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Title:
A SYSTEM FOR REDUCING UN-BURNT CARBON CONTENT IN ASH PARTICLES
Document Type and Number:
WIPO Patent Application WO/2017/025875
Kind Code:
A2
Abstract:
The system disclosed relates to the field of mechanical engineering. The system reduces carbon content present in ash. The ash particles are conveyed from a first hopper to a carbon burnout unit. The ash particles are fluidized in the carbon burnout unit by a fluidizing medium supplied by a first blower, thereby combusting the un-burnt carbon present in the ash particles, and generating residual ash and flue gases. A cyclone separator separates a first portion the flue gases containing ash particles having size greater than 7.5 microns, and releases a second portion of the flue gases containing fly ash. The heat from the second portion is extracted by a heat recovery unit. The second portion of the flue gases is then fed to an air pollution control unit to separate the fly ash from the flue gases. The flue gases are released to the atmosphere by a second blower.

Inventors:
KARVE PRAKASH SHAMRAO (IN)
GAIKWAD JALINDAR UTTAM (IN)
KULKARNI UMESH SURYAKANT (IN)
Application Number:
IB2016/054735
Publication Date:
February 16, 2017
Filing Date:
August 05, 2016
Export Citation:
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Assignee:
THERMAX LTD (IN)
International Classes:
F23G5/00
Attorney, Agent or Firm:
DEWAN, Mohan (S. A. Brelvi Road Fort, Mumbai, Maharashtra, IN)
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Claims:
CLAIMS:

1. A system for reducing un-burnt carbon content in ash particles (100), said system (100) comprises: a first hopper (10) adapted to receive said ash particles majority of which, have a particle size in the range of 7 microns to 15 microns entrained therein; a conveying unit (12) adapted to convey said ash particles received from said first hopper (10); a carbon burnout unit (14) adapted to receive said ash particles from said conveying unit (12), wherein said carbon burnout unit (14) is configured to fluidize said ash particles at a temperature in the range of 950° C to 1000° C by a fluidizing medium, thereby combusting said un-burnt carbon present in said ash particles to generate a residual ash (RA) and flue gases; a first blower (20) configured to supply said fluidizing medium to said carbon burnout unit (14); at least one cyclone separator (21) configured to receive said flue gases from said carbon burnout unit (14), said at least one cyclone separator (21) further configured to separate said ash particles having a particle size greater than 7.5 microns from said flue gases, and re -circulate a first portion of said flue gases containing said ash particles having a particle size greater than 7.5 microns into said carbon burnout unit (14), said at least one cyclone separator (21) further configured to release a second portion of said flue gases containing fly ash particles having a particle size less than 7.5 microns; a heat recovery unit (24) configured to receive said second portion of flue gases containing said fly ash particles, said heat recovery unit (24) further configured to extract heat from said second portion of flue gases received from said at least one cyclone separator (21); and at least one air pollution control unit (26) configured to receive said second portion of said flue gases from said heat recovery unit (24), wherein said at least one air pollution control unit (26) is configured to separate said fly ash particles from said second portion of said flue gases, and discharge said second portion of said flue gases to the atmosphere via a second blower (28).

2. The system as claimed in claim 1, wherein said conveying unit (12) is a screw feeder.

3. The system as claimed in claim 1, wherein said system further includes a first conduit (PI) connected to said first blower (20) and said operative first portion (I) of said carbon burnout unit (14), said first conduit (PI) configured to facilitate feeding of said fluidizing medium to said carbon burnout unit (14) from said operative first portion (I) of said carbon burnout unit (14).

4. The system as claimed in claim 3, wherein said fluidizing medium is air.

5. The system as claimed in claim 1, wherein said system further includes a second conduit (P2) connected to said first blower (20) and said operative second portion (II) of said carbon burnout unit (14), said second conduit (P2) configured to facilitate a passage of a stream of air therethrough, to said operative second portion (II) of said carbon burnout unit (14) for aiding combustion.

6. The system as claimed in claim 1, wherein said at least one air pollution control unit (26) includes a second hopper (27) for collecting said fly ash.

7. The system as claimed in claim 1, wherein said at least one cyclone separator (21) has a refractory comprising silicon carbide bonded with nitride.

8. The system as claimed in claim 1, wherein said at least one air pollution control unit (26) includes at least one electrostatic precipitator and a bag filter.

9. A process for reducing un-burnt carbon content in ash particles in said system as claimed in any of the claims 1 to 8, said process comprising the following steps: a. receiving said ash particles majority of which, have a particle size in the range of 7 microns to 15 microns entrained therein from said first hopper (10); b. conveying said ash particles received from said first hopper (10) to said carbon burnout unit (14); c. fluidizing said ash particles in said carbon burnout unit (14) at a temperature in the range of 950° C to 1000° C by said fluidizing medium supplied by said first blower (20), thereby combusting said un-burnt carbon in said ash particles to generate said residual ash (RA) and flue gases; d. receiving said flue gases in said at least one cyclone separator (21) from said carbon burnout unit (14), and separating said ash particles having a particle size greater than 7.5 microns from said flue gases; e. recirculating said first portion of said flue gases containing said ash particles having a particle size greater than 7.5 microns into said carbon burnout unit (14); f. releasing said second portion of said flue gases containing said fly ash particles having a particle size less than 7.5 microns; g. introducing said second portion of said flue gases containing fly ash particles into said heat recovery unit (24); h. extracting heat from said second portion of said flue gases having said fly ash particles; and i. allowing said second portion of said flue gases to pass through said at least one air pollution control unit (26) from said heat recovery unit (24) to separate said fly ash particles having a particle size less than 7.5 microns from said second portion of said flue gases, and discharging said second portion of said flue gases to the atmosphere by said second blower (28).

10. The process as claimed in claim 9, wherein said residual ash (RA) contains less than 5% un-burnt carbon.

Description:
A SYSTEM FOR REDUCING UN-BURNT CARBON CONTENT IN ASH

PARTICLES

FIELD

The present disclosure relates to the field of mechanical engineering and more particularly, relates to a process for reducing un-burnt carbon content in ash particles.

DEFINITIONS As used in the present disclosure, the following terms are generally intended to have the meaning as set forth below, except to the extent that the context in which they are used indicate otherwise.

Carbon burnout: The term "carbon burnout" hereinafter in the complete specification refers to the combustion of a carbon from carbon bearing material as a fuel. Ash: The term "ash" hereinafter in the complete specification refers to mineral containing residues left after the combustion of coal and other fuels in power plants and boilers.

BACKGROUND

A significant amount of ash is generated in power plants and boilers. The ash generated needs to be disposed off. This disposal is a major issue because the generated ash also contains un- burnt carbon. Disposing in landfill or as an additive in cement requires the carbon content of ash below a pre-defined threshold. Moreover, the un-burnt carbon in ash is environment polluting. Further, disposal of ash containing un-burnt carbon is a loss of energy contained in the un-burnt carbon.

Therefore, there is felt a need for a system that reduces un-burnt carbon content in ash particles.

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 ameliorate one or more problems of the prior art or to at least provide a useful alternative.

An object of the present disclosure is to provide a system that effectively reduces un-burnt carbon present in ash. Another object of the present disclosure is to provide a system for reducing un-burnt carbon content in ash particles that recovers energy from ash by using the ash as a fuel.

Other objects and advantages of the present disclosure will be more apparent from the following description, which is not intended to limit the scope of the present disclosure.

SUMMARY The present disclosure envisages a system for reducing un-burnt carbon content in ash particles. The system includes a first hopper, a conveying unit, a carbon burnout unit, a first blower, at least one cyclone separator, a heat recovery unit, at least one air pollution control unit, and a second blower. The first hopper is adapted to receive the ash particles majority of which have a particle size in the range of 7 microns to 15 microns entrained therein. The conveying unit is adapted to convey the ash particles received from the first hopper. The carbon burnout unit is adapted to receive the ash particles from the conveying unit. The carbon burnout unit is configured to fluidize the ash particles at a temperature ranging from 950° Celsius to 1000° Celsius by a fluidizing medium, thereby combusting the un-burnt carbon in the ash particles entrained therein to generate a residual ash and flue gases. The first blower is configured to supply the fluidizing medium to the carbon burnout unit. The at least one cyclone separator is configured to receive the flue gases from the carbon burnout unit. The at least one cyclone separator is further configured to separate the ash particles having a particle size greater than 7.5 microns from the flue gases and recirculate a first portion of flue gases containing the ash particles having a particle size greater than 7.5 microns into the carbon burnout unit. The at least one cyclone separator is further configured to release a second portion of the flue gases containing fly ash particles having a particle size less than 7.5 microns. The heat recovery unit is configured to receive the second portion of the flue gases containing the fly ash particles. The heat recovery unit is further configured to extract heat from the second portion of the flue gases received from the at least one cyclone separator. The at least one air pollution control unit is configured to receive the second portion of the flue gases from the heat recovery unit, wherein the at least one air pollution control unit is configured to separate the fly ash particles from the second portion of the flue gases, and discharge the second portion of the flue gases to the atmosphere via a second blower.

In a preferred embodiment, the conveying unit is a screw feeder. In a preferred embodiment, a first conduit is connected to the first blower and the operative first portion of the carbon burnout unit. The first conduit is configured to facilitate feeding of the fluidizing medium to the carbon burnout unit from an operative first portion of the carbon burnout unit.

In a preferred embodiment, a second conduit is connected to the first blower and the operative second portion of the carbon burnout unit. The second conduit is configured to facilitate a passage of a stream of air therethrough, to an operative second portion of the carbon burnout unit for aiding combustion.

In a preferred embodiment, the at least one air pollution control unit includes a second hopper that is configured to collect the fly ash. In a preferred embodiment, the at least one cyclone separator has a refractory comprising silicon carbide bonded with nitride.

In a preferred embodiment, the at least one air pollution control unit includes at least one electrostatic precipitator and a bag filter.

The present disclosure provides a process for reducing un-burnt carbon content in ash particles. During the process, the ash particles majority of which have a particle size in the range of 7 microns to 15 microns are conveyed from the first hopper to the carbon burnout unit. The ash particles are fluidized by the fluidizing medium supplied by the first blower at a temperature ranging from 950° C to 1000° C in the carbon burnout unit, thereby combusting the un-burnt carbon present in the ash particles, and generating the residual ash and flue gases. The residual ash contains less than 5% un-burnt carbon. The generated flue gases along the ash particles enter the at least one cyclone separator where the ash particles having particle size greater than 7.5 microns is separated from the flue gases and a first portion of the flue gases containing ash particles having a particle size greater than 7.5 microns is recirculated into the carbon burnout unit. Further, a second portion of the flue gases containing fly ash particles having particle size less than 7.5 microns is released from the at least one cyclone separator. The second portion of the flue gases containing the fly ash particles enters the heat recovery unit. The heat recovery unit extracts the heat from the second portion of the flue gases and passed through the at least one air pollution control unit. The air pollution control unit separates the fly ash particles having a particle size less than 7.5 microns from the second portion of the flue gases, and discharges the second portion of the flue gases into the atmosphere, via a chimney, by the second blower.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWING

A system for reducing un-burnt carbon content in ash particles, of the present disclosure, will now be described with the help of the accompanying drawing in which:

Figure 1 illustrates a schematic view of a system for reducing un-burnt carbon content in ash particles in accordance with the present disclosure.

LIST OF REFERENCE NUMERAL

100 - System for reducing un-burnt carbon content in ash particles 10 - First hopper

12 - Conveying unit

14 - Carbon burnout unit

16 - Distributor plate

18 - Burner 20 - First blower

21 - At least one cyclone separator

22 - Return leg

24 - Heat recovery unit

26 - At least one air pollution control unit 27 - Second hopper

28 - Second blower 30 - Chimney

I - First portion II - Second portion

RA - Residual ash

B - Fluidized bed

PI - First conduit

P2 - Second conduit DETAILED DESCRIPTION

Conventional fluidized bed combustors use ash containing un-burnt carbon as fuel having a particle size up to 6 mm. The bed material is recirculated in the conventional fluidized bed reactor by a riser velocity, which is above 4 m/s. Due to the high riser velocity, the fine ash particles containing un-burnt carbon is carried away along with the combustion products. The cyclones working with conventional fluidized bed combustors operate at a velocity in the range of 15-20 m/s. At this velocity, the conventional cyclones are unable to capture particles having the particle size less than 50 microns.

However, some limitations associated with the use of the conventional fluidized bed combustors are that on the one hand, relatively small sized fluidized bed particles leave the fluidized bed and enter the cyclone, and on the other hand, the cyclones are unable to scavenge sufficient quantities of these particles.

In order to overcome the afore-stated drawbacks, the present disclosure envisages a system for reducing un-burnt carbon content in ash particles.

The system and process of the present disclosure envisages use of ash as a fuel that is generated from power plants, and boiler. The generated ash contains un-burnt carbon, which is difficult to burn as it has already passed through high temperature zones in boiler, thereby leaving behind very little volatile matter. The un-burnt carbon in ash can be reduced by a carbon burnout unit and the energy released during combustion of the un-burnt carbon can be recovered by a heat recovery unit that is coupled to the carbon burnout unit.

A preferred embodiment of a system for reducing un-burnt carbon content in ash particles, of the present disclosure, will now be described in detail with reference to the accompanying drawing. The preferred embodiment does not limit the scope and ambit of the disclosure.

Figure 1 illustrates a system for reducing un-burnt carbon content in ash particles.

The present disclosure envisages a system for reducing un-burnt carbon content in ash particles (hereinafter referred as "the system 100")· The system 100 includes a first hopper 10, a conveying unit 12, a carbon burnout unit 14, a first blower 20, at least one cyclone separator 21, a heat recovery unit 24, at least one air pollution control unit 26, a first conduit PI, a second conduit P2, and a second blower 28. The first hopper 10 is adapted to receive the ash particles majority of which have a particle size in the range of 7 microns to 15 microns. The conveying unit 12 is adapted to convey the ash particles received from the first hopper 10. The carbon burnout unit 14 has an operative first portion I and an operative second portion II. The carbon burnout unit 14 is adapted to receive the ash particles containing un-burnt carbon from the conveying unit 12. The carbon burnout unit 14 is further configured to fluidize the ash particles at a temperature in the range of 950° Celsius to 1000° Celsius by a fluidizing medium, thereby combusting the un-burnt carbon present in the ash, and generate a residual ash and flue gases. In an embodiment, the fluidizing medium is air. The first blower 20 is configured to supply the fluidizing medium to the carbon burnout unit 14. The first conduit PI is connected to the first blower 20 and the operative first portion I of said carbon burnout unit 14. The first conduit PI is configured to facilitate feeding of the fluidizing medium to the carbon burnout unit 14 from the operative first portion I of the carbon burnout unit 14. Further, the second conduit P2 is connected to the first blower 20 and the operative second portion II of the carbon burnout unit 14. The second conduit P2 is configured to facilitate a passage of a stream of air therethrough, to the operative second portion II of the carbon burnout unit 14. The stream of air is fed in order to aid combustion of the ash particles. The at least one cyclone separator 21 is configured to receive the flue gases from the carbon burnout unit 14. The at least one cyclone separator 21 is further configured to separate the ash particles having a particle size greater than 7.5 microns from the flue gases and recirculate a first portion of the flue gases having a particle size greater than 7.5 microns into the carbon burnout unit 14. The at least one cyclone separator 21 is further configured to release a second portion of the flue gases containing fly ash particles having a particle size less than 7.5 microns. The heat recovery unit 24 is configured to receive the second portion of the flue gases containing fly ash particles. The heat recovery unit 24 is further configured to extract heat from the second portion of the flue gases received from the at least one cyclone separator 21 containing the fly ash. The at least one air pollution control unit 26 is adapted to receive the second portion of the flue gases from the heat recovery unit 24, wherein the at least one air pollution control unit 26 is configured to separate the fly ash particles from the second portion of the flue gases, and discharge the second portion of the flue gases to the atmosphere via the second blower 28.

In an operative configuration, the ash produced in power plants and boilers is filled in the first hopper 10. The ash obtained from the power plants is at least one of, but not limited to, residual ash or fly ash. The particle size of the ash containing un-burnt carbon content ranges between 7 microns to 15 microns. The ash from the first hopper 10 is introduced into the conveying unit 12 via rotary feeders (not exclusively labelled in the drawing). In a preferred embodiment, the conveying unit 12 is a screw feeder. The ash from the conveying unit 12 is then introduced into the carbon burnout unit 14 at a pre-determined velocity for combustion. In order to initiate the combustion of the ash in the carbon burnout unit 14, a pre-determined temperature ranging from 950° C to 1000° C is maintained in the carbon burnout unit 14 by using a support fuel and a burner 18. In a preferred embodiment, the support fuel is coal or oil. In another embodiment, if the calorific value of the ash introduced into the carbon burnout unit 14 exceeds 1500 kcal/kg, then use of the support fuel and the burner 18 is obviated for maintaining the pre-determined temperature in the carbon burnout unit 14. The ash introduced in the carbon burnout unit 14 itself acts as a bed material. In an embodiment, the carbon burnout unit 14 is a fluidized bed combustor.

The fluidizing medium from the first blower 20 is fed to the carbon burnout unit 14 from the operative first portion I, via the first conduit PI, by the first blower 20. In a preferred embodiment, the first blower 20 is a forced draft fan. The fluidizing medium is introduced into the carbon burnout unit 14 from the operative first portion I at a very low velocity of 1 to 1.2 m/s. The fluidizing medium is introduced into the carbon burnout unit 14 via a distributor plate 16 to fluidize the ash, thereby facilitating the combustion of the un-burnt carbon present in the ash, and generating residual ash RA and flue gases. The stream of air is fed to the carbon burnout unit 14 from an operative second portion II thereof via a second conduit P2 to facilitate combustion of the un-burnt carbon present in the ash particles. The combustion of the un-burnt carbon present in the ash reduces the amount of the un-burnt carbon present in the ash. In an embodiment, the velocity of the fluidizing medium is controlled to optimize the residence time of the ash in the carbon burnout unit 14. In a preferred embodiment, the second conduit P2 is attached to the carbon burnout unit 14 at the operative second portion II above fluidized bed B.

The flue gases bearing the ash particles leads to the at least one cyclone separator 21. In a preferred embodiment, the at least one cyclone separator 21 is configured to handle flue gases having a velocity in the range of 40 m/s to 60 m/s. The at least one cyclone separator 21 separates the ash particles having a particle size greater than 7.5 microns from the flue gases, and recirculates the first portion of the flue gases containing the ash particles having a particle size greater than 7.5 microns to the fluidized bed B of the carbon burnout unit 14, via a return leg 22. In another embodiment, the at least one cyclone separator 21 has a refractory comprising a special type of silicon carbide bonded with nitride.

The residual ash RA, formed as a result of combustion of the ash particles, is collected from the operative first portion I of the carbon burnout unit 14. In an exemplary embodiment, the residual ash RA contains less than 5% of un-burnt carbon. The residual ash RA can be blended with cement directly and can be used for manufacturing of concrete blocks. The second portion of the flue gases containing fly ash particles having a particle size less than 7.5 microns are introduced into the heat recovery unit 24 from the cyclone separator 21. The heat from the second portion of the flue gases is extracted by passing the flue gases through the heat recovery unit 24. In an embodiment, the heat recovery unit 24 extracts the heat from the second portion of the flue gases. The heat extracted is further used for various applications such as heating, cooling, drying, refrigeration, and the like. In a preferred embodiment, the heat recovery unit 24 is a heat exchanger.

The second portion of the flue gases containing the fly ash particles leaving the heat recovery unit 24 are introduced into the at least one air pollution control unit 26. The at least one air pollution control unit 26 arrests and separates the fly ash particles having particle size less than 7.5 microns from the second portion of flue gases. In a preferred embodiment, the at least one air pollution control unit 26 is at least one of, but not limited to, an electrostatic precipitator and a bag filter. The separated fly ash particles are collected in a second hopper 27. The fly ash particles having particle size less than 7.5 microns is used in manufacturing of cement.

The second portion of the flue gases from the at least one air pollution control unit 26, after separation of the fly ash particles therefrom, are discharged into the atmosphere, via a chimney 30, by the second blower 28. In an embodiment, the second blower 28 is an induced draft fan. The fly ash particles separated from the at least one air pollution control unit 26 contains less than 5% of un-burnt carbon.

TECHNICAL ADVANCES AND ECONOMICAL SIGNIFICANCE The present disclosure described herein above has several technical advantages including but not limited to the realization of a system for reducing un-burnt carbon content in ash particles that:

- effectively reduces un-burnt carbon present in ash; and

- recovers heat energy from ash. The disclosure has been described with reference to the accompanying embodiments which do not limit the scope and ambit of the disclosure. The description provided is purely by way of example and illustration.

The embodiments herein and the various features and advantageous details thereof are explained with reference to the non-limiting embodiments in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

The foregoing description of the specific embodiments so fully revealed the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

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 disclosure 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 disclosure. It is not to be taken as an admission that any or all of these matters form a part of the prior art base or were common general knowledge in the field relevant to the disclosure as it existed anywhere before the priority date of this application.

While considerable emphasis has been placed herein on the components and component parts of the preferred embodiments, it will be appreciated that many embodiments can be made and that many changes can be made in the preferred embodiments without departing from the principles of the disclosure. These and other changes in the preferred embodiment as well as other embodiments of the disclosure 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 disclosure and not as a limitation.