Energy efficient combined superheated steam dryer/MED

A new drying method of combined superheated steam and microwave drying is being proposed. The drying rates of sintered glass beads in combined superheated steam and microwave drying are experimentally and theoretically investigated. Drying experiments have been carried out in a waveguide where a standing wave is formed to uniformly heat a small sample. Concerning drying rate curves in combined superheated steam and microwave drying, a distinct constant rate period has been observed. For the falling rate period, high drying rates have been observed. For both periods, the drying rates in combined superheated steam and microwave drying are higher than those in superheated steam alone. Also, in comparison with the results of combined nitrogen and microwave drying, the normalized drying rates in combined superheated steam and microwave drying are higher than those at less than the critical moisture content in combined nitrogen and microwave drying. Moreover, theoretical drying rates for the falling rate period (predicted by a modified receding evaporation front model) in combined superheated steam and microwave drying, are in good agreement with the observed drying rates. The combined superheated steam and microwave drying method can attain higher drying rates under mild external conditions.

The effect of superheated steam (SS) drying and hot air (HA) drying on drying kinetics and changes in the color, crude protein, and amino acid concentrations (in particular, lysine content) of corn/wheat wet distillers grains (WDG) and centrifuged solubles (CS) was evaluated. An inversion temperature was reached at 139°C for WDG and 132°C for CS, above which moisture evaporation rate and qualitative changes under SS drying conditions exceeded the values noted in HA, and below which the reverse was observed. A significant decrease (from 8 to 50%) in the lysine content of WDG and CS was reported during SS and HA. The overall changes in the color (ΔE*) of corn/wheat WDG and CS ranged from 7.9 ± 2.6 to 27.2 ± 1.9 during SS drying and from 11.9 ± 3.7 to 32.0 ± 0.5 during HA drying. The observed deterioration in color was attributed mainly to changes in lightness (L*) and yellowness (b*) of dried samples. The values of L* and b* were reliable predictors of the lysine content of corn/wheat distillers co-products.

Superheated steam (SS) drying is known to be a more energy efficient alternative to conventional hot air drying. In food drying, burning and destroying the food product can be a problem for temperature sensitive material, such as fruits and vegetables, due to the high temperature required in SS drying. A solution is to create a drying environment having a sub-atmospheric SS pressure, which is often referred to as low pressure or vacuum drying. The objective of this study was to design, fabricate, and test a SS drying system that could operate at sub-atmospheric pressure.

Drying is an extremely energy-intensive process. Superheated steam as a drying medium can improve the energy efficiency of the drying processes. In superheated steam drying, waste heat can be recovered by condensing the exhaust steam or raising its specific enthalpy. Spray drying is widely used in industry, even though its energy efficiency is often low. Substitution of air by superheated steam as a drying medium in a spray dryer may reduce the energy consumption of the drying process by 20–30%; moreover, if excess steam generated by moisture evaporation is upgraded to a higher temperature level and reused for drying, the energy demand could be decreased by even 80%. A literature review showed that superheated steam spray drying was successfully applied for both thermally resistant and a wide range of thermally sensitive materials. Superheated steam drying gives a number of advantages in terms of product properties, i.e., higher particle porosity due to rapid moisture evaporation results in improved powder rehydration properties. Additionally, steam drying may be applied for in situ particle crystallization. Taking into account the advantages of superheated steam drying and the potential application of this technology in spray drying systems, there is a great need for further research in this field. This literature review aimed to present an energy-saving solution, i.e., superheated steam spray drying process, showing its advantages and potential applications, followed by drying kinetics, providing analysis of the research papers on experimental studies as well as mathematical modeling of this drying technique.

Breaking and disintegrating of biomass compacts while they are being dried in superheated steam (SS) is a common problem observed during the initial stage of SS drying. The present work investigated the moisture and temperature changes, volume and density variation, crushing resistance, and tensile strength of single cylindrical compacts produced from wet distiller's spent grain (WDG) under SS drying conditions. The wet compacts were dried in SS at 110, 130, and 150°C with SS velocities of 0.9, 1.1, and 1.4 m/s. For a specific temperature and velocity, the compacts were exposed to SS for time periods of 5, 120, 300, and 600 s and the changes in physical properties were analyzed. An increase in a percentage increase in volume by 78–130% and a decrease in density by 51–61% were observed as a result of drying the compact in SS. The results obtained from the study were compared with hot-air dried compacts for 600 s, indicating that SS drying had a substantial role in stimulating the relaxation of stresses stored in the compacts as compared with a convection hot-air drying process.

