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Bottom-Segment Slag Calculations
C H A P T E R
34 Bottom-Segment Slag Calculations O U T L I N E 34.1 Coke Ash Contribution to Blast Furnace Slag
291
34.2 New Variables
292
34.3 Al2O3 in Descending Coke Equation
292
34.4 SiO2 in Descending Coke Equation
293
34.5 Altered Bottom-Segment Al2O3 and SiO2 Mass Balances
293
34.1 COKE ASH CONTRIBUTION TO BLAST FURNACE SLAG
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00034-8
294
34.7 Matrix and Calculations
294
34.8 Results
294
34.9 Summary
294
Exercises
297
The matrix table in this chapter determines how the coke ash SiO2 and Al2O3 affect the amounts of;
Chapter 32, Bottom-Segment Slag Calculations - Ore, Fluxes, and Slag, showed us how to include (1) iron ore’s impurity oxides and (2) flux oxides in our blast furnace calculations. This chapter shows us how to include coke ash oxides, Fig. 34.1. Top-charged coke of Fig. 34.1 contains; • 90 mass% C, • 7 mass% SiO2, and • 3 mass% Al2O3.
34.6 Altered Enthalpy Balance
• C-in-coke and • O2-in-blast that are needed to steadily produce 1500 C molten iron and molten slag with this coke charge. We continue with the specification of Chapter 32, Bottom-Segment Slag Calculations Ore, Fluxes, and Slag, that the blast furnace slag must contain; • 10 mass% Al2O3, • 41 mass% CaO,
291
© 2020 Elsevier Inc. All rights reserved.
292
34. BOTTOM-SEGMENT SLAG CALCULATIONS
mass Al2 O3 in descending coke
and
mass SiO2 in descending coke
These new variables require two additional equations in bottom-segment matrix of Table 32.1, as follows.
34.3 Al2O3 IN DESCENDING COKE EQUATION FIGURE 34.1 Blast furnace top and bottom segments including Al2O3 and SiO2 in top-charged coke.
Matrix Table 32.1 already includes the variable;
• 10 mass% MgO, and • 39 mass% SiO2 for it to be safely molten at 1500 C and useful when the slag solidifies. The objectives of this chapter are to; 1. add coke ash variables and equations to the bottom-segment matrix Table 32.1; 2. calculate the amounts of a. C-in-coke, b. O2-in-blast, and c. Al2O3, CaO, and MgO fluxes that are needed to steadily produce 1500 C molten iron and slag with Al2O3 and SiO2 in the top-charged coke; and 3. calculate the mass of product molten slag including coke’s Al2O3 and SiO2.
with our specified 90 mass% C, 3 mass% Al2O3, and 7 mass% SiO2 coke; this variable is connected to;
mass Al2 O3 in descending coke
by the equation;
mass Al2 O3 in 3 mass% Al2 O3 in descending coke descending coke 5 5 0:0333 mass C in 90 mass% C in descending coke descending coke (34.1)
or
mass Al2 O3 in mass C in 15 0:0333 descending coke descending coke mass Al2 O3 in 1 from both subtracting descending coke
or sides;
mass Al2 O3 in
1 descending coke mass C in 1 0:0333 descending coke
05
34.2 NEW VARIABLES Al2O3-in-coke and SiO2-in-coke introduce two new variables into Table 32.1 matrix. They are:
mass C in descending coke
(34.2)
where the masses are per 1000 kg of Fe in product molten iron.
BLAST FURNACE IRONMAKING
293
34.5 ALTERED BOTTOM-SEGMENT Al2O3 AND SiO2 MASS BALANCES
This equation requires, of course, that there is no C-in-coke oxidation in the blast furnace top segment, as specified in Section 7.12.
34.4 SiO2 IN DESCENDING COKE EQUATION
mass SiO2 in mass C in 15 0:0778 descending coke descending coke mass SiO2 in 1 from both subtracting descending coke
mass SiO2 in mass SiO2 in 5 descending ore molten slag
(32.3)
becomes;
05
(34.4)
where the masses are per 1000 kg of Fe in product molten iron.
