DEVELOPMENT OF A MOBILE NATURAL CONVECTION DRYER FOR NATURAL FIBERS

Transcription

1 DEVELOPMENT OF A MOBILE NATURAL CONVECTION DRYER FOR NATURAL FIBERS Abstract A study was conducted to develop a mobile natural convection dryer for natural fibers with the following design considerations: low-cost compared to existing designs of dryers, indirect convection type, could be fueled by coconut husk with shell, coconut shell and fuel wood, replicable design, and simplicity in terms of operation. Tests were conducted to determine the suitable interval and feeding rate of each biomass fuel, determine whether significant differences existed between the different drying trays in the dryer, and evaluate the performance of the developed dryer in terms of the drying time, capacity and cost of utilization. Results revealed a significant difference in the average drying temperature of the drying trays. Succeeding tests were conducted by switching the load between the drying trays every two hours in order to obtain uniform moisture content of the leaves inside the drying bin. Cost analysis revealed that coco husk with shell gave the least cost for every hour of drying. The features that make the dryer promising and attractive to use is its mobility, less energy requirement, low investment cost, less space requirement, versatility in terms of fuel to use and adaptability to the rural setting. Keywords: dryer, convection dryer, natural fiber, mobile dryer 1.0 Introduction Region 8 is rich in natural fibers. Besides being the top producer of abaca fiber and fiber craft in the country, it has also produced fiber products from other natural sources such as tikog, romblon, and piña. Some places in the region utilize tikog and romblon as excellent materials for quality mats. These natural fibers are considered indigenous raw materials with potential for creating future markets for the gifts, toys, and house wares (GTH) sector. With the declining production of abaca fiber due to the outbreak of the bunchy top disease, it is imperative to utilize and maximize also the use of other natural fiber sources as means to create livelihood and thereby increase the productivity of rural communities. One of the important postharvest processes of these natural fibers is drying. Freshly harvested or decorticated/stripped fibers should be dried immediately in order to preserve the quality of the product. Poorly dried fiber will result in discoloration, and texture and tensile strength deterioration.

2 Traditional practice involved drying the fiber directly under the heat of the sun or by ambient air drying. This practice, however, have several limitations. Abit et al. (1987), in their study on the uses and current production of tikog (Fimbristylis globusa) in Region 8 found that 53.33% and 40% of the tikog growers and gatherers, respectively, had difficulty in drying the harvested tikog stalks, especially during rainy seasons. Discoloration of tikog stalks occurred when it was not dried immediately. Hence, some processors use mechanical dryers in order to increase and maintain production despite bad weather condition. The use of mechanical dryers require considerable investment and technical know-how on its operation. Though there are a lot of technology and dryer designs available today, most fiber processors still have not adapted the technology due to the high investment cost and lack of technical know-how on the proper use and maintenance of the dryer. The operation cost is high that these small-scale processors cannot meet the requirements to fully utilize the dryer. The Visayas State University (VSU) developed a stationary solar tunnel dryer for romblon (Pandanus tectorius) raw material. It is now used by the Iyusan Romblon Craft Weavers Cooperative in Brgy. Iyusan, Almeria, Biliran (DOST 8 Annual Report, 2003). The dryer requires only sunlight as the source of heat and electricity to power the blower. A similar dryer was also developed by the Bureau of Postharvest Research and Extension 52 (BPRE) in Nueva Ecija.The advantage of this type of dryer is that it is much more economical in terms of operational cost compared to other mechanical dryers. However, its limitation is that its use is limited only to sunny days. Drying is no longer possible during night time and rainy periods. In addition, initial investment is also higher as some of the materials used in this dryer are not available in the region. Investment cost for the multicommodity solar tunnel dryer of the BPRE was P80, Using this dryer, recovery period may be longer, because its effective use is only during sunny days. There is a need to develop a dryer which requires less investment, could be fully utilized at any time, has lower operational cost, and could easily be maintained. Hence, this study was conducted in an attempt to improve the existing dryers in relation to adaptability and suitability for small-scale fiber processors. 2.0 Methodology In order to achieve the above -mentioned objectives, the following procedures were followed. Over-all Design Considerations The following considerations served as basis in the design of the dryer: 1. A dryer that is low-cost compared to existing designs of dryers so that it could be

