Air Stoichiometric Ratio Research Articles

The influence of oxygen-stoichiometry on desulfurization during FBC: A simple sure modeling approach

In this paper an extension is presented cf the simple SUlfur REtention SURE model which was published earlier by the authors (Schouten and Van den Bleek, 1987). The present model explains the effect of a decreasing desulfurization efficiency during staged Fluidized Bed Combustion of coal by the relatively fast formation of SO 3 as a gaseous intermediate reactant in the sorbent sulfation reaction. The SURE model provides an analytical expression for the molar (Ca/S) ratio in the reactor feed as a function of the degree of sulfur retention, the maximum sorbent conversion and three dimensionless model parameters. These parameters are functions of fluid bed operating conditions, coal and sorbent properties and the stoichiometric air ratio. It is shown that the oxygen concentration and the decrease in sulfur retention at lower stoichiometric air ratios can readily be described by the model equations. Furthermore, the SURE model is applied as a diagnostic tool for the analysis of plant operational data obtained from the recent literature. It is concluded from an evaluation of SURE model calculations and experimental data that the sorbent residence time is a crucial system parameter. It is demonstrated that the observed neglect of the influence of the sorbent residence time on the steady state character of many retention experimentations gives rise to serious doubt on the reliability and usefulness of these measurements for model verification purposes.

Fluidized Bed Combustion of Petroleum Pitch

Fluidized bed combustion has been studied as a way for utilizationof petroleum pitch which is secondary product in the cracking processes of residual oil. Combustibility and combustion efficiency, effects of staged combustion and division of secondary air on the NOx formation, desulfurization by limestone and effect of NaCladdition to limestone were studied. The following test results were obtained.1) Petroleum pitch had higher ignition temperature and less combustibility in com-parison with Taiheiyo coal, and so combustion efficiency became few percent lower than that of Taiheiyo coal.2) Increasing bed temperature enhanced NOx abatement in the two staged combustion.3) A significant farther reduction in NOx formation was achieved by dividing secondary air into three parts and injected into free boad, and then unburned substance in flue gas, such asCO and hydrocarbon, disappeared.4) SO2 capture by limestone increased with increasing of first stage stoichiometric air ratio. Increasing bed temperature above 850° caused a rapid lowering in desulfurization, and enhanced the decrease of SO2 capture by limestone in the low range of first stage stoichiometric air ratio.5) SO2 capture by limestone could be increased by adding NaCl to limestone.