KR100761974B1 - Natural gas liquefaction apparatus capable of controlling load change using flow control means of a working fluid - Google Patents

Abstract

The present invention relates to a liquefaction apparatus of natural gas, in particular, in response to the load fluctuations of the natural gas evaporated in the liquefaction of the natural gas evaporated from the storage tank of the carrier transporting cryogenic liquefied natural gas. The present invention relates to a natural gas liquefaction device having a flow rate control means capable of adjusting the flow rate of a fluid (refrigerant).

Natural gas liquefaction apparatus according to the present invention, the natural gas compression unit for pressurizing the natural gas of the gas state generated in the storage tank in which the natural gas of the liquid state is stored; A working fluid compressor connected to a plurality of working fluid compressors and coolers such that pressurization and cooling processes are repeated to pressurize and cool the working fluid in a cryogenic refrigeration cycle for liquefying the natural gas; A cold box unit for liquefying the natural gas in the gas state by exchanging the working fluid in the working fluid compression unit at a cryogenic temperature and exchanging heat with the natural gas in a condenser; And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit, and recycling a part of the working fluid to the working fluid compression unit through the bypass pipe to adjust the flow rate of the working fluid supplied to the cold box unit. A natural gas liquefaction apparatus including a regulating means, wherein the natural gas liquefied by the cold box unit is returned to the storage tank, and the pressure of the working fluid flowing into the working fluid compression unit in the bypass pipe of the flow adjusting means. Or it is characterized in that the expansion valve is installed to lower the temperature.

Natural gas, liquefaction equipment, working fluid, flow control means, bypass piping

Description

NATURAL GAS LIQUEFACTION APPARATUS CAPABLE OF CONTROLLING LOAD CHANGE USING FLOW CONTROL MEANS OF A WORKING FLUID}

1 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a buffer tank shown in the applicant's prior application;

2 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a first embodiment of the present invention;

3 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a second embodiment of the present invention;

4 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a third embodiment of the present invention;

5 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a fourth embodiment of the present invention;

6 is a block diagram showing the concept of a natural gas reliquefaction apparatus according to the present invention.

Explanation of symbols on the main parts of the drawings

1: natural gas compression unit 2, 2a, 2b, 2c: cold box unit

3: flow control means 4: working fluid compression

10: storage tank 11: the first natural gas compressor

12: second natural gas compressor 13: safety valve

14: recirculation valve 15: gas-liquid separator

20: condenser 21, 21a: first heat exchanger

22: second heat exchanger 23: third heat exchanger

24, 26: expansion turbine 25, 30: expansion valve

31: first valve 32: second valve

33: third valve 34: fourth valve

35: precooler 41: first working fluid compressor

42: second working fluid compressor 43: third working fluid compressor

44: first cooler 45: second cooler

46: third cooler 47: surge valve

The present invention relates to a liquefaction apparatus of natural gas, and in particular, boil off gas (BOG) generated by evaporation of natural gas in a storage tank of a carrier transporting cryogenic liquefied natural gas (LNG). Liquefied "BOG" or "evaporated natural gas" relates to a natural gas liquefaction apparatus equipped with a flow control means capable of adjusting the flow rate of the working fluid (refrigerant) in response to the load variation of the evaporated natural gas .

In general, not only storage tanks of LNG (LNG) installed on land, but also storage tanks of carrier ships transporting LNG, generally 0.1% of the day, regardless of the shape of the storage tanks such as moss type or membrane type Up to 3% of LNG is evaporated as a result of the inflow of external heat through the insulators surrounding the storage tank, and when the amount of LNG BOG increases, the pressure inside the storage tank increases, which can cause dangerous situations such as explosion of the storage tank. Will result.

As described above, LNG boil-off gas generated inside the LNG storage tank has been typically used as an auxiliary fuel source for powering a boiler or generator of a carrier, but in recent years, the design of an LNG carrier has a turbine according to steam driving. Since diesel engines are used rather than engines, the need for using boil-off gas generated inside the LNG storage tank as a secondary fuel source is rapidly decreasing.

Therefore, recently, a reliquefaction system for recovering such LNG boil-off gas and reliquefaction it into LNG and sending it back to the LNG storage tank has been introduced. And a reliquefaction system as described in the above.

The reliquefaction system uses the cryogenic cold heat obtained through the compression and cryogenic expansion of the working fluid circulated by a cooling system composed of a closed system in order to reliquefy the LNG evaporated gas generated in the LNG storage tank. The BOG is liquefied and then returned to the storage tank.

However, the LNG boil-off gas is required to adjust the load of the cooling device according to the increase or decrease of the amount of generation according to the external temperature conditions during the transport and storage of LNG, the above-mentioned reliquefaction system is operated inside the closed system It is difficult to control the refrigeration load because it is impossible to control the flow rate of the fluid.

The natural gas liquefaction apparatus was devised to solve this problem.

1 is an unpublished application of the present applicant, and the natural gas liquefaction apparatus capable of controlling the load fluctuation by using the flow control means of the working fluid is characterized in that the multi-stage of the natural gas evaporated from the storage tank of the liquefied natural gas. Natural gas compression unit for pressurizing with a natural gas compressor; A working fluid compressor installed with a plurality of working fluid compressors and coolers to repeat the pressurizing and cooling processes to pressurize and cool the working fluid in the cryogenic refrigeration cycle for liquefying the natural gas; A cold box unit for liquefying the natural gas in the gas state by exchanging the working fluid in the expansion fluid cryogenically in an expansion turbine and then exchanging heat with the natural gas in a condenser; And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit, installing a buffer tank in the bypass pipe, recovering and storing a part of the working fluid into the buffer tank through the bypass pipe, or storing the stored working fluid. And a flow rate adjusting means for adjusting the flow rate of the working fluid supplied to the cold box unit by supplementing with the fluid compression unit, and the natural gas liquefied by the cold box unit is returned to the storage tank.

In addition, in the bypass pipe in which the buffer tank is installed, valves for controlling the inflow and outflow of the working fluid are respectively installed at the inlet and the outlet of the buffer tank, so that the flow rate of the working fluid is reduced in accordance with the decrease in the refrigeration load. In order to recover the working fluid by opening the valve on the inflow side and to increase the flow rate of the working fluid according to the increase of the refrigeration load, the operation supplied to the cold box unit by opening the valve on the supply side and supplying the working fluid. Adjust the circulating flow rate of the fluid.

The natural gas liquefaction apparatus is provided with a flow rate adjusting means of the working fluid to cope with the refrigeration load according to the amount of evaporated gas, but the flow rate adjusting means must be provided with a buffer tank for storing the working fluid.

In order to operate a refrigeration cycle, the working fluid is repeatedly compressed to high pressure by the working fluid compression unit and expanded to low pressure by expansion means such as an expansion turbine and an expansion valve. In order to reduce the flow rate of the working fluid in accordance with the reduction of the refrigeration load during operation, the high pressure compressed working fluid has to be recovered to the buffer tank.

In addition, the flow rate adjusting means including the buffer tank is not provided with a decompression means, the working fluid is stored in the buffer tank in a high pressure state, the operation of the high pressure stored in the buffer tank due to the increase of the refrigeration load during the operation of the refrigeration cycle When replenishing the fluid, the pressure of the line flowing into the working fluid compression unit and the low pressure line of the condenser outlet is increased, and as a result, the pressure difference at the inlet and outlet of the expansion turbine is reduced, thereby greatly reducing the efficiency of the refrigeration cycle.

In addition, in recent years, as the LNG carrier is enlarged, the volume of the buffer tank installed in the natural gas reliquefaction apparatus is also increased, which makes it difficult to install in a limited space. For example, natural gas reliquefaction equipment mounted on 210K LNG carriers uses nitrogen as the working fluid of the refrigeration cycle.In this case, the volume of the nitrogen buffer tank is approximately 30m3, so the installation space must be provided when designing the device. .

As described above, Korean Patent Publication No. 2005-94798 discloses a related art for controlling a nitrogen circulation amount by providing a nitrogen buffer tank. However, the patent application describes only a bypass line and a nitrogen storage tank. .

The present invention has been made to solve the conventional problems as described above, an object of the present invention is to form a bypass pipe in the working fluid inlet and outlet pipe of the cold box unit, a portion of the working fluid through the bypass pipe to the working fluid By recirculating to the compression section to adjust the flow rate of the working fluid supplied to the cold box unit, but to reduce the pressure and temperature of the working fluid supplied to the working fluid compression unit installed expansion valve in the bypass pipe to increase and decrease the evaporated natural gas It is to provide a natural gas liquefaction apparatus for adjusting the working fluid circulation flow rate supplied to the condenser of the cold box unit to cope with the fluctuation of the refrigeration load.

