JPH04181100A - Cooling standby holding method for shell-and-tube type liquefied gas vaporizer using intermediate heat medium - Google Patents

Abstract

PURPOSE:To perform stable temperature control by changing either one or both of the flow of the heat source fluid of a vaporizer and a gasification liquid, keeping the pressure or temperature of an intermediate heat medium constant, and holding the cooled state of the portion required to be kept cooled. CONSTITUTION:A pressure detection section 12 for detecting the pressure of an intermediate heat medium on a vaporizer 1 is provided on it, the opening of an auxiliary control valve 8a is regulated by a command from the detection section 12, and the flow of a gasification liquid is controlled so that the pressure of the intermediate heat medium is kept constant. The intermediate heat medium quickly responds to the balance between the heating by a heat source fluid and the cooling by the gasification liquid, thus resulting in the pressure change, i.e., temperature change, when it is used for the control subject, the control delay can be shortened from 10min to about 0.5min, for example. The pressure of the intermediate heat medium may be kept constant by the flow control of both the gasification liquid and the heat source fluid.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for holding a shell-and-tube type liquefied gas vaporizer using an intermediate heat medium while waiting for cooling.

Conventional technology and its problems Conventionally, vaporizers for liquefied gases such as liquefied natural gas have been used, such as open rack type vaporizers using seawater as a heat source fluid, shell-and-tube type vaporizers using an intermediate heat medium, and vaporizers installed in water tanks. Submerged vaporizers are known that are installed and vaporize water in an aquarium by heating it from the outside.

When both vaporizers are in operation, i.e., on standby in preparation for vaporizing the liquid to be vaporized, the temperature of the part where the liquid is introduced must be maintained below a certain level, even at night when demand for city gas is low. Must not be.

This is because if the temperature at the introduction part is not low enough, a large thermal stress will occur due to the sudden temperature change due to the flow of the liquid to be vaporized at the start of vaporization operation, and the thermal stress will act repeatedly, which will reduce the mechanical life of the vaporizer. This is to reduce the temperature due to thermal fatigue.

Therefore, whenever the vaporizer is on standby, the temperature is kept within a range where thermal stress does not shorten the mechanical design life even when the introduction of the liquid to be vaporized is started and the amount is increased at a predetermined rate. This is an important technology.

Among the above vaporizers, shell-and-tube vaporizers that use an intermediate heat medium can be kept cool during standby by allowing a small amount of the liquid to be vaporized to flow through the vaporizer, and by draining the heat source such as seawater. This is achieved by reducing the flow rate. As a control object, a temperature detection end is provided in the liquid introduction part, and the flow rate of the liquid to be vaporized and/or the heat source fluid is controlled so that the temperature thereof is kept constant, but there are the following problems.

■ If the conduit in the liquid introduction section is thick and has a large heat capacity, the control delay will be large and stable temperature control will not be possible.

(2) If the flow rate of the liquid to be vaporized is limited and the flow rate of the heat source fluid is large, the temperature may not drop to a predetermined level.

On the other hand, if the flow rate of the heat source fluid is low, the flow rate balance between the liquid to be vaporized and the heat source fluid may be disrupted, and the heat source fluid may freeze.

The present invention has been made with the aim of eliminating the above-mentioned conventional problems.

Means for Solving the Problems As a result of extensive research in order to eliminate the above problems, the inventors of the present invention did not directly control the temperature of the liquid introduction part, but rather controlled the heat input from the heat source fluid (for example, seawater). , discovered that all of the above problems can be solved when the pressure or temperature of an intermediate heat medium that quickly reflects the balance of cooling by the liquid to be vaporized (for example, liquefied natural gas) is controlled,
This invention led to the completion of the invention.

That is, in the present invention, when a shell-and-tube type liquefied gas vaporizer using an intermediate heat medium is in a standby state, by changing either or both of the flow rates of the heat source fluid of the vaporizer and the liquid to be vaporized, the intermediate heat medium is A shell-and-tube vaporizer for liquefied gas using an intermediate heat medium, which is characterized by maintaining the cooled state of parts that need to be kept cool, such as the liquid introduction part of the vaporizer, by keeping the pressure or temperature constant. This relates to a cooling standby holding method.

EXAMPLE A state of implementation of the method of the present invention will be described below based on the accompanying drawings.

FIG. 1 shows a conceptual diagram of a control loop in an embodiment of the method of the present invention.

Shell and tube vaporizer using intermediate heat medium (1)
In this case, the heat source fluid such as seawater is supplied from the supply line (2) to the tube (4) installed in the lower part of the shell (3) as usual.
), and while passing through the tube (4), the shell (3)
Heat is applied to the liquid phase part of the internally enclosed intermediate heat medium (not shown) to vaporize it, which is then discharged to the outside through a discharge line (5) equipped with a main flow control valve (6).

On the other hand, liquids to be vaporized such as liquefied natural gas are
8), and enters the tube (10) installed in the lower part of the shell (3) through the supply line (7) and the liquid introduction part (9). It absorbs heat from the gas phase of the gas, evaporates, and becomes gas, which flows through the exhaust line (
11) and collected. The liquid to be vaporized is
Examples include liquefied natural gas, liquefied nitrogen, liquefied oxygen, and liquefied ethane.

The above structure of the vaporizer (1) is not substantially different from the conventional one.

When the vaporizer (1) is on standby, a small amount of the liquid to be vaporized (cold heat source) is flowed into the vaporizer (1) as usual in order to maintain the liquid introduction part (9) below a certain temperature. It becomes necessary. Meanwhile, the flow rate of the heat source fluid is reduced to an amount corresponding to the flow rate of the liquid. For this purpose, branch pipes (5a) and (7a) are attached to the heat source fluid discharge line (5) and the vaporization target liquid supply line (7), respectively. 7a) are respectively equipped with auxiliary control valves (6a) and (8a) for cooling maintenance, and during standby, the main flow control valves (6) and (8) are closed, and the auxiliary control valve (6a) is closed.
), (8a') are operated in the open state.

During this cooling maintenance operation, in order to maintain the temperature of the liquid introduction part (9) constant, it is necessary to control, for example, the flow rate of the liquid to be vaporized (cold heat source).

Conventionally, as shown in Fig. 4, a temperature detection end (a) is provided in the liquid introduction part (9), and the flow rate of the liquid to be vaporized is controlled so that the temperature is constant. The problem with the control method is that it takes a considerable amount of time, for example, about 100 minutes, for the balance between heat input and cooling in the vaporizer (1) to be reflected in the temperature of the liquid introduction part (9), resulting in a large control delay. There is a point.

In the present invention, in order to solve such conventional problems, as shown in FIG. Equipped with
For example, the auxiliary control valve (8) is
The opening degree of a) is adjusted to control the flow rate of the liquid to be vaporized so that the pressure of the intermediate heat medium is maintained constant.

The intermediate heat medium quickly responds to the balance between the heat input by the heat source fluid and the cooling by the liquid to be vaporized, resulting in pressure changes and temperature changes. For example, it can be shortened from 10 minutes to about 0.5 minutes.

Figures 2 and 3 show other embodiments of the method of the present invention;
The figure shows a case in which the flow rate of the heat source fluid alone is controlled, and FIG. 3 shows a case in which the pressure of the intermediate heat medium is held constant by controlling the flow rate of both the liquid to be vaporized and the heat source fluid. In either embodiment, the same effects as the embodiment shown in FIG. 1 can be obtained.

Effects In the present invention, unlike the conventional method of directly controlling the temperature of the introduction part of the liquid to be vaporized, the pressure of the intermediate heat medium quickly reflects the balance between the heat input by the heat source fluid and the cooling by the liquid to be vaporized. Since the temperature is controlled, the following effects can be obtained.

■ Reduce control response delay from the conventional 10 to 0.5, for example.
The time can be shortened to about 1 minute, improving controllability.

(2) The temperature can be maintained at a predetermined temperature or lower with an extremely small flow rate (for example, about 2% of the rated load) of the liquid to be vaporized (for example, liquefied natural gas).

■ Since the controllability is improved as described above, the risk of freezing of the heat source fluid in the vaporizer can be avoided.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of a control loop showing an embodiment of the method of the present invention;
FIGS. 2 and 3 are conceptual diagrams of a control loop showing another embodiment of the method of the present invention, and FIG. 4 is a conceptual diagram of a control loop showing an example of the conventional method. In the figure, (1) is the vaporizer, (2) is the supply line, and (3) is the vaporizer.
) is the shell, (4) is the tube, (5) is the discharge line,
(6) is the main flow control valve, (7) is the supply line, (8) is the main flow control valve, (9) is the liquid introduction part, (10) is the tube, (11) is the discharge line, (12) is This is a pressure detection section. (that's all)

Claims (1)

[Claims] (1) In the standby state of a shell-and-tube liquefied gas vaporizer using an intermediate heat medium, by changing either or both of the flow rates of the heat source fluid of the vaporizer and the liquid to be vaporized, the pressure of the intermediate heat medium is Or standby for cooling of a shell-and-tube liquefied gas vaporizer using an intermediate heat medium, which is characterized by maintaining the cooled state of parts that need to be kept cool, such as the liquid introduction part of the vaporizer, by keeping the temperature constant. How to hold it.