Dry Process Kiln

Dry process kiln systems ■

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Efficient energy utilization

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Main features

S M E T S Y S N L I K

• High Highly ly re reli liab able le systems for any production level • A wid wide e ran range ge of calciner systems to suit specific requirements • Highly Highly ef effici ficient ent low pressure cyclones • Effe Effect ctiv ive e emissi emission on control technology • Opti Optimi mize zed d fuel fuel and and power consumption • Suit Suitab able le for for wast waste e fuels • Compact, space-saving preheater designs • Matc Matchi hing ng sta state te-o -offthe-art technologies for clinkerization, cooling and firing: ROTAX-2 two-support kiln, SF Cross-Bar™ clinker cooler and Duoflex kiln burner

F.L.Smidth offers a range of six standard dry-process kiln systems, each with its unique advantages depending upon the particular application. In this way we are able to provide the industry with the most suitable kiln system configuration for any given set of conditions and requirements. F.L.Smidth has supplied over 2500 rotary kiln systems and more than 3500 clinker coolers. This experience, coupled with the latest advances in pyroprocessing system design, makes our technology the logical choice for both new installations and modernisation of existing cement making facilities. In modern cement plants, raw meal is preheated to calcination temperature in a multi-stage cyclone preheater and most of the calcination process takes place in a separately fired calciner. calciner. The remaining calcination and clinkerization process takes place in a short length-to-diameter rotary kiln without internals.

Preference is commonly given to the cooling of clinker in the SF Cross-Bar™ cooler in which the two main functions, conveying and cooling of clinker, are completely separated. The introduction of stationary air distribution plates with self-regulating mechanical flow regulators (MFR) has revolutionized cooler operation. This brochure describes each of the six preheater/calciner system configurations in detail and presents general guidelines for their selection depending upon capacity requirements and whether the system is new or an upgrade of an existing installation. System components other than cyclones and calciners are dealt with in separate brochures that describe their mechanical and operational features.









Six standard Dry-process kiln system configurations SP: Suspension Preheater kiln

ILC-E: In-Line Calciner using Excess air

ILC: In-Line Calciner

SLC-D: Separate Line Calciner – Downdraft

SLC: Separate Line Calciner









SP: Suspension Preheater kiln

Special advantages

Features

• For small small cap capacit acities ies – the economical solution. • Ve Very ry low specific specific power power consump consumption tion – with planetary cooler. • Sim Simple ple oper operati ation on – well suited for manual control. • Accept Acceptss higher higher input of chlorides chlorides than than precalcining systems with tertiary air duct (without bypass).

• • • •

Normal capacity Normal capacity range: 700-45 700-4500 00 tpd. Ratio of of firing firing in riser riser duct: duct: 0-15%. 0-15%. Bypass Byp ass of kiln kiln gas: gas: 0-30% 0-30%.. Planetary Planet ary cooler cooler can can be employed employed..

material

-350mm WG

gas

282 C °

fuel 1. Ra Raw w meal meal fee feed d 2. Ex Exha haus ustt gas gas 454 C °

3. Kiln gas by-p by-pass, ass, if any any 4. Cl Clin inke kerr 5. Ki Kiln ln bur burne nerr

608 C °

6. Rise Riserr duct duct firing, firing, if any any 7. Co Coole olerr exces excesss air air 734 C °

820 C °

5-stage SP kiln system and SF Cross-Bar™ cooler Typical temperatures in the system are indicated together with the negative pressure in the exhaust gas exit based on a system designed for minimum overall pressure drop. This type of kiln system can be converted to the SLC precalcining system by adding an extra calcining string. If no future capacity increase is to be considered, a planetary cooler may be









ILC-E: In-Line Calciner using Excess air

Special advantages

Features

• Most economic economical al solution solution for for small and medium capacities. • Low specific specific power power consump consumption tion with with planetary cooler cooler.. • Easy operatio operation n due to high excess excess air air percentage in kiln. • Low coating coating tendenc tendencyy in kiln kiln inlet inlet and riser duct. • Long kiln kiln lining lining life due due to stable stable kiln kiln coating. • Less sensitiv sensitive e to chlorides chlorides and sulphur sulphur than precalcining systems with tertiary air duct (without bypass). • Smaller kiln dimensio dimensions ns than than SP system. system.

