KR20210081176A - Boil-off gas recondenser with pche installed inside for improvement of temperature controllability of outlet stream - Google Patents

Abstract

The present invention relates to a PCHE built-in LNG boil-off gas (BOG) recondenser to control outlet subcooling degree, which is to improve the performance of a boil-off gas recondenser by adjusting the subcooling degree of the outlet flow discharged from a BOG recondenser, which is used to recondense boil-off gas of LNG fuel, which is emerging as a clean fuel.

Description

PCHE built-in LNG boil-off gas recondensation system for controlling outlet subcooling {BOIL-OFF GAS RECONDENSER WITH PCHE INSTALLED INSIDE FOR IMPROVEMENT OF TEMPERATURE CONTROLLABILITY OF OUTLET STREAM}

The present invention relates to a PCHE built-in LNG BOG recondensing device for controlling the degree of subcooling at an outlet, and more particularly, to a BOG Recondenser (BOG recondensing) used for recondensing BOG of an LNG fuel floating as a clean fuel. It relates to a PCHE built-in LNG boil-off gas recondensation device for controlling the outlet supercooling degree to improve the performance of the BOG recondensation device by controlling the supercooling degree of the outlet flow discharged from the device).

In general, LNG is emerging as a clean fuel that can reduce harmful substances such as SOx, NOx and carbon dioxide and greenhouse gases compared to conventional fossil fuels, and its application is very wide not only on land but also in the ocean, that is, in shipbuilding and ship fields. is the trend

LNG exists as a cryogenic liquid at -162°C under atmospheric pressure and is stored in cryogenic tanks before being supplied to individual consumers. For reference, the pressure of the main pipeline supply chain of natural gas that is connected to the main demand varies from country to country, but it is usually operated in the range of 70-120 bar.

The LNG stored inside the storage tank is suppressed from heat inflow through the use of insulating materials, but due to the temperature difference between the atmospheric temperature and the inside of the tank, it inevitably causes heat inflow. With the recent development of insulation technology, in the case of membrane tanks used in ships, It is known that 0.15% vol% of stored LNG is evaporated on a daily basis. The evaporated BOG is compressed by the BOG compressor, and the LNG stored in the tank is pressurized to the pressure of the main pipeline supply network through a low-pressure pump and a high-pressure pump, and then is vaporized and sent out.

BOG recondensation device is a device that cools/liquefies BOG with sub-cooled sensible heat of LNG by directly contacting the first boosted LNG with the low pressure pump and the pressurized BOG. Finally, BOG liquefied LNG is transferred to a high-pressure pump. The BOG recondensation device itself is a technology that has been developed and used for over 20 years.

BOG re-condensation equipment typically operates in the operating pressure range of 3 to 9 barg, and at this time, the expected problem is that the incoming BOG and the incoming LNG directly contact and liquefied LNG may exist in a saturated state. When LNG is transferred to a high-pressure pump, there are cases in which the degree of subcooling required by the high-pressure pump cannot be met. The fluid introduced into the pump must match the degree of supercooling required by the pump, and if this is not met, air bubbles may be generated inside the pump, which may cause deterioration of pump performance and damage.

Therefore, when transporting liquefied LNG from the inside of the BOG re-condensation device to the high-pressure pump, the normally supercooled LNG is injected into the Drum of BOG Recondenser and mixed with the LNG inside to achieve the degree of subcooling. , or by injecting supercooled LNG between the boil-off gas re-condensation device and the high-pressure pump to adjust the degree of supercooling.

Looking at the problems of the existing method, when subcooled LNG is put in the drum, it is necessary to secure enough liquid hold-up or Liquid Residence Time (usually 1 to 10 minutes) to receive the incoming LNG. The size of the drum unit should be large enough, and even when subcooled LNG is injected between the boil-off gas recondensation device and the high-pressure pump, there is a disadvantage of additionally utilizing (or injecting) the subcooled LNG flow rate as separate cold LNG is injected. exist.

