Digital control method for reciprocating piston compressor

Abstract

The invention discloses a digital control method for a reciprocating piston compressor. The method comprises the following steps: 1) re-checking the inter-stage pressure of each stage according to a power-saving principle or a manual given process; (2) the working volume and the state volume of each stage (column) virtual cylinder are calculated according to the operation conditions of each stage; 3) calculating to obtain a complete set omegai of a stepless backflow adjusting device loading state data pair (thetaaxi, thetacyi); and (4) dynamic safety rechecking and reverse angle maximization optimization of each column are conducted on each data pair (theta axi and theta cyi) in the complete set omega i, an instruction solution set phi i for regulating and controlling the stepless backflow adjusting devices of all stages (columns) is obtained, any data pair solution (theta axi and theta cyi) in the solution set phi i can generate a control instruction, and the method is a virtual cylinder concept, multi-variable synchronous regulation and control are achieved, and the control efficiency is improved. The invention relates to a reciprocating piston compressor control method based on inter-stage pressure dynamic distribution and a digital framework technology. The regulation and control efficiency of the large reciprocating compressor is improved, the equipment utilization rate of the large reciprocating compressor is improved, and the service life of the equipment is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of compressor design and manufacturing, and specifically relates to a digital control method for a reciprocating piston compressor. Background Technology

[0002] Reciprocating piston compressors have wide applications in many fields and industries. They are typically designed and manufactured based on the maximum flow rate and maximum pressure ratio for the applied operating conditions. Furthermore, reciprocating piston compressors have the characteristic of maintaining a relatively constant volumetric flow rate under design operating conditions. These factors influence their operation and control under varying operating conditions. Currently, large reciprocating piston compressors are often used in single-variable applications (where there is only one main variable in the control process, and other operating parameters need to remain stable). Control methods include setting clearance chambers, bypass return lines, full-stroke open suction valves, and partial-stroke open suction valves. These control methods can be used individually or in combination, each with its own characteristics in terms of equipment investment, energy saving, and applicability. The partial-stroke open suction valve, through a dedicated actuator, precisely controls the closing time of the suction valve, allowing gas in the cylinder to flow back to the suction chamber before compression, thus changing the actual flow rate of the compressed gas. This allows for stepless adjustment during the control process, and this stepless backflow control device is a very important control method.

[0003] When large reciprocating piston compressors are used in single-variable applications, the commonly used control methods are relatively simple. The basic control means is to stabilize the interstage pressure of each stage. This control approach leads to poor compressor performance in some situations. For example, when the compressor inlet pressure fluctuates significantly (inlet pressure is the main variable), while downstream demand (outlet pressure and gas flow rate) remains stable, the conventional control method is as follows: as the inlet pressure fluctuates significantly, the compressor maintains stable outlet pressures at each stage. At this time, each stage tracks and controls the standard flow rate of each stage through the return line regulating valve to keep it constant. When the compressor inlet pressure decreases or increases to the outlet pressure of a certain stage, the intake valve of that stage is forcibly unloaded, realizing the no-load operation of the cylinder of that stage, thereby achieving follow-up control of the single variable of inlet pressure. However, the above control method will produce the following problems: 1. The intake valve unloading needs to be coordinated with the return line regulating valve, the operation process is complex, backflow power consumption cannot be avoided, and the long-term operation of the unloaded cylinder is risky. 2. The compressor's imbalance of piston force between moving parts increases the difference in piston force load between stages, deteriorates the uniformity of crankshaft tangential force, and challenges the compressor's operational stability. 3. The compressor's pressure ratios at each stage are not properly allocated, and the interstage cooling is not fully utilized to reduce the compression work of the next stage and lower the exhaust temperature, resulting in increased compressor energy consumption.

[0004] When reciprocating piston compressors are used in multi-variable applications (where there are two or more main variables in the control process, and other operating parameters are required to remain stable), such as in the example above where the outlet pressure fluctuates along with the compressor inlet pressure (dual-variable operation), the control scheme becomes limited and even difficult due to the constraints of the original control method. This is because the stepless backflow control method has not been deeply digitally integrated with the reciprocating compressor control, and the existing control process has not been innovated. Therefore, it is essential to propose a digital control method for reciprocating piston compressors to more rationally and efficiently meet the multi-variable operation requirements of piston compressors. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application employs a virtual cylinder concept, a multi-variable synchronous control, and a dynamic distribution of interstage pressure, and discloses a digital control method for a reciprocating piston compressor.

[0006] This invention provides a digital control method for a reciprocating piston compressor. A stepless backflow adjustment device is installed on both the shaft side and cover side of each stage (row) of the compressor cylinders. When the control variable changes, a control command for the stepless backflow adjustment device is generated through the following steps to complete the regulation of the compressor operation:

[0007] 1) Re-evaluate the pressure between each stage using power-saving principles or a manually assigned process;

[0008] 2) Calculate the working volume and cylinder state volume of each level (train) of virtual cylinders based on the operating conditions at each level;

[0009] 3) Calculate and obtain the loading state data of the continuously variable flow regulator (θ) axi ,θ cyi Complete series Ω i ;

[0010] 4) For the complete set Ω i Each data pair (θ) axi ,θ cyi The dynamic safety was verified and the optimal reverse angle of each column was maximized to obtain the instruction set Φ for regulating the stepless backflow control device at each stage (column). i Solution set Φ i Any data pair in the solution (θ) axi ,θ cyi It can generate control commands.

