Overview of E-Learning Environment for Web-Based Study of Testing and Diagnostics of Digital Systems

In this paper, we present an overview of latest developments taking place at Tallinn Technical University (TTU) in the area of e-learning supported by Europea

Axial Concentration Profiles and NO Flue Gas in a Pilot-Scale Bubbling Fluidized Bed Coal Combustor

Atmospheric bubbling fluidized bed coal combustion of a bituminous coal and anthracite with particle diameters in the range 500-4000 ím was investigated in a pilot-plant facility. The experiments were conducted at steady-state conditions using three excess air levels (10, 25, and 50%) and bed temperatures in the 750-900 °C range. Combustion air was staged, with primary air accounting for 100, 80, and 60% of total combustion air. For both types of coal, high NO concentrations were found inside the bed. In general, the NO concentration decreased monotonically along the freeboard and toward the exit flue; however, during combustion with high air staging and low to moderate excess air, a significant additional NO formation occurred near the secondary air injection point. The results show that the bed temperature increase does not affect the NO flue gas concentration significantly. There is a positive correlation between excess air and the NO flue gas concentration. The air staging operation is very effective in lowering the NO flue gas, but there is a limit for the first stage stoichiometry below which the NO flue gas starts rising again. This effect could be related with the coal rank

STUDY OF ACTIVATION OF COAL CHAR

This is the final report on a project whose aim is to explore in a fundamental manner the factors that influence the development of porosity in coal chars during the process of activation. It is known that choices of starting coal, activating agent and conditions can strongly influence the nature of an activated carbon produced from a coal. This project has been concerned mainly with the process of physical activation, which in fact involves the gasification of a char produced from a coal by oxidizing gases. This is of interest for two reasons. One is that there is commercial interest in production of activated carbons from coal, and therefore, in the conditions that can best be used in producing these materials. Much is already known about this, but there is a great deal that is in the realm of ''trade secret'' or just ''industry lore''. The second reason for interest in these processes is that they shed light on how porosity develops during any gasification process involving oxidizing gases. This has implications for understanding the kinetics and the role that ''surface area'' may play in determining kinetics. In earlier reports from this project, several conclusions had been reached upon which the present results rest. There is an often-cited difference in use of nitrogen and carbon dioxide as molecular probes of carbon porosity when using vapor adsorption techniques. Carbon dioxide is often ''preferred'' since it is argued that it offers greater access to fine microporosity, due to the higher temperature of carbon dioxide as opposed to nitrogen measurements. The early phases of this work revealed that the extreme differences are observed only in chars which are not much activated, and that by a few weight percent burnoff, the difference was negligible, provided a consistent theoretical equation was used in calculating uptake or ''surface area''. In another phase of this study, it was noted in a preliminary way how the use of different oxidizing environments would lead to very different porosity development in the same char. There did not seem to be a link to the overall inherent reactivity of the gas-char combination to the pattern of porosity development. In another portion of this study, it was observed that the expected pattern of porosity development could be seen, as a function of whether the process was carried out in a pure chemical kinetic control regime (Zone I) or in a partially mass transfer control regime (Zone II). This portion of the study was useful in suggesting that the unburned carbon from many practical pulverized coal combustion processes had actually emerged from a Zone II environment. This confirms other published hypotheses, and strongly suggests that the material does not survive the boiler environment because it was produced in a purely oxygen mass transfer limited zone (so-called Zone III) or because it was simply so unreactive that it could not burn up in the allotted time (a pure Zone I argument). Moreover, it is believed that the very rapid initial opening of porosity that is revealed by the rapid disappearance of nitrogen and carbon dioxide accessible porosity may be associated with a very thin surface layer of pyrolytically-formed carbon that effectively blocks the bulk char structure from nitrogen. Once removed by low extent of burn-off this phenomenon disappears. Finally, the project turned to comparing the relative influences of the starting coal and the oxidizing environment on the nature of porosity that was developed. Once again, the Argonne Premium coal suite served as a source of chars that would be representative of the broad range of coals found an utilized in the US. The conclusion is that the starting coal has a profound influence upon the ability of an oxidizing agent to develop porosity in the char. This is the single most important factor. Beyond this, however, there was a surprise to the extent that the ordering of porosity development did not follow a simply predictable pattern related to the reactivity of the activating agents. Oxygen is a very effective activating agent, if operation can be kept under control under so-called Zone I conditions. Its effectiveness is comparable to that of the more widely-employed steam

Turbo Tester - Diagnostic Package for Research and Training

This paper describes a diagnostic software package called Turbo Tester. It contains a variety of tools related to the area of testing and diagnosis of integrated circuits. The range of tools includes test generators, logic and fault simulators, a test optimizer, a module for hazard analysis, builtin self-test simulators, design verification and design error diagnosis tools. The range of compatible diagnostic tools forms, via their interaction and complementary operation, a homogeneous research environment, which provides good possibilities for experimental research. Due to this fact, there are a number of scientific papers became possible. These papers have been presented at international conferences and published in reviewed journals. We give a couple of examples of such experiments in this paper. We also describe some laboratory work scenarios for students