Collection of Air Compressor Post-Treatment Equipment

Compressed air contains moisture, oil, dust and various odor components. Equipment that removes these contaminants from compressed air via physical filtration is referred to as post-treatment equipment.
1 Air Receiver
Model Identification of Air Receiver
Example: C-0.3/8
"C" stands for air receiver;
"0.3" indicates the volume of 0.3 m³;
"8" represents the maximum allowable working pressure of 8 bar.
Functions of Air Receiver
a. Store compressed air;
b. Stabilize pressure. The pressure of air discharged by the compressor fluctuates within a certain range. Installation of an air receiver enables more stable compressed air pressure at the consumption side.

c. Pre-separate moisture. Part of the water vapor in compressed air turns into liquid droplets after compression. Most droplets settle at the bottom of the air receiver. 

A blowdown valve fitted at the bottom discharges condensate manually or automatically.

Selection Guidelines for Air Receiver

The rated pressure of the air receiver shall match the operating pressure of the air compressor. The recommended volume is 1/5 to 1/10 of the volumetric flow rate of the air compressor. 

If site conditions permit, a larger-volume air receiver is preferred for greater air storage capacity and improved preliminary water separation. (Inspection and filing requirements shall be taken into consideration.)

2 Air Dryers
Air dryers are categorized into refrigerated type, desiccant type (also known as heatless regenerative type), micro-heat regenerative type and combined type. The refrigerated air dryer is the most widely adopted model.
Model Identification of Refrigerated Air Dryer
Example: DA-55
"DA" represents refrigerated air dryer;
"55" indicates the processing capacity (purification flow) of 5.5 m³/min.
Functions of Refrigerated Air Dryer

Compressed air holds moisture at 100% relative humidity. Moisture precipitates when air cools down in pipelines, resulting in numerous adverse impacts on air-consuming equipment. 

A refrigerated air dryer adopts refrigeration technology to forcibly cool compressed air to the required dew point temperature (2–10°C), condensing water vapor into liquid droplets which are discharged out of the unit through drainers.

Selection Guidelines for Refrigerated Air Dryer

Select a dryer with a processing capacity close to the volumetric flow of the air compressor and matching operating pressure. For industries demanding high-quality compressed air, 

refrigerated air dryers are not suitable; desiccant air dryers or combined dryers shall be selected instead.

3 Functions and Selection of Desiccant, Micro-Heat Regenerative and Combined Dryers
Desiccant air dryers operate on the Pressure Swing Adsorption (PSA) principle.

They adopt a dual-tower structure filled with desiccant (activated alumina). When compressed air enters the tower and contacts the desiccant, 

compressed air is dried through pressure swing adsorption, achieving a pressure dew point below -40°C.

The sizing principle for desiccant air dryers is consistent with that for refrigerated air dryers.
4 Differences Between Refrigerated Air Dryers and Desiccant Air Dryers
Differences in Working Principle

A refrigerated air dryer follows the refrigeration dehumidification principle. Saturated compressed air from upstream exchanges heat with refrigerant and is cooled to a specified dew point. 

A large amount of liquid water condenses, separated by an air-water separator and automatically discharged, thereby realizing moisture removal.

A desiccant air dryer follows the pressure swing adsorption principle. Under certain pressure, saturated compressed air from upstream contacts desiccant, 

and most moisture is adsorbed by the desiccant. Dried air flows downstream to achieve deep drying.

Differences in Moisture Removal Performance
Restricted by its working principle, a refrigerated air dryer will experience icing at excessively low temperatures. Therefore, its pressure dew point is normally maintained at 2~10°C.
A desiccant air dryer does not rely on temperature variation. Desiccants (activated alumina) enable deep drying, so its outlet dew point can generally reach below -20°C to realize thorough drying.
Differences in Energy Consumption
Refrigerated air dryers require refrigerant compression for cooling, leading to relatively high power consumption.
Desiccant air dryers only need an electric control box to operate valves, with typical power consumption of merely tens of watts and low electricity loss.
Differences in Air Consumption
Refrigerated air dryers remove moisture by temperature variation, and condensate is discharged via automatic drainers, so there is no compressed air consumption.
Desiccant air dryers require roughly 12–15% purge air for regeneration after the desiccant becomes saturated with water.
Differences in Failure Rate

Refrigerated air dryers feature relatively complex refrigerant systems, air circuits and electrical components. For desiccant air dryers, frequent valve switching is the primary potential source of faults. 

Generally speaking, desiccant air dryers have a lower failure rate than refrigerated air dryers.

In summary, desiccant air dryers outperform refrigerated air dryers in stability and drying effect. Nevertheless, customers need to weigh the pros and cons owing to the consumption of purge air. 

Currently, an increasing number of manufacturers choose desiccant air dryers, which has become a prevailing trend.

5 Compressed Air Filters
Model Identification of Filters
** represents filtration accuracy grade (refer to the table for filtration accuracy grades).
Example: SF18-**
"SF" stands for filter;
"18" indicates the processing capacity (purification flow) of 1.8 m³/min.
Functions of Filters
Compressed air contains moisture, oil, dust and various odor components. Equipment that removes these compressed air contaminants via physical filtration is defined as a filter.
a. Particle retention size: The maximum diameter of solid particles that can pass through the filter under specified test conditions, expressed in μm (micrometer).

b. Residual oil content: Mass of oil (including oil droplets, suspended particles and oil vapor) contained in unit volume of compressed air, converted to standard atmospheric conditions: 

absolute pressure 1 bar, temperature 20°C and relative humidity 65%.

Residual oil content of filtered compressed air is expressed in ppm, where 1 ppm ≈ 1.2 mg/m³.
Selection Guidelines for Filters
Filters shall be selected progressively in accordance with the sequence of filtration accuracy grades. Higher-grade filters cannot be selected directly without matching preceding filter grades.
For example: Grade P (pre-filter) must be installed first, followed by Grade A, then Grade F (fine filter), Grade AC (activated carbon odor removal filter), Grade AD (sterile filter), in this exact sequence.
The flow capacity of the filter shall match the volumetric flow of the air compressor.