05 Combustion

Rev. 2002

5. COMBUSTION & FUELS

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

5.1

Rev. 2002

1. Fuel Theory

a) Low Heating Value

• LHV is calculated from the Higher Heating Value (obtained by bomb calorimeter)

• Considering that :

- Water created by the combustion doesn’t condense - The reaction takes place under constant pressure

LHV = HHV - 567W (at std. Temp = 25oC) in metric units LHV = HHV – 1020W (std. Temp = 60oF) in english units

- LHV, HHV in kcal/kg (BTU/lb)

- W in kg (lb) water vaporized per kg (lb) or fuel

W = H₂O contained in the fuel + H₂O created by the combustion H₂O created by the combustion : 2H + ½ O₂-> H₂O W = % (H₂O)+ 9*% (H) where % expressed in weight in the fuel

• The difference between the HHV and the LHV will vary with fuel type. The greater the proportion of hydrogen in a fuel, the lower the resulting LHV:

Fuel %H HHV (Btu/lb) LHV (Btu/lb) LHV (kcal/kg) LHV as a % of HHV Coal 5 12,000 11,540 6410 96 Coke 4 14,000 13,630 7570 97 Waste Fuel 10 9,000 8,070 4480 90 Fuel oil 10 19,000 18,070 10040 95 Nat. gas 25 23,000 20,680 11490 90 Rule of thumb:

• One cubic foot of air (+stochiometric amount of NG or oil) releases 100 Btu of heat (for fuel), 1m3 air releases about 900 kcal.

b) Volatile Matter

• Volatile matter is the loss in weight, corrected for moisture, of a sample heated to 950oC in the absence of air.

% VM

Ignition Temperature C

5.2

Rev. 2002

c) Ash

• Ash is the inorganic residue remaining after burning coal heated to 750oC in an oxidizing atmosphere until there is not weight change. It is composed chiefly (95-99%) of oxides of Si, Al, Fe, and Ca; Mg, Ti, S, Na, K, and trace elements can also be present.

d) Fixed Carbon

• Fixed carbon is the residue left after the volatile matter is driven off and is calculated as: F.C. = 100 – (% ash + % moisture + % volatile matter)

e) Flammability

Limit flammability in air Temp auto flame Inf limit (%) Sup limit (%) in air (°C)

H₂ 4 75 570 CO 12.5 74 610 CH₄ 5 15 580 C₂H₆ 3 12.5 490 C₃H₈ 2.2 9.5 480 C₄H₁₀ 1.7 8.5 420

f) Combustion Reaction Time

Coal Heavy oil Light oil Gas

0.1to 1 second 0.1 0.01 to 0.001 0.001

In second, at atmospheric pressure

2. Solid Fuel

2.1 Coal

a) Main Coal Characteristics

Approximate Analysis and bulk density for Various Coals

Group Fixed carbon (%) Volatile matter (%) Heat value (Btu/lb.) Kg/m3 ≥than <than >than <than ≥than

Anthracite Meta anthracite Anthracite Semi anthracite 98 92 86 98 92 2 2 8 8 14 800-930 Bituminous Low-vol Med volatile High vol A High vol B High vol C 78 69 86 78 69 14 22 31 22 31 13,000 11,500 670-910 Subbituminous A B C 10,500 9,500 8,300 Lignitic A B 6,300 640-860

5.3

Rev. 2002

b) Combustion Calculation for Coal Proximate Analysis

Volatile 22.19 % dry

Free carbon 64.29 % dry

Moisture 6.5 %

Ash 12.5 % dry

HHV 7.259 kcal/kg coal dry

LHV = HHV –5218 H (kcal/kg) @ 25° C, or

LHV = HHV –93.9196*H _(Btu/lb)

Where: H is the mass fraction of hydrogen in the fuel.

