Kazunori Shoji

Breakage of coals in ring-roller mills. Part I. The breakage properties of various coals and simulation model to predict steady-state mill performance

The objectives of the present study are to clarify breakage properties of coals in ring-roller mills and to develop a mathematical mill model capable of predicting steady-state mill performance in full scale mills. It was found that ring-roller mills have a higher coal grinding capability than ring-ball mills with an equal grinding efficiency. It was also demonstrated that breakage characteristics of coals in the mill could not be predicted by the conventional Hardgrove grindability index, HGI, under low filling conditions. On the basis of basic experimental results, a mathematical model was constructed to describe the behaviour in the mill. The model proposed here is based on breakage parameters determined form a batch ring-roller mill and utilizing a new scale-up rule employing apparent grinding energy rates in the batch ring-roller mills as well as large scale ring-roller mills. Furthermore, empirical rule of classification were also added to the mill model. The validity of the model was verified thereafter in large scale mills.

Breakage of coals in ring-roller mills Part 2. An unsteady-state simulation model

A mathematical model has been developed for predicting unsteady behavior of a ring-roller mill. The model is based on specific rates of breakage, primary breakage distributions, classification actions of particles in the mill and mass transport relation of mill hold-up and flow rates through the mill. The validity of the model was verified by pilot mill testing. Transient behavior of the mills during rapid changes of load, feed and operating conditions were then demonstrated.

Effect of adsorption characteristics of dispersant on flow and storage properties of coal-water mixtures

Abstract The flow and storage properties of coal—water mixtures (CWM) have been studied with respect to adsorption of anionic dispersants. The amount of adsorbed dispersants increased slightly for several days after the formulation of the CWM and then reached equilibrium, but was further increased by agitation. The adsorption of the dispersants increased as the surface property of coals became more hydrophobic and increased with the apparent surface area for a given coal. The adsorption also increased with the molecular weight of dispersants. The apparent viscosities of CWM depended on the amount of adsorbed dispersant and the viscosity of the carrier liquid. The yield stress at a given viscosity became larger as the adsorption of the dispersant increased, while the viscosity index decreased. There was a good relationship between the rheological behavior and the flow property and static stability. The optimum yield stress and viscosity index were found to be 1 – 5 Pa.s and 0.7 – 0.8, respectively.

Effect of coal particle and spray droplet sizes on combustion characteristics of coal—water mixtures

Abstract An experimental study was carried out to clarify the effect of the droplet and coal particle sizes of coal—water mixtures (CWM) on combustibility, using a twin-fluid atomizer in a small-scale test furnace of 80 kg CWM/h. It was found that the spray mean droplet size became smaller as the coal particle size decreased, while other conditions remained constant, giving rise to better combustibility. However, the combustion efficiency decreased by the blow-off of flame phenomena when the atomizing speed increased even though the spray mean droplet size decreased. It was also confirmed that the combustion efficiency was influenced by the specific surface area of coal particles even if the spray mean droplet sizes did not change. When CWM with a nominal top size of 150 μm was compared with that of 590 μm but containing more fines of less than 5 μm, the size distribution of fly ash was found to be independent of coal particle size distributions of CWM, resulting in no difference in the unburned content in the fly ash.

Coal burners for the entrained flow gasifier.

Gasification characteristics were studied in a single-burner gasifier and a four-burner gasifier to determine the upper and lower burner structures for two-stage circling gasifiers. In order to achieve high efficiencies under stable gasification conditions, it is necessary to obtain long residence times of reactive chars injected from the upper burners and to obtain short flames for the lower burners. It was found that an internal mixing-type burner could achieve a better coal/oxygen mixture than an external type, and favorable mixing was easily attained by adding swirling action to both burner types. The flame length of the internal mixing burner with swirl was shorter than that of the other burner without swirl. Carbon conversion of the internal mixing burners with strong angular momentum was higher than that of the other type of burner.