Effects of adherence in the drying of brewer’s spent grain with rotating equipment

Effects of adherence in the drying of brewer’s spent grain with rotating equipment | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Effects of adherence in the drying of brewer’s spent grain with rotating equipment Guilherme Henrique Alves Pinto, Jose Teixeira Freire, Flávio Bentes Freire, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2837473/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 07 Dec, 2023 Read the published version in Waste and Biomass Valorization → Version 1 posted 5 You are reading this latest preprint version Abstract Brewer's spent grain (BSG) is a biomass with a high lignocellulosic content that can be reused in thermal processes, however it has high moisture content, which avoids it from being used in these processes. Pretreatment by drying rotating equipment turns out to be a suitable alternative. This work studied the rotational drying of BSG analyzing the effects of adhesion of solids. To do this, a standard pan combined with an external blower was chosen as a rotary dryer due to the easy access to the bed and the inner surface of the dryer. In addition, this type of dryer made possible to determine the relationship between BSG moisture and adhesion force. Under the operating conditions of the experiments, the moisture content of BSG decreased from 80 to 8.6% (wb), making it possible for the biomass to be utilized in thermal processes. Moisture ratios higher than 0.6 led to greater adherence and consequent agglomeration of solids, reducing their mobility and heat transfer with the internal surface of the dryer. At the start of drying, the bed’s rotational speed rate of BSG was approximately 14 rpm, half of the maximum rate of 28 rpm, also the temperatures of the BSG and the inner wall of the tray were in equilibrium, showing that changes in biomass adhesion would take non-uniform drying. Drying Biomass Adhesion forces Agglomeration Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Novelty Statement Understanding of the drying of spent grain with focus on adhesion and cohesion mechanisms allows adequate strategies to reduce negative effects of agglomeration, allowing the reuse of this biomass. 1. Introduction Beer making processes produce high amounts of brewer's spent grains (BSG), or malt bagasse, the main by-product of brewing industry, despite technological advances and improvements in resource efficiency. BSG contains mainly water, with a wet basis moisture content of 70 to 80% (wb), as well as lignin, hemicellulose and cellulose [1,2]. BSG are often used as a supplement livestock feed, providing proteins, fibers, phenolic acids with several biofunctions and energy that can be useful in human diets [3,4]. The high moisture content and the presence of fermentable sugars make BSG susceptible to contamination by various microorganisms [1,5]. Drying is an alternative to inhibiting the growth of microorganisms in BSG, thus increasing storage time while also significantly reducing product weight and transportation costs. Furthermore, drying can be used in biomass processing to increase energy efficiency and decrease socio-environmental impacts [6]. However, the high moisture content of malt bagasse is directly related to its strong adhesion, which increases handling and drying costs [1]. Adhesion forces also have negative effects on other industrial processes [7,8]. The resultant adhesion is the sum of different interaction mechanisms, the van der Waals attraction, electrostatic repulsion/attraction, capillary and repulsive force [9]. In high humidity conditions, the capillary force is dominant over the other mechanisms and the contact is established through a process known as “wetting” [10]. Additionally, the resultant adhesion depends on the adherent surface energy and the adhesive properties [11]. According to the authors, to achieve wetting, the surface energy of the solid material should be higher than that of the liquid. Inorganic materials usually have higher surface energy than organic material. In other words, organic materials have poor wettability (less tendency to cause sticking of materials). Metals, on the other hand, have high surface energy, therefore, materials tend to stick to it. Also, materials rich in sugar, such as the brewer’s spent grain, have stronger interactions with metal surfaces [12]. The capillary force is usually related to the formation of a liquid film on the surfaces prior to contact, especially from water condensation [13] and, consequently, moisture could be related to the agglomeration behavior of biomasses [14]. Stroem et al. (2009) dried brewer’s spent grain in a rotary dryer with superheated steam and observed the agglomeration profile through the drum. The biomass had stronger adherence closer to the solids inlet and, according to the authors, the water condensation controlled the contact between the phases [5]. Based on the situation, it's critical to comprehend how malt bagasse adheres to surfaces and how that affects how agglomerates develop during drying operations. This information is necessary to define strategies that enable the reuse of malt bagasse commercially viable. The present study aimed to evaluate how the moisture content of malt bagasse, through adhesion and cohesion phenomena, influences the drying process in rotating equipment. To do this, a standard pan was selected as a characteristic of rotary dryers and was associated with an external blower to promote the drying of brewer's malt bagasse. This equipment was selected because, due to its frontal opening, it allows a complete observation of the bed movement, ease of sampling solids without needing to interrupt the process and direct access to measurements on the inner surface of the dryer. Furthermore, the centrifugal method was used to determine adhesion forces between malt bagasse and metallic surfaces as a function of moisture content. Finally, the drying rate as a function of the moisture content of the malt bagasse was determined using an oven with air renewal. 2. Materials and Methods 2.1 Materials Brewer’s spent grains (BSG) came from an independent commercial microbrewery, immediately after the filtration step, and kept under continuous refrigeration at 3°C. To maintain (within a small variation margin) the same properties as biomass, BSG was obtained exclusively from Indian Pale Ale production. The BSG has been tested for porosity and particle distribution. Indian Pale Ale beers are made exclusively from barley malt and hops, the proportion of it being a choice of brewers. It is evident that the porosity of the wet material is much lower than the dry material, being 0.397 for the wet BSG, while for the dry BSG it is 0.830. It was observed that after being subjected to drying processes, the porosity of the material increases and this increase in porosity is very similar to that found by other authors [ 15 ]. Regarding the particle distribution, an average distribution of 3.17 mm has been found, very similar to that found in other studies [ 16 ]. In Fig. 1 , the particle distribution of BSG used in this work is shown. 2.2 Equipment Figure 2 shows a schematic sketch of the dryer setup, consisting of a semi-spherical standard PRIMAR® copper pan, which was 285 mm in diameter and 195 mm deep, and hot air from an external blower (Fabbe-Primar, model 128). The pan was fixed on a spindle that was part of a pulley system that converted the rotary motion of a model 56-RC-6334 engine, with 250 W of power and 174 rpm of frequency, into the rotary motion of the pan. The pan rotational speed was set at 33.9 rpm. At the blower's air outlet, there was a "J" type thermocouple connected to a Digi-Sense digital system to measure the air temperature. The electric resistance heater had 1000 W of power. The air velocity at the blower’s outlet was 6.76 ± 0.04 m/s. The inner surface of the pan was modified so that the movement of the solid was as close as possible to that of a rotating drum, raising the grains to certain heights and dropping them by gravity into a cascade of solids. To prevent the retention of grains on the dryer surface, an 8 cm long and 1.5 cm thick rubber strip was placed on the inner bottom of the pan to mechanically stir the adherent material. In addition, six equally spaced strips that were 15 cm long, 1.5 cm wide, and 0.5 cm thick were placed on the lower inner surface of the dryer to improve the motion of the solids. Figure 2 shows a schematic sketch of the dryer. An oven with air circulation and renewal, model TECNAL TE-394/1, was used to obtain the drying kinetics of the malt bagasse. In the center of the oven there was a metal cell that was 2 cm high and 7 cm in diameter, inside of which the biomass sample to be dried was confined. The metal cell was attached to a digital scale, placed on the oven, which was connected to a computer for the data acquisition of both sample mass and drying time using HyperTerminal software. The BSG's adherence to the dryer surface was determined by a centrifuge with a maximum rotational speed of 10,000 rpm, in which the adhesion force equals the centrifugal force required to remove the adhered solids [ 17 ]. The centrifuge was modified to meet the objectives by pinning two 6.30 by 6.30 cm and 0.40 cm thick square iron blades welded to a 0.80 cm thick iron cylinder to the centrifuge spindle. Copper sheets with a thickness of 1.0 mm were fixed on the iron blades to provide the same conditions for adhesion of the material on the surface of the rotary pan (Fig. 3 ). 