Brine
Purification for I.E.M
I.E.M brine unit provides feed of brine solution to ion exchange membrane Cell room. The brine solution feed must be ultra pure. The ideal concentration Of brine is 300g/l. Following are the main components of I.E.M brine unit.
1.
Saturator
2.
Purifier
3.
Settler
4.
Primary and Secondary Filters
5. Ion
Exchange Unit
Saturator
Saturator
consists of large storage of rock salt. At the rock salt, depleted and de chlorinated
brine having 220 g/l concentration which exist from the anode of iem cells
called anolite is showered in order to concentrate it through a 10 inch dia
pipe line. From saturator saturated brine goes to pits. There are three primary
and two secondary pits. From secondary pits saturated
solution at 300g/l concentration and 60-650C temp. is pumped via centrifugal pump having 60 hp and 2900 rpm into purification section.
Purifiers
There are two purifiers both have capacity 70 m3.
In first purifier solution of barium carbonate has been added to remove
sulphate ions. Excess carbonates are maintained in
the solution to insure removal of sulphate ions. Sludge formed is periodically
remove from bottom of the first purifier and is send to the recovery pits.
Overflow from first purifier goes to second purifier where caustic solution is
added into it. This will settle Mg as Mg (OH) 2.
Purpose of adding caustic in purifier 2 is of dual purpose:
·
Maintaining
conc. Of Na+ ions in brine feed.
·
To convert Mg+
to Mg(OH)2.
One important thing is that If we don’t add
BaCO3 in first purifier then we add calcium chloride in CaCl2 pits
and also add Na2CO3 in first purifier.From purifier the brine is transferred to settler prior to
the introduction of Brine into the settler, a flocculent named “Accofloc” is
added which solution is prepared into accofloc storage tank. Purifier is made of
mild steel and lined with fiber glass. Following are the reactions involved in
purifiers
Ba2co3+Na2so4 -----------à Baso4+Na2co3
Na2co3+Cacl2 ----------à Caco3+2Nacl
Mgcl2+2NaoH ----------à
Mg (OH) 2+2Nacl
Settler
Settler has capacity of 1000m3, brine overflows from settler after settling. A Scraper is also installed in the center; it takes 8 min and 53 sec to complete one revolution or 6.75 rev/hr near the bottom of the settler to push the sludge settled, towards the bottom of the tank where an automatic pneumatic control valve is opens for 30 sec after every 45 mint. The sludge from the settler is send to the recovery pits and from the recovery pit brine is send to the purifier one. From settler, the brine moves to a clarified tank. Settler is made of mild steel and coated with a type of resin which is corrosion resistant.
Primary and Secondary Filters
From settler, the brine moves to a series of filters where 5 different layers of Pebbles are used to filter the brine solution. The layer at the top is of Anthracite and remaining layer are of pebbles whose size increases from top to bottom. Here further purification from any sort of suspended impurity takes place. Backwash of these Primary filters takes place once in 24 hours.
Steps for Backwashing of Primary Filters:
To
backwash a primary filter following steps should b followed:
·
Close inlet and outlet
valves simultaneously
·
Open the vent valve
·
Open the valve of the line
going to the backwash from the top
·
Open the drain valve for
5-10min and drain it to recovery pit
·
Close the drain and
recovery pit valve
·
Open the water valve
connected to the drain line
·
Backwashing will start in a
while and water will start coming out of the backwash pipe at the top
·
When water becomes clear it
means filter is clean now close the water inlet valve and open the drain valve
and drain the water into drain line
·
Now close the drain valve
and backwash valve
·
Open the inlet valve
·
When brine starts coming
out the vent then open the outlet valve and close the vent valve the filter
will into the circuit again
. After primary filter brine is passing in to 2 storage tanks. Now it is pumped to secondary FILTERS (for suspended / insoluble impurities), containing tubes in it 137 in no. with 10 openings for each tube, and above flanged portion (that is hollow) brine is accumulated. Alfa cellulose solution is prepared in agitated tank and pumped to secondary filter to form a coating, in order to remove suspended impurities. There are three secondary filters 2 in circuit at a time and 1 under coat layer formation for 30 mins. One of the circuited filters is made to be refreshed when its coating is chocked resisting further flow and developing pressure which is then drained with great pressure and newly coated filter is in circuited.Following are the steps involving in the backwashing of the secondary filters.
