JP2004019445A - Screw compressor and operation control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw compressor capable of conducting rotation control by an inverter device in all loaded areas. <P>SOLUTION: The screw compressor is operated as an oil-free screw compressor by rotation control by the inverter device 4 in an operation range where an air consumption ratio for a specified air volume is not less than a predetermined air consumption ratio. The rotation control by the inverter device 4 can be made in all loaded areas, and is operated as a water injection screw compressor by injecting water into a compression working chamber of a compressor body 1, in an operation range where the air consumption ratio is not larger than the predetermined air consumption ratio so as to enable the rotation control by the inverter device 4 in all loaded areas. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a screw compressor and an operation control method of a screw compressor which enable operation of a compressor body in all load regions from full load to no load by controlling the rotation speed by an inverter device.
[0002]
[Prior art]
Although air compressors are used in various industries, oil-free screw compressors that do not require lubricating oil to be supplied to the compression working chamber are used in industries such as electronics, food, and chemicals that do not want to mix oil. Many are adopted.
In addition, since the air compressor is used in a state where the discharge pressure is kept constant, it is necessary to control the amount of discharge air according to the amount of air used by the user, and the power consumption of the air compressor is reduced by the cost of factory equipment. Occupies about 25% of the electric power cost in Japan, an air compressor compatible with energy saving is demanded.
[0003]
On the other hand, there is a suction throttle control system as a general control system of an oil-free screw compressor. With this suction throttle control method, when the usage of the compressed air supply destination decreases and the discharge pressure becomes higher than the set pressure value, the valve provided at the suction port is closed to limit the suction amount and simultaneously open the discharge side to the atmosphere. This is a control method for reducing the amount of compression work under a low load.
In contrast to the suction throttle control method, as an operation control method capable of obtaining high energy efficiency in response to a change in the load of the screw compressor, there is a rotation speed control method using an inverter device. As a screw compressor adapted to perform the above, for example, a "screw compressor and its operation control method" described in JP-A-2001-342982 is known.
[0004]
According to the “screw compression apparatus and operation control method thereof” of the above publication, in a low load area that is equal to or less than a set consumption air amount, the compressor is operated at a rotation speed corresponding to the set consumption air amount ratio, and the compressor is operated. When the discharge pressure of the compressor reaches the upper limit pressure, the capacity control for discharging the discharge air of the compressor to the atmosphere is also used, and the set air consumption ratio is maintained until the air consumption ratio reaches the set air consumption ratio. The engine is operated at a rotation speed lower than the corresponding rotation speed, whereby the effect of reducing power consumption during no-load operation can be obtained.
[0005]
[Problems to be solved by the invention]
FIG. 4 is a diagram showing the power consumption characteristics of each operation control method of the oil-free screw compressor when the power consumption ratio and the air consumption ratio at full load are each set to 100%. And the solid line b shows the power consumption characteristic of the rotation speed control method using the conventional inverter device.
A dotted line c indicates an ideal power consumption characteristic in which the power consumption under no load is 0, and the change in power consumption with respect to the load from full load to no load is constant.
[0006]
However, in the conventional suction throttle control method indicated by the broken line a in FIG. 4, even when the load is low, the rotor rotation speed is not different from that at the time of full load, so that the compression work decreases but the mechanical loss does not decrease. There is a problem such as lowering.
Compared with the suction throttle control method, in the conventional rotation speed control method using the inverter device, the power consumption ratio in the high load region is small and the energy efficiency is high, but in the low air consumption ratio, that is, in the low load region, the displacement air is displaced. Since the ratio of the amount of internal air leakage to the amount of air increases, air leaking upstream in the compression working chamber is recompressed, and the temperature of the compressed air increases.
[0007]
The present invention has been made to solve such a conventional problem, and a screw compressor and an operation of a screw compressor which enable rotation speed control by an inverter device in all load ranges from full load to no load. It is an object to provide a control method.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the screw compressor of the present invention is a screw compressor that controls the number of revolutions of an electric motor that drives a compressor main body by an inverter device, and a discharge pressure exceeds an allowable range than a preset pressure. When the discharge pressure is lower than a preset pressure beyond an allowable range, the inverter device instructs to decrease the rotation speed of the motor when the motor pressure is higher than the preset pressure. A water injection means for injecting water into a compression working chamber of the compressor body when a consumption air amount or a load amount of a supply destination of the compressed air discharged from the compressor body becomes equal to or less than a predetermined amount. It was done.
