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  1. 1. Boiler Water Treatment <ul><li>Training Handouts . </li></ul><ul><li>AGD </li></ul>
  2. 2. Boiler Water System pre-treatment Feed Tank Feed pump Condensate Continuous Blowdown s s s s Boiler s s s s Sample point Plant Process Water Column Receiver
  3. 3. Benefits Of Using Steam <ul><li>High Heat Content. </li></ul><ul><li>Gives up heat at constant temperature. </li></ul><ul><li>Produced from water which is cheap and readily available. </li></ul><ul><li>It is clean, odourless and tasteless. </li></ul><ul><li>Can be used to generate power. </li></ul><ul><li>Can be easily distributed and controlled. </li></ul>
  4. 4. Types 0f Boilers <ul><li>Coil type </li></ul><ul><li>Smoke tube </li></ul><ul><li>Water tube </li></ul><ul><li>Spreader stroker </li></ul>
  5. 5. Major Problems <ul><li>Scaling </li></ul><ul><li>corrosion </li></ul><ul><li>Priming / Foaming </li></ul><ul><li>Silica carryover </li></ul><ul><li>Caustic embrittlement / cracking </li></ul>
  6. 6. Problems Caused By Impurities
  7. 7. Water <ul><li>Impurities </li></ul><ul><li>Dissolved Gases O 2 /CO 2 </li></ul><ul><li>Hardness </li></ul><ul><li>High TDS, SS, Alkalinity and Organic Matter </li></ul><ul><li>High OH - Alkalinity </li></ul><ul><li>Problems </li></ul><ul><li>Corrosion </li></ul><ul><li>Scaling </li></ul><ul><ul><li>Ca/Mg salts </li></ul></ul><ul><ul><li>Carbonates </li></ul></ul><ul><ul><li>Phosphates </li></ul></ul><ul><ul><li>Silicates </li></ul></ul><ul><li>Foaming/Priming </li></ul><ul><li>Caustic embrittlement/ Grooving </li></ul>
  8. 8. EFFECT OF SCALING, CORROSION, CARRY-OVER ON BOILER SYSTEM <ul><li>Reduction in heat transfer </li></ul><ul><li>Severe elevation of metal/tube temperature </li></ul><ul><li>Promotes under deposit corrosion - pitting </li></ul><ul><li>Loss of construction material </li></ul><ul><li>Failure of boiler tubes </li></ul><ul><li>Water losses </li></ul><ul><li>Increased maintenance cost </li></ul><ul><li>Unplanned shut downs </li></ul><ul><li>Ultimately, increased operational costs and loss of productivity. </li></ul>
  9. 9. Pretreatment Internal Boiler Condensate return line treatment Heat Treatment
  10. 10. 1.0 System: Feed
  11. 11. 2.0 System : Boiler Drum
  12. 12. 2.0 System: BoilerDrum
  13. 13. 3.0: System:Steam / Condensate
  14. 14. Boiler Water Treatment <ul><li>No Scale : Heat transfer surfaces . free from Scale, sludge, . & deposits </li></ul><ul><li>No corrosion : Surfaces covered . by film of magnetite </li></ul><ul><li>Pure steam :Elimination of . carryover </li></ul><ul><li>Safe Operation : Prevention of . sludge in the water . level & blow down control . </li></ul>
  15. 15. Deposit Formation
  16. 16. Deposit Formation <ul><li>Caused by hardness salts ppting,- Reduced solubility with increased temp.& increased conc. due to steam formation </li></ul><ul><li>Scale: occurs at the point of steam . generation sludge: occurs in bulk water & deposit on . metal surfaces </li></ul><ul><li>Lowers thermal conductivity </li></ul><ul><li>Reduces boiler efficiency </li></ul><ul><li>Increases fuel consumption </li></ul>
  17. 17. Deposits - Effects on Metal <ul><li>Furnace temp. over 2500 deg F </li></ul><ul><li>Metal deforms at 900 deg F </li></ul><ul><li>Water temp 338 deg F (100 psig) . 546 deg F (1000 psig) </li></ul><ul><li>Deposits form insulating barrier, tolerence depends on nature & heat tranfer of deposite </li></ul>
