Internship Report
BRINE SECTION
SUBMITTED BY:
Mobin
CHEMICAL ENGINEER
CONTENTS
SATURATOR
SETTLER
SECONDARY FILTERS
ION EXCHANGE UNIT
CHEMICAL ANALYSIS OF BRINE
PURIFIER
UTILITY UNIT
WATER UTILITY
Dryer:
INTRODUCTION
ITTEHAD Chemicals is a leading chemical manufacturing company in Lahore. It
produces mainly caustic soda and chlorine by electrolysis process. It was
formed by CHAMI group of industries in 1964 with initial installed production
of 60 MT/day of Caustic soda and 54 MT/day of chlorine. The First expansion
phase was carried out in 1969 enhancing capacity to 90 MT of caustic soda and
81 MT of chlorine. Before the period of nationalization the unit was known as
United Chemicals and renamed by the Govt. as ITTEHAD Chemicals after
nationalization in 1973 and put under the control of Federal Chemicals and
Ceramics Corporation Ltd. (FCCCL). The current production of all the cells is
350 MT/day of caustic soda and 315 MT/day of chlorine
The report is detailed on brine purification process. It is divided into two sections:
I. Brine purification unit for IEM and DS
II. Utility unit
Brine
purification section is discussed with working, material of construction,
material balance, heat balance, process parameters, specification, safety and
process control. Whereas in utility section, water, steam and instrument air
are mainly discussed.
I.E.M BRINE PURIFICAITON
Chlor
Alkali plant (CAP) produces caustic soda, chlorine and hydrogen (by product)
using brine and electricity. Purification of brine to ultra pure level is
essential for Ion Exchange Membrane (IEM) technology because alkaline earth
metal cause severe problem in membrane. So, the following are six steps used for
IEM brine purification process.
§ Saturator
§ Purifier
§ Settler
§ Primary
filters
§ Secondary
filters
§ Ion
exchange
BRINE
is solution of NaCl (sodium chloride) salt in water. The low
concentrated Na ions (brine) which is coming from the cell room lose its sodium
ions concentration i.e. 220 g/l due to
electrolysis to from caustic soda, so it is recycled back to gain its
concentration up to 300 g/l level. Saturator of 277 m3 used to
saturate the brine by showering de-chlorinated brine on northern and southern
bed of NaCl rock salt with
temperature 65-70 0C
and flow rate 100 m3/hr. industrial water pipe of 2’’ is also shower
on salt bed for brine make up purposes. When low concentration of sodium ion
de-chlorinated brine passes through 13 ft height of rock salt bed then it
enters into primary pits through channel line.
|
Rock salt Components |
Weight percentages |
|
NaCl |
93% |
|
Na2SO4 |
2.2% |
|
Ca++ |
0.35% |
|
Mg++ |
0.35% |
|
others |
4% |
There are three
primary pits, two secondary pits and two calcium chloride pits.
Three
primary pits of 415 m3 each are used to sediment the 4% remaining
impurities like mud, silicate, granules and other settle down impurities, it
takes 4 hour of retention time to settle down impurities. Out of three pits,
second pit is used as standby pit. When one pit become full of sludge then it
cut off from the circuit and other clean and de-sludge ready for use is put
into circuit. Pits are made inclined for the removal of sludge by external
means.
Two
secondary pits of 35 m3 each are used to remove the further
impurities which are not removed by primary pits. One pit is used as standby
for removal of remaining settle down impurities. Other purpose for formation of
secondary pits is the addition of chemicals such as sodium sulfite of 5 m3
tank is used when chlorine present in primary pits. Similarly, sulfate treated
brine from calcium chloride pit is also added into secondary pits. A titanium
coated or fiber pipe with number of holes of half centimeter size is used as
filter media attached at end side of secondary pit from where pump suction
start. At the end two centrifugal pump of 60 hp (one as standby) are used to
transfer brine to purifier.
Two
calcium chloride pits of 350 m3 each are used for treatment of
sulfate ions present in brine come from primary pits and the de-chlorinated
brine before showering at the flow rate of 20 m3. One pit is used as
standby for sludge removal. The purpose of CaCl2 pit is to minimize
the sulfate ions present in brine otherwise an alternate method for sulfate
removal by using barium carbonate will apply which is very costly than CaCl2
treatment. Firstly, (30-35%) calcium chloride solution comes from CaCl2
plant stored into 30 m3 of storage tank. After this CaCl2
solution is added into calcium chloride pit whose amount depend upon sulfate
ions. Accoflock is also added into CaCl2 pits to minimize the
suspended solid particles.
Concentration of sulfate ions in de-chlorinated brine = 12 g/l (it may change)
Concentration of sulfate
ions in rock
salt = 2.2 g/l
Total concentration =
14.2 g/l
Amount of sulfate ions in CaCl2 pit = 14.2 kg/m3 x350 m3 = 4970 kg
Mole of Na2So4
= 4970/138 (M.weight of Na2So4)
|
CaCl2 Required = 3.9 Ton
|
Mole of Na2So4 = 36 mole
Amount of CaCl2 required = 36 x111 (M.weight of CaCl2)
From CaCl2 amount we can find the level (mm)
of tank by using formula given below:
CaCl2 (MT) =
Sp.gravity x concentration of CaCl2
x Level
100
CaCl2
pit is prepared after 8 hours circulation of calcium chloride or brine solution
and pit consumed after 18 hours. When lab results show that sulfate ion is
within limit, calcium ions in excess and NTU <1 then solution transferred
into two CaCl2 tanks of 6
m3 and 7 m3 separately with the help of centrifugal pump
of 40 hp. Overflow of CaCl2 tank again send to pits for circulation.
PURIFIER
is a reactor or vessel contains a chemical reaction. Two open tank CSTR
(continuous stirred tank reactor) purifier of 70 m3 each are used to
produce adequate particles size that can be easily agglomerate with flocculent
in settler. Paddle agitator is used to provide mixing energy in such way that
particles do not disintegrate. Three reactant chemicals are added in purifier to achieve
large particle size of the impurities so that they are bound by flocculants and
are easily settles down and hence removed.
§ Barium
carbonate
§ Sodium
carbonate
§ Accoflock
These reactant chemicals
maintain excess carbonate and hydroxyl ions in two purifiers.
Saturated brine
from secondary pits enters into purifier#1 from bottom side and emit from top
side after retention time of 45 minute. A bypass line is attached with inlet of
brine to purifier which is used for distribution of additive chemical either from
top or bottom of purifier. Two type of reactant chemicals are used to remove
sulfate and calcium ions from brine as fellow:
I.
Barium carbonate
II.