[0011] In step 1),

[0012] The pressure between each stage can be re-evaluated by the principle of saving power or by manually assigning a process. This can be achieved by changing the compressor's operating mode. The compressor operating mode can be divided into three types: equal compression mode for each stage, equal load compression mode for each stage, and manual allocation of pressure ratio for each stage.

[0013] When the equal-ratio compression mode is selected, the pressure ratios at each stage are equal, and the relationship is expressed as follows:

[0014]

[0015] Where, ε i P represents the pressure ratio of the i-th stage. si P represents the i-th stage intake pressure (MPa, a). s(i+1) P represents the intake pressure (MPa, a) of stage (i+1). s P represents the compressor intake pressure (MPa, a). d The value represents the final discharge pressure of the compressor (MPa, a), N represents the total number of stages of the compressor, and i represents the stage variable of the compressor, with a value range of (i = 1, ..., N).

[0016] When the equal-load compression mode is selected, it indicates that the shaft power of each compression process is equal or similar, and the corresponding compression ratio (P) of each stage is equal. s(i+1) / P si ) Calculate the shaft power N of each stage using interpolation method i After equalization, the power N of the i-th stage shaft is obtained. i The calculation expression is

[0017]

[0018] Where, N i V represents the power of the i-th shaft (kW). dsi Represents the state volume (m) of the i-th stage cylinder 3 / r), η mi Represents the i-th level mechanical efficiency (values ​​range from 0.86 to 0.96 for medium and large machines, and η for small machines). mi The value ranges from 0.85 to 0.92, where m represents the process index, n represents the compressor speed (r / min), and q represents the number of cylinders in the i-th stage.

[0019] When the manual allocation mode for each stage of pressure ratio is selected, the pressure ratio for each stage is obtained by manual input. After the compressor operation mode is selected, the pressure ratio for each stage and the interstage pressure verification value for each stage will be generated.

[0020] In step 2),

[0021] The working volume V of each level (column) of the virtual cylinder is calculated based on the operating conditions at each level. fi Cylinder volume Vdsi When, the calculation expression is

[0022]

[0023] V dsi =V fi ·η vi

[0024] V fi =V si ·ψ fti (i = 1, ..., N)

[0025] Among them, V dsi V represents the volume of the i-th stage cylinder. fi V represents the working volume of the i-th stage virtual cylinder. si P represents the actual working volume of the i-th stage cylinder. si T represents the i-th stage intake pressure, Q0 represents the volumetric flow rate under standard conditions, and T represents the volumetric flow rate. si η represents the intake air temperature of stage i, n represents the compressor speed, q represents the number of cylinders in stage i, and η represents the number of cylinders in stage i. vi Ψ represents the volumetric efficiency of the i-th level. fti represents the total unloading coefficient of the i-th stage, N represents the total number of stages of the compressor, and i represents the stage variable of the compressor, with a value range of (i = 1, ..., N);

[0026] The total unloading coefficient Ψ fti When the i-th stage cylinder is a double-acting type and the piston rod does not penetrate, the axial unloading coefficient Ψ fai And the unloading coefficient Ψ of the cover side fci The expression representing the volume allocation ratio is as follows:

[0027]

[0028] S fai =S·ψ fai

[0029] S fci =S·ψ fci

[0030] Among them, D i d represents the actual cylinder diameter of the i-th stage, d represents the piston rod diameter, and S represents the actual piston stroke. fai S represents the i-th level axle-side virtual travel. fci Represents the virtual travel of the i-th level cover side;

[0031] When the cylinder shaft-side or cover-side stepless backflow adjustment device is applied to the cylinder, the crank angle θ and the virtual stroke S of the i-th stage shaft-side or cover-side are respectively adjusted. fai or S fciThe relational expression is as follows:

[0032]

[0033]

[0034] Where r represents the crank radius, λ represents the ratio of the crank radius (r) to the connecting rod length (l) (λ = r / l, or simply the connecting rod ratio), and θ represents the crank angle, which is the angle between the crank and the cylinder centerline. The crank angle is set with the piston's outer dead center as the starting angle, and the minimum division angle of θ is set to 1°. The range of θ is (0° ≤ θ ≤ 360°). ai θ represents the crank angle corresponding to the axial loading of the i-th stage cylinder. ci This represents the crank angle corresponding to the i-th stage cylinder head side loading;

[0035] In step 3),

[0036] Solve for the load state data pair (θ) of the continuously variable flow regulator. axi ,θ cyi Complete series Ω i The method is as follows:

[0037] The θ ai and θ ci The i-th stage cylinder loading state data pair (θ) is formed. ai ,θ ci For a compressor at a certain standard state volumetric flow rate Q, z0 The i-th level can correspond to multiple combinations of cylinder shaft-side and cover-side loading states (meeting their flow requirements), that is, multiple data pairs (θ). axi ,θ cyi ), record the flow Q z0 The corresponding i-th level data pair is Ω for the entire set. i The relational expression is as follows:

[0038] Ω i (Q z0 )={(θ a1i ,θ c1i ),(θ a2i ,θ c2i ),…,(θ axi ,θ cyi (i = 1, ..., N)

[0039] For a certain standard state volumetric flow rate Q z0 The state volume V of the i-th stage cylinder dsi With loading state data to the entire set Ω i (Q z0 There exists a functional relationship f1 between them, and the expression is:

[0040] V dsi =f1(Ω) i (Q Z0 (i = 1, ..., N)

[0041] By obtaining the loading status data of the continuously variable flow regulator (θ) axi ,θ cyi Complete series Ω i This enables full-domain control of the virtual cylinder volume and cylinder state volume at each stage (column), ensuring the re-verified interstage pressure of the compressor.