(34.6)
Likewise, SiO2 mass balance equation of Chapter 32, Bottom-Segment Slag Calculations—Ore, Fluxes, and Slag;
mass SiO2 in 1 descending coke mass C in 1 0:0778 descending coke
or sides;
mass Al2 O3 in
1 descending flux mass Al2 O3 in 1 descending coke mass Al2 O3 in 1 1 molten slag
052
or
mass Al2 O3 in mass Al2 O3 in 1 descending flux descending coke mass Al2 O3 in (34.5) 5 molten slag mass Al2 O3 in or subtracting descending flux mass Al2 O3 in 1 from both sides; descending coke
The new SiO2 in descending coke equation is developed exactly like the above Al2O3 in descending coke equation. With 7 mass% SiO2 and 90 mass% C in the coke, the basic equation is; mass SiO2 in 7 mass% SiO2 in descending coke descending coke 5 5 0:0778 (34.3) mass C in 90 mass% C in descending coke descending coke
or
mass SiO2 in
1
mass SiO2 in
descending ore descending coke mass SiO2 in 5 (34.7) molten slag mass SiO2 in mass SiO2 in 1 subtracting descending ore descending coke
from both sides
34.5 ALTERED BOTTOM-SEGMENT Al2O3 AND SiO2 MASS BALANCES Descent of Al2O3-in-coke and SiO2-in-coke into the bottom-segment changes both of their mass balances. Al2O3 mass balance equation of Chapter 32, Bottom-Segment Slag Calculations—Ore, Fluxes, and Slag;
mass Al2 O3 in mass Al2 O3 in 5 descending flux molten slag
mass SiO2 in 1 descending ore mass SiO2 in 1 2 descending coke mass SiO2 in 1 1 molten slag
05
(34.8)
This equation specifies that there is no reduction of SiO2 to Si (‘)in molten iron. Chapter 35, Bottom Segment Calculations - Reduction of SiO2, removes this restriction.
becomes;
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34. BOTTOM-SEGMENT SLAG CALCULATIONS
34.6 ALTERED ENTHALPY BALANCE
2. new Al2O3-in-coke and SiO2-in-coke concentration specification equations, 3. altered Al2O3 and SiO2 mass balance equations, and 4. an altered enthalpy balance equation.
This chapter’s two new variables;
mass Al2 O3 in descending coke
34.8 RESULTS
and
mass SiO2 in descending coke
change the bottom-segment enthalpy balance Eq. (32.11) to; 2 320 5 ½mass Fe0:947 O into bottom segment ð3:152Þ ½mass C in descending coke 1:359 ½mass O2 in blast air 1:239 ½mass N2 in blast air 1:339 ½mass Al2 O3 descending in flux ð15:41Þ ½mass Al2 O3 in descending coke ð15:41Þ
Figs. 34.2 and 34.3 show the effect of the mass (Al2O3 1 SiO2)-in-coke on steady-state bottom segment and hence whole furnace C-in-coke and O2-in-blast requirements. Both increase. This is because coke’s SiO2 and Al2O3 in ash must be heated and melted in the bottom segment, requiring more combustion of C-in-coke by O2-in-blast.
½mass CaO descending in flux ð10:50Þ
34.9 SUMMARY
½mass MgO descending in flux ð13:84Þ ½mass SiO2 in descending ore ð14:13Þ ½mass SiO2 in descending coke ð14:13Þ 1 ½mass Fe out in molten iron 1:269 1 ½mass C out in molten iron 5 1 ½mass CO gas out in ascending gas ð2:926Þ 1 ½mass CO2 out in ascending gas ð7:926Þ 1 ½mass N2 out in ascending gas 1:008 1 ½mass Al2 O3 out in molten slag ð13:58Þ
This chapter shows how; • Al2O3-in-coke, and • SiO2-in-coke are included in our blast furnace calculations. Mass% Al2O3-in-coke and mass% SiO2-incoke are specified, and two new variables;
1 ½mass CaO out in molten slag ð8:495Þ 1 ½mass MgO out in molten slag ð11:14Þ 1½mass SiO2 out in molten slag ð13:28Þ (34.9)
mass Al2 O3 in descending coke
and
mass SiO2 in descending coke
are introduced then related to;
34.7 MATRIX AND CALCULATIONS Tables 34.1 and 34.2 are bottom-segment matrix Tables 32.1 and 32.2 plus;
mass Al2 O3 in mass SiO2 in 1. new descending and descending coke coke
variables,
mass C in descending coke
Al2O3, SiO2, and enthalpy balances of matrix Table 32.1 are then altered to include the new variables as shown in Table 34.1. The results show that a blast furnace’s steady-state C-in-coke and O2-in-blast are both
BLAST FURNACE IRONMAKING
TABLE 34.1
Bottom-Segment Matrix of Fig. 34.1
7 mass% SiO2 in 3 mass% Al2 O3 in descending coke descending coke and 0.0333 in Cell E14 is . Remember that 0.0778 in Cell E5 is 90 mass%C in 90 mass% C in descending coke descending coke This is Table 32.1 with two new variables (mass Al2O3 and SiO2 in descending coke) and two new equations (mass Al2O3-in-coke and mass SiO2-in-coke) plus modified Al2O3, SiO2, and enthalpy balances. The calculated results are shown in Table 34.2.
