Preparation Of Wood-SiO₂ Aerogel Composite Material And Its Application In Thermal Insulation Of Drying Kiln Shell

Wood drying is the largest energy consumption link in the production process of wood products,accounting for about 40-70%of the total energy consumption of the production,and the heat loss of the wood drying chamber shell is as high as 20-30%of the total energy consumption of the drying.Therefore,the improve of the kiln shell insulation has great significance.The unique nano-network structure of SiO₂aerogel makes it have excellent characteristics such as low density,high porosity,and low thermal conductivity,and it has broad application prospects in the field of thermal insulation.However,the mechanical strength of SiO₂ aerogel is poor,and the commonly used supercritical drying has high preparation cost,complicated process and high risk.In this paper,the sol-gel method was used to prepare SiO₂ aerogel by ambient pressure drying and freeze-drying,and on this basis,wood-SiO₂ aerogel composite insulation materials were prepared to discuss its application in the insulation of wood drying kiln shell.The main conclusions are as follows:?1?Both SiO₂ aerogels can be successfully prepared under normal pressure drying and freeze-drying.The SiO₂aerogels obtained after n-hexane replacement and trimethylchlorosilane surface modification have the best performance and the density of composite material is 0.117 g/cm³,thermal conductivity of composite material is 0.0227 W/?m·K?,specific surface area of composite material is 956 m²/g,average pore diameter of composite material is 11.5 nm,porosity of composite material is 95%,and thermal stability is good.?2?Ambient pressure drying is used to produce wood-SiO₂ aerogel composite materials with low density,excellent thermal insulation performance,good thermal stability and good hydrophobicity.The density of the composite material obtained by direct immersion injection is 0.133 g/cm³,the thermal conductivity is as low as 0.0362 W/?m·K?,the thermal stability is good,the oxygen index is 22.4%,and the contact angle is 154.7°.The gel time,density,thermal conductivity,and contact angle of the composite material prepared by the gel integral molding method increase as the particle size of the wood flour decreases,the density of composite material is 0.159-0.191 g/cm³,and the thermal conductivity of composite material is 0.0302-0.0350 g/cm³,the contact angle of composite material is 144.6°-165.9°.?3?In the metal-assembled wood drying room,the heat loss of the frame with a small area is serious,up to 15%of the heat loss of the shell,and the heat loss of the H-shaped aluminum web portion of the frame structure is the most serious,accounting for 73%of the frame.The wood-SiO₂ aerogel composite material was applied to the wood drying kiln shell to enhance its insulation performance,and four different improvements were designed:the insulation material rock wool in the shell was replaced with wood-SiO₂aerogel composite insulation material;a composite insulation material layer is added at the double-sided frame of the casing;a composite insulation material layer is added to the aluminum plate on one side of the casing;and a composite insulation material layer is added to the aluminum plate on both sides of the casing.The study found that the heat loss of the frame with the double-sided composite shell structure was greatly reduced,in which the heat loss of the H-shaped aluminum web part was reduced by 77-82%,and the shell heat loss was reduced by 18-21%.