Densified Biofuel - an Alternative Source of Environmentally Sound and Renewable Energy

Advantages of densified biofuels as promising renewable and environmentally sound source for sustainable heat and power generation are discussed. Combustion characteristics of single particles of seven pelletised and three natural biofuels in a fluidized bed have been experimentally studied. The data obtained are described by mathematical models of devolatilisation and char combustion and empirical correlations

Estimates of turbulence effects in CFB boilers

A simplified physical model of turbulence in a circulating fluidized bed (CFB) combustor is presented. The existence of a dense bubbling bottom bed, a splash zone with pronounced clustering effects and a transport zone with predominantly disperse solids flow in the core is accounted for. The energy dissipation rate evaluated from the total energy supply and the macro-scale of the bubble-induced turbulence are used as defining parameters for order of magnitude estimates of turbulence effects in a 0.7 m wide cold rig and a 12 MW CFB boiler. The results obtained show a reasonable agreement with available experimental data

Estimates of turbulence mechanisms in circulating fluidized bed combustors

Estimates of the characteristic time scales (particle relaxation time, eddy-particle interaction time, interparticle collision time), and the energy dissipation mechanisms are performed together with a turbulent kinetic energy budget, for a simple equilibrium shear flow with conditions similar to those of a circulating fluidized bed (CFB) combustor. Based on dimensional analysis, the influence of five parameters is investigated: the Eulerian integral length scale in the gas phase, the gas-particle density ratio, the mean velocity gradient, the particle diameter, and the particle volume fraction. The results show significant differences between particles of Geldart groups A and B regarding response to gas phase turbulence, transition from dense to dilute suspensions, pressure and temperature dependence, and also energy dissipation mechanisms