A capacity control method for a series centrifuge unit

Abstract

This invention relates to the field of centrifuge unit technology and discloses a capacity control method for a series centrifuge unit, including a startup phase: the high-stage suction guide vane operates according to the set minimum opening degree XL, and the low-stage suction guide vane operates according to the set minimum opening degree YL; when the outlet water temperature SP > the target temperature SV+Ta, the unit obtains the opening degree X of the high-stage suction guide vane through PID calculation and outputs the opening speed of the high-stage suction guide vane to the high-stage compressor, and the opening degree Y of the low-stage suction guide vane follows the opening degree X of the high-stage suction guide vane; otherwise, S40 is executed; when the outlet water temperature SP ≤ the target temperature SV+Ta, or the interruptor control time ≥ tc, S40 is executed; otherwise, S20 is executed; capacity PID control: the opening degree of the low-stage suction guide vane follows the opening degree of the high-stage suction guide vane. This invention effectively solves the problem of capacity and air volume mismatch when different series compressors are used together.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of centrifugal unit, in particular to a capacity control method of series connection type centrifugal unit. BACKGROUND

[0002] With the development of high-temperature heat pump and low-temperature freezing in recent years, a single centrifugal compressor cannot meet the demand of high-pressure working condition. The series connection type centrifugal unit can solve the limitation of high pressure ratio by connecting two compressors in series, but the capacity control of two compressors is more complex than that of a single compressor. Whether the capacity control is reasonable and matched is related to the achievement of the unit operation target and the reliable and smooth operation.

[0003] The existing control method is to perform PID operation on the target value of the refrigeration or heating outlet temperature by a temperature controller to obtain the guide vane opening degree of the low-stage and high-stage compressors. This control method is suitable for compressors of the same series, and can achieve the unit operation target and smooth operation because the guide vane characteristics and air volume curve of the compressors of the same series are similar. However, the working condition of this control method is single.

[0004] With the development of various industries and the demand of different industries, series connection type centrifugal units will have a mixed use of compressors of multiple series. The guide vane characteristics and air volume curve of compressors of different series are quite different. If the above control method is used, the capacity and air volume of the two compressors will not be matched, and there will be a situation that the capacity and air volume are matched at a certain load but deviated at other loads. When the exhaust capacity of the low-stage compressor is greater than the suction capacity of the high-stage compressor, the intermediate economizer is high in pressure, and the low-pressure compressor is noisy, vibrates intensively, and even surges. When the suction capacity of the high-stage compressor is greater than the exhaust capacity of the low-stage compressor, the intermediate economizer is low in pressure, and the high-stage compressor surges. Therefore, in order to meet the demand of mixed use of compressors of different series, if the existing control method is used, the compressors will not operate stably, the system circulation will not be smooth, and the use demand of the customer cannot be met. SUMMARY

[0005] The present application provides a capacity control method of series connection type centrifugal unit to solve the above technical problems.

[0006] The technical solution of the present application to solve the above technical problems is as follows: a capacity control method of series connection type centrifugal unit, comprising a low-stage compressor, an intermediate cylinder economizer and a high-stage compressor connected in series, the output end of the high-stage compressor is connected with a condenser, the condenser is connected with the intermediate cylinder economizer, the intermediate cylinder economizer is connected with an evaporator, the evaporator is connected with the low-stage compressor, the low-stage compressor comprises a two-stage impeller and a low-stage suction guide vane, the high-stage compressor comprises a two-stage impeller and a high-stage suction guide vane, and the method comprises the following steps:

[0007] S10, Start-up phase: The high-stage compressor's high-stage suction guide vane runs for time ta at the set minimum opening of the high-stage suction guide vane XL, and then the low-stage compressor's low-stage suction guide vane runs for time tb at the set minimum opening of the low-stage suction guide vane YL.

[0008] S20. When the outlet water temperature SP > the target temperature SV+Ta, the unit calculates the opening degree X of the high-stage intake guide vane through PID calculation and outputs the opening speed of the high-stage intake guide vane to the high-stage compressor. The opening degree Y of the low-stage intake guide vane follows the opening degree X of the high-stage intake guide vane and controls the output of the opening degree Y of the low-stage intake guide vane to the low-stage compressor. Otherwise, execute S40.

[0009] S30. When the outlet water temperature SP ≤ target temperature SV + Ta or the interruptor control time ≥ tc, execute S40; otherwise, execute S20.

