The role of the main components of the refrigerated dryer
1. Refrigeration compressor
Refrigeration compressors are the heart of the refrigeration system, and most compressors today use hermetic reciprocating compressors. Raising the refrigerant from low to high pressure and circulating the refrigerant continuously, the system continuously discharges internal heat to an environment above the system temperature.
2. Condenser
The function of the condenser is to cool the high-pressure, superheated refrigerant vapor discharged by the refrigerant compressor into a liquid refrigerant, and its heat is taken away by the cooling water. This allows the refrigeration process to continue continuously.
3. Evaporator
The evaporator is the main heat exchange component of the refrigeration dryer, and the compressed air is forcibly cooled in the evaporator, and most of the water vapor is cooled and condensed into liquid water and discharged outside the machine, so that the compressed air is dried. The low-pressure refrigerant liquid becomes low-pressure refrigerant vapor during the phase change in the evaporator, absorbing the surrounding heat during the phase change, thereby cooling the compressed air.
4. Thermostatic expansion valve (capillary)
The thermostatic expansion valve (capillary) is the throttling mechanism of the refrigeration system. In the refrigeration dryer, the supply of the evaporator refrigerant and its regulator is realized through the throttling mechanism. The throttling mechanism allows refrigeration to enter the evaporator from the high-temperature and high-pressure liquid.
5. Heat exchanger
The vast majority of refrigeration dryers have a heat exchanger, which is a heat exchanger that exchanges heat between air and air, generally a tubular heat exchanger (also known as a shell and tube heat exchanger). The main function of the heat exchanger in the refrigeration dryer is to “recover” the cooling capacity carried by the compressed air after being cooled by the evaporator, and use this part of the cooling capacity to cool the compressed air at a higher temperature carrying a large amount of water vapor (that is, the saturated compressed air discharged from the air compressor, cooled by the rear cooler of the air compressor, and then separated by air and water is generally above 40 °C), thereby reducing the heating load of the refrigeration and drying system and achieving the purpose of saving energy. On the other hand, the temperature of low-temperature compressed air in the heat exchanger is recovered, so that the outer wall of the pipeline transporting compressed air does not cause “condensation” phenomenon due to the temperature below the ambient temperature. In addition, after the temperature of the compressed air rises, the relative humidity of the compressed air after drying is reduced (generally less than 20%), which is beneficial to prevent the rust of the metal. Some users (e.g. with air separation plants) need compressed air with low moisture content and low temperature, so the refrigeration dryer is no longer equipped with a heat exchanger. Since the heat exchanger is not installed, the cold air cannot be recycled, and the heat load of the evaporator will increase a lot. In this case, not only does the power of the refrigeration compressor need to be increased to compensate for energy, but also the other components of the entire refrigeration system (evaporator, condenser and throttling components) need to be increased accordingly. From the perspective of energy recovery, we always hope that the higher the exhaust temperature of the refrigeration dryer, the better (high exhaust temperature, indicating more energy recovery), and it is best that there is no temperature difference between the inlet and outlet. But in fact, it is not possible to achieve this, when the air inlet temperature is below 45 °C, it is not uncommon for the inlet and outlet temperatures of the refrigeration dryer to differ by more than 15 °C.
Compressed Air Processing
Compressed air→ mechanical filters→ heat exchangers (heat release), →evaporators→ gas-liquid separators→ heat exchangers (heat absorption), → outlet mechanical filters→ gas storage tanks
Maintenance and inspection: maintain the dew point temperature of the refrigeration dryer above zero.
To reduce the compressed air temperature, the evaporation temperature of the refrigerant must also be very low. When the refrigeration dryer cools the compressed air, there is a layer of film-like condensate on the surface of the fin of the evaporator liner, if the surface temperature of the fin is below zero due to the decrease in the evaporation temperature, the surface condensate may freeze, at this time:
A. Due to the attachment of a layer of ice with a much smaller thermal conductivity on the surface of the inner bladder fin of the evaporator, the heat exchange efficiency is greatly reduced, the compressed air can not be fully cooled, and because of the insufficient heat absorption, the refrigerant evaporation temperature may be further reduced, and the result of such a cycle will inevitably bring many adverse consequences to the refrigeration system (such as “liquid compression”);
B. Due to the small spacing between the fins in the evaporator, once the fins freeze, the circulation area of compressed air will be reduced, and even the air path will be blocked in severe cases, that is, “ice blockage”; In summary, the compression dew point temperature of the refrigeration dryer should be above 0 °C, in order to prevent the dew point temperature from being too low, the refrigeration dryer is provided with energy bypass protection (achieved by bypass valve or fluorine solenoid valve). When the dew point temperature is lower than 0 °C, the bypass valve (or fluorine solenoid valve) automatically opens (the opening increases), and the uncondensed high-temperature and high-pressure refrigerant steam is directly injected into the inlet of the evaporator (or the gas-liquid separation tank at the compressor inlet), so that the dew point temperature is raised to above 0 °C.
C. From the perspective of system energy consumption, the evaporation temperature is too low, resulting in a significant decrease in the compressor refrigeration coefficient and an increase in energy consumption.
Examine
1. The pressure difference between the inlet and outlet of compressed air does not exceed 0.035Mpa;
2. Evaporation pressure gauge 0.4Mpa-0.5Mpa;
3. High pressure pressure gauge 1.2Mpa-1.6Mpa
4. Frequently observe the drainage and sewage systems
Operation Issue
1 Check before booting
1.1 All valves of the pipe network system are in normal standby state;
1.2 The cooling water valve is opened, the water pressure should be between 0.15-0.4Mpa, and the water temperature is below 31Ċ;
1.3 The refrigerant high pressure meter and the refrigerant low pressure meter on the dashboard have indications and are basically equal;
1.4 Check the power supply voltage, which shall not exceed 10% of the rated value.
2 Boot procedure
2.1 Press the start button, the AC contactor is delayed for 3 minutes and then started, and the refrigerant compressor starts to run;
2.2 Observe the dashboard, the refrigerant high-pressure meter should slowly rise to about 1.4Mpa, and the refrigerant low-pressure meter should slowly drop to about 0.4Mpa; at this time, the machine has entered the normal working state.
2.3 After the dryer runs for 3-5 minutes, first slowly open the inlet air valve, and then open the outlet air valve according to the load rate until full load.
2.4 Check whether the inlet and outlet air pressure gauges are normal (the difference between the readings of the two meters of 0.03Mpa should be normal).
2.5 Check whether the drainage of the automatic drain is normal;
2.6 Check the working conditions of the dryer regularly, record the air inlet and outlet pressure, high and low pressure of cold coal, etc.
3 Shutdown procedure;
3.1 Close the outlet air valve;
3.2 Close the inlet air valve;
3.3 Press the stop button.
4 Precautions
4.1 Avoid running for a long time without load.
4.2 Do not start the refrigerant compressor continuously, and the number of starts and stops per hour shall not be greater than 6 times.
4.3 In order to ensure the quality of gas supply, be sure to abide by the order of starting and stopping.
4.3.1 Start: Let the dryer run for 3-5 minutes before opening the air compressor or inlet valve.
4.3.2 Shutdown: Turn off the air compressor or outlet valve first and then turn off the dryer.
4.4 There are bypass valves in the pipeline network that span the inlet and outlet of the dryer, and the bypass valve must be closed tightly during operation to avoid untreated air entering the downstream air pipe network.
4.5 The air pressure shall not exceed 0.95Mpa.
4.6 The inlet air temperature does not exceed 45 degrees.
4.7 The temperature of the cooling water does not exceed 31 degrees.
4.8 Please do not turn on when the ambient temperature is lower than 2Ċ.
4.9 The time relay setting in the electric control cabinet shall not be less than 3 minutes.
4.10 General operation as long as you control the “start” and “stop” buttons
4.11 The air-cooled refrigeration dryer cooling fan is controlled by the pressure switch, and it is normal for the fan not to turn when the refrigeration dryer works at a low ambient temperature. As the refrigerant high pressure increases, the fan starts automatically.