JP2011226418A - Compression device and method of operating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compression device capable of maintaining gas pressure on a demand side at a constant level while using a slide valve and a spill-back valve.SOLUTION: A discharge flow rate of a screw compressor 2 is calculated from the position of the slide valve 3 and pressure Ps of a suction flow passage 4, and a gas circulation flow rate from a discharge flow passage 5 to the suction flow passage 4 is calculated from an opening of the spill-back valve 7, the pressure Ps of the suction flow passage 4 and pressure Pd of the discharge flow passage 5. Based on a gas supply flow rate to the demand side 14 via a supply flow passage 13 obtained by subtracting the circulation flow rate from the discharge flow rate, a target value of the pressure Pd of the discharge flow passage 5 is determined to maintain terminal pressure Pc on the demand side 14 at predetermined pressure by compensating pressure loss in the supply flow passage 13. At least either of the position of the slide valve 3 or the opening of the spill-back valve 7 is controlled so that the pressure Pd of the discharge flow passage 5 becomes the target value.

Description

  The present invention relates to a compressor and a method for operating the compressor.

  Generally, a compression device that compresses gas is controlled so as to keep the discharge pressure constant. When the compressor and the customer are separated, there is a pressure loss in the flow path from the compressor to the customer, and the terminal pressure at the customer is lower than the discharge pressure of the compressor. Since such pressure loss increases as the flow rate increases, the end pressure varies depending on the amount of gas consumed. For this reason, the discharge pressure of the compression device is set so that the terminal pressure becomes the required pressure when the gas consumption at the demand destination is the maximum, and when the gas consumption is small, the gas is supplied with an excessive pressure and an excessive pressure is supplied. It consumes energy.

  In Patent Document 1, the flow rate loss to the customer is determined on the assumption that the discharge flow rate of the compressor driven by the inverter is determined by the rotation speed and the flow rate loss to the customer depends on the gas flow rate. There is described a compression device that achieves energy saving by making an estimation based on the number of rotations of the compressor and changing the target value of the discharge pressure so as to keep the terminal pressure constant.

  On the other hand, as described in Patent Document 2, for example, the discharge pressure of the compressor is not controlled by the rotation speed of the compressor but by a slide valve that adjusts the capacity of the compressor or a spillback valve that circulates the discharge gas to the suction side There is also a compression device for controlling the above. In such a compression apparatus, the method of Patent Document 1 cannot be applied.

JP 2008-19746 A JP-A-11-201069

  In view of the above-described problems, an object of the compression device according to the present invention is to provide a compression device that can keep a gas pressure at a demand destination constant while using a slide valve or a spillback valve.

  In order to solve the above problems, a compression apparatus according to the present invention has a screw compressor that compresses gas sucked from a suction flow path by a screw rotor accommodated in a rotor chamber and discharges the gas into a discharge flow path. A compression device for supplying compressed gas via a supply flow path, wherein the slide valve changes the compression capacity by changing the opening of the rotor chamber, and a part of the gas discharged to the discharge flow path is the suction flow A spillback valve that circulates to the passage, a suction pressure detector that detects the pressure of the suction flow path, a discharge pressure detector that detects the pressure of the discharge flow path, the position of the slide valve, and the suction flow path The discharge flow rate of the screw compressor is calculated from the pressure, and the amount of gas from the discharge flow path to the suction flow path is calculated from the opening of the spillback valve, the pressure of the suction flow path, and the pressure of the discharge flow path. Calculate the ring flow rate and Based on the gas supply flow rate to the demand destination obtained by subtracting the ring flow rate from the output flow rate, the pressure loss in the supply flow path is compensated to maintain the terminal pressure at the demand destination at a predetermined pressure. Control means for determining a target value of the pressure of the discharge flow path and adjusting at least one of the position of the slide valve and the opening of the spillback valve so that the pressure of the discharge flow path becomes the target value It shall have.

  According to this configuration, the flow rate of the compressed gas supplied to the supply channel is calculated according to the position of the slide valve and the opening of the spillback valve, the pressure loss in the supply channel is calculated, and the desired pressure is applied to the supply channel. By supplying compressed gas having a pressure higher than the pressure loss, wasteful energy consumption can be suppressed.

  In the compression apparatus of the present invention, the control means may determine the target value by the following formula 1.

