In the present study,the influence of the dynamic and anistropic pore microstructure of wood and char samples on the intra-particle flow permeability and tortuosity was investigated.To this end,a beech wood sphere was...In the present study,the influence of the dynamic and anistropic pore microstructure of wood and char samples on the intra-particle flow permeability and tortuosity was investigated.To this end,a beech wood sphere was pyrolysed at different temperatures(100℃,200℃,300℃,400℃,and 500℃)and characterised,after each pyrolysis step,by X-ray micro-computed tomography(μ-CT).From theμ-CT images,the structural geometry of the particle at the different conversion degrees achieved at each temperature level was extracted.The porosity evolution was characterised,accounting for pores larger than 15μm,which was the limit of resolution forμ-CT imaging in this study.The structural geometry was divided in subdomains and used for CFD(computational fluid dynamics)simulations,where the pressure loss at different velocities and in different directions with respect to the main pores(vessel cells)was determined and used to estimate the dynamic and anisotropic permeabilities.The permeability differed by an order of magnitude in the direction of the main pores(vessel cells)in comparison to the perpendicular directions,supporting the need to develop permeability tensors for improved simulations of the pyrolysis process at particle level,accounting for the coupled effects of microstructure,transport,and reaction.展开更多
Pyrolysis of thermally thick beech wood blocks with a size of around 2.5×8×6 cm^(3)(width×length×height)was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz,operated,both,a...Pyrolysis of thermally thick beech wood blocks with a size of around 2.5×8×6 cm^(3)(width×length×height)was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz,operated,both,at 300 W and 600 W under inert conditions,using N_(2) at around 400 mbar absolute pressure.The microwave cavity had a size of 20×20×20 cm^(3).The specific energy supply referred to the untreated wood block was 4-8 W/g,with slight variations depending on the initial water content.The mass loss and the reflected microwave power were in-situ monitored during the experiments.The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple,respectively.Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials.It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process,with increasing heating properties as the conversion process evolved.This was easily achieved using 60o W without susceptors.However,300 W was not enough to achieve a high conversion degree,independently of the irradiation time.This,together with the physico-chemical analyses of the solids,hinted to the importance of the transport kinetics in thermally thick materials,although further investigationis still required.展开更多
基金the funding by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287.
文摘In the present study,the influence of the dynamic and anistropic pore microstructure of wood and char samples on the intra-particle flow permeability and tortuosity was investigated.To this end,a beech wood sphere was pyrolysed at different temperatures(100℃,200℃,300℃,400℃,and 500℃)and characterised,after each pyrolysis step,by X-ray micro-computed tomography(μ-CT).From theμ-CT images,the structural geometry of the particle at the different conversion degrees achieved at each temperature level was extracted.The porosity evolution was characterised,accounting for pores larger than 15μm,which was the limit of resolution forμ-CT imaging in this study.The structural geometry was divided in subdomains and used for CFD(computational fluid dynamics)simulations,where the pressure loss at different velocities and in different directions with respect to the main pores(vessel cells)was determined and used to estimate the dynamic and anisotropic permeabilities.The permeability differed by an order of magnitude in the direction of the main pores(vessel cells)in comparison to the perpendicular directions,supporting the need to develop permeability tensors for improved simulations of the pyrolysis process at particle level,accounting for the coupled effects of microstructure,transport,and reaction.
基金the funding by the Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)-Project-ID 422037413-TRR 287.
文摘Pyrolysis of thermally thick beech wood blocks with a size of around 2.5×8×6 cm^(3)(width×length×height)was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz,operated,both,at 300 W and 600 W under inert conditions,using N_(2) at around 400 mbar absolute pressure.The microwave cavity had a size of 20×20×20 cm^(3).The specific energy supply referred to the untreated wood block was 4-8 W/g,with slight variations depending on the initial water content.The mass loss and the reflected microwave power were in-situ monitored during the experiments.The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple,respectively.Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials.It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process,with increasing heating properties as the conversion process evolved.This was easily achieved using 60o W without susceptors.However,300 W was not enough to achieve a high conversion degree,independently of the irradiation time.This,together with the physico-chemical analyses of the solids,hinted to the importance of the transport kinetics in thermally thick materials,although further investigationis still required.
