TECHNICAL FIELD
The present disclosure relates to a fluidized bed coal gasifier. In particular, the present disclosure relates to fines capture system for high pressure and temperature fluidized bed coal gasifier.
BACKGROUND
Coal gasification involves conversion of solid coal fuel into gaseous fuel known as "Synthesis Gas" or "syngas" (CO & H2 as major components) when reacted with oxygen or air under reducing atmosphere. The process involves reaction of sub-stoichiometric oxidant (air/oxygen) with coal. The coal first devolatilizes to release volatile components. Devolatilized coal i.e. char, then gasifies in presence of oxidant (air/oxygen) and steam and is converted to syngas and ash. Two types of ash forms during the process, 1) fly ash fines which are entrained along-with synthesis gas; 2) the rest being denser course bottom ash, which gets removed in the bottom section of the reactor. At any time, the fluidized bed contains ash, char (devolatilized coal) and partially gasified char. The reaction involved in the gasification are
Devolatalizes in heat
Coal > Char + ash (1)
Gasification
Char + 02 or Air + H20 > H2 + CO + Other gases (2)
Fluidized bed coal gasifier requires uniform mixing of reacting (feed) gases i.e. air/02 + steam and coal/char in the gasifier bed for a better performance like avoiding hot spots which leads to agglomerate formation, leading to bed defluidization. Better control of temperature below ash softening temperature of ash, high carbon conversion efficiencies etc are desired for best possible operation.
Gasifier bed mainly consists of particles of ash and char with size varying from 0.2 mm to 2 mm. Also, fluidized bed gasifier requires continuous removal of ash through the bed to ensure constant pressure drop inside the bed. But the existing systems do not address this problem and thus there is always a certain fraction of coal that gets out along with ash which has a impact on carbon conversion rate. So, a special provision for ash withdrawal is required to be made in distributors.
2

In prior arts, the distributors like conical, central pipe etc. limits the utilization of carbon owing to lower operating temperatures as a consequence of agglomerate formation due to improper mixing. Higher temperature operation is desired in these systems, but this leads to agglomeration of gasifier bed material due to non-uniformity of hot air + steam flow. This in turns give operational problems and difficulties in ash discharge.
Reference is made to the Indian Patent number 240767, which discloses water cooled flat distributor in which cooling tubes are parallel pipes and coolant water enters at one end of distributor and exits at the other end of distributor. Considerable temperature gradient on the plate results in the inefficient cooling. This distributor has ash removal system in the form of simple cylindrical pipe with uniform cross section. As the bed is mixed uniformly, there is always certain fraction of unreacted coal that gets out along with ash. So, the main drawback of the prior art is that it impacts the carbon conversion through the lost carbon fines through ash withdrawal pipe. Also, this disclosure requires more surface area and coolant for cooling.
Reference is made to US Patent Number 4435364, which discloses the apparatus for withdrawing agglomerated solids e.g. ash particles fused together, from a fluidized bed in which internals viz. spiral or descending ridges are positioned on the interior surface of constricted cylindrical opening of the venturi to permit variable and increased rates of agglomerates discharge with improved separation and classification of the solid material. However, this venturi assembly is attached to the conical type of distributor.
Furthermore, there is a specific provision to deliberately make ash agglomerate of sufficient size that will eventually fall. Char fines are combusted in the venturi to convert them into agglomerates. The drawback with respect to this disclosure is that, precisely controlled agglomerate formation is required and if bigger agglomerate that form inside the bed itself, get choked due to internals placed inside the venturi and overall effects the efficiency of the system.
Thus, in view of the drawbacks of hitherto prior arts, there is a dire need for the present disclosure which is suitable for gasifier and helps in proper distribution of feed/reacting gases and smooth ash discharge with fines capture at high pressure & high temperature. Further, a system is required with high carbon conversion as some of it is lost with the ash. Accordingly, the present disclosure provides an improved distributor system which overcome the aforesaid limitations of the prior art.

