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  1. 1. International Journal of Advanced Research in Engineering RESEARCH IN ENGINEERING INTERNATIONAL JOURNAL OF ADVANCED and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online)TECHNOLOGY (IJARET) AND Volume 4, Issue 7, November – December (2013), © IAEME IJARET ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 4, Issue 7, November - December 2013, pp. 228-235 © IAEME: Journal Impact Factor (2013): 5.8376 (Calculated by GISI) ©IAEME AMELIORATING THE ENERGY PERFORMANCE OF ELECTRIC DRYER FOR AGRO-FOOD PRODUCT. CASE STUDY: THE DRYER OF THE TRANSFORMATION UNIT FOR CASSAVA AT POUMA IN CAMEROON Abraham Kanmognea*, Yves Jannotb, Jean Nganhoua a b Laboratoire d’Energétique, ENSP, BP 8390 Yaoundé, Cameroun LEMTA, Nancy-Université, CNRS, 2, avenue de la Forêt de Haye, BP 160, 54504 Vandoeuvre Cedex, France SUMMARY In this article, we-have carried out the power control of a dryer, all which uses forced air circulation, imported from Ghana and installed in Pouma for drying cassava in Cameroon. The performance of the dryer does not meet up with the expected needs. This power control has made us detect the causes of a high power consumption rate of the dryer and therefore carry out by changes to Obtain Optimal Functioning year; we-have added a scythe of ceiling, blown out Mittal heating resistors, changed air ventilation turbines, Multiplied and Uniformly Redistributed sections for the heated air passages in the dryer. We have identified the different dead zones in the dryer. The changes made on the dryer-have led to a reduction in power control of about 20%. Keywords: Power Control, Dryer, Energy Savings, Cassava, Cameroon. 1. INTRODUCTION Agriculture occupies a prominent place in the economy of African countries, particularly in the tropics south of the Sahara. It contributes nearly 80% to exports and employs about 70% of the population [1]. Agricultural production are often characterized by the temporal surplus crops, the development of appropriate techniques can allow conservation to reduce post-harvest losses. Drying, being the oldest conservation methods one of the most appropriate techniques. However, drying problems are numerous and do not seem to be resolved despite the transfer of efficient technologies. The mastery and analysis of the operation of the drying technology can lead to reduced operating costs of exploitation by reducing its energy consumption. A study was conducted on an electric dryer belonging to a Cameroonian NGO, the AID-Cameroon in its processing cassava plant. Pouma, geographic coordinates latitude 3° 51 'north and longitude 10 ° 31 ' east [2], a locality in the Littoral region on the Yaoundé-Douala main road 150 km from Yaoundé. The objective in this work 228
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME is to modify the electric dryer to address the various causes of malfunctioning registered so as to improve energy efficiency and reduce the drying time. To attain our goal, we have assumed that the mode of fresh and warm air circulation in a dryer, hot and fresh air flow in the drying channel all influence the energy consumption of a dryer, and even on the reduction of the drying cost. An energy audit of the dryer was conducted to determine the causes of excessive consumption and measures prescribed have been implemented to increase the energy performance of the dryer and reduce drying time. 2. MATERIALS AND METHODS 2.1. Technical equipment 2.1.1 Dryer The dryer at the cassava processing unit (UTM) Pouma is the electric type with internal dimensions 3.7 m long; 1.6 m wide and 1.85 m in height [3] (cf. Figure 1). Figure 1: Drawings of the electric dryer of the Cassava Processing unit (UTM) Pouma 229
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME The side and top walls are made of two steel plates separated by the glass wool used for thermal insulation. The floor of the drier consists of a steel sheet resting on the rafters. The circulation of air in the dryer is provided by two centrifugal fans. The motors are attached to the outside on the roof of the dryer. The turbines of the motor-fans are coupled to the engines and are positioned inside the dryer at about 15 cm from the ceiling. Turbines take in air through the drying chamber and propel the air into a 25 cm wide space between one side of the wall and a plate arranged parallel to it. In this space are arranged 30 regularly spaced electrical resistors in the direction of the length of unit power 1.7 kilowatts. The electrical supply to these resistors is controlled in all or nothing law by an adjustable thermostat connected to a temperature probe placed inside the dryer. The thermostat cuts off the power supply of the resistors when the temperature inside the dryer has reached the required temperature set-point. Four vertical slits each of 2 cm width