Heat & Mass Balance in Cement Plant

© Confederation of Indian Industry
Heat & Mass Balance Study

Objective
 Overall assessment of the plant as a 90% energy
consumption from thermal.
 Thermal efficiency is one of the most important factors
which decides the overall variable cost of the cement
 By doing an HMB study plant can easily find the major
concern area of thermal losses
 Overall productivity and energy efficiency of the plant
mainly depends upon thermal energy consumption
 The cost of fuel is increasing day by day therefore saving
energy through fuel mainly impacts the overall
manufacturing cost

Basic concept of HMB study
 First define system boundary across which heat
and mass balance study is to be carried out.
 Then define basis such as per kg, per kg mol, etc
 After identifying system boundary, evaluate the
following parameters are as below:-
 Identify Input streams
 Identify Output streams
 Identify the accumulation & formation inside the
process .
INPUT-OUTPUT=ACCUMULATION+FORMATION

Heat And Mass Balance Inputs
Fuel
Primary air
Kiln feed
Fuel-calciner
Cooling air False air
Kiln HB
border
Cooler HB
border
System
boundary
Conveying
air

r
Heat and Mass Balance Outputs
Clinker
Cooler Vent
Air
Radiation
and
Convection
PH
exhaust
gas/dust
Kiln HB
border
Cooler HB
border

Approach
 Do Overall mass balance by taking input and
output streams.
 Cross check with cooler balance if everything is OK
then go further steps.
 Lastly, if false air across the system comes within
the acceptable range then go ahead for energy
balance.
 Acceptable range of false air up to10 %

Overall Mass balance
System Boundary
Kiln feed
Fuel
Input
cooling air
Primary
air & coal
conveying
air
Preheater exit
gases
Cooler vent gases
Return dust
Clinker
Water spray
in cooler
Basis-per kg clinker
ESP Clinker dust

Pyro process Optimization
Overall Mass Balance
Input Parameters
(kg/kg clinker)
Output Parameters
(kg/kg clinker)
Kiln feed Clinker
Cooling air Cooler vent gases
Fuel Preheater exit gases
Primary air Raw meal return dust
Conveying Air ESP Clinker dust
Fuel Moisture
Kiln feed moisture
Water Spray in cooler

Case Study-ABC plant
Basis :- kg/kg clinker.
Input Streams
(kg/kg clinker)
Kiln Feed 1.6
Input Cooling Air 2.36
Primary Air 0.049
Fuel Consumption 0.088
Coal Conveying Air 0.053
Input Moisture 0.012
Water spray 0.056
Total 4.216
Output Streams
(kg/kg clinker)
Clinker 1
Cooler Vent Air 1.35
Preheater gases 1.921
ESP return dust 0.05
Return dust loss 0.08
Total 4.40

HMB Study
Given:-
Kiln Feed = 405 TPH
Clinker factor = 1.6 TPH
Height above sea level = 165 m
Top cyclone Efficiency = 95%
Ambient Air Temperature = 32 degree C
Fuel Consumption kiln = 7.9 TPH
Fuel Consumption Calc. = 14.6 TPH
Coal Dust temp = 72o C
Moisture in Kiln Feed = 0.65% by weight
Moisture in Coal dust = 1.85% by weight

HMB Study
Clinker temp at cooler inlet = 1400o C
Kiln feed Temp = 75o C
Pitot Constant = 0.85
Clinker dust ESP = 5% of Clinker
Water Spray in cooler = 14 m3/hr
Density of air = 1.29 kg/Nm3
Clinker Analysis %
silica 21.26
alumina 5.89
iron 4.83
lime 63.91
MgO 0.99
SO3 1.42

Methodology-Overall Mass Balance
 Step1
 Measure cooler Fan flows
 Then, measure primary air and conveying air
 Calculate fuel consumption on basis of kg fuel per
kg clinker.
 Important thing to keep in mind the kiln should be in
stable condition
 No dusty condition & variation in secondary air temp

Methodology-Overall Mass Balance
 Finally add all input parameters
Cooler Fan flow = kg air/kg clinker…………1
Primary Fan Flow = kg air/kg clinker…………2
Conveying air Flow = kg air/kg clinker…………3
Fuel = kg fuel/kg clinker………..4
Kiln feed = kg /kg clinker…………….5
Input moisture = kg/kg clinker………………6
Water Spray = kg/kg clinker……………….7
Input = 1+2+3+4+5+6+7

Methodology-To Measure cooler fan Flows
Cooler Fan Flows
 Before starting the measurement to put all fans in
manual mode until the entire activity is not
finished(Complete HMB study).
 For cooler fan velocity, the vane anemometer should
be used and reading should be taken in such a way
that it covers the entire section area of the fan.
 Certain precautions should be taken during the
measurements such as don’t hold the anemometer
on screening it means that reading is to be taken in a
random manner & fast.

