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FIELD OF INVENTION:
This invention generally relates to a fluidtsed bed coal gasification reactor for effective
gasification or combustion of coal or carbonaceous particles. More particularly, the
invention relates to an improved pressurized fluidized bed gasification reactor adaptable*
in particular in a coal baaed combined cycle power plant
BACKGROUND OF THE INVENTION
Fluidised bed reactors are used to gasify coal tor power generation, production of
chemicals combustion and steam generation Typically they consist of a reactor chamber
and a lower distributor plate for supporting a bed of paniculate materials which usually
comprise carbonaceous or fuel material, inert bed material such as coal ash and
adsorbents tor removal of Sox. The distributor plate has typically a plurality of nozzles or
openings to allow passage of the fluidising/reacting gaseous media into the reactor, A
wind box or air plenum is disposed below the grid plate and gas or air is introduced into
the reactor above which keeps the bed above in a suspended stale. A compressor or
blower is used to deliver gases into the plenum chamber at the required pressure. Hie gas
flows upwardly into the fluidised b&& reactor through th? nozzles located on th$
distributor plate and enables the particulates in the bed to be suspended in a stream of air
or gases. As a result of this suspension of particulates in the flutdising media good mixing
of the particulates and gases is achieved in the reaction chamber. This results in
essentially uniform temperatures over die height of the fluidised bed resulting in effective
gasification or combustion of the coal or carbonaceous particles wilh good heat and mass
transfer characteristics.
Pressurised Fluidised Bed Coal Gasification Reactor is a preferred means to convert coal
into fuel gases for burning in a gas turbine combustor to generate electric power. The
process is especially suited for conversion of high ash coals, such as Indian coals
containing mineral matter in the range of 30 to 40%. The thermal energy in the exhaust of
the gas turbine is utilised in a bottoming cycle, for example a Ranking* cycle, to generate

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additional electric power. Tliere are several configurations utilising a gas turbine or aiuel
cell which depend on tlie fluidised bed coal gasifler to provide the fuel £&£«& for power
generation. Capacities required of the pressurised fluidised bed coal gasification reactors
has to be high for power generation applications. Increase in capacities of fluidised bed
coal gasifiers are obtained either by increasing the pressure of operation of the gasifier or
fay an increase in the diameter of the fmidiaed bed 2one in the coai gasification reactor.
However the maximum pressure for which the gasifier can be designed to maximise the
cycle efficiency is mainly dependent on the fuel gas entry specifications of the gas
turbine. And operating the gasifier beyond this maximum pressure wilt be detrimental to
overall cycle efficiency. After the optimum gasifier pressure is determined based on gas
turbine requirements the only way to increase the capacity of a single gasiiier is to
increase the gasitler diameter. It is well appreciated and accepted that increase in
diameter of a fluidited bed gasifier has limitations mid requires extensive testing because
of changes in the hydrodynamic behavior with reactor diameter which affects coal
conversion. Attempts to scale up from pilot sized gasifiers (400-50Gmm ID) to sizes
larger than 2m ID have resulted in several failures. On the other hand recourse to a
number of smaller gasifiers to meet the fuel gas requirements will be detrimental to the
overall economics of the power plant* in addition to the cost and complexity of increasing
the number of downstream gas treatment and heat recovery streams.. The present
invention provides a means to increase the capacity of a fluidised bed coal gastfier, by
providing atleast of two fluidised bed reactors inside a single pressure housing* such that
the diameter of the reactor bed is kept within safe limits from hydrodynamics point of
view, established by testing or within experimentally validated zone of hydrodynamics of
the process. Such a configuration has the added advantage of having a single stream of
cyclone separators and heat recovery boiler as opposed to having multiple units having
the same reactor diameter for the fluidised bed coal gasitler.

