Two-stage compression centrifugal unit and intermediate air supplement control method of two-stage compression centrifugal unit

Abstract

The present application relates to a kind of double-stage compression centrifugal unit.The present application aims to solve the technical problem that the air supplement amount of existing double-stage compression centrifugal unit is not in the optimal air supplement amount range.The double-stage compression centrifugal unit includes a double-stage centrifugal compressor, an evaporator and a condenser, a primary suction port of the double-stage centrifugal compressor is connected to a gas outlet of the evaporator, a secondary exhaust port of the double-stage centrifugal compressor is connected to a gas inlet of the condenser, an economizer and an air supplement valve, the economizer is connected between a gas inlet of the evaporator and a gas outlet of the condenser, the economizer is connected to a primary exhaust port and a secondary suction port of the double-stage centrifugal compressor through the air supplement valve, respectively, a calculation module, the calculation module calculates the actual air supplement amount and the optimal air supplement amount according to the operating parameters of the double-stage compression centrifugal unit, to adjust the opening of the air supplement valve.The actual air supplement amount of the adjusted air supplement valve is in the optimal air supplement amount range.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of refrigeration, and particularly relates to a two-stage compression centrifugal unit and a middle air supplement control method of the two-stage compression centrifugal unit. BACKGROUND

[0002] The part provided in this section is merely background information related to the present disclosure, which does not necessarily have to be prior art.

[0003] The two-stage compression centrifugal unit adopts an inter-stage configured economizer to perform middle air supplement and enthalpy increase to improve energy efficiency, but there are the following problems in the control scheme of the middle air supplement.

[0004] The air supplement amount is not controlled, the energy efficiency is poor, and there is a risk of air supplement liquid carrying. No valve is added to the air supplement pipeline, and the air supplement amount is not adjusted. The size of the economizer air supplement pipeline is determined according to the air supplement amount at full load under a single nominal design condition. When the unit is operated under part load or variable conditions such as ice storage and air conditioning dual conditions, air conditioning and heat recovery dual conditions, etc., the air supplement amount is too large or too small, which results in that the air supplement and enthalpy increase effect cannot be played, and seriously affects the reliable operation of the unit.

[0005] In order to solve the above problems, an air supplement valve is added to control the air supplement amount, but the air supplement amount is not precisely adjusted by simply preventing the risk of air supplement liquid carrying, which results in that the air supplement amount is not in the optimal air supplement amount interval, and the air supplement control cannot be dynamically adjusted by following the changes of load and operating conditions such as pressure ratio, outlet water temperature, supercooling degree, etc., which results in that the air supplement and enthalpy increase effect cannot be optimally played, and the unit cannot be operated efficiently and stably under all conditions. SUMMARY

[0006] The present application aims to at least solve the technical problem that the air supplement amount of the existing two-stage compression centrifugal unit is not in the optimal air supplement amount interval.

[0007] To achieve the above-mentioned purpose, the present application provides a two-stage compression centrifugal unit in a first aspect, which comprises: a two-stage centrifugal compressor; an evaporator and a condenser, a primary suction port of the two-stage centrifugal compressor is connected with an outlet of the evaporator, and a secondary exhaust port of the two-stage centrifugal compressor is connected with an inlet of the condenser; an economizer and an air supplement valve, the economizer is connected between an inlet of the evaporator and an outlet of the condenser, and the economizer is connected with a primary exhaust port and a secondary suction port of the two-stage centrifugal compressor through the air supplement valve; and a calculation module, which calculates an actual air supplement amount and an optimal air supplement amount according to operating parameters of the two-stage compression centrifugal unit, so as to adjust an opening degree of the air supplement valve.

[0008] The double-stage compression centrifugal unit provided by the application comprises a calculation module, which obtains operation parameters of the double-stage compression centrifugal unit, and calculates an optimal air supplement amount and an actual air supplement amount according to the operation parameters of the double-stage compression centrifugal unit, so as to adjust the opening of an air supplement valve, and the actual air supplement amount of the air supplement valve after adjustment is within the optimal air supplement amount interval.

[0009] In addition, the double-stage compression centrifugal unit according to the application can further have the following additional technical features.

[0010] In some embodiments of the application, the calculation module calculates the actual air supplement amount δm according to the following formula:

[0011] Wherein:

[0012] m1: refrigerant mass in primary circulation compression of the double-stage centrifugal compressor;

[0013] W comp : input power of the double-stage centrifugal compressor;

[0014] Q loss : total heat exchange amount of the double-stage centrifugal compressor;

[0015] h 0[] : enthalpy value of the primary suction port;

[0016] h 0[] : enthalpy value of the air supplement valve;

[0017] h 0[] : enthalpy value of the secondary suction port;

[0018] h 0[] : enthalpy value of the secondary exhaust port;

[0019] h 0[] : enthalpy value of the condenser;

[0020] h 0[] : enthalpy value of the economizer outlet.

[0021] In some embodiments of the application, the calculation module calculates the optimal air supplement amount Tδm according to the following formula:

[0022] Wherein:

[0023] m1: refrigerant mass in primary circulation compression of the double-stage centrifugal compressor;

[0024] W comp : input power of the double-stage centrifugal compressor;

[0025] Q loss : total heat exchange amount of the double-stage centrifugal compressor;

[0026] h 0[] : enthalpy of primary suction port;

[0027] h 0[] : enthalpy of air injection valve;

[0028] h 0[] : enthalpy of optimal secondary suction port;

[0029] h 0[] : enthalpy of secondary exhaust port;

[0030] h 0[] : enthalpy of condenser;

[0031] h 0[] : enthalpy of economizer outlet.

[0032] In some embodiments of the present application, the operating parameters include temperature parameters and pressure parameters, and the calculation module is capable of obtaining h 0[] , h 0[] , h 0[] , h 0[] , h 0[] , h 0[] and h 0[] according to the temperature parameters and the pressure parameters with reference to a temperature-pressure-enthalpy table and / or a pressure-saturation-enthalpy table.

