FIELD OF INVENTION
The present invention generally relates to the field of converting
carbonaceous materials such as biomass, waste, coal, organic materials etc.
to synthesis gas (syngas), typically obtained from indirect or oxygen-blown
gasification that is essentially free of tar or tar forming compounds and
wherein carbon conversion and yield of syngas in increased. More
particularly, the present invention relates to a one-stage bubbling fluidized
bed gasification system and method for producing low tar syngas under
adiabatic conditions. The gasification system and process must be designed
to be simple in terms of construction and operation however should
maximize carbon conversion efficiency leading to production of syngas with
near zero tar concentration.
BACKGROUND OF THE INVENTION
When carbonaceous materials are heated during a gasification process,
gaseous species of varying molecular weights are released as syngas
Production of syngas via gasification of renewable resources has been a
focus for researchers for decades. For this purpose, carbonaceous materials
include but are not limited to biomass, waste, coal, etc. Syngas as used
herein is a mixture of hydrogen (H2), carbon monoxide (CO) and other
combustible and non-combustible gases whereas the hydrogen and carbon
monoxide concentrations are maximized, and can be considered as either a
fuel gas where it is typically burned directly as fuel to produce heat and/or
electric power or as an intermediate for multiple uses, such as synthesis of
liquid fuels, chemicals, or other materials.

Carbonaceous species in syngas with molecular weights greater than
benzene (MW=78) are generally classified as tars. As initially produced,
these tars are reactive or tricky due to their chemical functional groups
including but not limited to: hydroxyls, aldehydes, ketones, carboxylic acids,
alkenes, alkynes, heterocyclic structures, in any combination, which can
allow them to polymerize and thereby cause plugging, form coke or other
solid deposits, cause equipment to seize, or have other deleterious effects.
The presence of these reactive or problematic tars in syngas has plagued
most gasification projects and has been the Achilles heel of gasification.
The gasification process uses several reactors, which can be classified
according to the relative movement of the fuel and the gasifying medium as
either fixed beds (updraft, downdraft and crossdraft) or fluidized beds
(bubbling, circulating, spouted and swirling). The three basic types of
processes that exist for the thermo-chemical production of syngas from the
carbonaceous materials or gasification of carbonaceous materials include:
(1) fixed-bed gasification, (2) fluidized-bed gasification and (3)
suspension/entrainment gasification. For the low power range, fixed-bed
gasifiers in a number of variants pre-dominate. Fixed-bed gasifiers are
reliant on a consistently high quality of the carbonaceous materials and are
not suited for the production of high-quality tar free synthesis gas suitable
enough for further processing into hydrogen. Further, the entrained flow
gasifier is particularly well suited to high powers of 1 GW upwards, since
the reactor size of the entrained flow gasifier is relatively small. Thus, for
small-scale plants the entrained-flow gasifier is uneconomic because of the
high-cost of the equipment. Additionally, the entrained flow gasifier requires
extensively dry biomass/primary products/carbonaceous materials since at

high temperatures the entrained-flow gasifier works with pure oxygen.
Moreover, the ashes produced as a byproduct are unsuitable to be used as
fertilizers, thereby causing the fertilizers to become more expensive and
scarce. Furthermore, the fluidized bed gasifier finds suitability in the
medium industrial power range of 1MW to 1 GW. Unlike fixed bed
reactors, models with a fluidized bed have no distinct reaction zones—
drying, pyrolysis and gasification occur simultaneously in the reactor—as
the reactor is mixed and, thus, closed to isothermal. Fluidized bed reactors
can be classified by configuration and the velocity of the gasifying agent,
e.g., bubbling, circulating, spouted, and swirling fluidized beds as mentioned
aforesaid. In methods using fluidized-bed gasifiers, there is a distinction
wherein the gasification may be auto thermal or allo thermal. The major
advantages of the fluidized-bed gasifiers are its simplicity, high charcoal
burn-out and internal heat exchange leading to low gas exit and shorter
residence time of carbonaceous materials in a fluidized bed gasifier.
In US8252073B2 to Tsang discloses a tar-free gasification process and
system is disclosed that involves the partial combustion of recycled dry
solids and the drying of a slurry feedstock comprising carbonaceous material
in two separate reactor zones in a two stage gasifier, thereby producing
mixture products comprising synthesis gas. The synthesis gas produced from
the high temperature first stage reaction zone is then quenched in the second
stage reaction zone of the gasifier prior to introduction of a slurry feedstock.
The temperature of the final syngas exiting the second stage reaction zone of
the gasifier is thereby moderated to be in the range of about 350-900° F.,
which is below the temperature range at which tar is readily formed,

