FIELD OF INVENTION
This invention relates to a method for achieving higher cooling rates of hydrogen
during bypass cooling in a batch annealing furnace of cold rolling mills. The
invention further relates to an apparatus for implementing the method.
BACKGROUND OF INVENTION
In a cold rolling mill, hot rolled steel strips are rolled at room temperature to
achieve improved surface quality and mechanical properties of the final cold
rolled products. However, extensive deformation of the steel at room
temperature during the cold rolling operation significantly reduces the ductility of
the cold rolled sheets. In order to render the cold rolled sheets amenable for
subsequent operations, e.g. deep drawing of auto body parts, the cold rolled
steel coils need to be annealed.
During the annealing operation, deformed microstructures of the cold rolled
sheets are stress relieved, and accordingly recovery, recrystallisation, and grain
growth take place.
Thus, the cold Rolled steel coils need to be annealed to obtain desired
metallurgical properties in terms of strength and ductility levels. To achieve this,

this cold rolled steel coils are stacked one above other and placed in a heating
chamber. The heating chamber heats the coils upto temperatures of 400~500°C.
The heating process is followed by a cooling cycle. The cooling cycle uses
hydrogen to take the heat away indirectly by cooling a hood of the furnace.
Efficiency of the cooling cycle depends on the rate at which heat can be
extracted from the hydrogen within the confinements of the system.
Batch annealing furnace typically comprise a base unit provided with a
recirculation fan and cooling means. On the base unit, several cold rolled steel
coils are placed one above the other, separated by a plurality of circular
convector plates. These cylindrical shaped coils with outer diameter (OD) in the
range of 1.5-2.5 m, inner diameter (ID) 0.5-0.7 m, and widths of 1.0-1.4 m,
weigh around 15-30 t each. These are the typical data, which widely vary from
plant to plant depending upon the overall material design. After loading the base
with the coils, a protective, gas tight cylindrical cover is put in place and
hydrogen gas is circulated within this enclosure. A cylindrical hood for the gas or
oil fired furnace hood is placed over this enclosure. The protective cover is
externally heated through radiative and convective modes of heat transfer, which
heats the circulating hydrogen gas. The outer and inner surfaces of the coils get
heated by convection from the circulating hydrogen gas and by radiation
between the cover and the coil. The inner portions of the coils are heated by
conduction.

During the cooling cycle, the furnace hood is replaced with a cooling hood and
the circulating gas is cooled.
There are generally three known strategies that are followed in batch annealing
furnace, namely:
(a) AIR/JET cooling in which compressed air hits the cooling hood at high
pressures.
(b) SPRAY cooling in which water is sprayed directly onto the cooling hood.
(c) BY-PASS cooling in cooling in which a gas flowing in the inner cover is
tapped and cooled using a heat exchanger. The efficiency of the heat
exchanger determines the rate of cooling of the gas.
Commonly used mechanism for increasing the heat transfer rate, are:
(a) Increasing the number of tubes and corrugations per tube inside the heat
exchanger.
(b) Using water at a lower temperature obtained from a chilled water line.
Both methods (a) and (b) are costly and hence do no find acceptance under the
present circumstances.

OBJECTS OF INVENTION
It is therefore an object of the present invention to propose a process for
achieving high cooling rates of a heated gas in a batch annealing furnace of cold
rolling mills.
Another object of the present invention is to propose a process for achieving
higher cooling rates of a heated gas in a batch annealing furnace of cold rolling
mills, which is implemented during the bypass cooling mode.
A further object of the invention is to propose an apparatus for achieving higher
cooling rates of an atmospheric gas in a batch annealing furnace of cold rolling
mills.
SUMMARY OF INVENTION
Accordingly in a first aspect of the invention there is provided an apparatus for
achieving higher cooling rates of a gas during bypass cooling in a batch
annealing furnace of cold rolling mills, comprising a nanocoolant preparation unit
for preparing a nanofluid, and for supplying the nanofluid to a heat exchanger at
a described flow rate, temperature and pressure, the nanofluid being prepared
by mixing industrial grade water with nanoparticles including dispersants by
adapting a high speed shear mixture. A batch annealing furnace accommodating
the cold rolled steel coils on a base and heating the coils by placing a furnace
hood on the top, the furnace having a cooling hood, a gas inlet and a gas outlet.

