Some statistical parameters for Miscanthus giganteus and Salix viminalis grinding using hammer mills

Abstract

Abstract. In the present paper we present values of some parameters of the grinding process experimentally determined for a hammer mill used for grinding miscanthus stems and willow harvested with specific harvesting machines. The grinding energy according to three tuning parameters was determined: hammer rotor frequency, feeding flow and mill sieve orifice diameter, for two types of hammers (one or twoedge corners). Value sets of energy-feeding flow, energy -rotor rotation frequency, energy -sieve orifice diameter, were analyzed, statistically determining the correlation between them, as well as other statistical parameters, using Excel MS Office (ex.covariance or kurtosis). If grinded biomass is willow, for the link between the energy and sieve orifice diameter the correlation shows a weak relation for one and two edge corner hammers, the two parameters being inversely proportional. Keeping in mind the fact that in the seven out of eight cases the correlation energy sieve orifice diameter presents an inversely proportional dependency, we can accept the hypothesis of reverse proportionality of the two parameters. In the paper, other comments are added regarding values obtained for all statistical parameters analyzed for the two types of grinded biomass.Keywords: biomass, grinding, energy consumption, frequency, feeding flow, statistical parameters. IntroductionBetween the constructive and functional parameters with a high influence on the hammer mill work rate, we can count: hammer rotor dimensions, dimension and shape of the hammer, dimension and form of the sieve orifices, rotor speed, feeding flow, etc.The authors [1] have studied the consumed specific energy variation in hammer mills according to the sieve orifice diameter and grinded vegetal material (alfalfa) mechanical properties. The first conclusion of the article is that specific energy consumption rises with lowering the sieve orifice diameter. Using only linear regression, the authors [1] obtain a regression coefficient with the values of 0.68-0.7. Using polynomial non-linear regressions, regression coefficients of over 0.7 were obtained, reaching over 0.9.The authors [2] confirm direct dependency of energy consumption on hammer mills with the rotation speed, which seems normal, the same thing being confirmed by the authors of the paper [3], which additionally shows reverse dependency of the same energy with the sieve orifice diameter.Reverse dependency of energy with the sieve orifice size is presented in [4], in which it is stated that the linear model of dependency of consumed energy on model parameters gave the best results. In paper [5], the rise in consumed energy with lowering of the sieve orifice dimensions is outlined, but also the rise of energy consumption with material humidity, of course, for the interval of humidity levels taken into consideration.The authors [6] confirm the same types of dependency, and the authors [7] confirm direct dependency of energy consumption on the work flow (which also means productivity in this case), but al...

Study of Selected Physical-Mechanical Properties of Corn Grains Important from the Point of View of Mechanical Processing Systems Designing

“…Similar conclusions are presented for other biomaterials, for example, rice [ 38 ], wheat [ 84 , 85 ] grains, etc. [ 86 ]. The presented crack propagations of brittle materials, e.g., are provided in [ 59 ].…”

Optimization Issues of a Hammer Mill Working Process Using Statistical Modelling

“…The dimension of the stalks measured after harvesting process were about 125 mm. The moisture content measured for the samples during the experimental testing (approximately 3 and a half months after harvesting) revealed that the value for Miscanthus Giganteus samples were between 8.11-11.31% and a value between 8.89-11.99% was revealed for Salix Viminalis [28]. Also, it must be said that for grinding energy consumption we had to consider the following: the material feeding flow values, the dimensions of mill sieve orifices, the type of hammer used for the experiment (four types: one, two and three step edge hammer, triangle edge hammer), and the rotor frequencies applied for testing (50 Hz, 47.5 Hz, 45 Hz, 42.5 Hz, 40 Hz).…”

“…Also, the positioning diameter of hammers on the rotor is 220 mm and the hammer mill rotors length is of 500 mm. [27,28] The MC 22 hammer mill was equipped with 24 hammers that were set up in a parallel distribution. The hammers used for testing had a length of 153 mm and a width of 60 mm, and they had different edges as it can be seen in Figure 2.…”

“…(a) Hammer mill MC 22 (hammer mill; 2. exhauster; 3. cyclone with support and dust collector bag; 4. grinding material evacuation vent; 5. electrical engine; 6. grinded material. ); (b) hammer mill rotor[27,28]…”