Ultimate Analysis (Dry Basis)

% weight nb moles/kg Carbon 74.87 C: 62.33 Hydrogen 3.78 H2: 18.75 Sulfur 2.24 S: 0.70 Nitrogen 1.93 N2: 0.69 Chlorine 0.08 Cl: Oxygen 3.53 O2: 1.10 Ash 13.57 Combustion Equations • C+O₂ →CO₂+7,829 kcal/kg C • O H O 2,8641kcal/kg H 2 1 H₂+ ₂ → ₂ + • S+O₂ →SO₂+2,213 kcal/kg S - the oxydation of coal is very quick: 0.1 to 0.3 seconds

Heat Value Calculation

• If (x) is the ponderal % of x, the heat value can be calculated with the following formula:

- LHV (kcal/kg) =

( )

( )

( ) ( )

6W,whereWisH Ocontentof the fuel

8 O H * 287 S 45 . 22 C 8 . 80 − ₂     ₋ + + - HHV = 80.8

( )

C +22.45

( )

S +339.4

( )

H −35.9

( )

O

Neutral Combustion Air for Coal

• Input in mass % V=

( )

( )

( )

( )

   

₊

₊

₋

99

.

15

*

2

01

.

1

*

4

06

.

32

01

.

12

*

21

4

.

22

C

S

H

O

Rule of thumb • 7.6 Nm3/kg of dry coal Neutral Combustion Products

Nm3/kg Kg/kg %vol %weight Combustion CO₂ 1.306 2.564 17.4 25.3 H₂O 0.393 0.316 5.2 3.1 SO₂ 0.015 0.042 0.2 0.4 N₂ 5.721 7.152 76.1 70.5 Moisture H₂O 0.081 0.065 1.1 0.7 Total 7.515 10.138

5.4 2.2 Coke

• Coke is the solid, cellular, infusible material remaining after carbonization of coal, pitch, petroleum residue and other carbonaceous materials. Thus, its oxydation takes more time: 1 to 2 seconds.

3. Fuel Oil

3.1 Main Characteristics Comp Nº1 Nº2 Nº4 Nº6 FO Nº6 C H O N S Ash C/H ratio 86.4 13.6 0.01 0.003 0.09 <0.01 6.35 87.3 12.6 0.04 0.006 0.22 <0.01 6.93 86.47 11.65 0.27 0.24 1.35 0.02 7.42 87.26 10.49 0.64 0.28 0.84 0.04 8.31 84.67 11.02 0.38 0.18 3.97 0.02 7.62 Specific Gravity 0.849 0.902 0.965 • 131.5

(

for SG 1

)

Gravity Specific 5 . 141 Gravity Api = − < 3.2 Viscosity Theory

• The viscosity of a fluid is a measure of its internal resistance to flow. Viscosity is the opposite of fluidity. - abs visc is absolute viscosity,µmeasured in cp (centipoise);

- kin visc is kinematic viscosity, C measured in cs or cSt (centistokes) - abs visc in cp = kin visc cs * specific gravity

1 poise = 100 cp = 1 dyne.s/cm2+ = 1 g/s*cm, 1 stoke = 100 cs = 0.000 1 m2/s Viscosity - temperature information for selected fuel oils

• The far right-hand columns list temperatures required to reduce the oil viscosity to levels often required for easy pumping (440cSt) and for atomization (20.7cSt).

• Required:

- Viscosity: 20-25cSt, filtration<125µm (abrasion and clogging: 3-stage filtration at 35, 60 and 120#) - Variation at the pump should not be higher than 5cSt

Delayed Coke Fluid Coke

LHV MJ/t 34,300 31,000 % C 88 – 90 87 – 88 % H 3.9 – 4.5 2 – 3 C/H Ratio 21 35 % S 2 – 6 5 – 8 ASH content (%) 0.5 – 1.5 2 – 8 Volatile matter (%) 10 – 15 5 – 10 Granulometry (mm) 0 – 50 0 – 8 Moisture content (%) 7 – 10 5 – 10 Ignition Temperature 220 - 250 230 – 250

5.5 Oil temperature (in C)

required for Type of oil Viscosity (ν) at 38C (cs)

pumping Atomisation #6 max 2200 59 129 #6 min 220 28 91 #5 max 165 22 83 #5 min 32.1 -7 50 #4 max 20.7 -17 38 #4 min 6.9 -59 -3 #2 max 3.5 -17 Other Viscosities

