Automation of refrigeration plants involves equipping them with automatic devices (devices and automation tools), with the help of a safe operation and carrying out a production process or individual operations without direct participation of service personnel or with partial participation.
Automation objects in conjunction with automatic devices form automation systems with different functions: control, signaling, protection, control and control. Automation increases economic efficiency The works of refrigeration units, as the number of service personnel decreases, the flow rate of electricity, water and other materials is reduced, the service life of the installations is increasing due to maintaining automatic devices of the optimal mode of their operation. Automation requires capital expenditures, so it is necessary to carry out it, based on the results of technical and economic analysis.
The refrigeration unit can be automated partially, completely or complex.
Partial automationit provides for all refrigeration installations automatic protection, as well as control, signaling and often control. The service personnel regulates the main parameters (temperature and humidity of air in the chambers, the boiling point and condensation of the refrigerant, etc.) when they deviates them from the specified values \u200b\u200band disruption of the equipment, which is informed by the control and alarm systems, and some auxiliary periodic processes ( Towing it from the surface of cooling devices, removing the oil from the system) are performed manually.
Full automationencompasses all processes related to maintaining the required parameters in cooled rooms and elements. refrigeration Installation. The service personnel may be present only periodically. Fully automate the small refrigeration units, reliable and durable.
For large industrial refrigeration plants more characteristic comprehensive automation(automatic control, alarm, protection).
Automatic control provides remote measurement, and sometimes recording parameters that determine the operation mode of the equipment.
Automatic alarm - Notification using a sound or light signal about achieving specified values, certain parameters, turning on or off elements, refrigeration unit. Automatic signaling is divided into technological, warning and emergency.
Technological alarm system - light, informs about the operation of compressors, pumps, fans, the presence of voltage in electrical circuits.
Warning alarm on protective, circulating receivers reports that the magnitude of the controlled parameter is approaching the maximum permissible value.
Alarm light and sound signals notifies that automatic protection worked.
Automatic protection that ensures the safety of the service personnel is required for any production. It prevents emergency situations, turning off individual elements or installation as a whole, when the controlled parameter reaches the maximum valid value.
Reliable protection in the event of a dangerous situation should provide an automatic protection system (SAZ). In the simplest SAZ variant consists of a sensor-relay (protection relay), which controls the value of the parameter and generating a signal when its limit value is reached, and the device that converts the protection relay signal into a stop signal, which is sent to the control system.
On the refrigeration plants of high power, the SAZ is performed so that after responding to the protection relay, the automatic launch of the refused element without eliminating the cause caused the cause has been impossible. On small refrigeration units, for example, in trade enterprises, where the accident cannot lead to serious consequences, there is no permanent maintenance, the object turns on automatically if the value of the control system of the parameter is returned to the permissible area.
Compressors have the largest number of protection species, since 75% of all accidents on refrigerated installations occur with them.
The number of parameters controlled by SAZ depends on the type, compressor power and the view of the refrigerant.
Compressor Protection Types:
from an unacceptable increase in pressure pressure - prevents the density of the compounds or the destruction of the elements;
invalid reduction of suction pressure - prevents the load on the compressor seal, foaming oil in the crankcase, freezing the coolant in the evaporator (high and high relays low pressure, almost all compressors are equipped);
reducing the pressure difference (before and after the pump) in the oil system - prevents emergency wear of the driving parts and the encoding of the mechanism of the compressor movement, the pressure difference relay controls the pressure difference on the discharge side and suction of the oil pump;
incassive increase in the discharge temperature - prevents the cylinder lubrication mode and emergency wear of the driving parts;
enhance the temperature of the winding of the built-in electric motor of hermetic and non-alternating refrigeration compressors - prevents overheating, rotor jamming and operation on two phases;
hydraulic impact (entering a liquid refrigerant in the compression cavity) - prevents a serious accident of the piston compressor: the density violation, and sometimes destruction.
Types of protection of other refrigeration elements:
from the freezing of the coolant - prevents the evaporator pipe break;
the overflow of the linear receiver - protects against the reduction of the efficiency of the condenser as a result of filling the part of its volume with a liquid refrigerant;
emptying linear receiver - prevents breakthrough gas high pressure In the evaporation system and the danger of hydraulic impact.
Preventing an emergency provides protection against an invalid concentration of ammonia indoors, which can cause a fire and an explosion. The concentration of ammonia (maximum 1.5 g / m 3, or 0.021% by volume) in the air is controlled by a gas analyzer.
Installations of propane cooling of natural gas are intended for simultaneously providing the required parameters of the point of dew on water and hydrocarbons by condensation of the aqueous and hydrocarbon fraction (HC) low temperatures (up to minus 30 0 s). The source of the cold is an external propane refrigeration cycle.
