Title of Invention	A NOVEL PROCESS FOR THE PREPARATION OF HYDRATION RESISTANT TIME.
Abstract	Calcium Oxide is an excellent refractory material and as per Ellingham diagram is the most stable of all the oxide materials used as refractory. Plenty of pure raw materials containing calcium oxide are available in nature abundantly. The material at present is not or rather cannot be used as a refractory material owing to its extreme hydration tendency in atmosphere. Once the hydration resistant calcium oxide is available the same can be used for developing various refractory products for particular areas of applications in metallurgical industry. The process of making calcium oxide hydration resistant through sintering or fusion either takes a lot of time or is not techno-economically viable. Hydration resistant calcium oxide with low porosity can be developed in a moving bed plasma reactor in a span of 1-3 minutes. Proper control of particle size distribution, controlling the plasma parameters and suitable additives can achieve the same.

Title of Invention

A NOVEL PROCESS FOR THE PREPARATION OF HYDRATION RESISTANT TIME.

Abstract

Calcium Oxide is an excellent refractory material and as per Ellingham diagram is the most stable of all the oxide materials used as refractory. Plenty of pure raw materials containing calcium oxide are available in nature abundantly. The material at present is not or rather cannot be used as a refractory material owing to its extreme hydration tendency in atmosphere. Once the hydration resistant calcium oxide is available the same can be used for developing various refractory products for particular areas of applications in metallurgical industry. The process of making calcium oxide hydration resistant through sintering or fusion either takes a lot of time or is not techno-economically viable. Hydration resistant calcium oxide with low porosity can be developed in a moving bed plasma reactor in a span of 1-3 minutes. Proper control of particle size distribution, controlling the plasma parameters and suitable additives can achieve the same.

