OCR Text |
Show 2.3 The Experimental Variables 5 The coal-water slurry used in the experiments was prepared and provided by the Occidental Research Corporation. The coal used in their formulation is an Eastern Kentucky bituminous coal of the Island Creek Coal Company. The coal was ground to a fineness of 85/6 < 74 nm. 25% of the coal was ground to below 10jim size to produce a bimodal size distribution which facilitated an increased mass loading, 70/6, of the CVS. Data from coal and ash analyses are given in Table 2. The effects of the following input parameters have been studied to date: o atomizer design, o combustion air swirl and exit velocity from the burner, and o heat extraction from the combustion chamber. Initially, scoping trials were carried out in which the effects of these input parameters on CVS ignition, flame stability, and quality were visually examined. Based upon these trials several sets of input conditions were selected for more detailed flame structure studies. The measurements (Table 3) carried out for first detailed flame structure studies considered in the program included determinations of gas temperature, gas velocity (axially directed), gaseous species concentrations (0^, CO^, CO, NO^), total solids concentration, and carbon burn-out along the flame axis. In addition, radiative heat flux incident on the furnace wall along its length was measured, and a number of in-flame solids and ash deposit samples were characterized by scanning electron microscopy and energy dispersive x-ray spectrometry. 3.0 Preliminary (Scoping) Trials 3.1 Light-up Procedure Since flame stabilization was considered to be one of the more critical problems of CVS combustion the light-up sequence for the slurry was carried out in a manner which ensured a high energy input to the fuel as it entered the combustion chamber. A diagram of the coal-water slurry fuel injection gun used in the CRF is shown in Figure 5. The design permits the co-injection of natural gas and/or oxygen with the CVS during the light-up sequence. The procedure for light-up was as follows: o the furnace was preheated with an oil flame until the refractory surfaces reached a steady state temperature of about 1000 C (1800 F); o the oil flame was shut down and the fuel gun was changed to that for the CVS delivery (Figure 5); o a natural gas flame was established around the spray nozzle; o CVS was started with the combustion air preheated to about 250 C (5005F) |