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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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