JP2006124468A - Method for producing gas hydrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the blockage of the filtrate recovery line for returning the filtrate separated in the dehydrator to the gas hydrate forming tank. <P>SOLUTION: In the gas hydrate forming tank 11, the starting gas G and water W are allowed to react each other to form the gas hydrate N, and the gas hydrate slurry S comprising the gas hydrate N and unreacting water W is fed to the dehydrator 12 to effect dehydration and the filtrate solution W' separated from the dehydrator via the filtrate recovering line 35 to the gas hydrate-forming tank 11. When the concentration of the filtrate in the filtrate recovering line 35 exceeds a prescribed value, water W is fed to the filtrate recovering line 35 and the concentration of the filtrate solution in the recovering line 35 is lowered to less than the prescribed value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, a gas hydrate is produced by reacting a raw material gas and water in a gas hydrate production tank, and a gas hydrate slurry comprising the gas hydrate and unreacted water is supplied to a dehydration tower for dehydration. The present invention relates to a filtrate recovery method in which the filtrate separated from the gas hydrate by the dehydration tower is returned to the gas hydrate production tank through a filtrate recovery line.

  At present, as a method of storing and transporting natural gas mainly composed of hydrocarbons such as methane, after collecting natural gas from a gas field, it is cooled to a liquefaction temperature and stored in a liquefied natural gas (LNG) state. The method of transport is generally adopted.

  However, as described above, in order to store and transport natural gas by converting it to LNG, advanced equipment and a great deal of cost are required.

  Therefore, in recent years, it has been studied to hydrate natural gas with water to produce a solid state hydrate, that is, natural gas hydrate (NGH), which is stored or transported as it is. This natural gas hydrate can be produced under temperature and pressure conditions that are relatively easily obtained. Therefore, manufacturing, storage, and transportation costs are reduced as compared with LNG, and attention has been paid to this field.

  By the way, natural gas hydrate is obtained by bringing a raw material gas and water into contact with each other to be solidified as a hydrate, and is usually a slurry containing a large amount of water. Therefore, if the slurry-like natural gas hydrate is stored and transported, the cost for storage and transport becomes enormous.

Therefore, in order to reduce the cost for storage and transportation of natural gas hydrate, it is necessary to introduce slurry-like natural gas hydrate into a dehydrator to remove unreacted water. As this type of dehydrating apparatus, a horizontal screw press type dehydrating apparatus is known (for example, see Patent Document 1).
JP 2003-105362 A (page 7-10, FIG. 2)

  However, such a screw press type dewatering device has a double structure of a meshed inner wall and a cylindrical body that is outside the inner wall and constitutes the outer shell, and is provided by a screw shaft installed in the inner wall. Water is forcibly removed from the mesh processed into the inner wall by forcibly advancing the slurry-like natural gas hydrate.

  For this reason, during dehydration, most of the natural gas hydrate passes through the mesh holes in the inner wall together with water, and as a result, there is a problem that the recovery rate of natural gas hydrate is lowered. In addition, there is a problem in that a power cost for rotating the screw shaft with high torque is required. Furthermore, since high torque is generated in a state where the inside is at a high pressure, the entire equipment is overloaded, and it is necessary to apply the seal of the screw shaft in a wide range from high pressure to atmospheric pressure.

  In order to solve such a problem, the present inventors examined a dehydration tower using gravity instead of the conventional mechanical forced dehydration.

  As shown in FIG. 3, the dehydrator 1 includes an introduction unit 4 for introducing a gas hydrate slurry s having a predetermined slurry concentration (for example, about 20%), and a draining unit 6 for dehydrating the gas hydrate slurry s. , A vertical tower body 2 composed of a lead-out section 5 that discharges a gas hydrate n having a low water content (for example, a water content of 50%) dehydrated in the draining section 6, and a filtrate (recovery) collected by the draining section 6 Water) is formed by a dewatering gathering part 3 for gathering w. Then, the filtrate (recovered water) w in the dewatering assembly 3 is returned to a gas hydrate generator (not shown) via the filtrate recovery line 7.

  The filtrate concentration returned to the gas hydrate generator via the filtrate recovery line 7, that is, the slurry concentration is normally close to 0 wt%. For example, when the slurry concentration supplied to the dehydration tower 1 is increased. It is expected that the gas hydrate n passing through the draining part 6 increases (for example, 20% to 60%), and the slurry concentration returned to the gas hydrate generator via the filtrate recovery line 7 is increased.

  When the slurry concentration in the filtrate collection line 7 becomes high, gas hydrate is deposited while passing through the filtrate collection line 7 and adheres to the tube wall. Then, the accumulation of gas hydrate increases with the passage of time, and the filtrate recovery line 7 may eventually be blocked.

