OCR Text |
Show Sticking Behavior of Slag Droplets and Initiation of Slag Deposit on Cooled Metal Surfaces (con't.) Some preliminary investigations were made to study the deposit initiation and sticking behaviour of the slag droplets using the Texas lignite at a firing rate of 93,910 Btu/hr. (10 lbs/hr.) using 10 percent excess air stoichiometry. The gas temperature around the probe was 1060 C. During these investigations only the mild steel substrate was used. The results obtained for slag deposition with the Texas lignite indicated that there was slow deposit growth even at or below 280 C substrate temperature. However, at 400 C substrate temperature, the initiation time was longer than that of Illinois No. 6 coal. At higher temperatures, the initiation time was, accordingly, found to be decreased. These results merely revealed that perhaps the iron content in Illinois No. 6 coal lowers the melting temperature of the reacting minerals, forming a low temperature eutectic, which results in a shorter initiation time. It was observed that at 400 C, the particles obtained from lignite combustion seem to develop a sticky surface on which any other particle will stick after impingement. The SEM analysis of these particles indicated that they were composed of Al, Si, Ca, Mg and Fe. Under the microscope, these particles were highly reflective. On the other hand, at 560 C, the sticking particles were spherical and, on occasion, were even fused together. 2-33 |