[0033] In some embodiments of the present application, a control module is further included, which takes the optimal air injection amount as a control target and takes the actual air injection amount as a feedback amount to adjust the opening degree of the air injection valve.

[0034] The second aspect of the present application provides a method for controlling air injection in a two-stage compression centrifugal unit, which is implemented according to the two-stage compression centrifugal unit of the first aspect of the present application, and includes the following steps:

[0035] Receiving operating parameters of the two-stage compression centrifugal unit;

[0036] Calculating an optimal air injection amount and an actual air injection amount according to the operating parameters of the two-stage compression centrifugal unit to adjust the opening degree of the air injection valve.

[0037] The method for controlling air injection in a two-stage compression centrifugal unit provided by the present application calculates an optimal air injection amount and an actual air injection amount according to the operating parameters of the two-stage compression centrifugal unit, and adjusts the opening degree of the air injection valve according to the optimal air injection amount and the actual air injection amount, so that the actual air injection amount of the air injection valve can be within the range of the optimal air injection amount.

[0038] In some embodiments of the present application, the actual air injection amount δm is calculated according to the formula: δm = (h 0[] - h 0[] ) / (h 0[] - h 0[] ) * (h 0[] - h 0[] )

[0039] m1: the mass of refrigerant in the first cycle compression of a two-stage centrifugal compressor;

[0040] W comp : Two-stage centrifugal compressor input power;

[0041] Q loss : Total heat exchange capacity of two-stage centrifugal compressor;

[0042] h 0[] : enthalpy of the first-stage suction port;

[0043] h 0[] : enthalpy of air supply valve;

[0044] h 0[] : enthalpy of the secondary air intake;

[0045] h 0[] : enthalpy of the secondary exhaust port;

[0046] h 0[] : condenser enthalpy;

[0047] h 0[] : Economizer outlet enthalpy.

[0048] In some embodiments of the present invention, according to the formula: Calculate the optimal gas supply volume Tδm, where:

[0049] m1: the mass of refrigerant in the first cycle compression of a two-stage centrifugal compressor;

[0050] W comp : Two-stage centrifugal compressor input power;

[0051] Q loss : Total heat exchange capacity of two-stage centrifugal compressor;

[0052] h 0[] : enthalpy of the first-stage suction port;

[0053] h 0[] : enthalpy of air supply valve;

[0054] h 0[] : enthalpy of the optimal secondary air intake;

[0055] h 0[] : enthalpy of the secondary exhaust port;

[0056] h 0[] : condenser enthalpy;

[0057] h 0[] : Economizer outlet enthalpy.

[0058] In some embodiments of the present application, the method further comprises the step of: adjusting the opening degree of the air supplement valve to a first opening degree, with the optimal air supplement amount as a control target and the actual air supplement amount as a feedback amount.

[0059] In some embodiments of the present application, the method further comprises the steps of:

[0060] obtaining a secondary suction gas superheat degree at the secondary suction port;

[0061] determining whether the secondary suction gas superheat degree is within a preset range;

[0062] maintaining the air supplement valve at the first opening degree according to the secondary suction gas superheat degree being within the preset range;

[0063] performing opening degree reduction control on the first opening degree according to the secondary suction gas superheat degree being less than a preset lower limit of suction gas superheat degree;

[0064] performing adjustable control on the first opening degree according to the secondary suction gas superheat degree being greater than a preset upper limit of suction gas superheat degree.

[0065] In some embodiments of the present application, the method further comprises the steps of:

[0066] obtaining a secondary exhaust gas superheat degree at the secondary exhaust port;

[0067] determining whether the secondary exhaust gas superheat degree is within a preset range;

[0068] maintaining the air supplement valve at the first opening degree according to the secondary exhaust gas superheat degree being within the preset range;

[0069] performing opening degree reduction control on the first opening degree according to the secondary exhaust gas superheat degree being less than a preset lower limit of exhaust gas superheat degree;

[0070] performing adjustable control on the first opening degree according to the secondary exhaust gas superheat degree being greater than a preset upper limit of exhaust gas superheat degree. BRIEF DESCRIPTION OF DRAWINGS

[0071] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a better understanding of the preferred embodiments, and are not to be considered limitations of the present application. Moreover, in the drawings, like reference numerals refer to similar components throughout the several views. In the drawings:

[0072] Figure 1 A structural schematic diagram of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0073] Figure 2A pressure and enthalpy diagram of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0074] Figure 3 A flow chart of a method of intermediate charge air control of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0075] Figure 4 A flow chart of a method of intermediate charge air control of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0076] Figure 5 A flow chart of a method of intermediate charge air control of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0077] Figure 6 A flow chart of a method of intermediate charge air control of a two-stage compression centrifugal unit according to an embodiment of the present application is schematically shown.

[0078] Wherein the reference numerals are as follows:

[0079] 100, two-stage compression centrifugal unit;

[0080] 1, intake line; 11, first pressure sensor; 12, first temperature sensor;

[0081] 2, two-stage centrifugal compressor;

[0082] 3, connecting line; 31, second pressure sensor; 32, second temperature sensor;

[0083] 4, exhaust line; 41, third pressure sensor; 42, third temperature sensor;

[0084] 5, condenser;

[0085] 6, charge air valve; 61, fourth pressure sensor; 62, fourth temperature sensor;

[0086] 7, economizer;

[0087] 8, evaporator;

[0088] 9, fifth pressure sensor;

[0089] 10, primary throttle valve;

[0090] 13, sixth pressure sensor;

[0091] 14, secondary throttle valve. DETAILED DESCRIPTION

[0092] Exemplary embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. While example embodiments of the present disclosure are shown in the drawings, it is understood that the present disclosure can be embodied in many forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

[0093] It is to be understood that the terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes", "including" and the like are to be construed to be inclusive (i.e., to include both instances of open ended terms and instances of terms limiting to a specific number) unless otherwise indicated as otherwise limited by context. The methods described herein can be implemented as a method, an apparatus, a system, a computer program product, computer-readable medium, computer program, or a combination thereof.

