3 Energy Conservation In Induction Furnace

Energy Conservation in Induction furnace Programme on Energy Conservation in Foundry Industry E Nand Gopal The Energy and Resources Institute 11th August2014

Contents

Introduction and working principle Losses in induction furnace Energy conservation measures Selection and sizing Best operating practices Case Studies 2

Melting furnaces Melting furnace Arc furnace Secondary refining furnace

Electric furnace

Melting furnace

Medium frequency furnace Induction furnace

Mains frequency furnace

Coke

Channel type furnace

Cupola Natural gas

Reverberatry furnace

Heavy oil

3

Introduction and working principle Two main types

• Coreless • Channel

Medium frequency coreless type

• Frequency: 500 – 2000 Hz • Crucible size: 50 kg – 20MT • Switching device: SCR or IGBT

Laws governing induction heating

• Electromagnetic induction • The joule effect 4

Introduction and working principle

5

Losses in induction furnace Transmission losses Converter losses Capacitor bank losses

Conduction heat loss Radiation losses Coil losses 6

Losses in induction furnace

7

Energy conservation measure Selection and sizing

Best operating practices

• • • •

Induction furnace selection Technology: SCR or IGBT Furnace sizing Cooling water circuit installation

• • • • •

Charge preparation and charging Melting and making melt ready Emptying the furnace Furnace lining Energy monitoring and data analysis 8

Selection and sizing – Before installation

Crucible size

• Melt rate handling capacity • Moulding capacity • Number of crucible

Panel capacity and type

• Technology: SCR or IGBT • Panel capacity: Power density (kW / kg)

Cooling water circuit

• Pump specification • Type of piping and size of piping

9

Selection and sizing – Before installation

Pump specification

Piping

• • • •

Flow rate, lpm (litres per minute) Head, m Power rating, hp / kW Pump-motor set efficiency, % • 34%, 37%, 40%, 47%, 59%

• To minimize friction loss • Water velocity typical design 1.8 – 2.0 m/s • Based on economics

10

Specific energy consumption • Typical values for cast iron foundries

SEC (kWh/tonne)

650

624

603

600 550

571

539 511

507

500

Average Best

450

400 Kolhapur

Belgaum

Europe

Kolhapur – 63 units Belgaum – 15 units Europe – WB report 2012

11

Analysis – Power Curve 600

Induction furnace power curve

500

Power, kW

400 300

Delay in spectro analysis

200 100 0

12

250

200

1:05:00 PM 1:07:00 PM 1:09:00 PM 1:11:00 PM 1:13:00 PM 1:15:00 PM 1:17:00 PM 1:19:00 PM 1:21:00 PM 1:23:00 PM 1:25:00 PM 1:27:00 PM 1:29:00 PM 1:31:00 PM 1:33:00 PM 1:35:00 PM 1:37:00 PM 1:39:00 PM 1:41:00 PM 1:43:00 PM 1:45:00 PM 1:47:00 PM 1:49:00 PM 1:51:00 PM 1:53:00 PM 1:55:00 PM 1:57:00 PM 1:59:00 PM 2:01:00 PM 2:03:00 PM 2:05:00 PM 2:07:00 PM

Power, kW

Analysis - Discussion 500

450

400

Temperature drop

350

300

Delay in spectro analysis

150

100

50

0

13

150

100

50

10:38 AM 10:40 AM 10:42 AM 10:44 AM 10:46 AM 10:48 AM 10:50 AM 10:52 AM 10:54 AM 10:56 AM 10:58 AM 11:00 AM 11:02 AM 11:04 AM 11:06 AM 11:08 AM 11:10 AM 11:12 AM 11:14 AM 11:16 AM 11:18 AM 11:20 AM 11:22 AM 11:24 AM 11:26 AM 11:28 AM 11:30 AM 11:32 AM 11:34 AM 11:36 AM 11:38 AM 11:40 AM 11:42 AM

Power, kW

Analysis - Discussion Induction furnace power curve

450

All moulds not ready

400

350

300

250

200

Small ladle pouring, power loss during pouring

0

14

250

4:10 PM 4:12 PM 4:14 PM 4:16 PM 4:18 PM 4:20 PM 4:22 PM 4:24 PM 4:26 PM 4:28 PM 4:30 PM 4:32 PM 4:34 PM 4:36 PM 4:38 PM 4:40 PM 4:42 PM 4:44 PM 4:46 PM 4:48 PM 4:50 PM 4:52 PM 4:54 PM 4:56 PM 4:58 PM 5:00 PM 5:02 PM 5:04 PM 5:06 PM 5:08 PM 5:10 PM 5:12 PM 5:14 PM 5:16 PM

Power, kW

Analysis - Discussion Induction furnace power curve

450

400

350

300

???

