Study Of Pyrolysis Kinetics And Fire Spread Characteristics Of Pine Needle

The proliferation of forest fires and building fires has had a significant impact on human life and property,ecosystems and other valuable resources globally.The main combustible materials in these fire scenarios are biomass materials.Also,as renewable energy widely exists in nature,biomass materials can be transformed into various forms of energy through different technical methods.In this paper,pine needles were selected as a typical forest surface combustible material to carry out pyrolysis and fire spread experiments.The pyrolysis and fire spread characteristics were investigated.In this paper,the pyrolysis of pine needles at different heating rates was studied by using TG-FTIR.The results show that three characteristic peaks appear in the TG curves of pine needles.Then,the values of the activation energy were calculated using Flynn-Wall-Ozawa（FWO）and Kissinger-Akahria-Sunose（KAS）methods based on the thermogravimetric data.The Distributed activation energy（DAEM）method was selected to calculate the corresponding pre-exponential factor.The pine needle pyrolysis was divided into three stages according to the evolution of activation energy with the conversion rate.The three stages correspond to the pyrolysis of hemicellulose,cellulose and lignin,respectively.A three-component parallel pyrolysis model was developed based on the Shuffled Complex Evolution（SCE）optimization algorithm.The related kinetic parameters were optimized.In addition,the FTIR spectra showed that most of the gaseous products and functional groups were produced between 450 K and 850 K,which was in agreement with the evolution of DTG curves.It was determined that gaseous products such as H₂O,CH_4,CO₂,CO,ketones,aldehydes and esters are produced during the pyrolysis of pine needles.Based on the characteristics of pine needle powder,a multi-component biomass pyrolysis solver biopyrolysis Foam was developed based on the Open FOAM platform to simulate the pyrolysis of the pine needle.The porous medium model,heat and mass transfer model and multi-component pyrolysis reaction model were developed with emphasis.Among them,the multi-component pyrolysis reaction model was based on the pyrolysis kinetics of pine needle.The mass fraction of char was obtained by the SCE global optimization algorithm.The volatiles produced by pyrolysis exists in the form of pyrolysis gases CH₄,H₂,CO and CO₂,and the stoichiometric number of each gas is determined experimentally.The simulation results fit well with experimental results on thermogravimetric data at different rates.It fully demonstrates the reliability of the pyrolysis reaction model of the pine needle.Meanwhile,the evolution of density of the solid component and the mass fraction of the gas component during the pyrolysis process also can be obtained.Finally,this paper conducts an experimental study on the fire spread of pine needle.For the linear fire spread experiment,the rate of fire spread increases with the width of the fuel layer due to the combined effect of convection and radiation.The inertial force dominates the flame height and the buoyancy force plays a smaller role when the rate of fire spread increases.In addition,the rate of fire spread decreases with increasing thickness,while the flame height increases as the thickness increases.For the flame residence time,the time increases with the increaseing width and thickness.It is caused by the flame propagation time in the vertical direction of the fuel layer becoming longer with the thickness of the fuel layer increaseing.Moreover,the heat transfer for fire spread is also analyzed.Convection and radiation are considered in the whole heat transfer process.As the width of the fuel layer increases,the role of convection will gradually become weaker and the role of radiation will be enhanced.The cylindrical flame radiation model is selected to establish the expression of the view factor.Then,the radiation of the flame front surface in the virgin zone is calculated by the integral method.For the V-shaped fire spread experiment,the fuel layer is divided into A and B zones.We focus on the fire spread characteristics of the B zone.When the flame front surface moves to the front part of the B zone,the fire spread rate will suddenly increase,which is defined as the accelerated zone.Under the effect of radiation preheating and air indraft,the fire spread rate decreases with increasing angle.The variations of flame height and the flame residence time are consistent with the fire spread rate.