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Show While the above program would ini tially be directed toward coal injection, the co-injection of other solid materials such as flux, ore, plastics, etc., should also be tested. Natural gas injection will continue to playa major role in North American blast furnace practice even after all companies likely to adopt coal injection have done so. 4.2.1.2 Blast Furnace Operating Improvements. The fuel used in an integrated plant's boilers accounts for a significant portion of the total plant fuel conswnption. A large portion of the boilers' steam output is used to drive the turbo-blowers that provide the wind for the blast furnaces . The advent of larger, modern blast furnaces has resulted in larger, more powerful turbo-blowers capable of producing greater air flows at higher pressures. This results in a cost factor that could be mitigated by a process change. Technology affecting boiler efficiencies, steam cycle efficiencies, condensers, and blower efficiencies is very well understood, and there are few areas of opportunity where further research would bring energy savings not already available. However, the following opportunity should be investigated to establish if significant energy savings can be achieved by making changes to the iron making processes of the integrated plants. • Modification of the blast furnace process using heated recycled reducing gases. Russian experimental work has demonstrated a process that uses recycled blast furnace top gas enriched with 95 percent purity oxygen instead of air for blast furnace blowing purposes. The top gas would be compressed, stripped of CO2, heated in modified blast furnace stoves, and blown into the furnace through the tuyeres. While a demonstration plant has been built in Russia, the process is untried in this COW1try. An evaluation of the process, its economics, and a possible field test in this country is needed. 4.2.1.3 Burner Enhancement Projects - Reheat Furnaces. Reheat furnaces are generally fued with recuperative burners of various sizes using combustion air temperatures up to 900°F. While temperatures greater than 900°F have been used, the cost of burner and recuperator materials goes up appreciably, and maintenance increases disproportionately, particularly if fuels other than natural gas are used. Burners are sized and applied by carefully taking into account the furnace heat loads that must be satisfied. However, the variability of the material heated (length and thickness as well as furnace loading pattern) makes the burner selection process a series of compromises. Modern computer control systems are now available to control furnace temperatures to respond to the varying production and temperature requirements for heated steel to be rolled by the mill. These computer programs are intended to model the radiant and convective heat transfer of the burner flames to the furnace refractory and steel. Furthermore, there is a whole spectrum of low NOx burners and oxy-fuel burners available in the marketplace. Additionally, there are several regenerative burner systems available. Pulse combustion burner systems are also being proposed by some suppliers for improving the efficiency of certain funlace types. Burner types supplied by the major manufacturers should be tested, evaluated, and modified, as required to: • Improve unifonnity of generation and application of heat to the steel. This includes a thorough evaluation of the heat transfer aspects of the burner types to confinn that existing computer models properly account for the burner characteristics. • Further reduce NOx emissions. • Improve the range over which bunlers can properly apply a wliform temperature field over the steel to be heated. • Improve burner long-tenn durability. A detailed examination of the benefits or disadvantages of using oxygen enrichment of the combustion air should be conducted. This should cover the full range of combustion air oxygen from 21 to 1000/0. It is clear that NO generation rises with the increase of combustion air oxygen content and the resultant flame temperature. The question x that must be addressed is whether or not the savings in fuel is a linear function of NOx per Btu of fuel fued so that the net NOx emission per ton of steel heated is reduced. 4.2.1.4 Direct Steel Temperature Measurement. While every major steel company now has very elaborate and complex computer models to simulate the heat transfer process that occurs in the reheat furnace and to predict the temperature of every slab in the furn ace, such models require direct steel temperature measurement to 9 |