Infrared assisted dry-blanching and hybrid drying of carrot

Infrared (IR) blanching and IR assisted hot air (hybrid) drying of carrot slices were attempted and their performance (processing time, retention of vitamin C and rehydration characteristics) was compared with conventional blanching and drying techniques. Intermittent heating of carrot slices using IR radiation (chamber maintained at 180–240 °C) for 8–15 min resulted in desired level of enzyme inactivation. The time required for blanching of carrot slices (10 mm thick) using hot water, steam and IR radiation was 5, 3 and 15 min, respectively. Retention of water soluble vitamin C was higher (62%) in IR blanched carrot as compared to water (43%) and steam (49%) blanching. IR blanching reduced the moisture content by 13–23% (absolute). IR blanched samples dried by hybrid mode took ～45% lesser time compared to water blanched–hot air dried samples. Higher rehydration moisture of dried samples indicated the retention of cell structure during IR blanching. Vitamin C retention was ～39% higher in IR blanched–hybrid dried slices compared to water blanched–hot air dried. The study shows the potential application of dry-blanching and IR assisted hybrid drying in food processing for improving product quality.     

Effects of thermal pretreatment in helium on the pyrolysis behaviour of Loy Yang brown coal

A wire-mesh reactor capable of multi-step heating/holding and minimising secondary reactions of volatiles was used to investigate the effects of thermal pretreatment in inert gas on the subsequent rapid pyrolysis behaviour of Loy Yang brown coal. Our results indicate that the presence of small amounts (<10 wt%) of moisture in brown coal has little influence on the tar and char yields from the pyrolysis of brown coal at 1000 K s⁻¹. While the hydrogen bonds between the moisture and the O-containing functional groups in the brown coal have little effects on its pyrolysis behaviour, the hydrogen bonds among the O-containing functional groups tend to induce cross-linking reactions to reduce the tar yields. Preheating the brown coal at >250 °C leads to reduced tar and increased char yields. However, the characterisation of tars using UV-fluorescence spectroscopy indicates that significant decreases in the release of larger aromatic ring systems are only observed after preheating at >380 °C for 30 min. The presence of ion-exchangeable cations (e.g. Ca²⁺) in the brown coal tends to stabilise the carboxylate groups and only preheating at >350 °C would result in changes in pyrolysis yields during the subsequent pyrolysis at 1000 K s⁻¹. These results may be explained by considering the formation of cross-links involving peripheral groups at low preheating temperatures and the formation of cross-links involving aromatic ring systems at elevated temperatures.     

Effect of Drying Conditions on Moisture Re-Adsorption Performance of Dewatered Lignite

In order to improve the drying efficiency of lignite and restrain the moisture re-adsorption of dewatered coal, the drying characteristics of typical Chinese lignite, the re-adsorption performances of dewatered samples and the change in pore structure throughout the entire processes were investigated in this study. Lignite samples with four different particle size fractions were dried in a fixed-bed reactor in the temperature range 60–160°C. The re-adsorbing moisture behaviors of dewatered coal samples containing different water contents were investigated at temperatures of 20–40°C and humidities of 55–95%. The changes in the pore structure of raw coal and different dried samples were measured by mercury intrusion porosimetry (MIP) and the relations between their re-adsorption performance and change in pore structure were explored. The moisture removal yields of lignite increased with an increase in drying time and temperature and was close to 100% above 120°C and over 100% after holding 40 and 15 min at temperatures of 140 and 160°C due to the release of CO₂ from the decomposing carboxyl group in the coal matrix. The re-adsorbed moisture content in dewatered coal was influenced by drying temperature and coal particle size through varying pore structure. The temperature and relative humidity in the re-adsorbing process were the main factors that influenced the moisture re-adsorption capacity of dewatered lignite, in which the re-adsorbing temperature mainly operated by varying the bonding ability of water on the surface of dewatered coal, and the relative humidity was connected with the pore structure as well. The mesopore was the main factor that influenced the re-adsorption of dewatered coal and the re-adsorption of moisture in dewatered coal at 100°C was highest due to the narrow range of the pore radius and because the relative volume ratio of 5 to 50 nm mesopore (above 91%) was high. The water loss yield of lignite with smaller particle size was higher due to its larger pore volume and surface area, but its re-adsorption capacity was lower because of lower volume ratio of 5 to 50 nm mesopore volume in dewatered coal obtained from the smaller size lignite.     

