If you work in the plastic processing industry, you know resin can begin to absorb moisture from the atmosphere throughout the procedures.
Although non-hygroscopic resins such as PVC, polystyrene, polyethylene and polypropylene can contain moisture only on the surface, most engineering plastics are more or less hygroscopic.
These hygroscopic resins (i.e. ABS, acrylic, nylon, PET, PBT, polycarbonate, polyurethane, etc.) absorb water vapor from the air. As the vapor pressure in the pellet increases, the vapor pressure surrounding the pellet also increases, causing moisture equilibrium.
If the pellets are not dried before processing, the water will react with the molten polymer at the processing temperature, causing a change to the molecular structure of the polymer. The chemical reaction is known as hydrolysis and will result in parts that have lesser physical properties, such as reduced impact strengths and tensile.
This is why it is so important to remove the moisture from the resins before processing. Unfortunately, you cannot remove the internal moisture from hygroscopic resins with hot air alone.
When you reach this point, it may be best to examine other drying solutions, such as desiccant dryers. For years, desiccant dryers have been a reliable and efficient solution for removing moisture from plastic resins throughout the plastic processing industry.
What is a Desiccant Dryer?
The term “desiccant dryer” actually refers to a broader class of drying machines. Some other names for this type of unit are:
- Regenerative Dryer
- Twin-Tower Dryer
- Adsorption Dryer (although, this term is used less frequently)
There are three basic styles of desiccant dryers: twin-tower, carousel designs with two or more desiccant beds and “honeycomb” wheel desiccants with a rotating design.
Desiccant drying is different from other forms of plastic drying such as hot air or compressed air drying in that these dryers use materials called desiccants to remove the moisture from the resins.
The air in a desiccant dryer is circulated in a closed loop between the drying hopper and dryer to ensure low air humidity at all times. During the process, the dryer deposits moisture from the hygroscopic material (resin) into the desiccant before releasing it into the ambient air.
Before we get too far into how a desiccant dryer works, we should first explain what a desiccant is and its important role in the drying process.
What is a Desiccant?
A desiccant is a type of hygroscopic substance that can help induce or sustain a state of dryness within its vicinity. Desiccants are chemically stable or chemically inert, which is what makes them so popular among a variety of industries.
The most common desiccant is silica, a nontoxic, water insoluble white solid used in a number of industries. Some other desiccants include activated charcoal, calcium chloride, calcium sulfate and molecular sieves.
For desiccant dryers, the desiccant is in the form of thousands of small beads, usually silica gel or activated alumina. During the drying process, it is the duty of the desiccant material to bring the dew point of the compressed air to a level where water will no longer condense or remove as much water from the resin as possible.
How Does Desiccant Drying Work?
Although there are several different types of desiccant dryers, they all work very similarly. One unique thing about desiccant dryers compared to other plastic dryers is that they use heated dry air to remove the moisture from resin pellets, rather than ambient air.
In desiccant drying systems, the air is circulated in a closed-loop process, preventing air from exiting the top of the hopper and into the ambient air. Instead, the machine recirculates the air back into the dryer, using it repeatedly to remove moisture from the resin.
Here is the step-by-step process of how a desiccant dryer works:
- Air is first sucked from the hopper to the dryer and sent through the filer and the cooling heat exchanger.
- From there, the distributors guide the air through the first of two containers filled with desiccant.
- As the air passes through the container, the desiccant absorbs the moisture.
- The dried air travels to the suction side of the blower through the distributor and is blown through the heater and distributor at the bottom of the hopper by the blower.
- Over time, as the amount of moisture in the desiccant in the container increases, the desiccant will need to be regenerated.
- The dryer uses dew point monitors to keep track of moisture levels in the containers, signaling the central control unit to switch towers.
- Thus, as the air passes through one container, the desiccant in the second container is going through the regeneration process.
In order to be able to reuse the desiccant, water needs to be removed in a process called regeneration. There are two ways to regenerate desiccant: with hot air or dried compressed air. This regeneration process is important in keeping your machine and facility running efficiently.
Here is a look at the regeneration process using hot air:
- The heater heats the regeneration air to high temperatures before guiding it to the desiccant in the container through the distributor.
- As the regeneration air removes the moisture contained in the desiccant, it releases into the ambient air.
- Using ambient air, the machine then cools down the heated desiccant before using it as drying process air.
- The desiccant rotor, or wheel, rotates through the process, switching over to the opposite container.
What are the Advantages to Using a Desiccant Dryer?
Desiccant plastic dryers have many advantages over other types of drying units, including increased efficiency, cost effectiveness and state-of-the-art technology.
Productivity and Efficiency
With desiccant drying, you can increase efficiency in your facility and make your company more energy efficient at the same time. Since these desiccant drying machines provide continuous, closed-loop drying, they allow different sections to work through the drying, regeneration and cooling processes simultaneously.
This allows the desiccant to absorb moisture at a more constant rate and keeps the resin moving from process to process in a quicker manner.
Most desiccant dryers come equipped with a number of key components that make it a more energy-efficient choice over time. In fact, some technologies found in desiccant dryers can reportedly cut energy use by 25 to 30 percent.
Although desiccant dryers tend to be at a higher price point compared to other drying options, they are worth it in the long run. In fact, it’s a value you will recognize after the first use.
In addition to increasing your facility’s overall efficiency, which can help you increase revenue and cut down on operating costs, desiccant dryers also help cut down on other additional costs.
For example, the desiccant drying technology requires less maintenance and eliminates contamination problems in the desiccant beds that were common with older models. Also, the machine’s ability to reuse desiccant and monitor dew points helps cut down on material costs.
There is a reason why desiccant dryers are one of the most common and trusted dryers in the industry. Their unique ability to simultaneously perform three tasks – drying, regeneration and cooling – puts these systems at a much higher level than their counterparts. This closed-loop drying technique helps eliminate contamination problems associated with desiccant beds while also reducing air contamination within your facility.
Desiccant dryers also come equipped with a variety of technological advancements that make them far more efficient and more reliable than other plastic dryers. These include the dew point controller, integrated controller, a timing belt and much more.
So Why Choose a Desiccant Dryer From Shini USA?
Shini USA (a division of Budzar Industries) offers equipment designed for all elements of plastic processing, including a line of drying and dehumidifying equipment.
We carry a variety of drying equipment, which includes several desiccant dryer machines designed with features to fit your company’s specific needs. They are equipped with the very latest in rotary wheel technology, allowing them to seamlessly integrate into your facility’s current processes.
As with most desiccant dryers, our machines allow you to simultaneously complete dehumidifying, regeneration and cooling cycles easily and efficiently. One thing that sets our dryers apart from the competition, though, is their compact design and ability to provide you with a 35 percent operating savings. Our dryers also boast a timing belt drive that eliminates slippage problems and broken drive teeth.
We believe in providing excellent products and services that will last for years, which is why all of our dryers come with an unlimited service life.
Our line of dryers with desiccant technology include:
- Honeycomb Desiccant Wheel Cabinet Dryer
- Portable Desiccant Wheel Drying Cart
- All-in-One Dryer
- Central Drying System
Whether you choose our portable cart or the central drying system, each desiccant dryer has specific attributes such as size, mobility, temperature controls and more that allow them to fit the needs of your facility. Each system’s individual features are designed to enhance performance and ensure reliable drying cycles.
Plus, as with all of our products, our desiccant dryers for plastics are backed by our excellent customer service standards.
How to Get Started With Your Desiccant Dryer
Throughout the years, desiccant drying has been a trusted and reliable drying solution for plastic processing companies. A dryer’s compact design and advanced technology make it ideal.
Need small desiccant dryers for injection molding machines? We’ve got you covered. Need a complete central drying system that allows for different configurations of hopper and dryer sizes? We’ve got that, too.