2.3 Experimental procedures 2.3.1 Pan drying tests The temperature was kept constant at the blower outlet before starting the drying experiments. After stabilizing the temperature value, a grain load with known mass, m s 0 , was fed to the rotating pan. The blower was positioned in the center of the front opening of the rotating pan, with a slope angle of 60° in relation to its vertical. Grain samples have been taken at predefined intervals to measure the temperature and frequency of solid mixing. The air temperature at the blower outlet, T a O , was measured with a thermocouple, while the spent grain temperature, T s , and the dryer wall temperature, T w , were measured with an UT300A infrared thermometer. The motion of the solids, Ω s , was measured by tracking the trajectory of an aluminum spherical tracer with a diameter of 1 cm. The tracer follows the cyclical movement together with the solids, in which Ω s is the ratio between the number of cycles and the sampling time. To compare the heating rates between the BSG particles and between BSG and the dryer wall, the dimensionless temperature θ, which is the ratio between T s and T w , was defined. Two different values of m s 0 and T a 0 were chosen to analyze the influence of these parameters on the operation of the dryer. The values used in the experimental essays are shown in Table 1 , and each experiment was repeated three times. Table 1 Operating variables in drying of brewer’s spent grain. Runs T a 0 (°C) m s 0 (kg) 1 101.2 1.0 2 101.2 1.5 3 67.7 1.0 4 67.7 1.5 2.3.2 Adhesion tests in the centrifuge The relationship between the adhesion forces and the moisture content of the spent grain was derived experimentally with eleven samples of different humidity, obtained in an oven with air circulation, setting eleven different drying times ranging from 0 to 24 hours. The moisture contents of the samples were determined through the gravimetric method (ISO 11461). The adhesion forces were determined through the centrifugal method, shown in Fig. 3 , where the adhesion force between the biomass and the copper surface would be equal to the centrifugal force necessary to detach the adhered particles. At first, BSG samples were mechanically adhered to the surface by placing them on the copper plates, covering their entire surface, and then the second copper plate of the same area was placed on the bagasse, and a weight of 0.80 kg was placed on a second plate for 5 minutes, mechanically compressing the material. After compression, the upper plate was removed, and the lower plate with adhered material was weighed, and it was then fastened to the centrifuge shaft. The rotational speed was progressively increased until the mass dropped, and the remaining material adhered to it was weighed again. The adhesion force F ad was determined by the following equation: $${F}_{ad}={F}_{cent}={m}_{det}w2r$$ 1 where F cent is the centrifugal force, m det is the detached BSG mass, w is the angular speed and r is the support radius. 2.3.3 Kinetics and oven drying rate In the tests to determine the kinetics and drying rate, the air velocity inside the oven was set at approximately 1.0 m·s − 1 and measured using a digital anemometer model (LCA 6000). Three different temperatures were used in the experiments: drying temperatures of 50, 60, and 70°C, respectively. For each drying test, approximately 11 g of raw malt bagasse were added to the metallic cell, filling it completely. After adding the metal cell to the oven, the mass loss of the sample was monitored through the LabView software in each second of drying until the biomass reached its dynamic equilibrium. The dry basis moisture of the sample, X s,db , was calculated using the following equation: $${X}_{s,db}\left(t\right)=\frac{\left({m}_{s}\left(t\right)-{m}_{s}^{0}\bullet {X}_{s,wb}^{0}\right)}{\left({m}_{s}^{0}\bullet {X}_{s,wb}^{0}\right)}$$ 2 where m s (t) is the mass of the sample at drying time t, m s 0 is the initial mass of the sample and X s 0 ,db is the initial moisture of the sample on a wet basis. Finally, the drying rate was calculated using the following equation: $${DR}_{i}=-\left[\frac{\left({X}_{s,db\left(i\right)}-{X}_{s,db(i-1)}\right)}{\left({t}_{\left(i\right)}-{t}_{(i-1)}\right)}\right] i\ge 1$$ 3 where DR i is the drying rate observed in the drying interval i. 3. Results and Discussion 3.1 Drying brewer’s spent grain in a pan Figure 4 shows that, under the conditions evaluated, the increase in drying air temperature and the decrease in the initial biomass load favored drying, reducing the time required to reach dynamic equilibrium. For example, by keeping the initial load at 1.5 kg and increasing the drying air temperature from 67.7°C to 101.2°C, a decrease was observed in the total drying time from 420 min to 240 min. By keeping the drying air temperature at 67.7°C and decreasing the initial load from 1.5 kg to 1.0 kg, a decrease was observed in the total drying time from 420 min to 330 min. The results indicated the potential use of rotary dryers in the processing of malt bagasse, reducing its initial moisture from approximately 80% (wb) to a moisture of approximately 8.5% (wb) in dynamic equilibrium in the four conditions evaluated. The product obtained is suitable for thermal conversion through combustion, gasification or pyrolysis, since the biomass must have a moisture content between 5 and 25% (wb) [ 6 ]. 3.2 Oven drying rate Figure 5 shows the drying rate as a function of malt bagasse moisture for the three different temperatures evaluated. Under the conditions evaluated, two distinct periods were identified, a stabilization period in which an increase in the drying rate was observed until the biomass reached a moisture ratio of approximately 0.9, followed by a period with a decreasing drying rate that extended until the end of the operation. The absence of a well-defined drying period at a constant rate is a strong indication that there was no excess of free water on the surface of the BSG and that the diffusion of water molecules from the inside of the BSG particles to its surface controlled drying mechanisms. It was also observed that the increase in drying rate was favored by the increase in air temperature. In Figs. 4 and 5 , the results of the drying rates are shown, which indicate that the total processing time and the drying rate are highly dependent on the temperature of the drying air and that the process can be controlled through this variable. 3.3 Adhesion forces in brewer’s spent grain Figure 6 shows that there was a reduction in the adhesion forces between the brewer’s spent grain and the copper surface by removing water from the particles. It was observed that the decrease in the moisture ratio from 1.0 to 0.25 was sufficient to reduce the adhesion force per surface area from approximately 1.4 to 0.14 N·cm − 2 . When the moisture ratio was less than 0.05, the adhesion forces were considered zero since no adhesion of the BSG particles to the copper surface was observed. Other authors have observed a decrease in the adhesion force as water is removed from the materials since, in conditions of high humidity, capillary forces prevail over other mechanisms of surface interaction, such as van der Waals forces and electrostatic forces [ 18 ]. The presence of water between the surfaces of the adhesive and the adherent would be responsible for the formation of liquid bridges through a process known as "wetting", and the water may come from steam condensation on the surface, the presence of excess water, or migration inside the solid particles [ 10 ]. Moreover, expressive adhesion forces between the spent grain and the surface showed that high sugar content led to a stronger interaction with metal surfaces and a tendency for agglomeration [ 12 ]. Deng et al. (2020) evaluated the influence of humidity on the forces that cause urban sewage to adhere, identifying a relationship between humidity and the shear and tensile stresses involved in the adhesion of the material and between humidity and the forces of compression involved in the cohesion of the material [ 19 ]. Kobayashi et al. (2021) used resins as accelerators in the drying of urban sewage and observed that, regardless of the presence of resin, moisture directly influenced the contact angle [ 20 ]. The influence of the moisture content of the spent grain on the adherence seems to be consistent with the work of Stroem et al. (2009) who evaluated the agglomeration profile of the biomass in a rotary drum dryer. According to their work, brewer’s spent grain tends to adhere to the dryer walls, especially close to the solids feed, where there was a higher moisture content and the adherence mechanisms were associated to the water condensation from the superheated steam [ 5 ]. However, in the present work, the atmosphere had controlled humidity during the adhesion tests and, consequently, vapor condensation would not have a significant influence on the adhesion mechanisms. It is possible, therefore, that the moisture inside the biomass particles controlled the interaction between the phases. 