depending upon the type of carbonaceous feedstock utilized. More
specifically, said invention discloses a two-stage entrained type gasifier for
producing low tar syngas by providing solid residence time in 1st and 2nd
stage of 4-6 seconds and 5-10 seconds respectively. Further, the gasifier
utilized in said invention operates at a temperature above 1300 degree
centigrade leading to increase in heat losses and difficulty in slag
management.
To the knowledgeable skill in the art it would be abundantly clear from the
above discussions that fluidized bed gasifier may be preferred over the other
gasifiers due to its distinct advantages over other gasification reactors,
including strong gas solids contact, excellent heat transfer characteristics,
better temperature control, large heat storage capacity, good degree of
turbulence, and high volumetric capacity. Furthermore, among the fluidized
bed reactors/gasifiers i.e. bubbling, circulating, spouted, and swirling
fluidized beds, the bubbling fluidized bed reactors are often preferred in
small-scale plants with fuels having low heat value and high moisture
content. In bubbling bed particle size used are larger than circulating
fluidized bed so power requirement for sizing is less. Thus, sensible heat
loss will be less in bubbling fluidized as air to solid is less in bubbling
fluidized bed than in a circulating fluidized bed.
Further, like all fluidized beds, bubbling fluidized beds are categorized as
either a single fluidized bed or multi-fluidized beds which also includes dual
fluidized bed gasifier. Sadaka has demonstrated that the single fluidized bed

gasifier consists of only one bed into which the feedstock and gasifying
agent enter and out of which the produced gas and char exit. The advantages
of the system include: (1) lower cost than dual and multi-fluidized beds; (2)
less maintenance; and (3) the produced gas is ready for utilization. On the
other hand the system has some disadvantages. These include: (1) heating
value of the produced gas is lower than that produced by the dual bed; (2)
inorganic materials in the feedstock cannot be separated; and (3) pyrolysis
occurs at the bottom of the gasifier leading to a non-uniform temperature
distribution. Further, Sadaka about dual and multi-fluidized beds gasifier
suggests that such gasifiers consist of more than one bed. The first bed is
usually used to burn some of the char to produce the energy for the second
bed, which is where the pyrolysis occurs. The advantages of the dual bed
system include: (1) the gas heating value is larger because char combustion
occurs in a separate reactor and hence the combustion gas does not dilute the
pyrolysis gas; (2) inorganic materials in the feed can be separated; and (2)
heat of pyrolysis in the reactor is distributed evenly, thus pyrolysis occurs at
a relatively uniform temperature. Higher construction costs and greater
maintenance are the disadvantages of this system.
Furthermore, the other design consideration lies in the selection of the
reactor or gasifier arrangement which may be a single-stage or a two/multi
stage gasification process. The aim of a ‘single-stage’ fluid bed gasifier is to
convert organic substances entirely in one reactor. Depending on the type of
operation, the solid fuel is injected into the hot environment, together with
oxygen and steam. As the fuel particles devolatize, the hydrocarbons

