New and efficient high‐temperature processes with circulating fluid bed reactors

Abstract

Starting with a brief review of the development of the circulatingfluid bed (CFB) reactor principle, its main features as an important tool for efficient and thus environmentally acceptable processing of fine particulate solids, typically less than 150 Fm diameter, are discussed. Various new industrial processes and high temperature process options starting with alumina calcination are described. Developing applications in the cement, metallurgical and chemical industries are approaching large-scale industrial importance. Efficient combustion or pressure gasification of fossil fuels and carbon-containing residues, fulfilling increasingly strict environmental legislation, is by far the most rapidly expanding field of application. In support of these developments our fundamental understanding of the fluid dynamics of CFB riser and of cyclone precipitation at high solid loadings has to be steadily improved. The reaction behaviour of aggregating fine particulate solids of varying size distributions also remains an open question.

Factors affecting solids segregation in circulating fluidized‐bed riser

“…A major feature of the CIRCOFER process where iron ore is directly reduced to metallic iron by char (Hirsch et al, 1985) is the continuous segregation with a separation of the char and iron ore particles in the CFB riser (Bresser et al, 1993;Reh, 1995). Mainly char particles are entrained by the gas and circulated through the CFB loop, while the heavy iron ore particles will preferentially remain in the riser.…”

Mass transfer and influence of the local catalyst activity on the conversion in a riser reactor

“…Contractor and Chaouki, 1991;Patience et al, 1992). Several industrial processes are carried out in a riser reactor, like for instance, the Fluidized Catalytic Cracking (FCC), the Fischer-Tropsch synthesis, the calcination of aluminium trihydrate to high purity alumina (Reh, 1986(Reh, , 1995, and the combustion or gasification of coal and biomass. Commercial and potential processes that employ riser systems are reviewed by Bermti et al (1995).…”

CO2 capture from the calcination of CaCO3 using iron oxide as heat carrier

“…For the stream characteristics listed in Table 2 and assuming a gas velocity of about 5 m/s in the air reactor (standard in many CFBCs), a cross-sectional area of around 23 m 2 is obtained for carrying out the oxidation stage, which means that the reactor diameter will be of the order of 5.4 m. Under these conditions, the solids circulation rate would be close to 18 kg/m 2 s, which is within the range of the 5e50 kg/m 2 s of most large-scale CFB systems (Reh, 1995). For the fuel reactor calciner, the same cross-sectional area would involve gas velocities of around 0.7 m/s.…”