[0094] Although the terms first, second, third, and the like can be used herein to describe various elements, components, regions, layers and / or sections, these elements, components, regions, layers and / or sections should not be limited by these terms. These terms can be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as "first", "second", and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0095] For ease of description, spatially relative terms can be used herein for the purpose of illustrating one element's or feature's relationship to another element or feature as shown in the figures. Such spatially relative terms include "internal", "external", "inward", "outward", "under", "below", "above", "on", "above", and the like. These spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device is inverted, then an element that is described as "below" or "beneath" another element or feature would be oriented "above" or "over" the other element or feature. Thus, the example term "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0096] Figure 1 The structural schematic diagram of the two-stage compression centrifugal unit according to the embodiment of the present application is schematically shown. Please refer to Figure 1 An embodiment of the first aspect of the present application provides a two-stage compression centrifugal unit 100, which comprises a two-stage centrifugal compressor 2, an evaporator 8, a condenser 5, an economizer 7, a makeup gas valve 6 and a calculation module (not shown in the figure).

[0097] The suction port of the first stage of the two-stage centrifugal compressor 2 is connected with the gas outlet of the evaporator 8, the exhaust port of the second stage of the two-stage centrifugal compressor 2 is connected with the gas inlet of the condenser 5, the gas inlet of the evaporator 8 and the gas outlet of the condenser 5 are provided with the economizer 7, the economizer 7 is further connected with the exhaust port of the first stage and the suction port of the second stage of the two-stage centrifugal compressor 2 through the makeup gas valve 6. The calculation module receives the operating parameters of the two-stage compression centrifugal unit 100 and calculates the optimal makeup gas amount and the actual makeup gas amount according to the operating parameters of the two-stage compression centrifugal unit 100 to adjust the opening of the makeup gas valve 6.

[0098] The two-stage compression centrifugal unit 100 provided by the present application comprises a calculation module, which receives the operating parameters of the two-stage compression centrifugal unit 100 and calculates the optimal makeup gas amount and the actual makeup gas amount according to the operating parameters of the two-stage compression centrifugal unit 100 to adjust the opening of the makeup gas valve 6, and the actual makeup gas amount of the makeup gas valve 6 after adjustment is within the optimal makeup gas amount interval.

[0099] The two-stage centrifugal compressor 2 comprises a first stage compressor and a second stage compressor, the first stage compressor comprises a first stage suction port and a first stage exhaust port, and the second stage compressor comprises a second stage suction port and a second stage exhaust port. Figure 1The arrows in the figure indicate the flow direction of the refrigerant. The suction port of the first stage of the two-stage centrifugal compressor 2 is connected to the evaporator 8 through the suction pipe 1, and a first pressure sensor 11 and a first temperature sensor 12 are arranged on the suction pipe 1 to measure the first stage suction pressure P1 (the pressure of the refrigerant at the first stage suction port) and the first stage suction temperature T1 (the temperature of the refrigerant at the first stage suction port). The first stage discharge port is connected to the second stage suction port through the connecting pipe 3, and the refrigerant discharged from the first stage discharge port is transported to the second stage suction port through the connecting pipe 3, and a second pressure sensor 31 and a second temperature sensor 32 are arranged on the connecting pipe 3, the second pressure sensor 31 is used to measure the second stage suction pressure P3' (the pressure of the refrigerant at the second stage suction port), and the second temperature sensor 32 is used to measure the second stage suction temperature T3' (the temperature of the refrigerant at the second stage suction port). The discharge port of the second stage of the two-stage centrifugal compressor 2 is connected to the condenser 5 through the discharge pipe 4, and a third pressure sensor 41 and a third temperature sensor 42 are arranged on the discharge pipe 4 to measure the second stage discharge pressure P4 (the pressure of the refrigerant at the second stage discharge port) and the second stage discharge temperature T4 (the temperature of the refrigerant at the second stage discharge port). The two-stage centrifugal compressor 2 receives low-temperature and low-pressure refrigerant from the evaporator 8 through the suction pipe 1, and performs two-stage compression to obtain high-temperature and high-pressure refrigerant, and transports the high-temperature and high-pressure refrigerant to the condenser 5 through the discharge pipe 4.

[0100] The economizer 7 is communicated with the connecting pipe 3 through the supplementary gas pipe, and the supplementary gas valve 6 is arranged on the supplementary gas pipe. The function of the economizer 7 is to supplement the intermediate gas for the two-stage centrifugal compressor 2, that is, the economizer 7 transports additional refrigerant to the connecting pipe 3 through the supplementary gas pipe, and the additional refrigerant is transported to the second stage suction port of the two-stage compressor together with the refrigerant discharged from the first stage discharge port in the connecting pipe 3, and the supplementary gas flow of the economizer 7 is adjusted through the supplementary gas valve 6. The fourth pressure sensor 61 and the fourth temperature sensor 62 are both arranged on the supplementary gas pipe, and specifically, the fourth pressure sensor 61 and the fourth temperature sensor 62 are both arranged on the segment of the supplementary gas pipe between the supplementary gas valve 6 and the connecting pipe 3, so that the fourth pressure sensor 61 and the fourth temperature sensor 62 measure the pressure and temperature of the refrigerant output by the supplementary gas valve 6. The fourth pressure sensor 61 is used to measure the pressure of the refrigerant output by the supplementary gas valve 6, which is defined as the supplementary gas pressure P6, and the fourth temperature sensor is used to measure the temperature of the refrigerant output by the supplementary gas valve 6, which is defined as the supplementary gas temperature T6. The fifth pressure sensor 9 is used to measure the pressure of the refrigerant in the condenser 5, which is defined as the condenser pressure P5, and the sixth pressure sensor 13 is used to measure the pressure of the refrigerant in the evaporator 8, which is defined as the evaporator pressure P8.