Sodium carbonate
Barium
carbonate:
Barium
carbonate has ability to remove sulfate ions present in brine in form of barium
sulfate. Amount of BaCo3 required removing impurities depend on
sulfate ions and can be find by formula given below:
Amount
of BaCo3 = load x44(factor calculated from sulfate)
Solution
tank of barium carbonate:
Barium
carbonate solution of 8 % w/w is prepared in 7m3 of fiber or mild
steel with rubber lining tank. Brine from primary filter is used as solvent for
BaCo3 solution to maintain sodium ions in purifier#1. A motor driven
mixer of 70 rpm (revolution per minute) is used to provide mixing energy for
solution formation. When 2 hours batch of BaCo3 is prepared then it
transferred to purifier from top side position with the help of two centrifugal
pumps (one as standby) to purifier.
Solution
tank of sodium carbonate:
Sodium carbonate solution of 8% w/w
is prepared in 7 m3 of fiber or mild steel with rubber lining tank.
Brine is used as solvent for solution formation. A peddle type motor driven
mixer with30 rpm is used to provide mixing energy.
One batch of 2 hours is added to
purifier in bypass line of brine to distribute the solution partially from top
and bottom.
Reaction:
BaCO3
+ Na2SO4 ---------
> BaSO4 + Na2CO3
Na2CO3 + CaCl2 ---------- > CaCO3 + 2NaCl
Brine enters
from bottom side into purifier#2 after emitting from top side of purifier#1. In
this purifier caustic soda 31% solution is added by gravity from overhead tank
and its flow can be adjusted through rotameter. A stand by tank can also be
used is case of NaOH solution shortage. Sodium hydroxide is used to precipitate
the magnesium ion impurity in form of magnesium hydroxide. NaOH is added into
purifier#2 because reaction of caustic soda with magnesium is fast as compared
to reaction of barium and sodium carbonate with sulfate or calcium ions.
Reaction:
2NaOH
+ MgCl2 --------------- > Mg (OH) 2 +
2NaCl
Solution
tank of Accoflock:
Accoflock
solution of 1% w/w is prepared in 7 m3 of fiber or mild steel with rubber
lining tank. First of all 700 gram cationic polymer accoflock is added into 1/2
m3 tank with (DI)
de-ionized water as solvent mixed by using tee mixer 42 rpm. Then this solution
is transferred into 7 m3 tank filled with industrial water as
solvent for further dilution. Sodium sulfite tank is also present for addition
into accoflock tank if chlorine present in settler. When all these additives
are mixed with peddle mixer 50 rpm to form uniform mixture then it transferred
to small tank place between purifier and settler by using two centrifugal pumps
(one as standby).
Conditions
for addition of BaCo3 and Na2Co3:
I.
If BaCo3 is injecting into purifier#1 then
injection of CaCl2 pits solution into secondary pits and Na2Co3
into Purifier#1 will be stop because Barium carbonate give double reaction with
impurities.
II.
If CaCl2 pit solution is injecting into secondary
pit then we can start BaCo3 injection two hours later after
termination the CaCl2 addition.
III.
If CaCl2 pit solution is injecting into secondary pit then
we only use Na2Co3 in purifier#1 because sulfates ions already removed by
Calcium chloride solution.
At the last,
sludge is removed from the bottom end of both purifiers once in a day for 2
minute opening and send into sludge pits. Two brine recovery sludge pits are
used to recover brine after giving settling time of approximately 45 minutes. Two centrifugal pumps (one as standby) are
used to transfer recovered brine into purifier#1. Brine is also recovered from
drain of primary filter during backwashing process which also use again in
purifier#2 with the help of centrifugal pump.
Settler
is a clarifier used to remove solid particulates or suspended solids from brine
by sedimentation process.
The 1k4 brine settler is solid contact type clarifier like a huge bowl which is broad from the top and narrows at the bottom. A big high efficiency marine propeller type agitator is fitted at the centre of the settler which completes its one revolution in 9 minute and 6.6 revolutions per hour keeps on fluid in slight motion. It is made up from mild steel material with titanium coating from interior side and has capacity of 1000 m3 which takes 10 hours of retention time for settling.
First of all
brine enters into settler from the center with accoflock into primary mixing
zone of settler, here flocculation mixing with suspended particles present in
brine occur. After this it enters into secondary mixing zone of settler, here
charge reduction and agitation increase the particles collision and then
particles move down (settle) by gravity due to its weight and size increased by
flocculating medium. The impurity particles bound with each other to form
bigger size particles called as Sludge which settles down at the bottom of the
settler and send to sludge pits. Brine recovered from sludge pits send to
purifier #1 and sludge dumped to drain well. An automatic instrument air
control pneumatic valve is attached with bottom end for de-slugging which open
after every 45 minutes for 30 second valve opening. At the top section
clarified brine overflow and move toward clarifier tank by gravity and overflow
from tank again move toward settler top side. After every two hours down take
sample analyze the excess carbonate and hydroxyl ions. Test result tells us how
much amount of reactant chemicals are needed in purifiers. Brine is send toward
primary filter from clarifier by using two centrifugal pumps (one as stand by)
of 60hp.
Brine
primary filters are required to remove the suspended solids overflowing with
the brine from the settler/clarifier. There are five number of flowing gravity
sand filters operated in parallel.
Primary filters are made up of mild
steel of total volume of 13 m3 consists of a multilayered
pebbles and stone filtering bed and one upper layer of anthracite coal of low
choric value. The bed of these
multilayered pebbles and stones are formed according to their size increase
from top bed to bottom and anthracite coal at upper most bed of filter.
Designing of bed according to size of pebbles and stones as fellow:
|
Pebbles size |
Bed volume |
|
40-50 mm |
2.7 m3 |
|
16-30 mm |
1.3 m3 |
|
11-15 mm |
0.55 m3 |
|
5-10 mm |
0.55 m3 |
|
3-4 mm |
0.55 m3 |
|
0.8-2 mm |
4.3 m3 |
|
Total |
10 m3 |
Brine
enters into primary filter from top side and out from bottom after passes
through bed of anthracite coal and multilayered bed of pebbles. Impurities like
excess carbonate and hydroxide ions stuck with porous part of pebbles and brine
out with impurities reduce up to 10ppm (parts per million). Pressure gauge is
attached with top of filter which tells us about backwashing indication. If
pressure increase from 1 bar then it means filtering media become full of
suspended particles. By using backwashing we can reuse our filtering medial
again.
To
backwash a primary filter for 45 minutes the following steps should be
followed:
·
Close inlet and outlet valves of brine simultaneously
·
Open the vent valve for air removal
·
Open the drain valve for 5-10min and let the
drain into recovery pit
·
Close the drain and recovery pit valve after
draining all brine
·
Open the industrial water valve for
backwashing
·
Backwashing water enter from bottom and coming
out of the backwash pipe at the top
·
When water becomes clear then close the water
inlet valve and open the drain valve to drain the water into drain channel
·
Now close the drain valve and backwash valve
·
Open the inlet and outlet valve of brine and
at the end close the vent valve
The brine from the primary filter
storage tank is pumped to the three secondary filters arrange in parallel
operation to remove the further impurities that are not removed from primary
filters.
