Details

Autor(en) / Beteiligte

• Bunt, J R
• Waanders, F B

Titel

Review article: An understanding of lump coal physical property behaviour (density and particle size effects) impacting on a commercial-scale Sasol-Lurgi FBDB gasifier

Ist Teil von

• Fuel (Guildford), 2008-10, Vol.87 (13-14), p.2856-2865

Erscheinungsjahr

2008

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Thermal processes which utilize coarse coal, such as fixed-bed gasification and chain grate stoker boilers, are dependant on a stable particle size for stable operation. During coarse coal utilization, thermal fragmentation of lump coal (upon heating) produces hydrodynamic effects (pressure drop fluctuations) manifesting itself in a variety of ways, and include: channel-burning and solids elutriation. Primary thermal fragmentation occurring in the drying zone of a fixed-bed reactor is primarily a function of moisture content release with ensuing particle size reduction. Large particles tend to fragment more than finer particles, thus leading to hydrodynamic problems. From fragmentation studies it was elucidated that a thermal 'stable size' is reached through the process of thermal fragmentation for optimum heat transfer and utilization during the drying and pyrolysis zone regions of the coarse coal utilization process. In this paper, the Sasol-Lurgi MK IV FBDB gasifier turn-out physical property profiles (bulk density and particle size distribution) results will be discussed. It was found that these profiles provided significant insight into the complex heterogeneous nature of the coal transformation processes occurring within the fixed-bed reactor. In the case of the bulk density profile, a shrinking core and flaking mechanism was proposed to explain the increase in density occurring in the bottom half of the gasifier. The +25 mm size fraction distribution profile was found to clearly show the fragmentation effects occurring within the reactor. Primary fragmentation was inferred as the mechanism responsible for causing breakage of this size fraction down to a remaining ca. 15% +25 mm fraction. The significant breakage of the coarse +25 mm fraction is expected to influence unstable gasifier conditions in the top part of the gasifier, due to pressure drop fluctuations caused by void packing. A good correlation was obtained for the relationship between bulk density versus the -25 mm + 6.3 mm size fraction content, indicating that the bed-packing density is highly dependent on the relative abundance of this intermediate size fraction.