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Highly reliable Low emission levels Efficient energy utilization Dry process kiln systems

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Page 1: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

■ Highly reliable

■ Low emission levels

■ Efficient energy utilization

Dry process kiln systems

1349_M_FLS_DryProcessKiln 28/11/02 9:16 Side 1

Page 2: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

2 · Dry process kiln systems

F.L.Smidth offers a range of six standarddry-process kiln systems, each with itsunique advantages depending upon theparticular application. In this way we areable to provide the industry with the mostsuitable kiln system configuration for anygiven set of conditions and requirements.

F.L.Smidth has supplied over 2500 rotarykiln systems and more than 3500 clinkercoolers. This experience, coupled with thelatest advances in pyroprocessing systemdesign, makes our technology the logicalchoice for both new installations and mod-ernisation of existing cement making facilities.

In modern cement plants, raw meal is pre-heated to calcination temperature in a mul-ti-stage cyclone preheater and most of thecalcination process takes place in a separate-ly fired calciner. The remaining calcinationand clinkerization process takes place in ashort length-to-diameter rotary kiln withoutinternals.

Preference is commonly given to the coolingof clinker in the SF Cross-Bar™ cooler inwhich the two main functions, conveyingand cooling of clinker, are completely sepa-rated. The introduction of stationary air dis-tribution plates with self-regulatingmechanical flow regulators (MFR) has revo-lutionized cooler operation.

This brochure describes each of the six pre-heater/calciner system configurations indetail and presents general guidelines fortheir selection depending upon capacityrequirements and whether the system isnew or an upgrade of an existing installa-tion. System components other thancyclones and calciners are dealt with in sepa-rate brochures that describe their mechanicaland operational features.

• Highly reliable systems for any production level

• A wide range of calciner systems tosuit specific require-ments

• Highly efficient lowpressure cyclones

• Effective emissioncontrol technology

• Optimized fuel andpower consumption

• Suitable for wastefuels

• Compact, space-savingpreheater designs

• Matching state-of-the-art technologiesfor clinkerization,cooling and firing:ROTAX-2 two-supportkiln, SF Cross-Bar™clinker cooler andDuoflex kiln burner

Main features

KI

LN

S

YS

TE

MS

1349_M_FLS_DryProcessKiln 28/11/02 9:16 Side 2

Page 3: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

Six standard Dry-process kiln systemconfigurations

SP: Suspension Preheater kiln

ILC: In-Line Calciner

SLC: Separate Line Calciner

ILC-E: In-Line Calciner using Excess air

SLC-D: Separate Line Calciner – Downdraft

SLC-I: Separate Line Calciner with In-line Calciner

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Page 4: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

-350mm WG

282° C

608° C

820° C

280° C

100° C

454° C

734° C

4 · Dry process kiln systems

Special advantages • For small capacities

– the economical solution.• Very low specific power consumption

– with planetary cooler.• Simple operation

– well suited for manual control.• Accepts higher input of chlorides than

precalcining systems with tertiary air duct(without bypass).

SP: Suspension Preheater kiln

Features • Normal capacity range: 700-4500 tpd.• Ratio of firing in riser duct: 0-15%.• Bypass of kiln gas: 0-30%.• Planetary cooler can be employed.

5-stage SP kiln systemand SF Cross-Bar™cooler Typical temperatures inthe system are indicatedtogether with the neg-ative pressure in theexhaust gas exit basedon a system designedfor minimum overallpressure drop. This typeof kiln system can beconverted to the SLCprecalcining system byadding an extra calcin-ing string. If no futurecapacity increase is tobe considered, a plane-tary cooler may beconsidered.

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Riser duct firing, if any

7. Cooler excess air

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Page 5: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

-395mm WG269° C

594° C

840° C

437° C

727° C

280° C

100° C

Dry process kiln systems · 5

Special advantages • Most economical solution for small and

medium capacities.• Low specific power consumption with

planetary cooler.• Easy operation due to high excess air

percentage in kiln. • Low coating tendency in kiln inlet

and riser duct. • Long kiln lining life due to stable kiln

coating. • Less sensitive to chlorides and sulphur

than precalcining systems with tertiary airduct (without bypass).

• Smaller kiln dimensions than SP system.

ILC-E: In-Line Calciner using Excess air

Features • Normal capacity range: 800-5500 tpd.• Ratio of firing in calciner: 10-25%.• Bypass of kiln gas: 0-25%.• Calcination at kiln inlet: 50-70% (com-

pared to 30-40% for SP operation).• Planetary cooler can be employed.