Therefore, in order to solve this problem, an integrated system of an after-cooler installed with an after-cooler at the outlet end of the BOG re-condensation device and an BOG re-condensation device is required.

Korean Patent Publication No. 10-2018-0093405

The present invention is to solve the above problems, by controlling the degree of subcooling of the LNG discharged from the outlet end of the boil-off gas recondensation device and transferred to the high-pressure pump, by injecting additional subcooled LNG into the drum part of the boil-off gas recondensation device. An object of the present invention is to provide a PCHE built-in LNG boil-off gas recondensation device for adjusting the degree of outlet subcooling to solve the problems of increasing the drum unit size and additionally injecting additional subcooled LNG that may be unnecessary.

In addition, the present invention can supercool the LNG at the outlet of the boil-off gas recondensation device, and in particular, it is smaller in size than the conventional aluminum plate fin heat exchanger (Al PFHE) and the heat transfer performance (heat transfer area) is relatively large. By installing the printed circuit heat exchanger (PCHE) inside the BOG re-condensing device, we want to provide a system with higher space efficiency than when the heat exchanger and BOG re-condensing device are installed independently.

The PCHE built-in LNG boil-off gas recondensation device for controlling the degree of outlet subcooling according to an embodiment of the present invention is installed in a housing connected to an LNG storage tank and an inner lower portion of the housing, and includes a first pressure pump connected to the LNG storage tank. and a heat exchanger for controlling the degree of subcooling of the LNG discharged from the housing toward the second pressure pump through the LNG discharge pipe by using the cooling heat of the first pressure LNG supplied through it.

In an embodiment, the heat exchanger may be a printed circuit heat exchanger (PCHE).

In one embodiment, the heat exchanger is manufactured by etching the flow path by a chemical etching method on a thin metal plate, which is a base meterial, and then performing diffusion bonding on the etched thin metal plate, A distributor for discharging LNG from the heat exchanger may be welded.

In one embodiment, as the heat exchanger is welded to the nozzle surface of the LNG discharge pipe, a separate pipe may not be provided between the heat exchanger and the LNG discharge pipe.

In one embodiment, the present invention determines whether the controlled value of the degree of subcooling of the LNG through the heat exchanger reaches a required value of the second pressure pump connected to the LNG discharge pipe, and if the required value is not reached When the flow rate of the first pressure LNG supplied from the LNG storage tank to the housing is increased, and when the required value is reached, the first pressure LNG in the LNG storage tank is bypassed by It may further include an LNG subcooling degree determination unit to be supplied to the gas-liquid distributor in the LNG storage tank.

According to one aspect of the present invention, as the LNG is cooled (supercooled) through the existing heat exchanger, it is possible to solve a problem due to abnormal flow that may occur between the LNG discharged from the BOG recondensation device, and accordingly, in the pre-cooler, BOG can be partially or completely liquefied by using the supercooling heat of high-pressure LNG regardless of whether BOG is liquefied, and has the advantage of higher space efficiency than when the heat exchanger and the BOG recondensing device are installed independently.

In addition, according to one aspect of the present invention, since a separate pipe is not provided between the heat exchanger and the LNG discharge pipe of the boil-off gas recondensation device, problems such as vibration, noise, and pipe damage that may occur in the pipe compared to the existing one are fundamentally reduced. have the advantage of being excluded.

In addition, according to one aspect of the present invention, when the boil-off gas is not sufficiently cooled or liquefied, the cooling performance required in the heat exchanger can be appropriately increased by increasing the flow rate of low-pressure LNG.

In addition, according to one aspect of the present invention, as the heat exchanger is installed inside the boil-off gas recondensation device, even if problems such as puncture or destruction occur due to the failure of the heat exchanger, the boil-off gas recondensation device itself is a sealed pressure vessel. It has the advantage that LNG does not leak to the external environment.

