CN116293613A - A system and control method for deep recovery and utilization of exhausted steam in continuous drainage - Google Patents

Abstract

The invention discloses a system machine control method for deep recycling of waste steam of continuous drainage, which comprises the following steps: a first flash tank; one side of the first flash tank is connected with a continuous blowdown flash tank of the boiler, the upper side of the first flash tank is connected with a hot water heater, the lower side of the first flash tank is connected with a second flash tank through an electric valve, and prediction control is carried out through liquid levels of the first flash tank and the second flash tank and vacuum degree of the second flash tank; the device combines the deep recovery of continuous drainage and exhaust steam together, realizes full-automatic operation, integrates the parameters of the system such as an electric valve, a water pump frequency, flow characteristics and the like into a fitting formula into an algorithm of the system, prejudges the variation trend of liquid level and vacuum degree in advance, ensures the accurate and stable operation of the system, and avoids the hysteresis quality of the traditional PID regulation.

Description

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

technical field

The invention relates to the technical field of waste steam and waste heat recovery, in particular to a system and a control method for deep recovery and utilization of continuous drainage waste steam.

Background technique

In order to ensure the safety of the unit and the economy of operation, the power plant puts forward strict requirements on the cleanliness of the steam. For this reason, the boiler is equipped with a sewage discharge device and a deaerator emptying device. Under normal circumstances, the sewage discharge of the condensing steam power plant The discharge rate of the thermal power plant is 2% to 5%. The exhaust steam of the deaerator accounts for 4‰ of the inlet water. And exhaust gas emissions and cannot be recycled.

At present, the waste heat recovery of high-pressure deaerator exhaust steam and continuous drainage at home and abroad is mostly carried out by power plants. The waste heat recovery of high-pressure deaerator exhaust steam is mainly divided into the following categories:

(1) Pressurized water sucks exhaust steam through jet pump to heat domestic water

Since the user side has no requirements on the oxygen content of the steam, etc., this scheme is feasible, but for most thermal power plants, there is no such heat user, so this technology has great application limitations.

(2) High-pressure steam is sucked and exhausted by jet pump for industrial steam extraction

Using injection technology, the high-pressure steam is passed through the supersonic nozzle to form a high-speed steam flow, and the exhaust steam of the deaerator is inhaled, mixed, and diffused to form the steam at the pressure required by the heat user. The ejection coefficient of the jet pump is the difference between the low-pressure steam and the high-pressure steam. The ratio is related to the pressure and temperature of the high and low pressure steam and the pressure of the output steam. The higher the ejection coefficient, the more low pressure steam is inhaled, and the better the economy. The cold resteam is used to inject the exhaust steam of the deaerator through the pressure matcher for external industrial extraction. Due to the large deviation between the pressure of the cold resteam and the exhaust steam of the deaerator, it is found that the exhaust gas of the deaerator cannot be pumped under some working conditions during operation. steam, causing the dissolved oxygen in the feed water to exceed the limit. At present, the equipment has been abandoned.

(3) Install a hybrid heat exchanger to recover the exhaust steam to the thermal system

By adding a hybrid heat exchanger, the exhaust steam is recovered to the thermal system of the steam turbine. The main problem of this method is that the oxygen in the exhaust steam of the deaerator cannot be effectively evacuated, and part of it returns to the thermal system. Adding a deaerator burden.

Waste heat recovery methods for continuous drainage are mainly divided into the following types:

(1) Heating heating water or turbine condensate with drainage

In the form of adding a partition-type heat exchanger, the heat of the continuous drainage is recovered to the heating water or the condensed water of the steam turbine, and the continuous drainage after cooling is used for sewage treatment. This method can achieve waste heat recovery, but it cannot concentrate the sewage. emission reduction.

(2) Concentration by flash evaporation with drainage

The flash technology is used to recover part of the heat of high-temperature continuous drainage, generate low-pressure steam, and discharge the rest. Most of this method can only use a small part of the highest-grade heat, and the amount of flash evaporation is very small, so the concentration enhancement effect is limited.

