OCR Text |
Show The blast furnace provides a simple but effective means of burning coal. The blast air is preheated to temperatures which at some facilities can exceed 1200°C. The blast air is then injected at a high velocity, of about 200 m/s, into the raceway region. The current method of coal injection is to mix the coal directly with this hot blast as described in fig. 6. This results in extremely fast, convective heating of the coal particles, accelerated to an even faster rate through the high initial slip velocity between the coal and blast air. The potential inefficiency in the blast furnace injection system, is the current method of mixing the coal with the blast air. The coal with cold transport air is injected through a straight pipe as shown in fig. 6. Although some mixing of the coal with the blast air will result from the existance of a high initial velocity component of the coal jet in the direction normal to that of the blast air, this mixing is directional in nature. The remainder of the mixing process must occur through turbulent diffusion. The poor global mixing resulting from this system would be expected to generate local fuel rich regions and a delay in the heterogeneous and volatile combustion. However, the desire to remain with a simple system is the reason for chosing a single axial pipe injection system in a blast furnace. It was to clarify the combustion process of coal under these special conditions of very high heating rates, about 105C/sec, with relatively poor mixing that these experiments were performed. The experiments were conducted in the IFRF furnace rather than an actual blast furnace in order to facilitate visualization of the flames and to make possible measurements at accurately known spatial locations. The overall purpose of this programme was to understand the influence of some variable parameters on the combustion of pulverized coal under conditions simulating injection into a blast furnace. The parameters which were varied, were deliberately restricted to parameters which could be altered in a blast furnace system namely: - coal type and particle size; - air blast temperature; - coal flow rate; - coal injection mode (position of coal lance, injector size). 10-3 |