Ship's vapor reliquefaction system

Abstract

The present invention discloses an evaporation gas reliquefaction system for a ship. The evaporation gas reliquefaction system for a ship includes a first compressor that compresses evaporation gas generated from liquefied gas in a cargo tank installed on the ship and a second compressor that compresses the evaporation gas compressed by the first compressor, a compression unit that compresses the evaporation gas in multiple stages, an intercooler that cools the evaporation gas compressed by the first compressor and supplied to the second compressor, a condenser that cools the evaporation gas compressed in the compression unit, a reliquefaction gas recovery line that recovers the cold energy of the liquefied gas from the liquefied gas cooled and condensed in the condenser using the intercooler and then supplies the liquefied gas to the cargo tank, and a first temperature control line that branches the liquefied gas from the reliquefaction gas recovery line and injects it into the upper part of the intercooler.

Description

[Technical Field]

[0001] The present invention relates to an evaporation gas reliquefaction system for a ship, and more particularly to an evaporation gas reliquefaction system for a ship that compresses and reliquefies evaporation gas generated from liquefied gas stored in a cargo tank, thereby recovering the evaporated gas. [Background technology]

[0002] Consumption of liquefied gases such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) is rapidly increasing worldwide. Liquefied gases are transported in a gaseous state via onshore or offshore gas pipelines, or stored in a liquefied state on liquefied gas carriers and transported to distant destinations. Liquefied gases such as LNG and LPG are obtained by cooling natural gas or petroleum gas to extremely low temperatures (approximately -163°C in the case of LNG). Furthermore, liquefied gases are highly suitable for long-distance transportation via sea routes because their volume is significantly reduced compared to their gaseous state.

[0003] Conventional LPG carriers and the like employ fuel supply systems that use relatively inexpensive heavy oil, such as bunker C oil, as fuel for the ship's propulsion engine. Due to stricter international exhaust gas emission regulations regarding the use of heavy fuel oil, these fuel supply systems are now required to have a separate low-sulfur heavy oil (LSHFO) fuel tank. Given these circumstances, there is a demand for environmentally friendly fuel supply systems that comply with international environmental regulations.

[0004] In recent years, an increasing number of LPG and LNG carriers have adopted fuel supply systems that use LPG, LNG, or the evaporated gases generated from them as fuel for their propulsion engines. In addition, with the strengthening of international exhaust gas emission regulations, an increasing number of ships other than LPG and LNG carriers also use LPG, LNG, etc. as fuel for their propulsion engines.

[0005] In particular, LPG is easier to store than LNG, which must be liquefied at cryogenic temperatures. Its specific energy and energy density are comparable to those of conventional HFO. Furthermore, it has a lower SO x , NO x It has excellent properties such as being able to reduce emissions of CO2, PM, etc. Summary of the Invention [Problem to be solved by the invention]

[0006] The liquefaction temperature of petroleum gas is a low temperature of approximately -42°C under standard atmospheric pressure, and it can be stored in liquid form up to a temperature of approximately 45°C under a pressure of 18 bar, and up to a temperature of approximately 20°C under a pressure of 7 bar. Furthermore, since LPG evaporates when its temperature rises above -42°C under standard atmospheric pressure, LPG storage tanks installed on ships are insulated. However, as external heat is continuously transferred to the LPG inside the storage tank, the LPG naturally evaporates during the LPG transportation process, generating boil-off gas inside the storage tank.

[0007] If evaporated gas accumulates in a storage tank, the pressure inside the tank may rise excessively, threatening the safety of the ship and its crew. For this reason, storage tanks are equipped with pressure-resistant structures, and evaporated gas re-liquefaction equipment is used to process evaporated gas generated inside the storage tank.

