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2012, International Journal of Mineral Processing
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Comminution of wide range of densified biomass in four mills. Shape factors do not change significantly compared to particle size with milling. Shape will only noticeably change below the critical particle size for comminution. Mill choking linked to the particle size, shape and classifier Stokes condition. Classification requirements should inform biomass pellet particle sizes. a b s t r a c t The impact of different mill fracture mechanisms were examined for a wide range of densified biomass pellets to provide a comprehensive analysis of biomass milling behaviour for pulverised fuel combustion. The milling behaviour of 7 woody, herbaceous, fruit, and thermally treated densified biomasses were investigated for four distinct types of comminution fracture mechanism using traditional milling indices and novel application of 3D imaging techniques. For the coal mill trials, a reference coal was used to provide a milling performance comparator. For the pre-milled samples, woody and herbaceous pellets have the least spherical particles (u 0.324–0.404), followed by thermally treated pellets (u 0.428), La Loma coal (u 0.503), with olive cake having the most spherical particles (u 0.562). This trend was noted for all the shape factors. Conventional comminution did not significantly impact biomass particle shape, even after a significant change in particle size. Therefore biomass pellet process history plays a key role in determining the comminuted particle shape. La Loma coal had significantly enhanced milling performance in comparison to the biomasses in the coal mills. Significant improvements in grindability and shape factors were observed for the thermally treated pellets. Mill choking was experienced for several of the woody and herbaceous samples, which resulted in a significant energy penalty. The mechanisms of mill choking were found to be intrinsically linked to the critical particle size of comminution through compression, particle shape factors, and the Stokes conditions set for the classifier and burners in pulverised fuel combustion systems. The study showed that for optimal milling performance, biomass pellets should be composed of particles which meet the Stokes requirements of the mill classifier. This would minimise the potential for mill choking and milling energy penalties, and ensure maximum mill throughput.
Bond Work Index (BWI) & Hardgrove Grindability Index (HGI) tests for biomass & coal. BWI can predict the potential for mill choking of biomass in a tube and ball mill. HGI is a poor method of predicting grindability of biomass in vertical spindle mills. Pellets should be composed of pre-densified particles close to the target size. Approximate correlation between HGI and BWI found for some biomass samples. a b s t r a c t With increasing quantities of biomass being combusted in coal fired power stations, there is an urgent need to be able to predict the grindability of biomass in existing coal mills, but currently no standard bio-mass grindability test exists. In this study, the applicability of the Hardgrove Grindability Index (HGI) and Bond Work Index (BWI) as standard grindability tests for biomass were investigated for commercially sourced wood pellets, steam exploded pellets, torrefied pellets, sunflower pellets, eucalyptus pellets, mis-canthus pellets, olive cake and Colombian La Loma coal. HGI predicts the behaviour of fuels in vertical spindle mills and BWI for tube and ball mills. Compared to La Loma (HGI of 46), all biomasses tested performed poorly with low HGI values (14–29). Miscanthus pellets had the highest BWI or W i at 426 kW h/t. Despite similar HGI values, some untreated biomasses showed lower BWI values (Eucalyptus pellets W i 87 kW h/t, HGI 22) compared to others (sunflower pellets W i 366 kW h/t, HGI 20). Torrefied pellets had the lowest W i (16 kW h/t), with La Loma coal at 23 kW h/t. Wood, miscanthus and sunflower pellets exhibited mill choking during the BWI test, as the amount of fines produced did not increase with an increasing revolution count. An approximate correlation between HGI and BWI was found for the bio-mass samples which did not experience mill choking in the BWI test. Milling results in this paper suggest that biomass pellets should be composed of pre-densified particles close to the target size in order to minimise the energy use in mills and possibility of mill choking. Our findings would also suggest that the BWI is a valid test for predicting the potential for mill choking of biomass in a tube and ball mill. HGI, however, appears to be a poor method of predicting the grindability of biomass in vertical spindle mills. A new standard grindability test is required to test the grindability of biomasses in such mills.
The potential benefits of dry comminution in a knife mill for a diverse range of biomass pellets are explored. The impact of dry comminution on energy consumption, particle size and shape, is examined as well as the link between milling and mechanical durability. Biomass pellet comminution energy was significantly lower (19.3e32.5 kW h t À1 [fresh] and 17.8e23.2 kW h t À1 [dry]) than values reported in literature for non-densified biomass in similar knife mills. The impact of drying was found to vary by feedstock. Dry grinding reduced milling energy by 38% for mixed wood pellets, but only 2% for steam exploded pellets. Particle size and shape, particle distribution dispersion, and distribution shape parameters changes between fresh and dry milling were also material dependent. Von Rittinger analysis showed that to maximise mill throughput, pellets should be composed of particles which can pass through the screen and thus have a neutral size change. A strong correlation was found between pellet durability and energy consumption for fresh biomass pellets. Dry grinding has the potential to significantly reduce energy consumption without compromising the product particle size, as well as enhancing product quality and opti-mising biomass pellet comminution and combustion.
