External Water Treatment
Ion-exchange process (softener plant)
• Water passes through bed of natural zeolite of synthetic resin to
remove hardness
• Calcium (Ca) and magnesium (Mg) replaced with sodium (Na) ions
• Does not reduce TDS
1
Softener Plant
2
DM System
3
4
External Water Treatment
Osmosis
• Solutions of differing concentrations
• Separated by a semi-permeable membrane
• Water moves to the higher concentration
5
External Water Treatment
Reversed Osmosis (RO)
• Higher concentrated liquid pressurized
• Water moves in reversed direction
6
RO System
7
8
Electrodialysis
9
Electrodialysis for Water Treatment
10
External Water Treatment
&
Internal Water Conditioning
11
Internal Water Conditioning
Prevention of internal scale by forming
deposits in sludge shape
Injection of chemicals
•Different chemicals for different water impurities
•Conditions:
For low amounts of feed water impurities
For low pressure boilers, TDS content has higher
limits
Internal treatment alone not recommended
12
Internal Water Conditioning
Scale control
Injection of chemical additives
• Minerals (Na2CO3, Na3PO4, Na2HPO4,
NaH2PO4, (NaPO3)6 ,…)
• Organics (Chelants, Lignins, Starches,
Tannins, …)
• Minerals + Organics
Chelants (NTA, EDTA, …)
13
External Water Treatment
De-aeration
• Removal of various dissolved gases from
water (O2, CO2, …)
• These gases are corrosive.
• De-aerator can decrease amount of dissolved
gases in water.
14
External Water Treatment
Mechanical de-aeration
• O2 and CO2 removed by heating
feed water
• Economical treatment process
Vent
Spray Nozzles
Boiler Feed
Water
• Vacuum type can reduce O2 to 0.02
mg/L
Steam
Scrubber
Section (Trays)
• Pressure type can reduce O2 to
0.005 mg/L
Storage Section
De-aerated
Boiler Feed
Water
15
Removal of Dissolved Oxygen Trace
Pitting Corrosion control
• Sodium sulphite:
2Na2 SO3  O2  2Na 2SO4
Increases TDS: increased blow down
• Hydrazine
N 2 H4 (NH 2  NH 2 )  O2  2H 2O  N 2
Does not increase TDS: used in high pressure
boilers
16
Causes of Carry Over
Mechanical (Boiler design)
High level of water in drums
Deficiency on separator operation
Sudden increasing boiler load (reduction of pressure)
Chemical
High TDS
High alkalinity
Oil and organic impurities
17
Water Conditioning
Corrosion & scale control
Acid (H+) attack
Adjustment of water pH based on
manufacturer recommendation
18
Water Conditioning
Caustic embrittlement control
Adjustment of water NaNO3/NaOH ratio
depending to boiler pressure (According to
manufacturer recommendation)
19
Boiler Blow Down
• Controls TDS of the boiler water
• Boiler sludge conditioning
• Blows off water and replaces it with feed water
• Conductivity measured as indication of TDS levels
20
Boiler Blow Down
Benefits
• Lower pretreatment costs
• Reduced maintenance downtime
• Increased boiler life
• Lower consumption of chemicals
21
Boiler Blow Down
Types of blow down
• Batch (Periodic)
• Manually operated valve reduces TDS
• Large short-term increases in feed water
• Substantial heat loss
• Continuous
• Ensures constant TDS and steam purity
• Heat lost can be recovered
• Common in high-pressure boilers
22
Water/Chemical Economics / Optimization
• Application of proper external treatment
• Application of accurate internal conditioning
• Amounts of used chemical
• Amounts of produced wastes/sludge
• Amounts of wasted water (blow down)
• Cost of monitoring & Control
• Economy of water treatment/conditioning
• Recirculation of used steam
23
THANKS
FOR YOUR
ATTENTION