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Top-Segment Enthalpy Balance
C H A P T E R
21 Top-Segment Enthalpy Balance O U T L I N E 21.1 Top-Segment Enthalpy Balance
199
21.5 Summary
203
21.2 Top-Segment Input Enthalpy
199
Exercises
204
21.3 Top-Segment Output Enthalpy
200
Reference
204
21.4 Calculated Values
203
21.1 TOP-SEGMENT ENTHALPY BALANCE
21.2 TOP-SEGMENT INPUT ENTHALPY
This chapter calculates Fig. 21.1’s;
Fig. 21.1 inputs are;
1. top-segment input enthalpy, and 2. top-segment output enthalpy. Our objective is to provide enthalpy information for calculating the top gas temperature of Fig. 21.1. Top gas temperature is important because it strongly affects the rate and efficiency of (1) charge moisture evaporation, and (2) carbonate flux decomposition1.
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00021-X
• • • • •
shows
that
the
top-segment
Fe2O3 in ore charge, C-in-coke charge, CO ascending from bottom segment, CO2 ascending from bottom segment, and N2 ascending from bottom segment.
Fig. 21.1 also shows their respective input temperatures.
199
© 2020 Elsevier Inc. All rights reserved.
200
21. TOP-SEGMENT ENTHALPY BALANCE
2 6 4
top segment input enthalpy; MJ per 1000 kg of Fe
3 7 5
in product molten iron 1431 kg Fe2 O3 ð 25:169Þ 5 in furnace charge 392 kg C-in1 0 coke charge 558 kg CO ascending 1 ð 22:926Þ from bottom segment 387 kg CO2 ascending ð 27:926Þ 1 from bottom segment 983 kg N2 ascending 1:008 1 from bottom segment
FIGURE 21.1 Sketch of conceptual blast furnace top segment with inputs and outputs. It is a copy of Fig. 20.2. This is a central vertical slice through the top of the blast furnace of Fig. 1.1.
(21.1b)
from which;
The combined enthalpy of all these inputs is described by; "
top segment input enthalpy
#
" 5
mass Fe2 O3 in
1
mass C-incoke charge
" 1
1
CðsÞ
top segment input enthalpy
MWC
mass CO ascending
mass CO2 ascending
mass N2 ascending from bottom segment
5 AC18 2 5:169 1 AC19 0 1 AC20 2 2:926 1 AC21 2 7:926
#
H930 C CO g
1 AC22 1:008
MWCO
where the cell addresses refer to Table 21.2. The equal sign and the right side of this equation are typed into Cell AG33 of Table 21.2.
H930 C
#
from bottom segment "
5 11; 105 MJ=1000 kg of Fe in product molten iron
# H 25 C
input enthalpy
Eq. (21.1b) may be expressed in spreadsheet form as;
Fe2 O3 ðsÞ
MWFe2 O3
from bottom segment "
1
#
furnace charge "
H25 C
top segment
CO2 g
MWCO2 H930 C
#
(21.2)
N2 g
MWN2 (21.1a)
Masses of Eq. (21.1a) are obtained from Table 21.2. The enthalpy values are obtained from Table J.1. Together, they give;
21.3 TOP-SEGMENT OUTPUT ENTHALPY Top-segment output enthalpy of Fig. 21.1 is given by the equation;
top segment top segment 5 output enthalpy input enthalpy 2 3 conductive; convective 6 7 2 4 and radiative heat loss 5 from the top segment (21.3)
BLAST FURNACE IRONMAKING
TABLE 21.1 Fig. 20.1 Bottom-Segment Matrix
This is the same as matrix Table 20.1. This chapter uses it to calculate top-segment input and output enthalpies of Fig. 21.1.
TABLE 21.2
This is Matrix Table 20.2 Plus Eqs. (21.2), (21.5a) and (21.5b)
Cell AG33 5 AC18 (25.169) 1 AC19 Cell AG34 5 AG3380
0 1 AC20 (22.926) 1 AC21 (27.926) 1 AC22 1.008
203
21.5 SUMMARY
In Section 5.4, the whole furnace conductive, convective and radiative heat losses are assumed to be 400 MJ/1000 kg of Fe in product molten iron based on actual measurements. Section 7.8 indicates that the bottom-segment conductive, convective plus radiative heat loss is 320 MJ/1000 kg of Fe in product molten iron. This means that the top-segment conductive, convective and radiative heat loss is 80 MJ/1000 kg of Fe in product molten iron. This small value is due to the low temperature of the top-segment’s contents which leads to relatively slow heat transfer. The top-segment conductive, convective and radiative heat loss gives;
top segment top segment 5 output enthalpy input enthalpy 2 3 80 MJ conductive; convective 6 7 and radiative heat loss 24 5 from the top segment (21.4)
where the terms are all MJ per 1000 kg of Fe in product molten iron. Section 21.2 gives a top-segment input enthalpy of 211,105 MJ/1000 kg of Fe in product molten iron. The top-segment output enthalpy is, therefore;
top segment 5 11;105 80 output enthalpy MJ per 1000 kg of Fe 5 11;185 in product molten iron
(21.5a)
top segment 5 AG33 2 80 output enthalpy
Table 21.2. Fig. 21.2 plots the latter as a function of blast temperature. It shows that top-segment output enthalpy becomes less negative with increasing blast temperature. We can now calculate top gas enthalpy and top gas temperature from calculated values of;
Eq. (21.5a) may be expressed in spreadsheet form as;
FIGURE 21.2 Top-segment input and output enthalpies as a function of blast temperature. Both become less negative with increasing blast temperature. This is the result of all the equations in our spreadsheets. We may postulate that they are due to the increasing enthalpy of the blast furnace’s blast air with increasing blast temperature - the consequent increasing amount of enthalpy rising into the top segment. The enthalpy values have been obtained by varying blast temperature in Cell D13 of Table 21.1. All are per 1000 kg of Fe in product molten iron.
