Disintegration of thermally converting particles
Wood is a strongly anisotropic material and likewise the char produced by pyrolysis of wood is characterized by a strong anisotropy. This anisotropic behaviour allows relatively easy transport of gas in the longitudinal(L) direction of the wood, but the transport is much less easy in the radial@) and in the tangential(T) directions. The present project study the influence of the anisotropy on the reactivity of thermally thick char particles during gasification using a macro TGA equipment.
The purpose of the project is to establish physical knowledge on the conversion of char particles emphasising geometry and fragmentation during conversion both in suspension, fixed bed and grate fired reactors. Experimental results and modelling of such gasification and combustion reactors have exposed the need for better understanding of the conversion of char particles, including mechanisms causing disintegration of particles and quantification of the amounts of produced fragments. Such knowledge will help modelling efforts to better describe the processes qualitatively as well as quantitatively, fascilitating better reactor design and process optimisation
In the present work the process occurring in structures of slowly pyrolysed beech wood char during thermal gasification have been investigated. Emphasis was put on physical changes and gas transport properties during conversion. The highly anisotropic structure of wood was preserved in its char. Direct observation of the microscopic char structure during gasification in CO2 at 735 C showed that the basic structure was nearly intact up to degrees of conversion of 0.6 - 0.7. Uni-axial measurements of diffusion coefficients and permeabilities revealed differences of 3-4 order of magnitudes between the longitudinal and the other directions in freshly pyrolysed beech wood char. Radial and tangential diffusion was controlled by Knudsen diffusion through the pits in wood cell wals for degrees of conversion by gasification up to at least 0.5
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Contact
Studentertorvet, Bygning 402
DK-2800 Kgs Lyngby, Denmark
www.bgg.mek.dtu.dk
Henriksen, Ulrik , 45254172, ubh@mek.dtu.dk
Øvr. Partnere: KT-DTU
