Title of Invention

PRESSURISED FLUIDIZED BED GASIFIER WITH INTEGRATED CHAR COMBUSTOR

Abstract

A fluidized bed char combustion device adaptable to a fluidized bed gasification system comprising of a gasifier (1), atleast one particulate collection means (2) to retain the ash and char particles separated from the gas and a bulk solid recirculator provided optionality for recycling the solids into the gasifier (1) is comprised of a separation means (3) for diverting the solid from the collection means to the gasifier (1) via a parallel stream (PS), a first fluidized bed char combustor [4(1)] for inputting air and air-oxygen mixture in the first combustor [4(1)]. The first combustor controls the temperature of the input and of fluidized bed and achieves combustion of the char materials present in the solid input. The gasifier (1) receives the generated flue gas that includes left out char. The resultant coarse ash including further left out char is extracted from the bottom of the gasifier (1). The device is further comprised of a second fluidized bed char combustor [4(2)] having at least one heat transfer coil and receives the coarse ash including further left out char particles from the gasifier (1) for combustion therein. The flue gas generated is being passed to a heat recovery means [5(2),6]. The coarse ash is then disposed in two stages firstly via the bottom of the combustor 4(2) and secondly via the heat recovery means (6).

Full Text

FIELD OF INVENTION The invention relates to pressurized fluidized bed combustion / gasification systems. More particularly, the present invention relates to a fluidized bed char combustion device adaptable to a fluidized bed gasification system. BACKGROUND OF THE INVENTION Gasification of coal, lignite and other fuels in pressurized fluidized / entrained bed systems are being adapted extensively for application in Integrated gasification combined cycle. In these systems, the fuel is gasified in an oxygen deficient environment. Hence the presence of un-burnt carbon-char in the fly ash as well as in the bottom ash is high compared to the combustion system where the oxygen required for reaction is provided. Even after recycling of these ash, the carbon-char in the ash is high in fluidized bed systems where the temperature of operation of the bed is influenced by the ash properties. To improve the carbon utilization, combustion of these char in a separate device is adapted. In order to enable an easy handling and further to effect pressure seal, the ash is generally cooled before taking it to the char combustor. US patent no. 5666801 dated 16th September 1997 under the Combined cycle power plant with integrated CFB devolatilizer and CFB boiler by Mr. Rohrer: John W. discloses a method in which coal is de-volatalized in a Circulating Fluidized Bed devolatiliser / Thermal Cracker and the char is burnt in a CFB Boiler. The fluidized bed could be a classical bubbling bed, a fast bed or a circulating bed where generally high volatile and high reactive bituminous, sub bituminous or lignite fuel is gasified in the gasifier to the maximum extent and un-burnt char along with the ash (either in full or partly) is burnt in conventional bubbling type combustor. The ash along with the char from the bottom of the bed and fly ash are removed through a cooler, extractor (to control the rate of removal) and a lock system consisting of vessels, isolation devices (ball valves), pressurizing / depressurizing means, before discharging through a suitable means into the char combustor. The char combustors mostly work at atmospheric pressure. This leads to a large system for ensuring proper combustion especially for fly ash. Even when the combustor is operating at elevated pressure, the ash is cooled to facilitate extraction. Such a method not only requires the additional equipment, but also cooling the ash / char results in lower efficiency of combustion / heat utilization. It also requires support fuel to maintain the high bed temperature for efficient combustion of char. OBJECTS OF THE INVENTION It is an object of the present invention to provide a fluidized bed char combustion device adaptable to a fluidized bed gasification system which eliminates the disadvantages of the prior art. Another object of the present invention is to provide a fluidized bed char combustion device adaptable to a fluidized bed gasification system which ensures efficient combustion of char present in the combustible material. A further object of the present invention is to provide a fluidized bed char combustion device adaptable to a fluidized bed gasification system which uses the sensible heat of the ash / char to aid combustion without the need of any support fuel thereby making the fluidized bed gasification system efficient and cost effective. A still further object of the present invention to provide a fluidized bed char combustion device adaptable to a fluidized bed gasification system which is compact and does not require additional means for cooling the ash / char to facilitate extraction. SUMMARY OF THE INVENTION Accordingly there is provided a fluidized bed char combustion device adaptable to a fluidized bed gasification system, the system comprising a gasifier, atleast one particulate collection means retaining the ash and char particles separated from the gas, and a bulk solid recirculator provided optionally for recycling the solids into the gasifier, the device comprises a diversion means for diverting the solid from the collection means to the gasifer via a parallel stream; a first fluidized bed char combustor for inputting one of air and air-oxygen mixture in the combustor, the first fluidized bed char combustor simultaneously controlling the temperature of the input including the temperature of the fluidized bed independently and/or combinedly thereby achieving combustion of the char material present in the solids input; the generated flue gas including left-out char being admitted to the gasifier, the resultant coarse ash including further left out char particles being extracted from the bottom of the gasifer; a second fluidized bed char combustor having atleast one heat transfer coil, and receiving the coarse ash including further left-out char particles from the gasifier for combustion therein, the flue gas generated being passed to a heat recovery means, the coarse ash being disposed in two stages firstly via the bottom of the combustor and secondly via the heat recovery means. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 - Shows a block diagram of a fluidized bed char combustion device adaptable to a fluidized bed gasification system according to the present invention. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The gasification system consists of a pressurized fluidized bed gasifier (1) where the gasification is carried out to the maximum extent unlike only devolatilising/cracking. In this system, the coal is fed either directly by pneumatic injection or through a bulk solid recirculator into the gasifier bed being kept actively fluidized by air, air-stream mixture distributed uniformly through the air distributor. Gasification reaction takes place in the bed and the product gas along with finer ash and char particles leave the gasifier vessel at the top. Relatively coarser ash and char particles retained in the bed is extracted through the bottom. In a particulate collection means (2) like cyclone (s), most of the particle carried by the gas is separated. The gas leaving the collection means (2) is then cooled in a heat recovery means (7) like steam generator and/or air heater and cleaned further for removing the remaining dust such that the product gas is suitable for applications like burning in a gas turbine combustor. The particles removed in the collection means (2) is then recycled into the gasifier (1) with a bulk solid recirculator (not shown). The device is provided with a parallel stream (PS) to divert the solid from the collection means (2) to the gasifier (1) directly by a diverting means (3) like cone valves or siphon seal or loop seal or seal pot, without passing it through a fluidized bed char combustor 4(1). The proportion of the material diverted could be varied from 0 to 100%. Alternatively, the device may consist of a single stream (ss) to recirculate the entire material through a first fluidized bed char combustor (4 (1)). The first fluidized bed char combustor 4(1) comprising a vessel for ensuring proper fluidisation velocity and residence time, an air distributor, an inlet connection from the separating means (3) and a return line to the gasifier (1). By admitting required quantity or air, air-oxygen mixture and controlling the temperature of the ash diverted, air supply, cooling coils and bed segments independently or combinedly combustion of the char present in the material is achieved. The flue gas formed along with the ash and any left out char is admitted into the gasifier (1). Provision is also made to remove the ash from the first combustor (4(1)) for disposal directly or through a second char combustor 4(2) described below. The coarse ash and char particles extracted from the bottom of the gasifier (1) is taken to a second char combustor 4(2) for burning the char. The flue gas from the combustor is cooled and cleaned in a heat recovery means (5(2), 6). When the proportion of char in the ash extracted from the bottom is within acceptable level for disposal- for some coals or certain operating conditions- the second combustor 4(2) is used for cooling the material extracted. The gas can also be used for pressurizing of locks. The material of construction of the components have either the capability to withstand the temperature- in which case it is insulated outside to prevent heat loss and for safety- or it may be cooled or refractory lined. The fluidizing medium for the first char combustor 4(1) is air and / or oxygen. By having heat transfer coils immersed in the bed of the second char combustor 4(2) and controlling the ash/char feed and air/oxygen to the bed, the temperature of the bed is maintained within a desired range. We Claim ------------- 1. A fluidized bed char combustion device adaptable to a fluidized bed gasification system, the system comprising a gasifier (1), atleast one particulate collection means (2) retaining the ash and char particles separated from the gas, and a bulk solid recirculator provided optionally for recycling the solids into the gasifier (1), the device comprising: - a separation means (3) for diverting the solid from the collection means (2) to the gasifer (1) via a parallel stream (PS); - a first fluidized bed char combustor (4(1)) for inputting one of air and air-oxygen mixture in the first combustor (4(1)), the first combustor (4(1)) simultaneously controlling the temperature of the input including the temperature of the fluidized bed independently and/or combinedly thereby achieving combustion of the char material present in the solids input, the generated flue gas including left-out char being admitted to the gasifier (1), the resultant coarse ash including further left out char particles being extracted from the bottom of the gasifer (1); - a second fluidized bed char combustor (4(2)) having atleast one heat transfer coil, and receiving the coarse ash including further left-out char particles from the gasifier (1) for combustion therein, the flue gas generated being passed to a heat recovery means (5(2),6), the coarse ash being disposed in two stages firstly via the bottom of the combustor 4(2)) and secondly via the heat recovery means (6). 2. The device as claimed in claim 1, wherein the char combustors 4(1), 4(2), the heat recovery means 5(2), 6 and the separation means (3) are outwardly insulated to prevent heat loss. 3. The device as claimed in claim 1, comprising a single stream (SS) for recirculating the entire solids via the first fluidized bed char combustor 4(1) instead of parallelly diverting a portion via the bulk-solid recirculator. 4. A fluidized bed char combustion device adaptable to a fluidized bed gasification system as herein substantially described and illustrated with reference to the accompanying drawing. A fluidized bed char combustion device adaptable to a fluidized bed gasification system comprising of a gasifier (1), atleast one particulate collection means (2) to retain the ash and char particles separated from the gas and a bulk solid recirculator provided optionality for recycling the solids into the gasifier (1) is comprised of a separation means (3) for diverting the solid from the collection means to the gasifier (1) via a parallel stream (PS), a first fluidized bed char combustor [4(1)] for inputting air and air-oxygen mixture in the first combustor [4(1)]. The first combustor controls the temperature of the input and of fluidized bed and achieves combustion of the char materials present in the solid input. The gasifier (1) receives the generated flue gas that includes left out char. The resultant coarse ash including further left out char is extracted from the bottom of the gasifier (1). The device is further comprised of a second fluidized bed char combustor [4(2)] having at least one heat transfer coil and receives the coarse ash including further left out char particles from the gasifier (1) for combustion therein. The flue gas generated is being passed to a heat recovery means [5(2),6]. The coarse ash is then disposed in two stages firstly via the bottom of the combustor 4(2) and secondly via the heat recovery means (6).

Documents:

357-KOL-2005-FORM-27-1.pdf

357-KOL-2005-FORM-27.pdf

357-kol-2005-granted-abstract.pdf

357-kol-2005-granted-claims.pdf

357-kol-2005-granted-correspondence.pdf

357-kol-2005-granted-description (complete).pdf

357-kol-2005-granted-drawings.pdf

357-kol-2005-granted-examination report.pdf

357-kol-2005-granted-form 1.pdf

357-kol-2005-granted-form 18.pdf

357-kol-2005-granted-form 2.pdf

357-kol-2005-granted-form 3.pdf

357-kol-2005-granted-gpa.pdf

357-kol-2005-granted-reply to examination report.pdf

357-kol-2005-granted-specification.pdf