3.4 Biomass movement As shown in Fig. 7 , the average motion of solids inside the rotating dryer was strongly dependent on the moisture content of the biomass. The results indicate that with high moisture content, at the beginning of drying, the solids had low fluidity, but as the moisture ratio reached 0.6, fluidity increased. A decrease in the movement of solids was observed when the water was removed, from a moisture ratio of 0.6 to dynamic equilibrium. The differences in motion of solids inside the rotating dryer could be visually noticed through its opening. Under conditions of high moisture content, the biomass formed a single agglomerate of solids with low mobility. By removing water from the biomass, some particles were detached by the mechanical action of the strips and started moving with higher mobility compared to the agglomerated particles. As the moisture ratio was close to 0.6, the agglomerated biomass was completely detached, and the solids reached their maximum motion. To this point, the solid-wall interaction played a key role in the solid motion as they were adhered to the surface, lifted to a specific height, and dropped, finally returning to the bottom bed through an "avalanche" movement. As the water evaporated, the adhesion between the solids and the walls of the dryer decreased, and consequently, they were not lifted by the rotation movement but were mixed by the strips. These results agree with those obtained by Ma et al. (2019), who used a three-dimensional discrete element model to study the surface interactions between individual particles and their surroundings through capillary bridges. The moisture content of the solids had an influence on the repose angle, varying from 13.76° for dry materials to 18.94° for wet materials, showing that dry solids have higher flowability. Furthermore, in the rotating drum, the dry particles had a lower surface angle and rolled down the slope in an unsteady flow, while the wet particles showed a higher surface angle due to the capillary effect. The particles fell as a coherent whole with uniform velocity in an "avalanche" motion [ 21 ]. Thus, it can be understood that the variation in solids’ movement, shown in Fig. 7 , is caused by the formation of agglomerates and by the interaction between the BSG particles and the internal surface of the dryer. In addition, it has been shown that the decrease in biomass humidity makes the movement of particles closer to what is considered ideal for rotating equipment. This behavior results in a homogeneous mixture and free movement of the particles. 3.5 Thermal behavior of malt bagasse drying Figure 8 shows the increase in the temperatures of the internal surface of the pan and the biomass during drying. It can be observed that the temperature profile was similar in all conditions evaluated, even with the constant increase of T w and T solids . At the beginning of the process, T w and T solids presented similar values; later, T w presented higher values, indicating more intense heating on the pan surface; and finally, T solids presented higher values at the end of the process. It can be observed that the increase in the maximum temperature reached by the internal surface of the pan and by the malt bagasse, as expected, was mainly associated with the air temperature at the blower outlet. The biomass was heated to a maximum temperature of approximately 46.5°C with the drying air at 67.7°C, while for the drying air at 101.2°C the maximum temperature reached by the biomass was considerably higher, approximately 65°C. The same was observed for the temperature of the internal surface of the pan, with maximums of approximately 41°C and 59°C for the drying air at 67.7°C and 101.2°C, respectively. The increase in the total mass of biomass did not change the temperatures in the dryer, influencing only the total processing time. Figure 9 presents the results obtained from the dimensionless temperature θ analysis through the drying. It can be noticed that the drying could be divided into three different regions. It can be observed that in Region 1, with a moisture ratio greater than 0.6, the dimensionless moisture remains practically constant, with values close to 1.0 due to the proximity between the temperatures of the biomass and the internal surface of the pan, indicating the thermal equilibrium between the phases. In Region 2, with a humidity ratio between 0.6 and 0.25, a constant reduction of the dimensionless humidity to values close to 0.85 is observed, indicating a more intense heating of the internal surface of the pan in relation to the BSG. Finally, in Region 3, with a humidity ratio lower than 0.25, a constant increase in θ could be observed with the decrease in humidity to values close to 1.1. This indicates that in this region, unlike Region 2, the BSG temperature increased more rapidly relative to the inner surface of the pan. The variation of θ as a function of humidity is a strong indication that the heat transfer between the BSG particles and the dryer wall was more efficient in conditions of high humidity. These results match those observed in earlier studies, as adhesion and cohesion in wet conditions usually affect the interface area [ 12 ] and there are differences between heat transfer coefficients in free-flowing and sticky materials [ 22 ]. Drying in a rotary dryer has allowed an approach to biomass drying, especially the BSG, in which it was possible to corroborate that this type of reactors can improve drying efficiencies. A drying ratio of 0.6 has proven to be the best to achieve fluidization in the rotary dryer. A single pan proves to be very efficient in the drying and fluid dynamic behavior of the BSG, as evidenced in Figs. 4 , 5 , and 6 . This information is relevant in drying processes, especially for biomass from the brewing industry, because it can predict drying behavior in this type of reactor. It is then necessary to continue testing with more developed equipment and larger dimensions to corroborate the good behavior shown in this study. The pretreatment of this type of residual biomass turns out to be quite interesting because barley, which is the main raw material used in the beer industry, and its residues have a relatively small average particle size (2 mm). This size is normally the same, with even slightly larger sizes up to 3 mm (Fig. 1 ), but it is always the same because, due to the beer process, they must be small particles, which means that the drying pretreatment does not need crushing or grinding. Finally, dry BSG waste is interesting for its use in thermal processes due to its calorific value of 21 MJ kg − 1 , which could be used in the same industry to obtain energy and use it within industrial plants, reducing some costs [ 16 , 23 ]. Instead, its use in pyrolysis or gasification turns out to be quite interesting, due to the possible obtaining of by-products such as H 2 , which can be used as raw material in refinery processes and as biofuel. Likewise, some authors have verified that BSG residues have high contents of phenolic waste that can be used in the cosmetic industry. Becoming a low-cost raw material for this industry and a raw material of sustainable origin for polyphenols as well as other bioactive molecules [ 24 ]. 4. Conclusion The drying of malt bagasse in pans was able to significantly reduce the biomass moisture, from 80 to 8.7% (wb), a necessary condition in several applications, such as gasification and combustion. However, the high biomass moisture, especially at the beginning of the operation, negatively affected the drying process due to the intense surface interactions. The formation of agglomerates, due to cohesion forces, and the adhesion of biomass to the internal walls of the dryer, due to adhesion forces, altered the movement of solids and the transfer of heat between the phases, preventing uniform drying throughout the process. Although the pan has proved to be an interesting piece for rotating equipment in obtaining information about the drying process due to its frontal opening and easy access to the moving bed and the internal surface of the dryer, further investigations into the mechanisms of bagasse adhesion to malt are necessary to define more efficient strategies and minimize the negative effects of agglomeration. Declarations Funding The authors gratefully acknowledge the financial support of the National Council for Scientific and Technological Development. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Finance Code 001. Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Guilherme Pinto, José Freire and Fábio Freire. The first draft of the manuscript was written by Guilherme Pinto and Fábio Freire and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. References Mussatto SI, Dragone G, Roberto IC. Brewers’ spent grain: Generation, characteristics and potential applications. J Cereal Sci. 2006;43(1):1–14. Ravindran R, Jaiswal S, Abu-Ghannam N, Jaiswal AK. A comparative analysis of pretreatment strategies on the properties and hydrolysis of brewers’ spent grain. Bioresour Technol [Internet]. 2018;248:272–9. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2837473","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":201949862,"identity":"e16d25f9-48c6-464a-99f2-350fd12f18c4","order_by":0,"name":"Guilherme Henrique Alves Pinto","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/klEQVRIiWNgGAWjYFACxjYQyQPl2YBEGg+QoiUNJNJAQAsDGzLnMJjEq0U+Irntwccd92T4biQfYPi547zd2vbDQFtqbKJxaTG8kdhuOPNMMY/kjbQExt4zt5O3nUkEajmWltuAS8uMxDZp3rYEHoMbOQYMvG23k80OALUwNhzGr+UvWEv+B8a/beeSzc4/xK9FXgKohRFiCwMzb9sBO7MbBGwx4HnYJtkL1CJ55pnBYdkzyQlmN4C2JODxi3x7+jOJn20J9nzHkx8+fLvDzt7sfPrDBx9qbHDbcgDGAjKA7mFIBKtMwKEcbAvcLJBeoBZ7PIpHwSgYBaNghAIAj6FnR9UHoSwAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-0896-7385","institution":"UFSCar: Universidade Federal de Sao Carlos","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Guilherme","middleName":"Henrique Alves","lastName":"Pinto","suffix":""},{"id":201949863,"identity":"e388c36b-7813-4ae6-9201-7df1ae2adda2","order_by":1,"name":"Jose Teixeira Freire","email":"","orcid":"","institution":"UFSCar: Universidade Federal de Sao Carlos","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jose","middleName":"Teixeira","lastName":"Freire","suffix":""},{"id":201949864,"identity":"621b9d5d-3a02-435a-83b2-aab790ee979e","order_by":2,"name":"Flávio Bentes Freire","email":"","orcid":"","institution":"Universidade Tecnológica Federal do Paraná: Universidade Tecnologica Federal do Parana","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Flávio","middleName":"Bentes","lastName":"Freire","suffix":""},{"id":201949865,"identity":"7b399394-eb19-493a-9cc6-bd1010dde65e","order_by":3,"name":"Juan Saldarriaga","email":"","orcid":"","institution":"University of the Andes: Universidad de Los Andes","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Juan","middleName":"","lastName":"Saldarriaga","suffix":""},{"id":201949866,"identity":"ba047958-ad32-4339-9f08-cba51ccac702","order_by":4,"name":"Fábio Bentes Freire","email":"","orcid":"","institution":"Universidade Federal de São Carlos: Universidade Federal de Sao Carlos","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Fábio","middleName":"Bentes","lastName":"Freire","suffix":""}],"badges":[],"createdAt":"2023-04-19 15:21:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2837473/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2837473/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12649-023-02329-8","type":"published","date":"2023-12-07T15:01:38+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":37333981,"identity":"d3221c02-a28f-4e11-ac2f-db6151e1b8a2","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":60507,"visible":true,"origin":"","legend":"\u003cp\u003eBrewer’s spent grain particle size distribution\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/e2a1e8492774d2b7d3f7dde1.png"},{"id":37333983,"identity":"07fde3e9-c1e3-4922-b46d-8155fa58dce0","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":52081,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic sketch of the dryer set up, comprising a standard rotary pan and an external blower\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/35b45ad1cbf3045fe307449a.png"},{"id":37333987,"identity":"fedf39cf-67af-423e-8605-387dbe878e90","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":242559,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic sketch of the centrifuge method to determine the adhesion forces: (1) centrifuge shaft, (2) iron blades, (3) copper sheets, (4) adhered BSG particles, (5) detached BSG particles\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/d8f08a1753cc703363490b83.png"},{"id":37335230,"identity":"aa353ec6-3f5f-4979-a0e7-85c9ca99ecba","added_by":"auto","created_at":"2023-05-22 15:36:42","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":402384,"visible":true,"origin":"","legend":"\u003cp\u003eMoisture ratio of brewer’s spent grain as a function of time during drying using a rotating pan\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/6e624c6409143d3122a7f88a.png"},{"id":37333990,"identity":"0501f0f2-7205-491b-ae3a-6ae8a370188b","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":612809,"visible":true,"origin":"","legend":"\u003cp\u003eDrying rates as a function of moisture ratio during BSG drying in an oven with air circulation\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/fec1b4a4ad20359486abd6d7.png"},{"id":37335233,"identity":"370d046c-2cd8-4fe6-abf5-7a6c054d33a9","added_by":"auto","created_at":"2023-05-22 15:36:42","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":596957,"visible":true,"origin":"","legend":"\u003cp\u003eAdhesion forces of brewer’s spent grain on copper surface as a function of the moisture ratio of the biomass. The adhesion force was set as 0 when there was no observed adherence\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/3b4c7bba78dd4b94e1763532.png"},{"id":37335636,"identity":"eef5e462-247e-412c-8aba-3909cfac0617","added_by":"auto","created_at":"2023-05-22 15:44:42","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":400460,"visible":true,"origin":"","legend":"\u003cp\u003eIntensity of solids motion as a function of the moisture content of the spent grain. The average standard deviation was ±2.2 rpm\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/df93436f653285400e2e3848.png"},{"id":37335232,"identity":"ec6a38cd-ec21-4f46-97d5-e7182d6db32a","added_by":"auto","created_at":"2023-05-22 15:36:42","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":498739,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature of the dryer walls and temperature of the spent grain as a function of the drying time, where: a) T\u003csub\u003eair\u003c/sub\u003e=67.7 °C and m\u003csub\u003esolids\u003c/sub\u003e=1.0 kg; b) T\u003csub\u003eair\u003c/sub\u003e=101.2 °C and m\u003csub\u003esolids\u003c/sub\u003e=1.0 kg; c) T\u003csub\u003eair\u003c/sub\u003e=101.2 °C and m\u003csub\u003esolids\u003c/sub\u003e=1.5 kg; d) T\u003csub\u003eair\u003c/sub\u003e=67.7 °C and m\u003csub\u003esolids\u003c/sub\u003e=1.5 kg\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/a64f1ad1c8a2c8e1dceadbcc.png"},{"id":37333989,"identity":"aee114ca-2490-4b5b-929e-9e3ac016c767","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":220406,"visible":true,"origin":"","legend":"\u003cp\u003eDimensionless temperature as a function of the moisture content of the spent grain. Drying was divided into three different regions: the beginning of drying with a moisture ratio greater than 0.6, an intermediate period and the end of drying with a moisture ratio lower than 0.25\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/baf9ea0ceabf25a4372046ca.png"},{"id":47989674,"identity":"0e12a6d0-4c73-4fdb-be22-81fcb6f2888c","added_by":"auto","created_at":"2023-12-11 15:10:28","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2384687,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/13f36530-c744-4e49-9c00-1bf0dbc95cf9.pdf"},{"id":37333984,"identity":"45c30682-0a43-44a5-9717-ceb33c474bd9","added_by":"auto","created_at":"2023-05-22 15:28:42","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":110086,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2837473/v1/ca2512af12573aa2fe3ff04d.pdf"}],"financialInterests":"","formattedTitle":"Effects of adherence in the drying of brewer’s spent grain with rotating equipment","fulltext":[{"header":"Novelty Statement","content":"\u003cp\u003eUnderstanding of the drying of spent grain with focus on adhesion and cohesion mechanisms allows adequate strategies to reduce negative effects of agglomeration, allowing the reuse of this biomass.\u003c/p\u003e"},{"header":"1. Introduction","content":"\u003cp\u003eBeer making processes produce high amounts of brewer\u0026apos;s spent grains (BSG), or malt bagasse, the main by-product of brewing industry, despite technological advances and improvements in resource efficiency. BSG contains mainly water, with a wet basis moisture content of 70 to 80% (wb), as well as lignin, hemicellulose and cellulose\u0026nbsp;[1,2]. BSG are often used as a supplement livestock feed, providing proteins, fibers, phenolic acids with several biofunctions and energy that can be useful in human diets\u0026nbsp;[3,4]. The high moisture content and the presence of fermentable sugars make BSG susceptible to contamination by various microorganisms\u0026nbsp;[1,5]. Drying is an alternative to inhibiting the growth of microorganisms in BSG, thus increasing storage time while also significantly reducing product weight and transportation costs. Furthermore, drying can be used in biomass processing to increase energy efficiency and decrease socio-environmental impacts\u0026nbsp;[6].