Novel configurations and variants

Compared with conventional bubbling and turbulent fluidized beds, circulating fluidized beds have many advantages including better gas—solids contacting and reduced backmixing (Lim et al., 1995). However, due to the core-annulus structure, particle backmixing along the wall can still be significant. Gas—solids contacting is not optimal given the non-uniform distribution of gas and particle flow in the riser. Significant solids backmixing also occurs in the bottom solids-acceleration zone, often covering a significant portion of the riser. Backmixing can also occur at the riser exit if a strong constriction is used. For fast reactions such as fluid catalytic cracking where the intermediate is the product, uniform residence time distributions of gas and solids are very important. To further reduce backmixing and to improve gas—solid contact, internals can be installed inside CFBs to modify the flow pattern and many novel inlet and exit configurations can be employed. The first two sections of this chapter discuss the various available internals and novel geometry structures and their effects on gas and solids flow. The third section describes two special configurations where solids upflow and downflow are accommodated within a single vessel containing concentric upflow and downflow regions and the N-shape CFB loop.

[1]  Yong Jin,et al.  Synthesis of linear alkylbenzene in a liquid–solid circulating fluidized bed reactor , 1995 .

[2]  J. Baeyens,et al.  Fluidization and its Applications : Proceedings of the International Symposium held in Toulouse, France, in 1973; pp. 729, £30.00. , 1976 .

[3]  C. Adams.  GAS MIXING IN FAST FLUIDISED BEDS , 1988 .

[4]  Herbert Baumann,et al.  Pyrolysis of some gaseous and liquid hydrocarbons in hydrogen plasma , 1988 .

[5]  M. J. Rhodes,et al.  Gas mixing in gas-solids risers , 1993 .

[6]  Ce Davies,et al.  Pressure Drop Reduction by Wall Baffles in Vertical Pneumatic Conveying Tubes , 1988 .

[7]  Zhu Yu,et al.  Flow regimes of the three‐phase circulating fluidized bed , 1995 .

[8]  Liang-Shih Fan,et al.  On the operating regimes of cocurrent upward gas—liquid—solid systems with liquid as the continuous phase , 1987 .

[9]  Leo A. Behie,et al.  The internally circulating fluidized bed (ICFB): A novel solution to gas bypassing in spouted beds , 1992 .

[10]  John R. Grace,et al.  Voidage profiles in a circulating fluidized bed of square cross-section , 1994 .

[11]  Yong Jin,et al.  Cocurrent downflow circulating fluidized bed (downer) reactors — A state of the art review , 1995 .

[12]  Yong Jin,et al.  The axial distribution of the cross-sectionally averaged voidage in fast fluidized beds , 1992 .

[13]  J. M. Kim,et al.  Pressure drop for cocurrent downflow of gas‐solids suspensions , 1983 .

[14]  A. Avidan,et al.  Bed expansion in high velocity fluidization , 1982 .

[15]  Cedric Briens,et al.  Application of fiber optic reflection probes to the measurement of local particle velocity and concentration in gas—solid flow , 1994 .

[16]  Aloysius G.J. van der Ham,et al.  Hydrodynamics and mass transfer in a regularly packed circulating fluidized bed , 1990 .

[17]  Fei Wei,et al.  Effect of flow direction on axial solid dispersion in gas—solids cocurrent upflow and downflow systems , 1996 .

[18]  R. C. Senior.  Circulating fluidised bed fluid and particle mechanics: modelling and experimental studies with application to combustion , 1992 .

[19]  Yong Jin,et al.  Dispersion of lateral and axial solids in a cocurrent downflow circulating fluidized bed , 1994 .

[20]  John R. Grace,et al.  High-velocity fluidized bed reactors , 1990 .

[21]  F. Wei,et al.  Gas mixing in the cocurrent downflow circulating fluidised bed , 1995 .

[22]  J. F. Large,et al.  OVERALL AND LOCAL CHARACTERISATION OF FLOW REGIMES IN A CIRCULATING FLUIDIZED BED , 1986 .

[23]  J. Grace,et al.  Hydrodynamics of gas-solid fluidization , 1995 .

[24]  M. Martín,et al.  Catalytic cracking in riser reactors : core-annulus and elbow effects , 1992 .

[25]  Wolfgang Wöhlk,et al.  Die Kristallisationstheorie in der Praxis , 1991 .

[26]  U. Arena,et al.  HIGH VELOCITY FLUIDIZATION BEHAVIOR OF SOLIDS IN A LABORATORY SCALE CIRCULATING BED , 1986 .

[27]  J. Grace,et al.  Local heat transfer, solids concentration and erosion around membrane tubes in a cold model circulating fluidized bed , 1995 .

[28]  Miao Guo.  GENERALIZED FLUIDIZATION II.ACCELERATIVE MOTION WITH STEADY PROFILES , 1964 .

[29]  J. Grace,et al.  FAST FLUIDIZATION IN A CONCENTRIC CIRCULATING BED , 1986 .

[30]  Leon Lapidus,et al.  Mechanics of vertical‐moving fluidized systems , 1957 .

[31]  Ryozo Echigo,et al.  Experimental study on the pressure drop and the entry length of the gas-solid suspension flow in a circular tube , 1978 .

[32]  C. Briens,et al.  Reactor development for the ultrapyrolysis process , 1989 .

[33]  Yong Jin,et al.  Hydrodynamics of cocurrent downflow circulating fluidized bed (CDCFB) , 1992 .

[34]  Hiromi Takeuchi,et al.  Regime classification of macroscopic gas-solid flow in a circulating fluidized bed riser , 1992 .

[35]  Aloysius G.J. van der Ham,et al.  Hydrodynamics of a pilot plant scale regularly packed circulating fluidized beds , 1992 .

[36]  T. M. Knowlton,et al.  NONMECHANICAL SOLIDS FEED AND RECYCLE DEVICES FOR CIRCULATING FLUIDIZED BEDS , 1988 .

[37]  Daizo Kunii.  CHAPTER 8 – High-Velocity Fluidization , 1991 .

[38]  Liang-Shih Fan,et al.  Fundamentals of gas‐liquid‐solid fluidization , 1985 .

[39]  Hsiaotao Bi,et al.  Static instability analysis of circulating fluidized beds and concept of high‐density risers , 1993 .

[40]  J. R. Murphy.  Evolutionary design changes mark FCC process , 1992 .

[42]  Hsiaotao Bi,et al.  Types of choking in vertical pneumatic systems , 1993 .

[44]  J. Grace.  Contacting modes and behaviour classification of gas—solid and other two-phase suspensions , 1986 .

[45]  Hsiaotao Bi,et al.  Baffle effects on performance of catalytic circulating fluidized bed reactor , 1991 .

[46]  W. Prins,et al.  A small scale regularly packed circulating fluidized bed. Part I: Hydrodynamics. , 1994 .