At ºC Water Air Natural gas

µ(cp) 1.124 0.0180 0.011

ν(cs) 1.130 14.69 14.92

• Approximate viscosity of water at 21C is 1 cp and 1 cs

4. Waste Fuel

a) Waste Fuel Specification

Heat Content < 23 GJ/T (9900 Btu/lb) ASTM D-240-76 range 28-32 GJ/T (12000-13800

Btu/lb)

Ash content < 7%

Specific gravity < 1.2 kg/L

Suspended solids < 30% (after being screened through a 30 mesh sieve)

Water < 1% (as separated phase)

Total halogens < 2%

Sulphur < 3%

Nitrogen < 1%

Inorganic acids and bases Extractable pH of 4 of 11

Barium < 3000 ppm Chromium < 300 ppm Lead < 3000 ppm Zinc < 3000 ppm Vanadium < 200 ppm PCB and PBB < 50 ppm Benzene < 0.5%

5.6 b) Approximate Properties of some By-product and Waste Fuels

• Different moisture contents may change these values considerably.

% Ash / Density Gross Heat Value

By Product or Waste Moisture _{Lb/ft3 Kg/m3} Btu/lb Kcal/kg

Animal fats 50-60 801-961 17,000 9,445

Brown paper 1.0/5 7 112 7,250 4,028

Corn cobs 3/5 10-15 160-240 8,000 4,445

Paint 8,000 4,445

Rubber waste 20/30 62-125 993-2000 10,000 5,556

Waste, type 0, trash 5/10 8-10 128-160 8,500 4,723

Waste, type 1, rubbish 10/25 8-10 128-160 6,500 3,611

Waste, type 2, refuse 5/70 15-20 240-320 4,300 2,389

Waste, type 3, garbage 5/70 30-35 481-561 2,500 1,389

Waste, type 4, pathological 5/85 45-55 721-881 1,000 556

Waste, type 6, compact 35-50 561-801 7,500 4,167

Wood 3/10 20 320 9,000 5,000

• Tires are usually high volatile content and high S and Fe/Zn content (if steel belts are not removed).

• Biomass fuels contain usually high level of moisture and O2 and may have a higher char reactivity than coal.

5. Natural Gas

a) Gas Characteristics

Typical example Content (%) _{LHV (Kcal/Nm3) Sp weight (kg/Nm3)}

CH4 93.93 8,556 0.7143 C2H6 2.42 15,223 1.3393 C3H8 0.26 21,795 1.9643 C4H10 (ISO+N) 0.002 28,336 2.589 C5H10 (ISO+N) 0 32,123 3.2143 S 0 CO2 0.34 1.9643 N2 3.05 1.2500 H2 0 0.0893 He 0 0.1339 O2 0 1.4286 Total 8462 0.7533 b) Combustion

Combustion Equations for Natural Gas

• CH₄ +2 O₂ →CO₂ +2 H₂O • O 2CO 3 H O 2 7 H C_{2 6} + ₂ → ₂ + ₂ • C₃H₈ +5O₂ →3CO₂ +4H₂O • O 4CO 5H O 2 13 H C_{4 10} + ₂ → ₂ + ₂ • C₅H₁₂ +8O₂ →5CO₂ +6H₂O • O H O 2 1 H₂ + ₂ → ₂ • S +O2 →SO2

5.7 Neutral Combustion Air for natural gas

• If[x] is the volume fraction of x, the neutral combustion air is:

[

]

[

]

[

]

[

]

[

]

[ ]

[ ] [ ]

      _{+ + + + + + −} 2 2 12 5 10 4 8 3 6 2 4 * H 1* S O 2 1 H C * 8 H C * 2 13 H C * 5 H C * 2 7 CH * 2 * 21 . 0 1 Rule of thumb

• 9.412 Nm3/Nm3gas (for the example) Neutral Combustion Products for natural gas

Nm3/Nm3 gas kg/Nm3 gas % volume % weight

CO2 0.999 1.962 9.58% 15.25%

SO2 0.000 0.000 0.00% 0.00%

H2O 1.962 1.576 18.81% 12.25%

N2 7.466 9.332 71.60% 72.51%

Total: 10.426 12.871

Natural Gas Heat Value

• kcal/m3 =90.3

[

CH4

]

+159.2

[

C2H6

]

+229

[

C3H8

]

.