[0008] In view of the above, the present invention provides an evaporated gas reliquefaction system for ships that can adjust the pressure inside a storage tank by reliquefying evaporated gas generated from liquefied gas such as LPG and recovering it in the storage tank, and that can reduce the amount of equipment required, thereby reducing equipment installation costs and improving the price competitiveness of the ship. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides an evaporated gas reliquefaction system for a ship, which is provided with a first compressor that compresses evaporated gas generated from liquefied gas stored in a cargo tank installed on the ship, and a second compressor that compresses the evaporated gas compressed by the first compressor, and is equipped with a compression section that compresses the evaporated gas in multiple stages, an intercooler that cools the evaporated gas compressed by the first compressor and supplied to the second compressor, a condenser that cools the evaporated gas compressed in the compression section, a reliquefaction gas recovery line that recovers the cold energy of the liquefied gas from the liquefied gas cooled and condensed in the condenser using the intercooler, and then supplies the liquefied gas to the cargo tank, and a first temperature control line that branches the liquefied gas from the reliquefaction gas recovery line and sprays it into the upper part of the intercooler.

[0010] Preferably, the system further includes a first temperature sensor that detects the temperature of the evaporated gas cooled by the intercooler and supplied to the second compressor, and a first temperature control valve that adjusts the flow rate of the liquefied gas that is branched from the reliquefied gas recovery line to the first temperature control line, and the temperature of the evaporated gas supplied to the second compressor is adjusted by controlling the first temperature control valve in accordance with the temperature of the evaporated gas detected by the first temperature sensor.

[0011] Preferably, the system further includes a liquid level adjustment line branching off from the re-liquefied gas recovery line to supply liquefied gas into the intercooler, a liquid level sensor to detect the liquid level of the liquefied gas in the intercooler, and a liquid level adjustment valve to open and close the liquid level adjustment line, and by controlling the liquid level adjustment valve in accordance with the liquid level of the liquefied gas detected by the liquid level sensor, the liquid level of the liquefied gas in the intercooler is maintained within a predetermined range, and the evaporated gas compressed by the first compressor is supplied through an injection nozzle into the liquefied gas filled in the intercooler and cooled.

[0012] Preferably, the system further includes a knock-out drum that receives the evaporated gas discharged from the cargo tank, separates the gas components, and supplies them to the first compressor of the compression section, and a second temperature control line that branches off from the reliquefied gas recovery line downstream of the intercooler of the reliquefied gas recovery line and is connected to the knock-out drum, and the evaporated gas that is supplied to the compression section is cooled by supplying the liquefied gas branched off from the reliquefied gas recovery line to a lower part inside the knock-out drum via the second temperature control line.

[0013] Preferably, the system further includes a second temperature sensor that detects the temperature of the evaporated gas compressed by the first compressor and supplied to the intercooler, and a second temperature control valve that adjusts the flow rate of the liquefied gas branched from the reliquefied gas recovery line to the second temperature control line, and the flow rate of the liquefied gas supplied to the lower part of the knockout drum is adjusted by controlling the second temperature control valve in accordance with the temperature of the evaporated gas detected by the second temperature sensor.

[0014] Preferably, the system further includes a reliquefaction gas receiver located upstream of the intercooler in the reliquefaction gas recovery line, for storing the reliquefaction gas cooled by the condenser, and the gas components separated in the reliquefaction gas receiver are discharged to the vent line.

[0015] Preferably, the liquefied gas is LPG and the compression section is a three-stage centrifugal compressor or a three-stage reciprocating compressor. [Effects of the Invention]

[0016] According to the present invention, evaporated gas generated from liquefied gas stored in a cargo tank is compressed, cooled, and re-liquefied before being collected in the cargo tank. Furthermore, the cooling effect of the intercooler is maximized, taking into consideration the evaporated gas containing multiple components with widely varying physical properties. Furthermore, the power consumption of the compression section is reduced, and the efficiency of re-liquefying the evaporated gas is improved.

[0017] Furthermore, the present invention reduces the number of required facilities, thereby reducing the cost of installing the facilities and improving the price competitiveness of the ship. Furthermore, by re-liquefying the evaporated gas and recovering it in the cargo tank, the pressure inside the cargo tank can be maintained within a safe range, and the transportation efficiency of LPG is improved. [Brief explanation of the drawings]

[0018] [Figure 1] Schematic diagram showing a conventional example of a system for re-liquefying evaporated gas generated from LPG. [Figure 2] 1 is a schematic diagram showing an evaporated gas reliquefaction system for a ship according to a first embodiment of the present invention. [Figure 3] FIG. 4 is a schematic diagram showing an evaporated gas reliquefaction system for a ship according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] For a full understanding of the operating advantages and objects attained by the embodiments of the present invention, reference should be made to the accompanying drawings, which illustrate preferred embodiments of the invention and the contents thereof.

