Clinker Cooler

Chapter 3.8

Clinker Coolers

by Hans Hans E. Steu Steuch* ch*

In cement cement manufacturing, manufacturing, formation of clinker nodules nodules occurs at the entrance entrance to the hottest part of the kiln with a material material temperature temperature of around 1280°C. 1280°C. The clinker clinker is preferably preferably in the form of 10-mm to 25-mm size nodules nodules that exit from the front front end of the kiln into the cooler. cooler. It is critical that cooling of the clinker is rapid to secure a phase composition that imparts adequate cementicementitious properties. It is equally important that the heat exchange between between clinker and air is efficient to ensure proper proper cooling, and at the same time maximize maximize the recovery recovery of heat to secondary secondary air, tertiary air, air, and the related related process process requirement. requirement. The modern cooler cooler must accomplish accomplish all of these tasks efficiently and simultaneously. Like other processing equipment, clinker coolers have undergone significant development over the past years. This chapter describes describes the advent advent of clinker coolers coolers with discussion discussion and description description of various types of coolers presently presently available. available. The chapter also also focuses on the reciprocatin reciprocatingg grate

Figure 3.8.1. Grate clinker clinker coolers. *Technical Director, *Technical Director, Western Region, Ash Grove Cement Co., Co., 6720 SW Macadam Ave. Ave. #300, Portland, Oregon 9721 97219, Tel: (503) 293-2333. 293-2333.

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Innovations in Portland Cement Manufacturing

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cooler and the latest developments developments in cooler designs, while tracing the historical development of the reciprocating grate cooler in relation to increasingly fuel-efficient fuel-efficient kiln systems. The theoretical mass and heat balance equations that describe the steady state and heat recuperating efficiency are presented, present ed, followe followed d by a more practical discussion of how to automate automate and optimize the operation operation of the cooler. cooler. Figure 3.8.1 3.8.1 shows the interior interior of most commonly commonly operated operated grate coolers in cement manufacturing. At the discharge discharge end of the kiln, the clinker clinker is red hot and contains contains around around 1.0 million Btu Btu per short ton thermal energy. The clinker is also to some extent still reacting chemically toward toward creation of various clinker clinker minerals. The purpose purpose of the clinker clinker cooling is to recoup some of the heat in the clinker, clinker, thereb therebyy making it cool enough to handle. We also want to stop the chemical reactions in the clinker at the point most favorable to the cement quality.

TYPES OF CLINKER COOLERS What governs governs the design and selection selection of a clinker cooler? cooler? Surely, Surely, today today,, any design project project would include some some of the following following requiremen requirements: ts: low capital capital cost; optimum cooling cooling rate rate for good good clinker quality; quality; low clinker clinker discharge temperature; temperature; least possible impact impact upon the environment; environment; high heat recovery; recovery; low power power consumption; consumption; low wear and maintenance maintenance cost, and reliable reliable to operoperate, causing minimal minimal downtime; downtime; and easy to to control control so it delivers delivers a steady flow flow of combust combustion ion air at an unvarying temperature temperature to the kiln and calciner calciner.. These criteria are of immediat immediatee interest interest to a manufacturer manufactu rer of cement who who buys a cooler cooler for clinker clinker.. The designer designer of the clinker clinker cooler looks looks at these criteria criteria and tries tries to optimize the design, design, dependin dependingg upon the weight of each of these individindividual criteria. Over the years, the criteria that that are used used to select select coolers have changed. changed. The technology technology of clinker cooling has developed developed as well, so that many different different types of clinker coolers coolers have been been applied since the infancy infancy of the portland cement cement manufacturing manufacturing industry in the late late l9th century. century. The following sections will describe the most common clinker coolers with particular emphasis on the reciprocating grate cooler. Planetary Coolers

The name of the planetary planetary cooler is derived from the fact that it circles the kiln like planets planets circle the the sun. A planetary cooler cooler consists consists of a number number cooler. of cooling tubes tubes mounted mounted around around the Figure 3.8.2. Planetary cooler. circumference circumfer ence of of the kiln shell (Figure 3.8.2). The advantage advantage of the planetary planetary cooler cooler is its simplicity: simplicity: it requires requires no no excess excess air air to handle, no fans or motors, motors, and no instrumen instruments. ts. It is self-adjustin self-adjusting. g. The power power consumption consumption is only about 0.5 to 1 kilowatt-hour kilowatt-hourss per ton of clinker added added to the kiln drive drive and exhaust exhaust fan, making it

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the lowest for any any kind of clinker cooler cooler.. The heat losses through radiation radiation and sensible heat in clinker are between between 0.40 and 0.45 mega-joules per kilogram of clinke clinkerr for an economical dryprocess kiln even and lower for wet-process kilns. Planetary coolers have been used successfully for kilns as big as 4000 metric tons per day, though not in North America. These coolers were popular in the 1960s and 1970s when many dry process 4-stage preheater kiln systems were built built around the world. world. In North North America, most of the dry process process kilns were were supplied with grate coolers. The planetary planetary cooler does not allow allow withdrawal of tertiary air for a calciner. calciner. As most kiln systems systems built today today have calciners, the planetary planetary cooler cooler is becomin becomingg a relic of the past. past. One weakness weakness of the planetary coolers is that they can be costly to maintain. The cooler inlets often wear out too fast due to the thermal, thermal, mechanical, and abrasive abrasive stress to which which they are subjected. subjected. To decrease the resulting maintenance and downtime, over the years there has been continuing improvement by trials with inlets made of high temperature metal metal alloys or ceramic materials. materials. Rotary Coolers

Some of the earlier earlier coolers coolers were were almost like another kiln following the clinker burning burning tube or, or, using another picture, picture, take the the planetary coolers, combine them them into one one tube with its own support and drive, and you have have a rotary cooler cooler (Figure 3.8.3). Figure 3.8.3. Rotary cooler. cooler.

The modern rotary cooler is equipped with ceramic lining and lifters based upon the development of the planetary cooler cooler.. Special seals at the the kiln outlet and and the cooler inlet are are required. required. To avoid spillage from from the inlet, the cooler is inclined 2.5° and giv given en a spee speed d of rot rotation ation of 3 rpm. rpm. The power consumption for the drive is about 3.5 kWh/ton. kWh/t on. The clinker temperature temperature is 200°C to 250°C, but is reduced to about 150°C 150°C by water injection in in the outlet. outlet. Prese Presently ntly,, no cooler of this type is used in North America. Shaft Coolers

As a curiosity, curiosity, we should mention the shaft coolerr (Figure 3.8.4), which has been operating coole with a 3000 metric ton per day kiln in Europe Figure 3.8.4. Shaft cooler. cooler.


