• FIELD OF THE INVENTION
The present invention relates to Rotary kiln having an improved refractory lining for different zones preferably suited for lime calcinations adapted to favour higher hot strength and abrasion resistance and longer operating life before relining. The invention advantageously provides selective refractory for the different zones of the Rotary Kiln such that the charging and discharging end are abrasion resistant with superior thermo-mechanical properties which achieve better performance than conventional castables and also the basic bricks in the calcinations zone have superior thermo-mechanical properties favouring low erosion and corrosion of the bricks as compared to existing linings. The refractory lining arrangement in the rotary kiln of the invention is further adapted such that it is possible to achieve considerable reduction in the shell temperature therby favouring improved performance of the lining. Importantly, the selective refractory lining in the rotary kiln of the invention would fvaour overall improved performance as compared to conventional linings of rotary kilns. The lining configuration of the present invention would thus favour low down time, higher yield/productivity and improved fuel economy, making it worthy of wide industrial applications in Rotary Kilns especially for Lime calcinations in steel plants and the like.
BACKGROUND ART
The Rotary kilns are conventionally used for pyro-processing of bulk solids in numerous industrial application and is basically a rotating cylinder with its axis at an selective inclination, within which such processing take place. The pyro-processing comprising steps of drying, calcining, heating and cooling wherein various endothermic and exothermic reactions takes place. Solid retention time is a critical parameter for rotary kiln operation and is determined by selection of appropriate diameter, length, speed of rotation, slope and internal configuration.
While the conventional configuration include two variations of rotary kilns- Direct fired and Indirect fired, depending on whether the combustion of fuel for desired heating of the solid mass to be pyro-processed takes place inside the kiln or outside of it, respectively. The present problem primarily deals with the direct fired rotary kiln wherein the hot flue gases passes through the kiln. The products of combustion of fuel are in intimate contact with the bulk of material being processed. The radiation from the flames is the principal mode of heat transfer in such processes.

JPH01257170 disclosed a monolithic refractory lining comprising a mixture consisting of 47-64wt.% classified fireproof aggregate, 35.-45% fireproof fine powder of <74um particle size and 1-8% alumina cement is blended with 0.1-3% composite binder prepd. by combining acid clay as a base with sodium phosphate and sodium silicate to obtain monolithic refractories. The chemical composition of the binder consists of 50-58% Si02, 5-12% P205 and 12-18% Na20. By using the refractories, even a furnace having a wide service temp, range such as a torpedo car or a rotary kiln can be subjected to seamless with uniform quality. This prior art uses monolithic refractory of same composition along the entire length of the kiln. The present invention provides a rotary kiln having selective refractory lining in different zones of the kiln.
JPH11287561 disclosed refractory lining structure of rotary kiln wherein an iron plate is interposed between a kiln rotary cylinder (an outer cylinder) and a lining fire resisting material .Lining with a monolithic refractory as the refractory material is effected, a long one in a rotary direction is interposed as the iron plate , but a shaped baked or not-baked refractory may also be used. Further, the iron plates having a given size are interposed at the backs of respective shaped refractory. This structure prevents a kiln rotary cylinder from corrosion due to a material containing alkali, chlorine, or sulfur, a mixture thereof, and variation in oxidation and reduction, and widely suppresses so that the mechanical damage of a lined refractory material is prevented from acceleration owing to the increase of deformation and bending of a kiln. Thus this cited art described about the lining structure to protect the inner surface of the main rotary kiln shell from corrosion. The document suggested use of a iron plate interposed between rotary kiln shell and refractory monolithic lining. The present invention provides a rotary kiln having selective refractory lining in different zones of the kiln.
W09746843 disclosed a rotary kiln having monolithic refractory lining cast with conventional castable( containing 10-40 % calcium aluminte cementitious agent) having specially designed internal configuration (non-uniform)of the lining wherein a plurality of lifting sections extend along the interior surface at spaced intervals for

