In the drying gas path, the drying temperature should be detected at the material inlet to compensate for the heat loss of the dehumidifying drying equipment in the hose. Low air temperature at the drum inlet may be due to improper controls and lack of insulation, or a malfunctioning heater element, heater contactor, thermocouple, or controller. Additionally, it is important to monitor the drying temperature throughout the desiccant dryer drying process.
If the material does not dry properly after coming out of the dryer, check that there is enough space in the drying bin to provide adequate and efficient drying time. Effective drying time refers to the time during which the particles are actually exposed to the appropriate drying temperature and dew point. If the particles do not stay in the silo for enough time, they will not dry properly. Therefore, attention should be paid to the size and shape of the particulate or pulverized material, which will affect the bulk density and residence time of the dried material.
To determine if the airflow to the desiccant dryer is adequate, the temperature profile in the drying chamber can be measured and special attention should be paid to the temperature at 4 hours (400 lbs). If the temperature at the 400 lb level in the drying bin reaches the set point, the air flow rate can be considered sufficient, if only the material in the 1 hour, 2 hour or 3 hour position in the drying bin is fully heated, the air flow rate will not complete the material at the predetermined output Heat and dry. Insufficient heating may indicate that the drying drum is too small for this production rate, or that air flow is restricted due to things like clogged filters or damaged hoses. Excess air volume can also cause problems, not only wasting energy, but also causing return air temperatures to be too high, compromising the performance of the desiccant.
A return air filter prevents filamentary material from contaminating the wheel and affecting its moisture absorption properties. These filters must be kept clean to ensure adequate air flow. When the dry air comes out of the top of the dryer, most of the heat has already been released. Most dryers work effectively when the desiccant temperature is in the range of 120°F to 150°F. If the return air overheats the desiccant, it reduces the ability of the desiccant to absorb moisture from the drying air.
When the temperature of the return air is high, this may indicate that the desiccant dryer size is too large for this production rate, or that the temperature of the material entering the drying bin is high, for example polyester has crystallized before drying, or that only some materials have a high drying temperature within the normal temperature range. In order to prevent the return air temperature from becoming high, as long as a heat exchanger is installed on the return air path, the desiccant can effectively remove the moisture in the dry air.