volatiles undergo gas-phase reaction with the most reactive species in the
ambient gas, that is, oxygen. Thus, the oxygen or Air supplies the required
heat by reacting with the reactive volatiles. The two-stage concept design
physically separates the principal unit operations of pyrolysis-preliminary
gasification zone from the final conversion zone, involving two different
levels of heat intakes. Most of this type of advanced thermal processes
eliminates char gasification as a limiting process step and, consequently, the
efficiency of the process depends on how the conversion is organized. In a
single stage process, the residual char reacts heterogeneously with the steam
and CO2 with a slow and highly endothermic process that is often
accelerated to practical rates by the use of additional oxygen to keep the
temperature high. The concept of two-stage gasification is based on
providing longer residence time whilst making a more efficient use of the
oxygen or Air required supporting the endothermic steam reactions.
In US 9353321B2 to Paskach teaches a system and method for producing
substantially tar free product gas from gasification of carbonaceous material.
The assembly as disclosed in said invention preferably includes a first stage
gasifier to produce char-ash and tar laden product gas and a second stage
gasifier which has a char-ash heating zone, at least one cyclone, and at least
one standpipe for the purpose of allowing selective delivery of char-ash to
the char-ash heating zone. A char-ash heating zone that utilizes oxidation of
char-ash is preferred and this results in the heat required to convert tar,
additional yield of product gas, and an oxidized, activated carbon surface to
facilitate tar conversion in the riser, thereby reducing the temperature

required to achieve the desired tar conversion. Alternatively, external heat is
supplied to the heating zone. The aforesaid system apart from utilizing
external heating is also more complex in terms of structure and operation,
thereby also increasing the cost.
In WO2014093308A1, the disclosure is related to a two stage fluidized bed
gasifier where syngas from 1st stage fluidized bed gasifier flows to the
second stage fluidized bed gasifier achieving low tar concentration with 95%
carbon conversion efficiency but the clear drawback is the disclosed system
requiring at least two fluidized bed gasifiers which makes the overall system
structurally complex and expensive.
Further, EP2927305A1 discloses implementing fluidized bed gasifier in
which monlith or honey comb type catalyst layer is provided in the free
board area of the gasifier to reduce tar to smaller molecules. However, the
above arrangement requires the use of catalyst for reducing the tar
concentration in the syngas.
Furthermore, US9011724B2 discloses a technique for producing low-tar
synthesis gas from biomass. The steps involve decomposing the biomass
into at least the components such as pyrolysis gas and pyrolysis coke in at
least one first fluidized bed reactor and feeding the pyrolysis gas generated
in the first fluidized bed reactor as fluidizing gas to at least one subsequent
fluidized bed reactor. However, the approach requires two fluidized bed
gasifier as well as heating of the gas from the 1st gasifier and feeding into

the 2nd gasifier which again makes the approach complex and commercially
expensive for carbonaceous material gasification.
The other design consideration finds home in developing and deciding a
scheme or a procedure for reducing flyash disposal with a carbonaceous
material drying procedure. The drying scheme needs to be selected in a
manner such that the syngas produced has a minimum tar concentration
along with the above scheme facilitating in the reduction of the design
complexity of the gasification system. WO2010144544A1 teaches
implementing a multiple stage cyclone filters can be located before the
sulfur remediation unit to allow un-reacted biomass recycling with cyclone
separation. A first heavy cyclone stage can be constructed to remove heavy
particles and a second lighter cyclone stage can be constructed to remove
lighter particles consisting mainly of un-reacted biomass and then the
substantially particle- free syngas is passed into the sulfur remediation unit.
However, the approach requires two cyclone stages again making the system
more complex commercially unviable.
Evidently, Capital needs for conversion of carbonaceous materials to syngas
are substantial and available processes and equipment still leave much to be
desired by way of efficiency of production and ease of operation and
maintenance. Although the process of gasification has been practiced for
decades, and numerous gasifier designs have been invented, no gasifier
exists that can produce a syngas with near zero concentration of tar at
commercial scales appropriate for economically compelling conversion of

carbonaceous materials into liquid fuels, electric power, or chemicals along
with reduction in the construction, operational and maintenance costs. Thus
it is desirable to come up with a appropriate gasifier model by considering a
multitude of constraints including but not limited to gasifier design
arrangement, number of beds in a gasifier, drying scheme, bed temperature,
pressure and height, residence time, fluidization velocity particle size, and
moisture content of feed material for producing syngas with near zero
concentration of tar at commercial scales for small plants.
OBJECTS OF THE INVENTION
An object of the invention is to overcome the aforementioned and other
drawbacks existing in prior art systems and methods.
Another object of the invention is develop a single stage air blown
fluidized bed gasifier operating under bubbling fluidization regime to
generate very low tar concentration syngas for power generation using
reciprocating engine or for chemical synthesis.
Still another object of the invention is to reduce the complexity of the system
by through implementing adiabatic single gasifier by eliminating the need of
external heating or cooling.
Yet another object of the invention is to develop a gasifier operating at
optimal temperature and having residence time specifically defined for
conversion of tar components into lighter hydro carbon.

