Kinds Of Mills Research Articles

Technique to Investigate Pulverizing and Abrasive Performance of Coals in Mineral Processing Systems

The operating costs of breaking coal particles into fine powder, to achieve optimum combustion for the boilers in a power plant, are made up of power input to carry on an energy intensive comminution mechanism and to overcome friction losses within pulverising machines. The operating costs also include the cost of the replacement of the processing system’s components due to wear. This study presents the development and application of an attrition test machine that enables an investigation of the factors that influence pulverizing efficiency. The attrition tester simulates grinding conditions in real vertical spindle mills. In this kind of mill, as with the tester, the size reduction process results from a shearing action during the redistribution of the coal particles. The redistribution and attrition within the coal bed are forced by movement of the rollers (or by a disc rotation, in the case of the tester). The testing method was oriented toward mechanical properties, i.e., internal friction shear strength, abrasiveness and grindability. This method enables facilitated testing procedures and a more exact simulation of grinding in vertical spindle coal mills. Ball-race mills and Loesche roller mills were used.

The use of hydropower potential of the rivers of Moscow basin

The purpose of this article is to study the changes in the ways of using the energy potential of the rivers of the Moscow River basin in the XVIII-XXI centuries. Analysis of the data of the General Survey suggests that in XVIII century the energy of flowing water was used for several kinds of mills: gristmills, saw mills and fulling mills. Energy of flowing water was applied for oil mills and blacksmith hammers. Analysis of literary data shows that the number of mills reduced at the end of XIX century. Only mills built on large rivers continued to work. At the turn of the 19th and 20th centuries small hydroelectric power stations were built instead of mill dams, and the modern hydropower facilities in Moscow basin are small stations of local meaning only. As a result, the maps showing the location of different kinds of mills in the Moscow river basin in XVIII century were composed for the first time. These maps are unique for this territory.

Improving energy efficiency of existing recovery boilers

Due to the increased global energy demand, increased electricity price, and incentives for renewable energy, it is in many cases profitable to maximize electricity output both from power boilers and from recovery boilers. Another motive for maximizing electricity output from recovery boilers is to decrease fuel input to power boilers. In cases where the saved fuel is fossil fuel, the carbon footprint of the mill can be decreased as well. In recent years, many different electricity efficiency increasing features have been installed on new and existing recovery boilers. In this paper, these recovery boiler-related, so-called high power features are applied to existing recovery boilers. The goal is to show how different kinds of mills with existing recovery boilers benefit from high power features. Some of these features can have certain limitations due to constraints set by the existing boilers, and these limiting factors are also discussed. In this study, electricity generation of two example cases are calculated with the following high power features: high black liquor dry solids, air preheating, fully pressurized feedwater tank, feedwater preheating, heat recovery from vent gases, heat recovery from flue gases, and high main steam parameters.

Mechanochemical Polymorphic Transformation of Photocatalyst Material TiO<sub>2</sub> and its Dependence on the Milling Operation

Some dry and wet grinding experiments have been respectively conducted on titanium dioxide which is a noble photocatalyst material in a mortar, a tumbling mill and a planetary mill. Anatase is apt to transform to rutile via a metastable phase brookite in every kind of mills in the case of dry grinding. And it hardly takes place for phase transformation from rutile to other forms. It is shown that the kind of mill has not decisive effect on the mechanochemical polymorphic transformation of titanium dioxide, which merely influences the rate of phase transformation. On the other hand, the addition of other liquid media, such as water and acetone, is helpless for phase transformation of anatase. Only anatase can transform to metastable phase brookite by wet grinding. When ground titanium dioxide is heated, the amorphous phase is easier to transform to rutile than metastable phase brookite at lower temperature.