但し、Ｐ１は前記目標値、Ｚは前記スライド弁の位置、ｆ（Ｚ）は予め与えられた前記スクリュ圧縮機の特性関数、Ｘは前記スピルバック弁の開度、ＣＶ（Ｘ）は予め与えられた前記スピルバック弁の特性関数、Ｐ２は前記需要先において望まれる圧力、Ｐｓは前記吸込流路の圧力、Ｐｓｏは前記スクリュ圧縮機の設計吸込圧力、Ｐｄは前記吐出流路の圧力、ΔＰｍａｘは前記供給流量が前記スクリュ圧縮機の定格流量であるときの前記供給流路における圧力損失、Ｑｔｙｐは前記スクリュ圧縮機の定格流量、Ａは圧縮するガスの物性により定まる定数である。

However, P1 is the target value, Z is the position of the slide valve, f (Z) is a characteristic function of the screw compressor given in advance, X is the opening of the spillback valve, and CV (X) is given in advance P2 is the pressure desired at the customer, Ps is the pressure of the suction passage, Pso is the designed suction pressure of the screw compressor, Pd is the pressure of the discharge passage, and ΔPmax. Is the pressure loss in the supply flow path when the supply flow rate is the rated flow rate of the screw compressor, Qtyp is the rated flow rate of the screw compressor, and A is a constant determined by the physical properties of the gas to be compressed.

  In the above Equation 1, the value in {} on the right side indicates the ratio of the gas supply flow rate to the supply flow path to the rated flow rate Qtype of the screw compressor. Since the pressure loss in the supply flow path is proportional to the square of the flow rate, Formula 1 uses the pressure obtained by adding the pressure loss in the supply flow path to the desired end pressure P2 as the target value P1 for the discharge pressure Pd of the screw compressor. Means that

  In the compression device of the present invention, when the control means receives a signal indicating a sudden change in the gas consumption of the demand destination, the control means outputs in advance a control output for at least one of the slide valve and the spillback valve. A predetermined addition value may be added. As a result, the compressor can be operated stably even with respect to discontinuous load fluctuations at the demand destination.

  Further, according to the present invention, the screw compressor that compresses the gas sucked from the suction passage by the screw rotor housed in the rotor chamber in the compression device and discharges it to the discharge passage through the supply passage to the customer. A compression device for supplying compressed gas, wherein the slide valve changes the compression capacity by changing the opening of the rotor chamber, and the spillback that circulates part of the gas discharged to the discharge flow path to the suction flow path The control method of the compression device having a valve calculates the discharge flow rate of the screw compressor from the position of the slide valve and the pressure of the suction flow path, and the opening degree of the spillback valve and the pressure of the suction flow path The flow rate of the gas from the discharge flow channel to the suction flow channel is calculated from the pressure of the discharge flow channel and the pressure of the discharge flow channel, and the gas supply flow rate to the demand destination obtained by subtracting the ring flow rate from the discharge flow rate is obtained. Based on The target value of the pressure of the discharge channel is determined so as to compensate the pressure loss in the supply channel and maintain the end pressure at the demand destination at a predetermined pressure, and the pressure of the discharge channel is set to the target value So that at least one of the position of the slide valve and the opening of the spillback valve is adjusted.

It is a lineblock diagram of the compression device of one embodiment of the present invention. It is a flowchart of control in the control apparatus of FIG. It is a figure which shows the flow volume according to the position of the slide valve of the screw compressor of FIG. It is a figure which shows the flow volume according to the opening degree of the spillback valve of FIG.

  Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a compression apparatus 1 according to one embodiment of the present invention. The compression device 1 includes a screw compressor 2 that houses a pair of male and female screw rotors in a rotor chamber. The screw compressor 2 has a slide valve 3 that changes the effective compression capacity by changing the opening of the suction port, sucks air (gas) from the suction flow path 4, compresses it by the screw rotor, and compresses it. Air is discharged into the discharge flow path 5. The slide valve 3 is positioned and driven by a fluid pressure actuator 6.

  The compressor 1 also includes a spillback valve 7 that circulates a portion of the compressed air discharged from the discharge flow path 5 to the suction flow path 4, and a discharge pressure that detects the pressure (discharge pressure) Pd of the discharge flow path 5. A detector 8, a suction pressure detector 9 for detecting the pressure (suction pressure) Ps of the suction flow path 4, a discharge air tank 10 serving as a buffer connected to the discharge flow path 5, and a buffer connected to the suction flow path 4 And an intake air tank 11. The position Z of the slide valve 3 and the opening X of the spillback valve 7 are adjusted based on the detection results of the discharge pressure detector 8 and the suction pressure detector 9 by a control device 12 comprising a computer.

  Compressed air is supplied from the compressor 1 to a customer 14 that consumes compressed air through a supply flow path 13 made of piping. In the compressor 1, the controller 12 cannot directly detect the pressure (terminal pressure) Pc of the compressed air at the demand destination 14, but in order to maintain the terminal pressure Pc at a predetermined pressure P2, a screw compressor It is programmed to change the target value P1 of the discharge pressure of 2. Further, the control device 12 can receive a contact signal indicating load interruption from the customer 14.