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since 1976, 1976, but apparently has not gained a foothold foothold in the cement industry. industry. The cooler requires fairly even clinker size distribution. The upper part is operated as a fluid bed in order to avoid avoid agglomeration and to ensure even even distribution. The power consumption is high, 10 to 12 12 kWh/ton, because the cooling air has to be compressed compressed to about 20 kPa. kPa. With minimum air to the cooler, cooler, the clinker temperature is 300 °C – 350°C, but it is reduced by water injection in the lower part. It should be added added that shaft coolers coolers of somewhat different different design, design, such as the Niems Niems cooler, cooler, have been used very successfully successfully for modern lime burning kilns. Burnt lime has a rather uniform grain size distribution and therefore is much easier to cool in a shaft cooler than cement clinker. Traveling Grate Coolers

It should be mentioned mentioned that travelling travelling grate coolers coolers have have been used in the the past; but, generally generally,, they were never never developed to the same high standard of operationa operationall reliability as the reciprocating grate cooler. Travelling grate coolers have been used mostly in connection with grate preheater kilns, which produce a very uniform clinker size. The travelling travelling grate cooler has the disadvantage that the clinker is conveyed conveyed as a solid bed. To obtain effective clinker clinker and air distribution, it is often necessary to use pulsating air. Grate Coolers

The grate cooler is by far the most common clinker cooler in North North America. Where the air and clinker move move in opposite directions (also called counter counter current) in the planetary, planetary, rotary rotary,, and shaft coolers, the grate cooler cooler is based on the cooling cooling air moving cross cross current to to the direction of of the clinker movemen movement. t. This type of cooler can produce produce clinker clinker discharge temperatures temperatures around around 80°C; but it needs more air for cooling than can be used in the kiln, and the excess air has to be removed and dedusted. dedusted. The amount of air needed varies according according to the clinker clinker size distribution and and to the clinker temperature temperature required. required. It is costly to cool to low temperatures. temperatures. The amount generally lies between 2.3 and 3.3 3.3 kg of air per kilogram kilogram of clinke clinker; r; but in order order to cope cope with forced forced conditions conditions and fluctuations, fluctuations, the cooling fan capacity is normally designed designed to allow allow the introduction introduction of 4.5 kg of air per kilogram of clinker clinker.. The specific load load on grate coolers coolers built since the mid-1 mid-1970’ 970’ss is often 35 to 45 metric ton per day per square meter grate area compared to 20 for grate coolers built in earlier times. This is the result of the tendency tendency to improve improve heat recuperation by by working with a thicker clinker bed on the grate. The cooler consists consists of one or several several grate sections. sections. The sections are are defined by by their location or their function, or by whether they are connected connected to a certain drive drive (for instance, ‘inlet grate,’ grate,’ ‘2nd movable mov able grate grate,,’ etc. etc.). ). Each grate grate consi consists sts of of a certain certain numbe numberr of row rowss of plat plates. es. The plate platess have have been the subject subject of much development development in the 1990s, 1990s, as will be described later later.. The air to the grates grates is supplied in various ways: through air blown into compartments compartments under the grates or blown into ducts (often called ‘airbeams ‘airbeams’) ’) connected directly directly to a limited number of grates.

Clinker Coolers

A typical cooler built between 1970 1970 and 1990 1990 works in the following fashion. From the kiln, the clinkerr drops onto a stationary clinke stationary air-quenching air-quenching grate. This grate may be horizontal horizontal or inclined. It consists of one or several rows of plates. In the cooler shown shown in Figure 3.8.5, there are are three movable grates; the first is with an inclination inclination of a few degrees, degrees, and the other other two are are horizontal. horizontal. Below the grate, the cooler is divided into into a number number of compartme compartments, nts, each provided provided with fans equipped with adjustable guide vanes for automatic air flow control and minimum power consumption. consump tion. Clinke Clinkerr spillage through the grate is collected in hoppers and remov removed ed through airtight flap valves to the clinker conveyor conveyor.. Since the 1990s 990s,, the unders underside ide of the plates in the quench grate and the first grate have been connected directly to cooling fans. This has allowed better individual adjustmentt of air to differadjustmen Figure 3.8.5. Reciprocating grate cooler – side view. entt parts en parts of of the gra grate te.. The efficient sealing between the compartments permits operation at high and different pressures in the various compartme compartments. nts. With a normal normal clinker clinker bed thickness thickness of 600 mm, the pressure pressure drop drop at a constant air flow per unit area will decrease from about 5.9 kPa in the hot end to about 2.0 kPa in the cold end. The fans are sized accordingly so that the maximum pressure decreases from 7.3 kPa kPa to 2.9 kPa. kPa. For trouble-free trouble-free operation, operation, it is an advantage to use more more air per grate or unit area in the hot end, end, up to 200 kg/min/m2, and less less in the cold cold part, say 40 40 kg/min/m kg/min/m2. The width of the grate is reduced in the inlet in order to spread the clinker more evenly evenly.. Together with the high air flow and the thick layer of clinker clinker,, this helps to provide a uniform uniform clinker bed bed thickness, which in turn gives a uniform uniform air flow flow over over the width of the grate. This is essential essential not only to avoid avoid local overheating overheating of the grate, but also to avoid avoid “snowmen “snowmen”” – the clinker is kept kept moving throughout the whole grate until the individual particles have lost their stickiness and ability to cling together. The clinker clinker is pushed through through the cooler by the the reciprocating reciprocating movement movement of rows of plates. Us Usually ually,, every second second row of plates in a grate is movable. movable. The other rows rows are stationary. stationary. A crank arm moves moves the movable movable frame on older coolers. coolers. The rows of of plates are are moved by by a connecting connect ing rod which is centrally fixed fixed to the movable frame, frame, so that twisting is avoided. avoided. The rod goes through the wall via an airtight seal and is driven by a direct current motor or by a hydraulic piston. In the 1980s 1980s one supplier supplier started to offer a pendulum pendulum suspended suspended frame, such as shown in

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482

Figure 3.8.6. Grate cooler – pendulum frame for moving grate plates.

Figure 3.8.6. Figure 3.8.6. This method method of movi moving ng the frame frame is claimed to be particularly effective at keeping tight tolerances tolerances of moveme movement nt to minimize minimize wear on side castings. The activation by by a single hydraulic cylinder with an asymmetric stroke (slow (slo w forward, forward, fast back), back), help helpss minimize minimize mixing mixi ng of the clinker clinker and, ther thereby eby,, bed resistan resistance ce to airflo airflow. w. The speed speed of frame frames, s, whate whatever ver way way they are moved, moved, can be varied between 3 and 30 strokes stro kes/min /min.. In normal normal operation, operation, 5 stro strokes kes/min /min is adequate, providing ample spare spare capacity.