Steps for backwashing
of Secondary Filters:
·
Close the inlet and outlet
valves simultaneously
·
Open the vent valve for the
removal of air
·
Open the drain valve and
drain the filter into the pit
·
Brine will drain at a high
rate because of the compressed air entrap inside the filter
·
Close the drain valve
·
Open the backwash water
valve the water will start coming out from the top of the filter
from the watch glass
line and close the vent valve
·
When the filter become
clear close the water valve
·
Open the drain valve and
drain the water and then close darin valve
·
pump the arbocell in the filter it comes out
from the top and will move to the arbocell tank
·
Watch glass will show milky
liquid coming out of the filter when it becomes clear the coating will complete
close the arbocell coating
·
Close the arbocell coating
valve
After passing through it, feed is sending to feed to ionizer tank. By pump brine is send to feed to ionizer.
Ion Exchange Unit
Freshly
regenerated resin of sodium zeolite is called as a polisher since it provide
final touch to remove any dissolved impurity if any, and when it contains
enough amount of soluble impurities it is called ionizer since it actually
removes solubility’s. Ionizer contains cations and zeolite, which when acting as a ionizer removes Ca+2
and Mg+ by converting to calcuim zeolite and magnesium zeolite. Two
out of three ionizers/polishers are in circuit at a time one as ionizer and
other as polisher, and third one under regeneration. Then this regenerated one
is made as ionizer and polisher as ionizer. This transition depends on feed
quality.
Regeneration
of Resin
To regenerate resin HCl along with NaOH is used. Sodium sulphide is added in order to remove chlorine gas. S-2 are also present in small extent. For regeneration first caustic is drained, followed by the displacement ( water wash) and backwashing with water. Acid HCl (dechlorinated with sodiumsuphite) is showered after diluting it 4% from 30% else it will damage resin. Once again it is displaced with water. Ca+2 and Mg+ adsorbed on resin will remove using HCl and HCl is displaced by water. NaOH is injected in order to add Na+2 and OH-1ions in resin. All of the ions are removed and converted into respective compounds. Temperature of the feed to ion exchange is maintained via heat exchanger.
Steps for Regeneration of Resin:
Ø Brine Drain:
Drain
the brine before regeneration.Open Drain valve and also open manual and
automatic valves so that brine could drain easily.
Ø Brine displacement:
After
the brine is completely drained, open water inlet valve as the drain valve is
already open. Check if drain is complete. If so close the water inlet valve and
drain valve. Backwash it
Ø Back Washing:
This
procedure takes place from bottom to top. Open the backwash valve and outlet
valve. Adjust the water manual valve so that resin does come out of the
vessel. And all the suspended particles
go out through it. Close the back wash valves.
Ø Water Drain:
To
drain water after backwash, open drain valve and vent valve so that water can
be drained easily and early. After drain is complete, prepare acid injection.
Ø HCL Injection
To
remove 32% free chlorine from acid tank, inject sodium sulphite and check from
the laboratory that chlorine is completely removed. After the removal of free
chlorine, open chemical valve and to reduce 32% acid to 4%, adjust the water
manual valve and start 32% acid pump. Open the suction and delivery valves.
Adjust the pump stroke to 78%. Check the concentration of acid from sample
point. It should be 4%. After 1 hour, check the acid concentration from the
drain valve and if this concentration is equal to the inlet concentration, acid
injection is complete. If this concentration is not equal to 4% then continue
acid injection.
Ø Acid Displacement:
To
remove the excess acid from ion exchanger, open the water inlet valve and check
the pH of water coming out of drain valve. Continue this process until pH is
normal and when the excess acid is completely removed. Close the water inlet
valve and completely drain the water.