[0042] In step 4),

[0043] For the complete series Ω i Each data pair (θ) axi ,θ cyi When performing dynamic safety verification and optimizing the maximum reverse angle of each column, the method is as follows:

[0044] Using the cylinder loading state data in column i to analyze the entire set Ω i (Q z0 Let θ be the sample space, and calculate the different data pairs (θ) axi ,θ cyi Under loading conditions, the reciprocating friction force F of each column within its full circumference working range fi reciprocating inertial force F si and gas force F gi The combined piston force F of each column is synthesized by superimposing the phase angles. pi This is to perform dynamic safety verification and optimize the maximization of the reversal angle of each column. (Subsequently, "level (column)" will be abbreviated as "column" to meet the requirements of dynamic verification.)

[0045] The gas force, reciprocating inertial force, and reciprocating friction force of each cylinder in the compressor are all along the cylinder centerline. Their algebraic sum is called the combined piston force, and its calculation expression is:

[0046] F pi =F gi +F si +F fi

[0047] Among them, F pi F represents the combined piston force in column i. gi F represents the gas force in the i-th column. si F represents the reciprocating inertial force of the i-th column. fi Represents the reciprocating friction force in the i-th column;

[0048] The i-th column of the combined piston force F pi It should be less than or equal to the compressor's maximum permissible combined piston force, with a safety margin. Its expression is:

[0049] F pi ≤(80%~95%)·F pmax

[0050] Among them, F pmax This represents the maximum permissible combined piston force of the compressor;

[0051] The i-th column of gas force F gi This force is generated by the gas pressure difference. Generally, the tensile gas force on the piston rod is considered positive, and the compressive gas force on the piston rod is considered negative. When the i-th cylinder is a double-acting cylinder and the piston rod does not penetrate through the gas, its calculation expression is:

[0052]

[0053] Among them, P ai P represents the pressure of the i-th column of shaft-side cylinders. ci P represents the pressure of the i-th column cover-side cylinder. b P represents atmospheric pressure. ai With P ci The range of variation is the intake and exhaust pressure (P) in column i. si ,P s(i+1) );

[0054] The i-th column of gas force F gi It should be less than or equal to the compressor's maximum permissible gas force, with a safety margin, and its expression is:

[0055] F gi ≤(80%~95%)·F gmax

[0056] Among them, F gmax This represents the maximum permissible gas force of the compressor;

[0057] The i-th column reciprocating inertial force F si Its expression is

[0058] F si =m si ·r·ω 2 (cosθ+λcos2θ)

[0059] Where ω represents the rotational angular velocity, ω=n·π / 30, and it is generally defined that the inertial force causing tension in the piston rod is positive, and the inertial force causing compression is negative, m si Let be the total mass of the i-th column of reciprocating motion;

[0060] The reciprocating friction force F in the i-th column fiThe reciprocating friction force is opposite to the direction of movement of the moving parts. It is generally stipulated that the reciprocating friction force during the axial stroke always points towards the cover side along the cylinder centerline and is defined as a positive value, while the reciprocating friction force during the cover stroke always points towards the axial side along the cylinder centerline and is defined as a negative value, with the reciprocating friction force at the dead center being zero. For simplified calculations, F can be taken as... fi It is a certain value.

[0061] The i-th column of the combined piston force F pi It is a function of the crank angle θ, when F pi A value of zero indicates that the force direction on the crosshead bearing has begun to reverse. Within one working cycle, if F... pi If a zero value appears only once, the working reverse angle of the pin bearing is 180°. If F pi If two or more zero values ​​appear, the corresponding crank angles θ1, θ2, ... θ need to be calculated. n (where n is an even number), the formula for calculating the working reverse angle of the pin bearing is θ. α =min(sum((θ2-θ1)+…+(θ)) n -θ n-1 )),360°-sum((θ2-θ1)+…+(θ n -θ n-1 )))

[0062] Where, θ α The working reversal angles of the crosshead bearing per revolution are θ1, θ2, ... θ n (n is an even number) represents the crank angles corresponding to the total piston force being zero;

[0063] The i-th column of cylinder shaft-side and cover-side loading state data pair (θ) axi ,θ cyi ) and the working reverse angle of the pin bearing (θ) αi There exists a functional relationship f2 between them, and the expression is:

[0064] θ αi =f2(θ) axi ,θ cyi )

[0065] Where, θ αi f1 represents the working reversal angle of the crosshead pin bearing per revolution of the i-th cylinder, and f2 represents the functional relationship.

[0066] For a compressor at a certain standard volumetric flow rate Q z0 The maximum working reverse angle of the pin bearing is max(θ). αi ) and loading status data for the entire set Ω i (Q z0 The relationship expression between ) is

[0067] max(θ αi )=max(f2(Ω i (Q Z0 (i = 1, ..., N)

[0068] At the same time, the maximum working reverse angle of the pin bearing should be greater than or equal to the minimum allowable value of the compressor, with a safety margin. The expression for this is:

[0069] max(θ αi )≥(15°~90°)(i=1,…,N)

[0070] As mentioned above, for the complete set Ω i Each data pair (θ) axi ,θ cyi To perform dynamic safety verification and maximize the selection of each column of reverse angles, it is necessary to solve the solution set of the following functional equations.

[0071]

[0072] Label the data pairs (θ) that satisfy the above functional equation. axi ,θ cyi The solution set is Φ i (Q z0 ), retrieve Φ i (Q z0 Solving any pair of data in the table will generate a set of control commands for the shaft side and cover side of the stepless backflow regulating device.