Before the 1990s, 1990s, all grate grate plates, plates, both the movable and stationary stationary,, were of identical design. They were cast with circular circular holes – in the front front part of the cooler they were were made of heat-res heat-resistant istant steel; steel; in the cold cold part, of cast steel. steel. The shoes of the plates plates were bolted to a cross cross beam away from the heat. All designs allow removal removal from underneath where where there is easy access to the grate through the undergrate compartments. Bolt for In the late 1980s a new type Air Cooling Jet nozzle of grate plate plate connected connected to an slot rib nozzle Hinge assembly airbeam was was introduced. introduced. This Seal plate contains inclined and Bolt for curved slots rather than holes Seal nozzle (Figure 3.8.7). 3.8.7). The slots are assembly Through rod shaped by small blades that Grate beam are easily replaced from the T-Bolt top of the plate plate.. This inno innovavaLock tion was so effective that by Stop nut the 1990s all major suppliers Figure 3.8.7. Air beams and grates with slots. were offering grate plates with slots instead of holes for for the hot part part of the cooler. cooler. The suppliers’ suppliers’ plate designs designs varied, varied, but they all contained contained a pocket where cooled clinker clinker could rest and minimize metal wear, wear, and they were all connected directly directly via an airbeam to a fan rather than being supplied supplied with air through an undergrate compartment. compartment. These changes resulted resulted in better protection protection of the grate from thermal and abrasive stress stress caused by hot moving/sliding moving/slid ing clinker and and improved improved cooling of the clinker by by better control control of air flows.

The clinker discharges from the cooler across a grizzly to a hammer mill or hydraulic roll crusher located in the cooler outlet. outlet. The crusher may be installed in the middle of the cooler, cooler, before the last grate, to break up up lumps and large large clinker, clinker, and to ensure ensure their efficient efficient cooling. The thermal stress on the crusher is obviously obviously greater in the middle than at the end of the cooler. cooler.

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When a cooler is operating with a thick clinker bed and evenly distributed distributed clinker and air, air, and is designed with sufficient sufficient retention retention time of clinker in the cold cold end, hot lumps do not cause severe severe problems. Grate Coolers Without Excess Air Vent Stack

The excess air from the grate cooler normally has to be dedusted and exhausted through a stack. This is costly and may be difficult to get permission for from licensing authorities. To avoid these problems, problem s, some plants have have installed installed a combination combination of a short grate cooler and and a gravity or “G-cooler” “G-coo ler” or they have installed installed recirculation recirculation of the excess excess air. air. 500 C °

V = 2–3 cm/min

80 C °

Figure 3.8.8. Grate cooler followed by G-cooler

The gravity cooler (Figure 3.8.8) is used in connection with a short grate cooler, cooler, furnished with just the amount of air needed for combustion in the kiln and calciner. calciner. The clinker discharged from the grate at a temperatur temperaturee of about 500°C 500°C is crushed and carried carried to the top of the gravity cooler cooler,, through throu gh which it drops slowly at 2 - 3 cm/min, while cooled cooled indirectly indirectly by ambient air blown through throu gh cooling tubes. tubes. Afte Afterr about two hours of slow downward downward travel, travel, the clinker clinker is discharged at a temperatur temp eraturee of about 100°C. 100°C. The power power consumption consumption for the fans fans of the G-cooler G-cooler is around around 1 to 2 kWh/ton. kWh /ton. Contr Control ol of hood pressure pressure and the conveying conveying of occasio occasionally nally very very hot clinker between between grate and gravity cooler requires special attention to make this system operate well. Another way to avoid dedusting the excess air from a grate cooler is to cool the air in a heat exchanger and then recirculate it to the 2 kg/kg clinker r e 250°C k grate (Figure 3.8.9). n i l C The heat exchanger 1.1 kg/kg kg/ kg Clinker Cli nker g k / 100°C is designed so that g k 0 ambient air is blown 2 on the the outside outside of the cooling tubes 2 kg/kg Clinker 60°C through which the excess air from the cooler is drawn. Figure 3.8.9. Grate cooler with recirculation of excess air air..


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Cross-Bar ™ Cooler

In the late 1990s, 1990s, a new type of clin clinke kerr cooler cooler was introduced. introduce d. It shares shares the horizontal conveying of clinker through which a vertically moving mass of cooling air is blown with the reciprocating clinker cooler,, but has several cooler several innovative and unique features.. The most features most striking Figure 3.8.10. Cross-Bar cooler. is th that at cl clin inkker ar aree no longer conveyed by rows of grate plates moving moving back and and forth, but by wedge-shaped wedge-shaped bars suspended suspended above above the grates, which are all stationary (Figure 3.8.10). 3.8.10). These bars move back and forth and have inspired inspired the name “Cross-Bar™ Cooler. Cooler.”” ™

Since the plates plates no longer move, move, they have been been made larger larger.. The traditional traditional size of a cooler grate is 30x30 cm; cm; the cross bar cooler plates are are 1x1 m. Furthermor Furthermore, e, each plate is supplied with an amount of air that is individually individually and dynamically dynamically adjusted adjusted to fit the cooling cooling needs of the moment. moment. This is accomplished by a mechanical flow regulator valve located in the air supply channel affixed underneath undernea th the grate plate. This regulator passes air from the undergrate undergrate chamber to the holes in the plate as shown in Figure 3.8.11. This eliminates the need for airbeams between between cooler fans and grate plates, plates, and the meNon-uniform clinker chanical problems associated with them. Curren Currently tly,, there are only a few crossbar coolers in cement High bed Low bed operation. The vendo vendorr resistance claims the cooler is consid- resistance erably more efficient at heat recuperation than ordinary reciprocat reciprocating ing grate coolers. coolers. The amount amount Lower Higher of cool cooling ing air is reduce reduced d valve ∆P valve ∆P from 2.8 to 1.9 kg air per kilogram clinker clinker,, resultin resultingg in a low power consumption tio n of 4. 4.00 kW kWh/t h/ton on of of Figure 3.8.11. Mechanical air flow regulator. regulator. clinker cooled.

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COMPARISON OF DIFFERENT COOLER TYPES A study made in 1980 1980 of the investment investment costs costs for grate coolers coolers with different different types of dust collectors and grate coolers operating without excess air led to the surprising result that the total installed equipment equipment costs are the same within ±5%. The decisive factors factors for choosing between these clinker cooling solutions are therefore their operational costs and reliability. Typical operational data for the different cooler types are tabulated in Table 3.8.1.