Ø Caustic Injection:
After complete water drain, start caustic injection. Open chemical valve and adjust the water manual valve so that the concentration of caustic is 4%. Start the caustic injection pump and open its suction and delivery valves. Keep the pump strokes to 66%. Check the caustic
Material
Balance of IEM Brine:
Basis: - 150ton/day
Brine required/salt requirement
2Nacl+2H2 O
--------à 2NaOH+H2 +Cl2
NaOH : Nacl
2 : 2
1 : 1
1*40 : 1*58.5
40g : 58.5g
40g
caustic required Nacl=58.5g
1g
caustic required Nacl=58.5/40
150,000,000g
caustic required Nacl=585/40*150,000,000
=219375000g
=219 ton
|
Nacl required=219 |
Nacl =94%
Sulphate =2.2%
Ca =0.35%
Mg =0.35%
Others =3%
Fe =0.002%
Rock
Salt Required to be charge:-
94 ton Nacl is present in rock salt=
100 ton
1 ton Nacl is present in rock salt =
100/94
219 ton Nacl is present in rock salt=
100/94*219
= 233 ton
So rock salt required= 233 ton
|
Rock salt required= 233 ton |
Sulphate in rock salt= 233*2.2/100=
5.126 ton
Ca in rock salt = 233*0.35/100= 0.8 ton
Mg in rock salt = 233*0.35/100= 0.8 ton
Others in rock salt = 233*3/100 = 7 ton
Fe in rock salt = 233*0.002/100= 0.005 ton
BaCo3 Required:-
BaCo3+Na2 So4 -------à BaSo4+Na2
Co3
Mass
of Na2 So4 = 5.126 ton
Molar
mass of Na2 So4 = 118 ton
Moles = 5.126/118= 0.043
BaCo3 : Na2
So4
1 : 1
0.043 : 0.043
BaCo3 Required= 0.043*137
BaCo3 Required= 5.891
BaCo3 Required= 5.8 ton
|
BaCo3 Required= 5.8 ton |
Na2 Co3 : Na2 So4
1 : 1
0.043 : 0.043
Na2
Co3 Produced= 0.043*94= 4
|
Na2 Co3 Produced= 4
ton |
Na2 Co3+CaCl2 --------à CaCo3+2NaCL
Mass of CaCl2 = 0.8 ton
Molar Mass of CaCl2 = 40
Moles = 0.8/111 = 0.007
= 0.07
Na2 Co3 : CaCl2
1 : 1
0.07 = 0.07
Na2
Co3 required = 94*0.07 = 6.6 ton
Amount
of Na2 Co3 required= 6.6 ton
|
Amount of Na2 Co3 required= 6.6 to |
NaOH
Required:-
MgCl2+2NaOH
------à Mg (OH) 2+2NaCl
Mass of MgCl2 = 0.8
Molar Mass = 90
Moles = 0.8/90 = 0.01
NaOH :
MgCl2
2 : 1
0.02 : 0.01
NaOH Required to remove MgCl2
=0.02*40 = 0.8 ton
NaOH required to remove MgCl2
= 0.8 ton
|
NaOH required to remove MgCl2 = 0.8 ton |
FeCl2+2NaOH ---------à Fe (OH) 2+2NaCl
Mass of FeCl2 = 0.005 ton
Molar Mass = 55.8g/mole+70 = 125.8
Moles = 0.005/125.8 = 3.9*10-5
FeCl2 : NaOH
1 : 2
3.9*10-5 : 2*3.9*10-5
: 7.9*10-5
: 7.9*10-5 *40
0.03 ton
NaOH required to remove FeCl2
= 0.03 ton
|
NaOH required to remove FeCl2 = 0.03 ton |
NaOH required= 0.8+0.03
= 0.83 ton
NaOH required= 1 ton
|
NaOH required= 1 ton |
Results:
Nacl required=219
Rock salt required= 233 ton
BaCo3 required= 5.8 ton
Na2 Co3 required=
1 ton
Na2 Co3 Produced=
4 ton
NaOH required to remove MgCl2
= 0.8 ton
NaOH required to remove FeCl2
= 0.03 ton
NaOH required= 1 ton
Material
Injections:
Baco3= 5.8 tons
NaOH=
1 ton
All pumps have volumetric flow rate
110 m3/hr and working on 80% effienency and maximum 2900 rpm.
|
Pump |
Max RPM (a) |
Given RPM (b) |
88/2900 *b |
Flow rates (m3/hr) |
|
Crude Brine |
2900 |
1050 |
.0303*1050 |
31.86 |
|
I.E |
2900 |
1650 |
.0303*1650 |
49.99 |
|
Secondary Storage Tank |
2900 |
2150 |
.0303*2150 |
65.154 |
|
Clarifier |
2900 |
2700 |
.0303*2700 |
81.81 |
IEM Brine Block diagram
Brine
Purification for D.S.A
DSA brine unit provides brine to DSA cell rooms. The purity level of brine solution required here is not that mush high as that for I.E.M cell room. That’s why lesser purifiers is installed into this unit. Another distinguishing feature of the unit is that brine is de‐chlorinated in this unit as oppose to I.E.M brine unit where de‐chlorinated brine is received from cell room. The unit consist of following sub units.