formed in the sheet allow the entry of hot air heated by the resistors inside the dryer. Two holes of diameter 9 cm on the roof of the dryer ensure the intake of the new air into the dryer. Two other openings 15 cm in diameter located just above the air outlet of the centrifugal fan permit the extraction of moist air from the dryer. Be it at the intake or extraction port, air flow is manually adjustable through a butterfly valve mounted in the holes. When opened, part of the exterior air enters the dryer (Case of the intake valve) through the inlet opening or a portion of the interior moist air leaves the dryer (case of the extraction valve) through the extraction port. The degree of valve opening is adjustable manually by means of a command stem. 2.1.2. Trolleys and Grid In the dryer, cassava is arranged on grids carried by trolleys. The dryer can hold 10 trolleys with 3 of 14 grids and 7 of 11 grids. The average dimensions of the grids are 0.6 m wide and 0.75 m long, giving a total area of the drying grid of 53.5 m 2 for 119 grids. The grids are made up of thick mesh (expanded metal) and their frames are made of angles 3 cm tile-gutters. On the thick mesh is a plastic mosquito netting on which is placed the cassava to be dried. The frame of the mosquito netting is made of white wooden that can slide within the frame bracket allowing loading and unloading of the material to be dried. Trolleys are made of tile-gutter of 4 cm. The medium size of each carriage is of width 0.7 m , 0.8 m in length and 1.5 m in height. On a carriage, the grids are placed one above the other at 14 or 11 per trolley. 2.2. Measuring equipment The measuring equipment consists of : − A thermo anemometer of the Testo brand for measuring the velocity of the air through the slits 2 cm in the dryer ; − A digital thermo hygrometer for measuring the air humidity and the temperature in the dryer ; − An electronic scale for measuring the weight of the product ; − A ventilated oven [4] to determine the water content of the lumped cassava ; − A tape measure for different measurements relating to the dryer [5]; − An electronic timer to measure the dryer’s operating time; − An energy meter for measuring the electric power consumption of the dryer ; − A digital multi-meter. 2.3. Method Before changing the dryer, vacuum and load tests of the dryer has been made. Careful inspection and a number of measurements were carried out on the dryer : 230
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Dryer off The 30 resistors heaters were dismantled and the values of their electrical resistance were verified using the digital multi-meter. The different compartments of the dryer (control table, drying chamber, trolley and grid) were inspected. Dryer running and empty The thermostat is set to a fixed temperature above the ambient temperature. Both fan motors rotate, using the thermo anemometer, we measured the temperature at different points within the dryer and the hot airflow over the four slots at 3 mid-planes; 0.35 m, 0.9 m and 1.50 m from the ceiling of the dryer. The thermostat was then set to a temperature below room temperature. Both fan engines were functional and we noted the indicator of the time and energy counter of the fans, using an electronic timer. Dryer running and loaded with cassava The exhaust air valves are set at a given position. Lumped Cassava is loaded on the grid with the cup. The weight of the lumped cassava is measured in advance by using the electronic balance. The racks are always loaded on carriages which are introduced into the dryer. Using a hygrometer, the humidity of the air at the outlet of the extraction orifice is measured at predetermined time intervals. The ambient temperature is measured using the thermo-anemometer. A sample mass of cassava is weighed at regular time intervals. At the end of the cycle, the dry mass of the sample is determined using the balance and the ventilated oven. This mass is used to determine the water content of the product. The maximum temperature for drying of the product should be 80°C [6]. Product is dry if the water content on a dry basis is between 0.12 and 0.15. After modifications on the dryer, we repeated the same tests as above when the dryer was running and empty. When the dryer was running and loaded, the only difference was that measurements of the velocity of the air will be made on 12 slots instead of 04 as previously. 