2. Heat loss from shell radiation
Heat loss in
product
Heat loss in
Preheater
Exit gas
Cooler exit air
Where does the heat go ?
3. 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.
4. 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
5. 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
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
15. 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.”
16. 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,...
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
• 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
20. 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
23. 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
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= −
26. 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
27. 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.
28. 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
29. 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
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
• 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)
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 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.
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 : 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
36. 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
37. 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
40. 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
41. 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)
42. 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
43. 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
44. 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
45. 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.
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
• 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.
49. 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
50. 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 ?
51. • 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
52. 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
53. 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
54. 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
55. 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
56. 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
57. 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
58. 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
59. 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
62. 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
64. 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
65.
66.
67. 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
68. 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
69. 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
71. 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
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 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
74. 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
75. 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
