05 Combustion

CEMENT PROCESS ENGINEERING VADE-MECUM

5. COMBUSTION & FUELS

Rev. 2002


SECTION 5 – COMBUSTION & FUELS

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

Index - i 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 Coal Coke Waste Fuel Fuel oil Nat. gas

%H 5 4 10 10 25

HHV (Btu/lb) 12,000 14,000 9,000 19,000 23,000

LHV (Btu/lb) 11,540 13,630 8,070 18,070 20,680

LHV (kcal/kg) 6410 7570 4480 10040 11490

LHV as a % of HHV 96 97 90 95 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. Ignition Temperature C

300

% VM

5.1 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 H2

Limit flammability in air Inf limit (%) Sup limit (%) 4 75

Temp auto flame in air (°C) 570

CO CH4

12.5 5

74 15

610 580

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 0.1to 1 second 0.1 0.01 to 0.001 In second, at atmospheric pressure

Gas 0.001

2. Solid Fuel 2.1 Coal a) Main Coal Characteristics Approximate Analysis and bulk density for Various Coals Group Anthracite Meta anthracite Anthracite Semi anthracite Bituminous Low-vol Med volatile High vol A High vol B High vol C Subbituminous A B C Lignitic A B

Fixed carbon (%) < than

Volatile matter (%)

≥ than

> than

98 92 86

98 92

2 2 8

86 78 69

14 22 31

Heat value (Btu/lb.) ≥ than

< than

Kg/m3 800-930

8 14 670-910

78 69

22 31 13,000 11,500 10,500 9,500 8,300 640-860 6,300

5.2 Rev. 2002



b) Combustion Calculation for Coal Ultimate Analysis (Dry Basis)

Proximate Analysis Volatile Free carbon Moisture Ash HHV

22.19 64.29 6.5 12.5 7.259

LHV = HHV – 5218 H LHV = HHV – 93.9196*H

% dry % dry % % dry kcal/kg coal dry (kcal/kg) @ 25° C, or (Btu/lb)

Carbon Hydrogen Sulfur Nitrogen Chlorine Oxygen Ash

% weight 74.87 3.78 2.24 1.93 0.08 3.53 13.57

C: H2: S: N2: Cl: O2:

nb moles/kg 62.33 18.75 0.70 0.69 1.10

Where: H is the mass fraction of hydrogen in the fuel. Combustion Equations • C + O2 → CO2 + 7 ,829 kcal / kg C • 1 • H 2 + O2 → H 2 O + 2 ,8641 kcal / kg H 2 - the oxydation of coal is very quick: 0.1 to 0.3 seconds

S + O 2 → SO2 + 2 ,213 kcal / kg S

Heat Value Calculation • If (x) is the ponderal % of x, the heat value can be calculated with the following formula: (O )  − 6W , where W is H O content of the fuel  - LHV (kcal/kg) = 80.8(C ) + 22.45(S ) + 287 * (H ) − 2 8   - HHV = 80.8(C ) + 22.45(S ) + 339.4(H ) − 35.9(O ) Neutral Combustion Air for Coal •

Input in mass % V=

(S ) + (H ) − (O )  22.4  (C ) * + 21 12.01 32.06 4 *1.01 2 *15.99 

Rule of thumb • 7.6 Nm3/kg of dry coal Neutral Combustion Products Nm3/kg Combustion CO2 1.306 H2O 0.393 SO2 0.015 N2 5.721 H2O 0.081 Moisture Total 7.515

Kg/kg 2.564 0.316 0.042 7.152 0.065 10.138

%vol 17.4 5.2 0.2 76.1 1.1

%weight 25.3 3.1 0.4 70.5 0.7

5.3 Rev. 2002



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.

