The air is compressible, easy to transport and inexhaustible on the ground. In industry, compressed air is widely used and has many good features and features that are easy to use. All trades and occupations have different requirements on the quality of compressed air. To properly allocate compressed air treatment equipment can it save equipment investment and operating costs while meeting the requirements of industrial production.
1. Compressed air quality requirements In the context of food engineering, the production process of compressed air quality requirements include the following categories: First, the biological fermentation project. Such as: amino acid fermentation, vitamin fermentation and other aerobic fermentation, the production requires pressure dew point <-40 ° C, particle size<0.01pm, oil <0.03ppm; Second, the transport and packaging of flour. Such as: milk powder, soy flour, such as the pneumatic conveying and canning, dew point liquid production requirements, granular food packaging. Pressure dew point instrumentation valves used in the production of gas. Requirements of pressure dew point <2, particle size <1 m, oil <1ppm. According to the above requirements, usually take the air meter drying, filtration, to achieve the appropriate quality level requirements.
2. The choice of air dryer Air dryer commonly used equipment are mainly frozen dryer, adsorption dryer, a composite freeze-drying dryer, each dryer has its own characteristics.
The refrigeration dryer consists of a refrigeration compressor, a condenser, an evaporator, a heat exchanger, a gas-liquid separator and the like. The principle of the refrigeration dryer is to reduce moisture content by dew condensation of moisture in the air by reducing air temperature. The pressure dew point of a freeze dryer is typically 2 ° C, depending on the setting of the evaporator. Although the pressure dew point is much higher than the adsorption dryer, its operating cost is 1/31 of the adsorption dryer / 5, therefore, the pressure dew point less demanding occasions, it is appropriate to use the frozen dryer, but the cold area outside the long distance pipeline delivery conditions.
Adsorption dryers usually use twin towers, one for adsorption and the other for desorption. According to the regeneration method is divided into no heat regeneration dryer, micro heat regenerative dryer, heat regenerative dryer. Non-thermal regenerative dryer actual work points sub-adsorption, pressure, regeneration of three, micro heat and heat regenerative dryer sub-adsorption, regeneration, blowing cold, pressure equalized four stages, constitute a cycle. In operation, the compressed air alternately flows through two tower containers filled with adsorbents. When one tower is adsorbed at working pressure, the other tower is desorbed at near atmospheric pressure or under heat and the two towers alternately switch work.
The main factors that affect the operation of adsorption dryers are inlet air temperature and working pressure. In general, the compressed air entering the dryer is saturated or supersaturated air. Under the same pressure conditions, the saturated water content will increase about 30% for each temperature increase of 50 ° C, that is, the moisture load into the dryer will increase by 30% In addition, the adsorption capacity of the adsorbent decreases with increasing temperature, so the desiccant's drying efficiency decreases with the increase of the temperature of the intake air. The reduction of working pressure also leads to the decrease of the drying efficiency of the drier because the working pressure is reduced and the quantity of regenerated gas is reduced, so that the drying efficiency of the drier is decreased. In addition, the pressure drop also increases the volume flow rate in the adsorption tower, resulting in Dynamic adsorption flow rate decline, these factors will inevitably reduce the adsorption capacity, causing the adsorber gas dew point rise.
Three types of adsorption dryer performance indicators and the scope of the different. Non-thermal regenerative dryer minimum working pressure 4bar, regeneration gas consumption 20% -25%, dry gas pressure dew point -40 ° C, the economic capacity of 3m³ / min-20m³ / min, the advantage of simple structure, equipment investment Less regenerative gas consumption, frequent switching; minimum working pressure of micro heat regenerative dryer 1bar, regenerative gas consumption 10% -15%, dry gas pressure dew point -40C-60 ° C, economic treatment capacity 10m³ / min-200m³ / min, which combines the advantages of non-thermal regeneration and thermal regeneration, comprehensive economic and technical indicators are good; thermal regeneration dryer minimum working pressure Ibar, renewable gas consumption of 5% -8%, dry gas pressure Dew point -40C a 80 ° C, the economic capacity of 10m³ / min200m3 / min, the advantage of less consumption of renewable gas, long working cycle, low operating costs, but its complex structure, equipment, one-time investment in high; Is the combination of the advantages of a low dew point of the regenerative dryer without exhaust gas pressure and the advantages of a regenerative dryer with no loss of regenerative dryer and a low dew point and low energy consumption of the dryer with a final result of -700 ° C below the dew point, renewable gas 5% air. This composite dryer low operating cost, the compressed air quality is good, suitable for high intake air temperature occasions, but the complex structure, high equipment costs.
3. Air filtration After drying the air also needs filtration treatment. According to different requirements of the user on the air source dust content, configure different levels of filters. It is usually required that compressed air with a particle size of 1 m and an oil content of 1 ppm need only be equipped with a degreasing filter and a primary filter. In general, oil-free air compressors and screw-type air compressors, the exhaust there is still a certain amount of oil exists, usually 5mg / m³-15mg / m³. If so much oil into Adsorption dryers, over time and again bound to cause the adsorbent poisoning, adsorption dryer in the import before, should be set degreasing filter, can greatly extend the life of the adsorbent. Primary filter cartridge type stainless steel fiber sintered felt, filter particle size 0.3m called Gong separation efficiency of 98% or more.
Compressed air used in bio-fermentation engineering requires high air volume, low pressure, air aseptic, while the particle size of the bacteria is between 0.25 m and several dozen pm and the virus particles are in the range of 0.1 pm-0.01 pm, so the supplied Compressed air in the primary filter on the basis of the need to fine filter to remove more than 0.1m particles, further sterile filtration to remove 0.01pm above particles. The compressed air used for the delivery of the milk powder can not only ensure the sterility, but also need activated carbon to remove odors to ensure the product quality.
In short, in practical applications, according to the different requirements of users on compressed air quality, according to the choice of air compressor, configure the appropriate air dryer and air filter, in order to achieve economic and reasonable.