SUMMARY
The following presents a simplified summary of the disclosure in order to provide a basic understanding of some aspects of the disclosure. This summary is not an extensive overview. It is not intended to identify the key/critical elements of the disclosure or to delineate the scope of the disclosure. Its sole purpose is to present some concept of the disclosure in a simplified form as a prelude to a more detailed description of the disclosure presented later.
The main objective of the present disclosure is to provide a system comprising of flat plate type distributor with circular or spiral water cooling pipe arrangement and fines capture system in distributor leg with venturi effect, for high pressure and temperature fluidized bed coal gasifier.
The present disclosure discloses an ash withdrawal pipe for a flat plate type distributor of a fluidized bed gasifier. The said ash withdrawal pipe has an ash withdrawal passage defined by the ash withdrawal pipe for withdrawal of ash from the fluidized bed gasifier, the ash withdrawal passage having a first end to receive the ash and a second end for disposal of ash. The ash withdrawal pipe further has a steam inlet defined towards the second end of the ash withdrawal pipe. The steam inlet is configured to receive pressurized steam in the ash withdrawal passage. The ash withdrawal passage is defined by venturi between the first end and the steam inlet. The ash withdrawal pipe of the disclosure has a body defining the ash withdrawal passage and a cooling passage provided on an outer surface of the body for distribution of cooling water for cooling the body. The first end of the ash withdrawal pipe is configured for connection to a central portion of the flat plate type distributor. The flat plate type distributor comprises one or more flat fins (2) and one or more chimneys (7) extending upwardly from the distributor plate. Further, the flat plate type distributor has a cooling passage (water circulation pipes) running along the distributor plate for cooling the distributor plate. The said cooling passage for flat plate type distributor is in the shape of a spiral hexagon.
The disclosure mentions a fluidized bed coal gasifier having a casing of hollow interior and the ash withdrawal pipe and flat plate distributor as mentioned above. The gasifier have a primary inlet at the lower portion of the casing for receiving the reactant gas into the gasifier, a secondary inlet at the upper portion of gasifier for passing the fuel into the reactor, a primary

The present invetion provides modification of conventional apparatus of ash removal system by the way of venturi. In the present disclosure ash is not agglomerated but withdrawn as a free dry ash. Also, the char fines are recycled back to the bed. Furthermore, in the present disclosure the cooling arrangement is either, circular or spiral which is beneficial since, there exists turbulence inside cooling tubes due to continuous change in direction of coolant which helps in increased heat removal rate. So, saving on coolant for the same geometry and/or reduced pipe diameter of cooling tubes. The present disclosure also allows one to manipulate with respect to geometrical arrangement and number of chimneys in order to have desired uniform distribution as a result of efficient cooling arrangement.
BRIEF DESCRIPTION OF FIGURE
The above and other aspects, features, and advantages of certain exemplary embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings in which:
Figure 1 illustrates a schematic view of water cooled flat plate distributor integrated with ash withdrawal system.
Figure 2 illustrates a top view of the flat plate type distributor with water circulation system.
Figure 3 illustrates a front view of the flat plate distributor integrated with ash withdrawal system.
Figure 4 illustrates a schematic view of the flat plate distributor.
Figure 5 illustrates a schematic view of the gasifier system.
A persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may have not been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE DISCLOSURE
The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the disclosure. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.
Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the disclosure. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.
The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present disclosure are provided for illustration purpose only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.
It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.
By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.
Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.
It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not

preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
Coal gasification involves conversion of solid coal fuel into gaseous fuel known as "Synthesis Gas" or "syngas" (CO & H2 as major components) when reacted under reducing atmosphere with oxygen or air. The process involves reaction of sub-stoichiometric oxidant (air/oxygen) with coal. The coal first devolatilizes to release volatile components. The devolatilized coal is known as char. The char then gasifies in presence of oxidant (air/oxygen) and steam and is converted to syngas and ash. Two types of ash forms during the process, 1) fly ash fines which is entrained along-with synthesis gas. 2) The rest being denser course bottom ash, which gets removed in the bottom section of the reactor. At any time, the fluidized bed contains ash + char (devolatilized coal) + partially gasified char.
The gasifier of the present disclosure has a casing of hollow interior,
a primary inlet located in the lower portion of gasifier for passing reactant gas or gasifying
agent (10) inside the gasifier,
a secondary inlet for located at the top portion of the gasifier for inlet of coal/fuel (13),
a primary outlet located in the upper portion of the gasifier for extracting the product gas (14)
from the gasifier,
a secondary outlet located at the lower portion of the gasifier for extracting the ash (15) through
an ash discharge system,
a flat plate type distributor (16) is placed above the secondary inlet and the secondary outlet
and below the primary outlet and the primary inlet, for admission of the gasifying agent
(air/02+steam) or distribution of the reactant gas inside the casing of the gasifier,
a flat plate type distributor plate placed above the secondary inlet and the secondary outlet,
an ash withdrawal pipe configured for connection to the flat plate type distributor for withdrawing ash from the gasifier;
Bed material or gasifying media (17) is located above the distributor plate. The gasifier oxidizes the feed and converts it to a Synthesis Gas ("Syngas") as per reactions (1) and (2) specified above. During the process, the bed level & temperature is maintained at desired value to obtain the optimum carbon conversion. In an alternate embodiment the fluidized bed gasifier can operate at higher temperatures and high pressure. In another alternate embodiment the fluidized bed gasifier can operate at low temperatures and pressure.