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OBJECTS OF INVENTION:
It is an object of this invention to propose an improved pressurized ilmdized bed
gasification reactor adaptable, in particular in a coal based combined cycle power plant,
which provides higher per-unit conversion capacity.
A further object of the invention is to propose an improved pressurized fluidized bed
gasification reactor adaptable, in particular in a coal based combined cycle power plant.
which limits the diameter of the flmdistng zone of the reactor to values within The ranges
of hydrodynamic scalability as established by experimental testing or analytical methods.
It ia atill further an object of this invention to propose an improved pressurized fluidized
bed gasification reactor adaptable, in particular in a coal based combined cycle power
plant, which reduces the number of independent fluidified bed gasifier units to cater for
the requirements of, for example a gas turbine, in a coal based combined cycle power
plant
It is another object of this invention to propose an improved pressurized fluidizsd bed
gasification reactor adaptable, in particular in a coal based combined cycle power plant
which minimizes the number of heat recovery and dust removal streams required to meet
the load requirements of a gas turbine in a coal based combined cycle plant.
It ia yet another object of this invention to propose an improved pressurized fiuidized bed
gasification reactor adaptable, in particular in a coal based combined cycle power plant
which reduces the numbers of coal feeders and ash removal equipment per unit of gasifier
throughput, thereby effecting reduction ia installed cost of the plant.
It is yet a further object of this invention to propose an improved pressurized fluidized
bed gasification reactor adaptable, in particular in a coal based combined cycle power
plant.

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which be configured with atleast two iluidised bed reactor zones within a common
pressure housinc, to fetch the attendant benefits of cost reduction, smaller overall plant
area requirement as opposed to the prior art reactors.
It is still another object of mis invention to propose an improved pressurised fluidized
bed gasification reactor adaptable, in particular in a coal based combined cycle power
plant, in which suitable material transfer port be provided between the two reactor beds
housed inside a common pressure housing, to enhance uniformity in process conditions
such as reactor bed temperatures and gas compositions in the congmently disposed
fluidised bed zones, which in turn improve the performance of die gasifier.
It is also an object of this invention to propose an improved pressurized fhiidized bed
gasification reactor adaptable, in particular in a coal based combined cycle power plant,
in which independent plenums be designed for introducing the tluidising media into the
two fluidised bed zones, so that it is made possible to start bed ignition and startup of one
of the beds initially, and subsequently build up the bed in the other fluidised bed by
enabling transfer of hot bed material from the first bed into the other through specially
provided transfer ports or openings in the common metal supported refractory lined
reactor wall between the two beds. This is achieved after initial ignition and start up of
the bed in a static mode and subsequent increase in height of the expanded bed by
constant fuel addition in the first bed and causing hot bed material to move into the
adjacent bed through ports provided tor die same, till such time that both beds build up to
die same bed height, whereupon fuel and fhiidisiog media are introduced mio me othelr
bed also and the two start operating in unison at the same bed height
It is also a further object of this invention to propose an improved pressurized fluidtzed
bed, gasification reactor adaptable, in particular in a coal based combined cycle power
plant, which has atleast two independent plenums for the two iluidised bed reactors
housed inside a common pressure housing, to achieve better distribution of the iluidising
media across the individual fluidised bed zones* to improve the process efficiency, by
improved gas-particle contact

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It is again an object of this invention to propose an improved pressurized fluidized b$d
gasification reactor adaptable, in particular in a coal based combined cycle power plant,
which be provided with openings in the common wall separating the two flutdising b^d
reactors at a height from the bottom of the gasifier of approximately one diameter of the
fluidised bed reactor, whereby initial heating and start up of the fluidised bed can be done
by starting only one of the beda and subsequently transferring the hot bed material from
the first one into the other after the first bed is fluidised and constant coal feed is initiated.
This provision be planned to minimise startup energy requirements in addition to other
benefits detailed above.
It is yet again an object of this invention to propose an improved pressurized fkudized
bed gasification reactor adaptable, in particular in a coal based combined cycle power
plant, in which the independent plenums for the two fhiidised bed zones, in combination
with the material transfer ports or openings reduces the bubble growth in the axial
direction of the fluidised bed, because of pressure perturbations caused by transfer of
material across the transfer ports.
Accordingly, there is provided an improved pressurized fluidized bed gasification reactor
adaptable, in particular in a coal baaed combined cycle power plant, comprising :
Atleast one free board zone acting as a common zone provided with a gas outlet a
fiuidized bed reactor zone having atleast one fluidizing gas plenum for entry of
fluidizing media; atleast one ash removal pipe flowably connected at one end with the
reactor zone, the other end leading to a bottom ash discharge port; atleast one coal inlet
for provision of coal into the reactor zone,
Hie fluidized bed reactor zone is configured as atleast two separate reaction zones
having identical internal diameter to correspond together the cross-sectional area of the
undivided reactor zone, and in that a separating member is disposed between the atleast