SUMMARY OF THE INVENTION
The present application discloses a one- stage bubbling fluidized bed
gasification method having adiabatic single gasifier for generating low tar
concentration syngas from carbonaceous material. In a preferred form said
method includes introducing the carbonaceous material into a gasification
reactor of a one-stage bubbling fluidized bed gasifier and combining it with
transport air and further for fluidizing fuel material, feeding fluidizing air
into the gasification reactor. In an aspect, the fluidizing air is fed in the
pressure range of 1-5 bar and further contacting of the fluidized air and the
fuel material, produces tar-laden syngas. In another aspect, the tar-laden
syngas further includes fly-ash containing at least fuel char. Furthermore, the
method includes, passing the tar-laden syngas produced from a reactor lower
section of the one-stage bubbling fluidized bed gasifier to a freeboard upper
section of the one-stage bubbling fluidized bed gasifier, thereby breaking the
tar-laden syngas in the reactor lower section and the freeboard upper section.
In an aspect, the reactor lower section and the freeboard upper section is
maintained at a temperature ranging between 800-1100 degree centigrades;
Further, the method includes drying adiabatically the tar-laden syngas for
producing syngas with tar concentration of 0-3 mg/NM^3 at an outlet of the
one-stage bubbling fluidized bed gasifier.
In another preferred form, the present application discloses a system for one-
stage bubbling fluidized bed gasification for generating low tar
concentration syngas from carbonaceous material. The system in an aspect
includes: a) a gasification reactor comprising a reactor lower section and a
free board upper section adapted for operation at temperatures between 800-

1100 degree centigrades, b) a feed hopper for introducing carbonaceous
material into the gasification reactor via a feed lock and a feed receiver; c) a
compressor, d) an air receiver, e) an air control valve comprising: a
fluidizing air control valve and a transport air control valve, f) a cyclone
zone containing a cyclone recycle line, g) a bottom ash receiver and a
bottom ash valve; h) a controller adapted to maintain the pressure difference,
i) plurality of knockout drums, j) a liquid trap.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 is a schematic illustration of the process flow type showing an
embodiment wherein a Single stage fluidized bed gasifier operating under
adiabatic conditions discards the fly ash separated via a cyclone from the
syngas.
Fig. 2 is a schematic illustration of the process flow type showing an
embodiment wherein a Single stage fluidized bed gasifier operating under
adiabatic conditions recycles the fly ash separated via a cyclone from the
syngas back to said gasifier.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF
THE INVENTION
Although the disclosure hereof is detailed and exact to enable those skilled
in the art to practice the invention, the physical embodiments herein
disclosed merely exemplify the invention which may be embodied in other
specific structure. While the preferred embodiment has been described, the

details may be changed without departing from the invention, which is
defined by the claims.
It will be apparent, however, to one of ordinary skill in the art that the
present invention may be practiced without specific details of the well
known components and techniques. In other instances, well known
components or methods have not been described in detail but rather in
schematic diagrams in order to avoid unnecessarily obscuring the present
invention. Further specific numeric references should not be interpreted as a
literal sequential order. Thus, the specific details set forth are merely
exemplary. The specific details may be varied from and still be
contemplated to be within the spirit and scope of the present invention. The
features discussed in an embodiment may be implemented in another
embodiment.
Further, the reference to the conventional system is made in order to better
distinguish the present inventive disclosure discussed later in greater detail.
The details of the conventional process related to the general process of
converting carbonaceous material to syngas using single/multi stage
fluidized bed gasification which are well-known in the are described herein
only in the detail required to fully disclose the present invention.
Improving upon the conventional techniques discussed at length above, in
the present disclosure, in a preferred form, the fluidized bed adiabatic
gasifier operating under bubbling fluidization regime is configured to