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Calciner burners

7. Cooler excess air

ILC-E kiln system withfive-stage preheaterand SF Cross-Bar™coolerTypical temperatures inthe system are indicat-ed, together with thenegative pressure in theexhaust gas exit, basedon a system designedfor minimum overallpressure drop. If nofuture capacity increaseis to be considered, aplanetary cooler maybe considered.

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Page 6: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

-465mm WG293° C

650° C

890° C

478° C

799° C

1000° C

280° C

100° C6 · Dry process kiln systems

Special advantages • High material and gas retention time in

calciner due to its large volume and moderate swirl.

• Regulation range of up to 30% bypass of kiln gas using ILC-I version.

• Well suited for low-grade fuels.• Long refractory life due to low thermal

kiln load and stable kiln coating.• Lowest NOx emission among traditional

calciner kiln systems.

ILC: In-Line Calciner

Features • Normal capacity range: 1500-6000 tpd,

with multiple strings > 10,000 tpd.• Ratio of firing in calciner: 55-65%. • Normal bypass of kiln gas: 0-60%. • Maximum bypass of kiln gas:

0-100% using ILC-I version.• Built-in low-NOx capabilities.• Calcination at kiln inlet: 90-95%.

ILC kiln system with five-stage preheater and SF Cross-Bar™ cooler Typical temperatures in thesystem are indicated,together with the negativepressure in the exhaust gasexit, based on a systemdesigned for minimum over-all pressure drop. Whendesigned for bypassing 30% or more of the kiln gases,the layout of the system willbe slightly different, as thetertiary air duct is connectedto the kiln riser duct at apoint below the calciner.This system is called the ILC-I calciner system. (See page 13)

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Calciner burners

7. Tertiary air duct

8. Tertiary air duct damper

9. Cooler excess air

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Page 7: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

-475mm WG300° C

657° C

890° C

487° C

803° C

886-1100° C

1000° C280° C

100° C

Dry process kiln systems · 7

Special advantages • High material and gas retention times in

the calciner/ combustion chamber whosedimensions are minimal since the kilngases do not pass through it.

• Very well suited for all fuel types, espe-cially low-volatile fuels, as the combustionin the calciner takes place in hot atmos-pheric air and the combustion tempera-ture in the calciner can be controlledindependently of the temperature of thecalcined material fed to the kiln.

• Low NOx operation is possible.• Smallest possible tower dimensions, as

the calciner can be installed separatelyfrom the cyclone tower.

• Especially well suited for retrofits of existing SP or ILC preheaters due to very short down time.

SLC-D: Separate Line Calciner – Downdraft

Features • Normal capacity range: 1500-6000 tpd,

with multiple strings > 10,000 tpd.• Firing in calciner: 55-60%.• Bypass of kiln gas: 0-60%.• Maximum bypass regulation range: 30%.• Calcination at kiln inlet: 90-95%.

SLC-D kiln system with five-stage preheater and SF Cross-Bar™ coolerTypical temperatures in thesystem are indicated,together with the negativepressure in the exhaust gasexit, based on a systemdesigned for minimumoverall pressure drop. Forproduction capacitiesexceeding approximately6000 tpd, the system isequipped with two or morepreheater strings, this alsobeing the case if a particu-larly low preheater tower isrequired.

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Calciner burners

7. Tertiary air duct

8. Tertiary air duct damper

9. Cooler excess air

10.Raw meal dividing gate

11.Slide damper

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Page 8: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

Special advantages • High material and gas retention times in the

calciner whose dimensions are minimalsince the kiln gases do not pass through it.

• Very well suited for all fuel types, evenlow-volatile fuels, as the combustion inthe calciner takes place in hot atmosphericair, and (as an option) the combustiontemperature in the calciner can be con-trolled independently of the temperatureof the calcined material fed to the kiln.

• Long refractory life due to low thermalkiln load and stable kiln coating.

• Independent and accurate draft controlfor kiln and calciner strings by adjustingspeed of individual fans.

• No damper in tertiary air duct. • Production down to 40% of capacity

using kiln string only.

SLC: Separate Line Calciner

-445mm WG294° C

469° C

750° C

484° C

822° C

664° C

890° C

280° C

100° C

1000° C

842° C

623° C

293° C-350mm WG

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Calciner burners

7. Tertiary air duct

8. Cooler excess air

9. Raw meal dividing gate

10.Raw meal change-over gate

SLC kiln system with SFCross-Bar™ cooler and five-stage preheater in the kilnand the calciner strings Typical temperatures in thesystem are indicated, togetherwith the negative pressurein the exhaust gas exits,based on a system designedfor minimum overall pressuredrop. The system offers thepossibility of controlling thetemperature level inside thecalciner, as part of the rawmeal from the second-low-est cyclone stage in the cal-ciner string can be feddirectly to the kiln riser and/or the upper portion of thecalciner vessel.

