There is an old saying among steel producers that if you have not made your money by the time you cast, you will not. Even with the ever-changing global market conditions of today, profits can and should be made by the time the steel is cast. As technological advances continue to increase, greater steelmaking profits are possible.

There is a more than a 20-percent decline in variable costs to produce steel today compared with 10 years ago. These cost drops have occurred by applying new technology. The decrease in electrode consumption per ton of steel produced is over 60 percent. This comes from higher secondary voltages and the application of effective water spray rings. In the last two years, with the use of slag engineering, no gunning needs to be done and production costs have been eliminated. The North American steelmakers have Dr. E. B. Pretorius of Baker Refractories and the U.S. Department of Energy’s Albany Research Center to thank for North America leading the world in slag engineering.

Closed-furnace operation with five sources of energy available has cut over 100 kWh/L.S. ton from the electric energy consumption. Closed-furnace operation makes oxygen lances through the door obsolete. The closed charging door results in over 40 kWh/L.S. ton savings. Tap-to-tap times of less than one hour are standard. Except for escalating energy costs, all other cost centers for North American steelmakers have decreased. Presently, over $15/L.S. ton is spent on energy whereas less than one-half hour of labor costs are spent; labor costs are now less than energy costs and will continue to decrease.

The problem is that all technologies have not been applied, training of steel plant personnel has not been done, and an understanding of the technologies possessed by the suppliers has not been widely communicated. For these reasons, the U.S. Department of Energy earlier this year awarded a three-year contract to D. L. Schroeder & Associates for “Improving the Efficiency of Electric Arc Furnaces in the United States” (AMM, Jan. 29). The contract, which carries a price tag of $3 million, looks to reduce energy consumption and environmental impacts while boosting the productivity of the steelmaking process.

The contract calls for the development of a “Steelmaker Pilot,” utilizing technologies to apply, guide, and control the electric arc furnace process in the United States. According to early estimates, the aim of the Steelmaker Pilot control technology is to save electric furnace producers $4 to $10 per ton on manufacturing costs by improving refractory life.

As reported, Tamco Steel, Rancho Cucamonga, Calif., is the first demonstration site. Tamco annually produces around 600,000 tons of rebar. Steelmaker Pilot will be installed at Tamco in January 2002. The system will control a 105-ton electric arc furnace. There will be at least one more demonstration site besides Tamco before Steelmaker Pilot is launched as a commercial product in 2003.

The Steelmaker Pilot system is implemented on a network of personal computers (PCs) and programmable logic controllers (PLCs). Suppliers would connect their equipment to the Ethernet network of PCs and PLCs. The basic concept involves accurately establishing and maintaining optimum heat profiles throughout the sequence of events for steel production. With the optimum set points established for sequencing the heat, the heat is sequenced by Q-VAR, a dynamic sequencer. Capturing all data in time-stamped records in a data base management package allows the heat to be rerun for diagnostic and training purposes.

The Steelmaker Pilot sets up the heat by running a charge design calculation that includes slag engineering and energy optimization. The silicon and alumina in the raw materials are important due to the need to control the B4 basicity of the slag to between 1.8 and 2.3, according to a technical paper published by E.R. Wunsche and R. Simcoe. Using slag engineering, the MgO in the slag is controlled so as to be neutral to the MgO in the lining. The shunted arc at a B4 basicity of approximately two leads to lower arc resistance and a power increase of six to 15 percent.
All this means faster heats with virtually no gunning repairs. Recently, the melt shop superintendent of a million-ton plus shop said zero gunning is impossible. However, Nucor Steel, Gerdau-MRM, and others already have accomplished this.

The required production rate, time-of-day the heat is to be made, and the energy costs will determine which energies and their amounts that are to be used. With energy costs escalating, the energy optimization routine is an effective tool in setting up the energy sequence. Wise usage of carbon dioxide that will be allotted annually also has to be considered. Maximum use of chemical energy may be dictated during pick electric energy costs.

Artificial intelligence can be used to predict the foamy slag index, according to Eric Wilson, department of Aerospace Engineering and Mechanics at the University of Alabama (at Tuscaloosa). Post combustion efficiency also can be predicted. Adjustments are made by carbon and/or dolomitic lime injection to maintain the foamy slag height and post combustion efficiency that has proven to be optimal based upon experience. Having a more or less constant foamy slag height results in a constant heat loss. This allows a precise prediction of bath temperature.

As the heat end point is approached, bath carbon and temperature are measured so specified end point carbon and temperature can be reached simultaneously. The problem has been in stopping the heat to take and analyze a sample for carbon. Three to five minutes are wasted. Utilizing the power analyzer, developed by UHP International Inc., Williamsville, N.Y., carbon is determined instantaneously for AC furnaces and within 10 seconds for DC furnaces. No time loss and/or loss of foamy slag is experienced. Tapping occurs at the correct carbon and temperature.

Faster heats coupled with higher oxygen usage has led to over-blowing to low carbons (this has become common). Loss of yield, higher oxygen usage, and longer heats result in higher cost steelmaking. With catch carbon, this does not occur. Savings of three percent in yield and one minute in heat time are common.

Dr. David L. Schroeder is president of D.L. Schroeder & Associates, a consulting firm based in Pittsburgh.
© 2001 American Metal Market LLC, a division of Metal Bulletin Plc. All rights reserved.

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