In addition, according to one aspect of the present invention, as the heat exchanger is installed inside the BOG recondensing device, the need for insulation is solved, and heat leakage generated from the incoming high-pressure, subcooled LNG is rather reduced by the BOG inside the BOG recondensing device. As the temperature is cooled, a separate space in which the cold box is to be installed disappears and spatial efficiency is improved.

1 is a diagram schematically illustrating the configuration of a PCHE-embedded LNG boil-off gas recondensation apparatus 100 for controlling the degree of outlet subcooling according to an embodiment of the present invention.

Hereinafter, preferred examples are presented to help the understanding of the present invention. However, the following examples are only provided for easier understanding of the present invention, and the content of the present invention is not limited by the examples.

1 is a diagram schematically illustrating the configuration of a PCHE-embedded LNG boil-off gas recondensation apparatus 100 for controlling the degree of outlet subcooling according to an embodiment of the present invention.

Referring to Figure 1, the PCHE built-in LNG boil-off gas recondensation device 100 for controlling the degree of subcooling of the outlet according to an embodiment of the present invention is largely installed in the lower housing 110 and the housing 110 connected to the LNG storage tank. It may be configured to include a heat exchanger (120).

More specifically, at one side of the LNG storage tank, a low-pressure LNG inlet pipe for receiving the first pressure LNG, which is low-pressure LNG, from the first pressure pump corresponding to the low-pressure pump is provided. In addition, a gas-liquid distributor is provided inside.

In this case, the first pressure pump may mean a low pressure pump, and the second pressure pump to be described later may mean a high pressure pump.

The housing 110 is connected to the LNG storage tank at the lower side of the LNG storage tank.

The first pressure LNG (low pressure LNG) supplied through the low-pressure LNG inlet pipe of the LNG storage tank is supplied to the housing 110, in which case the heat exchanger 120 has the first pressure LNG supplied through the low-pressure LNG inlet pipe. The LNG (liquefied LNG) discharged from the housing 110 is cooled by using the cooling heat.

The heat exchanger 120 is connected to the LNG discharge pipe provided in the housing 110 at the lower inner side of the housing 110 , and in this case, the LNG discharge pipe faces the second pressure pump corresponding to the high-pressure pump.

The heat exchanger 120 has a smaller size than an aluminum plate fin heat exchanger (Al PFHE) and a printed circuit heat exchanger (PCHE) having a relatively large heat transfer performance (heat transfer area) may be applied.

The heat exchanger 120 forms a flow path by etching a thin metal plate, which is a base meterial, by a chemical etching method, then stacks a plurality of etched thin metal plates on top of each other and performs diffusion bonding. , is manufactured by welding the distributor of each fluid to the heat exchanger 120 .

In the case of the heat exchanger 120 manufactured in this way, since it is directly welded to the nozzle face of the LNG discharge pipe from the inner lower part of the housing 110 , the LNG stored in the lower part of the housing 110 is directly transferred to the heat exchanger 120 . is introduced into Therefore, since there is no pipe between the heat exchanger 120 and the LNG discharge pipe, problems such as vibration, noise, and pipe damage that may occur in the pipe can be fundamentally excluded.

Meanwhile, in the present invention, the flow rate of the low-pressure LNG supplied from the first pressure pump (low-pressure pump) is adjusted according to the degree of subcooling of the LNG through the heat exchanger 120 , or the low-temperature LNG is directly transferred without passing through the heat exchanger 120 . It has a configuration for supplying a gas-liquid distributor, and we will look at this.

In one embodiment, in the PCHE built-in LNG boil-off gas recondensation device 100 for controlling the degree of outlet subcooling according to the present invention, the LNG subcooling degree control value of the heat exchanger 120 is the required value of the second pressure pump (high pressure pump) Based on the result of determining whether to reach , increase the flow rate of the first pressure LNG (low pressure LNG) supplied to the housing 110 from the LNG storage tank, or the first pressure LNG (low pressure LNG) to the gas liquid distributor It may further include an LNG subcooling degree determination unit 130 to be supplied by bypassing in the direction.

