A Study of the Limitations to Spray Dryer Outlet Performance

Abstract

The concept of the product moisture locus was tested in this work using a pilot-scale modified Niro spray dryer (diameter 0.8 m, height 2 m), where the residence time of the particles inside this spray dryer is lower compared with larger industrial spray dryers. The moisture contents of skim milk powder produced from spray drying skim milk (solids content 8.8% w/v) at different operating conditions, namely different swirl vane angles (0°, 25°, 30°), inlet air temperatures (170°C, 200°C, 230°C) and process fluid flowrates (1.4 kg h^?1, 1.6 kg h^?1, 1.8 kg h^?1), were compared with the predicted equilibrium moisture contents. In addition, the residence time of the particles was also increased in the spray dryer by decreasing the inlet air mass flowrate from 0.016 to 0.013 kg s^?1. The outlet moisture contents of the skim milk powder for all the 23 runs carried out in this work were within 0.4% of the equilibrium values. Thus, the skim milk powder particles were in close equilibrium with the gas inside the drying chamber. These equilibrium limitations are confirmed by other literature data (Boonyai, P. Comparative Evaluation of Soymilk Drying in a Spray Dryer and Spouted Bed of Inert Particles. M.Sc. Thesis. Asian Institute of Technology: Bangkok, Thailand, 2000; 90 pp; Harvie, D.J.E.; Langrish, T.A.G.; Fletcher, D.F. A computational fluid dynamics study of a tall-form spray dryer. Trans IChemE 2002, in press). The use of this finding to predict spray dryer performance is demonstrated by mass and energy balance calculations.     

Changes in Specific Gravity and Equilibrium Moisture Content in Heat-Treated Fir (Abies nordmanniana subsp. bornmülleriana Mattf.) Wood

The goal of this study was to determine the changes in specific gravity and equilibrium moisture content of fir (Abies nordmanniana subsp. bornmülleriana Mattf.) wood after heat treatment at different temperatures and durations. In this study, the effects of three different temperatures and three different durations were investigated. The temperatures were 170, 190, and 210°C, and the durations were 4, 8, and 12 h. The equilibrium moisture contents of the heat-treated specimens were determined at 20°C at relative humidities of 35, 50, 65, 80, and 90%, and the results were compared with control specimens. The results indicated that increasing temperatures increased the weight loss of the specimens. With respect to dimensional stabilization, the heat-treated specimens had lower equilibrium moisture contents than did the control specimens.     

Optimization of thermopressing conditions for the production of binderless boards from a coriander twin‐screw extrusion cake

A deoiled press cake resulting from twin‐screw extrusion of coriander fruits was used as a raw material for the production of self‐bonded boards. The operating parameters for thermopressing were varied and include the applied pressure (19.6–39.2 MPa), molding time (60–300 s), and molding temperature (155–205 °C). The optimized process conditions (21.6 MPa, 300 s, 205 °C) resulted in a board with a density of 1323 kg/m³, a flexural strength of 23 MPa, a modulus of elasticity of 4.4 GPa, and a thickness swelling of 31%. The thickness swelling was effectively reduced to 20% through the application of a heat treatment at 200 °C after thermopressing. A variation of the moisture content of the press cake between 3 and 8% showed that increased moisture contents do not lead to improved mechanical properties of the resulting board and further induce internal fracturing of the board during thermopressing. The manufactured binderless boards may act as environmentally friendly alternatives to commercial wood‐based boards such as oriented strand board and particleboard. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44650.     

Effects of superheated steam treatment on moisture adsorption and mechanical properties of pre-dried rubberwood

Abstract

Rubberwood (Hevea brasiliensis) was treated with superheated steam (140–160?°C) for 1–3?h and then its adsorption ability, mechanical properties, and color changes were investigated. The results of adsorption show decreased equilibrium moisture content (EMC) for all heat-treated cases throughout the hygroscopic range. The Hailwood–Horrobin model was used to analyze the sorption isotherms and determine the monolayer and polylayer moisture contents for untreated and heat-treated rubberwood. The monolayer moisture content clearly decreased with treatment temperature and duration, whereas the reduction in polylayer moisture was relatively smaller. Moreover, the least density of water adsorption sites was found in wood after treatment at 160?°C for 3?h, indicating this as the cause for reduced equilibrium adsorption. All treatment conditions had improved mechanical properties, including compression parallel-to-grain, hardness, and tensile strength. The total color difference of the wood surface increased with increasing temperature and treatment duration.     

