FIELD OF INVENTION
The invention relates to pressurized fluidized bed gasification. More particularly, the present invention relates to a fluidized bed gasification system with integrated char gasifier fluidizing with steam.
BACKGROUND OF THE INVENTION
Gasification of coal, lignite and other fuels in pressurized fluidized/entrained bed systems are being adopted extensively for application in Integrate gasification combined cycle and other use. 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 bottom ash is high compared to the combustion system where the oxygen required for reaction is provided. Even after recycling of these ashes, the carbon-char-in the ash is high in fluidized bed systems where the temperature of operation of the bed is decided by the ash properties. To improve the carbon utilization, combustion of these char in a separate system is adopted. In order to enable handling and 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 title Combined cycle power plant with integrated CFB devolatilizer and CFB boiler by Mr. Rohrer:John W. discloses a method in which coal is de-volatilized in a Circulating Fluidized Bed de-volatilizer/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 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. Besides the additional equipment, 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.
Another US patent no. 3803023 dated April 9. 1974 titled "Steam Gasification of coke" relates to coking process.
Indian patent IN233674 "pressurized fluidized bed gasifier with integrated char combustor" is for a similar application. However the patent envisages combustion of the char to improve the carbon conversion. Though combustion improves the carbon utilization, the resultant steam is used only in steam cycle, which is less efficient.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a system of pressurized fluidized gasification with integrated char gasifier fluidizing with steam which eliminates the disadvantages of the prior art.
Another object of the invention is to propose a system of pressurized fluidized gasification with integrated char gasifier fluidizing with steam which ensures efficient gasification of char present in the material.

Yet another object of the invention is to propose a system of pressurized fluidized gasification with integrated char gasifier fluidizing with steam which is capable to use the sensible heat of the ash/char to aid gasification without the need for any support fuel thereby making the fluidized bed gasification system efficient and cost effective.
A further object of the invention is to propose a system of pressurized fluidized gasification with integrated char gasifier fluidizing with steam which provides fluidized bed char gasifiers which are compact and do not require additional means for cooling the ash/char to facilitate extraction.
SUMMARY OF THE INVENTION
Accordingly there is provided a fluidized bed char gasification device adaptable to a fluidized bed gasification system comprising a gasifier, at least 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 gasifier via a parallel system; a first fluidized bed char gasifier for inputting steam in the gasifier, the first fluidized bed char

gasifier simultaneously controlling the temperature of the fluidized bed independently and/or combinedly thereby achieving gasification of the char present in the solids input.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - shows a block diagram of a fluidized bed char gasification device adaptable to a fluidized bed gasification system according to the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION
As shown in Fig.l, the gasification system consists of a pressurized fluidized bed gasifier (1) where the coal is fed either directly by pneumatic injection or through the bulk solid recirculator into the gasifier bed kept actively fluidized by air (13), air-steam 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 are extracted through the bottom. In a particulate collection device (2) like cyclone (s), most of

the particle carried by the gas is separated. The gas leaving the collection device (2) is then cooled in a heat recovery means (5) 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 (char + Ash) (15) 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 gasfier (1) through a fluidized bed char gasifier 4(1) by a diverting means (3) like cone valves or siphon seal or loop seal or seal pot. The proportion of the material diverted could be varied from 0 to 100%. Alternatively, the device may consist of only one stream (SS) to recirculate the entire material through the first fluidized bed char gasifier 4(1). The first fluidized bed char gasifier 4(1) comprising a vessel for ensuring proper fluidization velocity and residence time, steam distributor, an inlet connection from the separating means (3) and a return line (6) to the gasifier (1). By injecting required quantity of steam (9), and controlling the temperature as required by controlling the ash diverted and/or adding material which acts as a catalyst (10), gasification of the char present in the material is achieved. The fuel 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 (11) form the first char gasifier 4(1) for disposal directly.
The coarse ash and char particles extracted from the bottom of the gasifier (1) is taken to a second char gasifier 4(2) for gasifying the char. The fuel gas from the second char gasifier 4(2) is taken to gasifier (1) to mix the syngas. When the proportion of char in the ash extrcated from the bottom is within acceptable limit for disposal-for some colas or certain operating conditions- the second gasifier is not used, but when used, provision is made to remove the ash (14) from the second char gasifier 4(2) directly for disposal. 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 char gasifiers 4(1) and 4(2) is steam (7, 8).
The present invention uses the sensible heat of the ash/char to aid gasification without the need for any support fuel thereby making the fluidized bed gasification system efficient and cost effective. Also the invention provides fluidized bed char gasifiers 4(1), 4(2) which are compact and do not require additional means for cooling the ash/char to facilitate extraction.

