Essentials for a Sound Boiler Water Treatment Program. Presented by Steve Connor & Debbie Bloom April 23, 2014

Transcription

1 Essentials for a Sound Boiler Water Treatment Program Presented by Steve Connor & Debbie Bloom April 23, 2014

2 Today s Topics Chemical Aspects The Necessity of Water Treatment Mechanical Aspects Essentials for a Sound Boiler Water Treatment Program What needs to be removed from the water? Most Economical Long-Term Approach Tolerances are Based on Pressure & Temperature 2

3 Boiler Water Treatment 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. 3

4 Boiler Water Treatment Steam Systems Hot Water Systems 4

5 Necessity of Boiler Water Treatment Scaling Porous Deposition Corrosion Efficiency Loss Life of the Asset Steam Quality % moisture Steam Purity Silica Sodium ion 5

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 Waterside Corrosion Waterside Scale 6

7 Tolerances are Based on Pressure & Temperature Water Constituent Tolerance: operating psig Oxygen Feed Water Iron & copper Total Hardness ph Non-Volatile TOC (Total Organic Carbon) Oily Matter Boiler Water Silica Total Alkalinity Free OH Alkalinity Specific Conductance ASME Guidelines: Broken down by feed water and boiler water, and then by firetube and watertube boilers. 7

8 Most Economical Long-Term Approach Mechanical Chemical 8

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 Most Economical Long-Term Approach Mechanical Chemical 10

11 Mechanical Removal Removes Calcium Magnesium Water Softener (Resin Tanks) Brine Tank 11

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 Cation Exchange Process Service Cycle Na+ ions are exchanged for Ca++ and Mg++ ions Hard Water Soft Water Ca++ & Mg++ Na+ 13

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 Mechanical Process Removes Dealkalizer Bicarbonate & Carbonate Alkalinity Sulfate Nitrate 16

17 Anion Exchange Process Service Cycle Chloride (Cl-) ions are exchanged for Carbonates of Alkalinity (-) Alkaline Water Dealkalized Water 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 Waterside Corrosion Waterside Scale 18

19 Oxygen Corrosion 50 F 86 F 122 F RULE OF THUMB Almost 2 times more corrosive at 122 o F than at 86 o F Dissolved Oxygen is ~ 10 times more corrosive than CO 2 Reference Chart Courtesy of: 19

20 Mechanical Removal Deaeration Removes Oxygen Free Carbon Dioxide Heat Agitate Liberate 20

21 Mechanical Removal Column Spray Tray 21

22 Packed Column Deaerator Venting Out Water In Steam In Column Packing Rings Boiler Feed Tank 22

23 23 Spray Deaerator

24 Tray Deaerator Water Vent Steam Trays 24

25 Mechanical Removal Automatic blowdown system senses anything that adds conductivity Calcium Magnesium Sodium Silica Sulfate Chloride Iron Conductivity Sensor 25

26 TDS Control with Blowdown Heat Recovery Separator? Heat exchanger To drain To drain Water inlet

27 Most Economical Long-Term Approach Mechanical Chemical 27

28 Treatment for Steam Boiler Systems 28

29 Guidelines ASME ABMA OEM guidelines Water treatment companies 29

30 ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired - Feedwater Table 2 Drum Operating Pressure psig (MPa) Dissolved Oxygen ppm (mg/l) O 2 measured before chemical scavenger addition (0-2.07) <0.007 Total iron ppm (mg/l) Fe 0.1 Total copper ppm (mg/l) Cu 0.05 Total hardness ppm (mg/l) as CaCO o C Chemicals for preboiler system protection Nonvolatile TOC ppm (mg/l) C <1 Oily matter ppm (mg/l) <1 NS 30

31 ASME Suggested Water Chemistry Limits Industrial Watertube, High Duty, Primary Fuel-Fired Boiler Water Table 2 Drum Operating Pressure psig (MPa) Silica ppm (mg/l) SiO (0-2.07) 150 Total Alkalinity ppm (mg/l) as CaCO 3 <1000 Free OH Alkalinity ppm (mg/l) as CaCO 3 Specific Conductance µmhos/cm 25 o C <7000 NS 31

32 Improperly Controlled Water Chemistry Scale and Deposits Boiler Corrosion Carryover 32

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 Boiler Treatment for Scale / Deposition - Precipitating Programs 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 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 Boiler Treatment for Scale / Deposition - Solubilizing Programs 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 37

38 Approximate ph Value at 25 o C/77 o F Mild Steel Corrosion Relative Corrosion Attack 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

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 Treatment for Hot Water Boiler Systems 40

41 Hot Water Systems Hot water boilers are used for many applications from 140 o F to over 400 o F 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: CaCO 3, MgSiO 3 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 <300 o F and oxygen <1-2 ppm Maintain Nitrite levels at 1000 ppm or higher Azole 10 ppm 2. Combination Molybdate/Nitrite/Azole program Temperature <300 o F 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 >250 o F) 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

47 Monitoring and Control 47

48 Boiler Cycles and % Blowdown Steam 966,700 0 ppm TDS Boiler Feedwater 1,000, ppm TDS = 100 lb/day Solids Boiler 30 Cycles = 3000 ppm TDS Boiler Blowdown Based on Chemistry blowdown ion feedwater ion = cycles 30 = = 3.33% BD = Heat 30 Cycles % of Feedwater 33, ppm = 100 lb/day Solids

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 And Can Save Water and Energy % of Feedwater Going to the Blowdown 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% 5 to 10 cycles saves 10% FW Cycles of Concentration to 40 cycles saves 2.5% FW

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

53 Midwestern University Case History

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 Feedwater Product (ppm) 55

56 Scale Inhibitor vs. Steam Flow Feedwater Product (ppm) Product Pump Out % 56

57 Automation Maintains Desired Feedwater Reductant Levels to Minimize Corrosion Corrosivity (mv) % Sulfite Pump Output Time (2 weeks) 57

58 Energy and Water Savings ($/yr) 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 58

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 Tom Leunig Product Manager, Packaged Water Systems Debbie Bloom Principal Consultant, Technical Expertise Center