The main advantage of such installations is the low loss of the feedstock pressure (the throttle of the natural gas flow is not required) and the ability to extract the C3 + production fraction.
To prevent hydrate formation, an injector injection is used: ethylene glycol (for temperatures not lower than minus 35 0 s) and methanol (for temperatures up to minus 60 0 s).
Reliability
Efficiency
Possible options
The well-saturated stream of natural gas is fed to the input separator (1), in which free water and HC faction are removed from the stream. The gas fraction is sent to the gas gas-gas (2) heat exchanger for pre-cooling with a flow of dry rebno gas from a cold separator. To prevent hydrate formation in the heat exchanger, nozzle devices for the injection of an inhibitor (methanol or ethylene glycol) are provided.
Fig. 3. Schematic scheme propane refrigeration unit
After pre-cooling in the gas-gas heat exchanger, the stream is fed to the gas-propane heat exchanger (chiller) (4), in which the flow temperature is reduced to a given value by means of heat exchange with a flow of boiling propane. The raw flow is in the pipe beam, which in turn is immersed in the volume of refrigerant.
The pair-forming mixture formed as a result of cooling comes to the division into a low-temperature three-phase separator (5), where it is separated on the streams of the reinforcement gas, condensate and saturated water inhibitor of the hydrate formation.
Dry reheated gas (SHC) is supplied to the countercurrent gas-gas (2) heat exchanger and then returned beyond the installation.
Liquid fractions are discharged by independent automatic level conclusions in the corresponding lines.
One of our main tasks is the fight against the myth that gas processing is difficult, long and expensive. Surprisingly, the projects that in the United States are implemented in 10 months, in the territory of the CIS takes up to three years. Installations in the USA 5000 m2, in the territory of the CIS, are difficult to fit for 20,000 m2. Projects paying in the United States in 3-5 years, even with a significantly lower value of the product implementation, never pay off in Russia and Kazakhstan.
From dangerous regimes
In progress refrigerators and installations due to failures of individual nodes or aggregates, as well as due to violations in energy and water supply systems, hazardous modes can occur: increase pressure and temperature, fluid level in separate devices or machine nodes, cessation of rubbing pairs, lack of cooling water etc. If timely measures are not taken, compressors, heat exchangers or other installation elements can be damaged or destroyed. At the same time, there is a serious danger to the health and life of the staff.
The protection of refrigeration machines and installations includes a whole range of technical and organizational events providing them. safe operation. This chapter will consider only those that are performed on the basis of automatic devices and devices.
Ways to protect
The protection methods include the stopping of the machine or the entire installation, the inclusion of alarm devices, the production of the working substance into the atmosphere or the projection into other devices.
Stopping machine or all installation. This method is carried out using the automatic protection system (SAZ), which consists of primary devices - sensors-protection relay (or simply protection relays) and the electrical circuit transforming signals from the protection relay into the stop signal. This signal is transmitted to the automatic control circuit.
Protection relays perceive controlled technological values \u200b\u200band, when they reach the maximum allowable values, produce alarm. These devices possess most often relay two-position characteristics. The number of sensor-relays included in the SAZ is determined by the minimum necessary number of controlled values.
Electrical circuit It is performed in one of three options, in accordance with the SAZ there are once, with repeated inclusion and combined.
Sale of a single action Carries out a stop of the machine or installation when you trigger any protection relay and makes it impossible automatic starts before the intervention of the service personnel. This type of SAZ is distributed mainly on large and medium-sized machines. If the installation works without continuous maintenance and the equipment does not automatically turn on the reserve, the SAZ is complemented by a special alarm for emergency call for personnel.
SAZ with re-inclusion stops the machine when the protection relay is triggered and does not interfere with it automatically turning on when the relay returns to the normal state. It is used mainly in small trading types, where they seek to simplify the automation scheme.
In combined Saz A part of the protection relay controlling the most dangerous parameters is included in the electrical circuit of a single action, and a part with less dangerous parameters is to a repeated inclusion circuit. This allows, without resorting to help personnel, again automatically let the car, if it is not associated with the danger of the accident.
In practice, a variation of protection called blocking is also found. Its difference is that the signal is not received from the protection relay, but from the control circuit element or control a different unit or installation node (for example, a pump, fan, etc.). The blocking eliminates the start or operation of the machine when the specified order of the start of controlled aggregates is not fulfilled. Typically, the lock is performed according to the repeated circuit.
Enabling emergency devices. This method is also carried out by SAZ.
