Title of Invention

A DEVICE FOR IMPROVED FLY ASH RECYCLING IN BUBBLING FLUIDIZED BED COMBUSTION SYSTEMS

Abstract

This invention relates to a device for improved fly ash recycling in bubbling fluidized bed combustion systems at high temperature of fly ash having partly and / or fully unburnt carbon in operating compartments or segments of fluidized bed systems, the device characterized by comprising: -at least one fly ash dust collection means (1) collecting a predetermined quantity of dust from the flue gas;- -at least one stand pipe (2) sealingly coupled to the collection means (1) for leading the collected material of residual carbon in fuel burn to a return leg (3); -the atleast one return leg (3) is angularly disposed in reference to the stand pipe (2) such that the collected material finds a free slide down by means of fluidizing air into at least one active fluidized bed compartment or a bed segment (4); - a drain pipe (6) connected to the stand pipe (2) for disposal of the excess collection; and - at least one gravity flow interconnection (5) between each two bed segments (4) for transferring ash in an event of slumping any or more bed segments (4) to the adjoining return leg (3) via the said interconnection (5).

Full Text

Title: Fly ash recycling systems for fluidized bed System Field of Invention. This invention relates to Atmospheric fluidized Combustion systems using the conventional bubbling Fluidized Beds. The invention more particularly relates to a device for improved fly ash recycling in bubbling fluidized bed combustion systems. Background of the art: Atmospheric fluidized bed combustion ( AFBC) boilers and systems are being adopted extensively for coal, lignite, washery rejects and other waste fuels. In this system, the fuel is fed to a fluidized bed or inert/ ash particles maintained at 550 to 1200° C. Due to the fluid like property of the bed, the fuel particle is instantaneously heated by the inert particles and the fuel burns in the presence of oxygen available in the air being used for fluidizing the bed particles. A part of the ash which is coarser in size having unburnt carbon of about 1% is removed via overflow/bottom drains. Rest of the ash which is generally of finer size along with the unburnt particles ( the proportion of un-burnt is usually higher than that in the bottom ash and is a function of many variables like the coal size distribution, attrition characteristics of the coal ash, fluidizing velocity) is elutriated with the flue gas. The carbon conversion/combustion efficiency obtained in this system is low compared to the Circulating Fluidized Bed Combustion ( CFBC) Systems in which the fly ash is separated in high efficiency cyclones and recycled back into the combustor, thus giving the carbon particles several cycles for completing the combustion. While the ABFBC boilers and systems are adopted for smaller sizes, CFBCs are preferred for larger capacity because of higher combustion efficiency even though CFBCs investment costs are higher . This invention facilitates increase in carbon conversion efficiency in atmospheric bubbling fluidized bed boiler( ATBC) thereby optimizing the overall economic competitiveness at least in a specific capacity range of systems, apart form increasing the boiler turn down capability. Fly ash recycling is adopted only in select ABFBC boilers and systems. In order to improve the carbon burn up, the fly ash which has some unburnt carbon particles are collected in a mechanical device and re-injected back into the bed by methods like gravity flow or pneumatic transport. Unlike the CFBC, the quantum collected and recycled is usually only a limited portion due to the problems associated with high-scale re-injecting. Since the fly ash collection is done after economizer, the temperature of ash would be of the order of 350° C only. This low temperature ash would naturally absorb heat from the furnace, which will ultimately result in reduced efficiency. While the gravity method warrants that the material is put back above the bed, thereby increasing he chances of the material getting carried away again by the flue gas without a chance for the unburnt carbon particles to reside/ remain long enough in the bed/ combustion system. Further pneumatic recycle system disturbs the bed and also puts a limitation on the quantity of ash that could be reinjected. In CFBC the furnace has a single fluid bed compartment. In ABFBC, depending on the boiler capacity there are multiple compartments and the fly ash is to be recycled to each compartment by each dedicated feed system. Even in CFBC boiler with increased boiler capacities, there is a need to opt an interlinked multiple feeding system. Objects of the invention. It is an object of the present inyention to provide a device for improved fly ash recycling in bubbling fluidized bed combustion system. Another object of the invention is to provide a device adaptable to bubbling fluidized bed combustion systems which can achieve improved burn-up of residual carbon in the fuel-burn. Yet another object of the invention is to provide a device which facilitates adaptation of the existing fluidized beds to feed maximum quantity of fuel-burn for recycling at an optimum temperature. Still another object of the invention is to provide a device for selective fly ash recycling and /or disposal from any desired bed compartment in the event of segmental operation of the fluidized bed combustor. A further object of the invention is to provide a device for improved fly ash recycling having means to bypass recycling fly ash of one or more bed compartments in case of segmental operation of the fluidized bed combustor. Summary of the Invention. Accordingly, there is a provided a device for repeated recycling at high temperature of fly ash having partly and /or fully unburnt carbon in operating compartments or segments of fluidized bed systems, the device comprising at least one fly ash dust collection means collecting a predetermined quantity of dust from the flue gas; at least one stand pipe sealingly coupled to the collection means for leading the collected material to a return leg , the atleast one return leg is angularly disposed in reference to the stand pipe such that the collected material finds a freeslide down by means of fluidizing air into at least one active fluidized bed compartment or a bed segment; a drain pipe connected to the stand pipe for disposal