An Experimental Study of the Thermal Performance of a Screw Conveyor Dryer

ABSTRACT

In the present study drying of fine crystalline solid was carried out in a non-insulated jacketed screw conveyor dryer SCD of 3 m length and 0.072 m screw diameter. It is nitrogen-swept to carry off the evaporated moisture. Dryer performance was evaluated in terms of the final moisture content, heat-transfer coefficient, thermal efficiency and power consumption. From the experimental results it was observed that drying under low pressure gives 92% moisture removal compared to 30–40% using low flow rates of nitrogen. The initial moisture content was in the range of 5 to 6%. Over the parameter range studied, the overall heat transfer coefficient was found to be in the range of 46–102 W/m²K. The average rise in the temperature of the product was 40 to 50°C. Thermal efficiency (based on sensible and latent heat) of the dryer obtained was found to be in the range of 25–62%, typical values obtained in falling rate drying period. Power consumption per metric ton of dried material was found to be a strong function of screw speed and material feed rate, material properties, and drive efficiency.     

Study of Residence Time Distribution in a Pilot-Scale Screw Conveyor Dryer

The screw conveyor dryer (SCD) finds varied applications in the process industries either as a pre-dryer or for post-drying operation. In certain cases, it can be used as the main dryer. The full potential of SCD has not been exploited for the lack of its understanding. The conveying of paste or particles through a screw conveyor may follow a near plug flow behavior; however, it is essential to ascertain a desired level of inter-particle mixing during the course of drying/conveying so as to obtain the desired drying conditions. The effects of feed rate (15–176 kg/h) and screw speed (10.8–28 rpm) on the RTD were studied for the conveying of sand in a pilot-scale SCD using pulse input of a tracer (dye-coated sand). Two new parameters defining the relative stagnancy and screw effectiveness were introduced to study the flow performance of SCD. The flow in the SCD approaches plug flow with an increase in feed rate or by decrease in the screw speed. A low value of the holdback, a parameter of relative stagnancy, indicates the flow in SCD to be near plug flow. Mean residence time was found to be 3 to 4 times longer than the linear residence time due to lower values of screw effectiveness (0.24–0.32).     

Processing‐structure‐property relationship in rigid polyurethane foams

Rigid polyurethane (PU) foam is used as a thermal insulating and supporting material in domestic refrigerator/freezers and it is produced by reaction injection molding (RIM) process. There is a need to improve the thermal property of rigid PU foam but this is still a challenging problem. Accordingly, this work investigates the RIM process parameters to evaluate their effects on rigid PU foam's structure and hence property. It has been found that mold temperature is a key parameter whereas curing time has negligible effect on structure of PU foam. Cell size, strut thickness, and foam density have been found very critical in controlling the thermal and mechanical properties. Upper and lower values of 30 to 32 kg/m³ density are critical to observe contribution of radiation and solid conductivity separately. Finally, PU foam with 160 µm average cell size, 16 µm strut thickness, below 10% open cell content, and 30 to 32 kg/m³ density allow obtaining better thermal insulation without significant reducing in the compressive strength. The presented work provides a better understanding of processing‐structure‐property relationship to gain knowledge on producing high‐quality rigid PU foams with improved properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44870.     

Drying Characteristics of Barley Grain Dried in a Spouted-Bed and Combined IR-Convection Dryers

A study was performed to determine the drying characteristics and quality of barley grain dried in a laboratory scale spouted-bed dryer at 30, 35, 40, and 45°C and an inlet air velocity of 23 m/s^?1, and in an IR-convection dryer under an infrared radiation intensity of 0.048, 0.061, 0.073, and 0.107 W cm^?2 at an air velocity of 0.5 m/s^?1. The results show that the first, relatively short, phase of a sharp decrease in the drying rate was followed by the phase of a slow decrease. The time of barley drying depended on temperature of inlet air in a spouted-bed dryer and on radiation intensities in an IR-convection dryer. Barley drying at 45°C in a spouted-bed dryer was accompanied by the lowest total energy consumption. The average specific energy consumption was lower and the average efficiency of drying was higher for drying in a spouted-bed dryer. The effective diffusivities were in the range 2.20–4.52 × 10^?11 m² s^?1 and 3.04–4.79 × 10^?11 m²/s^?1 for barley dried in a spouted-bed and in an IR-convection dryer, respectively. There were no significant differences in kernel germination energy and capacity between the two drying methods tested.     

