Intermediate fluid type vaporizer, and natural gas supply method using the vaporizer

An intermediate fluid type vaporizer has an intermediate fluid evaporator for containing an intermediate fluid. The intermediate fluid evaporator includes heat source tubes for evaporating the intermediate fluid, and a low-temperature liquid evaporating section for evaporating a low-temperature liquid by exchanging heat between the low-temperature liquid and the evaporated intermediate fluid. In the intermediate fluid evaporator, members for dividing the intermediate fluid, and cover plates for covering both ends of the intermediate fluid level from above are provided to prevent the intermediate fluid level from changing due to the shaking of the intermediate fluid evaporator itself. This vaporizer and an LNG tank are mounted on a ship so as to vaporize LNG in the ship and to supply the LNG to an onshore consumer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an intermediate fluid type vaporizer that 
heats and vaporizes low-temperature liquid, such as liquefied natural gas 
(hereinafter referred to as "LNG"), by using an intermediate fluid such as 
propane. The present invention also relates to a natural gas supply method 
using the vaporizer. 
2. Description of the Related Art 
As a means for continuously vaporizing low-temperature liquid, such as LNG, 
in a compact structure, an intermediate fluid type vaporizer is known 
which uses an intermediate fluid in addition to a heat source fluid 
(Japanese Unexamined Patent Publication No. 53-5207, etc.). 
FIG. 5 shows an LNG vaporizer as an example of the intermediate fluid type 
vaporizer. The LNG vaporizer comprises an intermediate fluid evaporator 
E1, an LNG evaporator E2, and a natural gas (hereinafter referred to as 
"NG") heater E3. The LNG vaporizer further comprises an inlet channel 10, 
multiple heat source tubes 12, an intermediate channel 14, multiple heat 
source tubes 16, and an outlet channel 18 that are provided, in that 
order, so as to form a path through which a heat source fluid (sea water 
in this example) flows. The heat source tubes 12 are disposed in the NG 
heater E3, and the heat source tubes 16 are disposed in the intermediate 
fluid evaporator E1. The intermediate fluid evaporator E1 contains an 
intermediate fluid (e.g., propane) 17 whose boiling point is lower than 
that of sea water serving as the heat source fluid. 
The LNG evaporator E2 comprises an inlet channel 22 and an outlet channel 
24 that are divided by a partition plate 20, and multiple heat transfer 
tubes 23 that link both the channels 22 and 24. The heat transfer tubes 23 
are approximately U-shaped, and project above the intermediate fluid 
evaporator E1. The outlet channel 24 is connected to the inside of the NG 
heater E3 via an NG piping 26. 
In such a vaporizer, sea water serving as the heat source fluid passes 
through the inlet channel 10, the heat source tubes 12, the intermediate 
channel 14, and the heat source tubes 16, and reaches the outlet channel 
18. While passing through the heat source tubes 16, the sea water 
exchanges heat with the intermediate fluid 17 in the intermediate fluid 
evaporator E1, thereby evaporating the intermediate fluid 17. 
On the other hand, LNG to be vaporized is introduced from the inlet channel 
22 into the heat transfer tubes 23. The LNG in the heat transfer tubes 23 
and the evaporated intermediate fluid 17 in the intermediate fluid 
evaporator E1 exchanges heat with each other, and the intermediate fluid 
17 is thereby condensed. By receiving the heat of condensation, the LNG is 
evaporated into NG inside the heat transfer tubes 23. The NG is introduced 
from the outlet channel 24 into the NG heater E3 through the NG piping 26, 
is further heated by heat exchange with sea water that flows through the 
heat source tubes 12 in the NG heater E3, and is then supplied to a 
consumer. 
Therefore, this intermediate fluid type vaporizer allows LNG to be 
continuously vaporized by repeating evaporation and condensation of the 
intermediate fluid 17. 
The above-described intermediate fluid type vaporizer is more compact and 
has a lower profile than an open-rack type vaporizer. So, for example, 
even when there are no LNG supply facilities on the land, LNG can be 
vaporized off shore and supplied to an onshore consumer by installing both 
this vaporizer and an LNG tank on a ship or a barge plant floating on the 
sea. When the above-described intermediate fluid type vaporizer is 
installed on the sea, however, the entire vaporizer shakes together with 
the ship or the like due to waves or the like, and the level of the 
intermediate fluid 17 in the intermediate fluid evaporator E1 greatly 
changes, which may produce adverse effects on vaporization ability. 