[0020] The structure and operation of the present invention will be described in detail below with reference to the accompanying drawings. Note that when referring to components in each drawing, the same components are denoted by the same reference numerals whenever possible, even if they appear in different drawings.

[0021] The vessels of the embodiments of the present invention described below include all kinds of vessels, including self-propelled vessels such as LPG carriers, very large gas carriers (VLGCs), LNG carriers, liquid hydrogen carriers, and LNG regasification vessels (LNG RVs), as well as floating offshore structures that do not have self-propelling capabilities, such as LNG floating production storage offloading vessels (FPSOs) and LNG floating storage regasification units (FSRUs).

[0022] Furthermore, embodiments of the present invention can be applied to any type of liquefied gas that can be liquefied at low temperatures for transportation and generates evaporative gas during storage. Examples of such liquefied gases include liquefied petrochemical gases such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, and liquefied propylene gas, as well as ammonia. Note that in the embodiments described below, LPG, one of the representative liquefied gases, will be used as an example.

[0023] Figure 1 shows a conventional example of a system for re-liquefying evaporated gas generated from LPG.

[0024] As shown in Figure 1, in a conventional system, evaporated gas generated in a cargo tank is supplied to a compression section 20 via a knockout drum 10, compressed, cooled and re-liquefied in a condenser 50, and then returned to the cargo tank via a re-liquefied gas container 60 and an intercooler 30.

[0025] To compress the evaporated gas to the pressure required for re-liquefaction, the compression section 20 uses a multi-stage compressor, for example a three-stage compressor, which is usually operated at a constant speed. To improve the operating efficiency of the compression section 20, the evaporated gas compressed by the first compressor of the compression section 20 is cooled by an intercooler 30 before being supplied to the second compressor. The intercooler 30 utilizes the cold energy of the re-liquefied LPG.

[0026] However, since the evaporated gas generated from LPG in the cargo tank contains multiple components such as ethane, propylene, ammonia, etc. in addition to propane and butane (I-butane / N-butane), the physical properties of the evaporated gas vary widely.

[0027] In order to effectively cool the evaporative gas (containing multiple components) whose physical properties fluctuate widely, improve compressor efficiency, and improve re-liquefaction efficiency, this system is provided with a trim cooler 40 that additionally cools the evaporative gas before it is supplied to the second compressor after being cooled by the intercooler 30. Another intercooler may also be additionally installed between the second compressor and the third compressor.

[0028] However, while the compressor is operated at a constant speed, the amount of evaporative gas (containing multiple components) supplied to the compressor fluctuates greatly, making it difficult to effectively control the temperature of the evaporative gas supplied to the second compressor via an intercooler 30, trim cooler 40, etc. In particular, if evaporative gas is supplied to the compressor without being sufficiently cooled, the compressor's power consumption increases and the final reliquefaction efficiency decreases. For this reason, complete reliquefaction of evaporative gas is practically difficult, and evaporative gas that is not reliquefied is processed via a separate vent gas system. The reliquefaction system of the embodiment of the present invention described below solves this problem and effectively cools evaporative gas (containing multiple components) with widely varying physical properties, thereby reducing the compressor's power consumption and improving reliquefaction efficiency. It also reduces equipment installation costs.

[0029] Fig. 2 schematically shows an evaporated gas reliquefaction system for a ship according to a first embodiment of the present invention, and Fig. 3 schematically shows an evaporated gas reliquefaction system for a ship according to a second embodiment of the present invention.