[0073] The compressor is equipped with stepless backflow adjustment devices on the shaft side and cover side of each stage (row) of cylinders. The stepless backflow adjustment device can be implemented in various ways. Its typical feature is that the closing time of the intake valve is controllable, so that the gas in the cylinder can flow back to the intake chamber before being compressed.

[0074] The data required for the compressor calculations mainly comes from three sources: control variables, state parameters, and mechanical modeling data. The control variables of the external control system can be single or multiple variables; these variables can be real-time transmitted data or manually input data. State parameters are provided by the external control system, and the mechanical modeling data originates from manually input basic data.

[0075] The acquisition of the controlled variables or state parameters originates from the following equipment connections: the compressor inlet pipeline is connected to the inlet of the primary inlet gas collector V1; the primary inlet gas collector V1 is equipped with primary inlet pressure P1 and primary inlet temperature T1 measuring instruments; the outlet of the primary inlet gas collector V1 is connected to the inlet of the primary cylinder of the compressor; the primary cylinder operates in a double-acting mode; a primary cylinder shaft-side stepless backflow regulating device SA1 is installed on the primary cylinder shaft side; a primary cylinder head-side stepless backflow regulating device SC1 is installed on the primary cylinder head side; the primary cylinder outlet is connected to the inlet of the primary outlet cooler, and then connected to the inlet of the secondary inlet gas collector V2 via the primary outlet cooler outlet; the secondary inlet gas collector V2 is equipped with secondary inlet pressure P2 and secondary inlet temperature T2 measuring instruments. The outlet of the secondary inlet gas collector V2 is divided into two paths. One path connects to the secondary cylinder inlet of the compressor, and the other path connects to the inlet of the primary outlet return line regulating valve B1 through the primary outlet return line. The outlet of the primary outlet return line regulating valve B1 is connected to the primary cylinder inlet pipeline of the compressor. The process connection relationship between the second and third stages of the compressor follows the same pattern. Finally, the compressor is connected to the compressor outlet pipeline through the outlet of the tertiary outlet gas collector V4. The inlet and outlet pressure (P1, P2, P3, P4) and inlet and outlet temperature (T1, T2, T3, T4) of each stage of the compressor are sent to the external control system (DCS). The external control system (DCS) maintains data exchange with the compressor digital analog control system, completing the external data input to the compressor digital analog control system.

[0076] The present invention has the following beneficial effects:

[0077] (1) Within the permissible range, the compressor can operate in various ways such as equal load compression at each stage, equal ratio compression at each stage, or operation according to the pressure ratio of each stage given by the user. This fundamentally improves the control efficiency of large reciprocating compressors and enhances the equipment utilization rate of large reciprocating compressors.

[0078] (2) The real-time variable virtual cylinder concept of reciprocating piston compressor fully represents and embodies the real-time multi-variable operation requirements and control essence. Through real-time control of the stepless backflow adjustment device, the reciprocating compressor, which is characterized by a relatively fixed cylinder volume, can pioneeringly meet the multi-variable operation requirements.

[0079] (3) When the compressor operates under equal load at each stage, the total power consumption is distributed evenly to each stage in real time. The interstage cooling is fully utilized to reduce the compression work of the next stage and lower the exhaust temperature. The compressor reflux regulation mode is eliminated, maximizing energy saving and consumption reduction. This avoids the problems of complex operation, high energy consumption of reflux regulation, long cycle operation risk of unloading cylinder, and poor compressor safety that exist when the original large reciprocating compressor operates under different working conditions.

[0080] (4) Large reciprocating compressors are mostly symmetrical and balanced. When each stage of the compressor operates under equal load, the force on the moving piston can be effectively balanced, the horizontal force on the crankshaft is equal, the uniformity of the crankshaft tangential force is good, and the service life of the equipment is long. Attached Figure Description

[0081] Figure 1 This is a schematic diagram of the compressor pipeline flow and control connections;

[0082] Figure 2 This is a schematic diagram of a single-row compressor structure.

[0083] In the diagram: V1, primary inlet gas collector; V2, secondary inlet gas collector; V3, tertiary inlet gas collector; V4, tertiary outlet gas collector; T1, primary inlet temperature; T2, secondary inlet temperature; T3, tertiary inlet temperature; T4, tertiary outlet temperature; P1, primary inlet pressure; P2, secondary inlet pressure; P3, tertiary inlet pressure; P4, tertiary outlet pressure; SA1, primary cylinder shaft-side stepless backflow regulating device; SC1, primary cylinder head-side stepless backflow regulating device; SA2, secondary cylinder shaft-side stepless backflow regulating device; SC2, secondary cylinder head-side stepless backflow regulating device; SA3, tertiary cylinder shaft-side stepless backflow regulating device; SC3, tertiary cylinder head-side stepless backflow regulating device; B1, primary outlet return line regulating valve; B2, secondary outlet return line regulating valve; B3, tertiary outlet return line regulating valve.

[0084] Explanation of formula symbols:

[0085]

[0086] Detailed Implementation

[0087] The present invention will now be further described with reference to the accompanying drawings.

[0088] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments are merely specific illustrations of the present invention, intended to enable those skilled in the art to better understand the technical solutions of this application, and should not be regarded as limitations on the present invention.

[0089] Example

[0090] like Figures 1-2 As shown, this embodiment takes a hydrogen booster compressor as an example and invents a digital control method for a reciprocating piston compressor. The method achieves control functions through a compressor digital-analog control system. Specific steps include:

[0091] (1) The data sources required for compressor calculation are mainly divided into three parts: control variables, compressor state parameters, and compressor mechanical modeling data.

