Hot Blast Superheating - A Scalable Technology to Reduce Coke Consumption
In 1984, Ferromanganèse de Paris-Outreau, France implemented Aerospatiale plasma torches on their blast furnace. The torches were positioned in the tuyere assembles to superheat the hot blast just before it entered the furnace. Three 2-MW plasma torches were installed to test the validity of the concept and to create experimental velocity and temperature fields. With the torches operating, the blast furnace production increased, coke consumption was reduced, and operational flexibility improved. By 1986, eight 2-MW torches were installed to enhance the blast furnace operation. Torch reliability and maintainability proved difficult and as a result, the technology was not adopted on other commercial scale blast furnaces. Since the mid-1980s, Westinghouse Plasma Corporation has improved the reliability and maintainability of their plasma torches for industrial use. With increasing awareness of greenhouse gas (GHG) emissions, carbon taxes and the high cost of coke, Hatch evaluated the benefits of superheating hot blast with plasma torches as a means to introduce electrical power as a blast furnace fuel source.
The concept and benefits of retrofitting a cold blast mixer with plasma torches to heat the hot blast air will be described. A ‘hot-mixer’ that would top-up hot blast temperatures normally achieved during the stove firing cycle and eliminate the need for cold blast air mixing will be presented. Installation and maintenance of the torches in the mixer is simple when compared to installation as part of the tuyere assembles. Hot blast superheating is scalable; the benefits provided by plasma torches to reduce coke consumption and greenhouse gas emissions increases proportionally to the number of torches installed. The current and future effects of carbon taxation and emissions trading on the blast furnace operation will be discussed. Blast furnace operational scenarios were prepared using rules of thumb; this allowed for the exploration of the effect of superheating hot blast on CO2 emissions and cost to produce hot metal.