Lime Kiln Principles And Operations
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1. The document discusses principles and operations of lime kilns, including equipment like flames, chains, refractories, product coolers, and external mud dryers. 2. It provides details on improving lime kiln energy efficiency through factors like refractory systems, fuels, chain systems, fans and draft, and external drying of lime mud. 3. The document gives examples of calculating heat rate and how parameters like mud dry solids, refractory upgrades, fuel type and excess air can impact the heat rate.
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Lime Kiln Principles And Operations
- 1. 1 Lime Kiln Principles And OperationsLime Kiln Principles And Operations Terry N. AdamsTerry N. Adams Technical ConsultantTechnical Consultant Seattle WASeattle WA Slide 2 OutlineOutline •• Lime kiln equipmentLime kiln equipment –– flames, chains, refractoriesflames, chains, refractories –– product coolers, external mud dryersproduct coolers, external mud dryers •• Lime kiln energy efficiencyLime kiln energy efficiency •• Alternative fuels for lime kilnsAlternative fuels for lime kilns
- 2. 2 Slide 3 Exterior Of A Lime Reburning KilnExterior Of A Lime Reburning Kiln BurnerBurner Flue gasFlue gas to the ID fanto the ID fan Reburn limeReburn lime dischargedischarge LimeLime mudmud slurryslurry Slide 4 Interior Of A Lime Reburning KilnInterior Of A Lime Reburning Kiln DamDam FlameFlame RefractoryRefractory LiftersLifters ChainsChains
- 3. 3 Slide 5 Rotary Kiln Flame ShapesRotary Kiln Flame Shapes Long lazyLong lazy flameflame Short bushyShort bushy flameflame CompactCompact mediummedium-- length flamelength flame Slide 6 Rotary Kiln Chain SystemsRotary Kiln Chain Systems LowLow--densitydensity curtain chaincurtain chain HighHigh--densitydensity curtain chaincurtain chain GarlandGarland chainchain
- 4. 4 Slide 7 Lime Kiln Chain SystemsLime Kiln Chain Systems Slide 8 Rotary Kiln Refractory SystemsRotary Kiln Refractory Systems SingleSingle--Brick SystemBrick System TwoTwo--Brick SystemBrick System Refractory bricks Refractory bricks Insulating bricks Steel ShellSteel Shell
- 5. 5 Slide 9 Refractory WastageRefractory Wastage •• Most refractory damage due to wastageMost refractory damage due to wastage –– Smooth,Smooth, ““bird bathbird bath”” refractory thinningrefractory thinning •• Due to high temperature chemical attackDue to high temperature chemical attack •• Protect refractory with a coating of limeProtect refractory with a coating of lime •• Operate kiln for lower refractory face tempOperate kiln for lower refractory face temp –– Low primary air flow, avoid flame impingementLow primary air flow, avoid flame impingement –– ColdCold--end excess Oend excess O22 > 1> 1½½%% Slide 10 Refractory Damage PhotosRefractory Damage Photos Refractory Wastage Refractory Collapse
- 6. 6 Slide 11 Lifters And Discharge DamsLifters And Discharge Dams Lifters Cold end of kiln Lifters Lime bed Hot end of kilnDam Discharge Dam Slide 12 Rotary Kiln Product CoolersRotary Kiln Product Coolers Satellite Product CoolersSatellite Product Coolers InducedInduced secondary airsecondary air Reburned limeReburned lime
- 7. 7 Slide 13 External Lime Mud DryingExternal Lime Mud Drying Electrostatic precipitator PrecipitatorPrecipitator catchcatch Kiln CycloneCyclone GasGas Mud screwMud screw Slide 14 Fans, Draft, And OFans, Draft, And O22 •• PA fan only for flame shapingPA fan only for flame shaping •• ID fan is main air moving fanID fan is main air moving fan –– Use ID fan to control OUse ID fan to control O22 –– Often limits production capacityOften limits production capacity –– Wet scrubber is main flow restrictionWet scrubber is main flow restriction
- 8. 8 Slide 15 Lime Kiln Heat RateLime Kiln Heat Rate •• Heat rate is a measure of energy efficiencyHeat rate is a measure of energy efficiency –– Units are MM Btu/ton CaO or GJ/Units are MM Btu/ton CaO or GJ/tonnetonne CaOCaO –– Often stated as MM Btu/tonOften stated as MM Btu/ton ““productproduct”” •• Typical rangeTypical range –– 5 to 9 MM Btu/ton CaO5 to 9 MM Btu/ton CaO –– 5.8 to 10.5 GJ/5.8 to 10.5 GJ/tonnetonne CaOCaO –– Lower is betterLower is better Slide 16 Lime Kiln Energy Balance ComponentsLime Kiln Energy Balance Components •• DryingDrying •• Calcining : CaCOCalcining : CaCO33 + heat+ heat CaO + COCaO + CO22 •• LossesLosses –– Heat loss through shellHeat loss through shell –– Heat loss in hot lime productHeat loss in hot lime product –– Heat loss with gas and dust exiting at cold endHeat loss with gas and dust exiting at cold end •• A portion of fuel higher heating value is unavailableA portion of fuel higher heating value is unavailable –– HHV is measured and reportedHHV is measured and reported –– Only Lower Heating Value (LHV) is actually availableOnly Lower Heating Value (LHV) is actually available
