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A Boiler is a Pressure VesselWith a Burner orOther Energy Source UsedTo Convert ThermalEnergy FromOne Form to AnotherExampleBurn Natural Gas to Generate Steam3
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Average Steam System EfficiencyAn energy survey and load balance on a typical steamsystem in average condition will yield the following lossesBoiler Room LossesStack losses 21%Blowdown losses 4%Boiler radiation losses 3%Total Boiler Room Losses 28%Distribution LossesInsulation losses 7%Steam leaks 6%Blowing steam traps 7%Flash steam losses 13%Return System losses 9%Total Distribution Losses 42%Total Steam System Losses 70%Placed in perspective, if you are spending $500,000 per year forboiler fuel, only about $150,000 of thermal work is being deliveredinto your product or process.Average Steam System EfficiencyAn energy survey and load balance on a typical steamsystem in average condition will yield the following lossesBoiler Room LossesStack losses 21%Blowdown losses 4%Boiler radiation losses 3%Total Boiler Room Losses 28%Distribution LossesInsulation losses 7%Steam leaks 6%Blowing steam traps 7%Flash steam losses 13%Return System losses 9%Total Distribution Losses 42%Total Steam System Losses 70%Placed in perspective, if you are spending $500,000 per year forboiler fuel, only about $150,000 of thermal work is being deliveredinto your product or process.4
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SteamBoilerEnergy Sources•Natural gas•Oil•Waste gas•Coal•Wood•OtherSteamHeating Hot WaterHeating AutoclavesHeating Metal PlatensHeating Rotating DryersHeating Process AirHVAC EquipmentsOther ApplicationsProcess and HVAC EquipmentDeaeratorFeedwater5Boilers Convert PrimaryEnergy Sources to EnergyIn the Form of SteamThe Basic Steam LoopFor the most efficient operations, boiler operations should be integrated with steam demand.
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• Thermal energy is used in a wide range of applications to manufactureproducts as well as provide comfort during cold weather. Take amoment and glance around your current location and see if you canidentify anything you might see which did not use thermal energy toproduce it.• BTU is the amount of heat to raise one pound of water one degreeFahrenheit.• One pound of water yields one BTU of thermal energy when cooledone degree Fahrenheit.• One pound of steam yields approximately 1000 BTU’s whencondensed.• Steam is a common heat transfer media due to the large amount ofheat which can be transmitted through a pipe. Other heat transfermedia are offered such as thermal oils. We will limit our discussionsto steam and hot water for this presentation since the basic principalsand equipment are similar. 6
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ENERGY DATA ALL ARE EQUAL TO1,000,000 BTU• 1 MCF of natural gas• 1,000 cubic feet of natural gas• 1 decatherm of natural gas• 10 therms of natural gas• 293.1 KW of electricity• 7.29 gallons of # 2 oil• 10.93 gallons of propane• 1,000 lbs of steam• 29.31 boiler horsepower• 1 MCF of natural gas• 1,000 cubic feet of natural gas• 1 decatherm of natural gas• 10 therms of natural gas• 293.1 KW of electricity• 7.29 gallons of # 2 oil• 10.93 gallons of propane• 1,000 lbs of steam• 29.31 boiler horsepower7
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Gas Cost (MCF) # 2 Oil (gallon) Propane (gallon) Electricity(KWH)$5.00 $.82 $.46 $.01718If natural gas costs $5.00 per million BTU’s-•Number 2 oil would have to cost $.82 per gallon•Propane would have to cost $.46 per gallon•Electricity would have to cost $.0171 per KWHEnergyCross Over Costs
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Combustion EfficiencyThe optimum pointfor most boilers is3% O211Heat up thestackSmoke
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Fuel to Steam Efficiency =Output BTUsInput BTUsEfficiency and Radiation Loss• Efficiency is the ratio of output from a piece of equipment as compared to the input• Radiation loss is the heat lost from the boiler shell• The larger the boiler, the larger the radiation loss• Typical values for radiation loss are ~ 4% of full capacity• Boilers are typically under fired and operate in the 40-60% load range• A boiler operating at a 50% firing rate would have a radiation loss of 8%• As an example assume the combustion efficiency is 81% and the blow down losses are 2%• The predicated Fuel to Steam Efficiency would be 71% (81%-8%-2%)12
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Radiation Loss13Radiation loss is rated as apercentage of 100% boiler outputand is typically 4% for most firetubeboilersSince the radiation loss off a boiler does not change,a boiler operating at a 75% firing rate will have aradiation loss of 6% as a percentage of boiler output.At a 50% firing rate, the radiation loss rises to 8%.The lower the percentage load, the higher theradiation losses become since fuel is being wastedto keep the boiler hot.Boilers which cycle in and out of operation havevery high losses due to radiation and purge losses.
