Evaluation of the energy efficiency of combined drying and heat treatment by superheated steam

This study compares energy efficiency of a combined drying and heat treatment with that of conventional hot air heat treatment, the theoretical heat consumptions required for each treatment were determined, and the actual heat consumptions for each treatment were measured at a pilot scale. Conventional heat treatment method separately performs kiln-drying and heat treatment for wood with hot air in different equipment. On the contrary, in the combined treatment, the wood is simultaneously dried and heat-treated in the same enclosed space. Because of the time and energy savings, the economic feasibility of combined treatment is much higher than that of conventional heat treatment. Although the theoretical required energy of the combined treatment was similar to that of the two-stage method, the actual energy consumption of combined treatment was less than that of the two-stage method. And, the energy efficiency of the combined treatment was calculated to be two times higher than that of the two-stage method. From the results of this study, decreases in the processing time and energy consumption and increases in the energy efficiency of the combined treatment by superheated steam were quantitatively shown when compared to two-stage method.     

Discrete pore network modeling of superheated steam drying

A nonisothermal two-dimensional pore network model is developed to describe the superheated steam drying of a capillary porous medium. The complex void space is approximated by a network of spherical pores interconnected by cylindrical throats. In this model, the condensation of water vapor at the network surface as well as the network drying are taken into account. During the network drying period, the liquid transport is driven by capillary action, whereas vapor transport occurs because of convection. The condensation of water vapor within the pores is modeled based on newly formulated liquid invasion rules. The simulation results, presented as temperature and moisture content profiles over time, indicate qualitative agreement with available experimental observations. The inclusion of the liquid invasion rules is shown to accommodate more of the condensed water mass compared to earlier models, in which condensation is only partly treated. Due to the viscous vapor flow, the vapor overpressure within the network, which is the driving force of vapor transport, is reproduced in these simulations. The influence of vapor overpressure on the disintegration of the liquid phase is also discussed.     

Reducing energy requirement for drying of beet-pulp: Simulation of energy integration between superheated steam and air drying systems

Beet-pulp dehydration in the sugar industry is a highly energy intensive unit operation. Producing 1?kg of dried beet-pulp requires ～2–3?kg of water to be removed. The cost saving is a real challenge in sugar factory as the current dryers are underperforming (around 3?MJ/kg of water evaporated) because the heat recovery is limited and only a small proportion of dryer exhaust can be reused. The aim of this study was to investigate by simulation the energy efficiency of an independent multistage drying method that combines superheated steam drying (SHSD) and hot air drying (AD). Two case studies awarding the two types of energy coupling (AD then SHSD or SHSD then AD) are presented and compared. An approach of optimization is developed from energy balance. A number of operating parameters of the two drying configurations are investigated using sensitivity analysis. It proves that both cases allow an energy economy around 40% compared to the conventional dryer. Nevertheless, the SHSD-AD plant may present more benefits for a better quality product.     

油页岩过热蒸汽的干燥动力学

以油页岩颗粒作为干燥物料,以过热蒸汽和热空气分别作为干燥介质,进行了油页岩干燥实验的研究。当颗粒粒径减小时,油页岩干燥速率越大;过热蒸汽和热空气温度增大时,干燥速率也越大。对比相同条件下过热蒸汽和热空气干燥油页岩的平均干燥速率,发现当干燥介质温度超过逆转点温度时,过热蒸汽条件下的平均干燥速率大于热空气下的数值。实验得出粒径分别为9,7,5 mm的油页岩颗粒逆转点温度值分别是154,179,177℃;逆转点温度值是个变量,随颗粒粒径大小变化而变化。颗粒粒径越大时逆转点温度值越小,粒径较小时逆转点变化不大。采用薄层干燥模型对油页岩的干燥数据进行动力学模拟,可得修正Page模型(Ⅱ)干基水分比w模拟值与实验值的最大绝对偏差是12%,综合比较发现修正Page模型(Ⅱ)能较好地描述油页岩在过热蒸汽条件下的干燥过程。     

Drying paper by impinging jets of superheated steam. Part 1: Constant drying rate in superheated steam

Over a wide range of operating conditions, the drying of paper by impinging jets of superheated steam proceeds by a constant rate period followed by a falling rate period. The constant drying rate, investigated here in the jet temperature range 150 ≤ T_j/ ≤ 465°C and over jet Reynolds numbers of 1000 ≤ Re_j ≤ 12000, is predicted within + 12% by a heat transfer expression using Martin's (1977) correlation for the heat transfer coefficient corrected for mass transfer by the Couette flow approximation factor, and a property ratio to account for the large temperature difference between the jet and the paper.     

