CN111578566A - Control System of Gas Bearing Centrifugal Compressor - Google Patents

Abstract

The invention discloses a control system of a gas bearing type centrifugal compressor, and relates to the technical field of compressors. The compressor adopts an auxiliary gas pressurization injection flow regulating valve or a gas bearing type centrifugal compressor adopting an auxiliary liquid pump to supply liquid, and is applied to a refrigeration system, each mode is used for controlling the stable gas supply pressure difference of a gas bearing, the pressure of an oil groove is balanced to the low-pressure evaporation pressure side through a balance pipe, the oil supply of an oil film bearing is realized after low-pressure lubricating oil is lifted to higher pressure through the action of an oil pump, the oil supply pressure difference is the difference value of the oil supply pressure and the evaporation pressure, so the control target of the refrigeration system is to keep the outlet water temperature of chilled water stable, namely the evaporation pressure is stable, and the pressure of the oil groove is always stable.

Description

Control System of Gas Bearing Centrifugal Compressor

technical field

The invention relates to the technical field of compressors, in particular to a control system of a gas bearing centrifugal compressor.

Background technique

The principle of gas bearing and oil film bearing is the same, both are high pressure dynamic pressure oil film or high pressure dynamic pressure air film bearing design. The high pressure oil supply enters the bearing or the high pressure air supply enters the bearing, forming a stable dynamic pressure oil film or air film, the thickness of the dynamic pressure oil film, the wedge angle of the oil film surface of the thrust bearing, the wedge angle of the oil film ring of the radial bearing, the shaft/ The eccentric angle and eccentricity of the bearing, the stiffness and damping of the oil film have adaptive stability characteristics to ensure the stable bearing and operation of the shafting. Dynamic pressure bearings are used in centrifugal compressors and refrigeration systems. Due to changes in operating conditions, the discharge pressure and suction pressure fluctuate, and the variable operating conditions deviate from the design operating conditions. At the same time, due to changes in air conditioning loads, the compressor needs to be unloaded to reduce Rotation speed and variable load deviate from the design operating conditions; in variable operating conditions and variable load operation, the generated axial and radial loads (for radial bearings) and axial loads (for thrust bearings) are changing at any time. Film/oil film thickness, oil film/air film surface wedge angle, oil film/air film ring wedge angle, eccentric angle and eccentricity of the shaft center relative to the bearing center will change, and the stiffness and damping of the air film and oil film will also change to automatically It can adapt to the change of load and maintain the stable operation of the shaft system.

In order to realize high pressure dynamic pressure oil film bearing design or high pressure dynamic pressure air film bearing design, ensure stable and reliable axial bearing capacity and radial bearing capacity of the bearing, and form an oil film or gas film with stable stiffness and damping between the bearing and the shaft; The oil supply pressure difference or the supply air pressure difference must be constantly controlled, and the supply air temperature and oil supply temperature must be constantly controlled.

SUMMARY OF THE INVENTION

In view of the above technical problems, the present invention overcomes the shortcomings of the prior art, and provides a control system for a gas bearing centrifugal compressor.

In order to solve the above technical problems, the present invention provides a control system of a gas bearing centrifugal compressor.

The use of gas bearings is used in semi-hermetic or open centrifugal compressor systems. In Figures 3 and 4, the auxiliary gas booster ejection flow regulating valve is used; in Figures 5, 6 and 9, the auxiliary liquid pump is used for boosting; in Figures 7, 8 and 10, the auxiliary gas booster is used. The pressure ejection flow regulating valve also adopts the auxiliary liquid pump for liquid pressurization.

The auxiliary gas booster ejection flow regulating valve and the auxiliary liquid pump booster, each of which is used to control the stable supply pressure difference of the gas bearing. The meaning of their use is that when the supply pressure difference of the refrigeration system meets the gas bearing pressure difference When the minimum supply pressure difference of the gas bearing is not met, the auxiliary gas booster ejection flow regulating valve remains closed, and the auxiliary liquid pump remains closed; when the minimum supply pressure difference of the gas bearing is not met, the auxiliary liquid pump starts, or the auxiliary gas increases The pressure jet flow regulating valve opens to provide additional boost supply differential pressure. The booster ejection flow regulating valve is a part of the gas drawn from the high pressure exhaust gas of the compressor. The different percentage openings of the regulating valve will change the gas flow and gas pressure entering the ejector 16, and ultimately change the gas supply to the gas bearing Differential pressure, no power dissipation element; liquid pump is a power dissipation element.