Such an object of the present invention, the natural gas compression unit for pressurizing the natural gas of the gas state generated in the storage tank in which the natural gas of the liquid state is stored; A working fluid compressor connected to a plurality of working fluid compressors and coolers such that pressurization and cooling processes are repeated to pressurize and cool the working fluid in a cryogenic refrigeration cycle for liquefying the natural gas; A cold box unit for liquefying the natural gas in the gas state by exchanging the working fluid in the working fluid compression unit at a cryogenic temperature and exchanging heat with the natural gas in a condenser; And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit, and recycling a part of the working fluid to the working fluid compression unit through the bypass pipe to adjust the flow rate of the working fluid supplied to the cold box unit. A natural gas liquefaction apparatus including a regulating means, wherein the natural gas liquefied by the cold box unit is returned to the storage tank, and the pressure of the working fluid flowing into the working fluid compression unit in the bypass pipe of the flow adjusting means. Or it is achieved by a natural gas liquefaction apparatus that can adjust the load fluctuation using the flow control means of the working fluid, characterized in that the expansion valve is installed to lower the temperature.

Preferably, the front and rear sides of the expansion valve installed in the bypass pipe is characterized in that each valve for adjusting the flow rate is installed.

More preferably, the inlet of the expansion valve and the outlet of the last working fluid compressor of the working fluid compression unit is connected to the bypass pipe, characterized in that the valve for adjusting the flow rate is installed.

In addition, the outlet of the expansion valve and the outlet of the cold box unit is connected to the bypass pipe, the high temperature part working fluid through the heat exchange between the low temperature expansion working fluid introduced into the cold box unit and the low temperature expansion working fluid by the expansion valve A precooler is installed in the bypass pipe to precool the valve, and a valve for adjusting the flow rate is installed in the bypass pipe.

In addition, the outlet of the liquefied natural gas of the cold box unit and the outlet of the storage tank is connected to the bypass pipe, a valve for adjusting the flow rate is installed here, a part of the liquefied natural gas supplied through the bypass pipe and the The natural gas supplied from the storage tank is mixed so as to precool the natural gas supplied to the natural gas compression unit.

delete

In addition, a gas-liquid separator is installed at the outlet of the cold box unit so that the natural gas in the liquid state is returned to the storage tank by a pump or re-introduced into the natural gas compression unit through the bypass pipe, and the natural gas in the gas state is natural gas. It is characterized in that the re-injection or discharge into the compression unit.

The cold box unit may further include: a first heat exchanger connected to an outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid passing through the condenser; An expansion turbine connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And a condenser connected to the outlet of the expansion turbine to exchange heat between the cryogenic working fluid passing through the expansion turbine and the natural gas introduced from the natural gas compression unit to liquefy the natural gas.

The cold box unit may further include: a second heat exchanger connected to an outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; A first heat exchanger connected to the outlet of the second heat exchanger for cooling the precooled working fluid to the low temperature operating fluid passing through the condenser; By bypassing a part of the working fluid flowing into the first heat exchanger and expanding it at a low temperature, it is mixed with the low temperature working fluid passed through the condenser and re-introduced into the first heat exchanger to further pass the pre-cooled working fluid passing through the first heat exchanger. Expansion turbine for cooling; An expansion valve connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And a condenser connected to the outlet of the expansion valve to allow the cryogenic working fluid and the natural gas introduced from the natural gas compression unit to pass through the expansion valve to liquefy the natural gas.

The cold box unit may further include: a second heat exchanger connected to an outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; It is connected to the outlet of the second heat exchanger to form three paths through which the pre-cooled working fluid, the natural gas flowing from the natural gas compression unit and the low-temperature section working fluid passing through the condenser, and the pre-cooled working fluid and natural A first heat exchanger for cooling gas to the cold working fluid; By bypassing a portion of the working fluid flowing into the first heat exchanger and expanding it at a low temperature, it is mixed with the low temperature working fluid passed through the condenser and re-introduced into the first heat exchanger to pass through the first heat exchanger and the pre-cooled working fluid and natural Expansion turbine for further cooling the gas; An expansion valve connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And a condenser connected to the outlet of the expansion valve to exchange the cryogenic working fluid passing through the expansion valve and the natural gas passing through the first heat exchanger to liquefy the natural gas.

The cold box unit may further include: a second heat exchanger connected to an outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; It is connected to the outlet of the second heat exchanger to form three paths through which the pre-cooled working fluid, the natural gas flowing from the natural gas compression unit and the low-temperature section working fluid passing through the condenser, and the pre-cooled working fluid and natural A first heat exchanger for cooling gas to the cold working fluid; A third heat exchanger connected to the outlet of the first heat exchanger for cooling the high temperature part working fluid introduced from the first heat exchanger to the low temperature part working fluid passing through the condenser; By bypassing a portion of the working fluid flowing into the first heat exchanger and expanding at low temperature, mixed with the low-temperature operating fluid passed through the third heat exchanger and re-introduced into the first heat exchanger to pass the pre-cooled working fluid passing through the first heat exchanger And an expansion turbine for further cooling natural gas; An expansion valve connected to the outlet of the third heat exchanger to cryogenically expand the working fluid; And a condenser connected to the outlet of the expansion valve to exchange the cryogenic working fluid passing through the expansion valve and the natural gas passing through the first heat exchanger to liquefy the natural gas.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The temperature and pressure described below show one example, and the present invention is not limited to these numerical values.

The liquefaction apparatus according to the present invention is a natural gas compression unit (1) for pressurizing the natural gas of the gas state generated in the storage tank 10 in which the liquid natural gas is stored as shown in the block diagram of the present invention shown in FIG. ), A working fluid compressor (4) connected with a plurality of working fluid compressors and a cooler to repeat the pressurizing and cooling processes to pressurize and cool the working fluid in a cryogenic refrigeration cycle for liquefying the natural gas. Cold working unit (2) and the working fluid inlet and outlet piping of the cold box unit (2) for liquefying the natural gas in the gas state by heat exchange with the natural gas in the condenser after cryogenic expansion of the working fluid of (4) Forming a bypass pipe in the air, and recycling a part of the working fluid to the working fluid compression unit (4) through the bypass pipe to supply the cold box unit (2) It is largely composed of a flow rate control means (3) for controlling the flow rate of the fluid. The bypass pipe of the flow rate control means 3 is provided with expansion means for lowering the working fluid flowing into the working fluid compression unit 4 by expanding the working fluid at low temperature.

   This will be described in detail by dividing each embodiment as follows.

(First embodiment)

2 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a first embodiment of the present invention.

In the natural gas liquefaction apparatus according to the first embodiment of the present invention, the load fluctuation of the evaporated natural gas is added to the configuration described in the patent application No. 2005-65501 filed by the applicant of the present invention. In response to the device configured to perform the operation.

The natural gas liquefaction apparatus according to the first embodiment of the present invention extracts the gaseous natural gas (evaporated natural gas) generated in the storage tank 10 and liquefies it by heat exchange with the cryogenic refrigeration cycle and then again It is a device for returning to the storage tank (10) for storage.

In the natural gas liquefaction apparatus according to the first to fourth embodiments of the present invention, the cryogenic refrigeration cycle is composed of a closed system, the working fluid (refrigerant) circulating inside the closed system liquefied natural gas Nitrogen, helium, argon, or the like may be used as the material that can be cooled below the point (−162 ° C.). In the present invention, operation using nitrogen as a working fluid will be described.

Natural gas liquefaction apparatus according to the first embodiment of the present invention shown in Figure 2 is a natural gas compression unit (1) for pressurizing the natural gas of the gas state generated in the storage tank 10 in which the liquid natural gas is stored ; A plurality of working fluid compressors (41, 42, 43) and coolers (44, 45, 46) are connected so that the pressurizing and cooling processes are repeated to pressurize and cool the working fluid in the cryogenic refrigeration cycle for liquefying the natural gas. Fluid compression section 4; A cold box unit (2) for liquefying the natural gas in a gaseous state by cryogenic expansion of the working fluid of the working fluid compression unit (4) and then heat exchange with the natural gas in a condenser (20); And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit 2, recycling some of the working fluid to the working fluid compression unit 4 through the bypass pipe, and supplying it to the cold box unit 2. It is configured to include a flow rate control means (3) for adjusting the flow rate of the working fluid, which is configured to return the natural gas liquefied by the cold box unit (2) to the storage tank (10).

Here, the expansion pipe 30 is installed in the bypass pipe of the flow rate control means 3 to lower the pressure and temperature of the working fluid flowing into the working fluid compression unit 4 by expanding the working fluid at low temperature.

Referring to Figure 2 in more detail with respect to the above-described configuration, first, the system for supplying and reclaiming the system to extract and re-liquefy the evaporated natural gas of the liquid natural gas stored in the storage tank 10 is a storage tank 10, the natural gas compression unit 1, the condenser 20 and the pump (P).

A discharge port is formed in the upper portion of the storage tank 10 so that the evaporated natural gas can be discharged and extracted, and is connected to the natural gas supply pipe, and the natural gas inside the storage tank 10 is predetermined in the natural gas supply pipe. When the pressure rises above (about 1.03 bar), the safety valve 13 is formed to open and close to lower the pressure of the storage tank 10 below a predetermined pressure.