[0009]
With the above configuration, the screw compressor can be operated by the rotation speed control by the inverter device in all the load ranges from full load to no load, and the compression of the compressor body is reduced in the low air consumption ratio, that is, in the low load range. Since the space between the rotors is sealed by the water injected into the working chamber, the ratio of the internal air leakage to the displacement air does not increase.
As a result, the air leaking to the upstream side is not recompressed in the compression working chamber, and at the same time, the compressed air is cooled by the water injected into the compression working chamber. And a screw compressor with less pressure fluctuation can be obtained.
[0010]
In order to achieve the above object, a screw compressor of the present invention is provided with a water injection device that injects water also to an air suction side of a compressor body when a consumed air amount or a load of a supply destination of compressed air becomes a predetermined amount or less. Means are provided.
[0011]
According to the above configuration, the atomized water is mixed with the air sucked into the compressor main body, and the cooling effect of the air during the compression process can be enhanced, so that the energy efficiency can be improved.
[0012]
In order to achieve the above object, an operation control method for a screw compressor according to the present invention is an operation control method for a screw compressor in which the number of revolutions of an electric motor that drives a compressor body is controlled by an inverter device. In the operation range where the amount ratio is equal to or higher than the preset air consumption ratio, the operation as an oil-free screw compressor is performed by controlling the rotation speed by the inverter device, and the operation in which the air consumption ratio is equal to or lower than the preset air consumption ratio. In this range, the compressor is operated as a water-injection screw compressor by injecting water into the compression working chamber of the compressor body.
[0013]
According to the above method, the screw compressor can be operated by the rotation speed control by the inverter device in all load regions from full load to no load, and the compression of the compressor body is reduced in the low air consumption ratio, that is, in the low load region. Since the space between the rotors is sealed by the water injected into the working chamber, the ratio of the internal air leakage to the displacement air does not increase.
This prevents the air leaking upstream from being recompressed in the compression working chamber, and at the same time cools the compressed air by the water injected into the compression working chamber, so that the energy efficiency is high and the pressure fluctuation of the discharge air. It is possible to provide an operation control method of a screw compressor with less trouble.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a configuration diagram of a screw compressor according to a first embodiment, in which a compressor body 1 mainly using air as a working gas and water is discharged from discharge air of the compressor body 1 during a water injection operation. A separator 7 for storing separated and separated water, an aftercooler 8 for cooling discharged air, an electric motor 3 and a speed increasing device 2 for driving the compressor body 1, and an inverter for controlling the number of revolutions of the electric motor 3. A pressure sensor 13 mounted on a compressed air supply pipe 25 connected downstream of the aftercooler 8 to measure a discharge pressure in the compressed air supply pipe 25; The main parts are constituted by a bearing (not shown) of the compressor body 1, an oil pump 9 for supplying lubricating oil to the timing gear 1f and the gearbox 2, and an oil cooler 10.
[0015]
The compressor main body 1 includes a pair of meshed male screw rotors 1a and female screw rotors 1b, both of which are accommodated in bores formed in a casing 1c. Both shaft ends of both screw rotors 1a and 1b are rotatably supported by bearings.
For example, four teeth are formed in a screw shape on the outer peripheral portion of the male screw rotor 1a, and, for example, six teeth are formed in a screw shape on the outer peripheral portion of the female screw rotor 1b. A shaft sealing device (not shown) is provided between a bearing for supporting both shaft ends of the screw rotors 1a and 1b and a tooth portion of the screw rotors 1a and 1b, respectively. Of the air, water, and lubricating oil are prevented, and the bearing and the shaft sealing device are each held in a casing.
[0016]
A drive shaft 1d protruding from a male screw rotor 1a housed in the compressor body 1 projects toward the speed-increasing gear 2 side of the compressor body 1 and is provided in the speed-increasing gear 2 The screw rotors 1a and 1b of the compressor main body 1 are connected to the rotating shaft 3a of the electric motor 3 via the gears 2a and 2b, and are driven by the power of the electric motor 3.
[0017]
During a steady operation in which the discharge air amount ratio is equal to or higher than the preset discharge air amount ratio, air sucked from outside air together with the operation of the compressor main body 1 passes through the filter 6 and the suction pipe 22 and passes through the compressor main body. 1 and is sucked into a compression working chamber formed by a pair of rotating screw rotors 1a, 1b and a casing 1c, and the volume of the compression working chamber is reduced by the rotation of the screw rotors 1a, 1b. Pressed. After the compressed air is discharged from the compression working chamber, the air is guided to the aftercooler 8 through the air pipe 23, the separator 7, and the compressed air supply pipe 24, and is cooled by the aftercooler 8, and then compressed. The air is supplied to the supply destination through the air supply pipe 25 and the check valve 14. Reference numeral 15 denotes a safety valve.