2011, Industrial Crops and Products
A PROJECT ON THE DESIGN AND FABRICATION OF A MILL PULVERIZER FOR PROCESSING GRAINS
Mineral Processing Technology mineria procesamiento de minerales
2012, Journal of Biomedicine and Biotechnology
2006, 2006 Portland, Oregon, July 9-12, 2006
2009, Powder Technology
2008
2020
Paddy straw is one of the major agriculture waste produced in India. Burning of paddy straw is one of the easy options for farmers due to its difficult handling which produces environmental problem generating greenhouse gases. Size reduction of paddy straw is necessary for almost it’s every possible utilization for biofuel production. Torrefaction mainly used to process lignocellulosic biomass that makes them easily cut, chop or grind. Torrefaction was carried out at 250°C for 20 and 30 minutes and compared its effect on energy requirement for size reduction with that of raw paddy straw. In this study, effect of torrefaction on physiochemical properties were evaluated in terms of proximate analysis, calorific value, mass yield, energy yield and cutting force of torrefied and untorrefied paddy straw. Cutting force of untreated paddy straw was measured as 2.18 kg using texture analyzer while paddy straw after torrefaction for 20 minutes and 30 minutes was 1.31 and 0.44 kg respectively.
Emerging biomass conversion technologies, such as small scale mobile biochar or pyrolysis/torrefaction machines, aim to use forest residues left after extracting merchantable timber from timber harvest or fuel reduction thinning operations. The residues generated from these operations typically produce low quality feedstock which may not be suitable for new biomass conversion technologies. In an effort to increase feedstock quality, our study separated sub-merchantable trees and tops from piled limbs during the timber harvest. A portion of the separated material was further processed to remove limbs to create five material types: processed and unprocessed, conifer and hardwood stem wood, and slash (stems, limbs and chunks). These materials were comminuted with a disc-chipper or a grinder. The quality of the feedstock produced was characterized by moisture content, particle-size distribution, bulk density, and ash content. Moisture content of sample collected ranged from 19 to 29%. The mean geometric lengths for unprocessed hardwood, unprocessed conifer, processed hardwood, processed conifer, and slash were 20.60, 18.27, 18.16, 17.41, and 47.47 mm, respectively. The bulk density of the five material types ranged from 137.20 – 322 kg/m 3. The least amount of ash were observed in processed conifer samples (0.27%) and greatest in ground slash (1.5%). The results showed that a high quality feedstock can be produced by separating stem wood from other residues during a harvest.
The use of olive mill wastes (orujillo) within coal fired power stations in the UK has led to unexpected difficulties with material caking within the fuel handling plant. This study replicated orujillo caking on a laboratory scale using a planetary ball mill and explored the impact of mill parameters (speed, volume, and duration) on the caking phenomenon. The impact of orujillo composition was examined for 4 sections of fresh and dried orujillo (whole, pulp 0–850 m, pulp 850–3350 m, and cluster 3350 m+) for set milling conditions. Caking was induced by heat generation within the mill and was most prevalent in the pulp section of orujillo. Caking was brought on by a glass transition step, which was measured to be around 97–98 • C for a moisture content of 6–7% in a differential scanning calorimeter (DSC). Caking was the result of the bulk moisture content (14–18%) being higher than the standard moisture content of orujillo (<12%), and can be mitigated through drying. Thus the key to overcoming orujillo caking in fuel handling plants is through moisture content control. Additionally, as the caking issue is most prevalent in the pulp section, all fines below the required combustion particle size (typically <1 mm) should be removed prior to comminution and sent directly to the burner. This would also reduce the comminution load by nearly 50%, increase the energy potential of the fuel, and remove the most problematic section of orujillo from the fuel handling plant.
2009, Bioresource Technology
Within pharmaceutical manufacturing, size reduction is one of the most extensively used and vital unit operations. Size reduction is a process of reducing large solid unit masses into small unit masses, coarse particles or fine particles. Size reduction process is also termed as Comminution or Diminution or Pulverizations. There are many types of size-reduction equipment, which are often developed empirically to handle specific materials and then are applied in other situations. Knowing the properties of the material to be processed is essential. Probably the most important characteristic governing size reduction is hardness because almost all size-reduction techniques involve somehow creating new surface area and this requires adding energy proportional to the bonds holding the feed particles together. Size Reduction is an important operation in many pharmaceutical applications. The important reasons for size reduction are easy handling, increase in surface area per unit volume and separation of entrapped components.
Basics in Minerals Processing BASICS IN MINERAL PROCESSING CONTENT