• • • •

-395mm WG

material

269° C

gas

Normal capacit capacityy range: range: 800-5500 800-5500 tpd. tpd. Ratio of firing firing in calcine calciner: r: 10-25%. 10-25%. Bypass Bypa ss of kiln kiln gas: gas: 0-25%. 0-25%. Calcination Calcina tion at kiln inlet: inlet: 50-70% 50-70% (com(compared to 30-40% for SP operation). • Planeta Planetary ry cooler cooler can be employed. employed.

fuel 1. Ra Raw w meal meal fee feed d 437° C

2. Ex Exha haus ustt gas gas 3. Kiln gas by-p by-pass, ass, if any any 4. Cl Clin inke kerr 5. Ki Kiln ln bur burne nerr

594° C

6. Cal Calcin ciner er burne burners rs 7. Co Coole olerr exces excesss air 727° C

840° C

ILC-E kiln system with five-stage preheater and SF Cross-Bar™ cooler Typical temperatures in the system are indicated, together with the negative pressure in the exhaust gas exit, based on a system designed for minimum overall pressure drop. If no future capacity increase is to be considered, a planetary cooler may be considered.









ILC: In-Line Calciner

Special advantages

Features

• High material material and gas gas retention retention time time in calciner due to its large volume and moderate swirl. • Regula Regulation tion range range of up up to 30% 30% bypass bypass of kiln gas using ILC-I version. • Well suited suited for for low-grade low-grade fuels. • Long refracto refractory ry life due due to low thermal thermal kiln load and stable kiln coating. • Lowest NOx emission emission among traditi traditional onal calciner kiln systems.

• Normal Normal capacity capacity range: 1500-6 1500-6000 000 tpd, tpd, with multiple strings > 10,000 tpd. • Ratio of of firing firing in calciner: calciner: 55-65%. 55-65%. • Norma Normall bypass bypass of kiln kiln gas: gas: 0-60%. 0-60%. • Maximu Maximum m bypass bypass of of kiln kiln gas: gas: 0-100% using ILC-I version. • BuiltBuilt-in in low-NOx low-NOx capabil capabilities. ities. • Calcin Calcination ation at kiln inlet: 90-95 90-95%. %.

-465mm WG

material

293° C

gas fuel 1. Ra Raw w meal meal fee feed d 478° C

2. Ex Exha haus ustt gas gas 3. Kiln gas by-p by-pass, ass, if any any 4. Cl Clin inke kerr

650° C

5. Ki Kiln ln bur burne nerr 6. Cal Calcin ciner er burn burners ers 7. Tert ertiar iary y air duct duct 799° C

8. Tertia ertiary ry air duct dampe damperr 9. Co Coole olerr exces excesss air air

890° C

ILC kiln system with five-stage preheater and SF Cross-Bar™ cooler Typical temperatures in the system are indicated, together with the negative pressure in the exhaust gas exit, based on a system designed for minimum overall pressure drop. When designed for bypassing 30% or more of the kiln gases, the layout of the system will be slightly different, as the tertiary air duct is connected to the kiln riser duct at a point below the calciner. This system is called the ILC-I calciner system.











SLC-D: Separate Line Calciner – Downdraft Special advantages

Features

• High material material and and gas retentio retention n times in the calciner/ combustion chamber whose dimensions are minimal since the kiln gases do not pass through it. • Ve Very ry well suited suited for all all fuel types, types, espeespecially low-volatile fuels, as the combustion in the calciner takes place in hot atmospheric air and the combustion temperature in the calciner can be controlled independently of the temperature of the calcined material fed to the kiln. • Low NOx NOx operation operation is possib possible. le. • Smalles Smallestt possible possible tower tower dimensions, dimensions, as the calciner can be installed separately from the cyclone tower tower.. • Especia Especially lly well suited suited for for retrofits retrofits of existing SP or ILC preheaters due to very short down time.

• Normal capacit capacityy range: range: 1500-6000 1500-6000 tpd, tpd, with multiple strings > 10,000 tpd. • Firi Firing ng in calcine calciner: r: 55-60%. 55-60%. • Bypa Bypass ss of kiln kiln gas: gas: 0-60%. 0-60%. • Maximum bypass regul regulation ation range: range: 30%. 30%. • Calcina Calcination tion at at kiln inlet: 90-95% 90-95%..