  18. 18. Thermal Conductivities ( BTU .ft / ft2.hr.deg F ) <ul><li>CaCO3 1.10 </li></ul><ul><li>Ca3(PO4)2 2.20 </li></ul><ul><li>CaSO4 0.90 </li></ul><ul><li>Fe2O3 0.35 </li></ul><ul><li>SiO2 (Quartz) 0.97 </li></ul><ul><li>Carbon steel 30.0 </li></ul><ul><li>Copper 218 </li></ul>
  19. 19. Scale Deposition Potential Steam Production kg/hr 10,000 20,000 30,000 40,000 0.5 4 10 ppm hardness 5 ppm hardness 2ppm hardness Tonnes 1.0 1.5 2.0 2.5 3.0 3.5 Tonnes/Year Entering Boiler
  20. 20. SCALE / DEPOSIT CONTROL
  21. 21. Deposit Control <ul><li>Correct Pre-Treatment of Feed Water </li></ul><ul><li>Hardness Precipitation. </li></ul><ul><ul><li>ppted as CO 3 -2 or PO 4 -3 in presence of alkali. </li></ul></ul><ul><ul><li>Add sludge conditioners-polymers . </li></ul></ul><ul><li>Metal Oxides </li></ul><ul><ul><li>Dispersed with phosphonate + polymer. </li></ul></ul><ul><li>Silica </li></ul><ul><ul><li>Mainly present as Silicic acid H 2 SiO 3 </li></ul></ul><ul><ul><li>Decomposes above pH 9.4 into ions </li></ul></ul><ul><ul><li>Treatment </li></ul></ul><ul><ul><ul><li>pH>9.4 </li></ul></ul></ul><ul><ul><ul><li>Keep below limits specified </li></ul></ul></ul>
  22. 22. pH and PO 4 Concentration Below curve all alkalinity in the form of phosphate Above curve Free caustic present PO 4 - conc in ppm 10 30 20 40 50 60 70 pH 9.2 9.4 9.6 9.8 10.8 10.0 10.6 10.2 10.4 80 90
  23. 23. CORROSION CONTROL
  24. 24. Corrosion <ul><li>Presence of Oxygen, causing ferric oxide rust ,Fe2O3 </li></ul><ul><li>Fe +2H2O ---> Fe(OH)2 + H2 </li></ul><ul><li>Under favourable conditions oxide reduces to magnetite,Fe3O4,a very thin protective adherent film/layer 3Fe(OH)2 ---> Fe3O4 + 2H2O + H2 </li></ul><ul><li>Magnetite film is most stable between pH 10.5 - 11.5 </li></ul>
  25. 25. Corrosion Control <ul><li>Removal of oxygen *Mechanical Deaeration *Scavenging by chemicals </li></ul><ul><li>Neutralising carbon dioxide </li></ul>
  26. 26. Mechanical Deaeration <ul><li>Steam or Vacuum is used </li></ul><ul><li>Design to remove gases depends on: - Solubility of gases - Partial pressures - Operating temperatures </li></ul><ul><li>Technique employed : - To reduce partial pressure - Continuously extract evolved gases </li></ul>*
  27. 27. Vacuum Deaerator
  28. 28. Oxygen Scavenger Reactions <ul><li>Hydrazine </li></ul><ul><li>N 2 H 4 + O 2 ----------> N 2 + 2H 2 O </li></ul><ul><li>Sulphite </li></ul><ul><li>2Na 2 SO 3 + O 2 ---------->2Na 2 SO 4 </li></ul><ul><li>Diethylhydroxylamine (DEHA) </li></ul><ul><li>C 2 H 5 </li></ul><ul><li>NOH + [O] --> 2CH 3 COOH + 2N 2 + H 2 O </li></ul><ul><li>C 2 H 5 </li></ul>
  29. 29. Sulphite <ul><li>Limitations: </li></ul><ul><li>Adds to boiler water TDS </li></ul><ul><li>Reaction slower at low temp </li></ul><ul><li>At max temp/press (540 0 F /950 psig) </li></ul><ul><li>Na2SO 4 + H2O---> NaOH + H2SO3 </li></ul><ul><li>H2SO3-------> H2O + SO2 </li></ul><ul><li>It can undergo auto-oxidation/reduction </li></ul><ul><li>4Na2SO3------>3Na2SO4 + Na2S </li></ul><ul><li>Both SO2 and Na2S are corrosive </li></ul>
  30. 30. Hydrazine <ul><li>Any Excess Hydrazine breaks down to give Ammonia </li></ul><ul><li>3N 2 H 4 ------> 4NH 3 + N 2 </li></ul><ul><li>Small amounts < 0.5 ppm useful to neutralise CO 2 </li></ul><ul><li>Metal Passivator </li></ul><ul><li>6Fe 2 O 3 + N 2 H 4 -----> 4Fe 3 O 4 + 2H 2 O + N 2 </li></ul><ul><li>Non-Volatile -----> Not available in return line </li></ul><ul><li>Carcinogenic </li></ul>
