FIELD OF THE INVENTION
An improved on-line acid heating system for pickling line. The on-line acid
heating system for pickling line in cold rolling consisting of closed loop acid circulation
for bath agitation having temperature of mother liquor at 65 C before entering the tank
operating with line speed of 1 5 m/s to 2 5m/s during the mother liquor addition period
BACKGROUND OF THE INVENTION
Research and Development Centre for Iron and Steel (RDCIS), Ranchi and
Bokaro Steel Plant (BSL). Bokaro have designed and installed an improved system for
on-line heating of mother liquor coming from Block of Chemicals (BOC) to pickling line
l(as shown in figure) of Cold Rolling Mill at BSL. Bokaro.
In the pickling process the material is dipped into an acid solution to remove rust,
oxides, and mill scale. The most common acids tor use in pickling tanks are hydrochloric
acid and sulfuric acid, both being highly corrosive
The pickling process is largely dependent on thermal condition, bath reactivity
and types of scale structure. Improper bath temperature and bath reactivity in pickling
lead to poor strip quality and loss in production Inefficient strip rinsing system causes
acid carry-over resulting in poor strip surface.
Fresh mother liquor is pumped from Block of Chemicals (BOC) to pickling line
I (as shown in figure) at ambient temperature to make up for the loss of acid
concentration. This leads to decrease in acid bath temperature for about 4 hours and
consequent decrease in line speed from 2 5m/s to 1.5 m/s. On-line heating of the
incoming mother liquor has lead to improvement in temperature condition of the bath and
thereby increase in the line speed during the addition of mother liquor to the pickling
tank.
The US5466309 document discloses metal strip treatment installation comprising
a cold rolling mill including at least one rolling stand comprising a plurality of rolls and
means for spraying rolling fluid onto the rolls and strip, and a pickling line made up of a
series of tanks through which the metal strip is continuously passed, the tanks being filled
with a pickling solution and associated with means for heating such solution
The document US 4086321 discloses a method and apparatus for producing pre
metallic oxides by dissolving the meal or oxide in heated dilute hydrochloric acid to
form metallic chloride in a water solution (which solution may instead, be a waste
product from a steel strip pickling line), reacting said solution in a reactor in the presence
of heated oxygen to form metal oxide, part of which oxide being carried over in vapor
form to a variable throat venturi where it is redissolved and reintroduced into the reactor
to insure that only low chloride oxide will be discharged as a product. The document US
4086321 discloses a novel process and apparatus for producing metallic oxides by high
temperature hydrolysis of aqueous metallic chloride solutions The method recited in the
document US 4086321 wherein the dissolving tank is heated indirectly by heat
exchangers and compressed air/direct steam sparging is used to agitate the aqueous
hydrochloric acid solution.
The present invention relates to an improved new design for an on-line acid
heating system for pickling line in cold rolling mills to increase the temperature of
mother liquor from ambient to 65°C, which has led to improvement in line speed and in
turn increase in productivity commensurate with strip surface quality. The present
invention is advantageous over the prior art by maintaining temperature of the mother
liquor at 65°C before entering tank and also the present invention attains high speed
during the operation. The main inventive feature of the present invention lie in the new
improved design for an on-line acid heating system having a closed loop acid circulation
to improve bath agitation and ensure tank entry temperature of mother liquor at 65°C
The increased temperature of mother liquor facilitates operation of the line at higher
speed (1 5m/s to 2.5 m/s) during the mother liquor additi period.
OBJECT OF THE INVENTION
It is an improved new design to increase the temperature of mother liquor from
ambient to 65°C. which has led to improvement in line speed and in turn increase in
productivity commensurate with surface quality.
