Note: Descriptions are shown in the official language in which they were submitted.
CA 02741100 2013-05-14
High Pressure Oxy-Fuel Combustion System (HiPrOx) Bottoming Cycle
Field of the Invention
This invention relates to combustion systems for industrial processes,
including but not
limited to electric power generation. More particularly, the invention relates
to a high
pressure oxy-fuel system, and the delivery of thermal energy from condensation
from the
flue gas of the high pressure oxy-fuel system to an organic Rankine cycle
system.
Concurrently, direct thermal energy from the combustion in the system of the
invention
can be provided to a Rankine cycle or a wide variety of other systems.
Background of the Invention
In the ongoing aim to reduce the emission of greenhouse gases in industrial
processes
which generate carbon dioxide, but while continuing to use fossil fuels which
are
generally otherwise preferable over other fuels for practical and economic
reasons,
attempts have been made to simplify the isolation of the carbon dioxide so
that it can be
removed from the processes for sequestration or other containment or use. In
particular, it
has been found that the replacement of ambient air by concentrated oxygen in
what are
known as oxy-fuelled or oxy-fired combustion processes is advantageous in that
the
absence of the high levels of nitrogen and other constituents in air, thus
avoiding the need
to separate either the nitrogen or other constituents. Further, the absence of
nitrogen
avoids the formation of NOx and other problematic compounds, and the high
costs in
situations where these are required to be separated. Oxy-fuel systems thus
result in a flue
gas which has a high purity level of carbon dioxide and requires minimal or no
further
separation treatment before being prepared, for example by pressurization, for
sequestration or use.
Oxy-fuel systems are advantageous in that they provide relatively simple
solutions which
are applicable to new systems or the retrofit of existing systems. However,
such systems
when operated at ambient pressure suffer from disadvantages of inefficiency,
as well as
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the higher costs arising from the need for an air separation unit for
provision of the
oxygen, and the costs of the carbon dioxide product recovery train.
Oxy-fuel systems operate at significantly higher temperatures than air-fired
systems, and
thus require temperature control. There are various known methods of
temperature
moderation, including staging, the use of fluid beds, or the recirculation of
a portion of
the flue gas back to the combustor.
It has therefore been proposed to use high pressure for oxy-fuel systems, to
address at
least some of the above disadvantages, and to allow for a significant
reduction in size for
the structures used. For example, US 6,196,000 (Fassbender) proposes a
pressurized
Rankine cycle oxy-fuel system, allowing for reduced equipment size, and for
condensing
the carbon dioxide at ambient heat-sink temperatures, thus minimizing the need
for multi-
stage compression and refrigeration; and for increased efficiency from the use
of waste
heat to replace regenerative extraction from the turbine. However, the
proposed system
suffers from various disadvantages, some of which apply to oxy-fuel systems in
general,
including increased costs for high pressure oxygen feed, and difficulty in
achieving
temperature moderation using flue gas as recirculation. The proposed system
included the
variation in the conventional configurations of feedwater heaters, by removing
some of
them and instead using heat from condensed moisture in the flue gas. However,
conventional feedwater heater arrangements are highly developed and efficient,
and any
changes in those result in the need to adjust various other aspects of the
system, including
to address the effects of altering the regenerative extraction from the
turbine; problems in
making such adjustments present a significant disadvantage of the proposed
system.
One advantage of high pressure operation is that it changes the temperature
condition at
which the gas to liquid phase change occurs for the flue gas, which thus
allows for water
vapour in the flue gas to be condensed at much higher temperatures than in air-
fired
systems. For example, moisture in the flue gas condenses in the range of 150 C
to 200 C
at 80 bar, as compared with 50 C to 55 C in ambient pressure oxy-fuel systems.
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It has now been found that this, and other advantages, makes the condensate
from the flue
gas of a pressurized oxy-fuel system a suitable heat source for use in various
processes,
including but not limited to power generation systems and similar systems,
including
Brayton cycles, Rankine cycles and binary fluid cycles, and it is particularly
advantageous to use such flue gas condensate to provide heat to organic
Rankine cycles.
It has further been found advantageous to use the direct heat of the combustor
of the
system and the method of the invention to provide a direct heat energy source
for various
secondary systems, including but not limited to Brayton cycles, Rankine cycles
and
binary fluid cycles. Further, it has been found to be particularly
advantageous to provide
the heat of the condensate as a bottoming cycle to an organic Rankine cycle
system, and
to provide the direct heat of the combustion within a secondary Rankine cycle
system,
without making any modification to the conventional feedwater heater
arrangements.
