ENERGY REQUIREMENTS FOR DRYING LARGE ROUND BALES

Uniform density and softcore large round forage bales were dried under a variety of airflow and temperature regimes. The energy required to operate the fans and heaters was measured as the bales dried to an average final moisture content of 18 percent, wet basis. The energy requirement for drying both types of bales was found to be 33 kWh/tonne dry matter/moisture point reduction.

The soft-core bales tended to dry at a faster rate than the uniform density bales. Also, the final moisture content variation within the softcore bales was less than that within uniform density bales.     

COMPARISON Of STRATEGIES FOR AMBIENT-AIR DRYING OF LARGE ROUND BALES

A comparison of the drying efficacy of ambient-air drying of large forage bales was made between positive and negative pressure systems. Both systems effectively dried the bales to the desired average moisture content, but regions of higher moisture content within the bales were measured with the two systems. Energy consumption as expressed as the ratio of the energy consumed/weight of moisture removed was similar for both drying systems. Final configuration of the drying system will depend on whether heat is required to speed the drying process in order to meet the capacity of the harvesting system.     

COMPARISON Of STRATEGIES FOR AMBIENT-AIR DRYING OF LARGE ROUND BALES

ABSTRACT

A comparison of the drying efficacy of ambient-air drying of large forage bales was made between positive and negative pressure systems. Both systems effectively dried the bales to the desired average moisture content, but regions of higher moisture content within the bales were measured with the two systems. Energy consumption as expressed as the ratio of the energy consumed/weight of moisture removed was similar for both drying systems. Final configuration of the drying system will depend on whether heat is required to speed the drying process in order to meet the capacity of the harvesting system.     

Kiln-drying optimization for quality pacific coast hemlock timber

The pacific coast hemlock or “hem-fir” is a dominant species mix in British Columbia that is difficult to kiln-dry; hence, many mills are quite conservative with their drying schedules. Furthermore, mills tend to dry hem-fir with no green moisture content presorting, thus promoting high moisture differences within and between dried timbers. In this study, application of green chain moisture-based sorting, coupled with a modified drying schedule, was considered to be a potential way to improve drying times, moisture content spreads, and lumber quality. Modified schedules coupled to three-group green moisture content presorting, i.e., mixed, low, and high, were compared to a standard industrial one. To evaluate the process and product quality, final moisture content variation between and within lumbers, drying rates, warp, surface and internal checks, shrinkage, and casehardening were assessed. Data analysis revealed that there was no significant difference between the drying runs in terms of final moisture content variation, except in the high initial moisture content group. In regard to the sorting, high initial moisture content sorting helped to reduce the final moisture content variation. In particular, the modified schedule, when there was a high initial moisture content sorting, did improve the uniformity of final moisture content in comparison to the industrial one.     

An optimal operational strategy for wood in batch drying system

A complete model based on the wood drying mechanism and incorporating a multi-period operation was established for wood in batch drying systems. Both energy savings and improvement of wood quality were obtained by an optimal strategy proposed in this study. Energy saving was indicated by the numerical results to be roughly 22.5% for drying of soft wood under the conditions of a given drying time and final moisture content. The gradient of moisture content within the dried wood could be minimized for the sake of enhancing the quality of wood by applying the proposed operational model.     

EFFECT OF DRYING METHOD ON SHRINKAGE AND POROSITY

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density p_w, the dry solid density p_s, the dry solid bulk density p_bo and the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.     

COMPARISON OF DRYING LARGE ROUND BALES BY ALTERNATE AIR CONDITIONING METHODS

A comparison was made between alternate air conditioning methods used to dry large round forage bales. Energy consumption durin drying and the final nutritional qualit of the bales were measured durin ti% study. The methods used to increase tge drying potential of the air incfuded using a desiccant to dehumidify the drying air; a gasoline engine to drive the fan and heat the drying air and the use of direct electric heat to increase the temperature of the dr ing air.

The results from the study indicate that the energy consumption was least with the use of a desiccant but the regeneration ma only be economically feasible where waste heat is available to provide tKe enery The gasoline engine was less efficient than the application of electric;. No difference in the nutritional quality of the forage due to heat damage during the drying process was noted.     

