TECHNICAL FIELD
The present invention relates to a system for regasification of liquefied gas and a
method for regasification of liquefied gas.
5
BACKGROUND ART
' In a gas turbine generator, the fuel gas and the air for 'combustion are supplied to
the burner to burn the combustion gas, and the high temperature gas thus produced is
supplied to the turbine to rotate it. The rotational-drive force of the turbine turns the
10 generator to generate electrical power as well as to turn the air compressor to compress the
air required for combustion.
Here, when a seasonal variation in air temperature causes a rise in temperature of
the air for combustion, the air density decreases. Due to the lower air density, the
combustion efficiency in the burner is reduced and the output power of the generator is
15 reduced.
Consequently, a means to lower the temperature of air for combustion in order to maintain
the level of output power of a gas turbine generator is desired.
In case in which the LNG (liquefied natural gas) is used as a fuel gas, the cold
20 energy held in LNG could be utilized to lower the temperature of combustion air. That is,
concerning the lowering of combustion air temperature by utilizing the cold energy held in
LNG, there is background art by the applicant et al. of the present invention (Patent
Document 1) and similar art.
However, these arts also entail a problem in handling the he1 in that the moisture
contained in the combustion air freezes, and since, in making use of the cold energy of
LNG, it is necessary to avoid as much as possible letting the flammable LNG circulate in
the vicinity of a gas turbine operating at a high temperature, further efforts for
improvement are desired.
5
CITATION LIST
Patent Documents
[Patent Document I] Japanese Patent No. 3706436
10 SUMMARY OF INVENTION
Technical Problem to be Solved by the Invention
In view of the above circumstances, the present invention has as an object to
provide a system for regasification of liquefied gas and a method for regasification of
liquefied gas that enable to maintain the output power of a gas turbine generator through
15 lowering the temperature of combustion air by utilizing, in an appropriate manner, the
coldness in the liquefied gas.
SOLUTION TO PROBLEM
In order to attain the aforementioned object, the system for regasification of
20 liquefied gas in accordance with the present invention is characterized in that it is
equipped with
a) a device for cooling refrigerant to supply the necessary cold calorific power from the
liquefied gas to the object needing the coldness through the intermediary of a refrigerant,
and
b) a heat exchanger installed side by side with the device for cooling the refrigerant, the
purpose of the heat exchanger being the heat exchange of residual cold energy for
vaporizing the aforementioned liquefied gas.
In view of the object, the appropriate matter as the object needing coldness is the
5 combustion air for a gas turbine. However, in addition to the combustion air for the
turbine, we can also select other matters or systems as the object, such as refrigerators in
general used in other various facilities needing coldiess, including storage facilities for
fishery products, air conditioners, facilities for manufacturing frozen carbon dioxide, or
"dry ice", etc.
10 As a device for cooling refrigerant, one can apply a system comprising a heat
exchanger of shell-and-tube type which effects the heat exchange between the liquefied
gas and the refrigerant, and another unit of a heat exchanger to which the chilled
refrigerant is fed and which effects the heat exchange between the refrigerant and the
object matter.
15 Here, it is desirable to make use of, as a refrigerant, a non-flammable liquid with
a low freezing point as well as a high thermal conductivity. As such a refrigerant, one
can cite hydrofluorocarbons (HFC), hydrochlorofluorocarbons (HCFC), particularly
HFC-23, HCFC-22, HCFC-124, HCFC-134a, HFC-32 or their mixtures.
In another aspect, the present invention relates to a method for regasification of
20 liquefied gas characterized in that the necessary coldness is supplied from liquefied gas to
the object needing the coldness through the intermediary of refrigerant by means of a
device for cooling refrigerant, and in that, in order to vaporize the liquefied gas, the
residual cold energy is transferred through a heat exchanger installed side by side with the
device for cooling refrigerant.
Advantageous Effects of the Invention
The present invention provides a system and a method for regasification of
liquefied gas that enable maintaining the output power of a gas turbine generator by
5 making use of the coldness held in liquefied gas in an appropriate manner for reducing the
temperature of the combustion air.