Table 3.8.1. Typical Operational Data for Different Cooler Used in Dry Process Kilns

Planetary Rotary

Air (kg (kg/kg /kg cli clinke nker) r) F r e s h c o o li n g a ir Excess air to vent Clinker temp 1, °C After cooler After cooler, with water After secondar y cooler

Shaft

Grate + Grate + recirc. Grate G-cooler vent ai a ir

Pendulum

Cross ba r

1 .1 0

1. 1 0

1.3 0

2 .8 1 .7

1. 1 0

1.1 0

1.9 0 .8

1.9 0. 8

160 1 20

220 16 0

360 15 0

80

4 90

100

10 0

100

80

Power consumption (kWh/ton) cooler only

0.8

3. 5

12

7

8 .5

9.5

4

4

Thermal efficiency2, %

67

70

74

60

64

63

71

71

1 Clink Clinker er

from kiln: kiln: 1300° 1300°C C

2 The Thermal rmal

efficien effic iency cy = (He (Heat at in cli clinke nkerr from from kil kiln n – hea heatt loss losses) es) *10 *100 0 Heat in clinker from kiln

OPERATION OF GRATE CLINKER COOLERS Mass and Heat Balances

In the previous chapters we have mentioned mentioned the varying amounts of seconda secondary ry air and temperatures found in different different types of clinke clinkerr cooler systems. systems. To better understand understand these difference differences, s, we might ask how much of the heat contained in the clinker dropping dropping into the cooler has been recuperated to the air returned from the cooler to the kiln system? Some of the heat entering entering the cooler will be be lost in the cooled clinker clinker,, radiation, and possibly possibly the vent air air.. The amount amount recuperated recuperated is a measure measure of the thermal thermal efficiency efficiency of the cooler. cooler. The more more recuperated, recuperat ed, the more thermally-efficient thermally-efficient it is. To calculate the thermal efficiency, efficiency, it is necessary necessary to establish mass mass flows, temperatures, and heat flows. Figure 3.8.12 3.8.12 shows a typical clinker cooler with its heat inputs and outputs. The thermal efficiency of the cooler is defined as the relationship relationship between the heat recuperated recuperated and total total heat input


486

Secondary air H "SA

Tertiary air and/or coal mill air, H" TA + CMA

Clinker, H' Cl Heat recuperating zone

Radiation & convection H"R + C

Vent air H" VA

Definitions  = efficiency H = enthalpy ' = input " = output

Final cooling zone

Clinker, H" Cl Clinker air, H' CA Heat in secondary, tertiary Heat recuperated and coal mill air Cooler = x 100% = x 100% efficiency () Heat input Heat input =

H"SA + H"TA + CMA H'Cl + H'CA

Figure 3.8.12. Mass and heat balance.

as shown in the equation equation in the figure. figure. The lower lower the heat losses in clinker clinker,, vent air, air, radiatio radiation, n, and convecti con vection, on, the higher the amount amount of heat recuperated recuperated in secondary secondary air and the higher the thermal efficiency. Heat flow flow is a function function of mass and temperatur temperature. e. The higher the mass and temperatu temperature re of second second-ary air, the more heat heat is recuperated. recuperated. The air used for combustion combustion in the kiln and calciner calciner,, plus the air excess creating creating the oxygen we measure measure in the kiln system, comes from the primary air supplied through the burner(s), burner(s), and the secondary secondary and possibly tertiary air drawn from the cooler. cooler. For a given combustion combustion air need, need, to get the amount amount of secondary air and thus thus the cooler thermal thermal efficiency to increase increase,, the quantity quantity of primary air and/or and/or infiltration infiltration air must be decrease decreased. d. It is important to maximize maximize the amount of seconda secondary ry air by minimizing primary and air infiltration rates and to maximize the secondary air temperature by minimizing cooler heat losses. Since the amount of combustio combustion n air depends on the overall overall fuel consumption, consumption, it becomes clear clear that the type of kiln system influences influences the thermal cooler efficiency efficiency considerably considerably.. A modern-type preheater preheater kiln, consumi consuming ng 3.0 million Btu per short ton clinker clinker,, should be operated at at a thermal thermal efficiency efficiency between 64% and and 68%, 68%, if well adjusted. adjusted. A long dry kiln, consum consuming ing 4.0 million Btu Btu per short ton, ton, should run run between between 68% 68% and 72%; and a wet-type kiln, kiln, consumin consumingg 5.0 million Btu per short ton, ton, between 70% and and 75%. Nev Nevertheless, ertheless, many clinker coolers are operoperated at considerably considerably lower thermal efficiencies. efficiencies. It is evident that operating a clinker cooler at peak thermal efficiency improves overall heat consumption considerably.

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For any any given grate grate cooler, cooler, one can usually usually measure the amount amount of cooling air blown blown into it, as well as the amount amount of vent air air and coal mill mill air exhausted. exhausted. The amount of seconda secondary ry air is calculated calculated by differe diff erence nce or, or, perh perhaps, aps, fro from m the amount amount of coal coal,, back backend end oxyge oxygen, n, and primary primary air used. used. Typical mass balances are shown in Table 3.8.2.

Table 3.8.2. Air Mass Balance for Grate Cooler 4.00 ) r e k n i l c b l / r i a b l ( r e k n i l c g k / r i a g k

3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 Wet kiln

D r y k iln

Preheater kiln

Vent air

0.99

1.59

2.24

Coal mill air

0.65

0.50

0.34

Secondar y air

1.96

1.51

1.02

Table 3.8.3. Heat Balance for Grate Cooler BTU/lb clinker Wet kiln

Dry kiln

Preheater kiln

Btu/lb clinker Btu/lb clinker

534 0

534 0

534 0

Recovered heat out Secondar y air Btu/lb clinker Coal mill air Btu/lb clinker Total Btu/lb clinker

352 86 438

337 67 404

322 45 367

17 22 57 96

17 22 91 130

17 22 128 167

82

75

68

Heat in Clinker in Cooling air in

Heat losses Clinker out Radiation Vent air Total

Btu/lb Btu/lb Btu/lb Btu/lb

Cooler efficiency1, % 1

clinker clinker clinker clinker

(Efficiency = recovered heat out/heat in) x 100%.


