Present situation and development countermeasure of low carbon technology of metallurgical lime

Carbon emissions from lime production

Sources of carbon emissions from lime production

Calcination of ore raw material produces carbon emission. The lime production process is mainly the calcination process of limestone in lime kiln, and the main composition of limestone is calcium carbonate (CaCO3). Under calcination conditions ranging from 900 degrees Celsius to 1100 degrees Celsius, calcium carbonate decomposes to calcium oxide (CaO) and carbon dioxide (CO2).

Fuel combustion and electricity consumption produce carbon emissions. Lime production fuels are usually coal, coke and other solid fuels, heavy oil and other liquid fuels, as well as coke oven gas, converter gas, blast furnace gas, calcium carbide furnace gas, natural gas and other gas fuels, fuel combustion reaction generated carbon dioxide into the atmosphere with the flue gas. In addition, lime production also indirectly contributes to carbon emissions by consuming electricity.

Carbon emissions from metallurgical lime production

According to the "China Iron and Steel Production Enterprises Greenhouse Gas Emissions Accounting Methods and Reporting Guidelines (Trial)" (hereinafter referred to as the "Guidelines"), metallurgical lime production process carbon emissions by industrial production process carbon emissions, fuel combustion carbon emissions, electricity consumption carbon emissions from three aspects.

According to the "Guidelines", the calculation of carbon emissions from industrial production processes, fuel combustion, and electricity in metallurgical lime production is as follows:

Carbon emission in industrial production process = raw material consumption × emission factor

Carbon emission from fuel combustion = average low calorific value of fuel × fuel consumption × carbon content per unit calorific value of fuel × carbon oxidation rate ×44/12

Carbon emissions generated by electricity = power consumption × power emission factor

According to metallurgical lime production experience data: Ore ratio of 1.8 tons/ton, anthracite consumption of 160 kg/ton (under single fuel condition), converter gas consumption of 550 cubic meters/ton (under single fuel condition), power consumption of 50 KWH/ton, and power emission factors are temporarily calculated based on the average emission factors of the base lines of China's regional power grids in 2017 emission reduction projects. The carbon emissions per ton of product in the industrial production process are 0.792 tons, the carbon emissions per ton of product in the fuel combustion process are 0.308 tons (using anthracite as fuel) ~0.832 tons (using converter gas as fuel), and the carbon emissions per ton of product generated by electricity are 0.046 tons.

According to the above analysis, when anthracite is used as fuel, the production of each ton of lime products produces about 1.1 tons of carbon dioxide; When using converter gas as fuel, the production of each ton of lime product produces about 1.7 tons of carbon dioxide. According to statistics, the output of metallurgical lime in 2018 was about 110 million tons, that is, the production of carbon dioxide was about 121 million tons to 187 million tons, and the equivalent ton of steel produced carbon dioxide was about 0.13 tons to 0.20 tons.

At present, China's long process steel enterprises have carbon emissions of about 2.0 tons per ton of steel, short process steel enterprises have carbon emissions of about 0.6 tons per ton of steel, and short process crude steel production accounts for about 11% of total crude steel production. According to this calculation, the amount of carbon dioxide emitted by metallurgical lime production reaches about 7% to 11% of the total carbon emissions of the steel industry.

The above calculation is based on the rough estimate of anthracite coal and converter gas as two representative fuels in the process of metallurgical lime production, for reference only.

Review of low carbon technology of metallurgical lime

Through the unremitting efforts of industry research workers and practitioners, the low-carbon technology of metallurgical lime has made great progress in recent years. By strengthening combustion, improving furnace insulation performance and life, recycling waste heat resources, separation and purification of carbon dioxide in waste gas, they gradually promote the metallurgical lime industry to achieve energy-saving and low-carbon development. Low carbon technologies in metallurgical lime industry are summarized as follows:

Oxygen-enriched combustion technology

Oxygen-enriched combustion technology is a high-efficiency and energy-saving combustion technology that burns oxygen-containing gas with higher oxygen content than air. By increasing the oxygen content in the combustion air, the air requirement is reduced, the flue gas production is reduced, and the heat loss taken away by the flue gas is reduced. In addition, the oxygen-rich combustion technology can also increase the theoretical heating temperature and theoretical combustion temperature, so that the fuel is completely burned, reduce flue gas pollution, can improve the theoretical combustion speed, so that the combustion reaction is faster and more complete. The research shows that the application of oxygen-enriched combustion technology to lime kiln has great technical advantages, and has achieved remarkable effect of energy saving and consumption reduction.