JP2002156098A - Vent gas treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vent gas treatment method capable of suppressing the suction of heavy substance that vent gas contains into a BOG line when recovering vent gas generated in LNG facility and returning it into a tank. SOLUTION: The vent gas led by a vent gas line 2 is sucked into an ejector 4 using LNG led by an LNG line 3 as driving fluid and is returned into the tank 1 together with LNG. Consequently, since the vent gas and LNG confluent in the ejector are stirred and mixed and the vent gas is fed into the tank while at least the heavy substance that the vent gas contains is sucked into LNG, it is possible to suppress the suction of the heavy substance that the vent gas contains into the BOG line 11, even if a feed port for the vent gas and an exhaust port for BOG are arranged in close proximity each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vent gas processing method for recovering a vent gas generated in a facility handling low-temperature liquefied gas such as LNG and returning it to a low-temperature liquefied gas storage tank.

[0002]

2. Description of the Related Art In an LNG facility such as an LNG receiving base,
Although vent gas is generated in the process of purging various components and analyzing the composition, it is environmentally and economically desirable to collect this vent gas without discarding it and return it to an appropriate LNG storage tank.

[0003]

However, in a tank for storing LNG at a low temperature, an outlet for sending out BOG (boil-off gas) generated by heat input is opened in the gas phase, and this BOG outlet is provided. When the vent gas is sucked, the vent gas is cooled in the BOG line, and heavy components are condensed, which may hinder the operation of the compressor for BOG treatment.

[0004] On the other hand, if the vent gas inlet and the BOG outlet opened in the tank are sufficiently separated from each other, suction of the vent gas into the BOG line can be suppressed. In some cases, it is difficult to place the two well separated due to severe restrictions on the location, and if the vent gas floats in the gas phase, it can be reached even if the distance is long enough. Is hard to say.

[0005] The present invention has been devised to solve such problems of the prior art, and its main objects are as follows.
It is an object of the present invention to provide a vent gas treatment method capable of suppressing suction of heavy substances contained in vent gas into a BOG line regardless of the positions of a vent gas inlet and a BOG outlet inside a tank. .

[0006]

According to the present invention, a vent gas generated in a facility for handling low-temperature liquefied gas is collected and returned to a low-temperature liquefied gas storage tank. Is sucked by an ejector using the low-temperature liquefied gas as a driving fluid, and returned to the tank together with the low-temperature liquefied gas.

According to this, the vent gas and the low-temperature liquefied gas are joined and stirred and mixed in the ejector that sucks the vent gas using the low-temperature liquefied gas as a driving fluid, so that at least heavy components contained in the vent gas are liquefied at a low temperature. It is sent to the tank in a state where it has been absorbed by the gas. For this reason, even if the inlet for the vent gas and the outlet for the BOG are arranged close to each other, the heavy BOG contained in the vent gas may be used.
Suction into the line can be suppressed. Moreover,
Since the vent gas line is maintained at a low pressure by the suction effect of the ejector, it is convenient for discharging the vent gas from various facilities. In addition, since the ejector has a simple structure and no moving parts, the ejector has few failures, is easy to maintain, and can be easily incorporated into existing equipment.

The low-temperature liquefied gas serving as the driving fluid is not particularly limited as long as the required pressure can be secured. The low-temperature liquefied gas may be taken out from an appropriate line in the low-temperature liquefied gas facility. A liquid or a circulating liquid for cooling a pipe is preferable.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows a main part of an LNG facility to which a vent gas treatment method according to the present invention is applied. Here, in collecting the vent gas generated in the LNG facility and returning it to the tank 1, the vent gas led by the vent gas line 2 is sucked by the ejector 4 using the LNG led by the LNG line 3 as a driving fluid, and the LNG is sucked. With tank 1
To return to.

In the ejector 4, LNG as a driving fluid is used.
Is ejected from the nozzle 6, the vent gas in the vent gas line 2 is sucked into the suction chamber 7, and then the diffuser 8 decelerates and raises the pressure and simultaneously mixes the gas and liquid with the vent gas and LNG. The mixing of the vent gas and LNG is also continuously performed in the feed line 9 downstream of the ejector, and at least heavy components contained in the vent gas are LNG.
Cooled and liquefied and absorbed.

In the tank 1, an inlet 10 of a vent gas inlet line 9 and an outlet 12 of a BOG line 11 are open in the gas phase, and both are arranged close to each other. The heavy fraction of the gas flows down from the inlet 10 while being absorbed by the LNG, and does not float and diffuse in the gas phase of the tank 1, so that the heavy fraction derived from the vent gas in the tank 1 is discharged from the BOG line 11. It is possible to suppress heavy components from condensing in the BOG line 11 without being directly sucked into the BOG line 12, thereby ensuring stable operation of the BOG processing compressor.

[0013]

EXAMPLE When an ejector 4 was actually installed at an LNG facility and an experiment was conducted, the ratio of LNG to vent gas was reduced to 1/10 by volume ratio, and it was possible to treat the vent gas with high efficiency. Is the processing amount of L
It was found that as the flow rate of the NG was increased, and as the pressure downstream of the ejector was decreased, the flow rate increased.

Further, LNG caused by the reduced pressure in the ejector 4
It is confirmed that LNG is hardly generated. Particularly, it is confirmed that LNG does not flash even when LNG is circulated to the ejector 4 with the valve V1 on the vent gas line 2 side closed and the suction chamber 7 shows a negative pressure. For this reason, it is possible to set the pressure of the downstream inlet line 9 to a lower pressure condition than that in the experiment, and it is expected that highly efficient vent gas processing exceeding the above-mentioned processing capacity can be performed.

In the example shown in FIG. 1, the conventional feed line 14 for vent gas is also left, but the valve V2 on this feed line 14 is closed when the ejector 4 is operated.

[0016]

As described above, according to the present invention, even if the inlet for the vent gas and the outlet for the BOG are arranged close to each other, it is possible to suppress the suction of heavy substances contained in the vent gas into the BOG line. As a result, there are no restrictions on the locations of vent gas inlets and BOG outlets.
Moreover, it is possible to prevent the BOG line from being damaged due to the vent gas being fed into the tank.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a main part of an LNG facility to which a vent gas treatment method according to the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tank 2 Vent gas line 3 LNG line 4 Ejector 6 Nozzle 7 Suction chamber 8 Diffuser 9 Inlet line 10 Inlet 11 BOG line 12 Outlet 14 Inlet line V1 / V2 valve

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koichi Tanimura 4-1 Ogishima, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Tokyo Gas Co., Ltd. (72) Yukihiro Yamamoto 2--12, Tsurumi-chuo, Tsurumi-ku, Yokohama-shi, Kanagawa No. 1 Chiyoda Kako Construction Co., Ltd. (72) Inventor Kenji Watanabe 2-12-12 Tsurumi Chuo, Tsurumi-ku, Yokohama-shi, Kanagawa F No. 1 Chiyoda Kako Construction Co., Ltd. F term (reference) 3E073 AA01 BB00

Claims (1)

[Claims] 1. A vent gas treatment method for collecting vent gas generated in a facility handling low-temperature liquefied gas and returning the vent gas to a low-temperature liquefied gas storage tank, wherein the vent gas is supplied to an ejector using the low-temperature liquefied gas as a driving fluid. A method of treating a vent gas, comprising: sucking and returning to the tank together with the low-temperature liquefied gas.