[0010] S40, Capacity PID Control: The opening or closing speed of the high-section intake guide vane is 1° / s-5° / s. If the opening degree of the high-section intake guide vane is greater than or equal to the minimum opening degree XL, then the opening degree of the low-section intake guide vane follows the opening degree of the high-section intake guide vane; otherwise, S20 is executed.

[0011] Based on the above technical solution, the present invention can be further improved as follows:

[0012] Furthermore, in S40: when the opening degree of the high-stage intake guide vane X:Xn<X≤Xn+1, then the opening degree of the low-stage intake guide vane... , where n is a positive integer.

[0013] Furthermore, it also includes S50, where, when the machine stops, the opening of the low-stage intake guide vane closes in stages, following the opening of the high-stage intake guide vane.

[0014] Furthermore, S50 also includes the following: when the opening degree X of the high-section intake guide vane is less than the minimum opening degree XL of the high-section intake guide vane, and the opening degree of the low-section intake guide vane is less than the minimum opening degree YL of the low-section intake guide vane; or, when the closing time of both the high-section intake guide vane and the low-section intake guide vane is td, then the high-section compressor and the low-section compressor stop operating, and both the high-section intake guide vane and the low-section intake guide vane are closed.

[0015] Furthermore, in S10, the minimum opening XL of the high-section intake guide vane has an operating time ta of 8s-10s, and the minimum opening YL of the low-section intake guide vane has an operating time tb of 4s-5s.

[0016] Furthermore, the outlet water temperature SP is the outlet water temperature of the condenser or the outlet water temperature of the evaporator.

[0017] Furthermore, in S20, the opening speed of the high-section intake guide vane opening X is ≤3° / 20s and is output to the high-section compressor.

[0018] The beneficial effects of this invention are as follows: By employing a control method where the opening of the low-stage suction guide vane follows the opening of the high-stage suction guide vane, this invention effectively solves the problem of capacity and airflow mismatch when different series of compressors are used together. During the startup phase, minimum openings and running times are set for both the high-stage and low-stage suction guide vanes to ensure a smooth start-up of the unit. During operation, based on the comparison between the outlet water temperature and the target temperature, the opening of the high-stage suction guide vane is adjusted through PID calculations, and the opening of the low-stage suction guide vane follows suit, achieving precise control of the unit's capacity.

[0019] In the capacity PID control step, the opening of the low-stage intake guide vane is calculated using a specific formula, so that the capacity and air volume of the low-stage compressor and the high-stage compressor can be better matched, avoiding high or low pressure in the intermediate economizer and preventing unstable operation phenomena such as compressor surge.

[0020] When the unit is shut down, the opening of the low-stage intake guide vane closes in stages, following the opening of the high-stage intake guide vane. Furthermore, the compressor stops running and the guide vanes close when certain conditions are met, ensuring the safe shutdown of the unit.

[0021] The control method of this invention is applicable to the mixed use of various compressor series, expanding the applicable operating conditions of tandem centrifugal chiller units, improving the reliability and stability of unit operation, and better meeting the needs of different customers, resulting in significant economic and social benefits. Furthermore, the control method is logically clear and easy to implement, providing an effective solution for capacity control of tandem centrifugal chiller units. Attached Figure Description

[0022] Fig. 1 This is a schematic diagram of the series-connected centrifuge unit used in this invention;

[0023] Fig. 2 This is the characteristic curve of the guide vane of the present invention;

[0024] Fig. 3 This is a curve showing the correspondence between the opening degree of the high-section intake guide vane and the opening degree of the low-section intake guide vane in this invention.

[0025] Fig. 4 This is a schematic diagram of the control process of the present invention.

[0026] The attached diagram is labeled as follows: 1. Low-stage compressor; 2. High-stage compressor; 3. Condenser; 4. Intermediate cylinder economizer; 5. Evaporator. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0028] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "vertical," "upper," "lower," "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0029] Reference Figs. 1 to 4 As shown, this invention discloses a capacity control method for a series centrifuge unit, including a low-stage compressor 1, an intermediate cylinder economizer 4, and a high-stage compressor 2 connected in series. The output end of the high-stage compressor 2 is connected to a condenser 3. The condenser 3 is connected to the intermediate cylinder economizer 4. The intermediate cylinder economizer 4 is connected to an evaporator 5. The evaporator 5 is connected to the low-stage compressor 1. The low-stage compressor 1 includes a two-stage impeller and a low-stage suction guide vane. The high-stage compressor 2 includes a two-stage impeller and a high-stage suction guide vane.