The natural gas compression unit 1 is composed of a motor (M), a plurality of natural gas compressors (11, 12) and pipes interconnecting them, and the natural gas compressors (11, 12) are connected to the motor (M). It is connected to be driven by.

The first and second natural gas compressors 11 and 12 are sequentially connected by pipes so that the natural gas supplied from the storage tank 10 may be compressed and transported step by step by the natural gas compressors 11 and 12. It is. Here, the natural gas compression unit 1 according to the present invention compresses and transports natural gas in two stages, so that the first and second natural gas compressors 11 and 12 are connected in series by pipes.

The condenser 20 is a device for liquefying the compressed natural gas by heat exchange with the cryogenic expanded working fluid and is installed inside the cold box unit 2, and the compressed natural gas and the cryogenic expanded working fluid pass through. The flow path is formed inside so that it may be. The gas-liquid separator 15 is installed in the natural gas outlet pipe of the condenser 20 so that the natural gas in the condensed state is returned to the storage tank 10 by a pump P or compressed by natural gas through a bypass pipe described later. It is re-injected to the part (1). In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

In addition, a branch pipe is connected to the storage tank 10 by branching a return pipe of the outlet side of the cold box unit 2 to control a supply temperature of the evaporated natural gas supplied to the natural gas compression unit 1. The other pipe is connected to a supply pipe connecting the outlet of the storage tank 10 and the inlet of the natural gas compression unit 1 to form a bypass pipe, and supply to the natural gas compression unit 1. When the temperature of the natural gas is increased, a portion of the natural gas condensed through the bypass pipe is recycled to precool the natural gas to adjust the temperature by mixing the evaporated natural gas with the condensed natural gas.

Here, the recirculation pipe is formed with a recirculation valve 14 to adjust the recycle amount of the condensed natural gas, the control method of the recirculation valve 14 to manually open or close the valve or the outlet of the storage tank 10 Alternatively, a temperature sensor (not shown) may be formed at the inlet of the natural gas compression unit 1 to automatically control the opening and closing degree of the recirculation valve 14 according to the supply temperature of the natural gas. The automatic control of the recirculation valve 14 by the temperature sensor is controlled only until the temperature supplied to the natural gas compression unit 1 reaches a steady state, after which the recirculation valve 14 is closed and the condensed natural gas is It is returned to the storage tank (10).

The cold box unit 2 is connected to the outlet of the flow control means 3 (may be connected directly from the working fluid compression unit 4 without passing through the flow control means 3) the flow control means ( A first heat exchanger 21 for precooling the working fluid introduced from 3) to the low temperature part working fluid passing through the condenser 20; An expansion turbine 24 connected to the outlet of the first heat exchanger 21 to expand the working fluid to cryogenic temperature; And a cryogenic working fluid which is connected to an outlet of the expansion turbine 24 and passes through the expansion turbine 24 and natural gas introduced from the natural gas compression unit 1 to liquefy the natural gas. It comprises a condenser 20.

Hereinafter, the cold box unit 2 of the natural gas liquefaction apparatus according to the present invention is provided with an expansion turbine 24 for cryogenic expansion of the working fluid, but the present invention is not limited thereto, and the expansion turbine 24 is replaced with an expansion valve. It is also possible to use.

Here, the low temperature operating fluid is cryogenic expansion by the expansion turbine 24 of the cold box unit 2 and the heat exchange with the natural gas in the condenser 20 after the operation is returned to the working fluid compression unit (4) The fluid is defined as the fluid, and the high temperature working fluid is defined as the working fluid from the working fluid compression section 4 to the expansion turbine 24.

A generator G is connected to the rotary shaft of the expansion turbine 24 to use electric energy generated by the expansion turbine 24 as driving energy of the working fluid compression unit 4 or the natural gas compression unit 1. It is also possible.

The cold box unit 2 is formed as a single module, which shortens the pipe between the components by condensing the first heat exchanger 21, the expansion turbine 24, and the condenser 20 in a limited space. The heat loss through the pipe can be minimized. That is, the length of the pipe connecting the expansion turbine 24 and the condenser 20 is shortened so that the cryogenic state of the working fluid at the outlet of the expansion turbine 24 can be stably maintained.

In addition, by modularizing the cold box unit 2, it is possible to miniaturize the cold box unit 2 and the natural gas liquefaction apparatus, and can be easily mounted on the ship.

In addition, the cold box unit 2 is preferably insulated with a generally known heat insulator.

The working fluid compression unit 4 compresses the working fluid (nitrogen) to a high pressure (about 58 bar) so that the working fluid (nitrogen) can be sufficiently cryogenically expanded in the expansion turbine 24 and through the flow control means 3, the cold box unit. (2) acts as a means to pressurize and supply a plurality of working fluid compressors (41, 42, 43) for compressing the working fluid in multiple stages, the heating operation by the compression operation of the working fluid compressor (41, 42, 43) Working fluids during compression operation of the plurality of coolers 44, 45, 46 and the working fluid compressors 41, 42, 43 installed between the working fluid compressors 41, 42, 43 to cool the fluid. Surge to rapidly increase the pressure or to increase the flow rate of the entire system, that is, the natural gas liquefaction device is abnormally operated to bypass the flow to the working fluid compressor (41, 42, 43) It consists of piping. Here, the surge pipe is provided with a surge valve 47 for controlling the flow rate.

The first to third working fluid compressors 41, 42, and 43 are sequentially connected to the working fluid compression unit 4 of the natural gas liquefaction apparatus according to the present invention in order to compress the working fluid in three stages. The outlets of the working fluid compressors 41, 42, and 43 are connected to the first to third coolers 44, 45, and 46 for heat exchange with seawater. Here, the first to third working fluid compressors (41, 42, 43) are aligned to rotate in engagement with one rotation shaft, the rotation shaft is connected to be driven by a motor (M).

In addition, the first to third coolers 44, 45 and 46 operate and cool only when the working fluid is raised above a predetermined temperature by the first to third working fluid compressors 41, 42 and 43. When the thermal stress is applied to the working fluid compression unit 4 because the temperature of the working fluid recovered from the cold box unit 2 is low, the first to third coolers 44, 45, and 46 are applied. It is desirable to control the operation of the.

The flow rate adjusting means 3 is located between the working fluid compression unit 4 and the cold box unit 2 to adjust the flow rate and temperature of the working fluid supplied from the working fluid compression unit 4 by pressure Three bypass pipes connected by the control means for supplying the cold box unit 2 to recycle the part of the pressurized working fluid to the working fluid compression unit 4 through various paths, by the bypass pipes. Four valves 31, 32, 33, 34 installed on each path to be determined and the expansion valve 30 is installed in a specific pipe of the bypass pipe to expand the working fluid at low temperature.

The installation positions of the plurality of bypass pipes, the expansion valve 30 and the plurality of valves 31, 32, 33, and 34 will be described as follows.

First, the first bypass pipe is a pipe for controlling a flow rate of the working fluid by bypassing a part of the working fluid supplied to the cold box unit 2 when the refrigeration load is changed, and the third working fluid compressor 43 at the end. Branched from the working fluid supply pipe extending from the third cooler 46 connected to the pipe is connected to the recovery pipe connecting the outlet of the cold box unit 2 and the inlet of the working fluid compression unit (4). An expansion valve 30 is installed in the first bypass pipe, and a first valve 31 is installed in a front (inlet) side pipe of the expansion valve 30, and after (outlet) of the expansion valve 30. The 2nd valve 32 is provided in the side piping.

The flow rate control of the working fluid passing through the first bypass pipe can be controlled by operating a valve provided in front and rear of the expansion valve (30).

Next, the second bypass pipe is a pipe connecting the outlet of the third working fluid compressor 43 of the last end and the inlet side pipe of the expansion valve 30 installed in the first bypass pipe. Three valves 33 are provided.

The second bypass pipe is the last stage when the refrigeration load of the refrigeration system is reduced when the temperature of the working fluid compressed by the third working fluid compressor 43 of the last stage is not heated to about 40 ° C. or more. It is a pipe for controlling a flow rate of the working fluid by bypassing a part of the working fluid without passing through the third cooler 46 connected to the third working fluid compressor 43. Here, the reason for the temperature condition for bypassing a part of the working fluid to the second bypass pipe is about 40 ° C is generally operated by being compressed by the working fluid compression unit 4 and supplied to the cold box unit 2. This is because the temperature of the fluid is about 40 ° C. If a part of the working fluid is diverted to the expansion valve 30 installed in the first bypass pipe in the state where the temperature of the working fluid is cooled to 40 ° C. or lower by the third cooler 46 of the last stage, the expansion valve ( The temperature of the working fluid expanded by 30) is lowered to minus tens of degrees (° C.), and when the working fluid cooled below zero is recovered to the working fluid compression unit 4, the working fluid compression unit 4 Since thermal stress may be applied, it is desirable to maintain the temperature of the working fluid at an appropriate temperature.