Dehydration of Concentrated Ganoderma lucidum Extraction by Combined Microwave-Vacuum and Conventional Vacuum Drying

Combination of microwave-vacuum drying and conventional vacuum drying was investigated as a potential method for drying concentrated Ganoderma lucidum extraction. The Ganoderma lucidum was extracted by hot water (60-65°C) and then concentrated to moisture of about 70% (wet basis) in a rising-film evaporator. The concentrated sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional vacuum drying at the temperature of 55-60°C to final moisture content about 6% (wet basis). The retention of polysaccharide and triterpenes of Ganoderma lucidum dried by this method were evaluated and compared with those dried by freeze drying and conventional vacuum drying alone. The comparison showed that the quality of extraction dried by the current method was close to that of freeze-dried extraction and much better than that of conventional vacuum-dried ones.     

Analysis of the drying process of a biopolymer (poly-hydroxybutyrate) in rotating-pulsed fluidized bed

A rotating-pulsed fluidized bed (RPFB) dryer was employed to conduct the drying of poly-hydroxybutyrate (PHB) cohesive granules. Along the experiments, it was possible to identify, visually, 3 different dynamic regimes that were related with the temperature profile, the drying kinetics and the fluid dynamic behavior. The drying kinetics of PHB showed a short constant drying rate period followed by a decreasing drying rate period. The constant drying rate (N_c) and final moisture content (dry basis) were related to the rotation frequency (responsible for the pulsation effect), temperature and velocity of the inlet air. Furthermore, measurements of molecular mass (gel permeation chromatography analysis) and Carr Index (flowability test) on PHB samples were done before and after the drying. The RPFB dryer showed to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamic behavior that provided uniform drying of the solid. The best conditions of drying were identified at 7 Hz of rotation frequency, 90 °C and 0.55 m/s of inlet air temperature and velocity. At these conditions the dried PHB reached final moisture content of 0.56% (wet basis) after 2 h of drying.     

Drying Characteristics of Thick Lumber in a Laboratory Radio-Frequeocy/Vacuum Dryer

ABSTRACT

A series of forty two drying runs of two wood species and two cross-sectional dimensions of wood squares were carried out in a laboratory radio-frequency/vacuum (RF/V) dryer. The experimental temperature, pressure and moisture content levels as functions of space and time are presented. The results showed that western red cedar and western hemlock can be dried to a final moisture content of 15% in about 24 and 32 hours, respectively. The quality of the dried specimens was exceptional- Detailed analysis revealed the absence of internal drying stresses, internal and external checking and surface discoloration. Furthermore, evaluation of moisture content distribution in the longitudinal and transverse direction showed minimum variation compared to conventional kiln drying. The experiments also revealed that RF/V drying rates are directly affected by the level of the electrode plate voltage. Drying rates decreased with time when the voltage remained constant throughout the drying cycle thus resulting in long drying times. That was because of the changing dielectric properties of wood due to moisture content reduction during drying. Raising the voltages with time though, resulted in constant drying rates and shorter diying times.     

EXPERIMENTAL INVESTIGATION ON SOLAR DRYING OF FISH USING SOLAR TUNNEL DRYER

This paper presents field level performance of the solar tunnel dryer for drying of fish. The dryer consists of a transparent plastic covered flat plate collector and a drying tunnel connected in series to supply hot air directly into the drying tunnel using four d.c. fans, operated by two 40 watt solar modules. This dryer can be used to dry upto 150 kg of fish and three sets of full scale field level drying runs for drying silver jew (Johnius argentatus) fish were conducted in February-March, 1999. The temperature of the drying air at the collector outlet varied from 35.1 ° C to 52.2 ° C during drying. The fish was initially treated with dry salt and stacked for about 16 hours before drying. The salt treated fish was dried to a moisture content of 16.78% (w.b.) from 67% (w.b.) in 5 days of drying in solar tunnel dryer as compared to 5 days of drying in the traditional method for comparable samples to a final moisture content of 32.84%. In addtion, the fish dried in the solar tunnel dryer was completely protected from rain, insects and dust, and the dried fish was a high quality product.     

