Load sharing control method for series compressor units

Abstract

This invention relates to a load distribution control method for a series compressor unit, comprising the steps of determining the distance from the operating point of each compressor to the anti-surge line, calculating the theoretical operating point of each compressor, and adjusting the speed of each compressor to ensure equidistant operation. The series compressor unit consists of two or more compressors connected in series. Pressure and flow monitoring are installed at the inlet and outlet of each compressor, and the compressor speed is monitored via a UCP (Unified Pressure Processing Unit). By automatically adjusting the speed of each unit to ensure that the distance from its operating point to its respective anti-surge line is relatively equal, the load on each compressor is relatively balanced. During operation, this effectively prevents surge and achieves efficient and stable operation of the compressor unit.

Description

Technical Field

[0001] This invention belongs to the field of automatic control technology for large rotating equipment, specifically a load distribution control method for series compressor units. Background Technology

[0002] Compressors operate on the principle of converting kinetic energy into potential energy. They use high-speed rotating impellers / blades to accelerate gas, then decelerate and change its flow direction, thus converting kinetic energy into potential energy (pressure). In certain industrial fields, such as blast furnace smelting, natural gas pressurization and transportation, and air energy storage, compressors play a very important role and are one of the core pieces of equipment.

[0003] like Figure 1 As shown, the load and anti-surge control circuit of the electric compressor unit includes compressor 1, motor 2, frequency converter 3, compressor control system UCP 4, inlet flow meter 5, inlet pressure transmitter 6, outlet pressure transmitter 6, inlet temperature transmitter 7, and anti-surge valve 8. Its working principle is as follows: motor 2 controls the speed of compressor 1 through frequency converter 3, thereby increasing the medium pressure to the required level. Because the work capacity (compression ratio) of a single compressor is limited, multiple compressors are often connected in series for operation, such as... Figure 2 As shown, from left to right along the gas flow direction are compressor #1 and compressor #2, and the gas paths of the two compressors are connected in series. In the past, the load distribution control of multiple compressors was mainly achieved through the following two methods: (1) directly loading the first few compressors to the rated load, and controlling the final exhaust pressure / flow rate to meet the process requirements by adjusting the speed / guide vane of the last compressor; (2) the operator manually adjusts the speed / guide vane of multiple units until the final exhaust pressure / flow rate meets the process requirements.

[0004] In summary, the above two adjustment methods have the following disadvantages: (1) The distance between the operating points of each series-running compressor and the surge line varies greatly, which can easily cause the unit to surge or overpower due to process fluctuations; (2) The manual loading process is time-consuming and laborious, requiring operators to have rich experience, and the degree of automation is low, which is not conducive to achieving unmanned operation. Summary of the Invention

[0005] In order to overcome compressor surge or overpowering caused by unbalanced loads among compressors in the operation of series compressor units and to improve the automation level of compressor unit control, this invention proposes a load distribution control method for series compressor units.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A load sharing control method for a series compressor unit includes the following steps:

[0008] Step 1: Calculate the distance from each compressor operating point to the anti-surge line.

[0009] The implementation target is a series compressor unit.

[0010] During the operation of the series compressor unit, the inlet flow rate, inlet pressure, and discharge pressure of each compressor unit are measured to mark the operating point, i.e. the position of the compressor's flow rate and pressure ratio on the performance curve, and the actual distance from the operating point of each compressor to the anti-surge line is calculated.

[0011] Step 2: Calculate the theoretical operating point of each compressor.

[0012] When all compressors are at equal intervals, calculate the theoretical operating point of each compressor to obtain the theoretical pressure ratio of each compressor.

[0013] Step 3: Adjust the speed of each compressor to ensure that they are at equal intervals.

[0014] While ensuring the total pressure ratio equals the set value, the compressor speed is adjusted by the compressor control system (UCP) to make the pressure ratio of each compressor equal to the theoretical pressure ratio, thus achieving equidistant operation of all compressors. This equidistant operation means that the distance from the operating point of each compressor to the anti-surge line is equal.

[0015] The above-described load distribution control method for a series compressor unit includes two compressors, referred to as compressor #1 and compressor #2, respectively.

[0016] Step 1: Calculate the distance from the operating point of compressor #1 and compressor #2 to the anti-surge line.

[0017] The distances from the operating points of compressors #1 and #2 to the anti-surge line are respectively ΔP A , △P B The calculation formula is as follows:

[0018] △P A =(P dmA -P dA ) / P dmA (1)

[0019] △P B =(P dmB -P dB ) / P dmB (2)

[0020] In equations (1) and (2), P dmA P dmB These are the maximum allowable pressure ratios of compressor #1 and compressor #2, respectively, P dA P dB These are the pressure ratios of compressor #1 and compressor #2, respectively.

[0021] The total pressure ratio P of the compressor unit is calculated by the following formula:

[0022] P = P o / P s (3)

[0023] In equation (3), P o P is the inlet pressure of the compressor unit. s This refers to the discharge pressure of the compressor unit.

[0024] Step 2: Calculate the theoretical operating points of compressor #1 and compressor #2.

[0025] When compressors #1 and #2 are equidistant, we get:

[0026] (P dmA -P diA ) / P dmA =(P dmB -P diB ) / P dmB (4)

[0027] In equation (4), P diA P is the theoretical pressure ratio of compressor #1. diB This is the theoretical pressure ratio of compressor #2.

[0028] The product of the pressure ratios of compressor #1 and compressor #2 equals the total pressure ratio P of the compressor unit, that is:

[0029] P diA ·P diB =P (5)

[0030] Combining equations (4) and (5), we can obtain the theoretical pressure ratio P of compressor #1. diA The theoretical pressure ratio P of compressor #2 diB .

[0031] Step 3: Adjust the speeds of compressor #1 and compressor #2 to ensure they are equidistant.

[0032] In the UCP monitoring system, the pressure ratio of compressor #1 and compressor #2 is set to the theoretical pressure ratio. The speeds of compressor #1 and compressor #2 are adjusted so that the total pressure ratio of the compressor group is equal to the set value, that is, compressor #1 and compressor #2 are equidistant.

[0033] A series compressor unit includes a compressor unit, monitoring instruments, and a compressor control system (UCP).

[0034] The compressors are connected in series. The compressor control system (UCP) monitors and controls the compressor's inlet pressure, outlet pressure, flow rate, and speed in real time, and adjusts the compressor speed in real time.

[0035] The aforementioned series compressor unit has two or more compressors.

[0036] The beneficial effects of this invention are:

[0037] A load distribution control method for series compressor units links multiple units operating in series, avoiding compressor surge or overpowering due to different distances between the operating points of each compressor and the anti-surge line, thereby improving the overall operating efficiency of the unit. In addition, this method improves the automation control level of the unit and eliminates some of the drawbacks of manual load adjustment in the past.

[0038] A load distribution control method for series compressor units is proposed. Pressure and flow monitoring are designed at the inlet of each compressor, and pressure monitoring is set at the outlet of each compressor. The compressor speed is connected to the UCP for monitoring. By automatically adjusting the speed / guide vane of each unit to make the distance between its operating point and its respective anti-surge line equal, that is, the load of each compressor is relatively balanced. This enables multiple compressors to operate in series, prevents the occurrence of compressor unit surge, and achieves efficient and stable operation of the unit group.

[0039] A load distribution control method for series compressor units is proposed, which can be applied to the operation of multiple compressor units in series. It has strong scalability and adaptability, and has important application significance in fields such as natural gas compressors and air energy storage compressors. It can improve the overall operating efficiency and reliability of the units. At the same time, series load distribution is also a necessary condition for realizing unmanned operation of compressor units. When the process setpoint changes, multiple series units can adjust the unit load together to meet the requirements, instead of manually adjusting or distributing the unit load as before. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the load and anti-surge control circuit of the electric compressor unit;

[0041] Figure 2 This is a schematic diagram of the gas path for two compressors operating in series.

[0042] Figure 3 yes Figure 2 Performance curve of compressor #1;

[0043] Figure 4 yes Figure 2 Performance curve of compressor #2.

[0044] In the diagram: 1. Centrifugal compressor; 2. Motor; 3. Frequency converter; 4. Compressor control system (UCP); 5. Inlet flow meter; 6. Pressure transmitter; 7. Temperature transmitter; 8. Anti-surge valve. Detailed Implementation

[0045] Example 1

[0046] This invention proposes a load distribution control method for series operation by studying the characteristics of compressors and the technological principles of series compressor unit operation. To achieve load distribution in series operation, pressure and flow monitoring needs to be designed at the inlet of each compressor, pressure monitoring needs to be installed at the outlet of each compressor, and the compressor speed needs to be monitored by connecting it to the compressor control system (UCP).

[0047] The specific principle of load distribution control in series operation is explained as follows:

[0048] The following explanation uses two compressors running in series as an example, assuming that all compressors have started and finished, are fully loaded, have their anti-surge valves closed, and the compressor unit has reached the set load required by the process.

[0049] A load sharing control method for a series compressor unit includes the following steps:

[0050] Step 1: Calculate the distance from each compressor operating point to the anti-surge line.

[0051] like Figure 3 and Figure 4 As shown, compressor #1 operates at point A on the performance curve, and compressor #2 operates at point B on the performance curve. The unit's gas path is connected in series, and the inlet flow rate F of the two compressors is... A and F B They are the same, but the pressure ratios are different. The pressure ratio of compressor #1 is P. dA The pressure ratio of compressor #2 is P. dB Calculate the inlet flow rate as F A or F B Time (F) A =F B The maximum allowable pressure ratios for each compressor are P. dmA and P dmB The distance from the operating point of compressors #1 and #2 to the anti-surge line is ΔP. A and △P B And it is defined as follows:

[0052] △P A =(P dmA -P dA ) / P dmA (1)

[0053] △P B =(P dmB -P dB ) / P dmB (2)

[0054] As can be seen from the above definition, this distance is a relative value (percentage), which means the safety margin of the compressor at a specific flow rate.

[0055] Assume the compressor inlet pressure is P. s The required exhaust pressure for the process is P. o Therefore, the total pressure ratio of the compressors operating in series should be:

[0056] P = P o / P s (3)

[0057] Step 2: Calculate the theoretical operating point of each compressor.

[0058] Equidistant means △P A =△P B ,Right now

[0059] (P dmA -P diA ) / P dmA =(P dmB -P diB ) / P dmB (4)

[0060] and

[0061] P diA ·P diB =P (5)

[0062] In equations (4) and (5), P diA P is the theoretical pressure ratio of compressor #1. diB P represents the theoretical pressure ratio of compressor #2. dmA P dmB P can be obtained through instrument measurement or system calculation. Therefore, equations (4) and (5) form a system of two linear equations in two variables. P can be calculated by solving the system of equations. diA and P diB .

[0063] Step 3: Adjust the speed of each compressor to ensure that they are at equal intervals.

[0064] The theoretical equidistant operating point of the unit is calculated using the above method as P. diA and P diB Then, this pressure ratio is used as the set value for the compressor pressure ratio, and the pressure ratio is controlled by adjusting the compressor speed, which is P respectively. diA and P diB While ensuring the exhaust pressure (total pressure ratio), the compressor speed is controlled to increase / decrease at equal intervals.

[0065] It should be noted that the process of equidistant control is a dynamic adjustment process. During the adjustment process, the instruments and control system continuously measure or calculate the relevant variable values ​​to achieve equidistant operation of the unit.

