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Heat optimisation pradeep kumar

This document discusses heat optimization in cement production processes. It identifies major areas of heat loss, including through shell radiation, unused heat in exit gases and cooler exit air. The goal of design engineers is to minimize heat losses and optimize consumption. Key factors that influence heat losses are discussed for the preheater, calciner, kiln and cooler systems. Different burner and flame types are also examined in relation to combustion efficiency and heat distribution in the kiln. Heat balances are provided as examples to account for all heat inputs and outputs in the clinker production process.

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Optimisation of heat consumption
Heat loss from shell radiation Heat loss in product Heat loss in Preheater Exit gas Cooler exit air Where does the heat go ?
For perpetual pyro process in a kiln the heat required is only heat of clinker mineral formation, ie., 380 - 400 Kcal/kg clinker. 280 – 350 Kcal/kg clinker is wasted which is about 40 - 45 % . The dream of design engineer is to make heat losses to minimum and how to optimize the heat consumption.
The preheater heat losses Pre heater gas temperature Design of cyclones No of stages Dust loss Inlet / out let velocity ratio Location of meal distribution boxes Preheater( Surface) heat losses through radiation Calciner gas retention time Combustion effciency Coal residue & raw meal residue Location of firing nozzles
Different flames Normal flame Flame with low Secondary air temp Distorted nozzle Flame –poor hood geometry Or distorted nozzle Flame at the center Flame downward Flame upward
Flame length Long flame, unstable coating, High back end temp Low shell temperature Short intense divergent flame Good for burning Low back end temperature Poor refractory life, high Shell temperature Convergent flame Good for burning Good for refractory Stable coating Low shell temperature
The Ideal Flame hot ! short ! stable ! T"long" flame "short" flame Complete combustion: - CO = 0 - SO2, NOX ↓ Homogeneous: - no temperature peaks - no local CO on the clinker bed Longer flame increase the back end temperature resulting in Heat loss at kiln exit and hot meal clogging
Burning zone, Flame-profile • Low momentum burner • High momentum burner rings12m (~3xD) burning zone Rotaflam ~16 m Flame !☺! rings ~23 m Flame 17m (~4xD) burning zone ! ! Burner Operation
Duo Flex burner M.A.S burner, unitherm
Pyrojet Greco
Lafarge Multi Channel burner
Pillard Roto Flame
Cement kiln flame types Straight flame – essentially external recirculation Type-1 flame Weak internal recirculation & external recirculation Type-2 flame Strong internal recirculation & external recirculation
Objectives “It is desirable to operate the kiln at the lowest fuel consumption. This must be consistent with the highest practical output at an acceptable market quality.”
WHY TO DO IT • To get a detailed view of the kiln line performance • Evaluate exact data for heat consumption, production,... • Basis for comparison – impact of investment or modifications carried out – comparison to other plants • Detect weak points - Action Plan • Detect optimization potential • Check of sensors, weigh feeder,...
Σ massin = Σ massout MASS BALANCE Σ heatin = Σ heatout HEAT BALANCE “Energy cannot be created or destroyed but may be converted from one form to another” Energy in = Energy out
Boundary selection • Any boundary shape can be chosen. • Every stream that crosses the envelope must be taken into account. • The boundary line is chosen so that the boundary points are: – useful for the balance goals – easily accessible for reliable measurements
KilnKiln P/HP/H CoolerCooler Boundary selection
Dust Exists System Dust Does Not Exit Boundary Kiln System Dust Kiln Feed Measuring point (t/h) Kiln System Dust Kiln Feed Clinker Clinker Boundary selection and streams
Kiln System Primary air Clinker Fuel cooling air False air Kiln feed Kiln exit gases Water spray Exit dust Return dust S heatin = S heatout Wall losses Heat balance Cooler exhaust gas Bypass gas and dust
Heat Transfer MechanismsHeat Transfer Mechanisms • Conduction • Convection • Radiation 200°C 50°C heat
ConductionConduction • Transfer of heat from the hotter to colder part of a body • By direct molecular contact Furnace wall Hot gas 1200°C Cold air 25°C L Q kA T T L h c = −Q
ConvectionConvection • Natural convection: – fluid moving from difference of density due to different temperatures • Forced convection: – fluid is moved by the action of an external device hot air hot aircold air cold air natural convection forced convection ( )Q hA T Tw f= −
RadiationRadiation • Energy transferred by electro-magnetic radiation ( )Q A T T= −σ 1 4 2 4 2000°C 50°C Q
HEAT TRANSFER • Radiant heat transfer • Free convection (occurs by natural thermal draft, at low wind velocities) • Forced convection (occurs at high wind velocities) Convection Radiation Air
Chemical Reaction • Endothermic reaction - heat is consumed – Calcium Carbonate breaks down to CaO (lime) and CO2 when heated – it takes heat in Þ the reaction is endothermic. • Exothermic reaction - heat is released – CaO (lime) reacts with Silica and the cement minerals are formed – the process gives out heat Þ the chemical reactions is exothermic.
Two types of heat Latent Heat Linked to modification by chemical reaction, change in state, change in structure Sensible Heat Absorbed or released by a substance
The heat to remove from a material to cool it down to the reference temperature (usually 0ºC). Q = M × Cp (T) × (T - T0) M = specific mass Cp (T) = specific heat of a material at temperature T T = temperature of M Sensible heat
Qf = mf × ( LHVf + Cpmean f (Tf) × Tf ) Qf : heat from fuel (kcal/h) mf : fuel flow rate (kg/h) LHVf : fuel low heat value (kcal/kg) Cpmean f : mean specific heat of fuel (kcal/kg.ºC) Tf : fuel temperature (ºC) OR h = m • CV h : heat from fuel (kcal/kg clk) m : specific fuel consumption (kg/kg clk) CV : calorific value of fuel (kcal/kg fuel) Heat from fuel
Incomplete combustion • The kiln exit gases might contain some un burnt gases (CO, H2, CH4) • The combustion heat from those fuels must be included as a out stream Qic = mCO ×LHVCO + mH2 × LHVH2 + mCH4 ×LHVCH4 The heat loss through the gas can be calculated to: h = m•(CO%•12640+H2%•10800+ CH4% • 35 840) m = specific gas quantity (Nm3/kg clk)
Heat of Reaction • Heat of reaction is the difference between the heat absorbed in decarbonating the limestone and the heat released in forming the clinker minerals • It should be noted that raw meal chemistry affects the reaction heat, the heat absorbed by the process gets bigger as the LSF of the materials rises • 420 kcals/kg clinker is used if little else is known
Clinker theoretical heat of formation • The heat required to form clinker from dry raw mix • ZKG formula (German formula): Qt = 4.11 Al2O3 + 6.47 MgO + 7.64 CaO - 5.11 SiO2 - 0.60 Fe2O3 • If no clinker analysis: assume Qt = 420 kcal/kg ck • Must be added to the clinker heat content as latent heat or as a separate output heat stream. CaF2 addition reduce the heat of reaction considerably but It has the other implications.