[0092] In this embodiment, two control variables are used: the first-stage inlet pressure (P1) and the gas flow rate (Q0). That is, when the compressor is working, P1 and Q0 fluctuate within a certain range: P1 fluctuates from 0.39 to 1.49 MPa, and Q0 fluctuates from 4200 to 14000 Nm. 3 The compressor operates at a constant speed of 0.5 min, with other operating parameters remaining stable. The inlet temperature of each stage is 313 K, and the rated outlet pressure is 3.29 MPa. P1 is input after real-time data acquisition from the external control system (DCS), while Q0 is manually set. In this embodiment, P1 is set to 0.39 MPa and Q0 to 14000 Nm. 3 When the compressor is operating at its rated capacity (condition 1), P1 is 0.80 MPa and Q0 is 7000 Nm. 3 Explanation of the multivariable control method for condition 2 (min) (hereinafter referred to as condition 2).

[0093] The compressor status parameters are input after real-time data is collected by the external control system (DCS). These parameters mainly include the inlet and outlet pressures of each stage (P1, P2, P3, P4), the inlet and outlet temperatures of each stage (T1, T2, T3, T4), the outlet return line regulating valve signals of each stage (B1, B2, B3), and the stepless backflow regulating device signals of each stage cylinder shaft side and cover side (SA1, SC1, SA2, SC2, SA3, SC3), etc.

[0094] The compressor mechanical modeling data was manually input, including a symmetrical balanced layout, three-stage four-row compression, a dual-cylinder first stage, a single-cylinder second and third stage, pure hydrogen as the gas component, a hydrogen process index m of 1.4, a hydrogen compressibility coefficient Z ranging from 1.0010 to 1.0080, a first-stage cylinder diameter of 0.545 m, a second-stage cylinder diameter of 0.535 m, a third-stage cylinder diameter of 0.410 m, a piston stroke of 0.140 m, a piston rod diameter of 0.075 m, relative clearance volumes of the first-stage cylinders of 21.06% / 23.72% (shaft-side / cover-side), the second-stage cylinders of 22.30% / 22.76% (shaft-side / cover-side), and the third-stage cylinders of 28.33% / 28.17% (shaft-side / cover-side), a crankshaft speed of 741 r / min, and the reciprocating mass m of each row in the first stage. s1 The total mass of the second reciprocating motion is 285.09 kg. s2 The total mass of the third reciprocating motion is 292.13 kg. s3 The maximum permissible gas force is 284.77 kg. gmax The maximum permissible combined piston force is 40 kN. pmax The reciprocating friction force is 32 kN. fi Take 76N, and the mechanical efficiency η of each stage. miTaking 96%, the connecting rod ratio λ is taken as 0.187, and the maximum working reverse angle of the pin bearing is max(θ). αi The crank angle is ≥75°, and the minimum division angle of the crank angle θ is 1° (0°≤θ≤360°). After the control variables, state parameters, and mechanical modeling data are input, this control method completes the data input.

[0095] (2) When determining the pressure between each level, the control method includes three options: proportional compression of each level, equal load compression of each level, or manual allocation of the pressure ratio of each level.

[0096] When selecting stage-by-stage proportional compression, the calculation uses classical engineering thermodynamic formulas to calculate the pressure ratio of each stage and the interstage pressure values, and generates the interstage pressure values ​​for each stage. The calculation formulas are as follows:

[0097]

[0098] When selecting equal-proportional compression at each stage, the calculation uses classical engineering thermodynamic formulas and interpolation to determine that the shaft power is equal at each stage, and obtains the corresponding pressure ratio (P) at each stage. s(i+1) / P si The system generates pressure values ​​between each stage. In this embodiment, equal load compression operation is selected for each stage, and the state volume of each cylinder in each stage is calculated. The calculation formula is as follows:

[0099]

[0100]

[0101] Under operating condition 1, the shaft power N of each stage under equal load compression is calculated. i The power rating is 447KW. The secondary inlet pressure P2 is 0.80 (MPa, a), and the tertiary inlet pressure P3 is 1.50 (MPa, a). V ds1 =0.0500m 3 / r (single-row cylinder), V ds2 =0.0496m 3 / r,V ds3 =0.0249m 3 / r;

[0102] Under operating condition two, the shaft power N of each stage under equal load compression is calculated. i The power rating is 149KW, the secondary inlet pressure P2 is 1.30 (MPa, a), the tertiary inlet pressure P3 is 2.05 (MPa, a), and V... ds1 =0.0235m 3 / r (single-row cylinder), V ds2 =0.0149m 3 / r,V ds3 =0.0094m 3 / r;

[0103] When manually allocating the pressure ratios of each stage, manual interstage pressure settings can be implemented to improve the first-stage volumetric efficiency, prevent excessive exhaust temperature in the last stage, balance the reverse angles of each stage, and balance the piston forces of each stage, thus meeting the manually set operational requirements. The calculation process is the same as above, generating the interstage pressure values ​​for each stage.