• Production down to 20% of capacity forthree-string version.

Features • Normal capacity range:

3000-7500 tpd (one C-string), 7500-12,000 tpd (two C-strings)

• Firing in calciner: 55-60%.• Bypass of kiln gas: 0-100%• Maximum bypass regulation range: 30%. • Calcination at kiln inlet: 90-95%.

8 · Dry process kiln systems

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Page 9: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

-445mm WG304° C

486° C483° C

774° C830° C

890° C

280° C

100° C

1000° C

655° C

-445mm WG305° C

643° C

850° C

Dry process kiln systems · 9

Special advantages • Very well suited for all fuel types, even

low-volatile fuels, as the combustion inthe SLC calciner takes place in hot atmos-pheric air, and (as an option) the combus-tion temperature in the SLC calciner canbe controlled independently of the tem-perature of the calcined material fed tothe kiln.

• Independent and accurate draft controlfor kiln and calciner strings by adjustingspeed of individual fans.

• Production up to 50% of capacity usingkiln string only (ILC or ILC-E).

• Same cyclone sizes and feed systems forboth strings.

Features • Normal capacity range: 6500-11,000 tpd.• Firing in kiln string ILC: 10-15%.• Firing in calciner string SLC: 40-50%.• Bypass of kiln gas: 0-30%.• Calcination at kiln inlet: 90-95%

SLC-I: Separate Line Calciner with In-line Calciner

SLC-I kiln system with SFCross-Bar™ cooler and five-stage preheaters in boththe kiln and calciner strings Typical temperatures areindicated, together with thenegative pressure in theexhaust gas exits, based ona system designed for mini-mum overall pressure drop.The system has the addedadvantages of having equalcyclone sizes in both strings,as well as increased capacityand improved fuel consump-tion when only the kiln stringis in operation.

material

gas

fuel

1. Raw meal feed

2. Exhaust gas

3. Kiln gas by-pass, if any

4. Clinker

5. Kiln burner

6. Calciner burners

7. Tertiary air duct

8. Cooler excess air

9. Raw meal dividing gate

10.Raw meal change-over gate

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Page 10: Dry process kiln systems - ximang.vn · • Long refractory life due to low thermal kiln load and stable kiln coating. • Independent and accurate draft control for kiln and calciner

10 · Dry process kiln systems

Selecting the proper kiln system configurationfor a given project is a complicated task thatinvolves a number of considerations. Duringthe initial planning stage it will often beuseful to consult F.L.Smidth who has gaineda wealth of experience from a large varietyof cement projects. As a general guide tochoosing the most suitable new kiln system,a number of criteria should be considered,the most important of which are as follows:

Production capacity and investment costs For any given production capacity, a precal-cining system requires considerably smallerrotary kiln dimensions than a simple suspen-sion preheater system.

F.L.Smidth normally recommends a rotarykiln diameter not exceeding 6 metres toensure reasonably long lining life. For thisreason, it is advisable to employ a precalcin-ing system (with tertiary air duct) for kilnproductions above 4000 tpd.

On the other hand, the simplicity of theILC-E kiln system equipped with a planetarycooler makes it the most economical solutionfor production capacities up to about 4500tpd. Of course, the lowest-possible heatconsumption and clinker temperature areattained by replacing the planetary coolerwith a modern SF Cross-Bar™ cooler. For thisreason, the grate cooler is the logical choicefor most new kiln installations – particularlywhen taking future expansion into account.

Single-string preheaters are preferred aslong as the cyclone diameter remains withinreasonable limits. This allows the SP andILC-E systems to be used as single stringsup to a production capacity of 4000-4500tpd. Similarly, the ILC and SLC-D systemscan be used as single strings up to about6000 tpd. In contrast, the SLC and SLC-I

Type selection guidelines

Three stringTwo stringOne string

TPD Production Three-support kiln

12000

11000

10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

0SP ILC-E ILC SLC SLC-I SLC-D

6.00 x 95

5.75 x 91

5.50 x 87

5.25 x 82

5.00 x 78

4.75 x 74

4.55 x 71

4.35 x 67

4.15 x 64

3.95 x 60

3.75 x 57

3.60 x 54

3.30 x 49

Two stringOne string

TPD Production ROTAX 2 kiln, L/D~13

10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

0SP ILC-E ILC SLC SLC-I SLC-D

6.00 x 72

5.75 x 69

5.50 x 66

5.25 x 62

5.00 x 60

4.55 x 54

4.75 x 56

4.35 x 51

4.15 x 49

3.95 x 46

3.75 x 44

3.60 x 42

3.45 x 40

Table 1b

Table 1a

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systems always have at least twopreheater strings and, therefore, willnormally only be considered forcapacities above 5000 tpd.