Full Text	Field of Invention The present invention relates to a novel process for the preparation of hydration resistant lime suitable for use as a refractory material through plasma processing. Background of Invention and Description of Prior Art Marble/Limestone -CaC03- is available in nature in abundant quantity at a cost which is much lower compared to the other oxide materials. CaO has the distinction of being the most stable oxide amongst all the commonly available oxides over a large temperature range as can be clearly seen from the Ellingham diagram. The melting point of CaO is also very high about 2572°C. In view of all these excellent superior high temperature properties, CaO can be used as an ideal refractory material in many metallurgical pyroprocessing vessels. The excellent refractoriness and thermodynamic stability of CaO make it a superior refractory in many application areas compared to dolomite and magnesite based refractories. However, all these superior properties of CaO as a refractory material are nullified by one characteristic property of CaO. The material CaO has a very high hydration tendency. In the presence of moisture, it is converted very easily into Ca(OH)2 and the conversion disintegrates the material. Hence, unless CaO can be made hydration resistant, it cannot be used as a refractory material. Reference may be made to the work of L.L. Wong and R.C. Bradt [Am. Ceram. Soc. Bull. 69 (7) 1183-89 (1990)] wherein it was shown that limestone containing impurities cannot be sintered to a high density lime aggregate at 1600°C. Reference may be made to the work of L. Xintin et al [Brit. Ceram Trans. 93(4) 150-153 (1994)] wherein it was shown that CaO aggregates can be developed through sintering with improved hydration resistance by the incorporation of AI2O3. Reference may be made to the work of Vezikawa et al wherein lime aggregates were sintered with the incorporation of TIO2 by firing at 1700°C. Reference may be made to Polish Patent 44,408 of 29.05.1961, wherein a process of making CaO refractories based on hydration resistant lime has been described. Here also the route followed was CaO sintering in the presence of additives. Reference may be made to the German Patent 1,187,594 dated 12.10.1961, wherein fused lime grains were prepared for refractory applications. H.W. Grunling & H.E. Schwiete further investigated the development of fused CaO grain for refractory application as reported in Naturwissenschaffen 52 (1965), 58. G. Routschka also developed sintered and direct bonded CaO material for refractory applications; Keramo-Technik 21 (1970), 325. In case of fused CaO grain, it was found that their hydration resistance is not very superior to sintered aggregates. Addink et al [U.S. Pat. No. 4795,725 (1989)] used thermosetting novolak type phenol resin to coat the CaO grains for preventing hydration and developed lime refractory from the same. Cassens [U.S. Pat No. 4463100 (1984)] developed a refractory material based on lime by converting it into 2CaOSi02 which solved the problem of hydration of lime. Neville et al (U.S. Pat No. 4,843,044) (1984) developed a lime refractory based on lime sinter which was developed by incorporating monosodium phosphate and metal poly phosphate but basically it contained MgO aggregates above 90% of the total mix. Banerjee et al (US Pat No.6245315) (2001) developed hydration resistant lime through the sintering route. Limestone was initially calcined in the temperature range of 1000 to 1150°C for a period of 2 to 3 hours. Subsequently the material was hydrated and the hydrated mass was pelletised at a pressure of 1000 Kg/cm2. The pellets were sintered at a temperature of 1500 to 1650°C and the whole sintering time was in the range of 24 hours. In all the aforesaid processes, for the improvement in the hydration resistance of lime as well as densification, the processing route followed is the introduction of additive and then sintering the CaO at a specified temperature. Normally, the processing takes 10 to 25 hours to convert the raw CaO into a lime aggregate which is hydration resistant and has high density. The hydration resistant CaO aggregate can then be processed further for the development of CaO based refractory. Objects of the Invention The main object of the present invention is thus to provide a process for the production of hydration resistant lime suitable for use as a refractory material through plasma processing which obviates the drawbacks of the hitherto known prior art as detailed above. Another object of the present invention is to develop hydration resistant lime in a 'Moving bed plasma reactor'. Yet another object of the present invention is to shorten the time required for the entire process of making the CaO hydration resistant to around 1-4 minutes as opposed to the prior art processes which take about 10-15 hours. Still another object of the present invention is to provide hydration resistant CaO which when exposed to atmosphere will have a shelf life of at least 30 days. Summary of the Invention Ca bearing raw materials, additives and if need be an organic binder are mixed in the desired proportions. The batch is pressed into briquettes or plates and dried at a temperature of 105 to 110°C. The pressed briquettes or plates are processed under a thermal plasma in a moving bed plasma bed reactor under optimum plasma processing conditions so that