Purpose

Propane natural gas cooling units are designed to simultaneously provide the required dew point parameters for water and hydrocarbons by condensing the water and hydrocarbon fractions (HC) at low temperatures ah (up to minus 30 0 С). The cold source is an external propane refrigeration cycle.

The main advantage of such plants is the low pressure loss of the feed stream (throttling of the natural gas stream is not required) and the possibility of extracting the C3+ production fraction.

To prevent hydrate formation, injection of an inhibitor is used: ethylene glycol (for temperatures not lower than minus 35 0 С) and methanol (for temperatures up to minus 60 0 С).

Main advantages

Reliability

• A continuous process based on the condensation of water and hydrocarbon fractions in the presence of a hydrate inhibitor.
• No cyclic fluctuations.
• Shell and tube gas-gas heat exchanger with low temperature difference.
• The service factor of the refrigeration compressor motor is 110%.
• Automatic pressure maintenance system in the receiver when operating in cold climates.
• Electrical heating of the inhibitor collector in a three-phase separator.

Efficiency

• Cold separator with efficient coalescers and long residence time.
• Gas-propane heat exchanger (chiller) with submerged tube bundle.

Possible options

• Refrigeration cycle economizer (standard for systems over 150 kW and evaporation temperatures below minus 10 0 С).
• input separator.
• Gas-liquid heat exchanger (allows to reduce the power consumption of the compressor).

Technology system

The moisture-saturated natural gas stream is fed into the inlet separator (1), in which free water and hydrocarbon fractions are removed from the stream. The gas fraction is sent to the gas-gas heat exchanger (2) for pre-cooling with a stream of dry stripped gas from the cold separator. To prevent hydrate formation in the heat exchanger, nozzles are provided for injection of an inhibitor (methanol or ethylene glycol).

Rice. 3 Schematic diagram of a propane refrigeration plant

After pre-cooling in the gas-gas heat exchanger, the flow is fed to the gas-propane heat exchanger (chiller) (4), in which the flow temperature is lowered to a predetermined value by heat exchange with the boiling propane flow. The feed stream is located in the tube bundle, which in turn is immersed in the refrigerant volume.

The vapor-liquid mixture formed as a result of cooling enters the low-temperature three-phase separator (5) for separation, where it is divided into streams of stripped gas, condensate and water-saturated inhibitor of hydrate formation.

Dry stripped gas (DSG) is supplied countercurrent to the gas-gas heat exchanger (2) and then discharged outside the plant.

Liquid fractions are diverted by independent automatic level controllers to the appropriate lines.

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Gas processing made easy

One of our main tasks is to fight the myth that gas processing is difficult, time consuming and expensive. Surprisingly, projects that are implemented in the US in 10 months take up to three years in the CIS. Installations occupying 5,000 m2 in the USA can hardly fit on 20,000 m2 in the CIS. Projects that pay off in the US in 3-5 years, even at a significantly lower cost of selling a product, never pay off in Russia and Kazakhstan.

Automation systems. Automation of the operation of refrigeration machines, depending on the functions performed, is divided into systems:

– regulation , supporting the set value of the controlled variable (temperature, pressure, amount of refrigerant, etc.);

–protection, i.e. to turn off the installation in case of excessive deviation of the parameters of its operation mode;

– signaling , i.e. to turn on a visual and (and) audible signal in case of violation of the operating mode of the refrigeration unit;

– control when it is necessary to control any operating parameters of the refrigeration machine.

Depending on the drive, automation systems are electrical, pneumatic and combined, and according to the principle of action - positional and continuous.

The automatic control system of the refrigeration unit allows you to provide the specified temperature regime for the transported cargo without the participation of maintenance personnel.

An automation system is a set of an automation object and automatic devices that allow you to control the operation of this object without the participation of personnel. The object of automation can be a refrigeration plant as a whole or its individual units, units, apparatuses, etc. Automation systems can be closed and open.