Due to the different working fluids of the above two kinds of waste heat recovery, it is difficult to determine the temperature of waste heat recovery for heat exchange in an appropriate range, so it is difficult to combine the two, and the traditional control method is based on PID adjustment, such as a given flash Tank liquid level value, when the water discharge suddenly increases and the liquid level exceeds a given value, the opening of the liquid outlet regulating valve increases, and the liquid level falls below the set value, and the opening of the liquid outlet valve decreases again. There will always be a certain degree of hysteresis in the control method of tracking the adjusted parameters, which will bring a certain degree of instability to the system.

Contents of the invention

The purpose of the present invention is to solve the shortcomings existing in the prior art, and propose a system and control method for the deep recovery and utilization of exhausted steam in continuous drainage, realize the deep concentration of continuous drainage through two flashes, and achieve Maximize the utilization of the energy of the exhaust steam, and simultaneously extract the heat of the exhaust steam and continuous drainage to heat the desalted water.

In order to achieve the above object, the present invention adopts the following technical scheme: a system for deep recovery and utilization of exhaust steam in continuous drainage, comprising:

first flash tank;

One side of the first flash tank is connected to the continuous blowdown expansion vessel of the boiler, the upper part is connected to the hot water heater, and the lower part of the first flash tank is connected to the second flash tank through an electric valve. Tank and the liquid level of the second flash tank and the vacuum level of the second flash tank are predictively controlled.

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

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

As a further description of the above technical solution: the output of the expansion valve of the continuous blowdown of the boiler drains water into the first flash tank, and after concentration, the primary steam is transported to the second flash tank for secondary concentration.

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 concentrated water heat exchanger through the continuous row output pump, and the exhaust steam heat exchanger will exchange heat The final continuous drainage is transported into the second flash tank through the temperature element and pressure transmitter for recirculation, and the concentrated water heat exchanger conducts heat exchange and then transports the continuous drainage to the boiler's regular blowdown expansion vessel.

As a further description of the above technical solution: the exhaust steam of the high-pressure deaerator enters the steam ejector through the electric valve, temperature element and pressure transmitter, and is transported to the exhaust steam heat exchanger through the steam ejector, It is monitored again through the temperature element and the pressure transmitter, and the exhaust steam heat exchanger performs heat exchange, and discharges the exhaust steam condensate after condensation.

As a further description of the above technical solution: the desalted water incoming water is transported to the concentrated water heat exchanger through the pressure transmitter through the desalted water booster pump for heat exchange, and the desalted water booster pump is exchanged with the concentrated water There is a temperature element between the heat exchangers, and the concentrated water heat exchanger sends the desalted water to the condenser through the temperature element for heat exchange with the secondary steam, and then sends it to the balance pipe of the deaerator, and the condenser A pressure transmitter, a temperature element and a flow transmitter are arranged between the balance pipe of the deaerator.

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

As a further description of the above technical solution: the condensation port of the condenser and the steam ejector are connected through an electric valve.

A control method for the deep recovery and utilization of continuous drainage waste steam, the method is suitable for the system described in any one of the above technical solutions, including:

S1: Prediction function f1, which can judge in advance the change of the liquid level of the first flash tank at the next moment according to the change of the indication of the upstream continuous drainage flowmeter, and combine the fluctuation of the upstream continuous drainage to reach the first flash tank calculation time, the system is prepared to deal with disturbances in advance, and the liquid level of the first flash tank is kept basically unchanged;

f1 is the predictive control function of the liquid level 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;

f ₁ =f(p)=4.0339ln(p)-14.371

p=ρgL _t0106

Among them, p—the pressure in front of the electric valve; ρ—the drainage density; L ₀ —the design liquid level value of the first flash tank; Q ₀ —the design drainage flow rate; The length of a flash tank pipeline; r—the radius of the first flash tank; Q _s —the flow rate entering the upstream continuous blowdown expander; Q—the instantaneous flow rate entering the first flash tank;

