Evaluation and Improvement of Circumferential Uniformity for Blast Furnace Raceway

Abstract

The bustle pipe model of a running 2500 m³ blast furnace was established. The local and overall uniformity indexes of the raceway were defined and constructed. And then the effects of blast flow rate, the diameter and length of all tuyeres or No. 2 tuyere on the circumferential uniformity of raceway were quantitatively evaluated. It was shown that the circumferential uniformity of raceway decreased with the increasing blast flow rate, and when the blast flow rate increased from 4300 m³/min to 4700 m³/min, the circumferential uniformity index of raceway decreased from 0.1715 to 0.0760. The diameter of tuyere had a significant effect on the circumferential uniformity, while the length of tuyere showed little influence. The circumferential uniformity of raceway could be improved by increasing the diameter of all tuyeres or No. 2 tuyere with the minimum blast kinetic energy. When the diameter of all tuyeres increased to 140 mm, the overall uniformity index of raceway increased to 0.207, but the blast kinetic energy was only about 64 kJ/s which couldn’t meet the smelting. requirement. While the diameter of No. 2 tuyere near the hot blast main increased to 126 mm, the overall uniformity of the raceway increased to 0.124, and the blast kinetic energy was 120.11 kJ/s which was still within the reasonable range. it was feasible to improve the circumferential uniformity of raceway by adjusting the diameter of one or some off-average tuyeres but not all.

1. Introduction

The raceway was the important reaction zone of blast furnace (BF), which directly affected the distribution of gas flow, the heat and mass transfer, the production indexes and cost.^1,2,3,4,5) The circumferential unevenness of raceway would lead to the inconsistency of circumferential hearth activity, resulting in the deterioration of burden descent, the bad smelting environment, the decrease of pig iron quality, and the damage of BF service life.^6,7,8,9,10) Therefore, the research on the circumferential uniformity of raceway had attracted much attention in recent years.^{11,12,13,14,15,16,17,18)}

Bugaev et al found that the blast temperature difference among all the tuyeres was 150–250°C and the maximum adiabatic combustion temperature difference of raceway was corresponding to 508°C (1772–2280°C), when the blast flow rate difference along circumferential direction was115–300 m³/min.⁷⁾ Lyalyuk et al studied a running 5000 m³ BF and indicated that the blast flow rate, theoretical flame temperature, bosh gas rate, and blast kinetic energy along the circumferential direction of the tuyeres had similar changing trends, and they all showed great inhomogeneity. Among them, the blast flow rate in front of No. 34 and No. 35 tuyere is 162 m³/min and 249 m³/min respectively, and its difference reaches 87 m³/min.⁸⁾ V. G. Druzhkov et al.’s work showed that the geometry of tuyere was one of the reasons for the uneven distribution of hot blast flow rate, and this uneven distribution was improved by modifying the hot blast duct.¹¹⁾ Mei Yaguang et al. applied numerical simulation to study the influences of tuyere parameter adjustments on the homogeneity of the raceway in three BFs with different volume, and found that the non-uniformity of blast flow rate was much obvious when the volume of BF was relatively large.¹⁴⁾

A large number of studies had proved that the circumferential uniformity of raceway played an important role in blast furnace production.^{19,20,21,22,23,24)} However, the circumferential uniformity was usually evaluated by investigating the distribution of each relative parameter along the circumferential direction, and no effective characterization and quantitative evaluation methods of the circumferential uniformity of raceway had been proposed. Considering the important influence of the blast kinetic energy on the shape of the raceway and the distribution of gas flow, the blast kinetic energy was normalized by the principle of statistics, and the circumdirectional uniformity index of the tuyere raceway was put forward in this work, which can be used to quantitatively evaluate the uniformity of raceway. Meanwhile, the hot bustle pipe model of a running 2500 m³ BF in China was established to investigate the influences of the blast flow rate, the diameter and length of all tuyere and No. 2 tuyere on the circumferential uniformity of raceway. And the uniformity of raceway was quantitatively evaluated and the adjustment measures for the good circumferential uniformity were finally obtained.

