Dry process kiln systems - · PDF filekiln, SF Cross-Bar™ clinker cooler and Duoﬂex kiln burner Main features KILN SYSTEMS. Six standard Dry-process kiln system

■ Highly reliable

■ Low emission levels

■ Efficient energy utilisation

Dry process kiln systems

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 kilnsystem configurations in detail and presentsgeneral guidelines for their selectiondepending upon capacity requirements andwhether the system is new or an upgradeof an existing installation. System compo-nents other than cyclones and calciners aredealt with in separate brochures that describetheir mechanical and 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

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


Special advantages • For small capacities

– the economical solution.• Very low specific power consumption.• 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: 700-2800 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

Dry process kiln systems · 5

Special advantages • Most economical solution for small and

medium capacities.• Low specific power consumption.• 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: 800-3500 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


4. Clinker

5. Kiln burner

6. Calciner burners


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.


Special advantages • High material and gas retention time in

calciner due to its large volume and moderate swirl.

• Regulation range of up to 60% 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: 1500-5000 tpd,

with multiple strings > 10,000 tpd.• Ratio of firing in calciner: 55-65%. • Normal bypass of kiln gas: 0-30%. • 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-Icalciner system.

material

gas

fuel

1. Raw meal feed

2. Exhaust gas


4. Clinker

5. Kiln burner

6. Calciner burners

7. Tertiary air duct

8. Tertiary air duct damper



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: 1500-5000 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 approximately5000 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


4. Clinker

5. Kiln burner

6. Calciner burners


8. Tertiary air duct damper


10.Raw meal dividing gate

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. • Production down to 20% of capacity for

three-string version.

SLC: Separate Line Calciner

material

gas

fuel

1. Raw meal feed

2. Exhaust gas


4. Clinker

5. Kiln burner

6. Calciner burners



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.

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%.



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: 6500-9000 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


4. Clinker

5. Kiln burner

6. Calciner burners



9. Raw meal dividing gate

10.Raw meal change-over gate

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 3500 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 3000tpd. 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 3000-3500tpd. Similarly, the ILC and SLC-D systemscan be used as single strings up to about5000 tpd. In contrast, the SLC and SLC-Isystems always have at least two preheaterstrings and, therefore, will normally only beconsidered for throughput capacities above3500-4500 tpd.

Table 1 shows the six different preheater/ pre-calciner configurations as a function of pro-duction capacity along with standard kilnsizes. The SP kiln system is also shown for com-parison, although this would not normally bea preferred solution for a new installation.

Operation and maintenance These days, precalciner systems are generallypreferred to SP-type kiln systems due to thefixed degree of calcination of the materialentering the kiln and the shorter materialretention time in the system. Longer lininglife and lower kiln refractory weight enableprecalcining kiln systems to remain in oper-ation for longer periods than SP kilns, thusreducing down time and refractory costs.

Type selection guidelines

Generally, the maintenance costs of a single-string kiln system are lower than those of adouble-string kiln system. Consequently, asingle-string preheater is always preferableto a double-string preheater for small-to-medium production capacities, provided thereare no tower height limitations.

Fuel types and gradesAll F.L.Smidth kiln systems can be fired withnatural gas, heavy fuel oil, standard coalgrades or a combination of these fuels.Special fuels, however, require special con-siderations when selecting the appropriatekiln system configuration:

Low-volatile fuels Fuels such as anthracite, petroleum coke, andother low-reactive fuels pose no problem inthe kiln which operates at a high tempera-ture. The kiln burner, however, should be ofthe modern flame-shaping type, such as theDUOFLEX which has a suitable flow patternthat ensures rapid and stable ignition.

The use of low-volatile fuels in calciners (thatusually operate at a temperature around900°C) can cause problems unless the systemis provided with a high-temperature calciner.All our calciner systems are suited for theuse of low-volatile fuels as they are designedto allow raising the temperature in the com-bustion chamber without affecting the restof the system. This is accomplished by meansof a dividing gate that leads a relatively largeamount of raw meal to the calciner and/orthe kiln riser duct.

Low-calorific fuels Fuels with high ash contentrarely cause problems inthe calciner because theash is intimately mixed intothe raw meal as a conse-quence of the turbulence andhigh material retention time.However, the use of such fuelsfor kiln firing can cause prob-lems such as (1) the inability to

reach sufficiently high flame temperature,and (2) the non-homogeneous mixing ofash into the kiln charge which is alreadynodulised and partially fused. For this rea-son, a precalcining system is always pre-ferred when using low-grade coals becausethe total input ash content to the kiln burn-ing zone is greatly reduced. Each type offuel should be considered separately.Typically, the lower limit for net heating val-ue will be 3800 kcal/kg for the calciner and4000 kcal/kg for the kiln. The separate com-bustion chamber design of the SLC-D sys-tem often allows using alternative fuels of anet heat value as low as 2800 kcal/kg.

