Marcelo Figueira de Mello PrecoppeDevelopment of an Energy Efficient Drying System for High Quality Litchi Processing in Smallholder Cooperatives | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ISBN: | 978-3-8440-2592-7 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Series: | Schriftenreihe des Lehrstuhls für Agrartechnik in den Tropen und Subtropen der Universität Hohenheim Herausgeber: Prof. Dr. Joachim Müller Stuttgart | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Volume: | 08,2014 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Keywords: | convective drying; dehydration; hot-air dryer; energy efficiency; heat consumption; consumer preference; product optimization; product quality; lychee | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Type of publication: | Thesis | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Language: | English | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Pages: | 118 pages | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figures: | 22 figures | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Weight: | 174 g | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Format: | 21 x 14,8 cm | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Binding: | Paperback | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Price: | 30,80 € / 38,50 SFr | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Published: | March 2014 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Abstract: | Agriculture accounts for most of the land use in Southeast Asia’s mountainous regions, and here farming is mostly undertaken by smallholders, within fragile ecosystems in which it is difficult to carry out sustainable agricultural production. Thailand’s mountainous regions are mostly located in the north of the country, where litchi (Litchi chinensis Sonn.) production is significant and constitutes an important part of the region’s economy. After 1960, Thailand experienced rapid economic growth, but the mountainous regions remained largely isolated from this process at the time, as they were populated largely by ethnic minority groups who practiced swidden agriculture and grew opium poppies in fields located at higher altitudes. Then, during the 1970s and 1980s, many rural development projects were introduced in order to replace poppy cultivation, and the most common crop used to do this was litchi. As a consequence, by the early 1990s, litchis had become one of the area’s key crops and had made Thailand one of the world’s major producers. However, in the late 1990s, the domestic market for the fruit reached saturation, and as a result prices started to decline. This fall in prices led to the replacement of litchi orchards with seasonal crops, the cultivation of which led to an increase in erosion, plus pesticide and water use. In an attempt to make litchi growing profitable again, scientists from The Uplands Program, a Thai-Vietnamese-German interdisciplinary research project, set up a project aimed at promoting litchi drying among farmers’ cooperatives, as a way to cope with the saturated fresh-litchi market. Village-based litchi drying requires low-cost and easy-to-use equipment, but at that time there was a lack of such dryers on the market that is both, energy efficient and able to yield a high-quality product. In this context, the objective of the present study was to develop a low-cost energy-saving dryer, able to produce high-quality dried fruit. The project was performed with participation of a Chiang Mai based dryer manufacturer and a Hmong farmers’ cooperative. Dried litchis are popular in Asia, but Thai consumer preferences in terms of appearance, texture and taste had not been determined prior to this research. Six different dried litchi products were submitted to analysis of colour, texture, acidity and sugar content and evaluated by consumers in a survey. The results were then integrated using circular ideal-point regression analysis. Response surface methodology was used to determine the optimum colour, sugar/acidity ratio and hardness. It was found that Thai consumers prefer a goldenyellow dried litchi with a soft texture and a sweet taste. In 2008, the performance of the cabinet dryer used by the Hmong farmers in Mae Sa Mai to dry their litchis was analysed to reveal the reasons behind the excessive gas consumption and low product quality obtained during the previous year. Three replications of each of the drying experiments were performed, with drying conditions, energy consumption and product quality monitored. Regarding the excessive gas consumption, it was found that the energy efficiency of the dryer was rather low (29.8%), mainly due to the large amounts of heat lost via the unsaturated exhaust air (38.4%) and absence of thermal insulation (17.6%). In terms of product quality, it was found that significant differences in air velocity above the trays led to non-uniform temperature distribution and as a consequence, a non-uniformly dried product. In light of these findings, in 2011 the dryer was modified to reduce heat losses and also gas consumption. The air duct and blower located at the top of the dryer were insulated, and at the outlet, a metal sheet was installed as a sliding-door, allowing the farmers to adjust its size and so the amount of air being recirculated. The performance of the modified dryer was then compared with the unmodified version over a total of three replications for each design. Gas consumption, electricity consumption and drying parameters were recorded, and both fresh and dried fruit samples were collected for moisture analyses. It was found that closing the dryer’s outlet during the drying process significantly reduced exhaust heat losses, without increasing drying time. Insulation added to the section of the dryer where air temperatures were highest also reduced losses to the ambient air. The combined effect of these modifications was a significant energy saving, with the energy efficiency of the dryer reaching 39%, which is an increase 9.2%. In 2012, after performing a thermodynamic analysis of the dryer, an attempt was made to improve batch uniformity and the energy efficiency of the equipment using a low-cost modification. In the original dryer design, the chamber’s air inlet was composed of two slits, so it was decided to reduce this to a single slit. The two designs were then compared during an experiment in which three replications were carried out for each dryer type. Air velocity and temperature were measured above the dryers’ trays, and fruit samples were collected for moisture content analyses. The reduced size of the drying chamber’s hot air inlet increased the differential pressure – equalizing air velocity between the trays, and this led to a more uniform temperature distribution, and as a result, a more uniformly dried product. This modification also reduced the average air mass flow within the dryer, without decreasing the drying rate, so reducing the required heat input and increasing the energy efficiency of the dryer to 42%. Due to these modifications, the drying equipment became more energy efficient and able to yield a product of more uniform quality. The Chiang Mai-based dryer manufacturer incorporated these modifications into its production process with no impact on costs and; therefore, the technology is now readily available for smallholder farmers’ cooperatives throughout Thailand. However, after the research project had finished, the Hmong farmers’ cooperative in Mae Sa Mai stopped drying litchi, due to the small profit margins. Still, it is expected that market and technological developments in the near future should help reduce the costs and increase the revenue generated by such operations, possibly attracting farmers back to the dried litchi market and making use of the new dryer design |