Title of Invention	A PROCEES FOR MANUFACTURE OF COLD BONDED AGGREGATE PELLET FROM FLY ASH OF THERMAL POWER PLANT FOR CONSTRUCTIONAL USE
Abstract	The present invention relates to a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use. The process steps are:characterised in that mixing and grinding fly ash in presence of a hydraulic binder in the mixture is in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising powdery mixture in the presence of water by disc or drum pelletiser to make ball like pellets of various sizes, curing the above said pelletised material for 7 to 28 days by water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1100 to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion value.

Title of Invention

A PROCEES FOR MANUFACTURE OF COLD BONDED AGGREGATE PELLET FROM FLY ASH OF THERMAL POWER PLANT FOR CONSTRUCTIONAL USE

Abstract

The present invention relates to a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use. The process steps are:characterised in that mixing and grinding fly ash in presence of a hydraulic binder in the mixture is in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising powdery mixture in the presence of water by disc or drum pelletiser to make ball like pellets of various sizes, curing the above said pelletised material for 7 to 28 days by water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1100 to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion value.

Full Text	The present invention relates to a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use. Cold bonded aggregate pellet of various sizes made from fly ash of thermal power plant having enough mechanical strength can find wide application in making various building materials, concrete, road, pavement and embankment by replacing natural stone aggregates, gravel and sand. Also, it can be used as filler for low lying areas, mines and as covering material for ash ponds to protect from wind erosion and leaching of heavy metals and as absorbant media for treatment of various waste water containing toxic metal and oil. Present rate of generation of fly ash from different coal fired thermal power plants in the country is quite alarming due to its gradual accumulation and creation of environmental pollution. Development of suitable processes for gainful utilisation of fly ash in larger scale is a serious matter to get rid of disposal and environmental pollution. Utilisation of fly ash in various constructional activities is one of the avenues to save the use of various natural resources. Conventionally, natural aggregates produced by breaking hills and destroying forest lands are used to a large extent for various constructional works because of the size, strength and durability. Although, the fly ash of thermal power plant is chemically and mineralogically alike to many naturally occurring rocks, minerals and clay, but due to its powdery nature, the use of fly ash in various constructional activities like natural aggregates is very limited. Conversion of powdery form of fly ash into stone like aggregate is one of the options for wide application like natural aggregate in various constructions. Presently, only sintering processes have been developed for conversion of fly ash to produce stone like aggregates, porous aggregates and light weight aggregates for application in making building bricks, blocks, concrete, roads, skid resistant pavements by replacing natural aggregates, gravels and sand. References may be made to some of the patents and available publications as mentioned below: 1. Kettenbauer, Frazn : Fly ash sinter pellets, Ger. offen 1, 940. 169 (Cl. C04b), 25 Feb. 1971,Appl. 07Augl969. 2. Gal'pern, E.I.; Kotkina, L.A. and Mnskin, I.O. : Porous aggregate from beneficiated thermal power plant ash (USSR), Energ. Stroit, 1990 (2) pp. 38-39. 3. Rose, Jerry, G. and Stewart Orville, W. : Use of an improved continuous sintering grate for light weight aggregate production from bituminous coal refuse (Inst. Min. Miner. Res. Univ., Kentucky, Lexinton, KY), Proc. Bienn. Conf. Inst. Briquet. Agglom. 1977 (Pub. 1978), 15, pp. 41-56. 4. Sugimoto, Satoru : Manufacture of porous fly ash sinters (Ogawa Denki K.K.) Jpn. Kokai. Tokkyo. Koho JP 04, 270, 184 [92, 270, 184] (Cl. C04 B 38/00), 25 Sept. 1992. Appl. 91/53. 858,25 Feb 19991, pp. 5. Watanabe, Hikoitsu : Artificial stone from fly ash for building materials, Jpn. JCokai Tokkyo oho JP..02. 116, 653.[90, 116, 653] (Cl. C04 B28/02) ol May 1990. AppJ. 88/267, 239, 25 Oct 1988, pp.2. 6 Styron Robert, W. (Resource Technology Inc.) U.S. : Process for forming light weight aggregate pellet US .4, 741, 782 (Cl. 106-309; C04 B14/00) 03, May 1988,US Appl.669: 284. 