[0101] Please refer to Figure 2, where 4 to 5 indicates that the refrigerant flows through the condenser 5, and the high-temperature and high-pressure refrigerant gas exchanges heat with the cooling water in the condenser 5, transferring the heat to the cooling water and taking it away, while the refrigerant gas condenses into a high-pressure liquid. In this process, the pressure of the refrigerant remains unchanged but the enthalpy decreases, that is, the temperature decreases; 5 to 6 indicates that the refrigerant flows through the primary throttle valve 10. In this process, the refrigerant flow is restricted, so the temperature remains unchanged and the pressure decreases; 7 to 8 indicates that the refrigerant flows through the secondary throttle valve 14. In this process, the refrigerant is The refrigerant flow is restricted, so the temperature remains unchanged and the pressure decreases; from 8 to 1, it means that the refrigerant flows through the evaporator 8. During this process, the refrigerant pressure remains unchanged and the enthalpy value increases, that is, the temperature increases, indicating the evaporation of the refrigerant; from 1 to 3 represents the operation process of the first-stage compressor. During this process, the refrigerant pressure increases and the temperature rises; from 3 to 3ˊ represents the air replenishment process. During this process, the pressure remains unchanged and the enthalpy value increases; from 3ˊ to 4 represents the operation process of the second-stage compressor. During this process, the refrigerant pressure increases and the temperature rises.

[0102] The first pressure sensor 11, the first temperature sensor 12, the second pressure sensor 31, the second temperature sensor 32, the third pressure sensor 41, the third temperature sensor 42, the fourth pressure sensor 61, the fourth temperature sensor 62, the fifth pressure sensor 9, and the sixth pressure sensor 13 are all communicatively connected (specifically, electrically connected) to the computing module, and the computing module is capable of receiving in real time the pressure parameters measured by the pressure sensors and the temperature parameters measured by the temperature sensors. The first pressure sensor 11, the first temperature sensor 12, the second pressure sensor 31, the second temperature sensor 32, the third pressure sensor 41, the third temperature sensor 42, the fourth pressure sensor 61, the fourth temperature sensor 62, the fifth pressure sensor 9, and the sixth pressure sensor 13 constitute an acquisition module.

[0103] The acquisition module also collects the input power W of the two-stage centrifugal compressor in real time comp And the total heat exchange of the compressor Q loss And send it to the calculation module. The calculation module can also receive the input power W of the two-stage centrifugal compressor in real time. comp And the total heat exchange of the compressor Q loss Two-stage centrifugal compressor input power W comp It can be obtained by multiplying the current and voltage input to the two-stage centrifugal compressor 2, so that the calculation module can obtain W in real time. comp The total heat exchange capacity of the compressor is Q loss =Q air.con +Q air.rad +Q ref .Q air.con is the heat exchange between the two-stage centrifugal compressor and the air, Q air.rad is the radiation heat transfer of the two-stage centrifugal compressor, Q refHeat carried away by the refrigerant.

[0104] The calculation module stores a table of temperature, pressure and enthalpy values corresponding to various refrigerants and a table of saturation pressure and enthalpy values. For a specific refrigerant, when its temperature and pressure are determined, its enthalpy can be uniquely determined from the table of temperature, pressure and enthalpy values. The refrigerant can be R134A, R123, R245fa, R1233zd(E), R1336mzz(Z), R1224yd(Z), R514A, R1234ze(E), R513A, R5158B. In the present embodiment, the refrigerant is R134A. After obtaining the first-stage suction pressure P1 and the first-stage suction temperature T1 by means of the table of temperature, pressure and enthalpy values of R134A, the enthalpy value h 0[1] at the first-stage suction port can be determined. After obtaining the second-stage suction pressure P3' and the second-stage suction temperature T3', the enthalpy value h 0[3′] at the second-stage suction port of the compressor can be determined. After obtaining the second-stage discharge pressure P4 and the second-stage discharge temperature T4, the enthalpy value h 0[4] at the second-stage discharge port can be determined. After obtaining the subcooler pressure P6 and the subcooler temperature T6, the enthalpy value h 0[3] at the subcooler valve can be determined. The condenser enthalpy value h 0[5] represents the enthalpy value of the refrigerant in the condenser 5. After obtaining the condenser pressure P5, in one embodiment (the condenser has no subcooling degree), the condenser pressure P5 is the saturation pressure of the refrigerant in the condenser, which is measured by the fifth pressure sensor 9, and the condenser enthalpy value h 0[5] can be determined according to the table of saturation pressure and enthalpy values; or in one embodiment (the condenser has a subcooling degree), the condenser pressure P5 is the pressure of the refrigerant at the outlet of the condenser, and the condenser enthalpy value h 0[5] can be determined according to the table of temperature, pressure and enthalpy values by further measuring the temperature of the refrigerant at the outlet of the condenser. 0[7] represents the economizer outlet enthalpy value, but according to the pressure and enthalpy diagram of Figure 2 , it can be concluded that the enthalpy value does not change from the economizer 7 to the evaporator 8, and therefore, although the second-stage throttling valve 14 is arranged between the economizer 7 and the evaporator 8, the second-stage throttling valve 14 does not change the pressure and the enthalpy value, and the economizer outlet enthalpy value h 0[7] is equal in value to the evaporator enthalpy value, which represents the enthalpy value of the refrigerant in the evaporator, and therefore, the evaporator pressure P8 can be obtained by measuring the evaporator pressure P8 by means of the sixth pressure sensor 13. In one embodiment, the evaporator pressure P8 is the saturation pressure of the refrigerant in the evaporator, and the evaporator enthalpy value can be determined according to the table of saturation pressure and enthalpy values, which is used as the economizer outlet enthalpy value h 0[7] for calculation.