Operating Conditions for Drying Paddy in a Rotating Drum with Sand Medium

ABSTRACT

Batches of wddv rewened to 18% or 24% moisture content were dried in a sealed rotating drum containing ; preheated sand. For each initial moisture content, all combinations of the following variables were replicated three times: sand patilcle size (0.3 and 0.6mm). residence time (60, 120 and 180 s), sand-to-grain mass ration ( 3:1, 6:1 and 9:1) and initial sand temperture ( 100, 150 and 200°). The dried paddy was shelled and milled and the percentage of whole grain kernels was determined. In general. the paddy starting at 18% mc led to lower final moisture contents than that starting at 24%. For equivalent final moisture contents, milling yields of whole rice were equivalent. Best yields were generally associated with lower energy input (ie. low to intermediate initial sand temperature and sand-to-grain mass ratios below 4.7:1) Residence time was not critical in determining milling yieid. This study indicates that particulate medium drying of paddy is an interesting alternative to traditional drying since it greatly accelerates drying timee without reducing milling yields. Solar preheating of the sand could permit substantial energy savings.     

GROUPING TROPICAL WOOD SPECIES FOR KILN DRYING USING MATHEMATICAL MODELS

Because of the large variety and diffuse occurrence of tropical hardwood species in the forest, an efficient method to kiln dry these hardwoods in groups is needed. However, tropical hardwoods have a wide variety of drying properties, which makes drying mixtures of species difficult. This paper describes a mathematical model for grouping species by similar drying times. Our goal is to kiln dry so that all species emerge at the same time within set limits of moisture content. The model, which uses previously reported data, incorporates specific gravity, initial moisture content, and thickness as criteria for grouping species based on estimated drying time. The model can be used to calculate drying times and moisture content distributions within multiple-step kiln schedules, followed by calculations to equalize all members of the mixture within final moisture content specifications. The model can also be used to base grouping on green weight density, thus eliminating the need for direct information on specific gravity and initial moisture content. Plans are to evaluate the dry-kiln grouping system in field tests.     

Variation in Drying Behavior and Final Moisture Content of Wood during Conventional Low Temperature Drying and Vacuum Drying of Betula pendula Timber

Conventional and vacuum drying experiments were conducted on Betula pendula timber, which was sawn from trees felled during three different seasons. The influence of the wood procurement season on drying behavior differed, on the one hand, between the drying phases above and below 30% moisture content in the conventional drying, and, on the other hand, between the conventional and vacuum drying methods. During the first steps of the conventional drying process, relative humidity in the kiln, as well as drying time and drying rate, varied according to the felling season. Variations in environmental conditions outside the kiln and the seasonal variation in the physical properties of the wood were presumed to be the reasons for differences in drying behavior. The difference in moisture content gradient, i.e., the difference in final moisture content between the inner wood and the surface layer of boards, was greater in conventionally dried timber than in vacuum-dried timber. In conventionally dried timber there was a clear seasonal variation in the gradient of final moisture content, which was greatest for winter-felled wood. The premature drying of the surface layer during the first steps of the conventional drying process of winter-felled wood was the reason for the higher gradient of moisture content. Storage of wood as logs decreased the standard deviation of the final moisture content.     

Modeling of Diffusion with Shrinkage and Quality Investigation of Banana Foam Mat Drying

A diffusion model including shrinkage has been developed for predicting the change of moisture content in banana foam mats during drying. Two solution methods, moving boundary using variable grid and immobilizing boundary using the Lagrangian referential coordinate, were used in exploring their capabilities to predict the moisture change. Banana foam mats with initial foam densities of 0.3, 0.5, and 0.7 g/cm³ were dried at 60, 70, and 80°C and superficial air velocity of 0.5 m/s. The qualities of the final products in terms of texture and microstructure were determined. The moving boundary method can predict the moisture content more accurately than the immobilizing boundary method especially in the case of low-density foam. The quality determinations showed that the initial foam density strongly affected hardness, crispness, and morphology of dried banana foam mats, whereas the drying temperature had no significant effect on those qualities.     