Emergency devices include:
Warning alarms about hazardous modes that are used on particularly large installations with continuous maintenance, so that it is possible to avoid stopping the machine;
An emergency signaling that informs the personnel on the operation of protection, as well as the decrypting specific cause of the emergency response;
Emergency ventilation included with the local or overall concentration in the air of explosion and fire-hazardous, as well as toxic working substances (for example, ammonia).
Release of the work substance into the atmosphere or bypass to other devices. This method is carried out by special safety devices (safety valves, safety plates, fuse plugs, etc.), not included in the SAZ. Their appointment is to prevent destruction or explosion of vessels and apparatuses when the pressure is raised as a result of the malfunction of the installation, as well as in the event of a fire. Selecting safety devices and rules for their use are determined. regulatory documents In accordance with the rules of safety and operation of pressure vessels.
Construction of protection systems
Protection systems differ depending on the type of refrigeration unit, its size, adopted method of operation, etc. When constructing all SAZ, it is necessary to take into account general principlesensuring the most important safety of work. As an example, a schematic diagram of a compression refrigeration unit consisting of a compressor of a CM with an electric motor D, heat exchangers of that and auxiliary devices of Wu - pumps, fans, etc. (Fig. 7.1). The scheme is represented by B. general Without specifying specific values \u200b\u200band parameters subjected to control.
Fig. 7.1. SAZ schematic diagram
It should be agreed that the SAZ is designed to stop the compressor when one of the parameters is maximum permissible value.
SAZ has ten protection channels. Channels 1-8 operate from the corresponding protection relays that perceive technological parameters. Channels 9 and 10 provide compressor lock and auxiliary devices.
The system includes a key with which if necessary (in samples and running), you can turn off part of the protective relays and blocking chains (2, 3, 5, 6, 8, 9, 10). The protection that should function in any installation mode is not to be turned off.
The SAZ electrical circuit consists of two parts. The first part in which the channels 2, 5, 9 and 10 are included in the re-enabled method, and the second with the other channels provides protection operating on the principle of a single action and controls the most responsible parameters. When they reach the maximum permissible SAZ values \u200b\u200bstops the compressor. Its subsequent starts is possible only after the staff intervention, which uses a special input button to work protection.
The signals from the SAZ electrical circuit are fed into the automatic control circuit of AU. These signals stop the compressor motor, regardless of the OU operational control signals.
In addition to the main function of the saz emergency stopping of the compressor, it performs and auxiliary operations: enabling the necessary alarms, as well as light and sound alarm. The decipheering alarm of repeated protection protection is valid only until the controlled parameter entered the normal limits. Alarm protection of a single action remains enabled after the triggement before pressing the input button to work, regardless of the actual state of the controlled parameter. Such a scheme seems to "remember" the triggering of protection and informs staff for an unlimited time.
The scheme presented can only be considered as an example of the construction of the SAZ. Specific systems can differ from it with the number of channels and methods of their inclusion.
The main requirement to the SAZ is high reliability, which is achieved by the use of highly reliable protection relays and elements of electrical circuits, reservation of relays and other elements of protection in particularly responsible cases, decrease in the number of elements consistently included in the SAZ, using the most secure electrical schemes, the organization of preventive inspections and Repairs in the process of operation.
The use of highly reliable protection relays and electrical circuit elements is the easiest and most natural way, since other things being equal to the use of more reliable elements allows you to create a more reliable system. It should only be borne in mind that when operating the relay and other elements of the SAZ have a very small cyclic operation (a small number of triggered). Therefore, when evaluating reliability in the calculation, there should be not cyclic durability and cyclic developments on the refusal, but other indicators characterizing the ability of elements to keep readiness for triggering (for example, a time for refusing to time). At the same time, any violation of the ability of the element to triggering is taken.
Reservation is a parallel inclusion of two or more homogeneous and jointly working elements that perform the same functions. The failure of one of them does not violate the efficiency of the system as a whole. Reservations are used in particularly dangerous cases when the sudden refusal of the SAZ may lead to serious consequences. Such cases include, for example, protection against liquid ammonia in the piston compressor. To do this, on the vessels in front of the compressor, the main and backup level relays are set.
The simplified scheme (Fig. 7.2) shows a separator of a liquid ammonia of the coolant, mounted between the evaporator and the compressor KM. With normal operation, liquid ammonia in the liquid separator is absent. When emissions of fluid from the evaporator, it accumulates in a separator of liquid ammonia, and if its level reaches a permissible limit, the relay is triggered by the RZ 1 and RZ 2 (the diagram shows their primary converters). Both relays are constantly included in the work and perform the same function. Such reservation significantly increases reliability, since the probability of simultaneous failure of both relays is extremely small.