The hydrogen gas from the heat exchanger is allowed to enter the furnace via
the gas inlet, the cooled hydrogen exiting the heat exchanger via the gas outlet.
A heat exchanger receiving the nanofluid from a reservoir at a desired flow-rate,
the reservoir being supplied with the nanofluid from the preparation unit, the
nanofluid exchanging heat with the hydrogen at a higher rate, and exiting via an
outlet provided in the heat exchanger.
According to a second aspect of the invention, there is provided a method for
achieving a higher cooling rate of hydrogen during bypass cooling in a batch
annealing furnace of cold rolling mills, the method comprising the steps of filling-
up of the preparation unit with industrial grade water maintained at ambient
condition. Measuring in a first measuring and control device the nanoparticles
including dispersants at a lot-size determined based on the type of steel coils to
be cooled. The first device is controlling the flow rates, pressure, and
temperature of the produceable nanofluid to be supplied to the heat exchanger.
Mixing the nanoparticles including the dispersants with the industrial grade water
at a preferable volumetric ratio of 0.1% in the preparation unit. Supplying the
prepared nanofluids from the preparation unit to the reservoir by using a pump.
Delivering the hydrogen gas to the heat exchanger at a temperature between
400 to 600°C, and delivering the nanofluid at a predetermined flow-rate,
temperature, and pressure from the reservoir to the heat exchanger. Supplying
the hydrogen gas from the heat exchanger to the furnace for cooling the heated
steel coils and the hydrogen being returned to the heat exchanger from the
furnace. The nanofluids is delivered to the heat exchanger exchanging the heat

within the hydrogen; and the nanofluid exiting the heat exchanger via a first
outlet. The cooled hydrogen exiting the heat exchanger via a second outlet, the
hydrogen getting cooled at a rate between 1 to 2°C/min.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 : is a schematic view showing the operating principle of the invention.
Figure 2 : shows a detailed layout of a batch annealing process of Figure - 1.
Figure 3 : shows a detailed view of the heat exchanger of Figure - 1.
Figure 4 : shows a detailed view of a nanocoolant - preparation unit of Figure
1.
DETAIL DESCRIPTION OF THE INVENTION
The present disclosure covers the following main aspects of the invention:
(a) Nanocoolant preparation process
(b) Batch Annealing furnace process
(c) Proposed Circuit for achieving higher cooling rates of hydrogen.

Nanocoolant preparation process
Nanocoolants are aqueous based solution having controlled volumes of stable
dispersions of nano-sized oxide particles. Commonly used nano-sized particles
are oxides of alumina, copper and titanium that exhibit higher heat transfer
capacities compared to the bulk oxides of alumina, copper and titanium.
Nanosized particles of the oxides species of alumina, copper, titanium are
prepared using a high speed mixer as described in our Patent application no;
dated 16.02.2009
Batch annealing process
Cold Rolled steel coils need to be annealed to obtain desired metallurgical
properties in terms of strength and ductility levels. To achieve this, the cold
rolled steel coils are stacked one above other and placed in a heating chamber.
The heating process heats the coils upto temperature of 400~500°C. The heating
process is followed by a cooling cycle. The cooling cycle uses hydrogen to take
the heat away indirectly by cooling a cooling hood (3). Figure 2 shows the
schematic arrangement.
During the cooling process, hydrogen enters the hood (3) through an ambient
gas inlet (4), and picks up the heat by convection from the surface of the coils
(2) and comes out of the hood (3) through a hot gas outlet (5).

To ensure the effectiveness of the cooling process, it is essential to cool down
the hydrogen so that it enters the hood (3) at near ambient temperature. For
this, a commercially available gas-liquid heat exchanger (B) is employed.
Figure - 1 shows a schematic overall view depicting the principle of the present
invention. In a batch annealing furnace (c), cold rolled steel coils (2) are stacked
and heated upto a temperature of 400 to 500°C. The heating process is followed
by a cooling cycle in a heat exchanger (B) which uses hydrogen gas. The batch
annealing furnace (A) as shown in Fig - 2, comprises a base (1) for loading the
cold rolled steel coils (2), a cooling hood (4) to allow entry of the hydrogen gas
through an ambient gas inlet (4) which picks up the heat by convection from the
surface of the coils (2) and exits the furnace (A) via a hot gas outlet (5).
Figure - 3 shows a details of the heat exchanger (B) of Fig 1. The heat
exchanger (B) is having an inlet (7) for the nanofluid to enter the heat echanger
(B) from a Nanofluid preparation unit (C). After exchanging the heat, the
nanofluid is allowed to exit through a nanocoolant outlet (7).
Figure - 4 shows in details the nanofluid preparation unit (C) of fig - 1. The unit
(C) comprises a mixing device (8) in which industrial grade water and
nanoparticles including dispersants in a volumetric ratio of 0.1% is mixed in
ambient conditions. A pump is utilized to supply the nanofluid from the mixing
device (8) to a reservoir (10). From the reservoir (10) the nanofluid is pumped
into the heat exchanger (B) by a pumping unit (9) via an outlet (7). The

