The steelmaking process generates approximately 7 to 8 percent of the total greenhouse gas emissions worldwide. Therefore, the steel industry contributes significantly to carbon dioxide emissions. In fact, green steel refers to steel where less carbon is used in its production.
The process of green steel production
Any method that can produce steel with less carbon is referred to as green steel production. One efficient method of producing green steel is direct reduction of iron ore based on hydrogen. This process involves chemically reducing solid iron ore using hydrogen to produce an intermediate product called sponge iron(Direct Reduced Iron). The sponge iron is then melted in an electric arc furnace to produce steel.
Instead of using coke in a traditional blast furnace, the primary input energy during this process is electricity, which reduces greenhouse gas emissions. Significant reductions in greenhouse gas emissions can be achieved if electricity comes from reduced carbon or green sources.
Another approach to reduce carbon dioxide and greenhouse gas emissions, where feasible gas is available, is using natural gas as a fuel instead of coal in blast furnaces.
Production of green steel in Iran
In line with reducing greenhouse gas emissions, steel-producing countries worldwide must review their production processes by 2060, and Iran is no exception to this rule. Therefore, Iran’s Mines and Mining Industries Development and Renovation Organization (IMIDRO) has prioritized the “Feasibility Study of Green Steel Production” project, considering technical and economic parameters.
Collaboration for green steel production in Iran involves a memorandum of understanding between IMIDRO and companies such as Iran National Steel Industries Group , Iran International Engineering Company (IRITEC), IRASCO Company, Mobarakeh Steel Company, Khuzestan Steel Company, ChadorMalu lndustrial Complex Company, Golgohar Mining and Industrial Company, and Goharzamin Iron Ore Company.
The amount of carbon dioxide produced per ton of steel
The majority of pollution in the steel industry comes from iron smelting, while rolling mills have lower pollution levels due to their use of natural gas. For every ton of raw steel produced, iron smelting generates between 6 to 18 kilograms of carbon dioxide. The rate of iron production depends on the type and charge composition of the furnace.
Steel factories produce pollution in two ways:
1. Directly, through the production of carbon dioxide gas from smelting plants.
2. Indirectly, through power plants.
The lowest level of pollution pertains to furnaces that are fully charged with scrap iron. In these furnaces, 6.2 kilograms of carbon dioxide gas is produced per ton of crude steel. If the furnace charge consists of 80 percent cold sponge iron, 18.1 kilograms of carbon dioxide gas is produced per ton of crude steel, which is three times the amount produced by a furnace with 100 percent scrap iron charge. On the other hand, sponge iron contains 1.5 to 2 percent carbon, which leads to the production of carbon dioxide gas.
Considering that there is not enough scrap iron available in Iran, it is possible to reduce the energy consumption of electric arc furnaces and consequently the amount of pollutant gases produced by processing and preheating the scrap with high-temperature gases emitted from the furnace. If the scrap is sorted and shredded, it can reduce the carbon dioxide gas production to 6.2 kilograms per ton of crude steel.
In the field of sponge iron, the carbon content should be reduced as much as possible. Additionally, in steel melting, high-temperature sponge iron (hot charge) can be used. With these simple measures, it is possible to reduce the carbon dioxide emissions from 18.1 to 15.5 kilograms per ton of crude steel.
There is a direct relationship between energy consumption and the carbon dioxide gas produced. Therefore, to reduce pollution, we need to reduce gas consumption.
There are many ways to reduce energy consumption in the steel industry, including increasing the arc length in electric arc furnaces, reducing the interval times during melting, and so on.
Recycling industrial wastewater is another effective measure in producing green steel.
