Baskar Vairamohan Project Manager Industrial Center of Excellence December 17, 2014 Energy Savings with Induction Process Heating Overview, Applications and Case Studies
Jul 11, 2015
Baskar Vairamohan
Project Manager
Industrial Center of Excellence
December 17, 2014
Energy Savings with Induction Process Heating
Overview, Applications and Case Studies
2 © 2014 Electric Power Research Institute, Inc. All rights reserved.
Agenda
• Heat Transfer Modes
• Induction Fundamentals
–Heating
–Melting
• Applications
• Case Studies
•Benefits of Electrotechnologies
• Summary
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Facility HVAC
4.2%
Process Cooling
and Refrigeration
1.5%
Electrochemical
Processes
1.3%
CHP and/or
Cogeneration
8.5%
Conventional
Boiler Use
9.9%
Machine Drive
10.6%
Process Heating
21.0%
Other
3.9%
End Use Not
Reported
39.1%
Facility HVAC
4.2%
Process Cooling
and Refrigeration
1.5%
Electrochemical
Processes
1.3%
CHP and/or
Cogeneration
8.5%
Conventional
Boiler Use
9.9%
Machine Drive
10.6%
Process Heating
21.0%
Other
3.9%
End Use Not
Reported
39.1%
Break-down of All Energy Use in Industries
• Process heating accounts for
– 21% of total industrial energy use
– 2 to 15% of total industrial production cost
• Process temperature range: 300 – 5,000+oF
Source: Energy Information Administration, 2010 Manufacturing Energy Consumption Survey
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Other
6.6%
Process
Heating
12.1%
Facility HVAC
9.3%
Electro-
Chemical
Processes
7.2%
Facility
Lighting
6.9% Process
Cooling and
Refrigeration
7.2%
Machine Drive
50.6%
Other
6.6%
Process
Heating
12.1%
Facility HVAC
9.3%
Electro-
Chemical
Processes
7.2%
Facility
Lighting
6.9% Process
Cooling and
Refrigeration
7.2%
Machine Drive
50.6%
Industrial Net Electricity Consumption (End
Use)
• Process Heating uses 12.1% of total net electricity in manufacturing
• Total Industrial Net Electricity Consumption
= 2,850 Trillion Btu (= 835 Billion kWh) • Source: Energy Information Administration, 2010 Manufacturing Energy Consumption Survey
~100 Billion
kWh
http://www.eia.gov/consumption/manufacturing/
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Process Heating - Electricity Use by Industry
Sector
Primary Metal Manufacturing
– Largest electricity user
(39.4 billion KWh)
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Heat Transfer Modes
• Heat transfer happens in three ways:
– Conduction
• Heat transfer occur when adjacent atoms vibrate against one another
– Convection
• Transfer of heat vis mass flow (transfer).dominant form of heat transfer in liquids (also molten metals) and gases.
– Radiation
• Transfer of heat energy by means of photons in electromagnetic waves
Source: https://www.nsa.gov/research/tnw/tnw202/article4.shtml
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Induction Heating
• Induction heating makes use of I2R
losses, the same as the elements in
a resistance furnace or toaster.
• The difference is that the current is
“induced” with magnetic flux field,
rather than “applied” through
physical contact.
Network 60 Hz Frequency converter Filters
Chiller
Water cooling circuit
Inductor
and heated
piece
Transformer
Image Courtesy: Electricity de France (EDF)
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Induction Heating
• Used for heating directly, heat
treating or melting conductive
materials, typically metals.
• Similar to the operation of
transformer
• Plastics and other nonconductive
materials (e.g., chemicals) often
can be heated by first heating a
conductive material that transfers
heat to the nonconductive material.
• Generates heat within the
workpiece
Workpiece
Induction
coil
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Induction Heating Types
• Direct induction heating:
– It occurs when the material to be heated is in
the direct alternating magnetic field.
– The frequency of the electromagnetic field and
the electric properties of the material determine
the penetration depth of the field, thus enabling
the localized, near-surface heating of the
material.
– Comparably high power densities and high
heating rates can be achieved.
– Direct induction heating is primarily used in the
metals industry for melting, heating, and heat
treatment (hardening, tempering, and
annealing).
Examples of
Induction
Coils
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Induction Heating Types
• Indirect induction heating:
– a strong electromagnetic field generated by
a water cooled coil induces an eddy
current into an electrically conducting
material (susceptor), which is in contact
with the material to be treated.
