As the technology develops, now many people realize that the traditional air drying takes too long and it is with high risks of grade decline, so more and more kilns have been built to meet this need, there are many different types of kilns now on the market and it is always hard to choose a proper one, in fact for many operators, Kiln-dried wood already means a lot, but it is important to keep an eye on the market always and learn the latest technology, just like that you will never make it a success by investing a lot of money on telephones when everybody is using the smartphones.
Now in the markets, there are mainly the below five kinds of kilns which are widely used as follows:
1.The traditional kilns with boilers can burn the wood and other scraps, let’s call it TKS for short.
2. The Kilns are very similar to the traditional ones, but the boiler is powered by electricity, the kilns will be made of metal boards and they could be controlled by computers, we use TKE to stand for this kind of kiln.
3. When people realize that high temperature always causes serious defects in the wood, people began to use the vacuum drying, which allows the whole drying process to happen at a low temperature like 50℃， the third type of kiln is the one with vacuum drying chamber, and because the low content of air, it uses electricity to heat the water or oil in the metal plates, and then use the plates to dry the wood boards, Namely Thermal Vacuum Drying.
4. For the above three kinds of drying kilns, belong to the heat conduction heating method, meanwhile the following two belong to the electric field radiation heating. Just like the microwave oven in our kitchen, there is also Microwave drying in the wood drying field, and it also adopted the vacuum drying chamber. We call it MWV for short.
5. The Microwave is of high energy, but its wave is short which means low penetrate ability, so technicians use radiofrequency instead of the microwave, that is the last type, high-frequency vacuum wood drying kiln, HFV for short.
Now let us do a comparison as the table.
| Type/Items | TKS | TKE | TVD | MWV | HFV |
| Heating methods | Burn sawdust waste wood, etc., and heat water to generate steam | Electric heating of water, heat transfer oil, or direct resistance heating | Electric heating water or heat transfer oil, heat is transferred from the hot plate to the wood, the vacuum reduces the boiling point of water, improves the efficiency, and prevents cracking due to excessive temperature | Electricity is converted into an electromagnetic field to heat the water inside the wood, vacuum reduces the boiling point of water, improves efficiency, and prevents cracking due to excessive temperature | Electricity is converted into an electromagnetic field to heat the water inside the wood, vacuum reduces the boiling point of water, improves efficiency, and prevents cracking due to excessive temperature |
| Volume | Large capacity, hundreds of cubic meters are very common, need to add spacers | Same as TKS | Smaller capacity, the heat plate takes up most of the space | The capacity is small and the wood needs to have gaps | Small capacity, no space needed for electrode plates, no gaps, and no spacers, make the best use of a vacuum chamber. |
| Drying time | Several weeks and months | Same as TKS | 1-2 weeks | Within 100 hours | 4-10 days |
| Drying results | If the worker controls well, the drying effect is good. otherwise, it is easy to crack and deform or the moisture content is uneven. | Same as TKS, but if adopted the computer-aided system, the results are better than the former | The drying effect is good, and the surface carbonization is easy to occur if the control is not good. | The drying effect is good | The drying effect is good |
| Control methods | Human control and on duty | Same as TKS | Semi-auto or automatic | Semi-auto or automatic | Semi-auto or automatic |
| Power consumption | Because some waste could be reused, the cost is low | To dry per Cbm wood the electricity needed is about 200-240 Kwh | The electricity consumption is similar to TKS | The cost is higher than the before 3 kinds | 100-200Kwh depending on thickness |
| Limits | It occupies a large area, the drying capacity is relatively large, the time is too long, it is suitable for mass drying and not suitable for rapid turnover, and the thick wood is basically unable to be dried, and there is a fire risk. | Similar as TKS | Small drying capacity, not suitable for mass drying, suitable for fast turnover, not suitable for drying wood over 4cm, the hot plate occupies about half of the space, and the cost of hot plate replacement is high | The cost of electricity consumption is high, the drying capacity is small, and wood over 3cm cannot be dried | the drying capacity is small |
| Recommend Applications | Large Lumber factory and no environmental limits | Large Lumber factory, where labor cost is low | Some small and softwood producer | Pallet manufacturer | Sawmill factory, furniture manufacturer, and woodworking |
Conclusion： The traditional heat conduction type namely the steam kiln is suitable for mass drying, the drying quality will be uneven due to the different experiences of workers, there is a fire risk, and it may cause environmental problems. At the same time, it cannot dry thick boards. Microwave drying is suitable for thin board drying and requires strict control of temperature and speed. The core of thick boards cannot be dried, and high-frequency vacuum drying may consume high power. It has absolute advantages, no professional operation is required, basically no wood waste, extremely low maintenance costs in the later period, and high comprehensive benefits.
