Cacacs

Energy in Agriculture, 4 (1985) 41--55
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands

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EXPERIMENTAL RESULTS AT A PILOT SOLAR STATION USED FOR CURING TOBACCO IN A BULK-CURING SYSTEM - - ECONOMIC IMPLICATIONS
V.L. F A R A ' , R. G R I G O R E S C U ' , P. M A R I N E S C U 2 and V. D O G ~ R E S C U 2

2Solar Energy Laboratory, Department of Physics,Polytechnical Institute of Bucharest, Splai Independentei 313, sect. 6, Bucharest (Romania) 2Research Institute for Tobacco, SiT. G~rlei, Sect. 1, Bucharest (Romania)
(Accepted 6 June 1984)

ABSTRACT Fara, V.L., Grigorescu, R., Marinescu, P. and Dog~trescu, V., 1985. Experimental results at a pilot solar station used for curing tobacco in a bulk-curing system -- economic implications. EnergyAgric., 4 : 41--55. This paper summarizes research activity between 1979 and 1981 with a view to give a better understanding of industrial solar tobacco curing installations and their operating conditions. A brief presentation of the operating regime of the installation and of the physical parameters measured, is followed by a detailed analysis of the experimental results obtained both in thecollector field and 'at the user'. The study of the thermal balance of the installation allows the specification of its thermal performance. The economic advisability of the installation is presented in terms of the reduction obtained in conventional fuel consumption.

INTRODUCTION

During 1980--1981 a solar energy collecting installation (SECI) for curing bulk-cured tobacco was tested. It comprised168 small-concentration water solar collectors to form a 209 m 2 collecting surface. These collectors were m o u n t e d on the r o o f of a bulk-curing barn, in six groups each having 28 collectors. The reason for choosing small-concentration water collectors was the high temperature level obtained with no major technological requirements: the SECI of 5000 1 and 800 1, respectively, required fourfinned-coil heat exchangers (water--air), two water pumps and control equipment. The solar station was connected to four chambers of a bulk-curing barn. Solar energy was used during the yellowing stage in two chambers simultaneously, and also to preheat fresh air in the colour fixing stage.
MATERIALS AND DESIGN

Two approaches have been reported concerning the use of solar energy for0167-5826/85/$03.30

© 1985 Elsevier Science Publishers B.V.

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curing Virginia type 1 tobacco: the adaptation of solar energy collecting installations (SECI) to the existing bulk-curing barns (Dimitrov and Vatchov, 1978; Johnson, 1980; Fara et al., 1981b); and the construction of new types of multifunction barns having a specific architecture (Huang and Bowers, 1976). It is well known that ahigh quality of Virginia type 1 tobacco is obtained only if curing is performed immediately after harvest, following a certain technology which consists of the following phases: yellowing of the leaf, which takes place at 38°C under high humidity and gives rise to a high biochemical activity; colour fixing, which takes place at 40--50 ° C, when a high quantity of water is eliminated from the leaf;drying of the leaf limb, which takes place at 60 ° C; and drying of the ribs which takes place at 70--75 ° C. Table I shows the energy consumption for each phase, giving a total average daily consumption of 2891 kWh of which 46% takes place at temperatures under 45 ° C.
TABLE I Characteristics of phases of tobacco curing Phase Time interval (h) 48 34 12 16 Temperature (° C) 38 40--50 60 70--75Energy consumption (kW h) 3865 6423 2671 4352

Yellowing of the leaf Colour fixing Drying of the leaf limb Drying of the ribs

The hydraulic installation design provides a three-mode operation: direct circuit (pumps, collectors, coils); heat storage circuit (pumps, collectors, heat storage tanks, coils); and night circuit (pumps, heat storage tanks, coils). Mode switching is done either...