OIL IN THE STEEL INDUSTRY.
In the open hearth process of making steel the impurities in the pig iron are removed by the action of the flame upon an open bath of the molten metal. A very high temperature must be maintained in such a furnace to keep the iron thoroughly melted, and for this reason the air for combustion is heated to over 1000 deg. F. before it enters the combustion chamber. Measured quantities of ore, iron scale, or other oxides are added to the bath of molten metal, and these, re acting with the impurities present, serve to keep it thoroughly agitated. If the pig iron or scrap contains too much phosphorus, burnt lime is added to the charge, and the resulting slag absorbs the phosphorus.
There are many advantages in the use of oil as a fuel for open hearth furnaces. The cost of keeping such a furnace in repair is approximately 40 per cent less than when gas is used. The heat of the furnace is easily regulated, and a more even temperature may thus be maintained. Different chemical reactions take place in the furnace, producing a superior quality of castings ; and a lower grade of scrap iron can be used with fuel oil than with producer gas. As a result of these advantages many large steel plants in the East have equipped their furnaces for the use of fuel oil. In localities where natural gas is abundant and coal is cheap, the oil installation is merely an auxiliary ; it does not in any way interfere with the regular opera tion of the furnace with the other fuel, and is ready for use at a moment's notice.
Open hearth furnaces may be very simply and inexpensively equipped to burn oil. Fig. 77 shows the general arrangement of piping, burners, pumping sys tems, reversing stand and storage tank for a plant having two furnaces. The necessary apparatus for one open hearth furnace consists of two burners (one for each end of the furnace), a reversing stand located back on the charging floor for reversing the flow of the oil and the atomizing agent as the furnace is re versed, a pumping system for pumping oil from stor age tank and heating and regulating the supply to the burners, a reducing valve for regulating the atom izing agent (air or steam) and the necessary valves, pipe, tank and fittings as shown. The reversing stand shown in Fig. 78 is used in the regenerating type of furnaces, in which the draft is changed at certain inter vals from one side to the other, thus allowing the air to pass through the regenerative chamber, which is built of checkered brickwork. The waste gases flow ing from one side of the furnace pass into this cham ber and the brickwork absorbs a large part of the heat which they contain ; by reversing the flow of the gases from one side to the other, the air for combustion comes in contact with these hot bricks and is pre heated.
A swinging burner is commonly used for firing open hearth furnaces. When the furnaces are close together, or the end of the furnace is so near to the wall of the building that there is not room for the use of a swinging burner, a water-cooled burner is used, as illustrated in Fig. 79. Such a burner remains permanently in the furnace, both the burner and the water-cooled nozzle being swung in a yoke, so that the nozzle may be elevated or lowered as required. A circulation of water through a 4 in. pipe prevents the burner from being melted off by the heat of the furnace.
Fig. 80 illustrates the application and use of the ladle drying burner. It is provided with a swinging stand and is located at a convenient place on the charg ing floor, or bolted against the columns of the build ing. It is arranged to lower into the ladle when in use, and to raise up when not in service. A long noz zle is proved for reaching well down into the bottom of the ladle so that the heat is evenly distributed over the bottom and up the sides. A sheet iron cover is put over the ladle to protect the burner and retain the heat and help to distribute it to the sides of the ladle.
Some plants making merchant bar iron from scrap, use a furnace in which the waste heat is utilized by the installation of a boiler at the end of the fur nace. Data secured at one plant using this arrange ment show the consumption of oil per ton of iron to be 47 gal. The waste heat secured from the two fur naces was sufficient to furnish the necessary steam for operating the engines driving the rolls, pumping water and generating the electricity and steam used throughout the plant.
The report below was received from a rolling mill in which fuel oil has been used for many years. The manager states that the quality of iron produced from the scrap material is much better with oil than with coal as a fuel. When running through the rolls, the percentage of weight lost is much lower, as the metal is better able to withstand the compression, vibratory and torsional stresses of the rollers. The same size of furnace with coal fuel would only handle from 30 to 32 tons of material daily ; and the expense of up keep is about 35 per cent less than with coal. Vari ous atomizing agents have been tried, including steam, high pressure air, and steam and low pressure air combined ; but it has been found that much better results are obtained from low pressure air.