Effect of temperature on hot-air drying rate and on retention of antioxidant capacity in apple leathers

Fruit leathers are pectic gels, eaten as snack or dessert, obtained by dehydrating fruit purees. In this work, apple leathers were prepared by a hot-air drying process which allows the formation of a gel, following the “saccharide–acid–high methoxyl pectin” gelation mechanism. Leathers were produced at 50, 60 and 70 °C, from two formulations: control and added with potassium metabisulphite (KM) as antioxidant. The drying process was studied applying a diffusive model, while antioxidant capacity (AC) losses were represented by a first-order model. Activation energy for drying (20.6 kJ/mol) was lower than those estimated for AC losses in control (31.5 kJ/mol) and KM-added (37.9 kJ/mol) leathers. Therefore, the drying time reduction achieved by increasing air temperature is not sufficient to decrease AC losses in the range covered. AC retention decreased in both formulations at increasing air temperature. KM-added samples showed higher AC retention than the controls, except for those dried at 70 °C. Kinetic constants were lower for KM-added samples, suggesting a protective effect of the additive, especially at moderate air temperatures. In the most favorable situation, AC retention was of only 16%. Therefore, the functional character of these products may not be preserved if dried with hot air and the research on economically viable, less-severe drying technologies should be intensified.     

Optical and mechanical properties of cocona chips as affected by the drying process

The effect of the application of a pre-osmotic treatment to obtain hot air dried cocona (Solanum sessiliofurum Dunal) chips was studied. The drying kinetics and the optical and mechanical properties of cocona chips obtained by the combined method of osmotic dehydration and hot air drying (OD + HAD) and by only hot air drying (HAD) were compared. Samples were dried by hot air at 60 °C. For the combined method, they were pre-dried to a moisture content of 75 g_water/100 g, immersed in a 55 °Brix sucrose solution at 25 °C for 48 min. The pre-osmodehydration applied did not influence the subsequent hot air drying kinetics, resulting in a final product with 0.055 ± 0.005 g_water/g_cocona. The optical properties of OD + HAD chips were more favorable, exhibiting a smaller color change with respect to the fresh fruit (±15 units) than the HAD samples (±23 units). On the other hand, the OD + HAD chips presented more fracture peaks than HAD ones, this related with a structure with a higher degree of crispness, a very desirable property for a chip product.     

Combustion and Pollutant Emission Characteristics of Lignite Dried by Low Temperature Air

Lignite is a kind of coal that has high moisture content and needs to be dried before being utilized. In this article, a Chinese lignite was dried in air at 120–180°C and the changes in its physical and chemical structures after drying were investigated. The results showed that the pore volume and specific surface area of the lignite decreased after drying. Some of the methylene and methyl groups were oxidized by the oxygen in the drying air, resulting in an increase in oxygen functional groups. The combustion characteristics of the dried coals and parent coal (dry basis) were studied via thermogravimetric analysis. The total volatile yields of the dried coals increased compared to the parent coal. The burnout temperatures of the dried coals were higher than the parent coal, whereas the ignition temperatures stayed almost unchanged. An entrained flow system was set up to study the release of nitrogenous gas products during rapid pyrolysis and combustion. The HCN yields of the dried coals during pyrolysis were higher than that of the parent coal, and a similar trend was found for the NO yield during combustion. The mechanism changes of combustion and pollutant emission characteristics were discussed according to the results of the physical and chemical structure analyses.     

