FABRICATION AND EVALUATION OF PADDY HUSK DRIVEN UP-DRAUGHT HOT AIR DRYER FOR PADDY DRYING

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1 FABRICATION AND EVALUATION OF PADDY HUSK DRIVEN UP-DRAUGHT HOT AIR DRYER FOR PADDY DRYING Dilotharaj.P.A 1, Kannan.N 2, Prabhaharan.M 3 and Alvappillai.P 4 Department of Agricultural engineering, Faculty of Agriculture, University of Jaffna, Sri Lanka Abstract Drying is an important step in paddy processing. Sun drying is commonly practiced in northern Sri Lanka to dry paddy grains with many difficulties during rainy season. Hence, an attempt was developed to design an eco-friendly up-draught hot air dryer with the hypothesis that the drying rate of grains in designed dryer is greater than that of sun drying. Dryer was fabricated properly and experiment was conducted in Completely Randomized Design (CRD) to check its efficiency in terms of moisture removal of paddy grains. Results revealed that the final moisture content of all such paddy grains dried under conditions, T 1 and T 2 is significantly different (α=0.005) from sun drying. Further, variety and storage period influence drying of paddy grains. As designed dryer yields quick and uniform drying of different paddy grains compared to sun drying, it is very useful to dry paddy grains successfully throughout the year. Key words: Fabrication, Evaluation, Up-draught, Hot air, Paddy drying Introduction Paddy is on of important cereals in the world. Paddy production of Northern and Eastern provinces of Sri Lanka has contributed more than 34 percent of the total production in 2013 Yala season (Department of senses and statistics 2013). Total Production is around 1,865,260 Mt in Yala season in the year 2014 (Department of Agriculture, 2014). Most of the rural people in Sri Lanka cultivate paddy in both Maha and Yala seasons, as it is a staple food (Banda, 1999). Different varieties are used in different areas to suit existing climatic conditions (Department of Census and Statistics, 2013). Influences of environmental factors are highly significant as far as paddy processing is concerned. Paddy grains can be processed by two major methods namely raw rice processing and parboiling. However, these methods have their own merit and demerit as far as rice quality is concerned (Wimberly, 1983). Parboiling is a hydro thermal treatment of paddy grains before milling to increase milling recovery (Sareepuang et al., 2008). It involves three major steps, soaking, steaming and drying. Soaking is to increase the moisture content from 14% (Wb) to 30% (Wb) before steaming. 86

2 Steaming is done thereafter to gelatinize starch and to increase moisture content to 38% (Wb). Many physiochemical changes are taken place during steaming, which make the grains suitable for energy efficient milling. Drying is one of the challenging tasks to perform as it influences grain quality after milling. Drying is to reduce the moisture content from 38 % (Wb) to 14% (Wb) before milling (Navarro and Noyes, 2010). Quick drying is not preferred for quality milled rice as it cripples its physical properties (Wimberly, 1983). Drying is done in two stages. Stage one is to reduce moisture content from 38% (Wb) to 18% (Wb), whereas second stage is to reduce moisture content from 18% (Wb) to 14% (Wb) (Jittanit, 2007). First stage is quick and second stage is relatively slow because of the reduced moisture gradient. The drying process should be stopped at about 18% (Wb) moisture to allow the paddy to temper or equalize for several hours before continuing the drying to 14%(Wb) (Wimberly, 1983). There are different types of drying methods available for paddy grains, out of which sun drying is commonly used. Sun drying works well in the dry season when it takes about 24 hours to get the moisture content of rice down to 14% (Wb) (Patil, 2011). During cloudy weather, drying takes 48 hours to reach desired moisture content. Therefore, delayed drying, in the wet season, causes falling in grain value by between 5% and 58% (Wimberly, 1983). However, based on air flow rate and velocity, rest of the water is taken out from grains gradually to reach desired moisture content which is essential for energy efficient milling (Wimberly, 1983).Sun drying has been practiced by processers in Sri Lanka for long period of time, where paddy grains are spread on cement floors to remove the moisture. However, large number of workers is needed to constantly turn and mix the paddy to achieve rapid and uniform drying. It requires capital investment in land and water proof roofing. It further leads to unwanted losses of paddy grains by rodents and birds (Wimberly, 1983). Different types of dryers are commonly used for drying. However, they have their own specifications. Number of modifications has been made in the drying chamber to make drying process effective to get optimum milling recovery (Wimberly, 1983). It is obvious that few mills located in 87