Finally, the third bypass pipe is a pipe connecting the outlet of the expansion valve 30 installed in the first bypass pipe and the outlet side return pipe of the cold box unit 2, and the fourth valve in the third bypass pipe. 34 is provided, and a precooler 35 is formed so that the third bypass pipe and the inlet-side supply pipe of the cold box unit 2 cross each other to perform heat exchange.

The third bypass pipe is cooled by the third cooler 46 at the end and is installed in the first bypass pipe when the temperature of the high temperature part working fluid supplied to the cold box unit 2 flows into 40 ° C. or more. As a pipe for precooling the working fluid at low temperature by the expansion valve 30, a precooler 35 having a heat exchanger type must be formed.

On the other hand, in the cryogenic refrigeration cycle using nitrogen, by supplying a small nitrogen buffer tank near the front end of the first working fluid compressor 41 to supplement or adjust the small amount of nitrogen that is increased or decreased during the operation of the cryogenic refrigeration cycle. It is also possible.

Each operation mode for controlling the flow rate and temperature of the working fluid by various methods using the first to fourth valves 31, 32, 33, 34 installed in the first to third bypass pipes will be described later. The operation method of the natural gas liquefaction apparatus will be described in detail.

The operation method of the natural gas liquefaction apparatus according to the first embodiment of the present invention will be described by dividing the natural gas circulating process and the refrigeration cycle for the working fluid (nitrogen).

First, when the circulating process of the evaporated natural gas, when the natural gas of the liquid state stored in the storage tank 10 is evaporated by an external temperature difference, and the internal pressure rises above the set pressure, the storage tank 10 The safety valve 13 formed at the outlet is opened and the evaporated natural gas is discharged. At this time, when the temperature of the evaporated natural gas is a set temperature, that is, -120 ° C or more, the liquid natural gas stored in the storage tank 10 or a part of the liquefied natural gas introduced from the condenser 20 is evaporated. Natural gas supplied to the natural gas compression unit 1 by mixing with the natural gas is maintained at 1.03 bar, -120 ℃. Here, in order to recycle the liquefied natural gas, a recirculation valve 14 installed in the bypass pipe of the return pipe is opened so that a part of the liquefied natural gas is introduced and mixed with the evaporated natural gas. In addition, in order to inject the natural gas of the liquid state stored in the storage tank 10 to form a pipe so that the pipe (not shown) formed in the lower portion of the storage tank 10 is connected to the supply pipe of the evaporated natural gas. desirable.

The evaporated natural gas introduced into the natural gas compression unit 1 is compressed to 3.2 bar and −50.83 ° C. in the two-stage natural gas compressors 11 and 12 to be superheated at high temperature and high pressure.

The compressed natural gas is heat-exchanged with a cryogenic expanded working fluid (nitrogen) by a nitrogen refrigeration cycle in the condenser 20 of the cold box unit 2 to be liquefied into a 3.0bar, -154.7 ° C supercooled liquid.

The liquefied natural gas is returned to and stored in the storage tank 10 through a pump (P) installed in the return pipe, and during the initial operation of the natural gas liquefaction apparatus or the natural gas discharged from the storage tank 10 is hot When discharged to a portion of the liquefied natural gas is re-introduced to be mixed with the evaporated natural gas through the recirculation valve (14). Here, the method of returning the liquefied natural gas to the storage tank 10 has a method of spraying through the spray head from the upper portion of the storage tank 10 or supplying to the bottom of the storage tank 10. When flowing into the bottom of the storage tank 10, the nitrogen component of the uncondensed gas contained in the liquefied natural gas is dissolved in the liquefied natural gas to maintain a low nitrogen ratio in the gas phase. Since nitrogen has a lower liquefaction point than methane, which is a main component of liquefied natural gas, preventing an increase in nitrogen content in evaporated natural gas can reduce the load of the two-stage natural gas compressors 11 and 12 or the condenser 20.

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.2bar, 35.46 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through the pressure is increased to 58bar, 43 ℃ pressure, the compressed working fluid (nitrogen) is a flow path is determined according to the operating mode of the flow rate control means (3) through the cold pipe unit (2) Is supplied.

The nitrogen gas supplied to the cold box unit 2 is cooled to 58 bar and −105 ° C. by heat exchange with a low temperature operating fluid that has passed through the condenser 20 in the first heat exchanger 21, and the high pressure working fluid. While passing through the expansion turbine 24 is expanded to a cryogenic, low-pressure gas of 10.5 bar, 167 ℃ is further cooled.

The cryogenic working fluid is heat-exchanged with the evaporated natural gas supplied from the natural gas compression unit 1 in the condenser 20 to liquefy the natural gas into a supercooled liquid of 3.0 bar and -154.7 ° C. The cryogenic working fluid is heated to 10.3 bar, -134 ° C.

The working fluid is heated to 10 bar, 40 ° C. by heat exchange with the high temperature part working fluid supplied from the working fluid compression part 4 in the first heat exchanger 21, and then the flow control means 3 through the recovery pipe. Re-injected into the working fluid compression section 4 to complete the cryogenic refrigeration cycle.

At this time, when the working fluid flowing from the cold box unit (2) is introduced below 40 ℃, the flow control means (3) is switched to the appropriate operating mode to bypass a portion of the high temperature operating fluid mixed with the low temperature operating fluid It is necessary to control the temperature of the working fluid flowing into the working fluid compression unit (4).

The operation mode for determining the flow path of the working fluid passing through the flow regulating means 3 is basically defined as four cases, but is not limited thereto and operates by mixing at least two operation modes according to the change in the cryogenic refrigeration load. It is also possible to circulate the fluid.

Here, the liquefaction operation load of the evaporated natural gas can be adjusted in the range of 70 to 100% according to the change of the operation mode of the flow rate control means (3).

Run Mode 1

The operation mode 1 of the flow rate adjusting means 3 is to the cold box unit 2 through the first bypass pipe when the operating load (natural gas supply amount / liquefied natural gas amount) of the natural gas liquefaction apparatus is 100% or less. By bypassing a part of the working fluid supplied is a mode of operation to reduce the flow rate of the working fluid supplied to the condenser 20 of the cold box unit (2).

To this end, the first and second valves 31 and 32 installed in the first bypass pipe are opened, and the third valve 33 installed in the second bypass pipe and the fourth valve 34 installed in the third bypass pipe. ) To form a bypass path for the working fluid.

When the bypass path is formed in the above-described manner, a part of the working fluid compressed by the working fluid compression unit 4 is expanded by low temperature through the expansion valve 30 installed in the first bypass pipe, which bypasses the cold box. It is mixed with the low temperature part working fluid recovered through the outlet of the unit 2 and introduced into the working fluid compression part 4. At this time, the working fluid passing through the expansion valve 30 is preferably expanded at low temperature close to the temperature and pressure of the working fluid recovered from the cold box unit (2), in particular the temperature of the mixed working fluid is a suitable temperature It is important to prevent the compression efficiency from being lowered below to act as a thermal stress on the first to third working fluid compressors 41, 42 and 43, or to increase the pressure of the mixed working fluid to be higher than an appropriate pressure.

The flow rate of the working fluid passing through the first bypass pipe is adjusted according to the opening degree of the first and second valves 31 and 32, which is a variation of the amount of evaporated natural gas supplied to the natural gas liquefaction apparatus (load Adjustable).

Run Mode 2

In the operation mode 2 of the flow regulating means 3, the operating load (natural gas supply amount / liquefied natural gas amount) of the natural gas liquefaction apparatus is 100% or less, and at the exit of the third working fluid compressor 43 When the working fluid temperature is less than a predetermined temperature (about 40 ℃) bypass the part of the working fluid supplied to the cold box unit 2 through the second end of the second bypass pipe and the first bypass pipe to the cold box unit ( It is an operation mode to reduce the flow rate of the working fluid supplied to the condenser 20 of 2).

To this end, the first valve 31 installed in the first bypass pipe is closed, the second valve 32 installed in the first bypass pipe and the third valve 33 installed in the second bypass pipe are opened, and The fourth valve 34 installed in the third bypass pipe is closed to form a bypass path of the working fluid.

When the bypass path is formed in the above manner, a portion of the compressed working fluid is supplied through the second bypass pipe connected to the outlet of the third working fluid compressor 43 of the last stage, and the expansion installed in the first bypass pipe is supplied. The low temperature expansion at the valve 30 is bypassed through the rear end of the first bypass pipe, which is mixed with the low temperature operating fluid recovered through the outlet of the cold box unit 2 and introduced into the working fluid compression unit 4. do. At this time, the working fluid passing through the expansion valve 30 is preferably expanded at low temperature close to the temperature and pressure of the working fluid recovered from the cold box unit (2), in particular the temperature of the mixed working fluid is a suitable temperature It is important to prevent the compression efficiency from being lowered below to act as a thermal stress on the first to third working fluid compressors 41, 42 and 43, or to increase the pressure of the mixed working fluid to be higher than an appropriate pressure.