07 Nov. 1984, pp. 9 Cont-in-part of US, 4, 624, 711. 7, Tomari Masao (Nippon Magnetic Dressing Co. Ltd. : Utilisation of coal ash. Jpn Tokkyo Koho JP 02, 271, 943 [90, 271, 943] (Cl. CO4B 18/08) 06 Nov. 1990. Appl. 89/92, 376, 11 Apr 1989, pp. 5. Wherein the fly ash has been used to convert into pellet like aggregate firing at 1000 to 1500°C temperature in the rotary kiln or continuous chain grate sintering systems. The drawbacks of the above processes are the use of natural oil, gas and solid carbon as fuel for sintering the fly ash to make aggregates. These processes are also very energy intensive and costly which require high capital investment, number of plant machineries and large number of manpower for production of fly ash aggregate in commercial scale. Presently, no other process except the sintering route has been adopted in making aggregate from fly ash for use as construction material. The main object of the present invention is to provide a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power lent for constructional use which obviates the drawbacks as detailed above. Another object of the present invention is to avoid the sintering route and use of costly fuel and plant machineries in manufacture of fly ash aggregate pellet by cold bonding method at a cheaper cost suitable for multipurpose use in various constructional activities and as filler and absorbent material. Still another object of the project invention is the use of hydraulic binders which are commercially available or prepared by combinations of various industrial solid wastes as binding agent with fly ash to make stone like aggregate by pelletisation technique. Yet another object of the present invention is to make high strength and low porosity aggregate pellets from fly ash of various sizes ranging from 2 to 50 mm for easy handling, disposal and utilization in place of natural aggregate, gravel and sand for various constructions. Yet another object of the present invention is the adoption of easy and lowest processing route which can be translated into small and large scale for complete utilization of thermal plant fly ash as construction and filling material. Yet another object of the present invention is the fixation of leach able heavy metal compounds of fly ash by making aggregate in presence of hydraulic binders to avoid the contamination of ground and surface water. Accordingly, the present invention provides a process for the manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use which comprises; characterised in that mixing and grinding fly ash in presence of a hydraulic binder in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising powdery mixture in the presence of water by disc or drum pelletiser to make ball like pellets of various sizes, curing the above said pelletised material for 7 to 28 days by water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1 100 to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion value. In an embodiment of the present invention, the fly ash and binder used in the mixture is in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively. In an another embodiment of the present invention, the dry fly ash used is collected from hoppers and is having less than 6 of unburnt carbon. In yet another embodiment, the binder used is selected from the group consisting of hydraulic cement, lime, silica bearing pozzolanic waste material, calcined clay, gypsum, red brick, silica brick powder, calcined rice husk and a mixture thereof. In yet another embodiment, the ratio of CaO to (SiC^+AbOa) is maintained from 0.20 to 1.0 in the mixture prepared from the various combination of fly ash and binders. In still another embodiment, the water used for pelletisation of powdery mixture is in the range of 10-18 wt.% to make compact ball like pellets ranging from 2 to 50 mm size in the disc or drum pelletiser. The process of the present invention is described as below: Dry fly ash of thermal power plant having less than 6% residual carbon and binding materials which set hydraulically are the essential ingredients for making cold bonded fly ash pellets. The binders are like conventional cements, special cements, hydrated lime, lime and gypsum bearing waste materials, blast furnace slag, pozzolanic materials, reactive silica, calcined clay and gypsum, red brick and silica brick powders, calcined rice husk, etc. These binders are used itself or in combinations with the fly ash to prepare the mixture keeping in view to maintain the CaO/(SiO2+Al2O3) ratios from 0.2 to 1.0 or above depending the reactiveness of fly ash and binder compounds. The mixture may contain 65 to 