Heat of formation • Heat of dehydration of clay (endothermic) • Heat of decarbonation of CaCO3 + MgCO3 (endothermic) • Heat of formation of clinker (exothermic!) • General assumption for the three: 1750 kJ / kg clk 0r • 400 Kcal/kg cl
Qw : heat loss through wall (W) atot : total heat transfer coefficient (W/m².C) A : shell area (m²) T : shell temperature (ºC) Ta : ambient temperature (ºC) ( )Q A T Tw tot a= −α Heat loss through kiln shell
0 5 10 15 20 25 30 35 40 45 50 55 60 65 100 200 300 400 500 600 T - T° (C) W/M2C v = 14 m/s wind 13 12 11 10 9 8 7 6 5 4 3 2 1 v = 0 m/s (free convection) SS = 0.9 Ambient T° - 20°C Global heat transfer coefficient Radiation and convection heat transfer coeffcient ( Total) Radiation and Convection
Shell Losses vs Shell Temperatures Wind Velocity 0 m/s Wind Velocity 1.5 m/S SHELL TEMPERATURE ºC Kcal/(m2.min) 25 0 22 5 20 0 17 5 15 0 12 5 10 50 100 150 200 250 300 350 400
Radiation losses = 4*10 -8 * ( T4- Ta4) Kcal/h m2 Convection losses = 80.33*((T+Ta)/2) -0.724*(T-Ta)1.333 Convection losses = 28.03*((T+Ta)/2) -0.351*V 0.805(T-Ta) *D -0.195*(T –Ta) If wind velocity is > 3 m/s Surface heat losses
0 2 4 6 8 1680 1690 1700 1710 1720 1730 700 750 800 850 900 950 1000 Exit Oxygen % kcal/kgwet kcals/kg(dry) WET DRY Kiln Heat Consumption Effect of Kiln Exit Oxygen
How is cooling accomplishedHow is cooling accomplished Heat transfer by radiation and convectionHeat moves to clinker edge by conduction Air flows over clinker cooling surface
Heat Transfer in ClinkerHeat Transfer in Clinker • Convection - Surface to Air • Conduction - Inside to Surface • Heat transfer is driven by temperature difference • Takes place at the clinker surface • To maximize it: – Increase the air/material contact time with: • Deeper bed ( ⇒ more power) • Slower air flow (⇒ larger cooler)
Heat Exchanger TypesHeat Exchanger Types CounterflowParallel flow Co-current Air Material Air Material Cross-flow Material Air material air T material air T material T
Old conventional grate plates create sand blasting effect or fluidization This creates poor heat exchange Modern cooler plates flow resistance branch off the air , creates less fluidization , better heat exchange Cross flow Counter current Mechanical flow regulator
Heat Exchange Between Clinker and AirHeat Exchange Between Clinker and Air Temperature Bedthickness clinker air Fixed bed Fluidized bed Air in Air out Clinker Air in Air out Clinker Temperature Bedthickness clinker air More efficient recovery with fixed bed
General Truths (All Coolers)General Truths (All Coolers) 1. The hotter the inlet temperature the hotter the clinker outlet temperature. 2. The hotter the cooling air temperature the hotter the clinker outlet temperature. 3. The longer the air/material contact time the cooler the clinker outlet temperature.
SYSTEM DATA COLLECTION • Process • Type of kiln • Nominal capacity • Supplier • Fuel and firing system • Type of burner nozzle • Dust reintroduction system • Dimensions of main equipment • Data on fans, drives, etc.
OPERATING DATA • Various operating data (rpm, kW, temperature and pressure profiles along kiln system, grate speed, undergrate pressures, etc.) • Electric power readings (before / after test) • Chemical analysis of raw meal, dust(s) and clinker, LSF, SR, AR, etc.
Kiln Gas outlet Wall losses misc Clinker formation Clinker heat Cooler vent Sec.air Tert.air fuel Sec.air misc Tertiary air Kiln Heat balance
Cooler heat losses Optimised air flow & air distribution & sealing Clinker nodules Finer fraction & big balls causes bad heat exchange Radiation losses from walls Exit air temperature
Measurement Plan • Duration of an audit ? • What to measure? How to measure? – Material balance – Gas flows – Heat Balance • Frequency of sampling and measurements? • Which analyses have to be carried out ? • Which further data are to be collected ?
