Ship 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 gas reliquefaction line for reliquefying the evaporation gas generated from the liquefied gas and discharged from the cargo tank, a compression section provided in the gas reliquefaction line for compressing the evaporation gas, and a condenser provided in the gas reliquefaction line for cooling and reliquefying the evaporation gas compressed in the compression section, the compression section includes a first compressor for compressing the evaporation gas, and a second compressor for additionally compressing the evaporation gas compressed in the first compressor and supplying it to the condenser, and the first and second compressors are centrifugal compressors.

Description

[Technical Field]

[0001] The present invention relates to an evaporation gas reliquefaction system for ships, and more particularly to an evaporation gas reliquefaction system for ships that compresses and reliquefies evaporation gas generated from liquefied gas using a centrifugal compressor. [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 liquid 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 heavy oil, such as relatively inexpensive bunker C oil, as fuel for the ship's propulsion engine. Due to stricter international exhaust gas emission regulations regarding the use of heavy oil fuel, fuel supply systems that use such heavy oil as fuel are required to install a separate fuel tank for low-sulfur heavy oil (LSHFO), which has a low sulfur content. Given these circumstances, there is a demand for environmentally friendly fuel supply systems that comply with international environmental regulatory standards.

[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 extremely low temperatures, and its specific energy and energy density are comparable to those of HFO. Furthermore, LPG has superior properties in that it can reduce emissions of SOx, NOx, CO2, PM, etc. compared to HFO. 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 the temperature rises above -42°C under standard pressure, the storage tanks on ships in which LPG is stored are insulated. However, because heat from outside the storage tank is continuously transferred to the LPG inside the storage tank during transportation, the LPG inside the storage tank naturally evaporates, generating boil-off gas inside the storage tank.

[0007] If evaporation continues to occur in a storage tank, the pressure inside the storage 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 evaporation re-liquefaction equipment is used to process the evaporation generated inside the storage tank.

[0008] In view of the above, the present invention proposes a reliquefaction system that reliquefies evaporated gas generated from liquefied gases such as LPG and recovers it in a storage tank, while improving the price competitiveness of the reliquefaction system, reducing the installation area, and enabling stable operation of the reliquefaction system. [Means for solving the problem]

[0009] In order to solve the above problem, an embodiment of the present invention provides an evaporated gas reliquefaction system for a ship, comprising: a cargo tank installed on a ship in which liquefied gas is stored; a gas reliquefaction line that reliquefies evaporated gas generated from the liquefied gas and discharged from the cargo tank; a compression unit installed in the gas reliquefaction line that compresses the evaporated gas; and a condenser installed in the gas reliquefaction line that cools and reliquefies the evaporated gas compressed by the compression unit, wherein the compression unit comprises a first compressor that compresses the evaporated gas and a second compressor that further compresses the evaporated gas compressed by the first compressor and supplies it to the condenser, and wherein the first compressor and the second compressor are centrifugal compressors.

[0010] Preferably, the system further comprises a re-liquefaction gas container for storing the liquefied gas re-liquefied by the condenser, a pressure transmitter for detecting the pressure downstream of the condenser, and a first valve and a second valve arranged in parallel in a vent line for discharging vent gas from the re-liquefaction gas container, and the first valve is controlled based on the pressure detected by the pressure transmitter to maintain the pressure downstream of the second compressor in the gas re-liquefaction line at a predetermined pressure, and the second valve can prevent an excessive rise in pressure in the re-liquefaction gas container in the event of an abnormality in the re-liquefaction system.

[0011] Preferably, the system further includes a reliquefied gas recovery line connecting the reliquefied gas container and the cargo tank, and an economizer provided in the reliquefied gas recovery line, and the evaporated gas compressed by the first compressor is cooled by the economizer and then compressed by the second compressor.

[0012] Preferably, the first compressor is a centrifugal compressor having a first-stage compression section and a second-stage compression section connected to a motor shaft, and the evaporated gas compressed in the first-stage compression section is supplied to the intercooler and cooled by the liquefied gas supplied from the reliquefaction gas container to the cargo tank, compressed in the second-stage compression section, and further compressed in the second compressor.

[0013] Preferably, a knock-out drum is provided on the gas reliquefaction line upstream of the compression section, to which evaporated gas discharged from the cargo tank is supplied and which supplies gas components to the compression section. [Effects of the Invention]

[0014] The present invention provides a reliquefaction system that compresses and cools evaporated gas generated from liquefied gas stored in a cargo tank to reliquefy it, and then returns the reliquefied gas to the cargo tank. The system uses a centrifugal compressor in the compression section that compresses the evaporated gas. The use of a compact centrifugal compressor in the reliquefaction system of the present invention reduces the installation area of ​​the reliquefaction system compared to systems that use a reciprocating compressor, thereby contributing to space conservation on board the ship and reducing the installation costs of the reliquefaction system, thereby improving price competitiveness. Furthermore, the use of a centrifugal compressor in the system of the present invention eliminates the need for auxiliary equipment such as dampers that reduce vibrations and noise caused by reciprocating pistons, which are required when using a reciprocating compressor, and also prevents increased system maintenance and repair costs due to pulsation phenomena and the like. [Brief explanation of the drawings]

[0015] [Figure 1] An example of a re-liquefaction system that re-liquefies evaporated gas generated from LPG is shown below. [Figure 2] 1 shows a schematic diagram of a vapor re-liquefaction system for a marine vessel according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The operating advantages of the present invention and the objects achieved by embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: FIG.

