Experimental And Theoretical Study On The Behavior And Gas Products Of Smoldering Of Peat

In forests,abundant natural fuels,such as decayed plant litters and animal remains,can deposit and form humus or peat after a long time.These fuels can be easiely ignited by lightning or human activity of incineration,causing destructive fires finally.The smoldering fires of humus or peatlands are the great destructive ground fires on earth.Peatlands store a large amount of soil carbon,which will release considerable greenhouse gases once smoldering is initiated,causing serious threat to global climate balance and human health.Along with the global warm climate,large-scale smoldering fires are happened frequently.The research about peat smoldering is getting more and more attentions.At present,abundant volatile gas species are evolved from smoldering but it is rarely reported except some qualitative analysis for pyrolysis products by TG/FTIR,TG/MS,and TG/GC coupling technique.The reported major products evolving from smoldering of peat are CO₂,CO,CH₄.As for theoretical model of peat smoldering,most models focus on the smoldering thresholds between basic components and are limited to one-dimensional simulation.And there are no models to explain the mechanism of horizontal smoldering of peat,also no models to consider the wind effect on horizontal smoldering.The summary of this thesis is as follows.Firstly,the pyrolysis behavior of peat under inert atmosphere was analyzed by coupling technique of TG-FTIR-MS,and the kinetic model,based on the assumption that peat decomposition is the summation of decomposition of three pseudo components of hemicellulose,cellulose and lignin,was proposed.The kinetic parameters were optimized by genetic algorithm?GA?.The pyrolysis temperature ranges for each condensed species were simulated.The FTIR/MS anlysis identified the major gas products evolving from peat pyrolysis.Combined the temperature regions between gas production and condensed species decomposition,the generation sources of major gas products were identified.Similarly,TG-FTIR coupling technique was used to study the combustion behavior of peat,and a kinetic model including moisture evaporation,peat pyrolysis,peat oxidation,?-char,?-char oxidation was proposed.A natural downward smoldering experimental platform was established.The effects of inorganic content and initial bed height on smoldering temperature,velocity of pyrolysis and oxidation front,surface regression,were studied.Meanwhile,a 1-D numerical model considering the surface regression,which was simulated by the moving mesh technology in COMSOL Multiphysics,was proposed.This thesis extended the 1-D numerical model to the 2-D model and obtained the 2-D smoldering stucture.The effects of lateral heat loss and inorganic content on the velocity and lasting time of smoldering were predicted by the 2-D model,and validated by experimental observations.The predicted results provide us a better understanding of smoldering fires of peat with high inorganic content.A small-scale wind tunnel was established and the effect of oxygen concentration on shallow lateral smoldering was studied.The major gas products of CO₂,CO,CH₄ were measured by NOVA PLUS multi-functional flue gas analyzer.A 2-D numerical model was proposed to study the lateral smoldering structure and this model well predicted the experimental phenomenon.The combination between experiments and numerical simulation provide us a better insight into the shallow smoldeing mechanisms under different conditions.