Microwave Heat Treatment of Spinach: Drying Kinetics and Effective Moisture Diffusivity

The effect of microwave drying technique on moisture content, moisture ratio, drying rate, drying time, effective moisture diffusivity, and porosity of spinach (Spinacia oleracea L.) were investigated. By increasing the microwave output powers (180–900 W) and the sample amounts (25–100 g), the drying time decreased from 18 to 3.5 min and increased from 7.7 to 25 min, respectively. To determine the kinetic parameters, the drying data were fitted to various models based on the ratios of the differences between the initial and final moisture contents and equilibrium moisture content versus drying time. Among of the models proposed, Page's model gave a better fit for all drying conditions applied. The activation energy was calculated using an exponential expression based on Arrhenius equation. The relationship between the drying rate constant and effective moisture diffusivity was also estimated and gave a linear relationship.     

Use of FTIR combined with forms of water to study the changes in hydrogen bonds during low-temperature heating of lignite

The changes in the hydrogen bonds (HBs) of three types of Indonesian lignite during low-temperature heating were investigated. The amount of water loss was determined by weighing the samples before and after heating in an oven. The changes in the number of the different types of HBs were determined using Fourier transform infrared spectroscopy coupled with types of water in lignite. The number of peak positions and absorption bands in each spectrum was determined by curve-fitting analysis with a Gaussian function. The quantified integrated area of aromatic hydrogen atoms was used to accurately investigate the changes in the HBs. The results show that at low temperatures (T ≤ 50°C), free water is mainly removed, and the HBs broken are those between free water molecules. However, at medium temperatures (50 <T ≤ 100°C), bound water is mainly removed. The number of HBs significantly changes because of the breaking of bound water molecule HBs and bound water cluster–carboxyl group HBs, and the formation of nonfreezable moisture HBs. At high temperatures (100 <T < 125°C), nonfreezable moisture can be released. The number of HBs changes as a result of competition between the removal of nonfreezable moisture and the increase in the number of carboxyl groups. At higher temperatures (T ≥ 125°C), the moisture remaining in lignite is thermal decomposition moisture. In addition, the rate of decomposition of carboxyl groups is higher than the rate of generation, which means that the number of HBs markedly decreases at higher temperatures.     

THE MOISTURE SORPTION ISOTHERMS OF CEFOTAXIME SODIUM SALT

ABSTRACT

The water sorption isotherms of the cefotaxime sodium salt were determined at 30 and 40° C. Cefotaxime sodium salt was maintained at equilibrium relative humidities ranging from 40 to 80 %. Equilibrium moisture content was determined by the Karl Fischer method. The moisture sorption isotherms showed that the equilibrium moisture decrease while the temperature increase. The experimental curves of equilibrium humidity were fitted by different models (Bradley, Halsey, Henderson, Kuhn, Smith and Iglesias and Chirife and GAB). Parameters of each equations were determined by non-linear regression analysis. The best fit was obtained by Iglesias and Chirife model. The isosteric heat of moisture sorption calculated by Claussius Clapeyron equation varied from 64·45 to 48·03 kJ/mol when moisture content changed from 7 to 9·5 %.     

Studies on moisture sorption in coir fibers (cocos nucifera L)

Moisture desorption characteristics in coir fibers have been studied at several temperatures (53°C, 68°C, 86°C, and 105°C) as a function of time. Moisture absorption at room temperature after heating to 53°C, 68°C, 86°C, and 105°C are also reported. The results indicate that the relation between percentage moisture loss (A) (moisture loss is the ratio of the difference between initial moisture and final moisture to initial moisture) and temperature (T°K) is of the type A = A_oe^?B/T in the range of intervals studied. The constants A_o and B are dependent on time, and they decrease with time. The fraction moisture loss/gain (w) is related to time (t) by the equation w = m/t + b₀ at all temperatures investigated. The constant m decreases with temperature while b₀ increases with temperature. The equilibrium moisture content (the condition reached by the sample when it no longer takes up moisture from or gives up moisture to the surrounding atmosphere) increases with increase in relative pressure and decrease in temperatures. As the moisture content in the fiber increases, the tensile strength (tenacity) decreases and the % elongation increases. The observed results are explained on the basis of structural rearrangement on heating/cooling of lignocellulosic material.     