SUMMARY OF THE INVENTION
The system has been designed and installed for on-line heating of mother liquor
coming from Block of Chemicals (BOC) to pickling line l(as shown in figure) of Cold
Rolling Mills at BSL. Bokaro. The system consists of shell and tube type heat exchanger
complete with acid proof flanges on both ends, piping for steam and acid, temperature
sensing and indication, valves and fittings supporting structures etc. The heat exchanger
has been designed based on the design parameter as given below. The tube material is
able to sustain the corrosive environment of the mother liquor, i e the temperature and
concentration. The tube material is stainless steel grade 316L. The shell material is boiler
quality i.e. ASTM 106 Grade B. Steam supply has been tapped from 100 NB steam
supply line available in the battery limit, after providing an isolation valve. The pipeline
has been laid and lagged from this source point to the heat exchanger. The steam
condensate line from the heat exchanger is connected to the existing condensate line of
the shop. The condensate line has also been lagged from the heat exchanger to the exit
point. There is a provision for temperature sensing of the incoming mother liquor before
heat exchanger as well as outgoing mother liquor from the heat exchanger to the acid
tank 5(as shown in figure). The temperature sensors are installed with sheathing to
counter the acid attack. The temperatures sensed at both the points are continuously
indicated on the panel installed in the vicinity of the system. This provision has been
made in order to visualize and evaluate the efficiency of heating. There has been made
provision for flushing arrangement of the acid tubes after heating. After heating is over,
the inlet and outlet lines of acid are closed and water inlet and outlet lines are opened
This facilitates cleaning the acid/salt left over the tube surface. The general arrangement
of the system has been given in drawing no RD/D&E-BSL/356363/001 (R-0).
The on-line acid heating system for pickling iine in cold rolling is characterized
by closed loop acid circulation for bath agitation having temperature of mother liquor at
65°C before entering the tank operating with line speed of 1.5 m/s to 2.5 m/s during the
•mother liquor addition period comprising the steps of
? a shell and tube type heat exchanger. whith auxiliary components like piping for
steam and acid, temperature senser and indicator and control valves. all made of
acid proof material.
a said heat exchanger has being connected in parallel flow with existing set of
polvblock heat exchangers, of which one is on working mode and the other
stand by.
? an inlet for make up mother liquor from existing block of chemicals.
?a a steam inlet from existing main steam header,
? a condensed steam out let connected to existing stem condensate line,
? an outlet for pre-heated mother liquor connected to the pickling tank;
? there being provided Resistance Temperature Detectors (RTD), both at the
mother liquor inlet line and at the pre-heated mother liquor outlet iine;
a said RTD being connected to single panel.
In the present on-line acid heating system the mother liquor inlet to the sheil and
tube heat exchanger is provided with a glove. Further the stream inlet to the shell and
tube heat exchanger is provided v. ; in on ,' off gate valve, followed by a strainer for
steam. Also, the mother liquor outlet of shell and tube heat exchanger is provided with an
on /off gate valve.
The following design parameters were taken into consideration in designing the
on-line acid heating system

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The system consists of a shell and tube type heat exchanger complete with acid
proof flanges on both ends, piping for steam and acid, temperature sensing and
indication, valves and fittings, supporting structures etc. The heat exchanger has been
designed based on the design parameter as given above. The shell and tube heat
exchanger has been installed in parallel with the existing two numbers of Polyblock heat
exchangers; one working and the other stand by. Mother liquor line coming from block of
chemicals (BOC) has been extended to the shell and tube heat exchanger after providing
an isolation valve Separate outlet line of mother liquor has been laid with provision of
outlet valve in the line. This has been done to facilitate the use of both types of heat
exchangers by closing the isolation valve of the heat exchanger not in use and opening of
acid inlet valve of the heal exchanger under. use. "Tapping of steam has been taken from
the existing 100 NB line available at the pickling line after providing an isolation valve.
A strainer has been installed to remove foreign elements from the steam. The steam outlet
line from the heat exchanger has been connected to the plant steam condensate line
Resistance Temperature Detectors (2 numbers) have been installed one each in acid inlet
and outlet line to sense the temperature. Panel has been installed with digital temperature
indicators to display continuously the temperature of inlet acid from BOC and outlet acid
from heat exchanger. Drawing no. RD/D&E-BSL/3 56363/001 (R-0) show general
arrangement of the system.
EQUIPMENT SPECIFICATION

TECH NO-ECONOMIC BENEFITS:
On-line acid heating system has resulted in improved performance of the pickling
line at Cold Rolling Mills, Bokaro Steel Plain.
The process line speed of the pickling line has improved from 1 5m's to 2.5 m/s
This has given rise to improvement in production rate of the mill.
