**1. Introduction**

Steel is the world's most popular construction material due to its durability, processability, and cost cheapness. However, producing steel brings high energy consumption and CO2 emissions, especially in ironmaking process. In order to minimize the energy consumption and CO2 emissions of the ironmaking process, some alternative liquid iron production technologies to blast furnace (BF), such as the COREX process and the FINEX process, have been developed [1]. The COREX process is a smelting-reduction process developed by Siemens Voest-Alpine Industrieanlagenbau Gmbh & Co. (VAI) in the 1970s, for cost-efficient and environment-friendly production of hot metal from iron ore and non-coking coal. Eight COREX units in the world have been put into use and successfully commercialized in different areas, e.g., South Africa, India, and China; therein, two of them are the latest generation of COREX with a capacity of 1.5 million tons of liquid iron per year and were built in China at the Baosteel Luojing steel plant.

In the COREX process [2], all the metallurgical reactions take place in two separate process reactors, the upper shaft furnace (SF) for the iron ore pre-reduction and the lower melter gasifier (MG) for final reduction and smelting. A schematic process flow sheet is shown in Figure 1. Iron ore (lump ore, pellets, or a mixture thereof) is charged into the upper SF where the burden is reduced to direct reduced iron (DRI) by the reduction gas arising from the lower MG. Discharge screws convey the DRI from the SF into the MG where final reduction and melting take place in addition to all other metallurgical reactions. In comparison with a conventional BF, COREX MG is equipped with a more complicated top charging system consisting of one gimbal distributor for coal and eight flap distributors for DRI.

**Figure 1.** Schematic flow sheet of COREX process.

The BF concept is used, but the BF is virtually split into two parts at the cohesive zone interface (cf. Figure 2) in a COREX process. Compared with the conventional BF route, non-coking coal can be directly used for ore reduction and smelting in a COREX process, which eliminates the need for coke making units. The use of lump ore or pellets also dispenses with the need of sinter plants. Since coking and sintering plants are not required for the COREX process, substantial cost savings of up to 20% can be achieved in the production of hot metal, of a grade similar to that of the blast furnace [3].

**Figure 2.** Comparison of concepts between blast furnace (BF) route and COREX route.

Since the distribution of charged burden plays a crucial role in determining the gas flow and thus in achieving a stable operation in BF and SF, it is of considerable importance to investigate the burden distribution influenced by the complicated charging system of COREX MG. The top charging system of COREX MG consists of one coal-gimbal distributor and eight DRI-flap distributors. The gimbal distributor distributes the coal to different radial positions in the furnace by adjusting the angle of the chute. The DRI-flap distributors can charge DRI into the furnace by changing the angle of the flap. The burden distribution is affected by many factors, such as loading equipment and charging patterns. However, as a closed high-temperature reactor, it is difficult to observe directly the burden surface profile and internal structure in the COREX MG. Therefore, it is necessary to establish a mathematical model to predict the profile of the burden surface and the internal structure of burden column.

Many studies [4–7] have established mathematical models of BF and SF charging with chute distributors, and compared with physical experiments [8] or data from industrial onsite experiments [9], and the rationality and accuracy of the models have been verified. However, the mathematical model studies on the charging process in COREX MG remain scarce. In recent years, more and more detailed research works have been carried out on the flow trajectory of the DRI-flap distributor and the coal-gimbal distributor by some research groups [10–16]. Although many physical experiments and numerical simulations have been conducted, sophisticated forecasting software or mathematical models similar to the fast evaluation model of BF charging [17–19] for predicting the burden surface profile and internal layer structure have not been formed.

The authors' experimental studies on COREX MG charging [11,12] has shown that, due to the high free space (low stockline) and small flow rate of burden charging in the COREX MG, the formation of burden pile is in a developing phase with growing pile angles, while that in a BF is commonly recognized as in a fully-developed phase with stable pile angles. The experimental measurement showed also that the pile width was practically the same as the width of burden flow arriving at the burden surface. This makes the formation of burden pile in COREX MG being different from that in a BF. Therefore, this work will focus on the formation process of burden pile when certain material reaches the burden surface, and thereby a thorough understanding of the charging process as well as burden pile evolution can be expected, especially for the mechanism of developing growing with developing pile angles.

### **2. Mathematical Model**

The charging system of MG involves one coal-gimbal distributor and eight DRI-flap distributors. Reasonable charging processes are completed by various combinations of the two sets of equipment. The coal-gimbal distributor consists of consecutively a coal hopper, a down-comer, and the rotating chute; while a DRI-flap distributor consists of consecutively a vertical pipe, an inclined-pipe, and the angle-adjustable flap.