Vacuum Frying of Desalted Grass Carp (Ctenopharyngodon idellus) Fillets

The objective of this study was to investigate the effects of vacuum frying on the product quality of desalted grass carp fillets. Parameters of included moisture content, oil content, color values, and textures (hardness, chewiness, and springiness) were used to evaluate the product quality. Results showed that with increasing vacuum frying temperature and time, the moisture content of fillets decreased while the oil content increased, and hardness increased quickly. The hardness and chewiness values of vacuum-fried samples were both higher than those of atmospheric fried samples. However, there was no significant change in L* among four different temperature/vacuum-frying combinations. The results also indicated that vacuum frying at 0.08 MPa and 100°C–110°C for 15 min can produce crisp grass carp fillets with lower moisture and oil contents as well as good color and texture quality.     

The rheological behavior and dynamic mechanical properties of syndiotactic 1,2‐polybutadiene

The rheological behavior and the dynamic mechanical properties of syndiotactic 1,2‐polybutadiene (sPB) were investigated by a rotational rheometer (MCR‐300) and a dynamic mechanical analyzer (DMA‐242C). Rheological behavior of sPB‐830, a sPB with crystalline degree of 20.1% and syndiotactic content of 65.1%, showed that storage modulus (G′) and loss modulus (G″) decreased, and the zero shear viscosity (η₀) decreased slightly with increasing temperature when measuring temperatures were lower than 160°C. However, G′ and G″ increased at the end region of relaxation curves with increasing temperature and η₀ increased with increasing temperature as the measuring temperatures were higher than 160°C. Furthermore, critical crosslinked reaction temperature was detected at about 160°C for sPB‐830. The crosslinked reaction was not detected when test temperature was lower than 150°C for measuring the dynamic mechanical properties of sample. The relationship between processing temperature and crosslinked reaction was proposed for the sPB‐830 sample. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Effect of Fluidized Bed Drying Temperature on Various Quality Attributes of Paddy

Abstract

As reported by many researchers, it was found that fluidized bed paddy drying using high drying air temperatures of over 100°C affected the head rice yield and whiteness of dried rice. However, only a few studies on fluidized bed paddy drying with drying air temperatures below 100°C were so far reported. The main objective of this work was therefore to study the effect of fluidized bed drying air temperature on various quality parameters of Suphanburi 1 and Pathumthani 1 Indica rice. Paddy was dried from the initial moisture contents of 25.0, 28.8, and 32.5% dry basis to 22.5 ± 1.2% dry basis using inlet drying air temperatures between 40 and 150°C at 10°C/step. After fluidized bed drying, paddy was tempered and followed by ambient air aeration until its final moisture content was reduced to 16.3 ± 0.5% dry basis. The results showed that the head rice yield of Suphanburi 1 was significantly related to the inlet drying temperature and initial moisture content whilst there was no significant relationship between the head rice yield, drying temperature and initial moisture content for Pathumthani 1. The whiteness of the two rice varieties was slightly decreased with increase in drying air temperature and initial moisture content. It was also found that the hardness of both cooked rice varieties exhibited insignificant difference (p < 0.05) comparing to rewetted rice, which was gently dried by ambient air aeration in thin layer. The thermal analysis by DSC also showed that partial gelatinization occurred during drying at higher temperatures. Using inlet drying air temperatures in the range of 40–150°C therefore did not affected the quality of cooked rice and paddy. The milling quality of paddy was also well maintained.     

Measurement of water content and moisture distribution in sludge by 1H nuclear magnetic resonance spectroscopy

Moisture distribution in sludge is essential for the examination of dewatering problems; however, sufficiently rapid and accurate methods of sludge moisture measurement are currently lacking. Hence, this study investigated a low-field ¹H nuclear magnetic resonance (NMR) method for measuring water content and moisture distribution in sludge. Moisture content measured by NMR was closely correlated with the thermal drying method (R² = 0.999). The loss of mechanical bound water from sludge was the primary cause of the decrease in water content from 96 to 37% during thermal drying at 40°C. NMR is more accurate, rapid, and nondestructive than other water distribution measurement methods.     

