JPH10227398A - Disposal facility of boiloff gas and method thereof, manufacturing facility of natural gas and method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce cost by mixing liquefied natural gas(LNG) with a boiloff gas(BOG) line on the intermediate stage of multistage compression while regulating the flow through the mixing line. SOLUTION: BOG 2 accumulated in the upper part of a tank 1 is introduced to a BOG disposal facility 8 by the pressure through a BOG piping 5. The facility 8 is provided with a first stage compressor 81, a second stage compressor 82, a third stage compressor 83, an intercooler 84, an aftercooler 85, a LNG feed piping 86 as a LNG mixing line L-mix, a LNG flow regulating valve 87, and a BOG/LNG mixing nozzle 88. Because LNG pressure in a LNG piping 6 is higher than BOG pressure compressed by the compressor 82, they can be easily mixed by the mixing nozzle 88, compressed mass flow at the compressor 83 is increased but the suction temperature is lowered, and the required load of the compressor is lowered. Consequently, by appropriately regulating the LNG flow to be mixed, the compressor load is reduced, and hence the cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for producing natural gas used as city gas and the like, and relates to a boil-off gas generated from a storage facility or the like of liquefied natural gas (hereinafter referred to as LNG) as a raw material. (Hereinafter referred to as BOG)
Related to technology that utilizes

[0002]

2. Description of the Related Art In the production of city gas, LNG is used as a main raw material, which is heated in a vaporizer and then pressurized to obtain natural gas at a predetermined temperature and pressure. Therefore, the LNG base is provided with storage facilities for storing LNG and a piping system connected to the storage facilities. In such storage facilities and piping systems, BOG is generated due to heat input from the outside. This B
The amount of OG generation is not negligible, and such BO
G has been used by raising the temperature and pressure to a predetermined temperature and pressure state. A typical example of such an example is found in the conventional example shown in FIG. 4. In this example, BOG 2 generated from the LNG tank 1 is compressed in multiple stages, and the pressure and temperature are appropriately adjusted. The BOG2 can be used by adjusting it to join the natural gas production line. The natural gas production facility shown in FIG. 4 is a storage facility (LNG) for storing liquefied natural gas.
A natural gas supply line L-LN which is provided with a tank 1) and which raises and raises the temperature of the liquefied natural gas supplied from this storage facility to obtain a natural gas having a second temperature and a second pressure higher than the atmospheric pressure.
G, and BOG generated from liquefied natural gas
And a boil-off gas processing line L-BOG for obtaining a boosted boil-off gas at a first temperature and a first pressure higher than the atmospheric pressure by multi-stage compression by a compressor. Supply line L-LNG
To the downstream side to use BOG.

[0003] The natural gas supply line L-LNG is provided with a vaporizer 7 and a pressure regulating valve 9. On the other hand, in the boil-off gas processing line L-BOG, three compressors 81,
82 and 83, an intercooler 84 is provided between the second compressor 82 and the third compressor 83, and an aftercooler 85 is provided on the downstream side (downstream) of the third compressor 83. By adopting such a structure, natural gas derived from BOG can be favorably mixed with natural gas that has passed through the natural gas supply line L-LNG, and can be used for subsequent uses.

[0004]

