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Page 2

CEMENT PROCESS ENGINEERING SECTION 5 � COMBUSTION & FUELS
VADE-MECUM

Index - i
Rev. 2002

Table of Contents

1. Fuel Theory.......................................................................................... 5.1

2. Solid Fuel.............................................................................................. 5.2
2.1 Coal .............................................................................................5.2
2.2 Coke.............................................................................................5.4

3. Fuel Oil................................................................................................. 5.4
3.1 Main Characteristics.....................................................................5.4
3.2 Viscosity ......................................................................................5.4

4. Waste Fuel............................................................................................ 5.5

5. Natural Gas.......................................................................................... 5.6

6. Flame Theory....................................................................................... 5.7
6.1 Definition.....................................................................................5.7
6.2 Flame Speed.................................................................................5.7
6.3 Flame Radiation ...........................................................................5.7
6.4 Factors Influencing the Flame Temperature ..................................5.7

7. Burner Pipes ........................................................................................ 5.8
7.1 Number of Air Circuits.................................................................5.8
7.2 Primary Air ..................................................................................5.8
7.3 Transport air.................................................................................5.9
7.4 Specific Impulse...........................................................................5.9
7.5 Swirl .......................................................................................... 5.10
7.6 Examples of Burner Tip.............................................................. 5.10

8. Fuel Grinding and Dosing ................................................................. 5.12
8.1 Solid Fuel Grindability ............................................................... 5.12
8.2 Solid Fuel Fineness .................................................................... 5.12
8.3 Dosing........................................................................................ 5.13
8.4 Safety Considerations................................................................. 5.13
8.5 Fuel Grinders ............................................................................. 5.13

Page 14

CEMENT PROCESS ENGINEERING SECTION 5 – COMBUSTION & FUELS
VADE-MECUM

5.12

8. Fuel Grinding and Dosing

8.1 Solid Fuel Grindability
• The Hardgrove Grindability Index (HGI) indicates the ease of grinding solid fuel.
• A standard coal in the cement industry has a HGI of 65 or 76.
• HGImix = x * HGI coal + y * HGI coke.

Bowl Mill (Raymond) Capacity

0.6 0.8 1.0 1.2 1.4
20

40

60

80

100

90% Raymond
85% Raymond
80% Raymond
75% Raymond

Mill Capacity Factor

F
u

e
lG

ri
n

da
bi

lit
y

(H
a

rd
gr

ov
e

)

Passing 75um (#200)

• 0.10 mill capacity factor for 5 HGI

8.2 Solid Fuel Fineness
Fineness S / A< 1.2 S /A> 1.2

70 Mesh >99% >99.9%
200 Mesh 98 � 0.7 * % VM 98 � 0.6 * % VM

• S/A (molar ratio) =%SO3/80*(1/(%Na2O/62+%K2O/94))
where: % are expressed in weight, VM = Volatile Matter, S = Sulfur, A = Alkali Equivalent (in the mix and
fuel ashes).

• When S/A (molar ratio) > 1.2, risk of volatilization: need better combustion.

Rules of thumb
• 5% more passing at 200# yields to 15-20% less mill capacity.
• Addition of HES: 5% production increase at constant fineness.

Relationship: Burning Time & Particle Size

1.1.01
.1

1

10

Diameter of coal particle (mm)

B
u

rn
in

g
T

im
e

(s
e

co
n

d
s)

Combustion Temp.
= 1500°C

Combustion Temp.
= 900°C

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