Comparative Study On Five Drying Methods Of Plantation Pinus Sylvestris Wood In 40mm Thick

Pinus sylvestris is a very tenacious tree with very strong vitality.It grows quickly,has a long lifespan,a strong root system,and has good soil and wind resistance.Therefore,it is often used as one of the dominant tree species in the north.Since the ban on logging of natural forests,in order to alleviate the shortage of domestic timber supply,it is necessary to further overcome the shortcomings of planted forests,improve the high-quality utilization rate of wood,give full play to the advantages of artificial fast growing forest,and realize the goal of large use of small wood and superior use of inferior wood.Wood drying is the most important process in the processing of wood products.It is an important technical measure for rational use of wood and saving wood.It is the key to directly affecting the quality of wood products.It plays a very important role in energy saving,consumption reduction,and emission reduction.This article takes40 mm thick plantation Pinus sylvestris as the research object,and explores its drying characteristics in the solar drying,solar-high temperature combined drying,solar-conventional combined drying,high-temperature drying and conventional drying processes,mainly including drying quality,drying time,drying speed,drying energy consumption,and changes in resin content before and after drying.At the same time,a comprehensive evaluation system model for wood drying was established through the analytic hierarchy process,and the five drying methods were comprehensively evaluated.The main findings are as follows:1.Conventional drying by plantation Pinus sylvestris material initial moisture content of 76.08%,drying and moisture content of 11.69%,the whole drying time of 72 h;After conventional drying,the average final moisture content,drying uniformity and the deviation of moisture content in thickness of wood all reached the second grade of drying quality,and the residual stress reached the third grade of drying quality.Its degreasing rate is 27.20%.The maximum energy consumption of conventional drying is 459.095 k W · h/m~3.In the whole drying process,more energy consumption is needed in the late drying period,and the energy consumption in the late drying period accounts for 50% of the whole drying process.2.The high temperature drying plantation Pinus sylvestris from initial moisture content of 83.18%,dry to a moisture content of 10.42%,the whole drying process sharing 24 h.The drying speed of high temperature drying is 3.4 times that of conventional drying.After high temperature drying,the average final moisture content,the drying uniformity,the deviation of moisture content on the thickness of wood all reached the drying quality grade 2,and the residual stress reached the drying quality grade 3.The degreasing rate is about 25.64%,and the energy saving of high temperature drying is 73% compared with that of conventional drying.The energy consumption in the late stage of high temperature drying accounts for 32% of the energy consumption in the whole drying process,and high temperature drying is more energy saving in the late stage of drying.3.It takes 360 h to complete solar drying of plantation Pinus sylvestris.The whole drying process is relatively slow,and the drying speed in the daytime is about 4 times as fast as that at night.The average final moisture content,drying uniformity,moisture content deviation on thickness and residual stress of complete solar drying reached the second grade of drying quality.The degreasing rate of complete solar drying is 50.14%,which is the largest degreasing rate and the best degreasing effect.The energy consumption of complete solar drying is the minimum,which is 45.429 k W ·h/m~3.4.The total time of solar-conventional combined drying of plantation Pinus sylvestris wood is 203 h.The average final moisture content and drying uniformity of the solar-conventional combined drying were up to Grade 3 of drying quality,and the residual stress was relatively large,exceeding 5%,but no serious visible defects were found.The degreasing rate of solar energy combined with conventional drying is 31.02%,which is about 4.4 times that of solar-conventional combined with solar-high temperature drying.The energy consumption of solar-conventional combined drying is 148.404 k W ·h/m~3,which is the largest energy consumption in solar drying.5.The solar-high temperature combined drying of plantation Pinus sylvestris takes194 hours.The solar-high temperature combined drying cycle is 46% shorter than the complete solar drying,the average drying speed is completely solar drying and solar-conventional drying of 1.7 times and 1.1 times.The deviation of average final moisture content,drying uniformity and moisture content on thickness of solar energy and high temperature combined drying reaches the second grade of drying quality.The degreasing rate of solar-high temperature combined drying is only 6.99%.The energy consumption of solar-high temperature combined drying is 47% more energy saving than that of solar-conventional combined drying,and 22% more energy consumption than that of complete solar drying.6.Using the analytic hierarchy process(AHP),based on the comprehensive evaluation of wood drying system modeling,the five kinds of drying methods of quantitative evaluation on the evaluation index,calculated the high temperature,dry weight,the largest comprehensive evaluation of the effect is best,which compared with other four kinds of drying methods,high temperature drying in the drying quality,drying speed and drying energy consumption aspect of comprehensive performance is better.