  31. 31. Di-Ethyl-Hydroxyl-Amine DEHA <ul><li>Non-Toxic </li></ul><ul><li>LD 50 values---> 2190 mg/kg </li></ul><ul><li>(RATS, ORAL) </li></ul><ul><li>-------> 59 mg/kg for N 2 H 4 </li></ul><ul><li>Volatile : Available in return condensate line </li></ul><ul><li>Does not impart any solids to Boiler Drum Water </li></ul><ul><li>1.24 ppm DEHA  1 ppm O 2 </li></ul><ul><li>Forms stronger magnetite film </li></ul>
  32. 32. Reaction Rates Of Oxygen Scavengers At 70 0 F And pH 8.5 10 20 2.0 4.0 6.0 8.0 10.0 DEHA Catalysed Hydrazine Hydrazine Catalysed Sulphite D.O. ppm Catalysed DEHA Sulphite Contact Time In Minutes
  33. 33. Reaction rates of oxygen scavengers at 70 0 F& pH 11 1.0 2.0 3.0 2.0 4.0 6.0 8.0 10.0 Catalysed Hydrazine Catalysed DEHA Catalysed Sulphite Time Minutes D.O.,ppm
  34. 34. Ammonia Generated By DEHA and Hydrazine 100 200 300 400 500 0.2 0.4 0.6 0.8 1.0 DEHA Hydrazine Temperature ( 0 F) ppm NH 3 Generated per ppm Product
  35. 35. Ability Of Catalysed Hydrazine to reduce ferric iron to ferrous 0.1 0.2 0.3 0.4 0.5 0.6 2.0 4.0- 6.0 8.0 10.0 Catalysed Hydrazine Uncatalysed Hydrazine Catalysed Sodium Sulphite Hydrazine Concn in Feed Water (ppm ) Iron reduced from ferric to ferrous
  36. 36. Tannins <ul><li>Vegetable Tannins--Absorb O 2 in alkaline Condition </li></ul><ul><li>Tannins form metal complexes & act as corrosion inhibitors </li></ul><ul><li>Decompose at high temp. Used in low press. boilers </li></ul><ul><li>useful at low temp. ,for protecting feedline </li></ul>
  37. 37. Carbon dioxide Corrosion <ul><li>Carbon dioxide is present both in free & combined form </li></ul><ul><li>CO2 + H2O <---> H2CO3 ( H2O.CO2 ) . - + H2CO3 <--->HCO3 + H (pK=4.2 ) . -2 + HCO3 <---> CO3 + H (pK=8.3) </li></ul><ul><li>Free CO2 is zero above pH 8.3 ,BFW is therefore neutralised to pH 8.5 ~ 9.0 </li></ul>
  38. 38. Carbon Dioxide Corrosion <ul><li>CO2 is released on heating in the drum </li></ul><ul><li>_ _2 </li></ul><ul><li>2HCO3 + Heat ----> CO3 + H2O +CO2 </li></ul><ul><li>_2 _ </li></ul><ul><li>CO3 + H2O + Heat ----> OH + CO2 </li></ul><ul><li>Fe + 2H2CO3 ----> Fe[HCO3]2 + H2 </li></ul><ul><li>Soluble </li></ul><ul><li>Fe(HCO3)2 Can Precipitate as FeO, Fe3O4, FeCO3 in presence of O2 in codensate line </li></ul>
  39. 39. Return Lines Corrosion <ul><li>When steam condenses O 2 & CO 2 dissolve and produce dil.carbonic acid containing O 2 </li></ul><ul><li>This codensate will corrode return system </li></ul><ul><li>O 2 causes pitting, while CO 2 will channel out as grooving </li></ul><ul><li>Corrosion products will deposit in traps & strainers, and may block narrow-bore returns </li></ul>
  40. 40. Return Line Corrosion Protection <ul><li>Pretreatment - De-alkalisation / . De-mineralisation * . Deaeration </li></ul><ul><li>Oxygen Scavenging (Volatile) - D.E.H.A </li></ul><ul><li>Use of Volatile Neutralising Amines to keep BFW & condensate pH > 8.5 </li></ul><ul><li>Filming Amines </li></ul><ul><li>*Softening Will not remove alkalinity & should be avoided </li></ul>
  41. 41. Volatile Oxygen Scavenging (V.O.S) <ul><li>DiEthylHydroxylAmine (D.E.H.A) </li></ul><ul><li>Volatile hence passed into steam (Distribution ratio 1.26). </li></ul><ul><li>Removes Oxygen directly from the condensate </li></ul><ul><li>Reduces corrosion and also promotes formation of an adherent magnetite film which gives additional corrosion protection. </li></ul>