，液体泵的扬程为

，泵的转速

。In FIG. 1 and FIG. 2 , the gas in the gas return header 110 of the gas bearing is returned to the evaporator of the refrigeration system by means of differential pressure. The evaporator itself is provided with a pressure sensor 301 for controlling the secondary throttle expansion valve. 5 liquid supply and control the small temperature difference of the evaporator; a pressure sensor 302 is provided on the shell of the flash economizer itself, which is used to control the liquid supply of the primary throttle expansion valve 4 and the subcooling degree of the condenser. 301 and 302 are pressure sensors that are generally equipped in refrigeration systems, which are used for flow regulation control of the refrigeration system itself. Therefore, in addition to the pressure sensor configured in the existing refrigeration system, it is necessary to additionally arrange the pressure sensor 303 on the liquid supply circuit 106 of the liquid pump 7 and the pressure sensor 304 on the air supply circuit 107 of the gas bearing. The supply pressure difference of the gas bearing is

, the head of the liquid pump is

, the speed of the pump

.

(1)

(1)

(2)

(2)

(3)

(3)

(4)

(4)

，如果供气压差不足时，即

，则启动液体泵进行液体加压或者打开气体增压引射流量调节阀进行气体加压，大部分的制冷系统的运行工况下，当实际供气压差

大于此供气压差设定值300kPa时，液体泵或者气体增压引射流量调节阀是不需要开启的；当实际供气压差

小于此供气压差设定值300kPa时，液体泵或者气体增压引射流量调节阀才需要运行，气体或者液体的增压最终都是提高气体轴承的供气压力。液体泵从停机到启动到最小转速运行，必然会产生供气压力的突变，也必然导致供气流量突然增大从而引起轴承的载荷以及刚度、阻尼等轴承特性会有较大的变化，影响正常的离心压缩机的运行，所以采用变频液体泵或者定频液体泵加内压差调节阀来缓慢的提高供气压力。变频液体泵的原理比较简单，泵的流量与转速的平方成正比，泵的流量和泵的扬程为二次曲线关系，因此随着转速从0逐渐增大，泵的流量和出口压力也逐步增大，这是一个比较平缓的过程，最终的泵的转速和气体轴承的供气压差之间也会是二次曲线的关系。公式（3）为泵的转速

和气体轴承的供气压差

的关系曲线，需要实际测定不同的转速运行时，气体轴承的供气压差差，通过非线性拟合即可得到公式（3）的各系数

，

，

，不同的液体泵的选型，气体轴承的设计，这个关系式不同的，但是原理和方法是相同的。First, set the minimum supply pressure differential for the gas bearing

, if the supply air pressure difference is insufficient, namely

, then start the liquid pump to pressurize the liquid or open the gas pressurization ejection flow control valve to pressurize the gas. Under most operating conditions of the refrigeration system, when the actual supply pressure difference

When the set value of the supply pressure difference is greater than 300kPa, the liquid pump or gas booster ejection flow control valve does not need to be opened; when the actual supply pressure difference

When it is less than the set value of the supply pressure difference of 300kPa, the liquid pump or the gas booster ejection flow control valve needs to be operated, and the booster of the gas or the liquid ultimately increases the gas supply pressure of the gas bearing. When the liquid pump runs from shutdown to startup to the minimum speed, there will inevitably be a sudden change in the air supply pressure, which will inevitably lead to a sudden increase in the air supply flow, which will cause the bearing load, stiffness, damping and other bearing characteristics to change greatly, affecting the normal operation. Therefore, a variable frequency liquid pump or a fixed frequency liquid pump and an internal differential pressure regulating valve are used to slowly increase the air supply pressure. The principle of the variable frequency liquid pump is relatively simple. The flow rate of the pump is proportional to the square of the rotational speed. The flow rate of the pump and the head of the pump are in a quadratic curve relationship. Therefore, as the rotational speed gradually increases from 0, the flow rate and outlet pressure of the pump also gradually increase. Large, this is a relatively smooth process, and the final relationship between the pump speed and the supply pressure difference of the gas bearing will also be a quadratic curve. Equation (3) is the rotational speed of the pump

Supply pressure difference with gas bearing

It is necessary to actually measure the difference in supply pressure of the gas bearing when running at different speeds. The coefficients of formula (3) can be obtained by nonlinear fitting.