The secondary brine filters reduce the concentration of suspended solids
(mostly CaCO3 and Mg (OH) 2) to < 1 ppm with particle
size < 0.5 micron.
The
Secondary brine polishing filters are vertical tubular backwash filters that
utilize a cellulose fiber pre-coat to achieve such level of filtration that
protect the ion exchange system from suspended solids which would otherwise
plug the column.
The
secondary brine filters contain 139 tubes with 3 tubes opening suspended
vertically from a tube sheet. The filter tubes are constructed of C-PVC
(chlorinated polyvinyl chloride) with a polypropylene sleeve and are covered
with a seamless polypropylene sock type covering. The conical shaped bottom
facilitates the backwash by directing the filtered solids cake to the dump
(drain) connection during the backwash. All other internal hardware (fasteners
etc.) is constructed of titanium or plastic and gaskets are constructed of EPDM
(ethylene propylene diene monomer) to minimize metals contamination of the
brine.
Brine
enters the filter through the bottom conical section and is evenly distributed
throughout the filter chamber.
Brine
cross exchanger is located upstream of the secondary filter. The brine cross exchanger
is designed to exchange thermal energy between the brine primary storage tank
to the secondary filters. Filtration is from the outside of the tubes to the
inside. As the brine passes through the cake and tubes, suspended solids are
deposited on the outside diameter of the tubes. The collection of these
suspended solids forms a cake layer on the tubes. The formation of this cake
layer results in increased pressure drop from 2.5 kg/cm2 to above and
eventually necessitates backwashing of the filtered brine. Filtered brine flows
up through the inside diameter of the tubes and enters the top head of the
filter through the openings in the tube sheet. Filtered brine is then
discharged from the top head through the main filtered brine outlet and stored
in 70 m3 storage tanks.
The
pre-coating solution tank is used for mixing pre-coat material and brine.
The 7 m3 tank is an open top
FRP vessel with peddle type agitator 32 rpm provided to ensure a homogenous
mixture. Industrial and DI water can be use as solvent but mostly brine is used
as solvent to form 20 % w/w of Alfa cellulose by adding pre coating material of
17.5 kg (one bag) in the tank.
Backwashing and
pre-coating steps:
To
backwash a primary filter for 35 minutes the following steps should be
followed:
·
Close the inlet and outlet valves of brine simultaneously
·
Open the drain pneumatic valve and drain all
the filter cake solution into the pit
·
Brine will drain at a high rate because of
the compressed air entrap inside the filter doom
·
Close the drain valve after complete draining
of brine and filter cake
·
Turn on the arbocell pump for circulation
·
Open the inlet and outlet pre-coat valve to
circulate a brine solution containing the pre-coat material through the filter
until a uniform layer of pre-coat is applied
·
Watch glass will show milky liquid coming out
of the filter when it becomes clear (coating will complete) then close the
arbocell coating
·
Close the inlet pre-coat valve
·
Open the inlet and outlet valve of brine
·
At the end close the outlet of pre-coat valve
and turn off the pump of arbocell
If
the brine feed stream contains a large percentage of fines (small) or slimy
solids, then the pressure drop across the filter may rise rapidly, giving short
cycle times. This is often the case when the brine has a poor Ca to Mg ratio
(less than 2:1).
Filtered
brine from the secondary brine filters flows into the FRP made Ion Exchange
Feed Tank. Brine exiting the ion exchange feed tank is pumped through the brine
cross exchanger which is located upstream of the ion exchange system. The brine
cross exchanger is designed to exchange thermal energy between the brine feed
stream to the ion exchange system. The brine cross exchanger is a plate and
frame heat exchanger constructed of titanium plates used to steam heat the brine feed to the brine ion
exchange system as required to maintain the temperature in the range of 55 to 60ºC.
Brine
passé through secondary filter still has enough particles of size less the 0.5
microns may damage the membrane of electrolysis cell. So the special unit
called ion exchange resin applied to remove unwanted impurities of calcium and
magnesium ions.
Ion Exchange resins are insoluble
granular substances which have in their molecular structure acidic radicals
that can be exchanged. The positive ions fixed on these radicals are replaced
by ions of the same sign in brine solution in contact with them.
The
ion exchange vessels are typically constructed of rubber lined steel to
minimize impurities pick up by the passing brine. Internal piping is typically
constructed of Titanium, Hastelloy C-276, or C-PVC (plastic only for the top
inlet distributor). External piping is typically constructed of C-PVC or FRP.
The vessel under-drain system must be constructed of metal (Titanium and/or
Hastelloy C-276), and must be spiral wound wedge (well screen) design. Plastic
is not allowed to be used for the bottom under-drain system, and cloth wrapped
laterals are forbidden. An ion-exchange resin or ion-exchange polymer is an
insoluble matrix normally in the form of small (0.5-1 mm diameter) beads,
usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous, providing a
high surface area. Ion exchange resin type is a chelating resin
of micro porous structure with polystyrene matrix cross-linked with di-vinyl
benzene substituted with weakly acidic amino-phosphonic active groups. The characteristics reactions are
shown below:
2RCH2NHCH2PO3Na2
+ Ca+2 ------> (RCH2NHCH2PO3)2CaNa2
+ 2Na+
Regeneration to Hydrogen Form:
(RCH2NHCH2PO3)2CaNa2+4HCl--->2RCH2NHCH2PO3H2+CaCl2+2NaCl
Conversion to Sodium Form:
RCH2NHCH2PO3H2
+ 2NaOH ---------> RCH2NHCH2PO3Na2 +
2H2O
The
chemical structure of this resin facilitates the formation of complexes with
metallic ions such as calcium and magnesium. The relative affinities for metals
in an alkaline brine environment are as follows;
Mg+2 > Ca+2 > Sr+2 > Ba+2
There are three ion exchange resin units operate in series, one unit use as ionizer (primary column), second as polisher (secondary column) and the third one as standby for regeneration. Alkaline brine enters the top of the column and flows downward through the resin bed. As the brine contacts the resin, calcium ions in solution are “exchanged” for sodium ions in the resin. Two sodium ions are exchanged for each calcium ion. The resin bed becomes “exhausted” where there is too few sodium ions left to exchange with the calcium ions, resulting in the “break-through” of calcium ions in concentrations exceeding 20 ppb in the exiting brine. Lab analysis of the brine downstream of the ionizer (primary calcium) every 8 hours is used to determine when break-through has occurred indicating the need to regenerate the ionizer (primary column).
Merry-go-round
Fashion:
After
regeneration, the regenerated column is placed in stand-by mode. When
the primary column (ionizer) is taken offline for regeneration, the stand-by
column is put into service as the secondary (polishing) column and the
secondary column becomes the primary column (ionizer). This cyclic operation
has been described as “merry-go-round” fashion.
