Industrial Drying Research Articles

Energy Performance, Environmental Impacts and Costs of a Drying System: Life Cycle Analysis of Conventional and Heat Recovery Scenarios

High energy consumption is one of the main problems of drying, a critical process for many industrial sectors. The optimization of drying energy use results in significant energy saving and has become a topic of interest in recent decades. We investigate benefits of heat recovery in a convective drying system by comparing two different scenarios. The Baseline Scenario is a conventional industrial dryer, and Scenario 1 includes the preheating of drying air by exhausts from the drying chamber. We show that the energy efficiency of the drying cycle is strictly related to the properties of the dried material and operative conditions, and performance improves significantly (by 59% to 87%) when installing a heat recovery unit (Scenario 1). Additionally, the temperature of drying air affects performance. We assess both scenarios by LCA analysis, measuring the environmental impacts and externalities of four different fuels (natural gas, light fuel oil, biomethane, and hardwood chips). Our findings indicate that heat recovery reduces environmental impacts, both when fossil and renewable fuels feed the system, but unexpected impact arises for some categories when renewable fuels are used.

Efficient Microwave Processing of Thin Films Based on Double-Ridged Waveguide

Microwave heating has a wide range of applications in the fields of industrial heating and drying. However, when microwave heating is applied to the thin film, it will be challenging due to its low loss and large heat dissipation area. In this paper, a double-ridged waveguide for thin-film heating is proposed. The double ridge structure is employed to enhance the electric field, thereby increasing the power-loss density in the thin film. Firstly, a double-ridged waveguide, in which the electric field strength can be about 2.5 times that of the conventional waveguide, was designed based on the transverse resonance method and the electromagnetic field simulation. Then, a multiphysics model was built to analyze the heating performance of the ridged waveguide, in which the electromagnetic field and heat transfer are coupled. The simulation results show that the heating performance of the proposed waveguide will be 35.0 times that of the conventional waveguide. An experiment was carried out to verify the proposed model, showing that the experimental results are in accordance with the simulation results. Finally, the influences of the thickness of the film, the permittivity, the distance between two ridges, and the working state on heating performance and heating uniformity were also discussed.

Multiphysics simulation for design and adjustment of efficient industrial drying modes of ceramic ware

Algorithms for design and adjustment of industrial drying regimes of ceramic ware, based on modeling and numerical simulation of coupled mass transfer and mechanical processes in the dried media, are developed. They allow prediction of efficient drying rate through estimation of the strain-stress processes in the dried bodies based on finite element analysis and experimentally determined material models. Thermodynamically relations are used to obtain and adjust the change mode of the relative humidity, temperature and velocity of the drying gas in the dryers.The proposed approaches were applied for estimation of the possibility for drying time reduction of ceramic bricks in continuous draying installation, and the subsequent technological effects.

Performance of industrial drying and soybean grains quality

Thus, the objective of this work was to evaluate the performance of industrial drying and the quality of soybean grains using a direct-fire furnace automatically fed by wood chips. To represent the grains before drying, four samples were collected together with the sampling of the loads in the trucks carried out to classify the product in the storage unit. At drying, performance evaluations and specific energy consumption were carried out. The grains were evaluated for moisture content, germination, electrical conductivity, apparent specific mass, color, acidity index, and PAHs. Drying showed an average efficiency of 75.50%. The average chip consumption was 0.4403 kg of chip/kg of evaporated water. The specific energy consumption was 8,099.50 kJ/kg of evaporated water. The grains showed differences after drying in the characteristics of germination, electrical conductivity, and chroma. Six PAHs were detected in the samples before drying: (B(a)A, Chr, 5 MC, B(j)F, Dib(ai)P, and IcdP). After drying, in addition to the PAHs obtained before drying, five more were detected (B(b)F, B(k)F, B(a)P, Dib(al)P, and Dib(ah)A). Mean PAH concentrations were higher than the maximum values ​​allowed by European Union legislation.