• All referred to 1 kg clinker Production = .... t/h • Reference temperature = 0°C Specific • Ambient temperature = ...°C Heat cons. = .... kJ/kg clk Specification Heat (kg/kg clk), Temp. (Nm3/kg clk) (kW etc.) °C (kJ/kg clk) (%) Fuel combustion - primary firing - - secondary firing - Burnable matter in kiln feed - Raw meal: sensible heat Fuel: sensible heat Primary air: sensible heat Cooler air: sensible heat - Total of inputs - 100% INPUT DATA SUMMARY
Specification Temp. Heat (kg/kg clk), (Nm3/kg clk) °C (kJ/kg clk) (%) (kW etc.) Heat of formation Water evaporation: - kiln feed - water spray (s) Exhaust gas: - sensible heat - dust sensible heat - dust CaO-loss - unburnt gases (CO, etc) Cooler: - waste air sensible heat - middle air sensible heat - clinker exit sensible heat Bypass losses: - sensible heat - dust sensible heat - dust CaO-loss - unburnt gases (CO, etc) Radiation and Convection: - Preheater - Rotary kiln - Cooler - Tert air duct Rest (difference) Total of outputs 100% OUTPUT DATA SUMMARY
1. INPUT from sensible heat FUEL from combustion RAW MEAL from sensible heat from sensible heat of water COMBUSTION AIR from sensible heat of all the air supplied (prim. sec.) Total input 2. OUTPUT Heat of formation Evaporation of water from raw meal Exhaust gas sensible heat Dust sensible heat Incomplete combustion (CO) Clinker exit temperature Cooler exhaust gases Losses due to radiation and convection Water cooling (Recupol inlet chute) Difference Total output kJ/kg clk 25 5560 25 71 67 5750 1750 2370 754 25 — 59 100 540 — 152 5750 % 0.4 96.7 0.4 0.2 1.2 100 30.4 41.2 13.1 0.4 — 1.0 1.7 9.4 — 2.6 100 Wet Process kJ/kg clk 15 3343 30 17 20 3425 1750 506 314 21 — 50 276 452 42 14 3425 % 0.4 97.6 0.9 0.5 0.6 100 51.1 14.8 9.2 0.6 — 1.5 8.1 13.2 1.2 0.4 100 Semi-Dry (Lepol) kJ/kg clk 13 3150 54 — 6 3223 1750 13 636 18 — 63 423 297 — 23 3223 % 0.4 97.6 1.7 — 0.2 100 54.3 0.4 19.7 0.6 — 2.0 13.1 9.2 — 0.7 100 Dry Preheater (4-Stage) HEAT BALANCE EXAMPLES
Cooler Balance Tertiary air Vent air 0,65 Nm³/kgck 1,14 Nm³/kgck Secondary air 719°C 293°C 0,27 Nm³/kgck Coal mill Raw mill 1029°C 0,00 Nm³/kgck 0,00 Nm³/kgck Clinker 95.600 1465°C Grate surface 52,20 m² Standard load 44,0 t/d/m² Cooling air Clinker 2,07 Nm³/kgck 95.600 4°C 107°C
Elements of Mass BalanceElements of Mass Balance Tertiary air Vent air Comp 1 Comp 2 Comp 3 Comp 4 Comp 5 Comp 6 Comp 7 Comp 8 Secondary air clinker clinker mCK1 mCK2 mSA mTA mCM mVA mF1 mF2 mF3 mF4 mF5 mF6 mF7 mF8 Coal mill air Raw mill air mRM
Elements of Heat BalanceElements of Heat Balance Tertiary air Vent air Comp 1 Comp 2 Comp 3 Comp 4 Comp 5 Comp 6 Comp 7 Comp 8 Secondar y air clinker clinker HCK1 HCK2 HSA HTA HCM HVA HF1 HF2 HF3 HF4 HF5 HF6 HF7 HF8 Wall losses HWL Coal mill air Raw mill air HRM
Mass BalanceMass Balance In Out clinker (mCK1) clinker (mCK2) cooling air (SmFi) secondary air (mSA) tertiary air (mTA) coal mill air (mCM) raw mill air (mRM) vent air (mVA) In = Out secondary air flow: calculated by difference should be validated against a kiln balance
Heat BalanceHeat Balance In Out clinker (HCK1) clinker (HCK2) cooling air (SHFi) secondary air (HSA) tertiary air (HTA) coal mill air (HCM) raw mill air (HRM) vent air (HVA) wall losses (HWL) In = Out secondary air heat : calculated by difference good to validate it against kiln heat balance secondary air temperature: calculated from secondary air heat
Temperature Stratification of air above Clinker BedTemperature Stratification of air above Clinker Bed Secondary & Tertiary air Air to coal mill Vent air 1400°C 300°C 250°C 200°C 175°C 125°C 100°C 1000°C 700° C 500°C 400°C 150°C
Measuring Actual Bed DepthMeasuring Actual Bed Depth floor
Cooling EfficiencyCooling Efficiency clinkerininputheat clinkerbylostheat =η inck outck inck outckinck h h 1 h hh −= − =η Qualifies the cooling of the clinker but not the clinker cooler. More cooling is possible with more air but that does not improve the cooler efficiency. An efficient cooler would give same cooling with less air.
