JPS58109179A - Desalting method of sea water by refrigeration in direct contact with lng - Google Patents

Abstract

PURPOSE:To desalt sea water efficiently by bringing LNG and sea water into direct contact with each other to produce hydrate, decomposing the same under reduced pressure, converting the same to ice and separating ice from the sea water. CONSTITUTION:Sea water 11 is pumped 12 into a crystallizing tank 13, where the sea water contacts directly with the LNG15 supplied into the tank by a pump 14. The LNG15 deprives the sea water 11 of heat and is discharged as NG16 from the tank 13. Part of the NG reacts with the sea water 11 and forms hydrate. The slurry consisting of the hydrate and the sea water is transferred into a decomposing tank 17, where the hydrate is decomposed under reduced pressure and is separated to the NG and water. The water is frozen to ice by the heat of decomposition. The decomposition is continued for >=7min. The slurry consisting of the sea water and the ice is fed into a decomposing tank 18, where the slurry is separated to ice and brine. The ice is washed with part 24A of the fresh water 24 formed in a thawing tank 23 and is then fed into the tank 23.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a seawater desalination method in which LNG (liquefied natural gas) and seawater are brought into direct contact.

In recent years, the amount of LNG used has been increasing year by year due to the deterioration of the oil situation and the trend towards clean energy.

LNG is cooled and liquefied at -160C at the production site.

transported to the place of consumption. At the point of consumption, it is heated and gasified. Since LNG has a cooling energy of about 200 KCat/9, effective utilization of LNG is important from the viewpoint of energy consumption.

Conventionally, LNG gasification methods have been adopted: (1) open rack method and (2) submerged method, but neither method can effectively utilize the cold energy that LNG has. Possible ways to utilize the cold energy of LNG include cold power generation, cold storage, and seawater desalination. Methods for seawater desalination include a method in which the cold energy of LNG is transferred to a high boiling point refrigerant and a method in which this refrigerant is brought into direct contact with seawater, and a method in which LNG and seawater are brought into direct contact. In the method of bringing LNG and seawater into direct contact, a heat exchanger has extremely good heat exchange characteristics, transfers the cold heat of LNG to seawater, and increases hNo.
t-No (natural gas). The flow of this direct contact method is shown in Figure 1. 1 is seawater, 2 is a seawater pump, 4 is LNG, 5 is a LNG pump;
and LNG4 are directly melted in the crystallization tank 8, and LNG4
transfers cold heat to seawater and becomes NG3. At this time,
By reducing the amount of seawater 1 relative to LNG 4, ice crystals and hydrates (hydrocarbon hydrates) are generated in the seawater. The amount of hydrate produced varies depending on the LNG composition, crystallization pressure, and crystallization temperature. Note that 6 is a pline pump and 7 is a pline. Figure 2 shows CH, 89mO4%
This shows the region where hydrates are formed in LNG, and when the pressure exceeds 1 oKy/cm"G, the formation becomes noticeable.Basic studies have shown that in the region where hydrates are formed, hydrates are stronger than ice. It has also been revealed that crystallization pressure is 10~/cm''.
It was found that below G, almost no hydrate is produced, and ice is preferentially produced. Hydrate is the third
As schematically shown in Figure (a Convert to. Hydrate is a crystalline substance, but the size of hydrate particles generated by direct contact between LNG and seawater is about 40 μm, so solid-liquid separation is difficult, and separation and cleaning in the hydrate state is difficult. The law is not practical.

The present invention was made in view of the above circumstances, and an object of the present invention is to effectively recover all of the hydrate produced by direct contact between LNG and seawater as fresh water.

That is, the feature of the present invention is that, in an LNG vaporization method for gasifying LNG, LNG and seawater are brought into direct contact with each other, and the hydrate produced by this direct contact is decomposed under reduced pressure and converted into ice. This method involves separating and melting this ice to desalinate seawater by directly catalyzing LNG.

An embodiment of the present invention will be described below with reference to FIG. 13
is a crystallization tank in which seawater 11 pumped in by a seawater pump 12 and LNG 15 supplied by an LNG pump 14 come into direct contact;
16 is a vaporized fcNG; 17 is a decomposition tank that decomposes the hydrate discharged from the crystallization tank 13 under reduced pressure and returns it to ice;
8 is a separation tank that separates a slurry consisting of seawater and ice into ice and prine, and 23 is a +dN tank that melts the ice by bringing it into direct contact with seawater 26. 19 is the ply separated in the separation tank 18, 20 is its pline pump, and 21 is the ply 19
A part of the water is circulated to the crystallization tank 13, 22 is the circulating water pump, 24 is fresh water generated in the melting tank 23, and a part of it is the washing water 24A for washing the ice in the separation tank 18.
used as. 25 is fresh water 2 generated in the melting tank 23
A circulation pump that circulates 4B to the separation tank 18, 27 a freshwater pump, 28 cold seawater, and 29 a wash water pump.

