This
study investigates by experiment the global characteristics
of both moderate or intense low-oxygen dilution (MILD) oxy-combustion
and air combustion of firing light oil and pulverized coal in a pilot-scale
furnace. There are three burner configurations used, i.e., (I) central
straight (primary) jet + swirl (secondary) jet, (II) central straight
(primary) jet + two side symmetrical (secondary) jets, and (III) central
straight (primary) jet + side asymmetrical jet. The furnace centerline
temperature, species concentrations, and exhaust emissions are measured
and compared for the MILD and conventional combustion cases. For light
oil and pulverized coal, the MILD air combustion or oxy-combustion
occurs with burner II or III, while the conventional combustion takes
place when using burner I. For the light oil, the MILD oxy-combustion
can be reached even using pure oxygen. As the MILD combustion is reached,
a fairly uniform temperature distribution and low emissions of NO
and CO are obtained. Note that burner III produces the largest internal
recirculation of the flue gas, lowest peak temperature, and most uniform
temperature, whereas the opposite occurs for burner I. Importantly,
the MILD combustion is found to reduce the NO emission much more effectively
in the oxy-combustion case than in the air combustion case. Moreover,
the appearance of the MILD combustion of light oil and pulverized
coal differs from the invisible MILD combustion of gaseous fuels.
Dark sparks from burning oil droplets or char particles are present
in the MILD combustion of light oil or pulverized coal. It is also
revealed that the char burnout under the MILD combustion is weaker
than that under the conventional combustion.
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