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Although the drying of plastic particles is a relatively simple process, however, in some cases, the particles can not be completely dry. The factors that affect the drying effect are:
The drying temperature:
Heat is the key to the ability to open water molecules and moisture absorption polymers. When the temperature is higher than a certain temperature, the gravitational attraction between the water molecules and the polymer chains will be greatly reduced, and the water vapor will be taken away by the dry air.
The dew point:
In the dryer, the wet air is removed first, so that it has a very low residual moisture content (dew point). Then, by heating the air to reduce its relative humidity. At this time, the steam pressure of dry air is low. By heating, the water molecules inside the particles get rid of the bonding force and the air around the particles.
- time:
In the air around the particles, the absorption of heat and the diffusion of water molecules on the surface of the particles need some time. Therefore, the resin supplier shall detail the time required to obtain an effective drying of the material at an appropriate temperature and dew point.
- air:
Hot air drying will transfer heat to the drying bin particles in the particle surface and then remove the moisture, moisture of the dryer in the back. Therefore, it is necessary to have enough air flow to heat the resin to the drying temperature, and to maintain the temperature at a certain time.
When there is a problem, the problem should be found in the following three aspects.
1, dryer condition
When checking the dryer, pay particular attention to the air filter and hose. The hose is blocked or compressed air filter will decrease, thus affecting the dryer operation; the damaged filter will pollute the desiccant, inhibit the absorption capacity of it; the air hose may be broken into wet dry air, causing premature drying moisture absorption and high dew point; thermal insulation hose measures adverse and will also affect the drying bin drying temperature.
2, dry gas road
In the dry gas path, should be in the silo entrance detection of drying temperature, heat loss in the hose in order to compensate the dryer. Hopper inlet air temperature is low, may be due to improper adjustment of controller and the lack of insulation layer, or heater element, the heater contactors, thermocouple or controller failure. In addition, monitoring the whole drying process of drying temperature, observe the change of temperature fluctuations in the desiccant is also very important.
If the material from the dryer after not dried properly, it should check whether the drying bin is large enough to provide adequate and effective drying time, drying time refers to particles of actual exposure at the appropriate drying temperature and dew point in time. If the particles are in the residence time is not enough, will not get the proper drying. Therefore, we should pay attention to the size and shape of the particle or the crushed material, which will affect the packing density and the retention time of the dry material.
A twisted hose or a blocked filter can limit the flow of air and affect the performance of the dryer. Therefore, if the inspection dryer did not find such problems, it is not sufficient to determine whether the air flow. Here, there is a quick, simple and accurate method to detect the drier air is sufficient, measuring the vertical temperature curve of material in the drying hopper.
Assuming that the material supplier recommended the drying time is 4h, the processing capacity of 100lb/h (1lb=0.4536kg). To determine the adequacy of air dryer, temperature curve, measuring the drying bin in here, we must pay special attention to the 4H (400lb) at the temperature. If the drying bin 400lb material where the temperature reaches the set value, then you can believe that gas flow is sufficient. If the drying bin only 1H and 2H or 3H where the materials are fully heating, heating of the air flow can not be scheduled to complete the material and drying rate. Insufficient heating may indicate that the productivity of the drying bin is too small, or because of air filter clogging or hose damage restricted. Gas is too large to be a problem, not only a waste of energy, but also lead to high temperature of the return air, the destruction of the performance of the desiccant.
The return air filter can prevent the pollution of the desiccant from the filamentous material, and affect its moisture absorption performance. These filters must be kept clean in order to ensure enough air flow.
Most of the heat is released when the dry air comes out from the top of the dryer. When the desiccant temperature in the range of 150oF ~ 120oF, most of the dryer can work efficiently. If the backflow air causes the desiccant to overheat, it will reduce the adsorption capacity of the moisture in the dry air.
To constantly test the return air temperature of the dryer. When the return air temperature is high, may account for the productivity, the dryer size is too large, or the material enters the drying bin when the temperature is high, for example, PET has been crystallized in the drying bin, or just some materials (such as PET) the drying temperature is higher than the normal temperature range. In order to prevent backflow air temperature becomes higher, as long as a heat exchanger is installed in the return air path, it is sure that the desiccant can effectively remove the moisture in the dry air.
3, desiccant regeneration and cooling
Desiccant's ability to absorb moisture is limited, so it must be cleared through the regeneration of the absorption of moisture. The process is: when the ambient air is inhaled, through a filter into the blower, and then be fed into a set of heaters. Heated air through the drying bed. When the temperature of the desiccant rises, it releases the absorbed moisture. When the hot air is absorbed