S2: The increase in the flow rate of the first flash tank is equal to the increase in the flow rate of the second flash tank, so the outlet output pump of the second flash tank is required to discharge the increased flow, so the frequency of the pump is preliminarily calculated for:

Since the circulating concentrated water pipeline is a self-operated electric valve, the increase in the frequency of the pump will lead to an increase in the flow of the circulating pipeline. According to the experimental data of the self-operated pressure regulating valve and the characteristics of the pipeline, the relationship between the flow of the circulating pipeline and the flow of the water pump is obtained:

f2 is the predictive control function of the liquid level of the second flash tank, and the control value is the frequency of the continuous output pump;

Among them, Q ₀ —design continuous drainage flow; Q—instantaneous flow into the first flash tank; q—single-rotation flow of continuous row output pump; n—rated speed of continuous row output pump; f ₀ —design continuous drainage flow Q ₀ The frequency of the pump when debugging is stable; Q ₂₁ —the water pump flow corresponding to f ₂₁ in the initial calculation; Q _x —the circulation pipeline flow;

S3: The negative pressure control of the second flash tank is mainly powered 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 main reason for the fluctuation of the exhaust pressure It is the fluctuation of the water intake of the deaerator, so according to the relationship between the water intake and the exhaust pressure of the high-pressure deaerator, the relationship between the exhaust pressure and the injection ratio, and the relationship between the injection ratio and the valve opening The adjustment of the pumping volume can be realized in advance, and the pressure of the second flash tank can be kept stable;

f ₃ is the pressure control function of the second flash tank, outputting the opening degree of the electric valve between the condenser and the steam ejector:

f ₃ =7.4302δ ³ -8.8455δ ³ +5.8077δ-1.0291

Among them, δ—injection ratio of steam ejector; p _f —exhaust pressure of high-pressure deaerator; Q _s —water intake of single deaerator.

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

1. Combine the deep recovery of continuous drainage and exhaust steam, and realize fully automatic operation. System parameters such as electric valve, water pump frequency, and flow characteristics are transformed into fitting formulas and integrated into the system algorithm to predict liquid in advance. The change trend of position and vacuum degree can be adjusted in advance to ensure the precise and stable operation of the system and avoid the hysteresis of traditional PID adjustment.

Description of drawings

Fig. 1 is a schematic diagram of the connection structure of a system and control method for the deep recovery and utilization of exhaust steam with continuous drainage proposed by the present invention.

illustration:

1. The first flash tank; 2. The second flash tank; 3. Continuous output pump; 4. Exhaust steam heat exchanger; 5. Concentrated water heat exchanger; 6. Steam ejector; 7. Demineralized water Booster pump; 8. Condenser; 9. Vacuum pump.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

Referring to Fig. 1, an embodiment provided by the present invention: a system for deep recovery and utilization of waste steam with continuous drainage, including: a first flash tank 1; Connect the hot water heater, the bottom of the first flash tank 1 is connected to the second flash tank 2 through the electric valve, and the liquid level of the first flash tank 1 and the second flash tank 2 and the second flash tank 2 Predictive control of the vacuum degree.

In this embodiment, through the connection of the first flash tank 1 and the second flash tank 2, the continuous water flowing through the interior can be further heated and concentrated, and the temperature and pressure of the input and output of the first flash tank 1 can be monitored. Change the value, monitor the degree of enrichment, and monitor according to the current liquid level values of the first flash tank 1 and the second flash tank 2, combined with the opening output curve of the electric valve at the output end, to realize the advance adjustment of the liquid level.

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

The exhaust steam of the low-pressure deaerator enters the second flash tank 2 through the temperature element, and after the exhaust steam of the low-pressure deaerator is subjected to heat exchange and condensation, it is discharged into the boiler periodic blowdown expansion vessel through the temperature element

After the low-pressure deaeration exhaust steam enters the second flash tank 2 for heating and concentration, after the exhaust steam temperature reaches 80°C, it is discharged as the exhaust steam condensate of the low-pressure deaerator. The second flash tank 2 is a negative pressure chamber, and the evaporation When the temperature is less than 100°C, the lack of steam will be condensed.

