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4 Spin-flash dryer. (From Devahastin, S. (Ed.), Mujumdar's Practical Guide To Industrial Drying-Principles, Equipment And New Developments, Exergex Corporation, Montreal, Canada, 2000. With permission.)
Source publication
Drying is a separation process that converts a wet solid, semisolid, or liquid feedstock into a solid product by evaporation of the liquid into a vapor phase via heating. Essential features of the drying process are phase change and production of a solid, dried product.
Citations
... Mechanical dryers for the production of high-quality cassava flour are available in a variety of forms, including the tunnel dryer, the rotary dryer, and the flash dryer. A pneumatic conveying dryer, also known as a flash dryer, is the most cost-effective and extensively used drying method for solids that have been dewatered or are naturally low in moisture Levy and Borde, 2014). One of the most frequent types of continuous convective drying systems is the ''flash dryer'', which utilizes an entrained fluidized bed to achieve its drying results (Brennan, 2011). ...
... For cassava drying, the temperature of the solid must remain below 64.3 • C in order to avoid starch gelatinization (Breuninger et al., 2009). Dryer designs therefore need to be adapted to the product, as each has its own set of characteristics (Levy and Borde, 2014). The design of a dryer is particularly dependent on the product's initial and final moisture content, temperature sensitivity, and particle size of the product being dried (Levy and Borde, 2014;Jayaraman and Gupta, 2014). ...
... Dryer designs therefore need to be adapted to the product, as each has its own set of characteristics (Levy and Borde, 2014). The design of a dryer is particularly dependent on the product's initial and final moisture content, temperature sensitivity, and particle size of the product being dried (Levy and Borde, 2014;Jayaraman and Gupta, 2014). In addition, it is necessary to customize dryer designs to meet the needs of specific target audiences (Chua and Chou, 2003). ...
... t/h). Usually gravimetric dosing systems, such as the ODM-WeighTUBE [3] are able to dose the material with an accuracy of +/-1% from the massflow setpoint. Therefore for a typical case, where 15t/h are transported to the combustion process the variation over time in the actual energy content of the infeed fuel are varying quite enormously. ...
... This gas stream (drying medium) also supplies the heat required for drying and carries away the evaporated moisture. Superheated steam can also be used as drying medium yielding sometimes to higher efficiencies and often to higher product quality (see also [3]). The large surface area for heat and mass transfer and the high convective heat and mass transfer coefficients, which take place at these units, result in high drying rates and as a result, high drying capacity. ...
Many alternative fuels (AF) are derived from waste streams and therefore are prone to changing material properties. Especially a high variation of the humidity leads often to challenging process situations, since the variation of the water content causes automatically a non-constant energy influx to the combustion process. One possibility to compensate for those problems is the integration of modern fuel flash dryers into the AF handling line. This article provides an overview of the functional principle of those machines and summarises typical characteristics of the operation of dryers, which need to be considered for the plant operator.
... Superheated steam can also be used as drying medium, yielding sometimes to higher efficiencies and often to higher product quality. 4 The large surface area for heat and mass transfer and the high convective heat and mass transfer coefficients, which take place at these units, result in high drying rates and as a result, high drying capacity. The size of particulates to be dried is usually in the range of 10 -500 mm. ...
Many alternative fuels (AF) are derived from waste streams and therefore are prone to changing material properties. A high variation of humidity especially can often lead to challenging process situations, since the variation of the water content causes a non-constant energy influx to the combustion process. One possible means of compensating for these problems is the integration of modern fuel flash dryers into the AF handling line. This article provides an overview of the functional principle of those machines and summarises typical characteristics of the operation of dryers, which need to be considered by the plant operators.
... The potential of increasing drying efficiency with the development of two-, three-or multi-stage dryers has been shown in earlier studies. These studies focus on the use of lower drying temperatures and exhaust air recycling systems, as well as adapting drying techniques to the drying rate, for example, a technique for drying below the fiber saturation point [10,[15][16][17][18][19][20]. Frodeson et al. (2013) have shown, based on industrial data, that pellet plants have the potential to increase their drying capacity as well as their energy efficiency by implementing a two-step drying technique [17]. ...
... In this study the thermal drying step is based on a packed moving bed dryer, often used at pellet plants for its potential to use low-temperature heat sources. However, a packed moving bed is not optimized for dry biomasses below fiber saturation point, where a flash or pneumatic dryer would be more suitable [10,[15][16][17][18][19][20]. Therefore, a concept with the CDP and a flash dryer could increase the drying rate even further. ...
The use of bioenergy has increased globally in recent years, as has the utilization of biomaterials for various new product solutions through various biorefinery concepts. In this study, we introduce the concept of using a mechanical dewatering press in combination with thermal drying in a pellet plant. The purpose of the study is to increase the understanding of the effects a mechanical dewatering press has in a pellet production chain and investigate whether a pellet plant could thus become a biorefinery. The evaluations in this study are based on industrial data and initial tests at the university. The results show that the concept of using the mechanical dewatering press together with a packed moving bed dryer reduces energy use by 50%, compared to using only a packed moving bed dryer. The press water could be used as a raw material for biogas, bioplastics, and biohydrogen. Hence, this study points out the possibilities of a pellet plant increasing the efficiency of the drying step, while moving towards becoming a biorefinery.