Tables 1a and 1b show the six differentpreheater/ precalciner configurationsas a function of production capacityalong with standard kiln sizes. The SPkiln system is also shown for compari-son, although this would not normallybe a preferred solution for a newinstallation.

OperationandmaintenanceThese days, precalciner systems aregenerally preferred to SP-type kilnsystems due to the fixed degree ofcalcination of the material enteringthe kiln and the shorter materialretention time in the system. Longerlining life and lower kiln refractoryweight enable precalcining kiln sys-tems to remain in operation forlonger periods than SP kilns, thusreducing down time and refractorycosts.

Generally, the maintenance costs ofa single-string kiln system are lowerthan those of a double-string kilnsystem. Consequently, a single-string preheater is always preferableto a double-string preheater forsmall-to-medium production capaci-ties, provided there are no towerheight limitations.

Fuel types and gradesAll F.L.Smidth kiln systems can befired with natural gas, heavy fuel oil,standard coal grades or a combina-

tion of these fuels. Special fuels,however, require special considera-tions when selecting the appropriatekiln system configuration:

Low-volatile fuels Fuels such as anthracite, petroleumcoke, and other low-reactive fuelspose no problem in the kiln whichoperates at a high temperature. Thekiln burner, however, should be ofthe modern flame-shaping type,such as the DUOFLEX, which has asuitable flow pattern that ensuresrapid and stable ignition.

The use of low-volatile fuels in calcin-ers (that usually operate at a temper-ature around 900°C) can cause prob-lems unless the system is providedwith a high-temperature calciner. Allour calciner systems are suited forthe use of low-volatile fuels as theyare designed to allow raising the tem-perature in the combustion chamberwithout affecting the rest of the sys-tem. This is accomplished by means ofa dividing gate that leads a relativelylarge amount of raw meal to the cal-ciner and/or the kiln riser duct.

Low-calorific fuels Fuels with high ash content rarelycause problems in the calcinerbecause the ash is intimately mixedinto the raw meal as a consequenceof the turbulence and high materialretention time. However, the use ofsuch fuels for kiln firing can causeproblems such as (1) the inability toreach sufficiently high flame temper-ature, and (2) the non-homoge-neous mixing of ash into the kiln charge which is already nodulised

and partially fused. For this reason,a precalcining system is always pre-ferred when using low-grade coalsbecause the total input ash contentto the kiln burning zone is greatlyreduced. Each type of fuel shouldbe considered separately. Typically,the lower limit for net heating valuecan be 3800 kcal/kg for the calcinerand 4000 kcal/kg for the kiln.

Alternative fuelsCombustible waste products can beused in all kiln systems as a substi-tute for fossil fuels, provided thatsuch substitution does not result innegative consequences for the kilnsystem operation.

Each type of waste product musttherefore be assessed on anindividual basis, by evaluation of theimpact on clinker quality, productioncapacity, kiln system stability andemissions. Also health and safetyissues must be taken into conside-ration.

For many solid waste products, thephysical size may be a challenge. Forslow-reacting waste products theSLC-D system might be suitable,due to the possibility of high-tem-perature calciner operation.However, high temperature opera-tion can also be introduced in theSLC type of calciners.

Some solid waste products mustalways be pretreated before feed-ing to the kiln or calciner. Thetraditional method is to operatecostly shredding and grinding sys-tems, but for the ILC system a HOT-DISC reactor may be used instead.This is a combustion chamber inte-grated with the calciner, allowingfor direct firing of lumpy wasteproducts at high substitution rates.

Dry process kiln systems · 11

DUOFLEX Kiln burner.