Improvements of the Tensile Properties of Recycled High Density Polyethylene (HDPE) by the Use of Carbonized Olive Solid Waste

Recycling of plastic poses several concerns to manufacturers. The most important concern is the unpredictable of their mechanical properties (modulus of elasticity, tensile strength and ductility). Olive solid waste, an abundant material usually thrown into land causing harms to environment was mixed with HDPE plastic and used as a filling material. The mixture was fed to a house made extruder operating at different speed and temperature. Two carbon particle sizes range (less than 150 µm and 180–250 µm) were used. The effect of carbon contents from 0 to 10% wt/wt and operating conditions were tested on the mechanical properties of the recycled HDPE plastic. It was found that up to 5% wt/wt carbon of less than 150 µm resulted in a noticeable improvement of modulus of elasticity and tensile strength. The optimum value of modulus at carbon particle size 180–250 µm was found at 2.5 olive solid carbon content. Increasing screw speed was found to increase tensile modulus and strength of used plastic. This was related to melt viscosity and reduction in particle size. An increase in processing temperature was found to improve tensile properties up to certain point where degradation of polymeric matrix begins to occur and therefore tensile properties deteriorate.     

Influence of Stress Whitening Pretreatment on Cell Structure,Foaming Behavior,and Mechanical Properties of AN/MAA Copolymer Foam

Stress whitening pretreatment on expandable acrylonitrile (AN)/methacrylic acid (MAA) copolymer was adopted to reduce the cell size of high-performance AN/MAA copolymer foam. The article studied the influence of stress whitening on cell structure and mechanical properties of AN/MAA copolymer foam, observed foaming behavior of stress- whitened copolymer by hot stage optical microscopy, and discussed its bubble nucleation mechanism. The results indicate that stress-whitening pretreatment makes the cell size of corresponding copolymer foam reduce sharply when stress whitening occurs. The cell size of copolymer foam with the density of 32 kg/m³ and 75 kg/m³ reduces from 1.07 mm to 0.37 mm and from 0.59 mm to 0.076 mm, respectively. It also causes residual fragmental films in cells. The defects created by stress whitening work first as a bubble nucleus, then expand and combine together as cells. Stress whitening creates new interface between gas and polymer phase and new volume of gas phase, reduces the change of interface free energy and volume free energy during bubble nucleation, and improves the bubble nucleation rate. The foaming phenomenon of stress whitened copolymer is in line with the defect nucleation mechanism. However, stress whitening pretreatment reduces the mechanical properties of final foam because of residual fragmental films.     

Performance of Two Industrial Dryers for Fish Feed

Performance and energy efficiency of two types of dryers for fish feed are compared. The first dryer was a belt dryer located at a fish feed production facility in Norway. The second dryer was a counterflow multideck dryer at a fish feed production facility in Chile. In both dryers there was only a slight decrease in drying rate over the dryer. Product samples showed a standard deviation of 0.45% on an average moisture content of 10.2% (wb) for the belt dryer and 0.49% on an average of 8.6% (wb) for the counterflow dryer. Mass and heat balances showed good accuracy. In order to compare the energy use of both dryers, normalized energy consumption and efficiency were calculated for equal feed and air inlet temperatures using two methods: the primary energy method and the energy difference method. The average normalized specific energy consumption for the belt dryer was 3,386 kJ/kg water evaporation (primary energy method) and 2,970 kJ/kg (energy difference method), with efficiencies of 56 and 64%, respectively. For the counterflow dryer the average specific energy consumption was 2,893 kJ/kg (primary energy method) and 2,393 kJ/kg (energy difference method), with efficiencies of 70 and 85%, respectively.     

Experimental Study on Optimization of the Agglomeration Process for Producing Instant Sugar by Conical Fluidized Bed Agglomerator

This study was conducted to determine the optimal processing conditions for manufacturing instant sugar. The instant sugar was produced with a batch fluid bed agglomerator under the following conditions: inlet air temperature 60–90°C; water flow rate 1–3 mL min^?1; and spraying time 1–10 min. The optimal conditions were estimated using response surface methodology as follows: inlet air temperature of 74.4°C, water flow rate of 2.85 mL min^?1, and spraying time of 10 min. Subsequently, particle density of 1,550 kg m^?3, poured density of 470.13 kg m^?3, tapped density of 599.8 kg m^?3, porosity of 62.1%, mean diameter of 324.66 µm, flowing time of 6.39 s, yield percentage of 78.96%, and desirability of 0.46 were obtained as optimal amounts. The results showed that the quadratic effects of water flow rate and spraying time on flowing time and particle density as well as the effects of spraying time and inlet air temperature on mean diameter and flowing time were significant. Within the temperature range of 60–90°C, the impact of spraying time and water flow rate on instant sugar properties had preference over inlet air temperature. Moreover, the optimal instant sugar required less dissolution time compare to various industrial sugar samples.     

