Coolers System

Cross flow heat exchange through clinker bed with cold air Reciprocating grate type Occurrence of waste air requires additional equipment for de-dusting Capacities of up to 10,000 t/d  Alternative forms with two stage cooling and air recirculation are possible Travelling grate type : poor clinker distribution &  movement on the grate and therefore lower efficiency

Separate tube with separate drive Internal heat transfer equipment (lifters) No waste air Capacities of up to 4500 t/d maximum, preferably up to 2000 t/d

Set of tube fixed to the kiln, therefore no separate drive required Internal heat transfer equipment (lifters) No waste air Not suitable for AS pre-calcining systems Capacities of up to 5000 t/d maximum, preferably up to 3500 t/d

Main function of clinker cooler

Recuperate the clinker heat by heating up the combustion air Maintain a minimum cooling velocity in order to avoid unfavorable mineralogical clinker phases and crystal size No waste air

Working principle of coolers

The clinker forms a bed which is transported along the grate by different mechanisms

Working principle of coolers Part of air can be used as combustion air The cooling air is blown from below the grate by fans & pass through the clinker bed in cross current

Working principle of coolers

The material & the cooling air are led in counter current through one or more slightly inclined rotating tubes

Working principle of coolers

Special lifters are installed which increase the active heat transfer area between clinker and cooling air

Working principle of coolers

 An ideal counter current heat exchange takes place between the clinker moving down by gravity and the rising cooling air.

Thermal cooler efficiency the heat of combustion air total heat content of the clinker leaving the kiln

Cooler efficiency depends on :  The required combustion air of the kiln system

- Identical heat consumption - Same excess air factor - Same primary air ratio

Diameter of the cooler is similar to that of a corresponding suspension preheater kiln. Rotating speed is in the same range as for the kiln (max. 3 rpm)

The length to diameter is approximately = 10 The inclination is comparatively high

 “in the order of 5%” 

Simplicity of cooler design, robust piece of equipment. No special mechanical problems (at least not more problems than on a rotary kiln). No control loop Easy commissioning No waste air , therefore no dedusting equipment required Electrical energy consumption is approx. 5 kwh/t lower than for a grate cooler Rotational speed can be adjusted, therefore upset kiln conditions can be handled more easily than planetary cooler. Suitable for pre-calcining system having a separate tertiary air duct (extraction of hot air is possible)..

Little experience available with large coolers (above 2000 t/d) Formation of buildups (snowman) in the inlet chute.  A water-cooled chute or a dislodging device is required in such a case . Clinker outlet temperatures tend to be high and therefore water injection is usually require & Due to large falling height wear protection in the tube must be reinforced (compared to a planetary cooler) . High kiln foundations are required. Cooler inlet seal can contribute to additional false air inlet

Shell extension Fixation of cooling tubes Design of cooler supports Cooler length Inlet openings

The heat transfer in a planetary cooler is based on a  counter heat exchange between clinker and cooling  air.

Items influence the efficiency The clinker must be brought in an intensive contact with the cooling air The quantity of available cooling air affects the efficiency The efficiency is not only determined by the machine itself, but also by the amount of cooling air. The granulometry of the clinker affects the cooling efficiency

Heat input by clinker 1200oC

100%

Heat output By secondary air

750oC

By shell losses By clinker outlet

68% 22%

170oC

10%

P n

x

1.5

D

x

L

=

t m2.5 x d

Clinker production in t/24 h Number of coolers tubes Length of cooler tubes in m Cooler tube diameter in m Satellite tube diameter in m

P n x

D2

x

π

/4

< 70 t/m2

Design and condition of the internal heat transfer equipment Operating conditions

External Water Spray

Internal Water Spray

Simplicity in design and operation. No control loops are required. No Exhaust air is produced and therefore de-dusting is required. Specific power consumption is by 6 Kwh /t lower than with grate cooler and by approximately 2 Kwh /t more than with rotary cooler. commissioning is easy.

 Virtually no control of cooler operation is possible ( critical in case of  material rushes ). There is also no control of the distribution of the clinker to the individual tubes which may often vary by up to 50 %. Since there is no exhaust air there is no cooler exhaust air utilization possible. In cases where this heat could be used for drying purposes this may become an argument against the planetary cooler.  A planetary cooler might become an important source of noise emission (depending on the clinker granulometry). If residential areas are in the vicinity sound protection measures may become necessary Clinker exit temperatures are comparatively high and call for fully metallic clinker conveying equipment and adequate cooling in the cement mill.

Spare capacity is relatively little. Cooler is sensitive to overload. The kiln outlet section is a complicated structure which has to resist high stresses and temperatures. The protective cast refractory mass in this area needs close attention. In case of refractory failure the kiln has to be stopped immediately. The kiln downtimes tend to be longer because relining work in the kiln and repair works in the plants have to be performed simultaneously The planetary cooler cannot be applied for precalcining kiln Systems having a separate tertiary air duct because there is no possibility to extract hot tertiary air. Therefore the planetary cooler is ruled out for very high kiln capacities (above4000 / 5000 t / d). The necessity of a bypass may also act against the planetary cooler.