90% of fly ash and 10 to 35% of binding material by weight. The mixture is further mechanically blended or ground in ball mill depending on the particle fineness for uniform mixing and homogenisation. The homogenised mixture consisting of fly ash and binding material is granulated with water by disc or drum granulator to form ball like pellets of various sizes ranging up to 50 mm. During the process of granulation, the powdery materials develop seed particles which grow in size by the effect of rolling. The ball like pelletised particles gradually get compacted and develop bonding. Depending on the particle fineness of the mixture and setting character of hydraulic binder, the pelletisation time in the disc or drum pelletiser may range 5 to 12 minutes. The green pellets containing 10 to 18% water is allowed to store for 24 hours in atmospheric air. Then the pelletised material is cured 7 to 28 days by spraying water or 1 to 3 hours by passing steam at normal atmospheric pressure to develop the bonding strength. The cold bonded pellets of various sizes (2-50 mm) obtained after curing possess 40 to 300 kg of compressive strength and less than 12% of water absorption which can find suitable application in various constructional works. Presence of lime in form of oxides, hydroxides, silicates, aluminates, ferrites, sulphates, etc. of the binder compounds helps to promote mechanical and chemical activation of fly ash mineral phases during the process of grinding and homogenisation of the mixture when the homogenised powdery mixture consisting of fly ash and binder compounds is pelletised with water and activators, hydration of binder compounds along with fly ash takes place in the pelletised mass. During the process of pelletisation, the bonding and compaction of particle to particle within the pellet takes place by the effect of rolling pressure in the drum or disc pelletiser. Particle fineness of the powdery mixture and period of granulation significantly influence on size and compaction of the pellets. Higher is the particle fineness of the mixture better is the compaction to make dense and low porosity pellets of various sizes. Cold bonding strength of the pellets develop by the hydration binder compounds. Hydrated structures of calcium silicate, alumino-ferrite, sulpho-aluminates, chlorosilicates, calcium aluminium silicates, etc. which develop during water or steam curing promote the cold bonding strength in the pellets. Gradual gain of strength in the cold pellets takes place by the process of curing and it attains 40 to 300 kg of compressive strength depending the reactivity of fly ash and type of binders. The following examples are given by way of illustration and therefore should not be constructed to limit the scope of the present invention. Example-1 : Dry fly ash collected from the hopper of a thermal plant and binder like hydrated lime and 33-grade portland cement are used to make cold bonded fly ash pellets. A dry powdery mixture of 50 kg is prepared by taking 42.5 kg of fly ash, 2.5 kg of hydrated lime and 5 kg of portland cement. The mixture altogether is ground in the ball mill for 30 minutes for homogenisation. The homogenised mixture contains 63% of below 53 micron and 37% of -105+53 micron size fractions. A laboratory model small disc pelletiser of size 1 metre diameter, 200 mm of collar height and variable 8 to 25 r.p.m. is used for pelletisation of the mixture. 50 kg of powdery mixture is pelletised by adding 8 kg of water by the disc pelletiser in three different batches. In each batch, 16 to 18 kg of mixture is charged to the disc pelletiser to prepare 2 to 50 mm size pellets by giving 8 minutes of granulation time. The granulated pellets after 24 hours is cured for 14 days by spraying water to make it hardened for use. Physical properties of the pellets depending on the size as follows : (a) 2 to 6 mm size pellets show 70 to 120 kg compressive strength, less than 14% water absorption, 1100 to 1300 kg/m3 bulk density and 1.60 to 1.85 g/cc apparent density. (b) 6 to 20 mm size pellets show 150 to 270 kg compressive strength, less than 10% water absorption, 1250 to 1500 kg/m3 bulk density, 1.80 to 2.40 g/cc apparent density and 8 to 12% apparent porosity. (c) 20 to 50 mm size pellets show 160 to 290 kg compressive strength, less than 12 % water absorption, 1200 to 1450 kg/m3 bulk density, 1.60 to 1.90 g/cc apparent density and 10 to 14% apparent porosity. (d) Crushing, impact and abrasion value of the pellets are 30 to 40%, 28 to 32% and 15 to 25% respectively. ExampJe-2 : 42.5 kg fly ash, 3.5 kg hydrated lime, 1.5 kg rice husk silica and 2.5 kg of Portland cement are mixed and ground altogether