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12 · Dry process kiln systems

Type selection guidelines

Table 2: Heat consumption, pressure drop & power consumption ( no kiln bypass )

SLC-kiln 5000 t/d ILC kiln 3000 t/d

(SF Cooler) (SF Cooler)

Heat balance in (kcal/kg clinker) 5-stage 6-stage 5-stage 6-stage

Heat in exhaust gas and dust 153 132 149 130

+ radiation loss from preheater 34 39 31 35

+ radiation loss from kiln 19 19 23 23

+ heat of reaction 405 405 405 405

+ free water 5 5 5 5

+ VDZ cooler loss 107 109 113 115

+ heat of clinker at amb. temp. 3 3 3 3

- heat in raw meal, air and fuel 30 30 30 30

- combustibles in raw meal 8 8 8 8

= Net specific heat consumption 688 674 691 678

K - C K - C

Exhaust gas temperature (C) 294 256 293 258

Pressure loss preheater (mmWG) 305 360 305 360

Pressure loss in the rest of the system 45-140 45-140 160 160

Total pressure loss (mmWG) 350-445 405-500 465 520

Power consumption (kWh/t clinker)

ID fan(s) 5,0 5,4 5,3 5,7

Cooler (drive + fans+ crusher) 5,5 5,5 5,5 5,5

Kiln drive 2,1 2,1 2,1 2,1

Primary air fan 1,0 1,0 1,0 1,0

Cooler vent system 1,4 2,2 1,7 1,1

Total specific power consumption 15,0 16,2 15,6 15,4

(1) (2) (2) (1)

Table 2: Typical process values of SLC and ILC kilnswith five and six-stage preheaters.

(1) Includes electrostatic precipitator, vent fan anddust conveying system.

(2) Includes fabric filter, heat exchanger, vent fanand dust conveying system.

Heat efficiencyThe specific heat consumption of the vari-ous kiln systems depends mainly on the sizeof the kiln, the number of preheater stages,the rate of kiln bypass (if any), the raw mixcomposition, and the fuel type.

Table 2 shows typical heat balances for five-stage and six-stage SLC and ILC kiln systems.As shown, the specific heat consumption ofthe six-stage preheater system is 10 kcal/kgclinker lower than that of the equivalentfive-stage system. By comparison, the specificheat consumption of the five-stage preheatersystem is 20-25 kcal/kg clinker lower thanthat of the equivalent four-stage system.

Pressure drop and power consumption The most power-consuming parts of a kilnsystem are the Induced Draft gas fanmotor(s), the cooler fan motors and the kilndrive motor.

The power consumption of the ID gas fan(s)mainly depends on the total pressure drop inthe kiln system. Most of this pressure dropoccurs in the preheater. Increasing the pre-heater cyclone dimensions will reduce thepressure drop, but for any given preheatergeometry stable preheater operation (with-out raw meal falling through the riser ducts)requires a certain minimum pressure drop.The Low Pressure (LP) cyclone, a standardcomponent in all FLS kiln systems, was deve-loped to ensure a low pressure drop in thepreheater while maintaining high efficiencyand reasonably small cyclone dimensions.

The table compares the specific power con-sumption of an SLC and an ILC kiln system,both equipped with LP cyclone preheaters.

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Dry process kiln systems · 13

It also shows a comparison between the twomodern types of cooler venting systems(electrostatic precipitator versus fabric filterand heat exchanger).

For many years, costs have favoured the useof electrostatic precipitators (EP) for this pur-pose because of the higher running costs offabric filters (FF) in terms of power consump-tion and maintenance (bag replacement).However, with the tightening of emissionstandards, FF will tend to be preferred forcooler venting installations, because the EPsize increases proportionately with tighteremission standards, while the FF size remainsconstant.

Raw materialsThe content of volatile components in theraw materials is an important factor whenchoosing the appropriate kiln system.

Volatile components in connection with kilnoperation are usually understood as mineralscontaining the elements potassium (K),sodium (Na), sulphur (S), and chloride (Cl).Small quantities of these components willinevitably enter the kiln system with the rawmix and the fuel. On reaching the kiln burn-ing zone, some of the volatile componentsevaporate and are carried with the kiln gasto the preheater where they condense.

The resulting internal circulation of volatilematter in the kiln system and the concentra-tion of these components in the kiln gasesflowing to the preheater eventually reachessuch levels that it affects kiln operation. Thehigher concentration of volatile matterincreases dust stickiness which in turn causescoating formation and cyclone blockages.

The type of process selected sets an upperlimit to the acceptable content of the variousvolatile components in the raw mix (and thefuel) used in a preheater kiln system withouta bypass. The upper limit is lower with a pre-calcining system (with tertiary air duct) thanwith an SP kiln system due to the higher

volatile concentration in the gases of a pre-calcining system which is caused by thelower specific gas flow through the kiln, seetable 3.

