RU2547344C2 - Cascade refrigerating unit - Google Patents

Abstract

FIELD: heating.

SUBSTANCE: invention can be used in conditioning systems, in food and chemical industry. Cascade refrigerating unit with different work media of cascades consists single-stage machines referred to as the bottom and the top cascade legs and connected by a common condenser evaporator, and includes compressors, heat exchangers, thermoinsulated frost accumulator. Top cascade leg is open and uses R718 work medium (water or aqueous solutions of salts) replenished from outside as frost carrier, where minor part of water is evaporated to remove total heat input, vacuumised condenser evaporator is connected to vacuum pump for water vapour removal to ambient environment. Bottom cascade leg is open and uses ambient air, and/or is closed, and condensers of bottom cascade leg are positioned inside the vacuumised evaporator of top cascade leg condenser.

EFFECT: stable operation of cascade refrigerating unit regardless of ambient temperature.

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Description

The invention relates to refrigeration and can be used in air conditioning systems, in the food and chemical industries.

The objective of the present invention is to eliminate the dependence of the functioning of the cascade refrigeration unit on the temperature of the external environment when heat is removed therein, to substantially reduce the amount of industrial refrigerants used in it while increasing the environmental friendliness and thermodynamic efficiency of the cascade refrigeration unit, and to reduce the consumption of external work for the unit drive.

The level of technology.

Known refrigeration cascade unit with various working substances, consisting of two single-stage refrigerators with closed refrigerant circuits, called the lower and upper branch of the cascade and combined by a common condenser-evaporator. The low pressure working medium is used in the lower branch of the cascade, which receives heat from a low temperature source in the evaporator of its closed circuit and boils, steam is compressed in the compressor and sent to a common condenser-evaporator, where it is condensed. The condensation heat of the working substance of the lower branch of the cascade is taken away by the working substance of the refrigerating machine of the upper branch of the cascade, as a rule, by the medium pressure medium, which boils in a condenser-evaporator. Vapors of the working substance of the upper branch of the cascade are compressed by the compressor with an increase in their temperature potential above similar values in the external environment, after which the heat of this cascade is transferred to the surrounding air to air or water through heat transfer (N.N. Koshkin, I.A. Sakun, E. M. Bambushek and other Refrigerators, L., Mechanical Engineering, 1985, p. 91-96).

Known refrigeration unit containing two refrigerant circuits, with the first and second circuits equally containing each - compressor, condenser, evaporator and liquid refrigerant separator. As a cold accumulator of the second - upper circuit (cascade), a container with a liquid that accumulates cold (for example, water) is used, through which a heat exchanger of the second circuit is passed. Depending on the external conditions and the state of the installation, the automatic control system displays it for the necessary operating modes, such as parallel operation of both circuits, air conditioning with cold storage, only cold storage, only the primary circuit, only the secondary circuit (US Patent 5323618).

The closest in essence is a refrigeration unit containing a closed circuit (cascade) of refrigerant, in which a compressor, a condenser, a heat exchanger, a throttle valve and three parallel evaporators are installed in series, the second and third evaporators being made in the form of technological and operating cold accumulators (RF Patent 2199706, IPC ₆ F25B 5/02. - Bull. No. 6, 02.27.2003).

The disadvantages of these devices include the dependence of the temperature of condensation of the refrigerant and the temperature of the liquid refrigerant in the upper cascade from changes in the temperature parameters of the external environment during the year to plus or minus 400% or more with respect to the average annual temperature in ° C, the need to regulate the working conditions of the refrigeration installations in such a wide annual range of atmospheric temperatures, accompanied by a significant pressure spread in the cascade from 4 to 12 bar for most of industrially used refrigerants, the multi-stage conversion of the extracted heat energy with an intermediate storage device, which is accompanied by losses and reduces the efficiency of the heat extraction system as a whole, the significant design complexity due to its inherent versatility, the required temperature return of closed sections of the circuits of each cascade to a certain range of their parameters in the beginning of the cycle, which reduces the thermodynamic efficiency of the refrigeration unit.

Disclosure of invention

The proposed device is based on the predominant use of universally available natural substances - water and air as environmentally friendly refrigerants coming from the natural environment and returned to it when the open circuits of the upper and lower cascades are realized in a refrigerator. The device is a synergistic system, being in its composition open dynamic and nonequilibrium, which exchanges energy with the environment without achieving thermal balance with it.