Effects of traditional and advanced drying techniques on the physicochemical properties of Lycium barbarum L. polysaccharides and the formation of Maillard reaction products in its dried berries

This study explored the effect of three different industrial drying methods on the physicochemical, nutritional, and safety profile of goji berries. The hot-air (HD) and microwave drying (MD) methods yielded berries with relatively high polysaccharide content, while vacuum freeze-drying (FD) yielded dried berries with better sensory qualities but relatively less polysaccharide content. The polysaccharides obtained from the HD and MD berries had lower molecular weight, high antioxidant activity and high degrees of Maillard reaction. Further investigations revealed that all three methods, in particular HD and MD, generated high levels of intermediate Maillard reaction products (55.8–86.3 mg/kg) and advanced glycation end-products (fluorescent intensity of 26784–51712), based on significant reduction of reducing sugar and amino acids in the HD and MD berries (p < 0.05). These findings highlight the need to scrutinize the effectiveness of traditional and emerging drying technologies used to produce safe fruits.

Temperature Field Simulation and Energy Analysis of a Heat Pump Tobacco Bulk Curing Barn

Recently, heat pump drying has been widely used in tobacco processing. Considering the importance of this issue, it is of significant importance to further investigate temperature distribution and energy analysis in the drying process. To develop an energy-saving, environmental-friendly, and high-quality tobacco drying method, temperature distribution, dehumidification performance, the economic issues, and thermal efficiency of a heat pump curing barn (HPCB) and a traditional coal-fired bulk curing barn (TCCB) were compared. The regional temperature eigenvalue model was applied to describe the temperature uniformity with HPCB and TCCB. Moreover, thermal efficiency was obtained through energy tests. The obtained results showed that HPCB is beneficial to improve the drying quality of tobacco. The performed analyses showed that the thermal efficiency of the TCCB and HPCB was 42.02% and 66.53%, respectively. Accordingly, heat pump technology is recommended for industrial drying of tobacco leaves and obtaining high-quality products.

Performance of Exergetic, Energetic and Techno-Economic Analyses on a Gas-Type Industrial Drying System of Black Tea

The purpose of this research work is to perform detailed exergetic, energetic and techno-economic analysis of the black tea drying process in the gas-type industrial dryer. Exergy–energy and techno-economic methodology was applied to investigate the heat loss, exergetic and energetic performance, exergy efficiency, improvement potential rate, sustainability index and techno-economic performance of a drying system. The results showed that the heat loss of exhaust air in the late drying process played a main contributing role in the heat loss and exergy loss of the whole drying system. Therefore, the exergy efficiency of the initial drying period and the redrying period varied from 38.08% to 65.09% and 24.76% to 26.97%, respectively. In addition, the improvement potential rate and sustainability index of the whole system varied from 6.93 kW to 12.94 kW and 1.33 to 2.86, respectively. The improvement potential obtained in the present work indicated that the drying operation is greatly in need of exergy performance improvement. Finally, the net present value and payback period obtained from techno-economic analysis were 179,442.03 USD and 5.3 years, the result is useful for investors or contractors to refer to and make investment decisions.

Effects of spray drying, freeze drying, and vacuum drying on physicochemical and nutritional properties of protein peptide powder from salted duck egg white.

Salted duck egg white contains many kinds of high quality protein, but it is often discarded as food factory waste because of high salinity and other reasons. The discarded salted duck egg white not only causes a waste of resources, but also causes environmental pollution. Using salted duck egg white as raw material, this study was completed to investigate the effects of three drying methods including freeze drying, vacuum drying, and spray drying on physicochemical and nutritional properties of protein powder from salted duck egg white. The results showed that the solubility, foaming and foaming stability, emulsification and emulsification stability of the protein peptide of salted duck egg white decreased to different degrees after drying. The scavenging rates of freeze-dried samples for superoxide anion, hydroxyl radical, and 1,1-Diphenyl-2-picrylhydrazyl (DPPH·) reached 48.76, 85.03, and 80.17%, respectively. Freeze drying had higher scavenging rates than vacuum drying and spray drying. The results of electron microscopy showed that freeze-drying had the least effect on the structure of protein peptide powder of salted duck egg white. The purpose of this experiment was to provide theoretical guidance and technical support for industrial drying of salted duck egg white protein solution.