  42. 42. Volatile Oxygen Scavenger (V.O.A) <ul><li>Some pH elevation may be attributed to DEHA </li></ul><ul><li>As a RLT DEHA should be dosed in combination with neutralising Amines. </li></ul>
  43. 43. Neutralising Amines <ul><li>Steam volatile Alkaline materials which prevent corrosion caused by carbon dioxide </li></ul><ul><li>Amine reacts with carbonic acid to form Amine Carbonates or Bicarbonates and fix CO 2 . Elevation of pH to above 8.5 minimises the corrosion rate </li></ul>
  44. 44. Neutralising Amines <ul><li>Distribution ratio </li></ul><ul><li>Concentration of Amine in vapour phase Concentration of Amine in liquid phase. </li></ul><ul><li>High D.R= High volatility - Protects Cold End </li></ul><ul><li>Low D.R. = Low Volatility - Protects Hot End </li></ul><ul><li>Single Neutralising Amines can be used but, more often blend of amines with differing Distribution Ratios is employed to maximise system protection. Neutralising Amines are also used in combination with V.O.S and with Filming Amines. </li></ul>
  45. 45. Neutralising Amines
  46. 46. Filming Amines <ul><li>Filming amines contain a cationic amine group & a long hydrocarbon chain (hydrophobic) </li></ul><ul><li>Form an impervious, Non-Wettable film on metal surfaces by attracting amine groups </li></ul><ul><li>Steam condenses as a film & insulates heat transfer surfaces. </li></ul><ul><li>With filming amines the hydrophobic film promotes condensation as droplets & increases heat transfer ( Very useful on a paper drying roller ) </li></ul>
  47. 47. Primary Amines <ul><li>Primary Amines form films which completely cover metal surface giving excellent corrosion protection ( Octadecylamine - 0.5 ~ 2.0 ppm ) </li></ul><ul><li>Insoluble - applied as an emulsion </li></ul><ul><li>Incompatible with other products - Separate Dosing system required. </li></ul>
  48. 48. Secondary Amines <ul><li>Secondary Amines form less efficient films. Should be used in conjunction with neutralising Amines (e.g. Blended products) </li></ul><ul><li>Compatible with other products - can use same Dosing system </li></ul>
  49. 49. Filming Amines <ul><li>Filming Amines dosed to maintain Film Integrity </li></ul><ul><li>Over Dosing can cause Blockages </li></ul><ul><li>Dosing must be carefully controlled especially when applied to a previously corroded system </li></ul><ul><li>Should be introduced on a gradual basis. </li></ul>
  50. 50. Silica Carryover <ul><li>Silica is present as silicic acid, Si(OH)4 </li></ul><ul><li>It dissociates in alkaline condition : . _ _ Si(OH)4 + OH ---> H2SiO3 + H2O </li></ul><ul><li>Volatile silicic acid gets converted to soluble silicate ion above pH 9.5 </li></ul><ul><li>As pressure increases ( B.P.Temp . Increases) Silica becomes more volatile,Silica content is therefore kept within limits as per boiler pressure </li></ul>
  51. 51. Silica in Boiler Water - Relationship with Pressure Boiler water pH > 10.3 Boiler water pH<9.0 Silica , ppm Maximum Silica Content in Boiler Water to keep silica < 0.02 ppm in steam 2500 2300 2100 1900 1700 1500 1300 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 Press.,psig