2. Experimental

2.1. Hot Bustle Pipe Model

According to the design parameters of a running 2500 m³ BF, shown in Table 1, the 3D model of BF hot bustle pipe model was established, including hot blast main hot blast bustle pipe, and 30 tuyeres, as shown in Fig. 1. The hot blast was treated as the isothermal incompressible fluid and described by three-dimensional Reynolds average Navier-Stokes equations. The pressure-velocity coupling was described by Simple algorithm. When the calculation residual was lower than 10⁻³, the calculation was considered to be convergent.

Table 1. Related parameters and dimensions of bustle pipe.

Volume of BF /m3	Number of tuyere /-	Diameter of main /mm	Diameter of bustle pipe /mm	Diameter of tuyere /mm	Length of tuyere /mm
2500	30	2700	2700	120	300

Fig. 1.

3D model of bustle pipe model for a running 2500 m³ BF. (Online version in color.)

2.2. Calculation of Raceway Shape and Properties

In this work, the relevant calculation formulas of raceway shape and properties were given as Eqs. (1), (2), (3), (4), (5), (6). Where, x_O2 is the oxygen enrichment, %; f is the blast humidity, g/m³; O₂ is the oxygen flow rate, m³/h; n is the number of tuyere, -; V_b is the dry blast flow rate, m³/min; t_b is the blast temperature, K; E is the blast kinetic energy, kJ/s; D_R is the depth of raceway, m; W_R is the width of raceway, m; H_R is the height of raceway, m; V_R is the volume of raceway, m³; p_f is the penetration factor, -; D_T is the diameter of tuyere, m; ρ₀—is the density of bosh gas, kg/m³; ρ_s is the real density of coke, kg/m³; V_g is the volume flow rate of nest, m³/min; T_r is the adiabatic combustion temperature, K; P_b is the pressure of blast, kPa; D_C is the diameter of coke in tuyere, m; S_T is the area of tuyere, m².   

$$\begin{array}{l}E=\frac{1}{2}\times \frac{\frac{[4\times (0.21+x_{O_2})+28]+\frac{f}{1\mathrm{\hspace{0.17em} }000}}{22.4}}{g}\\ \hspace{1em}\times {\left(\frac{V_b+\frac{O_2}{60}}{60}\right)}^3\times {\left(1+\frac{22.4\times f}{18\mathrm{\hspace{0.17em} }000}\right)}^2\\ \hspace{1em}\times {\left(\frac{1\mathrm{\hspace{0.17em} }033}{1\mathrm{\hspace{0.17em} }033+P_b}\right)}^2\times {\left(\frac{t_b}{273}\right)}^2\times \frac{1}{n^3\times {\left(\frac{\pi }{4}\times D_T{}^2\right)}^2}\end{array}$$(1)

  

$$D_R=0.409\times p_f{}^{0.693}\times D_T$$(2)

  

$$W_R=2.631\times {\left(\frac{D_R}{D_T}\right)}^{0.331}\times D_T$$(3)

  

$$\frac{4H_R{}^2+D_R{}^2}{H_R\times D_T}=8.78\times {\left(\frac{D_R}{D_T}\right)}^{0.721}$$(4)

  

$$V_R=0.53\times D_R\times W_R\times H_R$$(5)

  

$$p_f=\frac{{\rho }_0}{{\rho }_s\times D_C\times {10}^{-3}}{\left(\frac{60\times V_g}{S_T}\right)}^2\frac{T_r}{P_b\times 298}$$(6)

2.3. Definition of Local Uniformity Index and Overall Uniformity Index

This work is proceeded on a running 2500 m³ BF with 30 tuyeres. Due to the difference of the position of each tuyere from hot blast main, the blasting performance varied greatly. In order to describe the circumferential uniformity for raceway, the local uniformity index named U_i and the overall uniformity index named U were proposed according to the principle of statistical normalization, given as Eqs. (7) and (8). Where, E_i is the blast kinetic energy at the i th tuyere, kJ/s; E is the average blast kinetic energy, kJ/s; n is the number of tuyere, -.   