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eHowever, the high moisture content of malt bagasse is directly related to its strong adhesion, which increases handling and drying costs\u0026nbsp;[1]. Adhesion forces also have negative effects on other industrial processes\u0026nbsp;[7,8]. The resultant adhesion is the sum of different interaction mechanisms, the van der Waals attraction, electrostatic repulsion/attraction, capillary and repulsive force\u0026nbsp;[9]. In high humidity conditions, the capillary force is dominant over the other mechanisms and the contact is established through a process known as \u0026ldquo;wetting\u0026rdquo;\u0026nbsp;[10]. Additionally, the resultant adhesion depends on the adherent surface energy and the adhesive properties\u0026nbsp;[11]. According to the authors, to achieve wetting, the surface energy of the solid material should be higher than that of the liquid. Inorganic materials usually have higher surface energy than organic material. In other words, organic materials have poor wettability (less tendency to cause sticking of materials). Metals, on the other hand, have high surface energy, therefore, materials tend to stick to it. Also, materials rich in sugar, such as the brewer\u0026rsquo;s spent grain, have stronger interactions with metal surfaces\u0026nbsp;[12]. The capillary force is usually related to the formation of a liquid film on the surfaces prior to contact, especially from water condensation\u0026nbsp;[13]\u0026nbsp;and, consequently, moisture could be related to the agglomeration behavior of biomasses\u0026nbsp;[14]. Stroem et al. (2009) dried brewer\u0026rsquo;s spent grain in a rotary dryer with superheated steam and observed the agglomeration profile through the drum. The biomass had stronger adherence closer to the solids inlet and, according to the authors, the water condensation controlled the contact between the phases\u0026nbsp;[5].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the situation, it\u0026apos;s critical to comprehend how malt bagasse adheres to surfaces and how that affects how agglomerates develop during drying operations. This information is necessary to define strategies that enable the reuse of malt bagasse commercially viable. The present study aimed to evaluate how the moisture content of malt bagasse, through adhesion and cohesion phenomena, influences the drying process in rotating equipment. To do this, a standard pan was selected as a characteristic of rotary dryers and was associated with an external blower to promote the drying of brewer\u0026apos;s malt bagasse. This equipment was selected because, due to its frontal opening, it allows a complete observation of the bed movement, ease of sampling solids without needing to interrupt the process and direct access to measurements on the inner surface of the dryer. Furthermore, the centrifugal method was used to determine adhesion forces between malt bagasse and metallic surfaces as a function of moisture content. Finally, the drying rate as a function of the moisture content of the malt bagasse was determined using an oven with air renewal.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eBrewer\u0026rsquo;s spent grains (BSG) came from an independent commercial microbrewery, immediately after the filtration step, and kept under continuous refrigeration at 3\u0026deg;C. To maintain (within a small variation margin) the same properties as biomass, BSG was obtained exclusively from Indian Pale Ale production. The BSG has been tested for porosity and particle distribution. Indian Pale Ale beers are made exclusively from barley malt and hops, the proportion of it being a choice of brewers. It is evident that the porosity of the wet material is much lower than the dry material, being 0.397 for the wet BSG, while for the dry BSG it is 0.830. It was observed that after being subjected to drying processes, the porosity of the material increases and this increase in porosity is very similar to that found by other authors [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Regarding the particle distribution, an average distribution of 3.17 mm has been found, very similar to that found in other studies [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the particle distribution of BSG used in this work is shown.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Equipment\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows a schematic sketch of the dryer setup, consisting of a semi-spherical standard PRIMAR\u0026reg; copper pan, which was 285 mm in diameter and 195 mm deep, and hot air from an external blower (Fabbe-Primar, model 128). The pan was fixed on a spindle that was part of a pulley system that converted the rotary motion of a model 56-RC-6334 engine, with 250 W of power and 174 rpm of frequency, into the rotary motion of the pan. The pan rotational speed was set at 33.9 rpm.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the blower's air outlet, there was a \"J\" type thermocouple connected to a Digi-Sense digital system to measure the air temperature. The electric resistance heater had 1000 W of power. The air velocity at the blower\u0026rsquo;s outlet was 6.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 m/s. The inner surface of the pan was modified so that the movement of the solid was as close as possible to that of a rotating drum, raising the grains to certain heights and dropping them by gravity into a cascade of solids. To prevent the retention of grains on the dryer surface, an 8 cm long and 1.5 cm thick rubber strip was placed on the inner bottom of the pan to mechanically stir the adherent material. In addition, six equally spaced strips that were 15 cm long, 1.5 cm wide, and 0.5 cm thick were placed on the lower inner surface of the dryer to improve the motion of the solids. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows a schematic sketch of the dryer.\u003c/p\u003e \u003cp\u003eAn oven with air circulation and renewal, model TECNAL TE-394/1, was used to obtain the drying kinetics of the malt bagasse. In the center of the oven there was a metal cell that was 2 cm high and 7 cm in diameter, inside of which the biomass sample to be dried was confined. The metal cell was attached to a digital scale, placed on the oven, which was connected to a computer for the data acquisition of both sample mass and drying time using HyperTerminal software.\u003c/p\u003e \u003cp\u003eThe BSG's adherence to the dryer surface was determined by a centrifuge with a maximum rotational speed of 10,000 rpm, in which the adhesion force equals the centrifugal force required to remove the adhered solids [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. The centrifuge was modified to meet the objectives by pinning two 6.30 by 6.30 cm and 0.40 cm thick square iron blades welded to a 0.80 cm thick iron cylinder to the centrifuge spindle. Copper sheets with a thickness of 1.0 mm were fixed on the iron blades to provide the same conditions for adhesion of the material on the surface of the rotary pan (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Experimental procedures\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.3.1 Pan drying tests\u003c/h2\u003e \u003cp\u003eThe temperature was kept constant at the blower outlet before starting the drying experiments. After stabilizing the temperature value, a grain load with known mass, m\u003csub\u003es\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e, was fed to the rotating pan. The blower was positioned in the center of the front opening of the rotating pan, with a slope angle of 60\u0026deg; in relation to its vertical. Grain samples have been taken at predefined intervals to measure the temperature and frequency of solid mixing. The air temperature at the blower outlet, T\u003csub\u003ea\u003c/sub\u003e\u003csup\u003eO\u003c/sup\u003e, was measured with a thermocouple, while the spent grain temperature, T\u003csub\u003es\u003c/sub\u003e, and the dryer wall temperature, T\u003csub\u003ew\u003c/sub\u003e, were measured with an UT300A infrared thermometer. The motion of the solids, Ω\u003csub\u003es\u003c/sub\u003e, was measured by tracking the trajectory of an aluminum spherical tracer with a diameter of 1 cm. The tracer follows the cyclical movement together with the solids, in which Ω\u003csub\u003es\u003c/sub\u003e is the ratio between the number of cycles and the sampling time. To compare the heating rates between the BSG particles and between BSG and the dryer wall, the dimensionless temperature θ, which is the ratio between T\u003csub\u003es\u003c/sub\u003e and T\u003csub\u003ew\u003c/sub\u003e, was defined. Two different values of m\u003csub\u003es\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e and T\u003csub\u003ea\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e were chosen to analyze the influence of these parameters on the operation of the dryer. The values used in the experimental essays are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, and each experiment was repeated three times.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOperating variables in drying of brewer\u0026rsquo;s spent grain.