WIXLIB

By:Boiler – Fundamentalsand Best Practices

Boiler - FundamentalsSteam production and steam usesSteam purity and steam qualityTypes of boilersBasic boiler principlesBasic boiler calculations

Steam ProductionandSteam Uses

Steam ProductionWhen heat is added to water, itstemperature rises at a rate of 0.56 C(1 F) for each heat input of 2.095kJ/kg (1 Btu/lb)If we take water at 0 C (32 F) and weadd 419 kJ/kg (180 Btu/lb) then wewill increase the temperature of thewater by 100 C (180 F)This rise in temperature can bedetected and is called Sensible Heat(Specific Enthalpy - Water)

Steam TablesPressure Temperature Sensible Heatpsig 366339200388362Latent HeatBtu/lb971946929912882858838Total HeatBtu/lb1151116411731180119019971200Volume DrySaturated ft3/lb26.8013.909.306.603.892.762.14Pressure Temperaturebarg 48.802763.502781.702792.20Specific VolumeSteam 419.04505.60562.20640.70697.50781.60845.10

Steam ProductionSteamAt normal atmospheric pressure, anyfurther addition of heat to water at100 C will not increase thetemperature but will convert some ofthe water into steamIn order to convert water into steam2,257 kJ/kg (971Btu/lb) of additionalheat must be addedThis cannot be detected as a rise intemperature and is called the LatentHeat of Vaporisation (SpecificEnthalpy - Evaporation)

Steam ProductionSteamTotal Heat of Steam Sensible Heat Latent Heat of VaporisationSpecific Enthalpy :Steam Water EvaporationThus the Total Heat of Steam(Specific Enthalpy - Steam) is 2,676kJ/kg (1151 Btu/lb)This data is found in Steam Tables

Steam ProductionSteamFrom steam tables we can see that thetotal heat of steam does not vary agreat deal as the boiler pressureincreaseThe boiling point (b.p.) increases as thepressure increasesThus the sensible heat increases as thepressure increases, and the latentheat decreasesBoiler pressures are expressed in psia,psig, bar, kg/cm2, kpa

Steam UsesSpace heatingDrying - paper millProcess heatingSterilisationHumidificationPower generation

Steam PurityandSteam Quality

Steam PuritySteam purity is an expression of the quantity ofnon water components in the steamComponents can be dissolved in the steam,dissolved in water droplets entrained in thesteam or carried as discrete solid particles inthe steamSteam impurities are normally expresses as aquantity in parts per million (ppm) or parts perbillion

Steam QualitySteam quality relates to the quantity ofmoisture present in the steam100% quality specifying no moisturecontent0% quality specifying all liquidLiquid droplets entrained in the steamleaving a boiler contain dissolvedsolids

Types of Boilers

Types of Boilers Fire Tube Water Tube Waste Heat

Types of BoilersFire Tube BoilersWater Tube BoilersWaste Heat BoilersLow Pressure SystemsMedium to High PressureSystemsProcess applicationsHRSG

Fire Tube BoilersAlso referred to as smoke tube boilers, shellboilers, package boilersMultiple gas paths - 2, 3 and 4 passInternal furnace or fire box as the 1st passDry back or wet back designSingle fuel or dual fuel designLittle or no steam separation equipment

Fire Tube Boilers

Fire Tube Boilers

Fire Tube BoilersTypical designs are O, D and A type boilersSteam separation equipment - drumfurnitureCyclone separatorsDemister padsBaffle platesHave economisers and superheatersLarge water tube boilers are field erectedand may be unique design

Fire Tube BoilersSTEAM DRUMRISERSSUPERHEATERDOWNCOMERSSCREEN TUBESECONOMISERWATER WALLSAIR HEATERMUDDRUM

Fire Tube Boilers

Waste Heat BoilersVarious types and designsShell and tube exchangerLinked to processAmmonia plant

Waste Heat BoilerAmmoniaPlant

Heat Recovery SteamGenerators (HRSG)Various types and designsShell and tube exchangerWater tube boilerMultiple drum systemlow pressure (LP)medium pressure (MP)high pressure (HP)

Multi Pressure Boiler Systemwith Integral Deaerator

Steam GeneratorsCoil designs, vertical or horizontalBucket typesSteam water separatorBoiler water returned to feed tankMay include economiser and superheater