Modelling of dehydration–rehydration of instant rice in combined microwave-hot air drying

The drying operation is one of the critical steps in the preparation of instant rice. Drying methods and conditions play important roles in achieving the desired quality. In this study, instant rice was subjected to convective hot air, microwave and combined microwave-hot air dehydration. Three air temperature (70 °C, 80 °C, 90 °C) and three microwave power (210 W, 300 W, 560 W) settings were investigated to find the drying kinetics, rehydration kinetics and colour change. The results showed that combined microwave-hot air drying decreased the drying time required when compared to drying with either hot air or microwave energy alone. Predictive models were developed to describe dehydration and rehydration kinetics. Dehydration rate, rehydration rate and total colour change of rehydrated product generally increased with microwave level and air temperature. Combination drying with MW = 300 W and T = 80 °C was optimal in terms of drying time, rehydration time and colour.     

Quality evaluation of pineapple fruit during drying process

Pineapple (Anana comosus) slices were dried by hot-air convective drying technique at fixed temperature (45, 60 and 75 °C) and constant air velocity of 1.5 m/s. The effect of drying conditions (drying time and air temperature) on the pineapple quality was evaluated. The quality of dehydrated pineapple was analyzed by color and texture changes, l-ascorbic acid loss and the ability of water uptake during rehydration procedure. Water uptake during rehydration was described by Page model. Statistical analysis of data revealed not significant difference (p > 0.05) among color and mechanical characteristics of pineapple samples dried at different drying temperatures to preset moisture content. Pineapple samples dried at 45 °C had better rehydration ability and more l-ascorbic acid retention than those obtained by air drying 75 °C. Hence, 45 °C drying temperature was best condition for pineapple quality preservation.     

Simulation of coal pyrolysis by solid heat carrier in a moving-bed pyrolyzer

A one-dimensional, steady state, numerical model for coal pyrolysis by solid heat carrier in moving-bed has been developed. The multiple-reaction model of coal pyrolysis and the gas–solid–solid three phases heat transfer theory in packed bed have been applied to account for the pyrolysis process. The results show that the axial temperature distribution of the coal particles increase with a heating rate more than 600 K/min. Coal particle size has significant influence on the heating rate, while blending ratio is the determinant factor of pyrolysis temperature. Given the main operating parameters, product distributions (H₂, CO, CH₄, tar, etc) are calculated by the model. The modeling results are found to agree the experimental data using a moving-bed pyrolyzer with processing capacity 10 kg h^?1 of coal.     

Drying equations of Thai Hom Mali paddy by using hot air,carbon dioxide and nitrogen gases as drying media

The objective of this study was to develop a drying equation for predicting the thin layer drying kinetics of dried Thai Hom Mali paddy using different drying gases. Thai Hom Mali paddy cv. Khao Dok Mali 105 with initial moisture content of 32% dry basis was dried in a heat pump dryer at 0.4 m/s fixed superficial velocity, 60% fixed evaporator bypass air ratio, and varied drying temperatures of 40, 50, 60 and 70 °C using hot air, CO₂ and N₂ gases as drying media. Drying rate was not affected by drying gases but increased with drying temperatures. Moisture ratios, at any given time during the drying process, were compared among various models, namely, Newton, Page, Modified Page I, Henderson and Pabis, two-term, approximation of diffusion, and Midilli. The effect of drying air temperatures on the coefficients of the best moisture ratio model was determined by single step regression method. The R² coefficient, root mean square error (RMSE) and chi-square (χ²) were criteria for selecting the best model. The study found that the Midilli model was the best model for describing the drying behavior of Thai Hom Mali paddy in every evaluated drying gas. It should be possible to predict the moisture content of a product with a generalized model that shows the effect of drying air temperature on the model constants and coefficients.     