Modeling of effective moisture diffusivity and activation energy of distillers' spent grain pellets with solubles during superheated steam drying

A spray dryer was modified and tested with superheated steam as the drying medium. The effect of the inlet temperature on the recovery and morphology of the dried powder was then investigated. The results were compared with those obtained from hot-air spray drying. The results showed that the use of superheated steam and an increase in the inlet temperature led to an increase in the product recovery. The morphological results correlated with those of the product recovery in that superheated steam powder exhibited more inflated skin, leading to less adhesion of the sprayed droplets to the dryer wall. Keywords: morphology; product recovery; spray drying; superheated steam drying.

ABSTRACTThe effects of drying methods on equilibrated moisture content (MC) and swelling efficiency of Chinese cedar (Cryptomeria fortunei) wood were studied in this paper. Drying experiments were conducted with conventional (CON) drying and superheated steam (SHS) drying under atmospheric pressure. Specimens were equilibrated at two environment conditions to measure moisture and dimensional changes, and then the moisture excluding efficiency (MEE) and antiswelling efficiency (ASE) were determined. Results showed that the equilibrated MC of artificial-dried wood was lower than control samples (air drying), and the equilibrated MC of wood with SHS drying was lower than that with CON drying, which indicated that MEE was enhanced in SHS drying process. Similar results were found in swelling efficiency and ASE of artificial-dried wood and the control. The mechanism was studied by dynamic mechanical analysis (DMA) and X-ray diffraction analysis (XRD). The DMA results showed that both of relative storage modulus and relative loss modulus were the highest for SHS-dried wood and the lowest for the control samples. As for the crystalline structure assessed by changes of XRD, the results showed that the cellulose crystallinity and crystallite size of Chinese cedar wood with SHS drying were the highest, and control specimens were the lowest. All the analyses showed that Chinese cedar wood with low hygroscopic and high dimensional stability could be gotten through SHS drying process.

Superheated steam drying (SSD) of low rank coal (LRC) is applied to improve the heating value and thermal efficiency and to reduce greenhouse gas emissions and the danger of spontaneous combustion. It is essential to understand the fundamental aspects of drying LRC with superheated steam supported by funds in China and the development of clean coal technology. It is also important to promote the level of scientific technology relevant to safe energy strategies. The background of SSD based on China's unique energy structure and coal production situation are presented in this article. A comprehensive overview on progress and mechanisms of SSD is provided, including the status of drying technology supported by funds in China, distribution of project field and important research institutions, physical and chemical structure of water in coal, heat and mass transfer processes, mathematical models, and some results for wood, food, hot gas, etc., with particular reference to SSD in drying of LRC in China. There are still many challenges in the application of SSD of LRC in very large-scale power plants, drying equipment, and control technology. Advanced SSD sponsored by the fund project in China shows important significance to energy savings and reducing greenhouse gas emissions.

Superheated steam is a vital drying media due to inherently passive, nonpoisonous, no fire risk, antioxidant, and compatible with food products with superb thermophysical properties than hot air. Moreover, it will improve energy efficiency by energy-saving due to reusing the energy from exhausted steam, mainly by recirculation, and the use of partial exhaust of excess steam for other operations reduces the additional energy requirement. Additionally, the specific heat at constant pressure for superheated steam is nearly double that of the hot air, reducing the quantity required for drying. In general, superheated steam as a drying medium instead of hot air has significant potential. In this study, past, present, and prospects of the superheated steam drying (SSD) are critically analyzed and are presented systematically, such as classification, working, and recent developments. This study also focused on various areas such as analytical modeling, experimental work, and pilot-test of SSD with covering energy recovery and energy efficiency. Out of different drying systems, Fluidized bed dryers, Vacuum dryers, Rotary dryers, Flash dryers, Impingement dryers, and Spray dryers applicable for SSD are discussed in details as the current stage of development and probable potential. The SSD is having bright future for diverse applications including vegetable drying and fruit processing, chemical process industries, wood drying, chemicals, dyestuff and pigments recovery, effluent drying, etc.

