Energy Savings for the Metals Industry

The steel industry is energy intensive with many opportunities to apply advanced controls to save energy. Some of the possible energy saving applications in a steel mill and the potential annual savings are illustrated in the figure below.

Energy saving systems typically use variable frequency drives, mill feedback data, and expert mill operation knowledge to precisely control and reduce the energy flows through the equipment. Some of the actual savings achieved by TMEIC on hot strip mills are shown below.

Main Motor Cooling Fan – Energy savings through speed control of the cooling fan based on the load on the motor, winding temperature, and air temperature.
Auxiliary Motor Cooling – Energy savings through speed control of the cooling fan based on the load on the motor, winding temperature, and air temperature.
Fume Exhaust Fan – Energy savings through fan speed control based on the exhaust air flow.
Cooling Water Pump – Energy savings through pump speed control based on the tank level and calculated flow of cooling water to the run out table.
Scale Pit Pump – Energy savings through pump speed control based on position of the slab relative to the descaler.

The following table shows the energy saving technology for each facility in a steel plant.

Plan	Equipment	Mechanical equipment and system technology
Manufacture of Pig Iron	Combustion equipment	Coke oven combustion equipment Air heating furnace combustion equipment
	Collection of waste heat	Coke dry quenching (CDQ) Collection of exhaust gas heat in coke oven Collection of coke oven furnace gas heat Collection of heat from sinter cooler Blast Furnace dry-type TRT Heat collection of air heating furnace Material drying preheating equipment
	Other Processes	Pulverized coal injection (PCI) Coal moisture control equipment Dust collector speed control, or combustion blower
Steel Making	Waste Heat Recovery	Arc furnace optimum electrical control system Arc furnace electric pole variable speed drive hoisting equipment Ladle refining optimum operation control system Larger arc furnace transformer capacity
	Sintering Plant	Main Blower Cooling Fan
	Collection of waste heat	Material preheating equipment for electric furnace
	Electrical Energy Saving	Speed control of dust blower High-speed electric hoisting control, furnace cover control
Rolling/ Surface Treatment	Collection of waste heat	Boiler for waste heat utilization Heat accumulation type regenerator
Rolling/ Surface Treatment	Electrical Energy Saving	Speed control of auxiliary motor on main motor Speed control of roll cooling water pump Pressure control of de-scaling pump
Rod/ Shaping/ Fabrication	Heat utilization equipment	Speed control of furnace blower
	Collection of waste heat	Waste heat utilization Collection of annealing exhaust gas heat
	Electrical Energy Saving	Speed control of cooling fan motor for main motor Speed control of roll cooling water pump Change motor from DC to variable-speed AC
Other Energy Consumption Plant	Cogeneration equipment	Multiple-stage extraction steam turbine Back pressure turbine
	Electric power use equipment	Speed control of Fan or Pump Power factor improvement equipment High efficiency motor/ electric transformer
	Lighting system	High efficiency lighting system High frequency fluorescent lamp lighting

Abstract from "Type 1 specified Business Operator" the guide for mid and long term scenario- (4) Steel Plant publication in Japan by ECCJ, Japan 1999 with TMEIC's amendments from electrical point of view.

TMEIC introduces the following electrical energy saving technologies for metal mills:

Energy Saving System for Rolling Mills and Process Lines

Features

Providing optimal energy savings for complete rolling mills and process lines
Providing an energy saving system which can be easily added to an existing mill
Using a combination of PLC controllers and drives

Applications

Energy saving using variable speed drive control
Optimal cooling of drive motor
Energy savings for miscellaneous power, lighting, and heaters (example: Stop while idling)
Optimal operation using energy saving control model (example: heating furnace combustion control and mill pacing)
Waste heat recovery

Energy Saving Controls for Hot Strip Mills

Furnace combustion control

Improved fuel consumption using furnace combustion control model
Reduction of material heat emission using mill control model

Improvement of power factor

Improving efficiency and power factor by applying GCT/IEGT main drives
Monitoring power demand for the entire mill line
Reduction of electric power rates by improving power factor

Optimization of Ventilation cooling

Optimal control using variable speed control
Main motor cooling fan
Auxiliary motor cooling fan
Electrical room ventilation cooling fan

Applying Variable Voltage, Variable Frequency Control

Descaler pump
Air compressor
Heating furnace blower
Conveyor system

Energy saving operation

Energy saving control of miscellaneous power, lighting and air conditioning units

Introduction of energy saving equipment

Applying high efficiency motors
Applying high efficiency transformers
Replacing DC motors with AC motors and variable speed drives

Energy Saving Control System for Hot Strip Mill Main Motor Cooling Fan

In order to remove the heat generated in the main motor rotor and stator, cooling air is circulated through the unit cooler. The speed of the cooling fan motor is varied proportionally to the load of the main motor, thereby providing energy conservation.

Typical plot of Fan Frequency and Motor Temperature

This graph shows an example of controlling the main motor cooling fan speed so the temperature rise of the motor remains constant irrespective of the main motor load. By applying this technology, large energy savings have been realized as shown in the following table.

*Typical Change of Fan frequency and Motor Temperature*

This graph shows the power reduction by applying TMEIC's energy saving control system in a steel company.