TABLE 34.2
Solution to Matrix of Table 34.1
C-in-coke and O2-in-blast for steady production of molten iron and molten slag, 1500 C, are shown to be 415 kg C-in-coke and 338 kg O2-in-blast; with Al2O3-in-coke and SiO2-in-coke as compared to 408 kg C-in-coke and 326 kg O2-in-blast of Table 32.1; without Al2O3 and SiO2 in coke.
297
EXERCISES
As expected, SiO2-in-coke also increases slag mass. This is the result of the coke’s SiO2 plus the increased amounts of CaO and MgO flux that are required to maintain specified slag composition of Section 32.6. For the values used in this chapter, the coke’s Al2O3 has a negligible effect on blast furnace requirements because it merely lowers the requirement for Al2O3 flux. This can change when the Al2O3 input from ore and coke is very high as experienced in India and China for example. FIGURE 34.2 Effect of mass% (Al2O3 1 SiO2)-in-coke on C-in-coke and O2-in-blast requirement for steady production of molten iron and slag, 1500 C. Both increase. The Al2O3/SiO2 mass ratio in the coke is constant at 3/7. The lines are not straight because an increase in mass% (Al2O3 1 SiO2)-in-coke causes a commensurate decrease in mass% C-in-coke as discussed in caption of Fig. 32.4.
FIGURE 34.3 Slag mass as a function of mass% (Al2O3 1 SiO2) in top-charge coke. The increase is about 8 kg/mass% (Al2O3 1 SiO2)-in-coke. The line is not straight because an increase in mass% (Al2O3 1 SiO2)-in-coke causes a commensurate decrease in mass% C-in-coke (as described in the caption of Fig. 32.4).
increased by Al2O3-in-coke and SiO2-in-coke. This is because the SiO2-in-coke must be heated and melted in the bottom segment, requiring more oxidation of C-in-coke by O2-in-blast.
EXERCISES All masses in this problem set are in kg per 1000 kg of Fe in product molten iron. 34.1. A blast furnace company receives coking coal from a new supplier. The coke product from this new coal contains 5 mass% Al2O3 and 5 mass% SiO2, remainder carbon. What effect will this new coke have on; a. C-in-coke, b. coke, c. O2-in-blast, d. blast, e. Al2O3 flux, f. CaO flux, g. MgO flux, and h. SiO2 flux of Table 34.1 requirements for steady production of; a. 1500 C molten iron: 4.5 mass% C, 95.5 mass% Fe, and b. 1500 C molten slag: 10 mass% Al2O3, 41 mass% CaO, 10 mass% MgO, and 39 mass% SiO2? Also, what mass of slag will be produced by this operation? 34.2. A cement manufacturer wishes to try slag that contains; a. 12 mass% Al2O3, b. 40 mass% CaO,
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34. BOTTOM-SEGMENT SLAG CALCULATIONS
c. 10 mass% MgO, and d. 38 mass% SiO2. Blast furnace team of Table 34.1 wishes to ascertain what flux masses will be necessary to produce this slag while steadily producing
1500 C molten iron, 4.5 mass% C and 95.5 mass% Fe. Please determine these for them. Notice that this slag composition is the same as that in Exercise 32.1.
