The worldsteel methodology for the use of steel scrap in the steelmaking process and the production of steel scrap at the end-of-life of a product is described in detail in the following sections.
4.1 Terminology requiredA number of parameters relating to steel and recycling which will be used in the following equations are as follows:
Recovery rate (RR): the fraction of steel recovered as scrap during the lifetime of a steel product, including scrap generated after manufacturing the steel product under analysis. A value of 85 % has been used in Eq. 11.
Metallic yield (Y): the process yield (or efficiency) of the EAF. It is the ratio of steel output to scrap input (i.e. >1-kg scrap is required to produce 1-kg steel). This is calculated using Eq. 4 as 1.092 based on worldsteel data published in 2010.
LCI for BOF steel production (X BOF ): the LCI for steel production from the BOF, which includes scrap. The value used in Eq. 8 of 1.756 kg CO2 is from the worldsteel data published in 2010.
LCI for primary steel production (X pr ): the theoretical LCI for 100 % primary metal production, from the BOF route, assuming 0 % scrap input.
LCI for secondary steel production (X re ): the LCI for 100 % secondary metal production from scrap in the EAF, assuming scrap = 100 %. The value used in Eq. 8 of 0.386 kg CO2 is from the worldsteel data published in 2010.
The letter X in each of these terms refers to any LCI parameter, e.g. natural gas, CO2, water and limestone.
S is the amount of scrap used in the steelmaking process to make a specific product. The value of 0.121 kg used in Eq. 11 for hot rolled coil is from the worldsteel data published in 2010.
The methodology assumes the burdens of scrap input and the credits for recycling the steel at the end of the life of a product are equal, per kilogram, and that all scrap is treated equally. In reality, there are numerous grades of steel products, and therefore, steel scrap grades and a combination of these scrap types are used when making steel. It has not been feasible to calculate an LCI for each scrap grade, but this could be addressed in the future. As the use of scrap replaces the production of crude steel, and not a finished steel product, it is appropriate to assume a generic scrap grade for the purpose of these calculations. For coated or galvanised scrap grades, this will result in an overestimation of the burden for the scrap input (the yield will be lower) so will give more conservative results.
Collecting scrap at the end of the product’s life and recycling it through the steel making process enables the saving of primary, virgin steel production.
This is commonly referred to as the integrated or BOF steel making route, but in reality, some steel scrap is always required in the process as it acts as a coolant in order to maintain the thermal balance in the process. Thus, there is no process using 100 % virgin material (with 0 % scrap input), and this theoretical value therefore needs to be calculated (see Sect. 6.3).
Furthermore, it is not the scrap itself that replaces this primary steel, as the scrap needs to be processed or recycled to make new steel. The EAF process is an example of 100 % scrap recycling, though some EAFs also use hot metal or direct reduced iron (DRI) as an input to the process.
Finally, the EAF process is not 100 % efficient, i.e. it needs more than 1 kg of scrap to make 1-kg steel.
The LCI associated with the scrap, ScrapLCI, is thus equal to the credit associated with the avoided primary production of steel (assuming 0 % scrap input), minus the burden associated with the recycling of steel scrap to make new steel, multiplied by the yield of this process (see Fig. 4) to consider losses in the process (see Sect. 4.1 for definitions):
Fig. 4The yield of the EAF process
$$ ScrapLCI=\left({X}_{pr}-{X}_{re}\right)Y $$
(1)
The letter X in each of these terms refers to any LCI parameter, e.g. natural gas, CO2 and water. The CO2 for scrap would be calculated as follows:
$$ C{O}_2 Scrap=\left(C{O}_{2pr}-C{O}_{2re}\right)Y $$
(2)
Y is the process yield of the EAF (i.e. >1-kg scrap is required to produce 1-kg steel)
The values for X re and Y are known by the industry as these values come from the steel producers. However, the theoretical value of X pr needs to be calculated.
4.3 Theoretical value of 100 % primary BOF steel, X prThe theoretical value of 100 % primary steel is calculated based on the LCI of steel slab made by the primary, or BOF route. As the steel slab contains a certain amount of scrap, this needs to be ‘removed’ from the LCI so that only virgin steel is accounted for, see Fig. 5a.
Fig. 5a Determination of the theoretical value of 100 % primary BOF steel, X pr . b Theoretical value of 100 % primary BOF steel, X pr
The scrap input to the BOF process (m kg scrap per 1-kg steel produced) that needs to be removed would be melted in the EAF process producing mY kg steel, Y being the yield of the steelmaking process. Therefore, the theoretical 100 % primary route, X pr , needs to produce 1-mY kg steel, see Fig. 5b.