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRuns\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eT\u003csub\u003ea\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003em\u003csub\u003es\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e (kg)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e101.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e101.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e67.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e67.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.3.2 Adhesion tests in the centrifuge\u003c/h2\u003e \u003cp\u003eThe relationship between the adhesion forces and the moisture content of the spent grain was derived experimentally with eleven samples of different humidity, obtained in an oven with air circulation, setting eleven different drying times ranging from 0 to 24 hours. The moisture contents of the samples were determined through the gravimetric method (ISO 11461). The adhesion forces were determined through the centrifugal method, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, where the adhesion force between the biomass and the copper surface would be equal to the centrifugal force necessary to detach the adhered particles. At first, BSG samples were mechanically adhered to the surface by placing them on the copper plates, covering their entire surface, and then the second copper plate of the same area was placed on the bagasse, and a weight of 0.80 kg was placed on a second plate for 5 minutes, mechanically compressing the material. After compression, the upper plate was removed, and the lower plate with adhered material was weighed, and it was then fastened to the centrifuge shaft. The rotational speed was progressively increased until the mass dropped, and the remaining material adhered to it was weighed again. The adhesion force F\u003csub\u003ead\u003c/sub\u003e was determined by the following equation:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$${F}_{ad}={F}_{cent}={m}_{det}w2r$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere F\u003csub\u003ecent\u003c/sub\u003e is the centrifugal force, m\u003csub\u003edet\u003c/sub\u003e is the detached BSG mass, w is the angular speed and r is the support radius.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.3.3 Kinetics and oven drying rate\u003c/h2\u003e \u003cp\u003eIn the tests to determine the kinetics and drying rate, the air velocity inside the oven was set at approximately 1.0 m\u0026middot;s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and measured using a digital anemometer model (LCA 6000). Three different temperatures were used in the experiments: drying temperatures of 50, 60, and 70\u0026deg;C, respectively. For each drying test, approximately 11 g of raw malt bagasse were added to the metallic cell, filling it completely. After adding the metal cell to the oven, the mass loss of the sample was monitored through the LabView software in each second of drying until the biomass reached its dynamic equilibrium. The dry basis moisture of the sample, X\u003csub\u003es,db\u003c/sub\u003e, was calculated using the following equation:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$${X}_{s,db}\\left(t\\right)=\\frac{\\left({m}_{s}\\left(t\\right)-{m}_{s}^{0}\\bullet {X}_{s,wb}^{0}\\right)}{\\left({m}_{s}^{0}\\bullet {X}_{s,wb}^{0}\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere m\u003csub\u003es\u003c/sub\u003e(t) is the mass of the sample at drying time t, m\u003csub\u003es\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e is the initial mass of the sample and X\u003csub\u003es\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e\u003csub\u003e,db\u003c/sub\u003e is the initial moisture of the sample on a wet basis. Finally, the drying rate was calculated using the following equation:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$${DR}_{i}=-\\left[\\frac{\\left({X}_{s,db\\left(i\\right)}-{X}_{s,db(i-1)}\\right)}{\\left({t}_{\\left(i\\right)}-{t}_{(i-1)}\\right)}\\right] i\\ge 1$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere DR\u003csub\u003ei\u003c/sub\u003e is the drying rate observed in the drying interval i.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Drying brewer\u0026rsquo;s spent grain in a pan\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows that, under the conditions evaluated, the increase in drying air temperature and the decrease in the initial biomass load favored drying, reducing the time required to reach dynamic equilibrium. For example, by keeping the initial load at 1.5 kg and increasing the drying air temperature from 67.7\u0026deg;C to 101.2\u0026deg;C, a decrease was observed in the total drying time from 420 min to 240 min. By keeping the drying air temperature at 67.7\u0026deg;C and decreasing the initial load from 1.5 kg to 1.0 kg, a decrease was observed in the total drying time from 420 min to 330 min. The results indicated the potential use of rotary dryers in the processing of malt bagasse, reducing its initial moisture from approximately 80% (wb) to a moisture of approximately 8.5% (wb) in dynamic equilibrium in the four conditions evaluated. The product obtained is suitable for thermal conversion through combustion, gasification or pyrolysis, since the biomass must have a moisture content between 5 and 25% (wb) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Oven drying rate\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows the drying rate as a function of malt bagasse moisture for the three different temperatures evaluated. Under the conditions evaluated, two distinct periods were identified, a stabilization period in which an increase in the drying rate was observed until the biomass reached a moisture ratio of approximately 0.9, followed by a period with a decreasing drying rate that extended until the end of the operation. The absence of a well-defined drying period at a constant rate is a strong indication that there was no excess of free water on the surface of the BSG and that the diffusion of water molecules from the inside of the BSG particles to its surface controlled drying mechanisms. It was also observed that the increase in drying rate was favored by the increase in air temperature. In Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, the results of the drying rates are shown, which indicate that the total processing time and the drying rate are highly dependent on the temperature of the drying air and that the process can be controlled through this variable.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Adhesion forces in brewer\u0026rsquo;s spent grain\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows that there was a reduction in the adhesion forces between the brewer\u0026rsquo;s spent grain and the copper surface by removing water from the particles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt was observed that the decrease in the moisture ratio from 1.0 to 0.25 was sufficient to reduce the adhesion force per surface area from approximately 1.4 to 0.14 N\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. When the moisture ratio was less than 0.05, the adhesion forces were considered zero since no adhesion of the BSG particles to the copper surface was observed.\u003c/p\u003e \u003cp\u003eOther authors have observed a decrease in the adhesion force as water is removed from the materials since, in conditions of high humidity, capillary forces prevail over other mechanisms of surface interaction, such as van der Waals forces and electrostatic forces [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The presence of water between the surfaces of the adhesive and the adherent would be responsible for the formation of liquid bridges through a process known as \"wetting\", and the water may come from steam condensation on the surface, the presence of excess water, or migration inside the solid particles [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Moreover, expressive adhesion forces between the spent grain and the surface showed that high sugar content led to a stronger interaction with metal surfaces and a tendency for agglomeration [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Deng et al. (2020) evaluated the influence of humidity on the forces that cause urban sewage to adhere, identifying a relationship between humidity and the shear and tensile stresses involved in the adhesion of the material and between humidity and the forces of compression involved in the cohesion of the material [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Kobayashi et al. (2021) used resins as accelerators in the drying of urban sewage and observed that, regardless of the presence of resin, moisture directly influenced the contact angle [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe influence of the moisture content of the spent grain on the adherence seems to be consistent with the work of Stroem et al. (2009) who evaluated the agglomeration profile of the biomass in a rotary drum dryer. According to their work, brewer\u0026rsquo;s spent grain tends to adhere to the dryer walls, especially close to the solids feed, where there was a higher moisture content and the adherence mechanisms were associated to the water condensation from the superheated steam [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. However, in the present work, the atmosphere had controlled humidity during the adhesion tests and, consequently, vapor condensation would not have a significant influence on the adhesion mechanisms. It is possible, therefore, that the moisture inside the biomass particles controlled the interaction between the phases.