JP2005351169A - Screw compressor and its operation control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically expand a control range of suction throttle control operation having high energy efficiency in capacity control of a screw compressor. <P>SOLUTION: This screw compressor adjusts capacity by adjusting delivery pressure substantially constant by performing blow-off control by a blow-off valve 4 arranged on the delivery side in a low load area by performing suction throttle control for keeping delivery air pressure substantially constant by adjusting a delivery air quantity by opening and closing a suction throttle valve 3 arranged on the suction side in a high load area. The screw compressor continues the suction throttle control without performing the blow-off control until the pressure ratio Pd/Ps being the ratio of delivery air pressure to suction air pressure reaches a predetermined pressure ratio value by detecting the suction air pressure Ps and the delivery air pressure Pd of a compressor body 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an oil-free screw compressor that does not mix oil in discharged air, and more particularly to a screw compressor that enables a suction throttle control operation in a wide load region and an operation control system for the screw compressor.

  Air compressors are indispensable equipment in various industries, but there is a demand for oil-free screw compressors that do not mix oil in the discharge air in industries that dislike mixing oil, such as electronics, food, and chemicals. high.

  Generally, an air compressor is operated within a set control pressure range, and discharge air amount control according to a user's air usage is required. In addition, since the power consumption cost of the air compressor accounts for about 25% of the power cost of the factory facilities, compressors that can save energy are in the market.

There is a two-step control method as a general capacity control method of an oil-free screw compressor. The two-step control method detects the discharge air pressure P ₀ of the compressor and does not perform load operation so that P ₁ > P ₀ > P ₂ with respect to a certain set upper limit pressure P ₁ and lower limit pressure P ₂ . This is a capacity control system that operates the compressor within the set pressure range according to the amount of compressed air used by repeating the load operation (the rotating throttle is always rotated at a constant speed and the intake throttle valve is fully closed or This is a control that fully opens and simultaneously opens or closes the vent valve).

  Here, in the load operation, when the amount of compressed air used increases and the discharge pressure becomes lower than the set pressure value, the intake valve provided on the suction side is fully opened and the air discharge valve provided on the discharge port is closed. In this operation state, compressed air is continuously discharged. Also, no-load operation means that when the amount of compressed air used decreases and the discharge air pressure reaches the set pressure value, the intake valve provided on the intake side is closed and the air discharge valve provided on the discharge side is opened. Therefore, it is an operation state in which the compression work is not performed and the power of the compressor is reduced.

  However, in this two-step control method, the rotor rotational speed does not change even when the load is low, and the compression work is reduced but the mechanical loss is not reduced, so that the energy efficiency is lowered. In addition, it is necessary to ensure a certain pressure range, and accordingly, the average discharge air pressure is increased, so that the power consumption is increased. Moreover, since there is a pressure fluctuation, it becomes difficult to use depending on the use of compressed air.

  On the other hand, as a capacity control method capable of obtaining high energy efficiency in response to fluctuations in the load of the compressor, there is a rotation speed control method by inverter drive, in contrast to the two-step control method. The number of revolutions of the main motor can be changed by the inverter so that the discharge air pressure of the compressor becomes constant, and the power consumption can be reduced. Further, since the discharge air pressure can be controlled constantly, the average discharge air pressure can be reduced, and the power consumption can be reduced correspondingly, resulting in a high energy saving effect.

  However, as described in Patent Document 1 illustrating an inverter-driven rotation speed control method, when the rotation speed control is performed while maintaining the discharge air pressure of the compressor at the operating air pressure, the internal capacity with respect to the displacement air amount is low in the low rotation area. The ratio of air leakage increases, and the air leaked upstream in the compression chamber is recompressed. As a result, the temperature of the compressed air rises and the energy efficiency is greatly reduced. become. In view of this, it is necessary to perform capacity control by opening a discharge valve provided on the discharge side and discharging discharge air in a low load region or less than a set consumption air amount.

  Although it can be said that the rotational speed control by the inverter has a high energy-saving effect as a whole, the energy-saving effect is reduced in a high load region because of inverter loss. Further, the inverter device is very expensive particularly in the class having a large capacity, and the burden of the initial investment of the user is increased.

