Superheated Steam Drying Research Articles

Fluidized Bed Superheated Steam Dryer for Bagasse: Effects of Particle Size Distribution

Fluidized bed superheated steam drying is one of the technologies successfully applied to drying pulp in the sugar beet industry. It has the technological advantages of energy efficiency and safety (inert environment) required for use in drying bagasse. A comparison of the particle size distribution of bagasse and beet pulp was evaluated in terms of fluidization. The size distribution of bagasse particles is from 2 to 10 times broader than the equivalent distribution of beet pulp particles. The mean particle size of the bagasse is 1/3 of the mean size of the beet pulp. Fluidization tests proved that bagasse fluidization is possible. It was found that beet pulp and bagasse particles clearly differ on shape and size distribution which in turn will affect the design of the ancillary equipment and the fluidization systems if sugarcane bagasse is to be dried using superheated steam technology.

Drying of oil palm frond particles in a fluidized bed dryer with inert medium

Drying characteristic of oil palm frond fibres was investigated in a fluidized bed dryer with the presence of inert particles. Sand was used as inert material. Effects of air temperature (60, 70 and 80?C), air velocity (0.79 and 0.85 m/s) and mass ratio of fibres to sand (1:0, 1:1 and 1:2) on the drying curves were investigated. The results showed that the shortest drying time was obtained with the highest air temperature, air velocity and fibres to sand mass ratio. The experimental drying data were fitted to nine existing drying models namely Lewis, Page, Modified Page, Henderson and Pabis, Logarithmic, Two-term, Two-term exponential and Wang and Singh models and a proposed new model. The goodness-of-fit was determined based on the values of r2, c2 and RMSE. The results showed that the best quality of the fit was obtained using the proposed model. The new model was also validated for the superheated steam drying of oil palm empty fruit bunch from other work.

Master curve behaviour in superheated steam drying of small porous particles

A lump drying model was developed for superheated steam drying of porous particles. Using single particle drying data [1], a unique master curve drying characteristic was obtained for porous ceramic particles dried under different degree of superheating and relative velocities. Further analysis revealed that the mass transfer depression phenomenon is significant under such superheating condition, typically used in drying processes. This highlights the precaution required in the case of future model development. This approach can potentially be a versatile approach in modelling the drying of porous particles, such as brown coal, under superheated steam condition.

Effects of various pretreatments and drying methods on Salmonella resistance and physical properties of cabbage

The combined effects of pretreatment and drying methods on the resistance of Salmonella attached to vegetable surfaces as well as some physical properties, in terms of color and shrinkage, were investigated. Cabbage was used as a test vegetable and Salmonella Anatum was used as a test microorganism. Cabbage leaves were pretreated either by soaking in 0.5% (v/v) acetic acid for 5min, blanching in hot water for 4min or blanching with saturated steam for 2min prior to either hot air drying, vacuum drying (10kPa) or low-pressure superheated steam drying (10kPa) at 60°C. Based on an initial Salmonella contamination level of approximately 6.4logCFU/g, soaking in acetic acid, hot-water and steam blanching resulted in 1.6, 3.8 and 3.6logCFU/g reduction in the number of Salmonella, respectively. Drying without pretreatment could not completely eliminate Salmonella attached on the cabbage surfaces, while no Salmonella was detected on the pretreated samples at the end of the drying process. Volumetric shrinkage was not affected by the pretreatment and drying methods. Dried blanched samples exhibited greener and darker color than the dried acetic acid pretreated and untreated samples.

Application of computer vision technique for on-line monitoring of shrimp color changes during drying

The effects of drying temperature and drying medium velocity on color change kinetics of shrimp viz. lightness (L∗), redness (a∗), yellowness (b∗), total color difference (ΔE), chroma (CH), hue angle (H°), and browning index (BI) were on-lineally investigated. Drying experiments were carried out on dryer equipped with computer vision systems using hot air drying (HAD) temperatures of 50–90°C and superheated steam drying (SSD) temperatures of 110–120°C at drying medium velocities of 1–2m/s. Zero-, first-order, and fractional conversion models were utilized to describe the color changes of shrimps and the fractional conversion model successfully tracked the experimental data. The results showed that the color parameters were significantly influenced by the studied parameters. Lightness of the samples decreased, while other color parameters increased as drying proceeded. Generally, increasing drying medium temperature decreased L∗ and H°, whereas increased other color parameters. The color characteristic of the SSD finished products were acceptable than the HAD processed samples. Finally, dimensionless moisture content of shrimps during drying was accurately correlated to the color parameters and drying time using a quadratic regression model. Moisture ratio had strong relationship with the lightness change compared with the redness and yellowness variations.