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Biomass movement\u003c/h2\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the average motion of solids inside the rotating dryer was strongly dependent on the moisture content of the biomass. The results indicate that with high moisture content, at the beginning of drying, the solids had low fluidity, but as the moisture ratio reached 0.6, fluidity increased. A decrease in the movement of solids was observed when the water was removed, from a moisture ratio of 0.6 to dynamic equilibrium. The differences in motion of solids inside the rotating dryer could be visually noticed through its opening. Under conditions of high moisture content, the biomass formed a single agglomerate of solids with low mobility. By removing water from the biomass, some particles were detached by the mechanical action of the strips and started moving with higher mobility compared to the agglomerated particles. As the moisture ratio was close to 0.6, the agglomerated biomass was completely detached, and the solids reached their maximum motion. To this point, the solid-wall interaction played a key role in the solid motion as they were adhered to the surface, lifted to a specific height, and dropped, finally returning to the bottom bed through an \"avalanche\" movement. As the water evaporated, the adhesion between the solids and the walls of the dryer decreased, and consequently, they were not lifted by the rotation movement but were mixed by the strips.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese results agree with those obtained by Ma et al. (2019), who used a three-dimensional discrete element model to study the surface interactions between individual particles and their surroundings through capillary bridges. The moisture content of the solids had an influence on the repose angle, varying from 13.76\u0026deg; for dry materials to 18.94\u0026deg; for wet materials, showing that dry solids have higher flowability. Furthermore, in the rotating drum, the dry particles had a lower surface angle and rolled down the slope in an unsteady flow, while the wet particles showed a higher surface angle due to the capillary effect. The particles fell as a coherent whole with uniform velocity in an \"avalanche\" motion [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThus, it can be understood that the variation in solids\u0026rsquo; movement, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, is caused by the formation of agglomerates and by the interaction between the BSG particles and the internal surface of the dryer. In addition, it has been shown that the decrease in biomass humidity makes the movement of particles closer to what is considered ideal for rotating equipment. This behavior results in a homogeneous mixture and free movement of the particles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Thermal behavior of malt bagasse drying\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the increase in the temperatures of the internal surface of the pan and the biomass during drying. It can be observed that the temperature profile was similar in all conditions evaluated, even with the constant increase of T\u003csub\u003ew\u003c/sub\u003e and T\u003csub\u003esolids\u003c/sub\u003e. At the beginning of the process, T\u003csub\u003ew\u003c/sub\u003e and T\u003csub\u003esolids\u003c/sub\u003e presented similar values; later, T\u003csub\u003ew\u003c/sub\u003e presented higher values, indicating more intense heating on the pan surface; and finally, T\u003csub\u003esolids\u003c/sub\u003e presented higher values at the end of the process.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIt can be observed that the increase in the maximum temperature reached by the internal surface of the pan and by the malt bagasse, as expected, was mainly associated with the air temperature at the blower outlet. The biomass was heated to a maximum temperature of approximately 46.5\u0026deg;C with the drying air at 67.7\u0026deg;C, while for the drying air at 101.2\u0026deg;C the maximum temperature reached by the biomass was considerably higher, approximately 65\u0026deg;C. The same was observed for the temperature of the internal surface of the pan, with maximums of approximately 41\u0026deg;C and 59\u0026deg;C for the drying air at 67.7\u0026deg;C and 101.2\u0026deg;C, respectively. The increase in the total mass of biomass did not change the temperatures in the dryer, influencing only the total processing time.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e presents the results obtained from the dimensionless temperature θ analysis through the drying. It can be noticed that the drying could be divided into three different regions. It can be observed that in Region 1, with a moisture ratio greater than 0.6, the dimensionless moisture remains practically constant, with values close to 1.0 due to the proximity between the temperatures of the biomass and the internal surface of the pan, indicating the thermal equilibrium between the phases. In Region 2, with a humidity ratio between 0.6 and 0.25, a constant reduction of the dimensionless humidity to values close to 0.85 is observed, indicating a more intense heating of the internal surface of the pan in relation to the BSG. Finally, in Region 3, with a humidity ratio lower than 0.25, a constant increase in θ could be observed with the decrease in humidity to values close to 1.1. This indicates that in this region, unlike Region 2, the BSG temperature increased more rapidly relative to the inner surface of the pan. The variation of θ as a function of humidity is a strong indication that the heat transfer between the BSG particles and the dryer wall was more efficient in conditions of high humidity. These results match those observed in earlier studies, as adhesion and cohesion in wet conditions usually affect the interface area [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] and there are differences between heat transfer coefficients in free-flowing and sticky materials [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eDrying in a rotary dryer has allowed an approach to biomass drying, especially the BSG, in which it was possible to corroborate that this type of reactors can improve drying efficiencies. A drying ratio of 0.6 has proven to be the best to achieve fluidization in the rotary dryer. A single pan proves to be very efficient in the drying and fluid dynamic behavior of the BSG, as evidenced in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. This information is relevant in drying processes, especially for biomass from the brewing industry, because it can predict drying behavior in this type of reactor. It is then necessary to continue testing with more developed equipment and larger dimensions to corroborate the good behavior shown in this study. The pretreatment of this type of residual biomass turns out to be quite interesting because barley, which is the main raw material used in the beer industry, and its residues have a relatively small average particle size (2 mm). This size is normally the same, with even slightly larger sizes up to 3 mm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), but it is always the same because, due to the beer process, they must be small particles, which means that the drying pretreatment does not need crushing or grinding.\u003c/p\u003e \u003cp\u003eFinally, dry BSG waste is interesting for its use in thermal processes due to its calorific value of 21 MJ kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which could be used in the same industry to obtain energy and use it within industrial plants, reducing some costs [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Instead, its use in pyrolysis or gasification turns out to be quite interesting, due to the possible obtaining of by-products such as H\u003csub\u003e2\u003c/sub\u003e, which can be used as raw material in refinery processes and as biofuel. Likewise, some authors have verified that BSG residues have high contents of phenolic waste that can be used in the cosmetic industry. Becoming a low-cost raw material for this industry and a raw material of sustainable origin for polyphenols as well as other bioactive molecules [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe drying of malt bagasse in pans was able to significantly reduce the biomass moisture, from 80 to 8.7% (wb), a necessary condition in several applications, such as gasification and combustion. However, the high biomass moisture, especially at the beginning of the operation, negatively affected the drying process due to the intense surface interactions. The formation of agglomerates, due to cohesion forces, and the adhesion of biomass to the internal walls of the dryer, due to adhesion forces, altered the movement of solids and the transfer of heat between the phases, preventing uniform drying throughout the process. Although the pan has proved to be an interesting piece for rotating equipment in obtaining information about the drying process due to its frontal opening and easy access to the moving bed and the internal surface of the dryer, further investigations into the mechanisms of bagasse adhesion to malt are necessary to define more efficient strategies and minimize the negative effects of agglomeration.