[0104] (3) After obtaining the working volume and cylinder state volume of each level and column of virtual cylinders, calculate and obtain the loading state data pair of the stepless backflow regulating device (θ). axi ,θ cyi Complete series Ω i Calculate the total set Ω i Each data pair (θ) axi ,θ cyi Based on the gas force and combined piston force of each stage and column of cylinders, the working reversal angle of the crosshead pin bearings in each stage and column is calculated. Then, the reversal angle is maximized and optimized. The calculation formula of this control method is as follows:

[0105] V dsi =V fi ·η vi

[0106]

[0107] S fai =S·ψ fai

[0108] S fci =S·ψ fci

[0109]

[0110]

[0111] F pi =F gi +F si +F fi

[0112]

[0113] F si =m si ·r·ω 2 (cosθ+λcos2θ)

[0114]

[0115] For a time, the working conditions at all levels (Ψ) fti ,Ψ fai ,Ψ fciAll are taken as 100%, η v1 Take 78.5%, η v2 Take 80.5%, η v3 Taking 72.5%, we calculate V. s1 =V f1 =0.0635m 3 / r (single-row cylinder), V s2 =V f2 =0.0612m 3 / r,V s3 =V f3 =0.0346m 3 / r, at which point the reverse angles of each column are 151°, 174° and 173° respectively;

[0116] Under operating condition two, η v1 Take 76%, η v2 Take 79%, η v3 Taking 71%, we calculate V. f1 =0.0309m 3 / r (single-row cylinder), V f2 =0.0189m 3 / r,V f3 =0.0132m 3 / r, after reverse angle optimization, calculate (Ψ) for each level. fti ,Ψ fai ,Ψ fci The loading states of the cylinders at each level are as follows: Level 1 (49%, 64%, 34%), Level 2 (30%, 45%, 15%), and Level 3 (38%, 53%, 23%). The corresponding cylinder loading state data pairs (θ) are... axi ,θ cyi The levels are: Level 1 (74°, 289°), Level 2 (96°, 314°), and Level 3 (87°, 303°). The calculated reverse angles of each column are 180° for Level 1, 171° for Level 2, and 175° for Level 3. It can be seen that although the two operating parameters change significantly, after control and regulation, each column can participate in compression and maintain operation under conditions with a large reverse angle, and the calculation results are satisfactory.

[0117] (4) For the above loading state data pair (θ) axi ,θ cyi A dynamic safety margin review is performed, including a gas force review and a combined piston force review. The gas force is generated by the pressure difference acting on both sides of the compressor piston. The combined piston force is the algebraic sum of the gas load, inertial force, and reciprocating friction. The inertial force is generated by the mass acceleration of the reciprocating motion of the object. Finally, the instruction set Φ for regulating each stage (train) of the continuously variable flow control device is obtained. i If the solution set Φ iA certain data pair in the solution (θ) axi ,θ cyi The result of the calculation is satisfactory enough, and it is no longer necessary to continue with the entire set Ω. i The preferred data is within the specified range, while directly using this data to solve (θ) axi ,θ cyi The above process involves adjusting and outputting data, and the calculation formula is as follows:

[0118]

[0119] Under operating condition 1, the first-stage gas force is (+103KN, -109KN), the first-stage combined piston force is (+98KN, -105KN), the second-stage gas force is (+172KN, -180KN), the second-stage combined piston force is (+155KN, -179KN), the third-stage gas force is (+227KN, ​​-249KN), and the third-stage combined piston force is (+201KN, -232KN). Since the maximum permissible gas force F... gmax The maximum permissible combined piston force is 400 kN. pmax The rated capacity is 320 kN, so all compressors meet the safety margin requirements.

[0120] Under operating condition 2, the first-stage gas force is (+23KN, -29KN), the first-stage combined piston force is (+24KN, -27KN), the second-stage gas force is (+47KN, -56KN), the second-stage combined piston force is (+45KN, -54KN), the third-stage gas force is (+49KN, -64KN), and the third-stage combined piston force is (+51KN, -66KN). Therefore, all stages of the compressor meet the safety margin requirements.

[0121] The results of the mechanical safety margin verification show that the solution set Φ i This set of data is relevant to the solution (θ) axi ,θ cyi The results of the calculations for the first level (74°, 289°), the second level (96°, 314°), and the third level (87°, 303°) are satisfactory, so the calculation of the entire set Ω is not continued. i The data within the specified range is preferred, and this set of data is directly used to solve (θ). axi ,θ cyi ) to regulate data output.

[0122] (5) In the control method output stage, first determine whether each stepless backflow regulating device is normal. If the status is normal, the stepless regulation control command will be sent to the stepless backflow regulating devices (SA1, SC1, SA2, SC2, SA3, SC3) on the shaft side and cover side of each cylinder of each stage, and they will complete the control function. If the status is abnormal, the stepless regulation control command will be sent to the outlet return line regulating valves (B1, B2, B3) of each stage, and the return line regulating valves of each stage will complete the control function.

[0123] Condition 1: The bypass line of the compressor is completely closed, that is, the signals of the outlet return line regulating valves (B1, B2, B3) of each stage are all closed. At the same time, the output control signals of the stepless backflow regulating devices on the shaft side and cover side of each stage cylinder are all 100% (that is, the actuators SA1, SC1, SA2, SC2, SA3, SC3 do not operate). At this time, the compressor is running under rated conditions.

[0124] Operating condition two: The compressor bypass lines are all closed, meaning the signals of the outlet return line regulating valves (B1, B2, B3) at each stage are all closed. Simultaneously, the loading status data of each cylinder is compared with (θ). axi ,θ cyi The parameters at the first level (74°, 289°), the second level (96°, 314°), and the third level (87°, 303°) are converted into control signals and output to the corresponding stepless backflow adjustment devices (SA1, SC1, SA2, SC2, SA3, SC3) of each cylinder, so that the actuators can act and complete the control commands.

[0125] The above descriptions are merely typical examples of the present invention and do not impose any limitations on the present invention. Any changes or modifications made by those skilled in the art using the above technical content without departing from the scope of the present invention should be considered equivalent examples of equivalent variations. Any equivalent changes made to the above examples based on the technical essence of the present invention without departing from the content of the present invention are within the scope of the present invention.

