KR100572822B1 - Air refrigerating cycle - Google Patents

Abstract

The present invention relates to an air refrigeration cycle using a turbomachine, and in particular, the air refrigeration cycle according to the present invention includes a centrifugal compressor for sucking, compressing, and discharging air; An intermediate cooler configured to heat exchange air discharged after being compressed by the centrifugal compressor; A recovery heat exchanger for exchanging the air passing through the intermediate cooler with the air flowing out of the freezing chamber; A centrifugal turbine installed on the same shaft as the centrifugal compressor to expand air passing through the recovery heat exchanger; A motor installed on the same shaft connecting the centrifugal compressor and the old core turbine; An inverter connected directly to the motor to increase the rotation speed; And it is characterized in that the low-temperature air from the old core turbine is introduced, and the freezing chamber is discharged after a certain time, the air flowing out of the freezing chamber is circulated back to the centrifugal compressor through the recovery heat exchanger.

Turbomachinery, centrifugal compressors, centrifugal turbines, inverters, air bearings, heat exchangers

Description

Air Refrigeration Cycle

1 is a view showing a first embodiment of a conventional general air refrigeration cycle,

2 is a view showing a second embodiment of a conventional general air refrigeration cycle,

3 is a view showing the shape of the centrifugal compressor and the old core turbine of the air refrigeration cycle according to the present invention,

4 is a view showing an embodiment of an air refrigeration cycle according to the present invention,

5 is a view showing a thermodynamic state of the air refrigeration cycle according to the present invention.

<Description of Symbols for Main Parts of Drawings>

1: centrifugal compressor 2: old core turbine

3: motor 3a: stator

3b: rotor 4: inverter

5: Intercooler 6: Recovery Heat Exchanger

7: freezer 8: air journal bearing

9: air thrust bearing 13: motor

14: Gearbox 15: Oil Separator

16: heat exchanger 17: blower

The present invention relates to an air refrigeration cycle using a turbomachine, and more particularly, to configuring a low temperature freezing compartment through compression and expansion of air using a centrifugal compressor and a centrifugal turbine.

Currently, the world is gradually tightening energy use regulations due to global warming, and due to factors such as the reduction of atmospheric ozone layer by using Freon refrigerant, technology development is actively used to utilize natural refrigerant rather than current Freon refrigerant. It is developing.

Natural refrigerants include hydrocarbon-based methane, ethane, propane, butane, isobutane, propylene, ammonia (NH ₃ ), carbon dioxide, and air.

In these cases, the hydrocarbon series is composed of carbon and hydrogen only, which is not toxic, chemically stable, and has a low global warming index (GWP) of 3, which makes it appear to be a good natural refrigerant but has a high flammability, which is a disadvantage. , Ammonia (NH ₃ ) is a refrigerant with excellent thermodynamic properties and relatively high efficiency, but it is fatally toxic, highly flammable, and has a high operating pressure and requires special management.In the case of carbon dioxide (CO ₂ ), it is not toxic, flammable and stable. Although it is an excellent refrigerant, its low critical temperature (31 ° C) makes it difficult to access technically because of the trans-critical cycle of condensation (cooling) at super-critical pressure and evaporation at sub-critical pressure.

Therefore, the use of air as a natural refrigerant in these fields is considered to be the most suitable for low temperature refrigeration systems (below -40C), because it has a higher coefficient of performance (COP) and no toxicity or flammability than the use of freon refrigerant.

In other words, the refrigeration cycle using air is efficient and environmentally friendly in terms of energy utilization, and is expected to be very useful in livestock and fisheries.

The study on the configuration of the air refrigeration cycle has already been done in the United States and Japan.

From 1995 to 1999, Air Products & Chemicals, Inc. of the United States was founded by NIST, a division of the US Commerce Department Technology Administration. With the support of the National Institute of Standards and Technology, the company developed and completed the Closed Cycle Air Refrigeration (CCAR), the first commercial system to enable refrigeration and refrigeration for food storage and chemical plants.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the said CC. In Figure 1, the freezing load of the cycle is 175 kW, about 50 frozen tons (RT) to keep the warehouse at -73 ℃, compress the air to about 88 bar (COP), the coefficient of performance (COP) is about 0.6 This cycle is very useful when rapid freezing is required to maintain food quality. However, the speed increase gear 14 is used as a component in the case of the cycle.

