Theoretical Minimum Energies 

To Produce Steel 

for Selected Conditions 

March 2000

R.J. Fruehan 

O. Fortini 

H.W. Paxton 

R. Brindle 

Prepared under contract to 

Energetics, Inc. 

Columbia, MD 

For the 

U.S. Department of Energy 

Office of Industrial Technologies 

Washington., DC 

Carnegie Mellon University 

Pittsburgh, PA 

THEORETICAL MINIMUM ENERGIES TO PRODUCE STEEL 

FOR SELECTED CONDITIONS 

R. J. Fruehan 

O. Fortini 

H.W. Paxton 

R. Brindle 

Carnegie Mellon University 

Pittsburgh, PA 

May 2000 

Prepared under contract to 

Energetics, Inc. 

Columbia, MD 

for the 

U.S. Department of Energy 

Office of Industrial Technologies 

Washington, DC 

DISCLAIMER 

This report was prepared as an account of work sponsored by an agency of the United States 

Government. Neither the United States Government nor any agency thereof, nor any of their 

employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility 

for the accuracy, completeness, or usefulness of any information, apparatus, product, or process 

disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any 

specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise 

does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United 

States Government or any agency thereof. The views and opinions of authors expressed herein do not 

necessarily state or reflect those of the United States Government or any agency thereof. 
TABLE OF CONTENTS 

EXECUTIVE SUMMARY ..................................................... iii

1. INTRODUCTION .......................................................... 1

2. BASIC ASSUMPTIONS AND CASES CONSIDERED ........................... 1

3. METHODOLOGY .......................................................... 2

4. ABSOLUTE THEORETICAL MINIMUM ENERGY VALUES .................... 3

5. CASES APPROACHING ACTUAL CONDITIONS .............................. 4

6. PRODUCTION OF STAINLESS STEEL ....................................... 9

7. ROLLING ............................................................... 11

8. EFFECT OF YIELD LOSSES ON ENERGY ................................... 13

9. OTHER MAJOR ENERGY-CONSUMING ACTIVITIES ........................ 15

10. TOTAL THEORETICAL MINIMUM ENERGY TO PRODUCE STEEL ........... 16

11. SPECIAL CONSIDERATIONS ............................................. 16

12. COMPARISON OF TYPICAL ACTUAL AND 

THEORETICAL MINIMUM ENERGY ................................... 19

13. SUMMARY AND CONCLUSIONS ......................................... 20

REFERENCES .............................................................. 23

APPENDIX A: THEORETICAL CO2 EMISSIONS FROM 

STEELMAKING PROCESSES .......................................... 25

Theoretical Minimum Energies to Produce Steel for Selected Conditions i 
ii Theoretical Minimum Energies to Produce Steel for Selected Conditions 
-- -- --

EXECUTIVE SUMMARY 

The energy used to produce liquid steel in today’s integrated and electric arc furnace (EAF) 

facilities is significantly higher than the theoretical minimum energy requirements. This study presents the 

absolute minimum energy required to produce steel from ore and mixtures of scrap and scrap 

alternatives. Additional cases in which the assumptions are changed to more closely approximate actual 

operating conditions are also analyzed. The results, summarized in Table E-1, should give insight into 

the theoretical and practical potentials for reducing steelmaking energy requirements. The energy values 

have also been converted to carbon dioxide (CO2) emissions in order to indicate the potential for 

reduction in emissions of this greenhouse gas (Table E-2). 

The study showed that increasing scrap melting has the largest impact on energy consumption. 

However, scrap should be viewed as having "invested" energy since at one time it was produced by 

reducing ore. Increasing scrap melting in the BOF may or may not decrease energy if the "invested" 

energy in scrap is considered. 

Table E-1. Comparison of Theoretical Minimum Energy 

and Actual Energy Requirements for Selected Processes 

Process 

Energy (GJ/metric ton product) 

Actual 

Requirements 

[106 Btu/ton] 

Absolute 

Minimum 

[106 Btu/ton] 

% 

Difference 

Practical 

Minimum 

[106 Btu/ton] 

% 

Difference 

Liquid Hot 

Metal (5%C) 

13 - 14 

[11.2 - 12.1] 

9.8 

[8.5] 

25 - 30 10.4 

[9.0] 

20 - 26 

Liquid Steel 

(BOF) 

10.5 - 11.5 

[9.1 - 9.9] 

7.9 

[6.8] 

25 - 31 8.2 

[7.1] 

22 - 29 

Liquid Steel 

(EAF) 

2.1 - 2.4 

[1.8 - 2.1] 

1.3 

[1.1] 

38 - 46 1.6 

[1.4] 

24 - 33 

Hot Rolling Flat 2.0 - 2.4 

[1.7 - 2.1] 

0.03 

[0.03] 

99 0.9 

[0.8] 

55 - 63 

Cold Rolling 

Flat 

1.0 - 1.4 

[0.9 - 1.2] 

0.02 

[0.02] 

98 - 99 0.02 

[0.02] 

98 - 99 

18-8 Stainless 

Melting 

1.2 

[1.0] 

1.5 

[1.3] 

Notes: Actual includes yield losses and is the average of state-of-art and less-efficient operations for the United 

States, Japan, and Europe. All of the values exclude electrical generation and transmission losses.

BOF energy is primarily from hot metal; actual process consumes 0.2 to 0.4 GJ/t and, if CO is oxidized to

CO2, could theoretically produce 0.5 GJ.

For 18-8 stainless no estimates are available, in particular for HCFeCr.

In all cases, full credit is taken for the energy in off gas.

Theoretical Minimum Energies to Produce Steel for Selected Conditions iii 
-- --

Table E-2. Comparison of Theoretical Minimum 

and Actual CO2 Emissions for Selected Processes 

Process 

CO2 Emissions (kg/metric ton product) 

Actual 

Emissions 

[lbs/ton] 

Absolute 

Minimum 

[lbs/ton] 

% 

Difference 

Practical 

Minimum 

[lbs/ton] 

% 

Difference 

Liquid Hot 

Metal 

1,447 - 1,559 

[2,894 - 3,118] 

1,091 

[2,182] 

25 - 30 1,158 

[2,316] 

20 - 26 

Liquid Steel 

(BOF) 

189 - 207 

[378 - 414] 

144 

[288] 

24 - 30 144 

[288] 

24 - 30 

Liquid Steel 

(EAF) 

364 - 416 

[728 - 832] 

225 

[450] 

38 - 46 

[76 - 92] 

277 

[554] 

24 - 33 

Hot Rolling 110 - 132 

[220 - 264] 

2 

[4] 

98 

[196] 

50 

[100] 55 - 62 

Cold Rolling 173 - 243 

[346 - 486] 

4 

[8] 

98 

[196] 

4 

[8] 98 

18-8 Stainless 

Melting 

– 208 

[416] 

260 

[520] 

Note: Based on theoretical minimum energy consumption shown in Table E-1. 

Other conclusions that can be drawn from the findings are as follows: 

• Elimination of ore agglomeration and cokemaking, which are not theoretically necessary to 

produce steel, would yield significant energy savings. 

• Effective utilization of the energy contained in the off gases from the blast furnace, coke plant, 

and direction reduction process is essential. 

• The best scrap substitute with respect to energy usage is liquid pig iron or hot metal. 

• Gangue and ash in ore and coal increase minimum ironmaking energy by about 6%. 

• In BOF steelmaking, the energy to produce steel is less than the energy to produce iron 

because scrap is melted in the process. 

• Dirt in scrap and air entrainment in an EAF increase the energy required by about 25%. 

• When carbon is used in the EAF, about 38% of the CO must be post combusted to CO2 to 

equal electrical energy, even taking into account the production and transmission losses 

associated with electrical energy. 

• The melting energy for stainless steel is similar to the melting energy for carbon steel, but is 

much greater if the energy associated with ferrochrome is included. 

• Direct charging of slabs or billets reduces total rolling energy by about 80%. 

iv Theoretical Minimum Energies to Produce Steel for Selected Conditions 
1. INTRODUCTION 

The absolute theoretical minimum energies to produce liquid steel from idealized scrap (100% 

Fe) and ore (100% Fe2O3) are much lower than consumed in practice, as are the theoretical minimum 

energies to roll the steel into its final shape. This study presents the absolute minimum energy 

required to produce steel from ore and mixtures of scrap and scrap alternatives, clearly 

defining the necessary assumptions involved. The energy calculations are then repeated for a 

series of cases in which the assumptions are changed one by one to more closely approximate 

the actual conditions. 

The results should give insight as to what is theoretically and practically possible in terms of 

reducing the energy required to produce steel and will also indicate what factors cause significant 

increases in energy consumption. The theoretical minimum energies will be compared to typical actual 

energy consumptions to determine the potential energy savings for each process. In addition, the 

theoretical minimum energies will be converted to CO2 emissions (detailed in Appendix A), using 

assumptions as to the type of energy used and national averages for CO2 for the type of energy used. 

It is not the objective of this study to 

examine actual energy consumptions or CO2 

emissions. However, it is useful to compare 

approximate industry averages to the minimums 

to see what the potential energy savings are for 

each process. These comparisons also indicate 

the relative energy intensities of the different 

steelmaking processes. Particular attention is 

given to ironmaking, which consumes 70-80% of 

the energy in integrated steel production, and the 

electric furnace, which consumes the largest 

portion of the overall energy in scrap-based 

production. 

