Heating Up of Kilns

Drying out and heating-up of refractory linings Dirk Basten

Refractory installation of an entire plant

dynamic mainly bricks

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 % Æ 80 tonnes of water to be vaporized

Exact amount of water when mixing, gunning and wet casting Stitching of evaporation holes As much as possible time for natural evaporation Use of bricks

Trend in development of the product properties

RC-vibration castable REFRACLAY 40 20 wt.-%

LC- vibration castable REFRACLAY 40 LCC ~5 wt.-%

Water addition:

10 – 12 %

6–7%

Bulk density:

2.05 g/cm³

2.25 g/cm³

Apparent porosity:

20 – 22 %

14 – 15 %

35 – 45 N/mm2

90 – 110 N/mm2

19 – 20 cm³

4 – 5 cm³

1450 °C

1500 °C

Cement content:

Cold crushing strength: Abrasion loss: Application temperature: Alkali resistance:

1500

Aufheizdiagramm feuerfester Massen (LCC, MCC, SC, JC) DryingHeating out and heating-up diagramm of refractory diagramm of refractory concretes (LCC, MCC, SC, JC) castables/concretes (RCC, MCC, LCC, SC, JC)

1400 1300 1200

Temperature / °C

Temperatur / °C Temperature / °C

1100 1000 900

30 °C/h bis zur Einsatztemperatur up to temp. of application

800 700

Heating-up

600

10 h / 500 °C

500

Drying out

400

25 °C/h

300 20 h / 110 - 150 °C

200 15 °C/h

min. 24 h Erhärtungsdauer min. 24 hrs setting time

100 0 0

10

20

30

40

50

60

70

Time after installation / hrs

80

90

100

Zeit nach Einbau / h Time after installation / hrs

110

Two different kinds of water are found in the refractory lining: 1. Physically bonded water (free water): Æ removed at 100-150°C Conversion of physical and chemical bonded water to the vapour phase by evaporation or vaporisation. Evaporating already during setting process at room temperatures and normally vaporising at 100°C

2. Chemically bonded water (water of crystallization): Æ removed at 300-800°C water 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 process and within the heating-up process.

Physically bonded water Wet cutting of bricks (only Al-bricks! )

Too much water in castable

Physically bonded water in expansion joint material (rainwater)

Chemically bonded water under the scanning electron microscope (SEM)

Hydration of magnesium oxide Formation of cracks due to brucite (Mg(OH)2 ) formed in the sintered structure

Acc.V Spot Magn Det WD Exp 25.0 kV 4.0 540x SE 9.8 17 CRB Analyse Service GmbH

Acc.V Spot Magn Det WD Exp 25.0 kV 4.0 10000x SE 9.9 13 CRB Analyse Service GmbH

hexagonal brucite sheets

Acc.V Spot Magn Det WD Exp 25.0 kV 4.0 7800x SE 9.6 17 CRB Analyse Service GmbH

Behaviour

Drying rate

Drying rate (weight/h)

100

Behaviour of drying rate ofasdrying rateofas a function a function drying time

Phase 1

of drying time

Phase 2

90

Low vapour pressureÆLow drying rate

80 70 60

Const. Drying Rate

Decreasing Drying Rate

50 40 30 20 10 0 1

2

3

4

5

tkn6

7

8

Drying tim e

Drying time (h)

9

10

11

12

13

Phase 1: Pmeniscus > Poutlet Air flow

Inlet

Outlet

T [°C] 100°C /1 bar

Poutlet

Pmeniscus

20°C /0.02 bar

Pcapillary

Low temperature, constant gasflow with high ventilation

ΔP≈ 1 bar

Phase 1: Initial phase: Evaporation of physical bonded water is relevant

1

Evaporation commences already during setting process at T < 100°C: Water is partly incorporated into the mineral lattice structure > 24 h in room temperature! The longer, the better!

2

Vaporisation of free water at 100°C

3

Physical bonded water can be found in very fine capillaries Higher temperatures are necessary to overcome capillary forces Vaporisation of capillary water at >100°C Æ (100-150°C)

Evaopration holes stitched and protected with straw

s a tu ra tio n v a p o u r p re s s u re ( b a r)

Saturation vapour pressures vs temperature

250 200 150 100

1bar (Atmospheric Pressure)

50 0 0

50

100

150

200

250

300

350

Te mpe ra ture (°C )

Cold Face

Hot Face

400

Phase 2: Pmeniscus < Poutlet Inlet

Air flow

Outlet

T [°C] 350°C /165 bar

Poutlet

ΔP≈ 164 bar

Pmeniscus

100°C /1 bar

High temperature, low ventilation and air flow

Pcapillary

Bitumen application as vapour barrier

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

As they dry, LC castables cause more problems due to: Lower proportion of water

Lower porosity

Higher capillary forces

Lower water vapour pressure

Slower drying rates

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

1500

Aufheizdiagramm feuerfester Massen (LCC, MCC, SC, JC) Drying out and heating up diagramm of Heating diagramm of refractory concretes (LCC, MCC, SC, JC) refractory concretes, castables (RCC, MCC, LCC, SC, JC)

1400 1300 1200

Temperature / °C

Temperatur / °C Temperature / °C

1100 1000 900

30 °C/h bis zur Einsatztemperatur up to temp. of application

800 700

Heating-up

600

10 h / 500 °C

500 400

25 °C/h

300 20 h / 110 - 150 °C

200 15 °C/h

min. 24 h Erhärtungsdauer min. 24 hrs setting time

100 0 0

10

20

30

40

50

60

70

Time after installation / hrs

80

90

100

Zeit nach Einbau / h Time after installation / hrs

110

Illustration of an entire refractory installation alumina bricks gear

basic bricks tyre

static mainly monolithics

dynamic mainly bricks

static mainly monolithics

Why do we need to heat-up the system slowly? Different elements of the system have their individual and particular thermal behaviour and properties. Different expansion coefficient Different thermal conductivity Different elasticy Different strength Different temperatures within the same material All elements have to be treated as a whole system since they closely coexist to each other and are integrated therein accordingly.

