JP2005315506A - Two-stage screw refrigerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-stage screw refrigerator simplified in structure, reduced in size, and reduced in a load for maintenance. <P>SOLUTION: This two-stage screw refrigerator 1A comprises a first stage screw compressor 11, a second stage screw compressor 12, a condenser 13, an intermediate supercooler 14, a refrigerant/oil circulation flow passage I including a main expansion valve 15 and an evaporator 16, and a branch flow passage II branched from a portion between the condenser 13 and the intermediate supercooler 14 in the refrigerant/oil circulation flow passage I, and after passing the intermediate supercooler 14 through an expansion valve 17 for supercooling, converging, on the discharge side of the first stage screw compressor 11, to an intermediate stage part 18 positioned on the suction side of the two-stage screw compressor 12. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a two-stage screw refrigerator using a screw compressor and a supercooler arranged in series in two stages.

Conventionally, a two-stage screw refrigerator using a screw compressor and a supercooler arranged in series in two stages is known (for example, see Patent Document 1).
JP-A-5-296484

  The screw compressor is an oil-cooled screw compressor that injects oil into the rotor chamber for the purpose of sealing between the rotors, between the rotor and the inner wall surface of the rotor chamber, cooling of the temperature rising part accompanying compression, lubrication, etc. Oil-free screw compressors that do not inject oil into the rotor chamber, are completely cut off from the rotor chamber by a seal, and use synchronous gears to transmit rotational driving force between the male and female rotors. Is done. The structure of the compressor itself is much more complicated than the oil-cooled screw compressor, and the oil-free screw compressor is more complicated than the oil-cooled screw compressor. Thus, the oil-free screw compressor is more expensive because it is more complicated. In addition, the oil-free screw compressor has a larger gap between the rotor and the gap between the rotor and the inner wall surface of the rotor chamber than the oil-cooled screw compressor. Large amount of gas leaks. Therefore, oil-cooled screw compressors are generally used except for special applications where the compressed gas is not allowed to contain lubricating oil and only clean compressed gas is required. No screw compressor is used.

  In the two-stage screw refrigeration apparatus described in the above-mentioned Patent Document 1, although not specified, as is clear from the fact that an oil separator is used, oil-cooled first and second stage screw compressors are used. The refrigerant gas sucked into the first stage screw compressor is compressed by the first stage and second stage screw compressors and then discharged from the second stage screw compressor with oil. Further, the compressed refrigerant gas and oil are separated by an oil separator, and the separated oil is guided to the first stage and second stage screw compressors by an oil flow path provided with an oil cooler. It can be circulated repeatedly.

In the case of the conventional two-stage screw refrigeration apparatus described above, an oil separation and recovery unit, an oil cooler, and an oil pipe for the oil flow path are required, and the ratio of these to the entire volume of the apparatus is large, and the apparatus becomes bulky. In addition to an increase in installation space, the apparatus has a complicated structure, and the cost is increased. In addition, there is a problem that a heavy burden is imposed on maintenance.
The present invention has been made with the object of eliminating such conventional problems, and an object of the present invention is to provide a two-stage screw refrigerator capable of simplifying the structure, reducing the size, reducing the maintenance burden, and the like. .

  In order to solve the above-mentioned problems, the first invention is a refrigerant / oil circulation passage including a first stage screw compressor, a second stage screw compressor, a condenser, an intermediate supercooler, a main expansion valve, and an evaporator. The first stage screw compression is performed after branching from a portion between the condenser and the main expansion valve in the refrigerant / oil circulation flow path, passing through the intermediate supercooler via the supercooling expansion valve. On the discharge side of the machine, a branch flow path that joins the intermediate stage located on the suction side of the second stage screw compressor is provided.

  The second invention is a refrigerant / oil circulation system including a first stage screw compressor, a second stage screw compressor, a condenser, a first stage intermediate subcooler, a second stage intermediate subcooler, a main expansion valve and an evaporator. The first stage intermediate subcooler branches from the flow path and a portion between the condenser and the second intermediate cooler in the refrigerant / oil circulation flow path, and passes through a first stage subcooling expansion valve. A first-stage branch passage that merges with the intermediate stage located on the suction side of the second-stage screw compressor on the discharge side of the first-stage screw compressor, and the refrigerant / oil circulation passage Branching from a portion between the first stage intermediate cooler and the main expansion valve in the first stage, passing through the second stage intermediate subcooler after passing through the second stage subcooling expansion valve, It was set as the structure which provided the 2nd stage branch flow path which joins the gas compression space part in a screw compressor.

