FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE
Specification
(See section 10; rule 13)


RICE HUSK ASH
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area, R. D. Aga Road, Chinchwad,
Pune 411 019, Maharashtra, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED


Field of Invention:
The present invention is related to rice husk ash.
In particular, the present invention is related to a method of producing amorphous rice husk ash.
Background and Existing Knowledge:
Agriculture waste material such as rice husk, rice hull, rice straw, wheat chaff and straw have a potential fuel value and also contains significant amount of siliceous material derived from the cell structure of plant material. The husk generated during milling is mostly used as a fuel in the boilers for processing paddy or producing energy through direct combustion and / or by gasification. The rice husk has a calorific value of about 3000-3100 kcal/kg. The husk contains about 80 % of organic matter and the balance 20 % of the weight of this husk is converted into ash during the firing process. This ash is known as rice husk ash (RHA). The rice husk ash in turn contains around 85 % - 90 % silica. Generally, the residue (ash) left behind after burning the agricultural waste is disposed off by burying in the landfill. Thus, rice husk ash is a great environment threat causing damage to the land and the surrounding area in which it is dumped.
It is highly desirable that a commercially attractive and environment friendly means to disposal of RHA is devised.
Amorphous rice husk ash is a good super pozzolan and widely used in cement concrete mix. The particle size of the cement is about 35μ. There may be formation of void in the concrete mixes, if curing is not done properly which

reduces the strength and quality of the concrete. The amorphous rice husk ash is finer (25μ) than cement and fills the interstices between the cement aggregates, imparting strength and density to the cement aggregate. Rice husk when burnt in controlled temperature (below about 700°C) gives amorphous rice husk ash. The transformation of this amorphous state to crystalline state takes place if the ash is exposed to high temperature (above 800 °C). Thus, controlled temperature treatment is very important while converting rice husk to rice husk ash.
United States Patent No. 3,959,007 discloses a process and apparatus for incineration of organic material, particularly agricultural waste products, to produce usable energy and siliceous composition. The process consists of exposing the waste material to elevated temperature in an excess of air in a cylindrical furnace. The rice hulls are subjected to vertical and centrifugal forces in the initial combustion stages in an oxidizing atmosphere (cyclonic combustion). The rice husk ash obtained by this process contains about 12-14 % unburnt carbon and is black in color.
United States Patent No. 4,049,464 discloses a method for making low carbon, white husk ash suitable for use in manufacturing building material. The ash is prepared by first removing volatile constituents by heating the husk at relatively low temperature below ignition point of husk. Fixed carbon is then oxidized by heating the husk to a second temperature above the separation temperature but below the crystallization temperature of silica in the husk and finally at high temperature above the crystallization temperature of silica to produce uniform siliceous material. It is a three step process and requires different temperature zones.

Russian Patent No. 2,144,498 discloses a method of preparing highly pure amorphous silica and carbon from rice husk. The method comprises subjecting rice husk to acid etching, washing with water, drying, pre-combusting in closed reactor where smoke is sucked out and amorphous carbon is entrapped, grinding and oxidative combustion successively in current of air and oxygen. Oxidative combustion is carried out in oxygen current for 20-60 minutes to get high purity silica. Again, the process is a three step process and requires different temperature zones.
Chinese Patent No. 1,073,660 discloses industrialized continuous production method of porous silicon dioxide by using rice hulls as the raw material. The acid soaked and water washed rice hulls are placed in a baking compartment between roasting furnaces and dried using waste heat of furnace walls. The roasting layer temperature is controlled at about 650°C.
The main drawbacks of the prior art process are that either acid is used for treatment or the resident time of rice husk or any agricultural waste in the furnace is very long, the number of steps required to burn rice husk are comparatively more. Also, the furnace temperature for treatment is very high which results in the formation of black siliceous material.
OBJECTS OF THE INVENTION:
It is one of the objects of present invention is to provide a value added product from rice husk.
It is yet another object of present invention to provide a process for the preparation of amorphous rice husk ash with low carbon content.

