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Lime Kiln Principles And OperationsLime Kiln Principles And Operations
•• 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
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Slide 15Lime 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/ton Often 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 16Lime Kiln Energy Balance ComponentsLime Kiln Energy Balance Components
–– 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
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Slide 17Example for Kiln Heat RateExample for Kiln Heat Rate
KILN PARAMETERSFuel Nat GasProduction rate 250 TPDMud dry solids 78%Kiln exit O2 3%Lime availability 85%Dust loss 18%Product temp 600°FCold end gas temp 600°FShell Heat Loss 11.4 MM Btu/hr
Slide 18Lime 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 RemedyCalcining reaction 2.82 34% No change possibleHeat to evap water 1.75 21% Increase mud dry solidsHeat in exit gas 1.50 18% Decrease exit gas tempShell heat loss 1.10 13% Insulating refractoryLHV/HHV loss 0.82 10% Change fuelHeat in product 0.29 3% Product coolersHeat in dust 0.11 1% Improve chain system
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Slide 19Caution 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 20Impact of Mud Dry Solids on Heat RateImpact of Mud Dry Solids on Heat Rate