488

Once the temperatu temperatures res of the various material material streams, streams, their specific specific heat capacity capacity,, and the radiation losses have been determined, one can calculate a heat balance, such as the one shown in Table Table 3.8.3. When the balance is established, established, the cooler heat recuperation efficiency efficiency can be calculated as follows: (Heat entering entering cooler) – (Heat lost in excess air, air, clinke clinker, r, and radiation) (Heat entering cooler)

Long dry kiln fuel consumption 4.0 mbtu/st

x

100

Secondary air 0.99 mbtu mbtu/st /st 1350°F

st = short ton Excess air 0.38 mbtu/st

1.53 mbtu/st 0.44 mbtu mbtu /st

0.48 mbtu mbtu /st

Clinker air 1.40 mbtu mbtu /st 2500°F

450°F

Heat in clinker 0.06 mbtu mbtu /st

Radiation loss 0.04 mbtu/st

To coal mill 0.06 mbtu mbtu /st

Cooler efficiency = 100 x

1.53 – 0.48 = 69% 1.53

Relatively high cooler efficiency due to utilization of some vent gases for drying in coal mill. Figure 3.8.13. Grate cooler heat balance – long dry dry kiln.

An example is given in Figure 3.8.13. 3.8.13. As mentioned earlier earlier,, a modern clinker cooler cooler should have an efficiency of 64% or better better no matter matter what kiln it serves. serves. This means that it should should be able to move move about two-thirds two-thirds of the heat from the clinker exiting the kiln to the combustion combustion air entering the kiln system. Automatic Control of Grate Coolers

Three groups groups of machine adjustments adjustments are are usually automated automated to obtain: obtain: 1) constant constant air flow through thro ugh the clink clinker er bed in term termss of mass of air per unit unit area area and per mass mass of clin clinker ker,, and 2) constan constant, t, slightly negative negative pressure pressure (suction) (suction) in the kiln hood. An example example is shown schematischematically in Figure 3.8.14.

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Interlockings, kiln, transport P01 M

T1

R

R

M

SA

Supervisor amplifier

Syn R SA

SA

SA

P111 P1 K-10 O

K-16 M

K-15

K-14

K-13

K-12

K-11 M

M

M

M

M

M

Automatic air regulation Alarm system

Figure 3.8.14. Typical automatic cooler controls.

The primary objective of a clinker cooler control control system is to stabilize the cooler operation operation and therebyy provide a more uniform flow of heated air for combustion thereb combustion in the kiln and possibly the calciner.. The secondary objective calciner objective is to provide a controlled response during kiln upsets so that the upsets have a minimum impact on the primary objective. Single and cascade analog analog controllers controllers,, or digital equivalents equivalents of these controlle controllers, rs, are the most common common ones in use. Ideally Ideally,, the grate cooler is controlled by one algorithm which optimizes the cooler operation during normal operation while a second control algorithm steps in during upset kiln conditions to ensure that the cooler is not damaged by high temperatures or mechanical problems. The pressure pressure in the undergrat undergratee compartments compartments and air beams beams (if prese present), nt), the flow of air into or out of fans, and the speed speed of of the movable movable grate grate frame frame are all all controlled controlled by PID loops. Other paramet parameters ers are monitored simply to ensure they are within a desired operating range. These include fan motor current, curren t, kiln speed, speed, motor running running status, status, exce excess ss air, air, and grate plate plate temperature temperatures. s. Using undergrate pressure to control Using control grate speed is acceptabl acceptablee if cooler conditions conditions remain near ideal. To avoid problems problems associated with erratic first and second compartment compartment pressure, both first and second compartment pressures can be measured for determining a weighted average undergrate pressure. This smoothes out the undergrate pressure and often lets the cooler cooler run steadier. The finer the clinker clinker,, the harder it is to blow air through the bed. With the control control loop in automatic mode, a decrease in clinker clinker size will result in an increase increase in undergrate pressure, pressure, until the

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control loop has sped up the grate, causing a lowering of the clinker control clinker bed bed depth. depth. Conv Conversely ersely,, very large clinker will result in unusually low undergrate pressure which will decrease cooler speed and result in excess excess bed depth, and may even even overload the drive. drive. The cooler control control system should should include elements that detect and correct these conditions. In the case of a two- or three-drive three-drive cooler, cooler, the second drive drive should be controlled controlled by the undergrate pressure of its first compartment. compartment. When the second second drive’s drive’s first compartment compartment is too large for its pressure to be successfully successfully used in connection with speed control, control, the second drive has to follow the first drive. In that case, the first drive’s drive’s speed speed multiplied by a factor represents represents the second second drive speed. The second drive’s speed should always be higher than tha n the first drive’s speed to avoid clinker piling up between the two drives. Occasional high grate plate temperatures in the first and second compartments can represent an obstacle to optimizing cooler compartment compartment airflow distribution. During upset conditions where high grate plate temperatures occur, occur, one may have to increase the cooler movable grate frame speed for safety reasons. The grate plate temperature temperature is then permitted to manipulate manipulate the undergrate pressure setpoint. setpoint. As grate plate temperature temperature increases, it will decrease the undergrate pressure setpoint which speeds up the cooler movable grate frame drive. In one particular case, this safety interlocking resulted resulted in no grate plate failures for two years where, in the past, grate plate failures failures had been been an ongoing ongoing problem. problem. In some cooler systems, systems, high vent air temperatures temperatures will result in automatic automatic opening opening of a tempering damper in the vent airduct to protect downstream equipment from overheating. overheating. The vent air volume increase increase caused by the opening of this damper or even just by the high vent temperature may make make the total volume volume exceed exceed the capacity of the vent vent fan. If this is a constrain constraint, t, it may be prudent to automatically automatically reduce undergrate undergrate compartment compartment airflows in the latter part of the cooler to restore kiln hood draft control when the vent air temperature (measured before the introduction of temperin temperingg air) exceeds exceeds a certain threshold valve. valve. In applications where vent fan capacity and high clinker discharge temperatures are a problem, the kiln hood’s draft can be controlled controlled as well by by the last compartment compartment fan. By doing this, it is possible to increase the amount of cooling air and to lower the clinker discharge temperature during normal normal operation. operati on. In this mode of contr control, ol, the vent vent fan is run on fixed fixed speed close to maximum maximum capacity capacity.. During upset upset conditions, conditions, the amount of coolin coolingg air is reduced, resul resulting ting in a higher clinker clinker tempertemperature, which would have have happened anyway anyway.. In a few cooler coolerss with limite limited d venting capacities, capacities, this control approach has led to considerably lower overall clinker discharge temperatures. Finally, in order to minimize the need for control Finally, control room operator involvem involvement, ent, other attractive attractive controll features to strive for include automatic contro automatic initialization of dampers to the full closed position

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on fan startup, automatic reduction reduction in airflow on fan achievemen achievementt of maximum motor motor current, and automatic airflow increases programmed for kiln startup.

