Analyzing the effects of turbulence and multiphase treatments on oxy-coal combustion process predictions using LES and RANS

Numerical studies of pulverized coal swirl combustion in oxy-fuel atmosphere are carried out. Thereby two issues are especially addressed: (1) how LES and RANS impact differently the predictions of combustion properties even though, in both approaches, the same kinetic rates are used to represent the coal combustion processes; (2) how the numerical multiphase treatments may affect the prediction of micro-process interaction as well as the range in which these processes are not negligible. For that purpose a methodology is developed based on an Eulerian-Lagrangian oxy-coal combustion module which is designed relying on the state of the art models as implemented in the commercial code ANSYS Fluent 17. This especially includes three kinetic rates for the description of coal combustion, namely coal devolatilization, volatile combustion and char combustion. Based on an appropriate Stokes number consideration, a full two-way inter-phase coupling has been numerically adopted. To assess the prediction capability of the overall model, a new set of experimental data from a 60 kW(th) oxy-coal test facility is employed. First, the model validation is ensured by comparison of results in terms of flow field and products from volatile and char combustion. Then, an analysis is performed to elucidate how the two-phase turbulence modeling impacts the thermal flow predictions along with the evolution of multiphase oxy-coal combustion properties. Finally, it is demonstrated how the numerical multiphase treatments affect the prediction of micro process interaction in terms of coal devolatilization, coal particle distribution due to turbulent particle dispersion, and of gaseous heat release as well as char burnout. The range in which these interphase processes (subgrid scale particle dispersion) are not negligible is also pointed out in terms of subgrid scale Stokes number. (C) 2017 Elsevier Ltd. All rights reserved

Devastating Decline of Forest Elephants in Central Africa.

African forest elephants– taxonomically and functionally unique–are being poached at accelerating rates, but we lack range-wide information on the repercussions. Analysis of the largest survey dataset ever assembled for forest elephants (80 foot-surveys; covering 13,000 km; 91,600 person-days of fieldwork) revealed that population size declined by ca. 62% between 2002–2011, and the taxon lost 30% of its geographical range. The population is now less than 10% of its potential size, occupying less than 25% of its potential range. High human population density, hunting intensity, absence of law enforcement, poor governance, and proximity to expanding infrastructure are the strongest predictors of decline. To save the remaining African forest elephants, illegal poaching for ivory and encroachment into core elephant habitat must be stopped. In addition, the international demand for ivory, which fuels illegal trade, must be dramatically reduced

Analysis of CO2 adsorption in different lytotypes of lignite

Numerous protected areas (PAs) have been created in Africa to safeguard wildlife and other natural resources. However, significant threats from anthropogenic activities and decline of wildlife populations persist, while conservation efforts in most PAs are still minimal. We assessed the impact level of the most common threats to wildlife within PAs in tropical Africa and the relationship of conservation activities with threat impact level. We collated data on 98 PAs with tropical forest cover from 15 countries across West, Central and East Africa. For this, we assembled information about local threats as well as conservation activities from published and unpublished literature, and questionnaires sent to long-term field workers. We constructed general linear models to test the significance of specific conservation activities in relation to the threat impact level. Subsistence and commercial hunting were identified as the most common direct threats to wildlife and found to be most prevalent in West and Central Africa. Agriculture and logging represented the most common indirect threats, and were most prevalent in West Africa. We found that the long-term presence of conservation activities (such as law enforcement, research and tourism) was associated with lower threat impact levels. Our results highlight deficiencies in the management effectiveness of several PAs across tropical Africa, and conclude that PA management should invest more into conservation activities with long-term duration