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3.4 Low-Carbon Technologies for Monozukuri
3.4.1 Shift from Blast Furnaces to Electric Furnaces
While agriculture, forestry, and fisheries make use of biological resources derived
from solar energy, monozukuri (making things) is an activity to produce various
artificial objects using underground resources that did not exist in the material cycle
of the natural world. Here, I would like to take up steel, which has the highest
energy consumption in the monozukuri process.
Steel can be produced by the blast furnace process (hereinafter referred to as
blast furnace process) or the electric furnace process. Iron ore, which is a natural
resource, is used in the blast furnace process. Iron ore refers to iron oxide. If iron ore
is cast into a blast furnace together with coke, which consists primarily of carbon,
pig iron is produced as oxygen is removed from the iron oxide. Various steel products are created by processing this pig iron.
About 600 kg of coke (carbon) is used to produce one ton of iron. Theoretically,
the required amount of carbon is 202 kg, so it means that two-thirds are not used.
Although the overall iron and steel process has become more efficient because of
technological development, the processing and molding process is a multi-stage
process, so if a slight loss that occurs at each stage accumulates, this could turn into
a significant loss. In the future, to what extent efficiency can be increased depends
on investment, but it is not easy to reduce 600–400 kg.
Meanwhile, iron that is used in bridges, buildings, railroad tracks, automobiles,
etc. that exist in society is recovered as scrap once its service life as a product comes
to an end. The scrap iron, however, is melted in electric furnaces, molded, and used
as steel products once again. The energy used in the electric furnace process to produce one ton of iron can be calculated in terms of the amount of carbon required for
the process. This is about 300 kg, about half of the amount required in the blast
furnace process.
Energy required for processing and molding cannot be reduced significantly
even in the electric furnace process, but the direction of reducing the overall energy
consumption is visible. Currently, electricity is used to melt the scrap iron. Fossil
resources are burned, and the heat generated is converted into electricity, which, in
turn, is converted into heat to melt the iron. If the iron can be directly melted with
the fossil resources, the amount of carbon used per one ton of iron can be reduced
to about 150 kg.
Thinking in terms of energy, rather than mining iron ore and producing iron in
blast furnaces, far less energy is consumed by taking advantage of scrap iron and
producing iron in electric furnaces. In addition, the direction of technology development to reduce the energy consumption is visible in the case of the electric furnace
process. This applies not only to iron but also to cement, aluminum, etc. If a social
system in which resources that lie under urban mines are recovered and recycled can
be created, it is possible to significantly reduce carbon in the monozukuri sector.
3 Technology to Support Low-Carbon Society (Using Energy)
3.4 Low-Carbon Technologies for Monozukuri
3.4.1 Shift from Blast Furnaces to Electric Furnaces
While agriculture, forestry, and fisheries make use of biological resources derived
from solar energy, monozukuri (making things) is an activity to produce various
artificial objects using underground resources that did not exist in the material cycle
of the natural world. Here, I would like to take up steel, which has the highest
energy consumption in the monozukuri process.
Steel can be produced by the blast furnace process (hereinafter referred to as
blast furnace process) or the electric furnace process. Iron ore, which is a natural
resource, is used in the blast furnace process. Iron ore refers to iron oxide. If iron ore
is cast into a blast furnace together with coke, which consists primarily of carbon,
pig iron is produced as oxygen is removed from the iron oxide. Various steel products are created by processing this pig iron.
About 600 kg of coke (carbon) is used to produce one ton of iron. Theoretically,
the required amount of carbon is 202 kg, so it means that two-thirds are not used.
Although the overall iron and steel process has become more efficient because of
technological development, the processing and molding process is a multi-stage
process, so if a slight loss that occurs at each stage accumulates, this could turn into
a significant loss. In the future, to what extent efficiency can be increased depends
on investment, but it is not easy to reduce 600–400 kg.
Meanwhile, iron that is used in bridges, buildings, railroad tracks, automobiles,
etc. that exist in society is recovered as scrap once its service life as a product comes
to an end. The scrap iron, however, is melted in electric furnaces, molded, and used
as steel products once again. The energy used in the electric furnace process to produce one ton of iron can be calculated in terms of the amount of carbon required for
the process. This is about 300 kg, about half of the amount required in the blast
furnace process.
Energy required for processing and molding cannot be reduced significantly
even in the electric furnace process, but the direction of reducing the overall energy
consumption is visible. Currently, electricity is used to melt the scrap iron. Fossil
resources are burned, and the heat generated is converted into electricity, which, in
turn, is converted into heat to melt the iron. If the iron can be directly melted with
the fossil resources, the amount of carbon used per one ton of iron can be reduced
to about 150 kg.
Thinking in terms of energy, rather than mining iron ore and producing iron in
blast furnaces, far less energy is consumed by taking advantage of scrap iron and
producing iron in electric furnaces. In addition, the direction of technology development to reduce the energy consumption is visible in the case of the electric furnace
process. This applies not only to iron but also to cement, aluminum, etc. If a social
system in which resources that lie under urban mines are recovered and recycled can
be created, it is possible to significantly reduce carbon in the monozukuri sector.
3 Technology to Support Low-Carbon Society (Using Energy)