3 adaptable to small-scale fiber processors. A mobile type natural convection dryer was developed. 2. A dryer that is an indirect convection type in order to prevent smoke and other hazardous substances from the burning fuel to pass through the product, and to allow users the option to dry also food products in order to maximize the use of the dryer. A heat exchanger was designed for this purpose. 3. A dryer that could be fueled by coconut husk with shell, coconut shell, and fuelwood which are abundant in the rural areas. A furnace was designed for coconut husk, coconut shell and fuelwood. 4. Replicable design to use locally available materials. 5. Simple to operate in terms of loading and unloading of the product, feeding of fuel should require less attention. Design and Fabrication of the Dryer The dryer was fabricated in one of the local shops in Sogod, Southern Leyte through contract basis. The implementing agency provided the fabrication materials. In addition, the proponents provided the detailed drawings and supervised the fabricator in the actual fabrication of the dryer. Constant monitoring and supervision was conducted in order to ensure that the working drawings/ design was followed. The developed dryer is a natural convection utilizing selected biomass as fuel. The parts could be dismantled and could easily 53 be transported to another place using a trailer or any 4-wheeled vehicle. The original design and fabricated prototype has 4 main components, namely: 1. Drying Bin. The drying bin measures 2 m x 1.5 m x 2 m and is made up of 1 ½ angle bars framing which are joined together using ½ diameter bolts. The framing could be collapsed and dismantled into 16 separate angle bars and round bars. The drying trays are composed of 3 layers which measure 2 m x 1.5 m each and are equally spaced at 0.4 m. It is made of a 1 able bar frame and a 1 wire mesh. The cover is made of canvas with zippers provided at every corner of the drying bin to facilitate opening for loading and unloading of fibers to be dried. Air vents are provided at the bottom of the canvas to facilitate the supply of fresh air inside the drying bin. 2. Furnace. The furnace measured 0.40 m x 0.50 m x 0.50 m and is designed for biomass fuels. The frame and cover are made from 1 ½ angle bar and 2.33 mm B.I. sheet. The fuel tray was constructed out of 10 mm plain round bars and designed to be detached out from the furnace for easy replacement in case it will be worn out or if another fuel burner will be installed inside the furnace. 3. Heat Exchanger. The heat exchanger is positioned directly below the drying trays. It is made out of 2.3 mm

4 B.I sheet, 1.58 m in length and semi-cylindrical in shape. Heat dampers which are equally spaced at 0.40 m were provided to increase the heat transfer capacity of the heat exchanger. One end is connected to the furnace while the other end is connected to the chimney base support. 4. Chimneys. The developed dryer has two chimneys: 1) exhaust chimney for smoke and flue gas from the furnace, and 2) exhaust chimney for vapor-saturated air 54 from the drying bin. The exhaust chimney for smoke and flue gas a diameter of 0.20 m and a height of 1.8 m measured from the chimney base support. It is made from Ga. 26 G.I. sheet and is directly attached to the chimney based support. The exhaust chimney for vapor-saturated air is made of 8 mm round bars frame and canvas cover. Its height from the top of the drying bin is 0.91 m. Fig. 1 The canvas cover with zippers Fig. 2 The dryer s furnace on the sides to facilitate opening of the bin Initial Testing and Modifications Initial testing was conducted to assess the workability of the developed dryer in burning the selected biomass fuels. Three biomass fuels were used during testing: coco shell, coco husk with shell, and fuel wood. The firing time with different biomass fuels using paper or kerosene is 2 to 5 minutes. Constant combustion was attained using the different biomass fuels as exhibited by the fire generated in the furnace and the movement of flame towards