In effect,
$$ {X}_{BOF}=\left(1- mY\right)\left({X}_{pr}\right)+ mY{X}_{re} $$
(3)
where m is the scrap input to the BOF route (ScrapBOF) and Y is the inverse of the scrap input to the EAF, Scrapre, i.e.
$$ Y=\frac{1}{Scra{p}_{re}} $$
(4)
Therefore,
$$ mY=\frac{Scra{p}_{BOF}}{Scra{p}_{re}} $$
(5)
This would then give the following:
$$ {X}_{BOF}=\left(1-\frac{Scra{p}_{BOF}}{Scra{p}_{re}}\right)\left({X}_{pr}\right)+\left(\frac{Scra{p}_{BOF}}{Scra{p}_{re}}\right){X}_{re} $$
(6)
Rearranging this equation will enable the theoretical value for 100 % primary steel to be calculated:
$$ {X}_{pr}=\frac{X_{BOF}-\left(\frac{Scra{p}_{BOF}}{Scra{p}_{re}}{X}_{re}\right)}{1-\frac{Scra{p}_{BOF}}{Scra{p}_{re}}} $$
(7)
This value for X pr can now be included in the scrap LCI equation and will therefore be applied to each of the inputs and outputs of the LCI. The values that have been used are based on the current worldsteel LCI data collection.
$$ {X}_{pr}=\frac{1.756-\left(\frac{0.119}{1.092}0.386\right)}{\begin{array}{l}\kern1.44em 1-\frac{0.119}{1.092}\hfill \\ {}{\mathrm{X}}_{\mathrm{pr}}=1.92\;\mathrm{kg}\;{\mathrm{CO}}_2\hfill \end{array}} $$
(8)
It should be noted that if an extrapolation was carried out in order to determine the theoretical value for X pr with zero scrap input, based on the values of X BOF and X re , the same values would be reached for X pr of 1.92 kg CO2. Figure 6 plots the global EAF steel value which is based solely on steel scrap, together with the global BOF steel value which contains nearly 12 % scrap. Extrapolating this to a value of zero scrap input gives this value of 1.92 kg CO2.
Fig. 6Extrapolation to show CO2 emissions for 0 % scrap input
And for CO2, the equation would be as follows (i.e. X = CO2):
$$ \begin{array}{c}\hfill ScrapLCI=\left({X}_{pr}-{X}_{re}\right)Y\hfill \\ {}\hfill \begin{array}{c}\hfill ScrapLCI=\left[1.92-0.386\right]\frac{1}{1.092}\hfill \\ {}\hfill \mathrm{Scrap}\;\mathrm{L}\mathrm{C}\mathrm{I}=1.405\mathrm{kg}\;{\mathrm{CO}}_2\hfill \end{array}\hfill \end{array} $$
(9)
4.4 Summary of scrap LCI calculationsThe methodology for determining the LCI for steel scrap, as described in Sects. 6.2 and 6.3, is summarised in Fig. 7. The figure uses CO2 as an example and includes the scrap inputs to the EAF and BOF processes to calculate the LCI for each production route when including a burden for the scrap. As the impact if the two routes can be equated when the burden for scrap has been included, this means that the scrap LCI can then be calculated.
Fig. 7Overview of scrap LCI calculations
4.5 Applying the scrap LCI burden and creditThe scrap LCI, defined in Eq. (1) as ScrapLCI = (X pr − X re )Y, is applied to the steel product cradle to gate LCIs in order to include the end-of-life phase. A credit is given for the amount of steel scrap that will be recycled at the end-of-life of the product, and this is referred to as RR. However, in doing this, a burden needs to be applied to any scrap that is used in the steelmaking process, referred to as S.
Thus, the LCI of a product, from cradle to gate including end-of-life (LCIincluding EoL), can be calculated as
$$ LC{I}_{includingE\;oL}=X-\left(RR-S\right)\left({X}_{pr}-{X}_{re}\right)Y $$
(10)
where X is the LCI of the product being studied and is cradle to gate, i.e. including all upstream as well as steel production. The term (RR − S) is also known as the net scrap that is generated from the product system. When this value is negative that implies that there is more scrap consumed to make the steel than is recycled from the product at the end-of-life.
In order to calculate the LCI of a steel product, including end-of-life recycling, an example for CO2 emissions is shown in Fig. 8 and Eq. (11), for global hot rolled coil, using an end-of-life recycling rate of 85 %. This gives a net scrap value of 0.85 − 0.121 = 0.729 kg.
Fig. 8Example cradle to grave system
The value of scrap, (X pr − X re )Y, has been calculated above, and the CO2 emissions and scrap content of hot rolled coil are provided from the global average data published in February 2010. New data will be available at the end of 2015.
$$ \begin{array}{c}\hfill LC{I}_{includingE\;oL}=1.889-\left(0.85-0.121\right)*1.405\hfill \\ {}\hfill LC{I}_{includingE\;oL}=0.86kgC{O}_2\hfill \end{array} $$
(11)
CO2 is used in this example as it is one of the most commonly used LCI flows. The same calculation method applies to all inputs and outputs of the LCI.
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