Vibrofluidized Bed Drying Of Citrus Processing Residue For Byproduct Recovery

Author

Eric A. Roe, University of South Florida

Graduation Year

2003

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemical Engineering

Major Professor

Richard A. Gilbert, Ph.D.

Committee Member

William E. Lee, Ph.D

Committee Member

Carl J. Biver, Ph.D.

Committee Member

Renee M. Goodrich, Ph.D.

Keywords

vibrating fluidized bed, fluidized bed, citrus byproducts, animal feed

Abstract

Approximately 44% of the citrus that is processed becomes processing residue. The residue consists of the non-juice components of a citrus fruit, primarily peel and pulp, and is recovered by conversion to animal feed. The material is hygroscopic, agglomerating, has a wide particle size distribution, and must be carefully dried to avoid thermal damage to nutrients and flavors. This dissertation evaluates the possibility of utilizing a vibrofluidized bed dryer for citrus processing residue. Results demonstrate that it is possible to overcome the agglomeration difficulties associated with this material, offering an economically viable alternative processing methodology.

To properly analyze this proposed system, a benchtop vibrofluidized bed dryer was designed, constructed and instrumented. Vibrofluidization and batch drying trials were conducted and analyzed. An economic evaluation of the proposed process was undertaken. Two mathematical models of the drying process were developed and validated.

Characteristics that describe the vibrofluidized bed drying of the residue were determined. The conditions that facilitated fluidization were: 1) A particle size distribution of the dried residue that was lognormal, had a geometric mean diameter, d_gw, of 3.829 mm, and a geometric standard deviation, S_gw, of 2.49x10^-07 mm. 2) A vibrational acceleration, Aω²/g, of 2.54. 3) A minimum vibrofluidization velocity, U_mvf, of 4.2 cm/s. The controlling mechanism of the falling rate period was determined to be diffusion, with an effective diffusion coefficient, Deff, of 2.85x10^-5 cm/s, and critical moisture content, M_c, of 30%. Economic evaluation of the proposed method has a payback period of 4.34 years, and an estimated processing cost of $33 per ton of dried material.

Models were developed based on bed hydrodynamics and three-phase drying kinetics, and thin-layer drying. Both models accurately predicted the drying curves. The three-phase kinetic drying model solved a series of simultaneous equations, and differential equations, based on moisture and enthalpy balances. This complex model successfully predicted the bed hydrodynamic properties and serves to facilitate scale-up, design, and bed configuration investigations. For the thin-layer drying model, the drying constants, K & N, for Page’s equation were determined as a function of bed temperature. This computationally simple, single-parameter model would serve process control algorithms.

Scholar Commons Citation

Roe, Eric A., "Vibrofluidized Bed Drying Of Citrus Processing Residue For Byproduct Recovery" (2003). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/1460