The Effect of Coal Composition on Ignition and Flame Stability in Coaxial Oxy-Fuel Turbulent Diffusion Flames

Abstract

The purpose of the research reported here is to explore how minor coal composition changes can affect oxy-coal flame ignition. Whereas previous work focused on the stability of coaxial turbulent diffusion flames for a single coal, we explore here how two coals of similar rank, fired under aerodynamically identical input conditions, may show very different flame stability characteristics. Since oxy-coal combustion allows oxygen contents in primary and secondary oxidant streams to be varied, flame stability characteristics were determined here by effects of partial pressure of oxygen (P O 2 ) in the primary stream (with differing preheat temperatures in the secondary stream) and effects of P O 2 in the secondary stream (with zero O 2 in the primary stream), on the flame stand-off distance. The two coals investigated were a Utah Skyline bituminous coal and an Illinois #6 bituminous coal. Flame stability was quantified by probability density functions (PDF) of the flame stand-off distance, which were determined using photoimaging techniques developed in previous work. The location of ignition is defined here as the onset of the luminous zone of the flame since that is what an operator in the field might use to control flame stability. At a 420°C preheat temperature, the Illinois coal showed a more stable flame compared to that of the Utah coal. However, the flame stability of the Illinois coal was not significantly changed by increases in secondary oxidant inlet temperature, while that of the Utah coal was. Both coals were bituminous and had similar proximate and ultimate analyses. However, the variations in the results could be interpreted in the light of TGA analysis and solid state 13 C NMR analyses, since these suggested that the observed ignition differences between the two turbulent combusting coal jets might be explained through differences in the fundamental structure of these two coals, as well as differences in their pyrolysis behaviors. Thus, subtle differences in the fundamental chemistry of coals can play important roles in the stability of complicated turbulent diffusion flames, and this may have implications on coal ignition mechanisms in practical turbulent coal flames.

Investigating the combustion characteristic temperature of 28 kinds of Chinese coal in oxy-fuel conditions

“…Thus, some researchers have proposed the use of the fuel ratio to predict coal combustibility. This ratio is defined as the ratio of fixed carbon content to volatile matter content [43,44]. As Table 3 shows, R O2 suggests that O 2 concentration significantly affected by fuel ratio.…”

Twenty-two compositional characterizations and theoretical energy potentials of extensively diversified China's crop residues

“…Crop residues biomass has characteristically high levels of VM and low levels of ash. Crop residue has a lower ignition point and is easier to burn initially with a higher ratio of VM to FC [48], and this ratio is also in descending order for rape stalk, rice straw, corn stover, wheat straw, and cotton stalk. Rape stalk is rich in lipids, and cotton stalk has a high lignin level, therefore both stalks have high VM contents.…”

A comparative study of thermochemistry models for oxy-coal combustion simulation

“…where M v is the volatile molecular weight. In (23), the carbon coecient,c, is determined from a mass balance:c…”

“…In this work, an Oxy-Fuel Combustor (OFC) located at the University of Utah is simulated [23,24]. We choose this experimental dataset because the characterization of ame stand-o distance in this experiment is a good way to measure the coupling between devolatilization and gas phase chemistry which control ignition delay.…”

“…The velocity, temperature and composition of primary, secondary, and euent (product) streams are reported in Table 3. Further details of the OFC are reported in [23].…”