[0105] The energy conservation equation established with the two-stage centrifugal compressor 2 as the control body is stored in the calculation module:

[0106] m1h 0[1] +δmh 0[3′] +W comp =(m1+δm)h 0[4] +Q loss

[0107] The energy conservation equation established with the economizer 7 as the control body is: 0[7] +δmh 0[3] =(m1+δm)h 0[5] .

[0108] Through the above two formulas, the actual air supplement amount δm can be obtained:

[0109]

[0110]

[0111] In the above formulas:

[0112] m1: the refrigerant mass in the primary circulation compression of the two-stage centrifugal compressor;

[0113] W comp : the input power of the two-stage centrifugal compressor;

[0114] Q loss : the total heat exchange amount of the two-stage centrifugal compressor;

[0115] h 0[1] : the enthalpy value of the primary suction port;

[0116] h 0[3] : the enthalpy value of the air supplement valve;

[0117] h 0[3′] : the enthalpy value of the secondary suction port;

[0118] h 0[4] : the enthalpy value of the secondary exhaust port;

[0119] h 0[5] : the enthalpy value of the condenser;

[0120] h 0[7] : the enthalpy value of the economizer outlet.

[0121] In order to calculate the optimal air supplement amount Tδm, the energy conservation equation is established again: 0[1] +δmh 0[3″] +W comp =(m1+δm)h 0[4] +Q loss ; m1h0[7] + δmh 0[3] = (m1+ δm)h 0[5] , h 0[3′] is replaced by h 0[3″] , where h 0[3″] is the enthalpy of the optimal secondary suction port. The enthalpy h 0[3″] of the optimal secondary suction port is determined by combining the target secondary suction pressure Pmth and the temperature, pressure and enthalpy table stored in the calculation module. Wherein, the target secondary suction pressure Pmth = (P5*P8)^0.5, wherein P5 is the condenser pressure, and P8 is the evaporator pressure.

[0122] Again, through two energy conservation equations, the optimal amount of air supplement Tδm is calculated as follows.

[0123] Wherein,

[0124] m1: refrigerant mass in the primary circulation compression of the two-stage centrifugal compressor;

[0125] W comp : input power of the two-stage centrifugal compressor;

[0126] Q loss : total heat exchange amount of the two-stage centrifugal compressor;

[0127] h 0[] : enthalpy of the primary suction port;

[0128] h 0[] : enthalpy of the air supplement valve;

[0129] h 0[] : enthalpy of the optimal secondary suction port;

[0130] h 0[] : enthalpy of the secondary exhaust port;

[0131] h 0[] : enthalpy of the condenser;

[0132] h 0[] : enthalpy of the economizer outlet.

[0133] After the calculation module calculates the optimal air supplement amount Tδm and the actual air supplement amount δm, the optimal air supplement amount Tδm and the actual air supplement amount δm are sent to the control module, and an air supplement valve adjustment instruction is issued. The control module is in communication connection with the calculation module, and specifically, the control module can be electrically connected with the calculation module. The control module receives the optimal air supplement amount Tδm and the actual air supplement amount δm, and adjusts the opening degree of the air supplement valve 6 with the optimal air supplement amount Tδm as the control target and the actual air supplement amount δm as the feedback value. If the optimal air supplement amount Tδm is greater than the actual air supplement amount δm, the opening degree of the air supplement valve 6 is increased. If the optimal air supplement amount Tδm is equal to the actual air supplement amount δm, the opening degree of the air supplement valve 6 is kept unchanged. If the optimal air supplement amount Tδm is less than the actual air supplement amount δm, the opening degree of the air supplement valve 6 is decreased.

[0134] The control module further determines the amplitude of adjusting the opening degree of the air supplement valve 6 according to the difference between the optimal air supplement amount Tδm and the actual air supplement amount δm. After being adjusted, the opening degree of the air supplement valve 6 is the first opening degree. Through the calculation module, the actual air supplement amount δm of the air supplement valve 6 approaches the optimal air supplement amount Tδm in real time, and thus the actual air supplement amount δm can fall into the optimal air supplement amount interval, thereby obtaining a better air supplement effect.

[0135] After the opening degree of the air supplement valve 6 is adjusted to the first opening degree, the control module further acquires the secondary suction gas superheat Tsh3ˊ at the secondary suction port or the secondary exhaust gas superheat Tsh4 at the secondary exhaust port, and judges whether the secondary suction gas superheat Tsh3ˊ is within a preset range or whether the secondary exhaust gas superheat Tsh4 is within a preset range. If the secondary suction gas superheat Tsh3ˊ is within the preset range or the secondary exhaust gas superheat Tsh4 is also within the preset range, the air supplement valve 6 keeps the first opening degree unchanged.

[0136] The calculation method of the secondary suction gas superheat Tsh3ˊ is to acquire the secondary suction gas pressure P3ˊ and the secondary suction gas temperature T3ˊ, acquire the saturation temperature TP3ˊ corresponding to the secondary suction gas pressure P3ˊ through the secondary suction gas pressure P3ˊ, and the secondary suction gas superheat Tsh3ˊ = T3ˊ-TP3ˊ. The calculation method of the secondary exhaust gas superheat Tsh4 is to acquire the secondary exhaust gas pressure P4 and the secondary exhaust gas temperature T4, acquire the saturation temperature Tp4 corresponding to the secondary exhaust gas pressure P4 through the secondary exhaust gas pressure P4, and the secondary exhaust gas superheat Tsh4 = T4-Tp4.

