**3.4 Temperature distribution across length for different coal percentages**

Microwave heating depends upon coal percentage in samples, as shown in **Figure 7**. The maximum peak temperatures of the slab for different coal percentages of 6.5%, 7.5%, and 8.5% are 736°C, 743°C, and 753°C, respectively. Coal, a carbonaceous material, absorbs microwave energy, resulting in an increase in temperature.

*Simulation Study of Microwave Heating of Hematite and Coal Mixture DOI: http://dx.doi.org/10.5772/intechopen.106312*

#### **Figure 6.**

*Temperature distribution in the hematite slab of dimensions, 0.01 m* � *0.01 m (a), 0.05 m* � *0.05 m (b), and 0.1 m* � *0.1 m (c) for a constant heating period of 60 s and power of 1 MW/m*<sup>2</sup> *.*

#### **Figure 7.**

*Temperature distribution in the hematite slab of dimensions, 0.15 m* � *0.15 m and coal percentage (a), 6.5 (b), 7.5, and (c) 8.5 for a constant heating period of 180 s and power of 1 MW/m<sup>2</sup> .*

Xu et al. [24] reported that coal could enhance permeability, loss factor, and dielectric constant of mixture samples and ensure the optimal heating effect. Dp (depth of penetration) of microwave heating is directly proportional to ffiffiffiffi ε00 ε0 q , The loss tangent is defined as tanδ = <sup>ε</sup><sup>0</sup> <sup>ε</sup>00. The attenuation constant, *<sup>α</sup>* <sup>¼</sup> <sup>2</sup><sup>π</sup> *λ* ε0 2 ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi <sup>1</sup> <sup>þ</sup> ð Þ tan<sup>δ</sup> <sup>2</sup> q � 1 � � � � <sup>1</sup>*=*<sup>2</sup> represents the rate of absorption of the wave into the sample. Finally, the output of penetration depth is achieved by Dp = <sup>1</sup> <sup>2</sup>*<sup>α</sup>* , so the depth of penetration is inversely related to the attenuation. So, it means that coal increases the loss factor and the dielectric constant of the samples increases. For that, penetration depth of the samples, will be enhanced which also respond to temperature increases. The temperature peak (**Figure 7**) is seen at similar locations in all three samples because the Dp expression accounts for the loss factor and permeability also. During microwave heating, for lean iron ore (Fe – 58%, Si – 42%, NMDC, Hyderabad) beneficial (Fe2O3 to Fe3O4) purposes, coal percentage should be limited (7.5%) when coal composition is as per **Table 2**. Otherwise, the temperature will increase, and a non-magnetic phase (FeO) will be produced. Because above 800°C temperature, formation of FeO and Fe is dominant due to the high rate of carbon gasification. Therefore, more than 7.5% carbon is not a desirable carbon percentage for the reduction study in the microwave furnace for such type of lean iron ores

**Figure 8.** *Variations of temperature with blowing time-varying carbon 6.5%, 7.5%, and 8.5%, respectively.*

#### **3.5 Verification with experimental results**

Temperature variations of the samples for 6.5, 7.5, and 8.5 coal is shown in **Figure 8**. Our model predictions are consistent with experimental results, which found temperature increases from 791°C to 821°C when coal content in the samples increases from 6.5% to 8.5%.

#### **3.6 Sample preparation**

Received iron ore is pulverized in a ball mill for 30 min with 10 mm diameter steel balls. The milled powder is further sieved to below 100 μm (-100 mesh size). The composition of iron ore samples is (65 % Fe2O3 and 35% SiO2). The proximate analysis result of coal is given below in **Table 1**. 100 grams of iron ore and the stoichiometric amount of reducing agent like 7.5 gram coal are entirely mixed. Then, using this mixture, pellets are made with dimensions of 15 mm 15 mm by pressing the machine (5 T pressing m/c, VB Ceramic). The pressing condition is 2-ton load and dwells time, 2 min. Each pellet weighs about 6 gms. Three samples were made by changing carbon percentages to 6.5, 7.5, and 8.5.

#### **3.7 Microwave treatment**

A power (1 MW) and 2.45 GHz hybrid microwave oven (VB Ceramic, Chennai, India) was used for microwave heating. Samples were placed in the oven in a microwave in an alumina crucible. The crucible was located in the central position of the microwave chamber to minimize the effect of the field pattern variations in the oven. Then heating is performed at 800°C for 3 minutes.