GROUPING TROPICAL WOOD SPECIES FOR KILN DRYING USING MATHEMATICAL MODELS

ABSTRACT

Because of the large variety and diffuse occurrence of tropical hardwood species in the forest, an efficient method to kiln dry these hardwoods in groups is needed. However, tropical hardwoods have a wide variety of drying properties, which makes drying mixtures of species difficult. This paper describes a mathematical model for grouping species by similar drying times. Our goal is to kiln dry so that all species emerge at the same time within set limits of moisture content. The model, which uses previously reported data, incorporates specific gravity, initial moisture content, and thickness as criteria for grouping species based on estimated drying time. The model can be used to calculate drying times and moisture content distributions within multiple-step kiln schedules, followed by calculations to equalize all members of the mixture within final moisture content specifications. The model can also be used to base grouping on green weight density, thus eliminating the need for direct information on specific gravity and initial moisture content. Plans are to evaluate the dry-kiln grouping system in field tests.     

Dehydration of Garlic Slices by Combined Microwave-Vacuum and Air Drying

Combination of microwave-vacuum drying and air drying was investigated as a potential mean for drying garlic slices. The sample was dried by microwave-vacuum until the moisture content reached 10% (wet basis), and then by conventional hot-air drying at the temperature of 45°C to final moisture content less than 5% (wet basis). Pungency, color, texture, and rehydration ratio of garlic slices dried by this method were evaluated and compared with those dried by freeze drying and conventional hot-air drying. The comparison showed that the quality of garlic slices dried by the current method was close to that of freeze dried garlic slices and much better than that of conventional hot-air dried ones. The lab microwave-vacuum dryer which the materials to be dried could be rotated in the cavity was developed by the authors.     

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

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, 10-15 °C temperature rise above ambit was obtained during peak bright sunshine hours. Relatively high daily average collector Effciency of 76%, high drying effectiveness, drying uniformity, uniform air distribution and tight sealing of the stack were achieved which resulted in an attractive green color of hay, no mold growth on hay, and an overall system drying efficiency of about 79%. Compared to a conventional natural gas drying system or field-drying method, the payback period on extra investment costs recovered through drying cost savings of $3/ t to $6/ t or through over two times higher prices for high-quality hay produced by the solar drying system may be just one or two years, respectively.     

Impact of ammonia fiber expansion (AFEX) pretreatment on energy consumption during drying,grinding, and pelletization of corn stover

Pretreatment and densification of biomass can increase the viability of bioenergy production by providing a feedstock that is readily hydrolyzed and able to be transported over greater distances. Ammonia fiber expansion (AFEX?) is one such method targeted for use at distributed depots to create a value-added and densified feedstock for bioenergy use. However, the pretreatment process results in a high-moisture material that must be dried, further size reduced, and pelletized, all of which are energy-intensive processes. This work quantifies the energy consumption required to dry, grind, and densify AFEX-pretreated corn stover compared to non-pretreated stover and explores the potential of reduced drying as a means to conserve energy. The purpose of this work is to understand whether material property changes resulting from AFEX pretreatment influence the material performance in downstream formatting operations. Material properties, heat balance equations, and a rotary drum dryer model were used to model a commercial-scale rotary drum dryer for AFEX-pretreated corn stover, showing the potential to reduce dryer energy consumption by up to 36% compared to non-pretreated corn stover. Laboratory-measured grinding and pelleting energies were both very sensitive to material moisture content. Overall, the total energy required for drying, grinding, and pelleting amounts to a savings of up to 23 kWh/dry Mg for the AFEX-pretreated material when dried to a low moisture content, equating to up to 0.61 $/Mg savings for gas and electricity. Grinding and pelleting of high-moisture AFEX-pretreated stover was shown to be more costlier than the savings collected through reduced drying. Although the energy and cost savings shown here are modest, the results help to highlight operational challenges and opportunities for continued improvement.     

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, 10-15 °C temperature rise above ambit was obtained during peak bright sunshine hours. Relatively high daily average collector Effciency of 76%, high drying effectiveness, drying uniformity, uniform air distribution and tight sealing of the stack were achieved which resulted in an attractive green color of hay, no mold growth on hay, and an overall system drying efficiency of about 79%. Compared to a conventional natural gas drying system or field-drying method, the payback period on extra investment costs recovered through drying cost savings of $3/ t to $6/ t or through over two times higher prices for high-quality hay produced by the solar drying system may be just one or two years, respectively.