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Boilers 101
Asit Patel
ANP Energy Consulting Services
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Learning objectives
• Define what is a boiler?
• What are different classification of boilers?
• Define combustion efficiency, thermal efficiency, and fuel to fluid efficiency.
• Identify different type of boilers
• Criteria for boiler selection
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Lets look at what the Merriam-Webster dictionary says the BOILER IS…
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What is a boiler?
• A boiler is a closed metal container (pressure vessel) in which water is heated to produce steam and heated water
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Boiler Classifications
• Low Pressure:• Section IV of ASME Code (Heating Boiler)
• Steam: Up to 15 PSIG
• Water: Up to 160 PSIG and or 250°F
• High Pressure:• Section I (Power Boiler) of ASME Code
• Steam: Above 15 PSIG
• Water: Above 160 PSIG and or 250°F5
Boiler Efficiency Classification
• Standard Efficiency (80-84%)• Most Steel and Cast Iron Boilers
• Mid Efficiency (85-90%)• Copper Fintube Boilers
• High Efficiency (90%+)• Condensing Boilers
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Non-Condensing
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Defining Boiler Efficiency
• Combustion Efficiency - indicates a burners ability to burn fuel measured by unburned fuel and excess air in the exhaust.
• Thermal Efficiency - indicates the heat exchangers effectiveness to transfer heat from the combustion process to the water or steam in the boiler, exclusive radiation and convection losses .
• Fuel to Fluid Efficiency - indicates the overall efficiency of the boiler inclusive thermal efficiency of the heat exchanger, radiation and convection losses - output divided by input.
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Where do we get input and output information for a boiler?
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Boiler Brochure
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Boiler CapacityUnits of Measurement
• Input (Firing rate)
• GPH – Gallons per hour
• MBH (M = 1,000 btu)
• Output• BHP = Boiler Horse Power = 33,475 btu
• Sqft of steam = 240 btu
• lbs/hr (34.5 lbs of steam = 1 BHP)
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What is a BTU?
• British Thermal Unit (btu) = Unit of measurement of heat energy.
• Amount of heat energy required to raise one pound of water by one degree Fahrenheit.• one gallon of water = 8.33 lbs
• Approximate amount of heat released by one kitchen match.
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin tube type
• Condensing boilers
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Types of Boilers
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypesCast Iron Sectional
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Boiler TypesCast Iron Boilers
• Advantages• Modular Design
• High Number of Options
• Low Initial Cost
• Durable Construction
• Disadvantages• Low Pressure Only
• Limited to 200 horsepower
• Not Recommended For Process Applications
• Medium to High Level of Maintenance
• Low Efficiency in Field
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypeSteel Firetube Scotch
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Two Pass – Dryback
Three Pass – Wetback
Boiler TypeSteel Firetube Scotch - Four Pass - Wetback
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Boiler TypeSteel Firetube Scotch - Wetback
• Design Principles• Rear turnaround is totally surrounded by
water
• No expensive refractory to maintain
• Rear doors are either lightweight lift off type or split-hinged
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Boiler TypeSteel Firetube Scotch - Dryback
• Design Principles• Rear turnaround is a refractory wall
• Door refractory is a maintenance item
• Rear door is vessel-sized in diameter, extremely heavy, and hinged or davited
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Boiler Type –Steel Firetube Scotch - Dryback
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Boiler TypeSteel Firetube Scotch
• Advantages• Wide range of sizes• Both high and low
pressure• Higher Efficiency• Easy to clean• No mud legs• Longevity• No refractory floor• No rear door refractory
(3-Pass & 4-Pass Wetback Only)
• Disadvantages• Operating weight• Requires more floor
space• Space required for
tube removal & cleaning
• Refractory Maintenance (dryback design only)
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypeSteel - Firebox
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Boiler TypeSteel - Firebox
• Advantages• Wide range of sizes
• Compact (for places where Scotch will not fit)
• Easy to clean
• Longevity
• Disadvantages• Low Pressure ONLY
• Operating weight
• Refractory maintenance costs
• Space required for tube removal & cleaning (but not as much as Scotch)
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Boiler TypeModified Firebox (fits through 36” door)
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypeFlexible Watertube
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Boiler TypeFlexible Watertube
• Advantages• Lower Cost
• Lower operating weight
• Long life expectancy (40 Years)
• Wide range of sizes
• Knockdown capability
• Minimum space required for tube removal & cleaning
• Tubes easily replaced
• Disadvantages• Low Pressure
Application ONLY
• Water treatment more critical (difficult to clean)
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Boiler TypeSteel - Watertube
• D Type
• S Type
• A Type
• O Type
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Boiler TypeSteel Watertube
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Boiler TypeSteel - Watertube
• Advantages• High Pressure up to
900 psig
• Fast Steaming
• Low Water Content
• Quick Response to Load Demands
• Disadvantages• Steam Only
• Process Only
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypeCopper Fin Tube – Horizontal Lay-out
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Source: Hydronic Institute
Installation Guide: Residential hydronic heating – Guide 2000
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Boiler TypeCopper Fin Tube – Vertical Lay-out
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Boiler TypeCopper Fin Tube
• Advantages• Medium efficiency
• Low initial cost
• Low Mass
• Low operating weight
• Small footprint
• Lower stand-by losses
• Disadvantages• Gas only
• Water only
• Special vent requirements
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Types of Boilers
• Cast Iron Sectional
• Scotch Marine Steel• Firetube
• Firebox
• Watertube
• Low water content copper fin
• Condensing boilers
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Boiler TypeHigh Efficiency – Condensing Boilers
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True Operating Efficiency of Condensing Boiler
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Condensing boilers actually operate at higher part-load efficiency while in condensing mode.
