Induction Melting Solutions

How To Calculate The Furnace Efficiency

Power Losses in Furace Can Vary According Ta

  1. Manufacturer of Furnace
  2. Size of the Furnace
  3. Scrap Quality
  4. Plant Operational Specific Issue

Factors Effecting The Furnace Efficiency

In a foundry, most of the power consumed by the induction furnace is around 85% of the power.
Technically, what affects the furnace efficiency is as under:

Wrong selection of the furnace & operational practice.

  1. Small power supplied unit & big crucible.
  2. Wrong lining selection and relatively slow charging.
  3. Improper lining thickness.

Results into:
a) reduced lining life
b) poor coil lining life
c) increased power draw due to an increase in furnace losses.
d) reduced furnace utilization due to increased melting time.

Optimum furnace sizes, approximately be: For up to 1000 kw ~ 1.5 times the kw applied
For 1000 kw furnaces ~ 2.0 times the kw applied. (For Steel Melting)

Furnace down time:

(1) sintering and patching, Higher sintering & patching increase the cost of production and reduces efficiency.

Break down time:

Due to poor maintenance the total production stops sometimes.
Breakdown moment results in increase of cost of production

Low supplied power:

If the supplied voltage is low, so furnace draw less power. Causes slow melting & inefficient operation, resulting in increased cost of production

 

Wrong lining:

Sometimes, the material selection is wrong concerning metal.
Basic lining is better conductor of heat compared to acidic lining
Wrong lining selection increases breakdown, Furnace downtime and furnace losses, resulting in inefficient operation.

 

Besides above all points some more factors which can also effect the energy consumption per MT are:

A) poor coordination between the melting staff & contractor
B) absence of material handling equipment
C) poor moulding efficiency sothe  furnace is on hold
D) poor quality scrap, reducing lining life, takes more time to melt.
E) absence of thermal insulation between the lining & coil.

Total Theoretical Energy Required To Turn 1 Ton Of Different. Solid Metals To Melt @ Different Molten Temperature

Type of metal Specific Heat Require Latent heat require Total require kwh/Ton
Mild steel @ 1650°C Melting temp.
307 kwh
76 kwh
307 + 76 = 383 kwh
Aluminum @ 710°C Melting temp.
170 kwh
110 kwh
170 + 110 = 280 kwh
Copper @ 1190°C Melting temp.
118 kwh
59 kwh
118 + 59 = 177 kwh
Gold @ 1130°C Melting temp.
36.38 kwh
18.78 kwh
36.38 + 18.78 = 55.16 kwh

Furnace Efficiency =

Theoretical Total Heat Reqd For Melting (HT) In Kwh. For The Melting Of The Metal In Kwh

Actual Consumed Energy By The Furnace For Melting Of The Metal In Kwh (HA)

Theoretical Heat Reqd For Melting:

H1 in Kwh =

W×Specific Heat Of The Metal×(T2−T1)+Latent Heat Of The Metal×W

3600 ( 3600 Kj = 1kwh)

H2 in Kwh =

Heat Reqd For Slag. To heat And Melt Will Be 1.65x Ws

X3.6(Where 3.6 MJ = 1 Kwh)

Where

W = Weight Of The Metal To Melt

T2 = Melting Final Temp Of the Metal

T1 = Initial Or Charging Temp Of the Metal

Ws = Weight Of Slag Generated In Operation

Here,

HT = H1 + H2

And

Actual Consumption Of The Melting Can Be Measured From The Input Busbar Of The Furnace Panel In Kwh. (HA in Kwh)

So Difference Between HA And HT (HA – HT) Is Loss Due To Conduction Radiation And Other Losses.

And So Furnace Efficiency Is Ratio Of Theoretical Heat Reqd For Melting In Kwh To Actual Consumed Heat In Kwh.

Furnace Efficiency =

HT

HA

55% To 65% (Max) Overall Energy Efficient Furnaces Are Available.

For M.S. Scrap

Specific Heat = 0.162 Kcal / Kg Deg Centi.

Latent Heat = 272.0 KJ / Kg

Latent Heat Reqd. To Melt 1000Kgs Of M.S. Scrap Will Be, @ 1650°C

Kwh

1000×0.162×(1650−30)

3600

=

= 307 Kwh

Latent Heat Reqd, 272 x 1000 / 3600 = 76 Kwh.
Heat For Slag: 1.65 x 2.5 / 3.6 = 12 Kwh.

Total Kwh Theoretically Reqd For Melting is 395 Kwh

Approx 400 Kwh Reqd To Melt M.S Of 1000Kgs To 1650Deg Centigrade.

If The Furnace Consumes 625 Kwh/ton,
Then The Overall Efficiency Of The Furnace Is 64% [i.e. 400 ÷ 625 = 64% ]

Distribution Of Power Losses In An Induction Furnace:

Type of Loss % Loss
Power Loss In Generator / Panel
2% To 4%
Power Loss In Capacitor Bank
1% To 3%
Power Loss In Crucible
18% To 25%
Radiation Loss
7% To 9%