3 northern Sri Lanka use artificial dryers for drying paddy since dryers are very expensive and it requires skill operator for handling. Further, durability of such dryers are not up to the standard. It is therefore important to design a simple up-draught hot air dryer to overcome these consequences. Hence, an attempt has been taken to develop such dryer driven by an energy recovered from burning of paddy husk with an objective of achieving quick and uniform during of paddy to save energy and time during parboiling. Materials and Methods 2.1: Design of dryer The up-draught hot air dryer was designed with two major units namely drying cylinder and gasification unit for energy recovery from paddy husk. Two drying cylinders, inner and outer, were made by metal sheets, wire mesh and metal bars. Number of accessories such as regulatory valve, lid with rotary distributor sieve, exhaust fan, air distribution nozzles and heating system were connected to drying cylinder for easy operation. Two different types of inner cylinder, T 1 and T 2, were fabricated using metal nets for this experiment. Many machine operations were incorporated to mantle this dryer. Gasification unit was built by bricks and clay. It was fitted with the blower for efficient burning. Specifications of drying cylinder and gasification unit are represented in the table below. Table 1: Gasifier specification Gasifier specifications Item/ Description Specificatio ns Loading capacity of 3 kg gasifier Rice husk 2 kg/hr consumption Air flow rate m 3 /s Heat recovered from gasifier C C Gasifier efficiency 66.67% Surface area of m 2 Heating element Two types of inner cylinders were developed for the experiment as illustrated in Figure: 1 and 2. Such two different types were supported by welded circular frame and vertical iron rods and paddy regulating shapes were covered with the iron wire mesh. These cylinders were placed into outer cylinder for evaluation. Type-1(T 1 ) was designed with three valves for regulating the flow of paddy with a surface are of 3.78 m 2.These valves were placed at 0.3m from one another. Type-2 (T 2 ) was developed with two valves placed at 0.15 m and 0.75 m away from the bottom of the cylinder and surface area was set to be 3.6 m 2. 88

4 0.5m 0.1m 0.25m 1.05m 0.15m Figure 1: Type-1 inner cylinder 0.5m m 0.15m 0.15m 0.05m 0.05m Table 1: Drying cylinder specifications Drying cylinder specifications Loading capacity of 50kg dryer Total drying time per 3hrs batch Initial moisture 35% content Final moisture 15% content Total loading and 5min unloading time of dryer Air drying plenum C temperature Average moisture 8% removal/hr Average ambient temperature C (Jaffna) Initial weight of 50kg paddy before drying Final weight of paddy 42.5kg after drying (85%) 2.2: Sample selection 0.45m Figure 2: Type-2 inner cylinder 0.15m Nadu type long grains of 3 and 6 months of storage and samba type short grains of 3 and 6 months of storage paddy were selected for the experiment. Paddy sample was cleaned before experiment. 89

5 2.3: Experimental setup Experiment was planned to check the performance of the up-draught-hot air dryer. Temperature of 55±3 o C was selected for checking the efficiency of dryer. Paddy husk was burnet inside gasifier to keep such temperature profile. Sensitive thermometer was used to keep such value stable until the end of each trail. Soaking was performed for 12 hours for samba type and 24 hours for nadu type in each treatment to reach desired moisture content for steaming. Water was changed in every 12 hours to avoid fermentation of the nadu and samba type grains. Paddy samples were steamed by laboratory steamer for 45 minutes and dried before milling in both up-draught hot air dryer and sun drying (C) to moisture content of around 14% (Wb).Series of test runs were conducted to determine drying pattern of up-draught-hot air dryer. 2.4: Estimation of moisture content Standard oven dry method was used for the measurement of moisture content. A moisture can in its inverted lid was placed in a thermostatically controlled oven at 130 o C for about 30 minutes. The moisture can and lid were transferred to a desiccator, cooled and weighed. Thoroughly mixed paddy sample of 10 g was accurately weighed by using an electronic balance in previously weighed moisture can. The sample was then placed in an oven at 130 o C and dried for 24 hours (Jindal and Siebenmorgen 1987). After drying the lid was replaced on the can and was transferred to a desiccator and the can was weighed immediately after cooling. This procedure was repeated for each sample. Moisture content was expressed as follows, Moisture content, (Wb) 100 Figure 3: Experimental setup Moisture content gets reduced as drying progresses inside the dryer. Paddy drying is commonly influenced by air properties, grain characters and contact time (Pomeranz, 1976). Moisture reduction of grains dried on two different inner cylinders. T 1, T 2 is not significantly different upto 90 minutes of drying since first stage of drying is quick as of high moisture gradient existing inside the chamber (Pomeranz, 1976). Moisture reduction pattern of 90

6 grains dried in T 1 and T 2 yields significant difference from 18% (Wb) to 14% (Wb) and these values are highly significant compared to control sample. However, drying rate of 6 month storage sample grains is not significantly different at α 0.05 upto the end point. samba grains dried on T 2 and T 1 reach around 15% moisture (Wb) after 150 minutes of drying, whereas moisture content of control sample is around 22% (Wb). Consistent airflow and temperature profile inside the cylinder lead to this quick and uniform removal of moisture from the grains. Many studies prove that air flow and temperature profile influence drying of grains under controlled conditions (Luh and Mickus, 1991). Further, stage two drying (18% Wb to 14%Wb) is quick and uniform in such two different tray arrangements, T 1 and T 2 compared to control condition (Sun drying) and this moisture reduction in paddy grain samples is significantly different from sun dried paddy samples. Contentious airflow inside the dryer leads to this quick and uniform drying of grains. 2.5: Statistical Analysis All the experiments were designed in the Completely Randomized Design (CRD). Obtained data were statistically analyzed using statistical package SAS (Statistical Analysis System) version-9.1. Significance among the treatment was determined by LSD method (P < 0.05). Results and discussion 3.1: Moisture profile of paddy during drying 3.1.1: Moisture content of samba (BG 360) type of six months storage paddy during drying The figure : 4 shows the relationship between the moisture content and drying time of samba type paddy grains of 6 months storage type paddy sample dried in different types of inner cylinder of up-draught hot air dryer. This airflow facilitates favorable moisture gradient for efficient drying (Karel and Heidelbaugh, 1973). 40 Moisture content (Wb)(%) Samba old T2 Samba old C Samba old T Drying time (minutes) Figure 4: Relationship between the moisture content and drying time of samba six months storage paddy grains 91

7 3.1.2: Moisture content of samba (BG 360) type of three months storage paddy grain during drying The figure :5 shows the relationship between the moisture content and drying time of samba type paddy grains of 3 months storage, dried under three different conditions, T 1, T 2 and C. Moisture content of grains is reduced in all three conditions as drying time increases. This reduction is due to the evaporation of free water from the grains. Previous study (Boyce, 1965) revealed that the moisture content of grains is reduced as drying progresses due to the removal of free water from the grain. Difference in moisture reduction between control C and two different inner cylinders, T 1 and T 2 becomes significant after 60 minutes of drying. This difference is due to the two different drying conditions. In sun drying, paddy drying is influenced by number of environmental factors particularly by sun shine intensity (Teter, 1987). Drying would be slow and uniform if sun shine intensity is consistent. In contrast, grains are dried in two different conditions, T 1 and T 2 under control conditions and temperature profile is kept constant at 60 o C throughout drying period with reasonable air flow rate of m 3 /s. These conditions facilitate stage two drying to be uniform and quick. After 90 minutes of drying, moisture reduction of paddy samples dried in conditions, T 1 and T 2 is slightly significant compared to C (sun drying). However, the moisture reduction of samples dried in conditions, T 1 and T 2 is not significantly different (α=5%) from one another. A study revealed that consistent airflow facilitates uniform and quick drying of paddy grains. (Luh and Mickus, 1991). 40 Moisture content (Wb)(%) Samba New T2 Samba New C Samba New T Drying time (minutes) Figure 5: Relationship between the moisture content and drying time of samba three months storage paddy grains. 92

8 3.1.3: Moisture content of nadu (Aaddakkary) type of six months storage paddy grains during drying The figure 6 shows moisture reducing scenario of nadu type of 6 month storage paddy grains dried under three different conditions, T 1, T 2, and C. Moisture content of grains is reduced with drying time. Moisture reduction pattern is different for T 1, T 2, and C. Previous study revealed that air conditions specially RH and temperature and grain characteristics influence grain drying rate (Babalis and Belessiotis, 2004; Luh and Mickus, 1991). Moisture reduction becomes gradual in grain samples dried under condition, C. However, reduction rate under conditions, T 1 and T 2 is greater than the condition, C. Grains dried under conditions T 1 and T 2 have moisture content of around 15% after 150 minutes of drying whereas, grains dried under condition, C have moisture content of 25% which is highly significant to the final value of moisture reached in conditions T 1 and T 2 at α=0.05%. It is important to note that moisture reduction on paddy samples dried in conditions T 1 and T 2 is significant from each other at 90 minutes of drying because of high reduction of moisture in T 2 at that point. Further, sun drying is influenced by continues shaking during drying (Imoudu and Olufayo, 2000). Recent study revealed that removal of evaporated moisture from the chamber facilitates drying (Soponronnarit et al., 2006). Quick and uniform drying is due to the removal of evaporated moisture by moving air and consistent temperature profile (Tirawanichakul et al., 2009). 40 Moisture content (Wb)(%) Nadu Old T2 Nadu Old C Nadu Old T Drying time (minutes) Figure 6: Relationship between the moisture content and drying time of nadu type of six months storage paddy grains 93

9 3.1.4: Moisture content of nadu (Addakkary) type of three months storage paddy during drying The figure 7 shows the relationship between the moisture content and drying time of paddy grains of 3 months storage dried under three different conditions, T 1, T 2 and C. Moisture reduction rate of samples dried in condition C is lower than the samples dried in conditions T 1 and T 2. However, moisture reduction becomes significant for the samples dried in conditions; T 1 and T 2 compared to the condition, C. Conditions T 1, T 2 and C reach moisture contents of 15.5%, 17% and 27% respectively after 150 minutes of drying. Moisture content of grains dried under conditions T 1 and T 2 is highly significant at the end compared to the condition, C. However, moisture content of samples dried under conditions T 1 and T 2 are not significantly different from each other. Different inner cylinders have therefore no influence on moisture reduction of such grains. Previous study on sun drying (Imoudu and Olufayo, 2000) revealed that the drying rate of nadu grains in sun drying is lower than that of artificial dryers because of modified air properties suitable for drying. Figure 7: Relationship between the moisture content and drying time of nadu three months storage paddy grains 94

10 3.1.5: Moisture content of paddy during drying in type-1 of inner cylinder of updraught hot air dryer The figure 8 shows the relationship between the moisture content and drying time of samba type and nadu type paddy grains of 3 or 6 months storage dried in the condition,t 1. Moisture content of all such different grains dried under condition, T 1 is reduced with drying time. Moisture contents of samba type paddy grains of 6 month storage and 3 month storage is 13.5% and 14.5% respectively, after 150 minutes of drying whereas, moisture content of nadu type paddy grains of 3 month storage and 6 months storage is 15.5% and 16% respectively. However, these values are not significantly different from each other at α=0.05%. Moisture reduction rate of all types becomes quick after 60 minutes of drying, as of the heat migration into grains through conduction (Van Xuan et al., 1996). Moisture migration occurs from the center of the grain to the grain surface. As prevalence of consistent airflow, migrated moisture is evaporated quickly and moisture gradient is kept stable until the end of drying. Previous research (Kunze, 2009) revealed that quick and uniform drying of paddy grains has been observed after 30 or 60 minutes of drying due to heat migration and contentious removal of surface moisture.this statement can be taken to support this pattern of drying rate in this experiment 95

11 40 35 Moisture content (Wb)(%) Samba Old Samba New Nadu Old Nadu New Drying time (minutes) Figure 8: Relationships between the moisture content and drying time of paddy samples in T 1 type inner cylinder 3.1.6: Moisture content of paddy during drying in type-2 of inner cylinder of updraught hot air dryer The figure 9 shows the relationship between the moisture content and drying time of samba and nadu type paddy grains of 3 months and 6 months storage dried under condition, T 2. Moisture content of all grains is reduced with drying time. Moisture reduction rate of samba grains of 3 months and 6 months storage is different from that of nadu grains. This is obvious that moisture removal from grain is influenced by dryer properties and grain characters since these two types of grains have different chemical composition, surface area, thickness of bran layer and husk layer and thermal conductivity values, heat migration is influenced from one point to another point inside grains (Prakash, 2011). As heat transfer is deferred, drying rate is also not consistent. Previous study revealed that this heat migration is influenced by grains properties (Ng et al., 2005). This statement can be taken for supporting different removal rates for different grains. However, storage may lead to some chemical and enzymatic changes and influence available moisture in the grains. This may also influence the drying rate. It is reported that the storage has made number of changes in the grains itself (Houston et al., 1970). As of different conditions, moisture migration is influenced during drying. However, final moisture content of nadu grains is greater than samba grains after 150 minutes of drying as they have thin bran and husk layer compared to nadu grains. These thin layers facilitate moisture removal quickly compared to nadu grains. 96