The processing of such a BOG requires a predetermined power to the compressor,
Equipment costs for the intercooler and aftercooler, as well as these heat sources and operating costs are required. Where B
Since the occurrence of OG is inevitable as a facility, it is desired to reduce the cost for making this useful as much as possible. Accordingly, the present invention satisfies the above-mentioned demands, and it is an object of the present invention to provide a technology capable of minimizing the cost required for making BOG useful.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above object, BOG generated from liquefied natural gas according to the present invention is provided.
Is processed in a multistage by a compressor to obtain a boosted BOG at a first temperature and a first pressure higher than the atmospheric pressure. The characteristic configuration of the BOG processing equipment is that a boil-off gas line at an intermediate stage of the multistage compression is liquefied. There is an LNG mixing line that can mix natural gas while adjusting the flow rate. The power required for the compressor is the gas on the inlet side of the compressor (in this case, BOG and liquefied natural gas mixed with this BOG)
, Temperature, and pressure, and the temperature and pressure of the outlet gas. In general, such a BO
When using G, BOG after finishing the last stage
The temperature and pressure conditions required for the operation are uniquely determined. Therefore, the compression state in each compression stage including the heat exchange system is determined such that the temperature and pressure are at the stage after the final stage of compression is completed. In, even if a relatively low temperature state was obtained,
Performing continuous multi-stage compression may require more power than necessary, or the temperature may be too high in the final stage, requiring an intercooler or aftercooler. Therefore, in the configuration of the present invention, the BOG in the middle stage is
While adjusting the flow rate of LNG in a lower temperature state than OG,
Mix via LNG mixing line. In this case, LNG
Is adjusted. Therefore, the power required in the compression stage after the mixing section, the temperature and pressure after compression,
It can be adjusted according to this mixing flow rate. As a result, in the multi-stage compression process, the power required for compression can be reduced as much as possible, or the gas state obtained through the final stage can be matched to the subsequent use state of BOG (for example, natural gas after vaporization in that state). (So that it can merge with the gas). As a result, the BOG gas can be used efficiently and effectively.

[0006] As a natural gas production facility capable of achieving the above object, the following form is preferably adopted. That is, a natural gas is provided which has a storage facility for storing liquefied natural gas and which raises and raises the temperature of the liquefied natural gas supplied from the storage facility to obtain a natural gas at a second temperature and a second pressure higher than the atmospheric pressure. A gas supply line is provided, and boil-off gas generated from liquefied natural gas is compressed in multiple stages by a compressor to a first temperature higher than the first temperature and an atmospheric pressure.
A boil-off gas processing line for obtaining a pressurized boil-off gas is provided. The obtained pressurized boil-off gas is combined with a natural gas at a second temperature and a pressure, and the following configuration is applied to a natural gas production facility using the boil-off gas. to add. An LNG mixing line, which can mix liquefied natural gas with the boil-off gas in the middle stage of the multi-stage compression in the boil-off gas treatment line while adjusting the flow rate, is provided by branching off from the natural gas supply line. In this equipment, when an LNG mixing line is provided, this receives LNG from a natural gas supply line and supplies the received LNG to the intermediate compression stage of the multistage compression provided in the boil-off gas treatment line while adjusting the flow rate. And Therefore, with respect to the boil-off gas processing line, the operation and effect described above in the section relating to the boil-off gas processing equipment can be obtained.
Further, this configuration can be constructed only by providing an LNG mixing line provided with a flow control valve or the like at a predetermined position in a conventional natural gas production plant as shown in FIG. As a result, efficient and useful equipment can be obtained by remodeling a conventional plant or the like.

Here, the LNG is provided at an intermediate portion of each of a plurality of compression stages except for the first stage compression in the multistage compression.
It is preferred to provide separate mixing lines. In this case, the compression state of the BOG in each compression stage can be set not only from the operating conditions of the compressor but also from the conditions such as the temperature, pressure, and flow rate of the liquefied natural gas supplied separately. And more control. As a result, the compression in each compression stage can be finely adjusted to make it suitable for the operation setting of the entire equipment. In the case of constructing such an equipment system, an intercooler (or heater),
A facility that does not require any aftercooler (or heater) can be constructed. (Although there is a difference in the effects, it is possible to construct a facility system that does not require such a heat exchange system even when each compression stage is not necessarily provided with the LNG mixing line.)

The LPG mixing line is preferably joined to the LNG mixing line. In this case, not only is the calorific value of the natural gas obtained from the natural gas supply line on the main pipe side adjusted, but also the BOG side. The calorific value can be well adjusted.

In the boil-off gas processing equipment described above, the following processing method is adopted. That is, when a boil-off gas generated from liquefied natural gas is multi-stage compressed by a compressor to obtain a boosted boil-off gas having a first temperature and a first pressure higher than the atmospheric pressure, a boil-off gas in an intermediate stage of the multi-stage compression is obtained. Then, the liquefied natural gas is mixed while adjusting the flow rate to obtain a pressurized boil-off gas.