Methodology-To Measure cooler fan
Flows
 After taking the velocity, then measure the inlet
and outlet static pressure of the fan and parallelly
also take the electric power of the fan for
efficiency calculation.
 For calculation purposes, the average velocity is
to be evaluated.
 Do the hole of 3mm at fan inlet for static pressure
measurement(maximum plant don’t follow the
standard methodology) and cross check it with
instrument manometer reading

Sample calculation of cooler fans
Cooler Fan 1:-
Q(m3/hr) = A X Average Velocity
= 0.50 X 22.36x3600
= 40,438 m3/hr
Convert into Kg/hr = 40,438 x 1.13(corrected density at 32)
Kg air/kg clinker = 45,694.94
253.12 X 1000
= 0.180 kg air per kg clinker
Nm3/kg Clinker = 0.180
1.29
= 0.14 Nm3/kg clinker
Electrical power = 82 kW

Cooler Fan1 measurement
Static at fan inlet = -35 mmwg
Static at fan outlet = 645 mmwg
Fan head = 645-(-35)
= 680 mmwg
Mechanical power = Fan Head(mmwg) X QX9.8
3600 X 1000
= 680 x 40,438x9.8
3600 x1000
= 74.85 kW

Cooler Fan1 measurement
Motor efficiency = 96%
Fan efficiency = 74.85x100
84*0.96
= 92.7%
Similarly, we have to calculate for all other cooler fans

COOLER SHEET
Cooler
No
Average
Velocity(m/s)
Area of
Screenin
g
(m2)
Q=VXAre
a(m3/hr)
Density
of air at
ambien
t temp
Kg Air/kg
clinker
Nm3/kg
Clinker
FN1 22.36 0.5024 40438 1.13 0.18 0.14
FN2 16.47 0.9677 57371 1.12 0.25 0.20
FN3 15.67 0.8992 50722 1.12 0.22 0.17
FN4 15.55 0.9852 55152 1.12 0.24 0.19
FN5 13.72 0.8992 44400 1.12 0.20 0.15
FN6 13.40 1.400 67501 1.12 0.30 0.23
FN7 13.53 1.4000 68184 1.12 0.30 0.23
FN8 13.73 1.169 57781 1.12 0.26 0.20
FN9 18.16 0.63617 41590 1.13 0.19 0.14
FN10 20.79 0.6362 47608 1.13 0.21 0.16
Total 2.36 1.83

How to Calibrate CCR fan flow with actual ?
CCR Flow = k x sqrt(piezo pressure)
= m3/min
K=?
Step 1
Find velocity by using below formula:-
V = sqrt(2 x9.8 x piezo pressure) x constant-----------2
corrected density of air
Q = A X V
A = Area of screening where piezo ring is installed

Step2
Take 20-30 sets of reading of each cooler fan by vane
anemometer and put the constant value in equation 2 such a
way it matches with anemometer flow
Step 3
Try to match both the flow
Anemometer Flow should be equal to piezo flow by putting
the constant.
Step 4
When above activity is completed and both flow come almost
same then find K with help of equation No 1

K = Piezo flow (after matching with anemometer)
sqrt(piezo pressure)
CCR Flow = k x sqrt(piezo pressure)
= m3/min
 This is very important activity and plays an important role
in optimizing the kiln operation as well as to control the
excess air
 Once the calibration is completed then it saves lot of time
in future to avoid to take reading from anemometer
 If system resistance change then automatically K constant
would be changed such as removing the damper.

Primary Air fan Flow
Primary Air Fan Flow:-
Q(m3/hr) = A X V
= 0.212 x 14.44x3600
= 11,071 m3/hr
Convert into Kg/hr = 11,071 x 1.12
= 12,399.5 kg/hr
Kg air/kg clinker = 12,399.5
253.12 x 1000
Convert into Nm3/kg Clinker = 0.0379 Nm3/kg clinker
Electrical power = 73.95 kW
Static Pressure at fan inlet = -10 mmwg
Static pressure at fan outlet = 2109 mmwg
Fan head = 2109-(-10)
Fan efficiency = Fan Head(mmwg) X QX9.8
3600 X 1000

Conveying Air Calculations
 Kiln Blower:-
 Calculate velocity with the help of pencil type anemometer.
Q = A X V
= 6370 m3/hr
Mass flow rate = 6370 x1.12
Kgair/kg clinker = 0.0252
7.9x1000
6370x1.12
Phase density =1.10 kg coal per kgair =
Conveying pipe dia = 260 mm
Velocity = 33 m/s Blower
filter
Surroundin
g air
Calculate velocity at
this point

Concept of Phase density
 Higher phase density means less conveying air
required & Vice versa
 Higher phase density means less tendency of
False air infiltration
 Recommended phase density
 Coal-3-4 kg coal per kg air
 Pet coke-4-6 kg coal per kg air

Conveying Air Calculations
 Calciner Blower:-
 Calculate velocity with the help of pencil type anemometer.
Q = A X V
= 7007 m3/hr
Mass flow rate = 0.027 kg air per kg clinker
Phase density = 1.86 kg coal per kg air
Conveying Dia = 280 mm
Velocity in conv = 32 m/s
Higher phase density means less tendency of
False air infiltration
Pet coke-: 4-6
Coal:3-4
Blower filter
Surroundin
g air
Calculate velocity at
this point