The energy consumption and color analysis of freeze/microwave freeze banana chips

This study investigated the energy consumption of preparing banana chips by freeze drying (FD) and microwave freeze drying (MFD) methods. The results in this study showed that the energy consumption for 400 g fresh banana (about 95 g dried samples) by FD process and MFD process are about 35.73 × 10⁶ J (9.92 kW h) and 21.76 × 10⁶ J (6.57 kW h), respectively. Compared to the traditional FD process, MFD can save up to 35.7% energy and 40% drying time. Increasing the heating power in the secondary drying stage of MFD process had been confirmed to result in decrease in both the energy consumption and drying time. After increasing the microwave power in the secondary drying stage from 1.0 W/g to 1.5 W/g in MFD process, total energy consumption is about 18.12 × 10⁶ J (5.56 kW h) and drying time can be reduced from 360 min to 270 min. The sensory evaluation of produced banana chips at different drying conditions (1.0 W/g, 1.5 W/g and 2.0 W/g) revealed that the sensory properties are acceptable by the customers except the 2 W/g microwave power dried product. Thus, the method that increased the heating powder in the secondary drying stage of the MFD process could potentially be an effective method to reduce the energy consumption without seriously sacrificing the color of the end product.     

Microwave-heated pyrolysis of waste automotive engine oil: Influence of operation parameters on the yield,composition, and fuel properties of pyrolysis oil

The pyrolysis of waste automotive engine oil was investigated using microwave energy as the heat source, and the yield and characteristics of the pyrolysis oils (i.e. elemental analysis, hydrocarbon composition, and potential fuel properties) are presented and discussed. The microwave-heated pyrolysis generated an 88 wt.% yield of condensable pyrolysis oil with fuel properties (e.g. density, calorific value) comparable to traditional liquid transportation fuels derived from fossil fuel. Examination of the composition of the oils showed the formation of light aliphatic and aromatic hydrocarbons that could also be used as a chemical feedstock. The oil product showed significantly high recovery (90%) of the energy present in the waste oil, and is also relatively contaminant free with low levels of sulphur, oxygen, and toxic PAH compounds. The high yield of pyrolysis oil can be attributed to the unique heating mode and chemical environment present during microwave-heated pyrolysis. This study extends existing findings on the effects of pyrolysis process conditions on the overall yield and formation of the recovered oils, by demonstrating that feed injection rate, flow rate of purge-gas, and heating source influence the concentration and the molecular nature of the different hydrocarbons formed in the pyrolysis oils. The microwave-heated pyrolysis can be performed in a continuous operation, and the apparatus described which is fitted with magnetrons capable of delivering 5 kW of microwave power is capable of treating waste oil at a feed rate of 5 kg/h with a positive energy ratio of 8 (energy content of hydrocarbon products/electrical energy supplied for microwave heating) and a net energy output of 179,390 kJ/h. Our results indicate that microwave-heated pyrolysis shows exceptional promise as a means for recycling and treating problematic waste oil.     

Effect of different drying conditions on the vitamin C (ascorbic acid) content of Hayward kiwifruits (Actinidia deliciosa Planch)

In this study, drying kinetics of kiwifruit are investigated experimentally and theoretically under varying drying conditions. Experiments are conducted using air temperatures at 35, 45, 55 and 65 °C, mean velocities at 0.3, 0.6 and 0.9 m s^?1 and, relative humidity values at 40%, 55%, 70% and 85%. Initially, sorption isotherms of the dried kiwifruit slices are determined for different temperatures and equilibrium relative humidity values. The values of the moisture diffusivity, D_eff are obtained from the Fick's diffusion model. The effects of the governing drying parameters on the vitamin C content as well as on the total drying time are determined. The experimental moisture data were fitted to some models available in the literature, mainly the Henderson and Pabis model, the Lewis model and the two-term exponential model and, a good agreement was observed. In addition, it is disclosed that increasing drying air temperature causes more loss in vitamin C in the dried fruits while degradation of vitamin C is reduced with increasing relative humidity of drying air.     

