I. STEAM GENERATION, BOILER TYPES and BOILER PLANT SYSTEMS
and BOILER PLANT SYSTEMS
Steam Generation
• Water’s Unique Properties:
High Thermal Capacity (Specific Heat) High Critical Temperature
• Ideal Medium for Heat Delivery
• High Pressure Steam:
Higher Temperatures Reduced Volume
Reduced Volume
Contains More Energy
Potential for Greater Efficiency
• Continuous Steam Bubble Formation through … Nucleate Boiling and Convective Boiling at the steam-water interface.
stea ate te ace
Steam Generation, contd .
• Relatively high Heat Transfer Rates in modern
boilers in the first stages of boiling (Incipient Boiling P i t)
Point).
• Small bubbles of steam form on the waterside metal surface (Steam Bubble Nucleation) but collapse
surface (Steam Bubble Nucleation) but collapse contacted with the cooler bulk boiler water.
• Upon continued heating to localized Saturation Temperatures the steam bubbles move into the larger, bulk water Nucleate Boiling Region.
I d t i t i i H t T f
• In order to maintain maximum Heat Transfer
Efficiency, both External Pretreatment and Internal Water Treatment is vital!
A Catastrophic Event Underscoring the
N d f B il W T
Need for Boiler Water Treatment
Steam Generation Costs
D d Hi h Effi i !
Demand High Efficiency!
Proper Boiler Water Treatment Equates Into Energy Savings
70
• Scale Thickness (inches) vs. Boiler Fuel Losses (percent)
60 70
1/32"
Fuel Losses (percent).
0.031” 8.5%
0.040 9.3
0.050 11.1
40
50 1/25"
1/20"
1/16"
0 050
0.062 12.4
0.125 25.0
0.250 40.0
0 375 55 0
20 30
1/16"
1/8"
1/4"
0.375 55.0
0.500 70.0
• A clean boiler will save far more money in fuel than it would ever use
10 20
3/8"
1/2"
money in fuel than it would ever use in water treatment products!
• Energy savings and the prevention of equipment failure are two vital
Maximum Boiler Efficiency Requires A Complete System Review
Complete System Review
• Fuel Losses due to Scale vs.
Soot Accumulations.
70
Soot Accumulations.
• Common Practice - Monitor Stack Temperatures to
determine increase flue gas
40 50 60
Pe rce nt Fuel Loss
Scale
determine increase flue gas temperatures.
• Increased temperatures mean fuel loss and possible scale
10 20
Fue l Loss 30 - Scale
Fuel Loss
fuel loss and possible scale formation.
• Applicable only if there are no
0 10
1/32" 3/16"
- Soot soot accumulations!
• Recommendation – Tune up your boiler with seasonal
Typical Boiler System Schematic yp y
Feedwater
Boiler
Softener
Boiler
Raw Water
Inside The Boiler
Steam
¾ Feedwater Dissolved Solids
concentrate in the Boiler Water when steam is generated
Feedwater
Steam
when steam is generated.
¾ Boiler Blowdown prevents the over-concentration of
Dissolved Solids Dissolved Solids.
¾ Feedwater replaces water lost in steam generation and
bl d
blowdown.
¾ Excess Boiler Blowdown should be minimized.
¾ Blowdown is valuable heated and treated Feedwater.
Basic Boiler Types Basic Boiler Types
Fire Tube Fire Tube
Water Tube
Package
Package
Field Erected
Cast Iron Sectional
Cast Iron Sectional
Electric
Hybrid
Hybrid
Additional Boiler Details Additional Boiler Details
• Coil Boilers: Small industrial applications where rapid but intermittent steam demand is required rapid but intermittent steam demand is required.
• Industrial Boilers: Typically operating below 900
i f i h t t d t h ti d
psig for various hot water and steam heating, and some process applications.
C ti (C bi d C l ) B il T i ll
• Cogeneration (Combined-Cycle) Boilers: Typically operating from 450 – 1,500 psig, providing both electricity and process steam.y p
Boiler Details, contd.
• Utility Power Boilers: Most modern plants usually operate at 1,500-2,000 psig; older plants may only
t t 450 950 i operate at 450-950 psig.
• Marine Boilers: In the most modern ships, marine boilers have become relegated to auxiliary and heat boilers have become relegated to auxiliary and heat- recovery use only.
• Waste Heat and Special Purpose Boilers: Special
• Waste-Heat and Special Purpose Boilers: Special designs provide boilers for waste-heat and chemical recovery, waste-to-energy, combined cycle
installations, and others.
Boiler Details, contd.
Boiler Details, contd.
• Electric Resistance and Electrode Boilers
• Industrial Exhaust Gas Co-generation Boilers
• Power Exhaust Gas Combined-Cycle Boilers
• Fired/Non-Fired Waste Heat Boilers (WHB)
• Heat Recovery Steam Generators (HRSG).y ( )
Most Common Boiler Types
Firetube Boilers –
Combustion gases are on the inside of the
boiler tubes and water boiler tubes, and water is on the exterior sides of the tubes.