Cooler lossCooler loss cooler loss = all heat not recovered by combustion air (secondary or tertiary) cooler loss = heat content of clinker leaving cooler (hck out) + heat content of vent air + heat content of coal mill air + heat content of raw mill air + wall heat losses Often a specification in supplier process performance guarantee
Operating results cooler Coolerefficiency[%] Combustion air Nm³/kgKl. 0,75 0,8 0,85 0,9 0,95 60 65 70 75 80 85 Standard - cooler New - competition REPOL RS New-type coolers Old-type coolers
Heat saving 1.Run the plant stable , continously with consistent production 2.Minimise the false air ingress by giving efficient seals 3.Optimise the flame as per our requirement 4.Minimise the variation in airflow, meal flow and fuel flow rate 5.Reduce the radiation losses by giving proper insulation 6.Optimise the cooler operation and cooler efficiency 7.Optimise the cyclone efficiency in the preheater 8.Minimise the variation in chemistry of raw meal and ash in fuel by efficient blending. 9. Addition of mineralisers reduce the heat of reaction by 20 – 30 Kcal/ kg.cl after thorough study on the rheological properties of cement. CaF2, Dolomite and slag are good mineralisers. Set point Natural and acceptable variation high variation Not acceptable Variation is a devil in any process
Satellite cooler rotary cooler grate cooler Recuperation zone Cooling zone static grate direct aeration chamber aerationchamber aeration Grate cooler With stationary inlet Walking floor pyrofloor Cross bar cooler Im provem ent in technology Rotary disc cooler MMD cross bar IKN Poly track Pyro floor ? Pyro step
1.31Kg/kg cl0.1Dust in tertiary duct7 0.180.16%1Excess air in kiln12 -0.1-0.17Deg C10Temperature of primary air 11 0.220.22%1Excess air in calciner13 -0.25-0.17Kcal/kgcoal100Heat content in coal9 1615.7Kg/kgcl0.1False air through hood14 1918.7Kg / kg cl0.1False air through inlet seal 15 0.680.66%1Amount of primary air10 0.470.45%1Moisture in coal8 1.30.12Kg/kg cl0.1Dust from kiln6 1.11.11Kcal/kgcl1Heat of reaction5 -73-74.37%1Carbon in rawmeal4 5.65.6%1Hydrate water3 1.81.8%1Feed moisture2 -0.5- 0.57Deg c10Feed temperature1 Heat, kcal/kgcl ILC Heat, kcal/kgcl SLC unitbyA change ins.no Heat calculation
1.11.1Kg / kg cl0.1Raw meal27 1.2Kg/ kg cl0.1False air cyclone C122 19.1Kg/ kg cl0.1False air cyclone C526 1.21.1Kcal/kg cl1standard Cooler loss28 7.2Kg/ kg cl0.1False air cyclone C324 Cyclone efficiency29 - 0.1%1Cyclone- K129 12.4Kg/ kg cl0.1False air cyclone C425 3.4Kg/ kg cl0.1False air cyclone C223 1918.8Kg/ kg cl0.1False air cyclone K521 1210.9Kg/ kg cl0.1False air cyclone K420 6.95.8Kg/ kg cl0.1False air cyclone K319 3.32.6Kg/ kg cl0.1False air cyclone K218 1.10.82Kg/ kg cl0.1False air cyclone K117 1615.7Kg / kg cl0.1False air calciner16 Heat, kcal/kgcl ILC Heat, kcal/kg cl SLC unitbyA change ins.no
-0.26%1Cyclone- K533 -0.38-0.28%1Cyclone- C436 -23-21.8Change from 4 to 5 stage41 1.61.6%1By pass of kiln gases40 -11-10.0Change from 5 to 6 stages 42 0.13%1Recarbonation, KS38 43 44 0.510.37%1Recarbonation, CS39 0.82-0.74%1Cyclone- C537 -0.34- 0.24%1Cyclone- C335 -0.27-0.18%1Cyclone- C234 -0.21-0.14%1Cyclone- C134 -0.12%1Cyclone- K432 -0.10%1Cyclone- K331 -0.08%1Cyclone- K230 Heat, kcal/kgcl ILC Heat, kcal/kg cl SLC unitbyA change ins.no
Heat loss from shell radiation Insulation effect of refractories optimised coating ,300mm thk Flame Shape & flame length Ring formation shoots the gas velocity takes the heat farther into the kiln, increases the back end temperature Exit gas velocity at kiln inlet = 10 m/s v=15 -16 m/s Steady Feed rate With less Fluctuation Of calcination Heat losses from kiln Parasite air ( ingress of false air entry) at inlet , outlet hood& preheater. Primary air & coal transport air are all false entry. Fluctuations In process Hood take off V=5 m/s Well controlled air flow Fuel flow
4 –stage preheater 5 –stage preheater 6 –stage preheater Conversion of 4 stage preheater To 5 stage preheater saves 28 Kcal/kg cl Conversion of 5 stage preheater To 6 stage preheater saves 14 Kcal/kg cl calciner
769.34.40Total Output 6.0Radiation Loss from Cooler 20.2Radiation Loss from Kiln 37.1Radiation Loss from Preheater 4.8Heat of Evaporation of Moisture 20.91110.1881.0Heat Through Clinker 91.62930.2521.2Heat Through Cooler Vent 410.0Heat of Clinkerisation 7.93360.2360.1Heat of PH Exit Dust 170.83360.2472.1Heat of PH Exit Gases Kcal/kg clinkerdeg CKcal/kg degCkg/kg clinker HeatTemperatureSp.heat capacityMass flow Heat Output relative to 0 deg C 769.34.40Total Input 412.3Heat of Coal Combustion in Calciner 295.7Heat of Coal Combustion in Kiln 1.1560.2380.1Sensible heat of Coal and Conveying Air 2.8600.2870.2Sensible heat of Coal 1.3460.2380.1Sensible Heat of PH Leak Air 27.1460.2472.4Sensible heat of Cooling air 8.1Heat through combustibles in raw meal 21.0600.2121.6Sensible heat of Kiln Feed kcal/kg Clinkerdeg CKcal/kg degCkg/kg clinker HeatTemperatureSp.heat capacityMass flow Heat Input relative to 0 deg C Specific heat Consumption= Total heat output – Total sensible heat 769.3-61.3 = 709 Kcal/kg cl
433.63.43Total Heat output 6.0Radiation 20.90.1881111.00Clinker 91.60.2522931.24Excess air 6.70.2369490.03Tertiary air dust 176.30.2689490.69Tertiary air 5.00.2410490.02Secondary air dust 127.10.27110490.45Secondary air kcal/kg clinkerkcal/kg oCdeg Ckg/kg cl HeatSpecific heatTemperatureMass flow reference: 0 deg CHEAT OUTPUT 433.63.43Total Heat Input 4.6Fan energy 27.10.247462.38Cooling air 19.10.26414500.05Dust 382.80.26414501.00Clinker kcal/kg clinkerkcal/kg oCdeg Ckg/kg cl HeatSpecific heatTemperatureMass flow reference: 0 deg CHEAT INPUT NORMAL OPERATING CONDITION
Automation further helps to run the plant more stable by reducing the meal, fuel flow and air flow. Running the kiln continuously with consistent production is the best way to reduce the fuel and power bills. For consistent production we must have short , Convergent and intense flame, less chemistry variation of raw meal , less variation in ash content of fuel and stable cooler operation. Automation further helps to run
Thanks for your attention

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Heat optimisation pradeep kumar

  • 1.
  • 2.
    Heat loss fromshell radiation Heat loss in product Heat loss in Preheater Exit gas Cooler exit air Where does the heat go ?
  • 3.