  The present invention has been made to solve such problems, and an object of the present invention is to prevent clogging of the filtrate recovery line for returning the filtrate separated by the dehydrator to the gas hydrate generator. It is to provide a filtrate recovery method.

  In order to solve the above problems, the present invention is configured as follows.

  According to the first aspect of the present invention, a gas hydrate is produced by reacting a raw material gas and water in a gas hydrate production tank, and a gas hydrate slurry comprising the gas hydrate and unreacted water is used as a dehydrator. The filtrate concentration in the filtrate recovery line is set in the filtrate recovery method in which the filtrate separated from the gas hydrate by the dehydrator is returned to the gas hydrate production tank through the filtrate recovery line. When the value is exceeded, water is supplied to the filtrate collection line to reduce the filtrate concentration in the filtrate collection line below a set value.

  The invention according to claim 2 is characterized in that when the filtrate concentration in the filtrate recovery line exceeds a set value, water supplied to the gas hydrate production tank is directed to the filtrate recovery line. Item 2. The method for recovering a filtrate according to Item 1.

  According to a third aspect of the present invention, when the filtrate concentration in the filtrate recovery line exceeds a set value, the temperature of water to be replenished to the filtrate recovery line is 2.0 ° C. to 15.0 higher than the gas hydrate formation temperature. The method for recovering a filtrate according to claim 1, wherein the temperature is raised to about 0C.

  As described above, according to the first aspect of the present invention, a gas hydrate is produced by reacting a raw material gas and water in a gas hydrate production tank, and comprising the gas hydrate and unreacted water. In the filtrate recovery method, the slurry is supplied to a dehydrator and dehydrated, and the filtrate separated from the gas hydrate by the dehydrator is returned to the gas hydrate production tank through the filtrate recovery line. When the filtrate concentration exceeded the set value, water was replenished to the filtrate collection line to reduce the filtrate concentration in the filtrate collection line to less than the set value. Adhesion can be avoided in advance. As a result, obstruction of the filtrate recovery line due to gas hydrate accumulation can be avoided in advance.

  According to the second aspect of the present invention, when the filtrate concentration in the filtrate recovery line exceeds a set value, the water supplied to the gas hydrate production tank is directed to the filtrate recovery line. There is no need to install a line and it is economical.

  According to a third aspect of the present invention, when the filtrate concentration in the filtrate recovery line exceeds a set value, the temperature of water to be replenished to the filtrate recovery line is 2.0 ° C. to 15.0 higher than the gas hydrate formation temperature. Since the temperature is raised by about 0 ° C., the gas hydrate adhering to the tube wall of the filtrate collection line is decomposed, and the clogging of the filtrate collection line can be solved. Note that if the makeup water temperature is increased to a hydrate generation temperature plus 15.0 ° C. or higher, the gas hydrate in the gas hydrate generation tank may be decomposed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  In FIG. 1, 11 is a gas hydrate production tank, 12 is a dehydrator for dehydrating the gas hydrate slurry s produced in the gas hydrate production tank 11, and 13 is a gas hydrate n almost dehydrated by the dehydrator 12. It is a conveying apparatus which transfers to a process (not shown).

  The gas hydrate production tank 11 includes a pressure vessel 14, a sparger 15 that blows natural gas g, which is a raw material gas, into the water w in the form of bubbles, an agitator 16 that stirs the pressure vessel 14, and a raw material gas g. The circulation line 17 and the circulation pump 18 are circulated.

  Here, the water w in the water tank 19 is supplied to the pressure vessel 14 by the pump 20, but is cooled to a predetermined temperature (for example, 1 ° C.) by the cooler 22 provided in the water supply line 21. . The cooler 22 is located on the downstream side of the pump 20, but two valves 24 and 25 are provided on the refrigerant supply line 23. The two valves 24 and 25 are provided before and after the cooler 22. The water supply line 21 is provided with a first on-off valve 26 on the downstream side of the cooler 22.

  The dehydrator 12 includes an introduction unit 28 for introducing the gas hydrate slurry s, a draining unit 29 for removing water from the gas hydrate slurry s, and a lead-out unit 30 for guiding the gas hydrate n dehydrated by the draining unit 29. And a dehydrating and collecting part 32 for collecting the water w filtered by the draining part 29.

  The draining portion 29 is formed of a wire mesh cylinder or a porous cylinder, and the diameter of the fine holes is formed in a range of 0.1 to 5 mm. When this hole diameter is less than 0.1 mm, clogging is likely to occur, and conversely, when it exceeds 5 mm, gas hydrate is likely to pass through.

  The filtrate (recovered water) w ′ collected in the dehydration collecting section 32 of the dehydrator 12 is returned to the gas hydrate production tank 11 through the filtrate collection line 35. The filtrate collection line 35 is provided with a flow meter 36, a density meter 37, and a second thermometer 38 in this order from the dehydration tower 12 toward the gas hydrate production tank 11.