lifting limestone being calcined from a lower portion of the chamber to an upper portion thereof as the chamber rotates. This prior art , unlike the present invention make use of conventional castable monolithic refractory, lining containing 10-40 % calcium aluminte cementitious agent. The present invention provides a rotary kiln having selective refractory lining in different zones of the kiln.
GB1292089 disclosed a kind of to rotary kiln which is equipped with cooler tubes arranged in planetary fashion around the outlet end of the kiln and rotating with it to receive and cool the product such as cement clinker from the kiln by air flowing 1 through the tubes in countercurrent to the product These cooler tubes are generally connected to the kiln by radial chutes through which the product falls and slides.
Thus this cited art describes about a rotary kiln equipped with cooler tubes at the outlet rotating with the outlet end. The whole lining of the rotary kiln is monolithic. The present invention provides a rotary kiln having selective refractory lining in different zones of the kiln.
US3733045 concerns about lining of rotary kilns and particularly a method and apparatus for installing monolithic lining in rotary kiln with monolithic castable refractory materials The method and apparatus for lining cast monolithic refractory lining comprises rings made of segments preferably adjustably attached to each other so that the rings can be adjusted to desired circumference, the rings having removable spacer elements which support the rings on and space them from the kiln shell. This prior art states about method and apparatus for installing monolithic lining in rotary kiln and not regarding the constitution of the lining. The present invention provides a rotary kiln having selective refractory lining in different zones of the kiln.

There had been therefore, a persistent need to develop rotary kilns with an improved constitution and configuration/scheme of the refractory lining inside kiln for calcinations of limestone such as to eliminate the disadvantages in the conventional lining of different zones of the rotary kiln and thereby the lining life is increased without shutdown and the desired distribution is achieved to economize fuel consumption and to obtain desired quality characteristics of the calcined lime to be used as flux.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to developing a rotary kiln having an improved constitution and configuration of the refractory lining for its different zones of the direct fired kiln for calcinations of limestone with improved hot strength and abrasion resistance such as to reduce the erosion of lining in the burning zone to prevent hot spots and/or shell crack observed on lining in this zone, thus favoring increasing the operating life of the rotary kiln without shut down for repair/relining and thereby improving the kiln yield/productivity in lime calcinations.
A further object of the present invention is directed to an improved refractory lining constitution and configuration favoring advantageous attainment of desired high abrasion resistance of the refractory lining at the charging and discharging end for preferred counter flow movement of charge; wherein said charge of limestone subjects the preheating zone to high abrasion due to falling and movement of hard limestone.
A still further object of the present invention is directed to an improved refractory lining constitution and configuration for different zones of rotary kiln for calcinations of limestone, to reduce the number of joints in the lining and prevent falling of bricks from the lining.
Another object of the present invention directed to an improved constitution and configuration for refractory lining of rotary kiln for calcination of lime to improve overall performance and life of the lining up to about 12 months from existing 3-4 months or alternatively a lining life to produce about one lakh ton of calcined lime with minimum repairs, at the most on two or three occasions only in one campaign.
A still further object of the present invention directed to providing improved configuration and composition of the refractory lining of rotary kiln such as to favor controlled uniform

^ heating of charge to desired temperature in order to obtain calcined limestone with no residual core and at the same time avoid over heating of the stone surface and maintain desired optimum surface temperature and heatflux diffusion toward the reacting core, to avoid recrystallisation of CaO, to ensure desired reactivity and quality of calcined lime.
A still further object of the present invention directed to providing improved configuration and composition of the refractory lining of rotary kiln to favor recovery of the sensible heat of lime is transferred to the cooling air in the preheating zone and that the sensible heat of hot flue gases leaving the calcination zone is transferred to the limestone in the preheating zone, thereby the sensible heat of the lime is completely returned to the process.
A still further object of the present invention directed to providing improved configuration and composition at the different zones of the refractory lining of rotary kiln wherein ceramic paper is provided in between the shell and the working lining of calcination zone and thereby reducing considerably the shell temperature resulting in improved performance of the lining and less damage to shell wall.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a rotary kiln having refractory lining adapted for superior thermo-mechanical properties comprising:
selective refractories in different regions of the kiln along the length starting from the discharge end comprising of:
abrasion resistant charging and discharging end refractories obtained of highly abrasion and thermal shock resistant 70% Al203 new generation monolithic (NGM) and erosion resistant calcinations zone refractories obtained of mag-chrome bricks having low iron and low silica with superior thermo-mechanical properties.
Another aspect of the present invention is directed to said Rotary kiln having refractory lining adapted for superior thermo-mechanical properties, comprising:

^ selective refractories in different regions of the kiln along the length starting from the discharge end comprising of:
0-2.5m : 70 % Al203 New Generation Monolithic (NGM) & 70 % Al203 bricks;
2.5-30m: Mag-chrome bricks having low silica and low iron;
31-36m : 70% Al203 bricks;
37-57m :42% Al203 bricks;
58-73m :70% Al203 bricks; and
74-75m : 70% Al203 new generation Monolithic (NGM).
A still further aspect of the Rotary kiln according to the present invention having refractory lining for lime calcinations adapted for superior thermo-mechanical properties wherein the high alumina new generation monolithic lining comprise low cement content preferably CaO of 1.5 % max. for superior thermo-physical properties.
According to an advantageous aspect of the present invention directed to said Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties, comprising ceramic paper in between shell and working lining of calcinations zone preferably 5 mm thick ceramic fibre paper adapted for reduced shell temperature and improved performance of lining.
A still further aspect of the present invention directed to said Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties wherein said mag-chrome bricks have low iron and low silica content of Si02 as low as 1.5%.
According to an important aspect of the present invention directed to said Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties of the New generation Monolithic (NGM) castables comprising: Al203 (%) min. : 70

Fe203(%) max.:0.6 CaO (%),max.: 1.5 Grading (mm) 0-5
B.D.(g.cm"3),min (at 110° C/24h) :2.80
CCS (kg.cm"2),min (at 110°C/24h) 500;(at 800°C/3h) 700; and (at 1400°C/3h) 1000 PLC (%),max (at 1400°C/3h) :±0.2
HMOR (kg.cm"2),min (at 1400°C/30 min, on samples pre fired at 1500°C/3h): 50 Water required for casting (%) : 3.5-4.5.
According to yet another aspect of the Rotary kiln of the present invention having refractory
lining for lime calcinations adapted for superior thermo-mechanical properties comprising
basic Mag-crome bricks having:
MgO (%),min : 60
Cr203(%),min : 15
Si02 (%), max : 2.5
A P (%),max : 20
B D (g.cm"3),min : 3.04
CCS (kg.cm2) : 400
RUL, (ta°C),min :1700
PLC (%),max (at 1600°C/2h) ±0.5
A still further aspect of the present invention directed to a process for calcinations of limestone comprising carrying out the calcinations in a rotary kiln having selective refractories in different regions of the kiln along the length starting from the discharge end.
Advantageously, the present refractory lining pattern provide for highly abrasion resistant and thermal shock resistant 70% Al203 new generation monolithic, the strength of which increases exponentially right from the room temperature to service temperature. More importantly, there is no decrease in strength of the monolithic lining at any intermediate temperature range of 300°C -1000°C.
A further aspect of the present invention directed to rotary kiln having improved refractory lining also ensure proper rate of conductive heat transmission through the limestone lump from surface inward and thereby leaving no residual core and at the same time appropriate surface temperature is maintained, preferably not exceeding the range of 1100-1150°C for

the soft burnt«flux, avoiding thereby recrystallization of CaO and thus maintaining desired reactivity and favorable quality of the calcined lime for its subsequent use.
The present invention and its objects and advantages are described in greater details with reference to the non-limiting illustrative figures.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1: is the illustration of the modified lining pattern of the rotary kiln according to the invention providing improved lining life by introducing lining composition and configuration ensuring higher hot strength and abrasion resistance at different zones of the kiln.
Figure 2: is the illustration of three views for the shape configuration of the bricks for lining according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE ACCOMPANYING FIGURE
The present invention relates to Rotary kiln with an improved lining pattern for calcination of lime whereby it is possible to enhance the working life of the lining eliminating the problems such as the hot spots or shell cracking and the like, encountered in the conventional rotary kiln, more particularly, the direct fired type kilns operation for calcination of limestone.
As already described that there exist different zones in the Rotary kiln depending upon the nature of process carried out at a particular location within the kiln. These are the cooling zone , burning zone and preheating zone, starting correspondingly from discharge to charging end of the kiln. The rotary kilns are typically about 75m in length and about 3-4m in diameter. Each kiln is essentially provided with a cooler for cooling of the finished calcined lime and thereby heat up the cooling air flown in the zone. The Rotary kilns usually rotates at a predetermined RPM about a longitudinal axis along the kiln which is maintained at a selective slope to ensure reaction/retention time for calcinations and complete conversion of limestone to CaO, at a selective temperature ranging 900-1200°C without any residual core and avoiding recrystallisation of soft burnt flux, to ensure reactivity and quality

