Phani Adapa

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.

PELLETING CHARACTERISTICS OF FRACTIONATED SUN-CURED AND DEHYDRATED ALFALFA GRINDS

A pilot scale pellet mill was used to produce pellets using ground alfalfa leaf and stem fractions. Both sun-cured and dehydrated alfalfa chops were used in the experiments. The moisture content of the sun-cured and dehydrated chops was 8.4% and 9.6% (w.b.), respectively. A stack of two square sieves with different opening sizes and a pan were used to separate leaf and stem fractions. The leaf and stem fractions were further segregated into two sample lots and ground in a hammer mill using screen sizes of 3.20 and 1.98 mm (1/8 and 5/64 in.). The leaf and stem fractions from each sample lot of same grind sizes were combined to get five different samples with leaf contents ranging from 0% to 100% in 25% increments. The moisture contents and temperatures of the samples were raised to 10% to11% (w.b.) and 76.C, respectively, in a double chamber steam conditioner prior to the pelleting operation. The temperature of material was further raised to 95.C in the pellet mill due to the friction between its roller-die assembly. Average particle sizes of sample lots were determined. Temperatures and moisture contents of samples, after various pelleting stages, were recorded. High durability pellets were produced using fractionated sun-cured alfalfa, irrespective of grind size (except for 100% stems, which was low). Durability fluctuated between high and medium range for dehydrated alfalfa (except for 100% stems, which was low). Greener pellets were produced from dehydrated alfalfa, while harder pellets were produced from sun-cured alfalfa.

PERFORMANCE STUDY OF A RE-CIRCULATING CABINET DRYER USING A HOUSEHOLD DEHUMIDIFIER

ABSTRACT The performance and operating characteristics of a low temperature re-circulating cabinet dryer using a dehumidifier loop were studied using alfalfa. Chopped alfalfa, initially at 70% moisture content, was dried to 10% moisture content in the dryer. Two dryer setups were used. The dryers in each case had a partitioned cabinet with trays of material on one side and a stack of one or two small household dehumidifiers on the other side. Air was re-circulated through the material from bottom to the top and back through the dehumidifiers. Two drying configurations were tested. In one, the material was left on the trays until drying was complete (batch or fixed tray drying). In the other configuration, the trays were moved from top to bottom, introducing a new tray at the top while removing an old tray from bottom. Drying air temperature ranged from 25 to 45°C. The average air velocity through the material was 0.38 m/s. Alfalfa chops dried in 5 h in the fixed tray drying and in 4 h in the moving tray drying. The specific moisture extraction rate ranged from 0.35 to 1.02 kg/kWh for batch drying and stayed at an average value of 0.50 kg/kWh for continuous/moving tray drying.

Compression Characteristics of Non-Treated and Steam-exploded Barley, Canola, Oat, and Wheat Straw Grinds

Compaction of low bulk density agricultural biomass is a critical and desirable operation for sustainable and economic availability of feedstock for biofuel industry.A comprehensive study of the compression characteristics (density of pellet and total specific energy required for compression) of ground non-treated and steam-exploded barley, canola, oat, and wheat straw obtained from three hammer mill screen sizes of 6.4, 3.2 and 1.6 mm at 10% moisture content (wb) was conducted. Four preset pressures of 31.6, 63.2, 94.7, and 138.9 MPa were applied using an Instron testing machine to compress samples in a cylindrical die. Ground steam-exploded barley straw at screen sizes of either 3.2 or 1.6 mm produced high density compacts, while ground steam-exploded canola, oat, and wheat straw at screen sizes of 6.4, 3.2 or 1.6 mm produced high density compacts. Steam-exploded barley straw for 3.2 mm at 138.9 MPa produced compacts having 13% higher density and consumed 19% lower total specific energy compared to non-treated straw. Steam-exploded canola straw for 1.6 mm at 138.9 MPa produced compacts having 13% higher density and consumed 22% higher total specific energy compared to non-treated straw. Steam-exploded oat straw for 3.2 mm at 94.7 MPa produced compacts having 19% higher density and consumed 13% higher total specific energy compared to non-treated straw. Steam-exploded wheat straw for 6.4 mm at 138.9 MPa produced compacts having 17% higher density and consumed 17% higher total specific energy compared to non-treated straw. Three compression models, namely: Jones model, Cooper-Eaton model, and Kawakita-Ludde model were considered to determine the pressure-volume and pressure-density relationship of non-treated and steam-exploded straws. Kawakita-Ludde model provided the best fit to the experimental data having R2 values of 0.99 for non-treated straw and 1.00 for steam-exploded biomass samples. The steam-exploded straw had higher porosity than non-treated straw. In addition, the steam-exploded straw was easier to compress since it had lower yield strength or failure stress values compared to non-treated straw.