[0018]
On the other hand, at the time of low load operation in which the discharge air amount ratio is equal to or less than the preset discharge air amount ratio, air sucked from outside air passes through the filter 6 and the suction pipe 22 and enters the compressor body 1 as in the normal operation. Is drawn into a compression working chamber formed by a pair of rotating screw rotors 1a, 1b and a casing 1c and is compressed under pressure. During this compression process, a nozzle is formed from a water pipe 35 or a water pipe 36. Is injected into the compressor main body 1 through the compressor.
At the same time, water is injected into the suction pipe 22 from the water pipe 35 or the water pipe 36 via a nozzle, and the atomized water is mixed into the suction air to enhance the cooling effect of the air during the compression process. Improves energy efficiency.
[0019]
When the discharge air amount ratio becomes equal to or less than the preset discharge air amount ratio, the solenoid valve 21 is opened, and the water stored in the separator 7 is supplied to the water pipe 38 by the air pressure discharged from the compressor body 1. After being pushed out and cooled by the water cooler 37, the water is injected into the compression working chamber of the compressor body 1 by the nozzle through the water pipe 32, the water filter 20, and the water pipe 36.
When the water in the separator 7 is equal to or less than the set amount, the solenoid valve 21 is closed and the solenoid valve 19 is open, and water from the external water supply is supplied to the valve 39, the water pipe 26, the water filter 18, and the water pipe 27. , Through the water pipe 35, the nozzle is injected into the compression working chamber of the compressor body 1 by the nozzle, and the solenoid valve 19 and the solenoid valve 21 are both closed when the compressor is stopped and during steady operation. ing.
[0020]
The nozzle is formed in the middle of the casing 1c of the compressor body 1 and at a position where the compression working chamber forms a closed space. In the compression working chamber, the screw rotors 1a and 1b are formed by the sealing effect of the injected water. Even at low-speed rotation, air leakage is reduced, and at the same time, compression power is reduced by the cooling effect, so that energy efficiency does not decrease even during low-load operation.
Further, after the compressed air is discharged from the compression working chamber of the compressor body 1 in a state of being mixed with water, the compressed air reaches the separator 7 through the air pipe 23, and the water is separated from the compressed air by the separator 7, and only the water is removed. A compressed air supply pipe 24 is connected to the upper part of the separator 7 and stored in a lower part of the separator 7. A water supply pipe for supplying the above-described water to the compressor body 1 is provided on a side wall part near the bottom of the separator 7. 38 are connected.
[0021]
The compressed air discharged from the separator 7 reaches the aftercooler 8 through the compressed air supply pipe 24, is cooled by the aftercooler 8, and is cooled by the drain separator 8 a provided on the discharge side of the aftercooler 8. The drain is separated, and the compressed air is supplied to an external supply destination after passing through the compressed air supply pipe 25 and the check valve 14. The drain separated by the drain separator 8a passes through the water pipe 31 and the drain valve 40. It is designed to be discharged outside.
[0022]
On the other hand, the lubricating oil discharged from the oil pump 9 is used for lubrication of the gears 2a and 2b of the gearbox 2 for transmitting the power of the bearing and the timing gear 1f and the electric motor 3 to the compressor main body 1 in the compressor main body 1. However, this lubricating oil is stored in an oil tank 2d provided below the gear casing 2c of the speed increaser 2, circulated to an oil cooler 10 by an oil pump 9, cooled by the oil cooler 10, and then cooled by an oil filter. 11. The lubricating oil is supplied to the bearings in the compressor main body 1, the timing gear 1f, and the speed increasing gears 1a, 2b in the speed increaser 2 through the oil header 12. Is returned to the oil tank 2d below the gear casing 2c of the gearbox 2.
A part of the cooling water for cooling the compressor body 1 and the intake air is guided from the external water supply source into the oil cooler 10 through the valve 39 and the water supply pipes 26 and 28, and exchanges heat with the lubricating oil in the oil cooler 10. After cooling the lubricating oil, the lubricating oil is guided into the aftercooler 8 through the pipe 29, exchanges heat with the discharge air in the aftercooler 8, and further cools the compressed air. Is discharged to the outside through the water pipes 30, 49 and the valve 41.
