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Keywords:

  • carbon rate;
  • alternative ironmaking;
  • smelting reduction;
  • direct reduction

Abstract

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

From economic viability and sustainable development of view, the future alternative ironmaking processes, in general, may be classified into two representative routes, “Pre-reduction-Smelting reduction” process and “Direct reduction-Melting” process. In the present work, aimed for hot metal production, the carbon rate (in kg tHM−1) is considered as the yardstick for the measurement of the “goodness” of these two processes, because it reflects the consumption of coal and energy, and the amount of carbon dioxide eventually to be emitted to atmosphere. By the thermodynamic calculation, under the idealized conditions, the total adiabatic carbon rate along “Direct reduction-Melting” process is approximately 145 kg tHM−1 lower than that along “Pre-reduction-Smelting reduction” process. Therefore, direct reduction would likely lead to an alternative process with much lower carbon rate, and it should be reasonable and successfully developed.

1 Introduction

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

Liquid iron continually is the main supply to efficient steelmaking in the long future. As we all know, the blast furnace (BF) lead the ironmaking process in the past and next many decades. Basically the supplier of energy for BF is coke and coal. In commercial processes (or technologies in development) for the making of liquid iron, to the best knowledge of authors, none has (or would have) a coal-equivalent and energy consumption rate lower than modern BF. But in recent years, aimed for hot metal production from iron ore and coal, there are many attempts in searching for coke-free alternative ironmaking processes, which could be an efficient supplement to BF or treatment of special ores and waste iron oxides.[1-6]

At present, there are a fair number of direct reduction processes to produce direct reduced iron (DRI) commercially. The commercial viability of smelting reduction processes in different countries, in general, is still debatable. Any new processes must be compared in terms of a yardstick, such as consumption of raw material and energy, or disposal of by-products with respect to both economic and environmental consequences. The yardstick should be valid for concerns in sustainable development and not be influenced by engineering problems, which may be overcome in the future and local situations. Currently, greenhouse gas emission and energy efficiency are among the key words of the era of sustainable development.[7, 8] Iron and steel industry is one of the largest CO2 source among industrial processes, accounting for about 8% of global total CO2 emission. CO2 emission has become an important concern for iron and steel making. Development of an innovative technology is the key to responding to the request for further reduction of CO2 emission and sustainable development on a global scale. Therefore, in the present work, carbon rate (in kg tHM−1) is considered as the primary yardstick for the measurement of the “goodness” of a new process, because it reflects the consumption of coal and energy and the amount of CO2 to be eventually emitted to the atmosphere.

2 Goal of Present Work

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

In representing current views, the typical coke-free alternative ironmaking processes include, (1) direct reduction, e.g. shaft furnace, rotary kiln, rotary hearth furnace, and tunnel kiln etc. The product of these processes is DRI in solid state.[9-11] (2) Smelting reduction, e.g. Corex, Finex, Hismelt etc. The product of these processes is liquid iron.[12-14] Carbon rate cannot be compared between direct reduction and smelting reduction due to different product (solid iron and liquid iron). In order to compare between them, the raw materials and product must be the same, so the direct reduction is followed by melting to produce liquid iron. Then, the product is same as smelting reduction. Therefore, to produce liquid iron, the typical coke-free alternative ironmaking processes may be classified into two representative groups of “two-reactor” systems, which are shown in Figures 1 and 21 and 2.

  1. Pre-reduction-Smelting reduction. Hot charge pre-reduced iron ore to a smelting reduction vessel for hot metal production, and the exit gas from the vessel is used for pre-reduction of iron ore (Figure 1).
  2. Direct Reduction-Melting. Produce DRI from ore-coal composite, followed by melting the hot DRI in an oxy-coal converter to produce hot metal (Figure 2). As shown in Figure 2, there are two compartments in direct reduction reactor: “reduction compartment” and “oxidation compartment”. Carbon is used first as reducing agent for iron ore reduction (which is strongly endothermic) to produce DRI and CO in the “reduction compartment”. Then, CO is combusted to CO2 in “oxidation compartment” to liberate all the heat energy of carbon for the need of “reduction compartment”.
image

Figure 1. Schematic flow chart of “Pre-reduction-Smelting reduction” process.

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image

Figure 2. Schematic flow chart of “Direct reduction-Melting” process.

