Industrial-scale solar vegetable drying

An industrial-scale solar vegetable dryer with a capacity of 100 kg was designed, constructed and tested at a food factory in the North East of Thailand. The complete solar drying system consists of four dryers. The main parts of a dryer are as follows: a solar collector with an area of 73 m(2), a 2 kW blower, a drying cabinet and an air to steam heat exchanger. The dryer used solar energy and steam as heat resources for drying vegetables such as chopped spring onion, cabbage, ginger, turmeric, green banana, basil and chili. Total area of solar collector was 300 m(2). Steam was used to supplement solar energy at low intensity. A central boiler with capacity of 5 tons/h was used to supply the air to steam heat exchanger. Drying air temperature was controlled at 60 degrees C in each experiment. In operation, air was sucked from the solar collector, heated by air to steam heat exchanges if air temperature was lower than a set value, and blown into the drying cabinet. Vegetable with approximate initial moisture content of 75 - 85 % w.b. was dried to approximate final moisture content of 5 - 10 % w.b. within 4-6 h. Experimental results showed that drying efficiency, efficiency of solar collector and system efficiency were 43 %, 40 % and 17.4 %, respectively.