On the other hand, the natural gas production facility described above is provided with a storage facility for storing liquefied natural gas, and the liquefied natural gas supplied from the storage facility is heated and pressurized. A natural gas supply line for obtaining a natural gas at a second temperature higher than the atmospheric pressure at a second temperature, and boil-off gas generated from the liquefied natural gas is compressed in multiple stages by a compressor to obtain a natural gas at a first temperature higher than the atmospheric pressure. A boil-off gas processing line for obtaining a high pressure boil-off gas having a high first pressure, wherein the pressure boil-off gas is produced at the second temperature, where natural gas is combined with the natural gas having a pressure,
Liquefied natural gas is branched from the natural gas supply line to a multistage compression intermediate stage of the boil-off gas processing line,
Liquefied natural gas is mixed while adjusting the flow rate.

Now, when using the boil-off gas, since it is not sufficient in terms of calorific value, a so-called heat increase may be performed by adding petroleum gas. As described above, when the heat is to be increased, a conventional LPG vaporization mechanism (which includes at least a vaporizer for LPG vaporization) is provided, and the oil gas obtained by this mechanism is mixed with the boil-off gas. And had The reason for requiring such a mechanism is that LPG tends to remain as droplets in the boil-off gas, and it is difficult to make the mixing uniform. However, such a vaporization mechanism is not preferable in terms of equipment costs and operation costs. Naturally, even when the heat is increased in this way, it is necessary to increase the pressure and the temperature with the multi-stage compression of the boil-off gas. Accordingly, the boil-off gas generated from the liquefied natural gas is compressed in a multistage by the compressor, and the liquefied petroleum gas is mixed to be in the state of the first temperature and the first pressure higher than the atmospheric pressure. In the case of obtaining a pressurized heat-up boil-off gas with an increased pressure, the liquefied petroleum gas is mixed with liquefied natural gas to obtain a heat-up mixture, and this heat-up mixture is used in the first or intermediate stage of multistage compression. It is preferable to obtain a boil-off gas which is mixed with a certain boil-off gas to be pressurized and heated. When this method is adopted, the liquefied petroleum gas is once mixed with the liquefied natural gas, and the mixture obtained by this mixing is mixed with the boil-off gas at the first stage or the middle stage of the multistage compression. In the compression step, a highly homogeneous mixed state can be realized, and a boil-off gas in a good pressurized and heated state can be obtained.

Therefore, the following effects can be obtained by adopting the configuration as in the present application. 1. The power required for compressing the boil-off gas can be reduced. 2. Even when the degree of reduction in power is low, equipment for heat exchange such as an intercooler can be omitted, so that equipment costs can be reduced. 3. Further, the calorific value of the boiling gas can be adjusted with less equipment and power.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION A natural gas production facility according to the present invention installed at an LNG handling base will be described below.
This will be described with reference to the drawings. As shown in FIG. 1, LNG3, which is a gas source, is 0.05 kg / cm ² G at -162 ° C.
And stored in the LNG tank 1 which is a storage facility.
LNG is driven by the power of the LNG pump 4 according to demand.
Discharged through the G pipe 6 and vaporized by the LNG vaporizer 7 using seawater as a heat source. The vaporized gas is controlled to a required pressure by the pressure regulating valve 9. Thus, the natural gas of the second temperature and pressure referred to in the present application is obtained. This line is the natural gas supply line L-LNG referred to in the present application,
When the gas is used for city gas, the calorific value is adjusted by a calorie adjusting device (not shown), and the gas is then odorized by an odorizing device and sent to a demand destination.

