Anti-surge control method for series centrifugal compressor unit and air conditioning equipment

Abstract

The present invention discloses an anti-surge control method for a series centrifugal compressor unit and an air-conditioning device using the method. The anti-surge control method calculates the minimum guide vane opening value of the current working condition according to the pressure ratio of the current working condition and determines the guide vane opening limit value. When the guide vane opening is greater than the guide vane opening limit value, the guide vane opening is controlled to prevent the unit from surging; when the guide vane opening is equal to the guide vane opening limit value, the unit is prevented from surging through bypass. The present invention solves the anti-surge problem of a multi-stage compression system with large temperature rise and high pressure ratio composed of a series centrifugal compressor unit, and at the same time reduces the problems of low energy efficiency ratio and high noise caused by opening the hot gas bypass for anti-surge.

Description

Technical Field

[0001] The present invention relates to the technical field of air conditioners, and particularly to an anti-surge control method applicable to a series centrifugal compressor unit and an air conditioning device using the method. Background Art

[0002] Surge is an inherent characteristic of a centrifugal compressor. When the compressor flow rate decreases or the pressure difference increases, the centrifugal compressor is prone to surge. The reason for the formation of surge is that when the gas pressure at the compressor outlet is less than the condensation pressure, the air flow will reverse back to the compressor until the condensation pressure is lower than the compressor outlet pressure. After the compressor returns to normal operation, there will be a situation where the gas pressure at the compressor outlet is less than the condensation pressure again, and the gas will reverse again. This cyclic and periodic gas oscillation phenomenon is surge. Surge will cause serious damage to the compressor, resulting in a significant deterioration of the compressor performance, large fluctuations in gas parameters, pulsation of the current, increased noise, intensified vibration of the unit, and damage to compressor components in severe cases.

[0003] To prevent compressor surge, the currently commonly used method is to set a surge line to make the unit operate within a safe range. However, for a system using a multi-stage series centrifugal compressor, it has a large temperature rise and a high pressure ratio, and is still prone to surge. Therefore, it is necessary to design an anti-surge control method suitable for a series high-temperature unit to ensure the normal operation of the system. Summary of the Invention

[0004] The present invention provides an anti-surge control method applicable to a series centrifugal compressor unit and an air conditioning device using the method, so as to solve the anti-surge problem of a multi-stage series centrifugal compressor system with a large temperature rise and a high pressure ratio in the prior art.

[0005] The anti-surge control method of the series centrifugal compressor unit proposed by the present invention calculates the minimum guide vane opening value of the current working condition according to the pressure ratio of the current working condition and determines the guide vane opening limit value. When the guide vane opening is greater than the guide vane opening limit value, the guide vane opening is controlled to prevent the unit from surging; when the guide vane opening is equal to the guide vane opening limit value, bypass is used to prevent the unit from surging.

[0006] Preferably, the minimum guide vane opening value Ymin is calculated according to the following formula:

[0007] Ymin = A*P g 4 + B*P g 3 + C*P g 2 + D*P g + E;

[0008] Wherein A, B, C, D, and E are the calculation parameters of the minimum guide vane opening value, which are obtained by curve fitting according to the unit's ultimate pressure ratio test; P g is the ratio of the condensation pressure to the low-pressure exhaust pressure.

[0009] Then determine the guide vane opening limit value: First, set the maximum limit value Dmax, the minimum limit value Dmin, and the safety margin a of the minimum guide vane opening;

[0010] When Dmin - a < Ymin < Dmax, the minimum guide vane opening limit value Y 限定 is equal to Ymin;

[0011] When Ymin < Dmin - a, the minimum guide vane opening limit value Y 限定 is equal to Dmin - a;

[0012] When Ymin > Dmax, the minimum guide vane opening limit value Y 限定 is equal to Dmax.

[0013] When adjusting the guide vane opening, the guide vane opening cannot be less than (Y 限定 + b), where b is the set safety margin for the guide vane adjustment opening.

[0014] When the guide vane opening has reached (Y limit + b) and the unit has not reached the set requirements, the suction volume of the low-pressure stage compressor is adjusted through the bypass valve.