of calcined lime thus produced. The kiln is provided with adequate number of duplex burners for heating by burning coke oven gas or alternatively by PCM. The calcination temperature is around 1200°C.
To select the refractory quality for different zones of the rotary kiln, it is necessary to first understand the thermo-chemical processes occurring during calcination of limestone. In order to fully calcine the stone without any residual core left in finished lime, heat supplied to the limestone surface must penetrate via conductive heat transfer to the core. A temperature of 900°C has to be reached in the core at least for a short period of time. The thermo-chemical processes occurring in the rotary kilns for heat treatment of carbonate materials (iimestone) are highly energy intensive and complex.
It is an obvious requirement to first understand the details of the thermo-chemical process that occur during the calcinations of limestone in order to ascertain the requirement of composition and configuration/pattern of the Refractory lining at the different zones of the Rotary Kiln. The Thermo-chemical process involved in heat treating the Carbonate materials in Rotary kiln involves a process comprising a series of interdependent parameters such as fuel consumption, gas and material movement, heat and mass transfer and physico-chemical transformation of the burden materials. The temperature of the Calcination zone of rotary kiln is limited to the range 1200-1300°C, to ensure quick production of high quality metallurgical flux.
The calcination or burning of limestone and dolomite is simple oxidation process involving
uniting oxygen with any substance/element. In the flux kiln, the temperature of the
limestone is increased to a point above its dissociation temperature. This is called
calcination and the process to accomplish this requires a minimum temperature of
1648°F(898°C). At that point, the carbon to oxygen bonds in the carbonate group becomes
unstable. A carbon atom, and two of the three oxygen atoms, from the carbonate group,
forms the carbon dioxide, which leaves the reaction environment. The remaining oxygen
atom quickly forms a strong, high energy, ionic bond with the calcium atom. Thus the
formation of calcium oxide, commonly known as quicklime, is obtained by decomposition of
limestone on heating according to following equation:
CaC03 + 3180 KJ(760Kcal) approx. = CaO + C02
Calcium Carbonate Calcium Oxide Carbon Dioxide
(Limestone) (Quicklime)

In order to fully calcine the stone and to eliminate retention of unburnt residual core, heat supplied to the stone surface must penetrate via conductive heat transfer to the core. A temperature of 900°C has to be reached in the core at least for a short period of time. As there is created a pure C02 atmosphere inside the kiln , the stone surface must be heated to a temperature greater than 900°C to maintain the required temperature gradient and overcome the insulating effect of the calcined material deposited on the stone surface. Moreover, care has to be taken when the soft burnt flux is produced by calcination of limestone, the surface temperature must not exceed 1100°C-1150°C as otherwise re-crystallization of the CaO will occur and result in lower reactivity and poorer quality.
The rotary kiln for limestone calcination operate with counter flow of raw material charging/feeding direction and the combustion products/gas/flue flow direction inside the kiln. There are three technological zones : preheating, calcinations and cooling. Dissociation of CaC03 occurs in the calcinations zone at a temperature range between 870°C and 1250°C. In the cooler zone towards the discharge end of kiln, the sensible heat of lime is completely transferred to the cooling airflow, which enters the calcinations zone at the temperature of about 300-500°C to react with the fuel. Therefore, the sensible heat of the lime is completely returned to the process. The sensible heat of the gases leaving the calcinations zone is transferred to the limestone in the preheating zone towards the discharge end of kiln. The temperature of limestone at the bottom of the preheating zone reaches the temperature of calcinations. The gas leaving the preheating zone has a temperature range of 150°C-300°C. It is not possible to utilize this off-gas heat content completely, since the heat capacity of the gases in the preheating zone is higher than the heat capacity of the charge material. The counter-current flow is optimized for preheating and cooling. The process of heat transfer in these zones is very efficient. The dissociation of CaC03 at the calcination zone begins at about 900°C with the pressure close to atmospheric pressure, undergoing an endothermic reaction. The speed of dissociation increases exponentially as the temperature increases. The speed of dissociation reaches about ten times higher at 1200°C than the speed at 900°C. The results of micro-kinetic study shows, that the speed of dissociation can be limited by the speed of heat flux diffusion towards the reacting core of the carbonate material lumps. Thus maintaining a temperature for calcinations above 1150°C is preferable for accleration of heat transfer inside the lump of material and to increase the kiln productivity.

