RU2718094C1 - Refrigerating plant for production of ice water in plate evaporator - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to devices for producing ice water in plate evaporators of refrigerating plants and can be used in various industries, where it is necessary to use ice water with temperature of 0.1÷0.5 °C. Control of water pressure at inlet of plate evaporator provides protection against freezing of plate evaporator by short-term hot gas bypass to inlet of evaporator, with simultaneous control of cooling capacity of compressor depending on temperature of ice water at outlet of flow evaporator. Heat-insulated mixing tank is connected by means of the bypass pipeline with the ice water tank of the refrigerating unit.

EFFECT: reliable and safe production of water with maximum temperature close to 0 °C.

1 cl, 1 dwg

Description

The invention relates to refrigeration, in particular, to devices for producing ice water with a temperature close to 0 ° C in plate evaporators and is intended for use in various technological processes of the food, chemical and pharmaceutical industries.

Statistics of the refrigeration market show that the demand for ice water is increasing every year, since it most fully meets the hygienic and thermophysical requirements of production processes by technologists - the maximum cooling rate of the product and the biological inertness to it. For intensive cooling, the temperature of ice water should be as close as possible to the freezing temperature. Therefore, the temperature of ice water is the most important characteristic of such refrigeration units. For poultry processing and food production, the lower the temperature of ice water entering the cooling line, the higher the product quality and higher labor productivity.

Ice water is obtained in refrigeration units, using heat exchangers-evaporators of open and closed types for cooling water. The simplest type of open heat exchanger is an evaporator made in the form of a construction of pipes or flat panels, immersed in a thermally insulated tank filled with water. A refrigerant boiling inside the tubes or panels with a temperature of -10 ÷ -8 ° C cools the liquid in the tank, and ice forms on the outer surface of the tubes and panels. To intensify heat transfer, the liquid in the tank is forcedly mixed either with a mechanical stirrer or with air supplied to the lower part of the tank, which causes mixing. The water in the tank, in contact with ice, is cooled to a temperature of 1-2 ° C, after which it enters the consumer. A device for producing ice water with a panel-type ice accumulator is described on p. 120-123, fig. V-15 in the book "Various Applications of the Cold," ed. Agropromizdat, Moscow, 1986, and also in the patent SU 1794235 MKI 5 F25D 3/00 under the name "Device for cooling milk", and.with. 1346923 MKI 4 F25U 3/00, 7/00 1986, SU and many other publications. Installations for the production of ice water on ice accumulators are widespread due to their simplicity of design. Their disadvantages are significant specific energy consumption per 1 kW of cold and very large dimensions and metal consumption.

In the device for cooling milk on the farms of the North (patent RU 2132521), ice water is obtained in a battery - an ice heat exchanger, where ice accumulated during the winter period and atmospheric air during the cold season serve as a source of cold. The heat exchanger itself - the battery is made in the form of two cavities separated by a partition with holes. The upper cavity is for loading ice, the lower cavity is for collecting chilled water from which this water enters the consumer. Although with this scheme, the specific energy consumption of the chiller is noticeably reduced, its main drawback is its geographic attachment to the northern regions, since both ice and water are produced due to cold climatic conditions, so it is not widespread.

Another type of refrigeration units for producing ice water are units with open evaporation panels, the so-called film evaporators, in which the cooling of water to temperatures close to + 1 ÷ 2 ° C is achieved by draining a thin layer of water with a temperature of + 5 ÷ 6 ° C supplied from above to these evaporative panels. Water from the consumer is supplied to the tank located above the battery of flat evaporation panels. Water flows uniformly from the tank through vertically arranged evaporation panels having a negative temperature due to boiling inside the refrigerant panels at a temperature of -3 ÷ -5 ° C and enters the ice water tank for subsequent supply to consumers. The temperature of ice water at the outlet of the tank varies between + 1 ÷ + 2 ° C.

The disadvantage of such ice water refrigeration units is their high metal consumption and low energy efficiency, although it is higher than that of refrigeration units with ice accumulators, since liquid coolers with film evaporators have a boiling point of minus 4 ° С, while liquid coolers with batteries cold it is -8 ÷ -10 ° C. In terms of the electricity consumed, we get that a liquid cooler with film evaporators for 1 kW of electricity consumed by the compressor produces about 15-20% more cold.

A device for cooling a liquid, in particular milk, is known, according to the application of the Federal Republic of Germany No. 4134277 MKI 5 A01J 9/04, announced on 10/17/1991, published on 04/22/1993, the cooler includes a refrigeration unit, two plate heat exchangers and a brine circuit. Milk is collected in a container and is pumped to a flow-through plate heat exchanger, cooling is carried out with a brine solution, which, in turn, is cooled in another heat exchanger with refrigerant from the refrigeration circuit. The milk flow rate is regulated so that it is cooled to + 2 ÷ 4 ° C. Plate heat exchangers, which are structurally a set of thin specially shaped plates assembled in a single package, form adjacent channels through which the cooled liquid passes on the one hand and the refrigerant on the other hand, are the most suitable evaporators for ice water, since the refrigerant and the cooled liquid are separated very thin plates, which reduces the thermal resistance to heat transfer, while the speed of the media in the channels formed by the package is much higher than that of other evaporators ogih types.

The disadvantage of this device is the relatively high temperature of the outgoing ice water, which is explained by the danger of freezing it in a flow heat exchanger.

The closest solution, selected as a prototype, is a patent for utility model No. 148545, F25B 39/02 according to application No. 2014125879 dated 06/26/2014 under the name "Refrigeration unit for producing ice water in a flow evaporator", authors V. Velyukhanov. and Koptelova K.A.

In this installation, the compressor is equipped with a capacity controller electrically connected to a pressure sensor installed at the inlet of the evaporator, the pump is equipped with a capacity controller electrically connected with a temperature sensor installed in the water circuit at the outlet of the evaporator, while the pump performance is selected above the rated capacity at maximum ice water needs. A pressure regulator of the “up to” type is introduced into the water circuit, the regulator input is connected to the evaporator output after the temperature sensor, and the regulator output is connected to the input of the storage tank, while the output of the storage tank is hydraulically connected to the pump inlet.

The main disadvantage of the prototype circuit is an increase in the temperature of ice water at the outlet of the evaporator above a given value with a sharp increase in the thermal load on the evaporator, i.e. while increasing the temperature and flow rate of water from the consumer to the evaporator for cooling. With a significant increase in water consumption at the consumer, the pressure of ice water in front of the pressure regulator "to yourself" decreases and it stops the bypass of water into the tank. This leads to the fact that chilled water from the tank does not enter the pump inlet and does not mix with the warm water coming from consumers. If, at the same time, the water temperature of consumers significantly increases, then due to the termination of mixing cold water from the tank with it, the temperature at the inlet to the flow evaporator increases sharply, which leads to an increase in the water temperature at the outlet of the evaporator above a predetermined one. Thus, with sharp fluctuations in the heat load of the consumer, the refrigeration unit will not be able to provide the consumer with ice water of the required temperature.

The objective of the invention is to reduce the water temperature at the outlet of the plate evaporator and increase the reliability of its maintenance under any operating conditions of the refrigeration unit.

The technical essence of the invention lies in the fact that in a refrigeration unit with a plate evaporator, a normally open solenoid valve is introduced into the composition of the refrigerant circuit, the inlet of which is connected by a pipe to the compressor outlet, and the output is connected by a pipe to the refrigerant inlet to a plate evaporator, water composition is introduced pressure switch installed at the outlet of the water circuit pump, electrically connected to a normally open solenoid valve of the refrigerant circuit, controlling sensors temperature, installed in the water circuit at the outlet of the plate evaporator, electrically connected to the compressor capacity regulator, a heat-insulated mixing tank, installed at the same level as the heat-insulated ice water tank and an additional water pump, the water cavities of the heat-insulated ice water tank and the heat-insulated mixing tank are hydraulically connected between a heat-insulated bypass pipe below the water level, while the performance of the water pump the round is selected above the design capacity of the additional water pump, the outlet of the flow evaporator in the water circuit is connected to the insulated ice water tank, this tank is hydraulically connected to the inlet of the additional water pump, the outlet of this pump is connected to the inlet of the ice water consumer, the outlet of the ice water consumer is connected to the insulated mixing tank, this tank is hydraulically connected to the inlet of the water circuit pump, and the outlet of this pump is connected to the inlet of the plate evaporator through the water Nome contour, with all pipes of the water circuit are made insulated.

Thus, in the proposed technical solution introduced features of the invention, distinctive from the prototype.

The first distinguishing feature is that a normally open solenoid valve is introduced into the refrigerant circuit, the inlet of which is connected by a pipe to the compressor output, and the output is connected by a pipe to the refrigerant inlet to a plate evaporator, while a normally open solenoid valve is electrically connected to a pressure switch installed at the water pump output contour. The second distinguishing feature is the control temperature sensor installed in the water circuit at the outlet of the plate evaporator, electrically connected to the compressor capacity regulator. The third distinguishing feature is that a thermally insulated mixing tank is installed in the water circuit, installed at the same level as the insulated ice water tank and connected with it with a thermally insulated bypass pipe below the possible water level in any of these tanks. The fourth distinguishing feature is that an additional water pump is introduced into the water circuit, the inlet of which is hydraulically connected to the insulated ice water tank, and the outlet is connected by a pipe to the inlet of the ice water consumer, while the capacity of the additional water pump at the maximum ice water flow rate is selected below the design capacity of the main pump . The fifth distinguishing feature is that the inlet of the water circuit pump is hydraulically connected to the heat-insulated mixing tank, and the outlet of this pump is connected to the inlet to the water cavity of the plate evaporator.

The combination of all these distinguishing features allows you to achieve the set result, namely, to obtain the lowest possible temperature at the outlet of the plate evaporator, namely + 0.1 ÷ 0.5 ° C, while eliminating the possibility of freezing water inside the plate evaporator.

Thus, a pipeline introduced into the composition of the refrigerant circuit with a normally open solenoid valve connecting the compressor outlet and the inlet of the plate evaporator refrigerant cavity is intended for periodic short-term transfer of hot refrigerant in the gaseous phase in order to remove ice from the walls of the water cavity of the plate evaporator. In technology, it is customary to consider a valve to be a normally open solenoid valve, which in the de-energized state is in the open position, and when the voltage is applied to it, the valve closes. When the refrigeration unit is operating, this solenoid valve is energized in the closed position. If the voltage is removed, it will automatically open. This condition is necessary so that during an emergency shutdown of the compressor (for example, an accident in the power supply network), the solenoid is in the open state and hot refrigerant from the inertialess deenergized compressor enters the refrigerant cavity of the plate evaporator, in which the remaining refrigerant continues to boil, so as not to allow freezing of water in the water cavity of the evaporator. When ice freezes on the plates of the water cavity of the plate evaporator, the flow area of this cavity decreases and the water pressure at the inlet to the plate evaporator begins to increase. When the pressure of the water increases, the pressure switch gives a control pulse to remove the supply voltage from the solenoid valve energized when it is closed, after which it opens and the hot (about 90 ° С) compressed refrigerant vapor from the compressor enters the refrigerant cavity of the plate evaporator and provides ice discharge from the evaporator plates and carried away by a stream of water. As soon as the pressure at the entrance to the water cavity returns to normal, the pressure switch supplies the supply voltage to the solenoid valve and it closes. A control temperature sensor installed at the outlet of ice water from the plate evaporator, electrically connected to the compressor capacity regulator, controls the capacity of the refrigeration circuit depending on the temperature of the water leaving the plate evaporator. If the temperature of ice water at the outlet of the plate evaporator approaches 0 ° C in order to avoid ice formation on the evaporator plates, the temperature sensor provides a control signal to the compressor drive in order to reduce its performance. The introduction of a thermally insulated mixing tank hydraulically connected to the pump of the water circuit into the water circuit makes it possible to equalize the temperature of the water entering the inlet of the flowing evaporator by mixing the incoming warmer water from the consumer with the colder water located in the insulated storage tank. A heat-insulated bypass pipe between the tanks together with another sign - the volumetric capacity of the water pump taking water from the heat-insulated mixing tank must be greater than the capacity of the additional water pump supplying ice water to the consumer, so that the plate evaporator works in the minimum heat load mode for the consumer to cool the water in both tanks, which allows you to accumulate ice water in the tanks, and then use it to remove peak heat s load without increasing the cooling capacity of the installation, and also for mixing of ice water to the water entering the mixing tank thermally insulated from the consumer.

The proposed scheme of the refrigeration unit for producing ice water in a plate evaporator is shown in the drawing, where the numbers indicate:

1 - refrigerant circuit

2 - compressor

3 - performance regulator

4 - control sensor for the temperature of the water circuit

5 - capacitor

6 - thermostatic valve (TRV)

7 - plate evaporator

8 - normally open solenoid valve

9 - water circuit

10 - water circuit pump

11 - water pressure switch

12 - insulated ice water tank

13 - insulated bypass pipe

14 - thermally insulated mixing tank

15 - additional water pump

16 - ice water consumer

A compressor 2 with a capacity regulator 3, a control temperature sensor for the water circuit 4, electrically connected to a capacity regulator 3, a condenser 5, a thermostatic valve 6, and a plate evaporator 7 are installed in the refrigerant circuit 1. A normally open solenoid valve 8 is introduced into the composition of the refrigerant circuit 1, the inlet of which is hydraulically connected to the outlet of the compressor 2, and the output of this solenoid valve 8 is hydraulically connected to the inlet of the plate evaporator 7 along the refrigerant circuit 1. This plate evaporator 7 is connected in one cavity to the refrigerant circuit 1, a second cavity with a water circuit 9. In the water circuit 9, a water circuit pump 10 is installed, the output of which is hydraulically connected to the inlet of the plate evaporator 7 along the water circuit 9, while the pressure switch the water circuit 11 is installed in the water circuit 9 at the inlet to the plate evaporator 7 and is electrically connected to a normally open solenoid valve 8 of the refrigerant circuit 1. The heat-insulated ice water tank 12 is hydraulically connected by a heat-insulated bypass pipe 13 to a heat-insulated mixing tank 14, connected by a pipe to the outlet of the water cavity plate evaporator 7, as well as with the input of the additional water pump 15. The output of this pump 15 is connected by a pipe to the inlet of the consumer of ice water 16, and Exit consumer ice water conduit 16 is connected with an insulated mixing tank 14. Insulated mixing tank 14 is fluidly connected with the inlet of the water pump 10, and pump output 10 is connected to a water inlet of the cavity 7 of the plate evaporator, the water circuit all the pipes are made insulated. The volumetric flow rate of the pump 10 of the water circuit is selected greater than the volumetric flow rate of the additional water pump 15 at the maximum heat load on the consumer.

A refrigeration unit for producing ice water in a plate evaporator operates as follows.

In the refrigerant circuit 1, the refrigeration compressor 2 compresses the gaseous refrigerant, while the refrigerant is heated and under pressure enters the condenser 5, where it condenses by cooling with the surrounding air, turning into a liquid refrigerant. Then the liquid refrigerant under high pressure enters the thermostatic expansion valve (TRV) 6, after which the refrigerant turns into a vapor-liquid mixture with a low boiling point. The specific refrigerant boiling point is selected by calculation depending on the required ice water temperature. Further, the refrigerant in the form of a vapor-liquid mixture enters the refrigerant cavity of the plate evaporator 7, where during boiling it takes heat from the water entering the cavity of the water circuit of the plate evaporator 7. The evaporated refrigerant enters from the evaporator 7 to the inlet of compressor 2 and the refrigeration cycle is repeated. The normally open solenoid valve 8 when starting the compressor 2 receives the supply voltage and it closes. In the case when the water pressure at the inlet to the water cavity of the plate evaporator 7 exceeds the preset value, the pressure switch 11 disconnects the power supply from the solenoid valve 8, it automatically opens, after which the hot gaseous refrigerant with a temperature of 90 ° C enters the cavity of the plate refrigerant evaporator 7. The experiments showed that the disappearance of ice from the plates of the water cavity of the plate evaporator 7 occurs in several tens of seconds (20-30 seconds), after which the passage section of the water channels of the first cavity is restored to the initial value and the pressure switch 11 supplies power to the solenoid valve 8. It closes and gaseous hot refrigerant from the compressor 2 enters the condenser 5. The duration of the thawing process due to the flow of hot gas into the refrigerant cavity of the plate evaporator 7 and the presence of a thermally insulated tank with a supply of ice water 12 practically does not affect the temperature of ice water in this tank. From the insulated ice water tank 12 with an additional water pump 15, water with a temperature of + 0.1 ° ÷ 0.5 ° C is supplied to the ice water consumer 16, where it takes heat from the product to be cooled and leaves this consumer 16 with a temperature of, for example, 4 ° C. Water with such a temperature enters the heat-insulated mixing tank 14 and from this tank the water pump 10 is fed into the water cavity of the plate evaporator 7. In it, the water is cooled to a predetermined temperature of + 0.1 ° ÷ 0.5 ° C and again enters the heat-insulated ice tank water 12.

