Procedure for calculation of refrigeration unit for three boiling points - exchange rate

Automation Diagram Description

In modern technology, automation means a set of technical measures that partially or completely exclude the participation of people in a particular technological process. When talking about the automation of refrigeration machines and plants, they usually mean the automation of their operation during operation.

Automation of refrigeration machines and plants is carried out in order to increase their economic efficiency and ensure the safety of people's work. Increase of economic efficiency is achieved due to reduction of operating costs and expenses for equipment repair, and operation safety - by use of automatic devices protecting plants from operation in hazardous modes.

There are two degrees of automation - complete and partial.

With partial automation, automation devices control only some process operations. Therefore, continuous maintenance and supervision by technical personnel is required.

With complete automation of the device, automatics completely control the main processes, which allows you to abandon continuous maintenance. The service can be periodic (once a day, per week, etc.) or, if necessary, with the participation of personnel.

12.1 Justification of automation scheme selection

The refrigeration unit serves three boiling points: t1 = -10 ° С, t2 = -30 ° С, t3 = -40 ° С. The company uses a compound circuit with parallel compression and sequential throttling. For this installation we accept the integrated automation scheme. This makes it possible to reduce the number of serviced personnel of the compressor shop and reduce the cost of cold generation.

12.2 Description of controlled parameters of the refrigeration unit

12.2.1 Compressor unit automation

In the scheme of the refrigeration unit, one screw unit is installed for each boiling point. Compressor units operating in single-stage compression mode are equipped with the following devices in accordance with the purpose. Emergency protection providing emergency shutdown of the compressor.

• In case of excessive injection pressure increase;

• In case of excessive reduction of suction pressure;

• If the allowable discharge temperature is exceeded;

• If there is insufficient water flow in the compressor cooling system;

• If the oil pressure in the compressor lubrication system is insufficient.

Maximum permissible level sensors in circulation receiver are connected to compressor automatic protection system.

Compressors are started and stopped via compressor control system by signals from temperature sensors installed on liquid pipelines from circulation receivers to pumps and from pressure sensor installed on gas line of compound receiver.

Furthermore, it is necessary to be able to control the compressor capacity depending on the change in temperature of the liquid refrigerant or air in the chambers and on the change in pressure in the gas line recorded by the temperature and pressure sensors described above. When the compressors operate, the following parameters must be monitored:

• Suction refrigerant pressure and temperature to compressor (10, 13; 26, 29; 42, 45);

• Compressor discharge pressure and temperature (9, 12; 25, 28; 41, 44);

• Oil pressure in compressor lubrication system (78; 23-24; 3940).

Instruments monitoring the above parameters shall be installed in situ (on the compressor instrument panel). To provide centralized control of several compressors and to facilitate large refrigeration plants, it is recommended that local devices be duplicated with an electrical output sensor in order to output readings to the central control panel. All actuating, warning and emergency alarms are also displayed on the central control panel, and the alarm on the row with the light must be duplicated with sound.

12.2.2 Circulation Receiver Automation

The following devices are installed on the compound circulation receivers:

● from exceeding the maximum permissible level in the receiver there are two duplicate level relays included in the compressor automatic protection circuit (alarm) (55, 56, 66, 67, 76, 77);

● level relay (warning alarm) is installed from increased filling of circulation receiver (57, 68, 78);

● receiver operating filling level switch controls closing and opening of electromagnetic valve installed on liquid coolant line (58, 69);

● filling of compound receiver is controlled by closing and opening of electromagnetic valve, which receives signal from temperature relay installed on receiver (79, 80).

12.2.3 Automation of drainage and linear receivers

The drain and line receivers are provided with level sensors monitoring the upper and lower filling levels of the vessel, as well as pressure indicators (49, 50, 53, 90, 91, 93).

12.2.4Automatization of ammonia circulation pump

Sealed circulation pumps have system of independent cooling with liquid ammonia. For safe operation of the pump, the cooling jacket of the pump must always be filled with liquid ammonia. This is controlled by a level sensor (64, 75, 86) installed on the line connecting the cooling jacket of the pump to the steam part of the receiver. In order that the liquid from the cooling jacket does not flow into the receiver on the line connecting them, a control valve or diaphragm is installed behind the level sensor. For safe operation of the pump, it is necessary that the difference in liquid pressure at the suction to the pump and at the discharge is not less than the passport value, which is controlled by the on-off pressure switch (6263; 73-74; 8485). These pressures shall be monitored by means of pressure indicators installed on the respective pipelines. When the liquid level in the cooling jacket of the pump decreases or the pressure drop decreases, the pump is automatically shut down and an alarm signal is sent. Pump start-up is blocked with compressor start-up system. The compressor cannot be started until the pump is started.

12.2.5 Water Pump Automation

Water pumps shall be protected against flow failure, which is controlled by a pressure difference relay (96), the sensor of which is installed on the suction and delivery pipelines. Pressure indicator sensor (97) is installed on delivery pipeline.

