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Material transport in mineral processing systems
Published in Gülhan Özbayoğlu, Çetin Hoşten, M. Ümit Atalay, Cahit Hiçyılmaz, A. İhsan Arol, Mineral Processing on the Verge of the 21st Century, 2017
Processing plants of raw materials often involve the transport of particulates through cylindrical rotating devices. Ball mills, pelletizing drums, rotary kilns, ribbon mixers, dryers, coolers, etc. are the most common types of processing equipment employed in size reduction, size enlargement, calcination, clinkering, induration, cooling, and/or mixing unit operations. The material transport in pelletizing discs is also of interest. Feeders, screens, and chutes are transfer points in the material processing plants where transport of particulates takes place from one point to another or from one unit to the other. Flotation cells and flotation columns are the most widely used concentrating units in mineral processing where the role of material transport is very essential in the control and performance of the flotation operation. Tables, jigs, spirals, and concentrating cones are also processing units where the behavior of the flowing material control the separation process.
Biomass, Biofuels, Waste-to-Energy Recovery
Published in Radian Belu, Energy Storage, Grid Integration, Energy Economics, and the Environment, 2019
There are several pretreatment techniques, from the well-established mechanical techniques, consisting of simply chopping, chipping or milling the raw feedstock into ready to use materials for the subsequent conversion, to less well-established thermomechanical or thermochemical upgrading techniques that are increasing the biomass energy density. Pelletization, torrefaction and pyrolysis technologies are such examples. Pellets are small wood-based cylinders 6–12 mm in diameter and 10–30 mm in length, produced by compressing wood sawdust. The high pressure of the press causes the temperature of the wood to greatly increases, causing the wood lignin content to form glue that is binding the pellet together as it cools. Pelletizing is an efficient energy densification technique as pellets typically have a bulk density of 650 kg/m3, about 3.3 times higher than industrial softwood chips. Moreover, due to their very low water content, pellets also have a high net calorific value (or lower heating value) of about 17 MJ/kg, that is about 17% higher than wood chips. This property alone is making the material pelletization economically viable, reducing the transport and storage costs. Since pellets are mostly produced from sawdust, a sawmilling co-product, the quantity of the produced pellets depends on the volume of timber consumed in the wood industry. Biomass briquettes are fabricated in a similar way as pellets and have a typical dimension of 3–10 cm. Unlike pellets, which can be used for automaticallycharged stoves and boilers, briquettes require manual charging, making them a less user-friendly fuel. Torrefaction is a thermal process, involving slowly biomass heating at 200°C–300°C in the absence of oxygen. This degrades the biomass into a completely dry coal-like product that has lost the original biomass fibrous structure, and hence significantly improving grindability, net calorific value, from 19 to 23 MJ/kg and energy density. Torrefaction is a highly densification efficient means, with torrefied products retaining about 92% of the original feedstock energy. In addition, torrefaction transforms hygroscopic feedstocks into a hydrophobic material. This represents a significant advantage over traditional dried biomass such as pellets, since torrefied feedstock can be transported over long distances and stored outside without absorbing any moisture, hence without reductions of its calorific value. Although torrefaction is an old technique, it is not fully commercially available as a means of pre-treating method for biomass-to-energy production chains. While the torrefied biomass can be produced from a wide variety of biomass while yielding similar product properties, this upgrading technique is usually applied to wood feedstocks.
Characterization, density and size effects of fuels in an advanced micro-gasifier stove
Published in Biofuels, 2020
The results of the proximate analysis (moisture, volatile matter (VM), ash and fixed carbon (FC)) and HHV of TSP, CS and PJ, as well as corncob, rice husk and banana leaf pellet, are presented in Table 1. The HHV was determined in a static and adiabatic bomb calorimeter as directed by ASTM E-711, suggested for coal, pellet and other solid biomass fuels. The moisture contents of biomass and pellets conformed with the ideal moisture range for briquetting of biomass and seeds of 5–15% [17]. Excessive moisture content can cause detonation due to the establishment of steam during the briquetting (pellet making) process. This results in lower quality pellets with suboptimal burning, since part of the energy produced during the combustion process is used for the dehydration of the fuel, reducing energy efficiency. Another important factor is the decrease in HHV and thermal conductivity due to increase in moisture content [15,17]. Drying of the fuel in the briquetting process is suggested for moisture content > 15%. However, this process may require higher energy consumption, larger components and increased operating time to produce the pellets. Moisture from TSP was marginally lower when compared to the biomass wastes such as corncob and rice husk; and higher than CS, PJ and banana leaf pellet. These results can be explained by the small degree of heating that occurred naturally in the briquetting machine during waste compaction, thus reducing the final moisture of the briquettes. The pelletizing process also reduces biological degradation of the fuel during storage and transportation because of the reduction of the moisture content as compared with the natural bio-waste.
Forest biomass potential for wood pellets production in the United States of America for exportation: a review
Published in Biofuels, 2022
The pelleting process converts finely ground materials into dense, free-flowing, durable pellets. A pellet has uniform product characteristics in terms of size with length and diameter from 13–19 mm and 6.3–6.4 mm respectively, its shape is cylindrical, and unit densities vary from 1125–1190 kg/m3 [12]. Wood pellets must have high energy density, which makes them suitable for both commercial and industrial heating applications. A pellet with low compression resistance tends to disintegrate easily, due to moisture adsorption [13].
Comparison of mechanical properties of ground corn stover, switchgrass, and willow and their pellet qualities
Published in Particulate Science and Technology, 2018
Apoorva Karamchandani, Hojae Yi, Virendra M. Puri
To date, researches of biomass densification process have focused on physical factors of biomass feedstocks affecting the pelleting process and pellet quality (Colley et al. 2006; Mani, Tabil, and Sokhansanj 2006; Adapa, Tabil, and Schoenau 2009; Kaliyan and Morey 2009; Kaliyan et al. 2009; Karamchandani, Yi, and Puri 2015, 2016) including moisture content, temperature, and constituents of feedstocks. For example, the moisture content of biomass feedstock has been most comprehensively studied and it has been widely reported that the optimum moisture content for reliable biomass densification processes is in the range of 12–20% (wet basis, w.b.) at room temperature for some of nonwoody biomass (Kaliyan et al. 2009). In general, at moisture content more than 20%, densification may not be possible. Likewise, at low moisture content, the pellets may not form at all or they are fragile and/or of low quality. Colley et al. (2006) reported that ground switchgrass at a moisture content of about 20% (w.b.) produced high‐quality pellets. Particle size distribution of size-reduced bulk biomass also has been studied. For example, Kaliyan and Morey (2009) postulated that a mixture of different particle sizes would give an optimum pellet quality because the mixture of particles will produce better interparticle bonding with nearly no interparticle spaces. However, this postulated underlying mechanism of biomass densification has yet to be substantiated. Temperature of biomass during densification process has also been identified as a major factor determining biomass pellet qualities. According to Mani, Tabil, and Sokhansanj (2003), individual pellet density and durability are influenced by physical and chemical properties of the feedstock, temperature, and applied pressure during the pelleting process. Study conducted by Shaw and Tabil (2007) indicated that pellet density was improved by increasing the die temperature, decreasing the screen size (particle size) and feedstock moisture content.