If the volatile components in the raw mix(and fuel) are higher than these upper limits,the kiln system must be equipped with abypass that enables extracting some of thekiln gas from the system before it reachesthe preheater. In this way, internal circula-tion of volatile components is reduced.Bypassing a few per cent of the kiln gases issufficient to reduce the internal circulationof chloride in the kiln system to an accept-able level.

To produce low-alkali cement it may also bedesirable to remove large quantities of alkalisthrough a kiln bypass. This requires a highbypass rate, and a precalcining system withtertiary air duct will be appropriate. For agiven amount of kiln gas extracted, higheralkali reduction is obtained in a precalciningsystem than in a SP kiln system. A certainreduction of alkali in the clinker can beattained by the lowest-possible increase inthe specific fuel consumption.

The ILC-I and SLC kiln systems allow bypass-ing up to 100% of the kiln gas while theother kiln systems can be equipped with abypass carrying a maximum 25-60% of thekiln gas, which in most cases will suffice toensure smooth operation, even with low-grade raw materials.

Table 3: Allowable total input of volatile components for kiln systems without bypass on LOI free basis.

Normal limit

ILC, SLC & SLC-I

Chlorine as CI 0.023%

Sulphur as S-total 1.25%

SP & ILC-E

Chlorine as CI 0.029%

Sulphur as S-total 1.5%

Table 3: The normal limit applies toa raw mix of good burnability andan ideal sulphur/alkali ratio

Maximum by-pass version ILC-I

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14 · Dry process kiln systems

All six kiln systems are supplied with a four-stage, five-stage, or six-stage cyclone pre-heater equipped with Low Pressure (LP)cyclones.

The unique design of the LP cyclone ensureshigh thermal efficiency and low pressure dropwhile enabling moderate preheater towerdimensions.

A four-stage preheater can be designed fora pressure drop down to 250 mm WG acrossthe preheater itself, while a five-stage pre-heater can be designed for a pressure dropdown to 305 mm WG at nominal capacity.Even with these low nominal pressure drops,the preheaters operate smoothly down to70-80% of rated capacity without increasingthe percentage of excess air.

Since the LP cyclones have no horizontalsurfaces on the inside, no material will accu-

mulate and this, in turn, ensures smoothoperation.

The lowermost cyclone (exposed to gastemperatures of about 900°C) is equippedwith a cast, segmented central pipe (thimble)of special alloy which maximizes thermalefficiency while ensuring long life.

The central pipe is easy to install and, becauseit consists of segments, will fit any size ofcyclone both in new and existing preheaters.

To prevent the gas from bypassing up throughthe material chutes between the individualcyclone stages, the chutes are equippedwith tipping valves. Distribution boxes withadjustable spreader plates ensure correctmaterial distribution in the individual riserducts. Change-over gates and dividing gatesare used to efficiently distribute the raw meal.

Cyclone preheater

The segmented centralpipe (thimble).

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16 · Dry process kiln systems

In-Line Calciners:In-Line calciners are generally known togenerate lower NOx emissions than Separate-Line calciners since all of the kiln exhaustgases must pass through the calciner.

F.L.Smidth's patented Low NOx ILC design isbased on dividing the meal from the secondlowest preheater cyclone to (1) the kiln riserand (2) the calciner, which are separated byan expanded riser duct that forms a reducingNOx zone. That is, the calcining chamber isbuilt (at least partially) into the kiln riser. Inthis way, a very simple means of creating lowNOx emissions without splitting of tertiary airis attained. 100% of the fuel is fired to thekiln riser duct. As a result, it is possible toobtain both reducing conditions and high

temperature zone in one simple system (with-out multiple firing points) for the lowestpossible NOx emissions. The combustion airis drawn either through the kiln or through aseparate tertiary air duct. Because the kilncombustion gases are drawn through thecalciner, the calciner size is necessarily largerto attain the required gas velocity andretention time. Following the reductionzone, the calciner’s cylindrical section issequentially tapered. The resultant rapidchanges in cross-sectional areas createstrong vortexes ensuring effective mixing offuel, raw meal, and gas. The top of the cal-ciner is most often provided with a loop ductto ensure optimum gas retention time, mix-ing and complete combustion of the fuel.

In the ILC-E configuration, kiln exhaust gasenters the calciner axially through the bottomcone and the calciner exhaust gas leaves thecalciner through a side outlet at the top. Inthe ILC configuration, kiln exhaust gas entersthe calciner axially through the bottom coneand leaves through an outlet connected toa central outlet pipe. The mixing of the fuel,raw meal and gas is further enhanced bythe tertiary air duct being fitted tangentiallyon the calciner. This causes a moderate swirlin the calciner which further increases parti-cle retention time. When designed forbypassing 60% or more of the kiln gases,the tertiary air duct is connected to the kilnriser (in an ILC-I configuration – page 13)rather than tangentially connected to thecalciner.

