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The humid months can create issues with resin drying by imparting additional moisture during the process. Carefully monitoring and making small adjustments can save strain on your equipment – especially during the regeneration cycle.

A resin drying system’s regeneration cycle burns off moisture that resides in hygroscopic resins or on the surface of non-hygroscopic resins. When there is more humidity in the air, your drying system must work harder to remove the moisture. The wetter the air, the harder it is to regenerate the desiccant.  This is because most dryers use a mixture of ambient air with recirculated dry air to regenerate the desiccant bed.

Under these conditions, it is important to follow a strict maintenance regimen tailored specifically to your materials and your process. A general guideline would be to review and maintain your equipment at least once a month (user/process defined). But as the humidity increases, you might want to increase that frequency.  It is important that your dryer is providing proper design flow to the process and regenerating air circuits.

No matter what type of dryer(s) you use, they all function in a similar manner.  Once the process circuit removes moisture from the resin, it will enter a regeneration cycle to remove that moisture from the desiccant so the process can repeat. This is accomplished by either switching beds or by continuously rotating the desiccant wheel.  Knowing what parts of the system to monitor and maintain is the key to keeping your process running in good condition. 

Tips for good performance

The part of the resin drying system that is sending dry air to the hopper, contains multiple components that keep that function working. Be sure to check for and repair or replace:

• Cracked or crushed hoses
• Missing hopper covers or loose-fitting cover seals
• Hopper door seals or door clamp adjustments
• Damaged or burned out heaters
• Replace worn out desiccant if contaminated

If high-humidity air has any way to enter your drying system, desiccant beds will fill with moisture faster, leading to high dewpoints and bad parts.

Keep filters clean!

Checking the filters on the process and regeneration side of your resin drying system is a key component of your summer inspection regimen. Filters ensure adequate air flow to regenerate your desiccant and to provide the right amount of process air flow to dry your resin.

Filters and desiccant can become clogged from:

• Dust and fines from the material or plant air
• Plasticizer vapors released from resin
• Dirty material or regrind trapped in the return air stream

Ensure that your filters are clean and no housing gaskets are missing to prevent air leaks that can let additional moisture into your resins. Also ensure that your filter lid fits correctly and all fasteners are present and working. Ensure that the filter is properly seated in the housing to prevent contamination from going to the desiccant.

If you are primarily processing virgin resin, filters should be cleaned on a regular basis and replaced about every six months. If you are processing dirty material, high-glass content material or a lot of regrind, you will want to check and change your filters more frequently.  Your process conditions will determine the frequency of inspection and servicing.  Filters can only be cleaned a limited amount of times before the filter element pores become clogged.  When clogged, this will increase the pressure drop and reduce air flow.

Plasticizer contaminant released from resins can condense and coat your filters and other internal components of the dryer. This results in blockage, even though they might look clean. An aftercooler and plasticizer trap limits and removes vapor particles that can contaminate your filter or other internal components including the desiccant. If you are processing even a few degrees over the material supplier’s recommended drying temperature, more plasticizer can be released, impeding regeneration and creating high dewpoints and temperature spikes.

Maintain in your inventory enough spare filters to keep all your dryers running at peak efficiency during the harsh and humid summer weather.

Use monitoring capabilities

State-of-the-art drying systems offer self-monitoring capabilities to help adjust to periods of increased humidity.

For instance, monitoring the dryer’s dewpoint and regeneration cycle will ensure proper function during humid months. Regeneration cycle monitoring technology can automatically adjust system temperature and control the cycle to account for humid air.