Dynamic modeling of the circulating fluidized bed riser

Abstract Dynamic modeling is required to understand hydrodynamics of a circulating fluidized bed (CFB) riser as a function of time. The paper develops a dynamic model of the riser from the conservation of solid mass. Solid mass that flows out of the riser requires particle residence time to close the mass balance equation. The mean residence time of solids was derived as the riser length divided by the superficial riser gas velocity normalized by a ratio of solid concentration in the riser outlet to that in the riser itself. For bed materials including high-density polyethylene beads, glass beads, and cork, the percentage of solid concentration in the horizontal crossover pipe connecting the riser exit and the cyclone inlet was found to be 22% of the average concentration of solids in the riser. Upon finding the particle residence time, we calculated the solid flow rate out of the riser and along with the knowledge of solids flowing into the riser column we determined the riser inventory as a function of time. We used the estimated solid inventory to model overall pressure drop across the riser from the conservation of momentum. The momentum equation included the balance of pressure force by the hydrostatic head of solids, and the wall frictions due to gas and solids in a fully developed zone. The prediction of overall riser pressure drop compared well with its measured values at many dynamic conditions. Therefore, our dynamic model is useful for developing advanced control strategy or for improving existing control systems of the CFB plant. The residence time approach is also useful for the design of a transport reactor. The technique also comes handy when setting up the boundary condition for the overall pressure drop in the CFD modeling that can simulate incremental pressures along the riser height.

[1]  Octave Levenspiel,et al.  Effect of exit geometry on the vertical distribution of solids in circulating fluidized beds. Part I: solution of fundamental equations; Part II: analysis of reported data and prediction , 1995 .

[2]  Lawrence J. Shadle,et al.  Method and Prediction of Transition Velocities in a Circulating Fluidized Bed's Riser , 2011 .

[3]  Wen-ching Yang,et al.  Estimating the Solid Particle Velocity in Vertical Pneumatic Conveying Lines , 1973 .

[4]  Dong Hyun Lee,et al.  Pressure Balance Model for Circulating Fluidized Beds with a Loop-seal , 2002 .

[5]  B. L. Hinkle.  Acceleration of particles and pressure drops encountered in horizontal pneumatic conveying , 1953 .

[6]  P. Basu.  Combustion and gasification in fluidized beds , 2006 .

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

[8]  Lawrence J. Shadle,et al.  Standpipe models for diagnostics and control of a circulating fluidized bed , 2013 .

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

[10]  Frank Shaffer,et al.  Higher order statistical analysis of Eulerian particle velocity data in CFB risers as measured with high speed particle imaging , 2013 .

[11]  M. Rhodes,et al.  Characterising non-uniformities in gas-particle flow in the riser of a circulating fluidized bed , 1992 .

[12]  Masayuki Horio,et al.  A Comprehensive Pressure Balance Model of Circulating Fluidized Beds , 1998 .

[13]  D. Geldart.  Types of gas fluidization , 1973 .

[14]  Larry Lawson,et al.  A transient method for determination of saturation carrying capacity , 2001 .

[15]  J. Chaouki,et al.  Solids flow metering from pressure drop measurement in circulating fluidized beds , 1990 .

[16]  D. Gidaspow.  Multiphase Flow and Fluidization: Continuum and Kinetic Theory Descriptions , 1994 .

[17]  Chris Guenther,et al.  A CFD study of gas–solid jet in a CFB riser flow , 2012 .

[18]  Lawrence J. Shadle,et al.  Improvement of continuous solid circulation rate measurement in a cold flow circulating fluidized bed , 2008 .

[19]  W.P.M. van Swaaij,et al.  Shear stresses on the wall of a dense gas—solids riser , 1970 .

[20]  Hsiaotao Bi,et al.  Suspension densities in a high-density circulating fluidized bed riser , 1999 .

[21]  H. Weinstein,et al.  An evaluation of the actual density in the acceleration section of vertical risers , 1989 .

[22]  S. Ergun.  Fluid flow through packed columns , 1952 .

[23]  Leon R. Glicksman,et al.  Scaling relationships for fluidized beds , 1984 .

[24]  Jamal Chaouki,et al.  Scaling considerations for circulating fluidized bed risers , 1992 .

[25]  Mooson Kwauk,et al.  The Dynamics of Fast Fluidization , 1980 .

[26]  L. Shadle,et al.  Estimate of solid flow rate from pressure measurement in circulating fluidized bed , 2010 .

[27]  George E. Klinzing.  Gas-Solid Transport , 1981 .

[28]  Chris Guenther,et al.  Improvement in Precision, Accuracy, and Efficiency in Standardizing the Characterization of Granular Materials , 2013 .

[29]  Madhava Syamlal,et al.  Challenge problem: 1. Model validation of circulating fluidized beds , 2014 .

[30]  N. A. Weil,et al.  A theoretical‐empirical approach to the mechanism of particle entrainment from fluidized beds , 1958 .

[31]  Joachim Werther,et al.  ANALYSIS OF THE LOCAL STRUCTURE OF THE TWO PHASE FLOW IN A FAST FLUIDIZED BED , 1986 .

[32]  Ronald W. Breault,et al.  Carbon capture test unit design and development using amine-based solid sorbent , 2016 .

[33]  Shozaburo Saito,et al.  PNEUMATIC CONVEYING OF SOLIDS THROUGH STRAIGHT PIPES , 1969 .

[34]  Jamal Chaouki,et al.  Hydrodynamics of circulating fluidized bed risers: A review , 1995 .

[35]  L. R. Glicksman,et al.  Scaling relationship for fluidized beds , 1984 .

[36]  L. Shadle,et al.  Analysis of the Acceleration Region in a Circulating Fluidized Bed Riser Operating above Fast Fluidization Velocities , 2008 .