*3.2. Oxygen Enrichment Ratio*

The oxygen enrichment mode in the present work is that the flowrate of the hot blast is constant. Oxygen is added to the blast and forms a mixture of air and oxygen. The amount of coal changes with the oxygen enrichment ratio. Based on the practical data, the coke rate decreases by 5 kg·t <sup>−</sup><sup>1</sup> and produced hot metal increases by 3.3% when the oxygen enrichment ratio increases by 1%. As a result, the amounts of gas, coal, coke, and production can be determined, and the compositions of injected gas and top gas are then calculated based on the balances of Fe, C, H and O. Table 4 presents the typical parameters when the oxygen enrichment ratio varies from 1% to 5% at a step of 1%, where the production, coke rate and coal rate at 1–5% are calculated based on the above balance calculations. The temperature profiles at different oxygen enrichment ratios are shown in Figure 4. The carbon solution loss ratio is also calculated after simulation, as shown in Figure 5.

**Figure 4.** Temperature profiles at different oxygen enrichment ratios.

It can be seen from Figure 4 that the temperature increases in the lower zone of the blast furnace with the increase of oxygen enrichment ratio while decreases a little in the upper zone of the blast furnace. At 5% oxygen enrichment ratio, the facet average temperature at 4 m height (the average temperature of the horizontal plane at 4 m height) increases by 85 ◦C from the base model. This indicates that the cohesive zone narrows with the increase of oxygen enrichment ratio.

**Table 4.** Typical parameters when the oxygen enrichment ratio changes.


**Figure 5.** Carbon solution loss ratio at different oxygen enrichment ratio.

It can be seen from Figure 5 that the carbon solution loss ratio decreases gradually as the oxygen enrichment ratio increases. For each 1% increase of the oxygen enrichment ratio, the carbon solution loss ratio decreases by about 0.47%. The reason may be as follows. Firstly, productivity increases while the coke feed rate is kept constant after the oxygen enrichment, which reduces the proportion of coke in the solid. This results in less contact between the gas and the coke. Secondly, the increase of coal injected after the oxygen enrichment leads to an increase of CO content in the lower part of the blast furnace, which limits the carbon solution loss reaction. Thirdly, the burden descending velocity increases after the oxygen enrichment, which causes the residence time of burden to decrease. This makes the carbon loss solution less sufficient.

The carbon consumption decreases and blast furnace productivity increases with the increase of oxygen enrichment. Therefore a higher oxygen enrichment ratio is better for preserving carbon saving and increasing production. However, oxygen enrichment has a great impact on the temperature distribution of the blast furnace, and especially increases the theoretical combustion temperature around the raceway. In the present study, when the oxygen enrichment rate increases by 5%, the theoretical combustion temperature increases by 200 ◦C, which is still within the normal range of the blast furnace of Bayi Steel. The gas temperature in the top decreases by 44 ◦C, but is still higher than the 150 ◦C, which is acceptable for normal production. The actual average oxygen enrichment rate in Bayi Steel is about 3%, so it can be increased to 5% based on the above analysis.
