Furnaces used in industrial fields

1. Industrial
melting
furnaces

2. What are furnaces?
A furnace is a device used for high-
temperature heating.
It is used for many industrial applications
such as:
 Production of ceramics.
 The extraction of metal from ore.
**Ore: is a type of rock that contains sufficient
minerals with important elements including
metals.
 Providing heat to chemical reactions for
processes like cracking.

3. Furnace types
The heat energy to fuel a furnace may be supplied directly by
fuel combustion, by electricity such as the electric arc furnace,
or through induction heating in induction furnaces.
Furnace
types
Fuel fired
furnace
coal fired
furnace
cupola
furnace
Rotary
furnace
Pit
furnace
oil fired
furnace
gas fired
furnace
Electric
furnace
resistance arc induction

4. First: Fuel-fired furnaces:
 Also called (pulverized
 coal-fired boiler).
 Theory of operation:
Coal is ground to the size of a fine grain,
mixed with air and burned in the flue gas
flow. Biomass and other materials can also
be added to the mixture.
 This type of boilers dominates the
electric power industry.
A) Coal fired furnace:

5.  There are about three types of these pulverized
coal power plants shown in the next graph:
subcritical
pulverized coal
plants (SCPC)
• operate below
the critical point
of water (647.096
K and 22.064
MPa).
• 37% efficiency.
ultra-supercritical
pulverized coal
(USCPC) plants
• operate above
the critical point
of water.
• 42-45% range of
efficiency.
supercritical
pulverized coal
(SCPC) plants
• operate above
the critical point
of water.
• 40% efficiency.

6. Advantages & Disadvantages
of coal as fuel:
 Advantages:
1. Reliability
2. Affordability
3. Abundance
4. Safety
 Disadvantages:
1. Greenhouse gas emission
2. Mining destruction
3. Generation of millions of tons of waste
4. Emission of harmful substances

7. It was the primary method of
melting used in iron foundries.
 Application:
It is used as a melting unit
for cast iron.

8.  Construction of the furnace:
 consists of a vertical steel shell which is lined with a
refractory brick, bricks and fire clay.
 Charging door at the furnace top part.
 Typical internal diameters of cupolas are 450 mm to
2000 mm diameter.
 Air is injected by the tuyers at the furnace bottom part.
 Drop bottom for cleaning after operation.
 Tapered sand refractory is lined above the drop
bottom.
 Molten metal is collected from tapping hole at the
furnace bottom part.
 Slag hole is located above the tapping hole at the
furnace bottom part.

9.  Theory of operation:
1. Drop bottom is closed, sand bottom is rammed.
2. Tapping of the tapping and slag holes by the fire
clay.
3. Coke bed and wooden parts are charged, then
firing.
4. After ignition, charging continue in repeated
layers, having the following order: flux (lime
stone), metal charge and then coke.
5. After complete melting, the slag is drawn from
the slag hole.
6. Molten metal is drained from the tapping hole.
7. Furnace is cooled, lining is rebuilt, and
sequence repeated.

10. Cupola Zones:
1. Well Zone:
Lower furnace part
Collect the molten metal
2. Combustion (Oxidizing) Zone:
15 cm above the tuyers
Oxidizing most elements of the charge
Exothermic Reactions:
C + O2 → CO2 + Heat
Mn + O2 → MnO2 + Heat
Si + O2 → SiO2 + Heat
High heat and temperature (1850 ℃)

11. 3. Reducing Zone:
From the top of the combustion zone to the top of the
coke bed.
Protective, due to the existence of endothermic
reaction:
CO2 + C (coke) → 2CO – Heat
Less temperature (1200 ℃)
4. Melting Zone:
Upper part of metal charge
Molten metal drops through the coke bed
3 Fe + 2 CO → Fe2C + CO2
5. Preheating Zone:
Above the melting zone to the bottom of the charging door.
Reducing gases like Co2, Co, and N2 are present.
6. Stack Zone:
Above the charging door to the spark arrester.
Reducing gases like Co2, Co, and N2 are present.

