# Effect of Furnace Structure on Burden Distribution and Gas Flow in Sinter Vertical Cooling Furnace
## 3 Simulation Conditions  
In this study, a vertical cooling furnace made of Meishan Steel was taken as the research object, along with an existing furnace type that is described in detail in Ref. [21]. To address the serious problem of a \"short circuit\" of gas flow in the furnace, a Venturi furnace type is proposed in this paper. Its typical feature is that the side wall is inclined to the inside first and then to the outside, and the center vent cowl is raised. The two parts correspond to each other, which causes the width of the middle and lower furnace cavity to form a change of \"contraction-vertical-expansion\". The longitudinal sections and related dimensions of the existing furnace type and the Venturi furnace type are shown in Figure 1a,b. A two-dimensional (2-D) slot model with a thickness of 750 mm (five times the maximum particle size) was used to avoid the effect of wall friction on the motion of particles. According to the existing distribution mode, a virtual particle factory was set up in the hopper above the furnace to randomly generate sinter particles with different particle sizes. The vertical cooling furnace cavity was divided into two parts: the fluid domain (area with the purple color) and the coupling domain (area with the cyan color). The particles contained in the fluid domain did not participate in the coupling calculation and were only used to fill the distribution pipe. The coupling domain was used for the gas-solid coupling  
Figure 1: Existing furnace type and Venturi furnace type. (**a**) Model dimension. (**b**) Slot model. (**c**) Computational grid. calculation. The gas outlet was set on the surface of the fluid domain, and the pressure outlet condition was adopted. According to the actual situation on site, the pressure value was \(-200\) Pa. The velocity inlet condition was adopted for the center and edge tuyeres. According to the actual air consumption and tuyere area of the vertical cooling furnace, the velocity of the center and edge tuyeres of the existing furnace was 3 m/s. The area of the Venturi furnace tuyere increased relatively, and the flow velocity at the center and edge tuyere was 2.242 m/s. A symmetry condition was adopted for the symmetry plane. The rest of the wall was set under a wall condition. The computational domain was divided using tetrahedral grids. The gridding of the coupled DEM-CFD method was quite different from the gridding of the pure CFD simulation. Usually, to meet the grid independence of the particle volume fraction calculation within the grid, the grid size should be at least larger than the maximum particle size so that the grid can contain a sufficient number of particles. To balance the grid independence of the particle volume fraction calculation and the accuracy of simulation results, the minimum grid size was 1.5 times the maximum particle size. The specific grid division is shown in Figure 1c. After crushing, the obtained sinter was sent directly to the vertical cooling furnace through the charging burden truck; thus, the particle size range was 0-150 mm. Therefore, the upper limit of particles was set to 150 mm in this study. As for the lower limit of the particle size, the consideration of smaller particles can cause the simulation results to be more accurate, but it will bring a huge increase in the calculation cost. To take into consideration both the simulation results and the calculation ability, the lower limit of the particle size was raised to 10 mm. In the current situation, the ratio of the particle size between the maximum diameter and the minimum diameter can still reach 15:1, which can simulate the filling effect of relatively small particles in a large particle gap, so it is close to the real particle accumulation. The mass fraction of each particle size range was determined according to the actual production situation of a vertical cooling furnace made of Meishan Steel. The sinter particle size in each particle size range was generated randomly.