[0137] Further, if the secondary suction gas superheat Tsh3ˊ is less than a preset lower limit of suction gas superheat or the secondary exhaust gas superheat Tsh4 is less than a preset lower limit of exhaust gas superheat, the control module controls the opening degree of the air supplement valve 6 to be decreased, and if the secondary suction gas superheat is greater than a preset upper limit of suction gas superheat Tsh3ˊ or the secondary exhaust gas superheat Tsh4 is greater than a preset upper limit of exhaust gas superheat, the control module controls the opening degree of the air supplement valve 6 to be increased.

[0138] In one embodiment of the application, when the control module controls the opening degree of the supplementary air valve 6, the control module acquires the secondary suction pressure P3' and determines whether the secondary suction pressure P3' reaches the current target secondary suction pressure value Pmth, wherein if the secondary suction pressure P3' does not reach the current target suction pressure value Pmth, the control module controls the opening degree of the supplementary air valve 6 to increase / decrease, so that the secondary suction pressure P3' reaches the current target suction pressure value Pmth.

[0139] After adjusting the opening degree of the supplementary air valve 6 to the first opening degree, the above-mentioned second adjustment of the actual supplementary air amount δm avoids the risk of liquid entrainment, and realizes safe and reliable operation of the two-stage compression centrifugal unit 100.

[0140] The two-stage compression centrifugal unit 100 provided by the application has the following beneficial effects.

[0141] Firstly, the plurality of temperature sensors and the plurality of pressure sensors can be used to measure the primary suction pressure P1, the primary suction temperature T1, the secondary suction pressure P3', the secondary suction temperature T3', the supplementary air pressure P6, the supplementary air temperature T6, the secondary exhaust pressure P4, the secondary exhaust temperature T4, the condenser pressure P5, and the evaporator pressure P8 in real time; the calculation module receives these temperature parameters and pressure parameters and combines them with the input power W of the two-stage centrifugal compressor to calculate the optimal supplementary air amount Tδm and the actual supplementary air amount δm. comp and the total heat exchange amount Q of the compressor loss The calculation module of the two-stage compression centrifugal unit 100 substitutes the above-mentioned operating parameters into the energy conservation equation established by taking the two-stage centrifugal compressor 2 as the control body and the energy conservation equation established by taking the economizer 7 as the control body, thereby calculating the optimal supplementary air amount Tδm and the actual supplementary air amount δm, which are used to adjust the opening degree of the supplementary air valve 6. If the actual supplementary air amount δm is different from the optimal supplementary air amount Tδm, the module issues a supplementary air valve adjustment instruction. The control module receives the optimal supplementary air amount Tδm and the actual supplementary air amount δm, and takes the optimal supplementary air amount Tδm as the control target and the actual supplementary air amount δm as the feedback value to adjust the opening degree of the supplementary air valve 6, so that the actual supplementary air amount δm can be adjusted in real time to approach the optimal supplementary air amount Tδm. The adjusted actual supplementary air amount δm is within the optimal supplementary air amount interval.

[0142] Secondly, by setting pressure sensor and temperature sensor and increasing the calculation module, the actual gas supplement amount δm and the optimal gas supplement amount Tδm can be calculated, the low-cost precise detection of the two-stage compression centrifugal unit 100 is realized, the detection precision is higher, the actual gas supplement amount δm of the two-stage compression centrifugal unit 100 can be precisely controlled, the actual gas supplement amount δm of the gas supplement valve 6 is within the optimal gas supplement amount interval, the gas supplement amount is dynamically adjusted online and self-adapted with the load and operating condition changes without increasing the structural complexity of the two-stage compression centrifugal unit 100, and the advantages of the gas supplement and enthalpy increase of the two-stage centrifugal compressor 2 are fully utilized.

[0143] Figure 3 The flow chart of the intermediate gas supplement control method of the two-stage compression centrifugal unit 100 according to the embodiment of the application is schematically shown. Please refer to Figure 3 An embodiment of the second aspect of the application provides an intermediate gas supplement control method of a two-stage compression centrifugal unit, which is implemented according to the two-stage compression centrifugal unit 100 of the first aspect of the application, and includes the following steps:

[0144] Receiving the operating parameters of the two-stage compression centrifugal unit 100;

[0145] Calculating the actual gas supplement amount δm and the optimal gas supplement amount Tδm according to the operating parameters of the two-stage compression centrifugal unit 100 to adjust the opening degree of the gas supplement valve 6.

[0146] The operating parameters of the two-stage compression centrifugal unit 100 include the primary suction pressure P1, the primary suction temperature T1, the secondary suction pressure P3ˊ, the secondary suction temperature T3ˊ, the secondary discharge pressure P4, the secondary discharge temperature T4, the gas supplement pressure P6, the gas supplement temperature T6, the condenser pressure P5, and the evaporator pressure P8. According to the above temperature parameters, pressure parameters, and the temperature-pressure-enthalpy table and / or the pressure-saturation enthalpy table, h 0[] , h 0[] , h 0[] , h 0[] , h 0[] , and h 0[] are determined. Combined with the two-stage centrifugal compressor input power W comp and the total heat exchange amount Q loss of the compressor, the actual gas supplement amount δm is calculated by the formula

[0147] m1: the refrigerant mass in the primary cycle compression of the two-stage centrifugal compressor;

[0148] W comp : the input power of the two-stage centrifugal compressor;

[0149] Q loss : the total heat exchange amount of the two-stage centrifugal compressor;​

[0150] h 0[] : enthalpy of the primary suction port;

[0151] h 0[] : enthalpy of the supplementary air valve;

[0152] h 0[] : enthalpy of the secondary suction port;

[0153] h 0[] : enthalpy of the secondary exhaust port;

[0154] h 0[] : enthalpy of the condenser;

[0155] h 0[] : enthalpy of the economizer outlet.