WE CLAIM:
1. A system of pressurized fluidized gasification with integrated
char gasifier fluidizing with steam and a method for the same
comprising:
a gasifier (1) for gasification of coal;
at least one particle collection means (2) for retaining the ash
and char particles separated from the gas;
at least one separation means (3) for diverting the solid from the
collection means (2) to the gasifier (1) through a parallel stream
(PS); characterised in that a first fluidized bed char gasifier 4(1)
achieves gasification of the char present in the material diverted,
char and ash (15) from the collection means (2); and
a second fluidized bed char gasifier 4(2) receives the coarse ash
and char particles (12) from the bottom of gasifier (1) for
gasifying the char when a heat recovery means (5) collects,
cools and cleans the product gas.
2. A system of pressurized fluidized gasification as claimed in claim
1, wherein the char gasifiers 4(1), 4(2) are insulated to prevent
heat loss.

3. A system of pressurized fluidized gasification as claimed in claim
1, wherein the char gasifier 4(1) comprises of a vessel for proper
fluidization velocity and residence time, a steam distributor, an
inlet connection (16) from the separating means (3) and a return
line (6) to the gasifier (1).
4. A method of pressurized fluidized gasification with integrated
char gasifier by injected steam comprising:
feeding the coal into the gasifier (1) while keeping the gasifier
(1) bed actively fluidized by air (13), air-steam mixture;
gasifying the materials in the bed of gasifier (1);
collecting the product gas from the gasifier (1) in the collection
means (2);
allowing the product gas (15) to move into heat recovery means
(5); characterised in that the particles (char + ash) (15) is
recycled from the collecting means to the gasifier (1) with a solid
recirculator wherein the solid is diverted by a parallel stream to
the said gasifier through a fluidized bed char gasifier 4(1) by a
diverting means (3) and
a second fluidized bed char gasifier 4(2) receiving the coarse ash
and char particles from the bottom of gasifier (1) gasifies the
char that passes to the gasifier (1).

5. A method of pressurized fluidized gasification as claimed in claim 4, wherein the entire material is re-circulated through the first fluidized bed char gasifier (1) with a single stream (SS).
6. A method of pressurized fluidized gasification as claimed in claim 4, wherein gasification of the char present in the material is achieved by injecting required quantity of steam (9), controlling the temperature and controlling the ash diverted and adding material acting as catalyst (10).
7. A method of pressurized fluidized gasification as claimed in claim 4, wherein the fluidizing medium for the char gasifiers 4(1) and 4(2) is steam (7, 8).

A system of pressurized fluidized gasification with integrated char gasifier fluidizing with steam comprises of a gasifier (1) for gasification of coal, at least one particle collection means (2) for retaining the ash and char particles separated from the gas and at least one separation means (3) for diverting the solid from the collection means (2) to the gasifier (1) through a parallel stream (PS). A first fluidized bed char gasifier 4(1) achieves gasification of the char present in the material diverted, char and ash (15) from the collection means (2) and a second fluidized bed char gasifier 4(2) receives the coarse ash and char particles (12) from the bottom of gasifier (1) for gasifying the char when a heat recovery means (5) collects, cools and cleans the product gas (17) while char gasifiers 4(1) and 4(2) have provisions for ash disposal (11,14).