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two separate reaction zones And a separating member being provided with a transfer port
so as to maintain a continuous inter-transfer of bed material and gaseous reactants
between the atleast two separate reactor zones.
The invention will be better understood in the following description according to the
accompanying drawing in a non restrictive manner wherein
Fig. 1 represents a Schematic layout of an existing Integrated Gasification Combined
Cycle Plant with a Pressurised Fluidised Bed Gamfier.
Fig. 2 represents a schematic vertical cross sectional drawing of an existing Pressurized
Fluidised Bed Coal Gasifier.
Fig, 3 represents a Schematic showing the arrangement of two fluidised bed reactors
housed in a single pressure vessel.
Fig. 1 indicates the major equipment and sub systems which constitute an Integrated
Gasification Combined Cycle Plant, wherein the present invention is intended to be
employed.
Fig. 2 shows the configuration of a Presumed Fluidised Bed Coal Gasifier having an
internal diameter in the fluidising zone of *V2d*
Fig. 3 shows the present invention which substitutes two fluidised bed zones of internal
diameter *d9in place of a single fluidised zone of internal diameter sV2d\ inside a
common pressure housing.

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Fig. 1 shows a schematic layout of an Integrated Gasification Combined Cycle Plant
based on a Pressurised Fluidised Bed Coal Gasifier (1), indicating the present art. Several
variations of the scheme are possible which is centered on the Pressurised Fluidised Bed
Coal Gasifier (1), The Pressurised Fluidised Bed Coal Gasifier (1) typically has provision
for entry of coal {2} into the gasifier (1), provision at the bottom for ash removal (3),
provisions for entry of fluidising/gasifying media (4), provision for gas exit etc, The fuel
gas stream exiting the gasifier at temperatures of approximately. 1000 deg. € is typically
routed thfongh a series of dust, separation devices (eg: cyclone separators) followed by
heat recovery equipment where die fuel gas temperature is brought down to
approximately 125 to 150 deg C to enable use of pressure and flow control elements
which cannot be reliably designed or operated at the temperatures prevalent at the gasifier
outlet, before further gas cleaning and conditioning steps to achieve gas turbine
specifications for fuel gas admission into the turbine combusfor.
Fig 2 shows a vertical erosa sectional drawing of a Pressurised Fluidised Bed Gasifier for
coal, which is intended to convert coal or other carbonaceous materials in the solid state
into fuel gases. Tlie fluidised bed zone is configured as a single reactor without partition
or separator, which is the existing practice or art Hie gasifier has a fluidised bed reactor
zone (5) of internal diameter in the fluidising zone of W2 d\ a free board zone (6), a
distributor (7) for introducing me fluidiaing reaction media into the reactor disposed
above, located in the plenum (8), provision for coal entry (9) and fluidising media entry
(10). A nozzle for fuel gas outlet (11) is provided near the top of the reactor. The
tluidised bed reactor ta lined internally with refractory and insulation material (12).
Fig, 3 shows the arrangement of the present invention intended to be the equivalent of the
reactor described in fig.2 and consists of two fluidised bed reactor zones of internal
diameter *d\ the two distinct fluidised bed reactor zones together have a cross sectional
area equivalent to that provided in the fluidised bed reactor zone (5) referred above with