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the financial support of the National Council for Scientific and Technological Development. This study was financed in part by the Coordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior \u0026ndash; Brazil (CAPES) \u0026ndash; Finance Code 001.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Guilherme Pinto, Jos\u0026eacute; Freire and F\u0026aacute;bio Freire. The first draft of the manuscript was written by Guilherme Pinto and F\u0026aacute;bio Freire and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMussatto SI, Dragone G, Roberto IC. Brewers\u0026rsquo; spent grain: Generation, characteristics and potential applications. J Cereal Sci. 2006;43(1):1\u0026ndash;14. \u003c/li\u003e\n\u003cli\u003eRavindran R, Jaiswal S, Abu-Ghannam N, Jaiswal AK. A comparative analysis of pretreatment strategies on the properties and hydrolysis of brewers\u0026rsquo; spent grain. Bioresour Technol [Internet]. 2018;248:272\u0026ndash;9. Available from: https://doi.org/10.1016/j.biortech.2017.06.039\u003c/li\u003e\n\u003cli\u003eIkram S, Huang LY, Zhang H, Wang J, Yin M. Composition and Nutrient Value Proposition of Brewers Spent Grain. J Food Sci. 2017;82(10):2232\u0026ndash;42. \u003c/li\u003e\n\u003cli\u003eWen C, Zhang J, Duan Y, Zhang H, Ma H. 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Available from: https://doi.org/10.1080/07373937.2019.1644347\u003c/li\u003e\n\u003cli\u003eJaiser S, Sanchez Salach N, Baunach M, Scharfer P, Schabel W. Impact of drying conditions and wet film properties on adhesion and film solidification of lithium-ion battery anodes. Dry Technol. 2017;35(15):1807\u0026ndash;17. \u003c/li\u003e\n\u003cli\u003eThundat T, Zheng XY, Chen GY, Sharp SL, Warmack RJ, Schowalter LJ. Characterization of atomic force microscope tips by adhesion force measurements. Appl Phys Lett. 1993;63(15):2150\u0026ndash;2. \u003c/li\u003e\n\u003cli\u003eLi B, Wang F, Chi Y, Yan JH. Adhesion and Cohesion Characteristics of Sewage Sludge During Drying. Dry Technol. 2014;32(13):1598\u0026ndash;607. \u003c/li\u003e\n\u003cli\u003eBhandari B, Howes T. Relating the stickiness property of foods undergoing drying and dried products to their surface energetics. Dry Technol. 2005;23(4):781\u0026ndash;97. \u003c/li\u003e\n\u003cli\u003eKudra T. Sticky region in drying - Definition and identification. Dry Technol. 2003;21(8):1457\u0026ndash;69. \u003c/li\u003e\n\u003cli\u003eFeiler AA, Stiernstedt J, Theander K, Jenkins P, Rutland MW. Effect of capillary condensation on friction force and adhesion. Langmuir. 2007;23(2):517\u0026ndash;22. \u003c/li\u003e\n\u003cli\u003eMorris JD, Daood SS, Chilton S, Nimmo W. Mechanisms and mitigation of agglomeration during fluidized bed combustion of biomass: A review. Fuel [Internet]. 2018;230(February):452\u0026ndash;73. Available from: https://doi.org/10.1016/j.fuel.2018.04.098\u003c/li\u003e\n\u003cli\u003eHerbst G, Hamerski F, Errico M, L. Corazza M. Pressurized liquid extraction of brewer\u0026rsquo;s spent grain: Kinetics and crude extracts characterization. J Ind Eng Chem [Internet]. 2021;102:370\u0026ndash;83. Available from: https://doi.org/10.1016/j.jiec.2021.07.020\u003c/li\u003e\n\u003cli\u003eArranz JI, Sep\u0026uacute;lveda FJ, Montero I, Romero P, Miranda MT. 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Available from: https://doi.org/10.1080/07373937.2019.1615938\u003c/li\u003e\n\u003cli\u003eKobayashi N, Okada K, Tachibana Y, Kamiya K, Zhang B, Suami A, et al. Drying enhancement of sludge with resin-type drying accelerator and its mechanism. Dry Technol [Internet]. 2021;39(6):834\u0026ndash;45. Available from: https://doi.org/10.1080/07373937.2020.1725770\u003c/li\u003e\n\u003cli\u003eMa Y, Evans TM, Philips N, Cunningham N. Modeling the effect of moisture on the flowability of a granular material. Meccanica [Internet]. 2019;54(4\u0026ndash;5):667\u0026ndash;81. Available from: https://doi.org/10.1007/s11012-018-0901-8\u003c/li\u003e\n\u003cli\u003eHirosue H, Shinohara H. Volumetric Heat Transfer Coefficient and Pressure Drop in Rotary Dryers and Coolers. 1st Int Dry Symp. 1978;152\u0026ndash;9. \u003c/li\u003e\n\u003cli\u003eIdowu IA, Hashim K, Shaw A, Nunes LJR. Energy recovery from brewery spent grains and spent coffee grounds: a circular economy approach to waste valorization. Biofuels [Internet]. 2022;0(0):1\u0026ndash;10. Available from: https://doi.org/10.1080/17597269.2022.2135292\u003c/li\u003e\n\u003cli\u003eMacias-Garbett R, Serna-Hern\u0026aacute;ndez SO, Sosa-Hern\u0026aacute;ndez JE, Parra-Sald\u0026iacute;var R. Phenolic Compounds From Brewer\u0026rsquo;s Spent Grains: Toward Green Recovery Methods a\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"waste-and-biomass-valorization","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wave","sideBox":"Learn more about [Waste and Biomass Valorization](http://link.springer.com/journal/12649)","snPcode":"12649","submissionUrl":"https://submission.nature.com/new-submission/12649/3","title":"Waste and Biomass Valorization","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Drying, Biomass, Adhesion forces, Agglomeration","lastPublishedDoi":"10.21203/rs.3.rs-2837473/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2837473/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBrewer's spent grain (BSG) is a biomass with a high lignocellulosic content that can be reused in thermal processes, however it has high moisture content, which avoids it from being used in these processes. Pretreatment by drying rotating equipment turns out to be a suitable alternative. This work studied the rotational drying of BSG analyzing the effects of adhesion of solids. To do this, a standard pan combined with an external blower was chosen as a rotary dryer due to the easy access to the bed and the inner surface of the dryer. In addition, this type of dryer made possible to determine the relationship between BSG moisture and adhesion force. Under the operating conditions of the experiments, the moisture content of BSG decreased from 80 to 8.6% (wb), making it possible for the biomass to be utilized in thermal processes. Moisture ratios higher than 0.6 led to greater adherence and consequent agglomeration of solids, reducing their mobility and heat transfer with the internal surface of the dryer. At the start of drying, the bed’s rotational speed rate of BSG was approximately 14 rpm, half of the maximum rate of 28 rpm, also the temperatures of the BSG and the inner wall of the tray were in equilibrium, showing that changes in biomass adhesion would take non-uniform drying.\u003c/p\u003e","manuscriptTitle":"Effects of adherence in the drying of brewer’s spent grain with rotating equipment","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-05-22 15:28:37","doi":"10.21203/rs.3.rs-2837473/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2023-05-19T10:48:22+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-05-19T08:20:24+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Waste and Biomass Valorization","date":"2023-05-14T07:05:15+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-04-21T06:31:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Waste and Biomass Valorization","date":"2023-04-20T08:06:08+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"waste-and-biomass-valorization","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"wave","sideBox":"Learn more about [Waste and Biomass Valorization](http://link.springer.com/journal/12649)","snPcode":"12649","submissionUrl":"https://submission.nature.com/new-submission/12649/3","title":"Waste and Biomass Valorization","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f39167f1-ff98-4bde-b59e-2f027c8853f9","owner":[],"postedDate":"May 22nd, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-12-11T15:09:28+00:00","versionOfRecord":{"articleIdentity":"rs-2837473","link":"https://doi.org/10.1007/s12649-023-02329-8","journal":{"identity":"waste-and-biomass-valorization","isVorOnly":false,"title":"Waste and Biomass Valorization"},"publishedOn":"2023-12-07 15:01:38","publishedOnDateReadable":"December 7th, 2023"},"versionCreatedAt":"2023-05-22 15:28:37","video":"","vorDoi":"10.1007/s12649-023-02329-8","vorDoiUrl":"https://doi.org/10.1007/s12649-023-02329-8","workflowStages":[]},"version":"v1","identity":"rs-2837473","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2837473","identity":"rs-2837473","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}