Received Date: December 24, 2013; Accepted Date: January 30, 2014; Published Date: February 07, 2014
Citation: Swain S, Din M, Chandrika R, Sahoo GP, Roy SD (2014) Performance Evaluation of Biomass Fired Dryer for Copra Drying: A Comparison with Traditional Drying in Subtropical Climate. J Food Process Technol 5:294. doi:10.4172/2157-7110.1000294
Copyright: © 2014 Swain S, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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In tropical and sub-tropical Island climate, adverse effect of heavy rainfall (2800-3500 mm), temperature (25-35°C) and relative humidity (75-95%) year round render high microbial infection to the copra produced by farming communities using traditional methods, causing low quality of copra leading to lower income to the producers. Keeping in view, a biomass fired copra dryer has been designed, developed and tested in Andaman Islands. The aim was to increase in employment generation to the rural households who are engaged with traditional method of copra production. The results indicated that biomass fired copra took 22 hours to reduce initial moisture content from 57.4% (w.b) to 6.8% (w.b) which saved 40% and 47% of total drying time compared to two traditional methods e.g. Machan drying and sun drying. Coconut shell of 80-85 kg is used as fuel. Two persons are required to feed the fuel and maintain the constant temperature to obtain better quality copra. The copra obtained was graded as 82% MCG1, 13% MCG2 and 5% MCG3. The cost benefit ratio and payback period was found to be 1.4 and 1.5 month respectively. The coconut shell may be used for fuel which saves manpower and energy, thereby enhancing net return to the farmers.
Copra; Machan; Sun drying; Biomass fired dryer
India ranks as the third largest coconut-producing country in the world . Andaman and Nicobar Island, India which is located at 11°40’ N and 92°46’ E. is blessed with floral diversity where coconuts are abundantly grown in the typical congenial climate. These fragile Islands stand 11th position in area with annual production of 95 million nuts  and it is regarded as the main source of livelihood securities to the lower and middle farming communities in the form of copra. Copra, the dried edible part of coconut is produced after drying of coconut. During traditional open sun drying, Island farmers spread coconut on mats, cement floors, roof tops or even on soil along the roadsides so as to expose to solar intensity until the completion of drying . In this method the samples are exposed to direct sun light and consequently the coconut pieces heat up and internal temperatures rise without regulation which destroys colour, vitamins and flavor giving rise to low quality produce that cannot compete with the mainland product. Again, sun drying suffers from high product losses due to inadequate drying, fungal growth, encroachment of insects, birds and rodents, etc. Anonymous  reported that copra manufacture solely by sun drying can be effective only in coconut regions with long periods of sunny clear skies, high mid-day temperatures (30–35°C in the shade) and low humidity air (60–70% RH). But in Andaman Islands, there is very little chance of getting favourable climate during sun drying. Most of the coconuts are consumed without undergoing much processing and value addition where nearly 80% of the produce supplied to mainland (India) for processing rather to have very high potential here to process and market for its export to other countries. Humid coastal climate prevailing throughout the year is conducive to the microorganism to grow upon the product unless it is properly dried. Unavailability of coconut-based industries is a clear testimony to this fact. Moreover, local farmers use indigenous structure made up bamboo sticks, clays known as “Machan” where the quality of copra is not up to standard for consumer acceptability which in turn fetch lower price in the domestic market. This system is inefficient and tedious with respect to profitability. In this method, there is also the chance of firing of total structure as the farmers used bamboo sticks and clay for making the frame without any control and constant supervision. Sometimes, the coconut shells were either dumped to the waste yard or used for fuel purposes for domestic cooking, causing environmental threat to the Island ecosystem Thiruchelvam  reported kiln drying was completed within 62 hours while 6 days were needed to bring down the moisture content to around 10% in sun drying, some more days might be needed to bring down the moisture content to safe storage level. Grimwood  has reported that it is necessary to reduce the moisture content of the endosperm from about 55-57% (w.b.) to 6-7% (w.b.) in order to reduce the weight, prevent microbiological deterioration and concentrate the oil. On average, five nuts are required to produce 1 kg of copra, however this conversion rate varies (plus or minus 40%) from country to country . However, copra is considered as a low value product and sophisticated dryers are not appropriate. Considerable efforts have also been made to design and develop solar dryers with/without phase change materials for drying of agricultural products [7-11] and also tested to enhance the efficiency of drying operation, still the research is continuing for getting quality product. Moreover, no study have been conducted for mechanically designed dryer for coconut drying where there is very less chance of getting adequate solar light during drying. Hence, to overcome the problems attributed to the coconut grower in the Islands, a biomass fired dryer has been designed, developed and the performance evaluated with the locally produced coconut so that it could be recommended to farmers for high-quality copra production.
