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AEROMASTER LTD & CHICAGO PNEUMATIC CYPRUS | COMPRESSORS TOOLS
RDP series - Refrigeration compressed air dryers
Background
Compressed air contains contaminants such as water, oil and particulates which must be removed or reduced to the acceptable level based on specific application requirements. Standard ISO 8573-1 specifies air purity/quality classes for these contaminants. Humidity (water vapour content) is expressed in the terms of Pressure Dew Point (PDP) where Dew point is the temperature at which air is 100 % saturated with moisture. When the temperature of the air reduces to or below the dew point, condensation will occur. Reduction of water content down to pressure dew point +3 °C is usually achieved with refrigeration dryers.
Performance
RDP refrigeration dryers have been designed to efficiently separate water from the compressed air and lower pressure dew point all the way down to +3 °C. Drying is achieved on the principle of cooling which takes place inside a highly efficient and ultra-compact 3 stage heat exchanger. In the first stage (air-air heat exchanger) hot and humid inlet air is being precooled by the cold outgoing air. In the second stage (air-refrigerant heat exchanger) intensive water condensation takes place due to cooling of the air. All condensed water is separated from the main compressed air stream in the third stage by the integrated demister. A proven and robust design enables efficient and reliable operation, fast installation and simple maintenance.
Controller
The control panel contains all the information necessary for the management of refrigeration dryer RDP. It also contains the installed main power button to turn off the refrigerated dryer, dew point display and alarm mode.
Electronic condensate drain
Integrated electronic condensate drain EMD 12 is designed for fully automatic discharging of condensate without air losses. The special self-cleaning direct acting valve assures reliable operation. EMD 12 is equipped with operational alarm, led indicator, test button and capacitive level sensor.
Low/high pressure switch
Low/high pressure switches are control devices which are used as safety control. The compressor is stopped by cutting the power supply of the motor of the compressor whenever the refrigerant pressure becomes excessive. This is necessary to prevent the possible damage of equipment. Presence of switch depends on dryer size.
Thermal protection
High temperature in the refrigera- tion system can cause damage to the system components. High compressor temperature means that the compressor is overheat- ing. High condenser temperature means that the heat rejection to the ambient is insufficient. Both thermal protection actions are in- cluded in the control function of our controller. It’s algorithms en- sure easy and reliable operation with preventive alarm and com- pressor stop.
Hot gas by-pass valve
The main purpose of hot gas bypass valve is to prevent condensate from freezing on the surface of the evaporator coil when the system is operating at reduced load conditions.
Integrated heat exchanger
The incoming air enters into an air- to-air pre-cooler, where incoming air is cooled by output air. Then air passes through a refrigerant heat exchanger where the air is cooled by the cold evaporating refrigerant. This process causes moisture to condense in demister into liquid water. Condensate is drained from the system by condensate drain.
Efficent cooling system
The refrigeration compressor pumps hot high pressure gas refrigerant into the condenser which transfers the heat from the refrigerant gas to the ambient air as the gas condenses into a liquid.
Compressor
High efficiency piston and scroll refrigerant compressors assure the circulation of system refrigerant. Compressors have the innovative construction with reduced energy consumption and high reliability levels.
Operating scheme
Operation
Operation of refrigeration compressed air dryer can be divided into two independent circuits:
COMPRESSED AIR CIRCUIT
Warm and humid compressed air enters into three-stage heat exchanger. In the first stage “air-air” (a) incoming air is precooled by cold outlet air. This stage is important from energy saving point of view as well as for stable operation of entire system. In the second stage “air-refrigerant” (b) the air is cooled by the cold refrigerant. In this stage water vapour condenses into liquid water. In the third stage “demister” (c) separates all the liquid water from the air stream. Cold dry air then enters “First stage” (a) again where it is re-heated by the hot inlet air. Besides energy saving feature this stage also makes sure that dry air leaving the dryer is warm enough to prevent condensation on the external side of downstream piping. Condensed water is discharged from the system via electronic condensate drain.
REFRIGERANT CIRCUIT
Circulation of the refrigerant gas in the circuit is provided by highly efficient hermetically sealed compressor (4). Compressor rises the pressure of the gas which is then cooled down and condensed in the condenser (5). Electric fan on the condenser can be controlled by temperature or pressure sensor. Liquid refrigerant then flows through capillary tube or thermostatic expansion valve (8) which acts as a metering device to reduce the pressure of the refrigerant. Reduction
of the pressure is a design function to achieve target temperature inside the evaporator (lower pressure = lower temperature). Filter (7) which is installed upstream the metering device intercepts impurities and assures reliable operation of the system. Low pressure refrigerant in gas form then re-enters the compressor.
RDP dryers operate based on “non-cycling” operating principle which means that when the dryer is without load (e.g. no or low inlet flow of compressed air) “hot gas by-pass valve” (6) will release part of the hot refrigerant gas (from discharge side of the compressor) back to the suction side of the compressor. As a result evaporation pressure/ temperature will be constant at the factory pre-set value.
In case of high discharge temperature the controller stops the compressor before permanent damage occurs. Depending on size of the dryer additional safety/protection devices (e.g. low pressure switch, high pressure switch) are installed in on the refrigerant gas circuit.
All of our dryers are equipped with good control mechanisms. This allows for a very stable dew point. From the smallest dryer sizes on we offer excellent communication possibilities. Larger dryers are equipped with more powerful controllers offering advanced control and monitoring features.