Energy viability of industrial drying of wood chips

Moisture content (MC) is one of the physical properties of wood that most influences its energy efficiency as fuel. The aim of the present study was to analyze the viability of drying pine wood chips in comparison to undried chips, considering the balance of the energy content as the primary evaluation parameter. We also investigated whether the increase in the energy content of dried wood chips exceeds the energy required for the drying process, demonstrating energy viability. The base scenario was created using data from an industry that performs wood chip drying in a rotary dryer that reduces the MC by 15%. Based on the baseline scenario data, two new scenarios were estimated to represent variations in energy consumption to reproduce the same drying process, taking into account different combinations of MC in the input and output chips. The results showed that drying increased the energy content of wood chips by 44.96% (from 7,194 MJ.kg−1 to 10,429 MJ.kg−1). However, the energy balance of the drying process was negative in all scenarios evaluated, demonstrating that the energy expenditure required to dry wood chips exceeded the increase in energy content resulting from the reduction in MC under the conditions evaluated.

Solar drying Technologies: A review and future research directions with a focus on agroindustrial applications in medium and large scale

• Design, integration schemes, and economic analysis of Solar Dryer were discussed. • The most important works about industrial Solar Dryer were classified and tabulated. • The current state of the art and future development of Solar Dryers were presented. • Loads greater than 90 kg of fresh food or solar collection areas greater than 30 m 2 was analyzed. • Industrial drying literature was reviewed to identify opportunities for integrating solar thermal technologies. The food industry accounts for approximately 30% of global energy consumption. In addition, food-processing activities contribute almost 26% of total greenhouse gas emissions. Dehydration is an energy-intensive unit operation, and most foods require drying, at least partially, at some stage of processing. Solar food drying can help sustainable energy supply and contributes to the solution of environmental degradation problems. This review focuses on medium and large-capacity solar drying systems, some challenges for their implementation in the agro-industrial sector, and the analysis of the integration schemes of solar thermal systems to the most common drying processes in the agroindustry. A systematic information search was carried out by analyzing four reviews on industrial solar drying and more than 50 articles on medium to large scale solar food drying (i.e., fresh product load greater than 90 kg or solar collection area greater than 30 m 2 ); from 1991 to date. The solar technology with thermal convection systems is mature for industrial food drying on an industrial and semi-industrial scale. There is a niche opportunity to produce industrial size systems for small and medium producers, which can incorporate added value to their production.

Evaluation of heat pump dryers from the perspective of energy efficiency and operational robustness

Vapor compression heat pump dryers (HPDs) are widely applied in food and industrial drying. Many efforts have been devoted to evaluating the HPD performance from the perspectives of energy, exergy, economy, etc. The current work offers a perspective of both energy efficiency and operational robustness to evaluate HPDs, intending to measure their design and off-design performance for various drying applications. Based on the proposed method, a case study on conveyor seaweed drying is presented. The preferable system(s) are found out among three candidates in general use, i.e., the basic heat pump dryer HPDbasic, the HPD with air bypass HPDbypass, and the HPD with air bypass and subcooler HPDsubcooler. The results show that, HPDbasic is not applicable for seaweed drying due to the required huge circulating air flow rate. HPDbypass and HPDsubcooler are more preferred with better energy performance and operational robustness. Moisture extraction rate (MER) of 30.4 kg/h and specific moisture extraction rate (SMER) of 2.20 kg/kWh are reached in HPDbypass at the design condition (Tdb = 45 °C, RH = 0.4), and are further increased to 35.8 kg/h and 2.58 kg/kWh in HPDsubcooler. Meanwhile the off-design robustness indices are 0.14 and 0.22 for HPDbypass and HPDsubcooler, and can be enlarged to 0.19 and 0.33 after reselecting a compressor withstanding condensing temperature up to 58 °C (2 °C higher). Besides, HPDbypass and HPDsubcooler can bear at least 30% air leakage in operation. Finally, operational robustness on other applications is also discussed for conveyor and batch dryers.