for 30 minutes in a ball mill to make 50 kg of mixture powder of particle size below 100 micron. The powdery mixture is pelletised by the laboratory model disc pelletiser with 17% water to make 2 to 30 mm size pellets. The pelletisation period in the disc pelletiser is 10 minutes. The granulated pellets after 24 hours is cured by water for 14 days and steam for 2 hours separately. Physical properties of different type of curing samples are as follows : (a) Water curing method : 60 to 180 kg compressive strength, 1100 to 1375 kg/m3 bulk density, 8% water absorption, 1.55 to 1.68 g/cc apparent density and 10 to 13% apparent porosity. (b) Steam curing method : 70 to 220 kg compressive strength and other properties are same as above. Example-3 : 38.5 kg fly ash, 5 kg red brick, 1.5 kg calcined gypsum and 5 kg hydrated lime are mixed and ground for 1 hour in the ball mill to make 50 kg of powdery mixture of particle size less than 100 micron pellets of 5 to 20 mm size with 16% water are prepared by the laboratory model disc granulator. Pelletisation period is given for 12 minutes. The granulated pellets after 24 hours are cured with water for 20 days. Physical properties of the cured pellets are : 40 to 90 kg compressive strength, 1150 to 1350 kg/m3 bulk density, less than 16% water absorption, 1.45 to 1.65 g/cc apparent bulk density, 36 to 44% crushing value, 32 to 39% impact value and 39 to 48% abrasion value. Depending on hydraulic properties of the pozzolanic additives and cement products, these can be used in different combinations with fly ash to make hardened cold bonded pellets. Normal water curing may be adopted to the pellets containing hydraulic cements as binder. But in case of pozzolanic material and lime combinations as binder, steam curing of the pellets will be suitable to get early strength than the normal water curing method. As the strength and other physical properties of the cold bonded pellets depend on size, different fractions can be screened for specific use, particle fineness of mixture, hydraulic property of binder compounds, pelletisation time and size, nature of curing are the controlling factors to make the cold bonded pellets from fly ash according to the specifications of building material aggregate for various applications. The main advantages of the present invention are : 1. Manufacture of cold bonded pellets of different size and strength as per specifications of natural aggregate, gravel and sand using 65 to 90% fly ash without the sintering route. 2. The manufacturing cost of cold bonded pellets is less compared to the aggregate pellet produced by sintering process. 3. Use of commercially available hydraulic cements and other pozzolanic materials from various industrial wastes as binder. 4. The manufacturing process of cold bonded fly ash pellet is simple and it involves limited plant machineries. 5. Depending on the size and strength of the cold bonded pellets, it can be used in making road, pavement, building materials and as filler to cover the ash ponds. We Claim: 1. A process for the manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use which comprises; characterised in that mixing and grinding fly ash in presence of a hydraulic binder in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising powdery mixture in the presence of water by disc or drum pelletiser to make ball like pellets of various sizes, curing the above said pelletised material for 7 to 28 days by water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1100 to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion value. 2. A process as claimed in claim 1, wherein the size of particle fineness of powdery mixture used is up to 100 micron. 3. A process as claimed in claims 1-2, wherein the dry fly ash used is collected from hoppers and is having less than 6% of un burnt carbon. 4. A process as claimed in claims 1-3, wherein he binder used is selected from the group consisting of hydraulic cement, lime, silica bearing pozzolanic waste material, calcined clay, gypsum, red brick, silica brick powder, calcined rice husk and a mixture thereof. 5. A process as claimed in claims 1-4, wherein the ratio of CaO to (SiO2+A12O3) is maintained from 0.20 to 1.0 in the mixture prepared from the various combination of fly ash and binders. 6. A process as claimed in claims 1-5, wherein the water used for pelletisation of powdery mixture is in the range of 10-18 wt.% to make compact ball like pellets ranging from 2 to 50 mm size in the disc or drum pelletiser. 7. A process for the manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use substantially as herein described with reference to the examples.

