Search

In this study, considering different operational parameters for stirred media mill, change in specific energy was compared to the change in R x values, i.e. the cumulative weight of the material undersized to a specific sieve. R values, namely R 38 , R 75 , R 106 , were measured before and after grinding in stirred mill. The change in R x (ΔR x , %) values were calculated and they were used to evaluate the certain unit of effectual energy (E cb). This abovementioned calculation is performed by proportioning the Specific Energy (SE) to ΔR x values. The effectual part of SE is considered to be the ratio of the energy needed only for size reduction in grinding and it should be related to the ΔR x. The relative E cb ratios of different grinding conditions give the relative specific energy efficiency ratio (SE e). The relative specific energy efficiency ratio is inversely proportional to specific grinding parameters and ground product particle sizes. The relative specific energy efficiency can be considered as the relative amount of energy for various grinding conditions. The variation between relative energy amount and the previously specified particle size provides a realistic comparison of different grinding parameters. The abovementioned variation could be employed to understand the resistance particle size which is a new concept to describe the particle size at which the maximum effectual SE is directly used. In the context of this study, it was aimed to figure out the interrelation between specific energy efficiency and PSD variation along with the resistance particle size. [ABSTRACT FROM AUTHOR]

The unburned carbon (UBC) content of ash from coal-fired thermal power stations and plants that use massive amount of coal can sometimes be 6–7% or more; this simply means loss of carbon and decrease in efficiency. Carbon loss not only causes a decrease in efficiency but is also an economical issue. Decreasing the carbon content would provide the usage of ash from thermal power stations as cement additives. Many factors cause low combustion efficiency and a high amount of UBC. In the course of this study, fly ash and bottom ash were divided into size fractions and accumulation of UBC at coarser size fractions was observed. In this study, a ground coal sample from a mill was sieved, and the accumulation of UBC at coarser size fractions was associated to a lack of grinding of pulverized coal. Ground coal has a size distribution where 54.45% was below 75 µm, and 45.55% was still over this critical size. A significant amount (35.48%) of the UBC accumulated in the size fraction over 75 µm in fly ash, whereas almost 70% accumulated in the size fraction over 0.5 mm in bottom ash. Coal and ash samples were observed under a microscope to deduce origins of UBC. [ABSTRACT FROM AUTHOR]