  According to the two-stage screw refrigerator according to the first aspect of the present invention, a refrigerant with oil is circulated, and the screw compressor that has been conventionally oil-cooled for the first-stage and second-stage screw compressors. It is possible to use the same structure as the above, and equipment for separating and collecting refrigerant and oil, equipment for cooling the separated oil, piping for repeatedly circulating this oil, etc. There is an effect that it becomes unnecessary and simplification of the structure of the entire apparatus, miniaturization, reduction of maintenance burden, and the like are possible. In addition, when the refrigerant with oil reaches the main expansion valve directly from the condenser and is sent from here to the evaporator, the refrigerant also cools the accompanying oil in addition to cooling the target that needs to be cooled. As a result, the action of cooling the object is reduced, but the two-stage screw refrigerator according to the first invention improves this point. That is, according to this two-stage screw refrigerator, the refrigerant / oil that has exited the condenser is cooled by the intermediate supercooler, then led to the evaporator through the main expansion valve, and the temperature of the oil has already been lowered. Therefore, this oil does not hinder the cooling action by the refrigerant in the evaporator.

  According to the two-stage screw refrigerator according to the second aspect of the invention, in addition to the same as above, since the intermediate supercooler is provided in two stages, the temperature of the oil led to the evaporator is intermediate It is further lowered by the cooler, and the cooling effect by the refrigerant can be further improved.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a two-stage screw refrigerator 1A according to the first invention. The two-stage screw refrigerator 1A includes a first-stage screw compressor 11, a second-stage screw compressor 12, a condenser 13, and an intermediate subcooler. 14, the refrigerant / oil circulation passage I including the main expansion valve 15 and the evaporator 16, and a portion of the refrigerant / oil circulation passage I between the condenser 13 and the intermediate supercooler 14 are branched and supercooled. Branching flow that passes through the intermediate supercooler 14 via the expansion valve 17 and then merges with the intermediate stage portion 18 located on the suction side of the second stage screw compressor 12 on the discharge side of the first stage screw compressor 11 Road II.

  In the two-stage screw refrigerator 1A having the above-described configuration, the oil-containing refrigerant is compressed by the first-stage screw compressor 11 and the second-stage screw compressor 12, and heat is removed from the condenser 13 by heat exchange. On the way from the condenser 13 to the intermediate supercooler 14, the condensed refrigerant part including oil is branched into the branch channel II. The refrigerant containing the oil that has been diverted is squeezed and expanded through the supercooling expansion valve 17, and the temperature is lowered and the gas-liquid mixed state is passed through the intermediate subcooler 14. The refrigerant containing oil in the refrigerant / oil circulation passage I passing through the refrigerant is cooled and flows into the intermediate stage 18.

  On the other hand, the refrigerant containing the refrigerant in the oil circulation passage I cooled by the intermediate supercooler 14 is expanded through the main expansion valve 15 to further decrease in temperature and become a gas-liquid mixed state. 16, the evaporator 16 removes heat from the surroundings, returns to the first stage screw compressor 11 in a gas state, repeats the same state change as above, and circulates.

  FIG. 2 is a p (pressure) -i (enthalpy) diagram showing the state change of the refrigerant circulating in the two-stage screw refrigerator 1A shown in FIG. 1, a so-called Mollier diagram, and each alphabet (ag) shown in FIG. The state of the refrigerant at the position of) corresponds to the state indicated by the alphabet of the same sign in FIG. In addition, as an example, specific temperatures and pressures of the refrigerant in the two-stage screw refrigerator 1 </ b> A at several places in the pi diagram are shown.

  As shown in the figure, in the two-stage screw refrigerator 1A, the refrigerant containing the oil before reaching the evaporator 16 is first cooled from 40 ° C. to −15 ° C. by the intermediate supercooler 14, and the refrigerant is further supplied to the main expansion valve. 15, the temperature is lowered to -60 ° C. Considering the case where the intermediate supercooler 14 is not provided, the refrigerant needs to be cooled from 40 ° C. to −60 ° C. at the same time as cooling the refrigerant from 40 ° C. to −60 ° C. by the main expansion valve 15, The enthalpy of the refrigerant that is throttled and expanded by the main expansion valve 15 to become a gas-liquid mixed state is considerably increased. That is, in the process where the refrigerant passes through the main expansion valve 15, it is necessary to significantly reduce the temperature of the oil, so that the refrigerating capacity of the evaporator 16 with respect to the surroundings by the refrigerant is greatly reduced. On the other hand, in the two-stage screw refrigerator 1A, the intermediate supercooler 14 has already cooled the refrigerant containing oil to −15 ° C., so the main expansion valve 15 uses −15 The temperature difference is reduced from ℃ to -60 ℃. Therefore, the amount of heat that the refrigerant takes from the oil for cooling the oil in the main expansion valve 15 can be reduced, and the refrigerating capacity in the evaporator 16 is improved as compared with the case where the intermediate supercooler 14 is not provided.

For example, if the theoretical stroke volume of the first stage screw compressor 11 is 100 m ³ / hr and the volumetric efficiency is 0.8, the intermediate subcooler 14 is not provided and the branch flow path II joined to the intermediate stage portion 18 is provided. As compared with the case where only the expansion valve is interposed, as shown in FIG. 1, when the intermediate supercooler 14 is provided, more precisely, when the branch flow path II and the supercooling expansion valve 17 are further provided. The refrigerating capacity is improved by about 3% when the oil is contained by 3% by weight with respect to the refrigerant, and is improved by about 5% when the oil is also contained by 5% by weight.

  Further, in this two-stage screw refrigerator 1A, a working fluid that circulates a refrigerant containing oil is used, and an oil separation and recovery device, an oil cooler, an oil filter, and oil pipes for oil circulation including these are conventionally used. Equipment and piping that have been a factor in the volume of the entire device, an increase in the installation area, and an increase in cost are no longer necessary, and the structure is simplified. Further, along with this, in the two-stage screw refrigerator 1A, no oil-related maintenance, which has conventionally required considerable labor, is required.

FIG. 3 shows a two-stage screw refrigerator 1B according to the second invention. In this two-stage screw refrigerator 1B, parts common to the two-stage screw refrigerator 1A shown in FIG. The description is omitted.
In the two-stage screw refrigerator 1B, a first-stage intermediate subcooler 14x and a second-stage intermediate subcooler 14y are provided between the condenser 13 and the main expansion valve 15. As in the case of the intermediate subcooler 14 in FIG. 1, the first-stage intermediate subcooler 14x branches from the refrigerant / oil circulation flow path I between this and the condenser 13 to expand the first-stage subcooler 14x. The first-stage branch flow path IIx through which the valve 17x is interposed passes, and the first-stage branch flow path IIx is connected to the intermediate stage portion 18. Further, the second stage intermediate subcooler 14y branches from the refrigerant / oil circulation flow path I between this and the first stage intermediate subcooler 14x, and a second stage subcooling expansion valve 17y is interposed therebetween. The installed second stage branch channel IIy passes,
The second-stage branch flow path IIy communicates with a gas compression space that does not communicate with any part of the suction process and the discharge process of the first-stage screw compressor 11.

  In the two-stage screw refrigerator 1B configured as described above, the refrigerant containing oil in the refrigerant / oil circulation passage I is cooled by the first-stage intermediate subcooler 14x and further cooled by the second-stage intermediate subcooler 14y. Thus, as described below, the load for cooling the oil by the main expansion valve 15 is reduced, and the refrigerating capacity of the evaporator by the refrigerant is further improved.

  FIG. 4 is a Mollier diagram showing the change in state of the refrigerant circulating in the two-stage screw refrigerator 1B shown in FIG. 3, and the state of the refrigerant at each alphabet (a to j) position in FIG. The state indicated by the alphabet of symbols corresponds. In addition, as an example, specific temperatures and pressures of the refrigerant in the two-stage screw refrigerator 1B at several places in the pi diagram are shown.

  As shown in the figure, in the two-stage screw refrigerator 1B, the refrigerant containing the oil before reaching the evaporator 16 is first cooled from 40 ° C. to −15 ° C. by the first stage intermediate subcooler 14x, and further the second Cooling is performed from −15 ° C. to −35 ° C. by the stage intermediate subcooler 14 y, and the temperature of the refrigerant is lowered to −60 ° C. by the main expansion valve 15. When this two-stage screw refrigerator 1B is compared with the above-described two-stage screw refrigerator 1B, the temperature of the refrigerant containing gas on the primary side of the main expansion valve 15 is as low as −20 ° C. in this two-stage screw refrigerator 1B. Thus, the temperature drop reduces the load for reducing the temperature of the oil by the refrigerant in the main expansion valve 15, and the refrigerating capacity of the refrigerant in the evaporator 16 is improved accordingly.

For example, if the theoretical stroke volume of the first stage screw compressor 11 is 100 m ³ / hr and the volumetric efficiency is 0.8, the first stage intermediate subcooler 14x and the first stage intermediate subcooler 14y are not provided. Similar to the above, as shown in FIG. 3, the first stage intermediate subcooler 14x and the first stage intermediate subcooler are compared with the case where only the expansion valve is provided in the branch flow path that joins the intermediate stage portion 18. When 14y is provided, more precisely, when the first stage branch flow path IIx, the first stage subcooling expansion valve 17x, the second stage branch flow path IIy, and the second stage subcooling expansion valve 17y are further provided. The refrigeration capacity is improved by about 4% when the oil is contained by 3% by weight with respect to the refrigerant, and is improved by about 6.6% when the oil is also contained by 5% by weight.

  Similarly to the above, this two-stage screw refrigerator 1B also has a working fluid that circulates a refrigerant containing oil, an oil separator / recoverer, an oil cooler, an oil filter, and an oil pipe for oil circulation that includes these. The equipment and piping that have been the cause of the increase in the overall volume of the conventional apparatus, the installation area, and the cost increase are eliminated, and the structure is simplified. Further, along with this, even in the two-stage screw refrigerator 1B, no oil-related maintenance that has conventionally required considerable effort is required.

  The configurations of the intermediate supercooler 14, the supercooling expansion valve 17, and the branch flow path II in the two-stage screw refrigerator 1A are as follows from the refrigerant / oil circulation flow path I of the branch flow path II as shown in FIG. This branch portion may be the secondary side of the intermediate supercooler 14 and a supercooling expansion valve 17 may be interposed between the branch portion and the intermediate cooler 14 in the branch flow path II. Configuration of first stage intermediate subcooler 14x, first stage subcooling expansion valve 17x, and first stage branch flow path IIx, second stage intermediate subcooler 14y, second stage subcooling expansion valve 17y, Similarly to the configuration of the second stage branch flow path IIy, the branch point may be the secondary side of the first stage intermediate subcooler 14x and the second stage intermediate subcooler 14y.

In addition, the specific numerical value regarding the temperature and the pressure given in the said description and drawing is an example, and this invention is not limited to these numerical values at all.
Further, the amount of oil contained in the refrigerant is such that the decrease in heat transfer efficiency in the evaporator 16 due to this oil can be ignored in practice, and specifically, the upper limit is 5% by weight of the refrigerant.

It is a figure which shows the whole structure of the two-stage screw refrigerator which concerns on 1st invention. It is a Mollier diagram which shows the state change of the refrigerant | coolant in the two-stage screw refrigerator shown in FIG. It is a figure which shows the whole structure of the two-stage screw refrigerator which concerns on 2nd invention. It is a Mollier diagram which shows the state change of the refrigerant | coolant in the two-stage screw refrigerator shown in FIG. It is a figure which shows another form of the part of the intermediate | middle supercooler in the two-stage screw refrigerator shown in FIG.

Explanation of symbols

1A, 1B Two-stage screw refrigerator 11 First-stage screw compressor 12 Second-stage screw compressor 13 Condenser 14 Intermediate subcooler 14x First-stage intermediate subcooler 14y Second-stage intermediate subcooler 15 Main expansion valve 16 Evaporator 17 Supercooling expansion valve 17x First stage supercooling expansion valve 17y Second stage supercooling expansion valve 18 Intermediate stage
I Refrigerant / oil circulation passage
II Branch channel
IIx First stage branch flow path
IIy 2nd stage branch flow path

Claims (2)

A refrigerant / oil circulation passage including a first stage screw compressor, a second stage screw compressor, a condenser, an intermediate supercooler, a main expansion valve and an evaporator;
The first-stage screw compressor is branched from a portion between the condenser and the main expansion valve in the refrigerant / oil circulation flow path, passes through the intermediate supercooler through the supercooling expansion valve, and then passes through the intermediate supercooler. A two-stage screw refrigerator having a branch flow path that joins an intermediate stage located on the suction side of the second-stage screw compressor on the discharge side. A refrigerant / oil circulation passage including a first stage screw compressor, a second stage screw compressor, a condenser, a first stage intermediate subcooler, a second stage intermediate subcooler, a main expansion valve and an evaporator;
After branching from a portion between the condenser and the second intermediate cooler in the refrigerant / oil circulation flow path, passing through the first stage intermediate subcooler via the first stage subcooling expansion valve A first-stage branch channel that joins an intermediate stage located on the suction side of the second-stage screw compressor on the discharge side of the first-stage screw compressor;
Branches from a portion between the first stage intercooler and the main expansion valve in the refrigerant / oil circulation flow path, passes through the second stage intermediate subcooler via the second stage subcooling expansion valve. After that, a two-stage screw refrigerator comprising a second-stage branch flow path that joins the gas compression space in the first-stage screw compressor.

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