ion-exchange process (softener plant) water passes through bed of natural zeolite of synthetic resin...
TRANSCRIPT
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
External Water Treatment
1
Softener Plant
2
DM System
3
4
Osmosis• Solutions of differing concentrations
• Separated by a semi-permeable membrane
• Water moves to the higher concentration
External Water Treatment
5
Reversed Osmosis (RO)• Higher concentrated liquid pressurized
• Water moves in reversed direction
External Water Treatment
6
RO System
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8
Electrodialysis
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Electrodialysis for Water Treatment
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External Water Treatment
&
Internal Water Conditioning
11
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
Internal Water Conditioning
12
Scale control
Injection of chemical additives• Minerals (Na2CO3, Na3PO4, Na2HPO4,
NaH2PO4, (NaPO3)6 ,…)• Organics (Chelants, Lignins, Starches,
Tannins, …)• Minerals + Organics
Chelants (NTA, EDTA, …)
Internal Water Conditioning
13
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.
External Water Treatment
14
External Water Treatment
Steam
Storage Section
De-aerated Boiler Feed Water
Scrubber Section (Trays)
Boiler Feed Water
Vent
Spray Nozzles
• O2 and CO2 removed by heating feed water
• Economical treatment process
• Vacuum type can reduce O2 to 0.02 mg/L
• Pressure type can reduce O2 to 0.005 mg/L
Mechanical de-aeration
15
Removal of Dissolved Oxygen TracePitting Corrosion control
• Sodium sulphite:
Increases TDS: increased blow down
• Hydrazine
Does not increase TDS: used in high pressure boilers16
2 3 2 2 42Na SO O 2Na SO
2 4 2 2 2 2 2N H (NH NH ) O 2H O N
Mechanical (Boiler design) High level of water in drumsDeficiency on separator operationSudden increasing boiler load (reduction of pressure)
Chemical High TDSHigh alkalinityOil and organic impurities
Causes of Carry Over
17
Corrosion & scale control
Acid (H+) attackAdjustment of water pH based on
manufacturer recommendation
Water Conditioning
18
Caustic embrittlement control
Adjustment of water NaNO3/NaOH ratio depending to boiler pressure (According to manufacturer recommendation)
Water Conditioning
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• 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
Boiler Blow Down
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Benefits• Lower pretreatment costs
• Reduced maintenance downtime
• Increased boiler life
• Lower consumption of chemicals
Boiler Blow Down
21
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
Boiler Blow Down
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• 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
Water/Chemical Economics / Optimization
23
THANKSFOR YOUR ATTENTION
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