... Therefore, these dryers are suitable for heat-sensitive materials and also for eliminating external moisture. Because of the parallel flow of drying medium and wet solid, high inlet gas temperatures can be applied even to heat sensitive materials, whose temperature never exceeds the gas outlet temperature [10]. Pneumatic dryers are simple in construction and have low cost of capital and have a large effective surface area of the material to be dried since solids are well dispersed within the dryer and high drying capacity due to a continuous process [6]. ...
The purpose of this research is to investigate the specific energy consumption in S-PVC pneumatic drying. In the present work, computational fluid dynamics is utilized to predict the hydrodynamics and drying mechanisms of a three-dimensional, dilute-phase, gas-solid turbulent flow in a laboratorial-scale and the experimental study is carried out in two pilot-scale spiral pneumatic conveying. The influence of diameter and length of the dryer was investigated in two pilot-scale dryers. In addition, the effects of gas velocity and temperature, particle temperature, gas density and moisture content on the dryer performance were examined. The results of energy analysis show that by increasing the gas temperature by 50 K, the specific energy consumption will be decreased as much as 37.7, 42.1, 45 percent at flow rate of 35476, 42570, 49665 .
... The use of high-speed air and high temperature will cause the product to dry in a short time. The pneumatic dryer includes continuous dryer with a granule solid feed [4,5]. The solids are driven to duct drying by the hot air produced by the heater with the air from the blower and then the product passed to the cyclone. ...
Aren (Arenga pinata) tree is one type of palm plant that produces fruit, sap and starch or flour in the trunk. Industries aren flour usually in small and medium industries is dried by conventional method with dried under the sun. The main constraint is the low drying speed. Therefore, in this study aren flour with a water content of 40% was dried using a pneumatic dryer to moisture content below 15% (wet base). The aim of this research is to analyze the influence of drying air temperature, drying air flow rate and feeding speed to drying speed and energy analysis. Energy analysis was performed to determine the performance of pneumatic dryers. The energy analysis itself is done in the form of energy utilization and energy efficiency. The results show that the increase of dryer temperature from 60 to 100 will increase the utilization of energy from 0.61 to 1.39 J / s, energy efficiency is 33.4-45.1%. the results of a proximate analysis, an ash content of 0.39 grain fiber 0.18 white degree 92.93% which already fulfill SNI standard of Aren flour.
... In addition, that traditionally the two-fluid theory was widely used to model dilute phase flow while the Eulerian granular was used to simulate both dense and dilute phase flows. [15] De Pádua et al. [61] investigated a vertical venturi feeder with the conveying system operating in the dilute-phase regime with 1 mm spherical glass particles. The Eulerian granular model was used for the solid phase modeling. ...
... The study of reported industrial drying data shows that the range of solid loading ratio placed between 0.1 and 1.1 for the drying of alumina and PVC particles. [15,31] Laboratory data for drying of alumina and iron have also been presented in the range of 0.4-1.3 in Ref. [99] respectively. ...
... Using the efficient combined systems is a way to improve system performance. [15] The multi-flash drying technology allowed the production of dehydrated fruits with moisture content, water activity and mechanical properties similar to those observed for commercial freeze-dried fruits. [105] Using the flash dryers as a drying stage in more complex systems, for instance, as a predrying stage to a fluidized bed dryer (batch or continuous) or fluidized bed cooler, spray dryer, drum dryer, etc., can enhance system performance. ...
Pneumatic conveying drying (PCD) is a widely used process in the industries and is a combination of heat and mass transfer and pneumatic handling technology. Drying processes consume large amounts of energy and therefore reduction in operating cost will be extremely beneficial for the industry. Many studies have been conducted to model and optimize the pneumatic drying. This review article focuses on the different strategies used in the literature to model pneumatic drying processes. An analysis is provided of the different mathematical modeling and its components such as balance and complementary equations and modeling assumptions. Two-fluid Theory, Eulerian Granular, and the Discrete Element Method are reviewed as well as gas-solid flow modeling methods. In addition, the numerical methods and the main studied parameters in the field of pneumatic drying are investigated. To this end, heat and mass transfer coefficients, gas and dispersed phase properties are reviewed.
... The capital and maintenance costs incurred by both tunnel and pneumatic dryers are low, allowing them to be used within small-scale drying operations (Mujumdar 2008;Levy and Borde 2014). Tunnel dryers are convective dryers in which the products are placed on trays stacked on trolleys, and these trolleys then move along the drying chamber. ...
... However, dryer designs need to be tailored to the product being processed, as each has unique properties (Levy and Borde 2014). In particular, dryer design depends on the initial and final moisture content of the product, its temperature sensitivity and on the particle size of the material being dried (Jayaraman and Gupta 2014;Levy and Borde 2014). ...
