FIELD OF THE INVENTION
The present invention generally relates to cogeneration/Combined cycle power
plant using coal as the primary energy source and natural gas as secondary
energy source. In particular the invention relates to a Heat recovery steam
generator (HRSG) in a combined cycle/cogeneration plant, adaptable to
downstream of gas turbine fired by coal gas. More particularly, the present
invention relates to a heat recovery steam generator (HRSG) system in
integrated gasification combined cycle (IGCC) system in integrated gasification
combined cycle (IGCC) power plants. The present invention further relates to a
method of configuration a HRSG System by optimizing disposition of heating
surface including fuel firing device to maximize power generation upon failure of
the gasifier system.
BACKGROUND OF THE INVENTION
It is known that combined cycle or cogeneration plants which convert fossil fuel
energy into electrical energy is efficient in comparison to coal fired power plants
and they are relatively easy and inexpensive to construct. In a typical combined
cycle/cogeneration plant gaseous/liquid fuels are fired in gas turbine and HRSG.
The exhaust gases leave the gas turbine at about 550°C and contain a significant
amount of energy. To recover this energy, the typical combined cycle or
cogeneration plant has a heat recovery steam generator through which the hot
exhaust gases pass to produce steam for process or for use in steam turbine for
producing power. Considering the high efficiency of the combined cycle power
plants (CCPPs) as compared to conventional coal fired power plants, and further
considering the limited availability of high cost liquid/gaseous fuels used in
combined cycle power plants (CCPP), IGCC power plants using abundantly-
available coal but providing high generation efficiency, has received a preference
in power generation. In combined cycle power plants, the natural gas/liquid fuels
are fired in a gas turbine, the HRSG installed behind the Gas turbine recovers the
heat from the exhaust by generating steam which is fed to the steam turbine. In
the IGCC, the syngas required for firing in the gas turbine is generated in a
gasifier which is then cooled in a syngas cooler and cleaned before being
admitted into the gas turbine. The degree of superheat available in the steam is
the decisive factor towards the amount of steam generation in the syngas cooler
boiler. The superheated steam generated from the coal gas (syn gas) cooler
boiler is either fed to the steam turbine or gas turbine or to both. In a standard
IGCC plant, the gas turbine fuel is supplied to GT from the gasifier and the HRSG
is unfired.
As shown in figure 1, in the prior art IGCC steam system, the working steam for
the turbine is supplied from the steam generated in an unfired HRSG installed
behind the Gas turbine and the steam generated in the syngas cooler in the coal
gasification system. In this configuration a coal supply device (1) supplies coal to
a gasifier (2), the syn gas from the gasifier (2) is cooled in a syngas cooler boiler
(3) which consists of a first superheater (4), a first evaporator (5), and a first
economizer (6). The cooled syn gas is passed through a gas cleanup system (8).
A syngas cooler (3) generates steam (7) for feeding to a steam turbine (18). The
cooled cleaned syngas from the gas cleanup system (8) is fed to a gas turbine
combustor (9) of a gas turbine (10). Air for the gas turbine combustor (9) is
provided by an air compressor (11). An exhaust gas heat recovery steam
generator (12) consisting of a second superheater (17), a second evaporator
(14), and a second economizer (13), uses the exhaust gas supplied from the gas
turbine (10) as the heat source. The saturated steam-water mixture from the
second evaporator (14) passes through a drum (15) and after separation of
water in the drum (15), the mixture passes through a plurality of links (16) to
the second superheater (17) for further superheating. The steam generated
from the Heat recovery steam generator (12) is supplied to the steam turbine
(18). The steam exhaust from the steam turbine (18) is condensed in a
condenser (19), and is passed through a Deaerator (20). The feed water from
the Deaerator (20) is pumped by a pump (21) to a feed water system of the syn
gas cooler boiler (3) and the exhaust gas heat recovery steam generator (12).
Another prior art of the IGCC system of power generation is known, in which
saturated steam is first generated in the syngas cooler boiler, and the steam is
supplied into a drum of an exhaust gas heat recovery steam generator for
further superheating and use in the steam turbine. Figure 2 illustrates such an
IGCC system, wherein a syngas cooler boiler (3) consists of an evaporator (5)
and an economizer (6). The saturated steam (7) generated is fed to the drum
(15) of the exhaust gas steam generator (12). This steam along with the steam
generated from the HRSG is superheated in a superheater (17). The drum (15) is
sized to accommodate larger steam quantity.