Specifically, the adverse effects are as follows: 
A) Exposure of Heat Source Tubes 16 
In a case in which the intermediate fluid evaporator E1 shakes to tilt in 
the transverse direction (in the widthwise direction nearly orthogonal to 
the axial direction of the heat source tubes 16), as shown in FIG. 6A, or 
in a case in which the intermediate fluid evaporator E1 shakes to tilt in 
the longitudinal direction (in the lengthwise direction nearly parallel to 
the axial direction of the heat source tubes 16), as shown in FIG. 6C, an 
intermediate fluid level 17a greatly tilts relative to the evaporator E1, 
and this may incur a risk that some of the heat source tubes 16 will be 
exposed above the level 17a. In such exposed portions, heat exchange 
between the intermediate fluid 17 and the heat source fluid is impossible, 
which significantly impairs vaporization ability. 
B) Surface Wetting of Heat Transfer Tubes 23 
When the shaking in the longitudinal or transverse direction becomes large, 
there is a risk that the heat transfer tubes 23 of the LNG evaporator E2 
will be wetted due to a wave 17b of the intermediate fluid 17 striking the 
LNG evaporator E2, as shown in FIG. 6B, or because the end of the LNG 
evaporator E2 is soaked in the intermediate fluid 17, as shown in FIG. 6C. 
Such surface wetting significantly impairs the condensation ability of the 
intermediate fluid 17 on the surfaces of the heat transfer tubes 23. 
SUMMARY OF THE INVENTION 
In view of such circumstances, an object of the present invention is to 
provide an intermediate fluid type vaporizer that is able to maintain good 
vaporization ability even when installed under conditions where an 
intermediate fluid evaporator is shaken, and to provide an NG supply 
method using the vaporizer. 
In order to achieve the above object, according to one aspect of the 
present invention, there is provided an intermediate fluid type vaporizer 
having an intermediate fluid evaporator for containing an intermediate 
fluid, the intermediate fluid evaporator including a heat source tube for 
evaporating the intermediate fluid by exchanging heat between a heat 
source fluid and the intermediate fluid, and a low-temperature liquid 
evaporating section for evaporating a low-temperature liquid by exchanging 
heat between the low-temperature liquid and the evaporated intermediate 
fluid, wherein the intermediate fluid evaporator further includes means 
for preventing the level of the intermediate fluid in the intermediate 
fluid evaporator from changing due to shaking of the intermediate fluid 
evaporator itself. 
By using this construction, even when the intermediate fluid evaporator 
itself shakes, the level of the intermediate fluid therein is prevented 
from changing due to the shaking. Therefore, it is possible to prevent 
exposure of the heat source tube and surface wetting of the 
low-temperature liquid evaporating section, which result from the level 
change, and to thereby maintain good vaporization ability. 
A partition member for dividing the intermediate fluid that remains in the 
intermediate fluid evaporator may be provided in the intermediate fluid 
evaporator. In this case, the intermediate fluid is restrained from moving 
inside the intermediate fluid evaporator due to the tilting of the 
intermediate fluid evaporator. As a result, the level change of the 
intermediate fluid is prevented. 
Preferably, the partition member is placed within a height range including 
at least the level of the intermediate fluid in the intermediate fluid 
evaporator. This can prevent the level change more effectively. 
Preferably, the partition member divides the intermediate fluid, which 
remains in the intermediate fluid evaporator, in the widthwise direction 
nearly orthogonal to the axial direction of the heat source tube. In this 
case, the level change in the dividing direction can be prevented. 
Therefore, the vaporizer becomes more resistant to the shaking and tilting 
of the intermediate fluid evaporator in the dividing direction. 
The partition member may be provided at a plurality of positions arranged 
in the dividing direction. This further increases the effect of preventing 
the level change. 
Preferably, the partition member divides the intermediate fluid, which 
remains in the intermediate fluid evaporator, in the lengthwise direction 
nearly parallel to the axial direction of the heat source tube. In this 
case, the level change in the dividing direction is also prevented, and 
the vaporizer becomes more resistant to the shaking and tilting of the 
intermediate fluid evaporator in the dividing direction. 
The partition member may be provided at a plurality of positions arranged 
in the dividing direction. This further increases the level change 
preventing effect. 
Support plates for commonly holding a plurality of parallel heat source 
tubes may be disposed at a plurality of positions arranged in the 
lengthwise direction nearly parallel to the axial direction of the heat 
source tubes so as to extend to a position higher than the level of the 
intermediate fluid in the intermediate fluid evaporator. In this case, the 
support plates can be effectively utilized as partition members for 
preventing the level change. 
A lattice-shaped partition member may be provided to divide the 
intermediate fluid, which remains in the intermediate fluid evaporator, 
both in the lengthwise direction nearly parallel to the axial direction of 
the heat source tubes, and in the widthwise direction nearly orthogonal to 
the axial direction. In this case, it is possible to construct a vaporizer 
that is resistant to shaking in all directions, and that is hardly 
restricted by the direction of placement. 
Preferably, the partition member is placed within a height range including 
at least the level of the intermediate fluid in the intermediate fluid 
evaporator. This further increases the level change preventing effect. 
A covering member may be provided in the intermediate fluid evaporator to 
cover both ends of the level of the intermediate fluid that remains in the 
intermediate fluid evaporator. This makes it possible to prevent waves 
from rising from both ends of the level, and to thereby prevent surface 
wetting due to striking of waves against the heat transfer tubes. 
As described above, since the vaporizer of the present invention can 
maintain good vaporization in spite of shaking thereof, it is particularly 
suitable as a vaporizer to be placed on a ship or a barge plant installed 
on the water. Even when there are no liquefied natural gas vaporizing 
facilities on the land, natural gas can be rapidly supplied from the ship 
to a consumer by mounting such a vaporizer together with a liquefied 
natural gas tank on a ship or on a barge plant, and supplying liquefied 
natural gas contained in the liquefied natural gas tank to the land after 
vaporizing the liquefied natural gas by the intermediate fluid type 
vaporizer. 
Further objects, features, and advantages of the present invention will be 
apparent from the following description of the preferred embodiments with 
reference to the attached drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of the present invention will be described below 
with reference to FIGS. 1 to 4. The overall basic configuration of a 
vaporizer in this embodiment is equivalent to that shown in FIG. 5, and 
therefore, a description thereof is omitted. This description places 
emphasis on the internal structure of an intermediate fluid evaporator E1. 
As shown in FIGS. 1, 2, 3A, 3B, and 3C, the intermediate fluid evaporator 
E1 of this embodiment includes a cylindrical shell 30 extending parallel 
to heat source tubes 16, and tubesheets 32 fixed to both ends of the shell 
30, in which an intermediate fluid 17 is contained. To both the tubesheets 
32, both ends of the heat source tubes 16 are fixed to penetrate 
therethrough. 
In the lower part of the intermediate fluid evaporator E1, support plates 
34 stand at a plurality of positions that are arranged in the lengthwise 
direction nearly in parallel with the axial direction of the heat source 
tubes 16. Middle portions of the heat source tubes 16 are supported by the 
support plates 34 to penetrate therethrough. 
This vaporizer is characterized in that the height of the support plates 34 
is set to be large so that the top ends thereof are higher than a level 
17a of the intermediate fluid 17 in a state in which the level 17a is 
stationary (i.e., a state in which the vaporizer itself, although being 
driven, does not shake, but remains stationary; a state shown in FIGS. 1 
and 3A. There are small clearances between through holes formed in the 
support plates 34 and the heat source tubes 16 passing through the through 
holes, which allow the intermediate fluid 17 to move slightly back and 
forth through the support plates 34. 
In this vaporizer, baffles (partition members) 36 shown in FIGS. 2, 3A, and 
3B also stand at a plurality of positions (three positions in the 
illustration) that are arranged in the widthwise direction nearly 
orthogonal to the above-described axial direction. The baffles 36 extend 
in the longitudinal direction nearly in parallel with the axial direction, 
and intersect the support plates 34 at approximately right angles to form 
a lattice. The height of these baffles 36 is also set to be large so that 
the top ends thereof are higher than the stationary level 17a. The baffles 
36 have small through holes, through which the intermediate fluid 17 is 
allowed to move to the right and left sides of the baffles 36. 
Cover plates (covering members) 38 are fixed to the right and left inner 
side faces of the shell 30 so as to project inward. These cover plates 38 
are placed higher than the stationary level 17a of the intermediate fluid 
17 so that they cover the right and left ends of the level 17a from above. 
By using such a vaporizer, since the intermediate fluid 17 in the lower 
part of the intermediate fluid evaporator E1 is divided lengthwise and 
widthwise by the support plates 34 and the baffles 36, even when the 
evaporator E1 shakes to tilt transversely (FIG. 3B) or to tilt 
longitudinally (FIG. 4), the level 17a is prevented by the support plates 
34 and the baffles 36 from changing due to the shaking (the change 
relative to the evaporator E1 itself). Furthermore, since the right and 
left sides of the level 17a are covered with the cover plates 38, waves of 
the intermediate fluid 17 are inhibited from rising from both the sides, 
which prevents heat transfer tubes 23 from being washed over by the waves. 
By thus preventing the level change, it is possible to avoid the partial 
exposure of the heat source tubes 16 (FIGS. 6A and 6C) and the surface 
wetting of the heat transfer tubes 23 (FIGS. 6B and 6C) due to the level 
change, and to thereby maintain excellent vaporization ability. 
Accordingly, this vaporizer is particularly suitable for installation on a 
ship or a barge plant on the sea. For example, even when there are no LNG 
vaporizing facilities on the land, rapid NG supply is made possible by 
installing the vaporizer with an LNG tank on a ship or a barge plant so as 
to vaporize LNG into NG and to feed the NG to an onshore consumer. 
The present invention is not limited to the above-described embodiment, and 
for example, the following modifications are possible. 
In the present invention, the height range, where the partition members are 
placed, can be freely set as long as the partition members can be in 
contact with the intermediate fluid. For example, the baffles 36 may be 
provided in an area below the level of the intermediate fluid (e.g., only 
at the bottom of the shell 30). When the partition members are provided in 
the height range including the level of the intermediate fluid, however, 
it is possible to more effectively restrict the level change. For example, 
when the support plates 34 higher than the fluid level are provided, as 
shown in FIG. 3A, it is, of course, possible to more effectively restrict 
the level change than a case in which only low support plates 34' are 
provided, as shown in FIG. 3C. Separate from such support plates 34, a 
partition member may be provided only for the purpose of restricting the 
level change. 
While the vaporizer of the above embodiment includes all the members 
(support plates 34) for dividing the intermediate fluid 17 longitudinally, 
the members (baffles 36) for dividing the intermediate fluid 17 
transversely, and the cover plates 38, even if it has only one of these 
members, it is possible to obtain advantages that are superior to those of 
the conventional vaporizer. Specific shape and number of the partition 
members may be appropriately determined. 
In the present invention, the number and shape of the heat source tubes 16 
and the heat transfer tubes 23 to be placed also do not matter. For 
example, the heat transfer tubes 23 may be linearly shaped to extend from 
one of the tubesheets 32 to the other tubesheet, instead of being U-shaped 
as described above. Furthermore, it may be appropriately determined 
whether to install equipment other than the intermediate fluid evaporator 
E1, e.g., the NG heater E3 shown in FIG. 5. 
While the clearances between the support plates 34 and the heat source 
tubes 16, and small through holes formed in the baffles 36 are utilized as 
a means for passing the intermediate fluid 17 little by little through the 
partition members (i.e., a means for moving the intermediate fluid 17 
below the level), for example, the partition members may be provided with 
a cutout at the bottom thereof, or may be fixed to the positions in the 
shell 30 above the bottom thereof. 
While the present invention has been described with reference to what is 
presently considered to be the preferred embodiment, it is to be 
understood that the invention is not limited to the disclosed embodiment. 
On the contrary, the invention is intended to cover various modifications 
and equivalent arrangements included within the spirit and scope of the 
appended claims. The scope of the following claims is to be accorded the 
broadest interpretation so as to encompass all such modifications and 
equivalent structures and functions.