It is yet another object of the invention to produce useful heat energy from organic agricultural waste material.
It is still another object of the invention to provide a method for agro waste disposal that is environment friendly.
It is stiil another object of the invention to provide a process for producing rice husk ash along with a process for generating steam.
It is yet another object of the present invention to provide a process having single step.
It is yet another object of present invention to provide a process having lesser resident time for organic waste material in a furnace.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided an apparatus for converting rice husk to amorphous rice husk ash, said apparatus comprising;
i. a combustor chamber; ii. feeding means for feeding rice husk to the combustor
chamber; iii. air supplying means for supplying excess air to said
combustor chamber; iv. incinerating means provided inside said combustor chamber for incinerating the rice husk with the help of the air supplied

by air supplying means to generate flue gas containing suspended rice husk ash ; v. ash collecting means for extracting amorphous ash from flue
gases; vi. suction means for drawing said flue gas from said combustor
chamber to the ash collecting means; vii. at least one separation means provided online between the suction means and the ash collecting means for separating particulate matter of size greater than 25 microns from the flue gases and returning said separate particulate matter to said combustor chamber; and viii. circulating means adapted to circulate at least part of flue gas emanating from the ash collecting means and supplying the same to the combustor chamber for controlling the temperature profile of said flue gases in said combustor chamber to below the crystallizing temperature of the ash. Typically, the combustor chamber has an elongated configuration having incineration means at the bottom and void at the top.
Typically, at least one heat exchanger means is provided online between the separation means and ash collecting means.
Typically, the incinerating means is at least one means or a combination selected from a fluidized bed combustor and an in bed heat exchanger.
Typically, the incinerating means includes a start up burner cooperating with a booster fan.

Typically, the feeding means is a screw feeder preferably in combination with a silo.
Typically, the incineration means is a fluidized bed and feeding means is adapted to feed rice husk in a mode selected from a group of mode consisting of under bed, over bed, and both under bed and over bed.
Typically, the incineration means is in bed and feeding means is adapted to feed rice husk in a mode selected from a group of mode consisting of over bed, under bed, and both under bed and over bed.
Typically, the air supplying means includes means for supplying fluidization air, secondary air and tertiary air to said chamber.
Typically, the incinerating means is a fluidized bed and velocity of fluidization air ranges from minimum fluidizing velocity to about four times fluidizing velocity.
Typically, the separation means is at least one cyclone separators adapted to extend the residence time of rice husk in combustion chamber by 2 to 50 times.
Typically, the heat exchanger means includes a water source or thermal oil source for extracting heat from said flue gases and convert it into steam / hot water or hot thermal oil.

Typically, the ash extracting means is a means selected from a group of means consisting of dust collector typically a bag filter, cyclone separator and/or an electrostatic precipitator.
The invention also extends to a method in accordance with the present invention for producing amorphous rice husk ash from rice husk comprising the following steps;
i. incinerating rice husk in a combustor chamber in excess of air
to generate the flue gas containing suspended rice husk ash; ii. generating flue gas containing suspended rice husk ash; iii. extracting flue gas containing suspended rice husk ash from
the combustion chamber; iv. separating particulate matter of size greater than 25 microns from the flue gas and returning said separated particulate matter to the combustor chamber; v. separating the ash from the flue gases in ash collecting means and circulating the flue gases downstream of the ash collecting means to the combustor chamber for maintaining the temperature of flue gases below crystallizing temperature of the ash. Typically, a heat exchanger is provided for extracting heat from the flue gases before separation of ash and after removal of particulate matter of size greater than 25 microns.
Typically, a heat exchanger is provided for extracting heat from the flue gases after separation of ash in ash collecting means.

BRIEF DESCRIPTION OF THE DRAWING:
Figure 1 is a schematic diagram of various components of the apparatus and process in accordance with this invention.
Figure 2 describes another embodiment of the apparatus and process in accordance with this invention.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a schematic view of the apparatus for conducting the process of producing rice husk ash from rice husk, in accordance with this invention which is indicated generally by reference numeral 100.
In Figure 1, the apparatus 100 has a combustor chamber [1]. The combustor chamber |1] has an elongated configuration. Incinerating means [2] is provided at the operative bottom portion of combustor chamber [1]. The combustor chamber [1] has a void [4] space at its operative top portion. The incinerating means [2] provided at the operative bottom portion of combustor chamber [1] is a fluidized bed combustor with or without an "in bed heat exchanger" (IBH) [3]. The fluidized bed temperature ranges from 600-800 °C. The incinerating means [2] is capable of combusting rice husk. Rice husk is stored in a silo [5] and is fed into the combustor chamber [1] by any known means like a screw feeder [7]. Rice husk is fed either under the bed [9] to fluidized bed combustor and or over the bed [7] in case of in bed combustion to generate flue gases containing suspended rice husk ash. The excess air for combustion in combustor chamber [1] is supplied with the help of blower/blowers [ll].This air may be preheated in an air pre-heater (APH) [12] before passing through start up burner [13]. The velocity of fluidization air