1.
De‐Chlorination Unit
2.
Saturator
3. Purifier
4.
Settler
5.
Sand Filters
De- Chlorination Unit
Depleted brine from DSA is sent to storage tank(2D10) behind DSA , with storage temp. 800C, with such a low level that on addition of HCl Cl2 gas covers maximum volume available, extracted and sent via suction of blowers to HCl plant or else. There are two storage tanks and two pumps to pump depleted brine. 31% caustic is imported into storage tank via pump and lift upward to provide flow under gravity since it is more well controlled, and fast way. From overhead this brine is injected into depleted brine line coming by passing through air strippers installed in series in which brine is entered from middle and air is blown through it to DE chlorinate brine. This chlorinated air is sent to calcium hypo chlorite unit. Chlorine is reduced to 7.1-21.3 g/l.After injection of caustic through over head arrangment,it is stored into DE chlorinated brine tank(2D13 A,B). Here its pH is 8.5-9.5. The de‐chlorinated brine is sent to saturator in de‐chlorination unit, the chlorine contents in brine solution is reduced to 7.1 ppm
Saturator
The declorinated brine then pumped to the saturators where it showered on the rock salt and becomes saturated. Saturated brine (320 – 325gpl ) is difficult to handle due to the variation in temperature, causing crystallization of the salt in pipe lines and equipments. In order to control the concentration of NaCl to the desired 300gpl a bypass line of depleted brine is mixed with saturated brine in pits. Here in pits insoluble fractions are settle down and then after required time of settlement brine is pumped to the purifiers for further.
Purifiers
There are two purifiers both have capacity 70 m3.
In first purifier solution of barium carbonate has been added to remove
sulphate ions. Excess carbonates are maintained in
the solution to insure removal of sulphate ions. Sludge formed is periodically
remove from bottom of the first purifier and is send to the recovery pits.
Overflow from first purifier goes to second purifier. where caustic solution is
added into it. This will settle Mg as Mg (OH) 2.
Purpose of adding caustic in purifier 2 is of dual purpose:
Maintaining conc. Of Na+ ions in brine feed.
To convert Mg+ to Mg(OH)2.
From
purifier the brine is transferred to settler prior to the introduction of Brine
into the settler, a flocculent named “Accofloc” is added which solution is
prepared into accofloc storage tank. Purifier is made of mild steel and lined
with fiber glass. Following are the reactions involved in purifiers
Ba2co3+Na2so4 -----------à Baso4+Na2co3
Na2co3+Cacl2 -----------à Caco3+2Nacl
Mgcl2+2NaoH --------à Mg (oH) 2+2Nacl
Settler
Settler
has capacity of 2300m3, brine overflows from settler after settling. A Scraper
is also installed in the center, near the bottom of the settler to push the
sludge settled, towards the bottom of the tank where an automatic pneumatic
control valve is opens for 15 sec after every 30 mint. The sludge from the
settler is send to the recovery pits and from the recovery pit brine is send to
the purifier one. From settler, the brine moves to a clarified tank. Settler is
made of mild steel and coated with a type of resin which is corrosion
resistant.
From settler, the brine moves to a series of filters where 5 different layers of Pebbles are used to filter the brine solution. Internals of primary filters, 8 in no. and 6 in circuit, consists of rocky pebbles leading from smaller size to larger one supported via rod support at bottom that do not allow them to flow out. At the top there is a layer of small particles enough small that it looks like a layer of sand. Fluid is entered from bottom of filters. Here further purification from any sort of suspended impurity takes place. Backwash of these Primary filters takes place once in 24 hours.
