Intermediate fluid type vaporizer

Details Intermediate fluid type vaporizer Intermediate fluid type vaporizer

2001-01-17

2002-04-09

Lu, Jiping (Department: 3749)

Liquid heaters and vaporizers

Indirectly heated separate injected fluid

C122S033000, C062S050200

Reexamination Certificate

active

06367429

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an intermediate fluid type vaporizer for heating and vaporizing a low temperature liquid, such as liquefied natural gas (hereinafter referred to as “LNG”), by using an intermediate fluid such as propane.
2. Description of the Related Art
Hitherto, an intermediate fluid type vaporizer using an intermediate fluid in addition to a heat source fluid is known as means for continuously vaporizing a low temperature liquid, such as LNG, with a compact structure (see, e.g., Japanese Unexamined Patent Application Publication No. 53-5207).
FIG. 6
shows one example of such an intermediate fluid type vaporizer for LNG. This conventional vaporizer comprises an intermediate fluid evaporator E
1
, an LNG evaporator E
2
, and a natural gas (hereinafter referred to as “NG”) heater E
3
.
The intermediate fluid evaporator E
1
comprises a first shell
101
, an outlet chamber
102
formed at one end of the first shell
101
, an intermediate chamber
103
formed at the other end of the first shell
101
, and a large number of heat source tubes
104
disposed in a lower portion of an inner space of the first shell
101
and extending between both the chambers
102
,
103
. The first shell
101
contains therein an intermediate fluid (e.g., propane) having a boiling point lower than that of sea water as a heat source fluid. The LNG evaporator E
2
comprises an inlet chamber
111
and an outlet chamber
112
divided from each other by a partition wall
110
, and a large number of heat transfer tubes
113
for communicating both the chambers
111
and
112
with each other. Each of the heat transfer tubes
113
has a substantially U-shape and projects into an upper portion of the inner space of the first shell
101
. The NG heater E
3
comprises a second shell
120
provided in continuation with the intermediate chamber
103
, an inlet chamber
121
, and a large number of heat source tubes
122
extending between both the chambers
103
,
121
.
A heat source fluid (sea water in the illustrated related art) flows through the inlet chamber
121
, the large number of heat source tubes
122
, the intermediate chamber
103
, the large number of heat source tubes
104
, and the outlet chamber
102
successively in the order named. Of this route, the heat source tubes
122
are disposed in the NG heater E
3
and the heat source tubes
104
are disposed in the intermediate fluid evaporator E
1
. The outlet chamber
112
of the LNG evaporator E
2
is connected to the second shell
120
side of the NG heater E
3
through an NG conduit
123
.
In such a vaporizer, sea water as a heat source fluid flows into the outlet chamber
102
after passing through the inlet chamber
121
, the heat source tubes
122
, the intermediate chamber
103
, and the heat source tubes
104
. While passing through the heat source tubes
104
, the sea water is subjected to heat exchange with the intermediate fluid
105
of liquid phase in the intermediate fluid evaporator E
1
, thereby evaporating the liquid intermediate fluid
105
. On the other hand, LNG to be vaporized is introduced to the heat transfer tubes
113
through the inlet chamber
111
. The evaporated intermediate fluid
105
condenses with heat exchange between the LNG in the heat transfer tubes
113
and the intermediate fluid
105
of gaseous phase in the intermediate fluid evaporator E
1
. By receiving heat generated upon condensation of the gaseous intermediate fluid
105
, the LNG evaporates and becomes NG in the heat transfer tubes
113
. The produced NG is introduced to the NG heater E
3
from the outlet chamber
112
through the NG conduit
123
, and is further heated with heat exchange between the NG and the sea water flowing through the heat source tubes
122
in the NG heater E
3
. Thereafter, the NG is supplied to consumers.
With the intermediate fluid type LNG vaporizer having the above-described construction, LNG can be continuously vaporized through repeated evaporation and condensation of the intermediate fluid
105
.
In most of intermediate fluid type vaporizers that have been conventionally used, the heat source fluid is sea water. In some of stations employing intermediate fluid type vaporizers, however, another heat source fluid such as warm water or an aqueous solution of glycol has become used in a place where sea water cannot be used from the standpoint of environmental protection, or in the case where sea water is not used to combine the cold heat recovery system.
In a conventional intermediate fluid type vaporizer using sea water as a heat source, a temperature difference obtainable with sea water as a heat source for vaporization is in the range of 5-7° C. Meanwhile, in an intermediate fluid type vaporizer using another heat source fluid such as warm water or an aqueous solution of glycol instead of sea water, a relatively large temperature difference of about 20° C. can be utilized for vaporization.
In the latter vaporizer, therefore, a flow rate of the heat source can be reduced. However, the heat transfer efficiency is deteriorated because a flow speed of the heat source flowing through the heat source tubes
104
in the intermediate fluid evaporator E
1
and the heat source tubes
122
in the NG heater E
3
cannot be set to a sufficiently high value. Thus, it has been found that, in order to compensate for such a deterioration of the heat transfer efficiency, the overall size of an intermediate fluid type vaporizer must be enlarged, and the cost of a heat exchanger is increased.
One conceivable method for increasing a flow speed of the heat source in the heat source tubes is to reduce the number of the heat source tubes
104
in the intermediate fluid evaporator E
1
and the number of the heat source tubes
122
in the NG heater E
3
. However, reducing the number of the heat source tubes decreases a heat transfer area and hence gives rise to another necessity of increasing the lengths of the heat source tubes
104
in the intermediate fluid evaporator E
1
and the heat source tubes
122
in the NG heater E
3
. This means that, since the intermediate fluid evaporator E
1
and the NG heater E
3
are connected to each other in series as shown in
FIG. 6
, the above method requires a longer installation area in the longitudinal direction, impedes free layout in design due to restrictions imposed on an equipment layout plan at a factory site, and eventually needs a larger land for installation.
SUMMARY OF THE INVENTION
In consideration of the state of the art set forth above, it is an object of the present invention to provide an intermediate fluid type vaporizer which employs a heat source fluid capable of providing a relatively large temperature difference utilizable for vaporization, and which can make an overall size of the vaporizer more compact.
To achieve the above object, an intermediate fluid type vaporizer according to the present invention comprises an intermediate fluid evaporator constructed by providing heat source tubes in a shell, which contains an intermediate fluid therein, to evaporate the intermediate fluid of liquid phase with heat exchange between the heat source fluid and the liquid intermediate fluid, and a liquefied gas evaporator constructed by providing heat transfer tubes in the shell to evaporate liquefied gas with heat exchange between the liquefied gas and the evaporated intermediate fluid. The heat source tubes are formed by a plurality of straight tubes, i.e., straight tubes arranged so as to constitute two or more passes.
With the above features, by employing a heat source fluid that is capable of providing a relatively large temperature difference utilizable for vaporization, the required flow rate of the heat source fluid can be reduced. Also, by arranging the heat source tubes of the intermediate fluid evaporator so as to constitute two or more passes, a flow speed of the heat source fluid in each heat source tube can be increased, whereby the heat transfer efficiency is enhanced and a sufficient heat transfer area can be en

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