Essentials for a sound boiler water treatment program
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El agua de Calderas es la base del proceso de Generacion de Vapor. Esta presentacion de Cleaver Brooks y Nalco empresas de clase mundial nos dan los consejos precisos para la conservacion de la estructura de la caldera por corrosion acida y depositos de solidos minerales.Elige el tratamineto recomendable.
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Essentials for a sound boiler water treatment program
- 1. Essentials for a Sound Boiler Water Treatment Program Presented by Steve Connor & Debbie Bloom April 23, 2014
- 2. Mechanical Aspects What needs to be removed from the water? Most Economical Long-Term Approach Tolerances are Based on Pressure & Temperature Chemical Aspects The Necessity of Water Treatment Today’s Topics 2 Essentials for a Sound Boiler Water Treatment Program
- 3. Boiler Water Treatment 3 Water is an excellent heat transfer medium, but it must be properly treated in both steam and hot water systems or serious problems will ensue, robbing energy and reducing the life of the asset.
- 4. Boiler Water Treatment Steam Systems Hot Water Systems 4
- 5. Necessity of Boiler Water Treatment 5 • Scaling • Porous Deposition • Corrosion • Efficiency Loss • Life of the Asset • Steam Quality • % moisture • Steam Purity • Silica • Sodium ion
- 6. What Needs To Be Removed Dissolved Minerals • Hard Scale Formers • Calcium • Magnesium • TDS • Calcium • Magnesium • Sulfate • Sodium • Silica • Chloride • Alkalinity • Dissolved Gas • Free Oxygen • Free Carbon Dioxide 6 Waterside Scale Waterside Corrosion
- 7. Tolerances are Based on Pressure & Temperature 7 Feed Water Boiler Water Oxygen Silica Iron & copper Total Alkalinity Total Hardness Free OH Alkalinity pH Specific Conductance Non-Volatile TOC (Total Organic Carbon) Oily Matter ASME Guidelines: Broken down by feed water and boiler water, and then by firetube and watertube boilers. Water Constituent Tolerance: 0-300 operating psig
- 8. Mechanical Chemical 8 Most Economical Long-Term Approach
- 9. Most Economical Long-Term Approach Chemical Treatment Only • Phosphate Treatment • Polymers • Hybrid Phosphonate/Polymer • Sulfite Treatment • Precise Control & Monitoring • Extensive Blowdown • Wastes Water, Chemicals & BTU’s 9
- 10. Mechanical Chemical 10 Most Economical Long-Term Approach
- 11. Mechanical Removal Removes • Calcium • Magnesium 11 Water Softener (Resin Tanks) Brine Tank
- 12. Cation Resin Bead Composition Chemically engineered polystyrene beads (resin) with an affinity for positive ions. Will exchange weaker positive ions for stronger positive ions • Sodium (Na+) for Calcium (Ca++) and Magnesium (Mg++) 12
- 13. Hard Water Soft Water Cation Exchange Process 13 Service Cycle • Na+ ions are exchanged for Ca++ and Mg++ ions Ca++ & Mg++ Na+
- 14. Cation Exchange Process Exhausted Condition • Cation beads can be used in the service cycle until they are saturated with Ca++ and Mg++ • Requires regeneration Ca++ or Mg++ 14
- 15. Cation Exchange Process Regeneration or Brining • Sodium Chloride (NaCl) solution (brine) is passed through the resin to drive off the Ca++ and Mg++ ions to be rinsed away with the Cl- ions Resin bead will be replenished with Na+ Ca++ or Mg++ Na+ Cl- 15
- 16. Removes • Bicarbonate & Carbonate Alkalinity • Sulfate • Nitrate Dealkalizer 16 Mechanical Process
- 17. Alkaline Water Dealkalized Water Anion Exchange Process Service Cycle • Chloride (Cl-) ions are exchanged for Carbonates of Alkalinity (-) Alkalinity Cl - 17
- 18. What Needs To Be Removed Dissolved Minerals • Hard Scale Formers • Calcium • Magnesium • TDS • Calcium • Magnesium • Sulfate • Sodium • Silica • Chloride • Alkalinity • Dissolved Gas • Oxygen 18 Waterside Scale Waterside Corrosion
- 19. Oxygen Corrosion 50 F 86 F 122 F 19 RULE OF THUMB • Almost 2 times more corrosive at 122oF than at 86oF • Dissolved Oxygen is ~ 10 times more corrosive than CO2 Reference Chart Courtesy of: http://www.engineeringtoolbox.com/oxygen-steel-pipe
- 20. Mechanical Removal 20 Deaeration Removes • Oxygen • Free Carbon Dioxide Heat Agitate Liberate
- 21. Mechanical Removal 21 Column Spray Tray
- 22. Packed Column Deaerator 22 Water In Venting Out Column Packing Rings Steam In Boiler Feed Tank
- 25. Mechanical Removal Automatic blowdown system senses anything that adds conductivity • Calcium • Magnesium • Sodium • Silica • Sulfate • Chloride • Iron 25 Conductivity Sensor
- 26. TDS Control with Blowdown Heat Recovery Water inletTo drain To drain Separator Heat exchanger?