Combustible wasteUsed car tyres, wood, rice shells, etc. maybe used as partial substitution for ordinarytypes of fuel, provided they contain nochemical compounds that might damageclinker quality or hinder smooth kiln opera-tion. Normally, such fuels are fed into thekiln riser for subsequent complete combus-tion at the kiln inlet. With the ILC precalcin-ing system more than 50% of the fuel canbe replaced by combustible waste which isburned in a separate combustion chamberwith a HOTDISC. Due to its high tempera-ture and retention time (> 1200°C and > 2seconds), the kiln is well suited as an incin-erator for hazardous wastes which are thussafely disposed of while providing additionalheat. However, each type of waste must beconsidered individually, taking local emissionregulations and occupational health andsafety issues into account.


DUOFLEX Kiln burner.


Type selection guidelines

Table 2: Heat economy, pressure drop & power consumtion

SLC ILC

5-stage 6-stage 5-stage 6-stage

Heat balance in (kcal/kg clinker) 166 148 160 141

+ radiation loss from preheater 34 39 31 35

+ radiation loss from kiln 23 23 26 26

+ heat of reaction 390 390 390 390

+ free water 2 2 2 2

+ VDZ cooler loss 103 105 107 110

+ heat of clinker at amb temp. 4 4 4 4

- heat in raw meal, air and fuel 32 32 32 32

- combustibles in raw meal 8 8 8 8

= Net specific heat consumption 682 671 680 668

K - C K - C

Exhaust gas temperature (0C) 352-303 324-265 316 282

Pressure loss preheater (mmWG) 328-315 380-442 303 347

Pressure loss in rest of system (mmWG) 30-140 30-60 160 160

Total pressure loss (mmWG) 358-455 410-502 463 507

Power consumption (kWh/t clinker)

ID fan(s) 4.95 5.20 5.40 5.50

Cooler (drive + fans + crusher) 5.20 5.20 5.00 5.00

Kiln drive 2.00 2.00 1.60 1.65

Primary air fan 1.00 1.00 1.00 1.00

Cooler vent system 0.80 1.40 1.40 0.80

Total spec. power consumption 13.95 14.80 14.40 13.95

EP(1) FF(2) FF(2) EP(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 exhaust gas fan motor(s), thecooler fan motors and the kiln drive motor.

The power consumption of the exhaust gasfan(s) mainly depends on the total pressuredrop in the kiln system. Most of this pressuredrop occurs in the preheater. Increasing thepreheater 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 standard component in all FLS kiln systems, wasdeveloped to ensure a low pressure drop in the preheater while maintaining reasonablysmall cyclone dimensions.

The table compares the specific power con-sumption of an SLC and an ILC kiln system,both equipped with LP cyclone preheaters.It also shows a comparison between the two


modern 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 (FFs) in terms of power consump-tion and maintenance (bag replacement).However, with the tightening of emissionstandards, FFs 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 matter in the rawmaterials is an important factor when choos-ing the appropriate kiln system.

Volatile matter in connection with kiln oper-ation is usually understood as componentscontaining 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 tends to be slightlylower with a precalcining system (with tertiaryair duct) than with an SP kiln system due tothe higher volatile concentration in the gases

of a precalcining system which is caused bythe lower specific gas flow through the kiln,see table 3.

If the volatile content in the raw mix (andfuel) is higher than these upper limits, thekiln system must be equipped with a bypassthat enables extracting some of the kiln gasfrom the system before it reaches the pre-heater. In this way, internal circulation ofvolatile matter is reduced. Bypassing a fewper cent of the kiln gases is sufficient toreduce the internal circulation of chloride inthe kiln system to an acceptable level.Excessive sulphur circulation requires a some-what higher degree of kiln gas bypass.

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 conventional kiln system.A certain reduction of alkali in the clinker canbe attained by the lowest-possible increasein the 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 maximum 25-60% of thekiln gas, which in most cases will suffice toensure smooth operation, even with low-grade raw materials.

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

Normal limit High limit

ILC, SLC & SLC-1

Chlorine as CI 0.023% 0.029%

Sulphur as SO3 1.25% 1.9%

0.65 * K2O + Na2O 1.0% 1.5%

SP & ILC-E

Chlorine as CI 0.029% 0.044%

Sulphur as SO3 1.5% 2.25%

0.65 * K2O + Na2O 1.0% 1.5%

Table 3: The upper limits apply toa raw mix of good burnabilityand an ideal sulphur/alkali ratio.


