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Raceway Flame Temperature With Moisture in Blast Air
C H A P T E R
19 Raceway Flame Temperature With Moisture in Blast Air O U T L I N E 19.1 Moisture in the Blast Air and Its Impact on RAFT
19.9 Raceway Nitrogen Balance Equation
180
185
19.2 Modifying the Bottom Segment and Raceway Matrices 180
19.10 Raceway Matrix Results and Flame Temperature Calculation
185
19.3 Raceway H2O(g) Input Quantity Specification
182
19.11 Raceway Input Enthalpy Calculation
185
19.4 Raceway O2-in-Blast Air Input Specification
19.12 Raceway Output Enthalpy
186
182
19.5 Raceway Input N2-in-Blast Air Specification
19.13 Raceway Output Gas (Flame) Temperature
187
182
19.14 Calculation Results
187
19.6 Modified Raceway Carbon Balance Equation
184
19.15 Discussion
187
19.16 Summary
188
Exercises
189
19.7 Modified Raceway Oxygen Balance Equation
184
19.8 Modified Raceway Hydrogen Balance Equation
184
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00019-1
179
© 2020 Elsevier Inc. All rights reserved.
180
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
19.1 MOISTURE IN THE BLAST AIR AND ITS IMPACT ON RAFT Chapter 18, Raceway Flame Temperature With CH4(g) Tuyere Injection, calculated raceway flame temperature with tuyere-injected CH4(g). This chapter calculates the raceway adiabatic flame temperature (RAFT) with through-tuyere H2O(g) input, Fig. 19.1. Our objectives are to; 1. show how H2O(g) injection is included in our raceway flame temperature calculations, 2. indicate how H2O(g) injection affects raceway flame temperature, and 3. explain this flame temperature effect. Note that; 1. the H2O(g) enters the blast furnace and raceway at blast temperature, and 2. the H2O(g) enters blast furnace raceways in humid blast air plus injected steam, Chapter 12, Bottom Segment With Moisture in Blast Air.
19.2 MODIFYING THE BOTTOM SEGMENT AND RACEWAY MATRICES Our flame temperature calculation begins with matrix bottom-segment input and output masses of Table 12.1 (copied here as Table 19.1). It then prepares a tuyere raceway matrix from these results by; 1. specifying that all of H2O(g), O2, and N2-inblast air of matrix Table 12.1 enter the Fig. 19.1 raceway, and 2. preparing new raceway hydrogen and oxygen mass balances. It then determines; 3. all raceway’s input and output masses including mass input H2O(g); 4. the raceway input and output enthalpies from these masses and the raceway input temperatures; and
FIGURE 19.1 Sketch of blast furnace raceway with through-tuyere 1200 C H2O(g) input in humid air and steam. All H2O(g) enters the blast furnace through its raceways. In three dimensions, the raceway is a horizontal pear shape. It is full of gas and hurtling coke particles. This sketch is a vertical slice through the center of a raceway. The calculations in this chapter specify that the through-tuyere blast contains 15 g H2O(g)/Nm3 of dry air (Eq. 12.2).
BLAST FURNACE IRONMAKING
TABLE 19.1
Bottom-Segment Matrix With Through-Tuyere Input H2O(g).
It is a copy of Table 12.1. Row 14 describes the amount of H2O(g) entering the raceways with 15 g of H2O(g)/Nm3 of dry air in blast (Eq. 12.2). All mass is per 1000 kg of Fe in product molten iron.
182
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
5. the raceway output gas (flame) temperature from the raceway’s output enthalpy and output masses. The calculations are shown in Table 19.2. They are explained in Sections 19.319.13.
H2O(g), Cell C29. This is also the amount of O2 entering a furnace’s raceways in blast. This oxygen input value is included in our raceway matrix by means of the O2 specification;
mass O2 entering
raceway in blast 5 302 kg=1000 kg of Fe in product molten iron ðCell C20Þ
19.3 RACEWAY H2O(g) INPUT QUANTITY SPECIFICATION The raceway’s H2O(g) input mass specification is represented in Row 14 of the spreadsheet in Table 19.2. It is;
mass through-tuyere mass H2 O g 15 1 input H2 O g entering raceway
or in matrix form; 302 5
mass O2 entering raceway in blast
mass H2 O g entering raceway
1
(19.2)
Of course, this numerical value will change with different concentrations of H2O(g)-inblast. This is automatically taken care of by inserting the instruction;
or in the present case; "
5 C20
#
into raceway matrix Cell C33.
1
5 15 kg through-tuyere input H2 O; Cell C29
19.5 RACEWAY INPUT N2-INBLAST AIR SPECIFICATION
or in matrix form;
mass H2 O g 1 15 5 entering raceway
(19.1)
as shown in Row 39, all masses per 1000 kg of Fe in product molten iron. The numerical value is put into the raceway matrix by typing the instruction 5 C29 into raceway Cell C39. Note that it is for an H2O(g) in blast concentration of 15 g of H2O (g)/Nm3 of dry air.
Blast furnace steady-state N2 input varies with the amount of injected H2O(g). This affects the amount of N2-in-blast entering the raceway, hence raceway flame temperature. In this case, it is;
mass N2 entering
raceway in blast 5 995 kg=1000 kg of Fe in product molten iron ðCell C21Þ
or in matrix terms;
19.4 RACEWAY O2-IN-BLAST AIR INPUT SPECIFICATION Bottom-segment matrix results of Table 19.2 show that 302 kg of O2 in blast, Cell C20 is required for steady production of 1500 C molten iron with 15 kg of through-tuyere input
995 5
mass N2 entering 1 raceway in blast
(19.3)
The nitrogen input is automatically inserted into raceway Cell C34 by the instruction;
BLAST FURNACE IRONMAKING
5 C21
TABLE 19.2
Bottom-Segment and Raceway Matrices/Equations With Through-Tuyere Input H2O(g)
Cell C33 5 C20; Cell C34 5 C21; and Cell C39 5 C29. The blast contains 15 g of H2O(g)/Nm3 of dry air. The flame temperature under these conditions is shown to be 2290 C.
184
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
19.6 MODIFIED RACEWAY CARBON BALANCE EQUATION
or "
" mass C in falling
#
100 mass% C
#
in solid carbon 100% coke particles mass CO in raceway ½42:9 mass% C in CO 5 100% output gas
subtracting
1
mass O2 entering 1g raceway in blast " 052
mass C in falling mass CO in raceway 15 0:429 coke particles output gas
or subtracting
mass C in falling 1 coke particles
mass C in falling
2
from both
1
mass O2 entering
1
1
mass H2 O g 0:888 entering raceways
from both sides;
mass H2 O g
#
entering raceways mass O2 entering
0:888
1 raceway in blast mass CO in raceway
sides; 052
0:888 1
or
or
#
raceway in blast entering raceways mass CO in raceway 5 0:571 output gas
With H2O(g) injection, there is no C in the injectant so that the carbon balance reverts to; "
mass H2 O g
output gas
0:571
(19.4)
as shown in Row 36.
coke particles mass CO in raceway 1 0:429 output gas
(14.10)
19.8 MODIFIED RACEWAY HYDROGEN BALANCE EQUATION
as shown in Row 35.
19.7 MODIFIED RACEWAY OXYGEN BALANCE EQUATION
With through-tuyere input H2O(g), the raceway hydrogen balance becomes mass H entering raceway in H2 O g 5 mass H leaving raceway in H2 g
With H2O(g) input through the blast furnace tuyeres, the raceway oxygen balance becomes; mass O entering in injected H2 O 1 mass O entering in blast air 5 mass O leaving in CO
It expands to; " "
With inputs and outputs of Fig. 19.1, this equation expands to; "
mass H2 O g entering raceways 1
#
88:8 mass%
mass O2 entering
11:2 mass% H
#
in injected H2 O 100% 100 mass% H mass H2 in raceway in ascending H2 5 100% output gas
or
O in O2 100% raceway in blast mass CO in raceway ½57:1 mass% O in CO 5 100% output gas
#
entering raceway
O in H2 O 100% 100 mass%
mass H2 O g
mass H2 in raceway mass H2 O g 0:112 5 1 output gas entering raceway mass H2 O g 0:112 or subtracting from entering raceway
both sides;
BLAST FURNACE IRONMAKING
185
19.11 RACEWAY INPUT ENTHALPY CALCULATION
" 052 1
mass H2 O g
#
entering raceways mass H2 in raceway output gas
2
3 " # raceway mass H2 O g 6 7 4 input 5 5 entering raceway enthalpy
0:112 1
(19.5)
2
as shown in Row 37.
6 14
mass O2 entering raceway in blast
2
19.9 RACEWAY NITROGEN BALANCE EQUATION
6 14
mass N2 entering raceway in blast
The raceway nitrogen balance remains the same as in all the previous flame temperature calculation chapters. It is; 052 1
mass N2 entering
1 1
mass C in
1200 C H2 O g MWH2 O
H 1200 C O2 g 7 5 MWO2 3
H 1200 C N2 g 7 5 MWN2 3
H 1500 C
3
6 7 1 4 falling coke 5 particles
raceway in blast air mass N2 in raceway output gas
2
H
CðsÞ MWC
or (14.9)
as shown in Row 38.
2
3 " # raceway mass H2 O g 6 7 ð2 10:81Þ 4 input 5 5 entering raceway enthalpy 2 3 mass O2 entering 6 7 raceway in 14 5 1:239 blast 3 mass N2 entering 6 7 14 raceway in 5 1:339 2
19.10 RACEWAY MATRIX RESULTS AND FLAME TEMPERATURE CALCULATION
2
3
6 7 1 4 falling coke 5 2:488 particles
Our raceway matrix determines all raceway’s input and output masses, Cells C43C49. We are now ready to calculate; • raceway input enthalpy, • raceway output enthalpy, and • raceway output gas (flame) temperature
blast mass C in
(19.6)
where from Table J.1;
as described in the next three sections.
19.11 RACEWAY INPUT ENTHALPY CALCULATION With 1200 C H2O(g) injection, our raceway’s input enthalpy is;
BLAST FURNACE IRONMAKING
H 1200 C H2 O g 10:81 5 MWH2 O H 1200 C O2 g 1:239 5 MWO2 H 1200 C N2 g 1:339 5 MWN2
186
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
and
H 1500 C 2:488 5
H T blast N2 g Cell G13 5 MWN2
CðsÞ MWC
all MJ per kg of substance. Numerically, the input enthalpy is; 2
3
raceway 6 7 4 input 5 5 15 ð10:81Þ 1 302 1:239 enthalpy 1 995 1:339 1 237 2:488 5 2130MJ=1000kg of
The 5 and right-hand side of Eq. (19.7c) are inserted into Cell G52, which calculates input enthalpy as a function of mass throughtuyere input H2O(g), Cell C29, and blast temperature, Cell E15.
Fe in product molten iron (19.7a)
19.12 RACEWAY OUTPUT ENTHALPY
where 15, 302, 995, and 237 are from Cells C49, C43, C44, and C45 of Table 19.2. Another form of this equation is; 2
raceway
3
Raceway output enthalpy is needed to calculate raceway output gas (flame) temperature. As described in Chapter 14, Raceway Flame 1 C44 1:339 1 C45 2:488 5 2130MJ=1000kg of Temperature, it is calculated by the adiabatic Fe in product molten iron equation;
6 7 4 input 5 5 C49 ð10:81Þ 1 C43 1:239 enthalpy
(19.7b)
and including blast temperature-dependent cells; 2
3 raceway 6 7 4 input 5 5 C49 O13 1 C43 F13 1 C44 G13 enthalpy 1 C45 2:488 5 2130MJ=1000kg of Fe in product molten iron (19.7c)
where:
with zero conductive, convective, and radiative heat loss from the raceway to its surroundings. From Section 19.11, the raceway input enthalpy is 2130 MJ/kg of Fe in product molten iron so that;
H T blast H2 O g Cell O13 5 MWH2 O
H T blast O2 g Cell F13 5 MWO2
2 3 raceway raceway output 1 zero 5 4 input 5 ðflameÞ enthalpy enthalpy
3 raceway 6 7 5 4 input 5 ðflameÞ enthalpy enthalpy raceway output
2
5 2130MJ=1000kg of Fe in product molten iron (19.8)
Matrix Table 19.2 does this calculation with the instruction; 5 G52
in Cell G53.
BLAST FURNACE IRONMAKING
187
19.15 DISCUSSION
19.13 RACEWAY OUTPUT GAS (FLAME) TEMPERATURE Our raceway flame temperature calculations use spreadsheet Table 19.2’s; 1. raceway CO, N2, and H2 output masses, 552, 995, and 1.7 kg from Cells C46C48, and 2. raceway output gas (flame) enthalpy, 2130 MJ from Cell G53 all per 1000 kg of Fe in product molten iron. Flame temperature equation of Section 18.13, that is; (
2
raceway
6 4
3
2
mass CO in
3
7 6 7 output 5 2 4 raceway 5 ð 24:183Þ ðflameÞ enthalpy output gas mass N2 in raceway ð 20:2448Þ 2 output gas ) mass H2 in raceway ð2 4:130Þ 2 output gas (" # 5 Tflame ; C mass CO in raceway 0:001310 output gas " # mass N2 in raceway 1 0:001301 output gas " # ) mass H2 in raceway 1 0:01756 output gas (18.9)
is used. The numerical values are from the raceway output gas’s enthalpy versus flame temperature equations, Table J.4. They are; H
Tflame CO g 5 0:001310 Tflame 4:183 MJ=kg of COðgÞ MWCO H Tflame N2 g 5 0:001301 Tflame 0:2448 MJ=kg of N2 MWN2
and H Tflame H2 g 5 0:01756 Tflame 4:130 MJ=kg of H2 ðgÞ MWH2
For the numerical example in Table 19.2, the raceway flame temperature is; 2130 2 552 2 4:183 2 995 2 0:2448 2 1:7 2 4:130 552 0:001310 1 995 0:001301 1 1:7 0:01756 5 Tflame 5 2290 C (19.9)
In cell terms, this is; G53 2 C46 2 4:183 2 C47 2 0:2448 2 C48 2 4:130 C46 0:001310 1 C47 0:001301 1 C48 0:01756 5 Tflame 5 2290 C (19.10a)
For automatic calculation, we insert; 5
G532C46 24:183 2C47 20:24482C48 24:130 C46 0:0013101C47 0:0013011C48 0:01756 (19.10b)
in Cell G55.
19.14 CALCULATION RESULTS Table 19.2 shows that flame temperature of Fig. 19.1 with 15 g of H2O(g)/Nm3 of dry air blast is 2290 C.
19.15 DISCUSSION Fig. 19.2 plots the above calculated raceway flame temperature point and others and shows that raceway flame temperature decreases with increasing H2O(g) in blast. This is a consequence of all equations of matrix Table 19.2. We may speculate that it is mainly due to the input large negative enthalpy of H2O(g) which lowers the enthalpy and hence temperature of the raceway output gas Fig. 19.3 shows
BLAST FURNACE IRONMAKING
188
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
and carbon is required to satisfy the enthalpy balance of Table 19.2.
19.16 SUMMARY
FIGURE 19.2 Steady-state raceway flame temperature with through-tuyere input H2O(g). It has been plotted by varying the values in Cells F14 and G14 of Table 19.2 (as described in Appendix O) and plotting Cell C49’s H2O (g) input quantity versus Cell G55’s raceway flame temperature. As expected, flame temperature decreases with increasing through-tuyere H2O(g) input. Each additional kg of H2O(g) lowers the flame temperature by B5.5 C, but the line isn’t exactly straight.
All iron blast furnace blast air contains H2O(g), Fig. 19.1. Moisture promotes smooth burden descent and rapid furnace start-ups. It also lowers the raceway flame temperature and hence Si content in product molten iron. The H2O(g)-in-blast is made up of the H2O (g) in humid blast air topped up with steam to obtain a prescribed H2O(g) concentration of about 15 g of H2O(g)/Nm3 of dry air. This moist blast enters the furnace through its tuyeres and into the tuyere raceways. There: 1. the O2-in-blast reacts with falling coke particles to produce CO2(g) plus heat, 2. the resulting CO2(g) reacts further with the falling C-in-coke to produce CO(g), and 3. the input H2O(g)-in-blast reacts with the C-in-coke to produce H2(g). The resulting CO(g) and H2(g) then leave the raceway and begin the blast furnace iron oxide reduction process. Raceway flame temperature is the temperature at which CO(g) and H2(g) plus N2(g) from the blast air leave the raceway. It is readily determined by our:
FIGURE 19.3 Graph showing that the mass of hot nitrogen rising into the top segment increases with increasing H2O(g) concentration in blast. Our expectation is that this increase in hot nitrogen will result in hotter top gas, Figs. 28.2 and 28.3. All masses are kg/1000 kg of Fe in product molten iron.
that increasing H2O(g) concentration in the blast increases the mass of N2 rising into the top segment. This is because more blast air
1. raceway matrix, 2. input enthalpy and output (flame) enthalpy calculations, and 3. output gas (flame) temperature calculation. H2O(g) is readily included in these calculations, in much the same way as described for injected CH4(g), Chapter 18, Raceway Flame Temperature With CH4(g) Tuyere Injection. Raceway flame temperature decreases with increasing H2O(g) concentration in blast,
BLAST FURNACE IRONMAKING
EXERCISES
Figs. 19.2. This is the result of all our equations, but we speculate that it is mainly due to the large negative enthalpy of the input H2O (g) which lowers; 1. the enthalpy of the raceway inputs; 2. the enthalpy of the raceway outputs; and 3. the temperature of the outputs (i.e., the flame temperature).
EXERCISES 19.1. To smooth their blast furnace’s operation, blast furnace operators of Table 19.2 plan
189
to increase the H2O(g) concentration in their blast to 25 g of H2O(g)/Nm3 of dry air in blast by injecting steam. Please predict for them the change in raceway flame temperature that will result from this change. 19.2. Blast of Exercise 19.1 contains 25 g of H2O (g)/Nm3 of dry air in blast. Its humid air portion contains 9 g of H2O(g)/Nm3 of dry air. How much steam must be added to make the furnace’s 25 g H2O/Nm3 blast? Please express you answer in; 1. g=Nm3 of dry air, 2. kg=kg of dry air, and 3. kg=1000 kg of product molten iron.
BLAST FURNACE IRONMAKING
19 Raceway Flame Temperature With Moisture in Blast Air O U T L I N E 19.1 Moisture in the Blast Air and Its Impact on RAFT
19.9 Raceway Nitrogen Balance Equation
180
185
19.2 Modifying the Bottom Segment and Raceway Matrices 180
19.10 Raceway Matrix Results and Flame Temperature Calculation
185
19.3 Raceway H2O(g) Input Quantity Specification
182
19.11 Raceway Input Enthalpy Calculation
185
19.4 Raceway O2-in-Blast Air Input Specification
19.12 Raceway Output Enthalpy
186
182
19.5 Raceway Input N2-in-Blast Air Specification
19.13 Raceway Output Gas (Flame) Temperature
187
182
19.14 Calculation Results
187
19.6 Modified Raceway Carbon Balance Equation
184
19.15 Discussion
187
19.16 Summary
188
Exercises
189
19.7 Modified Raceway Oxygen Balance Equation
184
19.8 Modified Raceway Hydrogen Balance Equation
184
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00019-1
179
© 2020 Elsevier Inc. All rights reserved.
180
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
19.1 MOISTURE IN THE BLAST AIR AND ITS IMPACT ON RAFT Chapter 18, Raceway Flame Temperature With CH4(g) Tuyere Injection, calculated raceway flame temperature with tuyere-injected CH4(g). This chapter calculates the raceway adiabatic flame temperature (RAFT) with through-tuyere H2O(g) input, Fig. 19.1. Our objectives are to; 1. show how H2O(g) injection is included in our raceway flame temperature calculations, 2. indicate how H2O(g) injection affects raceway flame temperature, and 3. explain this flame temperature effect. Note that; 1. the H2O(g) enters the blast furnace and raceway at blast temperature, and 2. the H2O(g) enters blast furnace raceways in humid blast air plus injected steam, Chapter 12, Bottom Segment With Moisture in Blast Air.
19.2 MODIFYING THE BOTTOM SEGMENT AND RACEWAY MATRICES Our flame temperature calculation begins with matrix bottom-segment input and output masses of Table 12.1 (copied here as Table 19.1). It then prepares a tuyere raceway matrix from these results by; 1. specifying that all of H2O(g), O2, and N2-inblast air of matrix Table 12.1 enter the Fig. 19.1 raceway, and 2. preparing new raceway hydrogen and oxygen mass balances. It then determines; 3. all raceway’s input and output masses including mass input H2O(g); 4. the raceway input and output enthalpies from these masses and the raceway input temperatures; and
FIGURE 19.1 Sketch of blast furnace raceway with through-tuyere 1200 C H2O(g) input in humid air and steam. All H2O(g) enters the blast furnace through its raceways. In three dimensions, the raceway is a horizontal pear shape. It is full of gas and hurtling coke particles. This sketch is a vertical slice through the center of a raceway. The calculations in this chapter specify that the through-tuyere blast contains 15 g H2O(g)/Nm3 of dry air (Eq. 12.2).
BLAST FURNACE IRONMAKING
TABLE 19.1
Bottom-Segment Matrix With Through-Tuyere Input H2O(g).
It is a copy of Table 12.1. Row 14 describes the amount of H2O(g) entering the raceways with 15 g of H2O(g)/Nm3 of dry air in blast (Eq. 12.2). All mass is per 1000 kg of Fe in product molten iron.
182
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
5. the raceway output gas (flame) temperature from the raceway’s output enthalpy and output masses. The calculations are shown in Table 19.2. They are explained in Sections 19.319.13.
H2O(g), Cell C29. This is also the amount of O2 entering a furnace’s raceways in blast. This oxygen input value is included in our raceway matrix by means of the O2 specification;
mass O2 entering
raceway in blast 5 302 kg=1000 kg of Fe in product molten iron ðCell C20Þ
19.3 RACEWAY H2O(g) INPUT QUANTITY SPECIFICATION The raceway’s H2O(g) input mass specification is represented in Row 14 of the spreadsheet in Table 19.2. It is;
mass through-tuyere mass H2 O g 15 1 input H2 O g entering raceway
or in matrix form; 302 5
mass O2 entering raceway in blast
mass H2 O g entering raceway
1
(19.2)
Of course, this numerical value will change with different concentrations of H2O(g)-inblast. This is automatically taken care of by inserting the instruction;
or in the present case; "
5 C20
#
into raceway matrix Cell C33.
1
5 15 kg through-tuyere input H2 O; Cell C29
19.5 RACEWAY INPUT N2-INBLAST AIR SPECIFICATION
or in matrix form;
mass H2 O g 1 15 5 entering raceway
(19.1)
as shown in Row 39, all masses per 1000 kg of Fe in product molten iron. The numerical value is put into the raceway matrix by typing the instruction 5 C29 into raceway Cell C39. Note that it is for an H2O(g) in blast concentration of 15 g of H2O (g)/Nm3 of dry air.
Blast furnace steady-state N2 input varies with the amount of injected H2O(g). This affects the amount of N2-in-blast entering the raceway, hence raceway flame temperature. In this case, it is;
mass N2 entering
raceway in blast 5 995 kg=1000 kg of Fe in product molten iron ðCell C21Þ
or in matrix terms;
19.4 RACEWAY O2-IN-BLAST AIR INPUT SPECIFICATION Bottom-segment matrix results of Table 19.2 show that 302 kg of O2 in blast, Cell C20 is required for steady production of 1500 C molten iron with 15 kg of through-tuyere input
995 5
mass N2 entering 1 raceway in blast
(19.3)
The nitrogen input is automatically inserted into raceway Cell C34 by the instruction;
BLAST FURNACE IRONMAKING
5 C21
TABLE 19.2
Bottom-Segment and Raceway Matrices/Equations With Through-Tuyere Input H2O(g)
Cell C33 5 C20; Cell C34 5 C21; and Cell C39 5 C29. The blast contains 15 g of H2O(g)/Nm3 of dry air. The flame temperature under these conditions is shown to be 2290 C.
184
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
19.6 MODIFIED RACEWAY CARBON BALANCE EQUATION
or "
" mass C in falling
#
100 mass% C
#
in solid carbon 100% coke particles mass CO in raceway ½42:9 mass% C in CO 5 100% output gas
subtracting
1
mass O2 entering 1g raceway in blast " 052
mass C in falling mass CO in raceway 15 0:429 coke particles output gas
or subtracting
mass C in falling 1 coke particles
mass C in falling
2
from both
1
mass O2 entering
1
1
mass H2 O g 0:888 entering raceways
from both sides;
mass H2 O g
#
entering raceways mass O2 entering
0:888
1 raceway in blast mass CO in raceway
sides; 052
0:888 1
or
or
#
raceway in blast entering raceways mass CO in raceway 5 0:571 output gas
With H2O(g) injection, there is no C in the injectant so that the carbon balance reverts to; "
mass H2 O g
output gas
0:571
(19.4)
as shown in Row 36.
coke particles mass CO in raceway 1 0:429 output gas
(14.10)
19.8 MODIFIED RACEWAY HYDROGEN BALANCE EQUATION
as shown in Row 35.
19.7 MODIFIED RACEWAY OXYGEN BALANCE EQUATION
With through-tuyere input H2O(g), the raceway hydrogen balance becomes mass H entering raceway in H2 O g 5 mass H leaving raceway in H2 g
With H2O(g) input through the blast furnace tuyeres, the raceway oxygen balance becomes; mass O entering in injected H2 O 1 mass O entering in blast air 5 mass O leaving in CO
It expands to; " "
With inputs and outputs of Fig. 19.1, this equation expands to; "
mass H2 O g entering raceways 1
#
88:8 mass%
mass O2 entering
11:2 mass% H
#
in injected H2 O 100% 100 mass% H mass H2 in raceway in ascending H2 5 100% output gas
or
O in O2 100% raceway in blast mass CO in raceway ½57:1 mass% O in CO 5 100% output gas
#
entering raceway
O in H2 O 100% 100 mass%
mass H2 O g
mass H2 in raceway mass H2 O g 0:112 5 1 output gas entering raceway mass H2 O g 0:112 or subtracting from entering raceway
both sides;
BLAST FURNACE IRONMAKING
185
19.11 RACEWAY INPUT ENTHALPY CALCULATION
" 052 1
mass H2 O g
#
entering raceways mass H2 in raceway output gas
2
3 " # raceway mass H2 O g 6 7 4 input 5 5 entering raceway enthalpy
0:112 1
(19.5)
2
as shown in Row 37.
6 14
mass O2 entering raceway in blast
2
19.9 RACEWAY NITROGEN BALANCE EQUATION
6 14
mass N2 entering raceway in blast
The raceway nitrogen balance remains the same as in all the previous flame temperature calculation chapters. It is; 052 1
mass N2 entering
1 1
mass C in
1200 C H2 O g MWH2 O
H 1200 C O2 g 7 5 MWO2 3
H 1200 C N2 g 7 5 MWN2 3
H 1500 C
3
6 7 1 4 falling coke 5 particles
raceway in blast air mass N2 in raceway output gas
2
H
CðsÞ MWC
or (14.9)
as shown in Row 38.
2
3 " # raceway mass H2 O g 6 7 ð2 10:81Þ 4 input 5 5 entering raceway enthalpy 2 3 mass O2 entering 6 7 raceway in 14 5 1:239 blast 3 mass N2 entering 6 7 14 raceway in 5 1:339 2
19.10 RACEWAY MATRIX RESULTS AND FLAME TEMPERATURE CALCULATION
2
3
6 7 1 4 falling coke 5 2:488 particles
Our raceway matrix determines all raceway’s input and output masses, Cells C43C49. We are now ready to calculate; • raceway input enthalpy, • raceway output enthalpy, and • raceway output gas (flame) temperature
blast mass C in
(19.6)
where from Table J.1;
as described in the next three sections.
19.11 RACEWAY INPUT ENTHALPY CALCULATION With 1200 C H2O(g) injection, our raceway’s input enthalpy is;
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H 1200 C H2 O g 10:81 5 MWH2 O H 1200 C O2 g 1:239 5 MWO2 H 1200 C N2 g 1:339 5 MWN2
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19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
and
H 1500 C 2:488 5
H T blast N2 g Cell G13 5 MWN2
CðsÞ MWC
all MJ per kg of substance. Numerically, the input enthalpy is; 2
3
raceway 6 7 4 input 5 5 15 ð10:81Þ 1 302 1:239 enthalpy 1 995 1:339 1 237 2:488 5 2130MJ=1000kg of
The 5 and right-hand side of Eq. (19.7c) are inserted into Cell G52, which calculates input enthalpy as a function of mass throughtuyere input H2O(g), Cell C29, and blast temperature, Cell E15.
Fe in product molten iron (19.7a)
19.12 RACEWAY OUTPUT ENTHALPY
where 15, 302, 995, and 237 are from Cells C49, C43, C44, and C45 of Table 19.2. Another form of this equation is; 2
raceway
3
Raceway output enthalpy is needed to calculate raceway output gas (flame) temperature. As described in Chapter 14, Raceway Flame 1 C44 1:339 1 C45 2:488 5 2130MJ=1000kg of Temperature, it is calculated by the adiabatic Fe in product molten iron equation;
6 7 4 input 5 5 C49 ð10:81Þ 1 C43 1:239 enthalpy
(19.7b)
and including blast temperature-dependent cells; 2
3 raceway 6 7 4 input 5 5 C49 O13 1 C43 F13 1 C44 G13 enthalpy 1 C45 2:488 5 2130MJ=1000kg of Fe in product molten iron (19.7c)
where:
with zero conductive, convective, and radiative heat loss from the raceway to its surroundings. From Section 19.11, the raceway input enthalpy is 2130 MJ/kg of Fe in product molten iron so that;
H T blast H2 O g Cell O13 5 MWH2 O
H T blast O2 g Cell F13 5 MWO2
2 3 raceway raceway output 1 zero 5 4 input 5 ðflameÞ enthalpy enthalpy
3 raceway 6 7 5 4 input 5 ðflameÞ enthalpy enthalpy raceway output
2
5 2130MJ=1000kg of Fe in product molten iron (19.8)
Matrix Table 19.2 does this calculation with the instruction; 5 G52
in Cell G53.
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19.15 DISCUSSION
19.13 RACEWAY OUTPUT GAS (FLAME) TEMPERATURE Our raceway flame temperature calculations use spreadsheet Table 19.2’s; 1. raceway CO, N2, and H2 output masses, 552, 995, and 1.7 kg from Cells C46C48, and 2. raceway output gas (flame) enthalpy, 2130 MJ from Cell G53 all per 1000 kg of Fe in product molten iron. Flame temperature equation of Section 18.13, that is; (
2
raceway
6 4
3
2
mass CO in
3
7 6 7 output 5 2 4 raceway 5 ð 24:183Þ ðflameÞ enthalpy output gas mass N2 in raceway ð 20:2448Þ 2 output gas ) mass H2 in raceway ð2 4:130Þ 2 output gas (" # 5 Tflame ; C mass CO in raceway 0:001310 output gas " # mass N2 in raceway 1 0:001301 output gas " # ) mass H2 in raceway 1 0:01756 output gas (18.9)
is used. The numerical values are from the raceway output gas’s enthalpy versus flame temperature equations, Table J.4. They are; H
Tflame CO g 5 0:001310 Tflame 4:183 MJ=kg of COðgÞ MWCO H Tflame N2 g 5 0:001301 Tflame 0:2448 MJ=kg of N2 MWN2
and H Tflame H2 g 5 0:01756 Tflame 4:130 MJ=kg of H2 ðgÞ MWH2
For the numerical example in Table 19.2, the raceway flame temperature is; 2130 2 552 2 4:183 2 995 2 0:2448 2 1:7 2 4:130 552 0:001310 1 995 0:001301 1 1:7 0:01756 5 Tflame 5 2290 C (19.9)
In cell terms, this is; G53 2 C46 2 4:183 2 C47 2 0:2448 2 C48 2 4:130 C46 0:001310 1 C47 0:001301 1 C48 0:01756 5 Tflame 5 2290 C (19.10a)
For automatic calculation, we insert; 5
G532C46 24:183 2C47 20:24482C48 24:130 C46 0:0013101C47 0:0013011C48 0:01756 (19.10b)
in Cell G55.
19.14 CALCULATION RESULTS Table 19.2 shows that flame temperature of Fig. 19.1 with 15 g of H2O(g)/Nm3 of dry air blast is 2290 C.
19.15 DISCUSSION Fig. 19.2 plots the above calculated raceway flame temperature point and others and shows that raceway flame temperature decreases with increasing H2O(g) in blast. This is a consequence of all equations of matrix Table 19.2. We may speculate that it is mainly due to the input large negative enthalpy of H2O(g) which lowers the enthalpy and hence temperature of the raceway output gas Fig. 19.3 shows
BLAST FURNACE IRONMAKING
188
19. RACEWAY FLAME TEMPERATURE WITH MOISTURE IN BLAST AIR
and carbon is required to satisfy the enthalpy balance of Table 19.2.
19.16 SUMMARY
FIGURE 19.2 Steady-state raceway flame temperature with through-tuyere input H2O(g). It has been plotted by varying the values in Cells F14 and G14 of Table 19.2 (as described in Appendix O) and plotting Cell C49’s H2O (g) input quantity versus Cell G55’s raceway flame temperature. As expected, flame temperature decreases with increasing through-tuyere H2O(g) input. Each additional kg of H2O(g) lowers the flame temperature by B5.5 C, but the line isn’t exactly straight.
All iron blast furnace blast air contains H2O(g), Fig. 19.1. Moisture promotes smooth burden descent and rapid furnace start-ups. It also lowers the raceway flame temperature and hence Si content in product molten iron. The H2O(g)-in-blast is made up of the H2O (g) in humid blast air topped up with steam to obtain a prescribed H2O(g) concentration of about 15 g of H2O(g)/Nm3 of dry air. This moist blast enters the furnace through its tuyeres and into the tuyere raceways. There: 1. the O2-in-blast reacts with falling coke particles to produce CO2(g) plus heat, 2. the resulting CO2(g) reacts further with the falling C-in-coke to produce CO(g), and 3. the input H2O(g)-in-blast reacts with the C-in-coke to produce H2(g). The resulting CO(g) and H2(g) then leave the raceway and begin the blast furnace iron oxide reduction process. Raceway flame temperature is the temperature at which CO(g) and H2(g) plus N2(g) from the blast air leave the raceway. It is readily determined by our:
FIGURE 19.3 Graph showing that the mass of hot nitrogen rising into the top segment increases with increasing H2O(g) concentration in blast. Our expectation is that this increase in hot nitrogen will result in hotter top gas, Figs. 28.2 and 28.3. All masses are kg/1000 kg of Fe in product molten iron.
that increasing H2O(g) concentration in the blast increases the mass of N2 rising into the top segment. This is because more blast air
1. raceway matrix, 2. input enthalpy and output (flame) enthalpy calculations, and 3. output gas (flame) temperature calculation. H2O(g) is readily included in these calculations, in much the same way as described for injected CH4(g), Chapter 18, Raceway Flame Temperature With CH4(g) Tuyere Injection. Raceway flame temperature decreases with increasing H2O(g) concentration in blast,
BLAST FURNACE IRONMAKING
EXERCISES
Figs. 19.2. This is the result of all our equations, but we speculate that it is mainly due to the large negative enthalpy of the input H2O (g) which lowers; 1. the enthalpy of the raceway inputs; 2. the enthalpy of the raceway outputs; and 3. the temperature of the outputs (i.e., the flame temperature).
EXERCISES 19.1. To smooth their blast furnace’s operation, blast furnace operators of Table 19.2 plan
189
to increase the H2O(g) concentration in their blast to 25 g of H2O(g)/Nm3 of dry air in blast by injecting steam. Please predict for them the change in raceway flame temperature that will result from this change. 19.2. Blast of Exercise 19.1 contains 25 g of H2O (g)/Nm3 of dry air in blast. Its humid air portion contains 9 g of H2O(g)/Nm3 of dry air. How much steam must be added to make the furnace’s 25 g H2O/Nm3 blast? Please express you answer in; 1. g=Nm3 of dry air, 2. kg=kg of dry air, and 3. kg=1000 kg of product molten iron.
BLAST FURNACE IRONMAKING