    For perpetual pyroprocess in a kiln the heat required is only heat of clinker mineral formation, ie., 380 - 400 Kcal/kg clinker. 280 – 350 Kcal/kg clinker is wasted which is about 40 - 45 % . The dream of design engineer is to make heat losses to minimum and how to optimize the heat consumption.
  • 4.
    The preheater heatlosses Pre heater gas temperature Design of cyclones No of stages Dust loss Inlet / out let velocity ratio Location of meal distribution boxes Preheater( Surface) heat losses through radiation Calciner gas retention time Combustion effciency Coal residue & raw meal residue Location of firing nozzles
  • 5.
    Different flames Normal flame Flamewith low Secondary air temp Distorted nozzle Flame –poor hood geometry Or distorted nozzle Flame at the center Flame downward Flame upward
  • 6.
    Flame length Long flame,unstable coating, High back end temp Low shell temperature Short intense divergent flame Good for burning Low back end temperature Poor refractory life, high Shell temperature Convergent flame Good for burning Good for refractory Stable coating Low shell temperature
  • 7.
    The Ideal Flame hot! short ! stable ! T"long" flame "short" flame Complete combustion: - CO = 0 - SO2, NOX ↓ Homogeneous: - no temperature peaks - no local CO on the clinker bed Longer flame increase the back end temperature resulting in Heat loss at kiln exit and hot meal clogging
  • 8.
    Burning zone, Flame-profile •Low momentum burner • High momentum burner rings12m (~3xD) burning zone Rotaflam ~16 m Flame !☺! rings ~23 m Flame 17m (~4xD) burning zone ! ! Burner Operation
  • 9.
    Duo Flex burner M.A.Sburner, unitherm
  • 10.
  • 11.
  • 12.
  • 13.
    Cement kiln flametypes Straight flame – essentially external recirculation Type-1 flame Weak internal recirculation & external recirculation Type-2 flame Strong internal recirculation & external recirculation
  • 15.
    Objectives “It is desirableto operate the kiln at the lowest fuel consumption. This must be consistent with the highest practical output at an acceptable market quality.”
  • 16.
    WHY TO DOIT • To get a detailed view of the kiln line performance • Evaluate exact data for heat consumption, production,... • Basis for comparison – impact of investment or modifications carried out – comparison to other plants • Detect weak points - Action Plan • Detect optimization potential • Check of sensors, weigh feeder,...
  • 17.
    Σ massin =Σ massout MASS BALANCE Σ heatin = Σ heatout HEAT BALANCE “Energy cannot be created or destroyed but may be converted from one form to another” Energy in = Energy out
  • 18.
    Boundary selection • Anyboundary shape can be chosen. • Every stream that crosses the envelope must be taken into account. • The boundary line is chosen so that the boundary points are: – useful for the balance goals – easily accessible for reliable measurements
  • 19.
  • 20.
    Dust Exists SystemDust Does Not Exit Boundary Kiln System Dust Kiln Feed Measuring point (t/h) Kiln System Dust Kiln Feed Clinker Clinker Boundary selection and streams
  • 21.
    Kiln System Primary air Clinker Fuel cooling air Falseair Kiln feed Kiln exit gases Water spray Exit dust Return dust S heatin = S heatout Wall losses Heat balance Cooler exhaust gas Bypass gas and dust
  • 22.
    Heat Transfer MechanismsHeatTransfer Mechanisms • Conduction • Convection • Radiation 200°C 50°C heat
  • 23.
    ConductionConduction • Transfer ofheat from the hotter to colder part of a body • By direct molecular contact Furnace wall Hot gas 1200°C Cold air 25°C L Q kA T T L h c = −Q
  • 24.
    ConvectionConvection • Natural convection: –fluid moving from difference of density due to different temperatures • Forced convection: – fluid is moved by the action of an external device hot air hot aircold air cold air natural convection forced convection ( )Q hA T Tw f= −
  • 25.
    RadiationRadiation • Energy transferredby electro-magnetic radiation ( )Q A T T= −σ 1 4 2 4 2000°C 50°C Q
  • 26.
    HEAT TRANSFER • Radiantheat transfer • Free convection (occurs by natural thermal draft, at low wind velocities) • Forced convection (occurs at high wind velocities) Convection Radiation Air
  • 27.
    Chemical Reaction • Endothermicreaction - heat is consumed – Calcium Carbonate breaks down to CaO (lime) and CO2 when heated – it takes heat in Þ the reaction is endothermic. • Exothermic reaction - heat is released – CaO (lime) reacts with Silica and the cement minerals are formed – the process gives out heat Þ the chemical reactions is exothermic.
  • 28.
    Two types ofheat Latent Heat Linked to modification by chemical reaction, change in state, change in structure Sensible Heat Absorbed or released by a substance
  • 29.
    The heat toremove from a material to cool it down to the reference temperature (usually 0ºC). Q = M × Cp (T) × (T - T0) M = specific mass Cp (T) = specific heat of a material at temperature T T = temperature of M Sensible heat
  • 30.
    Qf = mf× ( LHVf + Cpmean f (Tf) × Tf ) Qf : heat from fuel (kcal/h) mf : fuel flow rate (kg/h) LHVf : fuel low heat value (kcal/kg) Cpmean f : mean specific heat of fuel (kcal/kg.ºC) Tf : fuel temperature (ºC) OR h = m • CV h : heat from fuel (kcal/kg clk) m : specific fuel consumption (kg/kg clk) CV : calorific value of fuel (kcal/kg fuel) Heat from fuel
  • 31.
    Incomplete combustion • Thekiln exit gases might contain some un burnt gases (CO, H2, CH4) • The combustion heat from those fuels must be included as a out stream Qic = mCO ×LHVCO + mH2 × LHVH2 + mCH4 ×LHVCH4 The heat loss through the gas can be calculated to: h = m•(CO%•12640+H2%•10800+ CH4% • 35 840) m = specific gas quantity (Nm3/kg clk)
  • 32.
    Heat of Reaction •Heat of reaction is the difference between the heat absorbed in decarbonating the limestone and the heat released in forming the clinker minerals • It should be noted that raw meal chemistry affects the reaction heat, the heat absorbed by the process gets bigger as the LSF of the materials rises • 420 kcals/kg clinker is used if little else is known
  • 33.
