Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02352474 2001-07-25
FIELD OF THE INVENTION
Retrofit conversion of existing conventional thermal fuelled electrical
power generators with a system utilizing natural gas and steam generators,
thereby reducing the amount of pollutants released into the atmosphere and
increasing the efficiency of the generating station, for a given unit value of
fuel.
BACKGROUND OF THE INVENTION
Existing conventional power stations presently fired by regulated fuel
sources, such as coal and oil burning generators, are considered major
polluters
of the environment. Key air pollutants are nitrogen oxides (NOx), sulphur
dioxide, (S02), carbon dioxide (C02) and mercury (Hg). Both NOx and SOZ
cause acid rain while NOx, along with volatile organic compounds (VOCs), is an
important precursor gas to ozone, a major component of smog. C02 is a key
greenhouse gas, contributing to the threat of climate change. Mercury is a
potent nerve-toxin that builds up in the food chain.
Burning of these fuels, is considered to be the predominant producer of these
gases and greenhouse gases. Since these fuels are non-renewable, continued
use of these fuel sources are taxing on the environment. It would be desirable
to
use alternative fuel sources that would be less taxing on the environment and
would burn cleaner and therefore reduce the amount of pollutants and
greenhouse gases released into the atmosphere. The same is also true for
different reasons for nuclear powered stations.
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However capital costs of constructing entire new generation plants, makes it
impractical to discard existing old coal, oil fired, and nuclear power plants,
and
replacing them with entirely new power plants. In most cases existing plants
have been written off in the past. They have virtually no resale value.
It is clearly desirable therefore to retain, as far as possible, existing
plants, but
convert the fuel system to a more efficient and less environmentally damaging
system.
This invention outlines the method of retrofitting existing polluting power
generating stations for use with natural gas fuel.
The invention also provides an apparatus for carrying out the method. The
invention also provides increased efficiency for a given unit value of fuel.
The invention also envisages partial attenuation of use of existing polluting
fuels
by less polluting fuels, where total replacement is not adequate.
BRIEF SUMMARY OF THE INVENTION
The invention seeks to provide the foregoing improvements by the method of
converting an existing thermal electrical generating station, from
conventional
fuels such as coal/oil, or nuclear power, to natural gas. The method used,
includes retaining the existing steam turbine electrical generator of the
existing
station or other systems which used steam turbines, such as water treatment
facilities. The method also includes erecting a gas turbine prime mover along
side the existing generating station. The erected gas turbine is used to
produce
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electrical energy by the method of connecting at least one gas turbine prime
mover to at least one electrical generator, for generating electricity to be
supplied
to a supply grid. The method also connects the hot exhaust from at least one
gas turbine to at least one heat recovery steam generator and connecting it to
the steam turbine of the existing generating plant and either disconnecting
the
steam boiler or reducing the fuel consumption at the existing generating
plant.
The method of operating at least one gas turbine to generate a first supply of
electricity, and supplying same to a grid and, operating the steam turbine of
the
existing generation plant to generate a second supply of electricity and
supplying
same to a grid.
The methods further comprises the steps of, connecting the steam outlet of the
steam turbine back to the heat recovery steam generator, whereby to recycle
calorific values of the waste steam.
The method further comprises operating at least one gas turbine by continuous
introduction of air, compressing the air, introducing gas into the compressed
air,
and igniting the gas and compressed air to create a high pressure exhaust of
combustion products of gas and air. A gas turbine shaft is coupled to drive a
generator to generate electrical power as aforesaid.
The r'nethod further comprises introducing feed water to at least one heat
recovery steam generator , and preheating the feed water with condensed steam
from the steam turbine of the existing plant.
The invention seeks to achieve the foregoing improvements by providing
apparatus for converting all or part of an existing conventional thermal
electrical
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generating station, from a fuel such as, coal/oil, or nuclear to natural gas,
while
retaining the existing steam turbine and at least one electrical generator of
the
existing station and in which a gas turbine prime mover is erected adjacent
the
existing electrical generating station, at least one electrical generator is
connected to at least one gas turbine, and is connected to supply power to a
grid. The apparatus also includes at least one heat recovery steam generator
connected to the exhaust of at least one gas turbine to generate steam. There
is
at least one steam connection between at least one heat recovery steam
generator, and the existing steam turbine, which in turn is connected to at
least
one electrical generator in the existing plant, whereby the gas powered plant
is
operable to generate a first electrical supply from the gas turbine powered
generators, and to supply steam to generate a second electrical supply from
the
existing steam turbine powered generator.
The apparatus also includes a steam condenser connected to at least one steam
turbine and connected back to at least one heat recovery steam generator.
The apparatus for converting an existing thermal electrical generating
station,
including a feed water supply connected between at least one heat recovery
steam generator and at least one steam condenser, for preheating the feed
water.
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IN THE DRAWINGS
Figure 1 illustrates Prior art of existing thermal fuel burning power plants,
wherein
duplicate components are shown in phantom;
Figure 2 illustrates retrofitted power plant using natural gas fuel, wherein
duplicate components are shown in phantom.
DESCRIPTION OF A SPECIFIC EMBODIMENT
Referring generally to Figure 1, labeled "Prior Art", it will be seen that the
existing
power plant, indicated as number (10), consists of an existing fuel source(11)
used
to fire a boiler(12). Boiler(12) produces steam(13) which is connected to a
steam
turbine(14). Steam turbine(14) is connected via a turbine shaft(not shown) to
an
electrical generator(16) for producing electricity which is delivered to a
power
grid(18). Steam turbine(14) is also connected to a condenser(20), in which
steam
(13) is condensed to hot water, typically known as condensate(24). The
condensate(24) is connected to a make-up water(26) source, a supplementary
source used to replace water lost due to evaporation and leakage. The
condensate(24) is cycled back to boiler(12). In the case of many existing
power
plants, coal or heavy oil(11) is used as fuel to fire the boilers to heat
water to
steam(13). These fuels are regulated resources, and there is public pressure
to
move away from burning these fuels, due to the high levels of solid and
gaseous
pollutants. Also, since these fuels are used for other purposes, the
conversion of
power generating stations will reduce the demand for such fuels, thereby
prolonging
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the lifetime of existing resources. We will refer to boilers using coal , oil
or nuclear
fuel sources as "existing fuels", throughout the description, for ease of
explanation.
It should be noted that this invention may also be applied to nuclear power
stations,
which also have many environmentally damaging properties, such as threat of
heavy
water leaks, or radiation contamination.
Currently, to change the fuel burned in a power plant, would entail replacing
the
boilers, and expensive retooling of the existing equipment. Alternatively,
completely
new power generating plants would have to be built. Both of these options are
expensive endeavors. The capital cost of either alternative would cause a
significant and unacceptable increase in the price charged to the consumers of
electrical power. It would be desirable to develop a system that could offer a
different means of powering the turbine while, use existing equipment as far
as
possible, and keep the costs of retooling down.
Figure 2 illustrates an embodiment of the invention. In this embodiment the
second
power plant(28) is erected beside the existing thermal power plant(10). Second
power plant(28) includes gas turbine(30), fired by natural gas(32). Gas
turbine(30)
is connected by a turbine shaft(not shown) to an electrical generator(33).
Electrical
generator(33) is connected to grid(18) to which electricity is delivered.
The exhaust(34) from the gas turbine(30) is connected to a heat recovery steam
generator(36). The heat from the exhaust(34) is used to produce high pressure
steam(38), which is connected to steam turbine(14) of the existing power
plant(10),
where it is used to produce electricity in a method well known in the art.