The flow rate of the working fluid passing through the rear end of the second bypass pipe and the first bypass pipe is adjusted according to the opening degree of the second and third valves 32 and 33, which is evaporated to the natural gas liquefaction apparatus. It can be adjusted according to the fluctuation of the amount of natural gas (load fluctuation).

Run Mode 3

In the operation mode 3 of the flow rate control means 3, the operating load (natural gas supply amount / liquefied natural gas amount) of the natural gas liquefaction apparatus is 100% or less, and is supplied to the cold box unit 2 through a supply pipe. When the temperature of the working fluid is a high temperature condenser of the cold box unit 2 by bypassing a part of the working fluid supplied to the cold box unit 2 through the front end of the first bypass pipe and the third bypass pipe ( 20) is an operation mode to reduce the flow rate of the working fluid to be supplied to the pre-cooled working fluid flowing through the supply pipe at the same time.

To this end, the first valve 31 installed in the first bypass pipe is opened, the second valve 32 installed in the first bypass pipe and the third valve 33 installed in the second bypass pipe are closed, and The fourth valve 34 installed in the third bypass pipe is opened to form a bypass path of the working fluid. Here, the third bypass pipe that crosses the supply pipe connected to the inlet of the cold box unit 2 is provided with a precooler 35 for heat exchange with a high temperature working fluid passing through the supply pipe.

When the bypass path is formed in the above-described manner, a part of the working fluid compressed by the working fluid compression unit 4 is supplied through the first bypass pipe to be expanded at low temperature in the expansion valve 30, and the low temperature expanded working fluid. Is a third bypass pipe connected to the outlet of the expansion valve (30) is heat exchanged with the high temperature working fluid in the precooler (35), and then the low temperature operating fluid recovered through the outlet of the cold box unit (2) Mixed with and flows into the working fluid compression unit (4). At this time, the working fluid passing through the expansion valve 30 is preferably expanded at low temperature close to the temperature and pressure of the working fluid recovered from the cold box unit (2), in particular the temperature of the mixed working fluid is a suitable temperature It is important to prevent the compression efficiency from being lowered below to act as a thermal stress on the first to third working fluid compressors 41, 42 and 43, or to increase the pressure of the mixed working fluid to be higher than an appropriate pressure.

The flow rate of the working fluid through which the first bypass pipe passes through the front end and the third bypass pipe is controlled according to the opening degree of the first and fourth valves 31 and 34, which is evaporated to the natural gas liquefaction device. It can be adjusted according to the fluctuation of the amount of natural gas (load fluctuation).

Run Mode 4

In the operation mode 4 of the flow regulating means 3, the operating load (natural gas supply amount / liquefied natural gas amount) of the natural gas liquefaction apparatus is 100% or less, and at the end of the third working fluid compressor 43 When the working fluid temperature is less than a predetermined temperature (about 40 ℃), the temperature of the working fluid supplied to the cold box unit 2 through the supply pipe is a high temperature through the second bypass pipe and the third bypass pipe Bypassing a part of the working fluid supplied to the cold box unit 2 to reduce the flow rate of the working fluid supplied to the condenser 20 of the cold box unit 2 and at the same time the high temperature working fluid passing through the supply pipe It is an operation mode to precool.

To this end, the first and second valves 31 and 32 installed in the first bypass pipe are closed, and the third valve 33 installed in the second bypass pipe and the fourth valve 34 installed in the third bypass pipe 34 are provided. ) To form a bypass path for the working fluid. Here, the third bypass pipe that crosses the supply pipe connected to the inlet of the cold box unit 2 is provided with a precooler 35 for heat exchange with a high temperature working fluid passing through the supply pipe.

When the bypass path is formed in the above-described manner, a portion of the compressed working fluid is supplied through the second bypass pipe connected to the outlet of the third working fluid compressor 43 of the last end to be expanded at low temperature in the expansion valve 30. The low temperature expanded working fluid is led to a third bypass pipe connected to the outlet of the expansion valve 30 to exchange heat with the high temperature working fluid in the precooler 35, and then to the outlet of the cold box unit 2. It is mixed with the low temperature working fluid recovered through the working fluid is introduced into the working fluid compression unit (4). At this time, the working fluid passing through the expansion valve 30 is preferably expanded at low temperature close to the temperature and pressure of the working fluid recovered from the cold box unit (2), in particular the temperature of the mixed working fluid is a suitable temperature It is important to prevent the compression efficiency from being lowered below to act as a thermal stress on the first to third working fluid compressors 41, 42 and 43, or to increase the pressure of the mixed working fluid to be higher than an appropriate pressure.

The flow rate of the working fluid passing through the second bypass pipe and the third bypass pipe is adjusted according to the opening degree of the third and fourth valves 33 and 34, which is evaporated natural gas supplied to the natural gas liquefaction device. It can be adjusted according to the fluctuation of gas amount (load fluctuation).

According to the present invention, a working fluid supplied to the cold box unit 2 by bypassing a part of the working fluid by one of the operation modes 1 to 4 or a mode in which at least two or more operation modes are mixed. Even when the flow rate is adjusted, the pressure and the total flow rate flowing into the working fluid compression unit 4 are always constant, so that the operation control of the first to third working fluid compressors 41, 42, 43 is simple. There is no worry of surge.

In addition, when the flow rate of the working fluid supplied to the cold box unit 2 by bypassing a part of the working fluid by the operation mode 3 or 4, the high temperature and high pressure working fluid supplied to the cold box unit 2 is Since the heat exchange in the pre-cooler (35) installed in the third bypass pipe by the working fluid expanded at low temperature by the expansion valve (30) is pre-cooled, the efficiency of the condenser 20 of the cold box unit 2 is improved have.

In addition, the low temperature expanded working fluid by the expansion valve 30 of the flow control means 3 is mixed with the working fluid flowing from the cold box unit 2 and then introduced into the working fluid compression unit 4 Therefore, it is possible to control the temperature of the working fluid flowing into the working fluid compression unit 4, and as a result, when a high temperature working fluid is introduced, the cooling water pump or the cooling fan used as the cooling means is not used. There is an effect to save power.

Second Embodiment

3 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a second embodiment of the present invention.

In the natural gas liquefaction apparatus according to the second embodiment of the present invention, the load variation of the natural gas evaporated by adding the flow rate adjusting means 3 to the configuration described in the patent application No. 2005-78588 filed by the applicant of the present invention. In response to the device configured to perform the operation.

In the natural gas liquefaction apparatus according to the second embodiment of the present invention, only the gas liquid separator 15 is added to the configuration of the cold box unit 2a and the outlet of the cold box unit 2a with respect to the first embodiment. The differences are different, and the rest of the configuration and the connection relationship between the respective configurations are the same as in the first embodiment. In addition, the second embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2a), the operation method for the remaining configuration, in particular, the operation method for the flow rate control means (3) is the first Same as the embodiment.

Therefore, in the second embodiment of the present invention, a description of portions overlapping with the first embodiment will be omitted, and a different configuration from the first embodiment will be described.

The cold box unit 2a is connected to the outlet of the flow regulating means 3 so as to precool the working fluid flowing from the flow regulating means 3 to the low temperature working fluid which has undergone heat exchange. 22); A first heat exchanger (21) connected to the outlet of the second heat exchanger (22) for cooling the precooled working fluid to the low temperature operating fluid passing through the condenser (20); By bypassing a portion of the working fluid flowing into the first heat exchanger 21 and expanding at a low temperature, it is mixed with the low temperature operating fluid passed through the condenser 20 and re-introduced into the first heat exchanger 21. An expansion turbine 26 for further cooling the precooled working fluid passing through the first heat exchanger 21; An expansion valve 25 connected to the outlet of the first heat exchanger 21 to expand the working fluid to cryogenic temperature; And a cryogenic working fluid which is connected to an outlet of the expansion valve 25 and passes through the expansion valve 25 and natural gas introduced from the natural gas compression unit 1 to liquefy the natural gas. It comprises a condenser 20.

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2a so that the natural gas in the liquid state is returned to the storage tank 10 by the pump P or the natural gas compression unit 1 through the bypass pipe. Is reinserted into). In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

As described above, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid, which has been low-temperature expanded by the expansion turbine 26, is re-introduced into the first heat exchanger 21 to provide the expansion valve 25. By further cooling the working fluid supplied to the) it is possible to stably maintain the temperature of the working fluid supplied to the expansion valve (25).

The cold box unit 2a is formed as a single module, which connects the first and second heat exchangers 21 and 22, the expansion valve 25, the expansion turbine 26, and the condenser 20 in a limited space. By compacting, short piping can be formed between each component, thereby minimizing heat loss through the piping.