Two drying treatments were applied to slices of beef: superheated steam and hot air. Drying kinetics and quality attributes such as color, water activity, and peroxide value were investigated for different drying conditions (drying medium temperature 130, 160, or 180°C; flow rate of the drying medium of 35, 45, or 55 kg/h; and sample thickness 3 mm, 6 mm, 9 mm, or minced beef). The experimental results show that superheated steam drying generally leads to shorter residence times in the dryer when the moisture content needs to be decreased below 8%. Superheated steam drying distinguishes itself by longer constant rate periods, lower critical moisture contents, and higher drying rates for the falling rate period compared to air drying. Reducing the sample thickness or increasing the transferred heat, by increasing the temperature or velocity of the drying medium, result in accelerating the drying process. Temperatures above 160°C, however, cause changes within the and its surface and prevent the bound moisture from getting to the meat's surface to evaporate. This so-called case-hardening effect is worse for air drying than for superheated steam drying and results in even longer drying times and higher final moisture contents. Superheated steam drying reduces the water activity faster than air drying at the beginning of the drying process, but the same values are reached at the end of the drying run. Furthermore, the study proves that the absence of oxygen during superheated steam drying leads to prevention or minimization of lipid oxidation reactions, thus resulting in low peroxide values. Undesired quality changes like off-flavors and off-odors hardly develop during superheated steam drying even at high temperatures and long drying times.

Conventional drying of the fibers from oil palm empty fruit bunches (EFB) using flue gas from diesel burners frequently causes browning and dust explosion. Replacing the drying medium with superheated steam is expected to improve the quality of EFB fibers as well as improve the safety of the dryer operation. In this study, the effects of steam temperature and steam velocity on the quality of steam–dried EFB fibers was investigated. The drying experiment was carried out at atmospheric pressure with steam superficial velocity in the range of 0.3 to 0.49 m s−1 and temperature in the range of 135 to 200°C. Three quality parameters of the EFB fibers, the color, strength, and microstructure, were used to assess the changes in EFB fiber quality as a result of superheated steam drying. The color of the EFB fiber was either improved or not significantly degraded. The strength of the superheated steam–dried EFB fibers was higher than that of undried and hot air–dried EFB fibers. The microstructure of fresh undried EFB fibers as seen by scanning electron microscopy (SEM) showed the presence of round silica particles of 10–20 µm in diameter all over the EFB fiber strand, which complicates pulping and bleaching. Superheated steam drying successfully removed the silica particles from the EFB fibers at temperatures of at least 200°C and a velocity of steam of at most 0.49 m s−1, which is better than hammering, which can only remove 88% of the silica particles. The high temperature of the superheated steam loosened the silica particles from their craters. The EFB fibers cracked and split at steam velocities at or above 0.49 m s−1 and high superheated steam temperatures at or above 200°C and as a consequence became weaker at these conditions. The removal of silica particles by superheated steam drying makes the EFB fiber amenable to pulping and bleaching. Superheated steam drying is therefore found to improve the overall quality of EFB fibers compared to hot air drying.

BackgroundConventional drying using heated air oven is commonly used as a method for preserving the product but often affects the nutritional value, taste, and texture. However, the heat from the drying method can oxidize and destroy heat-sensitive compounds. Superheated steam (SHS) drying uses superheated steam instead of hot air or combustion gases in a direct dryer and was reported better at preserving the nutritional values of food products.AimTo evaluate the effect of SHS drying on antioxidant properties of tea leaves. The study also compared SHS drying with conventional and freeze-drying methods.ResultsTea leaves dried using freeze drying retained the highest level of antioxidant properties compared to other drying methods. The leaves dried using SHS exhibited significantly higher radical scavenging activity, ORAC and FRAP values compared to oven drying method. At different drying temperatures (150 °C and 175 °C), oven dried leaves showed significantly higher (p < 0.05) antioxidant properties than that of SHS dried ones. Tea leaves dried for 60, 75, and 90 min using SHS showed significantly higher (p < 0.05) FRAP and ORAC values, and also total phenolic content compared to oven dried tea leaves.ConclusionTea leaves dried using SHS drying method retained higher level of antioxidant properties compared to oven drying. The drying method also retained lower antioxidant properties as drying time increased. Further study involving SHS drying in food-related fields should be conducted to support its usefulness.Graphical abstract