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As explained above, steam turbine(14) is connected to condenser(20), in which
steam (13) and high pressure steam(38) are condensed to hot water, typically
known as condensate(24). The condensate(24) is connected to make-up water(26)
which replaces water lost due to evaporation and leakage. Combined
condensate(24) and Make-up water(26) are connected to boiler(12).
Condensate(24) is also connected to make-up water (42). Make-up water(42) and
condensate(24) are connected to the heat recovery steam generator(36).
STATEMENT OF OPERATION
In operation of the original prior art plant, the existing fuels (11) are
burned in the
boiler (12) to heat the condensate (24) to steam (13). The steam (13) is then
injected into a steam turbine (14) causing the steam turbine shaft (not shown)
to
turn. The steam turbine shaft is connected to an electrical generator (16) to
produce electricity. The electricity is then exported to the consumer
typically using
a grid (18). After passing over the steam turbine shaft, the injected steam
(13) is
then condensed by the condenser (20) into hot water, typically called
condensate
(24). Make up water (26) is added to the condensate (24) to compensate for
evaporation and leakage throughout the system. The condensate (24) is then
pumped (not shown) into the boiler (12) to complete the cycle. This describes
the
normal, unmodified power plant.
When modified according to the invention the second power plant (28), which is
erected beside the existing power plant(10), will include a natural gas fired
gas
turbine (30).
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The gas turbine(30) is of conventional construction, similar in many respects
to an
aircraft jet engine. Air is inducted and compressed by intake fans. Natural
gas
(32) is injected into the compressed air and ignited. The combustion products,
or
exhaust(34), then pass through sets of turbine blades mounted on a central
turbine
shaft (not shown). All of this is well known and requires no illustration.
The combustion of the gas and compressed air create a high pressure/high
temperature exhaust of combusted products, and are passed from the gas turbine
(30) to the heat recovery steam generator (36) to heat the condensate (24)
producing high pressure steam (38) and low pressure steam/hot water (40). Make
-
up water(42) is added to the condensate(24) to compensate for evaporation and
leakage.
The gas turbine (30) turns the gas turbine shaft (not shown), which is
connected to
the electrical generator (33), causing the electrical generator (33) to
produce
electricity. The electricity is then exported to the consumer typically using
a grid
(18).
The high pressure steam (38) is the injected into the steam turbine (14) of
the
existing power plant (10) producing electricity. The imported high pressure
steam
(38) combined with steam (13), which is produced by the boiler (12), cause the
steam turbine shaft (not shown) to turn. The steam turbine shaft is connected
to an
electrical generator (16) to produce electricity. The electricity is then
exported to
the consumer typically using a grid (18).
After passing over the steam turbine shaft, the combined steam is then
condensed
into hot water, typically called condensate (24), by the condenser (20). A
portion of
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the condensate (24) is returned to second power plant(28). Make up water (42)
is
added to the condensate (24) to compensate for evaporation and leakage. The
condensate is then pumped into the heat recovery steam generator (36)
completing
the cycle.
The balance of the condensate (24), remaining in the existing power plant (10)
is
combined with the low pressure steam/hot water (40) thus increasing the amount
and temperature of the condensate. Alternatively, the low pressure steam/hot
water (40) could heat up the condensate (24) by the use of heat exchangers
(not
shown). Make up water (26) is added to the condensate (24) to compensate for
evaporation and leakage throughout the system. The condensate (24) is then
pumped (not shown) into the boiler (12) to complete the cycle.
The utilization of both the imported steam (38) and the low pressure steam/hot
water
(40) would significantly reduce the consumption amount of the existing fuels.
In the style of the existing plant(10) of Figure 1., in some cases it may be
possible to
dispense with the use of the existing boiler(12), and to discontinue use of
existing
fuel(11 ).
The foregoing is a description of a preferred embodiment of the invention
which is
given here by way of example only. The invention is not to be taken as limited
to
any of the specific features as described, but comprehends all such variations
thereof as come within the scope of the appended claims.
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