– Indirect induction heating is often used to
melt non-ferrous materials in crucibles
such as gold and precious metals.
– Plastics and other nonconductive materials
(e.g., chemicals) often can be heated by
indirect induction heating
Single/Double Push-
Out Furnaces
Courtesy: Inductotherm
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What is Heat-treating?
• Heat treating as a technology can be very broadly defined as any process involving controlled heating and/or cooling of a work piece for the purpose of developing a given set of physical and mechanical properties.
• In general, this means:
– heating the work piece to a specific temperature—well above room temperature—at which the desired metallurgical transformations occur, then
– holding it at that temperature for a period of time sufficient for the transformations to occur through the work piece.
– followed by cooling at a prescribed rate to either develop additional transformed structures, or maintain the structure developed at the higher temperature.
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What is Annealing?
• Annealing is a treatment that consists of:
– heating a work piece and holding it at a suitable temperature
– followed by cooling at an appropriate rate.
• E.g. A steel work piece is heated to 1600oF (871oC) and held at this temperature.
– Approximate time needed is one hour per 1 inch (2.54 cm) of section thickness.
– The work piece is then slowly cooled to room temperature.
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What is Quenching?
• Quenching is the process of rapidly cooling the work piece
from the austenitizing (or, in the case of aluminum or stainless
steels, solutionizing) temperature in order to harden the
workpiece.
• The quenching usually takes place in a water, oil or polymer
bath. Gaseous quenchants are also used.
• Quenching medium depends on the ability of the work piece
material to be hardened (called hardenability), the section
thickness and shape of the part, and the cooling rates
required to develop the desired microstructure.
• Liquid quenchants include: Oil, Water, Aqueous polymer
solutions, Water containing salt or caustic additives
• Gaseous quenchants: helium, argon and nitrogen
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What is Tempering?
• Tempering is defined as a process in which a previously hardened (quenched) or normalized steel is heated to a temperature below the lower critical temperature and then cooled at a rate that will increase ductility, toughness and grain size.
• Tempering can be performed in a wide variety of equipment:
– Convection furnaces
– Salt bath furnaces
– Oil bath furnaces
– Molten metal baths
– Induction equipment
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Induction Hardening
• Involves heating the work piece into the austenitic range by
placing the part in the magnetic field generated by high-
frequency alternating current flowing through an inductor.
• The part is then quenched with liquid.
• The process is extremely versatile and can be used for
uniform surface hardening, localized surface hardening,
tempering and thorough hardening.
• The depth of heating is inversely proportional to the
frequency, consequently very precise case thickness can
be developed.
Dp is Current penetration depth, material electrical resistivity (ρ), magnetic permeability (μ) and coil current frequency (f):
𝑫𝑷 = 𝟑𝟏𝟔𝟎𝝆
𝝁𝒇 inch
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Power Density for Various Metal Heating
Technologies
• Productivity increases are often synonymous with
increases in power density.
• Table below shows the transmitted power density range for
the rapid metal heating process technologies.
Process Power Density
(W/cm2)
Power Density
(kW/m2)
Gas 1-10 10-100
Infrared 1-30 10-300
Induction 5-5,000 50-50,000
Direct
Resistance
10-10,000 100-100,000
Plasma 100-105 1000-106
Electron Beam 1,000 -109 10,000 -1010
Laser Beam 10,000 -1015 100,000 -1016 Source: EPRI
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Induction Heating Applications
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Other Applications of Induction Technology
• Hot Metal Working - forging,
forming, rolling, extrusion, and
upsetting.
• Melting - ferrous and non-ferrous
materials for sand, permanent mold,
and investment casting.
• Heat Treatment - hardening,
tempering, annealing, normalizing,
and stress relieving.
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Applications of Induction Heating
Source: Induction Heating Study 2003, BNP Market Research
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Dual Frequency Gear
Induction Hardening
Parts
• Dual frequency systems are used
more for surface hardening parts with
varying contours, such as gear teeth.
• The gear is induction-heated by:
– medium frequency to the deep
region for several seconds and
– reheated by high frequency for a
short period (taking advantage of
the surface skin effect of high
frequencies)
– followed by quenching by water
spray.
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Dual Frequency Gear
Induction Hardening
Parts
Inductor Coils
Example:
• For instance, a conventional induction heat
treatment might use a single frequency of
25kHz for 2.8 seconds.
