JPS5824080Y2 - liquefied natural gas vaporizer - Google Patents

Description

[Detailed description of the invention] The present invention relates to a liquefied natural gas (LNG) vaporizer, and more specifically, an intermediate heat medium heat exchanger using seawater as a heat source and a shell-and-tube heat exchanger are connected in series. This invention relates to a highly efficient and economical LNG vaporizer.

LNG, whose main component is methane, has a boiling point of about -160° C. at normal pressure, so even when vaporizing it using hot water or steam as a heat source, the vaporizer is likely to be clogged due to freezing.

The LN currently in use has solved these problems.
There are mainly the following types of G vaporizers.

(i) Open rack type vaporizer: In this type of vaporizer, for the LNG sent upward through the heat transfer tube,
LN is produced by flowing seawater from above onto the outer surface of the heat transfer tube.
Evaporate G.

However, this type of vaporizer has the drawback that seawater tends to freeze on the surface of the lower portion of the heat transfer tube and impede heat transfer, thus increasing the heat transfer area, which means that the device must be larger and more expensive than necessary. There is.

(ii) Intermediate heat medium indirect heating vaporizer: In this type of vaporizer, an intermediate heat medium such as propane or fluorinated hydrocarbon sealed in the vaporizer body is heated with hot water or steam to vaporize it. , LNG by vaporized intermediate heat medium
The intermediate heat medium, which is vaporized and liquefied again through heat exchange with LNG, is subsequently heated with hot water or steam, and the same operation is repeated.

Although this type of vaporizer is less expensive to construct than an open rack vaporizer, it has the disadvantage of higher operating costs due to the need to use hot water or steam.

([11) Submerged combustion type vaporizer: In this type of vaporizer, combustion gas generated by a burner immersed in water is ejected into the water to heat LNG passing through a pipe installed in the water. Vaporize.

Although this type of vaporizer is relatively inexpensive to construct, the disadvantage is that it requires high heating costs.

In view of the current state of the technology as described above, and as a result of various experiments and research, the present inventor connected a shell-and-tube heat exchanger and an intermediate heat medium heat exchanger in series, and developed an intermediate heat medium heat exchanger. When exchanging heat between the natural gas that has already been vaporized in the vessel and seawater in a shell-and-tube heat exchanger, if the seawater temperature is high, the vaporized natural gas and seawater are exchanged in a countercurrent flow.
It has been found that when the seawater temperature is low, the various problems of the above-mentioned prior art can be solved by causing vaporized natural gas and seawater to exchange heat in parallel flow.

The present invention was completed based on such new knowledge.

Hereinafter, the present invention will be explained in more detail with reference to embodiments shown in the drawings.

In FIG. 1, an intermediate heat medium type heat exchanger 1 and a shell-and-tube type heat exchanger 12 are connected in series.

Seawater as a heat source in the intermediate heat medium heat exchanger 1 is
The line 2 enters the lower part 1a of the heat exchanger 1, and a low boiling point intermediate heat medium (refrigerant) such as propane, fluorohydrocarbon, etc.
After exchanging heat with and vaporizing it, it is discharged from line 3.

The vaporized intermediate heat medium rises to the upper part 1b of the heat exchanger 1, where it exchanges heat with the LNG supplied from the line 4 to the heat exchanger tubes 5, and is liquefied again to the lower part 1a.
Return to

The natural gas heated and vaporized by the intermediate heat medium in the upper part 1b enters the shell-and-tube heat exchanger 12 via line 6.

In the intermediate heat medium type heat exchanger 1, it is advantageous to use LNG and the intermediate heat medium under high pressure.

When the seawater temperature is relatively high (e.g. 5 to 30°C), the seawater flows through lines 7 and 8 branching from line 2.
It is sent to a shell-and-tube heat exchanger 12, where it undergoes countercurrent heat exchange with the incoming vaporized natural gas fed from line 6, and then discharged via lines 9, 10 and 11.

That is, in this case, only valves 13 and 14 are open, and the other valves are closed.

The vaporized natural gas further heated in the shell-and-tube heat exchanger 12 is
It is taken out of the system through line 15.

