Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02194897 2004-09-28
BOILER WITH PRESSURIZED CIRCULATING
FLUIDIZED BED FIRING
The invention relates to boilers and more particularly to
boilers with pressurized, circulating fluidized bed firing
which are part of a combined gas-steam power plant.
Boilers of this type are known, wherein the flue gases
produced in the fluidized bed fire box are transported to the
gas turbine after cleaning of the hot gas at the temperature
of the fluidized bed of 800 to 1000°C. In the combined
process, the advantageous combustion and emission properties
of a circulating fluidized bed firing, which operates at high
pressure, and the special heat uptake distribution from the
cooling of the flue gas and solids in the boiler can be
combined with the gas turbine operation for optimal energy
use. Boilers of this type, apart from the fluidized bed
burner chamber, generally include a hot flue gas cleaning
arrangement such as one or more cyclone separators for the
removal of solids and a flue gas cooling arrangement for the
harnessing of the heat energy stored in the flue gas.
It is an object of the invention to advantageously coordinate
the individual reaction and heat exchanger components of the
boiler.
This object is achieved in a known steam boiler by combining
the cooling arrangement and the hot gas cleaning arrangement
into one unit which is placed in a common pressure vessel.
Accordingly, the invention provides a boiler with pressurized,
circulating fluidized bed firing, comprising a fluidized bed
burner chamber; at least one cyclone separator connected by a
connecting conduit on the flue gas side to and in series after
the fluidized bed burner chamber; a fluidized bed cooler
respectively connected in series to each cyclone separator,
the cooler being connected on the one hand by way of a dip pot
with a solids output of the cyclone separator and on the other
hand with the fluidized bed burner chamber; a return flow
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conduit connected to the dip pot and discharging into the
fluidized bed burner chamber, and at least one pressure vessel
housing the fluidized bed burner chamber, the cyclone
separator and the fluidized bed cooler, wherein the fluidized
bed cooler, the dip pot and the cyclone separator are combined
into one unit and placed in a common pressure vessel.
In another aspect of the invention, there is provided a steam
generator with pressurized, circulating fluidized bed firing,
comprising: a fluidized bed burner chamber; at least one
cyclone connected to a flue gas side of said fluidized bed
burner chamber through a connecting conduit; said cyclone
having a solids output; a fluidized bed cooler connected
behind said cyclone; a dip pot connected to said solids output
of said cyclone and to said fluidized bed cooler; a return
flow conduit connected to said dip pot and entering into said
fluidized bed burner chamber; a plurality of pressure vessels,
one of said pressure vessels housing said fluidized bed burner
chamber; said fluidized bed cooler, said dip pot, and said
cyclone being combined into a unit, said unit being housed in
another of said pressure vessels; a gas turbine system with a
compressor connected to an intermediate space between said
unit and the respective pressure vessel and between said
fluidized bed burner chamber and the respective pressure
vessel, said intermediate space being subjected to air over
pressure from said gas turbine system; ducts connecting said
pressure vessels; said connecting conduit being positioned
between said fluidized bed burner chamber and said cyclone as
well as said return flow conduit from said dip pot and said
fluidized bed cooler and leading to said fluidized bed burner
chamber being passed through said ducts.