Reducing the number of elements consistently included in the SAZ is one of the ways to increase the reliability of electrical SAZ schemas. The most reliable system in which the protection relay is associated directly with the engine of the compressor engine without intermediate elements. However, this scheme is used only on the smallest installations. In larger installations, you have to use intermediate relays, which reduces reliability. Therefore, the number of consecutive intermediate elements included in the compressor emergency disconnection circuit must be minimal.
Fig. 7.2. Simplified scheme of liquid separator with reservation of protection relay
from the wet stroke of the compressor
When using the safest electrical circuits, a compressor is stopped in the occurrence of failures in the SAZ. The most characteristic refusal of the electrical circuit is the broken (disappearance of voltage or current), which may occur during the physical cutting of the wires, the burning of contacts, the failure of the radio electronic elements (diodes, transistors, resistors, etc.), disorders in the operation of power sources. In order for the specified refusals to be signaled as an emergency, it is necessary that in the protection circuits at a normal state circulated current, and the emergency stop signal corresponded to its termination. Consequently, the most secure is the electrical protection scheme for normally closed contacts or other elements.
Thus, in the diagram (Fig. 7.3) Contacts of the RZ 1 protection relay, RZ 2 and RZ 3 are closed if the controlled values \u200b\u200bare under normal limits, and open when the maximum permissible values \u200b\u200bis reached. These contacts are included in a circuit of the winding circuit of the electromagnetic relay, which, when trigging protection, turns off the magnetic starter winding (not shown in the diagram) and stops the compressor.
Fig. 7.3. Electrical protection scheme for normally closed contacts
When all the contacts are closed, the circuit of the electromagnetic relay can be entered into operation a short-term press of the KZO button. At the same time, the current flows through the winding of the electromagnetic relay, this relay will work and closes its contact of the RA. After the button is released, the chain remains under the current. It is fairly one of the relay protection to smash contact, as the electromagnetic relay releases and its contact will open. Re-enable will be possible only after pressing the button. This is a single-action scheme. In a diagram with a re-enable contact, the RA contact and the button are not required.
The organization of preventive inspections and repairs in the process of operation plays a decisive role in ensuring safe work installations. These measures, if they are performed through the necessary intervals, practically eliminate dangerous situations associated with sudden failures in SAZ.
To organize preventive inspections, it is necessary that the SAZ is supplied with devices and adaptations allowing full Check the performance of protection. It is desirable that the check does not cause the installation for the maximum permissible modes. So, in the diagram (see Fig. 7.2) Check the operation of the protection relay can be without filling the liquid separator.
With normal operation, the valves in 1 and in 2 are open, and the valve is closed. Primary relay converters Protect RZ 1 and RZ 2 connected to a vessel.
For checking, the valve is closed in 2 and open the valve in 3. From the pipeline, the liquid is supplied directly into the float chambers of the level relay and fills them. If the relay is working, then they triggered, give the corresponding signals.
After that, the valve is closed in 3, and the valve is open. The fluid flows into the vessel, which indicates the absence of clogging of the coupling pipe.
During operation, a graph of preventive inspections should be operated, the frequency of which should be selected taking into account the actual reliability indicators.
SAZ composition
The number of parameters controlled by the SAZ depends on the type of equipment, its size and performance, the type of refrigerant, etc. Usually the number of protection increases with an increase in the size of the equipment. More complex SAZ is usually used on ammonia installations.
In tab. 7.1 shows the recommended list of controlled parameters for the most common species refrigeration equipment. For some types of equipment, several options for the protection set are proposed, which are selected based on specific conditions. So, for sealed compressors You can use two options. An embodiment with built-in devices for protecting the temperature of the windings of electric motors is preferred, since with the same number of instruments, protection is provided from a larger number of faults.
In tab. 7.1 did not entered the compressors of household refrigerators and air conditioners.
Some of the protection included in the SAZ is not necessarily entering a single-acting scheme, if necessary, it is allowed to include them in a repeat-inclusion circuit.
On highly large installations with screw and centrifugal compressors, it is advisable to apply warning alarms. When the parameters reaches the maximum valid values, warning alarm is activated. The compressor stops only in the case when the parameter does not enter the normal limits at a given period of time. Parameters allowing inclusion through warning alarms are also marked in Table. 7.1. At the same time, attention should be paid to the reliability of the temporary delay device and, if necessary, take appropriate measures, such as reservation.