[0030] 2, the evaporated gas reliquefaction system of this embodiment is provided with a compression section 100 which is provided with a first compressor 100A which receives and compresses evaporated gas generated from liquefied gas stored in a cargo tank provided on a ship and a second compressor 100B which further compresses the evaporated gas compressed by the first compressor 100A, thereby compressing the evaporated gas in multiple stages; an intercooler 200 which receives and cools the evaporated gas compressed by the first compressor 100A and then supplies it to the second compressor 100B; a condenser 300 which cools the evaporated gas compressed by the compression section 100; a reliquefied gas recovery line RL which passes the liquefied gas cooled and condensed by the condenser 300 through the intercooler 200 to recover the cold energy of the liquefied gas and then supplies it to the cargo tank; and a first temperature control line TL1 which branches the liquefied gas from the reliquefied gas recovery line RL and injects it into the upper part of the intercooler 200.

[0031] A knock-out drum 500 is provided upstream of the compression section 100 on the gas reliquefaction line GL. Evaporated gas discharged from a cargo tank is supplied to the knock-out drum 500, and its gas components are supplied to the compression section 100. At this time, the evaporated gas generated in the cargo tank contains various components such as ethane, propylene, ammonia, etc. in addition to propane and butane. The evaporated gas containing such multiple components generated in the cargo tank is supplied to the knock-out drum 500 via the gas reliquefaction line GL, and the gas components separated in the knock-out drum 500 are supplied to the first compressor 100A of the compression section 100, where they are reliquefied through a reliquefaction process and then recovered in the cargo tank.

[0032] The compression unit 100 is a three-stage multi-stage compressor including a first compressor 100A that receives and compresses the evaporative gas, a second compressor 100B that additionally compresses the evaporative gas compressed by the first compressor 100A, and a third compressor 100C that additionally compresses the evaporative gas compressed by the second compressor 100B and then supplies the compressed gas to the condenser 300. The compression unit 100 may be configured as a three-stage centrifugal compressor including the first to third compressors 100A to 100C. Alternatively, the compression unit 100 may be configured as a three-stage reciprocating compressor including reciprocating pistons, as in a second embodiment shown in FIG. 3. The number of stages in the compression unit may be increased as necessary.

[0033] The evaporated gas compressed in the compression section 100 is supplied to the condenser 300 and cooled.

[0034] In the condenser 300, the evaporated gas compressed in the compression section 100 is cooled by heat exchange to re-liquefy the evaporated gas. Note that, as a heat source for cooling the evaporated gas, for example, seawater, which is easily available on ships, can be used.

[0035] The reliquefied gas cooled in the condenser 300 is received in the reliquefied gas receiver 400 via the reliquefied gas recovery line RL. The liquid in the reliquefied gas receiver 400 is recovered in the cargo tank via the reliquefied gas recovery line RL. In addition, the vent gas separated in the reliquefied gas receiver 400 is discharged via the vent line.

[0036] The reliquefied gas recovery line RL is connected to the cargo tank via an intercooler 200. In the intercooler 200, heat is exchanged between the evaporated gas compressed by the first compressor 100A and the reliquefied gas supplied to the cargo tank. As shown in FIG. 2, the evaporated gas compressed by the first compressor 100A of the compression section 100 is supplied to the intercooler 200 and intercooled by heat exchange with the reliquefied gas supplied to the cargo tank from the reliquefied gas receiver 400. The evaporated gas is then supplied to the second compressor 100B and compressed, and is further compressed by the third compressor 100C. The evaporated gas is then supplied to the condenser 300, where it is cooled and reliquefied.

[0037] Also provided are a liquid level adjustment line LL that branches off from the reliquefied gas recovery line RL and supplies liquefied gas into the intercooler 200, a liquid level sensor LIT that detects the level of the liquefied gas in the intercooler 200, and a liquid level adjustment valve LV that opens and closes the liquid level adjustment line LL. The liquid level of the liquefied gas in the intercooler 200 is maintained within a predetermined range by the liquid level controller LIC controlling the opening of the liquid level adjustment valve LV in accordance with the liquid level of the liquefied gas detected by the liquid level sensor LIT.

[0038] The evaporated gas compressed by the first compressor 100A is supplied via an injection nozzle into the liquefied gas filled in the intercooler 200. On the other hand, the liquefied gas flowing through the reliquefied gas recovery line RL via the reliquefied gas receiver 400 passes through a heat transfer tube located at the bottom of the intercooler 200 (i.e., provided in the liquefied gas filled in the intercooler 200), thereby supplying cold to the intercooler 200. As a result, the evaporated gas compressed by the first compressor 100A is cooled by the intercooler 200.