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 210 mm WG acrossthe preheater itself, while a five-stage pre-heater can be designed for a pressure dropdown to 280 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 maximises 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 excellentmaterial distribution in the individual riserducts. Change-over gates and dividing gatesare used to efficiently distribute the raw meal.

Cyclone preheater

The segmented centralpipe (thimble).


In-Line Calciners:In-line calciners are generally known to gen-erate lower NOx emissions than separate-linecalciners since all of the kiln exhaust gasesmust 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 reducingzone. That is, the calcining chamber is built(at least partially) into the kiln riser. In thisway, a very simple means of creating lowNOx emissions without splitting of tertiary airis attained by firing 100% of the fuel to thekiln riser duct which made possible by meansof a single meal split to this “reduction zone”.As a result, it is possible to obtain both reduc-ing conditions and high temperature calcina-tion in one simplistic system (without multiplefiring points) for the lowest possible NOxemissions. The combustion air is drawn eitherthrough the kiln or through a separate tertiaryair duct. Because the kiln combustion gasesare drawn through the calciner, the calcinersize is necessarily larger to attain therequired gas velocity and retension time.

Following the reduction zone, the calciner’scylindrical section sequintially tapered. Theresultant rapid changes in cross-sectionalareas create strong vortexes ensuring effec-tive mixing of fuel, raw meal, and gas. Thetop of the calciner is most often providedwith a loop duct to ensure optimum gasretention time, mixing and complete com-bustion 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 gasis further enhanced by thetertiary air duct being fitted tangentially onthe calciner. This causes a moderate swirl inthe calciner which further increases particleretention time. When designed for bypassing30% or more of the kiln gases, the tertiaryair duct is connected to the kiln riser (in anILC-I configuration) rather than tangentiallyconnected to the calciner.

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 calcinationboth of which are proven to sig-nificantly minimize NOx emis-sions. The elevated temperaturedesigns are also particularlysuited for the use of lowvolatile 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 orsolid fuels. The calciner burnersare placed so that the fuel iswell distributed across the calcin-er cross section so that it ignitesrapidly in the presence of terti-ary air. The downdraft calciner,for example, 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.F.L.Smidth calciner types are bestclassified into the followingthree groups:

ILC-E Calciner ILC Calciner

Separate-LineSeparate-line calciners are also known as“air-only” calciners since the calciningchamber is at least partially offset from thekiln riser. The combustion air is alwaysdrawn 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 plannedthrough an outlet cone connected to a cen-tral outlet pipe.

In the SLC-I configuration, a calciner is builtparallel to the kiln riser duct as describedabove and a second calciner is built into thekiln riser duct. This design effectively destroysthermal NOx generated in the burning zoneof the kiln. Fuel NOx generated in the cal-ciner is effectively minimized through hightemperature operation.

A unique feature of the high temperaturecalciner system is the fact that the tempera-ture inside the calciner is independently

controlled 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 approximately9000C. 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 strong vortex forma-tion in the bottom cone, ensuring effectivemixing of raw meal, fuel and tertiary air fora high particle-to-gas retention time (meas-ured to be approximately 4 in an industrial-scale calciner).

SLC Calciner


Downdraft typesThe downdraft calciner is specifically tailoredfor low-reactive and hard-to-burn fuels sincethe combustion air for the downdraft cal-ciner (DDC) is drawn solely from the clinkercooler. The separate-line features of this cal-ciner design minimize the height of the pre-heater structure since a substantial portionof the total retention time takes place paral-lel to the kiln riser duct. The placement ofthe combustion chamber outside the pre-heater structure makes this calciner designwell suited for retrofits since down time isminimized.

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 entrained 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 unforeseen.

SLC-D Calciner


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.The figures below clearly reflect the trendtowards large single production lines andpreviously unheard-of levels of fuel consump-tion for 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-ing 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 tabulated below.

By utilising its extensive mechanical andplant design capabilities, F.L.Smidth hasbeen able to implement the necessary mod-ifications with minimum interruption to theplant's normal operations. In this way, the“state of the art” has been advanced forexisting plants as well as greenfield facili-ties.

State-of-the-art system

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 conventionel cooler (3000 MTPD)Plant B – 4-stage SLC-I preheater w/conventionel 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)

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

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]

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

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

www.flsmidth.com

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

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Documents

Dry process kiln systems - · PDF filekiln, SF Cross-Bar™ clinker cooler and Duoﬂex kiln burner Main features KILN SYSTEMS. Six standard Dry-process kiln system