ranges from minimum fluidizing velocity to about four times fluidizing velocity. Nozzles [not shown] are also provided in the combustor chamber [1] for supplying secondary and tertiary air to the void [4], The tertiary air supply means [17] are located above secondary air supply means [15] in the void space [4].
The generated flue gas containing suspended rice husk ash is drawn to separation means [19]. Separation means can be a cyclone separator. The cyclone separator selected is designed to separate particulate matter of size greater than 25 microns from the flue gases. These particles are generally unburnt carbon particle which are returned to combustor chamber [1] for further incineration. In addition to the cyclone separator a secondary dust settling means [21] may be provided for creating additional volume to the flow of flue gases which in turn increases residence time of flue gases so as to reduce the carbon content present to some greater extent. The flue gas containing suspended rice husk ash may then be allowed to exchange heat in a heat exchanger [23] to recover the energy in the form of steam [24]. Heat exchanger [23] may be provided with a scraper arrangement so as to avoid deposition of amorphous rice husk ash inside the heat exchanger [23]. The water required for cooling in the heat exchanger [23] is pumped using pump [25]. The cooled flue gases containing suspended rice husk ash are then allowed to pass through ash collection means [27] in order to collect the amorphous rice husk ash [29] having low loss on ignition (LOI) and carbon content in the range of 0.5 % to 3 %. The particle size of amorphous rice husk ash ranges from 5 microns to 40 microns. The ash extracting means is a dust collector like bag filter, cyclone separator or electrostatic precipitator. Suction means is provided to draw the flue gas from the combustion chamber [1], separation means [19] and may be from the dust settling means [21] , the heat

exchanger [23] and from the ash collection means [27], From the suction means [37] a significant portion of the flue gas is circulated to the combustor chamber [1]. A secondary air fan [35] may be used to aid this circulation of exhausted flue gases. This circulated flue gas is at a temperature much lower than the flue gases generated in the combustor chamber [1]. Therefore this relatively cooled flue gases returned to combustor chamber [1| helps in regulating the temperature in void [4]. The recirculated flue gas can be used either alone or in combination with tertiary air to introduce in the void [4] space through to maintain the temperature of suspended ash below its crystallizing temperature.
Referring to figure 2 indicated generally by reference numeral 200, another heat exchanger [23A] or [23B] is provided alternatively for extracting heat from the flue gases after seperation of ash in ash collecting means and before releasing part of flue gas to stack- [33] from ash collecting means [27] to the combustor chamber [1]. Heat exchanger [23A]/ [23B] helps in recovering more heat from the part of flue gases exiting -from the ash collecting means. Heat exchanger [23A]/ [23B] has a scraper arrangement so as to avoid deposition of amorphous ash inside the heat exchanger [23A]/ [23B], Heat exchanger [23A] or [23B] may be adapted to use simultaneously or individually as per the requirement.
The invention will now be described with respect to the following examples, which do not limit the invention in any way and only exemplify the invention.
The rice husk obtained as agro waste is heterogeneous in nature. During first pass of trial runs, desired temperature was maintained and crystallinity of rice

husk ash was checked. Every batch needs to be checked for crystallinity of final rice husk ash. The heat exchanger temperature in the void was then controlled to eliminate crystallinity of rice husk ash. The heat exchanger temperature can be controlled by three methods: 1) By circulating part of flue gas from the outlet of ID fan through secondary air fan in to combustor chamber in void; 2) By supplying excess secondary and tertiary air and 3) By having a water wall membrane panel or jacket to the chamber.
Rice husk at a rate of 50 kg/hr was fed in to the fluidized bed combustor in over bed mode in one experiment and in under bed mode in another experiment. The bed temperature was maintained in the range of 600-800°C. Typically, 100 kg of rice husk gave 20 kg of silica ash, suitable for mixing pozzolan cement.
The product ash was collected from bag filter type ash collection device placed after the heat exchanger. It was observed that the ash properties were as follows:
BET Specific Surface Area: 51.13 m2
2. Silica: 85-90 %
3. Pozzolanic Activity index:
As per ASTM C 1240-98 : 115%
As per IS 1727 : 3 Day: 97
: 7 Day: 97 : 28 Day: 109
The final rice husk ash has lower unburnt carbon, typically less than 3 %. If this is further baked or treated in oven or furnace for about 1-6 hrs at

temperatures ranging from about 300 to 500 °C, the unburnt carbon content in the ash can be reduced to even less than 1 %. The final rice husk ash having particle size in the range of 5 micron to 40 micron, with lower carbon content is suitable for mixing with pozzolan cement.
Economic Significance:
1. Highly efficient system with maximum energy recovery.
2. Eliminates ash disposal cost.
3. Replacement of costly additive like micro silica in concrete,
4. Produces value added product (amorphous silica) with energy recovery (steam / hot water / hot thermal oil ).
While considerable emphasis has been placed herein on the specific structure of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