  On the other hand, there is a suction throttle control system that is widely used mainly as a capacity control system for oil-cooled screw compressors (in this suction throttle control system, the rotation speed of the rotating machine is constant, and the suction throttle valve (The present invention is an improved version of this suction throttle control system, which will be described later). This is a capacity control system in which a suction throttle valve is installed on the suction side, the suction throttle valve is opened and closed in proportion to the detected discharge air pressure, the intake air amount is limited, and the discharge air pressure is kept constant. In the case of an oil-free screw compressor, by restricting the suction throttle valve in the low load region, the pressure ratio between the intake air pressure and the discharge air pressure in the compressor body becomes large, and the discharge air temperature rises. Thus, there is a risk that the pair of rotors in the compressor main body may thermally expand and come into contact with each other.

  In order to avoid this over-compression state, the limit opening of the suction throttle valve that can be over-compressed under the most severe conditions that can be operated in the suction throttle control is set as the set minimum opening, and the suction throttle valve becomes low in load. When the opening of the valve reaches the set minimum opening, it is necessary to perform control to switch from suction throttle control to air discharge control that keeps the discharge pressure constant by opening the air discharge valve installed on the discharge side. is there. For example, when the throttle opening of the throttle valve set as the limit opening reaches 80%, control is performed to open the air discharge valve and switch to air discharge control.

In the suction throttle control method, the capacity control can be performed by the constant pressure control in the high load region, so that the power consumption is reduced by lowering the discharge average pressure, and the energy saving effect is high. In addition, since an expensive device or the like is not necessary, the cost can be kept relatively low.
JP 2001-342982

  However, the suction throttle control has a high energy saving effect in the high load region, but the energy saving effect becomes small because it is necessary to switch to the air discharge control in the low load region. The minimum opening of the suction throttle valve for suction throttle control is determined under the most severe conditions within the operating conditions (suction air temperature, pressure loss of the suction air filter, etc.). In many cases, the overcompressed state is not reached. Therefore, in order to enhance the energy saving effect of the suction throttle control, a control method that can automatically expand the suction throttle control range as much as possible in the actual operation state is desired.

  The objective of this invention is providing the screw compressor which can expand the control range of the suction throttle control with high energy efficiency.

In order to solve the above problems, the present invention adopts the following configuration.
In the high load area, the suction throttle control is performed to keep the discharge air pressure substantially constant by opening and closing the suction throttle valve installed on the suction side and adjusting the discharge air volume. In the low load area, the air discharge is installed on the discharge side. A screw compressor that performs discharge control by a valve and adjusts the discharge pressure to be substantially constant to adjust the capacity,
A configuration in which the intake air pressure Ps and the discharge air pressure Pd of the compressor body are detected, and the suction throttle control is performed until the pressure ratio Pd / Ps, which is the ratio of the intake air pressure and the discharge air pressure, reaches a predetermined pressure ratio value. And

Also, in the high load region, the intake air amount is adjusted by opening and closing the suction throttle valve installed on the suction side, and the suction throttle control is performed to keep the discharge air pressure substantially constant. In the low load region, the suction throttle valve is installed on the discharge side. A screw compressor that performs discharge control with a discharge valve and adjusts the discharge pressure to a constant level to adjust the capacity,
The configuration is such that the discharge air temperature of the compressor body is detected and the suction throttle control is performed until the discharge air temperature reaches a predetermined temperature.

  According to the present invention, the control range of the suction throttle control operation in which the discharge air pressure fluctuation is small and the energy efficiency is high can be automatically expanded at low cost and can be operated over a wide range.

  The operation control system of the screw compressor according to the embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2. FIG. 1 is a system configuration diagram of the operation control system of the screw compressor according to the first embodiment of the present invention, and FIG. 2 is a system configuration of the operation control system of the screw compressor according to the second embodiment of the present invention. FIG. Here, 1 is a compressor main body, 2 is an intake air filter, 3 is an intake throttle valve, 4 is an air release valve, 5 is an air release silencer, 6 is a check valve, 7 is a control device, and 8 is a discharge pressure detector. , 9 is a suction pressure detector, 10 is a discharge temperature detector, 11 is a suction pipe, 12 is a discharge pipe, 13 is a discharge secondary pipe, and 14 is an air discharge pipe. The oil-free screw compressor described as the first and second embodiments of the present invention is a single-stage machine without an aftercooler in order to simplify the description. Although the present invention can be applied to the case where an aftercooler is installed or the compressor main body is a two-stage compressor having two low-pressure stage main bodies and high-pressure stage main bodies, description thereof is omitted.