Boiler TypeHigh Efficiency – Condensing Boilers
• Advantages• Highest Efficiency
• Can be used in low RWT systems
• Various types
• Condensate will not harm properly designed boiler
• Standard features & Controls
• Smaller Venting
• Disadvantages• Water only
• Gas only
• Special venting
• Costly???
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TYPES OF BOILERSAtmospheric - Gas
Increased standby losses
– Air from building free to move through units and up through stack at all times
Types of Boilers
• Knockdown• Boiler (vessel) only
• Packaged• Boiler and burner
• May be the same manufacturer or may be two different manufacturers
• Mostly two different manufacturers
• Integral unit• Boiler and burner is one unit
• Most condensing boilers 42
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Criteria for boiler selection
• Application• Heating/Process
• Steam/Hot Water
• High Pressure/Low Pressure
• Fuel availability and venting options
• Space availability
• Budget
• Efficiency43
What makes one boiler more efficient than other?• Capability to transfer more BTU’s from
combustion process to make hot water or steam.
• Heat exchanger design and construction
• Lower jacket and stand-by losses
• Better insulation and heat exchanger isolation during off cycles.
• Capability to match the boiler’s output to actual load
• Better modulation capability (higher turn-down ratio) 44
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From operating perspective..
• The best boiler for your application is the one that is properly sized to match your load.• A boiler that runs non-stop.
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How do we achieve that…
• Multiple smaller capacity boilers…
• Larger boiler(s) with modulation burner• Turn down ratio
• Typical – 4:1 (100% – 25%) 5:1 (100% - 20%)
• Highest - 20:1 (100% - 5%)
• But then, what about part load efficiency?
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Part-Load Efficiency Curves of Non-condensing High Mass boiler
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Typical high mass boilers have low part-load efficiency.
Another concern is flue gas condensation.
Part Load Efficiency of Condensing Boiler
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Condensing boilers actually operate at higher part-load efficiency while in condensing mode.
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So What Makes Condensing Boiler Efficient?
• Condensation of water vapor.• Extraction of latent heat that is otherwise
going up the chimney in form of water vapor.
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Fuels and Combustion
• Fuels are “Hydro-Carbons” • Oxygen is 21% of air (78% is Nitrogen)
• HC + O2 • Good, “complete” combustion• CO2 + H20(vapor) + heat
• Incomplete combustion of gas• CO2 + CO + H2O + heat
• Incomplete combustion of oil • CO2 + CO + C + H2O + heat
Flame Quality
Carbon Monoxide hazard
Soot = $ lost
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Energy Improvement Opportunities Associated with Boilers/burners
• Maximize combustion efficiency• Minimize excess air
• Maximize heat exchange• Clean up fireside and waterside fouling
• Minimize stand-by losses• Jacket losses and cyclical losses
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How much excess air should we strive for?
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FEMP O&M Manual Ver. 3
P. 9.17
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Opportunity in field
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Lowering of excess air results in lower exhaust gas temperature and higher efficiency
Soot on Heat Exchanger
• Acts as an insulator
• Increases amount of heat lost through chimney
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Heating System Efficiency
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Scale on Water Side of Heat Exchanger
• Acts as an insulator• More heat lost through chimney
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Heating System Efficiency
Just so that you know that I am not making these things up.
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Optimization Opportunity (Minimize stand-by losses)
If this damper is left in open position, it can significantly impact the stand-by losses and if not adjusted properly can have significant impact on combustion process.
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Thank You
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Q & A
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