After the concentrated water heat exchanger 5 conducts heat exchange with the drain, it is discharged through the temperature element into the boiler's regular blowdown expansion vessel.

Boiler continuous sewage blowdown expansion valve output even drainage to the first flash tank 1, after enrichment, the primary steam is sent to the second flash tank 2 for secondary enrichment, the second flash tank 2 is connected to the drainage through The serial output pump 3 outputs to the exhaust steam heat exchanger 4 and the concentrated water heat exchanger 5, and the exhaust steam heat exchanger 4 transports the serial drain after heat exchange into the second flash tank through the temperature element and the pressure transmitter 2 for recirculation, and the concentrated water heat exchanger 5 conducts heat exchange and then transports the continuous drainage to the boiler's regular blowdown expansion vessel.

Boiler continuous blowdown expander transports continuous waste water to the first flash tank 1 and second flash tank 2 in sequence for two-stage enrichment. After the enrichment is completed, it is transported to the concentrated water heat exchanger 5 through the serial output pump 3 After heat exchange with the desalinated incoming water, the temperature is monitored by the temperature element to reach the predetermined temperature, and then it is transported to the expansion vessel for regular sewage discharge of the boiler; the waste steam heat exchanger 4 passes the heat-exchanged continuous drainage through the temperature element and pressure transmitter The exhaust steamer is transported into the second flash tank 2, and the exhaust steam heat after the ejector is recovered to the second flash tank 2.

The continuous drainage enters the first flash tank 1 for initial concentration at 157.5°C, and then enters the second flash tank 2 for secondary concentration at 110°C. After heat exchange in the heat exchanger 4, it is returned to the second flash tank 2, and the other part is drained until the temperature drops to 81°C, and then it is sent to the concentrated water heat exchanger 5 for heat exchange with the desalinated incoming water again. When the temperature drops to 50°C, it is transported to the boiler's periodic blowdown expansion vessel.

The exhaust steam of the high-pressure deaerator enters the steam ejector 6 through the electric valve, temperature element and pressure transmitter, and is transported to the exhaust steam heat exchanger 4 through the steam ejector 6, and passes through the temperature element and pressure transmitter To monitor again, the exhaust steam heat exchanger 4 performs heat exchange, and discharges the exhaust steam condensate after condensation.

The top of the second flash tank 2 sends the liquid to the condenser 8 through the pressure transmitter and temperature element for heat exchange, and after passing through the flow transmitter, it is discharged as condensed water of the unit, and is connected in parallel on the other side of the flow transmitter vacuum pump9.

In this embodiment, the exhaust steam of the high-pressure deaerator enters the steam ejector 6 at 158°C and 0.587MPa, and after a certain pressure is provided, it is transported to the exhaust steam heat exchanger 4 for heat exchange, and then at 80°C Output lean condensate.

The incoming desalted water is sent to the concentrated water heat exchanger 5 through the pressure transmitter through the desalted water booster pump 7 for heat exchange. A temperature element is installed between the desalted water booster pump 7 and the concentrated water heat exchanger 5. The water heat exchanger 5 transports the desalinated water and the incoming water passes through the temperature element to the condenser 8 for heat exchange with the secondary steam and then transports it to the balance pipe of the deaerator, and a pressure transmitter is set between the condenser 8 and the balance pipe of the deaerator devices, temperature elements and flow transmitters.

In this embodiment, the desalinated incoming water enters the concentrated water heat exchanger 5 at a dew point temperature of 33.5°C, heats up to 44°C and enters the condenser 8, heats up again to 73°C, and then discharges to Deaerator balance tube.

The electric valve is connected between the condenser 8 and the steam ejector 6, and the system detects the inlet pressure of the steam ejector 6, calculates the injection ratio and the opening of the electric valve, and achieves the purpose of controlling the pressure of the second flash tank 2 .