nanocoolant preparation unit (C) further comprises a first measurement and
control device (Ml) for the measurement of nanoparticles before mixing with the
industrial grade water, and for controlling the flow rates, temperature, and
pressure of the nanocoolant to be supplied to the heat exchanger (B); and a
second measurement and control device (M2) for measurement of the
nanocoolant exiting from the heat exchanger (B) including flow rates,
temperature and pressure; and a third measurement and control device (M3) for
measuring the ppm and pH level of the nanocoolant in the preparation unit (C).
The operation process is as follows:
(a) Industrial grade water is filled up in the nanocoolant mixer (8) to a
capacity of 1000 litres.
(b) Temperature of the industrial grade water is maintained between
20~30°C i.e. ambient conditions. No pre-processing of the industrial grade
water is done.
(c) Nanoparticles are measured by a measuring unit (Ml) in lot sizes of 250
gms along with dispersants in lot sizes of 250 gms.
(d) The quantity is decided on the basis of a pre-determined operating rule,
for example, of 1 gram in 1 litre of industrial grade water. This is a
volumetric ratio of 0.1%.

(e) The lot sizes of the nanoparticles can vary depending on the coil type and
weight of the steel coils (2) being cooled.
(f) The mixing is done using the high speed shear Nanocoolant Mixer (8).
(g) The mixing is completed within 1 to 2 minute after the nanoparticles and
dispersants are added to the system.
(h) A pump (not shown) is used to fill up the Nanocoolant reservoir (10). This
Nanocoolant reservoir (10) now has the nanofluid.
(i) Hydrogen gas enters the heat exchanger (B) through the inlet (4) at a
temperature of 525~425°C at a flow rate of 20~40 m3/hr.
(j) Nanofluid from the reservoir (10) is pumped-out by a Nanocoolant
Pumping unit (9), and delivered into the heat exchanger (B) through the
inlet (6) at a flow rate of 20~40 m3/hr.
(k) The nanofluid exchanges heat with the hydrogen in the heat exchanger
(B).
(I) The cooled hydrogen exits the heat exchanger (B) through the outlet (5).
(m)The nanofluid exits the heat exchanger (B) through an outlet (7).

(n) The hydrogen is cooled at a rate of 1.2~1.5°C/min using the nanofluid.
(o) When steps (a) to (m) are repeated with industrial grade water without
the nanofluid, all other parameters remaining same, the hydrogen is
cooled at a rate of 0.8~1.0°C/min, according to the present invention.
This means that using the method and apparatus of the invention, higher cooling
rates of hydrogen of the order of 1.2~1.5°C/sec can be obtained.

WE CLAIM
1. An apparatus for achieving higher cooling rates of a gas during
bypass cooling in a batch annealing furnace of cold rolling mills,
comprising :
- a nanocoolant preparation unit (C) for preparing a
nanofluid, and for supplying the nanofluid to a heat
exchanger (B) at a desired flow rate, temperature and
pressure, the nanofluid being prepared by mixing industrial
grade water with the nanoparticles including dispasants by
adapting a high speed shear mixture;
- a batch annealing furnace (A) accommodating the cold
rolled steel coils (2) on a base (1), and heating the coils
(2) by placing a furnace hood on the top, the furnace (A)
having a cooling hood (4), a gas inlet (4), and a gas outlet
(5), hydrogen gas from the heat exchanger (B) being
allowed to enter the furnace (B) via the gas inlet (4), the
cooled hydrogen exiting the heat exchanger (B) via the gas
outlet (5), and
- a heat exchanger (B) receiving the nanofluid from a
reservoir (10) at a desired flow-rate, the reservoir (10)
being supplied with the nanofluid from the preparation unit
(C), the nanofluid exchanging heat with the hydrogen at a

higher rate, and exiting via an outlet (7) provided in the
heat exchanger (B).
2. The apparatus as claimed in claim 1, comprising a pump for supply
of the nanofluid from the preparation unit (C) to the reservoir (10).
3. The apparatus as claimed in claim 1 or 2, comprising a pumping
unit (9) for delivering the nanofluid from the reservoir (10) to the
heat exchanger (B).
4. An apparatus as claimed in claim 1, where in the nanocoolant
preparation unit (C) adapts a high speed shear mixer (8) for mixing
the industrial grade water and the nanoparticles.
5. An apparatus as claimed in claims 1 to 4, wherein the heat
exchanger (B) is a gas-fluid shell tube or plate type heat
exchanger.
6. The apparatus as claimed in any of the preceding claims, wherein
the preparation unit (C) comprises a first measurement and control
device (Ml), a second measurement and control device (M2), and a
third measurement and control device (M3).
7. A method for achieving a higher cooling rate of hydrogen during
bypass cooling in a batch annealing furnace of cold rolling mills, the
method comprising the steps of :

