WO2015149548A1 - Control system and method for air ejector in water ring vacuum pump unit - Google Patents

Abstract

A control system and method for an air ejector in a water ring vacuum pump unit. The control system comprises a DCS, a pressure sensor (8), a temperature sensor (9), a gas circuit bypass valve (5), and a drive gas valve (6). The pressure sensor (8) is disposed on a pumping pipeline of the water ring vacuum pump unit. The temperature sensor (9) is disposed on a working water pipeline of a water ring vacuum pump (3). A signal of the pressure sensor (8) and a signal of the temperature sensor (9) are input into the DCS. The gas circuit bypass valve (5) is disposed on a pipeline connected to an air ejector (2) in parallel. The drive gas valve (6) is disposed on a drive gas inlet pipeline of the air ejector (2). Both the gas circuit bypass valve (5) and the drive gas valve (6) are connected into the DCS. By using the control system, the input moment and the withdrawal moment of the air ejector can be accurately controlled, cavitation can be effectively avoided, the vacuum of a pumped system can be declined, and the system can efficiently and stably operate.

Description

Atmospheric injector control system and control method thereof in water ring vacuum pump unit Technical field

The invention belongs to the field of vacuum equipment, and particularly relates to an atmospheric injector control system and a control method thereof in a water ring vacuum pump unit.

Background technique

At present, power plants generally use a liquid ring vacuum pump unit as a vacuum pumping device for the condenser. The higher the vacuum of the condenser, the higher the power generation efficiency of the power plant, so the liquid ring pump is operated at the ultimate vacuum (the ultimate vacuum here refers to the highest vacuum that can be achieved when the liquid ring pump is working). Since the liquid ring vacuum pump uses water as the working fluid, the liquid ring vacuum pump operates under extreme vacuum and cavitation will occur. Cavitation is a physical phenomenon. At a certain temperature, in the suction working area of the liquid ring pump, the pressure is low to a certain extent, a part of the gas dissolved in the working fluid will be precipitated from the liquid ring, and the lower the pressure (or the closer it is to When the saturated vapor pressure of the liquid ring is), the more bubbles are precipitated from the liquid ring, the faster the speed, when the suction pressure reaches the saturated vapor pressure of the liquid ring, the liquid ring is in a boiling state, and the pumping amount of the liquid ring pump will be zero. . From the suction working area of the liquid ring pump to the discharge working area, due to the gradual increase of the pressure, the bubbles which are precipitated from the liquid ring in the suction working area are sharply reduced and even broken. At the same time as the large bubble bursts, the liquid particle will fill the cavity generated when the bubble is broken at a high speed, and collide with each other to form a water hammer. The frequency of this water hammer is as high as 2500 Hz and the pressure is as high as 49 MPa, so that the surface of the blade is pocked. When it is serious, the metal on the surface of the blade peels off to form a honeycomb shape. In addition to the mechanical force, cavitation damage is accompanied by many complicated functions such as electrolysis and chemical corrosion. The cavitation site of the liquid ring vacuum pump has a rapid drop in pumping capacity, which generates a lot of noise and vibration, and the impeller is quickly damaged. The method of fundamentally avoiding the cavitation of the liquid ring vacuum pump is to add an atmospheric ejector in front of the liquid ring vacuum pump, and then compress the gas through the atmospheric ejector to enter the liquid ring vacuum pump, and the inlet pressure of the liquid ring vacuum pump is increased. The eclipse can be avoided. Moreover, the atmospheric ejector has the ability to further increase the vacuum of the condenser, so more and more power plants use the unit of the atmospheric ejector + liquid ring vacuum pump. The water ring vacuum pump unit of the present invention refers to the water ring vacuum pump + atmosphere. Assembly of all components such as injector + gas water separator + heat exchanger.