5 the heat exchanger and constant upward flow of smoke during the 30 minute testing. Maximum amount of fuel that could be accommodated in the furnace was fed, however it was observed that the canvas cover near the furnace and directly above the heat exchanger started to get loose and softened due to heat radiated from the heat exchanger. The testing was therefore stopped and the researchers decided to modify and replace the portion of the canvas cover near the furnace with G.I. sheet with heat shield and the other sides with 6 mm plywood. Modifications were made to the drying bin s cover (Fig.3). The G.I. sheet and plywood cover were 55 bolted to the drying bin s frame covering the area from the bottom up to the lowest layer of the drying tray. A 7 cm gap between the heat exchanger and the G.I. sheet cover was provided as the only passage way of fresh air from outside towards the inside of the drying bin. A heat shield measuring 20 cm in width was welded on the edge of the G.I. sheet cover forming an arch along the gap between the heat exchanger. The canvas zippers, provided at every corner of the drying bin were replaced with velcrews which will not corrode and could hold the canvas much stronger compared to the zippers. Figure 3. Modifications to the drying bin cover. 1) G.I sheet. 2) Plywood. 3) Velcrew. 4) Heat shield Operation of the Dryer Prior to operating the developed dryer, the following procedures were undertaken. Mounting and Assembling of Parts Since the developed dryer is mobile, its parts could be collapsed during transportation to reduce space and to allow easy transport. Hence, before the actual use of the dryer in its location, its parts should be assembled and mounted first on a

6 flat, level and elevated ground with a shed provided for protection in case of rains during operation. The sequence in assembling and mounting the original prototype could be done by two people in one hour. Assembling the modified dryer is easy as only the G.I. sheet and plywood is bolted in the frame before and after mounting the canvas cover. The only tools used to assemble the dryer are adjustable wrench to tighten the bolts and ball hammer to fit the other parts. Fibers to be dried could be loaded by opening any of the four sides of the canvas covering the drying bin. After uniformly spreading the fibers to be dried, the canvas cover will be closed and secured by fastening the velcrew in each corner of the drying bin. Preliminary Testing and Calibration Romblon was the only fiber used in this study since it is the only abundantly available natural fiber near Sogod area. Since there is no established data yet on the drying characteristics of romblon fibers, a laboratory experiment using an oven was conducted to determine the optimum drying temperature that could preserve the quality of the dried fiber comparable to its sundried counterparts. Based on the results of the tests, the optimum drying temperature was determined at 80 C. Beyond this temperature, fiber becomes brittle. However cooling the fiber for one day allows the fiber to recover from its brittleness and 56 return to a state similar to sun-dried fiber. Preparation of Fiber Samples to be Dried Romblon was the only fiber used in this study since it is the only abundantly available natural fiber near Sogod area. Fresh romblon leaves were obtained from Inopacan, Leyte and transported to the testing site at Southern Leyte State University (SLSU) Sogod. The leaves were grouped into bunches, each bunch consisting of 40 leaves and each leaf sliced into halves, each slice having a width of 2 cm. Moisture content of fresh romblon leaves were determined using the standard oven method. Preparation of Biomass Fuel Three biomass fuels were used in this study: fuelwood which utilized ipil-ipil (Leucaena leucocephala), coco shell, and coco husk with shell, which were procured from a farmer in Sogod, Southern Leyte. The fuels were dried under the sun to eliminate excess moisture and to ensure dryness and combustibility. There was no attempt to measure the moisture content of the fuels prior to its use. Drying Procedures Four bunches of romblon leaves were loaded in each tray for a total of 12 bunches in one loading. Moisture content of romblon leaves is 68.73% (w.b.). The above loading

7 57 Figure 4. Loading romblon leaves on the three trays of the convection dryer. volume was selected based on the observed capacity allowing for thin spreading of romblon leaves in each tray. The leaves were placed in the drying trays along or parallel to the direction of the heat exchanger. The fuel feeding rate in order to maintain an average drying bin s temperature of around 80 C which was determined through preliminary testing were: 10 kg/hr for fuelwood, 8.57 kg/hr for coco shell, and 8 kg/hr for coco husk with shell. Feeding interval for the three biomass fuels is presented in Table 1. Three randomly selected samples of Romblon leaves in each drying tray were taken out every hour for moisture content determination. Table 1.Fuel feeding rate and interval. Cost Analysis Equipment such as the fabricated natural convection dryer for natural fibers and other similar gadgets are tools of production that should be operated in a businesslike manner to produce its supposed output for the advantage of its user. Its performance will only be profitable when the equipment can add value to the products or processes beyond the usual system s cost of operation. The optimum goal is to attain minimum cost in the production process but overall profit maximization would be the ultimate target in operating a business. Thus, the economic performance of the equipment relative to its use should be measured in terms of pesos per unit output to determine its margin of contribution to the production process and income generation. In this study, the cost of drying twelve bunches of stripped romblon leaves