3. RESULTS AND DISCUSSIONS 3.1. Energy audit The tests and measurements on the dryer before modification yielded the following results. Of the 30 electrical resistors that provide heat to the air in the dryer we have: − 2 missing ; − 1 is defective ; − 7 are disconnected. It has been proposed to connect the disconnected resistors, replace blown resistors and complete missing resistors. The speeds of the air blown into the dryer were also measured and the average air flow blown into the dryer was evaluated at 2000 m3/h. The performances of the dryer had been limited from the designing by the fact that the heated air was admitted into the dryer by 4 slots of width 2cm disposed over a length of 3.7 m. So there were dead zones between these slots (spaces of 90 cm) where the air velocity was very low. It was proposed to develop other slots to increase the hot air flow to standardize the drying chamber. The spacing of the slots should not exceed 20 cm. The recovery of air blown by the turbines is done at the center of the dryer which means that part of the hot air blown is sucked by the turbine without passing through the product. It has been proposed to find a system that allows us to force the hot air to pass through the entire product before being sucked through the turbines. The solution to fix a false ceiling for channeling hot air on the cassava before being drawn to the side opposite the resistor has been advocated. Following the rupture of the turbine during the startup of the dryer, they were replaced. One of the 2 turbines is smaller than the turbine initially put in place, which provokes falling airflow pulsed through the heaters. It has been 231
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME proposed to replace the two existing turbines by 2 turbines of larger diameters to increase the air velocity in the dryer and overcome losses. The dryer can hold 10 trolleys; only 7 were manufactured. It is essential to make three additional trolleys to occupy the entire dryer and on allowing constant drying, to reduce the thickness of the layer of cassava on each grid. Stocking density of cassava must be between 10 and 11.2 kg/m2, which correspond to a specific surface area of the product between 0.09 and 0.10 m2/kg for good drying results [7]. The optimization of drying of cassava at UTM Pouma consists also to determine the drying channel which ensures minimal energy consumption. To do this, we conducted a series of tests in which we varied the cassava loading density on the grids and the airflow of extracted air in the dryer. Previously, we conducted a series of load tests to determine certain characteristics of the dryer. All these were done after the implementation of the measures recommended by the energy audit. 3. 2. Performance of the modified dryer The measured speeds are speeds of the air which is blown into the chamber through the 14 slots after passing over the heating resistors. We have measured the speed at three heights and varying the positions of the air extraction and intake valves. Figure 2 shows the distribution of an air flow per unit mass in the dryer. 6 Air velocity (m/s) 5 4 3 2 Extraction open 1 Extraction close 0 1 2 3 4 5 6 7 8 9 Slots number 10 11 12 13 14 Figure 2: Distribution of air flow per unit mass in the modified dryer at UTM Pouma The observation of speed profiles shows that in the top of the dryer speeds are very low (1.3 m/s – 1.6m/s) relative to the speed of the medium (2.2 m/s- 3.1 m/s) and those of the bottom of the dryer (2.6 m/s-3.6 m/s) This reveals the existence of a dead zone vis-à-vis these fans that is areas where air velocities are very low. This zone goes from 1.5 m from floor to the ceiling, which means that the load of the product will be limited to 1.5 m from the floor of the drier. Kinetics of drying The drying operation is to extract part of water from a product to obtain at the end of the treatment a solid product of given residual moisture [8]. The drying kinetics are either the variation of water content as a function of time (x = f (t)), or the variation of drying rate as a function of time or of the water content (dX / dt = f (t) or (dX / dt = f (X)). The water contents of the product at the instant t i on dry basis, is determined by relationship : Xi = (m i - Md)/md [9] where mi is the mass 232
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME of the product at time t i and md the mass of the anhydrous product. Figure 3 represents the variation of moisture of cassava for an initial mass of 781 kg and a final weight of 430 kg. Water content(kgeau/kgms) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 5 10 15 Drying time (h) 20 25 30 Figure 3: Variation of the water content during drying 781 kg of cassava with broken clods Heat balance of the dryer The total energy consumed by the dryer is determined by the equation : ET =EV+ER where EV is the energy consumed by fans and ER is the energy consumed by the heating elements. Neglecting the heat losses through the walls of the dryer and assuming that all the energy consumed by the heaters is transformed into heat energy, the transformation efficiency of electrical energy ER to thermal energy is equal to 1. ER is the useful energy for drying. Tests in the modified dryer yielded the results in table 1. Table 1: Energy Performance of modified drying Mass of cassava clods (kg) Mass of dry cassava (kg) Drying time (hours) Energy required (kWh) Loss (energy consumed by fans) kWh 781 430 21 398 78 572 305 18 337 67 425 235 16 306 59 Energy consumption of the modified dryer To assess the thermal consumption of dryers, we define a number of criteria which include the energy consumption per unit mass (ECM) of a dryer which is the amount of heat needed to dry 1 kg of water. For a dryer 3300 kJ/kg of water, ECM ≤ 6500 kJ/kg of water [10]. The ECM of the electric dryer for cassava in Pouma is: 4637 kg/kg of water. This is consistent with the theory for this type of dryer. 233