Other Inputs
Moisture from kiln Feed = 0.65 x 1.6
100
= 0.010 kg/kg clinker
Water Spray = 14 m3/hr
Water spray = 14 x1000
253.10
= 0.056 kg water/kg clinker
Moisture from fuel = 1.85 x (14.6+7.9)
100
= 0.002 kg fuel moisture/kg
clinker

Cooler Fan flow = 2.36 kg air/kg clinker……………………….....1
Primary Fan Flow = 0.049 kg air/kg clinker………………….…..…2
Conveying air Kiln = 0.0252 kg air/kg clinker………………….….…3
Conveying Air Calc. = 0.027 kg air/kg clinker…………………………4
Fuel = 0.088 kg fuel/kg clinker………………………..5
Kiln feed = 1.6 kg /kg clinker………………………………..6
Kiln feed moisture = 0.010 kg/kg clinker………………………………7
Water spray in cooler = 0.056 kg/kg clinker………………………………8
Fuel moisture = 0.002 kg/kg clinker………………………………9
Input = 1+2+3+4+5+6+7+8+9
= 2.36+0.049+0.0252+0.027+0.088+1.6+0.010+0.056+0.002
Total Input

Cooler Vent Losses
 Step 1:-
 To measure static ,dynamic pressure &
temperature at cooler outlet duct Which is
connecting to ESP.
 Duct should be straight & reading is to be taken
at least 2 opposite points for checking the
condition of laminar flow.
ESP
At this
point
reading is
to be taken

Cooler Vent Losses
Steps 1:-
First calculate density of Flue gases at 293 degree C by
applying density Correction factor.
Step 2:-
Then calculate Velocity
V = 0.85XSqrt(2x9.8xdynamic pressure)
Corrected density
Þn= {(Barometric pressure +static pressure)X273}X Þt
{ (273.15+T)X Atmospheric pressure}

Cooler Vent Losses
Step 3:-
Calculate Flow
Q = AXV
=
Step 4:-
Calculate mass flow kg air/ kg clinker
Mass flow = Corrected density x Q
Clinker Production

Cooler Vent Losses Sheet
Parameters Vent Flow
Static pressure(mmwg) -25
Average Dynamic Pressure
10
Temperature(degree C) 293
Corrected Density 0.61
Velocity(m/s) 15.25
Area of Duct(m2) 10.22
Flow(Q) m3/hr 5,60,929
Kg air/kg clinker 1.348

Cooler Balance
 Cross Verification by doing Cooler Balance
 Calculate total input air in kg air /kg clinker.
 Total Input air= Cooler Vent Air + Recuperation Air(all value on
mass basis)
 If kiln is running stable then amount of recuperation air-0.75 Nm3/kg
clinker(Normal Coal) &0.80 for Pet coke.
ESP
Cooler vent Air Recuperation air

Identification of Cooler Null point
Total input Air = 2.36 kg air/kg clinker
Cooler Vent = 1.348 kg air/kg clinker
Recuperation air = Total input Air-Cooler vent……….1
= 2.36-1.348
= 1.012
1.29
= 0.78 Nm3/kg clinker……..1
Null point = Equation no 1
Vent air = 1.04 Nm3/kg clinker
From cooler table we can easily find the null point:-
Total flow upto cooler fan 5 = 1.09 kg air per kg clinker

Identification of Cooler Null point
From above graph we can easily find the null point:-
Total flow upto cooler fan 5 = 0.85 Nm3 air per kg clinker
It means the null point is in between 4th & 5th fan
The amount of air is used after null point mainly contributes in cooling the
clinker

Preheater Gas Flow
Steps 1:-
First calculate density of Flue gases at 298 degree C by
applying density Correction factor.
Step 2:-
Then calculate Velocity
V = 0.85XSqrt(2x9.8xdynamic pressure)
Corrected density
Þn= {(Barometric pressure +static pressure)X273}X Þt
{ (273+T)X Atmospheric pressure}

Pre heater Gas Flow Measurement
Step 3:-
Calculate Flow
Q = AXV
=
Step 4:-
Calculate mass flow kg air/ kg clinker
Mass flow = Corrected density x Q
Clinker Production

Pre heater Gas Flow sheet
Parameters
Static pressure(mmwg) -595
Average Dynamic
Pressure(mmwg)
9.45
Temperature(degree C) 253
Corrected Density 0.68
Velocity(m/s) 14.04
Area of Duct(m2) 14.19
Flow(Q) m3/hr 717010
Kg air/kg clinker 1.921

Cooler Vent Flow = 1.348 kg air/kg clinker…1
Preheater Flow = 1.921 kg air/kg clinker……2
Return dust = 0.05 x 1.6kg /kg clinker……3
Clinker = 1 kg clinker…………………4
ESP clinker dust = 0.05 x 1 kg/kg clinker
= 0.05 kg/kg clinker…………5
Output = 1+2+3+4 +5
Total Output

Basis :- kg/kg clinker.
Input Streams
(kg/kg clinker)
Kiln Feed 1.6
Input Cooling Air 2.36
Primary Air 0.049
Fuel Consumption 0.088
Coal Conveying Air 0.053
Input Moisture 0.012
Water spray 0.056
Total 4.216
Output Streams
(kg/kg clinker)
Clinker 1
Cooler Vent Air 1.35
Preheater gases 1.921
Return dust loss 0.08
ESP clinker dust 0.05
Total 4.40

