| Biomass is a renewable energy and its thermochemical utilization plays an important role in solving energy shortage,environmental pollution and other issues.Due to the low efficiency of conventional pyrolysis and poor quality of products,Catalytic pyrolysis technology has received extensive attention.In this paper,the influence of potassium salt on the pyrolysis of sawdust is studied.Two kinds of potassium salts（K2CO3 and KOH）are selected as catalysts.The effects of catalyst addition amount,pyrolysis temperature and catalyst types on pyrolysis process and pyrolysis products of sawdust are investigated.The variation and distribution of pyrolysis products in different pyrolysis conditions are comprehensively analyzed and compared,and the suitable process condition is found.Combined with different kinetic analysis methods,it is deduced that the most suitable reaction mechanism of sawdust pyrolysis.Through the establishment of the pyrolysis model for the simulation prediction,the pyrolysis characteristics of sawdust catalyzed by potassium salts are further investigated.Pyrolysis characteristics of sawdust catalyzed by potassium salts are analyzed by thermogravimetric analyzer.It is found that the pyrolysis process of sawdust is divided into four stages:dehydration,initial pyrolysis,main weight loss zone of pyrolysis and carbonization.The increase of heating rate makes pyrolysis of sawdust move to high temperature,the maximum weight loss rate increase,and the total weight loss decrease.Adding two kinds of potassium salts,it is found that both of them promote the pyrolysis of sawdust,the pyrolysis temperature significantly decrease,which indicate that the pyrolysis process of sawdust change,the DTG curve become only one"maximum pyrolysis peak".It is considered that the catalytic effect of KOH is better than that of K2CO3 because of its low melting point and high strength basicity property.The kinetic parameters are calculated according to the results of thermogravimetric experiments.The reaction mechanism of the sample is speculated.The results show that the reaction mechanism of sawdust follow two-dimensional diffusion model and random nucleation and then generated model respectively under low and high temperature.After the addition of the catalyst,the reaction mechanism of sawdust follows the three-dimensional diffusion model and the chemical reaction model,respectively.Comparing the results of kinetic calculation,it is found that two kinds of catalysts reduce the activation energy of pyrolysis of sawdust at low temperature,and slightly increase the activation energy of pyrolysis of sawdust at high temperature.A model of pyrolysis reaction is established to predict the pyrolysis process.The results show that the model can better describe the pyrolysis process of sawdust,and the addition of catalyst promotes the pyrolysis reaction of raw materials and intermediate products at a more low temperature.The effects of different factors on the composition and yield of pyrolysis products were investigated by pyrolysis experiments.By analyzing the yield of products,it is found that the two catalysts increase the yield of pyrolysis syngas and char,and reduce the yield of pyrolysis oil.The excessive addition of K2CO3 could hinder the pyrolysis process,KOH is not subject to this limitation.Through the analysis of the product components,it is considered that two kinds of potassium salts increase the content of H2 and CO2 in the gas composition,decrease the content of CH4 and CO,enhance the quality of the pyrolysis oil,reduce the oxygen content in the pyrolysis oil,and meanwhile,the pore structure of char is also improved.Comparing two kinds of catalysts,it is considered that KOH has a more significant effect on the H2 upgrading in syngas and the promotion of aromatic hydrocarbons in pyrolysis oil,while K2CO3 improves the pore structure of char better.Tt is considered that the addition amount of K2CO3 is 10%,the pyrolysis temperature is 800℃,which is the most suitable gas making process. |