[0030] During operation, the refrigerant in evaporator 5 evaporates and absorbs heat, lowering its temperature by absorbing heat from the refrigerant flowing through it. The low-temperature, low-pressure refrigerant gas that has absorbed heat and evaporated passes through the low-stage suction guide vane (LIGV) and is compressed by the low-stage compressor 1, forming a high-temperature, high-pressure gas. This gas is then transported to the intermediate cylinder economizer 4, where it mixes with the refrigerant gas that has flashed in the economizer. The mixture then passes through the high-stage suction guide vane (HIGV) and is compressed by the high-stage compressor 2, forming an even higher-temperature, higher-pressure refrigerant gas. This gas is then transported to the condenser 3, where it releases heat to form a high-temperature, high-pressure liquid. This liquid heats the cooling water flowing through the condenser 3, forming hot water. The high-temperature, high-pressure refrigerant liquid is then throttled by the expansion valve. The refrigerant gas enters the intermediate cylinder economizer 4. The refrigerant gas emitted in the intermediate cylinder economizer 4, along with the exhaust gas from the low-stage compressor 1, is regulated by the high-stage suction guide vane (HIGV). After compression by the high-stage compressor 2, it again forms a gas with higher temperature and pressure. The refrigerant in the intermediate cylinder economizer 4 is then throttled by the expansion valve to form a low-temperature, low-pressure liquid refrigerant, which enters the evaporator 5. The low-temperature, low-pressure liquid in the evaporator 5 absorbs heat from the refrigerant to form a low-temperature, low-pressure refrigerant gas. This gas is regulated by the low-stage suction guide vane and compressed by the low-stage compressor 1. Both the low-stage compressor 1 and the high-stage compressor 2 are centrifugal compressors. This cycle repeats, and compared to a single compressor, the centrifugal chiller unit of this invention can obtain a lower and more stable refrigerant or a higher temperature hot water. The evaporator 5 and condenser 3 have a higher pressure ratio.

[0031] To cope with the series connection of compressors of the same or different series, capacity control between compressors, i.e., guide vane control, is extremely important.

[0032] According to the characteristic curve of the low-section intake guide vane, the low-section intake guide vane includes the minimum opening YL of the low-section intake guide vane and the maximum opening Ymax of the low-section compressor intake guide vane, and can be divided into multiple stages between the minimum opening YL and the maximum opening Ymax.

[0033] Based on the characteristic curve of the high-section intake guide vane, the high-section intake guide vane includes the minimum opening XL and the maximum opening Xmax, and can also be divided into multiple stages between the minimum opening XL and the maximum opening Xmax.

[0034] Specifically, the following steps are included:

[0035] S10. Start-up phase: When the start button is pressed, the high-stage compressor 2 receives the main motor operation command and starts running. The high-stage suction guide vane receives the forced opening command and runs at the set minimum opening XL for a time ta, where ta is 8s-10s. Then, the low-stage compressor 1 receives the operation command and starts running. The low-stage suction guide vane receives the forced opening command and runs at the set minimum opening YL for a time tb, where tb is 4s-5s. The unit then begins capacity control based on the required target temperature.

[0036] S20. To prevent over-adjustment (where over-adjustment refers to adjusting excessively beyond the target value), PID calculation and interruptor control are performed first. When the outlet water temperature SP > target temperature SV + Ta, where the outlet water temperature SP represents the setpoint of the outlet water temperature, the target temperature SV refers to the target temperature value, and Ta is 0℃ to 2℃, the unit obtains the opening degree X of the high-stage suction guide vane through PID calculation and outputs the opening or closing speed of the high-stage suction guide vane to the high-stage compressor 2. The opening or closing speed of the high-stage suction guide vane is ≤3° / 20s. Start-up... Initially, the high-stage compressor 2 operates at low speed, low flow rate, and low pressure ratio, placing the system on the edge of instability. Slow adjustment (≤3° / 20s) can achieve coordinated control of "speed and guide vane angle," preventing stall and ensuring a smooth transition of the high-stage compressor 2 to stable operating conditions, while also avoiding over-adjustment. The low-stage suction guide vane opening Y follows the high-stage suction guide vane opening X in segmented control, and the low-stage suction guide vane opening Y is output to the low-stage compressor 1. The opening or closing speed of the low-stage suction guide vane is 1° / s; otherwise, S40 is executed.