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Energetic gain of the dryer The useful energy for drying is proportional to the drying time. Figure 4 shows the tonnage of dried cassava with time used to dry for two configurations of the dryer: The original and the modified dryer. 700 Mass of dry cassava (kg) 600 500 400 After Modification Before Modification 300 200 100 0 0 5 10 15 20 Drying time (h) 25 30 35 40 Figure 4: Influence of changes in the dryer on the drying time It appears from the curves of the figure that for the same quantity of cassava with broken clods, the drying time is reduced by about 20% for the modified as compared to the drying time for the initial drying machine. This induces an energy consumption of about 20% less in the modified dryer. 4. CONCLUSION An energy audit of the UTM Pouma dryer was performed to determine deficiencies in the construction and operation of the dryer. The correction of these deficiencies has increased the flow rate per unit mass of drying air in the dryer, ensured uniform distribution of hot air in the dryer, rationalize the use of hot air in the drying chamber and define a dead zone in the dryer area in which we must not place the product to dry. These factors have enabled after comparing the energy performance of the original and the modified dryer to release an energy saving of around 20%. REFERENCES [1] [2] [3] Ahouannou C., 2001. Etude du séchage de produits agroalimentaires tropicaux : application au manioc, gingembre, gombo et piment rouge. Thèse de Doctorat, Université Nationale du Bénin, 219 p. Njomo D., 1986. Contribution de l’énergie solaire au développement des populations rurales du Cameroun. Séminaire international tenu à l’ENSP. Manga M., 1998. Etude du séchoir à manioc de l’UTM de Pouma. Mémoire de fin d’étude d’ingénieur, Ecole Nationale Polytechnique, 50 p. 234
  8. 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Kanmogne A., 2003, Contribution à l’étude du séchage du cacao au Cameroun. Conception, réalisation et modélisation d’un séchoir adapté aux conditions locales. Thèse de Doctorat Ph.D, Université de Yaoundé I, 142 p. Kanmogne A., Jannot T. et Nganhou J., 2012, Description concise et analyse des systèmes utilisées dans la région Sud du Cameroun pour le cacao. Tropicultura, 2012, 30, pp. 94-102. GRET-GERES, 1986, Le point sur le séchage solaire des produits alimentaires. Dossier N° 8, 215 p. Ahouannou C., Jannot Y., Lips B et Lallemand A., 2000. Caractérisation et modélisation du séchage de trois produits tropicaux : manioc, gingembre et gombo. Sciences des aliments, 20(2000) 413-432. J.J. Bimbenet, 1978. Le séchage dans les industries agricoles et alimentaires. Cahier du GIA, SEPAIC, Paris. Jannot Y., Batsale J.C., Ahouannou C., Kanmogne A., Talla A., 2002. Measurement errors processing by covariance analysis for an improved estimation of drying characteristic curue parameters.Drying technology, Vol. 20, N° 10, pp. 1919-1939. Bimbenet J., Duquenoy A., Trystram G., 2002. Génie des procédés alimentaires. Des bases aux applications, Edition DUNOD. Qasim Murtaza, “Simulation of Spray Dryer Chamber by the Standard K-Є, Reliable K-Є and Reynolds Stress Models used in the Production of Thermal Spray Powders”, International Journal of Design and Manufacturing Technology (IJDMT), Volume 1, Issue 1, 2010, pp. 24 - 44, ISSN Print: 0976 – 6995, ISSN Online: 0976 – 7002. Ajeet Kumar Rai, Shahbaz Ahmad and Sarfaraj Ahamad Idrisi, “Design, Fabrication and Heat Transfer Study of Green House Dryer”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 4, 2013, pp. 1 - 7, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. Singh, L.P., Choudhry V. and Upadhyay, R. K., “Drying Characteristics of a Hygroscopic Material in a Fabricated Natural Convective Solar Cabinet Drier”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 299 - 305, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. Phairoach Chunkaew, Aree Achariyaviriya, Siva Achariyaviriya, James C. Moran and Sujinda Sriwattana, “Operating Parameters Effects on Drying Kinetics and Salted Sunflower Seed Quality Utilizing a Fluidized Bed”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 6, 2013, pp. 256 - 268, ISSN Print: 0976-6480, ISSN Online: 0976-6499. 235