Distinctive features of the claimed technical solution from the prototype:

the use of rarefaction in the entire internal space of the evaporator-condenser, complete independence from the temperature parameters of the surrounding environment, an increased degree of environmental friendliness due to the use of water and air as refrigerants, an increase in the thermodynamic efficiency of the refrigerating cascade unit as a whole due to the use of the most thermodynamically advantageous and affordable substance - water , exclusions of intermediate heat transfer stages and the use of open cascades allowing Referring without creating additional costs in devices with them additional energy for each circuit branch in the reverse cascade refrigeration cycle. The determining conditions for the stable operation of the proposed refrigeration cascade refrigeration unit with an open cascade branch (open loop) is atmospheric pressure with a deviation range of plus or minus 2% of its average annual value and a difference strictly within 1 bar in the upper open cascade branch.

The synergetic super-cumulative effect in the proposed device is determined by the fact that a small part of the mass of the environmentally friendly working fluid of the upper cascade (an insignificant reason) is used in the energy-intensive phase transformation of the first kind by self-evaporation of small amounts of water due to the reduction of pressure below atmospheric to the boundary values between low and medium vacuum. Due to the redistribution of pressure with a decrease in the range from 100 to 0.1 kPa by means of a vacuum pump, to which mechanical work is applied externally, in addition to the mass transfer small-scale phenomenon (causes), a much more intense energy component of spatial inhomogeneity is realized in one of the objects of the cascade installation (evaporator) -capacitor), which creates an artificial temperature inhomogeneity, as a driving force in other objects of the installation - the lower branches of the cascade, the system as a whole. The numerical ratio of the evaporated mass of water 0.1 kg / s (cause) and the corresponding heat output of 250 kW heat removal (effect), as a unidirectional process, without the need to close the cycle with returning to the starting point of temperature indicators, confirms the presence of a synergistic effect of the specified energy transfer with naturally reduced by 20% energy consumption from the outside to the process.

The invention is illustrated by figures 1 and 2. In figure 1. shows a schematic diagram of a cascade refrigeration unit with accumulation of a cold reserve in the upper cascade; figure 2 in a single scale combined T-S chart for water, air and ammonia (R718 and R717) shows the display of heat removal in the upper and lower branches of the cascade refrigeration unit;

According to the circuit diagram (Fig. 1.), the upper open cascade of the installation contains a vacuum pump 1, a check valve 2, a sealed thermally insulated evaporator-condenser 3, in which a condenser of the lower open pneumatic cascade 11 and a condenser of the vapor compression cycle 24 are located. a cascade of water, or a water-salt solution, fills a thermally insulated storage tank 4, communicating with the atmosphere, a shut-off and control valve 5 provides a supply of a working fluid to the evaporator-condenser 3. About emny pump 6 with a check valve 7 after the return line are cooled working fluid - water in storage tank 4. refed pipe supplying purified water 8 intended to compensate for the decreasing amount of the working fluid - water during operation of the upper stage.

The lower open pneumatic cascade includes an air filter 9, a pneumatic compressor 10, a condenser of moisture in the compressed air 11, a moisture separator 12, a safety valve 13 for venting excess air over a predetermined value, a condensate drain 14, a non-return valve 15, and shut-off and control valves for drained cold air 16 and 17, the aerodynamic wave resonance tube of the static type 18, the vortex tube 19.

The lower closed branch of the cascade with a vapor compression cycle has a heat exchanger-evaporator 22 in the process, a compressor 23, a condenser 24, which is located inside the evaporator-condenser 3, a choke 25 on the line of liquid refrigerant.

Cascade refrigeration works as follows.

The upper open branch of the cascade: turn on the vacuum pump 1 and create a vacuum in a thermally insulated evaporator-condenser 3 to a value of the residual absolute pressure in it from 500 to 100 Pa (from 3.8 to 0.8 Torr). Water from a thermally insulated storage tank 4 is supplied to the evaporator-condenser 3 due to the pressure difference created by the vacuum pump outside and inside it, through a shut-off-control valve 5. Once in the evacuated space of the evaporator-condenser 3, water boils in the entire volume with the formation of low-temperature water vapor, which is accompanied by intensive heat removal from water in an amount of from 2500 to 2540 kJ / kg of water vapor obtained, while the temperature of the supplied amount of water drops sharply. Water vapor is removed by a vacuum pump 1 from the evaporator-condenser 3 into the atmosphere, regardless of its temperature indicators. Thus, a well-known physical phenomenon is realized - water cooling due to self-evaporation of its part up to the formation of fine-crystalline ice with crystals from 10 to 25 microns and obtaining a fluid ice-water suspension - binary ice. Cooled water and / or ice-water suspension is pumped from the evaporator-condenser 3 by a volumetric pump 6 into the storage tank 4, which creates a reserve of cold to cover the emerging peak demand for it. The consumed part of the water is replenished by supplying the required amount to the storage tank 4 through the pipe 8, and the added water is pre-purified to the desired low salt content.

