1. Condition of dust-free drying oven

When checking the dust-free drying oven, pay special attention to the air filter and hoses. Blocked filters or flattened hoses can reduce airflow, thereby affecting the operation of the dryer; Damaged filters can contaminate the desiccant and inhibit its moisture absorption capacity; A ruptured hose may introduce moist ambient air into the drying airflow, causing premature moisture absorption and high dew point of the desiccant; Poor insulation measures for hoses and drying silos can also affect the drying temperature.

2. Dry gas path

In the drying gas circuit, the drying temperature should be detected at the inlet of the silo to compensate for the heat loss of the dryer in the hose. The low air temperature at the entrance of the silo may be due to improper adjustment of the controller and a lack of insulation layer, or a malfunction of the heater components, heater current contactors, thermocouples, or controllers. In addition, it is also important to monitor the drying temperature at various locations throughout the entire drying process and observe the temperature fluctuations during desiccant replacement.

If the material has not been properly dried after coming out of the dryer, it should be checked whether the drying silo has sufficient space to provide sufficient and effective drying time. Effective drying time refers to the time during which particles are actually exposed to appropriate drying temperatures and dew points. If the retention time of particles in the silo is not enough, they cannot be properly dried. Therefore, attention should be paid to the size and shape of granular or crushed materials, as they can affect the stacking density and residence time of dry materials.

A twisted hose or a clogged filter can limit airflow and affect the performance of the dryer. So, if no such issues are found during the inspection of the dryer, it is impossible to determine whether the airflow is sufficient. Here, there is a fast, simple, and accurate method to detect whether the airflow of the dryer is sufficient, that is, to measure the vertical temperature curve of the material in the drying silo.

The return air filter can prevent filamentous materials from contaminating the desiccant and affecting its moisture absorption performance. These filters must be kept clean to ensure sufficient airflow.

When dry air comes out of the top of the dryer, most of the heat has already been released. Most dryers can operate efficiently when the temperature of the desiccant is within the range of 120 ° F to 150 ° F. If the return air causes the desiccant to overheat, it will reduce its adsorption capacity for moisture in the dry air.

Always check the return air temperature of the dryer. When the return air temperature is high, it may indicate that the dryer size is too large for the production rate, or the temperature when the material enters the drying silo is high. For example, PET has crystallized before drying, or only some materials (such as PET) have a drying temperature higher than the normal temperature range. In order to prevent the temperature of the return air from increasing, as long as a heat exchanger is installed on the return air path, it can ensure that the desiccant can effectively remove moisture from the dry air.

3. Regeneration and cooling of desiccants

The moisture absorption capacity of a desiccant is limited, so the moisture it adsorbs must be cleaned up through regeneration. The process is: when ambient air is sucked in, it enters the blower through a filter and is then fed into a set of heaters. The heated air passes through the desiccant bed. When the temperature of the desiccant rises, adsorbed moisture is released. When the hot air absorbs water vapor and reaches saturation, it is discharged into the atmosphere. The high-temperature regenerative desiccant must be cooled before returning to the drying loop in order to restore its moisture absorption function.

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