Separate-Line CalcinersSeparate-line calciners are also known as“air-only” calciners since the calciningchamber is at least partially offset from thekiln riser. The combustion air is always

Low NOx CalcinersIn the following pages, the threebasic types of calciners (In-Line,Separate-Line, and Downdraftcalciners) offered by F.L.Smidthare discussed in detail.

All F.L.Smidth calciners arespecifically designed to meettoday's most stringent emissionslimits by minimizing NOx andCO emissions among other pol-lutants. This is best accomplishedthrough the use of a cylindrical-ly-shaped vessel with a conicalbottom. The cylindrical designensures ample internal volumewhile minimizing calciner weightand surface heat loss.

All F.L.Smidth low NOx calcinersare designed for (1) localizedreducing conditions and/or (2)high temperature zone both ofwhich are proven to significant-ly minimize NOx emissions. Theelevated temperature designsare also particularly suited forthe use of low volatile fuels.

In fact, many F.L.Smidth calcinerdesigns are specifically tailoredfor today's demands for the fir-ing of low-reactive and hard-to-burn fuels. All calciners can befired with liquid, gaseous orpulverized fuels. The calcinerburners are placed so that thefuel is evenly distributed acrossthe calciner cross sectionenabling it to ignite rapidly inthe presence of tertiary air. The downdraft calciner, forexample, is equipped with avertical burner that makes itparticularly well suited for lowvolatile fuels.

All F.L.Smidth calciners (andpreheaters) are lined withwear-resistant refractory brickson all cylindrical and conicalsurfaces. The irregularly shapedareas are lined with castable.The wear-resistant lining is fittedon a back lining of insulatedblocks, which ensures a verylow heat loss from the calcinerand/or preheater surface.

ILC Calciner

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drawn through a separate tertiary air duct.Because the kiln combustion gases do notpass through the calciner, the calciner sizecan be reduced to attain the required gasvelocity and retention time. This oftenresults in a shorter preheater structure (anda shorter erection period for retrofits) sincethe calciner can be readily situated outsideof the preheater structure.

In the SLC configuration, the hot tertiary airfrom the cooler enters the calciner throughthe central inlet in the bottom cone andleaves through either a side outlet or (incase high temperature operation is planned)through an outlet cone connected to a cen-tral outlet pipe.

In the SLC-I configuration, a SLC calciner is built parallel to the kiln riser duct asdescribed above and a second ILC calcineris built into the kiln riser duct. This designeffectively destroys thermal NOx generatedin the burning zone of the kiln. Fuel NOxgenerated in the calciner is effectively mini-mized through high temperature operation.

A unique feature of the high temperaturecalciner system is the fact that the tempera-ture inside the calciner is independentlycontrolled by the position of the gate thatdivides the raw meal flow to the calcinerand to the kiln riser duct, respectively.

So, by feeding a relatively larger amount ofraw meal to the kiln riser duct and keepingthe fuel input to the calciner constant, themean temperature in the calciner vessel canbe brought up to 9500 – 10500C. The tem-perature of the exit gas and the degree ofcalcination of the raw meal leaving the cal-ciner will increase accordingly. However, whenmixing with the kiln exhaust gas that containsuncalcined raw meal, the temperature of thegas/particle suspension falls to approximately900oC. So a normal temperature level ismaintained in the calciner cyclone. Similarly,a normal degree of calcination of 90-95%is maintained for the raw meal supplied tothe kiln.

The higher temperature in the calcinerensures effective combustion of even low-reactive fuels and helps to greatly minimizefuel NOx formation.

The calciners of the SLC and SLC-I systemsare characterized by a vortex formation inthe bottom cone, ensuring effective mixingof raw meal, fuel and tertiary air for a highparticle-to-gas retention time ratio.

SLC Calciner

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18 · Dry process kiln systems

Downdraft CalcinersThe downdraft calciner is specifically tailoredto low-reactive fuels since the combustionair for the downdraft calciner (DDC) isdrawn solely from the clinker cooler. Theseparate-line features of this calciner designminimize the height of the preheater struc-ture since a substantial portion of the totalretention time is located parallel to the kilnriser duct. The placement of the combus-tion chamber outside the preheater struc-ture makes this calciner design well suitedfor retrofits since down time is minimized.

