Drying out and heating-up of refractory linings Stefan Thomas
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
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 refractory castables/concretes (RCC, MCC, LCC, SC, JC)
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
hexagonal brucite sheets
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 7800x SE 9.6 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
Behaviour of drying rate
Behaviour of drying rateasas a function of drying a function of drying time time Phase 1
Phase 2
90
Low vapour pressureÆLow drying rate
80 70 Drying rate
Drying rate (weight/h)
100
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
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
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)
Saturation vapour pressure as a function of temperature
Phase 1
Phase 1
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
Cold Face
Hot Face
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
Evaporation holes stitched and protected with straw
Phase 2: Pmeniscus < Poutlet Inlet
Air flow
Outlet
T [°C] 350°C /165 bar
ΔP≈ 164 bar
100°C /1 bar
High temperature, low ventilation and air flow
Poutlet
Pmeniscus
Pcapillary
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!
IIlustration of an entire refractory installation alumina bricks gear
basic bricks tyre
static high rate of monolithics
dynamic mainly bricks
static high rate of monolithics
Time is money! So why heating-up slowly? Spontaneous explosion 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. 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.
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
Thermal expansion of magnesia spinel bricks and kiln shell Hot face
Kiln shell
1200
400
1000 800 600
Compression Point of equal expansion
300 Safe zone 200
prau°C tem
400 200
thermal expansion of the kiln shell
rancetolis
100
-1 N/mm2
thermal expansion of magnesia spinel bricks 0 100 50
1 0
2 % relative expansion
Heating-up is limited by the tyres and other mechanical parts
Squeezing at the tyres
Girth Gear
Recommondation to heat-up installations with grate-cooler and tertiary air duct
Before drying, at least 24h conditioning time for all masses Closing kiln inlet and cooler outletopening (Ytong o.a.) Adjustment of air flow with TAD slider. Configuration of multiple high velocity burners and thermal elements Fuel, ideally gas or light fuel-oil
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
Riser
Drehofen Kiln
Cooler
Kühler
R Steigi T1 schacht 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
3. Drying out and heating-up using the central burner and calciner 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 Æ Danger of squeezing Too fast drying of castables/wear benches in the cooler as drying only commences after first clinker has arrived.
.0 6.
03
20 03
03
03
20
20
.0 6.
.0 6.
20
03
03
20
.0 6.
.0 6.
04
03
02
02
01
03
20
20
.0 6.
03
03
03
20
20
20
.0 5.
.0 5.
.0 5.
.0 5.
01
31
30
30
29
03
:5
3:
03
00
28
18
18
6:
1:
5:
5:
:3
:3
:1
:1
54
39
3:
1:
:3
12
22
08
18
03
:2
03
48
39
7:
7:
1:
:0
:0
:2
12
22
07
17
Temperatur in °C
Drying out curve with actual temperatures measured during the process
600
500 Sollwert
400 TC 1 Meßstelle 1
300 TC 2 Meßstelle 2
TC 3 Meßstelle 3
200 TC 4 Meßstelle 4
TC 5 Meßstelle 5
100
0
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 drying out Explosive character of steam
Burner Drying
Burner Drying
Burner Drying
Dry out or barbecue preparation in raw meal pipe?
Good idea to get rid of waste but please…
Professional drying of pipes with heater mats (max 450°C)
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 Drying 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 silicate 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
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 0 6. 20 8:1 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
Heating up protocol for comparison
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
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 Drying 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 Drying out with light oil burner Surface blackened but smooth
After drying out cooler section Drying out with light oil burner Lining appears black by carbon layer
