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Solar Thermal Drum Drying Performance of Prune and Tomato Pomaces

Rebecca R. Milczareka*| Jonathan J. Ferryb| Fatima S. Alleynea| Carl W. Olsena| Donald A. Olsona| and Roland Winstonb | bUniversity of California, Merced | aU.S. Department of Agriculture, Agricultural Research Service

Project Background

• Use of drum drying to remove water content from California specialty crop pomaces and purées.

• Provide heating power needed for drying from innovative solar thermal collectors.

•  Identify the feasibility of adapting solar thermal energy for use with existing drum drying technologies.

Drum Drying

• Consist of one or more rotating steel cylinders. • Traditionally powered by steam condensing on

the inside surface. • Highly versatile in the ability to adjust surface

temperature, rotation speed, and application thickness.

•  Ideal for agricultural and food processing where there is a solid/liquid combined byproduct or waste stream.

Types of Drum Dryers

Top Fed Double Drum Top Fed Single Drum

Bottom Fed Double Drum Bottom Fed Single Drum

The External Compound Parabolic Concentrator (XCPC)

•  Evacuated tubes with concentrating reflectors

•  Medium temperature range •  (100°C ≤ T ≤ 300°C)

•  High solar to thermal efficiency •  Non-Tracking

•  Low cost and low maintenance

XCPC Collector

•  Non-imaging optics reflector design. •  Ideal theoretical concentration ratio. •  Accepts both diffuse and direct light within

angular limit. •  Evacuated glass tube reduces heat loss from

conduction and convection. •  Mineral oil heat transfer fluid carries heat

from absorber.

Optical Design

Solar Integration of a Drum Dryer •  Drum dryer to be operated using mineral oil heat transfer fluid

rather than steam. •  Heating power to be provided by and XCPC array connected to a

double drum dryer via a heat exchanger.

Drum Drying Heating Power

Pomace Drying Results

Acknowledgements •  The authors gratefully acknowledge Papagni Fruit & Juice (Madera, CA)

and Ingomar Packing Company, LLC (Los Banos, CA) for providing the pomace samples. The authors would also like to thank the USDA-ARS, UC Solar, Dr. Roland Winston, Ron Durbin, Bennett Widyolar, Dr. Lun Jiang, Kaycee Chang, and Jordyn Brinkley.

•  This project was supported by the Specialty Crop Block Grant Program at the U.S. Department of Agriculture (USDA) through Grant 14-SCBGP-CA-0006. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.

•  * Corresponding author: Rebecca R. Milczarek

•  Email: rebecca.milczarek@ars.usda.gov

•  Mailing Address: USDA-ARS-WRRC-HPFR; 800 Buchanan Street; Albany, CA, USA 94710

•  Phone: 1-510-559-5656

•  Fax: 1-510-559-5851 Figures from Ramli, W., & Daud, W. (2014). Drum Dryers. In A. S. Mujumdar, Handbook of Industrial Drying, Fourth Edition (pp. 249-257).

Figure 1 – Illustrative diagram showing integration of a small double drum dryer with an XCPC solar array.

Experimental Procedure •  48 Prune and 48 Tomato pomace samples were tested in a split plot

experiment. •  Four independent variables were tested to determine optimum

drying conditions for the solar powered drum dryer. •  Temperature of the inlet oil to the drum dryer [C]

•  139°C, 151°C, 164°C •  Rotation speed of the drum [Hz]

•  12.57 Hz, 8.22 Hz, and 6.08 Hz •  Correlates to dwell time of pomace on drum surface [min]

•  2 min, 3 min, and 4 min respectively •  Maltodextrin added to the pomace as a carrier [% of total]

•  0% to 20% of total weight •  Pomace to water ratio [1:X]

•  X = 0 to 2 parts water

Figure 3 – Water activity results for Prune and Tomato Pomaces. Shelf stability for values less than 0.6

Figure 4 – Moisture content results for Prune and Tomato Pomaces.

(%)

0

0.1

0.2

0.3

0.4

0.5

135.0 140.0 145.0 150.0 155.0 160.0 165.0 170.0

η System

[%]

Drum Inlet Temperature[C]

The system thermal efficiency is defined as the ratio of the thermal power provided to the drum dryer to the solar thermal power provided to the heat exchanger:

𝜂↓𝑆𝑦𝑠𝑡𝑒𝑚 = 𝑄↓𝐷𝑟𝑢𝑚 𝐷𝑟𝑦𝑒𝑟 /𝑄↓𝑆𝑜𝑙𝑎𝑟  

Figure 2 shows a plot of the system efficiency vs the inlet drum temperature. It is apparent that system performance of the drum dryer is stable within the operating temperature range of the experiment. Major factors that influence the system performance are the solar collector efficiency, and excess heat loss through plumbing and the heat exchanger. Future work could characterize the integration of an XCPC solar array and a drum dryer to optimize performance.

Figure 2 – System Efficiency of a XCPC solar thermal powered double drum dryer

Poster By Jonathan J. Ferry