A generator G is connected to the rotary shaft of the expansion turbine 26 to use electrical energy generated by the expansion turbine 26 as driving energy of the working fluid compression unit 4 or the natural gas compression unit 1. It is also possible.

The operation method of the natural gas liquefaction apparatus according to the second embodiment of the present invention will be briefly described by dividing the evaporated natural gas circulation process and the refrigeration cycle for the working fluid (nitrogen).

First, when the circulating process of the evaporated natural gas, when the natural gas of the liquid state stored in the storage tank 10 is evaporated by an external temperature difference, and the internal pressure rises above the set pressure, the storage tank 10 The safety valve 13 formed at the outlet is opened and the evaporated natural gas is discharged. At this time, the evaporated natural gas is properly mixed with the liquefied natural gas to maintain 1.03bar, -120 ℃.

The evaporated natural gas introduced into the natural gas compression unit 1 is compressed to 2.5 bar and −73 ° C. in the two-stage natural gas compressors 11 and 12 to be superheated at high temperature and high pressure.

The compressed natural gas is heat-exchanged with a cryogenic expanded working fluid (nitrogen) by a nitrogen refrigeration cycle in the condenser 20 of the cold box unit 2a and liquefied into a supercooled liquid of 2.3 bar and -155 ° C.

The liquefied natural gas is returned to the storage tank 10 through a pump (P) installed in the return pipe after the gas and the liquid is separated from the gas-liquid separator 15 is stored, the natural gas During the initial operation of the liquefaction apparatus or when the natural gas discharged from the storage tank 10 is discharged to a high temperature, a portion of the liquefied natural gas is re-introduced to be mixed with the evaporated natural gas through the recirculation valve 14. . In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14bar, 35.4 ℃ to the three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through, the pressure is raised to 58 bar and 43 ° C., and the compressed working fluid (nitrogen) has a flow path determined according to the operation mode of the flow regulating means (3). Is supplied.

The nitrogen gas supplied to the cold box unit 2a is precooled to 57.3 bar and −83.5 ° C. by heat exchange with the low temperature part working fluid in the second heat exchanger 22, and the condenser 20 in the first heat exchanger 21. Cooled to 57.5 bar, -137.9 ℃ by heat exchange with the low temperature working fluid passed through the), the high-pressure working fluid is expanded to cryogenic, low pressure gas of 14.6 bar, -163 ℃ while passing through the expansion valve (25) More cool. Here, the low temperature part working fluid flowing into the first heat exchanger 21 bypasses a part of the high temperature part working fluid supplied to the first heat exchanger 21 to 14.5 bar and −140 ° C. in the expansion turbine 26. It is a working fluid mixed with the low temperature operating fluid passed through the condenser 20 after expansion at low temperature.

The cryogenic working fluid is heat-exchanged with the evaporated natural gas supplied from the natural gas compression unit 1 in the condenser 20 to liquefy the natural gas into a supercooled liquid of 2.3 bar and -155 ° C. The cryogenic working fluid is heated to 14.4 bar, -138.9 ° C.

The working fluid is heated to 14.2 bar, −106 ° C. by heat exchange with the hot part working fluid supplied from the working fluid compression part 4 in the first heat exchanger 21, and the second heat exchanger 22 is heated. After passing through 14bar, 35.4 ° C while passing through the flow control means (3) through the recovery pipe again to the working fluid compression unit (4) to complete the cryogenic refrigeration cycle.

(Third Embodiment)

4 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of a working fluid according to a third embodiment of the present invention.

In the natural gas liquefaction apparatus according to the third embodiment of the present invention, the load variation of the natural gas evaporated by adding the flow rate adjusting means 3 to the configuration described in the patent application No. 2005-109931 filed by the applicant of the present invention. In response to the device configured to perform the operation.

The natural gas liquefaction apparatus according to the third embodiment of the present invention has a different configuration of the cold box unit 2b with respect to the first and second embodiments, and the cold box unit 2b with respect to the first embodiment. Only that the gas-liquid separator 15 is added to the outlet of the gas is different, and the rest of the configuration and the connection relationship between the components are the same as in the first and second embodiments. In addition, the third embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2b), the operation method for the remaining configuration, in particular, the operation method for the flow rate control means (3) is the first Same as the embodiment.

Therefore, in the third embodiment of the present invention, a description of portions overlapping with those of the first embodiment will be omitted, and a configuration different from the first embodiment will be described.

The cold box unit 2b is connected to the outlet of the flow regulating means 3 to supply a second working heat exchanger for precooling the working fluid introduced from the flow regulating means 3 to the low temperature working fluid after the heat exchange process. 22); It is connected to the outlet of the second heat exchanger 22 to form three paths through which the precooled working fluid, the natural gas flowing from the natural gas compression unit 1 and the low temperature part working fluid passing through the condenser 20 pass. A first heat exchanger (21a) for cooling the pre-cooled working fluid and natural gas with the low temperature working fluid; By bypassing a part of the working fluid flowing into the first heat exchanger 21a and expanding it at a low temperature, it is mixed with the low temperature operating fluid passed through the condenser 20 and re-introduced into the first heat exchanger 21a. An expansion turbine 26 for further cooling the pre-cooled working fluid and natural gas passing through the first heat exchanger 21a; An expansion valve 25 connected to the outlet of the first heat exchanger 21a to expand the working fluid to cryogenic temperature; And a cryogenic working fluid connected to the outlet of the expansion valve 25 and passing through the expansion valve 25 and natural gas passing through the first heat exchanger 21a to liquefy the natural gas. It comprises a condenser 20.

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2b so that the natural gas in the liquid state is returned to the storage tank 10 by the pump P or the natural gas compression unit 1 through the bypass pipe. Is reinserted into). In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

The natural gas evaporated at the inlet of the condenser 20 even if there is a change in the amount or temperature of the natural gas evaporated by pre-cooling the natural gas compressed by the natural gas compression unit 1 in the first heat exchanger 21a as described above. The temperature of can be kept constant within the set range. In addition, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid, which is expanded at a low temperature by the expansion turbine 26, is re-introduced into the first heat exchanger 21a to the expansion valve 25. By further cooling the supplied working fluid, the temperature of the working fluid supplied to the expansion valve 25 can be stably maintained.

The cold box unit 2b is formed as a single module, and electrical energy may be obtained by connecting a generator G to a rotation shaft of the expansion turbine 26.

The operating method of the natural gas liquefaction apparatus according to the third embodiment of the present invention will be briefly described by dividing the natural gas circulating process and the refrigeration cycle for the working fluid (nitrogen).

First, when the circulating process of the evaporated natural gas, when the natural gas of the liquid state stored in the storage tank 10 is evaporated by an external temperature difference, and the internal pressure rises above the set pressure, the storage tank 10 The safety valve 13 formed at the outlet is opened and the evaporated natural gas is discharged. At this time, the evaporated natural gas is properly mixed with the liquefied natural gas to maintain 1.03bar, -120 ℃.

The evaporated natural gas introduced into the natural gas compression unit 1 is compressed to 3.6 bar and −41.98 ° C. in two stages of natural gas compressors 11 and 12 to be in a superheated state at high temperature and high pressure.

The compressed natural gas is cooled to 3.3 bar and −134 ° C. by heat exchange with a low temperature working fluid in the first heat exchanger 21 a having three paths formed therein, and then the condenser 20 of the cold box unit 2 b. Heat exchanged with the cryogenic expanded working fluid (nitrogen) by nitrogen refrigeration cycle and liquefied into 3.0bar, -154.7 ℃ supercooled liquid.

The liquefied natural gas is returned to the storage tank 10 through a pump (P) installed in the return pipe after the gas and the liquid is separated from the gas-liquid separator 15 is stored, the natural gas During the initial operation of the liquefaction apparatus or when the natural gas discharged from the storage tank 10 is discharged to a high temperature, a portion of the liquefied natural gas is re-introduced to be mixed with the evaporated natural gas through the recirculation valve 14. . In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.3bar, 36.08 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through the pressure is increased to 58bar, 40 ℃ pressure, the compressed working fluid (nitrogen) is a flow path is determined according to the operation mode of the flow rate control means (3) through the cold pipe unit 2b Is supplied.

The nitrogen gas supplied to the cold box unit 2b is precooled to 57.7 bar and −70 ° C. by heat exchange with the low temperature working fluid in the second heat exchanger 22, and in the first heat exchanger 21 a of three paths. It is cooled to 57.4 bar, -132 ° C by heat exchange with the low temperature operating fluid and the compressed natural gas passing through the condenser 20, and the high pressure working fluid passes through the expansion valve 25 to 15.2 bar, -162.6 ° C. It is expanded to cryogenic, low pressure gas and is cooled further. Here, the low temperature part working fluid flowing into the first heat exchanger 21a bypasses a part of the high temperature part working fluid supplied to the first heat exchanger 21a to 15.2 bar and −129.3 ° C. in the expansion turbine 26. It is a working fluid mixed with the low temperature operating fluid passed through the condenser 20 after expansion at low temperature.