  FIG. 2 shows a flow of control of the slide valve 3 and the spillback valve 7 performed by the control device 12 in the compression device 1. First, in step S1, the compressed air flow rate in the supply flow path 13 is calculated. The discharge flow rate Qc of the screw compressor 2 is determined by the suction pressure Ps detected by the suction pressure detector 9, the designed suction pressure Pso, the rated capacity (discharge amount) Qtyp, and the position of the slide valve 3 determined by the control device 12. The capacity characteristic function f (Z) indicating the ratio of the capacity of the screw compressor 2 to the rated capacity determined accordingly can be expressed as Equation 2.

  The capacity characteristic function f (Z) of the screw compressor 2 is specified by the model of the screw compressor 2 or the like, and has a relationship as shown in FIG. 3, for example. Therefore, the capacity characteristic function f (Z) is stored in advance in the control device 12 as data in a format such as a reference table that is a table showing the ratio of the capacity corresponding to the position Z of the slide valve 3.

  The recirculation flow rate Qb through the spillback valve is determined by the pressure Pd of the discharge passage 5 detected by the discharge pressure detector 8, the pressure Ps of the suction passage 4 detected by the suction pressure detector 9, and the control device 12. As shown in Equation 3, the capacity coefficient (CV value) CV (X) determined by the valve opening X of the spillback valve 7 determined by the formula (1) and the coefficient (flow rate ratio to water) A determined by the physical properties of the air Can be represented.

  The capacity coefficient CV (X) of the spillback valve 7 is determined by the model of the spillback valve 7 and is usually provided from the manufacturer of the valve in a specification or the like. The capacity coefficient CV (X) has a relationship as shown in FIG. 3, for example, and is stored in advance in the control device 12 as data in a format such as a reference table.

  Subsequently, in step 2, the pressure loss in the supply flow path 13 is calculated. Since the pressure loss depends on the flow rate of the compressed air flowing through the supply channel 13, the flow rate in the supply channel 13 is first calculated. The supply flow rate Q through the supply flow path 13 is a flow rate (Qc−Qb) obtained by subtracting the ring flow rate Qb through the spillback valve 7 from the discharge flow rate Qc of the screw compressor 2.

  Since the pressure loss ΔP is proportional to the square of the supply flow rate Q, the supply flow rate Q is maximum when the discharge amount Qb of the screw compressor 2 is maximum and the ring flow rate Qb through the spillback valve 7 is zero. It becomes. At this time, that is, when the supply flow rate Q is equal to the rated discharge amount Qtyp of the screw compressor 2, the pressure loss becomes the maximum value ΔPmax. Thus, the pressure loss P can be expressed by the following formula 4.

  In order to set the terminal pressure Pc of the supply flow path 13 to a desired pressure P2, the set value P1 that is a target value for controlling the pressure Pd of the discharge flow path 5 may be set to the sum of P2 and ΔP. Note that ΔPmax must be confirmed by experiments when the supply flow path 13 is attached or when the compression apparatus 1 is installed, and must be stored in the control device 12.

  Therefore, the control device 12 sets P1 to a value represented by the following formula 5 in step S3.

  In step S4, the control device 12 performs a spillback valve by a known PID calculation based on the deviation between the actual pressure Pd in the discharge flow path 5 detected by the discharge pressure detector 8 and the set value P1. 7 is calculated.

  Further, in step S5, the control device 12 confirms whether there is a signal input indicating a sudden change in the load of the demand destination 14. If no load fluctuation, that is, a sudden change in the consumption amount of compressed air is confirmed in step S5, the opening of the spillback valve 7 is adjusted in step S6 according to the calculation result of the PID control in step S4. If the load fluctuation is confirmed by the signal input in step S5, the control device 12 adds the addition value FF set in advance corresponding to the signal to the control output MV1 of the PID calculation in step S7. Is used to adjust the opening of the spillback valve 7. As a result, it is possible to offset the sudden load fluctuation and reduce the disturbance of the PID control.

  In this manner, the compression device 1 maintains the pressure Pd of the discharge flow path 5 at the set value P1 by adjusting the opening degree of the spillback valve 7 having a quick response in the short term. However, circulating the compressed air through the suction flow path 4 via the spillback valve 7 is equivalent to discarding the energy required for the compression. For this reason, in the compressor 1, the slide valve 3 is operated so that the opening degree of the spillback valve 7 can be reduced. Since the spillback valve 7 substantially changes the compression capacity of the screw compressor 2, the power consumption decreases as the discharge flow rate decreases.

  For this purpose, the control device 12 calculates a control amount MV2 for adjusting the position of the slide valve 3 by PID calculation in step S8, and drives the fluid pressure actuator 6 to position the slide valve 3 in step S9.

  The above control of steps S1 to S9 is repeated without rest while the compressor 1 is in operation.

  In this embodiment, the slide valve 3 excellent in energy efficiency and the spillback valve 7 excellent in responsiveness are used for controlling the discharge pressure Pd. That is, in the present embodiment, while utilizing the control characteristics of each of the slide valve 3 and the spillback valve 7, a compressed gas having a pressure higher than the desired pressure by the pressure loss in the supply flow path 13 is supplied, which is useless. Discharge pressure control that suppresses energy consumption (control of the discharge pressure Pd so that the end pressure Pc can be maintained at the desired pressure P2) can be realized.

DESCRIPTION OF SYMBOLS 1 ... Compressor 2 ... Screw compressor 3 ... Slide valve 4 ... Suction flow path 5 ... Discharge flow path 7 ... Spillback valve 8 ... Discharge pressure detector 9 ... Suction pressure detector 12 ... Control apparatus 13 ... Supply flow path 14 ... customers

Claims (5)

A compression device that has a screw compressor that compresses gas sucked from a suction flow path by a screw rotor housed in a rotor chamber and discharges the gas to a discharge flow path, and supplies the compressed gas to a customer through a supply flow path. And
A slide valve that changes the compression capacity by changing the opening of the rotor chamber, and a spillback valve that circulates a part of the gas discharged to the discharge passage to the suction passage;
A suction pressure detector for detecting the pressure of the suction flow path;
A discharge pressure detector for detecting the pressure of the discharge flow path;
The discharge flow rate of the screw compressor is calculated from the position of the slide valve and the pressure of the suction flow path, and the discharge is calculated from the opening of the spillback valve, the pressure of the suction flow path, and the pressure of the discharge flow path. Calculate the flow rate of the gas from the flow path to the suction flow path, and calculate the pressure loss in the supply flow path based on the supply flow rate of the gas to the demand destination obtained by subtracting the ring flow rate from the discharge flow rate. A target value of the pressure of the discharge flow path is determined so as to compensate and maintain the terminal pressure at the demand destination at a predetermined pressure, and the pressure of the slide valve is adjusted so that the pressure of the discharge flow path becomes the target value. And a control means for adjusting at least one of a position and an opening of the spillback valve. The compression device according to claim 1, wherein the control unit determines the target value according to the following equation.

However, P1 is the target value, Z is the position of the slide valve, f (Z) is a characteristic function of the screw compressor given in advance, X is the opening of the spillback valve, and CV (X) is given in advance P2 is the pressure desired at the customer, Ps is the pressure of the suction passage, Pso is the designed suction pressure of the screw compressor, Pd is the pressure of the discharge passage, and ΔPmax. Is the pressure loss in the supply flow path when the supply flow rate is the rated flow rate of the screw compressor, Qtyp is the rated flow rate of the screw compressor, and A is a constant determined by the characteristics of the gas to be compressed.   The control means adds a predetermined addition value to a control output for at least one of the slide valve and the spillback valve when receiving a signal indicating a sudden change in the gas consumption of the demand destination. The compression apparatus according to claim 1 or 2, characterized by the above. A compression device that supplies compressed gas to a customer through a supply flow path by a screw compressor that compresses gas sucked from a suction flow path by a screw rotor housed in a rotor chamber and discharges the gas to the discharge flow path.
In the compression device having a slide valve that changes the compression capacity by changing the opening of the rotor chamber, and a spillback valve that circulates a part of the gas discharged to the discharge flow path to the suction flow path,
The discharge flow rate of the screw compressor is calculated from the position of the slide valve and the pressure of the suction flow path, and the discharge is calculated from the opening of the spillback valve, the pressure of the suction flow path, and the pressure of the discharge flow path. Calculate the flow rate of the gas from the flow path to the suction flow path, and calculate the pressure loss in the supply flow path based on the supply flow rate of the gas to the demand destination obtained by subtracting the ring flow rate from the discharge flow rate. A target value of the pressure of the discharge flow path is determined so as to compensate and maintain the terminal pressure at the demand destination at a predetermined pressure, and the pressure of the slide valve is adjusted so that the pressure of the discharge flow path becomes the target value. A method for controlling a compressor, comprising adjusting at least one of a position and an opening of the spillback valve. 5. The method for controlling a compressor according to claim 4, wherein the target value is determined by the following equation.

However, P1 is the target value, Z is the position of the slide valve, f (Z) is a characteristic function of the screw compressor given in advance, X is the opening of the spillback valve, and CV (X) is given in advance P2 is the pressure desired at the customer, Ps is the pressure of the suction passage, Pso is the designed suction pressure of the screw compressor, Pd is the pressure of the discharge passage, and ΔPmax. Is the pressure loss in the supply flow path when the supply flow rate is the rated flow rate of the screw compressor, Qtyp is the rated flow rate of the screw compressor, and A is a constant determined by the characteristics of the gas to be compressed.

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