Hydrodynamic properteies and combustion characteristics in an internal circulating fluidized bed

Abstract

Hydrodynamic properties and combustion characteristics have been studied in an internal and in a high velocity circulation fluidized beds. Hydrodynamic properties(pressure drop, bed voidage, bubble chord length, chord length distribution, rising velocity, volume fraction, local frequency, and solids circulation rate) have been determined in an internal circulating fluidized bed (0.4m$\times$0.2m$\times$5m high) with a partition plate and a high velocity circulating fluidized bed (0.1m ID$\times$1.9m high) combined with an auxiliary bed equipped with a standpipe with an L-valve for silids circulation. In addition, the combustion efficiencies and the heat transfer coefficient have been determined in an internal circulating fluidized bed coal combustor. In the internal circulating fluidized bed, solids circulation rate increases with increasing orifice opening area (0.01$\sim$0.04$m^2$), the initial static bed height (0.5 and 0.6m) and superficial gas velocity in the fluidized (up to 0.635 m/s) and moving beds (up to 0.127 m/s) but, it decreases with increasing the partition plate height (0.55 and 0.65m). Pressure drop across an orifice opening increases with increasing the static bed height and gas velocity in the fluidized bed. Bed voidage in the fluddized bed increases with increasing gas velocity to the fluidized bed and the static bed height. However, it decreases with an increase in the gas velocity to the moving bed. Solids circulation rate has been correlated as follows:$$Ws=0.22\times10^{-2}(D_o/d_p)^{0.97}(F_{rf})^{0.95}(F_{rm})^{1.09}(H_s/H_p)^{0.88}$$ In the study of bubble properties in the internal circulating fluidized bed with a constant static bed height (0.6m) and orifice opening area (0.04$m^2$), the maasured bubble chord length distribution has been represented by a logarthmic normal distribution. The measured bubble chord length, volume fraction and rising velocity of bubbles increase with the bed height(0.1$\sim$0.46m) and gas velocity to the...