[0039] Furthermore, this embodiment is configured to allow fine adjustment of the temperature of the evaporated gas supplied from the intercooler 200 to the second compressor 100B, taking into consideration the wide range of fluctuations in the physical properties of the evaporated gas (including multiple components). This maximizes the cooling effect of the intercooler 200, reduces the power consumption of the compression section 100, and improves the efficiency of re-liquefying the evaporated gas.

[0040] For this purpose, the reliquefaction system of this embodiment is equipped with a first temperature control line TL1 that branches liquefied gas from the reliquefied gas recovery line RL and injects it into the upper part of the intercooler 200, a first temperature sensor TIT1 that detects the temperature of the evaporated gas that is cooled in the intercooler 200 and then supplied to the second compressor 100B, and a first temperature control valve TV1 that adjusts the flow rate of the liquefied gas that branches from the reliquefied gas recovery line RL to the first temperature control line TL1.

[0041] The first temperature control unit TI1 controls the opening of the first temperature control valve TV1 in accordance with the evaporative gas temperature downstream of the intercooler 200 detected by the first temperature sensor TIT1, so that a portion of the liquefied gas flowing through the reliquefied gas recovery line RL is branched into the first temperature control line TL1 and injected into the upper part of the intercooler 200. This allows the evaporative gas cooled in the lower part of the intercooler 200 to be additionally cooled, thereby adjusting the temperature of the evaporative gas supplied to the second compressor 100B. In addition, an injection nozzle for additional cooling for injecting the liquefied gas is provided at the end of the first temperature control line TL1 located inside the intercooler 200.

[0042] As described above, the intercooler 200 can improve the cooling efficiency of the evaporative gas that is compressed by the first compressor 100A of the compression section 100 and then supplied to the second compressor 100B, and can also finely adjust the temperature of the evaporative gas upstream of the second compressor 100B. This eliminates the need to install another intermediate cooling device between the second compressor 100B and the third compressor 100C, reducing equipment installation costs. Furthermore, the power consumption of the compression section 100 is reduced, and the efficiency of re-liquefying the evaporative gas is improved.

[0043] Furthermore, according to the reliquefaction system of this embodiment, the evaporated gas is reliquefied and recovered in the cargo tank, so that the pressure inside the cargo tank can be maintained within a safe range and the transport efficiency of LPG is improved.

[0044] The second embodiment of the evaporated gas reliquefaction system shown in Figure 3 is configured to further reduce the temperature of the evaporated gas supplied from the knockout drum 500 to the first compressor 100A of the compression section 100, thereby further reducing the power consumption of the compression section 100 and improving reliquefaction efficiency.

[0045] For this reason, as shown in Figure 3, the reliquefaction system of this embodiment further includes a second temperature control line TL2 that branches off from the reliquefied gas recovery line RL and is connected to the knockout drum 500 downstream of the intercooler 200 in the reliquefied gas recovery line RL, and the evaporated gas supplied to the compression section 100 is cooled by injecting a portion of the liquefied gas flowing through the reliquefied gas recovery line RL into the knockout drum 500.

[0046] The reliquefaction system of this embodiment further includes a second temperature sensor TIT2 that detects the temperature of the evaporated gas compressed by the first compressor 100A and then supplied to the intercooler 200, and a second temperature control valve TV2 that adjusts the flow rate of the liquefied gas branched to the second temperature control line TL2. The liquefied gas recovered in the cargo tank via the reliquefied gas recovery line RL may be subcooled. By controlling the aperture of the second temperature control valve TV2 in accordance with the temperature of the evaporated gas downstream of the first compressor 100A detected by the second temperature sensor TIT2, a portion of the subcooled (low-temperature) liquefied gas downstream of the intercooler 200 in the reliquefied gas recovery line RL is branched to the second temperature control line TL2 and supplied to the lower part of the knockout drum 500. By cooling the evaporated gas in the knockout drum 500, the temperature of the evaporated gas supplied to the first compressor 100A of the compression section 100 can be adjusted.

[0047] Note that a description of the configuration overlapping with the first embodiment will be omitted.

