Blast Furnace Circumferential Process Symmetry: The Effect of Flow Distribution In Hot Blast Systems

摘要

Blast furnace operators are continuously striving to decrease hot metal cost. A major part of the hot metal cost is the cost of coke. Therefore, blast furnace operation is moving towards lower and lower coke rates by increasing Pulverized Coal Injection (PCI) levels. Presently, annual average coke rates as low as 262 kg coke/tHM are reported (reference 1). In these situations pulverized coal injection PCI rates of 200-240 kg/tHM are required. In addition to this trend, it is well known, that blast furnace productivity can be increased by oxygen enrichment of the blast. While the mentioned levels of coal injection need 5-7% oxygen enrichment in the blast, oxygen enrichment of the blast up to 15-20% have been used; among others at the steel plants in IJmuiden and AK Middletown. High productivity can only be achieved if the circumferential symmetry of the process is good. In other words, if every tuyere is considered as part of a pie, every part has to produce the same amount of hot metal. The lower the coke rate and the higher the oxygen level in the blast, the more sensitive the process becomes for deviations in circumferential symmetry in blast distribution. For this paper, the asymmetry in the distribution of blast flow in hot blast systems has been modeled with a 3-dimensional Computational Fluid Dynamics model (3D CFD). The results of these simulations have been checked with the blast distribution as measured in three different operating furnaces, which were equipped with Delta-P measurements over the tuyeres. The results of the simulation show that there are relatively large fluctuations in blast distribution (10%). These fluctuations vary in position as well as over time because of the layout of the hot blast system and the stove in operation at any particular point in time. The variation in blast volume from tuyere to tuyere is much larger than expected.