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Boiler Size 200 HPFiring Rate 50%Delivered HP 100 BHPCombustion Eff. 81%Radiation Loss 8% (50% firing rate doubles the radiation loss)Fuel to Steam Eff. 73%Gas Use (MCF/Hr) 4.73Cost per Hour $33.116000 Hours/Year $198,66014Cost to Produce 100 BHPUsing Various Boiler SizesGas Cost $7.00 per Million BTU’s6000 Hours of Operation per yearBoiler Specification of Radiation Loss-4%
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Cost to Produce 100 BHPUsing Various Boiler SizesGas Cost $7.00 per Million BTU’s6000 Hours of Operation per yearBoiler Specification of Radiation Loss-4%Boiler Size 200 HP 135 HP 100 HPFiring Rate 50% 75% 100%Delivered HP 100 BHP 100 BHP 100 BHPCombustion Eff. 81% 81% 81%Radiation Loss 8% 6% 4%Fuel to Steam Eff. 73% 75% 77%Gas Use (MCF/Hr) 4.73 4.60 4.48Cost per Hour $33.11 $32.20 $31.366000 Hours/Year $198,660 $193,200 $188,16015Multiply these figures for larger or smaller boilers
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Lead Lag Boiler ControlsFiring Rate 50% 75% 100%Cost per Hour $33.11 $32.20 $31.3616Boiler1Boiler2Steam to PlantA Simple Example•Case 1-One boiler carries load at 100% firingrate with a cost of $31.36 per hour.•Case 2-Two boilers each firing at 50% carrythe load with a cost of $33.11 per hour.•Lead Lag Savings is ~6% by using a lead lagcontroller.Lead LagController
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Blow Down Considerations• As water is boiled, sediment in the water settles and scum rises to the surface.• Surface blowdown deals with the surface contaminants.• Bottom blow down deals with the sediment.• Proper water treatment on a daily basis if critical to the service life of a boiler.17Conductivity basedsurface blowdowncontrollerHeat exchanger bottomblowdown heat recoverysystem
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Fuel to BoilerFuel to BoilerSteam toPlantSteam toPlantBoilerConsiderMetersConsiderMeters18Measuring Fuel to Steam Efficiency1 GPM = 500 Lb/HrFeedwaterMeterMeterMeter
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Boiler LossesCombustion Efficiency 75-86%Radiation and Convection Losses 0.3-6%Boiler Design and Load Management 2-7%Scale Buildup in Boiler 7-11%Excess Boiler Blowdown 0.1-1%Excess Air 0-7.5%Range of Efficiency 42.5-76.6%(Source ASHRAE Journal September 1994)Boiler LossesCombustion Efficiency 75-86%Radiation and Convection Losses 0.3-6%Boiler Design and Load Management 2-7%Scale Buildup in Boiler 7-11%Excess Boiler Blowdown 0.1-1%Excess Air 0-7.5%Range of Efficiency 42.5-76.6%(Source ASHRAE Journal September 1994)19
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Watertube Boilers•Efficiencies to 76-80%•Gas, oil, coal and othersolid fuels•15,000 lb/hr and up•Large site built units forpower generation andvery large loads•Expensive to purchaseand maintain•The choice for large tovery large applications20
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Firetube Boilers•Efficiencies to 78-81%•Gas, oil, and propanefired•Limited options on solidfuels•10-1200 BHP (1BHP=34.5 lb/hr)•Work horse boiler for awide range of applications•Moderate cost topurchase and install•Construction and designspec’s can affect price21
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Electric Boilers and Heaters•Efficiencies to 98-99%•Electrode and resistance types•Sizes up to 1000 BHP•No products of combustion•No alternate fuel options•Expensive to operate•Expensive to install-power side•RTP rates can be very expensive•Power company will addincentives22
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Electric Boilers and Heaters•Efficiencies to 98-99%•Electrode and resistance types•Sizes up to 1000 BHP•No products of combustion•No alternate fuel options•Expensive to operate•Expensive to install-power side•RTP rates can be very expensive•Power company will addincentives23Electric Boilers-a few thoughts•Sold on the basis of 98-99% efficient, zero emissions, and simple installation.
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Electric Boilers and Heaters•Efficiencies to 98-99%•Electrode and resistance types•Sizes up to 1000 BHP•No products of combustion•No alternate fuel options•Expensive to operate•Expensive to install-power side•RTP rates can be very expensive•Power company will addincentives24Electric Boilers-a few thoughts•Sold on the basis of 98-99% efficient, zero emissions, and simple installation.•1.02 BHP = 10 kWh A 200 BHP boiler would require a 2000 kWh power source.•Cost of steam = 293.1 x kWh rate for an electric boiler ($.07 x 293.1 = $20.52 per million BTU’s.•Cost of steam for a gas fired boiler = (Gas cost)/(Efficiency) $5.00 at 80% = $6.25 per million BTU’s.•Power audits used to understand steam loads and switch customers from natural gas.•Carbon footprint for natural gas about 25% less than coal and oil.