$$U_i=\{\begin{array}{c}1;\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\overline{E}-0.01<E_i<\overline{E}+0.01\\ \frac{0.01}{\sqrt{{(E_i-\overline{E})}^2}};\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\mathrm{\hspace{0.17em} }\text{other}\end{array}$$(7)

  

$$U=\frac{0.01}{\sqrt{\frac{1}{n}}{\sum }_{i=1}^n{(E_i-\overline{E})}^2}$$(8)

The local uniformity index named U_i ranged from 0 to 1. If the value was close to 1, it was indicated that the uniformity had the small deviation from the average at this tuyere. Meanwhile, if the overall uniformity index is large, the circumferential uniformity showed good. Based above, the evaluation system for the circumferential uniformity of raceway was established.

2.4. Boundary Condition of Simulation

During the simulation, the blast system showed good insulation, the hot blast was treated as the isothermal incompressible turbulence and its temperature was constant while flowing, the standard K -ε two-equation model was used, the wall surface was set as a non-sliding wall surface, the flow near the wall surface was treated by wall function, and the exit boundary was treated by pressure condition. Meanwhile, the blast temperature, blast humidity, oxygen enrichment and coal pulverized coal injection ratio remained unchanged at 1450 K, 0.44 g/m³, 4.35% and 149 kg/t, respectively. The influences of the blast flow rate, the changes of all tuyeres’ parameters, the changes of No. 1 tuyere’s parameters on the circumferential uniformity of raceway were investigated in this work. The blast flow rate varied from 4300 to 4700 m³/min, the diameter of tuyere varied from 100 to 120 mm, and the length of tuyere varied from 200 to 400 mm. The base of these parameters was the value of the present running 2500 m³ BF, which was 4500 m³/min, 120 mm, and 300 mm, respectively.

3. Results and Discussions

3.1. Flow Field Analysis of Hot Bustle Pipe

The velocity distribution in front of No. 1–30 tuyere under the base condition was shown in Fig. 2. The velocity at the front of each tuyere showed a trend of symmetrical distribution along the center line of the hot blast main. As the distance between hot blast main and hot bustle pipe increased, the blast velocity reduced firstly and then increased, and it was symmetrical along the center line of the blast main. The velocity in front of No. 16 tuyere that far from hot blast main is the largest of 222.38 m/s, while it in front of No. 2 tuyere that near the hot blast main is the smallest of 220.0 m/s.

Fig. 2.

Radar diagram of the velocity distribution in front of each tuyere under base condition.

The distributions of velocity streamline (a) and pressure (b) in hot bustle pipe were shown in Fig. 3. At the junction of the hot blast main and hot bustle pipe, the hot blast velocity streamline dispersed outward with first loose and then dense tendency, and tended to be stable at the position far from hot blast main, after entering the branch pipe, and the velocity increased due to the decreasing diameter of branch pipe. Correspondingly, the pressure of hot blast gradually decreased and tended to be stable with the hot blast diffusing, after entering the branch pipe, the pressure increased greatly under the reduction of pipe diameter.

Fig. 3.

Distributions of velocity streamline (a) and pressure (b) in hot bustle pipe. (Online version in color.)

3.2. Effect of Blast Flow Rate on the Circumferential Uniformity of Raceway

The radar diagram of the raceway properties under different blast flow rates was shown as Fig. 4. With the increase of blast flow rate, the concerned parameters increased continuously. Meanwhile, the influence of changing blast flow rate on the blast kinetic energy, the depth and volume of raceway was greater than that on the linear velocity. When the blast flow rate increased from 4300 m³/min to 4700 m³/min, the maximum difference of blast kinetic energy increased from 2.418 kJ/s to 4.968 kJ/s correspondingly.