Biomass Feedstock Pre-Processing – Part 2: Densification

1.1 The need for densification Agricultural biomass residues have the potential for the sustainable production of bio-fuels and to offset greenhouse gas emissions (Campbell et al., 2002; Sokhansanj et al., 2006). Straw from crop production and agricultural residues existing in the waste streams from commercial crop processing plants have little inherent value and have traditionally constituted a disposal problem. In fact, these residues represent an abundant, inexpensive and readily available source of renewable lignocellulosic biomass (Liu et al., 2005). New methodologies need to be developed to process the biomass making it suitable feedstock for bio-fuel production. In addition, some of the barriers in the economic use of agricultural crop residue are the variable quality of the residue, the cost of collection, and problems in transportation and storage (Bowyer and Stockmann, 2001; Sokhansanj et al., 2006). In order to reduce industry’s operational cost as well as to meet the requirement of raw material for biofuel production, biomass must be processed and handled in an efficient manner. Due to its high moisture content, irregular shape and size, and low bulk density, biomass is very difficult to handle, transport, store, and utilize in its original form (Sokhansanj et al., 2005). Densification of biomass into durable compacts is an effective solution to these problems and it can reduce material waste. Densification can increase the bulk density of biomass from an initial bulk density of 40-200 kg/m3 to a final compact density of 600-1200 kg/m3 (Adapa et al., 2007; Holley, 1983; Mani et al., 2003; McMullen et al., 2005; Obernberger and Thek, 2004). Biomass can be compressed and stabilized to 7–10 times densities of the standard bales by the application of pressures between 400–800 MPa during the densification process (Demirbas and Sahin, 1998). Because of their uniform shape and size, densified products may be easily handled using standard handling and storage equipment, and they can be easily adopted in direct-combustion or co-firing with coal, gasification, pyrolysis, and utilized in other biomass-based conversions (Kaliyan and Morey, 2006a) such as biochemical processes. Upon densification, many agricultural biomass materials, especially those from straw and stover, result in a poorly formed pellets or compacts that are more often dusty, difficult to handle and costly to manufacture. This is caused by lack of complete understanding on the natural binding characteristics of the components that make up biomass (Sokhansanj et al., 2005).

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.

CUBING CHARACTERISTICS OF FRACTIONATED SUN-CURED AND DEHYDRATED ALFALFA CHOPS

A single cubing unit was designed and constructed to study the cubing characteristics of fractionated sun-cured and dehydrated alfalfa chops. The moisture content of dehydrated and sun-cured chops were 6% and 7% (wet basis), respectively. A forage particle separator was used to separate leaf and stem fractions. The leaf and stem fractions were combined to get five different samples each for sun-cured and dehydrated alfalfa with leaf content ranging from 0 to 100% in increments of 25%. A hydraulic cubing machine with a maximum capacity of 14.0 MPa was used to apply compressive pressures on the chops. The effect of chop moisture content (6%, 10%, and 14%), leaf content (0, 25%, 50%, 75%, and 100%), chop preheat temperature (50.C, 75.C, and 100.C), cube die temperature (75.C, 90.C, 150.C, and 200.C), applied pressure (2.5, 5.0, 7.5, 9.0, 10.0, 12.0, and 14.0 MPa) and chop residence time in the cubing unit (10, 12, 15, and 30 s) on cube quality was studied. Cube quality was assessed based on its density, color, long fiber content, durability and hardness. Results were subjected to statistical analysis to determine the effect of the processing and material variables on cube quality. The density of dehydrated and sun-cured cubes increased with an increase in pressure, residence time, leaf content and cube die temperature. Cube hardness increased with an increase in pressure and residence time. Cube durability increased with an increase in pressure, residence time, and die temperature. Change in leaf content had an insignificant effect on cube durability, except for dehydrated alfalfa at 50% leaf content and sun-cured alfalfa at 100% leaf content. Cube greenness decreased with a decrease in leaf content and residence time, however, greenness increased with an increase in die temperature.

Municipal Solid Waste - A Review of Classification System

The present study is performed to review existing municipal solid waste (MSW) classification systems in Canada and other countries and if desired, propose a novel classification system that could assist municipalities to make informed decisions regarding MSW processing and utilization. MSW is highly non-homogenous since it consists of residues of nearly all materials used. The content of MSW varies with location, lifestyle, season, trends in packaging, local recycling schemes and local authority collection policy. Therefore, detailed classification and quantification of MSW is desired in order to obtain accurate data concerning estimates of present and future production and composition of MSW for long-term efficient and economical waste management planning. In addition, universal classification systems are required that can be implemented by any municipality, irrespective of national or regional variations.

Physical Properties of Cubes from Fractionated Suncured and Dehydrated Alfalfa Chops

Physical properties of cubes manufactured from fractionated sun-cured and dehydrated alfalfa chops were studied using a single cubing unit. A hydraulic cubing machine having a maximum capacity of 14.0 MPa was used to apply compressive pressures on the fractionated chops. Separation of alfalfa into leaf and stem fractions was achieved using a forage particle separator. The fractions were re-combined to get five different samples each for sun-cured and dehydrated alfalfa with leaf content ranging from 0% to 100% in increments of 25%. The effect of chop moisture content (6, 10 and 14%), leaf content (0, 25, 50, 75 and 100%), chop preheat temperature (50, 75 and 100oC), cube die temperature (75, 90, 150 and 200oC), applied pressure (2.5, 5.0, 7.5, 9.0, 10.0, 12.0 and 14.0 MPa) and chop residence time in the cubing unit (10, 12, 15 and 30 s) on cube quality was studied. Cube quality was assessed based on its density, color, long fiber content, durability and hardness. Results were subjected to statistical analysis to determine the effect of processing and material variables on cube quality. Chop moisture content of 10% (wb) was considered as an optimum value. A chop preheat temperature below 100oC was deemed appropriate to avoid vapor pocket formation inside a cube, leading to cracks on a cube surface. The density of dehydrated and sun-cured cubes increased with an increase in pressure, residence time, leaf content and cube die temperature. Cube hardness increased with an increase in pressure and residence time. Cube durability increased with an increase in pressure, residence time and die temperature. The change in leaf content had an insignificant effect on cube durability, except for dehydrated alfalfa at 50% leaf content and sun-cured alfalfa at 100% leaf content. Cube greenness decreased with a decrease in leaf content and residence time, however, greenness increased with an increase in die temperature.