I
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a schematic diagram showing an embodiment of the system for
10 regasification of liquefied gas in accordance with the invention.
Embodiments of the Invention
In the following sections, the system and the' method for regasification of
liquefied gas in accordance with the invention are described in more detail with reference
15 to an embodiment presented in the attached drawing.
Figure 1 represents an embodiment of the system for regasification of liquefied
gas in accordance with the invention. The present embodiment is a regasification system
for liquefying LNG where the object matter needing the coldness is the combustion air to
be fed to a gas turbine.
20 In the regasification system in the present embodiment, a shell-and-tube type heat
exchanger 1 is installed side by side with an open-rack type vaporizer (ORV) 2. The heat
exchanger 3 serves for the purpose of heat exchange between the refrigerant and the
combustion air. Incidentally, the expression "install side by side" indicates that the two
systems are placed in parallel with each other in view of the flow direction of LNG.
The heat exchanger 1, the heat exchanger 3 and the refrigerant reservoir 4
constitute the principal components of the device for cooling refrigerant 5.
The shell-and-tube type heat exchanger 1 is equipped with the upstream header
5 into which LNG flows, a number of heat transfer tubes arranged in parallel and connected
to the upstream header, and the downstream header into which the LNG flows after having
I I I passed through the heat transfer tubes and ha$ing vaporized. The heat transfer tubes are
arrayed so that they penetrate through the refrigerant chamber encased in the hull
I
I
(normally in a cylindrical form) of heat exchanger. The refrigerant flows inside the
10 refrigerant chamber.
It is desirable to make use of, as a refrigerant, a liquid with a low freezing point as
well as a high thermal conductivity. As such a refrigerant, one can cite
hydrofluorocarbons (HFC), hydrochlorofluorocarbons (HCFC), particularly HFC-23,
HCFC-22, HCFC- 124, HCFC- 134a, HFC-32 or mixtures thereof.
15 Regarding the heat exchanger 1, the LNG flows into it through the line 7 which
branches off from the LNG inflow line 6. As mentioned previously, the LNG flows into
the upstream header of the heat exchanger 1.
From the downstream header, the regasified LNG, i.e., NG (natural gas), flows out to the
line 8.
20 At the same time, the heat exchanger 1 is constructed in such a way that the vapor
of refrigerant flows from the line 9 into the refrigerant chamber. The refrigerant vapor
having thus flowed in receives coldness from LNG flowing through heat transfer tubes in
the refrigerant chamber and liquefies. The liquefied refrigerant flows out from the heat
exchanger 1 through the line 10 and is stored in the refrigerant reservoir 4.
The refrigerant from the reservoir 4 flows out of its bottom part, then through the
line 11 and is fed by the delivery pump 12 to the heat exchanger 3 through the line 13.
The line 13 branches out to form the line 14.
The heat exchanger 3 is constructed in such a manner that the refrigerant and the
5 combustion gas effect heat exchange between them in a countercurrent fashion.
In the heat exchanger 3, the combustion air of gas turbine flows in from the line
15 and flows 6ut from the line 16. The line 15 branches out to form thre line 17.
The vaporizer 2 is constructed in the type of open rack. In the present
embodiment, it is constructed in the type equipped with a number of heat transfer tubes
10 arrayed in a form of flat-panel. The construction enables use of sea water as the heat
source that is sprinkled over the surface of heat transfer tubes to vaporize the LNG inside
the tubes. The vaporizer 2 functions as the heat exchanger to effect heat exchange of the
residual cold energy of LNG by being installed side by side with the device for cooling
refrigerant.
15 The vaporizer 2 is supplied with LNG through the line 18 branching off from the
line 6. The vaporized LNG, that is, NG (natural gas), flows through the line 19. The
line 19 joins the line 8 to become the line 20.
By describing the overall material flow in the system for regasification of the
construction of system components, we shall describe an embodiment of the method for
20 regasification of liquefied gas in accordance with the present invention.
In the method for regasification of liquefied gas in accordance with the
embodiment, the LNG from the storage reservoir is fed through the line 6 and pumped into
the heat exchanger 1 through the line 7. The LNG flows into the upstream header of the
heat exchanger 1 and then flows through a number of heat transfer tubes arrayed in
parallel with each other. The refrigerant vapor flows through the line 9 and enters into
the refrigerant chamber where the heat transfer tubes are encased.
Heat transfer takes place between LNG and refrigerant. The LNG vaporizes and
becomes NG (natural gas) by receiving the latent heat released when the refrigerant vapor
5 liquefies. Conversely, the refrigerant vapor liquefies.
The NG flows out from the downstream header of heat exchanger 1 and gets into
I the line 8.
,
The liquefied refrigerant flows through the line 10 to get into the refrigerant
reservoir 4. Moreover, by means of delivery pump 12, the refrigerant flows out of the
10 reservoir 4 through the line 13 to flow into the heat exchanger 3.
Here, the flow rate of refrigerant is monitored by a sensor hot shown in the
figure), and by regulating the aperture of a control valve (not shown in the figure), the
excess amount of refrigerant is returned to the refrigerant reservoir through the line 14.
Furthermore, a pressure sensor and a control valve (not shown in the figure) are installed
15 on the line 21, and by regulating the aperture of the valve, it is possible to maintain the
inner pressure of refrigerant reservoir 4 within a required range.
In the heat exchanger 3, the combustion air, the flow direction of which is
opposite to that of the refrigerant that flows in through the line 15 and exchanges heat with
the refrigerant. The refrigerant vaporizes rapidly and the combustion air is chilled by its
20 latent heat and flows out through the line 16.
The combustion air from the line 15 is made to branch off into the line 17. The
line 17 joins the line 16 to become the line 22. In order to regulate the temperature of the
line 22, it is monitored by a sensor (not shown in the figure (to regulate the aperture of a
control valve (not shown in the figure) installed on the line 17. These configurations of
control elements enable regulation of the volume of combustion air branching off into the
line 17 and to maintain within a desired range the temperature of combustion air fed to the
gas turbine through the line 22.
Meanwhile, it is possible to install a device for heating LNG 23 on the line 8 as
5 shown in the figure. In case in which one chooses the configuration installing such a
device for heating LNG 23, it is possible to control the temperature of combustion air fed
to the gas turbine so that it will not become too low. I
On the other hand, the fraction of LNG branching off into the line 18 and feeding
into the vaporizer 2 acquires the latent heat for regasification from the sea water through
10 its heat transfer tubes and vaporizes. Through this action, the residual coldness of LNG
undergoes the heat exchange process that effects the complete regasification of LNG from
the line 6.
The NG from the heat exchanger 1 and that from the vaporizer 2 join and flow
through the line 20 to feed into the burner of gas turbine.
15 An example of the relationships among temperatures in different lines is
presented here. If we assume that the temperature of LNG is - 157 "C, the LNG of nearly
the same temperature flows through the lines 7 and 18. The heat exchanger 1 is fed with
refrigerant vapor of 24 "C that exchanges heat with the LNG which in turn vaporizes to
become NG of 5 "C. The temperature of liquefied refrigerant becomes 5 "C, and it is fed
20 to the heat exchanger 3. The combustion air, the temperature of which may rise to 30 "C
depending on the season, is fed to the heat exchanger 3, and the temperature is lowered to
24 "C as a result of heat exchange with the refrigerant. The combustion air thus chilled is
supplied to the gas turbine through the line 22. The gas turbine is supplied with the NG
of 5 "C through the line 20 having joined the lines 19 and 8. In a case in which the
temperature of the combustion air supplied to the heat exchanger 3 varies depending on
the season, the temperature of the combustion air supplied to the gas turbine can be easily
maintained within a desired range by increasing or decreasing the volume of LNG diverted
to the heat exchanger 1.
5 As described about the present embodiment, in the regasification system in
accordance with the present invention, since the temperature of refrigerant for chilling the
combustion air remains to bi on the order of 5 "C whereas we deal with the matter bf low
temperature, there is no such inconvenience as the freezing of moisture contained in the
combustion air even if we take account of the heat lost as latent heat.
10 Moreover, as can be seen from the present embodiment, the heat exchanger 1 can be
installed separately from the supply line of LNG, and consequently, it is unnecessary to
extend such a supply line of LNG to the area in the vicinity of the gas turbine operating at
a high temperature..
As described above, in accordance with the present invention, it is possible to
15 exploit the coldness held in liquefied gas with no difficulty for lowering the temperature of
combustion gas, and thus, to maintain the power output of a gas turbine, and at the same
time to liquefy the liquefied gas in an efficient manner.
In the present embodiment, an open-rack type vaporizer (ORV) 2 has been
adopted. However, it is possible to adopt a shell-and-tube type heat exchanger as well.
20 The shell-and-tube type heat exchanger can be constructed as a compact unit and applied
with advantage to the regasification of LNG on floating bodies on the ocean like FSRU
(floating storage and regasification unit) or FPSO (floating production, storage and
offloading) and vessels like LNG tankers.
The regasification system and the regasification method in accordance with the
present invention, in their most appropriate application, take the form of regasification of
LNG and are exploited in the facilities for cooling the combustion air for a gas turbine by
means of the coldness of LNG.
5 List of Reference Symbols
1 Heat exchanger
2 Vaporizer
3 Heat exchanger
4 Refrigerant reservoir
10 5 Device for cooling the refrigerant
6 LNG flow-in line
12 Delivery pump
Claims
1. A system for regasification of liquefied gas, characterized in that the system
comprising:
5 a) a device for cooling refrigerant to supply the necessary cold calorific power
from the liquefied gas to the object needing coldness through the intermediary of
a refrigerant, and
b) a heat exchanger installed side by side with the device for cooling the
refrigerant, the purpose of the heat exchanger being heat exchange of residual
coldness to effect the regasification of the liquefied gas.
2. The system for regasification of liquefied gas according to claim 1, further
characterized in that the combustion air for the gas turbine has been selected as the
object needing coldness.
15
3. The system for regasification of liquefied gas according to claim 1 or 2, further
characterized in that the liquefied gas is LNG (liquefied natural gas).
4. The system for regasification of liquefied gas according to any one of claims 1 to 3,
2 0 further characterized in that the system is configured so that the heat exchange
between the refrigerant and the liquefied gas takes place across a shell-and-tube type
heat exchanger, the chilled refrigerant then being fed to another heat exchanger where
the heat exchange takes place between the refrigerant and the object needing
coldness.
5. The system for regasification of liquefied gas according to any one of claims 1 to 4,
further characterized in that the refrigerant is at least a solvent that has been selected
from among a group of substances comprising HFC-23, HCFC-22, HCFC-124,
HCFC-134a, HFC-32 or their mixtures.
6. A method for regasification of liquefied gas characterized in that the method
comprising:
a) providing the necessary cold calorific power from the liquefied gas to an object
10 matter needing coldness by means of a device for cooling the refrigerant and
through the intermediary of refrigerant; and
b) transferring the residual cold energy across a heat exchanger installed side by
side with the device for cooling the refrigerant, in order to effect the regasification
of the liquefied gas.
15
7. The method for regasification of liquefied gas according to claim 6, further
characterized in that the combustion air for a gas turbine has been selected as the
object needing the coldness.
20 8. The method for regasification of liquefied gas according to claim 6 or 7, further
characterized in that the liquefied gas is LNG (liquefied natural gas).
9. The method for regasification of liquefied gas according to any one of claims 6 to 8,
further characterized in that the device for cooling the refrigerant effects the heat
exchange between the refrigerant and the liquefied gas by a shell-and-tube type heat
exchanger, the chilled refrigerant then being fed to another heat exchanger where the
heat exchange takes place between the refrigerant and the object needing the cold
energy.
5
I
10. The method for regasification of liquefied gas according to any one of claims 6 to 9,
I
I further characterized in that the refrigerant is at least a soldent that has been selected
I from among a group of substances comprising HFC-23, HCFC-22, HCFC- 124,
I
I I HCFC-134a, HFC-32 or mixtures thereof.