Fig. 4.

Radar diagram of the raceway properties under different blast flow rates. (Online version in color.)

Based on the calculation results of the blast kinetic energy, the circumferential local uniformity index and overall uniformity index were analyzed and shown in Figs. 5 and 6 respectively. The local uniformity index was symmetrical along the center line of the blast main and had the maximum values at No. 8 and No. 23 tuyere, which meant that the kinetic energy at those tuyere were cloest to the average value. As the blast flow increased, the value of peaks on the local uniformity curves increased. The overall uniformity index decreased with the increasing blast flow rate, which was 0.1715, 0.1484, 01090, 0.0953 and 0.0760, respectively. Due to the increasing blast volume, the turbulence effects in the hot bustle pipe and branch pipe was intensified, the rubbing action between the pipe wall and hot blast was enhanced, and the drag losses of the hot blast increased, therefore, the overall uniformity of blast furnace raceway would be destroyed.

Fig. 5.

Circumferential local uniformity of raceway under different blast flow rates. (Online version in color.)

Fig. 6.

Circumferential overall uniformity of raceway under different blast flow rates. (Online version in color.)

3.3. Effect of Changing All Tuyeres’ Parameters on the Circumferential Uniformity of Raceway

3.3.1. Effect of Changing All Tuyeres’ Diameter

The changes of the raceway properties under different diameter of all tuyeres were given as Fig. 7. With the increasing diameter of all tuyeres, the velocity of hot blast in front of tuyere, the blast kinetic energy, the depth and volume of raceway gradually decreased, and the decrease of each parameter was much obvious. The raceway properties under different diameter were similair and showed the symmetrical distribution along the center line of the hot blast main. It could be attributed to the pressure loss caused by changing the diameter of all tuyeres were equally alloted to each tuyere. When the diameter of tuyere was 100 mm, the maximum kinetic energy difference was 7.351 kJ/s, while the diameter of tuyere was 140 mm, the kinetic energy difference was only 1.738 kJ/s. The reason for this phenomenon was that as the tuyere increased, the pressure loss in blast pipes were reduced, which had an important effect on the raceway properties.

Fig. 7.

Changes of the raceway properties under different diameter of all tuyeres. (Online version in color.)

The circumferential local uniformity of raceway under different diameter of all tuyeres was given in Fig. 8. The local uniformity index of raceway was symmetrically distributed along the center line of hot blast main, and the large local uniformity indexs distributed around No. 8 and No. 23. As the diameters of tuyeres increased, the local uniformity index curves rose and the indexes at No. 8 and No. 23 had an obvious increasing. The circumferential overall uniformity of raceway under different diameter of all tuyeres was shown as Fig. 9. When the diameter tuyere increased from 100 mm, 110 mm, 120 mm, 130 mm to 140 mm, the overall uniformity index of raceway was 0.0445, 0.0749, 0.109, 0.154, and 0.207, respectively, and the circumferential overall uniformity was significantly improved. As the increase of all tuyeres’ diameter, the drag losses of the hot blast in the pipes was reduced and would weaken the rubbing interactions between the pipes wall and hot blast. Then the steady flowing of the hot blast was improved. All of these would result in the increasing overall uniformity of raceway. However, the blast kinetic energy decreased dramatically when the diameter of all tuyeres increased. When the diameter was 140 mm, it was shown a remarkable drop in blast kinetic energy from about 256 kJ/s to 64 kJ/s which couldn’t meet the reasonable requirement of BF production.

Fig. 8.

Circumferential local uniformity of raceway under different diameter of all tuyeres. (Online version in color.)

Fig. 9.

Circumferential overall uniformity of raceway under different diameter of all tuyeres. (Online version in color.)