Four
important safety precautions for resin are as given below:
I.
The brine ion exchanges system must be free
from mercury because it is not stripped from the resin during regeneration and
it will permanently reduce the capacity of the resin, thereby shortening cycle
time (i.e. shortening the length of time between regenerations)
II.
Brine feed to the ion exchange system must
not have any free chlorine present. Free chlorine will oxidize the resin which
destroys the resin’s ion exchange capacity
III.
The feed brine temperature should be maintained
in the range of 55 to 60ºC and the pH should be maintained in the range of
9-10.
IV.
The brine flow rate is typically controlled
in the range of 10 to 30 BV per hour
An exhausted column that has been
taken off line must have the resin converted from the calcium form back to the
sodium form. This conversion procedure is called regeneration. It is not
possible to go directly from the calcium to the sodium form as with a classical
water softener resin. Sodium chloride is not used to place the resin in sodium
form since the chelated functionality of the cation resin is not able to split
a neutral salt.
Auxiliary
equipment required for the ion exchange system regeneration includes;
§
HCl
Measuring Tank (for 31% HCl)
§
NaOH
Measuring Tank (for 32% NaOH)
§
HCl
Metering Pump
§
NaOH
Metering Pump
Weak
acid and weak caustic are made by diluting strong acid and strong caustic with
de-ionized water for regeneration of the ion exchange resin. The metering pumps
are designed to provide the proper flow rates of strong chemicals so that the
final (diluted) concentrations are 4-5 wt% HCl/NaOH. Sodium sulfite must be
added into the HCl Measuring Tank as required to eliminating the chlorine
otherwise free chlorine will damage the ion exchange resin permanently, causing
reduced capacity. Free chlorine can also be generated by the reaction of HCl
with sodium chlorate. It is therefore important to completely rinse the column
of brine prior to the start of acid regeneration. Lastly, the de-ionized water
used for regeneration also must be free of chlorates and free chlorine.
A general outline of the sequence for this chemical addition is as follows;
|
Sr # |
Description |
BV/hr (Bed volume) |
Time (min) |
BV (Bed volume) |
Flow Direction |
Concentration |
|
1 |
DI water rinse |
3.0 |
60 |
3.0 |
Down flow |
Chlorine = Nill |
|
2 |
DI
water backwash |
8.8 |
30 |
4.4 |
Up flow |
Chlorine = Nill |
|
3 |
Acid regent(HCl) |
4.0 |
60 |
4.0 |
Down
flow |
4-5 wt % HCl |
|
4 |
DI water rinse |
3.0 |
60 |
3.0 |
Down
flow |
|
|
5 |
Caustic
conversion (NaOH) |
4.0 |
60 |
4.0 |
Down
flow |
4-5 wt % NaOH |
|
6 |
DI water rinse |
3.0 |
60 |
3.0 |
Down
flow |
Chlorine = Nill |
|
7 |
Brine rinse |
3.0 |
60 |
3.0 |
Down
flow |
There are nine steps needed to regenerate an exhausted
primary column (ionizer) as given below:
|
1-Brine
drain |
4- Water
drain |
7- caustic injection |
|
2-Brine
displacement |
5- Acid
injection |
8-
caustic displacement |
|
3-Backwashing
|
6- Acid
displacement |
9-
Brine rinse |
§ Brine Drain:
First
step is to drain all the brine before regeneration. Close inlet and outlet of
brine then open manual and automatic drain valve with opening air vent valve that
brine could drain easily.
§ Brine displacement:
After
the brine is completely drained, open DI water inlet valve as the drain valve
is already open. When brine is completely drain then close the water inlet valve
and drain valve.
§ Back Washing:
Backwashing is done from bottom to top. Open the backwash DI water inlet and outlet valve. Adjust the water manual valve so that resin does come out of the vessel. Air vent valve should close during backwash.
§ Water Drain:
To
drain water after backwash, open drain valve and vent valve so that water can
be drained easily and early.
§ HCL Injection:
After the removal of free chlorine from HCL
tank by suing sodium sulfite, open acid tank valve and adjust the water manual
valve to reduce 32% acid to 4%.Open the suction and delivery valves of acid
metering pump. Adjust the pump stroke to 78% and Check the concentration of
acid from sample point, it should be 4%. The concentration of acid 4% is used
because it provides roughly the same molarity as the brine solution which
reduces the likelihood that the resin will experience osmotic shock .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.
§ Acid Displacement:
After
acid injection remove the excess acid from ion exchanger, open the DI water
inlet valve and check the pH of water coming out of drain valve. Continue this
process until pH is normal (7.0) and when the excess acid is completely removed
then close the DI water inlet valve.
§ Caustic Injection:
After complete water drain, start caustic injection. Open caustic tank 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 by keeping the pump strokes to 66%. After 1 hour, check the caustic concentration from the drain valve and if this concentration is equal to the inlet concentration, caustic injection is complete. If this concentration is not equal to 4% then continue acid injection.
§ Brine rinse:
After
caustic injection the primary column is regenerated with sodium ions and can be
uses again after rinsing the bed with brine at the end to continue to process.
Now this regenerated column becomes secondary column (polisher)
Acid
concentration conversion 31% to 4%:
Formula: For
60 % stroke,
C1xV1 = C2xV2 Dosing
pump flow rate 3.6 liter/hr
C1 (concentration
of given acid) = 0.31 1000 liter acid = 7750 liter of water
C2 (required concentration
of acid) = 0.40 1 liter acid =
7750/1000 liter of water
V1 (Volume of
given acid) = 1000 liter 3.6
liter acid = (7.75) x 3.6 liter of water=28
V2 (Volume
of required water) =? Result:
V2 = 0.31 x 1000/0.04 = 7750 liter
At 60% doze = 28 liter/hr DI water flow
Required
to convert 31% acid to 4%
MATERIAL
BALANCE for IEM BRINE
Rock salt 93
% NaCL
|
SATURATOR
De-chlorinated brine
NaCl = 220 g/l
--------Ã ----------Ã NaCl =305 g/l
Flow rate = 100 m3/hr
Density = 1170 kg/m3
Impurities
4.1 % (mud, silicate and granules)
Basis: - 1 hour
Operation
NaCl consumed from rock salt = 305 -220 g/l
NaCl consumed =
85 g/l
Mass flow =
85 kg/m3x 100 m3/hr
Mass flow = 8500 kg/hr
93 kg NaCl in rock salt = 100
kg
1 kg NaCl in rock salt =
100/93 kg
8500 kg NaCl in rock salt = 100/93x8500 kg
|
Result: 9140 kg rock salt required for 1 hour operation.
Overall
reaction
2NaCl+2H2 O ------------ > 2NaOH+H2 +Cl2
Mole of NaCl = 9140/58(Mol.