- 27. Mechanical Chemical 27 Most Economical Long-Term Approach
- 28. 28 Treatment for Steam Boiler Systems
- 29. Guidelines • ASME • ABMA • OEM guidelines • Water treatment companies 29
- 30. ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired - Feedwater Drum Operating Pressure psig (MPa) 0 - 300 (0 - 2.07) Dissolved Oxygen ppm (mg/L) O2 – measured before chemical scavenger addition <0.007 Total iron ppm (mg/L) Fe ≤0.1 Total copper ppm (mg/L) Cu ≤0.05 Total hardness ppm (mg/L) as CaCO3 ≤0.5 pH @ 25oC 8.3-10.5 Chemicals for preboiler system protection NS Nonvolatile TOC ppm (mg/L) C <1 Oily matter ppm (mg/L) <1 30 Table 2
- 31. ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired – Boiler Water Drum Operating Pressure psig (MPa) 0 - 300 (0 - 2.07) Silica ppm (mg/L) SiO2 ≤150 Total Alkalinity ppm (mg/L) as CaCO3 <1000 Free OH Alkalinity ppm (mg/L) as CaCO3 NS Specific Conductance µmhos/cm (µS/cm) @ 25oC <7000 31 Table 2
- 32. Scale and Deposits Boiler Corrosion 32 Carryover Improperly Controlled Water Chemistry
- 33. Scale and Deposits Form in High Heat Flux Areas Where Steam is Generated Effect of Scale & Deposits: • Calcium, magnesium, and iron inhibit heat transfer • Raise tube metal temperature • Blisters/overheat – mostly water tube boilers • Efficiency loss – firetube boilers • Iron also causes under deposit corrosion 33
- 34. We Can Minimize Scale and Deposition and Impact Boiler Cycles of Concentration by… • Minimizing feedwater contaminants entering boiler • Using best treatment program for your system • Accurately controlling blowdown rate 34
- 35. • Phosphate based • Very old, reliable chemistry • Dosed based on hardness • Can be used with very high feedwater hardness • Requires higher blowdown rates • Amount of phosphate scale formed depends on hardness present Boiler Treatment for Scale / Deposition - Precipitating Programs 35
- 36. Threshold Scale / Deposition Inhibitor • Good fit for low-pressure boilers • Able to handle moderate to severe hardness upsets • Hybrid program that combines phosphonate (HEDP) and polymer • Functions by distorting the crystal structure and preventing scale formation 36
- 37. • All-polymer or chelant programs • Dosed based on hardness • Conditions sludge and solubilizes hardness • Clean boiler internals when fed at recommended dosage • Reduces blowdown requirements Boiler Treatment for Scale / Deposition - Solubilizing Programs 37
- 38. Mild Steel Corrosion • Mild steel used in boiler systems because of mechanical strength, high thermal conductivity and low cost • Corrosion minimized over pH range of 8.5 to 12.5 RelativeCorrosionAttack Approximate pH Value at 25oC/77oF 38
- 39. Chemical Oxygen Scavenger • Chemical removes trace oxygen left by deaerator/FW tank • Sulfite is typically scavenger of choice in low-pressure systems • Non-sulfite scavengers exist • Fed to deaerator/FW tank • Performance traditionally determined by scavenger residuals • Oxygen is not the only corrodent in the FW system 39
- 40. 40 Treatment for Hot Water Boiler Systems
- 41. Hot Water Systems • Hot water boilers are used for many applications from 140oF to over 400oF • Requirements to maintain all systems are similar 41
- 42. Corrosion in Hot Water Systems Water loss/make-up should not be more than 0.1 to 0.5% of system volume monthly (1.2 to 6% system volume yearly) • Special emphasis on finding and fixing leaks • As water make-up increases and water temperatures increase, oxygen pitting becomes the most likely cause of corrosion-related failures 42
- 43. Scale / Deposition in Hot Water Systems • Softened make-up is recommended for all hot water boiler applications • Primary species of concern: CaCO3, MgSiO3 • Scale potential is a function of: • Temperature: higher is worse • Holding Time: lower is worse since constant influx of make-up water may increase the scaling load on the system • Water Chemistry: pH and dissolved ion levels • Dispersant in Program 43