Full Text

The present invention relates to a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use.
Cold bonded aggregate pellet of various sizes made from fly ash of thermal power plant having enough mechanical strength can find wide application in making various building materials, concrete, road, pavement and embankment by replacing natural stone aggregates, gravel and sand. Also, it can be used as filler for low lying areas, mines and as covering material for ash ponds to protect from wind erosion and leaching of heavy metals and as absorbant media for treatment of various waste water containing toxic metal and oil.
Present rate of generation of fly ash from different coal fired thermal power plants in the country is quite alarming due to its gradual accumulation and creation of environmental pollution. Development of suitable processes for gainful utilisation of fly ash in larger scale is a serious matter to get rid of disposal and environmental pollution. Utilisation of fly ash in various constructional activities is one of the avenues to save the use of various natural resources. Conventionally, natural aggregates produced by breaking hills and destroying forest lands are used to a large extent for various constructional works because of the size, strength and durability. Although, the fly ash of thermal power plant is chemically and mineralogically alike to many naturally occurring rocks, minerals and clay, but due to its powdery nature, the use of fly ash in various constructional activities like natural aggregates is very limited. Conversion of powdery form of fly ash into stone like aggregate is one of the options for wide application like natural aggregate in various constructions. Presently, only sintering processes have been developed for conversion of fly ash to produce stone like aggregates, porous aggregates and light weight aggregates for application in making building bricks, blocks, concrete, roads, skid resistant pavements by replacing natural aggregates, gravels and sand.
References may be made to some of the patents and available publications as mentioned below:

1. Kettenbauer, Frazn : Fly ash sinter pellets, Ger. offen 1, 940. 169 (Cl. C04b), 25
Feb. 1971,Appl. 07Augl969.
2. Gal'pern, E.I.; Kotkina, L.A. and Mnskin, I.O. : Porous aggregate from
beneficiated thermal power plant ash (USSR), Energ. Stroit, 1990 (2) pp. 38-39.
3. Rose, Jerry, G. and Stewart Orville, W. : Use of an improved continuous sintering
grate for light weight aggregate production from bituminous coal refuse (Inst.
Min. Miner. Res. Univ., Kentucky, Lexinton, KY), Proc. Bienn. Conf. Inst.
Briquet. Agglom. 1977 (Pub. 1978), 15, pp. 41-56.
4. Sugimoto, Satoru : Manufacture of porous fly ash sinters (Ogawa Denki K.K.)
Jpn. Kokai. Tokkyo. Koho JP 04, 270, 184 [92, 270, 184] (Cl. C04 B 38/00), 25
Sept. 1992. Appl. 91/53. 858,25 Feb 19991, pp.

5. Watanabe, Hikoitsu : Artificial stone from fly ash for building materials, Jpn.
JCokai Tokkyo oho JP..02. 116, 653.[90, 116, 653] (Cl. C04 B28/02) ol May 1990.
AppJ. 88/267, 239, 25 Oct 1988, pp.2.

6 Styron Robert, W. (Resource Technology Inc.) U.S. : Process for forming light
weight aggregate pellet US .4, 741, 782 (Cl. 106-309; C04 B14/00) 03, May 1988,US Appl.669: 284. 07 Nov. 1984, pp. 9 Cont-in-part of US, 4, 624, 711. 7, Tomari Masao (Nippon Magnetic Dressing Co. Ltd. : Utilisation of coal ash. Jpn Tokkyo Koho JP 02, 271, 943 [90, 271, 943] (Cl. CO4B 18/08) 06 Nov. 1990. Appl. 89/92, 376, 11 Apr 1989, pp. 5.
Wherein the fly ash has been used to convert into pellet like aggregate firing at 1000 to 1500°C temperature in the rotary kiln or continuous chain grate sintering systems.
The drawbacks of the above processes are the use of natural oil, gas and solid carbon as fuel for sintering the fly ash to make aggregates. These processes are also very energy intensive and costly which require high capital investment, number of plant machineries and large number of manpower for production of fly ash aggregate in commercial scale. Presently, no other process except the sintering route has been adopted in making aggregate from fly ash for use as construction material.

The main object of the present invention is to provide a process for manufacture of cold bonded aggregate pellet from fly ash of thermal power lent for constructional use which obviates the drawbacks as detailed above.
Another object of the present invention is to avoid the sintering route and use of costly fuel and plant machineries in manufacture of fly ash aggregate pellet by cold bonding method at a cheaper cost suitable for multipurpose use in various constructional activities and as filler and absorbent material.
Still another object of the project invention is the use of hydraulic binders which are commercially available or prepared by combinations of various industrial solid wastes as binding agent with fly ash to make stone like aggregate by pelletisation technique.
Yet another object of the present invention is to make high strength and low porosity aggregate pellets from fly ash of various sizes ranging from 2 to 50 mm for easy handling, disposal and utilization in place of natural aggregate, gravel and sand for various constructions.
Yet another object of the present invention is the adoption of easy and lowest processing route which can be translated into small and large scale for complete utilization of thermal plant fly ash as construction and filling material.
Yet another object of the present invention is the fixation of leach able heavy metal compounds of fly ash by making aggregate in presence of hydraulic binders to avoid the contamination of ground and surface water.
Accordingly, the present invention provides a process for the manufacture of cold bonded aggregate pellet from fly ash of thermal power plant for constructional use which comprises; characterised in that mixing and grinding fly ash in presence of a hydraulic binder in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising powdery mixture in the presence of water by disc or drum

pelletiser to make ball like pellets of various sizes, curing the above said pelletised material for 7 to 28 days by water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1 100 to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion value.
In an embodiment of the present invention, the fly ash and binder used in the mixture is in the range of 65 to 90 wt.% and 10 to 35 wt.% respectively.
In an another embodiment of the present invention, the dry fly ash used is collected from hoppers and is having less than 6 of unburnt carbon.
In yet another embodiment, the binder used is selected from the group consisting of hydraulic cement, lime, silica bearing pozzolanic waste material, calcined clay, gypsum, red brick, silica brick powder, calcined rice husk and a mixture thereof.
In yet another embodiment, the ratio of CaO to (SiC^+AbOa) is maintained from 0.20 to 1.0 in the mixture prepared from the various combination of fly ash and binders.
In still another embodiment, the water used for pelletisation of powdery mixture is in the range of 10-18 wt.% to make compact ball like pellets ranging from 2 to 50 mm size in the disc or drum pelletiser.
The process of the present invention is described as below:

Dry fly ash of thermal power plant having less than 6% residual carbon and binding materials which set hydraulically are the essential ingredients for making cold bonded fly ash pellets. The binders are like conventional cements, special cements, hydrated lime, lime and gypsum bearing waste materials, blast furnace slag, pozzolanic materials, reactive silica, calcined clay and gypsum, red brick and silica brick powders, calcined rice husk, etc. These binders are used itself or in combinations with the fly ash to prepare the mixture keeping in view to maintain the CaO/(SiO2+Al2O3) ratios from 0.2 to 1.0 or above depending the reactiveness of fly ash and binder compounds. The mixture may contain 65 to 90% of fly ash and 10 to 35% of binding material by weight. The mixture is further mechanically blended or ground in ball mill depending on the particle fineness for uniform mixing and homogenisation.
The homogenised mixture consisting of fly ash and binding material is granulated with water by disc or drum granulator to form ball like pellets of various sizes ranging up to 50 mm. During the process of granulation, the powdery materials develop seed particles which grow in size by the effect of rolling. The ball like pelletised particles gradually get compacted and develop bonding. Depending on the particle fineness of the mixture and setting character of hydraulic binder, the pelletisation time in the disc or drum pelletiser may range 5 to 12 minutes. The green pellets containing 10 to 18% water is allowed to store for 24 hours in atmospheric air. Then the pelletised material is cured 7 to 28 days by spraying water or 1 to 3 hours by passing steam at normal atmospheric pressure to develop the bonding strength. The cold bonded pellets of various sizes (2-50 mm) obtained after curing possess 40 to 300 kg of compressive strength and less than 12% of water absorption which can find suitable application in various constructional works.
Presence of lime in form of oxides, hydroxides, silicates, aluminates, ferrites, sulphates, etc. of the binder compounds helps to promote mechanical and chemical activation of fly ash mineral phases during the process of grinding and homogenisation of the mixture when the homogenised powdery mixture consisting of fly ash and binder compounds is pelletised with water and activators, hydration of binder compounds along