[0017] Hereinafter, the configuration and operation of an embodiment of the present invention will be described with reference to the accompanying drawings. Note that in this specification and the accompanying drawings, the same components are designated by the same reference numerals.

[0018] 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).

[0019] Furthermore, embodiments of the present invention can be applied to a reliquefaction system for any type of liquefied gas that can be liquefied at low temperatures for transportation and generates evaporated 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. In the embodiments described below, LPG, one of the representative liquefied gases, will be used as an example.

[0020] Figure 1 shows an example of a re-liquefaction system that re-liquefies evaporated gas generated from LPG.

[0021] 1, in such a reliquefaction system, evaporated gas generated in a cargo tank T and discharged from the cargo tank T is supplied to a knock-out drum 10, compressed in a compression section 20, and cooled and re-liquefied in a condenser 30. The re-liquefied liquefied gas is supplied to a re-liquefaction gas container 40, an intercooler 50, etc., and then supplied to the cargo tank T.

[0022] Furthermore, in such reliquefaction systems, a reciprocating compressor manufactured by Buckhardt AG, for example, is used as the compressor section 20 that compresses the evaporated gas. However, this type of reciprocating compressor generates significant vibration and noise due to the reciprocating pistons, and therefore requires the installation of auxiliary equipment such as a damper to reduce these vibrations. Another problem is that pulsation phenomena increase the maintenance and repair costs of the reliquefaction system. Furthermore, certain companies are taking advantage of their global monopoly supplier status to maintain high prices, which reduces the price competitiveness of ships and makes it difficult to adjust supply schedules, resulting in problems such as the inability to smoothly manage ship delivery schedules.

[0023] To solve these problems, the embodiment described below provides a re-liquefaction system that uses a centrifugal compressor to compress the evaporated gas and effectively configures a corresponding evaporated gas flow path to maintain the pressure downstream of the compressor at a level that allows the evaporated gas to be completely re-liquefied.

[0024] FIG. 2 shows a schematic diagram of an evaporation gas reliquefaction system for a ship according to an embodiment of the present invention.

[0025] Referring to Figure 2, the evaporated gas reliquefaction system of this embodiment includes a cargo tank T installed on a ship in which liquefied gas is stored, a gas reliquefaction line GL that discharges evaporated gas generated from the liquefied gas stored in the cargo tank T from the cargo tank T and reliquefies it, a compression section 100 installed in the gas reliquefaction line GL that compresses the evaporated gas, and a condenser 200 installed in the gas reliquefaction line GL that cools the evaporated gas compressed in the compression section 100.

[0026] Furthermore, in the evaporated gas reliquefaction system of this embodiment, a knock-out drum D is provided upstream of the compression section 100 on the gas reliquefaction line GL. The knock-out drum D receives the evaporated gas discharged from the cargo tank T and supplies the gas components to the compression section 100. The evaporated gas generated in the cargo tank T may contain various components such as ethane, propylene, and ammonia in addition to propane and butane (I-butane / N-butane). The evaporated gas containing various components generated in the cargo tank T is supplied to the knock-out drum D through the gas reliquefaction line GL, and the gas components discharged from the knock-out drum D are then supplied to the compression section 100. The evaporated gas is then reliquefied through a reliquefaction process and recovered in the cargo tank T.

[0027] The compression section 100 includes a first compressor 110 that compresses the evaporated gas discharged from the knock-out drum D, and a second compressor 120 that further compresses (additionally compresses) the evaporated gas compressed by the first compressor and supplies it to the condenser 200. In this embodiment, centrifugal compressors are used for both the first compressor 110 and the second compressor 120.

[0028] The first compressor 110 is a centrifugal compressor including a first-stage compressor 110A and a second-stage compressor 110B, each connected via a motor shaft. The number of compression stages in each compressor may be increased as needed. In this embodiment, the compression section 110 uses a centrifugal compressor, which is less expensive, lighter, and smaller than a reciprocating compressor. This reduces the weight and installation area of ​​the reliquefaction system, facilitating installation of the reliquefaction system on a ship and contributing to the creation of more space within the ship. Furthermore, centrifugal compressors generate less vibration and noise than reciprocating compressors with reciprocating pistons, thereby reducing the cost and space required for installing auxiliary equipment such as shock absorbers to reduce noise and vibration. Furthermore, minimizing pulsation reduces maintenance and repair costs and enables stable, continuous operation.

