Waste and Biomass Valorization

, Volume 9, Issue 3, pp 443–449 | Cite as

New Experimental Rotary Dryer of Olive Stone: Design, Control and Modeling

  • Francisco J. Gómez-de la Cruz
  • Pedro J. Casanova-Peláez
  • Fernando Cruz-Peragón
  • José M. Palomar-Carnicero
Short Communication


Drying is the most important process to treat olive oil mill wastes. Olive stone is a by-product obtained in the olive oil extraction process. Crushed olive stone is separated from olive oil mill waste in the olive oil mills by means of mechanical procedures. Olive stone is mainly used as a biomass product for generating thermal energy for space heating in commercial buildings, residences and homes. Olive stone moisture content ranges from 20 to 30% (wet basis). Drying of olive stone is fundamental for its revaluation as biofuel, and the vast majority of this by-product is dried in rotary dryers. To improve the drying efficiency of olive stone in these dryers, we have designed and modeled an experimental rotary dryer that is intended to solve the heat and mass transfer equation in the sectioned models, both in a steady-state model and transient model, and to contribute to the development of a control system that is much more perfect.


Olive stone Rotary dryers Experimental equipment Drying Modeling Biofuels 


Latin letters

\( A_{j} \)

Effective cross section of the trommel (m2)

\( c_{p} \)

Specific heat capacity at constant pressure (kJ kg−1 K−1)

\( D \)

Trommel diameter (m)

\( F \)

Solid mass flow per unit section (kg h−1 m−2)

\( G \)

Gas flow per unit section (kg h−1 m−2)

\( H \)

Moisture content in the solid (wet basis)

\( H^{*} \)

Dryer holdup (%)

\( j \)

Percentage of the dryer cross section represents a free area for the air to pass (%)

\( K \)

Empirical constant for calculation volumetric heat transfer coefficient

\( L \)

Trommel length (m)

\( LMTD \)

Log mean temperature difference (K)

\( \dot{m} \)

Flow rate (kg h−1)

\( n \)

Empirical constant for calculation volumetric heat transfer coefficient

\( N \)

Trommel speed (rpm)

\( \dot{Q} \)

Total heat flux transferred (W)

\( \dot{Q}_{H} \)

Heat flux which raises the temperature in the gas (W)

\( \dot{Q}_{L} \)

Heat flux which raises liquid phase temperature in the product (W)

\( \dot{Q}_{s} \)

Heat flux which raises the product temperature (W)

\( \dot{Q}_{v} \)

Heat flux which evaporates a liquid portion in the product (W)

\( S \)

Trommel slope

\( T \)

Temperature (°C, K)

\( u_{P} \)

Permissible air mass velocity (kg s−1 m−2)

\( U \)

Volumetric heat transfer coefficient (Btu h−1 ft−3 K−1, kW m−3 K−1)

\( v \)

Drying air velocity (m s−1)

\( V \)

Volume (m3)

\( X \)

Moisture content in the solid (dry basis)

\( Y \)

Humidity of the air (dry basis)

Greek letters

\( \gamma \)

Heat loss factor

\( \eta \)

Thermal performance (%)

\( \lambda \)

Latent heat of vaporization of water (kJ kg−1)

\( \rho \)

Density (kg m−3)

\( \tau \)

Residence time (minutes)





Dry solid






Loss in rotary dryer











This work has been conducted with the financial support of the Spanish “Consejería Andaluza de Innovación, Ciencia y Empresa” through the research projects AGR-6131 (“Modelado y Control de secadero rotativo de orujo”) and AGR-6509 (“Producción de biocombustible utilizando hueso de aceituna y residuos de poda de olivo”) as part of the research program “Proyectos de Excelencia de la Junta de Andalucía 2010–2014”. The authors gratefully acknowledge the financial support provided.


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  1. 1.Department of Mechanical and Mining Engineering, Escuela Politécnica Superior de JaénUniversity of JaénJaénSpain
  2. 2.Department of Electronic Engineering and Automatics, Escuela Politécnica Superior de JaénUniversity of JaénJaénSpain

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