The advantages of atmospheric ejector are only manifested in high vacuum. When vacuuming, the pumping capacity is not good with liquid ring vacuum pump alone, so controlling the input and withdrawal of atmospheric ejector can ensure efficient operation of the unit. In the prior art, the atmospheric injector is controlled by setting a pressure switch at the suction port of the unit to set two pressure values. Therefore, the following disadvantages are caused: since the cavitation is related to the working water temperature of the water ring vacuum pump, the atmospheric injector is not put into the air injector according to the pressure setting in the case of high water temperature in summer, but the liquid ring vacuum pump has cavitation and vibration. , The noise is intensified, which greatly shortens the service life of the liquid ring vacuum pump. On the contrary, in the case of low water temperature in winter, there is no cavitation actually, but the atmospheric injector is put in, so that the pumping capacity of the whole set of equipment is reduced, resulting in condensation. The vacuum is reduced, which increases the cost of power generation; and when the method is switched, the pumping capacity of the pumping device changes greatly, which in turn affects the stability of the operation of the condenser and the turbine. The above situation also occurs in high vacuum processes such as pharmaceuticals, chemicals, and the like.

Summary of the invention

The technical problem to be solved by the present invention is to provide a control system and a control method for effectively controlling the timing of the injection and withdrawal of the atmospheric injector for the vacuum pump unit of the high vacuum industry in view of the deficiencies of the prior art.

The technical problem to be solved by the present invention is achieved by the following technical solutions:

An atmospheric injector control system in a water ring vacuum pump unit, comprising a distributed control system referred to as DCS, a pressure sensor, a temperature sensor, a gas bypass valve, a driving gas valve, wherein the pressure sensor is disposed on an air suction line of the water ring vacuum pump unit The temperature sensor is disposed on the working water pipe of the water ring vacuum pump, the signal input of the pressure sensor and the temperature sensor is input to the DCS, the gas path bypass valve is disposed on the pipeline parallel to the atmospheric injector, and the driving gas valve is disposed in the driving gas of the atmospheric injector On the inlet line, both the gas bypass valve and the drive gas valve are connected to the DCS.

Specifically, the atmospheric ejector is connected to the air outlet of the steam separator in the water ring vacuum pump unit through a driving gas inlet line, and the working water line of the water ring vacuum pump is connected to the water outlet of the steam separator. The temperature sensor is disposed at the heat exchanger inlet of the working water pipe of the water ring vacuum pump.

as well as:

The control method of the atmospheric injector control system in the water ring vacuum pump unit,

First, according to the experiment, the following functional relations are summarized:

(1) When the water ring vacuum pump generates cavitation, the working water temperature t of the water ring vacuum pump is a function of the pressure P of the pumping system: P1=F(t);

(2) Determine the minimum pressure increase value k1 according to the experiment, so that P2=F(t)+k1, and use P2 as the minimum allowable pressure value of the pumping system before the water ring vacuum pump unit is put into the atmospheric injector;

(3) Determine the maximum pressure increase value k2 according to the experiment, so that P3=F(t)+k2, and use P3 as the maximum allowable pressure value of the pumping system before the water ring vacuum pump unit withdraws from the atmospheric injector.

2. Input the above-mentioned function calculation program of P1, P2 and P3 with t in the DCS, so that the atmospheric injector control system operates as follows:

(1) The temperature sensor will measure the working water temperature t, the pressure sensor will be input to the DCS by the pumping system pressure measured value P, and the DCS will substitute the measured value of the working water temperature into the above-mentioned functional relationship between P1, P2 and P3 and t. The pressure calculation values P1, P2 and P3 are obtained, and the measured value P of the pumped system is compared with the pressure calculation values P1, P2 and P3;

(2) When P≤P2, close the gas bypass valve, open the driving gas valve, and put the atmospheric injector into the pumping;

(3) When P ≥ P3, open the gas bypass valve and close the driving gas valve to allow the atmospheric ejector to withdraw the suction.

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments.

DRAWINGS

FIG. 1 is a structural diagram of a system according to an embodiment of the present invention.

2 is a block diagram of an atmospheric injector control system of the present invention.

