Ovidiu Marin

Simulating the Impact of Oxygen Enrichment in a Cement Rotary Kiln Using Advanced Computational Methods

This work presents the simulation of a rotary kiln used to produce cement clinker. The effort uses an original approach to kiln operation modeling. Thus, the moving cement clinker is accurately simulated, including exothermal reactions into the clicker and advanced heat transfer correlations. The simulation includes the normal operation of a cement kiln, using coal in an air-fired configuration. The results show the flame characteristics, fluid flow, clinker and refractory characteristics. Two types of coal are employed, one with medium-volatile and one with low-volatile content, with significant differences noted in the kiln operation. A specific goal of this effort is to study the impact of oxygen enrichment on the kiln operation. For this purpose, oxygen is lanced into the kiln at a location between the load and the main burner, and the impact of oxygen enrichment on the kiln operation is assessed. Different oxygen injection schemes are also studied. Thus, varying the angle of the oxygen lance enables to handle various problems as reducing conditions, overheating in the burning zone or refractory wall. It is concluded that oxygen has a beneficial role in the fuel combustion characteristics, and its impact on refractory temperature and the clinker is negligible, in conditions of increased productivity and overall efficiency. The paper presents the impact of dust insufflation into the kiln, such as reduced temperature profile, resulting in a less stable combustion process. The work shows the beneficial influence of oxygen enrichment on kiln operation in the presence of dust, leading to an increase in the amount of dust capable of being insufflated into the kiln. The paper presents the impact of dust insufflation into the kiln, such as reduced temperature profile, resulting in a less stable combustion process. The work shows the beneficial influence of oxygen enrichment on kiln operation in the presence of dust, leading to an increase in the amount of dust capable of being insufflated into the kiln.

A One-Dimensional Model for Cooling of Optical Fibers

This paper presents a one-dimensional model for the cooling of optical fibers. Heat transfer between the fiber, gas and wall, by conduction, convection, and radiation, are taken into account. The model offers advanced features such as multiple inlets and outlets. Six different pure gases or their mixtures may be used to study the effect of gas composition. The forced convection heat transfer coefficient is computed using the correlation for the forced convection in tubes and conduits. This correlation is then corrected to account for the enhanced heat transfer due to the motion of the fiber. This factor is determined from the limited experimental data available in the literature. The mathematical model consists of a system of ordinary differential equations and is solved using the LSODE solver. The model was used to study the effect of various operational parameters. The results show that at the typical conditions used in a commercial draw tower, Helium is the most effective cooling medium. A smaller diameter exchanger is more effective in cooling the fiber. More cooling is achieved if the incoming gas temperature is lower as well as if the cooler wall is kept at a lower temperature. The most critical factor is the fiber draw speed. At higher draw speeds, the residence time is low, which leads to shorter contact time for the fiber and gas to exchange heat. The effect of gas flow rate is not very significant, provided the flow regime is laminar. The turbulence flow regime is, in general, not desirable as it may cause vibrations, which is detrimental to fiber properties such as diameter and strength. Comparisons of the one-dimensional model results with the results of a two-dimensional model as well as simulations using Fluent, a commercial CFD package, are also presented. The results of these simulations may be used for an improved design of an exchanger, providing more efficient cooling of optical fiber. An improved design of exchanger will be the focus of future work in this area.Copyright

Numerical Simulation of Full Oxy-Fired Oscillating Combustion

Oscillating combustion represents a complex process, leading to significant improvements in high temperature industrial applications. Field demonstrations of the oscillating combustion technology have shown a significant reduction in NOx emissions, increased efficiency and improved operation. To date, no modeling work has been able to quantify these impacts of the technology. This effort presents the results of a numerical simulation study of oscillating combustion in a 450 kW pilot furnace. The combustion process involves a pipe-in-pipe natural gas-fired burner using exclusively oxygen as oxidant. The fuel is introduced into the combustion chamber periodically, given a certain amplitude and a time period, while the oxidant is introduced continuously. The transient numerical simulation uses the Air Liquide proprietary computational fluid dynamic software ATHENA™, analyzing the combustion process at incremental timesteps. The results reported here clearly explain the phenomena observed in the lab, as well as in field demonstrations. Detailed analysis of the mixing process between the fuel and oxidant, combustion of the reactants and heat transfer to the furnace walls is included. It is concluded that oscillating combustion represents a powerful solution to many industrial applications, and that modeling can play an important role in explaining the process, and in optimizing the system operation.Copyright