Weight of NaCl) = 157 mole
Caustic
product
Sodium chloride reactant
NaOH (mole) : NaCl (mole)
2 : 2
1 : 1
157*40 : 157*58.5
Amount of NaOH formed = 157x40
Amount of NaOH formed per hour = 6280 kg /hr
Amount of NaOH formed per
day = 6280x24 kg
NaOH Produce per day =
151200 Kg
|
Na2CO3 =?
NaCl
= 305 g/l BaCO3 =?
PURIFIER#1 |
SO4 -- =2.2 g/l
Ca++ =3.5 g/l -------Ã PURIFIER#1 ------Ã Product
Density =1170 kg/ m3
BaSO4 and CaCO3
(As Impurities)
Basis:
- 1
hour Operation
Overall Mass flow rate =
1170 kg/m3x 100 m3/hr
Overall
amount of salts =
117,000 kg
Mass flow rate of Ca++ = 3.5 kg/m3x100 m3/hr
Amount
of Ca++ = 350 kg
Mass flow rate of SO4 -- = 2.2 kg/m3x100 m3/hr
Amount
of SO4 -- = 220 kg
Mole
of Na2SO4 =
220/138(Mol. Weight of Na2SO4)
Mole
of Na2SO4 =
1.59 mole
Mole of CaCl2 =
350 /111(Mol. Weight of CaCl2)
Mole of CaCl2 = 3.15 mole
BaCo3
Required:
Reaction:
1BaCO3
+ 1Na2SO4 -----------Ã 1BaSO4 + 1Na2CO3
Mole
of Na2SO4= 1.59 mole
BaCO3 (mole) : Na2SO4
(mole)
1 : 1
Amount of BaCO3 required =1.59*197(Mol.
Weight of Na2SO4)
BaCO3 Required = 313 kg
No. of Bag of BaCO3 required = 313kg/25kg (one bag)
|
Na2Co3
Required:
Reaction:
1 Na2CO3
+ 1 CaCl2 ----------Ã 1 CaCO3 + 2NaCl
Mole
of CaCl2= 3.15 mole
Na2CO3 (mole) : CaCl2 (mole)
1 : 1
Amount of Na2CO3 required =3.15*106(Mol.
Weight of Na2CO3)
Na2CO3 Required =
334 kg
No. of Bag of Na2CO3 required = 334 kg/50kg (one bag)
|
NaOH =?
NaCl
= 305 g/l
Mg++ = 0.45 g/l --------Ã PURIFIER 2 ---------Ã Product
Density =1170 kg/ m3
Mg (OH) 2
(As Impurities)
Basis:
- 1
hour Operation
Overall Mass flow rate =
1170 kg/m3x 100 m3/hr
Overall
amount of salts =
117,000 kg
Mass flow rate of Mg++ = 0.45 kg/m3x100 m3/hr
Amount
of Mg++ = 45 kg
Mole
of MgCl2 =
45/95 (Mol. Weight of MgCl2) Mole of MgCl2 =
0.47 mole
NaOH
Required:
Reaction:
2NaOH + 1MgCl2 --------Ã Mg (OH) 2 + 2NaCl
MgCl2 (mole) : NaOH (mole)
1 : 2
1*0.47 : 1*0.47
0.47 : 0.94
Amount of NaOH required =0.94*40
(Mol. Weight of NaOH)
|
Density of NaOH (32%) = 1130 kg/m3
Flow rate of NaOH to Purifier#2 = 38 kg/1130(kg/m3)
Flow rate NaOH =
0.034 m3 /hr
Flow rate NaOH =
0.034(m3/hr) x (1000 liter/1 m3)
|
Impurities
formation:
Amount of CaCO3 =3.15*100(Mol. Weight of CaCO3) =315 kg
Amount of BaSO4 =1.59*229
(Mol. Weight of BaSO4) = 364 kg
Amount of Na2CO3 =1.59*106(Mol. Weight of Na2CO3) =168
kg
Amount of Mg (OH)
2 =0.47*58(Mol. Weight of
Mg (OH) 2 = 27 kg
Daily
Material consumption
|
Material |
Amount needed |
|
Rock
salt |
219
Ton (219,360 kg) |
|
BaCO3 |
7.5 Ton (7,512 kg) |
|
Na2CO3 |
8.0 Ton (8,016 kg) |
|
NaOH |
816 liter
(912 kg) |
|
Accoflock |
8 kg |
On brine plant there are
three types of chemical tests performed as given below:
I.
NaCl Concentration test
II.
Alkalinity test
III. Free chlorine test
NaCl concentration can be
finding by further two methods.
By
using chemical reagent:
Data:
Sample =
5 ml
AgNO3 (silver
nitrate) =
0.05 N (Normality)
K2CrO4 (potassium
chromate) =
1 ml (Indicator)
PROCEDURE:
1. Take
5 ml sample of brine in 500 ml conical flask with the help of graduated
cylinder and dilute it by adding distilled water up to full
2. Take
10 ml sample of brine in 250 ml from dilute brine
3. Add 1
drops of K2CrO4 and yellow color appear when shake it
4. Titrate
with AgNO3 0.05 N till yellow color changes to colorless
5. Note the volume of AgNO3 used suppose “R” ml
CALCULATION:
NaCl g/l = Rx 29 (Factor)
Factor
calculation:
From dilution formula
N1xV2 = N2xV2
0.05NxR = N2x10ml
N2 = R*0.005
We know that:
Concentration (g/l) = Normality x Molecular weight of NaCl
=
0.005x 58 x 100 (Conversion factor)
|
By
using Temperature vs. Density:
Data:
Sample = 50 ml
Thermometer = 0-120 0C
Hygrometer = 1.100-1.200 g/cc
PROCEDURE:
1. First
of all measure the temperature using thermometer say “A”
2. Then
note the density using Hygrometer say ”B”
3. By
using table of temp vs density , we can note the concentration of NaCl say “C”
with A respective to B values
4. 15 factor will subtract from the answer to get actual concentration of NaCl such as C-15
Alkalinity test is used to find carbonate and hydroxyl
ions. There are two alkalinity tests as fellow:
P-
Alkalinity Test:
Data:
Sample =
50 ml
HCl (Hydrochloric
acid) =
0.1 N (Normality)
Phenolphthalein =
2 ml (Indicator)
PROCEDURE:
1. Take
50 ml sample of brine in 250 ml conical flask with the help of graduated
cylinder
2. Add 2-3
drops of Phenolphthalein and red color appear when shake it
3. Titrate
with HCl 0.1 N till red color changes to colorless
4. Note
the volume of HCl used suppose “R” ml
CALCULATION:
OH ions g/l = (A-B) x 0.08 (Factor)
Factor
calculation:
From dilution formula
N1xV2 = N2xV2
0.1NxR = N2x50ml
N2 = R*0.002
We know that:
Concentration (g/l) = Normality x Molecular weight of NaOH
OH ions Concentration (g/l) = 0.002x 40*R
|
M-
Alkalinity Test:
Data:
Sample =
50 ml
HCl (Hydrochloric
acid) =
0.1 N (Normality)
Methyl orange =
2 ml (Indicator)
PROCEDURE:
1. use
50 ml same sample of brine that used for P-Alkalinity
2. Add
2-3 drops of Methyl orange and orange color appear when shake it
3. Titrate
with HCl 0.1 N till orange color changes to colorless
4. Note
the volume of HCl used suppose “R” ml
CALCULATION:
OH ions g/l = (B) x 0.212 (Factor)
Factor
calculation:
From dilution formula
N1xV2 = N2xV2
0.1NxR = N2x50ml
N2 = R*0.002
We know that:
Concentration (g/l) = Normality x Molecular weight of Na2CO3
CO3 ions
Concentration (g/l) = 0.002x 106*R
|
Data:
Sample =
50 ml
KI (Potassium iodide) 5% =
10 ml
H2SO4
(Sulfuric acid) 6.5% =
5 ml (Indicator)
Na2S2O3
(Sodium Thiosulfate) =0.1
N (Normality)
PROCEDURE:
1. Take
50 ml sample of brine in 250 ml conical flask with the help of graduated
cylinder
2. Add 10