produce very low tar concentration syngas from biomass and other residue
having high amount of volatiles as shown in Fig.1 and Fig.2.
Further, as illustrated in Fig. 1, Fig. 2, biomass and other carbonaceous
material is fed from hopper and introduced in the fuidized bed gasifier via
lock and receiver system with transport air. The fluidizing air is introduced
through an air distributor. The fluidizing air to fuel ratio is fixed to maintain
gasifier temperature below the ash melting point and hydrodynamics of the
gasifier remains in bubbling fluidizing air regime. The entrained ash
particles from gasifier may be collected in cyclone 1 and recycled to gasifier
as shown in Fig.2. Ash from the bottom of the gasifier is extracted
continuously. In various embodiments, the bed gasifier may be of a single
bed type, a dual bed type or a multi-bed type. Further, oxygen for the
gasification reactions can be provided by either air or high purity oxygen
produced by a cryogenic air separation unit (ASU). Air-blown gasifiers
avoid the large capital cost of an ASU an air-blown gasifier will typically
produce syngas with a calorific value of 120 Btu/scf. This has a significant
impact on the design of the combustion system of the gasifier. Additionally,
because the nitrogen in air must be heated to the gasifier exit temperature by
burning some of the syngas, air-blown gasification is more favorable for
gasifiers which operate at lower temperature. In a preferred form, the
invention uses air blown gasifier for tapping the advantages as disclosed
above.

Further, the fluidized bed is preferred over the fixed bed gasifier in a
preferred embodiment due to the advantageous characteristics of the
“fuidized bed” i.e., good mixing and long residence time as explained in
greater detail later in the description. Further, in one aspect, the fluidizing air
is fed from air receiver in the pressure range of 1-5 bar into gasifier so that
fuel material is fludized in the bubbling fluidized bed regime. The fludising
air is used to fluidize the bed material primarily to increase solid-air contact.
while, transport air used to convey fuel in the fuel feed line smoothly into
the gasifier. In an aspect, the air and fuel contact produces syngas or
producer gas having N2, Co, Co2, CH4, H2, H2O, higher hydrocarbons and
tar. The produced tar-laden syngas travels from reactor zone to free board
zone with char ash particles. In one aspect, a portion of the char ash particles
gets settled in the free board zone due to low velocity and the rest of the
portion with high velocity gets entrained along with syngas into cyclone.
Further, in a preferred form, during gasification no heat is added or removed
maintaining perfectly adiabatic temperature.
The aforesaid approach may not avoid forming tars but are capable of
breaking tars in the reactor and free board zone. Thus, a ash separation
mechanism needs to be implemented. In a preferred embodiment, in order to
separate the flyash from the synthesis gas, the tar-laden syngas with fly ash
is forwarded via a line to a cyclone. In one aspect, great bulk of the flyash is
separated in the cyclone and the fly ash is removed from the cyclone via a
line and sent as waste as shown in Fig.1 In another aspect, the fly ash
separated via a cyclone from the syngas back to said gasifier(Fig.2).

In order to further clarify the embodiments related to producing syngas with
near-zero concentration of tar one of the following drying schemes may be
adapted to produce tar free- syngas.
Scheme 1 (Fig. 1)
In a preferred aspect, the syngas is produced from fluidized bed gasifier and
fly ash from gas is removed in the cyclone is discarded. The operation is
adiabatic and operated in the range of 800-1100 C The ash from cyclone is
discarded.
Scheme 2 (Fig. 2)
In another preferred aspect, the syngas is produced from fluidized bed
gasifier and fly ash from gas is removed in the cyclone and recycles back to
the reactor for further gasification. The operation is adiabatic and operated in
the range of 800-1100 C.
Again, as used herein, the term "zone", as employed in the specification and
claims, includes, where suitable, the use of segmented equipment operated in
series, or the division of one unit into multiple units to improve efficiency or
overcome size con-straints, etc. For example, multiple gasification reactors
may be employed, and only one or more need to supply flyash to the
fluidization zone described herein, a series of cyclones may be employed,
The foregoing is considered as illustrative only of the principles of the
invention. Furthermore, since numerous modifications and changes will
readily occur to those skilled in the art, it is not desired to limit the invention
to the exact construction and operation shown and described. While the
preferred embodiment has been described, the details may be changed
without departing from the invention, which is defined by the claims.