Figure 3 is a graph of the functional relationship of the present invention.

Fig. 4 is a graph showing the pumping capacity of the water ring pump under the working water conditions at different temperatures and the pumping capacity of the atmospheric injector and the suction pressure of the pumped system.

detailed description

1 is a schematic view of a water ring vacuum pump unit and an atmospheric injector control system thereof according to the present invention.

As shown, the gas from the pumping system passes through the inlet main valve 1, the atmospheric ejector 2, the water ring vacuum pump 3, and then into the gas water separator 4. A bypass valve 5 is provided between the atmospheric injector 2 and the water ring vacuum pump 3, and a driving gas valve 6 is installed between the atmospheric injector 2 and the gas-water separator 4. When the bypass valve 5 is closed and the driving gas valve 6 is opened, the gas in the gas-water separator 4 is compressed by the atmospheric ejector 2 and then enters the water ring vacuum pump 3, at which time the atmospheric ejector 2 is put into operation. When the bypass valve 5 is opened while the driving gas valve 6 is closed, the atmospheric injector 2 is withdrawn at this time, and the gas from the pumping system directly enters the water ring vacuum pump 3. After the gas-water mixture discharged from the water ring vacuum pump 3 is separated by the gas-water separator 4, the gas is discharged from the top exhaust port, and the water is collected at the bottom and cooled by the heat exchanger 7, and then returned to the liquid-ring vacuum pump 3 for recycling. . The unit inlet is equipped with a pressure sensor 8 for measuring the pressure P of the pumping system, and the gas water separator 4 to the heat exchanger 7 A temperature sensor 9 is installed in the pipeline, and the water temperature t discharged from the liquid ring vacuum pump 3 is measured, that is, the working water temperature in the pump body of the liquid ring vacuum pump 3. The values of the pressure sensor 8 and the temperature sensor 9 are operated by DCS logic, and then the intake and withdrawal of the atmospheric injector 2 are achieved by controlling the opening and closing states of the bypass valve 5 and the driving gas valve 6.

2 is a block diagram of an atmospheric injector control system of the present invention, as shown, including a distributed control system (DCS), a pressure sensor, a temperature sensor, a pneumatic bypass valve, a driving gas valve, and the pressure. The sensor and temperature sensor temperature inputs the measured signal into the DCS, and both the bypass valve and the driven gas valve are connected to the DCS.

The atmospheric injector control system operates as follows:

(1) The temperature sensor will measure the working water temperature t, the pressure sensor will be input to the DCS by the pumping system pressure measured value P, and the DCS will calculate the working water temperature measured value t into the functional relationship between P1, P2 and P3 and t. Calculating the pressure calculation values P1, P2 and P3, and comparing the measured value P of the pumped system with the pressure calculation values P1, P2 and P3;

(2) When P≤P2, close the gas bypass valve, open the driving gas valve, and put the atmospheric injector into the pumping;

(3) When P ≥ P3, open the gas bypass valve and close the driving gas valve to allow the atmospheric ejector to withdraw the suction.

Figure 3 is a graph of the functional relationship of the present invention.

As shown in the figure, the abscissa in Fig. 3 is the value of the working water temperature t, which is the value measured by the temperature sensor 9 in Fig. 1. In Fig. 3, the ordinate is the suction pressure P value (the unit of P is hPa, followed by abs to indicate the absolute pressure), that is, the value measured by the pressure sensor 8 in Fig. 1. The graph is derived from repeated trials and field experience.

In Figure 3, there are a total of three curves divided into three regions. The area below curve 2 is the working area of the atmospheric injector, the area above curve 3 is the working area of the liquid ring pump, and the area between curve 2 and curve 3 is the transition. region.

Curve 1 is the cavitation curve of the liquid ring vacuum pump. The functional relationship is P1=F(t). That is to say, when the liquid ring vacuum pump works in the area below this curve (ie, P≤P1), cavitation will occur.

