Coolers System

7/28/2019 Coolers System

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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 re-circulation 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, preferablyup to 2000 t/d



Set of tube fixed to the kiln, therefore noseparate drive required

Internal heat transfer equipment (lifters)

No waste air

Capacities of up to 5000 t/d maximum, preferablyup to 3500 t/d

Not suitable for AS pre-calcining systems



Recuperate the clinker heat by heating up thecombustion air

Maintain a minimum cooling velocity in orderto avoid unfavorable mineralogical clinker

phases and crystal size

No waste air

Main function of clinker cooler



The clinker forms a

bed which is

transported along

the grate by

different

mechanisms

Working principle of coolers



The cooling air

is blown from

below the grate

by fans & pass

through theclinker bed in

cross current


Part of air canbe used as

combustion air



The material & the

cooling air are ledin counter currentthrough one ormore slightlyinclined rotatingtubes




Special lifters are

installed whichincrease the activeheat transfer areabetween clinker

and cooling air




An ideal counter

current heatexchange takesplace betweenthe clinker

moving down bygravity and therising cooling air.




Thermal cooler efficiency

Cooler efficiency depends on :

The required combustion air of the kiln system

the heat of combustion air

total heat content of the clinker leaving the kiln



- Identical heat consumption

- Same excess air factor

- Same primary air ratio



Diameter of the cooler is similar to that of acorresponding suspension preheater kiln.

Rotating speed is in the same range as forthe kiln (max. 3 rpm)

The length to diameter is approximately = 10

The inclination is comparatively high “in the order of 5%”



Suitable for pre-calcining system having a separate tertiary airduct (extraction of hot air is possible)..

Simplicity of cooler design, robust piece of equipment.

No control loop

Easy commissioning

No waste air , therefore no dedusting equipment required

Electrical energy consumption is approx. 5 kwh/t lower thanfor a grate cooler

Rotational speed can be adjusted, therefore upset kilnconditions can be handled more easily than planetary cooler.

No special mechanical problems (at least not moreproblems than on a rotary kiln).



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 thereforewater injection is usually require & Due to large falling heightwear 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 contactwith 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 coolingefficiency



Heat input by clinker 1200oC 100%

Heat output

By secondary air 750oC 68%

By shell losses 22%

By clinker outlet 170oC 10%



Clinker production in t/24 h

Number of coolers tubes

Length of cooler tubes in m

Cooler tube diameter in m

P

n D1.5x Lx= t

m2.5 dx

Satellite tube diameter in m



< 70 t/m2 Pn D2x π/4x



Design and condition of the internal heattransfer equipment

Operating conditions



External Water Spray

Internal Water Spray



Simplicity in design and operation. No control loops arerequired.

No Exhaust air is produced and therefore de-dusting is

required.

Specific power consumption is by 6 Kwh /t lower than withgrate 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 theclinker to the individual tubes which may often vary by up to 50 %.

Since there is no exhaust air there is no cooler exhaust air utilizationpossible. 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 noiseemission (depending on the clinker granulometry). If residentialareas are in the vicinity sound protection measures may become

necessary

Clinker exit temperatures are comparatively high and call for fullymetallic clinker conveying equipment and adequate cooling in thecement mill.



The kiln outlet section is a complicated structure which has to resisthigh stresses and temperatures. The protective cast refractorymass in this area needs close attention. In case of refractory failurethe kiln has to be stopped immediately.

The kiln downtimes tend to be longer because relining work in thekiln and repair works in the plants have to be performedsimultaneously

The planetary cooler cannot be applied for precalcining kiln Systemshaving a separate tertiary air duct because there is no possibility toextract hot tertiary air. Therefore the planetary cooler is ruled out forvery high kiln capacities (above4000 / 5000 t / d). The necessity of a

bypass may also act against the planetary cooler.

Spare capacity is relatively little. Cooler is sensitive to overload.



Travelling Grate Cooler

Reciprocating grate cooler



Reduced cooler width, in order to operate the cooler with athick clinker bed & consequently a good cooling airdistribution and a high heat recuperation

Good sealing of the cooler compartment by means of discharge hoppers for grate riddlings.