hydration resistant CaO material is produced. Accordingly, the present invention provides a novel process for the preparation of hydration resistant lime suitable for use as a refractory material wherein the process steps comprise: [a] crushing and grinding limestone and subsequently milling the material to fineness of 60 -100 mesh BS sieve, followed by mixing with the dopant titania in the range of 0.5 to 2.0 wt% to obtain a slurry; [b] drying the slurry as obtained in step [a] at 105 to 110 degree C for 24 to 30 hours; [c] adding and mixing an organic binder of the kind such as herein described in the range of 5 to 10 % to the dry powder as obtained in step [b] to obtain processed powder; [d] uniaxial pressing of the processed powder as obtained in step [c] into briquettes at a pressure in the range of 500 - 1400 Kg/cm2; [e] loading the briquettes as obtained in step [d] in single/multiple layers in a moving bed thermal plasma reactor for about 1 to 3 minutes; [f] optionally repeating step [e] to obtain the desired hydration resistant lime. Detailed Description of the Invention Plasma consists of a collection of free moving electrons and ions - atoms that have lost electrons. Energy is needed to strip electrons from atoms to make plasma. The energy can be of various origins. Thermal, electrical or light (ultraviolet light or intense visible light from laser) with sufficient sustaining power, plasma recombine into neutral gas. Plasma processing has advantages in the production of advanced materials. Reaction temperatures much higher than what can be achieved by using fossil fuels are easily generated. The temperatures are sufficiently high so that the reactions take place in the gaseous phase. The high temperatures along with the chemically reactive species formed in plasma may accelerate reactions by several orders of magnitude. Residence time in the "Plasma" -high temperature zone is start and controllable. By suitable choice of feed gases, the atmosphere can be kept inert, oxidizing or reducing. The present invention provides a process for the production of hydration resistant lime useful as refractory aggregates which comprise mixing of limestone with TiO2 as dopant, mixing the batch in a slurry form and subsequently drying the slurry, uniaxial pressing of the processed powders to briquettes, plasma processing the briquettes in a moving bed thermal plasma reactor and then allowing the plasma processed materials to cool naturally. The briquettes were given more than one pass depending on the plasma parameters. In an embodiment of the present invention, the CaO can be used in the form of CaCO3 of both marble or limestone variety. In another embodiment of the present invention, the milling of limestone or marble may be done by ball milling or vibro-grinding or attrition milling. In yet another embodiment of the present invention the raw material is passed through -60 +100 mesh sieve. In still another embodiment of the present invention the solvent during milling may be isopropyl alcohol, acetone or hexane. In another embodiment of the present invention the binder used for processing limestone or marble may be polyvinyl alcohol, dextrin or glycol in the range of 4 to 8%. The plasma processed materials were characterized by (1) Phase analysis (2) Hydration resistance (3) Bulk Density, Porosity (4) Microstructure. Phase analysis was done by x-ray diffraction. Hydration resistance was carried out by measuring the percentage weight gain of the samples after keeping them for 3 hours at 50°C and 95% Relative Humidity. Microstructure of the polished and thermally etched sample was observed through scanning electron microscope. Bulk density and porosity of the material were measured through Archimedes' principle under vacuum. The prior art reveals that the present work based on the concept of hydration resistant CaO through processing in a moving bed plasma reactor is completely novel and never before it has been reported anywhere. Earlier hydration resistant CaO was obtained through the sintering route or converting the material into silicates, aluminosilicates as has been discussed in the prior art. The novelty of the present invention is in obtaining hydration resistant CaO through processing in a moving bed plasma reactor which earlier was obtained either by converting CaO into other phases or through sintering route. Thus the main inventive step in the present invention is thermal plasma processing of CaCO3 powder pressed into briquettes for developing extremely high hydration resistant CaO aggregates. The controlling of the thermal plasma parameters and the parameters of starting materials improve the hydration resistance and porosity of the CaO aggregate. The following examples are given by way of illustration of the working of the invention in actual practice and should not be construed to limit the scope of the present invention in any way. Example - 1 Limestone was crushed and ground in a jaw crusher and ball mill, so that the material passes through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 24 hours. The dried batch was mixed with an organic binder PVA solution (5 wt% in aqueous medium) to the tune of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. Gas flow Power Bed speed No. of passes 0.5 liter/ sec 10 KW 1.5 cm/min 2 Plasma processed material Characteristics Phases present : CaO only Hydration Resistance : 0.9 % (% wt. gain) Bulk Density : 3.13 gm/cc Apparent porosity : 6.80 % Example -2 0.2 liter /sec 12.5 KW 2.5 cm/min 2 Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 105 degree C for 28 hours. The dried batch was mixed with PVA solution (5 wt% in aqueous medium) to the time of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. Gas flow Power Bed speed No. of passes Plasma processed material Characteristics Phases present : CaO only Hydration Resistance : 1.2 % (% wt gain) Bulk Density : 2.98 gm/cc Apparent porosity : 8.2 % Example- 3 Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve: The material was dried at 105 degree C for 28 hours. The dried batch was mixed with an organic binder namely PVA solution (5 wt% in aqueous medium) to the time of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. Gas flow Power Bed speed No. of passes 0.5 liter/ sec 12.5 KW 3.0 cm/min 3 Plasma processed material Characteristics Phases present : CaO only Hydration Resistance : 0.7 % ( % wt gain) Bulk Density : 3.12 gm/cc Apparent porosity : 1.05% Example- 4 Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 20 hours. The dried batch was calcined at 950 degree C to convert the carbonate into CaO. Subsequently the batch was hydra ted to calcium hydroxide. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. Gas flow Power Bed speed No. of passes 0.5 liter/ sec 10 KW 1.5 cm/min 2 Plasma processed material Characteristics Phases present : CaO only Hydration Resistance : 0.9 % ( % wt gain) Bulk Density : 3.13 gm/cc Apparent porosity : 6.80 % Example- 5 Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 105 degree C for 30 hours. The dried batch was calcined at 950 degree C to convert the carbonate into CaO. Subsequently the batch was hydrated to calcium hydroxide. The powder was then uniaxially pressed into 50 x 50 x 5 mm Gas flow Power Bed speed No. of passes briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. 0.2 liter/ sec 12.5 KW 2.0 cm/min 2 Plasma processed material Characteristics Phases present Hydration Resistance (% wt gain) Bulk Density Apparent porosity CaO only 1.0% 2.97 gm/cc 8.4 % Example - 6 Limestone was crushed and ground in a jaw crusher and ball mill in, so that the material passes through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 24 hours. The dried batch was mixed with Ti02 (1 wt%) & organic binder of dextrin solution (7 wt% in aqueous medium) to the tune of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters. Gas flow Power Bed speed No. of passes 0.5 liter/ sec 12.5 KW 2.0 cm/min 2 lasma processed material Characteristics Phases present : CaO only Hydration Resistance : 0.6 % (% wt gain) Bulk Density : 3.01 gm/cc Apparent porosity : 6.60 % The main advantages of the present invention are: 1) Production of hydration resistant lime aggregates through thermal plasma processing route leads to a drastic reduction in time to only a few minutes. 2) The initial attempts to make lime hydration resistant have been to completely melt the material in a conventional furnace. The process takes a long time and is energy intensive. Moreover the process did not remain viable because of the short life of the conventional furnace/container utilised for fusing the material. In case of plasma processing the time taken is only a few minutes and there is no damage to the container materials. 3) It opens up the possibility of utilizing an extremely thermodynamically stable material as a refractory material by overcoming its major weakness, which till date has not allowed the exploitation of other superior properties being prone to hydration. We claim: 1. A novel process for the preparation of hydration resistant lime suitable for use as a refractory material wherein the process steps comprise: [a] crushing and grinding limestone and subsequently milling the material to fineness of 60 -100 mesh BS sieve, followed by mixing with the dopant titania in the range of 0.5 to 2.0 wt% to obtain a slurry; [b] drying the slurry as obtained in step [a] at 105 to 110 degree C for 24 to 30 hours; [c] adding and mixing an organic binder of the kind such as herein described in the range of 5 to 10 % to the dry powder as obtained in step [b] to obtain processed powder; [d] uniaxial pressing of the processed powder as obtained in step [c] into briquettes at a pressure in the range of 500 - 1400 Kg/cm2; [e] loading the briquettes as obtained in step [d] in single /multiple layers in a moving bed thermal plasma reactor for about 1 to 3 minutes; [f] optionally repeating step [e] to obtain the desired hydration resistant lime. 2. A process as claimed in claim 1, wherein the limestone used is marble stone powder, whose CaO content on loss free basis is above 97%. 3. A process as claimed in claim 1, wherein the Titania used is of reagent grade chemical having a minimum assay of 98.5% purity. 4. A process as claimed in claim 1, wherein milling is done by conventional processes such as ball milling, vibrogrinding or attrition milling. 5. A process as claimed in claim 1, wherein the organic binder is preferably selected from PVA or dextrin. 6. A process as claimed in claim 1, wherein the solvent during milling is selected from the group consisting of isopropyl alcohol, acetone, and hexane. 7. A novel process for the preparation of hydration resistant lime substantially as herein described with reference to the foregoing examples.

