E.A. Arinze

Aerodynamic Separation and Fractional Drying of Alfalfa Leaves and Stems—A Review and New Concept

Abstract This article examines the state-of-the art on aerodynamic separation and drying of leaves and stems. Relevant aerodynamic and drying characteristics of alfalfa leaves and stems, important in the design and functional performance evaluation of appropriate drying and separation systems, are presented. General features and design parameters of rotary drum dryers are discussed. A new efficient approach to combined drying and separation in a rotary drum dryer is described in which fresh or pre-wilted alfalfa mixture is dried at a moderate temperature, and in the same operation the dry leaf fraction is aerodynamically separated from the stem fraction. Preliminary test data obtained from the dryer indicated that the separated product stream had comparatively high leaf purity, confirming the feasibility of the new approach.

Design and experimental evaluation of a solar dryer for commercial high-quality hay production

Design, experimental functional performance and economic evaluation of an energy efficient commercial-type solar energy dryer for production of high-quality hay, especially for the export market, are presented. The newly developed solar hay dryer consists of a solar collector with aluminum absorber plate and spaced fins, a drying shed with perforated metal grate floor above the ground level, swing-away plywood frames and polyethylene curtains for effectively sealing the hay stack during drying operations, an insulated duct, and a crawl space below the floor where a 3-hp in-line centrifugal fan is housed for air circulation by suction. In late August and in early September, 1996, 160 small rectangular bales of alfalfa hay with about 25% bromegrass were successfully dried from 33% initial moisture content to 13% moisture and from 25% to 11% moisture in 4 and 3 days, respectively, under average weather conditions in Saskatoon, Canada. The air temperature rise above ambient was 13–15 °C during peak bright sunshine hours in August and 10–13 °C in September. Ambient relative humidities ranged from 30–90%. Unlike field-cured hay, the hay produced by the dryer was of high-quality and remained green in colour and attractive after drying. Compared to field drying or conventional natural gas drying system, the payback period on investment in full-scale solar hay drying system may be just one to two years.

Simulation and optimization of energy systems for in-bin drying of canola grain (rapeseed)

Energy utilization systems optimization and management strategies for in-bin drying of canola were investigated by using a validated computer simulation model and typical weather data for a prairie location in North America. The use of different energy systems, including natural gas, propane, electricity, solar energy, and combined natural gas and solar energy for drying grain within 15 days with airflow rates of 0.5–2 m3/min t, initial grain moisture contents of 13, 16 and 19%, and three harvest dates in August, September and October, was simulated for 10% and 8% moisture contents average-dry and through-dry policies. The drying systems were optimized by considering the total annual cost of a drying system within set bounds of drying time (⪕15 days) and spoilage index (SI < 1.0). Continuous fan operation with 1.5–2 m3/min t ambient air with about 9–26 MJ/t fan energy consumption was required to dry canola grain to 10% and 8% average-dry and through-dry moisture contents in 15 days or less August at 19% initial moisture content or less. Supplemental heat, by raising the ambient temperature by 5–10°C, maintaining the plenum temperature at 20°C and solar heating, must be applied to successfully dry the product in September and October. Solar heating for drying was found to be more cost effective than other supplemental heat systems provided a well designed flat-plate solar collector for air heating can be found for use in locations with good solar energy availability. Heating the drying air with natural gas or propane was the cost effective for situations where the use of conventional energy systems is preferable to renewable energy sources in grain drying operation.

Modeling the Fractional Drying and Aerodynamic Separation of Alfalfa into Leaves and Stems in a Rotary Dryer

A computerized mathematical model was developed to predict fractional drying and aerodynamic separation of alfalfa into leaves and stems in one process in a rotary dryer. Aerodynamic separation was characterized by separation efficiency or the total amount of the desired component (leaf or stem) recovered, relative to the amount entering the process, and by purity of leaf or stem component collected at exit ports of the dryer. The model development assumed 100% separation efficiency and purity. The model was validated by comparing model predicted results with measured experimental and field test data obtained from a small industrial rotary dryer and a full-scale industrial dryer. Changes in leaf, stem, and drying gas moisture contents and temperatures were measured and predicted by the model under various drying conditions. The model-predicted results agreed well with measured data. The model was also used to simulate the performance of industrial rotary dryers under various operating conditions. The model can be used to determine the optimum drying and aerodynamic separation parameters. It can also be used to design and redesign new and existing industrial rotary dryers in order to combine drying and aerodynamic separation into one process.

A dynamic performance simulation model of flat-plate solar collectors for a heat pump system

Abstract Flat-plate collectors are inherently exposed to time-varying meteorological and system parameters. Thus, dynamic modeling, rather than the commonly used steady-state models, is a more accurate approach for the design and performance evaluation of flat-plate solar collectors. The dynamic model presented in this study describes the fluid, plate and cover temperatures of the collector by three different differential equations. Taylor series expansion and the Runge-Kutta method are used in the solution of the differential equations. The accuracy of the dynamic model was tested by comparing the results predicted by the model with experimental performance data obtained for a liquid-cooled flat-plate solar collector with a corrugated transparent fiberglass cover. The predicted results by the dynamic model agreed favorably with the measured experimental data for the flat-plate solar collector. Experimentally determined collector temperatures varied by a maximum of ± 3°C from values predicted by the model. Various changes in meteorological and system parameters were investigated with the model. The model was further used to design a flat-plate collector (generator) for a 1 kW ammonia-water absorption refrigeration system with an ammonia concentration of 30% by weight and fluid inlet temperature of 30°C. Measured experimental results and calculated results by the dynamic model show that the linearized model is an effective design and simulation tool. The dynamic effects of collector performance are well handled by the model. The model is a useful tool in parametric evaluation and design of collectors using various fluids and with various configurations for heat pump systems.