Moisture sorption/desorption behavior of various manmade cellulosic fibers

The kinetics of dynamic water vapor sorption and desorption on viscose, modal, cotton, wool, down, and polyester fibers and lyocell knit fabrics were investigated according to the parallel exponential kinetics (PEK) model. The total equilibrium moisture regain (M_inf(total)) in all the materials decreased with increasing temperature. However, the partial equilibrium fast sorption, determined by PEK simulation at 60% relative humidity (RH) and 36°C, was larger than that at 20°C, whereas the partial equilibrium slow sorption was smaller. The characteristic times in fast sorption (τ₁) and in slow sorption (τ₂) for lyocell were reduced when the conditions were changed from 60% RH and 20°C to 36°C, whereas those for the other fibers increased. Lyocell exhibited the highest M_inf(total) value and the lowest τ₁ and τ₂ values, and this suggested high equilibrium moisture content and fast moisture uptake/release, that is, high moisture accessibility for lyocell. The relationships between the moisture regain, hysteresis, water retention capacity, and Brunauer–Emmett–Teller surface volume in the materials were also examined. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1621–1625, 2005     

Drying Kinetics of Instant Asian Noodles Processed in Superheated Steam

The objective for this work was to develop a novel technique for creating instant noodles by determining the drying kinetics of noodles undergoing simultaneous drying and processing using superheated steam. The mathematical model of moisture ratio was differentiated to determine the drying rates of noodles during processing. There was a constant rate drying period for all temperatures at a steam velocity of 1.5 m/s but there was no constant rate drying period at a steam velocity of 0.5 m/s. The constant rate drying period suggested by measurement of internal noodle temperature is much longer and well defined for all processing conditions than from the drying curves. The constant drying rate period, was nearly 200 s at 110°C but decreased to 50 s at 150°C. Equilibrium moisture content isobars were determined from mass changes during superheated steam processing. It was determined that isotherm equations for equilibrium moisture content in hot air systems may be utilized to model isobars in superheated steam systems.     

Optimization of Vacuum Drying Characteristics of Date Powder

Kabkab, Khazravi, and Zark are three varieties of Iranian dates representing high, middle, and low sugar content, respectively. Under the vacuum conditions, powders from these dates were produced and placed in the optimized state for the dehydration reaction. The statistical analyses showed that the moisture reduction range of these three varieties at various conditions (100°C and 15.3 cm Hg, 93°C and 30.4 cm Hg, 84°C and 54.6 cm Hg, 68°C and 60.1 cm Hg) were 17.27±0.16, 20.89±0.19, and 7.61±0.02%, respectively. The analysis of variance (ANOVA) on date variety and thickness (0.2, 1, 2, 2.5, and 3 cm) in drying time indicated that the Zark variety with low moisture and sugar contents exhibited the lowest drying time (about 6 h), followed by Khazravi and KabKab. The optimum condition (85°C, 54.6 cm Hg, and 1 cm thickness during 7 h of drying time) was selected for its favorable effects on the moisture reduction, smell/color quality, energy usage, and economical feasibility.     

Evaluating a Solar Dryer for In-Shell Drying of Split Pistachio Nuts

Abstract

A thin-layer forced air solar dryer was designed to study the feasibility of drying pistachio nuts. The dryer was tested during the 2001 and 2002 drying seasons. The maximum temperature in the solar collector reached 56°C, which was 20°C above the ambient temperature. The required drying time was 36 h. During the first day of drying (0800 to 1700 h) the moisture content dropped to about 21% (wb). The final moisture content of the dried nuts was 6% wb, which was 1% below the recommended storage moisture. The drying constant of the pistachio nuts during solar drying was determined using two mathematical models, a one-term series solution of Fick's diffusion equation and an exponential decaying model. There was no significant difference between the two models (α = 0.05). In general, the quality of solar dried nuts was better than the conventional heated air due to slower drying rates.     

