The influence of coal-blending methods, such as out-furnace and in-furnace methods, on unburned carbon and NO emissions of blending coal combustion in a drop-tube furnace (DTF) has been analyzed using experimental and numerical approaches for binary coals (sub-bituminous and bituminous coals) used by Korean power plants. In the out-furnace method, as the blending ratio of sub-bituminous coal based on bituminous coal (SBR) increases up to 50%, the unburned carbon fraction gradually decreases. The worst condition is found at a SBR of 75%, which is caused by the occurrence of highly oxygen-deficient conditions in the furnace. Furthermore, the emission index of NO (EINO) is proportional to the SBR. In addition, the in-furnace blending method is applied using a modified DTF to improve the efficiency of unburned carbon fractions and the involvement of NO emissions. The results show that unburned carbon fractions as well as the EINO decrease over time because of improvements in oxygen deficiency and NO reduction mechanisms. The numerical modeling strongly supports these phenomena and provides insights into the mechanisms that affect the blending methods during the combustion of coal blends.

The influence of coal blending methods, such as out-furnace (external or premixed) blending and in-furnace (initially nonmixed) blending, with different excess oxygen (highest, medium, and lowest stoichiometric conditions) on unburned carbon and NO x emissions of blend combustion in an entrained flow reactor has been analyzed, using experimental and numerical approaches for binary coals used by Korean power plants. The results confirm that, under the medium condition, contrasting processes, such as reactive and unreactive effects, occur with SBRs in the out-furnace blending method. The in-furnace blending method results in an improvement in the efficiency of unburned carbon fractions and a further reduction in the NO x emission. Under the highest condition, the unburned carbon fraction in both the out-furnace and the in-furnace blending methods corresponds with the tendency under the medium condition with contrasting processes of lower magnitude, whereas the NO x emission in the highest condition increases slightly. Under the lowest conditions, the unburned carbon fraction in the out-furnace blending method gradually decreases as SBR decreases, without a competition effect. The reduction of NO x emission under the lowest conditions is more effective than those under other conditions for the two blending methods because of homogeneous and heterogeneous NO x reduction mechanisms. These results show that the phenomenon that occurs with coal blending methods under different excess oxygen conditions has been demonstrated and the in-furnace blending method below medium conditions would be an effective method to improve combustibility and NO x emission due to penalty of NO x under the highest condition. In general, the numerical results are in agreement with the measured values and give insight into the phenomena that affect the blending methods under different excess oxygen conditions.

The influence of the volatile matter content on fuel NO emissions from a coal-burning drop-tube furnace (DTF) was analyzed by means of a numerical model for 25 different coals utilized by Korean power plants. The numerical results were fully validated against experimental results obtained using an actual DTF. The results show that the numerical model incorporating the chemical percolation devolatilization submodel is more accurate than that incorporating the two-competing-rates submodel to predict combustion and emission, particularly the devolatilization process and NO. Furthermore, the conversion ratio of fuel N to NO decreases with increasing volatile matter content because the volatile matter releases HCN, which furthers NO reduction. The destruction ratio increases with the amount of HCN produced during the devolatilization process. This paper indicates that HCN is the predominant intermediate species and the volatile matter content has a significant impact on NO emissions from the combustion of coal.

Cities consist of infrastructure that enables transportation, which can be considered as topology in abstract terms. Once cities are physically organized in terms of infrastructure, people interact with each other to form the values, which can be regarded as the meta-information of the cities. The topology and meta-information coevolve together as the cities are developed. In this study, we investigate the relationship between the topology and meta-information for a street network, which has aspects of both a complex network and planar graph. The degree of organization of a street structure determines the efficiency and productivity of the city in that they act as blood vessels to transport people, goods, and information. We analyze the topological aspect of a street network using centralities including the betweenness, closeness, straightness, and information. We classify the cities into several groups that share common meta-information based on the centrality, indicating that the topological factor of the street structure is closely related to meta-information through coevolution. We also obtain the coevolution in the planned cities using the regularity. Another footprint is the relation between the street segment length and the population, which shows the sublinear scaling.In this study, we analyzed the urban street network of 22 cities in Korea. Each city has its own distinctive properties, and hence its street structures are diverse. For example, cities have different roles, and there include capital, satellite, farming, or industrial specialized cities. An industrial specialized city has a different street structure compared to a farming town. In addition, cities have different histories. Some cities were founded in the medieval era, while others were established in the modern era. Medieval cities have irregular street patterns with short or crooked streets, while modern cities have a hierarchical structure with regular, rectilinear, orthogonal, or tree-like patterns [18]. The topography is another factor that characterizes the street pattern; cities in flatlands, mountains, or by the seaside have their own distinctive street structures, which are determined by geographical constraints. Different cultural, social, and economic backgrounds determine the street patterns of a given city. For instance, most Americans prefer detached houses as opposed to apartments, but most Koreans have the opposite taste.The meta-information is basically information about information. Although the city has the physical structure, it is also composed of various kinds of information. For example, a person is the element of the city and is also information in the document. However, a whole collection of people, i.e. the population, is the meta-information because it is information about information. Above mentioned four properties are also kinds of the meta-information. Other types of meta-information include the area of the city, the gross regional domestic product (GRDP), the GRDP per capita, the total or average street segment...

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