Five hundred fresh mature coconuts were purchased from Central Agricultural Research Institute (CARI) farm. Good quality nuts were split into two halves in crosswise manner to remove coconut water.
Determination of moisture content
It was measured using AOAC method . Five mature coconuts were taken randomly and splitted into two halves. Then, these were cut into small cylindrical pieces and 20-30 g of coconut chips were placed into the oven at 105°C at until a constant weight is reached.
Experimental set up
Biomass fired dryer: A mechanical dryer (Figure 1) with capacity of 500 coconuts per batch was designed and fabricated using MS frame (2.4 m×1.2 m×1.6 m). The drying bed made of M.S bar grill kept at a height of 1.20 m above the ground level. A cylindrical shape heat exchanger was designed and fabricated using a 20 gauge metal sheet. The combustion chamber (2.5 m diameter) is made of 2 mm thick M.S. sheet. Two galvanized pipes have been connected at upper and lower side with combustion and drying chambers. The exhaust pipe is connected to the opposite end of the fuel inlet. A 50 cm gap is kept between combustion chamber and drying bed which are divided into two chambers for keeping splitted coconut. A door is provided for loading and unloading of fuel. Three tests were done to compare the yield of copra and its quality. At five different position of drying chamber the temperature was measured in each layer using a digital thermometer. Split coconut halves were loaded inside the drying chamber. Then, the fuel chamber is fired through coconut shell and wooden sticks. After every 2 hours, the temperature of the drying chamber is measured by digital thermo meter. Split coconut halves are kept upwards for 60% of total drying time and then downward for the rest drying period to enable homogeneous drying condition. It is necessary to reduce the moisture content of the coconut from 57% (w.b) to 6% (w.b) in order to reduce the weight, prevent microbiological deterioration and concentrate the oil. Two men were used to feed the fuel as well as to maintain constant temperature in the drying chamber by decreasing/increasing the fuel rate to the combustion chamber.
Traditional “machan” dryer
It consists of raised platform (Figure 2) where splitted coconut halves are spread on a bamboo platform. The coconut shell used for fuel are arranged horizontally below (70-80 cm gap) the platform. A door is provided to load and unload coconut shell. These shells were burnt underneath where the smoke and burnt gases directly contact the drying coconut cups placed above the raised platform. The farmers used to fire the shell in the morning and closed the door for 24 hours. Next day, the ashes are removed manually followed by filling the same with fresh shells. At the same time, coconut are removed from the shell manually and kept again in the platform and firing started. Next day, the dried copra are removed and stored in jute bags for selling to market.
Coconut cups (half splitted coconut) were spread on a black polyethylene sheet in a single layer directly facing the sun. The experiment was carried out at Garacharma farm, CARI Complex, Port Blair. Temperature sensors were fixed on the surface of the drying cups to measure the surface temperature. During night, the cups were covered completely by polyethylene. At the end of third/fourth consecutive day of sun drying, shells were removed from the cups manually and then dried for another three days. Samples were taken from seven cups at a time for the moisture determination at frequent intervals. To assure the quality, three replicates were conducted. At the end of the 7th day, based on the observation it was found that the copra had dried to sufficient moisture content and finally the grading was done. Moisture content was determined at every 2 hours intervals.
stimation of thermal efficiency
Thermal efficiency of biomass fired dryer was estimated using Equation (1). Moisture content of kernel was determined by taking a composite sample from randomly selected seven cups and drawing a representative sample from that
where M0 is the initial moisture content of coconut (%, wet basis), Mf is the final moisture content of coconut (%, wet basis), φ is the quantity of the final dried product at Mf moisture content (kg), γ is the latent heat of vaporization of water in 2.26 MJ/kg, W is the quantity of fuel used (kg) and C is the calorific value of fuel coconut shell (15.9 MJ/ kg), dry ash free.