Curve 2 is the atmospheric injector input curve, the relationship is P2 = F(t) + k1 (k1 is a constant), and when P ≤ P2, it is put into the atmospheric injector. K1 is a value given based on experimental experience and is equivalent to a safety margin, that is, it cannot be put into the atmospheric injector when P=P1. K1 should be as small as possible, as long as P2 is slightly larger Just P1. The value of K1 is determined according to the pressure reduction time of the pumping system and the time required to be put into the atmospheric injector. It must be ensured that the time required to input the atmospheric injector is less than the time required for the pumping system pressure to decrease from P2 to P1, thereby effectively avoiding Cavitation occurs, so the range of k1 is 5hPa-10hPa. According to the characteristics of the water ring vacuum pump, after the atmospheric ejector is put into operation, the energy consumption of the water ring vacuum pump will increase. Therefore, under the premise of ensuring the input time of the atmospheric ejector, the K1 value should be taken as small as possible, that is, the atmospheric ejector is reduced. Work area. However, if the atmospheric ejector can be used to increase the vacuum of the pumped system and increase the efficiency of the pumping system, then K1 can take a larger value, that is, increase the working area of the atmospheric ejector.

Curve 3 is the atmospheric injector withdrawal curve, the relationship is P3 = F(t) + k2 (k2 is a constant), and when P ≥ P3, the atmospheric injector is withdrawn. The maximum pressure increase value K2 is determined according to the pumping capacity of the water ring pump and the atmospheric ejector (m ³ /min of the pumping capacity) and the experimental relationship of the pressure relationship of the pumping system (see Fig. 4), and the range is 25hPa-40hPa. . According to the experiment, when the pumping system pressure P ≥ P3, the pumping capacity of the water ring pump is greater than the pumping capacity of the atmospheric ejector, so the atmospheric ejector should be withdrawn to keep the pumped system as low as possible. At the same time, K2 has a buffering effect, because if only P2=F(t)+k1, when the pressure P of the pumped system fluctuates around the value of P2, the DCS will continuously command the input and exit of the atmospheric injector. Therefore, under the premise of ensuring that the pressure fluctuation value of the pumping system after the evacuation of the atmospheric ejector does not cause repeated injection into the atmospheric ejector, the K2 value should be taken as small as possible, that is, the working area of the atmospheric ejector is reduced. However, if the atmospheric injector is used to reduce the pressure of the pumping system, that is, to increase the vacuum of the pumping system to increase the efficiency of the pumping system, then K2 can take a larger value, that is, increase the working area of the atmospheric injector.

In short, the selection of K1 and K2 values comprehensively considers the concept of avoiding cavitation, saving energy and reducing consumption, improving efficiency, different pumping equipment, different pumping systems, different working conditions, different equipment manufacturing and installation levels, etc. Other factors will affect the optimal selection of K1 and K2. The system can adjust the K1 and K2 values through DCS during equipment installation and commissioning, in order to achieve the best results.

The area below curve 2 in Fig. 3 is the working area of the atmospheric ejector, in which cavitation can be effectively avoided, and the pumping capacity of the atmospheric ejector is stronger than that of the liquid ring vacuum pump, and the effect of putting it into the atmospheric ejector is better. The area above curve 3 is the working area of the liquid ring pump. In this area, the pumping capacity of the atmospheric ejector is weaker than that of the liquid ring vacuum pump, and the effect of not putting it into the atmospheric ejector is better. The area between curve 2 and curve 3 is the transition zone where the pumping capacity of the atmospheric injector is comparable to that of a liquid ring vacuum pump, at which time the atmospheric injector can be cast or not.

The control system and method of the present invention can accurately control the timing of the injection and withdrawal of the atmospheric ejector, as shown by the three curves of Fig. 3, when the working water temperature is 33 ° C, correspondingly, the water ring pump of curve 1 Steam The corresponding pressure of the eclipse is 58.3hPa, the corresponding pressure of the atmospheric ejector input point of curve 2 is 63.3hPa, and the pressure of the withdrawal point of curve 3 is 83.3hPa; and when the working water temperature is 15°C, the corresponding curve 1 water ring pump The cavitation point pressure is 26.2 hPa, the curve 2 atmospheric injector input point pressure is 31.2 hPa, and the curve 3 withdrawal point pressure is 51.2 hPa.

If only the pressure switch and two pressure values are set according to the prior art to control the atmospheric ejector, if the atmospheric ejector is withdrawn when the pumping system pressure is set at 70hPaA, the pressure setting is set when the working fluid temperature is 33 °C. Withdrawal of the atmospheric ejector, since it is in the transition zone, there is no problem, but if the water temperature is 15 °C, 70hPaA is already higher than the atmospheric ejector withdrawal point 51.2hPa, which has already landed in the water ring pump working area, so It is not necessary to withdraw the atmospheric ejector at a pressure of 70 hPaA, but the atmospheric ejector should be withdrawn at more than 51.2 hPa. On the contrary, if the pressure of the pumping system is set to 40 kPa, the atmospheric injector is put at the set pressure value when the water temperature is 15 °C, because it falls in the transition zone, but if the water temperature is 33 °C. At the time, 40hPaA has been lower than the water ring pump cavitation point of 58.3hPa, and severe cavitation has occurred. Therefore, it should be put into the atmospheric injector when the pumping system pressure is greater than 58.3hPa, and should not be put into the atmospheric injector at 40hPaA.

Fig. 4 is a graph showing the pumping capacity of the water ring pump under the working water conditions at different temperatures and the pumping capacity of the atmospheric injector and the suction pressure of the pumped system. There are four curves in the figure, the abscissa is the suction pressure, and the ordinate is the pumping capacity.

Curve 1 is the pumping capacity curve of the water ring pump at 15 ° C water temperature;

Curve 2 is the pumping capacity curve of the water ring pump at 20 ° C water temperature;

Curve 3 is the pumping capacity curve of the water ring pump at 30 ° C water temperature;

Curve 4 is the pumping capacity curve of the atmospheric ejector. Since the atmospheric ejector does not use water as the working fluid, the pumping capacity of the atmospheric ejector has nothing to do with the water temperature, only one.

It can be seen from Fig. 4 that when the water temperature of the water ring pump is 15 °C, the curves 1 and 4 have no intersection, and at this time, the pumping capacity of the atmospheric injector is smaller than that of the water ring vacuum pump, so at 15 °C. The water temperature is not required to be put into the atmospheric injector.

When the working water temperature of the water ring pump is 20 ° C, the intersection of curves 2 and 4 is 60 hPa, and the pumping capacity of the water ring pump is equal to the pumping capacity of the atmospheric injector. When the suction pressure is greater than 60hPa, the pumping capacity of the water ring pump is greater than that of the atmospheric ejector. At this time, the atmospheric ejector should be withdrawn, otherwise the pressure of the pumped system will increase and the vacuum will decrease. When the suction pressure is less than 60hPa, when the water ring pump approaches the ultimate pressure of 50hPa, it is close to the cavitation point of the working water temperature of 20°C. At this time, it is put into the atmospheric injector to Increase the suction pressure of the water ring pump to avoid cavitation. Moreover, the pumping capacity of the atmospheric ejector at this time is greater than the pumping capacity of the water ring pump, and the pressure of the pumped system is kept constant or lower.

Similarly, when the water temperature of the water ring pump is 30 ° C, the intersection of curves 3 and 4 is at 100 hPa, and the pumping capacity of the water ring pump is equal to the pumping capacity of the atmospheric injector. When the suction pressure is greater than 100 hPa, the pumping capacity of the water ring pump is greater than the pumping capacity of the atmospheric injector, at which time the atmospheric injector is withdrawn. When the suction pressure is less than 100hPa, it is close to the cavitation point of the working water temperature of 30°C. At this time, the atmospheric injector should be put into the air to avoid cavitation, and at this time, the pumping capacity of the atmospheric injector is greater than the pumping capacity of the water ring pump. In addition, the pressure of the pumped system can be kept constant or lower.

In summary, the control system and method of the present invention can accurately control the input and withdrawal timing of the atmospheric ejector, and put into the atmospheric ejector before the liquid ring vacuum pump cavitation, thereby effectively preventing the occurrence of cavitation and improving the pumping of the unit. The ability to withdraw the atmospheric ejector when the atmospheric ejector pumping capacity is weaker than the liquid ring vacuum pump avoids causing the vacuum of the pumped system to drop, so that the pumping capacity of the entire unit is always at its highest state, ensuring stable operation of the system. The invention is applicable to the high vacuum industry, in particular to vacuuming the condenser of the power plant, which can improve the power generation efficiency of the power plant and ensure efficient and stable operation of the power plant.

Claims (6)

An atmospheric injector control system in a water ring vacuum pump unit, characterized in that it comprises a distributed control system referred to as DCS, a pressure sensor, a temperature sensor, a gas bypass valve, a driving gas valve, and the pressure sensor is arranged in a water ring On the suction line of the vacuum pump unit, the temperature sensor is disposed on the working water pipe of the water ring vacuum pump, the signal of the pressure sensor and the temperature sensor is input to the DCS, and the gas path bypass valve is disposed in parallel with the atmospheric injector. The driving gas valve is disposed on the driving gas inlet pipe of the atmospheric injector, and the gas bypass valve and the driving gas valve are both connected to the DCS. The atmospheric ejector control system of a water ring vacuum pump unit according to claim 1, wherein said atmospheric ejector is connected to an air outlet of a steam separator in a water ring vacuum pump unit through a driving gas inlet line, The working water pipe of the water ring vacuum pump is connected to the water outlet of the steam separator. The atmospheric ejector control system of a water ring vacuum pump unit according to claim 1, wherein said temperature sensor is disposed at a heat exchanger inlet of a working water pipe of the water ring vacuum pump. A method for controlling an atmospheric ejector control system in a water ring vacuum pump unit according to any one of claims 1 to 3, characterized in that: First, according to the experiment, the following functional relations are summarized: (1) When the water ring vacuum pump generates cavitation, the working water temperature t of the water ring vacuum pump is a function of the pressure P of the pumping system: P1=F(t); (2) Determine the minimum pressure increase value k1 according to the experiment, so that P2=F(t)+k1, and use P2 as the minimum allowable pressure value of the pumping system before the water ring vacuum pump unit is put into the atmospheric injector; (3) Determine the maximum pressure increase value k2 according to the experiment, so that P3=F(t)+k2, and use P3 as the maximum allowable pressure value of the pumping system before the water ring vacuum pump unit withdraws from the atmospheric injector. 2. Input the above-mentioned function calculation program of P1, P2 and P3 with t in the DCS, so that the atmospheric injector control system operates as follows: (1) The temperature sensor will measure the working water temperature t, the pressure sensor will be pumped system pressure The measured value P is input to the DCS. The DCS substitutes the measured value t of the working water temperature into the above-mentioned relationship between P1, P2 and P3 and t to calculate the pressure calculation values P1, P2 and P3, and then the measured values of the pressure of the pumped system. P is compared with pressure calculation values P1, P2 and P3; (2) When P≤P2, close the gas bypass valve, open the driving gas valve, and put the atmospheric injector into the pumping; (3) When P ≥ P3, open the gas bypass valve and close the driving gas valve to allow the atmospheric ejector to withdraw the suction. The control method of the atmospheric injector control system in the water ring vacuum pump unit according to claim 4, characterized in that the minimum pressure increase value k1 of the pumped system is 5-10 hPa. The control method of the atmospheric injector control system in the water ring vacuum pump unit according to claim 4, wherein the maximum pressure increase value k2 of the pumped system is 25-40 hPa.

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