[0015] Preferably, the bypass is provided with a bypass valve, and the bypass valve is provided with three gear opening judgment values: yn3, yn2, and yn1, where yn3 < yn2 < yn1,

[0016] When the bypass valve opening yn < yn3, increase the opening of the bypass valve;

[0017] When the bypass valve opening is in the range yn3 < yn < yn2, keep the bypass valve opening unchanged;

[0018] When the bypass valve opening is in the range yn2 < yn < yn1, decrease the bypass valve opening.

[0019] Preferably, the anti-surge control method further includes monitoring gas parameters. When the exhaust port pressure P p of the high-pressure stage compressor is less than the condensation pressure P c , it is determined that the unit has a surge, and at this time, a fault is reported and the unit is shut down.

[0020] Preferably, the anti-surge control method further includes monitoring current parameters. The control system reads the current parameters of the compressor motor to form a current curve. If the current curve fluctuates significantly, it is determined that the unit has a surge, and at this time, a fault is reported and the unit is shut down.

[0021] The present invention also provides an air conditioning device, comprising: a multi-stage series-connected centrifugal compressor unit, each stage of centrifugal compressor includes a first-stage impeller and a second-stage impeller, and an air supplement port is arranged between the first-stage impeller and the second-stage impeller; a multi-stage throttling device connected in series between a condenser and an evaporator; an inter-stage economizer is arranged between every two throttling devices, and a gas outlet of the inter-stage economizer is communicated with the corresponding air supplement port through a pipeline; and a bypass connecting an inlet of a low-pressure-stage centrifugal compressor and an outlet of a high-pressure-stage centrifugal compressor, and a bypass valve is arranged on the bypass.

[0022] In one embodiment, the air conditioning system comprises: a low-pressure-stage centrifugal compressor and a high-pressure-stage centrifugal compressor connected in series in two stages, both the low-pressure-stage centrifugal compressor and the high-pressure-stage centrifugal compressor include a first-stage impeller and a second-stage impeller, and an air supplement port is arranged between the first-stage impeller and the second-stage impeller; a first-stage throttling device, a second-stage throttling device, a third-stage throttling device and a fourth-stage throttling device connected in series between the condenser and the evaporator; a first and second-stage inter-stage economizer arranged between the first-stage throttling device and the second-stage throttling device, and a gas outlet thereof is communicated with the air supplement port of the low-pressure-stage compressor through a pipeline; a second and third-stage inter-stage economizer arranged between the second-stage throttling device and the third-stage throttling device, and a gas outlet thereof is communicated with an exhaust pipeline of the low-pressure-stage centrifugal compressor through a pipeline; a third and fourth-stage inter-stage economizer arranged between the third-stage throttling device and the fourth-stage throttling device, and a gas outlet thereof is communicated with the air supplement port of the high-pressure-stage compressor through a pipeline.

[0023] Preferably, a first pressure sensor is arranged on an exhaust pipe of the low-pressure-stage centrifugal compressor, and a second pressure sensor is arranged inside the condenser.

[0024] Further, the air conditioning system further comprises a gas parameter monitoring device arranged at an exhaust outlet of the high-pressure-stage centrifugal compressor for detecting an exhaust pressure, and when the exhaust pressure Pp is less than a condensation pressure Pc, it is determined that the centrifugal compressor unit has a surge and an alarm is given.

[0025] Further, the air conditioning system further comprises a current pulsation monitoring device for reading current parameter of a compressor motor to form a current curve, and if the current curve fluctuates significantly, it is determined that the unit has a surge and an alarm is given.

[0026] The air conditioning system provided by the present invention uses the above anti-surge control method.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. By adopting a multi-stage throttling device and a multi-stage inter-stage economizer to supplement air to each stage of compression impeller, the refrigerant flow rate of the compressor is fully guaranteed, and the anti-surge problem of a large temperature rise and high pressure ratio multi-stage compression system composed of a series-connected centrifugal compressor unit is solved;

[0029] 2. By preferentially adjusting the guide vane and then adjusting the bypass, not only the operating range of the unit is broadened, but also the comprehensive energy efficiency of the unit is improved.