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Summary of Boiler Types• Watertube Boilers (Many Brands)• Firetube Boilers (Many brands)• Low Volume Watertube Boilers (Miura)• Steam Generators (Clayton)• Electric Boilers (Many Brands)• Old Boilers• Best suited for high volume steamproduction from 25,000 lb/hr up tobuilding sized boilers.• Size range up to ~ 1200 HP (41,400lb/hr). Most boilers installed are FT’s .• Modular concept with high efficiencyand PLC based control. Small footprintand good for retrofit applications.• High efficiency coupled with highrange of operating pressures. Smallfootprint and good for retrofitapplications.• Suitable in specialized applicationssuch as no boiler stack possible, smallloads, point of use need for steam, noflame requirement and others.• New Boilers25
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Boiler Link-less ControlsImprove BoilerEfficiency 3-5%Most boilers use amechanical system tomanage the air fuelmixture. Mechanicalcombustion systems arehard to maintain, drift inadjustment and lead toextra fuel being burned tooperate your boilers.26
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Servo operator forair damperServo Operatorfor gas valve Servo operator forFGR controlsServo operatorfor oil valveControl PanelFull feature PLC controller allows for precise programmingof fuel, air, FGR and number 2 oil setting.•Complete data display of boiler operations.•Easily integrated with building management controlsystems.27
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28Boiler Stack EconomizersBoiler stack economizerswill typically increasecombustion efficiency by ~4%.The typical temperaturedrop across a stackeconomizer is ~ 100 F.The heat removed from thestack gas is used to boostthe feedwater temperaturesinto the boiler or preheatboiler feedwater.Stack dewpoint must becarefully considered toprevent acid formation inthe stack.
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Feedwater ConditioningRemoving O2 and CO229DeaeratorPressure VesselBoils feedwater to drive off gases225-227 F Water TemperatureOperating Pressure 5-7 psigFeedwater HeaterNon code VesselChemicals added to bind gases190-200 F Water TemperatureOperating Pressure O psigO2 Causes OxygenPitting on Boiler TubesCO2+H20 =Carbonic AcidCorrosionRed Brown Rust
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Boiler Feedwater Pumps30NPSHNet Positive Suction Head(NPSH)Required distance in feet toprevent pump cavitationCavitation occurs when wateris pumped out faster than itcan enter the pump whichleads to water vapor forminginside the pump whichdestroys seals and impellers
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Water SoftenersTypical Make Up Water Spec’s0 CaCo3 HardnesspH 7-9Less than.5 ppm O2Less than 30 mg/L ChloridesLess than 30 mg/L SilicaBelow .5 mg/L IronBelow .5 mg/L Manganese31
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Blow Down SeparatorsCold WaterInletSurface and BottomBlowdown fromBoilersSteam to Outside Vent160 F Boiler and CoolingWater to Drain32
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Older Boilers• The average boiler in service is typically 30+ years old.• Consider an 1979 automobile to a 2009 model.• Older boilers can be upgraded with linkage less controls, economizers, andbetter PLC based control systems.• Boilers should be tuned at least twice per year.• Boilers should be matched to the connected load.• Two boilers running in parallel to carry a load wastes fuel.• Lead lag systems typically reduce fuel use by at least 5%.• Consider setting back or shutting down boilers over a weekend-do the math.• Water treatment is critical to boiler life.• Water softeners are critical to boiler life.• Consider meters to provide a basis of system health.33
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Boiler Considerations-Before You Buy Be Aware• First cost vs. long term cost. A boiler will use 3-4 times thepurchase cost of the boiler installed in energy per year.• Understand boiler efficiency vs. manufacturer claims.• Be aware of efficiency claims by other utility companies.• Match the boiler to the connected load.• Emission requirements. All boilers over 10 million BTU’s mustbe air permitted and low NOx.• Fuel options and back up.• If a single boiler installation, will failure of the boiler shut downoperations?• Space and installation issues?• In most states, the installer must be licensed and the boilerpermitted.• Avoid buying a boiler. Buy a boiler room.34
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Average Steam System EfficiencyAn energy survey and load balance on a typical steamsystem in average condition will yield the following lossesBoiler Room LossesStack losses 21%Blowdown losses 4%Boiler radiation losses 3%Total Boiler Room Losses 28%Distribution LossesInsulation losses 7%Steam leaks 6%Blowing steam traps 7%Flash steam losses 13%Return System losses 9%Total Distribution Losses 42%Total Steam System Losses 70%Placed in perspective, if you are spending $500,000 per year forboiler fuel, only about $150,000 of thermal work is being deliveredinto your product or process.Average Steam System EfficiencyAn energy survey and load balance on a typical steamsystem in average condition will yield the following lossesBoiler Room LossesStack losses 21%Blowdown losses 4%Boiler radiation losses 3%Total Boiler Room Losses 28%Distribution LossesInsulation losses 7%Steam leaks 6%Blowing steam traps 7%Flash steam losses 13%Return System losses 9%Total Distribution Losses 42%Total Steam System Losses 70%Placed in perspective, if you are spending $500,000 per year forboiler fuel, only about $150,000 of thermal work is being deliveredinto your product or process.35