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Show DESCRIPTION OF EXPERIMENTAL AND NUMERICAL PROCEDURES A continuous, small flow-rate coal slurry atomizer and a laminar flow reactor system have been developed and described previously (Holve and Meyer, 1985). This system injects atomized slurry (or dry pulverized coal) at a uniform velocity and concentration into a 2 m m by 4 0 m m slot of a laminar flow reactor, which uses a methane-air mixture to produce uniform temperatures and oxygen concentrations in the reaction zone. The fuel feed system consists of an air assist atomizer and dry or slurried coal feed systems. The atomizer provides a conical spray which feeds into a converging section of the reactor leading to the slot exit. This arrangement selects a slice of spray across the entire diameter of the spray cone, thus providing a representative sample of the entire spray distribution while producing a uniform spray flow throughout the burner slot. A laser-based particle counter-sizer-velocimeter (PCSV) system is used to measure the concentration and size distribution of particles prior to and throughout the early combustion region of the flow reactor. The in situ P C S V system uses two independent laser beams and independent detection systems (Holve and Annen, 1984), and is capable of particle size measurements in the nominal size range of 0.3-120 //m, at high number densities (IO6 c m - 3 ) . In addition, the instrument obtains a particle velocity distribution for particles larger than approximately 10 /zm. This technique has been used previously to measure particle size distributions of both pulverized coal and coal/water slurries, and has been extensively documented and validated (Holve, 1985; Holve and Self, 1979). A one-dimensional coal combustion model (1-DICOG, described by Smith and Smoot, 1980) was used to calculate particle reaction times versus particle size for this experiment. This code was selected because it can be used to determine number densities for the discrete size distribution as well as to describe coal combustion characteristics. Some of the important features of the code that are pertinent to this study, such as the treatment of swelling and number density, have been briefly summarized in related work (Holve et al., 1985). R E S U L TS All measurements described here were obtained at either ambient air conditions (300 K) or combustion conditions of 1700 K and 3-4% O2. The size distribution data are presented in the form of logarithmic frequency distributions which allow presentation of both number density and solid volume density in a format that is independent of the instrument dynamic range (Holve and Meyer, 1984). A n equally important reason for using log-scaled frequency distributions is the ability to show the wide dynamic range of these particle size distributions. Figure 1 shows the number density size distribution evolution for an atomized coal/ water slurry (manufactured by A m a x ) compared with that of the constituent dried pulverized coal used to make the slurry. Although the pulverized coal is the same for these two fuel preparations (high volatile bituminous), the distributions of these two are significantly 3 |