[0030] 3. By setting different opening degrees of the bypass valve, problems such as low energy efficiency ratio and high noise caused by opening the hot gas bypass to prevent surge are reduced. Description of the Drawings

[0031] The present invention will be described in detail below in conjunction with the drawings and specific embodiments, where:

[0032] Figure 1 is a system diagram of a two-stage series centrifugal compressor unit;

[0033] Figure 2 is Figure 1 a partial enlarged view at position A in

[0034] Figure 3 is the anti-surge control capacity adjustment flow chart of the series centrifugal compressor unit proposed by the present invention.

[0035] In the figure, 1 is a low-pressure stage centrifugal compressor, 2 is a high-pressure stage centrifugal compressor, 3 is a condenser, 4 is an evaporator, 5 is an economizer between the third and fourth stages, 6 is an economizer between the second and third stages, 7 is an economizer between the first and second stages, 8 is a fourth-stage throttling device, 9 is a third-stage throttling device, 10 is a second-stage throttling device, 11 is a first-stage throttling device, 12 is a bypass valve, 13 is the air inlet of the low-pressure stage centrifugal compressor, 14 is the air inlet of the high-pressure stage centrifugal compressor, 15 is a first pressure sensor, 16 is a second pressure sensor, 17 is a first-stage impeller, and 18 is a second-stage impeller. Detailed Embodiments

[0036] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below in conjunction with the drawings and embodiments. It should be understood that the following specific embodiments are only used to explain the present invention and do not constitute a limitation to the present invention.

[0037] The anti-surge control method of the series centrifugal compressor unit proposed by the present invention includes three parts: First, air is supplemented to each stage impeller of the compressor through a multi-stage throttling device and a multi-stage economizer to ensure the refrigerant flow of the compressor; second, the minimum guide vane opening value under different pressure ratios is calculated to determine the minimum guide vane opening limit value, and according to different situations, the guide vane opening during the operation of the unit is controlled to prevent the unit from surging; third, when the guide vane opening reaches the minimum opening limit value and the capacity does not meet the requirements, hot gas bypass is used to prevent the unit from surging.

[0038] Figure 1This is a system diagram for anti-surge applicable to a series centrifugal compressor unit proposed by the present invention. The system includes: a low-pressure stage centrifugal compressor 1 connected in series, which includes a first-stage and a second-stage impeller, and a first air inlet 13 is provided between the first-stage and the second-stage impellers. A first pressure sensor 15 is arranged on the exhaust pipe of the low-pressure stage centrifugal compressor to detect the low-pressure stage exhaust pressure P d ; a high-pressure stage centrifugal compressor 2, which includes a third-stage and a fourth-stage impeller, and a second air inlet 14 is provided between the third-stage and the fourth-stage impellers; a condenser 3, and a second pressure sensor 16 is arranged inside it to detect the condensation pressure P c ; an evaporator 4; a set of throttling devices, including: a first-stage throttling device 11, a second-stage throttling device 10, a third-stage throttling device 9, and a fourth-stage throttling device 8; and a bypass connecting the inlet pipe of the low-pressure stage centrifugal compressor and the exhaust pipe of the high-pressure stage centrifugal compressor, and a bypass valve 12 is arranged on this bypass. An economizer 7 between the first-stage and the second-stage is arranged between the first-stage throttling device 11 and the second-stage throttling device 10, and the gas outlet of this economizer is communicated with the first air inlet 13 of the low-pressure stage centrifugal compressor 1 through a pipeline; an economizer 6 between the second-stage and the third-stage is arranged between the second-stage throttling device 10 and the third-stage throttling device 9, and the gas outlet of this economizer is communicated with the exhaust pipeline of the low-pressure stage centrifugal compressor 1 through a pipeline; an economizer 5 between the third-stage and the fourth-stage is arranged between the third-stage throttling device 9 and the fourth-stage throttling device 8, and the gas outlet of this economizer is communicated with the second air inlet 14 of the high-pressure stage centrifugal compressor 2 through a pipeline.

[0039] Figure 2 Show Figure 1 The position of the air inlet 13 between the first-stage impeller 17 and the second-stage impeller 18 of the low- and medium-pressure stage centrifugal compressor. The position of the air inlet of the high-pressure stage centrifugal compressor is similar to that of the low-pressure stage.