12 40 35 Moisture content (Wb)(%) Samba Old Samba New Nadu Old Nadu New Drying time (minutes) Figure 9: Relationships between the moisture content and drying time of paddy sample in T 2 type inner cylinder Table 3: Mean Final moisture content of paddy sample in different types of treatments Final moisture content in drying (%) Treatment Means of final moisture content (%) Type 1 cylinder samba 6 month 13.50±0.48 f storage Type 1 cylinder samba 3 month 14.50±0.48 e storage Type 1 cylinder nadu 6 month storage 16.25±0.50 b,c Type 1 cylinder nadu 3 month storage 15.50±0.48 c, d Type 2 cylinder samba 6 month 14.50±0.48 e storage Type 2 cylinder samba 3 month 15.25±0.50 d, e storage Type 2 cylinder nadu 6 month storage 16.50±0.48 a, b Type 2 cylinder nadu 3 month storage 17.25± 0.50 a *All the values from mean of four replicates Values having same letter in are not significantly different according to the least significant mean separation at.05 α and 95 % confidence interval. 97

13 The above table shows the ANOVA of for mean. Final moisture content of paddy samples in different treatment combination. Mean with sample better significant difference at α=0.05%. Whereas nears with same letter indicate no significant different at α=0.05%. Whereas nears with different letter indicate significant different at α=0.05%. Conclusions Moisture reduction rate of samba type and nadu type grains of 3 and 6 months storage dried under conditions T 1, T 2 is significantly different from C. Final moisture content of samba type paddy grains of 3 and 6 months storage dried under condition, T 1 is significantly different from each other. Further, final moisture content of nadu grains of 3 and 6 months storage dried under condition, T 1 is also significantly different from each other and compared to control as well. Final moisture content of samba and nadu types of paddy grains of 3 and 6 months storage dried under condition, T 1, is significantly different from each other and compared to control, C too. Acknowledgement Authors are indeed grateful to acknowledge the financial support provided by Council for Agriculture Research Policy (CARP),Sir Lanka for the successful completion of this research work. References Babalis, S.J., Belessiotis, V.G., Influence of the drying conditions on the drying constants and moisture diffusivity during the thin-layer drying of figs. Journal of food Engineering 65, Boyce, D., Grain moisture and temperature changes with position and time during through drying. Journal of agricultural engineering research 10, Houston, D.F., Houston, D.F., Kohler, G., Nutritional properties of rice. National Academies. Imoudu, P.B., Olufayo, A., The effect of sun-drying on milling yield and quality of rice. Bioresource technology 74, Jittanit, W., Modelling of seed drying using a two-stage drying concept. Ph. D. Thesis. The University of New South Wales. Sydney, Australia. Karel, M., Heidelbaugh, N.D., Recent research and development in the field of lowmoisture and intermediate-moisture foods. Critical Reviews in Food Science and Nutrition 3, Kunze, O.R., Effect of Drying on Grain Quality--Moisture Readsorption Causes Fissured Rice Grains. Agricultural Engineering International: CIGR Journal. 98

14 Luh, B.S., Mickus, R.R., Parboiled rice, Rice. Springer, pp Navarro, S., Noyes, R.T., The mechanics and physics of modern grain aeration management. CRC press. Ng, P., Law, C., Tasirin, S., Daud, W., Drying characteristics of Malaysian paddy: Kinetics and grain cracking quality. Drying technology 23, Patil, R., Post-Harvest Technology of Rice. Central Institute of Post Harvest Engineering and Technology, Punjab Agriculture University, Ludhiana (India). Rice Knowledge Management Portal: Directorate of Rice Research. Karel, M., Heidelbaugh, N.D., Recent research and development in the Pomeranz, Y., Scanning electron microscopy in food science and technology. Adv. Food Res 22, Prakash, B., Mathematical modeling of moisture movement within a rice kernel during convective and infrared drying. University of California, Davis. Soponronnarit, S., Prachayawarakorn, S., Rordprapat, W., Nathakaranakule, A., Tia, W., A superheated-steam fluidized-bed dryer for parboiled rice: Testing of a pilot-scale and mathematical model development. Drying technology 24, Teter, N., Paddy drying manual. Food and Agriculture Org. Tirawanichakul, S., Prachayawarakorn, S., Varanyanond, W., Soponronnarit, S., Drying strategies for fluidized-bed drying of paddy. International Journal of Food Engineering 5. Van Xuan, N., Vinh, T., Anh, P.T., Hien, P.H., Development of Rice-husk Furnaces for Grain Drying, Aciar Proceedings, pp Wimberly, J.E., Technical handbook for the paddy rice postharvest industry in developing countries. Int. Rice Res. Inst. Sareepuang, K., Siriamornpun, S., Wiset, L., Meeso, N., Effect of soaking temperature on physical, chemical and cooking properties of parboiled fragrant rice. World Journal of Agricultural Sciences 4,