200

150

100

50

0

15

400

10:02:00 AM 10:08:00 AM 10:14:00 AM 10:20:00 AM 10:26:00 AM 10:32:00 AM 10:38:00 AM 10:44:00 AM 10:50:00 AM 10:56:00 AM 11:02:00 AM 11:08:00 AM 11:14:00 AM 11:20:00 AM 11:26:00 AM 11:32:00 AM 11:38:00 AM 11:44:00 AM 11:50:00 AM 11:56:00 AM 12:02:00 PM 12:08:00 PM 12:14:00 PM 12:20:00 PM 12:26:00 PM 12:32:00 PM 12:38:00 PM 12:44:00 PM 12:50:00 PM 12:56:00 PM 1:02:00 PM 1:08:00 PM 1:14:00 PM

Power, kW

Analysis - Discussion 2000

1800

1600

Dual-trak furnace, poorly utilized

1400

1200

1000

800

600

???

200

0

16

Analysis - Discussion Induction furnace power curve 700 600

Power, kW

500 400

300

Almost Ideal

200 100 0

17

Best operating practices

Charge preparation and charging

Melting and making melt ready

Furnace lining

Emptying the furnace

Energy monitoring and data analysis

18

Charge preparation and charging Weighing and arranging the charge Free from sand, dirt, oil and grease. Rusty scrap: Less metal per charging. Clean, dry and dense: 10 kWh per ton Maximum size of charge: (1/3)rd of opening diameter Do not charge beyond coil level Proper charge sequence to be followed. Pig iron to be charged. Fill the gaps with turning and borings 19

Charge preparation and charging Foundry return should be tum/shot blasted. Contains 3 – 5% sand by weight Process control through melt managers, leads to less interruptions

Limit use of baled steel and loose boring

Use charge driers and pre-heaters to remove moisture and pre heat the charge 20

Charge preparation and charging

21

Charge preparation and charging

22

Melting and making melt ready Follow melt process, always run furnace at full power Use lid mechanism, 5 – 8 % energy lost through radiation Typically 20 – 30 kWh per tonne saving using lid Avoid build-up of slag on furnace walls Proper tools and techniques should be used for de-slagging Spectro-testing lab must be located near to melt shop Avoid un-necessary super-heating of metal. 50 °C leads to more than 25 kWh per tonne 23

Melting and making melt ready

24

Emptying the furnace Optimization of the ladle size to minimize the heat losses and empty the furnace in the shortest time Optimization of the ladle transportation Plan melting according to moulding. Metal should never wait for mould rather mould should be ready before metal Use of ladle pre-heater. Proper positioning of burner is important to get uniform heating Quantity of liquid metal returned to furnace must be as low as possible Glass-wool or ceramic-wool cover for pouring ladle Minimize plant breakdown by implementing a planned maintenance schedule 25

Emptying the furnace

26

Furnace lining Select the correct lining material Do not increase lining thickness at bottom or sidewalls. Increase in lining means reducing capacity of furnace Do not allow furnace to cool very slow. Forced air cooling helps in developing cracks of lower depth, this helps in faster cold start cycle Cold start cycle time should be ideally not more than 120% of normal cycle time Coil cement should be smooth, in straight line and having thickness of 3 to 5 mm While performing lining ensure that each layer is not more than 50mm. Compaction is better with smaller layer Monitor lining performance 27

Energy monitoring and data analysis Separate energy meter for furnace must be installed Monitor energy consumtion on heat by heat basis Analyse them in correlation with production data to arrive at specific energy consumption of furnace on daily basis Any peak or valley in data must be studied and investigated

ENERGY MONITORING is the first step for achieving ENERGY SAVING 28

Be the change you want to see in the world

E Nand Gopal +91 99715 17752 [email protected] [email protected]