-475mm WG

material

300° C

gas fuel 1. Ra Raw w meal meal fee feed d 487° C

2. Ex Exha ha t ga

SLC-D kiln system with five-stage preheater and SF Cross-Bar™ cooler Typical temperatures in the system are indicated, together with the negative pressure in the exhaust gas









SLC: Separate Line Calciner

Special advantages • High material and gas retention times in the calciner whose dimensions are minimal since the kiln gases do not pass through it. • Ve Very ry well suited suited for all fuel types, types, even even low-volatile fuels, as the combustion in the calciner takes place in hot atmospheric air, and (as an option) the combustion temperature in the calciner can be controlled independently of the temperature of the calcined material fed to the kiln. • Long refracto refractory ry life due due to low thermal thermal kiln load and stable kiln coating. • Indepe Independent ndent and and accurate accurate draft contro controll for kiln and calciner strings by adjusting speed of individual fans. • No damper damper in tertia tertiary ry air duct. • Produ Production ction down down to 40% of capacity capacity using kiln string only.

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

Features • Normal Normal capac capacity ity range: range: 3000-7500 tpd (one C-string), 7500-12,000 tpd (two C-strings) • Firing in calciner calciner:: 55-60%. 55-60%. • Byp Bypass ass of kiln kiln gas: gas: 0-100 0-100% % • Maximu Maximum m bypass bypass regulation regulation range: 30%. • Calcin Calcination ation at kiln inlet: 90-95 90-95%. %.

material

-445mm WG 294 C °

gas

-350mm WG

fuel

293 C °

1. Ra Raw w meal meal fee feed d 484 C °

2. Ex Exha ha t ga

SLC kiln system with SF Cross-Bar™ cooler and five stage preheater in the kiln and the calciner strings Typical temperatures in the system are indicated, together with the negative pressure









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

Features

• Very Very well suited suited for all all fuel types, types, even even low-volatile fuels, as the combustion in the SLC calciner takes place in hot atmospheric air, and (as an option) the combustion temperature in the SLC calciner can be controlled independently of the temperature of the calcined material fed to the kiln. • Indepen Independent dent and accurat accurate e draft contro controll for kiln and calciner strings by adjusting speed of individual fans. • Produ Production ction up up to 50% 50% of capacity capacity using using kiln string only (ILC or ILC-E). • Same cyclone cyclone sizes sizes and feed systems systems for both strings.

• • • • •

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

material

-445mm WG 304 C °

gas

-445mm WG

fuel

305 C °

1. Ra Raw w meal meal fee feed d 483 C °

2. Ex Exha ha t ga

SLC-I kiln system with SF Cross-Bar™ cooler and five stage preheaters in both the kiln and calciner strings Typical temperatures are indicated, together with the negative pressure in the









Type selection guidelines TPD Production

Three-support kiln Three string Two string One string

12000

6.00 x 95

11000

5.75 x 91

10000

5.50 x 87

9000

5.25 x 82

8000

5.00 x 78

Selecting the proper kiln system configuration for a given project is a complicated task that involves a number of considerations. During the initial planning stage it will often be useful to consult F.L.Smidth who has gained a wealth of experience from a large variety of cement projects. As a general guide to choosing the most suitable new kiln system, a number of criteria should be considered, the most important of which are as follows:

4.75 x 74

7000

4.55 x 71

6000

4.35 x 67

5000

4.15 x 64

4000

3.95 x 60

3000

3.75 x 57 3.60 x 54

2000

3.30 x 49

1000 0 SP

ILC-E

ILC

SLC

SLC-I

SLC-D Table 1a

Production capacity and investment costs For any given production capacity, a precalcining system requires considerably smaller rotary kiln dimensions than a simple suspension preh preheater eater system. system. F.L.Smidth normally recommends a rotary kiln diameter not exceeding 6 metres to ensure reasonably long lining life. For this reason, it is advisable to employ a precalcining system (with tertiary air duct) for kiln productions above 4000 tpd.

Table 1b

TPD Production

ROTAX 2 kiln, L/D~13 Two string One string

10000 6.00 x 72

On the other hand, the simplicity of the ILC-E kiln system equipped with a planetary cooler makes it the most economical solution for production capacities up to about 4500 tpd. Of course, the lowest-possible heat









systems always have at least two preheater strings and, therefore, will normally normal ly only be consid considered ered for capacit cap acities ies abo above ve 500 5000 0 tpd tpd..

tion of these fuels. Special fuels, however,, require special considerahowever tions when selecting the appropriate kiln system configuration:

Tab ables les 1a an and d 1b sho show w th the e six di diff ffer eren entt preheater/ precalciner configurations as a function of production capacity along with standard kiln sizes. The SP kiln system is also shown for comparison, although this would not normally be a preferred solution for a new installation.