6. Flame Theory

6.1 Definition

• The oxidation reaction is an exothermic reaction, which can be developed either slowly or quickly: The fast reaction leads to the flame.

6.2 Flame Speed

• In stable burner flames, the flame front appears to be stationary because the flame is moving toward the burner at the same speed that the fuel air mixture is coming out of the burner.

• Thus risk of blow off if mixture speed>flame speed.

• Natural gas flame speed in air: 0.3m/s and in Oxygen: 4 to 5m/s. 6.3 Flame Radiation • R =σ εT4 - σ= Boltsman constant - T = Flame temperature - ε: flame intensity: ≈ 1 solid fuel ≈ 0.8 – 0.95 heavy oil ≈ 0.25 – 0.70 gas 6.4 Factors Influencing the Flame Temperature

• ) prodct comb of heat specific ( * ) product comb of weight ( ) ion disssociat of effect ( ) fuel the of value heat net ( T = −

• An increase of flame temperature can be obtained by:

- Increasing combustion air temperature (ex: air temp: (200, 500, 900F) gives flame temp (3510, 3630, 3800)

- Decreasing inerts:

⇒ Avoid high excess air

⇒ O2 enrichment (ex: % O2 (21, 25, 29) gives flame temp (3650, 3900, 4150) in case of coal, air preheated at 510F)

5.8 - Completeness of combustion (full low heat value to be obtained):

⇒ Optimum excess air

⇒ High rate of mixing fuel and combustion air

• Water vapor in the flame decreases the flame temperature.

• Flue Gas.

Fuel Requirements

• To provide 1 000 000 Btu of available heat (fuel is CH4 and excess air=2%) then for instance with air (21% O2) it requires 4.6/2.3=2 times as much fuel

when preheat temp=500F as when

preheat is 1500F when flue gas

temperature is 3000F Temperature Impact F u e l Requ ir em e n t, M illio n B tu hhv %0 2 p reh ea t tem p era tu re , F

7. Burner Pipes

• The flame should be centered along the kiln axis. 7.1 Number of Air Circuits

• For solid fuels, the number of air circuits determines the degree of control on the flame shape. Single Circuit Burner Pipe

• Minimal control.

• The solid fuel has to be carried with the air.

• High velocities: Higher fan pressure requirement, higher wear in the circuit.

• Required burner tip velocity is of the order of 80 m/s. Two-circuit Burner

• Swirl + high velocity transport air.

• Additional control due to swirl but the problems of high pressure fan and high wear rate remain. Three-circuit Burner

• (swirl + high velocity axial + low velocity transport air).

• The most versatile one. The solid fuel does not have to be brought at a high velocity.

• Clearance of top guide vanes is critical since it will control eccentricity of flame. 7.2 Primary Air

Indirect System

• The primary air is usually controlled at below 12 % of the total combustion air. Direct system

• No recirculation of mill exit air, the primary air can be as high as 30 to 35 % of total combustion air. All of the air exiting the mill system enters the pyro-process.

5.9 Semi-direct system

• Primary air quantity varies (usually 18 to 25 %), depending upon the incoming fuel moisture.

• To keep a constant flow (10 to 15 % of total combustion air), it is possible to send the "overflow" to the kiln hood (for the direct or semi-direct system).

Primary air impact on heat consumption

Indirect Semi-direct Direct

Primary air 12% 20-25% 30-35%

kcal/kg 4-5 20-25 50

Tip velocity:

axial air swirl air transport air gas

80 to 250 m/s 50 to 250 m/s 20 to 40 m/s 200 m/s

Pressure drop within burner pipe:

For a three-circuit burner: Blower Design Pressure

• _{700 to 1000 mm H2O for axial air;} 3000 - 7000

• _{150 to 600 mm H2O for swirl air;} 200 - 2000

• _{600 to 1000 mm H2O for transport air (up to 1200 mm}

H2O for a modified three-circuit burner).

2000 - 3500

7.3 Transport air

Velocity

• The steadiest possible (25-35 m/s).