Table 7.1.
| Equipment | Pressure | Temperature | Liquid level | Axial shift Vala | Application area | |||||||||
| Boiling (Temperature) | Suction | Digging | Digging | Oil | oil reducer | Motor windings | Bearings | exiting coolant | ||||||
| Compressor piston hermetic | +* +* | +* +* +* +* | + | Claudone compressors of small refrigeration units (trade equipment, air conditioners, etc.) Same " | ||||||||||
| Compressor piston insalnikovy | + + + + + +* | + + + + + +* | + + + + | + | + + | Claudone compressors of average performance The same Claudone compressors of great performance The same Claudone compressors of small refrigeration units | ||||||||
| Compressor piston open | + + | + + | + + | + | Cladon and ammonia compressors of average performance The same, great performance | |||||||||
Ending table. 7.1.
| Equipment | Pressure | Pressure drop in oil system | Temperature | Liquid level | Axial shift Vala | Application area | |||||||
| Boiling (Temperature) | Suction | Digging | Digging | Oil | oil reducer | Motor windings | Bearings | exiting coolant | |||||
| Aggregate compressor helix | +** | + | + | +** | |||||||||
| Aggregate compressor cencing | +** | + | + | +** | +** | +** | +** | + | Ammonia and Claudon Units | ||||
| Ammonian shell-tube evaporator | +*** | Without limit | |||||||||||
| Cladonic evaporator with part-tube boiling | +*** | Also | |||||||||||
| Cladonic evaporator with intra-tube boiling | +*** | » | |||||||||||
| Liquid separator, Circulator receiver | + | » |
Note. An asterisk (*) means that protection is envisaged:
* It is allowed to turn on by a repeated circuit.
** It is allowed to stop the compressor after turning on the warning alarm.
*** It is allowed through the warning alarm.
Automation Systems
Air conditioning
Similar information.
The automated control system contributes to the creation of protection against various emergencies. Helps increase the life of the equipment used. Reduces the number of employees involved in the maintenance of equipment. This reduces the risk of the influence of the human factor, saves financial costs of labor, reduces the level of risk injury.
Automation of refrigeration equipment, refrigeration machines of different power allows you to adjust all parameters. The algorithm is able to regulate the submission of the refrigerant evaporators. It is responsible for moving liquids, pickles, water, other substances in refrigeration.
Automation of refrigeration systems allows you to run, scheduled compressor stop, electric motor, other mechanisms. At the same time, stopping the work of refrigeration equipment occurs when an emergency occurrence.
The blocking algorithm set does not allow the refrigeration machine to continue. It ceases to function before entering the permissive command. It happens when the refrigeration equipment is eliminated. Also the unit will stand still during the implementation repair work, service Enterprises.
Automation of the refrigeration unit makes it possible to adjust the indicators of the specified temperature mode of the room. If it is broken, the automation serves the corresponding beep.
In the occurrence of temperature failures of the propane refrigeration unit, an automatic reduction of cooling processes is allowed.
Competent automation of aggregates involves regulating a smooth or positional type. In the first case, automation performs a smooth change in the number of revolutions used. In the second - reducing the number of cylinder, compressors, other mechanisms included in the operation of devices.
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The service personnel of a non-automatic refrigeration unit allows and stops the refrigeration machine, adjusts the supply of a liquid agent to the evaporator, adjusts the temperature in refrigerated camerasah and cooling capacity of compressors, observes the operation of the devices, mechanisms, etc.
With automatic regulation of refrigeration machines, these manual operations disappear. Operation of the automated installation is much cheaper than the operation of the installation with manual adjustment (reducing the cost of maintenance of the service personnel). Automated installation cost-effective energy, more accurately supports the specified temperature modes. Automatics devices quickly react to all sorts of deviations from normal working conditions, and when the hazard occurs, the installation is turned off.
Apply various automatic devices - control, control, protection, alarm and control.
Automatic control devices include or turn off in a certain sequence of machine and mechanisms; include backup equipment during system overloads; Include auxiliary devices When pulling it from the surface of the cooling batteries, the production of oil, air, etc.
Automatic control devices are maintained under certain limits the main parameters (temperature, pressure, fluid level), on which the normal operation of the refrigeration unit depends, or regulate them in accordance with the specified program.
Automatic protection devices when hazardous conditions occur (excessive increase in pressure pressure, overflow by liquid ammonia, damage to the lubrication system), turn off the refrigeration unit or part of it.
Instruments automatic alarm Feed light or sound signals when the controlled value reaches the specified or maximum valid values.
N. D. Kochetkov
322 Automation of refrigeration units
Automatic control devices (self-inspection devices) Regient-powered parameters of the machine (temperature at different points, pressure, number of circulating agent, etc.).
Comprehensive automation provides for the equipment of the cooling equipment of the automatic control, control and protection devices. Control and alarm means are needed only to monitor the correct action of these devices.
