Rolling Mills

In rolling mills, intermediate steel products are given their final shape and dimension in a series of shaping and finishing operations.  Most of the slabs are heated in reheating furnaces and rolled into final shape in hot– or cold–rolling or finishing mills.   While some products (e.g. reinforcement bars, steel plates) only require hot-rolling, some others may require both hot– and cold–rolling (steel for cars and white-goods). Mechanical forces for cold rolling will create much more force and energy needs, while hot rolling happens much faster with less forces; however, there are significant energy costs to heat the metal to near eutectic temperatures (US EPA, 2010. p.25). In large integrated steel plants, the hot strip rolling process is the third largest user of energy after iron and steel making (IEA, 2007. p. 135).

In any hot rolling operation the reheating furnace is a critical factor to determine end-product quality, as well as the total costs of the operation. Energy use in a reheating furnace depends on production factors (e.g. stock, steel type), operational factors (e.g. scheduling), and design features. Based on seven sites, average total primary energy requirement of 1.2 GJ/t-cast steel is reported for hot rolling. According to IEA (2007), globally, typical hot rolling energy needs are 2 – 2.4 GJ/t.Upgrading existing furnaces will be another way of harvesting energy savings. 

According to IEA (2007) global average energy needs in cold rolling are  between 1 – 1.4 GJ/t. 

Rolling MillsSchematic

Rolling MillsTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Process Control in Hot Strip Mill

Estimated energy savings based on reducing rejects from 1.5% to 0.2% was 9% of fuel use, or approximately 0.3 GJ/t-product (US EPA, 2010. p.27). 

Emissions are reduced by 15.1kg CO2/t-rolled steel.

The investment costs for one plant in Belgium was $3.6 million for a hot strip mill with a capacity of 2.8 million tons, $1.29/t-product. The payback time is estimated as 1.2 years (US EPA, 2010. p. 27).

Commercial
Proper Reheating Temperature

A reduction of the heating temperature 100°C in the reheating furnace decreases unit fuel consumption by 9% to 10%. However under certain conditions total energy consumption may not decrease with a decrease in heating temperature.

Commercial
Throughput Optimisation in Rolling Mills

This technology ensures better utilization of rolling mill capacity and optimises throughput. Energy Saving occurs through improved product flow.

Coupling of work processes in case of interruptions, thereby less wear occurs.

Commercial
Oxgen Level Control and VSDs on Combustion Fans

A conservative approach estimates energy savings to be around 10%, or 0.33 GJ/t-rolled steel.
VSD on a combustion fan of a walking beam furnace at a UK based mill reduced the fuel consumption by 48%. 

Emissions are reduced by 16.6 kg CO2/t-rolled steel.

Retrofit capital costs are estimated at $0.79/t-rolled steel.
Installation of VSDs in a UK based mill had a payback time of 16 months  (US EPA, 2010. p.29). 

Commercial
Pressure Control for Furnace

LPG consumption was reduced by 83.3 tons/y in a drying furnace. Electric power savings were 24,734kWh/y.

Lower emissions due to energy savings by the technology.

Cost savings are ¥413,000/y.

Commercial
Avoiding Furnace Overloading

Energy consumption per unit production will decrease. 

CO2 reductions per unit production will decrease. 

Not available. 

Commercial
Energy Efficiency Drives for Rolling MillsHigh efficiency motors can save approximately 1-2% of the electricity consumption. Assuming an electricity demand of 220 kWh/t-hot rolled steel, the electricity savings are estimated to be 4 kWh/t-product (Worrell et al., 2010. p.100).

Emission reductions are estimated at 1.6 kg CO2/t-product. 

The additional cost of the high efficiency drives was estimated to be approximately $0.30/t-hot rolled steel. The payback time is estimated as 3.2 years (US EPA, 2010. p. 25).Commercial
Regenerative Burners for Reheating Furnaces

NEDO reports that using regenerative burners on a 110 t/h capacity billet reheating furnace (operating at 1050 oC) can reduce the energy consumption by 0.18 to 0.21 GJ/t-steel, as compared a conventional furnace.  Annual energy savings are reported to be 9.3 to 11.6 GWh ((NEDO, 2008. p. 88)

Up to 50% NOx reduction is possible with high temperature combustion.  CO2 emissions will also be reduced according to the reduced fuel consumption. 

Retrofiting costs for three pairs of regenerative burners for a 110 t/h furnace were ¥9 million for equipment and  ¥1 million for construction.
The payback time for the overall investment was 0.7 years (at a heavy fuel oil cost of ¥433/GJ) (NEDO, 2008. p. 89)

Commercial
Flameless Burners - Dilute Oxygen Combustion

EU Flag A plant in France reduced furnace fuel consumption by 40% by converting five pit furnaces to flameless oxyfuel furnaces- excluding additional electricity requirement for oxygen production. The production of 1 Nm3 of Oxygen requires approximately 0.5 kWh of electricity (Worrell et al., 2010. p. 102).