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The present work is to analyze the core characteristics of these two routes by the yardstick of “adiabatic carbon rate” along the idealized conditions. The thermodynamic data used in the present work is from literatures.[15, 16] The idealization in the processes include the assumptions of adiabatic condition, perfect heat transfer, using Fe2O3 and C instead of iron ore and coal, and that any problems related to refractory, mechanical equipment, and particular environmental regulations are ignored in this work.

3 Carbon Rate of Alternative Ironmaking Processes

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

3.1 Pre-Reduction-Smelting Reduction

According to the practical operation conditions, some assumptions are made to calculate the carbon rate of “Pre-reduction-Smelting reduction” process.

  1. The feed materials are Fe2O3 and C at 25°C, and the product is liquid Fe at 1550°C.
  2. Pre-reduced iron ore is hot charged to smelting vessel.
  3. Oxygen used in smelting vessel is pure O2.
  4. The exit gas of pre-reducer and FeOa in pre-reducer are in chemical equilibrium.
  5. The heat requirement for the operation of pre-reduction is assumed to be readily available from the sensible heat of hot exit gas from smelting vessel (or others).
  6. The variables are degree of pre-reduction of Fe2O3 and the percentage of CO2 in exit gas from smelting vessel. The degree of pre-reduction is defined as “Degree of Pre-reduction = [(Oxygen removed from iron oxides)/(Total original oxygen in iron oxides)] × 100%”.

If the chemical energy of gaseous product, CO, from smelting vessel partially post-combust (generate CO2) to supply heat to smelting vessel, there are two disadvantage effects: (1) increases the oxygen potential and result in re-oxidation of hot metal in smelting vessel at high temperature. (2) The reducing potential of CO/CO2 mixture gas is lower in pre-reduction. Therefore, the exit gas from smelting vessel cannot have a too high CO2 content, usually <20%.

For better understanding, the calculation procedures for “Pre-reduction-Smelting reduction” process, an example (Point M in Figure 3) is given below. For Point M, the parameters include, (1) the temperature of pre-reduction is 800°C, (2) the composition of exit gas from smelting vessel is 90% of CO and 10% of CO2, (3) and the degree of pre-reduction is 49%. Forty-nine percent of degree means FeO1.5 is pre-reduced to FeO0.76. So, in order to produce 1 mol Fe, 0.5 mol Fe2O3 is pre-reduced to 0.76 mol FeO and 0.24 mol Fe at 800°C in pre-reduction process, and these hot 0.76 mol FeO and 0.24 mol Fe are feed into smelting vessel. In smelting vessel, the calculation of carbon rate is listed in Table 1.

image

Figure 3. Carbon rate of “Pre-reduction-Smelting reduction” process.

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Table 1. Carbon rate in smelting reduction
 ItemΔH
Heat required0.76FeO + 0.68C = 0.76Fe + 0.62CO + 0.07CO2ΔH1 = 106 008 J
1 mol Fe is heated from 298 to 1823 KΔH2 = 70 991 J
0.62 mol CO is heated from 298 to 1823 KΔH3 = 30 692 J
0.07 mol CO2 is heated from 298 to 1823 KΔH4 = 5410 J
Heat supply0.76 mol FeO liberates heat from 1073 to 298 KΔH5 = 32 953 J
0.24 mol Fe liberates heat from 1073 to 298 KΔH6 = 6411 J
C + 0.55O2 = 0.9CO + 0.1CO2ΔH7 = 1 38 828 JΔHSup.1 = ΔH7–ΔH8–ΔH9 = 86 031 J mol C−1 (heat supply by combustion of 1 mol carbon: C + 0.55O2 = 0.9CO + 0.1CO2)
0.9 mol CO is heated from 298 to 1823 KΔH8 = 44 843 J
0.1 mol CO2 is heated from 298 to 1823 KΔH9 = 7954 J
C (As fuel) = [(ΔH1 + ΔH2 + ΔH3 + ΔH4) − (ΔH5 + ΔH6)]/ΔHSup.1 = ΔHReq.1HSup.1 = 2.02 mol
C (total) = C (As fuel) + C (As reductant) = 2.02 + 0.68 = 2.70 mol C mol Fe−1 (578 kg C tHM−1).

The hot exit CO/CO2 gas from smelting vessel is the reductant and heat source for pre-reduction. Then check if the reducing potential and heat of the gas is sufficient for pre-reduction. In pre-reduction process, 0.5 mol Fe2O3 is pre-reduced to 0.76 mol FeO and 0.24 mol Fe, which consumes 0.74 mol CO to generate 0.74 mol CO2. The mass balance, reducing potential check, heat check and chemical reaction equations are listed in Table 2.

