OSB Wood Shavings Drying Equipment Selection – Mesh Belt Low-Temperature Wood Shavings Dryer

Introduction

This paper introduces the simple structure of a drum-type single-channel medium/high temperature flue gas shaving dryer and a mesh belt-type low temperature shaving dryer for oriented strand board (OSB) production, and proposes suggestions for selecting shaving dryers based on the author's production experience.

1. Rotary drum type single-channel flue gas dryer

2. Mesh Belt Low Temperature Wood Shavings Dryer

This type of dryer was originally used in other industries. In Europe, it was first introduced in 2010 by the Italian IMAL & PAL Group when they built an oriented strand board (OSB) factory near Milan, producing unexpected results. For example: 1) Because hot water is used as the heat source, the wood shavings are not contaminated by smoke and dust, preserving the natural color of the original wood; 2) Compared to the low-temperature drying provided by flue gas, the wood shavings have a relatively low shrinkage rate; 3) Due to the low-temperature drying, the wood shavings are relatively flat, resulting in a relatively flat board blank during subsequent installation. This is one of the reasons why this production line does not need to move the large surface wood shavings to the core layer when producing fine-particle OSB; 4) Most importantly and sensitively, and also its significant advantage, is that without dedicated dust removal equipment, the dust content of the exhaust gas is ≤10 mg/m³, which fully meets the emission standards of some parts of my country. However, it is flammable, which is one of its so-called disadvantages. Analyzing the cause of the fire, the basic conditions for ignition are the presence of combustible material and an oxidizer. With both present, the temperature must reach the auto-ignition point of the combustible material, or an open flame must appear. Clearly, the possibility of the combustible material reaching its auto-ignition point due to high temperature can be largely ruled out. The only remaining cause of the fire is an open flame. There are two types of open flames: visible and hidden. Preventing visible open flames is relatively easy, while preventing hidden open flames is more difficult, as they are often caused by static electricity. Therefore, anti-static measures must be in place when using this type of dryer; otherwise, serious consequences may result.

3. Conclusion

As a crucial step in the production of oriented strand board (OSB), wood shavings drying is indispensable. For new production lines, selecting the right wood shavings dryer is an important task for technical personnel. This author believes that the selection of a wood shavings dryer should be considered from the following five aspects:

1) Safety of the dryer: Fires frequently occur during the production of oriented strand board (OSB) at this stage. Therefore, the dryer is a critical piece of equipment that companies must pay close attention to. Regarding the fire prevention of low-temperature wood shavings dryers, as analyzed earlier, as long as anti-static measures are in place, fires generally will not occur due to drying temperatures exceeding the auto-ignition point of wood. However, for medium/high-temperature wood shavings dryers, fires may occur due to high drying temperatures or the carbonization of fine wood shavings deposited in dead corners created by the dryer's internal structure.

2) The capacity of the dryer must be designed with a margin. Most particleboard production lines in my country are generally over-produced after normal operation, sometimes by more than 30%. At this point, it will be found that the drying process is the bottleneck restricting the increase in capacity. If it is modified, a lot of manpower, material resources and time will be wasted.

3) Energy consumption of the dryer: The energy consumption of wood shavings drying accounts for more than 65% of the total energy consumption of oriented strand board (OSB) production. Calculations show that drying 1000 kg of wet wood shavings with an initial moisture content of 100% at 20°C requires approximately 3.2 GJ of heat, regardless of the type of dryer. Energy saving can only be considered by reducing dryer resistance and minimizing heat loss from insulation. Calculations show that dry air provides significantly better insulation than rock wool. Electricity consumption for wood shavings drying: Under the same conditions, the amount of electricity consumed is mainly determined by the power of the main fan motor. The power configuration also depends on the system resistance; the greater the resistance, the greater the required motor power, and the higher the electricity consumption.

4) The quality of wood shavings drying can be considered from the following three aspects: First, the cleanliness of the wood shavings, because the smoke and dust pollution caused by the drying process will cause the original color of the wood shavings to change to varying degrees; second, the degree of change in the flatness and warping of the wood shavings after drying. Undoubtedly, the less warping, the better; third, the shrinkage rate of the wood shavings. Of course, the lower the better.

5) The reliability of the dryer is also crucial. Poor reliability and frequent malfunctions will affect the normal operation of the entire production line, leading to high maintenance costs, increased product costs, and reduced product competitiveness. By now, industry professionals should understand this perfectly.