Structure characteristics of dewatered lignite from different drying temperature and time and effects on its behaviors of re-adsorbing moisture

By changing the drying temperature and residence time, a series of different degree dewatered lignite samples were prepared in the fixed-bed reactor under inert gas and their adsorbing moisture behaviors were investigated under certain re-adsorption conditions. Using SEM, nitrogen adsorption and in-situ FTIR analysis methods, the structure changes of dewatered lignite were measured and associated with the drying and re-adsorption behaviors. The results show that the higher the drying temperature, the higher the drying efficiency and the more obvious structure change of dewatered lignite. But the moisture re-adsorption amount of dewatered lignite showed different changing trends. Under the drying condition of 140°C and 50min, the total moisture content of coal after moisture re-adsorption was the lowest. Most pores are mesoporous in lignite and the macropore structure collapsed into mesopore during drying. When the drying temperature was higher than 120°C, oxygen-containing functional groups began to decompose; with the increase of drying temperature and time, decomposition rate increased. The hydrophilic strengths of -OH and COOH groups are stronger than that of others.     

Multi-impregnating pitch-bonded Egyptian dolomite refractory brick for application in ladle furnaces

A method of preparation of multi-impregnated pitch-bonded Egyptian dolomite refractory brick for ladle furnace is described. Brick samples were prepared from blend of calcined dolomite mineral and coal tar pitch. The blend was hot mixed and pressed under a compression force up to 151 MPa. Green bricks were baked for 2 h at temperatures up to 1000 °C. Voids in the baked bodies were filled with carbon by multiple impregnations using low-softening point coal tar pitch. Each impregnation step (30 min) was followed by calcination at 1000 °C. Brick samples containing 8–12 wt.% coal tar pitch binder and pressed under 108–151 MPa acquired quantify crushing strength. However, multi-impregnating favored the mechanical strength of the baked brick samples and improved their hydration resistance (>45 days). Dolomite brick samples containing 10 wt.% coal tar pitch and pressed at 108 MPa gave high hydration resistance (more than 60 days in normal condition) compared to the hydration resistance of the commercial bricks (30 days). The prepared brick samples have acceptable density, chemical stability, outstanding resistance and good mechanical properties would meet the requirements of Ladle furnace (LF) for steel making industry. In addition, estimation of production cost of the brick indicates it is competitive with the market price based on durability and service life time aspects.     

Usage of solar-assisted spouted bed drier in drying of pea

The main objective of this study is to evaluate the effects of solar-assisted spouted bed and open sun drying on the drying rate and quality parameters of pea. Color, shrinkage, bulk and apparent densities, internal and bulk porosities, rehydration capacity and microstructure were the quality parameters investigated in dried product.Drying rate for solar-assisted spouted bed was about 3.5 times of drying rate for open sun drying. Air temperature changed between 20 °C and 27.4 °C during open sun drying while temperature of air at the inlet of solar-assisted spouted bed dryer varied between 35.3 °C and 65.5 °C during the experiments. Effective diffusivities were found to be 0.64 × 10^?10 and 3.27 × 10^?10 m²/s for open sun and solar-assisted spouted bed drying of pea, respectively. In color analysis, it was observed that a* value increased while b* value decreased for both drying methods. Bulk density and apparent density of peas dried under open sun was higher than that in solar-assisted spouted bed drier. In both drying methods, internal and bulk porosities decreased. Shrinkage was more for open sun dried samples. Rehydration capacity for solar-assisted spouted bed dried sample was higher than the one for open sun dried.     

Moisture transport in garlic cloves undergoing microwave-convective drying

A laboratory scale microwave dryer was used to dry the garlic cloves, applying microwave power in the range of 10–40 W, air temperature in the range of 40–70 °C and air velocity in the range of 1.0–2.0 m/s. Heat and mass transfer coefficient during the drying process varied in the range of 35.23–79.54 W/m²C and 4.26–6.34 × 10^?2 m/s. The temperature of the product rose rapidly in the early part of the drying and became almost stable thereafter. The Biot mass transfer number confirmed that moisture diffusion was the limiting factor in microwave drying of garlic. The effective moisture diffusivity, which ranged between 1.29–31.68 × 10^?10 m²/s increased with the increase in microwave power but decreased with increase in air velocity.     

