*Article* **Numerical Simulation of the Raceway Zone in Melter Gasifier of COREX Process**

**Ye Sun 1,2,\*, Ren Chen 1,2, Zuoliang Zhang 1,2, Guoxi Wu 1,2, Huishu Zhang 1,2, Lingling Li 1,2, Yan Liu 1,2, Xiaoliang Li 1,2 and Yan Huang 1,2**


Received: 28 September 2019; Accepted: 13 November 2019; Published: 20 November 2019

**Abstract:** The physical and chemical processes in the raceway zone of the COREX melter–gasifier express are similar to those inside the blast furnace. Based on the research achievements on blast furnaces, the unsteady numerical simulation of a gas-solid two-phase in the raceway was carried out by using computational fluid software. The formation process of the raceway in the COREX melter–gasifier was simulated. The shape and size of the raceway were obtained. Then, the effect of gas flow on the depth and height of the raceway was analyzed in this paper.

**Keywords:** COREX; raceway zone; numerical simulation; gas flow

### **1. Introduction**

COREX is the world's first commercially established and industrially proven smelting-reduction process [1,2]. It is a two-stage process that involves pre-reduction in a shaft furnace, followed by final reduction and separation in a melter gasifier [3–5]. The melter gasifier is the key reactor of the COREX process. Lateral injection of high-speed gas into the packed bed in a melter gasifier can cause the formation of granular circulation regions within the bed. These are commonly called 'raceways' due to the distinct shape of the path taken by entrained particles within the bed [6,7]. The raceway plays a critical role in providing energy and reducing agents for the successful and stable operation of the melter gasifier. Exploring the characteristics of the raceway in the COREX melter gasifier is beneficial for the design and optimization of the chemical process.

There are different approaches for the investigation of raceway phenomena in a packed bed. One method is cold model simulation. Two-dimensional or pseudo three-dimensional models were used to study the size of the raceway through photography [8–11]. However, due to the rather intensive particle-fluid interactions and high temperature environment, there are some deviations between the experimental results and the practice dates. The temperature measurement method is also a good way to explore the properties of the raceway zone. However, no matter the direct measurement method or non-contact measurement method, the size and volume of the raceway cannot be accurately obtained [12–14]. To overcome these difficulties in experimental and measurement studies, numerical simulations of the raceway have becomes more and more popular. For example, Sarkar et al. studied the raceway boundary using a continuum two-fluid model [15]. Frank et al. developed a computational fluid dynamics (CFD) model for describing the pressure field, temperature field, gas composition field, and so on [16]. Shen et al. established a series of CFD models to study coal combustion in the raceway zone [17–20]. Recently, a coupled CFD-DEM model was also developed to determine particle and

gas flow in the raceway in a blast furnace [21–23]. All these studies are useful for understanding the characteristics of the raceway in a blast furnace, whereas the difference between a blast furnace and a COREX process makes it impossible for the latter to draw experience directly from the blast furnace. Indeed, the raceway boundary and gas–solid flow behaviours of the raceway in a COREX melter gasifier were investigated by Sun et al. [24,25]. However, under pure oxygen injection in a COREX melter gasifier, the formation process of the raceway needs further research.

In this paper, a CFD model is developed to study the raceway zone in the melter gasifier of the COREX process. The raceway formation process is first discussed, and the influence of the amount of the blowing gas on raceway size is also studied. The findings of this work will be useful for the design, control, and optimization of COREX melter gasifier process operation.
