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Bottom Segment With Oxygen Enrichment of Blast Air
C H A P T E R
9 Bottom Segment With Oxygen Enrichment of Blast Air O U T L I N E 9.1 Benefits of Injecting Pure Oxygen With the Blast Air
93
9.2 Oxygen Injection Calculations 94 9.2.1 Injected Oxygen Quantity 94 9.2.2 Injected O2 in the Oxygen Mass Balance 94 9.2.3 Enthalpy Balance With Injected Pure Oxygen 95
9.1 BENEFITS OF INJECTING PURE OXYGEN WITH THE BLAST AIR Many iron blast furnaces inject purified oxygen into their unheated blast air. The airoxygen mixture is then;
95
9.4 Carbon Requirement
97
9.5 Summary
98
Exercises
98
Oxygen injection lowers the amount of nitrogen that is blown: • through the tuyeres, and • up the furnace shaft. The principle objectives of oxygen injection are to:
• heated to B1200 C, and • blown through the blast furnace tuyeres (Fig. 9.1).
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00009-9
9.3 Calculation Results
1. increase molten iron production without increasing gas flow rate, and
93
© 2020 Elsevier Inc. All rights reserved.
94
9. BOTTOM SEGMENT WITH OXYGEN ENRICHMENT OF BLAST AIR
1. a new oxygen quantity specification, 2. a modified steady-state oxygen balance, and 3. a modified steady-state enthalpy balance.
9.2.1 Injected Oxygen Quantity
FIGURE 9.1 Bottom segment with heated (air 1 oxy-
gen) blast, 1200 C. Pure oxygen is injected into unheated air. The mixture is then heated and blown into the blast furnace through its tuyeres. The drawing is a vertical slice through the center of the cylindrical furnace, Fig. 1.1. Modern blast furnaces inject up to 100 kg of purified oxygen per 1000 kg of Fe in product molten iron.
2. offset the cooling effect of hydrocarbon injectants (Chapter 11: Bottom Segment with CH4(g) Injection) in the furnace bottom segment. Objective (2) is a benefit that results from having to heat less nitrogen. The objectives of this chapter are to: 1. show how oxygen injection is included in our matrix calculations; 2. indicate how oxygen injection affects the upward blast furnace gas flows; 3. calculate steady-state bottom segment, and hence whole furnace, O2-in-blast air requirements with various amounts of injected oxygen; 4. calculate steady-state bottom segment C-incoke requirements with various amounts of injected oxygen; and 5. calculate steady state whole-furnace C-incoke charge requirements with various amounts of injected oxygen.
9.2 OXYGEN INJECTION CALCULATIONS Oxygen injection calculations are like carbon injection calculations. They require:
An example of oxygen quantity specification is:
mass O2 in injected
pure oxygen
5
30 kg per 1000 kg of Fe
in product molten iron
or, in matrix form, " 30 5
mass O2 in injected pure oxygen
# 1
(9.1)
9.2.2 Injected O2 in the Oxygen Mass Balance From Eq. (7.3), the bottom segment oxygen balance including injected oxygen is:
mass O2 in injected
100% O in O2 100% pure oxygen mass Fe0:947 O into 23:2 mass% O in Fe0:947 O 1 100% bottom segment mass O2 in 100% O in O2 1 100% blast air mass CO out 57:1 mass% O in CO 5 100% in ascending gas mass CO2 out 72:7 mass% O in CO2 1 100% in ascending gas
or
mass O2 in injected
11
mass Fe0:947 O into
pure oxygen bottom segment mass CO out mass O2 in 0:232 1 15 in ascending gas blast air mass CO2 out 0:727 0:571 1 in ascending gas
BLAST FURNACE IRONMAKING
9.3 CALCULATION RESULTS
95
2 320 5 1 1 1 1 1
½mass O2 in injected pure oxygen 1:239 ½mass Fe0:947 O into bottom segment ð 23:152Þ ½mass C in descending coke 1:359 ½mass O2 in blast air 1:239 ½mass N2 in blast air 1:339 ½mass Fe out in molten iron 1:269 ½mass C out in molten iron 5 ½mass CO gas out in ascending gas ð 22:926Þ ½mass CO2 out in ascending gas ð 27:926Þ ½mass N2 out in ascending gas 1:008
mass O2 in injected 1 pure oxygen mass Fe0:947 O into mass O2 in 0:232 1 1 1 bottom segment blast air
or subtracting
from both sides: " 05
mass O2 in injected
#
pure oxygen "
0:232
blast air "
0:571 1
mass O2 in
" 12
#
" 11
mass CO2 out in ascending gas
mass Fe0:947 O into
#
bottom segment mass CO out
#
in ascending gas
# 0:727 (9.2)
9.2.3 Enthalpy Balance With Injected Pure Oxygen
The enthalpy values are for the temperatures in Fig. 9.1. Note that the injected oxygen is heated to 1200 C before it enters the furnace. It has the same enthalpy content (per kg) as the O2 in blast air. Eqs. (9.1), (9.2), and (9.4) plus our unchanged bottom segment equations are shown in matrix Table 9.1.