  The set target discharge pressure of the screw compressor related to the present embodiment is determined by the use of compressed air, the pressure loss of compressed air to the equipment used, and the like. The pressure ratio is the ratio of the absolute pressure between the discharge air pressure and the intake air pressure (discharge air pressure / intake air pressure). The allowable pressure ratio is determined by the design conditions of the compressor body, and the thermal expansion of the rotor in the compressor body Determined by quantity.

The screw compressor is a positive displacement compressor and theoretically compresses air by an adiabatic compression process. When the intake air state is pressure Ps, volume Vs, and temperature Ts, and the discharge air state is pressure Pd, volume Vd, and temperature Td, Ps · Vs ⁿ = Pd · Vd ⁿ , Ts / Ps ^{(n−1) /} The relationship ⁿ = Td / Pd ^{(n−1) / n} is established. Here, n is a polytropic index, which is 1.4 in the case of adiabatic compression.

  In the compression process from the suction state to the discharge state, the pair of meshed rotors inside the compressor body rotate to reduce the intake air volume V, increase the compressed air pressure P, and increase the air temperature T. Rise. When the air temperature T rises, the rotor in the compressor body is heated and thermally expands, so that the gap between the two rotors is reduced. When the air temperature exceeds a certain allowable temperature, the rotor comes into contact. Since the discharge air temperature changes in proportion to the pressure ratio between the discharge air pressure of the compressor and the intake air pressure, the pressure ratio with respect to this allowable temperature is determined.

In other words, as can be seen from the relational expression Ts / Ps ^{(n-1) / n} = Td / Pd ^{(n-1) / n} , the discharge air temperature Td is determined by the ratio of Pd and Ps and Ts, If Td rises too much, an abnormal situation of rotor contact may occur, and Ps is determined by the opening degree of the suction throttle valve. Therefore, the minimum opening degree of the suction throttle valve, for example, 80% is set so as not to cause an abnormal situation. Therefore, when the minimum opening is reached, the air discharge valve is uniformly controlled to open.

  The control system according to the first embodiment of the present invention monitors the pressure ratio (Pd / Ps) without performing uniform control based on the set minimum opening of the suction throttle valve until the allowable pressure ratio is reached. It is determined that suction throttle control is possible, and the suction throttle control range is expanded (open / close control of the discharge valve is not performed). In the first embodiment, in a high load region, intake throttle control is performed by adjusting a discharge air amount by opening and closing a suction throttle valve installed on the suction side to keep a discharge air pressure constant (or a constant range). In the load area, in the screw compressor that performs discharge control by the discharge valve installed on the discharge side and adjusts the discharge pressure to adjust the capacity constant, the intake air pressure and the discharge air pressure of the compressor body are detected, The suction throttle control range is automatically expanded until the pressure ratio, which is the ratio between the discharge air pressure and the intake air pressure, reaches a predetermined pressure ratio value. That is, when the pressure ratio (Pd / Ps) is detected and reaches a predetermined value, the air discharge valve is opened while the opening of the suction throttle valve is maintained.

  Next, the operation control system of the screw compressor according to the first embodiment of the present invention will be specifically described with reference to FIG. In FIG. 1, the screw compressor is composed of a compressor main body 1, an electric motor for driving the compressor main body, an auxiliary pump such as an oil pump for circulating lubricating oil, and an oil cooler. The compressor body 1 includes a pair of meshed male screw rotor and female screw rotor, and both the rotors are accommodated in two overlapping cylindrical holes called bores formed in the casing. ing. Both shaft ends of these rotors are supported by bearings. Four teeth are formed in a screw shape on the outer peripheral portion of the male rotor, and six teeth are formed in a screw shape on the outer peripheral portion of the female rotor. A shaft seal device is provided between the bearing and the rotor tooth portion at both shaft end portions of the rotor, respectively, to prevent leakage of air and lubricating oil between the bearing and the compression working chamber. The bearing and the shaft seal device are each held in a casing.