Grading of copra was done after drying according to BIS: 6220-1971 (Table 1) by selecting 100 cups randomly. Chips in bulk sample were separated and weighed (% by weight). Wrinkled cups were separated and calculated their number as percentage of cups constituting bulk sample. Number of mouldy and black cups are counted and reported in percentage. Quality parameters include the moisture content; fatty acid content was measured using AOAC method . Along with these grades, total yield and efficiency of copra processing in each- process was calculated and compared.
|S. No.||Characteristics||MC Grade 1||MC Grade 2||MC Grade 3|
|1||Impurities, % by wt, Max||0.5||1||2|
|2||Mouldy cups, % by count, max||4||8||10|
|3||Black cups, % by count, max||5||10||15|
|4||Wrinkled cups, % by count||5||10||15|
|5||Chips, % by wt.||5||10||15|
|6||Moisture content, % by wt||6||6||6|
|7||Oil content(on moisture free basis), % by wt. Min||70||68||66|
|8||Acid value of extracted oil, Max||2||4||10|
|9||Grades of copra|
|Biomass fired copra dryer||82||13||5|
Table 1: Grading of copr.
Cost benefit analysis
It estimates and totals up the equivalent money value of the benefits and costs to the drying system to establish its profitability. The cost benefit analysis was carried out for each drying technique considering the fixed and the variable costs involved in the processing and the revenue from the sale of copra. The present market prices of different grades of copra were used in the analysis. According to these comparisons, the feasibility of drying system was determined.
Cost benefit ratio = Gross revenue/Total cost (2)
Payback period is the time required to recover capital investment was computed using following formula
Payback period = Capital investment/Net income (3)
The variation of moisture content with drying time is shown in (Figure 3). The average temperature recorded in the drying chamber was 52-55oC. It was observed that the temperature of lower chamber was 2-3°C higher than the above. The average moisture content of the coconut was reduced from about 57.4 % to 6.8% and 8.2% in the bottom and the top layer, respectively, after 22 hours. Biomass fired dryer took 22 hours to reduce initial moisture content from 57.4% (w.b) to 6.8 % (w.b) wherein traditional “machan” and sun drying took 34 hours and 42 hours respectively that implies biomass fired dryer saves 40 % and 47% of total drying time compared to two traditional methods.
In case sun drying, the variation of solar radiation and ambient temperature during experimentation is shown in (Figure 5). Maximum solar intensity of 1180 w/m2 was observed. The maximum drying air temperature recorded during peak sunshine hours was 35.9°C.
The average temperature reduced to 26.1°C during the night. The copra obtained from above methods is shown in (Figure 6). About 80- 85 kg of fuel (coconut shell) was used for the experimental study. It was observed that if the furnace was evaluated at the rate of 6.0 kg/h and the average temperature in the drying chamber was 65-69°C. If the feeding rate was more than 6.0 kg/h, the quality of dried products became hard. So, the rate of fuel consumed in the dryer was imperative to get quality products. Therefore, two man powers were needed for constant supervision of fuel rate and temperature.
Thermal efficiency of drying
About 187 kg of moisture was removed from 500 nuts to obtain about 135 kg of copra. The initial weight of 500 nuts with shells was measured to be about 350 kg. The thermal efficiency of the biomass fired dryer and machan dryer was estimated to be about 26% and 16% respectively by using Equation (1). Lozada reported that to enable the farmers to make copra more quickly, the use of drying kilns are resorted. And also sun drying may be affected by climatic factors, contamination of dust and other particle, mould development, birds and rodent activities. Therefore, at this ground, CRI kiln drying was considered as superior than that of sun drying. In our study, it was found that biomass fired dryer was superior to sun drying, machan drying and CRI kiln drying due to lesser humid environment as well as absence of microbial activity. Even though, the total copra yield was almost same in both drying techniques, cost involved and pricing system for different grades of copra were made considerable variations in cost benefit analysis. However, the revenue from sun drying was highly dependent upon the climate condition during drying period. As situated in sub-tropics, sun drying is inefficient for coconut drying. It has been argued that linking of farmers to the markets through efficient processing equipments would strengthen the value-adding activities by better technology and inputs, upgraded infrastructure and processing and exports .
Grading of copra
The copra obtained was graded as 82% MCG1, 13% MCG2 and 5% MCG3 (Table 1). Based on the grading of copra, it could be concluded that more than 80% of high-quality MCG1 could be produced in the biomass fired dryer. White copra has high market demand and high economic value. Good quality white copra provides best quality oil and also there is no contamination of smoke to produce polycyclic aromatic hydrocarbons. Therefore, at this point the sun drying technique was considered as superior than that of machan drying.
