Note: Descriptions are shown in the official language in which they were submitted.
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This is a division of Canadian patent application
Serial No. 586,153, filed December 16, 19~8 for "C7AS TURBINE
PLANT SYSTEM AND GAS PRESSURE STABILIZER THEREOF IN EMERGENCY".
BACKGROUND OF THE INVENTION
(l) Field of the Invention
This invention relates to a heat recovery gas turbine
plant system supplied with a low-pressure industrial by-product
gas, for instance, blast furnace gas, as a fuel, and more
particularly to a gas pressure stabilizer for safely returning
a high-pressure fuel gas on the discharge side of a fuel gas
compressor into a low-pressure industrial by-product gas pipeline
at the time of emergency shut-down of a gas turbine in such a
system. Such gas turbine system can be employed in various
process plant such as a paper manufacturing and pulp processing
plant, a Portland cement manufacturing plant, a petroleum
refinery plant or the like where a by-product gas is obtained.
(2) Description of the Prior Art
As a power generation system employing a by-product
gas fired gas turbine supplied with blast furnace gas as a fuel,
2~ there has recently been developed
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a large scale system in which, as disclosed in Japanese
Patent Application Laid-Open No. 58-57012 (1983), the
blast furnace gas i~ compressed to be a high-pressure
gas, which is mixed with compressed air and burned, and
the combustion gas is used to drive a gas turbine,
thereby generating electric power.
In such a power generation system, when an
emergency shut-down of the gas turbine is required, for
example, when a power transmis~ion system is failed and
a shut-down interlocking device is operated, it is
nece~cary to cut off the supply of the fuel to the gas
turbine, for the shut-down of the ga~ turbine.
For the purpose of the emergency shut-down of
the gas turbine, it i~ necessary for a gas ~upply shut-
off valve to be located as close as possible to the
inlet to the ga~ turbine. It i~ also necessary that the
shut-off operation can be performed at a sufficiently
high speed.
The rapid clo~ing action (for in~tance, in 0.5
to 1 sec) of the ga~ supply shut-off valve closes the
passage on the discharge side of a gas compressor
continuously discharging the high-pressure ga~,
resulting in a rapid increase in the discharge pressure.
In practice, therefore, a bypass pressure reducing valve
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for releasing the high-pressure gas into a bypass line
must be rapidly opened simultaneously with the rapid
closing action of the gas supply shut-off valve so that
the passage on the discharge side of the gas compressor
is not colsed.
The high-pressure gas on the discharge side of
the gas compressor has, for instance, a pressure of
about 12 kg/cm2G and a temperature of about 350C. The
pressure of the high-pressure gas is lowered by the
pressure reducing valve. Then, the gas is further
lowered in pressure by a gas cooler disposed on the
downstream side of the valve and is, simultaneously,
cooled by a water Rpray, and the resultant low-pre~sure
gas having a pressure of about 0.1 kg/cm2G and a
temperature of about 50C i~ returned into the
industrial by-product gas pipeline.
The pressure of the gas thus returned i8 not
determined by only the characteristics of the gas
compressor, bypass pressure reducing valve and gas
cooler, but is further affected by the volume of the
indu~trial by-product ga~ pipeline and the tide of the
industrial by-product gas at the moment of the emergency
~hut-down. Moreover, the pre~ure of the ga~ is
affected also by the in~tallation po~ition of a
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gasholder and by the volume absorption rate of the
gasholder.
For instance, where the quantity of ga~
consumed at the gas turbine is greater than the quantity
of blast furnace gas generated from the blast furnace,
it is difficult to control the pressure at the outlet of
the gas cooler to or below a predetermined value at any
time, as upon the emergency shut-down of the gas
turbine.
Upon the rapid closing action of the gas
supply shut-off valve for the emergency shut-down of the
gas turbine mentioned above, the gas turbine come~ to be
stopped. The gas compressor, on the other hand,
continues rotating due to inertia for a while;
therefore, until fully stopped, the compressor continues
discharging the gas at a pressure matching the dishcarge
resistance. particularly, at the moment (a few seconds)
of the emergency shut-down of the gas turbine, the ga~
compressor continues discharging the gas at the same
raté as immediately before the emergency shut-down.
Therefore, when the bypass pressure reducing
valve is rapidly opened in conjunction with the rapid
closlng of the gas ~upply shut-off valve for the gas
turbine, both the high-pressure gas accumulated in the
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high-pressure gas piping on the discharge side of the
compre~sor and the gas discharged continuou61y from the
compressor are returned into the industrial by-product
gas pipeline. In the industrial by-product gas
pipeline, therefore, not only the flow of gas toward the
gas turbine is shut off but the gas will be caused to
flow backward.
This phenomenon makes it more difficult to
recognize the condition of pressure setting in the
industrial by-product ga~ system including the
gasholder.
For in~tance, the gas absorption rate limit of
the gasholder may be exceeded and the gasholder be
broken. Further, ~ealing water contained in drain
discharge seal pots disposed at several positions of the
~industrial by-product gas pipeline may be blown out,
leading to a gas leakage accident.
For effective use of gases, it is practiced to
perform calorific value control by appropriately mixing
different by-product gases at positions in an indu~trial
by-product gas piping. For instance, blast furnace gas
having a lower calorific value is mixed with coke oven
gas having a higher calorific value to get a proper
calorific value of the mixed gas, thereby matching the
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calorific value of the gas with the characteristics of
the part at which the gas is used. Such a calorific
value control through mixing of gases is performed by
utilizing a low pressure difference of 500 to 1000 mm
~g, and is therefore heavily influenced by the above-
mentioned disturbance in the gas pressure in the
industrial by-product gas system.
In view of the above problems, it may be
contemplated for such a gas turbine plant system to
reduce the quantity of the gas returned at a lowered
pressure into the low-pressure gas piping upon the
closure of the gas supply shut-off valve, by reducing
the internal volume of the high-pressure gas piping from
the compressor to the gas turbine through shortening the
piping or reducing the diameter of the piping. Such an
approach, however, involve8 restrictions on layout or
increase the flow resistance in the high-pressure gas
piplng, and is therefore impracticable.
SUMMARY OF THE INVENTION
An object of this invention is to provide a
~ystem comprising an emergency gas pressure stabilizer
effective for lowering the pressure of a high-pressure
gas ~lowing backward upon emergency shut-down of a large
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gas turbine supplied with an industrial by-product gas as a
fuel.
According to the invention there is provided an
emergency gas pressure stabilizer for a gas turbine system sup-
plied with a low-pressure industrial by-product gas as a fuel
and equipped coaxially with a gas compressor for compressing the
fuel gas, the stabilizer being constituted of a water seal device,
the water seal device comprising a sealing water pipe, and an
outer cylinder disposed at the water seal end of the sealing
water pipe in a double tube form, the outer cylinder having such
a height as to extend from a bottom portion of the water seal
device to above the water level in the water seal de~ice and being
greater than the sealing water pipe in diameter.
According to a preferred feature the outer cylinder
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is provided near a bottom portion thereof with slit holes for
permitting communication between the interior and the exterior
of the outer cylinder.
. BRIEF DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a flow sheet of a gas turbine plant
system according-to this invention,
FIGURE 2 is a partially cutaway perspective view of
a major portion of an embodiment of an emergency gas pressure
stabilizer of this inventions
FIGURES 3a, 3b and 3c are an illustration of the
operation of a prior art water seal device;
FIGURES 4a, 4b and 4c are an illustration of the
operation of the emergency gas pressure stabilizer according to
this invention; and
FIGURE 5 is a flow sheet showing an exemplary
construction of a prior art gas turbine plant system.
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DESCRIPTION OF PREFERRED EMBODIMENTS
FIGURE 5 shows an example of a gas turbine
system in which blast furnace gas is used as a fuel.
The gas generated from a blast furnace 14 is drawn out of
a blast furnace gas main pipe 13 by a blast furnace gas
inducting pipe 12. On the other hand, a coke oven gas
supplied through a piping 15 is fed into the blast
furnace gas inducting pipe 12 through a control valve
16, to form a mixed gas having a predetermined calorific
value, for example, about 1000 Kcal/Nm3. The mixed gas
is passed through a dust catcher 11, a piping 10 and a
gas compressor 5, whereby the mixed gas is raised in
pressure to about 12 kg/cm2 to be a high-pressure gas.
The high-pressure gas i8 mixed with compressed air
supplied through an air compressor 2, and is burned, and
the resultant combustion gas is supplied to a gas
turbine 1. ~he gas turbine 1 drives a generator 6,
which generates electric power.
In such a power generation system, when a
power transmission system (not shown), for example, is
failed, a gas supply shut-off valve 3 for the gas
turbine 1 iR closed instantaneouly (for example, in 0.5
to 1 sec). Simultaneously, the high-pressure gas i9
reduced in pressure from 12 kg/cm2 to 0.1 kg/cm2 by a
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pressure reducing valve 7,-an~ the low-pressure gas is
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returned into a low-pressure.gas piping 8, The gas thus
lowered in pressure is led-through the.gas-piping 8 into
a gas cooler 9, where the gas is cooled from about 300C
to about.50C, and the cooled gas is returned into the.
blast furnace gas inducting pipe 12.
Normally, a.high-pressure gas supply pipe 5a
supplies the high-pressure gas from the gas compressor 5
to the gas turbine 1. ~ut,.when the gas supply shut-off
valve 3 is instantaneously closed due to, for instance,
the above-mentioned failure in the power transmission
system, the entire quantity of the high-pressure gas
having been supplied to the gas turbine 1 is returned
through the low-pressure gas piping 8 into the blast
furnace gas inducting pipe 12. ~esides, in a low-load
operation in which the gas turbine 1 is operated with a
gas quantity below the proper operation range of the gas
compressor 5, a portion of the high-pressure gas is
decompressed and bypassed into the blast furnace gas
inducting pipe 12 in order to prevent a surging
phenomenon of the gas compressor 5.
The present inventors have made intensive
studies of the system shown in FIGURE 1, before
at~aining this invention. As a result of the studies,
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it has been found that when a water seal device 20 is
provided on the outlet side of the cooler 9, the high-
pre~sure gas at a pressure of about 12 kg/cm2 blowing
backward upon the instantaneous closure of the gas
supply shut-off valve 3 is decompressed to 5 kg/cm2 by
the pressure reducing valve 7, is then decompressed to
800 mm ~2 by the cooler 9 and further pressure relief
i9 performed by the water seal device 20, whereby it is
possible to lower the pressure in the bypass piping up
to about 500 mm H20.
If the water seal device 20 comprises a
sealing water pipe 21 simply water sealed, as shown in
FIGURE 3(a), the construction being conventionally known
in the gas suppliers, the instantaneous rise in the gas
pressure results in a rising of the water surface 23, as
shown in FIGURE 3(b). When the gas subsequently breaks
the water sealing function, the pressure loss is so
large (FIGURE 3(c)) that the gas cannot flow through
and, therefore, the relief of the gas pressure i8 not
achievedl ~hus, the gas pressure of 800 mm ~2 at the
outlet of the cooler 9 at the time of emergency shut-
down of the gas turbine cannot be lowered to a pressure
not exerting a great effect on the low-pressure gas
piping 8, the blast furnace ga~ inducting pipe 12 or the
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low-pressure gas piping 13, namely, to a pressure of
about 500 mm H2O, which is higher than the pressure in
low-pressure gas system by 150 to 200 mm H2O.
In view of the above, it may be contemplated
to lower the height of the water surface 23 in the water
seal device 20. This approach, however,.may lead to
breakage of the water seal even under gas pressure
variations during normal operation, resulting in gas
leakage. Therefore, it is the usual practice to secure
a predetermined water level, and it is impossible to
lower the water level.
In consideration of the above, the present
inventors made experiments with a double tube
construction provided at a tip portion of a sealing
water pipe 21, a~ shown in FIGURE 2. In the double tube
construction, the sealing water pipe 21 constitutes an
inner cylinder, and an outer cylinder 24 is constituted
of an externally disposed pipe which is provided with a
multipllci~y of notch grooves 2g located at the boundary
of the water ~urface along the circumferential direction
and 18 provided near bottom portion thereof with a
multlplicity of lost portions, for instance, slit holes
2~ for communication between the interior and the
exterlor of the external pipe. As a result of the
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experiments, it has been found out that it is possible
to instantaneously lower the gas pressure at the outlet
of the cooler to 500 mm H20. This is due to a
phenomenon in which, as shown FIGURE 4(a), a gap 30
defined by the sealing water pipe 21 and the outer
cylinder 24 acts to cause water to be instantaneously
blown out of the gap 30 as shown in FIGURE 4~b), whereby
the water seal is broken and a passage being devoid of
water is securely formed, so that the gas pressure is
instantly released, as shown in FIGURE 4(c).
In FIGURE 2, an overflow pipe 25 is provided
for controlling the water level in the water seal
device, and a gas relief pipe 26 is provided for
discharging the gas to a high position in the air upon
the breakage of the water seal.
The outer cylinder 24 ia provided, near a
bottom portion 22 o~ the water seal device, with the
lost portions (slit holes for communication between the
interior and the exterior of the outer cylinder) 28
which permit the sealing water to pass therethrough.
The designated numerals in FIGURE 1 are the same as
those ln FIGURE 5.
The upper end notch grooves 29 and the alit
holes 23 ~hown in FIGURE 2 are provided for restoring
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the water seal broken. The moment the gas pressure iB
relea~ed, the surrounding water is permitted to flow in
through the upper end notch grooves 29 and the slit
holes 28 to form a water seal again.
The upper end notch grooves 29 are provided
for the following reason.
For a higher response to the instantaneous
rise in the gas pressure, it is necessary for the small
amount of sealing water sealing the Guter cylinder to be
blown out. In addition, for restoration of the water
seal upon the return of the pressure to a normal level
it is neces~ary for the water thus blown out to be
returned into the interior of the outer cylinder. The
upper end notch grooves are provided for effective
realization of the function to enhance the response.
The function of the slit holes 28 provided at
a lower portlon of the outer cylinder is as follows.
~ y observation of the behavior of sealing
water and the gas in the experiments (FIGURE 3), it has
been revealed that the repon~ive characteristics is
further raisable by providing slit holes in a lower
portion of the outer cylinder. Of the intended
function~ to prevent the instantaneous rise in the gas
pressure and to restore the water seal under normal
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pressure, the function to restore the water seal is not
satisfactorily ensured by providing the outer cylinder
and providing the notch grooves at the upper end of the
outer cylinder. Namely, once the gas pressure is
raised, the water seal cannot be restored easily, and
the gas is lePt blowing out. In consideration of this,
the slit holes are provided in a lower portion of the
outer cylinder so that the water pressure on the outer
cylinder is exerted on the inner cylinder and the water
seal is easily restorable.
According to the above considerations, when
the water seal device 20 is provided on the downstream
side of the cooler 9 as shown in PIGU~E 1, the gas
discharged from the cooler 9 at 800 mm H2O breaks
instantaneously the water seal with a pressure fall, Eor
instance, to 500 mm H2O, and a portion of the gas iB
released into the atmosphere through the diffuser pipe
26, while the ma~or portion of the gas is returnable
through the bypass piping ~ into the blast furnace gas
lnductlng plpe 12, namely, the low-pressure gas piplng
on the inlet side of the gas compressor 11.
Since the gas pressure has been lowered to
about 500 mm H2O, in this case, it is possible to
prevent the breakage of the gasholder 17 due to a rapid
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pressure increase in the gasholder and to prevent the
gas leakage accident due to blow-out of sealing water
from the seal pots.
The gas pressure of 500 mm H2O, mentioned by
way of example in the above explanation, is not
limitative. It i9 possible to select an appropriate
value of the ga~ pressure by modifying the initial
setting of the sealing water pressure through
modification of the position of the overflow pipe 25
according to the actual situation of the plant to which
the pre~ent sy~tem i~ applied.
This invention will now be explained more in
detail while referring to a particular example.
The emergency gas pressure stabilizer shown in
FIGURE 2 was fltted to a gas turbine power generation
equipment shown in FIGURE 1, in which blast Eurnace gas
and coke oven gas were mixed to have a calorific value
of 1000 Kcal/Nm3, the mixed gas was compressed to a
pressure of 12 kg/cm2 to produce a mixed gas at a rate
of 250,000 Nm3/H, and the thus obtained gas was supplied
to a 140 MW class gas turbine 1.
In an operation with a gas turbine load of 140
MWH (100%), an actual emergency shut-down test was
carried out on the ga~ turbine. When the gas supply
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shut-off valve 3 shown in FIGURE 1 was closed, the gas
pressure of 800 mm H2O on the outlet side of the cooler
9 was instantaneously lowered to 500 mm H2O, and it wa~
possible to return the high-pressure gas into the blast
furnace gas inducting pipe 12 and the blast furnace gas
main pipe 13 smoothly, without causing a rapid pressure
rise in the gasholder or blow-out of sealing water from
the seal pots.
The emergency gas pressure stabilizer
according to this invention utilizes the properties of
water and does not comprise mechanically moving
component parts such as valves; therefore, the emergency
gas pressure stabilizer operates securely, with only the
water level control by overflow, and is extremely high
in reliability.
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