[0048] As described above, a portion of the (low-temperature) liquefied gas is branched off into the second temperature adjustment line TL2 downstream of the intercooler 200 in the reliquefied gas recovery line RL and supplied to the knock-out drum 500, thereby cooling the evaporated gas supplied to the compression section 100. In addition, by injecting a portion of the (low-temperature) liquefied gas into the upper part of the intercooler 200 via the first temperature adjustment line TL1, it is possible to fine-tune the temperature of the evaporated gas before it is supplied to the second compressor 100B. This further reduces the power consumption of the compression section 100 and improves the final reliquefaction efficiency.

[0049] The present invention is not limited to the above-described embodiments, and it will be obvious to those skilled in the art to which the present invention pertains that various changes or modifications can be made without departing from the technical gist of the present invention.

Claims

1. a compression unit that compresses the evaporated gas in multiple stages, the compression unit including a first compressor that compresses evaporated gas generated from liquefied gas stored in a cargo tank provided on the ship and a second compressor that compresses the evaporated gas compressed by the first compressor; and an intercooler that cools the evaporated gas compressed by the first compressor and supplied to the second compressor; and a condenser for cooling the evaporated gas compressed in the compression section; and A re-liquefied gas recovery line that recovers the cold energy of the liquefied gas cooled and condensed in the condenser using an intercooler and then supplies the liquefied gas to the cargo tank; and a first temperature adjustment line that branches off the liquefied gas from the reliquefied gas recovery line and injects it into the upper part of the intercooler; Ship's vapor reliquefaction system.

2. a first temperature sensor that detects the temperature of the evaporated gas cooled by the intercooler and supplied to the second compressor; and a first temperature control valve that adjusts the flow rate of the liquefied gas branched from the reliquefied gas recovery line to the first temperature control line; The temperature of the evaporated gas supplied to the second compressor is adjusted by controlling the first temperature control valve in accordance with the temperature of the evaporated gas detected by the first temperature sensor.

2. The ship vapor reliquefaction system according to claim 1.

3. a liquid level adjustment line branching from the reliquefied gas recovery line to supply liquefied gas into the intercooler; and a liquid level sensor that detects the liquid level of the liquefied gas in the intercooler; and a liquid level control valve for opening and closing the liquid level control line; By controlling the liquid level adjustment valve according to the liquid level of the liquefied gas detected by the liquid level sensor, the liquid level of the liquefied gas in the intercooler is maintained within a specified range. The evaporated gas compressed by the first compressor is supplied to the liquefied gas filled in the intercooler through an injection nozzle and cooled.

3. The ship vapor reliquefaction system according to claim 2.

4. a knockout drum that receives the evaporated gas discharged from the cargo tank, separates the gas components, and supplies the gas components to the first compressor of the compression section; and a second temperature adjustment line branching off from the reliquefied gas recovery line downstream of the intercooler of the reliquefied gas recovery line and connected to a knockout drum; The liquefied gas branched off from the reliquefied gas recovery line is supplied to a lower part of the knock-out drum via a second temperature control line, thereby cooling the evaporated gas supplied to the compression section.

3. The ship vapor reliquefaction system according to claim 2.

5. a second temperature sensor that detects the temperature of the evaporated gas compressed by the first compressor and supplied to the intercooler; and a second temperature control valve that adjusts the flow rate of the liquefied gas branched from the reliquefied gas recovery line to the second temperature control line; a second temperature control valve being controlled in accordance with the temperature of the evaporated gas detected by the second temperature sensor, thereby adjusting the flow rate of the liquefied gas supplied to the lower portion of the knock-out drum; 5. The ship vapor reliquefaction system according to claim 4.

6. a re-liquefied gas receiver provided on the re-liquefied gas recovery line upstream of the intercooler and configured to receive the re-liquefied gas cooled by the condenser; The gas components separated in the reliquefaction gas receiver are discharged to a vent line. The ship vapor reliquefaction system according to any one of claims 1 to 5.

7. The liquefied gas is LPG, The compression unit is a three-stage centrifugal compressor or a three-stage reciprocating compressor.

7. The ship vapor reliquefaction system according to claim 6.

Images