The LNG subcooling degree determination unit 130 determines whether the LNG subcooling degree adjustment value through the heat exchanger 120 satisfies the supercooling degree required by the second pressure pump (high pressure pump) connected to the rear end of the LNG discharge pipe. However, if it is determined that the LNG is not sufficiently cooled, the LNG subcooling degree determination unit 130 controls the first pressure pump (low pressure pump) to supply the first pressure LNG (low pressure LNG) to the housing 110 . By increasing the flow rate of the heat exchanger 120 is increased the cooling performance required.

Conversely, when it is determined that the control value of the LNG subcooling degree through the heat exchanger 120 satisfies the supercooling degree required by the second pressure pump (high pressure pump) connected to the rear end of the LNG discharge pipe, the LNG subcooling degree determination unit ( In 130), the first pressure LNG (low pressure LNG) supplied from the first pressure pump (low pressure pump) is bypassed and supplied to the gas-liquid distributor in the LNG storage tank instead of the heat exchanger 120 .

As described above, according to the present invention, by using the cooling heat of the low-pressure LNG supplied from the first pressure pump (low-pressure pump) to cool the LNG in the liquefied state in the BOG re-condensation device, the second pressure from the BOG re-condensation device It is possible to further improve the performance of the boil-off gas recondensation device by adjusting the degree of subcooling of the LNG discharged to the pump (high pressure pump) to the degree of subcooling satisfied by the second pressure pump.

In particular, according to the present invention, since the heat exchanger is installed inside the boil-off gas recondensation device, even if problems such as puncture or destruction occur due to the failure of the heat exchanger, the boil-off gas recondensation device itself is a sealed pressure vessel, so it is not exposed to the external environment. As the LNG does not leak, the need for insulation is solved, and heat leakage from the incoming high-pressure, subcooled LNG rather cools the BOG temperature inside the BOG re-condensation device, a separate cold box is installed. There is an advantage in that the space disappears and the spatial efficiency is improved.

Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. You will understand that you can.

100: PCHE built-in LNG boil-off gas recondensation device for controlling outlet subcooling
110: housing
120: heat exchanger
130: LNG subcooling degree determination unit

Claims (5)

a housing connected to the LNG storage tank; and
It is installed in the lower inner portion of the housing and is discharged from the housing toward the second pressure pump through the LNG discharge pipe using the cooling heat of the first pressure LNG supplied through the first pressure pump connected to the LNG storage tank. A PCHE built-in LNG boil-off gas recondensation device for controlling the degree of subcooling at the outlet, comprising a heat exchanger for controlling the degree of subcooling.
According to claim 1,
the heat exchanger,
A PCHE built-in LNG boil-off gas recondensation device for controlling the degree of subcooling at the outlet, characterized in that it is a printed circuit heat exchanger (PCHE).
According to claim 1,
the heat exchanger,
The flow path is etched by chemical etching on a thin metal plate, which is a base meterial, and the flow path is etched, and then the etched thin metal plate is produced by diffusion bonding, and LNG is discharged from the heat exchanger. A PCHE built-in LNG boil-off gas recondensation device for controlling the degree of outlet subcooling, characterized in that the distributor for
According to claim 1,
the heat exchanger,
As it is welded to the nozzle surface of the LNG discharge pipe, a PCHE built-in LNG boil-off gas recondensation device for controlling the degree of outlet subcooling, characterized in that no separate pipe is provided between the heat exchanger and the LNG discharge pipe.
According to claim 1,
It is determined whether the control value of the degree of subcooling of the LNG through the heat exchanger reaches a required value of the second pressure pump connected to the LNG discharge pipe,
If the required value is not reached, increasing the flow rate of the first pressure LNG supplied from the LNG storage tank to the housing,
When the required value is reached, an LNG subcooling degree determination unit configured to bypass the first pressure LNG in the LNG storage tank and supply it to the gas-liquid distributor in the LNG storage tank; PCHE built-in LNG boil-off gas re-condensation device for controlling outlet subcooling.

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