Drying behavior of prina (crude olive cake) using different types of dryers

The purpose of this research is to investigate the drying kinetics and determine the suitable drying method of prina, which is obtained after pressing of olives in olive oil factories, and which cannot be used efficiently in certain sectors. Drying experiments were performed at drying temperatures of 60°C, 70°C, and 80°C at a fixed air velocity of 2 m/s using a hot air dryer and with microwave powers of 90 W, 360 W, and 600 W using a microwave dryer. The prina layer thicknesses were selected as 7, 9, and 11 mm for both drying methods. The minimum energy consumption values were measured as 42.0 Wh for 600 W power level and 7 mm layer thickness, and 10260 Wh for 7 mm layer thickness and 80°C temperatures. It was found that energy consumption during hot air drying was more than that of microwave drying. As a result, the suitable dryer and thickness of layer were selected as microwave dryer and 7 mm, respectively. The results of statistical analyses showed that the most suitable model to define the drying behavior of prina samples were found to be the Page model for the microwave dryer and Wang &; Singh model for the hot air dryer. Also, penetration depth, the loss tangent value (tanδ), dielectric constant of material (?^?), and dielectric loss factor (?^??) of dried prina were calculated as 34.51 cm, 0.1059, 75.65, and 8.01, at 2450 MHz, respectively.     

An Experimental Study of the Thermal Performance of a Screw Conveyor Dryer

In the present study drying of fine crystalline solid was carried out in a non-insulated jacketed screw conveyor dryer SCD of 3 m length and 0.072 m screw diameter. It is nitrogen-swept to carry off the evaporated moisture. Dryer performance was evaluated in terms of the final moisture content, heat-transfer coefficient, thermal efficiency and power consumption. From the experimental results it was observed that drying under low pressure gives 92% moisture removal compared to 30-40% using low flow rates of nitrogen. The initial moisture content was in the range of 5 to 6%. Over the parameter range studied, the overall heat transfer coefficient was found to be in the range of 46-102 W/m²K. The average rise in the temperature of the product was 40 to 50°C. Thermal efficiency (based on sensible and latent heat) of the dryer obtained was found to be in the range of 25-62%, typical values obtained in falling rate drying period. Power consumption per metric ton of dried material was found to be a strong function of screw speed and material feed rate, material properties, and drive efficiency.     

DRYING OF SOY PULP (OKARA) IN A BED OF INERT PARTICLES

ABSTRACT

Drying of okara, an insoluble pulp residue waste byproduct of tofu production, was investigated in a continuously moving bed of inert particles subjected to vortex-like motion. The experimental variables in their respective ranges included the mass of Teflon pellets used as inert particles (0.4–1.2 kg), feed rate (0.5–1.4 kg/h), inlet air temperature (100–145°C) and airflow rate (195–271 m³/h). The dryer showed good performance in general and produced dry okara with moisture content ranging from 5 to 33% wb depending upon the operating conditions. The product recovery ranged from 80 to 90% on dry basis in most experiments. The specific water evaporation rate in okara drying increased with increasing of the feed rate and mass of Teflon pellets. However, the specific heat consumption decreased with an increase in the okara feed rate. Results showed that specific heat consumption for okara drying in a bed of inert particles was about 3 to 4 times higher in comparison with that of free water.     