If the consumer of ice water 16 sharply increases the heat load, then the temperature of ice water at the outlet of the consumer can increase to + 7 ° C and with this temperature the water enters the insulated mixing tank 14, where it is mixed with water in this tank, which has a lower temperature , for example, 4 ° C. Suppose that the temperature in tank 14 becomes 1 ° C higher, i.e. 5 ° C. It is known from the theory of heat transfer that in a plate evaporator, liquid, including water, can be optimally cooled by no more than 5 ° C and this differential Δt for the evaporator will be constant at different temperatures of liquid inlet into the plate evaporator. Thus, at a water temperature of 5 ° C at the entrance to the water cavity of the plate evaporator 7, ice water at the outlet of this heat exchanger will be + 0.1 ° ÷ 0.5 ° C. This temperature is controlled by a control temperature sensor 4 and if the water temperature starts to continue to drop further, then from this sensor 4 a signal will be sent to drive 3 of compressor 2 to reduce compressor performance. When the refrigerating capacity of compressor 2 decreases, the flow rate of the refrigerant through the corresponding cavity of the heat exchanger-evaporator 7 decreases, the boiling point of the refrigerant rises and further cooling of the water in the adjacent cavity of the flow-through evaporator 7 is stopped, while the temperature of ice water at the outlet of the flow-through evaporator is close to 0 ° С. If suddenly, for some reason, this channel for regulating the temperature of ice water fails, then the pressure switch 11 installed at the inlet of the water circuit to the plate evaporator 7 will not freeze the water inside the flow evaporator 7. With a possible peak increase in heat load, the outlet water temperature from the consumer of ice water 16 can reach values of + 7 ÷ + 8 ° C. In this case, water with such a temperature is mixed in a thermally insulated mixing tank 14 with ice water with a temperature of + 0.1 ° ÷ 0.5 ° C entering it through a thermally insulated bypass pipe 13 from a thermally insulated ice water tank 12 due to the difference in the costs of additional water pump 15 (Gmax) and water circuit pump 10 (G). If the flow rate of the water circuit pump 10 is greater than the flow rate of the additional water pump 15, then ice water will always flow through the heat-insulated bypass pipe 13 from the heat-insulated ice water tank 12 to the heat-insulated mixing tank 14 and due to this, the temperature in the heat-insulated mixing tank 14 will decrease by 2- 4 ° C. In this case, the water supplied by the pump of the water circuit 10 for cooling into the water cavity of the flow evaporator 7 will have a temperature of 4 ÷ 5 ° C, which allows it to be guaranteed to cool to ice water temperature + 0.1 ÷ 0.5 ° C.

If the heat load of the consumer decreases, then the temperature of the ice water at the outlet from the consumer will increase slightly relative to the inlet temperature and due to the difference in costs (the flow rate of the water circuit pump is greater than the flow rate of the additional water pump), water cooling in the insulated mixing tank 14 will occur due to ice water from the tank 12 through the insulated bypass pipe 13. Thus, ice water is accumulated in two tanks. Therefore, if the consumer exceeds the rated heat load, the water leaving consumer 16 with a temperature exceeding the nominal value will be mixed in tank 14 with ice water coming from the heat-insulated ice water tank, and the operation of the refrigeration unit will be carried out in nominal mode, without increasing compressor performance 1.

The use of this invention allows reliable and safe for the design of a plate evaporator to obtain ice water with a temperature of + 0.1 ÷ 0.5 ° C in plate evaporators of refrigeration units. This reduces the energy cost of producing ice water, since ice water is produced at a boiling point of the refrigerant substantially higher than the boiling point of the refrigerant in film evaporators or panel batteries. The lower energy consumption of this refrigeration unit is due to the operation of its plate evaporator at a boiling point of -2 ° ÷ -3 ° C, which is 2 degrees higher than that of evaporative panels and 8 degrees higher than that of cold storage batteries. Therefore, 1 kW of electricity consumed by the compressor of the refrigeration unit generates about 5% more cold than evaporative panels and 24-25% more cold than cold storage batteries.

Claims (1)

A refrigeration unit for producing ice water in a plate evaporator, including a refrigerant circuit with a compressor, a capacity regulator, a condenser, a thermostatic valve and a water circuit with a pump, a heat-insulated storage tank and an ice water consumer, connected by a double-circuit plate evaporator, characterized in that in order to increase the accuracy and reliability of regulating the water temperature in a plate evaporator upon receipt of ice water with a temperature of 0.1 ÷ 0.5 ° C as part of the refrigerant circuit in a normally open solenoid valve has been installed, the input of which is connected by a pipeline to the compressor outlet, and the output is connected by a pipeline with the refrigerant inlet to a plate evaporator, a pressure switch is installed in the water circuit, installed at the outlet of the water circuit pump, electrically connected to a normally open solenoid valve of the refrigerant circuit, temperature control sensor installed in the water circuit at the outlet of the plate evaporator, electrically connected to the capacity controller RA, a thermally insulated mixing tank, installed at the same level as the thermally insulated ice water tank, and an additional water pump, the water cavities of the insulated ice water tank and the thermally insulated mixing tank are interconnected by a thermally insulated bypass pipe below the possible water level in each of these tanks, the capacity of the water circuit pump is selected above the design capacity of the additional water pump, the output of the plate evaporator in water the circuit is connected to a heat-insulated ice water tank, this tank is connected to the input of an additional water pump, the output of this pump is connected to the input of the ice water consumer, the output of the ice water consumer is connected to the heat-insulated storage tank, this tank is connected to the input of the water circuit pump, and the output of this the pump is connected to the inlet of the plate evaporator along the water circuit, while all the pipelines of the water circuit are thermally insulated.

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