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Raceway Flame Temperature With CH4(g) Injection
C H A P T E R
18 Raceway Flame Temperature With CH4(g) Injection O U T L I N E 18.1 Understanding The Impact of CH4(g) Injection on Raceway Adiabatic Flame Temperature
170
18.2 Matrix Setup
170
18.10 Raceway Matrix Results and Flame Temperature Calculation
174
18.3 Raceway Input CH4(g) SPECIFICATION
170
18.11 Raceway Input Enthalpy Calculation
175
18.4 Raceway O2-in-Blast Air Input Specification
18.12 Raceway Output Enthalpy
176
170
18.5 Raceway N2-in-Blast Air Specification
18.13 Raceway Output Gas (Flame) Temperature
176
173
18.6 Modified Raceway Carbon Balance Equation
18.14 Effect of CH4(g) Injection on Raceway Flame Temperature
177
173
18.15 Summary
177
18.7 Raceway Oxygen Balance Equation
173
Exercises
178
18.8 New Hydrogen Balance Equation
174
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00018-X
18.9 Raceway Nitrogen Balance Equation
169
174
© 2020 Elsevier Inc. All rights reserved.
170
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
18.1 UNDERSTANDING THE IMPACT OF CH4(g) INJECTION ON RACEWAY ADIABATIC FLAME TEMPERATURE In Chapter 17, Raceway Flame Temperature With Oxygen Enrichment, we calculated the raceway flame temperature with the injection of pure oxygen into the blast air. This chapter calculates the raceway adiabatic flame temperature (RAFT) with CH4(g) injection. Our objectives are to; 1. show how CH4(g) injection is included in our raceway flame temperature calculations, 2. indicate how CH4(g) injection affects raceway flame temperature, and 3. explain this flame temperature effect. CH4(g) is the main component of natural gas. CH4(g) injection adds a new variable to our flame temperature, the mass of H2 in the raceway output gas. To compensate, it adds a new equation-the raceway H balance. We specify that the only hydrogenous gas in the raceway output gas is H2 (Fig. 18.1). This is discussed in Appendices G and H. Fig. (18.1) is a sketch of the blast furnace raceway with CH4(g) injection.
18.2 MATRIX SETUP Our CH4(g) injection flame temperature calculation starts with the bottom-segment matrix result of Table 11.1, copied into Table 18.1. It then prepares raceway matrix Table 18.2 by; 1. setting up raceway C, H, N, and O mass balance equations, and 2. including bottom segment; a. mass tuyere-injected CH4(g), b. mass O2-in-blast air, and c. mass N2-in-blast air of Table 18.1 in these raceway mass balance equations. It then calculates the masses of the other raceway components, as shown in Table 18.2.
18.3 RACEWAY INPUT CH4(g) SPECIFICATION The CH4(g) input mass equation is taken from Cell C14 of the bottom-segment matrix. It is;
mass CH4 injected
into raceway 5 60 kg injected per 1000 kg of Fe in product molten iron
or in matrix form 60 5
mass CH4 injected 1 into raceway
(18.1)
For flexibility, this equation is put into Cell C39 of Table 18.2 by the instruction 5 C14
18.4 RACEWAY O2-IN-BLAST AIR INPUT SPECIFICATION FIGURE 18.1 Sketch of blast furnace raceway with CH4(g) injection. The drawing is a vertical slice through the center of a pear-shaped raceway. All blast furnaces’ blast air and injected CH4(g) enter the blast furnace through its raceways.
The bottom-segment matrix results of Table 18.2 show that; 323 kg O2 in blast air is required for steady production of molten iron 1500 C, Cell C20.
BLAST FURNACE IRONMAKING
TABLE 18.1
Bottom-Segment Matrix With Injection of 60 kg of CH4(g) per 1000 kg of Fe in Product Molten Iron
This is a copy of matrix Table 11.1. The enthalpies in Row 11 are from Table J.1.
TABLE 18.2
Matrices and Equations for Calculating Raceway Flame Temperature With 60 kg of Injected CH4(g)
Note the raceway matrix and raceway enthalpy and flame temperature equations, Rows 52, 53, and 55. The matrix equations are developed in Sections 18.218.8.
Cell F52 5 C49 2 4:667 1 C43 2 F11 1 C44 2 G11 1 C45 2:488 Cell F53 5 F52 Cell G55 5 ðF53 2 C46 2 4:183 2 C47 2 0:2448 2 C48 2 4:130Þ=ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ
173
18.7 RACEWAY OXYGEN BALANCE EQUATION
This is also the amount of O2 entering the blast furnace raceways in blast air. This oxygen is included in the raceway matrix by means of the O2 specification; 2 6 4
mass O2 entering raceway in
3 7 5
18.6 MODIFIED RACEWAY CARBON BALANCE EQUATION With CH4(g) injection, the carbon balance equation of Chapter 14, Raceway Flame Temperature, becomes; "
blast air 5 323 kg=1000 kg of Fe in product molten iron
# mass CH4 g injected into raceway
or in matrix form: 3 mass O2 entering 4 51 raceway in 323 5 blast air
2
1 (18.2)
Of course, this numerical value changes with different amounts of injected CH4(g). This is automatically taken care of in Table 18.2 by inserting the instruction;
mass C in falling
"
1
into raceway mass C in falling
5
6 4
mass N2 entering raceway in
" 052
1
# mass CH4 g injected
into raceway mass C in falling
blast air
1 coke particles mass CO in raceway
above equation and rearranging;
2
5 1064 kg=1000 kg of Fe in product molten iron
0:749
0:429 output gas mass CH4 g injected 0:749 or subtracting into raceway mass C in falling 1 1 from both sides of the coke particles
3 7 5
in injected CH4 100% 100 mass% C
# mass CH4 g injected
into raceway matrix Cell C33.
2
or
5 C20
The blast furnace steady-state N2-in-blast air input also varies with the amount of injected CH4(g). In this case, it is;
74:9 mass% C
in solid carbon 100% coke particles mass CO in raceway ½42:9 mass% C in CO 5 100% output gas
18.5 RACEWAY N2-IN-BLAST AIR SPECIFICATION
1 coke particles mass CO in raceway output gas
0:749
0:429 (18.4)
or in matrix form 2
3 mass N2 entering 51 raceway in 1064 5 4 blast air
(18.3)
This change is automatically taken care of in Table 18.2 by inserting the instruction 5 C21
into Cell C34.
as shown in Row 35 of raceway matrix of Table 18.2.
18.7 RACEWAY OXYGEN BALANCE EQUATION The raceway oxygen balance equation is the same as in Chapter 14, Raceway Flame Temperature. It is;
BLAST FURNACE IRONMAKING
174
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
2 6 0524 1
mass O2 entering raceway in
3
blast air mass CO in raceway output gas
or
7 51
"
0:571
(14.8)
as shown in Row 36.
# mass CH4 g injected 05 2 0:251 into raceway mass H2 in raceway 1 output gas
(18.5)
as shown in Row 37.
18.8 NEW HYDROGEN BALANCE EQUATION Injection of CH4(g) into the raceway requires a hydrogen mass balance. It is;
The nitrogen mass balance equation is the same as in Chapter 14, Raceway Flame Temperature. It is;
mass H into raceway 5 mass H out of raceway
This expands to; mass H in injected CH4 ðgÞ 5 mass H in raceway output gas
or because the only hydrogenous gas in the raceway output gas is H2(g); "
mass CH4 g injected into raceway 5
#
mass H2 in raceway output gas
25:1 mass% H
or subtracting both sides;
in H2 100%
mass CH4 g injected 0:251 into raceway
blast air mass N2 in raceway output gas
1
(14.9)
as shown in Row 38.
18.10 RACEWAY MATRIX RESULTS AND FLAME TEMPERATURE CALCULATION
# mass CH4 g injected 0:251 into raceway mass H2 in raceway 1 5 output gas
3 mass N2 entering 6 7 0524 raceway in 51 1
or "
2
in injected CH4 100% 100 mass% H
18.9 RACEWAY NITROGEN BALANCE EQUATION
Our raceway matrix determines all the raceway’s input and output masses, Cells C43C49. We are now ready to calculate;
from
• raceway input enthalpy, • raceway output enthalpy, and • raceway output gas (flame) temperature as described in the next three sections.
BLAST FURNACE IRONMAKING
175
18.11 RACEWAY INPUT ENTHALPY CALCULATION
18.11 RACEWAY INPUT ENTHALPY CALCULATION
H
1:339 5
With 25 C CH4(g) injection, our raceway’s input enthalpy is; 2
3 2 3 raceway mass CH4 ðgÞ 6 7 6 7 4 input 5 5 4 injected 5 enthalpy
into raceway
2:488 5
25 C CH4 g MWCH4
1500 C CðsÞ MWC H
2 4:664 5
H 1200 C mass O2 entering O2 g 6 7 14 raceway in 5 MWO2 blast air H 2 3 1200 C mass N2 entering N2 g 6 7 14 raceway in 5 MWN2 blast air 2 3 H 1500 C mass C in CðsÞ 6 7 1 4 falling coke 5 MWC particles 2
MWN2 H
H
1200 C N2 g
3
25C CH4 g MWCH4
all MJ/kg of substance. Numerically, the input enthalpy is; 2
raceway
3
6 7 4 input 5 5 60 4:664 1 323 1:239 1 1064 enthalpy 1:339 1 197 2:488 5 2036 MJ=1000 kg of Fe in product molten iron:
or 2
3 raceway 6 7 4 input 5 5 C49 4:664 1 C43 1:239 enthalpy
or 2
3
2
3
raceway mass CH4 ðgÞ 6 7 6 7 4 input 5 5 4 injected 5 2 4:664 enthalpy into raceway 2 3 mass O2 entering 6 7 raceway in 14 5 1:239 2 6 14 2
blast air mass N2 entering raceway in
3
(18.6)
7 5 1:339
blast air 3
mass C in
H
1:239 5
and including blast temperature-dependent cells: 2
3 raceway 6 7 4 input 5 5 C49 4:664 1 C43 F11 enthalpy
6 7 1 4 falling coke 5 2:488 particles
where from Table J.1
1 C44 1:339 1 C45 2:488 5 2036
1 C44 G11 1 C45 2:488 5 2036 (18.7a)
This equation is included in Table 18.2 by inserting the instruction; 5 C49 4:664 1 C43 F11 1 C44
1200 C O2 g MWO2
G11 1 C45 2:488
in Cell F52.
BLAST FURNACE IRONMAKING
(18.7b)
176
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
18.12 RACEWAY OUTPUT ENTHALPY Raceway output enthalpy is needed to calculate raceway output gas (flame) temperature. As described in Chapter 14, Raceway Flame Temperature, it is calculated by the equation; "
raceway output ðflameÞ enthalpy
#
2
3 raceway 6 7 1 zero 5 4 input 5 enthalpy
with zero conductive, convective and radiative heat loss from the raceway to its surroundings. From Section 18.11, the raceway input enthalpy is 2036 MJ/kg of Fe in product molten iron so that:
3 raceway 6 7 1 zero 5 4 input 5 5 F52 ðflameÞ enthalpy enthalpy raceway output
2
5 2036 MJ=1000 kg of Fe in product molten iron (18.8)
This included in Table 18.2 by inserting the instruction; 5 F52
of matrix Table 18.2 all per 1000 kg of Fe in product molten iron. We now; 1. modify flame temperature Eq. (14.16) of Chapter 14, Raceway Flame Temperature, to include H2(g) in raceway output gas, and 2. calculate the raceway flame temperature. The flame temperature equation (with two new H2 terms) is;
2
raceway output
ðflameÞ enthalpy mass CO in raceway
2
output gas mass N2 in raceway
2 ("
output gas mass H2 in raceway output gas mass CO in raceway
" 1 " 1
output gas mass N2 in raceway output gas mass H2 in raceway output gas
ð 24:183Þ
ð 20:2448Þ
ð2 4:130Þ #
5 Tflame ; C (18.9)
0:001310 # 0:001301 #
) 0:01756
is used. The numerical values are from the flame temperature range enthalpy versus temperature equations, Table J.4. They are;
in Cell F53.
H
18.13 RACEWAY OUTPUT GAS (FLAME) TEMPERATURE Our raceway flame temperature calculations uses; 1. raceway CO, N2, and H2 output (flame) masses, 565, 1064, and 15 kg from Cells C46, C47, and C48, 2. raceway output gas (flame) enthalpy, 2036 MJ from Cell F53
Tflame CO g 5 0:001310 Tflame 4:183 MJ=kg of CO g MWCO
H Tflame N2 g 5 0:001301 Tflame 0:2448 MJ=kg of N2 g MWN2 H Tflame H2 g 5 0:01756 Tflame 4:130 MJ=kg of H2 g MWH2
which are applicable in the Tflame temperature range of 18002400 C.
BLAST FURNACE IRONMAKING
18.15 SUMMARY
177
For the numerical example in Table 18.2, the raceway flame temperature is; 2036 2 565 ð 2 4:183Þ 2 1064 ð 2 0:2448Þ 2 15 ð 2 4:130Þ 565 0:001310 1 1064 0:001301 1 15 0:01756 5 Tflame 5 1976 C
or in automatic calculation form: ðF53 C46 4:183 C47 0:2448 C48 4:130Þ ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ 5 Tflame 5 1976 C
(18.10a)
This is included in Table 18.2 by inserting the instruction; ðF53 C46 4:183 C47 0:2448 C48 4:130Þ 5 ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ
(18.10b)
in Cell G55.
18.14 EFFECT OF CH4(g) INJECTION ON RACEWAY FLAME TEMPERATURE
FIGURE 18.2 Influence of 25 C CH4(g) injectant on raceway output gas (flame) temperature. The marked decrease is notable. Notice that the flame temperature decrease with CH4(g) injectant is much greater (B600 C/ 100 kg of injectant) than with C injectant (B120 C/100 kg of injectant), Fig. 16.2. This is a consequence of all the equations in our matrices, but we may speculate that it is mainly due to the large negative enthalpy (per kg of injectant) of the 25 C CH4(g) as compared to the zero enthalpy of 25 C pulverized carbon. The line is strongly curved, because Eqs. (18.9) and (18.10b) are not linear.
Fig. 18.2 shows the effect of CH4(g) injection on raceway flame temperature. The temperature drops significantly with increasing CH4(g) injection. This cooling effect is due to all the equations in the matrices. We can postulate that the cooling effect is mainly due the replacement of hot, highly positive enthalpy C-in-fallingcoke-particles with 25 C negative enthalpy CH4(g), Fig. 18.3. The line in Fig. 18.2 is noticeably curved, because the raceway products’ enthalpies are affected by raceway flame temperature.
18.15 SUMMARY This chapter shows how to calculate raceway flame temperature with CH4(g)
FIGURE 18.3 Effect of mass tuyere-injected CH4(g) on mass of C-in-coke falling into blast furnace raceways, both per 1000 kg of Fe in product molten iron. Falling C-in-coke mass decreases with increasing CH4(g) injection.
BLAST FURNACE IRONMAKING
178
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
injection through a blast furnace’s tuyeres. The calculations show that flame temperature decreases markedly with increasing CH4(g) injection. This decrease is mainly due to 25 C CH4(g)’s large negative enthalpy. The decrease in flame temperature may be offset by; 1. injecting pure oxygen, and 2. raising blast temperature while injecting the CH4(g).
EXERCISES 18.1. Blast furnace operators of Table 18.2 wish to raise their CH4(g) injection to 120 kg/1000 kg of product molten iron.
Please predict for them the flame temperature that will result from this amount of injection. 18.2. Operators of Exercise 18.1 now wish to operate at 2050 C flame temperature. They wish to know how much CH4(g) they will have to inject to obtain this temperature, kg per 1000 kg of Fe in product molten iron. Please calculate this for them. Use two methods of calculation. 18.3. Blast furnace plant of Table 18.2 has refurbished its blast heating stoves. It is now able to produce 1300 C blast. They still want to operate with a 2050 C flame temperature. Please calculate how much CH4(g) injection they will now need to obtain this flame temperature.
BLAST FURNACE IRONMAKING
18 Raceway Flame Temperature With CH4(g) Injection O U T L I N E 18.1 Understanding The Impact of CH4(g) Injection on Raceway Adiabatic Flame Temperature
170
18.2 Matrix Setup
170
18.10 Raceway Matrix Results and Flame Temperature Calculation
174
18.3 Raceway Input CH4(g) SPECIFICATION
170
18.11 Raceway Input Enthalpy Calculation
175
18.4 Raceway O2-in-Blast Air Input Specification
18.12 Raceway Output Enthalpy
176
170
18.5 Raceway N2-in-Blast Air Specification
18.13 Raceway Output Gas (Flame) Temperature
176
173
18.6 Modified Raceway Carbon Balance Equation
18.14 Effect of CH4(g) Injection on Raceway Flame Temperature
177
173
18.15 Summary
177
18.7 Raceway Oxygen Balance Equation
173
Exercises
178
18.8 New Hydrogen Balance Equation
174
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00018-X
18.9 Raceway Nitrogen Balance Equation
169
174
© 2020 Elsevier Inc. All rights reserved.
170
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
18.1 UNDERSTANDING THE IMPACT OF CH4(g) INJECTION ON RACEWAY ADIABATIC FLAME TEMPERATURE In Chapter 17, Raceway Flame Temperature With Oxygen Enrichment, we calculated the raceway flame temperature with the injection of pure oxygen into the blast air. This chapter calculates the raceway adiabatic flame temperature (RAFT) with CH4(g) injection. Our objectives are to; 1. show how CH4(g) injection is included in our raceway flame temperature calculations, 2. indicate how CH4(g) injection affects raceway flame temperature, and 3. explain this flame temperature effect. CH4(g) is the main component of natural gas. CH4(g) injection adds a new variable to our flame temperature, the mass of H2 in the raceway output gas. To compensate, it adds a new equation-the raceway H balance. We specify that the only hydrogenous gas in the raceway output gas is H2 (Fig. 18.1). This is discussed in Appendices G and H. Fig. (18.1) is a sketch of the blast furnace raceway with CH4(g) injection.
18.2 MATRIX SETUP Our CH4(g) injection flame temperature calculation starts with the bottom-segment matrix result of Table 11.1, copied into Table 18.1. It then prepares raceway matrix Table 18.2 by; 1. setting up raceway C, H, N, and O mass balance equations, and 2. including bottom segment; a. mass tuyere-injected CH4(g), b. mass O2-in-blast air, and c. mass N2-in-blast air of Table 18.1 in these raceway mass balance equations. It then calculates the masses of the other raceway components, as shown in Table 18.2.
18.3 RACEWAY INPUT CH4(g) SPECIFICATION The CH4(g) input mass equation is taken from Cell C14 of the bottom-segment matrix. It is;
mass CH4 injected
into raceway 5 60 kg injected per 1000 kg of Fe in product molten iron
or in matrix form 60 5
mass CH4 injected 1 into raceway
(18.1)
For flexibility, this equation is put into Cell C39 of Table 18.2 by the instruction 5 C14
18.4 RACEWAY O2-IN-BLAST AIR INPUT SPECIFICATION FIGURE 18.1 Sketch of blast furnace raceway with CH4(g) injection. The drawing is a vertical slice through the center of a pear-shaped raceway. All blast furnaces’ blast air and injected CH4(g) enter the blast furnace through its raceways.
The bottom-segment matrix results of Table 18.2 show that; 323 kg O2 in blast air is required for steady production of molten iron 1500 C, Cell C20.
BLAST FURNACE IRONMAKING
TABLE 18.1
Bottom-Segment Matrix With Injection of 60 kg of CH4(g) per 1000 kg of Fe in Product Molten Iron
This is a copy of matrix Table 11.1. The enthalpies in Row 11 are from Table J.1.
TABLE 18.2
Matrices and Equations for Calculating Raceway Flame Temperature With 60 kg of Injected CH4(g)
Note the raceway matrix and raceway enthalpy and flame temperature equations, Rows 52, 53, and 55. The matrix equations are developed in Sections 18.218.8.
Cell F52 5 C49 2 4:667 1 C43 2 F11 1 C44 2 G11 1 C45 2:488 Cell F53 5 F52 Cell G55 5 ðF53 2 C46 2 4:183 2 C47 2 0:2448 2 C48 2 4:130Þ=ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ
173
18.7 RACEWAY OXYGEN BALANCE EQUATION
This is also the amount of O2 entering the blast furnace raceways in blast air. This oxygen is included in the raceway matrix by means of the O2 specification; 2 6 4
mass O2 entering raceway in
3 7 5
18.6 MODIFIED RACEWAY CARBON BALANCE EQUATION With CH4(g) injection, the carbon balance equation of Chapter 14, Raceway Flame Temperature, becomes; "
blast air 5 323 kg=1000 kg of Fe in product molten iron
# mass CH4 g injected into raceway
or in matrix form: 3 mass O2 entering 4 51 raceway in 323 5 blast air
2
1 (18.2)
Of course, this numerical value changes with different amounts of injected CH4(g). This is automatically taken care of in Table 18.2 by inserting the instruction;
mass C in falling
"
1
into raceway mass C in falling
5
6 4
mass N2 entering raceway in
" 052
1
# mass CH4 g injected
into raceway mass C in falling
blast air
1 coke particles mass CO in raceway
above equation and rearranging;
2
5 1064 kg=1000 kg of Fe in product molten iron
0:749
0:429 output gas mass CH4 g injected 0:749 or subtracting into raceway mass C in falling 1 1 from both sides of the coke particles
3 7 5
in injected CH4 100% 100 mass% C
# mass CH4 g injected
into raceway matrix Cell C33.
2
or
5 C20
The blast furnace steady-state N2-in-blast air input also varies with the amount of injected CH4(g). In this case, it is;
74:9 mass% C
in solid carbon 100% coke particles mass CO in raceway ½42:9 mass% C in CO 5 100% output gas
18.5 RACEWAY N2-IN-BLAST AIR SPECIFICATION
1 coke particles mass CO in raceway output gas
0:749
0:429 (18.4)
or in matrix form 2
3 mass N2 entering 51 raceway in 1064 5 4 blast air
(18.3)
This change is automatically taken care of in Table 18.2 by inserting the instruction 5 C21
into Cell C34.
as shown in Row 35 of raceway matrix of Table 18.2.
18.7 RACEWAY OXYGEN BALANCE EQUATION The raceway oxygen balance equation is the same as in Chapter 14, Raceway Flame Temperature. It is;
BLAST FURNACE IRONMAKING
174
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
2 6 0524 1
mass O2 entering raceway in
3
blast air mass CO in raceway output gas
or
7 51
"
0:571
(14.8)
as shown in Row 36.
# mass CH4 g injected 05 2 0:251 into raceway mass H2 in raceway 1 output gas
(18.5)
as shown in Row 37.
18.8 NEW HYDROGEN BALANCE EQUATION Injection of CH4(g) into the raceway requires a hydrogen mass balance. It is;
The nitrogen mass balance equation is the same as in Chapter 14, Raceway Flame Temperature. It is;
mass H into raceway 5 mass H out of raceway
This expands to; mass H in injected CH4 ðgÞ 5 mass H in raceway output gas
or because the only hydrogenous gas in the raceway output gas is H2(g); "
mass CH4 g injected into raceway 5
#
mass H2 in raceway output gas
25:1 mass% H
or subtracting both sides;
in H2 100%
mass CH4 g injected 0:251 into raceway
blast air mass N2 in raceway output gas
1
(14.9)
as shown in Row 38.
18.10 RACEWAY MATRIX RESULTS AND FLAME TEMPERATURE CALCULATION
# mass CH4 g injected 0:251 into raceway mass H2 in raceway 1 5 output gas
3 mass N2 entering 6 7 0524 raceway in 51 1
or "
2
in injected CH4 100% 100 mass% H
18.9 RACEWAY NITROGEN BALANCE EQUATION
Our raceway matrix determines all the raceway’s input and output masses, Cells C43C49. We are now ready to calculate;
from
• raceway input enthalpy, • raceway output enthalpy, and • raceway output gas (flame) temperature as described in the next three sections.
BLAST FURNACE IRONMAKING
175
18.11 RACEWAY INPUT ENTHALPY CALCULATION
18.11 RACEWAY INPUT ENTHALPY CALCULATION
H
1:339 5
With 25 C CH4(g) injection, our raceway’s input enthalpy is; 2
3 2 3 raceway mass CH4 ðgÞ 6 7 6 7 4 input 5 5 4 injected 5 enthalpy
into raceway
2:488 5
25 C CH4 g MWCH4
1500 C CðsÞ MWC H
2 4:664 5
H 1200 C mass O2 entering O2 g 6 7 14 raceway in 5 MWO2 blast air H 2 3 1200 C mass N2 entering N2 g 6 7 14 raceway in 5 MWN2 blast air 2 3 H 1500 C mass C in CðsÞ 6 7 1 4 falling coke 5 MWC particles 2
MWN2 H
H
1200 C N2 g
3
25C CH4 g MWCH4
all MJ/kg of substance. Numerically, the input enthalpy is; 2
raceway
3
6 7 4 input 5 5 60 4:664 1 323 1:239 1 1064 enthalpy 1:339 1 197 2:488 5 2036 MJ=1000 kg of Fe in product molten iron:
or 2
3 raceway 6 7 4 input 5 5 C49 4:664 1 C43 1:239 enthalpy
or 2
3
2
3
raceway mass CH4 ðgÞ 6 7 6 7 4 input 5 5 4 injected 5 2 4:664 enthalpy into raceway 2 3 mass O2 entering 6 7 raceway in 14 5 1:239 2 6 14 2
blast air mass N2 entering raceway in
3
(18.6)
7 5 1:339
blast air 3
mass C in
H
1:239 5
and including blast temperature-dependent cells: 2
3 raceway 6 7 4 input 5 5 C49 4:664 1 C43 F11 enthalpy
6 7 1 4 falling coke 5 2:488 particles
where from Table J.1
1 C44 1:339 1 C45 2:488 5 2036
1 C44 G11 1 C45 2:488 5 2036 (18.7a)
This equation is included in Table 18.2 by inserting the instruction; 5 C49 4:664 1 C43 F11 1 C44
1200 C O2 g MWO2
G11 1 C45 2:488
in Cell F52.
BLAST FURNACE IRONMAKING
(18.7b)
176
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
18.12 RACEWAY OUTPUT ENTHALPY Raceway output enthalpy is needed to calculate raceway output gas (flame) temperature. As described in Chapter 14, Raceway Flame Temperature, it is calculated by the equation; "
raceway output ðflameÞ enthalpy
#
2
3 raceway 6 7 1 zero 5 4 input 5 enthalpy
with zero conductive, convective and radiative heat loss from the raceway to its surroundings. From Section 18.11, the raceway input enthalpy is 2036 MJ/kg of Fe in product molten iron so that:
3 raceway 6 7 1 zero 5 4 input 5 5 F52 ðflameÞ enthalpy enthalpy raceway output
2
5 2036 MJ=1000 kg of Fe in product molten iron (18.8)
This included in Table 18.2 by inserting the instruction; 5 F52
of matrix Table 18.2 all per 1000 kg of Fe in product molten iron. We now; 1. modify flame temperature Eq. (14.16) of Chapter 14, Raceway Flame Temperature, to include H2(g) in raceway output gas, and 2. calculate the raceway flame temperature. The flame temperature equation (with two new H2 terms) is;
2
raceway output
ðflameÞ enthalpy mass CO in raceway
2
output gas mass N2 in raceway
2 ("
output gas mass H2 in raceway output gas mass CO in raceway
" 1 " 1
output gas mass N2 in raceway output gas mass H2 in raceway output gas
ð 24:183Þ
ð 20:2448Þ
ð2 4:130Þ #
5 Tflame ; C (18.9)
0:001310 # 0:001301 #
) 0:01756
is used. The numerical values are from the flame temperature range enthalpy versus temperature equations, Table J.4. They are;
in Cell F53.