Purified brine with small amount of chlorine is pumped to 2D6 tank. After 2D6 tank HCl is added to adjust pH to 4-5, while its temperature is maintained by passing it through heat exchanger rising it to 700C. after heat exchanger brine is sent to overhead storage tank 2D7 where further from here it is sent to DSA cell rom.
Material
Balance of IEM Brine:
Basis: - 90
ton/day
Brine
required/salt requirement
2Nacl+2H2
O --------à 2NaOH+H2 +Cl2
NaOH : Nacl
2 : 2
1 : 1
1*40 : 1*58.5
40g : 58.5g
40g caustic required Nacl=58.5g
1g caustic required Nacl=58.5/40
150,000,000g caustic required
Nacl=58.5/40*90,000,000
=131625000g
=131 ton
|
Nacl required=131 |
Nacl =94%
Sulphate =2.2%
Ca =0.35%
Mg =0.35%
Others =3%
Fe =0.002%
Rock
Salt Required to be charge:-
94
ton Nacl is present in rock salt= 100 ton
1
ton Nacl is present in rock salt = 100/94
131
ton Nacl is present in rock salt= 100/94*131
= 139 ton
So
rock salt required= 139 ton
|
Rock salt required= 139 ton |
Sulphate
in rock salt= 139*2.2/100= 3.058 ton
Ca
in rock salt = 139*0.35/100=
0.5 ton
Mg
in rock salt = 139*0.35/100= 0.5
ton
Others
in rock salt = 139*3/100 = 4 ton
Fe in rock salt = 139*0.002/100= 0.003 ton
BaCo3 Required:-
BaCo3+Na2 So4 ----------à BaSo4+Na2
Co3
Mass of Na2 So4 = 3.058
ton
Molar mass of Na2 So4 =
118 ton
Moles = 3.058/118= 0.03
BaCo3 : Na2
So4
1 : 1
0.03 : 0.03
BaCo3
Required=
0.03*137
BaCo3 Required= 4.11
BaCo3 Required= 4.11 ton
|
BaCo3 Required= 4.11 ton |
Na2
Co3 : Na2 So4
1 : 1
0.03 : 0.03
Na2 Co3 Produced= 0.03*94= 3 ton
|
Na2 Co3 Produced= 3 ton |
Na2
Co3 Required:-
Na2
Co3+CaCl2 --------à CaCo3+2NaCL
Mass
of CaCl2 = 0.5 ton
Molar
Mass of CaCl2 = 40
Moles = 0.5/111 = 0.005
= 0.01
Na2
Co3 : CaCl2
1 : 1
0.05 = 0.05
Na2 Co3 required =
94*0.05 = 5 ton
Amount of Na2 Co3 required=
5 ton
|
Amount of Na2 Co3 required=
5 ton |
MgCl2+2NaOH ---------à Mg (OH) 2+2NaCl
Mass
of MgCl2 = 0.5
Molar
Mass = 90
Moles = 0.5/90 = 0.005
NaOH :
MgCl2
2
: 1
0.01 : 0.005
NaOH
Required
to remove MgCl2 =0.01*40 =
0.4 ton
NaOH
required to remove MgCl2
= 0.4 ton
|
NaOH required to remove MgCl2
= 0.4 ton |
Mass
of FeCl2 = 0.003 ton
Molar
Mass = 55.8g/mole+70 = 125.8
Moles = 0.003/125.8 = 2.4*10-4
FeCl2 : NaOH
1 : 2
2.4*10-4 : 2*2.4*10-4
: 4.8*10-4
: 4.8*10-4 *40
0.02 ton
NaOH
required to remove FeCl2 = 0.02 ton
|
NaOH required to remove FeCl2
= 0.02 ton |
= 0.42 ton
NaOH
required= 0.42 ton
|
NaOH required= 0.42 ton |
Results:
Nacl
required=131
Rock
salt required= 139 ton
BaCo3
required= 4.11 ton
Na2
Co3 required= 5 ton
Na2
Co3 Produced= 3 ton
NaOH
required to remove MgCl2 = 0.4 ton
NaOH
required to remove FeCl2 = 0.02 ton
NaOH
required= 0.42 ton
Material
Injections
Baco3=
4.11 tons
NaOH= 0.42 tons
DSA
Block diagram:
