FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2006
COMPLETE
Specification
(See Section 10 and Rule 13) CHAR FIRING SYSTEM
THERMAX LIMITED
an Indian Company
of D-13, MIDC Industrial Area,
R.D. Aga Road. Chinchwad,
Pune - 411 019, Maharashtra, India.
Inventors: a) Gaikwad Jalindar, b) Kulkarni Umesh, & c) Yadav Jeevan
The following specification particularly describes the invention and the manner in which it is to be
performed.

FIELD OF DISCLOSURE
The present disclosure relates to a fluidized bed combustion boiler. Particularly, the present disclosure relates to an atmospheric fluidized bed combustion boiler.
BACKGROUND
Char is a high ash solid fuel obtained as a by-product from the sponge iron plant process. Char has a high fixed carbon (FC) to volatile matter (VM) ratio, due to which it is difficult to burn. Further, due to the high ash content, the high FC/VM ratio, and high content of iron oxides which increase its bulk density; firing of char in a fluidized bed combustion boiler poses problems like clinker formation, de-fluidization of bed, erosion of in-bed coils, etc. Hence, char must be co-fired along with another fuel, generally coal, with a frequent fresh supply of the inert fluidization bed material. This limits the contribution of the char in the combustion, thereby reducing its energy output. Also, due to the high ash content intermittent draining of the bed material is essential. The present practice comprises intermittent draining of the bed material depending upon the increase in the bed height; where, a delay in removing the bed material results in clinker formation and subsequent chocking of the drainage system. Further, the draining rate is not consistent which results in variations in the bed temperature and loss of un-burnt carbon with the bed material. Also, to maintain the bed density, fresh bed material must be intermittently conveyed.
Summing-up, the disadvantages of the conventional fluidized bed combustion boilers using char include:
a) limitation in the percent of char used when co-firing, as char causes de-fluidization due to clinker formation, increase in the bed density and erosion of the in-bed coils; b) frequent feeding of fresh bed material to compensate for the loss of bed material during draining, this increases the operating cost and

operation time; and c) inconsistent bed draining resulting in fluctuations in the bed temperature, which thereby affects efficiency of the combustion process.
It is therefore required to provide a fluidized bed combustion boiler for firing char which overcomes the above-listed drawbacks of the known fluidized bed combustion boilers for firing char.
OBJECTS
Some of the objects of the present disclosure, which at least one embodiment herein satisfies, are as follows:
It is an object of the present disclosure to overcome the above-listed drawbacks of the known fluidized bed combustion boilers. Accordingly, an object of the present disclosure is to provide a fluidized bed combustion boiler for firing char which can be used to fire up to 100 % char without a need for co-firing with another fuel or use of a coal support.
It is another object of the present disclosure to provide a fluidized bed combustion boiler for firing char which eliminates the need to supply inert bed material intermittently during the combustion process.
It is yet another object of the present disclosure to provide an atmospheric fluidized bed combustion boiler for firing char which is cost-effective, minimizes wastage of energy through un-burnt carbon, maintains constant bed height and bed temperature, and reduces the power consumption, These objects and other advantages of the present disclosure will be more apparent from the following description.

SUMMARY
In accordance with the present disclosure, there is disclosed a fluidized bed combustion boiler system having:
a combustor comprising a fluidization chamber for combusting a solid fuel fluidized with a bed material, an air distributor plate arranged in the operative lower portion of said combustor immediately downstream of said fluidization chamber, said air distributor plate having a plurality of air ports for introducing hot combustion air to fluidize the bed material and fuel in said fluidization chamber, feeding means for supplying fuel to said fluidization chamber, an in-bed heat exchanger coil arranged in said fluidization chamber which in operation extracts heat from said fluidized bed, an upstream region extending upward from said fluidization chamber to the operative top of said combustor, said upstream region having a convention heat exchanger comprising a super heater and a boiler bank for extracting heat from flue gas generated by combustion in said fluidization chamber, a steam drum provided downstream from said convention heat exchanger, means for draining ash provided at the operative bottom of said combustor, said means comprising a discharge screw for controlled removal of ash and cooling water supply means adapted to cool said ash;
a plurality of external heat exchangers arranged in operative communication with said combustor for extracting heat from the flue gas downstream of said convention heat exchanger; and
dust collector arranged in operative communication with said external heat exchangers for separating particulate matter from the flue gas before discharge through a stack.
Typically, in accordance with the present disclosure, the solid fuel is selected from char, coal, and mixtures thereof.

Preferably, in accordance with the present disclosure, said feeding means supply the fuel to said fluidization chamber at a location above said air distributor plate.
Alternatively, in accordance with the present disclosure, said feeding means supply the fuel to said fluidization chamber at a location below said air distributor plate.
Typically, in accordance with the present disclosure, said plurality of external heat exchangers comprise an economizer and an air preheater. Preferably, an impact separator is placed between said economizer and said air preheater for separating dust particles from the flue gas. Typically, said air preheater is adapted to at least partly heat the combustion air by extracting heat from flue gas. Preferably, an air blower is provided in communication with said air preheater to provide the combustion air. Additionally, a start-up system is provided in operative communication with said air preheater to further heat the at least partly heated combustion air from said air preheater to obtain the hot combustion air to be fed to said combustor through said air distributor plate.
Preferably, in accordance with the present disclosure, said dust collector comprises a filtering medium.
Typically, in accordance with the present disclosure, the flue gas is conveyed to said stack via an ID fan.
In accordance with the present disclosure, there is provided a method for combusting a solid fuel in a fluidized bed combustion boiler system, said method comprising the steps of:
combusting a fluidized fuel by introducing hot combustion air in a fluidization chamber of a combustor via an air distributor plate arranged in the operative

lower portion of said combustor immediately downstream of said fluidization
chamber;
extracting heat from said fluidized bed by means of an in-bed heat exchanger
coil arranged in said fluidization chamber;
extracting heat from flue gas generated by the combustion in an upstream region
extending upward from said fluidization chamber to the operative top of said
combustor and having a convention heat exchanger comprising a super heater
and a boiler bank;
conveying the flue gas via a steam drum through a plurality of external heat
exchangers for extracting heat from the flue gas downstream of said convention
heat exchanger;
draining ash from the operative bottom of said combustor by means comprising
a discharge screw for controlled discharge of ash and cooling water supply
means adapted to cool said ash; and
separating particulate matter from the flue gas before discharge through a stack
by a dust collector.
Typically, in accordance with the present disclosure, the method comprises selecting the solid fuel from char, coal, and mixtures thereof.
Preferably, in accordance with the present disclosure, the method comprises at least partly heating the combustion air by extracting heat from the flue gas.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
The disclosure will now be described with the help of the accompanying drawing, in which,
FIGURE 1 illustrates a schematic of the fluidized bed combustion boiler in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWING
The disclosure will now be described with reference to the accompanying drawing which does not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.
The present disclosure envisages an atmospheric fluidized bed combustion boiler system, particularly suitable for firing char. The system of the present disclosure can be used to fire up to 100 % char without a need for co-firing with another fuel or use of a coal support. Preferably, between 30 - 100 % char can be fired in the boiler system. Also, the boiler system of the present disclosure eliminates the need for intermittent draining of the bed material and adding of fresh inert bed material, while maintaining the bed height and bed temperature. Further, the system of the present disclosure aims at reducing the wastage of energy through the loss of un-burnt carbon in drained bed material. A flat air-distributor plate design having an over-bed or under-bed fuel feeding system is used in the boiler system of the present disclosure.
FIGURE 1 of the accompanying drawings illustrates the atmospheric fluidized bed combustion boiler system of the present disclosure; the boiler system is referenced by numeral 100 in the FIG. 1. The boiler system 100 comprises a combustor 102. The combustor 102 comprises a fluidization chamber for combusting a solid fuel fluidized with a bed material. An air distributor plate 108 arranged in the operative lower portion of the combustor 102 immediately downstream of the fluidization chamber. The air distributor plate 108 comprises a plurality of air ports for introducing hot combustion air in the combustor 102 to fluidize the bed material and fuel in the fluidization chamber. An in-bed heat exchanger coil 112 is arranged within the fluidization chamber, which, in operation, extracts heat from the fluidized bed. The; in-bed heat exchanger coil 112 is coated with special refractory material to prevent erosion and thereby

enhance life of the coil. For holding the refractory material studs are welded on to the in-bed heat exchanger coil 112. The fuel is fed in the fluidization chamber by feeding means 110. The feeding means 110 are typically adapted to feed the fuel by gravity at a location above the air distributor plate 108. Alternatively, the fuel is fed at a location below the air distributor plate 108. Such type of feeding is identified as the under-bed feeding and is illustrated in the FIG. 1 by the numeral 121.
Hot air at the combustion temperature is fed into the combustor 102 through the air distributor plate 108 which is adapted to evenly distribute the hot air to cause a defined fluidization of the fuel and the bed material in the fluidization chamber and thereby give uniform combustion. Heat from the fuel and the heated bed material is extracted during the combustion process by means of the in-bed heat exchanger coil 112 provided within the fluidization chamber. Ash generated during the combustion process is controllably discharged by means 122 provided at the operative bottom of the combustor 102 to maintain the bed height. The means 122 comprise a discharge screw which provides a controlled discharge. The means 122 further comprise cooling water supply means 132 for supplying cooling water to cool the ash. The cooled ash is discharged at 130.
The discharge screw arrangement of the means 122 helps in adjusting the rate of draining of the ash. In a preferred embodiment of the present disclosure, means for continuous draining of the ash can be provided. Such draining means have provisions for variable draining capacity (adjustable speed). This continuous draining at a required rate helps in maintaining a constant bed height and bed temperature during combustion. The continuous draining means include the cooling water supply means 132 with variable speed function adapted to cool the ash before discharge, thereby assisting in handling of the drained material. By maintaining the draining rate in correspondence with the ash generated, the

bed level is maintained constant, resulting in constant wind box pressure and the bed height does not cross the safe limit. This system also maintains the required bed height by avoiding excess bed drain and thus eliminates the requirement for fresh inert bed material.
An upstream region which extends upward from the fluidization chamber to the operative top of the combustor 102 is defined. A convention heat exchanger comprising membrane panels 114, a super heater 116 and a boiler bank 118 is provided in the upstream region for extracting heat from flue gas generated by the combustion process in the fluidization chamber. A steam drum 128 is provided downstream from the convention heat exchanger for separating steam. A plurality of external heat exchangers, typically comprising an economizer 115 and an air preheater 116 are arranged in operative communication with the combustor 102 to receive the flue gas leaving the convention heat exchanger. The external heat exchangers are adapted to further extract the heat from the flue gas. An impact separator 127 is placed between the economizer 115 and the air preheater 116 for separating dust particles from the flue gas. The air preheater 116 is adapted to at least partly heat the combustion air to be fed to the combustor 102 by extracting heat from flue gas. An air blower 106 is provided in communication with the air preheater 116 to provide the flow of combustion air. A start-up system 104 is provided in operative communication with the air preheater 116 to further heat the at least partly heated combustion air from the air preheater 116 to obtain the hot combustion air which is fed to the combustor 102 through the air distributor plate 108. The start-up system 104 is typically a gas/oil assisted start-up boiler operatively located near the bottom portion of the combustor 102 at a point below the air distributor plate 108. A dust collector 120 is arranged in operative communication with the external heat exchangers (115, 116) for separating particulate matter from the flue gas before discharge through a stack 124. The dust collector 120 typically comprises a

filtering medium, such as a bag filter. An ID fan 126 is provided between the dust collector 120 and the stack 124, where the flue gas is conveyed to the stack 124 via the fan 126.
TECHNICAL ADVANTAGES
A fluidized bed combustion boiler particularly suitable for firing char, as described in the present disclosure has several technical advantages including but not limited to the realization of: the boiler can be used to fire up to 100 % char without a need for co-firing with another fuel or use of a coal support; the boiler eliminates the need to supply inert bed material intermittently during the combustion process; and the boiler is cost-effective, minimizes wastage of energy through un-burnt carbon, maintains constant bed height and bed temperature, and reduces the power consumption.
Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The use of the expression "at least" or "at least one" suggests the use of one or more elements or ingredients or quantities, as the use may be in the embodiment of the invention to achieve one or more of the desired objects or results. Any discussion of documents, acts, materials, devices, articles or the like that has been included in this specification is solely for the purpose of providing a context for the invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the invention as it existed anywhere before the priority date of this application.

The numerical values mentioned for the various physical parameters, dimensions or quantities are only approximations and it is envisaged that the values higher/lower than the numerical values assigned to the parameters, dimensions or quantities fall within the scope of the invention, unless there is a statement in the specification specific to the contrary.
In view of the wide variety of embodiments to which the principles of the present invention can be applied, it should be understood that the illustrated embodiments are exemplary only. While considerable emphasis has been placed herein on the particular features of this invention, it will be appreciated that various modifications can be made, and that many changes can be made in the preferred embodiments without departing from the principle of the invention. These and other modifications in the nature of the invention or the preferred embodiments 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. A fluidized bed combustion boiler system having:
a combustor (102) comprising a fluidization chamber for combusting a solid fuel fluidized with a bed material, an air distributor plate (108) arranged in the operative lower portion of said combustor (102) immediately downstream of said fluidization chamber, said air distributor plate (108) having a plurality of air ports for introducing hot combustion air to fluidize the bed material and fuel in said fluidization chamber, feeding means (110) for supplying fuel to said fluidization chamber, an in-bed heat exchanger coil (112) arranged in said fluidization chamber which in operation extracts heat from said fluidized bed, an upstream region extending upward from said fluidization chamber to the operative top of said combustor (102), said upstream region having a convention heat exchanger comprising a super heater (116) and a boiler bank (118) for extracting heat from flue gas generated by combustion in said fluidization chamber, a steam drum (128) provided downstream from said convention heat exchanger (116, 118), means (122) for draining ash provided at the operative bottom of said combustor (102), said means (122) comprising a discharge screw for controlled removal of ash and cooling water supply means adapted to cool said ash;
a plurality of external heat exchangers (115, 116) arranged in operative communication with said combustor (102) for extracting heat from the flue gas downstream of said convention heat exchanger (116, 118); and
dust collector (120) arranged in operative communication with said external heat exchangers (115, 116) for separating particulate matter from the flue gas before discharge through a stack (124).

2. The fluidized bed combustion boiler system as claimed in claim 1, wherein the solid fuel is selected from char, coal, and mixtures thereof.
3. The fluidized bed combustion boiler system as claimed in claim 1, wherein said feeding means (110) supply the fuel to said fluidization chamber at a location above said air distributor plate (108).
4. The fluidized bed combustion boiler system as claimed in claim 1, wherein said feeding means (110) supply the fuel to said fluidization chamber at a location below said air distributor plate (108).
5. The fluidized bed combustion boiler system as claimed in claim 1, wherein said plurality of external heat exchangers comprise an economizer (115) and an air preheater (116).
6. The fluidized bed combustion boiler system as claimed in claim 5, wherein an impact separator (127) is placed between said economizer (115) and said air preheater (116) for separating dust particles from the flue gas.
7. The fluidized bed combustion boiler system as claimed in claim 5, wherein said air preheater (116) is adapted to at least partly heat the combustion air by extracting heat from flue gas.
8. The fluidized bed combustion boiler system as claimed in claim 7, wherein an air blower (106) is provided in communication with said air preheater (116) to provide the combustion air.
9. The fluidized bed combustion boiler system as claimed in claim 7, wherein a start-up system (104) is provided in operative communication with said air preheater (116) to further heat the at least partly heated combustion air

from said air preheater (116) to obtain the hot combustion air to be fed to said combustor (102) through said air distributor plate (108).
10. The fluidized bed combustion boiler system as claimed in claim 1, wherein said dust collector (120) comprises a filtering medium.
11. The fluidized bed combustion boiler system as claimed in claim 1, wherein the flue gas is conveyed to said stack (124) via an ID fan (126).
12. A method for combusting a solid fuel in a fluidized bed combustion boiler system, said method comprising the steps of:
combusting a fluidized fuel by introducing hot combustion air in a fluidization
chamber of a combustor via an air distributor plate arranged in the operative
lower portion of said combustor immediately downstream of said fluidization
chamber;
extracting heat from said fluidized bed by means of an in-bed heat exchanger
coil arranged in said fluidization chamber;
extracting heat from flue gas generated by the combustion in an upstream region
extending upward from said fluidization chamber to the operative top of said
combustor and having a convention heat exchanger comprising a super heater
and a boiler bank;
conveying the flue gas via a steam drum through a plurality of external heat
exchangers for extracting heat from the flue gas downstream of said convention
heat exchanger;
draining ash from the operative bottom of said combustor by means comprising
a discharge screw for controlled discharge of ash and cooling water supply
means adapted to cool said ash; and
separating particulate matter from the flue gas before discharge through a stack
by a dust collector.

13. The method as claimed in claim 12, which comprises selecting the solid fuel from char, coal, and mixtures thereof.
14. The method as claimed in claim 12, which comprises at least partly heating the combustion air by extracting heat from the flue gas.