In 1996, Kajima Co. Ltd., in Japan, collaborated with three other companies to produce air, cooling, refrigeration, and freezing of foods using air cycles (AIRS; AIr Refrigerant). System).

2 shows a configuration diagram of the AILS.

It is selling three models with refrigeration and freezing loads of 7kW (2RT), 16kW (5RT) and 25kW (7RT). The temperature in the warehouse is based on -30 ℃ and the COP is about 0.55 ～ 0.60 level.

This is a typical bootstrap cycle that is still used for air conditioning in aircraft. It adopts a heat recovery recuperator to increase efficiency and features a low pressure system with a pressure level lower than 2 kgf / ㎠. to be.

In addition, a speed increase gear (not shown) is used for the blower 17 used as the first stage compressor. The oil separator 15 is used to separate the oil mixed in the air in the cycle.

In the case of domestic technology, in recent years, we have entered the development of aircraft air conditioning systems (ECS) using air cycles in connection with government-led aircraft development projects (KTX-1, KTX-2, and medium-sized aircraft development projects). We developed and developed air cycle design technology for aircraft centering on Aerospace Research Institute (KARI) and National Defense Research Institute (ADD), but we have prepared the prototype and performed the performance test after the imitation design through disassembly and analysis of overseas products. Could not escape. This was due to the lack of design and manufacturing technology for air-to-air heat exchangers, as well as the lack of design and manufacturing technology for products such as high-speed centrifugal compressors and centrifugal turbines.

In other words, it is no exaggeration to say that the development of applications to industrial refrigeration, refrigeration, and cooling equipment using air cycles has never been made in Korea.

Anyway, in the case of the embodiment of the conventional low temperature freezing chamber through the compression and expansion of the air using the centrifugal compressor and the centrifugal turbine shown in Figs. 1 and 2 described above, all the methods of increasing the RPM using the gearbox are used. . The disadvantage of this method is that the gearbox is an expensive workpiece and causes vibration and high maintenance costs. In addition, since all the mechanical losses generated are converted to heat, the lubricating oil must be circulated and cooled, which is disadvantageous in that it is not environmentally friendly.

In addition, when the gearbox is used, since the initial rising time to reach the steady state is long, it is impossible to use the air bearing, and to bypass the cooling load, it is necessary to use a bypass method. Problems will arise.

The present invention is characterized by applying an air bearing to drive the motor directly to the inverter in order to solve the above problems. That is, since the lubricant is not needed, the air supplied to the freezer compartment without waste lubricant is generated and only 100% pure cooling air is supplied.

In addition, since there is no speed increase gear, there is no mechanical loss of coupling part, which contributes to the improvement of efficiency, and significantly reduces vibration and noise.

In order to achieve the above object, the air refrigeration cycle according to the present invention comprises a centrifugal compressor for sucking, compressing and discharging air; An intermediate cooler configured to heat exchange air discharged after being compressed by the centrifugal compressor; A recovery heat exchanger for exchanging the air passing through the intermediate cooler with the air flowing out of the freezing chamber; A centrifugal turbine installed on the same shaft as the centrifugal compressor to expand air passing through the recovery heat exchanger; A motor installed on the same shaft connecting the centrifugal compressor and the old core turbine; An inverter connected directly to the motor to increase the rotation speed; And it is characterized in that the low-temperature air from the old core turbine is introduced, and the freezing chamber is discharged after a certain time, the air flowing out of the freezing chamber is circulated back to the centrifugal compressor through the recovery heat exchanger.

In a preferred embodiment of the present invention, the centrifugal compressor of the hermetic air refrigeration cycle includes an air bearing, so that oil components are not mixed in the air used as the refrigerant, so that a configuration such as an oil separator is unnecessary. do.

In addition, when the centrifugal compressor and the old centrifugal turbine are operated, the proper rotational speed is about 40,000 to 50,000 RPM. The initial time required for such rotational rotation is short so that the air bearings can function properly. This is a characteristic of the air bearing, because when the rotation speed is low at the initial operation, the air oil film does not play a role because the air is not sufficiently introduced between the air bearings.