Low-volatile fuels

Operationandmaintenance These days, precalciner systems are generally gener ally pref preferre erred d to SP-typ SP-type e kiln systems due to the fixed degree of calcination of the material entering the kiln and the shorter material retention time in the system. Longer lining life and lower kiln refractory weight enable precalcining kiln systems to remain in operation for longer periods than SP kilns, thus reducing down time and refractory costs. Generally, the maintenance costs of a single-string single-string kiln system are lower than those of a double-string kiln system. Consequently, a singlestring preheater is always preferable to a double-string preheater for

Fuels such as anthracite, petroleum coke, and other low-reactive fuels pose no problem in the kiln which operates at a high temperature. The kiln burner, however, should be of the modern flame-shaping type, such as the DUOFLEX, which has a suitable flow pattern that ensures rapid and stable ignition. The us use e of low low-v -vola olatil tile e fue fuels ls in cal calcin cin-erss (t er (tha hatt us usua uallllyy op oper erat ate e at a te temp mper er-ature atur e aroun around d 90 900° 0°C) C) ca can n ca cause use pr prob ob-lems le ms un unle less ss th the e sys syste tem m is pro provided vided with a high high-tem -temperat perature ure calci calciner ner.. All ourr cal ou calci cine nerr sy syst stem emss ar are e su suit ited ed fo forr the th e us use e of lo loww-vo vola lati tile le fu fuel elss as th they ey are ar e de desi sign gned ed to al allo low w ra rais isin ing g th the e te temmperatu per ature re in the com combus bustio tion n cha chambe mberr with wi thou outt af affe fect ctin ing g th the e re rest st of th the e sy sysstem. te m. Th This is is acc accom ompli plish shed ed by mea means ns of a di divi vidi ding ng ga gate te th that at le lead adss a re rela lati tive vely ly larg la rge e am amou ount nt of ra raw w me meal al to th the e ca callcine ci nerr an and/ d/or or th the e ki kiln ln ri rise serr du duct ct..

Low-calorific fuels Fuels with high ash content rarely cause problems in the calciner

and partially fused. For this reason, a precalcining system is always preferred when using low-grade coals because the total input ash content to the kiln burning zone is greatly reduced. Each type of fuel should be considered separately. Typically, the lower limit for net heating value can be 3800 kcal/kg for the calciner and 4000 kcal/kg for the kiln.

Alternative fuels Combustible waste products can be used in all kiln systems as a substitute for fossil fuels, provided that such substitution does not result in negative consequences for the kiln system operation. Each type of waste product must therefore be assessed on an individual basis, by evaluation of the impact on clinker quality, production capacity, kiln system stability and emissions. Also health and safety issues must be taken into consideration. For many solid waste products, the physical size may be a challenge. For slow-reacting waste products the SLC-D system might be suitable, due to the possibility of high-temperature calciner operation.











Type selection guidelines

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

Heat balance in (kcal/kg clinker)

SLC-kiln 50 5000 t/ t/d

ILC kiln 3000 t/ t/d

(SF Cooler)

(SF Cooler)

5-stage

6-stage

5-stage

6-stage

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

5

5

5

5

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

688

674

691

678

K-C

K-C

294

256

293

258

Heat in exhaust gas and dust

+ free water + VDZ cooler loss

= Net specific heat consumption Exhaust gas temperature (C)

Heat efficiency The specific heat consumption of the various kiln systems depends mainly on the size of the kiln, the number of preheater stages, the rate of kiln bypass (if any), the raw mix composition, and the fuel type. Table 2 shows typical heat balances for fivestage and six-stage SLC and ILC kiln systems. As shown, the specific heat consumption of the six-stage preheater system is 10 kcal/kg clinker lower than that of the equivalent five-stage system. By comparison, the specific heat consumption of the five-stage preheater system is 20-25 kcal/kg clinker lower than that of the equivalent four-stage system.

Pressure drop and









It also shows a comparison between the two modern types of cooler venting systems (electrostatic precipitator versus fabric filter and heat exchanger).

volatile concentrati concentration on in the gases of a precalcining system which is caused by the lower specific gas flow through the kiln, see table 3.

For many years, costs have favoured the use of electrostatic precipitators precipitators (EP) for this purpose becaus because e of the higher running running costs of fabric filters (FF) in terms of power consumption and maintenance (bag replacement). However, with the tightening of emission standards, FF will tend to be preferred for cooler venting installations, because the EP size increases proportionately with tighter emission standards, while the FF size remains constant.

