Drying-Out & Heating-Up of Refractory Linings [PDF]

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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



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: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