  52. 52. Caustic Embrittlement <ul><li>Under following conditions steel is subjected to intercrystalline cracking : </li></ul><ul><li>Boiler must be subject to high stress </li></ul><ul><li>Boiler water must contain free NaOH </li></ul><ul><li>Rivetted flanges & rolled-in tube ends are more prone </li></ul>
  53. 53. Inhibition Of Cracking <ul><li>For HP & MP boilers - use zero caustic / co-ordinated phosphate treatment (normally stress relieved tubes are used) </li></ul><ul><li>for LP boilers following chemicals may be used: *NaNO3 - keep NaNO3 / T.Alk as CaCO3 ratio above 0.4 *Na2SO4 - keep Na2SO4 / NaOH ratio above 2.5 </li></ul>
  54. 54. Priming <ul><li>Ejection of boiler water into the steam take-off </li></ul><ul><li>Reasons: *Too high drum water level *Operating boiler below design pressure *Operating at higher design capacity </li></ul><ul><li>Controlled by strictly adhering to operating conditions </li></ul>
  55. 55. Foaming <ul><li>Pure water does not foam & steam bubbles are large & burst quickly </li></ul><ul><li>Following causes foaming by altering surface tension- reduce bubble size: *High suspended solids *High alkalinity *High dissolved solids *Contamination of oils &other surfactant </li></ul><ul><li>0.1 - 0.5 ppm antifom(certain organic compounds) cause bubbles to coalse </li></ul>
  56. 56. Recommended Water Characterstics For Water Tube Boilers BS 2486 : 1978
  57. 57. Shell Boiler Operating Parameters All reserves are as ppm. Hardness and alkalinity reserves are expressesd as CaCO 3 . The operating caustic alkalinity is assumed to be half the maximum total alkalinity
  58. 58. Boiler Water Treatment Programming Calculations
  59. 59. Survey Data <ul><li>Raw water analysis </li></ul><ul><li>Pretreatment </li></ul><ul><li>Feed water analysis </li></ul><ul><li>Feed water Temperature </li></ul><ul><li>Steam output and input pressure </li></ul><ul><li>water consumption </li></ul><ul><li>Condensate Return </li></ul><ul><li>Steam Applications </li></ul>
  60. 60. Calculation steps <ul><li>!. Determine Feed water quality </li></ul><ul><li>2. Determine oxygen scavenger dose </li></ul><ul><li>3 . calculate the maximum permissible boiler </li></ul><ul><li>conc. </li></ul><ul><li>4. calculate Alkalinity demand </li></ul><ul><li>5. calculate phosphate requirement </li></ul><ul><li>6. calculate sludge conditioner dosage </li></ul><ul><li>7. calculate return line treatment requirement </li></ul><ul><li>8. Determine blow down rate </li></ul><ul><li>9. convert product dosage ppm to weight </li></ul><ul><li>10. calculate cost of programme </li></ul>
  61. 61. Determine Feed Water quality <ul><li>Condensate Return% = 1 - Feed water Cl . Makeup Cl </li></ul><ul><li>% Raw water usage = 100- Condensate . Return % </li></ul><ul><li>Feed water Quality= Make-up Quality x . % Make-up water used </li></ul><ul><li>(Assuming No Contamination of condensate has occurred) </li></ul>{ } x 100
  62. 62. Determine Oxygen Scavenger Dose <ul><li>Sulphite Requirement </li></ul><ul><li>[ Feed water O2(ppm) X 8 ] +Sulphite Reserve/C </li></ul><ul><li>Hydrazine Requirement </li></ul><ul><li>[Feed water O2(ppm) X 1 ] +Hydrazine Reserve/C </li></ul>