The effect of noncondensable gas on heat transfer in the preheater of the sewage sludge drying system

We used a shell-and-tube type preheater to investigate the effect of noncondensable gas on heat transfer. In the preheater of the drying system, heat is exchanged between steam-air mixed gas which is dryer outlet gas and sewage sludge. To evaluate the performances of the preheater, water was first used in the tube-side material instead of sewage sludge and steam-air mixed gas in the shell-side material. The test variables were as follows: mixed gas inlet temperatures range from 95 to 120 °C; inlet air content, m _air /m _steam from 55 to 83%; tube-side water flow rate from 42 to 62 kg/h. The shell-side heat transfer coefficient varied from 150 to 550W/m²K, which corresponds to the amount of noncondensable gas in the steam-air mixed gas and the overall heat transfer coefficient varied from 60 to 210W/m²K. Using sewage sludge as a tube-side material the overall heat transfer coefficient varied from 60 to 130W/m2K and the outlet temperature of sewage sludge was above 90 °C, which is high enough for reducing energy consumption in the dryer by preheating the sewage sludge.     

Thermal Processing of Particulate Solids in a Gas-Fired Pulse Combustion System

Abstract

An experimental study on thermal processing of particulate solids has been carried out on a valved pulse combustion unit. The test-bench consists of a 60 kW natural gas-fired valved (flappers) pulse combustor having a 4.63 × 10^?3 m³ combustion chamber, horizontal tailpipe with variable geometry, and a cylindrical drum. The particulate solid used is clean sand (311 µm and 2646 kg/m³), which flows within the tailpipe and the cylindrical drum located at its end. The sand flowrate was varied from 10 to 50 kg/h and it was heated from 20 to 600°C. Local pressure measurements showed clearly that the propagation of sonic waves remain stable when they are in direct contact with the sand particles. The heating time of sand particles in the pulsed system was found shorter than the one observed when operating with a conventional burner under the same conditions; this resulted in a 25.5% reduction of natural gas consumption.     

By-product gypsum from the tapioca starch process

By-product gypsum derived from the tapioca starch process was calcined in the laboratory and evaluated for use in the manufacture of plaster of Paris and plaster products. The gypsum had a purity of about 98%, was fine (1 %, + 150μm) and had a low bulk density (600 kg/m³). The laboratory calcined material had a higher than normal water requirement of 120–130 ml/100 g, and a long setting time of 65 min. Specimens cast at a water/solids ratio of 1·0 had a low compressive strength of 2·4–3·4 MPa. However, the mechanical strength could be improved by the addition of water-reducing admixtures, and a strength of 7·6 MPa was obtained at a water/solids ratio of 0·6 and a resulting density of 1190 kg/m³. The waste gypsum derived from the manufacture of tapioca starch appears to be suitable for the manufacture of plaster of Paris and plaster products after the incorporation of water-reducing admixtures into the plaster slurry.     

Analysis of Energy and Environmental Parameters during Solar Cabinet Drying of Apple and Carrot

A modular solar cabinet dryer equipped with an air collector including a drying chamber with different tray arrangements was developed to determine moisture changes in different sizes and forms (slices and cubes) of apple and carrot pieces and to carry out serial measurements of temperatures, solar radiation, and air humidity distributions during the drying process. The initial and final moisture contents (w.b.) of fresh products were 88 and 26% for apple and 71 and 13% for carrot with initial weights of 1.56 and 3 kg, respectively. The results revealed that the temperature inside the chamber was strongly negatively correlated with air humidity (R² = 0.91) and that the length of the drying period was influenced by the weather conditions, as the cloudy weather retarded drying of carrots. It was possible to reach an air drying temperature over 41°C with a daily total solar energy incident on the collector's surface of 857.2 kJ/(m² day) for apples and 753.20 kJ/(m² day) for carrots. The analysis of energy requirements to remove moisture from apples and carrots during the total drying period showed values of 3300.19 and 7428.28 kJ/kg, respectively. The amount of air to remove water from the samples was also determined as 126.93 m³ for apples and 928.56 m³ for carrots.     

Energy and Exergy Analyses of Thin-Layer Drying of Potato Slices in a Semi-Industrial Continuous Band Dryer