Currently, the installation is small and much of the average performance settings are automated completely; Large installations in most cases are automated partially (semi-automatic installations).
Automatic refrigeration control
Installations
The automatic control devices used are distinguished by a variety of functions performed and action principles.
Each automatic regulator consists of a sensitive element that perceives the change in the adjustable parameter; controller; Intermediate bond connecting the sensitive element and regulating body. Consider ways to regulate the main parameters and the most characteristic devices.
Regulating the temperature of refrigeration chambers. In refrigeration chambers, it is necessary to maintain constant temperatures, even if the thermal load on the cooling batteries is changing.
The constant temperature is maintained by adjusting the cold-performance batteries. Simple and distributed is a two-position regulation system. With this system, an individual temperature relay is installed in each chamber, for example, the type of TDDa is a two-position remote thermaller (Fig. 193), or other types. On the pipeline of the liquid refrigerant or brine before entering the battery, a solenoid valve is installed (Fig. 194). With an increase in the temperature of the air to the upper specified limit, the temperature controller automatically closes the electrical circuit of the solenoid valve. The valve is fully opened, and the coolant enters the battery; Cameras are cooled. When the air temperature drops to the lower specified limit, the temperature controller, on the contrary, opens the valve chain, stopping the flow of cold fluid in the battery.
Termobalon 1
(sensitive cartridge) Temperature controller TDDA (see Fig. 193), partially filled with liquid phone-12,
Automatic refrigeration adjustment 323
placed in the refrigeration chamber, the temperature of which is required to be adjusted. Freon pressure in the thermobalone depends on its temperature, which is equal to the air temperature of the camera. With an increase in this temperature, the pressure in the thermobalone increases. Increased pressure through the capillary tube 2 is transmitted to the chamber 3, in which the bellows 4, representing
a corrugated tube. The siltphone is compressed and moves in the axial direction to the needle 5, which turns the angular lever 6 (see also the scheme to the right) around the axis 7 counterclockwise, overcoming the resistance of the spring 22. Lever 6 peashes on itself a plate-in-one with an 8-hinged PRA Which when moving the lever counterclockwise moves to the left. The finger 10 is bonded with a finger 10, moving in the slots of the contact plate 12. At some point, the finger comes into contact with the lever 9 and turns this lever, as well as the contact plate 12 (which is associated with the spring arm 11) around the axis 13 (in this case counterclockwise ). In it
324 Automation of refrigeration units
the bottom end of the contact plate is approaching a constant horseshoe magnet 18 and is rapidly attracted by it. The main 17 and the sparkling 26 contacts are closed. Chain control of the solenoid valve installed on liquid line, closes, the valve opens, th liquid enters the battery.
With a decrease in the air temperature, the pressure in the thermobalone and in the chamber 3, where the bellows is located, decreases and the angular lever 6 under the action of the spring 22 is rotated clockwise. Finger 10 moves from the lever 9 to the end of the slot in the contact plate 12 (free stroke), presses on the plate and, overcoming the magnet attraction, turns sharply clockwise. At this point, the electrical contacts are blocked, the solenoid valve is closed and the flow of fluid in the battery stops.
Automatic regulation of refrigeration settings 325
The temperature of the chamber at which electrical con-clocks is blocked, is mounted depending on the springs tension 22. To adjust the device to a certain point of opening, the carriage 21 with a pointer 20 to the corresponding division of the temperature scale 19, which is achieved when rotating the screw 23 handle 24.
The device is regulated by a certain difference in closure temperature and opening of electrical contacts. This difference depends on the magnitude of the free move 10 in the slot of the contact plate. The free move changes when moving the top end of the lever 9 along the slot, which is achieved when the cam is turned around around the axis 13. The more the cam radius in the touch of the lever 9, the greater the free move and the greater the difference in the temperature of the closure and opening of contacts.
The TDDA temperature controller ensures that the solenoid valve is turned off within the temperature scale from -25 to 0 ° C. Possible error of ± 1 ° C. The minimum differential of the device is 2 ° C, the maximum is at least 8 ° C. Mass of the device is 3.5 kg , Capillary length 3 m.
For large refrigerators, a multipoint centralized system of automatic temperature control in the chambers is developed - Amur machine. Such machines are manufactured by Pa 40, 60 and 80 adjustment points. They can be used not only to regulate the air temperature, but also the boiling point of the refrigerant, the temperature of the brine, etc. The machine has devices for measuring temperature at the control points.
Solenoid (electromagnetic) valves (see Fig. 194) work as follows. When the voltage is submitted to the electromag-nita coil arises electric fieldwhich draws the core; The unloading valve associated with it is lifted by opening the saddle of the small diameter. After that, the fluid from the discharge side, i.e., from the cavity above the valve (in the VAT) or above the membrane (in the VVM ventilator) through the through holes n small saddle enters the cavity under the valve. The valve is unloaded from the pressure, which pressed it to the saddle, and opens for fluid duct under pressure from the injection pipeline. After turning off the solenoid coil, on the contrary, the header with the discharge valve is lowered down, overlapping the saddle of the small diameter. The pressure on top to the main valve increases, and it is under the action of its own weight and spring is lowered onto its saddle, overlapping the fluid flow.
Solenoid valves are among the most common devices for ammonia and freon refrigeration
326 Refrigeration Automation
novok. For liquid and gaseous freon and ammonia, brine and water, solenoid valves are produced with a diameter of a conditional pass from 6 to 70 mm. Previously used predominantly piston solenoid valves of type SPE; Recently, membrane valves of the TSM type of improved design are used. The temperature of the working environment may vary from -40 to + 50 ° C. The solenoid valve (with a filter in front of it) is installed on a horizontal section of the pipeline in a vertical position.
The adjustment of the air temperature is also possible by changing the temperature or consumption of the refrigeration agent (when cooled cooling) in batteries using proportional-nyline PRT temperature regulators. Such regulators are rarely used.
To automatically control the temperature of the air with the use of small freon settings with one cooled object-volume, the compressor is turned on and off. To turn on and off, use devices that react to the temperature or boiling pressure in the evaporator, or directly at the air temperature of the camera.
Regulation of the cooling capacity of compressors. The heat-loading of refrigeration chambers can vary widely depending on the number and temperature of the incoming products, ambient temperature and other factors. The cooling and dity of the installed compressors is chosen with the calculation of maintaining the required temperatures under the most difficult conditions.
In small freon installations of direct evaporation, the performance of compressors is adjusted simultaneously with adjusting the temperature of the cooled object by the start and stop method at the corresponding values \u200b\u200bof one of the adjustable parameters.
In brine cooling machines, the most convenient parameter for regulating the performance of the compressor is the pickle of the brine when leaving the evaporator. In the case of a decrease in the thermal load, the toll temperature in the evaporator is quickly reduced to the lower specified limit and the temperature controller (for example, the type of TDDA), the erosion chain of the magnetic starter coil, remains-lifts the compressor electric motor. With increasing temperature to the top specified limit, the temperature controller includes a new compressor to work. The greater the thermal load on the evaporator (cooling batteries), the longer the compressor works. Changing the working time coefficient achieved the necessary Automatic regulation of refrigeration settings 327
the average performance of the compressor.
In medium and large installations, the system contains a large number of batteries intended for cooling many rooms. When the specified temperatures are reached in separate rooms, part of the cooling batteries must be turned off with the cooling capacity of the compressors, respectively, is reduced.
The most acceptable in this case is a multi-position (stepwise) regulation by changing the working volume, described by pistons of compressors. In settings with several compressions, the multi-position control is carried out on and off the individual compressors controlled by temperature controls with offset settings. The presence of two identical compressors allows three stages of cold-productivity: 100- 50-0%. Two AV-100 and AU-200 compressors give four stages of cooling capacity: 100-67-33-0%. The stepwise regulation of multi-cylinder nonmediate computers may be turned off from the work of individual cylinders by pressing the suction valves with a special mechanism controlled by low pressure relay.
Much less often use smooth regulation of the manufacturer of the compressor-throttling of the suction steam, the change in the magnitude of the dead volume of the compressor, etc. These methods of energy-ki are disadvantageous. Comparatively promising is the method of regulating the cooling capacity by changing the number of revolutions of the compressor (the use of multi-speed electric motors).
Regulation of refrigerant supply to the evaporator. Regardless of the magnitude of the heat load, automatic control devices must ensure proper filling of the evaporator with a refrigerant. Excess fluid in the evaporator can not be allowed, as it leads to a decrease in the cost-effectiveness of work and to the occurrence of hydraulic impact ("wet stroke").
In the event of a lack of fluid, some of the surface is not used, which also worsens the operation of the operation due to the decrease in evaporation rate.
The devices that regulate the supply of fluid into the evaporator are the thermoregulating valves of the TRV and float control valves PRV. In the same devices, the process of throttle fluid is carried out.
The main type of productable thermal control valves -Mambrane, in a metal case. The inclusion scheme of TRV is shown in Fig. 195. The effect of the device depends on the overheating of the feather coming out of evapo-
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tel. The absence of overheating indicates excess fluid in the evaporator and the possibility of entering it into the suction line and into the compressor. In this case, TRV automatically stops supplying the fluid to the evaporator. A large overheating of the chest of refrigerant during suction is, on the contrary, a sign of a shortage of it in the evaporator. At the same time, the TRV condition enhances fluid supply.