Table 2. Mass balance, reducing potential check and heat check in pre-reduction
 Input to pre-reduction Output from pre-reduction
Mass balance0.5 mol Fe2O3 at 298 K0.76 mol FeO at 1073 K
 0.24 mol Fe at 1073 K
2.43 mol CO at 1823 K (90% of exit gas from smelting vessel)1.69 mol CO at 1073 K
0.27 mol CO2 at 1823 K (10% of exit gas from smelting vessel)1.01 mol CO2 at 1073 K
Reducing potential CheckFeO + CO = Fe + CO2 K1073K = 0.60
For the output gas from pre-reduction, (%CO2)/(%CO) = 1.01 mol/1.69 mol = 0.60 = K1073K. So, the reducing potential of the output gas from pre-reduction is sufficient for the metallic iron to stable exist.
But if (%CO2)/(%CO) > K1073K, extra carbon (or CO) is required to sustain the reducing potential, until (%CO2)/(%CO) ≤ K1073K. That's why the curve of carbon rate increases with the increase of pre-reduction degree at later stage (Fig. 3).
Heat checkHeat required0.76 mol FeO is heated from 298 to 1073 KΔH10 = 32 952 J
0.24 mol Fe is heated from 298 to 1073 KΔH11 = 6411 J
1.69 mol CO is heated from 298 to 1073 KΔH12 = 40 702 J
1.01 mol CO2 is heated from 298 to 1073 KΔH13 = 37 311 J
0.38Fe2O3 + 0.38CO = 0.76FeO + 0.38CO2ΔH14 = 3603 J
0.12Fe2O3 + 0.36CO = 0.24Fe + 0.36CO2ΔH15 = −3315 J
ΔHReq.2 = ΔH10 + ΔH11 + ΔH12 + ΔH13 + ΔH14 + ΔH15 = 1 17 665 J
Heat supply2.43 mol CO liberates heat from 1823 to 298 KΔH16 = 1 21 075 J
0.27 mol CO2 liberates heat from 1823 to 298 KΔH17 = 21 475 J
ΔHSup.2 = ΔH16 + ΔH17 = 1 42 550 (from the hot exit gas of smelting vessel)
ΔHSup.2 > ΔHReq.2, so the sensible heat from the hot exit gas of smelting vessel is sufficient for pre-reduction process, no extra carbon in pre-reduction is required.
Therefore, the total adiabatic carbon rate for Point M [DOUBLE BOND] C (in smelting) + C (in pre-reduction) = 578 + 0 = 578 kg tHM−1.

From Tables 1 and 21 and 2, the calculated total adiabatic carbon rate of “Pre-reduction-Smelting reduction” process is the sum of that used as reductant and that used as fuel. So the carbon rate is a function of pre-reduction degree (mixtures of hematite, magnetite, wustite, and metallic iron), exit gas composition, and pre-reduction temperature. The calculations about carbon rate at different conditions are similar with Point M, and are shown in Figure 3. In the figure, the percentage of CO2 is 0, 10, and 20% respectively, and the temperature of pre-reduction is 800 and 1000°C, respectively.

The exit CO/CO2 mixture gas from smelting vessel is by-product, but it is the input as reductant and heat source in pre-reduction reactor. So it serves as coupling link of these two reactors. If the CO/CO2 gas from smelting vessel is the source of pre-reduction, there are contradictory requirements in smelting vessel and pre-reduction. (1) When the degree of pre-reduction is lower, the work load in smelting vessel is higher, and result that the carbon rate in smelting process is higher. (2) On the other hand, in order to lower the work load in smelting vessel, the iron ore should have higher degree of pre-reduction, i.e. more CO/CO2 mixture gas of higher reducing potential is needed in pre-reduction. However, the smelting vessel which is charged with ore of higher degree of pre-reduction will produce less CO gas, instead of more CO to satisfy the increased need in pre-reduction. In order to sustain the pre-reduction operation, other extra carbon in addition to CO from smelting vessel may be used to supply reducing potential and heat. Therefore, the total adiabatic carbon rate first decreases and then increases with the increase of degree of pre-reduction (Figure 3).