The aim of this study is to investigate the effect of different range of inlet fluid temperature on both electrical and thermal efficiency for a serpentine PV/T collector. The variation of the inlet fluid temperature used in this study is above and below ambient temperature. The thermal performance test uses the EN 12975 under indoor system with a solar simulator. The results showed that hybrid PV/T solar collectors with the inlet fluid temperature below ambient temperature have higher values for both heat loss coefficient and electrical efficiency when they compared to those obtained from the above ambient temperature. Meanwhile, the collector with the inlet fluid temperature below ambient temperature and mass flow rate of 0.015 kg/s has a higher value of heat loss coefficient of 2.2 W/m²K if they compared to those obtained from above ambient temperature and also there is an increase of 1% electrical efficiency with average temperature surface of PV/T collector 46.76ºC. The application of different range of inlet fluid temperature has no significant effect on zero efficiency of PV/T collector.Penelitian ini bertujuan untuk mengetahui pengaruh penerapan perbedaan temperatur fluida masuk pada kolektor surya hybrid PV/T aliran serpentine baik secara thermal maupun daya elektrik yang dihasilkan. Perbedaan temperatur fluida masuk yang digunakan adalah di atas dan di bawah temperatur lingkungan. Pengujian unjuk kerja thermal ini menggunakan standar EN 12975 sistem indoor dengan simulator surya. Hasil penelitian menunjukkan bahwa kolektor surya hybrid PV/T dengan temperatur fluida masuk di bawah temperatur lingkungan memiliki koefisien kerugian panas dan efisiensi listrik yang lebih tinggi jika dibandingkan dengan kondisi pengujian di atas temperatur lingkungan. Sementara itu kolektor surya hybrid PV/T dengan temperatur fluida masuk di bawah temperatur lingkungan dan laju aliran massa fluida 0.015 kg/s memiliki koefisien kerugian panas lebih tinggi 2.2 W/m²K dibandingkan dengan kondisi pengujian yang sama ketika temperatur fluida masuk di atas temperatur lingkungan dan terjadi peningkatan efisiensi daya listrik 1% dengan temperatur rata rata permukaan kolektor PV/T 46.76ºC. Sedangkan penerapan variasi temperatur fluida masuk di bawah dan di atas temperatur lingkungan tidak berpengaruh signifikan terhadap efisiensi zero pada kolektor surya hybrid (PV/T) aliran serpentine ini.Kata kunci : Energi matahari, Photovoltaic thermal (PV/T), EN 12975.

ABSTRACTInitial condensation on the sample surface during superheated steam (SS) drying leads to increased sample moisture affecting its mechanical and thermal properties. A study was conducted to understand the effect of temperature and velocity of SS on the amount of initial condensation on distillers’ spent grain pellets with an initial moisture content of 25% (wet basis). These pellets were dried using SS at 120, 150, and 180°C with velocities 0.5, 1.0, 1.2, and 1.4 m/s. Separate experiments were conducted for recording mass and surface temperature of the pellets during SS drying. Mass recorded over the drying period was then compared with the predicted mass obtained by solving the standard heat balance and film condensation equations. The predicted values of mass flux due to initial condensation were in close agreement with directly measured values with a maximum mean square error of 0.20. There was a 60–64% decrease in the amount of initial condensation as the temperature of SS was increased from 120 to 180°C. The results indicate that the initial condensation can be minimal when the temperature of SS is equal or above 180°C with SS velocity equal or above 1 m/s using a preheated drying chamber.