    Clinker theoretical heatof formation • The heat required to form clinker from dry raw mix • ZKG formula (German formula): Qt = 4.11 Al2O3 + 6.47 MgO + 7.64 CaO - 5.11 SiO2 - 0.60 Fe2O3 • If no clinker analysis: assume Qt = 420 kcal/kg ck • Must be added to the clinker heat content as latent heat or as a separate output heat stream. CaF2 addition reduce the heat of reaction considerably but It has the other implications.
  • 34.
    Heat of formation •Heat of dehydration of clay (endothermic) • Heat of decarbonation of CaCO3 + MgCO3 (endothermic) • Heat of formation of clinker (exothermic!) • General assumption for the three: 1750 kJ / kg clk 0r • 400 Kcal/kg cl
  • 35.
    Qw : heatloss through wall (W) atot : total heat transfer coefficient (W/m².C) A : shell area (m²) T : shell temperature (ºC) Ta : ambient temperature (ºC) ( )Q A T Tw tot a= −α Heat loss through kiln shell
  • 36.
    0 5 10 15 20 25 30 35 40 45 50 55 60 65 100 200 300400 500 600 T - T° (C) W/M2C v = 14 m/s wind 13 12 11 10 9 8 7 6 5 4 3 2 1 v = 0 m/s (free convection) SS = 0.9 Ambient T° - 20°C Global heat transfer coefficient Radiation and convection heat transfer coeffcient ( Total) Radiation and Convection
  • 37.
    Shell Losses vsShell Temperatures Wind Velocity 0 m/s Wind Velocity 1.5 m/S SHELL TEMPERATURE ºC Kcal/(m2.min) 25 0 22 5 20 0 17 5 15 0 12 5 10 50 100 150 200 250 300 350 400
  • 38.
    Radiation losses =4*10 -8 * ( T4- Ta4) Kcal/h m2 Convection losses = 80.33*((T+Ta)/2) -0.724*(T-Ta)1.333 Convection losses = 28.03*((T+Ta)/2) -0.351*V 0.805(T-Ta) *D -0.195*(T –Ta) If wind velocity is > 3 m/s Surface heat losses
  • 39.
    0 2 46 8 1680 1690 1700 1710 1720 1730 700 750 800 850 900 950 1000 Exit Oxygen % kcal/kgwet kcals/kg(dry) WET DRY Kiln Heat Consumption Effect of Kiln Exit Oxygen
  • 40.
    How is coolingaccomplishedHow is cooling accomplished Heat transfer by radiation and convectionHeat moves to clinker edge by conduction Air flows over clinker cooling surface
  • 41.
    Heat Transfer inClinkerHeat Transfer in Clinker • Convection - Surface to Air • Conduction - Inside to Surface • Heat transfer is driven by temperature difference • Takes place at the clinker surface • To maximize it: – Increase the air/material contact time with: • Deeper bed ( ⇒ more power) • Slower air flow (⇒ larger cooler)
  • 42.
    Heat Exchanger TypesHeatExchanger Types CounterflowParallel flow Co-current Air Material Air Material Cross-flow Material Air material air T material air T material T
  • 43.
    Old conventional grateplates create sand blasting effect or fluidization This creates poor heat exchange Modern cooler plates flow resistance branch off the air , creates less fluidization , better heat exchange Cross flow Counter current Mechanical flow regulator
  • 44.
    Heat Exchange BetweenClinker and AirHeat Exchange Between Clinker and Air Temperature Bedthickness clinker air Fixed bed Fluidized bed Air in Air out Clinker Air in Air out Clinker Temperature Bedthickness clinker air More efficient recovery with fixed bed
  • 45.
    General Truths (AllCoolers)General Truths (All Coolers) 1. The hotter the inlet temperature the hotter the clinker outlet temperature. 2. The hotter the cooling air temperature the hotter the clinker outlet temperature. 3. The longer the air/material contact time the cooler the clinker outlet temperature.
  • 46.
    SYSTEM DATA COLLECTION •Process • Type of kiln • Nominal capacity • Supplier • Fuel and firing system • Type of burner nozzle • Dust reintroduction system • Dimensions of main equipment • Data on fans, drives, etc.
  • 47.
    OPERATING DATA • Variousoperating data (rpm, kW, temperature and pressure profiles along kiln system, grate speed, undergrate pressures, etc.) • Electric power readings (before / after test) • Chemical analysis of raw meal, dust(s) and clinker, LSF, SR, AR, etc.
  • 48.
    Kiln Gas outlet Wall losses misc Clinkerformation Clinker heat Cooler vent Sec.air Tert.air fuel Sec.air misc Tertiary air Kiln Heat balance
  • 49.
    Cooler heat losses Optimisedair flow & air distribution & sealing Clinker nodules Finer fraction & big balls causes bad heat exchange Radiation losses from walls Exit air temperature
  • 50.
    Measurement Plan • Durationof an audit ? • What to measure? How to measure? – Material balance – Gas flows – Heat Balance • Frequency of sampling and measurements? • Which analyses have to be carried out ? • Which further data are to be collected ?
  • 51.
    • All referredto 1 kg clinker Production = .... t/h • Reference temperature = 0°C Specific • Ambient temperature = ...°C Heat cons. = .... kJ/kg clk Specification Heat (kg/kg clk), Temp. (Nm3/kg clk) (kW etc.) °C (kJ/kg clk) (%) Fuel combustion - primary firing - - secondary firing - Burnable matter in kiln feed - Raw meal: sensible heat Fuel: sensible heat Primary air: sensible heat Cooler air: sensible heat - Total of inputs - 100% INPUT DATA SUMMARY
  • 52.
    Specification Temp. Heat (kg/kgclk), (Nm3/kg clk) °C (kJ/kg clk) (%) (kW etc.) Heat of formation Water evaporation: - kiln feed - water spray (s) Exhaust gas: - sensible heat - dust sensible heat - dust CaO-loss - unburnt gases (CO, etc) Cooler: - waste air sensible heat - middle air sensible heat - clinker exit sensible heat Bypass losses: - sensible heat - dust sensible heat - dust CaO-loss - unburnt gases (CO, etc) Radiation and Convection: - Preheater - Rotary kiln - Cooler - Tert air duct Rest (difference) Total of outputs 100% OUTPUT DATA SUMMARY
  • 53.
