Characteristics And Product Distribution Of Chestnut Shell Pyrolysis

China is rich in chestnut shell resources,but the existing treatment methods are generally incineration or random disposal,which not only causes waste of resources,but also causes serious environmental pollution.Pyrolysis is a commonly used treatment method for chestnut shells at present.The products of pyrolysis have good economic and utilization value,but their processing efficiency is low.Therefore,in order to further improve the efficiency of pyrolysis of chestnut shells and achieve their efficient pyrolysis,this study aims to design a fast thermal pyrolysis pilot-plant unit for chestnut shells,through the composition and thermogravimetric analysis of chestnut shells,and the products of thermal cracking Research on the characteristics and relevant conclusions can provide guidance for the industrial application of chestnut shells.The main findings are as follows:(1)The self-developed fast thermal pyrolysis pilot-plant unit includes includes: cutting system,reaction system,filtration system,condensation system,heating system,nitrogen production system and control system.The power supply of each component is automatically controlled by the computer,which is safe and convenient.The feed rate can reach 1 kg / h,the maximum pyrolysis temperature can reach 800 °C,and the pyrolysis gas cooling temperature is 4 °C.The fast pyrolysis device can also achieve slow thermal pyrolysis of biomass,with a single processing capacity of 2 kg chestnut shell powder and a maximum pyrolysis temperature of 800 °C.(2)Chestnut shell characterization analysis results show that its composition is N(1.09%),C(44.53%),S(0.91%),H(5.58%),moisture(11.63%),volatile matter(75.58%)Ash(1.61%)and fixed carbon(25.81%).The process of pyrolysis is mainly divided into four stages: the low temperature section at a temperature <130 ° C,mainly the evaporation of water in the chestnut shell sample;at 180-320 ° C,the main thermal decomposition of hemicellulose;320-450 °C It is mainly pyrolysis of cellulose;260-600 °C,mainly pyrolysis of lignin.At 420 °C,the chestnut shell has been basically pyrolysised,and then it is mainly carbonized.(3)Py-GC/MS technology was used to analyze the pyrolysis behavior of the chestnut shell,which showed that the higher the temperature,the higher the single-stage thermal cracking,the higher the product yield.For two-stage rapid thermal cracking,the first-stage temperature has little effect on total product yield,which is equivalent to the single-stage pyrolysis at 450 °C.At 350 °C,only a small amount of decomposition occurred.When the temperature was increased to 450 °C,the chestnut shell was almost completely decomposed.In order to get the most products from the thermal cracking of chestnut shells,single-stage pyrolysis shall be used,at a temperature higher than 450 °C.In single-stage pyrolysis,the total number of compounds increased with temperature.In the two-stage pyrolysis,the higher the first-stage temperature,the higher the number of compounds.Pyrolysis products were mainly nitrogen-containing compounds,sugars and acids,of which D-allose and acetic acid content were the highest.For single-stage pyrolysis at 500 °C,the concentration of D-allose reached 17.0%.For two-stage pyrolysis,when reaction temperatures were set at 450 °C and 600 °C for the first and second stages,the acetic acid concentration can reach 15.9%.(4)Pilot-plant fast pyrolysis experiments showed that the total amount of products decreases with an increasing pyrolysis temperature,and the water content of the product increases.Pyrolysis temperature should be set at 450 °C to obtain the highest yield of pyrolysis products,mainly including sugars,acids,phenols and ketones.For a highest nitrogencontaining products the temperature should be set at 600 °C,with total product yield less than at 450 °C.A lower pyrolysis temperature is conducive to obtaining bio-oils with a high proportion of acids,phenols,and esters.A high pyrolysis temperature increase the proportion of nitrogen,ketones,and alkanes,and it is easier to obtain bio-oils with a more uniform distribution of various substances.The total number of product chemicals showed a trend of decreasing first and then increasing when the reaction temperature was increased.When fast pyrolysis temperature increases,nitrogen-containing macromolecular compounds are gradually cracked into small molecular compounds.Sugars,esters,and benzenes are basically harvested at 450 °C.A higher pyrolysis temperature does not change much the total yield and the number of chemical species.Acids can account for up to 49.7%,phenols for up to 9.7%,alkanes for up to 10.6%,and esters for up to 16.5% in the resulting pyrolysis bio-oil.(5)Pilot-plant slow pyrolysis experiments showed that: For single-stage slow pyrolysis,the product yield was the largest at 500 °C,with products mainly were nitrogen-containing compounds,sugars,ketones,benzenes,and alkanes.The total yield was low at 600 °C,but with more acids and esters: 25.7% of sugars,39.8% of acids,21.6% phenols,and 12.1% of ketones.When the pyrolysis temperature was 400 °C or 700 °C,most of the pyrolysis products were sugar acids,phenols and ketones;When the temperature was 500 °C or 600 °C,the products mainly contained sugars,acids,phenols and ketones.Therefore,at 400 °C the sugar had not been completely produced,but when the temperature reached 700 °C,it is not good for the formation of sugars.To obtain a high content of sugars,a pyrolysis temperature of 500 °C was desired.In single-stage slow pyrolysis at 500 °C,the number of product species is up to 182.Generally speaking,500 °C is the best temperature for single-stage slow cracking.(6)The effect of residence time on total yield during the slow pyrolysis in stages was not significant,and the residence time had basically no effect after 60 min.When the residence time was 45 min,it was easier to obtain high yields of sugars,alkanes,and esters;At 60 min it was easier to obtain high yields of nitrogen-containing and phenolic compounds;At 75 min,it was easier to obtain acids,ketones,and benzenes.The number of products increased with residence time.At the residence time of 75 min the total number of products was 190.In the staged slow pyrolysis,the distribution of products at different residence times and stages were very similar.