If the volatile components in the raw mix (and (a nd fu fuel el)) ar are e hi high gher er th than an th thes ese e up uppe perr li limi mits ts,, the kiln system must be equipped with a bypass that enables extracting some of the kiln gas from the system before it reaches the preheater. In this way, internal circulation of volatile components is reduced. Bypassing a few per cent of the kiln gases is sufficient to reduce the internal circulation of chloride in the kiln system to an acceptable level.

Raw materials

To produce low-alkali cement it may also be desirable to remove large quantities of alkalis through a kiln bypass. This requires a high bypass rate, and a precalcining system with tertiary air duct will be appropriate. For a given amount of kiln gas extracted, higher alkali reduction is obtained in a precalcining

The content of volatile components in the raw materials is an important factor when choosing the appropriate appropriate kiln system. Volatile components in connection with kiln operat ope ration ion are usu usually ally und unders erstoo tood d as min minera erals ls

Maximum by-pass version ILC-I









Cyclone preheater

















I n the following pages, the three basic types of calciners (In-Line, Separate-Line,, and Downdraft Separate-Line calciners) offered by F.L.Smidth are discussed in detail.

Low NOx Calciners

All F.L.Smidth calciners are specifically designed to meet today's most stringent emissions limits by minimizing NOx and CO emissions among other pol pollutants. This is best accomplished through the use of a cylindrically-shaped vessel with a conical bottom. The cylindrical design ensures ample internal volume while minimizing calciner weight and surface heat loss. All F.L.Smidth low NOx calciners are designed for (1) localized reducing conditions and/or (2) high temperature zone both of which are proven to significantly minimize NOx emissions. emissions. The elevated temperatu temperature re designs are also particularly suited for the use of low volatile fuels. In fact, many F.L.Smidth calciner designs are specifically tailored for today's demands for the fir-

ILC Calciner

temperature temperat ure zone in on onee sim simpl plee sys syste tem m (w (wit ithhout multiple firing points) for the lowest possible NOx emissions. The combustion air is drawn either through the kiln or through a separate tertiary air duct. Because the kiln combustion gases are drawn through the calciner, the calciner size is necessarily larger to attain the required gas velocity and retention time. Following the reduction zone, the calciner’s cylindrical section is sequentially tapered. The resultant rapid changes in cross-sectional areas create strong vortexes ensuring effective mixing of fuel, raw meal, and gas. The top of the calciner is most often provided with a loop duct to ensure optimum gas retention time, mixing and complete combustion of the fuel.











drawn through a separate tertiary air duct. Because the kiln combustion gases do not pass through the calciner, the calciner size can be reduced to attain the required gas velocity and retention time. This often results in a shorter preheater structure (and a shorter erection period for retrofits) since the calciner calciner can be readily readily situated outside of the preheater structure. In the SLC configuration, the hot tertiary air from the cooler enters the calciner through the central inlet in the bottom cone and leaves through either a side outlet or (in case high temperature operation is planned)

So, by feeding a relatively larger amount of raw meal to the kiln riser duct and keeping the fuel input to the calciner constant, the mean temperature in the calciner vessel can be brought up to 950 0 – 10500C. The temperature of the exit gas and the degree of calcination of the raw meal leaving the calciner will increase accordingly. However, However, when mixing with the kiln exhaust gas that contains uncalcined raw meal, the temperature of the gas/particle suspension falls to approximatel approximatelyy o 900 C. So a normal temperature level is maintained in the calciner cyclone. Similarly, a normal degree of calcination of 90-95% is maintained for the raw meal supplied to









Low NOx Calciners

multi-channel vertical burner located in the roof of the DDC under high temperature conditions to minimize fuel NOx. In the SLC-D configuration, raw meal entrained in hot tertiary air enters the DDC at the top through a 180 degree involute (similar to an LP cyclone) and exits through a truncated cone which forms a circular duct transition









State-of-the-art systems

State-of-the-art State-of-the-a rt systems Designing equipment and systems for the manufacture of cement has always been a challenging task due to the variations in raw materials, the multitude of cement products required for the marketplace, and the need to minimize investment costs. In addition, integrating high-efficiency concepts with

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

Plant A Mexico

Plant B Indonesia

Plant C USA

Plant D Thailand

134

184

135

182

Heat in free water evaporation

2

2

5

4

Heat in bypass gas

0

0

39

0

Heat in exhaust gas and dust









Dry Process Kiln

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