    1. INPUT fromsensible heat FUEL from combustion RAW MEAL from sensible heat from sensible heat of water COMBUSTION AIR from sensible heat of all the air supplied (prim. sec.) Total input 2. OUTPUT Heat of formation Evaporation of water from raw meal Exhaust gas sensible heat Dust sensible heat Incomplete combustion (CO) Clinker exit temperature Cooler exhaust gases Losses due to radiation and convection Water cooling (Recupol inlet chute) Difference Total output kJ/kg clk 25 5560 25 71 67 5750 1750 2370 754 25 — 59 100 540 — 152 5750 % 0.4 96.7 0.4 0.2 1.2 100 30.4 41.2 13.1 0.4 — 1.0 1.7 9.4 — 2.6 100 Wet Process kJ/kg clk 15 3343 30 17 20 3425 1750 506 314 21 — 50 276 452 42 14 3425 % 0.4 97.6 0.9 0.5 0.6 100 51.1 14.8 9.2 0.6 — 1.5 8.1 13.2 1.2 0.4 100 Semi-Dry (Lepol) kJ/kg clk 13 3150 54 — 6 3223 1750 13 636 18 — 63 423 297 — 23 3223 % 0.4 97.6 1.7 — 0.2 100 54.3 0.4 19.7 0.6 — 2.0 13.1 9.2 — 0.7 100 Dry Preheater (4-Stage) HEAT BALANCE EXAMPLES
  • 54.
    Cooler Balance Tertiary airVent air 0,65 Nm³/kgck 1,14 Nm³/kgck Secondary air 719°C 293°C 0,27 Nm³/kgck Coal mill Raw mill 1029°C 0,00 Nm³/kgck 0,00 Nm³/kgck Clinker 95.600 1465°C Grate surface 52,20 m² Standard load 44,0 t/d/m² Cooling air Clinker 2,07 Nm³/kgck 95.600 4°C 107°C
  • 55.
    Elements of MassBalanceElements of Mass Balance Tertiary air Vent air Comp 1 Comp 2 Comp 3 Comp 4 Comp 5 Comp 6 Comp 7 Comp 8 Secondary air clinker clinker mCK1 mCK2 mSA mTA mCM mVA mF1 mF2 mF3 mF4 mF5 mF6 mF7 mF8 Coal mill air Raw mill air mRM
  • 56.
    Elements of HeatBalanceElements of Heat Balance Tertiary air Vent air Comp 1 Comp 2 Comp 3 Comp 4 Comp 5 Comp 6 Comp 7 Comp 8 Secondar y air clinker clinker HCK1 HCK2 HSA HTA HCM HVA HF1 HF2 HF3 HF4 HF5 HF6 HF7 HF8 Wall losses HWL Coal mill air Raw mill air HRM
  • 57.
    Mass BalanceMass Balance InOut clinker (mCK1) clinker (mCK2) cooling air (SmFi) secondary air (mSA) tertiary air (mTA) coal mill air (mCM) raw mill air (mRM) vent air (mVA) In = Out secondary air flow: calculated by difference should be validated against a kiln balance
  • 58.
    Heat BalanceHeat Balance InOut clinker (HCK1) clinker (HCK2) cooling air (SHFi) secondary air (HSA) tertiary air (HTA) coal mill air (HCM) raw mill air (HRM) vent air (HVA) wall losses (HWL) In = Out secondary air heat : calculated by difference good to validate it against kiln heat balance secondary air temperature: calculated from secondary air heat
  • 59.
    Temperature Stratification ofair above Clinker BedTemperature Stratification of air above Clinker Bed Secondary & Tertiary air Air to coal mill Vent air 1400°C 300°C 250°C 200°C 175°C 125°C 100°C 1000°C 700° C 500°C 400°C 150°C
  • 60.
    Measuring Actual BedDepthMeasuring Actual Bed Depth floor
  • 61.
    Cooling EfficiencyCooling Efficiency clinkerininputheat clinkerbylostheat =η inck outck inck outckinck h h 1 h hh −= − =η Qualifiesthe cooling of the clinker but not the clinker cooler. More cooling is possible with more air but that does not improve the cooler efficiency. An efficient cooler would give same cooling with less air.
  • 62.
    Cooler lossCooler loss coolerloss = all heat not recovered by combustion air (secondary or tertiary) cooler loss = heat content of clinker leaving cooler (hck out) + heat content of vent air + heat content of coal mill air + heat content of raw mill air + wall heat losses Often a specification in supplier process performance guarantee
  • 63.
    Operating results cooler Coolerefficiency[%] Combustionair Nm³/kgKl. 0,75 0,8 0,85 0,9 0,95 60 65 70 75 80 85 Standard - cooler New - competition REPOL RS New-type coolers Old-type coolers
  • 64.
    Heat saving 1.Run theplant stable , continously with consistent production 2.Minimise the false air ingress by giving efficient seals 3.Optimise the flame as per our requirement 4.Minimise the variation in airflow, meal flow and fuel flow rate 5.Reduce the radiation losses by giving proper insulation 6.Optimise the cooler operation and cooler efficiency 7.Optimise the cyclone efficiency in the preheater 8.Minimise the variation in chemistry of raw meal and ash in fuel by efficient blending. 9. Addition of mineralisers reduce the heat of reaction by 20 – 30 Kcal/ kg.cl after thorough study on the rheological properties of cement. CaF2, Dolomite and slag are good mineralisers. Set point Natural and acceptable variation high variation Not acceptable Variation is a devil in any process
  • 67.
    Satellite cooler rotary cooler gratecooler Recuperation zone Cooling zone static grate direct aeration chamber aerationchamber aeration Grate cooler With stationary inlet Walking floor pyrofloor Cross bar cooler Im provem ent in technology Rotary disc cooler MMD cross bar IKN Poly track Pyro floor ? Pyro step
  • 68.