The technical solution of the present invention also includes an embodiment of a control method for the deep recovery and utilization of continuous drain waste steam, and the method is applicable to the system in any one of the above technical solutions.

Including: S1: prediction function f1, which can judge in advance the change of the liquid level of the first flash tank 1 at the next moment according to the change of the indication of the upstream continuous drainage flowmeter, and combine the fluctuation of the upstream continuous drainage to reach the first flash tank 1 The calculation time of the calculation time, let the system prepare for the disturbance in advance, and keep the liquid level of the first flash tank 1 basically unchanged;

f1 is the predictive control function of the liquid level 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, and the electric valve is a liquid outlet regulating valve;

f ₁ =f(p)=4.0339ln(p)-14.371 (1-1)

Among them, p—the pressure in front of the electric valve; ρ—the drainage density; L ₀ —the design liquid level value of the first flash tank; Q ₀ —the design drainage flow rate; The length of a flash tank pipeline; r—the radius of the first flash tank; Q _s —the flow rate entering the upstream continuous blowdown expander; Q—the instantaneous flow rate entering the first flash tank;

In formula 1-1, according to the valve flow adjustment curve of the electric valve at the output end of the first flash tank 1, combined with the relationship between the opening of the electric valve and the pressure in front of the valve, through the monitoring of the liquid level gauge, the first The instantaneous flow rate of the first flash tank 1 and the flow rate of the continuous drainage, the value of the instantaneous flow rate entering the first flash tank 1 is verified by formula 1-4, according to the flow rate before the continuous blowdown expansion of the upstream boiler and the thermal power of the continuous blowdown expansion vessel The characteristics are obtained by theoretical calculation and data fitting of monitoring.

S2: The increase in the flow rate of the first flash tank 1 is equal to the increase in the flow rate of the second flash tank 2, so the output pump at the outlet of the second flash tank 2 is required to discharge the increased flow rate, so the preliminary calculation of the pump frequency is:

Since the circulating concentrated water pipeline is a self-operated electric valve, the increase in the frequency of the pump will lead to an increase in the flow of the circulating pipeline. According to the experimental data of the self-operated pressure regulating valve and the characteristics of the pipeline, the relationship between the flow of the circulating pipeline and the flow of the water pump is obtained:

f2 is the predictive control function of the liquid level of the second flash tank 2, and the control value is the frequency of the serial output pump 3;

Among them, Q ₀ —design even drainage flow; Q—instantaneous flow into the first flash tank. q—the single-rotation flow rate of the continuous output pump; n—the rated speed of the continuous output pump; f ₀ —the frequency of the pump when the designed continuous drainage flow Q ₀ is debugged and stabilized; Q ₂₁ —the initial calculation of the pump flow corresponding to f ₂₁ ; Q _x — Circulation pipeline flow;

Maintain the stability of the system loop by monitoring the liquid level of the second flash tank 2, monitor the temperature element and pressure transmitter, and obtain the flow rate of the second flash tank 2 by monitoring the flow increase of the first flash tank 1 The amount of increase is calculated according to the single-turn flow rate and frequency of the output pump 3 at the output end of the second flash tank 2, and the flow rate of the circulation pipeline is calculated, which is calculated with the flow rate of the output pump 3 to obtain the liquid in the second flash tank 2. Bit prediction calculation formula.

S3: The negative pressure control of the second flash tank 2 is mainly powered 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 main reason for the fluctuation of the exhaust pressure It is the fluctuation of the water intake of the deaerator, so according to the relationship between the water intake and the exhaust pressure of the high-pressure deaerator, the relationship between the exhaust pressure and the injection ratio, and the relationship between the injection ratio and the valve opening The advance adjustment of the pumping volume can be realized, and the pressure of the second flash tank 2 can be kept stable;

f ₃ is the pressure control function of the second flash tank 2, which outputs the opening degree of the electric valve between the condenser 8 and the steam ejector 6, and the electric valve is an air extraction regulating valve:

f ₃ =7.4302δ ³ -8.8455δ ³ +5.8077δ-1.0291 (3-1)

Among them, δ—injection ratio of steam ejector; p _f —exhaust pressure of high-pressure deaerator; Q _s —water intake of single deaerator.