Taking economic analysis, About 135 kg and 95 kg of quality copra obtained in the biomass fired dryer and traditional “Machan” dryer from 500 nuts if the quality characteristics are properly maintained. (Table 2) below provides the clear picture for cost benefit ratio of two dryers. The B/C ratio was found to be more (1.4) as compared machan dryer (1.19). The payback period was calculated to be 1.5 months only. Hence, taking monthly calculation of cost involved in producing quality copra and benefit from selling those products, it could be concluded that the biomass fired dryer is superior to traditional drying system based on quality and profitability.
|Biomass fired dryer||“Machan” dryer|
|I. Cost of equipment||Rs. 45,000||Rs. 6,000*|
|A. Fixed Cost|
|II. Cost of raw coconut/batch (@Rs.8 per nut)||4000||4000|
|B. Variable cost (Rs.)|
|III. Labour cost/batch||600 (2 days)||-|
|IV. Cost of fuel/batch||800||300|
|V. Monthly production of copra||2025 kg (Taking 135 kg in 2 days. So, it is 135*15=2025 kg/month)||950 kg (Taking 95 kg in 3 days. So, it is 95*10= 950 kg/month)|
|VI. Maintenance cost/month||500||200|
|VII. Depreciation cost/month (@10%/annum) on equipment||375||50|
|VIII. Interest (@11%)||412.5||-|
|IX. Revenue/month||1,03,275 (@Rs. 51/kg||48,450 (@Rs. 51/kg)|
|X. Total cost (II+III+IV+V+VI+VII+VIII)||**73,287.5||**40,550|
|XI. Profit/month (IX-X)||29,987.5||7,900|
|B/C ratio (IX/X)||1.40||1.19|
|Payback period||1.5 month||-|
*(Taking in account the cost of bamboo platform, dryer roof, raised platform made of wooden plates/sticks though it is totally indigenously made by tribal’s /farmers), ** calculation on monthly basis.
Table 2: Calculation of Cost-benefit (B/C) ratio.
The temperature inside the biomass fired dryer was higher and relative humidity was lower than the ambient temperature as a result of which drying rate is more as compared to open sun drying and “Machan”. At the beginning of drying process, surface moisture was evaporated and the drying rate was high. Reduction was observed due to evaporation of free moisture migration from outer surface layer and gets reduced afterwards due to internal moisture migration from inner layer to surface. The drying rate decreased with an increase in the drying time. Drying occurs in the falling rate period with a steep fall in the moisture content in the initial stages of drying which becomes very slow in the later stages (Figure 4). It may be noted that during traditional drying, smoke is in direct contact with coconut cups and hence, good quality copra could not produced. The reason may be due to formation of high acid content and polycyclic aromatic hydrocarbon in copra . Nathanael supported this result as during the ensuring of hot air curing with intermittent cooling, a moisture gradient is established within the kernel, where moisture gradually migrates from deeper layers to the surface, resulting in a process of uniform dehydration of the kernel. In Machan drying, hot fumes and burnt gases were in contact with drying bed and, due to deposition of dust and smoke particle on wet kernel, the quality is also poor. It is also found that if the combustion chamber was evaluated at the feeding rate of 4kg/h, the average temperature recorded in the drying chamber was 45°C. This temperature was not enough to maintain the drying temperature of 50-55°C. A high drying rate at a rate of 0.094 g of water/g of dry matter hour was observed during the initial stage of drying. The drying rate of copra in the biomass fired dryer was high compared to sun drying and machan drying due to its high heat and mass transfer coefficients. Best quality copra was produced from biomass fired dryer. Again, based on financial calculation, monthly profit was calculated to be approx. 30,000 and 8,000 respectively for two dryers.
A biomass fired drier was designed, fabricated and tested for drying copra in sub-tropical climate. It reduces the moisture content from 57% to 6% (w.b). Copra produced (82 % of high quality) was free from dust, black/brown patch, birds etc. Poor quality copra obtained from traditional means mainly due to its exposure to tropical climate which may induce formation of carcinogenic substances in copra. Biomass forced copra dryer is more suitable in Andaman and Nicobar Islands for getting quality copra that could compete with the same produced in mainland for small and marginal holders. The copra obtained was graded as 82% MCG1, 13% MCG2 and 5% MCG3 with average thermal efficiency of about 26%. The cost benefit ratio was calculated to be 1.4 and 1.19 for two dryer tested for quality copra production. The monthly profit (Rs. 30,000) by biomass fired dryer could be a better source for revenue generation to support livelihood securities. The payback period was calculated to be 1.5 months only. Since, the results reflect their performance regarding the uniformity of drying, labour requirements and quality of product, it was found that there is a paramount importance to develop biomass fired dryer to cater the need of Islanders.
The Author is thankful to Director, Central Agricultural Research Institute (CARI) for his kind assistance, support and encouragement.