Drying of soy sauce residue in superheated steam at atmospheric pressure

Soy sauce residue needs drying to avoid fermentation and oxidation during storage and transportation, and its reutilization as a useful resource is expected. Superheated steam drying was applied to investigate the effects of drying conditions on the drying characteristics and the content changes of salt and protein. The results showed that the inversion temperature was about 130°C, beyond which superheated steam drying was faster than hot air-drying. The drying time approaching equilibrium moisture content was reduced with elevated drying temperature as well as higher steam mass flow rate in the present experimental conditions. The effect of bed thickness on drying time was not obvious when drying temperature increased. Interestingly, the salt content of soy sauce residue could be decreased by 34.8% due to condensate water in the initial drying period (wetting), while protein content had no significant loss (p?相似文献   

Comparative study of moisture absorption and dimensional stability of Chinese cedar wood with conventional drying and superheated steam drying

The 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.     

Convective drying of wood-waste in air and superheated steam

The convective batch drying of Western Hemlock hog fuel-sized particles in fixed beds under various operating conditions quantiatively established the effect of factors which govern the drying process. A correlation was obtained for the Nusselt number during the heat transfer controlled period. Under specific conditions, the existence of a unified characteristic drying rate curve was confirmed. Drying behaviour as described by the receding plane model provided a mathematical expression for such a curve. The existence of an inversion point temperature was experimentally confirmed.     

过热蒸汽对氧化铝蒸发传热效率的影响及解决方案

在氧化铝的生产过程中,需要保持系统的水平衡和盐平衡,一般采用多效真空蒸发的生产工艺,换热设备大都采用列管式换热器,Ⅰ效多采用0.6 MPa的新蒸汽作为热源.由于铝酸钠溶液成分十分复杂,含有碳酸盐、硫酸盐等多种杂质,在蒸发过程中会以盐类结晶形式析出而附着在换热管壁上形成结疤,进而影响蒸发器的效率和运转率.作为热源的新蒸汽是由热力锅炉提供,由于输送路程较长,多采用过饱和蒸汽(其温度远远高于饱和蒸汽温度),这样虽然提高了蒸汽输送效率,但是却加剧了蒸发器结疤的形成.通过系统分析认为:用饱和蒸汽替代过饱和蒸汽作为蒸发器热源,可以有效地提高传热效率和蒸发强度,显著地降低能耗.     

过热蒸汽流化床制备粒状磷酸一铵的实验研究

实验研究了过热蒸汽流化床反应干燥一步法制备粒状MAP的工艺条件,在70 kPa,100～130℃,进料n(NH3)/n(H3PO4)为1.2～1.6条件下,床层操作稳定,制得了性状良好的球形磷酸一铵产品。     

Experimental analysis and CFD simulation of infrared apricot dryer with heat recovery

Drying is one of the easily accessible and the most widespread processing technologies that have been used since ancient times for preserving fruits. Drying is an energy-intensive and time-consuming process, so reducing energy demand is important. The main aim of this paper is to analyze the heat and mass transfer characteristics of product in the drying chamber and in addition to this, three-dimensional (3-D) computational fluid dynamic (CFD) simulation was performed. The analyses of heat and mass transfer were investigated theoretically and experimentally in infrared dryer (IRD). The dryer consists of air to air heat recovery unit and proportional temperature controller. Experiments were performed at 0.5 and 0.25?m/s air velocities and at 60 and 65°C apricot surface temperatures which were controlled by three thermocouples contacted on top side of the product. In order to use energy more effectively and improve the drying characteristics of apricot, analyses were performed under different drying conditions. Since the heat recovery unit has a key role in this system, the performance of this unit was investigated and recovered energy ratio was between 58 and 62%. The calculated moisture diffusivity values varied from 1.7?×?10^?10 to 1.15?×?10^?9 for apricot, and the highest value of average energy efficiency was obtained as 16.43% at 65°C temperature and 0.25?m/s air velocity. Theoretical and experimental results are in line with each other.     