A pressure transmitter is installed at the input and output ends of the second flash tank 2 to monitor the pressure of the high-pressure deaerator exhaust steam entering the second flash tank 2. By monitoring the water intake of a single deaerator and the second flash tank 2 Calculate the injection ratio of the steam ejector 6 connected to the output end to obtain the pressure control calculation formula of the second flash tank 2, and perform pre-adjustment in combination with the monitored pressure data.

There are three main control parameters of the system. One is the liquid level of the first flash tank 1. Whether the liquid level is stable or not is related to the amount of first-stage enrichment and whether the system can run continuously. The liquid level of the first flash tank 1 is influenced by The impact of lingering displacement, primary steam volume, and the electric valve of the first flash tank 1; the second is the liquid level of the second flash tank 2, and the stability of the liquid level of the second flash tank 2 is the key to the success of the entire system; The liquid level of the second flash tank 2 is affected by the frequency of the liquid outlet valve of the first flash tank 1 and the frequency of the drainage output pump; the third is the vacuum degree of the second flash tank 2, and the vacuum degree of the second flash tank 2 is guaranteed A key indicator of system concentration. Wherein, the vacuum degree of the second flash tank 2 is related to the electric valve at the steam ejector 6 and the vacuum pump 9 .

Finally, it should be noted that: the above 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, for those skilled in the art, it still It is possible to modify the technical solutions recorded in the foregoing embodiments, or to perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present invention shall be included in the within the protection scope of the present invention.

Claims (10)

1. A system for deep recovery and utilization of waste steam in continuous drainage, characterized in that it comprises: a first flash tank (1); One side of the first flash tank (1) is connected to the continuous blowdown expansion vessel of the boiler, and the upper part is connected to a hot water heater, and the bottom of the first flash tank (1) is connected to the second flash tank (2) connection, predictive control is performed through 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). 2. A system for deep recovery and utilization of waste steam with continuous drainage according to claim 1, characterized in that: said first flash tank (1) and said second flash tank (2) are provided with liquid level gauge. 3. A system for deep recovery and utilization of exhaust steam with continuous drainage according to claim 1, characterized in that: the exhaust steam of the low-pressure deaerator enters the second flash tank (2) through the temperature element, and the low-pressure After the exhaust steam of the deaerator is condensed by heat exchange, the exhaust steam condensate of the low-pressure deaerator is output. 4. A system for deep recovery and utilization of waste steam with continuous drainage according to claim 3, characterized in that: the output of the expansion valve for continuous blowdown of the boiler is connected to the first flash tank (1), and after thickening The primary steam is sent to the second flash tank (2) for secondary enrichment. 5. A system for deep recycling of waste steam with continuous drainage according to claim 3, characterized in that: the continuous drainage in the second flash tank (2) is output to the waste steam through the continuous output pump (3). In the heat exchanger (4) and the concentrated water heat exchanger (5), the exhaust steam heat exchanger (4) transports the continuous water after heat exchange into the second flash vaporizer through a temperature element and a pressure transmitter The tank (2) performs recirculation, and the concentrated water heat exchanger (5) conducts heat exchange and then transports the continuous drainage to the boiler's regular blowdown expansion vessel. 6. A system for deep recovery and utilization of exhausted steam with continuous drainage according to claim 5, characterized in that: the exhausted steam of the high-pressure deaerator enters the steam ejector (6) through the electric valve, temperature element and pressure transmitter In the process, it is transported to the exhaust steam heat exchanger (4) through the steam ejector (6), and is monitored again through the temperature element and pressure transmitter, and the exhaust steam heat exchanger (4) conducts Heat exchange, discharge the exhausted condensed water after condensation. 7. A system for deep recovery and utilization of exhaust steam with continuous drainage according to claim 6, characterized in that: desalted water incoming water is transported to the concentrated water exchange unit through a pressure transmitter and a desalted water booster pump (7). heat exchange in the heat exchanger (5), a temperature element is provided between the desalted water booster pump (7) and the concentrated water heat exchanger (5), and the concentrated water heat exchanger (5) transports desalted water The incoming brine water passes through the over-temperature element to the condenser (8) for heat exchange with the secondary steam and then is sent to the balance pipe of the deaerator, and a pressure is set between the condenser (8) and the balance pipe of the deaerator. Transmitters, temperature elements and flow transmitters. 8. A system for deep recovery and utilization of waste steam with continuous drainage according to claim 1, characterized in that: the top of the second flash tank (2) transmits the liquid to the condenser through a pressure transmitter and a temperature element (8) for heat exchange, after passing through the flow transmitter and discharged as condensed water of the unit, a vacuum pump (9) is connected in parallel on the other side of the flow transmitter. 9. A system for deep recycling of waste steam with continuous drainage according to claim 7, characterized in that: between the condensate port of the condenser (8) and the steam ejector (6), an electric valve connection. 10. A control method for the deep recovery and utilization of waste steam in continuous drainage, characterized in that the method is suitable for the system described in any one of claims 1-9, including: S1: Prediction function f1, which can judge in advance the change in the liquid level of the first flash tank (1) at the next moment according to the change of the indication of the upstream continuous drainage flowmeter, and achieve the first flash evaporation in combination with the fluctuation of the upstream continuous drainage flow The calculation time of the tank (1) allows the system to prepare for the disturbance in advance, and maintains the liquid level of the first flash tank (1) basically unchanged; f1 is the predictive control function of the liquid level 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); f ₁ =f(p)=4.0339ln(p)-14.371 p=ρgL _t0106