Different embodiments of the invention are possible to achieve the best method of
performance and to obtain the product as slated above to meet the object of the invention
It will be understood that skilled persons with many modifications, variations and
adaptations may carry out the„invention into practice without departing from its spirit or
exceeding the scope of claims in describing the invention for the purpose of illustration.

1. WATER SUPPLY LINE
2. EXISTING MAIN STEAM HEADER
3. EXISTING BLOCK OF CHEMICALS (BOC)
4. RTD
5. MOTHER LIQUOR
6. STEAM LINE
7. PICKLING TANKS
8. SHELL & TUBE HEAT EXCHANGER
9. EXISTING GRAPHITE HEAT EXCHANGER
10. SIGNAL CABLE
11. EXISTING STEAM CONDENSATE LINE
12. CONTROL PANEL
13. EXISTING WASTE LIQUOR
DISPOSAL LINE
14. POWER CABLE
15. TEMPERATURE INDICATOR
WE CLAIM:
1. An on-line acid heating system for pickling line in cold rolling characterized
by closed loop acid circulation for bath agitation having temperature of
mother liquor at 65°C before entering the tank operating with line speed of 1.5
m/s to 2.5 m/s during the mother liquor addition period comprising the steps
of:
(a) a shell and tube type heat exchanger, with auxiliary components like
piping for steam and acid, temperature sensor and indicator and control
valves, all made of acid proof material;
(b) said heat exchanger has being connected in parallel flow with existing set
of polyblock heat exchanger of which one is on working mode and the
other stand by,
(c) an iniet for make up mother iquor from existing block of chemicals.
(d) a steam inlet from existing main steam header;
(e) a condensed steam out let connected to existing stem condensate line,
(t) an outlet for pre-heated mother liquor connected to the pickling tank;
(g) there being provided Resistance Temperature Detectors (RTD), both at the
mother liquor inlet line and at the pre-hcated mother liquor outlet line;
(h) said RTD being connected to single panel.
2. An on-line acid heating system as claimed in claim 1 wherein, the mother
liquor inlet to the shell and tube heat exchanger is provided with a glove.
3. An on-line acid heating system as claimed in claims I and 2 wherein, the
stream inlet to the shell and lube heat exchanger is provided with an on /' off
gate valve, followed by a strainer for steam.
4. A on-line acid heating system as claimed in claims 1 to 3 wherein, the mother
liquor outlet of shell and tube heat exchanger is provided with an on / off gate
valve.
5. A system for on-line acid heating for pickling liquid substantially as herein
described with reference to the accompanying drawings.

The system has been designed and installed for on-line heating of mother liquor coming from Block of Chemicals (BOC) to pickling line l(as shown in figure) of Cold Rolling Mills at BSL. Bokaro. The system consists of shell and tube type heat exchanger complete with acid proof flanges on both ends, piping for steam and acid, temperature sensing and indication, valves and fittings supporting structures etc. The heat exchanger has been designed based on the design parameter as given below. The tube material is
able to sustain the corrosive environment of the mother liquor, i e the temperature and
concentration. The tube material is stainless steel grade 316L. The shell material is boiler
quality i.e. ASTM 106 Grade B. Steam supply has been tapped from 100 NB steam supply line available in the battery limit, after providing an isolation valve. The pipeline has been laid and lagged from this source point to the heat exchanger. The steam condensate line from the heat exchanger is connected to the existing condensate line of the shop. The condensate line has also been lagged from the heat exchanger to the exit point. There is a provision for temperature sensing of the incoming mother liquor before heat exchanger as well as outgoing mother liquor from the heat exchanger to the acid
tank 5(as shown in figure). The temperature sensors are installed with sheathing to counter the acid attack. The temperatures sensed at both the points are continuously indicated on the panel installed in the vicinity of the system. This provision has been made in order to visualize and evaluate the efficiency of heating. There has been made provision for flushing arrangement of the acid tubes after heating. After heating is over, the inlet and outlet lines of acid are closed and water inlet and outlet lines are opened. This facilitates cleaning the acid/salt left over the tube surface. The general arrangement of the system has been given in drawing no RD/D&E-BSL/356363/001 (R-0).