... However, dryer designs need to be tailored to the product being processed, as each has unique properties (Levy and Borde 2014). In particular, dryer design depends on the initial and final moisture content of the product, its temperature sensitivity and on the particle size of the material being dried (Jayaraman and Gupta 2014;Levy and Borde 2014). Dryer designs also need to be tailored to the users' characteristics (Chua and Chou 2003). ...
In sub‐ S aharan A frica, cassava is grown by smallholder farmers and is the principal source of calories for the local population. However, the short shelf life of cassava associated with poor infrastructure in the region results in significant postharvest losses. The expansion of small‐scale cassava processing could reduce these losses, but the availability of drying equipment suitable for use in such operations is limited. The objective of this research was to contribute to the development of cassava dryers suitable for use by smallholder farmers. A tunnel dryer and a pneumatic dryer being operated in T anzania were evaluated using mass and energy balance analysis. It was found that the energy efficiency of the tunnel dryer was 29% and of the pneumatic dryer 46%. For the tunnel dryer, most of the heat losses were through unsaturated exhaust air, while for the pneumatic dryer, most losses were through radiation and convection.
Practical Applications
In this study, a tunnel dryer and a pneumatic dryer suitable for use by smallholder farmers were evaluated during processing centers' usual cassava drying operations. The sources and extent of heat losses were identified, and then guidelines developed on how to reduce such losses. For both dryer types, improvements to the thermal insulation used could reduce heat losses to the ambient. For the tunnel dryer, decreasing the air mass flow rate by 57% would help to minimize exhaust heat losses without producing condensation inside the unit. For the pneumatic dryer, air mass flow rate could be reduced by 9%, improving energy performance without having a negative impact on the pneumatic conveying of the product. Those two modifications would be easy to implement and represent a significant contribution to the development of small‐scale cassava drying technology.
... Designers of dryers consider the "falling rate" period to be much slower, which has led to the development of two-stage, or three-stage dryers. By running each step more slowly than the preceding step in a three-stage bed dryer, the drying rate can increase and the retention time can be achieved [18,26,27]. The multistage drying technique uses a lower drying temperature, and, thus, as compared to the single stage dryer, the emissions can be kept at a lower level at the same time as the energy efficiency increases [28]. ...
The use of wood fuel pellets has increased worldwide in recent years, and pellet producers conclude that the lack of drying capacity is a barrier to increased production. In this study, we develop a concept of two different dryers called the two-step drying technique. The aim is to show the potential for increasing the drying capacity and improving energy efficiency when introducing a second dryer into the pellet plant. The study is theoretical and based on an industrial packed moving bed dryer. It shows that the drying capacity increased by 22% when a pneumatic second dryer was used.
... Also the drying time and possible material residues remaining in the dryer have to be considered. A widely used drying system in the chemical industry is pneumatic or flash drying [7]. There the feed is dispersed in a hot air stream leading to large surface area benefitting the heat and mass transfer. ...
... In pneumatic drying solid or high viscous fluid feed is dispersed in a hot air stream of high velocity [7]. As the material is conveyed with the air the particles dry. ...
... 5. The air stream first is heated (2) and enters the SFD tangentially at the bottom, passing through a small gap (7). By passing through the gap the air stream is distributed homogeneously along the circumference. ...
The spin-flash dryer (SFD) is a pneumatic dryer capable of handling a large variation of feed composition. In the SFD particles are dried in an agitated fluidized bed and ejected when dry. In the chemical industry the SFD is well implemented in production processes. To answer the demand of the pharmaceutical industry for new production processes the SFD was investigated mathematically, experimentally and with statistical analyses. The goal was to answer whether the SFD is of use for pharmaceutical drying operation or not.
A full fractional experimental plan was set up by use of design of experiments. Drying
settings were investigated using adipic acid and ibuprofen as model substances. The influence of energy via heat was investigated with an extra set of experiments using lactose as the model substance. The importance of not exceeding critical material temperature during drying was shown for ibuprofen. Important product attributes are the residual moisture and the material damage. For all experiments the residual moisture was well below acceptable limits of 2wt%. Additional experiment conducted with flour led to inacceptable results. The feed formed dough couldn’t be dried as consequence of its structure. Material damage was observed for all experiments. The extent depends on the material size, the agitator speed and the drying-air throughput. By SEM analyses debris or actual particle breakage could be identified. In addition changes of pore structure was found for adipic acid. Material residues had been found in the dryer during experiments. The amount of residue depends on the dryer settings as well as on the material itself. Different agitator concepts are suggested to minimize the material residues on the wall.
In the mathematical calculation the dryer performance for various feed flux and feed
composition was investigated. For adipic acid the operational field was calculated. In
agreement with the experimental results the feed conditions always led to residual moisture below the limit. It could be shown that the relative humidity of the inlet air has a significant impact on the operational field and the drying kinetics. Drying operations containing toxic solvents or particles can be calculated with these equations. The critical particle size in dependence on the air throughput was calculated. It shows that material breakage exhibited for adipic acid particles also results from the fact that feed particles are bigger than the critical particle size.
Concluding, it could be shown in this work, that the SFD can be used for drying in the
pharmaceutical industry but with restriction in particle size and feed consistency.