LHV MJ/t %C %H C/H Ratio %S ASH content (%) Volatile matter (%) Granulometry (mm) Moisture content (%) Ignition Temperature Hard Grove (HGI)

Delayed Coke 34,300 88 – 90 3.9 – 4.5 21 2–6 0.5 – 1.5 10 – 15 0 – 50 7 – 10 220 - 250 90 – 100

Fluid Coke 31,000 87 – 88 2–3 35 5–8 2–8 5 – 10 0–8 5 – 10 230 – 250 10 - 30

3. Fuel Oil 3.1 Main Characteristics Comp C H O N S Ash C/H ratio Specific Gravity •

Api Gravity =

Nº1 86.4 13.6 0.01 0.003 0.09 <0.01 6.35

Nº2 87.3 12.6 0.04 0.006 0.22 <0.01 6.93 0.849

Nº4 86.47 11.65 0.27 0.24 1.35 0.02 7.42 0.902

Nº6 FO 87.26 10.49 0.64 0.28 0.84 0.04 8.31

Nº6 84.67 11.02 0.38 0.18 3.97 0.02 7.62 0.965

141.5 − 131.5 ( for SG < 1) Specific Gravity

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, µ measured 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

5.4


Type of oil

Viscosity (ν) at 38C (cs)

#6 max #6 min #5 max #5 min #4 max #4 min #2 max

2200 220 165 32.1 20.7 6.9 3.5


Oil temperature (in C) required for pumping Atomisation 59 129 28 91 22 83 -7 50 -17 38 -59 -3 -17

Other Viscosities At ºC Water Air Natural gas 1.124 0.0180 0.011 µ (cp) 1.130 14.69 14.92 ν (cs) • Approximate viscosity of water at 21C is 1 cp and 1 cs

4. Waste Fuel a) Waste Fuel Specification Heat Content < Ash content

<

Specific gravity Suspended solids Water Total halogens Sulphur Nitrogen Inorganic acids and bases Barium Chromium Lead Zinc Vanadium PCB and PBB Benzene Odor

< < < < < < < < < < < < <

23 GJ/T (9900 Btu/lb) ASTM D-240-76 range 28-32 GJ/T (12000-13800 Btu/lb) 7% 1.2 kg/L 30% (after being screened through a 30 mesh sieve) 1% (as separated phase) 2% 3% 1% Extractable pH of 4 of 11 3000 ppm 300 ppm 3000 ppm 3000 ppm 200 ppm 50 ppm 0.5% Characteristic of solvents as per ASTM 1296-69

5.5



b) Approximate Properties of some By-product and Waste Fuels • Different moisture contents may change these values considerably. By Product or Waste Animal fats Brown paper Corn cobs Paint Rubber waste Waste, type 0, trash Waste, type 1, rubbish Waste, type 2, refuse Waste, type 3, garbage Waste, type 4, pathological Waste, type 6, compact Wood

• •

% Ash / Moisture 1.0/5 3/5 20/30 5/10 10/25 5/70 5/70 5/85 3/10

Density Lb/ft3 Kg/m3 50-60 801-961 7 112 10-15 160-240 62-125 8-10 8-10 15-20 30-35 45-55 35-50 20

993-2000 128-160 128-160 240-320 481-561 721-881 561-801 320

Gross Heat Value Btu/lb Kcal/kg 17,000 9,445 7,250 4,028 8,000 4,445 8,000 4,445 10,000 5,556 8,500 4,723 6,500 3,611 4,300 2,389 2,500 1,389 1,000 556 7,500 4,167 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 CH4 C2H6 C3H8 C4H10 (ISO+N) C5H10 (ISO+N) S CO2 N2 H2 He O2 Total

Content (%) 93.93 2.42 0.26 0.002 0 0 0.34 3.05 0 0 0

LHV (Kcal/Nm3) 8,556 15,223 21,795 28,336 32,123

Sp weight (kg/Nm3) 0.7143 1.3393 1.9643 2.589 3.2143

8462

1.9643 1.2500 0.0893 0.1339 1.4286 0.7533

b) Combustion

Combustion Equations for Natural Gas • CH 4 + 2 O2 → CO2 + 2 H 2 O 7 • C 2 H 6 + O2 → 2 CO2 + 3 H 2 O 2 • C 3 H 8 + 5 O2 → 3 CO2 + 4 H 2 O 13 • C 4 H 10 + O 2 → 4 CO2 + 5 H 2 O 2