We Claim:
1. An apparatus for converting rice husk to amorphous rice husk ash,
said apparatus comprising; i. a combustor chamber;
ii. feeding means for feeding rice husk to the combustor chamber;
iii. air supplying means for supplying excess air to said combustor chamber;
iv. incinerating means provided inside said combustor chamber for incinerating the rice husk with the help of the air supplied by air supplying means to generate flue gas containing suspended rice husk ash ;
v. ash collecting means for extracting amorphous ash from flue gases;
vi. suction means for drawing said flue gas from said combustor
chamber to the ash collecting means; vii. at least one separation means provided online between the suction means and the ash collecting means for separating particulate matter of size greater than 25 microns from the flue gases and returning said separate particulate matter to said combustor chamber; and viii circulating means adapted to circulate at least part of flue gas emanating from the ash collecting means and supplying the same to the combustor chamber for controlling the temperature of said flue gases in said combustor chamber to below the crystallizing temperature of the ash.

2. An apparatus as claimed in claim 1, wherein the combustor chamber has an elongated configuration having incineration means at the bottom and void at the top.
3. An apparatus as claimed in claim 1, wherein at least one heat exchanger means is provided online between the separation means and ash collecting means.
4. An apparatus as claimed in claim 1, wherein the incinerating means is at least one means or a combination selected from a fluidized bed combustor and an in bed heater.
5. An apparatus as claimed in claim 1, wherein the incinerating means includes a start up burner cooperating with a booster fan.
6. An apparatus as claimed in claim 1, wherein the feeding means is a screw feeder preferably in combination with a silo.
7. An apparatus as claimed in claim 6, the incineration means is a fluidized bed and feeding means is adapted to feed rice husk in a mode selected from a group of mode consisting of under bed, over bed, and both under bed and over bed.
8. An apparatus as claimed in claim 6, the incineration means is in bed and feeding means is adapted to feed rice husk in a mode selected from a group of mode consisting of over bed, under bed, and both under bed and over bed.

9. An apparatus as claimed in claim 1, wherein the air supplying means includes means for supplying fluidization air, secondary air and tertiary air to said chamber.
10. An apparatus as claimed in claim 1, wherein the incinerating means is a fluidized bed and velocity of fluidization air ranges from minimum fluidizing velocity to about four times fluidizing velocity.
11. An apparatus as claimed in claim 1, wherein the separation means is at least one cyclone separators adapted to extend the residence time of rice husk in combustion chamber by 2 to 50 times.
12. An apparatus as claimed in claim 1, wherein the heat exchanger means includes a water source or thermal oil source for extracting heat from said flue gases and convert it into steam / hot water or hot thermal oil.
13. An apparatus as claimed in claim 1, wherein the ash extracting means is a means selected from a group of means consisting of dust collector typically a bag filter, cyclone separator and/or an electrostatic precipitator.
14. A method for producing amorphous rice husk ash from rice husk comprising the following steps;
i. incinerating rice husk in a combustor chamber in excess air to generate the flue gas containing suspended rice husk ash;

ii. generating flue gas containing suspended rice husk ash; iii. extracting flue gas containing suspended rice husk ash from
the combustion chamber; iv. separating particulate matter of size greater than 25 microns
from the flue gas and returning said separated particulate
matter to the combustor chamber; v. separating the ash from the flue gases in ash collecting means
and circulating the flue gases downstream of the ash collecting
means to the combustor chamber for maintaining the
temperature of flue gases below crystallizing temperature of
the ash.
15. A method for producing amorphous rice husk ash from rice husk as claimed in claim 14, wherein a heat exchanger is provided for extracting heat from the flue gases before separation of ash and after removal of particulate matter of size greater than 25 microns.
16. A method for producing amorphous rice husk ash from rice husk as claimed in claim 14, wherein a heat exchanger is provided for extracting heat from the flue gases after separation of ash in ash collecting means.