of the excess collection; and at least one gravity flow interconnection between each two bed segments for transferring ash in an event of slumping any or more bed segments . Brief Description of the Accompanying Drawing. Fig. 1. shows a schematic block diagram of elevational, plan and side sectional view of an embodiment of the present invention incorporated in an ABFBC system. , Detailed Description of a Preferred Embodiment of the Invention. As shown in the Fig. 1, the novel recycling device consists of at least one ash separation means (1) which removes required proportion of the dust in the flue gas, a stand pipe (2) which leads the ash/ unburnt carbon to a return leg (3). The return leg (3) feeds the material into an active fluidized bed (4). Air is used as the fluidizing medium for the return leg (3) and optionally from the stand pipe (2). The angular disposition of the return leg (3) corresponds to achieve a free slide down of the material by means of the fluidizing air. The material of construction of the device components (1, 2, 3, 4) is selected to have a capability to withstand the temperature of the material (in which case it is insulated from outside to prevent heat loss and for safety). Alternatively, the selected materials should be capable of being cooled or refractory lined. The collection means may be the conventional cyclones (s) configured as a square/rectangular enclosure with suitable vortex finders or mechanical impingement type separator as required. During operation, the dust collection means (1) separates the ash/unburnt carbon particles and through the stand pipes (2) ( at least one per bed segment) feeds the return leg (3). The number of the collection means (1) may correspond the number of stand pipes (2), or could be increased in multiples of the number of stand pipes (2) for improved distribution. If, for operational and other requirements, one or more of the bed segments (4) are slumped, the ash through the corresponding stand pipe (2) is transferred to the adjoining return leg (3) through fluidized/gravity flow interconnection (5) and /or sent to disposal through drain pipes (6). During this time the fluidization air to a second compartment is cut off and thereby the ash recycling to the slumped bed is cut-off. This is in contrast to the existing practice of CFBC boilers in which there is no demarcation called "segments" and hence the need of by passing the return leg is not encountered. Due to the unique requirement of segmental operation in ABFBC boilers, there exists a need for return leg bypassing. This is achieved by the unique construction of the device as shown in the figure 1. WE CLAIM: 1. A device for improved fly ash recycling in bubbling fluidized bed combustion systems at high temperature of fly ash in operating compartments or segments of fluidized bed systems, the device characterized by comprising; - at least one fly ash dust collection means (1) collecting a predetermined quantity of dust from the flue gas; - at least one stand pipe (2) sealingly coupled to the collection means (1) for leading the collected material of residual carbon in fuel burn to a return leg (3); - the atleast one return leg (3) is angularly disposed in reference to the stand pipe (2) such that the collected material finds a, free slide down by means of fluidizing air into at least one active fluidized bed compartment or a bed segment (4); - a drain pipe (6) connected to the stand pipe (2) for disposal of the excess collection; and - at least one gravity flow interconnection (5) between each two bed segments (4) for transferring ash in an event of slumping any or more bed segments (4) to the adjoining return leg (3) via the said interconnection (5). 2. The device as claimed in claim 1, wherein the construction materials of the at least one collection means (1), the at least one stand pipe (2), the at least one return leg (3), and the fluidized bed compartment (4) is selected from material having capability to withstand high temperature 3. The device as claimed in claim 1 or 2, wherein the collection means (1), the m materials having capability to withstand high temperature stand pipe (2), the return leg (3) and the fluidized bed compartment (4) each is externally insulated and/ or provided with refractory lining to prevent heat loss. 4. The device as claimed in claim 1or 2, wherein the collection means (1), is configured as a shaped enclosure having at least one vortex finder and / or a mechanical impingement type separator. 5. A device for Improved fly ash recycling in bubbling fluidized bed combustion system at high temperature of fly ash having partly and / or fully unburnt carbon in operating compartments or segments of fluidized bed systems, as herein described and illustrated with reference to the accompanying drawing. ABSTRACT TITLE: A DEVICE FOR IMPROVED FLY ASH RECYCLING IN BUBBLING FLUIDIZED BED COMBUSTION SYSTEM. This invention relates to a device for improved fly ash recycling in bubbling fluidized bed combustion systems at high temperature of fly ash having partly and / or fully unburnt carbon in operating compartments or segments of fluidized bed systems, the device characterized by comprising: -at least one fly ash dust collection means (1) collecting a predetermined quantity of dust from the flue gas;- -at least one stand pipe (2) sealingly coupled to the collection means (1) for leading the collected material of residual carbon in fuel burn to a return leg (3); -the atleast one return leg (3) is angularly disposed in reference to the stand pipe (2) such that the collected material finds a free slide down by means of fluidizing air into at least one active fluidized bed compartment or a bed segment (4); - a drain pipe (6) connected to the stand pipe (2) for disposal of the excess collection; and - at least one gravity flow interconnection (5) between each two bed segments (4) for transferring ash in an event of slumping any or more bed segments (4) to the adjoining return leg (3) via the said interconnection (5).

Documents:

201-KOL-2005-ABSTRACT.pdf

201-KOL-2005-CLAIMS.pdf

201-KOL-2005-CORRESPONDENCE.pdf

201-KOL-2005-DESCRIPTION (COMPLETE).pdf

201-KOL-2005-DRAWINGS.pdf

201-KOL-2005-EXAMINATION REPORT.pdf

201-KOL-2005-FORM 1.pdf

201-KOL-2005-FORM 18.pdf

201-KOL-2005-FORM 2.pdf

201-KOL-2005-FORM 3.pdf

201-KOL-2005-GPA.pdf

201-KOL-2005-REPLY TO EXAMINATION REPORT.pdf

201-KOL-2005-SPECIFICATION.pdf