While microwaves are nothing new when it comes to heating food, the technology has recently been approved by the international authorities for heat treating wooden packaging. The first test site has been in operation for more than a year at Scaroni Group, a pallet recycler and broker in northern Italy. The technology is completely different than conventional heat treatment. It is sort of like the difference between using an oven or a microwave to heat your meal. Both methods are safe and useful.
Angelo Scaroni, president of the Scaroni Group, said, “Dielectric Heating (DH) using a microwave is a completely different process from conventional heat treatment although it achieves the same result.”
Dielectric treatment involves heating the wood with a microwave or radiowave; the heating starts from the heart of the wood and it propagates toward the outside compared to conventional heat treatment that works from the outside toward the inside of the material.
John Janowiak, Ph.D., professor of wood products engineering at Penn State University, has studied the use of microwaves to heat treat pallets and wooden packaging. He said his research was able to prove the efficacy of dielectric heating using microwaves and similarly radio frequency treatment to kill significant wood pests species in compliance with ISPM-15.
International governing authorities have approved dielectric heating using microwaves as long as the wood is heated to 60 degrees for one minute, which is different from the 56 degrees for 30 minute standard for conventional heat treating.
Microwaves tend to work much faster than conventional heating, which can fully sterilize a pallet to ISPM-15 standards in less than three minutes compared to hours with a heat treatment chamber or dry kiln. Such a quick rate of treatment allows a microwave system to be put inline so that pallets can be treated without lots of unnecessary handling.
The microwave system used by Scaroni can accept a new pallet every 40 seconds, and it is capable of treating up to four pallets at once, which is about 100 pallets per hour. A fast automated nailing system can produce more pallets than the microwave system can process, but extra pallets can be staged in stacks awaiting treatment. Scaroni added that advancements in technology in the future may allow for higher production of pallets at once through the system.
According to Scaroni, the microwave system uses much less energy than conventional heat treating methods. It requires 100kW of electrical power to operate. Energy savings can be substantial compared to conventional heat treatment. Janowiak said, “If you have reasonably low industrial electrical power rates, than the cost of operating a microwave system can be less expensive than conventional heat treating.”
While a pallet is in the system, it is rotated to allow for even treatment compared to conventional heat treatment, which may have uneven treatment in areas. Michele Diaferia of EMitech, said, “The microwave system is ready to heat pallets immediately when the unit is turned on, no pre-heating is required.”
Scaroni further explained that the type of wood and the initial humidity (wood moisture) level can affect the treatment modality. It should be noted that the higher the humidity level of the wood, the better the dielectric heating process will function. The reason is that a microwave works by reacting with water molecules in the wood. The drier the wood, the less moisture is present to cause this heat reaction.
Some people worry about the security of a microwave system. But the entire chamber is shielded and doors prevent any dielectric energy as low-level radiation in terms of the applied electromagnetic field from leaking. Diaferia stated the EMitech microwave unit is completely safe. The unit has been functioning at the Scaroni plant since 2008. It is regularly tested and has shown no sign of problems or microwave leakage. Scaroni claims that he has treated 70,000 or more pallets through the system according to ISPM-15 standards, which proves the technology works well.
Janowiak explained, “It is easy to shield chambers so that no microwave leaks out. The technology is well proven, and safety is not an issue.” He added that microwaves are different from gamma or X-ray radiation. It is non-ionizing energy, which is the reason that people don’t have health problems after repeatedly using their kitchen microwave ovens.
Scaroni stated, “To date, the Scaroni microwave treatment system has exceeded all safety checks without any problems.”
The designers of the system claim the microwave process is effective for anti-mold sanitizing as well. Scaroni suggested, “When microwaved, the resin in the wood crystallizes almost like a varnish so that the material does not easily mold because air exposure is impeded.”
This process also helps to reduce the likelihood of future mold growth according to Scaroni. He claimed, “Using the dielectric heating method has helped to deal with my mold problem on pallets.”
Diaferia added that the process continues even after the pallet leaves the microwave chamber as the wood continues to push the resin out toward the surface.
Janowiak could not confirm the claims about anti-mold benefits of microwaves. But he did say it does heat differently, which means the technology might not have the surface moisture issue that can cause problems after conventional heat treating. He said that the ability to grow mold depends on the species and moisture content of the wood.
Janowiak commented, “I think microwave heating tends to create a situation where you have more dynamic moisture redistributions and soluble chemical extractives mitigation to the treated wood surface that may affect growth of sapstain or mildew type of fungal organisms. I see in theory how their claims can be true. But I have never collected data to prove those assertions.”
So will microwaves radically change the industry tomorrow? The reality is that even though the technology behind microwaves has been proven effective and is now officially authorized to be used for ISPM-15 pallet and packaging certification, it faces a number of challenges. For starters, the technology has yet to be commercialized outside of the test sites in Europe. And there is practical little experience running or servicing systems around the globe.
Scaroni commented, “There currently is no industrial production of dielectric systems, and the cost is still high for large-scale penetration in the market.” But the technology is evolving and has a number of significant advantages that could make dielectric heating more affordable and more widely available in the near future.
Another challenge for dielectric heating is extremely cold ambient temperatures. Diaferia stated, “Very cold outside temperatures reduce the final treatment output significantly.”
Another challenge is the treatment capacity compared to production of high-speed nailing machines. Scaroni commented, “We are studying improvements in the treatment process to speed up the system and allow the treatment of piles of pallets.”
The price tag is expected to be greater than a typical heat treatment system and yet cheaper than a very large dry kiln. Probably in the $200,000-$300,000 range. The unit at Scaroni Group is fairly long in terms of space requirements. It runs about the total length of an automated nailing line. Scaroni said, “We are actively evaluating the U.S. market potential right now.”
For more information on this technology, contact EMitech at m.diaferia@emitech.it or Angelo Scaroni at Angelo@scaroni.it.
Resources
EMitech www.EMitech.it
Scaroni Group http://www.scaroni.it/