Overall Mass Balance-Conclusion
 Do Overall mass balance by taking input & out put
stream flow by taking the basis on kg/kg clinker.
 Then calculate the percentage of false air for
cross verification.
 Acceptable range is upto10% if excess deviation
comes it means something is wrong.
 After completing the mass balance study
successfully then proceed for energy balance

Overall Mass Balance-Conclusion
False Air Calculation = (Output Stream –Input stream ) X100
(Input stream)
= 4.40 -4.216 x 100
4.216
= 4.33 %
It means the overall plant is good and there is minimum
leakages in the system
Indicators:-PH outlet temp:-253 degree C; SP volume:-1.35
Nm3/kg clinker

Energy Balance
System Boundary
Kiln feed
Fuel
Input
cooling air
Primary
air & coal
conveying
air
Preheater gas
losses
Cooler vent gas
losses
Return dust heat
losses
Heat losses
through Clinker
Input sensible heats
Radiation losses
Heat from fuel

Calculation of Input Heat
 Sensible heat from cooling air
= Input air(kg/clinker) x specific heat x (temperature difference)
= 2.36 x 0.237 x(32-0)
= 17.87 kcal/kg clinker………………………………….1
Temperature difference= Ambient Temp-Reference Temperature
 Sensible heat from kiln feed
= kiln feed x specific heat x( kiln feed temp-0)
= 1.6 x 0.213 x(75-0)
= 25.60 kcal/kg clinker………………………..…...2
 Sensible heat from Primary Air
= Primary air(kg air/kg clinker) x Specific heat x (Primary air temp-
reference temp)
= 0.049 x 0.237 x(32-0)
= 0.37 kcal/kg clinker……………………………………………………..3

Overall HMB Sheet-Input
 Sensible heat from Conveying Air
= conveying air(kg air/kg clinker) x Specific heat x (Primary air temp-
reference temp)
= 0.053 x 0.237 x 32
= 0.40 kcal/kg clinker…………………………………………………4
Sensible heat from fuel
= Fuel Consumption x specific heat x( Fuel temp-0)
= 0.0889 x 0.286 x(72-0)
= 1.83 kcal/kg clinker…………………………………………………5
 Sensible heat from cooler water spray
= water consumption x specific heat x (water temp-0)
= 0.056 x 0.447 x (25-0)
= 0.63 kcal/kg clinker…………………………………………………..6

Overall HMB Sheet-Input
 Sensible heat from Kiln feed moisture
= moisture(kg air/kg clinker) x Specific heat x (Kiln feed temp-
reference temp)
= 0.01 x 0.44 x (75-0)
= 0.349 kcal/kg clinker…………………………………………………7
Sensible heat from fuel moisture
= Fuel moisture x specific heat x( Fuel temp-0)
= 0.002 x 0.447 x(72-0)
= 0.057 kcal/kg clinker………………………………………………..8

Total Input Heat
Q input = 1+2+3+4+5+6+7+8+heat from fuel
Q input = 47.11 + Heat from fuel
Heat from fuel = ?
Heat from fuel is to be calculated by doing overall heat
balance
Heat input = Heat Output
Heat from fuel = Heat output-47.11………………….9
Note:-
:- Reference temperature is considering zero in all calculations
 Specific heat is to be calculated by a,b,c & temperature values and
separate excel sheet will be shared for calculation purpose.

Calculation of Output Heat
 Sensible heat from preheater gases
= Gases(kg/clinker) x specific heat x (temperature difference)
= 1.921 x 0.24 x(253-0)
= 116.63 kcal/kg clinker…………………………………………….1
 Sensible heat from return dust losses
= Dust losses x specific heat x( kiln feed temp-0)
= 0.08 x 0.23 x (75-0)
= 4.67 kcal/kg clinker………………………………………………….2
 Sensible heat from cooler vent losses
= Vent air(kg air/kg clinker) x Specific heat x (vent air temp-
reference temp)
= 1.292 x 0.2437 x (293-0)
= 92.25 kcal/kg clinker…………………………………………………3

Calculation of Output Heat
 Heat losses from water evaporation
= Sensible heat from 25 degree C to 100 degree C + latent heat +
sensible heat from 100 degree C to 293 degree C
= 0.056 x0.4470 x(100-25) + 0.056 x540 +(0.056 x.4470 x(293-100))
= 37.66 kcal /kg clinker…………………………………………………….4
Heat losses from clinker
= clinker x specific heat x( Clinker temp-0)……
= 1 x 0.19 x(140-0)
= 26.88 kcal/kg clinker……………………………………………………..5
Heat loss due to ESP clinker dust
= 0.050 x 0.19 x(293-0) = 2.81 kcal/kg clinker…………………6
Heat of Formation
= 408 kcal/kg clinker………………………………………………………7
Heat of Formation
= 4.11 x Al2O3 + 6.48 x MgO+ 7.646 x CaO -5.11 xSiO2 -0.59 x Fe2O3