Fingerless plates supports, allowing a quick replacement of grate plates from the undergrate chamber

Good accessibility of the spillage drag chain

Important design features of modern grate coolers



Hydraulic drive for each individual grate, with speed range0 to 25 strokes per minute

Full width clinker beaker

Total cooling air quantity installed in the range of 3 - 3.5Nm3/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

p g g



Grate Speed

Air Flow

Hood Draft



Normaloperation

Kiln inUpset

Conditions

Air flow(actual volume)

% 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

Cooler de-dusting

Comparison of de

-

dusting equipment for clinker coolers



Type of Collector Advantage Disadvantage

Multiclone

Simple

Low investment cost

Low space requirement

Not sensitive to temperature peaks

Good experience for may years

Poor efficiency for particles < 20

um

Efficiency sensitive to gas flowfluctuation

Comparatively high pressure loss

High operating cost

Electrostatic

Precipitator

High efficiency

Low pressure lossLow operating cost

Low maintenance cost

Bit unit required or use of pulse

generator high investment cost Possibly water injection required

Gravel Bed FilterHigh efficiency

Not sensitive to temperature peaks

Experience with many units in

operation

Highest investment cost

Highest pressure loss

High operating cost

Bag Filter

High efficiency

Relatively low investment cost

No bags withstanding

temperatures up to 450C pre-cooling required

High pressure loss

High operating cost

High maintenance cost

l i l



• Simple

• Low investment cost

• Low space requirement

• Not sensitive to temperature peaks

• Good experience for many years

Multiclone

• Poor efficiency for particles < 20 micron• Efficiency sensitive to gas flow flLldu1n1

• Comparatively high pressure loss

• High operating cost



Type of

Collector Advantage Disadvantage

Multiclone

• Simple• Low investment

cost

• Low space

requirement• Not sensitive to

temperature peaks

• Good experience

for may years

• Poor efficiency for

particles < 20 micron

• Efficiency sensitive to

gas flow flLldu1n1• Comparatively high

pressure loss

• High operating cost

Electrostatic

Precipitator

• High efficiency

• Low pressure loss

• Low operating cost

• Low maintenance

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

Heat recovery possible

Moderate maintenance cost

Moderate operating cost

Extension possible by adding further heatexchange units



Possible wear of fan blades

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

Material temp & undergrate pressure of grate



Material temp. & undergrate pressure of grate

cooler

Temp of secondary air



Temp. of secondary air

Notation:

X = Specific heat consumption of the kiln,kca/kg clinker

Number of coolers tubesn =

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

The figures 3250 & 347 are constants

Temp. of secondary air



e p o seco da y a

Assume

Specific heat consumption = 830 kcal/kg

Heat loss of the cooler =

Excess air number of = 1.1

92 kcal/kg clinker

t =3250 ( 347 - 92 )

( 830 x 1.1 )

Criteria used for judging the cooler efficiency



Cooler Thermal Efficiency:

It is the ratio of the heat reclaimed from thehot clinker, and utilized in the burningprocess, to the total heat content of the

clinker leaving the kiln.

100*A

B-A=


1





100*A

B-A=Notation:

A = Heat content of clinker leaving the kiln

Heat losses of clinker coolerB =

B consists of =

Heat loss in cooler exit airHeat loss in clinker leaving cooler

a =

Heat loss by radiation

b =

c =



The temp. difference between the hot clinkerentering the cooler and the hot secondary air leavingthe cooler


2

Heat balance of satellite cooler



Heat balance of satellite cooler

Coolers thermal efficiency



Coolers thermal efficiency

Range of application



Range of application

Type of Cooler

OptimumCapacity range

3)

(t/d)

MaximumCapacity (t/d)

Suitability for AS1)

Pre-calcining

Systems

De-dustingEquipment for

Waste air

Required

Remarks

Reciprocating

Grate

7000-3000

10,000

YES

YES2)

Rotary Cooler

500-2000

4,000

YES

NO

Planetary

Cooler

1500-3500

5,000

NO

NO

Criteria influence the selection of a cooler



Criteria influence the selection of a cooler

Layout possibilities

Old equipment which can be incorporated in a newplant

Granulometry of clinker

Noise emission

Possibility to extend capacity in a later stage

T fil i th li k b d



Temp. profile in the clinker bed

Cli k t t



Clinker transport

Surface transport

Pneumatic transport

The travelling of big chunk or heavy coating from the fixed inlet tothe moving grates is effected by two transport mechanisms

Coolers System

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