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

Squeezing at the tyres

Girth Gear

Temperature distribution in brick and kiln shell during heating-up

Hot Face of Brick Temperature in °C

Mid-Depth of Brick Cold Face of Brick

Kiln Shell

Time in hrs

Rapidly heating-up

Axial and radial pressure Æ Risk of thermal spalling

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

Loose bricks Æ Risk of Displacement

Heating-up process:

After Drying out it is usefull to start the Heating-up immediately and to bring the whole plant to normal operating temperature. RT provides guide lines as part of the installation documentation 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°C 1/3 revolution every 30 minutes

In the temperature range of 900-1200°C continuous rotation required

In the temperature range of 600-900°C 1/3 revolution every 15 minutes

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

Drying out and heating- up using exclusively the central 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 drying out and heating-up is limited to 72 hours. (Drying out should take max. 36 hours.Heating-up is to start immediately afterwards 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 a squeezing of the rotary kiln by the tyre. In emergency case cooling of kiln shell may be required.

Drying out and heating-up using exclusively the central burner T2 ILC T3

Drehofen Kiln

Cooler

Kühler

SteigRRiser T1 schacht i s e r

FLS Kuwait

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

Raw meal feeding is started in KHD and Polysius plants if the inlet chamber temperature 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

2. Drying out and heating-up using exclusively the calciner burner Expected temperatures at Kuwait Cement Co., (FLS)

2. Drying out and heating up using exclusively the calciner burners Actual temperatures at Kuwait Cement Co., (FLS)

Practically not advisable

29 .0 5. 20 30 03 .0 1 5. 20 7:0 30 7: 03 48 .0 07 5. 20 :0 31 7: 03 03 .0 22 5. 20 :2 01 1: 03 39 .0 12 6. 20 :2 01 1: 03 39 .0 03 6. 02 200 :33 :5 3 .0 4 18 6. 20 : 02 03 15:1 .0 8 08 6. 20 :1 03 5: 03 18 .0 22 6. 20 :3 04 1: 03 28 .0 12 6. 20 :3 6: 03 00 03 :5 3: 03

Temperatur in °C

Drying out curve with actual temperatures measured during the process 600

500 Sollwert

400

300

200

100

0 TC 1 Meßstelle 1

TC 2 Meßstelle 2

TC 3 Meßstelle 3

TC 4 Meßstelle 4

TC 5 Meßstelle 5

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

4.1. Plants without tertiary air duct Distribution of auxiliary burners: Two auxiliary burners in the cooler Two auxiliary burners in the kiln hood Two auxiliary burners in the inlet chamber Two auxiliary burners in the lower cyclones When applying this method, drying will take longer than with the main burner 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 drying is 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 Drying and heating time is not limited but recommended to range between 100 and 125 hours. It is easy to follow up the drying and heating-up scedule as well as to follow the holding time. When applying this method it is possible to do the final heating at a later stage 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

Burner Drying

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 waste but please…

Drying out cooler section Grate plates covered with insulationboards Bulkhead at the end

Before Drying out cooler section

Thick layers like wear banks require special care Dry out is a must LCC castable sensitive due to high amount of chemically bonded water Installation of wear banks always in the end

Drying out cooler section

Clinker for protection of the grate plates Lower part fo wearbanks have been cleared again to ensure temperature access during dry out Prevention of thermal shock

Drying out cooler section

Grate plates covered with clinker Bulkhead at the end

Bulkheaded kiln outlet

Bulkheaded kiln outlet

Rockwool and scaffolding

Bulkheaded kiln outlet

Calcium silikate boards with metal framing

Bulkheading of a cooler exhaust gas duct

Drying out cooler section

Closing of secondary air with rock wool

Drying out, equipment , gas tanks

Drying out equipment

Support burner

Lightoil burner in action

Drying out cooler section

Positioning of support burners at cooler side wall door

Drying out, equipment

Single burner control

Drying out cooler section

Positioning of support Burners at cooler side wall Openings closed tightly False air prevention

support burners squeezed in cooler side door

Drying out cooler section

Positioning of support burner at cooler side wall

Drying out cooler section

Positioning of support burner at cooler side wall Burner pointing into the cooler but not at the roof

Drying out cooler section

Support burner pointing into the cooler Direct flame contact to be avoided Grate covered with clinker

Cooler Drying out

Oil leaking down into cooler

Drying out cooler section

First clinker arrives at cooler Serious thermal shock for side walls

Drying out cooler section

Thermal shock at castable surface causes cracks. Typical in cooler section Hot clinker in direct contact to thick castable layer. Explosive mixture

After Drying out cooler section

Dry out with gas Clean and smooth surface

After Drying out cooler section

Smooth surfaces No cracks No damage Expansion joints clear

After Drying out cooler section

View box in good shape No cracks

After Drying out cooler section

Dry out with light oil burner Surface blackened but smooth

After Drying out cooler section

Dry out with light oil burner Lining appears black by carbon layer