OPTIMIZATION OF GRATE COOLER OPERA OP ERATION TION A smooth cooler cooler operation depends depends upon many many factors. In the preceding preceding paragraphs several several of the important design design features features that affect affect the operation, operation, such as burner burner pipe location, location, cooler width, and control contr ol loops, have been been mentioned. mentioned. In the following following section, these points have have been revisited, revisited, while also dwelling dwelling on the fact that optimization of a clinker cooler cooler can be divided into three tasks: tasks: 1) maximizing maximizing the amount amount of seconda secondary ry air, 2) maximizing maximizing the secondary secondary air temperature temperature,, and 3) max maximiz imizing ing the uniformi uniformity ty of the operatio operation. n. Burner Pipe Position

The first step in optimizing a cooler operation begins begins in the kiln. kiln. The burner position has a crucial influence upon the kiln and cooler performance. performan ce. Long wet and dry kilns with a fuel consumption of more than 4.0 million Btu per short ton of clin clinke kerr, which were were common common in the past, past, needed high high amounts of combustion combust ion air. air. Low secondary secondary air temperatures ensured a fast clinker cooling inside inside the kiln, kiln, and the overall thermal efficiency efficiency of the cooler was acceptable. Today’s lowfuel-consuming kiln systems have low combustion air requirements, thus giving high secondary air temperatures and slower clinker cooling.

+2" W.G.





7 SCFT/lb  1900°F 



2500°F



7 SCFT/ SCFT/ lb  1400°F  2200°F 

750°F

Heat consumption:  2.7 x 10 6 BTU/st Production: 1500 + tpd clinker Incl. of grate: 0-3°

+18" W.G.

+16" W.G.





’

Figure 3.8.15. 3.8.15. Typical 1970 s burner pipe position.

0.4" W.G.





Figures 3.8.15 and 3.8.16 show the difference between two burner pipe positions. Posit Positioning ioning the burner burner tip at the kiln nose or even into the kiln hood (Figure 3.8.15) means that the flame ignition takes place close to the kiln’s kiln’s discharge, discharge, thus keeping

2650°F

2650°F



2500°F

Heat consumption:  2.7 x 10 6 BTU/st Production: 1500 + tpd clinker Incl. of grate: 0-3° > + 24" W.G.

13 SCF/lb 1650°F  2200°F  



+14" W.G.



+12" W.G.

+14" W.G.



Figure 3.8.16. Recommended 1990’s 1990’s burner pipe position.

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the clinker hot until they drop into the cooler. cooler. This can have several undesirable consequences as follows: • The clinker clinker discharged discharged onto onto the clinker clinker bed can form large large clinker clinker agglomerations, agglomerations, leading to poor cooling rates because only the clinker closest to the grates are rapidly cooled. • High temperature temperature clinker reaches the discharge discharge end of the cooler cooler, resulting in elevated elevated clinker clinker discharge and vent air temperatures. temperatures. The overall cooler thermal efficiency decreases decreases and fuel consumption increases. • High secondary air and kiln clinker discharge temperatures can result in a severe “snowman” formation, especially if coals with high ash conten contentt are used. used. In addition to all these disadvantages, operational and maintenance maintenance problems problems are likely to occur. In contrast, positioning the burner tip approximately 1 to 2 m into the kiln (Figure 3.8.16) 3.8.16) improves the kiln’s own heat recuperating and cooling zone. The pre-cooled clinker drops at a lower temperature into the cooler and the secondary air temperature drops. The requirement requirement to cool the clinker quickly is fulfilled. fulfilled. The clinker reaches reaches the latter clinker cooler zones zones at a lower temperature, temperature, which results in lower clinker discharge and vent temperatures. temperatu res. Less required cooling air relieves relieves the vent air system and saves considerable considerable electrical energy.. The overall energy overall cooler thermal thermal efficiency efficiency improves. improves. In addition, addition, the cooler now now runs at a higher availability availabil ity and lower maintenance maintenance cost. cost. The formation formation of “sno “snowmen wmen”” is unlikely. unlikely. There may be one drawback in pushing the burner into the kiln – it might represent a problem in regard to burner refractory refractory life. Good results were experienced experienced with extreme high strength lowcement type refractories on burner pipes in very severe applications. Maximizing the Amount of Secondary Air

Low primary air and low air infiltration rates at the kiln discharge maximize the amount of secondary air. air. Low primary air rates can only be accomplis accomplished hed with semi-direct and indirect firing systems that offer offer primary air rates as low as 6%. Low air infiltration infiltration rates at the kiln discharge can be accomplished with good hood sealing and an effective kiln discharge seal. Many plants plants now employ an effective effective leaf-type kiln discharge seal where overlapping overlapping sheets of high quality steel ride on the kiln cowling. This arrangement exhibits exhibits little tendency for clinker clinker to pry open the seal. A puffing kiln hood does not open a gap between between leaves leaves and the air cowl. This seal has proven proven itself in many applications. applications. Repairs are are easy and overall costs costs are low. low. If the kiln system system has a calciner, calciner, it is important that as much of of the air as possible possible used used for combustion comes from the clinker cooler. Thus any potential opening to ambient air between the calciner and the cooler should be kept kept as tight as possible. Such openings could could be inspection

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doors, material discharge discharge flaps and damper damper housings housings on tertiary air ducts, and kiln material material inlet seal and kiln riser riser poke holes holes if an in-line calciner calciner is used. Maximizing Secondary Air Temperature

Maximizing the secondary air temperature means getting the best heat transfer between clinker and cooling cooling air. air. The heat transfer transfer is optimized optimized by 1) optimization optimization of clinke clinkerr bed distribution, distribution, and 2) optimization optimization of the cooling cooling air distribution. distribution. A clinker cooler cooler basically is a heat exchanger exchanger.. In contrast to most most heat exchangers, exchangers, both mediums – clinker and air, air, come in direct contact contact with each other. other. Therefo Therefore, re, the effectiven effectiveness ess of heat exchange exchan ge largely depends upon the surface surface with which both mediums come into contact. contact. In a clinkerr cooler, clinke cooler, the more uniform the clinker clinker size distribution and the clinker granulometry granulometry,, the more effective the heat transfer. While the clinker clinker size, size, for the most part, cannot be altered, altered, the overall heat heat transfer can be be optimized with a good, uniform clinker clinker bed distribution. Fine

Coarse Clinker

Compartment #1 #2

Kiln Capacity 2300 St/d Clinker

#3

#4 Dead Grates Grates W/O Holes Wedge Grates #5

#6

Figure 3.8.17. Grate arrangement to cope with “red “red rivers.” rivers.”