Therefore, a sure way to solve this problem is to increase the number of revolutions by using an inverter, which increases the initial rising time to reach a steady state rather than increasing the speed by using a conventional gearbox. By reducing the pressure, it is easy to use the air bearings, as well as the variable capacity to suit the desired load, and by-pass method to change the cooling load when using the conventional gearbox It will free you from the hassle of using it.

The air bearings are used as journal bearings and thrust bearings.

3 is a cross-sectional view of a centrifugal compressor and a centrifugal turbine of an air refrigeration cycle according to the present invention. As shown in FIG. 3, the journal bearing 8 and the axial load are supported to support a radial load. Thrust bearing 9 is employed.

For a more preferred embodiment of the present invention, the intercooler 5 of the hermetic air cooling cycle is a water-cooled heat exchanger, and the heat recovery heat exchanger 6 is an air-cooled heat exchanger.

This is because the intermediate cooler aims at reliable heat exchange in a situation where heat exchange is required first.

Hereinafter, the configuration and operation of the air refrigeration cycle according to the present invention will be described in detail by the accompanying drawings.

Figure 4 is a view showing an embodiment of the air refrigeration cycle according to the present invention, the overall configuration is a centrifugal compressor (1) and the old core turbine (2) is connected on the same axis, the shaft is a stator constituting a motor 3a and the rotor 3b are directly connected to the inverter 4 to increase the rotation speed. Thus, the system is simplified compared to the conventional configuration.

The shaft connecting the centrifugal compressor 1 and the centrifugal turbine 2 is supported by the air journal bearing 8 and the air thrust bearing 9 shown in FIG. Compared with the fact that waste lubricant is not generated, as well as no oil component is generated in the air circulating the cycle, the configuration such as the oil separator 15 shown in FIG. 2 is not necessary, thereby simplifying the system configuration. It can be said.

Therefore, the pure air introduced into the centrifugal compressor (1) is compressed and then primarily heat exchanged by water in the intermediate cooler (5), and flows into the old centrifugal turbine (2) installed on one side of the same shaft. The process becomes an expansion process as shown in FIG.

5 is a view showing a thermodynamic state of the air refrigeration cycle according to the present invention, both the temperature and the pressure is lowered in the expansion process.

The expanded air flows into the freezing chamber (7) to cool the food, and then heat exchanges with the compressed air in the recovery heat exchanger (6) to form a closed cycle that is sucked into the centrifugal compressor (1) again. In this way, it is possible to implement an air refrigeration cycle characterized in that the motor 3 is increased and driven directly by the inverter 4, and the centrifugal compressor 1 and the old core turbine 2 are supported by air bearings. And it can be applied to a variety of fields that need refrigeration, such as fisheries.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and the scope of application of the present invention is not limited thereto, and may be appropriately changed within the scope of the same idea.

As described above, the air refrigerating system according to the present invention applies an air bearing and drives a motor directly to an inverter, thereby eliminating the need for lubricating oil, thus eliminating waste lubricants, and supplying only 100% pure cooling air to the freezing compartment. As it is more suitable for storage of food, etc., there is no speed increase gear, so there is no mechanical loss of coupling part, which contributes to the improvement of efficiency and significantly reduces vibration and noise.

Claims (4)

A centrifugal compressor that sucks air, compresses it, and discharges the air; An intermediate cooler configured to heat exchange air discharged after being compressed by the centrifugal compressor; A recovery heat exchanger for exchanging the air passing through the intermediate cooler with the air flowing out of the freezing chamber; A centrifugal turbine installed on the same shaft as the centrifugal compressor to expand air passing through the recovery heat exchanger; A motor installed on the same shaft connecting the centrifugal compressor and the old core turbine; An inverter connected directly to the motor to increase the rotation speed; And Low temperature air from the old core turbine is introduced, and the freezer compartment flows out after a certain time The air-tight cycle, characterized in that the air flowing out of the freezing chamber is circulated back to the centrifugal compressor through the recovery heat exchanger. 2. The hermetic air refrigeration cycle according to claim 1, wherein the centrifugal compressor comprises an air bearing. The closed air cooling cycle according to claim 1, wherein the intercooler is a water-cooled heat exchanger. The closed air cooling cycle according to claim 1, wherein the heat recovery heat exchanger is an air-cooled heat exchanger.

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