[0040] Figure 1The illustrated example adopts two two-stage compressors connected in series to form a four-stage compression system. The refrigerant liquid at low temperature and low pressure evaporates and absorbs heat in the evaporator 4, turns into a gas at low temperature and low pressure and is discharged, and enters the low-pressure centrifugal compressor 1. This centrifugal compressor is configured with two-stage impellers. The gas undergoes primary compression through the first-stage impeller in the low-pressure centrifugal compressor, and then mixes with the refrigerant gas coming out of the economizer between the first and second stages and entering through the first air supplement port 13, and enters the second-stage impeller to complete the secondary compression and discharge high-pressure gas; then it mixes with the gas discharged from the economizer 6 between the second and third stages in the pipeline between the low-pressure centrifugal compressor and the high-pressure centrifugal compressor, enters the high-pressure centrifugal compressor 2. After the refrigerant completes the tertiary compression in the third-stage impeller, it mixes with the gas entering through the second air supplement port and discharged from the economizer 5 between the third and fourth stages, enters the fourth-stage impeller for compression, and the discharged high-temperature and high-pressure gas enters the condenser 3 to release heat and condense into a liquid, and then enters the throttling device to reduce pressure. In this embodiment, the refrigerant undergoes four-stage throttling, and the refrigerant gas generated by the inter-stage throttling is sent back to the corresponding air supplement port to be added to the next round of compression. The low-temperature and low-pressure liquid after four-stage throttling enters the evaporator to absorb heat and gasify, and then returns to the compressor for circulation.

[0041] As pointed out in the prior art, in the case of large temperature rise and high pressure ratio, centrifugal compressors are prone to surge. To solve this technical problem, the anti-surge control method for the series centrifugal compressor unit proposed by the present invention obtains the calculation formula for the minimum guide vane opening of the impeller based on the curve fitted from the test results of the ultimate pressure ratio of the unit, and uses this formula to calculate the minimum guide vane opening values under different working conditions and determine the minimum guide vane opening limit value Y. 限定 During the operation of the unit, it is specified that the guide vane of the unit cannot be adjusted below the minimum opening limit value of the guide vane to avoid the occurrence of unit surge; when the guide vane has already been at the minimum guide vane opening limit value and still cannot meet the working condition requirements, then the high-pressure exhaust gas is returned to the low-pressure compressor inlet through the bypass to increase the flow rate and prevent surge.

[0042] The anti-surge control method proposed by the present invention gives priority to adjusting the guide vane, and only when the guide vane is adjusted to the minimum opening limit value and still cannot meet the working condition, the bypass valve is adjusted. The advantage of doing this is that it can reduce problems such as low energy efficiency ratio and high noise caused by opening the hot gas bypass for anti-surge.

[0043] Figure 3 is the flow chart of the anti-surge control capacity regulation proposed by the present invention, including the following steps:

[0044] (1) Calculate the minimum guide vane opening values of the two compressors.

[0045] The calculation formula is: Ymin = A * Pg 4 + B * Pg 3 + C * Pg 2 + D * Pg + E

[0046] Wherein, Pg is the operating pressure ratio of the high-pressure stage compressor, and Pg = condensation pressure / low-pressure exhaust pressure.

[0047] Wherein A, B, C, D, and E are the calculation parameters for the minimum guide vane opening value and are adjustable.

[0048] The above calculation formula and calculation parameters are obtained by curve fitting based on the test of the ultimate pressure ratio of the unit, and the calculation parameters of different units are different.

[0049] (2) Determine the limit value of the minimum guide vane opening.

[0050] To prevent the compressor from surging, the maximum limit value Dmax and the minimum limit value Dmin of the minimum guide vane opening are set, and both the maximum limit value and the minimum limit value can be adjusted according to different units.

[0051] When the minimum guide vane opening is in the range Dmin - a < Ymin < Dmax, the limit value of the minimum guide vane opening is equal to the calculated value, Y 限定 = Ymin;

[0052] When the minimum guide vane opening is less than Dmin - a, Ymin < Dmin - a, the limit value of the minimum guide vane opening is equal to the difference between the maximum limit value Dmax and a, Y 限定 = Dmin - a;

[0053] When the minimum guide vane opening is greater than Dmax, Ymin > Dmax, the limit value of the minimum guide vane opening is equal to the maximum limit value Dmax, Y 限定 = Dmax;

[0054] The above a is the safety margin of the minimum guide vane opening and is obtained from experimental data.

[0055] (3) Perform capacity adjustment according to the current working condition.

[0056] In the present invention, the limit value of the minimum guide vane opening is obtained through calculation and judgment. In the control system, when the guide vane opening is greater than the limit value of the minimum guide vane opening, only the guide vane is used to adjust the operating condition of the unit to prevent the unit from operating at the surge point.

[0057] Set the safety margin b for the guide vane adjustment opening. When adjusting the guide vane opening Y, the opening cannot be less than Y 限定 + b. When the guide vane opening Y is greater than Y 限定 + b and the capacity has reached the requirements of the unit, the capacity adjustment is completed;

[0058] When the guide vane opening has reached Y 限定 + b and the unit has not yet reached the set working condition requirements, the guide vane opening value is maintained at Y 限定+b, then open the bypass valve 12, and lead the exhaust gas of the high-pressure centrifugal compressor 2 to the suction port of the low-pressure centrifugal compressor 1 through the bypass to increase the flow rate of the compressor.

[0059] In this embodiment, there are three levels of opening judgment values for the bypass valve 12: yn3, yn2, yn1, where:

[0060] yn3 < yn2 < yn1, and the specific values of the judgment values can be adjusted.

[0061] When the opening of the bypass valve 12 is yn < yn3, the bypass capacity decreases, and at this time, the hot gas bypass valve is adjusted larger;

[0062] When the opening of the bypass valve 12 is in the range of yn3 < yn < yn2, the bypass capacity remains unchanged, and the opening of the bypass valve 12 remains unchanged;

[0063] When the opening of the bypass valve 12 is in the range of yn2 < yn < yn1, the capacity increases, and the hot gas bypass valve is adjusted smaller;

[0064] When the opening of the bypass valve 12 is yn < yn1, the opening is adjusted smaller and a fault is reported.

[0065] The method proposed by the present invention prevents the compressor from surging and ensures the normal operation of the unit through three aspects: air supplement, adjusting the guide vane opening, and increasing the hot gas bypass.

[0066] During the compressor capacity adjustment process, the anti-surge control method proposed by the present invention first calculates the minimum guide vane opening value of the current working condition by detecting the low-pressure exhaust pressure and the condensation pressure, sets the minimum value safety margin a, and determines the final minimum guide vane opening limit value. The compressor capacity is adjusted within this range to avoid surging; when the adjustment to the minimum guide vane opening limit value still cannot meet the required capacity, the hot gas bypass adjustment is used to achieve the required capacity. In this way, a larger allowable adjustment range, better comprehensive energy efficiency can be achieved while ensuring that the unit does not surge, and the noise generated by opening the hot gas bypass can be reduced.

[0067] As a supplement, it is also possible to judge whether the unit has stalled or surged by monitoring the exhaust pressure and current fluctuation of the unit. After determining the stall and surge, stop the machine for protection to prevent the damage caused by surging to the unit. After stopping the machine to check and eliminate the fault, restart the machine. For example, a gas parameter monitoring device or a current pulsation monitoring device can be set to judge whether the unit is in a stall or surge state. If it is in a stall and surge state, an immediate shutdown command is issued to protect the unit, and after the unit maintenance personnel check, restart the machine if conditions permit.

[0068] The gas parameter monitoring device can be a pressure sensor set at the exhaust port of the high-pressure compressor to detect the high-pressure exhaust pressure P p。If the high-pressure exhaust pressure is less than the condensation pressure, P p <P c , it is determined that the unit has surging. At this time, a fault is reported and the unit shuts down.

[0069] The current pulsation monitoring device can be that the control system reads the current parameters of the compressor motor to form a current curve. If the current curve fluctuates significantly, it is determined that the unit has surging. At this time, a fault is reported and the unit shuts down.

[0070] The above are only specific embodiments of the present invention. It should be noted that any modifications, equivalent replacements, and changes made within the spirit and framework of the concept of the present invention should be included in the protection scope of the present invention.

Claims

1. An anti-surge control method for a series centrifugal compressor unit, the series centrifugal compressor unit comprising: Bypass connecting the suction port of the low-pressure stage centrifugal compressor and the discharge port of the high-pressure stage centrifugal compressor; A multi-stage throttling device connected in series between the condenser and the evaporator, with an inter-stage economizer provided between every two throttling devices. The gas outlet of the inter-stage economizer is connected to the gas supplement port corresponding to each stage of the centrifugal compressor through a pipeline. It is characterized in that the anti-surge control method includes: First, supplement gas to each stage of the impeller of the compressor through the multi-stage throttling device and the multi-stage economizer to ensure the refrigerant flow rate of the compressor; Second, determine the minimum guide vane opening limit value by calculating the minimum guide vane opening value at different pressure ratios, and prevent the unit from surging by controlling the guide vane opening during the operation of the unit; Third, when the guide vane opening reaches the minimum opening limit value and the capacity does not meet the requirements, prevent the unit from surging through hot gas bypass; The minimum guide vane opening value Ymin is calculated by the following formula: Ymin = A * P g 4 + B * P g 3 + C * P g 2 + D * P g + E; where P g is the ratio of the condensation pressure to the low-pressure exhaust pressure, and A, B, C, D, and E are the calculation parameters for the minimum guide vane opening value. The calculation formula and calculation parameters are obtained by curve fitting based on the curve of the unit's ultimate pressure ratio test.

2. The anti-surge control method according to claim 1, wherein Set the maximum limit value Dmax, the minimum limit value Dmin of the minimum guide vane opening, and the safety margin a of the minimum guide vane opening; When Dmin - a < Ymin < Dmax, the minimum guide vane opening limit value Y 限定 is equal to Ymin; When Ymin < Dmin - a, the minimum guide vane opening limit value Y 限定 equals Dmin - a; When Ymin > Dmax, the minimum guide vane opening limit value Y 限定 is equal to Dmax.

3. The anti-surge control method according to claim 2, wherein When adjusting the guide vane opening, the guide vane opening shall not be less than Y 限定 +b, where b is the set safety margin for the guide vane adjustment opening.

4. The anti-surge control method according to claim 3, wherein When the guide vane opening has reached Y 限定 +b and the unit has not reached the set requirements, the suction volume of the low-pressure stage compressor is adjusted through the bypass valve.

5. The anti-surge control method according to claim 4, characterized in that, A bypass valve is provided on the bypass, and the bypass valve is provided with three opening judgment values: yn3, yn2, and yn1, where yn3 < yn2 < yn1, When the bypass valve opening yn < yn3, increase the opening of the bypass valve; When the bypass valve opening is in the range yn3 < yn < yn2, keep the bypass valve opening unchanged; When the bypass valve opening is in the range yn2 < yn < yn1, decrease the bypass valve opening.

6. The anti-surge control method according to claim 1, characterized in that, It also includes monitoring gas parameters. When the pressure P at the exhaust port of the high-pressure stage compressor p is less than the condensation pressure P c , it is determined that the unit has a surge. At this time, a fault is reported and the unit stops.

7. The anti-surge control method according to claim 1, wherein It also includes monitoring the current parameter. The control system reads the current parameter of the compressor motor to form a current curve. If the current curve fluctuates significantly, it is determined that the unit has surged, and at this time, a fault is reported and the unit is shut down.

8. An air conditioning device, comprising a series-connected centrifugal compressor unit; a bypass connecting the suction port of the low-pressure stage centrifugal compressor and the discharge port of the high-pressure stage centrifugal compressor; a multi-stage throttling device serially arranged between the condenser and the evaporator, and an inter-stage economizer is provided between every two throttling devices, and the gas outlet of the inter-stage economizer is communicated with the air make-up port corresponding to each stage of centrifugal compressor through a pipeline; characterized in that, The air conditioning equipment uses the anti-surge control method according to any one of claims 1 to 7.

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