,

,

, The selection of different liquid pumps, the design of gas bearings, this relationship is different, but the principle and method are the same.

However, the process of gradually opening the gas booster ejection flow regulating valve from the closed state of 0% opening is relatively gentle, which can basically completely avoid the sudden change of the gas supply pressure of the gas bearing. However, the gas booster ejection flow control valve draws out a small part of the high-pressure refrigerant gas from the high-pressure exhaust of the compressor of the refrigeration system. It does not do work itself, so it is a passive adjustment mechanism, but the adjustment is relatively stable; the liquid pump does work The components belong to the active adjustment mechanism, and the adjustment process is relatively sudden. The use of variable frequency liquid pumps will achieve better stable adjustment effects. If the two are combined, as shown in Figure 7, Figure 8 and Figure 10, the effect will be better.

和气体轴承的供气压差

的关系曲线，需要实际测定不同的调节阀百分比开度（%）时，气体轴承的供气压差，通过非线性拟合即可得到公式（4）的各系数

，

，

，根据调节阀的线性特性和流量特性选型，以及气体轴承的设计，这个关系式不同的，但是原理和方法是相同的。Formula (4) increases the opening degree of the gas pressurized ejection flow control valve

Supply pressure difference with gas bearing

When it is necessary to actually measure the percentage opening (%) of different control valves, the supply pressure difference of the gas bearing can be obtained by nonlinear fitting to obtain the coefficients of formula (4).

,

,

, according to the selection of the linear characteristics and flow characteristics of the regulating valve, as well as the design of the gas bearing, this relationship is different, but the principle and method are the same.

满足之后才能再次关闭液体泵；同理，如果液体泵关闭之后，最小供气压差会降低，直至

满足之后才能再次开启液体泵。采用上行回差和下行回差设定，可以根据试验测定，保证液体泵不会频繁开启和关闭，也保证供气压差稳定在设定的小的区间内，轴承工作稳定。Further, the opening and closing of the liquid pump: after the liquid pump is turned on, the supply air pressure increases and the supply air pressure difference also increases, if it is greater than the set value of the minimum supply air pressure difference, until the

The liquid pump can be turned off again after it is satisfied; for the same reason, if the liquid pump is turned off, the minimum supply air pressure difference will decrease until

After this is satisfied, the liquid pump can be turned on again. The upward hysteresis and the downward hysteresis are set, which can be determined according to the test to ensure that the liquid pump will not be turned on and off frequently, and also ensure that the supply air pressure difference is stable within the set small interval, and the bearing works stably.

Further, the opening and closing of the liquid pump is associated with frequency conversion control.

The beneficial effects of the present invention are:

(1) In the present invention, the pressure of the oil tank is balanced to the low-pressure evaporation pressure side through the balance pipe, and the low-pressure lubricating oil is raised to a higher pressure through the action of the oil pump, so as to realize the oil supply of the oil film bearing and the oil supply pressure difference. It is the difference between the oil supply pressure and the evaporation pressure. In this way, since the control goal of the refrigeration system is to keep the outlet temperature of the chilled water stable, that is, the evaporation pressure is stable, the pressure of the oil tank is always relatively stable, and there will be no greater stability. The pressure before the oil pump is low, and the entire pipeline can also be designed for low pressure.