Claims

1. A digital control method for a reciprocating piston compressor, wherein stepless backflow adjustment devices are provided on both the shaft side and cover side of each stage (row) of the compressor cylinders, characterized in that: When the controlled variable changes, the following steps are taken to generate a control command for the stepless backflow regulating device, thereby controlling the operation of the compressor: 1) Re-evaluate the pressure between each stage using power-saving principles or a manually assigned process; 2) Calculate the working volume and cylinder state volume of each level (train) of virtual cylinders based on the operating conditions at each level; 3) Calculate and obtain the loading state data of the continuously variable flow regulator (θ) axi ,θ cyi Complete series Ω i ; 4) For the complete set Ω i Each data pair (θ) axi ,θ cyi The dynamic safety was verified and the optimal reverse angle of each column was maximized to obtain the instruction set Φ for regulating the stepless backflow control device at each stage (column). i Solution set Φ i Any data pair in the solution (θ) axi ,θ cyi It can generate control commands.

2. The digital control method for a reciprocating piston compressor according to claim 1, characterized in that: In step 1), The pressure between each stage can be re-evaluated by the principle of saving power or by manually assigning a process. This can be achieved by changing the compressor's operating mode. The compressor operating mode can be divided into three types: equal compression mode for each stage, equal load compression mode for each stage, and manual allocation of pressure ratio for each stage. When the equal-ratio compression mode is selected, the pressure ratios at each stage are equal, and the relationship is expressed as follows: Where, ε i P represents the pressure ratio of the i-th stage. s P represents the compressor intake pressure. d P represents the final discharge pressure of the compressor. s(i+1) This represents the intake pressure of stage (i+1). When the equal-load compression mode is selected for each stage, it indicates that the shaft power in each compression process is equal or similar, and the corresponding compression ratio (P) for each stage is... s(i+1) / P si ) Calculate the shaft power N of each stage using interpolation method i After equalization, the power N of the i-th stage shaft is obtained. i The calculation expression is Where, N i Represents the power of the i-th axis, η mi Represents the i-th level mechanical efficiency (values ​​range from 0.86 to 0.96 for medium and large machines, and η for small machines). mi The value range is 0.85 to 0.

92. When the manual allocation mode for each stage of pressure ratio is selected, the pressure ratio for each stage is obtained by manual input. After the compressor operation mode is selected, the pressure ratio for each stage and the interstage pressure verification value for each stage will be generated. In step 2), The working volume V of each level (column) of the virtual cylinder is calculated based on the operating conditions at each level. fi Cylinder volume V dsi When the expression is: V dsi =V fi ·η vi V fi =V si ·ψ fti (i=1,…,N) Among them, V dsi V represents the volume of the i-th stage cylinder. fi V represents the working volume of the i-th stage virtual cylinder. si P represents the actual working volume of the i-th stage cylinder. si T represents the i-th stage intake pressure, Q0 represents the volumetric flow rate under standard conditions, and T represents the volumetric flow rate. si η represents the intake air temperature of stage i, n represents the compressor speed, q represents the number of cylinders in stage i, and η represents the number of cylinders in stage i. vi Ψ represents the volumetric efficiency of the i-th level. fti represents the total unloading coefficient of the i-th stage, N represents the total number of stages of the compressor, and i represents the stage variable of the compressor, with a value range of (i = 1, ..., N); The total unloading coefficient Ψ fti When the i-th stage cylinder is a double-acting type and the piston rod does not penetrate, the axial unloading coefficient Ψ fai And the unloading coefficient Ψ of the cover side fci The expression representing the volume allocation ratio is as follows: S fai =S·ψ fai S fci =S·ψ fci Among them, D i d represents the actual cylinder diameter of the i-th stage, d represents the piston rod diameter, and S represents the actual piston stroke. fai S represents the virtual travel on the i-th axle side. fci Represents the virtual travel of the i-th level cover side; When the cylinder shaft-side or cover-side stepless backflow adjustment device is applied to the cylinder, the crank angle θ and the virtual stroke S of the i-th stage shaft-side or cover-side are respectively adjusted. fai or S fci The relational expression is as follows: Where r represents the crank radius, λ represents the ratio of the crank radius (r) to the connecting rod length (l) (λ = r / l, or simply the connecting rod ratio), and θ represents the crank angle, which is the angle between the crank and the cylinder centerline. The crank angle is set with the piston's outer dead center as the starting angle, and the value of θ ranges from 0° to 360°. ai θ represents the crank angle corresponding to the axial loading of the i-th stage cylinder. ci This represents the crank angle corresponding to the i-th stage cylinder head side loading; In step 3), Solve for the load state data pair (θ) of the continuously variable flow regulator. axi ,θ cyi Complete series Ω i The method is as follows: The θ ai and θ ci The i-th stage cylinder loading state data pair (θ) is formed. ai ,θ ci For a compressor at a certain standard state volumetric flow rate Q, z0 The i-th level can correspond to multiple combinations of cylinder shaft-side and cover-side loading states (meeting their flow requirements), that is, multiple data pairs (θ). axi ,θ cyi ), record the flow Q z0 The corresponding i-th level data pair is Ω for the entire set. i The relational expression is as follows: Oh i (Q z0 )={(θ a1i ,i c1i ),(θ a2i ,i c2i ),…,(θ axi ,i cyi )}(i=1,…,N) Corresponding to a certain standard volumetric flow rate Q z0 The state volume V of the i-th stage cylinder dsi With loading state data to the entire set Ω i (Q z0 There exists a functional relationship f1 between them, and the expression is: V dsi =f1(Ω i (Q Z0 ))(i=1,…,N) By obtaining the loading status data of the continuously variable flow regulator (θ) axi ,θ cyi Complete series Ω i This enables full-domain control of the virtual cylinder volume and cylinder state volume at each stage (train), ensuring the re-verified interstage pressure of the compressor; In step 4), For the complete series Ω i Each data pair (θ) axi ,θ cyi When performing dynamic safety verification and optimizing the maximum reverse angle of each column, the method is as follows: Among them, F gi F represents the gas force in the i-th column. gmax F represents the maximum permissible gas force of the compressor. pi F represents the combined piston force in column i. pmax θ represents the maximum permissible combined piston force of the compressor. αi f1 represents the working reversal angle of the crosshead pin bearing per revolution of the i-th cylinder, and f2 represents the functional relationship. Label the data pairs (θ) that satisfy the above functional equation. axi ,θ cyi The solution set is Φ i (Q z0 ), retrieve Φ i (Q z0 Solving any pair of data in the table will generate a set of control commands for the shaft side and cover side of the stepless backflow regulating device.