This problem exists in all smelting reduction process. In order to satisfy the reducing agent and heat requirement (carbon rate) both in pre-reduction and in smelting reduction, it could be worked out a compromise on mass balance and heat balance between smelting vessel and pre-reduction. For the illustration of such contradictory requirement, a minimum value of carbon rate (the compromise degree of pre-reduction) at a certain pre-reduction temperature and certain composition of exit gas from smelting vessel is shown in Figure 3 (point with lowest carbon rate in each curve). More or less than this degree of pre-reduction, the carbon rate will increase. From Figure 3, one can conclude that basically the total adiabatic carbon rate of “Pre-reduction-Smelting reduction” is more than 600 kg tHM−1.

3.2 Direct Reduction-Melting

Same as before, according to the practical operation conditions, some assumptions are made to calculate the carbon rate of “Direct Reduction-Melting” process.

  1. The feed materials are Fe2O3 and C at 25°C, and the product is liquid Fe at 1550°C.
  2. DRI is hot charged to melting converter.
  3. Oxygen used in “oxidation compartment” is air (20% O2 and 80% N2). In some oxygen-enriched cases, the percentage of O2 is 25% and 30%.
  4. Oxygen used in melting converter is pure O2.
  5. Without re-oxidation of nascent iron in direct reduction (because paired straight hearth (PSH) furnace can resolve the problem of re-oxidation).
  6. The variable is the temperature of direct reduction.

For better understanding the calculation procedures for “Direct reduction-Melting” process, an example (Point N in Figure 5) is given below. For Point N, the parameters include, (1) direct reduction temperature is 1200°C (1473 K), (2) Air is pre-heated at 450°C (723 K), the heat for pre-heating comes from the hot CO gas from melting, (3) and no oxygen-enriched. The calculations of carbon rate in direct reduction and in melting are listed in Tables 3 and 43 and 4, respectively.

Table 3. Carbon rate in direct reduction
 ItemΔH
Reduction compartment0.5Fe2O3 + 1.5C = Fe + 1.5COΔH18 = 2 44 865 J
1 mol Fe is heated from 298 to 1473 KΔH19 = 42 796 J
Oxidation compartment1.5CO + 0.75O2 = 1.5CO2 (1.5 mol CO comes from reduction compartment)ΔH20 = −4 24 470 J
0.75 mol O2 liberates heat from 723 to 298 KΔH21 = −9982 J
3 mol N2 liberates heat from 723 to 298 KΔH22 = −38 307 J
1.5 mol CO2 is heated from 298 to 1473 KΔH23 = 88 478 J
3 mol N2 is heated from 298 to 1473 KΔH24 = 1 11 546 J
ΔHReq.3 = ΔH18 + ΔH19 + ΔH20 + ΔH21 + ΔH22 + ΔH23 + ΔH24 = 14 926 J
C + O2 = CO2ΔH25 = 393 510 JΔHSup.3 = ΔH25 + ΔH26 + ΔH27–ΔH28–ΔH29 = 250182 J (Heat supply by complete combustion of 1 mol carbon: C + O2 = CO2)
1 mol O2 liberates heat from 723 to 298 KΔH26 = 13309 J
4 mol N2 liberates heat from 723 to 298 KΔH27 = 51076 J
1 mol CO2 is heated from 298 to 1473 KΔH28 = 58985 J
4 mol N2 is heated from 298 to 1473 KΔH29 = 148728 J
So. C (As fuel) = ΔHReq.3HSup.3 = 0.06 mol
C (In DR) = C (As reductant in reduction compartment) + C (As fuel in oxidation compartment) = 1.5 + 0.06 = 1.56 mol C mol Fe−1
Table 4. Carbon rate in melting
ItemΔH
1 mol Fe is heated from 1473 to 1823 KΔHReq.4 = 28195 J
C + 0.5O2 = COΔH30 = 110530 JΔHSup.4 = ΔH30 − ΔH31 = 60705 J (heat supply by incomplete combustion of 1 mol carbon: C + 0.5O2 = CO)
1 mol CO is heated from 298 to 1823 KΔH31 = 49825 J
C (in melting) = ΔHReq.4HSup.4 = 0.46 mol
Therefore, the total adiabatic carbon rate for Point N = C (in DR) + C (in melting) = 1.56 + 0.46 = 2.02 molC mol Fe−1 (433 kg tHM−1).

From Tables 3 and 43 and 4, the calculated total adiabatic carbon rate of “Direct reduction-Melting” process is the sum of that used as reductant and that used as fuel. So the carbon rate is a function of direct reduction temperature, air pre-heated, and oxygen-enriched. The calculations about carbon rate at different conditions are similar with Point N, and are shown in Figures 4 and 54 and 5.