3.3.2. Effect of Changing All Tuyeres’ Length

The changes of the raceway properties under different length of all tuyeres were shown as Fig. 10. With the increasing length of all tuyeres, the velocity of hot blast in front of tuyere decreased slightly, and the phenomenon was more distinct at the No. 2, No. 15, No. 16 and No. 29 tuyeres. Under the experimental conditions, the velocity of hot blast was between 220 m/s and 223 m/s. Compared with changing the diameter of all tuyere, changing the length of all tuyere had less effect on the velocity of hot blast. The variation trend of kinetic energy was consistent with that of velocity. As the length of all tuyeres increased, the blast kinetic energy decreased slightly. When the length of tuyere was 200 mm and 400 mm, the maximum difference of the blast kinetic energy was 3.129 kJ/s and 3.634 kJ/s, respectively.

Fig. 10.

Changes of the raceway properties under different length of all tuyeres. (Online version in color.)

The circumferential local uniformity and overall uniformity of raceway under different length of all tuyeres was shown as Figs. 11 and 12, repectively. As the increase of length of all tuyeres, the local uniformity indexes at No. 8 and No. 23 increased, and the circumferential uniformity of raceway decreased slightly. When the length increased from 200 mm to 400 mm, its uniformity was 0.1229, 0.1161, 0.1090, 0.1025 and 0.0944 separately.

Fig. 11.

Circumferential local uniformity of raceway under different length of all tuyeres. (Online version in color.)

Fig. 12.

Circumferential overall uniformity of raceway under different length of all tuyeres. (Online version in color.)

3.4. Effect of Changing No. 2 Tuyere’s Parameters on the Circumferential Uniformity of Raceway

According to the above study, it was indicated that the blast kinetic energy was greatly affected by changing the parameters of all tuyeres, which brought the bad influences of BF smelting. Especially, as the diameter of all tuyeres increased, it had a sharp decrease in the blast kinetic energy. Moreover, the blast speed at No. 2 and No. 29 tuyeres were relatively small and the minimum values appeared at No. 2. It means that the parameters of these two tuyeres had an significant effects on the uniformity of raceway. The circumferential uniformity for blast furnace raceway could be improved by increasing the blast kinetic energy of the two tuyeres especially the No. 2 tuyere. Therefore, the effect of changing No. 2 tuyere parameters on the circumferential uniformity of raceway was investigated and discussed.

3.4.1. Effect of Changing No. 2 Tuyere’s Diameter

The changes of the raceway properties under different diameter of No. 2 tuyere were shown as Fig. 13. With the diameter of No. 2 tuyere increasing, the blast velocity of No. 2 tuyere decreased distinctly, and the blast kinetic energy increased gradually. This phenomenon could be explained by two main reasons. Firstly, the area of No. 2 tuyere was enlarged and the blast velocity decreased. Secondly, as the diameter of No. 2 tuyere increased, the drag of hot blast in the pipe decreased, the volume of hot blast increased, and the blast kinetic energy increased. In fact, changing the single tuyere such as No. 2 tuyere had little effects on the other tuyeres, and both the velocities and blast kinetic energy of other tuyeres decreased a little. When the diameter of No. 2 tuyere was 114 mm and 126 mm, the velocity of hot blast, the blast kinetic energy, the depth and volume of raceway were 225.00 m/s and 214.46 m/s, 116.45 kJ/s and 120.11 kJ/s, 1.663 m and 1.688 m, 0.707 m³ and 0.684 m³, respectively.

Fig. 13.

Changes of the raceway properties under different diameter of No. 2 tuyere. (Online version in color.)

The circumferential local uniformity and overall uniformity of raceway under different diameter of No. 2 tuyere was shown as Figs. 14 and 15, respectively. With the increase of No. 2 tuyere diameter, the local uniformity index of No. 2, No. 8 and No. 23 raised obviously, and the overall uniformity was also improved. It was mainly because that the increase degree of the blast kinetic energy at No. 2 tuyere was evident and gradually tend to the equal value leading to the good uniformity of raceway. When the diameter of No. 2 tuyere gradually increased from 114 mm to 126 mm, the overall uniformity index of was 0.0723, 0.0932, 0.109, 0.119 and 0.124. Therefore, changing the diameter of No. 2 tuyere was benefit to enhance the uniformity, but the improvement was limited. In practice, the circumferential uniformity of raceway could be advanced by adjusting the diameters of some special and off-average tuyeres, such as the No. 29 tuyere near the blast main with low blast speed, the No. 15 and No. 16 tuyeres far from the blast main with high blast speed.

