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FIELD OF THE INVENTION
This invention generally relates to integrated gasification combined cycle power
plants (IGCC), which is particularly employ air blown gasification method. More
particularly, the invention relates to a system adaptable to enhance calorific
value of syngas in an IGCC employing the air blown fluidized bed gasification
method.
BACKGROUND OF INVENTION
In IGCC plants syngas is produced by the partial combustion of coal in the
present of steam using either oxygen or air. Oxygen is used in the entrained bed
gasifiers where ash is removed in the form of slag. IGCC plants are operated at
high pressure up to 30 kg/sq.cm to meet the gas tubine requirement. For high
ash coals or coals having high ash fusion temperature, air blown fluidized bed
gasification method is employed. Atmospheric air is used for gasification after
compression, Syngas produced is cleaned by series of cyclones arranged in the
gas path. This syngas is cooled by extracting heat with the help of heat recovery
system introduced in the syngas path and the gas is admitted to gas turbine for
power production.
In the IGCC plants employing the entrained bed gasification method, ash in the
coal is melted and removed in the form of slag for this oxygen is used to achieve
higher process temperature for melting ash in the gas. In turn the use of oxygen
in the process leads to reduce nitrogen content in the syngas and helps to
improve the calorific value of syngas. But this leads to high power consumption
for 02 separation and thereby increase in cost. This method is not suitable for

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high ash coals with high ash fusion temperature. However, the air blown
fluidized bed gasification method is suitable for this type of coals. In this process
the presence of more carbon di oxide nitrogen in the syn gas in contrast leads to
reduce the calorific value of syngas. Calorific value achieved in this method does
not meet the requirement of the existing gas turbines. Introduction of air
preheating device in the syngas path after dust removal in cyclones may lead to
mixing of air and gas in the air preheater in the event of leakage and causing fire
hazard, hence not desirable. Hence, a need exists to propose a system and
method which enhances the calorific value of syngas in an IGCC employing the
air blown fluidized bed gasification method.
OBJECT OF INVENTION
It is therefore an object of the invention to propose a system and method which
enhances the calorific value of syngas corresponding to gas turbine requirement
in an IGCC employing the air blown fluidized bed gasification method.
Another object of the invention is to propose a system and method which
enhances the calorific value of syngas corresponding to gas turbine requirement
in an IGCC employing the air blown fluidized bed gasification method, which
makes use of the available resources in the plant.
A still another object of the invention is to propose a system and method which
enhances the calorific value of syngas corresponding to gas turbine requirement
in an IGCC employing the air blown fluidized bed gasification method, which is
safe and reliable.

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A further object of the invention is to propose a system and method which
enhances the calorific value of syngas corresponding to gas turbine requirement
in an IGCC employing the air blown fluidized bed gasification method, which is
cost-effective.
SUMMARY OF INVENTION
Primarily the system uses the resources available in the plant i.e. syngas and
coal produced in the plant to enhance the calorific value of the syngas by
preheating the process air from the compressor. This preheater air provides
additional sensible heat to the process. As the operational temperature of the
gasifier remains same, the calorific value of the syngas enhances by the
reduction of carbon-di-oxide and corresponding increase of carbon mono oxide.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1. Shows a schematic diagram of a first embodiment of the system of the
invention to preheat the process air using syn gas to achieve calorific value
enhancement and to heat the syn gas before being admitted to the gas turbine
by utilizing heat available in the flue gas.
Fig 2. Shows a schematic diagram of an alternative embodiment of the invention
to preheat the process air using to achieve calorific value enhancement and to
heat the syn gas before being admitted to the gas turbine utilizing heat available
in the flue gas.

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DETAILED DESCRIPTION OF THE INVENTION
According to the embodiment of figure - 1, preheating of the process air is
achieved by tapping a portion of a first syngas (07) before being admitted to the
gas turbines through a pressure reducing valve (01) and firing the syngas (07) in
a burner (02), where combustion air is admitted by a forced draught fan (03) to
aid combustion. Heat produced by the first syngas (07) and the air from the FD
fan (03) is utilized in a tubular heat exchanger (04) having a flue gas (14) in a
shell side (04). Cold air (10) and steam (11) mixed in a mixer (12), is admitted to
a plurality of tubes (05), which normally operate at 30 kg/sq cm in the IGCC
plants. The flue gas (14) after transferring its heat to the air and steam is further
used to increase the temperature of a second syngas (08) coming from a gasifer
system (15) before being admitted to the gas turbine, and then the flue gas (14)
is released to atmosphere. Air and steam mixture (13) pick up heat from the flue
gas and then admitted to the gasifier for the process. This preheated air and
steam mixture (13) enhances calorific value of the syngas produced, utilizing the
additional sensible heat energy available for the process air. This process air with
higher sensible heat reduces Carbon di oxide content in the syngas and
enhances the calorific value of the syngas due to increase of Carbon monoxide.
Excess heat available in the flue gas (14), is utilized by introducing another set of
tubular heat exchanging coils (06) for heating the second syngas (08) from the
gasifier system (15) and a hot gas (09) is admitted to the gas turbine to suit gas
turbine inlet temperature.

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Fig 2. Shows the alternate embodiment of the system proposed to preheat the
process air using coal available in the plant and by using a fluidised bed heat
exchanger to achieve calorific value enhancement and utilizing heat available in
the flue gas to heat the syngas before being admitted the hot syngas is admitted
to gas turbine.
The air preheat system having, a fluidised bed combustor (01) using coal (02)
form a coal handling unit in the plant, and a FD fan (03) which provides
combustion air (04) for the fluidized bed combustion which acts as heat
generating source. Process air (05) and steam (06) mixed in a mixer (07) is
admitted to tubes (08) immersed in the bed. Operating pressure of this mixture
is normally at 30 Kg/sq cm in the IGCC plant. This flue gas (09) after transferring
its heat to the air and steam is further used to increase the temperature of
syngas (10) coming from the gasifer (11) before it is admitted to the gas
turbines, and then the flue gas (09) is released to atmosphere. Air and steam
mixture (05,06) pick up heat from the flue gas (09) and then admitted to the
gasifier (11) for the process. This preheated air and steam mixture (05, 06)
enhance the calorific value of the syngas produced, utilizing the additional
sensible heat energy available for the process air (05). This process air with
higher sensible heat reduces Carbon di oxide content in the syngas and
enhances the calorific value of the syngas due to increase of Carbon monoxide.
Excess heat available in the flue gas (09), is utilized by introducing another set of
tubular heat exchanging coils (12) housed in the fluidised bed heat exchanger
(13) for heating syngas exiting from the gasifier (11) to suit gas turbine inlet
temperature.

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WE CLAIM
1. A system adaptable to enhance the calorific value of syngas corresponding
to a value applicable to the gas turbine in an integrated gasification
combined cycle power plant (IGCC), the IGCC employing an air blown
fluidized bed gasification device, the system comprising:
- a first syngas (07) firable in a burner (02), the burner (02) further
receiving combustion air from a forced draught fan (03);
- a tubular heat exchanger (04) having a plurality of tubes (05), the
heat exchanger (04) further having in a shall side (04) a flue gas
(14);
- a mixture (13) of cold air (10) and steam (11) produced in a mixer
(12) for admitting into said plurality of tubes (05), the mixture (13)
receiving heat from the flue gas (14);
- the flue gas (14) transferring further heat by adapting a set of heat
exchanging coils (06) to a second syngas (08) exitting from a
gasifier system (15), the flue gas (14) after transfer of heat being
released to the atmosphere; and
- a hot gas (09) produced by heating the second syngas (08) via said
heat exchanging coils (06) ingressed into the gas turbine.

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2. A system adaptable to enhance the calorific value of syngas corresponding
to a value applicable to the gas turbine in an integrated gasification
combined cycle power plant (IGCC), the IGCC employing a fluidized bed
heat exchanger, the system comprising:
- a fluidized bed heat exchanger (13) having a plurality of tubes (08)
immersed into the bed, a fluidized bed combustor (01) generating
heat using coal (02), and a forced draught fan (03) providing
combustion air (04) for fluidized bed combustion;
- a mixer (07) mixing a process air (05) and steam (06) and
supplying the mixture to said plurality of tubes (08);
- a flue gas (09) produced by the fluidized bed combustion
transferring heat to said air-steam mixture (05, 06), and further
increasing the temperature of a syngas (10) coming from a gasifier
(11) for the process; and
- a set of tubular heat exchanging coils (12) housed in said fluidized
bed heat exchanger (13) for receiving said flue gas (09) after first
heat transfer and further heating the syngas (10) to increase its
before being admitted to the gas turbine.

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3. A system adaptable to enhance the calorific value of syngas corresponding
to a value applicable to the gas turbine in an integrated gasification
combined cycle power plant (IGCC), as substantially described and
illustrated herein with reference to the accompanying drawings.

The invention relates to a system adaptable to enhance the calorific value of
syngas corresponding to a value applicable to the gas turbine in an integrated
gasification combined cycle power plant (IGCC), the IGCC employing an air
blown fluidized bed gasification device, the system comprising; a first syngas
(07) firable in a burner (02), the burner (02) further receiving combustion air
from a forced draught fan (03); a tubular heat exchanger (04) having a
plurality of tubes (05), the heat exchanger (04) further having in a shall side
(04) a flue gas (14); a mixture (13) of cold air (10) and steam (11) produced
in a mixer (12) for admitting into said plurality of tubes (05), the mixture (13)
receiving heat from the flue gas (14); the flue gas (14) transferring further
heat by adapting a set of heat exchanging coils (06) to a second syngas (08)
exitting from a gasifier system (15), the flue gas (14) after transfer of heat
being released to the atmosphere; and a hot gas (09) produced by heating
the second syngas (08) via said heat exchanging coils (06) ingressed into the
gas turbine.