The fact that especially large diameter type kilns tend to discharge fine clinker on the kiln’s load side and coarse clinker on the opposite side can make it difficult to get good clinker distribut distr ibution. ion. Due to the high high air resistanc resistancee of a fine clinker clinker bed, “red rivers rivers”” often are are inevitable. Studies show show that “red rivers rivers”” can cause a variation variation in air distribution distribution of 1:6 between the fine and coarse clinker side and can even even cause cause clogging clogging of the bed. bed. This is why grate plates sometimes become red hot in places. “Red rivers” rivers” also cause an increase in in clinker discharge temperature. Measures for improving the clinker distribution should start at the cooler cooler inlet. Wher Wheree “snowmen “snowm en”” cause poor clinke clinkerr distribution, distribution, the cooler back and sidewalls can be kept clean with the help help of com compre pressed ssed air cannon cannons. s. Some improvements are possible by slowing down the movement movement of the fine clinker clinker bed and diverting more fine clinker to the coarse cooler side, thus increasing increasing the overall clinker clinker bed resistance which pushes more air through the

494


fine clinker bed. This diversion diversion can be done by using wedge-type grates with 125-mm or 200-mm high faces. The grates are arranged in a checkerboard pattern pattern as shown in Figure 3.8.17. 3.8.17. An often successful way to improve the situation is to narrow the cooler grate area on the fine clinker side. By doing so, the clinker bed becomes becomes narrower narrower and often eliminates a severe severe segregation of fine and coarse clinker clinker.. It is recommended recommended that the cooler inlet inlet grate width not exceed exceed 2.5 m for kiln capacities up to 2,500 metric tons per day of clinker clinker.. Figure 3.8.17 3.8.17 shows that some air holes in corner grates are blanked off. Corner areas often have a low clinker load which results in heavy air channeling channeling and bypassing the clinker load. Blanke Blanked d off air holes ensure that cooling air is diverted into the clinker load. When severe severe “red river” river” conditio conditions ns exist and loss loss of cooler grates are are experienced, experienced, “Ondufi “Ondufin” n” grates can be applied. The grates have cooling cooling fins on the underside which increase the cooling surface. The grates stay cooler cooler and last longer longer.. In addition, addition, if a grate is burned through, through, the fins preven preventt large clinker spillages for a considerable time. When “red “red river” conditio conditions ns in a pre-1990’ pre-1990’ss style cooler are extremely severe, compartmen compartments ts can be divided into two two sections. Two cooling fans, fans, one on each cooler cooler side, assure that both both grate areas, the fine and the coarse side, side, receiv receivee the proper proper amount amount of air air.. Or Or,, the design can be upgraded to to one with airbeams or mechanical air flow flow regulators regulators for small groups of grates. Some suppliers, borrowing from the airbeam technology, technology, offer a grate plate design for pre-1 pre-1990’ 990’ss coolers where the air has to travel travel through a labyrinth in the grate – first up, up, then down – before before exiting into the clinker clinker bed. This provides an effective effective clinker seal that reduces reduces the amount of clinker falling through the grate plates to the undergrate compartment. Increasing the clinker bed thickness generally improves the overall clinker distribution and heat transfer.. Good results have been transfer been experienced with clinker clinker beds up to 1 meter deep. deep. In addition, lower grate speed has had a positive effect upon grate wear rates. High undergrate pressures pressures and airflows adversely adversely affect the conv conveying eying action of a reciprocating grate. High air pressures pressures can reduce reduce the friction between between the clinker clinker and the grate, grate, which in turn can speed up the moveme movement nt of the clinker clinker toward toward the cooler discharge. discharge. The air, air, which expands as it rises in the bed, causes the clinker clinker at the surface to be fluidized. fluidized. The result might be that clinker clinker flows down the slope if the grate area is inclined or that the clinker clinker can only be moved moved with extremely high reciprocating speed on horizontal type coolers. To prevent clinker from flowing forward, the single grate surface should should be at least horizontal. Experience has shown shown that the best results can be attained attained with a maximum of 4.7 to 5.5 kPa kPa undergrate pressures pressures in horizontal and 3 degree inclined inclined coolers, and 2.0 to 2.5 kPa in old 10 degree inclined inclined coolers. coolers.

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AIR DISTRIBUTION VERSUS OVERALL COOLER EFFICIENCY Optimized air distribution also improves the overall thermal cooler efficiency and prevents damage to grates due to overheatin overheating. g. To achieve this goal, prede predefined fined amounts amounts of coolin coolingg air need to be established for every cooler compartment. Coolers with airbeams or mechanical air flow regulators can refine the air distribution even more to sections of grate plates or to individual plates. The optimization of airflow is especially especially important for the heat recuperating recuperating zone. Too high amounts of of air do not give give maximum maximum secondary secondary air temperature. temperature. Too low amounts amounts of air elevate elevate the clinker clinker discharge temperat temperature. ure. Too high amounts amounts of air also promote promote fluidization fluidization of the clinker. As the finer clinker particles are likely to be entrained in the locally intensified air flow, high amounts of dust cycles between between kiln and cooler are are likely. likely. Dust particles might also be picked up from highly fluidized areas and concentrate concentra te in others, thereby intensifying any “red “red rivers.” rivers.” Extremely high airflows also promote promote heavy air channeling, giving a poor heat exchange for a grate cooler of 1970’ 970’ss to mid-1990’ mid-1990’ss vintage. It is recommended that maximum airflow not exceed exceed approximately 140 140 normal cubic meters per minute per square square meter of cooler grate area. Figure 3.8.18 3.8.18 shows a chart of optimized cooling cooling air distribution for a typical eight-compartment eight-compartment reciprocating grate cooler. cooler. The first five compartments (including quench compartment) compartment) supply secondary air and tertiary air if applicable; compartment compartmentss #5 through #8 cool cool the clinker clinker to a final temperature temperature of of approximately appro ximately 100°C. 100°C. Lowering the clinker discharge temperature further with more air increases the electrical power consumption consumption considerably considerably.. Depending upon upon the total amount of cooling air used, the power consumption consumption for the cooling fans fans can run between 3 and and 8 kWh/ton of clinker clinker,, plus up to 4 kilowatt-hours for venting.

1st Grate drive

Undergate pressure, IWR

2nd Grate drive

3rd Grate drive

Air pr. grate area, SCFM/sq. ft.

20

600

15

450

10

300

5

150 Q

1

2

3

4

Figure 3.8.18. Air distribution in cooler. cooler.