  The compressor body 1 is rotated by an electric motor, and the intake air is sucked into the compressor from the suction air filter 2, the amount of intake air is adjusted by the suction throttle valve 3, and is sucked into the compressor body 1 through the suction pipe 11. The Compressed air compressed by the compressor body 1 is discharged from the compressor body 1, passes through the discharge pipe 12, and when the pressure on the secondary side is smaller than the primary side of the check valve 6, the check valve Since 6 is in the open state, it passes through the discharge secondary pipe 13, passes through the check valve 6, and compressed air is supplied to the line.

  When the air discharge valve 4 is in an open state, a part of the compressed air passes through the air discharge pipe 14, passes through the air discharge valve 4, and is released to the atmosphere from the air discharge silencer 5. An operation command signal is transmitted from the control device 7 to open and close the intake throttle valve 3 and the discharge valve 4.

  When the discharge air pressure Pd in the discharge pipe 12 is detected by the discharge air pressure detector 8 and Pd <P with respect to the set target discharge pressure P, an opening operation command signal is transmitted to the suction throttle valve 3. Then, the intake air volume is increased by widening the valve opening of the intake throttle valve 3 to increase Pd. When Pd> P, a closing operation command signal is transmitted to the suction throttle valve 3, and the intake air volume is reduced by reducing the opening degree of the suction throttle valve 3, thereby lowering Pd. When Pd = P, the opening / closing operation command signal is not transmitted to the suction throttle valve 3 and the opening degree of the suction throttle valve 3 is fixed, so that the discharge air pressure Pd becomes the target discharge pressure P. The capacity is controlled to be constant. At this time, a command signal for fixing the closed state is continuously transmitted to the air discharge valve 4 to keep the air release valve 4 in a fully closed state. This state is suction throttle control.

  Here, the suction pressure Ps in the suction pipe 11 is detected by the suction pressure detector 9, and the detected pressure ratio between the discharge air pressure Pd and the suction air pressure Ps, that is, Pd / Ps is calculated by the control device 7. The suction throttle control described above is continued in the case of a condition that is less than or equal to the set allowable pressure ratio determined by the design conditions of the main body of the compressor. A fixed opening signal is continuously transmitted to maintain the opening of the intake throttle valve 3, the discharge air pressure Pd in the discharge pipe 12 is detected by the discharge air pressure detector 8, and Pd <P with respect to the target discharge pressure P. In this case, a closing operation command signal is transmitted to the discharge valve 4, and the amount of the discharge air is reduced by reducing the valve opening of the discharge valve 4, thereby increasing Pd. Further, when Pd> P, an opening operation command signal is transmitted to the air discharge valve 4, and the air opening amount of the air discharge valve 4 is increased to increase the amount of the air discharge, thereby reducing Pd. When Pd = P, the command signal for opening / closing operation is not transmitted to the air discharge valve 4, and the valve opening of the air discharge valve 4 is fixed so that Pd becomes constant at the target discharge pressure P. Control. This state is air discharge control.

  Next, the operation control system of the screw compressor according to the second embodiment of the present invention will be specifically described with reference to FIG. In FIG. 2, the description of the parts common to the first embodiment is omitted.

  In FIG. 2, the switching condition between the suction throttle control and the discharge control range is determined by the control device 7 from the discharge air temperature Td in the discharge pipe 12 detected by the discharge air temperature detector 10. When the discharge air temperature Td is compared with the allowable discharge air temperature T determined by the design conditions of the compressor body 1 and Td <T, capacity control is performed by suction throttle control, and when Td> = T. Performs capacity control by ventilating control.

  As described above, in the high load region, the present invention performs the suction throttle control that adjusts the discharge air amount by opening and closing the suction throttle valve installed on the suction side to keep the discharge air pressure constant. In the screw compressor operation control system that adjusts the capacity by controlling the discharge with a discharge valve installed on the discharge side, the operation range of the suction throttle control, which is highly energy-saving under actual operating conditions, is expanded as much as possible. The present invention relates to a screw compressor that enables a suction throttle control operation in a wide load region, and an operation control system of the screw compressor.

