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Solar Thermal Powered Drum Drying of California Specialty Crops

Jonathan Ferry, Ph.D. Student | Dr. Roland Winston, Principle Investigator | University of California, Merced | U.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

Solar Resource

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 Characterization •! In order to determine how effective the drum is at drying different materials, a

characterization of the surface temperature and rotational speed is necessary. •! The drum rotation corresponds to how long a material will remain on the hot surface,

or its “dwell time.” •! The surface temperature of the drum corresponds to how much heat is being transfer

to a material in order to remove water content.

•! Each of these parameters will be used to set up a split plot experiment to determine the optimum parameters for drying different purees and pomaces.

Next Steps •! Using the parameters defined in the characterization of the double

drum dryer, a split plot experiment will be designed to dry several different fruit and vegetable pomaces and purees.

•! Dried products will be measured for their water content, color, as well as vitamin and mineral content in comparison to before drying.

•! Samples to be tested will have different starting water contents, dwell times, and surface temperature settings to bolster the split plot experiment design.

Acknowledgements •! The authors would like to thank Grimmway

Farms, (Arvin, California, USA) for supplying the carrot pomace for this study. 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 is 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. Figures from Ramli, W., & Daud, W. (2014). Drum Dryers. In A. S. Mujumdar, Handbook of Industrial Drying, Fourth Edition (pp. 249-257).

Map provided by NREL at http://www.nrel.gov/gis/solar.html

•! California has an abundant solar resource. •! Average direct

normal irradiance of 5.0-6.0 kW/m2/day.

•! Sunlight to heat conversion generally more efficient than sunlight to electricity.

•! Concentrating solar irradiation can improve heating power.

•! Solar thermal is a well established industry. y = 28.864x-1.048

R" = 0.99931

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0 5 10 15 20 25 30 35 40 45

Sur

face

Dw

ell T

ime

[min

]

Motor Frequency [Hz]

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

Figure 2 – Characterization of drum rotation speed and 65.5% surface dwell time.

Table 1 - Characterization of drum surface temperatures for various set point oil temperatures!

Tset [C]! mdot [g/s]! Tin [C]! Tout [C]! Ts_ave [C]!100! 89.8! 100.5! 98.8! 89.2!130! 90.2! 132.1! 129.3! 119.3!160! 92.3! 164.8! 160.1! 137.6!165! 92.5! 168.5! 163.7! 142.3!