Protein Content and Antioxidant Activity of Distillers’ Spent Grain Dried at 150°C with Superheated Steam and Hot Air

The quality of dried distillers’ grain (DDG) is of great importance, and due to concerns regarding drying efficiency, various drying methods have been proposed. The objective of this study was to evaluate the protein content and antioxidant activity of DDG using two different drying media: (1) hot air at 150°C and (2) and superheated steam (SS) at 150°C. The results were compared to a reference sample dried at near ambient air temperature of 30°C. Protein content ranged from 15.1 to 16.4% wb for all samples. With respect to phenolic content, ethanolic extraction (3.1–12.9 mg GAE/g) was more effective than aqueous extraction (0.87–2.9 mg GAE/g). The DDG samples dried with SS had the highest phenolic contents among the analyzed samples (p < 0.05). Antioxidant activity ranged between 0.32 and 0.44 mg Trolox/g for aqueous extracts and 0.54–0.57 mg Trolox/g for ethanolic extracts. The results indicate that SS drying can be a suitable method to dry distillers’ spent grain without the adverse effect on protein and phenolic contents.

Study of Chemical Structure Changes of Chinese Lignite upon Drying in Superheated Steam, Microwave, and Hot Air

Chemical changes of Chinese lignite upon drying in superheated steam, microwave, and hot air have been studied in this paper using the Fourier transform infrared (FTIR) spectroscopy technique. The infrared (IR) spectra of raw and dried samples were curve-fitted to a series of bands in aliphatic hydrogen (3000–2800 cm–1) and carbonyl absorption (1850–1500 cm–1) zones. It has been found that aliphatic hydrogen absorbance decreased slightly with an increasing temperature during superheated steam drying, while absorption of carboxyl (COOH) and carbonyl (C═O) groups decreased drastically, indicative of the loss of oxygen functionalities with an increasing drying temperature. During steam drying, aromatic carbon and aromatic ring stretch absorption remained relatively unchanged up to 250 °C and decreased significantly thereafter because of some pyrolysis reactions that took place at higher drying temperatures. Microwave heating of lignite resulted in a significant decrease in the concentration of oxygen-contain...

Generalized microstructural change and structure-quality indicators of a food product undergoing different drying methods and conditions

It is well recognized that changes of many physical characteristics of food during drying are due to changes of the product microstructure. However, since both the physical characteristic and microstructural changes depend on the drying methods and conditions, relationships between the physical and microstructural changes are difficult to be generalized. The aim of this work was to determine if it would be possible to develop a generalized indicator that could be used to monitor microstructural changes of a model food product (carrot cubes) undergoing three different drying methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying. Two types of indicators, i.e., normalized change of the fractal dimension (ΔFD/FD0) of the sample microstructure and normalized change of the average sample cell diameter (ΔD¯/D0¯), were tested. Further investigation was made to determine if the tested indicators could be used to correlate the microstructural changes to apparent physical characteristic changes (shrinkage and hardness). It was found that both ΔFD/FD0 and ΔD¯/D0¯ increased with a decrease in the product moisture content, corresponding to an increase in the irregularity of the sample microstructure and a decrease in the sample cell volume; the relationships between the changes of these indicators and product moisture content were similar among all the tested drying methods and conditions. However, ΔFD/FD0 seemed to be a more generalized structure-quality indicator than ΔD¯/D0¯.