The major disadvantages of the prior art as depicted in fig 1 & fig 2, are that the
amount of power generated from the steam turbine is less when there is no
export of saturated steam from the syn gas boiler of the IGCC system to HRSG
superheaters during failure of the gasifier, and wherein when the HRSG system
is unfired. The major disadvantage of the prior art is that they are not enabled to
utilize the full capacity of the steam turbine/total plant capacity when the gasifier
is not working and the gas turbine is fired with alternate natural gas in normal
combined cycle mode without import of steam from the syn gas cooler boiler
into the HRSG.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a firing device in a heat
recovery steam generator (HRSG) for dual-fuel integrated gasification combined
cycle (IGCC), for maximizing power generation from steam turbine, in absence of
saturated steam imported from syngas cooler boiler into HRSG drum/superheater
due to non-operational condition of gassifier and gas turbine operating with
alternate fuel natural gas instead of coal gas (syngas).
Another object of the invention is to propose a firing device in a heat recovery
steam generator (HRSG) for dual-fuel integrated gasification combined cycle
(IGCC), which allows generation of corresponding quantities of steam both in
IGCC mode (with gas turbine fired with syn gas from the gasifier and import
steam from the syn gas cooler superheated in the HRSG behind GT) and in
natural gas (NG) combined cycle mode (with NG as fuel for firing in gas turbine
(GT) and no import steam available to the HRSG superheater from the syn gas
cooler boiler) for achieving the rated capacity of the power plant even when the
gasifier system is in-operable.
A still another object of the invention is to propose a firing device in a heat
recovery steam generator (HRSG) for dual-fuel integrated gasification combined
cycle (IGCC), which includes a flexible auto sensing fuel input device enabled to
vary the steam generated from the HRSG to get maximum power from the steam
turbine irrespective of the GT loads and irrespective of operations of plant in
IGCC mode or Natural Gas fired Combined Cycle mode.
A further object of the invention is to propose a process of configurating a HRSG
system such that the fuel firing device is capable of firing syngas/natural gas and
other liquid and gaseous fuels to the HRSG corresponding to the plant power
requirements and pollution limits.
SUMMARY OF THE INVENTION
In accordance with the present invention a fuel receiving, distribution and firing
device is provided in the Heat recovery steam generator (HRSG) in the IGCC
system, for achieving the rated power output from the steam turbine without
availability of import steam by providing the required steam generation from the
HRSG. The heat recovery steam generator (HRSG) system, is flowably connected
to a gas turbine via a transition duct acting as a passage for the exhaust gas
from the gas turbine, the HRSG comprising a fuel receiving, distribution and
firing device, a superheater formed of a plurality of tubes, an evaporator
consisting of a plurality of configured tubes; an economizer located downstream
of the evaporator, an import steam receiving and distributing device receiving
saturated steam from the syngas cooler boiler including the HRSG evaporator
system, and allowing the mixed steam to enter a system consisting of
superheater and desuperheater for superheating the mixed saturated steam for
supply to the steam turbine. In accordance with the present invention, a fuel
receiving, distribution and firing device is additionally provided in the HRSG
System of IGCC, which is opened or closed based on operational mode of the
power plant such as normal combined cycle mode with natural gas in the gas
turbine (gasifier not in operation) or IGCC mode (with import steam from syn gas
cooler boiler) for achieving rated steam turbine power output.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 is a schematic presentation of a HRSG in IGCC system as per prior art.
Figure 2 is a schematic presentation of a HRSG in yet another type of IGCC
system as per prior art.
Figure 3 is a schematic view of the IGCC HRSG system that utilizes a fuel
receiving, distribution and firing system constructed in accordance with and
embodying the present invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
Figure 3 shows a coal handling system (1) feeding coal to a gasifier (2) which
generates high temperature coal'gas (syn gas). This high temperature syn gas is
cooled in a syn gas cooler boiler (3) having a first evaporator (5) and a first
economizer (6) which generates saturated steam (7) which is supplied to an
import steam receiving and distributing device (22). The cooled syn gases after
cleaning in a gas cleanup system (8) is fed to a combustion chamber (9) of a Gas
turbine (10). A compressor (11) of the gas turbine suppliers air to the
combustion chamber (9) of the gas turbine. The exhaust gases leaving the gas
turbine (10) is fed to a Heat recovery steam generator (12) consisting of a
superheater system (17), a second evaporator (14), and a second economizer
(13). The steam and water mixture generated from the second evaporator (14)
is passed through a drum (15) for separating the water from the mixture and the
separated saturated steam is supplied to the import steam receiving and
distributing device (22) through a plurality of links
(16). The steam received from the first evaporator (5) is also fed to the import
steam receiving and distributing device (22), the mixed steam (23) is supplied to
the superheater system (17). The steam from the HRSG superheater system (17)
is supplied to a steam turbine (18), the exhaust of the steam turbine is
condensed in a condenser (19). The condensate is heated in a deaerator (20)
and the deaerated water from the Deaerator (20) is pumped through feed pump
(21) to the first economizer (6) and the second economizer (13). When the
gasifier is not in operation, a separate natural gas line along with its valves (24)
is connected the combustion chamber (9) of the gas turbine (GT) for operation
of GT using natural gas. A fuel receiving, distribution and firing device (25) is
added into HRSG (12) for operation during natural gas firing in GT (10).
According to the present invention, as illustrated in Figure 3, the saturated steam
generated from the syngas cooler boiler (3) is fed to the import steam receiving
and distributing device (22). The saturated steam from the drum (15) of the heat
recovery steam generator system (12) is fed to the import steam receiving and
distributing device (22) through the links (16). The mixture of the saturated
steam received from syngas cooler boiler (3) and the HRSG (12) received in the
import steam receiving and distributing device (22) is further fed to the
superheater system (17) through a plurality of distributing links (23). The
introduction of the fuel receiving distribution and firing device (25) maintains the
power output from the total plant even when the gasifier is not in operation and
there is no import steam from the syngas cooler into the HRSG and the gas
turbine (10) is fed with natural gas fuel for utilizing the full steam turbine
capacity. The introduction of said fuel receiving, distribution and firing device
(25) in the HRSG (12) maintains the total power output from the plant even
when the gasifier is not in operation and the gas turbine is fed with natural gas
fuel.
Another aspect of present invention is to provide said plurality of connecting links
(26) to the firing device (25) that can be operated when the gasifier is not in
operation and the natural gas is available for firing in HRSG which facilitates
power augmentation in the steam turbine by producing required additional steam
from the HRSG.
A still another aspect of present invention is to maximize the power generation in
IGCC mode by firing syngas in the GT and NG in the HRSG even when the gas
turbine is in IGCC mode.
Yet another aspect of present invention is to maximize the power generation
from the plant and utilize the steam turbine capacity fully using any form of
available fuel for firing in the firing device (25).
A further aspect of the present invention is that the firing device (25) can be
made to fire any fuel to get the required steam quantity to utilize the maximum
capacity of the steam turbine.
A still further aspect of the present invention device (25) is that it automatically
senses the mode of operation either normal combined cycle mode (no import
steam from syngas cooler boiler) or in IGCC mode (Import steam from gasifier)
and either closes or opens the firing device.
WE CLAIM :
1. A heat recovery steam generator (HRSG) system in intergrated
gasification combined cycle (IGCC) for full capacity utilisation of
power plant in a condition that the gas turbine is devoid of coal gas
supply due to non-operation of the gassifier system, comprising:
a single pressure circuit having a superheater system (17), a second
evaporator (14), and a second economizer (13) or with multiple
pressure circuits and with or without condensate water preheater,
characterized by comprising :
a fuel receiving, distribution, and firing device (25) for receiving
natural gas from a natural gas piping (26) and firing in the IGCC HRSG
system (12) to supplement the steam supply to a steam turbine (18)
by compensating the loss of import steam from a syn gas cooler boiler
(3) when the gasifier system (2) is in-operable and the gas turbine
(10) being operated on Natural Gas.
2. The system as claimed in claim 1, wherein the device (25) comprising
an automatic control means to sense the Plant operation mode (IGCC
or Combined Cycle) including means to judge whether the gasifier (2)
is operational or otherwise so as to correspondingly open or close or
regulate the natural gas system pipe and valves (26) to activate the
firing device (25).
3. The system as claimed in claim 1, wherein the device (25) comprises
multiple fuel connections through syn gas piping with fittings (27) from
the gasifier (2) and through a liquid fuel piping with fittings (28) for
firing either syn gas or natural gas/or any other gaseous or liquid fuels
based on the adjudjed mode of operation.
4. The fuel receiving, distribution, and firing device (25) as claimed in
Claim1 provided with multiple fuel connections as claimed in claim3 can
be actuated for suitable selection of fuel by the automatic control system
as claimed in claim2 based on the availability of fuel(s) and regulation of
selected fuel to meet the plant's power requirement and emission levels.
5. A heat recovery steam generator (HRSG) system in intergrated gasification
combined cycle (IGCC) for full capacity utilisation of a power plant in a
condition that the gas turbine is devoid of coal gas supply due to non-
operation of the gassifier system as substantially described and illustrated
herein with reference to the accompanying drawings.
6. A method for full capacity utilization of a power plant in a condition when
the gas turbine is devoid of syn gas supply due to non operation of the
gasifier system, in a system as claimed in claim 1 system as substantially
described and illustrated herein with reference to the accompanying
drawings.

The invention relates to a Heat Recovery Steam Generator System and a
method for full capacity utilization of an IGCC power plant in a condition when
the gas turbine is devoid of syn gas supply due to non operation of the gasifier
system, in a system as claimed in claim 1. Unlike the prior art of IGCC system
which incorporates a HRSG meant to operate in recovery mode, when the gas
turbine is devoid of syn gas supply due to non operation of the gasifier system
and devoid of steam from syngas cooler boiler leading to under-utilisation of
capacity of steam turbine, the invention relates to a system and a method of
enhancing the steam output of HRSG to fully utilize the capacity of IGCC plant.