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Figure 4. Carbon rate of direct reduction process.

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Figure 5. Carbon rate of “Direct reduction-Melting” process with oxygen-enriched or pre-heating air.

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In Figure 4, the carbon rate of direct reduction (not include melting, similar with Table 3) is plotted in a wide range of direct reduction temperature (800–1400°C). In the figure, when the temperature is lower, the carbon rate is a constant and it is the stoichiometric value of 1.5 mol C mol−1 Fe (321 kg tHM−1). The reason is that the amount of carbon as reductant is “1.5 mol C mol Fe−1” and generates 1.5 mol CO. The heat liberated from the post combustion of this 1.5 mol CO (to CO2) exceed the amount of heat required in “reduction compartment”. Therefore, no additional carbon as fuel is required for direct reduction, and the carbon rate in direct reduction process keeps at a constant, that is “1.5 mol C mol Fe−1” or “321 kg tHM−1”. But at higher process temperature, the heat generated from post combustion of CO from “reduction comparment” is not sufficient for heat required in “reduction comparment”, additional post combustion of carbon as fuel is required to supply heat to “reduction comparment” and result that the carbon rate increases with the increase of direct reduction temperature.

The total adiabatic carbon rate for liquid iron production at different conditions is shown in Figure 5 (include direct reduction and melting, similar with Table 4). In case of hot charging DRI to melting converter at 1550°C, when the carbon rate of direct reduction is constant (Figure 4), higher temperature of DRI will result lower work load in melting process. That is why, the total adiabatic carbon rate firstly decreases in Figure 5. Same as before, when the temperature of direct reduction is higher, the heat generated from post combustion of CO is not sufficient for heat required in direct reduction, additional carbon as fuel is needed and result that the total carbon rate increases with the increase of direct reduction temperature (more carbon is required in direct reduction process, more air is required, more heat is required to heat N2 to high temperature, and more energy is wasted).

Both oxygen-enriched and pre-heating air are optimized methods to decrease carbon rate. So the carbon rate of “Direct reduction-Melting” process with oxygen-enriched (left section) and pre-heating air (right section) is plotted in Figure 5. The two top curves in each section are standard and consequent result of the curve in Figure 4 (no oxygen-enriched and no pre-heating). The hot gas (1550°C) from melting converter may be used as the source of pre-heating. From the figure, one can conclude that the oxygen-enriched and pre-heating air can effectively decrease the carbon rate. The total adiabatic carbon rate of “Direct reduction-Melting” process may be lower than 440 kg tHM−1. If both of these two optimized methods are simultaneously taken in direct reduction, the total carbon rate may be further decreased to lower than 400 kg tHM−1.

3.3 Comparison between these two Alternative Ironmaking Processes

The basics of these two routes of hot metal production along idealized conditions, both starting with hematite and carbon at ambient temperature to liquid iron at 1550°C, are summarized in Figures 3 and 53 and 5. Point M in Figure 3 and Point N in Figure 5 are close to the best possible conditions in each case. The operational parameters for Point M and Point N are listed in Table 5. From the table, the difference in total carbon rate based on “Pre-reduction-Smelting reduction” (Point M) and “Direct reduction-Melting” (Point N) is about 145 kg tHM−1. The mass balance and heat balance of these two selected alternative ironmaking processes are listed respectively in Tables 6 and 76 and 7. From the tables, one can conclude that the difference of carbon rate between these two routes is due to the efficient utilization of the element carbon.

Table 5. Operational parameters of Point M and Point N (the best possible conditions in each case)
Pre-reduction-Smelting reduction (Point M)Direct reduction-Melting (Point N)
Carbon rate578 kg tHM−1Carbon rate433 kg tHM−1
Degree of pre-reduction49%Temperature of direct reduction1200°C
Feed to smelting vessel76% FeO + 24% FeO2 content in air20%
Exit gas from smelting vessel90% CO + 10%CO2Pre-heating air450°C
Table 6. Heat and mass balance of selected “Pre-reduction-Smelting reduction” process (Point M)
InputOutput
ItemsT [°C]molΔH [kJ]ItemsT [°C]molΔH [kJ]
FeO8000.76−32.95Fe1550170.99
Fe8000.24−6.41CO15502.43121.08
C (reductant)250.680CO215500.2721.48
C (fuel)252.020    
O2251.110    
2.02C + 1.11O2 = 1.82CO + 0.2CO2−280.430.76FeO + 0.68C = 0.76Fe + 0.62CO + 0.07CO2106.01
Total  −319.79Total  319.56
Table 7. Heat and mass balance of selected “Direct reduction-Melting” process (Point N)
InputOutput
ItemsT [°C]molΔH [kJ]ItemsT [°C]molΔH [kJ]
  1. DR, direct reduction.