  Specifically, the operation control system of the screw compressor according to the embodiment of the present invention detects the pressure ratio between the intake air pressure and the discharge air pressure of the compressor body, and this pressure ratio is determined as an overcompressed state. This is a control system that automatically expands the suction throttle control range until the pressure ratio is reached. Since the control is performed by the pressure ratio between the intake air pressure and the discharge air pressure, the intake throttle control range can be automatically expanded as much as possible in each operation state and environment. Further, the operation control system of the screw compressor according to another embodiment of the present invention detects the discharge air temperature of the compressor main body, the rotor temperature inside the compressor main body becomes high temperature, and the thermal expansion occurs. This control system automatically expands the suction throttle control range until reaching the discharge air temperature at which there is a risk of contact with the pair of rotors. Since the discharge air temperature of the compressor changes depending on the intake air temperature, the pressure ratio between the intake air pressure and the discharge air pressure of the compressor body, etc., by controlling the discharge air temperature as much as possible in each operating state and environment The suction throttle control range can be automatically expanded. As described above, according to the embodiment of the present invention, when the intake air temperature is low or the target set discharge pressure is low, the suction throttle control range is automatically expanded without changing the setting or the like, and further energy saving effect is achieved. Can be obtained.

It is a system configuration | structure figure of the operation control system of the screw compressor which concerns on the 1st Embodiment of this invention. It is a system configuration | structure figure of the operation control system of the screw compressor which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor body 2 Suction air filter 3 Suction throttle valve 4 Breathing valve 5 Breathing silencer 6 Check valve 7 Control device 8 Discharge pressure detector 9 Suction pressure detector 10 Discharge temperature detector 11 Suction piping 12 Discharge piping 13 Discharge Secondary piping 14 Ventilation piping

Claims (4)

In the high load range, the intake air amount is adjusted by opening and closing the suction throttle valve installed on the suction side and the discharge air pressure is controlled to keep the discharge air pressure substantially constant. In the low load region, the discharge throttle installed on the discharge side is controlled. A screw compressor that performs discharge control by a wind valve and adjusts a discharge pressure to be substantially constant to adjust a capacity,
The suction air pressure Ps and the discharge air pressure Pd of the compressor body are detected, and the suction throttle control is performed until the pressure ratio Pd / Ps that is the ratio of the intake air pressure and the discharge air pressure reaches a predetermined pressure ratio value. Operation control system of screw compressor characterized by In the high load range, the intake air amount is adjusted by opening and closing the suction throttle valve installed on the suction side and the discharge air pressure is controlled to keep the discharge air pressure substantially constant. In the low load region, the discharge throttle installed on the discharge side is controlled. A screw compressor that performs discharge control by a wind valve and adjusts a discharge pressure to be substantially constant to adjust a capacity,
An operation control system for a screw compressor, characterized in that a discharge air temperature of a compressor body is detected and the suction throttle control is performed until the discharge air temperature reaches a predetermined temperature. An intake throttle valve provided on the air intake side of the screw compressor body, an air discharge valve provided on the air discharge side of the screw compressor body, an intake air pressure detector provided on an intake pipe of the screw compressor body; A screw compressor provided with a discharge air pressure detector provided in a discharge pipe of the screw compressor body,
Controlling the suction throttle valve and / or the discharge valve to make the discharge pressure substantially constant and adjusting the discharge air amount;
A screw compressor that performs suction throttling control without air discharge control until a pressure ratio between the discharge pressure from the discharge pressure detector and the suction pressure from the suction pressure detector reaches a predetermined value. A suction throttle valve provided on the air suction side of the screw compressor main body, a discharge valve provided on the air discharge side of the screw compressor main body, a discharge air temperature detector provided on a discharge pipe of the screw compressor main body, In a screw compressor equipped with,
Controlling the suction throttle valve and / or the discharge valve to make the discharge pressure substantially constant and adjusting the discharge air amount;
The screw compressor, wherein the suction throttle valve control is performed without performing the air discharge valve control until the temperature of the discharge air from the discharge air temperature detector reaches a predetermined value.

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