Among them, p—the pressure before the electric valve; ρ—the drainage density; L ₀ —the design liquid level value of the first flash tank; Q ₀ —the design drainage flow rate; The length of a flash tank pipeline; r—the radius of the first flash tank; Q _s —the flow rate entering the upstream continuous blowdown expander; Q—the instantaneous flow rate entering the first flash tank; S2: The increase in the flow rate of the first flash tank (1) is equal to the increase in the flow rate of the second flash tank (2), so the output pump at the outlet of the second flash tank (2) needs to be increased The flow is discharged, so the frequency of the pump is initially calculated as:

Since the circulating concentrated water pipeline is a self-operated electric valve, the increase in the frequency of the pump will lead to an increase in the flow of the circulating pipeline. According to the experimental data of the self-operated pressure regulating valve and the characteristics of the pipeline, the relationship between the flow of the circulating pipeline and the flow of the water pump is obtained:

f2 is the predictive control function of the liquid level of the second flash tank (2), and the control value is the frequency of the row output pump (3); Among them, Q ₀ —design continuous drainage flow; Q—instantaneous flow into the first flash tank; q—single-rotation flow of continuous shooting output pump; n—rated speed of continuous shooting output pump; f ₀ —design continuous drainage flow Q ₀ The frequency of the pump when debugging is stable; Q ₂₁ —the water pump flow corresponding to f ₂₁ in the initial calculation; Q _x —the circulation pipeline flow; S3: The main power of the negative pressure control of the second flash tank (2) comes from 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 exhaust The main reason for the fluctuation of air pressure is the fluctuation of the water intake of the deaerator, so according to the relationship between the water intake of the high-pressure deaerator and the exhaust pressure, the relationship between the exhaust pressure and the injection ratio, the injection ratio and the valve The relationship between the openings can realize the advancement of the pumping volume, and adjust to keep the pressure of the second flash tank (2) stable; f ₃ is the pressure control function of the second flash tank (2), outputting the opening of the electric valve between the condenser (8) and the steam ejector (6): f ₃ =7.4302δ ³ -8.8455δ ² +5.8077δ-1.0291

Among them, δ—injection ratio of steam ejector; p _f —exhaust pressure of high-pressure deaerator; Q _s —water intake of single deaerator.

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