WE CLAIM:
1. A one- stage bubbling fluidized bed gasification method having
adiabatic single gasifier for generating low tar concentration
syngas from carbonaceous material, said method comprising
the steps of:
a) introducing the carbonaceous material into a gasification
reactor of a one-stage bubbling fluidized bed gasifier and
combining therein with transport air and further for fluidizing
fuel material, feeding fluidizing air into the gasification reactor,
wherein the fluidizing air is fed in the pressure range of 1-5 bar,
and contacting therein of the fluidized air and the fuel material,
thereby producing tar-laden syngas, wherein the tar-laden
syngas further includes fly-ash containing at least fuel char;
b) passing the tar-laden syngas produced in a) from a reactor lower
section of the one-stage bubbling fluidized bed gasifier to a
freeboard upper section of the one-stage bubbling fluidized bed
gasifier, thereby breaking the tar-laden syngas in the reactor
lower section and the freeboard upper section, and wherein the
reactor lower section and the freeboard upper section is
maintained at a temperature ranging between 800-1100 degree
centigrade;
c) Separating ash in cyclone adiabatically the tar-laden syngas for
producing syngas with tar concentration of 0-3 mg/NM^3 at an
outlet of the one-stage bubbling fluidized bed gasifier.

2. The method of claim 1, the tar-laden gas comprises:
separating, by a cyclone the fly ash from the tar-laden syngas;
and
discarding the fly ash separated by the cyclone, wherein the
cyclone is generated in the cyclone zone.
3. The method of claim 1, the tar-laden gas comprises:
separating ,by the cyclone the fly ash from the tar-laden syngas
; and
recycling the fly ash to the one-stage bubbling fluidized bed
gasifier via the cyclone for further gasification.
4. The method of claim 1, wherein the freeboard upper section has
a diameter higher than the reactor lower section.
5. The method of claim 1, wherein the freeboard upper section has
a higher diameter than the reactor lower section.
6. The method of claim 1 or 4, wherein dimensions of the reactor
lower section and the freeboard upper section are adapted for
maintaining syngas residence time of the reactor lower section
and the freeboard upper section between 7sec-20 sec.

7. The method of claim 1 or 4, wherein dimensions of the reactor
lower section and the freeboard upper section are adapted for
maintaining fuel char residence time of the reactor lower
section and the freeboard upper section between 25-30 mins.
8. A System for one- stage bubbling fluidized bed gasification for
generating low tar concentration syngas from carbonaceous
material, comprising:

a) a gasification reactor comprising a reactor lower section and a
free board upper section adapted for operation at temperatures
between 800-1100 degree centigrades;
b) a feed hopper for introducing carbonaceous material into the
gasification reactor via a feed lock and a feed receiver;
c) a compressor to provide transport and fludising air
d) an air receiver to store air at higher pressure for supplying
transport and fluidisied air to gasifier
e) an air control valve comprising: a fluidizing air control valve
and a transport air control valve : to control the flow of
transport and fluidizing air.
f) a cyclone zone containing a cyclone recycle line : to separate
ash particle from gas and to recycle back the collected ash
particle to gasifier.
g) a bottom ash receiver and a bottom ash valve: to collect bottom
ash from gasifier bottom .

h) a controller adapted to maintain the pressure difference; To
maintain desired gasifier pressure
i) There is no knock out drum)
j) (No liquid trap)
9. The system of claim 8, wherein walls of the reactor lower
section, the free board upper section and the cyclone zone are
coated with insulating materials.