The present disclosure mainly relates to a system comprising of flat plate type distributor with and fine capture system in distributor leg with venturi effect, for high pressure and temperature fluidized bed coal gasifier. The flat plate type distributor of the present invetion has a distributor plate for uniform distribution of the gas, an ash withdrawal pipe configured for connection.
The casing of the gasifier is the outer most part of the gasifier which covers the inner structure and has a hollow interior. The casing is primarily in the shape of the cylinder as shown in Figures 1 & 5. The casing gasifier has a diameter of more than 1.2m. The material of the casing is carbon steel. In an alternate embodiment the casing can be in the shape of of differential diameter cylinder for effective reaction. In a further alternate embodiment, the gasifier has a diameter of less than 1.2mm. In a further alternate embodiment, the material can be hard steel.
The primary inlet and secondary inlet are located in the lower and upper portion of the gasifier. The primary and secondary inlets are nozzles for passing the reactant gas and the coal respectively. In an alternate embodiment inlets can be deviated nozzle for a simple pipe for passing the streams into the reactor
The primary outlet and secondary outlet are located in the upper and lower portion of the gasifier. The primary and secondary outlet are nozzles for retrieving the product gas and the coal respectively. In an alternate embodiment inlets can be deviated or straight nozzle or a simple pipe.
The flat plate distributor as shown in figures 1, 2 and 3 includes the water cooled flat plate distributor augmented with ash withdrawal system inside the gasifier reactor. The flat plate type distributor consists of flat fins (2) welded in between the water circulation pipes (3) with interconnection water pipes (4) for connecting all of the water circulation rings (3). Figure 4 shows the isometrics of flat plate distributor while the top view of the flat plate with water circulating pipe is depicted in figure 2 & the side view is depicted in figure3. The purpose of water circulation is to cool down the flat plate having temperature of 850 °C -1050 °C to a temperature that a material can withstand safely and safe disposal of ash. Cooling water (5) is circulated inside the distributor system through outer shell of ash withdrawal pipe (6). Flat fins (2) are provided with chimneys (7) in regular intervals with height in the range of 75 - 125 mm. Chimney (7) consists of orifice holes (8) on its circumference with top end closed (9) on top of

it. Orifice holes (8) on the chimney (7) provide uniform distribution of fluidizing medium/reacting gases i.e. air/02 + steam (10) into the gasifier reactor (1). The distributor is provided with an ash withdrawal pipe (6) with a venturi (11) effect by means of steam inj ection through steam nozzle (12) for ash extraction with minimal loss of carbon fines with ash.
The fines capture system as disclosed above comprises an ash withdrawal pipe having a a first end to receive the ash and a second end for disposal of ash. The fines capture system has a steam inlet located toward the second end of the ash withdrawal pipe for the venturi effect. The first end of the ash withdrawal pipe is connected to the distributor plate. The ash withdrawal pipe has a venturi between the first end and the second end of the ash withdrawal pipe. The ash withdrawal pipe has a converging section and a diverging section. The venturi of the ash withdrawal pipe takes the unreacted char or carbon particles, which comes along with the ash, back into reaction zone. The first end of the ash withdrawal pipe receives the ash (along with char) settling from the reaction and its passed into the converging section which speeds up the velocity of the ash. The steam which is passed from the second end of the ash withdrawal pipe also passes through converging section which speeds up the velocity. As the steam and the ash enters diverging section of the pipe though the venturi, the fine char particles are separated from the ash due to their difference in settling velocity. The steam takes the chars back to the reaction. The ash withdrawal pipe has a ratio of a maximum diameter (outer edges) to and a minimum diameter (venturi) as 0.2 to 0.8.
The ash withdrawal pipe distributor is provided with a cooling system/ cooling arrangement around the body of the ash withdrawal pipe. The arrangement of cooling pipe is beneficial since, there exists turbulence inside cooling tubes due to continuous change in direction (continuous boundary layer separation) of coolant, in this case cooling water, which helps in increased heat removal. The ash withdrawal pipe and the flat plate type distributor is made of carbon steel and the cooling system avoids melting of the material. In an alternate embodiment the ash withdrawal pipe and the flat plate type distributor can be made of hard steel.
The present disclosure provides uniform distribution of air/02 and steam in a high pressure (up to 30 bar) and high temperature (850 °C -1050 °C) in a fluidized bed gasifier with maximum carbon conversion. The present disclosure prevents defluidization thereby maintaining uniform fluidizing velocity. To remove the heat, cooling water enters through ash withdrawal pipe, a venturi, passes upwards and then through circular/spiral pipes. In the vicinity of distributor,

highest temperatures of the order of 900 C -1000 C prevails due to exothermicity of the coal + oxygen reaction.
In one embodiment, the ash withdrawal pipe has a body defining the ash withdrawal pipe and a cooling passage provided on an outer surface of the body for distribution of cooling water for cooling the body.
In another embodiment, the ash withdrawal pipe is configured for connection to the central portion of the flat plate type distributor.
In another embodiment, the flat plate type distributor connected with ash withdrawal pipe has chimneys (7) extending from the distributor plate.
In another embodiment the flat plate type distributor, a cooling passage running on or below the distributor plate of the flat plate type distributor for distribution of cooling water.
In another embodiment the cooling passage is circular or spiral water cooling passage.
In another embodiment the cooling passage is spiral hexagon for effective cooling.
In another embodiment, the gasification reactor has a diameter value of more than 1.2 m
In another embodiment, Single and long curving flow passages with a uniform cross-section ensure intense turbulence, and high heat transfer coefficients. So, saving on coolant for the same geometry and/or reduced pipe diameter of cooling tubes for given cooling duty can be designed. Thus, water circulation in circular/spiral tubes provides better cooling. As a result, the area occupied by cooling pipes on distributor plate is reduced. This allows additional space for accommodating more chimneys and also for arrangement for different pitched chimneys. This combined effect will enhance the uniform distribution in the bed and allows operator to operate at higher temperatures in order to get maximum conversion without clinker formation. Since, operations at higher temperatures may result in clinker formation if the air/oxygen distribution is not proper.
NOMENCLATURE

Numeral Reference
1 Gasifier reactor
2 Flat Fins
3 Cooling water rings
4 Interconnecting cooling pipes
5 Cooling water
6 Ash withdrawal pipe
7 Chimney
8 Holes on chimney
9 Closed top end
10 Air/02 + Steam
11 Venturi for carbon fines removal
12 Steam
13 Fuel/Coal
14 Product gas
15 Ash extracted
16 Flat plate type distributor
17 Bed material or gasifying media
18 Reactant gas
Working Example:
The fluidized bed gasifier having a diameter of greater than 1.2m is charged (through secondary inlet) with coal of C grade having 30% to 40% ash content. The reactant gas of oxygen and steam is send into the gasifier by the primary inlet. The steam is also sent to the lower portion of the ash withdrawal pipe. The ash withdrawal pipe is rigidly fixed centrally to the lower portion of the flat plate type distributor. The primary inlet is located in the flat plate type distributor and the gas is distributed inside the reactor through chimneys present on the flat plate type distributor. The flat plate type distributor has 74 to 80 chimneys for even distribution of gas.

The ash withdrawal pipe of the present invetion having a maximum diameter (outer edges) of 100mm and a minimum diameter (venturi) of 50 mm is used and the ash settled were analyzed. The settled ash contains 99% ash and 1% char.
The conventional ash withdrawal pipe with straight cross section is used and the ash collected are analyzed through mass spectrometer to find that the settled ash has 96% of ash and 4% of char. On comparison to this the present disclosure allows for the fines to be captured and taking back into the gasifier.
It is also found that there is a wide variation in size distribution of char (devolatilized coal) fines and ash particles. The Venturi effect of the present invetion takes advantage of this difference between size and density of ash (2200-2400 kg/m3) and char particle (<1000 kg/m3). Higher velocity (at the venturi throat), lifts the less denser char particles back into the bed, while ash which is denser, gets over the gas velocity in venturi pipe and settles down. The velocity in venturi is carefully controlled for the desired separation of char particles.
So, it has been advantageous of using the ash withdrawal pipe of the present invetion as the fines are redistributed back to the reaction, Hence, it is clearly evident that the present invetion has several advantages, the present disclosure provides combination of flat plate with venturi type ash leg (1) that will improve the gasifier carbon conversion by arresting back the char particles with bottom ash through venturi effect. The flat plate will provide the uniform distribution which will prevent any hot spot in bed, allowing higher operating temperatures. The combination results in the increase in efficiency of gasifier as well as operational longevity. The present disclosure will prevent costly, tedious & prolonged shut downs, if agglomerates forms in the bed. The venturi pipe (11) is externally provided with water cooling which provides cooling of ash before going to ash extraction system.