Full Text

Field of Invention
The present invention relates to a novel process for the preparation of hydration resistant lime suitable for use as a refractory material through plasma processing.
Background of Invention and Description of Prior Art
Marble/Limestone -CaC03- is available in nature in abundant quantity at a cost which is much lower compared to the other oxide materials. CaO has the distinction of being the most stable oxide amongst all the commonly available oxides over a large temperature range as can be clearly seen from the Ellingham diagram. The melting point of CaO is also very high about 2572°C. In view of all these excellent superior high temperature properties, CaO can be used as an ideal refractory material in many metallurgical pyroprocessing vessels. The excellent refractoriness and thermodynamic stability of CaO make it a superior refractory in many application areas compared to dolomite and magnesite based refractories.
However, all these superior properties of CaO as a refractory material are nullified by one characteristic property of CaO. The material CaO has a very high hydration tendency. In the presence of moisture, it is converted very easily into Ca(OH)2 and the conversion disintegrates the material. Hence, unless CaO can be made hydration resistant, it cannot be used as a refractory material.
Reference may be made to the work of L.L. Wong and R.C. Bradt [Am. Ceram. Soc. Bull. 69 (7) 1183-89 (1990)] wherein it was shown that limestone containing impurities cannot be sintered to a high density lime aggregate at 1600°C.
Reference may be made to the work of L. Xintin et al [Brit. Ceram Trans. 93(4) 150-153 (1994)] wherein it was shown that CaO aggregates can be
developed through sintering with improved hydration resistance by the incorporation of AI2O3.
Reference may be made to the work of Vezikawa et al wherein lime aggregates were sintered with the incorporation of TIO2 by firing at 1700°C.
Reference may be made to Polish Patent 44,408 of 29.05.1961, wherein a process of making CaO refractories based on hydration resistant lime has been described. Here also the route followed was CaO sintering in the presence of additives.
Reference may be made to the German Patent 1,187,594 dated 12.10.1961, wherein fused lime grains were prepared for refractory applications.
H.W. Grunling & H.E. Schwiete further investigated the development of fused CaO grain for refractory application as reported in Naturwissenschaffen 52 (1965), 58.
G. Routschka also developed sintered and direct bonded CaO material for refractory applications; Keramo-Technik 21 (1970), 325. In case of fused CaO grain, it was found that their hydration resistance is not very superior to sintered aggregates.
Addink et al [U.S. Pat. No. 4795,725 (1989)] used thermosetting novolak type phenol resin to coat the CaO grains for preventing hydration and developed lime refractory from the same.
Cassens [U.S. Pat No. 4463100 (1984)] developed a refractory material based on lime by converting it into 2CaOSi02 which solved the problem of hydration of lime.
Neville et al (U.S. Pat No. 4,843,044) (1984) developed a lime refractory based on lime sinter which was developed by incorporating monosodium phosphate and metal poly phosphate but basically it contained MgO aggregates above 90% of the total mix.
Banerjee et al (US Pat No.6245315) (2001) developed hydration resistant lime through the sintering route. Limestone was initially calcined in the temperature range of 1000 to 1150°C for a period of 2 to 3 hours. Subsequently the material was hydrated and the hydrated mass was pelletised at a pressure of 1000 Kg/cm2. The pellets were sintered at a temperature of 1500 to 1650°C and the whole sintering time was in the range of 24 hours.
In all the aforesaid processes, for the improvement in the hydration resistance of lime as well as densification, the processing route followed is the introduction of additive and then sintering the CaO at a specified temperature. Normally, the processing takes 10 to 25 hours to convert the raw CaO into a lime aggregate which is hydration resistant and has high density. The hydration resistant CaO aggregate can then be processed further for the development of CaO based refractory.
Objects of the Invention
The main object of the present invention is thus to provide a process for the production of hydration resistant lime suitable for use as a refractory material through plasma processing which obviates the drawbacks of the hitherto known prior art as detailed above.
Another object of the present invention is to develop hydration resistant lime in a 'Moving bed plasma reactor'.
Yet another object of the present invention is to shorten the time required for the entire process of making the CaO hydration resistant to around 1-4 minutes as opposed to the prior art processes which take about 10-15 hours.
Still another object of the present invention is to provide hydration resistant CaO which when exposed to atmosphere will have a shelf life of at least 30 days.
Summary of the Invention
Ca bearing raw materials, additives and if need be an organic binder are mixed in the desired proportions. The batch is pressed into briquettes or plates and dried at a temperature of 105 to 110°C. The pressed briquettes or plates are processed under a thermal plasma in a moving bed plasma bed reactor under optimum plasma processing conditions so that hydration resistant CaO material is produced.