Radiation and Conventional losses
Q radiation losses
𝑄𝑟𝑎𝑑 = 𝜀 × 𝜎 × ((𝑇𝑠 + 273.15) 4 − (𝑇a + 273.15) 4 ) × 𝐴𝑠
= 𝑘𝑐𝑎𝑙⁄ℎ
Qrad = Radiation loss
𝜎 = Stefan-Boltzmann Constant
= 5.67 x 10-8 (W/m2K4)
Ts = Surface temperature (degree c)
Ta = ambient air temperature(degree c)
As = Area of surface(m2)
𝜀 = Emissivity of the object
𝜀 = 0.86-0.90-Kiln shell
= 0.94-0.97 painted surface
= 1(black body)

Radiation and Conventional losses
VDZ equation for kiln, cooler, PH ,TAD & hood
𝑄𝑐𝑜𝑛 = 𝛼𝑐𝑜𝑛 × (𝑇𝑠 −𝑇a) × 𝐴𝑠 + 𝜀 × 𝜎 × ((𝑇𝑠 + 273.15) 4 − (𝑇a + 273.15) 4 ) × 𝐴s
𝛼𝑐𝑜𝑛 = Heat transfer coefficient
= 7 W/m2K
As = Area of surface(m2)
𝜀 = Emissivity of the object
𝜀 = 0.86-0.90-Kiln shell
= 0.94-0.97 painted surface
= 1(black body)
𝜎 = Stefan-Boltzmann Constant
= 5.67 x 10-8 (W/m2K4)
Ts = Surface temperature (degree c)
Ta = ambient air temperature(degree c)

Output Heat
Radiation Losses
 TAD
 Kiln
 Preheater
 Kiln hood & Cooler
Note:-Generally, radiation losses contribute 6-8% to
overall heat losses

Kiln Radiation Loss Sheet
Distance
(m)
Avg
Temp
Ambient
Temp
Area
(m2)
Radiation loss
(kcal/kg
clinker)
Convection
loss(kcal/kg
clinker)
Total
(radiation+
conventional loss)
1
2
-----
85 m
1 2 3 4 5…………………………………………………………………..85
Take temperature readings at every 1 meter from kiln outlet to kiln inlet

TAD Radiation Loss Sheet
Distance
(m)
Avg
Temp
Ambient
Temp
Area
(m2)
Radiation loss
(kcal/kg
clinker)
Convection
loss(kcal/kg
clinker)
Total
(radiation+
conventional loss)
1
2
-----
85 m
1 2 3 4 5…………………………………………………………………..85
Take temperature readings at every 1 meter from cooler inlet to PC inlet

Preheater Radiation Loss Sheet
cyclone
Av
g
Te
mp
Ambie
nt
Temp
Area
(m2)
Radiation loss
(kcal/kg
clinker)
Convection
loss(kcal/kg
clinker)
Total
(radiation+
conventional loss)
Cyclone no1
Slant portion
Cylindrical portion
Conical portion
Feed pipe(1-2)
Riser duct area
 Similarly to calculate in all other cyclones
 Detailed area calculations will be shared
through HMB excel sheet

Cooler & Kiln hood Radiation Loss Sheet
Area
Avg
Temp
Ambient
Temp
Area
(m2)
Radiation loss
(kcal/kg
clinker)
Convection
loss(kcal/kg
clinker)
Total
(radiation+
conventional loss)
Kiln hood
walls
Roof area
Cooler walls
Cooler roof
area

Heat Input
Parameters Input Heat
Sensible heat from cooling Air 17.87
Sensible heat from primary air 0.37
Sensible heat from conveying air 0.40
Sensible heat from kiln feed 25.60
Sensible heat from fuel dust 0.057
Sensible heat from water 0.63
Sensible heat from kiln feed moisture 0.349
Sensible heat from coal moisture 0.057
Heat From fuel Q
Total 47.11+Q

Heat Output
Parameters Output Heat(kcal/kg clinker)
Preheater losses 116.63
Cooler Vent losses 92.25
Return Dust losses 4.67
Water Evaporation losses 37.66
Heat of Formation 408
Kiln Radiation losses 14
TAD radiation losses 2
Cooler and Hood radiation losses 5
Preheater radiation losses 28
Heat Loss through Clinker Dust
Heat losses through Clinker 26.88
Total output 737.56

Overall Heat Balance
Heat from fuel is to be calculated by doing overall heat
balance
Heat input = Heat Output
Heat from fuel = Heat output-47.11…………….9
Heat from fuel = 737.56-47.11
= 690.45 kcal per kg clinker

Key Points-HMB
 Generally, radiation losses contribute 6-8% to overall heat
losses
 Acceptable range of cooler losses
 Vent+ Clinker:-110-120 kcal/kg clinker
 Preheat outlet temp:-240-260 degree C indicates good number
 Specific Volume of preheater exit gases
 :-1.30-1.50 Nm3/kg clinker(Coal)
 1.50 Nm3/kg clinker(Pet coke)
 Further fuel consumption can be reduced by taking more
sensible heat from input such as to increase the temperature
of kiln feed