Changes in physico-chemical and functional properties during convective drying of aloe vera (Aloe barbadensis) leaves

Aloe vera leaves were dried at different temperatures in hot air oven and powdered. The percent powder yield was found 2.60%, 2.60%, 2.55% and 2.52% at 50, 60, 70 and 80 °C respectively. Powder samples had the pH (1% solution) 3.51, 3.53, 3.52 and 3.53 with the rise of drying temperature in the selected range. Statistically, yield and pH indicated no significant difference (p < 0.5) due to drying temperature variation. Wettability of powder at 70 °C was 32 s as compared to 35, 35 and 37 s in the samples obtained at 50, 60 and 80 °C respectively. Water absorption capacity of powder at 70 °C was 359% as compare to 351%, 354% and 356% of 50, 60, and 80 °C powder samples. The HPLC chromatogram obtained for the sample dried at 80 °C shows that as the temperature increased from 50 to 80 °C, aloin content decreased from 10.6 to 1.7 ppm. The “a” values were found 2.028, 2.226, ?0.282 and 2.531 for the samples obtained after drying at 50, 60, 70 and 80 °C respectively. Samples obtained at 70 °C showed negative “a” value indicated that the sample was more greenish in colour as compared to other samples.     

Effect of drying methods on volatiles of Chinese ginger (Zingiber officinale Roscoe)

Fresh ginger slices were dehydrated by air drying (AD), microwave drying (MD), vacuum drying (VD), and freezing drying (FD). Volatiles were extracted from fresh ginger pulp and dried ground ginger powder with solid-phase microextraction (SPME), and identified by gas chromatography–mass spectrometry (GC–MS). Results indicated that, 19, 28, 21, 20, 31 and 20 novel compounds (70 in total) appeared in dried gingers treated by AD at 50, 60 and 70 °C, MD at 60 W, VD in 13.3 kPa at 60 °C and FD in 0.203 kPa at chamber temperature of 22 °C, respectively. Principal component analysis for the main volatiles indicated that drying increased the relative contents of benzene,1-(1,5-dimethyl-4-hexenyl)-4-methyl-, 1,3-cyclohexadiene,5-(1,5-dimethyl-4-hexenyl)-2-methyl-,[S-(R*,S*)]-, α-farnesene and cyclohexene,3-(1,5-dimethyl-4-hexenyl) -6-methylene-,[S-(R*,S*)]- while decreased those of 2,6-octadienal,3,7-dimethyl-,(Z) and 2,6-octadienal,3,7-dimethyl-. Cluster analysis disclosed that MD was the most favorite drying way, followed by AD at 60 °C, VD, FD, and AD at 50 and 70 °C.     

Spouted bed and microwave-assisted spouted bed drying of parboiled wheat

The effect of spouted bed and microwave-assisted spouted bed drying on drying rates of parboiled wheat was investigated. In addition, the effective moisture diffusivities of parboiled wheat were calculated. The drying experiments were performed using 200 g of parboiled wheat, at three different air temperatures (50, 70, 90 °C) and at two different microwave powers (3.5 W/g (db), 7.5 W/g (db)). Microwave-assisted spouted bed drying at microwave power of 3.5 W/g and 7.5 W/g reduced drying time by at least 60% and 85%, respectively compared to spouted bed drying. The effective diffusivity values were in the range of 1.44 × 10^?10–3.32 × 10^?10 in spouted bed drying while they were between 5.06 × 10^?10 and 11.3 × 10^?10 in microwave-assisted spouted bed drying at different experimental conditions.