(21.5b)
Its equal sign and right side are typed in Cell AG34 of Table 21.2.
1. top-segment output enthalpy, 2. top-segment output masses of Chapter 20, Top-Segment Mass Balance, and 3. H T =MW of Table J.5 versus top gas temperature equations, top gas
as described in Chapter Temperature Calculation.
22,
Top
Gas
21.4 CALCULATED VALUES
21.5 SUMMARY
The top-segment input and output enthalpy values with 1200 C blast air are shown in
Top gas temperature of Chapter 22, Top Gas Temperature Calculation, calculations start
BLAST FURNACE IRONMAKING
204
21. TOP-SEGMENT ENTHALPY BALANCE
with top-segment output enthalpy - which is readily calculated from; 1. top-segment input masses and temperatures, which we use to calculate top-segment input enthalpy, and 2. top-segment conductive, convective, and radiative heat loss. The basic equation is:
top segment output enthalpy
5
top segment
input enthalpy 2 3 conductive; convective 6 7 2 4 and radiative heat loss 5 from the top segment
Top-segment output enthalpy increases with increasing blast temperature, that is,
with increasing blast enthalpy, MJ per kg of blast.
EXERCISES 21.1. Please calculate top-segment input and output enthalpies of Exercise 20.1. 21.2. Please calculate top-segment input and output enthalpies of Exercise 20.2. Remember that the enthalpies of Fe2O3 and Fe3O4 are different.
Reference 1. Geerdes M, Chaigneau R, Kurunov I, Lingiardi O, Ricketts J. Modern blast furnace ironmaking, an introduction. 2nd ed. BV, Amsterdam: IOS Press; 2015. p. 164.
BLAST FURNACE IRONMAKING
21 Top-Segment Enthalpy Balance O U T L I N E 21.1 Top-Segment Enthalpy Balance
199
21.5 Summary
203
21.2 Top-Segment Input Enthalpy
199
Exercises
204
21.3 Top-Segment Output Enthalpy
200
Reference
204
21.4 Calculated Values
203
21.1 TOP-SEGMENT ENTHALPY BALANCE
21.2 TOP-SEGMENT INPUT ENTHALPY
This chapter calculates Fig. 21.1’s;
Fig. 21.1 inputs are;
1. top-segment input enthalpy, and 2. top-segment output enthalpy. Our objective is to provide enthalpy information for calculating the top gas temperature of Fig. 21.1. Top gas temperature is important because it strongly affects the rate and efficiency of (1) charge moisture evaporation, and (2) carbonate flux decomposition1.
Blast Furnace Ironmaking DOI: https://doi.org/10.1016/B978-0-12-814227-1.00021-X
• • • • •
shows
that
the
top-segment
Fe2O3 in ore charge, C-in-coke charge, CO ascending from bottom segment, CO2 ascending from bottom segment, and N2 ascending from bottom segment.
Fig. 21.1 also shows their respective input temperatures.
199
© 2020 Elsevier Inc. All rights reserved.
200
21. TOP-SEGMENT ENTHALPY BALANCE
2 6 4
top segment input enthalpy; MJ per 1000 kg of Fe
3 7 5
in product molten iron 1431 kg Fe2 O3 ð 25:169Þ 5 in furnace charge 392 kg C-in1 0 coke charge 558 kg CO ascending 1 ð 22:926Þ from bottom segment 387 kg CO2 ascending ð 27:926Þ 1 from bottom segment 983 kg N2 ascending 1:008 1 from bottom segment
FIGURE 21.1 Sketch of conceptual blast furnace top segment with inputs and outputs. It is a copy of Fig. 20.2. This is a central vertical slice through the top of the blast furnace of Fig. 1.1.
(21.1b)
from which;
The combined enthalpy of all these inputs is described by; "
top segment input enthalpy
#
" 5
mass Fe2 O3 in
1
mass C-incoke charge
" 1
1
CðsÞ
top segment input enthalpy
MWC
mass CO ascending
mass CO2 ascending
mass N2 ascending from bottom segment
5 AC18 2 5:169 1 AC19 0 1 AC20 2 2:926 1 AC21 2 7:926
#
H930 C CO g
1 AC22 1:008
MWCO
where the cell addresses refer to Table 21.2. The equal sign and the right side of this equation are typed into Cell AG33 of Table 21.2.
