1. Conventional drying technology
Conventional drying refers to the indirect heating of air with atmospheric wet air as the drying medium and steam, hot water, furnace gas or hot oil as the heat source. Conventional steam drying plays a leading role in wood drying in China, accounting for more than 80%, followed by conventional drying with furnace gas and hot water as energy.
China has recently developed a furnace gas (also known as hot air) drying equipment for burning wood waste in a cyclone combustion furnace. It changes from the direct heating of furnace gas in the initial stage to the conventional drying of wet air indirectly heated by furnace gas. It can not only treat the waste such as sawdust, shavings and waste materials in the wood processing plant, but also reduce the drying cost.
2. Dehumidification and drying
During dehumidification and drying, the wet air is closed circulated between the dehumidifier and the drying chamber, and the drying chamber is dehumidified by refrigeration and dehydration. The dehumidifier recovers the heat released by the dehumidification of the drying chamber, saving energy. Compared with steam drying, its energy-saving rate is 40% ~ 70%. It is an energy-saving equipment.
The performance of some products in China has reached the international level. For example, RCG series medium temperature and high temperature dual heat source dehumidifiers designed by Beijing Forestry University have made innovations in refrigerant subcooling mode, design of heat pump air inlet system and secondary air supplement mode, which has increased the energy-saving efficiency of dehumidifiers by 15% ~ 20% and reduced the manufacturing cost by 5% ~ 10%.
3. Solar drying
Solar energy is a clean and cheap renewable energy. China and many countries in the world are rich in solar energy resources. However, the scale of wood drying rooms using solar energy in various countries is very small. The total drying capacity of solar drying rooms in China accounts for about 0.2% of the total drying capacity of the country.
China has successfully developed trcw medium temperature and GRCT high temperature solar heat pump dehumidifier combined drying system. Its performance indexes in heating efficiency and drying energy consumption have reached the international advanced level of similar products.
4. Vacuum drying
Wood vacuum drying is to dry wood in a closed container below atmospheric pressure. The water in wood accelerates the migration speed of water under the action of internal and external pressure difference. At the same time, due to the low saturation temperature of water in vacuum, vacuum drying can achieve rapid drying at low temperature and good drying quality.Beijing Forestry University has preliminarily discussed the characteristics of wood vacuum superheated steam drying and heat and mass transfer under vacuum and negative pressure, and published relevant research papers.
5、Microwave And High Frequency Wood Dry Kiln
Both microwave and high-frequency drying use wet wood as dielectric. Under the action of microwave or high-frequency electromagnetic field, water molecules in wood polarize. At the same time, due to the frequent alternation of electromagnetic field, water molecules swing at high speed and frequently, friction generates heat, so as to heat and dry wood.
heated surface to the core wholly and uniformly. That is one of the reasons why the high frequency vacuum machine is 10 times faster than a conventional wood drying kiln.
The hardwood from 30% moisture content to 8-10%MC only take 4-6 days and the fresh cut wood only take 10-12 days to get 8-10% moisture content.
Our kiln also adopts vacuum dehydration technology. The stainless steel vacuum pump can make the vacuum oven reach -0.093Mpa condition. The vacuum condition is to make water vaporized in low temperature below 55 ℃,At the same time, vacuum can also suck the wood moisture out. The machine cooling system will separate the hot air and hot water out, then cool them and release them out. Wood is drying under a vacuum and wet condition at low temperature. That will ensure wood is no cracks and keep the wood nature color.