Simulation of natural and solar-heated air hay drying systems

Abstract There is a need for application of artificial drying techniques to reduce the risks of crop spoilage in field-drying of forage crops in the hay-making process in North America. As an important management tool in livestock production in the selection of appropriate drying systems for forage crops, a computer program was therefore developed in this study to simulate the solar-heated and natural air hay drying systems. The computer model was validated by comparing the model predicted results with the experimental data obtained from a batch dryer and field-drying for fresh alfalfa crop. The computer program was also run by using the long-term typical meteorological year data for Saskatoon in Western Canada as input parameters to the program. The simulation model is suitable for use in any other locations where meteorological data are available. Drying curves were produced and the program predicted the drying times for hay of various initial moisture contents when harvested at various times of the year. The effects of insolation, air flow rate, air temperature and humidity, initial moisture content and dry matter density, and stack height of hay on drying times to 18% safe storage moisture content were investigated. Time and fan power savings of about 30% and 45% were achieved by using the solar-heated air drying system as against natural air system in June and August, respectively, for Saskatoon. The significant time savings in using solar-heated air drying systems would mean higher quality of hay produced and less nutrient and yield losses.

Design and experimental evaluation of a new commercial-type mobile solar grain dryer provided with high efficiency fined-plate collector

Design features and experimental functional perforfance evaluation of a new mobile solar grain dryer suitable for commercial applications in the grain-producing areas of the Prairies and other locations in North America are presented. The solar dryer consists of the following main parts: (i) cylindrical metal drying bin with top and bottom cones and aeration facilities, and of capacity up to 90 tonnes of grain, (ii) solar collector mounted on a four-wheel trailer and the collector was provided with specially designed and coated fins attached to the 18 m2 absorber plate, and ultra-violet resistant transparent fiberglss top cover, and (iii) axial-flow fan and insulated flexible ducts for forced air circulation through the solar collector and drying bin. The dryer was evaluated for solar collector collection efficiency, system drying capability, and system drying efficiency.

Development of optimal management schemes for in-bin drying of canola grain (rapeseed)

Abstract As a management tool in grain drying and storage, a computer drying simulation model was developed, validated and used to investigate in-bin drying of canola grain (rapeseed) under typical weather conditions for a Canadian Prairie location. Different drying schemes with airflows of 0.5 to 2 m 3 min −1 per tonne, initial moisture contents of 13%, 16% and 19%, and three harvest dates in August, September and October were optimized by considering the total annual cost of drying for each scheme within set bounds of drying time (30 and 15 days) and grain spoilage. Continuous fan operation delivering an airflow of 1.0 to 2.0 m 3 min −1 per tonne of grain is adequate to successfully dry canola grain in 30 days or less when the initial moisture content of the grain is lower than or equal to 19% in August and September. Drying of grain in October requires supplemental heat. In September and October, however, supplemental heat must be added to air in order to successfully dry the product in 15 days or less. The drying time is about 50% higher when the drying front is allowed to sweep the entire grain bed (through-dry) as compared to drying grain to a bin average moisture content (average-dry). The combined drying cost and the hidden cost of over-drying grain (loss of weight) makes through-drying 30–100% more costly than average-drying. However, for long-term storage of the grain after drying, it is safer to dry all layers of the bin down to 8% through-dry. Small airflow rates of 0.5 m 3 min −1 per tonne show lesser drying costs but the drying time, risk and over-drying costs associated with these low airflow rates are significantly higher than for larger airflow rates. It is therefore, more economical to dry at airflow rate of 1.0–1.5 m 3 min −1 per tonne to minimize time delay in drying and these costs, especially over-drying cost in the through-dry policy. Amongst supplemental heat options, raising the ambient temperature by 5–10°C and maintaining plenum temperature at 20°C ensured complete grain drying in fall and are the most cost-effective schemes.

DESIGN, EXPERIMENTAL AND ECONOMIC EVALUATION OF A COMMERCIAL-TYPE SOLAR DRYER FOR PRODUCTION OF HIGH-QUALITY HAY

Abstract Design features, development, experimental functional performance and economic evaluation of an energy efficient solar energy dryer for commercial production of high-quality hay and processed forage products are presented. The solar hay dryer consists of an improved solar collector with selective coated aluminum absorber plate and spaced fins, and a drying shed connected to the collector by an insulated duct and having a perforated metal grate floor, swing-away plywood frames and polyethylene curtains for effectively sealing the hay stack, and a crawl space below the floor where a 3-hp in-line centrifugal fan is housed for air circulation by suction. In late August and in early September, 1996, 160 small rectangular bales of alfalfa hay with about 25% bromegrass were successfully dried from 33% initial moisture content to 13%, and from 25% to 11% moisture in 4 and 3 days, respectively, under average weather conditions in Saskatoon, Saskatchewan, Canada. With about 18 m3/min per tonne airflow, 10-...

Evaluation of energy conservation potential by exhaust air recirculation for a commercial-type heated-air batch hay dryer

Energy conservation in drying and processing operations is essential in order to improve the reliability of low and moderate temperature renewable energy systems, and to reduce operating costs and energy consumption in systems using high-energy content fossil fuels in farms and processing plants especially in industrialized economies. An experimental evaluation of energy conservation potential by recirculating exhaust air in a commercial heated-air batch hay dryer is presented. The design of the exhaust recirculation unit is such that only about 30% of the total exhaust air is recirculated through the heater inlet. Experimental tests were conducted on the dryer with and without exhaust air recirculation. Maximum energy savings of 27% and 17% were achieved with exhaust air recirculation during fall and summer dryer operation, respectively.