This article is concerned with the energy and exergy analyses of the continuous-convection drying of potato slices. The first and second laws of thermodynamics were used to calculate the energy and exergy. A semi-industrial continuous-band dryer has been designed and used for drying experiments. The equipment has a drying chamber of 2 m length and the inlet air used for drying is heated by gas power. The experiments were conducted on potato slices with thickness of 5 mm at three different air temperatures of 50, 60 and 70°C, drying air mass flow rates of 0.61, 1.22, and 1.83 kg/s and feeding rates of 2.31 × 10^?4, 2.78 × 10^?4, and 3.48 × 10^?4 kg/s. The energy utilization and energy utilization ratio were found to vary between 3.75 and 24.04 kJ/s and 0.1513 and 0.3700, respectively. These values show that only a small proportion of the supplied energy by the heater was used for drying. The exergy loss and exergy efficiency were found to be in the range of 0.5987 to 13.71 kJ/s and 0.5713 to 0.9405, respectively, indicating that the drying process was thermodynamically inefficient and much energy was vented in the exhaust air. In addition, the results showed that the feeding rate and the temperature and flow rate of the drying air had an important effect on energy and exergy use. This knowledge will provide insights into the optimization of a continuous dryer and the operating parameters that causes reduction of energy consumption and losses in continuous drying.     

Hydrodynamic Characteristics of a Pilot-Scale Screw Conveyor Dryer

This article presents results of an experimental study on the flow characteristics of a pilot-size screw conveyor dryer (SCD). In particular, the effects of granular solids flow rate (15.2–206 kg/h) and screw speed (10.8–28 rpm) on the residence time distribution (RTD) were studied using sand as the model material. The RTD was measured using a dynamic step change in the solids flow rate. Parameters such as solids holdup, degree of fullness, mean residence time, and uniformity of the discharge flow were studied. The solids holdup and hence the degree of fullness was found to decrease with increase in the screw speed and decrease with the solids flow rate. The mean residence time was found to decrease with an increase in the screw speed, as expected. The screw speed and the solids flow rate strongly affected the discharge uniformity. An optimum value of the degree of fullness was observed with regard to the solids flow rate. Over the operating range examined, the solids flow pattern was close to plug flow, as indicated by high values of N and Pe number.     

Preparation of Polymeric Stationary Phase for Use in Inverse Gas Chromatography

Abstract

The preparation of ground low‐density poly(ethylene) (LDPE), high‐density poly(ethylene) (HDPE), and poly(ethylene terephthalate) (PET) materials suitable for use by inverse gas chromatography (IGC) experiments is described. Materials prepared showed a smaller and more uniform particle size, 83–86 µm (200 mesh), than commercially available Chromosorb^® W solid chromatography support. In addition, the BET surface area of polymeric materials, 0.367–0.559 m²/cm³, was much greater than the surface area of 150‐ to 212‐µm‐diameter glass beads. The use of polymeric materials with uniform particle sizes and defined surface areas have several advantages over polymer coated Chromosorb^® W and glass beads in IGC experiments.     

Effect of Processing Parameters and Vibrating Field on Poly(Vinyl Chloride) Microcellular Foam Morphology

The effects of processing parameters such as processing pressure, temperature, mixing time and rotor speed on polyvinyl chloride foams were investigated by using a novel microcellular foaming setup. The experimental results show that a proper temperature and a high pressure can promote CO₂ dissolving in polymer, which makes cell density increase and cell size decrease. Increasing mixing time and rotor speed also promote CO₂ dissolving in PVC and speed up forming single-phase polymer/CO₂ solution. The effects of oscillatory shear on polyvinyl chloride cell morphology were also studied. The combined shear improves the mixing, and thus shortens the time needed for homogeneous polymer/supercritical CO₂ solution formation. Foamed samples with the cell density of 1.0 × 10⁷–3.5 × 10⁸ cells/cm³, average cell size of 15–60 µm and bulk density of 0.6–0.87 g/cm³ had been produced.     

MOBILE FLUIDIZED BED PADDY DRYER

ABSTRACT

The objectives of this research are to design, construct and test a mobile fluidized bed paddy dryer with a drying capacity of 2.5-4.0 t/h. Suitable drying conditions are recommended as follows : drying capacity 3.8 t/h, bed velocity 2.8 m/s, average drying air temperature 144 °C, bed height 13.5 cm, fraction of air recycled 0.8. Residence time of paddy was approximately 1.3 minutes. Test results showed that moisture content of paddy was reduced from 32.6 % dry-basis to 25.8 % dry-basis. Consumption of electrical power and diesel fuel was 12.9 kW and 21.71 1/h respectively. Primary energy consumption was 910.9 MJ/h. The dryer could evaporate water 218.8 kg/h. Specific primary energy consumption was 4.2 MJ/kg-water evaporated. Cost of paddy drying was 1.48 baht/kg-water evaporated of which 0.53 was fixed cost and 0.95 was energy cost (US$1 =34baht).