Summary

Numerical 12
N12
By arresting the leakages and certain modifications across the
preheater system the plant gets the benefit in terms of overall
specific heat consumption by 30 kcal/kg clinker
NCV of Coal- 6500 kcal/kg coal
Clinker production :-4500 TPD
Present Specific heat consumption:-730 kcal/kg clinker
Calculate the following:-
a) Present coal consumption per day
b) Coal consumption with improved thermal efficiency

Numerical 12
NCV of Coal = 6500 kcal/kg coal
Coal consumption = Specific heat
Coal NCV.
= 730
6500
= 0.112 kg coal per kg clinker
= 11.2%
= 700
6500
= 0.10769
= 10.769%

Numerical 12
= 0.112 – 0.10769
= 0.00431 x 4500 x1000
= 19.395 x1000
= 19395 kg coal saving per day
= 19.395 ton saving per day
Cost of fine coal per ton = Rs 7000
Total Saving = 19.395 x 7000
= Rs 1,35,765 per day

Impact of false air on Cement
manufacturing cost

What is false air?
 False air is any unwanted air entering the system
between two points.
 Exact amount of False air is difficult to measure.
 An indicator of false air amount can be the oxygen
increase between two points
 Applicable for the gas containing oxygen
percentage less than 21%
 Not applicable for Air
 Reasons for high false air:-
 Air follows the least path resistance

What is false air?
 False air is any unwanted air entering the system
between two points.
False air formula
= Oxygen % at point2- Oxygen % at point1 X 100
21- (Oxygen% at point1)
1 Gas flow 2

Disadvantages of false air
 Increase in electrical energy consumption.
 Increase in thermal energy consumption.
 Reduction in productivity
 Unstable and disturbed operation
 Frequent human exposure to unsafe areas while
arresting false air.
 Increase the overall variable cost of cement

Concept of ILC & SLC string
ILC System:-The secondary and tertiary air is premixed
when it entering into pre-calciner.
SLC System:-There is no mixing of secondary &
tertiary air and both are parallel to each other.
ILC System:-Low NOx burner is effective for reducing
the NOx at Preheater Outlet by decreasing NOx
formation in the calciner reduction zone.
SLC System:-NOx emission control is not so much
effective by using low NOx Burner.

ILC –Kiln System

SLC - Kiln System

ILC String –False Air Concept
O2-5%
1
2
3
4
PH FAN 5
6
Calcin
er
kiln
Kiln Feed
O2-2.5%
Measuring Points
1) Calciner Outlet
2) Preheater
down Comer
3) Fan Inlet

Calculations-ILC String
 Preheater Down Comer:-5%
 Calciner Outlet:-2.5%
Apply False Air Formula
= (Down Comer oxygen-Calciner outlet) X 100
( 21-calciner outlet oxygen)
= 5-2.5 X 100
21-2.5
= 13.5 %
Remarks:-
Norms -6-8 % false air is acceptable range across preheater section
Impact of false air on fuel consumption will be discussed in next module(Process
optimization)

Calculations-SLC String
SLC String
Kiln string
Kiln inlet O2 = 2%
PH outlet O2 = 4.5%
Calciner String
Calciner outlet O2 = 2.5%
Preheater Outlet O2 = 5%

Calculations-SLC String
Calciner string
(Down Comer oxygen-Calciner outlet) X 100
( 21-calciner outlet oxygen)
= (5-2.5) x 100
21-2.5
= 13.5%
Kiln String
= PH Outlet O2-Kiln Inlet O2
21 – kiln inlet oxygen
= 13.15%

Numerical 13
N12 :-If false air across the preheater system is reduced
by 5 % and present electrical power of preheater fan is
1400 kW ,then how much saving could be
achieved(Consider only electrical saving)
Given
Unit Cost:-Rs 5 kWh
Kiln running days:-300
b) Also calculate the cost saving in Rs per annum

Impact of False Air on Electrical power
Electrical Loss = Percentage of false airX electrical
power of fan
Electrical power = 1400 kW
Power loss = 0.05x1400
= 70 kW
Electrical cost = Rs 5 kWh
No of days per annum:
= 300
Annual Saving = 135x300x5x24
= 25.2 lakhs per annum

False air infiltration points across preheater
 Poking holes of cyclones
 Expansion joints of feed pipes and down
comer duct
 Feed pipe flap valve
 Cyclone doors

Cyclone Joints-Riser duct to cyclone

Feed pipe flap valves

Boxes for repairing the shell

Smoke Chamber doors

Expansion joints of feed pipes

Expansion joints in down comer duct.

Poking holes

False air infiltration points across VRM
 Mill body
 Gap between tie rods with mill body.
 Expansion joints of ducts
 Cyclone roof
 Below RAL of cyclones
 Separator body
 Fan suction box
Remarks:-
How to calculate false air across Raw Mill Section will be discussed in
Process Optimization module.