Accordingly, the present invention provides a novel process for the preparation of hydration resistant lime suitable for use as a refractory material wherein the process steps comprise:
[a] crushing and grinding limestone and subsequently milling the material to fineness of 60 -100 mesh BS sieve, followed by mixing with the dopant titania in the range of 0.5 to 2.0 wt% to obtain a slurry;
[b] drying the slurry as obtained in step [a] at 105 to 110 degree C for 24 to 30 hours;
[c] adding and mixing an organic binder of the kind such as herein described in the range of 5 to 10 % to the dry powder as obtained in step [b] to obtain processed powder;
[d] uniaxial pressing of the processed powder as obtained in step [c] into briquettes at a pressure in the range of 500 - 1400 Kg/cm2;
[e] loading the briquettes as obtained in step [d] in single/multiple layers in a moving bed thermal plasma reactor for about 1 to 3 minutes;
[f] optionally repeating step [e] to obtain the desired hydration resistant lime.
Detailed Description of the Invention
Plasma consists of a collection of free moving electrons and ions - atoms that have lost electrons. Energy is needed to strip electrons from atoms to make plasma. The energy can be of various origins. Thermal, electrical or light (ultraviolet light or intense visible light from laser) with sufficient sustaining power, plasma recombine into neutral gas. Plasma processing has advantages in the production of advanced materials. Reaction temperatures much higher than what can be achieved by using fossil fuels are easily generated. The temperatures are sufficiently high so that the reactions take place in the gaseous phase. The high temperatures along with the chemically reactive species formed in plasma may accelerate reactions by several orders of magnitude. Residence time in the "Plasma" -high temperature zone is start and controllable. By suitable choice of feed gases, the atmosphere can be kept inert, oxidizing or reducing.
The present invention provides a process for the production of hydration resistant lime useful as refractory aggregates which comprise mixing of limestone with TiO2 as dopant, mixing the batch in a slurry form and subsequently drying the slurry, uniaxial pressing of the processed powders to briquettes, plasma processing the briquettes in a moving bed thermal plasma reactor and then allowing the plasma processed materials to cool naturally. The briquettes were given more than one pass depending on the plasma parameters.
In an embodiment of the present invention, the CaO can be used in the form of CaCO3 of both marble or limestone variety.
In another embodiment of the present invention, the milling of limestone or marble may be done by ball milling or vibro-grinding or attrition milling.
In yet another embodiment of the present invention the raw material is passed through -60 +100 mesh sieve.
In still another embodiment of the present invention the solvent during milling may be isopropyl alcohol, acetone or hexane.
In another embodiment of the present invention the binder used for processing limestone or marble may be polyvinyl alcohol, dextrin or glycol in the range of 4 to 8%.
The plasma processed materials were characterized by (1) Phase analysis (2) Hydration resistance (3) Bulk Density, Porosity (4) Microstructure.
Phase analysis was done by x-ray diffraction.
Hydration resistance was carried out by measuring the percentage weight gain of the samples after keeping them for 3 hours at 50°C and 95% Relative Humidity. Microstructure of the polished and thermally etched sample was observed through scanning electron microscope. Bulk density and porosity of the material were measured through Archimedes' principle under vacuum.
The prior art reveals that the present work based on the concept of hydration resistant CaO through processing in a moving bed plasma reactor is completely novel and never before it has been reported anywhere. Earlier hydration resistant CaO was obtained through the sintering route or converting the material into silicates, aluminosilicates as has been discussed in the prior art.
The novelty of the present invention is in obtaining hydration resistant CaO through processing in a moving bed plasma reactor which earlier was obtained either by converting CaO into other phases or through sintering route. Thus the main inventive step in the present invention is thermal plasma processing of CaCO3 powder pressed into briquettes for developing extremely high hydration resistant CaO aggregates. The controlling of the thermal plasma parameters and the parameters of starting materials improve the hydration resistance and porosity of the CaO aggregate.
The following examples are given by way of illustration of the working of the invention in actual practice and should not be construed to limit the scope of the present invention in any way.
Example - 1
Limestone was crushed and ground in a jaw crusher and ball mill, so that the material passes through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 24 hours. The dried batch was mixed with an organic binder PVA solution (5 wt% in aqueous medium)
to the tune of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.