Description of drawings

Figure 1 is a structural layout diagram of a centrifugal compressor with a gas bearing;

Figure 2 is a structural layout diagram of a centrifugal compressor with a gas bearing;

Figure 3 is the flow chart of the refrigeration system - the high pressure liquid phase pipeline leads out liquid and pressurizes it with gas;

Figure 4 is the flow chart of the refrigeration system - the medium pressure liquid phase pipeline leads out the liquid and the gas is pressurized;

Figure 5 is the flow chart of the refrigeration system - the high pressure liquid phase pipeline leads out the liquid and has a liquid pump;

Figure 6 is the flow chart of the refrigeration system - the medium pressure liquid phase pipeline leads out the liquid and has a liquid pump;

Figure 7 is the flow chart of the refrigeration system - the high pressure liquid phase pipeline leads out the liquid and the liquid pump and the gas pressurization;

Figure 8 is the flow chart of the refrigeration system - the medium pressure liquid phase pipeline leads out the liquid and the liquid pump and the gas pressurization;

Figure 9 is the flow chart of the refrigeration system - the low pressure liquid phase pipeline leads out the liquid and the liquid pump;

Figure 10 is the flow chart of the refrigeration system - the low pressure liquid phase pipeline leads out the liquid and the liquid pump and the gas pressurization;

Figure 11 shows the start and stop control of the liquid pump.

Among them: 1-centrifugal compressor; 2-condenser; 3-flash economizer; 4-primary throttle expansion valve; 5-secondary throttle expansion valve; 6-evaporator; 7-liquid pump; 8 - impeller end gas radial bearing; 9 - non-impeller end gas radial bearing; 10 - thrust bearing; 11 - reverse thrust bearing; 12 - thrust collar; 13 - motor/rotor shaft assembly; 14 - motor Stator; 15-Impeller; 16-Venturi restrictor; 17-One-way valve; 18-Gas booster ejection flow regulating valve; 19-Impeller end landing bearing; 20-Impeller end landing bearing 100-Exhaust pipeline ; 101- suction pipeline; 102- condenser outlet liquid phase pipeline; 103- economizer gas phase pipeline 104- economizer liquid phase pipeline; 105- gas bearing liquid supply main pipe 106- liquid pump discharge main pipe; 107 - Gas bearing gas supply manifold; 108 - Bearing gas supply distribution pipeline; 109 - High pressure nozzle gas supply holes for each gas bearing; 110 - Gas bearing return gas manifold; 111 - Gas booster ejection pipeline; 112 - Evaporation 301-evaporation pressure sensor; 302-intermediate pressure sensor; 303-liquid supply pressure sensor; 304-air supply pressure sensor.

Detailed ways

This embodiment provides a control system for a gas bearing centrifugal compressor. In FIGS. 1 to 2 , a semi-hermetic centrifugal compressor using a gas bearing is used. The gas radial bearings 8 and 9 are distributed across the rotor/shaft of the motor. from both sides. Landing bearings 19 and 20 are distributed on the inner sides of the span of the motor rotor/shaft, and the clearance of the landing bearing is slightly smaller than that of the gas bearing. Dimension D is the clearance of the landing bearing, dimension D1 is the clearance of the gas bearing, D1>D. The impeller end radial bearing 8 and the non-impeller end gas radial bearing 9 provide radial load. The gas thrust bearing 10 provides a positive thrust towards the impeller end. When the centrifugal compressor operates stably in various high and low pressure differential conditions, the direction of the shafting force caused by the gas is towards the non-impeller end, so the thrust bearing 10 provides thrust against the gas force of this shafting. The reverse gas thrust bearing 11 provides the reverse thrust bearing force towards the non-impeller end. When the compressor is in the condition of small flow and large pressure difference, if shedding stall or surge occurs, the discharge pressure of the compressor will be reduced. Periodic oscillation will occur, and the exhaust pressure at the outlet of the impeller will flow backward to the suction side. At this time, the transient gas force of the compressor shaft system will be several times the reverse gas force toward the impeller end, so the reverse Thrust bearing 11 provides thrust against the transient gas forces of this shafting. The end faces on both sides of the thrust collar 12 rotating with the impeller shaft at high speed face the thrust bearing 10 and the reverse thrust bearing 11 on both sides respectively. The balance between the two bearings ensures the axial alignment of the shafting.

In Figures 3 and 4, gas radial bearings 8 and 9, gas thrust bearings 10 and 11, and their high pressure gas supply circuits are as follows: from the high pressure condenser outlet liquid phase line 102 (Figure 3), or in the middle The pressure economizer liquid phase line 104 (Fig. 4) leads out high pressure refrigerant saturated liquid or subcooled liquid (Fig. 3), or medium pressure refrigerant saturated liquid or subcooled liquid (Fig. 4), due to high pressure and The driving force of the low pressure differential pressure causes a small part of the liquid to enter the liquid supply main circuit 105 of the gas bearing through the liquid supply pipeline 102 (FIG. 3) or 104 (FIG. 4), and the refrigerant liquid flow is venturi throttled There will be a large amount of refrigerant liquid flashing gas after the device 16, the unflashed refrigerant liquid and the flashed refrigerant gas will be mixed, the flow rate will increase, the pressure will decrease, and flow through the gas supply main pipe 107 to the gas bearing at high speed, The gas-liquid mixture is then distributed to the respective bearings, radial bearings 8 and 9, and thrust bearings 10 and 11, respectively. The gas bearings 8-11 are provided with a number of tiny high-pressure nozzle air supply holes 109 in the circumferential and axial directions. The purpose of the high-pressure nozzle air holes is to completely flash the remaining refrigerant liquid in the gas-liquid mixture into gas, and finally the high pressure Air is supplied into the radial bearing annular wedge-shaped gap, as well as the wedge-shaped gap between the thrust bearing and the thrust collar 12 to form a high-pressure gas film with sufficient stiffness and damping to form a stable gas bearing capacity.

Optionally, in FIG. 5 and FIG. 6 , a gas pressurized ejection gas circuit 111 is used. From the exhaust pressure side of the compressor, the high-pressure gas is drawn out through the gas booster ejection pipeline 111, and the flow and pressure are adjusted by the gas booster ejection flow regulating valve 18, and then enters the ejector 16. When the control system detects that the gas supply When the pressure difference is insufficient, the flow rate of the high-pressure gas that ejects the pump liquid can be adjusted by the regulating valve 18. The function of the ejector 16 is also to pump the liquid of the high-pressure gas to pressurize the liquid in the liquid supply pipeline 105. The injector 16 is connected with the high-pressure gas to enter the gas supply circuit 107 of the gas bearing, and the flow and pressure of the gas and liquid in the gas supply circuit 107 are increased to ensure that the supply pressure difference of the gas bearing is stable within the range. The linear adjustment function of the valve 18 can achieve precise control of the supply air pressure difference.

Optionally, in FIG. 7 and FIG. 8 , a liquid pump 7 can be set on the gas bearing liquid supply main pipe 105 to increase the liquid supply pressure. When the liquid pump is started, it flows through the 106 pipeline and enters the 107 gas supply main pipe; the liquid When the pump is not started, it flows through the bypass line 110 and enters the gas supply main pipe 107 . The purpose of the one-way valve 17 is to ensure that when the liquid pump is not running, the refrigerant flows through the pipeline 110 into 107 through the pressure difference; and when the liquid pump is running, to prevent the backflow of the fluid. The purpose of the final liquid pump is to increase the air supply pressure of the gas bearing when necessary. When the centrifugal compressor runs in surge, or caused by a sudden load change, or operates in a low-pressure differential condition, it only depends on the high and low pressure of the refrigeration system. The driving force of the pressure difference, the air supply pressure of the gas bearing is low, and the bearing capacity is too small, the liquid pump can be started, and after the liquid is pressurized, a higher air supply pressure of the gas bearing is provided to improve the bearing capacity of the bearing.

Optionally, in FIGS. 9 and 10 , the refrigeration system has a liquid pump 7 and a gas booster ejection circuit 111 . More stable and reliable supply pressure differential control and stable operation of the gas bearing can be achieved. In Fig. 11, when the design with a liquid pump is adopted, the low-pressure refrigerant liquid can be directly drawn from the liquid phase area at the bottom of the evaporator, and the low-pressure refrigerant liquid can be drawn through the liquid pressurization and gas pressurization ejection circuit 111 of the liquid pump 7. After the refrigerant is raised to a higher refrigerant pressure, the gas supply of the gas bearing is realized. This design is similar to the design of high-pressure dynamic pressure oil film bearings. The pressure of the oil tank is balanced to the low-pressure evaporation pressure side through the balance pipe. Through the action of the oil pump, the low-pressure lubricating oil is raised to a higher pressure to realize the supply of oil-film bearings. Oil, the oil supply pressure difference is the difference between the oil supply pressure and the evaporation pressure, so because the control goal of the refrigeration system is to keep the outlet temperature of the chilled water stable, that is, the evaporation pressure is stable, then the pressure of the oil tank is always relatively stable. Larger stability occurs, the pressure before the oil pump is low, and the entire pipeline can also be designed according to low pressure. The design of low-pressure liquid injection or pumping liquid will be more stable from the control point of view.