9.3 CALCULATION RESULTS
Including injected O2, the bottom segment enthalpy balance Eq. (7.14) becomes: ½mass O2 in injected pure oxygen 1:239 1 ½mass Fe0:947 O into bottom segment ð 23:152Þ 1 ½mass C in descending coke 1:359 1 ½mass O2 in blast air 1:239 1 ½mass N2 in blast air 1:339 5 ½mass Fe out in molten iron 1:269 1 ½mass C out in molten iron 5 1 ½mass CO out in ascending gas ð 22:926Þ 1 ½mass CO2 out in ascending gas ð 27:926Þ 1 ½mass N2 out in ascending gas 1:008 3 2 320 MJ bottom segment conductive; 1 4convective and radiative heat loss per 5 1000 kg of Fe in product molten iron MWO2 : where 1.239 is H 1200 C O2 g
(9.4)
Fig. 9.2 shows the effect of pure oxygen injection on the, • amount of blast air
(9.3)
Subtracting the left side of Eq. (9.3) and the last term of the right side of Eq. (9.3) from both sides and rearranging:
that is required to produce molten iron, 1500 C. As expected, the blast air requirement decreases appreciably with increasing pure oxygen injection. This decrease in input blast air also markedly decreases N2 flow through the furnace (Fig. 9.3). It is this decrease in N2 flow that enables pure oxygen to; • increase molten iron production rate without • increasing the amount of gas that flows up the blast furnace shaft.
BLAST FURNACE IRONMAKING
TABLE 9.1
Bottom Segment Pure Oxygen Injection Matrix
The new O2 injection quantity specification and altered oxygen balance/enthalpy balance equations are shown. Steady-state reactant and product quantities at other oxygen injection levels are determined by putting various values in cell C12. Try it!
9.4 CARBON REQUIREMENT
FIGURE 9.2
Effect of pure oxygen in blast on blast furnace blast air requirement. The line is straight. The points have been calculated by altering mass O2 in injected oxygen, cell C12. Injected oxygen lowers blast air requirement by 3.9 kg of blast air per kg of injected pure oxygen.
97
FIGURE 9.4 Effect of pure oxygen in blast on steadystate whole-furnace C-in-coke requirement. Whole-furnace C-in-coke requirement increases by about 0.06 kg C per kg of added pure oxygen.
9.4 CARBON REQUIREMENT Fig. 9.4 shows the effect of pure oxygen injection on the whole-furnace C-in-coke requirement. This is the same as matrix Table 9.1’s bottom segment mass C in descending coke requirement (Eq. (7.16)). Carbon requirements in top-charged coke increase slightly with increasing amount of pure oxygen injected. This is the result of all of Table 9.1’s equations. We may speculate, however, that the smaller amount of N2 entering the blast furnace with oxygen injection;
FIGURE 9.3 Effect of pure oxygen injection on the amount of N2 entering the furnace in blast air. All N2 flows up the blast furnace shaft and out in top-gas (i.e., it doesn’t react in the furnace). Adding 1 kg of pure oxygen into the furnace reduces nitrogen flow by B 3 kg, both per 1000 kg of Fe in product molten iron. The line is straight.
1. brings less enthalpy into the bottom segment (per 1000 kg of Fe in product molten iron) which consequently, 2. requires more bottom segment carbon combustion to maintain the 930 C bottom segment exit gas temperature. This is confirmed by an equivalent slight increase in total O2-in-blast requirement (Fig. 9.5).
BLAST FURNACE IRONMAKING
98
9. BOTTOM SEGMENT WITH OXYGEN ENRICHMENT OF BLAST AIR
FIGURE 9.5 Effect of pure oxygen injection on steadystate total O2-in-blast requirement. The total oxygen requirement increases by about 0.1 kg/kg of injected pure oxygen, both per 1000 kg of Fe in product molten iron. The line is straight.