In a further aspect of the invention, there is provided a
steam generator with pressurized, circulating fluidized bed
firing, comprising: a fluidized bed burner chamber; at least
one cyclone connected to a flue gas side of said fluidized bed
burner chamber through a connecting conduit; said cyclone
having a solids output; a fluidized bed cooler connected
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behind said cyclone; a dip pot connected to said solids output
of said cyclone and to said fluidized bed cooler; a return
flow conduit connected to said dip pot and entering into said
fluidized bed burner chamber; a plurality of pressure vessels,
one of said pressure vessels housing said fluidized bed burner
chamber, said fluidized bed cooler, said dip pot, and said
cyclone being combined into a unit, said unit being housed in
another of said pressure vessels; said unit being suspended in
said other pressure vessel; said fluidized bed cooler having
an output end connected to said return flow conduit; said
return flow conduit being connected to said dip pot and to
said output end of said fluidized bed cooler; walls of tubes
welded gas-tight together and defining said fluidized bed
cooler, said cyclone, said dip pot, said return flow conduit,
said connecting conduit, and said fluidized bed burner
chamber; a common water-steam circuit operated under
continuous flow and connected to said walls of tubes arranged
in series with respect to said water-steam circuit; said walls
of tubes being connected directly free of intermediate
collectors positioned therebetween; said walls of tubes
arranged so that tubes with downward flow are adjacent tubes
with upward flow; ducts connecting said pressure vessels, said
connecting conduit being positioned in said ducts; said
connecting conduit and said return flow conduit comprise walls
of tubes and forming a connection between said walls of tubes
inside said pressure vessels; secondary air nozzles opening
into said fluidized bed burner chamber and open to an
intermediate space between an inner wall of said one pressure
vessel and wall of tubes of said fluidized bed burner chamber;
return flow blocking means in said nozzles; said fluidized bed
burner chamber, said dip pot, and said fluidized bed cooler
having a respective nozzle floor with separate air supply
conduits respectively; a gas turbine system with a compressor
connected to an intermediate space between said units and the
respective pressure vessel and between said fluidized bed
burner chamber and the respective pressure vessel, said
intermediate space being subjected to air over pressure from
said gas turbine system.
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In a further aspect of the invention, there is provided a
steam generator with pressurized, circulating fluidized bed
firing, comprising: a fluidized bed burner chamber, at least
one cyclone connected to a flue gas side of said fluidized bed
burner chamber through a connecting conduit; said cyclone
having a solids output; a fluidized bed cooler connected
behind said cyclone; a dip pot connected to said solids output
of said cyclone and to said fluidized bed cooler; a return
flow conduit connected to said dip pot and entering into said
fluidized bed burner chamber; a plurality of pressure vessels,
one of said pressure vessels housing said fluidized bed burner
chamber; said fluidized bed cooler, said dip pot, and said
cyclone being combined into a unit, said unit being housed in
another of said pressure vessels; said unit being suspended in
said other pressure vessel; said fluidized bed cooler having
an output end connected to said return flow conduit; said
return flow conduit being connected to said dip pot and to
said output end of said fluidized bed cooler; walls of tubes
welded gas-tight together and defining said fluidized bed
cooler, said cyclone, said dip pot, said return flow conduit,
said connecting conduit, and said fluidized bed burner
chamber; a common water-steam circuit operated under
continuous flow and connected to said walls of tubes arranged
in series with respect to said water-steam circuit; said walls
of tubes being connected directly; said walls of tubes
arranged so that tubes with downward flow are adjacent tubes
with upward flow; ducts connecting said pressure vessels, said
connecting conduit being positioned in said ducts; said
pressure vessels being connected through ducts enclosing said
connecting duct and said return flow duct; said connecting
duct and said return flow duct forming the connection between
said walls of tubes arranged within said pressure vessels.
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The invention provides a boiler arrangement with relatively
low space and material requirements. Furthermore, in the
arrangement of the invention, the characteristics of a low
pollution combustion reaction, including unavoidable
tolerances, are considered independently from a process point
of view. They are also considered independent of the
individually different characteristics of the solids transport
and the heat exchange and the also unavoidable associated
tolerances. This results in an especially flexible
arrangement which is stable over wide load ranges and can be
operated for any selected steam parameter. A further
advantage is the favourable exploitability of extreme steam
parameters by using highly alloyed materials at moderate
intake temperatures and in especially small amounts. The
current operational limits observed with boilers of known
construction operated with flexible fuels, which limits result
from the load capacity of the pipe walls surrounding the
burner chamber and their material specifications, thereby no
longer exist.
A preferred embodiment of the boiler in accordance with the
invention is shown in the drawing and will be further
described in the following by way of example only. The
drawing schematically illustrates a boiler arrangement.
Of a combined gas-steam power plant, only the boiler is shown.
The boiler is heated by way of a circulating fluidized bed
firing and includes a fluidized bed burner chamber 1. The
fluidized bed burner chamber 1 is defined by the walls 2 of
tubes which are surrounding the chamber and are welded
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together gas-tight. The cross section of the fluidized bed
burner chamber 1 is downwardly sonically tapered in the lower
part and along two opposing walls which are not shown in the
drawing. The tube walls 2 of the fluidized bed chamber 1 are
ceramically coated especially in the lower highly solids-
enriched part in order to prevent wear of the tubes. However,
the upper part of the fluidized bed burner chamber 1 which is
less loaded with solids can also be provided with a ceramic
coating with advantageous heat transfer characteristics to
protect it against wear by the solids. No heat exchange
surfaces are provided within the fluidized bed burner chamber
1. The fluidized bed burner chamber 1 is downwardly closed by
a nozzle floor 3. One or more connecting conduits 4 which
respectively lead to a cyclone separator 5 are connected to
the fluidized bed burner chamber 1. In the cyclone separator
5, the suspended solids are separated from the flue gas. The
solids-free flue gas is guided to a hot gas filter through a
dip conduit 6 of the cyclone separator 5. Subsequently, the
hot gas is guided, without cooling, to the not illustrated gas
turbine installation.
The solid's output of the cyclone separator 5 opens into a dip
pot 8 provided with a nozzle floor 7. The dip pot 8
principally operates as a syphon and as a solids return flow
check valve to prevent a short circuit on the flue gas side
between the fluidized bed burner chamber 1 and the cyclone
separator 5. The open side of the dip pot 8 is provided with
an overflow gate and connected to a return conduit 10. The
return conduit 10 discharges into the fluidized bed burner
chamber 1.
The dip pot 8 is provided with an opening for the removal of a
portion of the main solids return flow which opening is
closable by a control member 11. The control member 11 can be
an externally operable lancet-shaped valve provided with
ceramic or metallic wear and heat protection. However, an
overflow with gate can be used which is pneumatically operated
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with combustion air and the overflow edge of which can be
horizontal or slanted. The control of the pneumatic air flow
can be continuous, intermittent or pulsed. The height of the
overflow edge can be fixed or variably adjustable relative to
the height of the overflow of the dip pot 8.
The secondary solids flow which is divided out from the dip
pot 8 by way of the control element 11 is guided to fluidized
bed cooler 12 which is positioned below the dip pot 8. The
fluidized bed cooler 12 includes several chambers 13 which are
separated by a separation wall 14. Each chamber 13 of the
fluidized bed cooler 12 houses one heat exchanger bundle 15.
A nozzle floor is provided below each chamber 13 through which
air is blown for fluidizing the solids contents of the chamber
13. The nozzle floors of the chambers 13 can be supplied with
fluidizing air from the same or separate sources. In the
illustrated case, two chambers 13 are positioned side by side.
Especially at higher throughput, the chambers 13 can also be
positioned one above the other. The flow of the solids
through the chambers 13 can be upward or downward. The
chambers 13 of the illustrated fluidized bed coolers 12 are
connected to each other below the heat exchanger bundles 15
and through an opening 17 in the separation wall 14. In this
way, a downward flow is induced in the first chamber 13
exposed to the solids and an upward flow in the chamber 13
subsequently exposed to the same solids. It is also possible
to guide a partial solids stream downward and to directly
guide a make up solids stream to the subsequent chambers 13 by
appropriately selecting the height of the gate in the
separation wall 14 between the chambers 13.
The output end of the chamber exposed last is connected to the
return conduit 10. In this way, the solids as well as the
fluidizing air are guided from the fluidized bed cooler 12 and
the dip pot 8 through the return conduit 10 and into the
fluidized bed burner chamber 1. The solids transported from
the fluidized bed burner chamber 1 into the cyclone separator
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are used as heat carrier from which heat is extracted in the
fluidizing bed cooler 12 with the help of the fluidizing air
which is a portion of the combustion air. The solids thereby
develop a high heat transition capacity whereby large amounts
of heat can be transferred with the smallest heat transfer
surfaces. After the heat transfer, the cooled solids stream
is fully or partly mixed with the uncooled solids return
stream and returned to the fluidized bed burner chamber 1.
The cyclone separator 5, the dip pot 8, the fluidized bed
cooler 12, the connecting conduit 4 and the return flow
conduit 10 are defined by the walls of gas tight welded
together tubes, just as the fluidized bed burner chamber 1.
The tube walls are made of planar pipe panels and form a
polygon whereby the lowest number of corners is 4. The tube
walls are protected against unacceptable deformation by
appropriate external reinforcing bands.
To compensate the high gas counter pressure of the gas
turbine, the individual components of the boiler are housed in
separate, cylindrical pressure vessels with preferably
vertical axes. A first pressure vessel 18 encloses the
fluidized bed burner chamber 1. A further pressure vessel 19
houses respectively a cyclone separator 5 with the dip pot 8
positioned therebelow and the fluidized bed cooler 12. The
cyclone separator 5, the dip pot 8 and the fluidized bed
cooler 12 are combined into a unit which is suspended in the
respective pressure vessel 19 by way of anchors 20.
The cylindrical pressure vessels 18, 19 are connected by
cylindrical ducts 21, 22 having horizontal or inclined axes.
Positioned within these ducts 21, 22 are the pipe-shaped
connecting conduits 4 and return conduits 10 for the fluid and
solids transport from the fluidized bed burner chamber 1 to
the other components and vice versa. These pipe shaped
conduits 4, 10 at the same time provide the connection between
the pipe systems positioned in the individual pressure vessels
18, 19.
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The intermediate space between the pressure vessels 18, 19 and
the components positioned therein, which are surrounded by the
gas tight tube walls, is kept at a slight over-pressure
relative to the gas operating pressure in the interior of the
components. This over-pressure is produced by blowing
blocking air from the gas turbine compressor of the associated
gas turbine installation into the intermediate space by way of
an air conduit 25 and through a control valve 23. The
blocking air at the same time serves as secondary air for the
fluidized bed firing. Secondary air nozzles 24 are provided
for this purpose penetrate the tube walls 2 in the upper part
of the fluidized bed burner chamber 1, are open to the
intermediate space and are respectively provided with a return
flow check valve arrangement (not illustrated). The over
pressure is adjusted by way of the secondary air nozzles 24
and preferably self-regulating because of the dynamic
resistance of the fluidized bed burner chamber 1. In special
circumstances, the over pressure can be adjusted with the help
of a regulating arrangement. The remaining air flows, such as
the primary and fluidizing air for the fluidized bed burner
chamber 1 and the fluidizing air for the dip pots 8 and the
fluidized bed coolers 12 are necessarily guided to the
individual nozzle floors 3, 7, 16 by way of separate air
conduits 26, 27, 28 respectively.
On the water/steam side, the individual tubes of the tube
walls are connected in series and are part of a common
water/steam circuit. This water/steam circuit is operated
with continuous flow according to the Benson principle. The
serial connection in the water/steam circuit is carried out
in such a way that the flow preferably passes first through
the tube walls of one of the fluidized bed coolers 12 and the
associated cyclone separator 5 with dip pot 8 and subsequently
without intermediate collector through the connecting conduit
4 and the return conduit 10 which is positioned in the same
pressure vessel 19. In this way, the water/steam mixture
carrying pipe system is guided without additional connecting
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conduits into the fluidized bed burner chamber 1. The second
fluidized bed cooler-cyclone separator-group is connected in
reverse series to the pipe system of the fluidized bed burner
chamber with multiple upwards and downward flows. Thereafter
follow the heat exchanger bundles 15 of the fluidized bed
cooler 12, which are operated as further evaporators and as
superheaters. The economizer is positioned in the exhaust
heat vessel placed in series after the gas turbine.