12.2.6 Water Horizontal Condenser Automation

The following devices are installed on the water condenser:

● pressure gauge (103), which controls the pressure in the condenser;

● flow relay (102), which controls the supply of cold water to the condenser for cooling the refrigerant and controls the start and stop of the compressor motor.

12.2.7 Automation of oil separator and oil collector

Only pressure indicators (88.89) are installed on the oil separator and oil collector.

12.2.8 Cooling tower automation

The following instruments are installed on the cooling tower:

● temperature relay (99), which controls the temperature of the cooling water of the screw units and controls the start and stop of the fan motor of the cooling tower (98);

● level switch (100), which controls the addition of fresh water to the cooling tower and controls the closing and opening of the electromagnetic valve installed on the pipeline, fresh water (101).

12.2.9 Automation of cooling devices

To maintain the required air temperature in the room, individual power supply of cooling devices is used. In this scheme, liquid coolant is supplied to cooling devices using an electromagnetic valve according to signals from temperature sensors installed in the premises (106,110,114). The boiling pressure (temperature) is kept constant in the circulation receiver. For this purpose, temperature sensors (54, 65) are installed on the liquid line from the circulation receiver to the pump, according to the signals of which the compressor control system changes the capacity.

12.3 Automation Diagram Description

The thermostat (KP63, KP68, KP73) monitors the air temperature in the chambers, the liquid coolant filling control signal of the cooling devices (positions 105, 109, 113) through the electromagnetic valve (positions 106, 110, 114).

Thermostat (KP81, KP77, KP79) controls the discharge temperature, automatic protection signal (positions 12,28,44).

Low pressure switch KP1A (positions 10,26,42) controls the suction pressure, protection signal when the suction pressure drops below the allowable value.

High pressure switch KP5A, KP1A (positions 9,25,41) controls the discharge pressure, protection signal in case of excessive pressure increase.

The low pressure switch DEM 10502 monitors the discharge pressure of the water pump (position 96), the pressure relief protection signal.

The level switch PS501 controls the level of liquid coolant in the circulation receiver (positions 55, 56, 66, 67, 76, 77), the protection signal when the vessel filling limit is reached.

Level switch PMFL 801, PMFL 802 controls the level of liquid coolant in the circulation receiver (positions 58, 69), the filling control signal by closing or opening the electromagnetic valve (position 59.70).

The POC501 level switch regulates the level of filling with liquid coolant of a linear receiver (position 90, 91), a protection signal at achievement of the lower or top levels.

The POC501 level switch regulates the level of filling with liquid coolant of a drainage receiver (position 49, 50), a protection signal at achievement of the top or lower levels.

Description of refrigeration unit diagram

The design provides ammonia, compound circuit with sequential throttling and parallel compression (three temperature modes).

The first mode: temperature of boiling of to=10 wasps .

The second mode: temperature of boiling of to=30 wasps .

The third mode: temperature of boiling of to=40 wasps .

Two screw compressor units 26A28073 work for the first temperature condition. The unit includes: compressor, electric motor, oil cooler, electric oil pump, oil separator, automation board, fine and gas filter, bypass and check valve, etc. Giving of the refrigerating agent to devices of cooling we are carried out from a compound circulating receiver of RKTs1.25 by the pumps TsNG70M1.

Two screw compressor units 26A28077 work for the second temperature condition. The unit includes: compressor, electric motor, oil cooler, electric oil pump, oil separator, automation board, fine and gas filter, bypass and check valve, etc. Refrigerant is supplied to cooling devices from RTsZ4 circulation protective receiver by TsGG68 pumps.

Two screw compressor units 26A28077 work for the third temperature condition. The unit includes: compressor, electric motor, oil cooler, electric oil pump, oil separator, automation board, fine and gas filter, bypass and check valve, etc. Refrigerant supply to cooling devices is performed from circulating protective receiver RTsZ1,25 by pumps TsGG68.

Two water horizontal shell-tube condensers KTG125 and one linear receiver RLD 1.25 are included in the circuit, a drain receiver RLD 1.25 is provided for collecting liquid coolant. A common oil collector is installed in the engine room to collect oil from the refrigerating apparatus.

Filling the system with ammonia

The system is charged with ammonia through the manifold of the control station through a pipeline through a valve. The cylinders are connected to the valve by a swivel nut with a steel tube. During charging, supply of circulation receivers from the linear receiver is stopped, and ammonia is supplied from cylinders. In order for liquid to leave the cylinder, it is placed on a wooden sunbed, with a valve down. The movement of liquid from the cylinders is observed by icing the tube.

It is also provided for refueling the system from railway and car tanks. Liquid ammonia is transferred from tanks due to pressure difference. The pressure is quickly equalized and for further movements the pressure difference must be maintained by the operating CM.