Bottom open branch of the cascade. Turn on the compressor 10, pump 20 and open the shut-off and control valve 21. The air acting as a working fluid in the open lower stage is taken from the atmosphere through a filter 9. Compressed air having an elevated temperature after being compressed by the compressor is sent through a cooler-condenser 11, placed inside the evaporator-condenser 3, where they carry out the selection of cold water from the upper cascade, which is supplied by the pump 20 in an amount controlled by a shut-off and control valve 21. The heated water leaving the condenser 11 to the evaporator-condenser 3, partially immediately evaporate, with the removal of water vapor by the vacuum pump 1 of the upper stage. Compressed air is cooled in the process of heat removal to a temperature below the point of loss of moisture in it - condensate. Cooled air together with the condensate is supplied under pressure to the condensate separator 12, from where the condensate is removed through the steam trap 14 to the storage tank 4 due to the increased air pressure after the compressor 10, which exceeds the pressure of the atmosphere and the liquid column in the storage tank. Dried air under pressure is used to produce cold at the place of technological need for it by expanding this air to atmospheric pressure, which is accompanied by a significant decrease in temperature in the cold air supply zone. Depending on the required temperature values in places of cold supply, either a static type 18 aerodynamic resonant wave tube is used that implements the Hartmann-Sprenger effect with the removal of excess heat from its outer walls directly into the cold water of the storage tank 4, or a vortex tube 19 with separation of the supplied air into hot and cold streams, where the temperature of the cold stream is reduced to minus 60 ° C and below. To this end, the corresponding shut-off and control valves 16 and 17 are opened on the pneumatic line.

The lower closed branch of the cascade with a vapor compression cycle. They include a compressor 23 that draws in refrigerant vapor from an evaporator 22 installed in the production line. The vapor is compressed with a simultaneous increase in temperature, after which the compressed refrigerant vapor is sent to the condenser 24, which is placed in the evaporator-condenser of the upper cascade 3. To carry out the condensation process, cold water from the thermally insulated storage tank 4 is pumped to collect heat from the refrigerant vapor into the condenser 24 by pump 26 through a check valve 27, which passes the required amount of water. The insulated water leaving the condenser 24 into the evacuated space of the evaporator-condenser 3 and absorbing the heat of the circulating refrigerant is partially evaporated in the evaporator-condenser 3, water vapor is removed into the atmosphere by the vacuum pump 1 of the upper cascade. The refrigerant liquefied as a result of heat removal from it is supplied from the condenser 24 through the choke 25 to the evaporator 22, where the refrigerant is evaporated during the absorption of heat from the flows of the processed product of the technological production line.

According to the considered (figure 2) cascade mode of operation of the refrigeration unit in the combined T-S diagram for water (R718), air and ammonia (R717), interconnected processes are implemented in it as follows. Water vapor in the upper branch of the cascade with the initial state (point 2) is pumped out of the common evaporator-condenser by a vacuum compressor (process 2-1) and compress them (process 2-3) to a value above atmospheric pressure, which allows water vapor to be released into the atmosphere regardless of its temperature. By pumping out water vapor, the temperature in the common evaporator-condenser is lowered to 0 ° С and maintained by the first-order phase transition, which also ensures the temperature difference between the compressed refrigerant vapor of the lower cascade and the temperature of their condensation in the common evaporator-condenser. By means of evacuation, a temperature-related driving force is generated, which contributes to the removal of heat from the lower cascade. The mass consumption of water for evaporation and removal to the atmosphere is compensated by adding water to the storage tank from an external source (process 4-1), the amount of salts dissolved in it is previously reduced to the required value.

The processes carried out in the lower open branch of the cascade of the refrigeration unit using air are shown in FIG. 2 as follows: intake of atmospheric air at plus 20 ° C and its compression by the compressor to plus 90 ° C are shown by line 5-6. Air cooling with water and / or an ice-water mixture with condensation of the moisture contained in it occurs according to line segment 6-7. The expansion of air in a static-type aerodynamic resonant wave tube is reflected by line 7-8, and the separation of air in a vortex tube into cold and hot flows is shown by lines 7-9 and 7-10, respectively.