• Sufficient to prevent pulsations: 3-5 kg of coal/Nm3air, up to 7 kg/m3. Geometry

• Rising parts vertical and not diagonal.

• As short as possible.

Liquid fuel injection: use of injectors :

• MY type: 40 bars: when operation is stable.

• ZV2 (assisted pulverization): between 2 and 20 bars: when wide range of flow variation. 7.4 Specific Impulse

• Is = Characterizes approximately the primary/secondary air ratio irrespective of the kiln. Usually two thirds or more of the primary air (non included transport air).

• Momentum impulse: Q V * M Is= where:

-

Q

=

ki

ln

(

heat

power

)

inGJ

.

h

−1

- M=primary airflow(intheaxe)inkg.s−1 - V=AirSpeed in m.s−1

Rules of thumb

Specific impulse Long Kilns Short Kilns

Fuel Oil 1,2 N.h.GJ-1 1,2 N.h.GJ-1

Coal 1,5 N.h.GJ-1 1,5 N.h.GJ-1

5.10 7.5 Swirl

• Swirl is the ratio of the tangential component produced by the rotational air to the sum of the axial components Ix produced by the various primary air and gas circuits.

• It improves the stability by forming toroidal recirculation zones that recirculate heat and species (when Sw>0.3).

Rotational moment / axial moment ratio

Rot. circ. velocity: Vr Vry Vrx rg I_θr = Qmr . Vry I x = ΣΣΣΣ_i I x_i where:

SW

I r

I

De

r g x

=

θ

.

where: - I_θr = Ixrtg

α

- I_θ : tangential impulsion

- I_xr : rotational circuit axial impulsion

- α : swirl angle (usually between 20 and 35

degree: smaller for long dry kiln)

• The gyration radius defines, on the basis of the respective radius of the rotational circuit at the burner pipe tip.

- rg = 2/3 (re3– ri3) / (re2– ri2) - re = external radius

- ri = internal radius

• The equivalent diameter of the flow is given by:

χ Ι χ Ι ρ Π _m Qm 2 De= where:

- Qm = The total mass flowrate of the air injected - ρ_m = The average specific gravity of the air - Ιχ= The total axial impulse

Rules of thumb

swirl Long Kilns Short Kilns

Fuel, coal, coke 0,02 to 0.08 0,12 to 0.15

Gas 0,05 0,05

7.6 Examples of Burner Tip

Pillard Standard Axial Transport Swirl Gas Lafarge Burner Axial Transpor t Swirl Gas Tip velocity 100 m/s 10% of primary air

Axial Tip velocity: 250 m/s < 12% primary air

axial air holes rotational circuit air gun coal conveying circuit central air (flame catcher) 2 expansion seals

5.11 Burner Calculation (LAFARGE)

SWIRL AND MOMENTUM DETERMINATION Version 2.2

Original: CLV / S.THIERS Apr-95 PLANT :

Update: CTS / W.Oliveira Sep-99 Date : 24/02/2000

(Inputs are in bold characters) Name

COMMENTS :

TIP CROSS SECTION AREAS Diameters : % cross section reduction Dext : 355.6

(mm) thk : 9.525

AXIAL AIR 320.7 2667 mmWG

Holes 1, Vanes 2 : 1 218 m/s 291.7 71.6% 23 m/s 2360 Nm³/h

3963 mm² Dext : 273.1

247.7 thk : 12.7

TRANSPORT AIR 36 m/s 223.1 31 m/s Dext : 219.1

9096 mm² thk : 8.179

196.7 2500 mmWG

SWIRL AIR 212 m/s 172.8 56.2% 26 m/s 1437 Nm³/h

2491 mm² Dext : 141.3

thk : 6.553

DETAILS OF THE TIP Swirler Number slots groove width radial gap radius angle (o) of vanes width(mm) (mm) vanes(mm) raccord.

Swirl 35 20 12.0 9.800 0.5 1

Axial (if vanes)

-Axial (if holes) Number of holes : 24 Diameter : 14.50

GENERAL DATA

Kiln TYPE : AS PRODUCTION (T CK /d ) : 2630.00

NP : no preca, AT : air through, AS : air seperat. Specific heat consumpt.kJ/kg CK : 3486.00 FUEL ANALYSIS , AS FIRED (DRY BASIS) Swirl Air: F=Fan; B=Blower B

% C 70.26 % O 5.43 Percent of heat at back- end : 65.00

% S 2.03 NCA

% H 3.09 Nm³/kg fuel 6.96 Shell internal diameter (m ) : 4.14

Total combust. air ( Nm³/hr) : 99400.21 SPECIFIC HEAT CONSUMPTION Throughput L.H.V. Therm.power

AT THE BLAST PIPE kg/h KJ/kg GJ/h COKE/COAL 25/75 4760 28087 133.70

0.00 0.00

0.00 Recalculated SHC :

Total (GJ/h ) : 133.70 3486 kJ/kg CK GAS FLOW MEASUREMENTS Axial Swirl Transport

Static pressure in the tip (mm WG) 2667 2500

-Temperature in the pipe ( deg C) 100 100 100

Theoretical flow rate ( Nm³/h) 2360 1437 - Fuel to air ratio:

Bias coefficient : 1.00 1.00

Accepted flowrate ( Nm³/h) 2360 1437 860 4.05 kg coal/m³

Axial / Swirl distribution 62% 38%

RESULTS

FLOW VELOCITIES Axial Swirl Transport Is Swirl

Nature of flow subsonic subsonic velocity N.h/GJ

Release tip velocity (m/s) 218 212 36 2.14 0.18

Primary air rate, axial :

6.78% Targets: Fuel-Oil 1.2 0.15

swirl : 4.13% Coal 1.5 0.15

transport : 2.47% Coke 1.8 0.15

Axial + Transport: 9.26%

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 l G rin d a b ilit y (H a rd g ro v 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)

Bu rn in g T im e (seco n d s) Combustion Temp. = 1500°C Combustion Temp. = 900°C

5.13 8.3 Dosing

• Dosing should insure a regular and steady feeding of the burner. The targeted precision should be in the range of 1%(see Les Cahiers Techniques Combustion). Coal concentration up to 7kg/m3 of air.

8.4 Safety Considerations

• Process has to deal with safety. Recommendations

(to be adjusted plant by plant)

Sensor Threshold Sensor Threshold

Storage temperature, external, unpacted 50C Filter outlet temp (coke) 105C

Raw silo (lower base) 50C Temp difference (outlet-inlet) 10C

Raw silo (top) CO 1500 ppm Temp difference variation 10C

Grinding mill outlet temp (coke) 120C Filter outlet CO 2000ppm

Grinding mill outlet temp (Coal) 65C Filter hopper temp (coke) 85C

Mill inlet temp: (High VM : 40%) 200C Pulverized hopper CO 1000ppm

Mill inlet temp: (Low VM : 20%) 360C Pulverized hopper temp 85C

Filter outlet O2 (coke) 15% Fired fuel into the kiln (%H2O) 0.5-1.5%

Filter outlet (coal) 13% Transport air (non inert/inert) temp (Coal) 65/85C

(sources: PyroI, modified 2000, RdeB)

8.5 Fuel Grinders

• Feed size: 0-50mm, moisture content: 10-15%, exhaust gases dust load: 500-600g/m3.

• Hot gases temperature 250-400C, dew point: 20-70C, exhaust gases temperature: 80-100C.

• Moisture content in the blasted fuel below 1%.

Type of grinder Hammer mill Tube mill Roller mill Ring ball mill (Babcock)

kWh/t 20-30 25-30 10-13

Lifetime wear part 500-1000h Liners: 25-40000h 3-5000 h 9-12000h

Drying capacity 0-15% H2O 0-15% H2O 0-20% H2O

Tube mill Wear rate (g/t) Life (h) Rollermill Wear rate (g/t) Life (h)

Balls 80-200 Roller liners 5-20 4-9000

Liners 8-20 25-40000 Table liners 4-10 4-12000

Diaphragms 8-20 10-20000 Casting liners 3-5 2-12000

Rules of thumb:

• Mill sweep : 1.7 to 2.2 Nm3/kg fuel