[0156] The method for calculating the optimal supplementary air amount according to the operating parameters of the two-stage centrifugal compressor unit 100 comprises:

[0157] According to the primary suction pressure P1, the primary suction temperature T1, the target secondary suction pressure Pmth, the secondary suction temperature T3', the secondary exhaust pressure P4, the secondary exhaust temperature T4, the supplementary air pressure P6, the supplementary air temperature T6, the condenser pressure P5, the evaporator pressure P8, and the temperature-pressure-enthalpy table and / or the pressure-saturation enthalpy table, h 0[] , h 0[] , h 0[] , h 0[] , h 0[] , and h 0[] are determined. Combined with the input power W comp of the two-stage centrifugal compressor, the total heat exchange amount Q loss of the compressor, the optimal supplementary air amount Tδm is calculated through the formula , wherein:

[0158] m1: the refrigerant mass in the primary cycle compression of the two-stage centrifugal compressor;

[0159] W comp : input power of the two-stage centrifugal compressor;

[0160] Q loss : total heat exchange amount of the two-stage centrifugal compressor;

[0161] h 0[] : enthalpy of the primary suction port;

[0162] h 0[] : enthalpy of the supplementary air valve;

[0163] h 0[] : enthalpy of the optimal secondary suction port;

[0164] h0[] : enthalpy of the secondary exhaust port;

[0165] h 0[] : enthalpy of the condenser;

[0166] h 0[] : enthalpy of the economizer outlet.

[0167] Figure 4 A flow chart of the intermediate air injection control method of the two-stage compression centrifugal unit according to the embodiment of the present application is schematically shown. Please refer to Figure 4 After "calculating the actual air injection amount δm and the optimal air injection amount Tδm according to the operating parameters of the two-stage compression centrifugal unit 100 to adjust the opening degree of the air injection valve 6", the method further comprises the step of "adjusting the air injection valve to the first opening degree with the optimal air injection amount as the control target and the actual air injection amount as the feedback value".

[0168] Figure 5 A flow chart of the intermediate air injection control method of the two-stage compression centrifugal unit according to the embodiment of the present application is schematically shown. Please refer to Figure 5 After "adjusting the opening degree of the air injection valve 6 with the optimal air injection amount as the control target and the actual air injection amount as the feedback value, the air injection valve 6 is adjusted to the first opening degree", the method further comprises the following steps:

[0169] Obtaining the secondary suction superheat Tsh3ˊ at the secondary suction port;

[0170] Determining whether the secondary suction superheat Tsh3ˊ is within the preset range;

[0171] Keeping the air injection valve 6 at the first opening degree according to the secondary suction superheat Tsh3ˊ being within the preset range;

[0172] Controlling the first opening degree to be reduced according to the secondary suction superheat Tsh3ˊ being less than the preset lower limit of the suction superheat;

[0173] Controlling the first opening degree to be increased according to the secondary suction superheat Tsh3ˊ being greater than the preset upper limit of the suction superheat.

[0174] Please refer to Figure 6 Alternatively, after "adjusting the opening degree of the air injection valve 6 with the optimal air injection amount as the control target and the actual air injection amount as the feedback value, the air injection valve 6 is adjusted to the first opening degree", the method further comprises the following steps:

[0175] Obtaining the secondary exhaust superheat Tsh4 at the secondary exhaust port;

[0176] Determining whether the secondary exhaust superheat Tsh4 is within the preset range;

[0177] According to the secondary exhaust gas superheat Tsh4 being in a preset range, the air supplement valve 6 is kept at the first opening degree;

[0178] According to the secondary exhaust gas superheat Tsh4 being less than a preset lower limit value of exhaust gas superheat, the first opening degree is controlled to be reduced in opening degree;

[0179] According to the secondary exhaust gas superheat Tsh4 being greater than a preset upper limit value of exhaust gas superheat, the first opening degree is controlled to be adjusted.

[0180] The calculation method of the secondary suction gas superheat Tsh3' is that the secondary suction gas pressure P3' and the secondary suction gas temperature T3' are obtained, the saturation temperature TP3' corresponding to the secondary suction gas pressure P3' is obtained through the secondary suction gas pressure P3', and the secondary suction gas superheat Tsh3' = T3'- TP3'. The calculation method of the secondary exhaust gas superheat Tsh4 is that the secondary exhaust gas pressure P4 and the secondary exhaust gas temperature T4 are obtained, the saturation temperature Tp4 corresponding to the secondary exhaust gas pressure P4 is obtained through the secondary exhaust gas pressure P4, and the secondary exhaust gas superheat Tsh4 = T4-Tp4.

[0181] In an embodiment of the present application, when the air supplement valve 6 is controlled to be adjusted, the control module obtains the secondary suction gas pressure P3' at the secondary suction port, and judges whether the secondary suction gas pressure P3' reaches the current target secondary suction gas pressure value Pmth, wherein if the secondary suction gas pressure P3' does not reach the current target suction gas pressure value Pmth, the control module controls the air supplement valve 6 to be adjusted in opening degree to increase or decrease, so that the secondary suction gas pressure P3' reaches the current target suction gas pressure value Pmth.

[0182] After the air supplement valve 6 is adjusted to the first opening degree, the secondary suction gas superheat Tsh3' and the secondary exhaust gas superheat Tsh4 are compared with the preset range, and the air supplement valve 6 is adjusted again according to the comparison result, so that the air supplement with liquid is avoided.

[0183] The above describes the optional embodiments of the present application in detail with reference to the drawings, but the embodiments of the present application are not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the embodiments of the present application within the technical concept of the embodiments of the present application, and these simple modifications all belong to the protection scope of the embodiments of the present application.

[0184] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the embodiments of the present application.

