Evaluating The Effects Of KCI On Reaction Kinetics Of Medium Density Fiberboard (MDF) Pyrolysis

With the enhancement of people's awareness of environmental protection at present,wood panel is popular for its pollution-free,beautiful texture and easy processing.However,the world's forest resources are decreasing and there is a serious shortage of available timber.Medium density board(MDF)as an alternative to wood products of environmental protection building materials substitutes into the line of sight.But the wide use of medium density board in the construction field has laid a huge fire safety hazard for the indoor fire prevention of buildings.This makes the pyrolysis,as the initial stage of combustion,of medium density board occupies an important position in fire research.In fact,as a kind of composite material,the medium density board contains a variety of components,in addition to the main components of cellulose,hemicellulose and lignin,but also resin and a small amount of inorganic substances,resulting a very complex pyrolysis mechanism of medium density board.In this paper,the pyrolysis kinetics of medium density board is studied from the perspective of constructing the pyrolysis model of medium density board,solving the pyrolysis kinetic parameters,and studying the influence of inorganic matter on the pyrolysis of medium density board,which is conducive to understanding the pyrolysis mechanism of medium density board,and thus contributing to a deeper understanding of the fire process.This paper mainly contains the following three aspects:First,a multicomponent pyrolysis model considering secondary charring reactions was proposed.In this paper,the reaction of resin,cellulose,hemicellulose and lignin and the secondary reaction of intermediate product tar were considered.First,the kinetic study for pyrolysis of MDF was performed by a thermogravimetric analyzer over a heating rate range from 10 to 40 ?/min in a nitrogen atmosphere.Four stages related to the degradation of resin,hemicellulose,cellulose,and lignin could be distinguished from the thermogravimetric analyses(TGA).Then the reactions of these components were processed based on Arrhenius equation,and the kinetic parameters in the model were optimized by differential evolution method(DE).The optimized parameters are used to calculate the weightlessness curve of medium density board.Comparisons of the results between the calculated results and the experimental data showed that the the model considering secondary charring reactions were in well agreement with the experimental data.At this point,a multicomponent model for the analysis of medium density board pyrolysis with secondary charring reactions is established.At the same time,a reliable method for solving kinetic parameters of biomass pyrolysis was obtained.Senond,the effect of potassium chloride on pyrolysis kinetics of medium density board was studied.Pyrolysis experiments were carried out on medium density plate samples with different potassium chloride loading concentrations by TG-FTIR.It was found that potassium chloride had a great influence on the pyrolysis of medium density board.The main pyrolysis stage of medium density board is advanced.The concentration of gas products CH4 and C=O decreased with the increase of potassium chloride concentration,and the concentration of CO2 and CO increased with the increase of potassium chloride concentration.The total gas yield and char yield increased with the increase of potassium chloride concentration,while the tar yield decreased.Kinetic parameters of reactions of MDF components were estimated by differential evolution algorithm.It was found that the activation energies of the five reactions in pyrolysis model are affected obviously by the concentration of potassium chloride.For resin,hemicellulose and cellulose,the activation energies decrease with the concentration of potassium chloride,respectively.The effect of the potassium chloride on the activation energy of lignin is very small.At the same time,the activation energy of secondary charring reaction decreases with the concentration of potassium chloride.The analysis of activation energies showed that the reactions of resin,hemicellulose and cellulose are catalyzed by potassium.For lignin,potassium has little effect on its reaction.Besides,the secondary charring reaction of tar is catalyzed by potassium.Finally,numerical simulations of the effect of potassium chloride on the pyrolysis of medium density board were performed.Based on the established multi-component pyrolysis model which includes secondary charring reaction and optimized kinetic parameters,the Gpyro software was used to simulate the pyrolysis of medium density board with different potassium chloride loading concentrations.First,it is needed to verify the validity of the pyrolysis model.The pyrolysis model was verified from zero dimensions and one dimensions,respectively.The mass fraction curves of different situations were simulated by the thermogravimetric analysis model of Gpyro.Then,the FPA experiment of medium density board with a radiation of 20kW/m2 was simulated with one-dimension Gpyro.Both simulation results are in good agreement with experimental data.Then FPA experiments scenario is used as the physical model to simulate the pyrolysis of medium density plates with different potassium chloride loading concentrations.The simulation results show that with the increase of potassium chloride concentration,the time for the solid surface temperature to reach the peak temperature becomes shorter.When the concentration of potassium chloride increases,the degradation time of the resin begins to be forward,and the reaction rate increases,that is,potassium chloride catalyzed the degradation reaction of the resin.Similarly,with the increase of potassium chloride concentration,hemicellulose and cellulose began to decompose in advance,the reaction rate increased,and potassium chloride played a catalytic role in the degradation of hemicellulose and cellulose.For lignin,potassium chloride had little effect on the reaction.The reaction rate of the intermediate tar increased with the increase of the concentration of potassium chloride,and the yield of pyrolysis product char also increased.The effect of potassium chloride on the pyrolysis of medium density board is the coupling effect of primary pyrolysis and secondary charring reaction.