Blown refractories

Basic Oyygen Steelmaking. New Technology Emerges Proceedings of the Conference, Metallurgical Society of London, 1979. Contaias papers on refractories for conventional and new bottom-blown vessels. 

Top-Blown Basic Oxygen Process. The top-blown basic oxygen process is conducted ia a cylindrical furnace somewhat similar to a Bessemer converter. This furnace has a dished bottom without holes and a tmncated cone-shaped top section ia which the mouth of the vessel is located. The furnace shell is made of steel plates ca 50-mm thick it is lined with refractory 600—1200-mm thick (11). 

Furnace Design. Modem carbide furnaces have capacities ranging from 45,000 t/yr (20 MW) to 180,000 t/yr (70 MW). A cross-section of a 40 MW furnace, constmcted in 1981, having a 300 t/d capacity is shown in Figure 2. The shell consists of reinforced steel side walls and bottom. Shell diameter is about 9 m and the height to diameter ratio is shallow at 0.25 1.0. The walls have a refractory lining of 0.7 m and the bottom has a 1-m layer of brick topped by a 1.5-m layer of prebaked carbon blocks. The steel shell is supported on concrete piers and cooling air is blown across the shell bottom. A taphole to withdraw the Hquid carbide is located at the top of the carbon blocks. 

In a suspension roaster, the concentrates are blown into a combustion chamber. The roaster consists of a refractory-lined cylindrical shell, with a large combustion space at the top and two to four hearths in the lower portion. Additional grinding, beyond that required for a multiple-hearth furnace, is normally required to ensure that heat transfer to the material is sufficiently rapid for the desulfurization and oxidation reaction to occur in the furnace chamber. Suspension roasters are also unpressurized and operate at about 980°C (1800°F). 

The necessary heat may be supplied by passing the hydrocarbon gas or vaporised oil through a tube of refractory material which is externally heated, or the ingenious Rincker-Wolter method may be used. In this process the rough principle is to use a generator similar to a blue-gas generator filled with coke. By means of an air blast the temperature of the coke is raised to about 1200° C., then, when this temperature has been reached, the air supply is stopped and crude oil is blown in at the bottom of the hot coke. 

Liquid or pulverized solid fuels are blown into the kiln through a nozzle with primary air. Additional secondary air is drawn into the kiln through the clinker cooler. The flame in the rotary kiln must meet several requirements. The clinker must be correctly burned, so as to minimize its content of free lime, with the least expenditure of fuel. The ash from a solid fuel must be uniformly absorbed by the clinker. For normal Portland cements, the conditions must be sufficiently oxidizing that the iron is present as Fe however, for white cements, mildly reducing conditions may be preferable. Proper flame control also extends the life of the refractory lining of the kiln. Computer-aided or fully automated control of kiln operating conditions is increasingly used. 

Nothing much changed in iron or steelmaking for the next 200 years until the Bessemer process was introduced in the mid 1800s. In the Bessemer process, molten iron from the blast furnace was transferred to a separate refractory-lined vessel into which large quantities of cold air were blown to oxidize and remove the carbon. This was made possible by developments in air compression equipment. The modem steel age was bom. The availability of higher-quality, low-cost steel drove rapid expansion of the market for iron and steel and led to a rapid development of several new technologies. 

---