Fe2O3250.50Fe1550170.99
C (reductant)251.50CO212001.5692.01
C (fuel in DR)250.060N212003.24120.47
O2 (DR)4500.81−10.78CO15500.4622.92
N2 (DR)4503.24−41.37    
C (melting)250.460    
O2 (melting)250.230    
1.5CO + 0.75O2 = 1.5CO2 (DR)−424.470.5Fe2O3 + 1.5C = Fe + 1.5CO244.86
0.06C + 0.06O2 = 0.06CO2 (DR)−23.61    
0.46C + 0.23O2 = 0.46CO (melting)−50.84    
Total  −551.07Total  551.25

The net heat available by incomplete combustion of C to CO is much lower than its complete combustion to CO2 (the heat liberation of C + 0.5O2 = CO and C + O2 = CO2 is 110.53 and 393.51 kJ mol−1, respectively). This is the main reason for high carbon rate in “Pre-reduction-Smelting reduction” process (Table 6). In all pilot and demonstration plants of smelting reduction process, the reported coal rates are significantly higher than 650 kg tHM−1. By the fundamental analysis of smelting reduction in present work, there is no reason to expect any pleasant surprise in the effort to further lower its total carbon rate than what has been reported.

For “Direct reduction-Melting”, the reduction of iron ore is completed in “reduction compartment”, and the complete combustion of CO could be 100% (of cause, nascent metallic iron should be avoid to be re-oxidized). That is why the total carbon rate of direct reduction is lower (Table 7).

It must be pointed out that there are two key points in the development of a viable direct reduction process of lower carbon rate. (1) The challenge of the process is in the efficient heat transfer from “oxidation compartment” (where it is generated) to “reduction compartment” (where it is consumed by the endothermic reaction and sensible heat of substances). (2) The prevention of re-oxidation of nascent metallic iron by gaseous oxidants generated in “oxidation compartment” should be considered as one of the important tasks. PSH furnace is a considerable innovative direct reduction process to realize the perfect heat transfer and prevention of re-oxidation of DRI. There is not data available on PSH process yet at commercial level, but a project on it is in planning by the Northeastern University, China and its partners. Also, some detailed information about PSH can be viewed in some literatures.[17, 18]

4 Conclusions

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

Aimed for producing liquid iron from iron ore and coal, by analyzing the total adiabatic carbon rate of representative alternative ironmaking processes, the main findings could be summarized as follows:

  1. The total carbon rate of “Pre-reduction-Smelting reduction” process depends on degree of pre-reduction and exit gas composition from smelting vessel. The incomplete post combustion of carbon and contradictive requirements for carbon between pre-reduction and smelting reduction contribute to the limitations of process, and keep the total carbon rate at a higher level.
  2. The total carbon rate of “Direct reduction-Melting” process depends on the temperature of direct reduction and some optimized methods, such as oxygen-enriched and pre-heating air etc. The complete post combustion of carbon could be 100% in “oxidation compartment” if the nascent metallic iron can be effectively protected from re-oxidation. The chemical energy of carbon is first used as reducing agent in “reduction compartment”, and then the thermal energy of carbon is used as heat source in “oxidation compartment”. Therefore, all energy of carbon may be effectively used in the process, and the total carbon rate is lower.
  3. Under the idealized conditions, the total adiabatic carbon rate along “Direct reduction-Melting” process is approximately 145 kg tHM−1 lower than that along “Pre-reduction-Smelting reduction” process. Therefore, direct reduction would likely lead to an alternative ironmaking process with much lower carbon rate, and it should be reasonable and successfully developed.

Acknowledgements

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References

The authors wish to acknowledge the contributions of associates and colleagues in Northeastern University, China and McMaster University, Canada. Also, the financial support of Department of Liaoning Science and Technology (NSFLN: 2011010429-401) and Tangshan Outstanding Science and Technology Co. Ltd are very much appreciated.

References

  1. Top of page
  2. Abstract
  3. 1 Introduction
  4. 2 Goal of Present Work
  5. 3 Carbon Rate of Alternative Ironmaking Processes
  6. 4 Conclusions
  7. Acknowledgements
  8. References