A kinetic study of microwave and fluidized-bed drying of a Chinese lignite

The drying kinetics of Chinese lignite in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave were investigated. The changes in the mass as a function of drying time were measured under various drying conditions. The variations of moisture ratio with time were used to test ten different thin-layer empirical drying models given in the literature. In studying the consistency of all the models, some statistical tests, such as χ², residual sum of squares (RSS) and F-value were also used as well as coefficient of determination R². In nitrogen fluidized-bed and superheated steam fluidized-bed, the Midilli–Kucuk model best described the lignite drying process. Drying data in microwave were best described by the Page model, indicative of a difference in kinetics between the two drying methods. This difference was attributed to different heat transfer mechanisms under conventional and microwave drying conditions. The effects of drying parameters in nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying on the constants and coefficients of the selected models were studied by multiple regression analysis. The apparent diffusion coefficient of moisture in samples was obtained from the kinetics data and the apparent activation energies under nitrogen fluidized-bed, superheated steam fluidized-bed and microwave drying were found to be rather similar.     

聚酯长丝生产的能效分析及节能方案

对聚酯长丝生产工艺进行了简单介绍,并对聚酯及长丝的各个产品,如切片、POY、FDY和DTY的能耗情况进行了分析及评价,同时也给出了节能的解决方案.     

Mathematical modeling and influence of ultrasonic pretreatment on microwave vacuum drying kinetics of lotus (Nelumbo nucifera Gaertn.) seeds

The people of Southeast Asia often use lotus as a highly sought-after food source. Here, the effects of ultrasonic pretreatment on the drying kinetics of lotus (Nelumbo nucifera Gaertn.) seeds under microwave vacuum drying were investigated. The best fit model to predict the drying kinetics was also proposed. Lotus seeds were subjected to ultrasonic pretreatment at frequencies of 20, 35, and 80?kHz and power intensity of 0.75 and 1.50?W/g for 10?min using an ultrasonic bath and then to microwave vacuum drying. Five different mathematical models were fitted to the experimental data and a newly proposed model was selected based on model with highest regression coefficient (R²), lowest root mean square error (RMSE), sum square error (SSE), and chi-square (χ²), respectively. Time-domain nuclear magnetic resonance and field scanning electron microscope were used to describe the water state of ultrasonic samples and examine microstructure, respectively. The results showed that ultrasonic pretreatment performed at a relatively low frequency and relatively high power intensity had a positive effect on reducing the drying time (6.25–31.25%) during microwave vacuum drying because of the redistribution of water and the formation of microchannels. In parallel studies, the new model showed the best fit to the drying curve.     

2150kW背压式汽轮机节能改造实践与运用

介绍了2150 kW背压式汽轮机的结构原理,分析了汽轮机在生产运行过程中能效较低和运行故障频繁的原因,通过重新设计制造汽轮机,并对润滑系统和控制系统进行优化改造,前、后汽封平均蒸汽泄漏量由6 t/h降为0.45 t/h,蒸汽消耗量由25.06 t/h降到20.84 t/h,取得了良好的经济效益.     

Red pepper (Capsicum annuum L.) drying: Effects of different drying methods on drying kinetics,physicochemical properties,antioxidant capacity,and microstructure

Results of an experimental study are presented and discussed for pulsed vacuum drying (PVD), infrared-assisted hot air-drying (IR-HAD), and hot air-drying (HAD) on drying kinetics, physicochemical properties (surface color, nonenzyme browning index, red pigments, rehydration ratio, water holding capacity, and ascorbic acid), antioxidant capacity (ferric reducing antioxidant power and 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity), and microstructure of red pepper. As expected, the drying time decreased with an increase in drying air temperature, IR-HAD needed the shortest drying time, followed by HAD and PVD. The effective moisture diffusivity (D_eff) of red pepper under PVD, HAD, and IR-HAD was computed to be in the range 1.33–5.83?×?10^?10, 1.38–6.87?×?10^?10, and 1.75–8.97?×?10^?10 m²/s, respectively. PVD provided superior physicochemical properties of dried red pepper compared to samples dried by HAD and IR-HAD. In detail, PVD yielded higher rehydration ratio, water holding capacity, red pigment and ascorbic acid content, brighter color, lower nonenzyme browning index, and comparable antioxidant capacity compared to samples dried by HAD and IR-HAD at the same drying temperature. Furthermore, PVD promoted the formation of a more porous structure, while HAD and IR-HAD yielded less porous structure. The current findings indicate that PVD drying has the potential to produce high-quality dried red pepper on commercial scale.     