In order to achieve longer lining life under the above control parameters for the entire calcinations process carried out in the rotary kiln, following refractory pattern was adopted according to the present invention, along the length starting from the discharge end:
0-2.5m: 70% Al203 new generation monolithic lining & 70% Al203 bricks;
2.5-30m: Mag-chrome bricks having selectively low silica and low iron content;
31-36m: 70% Al203 bricks;
37-57m: 42% Al203 bricks;
58-73m: 70% Al203 bricks;
74-75m: 70% Al203 new generation monolithic refractory lining.
As already discussed , the lining at the charging and the discharge end are subjected to
high degree of abrasion due to either impact of falling and moving hard limestone lumps or
due to thermal shocks. The present refractory lining pattern provide .highly abrasion
resistant and thermal shock resistant 70% Al203 new generation monolithic. The strength of
this material increases right from the room temperature to service temperature.
Advantageously, there is no decrease in strength of the monolithic lining at any
intermediate temperature range e.g. 200-1000°C. The comparative characteristic properties
of the conventional versus the new generation monolithic castables are presented in the
following Table 1. _


In order to enhance the life of lining in the calcination zone avoiding erosion of refractories or damage due to formation of hot spot or cracked shell, the lining according to the present invention introduces mag-chrome bricks having low iron and low silica (Si02 as low as 1.5%). Thermo-mechanical properties of these bricks are much better having higher hot strength and abrasion resistance as compared to existing conventional mag-chrome bricks. In calcinations zone, 5mm thick ceramic fibre paper was used in between the working lining and the shell to prevent overheating of the shell and avoid shell cracking. The comparative characteristic properties of the two varieties of basic bricks used in the rotary kiln are given in the following Table 2.


Reference is now invited to Figure 1 that illustrates the configuration pattern for the Rotary kiln for calcinations of lime wherein the above monolithic lining or the mag-chrome bricks have been utilized in a selective manner in order to achieve the desired longer lining life and thereby longer run time before relining/repair, by way of providing higher hot strength and abrasion/erosion resistance through a selective constitution and lining pattern for the different zones of the rotary kiln. It is seen from the figure that the new generation monolithic (NGM) lining has been provided at the charging and discharge end of the rotary kiln over preferred length of about up to 2.5m at the discharge end and up to about lm at the charging end, to save the lining from abrasion due to impact of fall and movements of hard lumps of limestone or thermal shock due to sharp temperature gradient at the respective cooling and preheating zones. In between the monolithic castables there are the refractory brick lining as follows and as indicated in the accompanying Figure 1, 0-2.5m long 70% Al203 new generation monolithic lining and 70% Al203 bricks from discharge end, and then Mag-chrome bricks having selectively low silica and low iron content over a length after 2.5m and up to 30m in the calcinations zone, then 70% Al203 bricks over a stretch of about next 6 meters, then 42% Al203 bricks over about next 20 meters length, then again a stretch of about 6 meters is laid with 70% Al203 bricks and lastly the monolithic lining (NGM) again for the last stretch of about 2 m at the charging end. The accompanying Figure 2 shows three different views of the typical selective shape configuration of the bricks according to the refractory lining of the present invention.

It is thus possible by way of this invention to achieve a lining pattern for Rotary kiln for
calcinations of lime, providing longer lining life having higher hot strength and abrasion
resistance achieved through a new generation monolithic castable refractory lining of
selective composition and also bricks of selective composition. The 70% Al203 bricks/
castables provided in the lining pattern, and the mag-chrome bricks selectively comprising
low silica and low iron to achieve desired thermo-mechanical properties and the high
alumina new generation monolithic castable lining at the charging and the discharge ends
having low cement content of 1.5%(CaO) max, unlike the conventional 4-5%(CaO),
resulting in superior thermo-physical properties. Advantageously, the lining pattern of the
present invention where in there is no decrease in strength in the intermediate temperature
range (300-1000°C). the life of the lining is enhanced to the extent of up to 12 months as
compared to 3-4 months obtained in the conventional lining design for rotary kiln for
calcinations of limestone at desired temperature range without leaving any unburnt residual
core and avoiding recrystallisation of the soft burnt flux. The lining so configured showed
little erosion, abrasion or formation of hot spots or shell cracking even after six months of
continuous operation for the rotary kiln to produce calcined lime, thus favoring wide
industrial application in steel plants where the requirement of lime as flux is continuous in
large volume. >- . ____

WE CLAIM:
1. Rotary kiln having refractory lining adapted for superior thermo-mechanical properties
comprising:
selective refractories in different regions of the kiln along the length starting from the discharge end comprising of:
abrasion resistant charging and- discharging end refractories obtained of highly abrasion and thermal shock resistant 70% Al203 new generation monolithic (NGM) lining comprising low cement content preferably CaO of 1.5 % max. for superior thermo-physical properties and
erosion resistant calcinations zone refractories obtained of mag-chrome bricks having low iron and low silica of 2.5 % max. with superior thermo-mechanical properties.
2. Rotary kiln having refractory lining adapted for superior thermo-mechanical properties
as claimed in claim 1 comprising:
f selective refractories in different regions of the kiln along the length starting from the discharge end comprising of:
0-2.5m : 70 % Al203 New Generation Monolithic (NGM) & 70 % Al203 bricks;
2.5-30m: Mag-chrome bricks having low silica and low iron;
31-36m : 70% Al203 bricks;
37-57m :42% Al203 bricks;
58-73m :70% Al203 bricks; and
74-75m : 70% Al203 new generation Monolithic (NGM).

3. Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties as claimed in anyone of claims 1 or 2 wherein the high alumina new generation monolithic lining comprise low cement content preferably CaO of 1.5 % max. for superior, thermo-physical properties.
4. Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties as claimed in anyone of claims 1 to 3 comprising ceramic paper in between shell and working lining of calcinations zone preferably 5 mm thick ceramic fibre paper adapted for reduced shell temperature and improved performance of lining.
5. Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties as claimed in anyone of claims 1 to 4 wherein said mag-chrome bricks have low iron and low silica content of Si02 as low as 1.5%.
6. Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-mechanical properties as claimed in anyone of claims 1 to 5 comprising New generation Monolithic (NGM) comprising:
Al203 (%) min. : 70
Fe203 (%) max.:0.6
CaO (%),max.: 1.5
Grading (mm) 0-5
B.D.(g.cm"3),min (at 110° C/24h) :2.80
CCS (kg.cm"2),min (at 110°C/24h) 500;(at 800°C/3h) 700; and (at 1400°C/3h) 1000
PLC (%),max (at 1400°C/3h) :±0.2
HMOR (kg.cm"2),min (at 1400°C/30 min, on samples pre fired at 1500°C/3h): 50
Water required for casting (%) : 3.5-4.5.
7. Rotary kiln having refractory lining for lime calcinations adapted for superior thermo-
mechanical properties as claimed in anyone of claims 1 to 6 comprising bricks having:
MgO (%),min : 60
Cr203(%),min : 15 Si02 (%), max : 2.5 A P (%),max : 20 B D (g.cm"3),min : 3.04

CCS (kg.cm2) : 400 RUL, (ta°C),min :1700 PLC (%),max (at 1600°C/2h) ±0.5
8. A process for calcinations of limestone comprising carrying out the calcinations in a rotary kiln as claimed in anyone of claims 1 to 7 involving carrying out the calcinations sequentially in selective refractories in different regions of the kiln along the length starting from the discharge end comprising of:
0-2.5m : 70 % Al203 New Generation Monolithic (NGM) & 70 % Al203 bricks;
2.5-30m: Mag-chrome bricks having low silica and low iron;
31-36m : 70% Al203 bricks;
37-57m :42% Al203 bricks;
58-73m :70% Al203 bricks; and
74-75m : 70% Al203 new generation Monolithic (NGM).
such as to achieve proper rate of conductive heat transmission through the limestone lump from surface inward and leaving no residual core and maintaining surface temperature not exceeding the range of 1100-1150°C for the soft burnt, flux and in the process avoiding recrystallization of CaO and generating desired calcined lime.
Dated this 12th day of January, 2008

ABSTRACT

TITLE: ROTARY KILN HAVING REFRACTORY LINING ADAPTED FOR SUPERIOR THERMO-MECHANICAL PROPERTIES.
A Rotary kiln for lime calcinations having refractory lining at different zones providing higher hot strength and abrasion resistance and longer operating life before relining. The refractory lining uses highly abrasion and thermal shock resistant 70% Al203 containing new generation monolithic(NGM) refractory lining at charging and discharge ends. The refractory lining in the Calcination zone contains mag-chrome bricks having low iron and low silica (Si02 as low as 1.5%). Thermo-mechanical properties of the NGM are much superior e.g. CCS (kg-cm"2,min) at 1400°C/2h is 1000 and HMOR (kg-cm"2,min) is 50. The rotary kiln of the invention also uses Ceramic paper in between shell and working lining of Calcination zone for controlling shell temperature rise and improving performance of the lining. The lining with reduced joints and falling bricks, provides improved energy utilization and increased lining life up to 12 months as compared to conventional 3 to 4 months. The Rotary Kilns of the invention thus ensure low down time, higher yield/productivity with wide industrial applications in steel plants and the like. Figure 1.