[0185] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any changes or replacements within the technical scope disclosed by the present application, which can be easily thought by those skilled in the art, should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A two-stage compression centrifugal unit, characterized in that, The double-stage compression centrifugal unit comprises: a double-stage centrifugal compressor; an evaporator and a condenser, a suction port of a first stage of the double-stage centrifugal compressor being connected to an outlet port of the evaporator, and an exhaust port of a second stage of the double-stage centrifugal compressor being connected to an inlet port of the condenser; an economizer and a supplementary air valve, the economizer being connected between an inlet port of the evaporator and an outlet port of the condenser, and the economizer being connected to the exhaust port of the first stage and the suction port of the second stage of the double-stage centrifugal compressor through the supplementary air valve; a calculation module, the calculation module being configured to calculate an actual supplementary air amount and an optimal supplementary air amount according to operating parameters of the double-stage compression centrifugal unit, and to adjust an opening degree of the supplementary air valve based on the actual supplementary air amount and the optimal supplementary air amount; the calculation module being configured to calculate the actual supplementary air amount δm according to the following formula: wherein: m1: a refrigerant mass in a first-stage circulation compression of the double-stage centrifugal compressor; W comp : double-stage centrifugal compressor input power; Q loss : total heat exchange of two-stage centrifugal compressor h 0[1] : enthalpy of the primary air intake h 0[3] : enthalpy of the gas supply valve h 0[3′] : enthalpy of secondary air intake h 0[4] : enthalpy of secondary exhaust h 0[5] : condenser enthalpy h 0[7] : economizer outlet enthalpy or the calculation module being configured to calculate the optimal supplementary air amount Tδm according to the following formula: wherein: m1: a refrigerant mass in a first-stage circulation compression of the double-stage centrifugal compressor; W comp : input power of two-stage centrifugal compressor Q loss : total heat exchange of two-stage centrifugal compressor h 0[1] : enthalpy of primary air intake h 0[3] : enthalpy of the gas supply valve h 0[3″] : enthalpy of the optimal secondary air intake h 0[4] : enthalpy of secondary exhaust h 0[5] : condenser enthalpy h 0[7] : economizer outlet enthalpy 2. The two-stage compression centrifugal package of claim 1, wherein, The operating parameters include temperature parameters and pressure parameters, and the calculation module can obtain h 0[1] , h 0[3] , h 0[3′] , h 0[3′′] , h 0[4] , h 0[5] and h 0[7] according to the temperature parameters and the pressure parameters, with reference to a temperature-pressure-enthalpy table and / or a pressure-saturation-enthalpy table.

3. The two-stage compression centrifugal package of claim 1, wherein, and further comprising a control module, the control module being configured to adjust the opening degree of the supplementary air valve based on the optimal supplementary air amount as a control target and the actual supplementary air amount as a feedback amount.

4. A method for intermediate supplementary air control of a double-stage compression centrifugal unit, the method being implemented by the double-stage compression centrifugal unit according to any one of claims 1 to 3, and comprising the following steps: receiving operating parameters of the double-stage compression centrifugal unit; calculating an optimal supplementary air amount and an actual supplementary air amount according to the operating parameters of the double-stage compression centrifugal unit, and adjusting an opening degree of a supplementary air valve based on the actual supplementary air amount and the optimal supplementary air amount; The actual make-up amount δm is calculated according to the formula: wherein: m1: a refrigerant mass in a first-stage circulation compression of the double-stage centrifugal compressor; W comp : input power of two-stage centrifugal compressor Q loss : total heat exchange of two-stage centrifugal compressor h 0[1] : enthalpy of primary air intake h 0[3] : enthalpy of the gas supply valve h 0[3′] : enthalpy of secondary air intake h 0[4] : enthalpy of secondary exhaust h 0[5] : condenser enthalpy h 0[7] : economizer outlet enthalpy Alternatively, the optimal amount of air supplement Tδm is calculated according to the formula: wherein: m1: a refrigerant mass in a first-stage circulation compression of the double-stage centrifugal compressor; W comp : input power of two-stage centrifugal compressor Q loss : total heat exchange of two-stage centrifugal compressor h 0[1] : enthalpy of the primary air intake h 0[3] : enthalpy of the gas supply valve h 0[3′′] : enthalpy of the optimum secondary air intake h 0[4] : enthalpy of secondary exhaust h 0[5] : condenser enthalpy h 0[7] : economizer outlet enthalpy 5. The intermediate gas injection control method of a two-stage compression centrifugal compressor unit according to claim 4, characterized by, and further comprising the following steps: adjusting the opening degree of the supplementary air valve to a first opening degree based on the optimal supplementary air amount as a control target and the actual supplementary air amount as a feedback amount.

6. The intermediate gas injection control method of a two-stage compression centrifugal chiller unit according to claim 5, wherein and further comprising the following steps: obtaining a second-stage suction superheat degree at the suction port of the second stage; determining whether the second-stage suction superheat degree is within a preset range; maintaining the supplementary air valve at the first opening degree based on the second-stage suction superheat degree being within the preset range; performing opening degree reduction control on the first opening degree based on the second-stage suction superheat degree being less than a preset lower limit of suction superheat degree; performing adjustable control on the first opening degree based on the second-stage suction superheat degree being greater than a preset upper limit of suction superheat degree.

7. The intermediate gas injection control method of a two-stage compression centrifugal chiller unit as set forth in claim 5, wherein and further comprising the following steps: obtaining a second-stage exhaust superheat degree at the exhaust port of the second stage; determining whether the second-stage exhaust superheat degree is within a preset range; maintaining the supplementary air valve at the first opening degree based on the second-stage exhaust superheat degree being within the preset range; performing opening degree reduction control on the first opening degree based on the second-stage exhaust superheat degree being less than a preset lower limit of exhaust superheat degree; performing adjustable control on the first opening degree based on the second-stage exhaust superheat degree being greater than a preset upper limit of exhaust superheat degree.

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