A cooling material (not shown) is provided around the LNG tank 1 to prevent heat input from the atmosphere.
However, heat input cannot be completely prevented, and 8
Approximately 2t / h BO with one 000kL LNG tank
G2 occurs. In addition, L in the LNG pipe 6 in the base
BOG is also generated from NG and LNG tank 1
It is structured to gather in. The BOG 2 accumulated in the upper part of the tank is guided to the boil-off gas processing equipment 8 of the present invention through the BOG pipe 5 by its own pressure. The boil-off gas treatment equipment 8 includes a first-stage compressor 81, a second-stage compressor 82, a third-stage compressor 83, an intercooler 84, an aftercooler 85, an LNG supply pipe 86 as an LNG mixing line L-mix, an LNG Flow control valve (FCV)
87, a BOG / LNG mixing nozzle 88 is provided. The line passing through the boil-off gas processing equipment 8 is the boil-off gas processing line referred to in the present application. In this way,
Natural gas at the first temperature and pressure referred to in the present application is obtained. Here, the intercooler 84 and the aftercooler 85 compress the BOG and the temperature greatly exceeds the atmospheric temperature.
It is provided for cooling seawater as a refrigerant. FIG.
In the example shown in FIG. 7, the LNG mixing line is disposed on the lower side of the intercooler 84 and on the upper side of the third-stage compressor 83 so as to be merged. Symbols a to i denote positions, which are used to describe the state of gas at these positions.

The operation of the equipment will be described.
Since the pressure of LNG in the G pipe 6 is higher than the pressure of BOG compressed by the second-stage compressor 82, the mixing can be easily performed by the mixing nozzle 88. If LNG is mixed with BOG, the mass flow rate to be compressed by the third-stage compressor 83 increases, but the suction temperature decreases. Generally, as the mass flow rate increases, the required load on the compressor increases, but as the suction temperature decreases, the required load on the compressor decreases. Therefore, the load required for the compressor (the third stage compressor 83 in the example shown in FIG. 1) can be reduced by appropriately adjusting the flow rate of the mixed LNG. Table 1 shows values of flow rate / pressure / temperature at points a to i shown in FIG.
The BOG generated and processed in the entire base is 15 t / h.

[0016]

[Table 1]

Case 1 corresponds to the conventional method in which the inflow of LNG is set to 0 t / h, that is, the conventional method in which LNG is not mixed, and corresponds to the configuration of the natural gas production facility shown in FIG. In this case, the total load required for the compressor is 2441 kW. On the other hand, in case 2 in which 7 t / h LNG is mixed into the output side of the second stage compressor with respect to BOG of 15 t / h, the temperature at the inlet side of the third stage compressor decreases from 23 ° C. to −91 ° C. The required load of the stage compressor 83 is 20
1kW reduction, total load required for multi-stage compression is also 201kW
Will be reduced. The temperature of the BOG at the outlet of the third stage compressor is-
30 ° C., and in this case, the aftercooler 85 is heated to 17 ° C. as a heater. Further, in this configuration, the BOG at −30 ° C. on the third stage compressor side is f
If the BOG is precooled at this point, the compressor load can be reduced by the same amount with a smaller amount of LNG. Therefore, by adopting the technology of the present application, it becomes possible to provide the boil-off gas treatment equipment 8 that efficiently compresses gas with a small amount of power in this manner. In this case, the amount of LNG mixed on the BOG side via the LNG mixing line L-mix (86) is controlled to approach the target temperature while measuring the temperature at point g. Further, when the temperatures of LNG and BOG are stable, control may be performed so that the ratio between the two is constant.

The intercooler 84 shown in FIG.
It is also possible to cool directly by mixing LNG into BOG without installing the BOG. In this case, the installation cost of the intercooler 84 can be reduced. Under the assumption that the intercooler is omitted, the amount of LNG mixed is assumed to be the same as in the case 2 described above.
-1), the load of the third stage compressor is 735 k
W, but this also results in a reduction of 78 kW compared to Case 1 with no LNG contamination.