• A dual frequency induction system might
use:
– 3kHz frequency for 1.8 sec in
preheating
– 150 kHz for 0.18 sec during final
heating.
• This new technique produces the desired
thin-surface hardening with little distortion
and high compressive residual stresses.
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Energy Savings Opportunities for Induction
Heat Treatment • Instant On/ Off: When not in use, the induction power supply can be
turned off thus saving energy. No pre-heating required.
• Rapid Heating of Parts: Induction heating rapidly heats the parts or part
sections. Because high electrical currents are induced into the part, the
resistance to this current flow causes very rapid heating in the area of the
induced current flow.
• Scale/ Scrap and Remelting: Shorter heating times - characteristic of
induction heating - result in considerably less scale (25% less than gas
furnace).
– Scrap losses due to improper heating are higher in gas-fired furnaces
– Remelting of scrap consumes lot of energy
• Lower energy costs achieved by localized workpiece heating and no off-
cycle heating losses.
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Induction Heating – Non-Energy Benefits
• Ease of automation: Many manufacturers have
completely automated their induction heating equipment.
• Compact footprint: Induction heating installations are
generally much smaller than conventional gas fired heating
furnaces for equivalent throughput.
• Precise heat location
• Easier process control and monitoring: It is easier to
control repeatability and monitor the process on a part-by-
part basis since it is not a batch process.
• No On-site emissions with induction heat treatment.
Especially beneficial in non-attainment areas.
Source: Induction Heat Treating Marketing Kit –
A Sales and Marketing Support Guide- TR-111818-Final Report, February 1999
Induction Melting
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Induction Melting – Operating Principle
• An induction furnace operates on a similar
principle to a transformer.
• The induction coil acts as a primary coil, having
many turns, and the charge acts a secondary
coil, with only a single turn.
• When an alternating current is applied to the
induction coil of a furnace, a significantly larger
current is induced in the metallic charge
materials.
• The resistance to the passage of the induced
current within the furnace charge causes the
charge to heat up until it eventually melts.
• Once the metal is molten the magnetic field
generated creates a stirring action in the bath,
producing both homogenization of the chemical
composition and assimilation of any bath
additions.
• Two major types: Coreless & Channel Furnace
Coreless Melting Furnace
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Coreless Induction Furnaces
• Has refractory shell surrounded by the coil. Further
classified as:
• Line: 60Hz
• Medium: 200-1200Hz
• High: Over 1200 Hz
• Variable Frequency Units
• Best suited for melting turnings or clippings & for simple
charging and pouring operations
• Advantages:
– Furnace can be completely emptied to change an
alloy
– Can be sized to meet melting needs
– Very efficient – 55-80% compared to fossil-fuel (7-
50%)
• Disadvantages:
– Refractory cracks can cause premature lining failure Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000
Image courtesy: Good Practice Guide 50 – Efficient Melting in Coreless Induction Furnaces
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Channel Induction Furnace
• Inductor consists of water-cooled coil embedded in the refractory
• Channel is formed in the refractory through the coil and this channel forms a continuous loop with the metal in the main part of the furnace
• Hot metal in the channel circulates into the main body of the metal in the furnace and is replaced by colder metal
• Advantages:
– Higher efficiency than coreless and natural gas furnace
– Extremely effective at mixing to have homogeneous temperature
– Typically used for holding molten metal
Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000
http://www.fomet.com/P/24/INDUCTION-FURNACE/POURING-INDUCTION-FURNACE---PR---PRV.html
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Energy Efficiency Improvements with
Induction Melting
Electric
Induction
Melting
Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000
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Energy (kWh) Required to Melt Per Ton of
Metal (Approximate Values)
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Energy Savings Opportunities with Induction
Melting
• Energy efficient: Induction furnaces are energy-efficient.
The overall efficiency normally ranges from 55 to 75
percent, which is significantly better than combustion
processes.
• No preheating of furnace required – as in the case of
natural gas furnace – thus saving energy as well as wasted
heat
• Natural mixing (stirring) action eliminates stratification
– Results in uniform melting
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Energy Efficiency Improvements in Induction
Melting Systems
Power Supplies used in Induction Melting Systems
Latest Generation Induction Melting Systems
Source: Inductotherm
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Non-Energy Benefits of Induction Melting
• Higher yield: Due to the absence of combustion sources, induction furnaces reduce oxidation losses that can be significant in the melting process.