In addition to the above-described embodiments, the present invention may also have other embodiments. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims (4)

1. a control system of a gas bearing type centrifugal compressor, it is characterized in that: described compressor adopts auxiliary gas booster ejection flow regulating valve or adopts the gas bearing type centrifugal compressor that auxiliary liquid pump supplies liquid, it is applied to In the refrigeration system, each method is used to control the stable supply pressure difference of the gas bearing. The meaning of their use is that when the supply pressure difference of the refrigeration system meets the minimum supply pressure difference of the gas bearing, the auxiliary gas The booster ejection flow regulating valve remains closed, and the auxiliary liquid pump remains closed; when the minimum supply pressure difference of the gas bearing is not met, the auxiliary liquid pump is started, or the auxiliary gas booster ejection flow regulating valve is opened to provide additional Boost supply pressure differential. 2. The control system for a gas bearing centrifugal compressor according to claim 1, characterized in that: the compressor adopts the method of an auxiliary gas booster ejection flow regulating valve, and the opening percentage (%) of the regulating valve can be Change and adjust the flow rate of the high-pressure gas that ejects the liquid. The function of the ejector 16 is also through the pumping action of the high-pressure gas, and the liquid in the liquid supply pipeline 105 is pressurized and sucked into the ejector 16 and connected with the high-pressure gas to enter together. To the gas supply circuit 107 of the gas bearing, the flow and pressure of the gas and liquid in the gas supply circuit 107 are increased, and finally the supply pressure difference of the gas bearing is increased; formula (4) increases the pressure of the gas pressurized ejection flow control valve. opening

Supply pressure difference with gas bearing

When it is necessary to actually measure the percentage opening (%) of different control valves, the supply pressure difference of the gas bearing can be obtained by nonlinear fitting to obtain the coefficients of formula (4).

,

,

. 3. The control system of the gas bearing centrifugal compressor according to claim 1, wherein the auxiliary liquid pump adopts a variable frequency liquid pump flow/pressure regulation or a fixed frequency liquid pump with a built-in differential pressure flow/pressure regulation. or other variable flow/variable pressure head adjustment methods; the change of rotational speed and the adjustment of differential pressure can change the pressure head of the output liquid of the auxiliary liquid pump, the flow rate of the output liquid and finally adjust the total gas supply of the gas bearing. The pressure difference between the pressure and the supply gas ensures the stable operation of the gas bearing; the flow rate of the liquid pump is proportional to the square of the rotation speed, and the flow rate of the liquid pump and the pressure head of the liquid pump are in a quadratic curve relationship, so as the rotation speed gradually increases from 0 The flow rate of the liquid pump and the pressure at the pump outlet also gradually increase. This is a relatively gentle process. The final speed of the liquid pump and the supply pressure difference of the gas bearing will also be a quadratic curve relationship; the formula ( 3) The speed of the liquid pump in

Supply pressure difference with gas bearing

It is necessary to actually measure the difference in supply pressure of the gas bearing when running at different speeds. The coefficients of formula (3) can be obtained by nonlinear fitting.

,

,

. 4. The control system of the gas bearing centrifugal compressor according to claim 1, characterized in that: the opening and closing of the auxiliary liquid pump and the opening and closing of the liquid pump: after the liquid pump is turned on, the air supply pressure increases, and the When the air pressure difference is also increased, if it is greater than the minimum supply air pressure difference setting value, until the

The liquid pump can be turned off again after it is satisfied; for the same reason, if the liquid pump is turned off, the minimum supply air pressure difference will decrease until

The liquid pump can be turned on again only after it is satisfied; the setting of the upward hysteresis and the downward hysteresis can be determined according to the test to ensure that the liquid pump will not be turned on and off frequently, and also ensure that the supply pressure difference is stable within the set small interval. The bearing works stably.

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