Objectives 

• Compute the theoretical energy required in 

the major steelmaking processes for a 

number of conditions 

• Compare the theoretical minimum energies to 

typical actual energy consumptions to 

determine the energy saving potential for 

each process considered 

• Convert the theoretical minimum energies to 

CO2 emissions using the national averages 

for the type of energy used in the process 

2. BASIC ASSUMPTIONS AND CASES CONSIDERED 

The calculations performed are theoretical; the basic assumptions are given on the next page. 

The baseline calculations are the absolute minimum energy to produce liquid iron from pure ore and 

scrap. The theoretical minimum energy is then computed for a series of cases, including 

• blast furnace ironmaking, 

• direct reduction, 

• oxygen steelmaking, and 

• electric arc furnace (EAF) steelmaking. 

Also calculated is the energy required for production of hot and cold rolled sheet from conventional 

slab casters (254 mm or 10 inch) and thin slabs (50 mm or 1.97 inch) and for the production of bars 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 1 
(25.4 mm, or 1 inch) from a billet (10.16 mm sq, or 4 inch sq). A number of specific issues are also 

addressed, including the energy and CO2 emissions for calcining limestone, using carbon in EAF, the 

effect of yield losses, and the effect of air entrainment in the EAF. 

Assumptions Used in the Calculations 

• Only energy directly used in the process is considered. 

• Energy to produce materials such as alloys, oxygen, refractories, and electrodes is excluded. 

• Energy loss in producing and transmitting electrical energy is excluded in initial energy calculations. It 

is considered for CO2 emissions. 

• Energy and heat losses are excluded. For example, heat losses from furnaces and energy losses from 

mechanical and electrical equipment are not considered. 

• Energy credits are allowed but noted. For example, the chemical and thermal energy in the off gas from 

the blast furnace is credited to the process. 

• Energy used in ore agglomeration and cokemaking are excluded; these are treated separately. 

• Energy loss due to yield loss is not considered in the theoretical minimum calculations. However, the 

minimum energy loss resulting from yield losses is discussed in Section 8. 

3. METHODOLOGY 

Several different types of energy were considered in the calculations of theoretical minimum 

energy requirements, including 

• sensible or heating energy, 

• melting and phase transformation energy, 

• heats of reactions, and 

• heats of solution. 

The required thermodynamic data was taken from several sources.(1-6) Computer programs 

were developed that incorporated the energy and materials balance for the process being considered. 

The accuracy of the calculation depends on the accuracy of the data used. In general, the uncertainties 

of the calculated energies is 1 to 3%. 

Sensible or Heating Energy 

In all cases considered, input materials such as ore, carbon, oxygen, and scrap must be heated. 

The heat DH is given by: 

T2 

DH = CpdT �T1 

Cp = Heat capacity which is a function of temperature 

T1, T2 = the initial and final temperatures 

2 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Melting and Phase Transformation 

The energies associated with materials melted in the process or going through phase transformations are 

included. 

Heats of Reactions 

Chemical reactions either require energy (endothermic) or give off energy (exothermic). An 

example of an endothermic reaction is the dissociation or reduction by carbon of FeO: 

FeO = Fe + 1/2 O2 

FeO + C = Fe + CO 

Examples of exothermic reactions are the oxidation of carbon to CO or CO2 and of iron: 

C + 1/2 O2 = CO

C + O2 = CO2

Fe + 1/2 O2 = FeO

Heats of Solution 

When two or more components go into solution, heat can be given off or absorbed. These 

heats compared to the other types considered are usually small. Examples include the heat of mixing of 

CaO and SiO 2 and of Fe and carbon. 

4. ABSOLUTE THEORETICAL MINIMUM ENERGY VALUES 

The absolute theoretical minimum energy values for ore reduction and scrap melting are shown 

in Table 1 and discussed below. 

Ore Reduction 

The theoretical minimum energy to produce steel from ore was computed by assuming ore is 

pure Fe2O3 and is reduced at 298 K, with the resulting iron heated to its melting point and melted. Iron 

goes through a number of phase changes whose energies are included. For the theoretical minimum, no 

super heat is required and the product is cast into its final shape without finishing. For this case the 

energy is 8620 MJ/tonne. For moderate super heat to 1873 K the energy is 8673 MJ/tonne. 

Scrap Melting 

The theoretical minimum in this case is simply heated and melted. The energy is 1,274 

MJ/tonne. For super heating to 1873 K the energy increases to 1327 MJ/tonne. As in the previous 

case, it is assumed the product is cast into its final shape. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 3 
Table 1. Absolute Theoretical Minimum Energy to Produce Steel 

from Pure Ore (Fe 2O3) and Pure Scrap (Fe) 

Raw Material 

Absolute Theoretical Minimum Energy 

as a Function of Tap Temperature 

(MJ/t) 

1813 K 1873 K 

Ore (Fe2O3) 8,620 8,673 

Scrap (Fe) 1,274 1,327 

5. CASES APPROACHING ACTUAL CONDITIONS 

Blast Furnace Ironmaking 

Blast furnace ironmaking or any ironmaking process requires more energy and releases more 

CO2 than any other process to produce steel. The reduction of Fe2O3 to Fe is by far the most energyintensive step. The theoretical energy requirements to produce liquid hot metal for selected conditions 

along are presented below, with the specific assumptions. Liquid hot metal or pig iron is defined as iron 

containing 4% to 5% carbon. Full credit is given for the energy in the off gas. The ironmaking results 

are summarized in Table 2. 

Ironmaking Case I - Absolute minimum. The iron blast furnace does not produce pure iron 

but rather iron nearly saturated with carbon (typically about 5% C). The tap temperature is usually 

about 1723 K (1450°C). In this case the energy associated with the carbon is significant and there is a 

small positive heat of solution. The energy required to produce hot metal for this case is 9,805 MJ. 

For a tap temperature of 1773 K the energy increases to 9,918 MJ. The energy of carbon associated 

with the product (50 kg/t) at this point does not release any CO2; the CO2 is released during 

steelmaking. Also, the small heat of solution is given back during steelmaking as the carbon is burned. 

Ironmaking Case II - Effect of slag resulting from gangue in ore. Ore is not pure Fe2O3 

but contains gangue or impurities, primarily SiO 2 and Al2O3. An ore with 6% gangue and an assumed 

consumption of 4% SiO 2, 1% MnO, and 1% Al2O3 was considered. To form a blast furnace slag, lime 

(CaO) is added. A typical slag will have a basicity (B) of 1.2, where B is defined as 

B = 

(%CaO) 

(%SiO2 ) 

4 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
--

--

--

--

Table 2. Minimum Energies to Produce Liquid Hot Metal at 1723 K 

(1450°C or 2642°F) for Selected Conditions 

Metal Composition Gangue Ash 

Energy 

(MJ/t HM) 

Fe - 5%C No No 9,805 

Fe - 5%C Yes No 10,216 

Fe - 5%C - 0.5%Si - 0.5%Mn Yes No 10,268 

Fe - 5%C - 0.5%Si - 0.5%Mn Yes Yes 10,421 

Notes: Gangue - 4% SiO2 - 1% Al2O3 - 1% MnO of ore 

Ash - 5% of 500 kg of coal and coke or 25 kg/t HM 

Slag Basicity �

�%CaO�

� 

= 1.2 Ł %SiO2 ł 

Energy credit for off gas approximately 5,400 - 5,600 MJ/t HM in each case 

In this case all the gangue is assumed to enter the slag. In the calculation, the energy to heat and 

melt the gangue and CaO are included. There is a significant negative heat of solution or heat release of 

the slag components. Because of the presence of gangue, the energy increases to 10,216 MJ per 

tonne of hot metal. 

Ironmaking Case III - Effect of slag and reduction of SiO2 and MnO in slag. During 

ironmaking some of the SiO 2 and MnO is reduced. A typical metal composition is as follows: 

Fe 94% 

C 5% 

Si 0.5% 

Mn 0.5% 

When the energy for slag formation and reduction of SiO 2 and MnO is included, the energy is 10,268 

MJ per tonne of hot metal for a tap temperature of 1773 K. 

Ironmaking Case IV - Effect of coke ash. Coke and injected coal contain ash. For this case 

500 kg of coke plus coal per tonne of hot metal is assumed, with an average ash content of 5% (the ash 

is assumed to contain 4% SiO 2 , 1% Al2O3, and 1% MnO). The assumed 500 kg of coke plus 

coal/tonne hot metal is not the theoretical minimum but reflects typical actual values. The other 

conditions for slag and reduction are similar to Case III, and the energy increases to 10,421 MJ per 

tonne of hot metal. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 5 
Direct Reduction 

The production of direct reduced iron by a number of processes has increased dramatically in the 

past five years. For the purposes of this report direct reduction is defined as any process that converts 

ore into a solid product containing primarily metallic iron. The product will also contain gangue from the 

ore, along with reductant, carbon, and unreduced iron oxide (FeO). In most cases, natural gas (CH4) 

supplies the energy. Examples of such processes are Midrex, HyL, FINMET, CIRCORED, and Iron 

Carbide. 