We Claim:
1. An ash withdrawal pipe for a flat plate type distributor of a fluidized bed gasifier, the ash
withdrawal pipe comprising:
an ash withdrawal passage defined by the ash withdrawal pipe for withdrawal of ash from the fluidized bed gasifier, the ash withdrawal passage having a first end to receive the ash and a second end for disposal of ash;
a steam inlet defined towards the second end of the ash withdrawal pipe, the steam inlet configured to receive pressurized steam in the ash withdrawal passage; and
a venturi defined in the ash withdrawal passage between the first end and the steam inlet.
2. The ash withdrawal pipe as claimed in claim 1, wherein the ash withdrawal pipe comprises:
a body defining the ash withdrawal passage; and
a cooling passage provided on an outer surface of the body for distribution of cooling water for cooling the body.
3. The ash withdrawal pipe as claimed in claim 1, wherein the first end is configured for rigid connection to a distributor plate of a flat plate type distributor.
4. The ash withdrawal pipe as claimed in claim 3 wherein the ash withdrawal pipe is configured for connection to a central portion of the flat plate type distributor.
5. A flat plate type distributor for a fluidized bed gasifier comprising:
a distributor plate for distribution of the gas in a fluidized bed of the fluidized bed gasifier;
an ash withdrawal pipe configured for connection to a central portion of the distributor plate, an ash withdrawal passage defined by the ash withdrawal pipe for withdrawal of ash from the fluidized bed gasifier, the ash withdrawal passage having a first end to receive the ash and a second end for disposal of ash;
a steam inlet defined towards the second end of the ash withdrawal pipe, the steam inlet configured to receive pressurized steam in the ash withdrawal passage; and
a venturi defined in the ash withdrawal passage between the first end and the steam inlet.
6. The flat plate type distributor as claimed in claim 5, comprising one or more flat fins (2) and one or more chimneys (7) extending upwardly from the distributor plate.

7. The flat plate type distributor as claimed in claim 5, wherein the flat plate type distributor
has
a cooling passage running along the distributor plate for cooling the distributor plate.
8. The flat plate type distributor as claimed in claim 7, wherein the cooling passage is defined by one or more water circulation pipes (4).
9. The flat plate type distributor as claimed in claims 7 or 8 wherein the cooling passage is in the shape of a spiral hexagon.
10. A Fluidized bed coal gasifier comprising
a casing comprising a hollow interior;
a primary inlet (10) at the lower portion of the casing for receiving the reactant gas into the gasifier;
a secondary inlet at the upper portion of gasifier for passing the fuel into the reactor;
a primary outlet for as the upper portion of the gasifier for extracting the product gas;
a secondary outlet in the lower portion of the gasifier for extracting the ash;
a flat plate type distributor plate placed above the secondary inlet and the secondary outlet and below the primary outlet and the primary inlet, for distribution of the reactant gas inside the casing of the gasifier;
an ash withdrawal pipe configured for connection to the flat plate type distributor for withdrawing ash from the gasifier;
wherein the ash withdrawal pipe comprising:
an ash withdrawal passage defined by the ash withdrawal pipe for withdrawal of ash from the fluidized bed gasifier, the ash withdrawal passage having a first end to receive the ash and a second end for disposal of ash;
a steam inlet defined towards the second end of the ash withdrawal pipe, the steam inlet configured to receive pressurized steam in the ash withdrawal passage; and
a venturi defined in the ash withdrawal passage between the first end and the steam inlet.
11. The fluidized bed coal gasifier as claimed in claim 10, wherein the ash withdrawal pipe comprises:
a body defining the ash withdrawal passage; and

a cooling passage provided on an outer surface of the body for distribution of cooling water for cooling the body.
12. The fluidized bed coal gasifier as claimed in claim 10, wherein the flat plate type distributor comprises:
a distributor plate for distribution of the gas
a cooling passage running on or below the distributor plate of the flat plate type distributor for distribution of cooling water for cooling the distributor plate.