Boilers’ Feed Water Treatment/Conditioning & رایط آب و... · PDF file•...
Transcript of Boilers’ Feed Water Treatment/Conditioning & رایط آب و... · PDF file•...
In The Name of God
Boilers’ Feed Water
Treatment/Conditioning & Optimization
By: Arjomand MehrabaniAdjusted for The Second Meeting of Steam Technology
(By Packman Company)Modified: Fall 1394
Contents
• Definitions & Terminology
• Overview & Basic concepts
• Types & Classifications
• Structure & Parts
• Feed Water & Quality
• Water treatment & Conditioning (External/Internal)
• Methods & Materials
2
A closed vessel for heating of water to
make hot water / saturated steam /
superheated steam, or any combinations
by application of heat from combustible
fuels in a self-contained or attached
furnace.
What is a Boiler?
3
STEAM GENERATION REQUIREMENTS
Container
Thermal Energy
Water
4
Basic Units in boilers
regardless of size / usage:
Feed water system
(supply quality water)
Fuel system
(supply energy source)
Draft systems
(provide air for combustion)
Combustion system
Steam system
(collect and control produced steam)
Combusted gases transfer system
(starts: furnace and terminates: flue gas stack)
Other parts (controller, instruments, valves, …)5
Fire - Tube BoilersCombusted gases pass through the tubes
while the water and steam are round the tubes
6
Water - Tube BoilersWater is circulated inside the tubes and combusted gas
passes outside of the tubes.
7
Water-
Tube
Boilers
(Riser
Tubes)
Floor
Ceil
Walls
8
Boiler Classifications
Operational Pressure
• Boilers with pressure under 200psi (~15atm) are
considered as low pressure.
• Boilers with pressure between 200 and 500psi
(~35atm) are considered as medium pressure.
•
• Boilers with operational pressure between 500 and
2000psi (~135atm) are categorized as high pressure.
9
Boiler ClassificationsWater Circulation
Types:
Natural circulation: Water circulation is based on the
density difference between the temperature in riser
and down-comer tubes.
Forced circulation: A pump is used to help the better
circulation of water in tubes and drums.
10
Water
System
11
Water Impurities
• Dissolved Solids
Ionic
Non-Ionic
• Suspended Solids and Materials
Sands, Soils
Microorganisms, Bacteria, Algae
Oils
Emulsions, Collides, Colloidal Silica
• Gases 𝐍𝐇𝟑 , 𝐂𝐇𝟒 , 𝐇𝟐𝐒 , 𝐂𝐥𝟐 , 𝐎𝟐 , 𝐂𝐎𝟐
12
Anions Cations
-HCO3+++Al
--CO3+NH4
-Cl ++Ca
-F H+
-NO3++Fe
-OH +++Fe
PO4--- ++Mg
HPO4- ++Mn
H2PO4- +K
SO4-- +Na
Ions in Natural Water
13
System of Water Quality Maintenance
Boiler water is purified for:
• Reduction of fouling deposits Enhancing of thermal efficiency
Reduction of fuel consumption,
Prevention from overheating of tubes (formation of
hot spots)
Extending of operation period
Enhancing of maintenance, reduce repairments
Increasing of system life
Increasing system safety
… 14
15
16
System of Water Quality Maintenance
Boiler water is purified for:
• Minimizing of boilers’ systems corrosionEnhance maintenance, reduce replacements
Increase system life
Meeting safety regulations.
Enhancing steam quality.
…
17
18
19
System of Water Quality Maintenance
Boiler water is purified for:
• Avoiding of steam carry over
Various forms:
foaming
priming
spray/mist carry overEnhancing steam quality
Preventing deposition of solids over turbine blades,
valves, steam pipes, …
Preventing from thermal shocks
… 20
21
System of Water Quality Maintenance
Boiler water is purified for:
• Prevention from caustic embrittlementAn inter-crystalline cracking of boiler metal
without any prior deformation that results in boiler
explosion.
This is due to:
- Leakage of water in boiler’s body and
concentrating of dissolved solids.
- Presence of stress in metal
22
Results of Poor Water Treatment:
EXPLOSION
23
Deposit control:
• Reducing hardness salts of calcium and magnesium
• Alkaline hardness: removed by boiling
• Non-alkaline: not removed by boiling (special treatment)
• Reduction in silica contents (forms hard silica scales)
Feed Water Treatment
24
External water treatment:
• Removal of suspended/dissolved solids and dissolved gases
• Pre-treatment: sedimentation and settling
• First treatment stage: removal of dissolved solids
• Major Processes
a) Lime-Soda process
b) Ion exchange (Demineralization)
c) Reverse osmoses
d) Electrodialysis
…
Feed Water Treatment
25
Temporary Hardness
Lime Soda Process
External Water Treatment
26
Removal of Temporary Hardness
3 2 2 3 2
3 2 2 3 3 2
5
SP 3
3 2 2 3
14
SP 2
____________________________________________
Ca(HCO ) Ca(OH) 2CaCO H O pH 10 10.5
Mg(HCO ) Ca(OH) MgCO CaCO 2H O
K MgCO 2.6 10
MgCO Ca(OH) Mg(OH) CaCO
K Mg(OH) 4.0 10
:
__________________________________
3 2 2 2 3 2Mg(HCO ) 2Ca(OH) Mg(OH) 2CaCO 2H O
27
4 2 3 3 2 4
2 2 2 3 2 3
4 2 3 2 2 3 2 4
CaSO Na CO CaCO Na SO
MgCl Ca(OH) Na CO Mg(OH) CaCO 2NaCl
MgSO Na CO Ca(OH) Mg(OH) CaCO Na SO
Removal of Permanent Hardness
28
با سپاس از توجه شما
Solids-contact clarifier
29
30
Coagulation/Flocculation
Coagulation of colloidal particles
31
FiltersRemoval of suspended solids
32
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
7
8
Electrodialysis
9
Electrodialysis for Water Treatment
10
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 drums
Deficiency on separator operation
Sudden increasing boiler load (reduction of pressure)
Chemical
High TDS
High alkalinity
Oil and organic impurities
Causes of Carry Over
17
Corrosion & scale control
Acid (H+) attack
Adjustment 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
19
• 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
20
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
22
• 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
THANKS
FOR YOUR
ATTENTION