Watertube Boilers –
Water is on the inside of the tubes, and the
combustion gases are on the tube exteriors on the tube exteriors.
Modern Firetube Boil er
Stack Gases Boiler
Stack
¾ Maximum 300-psig. 4 Pass Boiler
¾ The bulk boiler
water surrounds the fire in the tubes.
e
¾ Variable boiler f efficiencies.
c d
¾ Increased boiler
efficiency with more passes. d
Burner Burner
Water Tube Boilers
Water is contained in the tubes
d i th t d d d Steam Drum
and in the steam and mud drums.
Risers and down-comers provide a path for boiler water circulation
Steam Drum
a path for boiler water circulation.
Rapid steaming capabilities.
Pressures up to 3 200 psig Down Risers
Pressures up to 3,200 psig.
Rated in lb/hr.
Various configurations: ‘O’ ‘A’
Down Comers
Various configurations: O , A , and ‘D’ types; others.
Higher Pressure Boilers
Water Tube Boiler Des ign g
Water Tube ‘D’-Type Boiler
Drums and Tubes
• Drums and Tubes.
• Refractory Brick.
• InsulationInsulation.
• Metal Skin.
• Boiler Water Flow.
• Tube Surfaces.
Water Tube Boiler Side Wall Headers
• Side Wall Headers (SWH).
P t ti l W t St ti
• Potential Water Starvation.
• Regular Blowdown is vital!
• Never excessively!y
• Avoid Sludge accumulation.
• 3-5 Second ‘Puff’ blows.
• One header at a time
• One header at a time.
• Once per shift.
• Sludge Conditioning is vital!
Hybrid Boilers
Hybrid Boilers
Sugar Cane Bagasse Boiler
Gas Plant Boilers
Vertical Tube Heat Recovery
Steam Generator (HRSG)
Boiler Steam Drum Internals
Water Tube Boiler Mud Drum
The lowest point in a p Water Tube Boiler.
Precipitated solids settle forming sludge settle forming sludge.
Sludge is removed with manual blow d
downs.
Blow down – a
succession of 5-sec
‘puff’ blows.
Boiler Fireside Slag Management
Steam Purity in Superheaters d T bi I C i i l!
and Turbines Is Critical!
Steam Drum with Cyclone Steam Separators
Steam Separators
Steam / Water Separation Factors
DESIGN FACTORS:
• Pressure
• Drum Length and DiameterDrum Length and Diameter
• Rate of Steam Generation
• Average Inlet Steam Quality
• Type and Arrangement of Steam Separators
A t f F d t S l d St Di h E i t
• Arrangement of Feedwater Supply and Steam Discharge Equipment
• Arrangement of Downcomer and Riser Connections OPERATING FACTORS:
• Boiler Load
• Boiler Load
• Type of Steam Load
• Chemical Analysis of Boiler Water
• Water Level
PRIMARY SEPARATION EQUIPMENT:
• Natural Gravity Driven Separation
• Baffle Assisted Separation
Low Water Cut ‐ Offs (LWCO)
¾ A
critical
safety device!¾ Shuts off burner to prevent a low boiler water condition.
¾ May also be used to activate a Feedwater Pump or to open a Feedwater Valve.
¾ Typically a Primary and a Backup LWCO.
¾ Primary usually includes a Site Glass and activates a Feedwater Pump.
¾ Secondary serves as a backup; usually manually reset.
¾ Float type commonly called the ‘McDonald Miller yp y
Checking LWCO Operation
¾ Follow Manufacturers Instructions!
¾ Regularly blow down “water
¾ Regularly blow down water columns” to:
– Verify operation of the LWCO.
– Keep the LWCO free of sludge and obstructions.
¾ During boiler inspections, check the bowl and cross tee for sludge and deposit accumulations.p
¾ Deposit samples taken from the LWCO may not epresent the
Boiler Blowdown Boiler Blowdown
Continuous or Surface - Removes concentrated boiler water to maintain Cycles of Concentration.
Bottom – Removes suspended solids.
Bottom Removes suspended solids.
Water Column – Keeps Level Controls clean to insure proper operation
proper operation.
Continuous Blow Down
The point from hi h th
which the majority of blow down is removed.
removed.
Control
conductivity at this point.
this point.
Remove sludge from the Mud Drum with
Drum with manual blow downs.
Continuous Automated Boiler Blowdown
Board – Mounted Continuous Boiler
Bl d S
Blowdown Systems
Steam/Condensate System Components Steam/Condensate System Components
¾ Steam Trapsp
¾ Condensate Receivers
¾ Condensate Return Pumps
¾ Condensate Return Lines
¾ Condensate Return Lines
Basic Steam Trap Designs
• Fixed Orifice
• Float
• Inverted Bucket
• Bellows Actuated