Rice. 4.26 - Closed-loop automation system

A closed system consists of an object ( About) and automatic device ( BUT), which are connected by a straight line ( PS) and inverse ( OS) connections, which are shown in Fig. 4.26. An input action is applied to the object via a direct connection X , on the reverse - the output value at , which affect BUT. System OS works on the deviation of the actual value at from the set value at h.

If the purpose of the system is to maintain the value at near the set value with changes in external influence f vn, then such a system is called an automatic control system ( SAR), and the automatic device - automatic regulator ( AR). Functional system SAR shown in fig. 4.27.

Rice. 4.27 - Functional diagram of the automatic
regulation ( SAR)

On the functional diagram SAR The direct link chain includes: amplifier, actuating mechanism (THEM) and the regulatory body ( RO). In chain feedback switched on sensor, with which the regulator AR accepts an adjustable value At and converts it to a value At p, convenient for further transmission. To one of the inputs of the comparison element ( ES) the converted value is supplied At n, and on its other input - a signal At from setter.

This signal in the converted form is exercise regulator. Amount of agreement d= At h - At n is a stimulating signal. Its power is increased in the amplifier by the supply of external energy E ext and as a signal D affects THEM, which converts the signal into a usable form of energy D x and rearranges to RO. As a result, the input to About energy flow, which corresponds to a change in the regulatory action X .

If the normal operation of the object proceeds at values at , different from at h, and when equality between them is reached, a signal is sent to the object X to shutdown, then such a system is called an automatic protection system ( SAZ), and the automatic device - protection device ( AZ). Such a functional system is shown in Fig. 4.28.

Scheme SAZ different from schema SAR the fact that in an automatic device AZ missing THEM and RO. The signal from the amplifier acts directly on About, turning it off in its entirety or its individual parts.

Rice. 4.28 - Functional diagram of the automatic protection system ( SAZ)

Rice. 4.29 - Open-loop automation system

An open system is a system in which one of the links (reverse or direct) is absent (Fig. 4.29). Parameter Z related to the output at and is perceived by the automatic device BUT. Setpoint deviation Z 3 causes impact changes X .

Evaporator Automation. One of the important management processes refrigeration machine is the automatic supply of evaporators by steam overheating and by the level of liquid in the evaporator. As an automatic superheat controller, they are mainly used thermostatic valves (TRV).

The expansion valve is installed in front of the evaporator. A capillary tube is soldered to the top of the valve (Fig. 4.30). 7 connecting the internal working part 6 thermostatic valve 8 . The upper power part of the valve is sealed. The bulb is tightly attached to the suction line connecting the evaporator to the compressor. The thermal bulb, capillary and space above the membrane are filled with a strictly metered amount of refrigerant during the manufacture of the valve. From the bottom of the membrane 5 rod goes down 4 with shut-off valve 3 , which is pressed against the seat by a spring 2 with adjusting screw 1 .

Rice. 4.30 - Scheme of expansion valve with internal equalization

The principle of operation of the expansion valve is based on comparing the boiling point of the refrigerant in the evaporator with the temperature of the vapors leaving it. The comparison is made by converting the vapor temperature perceived by the bulb t at the appropriate pressure R c in the power section of the device (see Fig. 4.30). Pressure acts on the diaphragm from above and tends to open the valve through the stem 3 for a larger cross section. This movement of the valve is prevented by the boiling pressure of freon in the evaporator R o acting on the membrane from below, as well as the spring force f and pressure R to the valve.

When the evaporator is properly filled, the vapor temperature at the outlet of it should not exceed 4.7°C. To do this, all the freon supplied through the expansion valve to the evaporator must boil away in the area from the valve 3 to point A. Here the freon temperature does not change and is t about. In the last turns of the evaporator from point A to the thermal bulb, freon, continuing to absorb heat from the refrigerated room, overheats to a temperature t in > t about. Temperature t c perceives the bulb, and pressure is set in the power system R with. At equilibrium R c = R o + f +R when the evaporator is allowed to be completely filled with refrigerant, and the refrigeration machine operates in the optimum mode.

