A waste heat recovery process for continuous feeding and preheating of scrap charge to an electric arc furnace after preheating it with furnace exhaust gases.
Tenova’s Consteel® process involves continuous feeding and preheating of scrap charge to an electric arc furnace (EAF). Charge is loaded from the scrap-yard to the charge conveyor, where it is continuously transferred to the EAF while being preheated by off-gases. Once preheated, the charge falls into the EAF and is melted by the liquid steel bath. Constant flat bath operation is an advance over conventional batch processes. Continuous charging results in increased productivity, lower energy use and improved safety. As of 2009, 36 plants globally used Consteel®.
Most EAF’s require 360 to 440 kWh per ton of liquid steel produced. EAF off-gases flow into the pre-heating tunnel above 900 ºC and preheat the scrap charge to an average temperature in the range of 300 to 400 ºC. With Consteel®, EAF electrical consumption can be reduced to approximately 305 to 325 kWh/ton—with typical energy savings ranging between 73 and 110 kWh/ton (savings of over 20%).
Additional advantages of preheating include elimination of scrap moisture, reduced electrode consumption, a reduction in dust, an increase in scrap yield, and a reduction in tap-to-tap times providing a 33% productivity increase. Scrap introduced into a hot molten bath is melted by immersion. The electric arc makes good contact when working on a hot bath instead of solid scrap with improved contact reducing harmonic and flicker problems.
Consteel® has been employed with EAF heat sizes ranging from 45 to 275 tons with liquid steel outputs from 60 to 300 tons/hour. There are 3 EAF facilities in the Northwest.
This is not an endorsement of Teranova or Consteel® but, to our knowledge, as of 2012 they are unique in offering this technology.
Status:
Baseline Description: Conventional EAF with no Charge Preheating Baseline Energy Use: 400 kWh per year per ton of steel
Most EAF’s require between 360 to 440 kWh in electrical energy consumption per ton of liquid steel produced. A value of 400 kWh/ton will be used as the baseline.
"Typical" Savings: 23% Low and High Energy Savings: 18% to 27% Energy Savings Reliability: 3 - Limited Assessment
With the ConSteel approach, EAF off-gases flow into the pre-heating tunnel at a temperature above 900 ºC and preheat the scrap charge up to a surface temperature above 600 ºC with an average temperature in the range of 300 to 400 ºC depending upon the type of scrap charged. Using the continuous melting Consteel approach, EAF electrical consumption can be reduced to approximately 305 to 325 kWh/ton. Typical energy savings range from 73 kWh/ton to 110 kWh/ton.
With a "typical" savings of about 91 kWh/ton, and with a 400 kWh/ton baseline, the energy savings amount to 22.7% of the input energy.
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
David Blazevic, 01/01/2012. The Evolution of Preheating and Importance of Hot Heel in Supersized Consteel Systems Iron & Steel Technology
Robert Schmitt, 09/11/2006. Electric Arc Furnace Scrap Preheating The EPRI Center for Materials Production
EERE, 10/27/2005. Process to Continuously Melt, Refine, and Cast High Quality Steel Industrial Technologies Program
Energetics, Inc., 06/20/2006. Steel Industry Marginal Opportunity Study Industrial Technologies Program
Dr. John Stubbles, 07/15/2004. Energy Use in the U.S. Steel Industry: An Historical Perspective and Future Opportunities Industrial Technologies Program
Tenova Group, 01/01/2013. Consteel System Tenova Group
Tenova Core, 01/10/2011. Tenova Core Contracted for Consteel Revamp Tenova Core