9.5 SUMMARY Purified oxygen is provided to the blast furnace by: 1. injecting pure oxygen into the blast air, 2. heating the airoxygen mixture to about 1200 C in the stove shown in Fig. 1.2, and 3. blowing the heated mixture through all the blast furnace tuyeres. Oxygen injection is readily represented in our blast furnace matrices. It requires a new mass O2 in injected oxygen specification and modified steady-state oxygen and enthalpy balance equations. Pure oxygen addition decreases nitrogen flows up the blast furnace, per 1000 kg of Fe in product molten iron. Purified oxygen injection can, therefore, give faster iron production without increasing the upward gas flow rate.
As Chapter 17, Raceway Flame Temperature with Oxygen Enrichment, shows, pure oxygen enrichment also increases tuyere raceway flame temperature and/or offsets the cooling effects of low enthalpy hydrocarbon tuyere injectants. These are both useful for steady production of 1500 C molten iron. Chapter 8, Bottom Segment with Pulverized Carbon Injection, and this chapter have examined carbon and purified oxygen injection. Our next task is to examine injection of less purified oxygen, 90 mass% O2(g) and 10 mass% N2(g).
EXERCISES 9.1. What are the two (maybe three) advantages of injecting pure oxygen into a blast furnace’s blast air (Fig. 9.1)? 9.2. Are there any costs for this injection? 9.3. Are there any safety issues with handling of large amounts of pure oxygen? 9.4. The Table 9.1 blast furnace operators increased their oxygen injection quantity specification to 65 kg per 1000 of Fe in product molten iron. By how much does this change its C-in-coke requirement and blast air requirement for steady production of 1500 C molten iron. We suggest that you first predict the direction of these changes (increase, decrease) then calculate them. Please express your answers in kg per 1000 kg of Fe in product molten iron. 9.5. Blast furnace management believes that the amount of N2 entering and leaving their blast furnace should be less than 700 kg per 1000 kg of Fe in product molten iron. More N2 than this tends to cause
BLAST FURNACE IRONMAKING
99
EXERCISES
fluidization of the furnace’s top-charged solids. Predict for them the minimum amount of injected pure oxygen (per 1000 kg of Fe in product molten iron) that will be needed to obtain this amount of N2 input/output. 9.6. What effect will blast temperature have on C-in-coke and blast air requirements
for steady-state production of 1500 C molten iron? Predict your answers (qualitatively) then calculate the results with 1150 C blast. Use Appendix J for the required enthalpy equations. Please express your answers in kg per 1000 kg of Fe in product molten iron.
BLAST FURNACE IRONMAKING
9 Bottom Segment With Oxygen Enrichment of Blast Air O U T L I N E 9.1 Benefits of Injecting Pure Oxygen With the Blast Air
93
9.2 Oxygen Injection Calculations 94 9.2.1 Injected Oxygen Quantity 94 9.2.2 Injected O2 in the Oxygen Mass Balance 94 9.2.3 Enthalpy Balance With Injected Pure Oxygen 95
9.1 BENEFITS OF INJECTING PURE OXYGEN WITH THE BLAST AIR Many iron blast furnaces inject purified oxygen into their unheated blast air. The airoxygen mixture is then;
95
9.4 Carbon Requirement
97
9.5 Summary
98
Exercises
98
Oxygen injection lowers the amount of nitrogen that is blown: • through the tuyeres, and • up the furnace shaft. The principle objectives of oxygen injection are to:
• heated to B1200 C, and • blown through the blast furnace tuyeres (Fig. 9.1).
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00009-9
9.3 Calculation Results
1. increase molten iron production without increasing gas flow rate, and
93
© 2020 Elsevier Inc. All rights reserved.
94
9. BOTTOM SEGMENT WITH OXYGEN ENRICHMENT OF BLAST AIR
1. a new oxygen quantity specification, 2. a modified steady-state oxygen balance, and 3. a modified steady-state enthalpy balance.
9.2.1 Injected Oxygen Quantity
FIGURE 9.1 Bottom segment with heated (air 1 oxy-
gen) blast, 1200 C. Pure oxygen is injected into unheated air. The mixture is then heated and blown into the blast furnace through its tuyeres. The drawing is a vertical slice through the center of the cylindrical furnace, Fig. 1.1. Modern blast furnaces inject up to 100 kg of purified oxygen per 1000 kg of Fe in product molten iron.
2. offset the cooling effect of hydrocarbon injectants (Chapter 11: Bottom Segment with CH4(g) Injection) in the furnace bottom segment. Objective (2) is a benefit that results from having to heat less nitrogen. The objectives of this chapter are to: 1. show how oxygen injection is included in our matrix calculations; 2. indicate how oxygen injection affects the upward blast furnace gas flows; 3. calculate steady-state bottom segment, and hence whole furnace, O2-in-blast air requirements with various amounts of injected oxygen; 4. calculate steady-state bottom segment C-incoke requirements with various amounts of injected oxygen; and 5. calculate steady state whole-furnace C-incoke charge requirements with various amounts of injected oxygen.