Fig. 14.

Circumferential local uniformity of raceway under different diameter of No. 2 tuyere. (Online version in color.)

Fig. 15.

Circumferential overall uniformity of raceway under different diameter of No. 2 tuyere. (Online version in color.)

3.4.2. Effect of Changing No. 2 Tuyere’s Length

The changes of the raceway properties under different length of No. 2 tuyere was shown in Fig. 16. When the length of No. 2 tuyere increased gradually, the concerned parameters of raceway changed little, and the circumferential distributions of all parameters were still symmetrical with the center line of hot blast main. The raceway properties of No. 2 tuyere showed a slight reduced trend with the increasing of No. 2 tuyere length. The circumferential local and overall uniformity of raceway under different length of No. 2 tuyere was seen in Figs. 17 and 18. With the length of No. 2 tuyere increasing, the circumferential local uniformity of the raceway fluctuated greatly, and the overall uniformity index increased from 0.1154, 0.1141, 0.1090, 0.1045, and 0.1027 sligtly. In general, changing the length of No. 2 tuyere near the hot blast main had little effect on the circumferential uniformity of raceway.

Fig. 16.

Changes of the raceway properties under different length of No. 2 tuyere. (Online version in color.)

Fig. 17.

Circumferential local uniformity of raceway under different length of No. 2 tuyere. (Online version in color.)

Fig. 18.

Circumferential local uniformity of raceway under different length of No. 2 tuyere. (Online version in color.)

4. Conclusion

(1) The velocity of hot blast in front of the tuyere was generally distributed symmetrically along the center line of the hot blast main, and the velocity at the far end of the hot blast main was large, while that at the near end was small. The increase of blast flow rate would lead to the decrease of circumferential uniformity of raceway. When the blast flow rate was 4700 m³/min, the circumferential overall uniformity index of raceway was only 0.0760, which was lower than 0.1715 when the blast flow rate was 4300 m³/min.

(2) The circumferential uniformity of raceway was improved by changing the diameter of all tuyeres, but the blast kinetic energy decreased gradually. When the diameter of all tuyere was 140 mm, the circumferential overall uniformity index of raceway was 0.207, which was obviously better than 0.0445 when the diameter was 100 mm, however, the blast kinetic energy was only about 64 kJ/s which couldn’t meet the requirement of BF smelting. On the other hand, changing the length of all tuyeres had little effect on the uniformity circumferential of raceway.

(3) With the diameter of No. 2 tuyere increasing, the blast velocity of No. 2 tuyere decreased distinctly and the blast kinetic energy increased gradually. Changing the single tuyere such as No. 2 tuyere had little effects on the other tuyeres. When the diameter of No. 2 tuyere increased from 114 mm to 126 mm, the overall uniformity of the raceway increased from 0.0723 to 0.124, and the blast kinetic energy increased from 116.45 kJ/s to 120.11 kJ/s. In addition, changing the length of No. 2 tuyere near the hot blast main had little effect on the circumferential uniformity of raceway.

(4) The diameter of tuyere had the most significant effect on the circumferential uniformity of raceway. Increasing the diameter of all tuyere or the tuyere near the hot blast main could enhance the circumferential uniformity to different degrees. In practice, it was feasible to improve the circumferential uniformity of raceway by adjusting the diameter of one or some off-average tuyeres but not all.

Acknowledgments

The authors are especially grateful to the National Natural Science Foundation of China (Grant No. 51904063), the Fundamental Research Funds for the Central Universities (N2025023), the Plan of Xingliao Talents (XLYC1902118), and 111 Project (B16009).

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