The processes of the lower branch of the cascade operating in a standard closed vapor compression cycle are shown in FIG. 2 as follows. The refrigerant vapor of the lower branch of the cascade (point 12) obtained when it absorbs process heat from the product being processed (line 11-12) is compressed by a compressor, which is reflected by line 12-13, and liquefied in a condenser located inside the evaporator-condenser (process along the line 13-14-15) at a temperature near zero, then the liquid refrigerant is throttled (process 15-11) and sent for evaporation to the process at point 11. This closes the cycle of the lower branch of the cascade of the refrigeration unit. The processes on the line 13-14-15-11 are aimed at returning the parameters of the refrigerant to its original state before the useful main working process.

When the lower branch of the cascade of the refrigeration unit is completely turned off, the upper branch of the cascade provides accumulation of cold in the form of ice water (ice suspension) in a thermally insulated storage tank as follows. When the vacuum compressor is turned on and there is no heat influx in the common evaporator-condenser from the lower branch of the cascade, the water in the common evaporator-condenser continues to be cooled (line 2-1) without heat influx from the outside, while a second phase transition of the first kind is observed in it with the appearance of ice crystalline suspensions (binary ice). This suspension is continuously pumped into a thermally insulated storage tank, thereby increasing the potential of the cold stored in it, and cooling water is continuously withdrawn from the tank in the same volume to the stage of obtaining an ice-cold crystalline suspension.

The technical result of the proposed device is:

- the stability of the refrigeration cascade installation, regardless of the external temperature conditions of the environment due to the use of an open refrigeration process of the upper branch of the cascade with a determining indicator of its work in atmospheric pressure in the deviation range of plus or minus 2% of the average annual atmospheric pressure in the area,

- increasing the thermodynamic and economic efficiency of heat removal due to the use of water as the working fluid of the upper branch of the cascade with two phase transformations of the first kind and the absence of the need to return the parameters of the working fluid to the beginning of the cycle,

- the preservation of environmental environmental indicators, mainly due to the use of environmentally friendly water and air in the upper and lower branches of the cascade, while significantly reducing the presence of industrially produced refrigerants in the cascade installation,

- reduction of specific energy consumption in the refrigeration cascade installation as a whole due to stabilization of the condensation temperature of the lower branch of the cascade at a level of plus 5 ° C plus or minus 2 ° C with a corresponding stabilization of the condensation pressure in it at lower pressures and temperatures,

- the lack of need for the upper branch of the cascade of the installation in the use of such a heat exchange structure as a cooling tower, in which biological fouling of open surfaces is observed over time,

- improving the operational safety of the cascade refrigeration unit,

- simplification of automation of the cascade refrigeration unit by reducing the number of adjustable heat transfer parameters and eliminating the dependence of the working process in the upper branch of the cascade on the temperature parameters of the external environment.

The technical result is achieved due to the fact that in a refrigerating cascade installation with various working substances of cascades, consisting of single-stage machines, called the lower and upper branches of the cascade with compressors, heat exchangers, a thermally insulated cold accumulator and combined by a common evaporator-condenser, the upper branch of the cascade is made open with the use of R718 working fluid replenished from the outside - water or aqueous solutions of salts as a coolant, with the evaporation of a small part of the water for the total heat influx, the evacuated evaporator-condenser is connected to a vacuum pump to remove evaporated water vapor from it into the environment, the lower branch of the cascade is open using atmospheric air and / or closed, and the condensers of the lower branch of the cascade are placed inside the evacuated evaporator - capacitor of the upper branch of the cascade.

The positive effect of the use of the device is determined by the preservation of environmental indicators of the environment, the increase in thermodynamic and economic efficiency of heat removal due to the use of water as the working fluid of the upper branch of the cascade with two first-order phase transformations and the absence of the need to return the working fluid parameters to the beginning of the cycle, reducing specific energy costs by drive to the operation of the cascade refrigeration unit up to 25%, excluding external temperature restrictions on the heat process swapping.

The implementation of the invention is possible with the use of industrially produced equipment and other components of technical refrigeration systems, massively present in the market of engineering products.

Claims (1)

Cascade refrigeration unit with various cascade working substances, consisting of single-stage machines called the lower and upper cascade branch and combined by a common evaporator-condenser, including compressors, heat exchangers, a thermally insulated cold accumulator, characterized in that the upper cascade branch is made open using replenished in it from the outside of the working fluid R718 - water or aqueous solutions of salts as a coolant, with the evaporation of an insignificant part of water to remove the total heat gain s, a vacuum evaporator-condenser is connected to a vacuum pump to remove vapor of evaporated water from it into the environment, the lower branch of the cascade is open using atmospheric air and / or closed, and the condensers of the lower branch of the cascade are placed inside the vacuum evaporator-condenser of the upper branches of the cascade.

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