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Analysis on Material and Energy Balances of Ironmaking Systems on Blast Furnace Operations with Metallic Charging, Top Gas Recycling and Natural Gas Injection
Hiroshi NOGAMI, Junichiro YAGI, Shinya KITAMURA and Peter Richard AUSTIN
( Department of Chemical Engineering, Japan)
(July 6, 2010)
The iron and steelmaking industry has been receiving social pressure to reduce energy consumption and environmental load as recent increase in the social awareness on environmental and resource problems. The ironmaking system consumes more than a half of overall energy input to the steelwork and its improvement is expected as a countermeasure for such problems. Numerous attempts through improving the blast furnace operation have been made.
This paper analyzes material and energy balances of ironmaking system that consists of hot stove, coke oven, CDQ, sintering and blast furnace. The operation statuses of the blast furnace with natural gas injection, metallic charging and top gas recycling that have been obtained by the kinetic-based numerical simulations are applied to this analysis. The results suggested that the metallic charging to blast furnace decreases both energy input and CO2 emission. The natural gas injection operation decreases the CO2 emission from the iron making system while the decrease in the energy input is small. The top gas recycling operation increases the CO2 emission due to the scrubbed CO2 from the recycled top gas.
Social awareness on problems of environment, waste treatment, resources and so on has been arising recent years. Among these problems, global warming attracts much attention because it is considered to cause natural disasters such as sea level rise and extreme weather events.
Accumulation of green house effect gases in atmosphere is recognized as one of the most important reasons of global warming. The industrial and urban activities of human being release huge amount of carbon dioxide which is included in the six major greenhouse effect gases to the atmosphere. Thus the social pressure to reduce carbon dioxide emission towards large scale industries is getting stronger.
The iron and steelmaking industry uses coal as the primary reducing agent. The carbon that is major component of coal is finally released to the environments as carbon dioxide. Therefore, the energy consumption in this industry is equivalent to carbon dioxide emission, and various efforts to improve energy efficiency have been being made.
They can be classified into several groups by their concepts, such as:
1) decreasing process operation temperature with keeping or increasing reaction rates, 2) replacing current reducing agent with hydrogen bearing materials,
3) decreasing energy for reduction of iron oxides,
4) effective use of reduction potential of carbonaceous materials,
5) development of new processes, and so on.
Examples of these attempts are:
1) Research Project on Innovative Ironmaking Reaction in New BF Aiming at Half Energy Consumption and Minimum Environmental Load,
2) plastic injection into tuyere, natural gas injection,
3) scrap or DRI charging,
4) top gas recycling,
5) reduction of carbon composite agglomerates in rotary hearth furnace, direct iron ore reduction process, and so on.
The authors examined some of these measures using the kinetic-based mathematical simulator of blast furnace operation.
These analyses showed that the blast furnace operations with metallic iron charge, natural gas injection and top gas recycling showed increase in hot metal productivity and decrease in reducing agent rate under appropriately selected conditions. This means that the energy consumption for the unit production of iron is expected to decrease under these operations.
The ironmaking system consists of various processes such as coke oven, sintering, hot stove, and so on as well as blast furnace. These processes provides raw materials, reducing agents and hot blast to the blast furnace, and the production rates of these processes depend on the operation of blast furnace. Additionally by-product gases of blast furnace and coke oven are utilized as fuel of some these processes. Therefore the variations of operation status of the processes included in the ironmaking system need to be evaluated for more detailed analysis on energy consumption for iron production. The ironmaking system not only consumes energy but also provides fuel to the downstream processes, like steel making, re-heating, forming, power plant and so on. Thus the energy and material flow analyses in the integrated steel works are frequently made. However, these are made based on actual operation results and/or thermodynamic analysis of blast furnace operation.
In this study, a method to analyze material and energy balances in ironmaking system based on the kinetic-bases simulations of blast furnace operation, and it is applied to the previously reported results on some novel operations made by the authors.
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