, characterized in that, The method is applicable to the system described in any one of claims 1-3, comprising: S1: Prediction function f1 can predict the change in the liquid level of the first flash tank (1) in advance based on the change in the reading of the upstream connected drainage flow meter. Combined with the calculation time of the fluctuation of the upstream connected drainage to the first flash tank (1), the system can prepare in advance to deal with the disturbance and keep the liquid level of the first flash tank (1) basically unchanged. f1 is the liquid level prediction control function of the first flash tank, and the control value is the opening degree of the electric valve between the first flash tank (1) and the second flash tank (2); in —Pressure before the electric valve; —including drainage density; —Design liquid level value of the first flash tank; —Design for continuous drainage flow; —To linger over the drainage flow rate; —Length of the pipeline from the continuous blowdown expansion tank to the first flash tank; —Radius of the first flash tank; —Into the upstream continuous sewage discharge expansion container flow; —Instantaneous flow rate into the first flash tank; S2: The increase in flow rate of the first flash tank (1) is equal to the increase in flow rate of the second flash tank (2). Therefore, the outlet pump of the second flash tank (2) needs to discharge the increased flow rate. Therefore, the pump frequency is initially calculated as follows: Since the circulating concentrate pipeline uses a self-regulating pressure regulating valve, an increase in pump frequency will lead to an increase in the flow rate in the circulating pipeline. Based on experimental data of the self-regulating pressure regulating valve and pipeline characteristics, the relationship between the circulating pipeline flow rate and the pump flow rate is derived as follows: f2 is the liquid level prediction control function of the second flash tank (2), and the control value is the frequency of the continuous output pump (3); in, —Design for continuous drainage flow; —Instantaneous flow rate into the first flash tank; —Single-cycle flow rate of the continuous output pump; —Rated speed of the continuous output pump; —Design for drainage flow rate The pump frequency when it is stable after commissioning; —Initial Calculation The corresponding water pump flow rate; —Flow rate in the circulation pipeline; S3: The negative pressure control of the second flash tank (2) is mainly driven by the ejection of the steam ejector (6), that is, the exhaust of the high pressure deaerator. According to the operating characteristics of the high pressure deaerator, the fluctuation of the exhaust pressure is mainly due to the fluctuation of the deaerator water inlet. Therefore, according to the relationship between the high pressure deaerator water inlet and exhaust pressure, the relationship between exhaust pressure and ejection ratio, and the relationship between ejection ratio and valve opening, the advance of the extraction volume can be achieved to adjust and maintain the pressure stability of the second flash tank (2). For the pressure control function of the second flash tank (2), output the opening degree of the electric valve between the condenser (8) and the steam ejector (6): in, —Steam ejector ejection ratio; —High-pressure deaerator exhaust pressure; —Water intake of a single deaerator.

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