The cryogenic working fluid is heat-exchanged with the evaporated natural gas supplied from the natural gas compression unit 1 in the condenser 20 to liquefy the natural gas into a supercooled liquid of 3.0 bar and -154.7 ° C. The cryogenic working fluid is raised to 14.9 bar, -145 ° C.

The working fluid is heated to 14.6 bar, −86.42 ° C. by heat exchange with the hot part working fluid supplied from the working fluid compression section 4 and the compressed natural gas in the first heat exchanger 21a, and the second heat exchange. Heated to 14.3 bar, 36.08 ℃ while passing through the machine 22 and is re-introduced to the working fluid compression unit (4) through the flow control means 3 through the recovery pipe to complete the cryogenic refrigeration cycle.

(Example 4)

5 is a system schematic diagram of a natural gas liquefaction apparatus capable of regulating load fluctuation by using a flow control means of a working fluid according to a fourth embodiment of the present invention.

In the natural gas liquefaction apparatus according to the fourth embodiment of the present invention, the load fluctuation of the evaporated natural gas is added to the configuration described in the patent application No. 2006-1271, filed by the applicant of the present invention. In response to the device configured to perform the operation.

In the natural gas liquefaction apparatus according to the fourth embodiment of the present invention, the configuration of the cold box unit 2c is different from that of the first to third embodiments, and the cold box unit 2c is different from the first embodiment. Only that the gas-liquid separator 15 is added to the outlet of the different, and the remaining configuration and the connection relationship of each configuration is the same as the first to third embodiments. In addition, the fourth embodiment of the present invention differs only in the operation method of the refrigeration cycle through the cold box unit (2c), the operation method for the remaining configuration, in particular, the operation method for the flow rate control means (3) described above Same as the embodiment.

Therefore, in the fourth embodiment of the present invention, a description of portions overlapping with those of the first embodiment will be omitted, and a configuration different from the first embodiment will be described.

The cold box unit (2c) is connected to the outlet of the flow rate control means 3, the second heat exchanger for pre-cooling the working fluid flowing from the flow rate control means (3) to the low-temperature operating fluid through a heat exchange process ( 22); It is connected to the outlet of the second heat exchanger 22 to form three paths through which the precooled working fluid, the natural gas flowing from the natural gas compression unit 1 and the low temperature part working fluid passing through the condenser 20 pass. A first heat exchanger (21a) for cooling the pre-cooled working fluid and natural gas with the low temperature working fluid; A third heat exchanger 23 connected to the outlet of the first heat exchanger 21a to cool the high temperature part working fluid flowing from the first heat exchanger 21a to the low temperature part working fluid passing through the condenser 20. ); Bypassing a part of the working fluid flowing into the first heat exchanger 21a and expanding it at a low temperature, then mixing it with the low temperature operating fluid passed through the third heat exchanger 23 and re-adding it to the first heat exchanger 21a. An expansion turbine (26) for further cooling the pre-cooled working fluid and natural gas passing through the first heat exchanger (21a); An expansion valve 25 connected to the outlet of the third heat exchanger 23 to expand the working fluid to cryogenic temperature; And a cryogenic working fluid connected to the outlet of the expansion valve 25 and passing through the expansion valve 25 and natural gas passing through the first heat exchanger 21a to liquefy the natural gas. It comprises a condenser 20.

A gas-liquid separator 15 is installed at the outlet of the cold box unit 2c so that the natural gas in the liquid state is returned to the storage tank 10 by the pump P or the natural gas compression unit 1 through the bypass pipe. Is reinserted into). In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

The natural gas evaporated at the inlet of the condenser 20 even if there is a change in the amount or temperature of the natural gas evaporated by pre-cooling the natural gas compressed by the natural gas compression unit 1 in the first heat exchanger 21a as described above. The temperature of can be kept constant within the set range. In addition, the working fluid is pre-cooled by the second heat exchanger 22, and the working fluid expanded at a low temperature by the expansion turbine 26 is re-injected into the first heat exchanger 21a to cool the high-temperature operating fluid. By further cooling the working fluid supplied from the third heat exchanger 23 to the expansion valve 25, the temperature of the working fluid supplied to the expansion valve 25 can be more stably maintained.

The cold box unit 2c is formed as a single module, and electrical energy may be obtained by connecting a generator G to a rotation shaft of the expansion turbine 26.

The operating method of the natural gas liquefaction apparatus according to the fourth embodiment of the present invention will be briefly described by dividing the natural gas circulating process and the refrigeration cycle for the working fluid (nitrogen).

First, when the circulating process of the evaporated natural gas, when the natural gas of the liquid state stored in the storage tank 10 is evaporated by an external temperature difference, and the internal pressure rises above the set pressure, the storage tank 10 The safety valve 13 formed at the outlet is opened and the evaporated natural gas is discharged. At this time, the evaporated natural gas is properly mixed with the liquefied natural gas to maintain 1.03bar, -120 ℃.

The evaporated natural gas introduced into the natural gas compression unit 1 is compressed to 3.2 bar and −50.83 ° C. in the two-stage natural gas compressors 11 and 12 to be superheated at high temperature and high pressure.

The compressed natural gas is cooled to 3.1 bar and −130 ° C. by heat exchange with a low temperature working fluid in the first heat exchanger 21 a having three paths formed therein, and then the condenser 20 of the cold box unit 2 c. Heat exchanged with the cryogenic expanded working fluid (nitrogen) by nitrogen refrigeration cycle and liquefied into 3.0bar, -154.7 ℃ supercooled liquid.

The liquefied natural gas is returned to the storage tank 10 through a pump (P) installed in the return pipe after the gas and the liquid is separated from the gas-liquid separator 15 is stored, the natural gas During the initial operation of the liquefaction apparatus or when the natural gas discharged from the storage tank 10 is discharged to a high temperature, a portion of the liquefied natural gas is re-introduced to be mixed with the evaporated natural gas through the recirculation valve 14. . In addition, the natural gas of the gas state separated from the gas-liquid separator 15 may be discharged as it is, or may be re-introduced into the natural gas compression unit 1 through a separate pipe not shown.

Next, the operation process of the refrigeration cycle for the working fluid (nitrogen), the nitrogen gas of 14.2bar, 35.46 ℃ three stage working fluid compressor (41, 42, 43) and the cooler (44, 45, 46) After passing through the pressure is increased to 58bar, 43 ℃ pressure, the compressed working fluid (nitrogen) is a flow path is determined according to the operation mode of the flow rate control means (3) through the cold pipe unit 2c Is supplied.

The nitrogen gas supplied to the cold box unit 2c is precooled to 57.9 bar and -77 ° C by heat exchange with the low temperature part working fluid in the second heat exchanger 22, and in the first heat exchanger 21a of three paths. It is cooled to 57.8 bar, -134 ° C by heat exchange with the low temperature working fluid passed through the third heat exchanger 23 and the compressed natural gas. The working fluid passing through the first heat exchanger 21a is further cooled to 57.7 bar and -137 ° C by heat exchange with the low temperature part working fluid passing through the condenser 20 in the third heat exchanger 23. The high pressure working fluid is expanded to cryogenic, low pressure gas of 14.6 bar, -163.3 ° C while passing through the expansion valve 25, and is further cooled. Here, the low temperature part working fluid flowing into the first heat exchanger 21a bypasses a part of the high temperature part working fluid supplied to the first heat exchanger 21a to 14.5 bar and −136.9 ° C. in the expansion turbine 26. It is a working fluid mixed with a low temperature operating fluid passed through the third heat exchanger 23 after the low temperature expansion.

The cryogenic working fluid is heat-exchanged with the evaporated natural gas supplied from the natural gas compression unit 1 in the condenser 20 to liquefy the natural gas into a supercooled liquid of 3.0 bar and -154.7 ° C. The cryogenic working fluid is heated to 14.5 bar, -150.7 ° C.

The working fluid is heated to 14.4 bar and −140 ° C. by heat exchange with the high temperature part working fluid passing through the first heat exchanger 21a in the third heat exchanger 23, and in the first heat exchanger 21a. Heated to 14.3 bar, −98.88 ° C. by heat exchange with the hot part working fluid supplied from the working fluid compression unit 4 and the compressed natural gas, to 14.2 bar and 35.46 ° C. while passing through the second heat exchanger 22. After being heated, it is re-introduced into the working fluid compression unit 4 through the flow rate adjusting means 3 through the recovery pipe to complete the cryogenic refrigeration cycle.

As described above, the natural gas liquefaction apparatus capable of regulating load fluctuation using the flow control means of the working fluid according to the present invention recovers or replenishes a part of the working fluid circulating the cryogenic refrigeration cycle according to the increase and decrease of the evaporated natural gas. In order to replace the conventional flow control means used to install a buffer tank in the bypass pipe formed at the inlet and outlet of the cold box unit in order to install an expansion valve in place of the buffer tank, to form a bypass pipe in various ways to pass through the expansion valve By controlling the flow rate and temperature of the high temperature operating fluid supplied to the cold box unit.