[0037] When the opening degree X of the high-stage intake guide vane is greater than the minimum opening degree XL during operation, even if the PID calculation value X < XL, the opening degree of the high-stage intake guide vane will be forced to be equal to XL to prevent excessive vibration and noise of the unit and extend the service life of the unit.

[0038] Furthermore, when the unit is used for cooling, the outlet water temperature is the same as the outlet water temperature at evaporator 5; when the unit is used for heating, the outlet water temperature is the same as the outlet water temperature at condenser 3, thus meeting the adjustment requirements under different operating conditions and improving the convenience and versatility of use.

[0039] S30. When the outlet water temperature SP ≤ target temperature SV + Ta, where Ta is 0℃ to 2℃, or the interruptor control time ≥ tc, where tc represents the control cycle and the time tc is 20min, execute S40; otherwise, execute S20.

[0040] S40, Capacity PID Control: The opening degree of the low-section suction guide vane follows the opening degree of the high-section suction guide vane. Based on the test data of each series of compressors, the guide vane characteristic curve corresponding to the air volume data of the suction guide vane of each series of compressors is obtained. The characteristic curve of the guide vane can be divided into stages such as ①, ②, ③, ④, etc. The corresponding series unit can be segmented with the low-section suction guide vane opening degrees Y2, Y3, Y4, Y5 of the low-section compressor 1 and the high-section suction guide vane opening degrees X2, X3, X4, X5 of the high-section compressor 2. The segmented opening degree can be the same as the maximum opening degree according to the guide vane characteristic curve. During the test of the series unit, the corresponding points of the segment are checked and adjusted. At the customer's site, the corresponding points of the segment can also be adjusted according to the customer's actual operation.

[0041] The opening or closing speed of the high-section intake guide vane is 1° / s-5° / s. In this embodiment, the opening or closing speed of the high-section intake guide vane is 1° / s. The faster adjustment speed can realize multi-variable coordinated control and improve the overall dynamic performance. The opening degree of the high-section intake guide vane X>XL. If not, then execute S40.

[0042] If so, it means that the opening degree of the high-stage intake guide vane X≥XL, and the opening or closing speed of the low-stage intake guide vane follows the opening or closing speed of the high-stage intake guide vane, both being 1° / s;

[0043] Wherein, when the opening degree X of the high-section intake guide vane satisfies: Xn<X≤Xn+1, where n is a positive integer, Xn represents the lower limit of the opening degree of the high-section intake guide vane in the nth opening degree interval, and Xn+1 represents the upper limit of the opening degree of the high-section intake guide vane in the nth opening degree interval, then the opening degree Y of the low-section intake guide vane is:

[0044] Wherein, Yn represents the lower limit of the opening of the low-section intake guide vane in the nth opening interval, and Yn+1 represents the upper limit of the opening of the low-section intake guide vane in the nth opening interval. In this embodiment, the value of n is from 1 to 4.

[0045] Specifically, when the opening degree X of the high-stage intake guide vane satisfies: X1 < X ≤ X2, the opening degree of the low-stage intake guide vane... :

[0046] ;

[0047] When the opening X of the high-stage intake guide vane satisfies: X2<X≤X3, the opening of the low-stage intake guide vane... :

[0048] ;

[0049] When the opening X of the high-stage intake guide vane satisfies: X3<X≤X4, the opening of the low-stage intake guide vane... :

[0050] ;

[0051] When the opening X of the high-stage intake guide vane satisfies: X4<X≤XMax, the opening Y of the low-stage intake guide vane is:

[0052] ;

[0053] Based on the guide vane characteristic curves of the low-section compressor 1 and the high-section compressor 2, the high-section suction guide vane and the low-section suction guide vane are controlled in segments, so as to match the air volume of the compressor and enable compressors of the same series or different series to operate smoothly.

[0054] S50. When the machine stops, the opening of the low-stage intake guide vane closes in stages, following the opening of the high-stage intake guide vane.

[0055] Specifically, when the opening degree X of the high-section intake guide vane is less than the minimum opening degree XL of the high-section intake guide vane, and the opening degree YL of the low-section intake guide vane is less than the minimum opening degree YL of the low-section intake guide vane; or when the closing time of both the high-section intake guide vane and the low-section intake guide vane is td, and td=60s, then the high-section compressor 2 and the low-section compressor 1 stop operating, and all the high-section intake guide vanes and the low-section intake guide vanes are closed, thereby achieving unit shutdown.

