heating up of kilns

Dirk Basten

Drying out and heating-up of refractory linings

dynamicmainly bricks

Refractory installationof an entire plant

How much water has to be removed?

In case of a preheater lined with 2000 tonnes of refractory materials, around 1000 tonnes thereof being refractory concretes

average water content of 8 % 80 tonnes of water to be vaporized

Exact amount of water when mixing, gunning and wet castingStitching of evaporation holesAs much as possible time for natural evaporationUse of bricks

Trend in development of the product properties

RC-vibration castable LC- vibration castable REFRACLAY 40 REFRACLAY 40 LCC

Cement content: 20 wt.-% ~5 wt.-%

Water addition: 10 – 12 % 6 – 7 %

Bulk density: 2.05 g/cm³ 2.25 g/cm³

Apparent porosity: 20 – 22 % 14 – 15 %

Cold crushing strength: 35 – 45 N/mm2 90 – 110 N/mm2

Abrasion loss: 19 – 20 cm³ 4 – 5 cm³

Application temperature: 1450 °C 1500 °C

Alkali resistance:

Aufheizdiagramm feuerfester Massen (LCC, MCC, SC, JC)Heating diagramm of refractory concretes (LCC, MCC, SC, JC)

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0 10 20 30 40 50 60 70 80 90 100 110

Zeit nach Einbau / hTime after installation / hrs

Tem

pera

tur /

°C

Tem

pera

ture

/ °C

10 h / 500 °C

min. 24 h Erhärtungsdauermin. 24 hrs setting time

20 h / 110 - 150 °C

15 °C/h

25 °C/h

30 °C/hbis zur Einsatztemperaturup to temp. of application

Heating-up

Drying out

Time after installation / hrs

Tem

pera

ture

/ °C

Drying out and heating-up diagramm of refractorycastables/concretes

(RCC, MCC, LCC, SC, JC)

Two different kinds of water are found in the refractory lining:

2. Chemically bonded water (water of crystallization):removed at 300-800°Cwater but more difficult to be removed.Removal by vapour-diffusion or vapour-flow. Decomposition of water containing minerals.Water will be expelled at 300-800°C at the end of the drying out processand within the heating-up process.

1. Physically bonded water (free water):removed at 100-150°CConversion of physical and chemical bonded water to the vapour phaseby evaporation or vaporisation.Evaporating already during setting process at room temperaturesand normally vaporising at 100°C

Physically bonded water

Too much water in castable

Wet cutting of bricks (only Al-bricks! )

Physically bonded water in expansion joint material(rainwater)

Chemically bonded water under thescanning electron microscope (SEM)

Hydration of magnesium oxide

Acc.V Spot Magn Det WD Exp25.0 kV 4.0 540x SE 9.8 17 CRB Analyse Service GmbH



Formation of cracks due to brucite (Mg(OH)2 )formed in the sintered structure hexagonal brucite sheets

Behaviour of drying rate as a function of drying time

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1 2 3 4 5 6 7 8 9 10 11 12 13

Drying time

Dry

ing

rate

tkn

Low vapour pressure Low drying rate

Behaviour of drying rate as a function of drying time

Drying time (h)

Dryi

ngra

te (w

eigh

t/h)

tkn

Phase 1

Const. Drying Rate

Phase 2

Decreasing Drying Rate

PoutletPmeniscus >

OutletInlet Air flow

100°C/1 bar

20°C/0.02 bar

Phase 1:

T [°C]

Poutlet

Pcapillary

Pmeniscus

ΔP≈ 1 bar

Low temperature, constant gasflow with high ventilation

Phase 1: Initial phase:

Evaporation of physical bonded water is relevant

2 Vaporisation of free water at 100°C

1Evaporation commences already during setting process at T < 100°C:

> 24 h in room temperature! The longer, the better!Water is partly incorporated into the mineral lattice structure

Physical bonded water can be found in very fine capillariesHigher temperatures are necessary to overcome capillary forces3

Vaporisation of capillary water at >100°C (100-150°C)

Evaopration holes stitched and protected with straw

Saturation vapour pressures vs temperature

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250

0 50 100 150 200 250 300 350 400

Te mpe ra ture ( °C )

satu

rati

on v

apou

r pr

essu

re (

bar)

1bar (Atmospheric Pressure)

Hot FaceCold Face

Poutlet

Pcapillary

Pmeniscus

T [°C]

OutletInlet Air flow

350°C/165 bar

100°C/1 bar

< PoutletPmeniscusPhase 2:

ΔP≈ 164 bar

High temperature, low ventilation and air flow

Bitumen application as vapour barrier

Desteaming holes are only necessary on the top of the cycloneroofs to control the desteaming progress

Lower proportion of water

Lower porosity Lower watervapour pressure

Slower drying ratesHigher capillary forces

As they dry, LC castables cause more problems due to:

Lower water content of castable does not mean faster drying out and heating up!

Aufheizdiagramm feuerfester Massen (LCC, MCC, SC, JC)Heating diagramm of refractory concretes (LCC, MCC, SC, JC)

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100

200

300

400

500

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900

1000

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1300

1400

1500

0 10 20 30 40 50 60 70 80 90 100 110

Zeit nach Einbau / hTime after installation / hrs

Tem

pera

tur /

°C

Tem

pera

ture

/ °C

10 h / 500 °C

min. 24 h Erhärtungsdauermin. 24 hrs setting time

20 h / 110 - 150 °C

15 °C/h

25 °C/h

30 °C/hbis zur Einsatztemperaturup to temp. of application

Heating-up

Time after installation / hrs

Tem

pera

ture

/ °C

Drying out and heating up diagramm of refractory concretes, castables

(RCC, MCC, LCC, SC, JC)

Illustration of an entire refractory installation

dynamicmainly bricks

staticmainly monolithics

staticmainly monolithics

alumina bricks

basic bricks

tyre

gear

Why do we need to heat-up the system slowly?

Different elements of the system have their individual and particular

thermal behaviour and properties.

All elements have to be treated as a whole system since they closely coexist

to each other and are integrated therein accordingly.

Different expansion coefficient

Different thermal conductivity

Different elasticy

Different strength

Different temperatures within the same material

Squeezing at the tyres

Heating-up is limited by the tyres and other mechanical parts

Girth Gear

Temperature distribution in brick and kiln shell during heating-up

Kiln Shell

Hot Face of Brick

Mid-Depth of Brick

Cold Face of Brick

Tem

pera

ture

in °

C

Time in hrs

Rapidly heating-up

Axial and radial pressureRisk of thermal spalling

Too slowly heating-up, too early turning of the kiln

Loose bricksRisk of

Displacement

Heating-up process:

After Drying out it is usefullto start the Heating-upimmediately and to bring the whole plant to normal operating temperature.

RT provides guide lines as part of the installationdocumentation

RT does not offer Dry – out or heating up services on their own but leave this to professional services of specialized companies .

Heating-up curve after short shutdowns(cooling down of the burning zone not below 300°C)

In the temperature range of 300-600°C1/3 revolution every 30 minutes

In the temperature range of 600-900°C1/3 revolution every 15 minutes

In the temperature range of 900-1200°Ccontinuous rotation required

In the temperature range from 1200°CUp to working temperature:Bring the kiln up to normal operation

Drying out and heating- up using exclusively thecentral burner

Drying out and heating-up has to be done in one step.

To protect the refractory lining in the rotary kiln, whole time for dryingout and heating-up is limited to 72 hours.(Drying out should take max. 36 hours.Heating-up is to start immediatelyafterwards and is to be finished after 72 hours).

Turning of rotary kiln should start at shell outside temperature of 100°C (aprox.6-8 hrs after ignition of flame).

Tyre clearance is to be controlled at regular intervals to avoid asqueezing of the rotary kiln by the tyre.

In emergency case cooling of kiln shell may be required.

Drying out and heating-up using exclusively thecentral burner

FLS Kuwait

Kühler

T1

T3

T2

Steig-schacht

Drehofen

ILC

Cooler

Kiln

Riser

Riser

1. Drying out and heating-up using exclusively the central burner

Raw meal feeding is started in KHD and Polysius plants if the inlet chambertemperature exceeds 850 °C.

In case of FLS plants, raw meel feeding commences once a temperature of 920 °C is reached in the lower cyclones.

Drying out and heating-up with calciner burner

2. Drying out and heating-up using exclusively the calciner burner

Theoretically possible and easily to be managed at first glance, but:

calciner burners are not designed for small quantities of fuel

danger of overheating of the brickwork opposite the burners

sufficient heat distribution up to the cooler benches not possible

Expected temperatures at Kuwait Cement Co., (FLS)

2. Drying out and heating-up using exclusively thecalciner burner

Actual temperatures at Kuwait Cement Co., (FLS)

Practically not advisable

2. Drying out and heating up using exclusively the calciner burners

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Tem

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tur i

n °C

SollwertTC 1 Meßstelle 1TC 2 Meßstelle 2TC 3 Meßstelle 3TC 4 Meßstelle 4TC 5 Meßstelle 5

Drying out curve with actual temperatures measured during the process

Typical auxiliary burner assembly situation for gas

Clean, easy manageable fuel but high safety requirements

Typical auxiliary burner assembly situation for light oil

Fuelstorage and distribution simple, but heavy smoke development

Distribution of auxiliary burners:

Two auxiliary burners in the coolerTwo auxiliary burners in the kiln hoodTwo auxiliary burners in the inlet chamberTwo auxiliary burners in the lower cyclones

4.1. Plants without tertiary air duct

When applying this method, drying will take longer than with the main burnermethod and is therefore advantageous to the kiln lining.

Heat distribution in all vessels is very equal, particulary drying in the cooler can becommenced at its optimum.

Total drying and heating-up time is limited and any interruption after dryingis not possible.

Turning of kiln necessary if shell temperature exceeds 100°C.

4.2. Plants with tertiary air duct

Rotary kiln has to be closed by a bulkhead.Cooler exhaust gas duct or connections have to be closed (bulkheaded)

Distribution of auxiliary burners:similar to previous method

It is easy to follow up the drying and heating-up scedule as well as tofollow the holding time.

Drying and heating time is not limited but recommended to range between100 and 125 hours.

When applying this method it is possible to do the final heating at a laterstage since the rotary kiln was cold and not affected by the heat.

Burner being introduced wet, without dry out

Explosive character of steam

Burner Drying

Professional drying of pipes with heater mats(max 450°C)

Dry out or barbecue preparation in raw meal pipe?

Good idea to get rid of wastebut please…

Drying out cooler section

Grate plates coveredwith insulationboards

Bulkhead at the end

Before Drying out cooler section

Thick layers like wear banksrequire special care

Dry out is a must

LCC castable sensitive dueto high amount of chemically bonded water

Installation of wear banksalways in the end


Clinker for protectionof the grate platesLower part fowearbanks have beencleared again to ensure temperatureaccess during dry outPrevention of thermal shock


Grate plates coveredwith clinker

Bulkhead at the end

Bulkheaded kiln outlet


Rockwool and scaffolding


Calcium silikate boardswith metal framing

Bulkheading of a cooler exhaust gas duct


Closing of secondary airwith rock wool

Drying out, equipment , gas tanks

Drying out equipment

Support burner

Lightoil burner in action


Positioning of supportburners at cooler side wall door

Drying out, equipment

Single burner control


Positioning of supportBurners at cooler sidewallOpenings closed tightlyFalse air prevention

support burners squeezed in cooler side door


Positioning of supportburner at cooler sidewall


Positioning of supportburner at cooler sidewall Burner pointing intothe cooler but not at the roof


Support burner pointinginto the coolerDirect flame contact to beavoidedGrate covered with clinker

Cooler Drying out

Oil leaking down into cooler


First clinker arrives at coolerSerious thermal shock forside walls


Thermal shock at castable surface causes cracks.Typical in cooler sectionHot clinker in directcontact to thick castable layer.Explosive mixture

After Drying out cooler section

Dry out with gasClean and smooth surface


Smooth surfacesNo cracksNo damageExpansion joints clear


View box in good shapeNo cracks


Dry out with light oil burner

Surface blackened butsmooth


Dry out with light oil burner

Lining appears black bycarbon layer

heating up of kilns

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