US flag A plant in the US reduced furnace fuel coonsumption by 60% by implementing a flameless oxy-fuel operation on its rotary-hearth steel-reheat furnace - compared to the original air-fuel operation. 

US flag In a US based plant, swithinc over to flameless oxyfuel burners reduced CO2 emissions by 60% and NOx emissions by 92%. 

Commercial
Walking Beam Furnace

Compared to three pusher type of furnaces, installation of a walking beam furnace together with a state-of-the-art control system reduced energy and fuel consumption by 25% and 37.5%, respectively. 

Lower operational costs compared to alternative transmission systems.

Commercial
Recuperative Burners

Recuperative burners in the reheating furnace can reduce energy consumption by as much as 30 percent. Although actual savings will be highly facility-specific, one estimate placed energy savings at approximately 0.7 GJ/t-product.

US flag tIn a US based plant, recuparator replacement reduced fuel consumption by 9%.

Japanese flag Another example in Japan shows that a newer model continuous slab reheating furnace can reduce energy consumption by 25% in comparison to an older furnaces recovering waste heat with a recuperator.

US flag tEmission reduction estimations are in 35.2 kg CO2/t-steel.

Retrofit Capital Cost is $3.9/tonne rolled steel.

Commercial
Thermochemical Recuperation for High Temperature Furnaces

This technology can reduce the fuel consumption in the furnace by 25% or more. 

CO2 and NOx emissions will be reduced. 

Demonstration
Installing Lubrication Systems

Installation of a lubrication system resulted savings of 4 kWh/t-product (Worrell et al., 2010. p. 100).

Savings are estimated at $0.31/t-product.

Commercial
Improved Insulation of Reheating Furnace

The potential energy savings for insulating a continuous furnace were estimated to range from 2 to 5% or around 0.16 GJ/t-rolled Steel.

Emissions reductions are estimated to be around 8.0 kg CO2/t-rolled steel.

Retrofit Capital cost of $15.6/tonne solled steel is estimated.

Commercial
Hot Charging

Energy savings of 0.06 GJ/t-rolled steel are estimated (US EPA, 2010. p.27). 

Japanese flag In a Japanese plant, hot charging has reduced specific fuel consumption in the heating furnace by 0.21 GJ/t-product (NEDO, 2008. p. 86)

Emissions reduction potential is estimated to be 30.2 Kg CO2/t-rolled steel. 

Retrofit capital costs and savings are estimated as $23.5/t-rolled steel and $1.15/t-hot charged steel with payback times of 5.9 years (US EPA, 2010. p.27).

Japanese flag In a Japanese plant total retrofiting costs were ¥250 million. With a heavy oil price of ¥433/GJ, the payback time was 2 years. 

Commercial
Cold Rolling - Reducing Losses on Annealing Line

 

Implementing loss reduction measures for a continuous annealing line, energy use can be reduced by up to 40-60% compared to furnaces without heat recovery (Worrell et al., 2010. p. 105).

Energy savings can amount to 0.3 GJ/t-product for fuel and 0.011 GJ/t-product for electricity (US EPA, 2010. p. 29).

Emission reductions are estimated to be 17.5 kg CO2/t-product.

Investment costs in a plant in Netherlands were estimated to be $4.2/t-product. The payback time is estimated as 4 years (US EPA, 2010. p. 29).

Commercial
Cold Rolling - Automated Monitoring and Targeting System.

A system installed at the UK based strip mill reduced energy demand of the cold rolling mill by approximately 15-20% (Worrell et al., 2010. p. 104) or approximately by 0.22 GJ/t-product (US EPA, 2010. p. 30).

US flag Emission reductions are estimated to be 35.3 kg CO2/t-product.

 

Installation costs were estimated to be $1.72/t-product, or $1.0/t-crude steel. The payback time is estimated as 0.8 years.

Commercial
Cold Rolling - Reduced Steam Use in the Acid Pickling Line

Steam use can be reduced by around 17% or by approximately 0.19 GJ/t-product (US EPA, 2010. p. 30). 

Emission reductions are estimated to be 9.9 kg CO2/t-product (US EPA, 2010. p. 10). .

 

Estimated capital costs were $4.4/t-product. The payback time is estimated as 7 years (US EPA, 2010. p. 30).

Commercial
Cold Rolling - Continuous Annealing Furnace

In a Japanese plant installation of this system reduced fuel consumption by 33%. >
Considerable differences in fuel consumption exist between different types of cooling equipment used in continuous annealing: the suction cooling roll uses only 14 percent of the power used by a gas jet system.  (US EPA, 2010. p.30)

US flag Installation of a facility with a capacity 450,000 t/yhas an estimated cost of $225 million.(US EPA, 2010. p.30)

Commercial
Heat Recovery to the Product

Annual cost savings of 32% compared to no-heat recovery.

Commercial
Heat Recovery from Cooling Water

Energy savings of 0.0 GJ/t-rolled steel is estimated by the implementation of the technology, with an increase of 0.17 kWh/t in electricity consumption (Worrell et al., 2010. p. 104).