- 9. 9 Slide 17 Example for Kiln Heat RateExample for Kiln Heat Rate KILN PARAMETERS Fuel Nat Gas Production rate 250 TPD Mud dry solids 78% Kiln exit O2 3% Lime availability 85% Dust loss 18% Product temp 600°F Cold end gas temp 600°F Shell Heat Loss 11.4 MM Btu/hr Slide 18 Lime Kiln Heat RateLime Kiln Heat Rate •• Overall Heat Rate = 8.4 MM Btu/ton CaOOverall Heat Rate = 8.4 MM Btu/ton CaO Contribution Heat rate Fraction Remedy Calcining reaction 2.82 34% No change possible Heat to evap water 1.75 21% Increase mud dry solids Heat in exit gas 1.50 18% Decrease exit gas temp Shell heat loss 1.10 13% Insulating refractory LHV/HHV loss 0.82 10% Change fuel Heat in product 0.29 3% Product coolers Heat in dust 0.11 1% Improve chain system
- 10. 10 Slide 19 Caution With Heat Rate CalculationCaution With Heat Rate Calculation •• Gives instantaneous valueGives instantaneous value –– DoesnDoesn’’t include down time, upsetst include down time, upsets •• Good to assess where improvements neededGood to assess where improvements needed •• Some changes affect more than one parameterSome changes affect more than one parameter –– Refractory changes shell loss & exit tempRefractory changes shell loss & exit temp –– Mud solids affects evaporation loss and exit tempMud solids affects evaporation loss and exit temp –– Fuel changes LHV/HHV, exit gas temp, and dust lossFuel changes LHV/HHV, exit gas temp, and dust loss Slide 20 Impact of Mud Dry Solids on Heat RateImpact of Mud Dry Solids on Heat Rate 0 1 2 3 4 5 6 7 8 60 65 70 75 80 85 90 Lime Mud Dry Solids, % HeatRate,GJ/tonneCaO Mill data
- 11. 11 Slide 21 Major Heat Rate ImprovementsMajor Heat Rate Improvements KILN PARAMETERS Base Refractory Fuel Type Chains Fuel Nat Gas Nat Gas Fuel Oil Nat Gas Production rate, TPD 250 250 250 250 Mud dry solids 78% 78% 78% 78% Kiln exit O2 3% 3% 3% 3% Lime availability 85% 85% 85% 85% Dust loss 18% 12% 18% 18% Product temp, °F 600 600 600 600 Cold end gas temp, °F 600 475 500 525 Shell Heat Loss, MM Btu/hr 11.4 6.3 11.4 11.4 Heat Rate, MM Btu/ton 8.4 7.0 7.4 8.0 Change -17% -11% -4% Slide 22 Minor Heat Rate ImprovementsMinor Heat Rate Improvements KILN PARAMETERS Base Excess air Dust Inerts Fuel Nat Gas Nat Gas Nat Gas Nat Gas Production rate, TPD 250 250 250 250 Mud dry solids 78% 78% 78% 78% Kiln exit O2 3% 2% 3% 3% Lime availability 85% 85% 85% 92% Dust loss 18% 18% 12% 18% Product temp, °F 600 600 600 600 Cold end gas temp, °F 600 575 600 600 Shell Heat Loss, MM Btu/hr 11.4 11.4 11.4 11.4 Heat Rate, MM Btu/ton 8.4 8.1 8.2 8.2 Change -3% -3% -2%
- 12. 12 Slide 23 Common Lime Reburning Kiln FuelsCommon Lime Reburning Kiln Fuels •• Nat gas and fuel oil are most commonNat gas and fuel oil are most common –– Fuel oil is more efficient, gives higher capacityFuel oil is more efficient, gives higher capacity •• Petroleum cokePetroleum coke –– Many applications, low costMany applications, low cost –– Sulfur and metals can be highSulfur and metals can be high –– Thermal NOx can be highThermal NOx can be high –– Improves heat rateImproves heat rate Slide 24 Other Solid/Liquid Kiln FuelsOther Solid/Liquid Kiln Fuels •• Wood and bark powderWood and bark powder –– NPEs can be highNPEs can be high –– Lime purge & makeup needed to control NPEsLime purge & makeup needed to control NPEs •• LigninLignin –– Sulfur can be highSulfur can be high •• Pyrolysis oilsPyrolysis oils –– Not currently used, pH &Not currently used, pH & μμ possible issuespossible issues
- 13. 13 Slide 25 Gasification FuelsGasification Fuels •• Coal, wood and other fuels can be gasifiedCoal, wood and other fuels can be gasified •• FuelFuel--gas can be used to fire kilngas can be used to fire kiln –– Similar to natural gasSimilar to natural gas –– Lower inert level, well established technologyLower inert level, well established technology –– OOnn--line availability ~ 85%line availability ~ 85% –– Wet gasifier feedstocksWet gasifier feedstocks deratederate kilnkiln –– Burner and chains must be designed for fuelBurner and chains must be designed for fuel--gasgas Slide 26 Fuels From the Pulp MillFuels From the Pulp Mill •• Turpentine or methanol liquidTurpentine or methanol liquid •• Stripper OffStripper Off--Gas (SOG)Gas (SOG) •• NonNon--condensable gas (NCG)condensable gas (NCG) –– Can be wet and sulfur level can be highCan be wet and sulfur level can be high •• Tall oil and tall oil pitchTall oil and tall oil pitch –– Can fire 100% tall oil, similar to fuel oilCan fire 100% tall oil, similar to fuel oil –– 16,000 Btu/lb and16,000 Btu/lb and low sulfurlow sulfur
- 14. 14 Slide 27 How To Improve Lime Kiln PerformanceHow To Improve Lime Kiln Performance •• Improve refractory systemImprove refractory system –– thicker bricks, twothicker bricks, two--brick systembrick system •• Switch fuelsSwitch fuels •• Improve chain systemImprove chain system –– amount for heat transfer, layout for dustamount for heat transfer, layout for dust •• Improve ID fan/scrubberImprove ID fan/scrubber •• Dry mud externallyDry mud externally