What factors affect the dew point of an adsorption dryer

In the adsorption dryer, the lower the dew point, the better the effect, but there will be many factors that affect the dew point of the adsorption dryer during operation, so which factors will affect the dew point of the adsorption dryer? Explain the dew point and influencing factors of adsorption dryer from eight aspects!

1. Adsorbent

The adsorbent is the material basis for the work of the adsorption dryer, and the type of adsorbent has a decisive influence on the final dew point of the compressed air being treated. At present, the most commonly used adsorbents in compressed air dehydration and drying are silica gel, activated alumina and molecular sieve. Due to the different degrees of surface micropores development, the effect of water adsorption they can achieve is also inconsistent (see figure below).

2. Adsorption rate

During the adsorption process, the adsorption rate has a great influence on the dew point of the outlet air. Taking silica gel as an example, at the beginning of adsorption, the adsorption efficiency is very high, and the outlet air dew point remains unchanged in a large range, which is the adsorption area of the dryer. When the air continues to flow through and the adsorbent process continues, the moisture adsorbed by the surface layer of the adsorbent particles gradually increases, the water content of the outlet air begins to rise, and when the surface layer is completely saturated with moisture, the adsorption equilibrium is reached - also known as the "conversion point" of the adsorbent.

3. Two-phase contact time

The structural parameters of the adsorption dryer mainly refer to the column diameter D and height H. The influence of these two parameters on the dew point of the outlet air is comprehensively expressed as the two-phase contact time T between the wet air and the adsorbent. The contact time T between the moist air flow and the adsorbent is determined by the ratio of the adsorption bed height H to the empty tower flow rate c: T=H/c

4. Residual water volume

For adsorption dryers, adsorbent regeneration is an extremely important link. Ideally, the moisture inside the adsorption bed must be resolved and taken out during the regeneration half-cycle, and this process consumes enough regeneration capacity. If the regeneration capacity is insufficient, residual water will appear in the adsorption bed. The residual water volume is equivalent to adding an additional adsorption capacity to the adsorbent, and after a long period of use, the end of the adsorption bed will produce the accumulation of residual water volume, so that this part of the adsorbent loses the adsorption capacity in advance, which is equivalent to shortening the height of the adsorption bed, reducing the contact time between the compressed air and the adsorbent, resulting in the rise of the outlet dew point.

5. Inlet air temperature

The increase in the inlet air temperature of the adsorption dryer will have a negative impact on the outlet dew point in two ways:

1. According to the adsorption characteristics of the adsorbent, the adsorption capacity is large at low temperature; High temperature is, small adsorption capacity.

2. The saturated water content in compressed air with high temperature is also more. The compressed air entering the dryer is generally in a saturated state, the higher the temperature, the more water content, the greater the dryer load, so that the outlet air dew point rises.

6. Adsorption cycle

There are two types of adsorption cycles of commonly used adsorption dryers. The heatless regeneration dryer based on pressure swing adsorption belongs to the short-cycle type, while all heated regeneration adsorption dryers belong to the long-cycle type. The shorter the adsorption time, the less water adsorbed by the adsorption bed at one time, and the greater the adsorption rate of the adsorbent. Generally speaking, the shorter the adsorption cycle, the better the drying effect.

7. Adsorbent deterioration

Adsorbent deterioration refers to the weakening of adsorption performance caused by fatigue or aging after a long period of use. Specifically, the adsorption "conversion point" decreases sharply and the outlet dew point rises rapidly.

8. Inlet pressure

The working pressure decreases, resulting in an increase in the air flow rate in the tower, a decrease in the contact time between the two phases, and an increase in the dew point of the outlet air. The decrease in working pressure will lead to an increase in the saturated moisture content, that is, an increase in the amount of water entering the dryer and an increase in the dew point of the outlet air. Therefore, the reduction of compressed air pressure will adversely affect the outlet air dew point of the dryer, and appropriately increasing the pressure of the inlet air is conducive to the reduction of the outlet air dew point.