Selection and Application of Air Compressor After-treatment Equipment

Classification and Application of Compressor After-treatment Equipment
Compressor after-treatment equipment is generally divided into three main categories. The most commonly used types include air receiver tanks, dryers (refrigerated and adsorption types), and filters.
Air Receiver Tank

The air receiver tank stores compressed air, eliminates pressure fluctuations and stabilizes pressure to guarantee continuous air output. As the discharge pressure from the compressor fluctuates, 

installation of an air receiver tank delivers more stable compressed air pressure at the consumption end. It balances air consumption and provides emergency air supply during equipment faults or temporary demand surges. 

In addition, it further separates moisture and oil from compressed air. Part of the water vapor turns into liquid droplets after air compression; most droplets settle at the tank bottom when compressed air flows through the tank. 

A drain valve is fitted at the bottom for manual or automatic condensate discharge.

Dryers (Refrigerated Type & Adsorption Type)
Dryers further remove moisture and oil from compressed air to produce dry air for systems consisting of pneumatic instruments and jet components that demand high-quality air supply.
At present, two main types of compressed air dryers are manufactured and applied domestically: adsorption dryers and refrigerated dryers.
Adsorption dryers are filled with adsorbents such as silica gel, activated alumina and molecular sieve inside two towers. When air passes through the dryer, adsorbents trap moisture to realize air drying.
Refrigerated dryers adopt refrigerant cooling to condense and separate moisture from air to achieve dehumidification.

After operation, adsorbents inside adsorption dryers require regeneration. Regeneration modes are categorized into heatless (self-regenerative) and heated regeneration. 

Heated regeneration includes external heating, internal heating, waste heat regeneration and low-heat regeneration.

Filters
Filters remove contaminants such as oil, water and dust from compressed air. Different application scenarios have different air filtration requirements. Filters are classified into primary filters, secondary filters and high-efficiency filters.
Primary filter (simplified filter): Installed after dryers inside air compressor stations. Materials such as filter screens, felts, silica gel and coke are used for adsorption and filtration, with dust removal efficiency ranging from 50% to 70%.
Secondary filter (water-air separator): Widely adopted in pneumatic systems, with dust removal efficiency of 70%~90%.
High-efficiency filter: Precision water-air separators with tiny filter element pores. Usually installed after secondary filters as tertiary filtration for pneumatic sensors and testing equipment, achieving dust removal efficiency up to 99%.
Filter Performance Indicators
Permissible particle size: The maximum diameter of solid particles that can pass through the filter under specified test conditions, expressed in μm (micrometers).
Residual oil content: Mass of oil (including oil droplets, suspended particles and oil vapor) per unit volume of compressed air, converted to standard atmospheric conditions: absolute pressure 1 bar, temperature 20°C, relative humidity 65%.
Residual oil content in filtered compressed air is expressed in ppm, where 1 ppm ≈ 1.2 mg/m³.
Principles for Selecting Air Compressor After-treatment Equipment
Select the purification system according to the rated air flow and pressure of the air compressor.
Determine the dryer capacity based on inlet air temperature, rated flow, rated pressure and ambient temperature.
Select the dryer type according to the required drying level, namely the dew point value.
Determine the number of filtration stages and filter types based on required residual oil and dust content indicators.
Specify pipeline layout and pipeline materials according to target dew point, oil content and dust content.
Install an intake air filter in heavily dusty working environments to protect compressors and ensure purification performance.
Other technical specifications shall comply with relevant provisions of Design Standard for Air Compressor Stations.

Air receiver tanks play a vital role in the whole compressed air system. They stabilize airflow, cool compressed air, discharge condensate and store air. Therefore, 

air receiver tanks shall be installed between compressors and purification equipment, as well as between purification equipment and terminal air consumption points.

Compressed air drying and purification involves continuous drying and filtration accompanied by temperature reduction. Temperature is a critical factor; inlet temperature and ambient temperature directly affect purification efficiency.

Model selection shall follow JB/T6432-1992 Method for Compiling Model of Compressed Air Purification Equipment. The combined purification unit shall have an appropriate model, 

and the matching scheme of after-treatment equipment can be clearly referenced in Figure 1.

Selection Guidelines for Air Compressor After-treatment Equipment
Selection of Air Receiver Tanks

The tank shell shall feature excellent ductility for uniform stress distribution and reasonable stress status. Safety signal holes shall be arranged on the cylinder to ensure operational safety. 

Good corrosion resistance is required; the inner cylinder shall adopt corrosion-resistant materials and receive stress relief heat treatment to avoid hydrogen sulfide stress corrosion. 

Superior fatigue resistance is necessary; finite element fatigue analysis is recommended during design.

Air receiver tanks belong to pressure vessels and shall be equipped with complete safety accessories including safety valves, pressure gauges and drain valves.
1000 L tank for compressors with displacement below 2~4 m³/min;
1500 L ~ 2000 L tank for compressors with displacement below 6~10 m³/min.
It is recommended to reuse existing tanks or connect tanks in series to reduce one-time investment.
Selection of Dryers
As core purification equipment, dryers must meet process air quality requirements while pursuing low investment, convenient maintenance and minimum energy consumption.
Two mainstream dryer types are widely used domestically: adsorption dryers and refrigerated dryers.
Industries with strict compressed air quality requirements cannot adopt refrigerated dryers; adsorption dryers or combined dryers are mandatory.

Unlike refrigerated dryers which consume no product air, all types of adsorption dryers consume a portion of treated air for regeneration, reducing effective air supply volume. Accordingly, 

different dryer types and air compressor specifications shall be selected based on total air consumption of process equipment, system leakage rate and air consumption for dryer regeneration.

Selection of Filters
As mentioned above, filters are divided into primary, secondary and high-efficiency types. Primary filters are only deployed inside air supply units.
Water-air separators shall be selected according to the required filtration accuracy and free air flow of pneumatic equipment. Normally installed upstream of pressure reducing valves, they can also be used independently.
Connect the inlet and outlet strictly following the arrow marking on the housing. Reversed connection is prohibited; the water cup cannot be installed upside down.