8 using three different fuel types was determined with due consideration of the fixed and variable costs in the use of the equipment. The fixed costs that were taken into consideration are equipment depreciation, interest of investment and shelter. The variable costs on the other hand included 58 costs of fuel used, repair and maintenance and labor. The straight -line depreciation method was used considering ten years of economic life of the equipment. The salvage value is ten percent of the purchase cost or the equipment cost itself. Depreciation is expressed as: The annual interest of investment is the product of the average investment and the interest rate which is currently 12% (Landbank Sogod Branch). The relationship is expressed as: The annual shelter cost of one percent (Hunt 1977) was adopted in this study, thus: Annual shelter cost = 0.01 P The labor cost of P per 8-hour work was based on the average farm daily wage. The repair and maintenance cost is two percent of the equipment cost per 100 hours of annual use (Hunt 1977). To be able to come up with a differential cost analysis in drying romblon leaves using the natural convection dryer and sundrying, data was gathered through interview with some of the mat weavers and romblon processors in Brgy. Plaridel, Baybay, Leyte. According to mat weavers and romblon processors, fresh romblon leaves sliced 2 cm in width has a usual drying time of 6 days using sunlight, and leaves sliced 1 cm has a drying time of three days.

9 Romblon leaves grouped in bunches are suspended from drying lines in the morning and kept in a shed late in the afternoon. With this set-up, one laborer could dry a maximum of 100 bunches or 157 kg of fresh romblon leaves per day and be paid P150.00/day. In this study, the drying time of 6 days under sunlight 59 was used as the comparison in the analysis due to the 2 cm slice of the leaves that were tested in the dryer. In addition the average weight of fresh romblon leaves was determined at 1.57 kg to parallel the 157 kg capacity of fresh leaves that are sundried per day. Table 2. Basic data used in the cost analysis. Statistical Analysis The experiment was carried out in completely randomized design (CRD). Analysis of variance was employed among the different drying trays using the least significance difference (LSD) test to compare treatment means. 3.0 Results and Discussion Drying temperature inside the drying bin Temperature generated inside the drying bin depends upon the fuel feeding rate. It was found on preliminary testing that the appropriate fuel feeding rate and interval should be employed in order to maintain a more uniform temperature inside the drying bin. The fuel feeding rates that were maintained during the experiment were 10 kg/hr, 8.57 kg/hr, and 8 kg/ hr for fuel wood, coco shell, and coco husk with shell, respectively. Table 5 presents the average drying temperature using the three

10 60 biomass fuels from the start of constant burning up to the time that fuel feeding was stopped. Using the fuel wood, the mean temperature inside the drying bin was found to be C. Analysis of variance (Table 4) showed that there is a significant difference between the temperature of the three drying trays. The bottom tray temperature (94.50 C) was significantly different from the middle (67.67 C) and top (72.50 C) tray s temperature. On the other hand, mean temperature of middle and top trays did not differ significantly. Table 3.Technical specifications of the developed dryer. Table 4. Statistical differences of drying temperature of the three drying trays using the three biomass fuels.