    1.31Kg/kg cl0.1Dust intertiary duct7 0.180.16%1Excess air in kiln12 -0.1-0.17Deg C10Temperature of primary air 11 0.220.22%1Excess air in calciner13 -0.25-0.17Kcal/kgcoal100Heat content in coal9 1615.7Kg/kgcl0.1False air through hood14 1918.7Kg / kg cl0.1False air through inlet seal 15 0.680.66%1Amount of primary air10 0.470.45%1Moisture in coal8 1.30.12Kg/kg cl0.1Dust from kiln6 1.11.11Kcal/kgcl1Heat of reaction5 -73-74.37%1Carbon in rawmeal4 5.65.6%1Hydrate water3 1.81.8%1Feed moisture2 -0.5- 0.57Deg c10Feed temperature1 Heat, kcal/kgcl ILC Heat, kcal/kgcl SLC unitbyA change ins.no Heat calculation
  • 69.
    1.11.1Kg / kgcl0.1Raw meal27 1.2Kg/ kg cl0.1False air cyclone C122 19.1Kg/ kg cl0.1False air cyclone C526 1.21.1Kcal/kg cl1standard Cooler loss28 7.2Kg/ kg cl0.1False air cyclone C324 Cyclone efficiency29 - 0.1%1Cyclone- K129 12.4Kg/ kg cl0.1False air cyclone C425 3.4Kg/ kg cl0.1False air cyclone C223 1918.8Kg/ kg cl0.1False air cyclone K521 1210.9Kg/ kg cl0.1False air cyclone K420 6.95.8Kg/ kg cl0.1False air cyclone K319 3.32.6Kg/ kg cl0.1False air cyclone K218 1.10.82Kg/ kg cl0.1False air cyclone K117 1615.7Kg / kg cl0.1False air calciner16 Heat, kcal/kgcl ILC Heat, kcal/kg cl SLC unitbyA change ins.no
  • 70.
    -0.26%1Cyclone- K533 -0.38-0.28%1Cyclone- C436 -23-21.8Changefrom 4 to 5 stage41 1.61.6%1By pass of kiln gases40 -11-10.0Change from 5 to 6 stages 42 0.13%1Recarbonation, KS38 43 44 0.510.37%1Recarbonation, CS39 0.82-0.74%1Cyclone- C537 -0.34- 0.24%1Cyclone- C335 -0.27-0.18%1Cyclone- C234 -0.21-0.14%1Cyclone- C134 -0.12%1Cyclone- K432 -0.10%1Cyclone- K331 -0.08%1Cyclone- K230 Heat, kcal/kgcl ILC Heat, kcal/kg cl SLC unitbyA change ins.no
  • 71.
    Heat loss fromshell radiation Insulation effect of refractories optimised coating ,300mm thk Flame Shape & flame length Ring formation shoots the gas velocity takes the heat farther into the kiln, increases the back end temperature Exit gas velocity at kiln inlet = 10 m/s v=15 -16 m/s Steady Feed rate With less Fluctuation Of calcination Heat losses from kiln Parasite air ( ingress of false air entry) at inlet , outlet hood& preheater. Primary air & coal transport air are all false entry. Fluctuations In process Hood take off V=5 m/s Well controlled air flow Fuel flow
  • 72.
    4 –stage preheater 5–stage preheater 6 –stage preheater Conversion of 4 stage preheater To 5 stage preheater saves 28 Kcal/kg cl Conversion of 5 stage preheater To 6 stage preheater saves 14 Kcal/kg cl calciner
  • 73.
    769.34.40Total Output 6.0Radiation Lossfrom Cooler 20.2Radiation Loss from Kiln 37.1Radiation Loss from Preheater 4.8Heat of Evaporation of Moisture 20.91110.1881.0Heat Through Clinker 91.62930.2521.2Heat Through Cooler Vent 410.0Heat of Clinkerisation 7.93360.2360.1Heat of PH Exit Dust 170.83360.2472.1Heat of PH Exit Gases Kcal/kg clinkerdeg CKcal/kg degCkg/kg clinker HeatTemperatureSp.heat capacityMass flow Heat Output relative to 0 deg C 769.34.40Total Input 412.3Heat of Coal Combustion in Calciner 295.7Heat of Coal Combustion in Kiln 1.1560.2380.1Sensible heat of Coal and Conveying Air 2.8600.2870.2Sensible heat of Coal 1.3460.2380.1Sensible Heat of PH Leak Air 27.1460.2472.4Sensible heat of Cooling air 8.1Heat through combustibles in raw meal 21.0600.2121.6Sensible heat of Kiln Feed kcal/kg Clinkerdeg CKcal/kg degCkg/kg clinker HeatTemperatureSp.heat capacityMass flow Heat Input relative to 0 deg C Specific heat Consumption= Total heat output – Total sensible heat 769.3-61.3 = 709 Kcal/kg cl
  • 74.
    433.63.43Total Heat output 6.0Radiation 20.90.1881111.00Clinker 91.60.2522931.24Excessair 6.70.2369490.03Tertiary air dust 176.30.2689490.69Tertiary air 5.00.2410490.02Secondary air dust 127.10.27110490.45Secondary air kcal/kg clinkerkcal/kg oCdeg Ckg/kg cl HeatSpecific heatTemperatureMass flow reference: 0 deg CHEAT OUTPUT 433.63.43Total Heat Input 4.6Fan energy 27.10.247462.38Cooling air 19.10.26414500.05Dust 382.80.26414501.00Clinker kcal/kg clinkerkcal/kg oCdeg Ckg/kg cl HeatSpecific heatTemperatureMass flow reference: 0 deg CHEAT INPUT NORMAL OPERATING CONDITION
  • 75.
    Automation further helpsto run the plant more stable by reducing the meal, fuel flow and air flow. Running the kiln continuously with consistent production is the best way to reduce the fuel and power bills. For consistent production we must have short , Convergent and intense flame, less chemistry variation of raw meal , less variation in ash content of fuel and stable cooler operation. Automation further helps to run
  • 76.
    Thanks for yourattention