Deciding the Optimal Operation Patterns of Steelmaking Facilities using a Network Diagram

Diverse steel products, which are bolstering the modern civilisation, are manufactured using irons produced at integrated steel mills as materials. Steelmaking at an integrated steel mill involves five processes (in the following order): unloading at a port, iron making, steelmaking, continuous casting, and rolling, which can be outlined as shown in Figure 1. The unloading process involves the unloading of iron ores (the raw materials used for the molten irons produced at a furnace), coals (the raw materials used for burning iron ores), and various submaterials for controlling the compositions, etc. from a ship at a port, and transporting them to storage warehouses. The iron making process proceeds as follows: (i) iron ores, cokes, and limestone are placed in a smelting furnace; (ii) high-temperature air is blown through the air heating furnace at the lower part of the smelting furnace; (iii) the cokes fabricated from coals are burned to emit carbon monoxide, which deoxidises the iron ores; and (iv) molten iron is manufactured. The molten iron with a high carbon content that is first produced at a smelting furnace is called pig iron. The steelmaking process progresses as follows: (i) the pig irons manufactured at a furnace are loaded onto a pig iron transportation vehicle (torpedo ladle car, TLC) and are delivered to a steelmaking plant; (ii) carbon is removed by oxidising the irons through the mixing of scrap irons and oxygen blowing; (iii) the silicon, manganese, phosphorus, and sulfur contents are decreased appropriately; and (iv) steel is manufactured. A series of such process is called tapping. The molten metal, whose carbon content decreased, whose impurities were removed, and whose composition (e.g., silicon, manganese, phosphorus, and sulfur) was adjusted at a steelmaking mill, is called steel. The continuous casting process, where the steel in liquid state is transformed into a solid object, progresses as follows: the steel is continuously supplied in liquid state into a mold, is made to pass through a casting machine, and is solidified through a cooling process; and intermediary materials such as slabs, blooms, and billets are manufactured. The rolling process hot-rolls the intermediary materials such as the slabs, blooms, and billets that were produced at the continuous casting plant and produces products such as Abstract