ml of KI 5% and yellow color appear when shake it
3. Add
5ml H2SO4 6.5% use as indicator to form acidic medium for
chlorine detection
4. Titrate
with Na2S2O3 0.1 N till yellow color disappear
5. Note the volume of Na2S2O3 used suppose “R” m
CALCULATION:
Free Chlorine (g/l) = Rx 0.71 (Factor)
Factor
calculation:
From dilution formula
N1xV2 = N2xV2
0.1NxR = N2x50ml
N2 = R*0.002
We know that:
Concentration (g/l) = Normality x Molecular weight of Cl2
Free Cl2 ions
Concentration (g/l) = 0.002x 71*R
Free Cl2 ions
Concentration (g/l) = 142/2(no. of H ion replaceable)*R
|
D.S.A BRINE PURIFICATION
DSA (Dimensionally stable anode) brine purification is
used to provide brine to mercury cell called southern cell room. Mercury is
used as cathode so purity level of ultra pure brine is not needed. The
following are four steps used fro DSA brine purification process.
§ De-chlorination
of Brine
§ Saturator
§ Purifier
§ Settler
§ Final
filtration
Brine
concentration of 240 g/l with temperature 75 0C coming form mercury
cell room contains free chlorine that must be removed otherwise it may cause
side reaction at saturator. From the SCR (southern cell room) the anolyte brine
stored into 2 D-10 storage tank.
2 D-10 storage tank of 32 m3 is used to store the anolyte brine and to remove free chlorine by using HCl (Hydrochloric acid). According to common ion effect chlorine ion become excess in solution by adding acid and free chlorine will displace in form of gas. From top of tank chlorine gas send to sodium or calcium hypo plant. Other purpose of addition of HCl acid is lower the ph of brine for stripping process. Ph decrease from 3.5 to 2.5 after acid addition and can be control by rotamete because HCl acid come from overhead tank by gravity. After this, two centrifugal pumps (one as stand by) of 50 hp used to transfer the depleted brine to stripper
REACITON:
HCl + HOCl -------Ã Cl2 + H2O
After
2 D-10 tank, depleted brine send to 4 strippers attached in series to remove
the further free chlorine which are not removed from 2 D-10 tank.
Principle:
Air
stripper is physical process that transferred volatile hypochlorite from brine
to an air stream by creating turbulence with compressor air.
Construction and Working:
Air
stripper is made up of mild steel with titanium coating inside. It hollow
cylinder from top side and conical shape from bottom side. Brine enters from
side bottom of first stripper from where conical section starts and emits from
upper side then enters into next stripper like same way. Air from compressor of
total pressure of 5.1 psi is distributed into four strippers with individual
pressure increase from 50mmH2O (first) to 150mmH2O (fourth)
strippers because fourth stripper need greater pressure of air than previous to
overcome the resistance and to remove the chlorine at maximum extent. From top
of all strippers there is common line of chlorine gas that was in suction by
blower placed in calcium hypo plant. When brine enters 30 ppm (parts per
million) chlorine is present and after stripping chlorine content decrease to
7-14 ppm. There are two sample point located before and after stripper with
cooler to check its ph and free chlorine concentration.ph should be less than2.5
(acidic) to facilitate the stripping process.
Brine
enters to 2 D-13 tank of 32 m3 from top side. In this tank caustic
soda is added by gravity from overhead tank whose flow rate can be control by
rotameter. In this tank Ph increase from 2.5 to 9 because alkaline brine
facilitates at saturator to remove impurities. From the top of tank free
chlorine removes if it carries from stripper. There is bypass line from 2 D-10
tank to 2 D-13 tank use in case of brine circulation in cell room and all brine
from 2 D-10 enters to 2 D-13 directly without going to stripper.
Saturator
is used to saturate the depleted brine of low concentration of sodium ion to
required limit. Depleted brine showered on eastern and western bed of rock salt
from 2 D-13 tank with temperature of
65-70 0C and ph 10. A bypass line is attached with depleted brine to
control the concentration of brine. If concentration of brine increases from
300 g/l to above then open the bypass line to adjust it.
There
are three primary pits eastern, central and western pits are used to sediment
the impurities like sand, mud and granules. One primary pit is working while
other two are standby. Two secondary pits are used to remove further impurities
from fine. One secondary pit is common for western and central primary pits.
Two centrifugal pumps (one as standby) are attached with both secondary pits to
transferred brine to purifier.
There
are two purifier of 70 m3 each used to treat the major impurities
like sulfates, calcium and magnesium ions by using barium carbonate, sodium
carbonate and sodium hydroxide as reactant or additives. Brine enters with 100
m3/hr into the bottom side of purifier#1 and emit from top side and
then enters into purifier#2 from bottom side and out from top.
In
purifier#1, a solution of barium carbonate and sodium carbonated added into
bypass pipe of brine inlet to purifier. The purpose of addition of BaCo3
and Na2Co3 into bypass line is to distribute the solution
into top or bottom. Similarly, brine recovered from sludge pit is also added
into this purifier. A sample point is attached with brine inlet to purifier
with cooler to analyze the ph and free chlorine concentration. In purifier#2,
caustic soda is added by gravity from overhead tank whose flow can be adjusted
by rotameter. Accoflock is also added into this purifier to stick the
particles. At the bottom of both purifier sludge is removed once in a day with
valve opening for 1 minute.