12.  Cupola Charge:
1. Metal Charge: Pig Iron. Cast Iron Scrap (New
and return), and Steel Scrap.
2. Coke.
3. Lime Stone ( CaCo3 ) as flux.
4. Air
Advantages:
 continuous in its operation.
 High melt rates.
 Relatively low operating costs.
 Ease of operation.

13. Applications:
 The rotary melting furnace is the most flexible and
universal design of equipment to recycle aluminum
scrap. Due to the nature of its operation all scrap forms
can be recycled with good results.
 It also may be used for producing other materials such
as:
 Cement Lime
 Refractories
 Titanium dioxide
 Alumina
 Vermiculite
 Iron ore pellets

14.  Construction:
 The basic components of a rotary kiln are the shell, the
refractory lining, support tyres and rollers, drive gear and
internal heat exchangers.
 Theory of operation:
 The kiln is a cylindrical vessel, inclined slightly to the
horizontal, which is rotated slowly about its axis.
 The material to be processed is fed into the upper end of the
cylinder.
 As the kiln rotates, material gradually moves down towards
the lower end, and may undergo a certain amount of stirring
and mixing.
 Hot gases pass along the kiln, sometimes in the same
direction as the process material (co-current), but usually in
the opposite direction (counter-current).
 The hot gases may be generated in an external furnace, or
may be generated by a flame inside the kiln. Such a flame is
projected from a burner-pipe (or "firing pipe") which acts like
a large Bunsen burner.
 The fuel for this may be gas, oil, pulverized petroleum coke
or pulverized coal.

15.  The pit furnace is a vertical orientation furnace
used for a variety of processes.
 Advantages:
1. Faster heating: The high pressure
recirculation blower forces the heated air
through the load in a vertical, top-down arrangement. A
high-suction return duct is located below the load to
draw the air through. This arrangement provides much
faster heating than most other conventional furnace
designs.
1. Saves floor space.
2. Easy to load.
3. Lower installation & start-up cost.

16. B) Gas fired furnace:
 Gas boilers and furnaces can be fueled by either
natural gas or propane.
 Propane is usually more expensive as a fuel.
C) Oil fired furnace:
 Oil-fired furnaces and boilers are a popular choice in
areas of the country with limited access to natural
gas.
 Oil-fired furnaces and boilers present an opportunity
to use renewable fuels to heat your home.
 A number of companies are now offering heating oil
blended with biodiesel, allowing their customers to
reduce their dependence on foreign oil.
 The biodiesel blends also produce less pollution than
pure heating oil.

17. Second: Electrical furnaces:
A. Electric arc furnaces :
 It may be categorized as direct arc or indirect
arc.
 Both types of units are suited for the melting
of high melting point alloys such as steels.
 They may be lined with acid or basic
refractories.

18. Direct arc furnaces:
 construction:
 Cylindrical steel shell which is lined with
acid or basic refractories. The roof
contains three carbon electrodes
operating on a high tension three-phase
power supply. These electrodes protrude
vertically through the roof and an electric
current passes directly through them and
into the metal bath. The distance
between the electrodes and the metal
bath is automatically controlled and
determines the power input into the bath.
 Some of the advantages of direct arc
furnaces include high melt rates, high
pouring temperatures and excellent
control of melt chemistry.
 Applications:
 melting of alloy steels
Indirect arc furnaces:
 construction:
 A horizontal barrel shape
steel shell lined with
refractories. Melting is
effected by the arcing
between two horizontally
opposed carbon
electrodes.
 Heating is via radiation
from the arc to the
charge.
Applications:
 Indirect arc furnaces are
suitable for melting a
wide range of alloys but
are particularly popular
for the production of
copper base alloys.

19. B. Induction furnaces:
 Theory of operation:
A high voltage electrical source from a primary coil
induces a low voltage, high current in the metal or
secondary coil.
 Applications:
Melting and alloying a wide variety of metals with
minimum melt losses.
 Advantages:
A clean, energy-efficient and well-controllable melting
process.
Most modern foundries use this type of furnace, and now
also more iron foundries are replacing cupolas with
induction furnaces to melt cast iron, as the former emit
lots of dust and other pollutants.

20. Introduced to:
Eng:Hesham Ahmed Dr/Tarek Moussa
Ain Shams University
Mechanical department