Energy economics management

Energy economics management1

M. E. [CONSTRUCTION ENGINEERING & MANAGEMENT]YEAR I (SEMESTER II)SNPIT&RC, UMRAKHGUJARAT TECHNOLOGICAL UNIVERSITYPREPARED BY : -PATEL TARUN (140490714006)PATEL JATIN (140490714014)

BOILER WATER TREATMENTCONTENTINTRODUCTIONBOILER FEEDWATERWATER FOR BOILERSTREATMENT METHODSIMPURITIES IN WATER AND ITS EFFECT ON BOILER2INTRODUCTIONTwenty to thirty years ago or longer, internal boiler feed water treatment chemicals (soda ash, starch, tannin, etc.) were applied directly to the boiler and the boiler itself was used as a softener. In these low heat release boilers, scale formation was reduced to a sufficient degree that relatively trouble-free operation resulted. The modern boiler, with water walls and smaller diameter tubes, employs higher heat transfer rates and is not designed for handling feed waters of high suspended solids content. Therefore, high quality make-up water of minimum hardness, suspended matter, and dissolved mineral content is required for efficient operation and minimum maintenance. 3BOILER FEEDWATERA boiler's efficiency is directly related to the quality of its feed water. The feed water system refers to de aerator, feed water pumps, and the piping to the boiler. Feed water is water added to a boiler to replace evaporation and blow down. Feed water composition therefore depends on the quality of the make-up water and the amount of condensate returned. Before water enters the boiler, oxygen must be removed or corrosion can occur throughout the boiler system, forming pits that eat away at the metal. Resulting leaks could lead to a blown boiler tube and ultimately could cause a power plant shutdown.4WATER FOR BOILERSAll natural waters contain varying amounts of suspended and dissolved solids as well as dissolved gases (O2, CO2)The type and amount of impurities in fresh water vary with the source (lake, river, well) Impurities in water are of importance when water is to be used for steam generation. For higher-pressure boilers, feedwater must be pretreated to remove impurities

5TREATMENT METHODSExternal TreatmentInternal Treatment

6EXTERNAL METHODS OF CONDITIONINGClarificationFiltrationIon exchangeMembrane separation

7CLARIFICATIONRemoves all types of solids & large particles sediments, oil, natural org. matter, colouretc.Consists of 4 steps screening, coagulation-flocculation, sedimentation, fine filtration.Screening protects downstream units from large, easily separable objects.Three types:Fine screening (spacing < 10 mm)Medium screening (spacing 10 40 mm)Coarse screening (spacing > 40 mm)Coagulation-flocculation removes suspended solids & colloidal particles.8CLARIFICATION (CONTD.)Important factors velocity gradient, time, pHFlotation to separate particles having density lesser than water.Three types:NaturalAidedInducedInduced flotation facilitated through bubbling of air; 2 types : Dissolved air flotation (DAF) (bubbles of 40 70 mm)Mechanical flotation (bubbles of 0.2 2 mm)9FILTRATIONSeparates un dissolved solids from water by means of a filter - porous substance, membrane or permeable fabric.Three types of filtration:Micro filtration (pore size 0.1 10 m)Ultra filtration (pore size 1-100nm)Nano filtration (pore size < 1 nm)Micro filtration removes bacteria; used for biological wastewater treatment, effluent treatment, separation of oil-water emulsions.Ultra filtration - separation of suspended solids, colloids, bacteria, virus. 10ION EXCHANGE Resins - acidic/basic radicals with ions fixed on them; exchanged with ions present in water.Theoretically removes 100 % of salts; does not remove organics, virus or bacteria.2 types of resins gel type (microporous) and macroporous or loosely cross-linked type.3 systems of resin beds:Strong acid cation + Strong base anionStrong acid cation + weak base anion + Strong base anionMixed-bed DeionizationIon exchange plant softens water, removes heavy metals, produces demineralized water.

11ELECTRODIONIZATIONCombines membrane separation and ion-exchange to provide high efficiency demineralization process. Electric potential transports & segregates charged aqueous species.Electric current continuously regenerates resin; no need for periodical regeneration.Deionization chamber - ion exchange resin, packed between cationic & anionic exchange membranes.12INTERNAL TREATMENT METHODSDeaerators:Dissolved non-condensibles: O2 and CO2 Pitting and corrosionMechanical deaeration: reducing solubility of gasesIncreased temperatureDecreased partial pressure over the waterCommonly used purge gas: steamAdvantages:No added impuritiesEasily availableAlso provides heatPressure/Vacuum operation, ~98% of total and free is removedCoupled with chemical scavengers for complete deaeration13IMPURITIES IN WATER AND ITS EFFECT ON BOILER

14PROBLEMS CAUSED BY IMPURITIES IN THE FEED WATER

ScalingWater Hardness is the primary source of scale in boiler equipment, Calcium and Magnesium are main cause of hardness in waterSilica in boiler feedwater can also cause hard dense scale with a high resistance to heat transfer.15BOILER SCALE ON WATER SIDE

16FAILED TUBES SHOWING SIGNS OF BOTH CORROSION FAILURE AND OVERHEATING

17CORROSIONOxygen and Carbon Dioxide cause corrosion The carbon dioxide by dissolving in the water and forming a weak carbonic acid which attacks the metal in boiler Oxygen is present in water reacts with Iron to form red iron oxideCorrosion reduces the thickness of the steam pipe metal18CORROSION CONTROLOxygen control: during operationChemical Scavengers added to feed water and condensateSodium sulfite, bi sulfite, hydrazineionone, acerbateCommon entry: between de aerator and storageSodium sulfite : easy to handle, safe, for pressures of < 70 bar, solid addition to system, decomposition to corrosive gasesHydrazine : no solid addition, high pressures, but toxic, handling issues, Ammonia liberation, slower reactionConstant sampling and monitoring19CORROSION CONTROL (CONTD.)Control: downtime and storageOxygen in-leakage and pH loweringDry storage: long downtime, month or moreCompletely driedApplied de secants like quicklime, silica gel, activated aluminaWet storage: short downtimeCleaning, inspection and filling with de aerated feed waterAddition of scavenger, heat addition20DEPOSITSScaling/deposition from carryoverCarbonate/Phosphate controlAddition of certain amounts of carbonate/phosphate for ensuring precipitate in the form of salts. Prevention of SulphatesFor removal of hardness, Ca and MgPrecipitation in bulk instead of at walls, non-adherentOrganic supplements: fluid sludge formation (polymer addition)Bottom blow down removes sludgeChelan controlCombination of additivesBlow down21THANK YOU22