5 6 7 Compartment number

8


496

As can be seen, the maximum maximum specific amount amount of air per unit of grate area area goes into into the quench quench compartmentt and compartment #1 to quench the clinker and assure low grate temperatures. compartmen temperatures. The specific airflows airflows per unit of cooler area area gradually decrease decrease toward toward the cold end of of the cooler. cooler. Some older coolers coolers still have one cooling cooling fan for up to three compartments. compartments. The distribution of air into each compartment is difficult since the cooling air will try to migrate into the compartment compartment with the lowest undergrate pressure. pressure. This is especially true when heavy loads travel down the cooler. Employing one air fan for each compartment and making sure they are well air-sealed from each other will result in a lower overall clinker discharge temperature and less air usage. In order to allow deep clinker clinker beds and defined airflows in each compartment, compartment, one needs good undergrate compartment compartment sealing, sealing, especially where where drag chains pass through compartments. compartments. Where drag chains are located below the cooler, cooler, the best sealing is accomplished with flap valves concontrolled by level indicators indicators located in the undergrate compartment. compartment. The flap valves are only operated if material inside inside the compartment compartment reaches reaches a certain certain level. level. Figure 3.8.1 3.8.199 shows this this arrangement. Efforts to avoid the mixture of low and and high temperat temperature ure cooler air above the clinker bed are important as well. If considerable considera ble amounts of air from the back-end compartments mix with air from the heat recuperating recuperating zone, the secondary air temperature drops while the vent air temperature temperatu re increase increases. s. We can take some steps to avoid secondary (and tertiary) air from mixing with the vent air.. At the point in the air the cooler where these two air streams split off off in different different directions, an arched arched brick wall wall or some hanging stainless steel dampers can be installed. From this this part of the cooler, cooler, the cooler cooler roof roof shou should ld be sloped at approximately 15° 15° as it approaches the cooler

Grate Line

Electronics High Limit Low Limit

Dust Gates

Figure 3.8.19. Undergrate clinker clinker discharge control.

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throat and and 5° to 10° 10° as it approaches approaches the the vent vent air take take off. off. The sloped sloped roof changes the the bullnose bullnose from 90° 90° to approximat approximately ely 75°. The resulting resulting lower lower velocity velocity in the lower lower part of the cooler throat reduces the the amount of fine particles returned returned to the kiln. kiln. Wherever possible, Wherever possible, the cooler throat velocity velocity should be held below 7 m/sec. New systems systems should even be designed with velocities as low as 3.5 m/sec. A proper proper and uniform uniform distribution distribution of of the clinker clinker upon upon the grate is is of importan importance, ce, as already already mentioned. Ideally Ideally,, you would like a giant stirrer to mix the large and small clinker clinker (that are segregated as they fall into the cooler) together again, and then have them spread out in an even layer layer upon the grate. grate. Equipm Equipment ent that has been been used for this purpose purpose includes: includes: 1) sloped inlet, inlet, 2) waterwatercooled adjustable steel steel impact inlet plate, 3) reducing effective grate width (horseshoe pattern of inlet grate grate plates), plates), 4) station stationary ary quench grates grates at the front front of the cooler cooler, and 5) spreader spreader beam beam across across the cooler cooler. In the 1990s 1990s another another interestin interestingg method was introduced introduced.. It consists consists of aeratio aeration n of a sloping bed at the inlet inlet end of the grate. This area is provided provided with a series of fix fixed ed windboxes windboxes arranged arranged stepwise and equipped with cast metal grate elements designed so that no particles can fall through them (Figure (Figure 3.8.20 3.8.20), ), that is, with the airbeam and pocket pocket grate technology technology mentioned mentioned earlier earlier. A considerable considerable pile is built up over the grate plates, plates, which contain pulsating pulsating air. air. The air expands the pile and in particular moves and mixes the finer clinker clinker with the coarser coarser.. At the same time making the upper upper portion of the pile slide gently into into the cooler while it is being spread out. out.

• Static Aeration Zone • Suitable Clinker Distribution to Avoid Red River • Autogenous Wear Protection of Cooler Inlet

Figuree 3.8.20. Examp Figur Example le of fix fixed ed cooler inlet. inlet.

Final Words

Clinker coolers coolers are an integral integral part of the kiln system. system. Select them carefully carefully,, keep working working at optimizing them, and overall plant performance performance is bound to improve! improve!


498

REFERENCES Gagnon, Denis, “Upgrad “Upgrading ing a Clinker Cooler, Cooler,” Proceedings 38th IEEE/PCA Cement Industry Technical Conference, Los Angeles, April 1996, 1996, pages 156-1 156-170. 70. Herchenbach, Horst, “Cemen Herchenbach, “Cementt Cooling - The Key To To An Economic Kiln Operation and Good Clinker Quality, Quality,”” Proceedings 21st International Cement Seminar, Rock Products, Products, Chica Chicago go,, Illin Illinois, ois, 1985, pages 41-54. 41-54. Keefe, Brian P., Keefe, P., and Christensen, Christensen, Kim Pandrup Pandrup,, “The Cross-Bar Cross-Bar Cooler: Cooler: Innova Innovative tive and and Proven, Proven,” lake City City,, Ut Utah, ah, Ma May y Proceedings 42nd IEEE-IAS/PCA Cement Industry Technical Conference, Salt lake 2000, pages 135-1 35-147. 47. Klotz, Bryan, “Design Features Features of the Polysius Polysius Clinker Clinker Cooler Cooler,,” Proceedings 42nd IEEE-IAS/PCA Cement Industry Technical Conference, Salt lake lake City, City, Utah, May 2000, 2000, pages 159-1 159-170. 70. Labahn/Kohlhaas, Cement Engineers Handbook, 4th Edition, Edition, Bauver Bauverlag lag GmbH, GmbH, Wiesba Wiesbaden den and and Berlin, Berl in, 796 pages, pages, 1983. Lecture 55, “Cooling of Clinker Clinker,,” ” FF. L. Smidth Smidth’s ’s Cement Cement Production Seminar Seminar,, 198 981. 1. Nobis, Rainer Rainer,, “Evalu “Evaluation ation and and Optimization Optimization of Clinker Cooler Operations Operations,,” P roceedings 25th International Cement Seminar, Rock Products, Products, Chicago, Illinois, 1989 pages 11 119-1 9-140. 40. von Wedel, Justus, “The IKN Pendulum Pendulum Cooler,” Proceedings 42nd IEEE-IAS/PCA Cement Industry Technical Conference, Salt lake lake City, City, Utah, May 2000, pages 149-1 149-157. 57.

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