Summary of the Invention
The invention therefore seeks to provide a combustion system for operational
connection
to an industrial process system, the combustion system comprising
(a) a combustor constructed and arranged to be selectively operable at a
selected
operational pressure exceeding atmospheric pressure, and comprising
(i) a combustor wall comprising a combustion chamber;
(ii) a burner;
(iii) at least a first fuel inlet constructed and arranged to deliver a first
fuel to the
burner at a delivery pressure exceeding the selected operational pressure;
(iv) at least one oxidant inlet constructed and arranged to deliver a supply
of
oxygen having a purity of at least 22% to the burner at a delivery pressure
exceeding the selected operational pressure;
(v) an outlet region having a flue gas outlet;
(b) a flue gas delivery means, constructed and arranged to be operatively
connected to the
flue gas outlet, to receive a supply of flue gas therefrom at a pressure
exceeding
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atmospheric pressure and to deliver at least part of the supply of flue gas to
a heat
removal means comprising
(i) at least one condensing means to produce condensate from the supply of
flue
gas; and
(ii) a heat delivery means to deliver heat from the condensate to the
industrial
process system.
Preferably, the condensing means and the heat delivery means comprise at least
one
condensing heat exchanger.
Preferably, the first fuel inlet is constructed and arranged to deliver a
first fuel selected
from at least one of a solid fuel, a liquid fuel, a gaseous fuel, and
combinations thereof
Preferably, the at least one oxidant inlet is constructed and arranged to
deliver a supply of
oxygen having a purity of at least 80%, more preferably at least 95%.
Optionally, the flue gas delivery means comprises a flue gas recirculation
outlet and the
combustor further comprises at least one flue gas recirculation inlet, and the
flue gas
recirculation outlet is constructed and arranged to selectively deliver a
supply of part of
the flue gas to selective ones of the at least one flue gas recirculation
inlet.
The industrial process system can be a power generation system, for example an
electric
power generation system. Alternatively, the combustion system is constructed
and
arranged to be operationally connected to and deliver the heat from the
condensate to a
low temperature power cycle system.
In some embodiments, the combustion system is constructed and arranged to be
operationally connected to and deliver the heat from the condensate to a
system selected
from a Brayton cycle system, a Rankine cycle system, and a binary fluid cycle
system.
Preferably, the combustion system is constructed and arranged to be
operationally
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connected to and deliver the heat from the condensate to an organic Rankine
cycle
system.
Where the combustion system is constructed and arranged to be operationally
connected
to a binary fluid cycle system, preferably that system is a Kalina cycle.
Preferably, the combustor is further constructed and arranged to be
operationally
connected to and deliver direct heat to a secondary system. Such secondary
system can be
selected from an engine, a secondary industrial process system and a secondary
power
system; and selected from a Brayton cycle system, a Rankine cycle system, and
a binary
fluid cycle system. Where the secondary system comprises a binary fluid cycle
system,
preferably it is a Kalina cycle.
In some embodiments, the secondary system is a secondary industrial process
system
comprising a Rankine cycle system having a flow path for a flow of working
fluid, the
flow path being constructed and arranged to deliver the flow through a low
pressure
turbine, and thereafter to deliver at least part of the flow selectively to an
evaporator in
the organic Rankine cycle system.
The invention therefore further seeks to provide a method of providing heat
energy to an
industrial process system, the method comprising the steps of
(a) providing a combustion system according to the invention and selecting an
operational pressure;
(b) connecting the flue gas delivery means to the heat removal means, and
connecting the
heat removal means to the industrial process system;
(c) delivering a supply of the first fuel to at least the first fuel inlet at
a delivery pressure
exceeding the selected operational pressure;
(d) delivering a supply of oxygen having a purity of at least 22% to the
burner at a
delivery pressure exceeding the selected operational pressure;
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(e) operating the combustor at the selected operational pressure to generate a
supply of
flue gas, and delivering at least part of the supply of flue gas to the heat
removal means;
(f) producing condensate from the supply of flue gas, and delivering heat from
the
condensate to the industrial process system.
Preferably, step (d) comprises delivering a supply of oxygen having a purity
of at least
80%, more preferably at least 95%.
Optionally, step (b) comprises providing the flue gas delivery means with a
flue gas
recirculation outlet and step (e) further comprises delivering at least a part
of the supply
of flue gas through the recirculation outlet and into the combustor.
The invention therefore further seeks to provide a method of providing heat
energy to an
industrial process system, the method comprising the steps of
(a) providing a combustion system according to the invention and selecting an
operational pressure;
(b) connecting the flue gas delivery means to the heat removal means, and
connecting the
heat removal means to the industrial process system;
(c) connecting the combustor to the secondary system;
(d) delivering a supply of the first fuel to at least the first fuel inlet at
a delivery pressure
exceeding the selected operational pressure;
(e) delivering a supply of oxygen having a purity of at least 22% to the
burner at a
delivery pressure exceeding the selected operational pressure;
(t) operating the combustor at the selected operational pressure to produce
heat energy
and generate a supply of flue gas;
(g) delivering heat energy to the secondary system and delivering at least
part of the
supply of flue gas to the heat removal means;
(h) producing condensate from the supply of flue gas, and delivering heat from
the
condensate to the industrial process system.
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Preferably, step (e) comprises delivering a supply of oxygen having a purity
of at least
80%, more preferably at least 95%.
Optionally, step (b) comprises providing the flue gas delivery means with a
flue gas
recirculation outlet and step (g) further comprises delivering at least a part
of the supply
of flue gas through the recirculation outlet and into the combustor.
Brief Description of the Drawings
The invention will now be described with reference to the drawings, in which
Figure 1 is a schematic representation of a conventional layout of a Rankine
cycle system
of the prior art;
Figure 2 is a schematic representation of a combustion system in an embodiment
of the
invention;
Figure 3 is a schematic representation of a combustion system in a second
embodiment of
the invention; and
Figure 4 is a schematic representation of a combustion system in a third
embodiment of
the invention.
Detailed Description of the Drawings
Referring to Figure 1, this is a schematic representation of a conventional
layout of a
Rankine cycle system 10 of the prior art. Various layouts are known and used,
but in
accordance with the principles of operation of such cycles, each includes at
least the
elements shown in Figure 1. In sequence, the working fluid (not shown) passes
through
boiler/evaporator 11, is expanded in turbine 13, passes through regenerator
(also known
as recuperator) 14, and thence to condenser 15. From condenser 15, the working
fluid is
pumped by pump P, and passed through regenerator 14 for preheating before
being
returned to boiler/evaporator 11.
Referring now to Figure 2, an embodiment of the invention is shown in a
schematic
representation, in which furnace 30 is operationally connected to an organic
Rankine
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cycle 220, and a secondary Rankine cycle 50. Organic Rankine cycle 220
comprises high
temperature evaporator 21, turbine 23, regenerator 24 and condenser 25, and
will have a
suitable working fluid selected from those known and permitted to be used
pursuant to
any applicable regulations.
Furnace 30 is designed for high pressure oxy-firing, and is fed by fuel supply
from line
32 at fuel inlet 33, and oxygen supply from line 34 at oxygen inlet 35. Oxygen
is supplied
at the selected level of purity, by known methods, for example from an air
separation unit
(not shown). Flue gas generated by the combustion leaves furnace 30 in flue
gas line 36.
Optionally, a recirculation stream can be separated from the flue gas stream
in flue gas
line 36, to be selectively recirculated back in flue gas recirculation line 38
to be
reintroduced to the furnace in a suitable manner, either through a separate
inlet (not
shown) or by joining the oxygen supply in line 34. The main flue gas stream is
delivered
to a condenser 40 at flue gas inlet 39. Condenser 40 can be of any known
construction,
and is preferably a condensing heat exchanger.
In condenser 40, water is condensed from the flue gas stream, the condensate
passes
through outlet 41 and condensate line 42 to be delivered to high temperature
evaporator
21 at condensate inlet 43, and the heat of condensation is provided to high
temperature
evaporator 21, to contribute to the heating of the working fluid in organic
Rankine cycle
220. The remaining gaseous portion of the flue gas stream, mostly pressurized
carbon
dioxide, leaves condenser 40 at outlet 44, and passes through line 45 to a
carbon dioxide
capture system 46, where impurities are removed by known means, and the carbon
dioxide product stream is removed for further processing, use or sequestration
.
Concurrently with providing heat of condensation to organic Rankine cycle 220,
furnace
can be used to provide direct heat of combustion to various types of system
requiring
heat energy. In the exemplary embodiment of Figure 2, furnace 30 is shown as
operationally connected to a Rankine cycle 50 of a conventional configuration
and shown
30 here as having water as the working fluid. In Rankine cycle 50, expanded
working fluid
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leaves intermediate pressure/low pressure turbine 52, passes through and is
condensed in
condenser 56, and passes to a first group of feedwater heaters 53, shown here
as
feedwater heaters 53a, 53b and 53c. Extracted heat can be selectively provided
to each of
feedwater heaters 53a, 53b and 53c from intermediate pressure/low pressure
turbine 52.
The working fluid then passes to a second group of feedwater heaters 55, shown
here as
feedwater heaters 55a and 55b. Extracted heat can be selectively provided to
each of
feedwater heaters 55a and 55b from high pressure turbine 54. The working fluid
then
passes to reheater 57, which is supplied with heat from furnace 30, and
delivered to and
expanded in high pressure turbine 54 to provide energy to the process or
system being
powered by Rankine cycle 50. Thereafter, the working fluid is reheated in
reheater 58,
which is also supplied with heat from furnace 30, before passing to and being
expanded
in intermediate pressure/low pressure turbine 52 to provide energy to the
process or
system being powered by Rankine cycle 50, and to complete the cycle.
In each of Figures 2 to 4, it will be appreciated that various known
structural elements
will be included in the embodiments of the invention, such as pumps, valves
etc. For
simplification, these are not included in the figures in general, but some of
the pumps are
included where this would assist in understanding the invention, and are
identified
generically as P.
Referring now to Figure 3, a second exemplary embodiment of the invention is
shown in
a schematic representation. In this embodiment, again furnace 30 supplies the
heat of
condensation of flue gas to organic Rankine cycle 320, in the same manner as
in the
configuration shown in Figure 2; and provides direct heat to Rankine cycle
350, which is
shown as having water as the working fluid. However, organic Rankine cycle 320
is
provided with a low temperature evaporator 22, which preheats the working
fluid of
organic Rankine cycle 320 after the working fluid leaves regenerator 24 and
before it
enters high temperature evaporator 21. Working fluid from Rankine cycle 350
leaving
intermediate pressure/low pressure turbine 52, instead of passing directly to
steam
condenser 56, passes in line 70 to low temperature evaporator 22, where it
provides heat
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to the working fluid of organic Rankine cycle 320. Thereafter the working
fluid in
Rankine cycle 350 returns in line 72 to steam condenser 56.
Referring now to Figure 4, a further exemplary embodiment of the invention is
shown in
a schematic representation. In this embodiment, again furnace 30 supplies the
heat of
condensation of flue gas to organic Rankine cycle 420, in the same manner as
in the
configurations shown in Figures 2 and 3; and provides direct heat to Rankine
cycle 450,
which is shown as having water as the working fluid. Further, in the same
manner as in
the configuration shown in Figure 3, organic Rankine cycle 420 is provided
with low
temperature evaporator 22, which preheats the working fluid of organic Rankine
cycle
420 after the working fluid leaves regenerator 24 and before it enters high
temperature
evaporator 21. However, in this embodiment, when the working fluid from
Rankine cycle
450 leaves intermediate pressure/low pressure turbine 52, it is split into two
streams, one
of which passes in line 470 to low temperature evaporator 22, where it
provides heat to
the working fluid of organic Rankine cycle 420, before returning in line 472
to the input
region 60 of steam condenser 56, where it is joined by the second stream
passing directly
to steam condenser 56 from intermediate pressure/low pressure turbine 52 in
line 474.
As noted above, the system and methods of the invention provide an
advantageous use
for condensate in the flue gas of a pressurized oxy-fuel system, which can be
readily
connected to many types of conventional systems, without requiring significant
modification to those systems, which is of particular significance in relation
to (1)
delivery of the thermal energy from condensation to all manner of organic
Rankine
cycles; and (2) connection to Rankine cycles for the provision of direct heat
from the
combustor, where the connection of the system of the invention to the Rankine
cycle can
be made without requiring any modification to the highly developed and complex
arrangements for the feedwater heaters.