Effects of aging and moisture on the dynamic viscoelastic properties of oriental lacquer (urushi) film

The effects of aging and moisture on the dynamic viscoelastic properties of three oriental lacquer films were investigated. With aging over 1000 days at room temperature, the glass‐transition temperature of the lacquer films (T_α) shifted to higher temperatures, the maximum loss tangent (tanδ_α) decreased, and the storage modulus at 20°C (E) increased. These changes were analogous irrespective of lacquers. With increasing moisture content, E decreased and tanδ increased at room temperature. Although the equilibrium moisture content of the virgin lacquer (sap) film was higher than that of the clear lacquer film, its E and tanδ were more stable with an increase of moisture content. It was speculated that the polysaccharides aggregated in the sap film did not effectively contribute to the mechanical properties of the film, while their hygroscopicity resulted in higher moisture content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2288–2294, 2002     

DRYING CHARACTERISTICS OF THE HAZELNUT

Abstract

Equilibrium moisture content isotherms for Spanish hazelnut (Corylus avellana L.) at different temperatures (30°C-80°C) were determined using static gravimetric method. Thin layer drying experiments were done with forced air circulation and were conducted with different operating conditions to determine the drying characteristics of hazelnuts. The effect of air temperature (30°C-70°C), air velocity (0.5 m/s - 2 m/s) and drying bed loading density (50 kg/m² - 150 kg/m²) on drying of unshelled and shelled hazelnuts was studied. Six mathematical models were used to fit the experimental equilibrium moisture content data, from which the G.A.B. model was found to give the best fit. Diffusion coefficients were determined by fitting experimental thin-layer drying curves to the Fick's diffusion model. Variation of the effective diffusion coefficient with temperature was of the Arrhenius type. The Page equation was found to describe adequately the thin layer drying of hazelnut. Page equation drying parameters k and n were correlated with air temperature and relative humidity.     

Effect of moisture absorption on the thermal properties of Bombyx mori silk fibroin films

Films of regenerated Bombyx mori silk are strongly affected by absorbed moisture, a phenomenon studied here by differential scanning calorimetry (DSC). Exposure of previously dried films to environments of controlled relative humidity produces test samples of well-defined equilibrium moisture content. Ultimate moisture uptake is as high as 20–23% (by weight) at 75% relative humidity. The glass transition temperature, T_g, drops by 40°C at moisture uptakes as low as 2%, and T_g depressions as large as 140°C are observed at higher relative humidity. The moisture-induced decrease of T_g is completely reversible, as a film remoistened and then redried possesses an unchanged T_g. Trends in T_g with water uptake correspond reasonably well to predictions of a classical thermodynamic theory, indicating that the plasticization effect of moisture on the combined silk-water system can be satisfactorily explained from macroscopic properties of the constituents without any reference to specific interactions. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 401–410, 1997     

DETERMINATION OF CROSS-GRAIN PROPERTIES OF CLEARWOOD SAMPLES UNDER KILN-DRYING CONDITIONS AT TEMPERATURE UP TO 140° C

ABSTRACT

Small specimens of Pinus radiata have been tested to determine the creep strain that occurs during the kiln drying of boards. The samples have been tested over a range of temperatures from 20°C to 140°C. The samples, measuring 150 × 50 × 5 mm, were conditioned at various relative humidities in a pilot-plant kiln, in which the experiments at constant moisture content (MC) in the range of 5-20% MC were undertaken to eliminate mechano-sorptive strains. To determine the creep strain, the samples were brought to their equilibrium moisture content (EMC), then mechanically loaded under tension in the direction perpendicular to the grain. The strain was measured using small linear position sensors (LPS) which detect any elongation or shrinkage in the sample. The instantaneous compliance was measured within 60 sec of the application of the load (stress). The subsequent creep was monitored by the continued logging of strain data from the LPS units.

The results of these experiments are consistent with previous studies of Wu and Milota (1995) on Douglas-fir ( Pseudotsuga menziesii ). An increase in temperature or moisture content causes a rise in the creep straw while the sample is under tension. Values for the instantaneous compliance range from 1.7 × 10^?3 to 1.28 × 10^?7 MPa^?1 at temperatures between 20°C and 140°C and moisture content in the range of 5-20%. The rates of change of the creep strains are in the Order of magnitude 10^?7to10^?8s^?1 for these temperatures and moisture contents. The experimental data have been fitted to the constitutive equations of Wu and Miloia (1996) for Douglas-fir to give material parameters for the instantaneous and Creep strain components for Pinus radiata.