The SLC-D configuration combines theadvantages of the well-known Separate-linecalciners with the low NOx features of theIn-line calciner when a portion of the calcinerfuel is directed to the kiln riser duct. Thiseffectively destroys thermal NOx formed inthe kiln. Most of the fuel is introduced via a

multi-channel vertical burner located in theroof of the DDC under high temperatureconditions to minimize fuel NOx. In theSLC-D configuration, raw meal entrained inhot tertiary air enters the DDC at the topthrough a 180 degree involute (similar to anLP cyclone) and exits through a truncatedcone which forms a circular duct transitionto the kiln riser duct. The 180 degree invo-lute ensures that the majority of the calcinedmeal is detained along the walls of the DDC.This effectively protects the refractory liningwhile promoting hot core conditions foroptimum combustion characteristics in thecentre of the calciner.

For the same production capacity, the calcinerof the SLC-D system has smaller dimensionsthan the ILC calciner since no kiln exhaustair is led through the calciner. This makesthe SLC-D system well suited for retrofitapplications even when low reactive fuelsare not planned.

SLC-D Calciner

Low NOx Calciners

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Dry process kiln systems · 19

State-of-the-art systems Designing equipment and systems for themanufacture of cement has always been achallenging task due to the variations in rawmaterials, the multitude of cement productsrequired for the marketplace, and the needto minimize investment costs. In addition,integrating high-efficiency concepts withthe requirement for reliability has tended toinhibit the development of new machineryand systems. However, widespread accept-ance of preheater and precalciner systemshas created the opportunity to evolve to thepresent high level of efficiency and reliability.Table 4 clearly reflects the trend towardslarge single production lines and previouslyunheard-of low levels of fuel consumptionfor the modern dry processes.

In the case of F.L.Smidth, the evolution ofour designs has been driven by the continuingperformance evaluation of existing systems,coupled with feedback which has identifiedthe obstacles to achieving optimum perform-ance of every system component. This hasbeen particularly true for kiln system upgrad-es and modernisation projects. It is com-monplace for F.L.Smidth to audit the per-formance of kiln systems before and aftermodification. In the process of establishingthe potential modification scenarios, eachpreheater stage, the kiln, cooler and othersystem auxiliaries are analysed and comparedto the standards of performance beingachieved by the most modern systems thathave been installed by F.L.Smidth worldwide.Some of the more notable achievements ofthese projects are shown in table 4.

By utilising its extensive mechanical andplant design capabilities, F.L.Smidth hasbeen able to implement the necessary mo-difications with minimum interruption tothe plant's normal operations. In this way,the “state of the art” has been advancedfor existing plants as well as greenfield facilities.

State-of-the-art systems

Table 4: Examples of F.L.Smidth plants operating with low heat consumptionHeat balance (kcal/kg clinker)

Plant location Plant A Plant B Plant C Plant DMexico Indonesia USA Thailand

Heat in exhaust gas and dust 134 184 135 182

Heat in free water evaporation 2 2 5 4

Heat in bypass gas 0 0 39 0

Radiation loss from preheater 37 22 48 35

Radiation loss from kiln 28 31 44 25

Total cooler loss 132 125 113 124

Heat of reaction 374 384 320 360

Free heat from air, fuel and feed -30 -29 -31 -33

Net specific heat consumption 677 719 673 697(651 w/o bypass)

Plant A – 6-stage ILC preheater w/2-support kiln and conventional cooler (3000 MTPD)Plant B – 4-stage SLC-I preheater w/conventional cooler (7800 MTPD)Plant C – 6-stage ILC preheater w/SF Cross-Bar cooler and 15% operating bypass (3700 MTPD)Plant D – 5-stage SLC preheater w/ conventional cooler (10,000 MTPD)

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Data in this brochure is intended for preliminary project planning only. Manufacturer reserves the right to modify equipment details and/or specifications without notice.

DENMARK F.L.Smidth A/SVigerslev Allé 77DK-2500 ValbyCopenhagenTel: +45 36 18 10 00Fax: +45 36 30 18 20E-mail: [email protected]

INDIAFuller India LimitedCapital Towers180, Kodambakkam High RoadNungambakkamChennai 600 034IndiaTel: +91 44-827-6030/8228623Fax: +91 44-827-9393E-mail: [email protected]

USAF.L.Smidth Inc.2040 Avenue CBethlehem, PA 18017-2188Tel: +1 610-264-6011Tel: +1 800-523-9482Fax: +1 610-264-6170E-mail: [email protected]

www.flsmidth.com

Up-to-date addresses of worldwidesubsidiaries and sales offices are available from our website

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