Heating Up of Kilns
description
Transcript of 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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Zeit nach Einbau / hTime after installation / hrs
Tem
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°C
Tem
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/ °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
Acc.V Spot Magn Det WD Exp25.0 kV 4.0 10000x SE 9.9 13 CRB Analyse Service GmbH
Acc.V Spot Magn Det WD Exp25.0 kV 4.0 7800x SE 9.6 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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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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Te mpe ra ture ( °C )
satu
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apou
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essu
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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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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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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
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 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
Drying out cooler section
Clinker for protectionof the grate platesLower part fowearbanks have beencleared again to ensure temperatureaccess during dry outPrevention of thermal shock
Drying out cooler section
Grate plates coveredwith clinker
Bulkhead at the end
Bulkheaded kiln outlet
Bulkheaded kiln outlet
Rockwool and scaffolding
Bulkheaded kiln outlet
Calcium silikate boardswith metal framing
Bulkheading of a cooler exhaust gas duct
Drying out cooler section
Closing of secondary airwith rock wool
Drying out, equipment , gas tanks
Drying out equipment
Support burner
Lightoil burner in action
Drying out cooler section
Positioning of supportburners at cooler side wall door
Drying out, equipment
Single burner control
Drying out cooler section
Positioning of supportBurners at cooler sidewallOpenings closed tightlyFalse air prevention
support burners squeezed in cooler side door
Drying out cooler section
Positioning of supportburner at cooler sidewall
Drying out cooler section
Positioning of supportburner at cooler sidewall Burner pointing intothe cooler but not at the roof
Drying out cooler section
Support burner pointinginto the coolerDirect flame contact to beavoidedGrate covered with clinker
Cooler Drying out
Oil leaking down into cooler
Drying out cooler section
First clinker arrives at coolerSerious thermal shock forside walls
Drying out cooler section
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
After Drying out cooler section
Smooth surfacesNo cracksNo damageExpansion joints clear
After Drying out cooler section
View box in good shapeNo cracks
After Drying out cooler section
Dry out with light oil burner
Surface blackened butsmooth
After Drying out cooler section
Dry out with light oil burner
Lining appears black bycarbon layer