Reciprocating grate cooler

Travelling Grate Cooler

Reduced cooler width, in order to operate the cooler with a thick clinker bed & consequently a good cooling air distribution and a high heat recuperation Good sealing of the cooler compartment by means of  discharge hoppers for grate riddlings. Good accessibility of the spillage drag chain Fingerless plates supports, allowing a quick replacement of  grate plates from the undergrate chamber

Important design features of modern grate coolers

Hydraulic drive for each individual grate, with speed range 0 to 25 strokes per minute Full width clinker beaker Total cooling air quantity installed in the range of 3 - 3.5 Nm3/kg cli, with fan pressures decreasing from 60-70 mbar in the first compartment to 20 to 30 mbar in the last one Possibility of re-circulation of the cooler vent air

Grate Speed  Air Flow Hood Draft

Cooler de-dusting

Normal operation

Kiln in Upset Conditions

%

100

up to 150

 Air temperature

°C

200 - 250

up to 450

 Air dew point

°C

5- 20

5-20

Dust load

g/Nm3

5-15

25-35

 Air flow (actual volume)

Comparison of de-dusting equipment for clinker coolers

Type of Collector

Multiclone

Electrostatic Precipitator

Gravel Bed Filter

Bag Filter

Advantage  Simple  Low investment cost  Low space requirement  Not sensitive to temperature  peaks  Good experience for may years  High efficiency  Low pressure loss  Low operating cost  Low maintenance cost  High efficiency  Not sensitive to temperature  peaks  Experience with many units in operation  High efficiency  Relatively low investment cost

Disadvantage  Poor efficiency for particles < 20 um  Efficiency sensitive to gas flow fluctuation  Comparatively high pressure loss  High operating cost  Bit unit required or use of pulse generator   high investment cost  Possibly water injection required  Highest investment cost  Highest pressure loss  High operating cost

 No bags withstanding temperatures up to 450C  precooling required  High pressure loss  High operating cost  High maintenance cost

Multiclone • Simple • Low investment cost • Low space requirement • Not sensitive to temperature peaks • Good experience for many years

• Poor efficiency for particles < 20 micron • Efficiency sensitive to gas flow flLldu1n1 • Comparatively high pressure loss • High operating cost

Type of  Collector 

Advantage

• Simple • Low investment cost • Low space Multiclone requirement • Not sensitive to temperature peaks • Good experience for may years • High efficiency • Low pressure loss Electrostatic • Low operating cost Precipitator  • Low maintenance cost

Disadvantage • Poor efficiency for  particles < 20 micron • Efficiency sensitive to gas flow flLldu1n1 • Comparatively high pressure loss • High operating cost • Bit unit required or use of pulse generator —* high investment cost • Possibly water inj ectioii required

Principle of non ventilating clinker cooler

No dust emission at all Simple Low investment cost Moderate maintenance cost Moderate operating cost Heat recovery possible Extension possible by adding further heat exchange units

Possible wear of fan blades

Maintenance and operating cost higher than conditional cooler de-dusting system with E.P.

Material temp. & undergrate pressure of grate cooler

Temp. of secondary air

Notation: X =

Specific heat consumption of the kiln, kca/kg clinker

n =

Number of coolers tubes

Cl =

Heat loss of the cooler cooler,, kcal/kg clinker

The figures 3250 & 347 are constants

Temp. of secondary air

Assume Specific heat consumption =

830 kcal/kg

Excess air number of =

1.1

Heat loss of the cooler =

92 kcal/kg clinker

t =

3250 250 ( 347 - 92 ) ( 830 x 1.1 )

Criteria used for judging the cooler efficiency

Cooler Thermal Efficiency: 1

It is the ratio of the heat reclaimed from the hot clinker, and utilized in the burning process, to the total heat content of the clinker leaving the kiln.

=

A-B A

* 100

Cooler Thermal Efficiency:

Notation:

=

A-B A

* 100

A = Heat content of clinker leaving the kiln B = Heat losses of clinker cooler B consists of = a = Heat loss in cooler exit air b = Heat loss in clinker leaving cooler c =

Heat loss by radiation

Criteria used for judging the cooler efficiency

2 The temp. difference between the hot clinker entering the cooler and the hot secondary air leaving the cooler

Heat balance of satellite cooler

Coolers thermal efficiency

Range of application

Type of Cooler

Suitability for AS1) Pre-calcining Systems

De-dusting Equipment for Waste air Required

10,000

YES

YES2)

500-2000

4,000

YES

NO

1500-3500

5,000

NO

NO

Optimum Capacity range3) (t/d)

Maximum Capacity (t/d)

Reciprocating Grate

7000-3000

Rotary Cooler

Planetary Cooler

Remarks

Criteria influence the selection of a cooler Layout possibilities Old equipment which can be incorporated in a new plant Granulometry of clinker Noise emission Possibility to extend capacity in a later stage

Temp. profile in the clinker bed