Experimental Study on Super-Heated Steam Drying of Lignite

This paper applies super-heated steam drying technology to improve the quality of lignite. A unique experimental system was built up. In order to obtain the optimum operation conditions, the drying kinetics was measured. The temperature range of super-heated steam was from 120 to 200°C. The results showed that the drying process of super-heated steam drying of lignite can be well depicted by two stages, as a constant drying rate stage followed by a falling drying rate stage. The comparison of drying process to the hot air drying showed the superior advantages of super-heated steam drying on safety, drying capacity and energy conservation. Analysis shows the huge application potential of lignite in power plants by means of the super-heated steam drying.

On Prediction of the Drying Rate in Superheated Steam Drying Process

The aim of the study was to determine how the drying rate in the falling drying rate period can be predicted in superheated steam drying. The study presents drying kinetics (determined experimentally) in the range of steam temperatures from 120°C to 200°C, with the superheated steam velocity from 0.18 to 0.40 m/s and under atmospheric pressure of a gypsum plate. In the study the drying rate based on the convective heat-transfer coefficient and steam-solid temperature difference was determined. It was proven that in order to predict drying rate in the falling rate period the surface temperature must be known.

Application of Image Processing to Analyze Shrinkage and Shape Changes of Shrimp Batch during Drying

In this article, variations in the top-view area and lateral-view area, average area, perimeter, Feret diameter, roundness, elongation, shape of the edge, and diameters of the shrimp in the batch parallel and perpendicular to the drying medium flow were investigated in defined intervals during drying. For this purpose, a thin-layer dryer based on machine vision was fabricated and image analysis techniques were used. Drying experiments were conducted in triplicate at five drying temperatures of 50, 70, 90, 110, and 120°C and three drying medium velocities of 1, 1.5, and 2 m/s. Purely near-atmospheric superheated steam drying (SSD) was used for the temperatures above the boiling point of water (110 and 120°C). Drying at the other temperatures was done using a hot air convective method. Analysis of batch area shrinkage, average area shrinkage, normalized Feret diameter, dimensionless perimeter, and diameters parallel and perpendicular to the drying medium flow showed that there are almost linear relations with moisture content. Drying medium temperature and velocity had a significant effect on all measured morphological parameters (P < 0.01). There was a significant difference between shrinkage of diameters parallel and perpendicular to the drying medium flow in all studied drying conditions, which implies that shrinkage of shrimp samples was nonisotropic. Moreover, comparing the top- and lateral-view areas of the shrimp batch showed that there was nonisotropic shrinkage in the shrimp samples during drying process. More regular and irregular edges of shrimp were obtained at low and high temperatures, respectively. Drying took place entirely in the falling rate period. Drying medium velocity had no significant effect on drying time. No regular trend regarding the effect of the studied drying medium velocities on the roundness and elongation of shrimp samples was found. More porous shrimp samples with a lower degree of shrinkage were obtained in superheated steam drying in comparison to hot air drying at high temperatures.

Comparative Evaluation of Mathematical Models for Release of Antioxidant from Chitosan Films Prepared by Different Drying Methods

Antioxidants are often added to many types of food packagings, especially packaging films, to enhance their effectiveness in protecting food from the environment. This positive action is possible due to release of the agents from the film matrix into food to reduce oxidation, thus extending the product's shelf life. For effective design of antioxidant-added films, the release characteristics of antioxidant from the films under various conditions need to be known and predicted. The aim of this study was to compare various simple mathematical models for prediction of the release of antioxidant from edible chitosan films into distilled water at room temperature. Chitosan films were prepared via hot air drying, vacuum drying, and low-pressure superheated steam drying. Models with different expressions for the effective diffusion coefficient were tested. The model equations were solved numerically using COMSOL Multiphysics software (Comsol AB, Stockholm, Sweden). The prediction efficiency of the models was verified by comparing the predicted release kinetics of the antioxidant, in terms of the total phenolics content (TPC), with the experimental data available in the literature. It was found that the model assuming the effective diffusion coefficient as a function of the phenolics concentration gave the best agreement with the experimental results.