Now, the seawater 11 is sent to the crystallization tank 13 by the seawater pump 12, and the LNG1 is supplied by the LNG pump 14.
Direct contact with 5. LNG15 takes away the heat from seawater11,
The NG becomes NG16 and is discharged from the crystallization tank 13, but a part of the NG reacts with the seawater 11 to generate hydrate. A slurry consisting of seawater and hydrate is transferred from the crystallization tank 13 to the decomposition tank 17. In the decomposition tank 17, the 21 idrate is decomposed under reduced pressure and separated into n, NG16 and water 71'.
Due to heat of decomposition, water is converted to ice. At this time, the decomposition time is 1
0 minutes or more. Next, the slurry consisting of seawater and ice is transferred from the decomposition tank 16 to the separation tank 18, where it is separated into ice and prine 19. Ply/19
is discharged as brine water/7" 20, and a part of it is sent to the crystallization tank 13 by the circulation pump 22 as circulating water 21. After washing with a portion 24A of fresh water 24A, fresh water 24Bt is circulated from the melting tank 23 by a circulation pump 25 and the ice is transferred to the melting tank 23. In the melting tank 23, seawater 26 is brought into direct contact with the ice to melt the ice, and the fresh water 24 The fresh water 24 is supplied to the utilization facility by a fresh water pump 27.The sea water 26 used for melting the ice is converted into cold sea water 289, and is used as part of the sea water to be input into the crystallization tank 13. This increases the effectiveness of cooling and heat utilization.

The present invention is based on the above-mentioned method, in which the treetop tray 1 is decomposed under reduced pressure and converted into ice crystals, the ice crystals are separated by prine force, and the fresh water is recovered by washing, as shown in Figure 3. Thus, when rapid decompression is carried out, the particle size of the ice crystals produced will be close to that of hydrate, and no improvement in separation performance from the pline can be expected. Figure 5 shows 141IJ1 when the pressure is reduced from the crystallization pressure to normal pressure and the particle size of the ice crystals generated at that time.

When the decomposition time is short, the particle size is small, but by increasing the decomposition time, it is possible to increase the size of the generated ice crystal particles.

to After 10 minutes or more, the grain size of the wrinkles approaches a constant value.

The particle size increases to about 75% of the saturation value after 7 minutes of decomposition time. Therefore, it is considered that 7 minutes or more is sufficient.

According to the present invention, the high tray 1 produced by direct contact between LNG and seawater can be effectively recovered as fresh water.

Brief explanation of the drawings □:□ Figure 1 is an explanatory diagram showing heat exchange through direct contact between LNG and seawater;
Figure wII2 is a diagram showing the hydrate generation region, Figure 3 is a schematic diagram of hydrate, Figure 4 is a block diagram showing an embodiment of the present invention, and Figure 5 is a diagram showing pressure reduction from crystallization pressure to normal pressure. FIG. 2 is a diagram showing the relationship between decomposition and the particle size of ice crystals.

11...Seawater, 15...LNG, 9...Crystallization tank,
17... Decomposition tank, 18... Separation tank, 23... Melt P
s tank, 24...Flame 1A + Zushokai 1 degree (°C) Kuzu 3 diagram (LL) (4) '@Ushizutomi 5 diagram OIO2o 3o 4-O Mejisuke folding θbeikai (i) Page 19 Continuation of 0 inventions Author: Sankichi Takahashi, 3-1-1, Saiwai-cho, Hitachi City, % stock % @Applicant: Hitachi, Ltd., 5-1, Marunouchi-chome, Chiyoda-ku, Tokyo

Claims (1)

[Claims] 1. I to gasify LNGt. In the NG vaporization method, L
NG and seawater are brought into direct contact, and the hydrate produced by this direct contact is decomposed under reduced pressure and transformed into ice.This water is then separated from the seawater and N! 1. A method for desalinating seawater by directly catalyzing LNG, which is characterized by desalinating seawater by decomposing LNG. 2. The LNG direct catalytic seawater desalination method according to claim 1, characterized in that the decomposition time under reduced pressure of the hydrate is 7 minutes or more. 3.L of Claim 1--, characterized in that seawater used on a sheet of ice is used for direct contact with LNG.
NG direct contact frozen seawater desalination method.