FIELD OF THE INVENTION
The invention relates to a heat recovery system from the cast houses of primary
metallurgy plants.
BACKGROUND OF THE INVENTION
In primary metallurgy processes, hot metal and slag are tapped from a furnace
and transported for casting or further processing. The place where hot metals
and slag are tapped is called cast house. For example, in a blast furnace, ore and
coke are charged at the top of 30-40m reactor and oxygen enriched air is blown
from the bottom. Burning of coke produces heat and carbon of coke act as a
reducing agent, which leads to reduction of iron bearing material to liquid iron.
This liquid iron is tapped at around 1700-1800K and transported into torpedo
ladles for casting or steelmaking. Surface area of the exposed runner surface in
the blast furnace varies from 25-45m2. Slag formed during the process is usually
granulated by water. The exposure of these hot liquids to open air causes huge
amount of radiation losses. The cast house becomes hot and is filled with fumes
and dust generated in the tapping process. Open runners poses risks to safety.
Existing heat recovery systems usually use heat exchangers to transfer heat from
a primary metallurgy plants. US-patent US 5033414 disclose a sheet recovery
system in which waste gaseous stream is combusted to heat an intermediate
fluid. The heat from this heat transfer fluid is transferred to an array of heat
exchangers. However, these systems have limitations of constant source of heat
and are not capable to handling excess heat. Further, the system also requires
heat exchangers, large amount of piping and adjacently disposed utilization

arrangement of the recovered heat. This is not possible in cast house of a blast
furnace.
Blast furnace cast house has space constraint because of huge amount of
machinery required for metal tapping. Installation of heavy machineries for heat
recovery is not desirable in order to meet the safety standards. The metal
runners of the plant from where the waste heat is recovered need constant
cleaning, and therefore any permanent structure cannot be installed over them.
In some of the blast furnaces, exhausts are installed to take away the excess
heat from the runners. Accordingly, the heat recovery systems should not be
designed so as to hamper the metal tapping process in any way. The metal may
even freeze in the runner if more heat is extracted, which is not desirable.
Thermionic generators that convert heat energy to electric energy are known in
the art. As discussed in US Patent US 5541464, the thermionic generator consists
of the cited invention, emitter and a collector. The space between the emitter
and collector is sealed and a low pressure is maintained between them. When
sufficient heat is supplied to the emitter, high-energy free electrons obtain
enough energy to escape from the emitter surface. This phenomenon is known
as thermionic emission. This electron is captured by the collector. The collector is
cooled by using a cooling circuit.
US 2001/0045309 A1 discloses a combustion chamber thermionic device for
automobile. Heat energy generated in a chamber due to combustion of fuel is
converted into electric energy through thermionic generator. Thus obtained
electric energy is used as the motive power for automobile wheels. This
arrangement shows that thermionic generators can be installed in small space.

The thermionic reactors in this cited invention do not face problems related to
deposition, because of high flow rates inside the combustion chamber.
US - 5247548 and 5219516 each describes thermionic reactor for providing
electric power, using heat produced by nuclear fuel. This type of arrangement
can be fixed inside an insulation layer protected from the surrounding hostile
conditions, and further provide better efficiency because of the fact that the
temperature generated by the nuclear fuel is very high.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a system for recovering
waste heat from cast houses of primary metallurgy plants, which eliminates the
disadvantages of prior art.
Another object of the invention to propose a system for recovering waste heat
from cast houses of primary metallurgy plants, which maintains a continuous
power supply at a rated power during tapping.
A further object of the invention to propose a system for recovering waste heat
from cast houses of primary metallurgy plants, which is provided with at least
two cleaning mechanisms selectively activateable depending on downward rated
power compared to a reference value.

SUMMARY OF THE INVENTION
Thermionic generators are used at various technical installations to convert heat
energy into electricity. However, a cast house of primary metallurgy plants is
required to capture the maximum waste heat so as to recovery system is
enabled to capture the waste heat from the cast house runners and waste hot
gases.
The system is configured to capture the maximum heat from the slag and metal
runners and provided with a cleaning mechanism, which is absent in known
thermionic generator setups. Further, the known thermionic generators are
susceptible to deposition of duct and suite produced in the cast house leading to
decrease in their power-generation efficiency. Therefore, the system of the
present invention is provided with a cleaning mechanism, which is selectively
activated or deactivated depending on decreased in power generation of the
plant.
The thermionic generators modules according to the invention is optimized to
capture the maximum heat from the cast house. A fin type structure is used to
maximize the exposed surface area. Individual thermionic generators are joined
in parallel so that the output is not substantially affected if one generator
malfunctions.
The energy generated by the thermionic modules is used for driving the cleaning
mechanism and other cast house equipments. The extra energy generated can
be used for any other applications.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows a general arrangement of a runner hood in the cast house of the
blast furnace.
Figure 2 shows a perspective view of a first thermionic converter module
according to the invention.
Figure 3 shows a simplified lay out of a thermionic generator.
Figure 4 shows a schematic view of the heat recovery system according to the
invention.
Figure 5 shows a perspective view of a second thermionic converter module
according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The heat recovery system of the invention consists of at least two thermionic
converter modules. The first module (18) is installed at the hot metal or slag
runners 11. The runners (11) carry slag/Hot metal, which is at a temperature
around 1400-1700 K. These runners (11) are covered with hoods (12) to reduce
radiation heat losses. The system of the invention captures these radiation losses
to convert into electricity through thermionic generators (18). Thermionic
converter module (18) is attached to the runner hood 12. The shape of the
runner hood (12) can be varied as per runner design. The runner hood (12) has
a coating of refractory (13) on it. The thermionic converter module is supplied
with a coolant to cool the collector plates. Pipes 15 and 16 are the inlet and