Brine
from purifiers enters into settler of 2300 m3 by gravity from
center. A high efficiency marine type propeller is used to provide
agglomerating energy by which particles stuck with each and due to increase in
size and weight particles start to settle by gravity called sedimentation. At
the top clarified overflow brine move toward 2 D-5 storage tank of 32 m3 size. A down take sample
point is attached with settler to check the alkalinity or excess of carbonate
(0.2-0.4 g/l) and hydroxyl (0.15-0.20g/l) ions. From bottom of settler a
automatic pneumatic instrument air driven valve is attached to remove the
sludge after every 50 minutes for 30 second valve opening.
Brine
from 2 D-5 storage tank enter into 7 filter of 13 m3 each arranged
in parallel operation used to remove the excess carbonates and hydroxyl ions
suspended solid to 10 ppm. Filter is made up of mild steel with multilayered
bed of pebbles and stops and at top upper side with anthracite coal. One filter
is backwash once a day to remove the stuck particles in filter medium by using
industrial water.
Braine
passes through seven sand filters then enters into two 2 D-6 storage tank
of 36 m3 of each. In 2 D-6
tank HCl is added again by gravity from overhead tank whose flow rate can be
adjusted by rotameter to lower the ph from 9 to 4. Overflow of two tanks fall
into sludge pit. A vertical shell and tubes type heat exchanger is used to
raise the temperature of 2 D-6 brine from 72 to 78 0C with flow rate
of100 m3/hr.
Brine from shell and tubes enter into 2 D-7 storage tank of 32 m3 with made up of fiber material place at overhead. Overflow of this tank again fall into 2 D-6 tank by gravity. A sample point is attached with cooler to check its ph (4-4.5), concentration (290-305 g/l), temperature (75-80 0C) and free chlorine which not exceed to 7 ppm. Brine move to cell room with uniform velocity to mercury cell from there control flow of brine to cell
ENERGY
BALANCE
Design of shell and tubes heat exchanger:
GIVEN DATA:
SHELL
SIDE (Brine)
TUBE SIDE (hot steam)
Mass flow rate = 117000 kg/hr Length = 3 m
Length of shell = 3 m Outer
dia (OD) = 25 mm (1 inch)
Outer dia (OD) = 323 mm (13 inch) N (no. of tubes) = 61 no
Inner dia (ID) = 305 mm (12 in) Temperature = T1
= 170 0C
Flow rate of
brine = 100 m3/hr Temperature
= T2 = 150 0C
Density = 1170 kg/m3 Thickness of
tube = 1.2 mm (0.47)
Baffles space =
B = 60 mm (2.3 inch) pass = 2 no
Clearance = “C = 0.287 inch steam pressure = 2 bar
Tube pitch = Pt = 1.2 inch Flow rate = 3000 kg/hr
Shell pass = 1
Temperature =t1 =55 0C
Ael type single segmental 44.8 % cut
Vertical shell and tube
FIND:
I.
t2 =?
II.
Uc and Ud =?
III.
Rd?
DESIGN STEPS
HEAT LOAD:
For Steam:
Q = m x λ (equation -1)
AT 160 oC;
λ=2135
Kj/kg (Fig-12 D.Q kern)
Putt
values in equation 1.
|
Q = 2135 x 3000
kg/hr (kj/kg)
t2 CALCULATION:
Q = m c deta (t)
Q = m x C x ( t2- t1) (equation -2)
Put
values in equation -2
6405960
= 117000x 3.2(t2 - 55)
|
|
TRUE MEAN TEMPERATURE:
R = T1 – T2 S = t2 – t1
---------- ----------
| T2 – t1 | ||||
|
||||
R = 20/ 17 = 1.17 S
= 17/ 115 = 0.14
Fr =
0.98 (using R and S values from Fig-18 DQ kern)
Del
(t) = LMTD X Fr (equation -3)
Put
values in equation-3
Del (t) = 0.98
x 100 = 98 0C
CHLORIC TEMPERATURE:
Th = T average Th
=160 0C
t c = t average t c = 63 0C
|
TUBE
SIDE (saturated steam) 1-FLOW AREA: at=Nt
x a”t /n at” = 4.1
x 10-4 (Table-10 D.Q kern)
at = 61 x 4.1 x 10-4/2 =0.012m2 2- MASS VELOCITY: Gt =
W/at
= 3000/0.012
Gt = 250000
kg/hr.m2 3-
At Tavg=160 oC μ=0.05 kg/m.hr (Fig-14 D.Q kern) 4- Di=0.023 m 5-
Re=D*Gt/ μ
= 0.023 x 250000/0.05 Re = 6- Jh=
280 (Fig-24 D Q kern) 7- T avg = 160 oC K = 1.6 kj/m.hr. oC; C =603 kj/kg. . oC 8- (Cp μ/k)⅓ = (603 x
0.05/1.6)1/3 = 2.6 9- hi =
50643 10-hio= hi x(ID/OD)
= 50643(0.023/0.025) hio = 46591
|
SHELL
SIDE (Brine) 1-FLOW AREA: as= ID x “C x B/144 x Pt
= 12 x 0.28
x2.3/144 x 1.2 =0.00437m2
2-MASS
VELOCITY: Gs
= W/as =117000/0.00437 Gs
=26773455 kg/m2.hr 3-Cloric
Temperature At tavg = 63oC μ=4.2
kg/ m.hr 4-Reynold
number Re=De*Gs/ μ Re =0.025 x 26773455/4.2 Re = 159365 5- Jh=525 (Fig-28 D Q
kern) 6- t avr =63 oC k=70 W/m. oC 7- (Cp μ/k)⅓ = (874 x
4.2/70)1/3 = 3.6 8- ho
=Jh.k/De Qs (Cp μ/k)⅓. H0
= 525 x(70/0.025)x 3.6 x1 ho=5292000
|
OVERALL CLEAN COEFFICEINT:
Uc
= hio
x ho (equation -4)
|
----------- Put values in equation -4
Uc = 46591 x 5292000
-----------------------
OVERALL DESIGN COEFFICEINT:
Q =
Ud x A x del t
(equation -5)
A = pi x D x L x N (equation
-6) (D = 0.618 from Table
-10 D.Q kern)
Put value in equation -6
A = 3.12 x 0.193 x 3 x
61 = 111 m2
Put
values in equation – 5
|
Ud = Q/ A x del t = 6405960/111 x98 = 589
DIRT FACTOR:
Rd = Uc – Ud (equation -7) put values in equation-7
|
|
-----------
Rd = 45283 – 589 = 0.00167
|
UTILITY UNIT
The objective of utilities unit is to provide desired quantity and
quality of certain utilities to brine purification units for smooth
functioning. These utilities include electricity, cooling water, instrument air,
fuel gas and steam network, Water, air and natural gas are the basic utility
raw materials, which are processed and improved in order to meet the plants’
criterion of quality and ensure a longer life and safety of equipment. In case of utility failure plant
has to face an emergency shutdown.
Major sub-divisions of utility
section are:
§ Water utility
§ Instrument Air Compression utility
§ Auxiliary Boilers and Steam Network
utility
Water utility at brine
purification plant is divided into two sub section as give below:
I.