3. The digital control method for a reciprocating piston compressor according to claim 2, characterized in that: The gas force, reciprocating inertial force, and reciprocating friction force of each cylinder in the compressor are all along the cylinder centerline. Their algebraic sum is called the combined piston force, and its calculation expression is: F pi =F gi +F si +F fi Among them, F si F represents the reciprocating inertial force of the i-th column. fi Represents the reciprocating friction force in the i-th column; The i-th column of gas force F gi and reciprocating inertial force F si When the i-th cylinder is a double-acting cylinder and the piston rod does not pass through, its calculation expression is: F si =m si ·r·ω 2 (cosθ+λcos2θ) Among them, P ai P represents the pressure of the i-th column of shaft-side cylinders. ci P represents the pressure of the i-th column cover-side cylinder. b P represents atmospheric pressure. ai With P ci The range of variation is the intake and exhaust pressure (P) in column i. si ,P s(i+1) ), ω represents the rotational angular velocity (ω=n·π / 30), m si Let be the total mass of the i-th column of reciprocating motion; The reciprocating friction force F in the i-th column fi Opposite to the direction of motion of the moving part, and the reciprocating friction force at the dead point is set to zero. For simplified calculations, F can be... fi It is considered to be a certain value. Set the minimum division angle of θ to 1°, and use the cylinder loading state data of the i-th column to apply to the entire set Ω. i (Q z0 Let θ be the sample space, and calculate the different data pairs (θ) axi ,θ cyi Under loading conditions, the reciprocating friction force F of each column within its full circumference working range fi reciprocating inertial force F si and gas force F gi The combined piston force F of each column is synthesized by superimposing the phase angles. pi This is to perform dynamic safety verification and optimize the maximum reverse angle of each column. The i-th column of the combined piston force F pi It is a function of the crank angle θ, when F pi A value of zero indicates that the force direction on the crosshead bearing has begun to reverse. Within one working cycle, if F... pi If a zero value appears only once, the working reverse angle of the pin bearing is 180°. If F pi If two or more zero values ​​appear, the corresponding crank angles θ1, θ2, ... θ need to be calculated. n (where n is an even number), the formula for calculating the working reverse angle of the pin bearing is as follows: i α =min(sum((θ2-θ1)+…+(θ n -θ n-1 )),360°-sum((θ2-θ1)+…+(θ n -θ n-1 ))) Where, θ α The working reversal angles of the crosshead bearing per revolution are θ1, θ2, ... θ n (n is an even number) represents the crank angles corresponding to the total piston force being zero; The i-th column of cylinder shaft-side and cover-side loading state data pair (θ) axi ,θ cyi ) and the working reverse angle of the pin bearing (θ) αi There exists a functional relationship f2 between them, and the expression is: i αi =f2(θ axi ,i cyi ) For a compressor at a certain standard volumetric flow rate Q z0 The maximum working reverse angle of the pin bearing is max(θ). αi ) and loading status data for the entire set Ω i (Q z0 The relationship expression between ) is max(θ αi )=max(f2(Ω i (Q Z0 )))(i=1,…,N) At the same time, the maximum working reverse angle of the pin bearing should be greater than or equal to the minimum allowable value of the compressor, with a safety margin. The expression for this is: max(θ αi )≥(15°~90°)(i=1,…,N) 4. The digital control method for a reciprocating piston compressor according to claim 1, characterized in that: The compressor's cylinders at each stage (row) are equipped with stepless backflow adjustment devices on the shaft side and cover side respectively. The stepless backflow adjustment device can be implemented in various ways. Its typical feature is that the closing time of the intake valve is controllable, so that the gas in the cylinder can flow back to the intake chamber before being compressed.

5. The digital control method for a reciprocating piston compressor according to claim 1, characterized in that: The data sources required for compressor calculations are mainly divided into three parts: control variables, state parameters, and mechanical modeling data. The control variables of the external control system can be single or multiple variables; the variables are real-time transmitted data or manually given; the state parameters are from the external control system; and the mechanical modeling data originates from manually input basic data.

6. The digital control method for a reciprocating piston compressor according to claim 1, characterized in that: When the compressor completes the control action, first determine whether each stepless backflow regulating device is normal. If the operating status is normal, the stepless backflow regulating device completes the control function. If its operation is abnormal, the control function is completed by the return line regulating valves at each level.

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