The general assumptions for direct reduction are the same as for ironmaking in a blast furnace. The 

gangue is assumed to be entirely SiO 2. It is also assumed that the ore is heated to 900°C and reduced. 

Full credit for the energy in the off gas is taken. In these processes the off gas is usually recycled back 

into the process, and the chemical energy is used but some thermal energy is lost. 

As in the reduction of liquid hot metal, the simplest case is considered first and then realistic 

computations such as gangue in the ore and carbon in the product are added. All energy values given 

are per tonne of product. Some products require more energy when used to produce liquid steel in an 

EAF, which is discussed in a later section of this report. The results of the five cases considered are 

given in Table 3. 

Table 3. Minimum Energies to Produce Direct Reduced Iron at 1173 K 

(900°C or 1620°F) Reduction Temperature for Selected Conditions 

Ore Product 

Energy 

(MJ/tonne) 

Pure Fe2O3 Fe 8,360 

Fe2O3 - 1.4% SiO 2 Fe - 2% SiO 2 8,380 

Fe2O3 - 1.4% SiO 2 Fe - 2% SiO 2 - 8% FeO 7,900 

Fe2O3 - 1.5% SiO 2 Fe - 2% SiO 2 - 8% FeO - 2% C 8,427 

Fe2O3 - 1.5% SiO 2 Fe - 2% SiO 2 - 7.7% FeO - 6% C 9,432 

Note: Full credit is assumed for off gas 

It is important to note that the energy per tonne of iron is different in each case and the energy to 

melt the materials varies. Later in this section, the total energy to produce steel is given for a 50% 

scrap - 50% DRI charge. 

Oxygen Steelmaking 

Oxygen steelmaking (OSM) does not in itself consume energy but instead generates it. In the 

process, the carbon, silicon, and other elements in the hot metal are oxidized, producing energy 

6 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
--

--

primarily used to melt scrap. The energy can also be used to melt and smelt (reduce) waste oxide 

briquettes or smelt ore. The amounts of these oxide-containing materials that can be used are 

significantly less than scrap because of the energy required to reduce the iron oxides. In the United 

States scrap is almost exclusively used as a coolant and is included in this analysis. 

Table 4 lists the amounts of scrap that can be melted per tonne of hot metal of selected 

compositions. Also given is the amount of liquid steel produced and the energy per tonne of liquid 

steel, computed by dividing the energy required to produce the hot metal by the amount of steel 

produced. 

Table 4. Energy to Produce Steel from Hot Metal and Scrap for Selected Conditions 

Hot Metal Slag 

Tap Tp 

(K) 

Scrap 

(kg/t HM) 

Steel 

(kg/t HM) 

Energy 

(MJ/t steel) 

Fe - 5% C 1873 290 1,240 7,907 

Fe - 5% C 1923 244 1,194 8,212 

Fe - 5%C - 0.5% Si 

(coke ash) 

B=3 

30% FeO 

1873 401 1,328 7,853 

Fe - 5%C - 0.5%Si 

(coke ash) 

B=3 

30% FeO 

1923 353 1,278 8,154 

Fe - 5%C - 0.5% Si 

(coke ash) 

B=3 

20% FeO 

1873 389 1,320 7,894 

Fe - 5%C - 0.5%Si 

(coke ash) 

B=3 

20% FeO 

1923 341 1,270 8,205 

Note: The decrease in energy per tonne of steel for oxidizing Si and Fe is due to increased scrap melting. 

The calculations assume CO to be the off gas no post combustion. For 5% C in the hot metal the 

potential energy in the off gas ranges from 950 MJ/t (steel) to1,000 MJ/t if the CO is oxidized to CO2. 

The results in Table 4 indicate that less energy per tonne of steel is obtained when silicon is present 

in the hot metal and iron is oxidized. This is somewhat misleading because the reduced energy per 

tonne of steel is from melting scrap using the additional energy from the oxidation of Si and Fe. Since it 

takes considerably more energy to produce hot metal from ore than to melt scrap, the energy per tonne 

of steel produced is reduced when melting more scrap in OSM. This important fact can be illustrated 

by considering a case in which the additional scrap melted by oxidizing Si and Fe was simply melted in 

another process. For the case when there is no silicon of iron oxidized to the slag, 290 kg of scrap is 

melted and the energy per tonne of steel is 7,907 MJ while for 30% FeO and 0.5% Si, 401 kg of scrap 

is melted and the energy is 7,853 MJ per tonne of steel. If the additional 111 kg of scrap was simply 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 7 
--

melted separately, it would require 146 MJ. This reduces the average energy per tonne of steel to 

7,200 MJ for no FeO or SiO 2 in the slag if the additional 111 kg of scrap was simply melted. 

Electric Furnace Steelmaking with Scrap 

A number of cases were considered for scrap and scrap alternative melting in an EAF. The results 

for 100% scrap melting are summarized in Table 5. The energy loss in producing electricity or the 

energy required to process the scrap is not considered. Only the energy consumed in the process is 

included, not the energy to produce other materials, such as electrodes and refractories. 

Table 5. Theoretical Minimum Energies to Produce Steel from Scrap for 

Selected Conditions, Tap Temperature 1873 K (1600°C or 2912°F) 

Scrap Slag 

Energy 

(MJ/t) 

Fe 1,327 

Fe - 0.1%C - 0.2%Si 

B = 2.5 

%FeO = 25% 1,289 

Fe - 0.1%C - 0.2%Si 

1% dirt 

B = 2.5 

%FeO = 25% 

1,352 

Fe - 0.1%C - 0.2% Si 

1% dirt 

B = 2.5 

%FeO = 35% 

1,325 

Fe - 0.1%C - 0.2%Si 

1% dirt 

100 Nm3 air entrainment 

B = 2.5 

%FeO = 25% 

1,577 

Note: The decrease in melting energy with FeO in slag is due to oxidation of Fe 

EAF Case I - Absolute Minimum to Melt Iron. The absolute minimum energy is 1,327 MJ/t, 

the amount of energy required to heat and melt scrap and super heat the metal to 1873 K. 

EAF Case II - Scrap Containing 0.1%C - 0.2%Si. In this case, it is assumed that the carbon 

remains in the steel and the silicon is oxidized to SiO 2. Flux (CaO) is also heated and melted, yielding a 

slag with a basicity of 2.5 and 25% FeO. The energy requirement is 1,289 MJ/t. The reduction in 

energy from Case I is due to the oxidation of Si and Fe to the slag, which results in a yield loss of 0.6%. 

EAF Case III - Scrap Containing 0.1%C - 0.2%Si + 1.0% (10 kg) "Dirt." Scrap also has 

other materials with it such as water, soil or dirt, and oil. Based on the final slag formed, considerable 

amounts of materials containing SiO 2 and Al2O3 (e.g., dirt) enter the furnace. 

8 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
--

For 10 kg per tonne of scrap of SiO 2 plus Al2O3 and maintaining a slag basicity of 2.5, the energy 

required is increased to 1,352 MJ/t, with a yield loss to the slag of 2.5% 

EAF Case IV - Air Entrainment. During EAF steelmaking large quantities of air can be 

entrained into the furnace through the furnace door and other openings. It is estimated that 100 

nm3/tonne of air can be entrained. If the N2 leaves at 1473 K or 1873 K, the heat associated is 165 

MJ and 225 MJ, respectively, increasing the energy from Case III to 1,517 MJ and 1,577 MJ/t, 

respectively. 

Electric Furnace Steelmaking with DRI and Scrap 

The energy required to produce steel with 50% scrap and 50% scrap substitute was calculated. 

The scrap was assumed to contain 0.2% Si and 10 kg dirt per tonne. There is no post combustion or 

air entrainment in the process. The slag is assumed to have basicity of 2.5 and 25% FeO. The energy 

required to produce steel (0.05%C) for several cases is given in Table 6. This table also shows the 

energy required to produce steel with solid and liquid pig iron as 50% of the charge. The total energy 

given in Table 6 includes the energy to produce the DRI (shown in Table 3). 

There are numerous other combinations of scrap and DRI and other assumptions with regards 

to slag and post combustion, which were covered in the AD Little report to AISI(7). 

6. PRODUCTION OF STAINLESS STEEL 

There are numerous grades of stainless steel produced in the United States. The most common is 

18-8 type stainless, which contains 18% Cr and 8% Ni. This analysis assumes the production of a 

generic 18-8 type stainless steel in an EAF-AOD (Argon Oxygen Decarburization) sequence, which 

accounts for over 90% of U.S. stainless steel production. 

In the EAF, a mixture of stainless steel scrap, steel scrap, high carbon ferrochrome (HCFeCr), and 

nickel are melted and the carbon content is reduced to about 1%. The metal is then transferred to an 

AOD vessel where a mixture of O2 - Ar or O2 - N2 gases oxidizes the carbon to its desired level. The 

AOD itself does not theoretically require energy and is therefore not considered. After the AOD, a 

reductant containing either silicon or aluminum is added to the slag to recover chromium, which is 

oxidized to slag. For the assumptions of the present study, this stage also need not be considered. 

A typical charge to the EAF per tonne of steel is as follows: 

Steel Scrap 350 kg 

Stainless Scrap -- 400 kg 

The carbon is combusted with oxygen down to 1.0%. The absolute minimum energy for melting 

the above charge is 1,213 MJ, which is less than melting Fe because of carbon oxidation. If the scrap 

contains 1% dirt and there is no air entrainment, the melting energy is 1,275 MJ/t. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 9 
--

--

--

Table 6. Theoretical Minimum Energies to Produce Liquid Steel at 1873 K (1600°C or 

2912°F) from 50% Scrap and 50% Scrap Substitute 

Scrap Substitute 

Melting Energy 

(MJ/t) 

Charge Energy 

(MJ/t) 

Total Energy 

(MJ/t) 

None (!00% Scrap Case) 1,289 1,289 

Fe - 2% SiO2 1,403 4,296 5,698 

Fe - 2%SiO 2 - 8%FeO 1,559 4,233 5,792 

Fe - 2%SiO2 - 8%FeO -2%C 1,483 4,565 6,048 

Fe - 2%SiO 2 - 7.7%FeO - 6%C 1,328 5,223 6,551 

Liquid Pig Iron 487 5,388 5,875 

Solid Pig Iron 1,145 5,388 6,533 

Notes: Liquid Pig (Hot Metal) charged at 1723 K, all others 298 K 

If air entrainment is included, it will add 238 MJ/t in each 

Slag has B = 2.5 and 25% FeO 

HCFeCr 250 kg 

Nickel 48 kg 

According to the initial assumptions and boundaries of the present calculations the energy to 

produce the high carbon ferrochrome is not included. The amount of alloys for carbon steel production 

is much smaller than it is for stainless steel. Since the energy in ferrochrome is so high, it is useful to 

estimate the theoretical minimum for its production. Only the very simplest case of the absolute 

minimum for the production of HCFeCr is considered. 

HCFeCr is produced from chromite ore whose composition depends on the specific mine 

location. The major component is FeCr2O4. For the absolute minimum, the ore is considered to be 

pure FeCr2O4 and the product 61% Cr - 33% Fe - 6% C. The absolute minimum energy is 11.7 

GJ/tonne of product. For the 250 kg used in the present example, the absolute minimum is 2,925 MJ 

per tonne of steel; the actual energy will be over 4,000 MJ. It should be noted that HCFeCr is not 

produced domestically and therefore no energy is used in the United States. If the minimum energy to 

produce ferrochrome is included, the total energy is increased to 3,200 MJ/tonne of 18-8 stainless 

steel. 

10 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
7. ROLLING 

There are two general types of rolling -- hot and cold. With hot rolling, the steel either is 

reheated or directly charged after casting. Reheating is the major energy consumer in the rolling 

process. For both hot and cold rolling, energy is also consumed in deformation, where the deformation 

energy (E) is given by 

E=sec 

where 

s = the yield stress 

e = strain or deformation 

c = a constant describing the shape of the stress strain curve, assumed to be an average of 0.7 

The strain is defined in terms of the initial and final dimensions, to and tf , respectively. 

e = ln to 

tf 

The yield strengths used in the following calculations were taken from the Making, Shaping 

and Treating of Steel.

(8) 

Cases included were hot and cold rolling for flat rolled carbon steel and 18-8 type stainless 

(starting from both normal slabs and thin slabs), as well as hot rolling of bars from billet. The effects of 

direct charging and billet splitting are also included in the analysis. 

For hot rolling, the deformation energy is low because the yield stress is low at high 

temperatures. For stainless steel, the yield stress is about three times higher than for carbon steel, while 

for bars it is slightly higher than for flat steel because the carbon content is generally higher. The energy 

used for heating is fossil fuel and for rolling electrical. Table 7 lists the minimum energies for rolling, 

assuming no energy or yield losses. 

The results in Table 7 indicate that reheating the slab or billet accounts for the vast majority of 

the rolling energy. If slabs of normal thickness are directly charged, as is the case for most thin slabs, 

the energy for rolling these slabs is similar to that for thin slabs. Strip casting a 2-mm strip does not 

significantly reduce the total energy if the normal slab is directly charged. The total energy for a thin 

slab with hot and cold rolling with direct charging is 33 MJ, compared to cold rolling a 2-mm strip to 1 

mm, which requires 17 MJ. 

During hot rolling the metal being processed cools and must be reheated or deformed at a 

lower temperature. These effects require more energy but are not considered. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 11 
--

--

--

--

--

--

--

--

Table 7. Theoretical Minimum Energies to Roll Steel for Selected Products and Conditions 

Bar Carbon (10 cm billet to 2 cm bar) 

a Slab temperature prior to rolling 

b Billet split into 4 pieces prior to rolling 

Rolling 

Type 

Rolling 

Temperature 

(K) 

Slab 

Temperature a 

(K) 

Reduction 

(mm) 

Energy 

(MJ/t) 

Heat 

Deformation Total 

Flat Carbon Slab (25.4 cm or 10 inch) 

Hot 1473 298 254 to 2 825 25 850 

Hot 1473 1173 254 to 2 270 25 295 

Hot 1473 1473 254 to 2 25 25 

Cold 298 298 2 to 1 17 17 

Flat Carbon Slab (5.0 cm or 1.97 inch) 

Hot 1473 298 50 to 2 825 16 841 

Hot 1473 1173 50 to 2 270 16 286 

Hot 1473 1473 50 to 2 15 16 

Cold 298 298 2 to 1 17 17 

Flat 18-8 Stainless Steel Slab (25.4 cm or 10 inch) 

Hot 1473 298 254 to 2 825 72 897 

Hot 1473 1173 254 to 2 271 72 342 

Hot 1473 1473 254 to 2 72 72 

Cold 298 298 2 to 1 51 51 

Hot 1473 298 10 sq to 2 sq 825 20 845 

Hot 1473 1473 10 sq to 2 sq 20 20 

Hot 1473 1173 10 sq to 2 sq 270 20 290 

Hotb 1473 1473 10 sq to 2 sq 11 11 

12 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
8. EFFECT OF YIELD LOSSES ON ENERGY 

The calculation of minimum energies assumed no process yield losses. However, yield losses 

occur in all processes, and their effect on energy depends on where the yield loss occurs and how much 

energy is "invested" in the iron or steel to that point. Some forms of yield loss have been taken into 

account and the energy reclaimed in the calculation. For example, in steelmaking Fe is oxidized to the 

slag, releasing energy that is used in the process. This energy release has been included in the 

steelmaking energy calculation. For oxygen steelmaking, this added energy increased the hot metal 

requirement and, therefore, the energy per tonne of steel. For scrap-based EAF, the "invested energy" 

in the scrap was not included. 

The following section addresses the impact of yield losses related to the various processes. In 

all cases, the energy invested in the product is assumed to be that for the most likely case for 

production. For example, for oxygen steelmaking the most likely case for production is the case for hot 

metal containing silicon. The most likely case for production in the EAF is assumed to include slag and 

air entrainment. A summary of the effect of yield loss on the minimum theoretical energy requirements 

to produce steel is summarized in Table 8. 

Ironmaking and Hot Metal Treatment 

Significant yield losses can occur during tapping, handling, and treatment of hot metal. In 

particular, iron is extracted with the slag during slag removal after hot metal desulfurization. Yield losses 

of 1% to 3% are typical; for a 1% yield loss of liquid pig iron the energy loss would be 104 MJ. If the 

iron is recovered from the slag and reused, only the sensible and melting energy (about 14 MJ) is lost. 

Steelmaking 

Yield losses in both oxygen steelmaking and EAF steelmaking can be significant. The highest 

yield loss is FeO to the slag, which can be 5% to 10%. This yield loss releases energy, which was 

considered, but more iron must be charged. Both of these effects were taken into account in the results 

given for OSM and the EAF. However, there is no energy charge for the increased scrap usage. 

Other yield losses can be vaporization of iron (which is oxidized to the dust), other iron losses to the 

dust, and losses during tapping and handling. 

Vaporization of iron consumes a considerable amount of energy in steelmaking. The energy is 

not recovered when the vaporized iron is oxidized in the off gas. For 1.0% iron vaporizing in the BOF 

and no energy recovery from iron oxidation, the energy loss is the energy invested in the steel (80 MJ) 

and the heat of vaporization (64 MJ), or a total of 144 MJ/t of steel. Typical losses by vaporization 

are about 0.5% to 1.0%. In the case of 1.0% iron vaporizing in the EAF, the invested energy in the 

steel is less (13 MJ) and the total energy loss is 77 MJ. 

The direct energy lost by vaporization, 64 MJ, can actually cause a larger decrease in energy 

for oxygen steelmaking. The energy loss will result in less scrap melting, which will cause a shift from 

scrap to hot metal. Since hot metal requires considerably more energy than melting scrap, the resulting 

increase in energy could be as high as 500 MJ. 

Iron is also lost to the dust by simple metal ejection. In this case, only the energy invested is 

lost. Again, the iron is oxidized in the off gas and little is recovered. For a 1.0% yield 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 13 
Table 8. Effect of Yield Loss on Minimum Theoretical Energies 

to Produce Steel for 1% Yield Loss 

Process Type of Loss Energy (MJ/t) 

Hot metal loss in pretreatment 

Hot metal loss to slag 

but recovered 14 

Hot metal loss in pretreatment 

Hot metal loss to slag 

not recovered 104 

Direct Reduction Fines lost 60 

Direct Reduction Fines recycled 6 

BOF Fe vaporized to dust 144 

EAF Fe vaporized to dust 102 

BOF Fe ejected to dust 80 

EAF Fe ejected to dust 16 

Hot rolling Fe lost but recovered 13 

Cold rolling Fe lost after reheating for 34 

Notes: Losses to slag in BOF and EAF were accounted for in the process. 

For rolling, if the metal is not recovered or oxidized, the energy invested in the steel is lost (about 

80 MJ for BOF and 16 MJ for EAF). 

The energy consumed by Fe vaporization reduces scrap melting, thus requiring more hot metal per 

tonne of steel. This could represent 500 MJ due to the higher energy associated with hot metal. 

loss by metal ejected, the energy loss is 80 MJ for OSM and 16 MJ for EAF steelmaking. The 

vaporization or loss of other metals, such as zinc, are possible but not considered. 

Direct Reduction 

Some material is lost as fines during the production of DRI/HBI. This material is often 

recovered and used to form briquettes or injected into an EAF, in which case there is no energy loss. 

However, if the material is lost or more likely recycled back into the direct reduction furnace, some 

energy is lost. Assuming the material does not reoxidize and is recycled into the process, the energy 

loss is 6.2 MJ/t for 1% material recycle. If the material is reoxidized, the energy loss per 1% is 84 

MJ/t. 

14 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Rolling 

One of the largest cost and energy consumers in rolling is yield loss. The yield loss is usually 

remelted, requiring about 13 MJ/t for a 1% loss of Fe. However, the yield loss often occurs later in the 

process when additional energy has been invested into the steel. For example, if the slab is reheated 

and hot rolled, the yield loss after cold rolling results in a 34 MJ/t loss. If the iron is oxidized or not 

recovered, the invested energy in the steel is lost. A 1% yield loss applied to the most likely production 

cases represents an additional loss of 80 MJ/t for BOF steel and 16 MJ/t for EAF steel. 

9. OTHER MAJOR ENERGY-CONSUMING ACTIVITIES 

Several significant sources of energy consumption were neglected in computing the theoretical 

minimum energies to produce steel for selected conditions. In some cases, estimates of the energy for 

these sources can be made while for others the conditions vary greatly and reasonable estimates are 

difficult. 

In theory, ore agglomeration and cokemaking are not necessary for integrated steel production 

and were not considered. However, these processes are virtually always part of actual integrated 

steelmaking. Ore agglomeration consists of taking ore fines or concentrate and sintering them into sinter 

or pellets. Cokemaking is achieved by heating coal under pressure, driving off volatiles and increasing 

the strength of the material. The theoretical minimum energies for these processes were determined by 

calculating the energy to heat idealized coal and ore to 1100°C and 1350°C, respectively. In 

cokemaking the heat of devolatilization is also required but is usually accounted for in computing the 

energy value of coal. The coke output was taken as 0.768 per tonne of the coal input. The volatiles 

represent the remainder, which is used as a fuel or for chemicals. The approximate minimum energies 

for these processes, along with typical actual consumptions, are given in Table 9. The actual energies 

are given as a range because the values vary according to the actual process and its efficiency. 

During cokemaking the volatiles are either used for producing chemicals with energy values and 

credits or as a fuel in the process itself. The process also produces a relatively rich off gas for which an 

energy credit is taken. The total credits are about 4.0 to 5.0 GJ/t steel or 11.8 to 14.5 GJ/t coke. The 

values given in Table 9 have taken into account all the energy credits. 

The actual and theoretical minimum energy requirements for ore agglomeration are reasonably 

close because of the simplicity of the process. For cokemaking the differences are greater because of 

process complications and yield losses. 

There are other energy-consuming process steps or materials used in steelmaking that were 

beyond the scope of this study. Often the energy consumption is very site-specific; the energy is 

consumed in another area or even country and depends on process details. These other steps include 

• mining of ore, coal, and limestone (integrated production), 

• scrap preparation (in scrap-based production), 

• transportation of materials to and within the plant, and 

• production of alloys, refractories, electrodes, special fluxes, and other materials 

consumed in steelmaking. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 15 
Table 9. Theoretical Minimum and Typical Energy Consumption 

in Cokemaking and Ore Agglomeration 

Process 

Theoretical Energy Actual Energy 

GJ/t (output) GJ/t (steel) GJ/t(output) GJ/t (steel) 

Cokemaking 2.0 0.8 5.4 - 6.2 2.2 - 2.6 

Ore Agglomeration 1.2 1.6 1.5 - 1.7 2.1 - 2.4 

Note: For cokemaking, full credit is taken for off gas and by-product energy, approximately 4-6 GJ. 

10. TOTAL THEORETICAL MINIMUM ENERGY TO PRODUCE STEEL 

It is difficult to adequately describe the total energy to produce final steel products because it 

depends on the process used (EAF or integrated), the raw or charge materials, and the conditions of 

rolling. Furthermore, the total does not give any insight as to where and how energy can be conserved. 

However, it is somewhat useful to compare process routes and theoretical to actual energy 

consumption requirements. 

Table 10 summarizes the total energy requirements for producing selected steel products for 

selected conditions. The most realistic minimum values are about 8,150 MJ/tonne for integrated 

production and 1,600 MJ/tonne for scrap-based production. Yield losses and other additional losses 

are not considered. 

11. SPECIAL CONSIDERATIONS 

This section discusses information regarding theoretical minimum energies that is beyond the 

primary scope of this report. Whereas the process primarily uses lime (CaO), the raw material is 

limestone (CaCO3). The conversion of limestone to lime requires energy and produces CO2. The 

impact of SiO 2 on gangue materials in the ore and coke on energy is followed through the process. 

The impact of post combustion and carbon in the BOF and EAF are also considered. 

Energy and CO2 in Producing CaO 

The major flux used in iron and steelmaking is CaO. CaO is obtained from limestone (CaCO3) 

by heating it and driving off the CO2 according to the following reaction: 

CaCO3 = CaO + CO2 

The reaction will only occur when the equilibrium pressure reaches one atmosphere. Therefore, the 

reactants must be heated to 1155 K and the energy of the reaction supplied. 

16 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Table 10. Total Theoretical Minimum Energies to Produce 

Selected Products for Selected Conditions 

Process Product Rolling Energy (MJ/t) 

BF-BOF 

(Conventional Slab) 

Hot Rolled Sheet Direct 

Reheat 

7,878 

8,703 

BF-BOF 

(Conventional Slab) 

Cold Rolled Sheet Direct 

Reheat 

7,895 

8,720 

EAF (Scrap) 

(Thin Slab) 

Hot Rolled Sheet Direct 

Reheat 

1,341 

2,166 

EAF Scrap 

(Thin Slab) 

Cold Rolled Sheet Direct 

Reheat 

1,358 

2,183 

EAF (50% DRI) 

(Thin Slab) 

Cold Rolled Sheet Direct 

Reheat 

6,081 

6,906 

EAF (Scrap) 

(Billet) 

Bar Direct 

Reheat 

1,345 

2,170 

EAF (50% DRI) 

Billet 

Bar Direct 

Reheat 

6,068 

6,893 

EAF-AOD 

Slab 

Cold Rolled 

18-8 Stainless 

Direct 

Reheat 

1,397 

2,223 

EAF-AOD-(HCFeCr) 

Slab 

Cold Rolled 

18-8 Stainless 

Direct 

Reheat 

4,323 

5,148 

Notes: Does not include ore preparation, cokemaking, or yield losses. 

Stainless for melting only and for production of required HCFeCr. 

Liquid steel energy:

BF-BOF 7853 MJ/t

EAF-scrap 1355 MJ/t

EAF-DRI 6048 MJ/t

EAF-AOD 1275 MJ/t

EAF-AOD-HCFeCr 4200 MJ/t

Theoretical Minimum Energies to Produce Steel for Selected Conditions 17 
To produce one tonne of CaO from CaCO3 requires a theoretical minimum energy of 4,670 

MJ. The product is CaO and CO2 at 1155 K. It is theoretically possible but highly impractical to 

utilize the heat contained in the CaO (1,471 MJ). In addition to the energy required, 0.79 tonnes of 

CO2 is released per tonne of CaO. 

Effect of SiO2 

Silica enters the steelmaking process primarily as gangue in the ore or coke ash. Silicon is also 

present in scrap. The silica requires energy in ironmaking and steelmaking because it must be heated 

and melted along with the appropriate amount of lime. The energy in ironmaking increases by about 

110 MJ for 1% extra silica in the gangue or ash. However, this SiO 2 requires CaO. Whereas the 

heating and melting is included in the 110 MJ, the production of the CaO is not for a slag basicity of1.2, 

which requires 12 kg CaO per 1% SiO 2. This requires an additional 5.5 MJ, and 0.008 tonnes of CO2 

is released from the limestone. 

Energy Credits in Off Gases 

Full energy credit was taken for the off gas for the processes of blast furnace ironmaking, 

cokemaking, and direct reduction. These credits are a large percentage of the total energy. This 

energy must be efficiently utilized for the processes to be energy-efficient. The off gases can be used in 

the process itself such as in blast furnace air preheating stoves, in reheating furnaces, or producing 

steam for electricity. For integrated steel production, including cokemaking, the total energy in off 

gases can be as high as 6-10 GJ per tonne of steel. Therefore, the efficient use of this energy is critical. 

Carbon in Steelmaking 

Carbon is usually used as a fuel in the EAF and is sometimes used to melt more scrap in a 

BOF. The carbon used in an EAF usually contains ash, which reduces its energy value by 5% to15%, 

depending on the amount. For these theoretical calculations the material is assumed to be pure carbon. 

The reaction product in the presence of carbon or iron is primarily CO. If the carbon is only oxidized 

to CO, it is much less efficient than using the same carbon to produce electrical energy. For the carbon 

to be as effective as electricity generation and transmission with an efficiency of 36% (which 

corresponds to 10 MJ/kWh), it must be post combusted (PC) to 37.6% with 100% of the energy 

going to the steel. The equation below represents the post-combustion percentage: 

CO PC= 2 (100) CO+ CO2 

These conditions are difficult to achieve in practice, and in the actual case the required PC 

would be higher because of the ash in the carbon. Therefore, using carbon does not reduce energy use 

in the EAF, even if the inefficiency of electric power production is considered. However, carbon 

oxidation does improve productivity and refining of the steel, which is its primary purpose. 

18 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Post Combustion 

In steelmaking processes, the equilibrium product for the oxidation of carbon is primarily CO, 

with less than 10% CO2. It has been recognized for decades that significant quantities of energy are 

available if the CO can be combusted to CO2 in such a way that the CO2 does not react with iron or 

carbon, and the energy can be transferred to the system. 

The post combustion reaction is 

CO + 1/2 O2 = CO2 

After accounting for the heating of the oxygen, the heat released at 1873 K is 255 KJ per mole 

of CO. For example, if 10% of the CO can be post combusted in OSM with 100% heat- transfer 

efficiency, the energy released is 106 MJ per tonne of hot metal. This energy can melt 80 kg of scrap 

per tonne of metal, which can significantly reduce the energy to produce steel because of the shift from 

ore to scrap. For OSM with a slag basicity of 3 and 30% FeO and a tap temperature of 1873 K, the 

energy per tonne of steel is reduced from 7,853 MJ to 7,401 MJ. The major reason for the energy 

savings is the use of more scrap. 

In the EAF, large amounts of charge carbon are initially oxidized to CO. About 16 MJ/t of 

energy is released for 10 kg carbon for each 10% post combustion to CO2 with 100% heat transfer. 

12. COMPARISON OF TYPICAL ACTUAL AND 

THEORETICAL MINIMUM ENERGY 

Table 11 shows the theoretical minimum energy for the most realistic case and the typical range 

of actual energy consumption for selected processes. The low value for the actual consumptions 

represents the lowest values for any country as reported by the International Iron and Steel Institute 

(IISI), not necessarily best practice.(9) For BOF steelmaking, the energies represent the energy of the 

hot metal; the steelmaking process itself does not consume significant energy. For hot rolling, the 

energy values represent a mixture of direct charging and reheating of conventional slabs. Most likely 

the majority of the slabs are reheated and the theoretical values include reheating. 

The results indicate that for ironmaking the absolute maximum energy savings available are 

about 20% to 25%. Similarly for EAF steelmaking, the absolute maximum savings are about 23% to 

33%. 

The potential energy savings for rolling are lower simply because the processes use less energy. 

Although it is not clear from Table 11, the potential for the greatest energy savings in finishing lies in 

direct charging of slabs and billets. This would require major equipment changes and improved clean 

steel practices in order to avoid inspection and grinding of slabs and billets. 

Table 8 showed the total energy in cokemaking and ore agglomeration to be about 5 GJ/t 

(steel). If an ironmaking process can be developed that uses coal and ore fines or concentrates, this 

energy could be eliminated. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 19 
--

Table 11. Practical Theoretical Minimum and Energy for Selected Processes 

Process 

Energy (GJ/t product) 

Absolute 

Minimum 

Practical 

Minimum 

Reported 

Consumption 

Liquid Hot Metal (5%C) 9.8 10.4 13 - 14 

Liquid Steel (BOF) 7.9 8.2 10.5 - 11.5 

Liquid Steel (EAF) 1.3 1.6 2.1 - 2.4 

Hot Rolling Flat 0.03 0.9 2.0 - 2.4 

Cold Rolling Flat 0.02 0.02 1.0 - 1.4 

18-8 Stainless Melting 1.2 1.5 

Notes: Actual includes yield losses and is the average of state-of-art and less-efficient operations for the United 

States, Japan, and Europe. 

BOF energy is primarily from hot metal; actual process consumes 0.2 to 0.4 GJ/t and, if CO is oxidized to 

CO2, could theoretically produce 0.5 GJ. 

For 18-8 stainless no estimates are available, in particular for HCFeCr 

In all cases, full credit is taken for the energy in off gas. 

13. SUMMARY AND CONCLUSIONS 

The theoretical minimum energies to produce several steel products for ore- and scrap-based 

processes were computed. In general, only the energy for the process itself was considered and not 

the energy used to produce input materials or electricity. The cases included ironmaking, direct 

reduction, oxygen steelmaking, scrap and scrap substitute, EAF steelmaking, production of 18-8 type 

stainless, and rolling of cast material to final shape. In addition, the effects of yield loss, gangue, and use 

of carbon post combustion (as well as other special cases) on energy consumption were estimated. 

Table 12 presents a comparison of the theoretical minimums to actual typical energy consumption 

values. Some additional findings are shown in the summary box. 

Increasing scrap melting has the largest impact on energy consumption. However, scrap should be 

viewed as having "invested" energy since at one time it was produced by reducing ore. Therefore, it 

should be used wisely. For example, oxidizing it to the slag may reduce energy in the process but the 

"invested" energy is lost. Also, increasing scrap melting in the BOF may or may not decrease energy if 

the "invested" energy in scrap is considered. Scrap supplies are not unlimited, and new iron from ore 

will always be required. 

20 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
-- -- --

Table 12. Comparison of Theoretical Minimum Energy 

and Actual Energy Requirements for Selected Processes 

Process 

Energy (GJ/t product) 

Actual Energy 

Requirements 

Absolute 

Minimum 

% 

Difference 

Practical 

Minimum 

% 

Difference 

Liquid Hot Metal 

(5%C) 

13 - 14 9.8 25 - 30 10.4 20 - 26 

Liquid Steel (BOF) 10.5 - 11.5 7.9 25 - 31 8.2 22 - 29 

Liquid Steel (EAF) 2.1 - 2.4 1.3 38 - 46 1.6 24 - 33 

Hot Rolling Flat 2.0 - 2.4 0.03 99 0.9 55 - 63 

Cold Rolling Flat 1.0 - 1.4 0.02 98 - 99 0.02 98 - 99 

18-8 Stainless 

Melting 

1.2 1.5 

Notes: Actual includes yield losses and is the average of state-of-art and less-efficient operations for the United 

States, Japan, and Europe. 

BOF energy is primarily from hot metal; actual process consumes 0.2 to 0.4 GJ/t and, if CO is oxidized to 

CO2, could theoretically produce 0.5 GJ. 

For 18-8 stainless no estimates are available, in particular for HCFeCr. 

In all cases, full credit is taken for the energy in off gas. 

Other conclusions that can be drawn from the findings are as follows: 

• Elimination of ore agglomeration and cokemaking, which are not theoretically necessary to produce 

steel, would yield significant energy savings. 

• Effective utilization of the energy contained in the off gases from the blast furnace, coke plant, and 

direction reduction process is essential. 

• The best scrap substitute with respect to energy usage is liquid pig iron or hot metal. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 21 
Additional Findings 

Effect of Gangue and Ash 

• Gangue and ash in ore and coal increase minimum energies by 0.6 GJ (about 6%) for ironmaking. 

Direct Reduction 

• Energy requirements for direct reduction per tonne of iron are similar to those for the blast furnace. 

Scrap in the BOF 

• In BOF (OSM) steelmaking, the energy to produce steel is less than the energy to produce iron 

because scrap is melted in the process. 

• Due to the "invested" energy in scrap any process that increases scrap melting lowers the total energy 

because of the substitution of scrap for ore. 

Variables in the EAF 

• Dirt in scrap and air entrainment in an EAF increase the energy required by 0.3 GJ/t (about 25% of the 

total energy). 

• Total energy increases dramatically when using scrap substitute such as DRI or pig iron with scrap in 

an EAF. The best scrap substitute with respect to energy usage is liquid pig iron or hot metal. 

Stainless Steel 

• The melting energy for stainless steel is similar to the melting energy for carbon steel. However, the 

energy is much greater if the energy associated with ferrochrome is included. 

Direct Charging 

• Direct charging of slabs or billets reduces total rolling energy by about 80%. 

Ore Agglomeration and Cokemaking 

• Ore agglomeration and cokemaking, which are not theoretically necessary to produce steel, have 

significant theoretical minimum energies (1.6 and 0.8 GJ/t steel, respectively) and actual energies (2.2 

and 2.4 GJ/t, respectively). 

Limestone Calcination 

• Calcination of limestone requires 4.7 GJ/t CaO and releases 0.79 tonnes of CO2. 

Post Combustion 

• Post combustion can significantly increase scrap melting in the BOF and decrease energy required in 

the EAF. 

Carbon in the EAF 

• When carbon is used in the EAF, about 38% of the CO must be post combusted to CO2 to equal 

electrical energy, even taking into account the production and transmission losses associated with 

electrical energy. 

Off-Gas Energies 

• Off-gas energies from the blast furnace, coke plant, and direct reduction were significant and were 

credited to the processes. For example, the total energy credit for coke and ironmaking is 6-10 GJ. 

22 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
REFERENCES 

1. V. F. Campos and R. M. Figueira, Dados Termodinamicos para Metalurgistas, EEUFMG, Belo 

Horizonte, Minas Gerais, Brazil, p. 392, 1977. 

2. O. Kubaschewski, E. Evans and C. B. Alcock, Metallurgical Thermochemistry, Pergamon Press, 

New York, NY 1967. 

3. S. Ban-ya, M. Hino, “Chemical Properties of Molten Slags,” ISIJ, p. 278, 1991. 

4. E. T. Turkdogan, “Physicochemical Properties of Molten Slags and Glasses,” The Metals Society, 1 

Carlton House Terrace, London, p. 516, 1983. 

5. M. W. Chase, Jr. et al. Ed: JANAF Thermochemical Tables, 3rd Ed., American Chemical Society, 

1985. 

6. J. F. Elliott, M. Gleiser and V. Ramakreshna: Thermochemistry for Steelmaking, Addison-Wesley 

Publishing, Reading, MA. 

7. “New and Emerging Sources of Iron,” R.J. Fruehan, Prepared for the American Iron and Steel 

Institute, 19xx? 

8. The Making, Shaping and Treating of Steel, 10th Edition, AISE, Pittsburgh, PA, 1985. 

9. “Energy Use in the Steel Industry, International Iron and Steel Institute, September 1998. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 23 
24 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
APPENDIX A 

THEORETICAL CO2 EMISSIONS 

FROM STEELMAKING PROCESSES 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 25
In this section, the CO2 emissions associated with the energies required to produce steel are calculated. 

The following tables present theoretical CO2 emissions from various steelmaking processes for a 

number of conditions. These conditions are based on those used in the preceding analysis of theoretical 

energy consumption for steel production. 

Emission factors were calculated by considering the heats of reaction for the following reactions: 

C + 1⁄2 O2 � CO2 - “Hrxn = 395.3 kJ/mol (1) 

H2 + 1⁄2 O2 � H2 O - “Hrxn = 247.3 kJ/mol (2) 

C + 2H2 � CH4 - “Hrxn = 91.0 kJ/mol (3) 

CH4 + 2O2 � CO2 + H2 O - “Hrxn = 798.9 kJ/mol (4) 

These reactions represent the basic reactions that occur when fuel (carbon or methane) is combusted. 

By using these heats of reaction and the energy requirements for each process (shown in the report), 

the necessary amount of moles of fuel can be calculated. Once the amount of fuel is known, 

stoichiometry dictates the amount of CO2 generated by the combustion of that fuel. Because the 

production of electricity is not a matter of simple chemical reaction, the emission factor for electricity 

(U.S. grid) accepted by the American Iron and Steel Institute (AISI) was used in this analysis (AISI 

1996). Table A-1 shows the emission factors used in this analysis according to the assumptions noted 

and compares them to the AISI emission factors for each fuel source considered. Some assumptions 

have been made to simplify calculations and are noted below: 

• The energy for ironmaking is assumed to come from 100% carbon and converted entirely to 

CO2 when consumed. 

• Natural gas is assumed to be 100% methane and converted entirely to CO2 and H2O when 

consumed. 

• Electricity emissions include efficiency and transmission losses. 

• Emissions for BOF steelmaking are a result of 50 kg C/tonne HM that remains in the liquid pig 

iron and is used as fuel during oxygen steelmaking. This carbon is not combusted to CO2 

during the ironmaking step and thus is not included in the emissions for ironmaking. Since 

oxygen steelmaking generates rather than consumes energy, this process has no additional 

combustion emissions beyond the 50 kg C/tonne HM remaining in the liquid pig iron. 

The minimum theoretical energy consumption data presented in the body of this report are not estimates 

but rather actual physical quantities. When those energy data are converted to CO2 emissions, a 

number of assumptions and approximations are necessary. Particularly, while the energy data are 

simply energy (no fuel type is specified), fuel types must be specified when calculating carbon 

emissions. Additionally, carbon emission factors have been estimated based on the composition of 

common fuel sources. The distinction between the theoretical minimum energy consumption as a 

physical quantity and the minimum CO2 as an estimate must be made clear. 

26 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Table A-1. Emission Factors Used to Convert Theoretical Energy Consumption 

to CO2 Emissions 

Fuel Source 

Theoretical Emission Factor 

(kg CO2/MJ) 

AISI Emission Factor 

(kg CO2/MJ) 

Difference 

(percent) 

Coke 0.111 0.109 1.8 

Natural Gas 0.055 0.050 9.1 

Hydrogen 0 0 0.0 

Electricity N/A 0.173 N/A 

Coke Oven Gas 0.055 0.046 16.4 

Source: Survey of Consumption of Energy in the U.S. Iron and Steel Industry, American Iron and Steel Institute, 

1996. 

Notes: Coke is assumed to be 100% carbon combusted to 100% CO2. 

Natural gas is assumed to be 100% methane and combusted to 100% CO2 and H2O. 

Electricity emission factor accounts for transmission and efficiency losses at the power plant (based on IISI 

value for the U.S. grid). 

Hydrogen used as fuel does not result in any CO2 emissions. 

Coke oven gas used as fuel is considered as natural gas when considering CO2 emissions. 

The remainder of this appendix consists of the following tables: 

Table A-2. Absolute Theoretical Minimum CO2 Emissions for Producing Steel from Pure Ore 

(Fe2O3) and Pure Scrap (Fe) 

Table A-3. Minimum CO2 Emissions to Produce Liquid Hot Metal at 1723 K for Selected 

Conditions 

Table A-4. Minimum CO2 Emissions to Produce Direct Reduced Iron at 1173 K Reduction 

Temperature for Selected Conditions 

Table A-5. Minimum CO2 Emissions to Produce Steel from Hot Metal and Scrap for Selected 

Conditions 

Table A-6. Minimum CO2 Emissions to Produce Steel from Scrap for Selected Conditions, Tap 

Temperature = 1873 K 

Table A-7. Minimum CO2 Emissions to Produce Liquid Steel at 1873 K from 50% Scrap and 

50% Scrap Substitute 

Table A-8. Minimum CO2 Emissions to Roll Steel for Selected Products and Conditions 

Table A-9. Effect of Yield Loss on Minimum CO2 Emissions to Produce Steel for 1% Loss 

Table A-10. Minimum and Typical CO2 Emissions in Cokemaking and Ore Agglomeration 

Table A-11. Practical Minimum CO2 Emissions for Selected Processes 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 27 
Table A-2. Absolute Theoretical Minimum CO2 Emissions 

for Producing Steel from Pure Ore (Fe 2O3) and Pure Scrap (Fe) 

Raw Material 

Temperature 

(degrees K) 

Carbon Emissions (kg CO2/tonne) 

Fuel = Carbon 

Fuel = Natural 

Gas 

Fuel = 

Electricity 

Ore (Fe2O3) 

1813 960 475 1,494 

1873 966 478 1,503 

Scrap (Fe) 

1813 142 70 221 

1873 148 73 230 

Notes: Based on theoretical minimum energy consumption shown in Table 1. 

Absolute theoretical minimum energy consumption is independent of fuel type and not based on any actual 

production process. Therefore, the three main sources of fuel have been used to calculate theoretical 

carbon emissions for each. 

Table A-3. Minimum CO2 Emissions to Produce Liquid Hot Metal 

at 1723 K for Selected Conditions 

Material Consumption Gangue Ash 

CO2 (kg/ 

tonne HM) 

Fe - 5% C No No 908 

Fe - 5% C Yes No 954 

Fe - 5% C - 0.5% Si - 0.5% Mn Yes No 960 

Fe - 5% C - 0.5% Si - 0.5% Mn0 Yes Yes 977 

Notes: Based on theoretical minimum energy consumption shown in Table 2. 

Gangue contains 4% SiO2, 1% Al2 O3, and 1% MnO. Ash content is 25 kg/tonne hm (5% of coal and coke 

used).

Fuel used in ironmaking is assumed to be 100% coke.

Carbon that remains in the hot metal (5% C, or 50 kg C/tonne HM) is subtracted from the overall carbon

emissions for liquid hot metal production shown in this table. Those carbon emissions are attributed to the

process in which that carbon is used as fuel (i.e., raw steel production from hot metal, see Table A-5).

28 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Table A-4. Minimum CO2 Emissions to Produce Direct Reduced Iron 

at 1173 K Reduction Temperature for Selected Conditions 

Ore Product CO2 (kg/tonne) 

Pure Fe2O3 Fe 461 

Fe2O3 - 1.4% SiO 2 Fe - 2% SiO 2 462 

Fe2O3 - 1.4% SiO 2 Fe - 2% SiO 2 - 8% FeO 435 

Fe2O3 - 1.5% SiO 2 Fe - 2% SiO 2 - 8% FeO - 2% C 391 

Fe2O3 - 1.5% SiO 2 Fe - 2% SiO 2 - 7.7% FeO - 6% C 300 

Notes: Based on theoretical minimum energy consumption shown in Table 3. 

The energy used to produce direct reduced iron is assumed to be 100% natural gas. 

When carbon remains in the final product (the final two rows in the table above), that carbon is subtracted 

from the overall CO2 emissions of the process. The subtracted CO2 is attributed to the process in which the 

carbon is used as fuel (i.e., liquid steel production from scrap and scrap substitute, Table A-7). 

Table A-5. Minimum CO2 Emissions to Produce Steel 

from Hot Metal and Scrap for Selected Conditions 

Hot Metal Slag 

Tap 

Temp. 

(K) 

Scrap 

(kg) 

Steel 

(kg/tonne 

HM) 

CO2 

(kg/tonne) 

Fe - 5% C – 1873 290 1,240 148 

Fe - 5% C – 1923 244 1,194 135 

Fe - 5% C - 0.5% Si B = 3; 30% FeO 1873 401 1,328 138 

Fe - 5% C - 0.5% Si B = 3; 30% FeO 1923 353 1,278 143 

Fe - 5% C - 0.5% Si B = 3; 20% FeO 1873 389 1,320 139 

Fe - 5% C - 0.5% Si B = 3; 20% FeO 1923 341 1,270 144 

Notes: Based on theoretical energy consumption shown in Table 4. 

Oxygen steelmaking is theoretically an energy-producing process due to the exothermic nature of the 

reactions taking place. Therefore, fuel consumption is theoretically not needed, and carbon emissions do 

not result from the combustion of fuels. 

The CO2 emissions shown are the result of the 5% carbon (50 kg/tonne HM) in the hot metal feed that is 

consumed during steelmaking. The carbon is actually used as a fuel source for melting scrap and is 

converted to CO2 in this process. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 29 
Table A-6. Minimum CO2 Emissions to Produce Steel from 

Scrap for Selected Conditions, Tap Temperature = 1873 K 

Scrap Slag CO2 (kg/tonne steel) 

Fe – 230 

Fe - 0.1%C - 0.2% Si B=2.5; 25% FeO 223 

Fe - 0.1%C - 0.2% Si -1% dirt B=2.5; 25% FeO 234 

Fe - 0.1%C - 0.2% Si -1% dirt B=2.5; 35% FeO 230 

Fe - 0.1%C - 0.2% Si -1% dirt -100 Nm3 air B=2.5; 25% FeO 275 

Notes: Based on theoretical energy consumption shown in Table 5. 

Energy is assumed to be 100% electricity, using a conversion factor of 10,500 Btu/kWh to include 

transmission and efficiency losses. 

Table A-7. Minimum CO2 Emissions to Produce Liquid Steel 

at 1873 K from 50% Scrap and 50% Scrap Substitute 

Input 

Melting Energy 

(MJ/tonne steel) 

Charge Energy 

(MJ/tonne steel) 

CO2 (kg/tonne 

steel) 

None (100% Scrap Case) 1,289 – 234 

Fe - 2% SiO 2 1,403 4,296 480 

Fe - 2% SiO 2 - 8% FeO 1,559 4,233 503 

Fe - 2% SiO 2 - 8% FeO - 2% C 1,483 4,565 548 

Fe - 2% SiO 2 - 8% FeO - 6% C 1,328 5,223 640 

Liquid Pig Iron 487 5,388 779 

Solid Pig Iron 1,145 5,388 893 

Notes: Based on theoretical energy consumption shown in Table 6. 

Liquid pig iron is charged at 1723 K, all others at 298 K; melting energy is assumed to be 100% electricity. 

Charge energy is assumed to be 100% natural gas for DRI and 100% coke for pig iron. 

In addition to the CO2 emissions generated from fuel consumption, the carbon contained in the input 

materials is converted to CO2 in this process (10.8 kg C/tonne, 2%C DRI; 33.2 kg C/tonne, 6%C DRI; 25.8 kg 

C/tonne pig iron). 

30 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Table A-8. Minimum CO2 Emissions to Roll Steel for Selected Products and Conditions 

Rolling 

Temperature 

(K) 

Slab 

Temperature 

(K) 

Reduction 

(mm) 

Energy (MJ/tonne) 

CO2 

Heat (kg/tonne)

Deformation 

Flat Carbon (25.4 cm slab) 

1473 298 254 - 2 825 25 50 

1473 1173 254 - 2 270 25 19 

1473 1473 254 - 2 – 25 4 

298 298 2 - 1 – 17 3 

Flat Carbon (5.0 cm slab) 

1473 298 50 - 2 825 16 48 

1473 1173 50 - 2 270 16 18 

1473 1473 50 - 2 – 16 3 

298 298 2 - 1 – 17 3 

Flat 18-8 Stainless (25.4 cm slab) 

1473 298 254 - 2 825 72 58 

1473 1173 254 - 2 270 72 27 

1473 1473 254 - 2 – 72 12 

298 298 2 - 1 – 51 9 

Bar Carbon (10 cm billet to 2 cm bar) 

1473 298 10 sq - 2 sq 825 20 49 

1473 1473 10 sq - 2 sq – 20 4 

1473 1173 10 sq - 2 sq 270 20 18 

1473 1473 10 sq - 2 sq – 11 2 

Notes: Based on theoretical energy consumption shown in Table 7. 

Heating energy is assumed to be 100% natural gas. 

Deformation energy is assumed to be 100% electricity. 

Theoretical Minimum Energies to Produce Steel for Selected Conditions 31 
Table A-9. Effect of Yield Loss on Minimum CO2 Emissions to Produce Steel 

for 1% Loss 

Process Type of Loss 

Energy 

(MJ/tonne) CO2 (kg/tonne) 

Hot metal loss in 

pretreatment 

Hot metal loss to slag but 

recovered 14 1.6 

Hot metal loss to slag, not 

recovered 104 11.6 

Direct Reduction 

Fines lost 60 3.3 

Fines recycled 6 0.3 

BOF 

Fe vaporized to dust 144 2.6 

Fe ejected to dust 80 1.4 

EAF 

Fe vaporized to dust 102 17.7 

Fe ejected to dust 16 2.8 

Hot Rolling Fe lost but recovered 13 2.3 

Cold Rolling Reheating for hot rolling, but 

recovered 34 5.9 

Notes: Based on theoretical energy consumption shown in Table 8. 

Energy lost in hot metal loss is assumed to be 100% coke. Energy lost in direct reduction fines is assumed 

to be 100% natural gas.

Energy lost in EAF and rolling operations is assumed to be 100% electricity.

For BOF steelmaking, emissions are calculated using the average emission rate for the BOF steelmaking

calculations (0.018 kg CO2/tonne/MJ). 

32 Theoretical Minimum Energies to Produce Steel for Selected Conditions 
Table A-10. Minimum and Typical CO2 Emissions 

in Cokemaking and Ore Agglomeration 

Process 

Theoretical Actual 

GJ/tonne 

output 

GJ/tonne 

steel 

CO2 

(kg/tonne 

output) 

GJ/tonne 

output 

GJ/tonne 

steel 

CO2 

(kg/tonne 

output) 

Cokemaking 2 0.8 0.11 5.4 - 6.2 2.2 - 2.6 0.30 - 0.34 

Ore Agglomeration 1.2 1.6 0.07 1.5 - 1.7 2.1 - 2.4 0.17 - 0.19 

Notes: Based on theoretical minimum energy consumption shown in Table 9. 

Energy used in cokemaking is assumed to be 100% natural gas. 

Energy used in ore agglomeration is assumed to be 100% coke breeze. 

Table A-11. Comparison of Theoretical Minimum and Actual CO2 Emissions 

for Selected Processes 

Process 

Absolute Minimum 

CO2 (kg/tonne 

product) 

Practical Minimum 

CO2 (kg/tonne 

product) 

Actual CO2 

(kg/tonne 

product) 

Liquid Hot Metal 1,091 1,158 1,447 - 1,559 

Liquid Steel (BOF) 144 144 189 - 207 

Liquid Steel (EAF) 225 277 364 - 416 

Hot Rolling 2 50 110 - 132 

Cold Rolling 4 4 173 - 243 

18-8 Stainless Melting 208 260 – 

Notes: Based on theoretical minimum energy consumption shown in Table 11. 

Actual includes yield losses and is the average of state-of-the-art and less-efficient operations for the 

United States, Japan, and Europe.

BOF energy is primarily from hot metal; the actual process consumes 0.2 to 0.4 GJ/tonne. Theoretically if

CO is oxidized, it could produce 0.5 GJ/tonne. 

For 18-8 stainless melting no estimates of actual emissions were available.

Theoretical Minimum Energies to Produce Steel for Selected Conditions 33 
34 Theoretical Minimum Energies to Produce Steel for Selected Conditions