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an internal diameter in the fluidismg zone of S2 d' the two fluidised bed reactor zones
(13) have a common fireedboard region (14) aad gas outlet connection (15). The two
fluidised bed reactor zones are provided with separate fluidismg gas plenums (16) tor
entry of me tluidising media such as air and steam and ash removal pipes (17). The ash
and agglomerates discharged from the two reactors are combined into one stream before
exiting the gasifier through an opening (18) provided for bottom ash discharge The two
fluid bed reactors share a common freeboard region (14) where the bigger particles-
disengage and fall back into the fluidised bed region (13) and the gases along with fine
participate materials leave the gasifier through a single exit (15) provided at the top. A
metallic supporting and separating member (19) is provided to separate the two fmidising
reaction zones. Transfer ports or opening (20) are provided on this separating member to
provide inter communication of bed material and gaseous reactanfrs and products between
the two tluidising reaction zones.
Examples-Preferred Embodiments;
The preferred embodiment is as shown in fig. 3 Two separate fluidised bed reaction
regions (13) of internal diameter *d* are provided inside a common pressure housing with
independent fluidising gas plenum (16) for introducing me fluidmng media into the
fluidising reaction zones. The gasifier is provided with required numbers of coal inlet
provision (21). However the two fluidised bed reactors share a common ireedboard, gas
exit provision and bottom ash removal provision. Hie ash and agglomerates exiting the
respective reaction zones enter the plenum by means of individual pipe connections,
before they combine into one stream to exit the gasifier through the bottom ash opening
(18).
The preferred embodiment provides two distinct tluidising reactor zones inside a
common gasifier pressure housing. Hie diameter of the individual fluidising reactor
zones are chosen in such a manner as to minimize scale up uncertainties as a consequence
of choosing a larger diameter single fluidised bed, especially on account of uncertain or
unknown bed hydrodynamics. As an example if me required diameter for a coal gasifier
with a single bed to meet fuel gas requirements is ci2 d* the same can be met with the

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preferred embodiment having two distinct fluidising zones each of diameter *d\ when the
hydrodynamics are well established at the diameter *d'.
The preferred embodiment retain? many of the advantages of having a single larger
diameter gasifier, such as, a common ash extraction system after the two ash streams
from the two imidised bed zones are combined into one, ahead of the bottom ash opening
as described above, a common gas exit connection, a common freeboard region ahead of
the fuel gas exit nozzle etc. The advantage of a single stream from the fuel gas exit nozzle
connecting to dust separation devices and heat recovery devices are maintained, just the
same as in the case of a gasifier having a single fluidising zone.
The preferred embodiment provides for interconnection of the two fluidising bed zones as
described above for the purposes of faster startup, reduction of startup energy
requirements. Hie interconnecting ports fcher improve the flmdising characteristics of
the beds by breaking bubbles formed in the fluidising zone above the distributor plate
because of small pressure fluctuations and differences caused in the two fluidieing zones
due to material exchange between the two fluidised bed zones.
The scope of the invention as narrated herein is defined in the appended claims.

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WE CLAIM
1. An improved pressurized fluidized bed gasification reactor adaptable, in particular
in a coal based combined cycle power plant, comprising ;
- one free board zone (14) acting as a common zone provided with a gas outlet
(15);
- a fluidized bed reactor zone (13) having atleast one iluidizing gas plenum (161 for
entry of fluidizing media;
- atleast one ash removal pipe (17) flowably connected at one end with the reactor
zone (13), the other end leading to a bottom ash discharge port (18);
- atleast one coal inlet (21) for provision of coal into the reactor zone (13),
characterized in mat the fluidized bed reactor zone (13) is configured as atleast two
separate reaction zones (13', 13") having identical internal diameter to correspond
together the cross-sectional area of the un-separated reactor zone (05), and in that a
separating member (19) is disposed between the atieast two separate reaction zones (13',
13"), the separating member (19) being provided with a transfer port (20) so as to
maintain a continuous inter-transfer of bed material and gaseous reactants between the
atieast two separate reactor zones (13', 13").
2. The gasification reactor as claimed in claim 1, wherein each reaction zone (13*,
13") is provided with associated flmdizing gas plenum (16).
3. An improved pressurized fluidized bed gasification reactor adaptable, in particular
in a coal based combined cycle power plant, as herein described and illustrated with
reference to the accompanying drawings.