Process Optimization Of Combined Solar/Air Energy Drying Of Poplar Wood

Wood drying is the most energy-consuming process in the wood processing process,accounting for about 40%to 70%of the total energy consumption in the production of wood products.In addition,the exhaust gas produced by conventional drying,which occupies a dominant position,contains a large amount of environmental pollutants such as CO2,SO2,and NO2.With the implementation of my country's relevant environmental protection laws and the deployment of air pollution prevention and control decisions,high energy consumption and environmental pollution has became the bottleneck for the development of the wood drying industry.The environmentally friendly drying method that uses clean energy such as solar energy and air energy is most in line with the energy-saving and environmentally-friendly wood drying theme.The intermittent heating drying method has the advantages of relieving drying stress and improving drying quality.In order to achieve the purpose of energy saving and environmental protection,and efficient use of wood resources and energy,it is very necessary to determine the optimal energy conversion threshold for air assist solar energy combined intermittent heating and drying and optimize the process.This research combined the research ideas of multi-energy complementarity,used 25mm poplar wood as the test material,applies the intermittent heating drying method to the air assist solar energy combined drying equipment built in the laboratory,and determined the appropriate intermittent limit of moisture content by improving the drying system Then adjusted the intermittent heating and drying benchmark in three aspects to optimize the combined drying process.The test results were as follows:(1)The initial cracking of poplar wood measured by 100? method was level 2,internal cracking was level 1,and cross-sectional deformation was 4 The initial temperature of 25mm poplar drying standard was 50? the difference between dry and wet bulb temperature was 5?,and the final drying temperature was 75?.(2)Used air assist solar energy combined drying equipment to verify and test the preliminary drying benchmarks,the combined drying quality reached the third-level standard.According to the performance test results of the combined drying equipment,it was proposed that the solar radiation value reached 400W/m2 as the heat collection The pump opening conditions were used to optimize the combined drying control system and make full use of solar radiation energy.It was proposed that the installation of high-power electric steam humidifiers can improve the combined air assist solar energy drying equipment and improved the performance and drying quality of the combined drying equipment.Optimize the combined drying process to provide technical support.(3)By analyzing the drying rate,stratified moisture content,drying stress and drying quality during the intermittent heating and drying process of poplar wood,it was concluded that the intermittent heating drying method promoted the core edge through the surface moisture absorption and moisture content gradient in the non-heating stage.The moisture of the junction wood and the heartwood moved to the sapwood,which improved the uniformity of the moisture inside the wood,and achieved the effect of increasing the drying speed and alleviating the drying stress during the heating stage.Finally,the moisture content of 30%?90%was determined as the application range of intermittent heating and drying.Among them,the moisture content of 60%was the transition point of the drying process with the intermittent rate of 33%and the intermittent rate of 66%;in order to ensure that the wood was fully heated through,a 1.5h pre-heat treatment was required before the heating phase starts.(4)By adjusting the intermittent heating.and drying benchmark and perfecting the air assist solar energy combined drying system,the optimized combined intermittent heating and drying process,compared with the continuous low-temperature drying before optimization,had a higher initial moisture content of 72.8%?81.72%,The drying rate was increased by 9%?37.5%;the drying quality was improved from the third level to the second level;the COP of the drying system was 2.74 and 2.80,respectively,which was 11.8%?14.3%higher than that of the continuous low-temperature drying system.In summary,the best drying process of 25mm poplar wood air assist solar energy combined was:adopt intermittent heating drying standard,in which the initial temperature was 55?,the temperature difference was 5.3?,the post-drying temperature was 85?;the moisture content was 90%?60%When the intermittent rate was 33%,and when the moisture content was 60%?30%,the intermittent rate was 66%..