Steam Generator - Coil

Basic Boiler Principles

Basic Boiler PrinciplesEXTERNALTREATMENTSATURATED STEAMEVAPORATED WATERMAKE UPWATERANDSOLIDSHOT WELLFEEDWATERDEAERATORWATERANDSOLIDSRETURNED CONDENSATEWATER AND HEATBlowdown - Removes boiler water witha high concentration of solids which isreplaced by feedwater containing a lowconcentration of solidsIntermittent blowdownto remove suspendedsolids in boiler waterContinuousblowdownto removedissolvedsolids inboiler water

Basic Boiler PrinciplesWater and solids enter the boilerWater leaves the boiler as steamSolids concentrate in the boilerTherefore the boiler water will contain more solidsthan the feedwaterThis Concentrating effect is calledThe Cycles of Concentration or The Cycles

Basic Boiler PrinciplesA boiler can only tolerate a specificnumber of cycles ofconcentrationThis will vary depending onType and pressure of the boilerType of external treatmentPercentage condensate return

Basic Boiler PrinciplesThe chemical factors which limit theboiler water cycles of concentration areSuspended solids (Total Hardness)Dissolved solidsTotal alkalinity (M Alkalinity)Silica

Basic Boiler PrinciplesHow do we determine the chemicalcontrol limits that we apply to anoperating boiler ? British Standard BS2486:1997 ASME Guidelines* 1994 Consensus on operating practices forthe control of feedwater and boilerwater chemistry in modern industrialboilers

Basic Boiler Calculations

Basic Boiler CalculationsMake UpFeedwaterCondensateReturn

Basic Boiler Calculations Feedwater Make up Condensate Return

Basic Boiler CalculationsSteam Make (Flow)FeedwaterFlowBlowdown

Basic Boiler Calculations Feedwater Make up CondensateReturn Feedwater Flow (FWF) Steam Make Blowdown

Basic Boiler Calculations Feedwater Make up Condensate Return Feedwater Flow (FWF) Steam Make Blowdown(BD) Feedwater Flow (FWF) Steam Make Steam Make Cycles 1

Basic Boiler Calculations Feedwater Make up Condensate Return Feedwater Flow (FWF) Steam Make Blowdown(BD) Feedwater Flow (FWF) Steam Make SteamMake Cycles -1 Blowdown Steam make or Cycles –1 % Blowdown FWFCycles1as a % of FWFCycles

Basic Boiler CalculationsCondensate Return is also expressed as % ofFWFIf Condensate Return 60% Make up 40%% Condensate % Make up 100% FWFAs the boiler water cycles of concentrationincrease then the feedwater flow and the steammake approach the same number

Basic Boiler CalculationsCalculate the feedwater composition (impurities)from make up and condensate analysis belowMake-UpTotal HardnessM AlkalinityTDSSilica% Condensate22003506Condensate01015050Feedwater

Basic Boiler CalculationsCalculate the feedwater composition (impurities)from make up and condensate analysis belowMake up Condensate Feed waterTotal HardnessM AlkalinityTDSSilica% Condensate22003506010150501105182.53

Boiler Water Best Practises

Boiler WaterInternal TreatmentTechnology

Why is Effective Internal BoilerWater Treatment Necessary ?

Effective Internal Boiler WaterTreatmentControls Deposition Corrosion Carryoverand

Enhances System Reliabilityand Efficiency Avoids unscheduled shutdowns Helps ensure uninterrupted production Reduces maintenance costs Reduces operating costs

What Operating Costs areAssociated with BoilerOperation ?

Boiler Operating Costs Fuel - Gas, Oil, Coal Water - Influent and Effluent Regenerants - Salt, Acid,Caustic Water Treatment

Boiler Operating Costs Fuel - Gas, Oil, Coal Water - Influent and Effluent Regenerants - Salt, Acid, Caustic Water Treatment

Boiler Operating Costs Need to minimise all operating costsReducing boiler water blowdown giveswater, energy and chemical savings Need to maximise efficiencyMaintain clean heat transfer surfacesHeat recovery systems

Effective Internal Boiler WaterTreatmentControlsDeposition

Boiler Water Deposit Control Hardness salts Calcium Magnesium Metal oxides Iron Copper

Comparison of Heat Transfer SurfacesWith and Without DepositsMetalFireside600 FMetalWatersideFiresideScaleWaterside800 Fandabove500 FWithout deposits500 FWith deposits

Energy Loss from Scale Deposits(from Energy Conservation Programme Guide for Industry & Commerce)Scale8ica7S il5Iron&Energy Loss ceS2101640.4 mm1320.8 mm3641.2 mm1161.6 mm5642.0 mmScale Thickness, inches or mm3322.4 mm

