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Drying systems are available in a variety of configurations, each with their own unique capabilities and advantages. Drying systems should be evaluated based on a processor’s overall throughput requirements, as well as other considerations like material changes, floor space and access to utilities.  Current and future needs should be considered so that you have designed in expansion for the system.

The most common resin drying systems include:

• Machine mount units
• Portable cart systems
• Portable cart systems with integrated conveying
• Central drying systems
• PET specialty systems

Central Resin Drying Systems

Central drying systems typically feature one large central dryer with multiple drying hoppers on a common piping and control platform. The dryer runs and provides full air flow in a large dryer loop. Manual or automatic air regulation valves control air flow to each individual drying hopper. One large central heater or smaller individual heaters are supplied to provide heated air to each drying hopper.

Another central drying configuration is designed to provide a grouping of smaller dryers in a row. Each dryer would be sized for the main throughput of the resin it is designed to process. In this case, the system provides ultimate control and processing of each resin. If there is a dryer problem, the rest of the system is unaffected and continues to operate. If another material is added, another dryer module can easily be added to the drying system hopper bank. In this case, each material is provided with the most efficient operating parameters and control to achieve proper drying and delivery of resin to the process.

 

Central resin drying systems are a failsafe against production slowdowns and stoppages because work can continue even if one drying unit fails. New dryer units are easy to add on, in any size and dimension.

While easy to expand, central systems still use less floor space. Central drying systems allow dryers, hoppers and even bins of material to be moved away from the area around the primary machine. This makes central drying systems safer and easier to clean.

A central system could be as simple as a single small dryer serving two or three hoppers on a cart. A central system can also be a series of smaller dryers/drying hoppers each sized for the specific volume of a dedicated resin. In the final scenario, the central system can consist of one large dryer supporting up to 12 drying hoppers on multiple carts. Central systems can be configured to dry from as little as one pound of material up to thousands of pounds of resin.

One dryer or multiple dryers?

A central resin drying system will feature either one large dryer with several drying hoppers connected or a row of individual dryers with integrated drying hoppers.

It is preferable to have individual dryers next to each other to make a central system dryer bank. This affords processors optimum control of each individual material and precise, individual control of air flow and temperature to get the optimum drying performance characteristics.

Alternatively, with only one dryer and multiple drying hoppers, processors are relying on one large unit to control material flow, temperature and air flow to several drying hoppers. In this case, the resin drying system might not be running as efficiently as it could. Worse, if a dryer encounters a problem, the processor might have to shut down the entire system rather than just one station. While individual drying cells require slightly more floor space, if one goes down, it can be removed from the line while the others are running. If the system is expanded, additional dryer modules can easily be added.

The total energy consumption of each type of system is comparable. With an individual dryer and drying hoppers, processors control the actual material and actual drying parameters for the material – the ideal scenario for the best drying performance. That configuration might use slightly more input power upon installation, but it will certainly require less operating power because it is using only the energy it needs to run and dry a specific material. A single-dryer system with multiple hoppers uses a larger main blower, which can be turned down only so much based on the total system requirement.

To achieve contemporary requirements for energy efficiency, modularity and functionality, having individual dryers set up in a bank provides more advantages overall.

 

Portable resin drying systems

Portable resin drying systems are often an interim solution between machine-side and centralized drying systems. They are also a good choice for custom molding operations.

Often mounted on a cart, portable resin drying systems feature a drying hopper, a unit to deliver material to the hopper and another unit to bring material to the machine.

Throughput for portable resin drying systems can be as little as 1 pound per hour up to 400 pounds an hour.

While multiple materials can be managed with multiple portable systems, navigating changeovers on valuable production floor space requires careful planning and execution.

Portable resin drying systems with integrated conveying

An all-in-one portable integrated conveying system allows operators to automatically convey material to the drying hopper and the process machine with integrated controls. This means that no additions or expansions to existing conveying systems are required. In addition, when equipped with an optional remote proportioning valve, two materials, typically virgin and regrind, can be automatically conveyed to the drying hopper, eliminating the need to mix the two prior to drying.

Machine-Mounted Dryers

Machine-mounted dryer/hopper configuration are generally designed for lower throughput.  On higher-throughput extrusion applications, a drying hopper can be mounted to the process machine, and the dryer would sit next to or near the machine to connect to the drying hopper.

Any machine movement or cycling could seriously affect the mechanical design integrity of the system. In these cases, it would be better to mount the dryer above the throat on a stand that straddles the process machine or on a mezzanine directly above the feed throat of the machine. This removes the dryer and hopper from direct mechanical impact and fatigue.

At one time, it was common practice to mount the dryer/drying hopper to the process machine.  In today’s production environment it is considered common practice to install the drying system next to or directly above the process machine feed throat.

PET Resin Drying Systems

Drying systems for PET often use a desiccant wheel dryer. These simple, energy-efficient units consist of the dryer, an energy-efficient drying hopper, a process heater, a cyclone to remove return air dust and a self-cleaning dust collector (pulse type).

In some cases, it might be practical to incorporate a gas-fired process heater, which can provide significant cost savings over electric – particularly when processing over 3,000 pounds or more of material per hour. With increased use of post-consumer and post-industrial PET, modern PET drying systems and crystallizers must process greater amounts of material.

Most PET applications require the final moisture content to be below 50 ppm and sometimes 30 ppm or less.

PET drying systems are important because:

• PET for beverage bottles must be dried properly not only for clarity but for strength to contain carbonated fluids and maintain the integrity of the product for a sustainable shelf life. 
• PET sheet packaging products require hot fill, to the freezer, to the microwave or oven without breaking.