Moderate or Intense Low-Oxygen Dilution Oxy-combustion Characteristics of Light Oil and Pulverized Coal in a Pilot-Scale Furnace

Abstract

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.

Mechanisms of NO formation in MILD combustion of CH 4 /H 2 fuel blends

“…To our best knowledge, there are four kinds of definitions of the MILD combustion, i.e., (1) the definition of Wü nning and Wü nning [11], (2) the definition of Kumar et al [47], (3) the definition of Cavaliere et al [8] and (4) the definition of the present authors [45,46,48]. Wü nning and Wü nning [11] defined the MILD combustion regime using the global parameters of gas recirculation rate (K v ) and furnace temperature.…”

“…This definition is based on the well-stirred reactor. The definitions of the MILD combustion of burning gaseous, liquid and solid fuels are discussed in our previous study [48]. For the present study of firing gaseous fuels, the MILD combustion in experiments is defined as the flameless combustion where no visible flame front occurs at all.…”

Moderate or Intense Low-Oxygen Dilution Combustion of Methane Diluted by CO2 and N2

“…Particularly, their investigation indicates that wet recirculation is more preferable in terms of NO x emission. Our recent study by Li et al 11 investigated the MILD oxy-combustion of firing both light oil and pulverized coal by experiment at a pilot-scale furnace of 300 kW and examined the effects of burner design and dilution level on the combustion appearance of liquid and solid fuels and emissions of CO and NO x . It was found that NO x reduction is more efficient under MILD oxy-combustion than the air case, while the burnout rate needs to be improved.…”

Numerical study of H 2 O addition effects on pulverized coal oxy-MILD combustion

“…Our group recently reported a coal oxy-fuel combustion experimental study operated with both conventional swirl and MILD burners [35]. The results revealed that a larger NO X reduction potential could be achieved in oxy-MILD combustion as compared to the air-MILD operation, and the coal burnout was improved likewise.…”

“…The applications also indicate a higher thermal efficiency under oxy-MILD combustion than conventional oxy-fuel combustion or air-MILD combustion. As for coal oxy-MILD combustion, the corresponding studies are quite sparse, however, the latest literatures still can be found elsewhere [32][33][34][35][36].…”