As the temperature in the refrigerated room decreases, the heat flow to the evaporator decreases. The boiling of the refrigerant at point A does not end, but continues to point B. The path of the vaporous refrigerant to the bulb is shortened, and the vapor superheat is reduced. The bulb senses a lower temperature and the power system is set to a lower value. R with. Under the action of the spring, the valve moves upward, reducing the flow area of ​​the valve and thereby the supply of refrigerant to the evaporator.

With a smaller amount of refrigerant, its boiling in the evaporator ends earlier, and overheating takes on a value close to the original one. The upward movement of the valve occurs until a new equilibrium is established between the reduced pressure and the reduced spring compression, i.e. R c = R o + f +R k. Vapor superheating in the evaporator is regulated by preloading the spring 2 with adjusting screw 1 .

thermal bulb 8 , capillary 7 and membrane 5 (see Fig. 4.30) are the main elements of manometric instruments - thermostats , which are used to automatically control the operation of diesel generators and refrigeration units on refrigerated rolling stock.

Automatic maintenance temperature regime in cargo spaces. To establish the required temperature regime in the cargo space of a refrigerated transport or storage module and automatically maintain it within the specified limits, the pressure switch-thermostat , the device of which is shown in Fig. 4.31.

Rice. 4.31 - Pressure switch device

The pressure switch is installed on the suction pipe between the evaporator and the compressor. It consists of a piston 1 , a rod rigidly connected to it 2 , springs 4 , handles 5 , two electrical contacts: rolling 6 and motionless 7 .

The piston is in the knee 3 connected to the suction pipe 8 . Under pressure R o, more than the twisting force of the spring 4 , the piston is in its uppermost position. At the same time, contacts 6 and 7 closed. The compressor is switched on and sucks off freon vapors from the evaporator. During the extraction process, the pressure R o decreases, becomes less than the twisting force of the spring. The moving contact piston moves to its lowest position and the compressor is switched off.

Due to the continuing boiling of freon in the evaporator, its specific volume increases, the pressure R o starts growing again. Contacts 6 and 7 will be closed, the compressor will begin to suck off freon vapors from the evaporator. The cycle is repeated.

The piston stroke is limited by special stops that can be adjusted. The force of the spring on the piston is regulated by the handle 5 . When the handle is set to the “cold” position, the spring force decreases. Consequently, less pressure will be established in the evaporator zone R Oh, and hence the low boiling point of freon.

Thus, the thermostatic pressure switch maintains the boiling pressure in the evaporator at the required level by controlling the amount of refrigerant flowing into the evaporator.

Automation refrigeration units involves equipping them automatic devices(instruments and automation equipment), which ensure safe operation and conduct production process or separate operations without the direct participation of the attendants or with their partial participation.

Automation objects, together with automatic devices, form automation systems with various functions: control, signaling, protection, regulation and control. Automation increases the economic efficiency of refrigeration units, as the number of maintenance personnel is reduced, the consumption of electricity, water and other materials is reduced, the service life of the units is increased due to the maintenance of the optimal mode of their operation by automatic devices. Automation requires capital expenditures, so it must be carried out based on the results of a feasibility study.

The refrigeration plant can be automated partially, completely or comprehensively.

Partial automation provides for mandatory automatic protection for all refrigeration units, as well as control, alarm and often management. The service personnel regulates the main parameters (temperature and humidity of the air in the chambers, the boiling and condensing temperature of the refrigerant, etc.) in case of their deviation from the set values ​​and the malfunction of the equipment, which is reported by the control and alarm systems, and some auxiliary periodic processes ( thawing of frost from the surface of cooling devices, removal of oil from the system) are performed manually.

Full automation covers all processes related to maintaining the required parameters in the refrigerated rooms and elements of the refrigeration plant. Service personnel may be present only occasionally. Fully automate refrigeration units of small capacity, trouble-free and durable.

For large industrial refrigeration plants, it is more typical complex automation(automatic control, signaling, protection).

Automatic control provides remote measurement, and sometimes recording of the parameters that determine the mode of operation of the equipment.

Automatic signaling - notification by means of a sound or light signal about the achievement of specified values, certain parameters, turning on or off the elements, the refrigeration unit. Automatic alarm subdivided into technological, preventive and emergency.

Technological signaling - light, informs about the operation of compressors, pumps, fans, the presence of voltage in electrical circuits.

A warning signal on protective, circulating receivers informs that the value of the controlled parameter is approaching the maximum permissible value.

Emergency signaling by light and sound signals notifies that automatic protection has been triggered.

Automatic protection, which ensures the safety of operating personnel, is mandatory for any production. It prevents emergency situations by turning off individual elements or the installation as a whole when the controlled parameter reaches the maximum permissible value.

Reliable protection in the event of a dangerous situation should be provided by an automatic protection system (ACS). In the simplest version, the SAS consists of a sensor-relay (protection relay) that controls the parameter value and generates a signal when its limit value is reached, and a device that converts the protection relay signal into a stop signal that is sent to the control system.

On high-capacity refrigeration plants, the SAS is performed so that after the protection relay is activated, the automatic start-up of the failed element without eliminating the cause that caused the stop was impossible. On small refrigeration units, for example, at trade enterprises, where an accident cannot lead to serious consequences, there is no permanent service, the object turns on automatically if the value of the controllable parameter returns to the permissible range.

Largest number compressors have types of protection, since, according to operating experience, 75% of all accidents at refrigeration plants occur with them.

The number of parameters controlled by the SAS depends on the type, capacity of the compressor and the type of refrigerant.

Compressor protection types:

from an unacceptable increase in discharge pressure - prevents violation of the density of joints or destruction of elements;

impermissible decrease in suction pressure - prevents an increase in the load on the compressor stuffing box, oil foaming in the crankcase, freezing of the refrigerant in the evaporator (high and low pressure, equip almost all compressors);

reducing the pressure difference (before and after the pump) in the oil system - prevents emergency wear of rubbing parts and jamming of the compressor movement mechanism, the pressure difference switch controls the pressure difference on the discharge and suction sides of the oil pump;

unacceptable increase in discharge temperature - prevents violation of the cylinder lubrication regime and emergency wear of rubbing parts;

increasing the temperature of the windings of the built-in electric motor of hermetic and glandless refrigerant compressors - prevents overheating of the windings, jamming of the rotor and operation in two phases;

hydraulic shock (liquid refrigerant entering the compression cavity) - prevents a serious accident of a reciprocating compressor: violation of density, and sometimes destruction.

Types of protection for other elements of the refrigeration unit:

from freezing of the coolant - prevents rupture of the evaporator pipes;

overflow of the linear receiver - protects against a decrease in the efficiency of the condenser as a result of filling part of its volume with a liquid refrigerant;

emptying of the linear receiver - prevents gas breakthrough high pressure into the evaporator system and risk of water hammer.

Prevention of an emergency provides protection against unacceptable concentrations of ammonia in the room, which can cause a fire and explosion. The concentration of ammonia (maximum 1.5 g/m 3 or 0.021% by volume) in the air is monitored by a gas analyzer.

Cold is used in the technologies of many processes of processing agricultural products. Thanks to refrigerators, losses during storage of products are significantly reduced. Refrigerated products can be transported over long distances.

Milk intended for processing or sale, as a rule, is pre-cooled. Before being sent to a dairy industry enterprise, milk may be stored for no more than 20 hours at a temperature not exceeding 10 °C.

In agriculture, meat is cooled mainly on farms and poultry farms. In this case, the following cooling methods are used: in air, cold water, in water with melting ice and irrigation with cold water. Poultry meat is frozen either by cold air or by immersion in cold brine. Air freezing is carried out at an air temperature in refrigerators from -23 to -25 ° C and an air speed of 3 ... 4 m / s. For freezing by immersion in brine, solutions of calcium chloride or propylene glycol are used with a temperature of -10 ° C and below.

Meat intended for long-term storage is frozen in the same way as freezing. Freezing

air is carried out at a temperature of the cooled air from -30 to -40 ° C, when freezing in brine, the temperature of the solution is -25 ... -28 ° C.

Eggs are stored in refrigerators at a temperature of -1 ... -2 ° C and a relative humidity of 85 ... 88%. After cooling to 2...3 °C they are placed in a storage chamber.

Fruits and vegetables are cooled in stationary storages. Fruit and vegetable products are stored in refrigerating chambers with cooling batteries, in which a cold agent or brine circulates.

In air-cooled systems, air is first cooled, which is then forced into the storage rooms by fans. In mixed systems, the products are cooled by cold air and from a battery.

In agriculture, cold is obtained both in a machineless way (glaciers, ice-salt cooling), and with the help of special refrigeration machines. During machine cooling, the heat from the cooled medium is removed to the external environment using low-boiling refrigerants (freon or ammonia).

In agriculture, steam compressors and absorption chillers are widely used.

The simplest way to get the temperature of the working fluid below the temperature environment is that this working fluid (refrigerant) is compressed in the compressor, then cooled to ambient temperature and then subjected to adiabatic expansion. In this case, the working body performs work due to its internal energy and its temperature decreases in comparison with the ambient temperature. Thus, the working fluid becomes a source of cold.

Any steam or gas can in principle be used as refrigerants. First refrigerating machines with a mechanical drive, air was used as a refrigerant, but already from the end of the 19th century. it was replaced by ammonia and carbon dioxide, since an air refrigeration machine is less economical and more cumbersome than a steam one, due to the high air consumption due to its low heat capacity.

In modern refrigeration systems, the working fluid is a vapor of liquids that, at pressures close to atmospheric, boil at low temperatures. Examples of such refrigerants are ammonia NH3, sulfur dioxide SO2, carbon dioxide CO 2 and freons - fluorochlorine derivatives of hydrocarbons of the C m H x F y Cl2 type. The boiling point of ammonia at atmospheric pressure is 33.5 °С, "Freon-12" -30 °С, "Freon-22" -42 °С.

Freons are widely used as refrigerants - halogen derivatives of saturated hydrocarbons (C m H n), obtained by replacing hydrogen atoms with chlorine and fluorine atoms. In technology, due to the wide variety of freons and their relatively complex naming, a conditional numerical designation system has been established, according to which each such compound, depending on the chemical formula, has its own number. The first digits in this number conditionally designate the hydrocarbon, of which this freon is a derivative: methane - 1, ethane - 11, propane - 21. If there are unsubstituted hydrogen atoms in the compound, then their number is added to these numbers. Further, to the resulting amount or to the original number (if all hydrogen atoms in the compound are substituted), a number is added as the next character, expressing the number of fluorine atoms. This is how the designations are obtained: R11 instead of monofluorotrichloromethane CFCI2, R12 instead of difluorodichloromethane CF 2 C1 2, etc.

In refrigeration, R12 is commonly used as a refrigerant, and R22 and R142 will be widely used in the future. The advantages of freons are relative harmlessness, chemical inertness, incombustibility and explosion safety; disadvantages are low viscosity, which promotes leakage, and the ability to dissolve in oil.

Figure 8.15 shows the circuit diagram vapor compressor refrigeration unit and its ideal cycle in the 75-diagram. In the compressor 1 wet refrigerant vapor is compressed, as a result of which (area a-b) dry saturated or superheated steam is obtained. Typically, the degree of overheating does not exceed

130 ... 140 "C, in order not to complicate the operation of the compressor due to increased mechanical stresses and not to use oils

Rice. 8.15.

/ - compressor; 2 - refrigerated room; 3- throttle valve; 4 - special grade condenser. Superheated steam from the compressor with parameters pi and 02 enters the cooler (condenser 2). In a condenser at constant pressure, the superheated steam gives off the heat of superheat to the cooling water (the process b-c) and its temperature becomes equal to the saturation temperature of 0 H2. Further giving off the heat of vaporization (the process c-d), saturated steam turns into a boiling liquid (point d). This fluid flows to the throttle valve 3, passing through which it turns into saturated steam of a small degree of dryness (x 5 \u003d 0.1 ... 0.2).

It is known that the enthalpy of the working fluid before and after throttling is the same, and the pressure and temperature decrease. The 7s diagram shows the dashed line of the constant enthalpy d-e, dot e which characterizes the state of the steam after throttling.

Next, wet steam enters a refrigerated container called a refrigerator. 4. Here, at constant pressure and temperature, the vapor expands (the process e-a), taking away a certain amount of heat. In this case, the degree of dryness of the steam increases (x| = 0.9 ... 0.95). Steam with state parameters characterized by a dot 1, is sucked into the compressor, and the operation of the installation is repeated.

In practice, the steam after the throttle valve does not enter the refrigerator, but into the evaporator, where it takes heat from the brine, which, in turn, takes heat from the refrigerator. This is due to the fact that in most cases the refrigeration unit serves a number of cold consumers, and then the non-freezing brine serves as an intermediate coolant, continuously circulating between the evaporator, where it is cooled, and special air coolers in refrigerators. As brines, aqueous solutions of sodium chloride and calcium chloride are used, which have fairly low freezing temperatures. Solutions are suitable for use only at temperatures above those at which they freeze as a homogeneous mixture, forming salt ice (the so-called cryohydrate point). The cryohydrate point for a NaCl solution with a mass concentration of 22.4% corresponds to a temperature of -21.2 "C, and for a solution of CaCl 2 with a concentration of 29.9 - a temperature of -55 °C.

An indicator of the energy efficiency of refrigeration units is the refrigeration coefficient e, which is the ratio of specific cooling capacity to the energy consumed.

The actual cycle of a vapor-compressor refrigeration plant differs from the theoretical one in that, due to the presence of internal friction losses, compression in the compressor occurs not along the adiabatic, but along the polytropic. As a result, energy consumption in the compressor is reduced and the coefficient of performance is reduced.

To obtain low temperatures (-40 ... 70 ° C), required in some technological processes, single-stage steam compressor units turn out to be either uneconomical or completely unsuitable due to a decrease in compressor efficiency due to high temperatures working fluid at the end of the compression process. In such cases, either special refrigeration cycles are used, or, in most cases, two-stage or multi-stage compression. For example, two-stage compression of ammonia vapors produces temperatures up to -50 °C, and three-stage compression up to -70 °C.

Main advantage absorption refrigeration units compared to compressor plants, the use of low and medium potential heat energy, rather than electrical energy, is used to generate cold. The latter can be obtained from water vapor taken, for example, from a turbine in combined heat and power plants.

Absorption is the phenomenon of the absorption of vapor by a liquid substance (absorbent). In this case, the temperature of the steam may be lower than the temperature of the absorbent that absorbs the steam. For the absorption process, it is necessary that the concentration of absorbed vapor be equal to or greater than the equilibrium concentration of this vapor over the absorbent. Naturally, in absorption refrigeration systems, liquid absorbents must absorb the refrigerant at a sufficient rate, and at the same pressures, their boiling point should be significantly higher than the boiling point of the refrigerant.

The most common are water-ammonia absorption plants, in which ammonia serves as a refrigerant and water as an absorbent. Ammonia is highly soluble in water. For example, at 0 °C, up to 1148 volumes of vaporous ammonia are dissolved in one volume of water, and heat of about 1220 kJ/kg is released.

Cold in the absorption unit is generated according to the scheme shown in Figure 8.16. This diagram shows the approximate values ​​of the parameters of the working fluid in the installation without taking into account pressure losses in pipelines and losses in the temperature head in the condenser.

In the generator 1 the evaporation of a saturated ammonia solution occurs when it is heated with water vapor. As a result, a low-boiling component is distilled off - ammonia vapor with a slight admixture of water vapor. If the temperature of the solution is maintained at about 20 °C, then the saturation pressure of ammonia vapor will be approximately 0.88 MPa. To ensure that the NH 3 content in the solution does not decrease, using a transfer pump 10 from the absorber to the generator is continuously fed a strong concentrated

Rice. 8.16.

/-generator; 2- capacitor; 3 - throttle valve; 4- evaporator; 5-pump; b-bypass valve; 7- refrigerated container; absorber; 9-coil; 10- pump

bath ammonia solution. Saturated ammonia vapor (x = 1), obtained in the generator, is sent to the condenser 2, where ammonia turns into a liquid (x = 0). after choke 3 ammonia enters the evaporator 4, at the same time, its pressure decreases to 0.3 MPa (/ n \u003d -10 ° C) and the degree of dryness becomes approximately 0.2 ... 0.3. In the evaporator, the ammonia solution is evaporated due to the heat supplied by the brine from the cooled tank 7. In this case, the temperature of the brine decreases from -5 to -8 °C. With a pump 5 it is distilled back into container 7, where it is again heated to -5 ° C, taking heat from the room and maintaining a constant temperature in it, approximately -2 ° C. Ammonia evaporated in the evaporator with a degree of dryness x = 1 enters the absorber 8, where it is absorbed by the weak solution supplied through the bypass valve 6 from the generator. Since absorption is an exothermic reaction, to ensure the continuity of the heat exchange process, absorbzite is removed by cooling water. Strong ammonia solution obtained in the absorber pump 10 pumped to the generator.

Thus, in the considered installation there are two devices (generator and evaporator), where heat is supplied to the working fluid from the outside, and two devices (condenser and absorber), in which heat is removed from the working fluid. Comparing circuit diagrams steam compressor and absorption units, it can be noted that the generator in the absorption unit replaces the discharge part, and the absorber replaces the suction part of the reciprocating compressor. Compression of the refrigerant occurs without the expenditure of mechanical energy, except for the small costs of pumping a strong solution from the absorber to the generator.

In practical calculations, the cooling coefficient e is also taken as an energy indicator of the absorption plant, which is the ratio of the amount of heat q2 perceived by the working fluid in the evaporator to the amount of heat q u spent in the generator. The COP calculated in this way is always less than the COP of the steam compressor system. However, a comparative assessment of the energy efficiency of the considered methods of obtaining cold as a result of a direct comparison of the methods of only the cooling coefficients of absorption and vapor compressor installations is incorrect, since it is determined not only by the amount, but also by the type of energy consumed. The two methods of obtaining cold should be compared by the value of the reduced coefficient of performance, which is the ratio of the cooling capacity q2 to fuel heat consumption q it i.e. ? pr = Yag I- It turns out that at evaporation temperatures from -15 to -20 °C (used by the bulk of consumers), e pr absorption plants are higher than steam compressor plants, as a result of which, in a number of cases, absorption plants are more profitable not only when supplying them with steam taken from turbines, but also when supplying them with steam directly from steam boilers.

Page 4 of 5

Automation system is a series connection by means of pipelines of all elements of the refrigeration unit, which ensures accurate maintenance of the set cooling temperature, continuous monitoring and protection of the machine from accidents, as well as operational reliability refrigeration equipment. The system must be able to easily adjust the temperature and economically operate the plant. The scheme of the automation system is selected depending on the cooling capacity and purpose of the installation.

Apply refrigeration automation systems with capacity control by depressing the solenoid valves, as well as turning the refrigeration units on and off. In transport, the most common automation systems are arranged according to the second principle.

The device of the automatic control system of a freon machine is determined by the type of compressor, evaporator and condenser, the method of changing the cooling capacity, as well as the number of compression stages or cooling stages.

A characteristic feature of the automation of ammonia refrigeration plants- increased requirements for operational safety due to the high toxicity of ammonia, its explosiveness, as well as the risk of destruction of compressors from hydraulic shocks.

In refrigerated rolling stock cars, restaurant cars, passenger cars with air conditioning, the following are used to cool cabinets and small chambers for short-term storage of products. automated freon refrigeration units:

• compressor-motor;
• compressor-condenser;
• evaporator-regulating station;
• evaporator-condenser;
• compressor-condenser-evaporator.

The compressors of these units are usually vertical or V-shaped, multi-cylinder crankcase, with air-cooled cylinders. There are also hermetic units in which the compressor, together with the electric motor, is placed in a sealed casing. These units include installations of home refrigerators.

Rice. 1 - Scheme of the refrigerator "ZIL" Moscow

Refrigerator "ZIL-Moscow" is equipped with a compressor (7) (Fig. 1) with an electric motor (5), condenser (1), evaporator (2), thermostat (5), capillary tube (4), filter (5), starting and power relay. The compressor has a fitting (6) for charging with freon-12. The operation of the unit is controlled by a thermostat, which automatically maintains the set temperature in the refrigerator. The electric motor is switched on by a starting relay, in one case with which a thermal relay is mounted, which protects the motor from overload.

Restaurant cars are equipped with FRU and FAK freon units for cooling refrigerated cabinets and chambers. A diagram of a freon rotary unit (FRU) is shown in (Fig. 2), and units with a piston compressor are shown in Fig. 3.

Rice. 2 - Scheme of a freon rotary refrigeration unit: 1 - evaporator; 2 - thermostatic valve; 3 - liquid line; 4 - fuses; 5 - suction line; 6 - pressure switch; 7 - reinforcing shield; 8 - switches; nine - socket outlet; 10 - magnetic starter; 11 - discharge valve; 12 - gas filter; 13 - rotary compressor; 14 - air condenser; 15 - electric motor; 16 - suction pipe; 17- check valve; 18 - filter for liquid; 19 - receiver; 20 and 21 - receiver shut-off valves

Rice. 3 - Scheme of the freon refrigeration machine IF-50: 1 - evaporative battery; 2 - thermostatic valve; 3 - magnetic starter; 4 - sensitive cartridge of the thermostatic valve; 5 - heat exchanger; 6 - pressure switch; 7 - compressor and condenser unit

The refrigeration equipment of the all-metal restaurant car consists of three automatic compressor and condenser units of the FAK-0.9VR type, equipped with a drive from electric motors direct current PNF-5 with a voltage of 50 V. Each unit cools two drawers or cabinets equipped with evaporative batteries and accumulation plates. The car has three undercar boxes for storing fish, meat and drinks. In the dispensing compartment there is a cabinet for storing confectionery; a refrigerated cabinet, which is located in the kitchen, serves to store gastronomic products; next to it is a cabinet for cold dishes.

The refrigeration units of dining cars use two cooling systems- with direct boiling of refrigerant and accumulation. To cool the undercarriage boxes and cabinets, tubular evaporators made of copper pipes with flat brass fins, as well as evaporators made of copper pipes with a cross section of 12 × 1 mm with fins made of thin brass tape. Accumulation plates are installed in the undercarriage box for drinks and a cabinet for confectionery. They are welded stainless steel tanks with tubular plate evaporators inside. The annular space inside the tanks is filled with water, which freezes during the operation of the unit and accumulates cold.

All drawers and cabinets are equipped with thermostatic valves. The cyclical operation of the refrigeration units is provided by the pressure switch RD-1, which automatically acts on the starting equipment of the electric motors.

Rice. 4 - Schemes of automated reciprocating refrigeration units with several cooled objects: a - with on-off control; b - when servicing two cameras; c - when controlling the temperature with the help of temperature controllers; 1 - compressor; 2 - receiver; 3 - capacitor; 4 - evaporator; 5 - thermostatic valves; 6 - pressure switch; 7 - magnetic starter; 8 - electric motor; 9 - automatic pressure throttle; 10 - check valve; 11 - intermediate relay; 12 - solenoid valve; 13 - thermostat; 14 - water control valve

Typical automation schemes for compression piston refrigeration units with several cooled objects can be made in various versions. Automation scheme for on-off control in one or two evaporators with the same chamber air cooling temperature (Fig. 4, a) provides for the use of an evaporator temperature switch, a chamber or a compressor low pressure switch. When one refrigerating machine serves two chambers with different temperatures(Fig. 4, b) use an automatic pressure throttle (9) (ADD). The temperature control scheme using temperature controllers is shown in Figure 4, c.