Filtration of nano-particles by a gas–solid fluidized bed

Removals of fly ash and NO in a fluidized-bed reactor with CuO/activated carbon catalysts

“…Because some catalysts may be elutriated from the fluidized-bed reactor and which would influence the exact amounts of particles passing through the fluidized-bed reactor, the elutriation tests must be carried out to determine the mass of elutriated particles from the catalysts. The detailed elutriation procedures have been described in our previous studies [1][2][3]28]. The mass of elutriated bed materials must be subtracted from the total mass of output particles to yield the exact concentrations of output particles.…”

“…The inhibition effect is related to the increase of particle concentration. Because Al 2 O 3 and SiO 2 particles have higher densities and hardness than CuO/AC-N catalysts, the strong impacts and accumulations on the surface of fluidized-bed catalysts are significant [1][2][3]. In addition, fine particles (4-10 m) can cover or block the surface of catalyst.…”

“…8(G)-(J) shows that Al 2 O 3 and SiO 2 particles are not aggregated on the surface of CuO/AC-N catalyst. Some filtration studies [1][2][3]29,30] have indicated that the filtered particles may accumulate on or inset into the surface of fluidized bed media. The results are caused by the strong inertial impacts and interceptions of particles on the surface of fluidized bed granular media [1,2,31,32].…”

“…The concentration of fly ash produced in thermal power plants ranges from 1000 to 10,000 mg m −3 and the mass medium diameter (MMD) locates at 4-40 m [1,2]. Previous studies have found that the compositions of fly ash are 43% SiO 2 , 22.5% Al 2 O 3 , 7.7% Fe 2 O 3 , and 7.5% CaO [2][3][4]. Conventional air pollution control devices (APCDs) used for removing acid gases and fly ash from the flue gas always comprise more than two apparatuses, such as an electrostatic precipitator integrated with a wet scrubber and an NO x converter (selective catalytic reduction with ammonia), or a semi-dry scrubber integrated with a bag filter and NO x converter [1][2][3].…”

“…The fluidized-bed reactor used for filtration and catalysis has the advantages of easy continuous operation and regeneration, less plugging phenomenon caused by fly ash, higher thermal/mass transfer efficiency, higher gas/solid or solid/solid contact efficiency, higher tolerance to variations in gas flow rate, and easy to replace or replenish the catalysts [24][25][26][27]. Moreover, the filtration of fly ash using a fluidized bed reactor has been well examined in our previous studies [1][2][3][4]. The results indicate that the optimum condition for fly ash filtration occurs at the ratio of operating fluidization velocity/minimum fluidization velocity (U o /U mf ) lower than 2.5.…”