  On the other hand, the water supply line 21 and the filtrate recovery line 35 are connected by a bypass line 40. Here, one end of the bypass line 40 is connected to the water supply line 21 between the cooler 22 and the first on-off valve 26, and the other end is connected to the bypass line 40 as close to the dewatering assembly portion 32 as possible. . The bypass line 40 is provided with a first thermometer 41 and a second on-off valve 42 in this order.

  The gas hydrate regeneration tank 11 and the dehydration tower 12 are connected by a slurry supply line 44 provided with a slurry pump 43.

  In the figure, reference numeral 50 denotes a control device that opens and closes the first on-off valve 26 and the second on-off valve 42 based on the detection signals of the flow meter 36 and the density meter 37, and the two valves 24 of the refrigerant supply line 25 open / close degrees are requested.

  Next, the operation of this gas hydrate production apparatus will be described.

  While the water w in the gas hydrate production tank 11 is being stirred by the stirrer 16, when the natural gas g, which is the raw material gas, is spouted into the water w from the sparger 15, the natural gas g reacts with the water w. As a result, a gas hydrate n is generated.

  As described above, since the inside of the gas hydrate production tank 11 is stirred by the stirrer 16, the gas hydrate n is in the form of a slurry, and its concentration is, for example, about 20%.

  The gas hydrate slurry s is supplied to the dehydrator 12 via the slurry supply line 44. The gas hydrate slurry s supplied to the dehydrator 12 rises in the introduction part 28 and reaches the draining part 29 above it. Then, the unreacted water of the gas hydrate slurry s permeates through the fine holes of the drainer 29 by the drainer 29 and flows down into the dewatering assembly 3.

  The gas hydrate n dehydrated in the draining unit 29 and having a low water content (for example, about 50%) is guided to the upper discharge device 13 by the outlet unit 30 of the dehydration tower 12, and then is discharged by the discharge device 13. It is transferred to the process.

  Then, the filtrate (recovered water) w ′ removed from the gas hydrate n by the dehydrator 12 is returned to the gas hydrate production tank 11 through the filtrate recovery line 35, but the gas hydrate n is removed from the draining portion 29. When the concentration (slurry concentration) of the filtrate (recovered water) w ′ exceeds a set value (for example, 20%) through the fine holes of the flow meter 36 and the density meter 37 disposed on the filtrate recovery line 35. The first opening / closing valve 26 is “closed” by the command of the control device 50 based on the detection signal from the first, and the second opening / closing valve 42 of the bypass line 40 is “opened” on the contrary.

  By such control of the on-off valve, water w in the water tank 19 is supplied to the filtrate collection line 35, and filtrate (collected water) w 'in the filtrate collection line 35 is diluted. At the same time, the opening of the two valves 24 and 25 provided in the refrigerant supply line 23 of the cooler 22 is adjusted so that the water temperature in the filtrate collection line 35 becomes a predetermined temperature (for example, 5.0 ° C.). To.

  This prevents the gas hydrate from adhering to the tube wall, while promoting the decomposition of the gas hydrate adhering to the tube wall.

  FIG. 2 shows an example in which a screw press type dewatering device 55 is used as the dewatering device. The same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

It is a schematic structure figure showing a 1st embodiment of the present invention. It is a schematic block diagram which shows the 2nd Embodiment of this invention. It is a schematic block diagram of the conventional dehydration tower.

Explanation of symbols

g Raw material gas n Gas hydrate s Gas hydrate slurry w Water w 'Filtrate 11 Gas hydrate production tank 12 Dehydrator 35 Filtrate recovery line

Claims (3)

A raw material gas and water are reacted in a gas hydrate production tank to produce gas hydrate, and a gas hydrate slurry comprising this gas hydrate and unreacted water is supplied to a dehydrator for dehydration, and the dehydrator In the filtrate recovery method in which the filtrate separated from the gas hydrate is returned to the gas hydrate production tank through the filtrate recovery line, when the filtrate concentration in the filtrate recovery line exceeds a set value, the filtrate recovery is performed. A method for collecting a filtrate, comprising replenishing the line with water to reduce the filtrate concentration in the filtrate collection line to less than a set value. The filtrate recovery method according to claim 1, wherein when the filtrate concentration in the filtrate recovery line exceeds a set value, water supplied to the gas hydrate generation tank is turned to the filtrate recovery line. When the filtrate concentration in the filtrate recovery line exceeds a set value, the temperature of water to be replenished to the filtrate recovery line is made higher by about 2.0 ° C. to 15.0 ° C. than the gas hydrate production temperature. The filtrate recovery method according to claim 1.

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