Pressure Effects on Gas-Solid Fluidized Bed Behavior

Abstract

The purpose of this paper is to review the state of our knowledge of the effects of operating pressure on the hydrodynamic behavior of fluidized beds. With the development of coal combustion and gasification fluidized bed processes in the early 1970s, many academic and industrial researchers have studied the effect of pressure on fluidized bed behaviour. This review covers experimental and theoretical studies of effects of elevated operating pressure on fluidization, published in the literature before August, 2002.The review begins with the discussion of the effect of pressurized conditions on non-bubbling fluidization and several methods for better prediction of minimum fluidization velocity at elevated pressure are presented. The effects of pressure on non-bubbling bed expansion in the region between minimum fluidization and minimum bubbling velocities are considered and areas of uncertainty or disagreement are highlighted. The influence of pressure on the dynamics of gas bubbles and bubbling bed expansion is described next. In addition to fundamental hydrodynamics of fluidization, bed-to-surface heat transfer, jet penetration, solids mixing and particle entrainment are mentioned.

Pressure Effect on Hydrodynamics of a High Pressure X-ray Transparent Polyethylene Fluidized Bed

“…Figure 2 shows the pressure drop during decreasing velocities at different pressures. This result was expected, as increasing system pressure causes U mf to decrease for particles sizes greater than 100 μm (Olowson & Almstedt, 1990;Sidorenko & Rodhes, 2003). The pressure drop for the fluidized bed is very close at different operating pressures.…”

“…Pressure effect on hydrodynamics is investigated through analyses of pressure fluctuation time series (standard deviation, power spectral) and bubble properties from X-ray images. Fluidization becomes smoother while increasing pressure due to the smaller bubbles at higher pressure and also the resulting bed is more homogeneous caused by the smaller differences between the minimum fluidization velocity of the smallest and largest particles (Sidorenko and Rodhes, 2003;Yang, 1998;Sciazko and Bandrowski, 1995). Superficial gas velocity and pressure effect on time series of pressure fluctuations measured at position 1 (2 and 17 cm above distributor) is shown in Figures 4 and 5.…”

“…The difference between the correlation and the experimental data obtained reflects that the correlations are not appropriate to represent this particular system due to the difference in particles, operating conditions and column dimensions. This behavior has been attributed to smaller bubbles at increased pressure (Sidorenko and Rodhes, 2003;Yang et al, 2002). In addition, the Werther correlation requires knowledge of the visible bubble fraction.…”

Particle Motion near the Wall of a Fluidized Bed at Elevated Pressure

“…The process and instrumentation diagram of the pressurized fluidized bed used in this study of the effects of pressure on fluidization is given elsewhere . The pressure vessel, capable of operating at pressures up to 2600 kPa, was 2.38 m high and was equipped with five glass observation ports.…”

Effect of bed particle size and temperature variation on the minimum fluidisation velocity: A comparison with minimum fluidisation velocity correlations for bubbling fluidised bed designs

“…The dense phase is an important parameter in determining the fluidised bed performance because it is widely believed that it has a direct influence on the chemical reactions taking place in the fluidised bed. 29 The dense phase affects the degree of gas–solid contact and heat and mass transfer.…”