9.2 OXYGEN INJECTION CALCULATIONS Oxygen injection calculations are like carbon injection calculations. They require:
An example of oxygen quantity specification is:
mass O2 in injected
pure oxygen
5
30 kg per 1000 kg of Fe
in product molten iron
or, in matrix form, " 30 5
mass O2 in injected pure oxygen
# 1
(9.1)
9.2.2 Injected O2 in the Oxygen Mass Balance From Eq. (7.3), the bottom segment oxygen balance including injected oxygen is:
mass O2 in injected
100% O in O2 100% pure oxygen mass Fe0:947 O into 23:2 mass% O in Fe0:947 O 1 100% bottom segment mass O2 in 100% O in O2 1 100% blast air mass CO out 57:1 mass% O in CO 5 100% in ascending gas mass CO2 out 72:7 mass% O in CO2 1 100% in ascending gas
or
mass O2 in injected
11
mass Fe0:947 O into
pure oxygen bottom segment mass CO out mass O2 in 0:232 1 15 in ascending gas blast air mass CO2 out 0:727 0:571 1 in ascending gas
BLAST FURNACE IRONMAKING
9.3 CALCULATION RESULTS
95
2 320 5 1 1 1 1 1
½mass O2 in injected pure oxygen 1:239 ½mass Fe0:947 O into bottom segment ð 23:152Þ ½mass C in descending coke 1:359 ½mass O2 in blast air 1:239 ½mass N2 in blast air 1:339 ½mass Fe out in molten iron 1:269 ½mass C out in molten iron 5 ½mass CO gas out in ascending gas ð 22:926Þ ½mass CO2 out in ascending gas ð 27:926Þ ½mass N2 out in ascending gas 1:008
mass O2 in injected 1 pure oxygen mass Fe0:947 O into mass O2 in 0:232 1 1 1 bottom segment blast air
or subtracting
from both sides: " 05
mass O2 in injected
#
pure oxygen "
0:232
blast air "
0:571 1
mass O2 in
" 12
#
" 11
mass CO2 out in ascending gas
mass Fe0:947 O into
#
bottom segment mass CO out
#
in ascending gas
# 0:727 (9.2)
9.2.3 Enthalpy Balance With Injected Pure Oxygen
The enthalpy values are for the temperatures in Fig. 9.1. Note that the injected oxygen is heated to 1200 C before it enters the furnace. It has the same enthalpy content (per kg) as the O2 in blast air. Eqs. (9.1), (9.2), and (9.4) plus our unchanged bottom segment equations are shown in matrix Table 9.1.
9.3 CALCULATION RESULTS
Including injected O2, the bottom segment enthalpy balance Eq. (7.14) becomes: ½mass O2 in injected pure oxygen 1:239 1 ½mass Fe0:947 O into bottom segment ð 23:152Þ 1 ½mass C in descending coke 1:359 1 ½mass O2 in blast air 1:239 1 ½mass N2 in blast air 1:339 5 ½mass Fe out in molten iron 1:269 1 ½mass C out in molten iron 5 1 ½mass CO out in ascending gas ð 22:926Þ 1 ½mass CO2 out in ascending gas ð 27:926Þ 1 ½mass N2 out in ascending gas 1:008 3 2 320 MJ bottom segment conductive; 1 4convective and radiative heat loss per 5 1000 kg of Fe in product molten iron MWO2 : where 1.239 is H 1200 C O2 g
(9.4)
Fig. 9.2 shows the effect of pure oxygen injection on the, • amount of blast air
(9.3)
Subtracting the left side of Eq. (9.3) and the last term of the right side of Eq. (9.3) from both sides and rearranging:
that is required to produce molten iron, 1500 C. As expected, the blast air requirement decreases appreciably with increasing pure oxygen injection. This decrease in input blast air also markedly decreases N2 flow through the furnace (Fig. 9.3). It is this decrease in N2 flow that enables pure oxygen to; • increase molten iron production rate without • increasing the amount of gas that flows up the blast furnace shaft.
BLAST FURNACE IRONMAKING
TABLE 9.1
Bottom Segment Pure Oxygen Injection Matrix
The new O2 injection quantity specification and altered oxygen balance/enthalpy balance equations are shown. Steady-state reactant and product quantities at other oxygen injection levels are determined by putting various values in cell C12. Try it!
9.4 CARBON REQUIREMENT
FIGURE 9.2
Effect of pure oxygen in blast on blast furnace blast air requirement. The line is straight. The points have been calculated by altering mass O2 in injected oxygen, cell C12. Injected oxygen lowers blast air requirement by 3.9 kg of blast air per kg of injected pure oxygen.
97
FIGURE 9.4 Effect of pure oxygen in blast on steadystate whole-furnace C-in-coke requirement. Whole-furnace C-in-coke requirement increases by about 0.06 kg C per kg of added pure oxygen.
9.4 CARBON REQUIREMENT Fig. 9.4 shows the effect of pure oxygen injection on the whole-furnace C-in-coke requirement. This is the same as matrix Table 9.1’s bottom segment mass C in descending coke requirement (Eq. (7.16)). Carbon requirements in top-charged coke increase slightly with increasing amount of pure oxygen injected. This is the result of all of Table 9.1’s equations. We may speculate, however, that the smaller amount of N2 entering the blast furnace with oxygen injection;
FIGURE 9.3 Effect of pure oxygen injection on the amount of N2 entering the furnace in blast air. All N2 flows up the blast furnace shaft and out in top-gas (i.e., it doesn’t react in the furnace). Adding 1 kg of pure oxygen into the furnace reduces nitrogen flow by B 3 kg, both per 1000 kg of Fe in product molten iron. The line is straight.
1. brings less enthalpy into the bottom segment (per 1000 kg of Fe in product molten iron) which consequently, 2. requires more bottom segment carbon combustion to maintain the 930 C bottom segment exit gas temperature. This is confirmed by an equivalent slight increase in total O2-in-blast requirement (Fig. 9.5).
BLAST FURNACE IRONMAKING
98
9. BOTTOM SEGMENT WITH OXYGEN ENRICHMENT OF BLAST AIR
FIGURE 9.5 Effect of pure oxygen injection on steadystate total O2-in-blast requirement. The total oxygen requirement increases by about 0.1 kg/kg of injected pure oxygen, both per 1000 kg of Fe in product molten iron. The line is straight.
9.5 SUMMARY Purified oxygen is provided to the blast furnace by: 1. injecting pure oxygen into the blast air, 2. heating the airoxygen mixture to about 1200 C in the stove shown in Fig. 1.2, and 3. blowing the heated mixture through all the blast furnace tuyeres. Oxygen injection is readily represented in our blast furnace matrices. It requires a new mass O2 in injected oxygen specification and modified steady-state oxygen and enthalpy balance equations. Pure oxygen addition decreases nitrogen flows up the blast furnace, per 1000 kg of Fe in product molten iron. Purified oxygen injection can, therefore, give faster iron production without increasing the upward gas flow rate.
As Chapter 17, Raceway Flame Temperature with Oxygen Enrichment, shows, pure oxygen enrichment also increases tuyere raceway flame temperature and/or offsets the cooling effects of low enthalpy hydrocarbon tuyere injectants. These are both useful for steady production of 1500 C molten iron. Chapter 8, Bottom Segment with Pulverized Carbon Injection, and this chapter have examined carbon and purified oxygen injection. Our next task is to examine injection of less purified oxygen, 90 mass% O2(g) and 10 mass% N2(g).
EXERCISES 9.1. What are the two (maybe three) advantages of injecting pure oxygen into a blast furnace’s blast air (Fig. 9.1)? 9.2. Are there any costs for this injection? 9.3. Are there any safety issues with handling of large amounts of pure oxygen? 9.4. The Table 9.1 blast furnace operators increased their oxygen injection quantity specification to 65 kg per 1000 of Fe in product molten iron. By how much does this change its C-in-coke requirement and blast air requirement for steady production of 1500 C molten iron. We suggest that you first predict the direction of these changes (increase, decrease) then calculate them. Please express your answers in kg per 1000 kg of Fe in product molten iron. 9.5. Blast furnace management believes that the amount of N2 entering and leaving their blast furnace should be less than 700 kg per 1000 kg of Fe in product molten iron. More N2 than this tends to cause
BLAST FURNACE IRONMAKING
99
EXERCISES
fluidization of the furnace’s top-charged solids. Predict for them the minimum amount of injected pure oxygen (per 1000 kg of Fe in product molten iron) that will be needed to obtain this amount of N2 input/output. 9.6. What effect will blast temperature have on C-in-coke and blast air requirements
for steady-state production of 1500 C molten iron? Predict your answers (qualitatively) then calculate the results with 1150 C blast. Use Appendix J for the required enthalpy equations. Please express your answers in kg per 1000 kg of Fe in product molten iron.
BLAST FURNACE IRONMAKING