- filling-up of the preparation unit (C) with industrial grade
water maintained at ambient condition;
- measuring in a first measuring and control device (Ml) the
nanoparticles including dispersants at a lot-size determined
based on the type of steel coils (2) to be cooled, the first
device (Ml) controlling the flow rates, pressure, and
temperature of the produceable nanofluid to be supplied to
the heat exchanger (B);
- mixing the nanoparticles including the dispersants with the
industrial grade water at a preferable volumetric ratio of
0.1% in the preparation unit (C);
- supplying the prepared nanofluids from the preparation
unit (C) to the reservoir (10) by using a pump;
- delivering hydrogen gas to the heat exchanger (B) at a
heated temperature;
- delivering the nanofluid at a predetermined flow-rate,
temperature, and pressure from the reservoir (10) to the
heat exchanger (B);
- supplying the hydrogen gas from the heat exchanger (B)
to the furnace (A) for cooling the heated steel coils (2),

and the hydrogen being returned to the heat exchanger
(B) from the furnace (A);
- the nanofluid delivered to the heat exchanger (B)
exchanging the heat within the hydrogen; and
- the nanofluid exiting the heat exchanger (B) via a first
outlet (7), the cooled hydrogen exiting the heat exchanger
(B) via a second outlet (5), the hydrogen is getting cooled
at a higher rate.
8. A method as claimed in claim 7, wherein the heated gases is
caused to pass through a heat exchanger (B).
9. A method as claimed in claim 8, wherein the heat exchanger (B)
uses a fluid as the heat exchange medium.
10. A method as claimed in claim 7, wherein the fluid is a water or oil
based.
11. A method as claimed in claims 7 or 10, wherein the fluid is water or
oil based with a stable nanocoolant with higher heat extraction
capabilities.
12. A method as claimed in claim 7, wherein the effectiveness of the
process is form 5% to 30% compared to water at ambient
temperatures in the same circuit.

13. A method as claimed in claim 1, wherein the heated gas is
hydrogen at normal or pressurized conditions.
14. A method as claimed in claim 7, wherein the nanocoolant contains
nano-particles in volumetric proportions of 0.01% to 5%.
15. A method as claimed in claims 7 or 11, wherein the nanocoolants
contains Titanium dioxide (Ti02) having nano-particles of sizes
varying between 5 to 200 nanometers.
16. A method as claimed in claims 7 to 15, wherein the nano-coolant
contains a stabilizer agent for example, Sodium hexa meta
phosphate in the same volumetric proportion.
17. A method as claimed in claim 16, wherein the nanocoolant is a
stable nanocoolant, the stability being determined by a non-setting
period or more than 240 hours.
18. A method as claimed in claims 7 to 17, wherein the flow rates of
the nanocoolant is from 5m3/hr to 100m3/hr.
19. A method as claimed in claim 7, wherein the nanocoolant is in a pH
range of 3 to 12.
20. A method as claimed in claim 7, wherein the nanocoolant is in a
temperature range of 10 to 60°C.

21. A method as claimed in claim 7, wherein the hydrogen is delivered
to the heat exchanger (B) at a temperature between 600° to
400°C.
22. A method as claimed in claim 7 or 21, wherein the hydrogen gas is
cooled at a rate of 1.0 - 2.0°C/min.
23. An apparatus for achieving higher cooling rates of a gas during
bypass cooling in a batch annealing furnace of cold rolling mills as
substantially described and illustrated herein with reference to the
accompanying drawings.
24. A method for achieving a higher cooling rate of hydrogen during
bypass cooling in a batch annealing furnace of cold rolling mills, as
substantially described and illustrated herein with reference to the
accompanying drawings.

The invention relates to a method and apparatus to increase the cooling rate of
gas used in a batch annealing furnaces (A) of cold rolling mills under bypass
cooling is disclosed. The invention makes use of the higher heat transfer
capacities of nano-coolants developed by a higher-shear mixing (8) of nano-
particles and stabilizers in a basic aqueous medium for cooling heated hydrogen
flowing through a heat exchanger (B) during bypass cooling of the batch
annealing furnace (A). The nanofluid is prepared in a nanofluid preparation unit
(C).