[0029] The evaporated gas compressed by the three-stage centrifugal compressors of the first and second compressors 110 and 120 is supplied to the condenser 200 .

[0030] In the condenser 200, the evaporated gas compressed in the compression section 100 is cooled and re-liquefied by heat exchange. Note that the heat source for cooling the evaporated gas in the condenser 200 can be, for example, seawater, which is easily available on ships.

[0031] The liquefied gas reliquefied in the condenser 200 is stored in a reliquefied gas container 300 and supplied to the cargo tank T through a reliquefied gas recovery line LL connecting the reliquefied gas container 300 and the cargo tank T.

[0032] Furthermore, a pressure transmitter PT is provided downstream of the condenser 200 on the gas reliquefaction line GL to detect the pressure downstream of the condenser 200. A first valve V1 and a second valve V2 are provided in parallel in the vent line through which vent gas is discharged from the reliquefaction gas container 300. The opening and closing of the first and second valves V1 and V2 is controlled based on the pressure detected by the pressure transmitter PT.

[0033] The compression pressure of the evaporated gas required for full liquefaction of the evaporated gas varies depending on the component composition of the evaporated gas. Therefore, in this embodiment, the opening of the first valve V1 is controlled based on the pressure detected by the pressure transmitter PT, thereby maintaining the pressure downstream of the second compressor 120 at the pressure required to fully re-liquefy the evaporated gas.

[0034] In addition, the second valve V2 is used to prevent the pressure inside the reliquefaction gas container 300 from rising excessively in the event of an emergency in the reliquefaction system, and in the event of an emergency, the second valve is opened to prevent excessive pressure from being applied to the reliquefaction gas container 300.

[0035] Furthermore, the reliquefied gas recovery line LL is provided with an economizer 400. In the economizer 400, heat is exchanged between the evaporated gas compressed by the first compressor 110 and the reliquefied liquefied gas supplied to the cargo tank T. As shown in FIG. 2 , the evaporated gas compressed by the first stage compression section 110A of the first compressor 110 is supplied to the economizer 400 and cooled by the reliquefied liquefied gas supplied from the reliquefied gas container 300 to the cargo tank T. Thereafter, the evaporated gas is compressed by the second stage compression section 110B, further compressed (additionally compressed) by the second compressor 120, and then cooled by the condenser 200 to be completely reliquefied.

[0036] The liquefied gas (LPG) reliquefied by the condenser 200 is supplied to the reliquefaction gas container 300 and the intercooler 400, and then supplied to the cargo tank T. In this way, in the present embodiment, by reliquefying the evaporated gas and recovering it in the cargo tank T, the transportation efficiency of the LPG is improved and the pressure inside the cargo tank T can be maintained at a safe pressure.

[0037] 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 and modifications can be made without departing from the technical gist of the present invention.

Claims

1. a cargo tank provided on a ship for storing liquefied gas; a gas reliquefaction line for reliquefying evaporated gas generated from the liquefied gas and discharged from the cargo tank; a compression unit provided in the gas reliquefaction line for compressing the evaporated gas; and a condenser provided in the gas reliquefaction line for cooling and reliquefying the evaporated gas compressed in the compression unit, the compression unit includes: a first compressor that compresses the evaporative gas; and a second compressor that additionally compresses the evaporative gas compressed by the first compressor and supplies the compressed gas to the condenser; the first compressor and the second compressor are centrifugal compressors, The system further comprises a re-liquefaction gas container for storing the liquefied gas re-liquefied by the condenser; a pressure transmitter for detecting the pressure downstream of the condenser; and a first valve and a second valve provided in parallel on a vent line for discharging vent gas from the re-liquefaction gas container. The first valve is controlled based on the pressure detected by the pressure transmitter to maintain the pressure downstream of the second compressor in the gas reliquefaction line at a predetermined pressure, and the second valve prevents an excessive increase in pressure in the reliquefaction gas container in the event of an emergency in the reliquefaction system. Evaporative gas reliquefaction system for ships.

2. a reliquefied gas recovery line connecting the reliquefied gas container and the cargo tank; and an intercooler provided in the reliquefied gas recovery line; The evaporated gas compressed by the first compressor is cooled by the intercooler and then compressed by the second compressor.

2. The system for reliquefying evaporated gas for a ship according to claim 1.

3. the first compressor is a centrifugal compressor having a first stage compression section and a second stage compression section connected to a motor shaft, the evaporated gas compressed in the first stage compression unit is supplied to the intercooler and cooled by the liquefied gas supplied from the reliquefaction gas container to the cargo tank, and then compressed in the second stage compression unit and further compressed in the second compressor.

3. The system for reliquefying evaporated gas for a ship according to claim 2.

4. a knock-out drum that receives evaporated gas discharged from the cargo tank and supplies gas components to the compression section is provided upstream of the compression section of the gas reliquefaction line. The system for reliquefying evaporated gas for a ship according to any one of claims 1 to 3.

Images