An Overview of Recent Developments and Some R&D Challenges Related to Drying of Foods

Thermal dehydration is the most common and cost-effective technique for preservation of foods and for the production of traditional as well as innovative processed products such as snacks with desired functionalities. The basic intent of this article is to provide a global overview of emerging and innovative thermal drying technologies that are already commercialized or show potential of industrial exploitation upon successful R&D to sort out some limitations. New drying technologies are needed to enhance quality, reduce energy consumption, improve safety, and reduce environmental impact. Mathematical modeling can be used for cost-effective development of untested novel designs to reduce the cost and time required for innovation. As examples of emerging drying technologies we consider selected dehydration techniques with imminent commercialization potential. These include heat pump–assisted drying, microwave-assisted drying, low-pressure superheated steam drying, pulse combustion spray drying, pulsed and ultrasound-assisted osmotic dehydration, as well as novel gas–particle contactors such as impinging streams and pulsed fluidized beds. Multistage drying, intermittent drying, and the use of hybrid drying technologies—which combine advantages of different dryers without some of their limitations—will be outlined. This article also discusses various methods of energy minimization, and the potential for use of renewable energy will also be discussed briefly. Although this overview emphasizes food dehydration, the themes covered are applicable to other materials as well.

Generalized desorption equilibrium equation of lignite in a wide temperature and moisture content range

Brown coal is the most abundant and economically viable source of energy. To increase the efficiency of power generation from brown coal predrying of lignite is probably the first step to be taken. Both air drying, or more energy efficient superheated steam drying, may be considered. For the design of both processes an equilibrium relationship between water activity, moisture content and temperature in a form of working desorption isotherm is needed. This work presents experimentally obtained results of sorption isotherms measurements at seven temperatures and one sorption isobar at atmospheric pressure obtained for Bełchatów brown coal. These results were compared to the results obtained by other authors for Australian and USA coals and due to relatively close fit of all data points one generalized equation of desorption equilibrium was fitted covering a wide range of temperatures from 5 to 260°C and moisture contents up to 1.5kg/kg. Adsorption isotherms are not described by the same equation since strong sorptional hysteresis was observed.

Thermal resistance of Salmonella enterica serovar Anatum on cabbage surfaces during drying: Effects of drying methods and conditions

The effects of selected drying methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD), on the heat resistance of Salmonella attached on vegetable surface, which are data that have never been reported elsewhere, were investigated at drying temperatures of 50-70 °C; vacuum drying and LPSSD were carried out at an absolute pressure of 10 kPa. The selected Salmonella serovar, i.e., S. Anatum, was used as a test organism. Cabbage was used as a vegetable model to represent uneven natural surface. The results showed that drying methods had a significant effect on the drying kinetics as well as the destruction rate of Salmonella. Higher drying temperatures resulted in higher destruction rates of S. Anatum. Hot air drying was noted to be the slowest drying process, while vacuum drying and LPSSD could be used to shorten the drying time. By considering the reduction in the number of Salmonella at the end of drying, LPSSD is recommended as it has proved to yield the highest degree of S. Anatum inactivation.

Inversion Temperature and Pinch Analysis, Ways to Thermally Optimize Drying Processes

This work studies the compatibility and suitability of a combined inversion temperature and pinch analysis with the process selection for air and superheated steam spray drying of milk solids. The inversion temperature is a good starting point for an energy analysis because it is a simplified rate-based approach to comparing the steam and air drying systems. pinch analysis enables process integration, at least on a heat recovery and heat exchanger network level. The resulting inversion temperature for the studied system was estimated as 182°C for the dryer inlet temperature. However, mass and energy balances showed that a minimum inlet temperature for spray drying of 184°C was required for the superheated steam dryer in order to ensure that the outlet solids temperature above the dew point temperature. The inversion temperature is still very relevant in the early stages of a design process because it allows a quick assessment of which drying medium should result in a smaller dryer. It was evident that the steam system is better from an energy perspective because of the recoverable latent heat of the water vapor carried out of the dryer with the recycled steam. The steam system has between 82 and 92% of thermal energy recovery potential as condensable steam, compared with 13–30% energy recovery of the air system. However, other important design and operational factors are not discussed here in detail. Combining the inversion temperature and pinch analysis suggests that superheated steam drying both gives better energy recovery and is likely to give smaller dryers for all operational conditions.