Industrial water
II.
DI (De-ionized) water
There
are six tube well 19, 19 A, 20, 20-A,
21, and 21-A of 50 Hp are present near form house in this factory. Four
tube well (19, 20, 20-A and 21) out of six are in working while other two (19-A
and 20-A) are not working due to problems in their motors. Here “A” with number
show the capacity of tube well 1 cusec/hr and number without “A” shows the
capacity of 2 cusec/hr. From this tube well Industrial water is pumped to
pumping station near calcium hypo plant with pressure 2 bar approximately. Old
connection of 4” and 3” pipe from pumping station attached with old DI water
softener which in not working now. From pumping station a 8’’ pipe line come
into header placed near chlorine compressor then from this header a 6’’ pipe
line is used for IEM or DSA brine purification plant and to cooling tower#1
(for water make up) with pressure of 4.5 kg/cm2 approximately.
Distribution of water to IEM Unit:
Industrial
water distribute to the following units of IEM as given below:
I.
To saturator by connecting water pipe with sodium sulfite pipe
II.
For accoflock solution making with 2” inch
pipe
III.
For primary filters backwashing with 3” inch
pipe
IV.
To sludge drain pipe of settler
V.
For arbocell solution making
VI.
To IEM
sludge pit for cleaning purposes
VII.
For cleaning purposes of plant areas
Distribution
of water to DSA Unit:
Industrial
water distribute to the following units of IEM as given below:
I.
To saturator for brine make up of 2” pipe
line
II.
For accoflock solution making
III.
For primary filters backwashing with 4” inch
pipe
IV.
To cooling tower with 4” pipe
V.
To sludge drain pipe of settler from pipe going to cooling tower
VI.
To sludge pit for cleaning purposes
VII.
For cleaning purposes of plant areas
DI
(De-ionized) water come form Reverse osmosis plant in 4” PVC pipe into 70 m3
tank made of fiber. DI water from this storage tank used for two sections as
given below:
I.
To IEM cell room
II.
To IEM and DSA brine purification units
To IEM cell room:
Tow
pipes of 4” and 3” are used to transfer DI water to IEM cell room with flow
rate of 4.5 kg/cm2. A 3 inch pipe line is send to cell room for
dilution of feed caustic and a 4 inch pipe line
send toward overhead DI water storage tank used for de-chlorination
vacuum pump by using two centrifugal pump (one as standby).
To IEM brine purification units:
A 4”
pipe line is used for following IEM brine units with flow rater of 3.5 kg/cm2
as given below:
I.
For accoflock, barium and sodium carbonate
solution making
II.
For regeneration of Ion exchange resin like
for brine, HCl acid , caustic displacement and for backwashing of resin
III.
For solution making of arbocell and sodium
sulfite tank
To DSA brine purification units:
A 4”
pipe line is used for following DSA brine units as given below:
I.
For solution making of accoflock , barium and
sodium carbonate
INSTRUMENT AIR COMPRESSION:
This section provides compressed air
for instrument of IEM and DSA brine purification units. Instrument air make
possible the functioning of pneumatic valves installed over multiple locations
on plant. This area is of extreme importance because in case of its failure,
many plants might lead to shut down.
Operation:
The compressor takes air from
atmosphere in its first stage and compresses it at to create high pressure.
Compression heats the air to 160°C, by which water is removed from it and it
becomes dry. Which is than cooled to 45°C in inter cooler before feeding to the
second stage of compression. The second stage discharges at 8 bars. Compressed
air is then passed though a damping vessel, fitted with baffles to remove any
condensate. Air is then passed through an after cooler, where it is cooled down
to 50°C.
Dryer:
The compressed air from is sent to
air drying section through a cooler and condensate separator. The air cools
down to 37°C while passing through the final cooler and condensate is
separated. The compressed air is then fed to air dryers (one in service and
other on standby).Dried air is finally passed through air filters, where
sub-micron particles are removed from air. The resulting dry and clean
instrument air is supplied to IEM and DSA brine plant at 7 bars.
Dry Instrument air to IEM and DSA brine plant:
A 2” pipe line is used for following IEM and DSA brine
units as given below:
I.
To pneumatic valves of Ion exchange unit for
opening and closing of acid or caustic injection and for ion exchange series
change valves
II.
To pneumatic valves of secondary filters
units for opening and closing of brine inlet or outlet valve and for brine
drain for recoating
III.
To pneumatic valves of both IEM and DSA
settler for opening and closing of sludge drainage to sludge pits
IV.
To
metering pump of HCl acid injection to Ion exchange unit
V.
To pneumatic valves of IEM primary filters
units for opening and closing of brine inlet or outlet valve of brine and for
backwashing
VI.
To maintenance workshop of IEM and DSA
STEAM UTILITY:
Boilers are designed to produce
steam as dry as possible at high temperature and pressure. There are ten boiler
installed with total capacity of 30 ton/hr in industry from which five boilers
are located at power plant with capacity of 4.5 ton/hr, one boiler is used for
sulfuric acid plant of 4.5 ton/hr capacity and four boiler are located near
sodium hypo plant of 15 ton/day, 10 ton/day, 7.5 ton/day capacity. These
boilers are of water tube and fire tube type boiler using natural gas or
furnace oil as heating medium.
Operation:
There is common line through which
saturated Steam from five power plants boilers and from four other boilers
mixed with each other and then distributed to the IEM cell, IEM or DSA brine
units,CaCl2, caustic, zinc and shaffaf plant in 4” carbon steel pipe
as given bellow :
|
units |
Amount of steam Ton/hr |
Monthly amount of steam (Ton) |
Steam temperature/pressure |
|
IEM
cell room |
6.5 |
4680 |
165
0C/10 bar |
|
Caustic
evaporation |
7 |
5143 |
165
0C/10 bar |
|
CaCl2 |
7 |
5343 |
165
0C/10 bar |
|
DSA
brine |
3 |
2169 |
165
0C/10 bar |
|
IEM
brine |
1 |
740 |
165
0C/10 bar |
|
Shaffaf |
1 |
721 |
165
0C/10 bar |
|
zinc |
1 |
651 |
165
0C/10 bar |
Steam to IEM and DSA
brine plant:
A 2” carbon steel pipe line cover with fiber cotton and
insulated sheet at outermost of saturated steam is used for following IEM and
DSA brine units as given below:
I.
To vertical shell and tube type heat
exchanger for DSA brine to raise the temperature 10 0C of 2 D-6 tank brine
II.
To cross flow plate and frame type heat
exchanger to raise the temperature 2 0C of ion exchange storage tank
brine
III.
To cross flow plate and frame type heat
exchanger to raise the temperature 2 0C of primary storage tank
brine
IV. Condensate of steam from shell & tube and Plate & frame type heat exchanger send to DI water storage tank by using centrifugal tank once in a day
Process Flow Diagram
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