11 1 Vivencio A. Pelesco and 2 Jose P. Monteroso J ournal Moisture content of dried romblon leaves Hourly average moisture content of the romblon leaves was noted in using the three biomass fuels. Analysis of variance (Table 5) revealed that using coco shell and coco husk with shell, average moisture content of romblon leaves already differed significantly in each drying tray, one hour from the start of drying. With fuelwood, moisture content of the leaves in the drying trays did not differ significantly for one hour. However after two hours, moisture content among the drying trays began to differ significantly. However after five hours of drying, analysis of variance did not reveal any significant differences in the bottom and middle trays, where fuelwood and coco shell was used. This implies that after five hours, of 61 Science, Engineering and Technology moisture removal rate of the bottom tray slows down since moisture content was already very low. At the end of five hours, moisture content of romblon leaves in the bottom and middle tray already fell below the moisture content of sun-dried romblon leaves which found to be 18% (wet basis) by experiment. It was observed that newly dried romblon leaves with moisture content below 18% became brittle and had to be allowed to cool for one day to return to a condition similar to that of sun-dried romblon leaves. Succeeding test were conducted by switching the load between drying trays every two hours in order to obtain a uniform moisture content inside the drying bin. Using the same fuel feeding rate, moisture content below 20% (wet basis) was attained after 5 hours of drying. Table 5. Average moisture content of romblon leaves at different drying times, and drying trays using three biomass fuels.

12 1 2 Vivencio A. Pelesco and Jose P. Monteroso Journal of Science, Engineering and Technology 62 Cost Analysis Across the different types of fuel tested, the use of coco husk with shell gave the least cost of P36.40 for every hour of drying of P for the while duration of drying which was 5 hours. In contrast, that of fuelwood gave the highest cost at P44.40 per drying hour or P in five drying hours. P1.41, P1.38, P1.03 and P3.00 were the costs for depreciation, interest on investment, shelter and repair and maintenance, respectively for every hour of drying twelve bunches of romblon leaves using the dryer. In terms of quantity of fuel used in drying a kilogram of fresh romblon leaves, the dryer using coco husk with shell consumed the least weight of fuel material of only 2.12 kg while in the use of fuelwood, the dryer consumed the most at 2.66 kg. the findings suggest that with the present features of the dryer, wouldbe users can maximally benefit from the use of the dryer in two ways. First, is to increase the number of hours of dryer utilization in a year. Increasing the number of dryer utilization like utilizing the dryer to dry other products such as peanut, mongo, roootcrop chips and others would reduce the hourly costs for depreciation, interest on investment, shelter and repair and maintenance. Second, other abundant materials in the locality should be utilized to reduce the costs for fuel. Table 6. Cost of drying 12 bunches of stripped romblon leaves.

13 Table 7. Quantity of fuel used per bunch and per kilogram of fresh romblon leaves by type of fuel Conclusion The developed dryer was found to be potentially applicable to dry also newly bleached and dyed natural fibers. Because the developed dryer uses only heated air to dry the product, the dryer does not pose a danger on the quality of other natural fibers. Since the developed dryer is of an indirect type and does not expose the product to smoke, it is also potentially applicable on food products that need drying such as fish, root crop chips and other products such as tobacco, peanut and mongo. for improved fiber quality. Proceedings of the 5 th farm resources and systems forum on Fiber Engineering Technology for Improved Fiber Quality. CSSAC, Pili, Camarines Sur. Bassey MW, Whitfield MJ, Korama EY Problems and solutions for natural convection solar crop drying. In: Solar drying in Africa.(url needed) Bassey MW, Schmidt OG. Food Drying Workshop in Dakar, Senegal.(url needed) 5.0 References Cited Abit SE, Escasinas AB, Garcia FC, Galenzoga AT Survey on the uses and current production practices of tikog (Fimbristylisglobusa). Visca, Baybay, Leyte. Andam CJ, Armada AB, Alamban RB, Lantican CM Fiber engineering technology Bhattacharya SC, Sidique AHMR, Manandari CP, Pham HL A study on improved institutional biomass stoves. A report of the renewable energy technologies in Asia: RET s in Asia. Energy program, Asian Technology of Technology, Bangkok. Department of Energy, Republic of the Philippines

14 64 Household Consumption Survey. Energy Guarte RC Modelling the drying behavior of copra and development of a natural convection dryer for production of high quality copra in the Philippines [dissertation]. Hohenheim, Germany. Guarte RC Design and development of a natural convection dryer for rice [thesis]. Bangkok: Asian Institute of Technology Hunt D Farm power and machinery management. Ames, Iowa: Iowa State University Press. 7 th ed. Mastekbayeva GA, Bhatta CP, Leon MA, Kumar S Experimental studies on a hybrid dryer. Paper presented at: ISES 99 Solar World Congress; Israel.