- 44. Chemical Programs 1. Nitrite/Azole program • Temperature <300oF and oxygen <1-2 ppm • Maintain Nitrite levels at 1000 ppm or higher • Azole ≥10 ppm 2. Combination Molybdate/Nitrite/Azole program • Temperature <300oF and oxygen <1-2 ppm • At least 1000 ppm Nitrite • Molybdate greater than 100 ppm • Azole ≥10 ppm 3. Molybdate/Azole program • Molybdate at 300 ppm or higher (500 ppm if temperature is >250oF) • Molybdate requires approximately 1 ppm oxygen to provide adequate corrosion protection 44
- 45. Sulfates & Chlorides • Corrosion rates sensitive to increased chlorides and sulfates • Both degrade nitrite and molybdate performance • Increase nitrite and molybdate dosage for chloride and sulfate levels >50 ppm 45
- 46. Sometimes Sulfite or Alternate Oxygen Scavengers are Used • Sulfite is not compatible with nitrite • Minimize water loss/make-up • Deoxygenate make-up if rates are high • Sulfite plus oxygen results in sulfate • Sulfate levels above 300 ppm increase yellow metal corrosion • Some non-sulfite scavengers can add ammonia • Ammonia is known to increase yellow metal corrosion 46
- 48. Boiler Steam Boiler Feedwater Boiler Blowdown Heat 966,700 lb/Day @ 0 ppm TDS 1,000,000 lb/Day @ 100 ppm TDS = 100 lb/Day Solids 3.33% of Feedwater 33,300 lb/Day @ 3000 ppm = 100 lb/Day Solids Based on Chemistry Cycles30 100 3000 ionfeedwater ionblowdown == 30 Cycles = 3000 ppm TDS BD3.33% 30 100 cycles 100 == Boiler Cycles and % Blowdown 48
- 49. Determining Boiler Cycles Conductivity • Good to use if feedwater conductivity is relatively high • Limited use if feedwater conductivity is low and contains ammonia or amines Trace chemicals can aid cycles determination • Inert fluorescent dye • Non-volatile • Non-precipitating • Non-reactive Other Measurements • Silica • Chlorides • Sodium 49
- 50. Blowdown Control Minimizes Chemistry Swings in the Boiler With Without Time 50
- 51. 0% 5% 10% 15% 20% 25% 30% 35% 40% 45% Cycles of Concentration %ofFeedwater GoingtotheBlowdown 1 10 1005 50 20 to 40 cycles saves 2.5% FW 5 to 10 cycles saves 10% FW 20 40 … And Can Save Water and Energy 51
- 52. Blowdown Control is Only Half the Issue • Perform chemical tests relative to treatment • Adjust chemical feed to maintain dosage • Maintain boiler parameters to prevent over-cycling • Testing can be automated with feedwater control 52
- 54. Background • 3 water tube boilers with economizers, 175-psig • Natural gas fired • Softened make-up water • Steam supplies absorption chillers, heat and reheat for campus, hospital, and laboratory buildings • Polymer fed relative to feedwater flow/steam load • Sulfite fed to maintain desired boiler water residual • Boiler blowdown controlled manually based on conductivity 54
- 55. Before / After Improvement in Scale Inhibitor Feed 55 FeedwaterProduct(ppm)
- 56. Scale Inhibitor vs. Steam Flow 56 FeedwaterProduct(ppm) ProductPumpOut%
- 57. Automation Maintains Desired Feedwater Reductant Levels to Minimize Corrosion 57 %SulfitePumpOutput Time (2 weeks) Corrosivity(mV)
- 58. Energy and Water Savings ($/yr) 58 Before Installation After Installation Difference Blowdown Energy Cost $38,147 $22,577 $15,570 Blowdown Sewer Cost $11,114 $6,578 $4,536 Make-up Water Cost $10,002 $3,198 $6,804 Subtotal (Costs) $59,263 $32,353 $26,910 Net Savings or Costs $/yr $26,910
- 59. Today’s Take-A-Ways • Proper water treatment is a combination of mechanical and chemical remediation • Has significant impact on efficiency and reliability attainment • Chemical treatment varies based on watertube, firetube, pressure/temperature. • Corrosion accelerates with temperature • Increasing cycles of concentration saves fuel dollars • Heat from continuous blow down for TDS control can be recouped • Hot water systems need to be chemically treated too • Monitoring and control is ESSENTIAL 59
- 60. Contact Us Debbie Bloom Principal Consultant, Technical Expertise Center dbloom@nalco.com 630-305-2445 60 Tom Leunig Product Manager, Packaged Water Systems tleunig@cleaverbrooks.com 414-577-3197