Bag house

Target values of false air
Section Target false air
Pyro Section across
preheater
Less than 6%
Raw mill (VRM) Less than 12%
Raw mill(Ball mill) Less than 19%
Coal mill(VRM) Less than 15%

Impact of false air in cement manufacturing cost
1% Increase in false
air
kWh loss
Kcal/kg
clinker
Cost per day(Rs
5 & Rs1150
Mkcal)
Calculation Basis
Raw mill 3.3 NA 333
Running hr-20 in a
day;1.58 kg gas/kg
material, capacity of
mill-300 TPH
coal mill 2.0 NA 200
Running hr-20 in a
day;1.58 kg gas/kg
material, capacity of
mill-38 TPH
Pre-heater 6.8 1.50 8691
Out let Temp-280 degree
Standard flue gas flow
at PH outlet -1.50
Nm3/kg for pet coke;
production:-190
TPH;Six stage
Remarks:-
Detail Calculations will be discussed in Process Optimization module.

Recommendations & Solutions
 Arrest the leakages by using sodium silicate solution with
glass wool.
 Oxygen profiling should be done every week to check false
air ingress
 In shut down check the flap valves and expansion joints
condition of preheater.
 Check the gap of vanes with body in gravel gate.
 Check the static pressure below RAL(rotary air lock) in bag
house as well as cyclones.

Recommendations & Solutions

Replace kiln outlet seal with efficient graphite seal
 Observations:
 Conventional seals are
installed at kiln section

 Observations:
 Impact of Conventional seals are
 Improper sealing
 False air infiltration
 Heat consumption increases

 Recommendations:
 Replace kiln outlet seals in with efficient
graphite seals
 staggered arrangement of
overlapping graphite blocks
 graphite blocks move independently
with the radial movement of the kiln
 Saving potential: 3-4 Kcal/ kg clinker

 Benefits :
 Increased sealing
capabilities
 Reduction in false air
infiltration
 Low maintenance cost
 Reduces specific energy
consumption
Replace kiln outlet seal with efficient graphite
seal

Annual Saving -Rs 40.00 Lakhs
Investment -Rs 75.00 Lakhs
Payback -22 months

Case Studies in pyrosection

SLC-Separate Line Calciner string

Dew Point
 The Dew Point is the temperature
where water vapor starts to condense
out of the air.
 The temperature at which air becomes
completely saturated.
 Above this temperature the moisture
stays in the air.
 If the dew-point temperature is close
to the dry air temperature - the
relative humidity is high
 if the dew point is well below the dry
air temperature - the relative humidity
is low

Dry Bulb & Wet Bulb temperature
 The Dry Bulb Temperature refers basically to the
ambient air temperature.
 The Wet Bulb temperature is the adiabatic saturation
temperature
 Wet Bulb temperature is always between the Dry Bulb
temperature and the Dew Point
 Wet bulb temperature always less than dry bulb
temperature

Psychometric Chart

How to find the dew point of the gas in
RABH & Coal mill?
 Put some wet cloth on thermocouple and then insert at
coal mill stack & observe the following observations;-
 At first stage temperature will be increased
 Then after some time it holds at particular temperature
 Finally when all water will be evaporated from cloth then
temperature would be increased very fast up to the
desire temperature of stack
 The temperature at which reading holds is called wet
bulb temperature.

Case Study -Coal mill
Readings & Curve
 25,26,27…………………………51…………………Stage1
 51,52……………………………..52…………….…Stage 2
 52,53,54……………………………73……….……Stage 3
 52 is the wet bulb temperature……………….Stage2
 With the help of psychometric chart one can easily find
the dew point but in cases of flue gas it always
equivalent to wet bulb

Wet Bulb Profile of coal mill
to Find Dew point

Importance of Dew point
 Gas temperature always greater than dew point by
20 degree C
 To avoid moisture inside the RABH and Coal mill
bag house the gas temperature should be greater
than dew pint by 20 degree C
 Recommended Temperature
 Coal mill :-72 degree C(Outlet)
 RABH:-100 degree C

Preheater Gas Estimation by theoretical Method
Heat Consumption :- 850 kcal/kg clinker
Coal consumption :- 12.7 % of total clinker
NCV Of coal = 6650 kcal/kg coal
Coal consumption = 850
6650
Ultimate analysis
Carbon:-80%
H:-5%
S:1%
O:5%

Basis 1kg clinker
 After combustion
C + O2 – CO2
H + O2-H20
S + O2- SO2
As per stoichiometry
1kg mol of C produce 1 kg mol of CO2
No of mol of C = Weight / Molecular weight
= 0.80 x 127 gm
12

 No of mol C = 8.46 gm per mol
CO2 = 8.46
Weight of CO2 = 44 X 8.46
= 372.24
Volume = 190 L(Avogadro’s)
Weight of O2 = 32 X 8.46
= 270.72 gm………….1
Similarly for H20
H2 +1/2 O2 - H2O
= 0.05 X127
2
= 3.175

No of mol H20 = 3.175 gm per mol
= 3.175 x 18
Weight = 57.15 gm
No of mol O2 is required to form H20 -1/2 of H20
Weight of O2 = ½ X 3.175 X32
= 50.8 gm ……………………2
Similarly for Sulphur
Amount of oxygen is required
= 1 gm……………………….3

Available oxygen for combustion
= 0.05 x 127
= 6.35 gm………………………………………………4
Amount of oxygen required
= (1+2+3)-(4)
= 323-6.35
= 317 gm
Now convert the oxygen amount in litre & NM3
Calculate No of moles = 317/32
= 9.90 gm per mol

