Air preparation system
Compressed air used in industry must be dry and clean. To obtain compressed air of high quality, besides the compressors, it is necessary to install an air preparation system that in most cases includes the following components:
- Refrigeration dryers
As a rule, the air supplied by the compressor, besides mechanical impurities, contains humidity. The consequences of ingress of moisture into the equipment can be very different: from corrosion of the installation and quality degradation of works / products produced till the complete running failure of the system. Thus, the moisture removal contained in compressed air is one of the most important ways to ensure the safety of pneumatic equipment.
At the moment, one of the most common and energy-efficient ways to reduce the moisture content of compressed air is the use of refrigeration dryers. As a refrigerating agent, the freon gas is used, precisely because of that, they are also called refrigeration ones.
In general, the working process of such dryers is quite simple:
1. At the first stage, air enters the heat exchanger "air-air", where it is precooled by the outflow of refrigerated air.
2. At the second stage, the compressed air reaches the condensing temperature as it passes through the refrigerated heat exchanger. The compressor provides the refrigerating agent circulation. All moisture remained in the compressed air condensates when the dew point temperature is reached and after that is automatically removed by the drain valve.
The main disadvantage of such devices can be considered a limited possibility of lowering the dew point temperature. It is limited by the moisture freezing temperature.
Adsorption dryers are used in systems where the presence of condensate is unacceptable - i.e. the supply of compressed air through street pipelines exposed to freezing in wintertime, transportation of hygroscopic materials, special production processes, chemical, pharmaceutical and laboratory equipment.
Depending on the ambient temperature and the required grade of air purity, adsorption dryers with dew points of -20°C, -40°C or -70°C are used, which corresponds to the 3rd, 2nd and 1st classes of air dehumidification, respectively.
A dryer of adsorption-type is represented by two columns in which alternately drying and regeneration processes take place. The moisture is absorbed by the surface layer of the adsorbent, in the function of which alumina, silica gel and molecular sieve are used. The adsorbent is sensitive to oil contamination coming from the air of the compressor, that is why filters must always be installed before the adsorption dryer. At the exit from the dryer, a dust filter should be placed, so that the adsorbent particles do not enter the dried air.
By type of regeneration, dryers are divided into devices with cold and hot regeneration. Regeneration is the process of restoring the adsorbent properties, i.e. removal of moisture from it. Cold regeneration is carried out by a dry air flow, hot regeneration is carried out by heated to high temperatures air. The choice of this or that type of desiccant dryer equipment depends on the economic efficiency. As a rule, with a compressed air flow of up to 20 m3/min dryers with cold regeneration are used; above this level, it is more useful to use dryers with hot regeneration.
Cleaning compressed air filters
The compressed air filters are used to purify air from solid particles and oil, as well as to separate water. These devices consist of a cleaning element placed in a metal or plastic cylindrical container. This equipment along with dryers and separators is an integral part of the compressed air cleaning system.
Air receivers are meant for accumulation and uniform supply of compressed air, they are used either in industry or in the domestic sphere. The air collector is a container that levels down the pressure and stabilizes the air flow. The use of the receiver eliminates the air pulsation, which is especially important when working with painting and sandblasting.
The air receiver undertakes the following functions:
- It creates a reserve of compressed air;
- It cools the air under pressure;
- It levels down of the air flow pulsation, which comes from the compressor unit;
- It stabilizes the pressure in the pneumatic system with a non-constant air flow;
- It gathers and removes accumulating moisture;
- It reduces the number of compressor restarts.
The receiver can be made of stainless or galvanized steel. In the case if it is necessary to use an air receiver that is resistant to corrosion, as a rule, the choice is the receiver made of steel with an increased chromium content.
Cyclonic separators (oil and moisture separators) are meant for primary compressed air cleaning from compressor condensate. As a rule, they are installed directly at the compressed air outlet from the final cooler of the air compressor.
The use of cyclonic separators can significantly reduce the load on the main filters and compressed air dryers, since inside of them about 99% of the large-sized moisture particles are removed. The efficiency of cyclonic separators in the area of removal of compressor oil is not declared, but a significant part of the oil is also hold. An important advantage of cyclonic separators is that they do not need an external power source, they do not contain filter elements and other wearing parts and they do not require maintenance.