  63. 63. Feedwater Temp Dissolved oxygen <ul><li>100 212 </li></ul><ul><li>95 203 </li></ul><ul><li>90 194 </li></ul><ul><li>85 185 </li></ul><ul><li>80 176 </li></ul><ul><li>75 167 </li></ul><ul><li>70 158 </li></ul><ul><li>65 149 </li></ul><ul><li>60 140 </li></ul><ul><li>55 131 </li></ul><ul><li>50 122 </li></ul><ul><li>45 113 </li></ul><ul><li>40 104 </li></ul><ul><li>35 95 </li></ul><ul><li>30 86 </li></ul><ul><li>25 77 </li></ul><ul><li>20 68 </li></ul><ul><li>0 </li></ul><ul><li>0.8 </li></ul><ul><li>1.6 </li></ul><ul><li>2.2 </li></ul><ul><li>2.9 </li></ul><ul><li>3.4 </li></ul><ul><li>3.9 </li></ul><ul><li>4.3 </li></ul><ul><li>4.7 </li></ul><ul><li>5.2 </li></ul><ul><li>5.6 </li></ul><ul><li>6.1 </li></ul><ul><li>6.6 </li></ul><ul><li>7.1 </li></ul><ul><li>7.5 </li></ul><ul><li>8.1 </li></ul><ul><li>8.8 </li></ul>0 C Temp. 0 F D.O.ppm
  64. 64. Determine Maximum Permissible Boiler Concentrations <ul><li>C Max TDS = ________ TDS MAX LIMIT_________ </li></ul><ul><ul><li>TDS FEED + SULPHITE DOSED </li></ul></ul><ul><li>C Max ALKALINITY = ALKALINITY MAXIMUM </li></ul><ul><li>TOTAL ALK. FEED - A </li></ul><ul><li>A is the Bisulphite allowance . Some Indion products are Bisulphite based, check product application guidelines for allowance. </li></ul><ul><li>C Max SILICA = MAX ALLOWABLE BOILER SILICA ACTUAL SILICA IN FEED </li></ul><ul><li>. </li></ul>
  65. 65. Alkalinity Demand <ul><li>Alkalinity Demand = </li></ul><ul><li>{(FWAlk - FW TH - Bisulphite Allowance) x Cmax}- Alk Res </li></ul><ul><li>Alkalinity reserve is normally taken as 850 ppm for low pressure boilers </li></ul><ul><li>If demand is negative then no extra alkali is required </li></ul><ul><li>Dose 0.8 ppm Sodium Hydroxide per 1 ppm of Alkalinity demand </li></ul>
  66. 66. Determination of Phosphate Requirement <ul><li>Assuming a product is 100% phosphate as PO 4 then dosage is given by </li></ul><ul><li>0.63 ppm product per 1 ppm CaH + 30/C max </li></ul>
  67. 67. Checking Sludge conditioner dosage <ul><li>Boiler Sludge Conditioner Dose = </li></ul><ul><li>Sludge Conditioner Conc ( 200ppm) COC X Product Factor </li></ul><ul><li>Typical Sludge conditioner levels are minimum 200 ppm for normal operations and minimum 300 ppm for on-line cleans </li></ul>
  68. 68. Calculate Return Line treatment requirement <ul><li>Dose of RLT Products is based on maintaining condensate pH  8.5 </li></ul><ul><li>This in turn depends on CO 2 generated in the boiler drum. </li></ul>
  69. 69. Determination Of Blowdown <ul><li>%Blowdown = 100 X S . T-S Calculated as %of Evaporation rate </li></ul><ul><li>% Blowdown = 100 . . C max Calculated as % of Feed water </li></ul><ul><li>Feedwater rate. </li></ul><ul><li>S - Feedwater TDS </li></ul><ul><li>T - Boiler water Maximum TDS </li></ul>
  70. 70. Conversion of dose rates to kg product per day <ul><li>Say, Water Usage (Evaporation + Blow Down) = F Tons/Day </li></ul><ul><li>Say, product dose = X ppm </li></ul><ul><li>Then, Product Required (Kg/Day) = F x X 1000 </li></ul>
  71. 71. Water Losses
  72. 72. Water Losses From Steam System <ul><li>Evaporation Of steam </li></ul><ul><li>Loss of Condensate </li></ul><ul><li>steam Boiler leaks </li></ul><ul><li>Blowdown </li></ul>
  73. 73. Uncontrolled water Losses <ul><li>Steam boilers </li></ul><ul><ul><li>Waste water </li></ul></ul><ul><ul><li>Waste fuel </li></ul></ul><ul><ul><li>Waste chemical </li></ul></ul><ul><ul><li>Lead to poor control of inhibitor reserves Lead to over running of pretreatment plant, Fuel, increased chemical consumption </li></ul></ul>

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