BLAST FURNACE IRONMAKING
34 Bottom-Segment Slag Calculations O U T L I N E 34.1 Coke Ash Contribution to Blast Furnace Slag
291
34.2 New Variables
292
34.3 Al2O3 in Descending Coke Equation
292
34.4 SiO2 in Descending Coke Equation
293
34.5 Altered Bottom-Segment Al2O3 and SiO2 Mass Balances
293
34.1 COKE ASH CONTRIBUTION TO BLAST FURNACE SLAG
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00034-8
294
34.7 Matrix and Calculations
294
34.8 Results
294
34.9 Summary
294
Exercises
297
The matrix table in this chapter determines how the coke ash SiO2 and Al2O3 affect the amounts of;
Chapter 32, Bottom-Segment Slag Calculations - Ore, Fluxes, and Slag, showed us how to include (1) iron ore’s impurity oxides and (2) flux oxides in our blast furnace calculations. This chapter shows us how to include coke ash oxides, Fig. 34.1. Top-charged coke of Fig. 34.1 contains; • 90 mass% C, • 7 mass% SiO2, and • 3 mass% Al2O3.
34.6 Altered Enthalpy Balance
• C-in-coke and • O2-in-blast that are needed to steadily produce 1500 C molten iron and molten slag with this coke charge. We continue with the specification of Chapter 32, Bottom-Segment Slag Calculations Ore, Fluxes, and Slag, that the blast furnace slag must contain; • 10 mass% Al2O3, • 41 mass% CaO,
291
© 2020 Elsevier Inc. All rights reserved.
292
34. BOTTOM-SEGMENT SLAG CALCULATIONS
mass Al2 O3 in descending coke
and
mass SiO2 in descending coke
These new variables require two additional equations in bottom-segment matrix of Table 32.1, as follows.
34.3 Al2O3 IN DESCENDING COKE EQUATION FIGURE 34.1 Blast furnace top and bottom segments including Al2O3 and SiO2 in top-charged coke.
Matrix Table 32.1 already includes the variable;
• 10 mass% MgO, and • 39 mass% SiO2 for it to be safely molten at 1500 C and useful when the slag solidifies. The objectives of this chapter are to; 1. add coke ash variables and equations to the bottom-segment matrix Table 32.1; 2. calculate the amounts of a. C-in-coke, b. O2-in-blast, and c. Al2O3, CaO, and MgO fluxes that are needed to steadily produce 1500 C molten iron and slag with Al2O3 and SiO2 in the top-charged coke; and 3. calculate the mass of product molten slag including coke’s Al2O3 and SiO2.
with our specified 90 mass% C, 3 mass% Al2O3, and 7 mass% SiO2 coke; this variable is connected to;
mass Al2 O3 in descending coke
by the equation;
mass Al2 O3 in 3 mass% Al2 O3 in descending coke descending coke 5 5 0:0333 mass C in 90 mass% C in descending coke descending coke (34.1)
or
mass Al2 O3 in mass C in 15 0:0333 descending coke descending coke mass Al2 O3 in 1 from both subtracting descending coke
or sides;
mass Al2 O3 in
1 descending coke mass C in 1 0:0333 descending coke
05
34.2 NEW VARIABLES Al2O3-in-coke and SiO2-in-coke introduce two new variables into Table 32.1 matrix. They are:
mass C in descending coke
(34.2)
where the masses are per 1000 kg of Fe in product molten iron.
BLAST FURNACE IRONMAKING
293
34.5 ALTERED BOTTOM-SEGMENT Al2O3 AND SiO2 MASS BALANCES
This equation requires, of course, that there is no C-in-coke oxidation in the blast furnace top segment, as specified in Section 7.12.
34.4 SiO2 IN DESCENDING COKE EQUATION
mass SiO2 in mass C in 15 0:0778 descending coke descending coke mass SiO2 in 1 from both subtracting descending coke
mass SiO2 in mass SiO2 in 5 descending ore molten slag
(32.3)
becomes;
05
(34.4)
where the masses are per 1000 kg of Fe in product molten iron.