Mechanochemical activation assisted synthesis of bismuth layered-perovskite SrBi4Ti4O15

Strontium bismuth titanate oxide (SrBi4Ti4O15) belongs to the Aurivillius structural type. The materials in this family are good candidates as lead-free ferroelectric materials for applications at high temperature due to their elevated Curie temperature. The mechanochemical activation method permits one to reduce the particle size of the initial products, so the specific surface is increased, improving in most cases its reactivity. In this paper we report on the synthesis of SrBi4Ti4O15 Aurivillius-type material from activated precursors, obtained though mechanical treatment in vibrating and planetary mills. In some samples a new transitory Sr-Bi-Ti-O fluorite-type phase appears, depending on the milling time and the kind of mill used. The synthesis of SrBi4Ti4O15 from activated precursors is obtained at a temperature about 450°C lower than it would have been required by a conventional solid-state reaction, with significantly reduced heating times.

Breakage behavior of quartz in a laboratory stirred ball mill

An investigation on the kinetics of grinding quartz was carried out in a laboratory stirred ball mill. In this study, the specific rate of breakage S and breakage function B were determined by one-size-fraction tests. The results showed that below a certain size, the breakage was firstorder and the breakage functions were normalizable. Compared with the breakage of same material in a tumbling mill, the S values in a stirred mill were more than a magnitude higher. Nevertheless, in contrast with the case in a tumbling mill, the simulation of size distribution by using these experimental S and B values gave no agreement with the observed data. The study showed that due to the environment effects by a high force action in this kind of mill, the breakage rate for small sizes was affected by large sizes, differing from the breakage of one size fraction. Considering this effect, a reasonable expression of S was given and gave a better simulation of grinding.

Ｗｏｒｋ Ｉｎｄｅｘ相当数による石灰石の微粉砕性評価

Comminution is the oldest mechanical unit operation for size reduction of solid materials and an important step in many processes where raw materials are converted into intermediate or final products. Limestone is self-sufficient mineral resource in Japan and has been using as a sample for grinding tests.Recently, a demand for fine or ultra-fine particles is increasing in many kinds of industries.The energy efficiency of comminution is very low and the energy required for comminution increases with a decrease in feed or produced particle size. Research and development to find energy-saving comminution processes have been performed. Then, it is necessary to estimate the comminution energy. Bond had proposed Work Index and it is an important factor in designing comminution processes and has been widely used. The measurement procedure of Work Index is closely defined by JIS. In a previous paper, the authors proposed a corresponding Work Index which is proportional to the Work Index. A corresponding Work Index could be estimated by the examination of the zeroorder increasing rate constant of mass fraction less than a evaluating size using an arbitrary ball mill.In this paper, ball mill, vibration mill and planetary mill grinding, compressive crushing of powder bed, and autogenous grinding with a stirred mill were carried out on limestone. The relationships between the corresponding Work Index and the evaluating size (sieving size) were studied.As a result, the corresponding Work Index had the minimum value when the evaluating size was approximately the grain size of limestone in the five kinds of mills.

Milling dynamics: Part II. dynamics of a SPEX mill and a one-dimensional mill

The dynamics of mechanical milling can be described in either local or global terms. Local descrip-tions consider aspects of powder deformation, fracture, and welding that transpire when powder is entrapped between grinding media during a typical media collision. Global descriptions consider heterogeneous aspects of milling in specific grinding devices; for example, the distribution of impact energies and powder segregation within a mill. In part I of this series, we described facets of attritor global dynamics. In this article, we do the same for a SPEX* mill and for a hypothetical one-dimensional vibratory mill. In a following companion article, we compare the dynamics of an attritor with a SPEX mill and, by extension, other kinds of mills. Specific attention is paid to the relative efficiencies of these devices and the characteristics of powder processed in them.

Effect of mill diameter on the rate of initial grinding in vibration ball mills

Vibration ball milling was carried out using three kinds of mills with the same internal volume but different diameters. The variations of specific surface area produced with time were investigated at a constant vibration intensity using feldspar with an initial size range of 74 – 149 μm. As a result, it was found that the specific surface area of product was markedly influenced by the difference in mill diameter even at the same vibrating conditions. According to an empirical equation proposed in a previous paper, the rate of initial grinding was also found to vary by a factor of 1.4 to 2.0, depending upon the mill used. The dependence of the rate of grinding on mill diameter can be explained by considering an effective area of mill shell capable of colliding with balls and a motion of balls in each mill. An available suggestion for designing a mill pot was obtained from this work.