Long Term Overheating

Boiler Water Deposit Control Removal of impurities Pretreatment plant Chemical treatment Controlled blowdown

Effective Internal BoilerWater TreatmentControls Deposition Corrosion

Boiler Water Corrosion Control Oxygen pitting Caustic corrosion Embrittlement or gouging Acidic attack

Oxygen Corrosion - Pitting

Caustic Gouging

Acid CorrosionAcid Corrosion

Effective Internal BoilerWater TreatmentControls Deposition Corrosion Carryover

Control of Boiler Water Carryover Effective mechanical steam separation Proper control of boiler water chemistry Antifoam, as needed Avoid major contaminant ingress Proper boiler operating practices

What Types ofInternal Boiler WaterTreatments areAvailable ?

Internal TreatmentProgrammesGeneral Classifications Precipitating Solubilising Combination

Internal TreatmentProgrammes Phosphate/Polymer Phosphonate/Polymer Chelant/Polymer Phosphate/Chelant/Polymer All Polymer Coordinated pH/Phosphate/Polymer All Volatile Treatment (AVT)

Boiler Water Polymersare Crucial to theSuccess of anyInternal TreatmentProgramme

How do Boiler Water PolymersFunction ?

Boiler WaterPolymersThe mechanisms by which boilerwater polymers function are Complexation / Solubilisation Crystal modification Dispersion

Calcium phosphate,magnesium silicatecrystals formed inboiler water withoutdispersant

Calcium phosphate,magnesium silicatecrystals formed inboiler water in thepresence of asulphonated polymer

Variables Affecting PolymerPerformance Functional group carboxylated (SCP/SCCP) sulfonated (SSP) phosphorylated (HTP) Polymer backbone Molecular weight

Typical Polymer StructuresCH2CH2C OO-CHCHCH2C OC OOHNH2XPolyacrylateAcrylate-Acrylamide CopolymerCH3CCH2CHCH2OC OCHCHCC OSO3O-X CHOXXPolymethacrylateSulfonated Styrene-MaleicAnhydride CopolymerY

Typical Polymer StructuresCH2ORP-OCHC OCH2O-O- H OCH2 O]m HPOHO-nPolyethylene glycol allyl ether (PEGAE)OCHEDP[CH2CH3 CH3 -OCH2P OPhosphonateOCHO-CH2CO PO-OHXPoly (isopropenyl phosphonic acid)PIPPA

DepositionPolymer PerformancevsMolecular WeightPolymer Molecular Weight

Programme SelectionConsiderations Boiler pressure, design Pre-treatment plant type Feedwater quality Hot well, deaerator type Steam turbine Control capabilities

Chemical Factors Total Dissolved Solids (TDS) Alkalinity Silica Suspended Solids

ASME Boiler Feedwater QualityGuidelines for Modern IndustrialWater-TubeBoilersHardnessCopperIronDrum Pressure (kg/cm²) 0 - 2122 - 3132 - 4243 - 5253 - 6364 - 7071 - 105 (ppm Fe)(ppm Cu)(ppm 020.0150.0150.010.300.300.200.200.100.050.0

Internal TreatmentProgrammes Phosphate/Polymer

Phosphate/Polymer Treatment Reactions:OHCa PO4 Ca(OH)PO4 Calcium Phosphate HydroxideHydroxyapatite Mg Mg(OH)SiO3 MagnesiumSiO3Silica OHHydroxideSerpentine

Phosphate/Polymer TreatmentCharacteristics Hardness controlled by precipitation Polymers used to control hardnesssludge and metal oxides Phosphate residual used for programmecontrol Hydroxide alkalinity required (pH : 10.5 12)

Phosphate/PolymerTreatmentBoiler Control Parameters Phosphate residual as PO4 depending onhardness in the feedwater usually associated with boiler pressure and environmental legislation M alkalinity of 700 ppm as CaCO3 (25 % ofTDS) Polymer : min 360 ppm as SP8100 Still the most used method for treating lowpressure boilers

Phosphate/PolymerTreatmentAdvantages Disadvantages Tolerates a wide range offeedwater hardness Is a precipitationprogramme (somedeposition is normal) Non corrosive treatment Suitable for low to mediumpressure systems Easy operator control Higher blowdown ratesmay be required

Internal Treatment Programmes Phosphate/Polymer Phosphonate/Polymer

Phosphonate/PolymerCharacteristics Organic phosphor donors combinedwith three synergistic polymers Complexes hardness, iron and copperions in BFW Disperses/solubilises contaminants inboiler minimising sludge formation