(34.6)
Likewise, SiO2 mass balance equation of Chapter 32, Bottom-Segment Slag Calculations—Ore, Fluxes, and Slag;
mass SiO2 in 1 descending coke mass C in 1 0:0778 descending coke
or sides;
mass Al2 O3 in
1 descending flux mass Al2 O3 in 1 descending coke mass Al2 O3 in 1 1 molten slag
052
or
mass Al2 O3 in mass Al2 O3 in 1 descending flux descending coke mass Al2 O3 in (34.5) 5 molten slag mass Al2 O3 in or subtracting descending flux mass Al2 O3 in 1 from both sides; descending coke
The new SiO2 in descending coke equation is developed exactly like the above Al2O3 in descending coke equation. With 7 mass% SiO2 and 90 mass% C in the coke, the basic equation is; mass SiO2 in 7 mass% SiO2 in descending coke descending coke 5 5 0:0778 (34.3) mass C in 90 mass% C in descending coke descending coke
or
mass SiO2 in
1
mass SiO2 in
descending ore descending coke mass SiO2 in 5 (34.7) molten slag mass SiO2 in mass SiO2 in 1 subtracting descending ore descending coke
from both sides
34.5 ALTERED BOTTOM-SEGMENT Al2O3 AND SiO2 MASS BALANCES Descent of Al2O3-in-coke and SiO2-in-coke into the bottom-segment changes both of their mass balances. Al2O3 mass balance equation of Chapter 32, Bottom-Segment Slag Calculations—Ore, Fluxes, and Slag;
mass Al2 O3 in mass Al2 O3 in 5 descending flux molten slag
mass SiO2 in 1 descending ore mass SiO2 in 1 2 descending coke mass SiO2 in 1 1 molten slag
05
(34.8)
This equation specifies that there is no reduction of SiO2 to Si (‘)in molten iron. Chapter 35, Bottom Segment Calculations - Reduction of SiO2, removes this restriction.
becomes;
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34. BOTTOM-SEGMENT SLAG CALCULATIONS
34.6 ALTERED ENTHALPY BALANCE
2. new Al2O3-in-coke and SiO2-in-coke concentration specification equations, 3. altered Al2O3 and SiO2 mass balance equations, and 4. an altered enthalpy balance equation.
This chapter’s two new variables;
mass Al2 O3 in descending coke
34.8 RESULTS
and
mass SiO2 in descending coke
change the bottom-segment enthalpy balance Eq. (32.11) to; 2 320 5 ½mass Fe0:947 O into bottom segment ð3:152Þ ½mass C in descending coke 1:359 ½mass O2 in blast air 1:239 ½mass N2 in blast air 1:339 ½mass Al2 O3 descending in flux ð15:41Þ ½mass Al2 O3 in descending coke ð15:41Þ
Figs. 34.2 and 34.3 show the effect of the mass (Al2O3 1 SiO2)-in-coke on steady-state bottom segment and hence whole furnace C-in-coke and O2-in-blast requirements. Both increase. This is because coke’s SiO2 and Al2O3 in ash must be heated and melted in the bottom segment, requiring more combustion of C-in-coke by O2-in-blast.
½mass CaO descending in flux ð10:50Þ
34.9 SUMMARY
½mass MgO descending in flux ð13:84Þ ½mass SiO2 in descending ore ð14:13Þ ½mass SiO2 in descending coke ð14:13Þ 1 ½mass Fe out in molten iron 1:269 1 ½mass C out in molten iron 5 1 ½mass CO gas out in ascending gas ð2:926Þ 1 ½mass CO2 out in ascending gas ð7:926Þ 1 ½mass N2 out in ascending gas 1:008 1 ½mass Al2 O3 out in molten slag ð13:58Þ
This chapter shows how; • Al2O3-in-coke, and • SiO2-in-coke are included in our blast furnace calculations. Mass% Al2O3-in-coke and mass% SiO2-incoke are specified, and two new variables;
1 ½mass CaO out in molten slag ð8:495Þ 1 ½mass MgO out in molten slag ð11:14Þ 1½mass SiO2 out in molten slag ð13:28Þ (34.9)
mass Al2 O3 in descending coke
and
mass SiO2 in descending coke
are introduced then related to;
34.7 MATRIX AND CALCULATIONS Tables 34.1 and 34.2 are bottom-segment matrix Tables 32.1 and 32.2 plus;
mass Al2 O3 in mass SiO2 in 1. new descending and descending coke coke
variables,
mass C in descending coke
Al2O3, SiO2, and enthalpy balances of matrix Table 32.1 are then altered to include the new variables as shown in Table 34.1. The results show that a blast furnace’s steady-state C-in-coke and O2-in-blast are both
BLAST FURNACE IRONMAKING
TABLE 34.1
Bottom-Segment Matrix of Fig. 34.1
7 mass% SiO2 in 3 mass% Al2 O3 in descending coke descending coke and 0.0333 in Cell E14 is . Remember that 0.0778 in Cell E5 is 90 mass%C in 90 mass% C in descending coke descending coke This is Table 32.1 with two new variables (mass Al2O3 and SiO2 in descending coke) and two new equations (mass Al2O3-in-coke and mass SiO2-in-coke) plus modified Al2O3, SiO2, and enthalpy balances. The calculated results are shown in Table 34.2.