[0056] This invention achieves a good match between compressor capacity and airflow by precisely controlling the high-stage and low-stage suction guide vanes during startup, operation, and shutdown. In practical applications, this method can effectively handle the series use of compressors of the same or different series, avoiding various problems caused by capacity and airflow mismatch, such as abnormal pressure in the intermediate economizer and compressor surge.

[0057] To meet different cooling or heating demands under varying operating conditions, this control method flexibly adjusts the opening of the high- and low-section intake guide vanes based on the actual outlet water temperature and target temperature, ensuring the unit always operates in a highly efficient and stable state. When cooling demand is high, the opening of the high-section intake guide vane is increased through PID calculations, and the opening of the low-section intake guide vane is adjusted accordingly, enabling the unit to provide sufficient cooling capacity. Conversely, when cooling demand is low, the guide vane opening is promptly reduced to decrease unit energy consumption.

[0058] Furthermore, this control method has clear logic, is easy to implement, and requires relatively low technical skills from operators. During the installation and commissioning of the unit, technicians can verify and adjust the corresponding points of each section according to the specific model of the unit and the actual needs of the customer, further optimizing the unit's operating performance.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for controlling the capacity of a series centrifugal compressor unit, comprising a low-stage compressor, an intermediate cylinder economizer and a high-stage compressor connected in series, the output end of the high-stage compressor being connected with a condenser, the condenser being connected with the intermediate cylinder economizer, the intermediate cylinder economizer being connected with an evaporator, and the evaporator being connected with the low-stage compressor, characterized in that, The low-stage compressor comprises a low-stage suction guide vane, and the high-stage compressor comprises a high-stage suction guide vane, and specifically comprises the following steps. S10, start-up stage: the high-stage suction guide vane of the high-stage compressor is operated at a set minimum opening degree XL for a time ta, and then the low-stage suction guide vane of the low-stage compressor is operated at a set minimum opening degree YL for a time tb; S20, when the outlet water temperature SP is greater than the target temperature SV+Ta, the high-stage suction guide vane opening degree X is obtained through PID operation of the unit, and the obtained opening speed of the high-stage suction guide vane is output to the high-stage compressor; the low-stage suction guide vane opening degree Y follows the high-stage suction guide vane opening degree X, and the low-stage suction guide vane opening degree Y is controlled and output to the low-stage compressor; if not, S40 is executed; S30, when the outlet water temperature SP is less than or equal to the target temperature SV+Ta or the intermittent control time is greater than or equal to tc, S40 is executed; Otherwise, S20 is executed; S40, capacity PID control: the opening or closing speed of the high-stage suction guide vane is 1° / s-5° / s, and if the high-stage suction guide vane opening degree is greater than or equal to the minimum opening degree XL, the low-stage suction guide vane opening degree follows the high-stage suction guide vane opening degree; Otherwise, S20 is executed.

2. The method of claim 1, wherein, In S40, when the high-stage suction guide vane opening degree X satisfies XnX≤Xn+1, the low-stage suction guide vane opening degree Y: where n is a positive integer.

3. The method of claim 2, wherein, Further comprising S50, when the unit is stopped, the low-stage suction guide vane opening degree follows the high-stage suction guide vane opening degree and is closed in stages.

4. The method of claim 3, wherein, In S50, further comprising: when the high-stage suction guide vane opening degree X is less than the minimum opening degree XL of the high-stage suction guide vane, and the low-stage suction guide vane opening degree is less than the minimum opening degree YL of the low-stage suction guide vane; or, the high-stage suction guide vane and the low-stage suction guide vane are closed for a time td, the high-stage compressor and the low-stage compressor stop operating, and the high-stage suction guide vane and the low-stage suction guide vane are all closed.

5. The method of claim 1 or 2, wherein In S10, the minimum opening degree XL of the high-stage suction guide vane is operated for a time ta of 8s-10s, and the minimum opening degree YL of the low-stage suction guide vane is operated for a time tb of 4s-5s.

6. The in-line centrifuge pack control method of claim 1, wherein, The outlet water temperature SP is the outlet water temperature of the condenser or the outlet water temperature of the evaporator.

7. The method of claim 1, wherein, In S20, the opening speed of the high-stage suction guide vane is ≤3° / 20s and is output to the high-stage compressor.

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