• Faster startup: Induction furnaces can take up to full power instantaneously, thus reducing the time to reach working temperature. Melting batch time from metal charging to molten metal tapping can be reduced to one to two hours.
• Better product: Induction furnaces allow precise control, resulting in dependable and consistent quality. Exact control of power input ensures that the optimum temperature is maintained throughout processing. Medium frequency magnetic fields give a strong stirring effect, resulting in a homogeneous melt.
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Non-Energy Benefits of Induction Melting
• Flexibility: Induction furnaces require no molten metal as the starting batch. This facilitates repeated cold starting and frequent alloy changes.
• Automatic operation: Precise automatic control of power reduces furnace operation manpower to that required only for charging, tapping and metallurgical measurements.
• Compact installation: High melting rates can be obtained from small induction furnaces. No space is required for fuel storage and handling.
• Better working environment: Induction furnaces are much quieter than gas furnaces, arc furnaces, or cupolas. No combustion gas is presented and waste heat is minimized.
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Energy Savings and Productivity Increase in a
Metal Heat Treatment Plant for Railroad Bearing
• Challenge: Increasing production demand for
railroad bearings required additional heating
capability. Excessive energy and maintenance
cost were associated with the initial gas fired
furnace operation.
• New Method:
– Induction heating systems from Pillar/ Ajax
Tocco were considered as an alternative to
conventional gas fired furnace.
– The new installation requirement is
evaluated to determine cost/performance
savings opportunities via use of induction
heating systems.
– Five new 2500 kW - 60/200 Hz induction
heating systems were installed.
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Metal Heat Treatment for Railroad Bearing
Payback and Other Benefits
1. Overall cost savings/ton was 25% to 30%, providing a payback period that ranged from 0.9 years to 1.25 years
2. Scale loss reduced by 75%
– Removal of scales results in wasted products that cannot be remelted or reused
3. Scrap reduced by 75%
– Reduction of scrap resulted in reduction of energy, otherwise spent on remelting of scrap
4. Operating labor reduced by 50%
5. Maintenance reduced by 50%
6. Cost: Total installed system cost was $600,000
Photo Source: www.freefoto.com
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References
1. Industrial Process Heating: Current and Emerging Applications of Electrotechnologies.
EPRI, Palo Alto, CA: 2010. 1020133.
2. Rapid Metal Heating: Reducing Energy Consumption and Increasing Productivity in
the Thermal Processing of Metals, EPRI, Palo Alto, CA: 2000. TR-114864.
3. Energy Efficiency Improvement and Cost Saving Opportunities for the Vehicle
Assembly Industry, Christina Galitsky and Ernst Worrell Energy Analysis Department,
Lawrence Berkeley National Laboratory, March 2008
4. Development of a Performance-Based Industrial Energy Efficiency Indicator for
Automobile Assembly Plants, Boyd, Gale A., Argonne National Laboratory, ANL/DIS-
05-3, 2005.
5. Electric Process Heating, Maurice Orfeuil, 1987 (Battelle Press) - Book
6. Electrotechnology Update, Induction Heating. EPRI, TB-110221
7. Electrotechnologies in Metal Heat Treating Systems—Marketing Kit, EPRI, Palo Alto,
CA: 2000.1000136
8. ENERGY STAR:
http://www.energystar.gov/index.cfm?c=in_focus.bus_motorveh_manuf_focus
9. DOE – Process Heating Source Book For the Industry:
http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/process_heating_s
ourcebook2.pdf
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References
• Induction Melting:
– Melting technologies for Aluminum and other Non-ferrous metals
– EPRI Technical Commentary –Product Id:1001205, 2000
– Induction and Cupola Melting: A cost comparison model: CR-
108697, CMP – Report No 89-4, 1989
– Efficient Electric Technologies for Industrial Heating, product Id
– 1014000, 2007
– Good Practice Guide 50 – Efficient Melting in Coreless Induction
Furnaces, 2000
– Ind Heat WS Code - Cost Comparison Worksheet for Induction
Heating, Version 1.0, EPRI Product Id: 1001500, May 2001
– http://www.fomet.com/P/24/INDUCTION-FURNACE/POURING-
INDUCTION-FURNACE---PR---PRV.html
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Questions
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Contact
Baskar Vairamohan
Project Manager, EPRI
Ph: 865-218-8189
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