TABLE 34.2
Solution to Matrix of Table 34.1
C-in-coke and O2-in-blast for steady production of molten iron and molten slag, 1500 C, are shown to be 415 kg C-in-coke and 338 kg O2-in-blast; with Al2O3-in-coke and SiO2-in-coke as compared to 408 kg C-in-coke and 326 kg O2-in-blast of Table 32.1; without Al2O3 and SiO2 in coke.
297
EXERCISES
As expected, SiO2-in-coke also increases slag mass. This is the result of the coke’s SiO2 plus the increased amounts of CaO and MgO flux that are required to maintain specified slag composition of Section 32.6. For the values used in this chapter, the coke’s Al2O3 has a negligible effect on blast furnace requirements because it merely lowers the requirement for Al2O3 flux. This can change when the Al2O3 input from ore and coke is very high as experienced in India and China for example. FIGURE 34.2 Effect of mass% (Al2O3 1 SiO2)-in-coke on C-in-coke and O2-in-blast requirement for steady production of molten iron and slag, 1500 C. Both increase. The Al2O3/SiO2 mass ratio in the coke is constant at 3/7. The lines are not straight because an increase in mass% (Al2O3 1 SiO2)-in-coke causes a commensurate decrease in mass% C-in-coke as discussed in caption of Fig. 32.4.
FIGURE 34.3 Slag mass as a function of mass% (Al2O3 1 SiO2) in top-charge coke. The increase is about 8 kg/mass% (Al2O3 1 SiO2)-in-coke. The line is not straight because an increase in mass% (Al2O3 1 SiO2)-in-coke causes a commensurate decrease in mass% C-in-coke (as described in the caption of Fig. 32.4).
increased by Al2O3-in-coke and SiO2-in-coke. This is because the SiO2-in-coke must be heated and melted in the bottom segment, requiring more oxidation of C-in-coke by O2-in-blast.
EXERCISES All masses in this problem set are in kg per 1000 kg of Fe in product molten iron. 34.1. A blast furnace company receives coking coal from a new supplier. The coke product from this new coal contains 5 mass% Al2O3 and 5 mass% SiO2, remainder carbon. What effect will this new coke have on; a. C-in-coke, b. coke, c. O2-in-blast, d. blast, e. Al2O3 flux, f. CaO flux, g. MgO flux, and h. SiO2 flux of Table 34.1 requirements for steady production of; a. 1500 C molten iron: 4.5 mass% C, 95.5 mass% Fe, and b. 1500 C molten slag: 10 mass% Al2O3, 41 mass% CaO, 10 mass% MgO, and 39 mass% SiO2? Also, what mass of slag will be produced by this operation? 34.2. A cement manufacturer wishes to try slag that contains; a. 12 mass% Al2O3, b. 40 mass% CaO,
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34. BOTTOM-SEGMENT SLAG CALCULATIONS
c. 10 mass% MgO, and d. 38 mass% SiO2. Blast furnace team of Table 34.1 wishes to ascertain what flux masses will be necessary to produce this slag while steadily producing
1500 C molten iron, 4.5 mass% C and 95.5 mass% Fe. Please determine these for them. Notice that this slag composition is the same as that in Exercise 32.1.
BLAST FURNACE IRONMAKING