In the ammonium valve of the TRV, the thermobalon (sensitive element of the device) is filled with freon-22, close to the working pressures to Ammon Aku. The thermobalon is tightly attached to the suction pipeline; It has ammonia vapor temperature overlooking the evaporator.
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When the temperature changes, the pressure in the thermobalone changes. The valve of the valve is mechanically connected to the membrane on which the pressure of the thermobalone pair is applied on top of the capillary tube, and the pressure from the evaporator along the equalization tube (through the fitting 7). From the difference in these pressures, proportional to the outlet of the vapor at the outlet of the evaporator depends on the displacement of the membrane, and at the same time the opening of the valve controlling the flow of fluid into the evaporator. Ammonia enters the TRP through the fitting 10. The throttling is performed and the valve opening and partially in the throttle tube 8, which provides a more relaxed and equal measuring agent through the valve.
During the operation of the machine, the Trp supports constant steam overheating; The overheating value corresponding to the adjustment can be changed from 2 to 10 ° C. The setting is carried out using the screw 4 and the adjusting gear associated with it. When rotating the screw, the tension of the spring 3 changes, opposing the valve opening.
TRP allows you to reliably regulate the supply of ammonia to evaporators different types At boiling temperatures from 0 to -30 ° C. Power of co-gas-tube evaporators for cooling brine is adjusted for small overheating (from 2 to 4 ° C). Different models of the TRP are produced, designed for cooling capacity from 6 to 230 kW (~ 5-200 μAL / h).
TRV for 12-190 kW 10-160 mcal / h) For freon installations in the design close to the valves of the TRP type. In small freon machines, membrane TRVs are used without equalizing lines.
The adjustment of the ammonia supply to evaporators and vessels with a free level of fluid is possible with the help of float controls of the Low PRV (Fig. 196).
PRV is set at the level, which is desirable to support the evaporator (or other vessel). The body of the device is connected to the evaporator with equalizing lines (liquid and steam). The change in the level of fluid in the evaporator leads to a change in the level in the PRV housing. At the same time, the position of the float inside the case is changing, which causes the valve to move and change the cross-sectional area for fluid flow from the condenser to the evaporator.
In the float valves of the indispensable type, the refrigeration agent Pos-le throttling in the valve opening comes directly into the evaporator, bypassing the float chamber. In the valves of the passage of the refrigerant, after throttling enters the float chamber, and from it is given to the evaporator.
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liquid level in evaporators and vessels. Unlike low pressure valves, PR-1 can be installed at different levels relative to the evaporator and condenser.
The fitting, connecting the valve with the bottom of the capacitor, is welded to the valve body. Inside the housing is a float associated with a lever with a needle valve. Ammonia through the hole in the valve seat, the channel and the throttle passes to the output
stacker and through it into the pipeline to the evaporator. Inside the body of the valve there is a capillary tube. The upper end is open, and the lower with the help of the channels is connected to the throttle tube. Pressure in the valve is set slightly lower than in the condenser; The liquid from it enters the valve body. Under the action of fluid float floats. The larger the fluid enters the housing of the pop shop, the more the valve opens to pass it into the evaporator. When using a valve type PR-1, the condenser is free from liquid. Therefore, the amount of ammonia in the system should be such that with the full flow of ammonia into the evaporator, the fluid level in it was not higher than between the first and second above the rows of the evaporator pipes. With this fill
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the risk of fluid ammonia into the suction line is also created. favorable conditions For intensive heat exchange in the evaporator.
For positional control of the level of fluid in the refrigeration unit, indirect level control regulators are often used from a level indicator (for example,
DU-4, RU-4, PRU-2) and the solenoid valve controlled. These devices are included in the circuit (Fig. 198) so that in the case of an excessive increase in the level of fluid in the device, the remote pointer is once-in the electrical circuit of the control of the solenoid valve and it closes, stopping the supply of the refrigerant in the evaporator.
If the level of fluid in the evaporator drops compared to op-tyrimal, then the remote pointer will again be closed by the electrical chain of the solenoid valve; Fluid supply will be resumed.
Regulation of the cooling water supply to the condenser.
The water on the condenser is supplied through the water regulating valve
(Fig. 199) supporting approximately constant pressure and temperature of condensation at different loads. Condensation pressure perceives the valve membrane or a bellows, changing the spindle position and the section for water passage. In installations with cooling towers, water-adjusting valves do not apply.
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