Gas flow Power Bed speed No. of passes

0.5 liter/ sec
10 KW
1.5 cm/min
2

Plasma processed material Characteristics
Phases present : CaO only
Hydration Resistance : 0.9 %
(% wt. gain)
Bulk Density : 3.13 gm/cc
Apparent porosity : 6.80 %
Example -2
0.2 liter /sec 12.5 KW 2.5 cm/min 2
Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 105 degree C for 28 hours. The dried batch was mixed with PVA solution (5 wt% in aqueous medium) to the time of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.
Gas flow Power Bed speed No. of passes
Plasma processed material Characteristics
Phases present : CaO only
Hydration Resistance : 1.2 %
(% wt gain)
Bulk Density : 2.98 gm/cc
Apparent porosity : 8.2 %
Example- 3
Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve: The material was dried at 105 degree C for 28 hours. The dried batch was mixed with an organic binder namely PVA solution (5 wt% in aqueous medium) to the time of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.

Gas flow Power Bed speed No. of passes

0.5 liter/ sec 12.5 KW 3.0 cm/min 3

Plasma processed material Characteristics

Phases present : CaO only
Hydration Resistance : 0.7 %
( % wt gain)
Bulk Density : 3.12 gm/cc
Apparent porosity : 1.05%

Example- 4
Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 20 hours. The dried batch was calcined at 950 degree C to convert the carbonate into CaO. Subsequently the batch was hydra ted to calcium hydroxide. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.

Gas flow Power Bed speed No. of passes

0.5 liter/ sec
10 KW
1.5 cm/min
2

Plasma processed material Characteristics
Phases present : CaO only
Hydration Resistance : 0.9 %
( % wt gain)
Bulk Density : 3.13 gm/cc
Apparent porosity : 6.80 %
Example- 5
Limestone was crushed and ground to pass through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 105 degree C for 30 hours. The dried batch was calcined at 950 degree C to convert the carbonate into CaO. Subsequently the batch was hydrated to calcium hydroxide. The powder was then uniaxially pressed into 50 x 50 x 5 mm

Gas flow Power Bed speed No. of passes
briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.
0.2 liter/ sec 12.5 KW 2.0 cm/min 2
Plasma processed material Characteristics

Phases present Hydration Resistance
(% wt gain) Bulk Density Apparent porosity

CaO only 1.0%
2.97 gm/cc 8.4 %

Example - 6
Limestone was crushed and ground in a jaw crusher and ball mill in, so that the material passes through 60 mesh BS sieve and retained over 100 mesh sieve. The material was dried at 110 degree C for 24 hours. The dried batch was mixed with Ti02 (1 wt%) & organic binder of dextrin solution (7 wt% in aqueous medium) to the tune of 5 wt%. The powder was then uniaxially pressed into 50 x 50 x 5 mm briquettes at a pressure of 200 Kg/cm2. Pressed briquettes were dried in air and subsequently processed in a moving bed plasma reactor after maintaining the following parameters.