Influence of different drying methods coupled with different process modes on physicochemical qualities and anthraquinones contents of Rheum palmatum L.

Rhubarb is a popular food in Europe with laxative properties attributed to anthraquinones. Industrially drying fresh Rheum palmatum easily lose color characteristics and bioactive anthraquinone (AQ) content. Hot air drying (HAD), sun drying (SD) and smoke pre-drying followed by hot air drying (SMD-HAD) were employed to preserve physicochemical qualities and AQ content of R. palmatum. Different growing years, process modes (segment length, diameter, drying temperature and whether or not peeled) were compared among different drying methods. Compared with HAD and SD, SMD-HAD maintained optimal levels of AQ content and shiny color, it also significantly shortened the drying time by 10–15 days than SD. The segment length of 5 cm and the whole rhizome of 4-year-old plants were suitable to meet the industrial drying. Treatments of keeping the peel showed the higher total and free AQ content (2.84% and 0.33%) than treatments of removing the peel (1.51% and 0.23%). Moreover, AQ content in periderm was much higher than in phloem + xylem part and pith part, this discovery will present theoretical basis for revising the stipulation that Rhubarb should be scraped in Chinese pharmacoeia. It can be concluded that SMD-HAD is an efficient technique for the industrial drying production of high-quality R. palmatum.

Industrial drying for agrifood by-products re-use: Cases studies on pomegranate peel (Punica granatum L.) and stoned olive pomace (pâtè, Olea europaea L.)

The effect of industrial drying processes on phenols and polysaccharides of olive pomace (pâté) and pomegranate peel was studied, with the aim to re-use pomegranate and olive oil by-products. Pomegranate peel (Wonderful and G1 varieties) was oven-dried at different temperatures, taking into account peel thickness and size. Pâté was freeze-dried and oven dried at 50–110 °C, at lab scale; then, an industrial drying system (150 °C) was compared to freeze-drying. All dried samples were analyzed in terms of phenolic and polysaccharides compounds. Drying at room temperature of small pieces of pomegranate peel guaranteed the highest humidity removal and recovery of phenols. Sugar analysis, DLS and 1H NMR confirmed that polysaccharide fractions were not significantly affected by the highest drying temperatures (42 °C for pomegranate, 150 °C for pâté). The two drying procedures at large scale were suitable for avoiding degradation of phenols, maintaining the same profiles of the corresponding freeze-dried samples.

A comparison of mixture and separated-phase models of heat transfer in a stationary wet granular bed

Solvent removal by thermal drying of granular mixtures is encountered in many industrial operations. A mixture model that treats the granular solid and the liquid solvent along with any interstitial gas phase as a single phase, is a useful first approximation to estimate the time required to heat the system to the wet-bulb temperature at which the solvent starts to vaporize. An analytical solution for the transient, axisymmetric temperature distribution in a stationary wet granular mixture in a heated cylindrical vessel is developed as an approximation to the typical geometry of an industrial dryer . Besides being a good first approximation to obtain an order-of-magnitude estimate of the heating time, the analytical solution serves as an excellent verification case for numerical simulations. A parametric study to assess the effect of fill height and wall temperature on the heating time is performed. Before analyzing the mass transfer aspects of the drying phenomena, it is critical to understand the fundamentals of interphase heat transfer in multiphase mixtures that can be found in such assemblies. Therefore, a 0-D separated-phase (multiphase) heat transfer model is developed to account for the effect of interphase heat transfer in the prediction of heating time of wet granular mixtures in cylindrical vessels. The 0-D model is extended to 3-D simulations using a newly developed OpenFOAM solver with multiphase heat transfer capability. The same problem that was solved using the analytical solution is solved using the 0-D model, and in 3-D using the newly developed OpenFOAM solver, to study the effect of interphase heat transfer on the prediction of heating time. It was found that inclusion of interphase heat transfer in the heat diffusion equations has a significant impact on the predictions of heating time. Further analysis of the problem results in the identification of the non-dimensional thermal interphase transfer number that determines the conditions under which a mixture model can be used in place of a separated phase model in problems involving heat transfer.

