Refrigeration – Storage of solidified or liquified gas – Liquified gas transferred as liquid
Reexamination Certificate
2000-06-02
2002-04-09
Doerrler, William (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Liquified gas transferred as liquid
C062S052100
Reexamination Certificate
active
06367265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vaporizer for vaporizing a low temperature liquid such as liquefied natural gas (hereinafter referred to as LNG) by using a heat exchange with a heating medium.
2. Description of the Related Art
As a means for vaporizing a low temperature liquid such as LNG, a heat exchange between a low temperature liquid and a heating medium is generally used. For example, Japanese Patent sho 53-5207 discloses an intermediate medium type vaporizer that uses an intermediate medium in addition to the heat source fluid, vaporizing LNG by using heat exchange between the intermediate medium and the LNG.
FIG. 7
shows an example of such a heat exchanger. The diagram shows a LNG vaporizer, which comprises an intermediate medium evaporator E
1
, a LNG evaporator E
2
, and a natural gas (hereinafter referred to as NG) heater E
3
. Further, as a path for the heat source fluid (which is sea water in the example shown), there are sequentially arranged an inlet chamber
10
, a large number of heat source tubes
12
, an intermediate chamber
14
, a large number of heat source tubes
16
, and an outlet chamber
18
, the heat source tubes
12
and the heat source tubes
16
being provided in the NG heater E
3
and the intermediate medium evaporator E
1
, respectively. In the intermediate medium evaporator E
1
, there is accommodated an intermediate medium (such as propane)
17
whose boiling point is lower than that of sea water, which is the heat source fluid.
As shown in
FIG. 8
, the LNG evaporator E
2
comprises a capsule-shaped shell
21
, the closed end portion of which is separated from the other portion by a tube plate
25
. Further, a horizontal partition
20
is secured in the closed end portion, whereby there are defined an inlet chamber
22
and an outlet chamber
24
, which are separated from each other, the chambers
22
and
24
communicating with a large number of substantially U-shaped heat transfer tubes
23
. The intermediate portion of each heat transfer tube
23
protrudes in the upper portion of the intermediate medium evaporator E
1
, and the end portions thereof pass through the tube plate
25
and secured thereto.
In the inlet chamber
22
, there is provided an LNG supply portion
28
for introducing LNG, the LNG supply portion
28
being connected to an LNG supply source through a supply passage (not shown). In the outlet chamber
24
, there is provided an NG discharge means
29
, which is connected to the interior of the NG heater E
3
through an NG duct
26
.
In this vaporizer, sea water, which is the heat source fluid, passes the inlet chamber
10
, the heat source tubes
12
, the intermediate chamber
14
, and the heat source tubes
16
before it reaches the outlet chamber
18
. Heat exchange is performed between the sea water passing through the heat source tubes
16
and the liquid intermediate medium
17
in the intermediate medium evaporator E
1
to vaporize the intermediate medium
17
.
LNG, which is the object of vaporization, is introduced into the heat transfer tubes
23
from the inlet chamber
22
. Through heat exchange between the LNG in the heat transfer tubes
23
and the evaporation intermediate medium
17
in the intermediate medium evaporator E
1
, the intermediate medium condenses, the heat of condensation vaporize the LNG and consequently NG is obtained. This NG is introduced into the NG heating chamber E
3
from the outlet chamber
24
through the NG duct
26
, and is further heated by heat exchange with the sea water flowing through the tubes
12
in the NG heating chamber E
3
and then supplied to the place where it is required.
In the above LNG vaporizer (and other low temperature liquid heating heat exchangers of various types), a large thermal stress is generated when the low temperature liquid is abruptly introduced at a great flow rate at the time of starting. In view of this, at the time of speaking, as shown in
FIG. 8
, the supply flow rate is reduced to perform slow cooling operation, in which LNG is supplied little by little from the LNG supply portion
28
to the inlet chamber
22
.
However, when the flow rate is thus reduced and LNG is caused to flow out little by little from the LNG supply portion
28
, the LNG first flows down to the bottom portion of the shell
21
, and then spreads over the entire inlet chamber
22
, so that the bottom portion of the inlet chamber
22
is locally cooled prior to the other portions. For example, in the structure shown in
FIG. 8
, a marked temperature gradient as shown in
FIG. 9
is generated during slow cooling, and thermal stress attributable to this temperature gradient is generated.
That is, it is difficult to effectively mitigate the thermal stress generated in the inlet chamber
22
solely by reducing the LNG supply flow rate as in the prior art. In particular, in a heat exchanger, which is frequently started/stopped, there is a fear of fatigue failure being generated in, for example, the welding portion between the shell
21
and the tube plate
25
or the welding portion between the tube plate
25
and the partition
20
. Further, a similar temperature gradient is liable to be generated not only at the time of starting but when the LNG flow rate is reduce to maintain slow cooling at the time of temporary interruption of the operation of the heat exchanger.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems. It is an object of the present invention to provide a vaporizer for vaporizing a low temperature liquid in which it is possible to effectively restrain the generation of thermal stress when effecting slow cooling at the time of starting, etc.
To achieve the above object, there is provided in accordance with the present invention a method for effecting slow cooling in a heat exchanger for heating a low temperature liquid which is equipped with an inlet chamber in which the low temperature liquid is introduced, wherein, when effecting slow cooling, the low temperature liquid is sprinkled in the inlet chamber at a flow rate lower than that at the time of normal operation.
In this method, the low temperature liquid is diffused and supplied to a wide region in the inlet chamber at a flow rate lower than that at the time of normal operation, so that the temperature gradient generated in the inlet chamber is reduced, thereby effectively mitigating the thermal stress.
More specifically, the inlet chamber is equipped with a normal operation supply means and a slow cooling supply means with a sprinkling function; during normal operation, the low temperature liquid is supplied at least from the normal operation supply means to the inlet chamber, and, during slow cooling, the low temperature liquid is supplied solely from the sprinkling means, whereby it is possible to supply a low temperature liquid suitable for slow cooling to the inlet chamber through the dedicated slow cooling supply means at the time of slow cooling, and, after the completion of the slow cooling, it is possible to supply an LNG suitable for normal operation by the normal operation supply means.
Further, in accordance with the present invention, the above methods is performed by a vaporizer comprising an inlet chamber, a heat transfer tube into which the low temperature liquid is introduced from said inlet chamber and in which the low temperature liquid is vaporized, and means for sprinkling the low temperature liquid in said inlet chamber.
As the means for sprinkling, various types can be adopted. For example, by constructing the means for sprinkling such that the low temperature liquid is sprinkled from a plurality of places in the inlet chamber, it is possible to further widen the sprinkling region than in the case in which the liquid is sprinkled from a single place.
Further, by installing the means for sprinkling such that at least a part of the upper half of the inner wall of the inlet chamber is included in the sprinkling region, the low temperature liquid gradually flows down after being sprinkled again
Nakaoki Kozo
Sugino Kuniteru
Terada Susumu
Ueno Yasuhiro
Yamamoto Shuji
Doerrler William
Kabushiki Kaisha Kobe Seiko Sho.
Reed Smith LLP
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