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The production of green turmeric has shown significant improvement in Punjab but for its use, it has to be processed, i.e., dried, polished, and grinded. As turmeric is an essential part of Indian cuisine, sustained growth in demand is expected for the product. As a part to diversify agriculture huge potential under turmeric cultivation has been envisaged. As per a simple economic estimate, one acre farm yields 80–90 quintals. For the last few years, the wholesale market price of raw turmeric is Rs 8–12 per kg whereas after processing about 5 kg of fresh turmeric yields 1 kg of dried turmeric powder and the branded turmeric powder is available at approx. Rs 200–250/kg and the unbranded is available at Rs 150/kg. At present, major portion of the produce is dried locally by spreading it on cemented floor in open exposed to solar radiation. The land area required for drying turmeric in open is large due to thin layer drying. The open sun drying has major drawbacks of slow drying and high land cost. Polishing losses are also more for turmeric dried in open sun drying.

To overcome the drawbacks of turmeric drying in open sun, a large forced circulation solar dryer called ‘PAU Forced Circulation Solar Dryer’ for turmeric has been designed in the School of Energy Studies for Agriculture at Punjab Agricultural University (PAU), Ludhiana as shown in Picture 1. The PAU Forced Circulation Solar Dryer has two main components, viz., greenhouse and solar air heating arrangement. The greenhouse contains tray-rack for initial drying and drying chamber for final drying of turmeric. The solar air heating arrangement has solar air heaters, connecting pipes, electric air blower, etc. The solar air heater was also designed at PAU and utilizes evacuated tubes. This solar air heater heats air efficiently to higher temperature as compared to the conventional solar air heaters. Air temperature up to 65° C can be attained in the greenhouse during turmeric drying months. The dryer needs electric energy input for electric air blower. This dryer also has control on the relative humidity of air in greenhouse for maximum utilization of the drying capacity of hot air. This dryer can be operated in batch as well as semi-continuous loading mode for better utilization of the dryer capacity. It is suggested to follow the semi-continuous mode for loading turmeric in solar dryer.

Picture 1: PAU Forced Circulation Solar Dryer installed at Farm Produce Promotion Society (FAPRO), Hoshiarpur

In semi-continuous mode after 3–4 drying days, fresh product can be added daily due to shrinkage of drying product in solar dryer. The first lot of dried product is removed after 8–10 drying days, thereafter the dried product can be removed daily. In semi-continuous mode this solar dryer has drying efficiency of 23–29 per cent. The drying time is reduced to almost half as compared to open sun drying. The quality parameters, viz., volatile oil content, curcumin content, colour, polishing loss, and polishing time of turmeric dried in this dryer was found to be better as compared to open sun.

The salient features of the dryer are:

  • Better quality parameters of the product dried in this solar dryer as compared to open sun drying due to lesser exposure time to solar radiations.
  • Product dried in solar dryer is free from dust, birds excreta, dead insects, etc.
  • Lesser area required as compared to open sun drying.
  • In comparison to open sun, no attention required during off-sunshine hours and in case of rain, storm, etc.
  • Higher shelf life of dried product due to lower final moisture content because higher temperature air from array of solar air heaters is used for final drying.
  • Heat of air in the greenhouse is better utilized by removing air only when it has high relative humidity by using automatic humidity controlled exhaust fan.
  • Faster and efficient drying due to drying at higher temperature and in semi-continuous mode.
Picture 2: Photograph of turmeric spread in open on concrete floor at FAPRO, Hoshiarpur

This dryer can be made to any desired capacity. A solar dryer of about 700 kg turmeric loading capacity has been designed. The designed dryer has greenhouse floor area of 6.60 m x 3.5 m and 3 m height. The greenhouse has north wall vertical and insulated with 5 cm thick thermocole insulation. For circulation of air inside the greenhouse two air circulating fans are fitted inside the greenhouse. Besides exhaust fan controlled with humidity controller has been provided in one side wall of the greenhouse to maintain required humidity level. The greenhouse is covered with 200 micron UV stabilized transparent plastic sheet. Inside the greenhouse, tray racks are provided on north and south side for initial drying of product. The tray racks have 58 trays each of size 80 cm x 80 cm x 2.5 cm with wire mesh base. The drying chamber has opening at bottom for hot air inlet from solar air heater and opening at top for air outlet in greenhouse. The drying chamber has eight trays. Solar air heater with aperture area of 2 m2 has been provided outside the greenhouse for heating air. The solar air heater works in recirculation mode with greenhouse and sucks in air from greenhouse for heating. The above designed solar dryer has been installed at two user locations, namely:

(i) Farm Produce Promotion Society (FAPRO) Village Ghugial, District Hoshiarpur, and

(ii) S Tejinder Singh, Village Kang Khurd, District Kapurthala.

Picture 3: Forced circulation solar dryer installed at the farm of Shri Tejinder Singh, Village Kang Khurd, District Kapurthala

FAPRO is a consortium of around 300 farmers. The farmers bring their produce under the umbrella of FAPRO. The processing, packaging and then selling are done by the society. The FAPRO processes turmeric from February to June each year. They have a concrete floor of about 50 m x 50 m, on which turmeric is spread for drying in open sun (Picture 2). The solar dryer was installed at FAPRO in May 2015 and its photograph is shown in Picture 1 . About 3 tonnes of turmeric was dried in this dryer from May to June 2015. The society is quite satisfied with the quality of dried turmeric. Picture 3 shows another installation of this solar dryer at the farm of Shri Tejinder Singh. Both the dryers are working satisfactorily. On an average 50 kg of dried turmeric is removed per day by operating solar dryer in semi-continuous mode. The quality of turmeric dried in this dryer is good and comparable to branded turmeric available in the market but the total cost for dried turmeric including cost of fresh turmeric and post harvest operations is much lower. The cost of drying operation in this solar dryer is Rs 1.12 kg of dried product. The approximate cost of other post-harvest operations, viz., washing, boiling, polishing, grinding, and packaging is Rs 16 per kg approximately. This makes total cost for obtaining 1 kg of turmeric powder to Rs 80 approximately. The payback period in terms of number of drying days to recover the initial investment in comparison to branded turmeric are about 30 and those in comparison to unbranded turmeric are 50 days.

Dr Sukhmeet Singh, School of Energy Studies for Agriculture, Punjab Agricultural University, Ludhiana, Punjab; Dr R S Gill, Mechanical Engineering Department, Punjab Agricultural University, Ludhiana, Punjab; and Dr V S Hans, School of Energy Studies for Agriculture, Punjab Agricultural University, Ludhiana, Punjab, India.