[0066] The series operation load distribution control method of the present invention can be applied to the operation of multiple compressor units in series. It has been verified through multiple experimental projects and has strong scalability and adaptability. It has important application significance in fields such as natural gas compressors and air energy storage compressors. It can improve the overall operating efficiency and reliability of the unit. At the same time, series load distribution is also a necessary condition for realizing unmanned operation of compressor units. When the process setpoint changes, multiple series units can adjust the unit load together to meet the requirements, instead of manually adjusting or distributing the unit load as before.

Claims

1. A load distribution control method for a series compressor unit, characterized in that, The main steps include the following: Step 1: Calculate the distance from each compressor operating point to the anti-surge line: Taking a series compressor unit as the implementation object, during the operation of the series compressor unit, the inlet flow rate, inlet pressure, and discharge pressure of each compressor unit are measured to mark the position of the compressor's flow rate and pressure ratio on the performance curve, and the actual distance from the operating point of each compressor to the anti-surge line is calculated. Step 2, calculate the theoretical operating point of each compressor: When the operating points of each compressor are at equal intervals, the theoretical operating point of each compressor is calculated to obtain the theoretical pressure ratio of each compressor; the equal intervals refer to the fact that the distance from the operating point of each compressor to the anti-surge line is equal. Step 3: Adjust the speed of each compressor to ensure they are evenly spaced. While ensuring that the total pressure ratio is equal to the set value, the speed of each compressor is adjusted by the compressor control system UCP so that the pressure ratio of each compressor is equal to the theoretical pressure ratio, that is, the compressors are equidistant. The series compressor unit includes two compressors, referred to as compressor #1 and compressor #2 respectively; Step 1: Calculate the distance from the operating points of compressors #1 and #2 to the anti-surge line. The distances from the operating points of compressors #1 and #2 to the anti-surge line are respectively ΔP A , △P B The calculation formula is as follows: △P A =(P dmA -P dA ) / P dmA (1); △P B =(P dmB -P dB ) / P dmB (2); In equations (1) and (2), P dmA P dmB These are the maximum allowable pressure ratios of compressor #1 and compressor #2, respectively, P dA P dB These are the pressure ratios of compressor #1 and compressor #2, respectively. The total pressure ratio P of the compressor unit is calculated by the following formula: P=P o / P s (3); In equation (3), P o P is the inlet pressure of the compressor unit. s This refers to the compressor unit's discharge pressure. Step 2, calculate the theoretical operating points of compressor #1 and compressor #2: When compressors #1 and #2 are equidistant, we get: (P dmA -P diA ) / P dmA =(P dmB -P diB ) / P dmB (4); In equation (4), P diA P is the theoretical pressure ratio of compressor #1. diB This is the theoretical pressure ratio of compressor #2; The product of the pressure ratios of compressor #1 and compressor #2 equals the total pressure ratio P of the compressor unit, that is: P diA ·P diB =P (5); Combining equations (4) and (5), we can obtain the theoretical pressure ratio P of compressor #1. diA The theoretical pressure ratio P of compressor #2 diB ; Step 3: Adjust the speeds of compressor #1 and compressor #2 to ensure they are equidistant. In the UCP monitoring system, the pressure ratio of compressor #1 and compressor #2 is set to the theoretical pressure ratio. The speed of compressor #1 and compressor #2 is adjusted so that the total pressure ratio of the compressor group is equal to the set value, that is, compressor #1 and compressor #2 are equidistant.

2. A series compressor unit, using the load distribution control method for a series compressor unit as described in claim 1, comprising a compressor and a compressor control system (UCP); The compressors are connected in series; the compressor control system UCP is connected to the compressor, and monitors and controls the compressor's inlet pressure, outlet pressure, flow rate, and speed in real time, and adjusts the compressor speed in real time.

3. The series compressor unit according to claim 2, characterized in that, The number of compressors is greater than or equal to 2.

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