A Critical Assessment of Industrial Coal Drying Technologies: Role of Energy, Emissions, Risk and Sustainability

Low-rank coals (LRCs) constitute about 45% of the total coal reserves and hence will soon be the fossil fuel of choice in many countries despite their high moisture content on mining, which varies from 30% to as high as 66%. It is important to reduce their water content to enhance the heating value and reduce transportation costs while enhancing combustion efficiency, safety, and reduction of emissions on combustion. The level of moisture to be achieved upon drying LRCs depends on the end application; it varies from as low as 0% for hydrogenation processes to 15% for briquetting and gasification processes. Numerous drying technologies have been proposed for drying coal; they include pulse combustion, vacuum, fluid bed, rotary, flash, microwave, and superheated steam drying. Each technology has some pros and cons, which are not always clearly spelled out in the literature. In addition, it is necessary to develop sustainable rather than just cost-effective drying systems for LRC. In this article we assess various coal drying techniques critically and identify their strengths and weaknesses. Some theoretical comparisons of different dryer types are carried out based on energy utilization and carbon footprints. The jury is still out on optimal drying technology for LRC and innovative design concepts should be evaluated before finalizing the selection.

The Effect of Using a Heating Tube in an Existing Spouted Bed Superheated Steam Dryer

Interest in the use of biofuels, such as pellets and briquettes, has continued to grow in the European market in recent years. In order to manage the increased use of biofuels, the dryer capacity must also increase. One possible way of accomplishing this is to install heating tubes into the already existing dryers. Therefore, industrially relevant and appropriate design data, such as energy efficiency and a possible increase in the capacity of developing drying systems, are needed. This article presents the experimental results obtained from drying sawdust in a continuous spouted bed using a heating tube submerged in the bed; the results are compared with those obtained from a bed without using a heating tube. Superheated steam is used as the drying gas in all tests. The drying test is performed with an almost constant inlet moisture content and at three different inlet and outlet temperatures. The drying efficiency increases when the heating tube is turned on. Some explanations of the relation between inlet and outlet gas temperature and moisture content are presented.

Mathematical model of pork slice drying using superheated steam

Superheated steam has received much attention as an effective technique for drying purposes because it produces dried products with high quality attributes. Although currently there are a number of works reporting the development of a mathematical model of superheated steam drying, they do not use a numerical method to estimate the effective moisture diffusivity value ( D eff value) of the product. The purposes of this work, therefore, were to develop a semi-empirical model for estimating the D eff value of pork, and for predicting the evolution of the moisture content and the center temperature of sliced pork during superheated steam drying. The model was based on mass and energy-balance equations and was divided into three periods: heating up, constant drying rate and falling drying rate period. It was solved using an explicit finite difference method and used a grid search method to estimate the D eff value of pork. The predicted results were compared with the experimental data of superheated steam drying of seasoned and unseasoned pork with slice thicknesses of 1 and 2 mm at a drying temperature of 140 °C. The comparison results showed that the developed model could estimate the ranges of the D eff value of pork fairly well ( D eff = 3.311–12.471 × 10 −10 m 2/s for seasoned pork, and 4.200–15.056 × 10 −10 m 2/s for unseasoned pork) and could reasonably predict the evolution of the moisture content of the sliced pork. The predicted center temperature of the sliced pork was higher than the experimental data in the heating up period and in the first 5 min of the falling drying rate period, but it agreed well in the constant drying rate period and after the drying time of 10 min. Moreover, it was found that the slice thickness and the seasoning had an influence on the drying curves only in the constant drying rate and falling drying rate period.

Drying kinetics and ANN modeling of paneer at low pressure superheated steam

Drying characteristics, selection of analytical model and development of artificial neural network (ANN) models of 1cm(3) paneer at low pressure superheated steam drying (LPSSD) were studied. Effects of steam temperature and pressure on drying rates were determined. Page's model was selected as the best predictive model. Second degree polynomial, non linear regression analysis resulted in a good agreement of defined model by changing the values of temperature and corresponding pressure. Optimized ANN models were developed for all data set. The correlation coefficient for all data set was >0.98 in all cases.