Short Drying Processes for Silicon Solar Cells

Herein, very short drying processes for the screen‐printed electrodes of passivated emitter and rear solar cells (PERC) are successfully demonstrated. The short drying processes are conducted in an in‐line heating system with vertical‐cavity surface‐emitting lasers (VCSEL) as its heat source, being a compact alternative to the conventional heating chamber. While the heating time of the conventional industrial drying process is believed to be about 20 s (to the best of the authors’ knowledge), the VCSEL system allows a significant reduction down to 0.15 s while maintaining a similar power conversion efficiency and contact adhesion quality.

Drying Microalgae Using an Industrial Solar Dryer: A Biomass Quality Assessment.

Microalgae are considered a promising resource of proteins, lipids, carbohydrates, and other functional biomolecules for food and feed markets. Competitive drying solutions are required to meet future demands for high-quality algal biomass while ensuring proper preservation at reduced costs. Since often used drying methods, such as freeze or spray drying, are energy and time consuming, more sustainable processes remain to be developed. This study tested an indirect and hybrid solar dryer as an alternative to conventional freeze drying of industrially produced Tetraselmis chui and Nannochloropsis oceanica wet paste. The effects of the drying method on biomass quality parameters, including biochemical profiles, functional properties, and microbial safety, were assessed. No significant differences were found between the applied drying technologies for total proteins, carbohydrates, lipids, and fatty acid profiles. On the other hand, some pigments showed significant differences, displaying up to 44.5% higher contents in freeze-dried samples. Minor differences were also registered in the mineral profiles (<10%). Analyses of microbial safety and functional properties of the solar-dried biomass appear adequate for food and feed products. In conclusion, industrial solar drying is a sustainable technology with a high potential to preserve high-quality microalgal biomass for various markets at expected lower costs.

Multiphysics Modeling to Assist Microwave Cavity Design for Food Processing

Microwave technology has many current applications. It is very useful for food processing, including domestic cooking and warming-up and industrial heating and drying. It heats faster than conventional applications; however, in most cases result in non-uniform temperature distribution. Adequate cavity and equipment designs can reduce the impact of these heterogeneities and using multiples magnetrons is a possibility to mitigate hot and cold spots. Yet, the literature lacks methods to evaluate and compare multiple magnetrons designs. This study aimed to develop a procedure to evaluate the number and position of magnetrons connected to an application cavity using multiphysics modelling and simulation of the microwave distribution and heating of a food model. It was based on evaluating the electric field distribution into a selected working volume filled with air or a mixture of air-potato and the consequent effective power absorbed and temperature distribution into the air-potato medium. The assisted methodology with process simulation offers an insight into food temperature distribution, which would be very difficult to obtain experimentally or in any equipment design methodology. In this case study, it was found that up to 6 magnetrons are good enough when active in approximately 0.16 m3 cavity with a load that fills 10% of its volume.