Gas flow Power Bed speed No. of passes

0.5 liter/ sec 12.5 KW 2.0 cm/min 2

lasma processed material Characteristics
Phases present : CaO only
Hydration Resistance : 0.6 %
(% wt gain)
Bulk Density : 3.01 gm/cc
Apparent porosity : 6.60 %
The main advantages of the present invention are:
1) Production of hydration resistant lime aggregates through thermal plasma processing route leads to a drastic reduction in time to only a few minutes.
2) The initial attempts to make lime hydration resistant have been to completely melt the material in a conventional furnace. The process takes a long time and is energy intensive. Moreover the process did not remain viable because of the short life of the conventional furnace/container utilised for fusing the material. In case of plasma processing the time taken is only a few minutes and there is no damage to the container materials.
3) It opens up the possibility of utilizing an extremely thermodynamically stable material as a refractory material by overcoming its major weakness, which till date has not allowed the exploitation of other superior properties being prone to hydration.

We claim:
1. A novel process for the preparation of hydration resistant lime suitable
for use as a refractory material wherein the process steps comprise:
[a] crushing and grinding limestone and subsequently milling the material to fineness of 60 -100 mesh BS sieve, followed by mixing with the dopant titania in the range of 0.5 to 2.0 wt% to obtain a slurry;
[b] drying the slurry as obtained in step [a] at 105 to 110 degree C for 24 to 30 hours;
[c] adding and mixing an organic binder of the kind such as herein described in the range of 5 to 10 % to the dry powder as obtained in step [b] to obtain processed powder;
[d] uniaxial pressing of the processed powder as obtained in step [c] into briquettes at a pressure in the range of 500 - 1400 Kg/cm2;
[e] loading the briquettes as obtained in step [d] in single /multiple layers in a moving bed thermal plasma reactor for about 1 to 3 minutes;
[f] optionally repeating step [e] to obtain the desired hydration resistant lime.
2. A process as claimed in claim 1, wherein the limestone used is marble
stone powder, whose CaO content on loss free basis is above 97%.
3. A process as claimed in claim 1, wherein the Titania used is of reagent grade chemical having a minimum assay of 98.5% purity.
4. A process as claimed in claim 1, wherein milling is done by conventional processes such as ball milling, vibrogrinding or attrition milling.
5. A process as claimed in claim 1, wherein the organic binder is preferably selected from PVA or dextrin.
6. A process as claimed in claim 1, wherein the solvent during milling is selected from the group consisting of isopropyl alcohol, acetone, and hexane.
7. A novel process for the preparation of hydration resistant lime substantially as herein described with reference to the foregoing examples.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=ezVX2FxaO9lFIc1/zvTxtw==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

269921

Indian Patent Application Number

1119/DEL/2008

PG Journal Number

47/2015

Publication Date

20-Nov-2015

Grant Date

18-Nov-2015

Date of Filing

02-May-2008

Name of Patentee

COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH

Applicant Address

AUSANDHAN HAWAN, RAFI MARG, NEW DELHI-110001,INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	GALGALI RAMCHANDRA KRISHNARAO	INSTITUE OF MINERALS & MATERIALS TECHNBOLOGY, BHUBANESWAR
2	MISHRA BARADA KANTA	INSTITUE OF MINERALS & MATERIALS TECHNBOLOGY, BHUBANESWAR
3	MAITI HIMADRI SEKHAR	CENTRAL FLASS & CERAMIC RESEARCH INSTITUTE, P.O. JADAVPUR UNIVERSITY, KOLKATA 700 032
4	MUKHERJEE BARUNDEB	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O. JADAVPUR UNIVERSITY, KOLKATA 700 032
5	GHOSH ARUP	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O. JADAVPUR UNIVERSITY, KOLKATA 700 032
6	TRIPATHI HIMANSU SEKHAR	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, P.O. JADAVPUR UNIVERSITY, KOLKATA 700 032
7	MUKHERJEE PARTHA SARATHI	INSTITUE OF MINERALS & MATERIALS TECHNBOLOGY, BHUBANESWAR.
8	GUMASTE JAYARAM LAXMAN	INSTITUE OF MINERALS & MATERIALS TECHNBOLOGY, BHUBANESWAR

PCT International Classification Number

C04B

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA