XDEM simulation of an industrial-scale rotary drum dryer for organo-mineral fertiliser

Biomass material such as forest and agricultural residues are moist after harvest. Drying is an established operation to prepare them for pelletization. Wood pellet manufacturer involves drying wet biomass from mill residue or forest down to 5–7% wet-basis moisture content. Moisture reduction occurs conventionally in rotary drum dryers operating at high inlet temperatures of 300–600 °C. Although rotary dryers were initially designed to dry nonfibrous materials, these dryers have been used for drying grains, herbs, woody biomass, and agricultural wastes. Biomass materials have heterogeneous size, shape, and density properties, and their flow characteristics inside the drum are not a known phenomenon. This article reviews the researchers’ efforts to determine the residence time of solid material in concurrent rotary drum dryers. This review article analyzes the developed empirical correlations and solid cascading approximation to determine the residence time. The outputs of various empirical correlations are compared for a consistent operating condition.

Turmeric is a challenging crop to dry because of its heat sensitive volatile content and browning characteristics. In this study, a pilot scale biomass fired rotary drum dryer was developed for drying turmeric rhizomes. The drying experiments were conducted at 50, 60, and 70°C air temperatures at an air velocity of 2 and 3 m/s and the drum speeds of 6 and 9 rpm. The turmeric rhizomes dried at a faster rate at the operating conditions of 70°C air temperature, 3 m/s air velocity and 9 rpm drum rotational speed. Among the evaluated thin layer drying models, Page model comparatively gave higher R2 values (0.998), lower sum of square error (0.001), and root mean square error (0.01) values. The effective moisture diffusivity of turmeric in the rotary dryer ranged from 0.33 to 0.5 × 10−10 m2 s−1. The calculated activation energy of turmeric rhizomes was 19,338 kJ/kg mol−1. The higher curcumin, oleoresin, starch, and color values such as lightness, redness, and yellowness value of 4.92%, 16.5%, 58.09%, and 59.87, 28.43, and 74.21, respectively, was observed at 50°C, 9 rpm drum rotational speed and 3 m/s air velocity. The results indicated that the color of turmeric could be retained by drying at 50°C.Practical ApplicationsThe present scenario, turmeric has been considered as an important crop against COVID‐19 due to its antiviral properties and also food applications such as natural coloring agent and flavor enhancer. The unit operations involved in turmeric processing is washing, boiling, drying, polishing, and size reduction. The amount of curcumin content presents in turmeric decides its value. Drying is the time‐consuming process compared to other unit operations and has an impact over the quality parameters of turmeric. Sun drying is the main traditional drying method normally practiced by the farmers for bulk drying of turmeric rhizomes. However, the sun‐dried turmeric rhizomes lost its product value because of poor quality end product (dark yellowish brown color). This could be due to longer exposure of the product in sun causes change in the volatiles and color in turn degrades the market value and fetches lower price to the farmer. And also decreased drying rate, prolonged drying time, non‐uniformity, and lesser energy consumption are the other factors that degrades further the quality of the product. Hence, a drying technology should be identified to overcome the problems faced by the farmers and also to dry the bulk capacities of the turmeric rhizomes at low cost. Rotary dryers are capable of processing larger capacities of various agricultural products having wide range of thermophysical and aerodynamic properties. The current research focused on developing a rotary dryer to reduce the drying time and also to retain the quality that benefits both farmers and industries by providing good quality product.

Drying agricultural seeds is a commonly used industrial process. The drying process of the material inside the rotary drum is directly related to the seed movement in the dryer. However, the movement of agricultural seeds inside the rotary drum dryer has never seriously been studied before. This paper adopts a mathematical model for simulating particle flow in rotary drum dryers for agricultural seeds using discrete element methods (DEMs). It is aimed to study the efficiency of the rotary drum dryer and how this is linked to the type and number of vans and positions of vans mounted inside the rotary drum dryer. The study parameters were performed by varying the rotational speed, inclination of the rotary drum installation with minimal impact on the flow of seeds, and segregation of the seeds in a rotary drum dryer. The simulation results show that different operating conditions were the most significant influences on the movement of seeds. Maximum height of the particle falling can be realized when the rotary drums are operating at an optimum condition for particle loading from the bottom drum.

Empty fruit bunches (EFB) of the oil palm have great potential to be used as industrial fibers in various industries, such as fiber board, mattress and cushion, erosion controller, thermoplastic filler, paper, acoustics control, sound insulator, and animal feed industries. A rotary drum dryer with a flue gas drying medium has been conventionally used to dry EFB fibers. However, this drying system tends to produce highly entangled and blackened fiber. Furthermore, the uneven contact between the flue gas and fiber in the rotary dryer may cause nonuniformity in the moisture content of the product. To overcome this problem, the present work uses superheated steam as the drying medium for EFB fiber drying. The drying experiments were carried out at the following conditions: atmospheric pressure; temperature range 112–172 °C; steam superficial velocity in the range 0.14‐4.3 m/s, distance from steam nozzle to EFB in the range 50–200 mm; and size of holes on plate in the range 10–200 mesh. The initial fiber moisture content was in the range 0.96‐1.46 kg/kg dry basis. The mass loss of EFB fiber during the drying process was periodically measured using an analytical balance connected directly to the wire mesh plate when the steam was diverted momentarily so that the effect of momentum transfer between the steam and the sample holder is minimized. In the temperature range 112–172 °C and at atmospheric pressure, the equilibrium moisture content isotherm is found to follow an exponential equation with coefficient ke = 15.365 kg/kg, ne = —0.001 °C−me and power index me = 1.869. It was found that for maximum moisture removal, the temperature and steam superficial velocity was 142 °C and 0.39 m/s, respectively. The effect of steam velocity is greater than that of steam temperature in decreasing the moisture content. The drying rate initially increases to a maximum and then falls off exponentially thereafter. A new drying model was developed for superheated steam for drying of EFB fiber, which is given by MR = 1 − atnexp(−ktm). The increasing drying rate is largely described by the exponential term with the coefficient k having values ranging from 1.945 to 5.351 s−n and the index m having values ranging from − 0.843 to 1.198. The falling drying rate is largely described by the power law term with the coefficient a ranging in value from 0.453 to 1.027 s−m and the power index n ranging in value from 0.0415 to 0.317. The drying is best carried out with the plate at a distance of 150 mm from the sample holder containing a 50 mesh plate. The superheated steam through the drying system can successfully reduce the moisture content by almost 100% in 15 min without steam condensation during the drying process. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd.

In this study, a new type of rotary dryer filled with inert alumina ceramic bead (ACB) fillers was introduced to treat the industrial wastewater, e.g., the high-salt wastewater and landfill leachate. Numerical simulations based on the Discrete Element Method (DEM) on the motion trajectory of ACB fillers in the rotary dryer were conducted, and the parameters of flight structure, rotational speed, and filling degree on the dynamic behavior of ACB fillers were optimized. Under various rotational speeds and filling degrees, the experimental results fit the numerical-simulated results very well. The optimized flight configuration was the straight flights with a length of 65 mm, and the optimized rotational speed and filling degree were 35 rpm and 15%, respectively. Under the optimized condition, both the response variables, the mass of particles in the airborne phase (MAP) and the percentage of occupied area in the airborne region (OAR), have the optimal values, in which the dryer will have a better drying performance. Besides, the lower-right area of the drum is empty which is convenient for the installation of the inlet pipe. The drying experiments of industrial wastewaters were also studied using this ACB filled rotary drum dryer under the optimized conditions. Under the optimal operational conditions, the evaporation capacities of the high-salt wastewater and landfill leachate could reach as high as 49.7 kg/h and 90 kg/h, respectively. This study highlights the integration of evaporation and drying processes of this novel ACB filled rotary dryer and provides an efficient and zero-liquid-emission strategy for the thermal treatment of industrial wastewater.

Product quality and energy consumption when drying peppermint by rotary drum dryer

Preliminary study in this article, the flow and the heat transfer of rotary drum dryer were simulated by using Computational Fluid Dynamics (CFD). A 3D modelling of rotary drum dryer including ambient air was created by considering transient simulation. The temperature distributions on rotary drum dryer surfaces of experimental setup during heating detected by using infrared camera were given to be boundary conditions of modelling. The average temperature at the surface of the drum lids was 80°C, and the average temperature on the heated surface of the drum was 130°C. The results showed that the internal temperature of air in drum modelling was increased relating on time dependent. The final air temperature inside the drum modelling was similar to the measurement results.

In the present study, the market wastes were treated and made as fine briquettes by using a portable rotary dryer. For the experimental purpose, a portable rotary dryer was designed and developed to determine the drying conditions of market waste. A U-type electric air heater of 1000 W were installed in the heating unit along with solar parabolic dish collector. The input parameters for the experiments are drying temperature (120 °C), rotation of dryer (3 rpm), air velocity (5 m/s), initial residue temperature (30 °C) and residue bulk density (200–250 kg/m3). Mixed market wastes are in the proportions such as: Briquette 1: watermelon lund 40% + drumstick pods 10% + beans pods 30% + drumstick peels 20%, briquette 2: watermelon lund 30% + drumstick pods 30% + beans pods 20% + drumstick peels 20%. The final product resulted in fiber form, which can be compacted to an even size of fuel briquettes which can be directly used for commercial and domestic heating. The performance of rotary dryer was analyzed based on inner rotary drum depth position (z = 0 m, z = 0.25 m, z = 0.5 m) and drying time (up to 150 min). The performance parameters like variation in moisture ratio, drying temperature, dry air humidity and air temperature were investigated in the present study. Residence time required for drying the mixed market waste up to milling moisture content (< 20%) in the developed dryer takes 150 min, while the sun drying takes 12–14 h generally. Calorific value of the fuel briquettes produced in the study is determined as 16.2–17.8 MJ/kg. The developed rotary air dryer provides a promising alternative to landfilling because of its low cost of construction, easy operation, green energy utilization and portability.

Rotary drum dryers operating in co-current mode are commonly used for drying food and feed in leaf form, reducing the damage caused by the high air temperatures typical of these dryers, as well as providing advantages including reduced drying times and increased energy efficiency. However, drying control to ensure a desirable product exit moisture content is strongly based on empirical practices, which are usually jealously guarded by producers and users, grounded in simplified mathematical modelling. To overcome these uncertainties, in this work, a more complete mathematical modelling approach, based on the solution of ordinary differential equations (ODEs), is developed. The ODEs describe the drying process in the drum dryer, where the air is continuously cooled and humidified as the product dries. The mathematical model developed was experimentally verified in a drum dryer by drying alfalfa, and the maximum relative error was found to be only 2.4%. Finally, a comparison between the complete model proposed here and a simplified model was conducted, using both for drying control to keep the product exit moisture content constant (i.e., at 0.111). The results indicated that the simplified model provided values of air inlet temperatures erroneously higher, up to +8.2%, with a consequent higher energy consumption, lower dried alfalfa quality, and a greater risk of fire, given that the product exit temperature was dangerously increased.

A rotary drum dryer having an internal rotating body was designed and tested in this study. It was shown that the developed dryer is effective for drying sewage sludge. The best operating conditions in the dryer were low energy input and almost 10% moisture content. The conditions are 255°C for the rotary drum temperature, 17 min for the sludge residence time, and 55 kg/m3 h for the dryer load. Under these conditions, the drying efficiency was 84.8%. The average diameter of dried sludge was less than 8 mm, and the weight reduction rate was 80%. Parametric screening studies achieved the following results. The drying efficiency increased with the increase of the internal temperature and the sludge residence time in the rotary drum, while the drying efficiency decreased when increasing the dryer load. In addition, it was shown that NH3 and CO2 were the primary components released from the sewage sludge drying process. The amounts of both of these components increased when the rotary drum temperature was increased.

The rapidly expanding US corn ethanol industry is producing increasing quantities of wet distillers grain and about 70 % of this material is dried to 10% moisture. Drying this material requires one-third of the energy used to operate an ethanol plant. Shivvers Inc of Corydon, Iowa has developed a rotary drum dryer which reclaims energy from the exhaust air stream. Tests of a pilot scale Shivvers rotary drum dryer showed it can dry distillers grain using about 2890 kJ/kg (846 Btu/lb) of water removed. This is less than half the energy usually required for a drum dryer or a grain dryer. Modifications are underway to further reduce energy use. Use of this dryer design scaled up to dry distillers grain at ethanol plants has the potential for large energy savings for the corn ethanol industry.

Sand and metallic charge materials are two essential and heavy raw materials that are needed for molding and casting. This chapter focuses on planning and provision for storage and handling of the raw materials needed for casting manufacturing. The major raw materials used for molding and casting are metallic charge materials and nonmetallic materials. The chapter also presents the advantages, limitations, and applications of drum or rotary dryers (also known as rotary kiln dryers) and fluidized bed dryers (also known as vibration fluidized bed dryers).

The developed mathematical description of heat treatment of the crushed wood in rotary drum dryers, and also the results of the mathematical description of the studied process is presented in the article. The results of mathematical modeling have shown that with increase in the diameter of a drum by 3 times its length can be reduced almost by 7 times due to the increase in the relative stay time of particles in flight. It provides the best interaction of particles with the heat carrier. Increase in speed of rotation of the drum twice also allows reducing its length almost by 3 times, but at the same time energy consumption increases and crushing of raw wood materials is observed. It was established that the practical speed of the heat carrier is 0.75-2.6 m/s, which limits the drum length to no more than 8-10 meters.

Pneumatic dryers, in which the moist solid is carried and transported by the drying air while being dried, are very cost-efficient dryers where short-time drying is sufficient. Their basic and most widely used form is the flash dryer. Most drying tasks requiring a longer drying time, however, could so far not be solved by pneumatic dryers. Long-time dryers like fluidized bed dryers or rotary drum dryers had to be used. In this paper, the cyclone dryer, a pneumatic dryer with significantly increased solid residence time, is described. Combined with a flash dryer as pre-dryer, it offers a straightforward and cost-efficient solution for many drying problems otherwise solved using fluidized bed or rotary drum dryers. The paper gives a brief description of design and working principles of the cyclone dryer and recalls the basic principles of parallel flow pneumatic drying. The dimensioning of flash dryer – cyclone dryer units for changing products in day-to-day practice is largely experimental due to the different and hardly predictable drying characteristics of the solids. A choice of products successfully dried on flash dryer – cyclone dryer units is presented.

This study determined the optimum effects of temperature, drum rotation and loading rate on the drying rate of cassava grates using the rotary drum dryer in removing moisture from cassava grates. A Central Composite Design was employed to evaluate a total of 15 fractional treatments derived from the 27 treatment combinations of temperature (75, 94 and 113°C), drum rotation (15, 20 and 25 RPM) and loading rate (5, 15, and 25 kg/h). The response surface regression obtained optimum conditions of the factors and predicted values on the stationary point on water loss as well as the rate of water removal. Results from the canonical analysis of response surface on plain water loss show an optimum combination of temperature of 107°C, drum rotation of 23 RPM and loading rate of 24 kg/h. At 25 kg/h loading rate regardless of any variation of temperature and drum rotation, the rotation of the drum could not be sustained due to heavy load caused by the accumulated weight of the grates inside the drums. The optimum conditions and predicted response values for rate of plain moisture loss were observed to be: temperature of 108°C, drum rotation of 23 RPM, loading rate of 26 kg/h. Response surface plots show the opposite effects between loading rates and temperature on the plain water loss as well as the rate of moisture loss. Response surface plots also revealed that RPM has no effect on the plain water loss and rate of moisture removal