H
18.13 RACEWAY OUTPUT GAS (FLAME) TEMPERATURE Our raceway flame temperature calculations uses; 1. raceway CO, N2, and H2 output (flame) masses, 565, 1064, and 15 kg from Cells C46, C47, and C48, 2. raceway output gas (flame) enthalpy, 2036 MJ from Cell F53
Tflame CO g 5 0:001310 Tflame 4:183 MJ=kg of CO g MWCO
H Tflame N2 g 5 0:001301 Tflame 0:2448 MJ=kg of N2 g MWN2 H Tflame H2 g 5 0:01756 Tflame 4:130 MJ=kg of H2 g MWH2
which are applicable in the Tflame temperature range of 18002400 C.
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18.15 SUMMARY
177
For the numerical example in Table 18.2, the raceway flame temperature is; 2036 2 565 ð 2 4:183Þ 2 1064 ð 2 0:2448Þ 2 15 ð 2 4:130Þ 565 0:001310 1 1064 0:001301 1 15 0:01756 5 Tflame 5 1976 C
or in automatic calculation form: ðF53 C46 4:183 C47 0:2448 C48 4:130Þ ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ 5 Tflame 5 1976 C
(18.10a)
This is included in Table 18.2 by inserting the instruction; ðF53 C46 4:183 C47 0:2448 C48 4:130Þ 5 ðC46 0:001310 1 C47 0:001301 1 C48 0:01756Þ
(18.10b)
in Cell G55.
18.14 EFFECT OF CH4(g) INJECTION ON RACEWAY FLAME TEMPERATURE
FIGURE 18.2 Influence of 25 C CH4(g) injectant on raceway output gas (flame) temperature. The marked decrease is notable. Notice that the flame temperature decrease with CH4(g) injectant is much greater (B600 C/ 100 kg of injectant) than with C injectant (B120 C/100 kg of injectant), Fig. 16.2. This is a consequence of all the equations in our matrices, but we may speculate that it is mainly due to the large negative enthalpy (per kg of injectant) of the 25 C CH4(g) as compared to the zero enthalpy of 25 C pulverized carbon. The line is strongly curved, because Eqs. (18.9) and (18.10b) are not linear.
Fig. 18.2 shows the effect of CH4(g) injection on raceway flame temperature. The temperature drops significantly with increasing CH4(g) injection. This cooling effect is due to all the equations in the matrices. We can postulate that the cooling effect is mainly due the replacement of hot, highly positive enthalpy C-in-fallingcoke-particles with 25 C negative enthalpy CH4(g), Fig. 18.3. The line in Fig. 18.2 is noticeably curved, because the raceway products’ enthalpies are affected by raceway flame temperature.
18.15 SUMMARY This chapter shows how to calculate raceway flame temperature with CH4(g)
FIGURE 18.3 Effect of mass tuyere-injected CH4(g) on mass of C-in-coke falling into blast furnace raceways, both per 1000 kg of Fe in product molten iron. Falling C-in-coke mass decreases with increasing CH4(g) injection.
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178
18. RACEWAY FLAME TEMPERATURE WITH CH4(G) INJECTION
injection through a blast furnace’s tuyeres. The calculations show that flame temperature decreases markedly with increasing CH4(g) injection. This decrease is mainly due to 25 C CH4(g)’s large negative enthalpy. The decrease in flame temperature may be offset by; 1. injecting pure oxygen, and 2. raising blast temperature while injecting the CH4(g).
EXERCISES 18.1. Blast furnace operators of Table 18.2 wish to raise their CH4(g) injection to 120 kg/1000 kg of product molten iron.
Please predict for them the flame temperature that will result from this amount of injection. 18.2. Operators of Exercise 18.1 now wish to operate at 2050 C flame temperature. They wish to know how much CH4(g) they will have to inject to obtain this temperature, kg per 1000 kg of Fe in product molten iron. Please calculate this for them. Use two methods of calculation. 18.3. Blast furnace plant of Table 18.2 has refurbished its blast heating stoves. It is now able to produce 1300 C blast. They still want to operate with a 2050 C flame temperature. Please calculate how much CH4(g) injection they will now need to obtain this flame temperature.
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