Heat pump drying of grape pomace: Performance and product quality analysis

Abstract

Grape is one of the most popular fruits and various types of grape have been cultivated by more than 100 countries around the World. The wine and juice industry produces large quantities of by-product, called grape pomace (GP) as an industrial waste and it consists of skins, seeds, and stems. Various processes such as separation, pressing, drying, and milling are applied to benefit from its health effects. In this study, the seeded black GP Kalecik karas? (Vitis vinifera) was dried in an assisted closed cycle heat pump dryer (HPD) designed for high-moisture products to investigate the drying behaviors of GP. The effects of drying air temperature on bioactive properties and the drying characteristics of GP, and performance of system have discussed. Experiments were carried out at two different temperatures (45 and 50°C) and air velocity of 1.0 m/s. It was seen that increasing temperature decreased the drying time, coefficient of performance of whole system (COP_ws), and specific energy consumption (SEC). The average values of COP_ws for temperatures 45°C and 50°C were calculated as 3.28 and 3.10, respectively. The drying efficiencies (DE) at drying air temperature of 45°C and 50°C ranged from 2 to 12% and from 2 to 15%, respectively. Additionally, result of analysis has indicated that using a HPD at lower temperatures increases performance of system despite of higher energy input. Bioactive properties of dried samples at drying air temperature of 45°C are better than 50°C. The results show that drying the GP at low temperature is more suitable for product quality. For this reason, heat pump may be preferred. It shows that this drying system with higher capacities in the future can be recommended as an alternative technique in terms of energy usage, drying time, and performance of system.     

Reaction Engineering Approach (REA) to model the drying kinetics of droplets with different initial sizes—experiments and analyses

Droplets with different initial sizes, which are typical in conventional liquid atomization for spray drying applications, will result in varying drying and crust formation histories. It is essential for any droplet drying model to accurately capture such fundamental phenomena. This study used a newly constructed glass-filament single droplet rig to evaluate the applicability of the Reaction Engineering Approach (REA) in describing such effect. For the three initial sizes (1, 2 and 3 μL) tested, the glass filament gravimetric method clearly distinguished the different drying kinetics and the crust formation phenomenon, delineated by the drying behavior. Analysis from the drying kinetics revealed that the main premise of the REA, which utilizes a material-specific master activation energy curve, is applicable to droplets of different initial sizes at all the three air temperatures tested. This allowed the REA to accurately predict the different temperature and moisture histories given by droplets with different initial sizes. The result supports the REA as a good modeling approach for a wide range of initial droplet conditions. A new master curve approach was proposed to predict the diameter change of droplets with different initial concentrations. Validation with the current and past experimental data revealed that this approach has strong potential to account for the different feed concentrations typically found in spray drying applications.     

Near-fluidizing microwave drying to stabilize encapsulated material: Analysis of kinetic,energy and quality elements

Dehydration of the encapsulated material containing nutritional ingredients was determined to be necessary for functional foods and probiotics production. The application of a suitable drying process was required. This study proposes the development of a new dehydration process, called near fluidizing microwave drying (NFMD), to minimize the problems observed in other drying processes, such as spray drying or lyophilization. Several heating strategies, which are employed in microwave applications under fluidizing conditions, were adequately modeled to analyze the effect of the operational variables. The fitting of experimental data has enabled the determination of the mass and heat transfer coefficients: diffusivity and heat convection. The drying phases were analyzed based on the obtained values of these parameters as basis for the selection of the most favorable operational conditions. Under these conditions, the NFMD process has been employed for the dehydration of the encapsulated probiotic Bifidobacterium animalis subsp. Lactis (BB12). The best results of the cell viability were around 90%, demonstrating the suitability of this novel technology for these thermo-sensitive materials.     

Thermodynamic characterization of single-stage spray dryers: Mass and energy balances for milk drying

Spray drying is an efficient unit operation applied in food drying that demands a high amount of energy compared to vacuum evaporation and membrane filtration. The objective of this work was to present a mathematical model-like basis for the construction of mass and energy balances. For this purpose, two lab-scale single spray dryers in milk drying with different evaporative capacities have been used as example. The values of the absolute humidity, mass and energy losses, energetic specific consumption (ESC), and the efficiency of the process were obtained by calculations developed in this work. The mathematical model was valid for the evaluation of mass and energy losses, and it allowed us to compare the efficiencies of spray dryers with different designs. From this model, it is possible to compare different drying processes and dryers.