outlet of the coolant respectively. Figure 2 shows the thermionic generators in
the form of fins (18) fitted inside the hood. Fin type structure 18 maximizes the
heat capture. Coolant water in coming through the pipe 15 and going out from
the pipe 16. The circulation of water inside the thermionic converter module is
shown by reference removal 19. The detailed view of the fin type thermionic
generator 18 is given in figure 3. Thermionic generator consists of at least
emitterf 22 and a collector 23. The emitters 22, is exposed to the hot surface of
slag/Hot metal and knock out electron, which are captured by the collector 23.
The coolant is used to keep the temperature of the collector (23) under control.
The coolant enters through an inlet 20 and leaves through an outlet 21. The
refractory coating 13 protects the heat loss. The thermionic converter module
consists of a plurality of thermionic generators attached in parallel. This ensures
a continuous current supply of power irrespective of malfunctioning of a single
generator. As shown in figure 2, thermionic converter module consists of a
semicircular cleaning brush 17. The cleaning brush (17) rides on a channel 14.
Circuit of this cleaning brush (17) is shown in figure 4. There is control unit 24,
which monitors the power generation from the thermionic module. If the power
generation goes below a reference value stored in reference unit 25, then the
control unit 24 transmits a signal to a driving unit 26 to activate the brush and
cleaning of the surface of the thermionic generators 18 is done. The energy
generated by the thermionic generators (18) is stored in a battery 27.
The Second thermionic module (30) is installed in the exhaust pipe 28 of a tilting
runner as shown in figure 5. The pipe carries high temperature gas with dust.
The second thermionic generator module 30 is installed in the form of fins to
maximize the heat transfer. An emitter 31 of the second thermionic generator
(30) gets heat from the exhaust gasses and knocks out electrons, which are
captured by a second collector 32. The second collector (32) is cooled by the

coolant entering through an inlet 33 and leaving via an outlet 34. The second
thermionic converter module (30) is supplied with a cleaning brush (35) to clean
the accumulated dust. The brush 35 is attached to a channel 36. Circuit of
cleaning the brush (35) is similar to the one mentioned earlier of the first
thermionic converter module (18).
The energy generated from both the thermionic converter modules (18, 30) is
stored into the battery, which can be used to drive the cleaning mechanism and
other cast house equipments.

WE CLAIM
1. A system for recovering waste heat from the cast houses and similar
technical installations of primary metallurgy plants, comprising :
- a first thermionic converter module to capture the waste heat from the
hot metal and slag runners in the cast house;
- a second thermionic converter module to capture the waste heat from the
exhaust gases from the cast house;
- a cleaning device for the first and second thermionic converter modules to
maintain a constant heat flow, the thermionic modules are configured as a
fin-type structure to maximize the heat capture, and wherein the first
module is fitted in the hood of the runner to provide structural support
and is fitted with a layer of refractory insulation to protect from outside
atmosphere, and to prevent heat loss.

2. The system as claimed in claim 1, wherein the first thermionic converter
module has a plurality of TEG devices parallely connected to ensure
continuous power supply in case of malfunctioning of a single TEG device.
3. The system as claimed in claim 1, wherein the first thermionic converter
module is supplied with cooling water for cooling the collector of the
thermionic converters.

4. The system as claimed in any of the preceding claims, wherein the first
thermionic converter module is optimized for high temperature working of
the runners.
5. The system as claimed in claim 1, wherein the converter modules are
each provided with a cleaning mechanism.
6. The system as claimed in claim 5, wherein the cleaning mechanism
comprises a reference unit that provides the reference value of the power
generated.
7. The system as claimed in claim 5 or 6, wherein the cleaning mechanism
comprises a control unit which compares the reference value with the
current power generation.
8. The system as claimed in claims 5 to 7, wherein comprises a driving unit.
9. The system as claimed in any of the preceding claims, wherein the
cleaning mechanism comprises a cleaning brush which removes any dust
sticking on the surface of the thermionic generators.
10. The system as claimed in claim 1, wherein the second thermionic
converter module is disposed on an exhaust pipe of the tilting runner and
covered with refractory lining for insulation.

11. The system as claimed in claim 1 or 10, wherein the second thermionic
converter module is supplied with cooling water for cooling the collector of
the thermionic converters. Thermionic converter modules is optimized for
lower temperature working for the exhaust gasses.
12. The system as claimed in claim 1, wherein the energy generated by the
modules is stored in a battery.

The invention relates to a system for recovering waste heat from the cast
housesand similar technical installations of primary metallurgy plants,
comprising a first thermionic converter module to capture the waste heat
from the hot metal and slag runners in the cast house; a second
thermionic converter module to capture the waste heat from the exhaust
gases from the cast house; a cleaning device for the first and second
thermionic converter modules to maintain a constant heat flow, the
thermionic modules are configured as a fin-type structure to maximize the
heat capture, and wherein the first module is fitted in the hood of the
runner to provide structural support and is fitted with a layer of refractory
insulation to protect from outside atmosphere, and to prevent heat loss.