• • •

C 5 H 12 + 8 O2 → 5 CO2 + 6 H 2 O 1 H 2 + O2 → H 2 O 2 S + O2 → SO2

5.6



Neutral Combustion Air for natural gas • If [x] is the volume fraction of x, the neutral combustion air is: 1  7 13 1  *  2 * [CH 4 ] + * [C 2 H 6 ] + 5 * [C 3 H 8 ] + * [C 4 H 10 ] + 8 * [C 5 H 12 ] + * [H 2 ] + 1 * [S ] − [O2 ] 0.21  2 2 2  Rule of thumb • 9.412 Nm3/Nm3gas (for the example) Neutral Combustion Products for natural gas Nm3/Nm3 gas 0.999 0.000 1.962 7.466 10.426

CO2 SO2 H2O N2 Total:

kg/Nm3 gas 1.962 0.000 1.576 9.332 12.871

% volume 9.58% 0.00% 18.81% 71.60%

% weight 15.25% 0.00% 12.25% 72.51%

Natural Gas Heat Value •

kcal / m 3 = 90.3 [CH 4 ] + 159.2 [C 2 H 6 ] + 229 [C 3 H 8 ] .

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 ε T4 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 • •

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

⇒ ⇒

5.7


⇒ ⇒

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

% 02preheat temperature, F

• •

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 Requirement, Million Btu hhv

-


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.

5.8



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 Primary air 12% 20-25% kcal/kg 4-5 20-25

Direct 30-35% 50

Tip velocity: axial air 80 to 250 m/s

transport air 20 to 40 m/s

swirl air 50 to 250 m/s

gas 200 m/s

Pressure drop within burner pipe: For a three-circuit burner: • 700 to 1000 mm H2O for axial air; • 150 to 600 mm H2O for swirl air;

•

Blower Design Pressure 3000 - 7000

600 to 1000 mm H2O for transport air (up to 1200 mm H2O for a modified three-circuit burner).

200 - 2000 2000 - 3500

7.3 Transport air Velocity • The steadiest possible (25-35 m/s). • Sufficient to prevent pulsations: 3-5 kg of coal/Nm3 air, 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: where: M *V Is = Q - Q = ki ln ( heat power )inGJ .h −1 -

M = primary airflow ( in the axe ) in kg .s −1

-

V = Air Speed in m.s −1

Rules of thumb Specific impulse Fuel Oil Coal Coke

Long Kilns 1,2 N.h.GJ-1 1,5 N.h.GJ-1 1,8 N.h.GJ-1

Short Kilns 1,2 N.h.GJ-1 1,5 N.h.GJ-1 1,8 N.h.GJ-1

5.9



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). where: Rotational moment / axial moment ratio - I θr = I xr t g α Vry Rot. circ. velocity: Vr

Vrx

Iθ r r g SW = I x . De

rg

where:

I θ r = Qmr . Vry Ix = Σ

•

I i xi

The equivalent diameter of the flow is given by: 2Qm Ιχ De =

Πρ mΙχ

-

Iθ : 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 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 Fuel, coal, coke Gas

Long Kilns 0,02 to 0.08 0,05

Short Kilns 0,12 to 0.15 0,05

7.6 Examples of Burner Tip air gun

Pillard Standard Axial Transport Swirl Gas

axial air holes

Tip velocity 100 m/s 10% of primary air

rotational circuit 2 expansion seals

Lafarge Burner Axial Transpor t Swirl Gas

coal conveying circuit

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

central air (flame catcher)

5.10



Burner Calculation (LAFARGE)

SWIRL AND MOMENTUM DETERMINATION Original: CLV / S.THIERS

Apr-95

Update: CTS / W.Oliveira

Sep-99

(Inputs are in bold characters) COMMENTS :

TIP CROSS SECTION AREAS AXIAL AIR Holes 1, Vanes 2 : 1 3963 mm² TRANSPORT AIR 9096 SWIRL AIR 2491

218 m/s

Version 2.2

PLANT : Date : 24/02/2000 Name

Diameters : (mm) 320.7 291.7

36 m/s

247.7 223.1

212 m/s

196.7 172.8

% cross section reduction

71.6%

23 m/s

2667 2360

31 m/s

mm²

56.2%

26 m/s

2500 1437

mm²

DETAILS OF THE TIP Swirl Axial (if vanes)

Swirler angle (o) 35 -

Axial (if holes) GENERAL DATA Kiln TYPE :

Number of vanes 20

Number of holes :

slots width(mm) 12.0

groove width (mm) 9.800

24

AS

355.6 9.525

273.1 12.7 219.1 8.179

141.3 6.553

radial gap vanes(mm) 0.5

radius raccord. 1

Diameter :

14.50

2630.00

PRODUCTION (T CK /d ) :

NP : no preca, AT : air through, AS : air seperat.

70.26 2.03 3.09

SPECIFIC HEAT CONSUMPTION AT THE BLAST PIPE COKE/COAL 25/75

3486.00

Specific heat consumpt.kJ/kg CK :

FUEL ANALYSIS , AS FIRED (DRY BASIS) %C %S %H

Dext : thk : mmWG Nm³/h Dext : thk : Dext : thk : mmWG Nm³/h Dext : thk :

%O NCA Nm³/kg fuel

5.43

Throughput kg/h 4760

L.H.V. KJ/kg 28087

Swirl Air: F=Fan; B=Blower

B

Percent of heat at back- end :

65.00

6.96

Total (GJ/h ) : GAS FLOW MEASUREMENTS Static pressure in the tip (mm WG) Temperature in the pipe ( deg C) Theoretical flow rate ( Nm³/h) Bias coefficient : Accepted flowrate ( Nm³/h)

Axial 2667 100 2360 1.00 2360

Swirl 2500 100 1437 1.00 1437

Axial / Swirl distribution

62%

38%

4.14

Shell internal diameter (m ) :

Total combust. air ( Nm³/hr) : 99400.21 Therm.power GJ/h 133.70 0.00 0.00 0.00 Recalculated SHC : 133.70 Transport 100 860

3486

kJ/kg CK

Fuel to air ratio: 4.05 kg coal/m³

RESULTS FLOW VELOCITIES

Axial

Nature of flow Release tip velocity (m/s) Primary air rate, axial : swirl : transport : Axial + Transport: Primary air rate

Swirl

Swirl

36

Is N.h/GJ 2.14

Fuel-Oil Coal Coke

1.2 1.5 1.8

0.15 0.15 0.15

Transport

subsonic

subsonic

velocity

218

212 Targets:

6.78% 4.13% 2.47% 9.26% 13.39%

THERMAL LOAD (MW/m² ) :

0.18

3.16

5.11



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

Fuel Grindability (Hardgrove)

100

80

60

Passing 75um (#200) 40

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

20 0.6

0.8

1.0

1.2

1.4

Mill Capacity Factor

•

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% 98 – 0.7 * % VM 98 – 0.6 * % VM 200 Mesh • 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 Burning Time (seconds)

10 Combustion Temp. = 900°C

1 Combustion Temp. = 1500°C

.1 .01

.1 Diameter of coal particle (mm)

1

5.12



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 Storage temperature, external, unpacted Raw silo (lower base) Raw silo (top) CO Grinding mill outlet temp (coke) Grinding mill outlet temp (Coal) Mill inlet temp: (High VM : 40%) Mill inlet temp: (Low VM : 20%) Filter outlet O2 (coke) Filter outlet (coal) (sources: PyroI, modified 2000, RdeB)

Threshold 50C 50C 1500 ppm 120C 65C 200C 360C 15% 13%

Sensor Filter outlet temp (coke) Temp difference (outlet-inlet) Temp difference variation Filter outlet CO Filter hopper temp (coke) Pulverized hopper CO Pulverized hopper temp Fired fuel into the kiln (%H2O) Transport air (non inert/inert) temp (Coal)

Threshold 105C 10C 10C 2000ppm 85C 1000ppm 85C 0.5-1.5% 65/85C

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 Balls Liners Diaphragms

Wear rate (g/t) 80-200 8-20 8-20

Life (h) 25-40000 10-20000

Rollermill Roller liners Table liners Casting liners

Wear rate (g/t) 5-20 4-10 3-5

Life (h) 4-9000 4-12000 2-12000

Rules of thumb: • Mill sweep : 1.7 to 2.2 Nm3/kg fuel • Drying efficiency : average 1200kcal/kgH2O for a residual moisture of 0.5 to 1.5%

5.13

05 Combustion

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