Insulation
Insulating key components of your resin drying system, including the hopper(s) and dryer(s), is essentially to retaining optimum heat throughout the resin drying process.
Drying hoppers generally are insulated. The thicker the insulation, the better the heat retention. Most drying hoppers have 2-inch thick or thicker insulation. For dryers, components that should be insulated include high-temperature flex hoses and hard metal ducting routed from the dryer to the drying hopper.
Insulate dryer hoses and piping that carry hot air from the dryer to the drying hopper inlet. The hose returning air from the top of the hopper to the dryer should never be insulated. It is important to reduce the dryer return air temperature to allow for optimum desiccant regeneration.
Component placement
In any dryer installation the placement of those components must be considered relative to the overall extrusion or molding process and the workflow.
Portable drying systems generally feature a dryer, hopper and loader on a rolling cart that can be moved from one machine to another. Larger systems should be more stationary and are not considered portable.
Mezzanine-mounted drying systems, located directly above process machines, save floor space and can supply resin to multiple machines.
Central drying systems
Central drying systems are optimal for use with multiple resin types requiring many changeovers. Central drying systems can be built with multiple dryers or a single dryer.
Application requirements are a key consideration for the layout of your resin drying system – if you are also blending and conveying materials.
Process heaters can be included in the dryer cabinet with small systems or on or near the drying hopper in large systems. This minimizes heat loss between dryer and hopper and maximizes the energy efficiency of the drying system.
Hose requirements
Resin drying systems use multiple hoses to convey air and materials from storage through drying to processing.
- Heated dry air to the drying hopper – insulate.
- Hot air within the dryer cabinet components – insulate.
- Returning air from the top of the hopper to the dryer – no insulation.
Material flow
When planning your equipment layout, consider the flow of resin from storage into the drying hoppers and then from the drying hoppers into the process. The design should consider optimum flow, minimal material degradation and protection of the dried material after it leaves the drying hopper and is conveyed to the process.
The distance from the drying hopper discharge to the process machine must take into account excessive heat loss by the resin and the amount of time the resin sits in the material lines. It is important to protect the resin and minimize the chance that it can regain moisture after it has been dried and before it is processed.
Consideration should be made to provide closed loop conveying, conveying with dry air and/or purging material from the drying hopper into the process machine. These would be discussed as separate topics during the system design process.
For long conveying distances between the drying hopper and process machine, it might be beneficial to add a small conditioning dryer/drying hopper near the process machine to bring the material back up to temperature and to condition the dried resin and prevent the material from absorbing ambient moisture from the environment.
Purging the material line each time material is conveyed from the drying hopper to the process machine is a good way to ensure dried resin is contained at the source and then used in minimal amounts (enough for the process machine throughput requirements plus a small reserve). In this type of system an insulated machine hopper can hold enough reserve material and keep it from losing too much heat prior to being used in the process. Care must be taken when designing this type of system due to convey time lost to the purging process. Your system design expert can properly size the system to avoid any chance of under sizing your throughput for the system.
Each resin has different material properties and different levels of moisture regain potential. Understanding this will allow you to design a system that addresses the concerns but does not create a system that is overengineered.
Controls
Contemporary dryer system control screens generally are set at the factory and are ready to perform right out of the box to communicate system parameters and maintain them.
In most cases, a resin drying recipe can simply be loaded into a controller’s recipe book with easy-to-use touchscreen controls. With stored resin drying recipes, once a material is loaded into the dryer control, it runs automatically at the prescribed temperature, air flow rate and drying time. Preset recipes can be overridden by expert processors.
System utilities
Planning the location of a resin drying system must consider the availability of and ease of access to an electrical supply, gas supply, compressed air and water. Always check and comply with local codes and installation requirements for all utilities. Your equipment supplier can provide specific requirements for the equipment you are installing for your process. In most cases, installation support can be quoted and sold as part of the new system purchase.