Emission reductions are estimated at 1.9 kg CO2/t-rolled steel (US EPA, 2010. p.10).

Retrofit Capital Cost is $1.3/t-rolled steel. Operation and maintenance costs can increase by $0.11/t-product (US EPA, 2010. p. 29). 

Commercial
Thin Slab Casting - Near Net Shape Casting

TSC is estimated to reduce energy consumption by 4.9 GJ/t-crude steel.
TSC with a tunnel furnace offers an energy savings 1.08 GJ/t-steel cast (US EPA, 2010. p. 24)

Thins slab casting is estimated to reduce CO2 emissions by 779 kg per ton of product. 

Investment costs for a large-scale plant were estimated to range from $234.9/t-product with a resultant cost savings of approximately $31/t-crude steel.
TSC is estimated to have a payback time of 3.3 years (US EPA, 2010. p. 24). 

Commercial
Endless Strip Production (ESP)

Specific energy consumption decreases by 40 – 60% as compared to a traditional rolling mill.

Environmental emissions will drastically decrease due to reduced energy consumption by avoiding reheat furnaces.

Commercial
Strip Casting – Castrip® Process

Compared to thick slab casting (hot rolling, pickling and cold rolling), the Castrip® process saves approximately another  2 GJ/t.

Correleating from the energy savings reported in APP (APP, 2010. p.94), the process is estimated to redcue CO2 emissions by 80-90% comparing to conventional casting. 

Commercial
Integrated Casting and Rolling

Energy savings can range from 35% to close to 100%.  

CO2 emissions are reduced due to reduced fuel consumption. 

Commercial
Thin Slab Casting

Energy savings are in range of 1 – 2 GJ of Primary Energy/t of product. Saving potential is 0.3-0.4 EJ/yr if this technology is applied to quarter of world production.

Estimated CO2 emissions savings are 20 - 40 Mt/yr.

Retrofit capital cost is $234.9/tonne hot rolled steel.

Commercial
Strip Casting

The savings over traditional thick slab continuous casting include 0.32-0.55 GJ/t for electricity and 1.2-1.5 GJ/t for fuel (US EPA, 2010. p.25). 

Commercial
Novel Post Combustion Method

Savings of up to 30% in fuel gas have been achieved relative to recuperative combustion air preheating systems.

Reduction of pollutants because flue gas is utilized.

Further cost reductions are possible due to the use of inexpensive low calorific-value gases such as process and biogas. 

Demonstration
Model Based Closed-Loop Oxygen Control

By reducing the oxygen content by 1.5 % in a heating furnace with a throughput of 450 t/h, energy consumption was reduced by 2.4 %.

For a 450 t/h capacity furnace, cost savings due to reduced energy consumption were €350 thousand/y.
The technology also reduced scale formation by 20% and this resulted in financial savings of €1.1 million/y. 

Demonstration
Preventing Scale Formation in Rolling

Energy consumption and material loss will be reduced. 

Reduced energy and material costs, and minimisation of subsequent corrective measures will reduce the costs. 

Research
Extended Universal Fuel Gas Measuring DeviceResearch
Innovative Reheat Furnace Management

This technology improves the performance of the furnace and its energy efficiency. It is possible to reduce the oxygen concentration to approximately 7 % by volume.

This technology lowers CO2 emissions.

The energy costs will be lowered. 

Demonstration
High Temperature Membrane Module for Oxygen Enrichment of Combustion Air

Savings of natural gas is estimated. Process gas can be reused.

This technology will decrease anthropogenic CO2 emissions.

If the O2 can be provided cost-efficiently,this will reduce operating costs of the technology.

Research
Development of Oxygen-rich Furnace System for reduced CO2 and NOx emissions

By applying this technology, fuel firing rate was decreased from 325-365 KW to 200-220 KW.

Potential savings are 40 – 45% in fuel usage. A corresponding reduction in CO2 emissions is obvious.

Fuel savings are offset to some extent by the cost of the Oxygen. However O2 production technologies are becoming more economical.

Demonstration
Oscillating Combustion

Efficiency or productivity increases by 5% or more. It improves heat transfer by up to 13%.

The technology reduces NOx emissions by up to 75%.

Demonstration

Rolling Mills Publications

Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry

The U.S. Environmental Protection Agency’s (EPA) energy guide, Energy Efficiency Improvement and Cost Saving Opportunities for the U.S. Iron and Steel Industry, discusses energy efficiency practices and technologies that can be implemented in iron and steel manufacturing plants. This guide provides current real world examples of iron and steel plants saving energy and reducing cost and carbon dioxide emissions.

Page Number: 

100-105

Global Warming Countermeasures: Japanese Technologies for Energy Savings / GHG Emissions Reduction

This revised 2008 version of the publication from New Energy and Industrial Technology Development of Japan includes information on innovative Japanese technologies for energy efficiency and for the reduction of COemissions.