Showing papers by "Vasudevan Raghavan published in 2020"

A Parametric Study of Spontaneous Ignition in Large Coal Stockpiles

Abstract: Self-heating of coal during its storage and transportation has been a serious problem for decades. Coal stored in large piles for long duration is subjected to weathering by atmospheric air that prevails with different temperatures and moisture content. Chemisorption of atmospheric oxygen results in low-temperature oxidation of pile, which generates heat due to exothermic reactions. If the local heat release rate is higher as compared to the heat dissipated, a significant increase in temperature is possible and this results in spontaneous ignition of the pile. The presence of moisture in coal delays the occurrence of self-heating. This motivates to analyze a scenario of using moist coal to delay or even prevent the self-ignition in dry coal until a given time period of its storage. The main objective of this work is to investigate the critical conditions, which may lead to spontaneous ignition in large coal stockpiles containing dry and moist coal layers. A one-dimensional numerical model is used for this purpose. A parametric study is carried out considering different porosity, superficial air velocity and reactivity values. The time period of coal pile storage is fixed as 360 days. The location and time taken for self-ignition in the pile within this period is reported for each case. In summary, considering several cases, the simulations systematically reveal that highly reactive coal with high pile porosity and higher superficial gas velocity takes the least time to reach the self-ignition temperature.

Burning characteristics and soot formation in laminar methyl methacrylate pool flames

Abstract: This study presents careful measurements from lab-scale experiments and predictions from comprehensive numerical model for the burning characteristics of laminar flames over MMA pools of different ...

Numerical study of characteristics of liquefied petroleum gas flames in coflow air

Abstract: Liquefied Petroleum Gas (LPG) is a fossil fuel mixture, widely used in domestic and industrial burners for several applications. Non-premixed flames are commonly preferred in these burners owing to their stability and controllability. However, based on operating conditions, non-premixed flames emit emissions such as CO and soot. Several techniques, including supply of coflow air and partial premixing of air with fuel, are used to abate these emissions. Due to multicomponent nature of LPG and its complex oxidation pathway, numerical studies on LPG flames are scarce in literature. However, such studies are helpful in the analysis of flames in several burners. With this motivation, systematic numerical simulations of canonical non-premixed coflow flames of LPG and air, without and with partial premixing of air in the fuel stream, have been presented. A two-dimensional axisymmetric domain is used to represent coflow burner. The numerical model includes sub-models to account for soot formation and its oxidation, and radiation energy loss due to participating species and soot. A short kinetic mechanism with 43 species and 392 elementary reactions is used. Results from the numerical model have been validated for flames of propane, n-butane and LPG. Coflow air is varied as proportions of stoichiometric air. Partial premixing of air to the fuel stream results in a reactant mixture that is not flammable. Characteristics of flames in all these cases are presented systematically using the fields of temperature, flow and species mass fractions. A relative comparison of soot production between all these cases is made. Results reveal that in coflow flames, the net soot emissions increase initially, reach a local maximum and then decrease. In partially premixed flames, soot emissions continuously decrease with an increase in the primary air and become almost negligible after a specified air addition to the fuel stream.

Influence of frictional packing limit on hydrodynamics and performance of gas-solid fluidized beds

Abstract: The influence of frictional packing limit (FPL) on prediction of hydrodynamics and performance of fluidized bed reactors was studied. Dense gas-solid flows in non-reactive (under isothermal cold and at elevated temperatures) and reactive atmospheres (fluidized bed gasifier) were simulated using Eulerian-Eulerian methodology considering a range of values for FPL. Simulations under cold flow conditions were conducted to establish a range of FPL values that provides physically realistic predictions. It is noticed that bed pressure drop increases with increasing value of FPL when superficial gas velocity (U) is less than or equal to the minimum fluidization velocity. For larger values of U, predicted pressure drop is unaffected by the choice of value of FPL. However, in these cases, the distribution of particles, their velocities and bubbling behavior are significantly affected by FPL. Effect of FPL at elevated temperatures is similar to the one observed at cold flow conditions. It is further noticed that FPL not only affects the predictions on bed hydrodynamics but also has profound influence on reactive flow characteristics such as bed temperature and product gas composition. Sensitivity analysis under cold flow conditions could reveal better predictions when the ratio of FPL to close packing limit is chosen between 0.9 and 0.97.

Numerical study of methanol flames in laminar forced convective environment using short chemical kinetics mechanism

Abstract: Due to recent interest in methanol economy, it is seen that a numerical study of combustion of methanol in a comprehensive manner is necessary. Motivated from this interest and based on the studies...