with fly ash takes place in the pelletised mass. During the process of pelletisation, the bonding and compaction of particle to particle within the pellet takes place by the effect of rolling pressure in the drum or disc pelletiser. Particle fineness of the powdery mixture and period of granulation significantly influence on size and compaction of the pellets. Higher is the particle fineness of the mixture better is the compaction to make dense and low porosity pellets of various sizes. Cold bonding strength of the pellets develop by the hydration binder compounds. Hydrated structures of calcium silicate, alumino-ferrite, sulpho-aluminates, chlorosilicates, calcium aluminium silicates, etc. which develop during water or steam curing promote the cold bonding strength in the pellets. Gradual gain of strength in the cold pellets takes place by the process of curing and it attains 40 to 300 kg of compressive strength depending the reactivity of fly ash and type of binders.
The following examples are given by way of illustration and therefore should not be constructed to limit the scope of the present invention.
Example-1 :
Dry fly ash collected from the hopper of a thermal plant and binder like hydrated lime and 33-grade portland cement are used to make cold bonded fly ash pellets. A dry powdery mixture of 50 kg is prepared by taking 42.5 kg of fly ash, 2.5 kg of hydrated lime and 5 kg of portland cement. The mixture altogether is ground in the ball mill for 30 minutes for homogenisation. The homogenised mixture contains 63% of below 53 micron and 37% of -105+53 micron size fractions. A laboratory model small disc pelletiser of size 1 metre diameter, 200 mm of collar height and variable 8 to 25 r.p.m. is used for pelletisation of the mixture. 50 kg of powdery mixture is pelletised by adding 8 kg of water by the disc pelletiser in three different batches. In each batch, 16 to 18 kg of mixture is charged to the disc pelletiser to prepare 2 to 50 mm size pellets by giving 8 minutes of granulation time. The granulated pellets after 24 hours is cured for 14 days by spraying water to make it hardened for use. Physical properties of the pellets depending on the size as follows :

(a) 2 to 6 mm size pellets show 70 to 120 kg compressive strength, less than 14%
water absorption, 1100 to 1300 kg/m3 bulk density and 1.60 to 1.85 g/cc apparent
density.
(b) 6 to 20 mm size pellets show 150 to 270 kg compressive strength, less than 10%
water absorption, 1250 to 1500 kg/m3 bulk density, 1.80 to 2.40 g/cc apparent
density and 8 to 12% apparent porosity.
(c) 20 to 50 mm size pellets show 160 to 290 kg compressive strength, less than 12 %
water absorption, 1200 to 1450 kg/m3 bulk density, 1.60 to 1.90 g/cc apparent
density and 10 to 14% apparent porosity.
(d) Crushing, impact and abrasion value of the pellets are 30 to 40%, 28 to 32% and
15 to 25% respectively.
ExampJe-2 :
42.5 kg fly ash, 3.5 kg hydrated lime, 1.5 kg rice husk silica and 2.5 kg of Portland cement are mixed and ground altogether for 30 minutes in a ball mill to make 50 kg of mixture powder of particle size below 100 micron. The powdery mixture is pelletised by the laboratory model disc pelletiser with 17% water to make 2 to 30 mm size pellets. The pelletisation period in the disc pelletiser is 10 minutes. The granulated pellets after 24 hours is cured by water for 14 days and steam for 2 hours separately. Physical properties of different type of curing samples are as follows :
(a) Water curing method : 60 to 180 kg compressive strength, 1100 to 1375 kg/m3
bulk density, 8% water absorption, 1.55 to 1.68 g/cc apparent density and 10 to
13% apparent porosity.
(b) Steam curing method : 70 to 220 kg compressive strength and other properties
are same as above.
Example-3 :
38.5 kg fly ash, 5 kg red brick, 1.5 kg calcined gypsum and 5 kg hydrated lime are mixed and ground for 1 hour in the ball mill to make 50 kg of powdery mixture of