H930 C
#
from bottom segment "
5 11; 105 MJ=1000 kg of Fe in product molten iron
# H 25 C
input enthalpy
Eq. (21.1b) may be expressed in spreadsheet form as;
Fe2 O3 ðsÞ
MWFe2 O3
from bottom segment "
1
#
furnace charge "
H25 C
top segment
CO2 g
MWCO2 H930 C
#
(21.2)
N2 g
MWN2 (21.1a)
Masses of Eq. (21.1a) are obtained from Table 21.2. The enthalpy values are obtained from Table J.1. Together, they give;
21.3 TOP-SEGMENT OUTPUT ENTHALPY Top-segment output enthalpy of Fig. 21.1 is given by the equation;
top segment top segment 5 output enthalpy input enthalpy 2 3 conductive; convective 6 7 2 4 and radiative heat loss 5 from the top segment (21.3)
BLAST FURNACE IRONMAKING
TABLE 21.1 Fig. 20.1 Bottom-Segment Matrix
This is the same as matrix Table 20.1. This chapter uses it to calculate top-segment input and output enthalpies of Fig. 21.1.
TABLE 21.2
This is Matrix Table 20.2 Plus Eqs. (21.2), (21.5a) and (21.5b)
Cell AG33 5 AC18 (25.169) 1 AC19 Cell AG34 5 AG3380
0 1 AC20 (22.926) 1 AC21 (27.926) 1 AC22 1.008
203
21.5 SUMMARY
In Section 5.4, the whole furnace conductive, convective and radiative heat losses are assumed to be 400 MJ/1000 kg of Fe in product molten iron based on actual measurements. Section 7.8 indicates that the bottom-segment conductive, convective plus radiative heat loss is 320 MJ/1000 kg of Fe in product molten iron. This means that the top-segment conductive, convective and radiative heat loss is 80 MJ/1000 kg of Fe in product molten iron. This small value is due to the low temperature of the top-segment’s contents which leads to relatively slow heat transfer. The top-segment conductive, convective and radiative heat loss gives;
top segment top segment 5 output enthalpy input enthalpy 2 3 80 MJ conductive; convective 6 7 and radiative heat loss 24 5 from the top segment (21.4)
where the terms are all MJ per 1000 kg of Fe in product molten iron. Section 21.2 gives a top-segment input enthalpy of 211,105 MJ/1000 kg of Fe in product molten iron. The top-segment output enthalpy is, therefore;
top segment 5 11;105 80 output enthalpy MJ per 1000 kg of Fe 5 11;185 in product molten iron
(21.5a)
top segment 5 AG33 2 80 output enthalpy
Table 21.2. Fig. 21.2 plots the latter as a function of blast temperature. It shows that top-segment output enthalpy becomes less negative with increasing blast temperature. We can now calculate top gas enthalpy and top gas temperature from calculated values of;
Eq. (21.5a) may be expressed in spreadsheet form as;
FIGURE 21.2 Top-segment input and output enthalpies as a function of blast temperature. Both become less negative with increasing blast temperature. This is the result of all the equations in our spreadsheets. We may postulate that they are due to the increasing enthalpy of the blast furnace’s blast air with increasing blast temperature - the consequent increasing amount of enthalpy rising into the top segment. The enthalpy values have been obtained by varying blast temperature in Cell D13 of Table 21.1. All are per 1000 kg of Fe in product molten iron.
(21.5b)
Its equal sign and right side are typed in Cell AG34 of Table 21.2.
1. top-segment output enthalpy, 2. top-segment output masses of Chapter 20, Top-Segment Mass Balance, and 3. H T =MW of Table J.5 versus top gas temperature equations, top gas
as described in Chapter Temperature Calculation.
22,
Top
Gas
21.4 CALCULATED VALUES
21.5 SUMMARY
The top-segment input and output enthalpy values with 1200 C blast air are shown in
Top gas temperature of Chapter 22, Top Gas Temperature Calculation, calculations start
BLAST FURNACE IRONMAKING
204
21. TOP-SEGMENT ENTHALPY BALANCE
with top-segment output enthalpy - which is readily calculated from; 1. top-segment input masses and temperatures, which we use to calculate top-segment input enthalpy, and 2. top-segment conductive, convective, and radiative heat loss. The basic equation is:
top segment output enthalpy
5
top segment
input enthalpy 2 3 conductive; convective 6 7 2 4 and radiative heat loss 5 from the top segment
Top-segment output enthalpy increases with increasing blast temperature, that is,
with increasing blast enthalpy, MJ per kg of blast.
EXERCISES 21.1. Please calculate top-segment input and output enthalpies of Exercise 20.1. 21.2. Please calculate top-segment input and output enthalpies of Exercise 20.2. Remember that the enthalpies of Fe2O3 and Fe3O4 are different.
Reference 1. Geerdes M, Chaigneau R, Kurunov I, Lingiardi O, Ricketts J. Modern blast furnace ironmaking, an introduction. 2nd ed. BV, Amsterdam: IOS Press; 2015. p. 164.
BLAST FURNACE IRONMAKING