[0023]
When the discharge pressure detected by the pressure sensor 13 is higher than a preset pressure (rated discharge pressure) exceeding an allowable range, the control device 5 that controls the inverter device 4 causes the inverter device 4 to rotate the electric motor 3. When the discharge pressure detected by the pressure sensor 13 is lower than a predetermined pressure (rated discharge pressure) exceeding an allowable range, the rotation speed of the electric motor 3 is increased by the inverter device 4. The rotation speed of the electric motor 3 is controlled so that the discharge pressure always falls within a permissible range of a preset pressure (rated discharge pressure). When the rotation speed of the motor 3 is input and the rotation speed of the electric motor 3 is equal to or lower than a preset lower limit rotation speed, a command to open the valve is output to the solenoid valve 19 or the solenoid valve 21, whereby the pressure is increased. It has ejects water to the compressed working chamber of the machine body 1.
[0024]
Next, a description will be given of an operation control method of the screw compressor configured as described above. In a steady operation in which the discharge air amount ratio is in an operation range equal to or higher than a preset discharge air amount ratio, the compressor is sucked in from outside air together with the operation of the compressor body 1. The compressed air is guided into the compressor main body 1 through the filter 6 and the suction pipe 22 and is pressurized by the compressor main body 1, and then is passed through the air pipe 23, the separator 7, and the compressed air supply pipe 24, and is subjected to after-sales. After being guided to the cooler 8 and cooled by the after cooler 8, it is supplied to the supply destination through the compressed air supply pipe 25 and the check valve 14.
[0025]
Further, when the discharge pressure detected by the pressure sensor 13 is higher than a preset pressure beyond an allowable range, the control device 5 instructs the inverter device 4 to decrease the rotation speed of the electric motor 3, and the pressure sensor When the discharge pressure detected at 13 is lower than the preset pressure by more than an allowable range, the discharge pressure is always set in advance by instructing the inverter device 4 to increase the rotation speed of the electric motor 3. The number of revolutions of the electric motor 3 is controlled so as to be within the allowable range of the pressure, whereby, for example, in a load region where the air consumption ratio is 100% to 40%, the screw rotors 1a and 1b of the compressor main body 1 have different rotation speeds. Since an air layer is formed between the screw rotors 1a and 1b, there is no contact between the screw rotors 1a and 1b. Load operation is possible.
[0026]
On the other hand, at the time of low load operation in which the discharge air amount ratio is equal to or less than the preset discharge air amount ratio, the solenoid valve 21 is opened by a command from the control device 5, and the water stored in the separator 7 is discharged from the compressor body. After being pushed out to the water pipe 38 by the air pressure discharged from the pipe 1 and cooled by the water cooler 37, the water is injected into the compression working chamber of the compressor body 1 by the nozzle through the water pipe 32, the water filter 20 and the water pipe 36. You.
Thus, in a low load region where the air consumption ratio is, for example, 40% to 0%, even if the screw rotors 1a and 1b rotate at a low speed, air leakage is reduced due to the sealing effect of the water injected into the compression working chamber. At the same time, since the compression power is reduced by the cooling effect of the water injected into the compression working chamber, low-speed operation of the oil-free compressor becomes possible by controlling the rotation speed by the inverter device 4, and at the time of low-load operation. In this case, the energy efficiency does not decrease.
[0027]
FIG. 2 is a graph showing the power consumption characteristics according to the operation method. A curve indicated by a dashed line d indicates the power consumption characteristics according to the embodiment, and a dashed line a indicates the power consumption characteristics of the suction aperture control method. , And the dotted line c shows the power consumption characteristic in an ideal state in which the change in the power consumption with respect to the load from full load to no load is constant.
In the first embodiment, the lower limit rotation speed of the electric motor 3 is set to the rotation speed at which the discharge air amount becomes 40% of the specified air amount, but it is not necessarily limited to 40%. What is necessary is just to select suitably according to the characteristics, capacity | capacitance, etc. of the compressor main body 1.
[0028]
On the other hand, FIG. 3 shows a second embodiment, in which water injected into the compression working chamber of the compressor main body 1 is supplied only from the outside, so that water is separated from discharge air during operation of the water injection screw compressor. A separator 7 for storing water is omitted, water is separated from discharge air in an aftercooler 8, and the separated water is discharged to the outside. Others are the same as those of the first embodiment. Since they have substantially the same configuration, the same parts are denoted by the same reference numerals and description thereof will be omitted.
[0029]
In the second embodiment shown in FIG. 3, at the time of low load operation in which the discharge air amount ratio is equal to or less than the preset discharge air amount ratio, air passes from the outside air through the suction filter 6 as in the steady operation. Is guided to the compressor main body 1 through the suction pipe 22 and pressurized in the compressor main body 1. At this time, the solenoid valve 19 is opened, and water from the external water supply source is supplied to the valve 39, the water pipe 26. The nozzle is injected through a nozzle through a water filter 18, a water pipe 27, and a water pipe 35 into a compression working chamber of the compressor body 1 and into the suction pipe 22, and at this time, the solenoid valve 19 is closed when the compressor is stopped and during steady operation. It has become.
[0030]
The nozzle is formed at a position between the suction pipe 22 and the casing 1c of the compressor body 1 and at a position where the compression working chamber forms a closed space, and the compressed air is discharged from the compression working chamber in a state of being mixed with water. After that, the compressed air is discharged to the aftercooler 8 through the air pipe 23, the compressed air is cooled by the aftercooler 8, and the water separated from the compressed air is discharged to the outside from the water pipe 31. The air is discharged to an external supply destination through the compressed air supply pipe 25 and the check valve 14.
[0031]
In addition, since the conventional water injection type screw compressor always uses a large amount of water to inject water into the compression working chamber, a method of saving external water supply by circulating water has been used. However, in the case of the circulation type, an expensive water quality preservation device is required to solve problems such as propagation of bacteria such as pathogenic bacteria in water and melting of metal ions.
However, according to the screw compressors according to the first and second embodiments, since water is injected only when the compressor body 1 is under a low load, the amount of water used is relatively small, and the second embodiment is not limited. Water is not required to be circulated according to the screw compressor in the form, so water supplied from the outside is injected into the compression working chamber, and water separated from the discharge air is discharged to the outside of the compressor as it is to maintain water quality. The burden on the device can be reduced.
[0032]
【The invention's effect】
As described in detail above, the present invention operates as an oil-free screw compressor by controlling the rotation speed by an inverter in an operation range in which the air consumption ratio with respect to the specified air amount is equal to or more than a preset air consumption ratio, In the operation range where the air consumption ratio is equal to or less than the preset air consumption ratio, by injecting water into the compression working chamber of the compressor body, the operation is performed as a water injection screw compressor, In all load ranges from full load to no load, the rotation speed control by the inverter device enables the operation of the screw compressor, and in the low air consumption ratio, that is, in the low load range, the screw compressor is injected into the compression working chamber of the compressor body. Since the water is sealed between the rotors, the internal air leakage ratio to the displacement air amount does not increase.
As a result, the air leaking to the upstream side is not recompressed in the compression working chamber, and at the same time, the compressed air is cooled by the water injected into the compression working chamber. And a method for controlling the operation of the screw compressor with less pressure fluctuation.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a screw compressor according to a first embodiment of the present invention.
FIG. 2 is a diagram showing power consumption characteristics of the screw compressor according to the first embodiment of the present invention.
FIG. 3 is a configuration diagram of a screw compressor according to a second embodiment of the present invention.
FIG. 4 is a diagram showing power consumption characteristics of a conventional screw compressor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Compressor main body 2 Gearbox 3 Motor 4 Inverter 5 Control device 6 Suction filter 8 Separator 9 Oil pump 10 Oil cooler 13 Pressure sensor 25 Compressed air supply pipe

Claims (3)

A screw compressor that controls the rotation speed of an electric motor that drives a compressor body by an inverter device, and when the discharge pressure is higher than a preset pressure beyond an allowable range, the rotation speed of the electric motor is reduced. Command, when the discharge pressure is lower than a preset pressure exceeding an allowable range, an inverter device for instructing to increase the rotation speed of the electric motor, and a supply destination of compressed air discharged from the compressor body. A screw compressor, comprising: water injection means for injecting water into a compression working chamber of the compressor body when an amount of consumed air or a load amount becomes equal to or less than a predetermined amount. 2. The screw compressor according to claim 1, further comprising water injection means for injecting water on the air suction side of the compressor body when the amount of consumed air or the load of the supply destination of the compressed air becomes equal to or less than a predetermined amount. Machine. An operation control method for a screw compressor in which an electric motor for driving a compressor body is controlled in rotation speed by an inverter device, wherein an air consumption ratio with respect to a specified air amount is equal to or greater than a preset air consumption ratio. By operating as an oil-free screw compressor by controlling the rotation speed of the device, in the operating range where the air consumption ratio is equal to or less than the preset air consumption ratio, water is injected into the compression working chamber of the compressor body, An operation control method for a screw compressor, which operates as a water injection screw compressor.

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