drying-out & heating-up of refractory linings

$: Drying-Out & Heating-Up of Refractory Linings$
Stefan Thomas

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

What measures help before drying out

Use exact amount of water (as less as possible during installation of all monolithics)Stitching of evaporation holes (castable layer thickness >150mm)As much as possible time for natural evaporation

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 the scanning 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

0

10

20

30

40

50

60

70

80

90

100

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

Drying out and heating-up diagramm of refractory concretes/castables(RCC, MCC, LCC, SC, JC)

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)

Temperature in °C Saturation vapour pressure in bar

20 0.02

50 0.12

100 1

150 5

200 15

250 40

300 86

350 165

Saturation vapour pressure as a function of temperature

Phase 1

Phase 1

Saturation vapour pressure as a function of temperature

Hot FaceCold Face

PoutletPmeniscus >Phase 1:

OutletInlet Air flow

100°C/1 bar

20°C/0.02 bar

T [°C]Poutlet

Pcapillary

Pmeniscus

ΔP≈ 1 bar

Low temperature, constant gasflow with high ventilation

Evaporation holes stitched and protected with straw

< PoutletPmeniscusPhase 2:

T [°C]

OutletInlet Air flow

350°C/165 bar

100°C/1 bar

ΔP≈ 164 bar

High temperature, low ventilation and air flow

Poutlet

Pcapillary

Pmeniscus

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!

IIlustration of an entire refractory installation

dynamicmainly bricks

statichigh rate of monolithics

statichigh rate of monolithics

alumina bricks

basic bricks

tyre

gear

Time is money! So why heating-up slowly?

Spontaneousexplosion of water

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

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

Thermal expansion of magnesia spinel bricks and kiln shell

0-1 1 2 %

100 50 0

1200

1000

800

600

400

200100

300

400

200

CompressionPoint of equal expansion

Safe zone

N/mm2

thermal expansion ofthe kiln shell

thermal expansion ofmagnesia spinel bricks

relative expansion

installationtolerance

Kilnshell

Hotface

temperature°C

Squeezing at the tyres

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

Girth Gear

Recommondation to heat-up installations with grate-cooler and tertiary air duct

Before drying, at least 24h conditioning time for all massesClosing kiln inlet and cooler outletopening (Ytong o.a.)Adjustment of air flow with TAD slider.Configuration of multiple high velocity burners and thermal elementsFuel, ideally gas or light fuel-oil

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 KuwaitKühler

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

3. Drying out and heating-up using the central burner andcalciner burner (no auxiliary burners)

Theoretically possible, but:

Drying out and heating-up time is limited (see process with central burner)

Early turning of rotary kiln is required.

Temperatures in rotary kiln do rise very fast Danger of squeezing

Too fast drying of castables/wear benches in the cooler as drying onlycommences after first clinker has arrived.

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600

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Tem

pera

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 mainburner method and is therefore advantageous to the kiln lining.

Heat distribution in all vessels is very equal, particulary drying in the cooler can be commenced 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 drying out

Explosive characterof steam

Burner Drying

Dry out or barbecue preparation in raw meal pipe?

Good idea to get ridof waste but please…

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

Drying out cooler section

Grate plates coveredwith insulationboards

Bulkhead at the end

Before drying out cooler section

Thick layers like wearbanks require specialcare

Drying out is a must

LCC castable sensitivedue to 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 silicate boardswith metal framing

Bulkheading of a cooler exhaust gas duct


Closing of secondaryair with rock wool

Drying out, equipment , gas tanks

Drying out equipment

Support burner

Lightoil burner in action


Positioning of supportburners at cooler sidewall door

Drying out, equipment

Single burner control

0

100

200

300

400

500

600

29.05

.2003

17:07

:48

30.05

.2003

07:07

:03

30.05

.2003

22:21

:39

31.05

.2003

12:21

:39

01.06

.2003

03:33

:54

01.06

.2003

18:15

:18

02.06

.2003

08:15

:18

02.06

.2003

22:31

:28

03.06

.2003

12:36

:00

04.06

.2003

03:53

:03

Tem

pera

tur i

n °C

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

Heating up protocol for comparison


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 tobe avoidedGrate covered with clinker

Cooler drying out

Oil leaking down intocooler


First clinker arrives at coolerSerious thermal shockfor side 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

Drying out with gasClean and smoothsurface


Smooth surfacesNo cracksNo damageExpansion joints clear


View box in good shapeNo cracks


Drying out with light oilburner

Surface blackened butsmooth


Drying out with light oilburner

Lining appears black bycarbon layer

drying-out & heating-up of refractory linings

Documents

saturation

static high

physically

chemically

100c 1 bar

air flow poutlet

bulkheaded

air flow