In this way, when using the multi-tubular heat exchanger 12 as a countercurrent heat exchanger, when setting the flow rate appropriately according to the heat transfer area, it is necessary to set the flow rate to an extent that does not cause blockage of the tubes over the entire surface of the heat transfer tubes. It was confirmed that even if swimsuits were to occur, there would be no problem with the operation, and this was therefore extremely advantageous in terms of equipment design.

On the other hand, when the seawater is at an extremely low temperature (for example, 0 to 5°C), the seawater is sent to the shell-and-tube heat exchanger 12 via line 7, line 16, and line 9 branching from line 2,
Here, after cocurrent heat exchange with the vaporized natural gas fed from line 6, it is discharged via line 8, line 17, and line 11.

In this case, only valves 18 and 19 are opened and valves 13 and 14 are closed.

Even if the seawater is at a low temperature, if the seawater flow rate is above a specified value, there is no problem in bringing the seawater and vaporized natural gas into countercurrent contact, but in the unlikely event that the seawater flow rate falls below the specified value. In such a case, ice formation inside the heat exchanger tubes may progress and cause blockage of the heat exchanger tubes.

Therefore, in the present invention, a valve mechanism is provided for cocurrent heat exchange between seawater and vaporized natural gas when the seawater is at a low temperature.

According to the present invention, the following effects are achieved.

(il) Because it has excellent heat exchange efficiency, only a small amount of seawater can be used as a heat source.

(il) Therefore, it is possible to reduce the size of the device by greatly reducing the heat transfer area and simplifying the water distribution system, and the construction cost is greatly reduced.

(1i[) Since heating fuel is not required and only a small amount of seawater can be used, operating costs are also greatly reduced.

(IV) Even when low-temperature seawater is used as a heat source, problems such as blockage of pipes and significant reduction in heat transfer efficiency do not occur due to valve switching.

Examples 1 to 4 LNG was vaporized and heated under the conditions shown in Table 1 using seawater as a heat source and the apparatus of the present invention shown in FIG. 1, and the results shown in Table 1 were obtained.

In addition, when an open rack type vaporizer having the same LNG vaporization and heating capacity as in Example 1 was used, the temperature was 6°C.
4,000 tons/h of seawater was required.

In addition, when an open rack type vaporizer equivalent to that in Example 3 is used, 4000 tons/h of seawater at a temperature of 5°C
required.

[Brief explanation of drawings]

FIG. 1 is a flow diagram showing an example of the device of the present invention. 1... Intermediate heat medium type heat exchanger, 1a...
・Heat exchange section between seawater and intermediate heat medium, 1b... Heat exchange section between intermediate heat medium and LNG, 2... Seawater supply line, 3... Seawater discharge Line, 4...
... LNG supply line, 5 ... heat exchanger tube, 6 ...
... Gasified natural gas supply line to shell-and-tube heat exchanger, 7.8.9.10.11.16.17 ... Seawater transfer line, 12 ... Multi-tubular heat exchanger Pipe type % type % ... Vaporized natural gas take-off line.

Claims (1)

[Scope of claim for utility model registration] In a liquefied natural gas vaporizer that uses seawater as a heat source, (:)
a heat exchanger body in which the upper part accommodates intermediate heat medium vapor that vaporizes the liquefied natural gas by exchanging heat with it, and the lower part accommodates the intermediate heat medium liquefied by heat exchange with the liquefied natural gas; A supply port for seawater that exchanges heat with the intermediate heat medium in the lower part and vaporizes it; A discharge port that discharges the seawater that has finished heat exchange with the liquefied intermediate heat medium to the outside of the system; A liquefied natural gas that exchanges heat with the above. An intermediate heat medium type indirect heat exchanger equipped with a supply port for supplying to the upper part of the vessel body; and a delivery port for supplying vaporized natural gas to the following shell-and-tube heat exchanger, (i[) above A supply port for the vaporized natural gas sent from the intermediate heat medium type indirect heat exchanger; a supply port for seawater to exchange heat with the vaporized natural gas and heat it to a temperature suitable for use; (**i) When the seawater temperature is high, the direction of flow of seawater in the shell-and-tube heat exchanger is changed according to the temperature of the seawater. The liquefied natural gas is characterized by being equipped with a valve mechanism for exchanging heat between the vaporized natural gas and seawater in a countercurrent flow, and for exchanging heat between the vaporized natural gas and seawater in a parallel flow when the seawater temperature is low. gas vaporizer.