As per Avogadro rule
1gm mole = 22.4 litre(STP)
Then total volume = 22.4 x 9.90
= 222 L
NM3 = 0.222 NM3
Amount of Nitrogen
= 79 X 0.222
21
= 0.835 NM3

CO2 Calculations from calcination
Kiln Feed LOI = 35 %
Basis:- Raw meal to produce 1 kg clinker
Then CO2 from calcination
= {(1000) - (1000)}
(0.65)
= 538 gm
Convert NM3
= 0.274 NM3
Total CO2 = Fuel + Calcination
= 0.464 NM3

Moisture in kiln feed:-0.5%
Kiln feed:1.65 kg raw meal per kg clinker
H20 = 1.65 X(0.0050)
= 8.25 gm
H2O = 0.01 NM3
Total H2O = 10L +71 L
= 0.081 NM3

 Exhaust gas volume with no excess air
CO2 :- 0.464 NM3
H2O :- 0.081 NM3
N2 :- 0.835 NM3
SO2 :- 0.001 NM3
= 1.38 NM3/kg clinker
CO2% = 33.5
N2 = 60.5%
H2O = 5.9
SO2 = 0.1%(1000 ppm)

Preheater Gas Estimation by Direct Formulae
40% CO2-Fuel
60 % CO2-Calcination
Standard value:-0.42-0.44 NM3/kg clinker
 Depends upon fuel consumption
Formulae (no excess oxygen)(Nm3/kg clinker)
Net Volume = (kcal/kg clinker x 0.00129) + 0.284------------1
Formulae (excess oxygen-n%)
Eq1 x {(1 + (n/21-n)}

Numerical
Heat Consumption:-840 kcal/kg clinker
Calculate Nm3/kg clinker at 2% excess oxygen
= (840 x 0.00129) + 0.284
= 1.3676 Nm3/kg clinker
Find excess air
= O2/21-O2
= 2
= 21-2
= 10.52%
Apply formulae
= 1.3676 x(1+.1052)
= 1.51 NM3/kg clinker

Key points
 Reducing system resistance, improving fan efficiency
and removing damper losses across fan creates the huge
saving potential in Process fans
 In house modifications such as bell mouth and suction
box of fan have enough saving potential with attractive
pay back period less than 6 months
 Through heat and mass balance study plant can reduce
the variable cost of cement
 By stabilizing the system and providing proper insulation
saves lot of thermal energy
 6-8% radiation losses in overall HMB

Key points
 Plant can reduce the overall losses due to false air by using
best practices
 1% increase in false air across preheater impact the overall
variable cost by approximately Rs 8591 per day
 Dew point temperature plays an important role in baghouse
therefore gas temperature should be greater than dew point
by 20 degree C
 Preheater gas estimation can be done theoretically by using
heat consumption of kiln

Question Bank
N1:-Preheater gas flow=568019 m3/hr;
Height above seal level=350 m
Temp=285 degree c;motor efficiency:-96%
Fan power = 1400 kW ;
Clinker production = 4000 TPD
Sp at traverse point = -500 mmwg
Sp at fan inlet before damper = -530 mmwg
Sp at fan inlet after damper = -565 mmwg
Sp at fan outlet = -35 mmwg
Oxygen percentage at Calciner outlet-2 %;
Oxygen percentage at PH Outlet :-4.5%
Oxygen at Fan inlet:-5.2%

Numerical No1
a) Calculate damper losses?
b) Fan efficiency?
c) If Fan efficiency come less than 70 % then retrofit it with
84% efficiency impeller with investment & ROI details and
also mention SEC saving in per ton clinker?
d) False air across preheater?
e) Energy losses due to false air.(Consider only electrical)

N2:-Raw mill Gas flow=700000 m3/hr;
Height above seal level=350 m
Mill outlet Temp=89 degree c;
Fan power =3500 kW ;Raw Mill Feed= 350 TPH;
Mill inlet temp =200 degree C
Sp at mill inlet=-50 mmwg
Sp at mill outlet =-910 mmwg
Sp at fan inlet before damper= -1010 mmwg
Sp at fan inlet after damper= -1050 mmwg
Oxygen at mill inlet-6 %; Oxygen at mill Outlet :-9%
Oxygen at Fan inlet;-9.5%
Numerical No2

Numerical No 2
a) Calculate damper losses and fan efficiency?
b) False air across system and energy losses due to it.
c) Nozzle ring velocity if nozzle area =0.80 m2
d) Calculate Pressure drop across mill and if static pressure at
fan inlet is reduced by 40 mmwg then how much electrical
savings could be achieved

Annexures

http://energy.greenbusinesscentre.com/
THANK YOU !
For any queries related to energy efficiency log in @
For latest updates on energy efficiency please visit
http://energy.greenbusinesscentre.com/sup/
@CII_GBC cii--godrej-gbc

Further contact details:-
Vaibhav Girdhar/vaibhav.girdhar@cii.in/9908518912
Nitin Asnani/nitin.asnani@cii.in/8963965157

Heat & Mass Balance in Cement Plant

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