FIG. 2 shows another embodiment of the natural gas production facility of the present invention installed at an LNG handling base for city gas. As can be seen at a glance from the drawing, the LNG mixing line L-mix
The LPG mixing line L-LPG 104 is configured to join. In this figure, 1 to 8 and 81 to 88 are the same as those shown in FIG. Reference numeral 101 denotes an LPG tank, and the LPG 102 stored inside the LPG tank
The PG is sent to the boil-off gas treatment facility 8 of the present invention via the LPG pipe 104 by the PG pump 103. At this time, the LPG flow control valve 89 controls the LPG so that the heat value at the point i is kept constant.
The flow rate is controlled and the LNG / LPG mixing nozzle 90
Mixed with. After this, the mixture of LPG and LNG is BOG
/ LNG is mixed with BOG by the mixing nozzle 88. BOG
As the proportion of the high boiling point with respect to LNG and LNG increases, mixing becomes difficult and droplets tend to be generated. In this configuration,
Immediately after mixing, it is sucked into the third-stage compressor 83, compressed, and the temperature of the BOG increases. Therefore, even when droplets are generated immediately after mixing, they can be uniformly mixed as gas in the third stage compressor 83.

FIG. 3 shows another embodiment of the natural gas production facility of the present invention installed at an LNG handling base for city gas. Compared to the configuration of FIG. 1, the second cooler does not include an intercooler and an aftercooler.
It is characterized in that an LNG mixing line L-mix is separately provided upstream of the stage compressor 82 and the third stage compressor 83. Flow rate of gas flowing through each line (unit: t /
h), pressure (kg / cm ² G) / temperature (° C.) are shown on the drawings with reference to required parts. This configuration can be contrasted with the configuration shown in FIG. The operating load of the compressor in this system is 813 kW, 735 kW, 73
5 kW, for a total of 2283 kW. As a result, a power reduction of 158 kW can be achieved as compared with the conventional example shown in FIG. Further, in this example, since it is not necessary to provide an intercooler and an aftercooler, it is possible to reduce equipment costs and operation costs. This effect is very large.

In the examples described so far, the current state of 37 kg / cm ² G as the natural gas pressure state after the temperature rise and pressure rise has been described. However, when transporting vaporized natural gas to a distant consumption area, it is necessary to further increase the pressure of the natural gas.
In this case, as an example, the pressure of natural gas is set to 72 kg / cm.
Attempts to raise up to about ² G have been made today. In this case, as shown in FIG. 7, when the compressor shown in FIG. 4 is used as a base, another extra compressor is required. Further, as is apparent from FIG. 5, in this example, two intercooler ICs and one aftercooler AC are required. Also in this figure, the flow rate (unit: t / h), pressure (kg / cm ² G) / temperature (° C.) of the gas flowing through each line are shown on the drawing with the required parts. In the case of this example, the operating load of the compressor is 756 in the first to fourth order.
kW, 755 kW, 755 kW, 755 kW, which is 3021 kW in total.

For comparison, FIGS. 5 and 6 show examples of the configuration of the present invention with respect to the configuration shown in FIG. FIG. 5 is an example corresponding to FIG. 1 and shows a plurality of LNG mixing lines L-m.
ix and the afterheater AH. On the other hand, FIG. 6 is an example corresponding to FIG. 3, in which the intercooler IC and the afterheater AH (these are so-called heat exchangers) are deleted. Comparing the required power in these examples, in the example shown in FIG. 5, 756 kW, 633 kW, 562 kW, 510 kW
kW, which is 2491 kW in total, which makes it possible to reduce the power by 530 kW and reduce the number of intercooler ICs, as compared with an example without the LNG mixing line L-mix. On the other hand, in the example shown in FIG. 6, 756 kW, 663 kW, 618 kW, and 732 kW are obtained in the first to fourth order, and the total is 2769 kW.
As compared with the example without the -mix, the power consumption is reduced by 252 kW and the heat exchanger such as the intercooler IC is not required.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a natural gas production facility of the present application.

FIG. 2 is a diagram showing a configuration example of a natural gas production facility of the present application provided with a mixed system of LPG.

FIG. 3 is a diagram showing a configuration example of a natural gas production facility of the present invention without a heat exchanger.

FIG. 4 is a diagram showing a configuration example of a conventional natural gas production facility.

FIG. 5 is a diagram showing a configuration example of a natural gas production facility of the present application.

FIG. 6 is a diagram showing a configuration example of a natural gas production facility of the present application from which a heat exchanger is eliminated.

FIG. 7 is a diagram showing a configuration example of a conventional natural gas production facility.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LNG tank (storage equipment) 8 Boil-off gas processing equipment 81 1st stage compressor 82 2nd stage compressor 83 3rd stage compressor 84 Intercooler 85 Aftercooler L-LNG Natural gas supply line L-BOG boil-off gas treatment line L-LPG LPG mixing line L-mix LNG mixing line

Claims (7)

[Claims] 1. A boil-off gas treatment facility, wherein boil-off gas generated from liquefied natural gas is multi-stage compressed by a compressor to obtain a boosted boil-off gas having a first temperature and a first pressure higher than the atmospheric pressure. In the boil-off gas line in the middle stage of multi-stage compression,
A boil-off gas treatment facility equipped with an LNG mixing line that can mix liquefied natural gas while adjusting the flow rate. 2. A storage facility for storing liquefied natural gas, wherein the liquefied natural gas supplied from the storage facility is heated and pressurized to produce natural gas at a second temperature and a second pressure higher than the atmospheric pressure. A boil-off gas processing line that includes a natural gas supply line that can supply the boil-off gas generated from the liquefied natural gas, and that compresses the boil-off gas from the liquefied natural gas in multiple stages to obtain a boosted boil-off gas at a first temperature and a first pressure higher than the atmospheric pressure. A natural gas production facility for combining the pressurized boil-off gas with the natural gas at the second temperature and pressure, wherein the boil-off gas in a multi-stage compression intermediate stage in the boil-off gas treatment line includes liquefied natural gas. A natural gas production facility comprising an LNG mixing line that can be mixed while controlling the flow rate of the natural gas by branching off the natural gas supply line. 3. The natural gas production facility according to claim 2, wherein the LNG mixing line is separately provided at an intermediate portion of each of the plurality of compression stages except for the first stage compression in the multistage compression. 4. An LPG mixing line for combining liquefied petroleum gas with the LNG mixing line.
Natural gas production equipment as described. 5. A method for treating a boil-off gas, wherein a boil-off gas generated from liquefied natural gas is multi-stage compressed by a compressor to obtain a boosted boil-off gas at a first temperature and a first pressure higher than the atmospheric pressure. For boil-off gas in the middle stage of multi-stage compression,
A method for treating a boil-off gas in which liquefied natural gas is mixed while controlling the flow rate to obtain the pressurized boil-off gas. 6. A storage facility for storing liquefied natural gas, wherein the liquefied natural gas supplied from the storage facility is heated and pressurized to produce natural gas at a second temperature and a second pressure higher than the atmospheric pressure. A boil-off gas processing line that includes a natural gas supply line that can supply the boil-off gas generated from the liquefied natural gas, and that compresses the boil-off gas from the liquefied natural gas in multiple stages to obtain a boosted boil-off gas at a first temperature and a first pressure higher than the atmospheric pressure. A method for producing natural gas wherein the pressurized boil-off gas is combined with natural gas at the second temperature and pressure, wherein the natural gas supply line branches to a multi-stage compression intermediate stage of the boil-off gas treatment line. And a method for producing natural gas by mixing liquefied natural gas while controlling the flow rate. 7. A boil-off gas generated from liquefied natural gas is compressed in a multistage by a compressor, liquefied petroleum gas is mixed, and the boil-off gas is in a state of a first temperature and a first pressure higher than the atmospheric pressure. A method of treating a boil-off gas to obtain an increased pressure-increased boil-off gas, wherein the liquefied petroleum gas is mixed with liquefied natural gas to obtain a heated mixture, and the heated mixture is subjected to the first stage of the multi-stage compression. Alternatively, a method of treating a boil-off gas, wherein the boil-off gas is mixed with a boil-off gas at an intermediate stage to obtain the boosted boil-off gas.