Study on the effect of circulating air volume on the performance of closed loop heat pump drying system

• 1. A closed heat pump drying system for high temperature industrial drying is proposed. • 2. The effect of circulating air volume on the system drying performance is studied. • 3. The maximum drying temperature of 71.1℃ can be obtained for drying metal parts. • 4. The system has high energy efficiency and excellent dehumidification performance. Considering the fact that high energy consumption and low drying temperature of current drying system was not appropriate for the high temperature industrial drying, a closed loop heat pump drying system with high drying temperature was designed, established and explored. As a key operation parameter, the circulating air volume was closely related to the drying temperature and could affect the system performance. The effect of circulating air volume on the circulating air temperature, coefficient of performance (COP), moisture extraction rate (MER) and specific moisture extraction rate (SMER) were all experimentally investigated in this study. The results showed that with the increase of circulating air volume, the circulating air temperature was gradually decreased, while the system COP was oppositely increased. And both the system MER and SMER firstly increased and then decreased with increasing air volume. The drying temperature could exceed 70 °C when the circulating air volume was below 539.8 m 3 /h, and reach its maximum value 71.11 °C when the circulating air volume was 388.5 m 3 /h, meeting the high drying temperature requirement. At the same time, both the system MER and SMER could reach their maximums (i.e., 3.27 kg/h and 1.40 kg/(kW·h)), showing the excellent dehumidification performance of this system. Besides, when the circulating air volume was 736.1 m 3 /h, the system COP could reach its maximum 6.56, indicating high energy efficiency. These results can provide guidance for the popularization and application of heat pump drying technology in the industrial drying field.

CFD-DEM-IBM simulation of particle drying processes in gas-fluidized beds

A great deal of industrial processes involves drying processes that removes water from the surface and interior of particles, where knowing the flow behavior, mass and heat transfer is crucial for proper design and optimization of industrial dryers. This work developed a CFD-DEM method for the simulation of particle drying processes, where the immersed boundary method (IBM) was used to handle the no-slip boundary condition of gas phase at the wall of complex geometries. The model was validated by comparing the numerical results to the experimental data of particle moisture and gas (particle) temperature in the dense bubbling bed and dilute pneumatic conveying bed, respectively. Compared with the experimental results, the maximum relative errors of outlet gas temperature, particle temperature and water content in the pneumatic conveying bed are 2.2%,2.2% and 7.9%, respectively. It was also found that considering the effect of Stefan flow on the drag correction did not affect the studied particle drying processes. Present study proved that CFD-DEM-IBM method is powerful for simulating the fluid flow, mass and heat transfer in gas-fluidized beds.

An Exergoeconomic Analysis of a Gas-Type Industrial Drying System of Black Tea.

The performance evaluation and optimization of an energy conversion system design of an energy intensive drying system applied the method of combining exergy and economy is a theme of global concern. In this study, a gas-type industrial drying system of black tea with a capacity of 100 kg/h is used to investigate the exergetic and economic performance through the exergy and exergoeconomic methodology. The result shows that the drying rate of tea varies from the maximum value of 3.48 gwater/gdry matter h to the minimum 0.18 gwater/gdry matter h. The highest exergy destruction rate is found for the drying chamber (74.92 kW), followed by the combustion chamber (20.42 kW) in the initial drying system, and 51.83 kW and 21.15 kW in the redrying system. Similarly, the highest cost of the exergy destruction rate is found for the drying chamber (18.497 USD/h), followed by the combustion chamber (5.041 USD/h) in the initial drying system, and 12.796 USD/h and 5.222 USD/h in the redrying system. Furthermore, we analyzed the unit exergy rate consumed and the unit exergy cost of water removal in different drying sections of the drying system, and determined the optimal ordering of each component. These results mentioned above indicate that, whether from an energy or economic perspective, the component improvements should prioritize the drying chamber. Accordingly, minimizing exergy destruction and the cost of the exergy destruction rate can be considered as a strategy for improving the performance of energy and economy. Overall, the main results provide a more intuitive judgment for system improvement and optimization, and the exergy and exergoeconomic methodology can be commended as a method for agricultural product industrial drying from the perspective of exergoeconomics.