In addition, since the operating fluid of the high temperature and high pressure was recovered to the buffer tank by the operating fluid compression unit, it was inconvenient to discharge it forcibly and replenish it afterwards for the decompression and cooling of the working fluid stored in the buffer tank. The flow rate control means according to the present invention bypasses a part of the working fluid supplied to the cold box unit to the bypass pipe in which the expansion valve is installed and continuously circulates it to the working fluid compression unit so that the flow rate of the working fluid circulating the cryogenic refrigeration cycle is increased. It can be kept constant all the time.

In addition, the natural gas liquefaction apparatus according to the present invention can reduce the size of the entire system by efficiently using the installation space of the buffer tank occupying a large volume by removing the high-pressure buffer tank, and next, risk factors for explosion Is essentially eliminated to ensure safety.

In the natural gas liquefaction apparatus according to the present invention, the liquefaction operation load of the evaporated natural gas can be adjusted in a range of 70 to 100% by appropriately adjusting the operation mode of the flow control means.

Specifically, the flow rate of the working fluid supplied to the cold box unit by bypassing a part of the working fluid by one of the operation modes 1 to 4 of the flow rate adjusting means or a mode in which at least two or more operating modes are mixed Even in the case of adjusting the pressure and the total flow rate flowing into the working fluid compression unit is always constant, the operation control of the plurality of working fluid compressor is simple, there is no fear of surge.

In addition, when the flow rate of the working fluid supplied to the cold box unit by bypassing a part of the working fluid by the operation mode 3 or 4, the high temperature and high pressure working fluid supplied to the cold box unit is low temperature by the expansion valve. Since the heat exchange in the precooler installed in the third bypass pipe by the expanded working fluid is pre-cooled, the condenser efficiency of the cold box unit is improved.

In addition, the temperature control of the working fluid flowing into the working fluid compression unit because the working fluid expanded at a low temperature by the expansion valve of the flow control means is mixed with the working fluid flowing from the cold box unit and then flows into the working fluid compression unit As a result, when a high temperature working fluid is introduced, the cooling water pump or the cooling fan used as the cooling means is not used, thereby reducing the power of the cooling means.

Claims (11)

A natural gas compression unit configured to pressurize the natural gas in a gaseous state generated inside a storage tank in which the natural gas in a liquid state is stored; A working fluid compressor connected to a plurality of working fluid compressors and coolers such that pressurization and cooling processes are repeated to pressurize and cool the working fluid in a cryogenic refrigeration cycle for liquefying the natural gas; A cold box unit for liquefying the natural gas in the gas state by exchanging the working fluid in the working fluid compression unit at a cryogenic temperature and exchanging heat with the natural gas in a condenser; And forming a bypass pipe in the working fluid inlet / outlet pipe of the cold box unit, and recycling a part of the working fluid to the working fluid compression unit through the bypass pipe to adjust the flow rate of the working fluid supplied to the cold box unit. A natural gas liquefaction apparatus including a control means, wherein the natural gas liquefied by the cold box unit is returned to the storage tank, By-pass pipe of the flow control means is a natural gas liquefaction apparatus that can control the load fluctuation using the flow control means of the flow fluid, characterized in that the expansion valve for lowering the pressure or temperature of the working fluid flowing into the working fluid compression unit is installed . The natural gas liquefaction apparatus of claim 1, wherein the front and rear sides of the expansion valve installed in the bypass pipe are provided with valves for adjusting flow rates, respectively. 3. The flow control means of claim 2, wherein an inlet of the expansion valve and an outlet of the last working fluid compressor of the working fluid compression unit are connected to a bypass pipe, and a valve for adjusting the flow rate is installed therein. Natural gas liquefaction apparatus that can control the load fluctuation using. The method of claim 2, wherein the outlet of the expansion valve and the outlet of the cold box unit is connected to the bypass pipe, and through the heat exchange between the low-temperature expansion working fluid and the high temperature operating fluid flows into the cold box unit by the expansion valve A pre-cooler is installed in the bypass pipe so as to pre-cool the high temperature operating fluid, and a valve for adjusting the flow rate is installed in the bypass pipe. . According to any one of claims 1 to 4, The outlet of the liquefied natural gas of the cold box unit and the outlet of the storage tank is connected to the bypass pipe, a valve for adjusting the flow rate is installed, the bypass By using some of the liquefied natural gas supplied through the pipe and the natural gas supplied from the storage tank to be mixed to pre-cool the natural gas supplied to the natural gas compression unit by using the flow control means of the flow control means Natural gas liquefaction apparatus with adjustable fluctuations. According to any one of claims 1 to 4, wherein the outlet of the cold box unit is a gas-liquid separator is installed, the liquid natural gas is returned to the storage tank by a pump, the gas natural gas is natural gas A natural gas liquefaction apparatus capable of regulating load fluctuation by using a flow control means of a working fluid, characterized in that the recommissioned or discharged to the compression unit. According to claim 5, At the outlet of the cold box unit is a gas-liquid separator is installed, the liquid natural gas is returned to the storage tank by a pump or re-introduced into the natural gas compression unit through the bypass pipe, the natural gas in the state A natural gas liquefaction apparatus capable of regulating load fluctuation using a flow control means of the working fluid, characterized in that the gas is re-introduced or discharged to the natural gas compression unit. The method according to any one of claims 1 to 4, wherein the cold box unit, A first heat exchanger connected to the outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid passing through the condenser; An expansion turbine connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And A working fluid connected to an outlet of the expansion turbine, the working fluid of which the cryogenic temperature passes through the expansion turbine and a natural gas flowing from the natural gas compression unit are heat-exchanged with each other to condense the natural gas. Natural gas liquefaction apparatus that can control the load fluctuation using the flow control means. The method according to any one of claims 1 to 4, The cold box unit, A second heat exchanger connected to the outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; A first heat exchanger connected to the outlet of the second heat exchanger for cooling the precooled working fluid to the low temperature operating fluid passing through the condenser; By bypassing a part of the working fluid flowing into the first heat exchanger and expanding it at a low temperature, it is mixed with the low temperature working fluid passed through the condenser and re-introduced into the first heat exchanger to further pass the pre-cooled working fluid passing through the first heat exchanger. Expansion turbine for cooling; An expansion valve connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And A working fluid connected to an outlet of the expansion valve and including a condenser for liquefying the natural gas by mutually exchanging the cryogenic working fluid passing through the expansion valve and the natural gas introduced from the natural gas compression unit; Natural gas liquefaction apparatus that can control the load fluctuation using the flow control means. The method according to any one of claims 1 to 4, The cold box unit, A second heat exchanger connected to the outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; It is connected to the outlet of the second heat exchanger to form three paths through which the pre-cooled working fluid, the natural gas flowing from the natural gas compression unit and the low-temperature section working fluid passing through the condenser, and the pre-cooled working fluid and natural A first heat exchanger for cooling gas to the cold working fluid; By bypassing a portion of the working fluid flowing into the first heat exchanger and expanding it at a low temperature, it is mixed with the low temperature working fluid passed through the condenser and re-introduced into the first heat exchanger to pass through the first heat exchanger and the pre-cooled working fluid and natural Expansion turbine for further cooling the gas; An expansion valve connected to the outlet of the first heat exchanger to cryogenically expand the working fluid; And And a condenser connected to the outlet of the expansion valve, the cryogenic working fluid passing through the expansion valve and the natural gas passing through the first heat exchanger mutually liquefying the natural gas. Natural gas liquefaction apparatus that can control the load fluctuation using the flow control means. The method according to any one of claims 1 to 4, The cold box unit, A second heat exchanger connected to the outlet of the flow regulating means for precooling the working fluid introduced from the flow regulating means to the low temperature part working fluid after the heat exchange process; It is connected to the outlet of the second heat exchanger to form three paths through which the pre-cooled working fluid, the natural gas flowing from the natural gas compression unit and the low-temperature section working fluid passing through the condenser, and the pre-cooled working fluid and natural A first heat exchanger for cooling gas to the cold working fluid; A third heat exchanger connected to the outlet of the first heat exchanger for cooling the high temperature part working fluid introduced from the first heat exchanger to the low temperature part working fluid passing through the condenser; By bypassing a portion of the working fluid flowing into the first heat exchanger and expanding at low temperature, mixed with the low-temperature operating fluid passed through the third heat exchanger and re-introduced into the first heat exchanger to pass the pre-cooled working fluid passing through the first heat exchanger And an expansion turbine for further cooling natural gas; An expansion valve connected to the outlet of the third heat exchanger to cryogenically expand the working fluid; And And a condenser connected to the outlet of the expansion valve, the cryogenic working fluid passing through the expansion valve and the natural gas passing through the first heat exchanger mutually liquefying the natural gas. Natural gas liquefaction apparatus that can control the load fluctuation using the flow control means.

Images