particle size less than 100 micron pellets of 5 to 20 mm size with 16% water are prepared by the laboratory model disc granulator. Pelletisation period is given for 12 minutes. The granulated pellets after 24 hours are cured with water for 20 days. Physical properties of the cured pellets are : 40 to 90 kg compressive strength, 1150 to 1350 kg/m3 bulk density, less than 16% water absorption, 1.45 to 1.65 g/cc apparent bulk density, 36 to 44% crushing value, 32 to 39% impact value and 39 to 48% abrasion value.
Depending on hydraulic properties of the pozzolanic additives and cement products, these can be used in different combinations with fly ash to make hardened cold bonded pellets. Normal water curing may be adopted to the pellets containing hydraulic cements as binder. But in case of pozzolanic material and lime combinations as binder, steam curing of the pellets will be suitable to get early strength than the normal water curing method. As the strength and other physical properties of the cold bonded pellets depend on size, different fractions can be screened for specific use, particle fineness of mixture, hydraulic property of binder compounds, pelletisation time and size, nature of curing are the controlling factors to make the cold bonded pellets from fly ash according to the specifications of building material aggregate for various applications.
The main advantages of the present invention are :
1. Manufacture of cold bonded pellets of different size and strength as per
specifications of natural aggregate, gravel and sand using 65 to 90% fly ash
without the sintering route.
2. The manufacturing cost of cold bonded pellets is less compared to the aggregate
pellet produced by sintering process.
3. Use of commercially available hydraulic cements and other pozzolanic materials
from various industrial wastes as binder.

4. The manufacturing process of cold bonded fly ash pellet is simple and it involves
limited plant machineries.
5. Depending on the size and strength of the cold bonded pellets, it can be used in
making road, pavement, building materials and as filler to cover the ash ponds.

We Claim:
1. A process for the manufacture of cold bonded aggregate pellet from fly ash of thermal
power plant for constructional use which comprises; characterised in that mixing and
grinding fly ash in presence of a hydraulic binder in the range of 65 to 90 wt.% and 10
to 35 wt.% respectively to prepare dry and homogenized powdery mixture, pelletising
powdery mixture in the presence of water by disc or drum pelletiser to make ball like
pellets of various sizes, curing the above said pelletised material for 7 to 28 days by
water or 1 to 3 hours by steam at normal atmospheric pressure to obtain the hardened
pellets having 40 to 300 kg compressive strength, less than 14% water absorption, 1100
to 1500 kg/m3 bulk density, 1.60 to 2.40 g/cc apparent pellet density, 8 to 14% apparent
porosity, 30 to 40% crushing value, 28 to 39% impact value and 15 to 48% abrasion
value.
2. A process as claimed in claim 1, wherein the size of particle fineness of powdery mixture
used is up to 100 micron.
3. A process as claimed in claims 1-2, wherein the dry fly ash used is collected from
hoppers and is having less than 6% of un burnt carbon.
4. A process as claimed in claims 1-3, wherein he binder used is selected from the group
consisting of hydraulic cement, lime, silica bearing pozzolanic waste material, calcined
clay, gypsum, red brick, silica brick powder, calcined rice husk and a mixture thereof.
5. A process as claimed in claims 1-4, wherein the ratio of CaO to (SiO2+A12O3) is
maintained from 0.20 to 1.0 in the mixture prepared from the various combination of fly
ash and binders.
6. A process as claimed in claims 1-5, wherein the water used for pelletisation of powdery
mixture is in the range of 10-18 wt.% to make compact ball like pellets ranging from 2 to
50 mm size in the disc or drum pelletiser.
7. A process for the manufacture of cold bonded aggregate pellet from fly ash of thermal
power plant for constructional use substantially as herein described with reference to the
examples.

Documents:

112-del-2001-abstract.pdf

112-del-2001-claims.pdf

112-del-2001-correspondence-others.pdf

112-del-2001-correspondence-po.pdf

112-del-2001-description (complete).pdf

112-del-2001-form-1.pdf

112-del-2001-form-19.pdf

112-del-2001-form-2.pdf

112-del-2001-form-3.pdf

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Patent Number

216945

Indian Patent Application Number

112/DEL/2001

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

20-Mar-2008

Date of Filing

31-Jan-2001

Name of Patentee

COUNCL OF SCIENTIFIC AND INDUSTRIAL RESEARCH,

Applicant Address

RAFI MARG, NEW DELHI-110 001,

Inventors:

#	Inventor's Name	Inventor's Address
1	BANSDHAR NAYAK	9 OF REGINAL RESEARCH LABORATORY BHUBANESWAR-751013

PCT International Classification Number

E04C 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA