KR20120089377A - A method and system for handling warm lpg cargo - Google Patents

Abstract

At least one reliquefaction unit (130) comprising a condenser (170) as a method for processing hot LPG cargo in at least one cargo tank (100, 110, 120) installed on an LPG carrier, during processing prior to shipment. Re-liquefying vapors discharged from the cargo in at least one cargo tank (100, 110, 120) to the at least one cargo tank (100, 110, 120). Sending step. The method comprises operating the at least one reliquefaction unit (130, 140, 150) and condenser (170) in a non-freezing manner to compress and condense steam and to remove hot condensate from the condenser (170). Flow to 160). Corresponding systems have been disclosed.

Description

High temperature LPG cargo handling method and system {A METHOD AND SYSTEM FOR HANDLING WARM LPG CARGO}

FIELD OF THE INVENTION The present invention relates to a method and system for reducing loading time at a loading port for tankers sailing seas carrying liquefied petroleum gas, commonly known as LPG (hereinafter referred to as LPG carriers), in particular cargo A method and system for reducing loading time when loading cargo at temperatures above the saturation temperature corresponding to tank pressure. In addition, secondary effects are obtained including omitting forced shaving during unloading and peak shaving during transportation.

A shipping port means an LPG export terminal, which is located on the coast or coast.

A cargo port means an import terminal, which is located on the coast or coast.

In the following, the cargo tank is to be understood as one liquid-tight container for accommodating LPG at the loading or unloading port. The cargo tank can be any tank, for example an integrated tank, a membrane tank or an independent tank.

In the following, the storage tank is to be understood as one liquid-tight container for accommodating LPG at the loading or unloading port.

LPG should be understood as various grades of petroleum gas or petroleum gas products that are stored and transported as liquid cargo. Of the various petroleum gases, propane and butane are the main examples, and propane generally contains any concentration of ethane from 0% to 5% by volume, but the butane content in propane is any from 0% to 20% by volume. Content can be. This mixture, which generally consists of 70 to 98% by volume of propane, is known as commercial propane and hereinafter referred to as propane.

Butane may be any mixture of iso-butane and normal-butane containing possible proportions of unsaturated hydrocarbons, hereinafter referred to as butane.

In addition to propane and butane, LPG should contain a minimum of ammonia, butadiene, butane-propane mixture (any mixture), butylene, diethyl ether, propylene, vinyl chloride.

LPG, stored and transported at temperatures below ambient temperature, naturally continue to produce a certain amount of steam. It is common practice to maintain the pressure in the cargo tank by extracting and liquefying the discharged vapor and returning it back to the cargo tank as condensate. In the following, a reliquefaction unit is to be understood as a refrigeration unit in which the duty liquefies the vapor, with the prefix "re" indicating that the vapor from the liquefied gas is liquefied.

In the following, condensate means liquefied steam, which means steam generated when loading the cargo, flash vapor generated from the loaded cargo, steam generated when the condensate returns from the reliquefaction unit, Refers to the product of flash steam generated from the returned condensate, steam formed by adding heat to the cargo tank.

Hot cargo is to be understood as loaded LPG at temperatures above the saturation temperature corresponding to the current cargo tank pressure.

LPG is transported in a liquid state at pressures above atmospheric pressure or below atmospheric temperature, or at pressures above atmospheric pressure and below atmospheric temperature. The present invention,

(1) LPG carriers known as fully refrigerated, carrying LPG, a liquefied cargo, at temperatures below ambient temperature;

(2) It relates to LPG carriers, known as semi refrigerated / semi pressurized, which carry LPG, a liquefied cargo, at sub-atmospheric and above atmospheric pressures.

For LPG trade transactions it is common for LPG carriers to carry different grades of LPG in some cases, and it is common for LPGs received and loaded at the loading port to have a saturation pressure above the maximum allowable working pressure of the cargo tank. . This means that the LPG carrier must cool the loaded cargo to the working pressure range of the cargo tank. Cooling is generally accomplished by flashing a liquid that lowers the cargo tank pressure and liquefying the generated steam. Depending on the saturation pressure, loading time can take from less than 24 hours to more than 4 days.

Reducing loading time will reduce shipping port costs and increase navigable time, thus reducing carbon emissions to the atmosphere due to reduced fuel consumption. At present, there is nothing characteristic available except to increase the refrigeration capacity of the reliquefaction unit of LPG carriers. Increasing the refrigeration duty of the reliquefaction unit built into the LPG carrier is not considered feasible. Minimum requirements for refrigeration duty are set out in international rules and regulations, and installed refrigeration duty is generally above the minimum requirement. An obvious but unacceptable solution is to release all steam to the atmosphere.

Super-large gas carriers with a cargo carrying capacity of approximately 80000 m ³ are usually equipped with four reliquefaction units and often only one or two units are intermittently used to cope with natural heat leaks during loading and voyage. Is activated. There is an imbalance in installed unit capacity and general heat leaks, and often continuous operation is interrupted while loading and navigating cargo. As mentioned above, the minimum required refrigeration capacity is controlled by international rules and regulations, but in reality the installed refrigeration capacity exceeds this requirement and the excess capacity is mainly due to the operating mode, for example the maximum load time that can be tolerated. This is at the owner's additional request. The additional capacity increase of the reliquefaction unit will increase the cost excessively and thus is not a viable solution.

In LPG trade transactions, although not common to all ships, in many cases it is also common for LPG carriers to have deck tanks capable of maintaining LPG at saturation pressures corresponding to warm atmospheric conditions. The purpose of the deck tank is to accommodate sufficient liquid to replace the vapor atmosphere of the cargo containment system when the gas in the cargo tank is emptied and vented before changing or anchoring the cargo class to be shipped. Mixing of different cargoes is undesirable. In some cases, however, very small amounts of propane and butane mixtures can be tolerated, as some cross contamination of the two cargoes is already very common before loading.

Some LPG cargoes such as propylene and butadiene are used as feedstock in the chemical industry. Contamination of these and other class cargoes can reduce their value as feedstock. Therefore, it is common to keep the containment system strictly clean against changes in vapor atmosphere.

Changing the vapor atmosphere is generally carried out by first replacing the original vapor atmosphere with an inert gas from an inert gas generator or nitrogen generator, for example exhaust gas. The type of cargo grade determines which inert gas can be used. After filling the entire containment system with inert gas, the inert gas is replaced by fresh cargo grade vapor to be loaded into the LPG carrier. This is done by opening the valve 310 of the line 12, vaporizing the LPG in the cargo evaporator 190, and flowing the vapor through the liquid line to replace the inert gas of the overall cargo receiving system (FIG. 2).

A cargo containment system is to be understood as a cargo tank with all relevant piping and equipment.

Another feature of LPG maritime transport is that it is very common for LPG carriers to refuse steam and replace LPG carriers from LPG carriers in order to replace the liquid volume removed from the cargo port. The liquefied gas evaporates as soon as the vapor pressure decreases, thus compensating to some extent the LPG pumped from the cargo tank. However, it is not clear whether the total pressure reduction in the cargo tank during the LPG unloading will be within the operating pressure range of the cargo tank. To avoid pressure problems during unloading LPG, it is common to evaporate some of the liquid discharged in a dedicated evaporator and return this steam back to the cargo tank. Other means are also possible, for example using a cargo compressor to warm up the steam atmosphere in the cargo tank. Warming up is accomplished by circulating steam through the cargo compressor and returning the steam back to the cargo tank without any cooling.

1 shows a typical prior art reliquefaction unit for reference. Liquid cargo flows in line 1 from the storage tank at the loading port. Loading line valves 261, 262 and 263 regulate the amount of cargo contained in each cargo tank. Steam from the cargo tanks 100, 101, 120 flows through the steam line 2 and enters the cargo compressor 200 where the steam is compressed to medium pressure. The steam not processed by the reliquefaction unit shown in FIG. 1 flows through a continuous steam line 2 placed in parallel with the operation unit not shown.

The cargo compressor 200 is generally the first stage of a multistage compressor.

The steam exiting the cargo compressor 200 enters via line 3 into a combined de-superheater / flash economiser 210 where the steam approaches saturation temperature. The steam then flows through line 4 from the combined superheater / flash economizer 210 to the cargo compressor 220, where the steam is at a temperature that can be obtained at the cargo compressor 170. It is compressed to the corresponding bubble point pressure.

The cargo compressor 220 is generally the second stage of the multistage compressor.

Compressed steam enters cargo condenser 170 through line 5 which condenses into sea water or a cooling medium, generally above sea water temperature. Seawater is the most commonly used heat sink for the cargo condenser 170 so far, but a mixture of water and antifreeze is also available. The antifreeze can be any suitable glycol.

The warm condensate exiting the cargo condenser 170 flows via line 7 to line 6 branched from line 7, where line 6 is the most necessary step of hot condensate. A portion flows through the level regulating valve 230 which provides interstage cooling and subcooling.

The remaining high temperature condensate to be returned to the cargo tanks 100, 110, 120 flows through the coil 215 in the superheater / flash economizer 210 via the condensation line 7 ′ and in the supercooled state. Exit 215). The subcooled condensate is now reduced in pressure by the pressure control valve 240 and the resulting two phase condensate and vapors are condensed flowing through the line 8 from the other reliquefaction unit 8. Mixed with water and steam. The mixed condensate and steam flows back through line 9 to cargo tanks 100, 110, 120.

Figure 2 shows a typical arrangement of an LPG carrier with three reliquefaction units and three cargo tanks, which do not return steam to land.

As mentioned above, LPG carriers may take any combination of cargo tanks and reliquefaction unit numbers, and as an example two LPG carriers with four cargo tanks according to Norwegian patent application No. 20092477. The unit can be installed.

LPG is loaded on the cargo tanks 100, 110, and 120 of the LPG carrier by the cargo loading line 1 from the loading port. Loading line valves 261, 262, 263 adjust the loading rate and prevent overfilling. In general, larger LPG carriers have more than three tanks, but the number is not relevant to the present invention. Some of the LPG flowing into the cargo tank will flash into the gas phase depending on the pressure difference between the pressure in the shipping port storage tank and the LPG carrier cargo tank pressure and the total heat inflow from the storage tank to the cargo tank.

Steam flows from the cargo tanks 100, 110, 120 to the reliquefaction unit 130, 140, 150 via the steam line 2, in which the vapor is reliquefied and condensate or more precisely The mixture of condensate and steam is sent back to the cargo tanks 100, 110, 120 via the condensate line 9. The valves 264, 265, 266 can flexibly return the condensate to one cargo tank, all cargo tanks, or any combination of tanks.

The loading rate is determined by the refrigeration duty of the reliquefaction unit, since during the LPG shipment there is clearly a certain amount of steam generation to be handled by the reliquefaction unit installed in the LPG carrier. The number of reliquefaction units generally depends on the size of the LPG carrier, and the number of reliquefaction units is not relevant to the present invention.

The cargo evaporator 190 shown in FIG. 2 does not operate during the loading operation. Generally this also applies to deck tank 160.

In use, deck tank 160 is filled with LPG directly via line 10 connected to loading line 1. Thus, during shipment, the deck tank is generally filled with cold cargo directly from the loading line 1, and alternatively the deck tank 160 can be filled during cargo unloading. During unloading of the cargo, the loading line 1 is used as an export line.

The isolation valve 320 opens when loading the deck tank 160. The deck tank 160 is not insulated and may be heated. When emptying the deck tank 160, the valve 310 opens to regulate the flow through the cargo evaporator 190 which vaporizes the liquid. The vapor product flows via line 12 and is connected to the liquid cargo header, although there are other connections, which are not relevant to the description. Isolation valve 340 prevents backflow to cargo evaporator 190 during normal shipping operations.

Steam from deck tank 160 flows via line 11 and is connected to the steam header. Isolation valve 330 isolates deck tank 160 from steam headers during normal operation.

35000 m ³ a typical medium size LPG tanker equipped with a storage tank of the load-carrying capacity is shipped from a shipping port propane which are storage tank having a vapor pressure of 0.42 bar g. It can be seen from the graph 1 below that the temperature of the LPG received is -38 ° C.

Graph 1

In this particular example, it is preferred that during the shipment the LPG carrier has a cargo tank pressure of 0.275 bar g. This particular example and the loading curve for the LPG carrier are shown in Graph 2 below.

Graph 2

From Graph 2 it can be seen that the loading capacity is approximately 170 tons / hour. The total load weight of the cargo is 19788 tons and the loading time will be 4,9 days.

There is no prior art solution that is environmentally friendly, i.e. a significant reduction in loading time can be achieved without releasing steam into the atmosphere.

The main object of the present invention is to solve the above problems.

According to a first aspect of the present invention, an object of the present invention is a method for the treatment of hot LPG cargo in at least one cargo tank installed in an LPG carrier, preferably during shipment, comprising a condenser. And re-liquefying vapor discharged from the cargo in at least one cargo tank to at least one reliquefaction unit and returning the reliquefied steam to the at least one cargo tank. The method also includes operating the at least one reliquefaction unit and condenser in a non-frozen manner, which only compresses and condenses steam, and flows hot condensate from the condenser to the deck tank.

According to a second aspect of the present invention, there is provided a system for processing hot LPG cargo in at least one cargo tank installed in an LPG carrier for processing, preferably during shipment, wherein steam is released from the cargo in the at least one cargo tank. Re-liquefied to at least one reliquefaction unit comprising a condenser and returning the re-liquefied vapor to the at least one cargo tank, wherein the at least one reliquefaction unit and the condenser only compress and condense the vapor. It is operated in a non-freezing manner and hot condensate from the condenser is introduced into the deck tank.

In order to condense, flow and direct the hot condensate to the deck tank, the vapor is compressed by a compressor device in at least one reliquefaction unit and then by a condenser arranged in connection with the compressor.

However, the vapor compressed to medium pressure can be flowed through a combined superheater and flash economizer, arranged in at least one reliquefaction unit in front of the condenser, and, if appropriate, the combined superheater and flash economizer. You can bypass it.

The steam may include: i) sending the steam back to the suction side of the cargo compressor, ii) sending the steam back to the discharge side of the first compression stage of the cargo compressor, and iii) sending the steam to the third cargo compressor to which the three stage compression stages are applied. It may be returned from the deck tank by either sending it back to the suction side, i) mixing the vapor with the loaded LPG.

In particular, the deck tank can be emptied into the cargo tank of at least one of the cargo tanks during unloading, in order to compensate for the pressure reduction during the unloading operation and at the start of the unloading at the intermediate tank pressure, wherein the hot steam is at least one Flow by pressure through the spray cooling nozzle arranged in the cargo tank of.

A section of at least one reliquefaction unit is operated including both the combined superheater and flash economizer such that the initial saturation pressure of the condensate entering the deck tank is below the maximum working pressure of the deck tank.

In addition, propane generated from hot condensate in deck tanks can be used as fuel for propulsion of LPG carrier engines by low pressure fuel pumps.

Other preferred embodiments are specified in the dependent claims and the following detailed description.

Briefly, loading time at the loading port for LPG carriers is reduced, especially when loading cargo at temperatures above the saturation temperature corresponding to the cargo tank pressure. As already explained, additional effects are obtained, for example, omitting peak saving during unloading and during transport.

The present invention will now be described in more detail with reference to the accompanying drawings.

1 and 2 are schematic diagrams of prior art reliquefaction units.
3-11 are schematic diagrams of preferred embodiments of a system for transporting liquefied petroleum gas, but not limited to, particularly to reduce LPG carrier loading time when loading hot cargo.

The present invention relates to a method and system for transporting liquefied petroleum gas, and more particularly to a method and system for reducing LPG carrier loading time when loading hot cargo. The present invention uses existing equipment typically installed on LPG carriers but differs from the structures currently known.

3 schematically illustrates the overall apparatus of the present invention and will be described below.

The LPG carriers receive LPG from the loading port via a cargo liquid line 1 extending into at least one cargo tank 100, 110, 120. LPG carriers can have any number of cargo tanks but are generally two to four.

Steam flows from the cargo tanks 100, 110, 120 to the reliquefaction unit via steam line 2. FIG. 3 shows one generalized reliquefaction unit 130 among reliquefaction units formed of a compressor device 400, a condensate subcooling device 500, and a condenser 170. While the compressor device typically includes at least a two stage compressor, the condensate subcooling device may have a different configuration, but both the compressor device and the condensate subcooling device both reduce the amount of flash gas in the cargo tank 160, To reduce the temperature of the gas to be compressed and to subcool the condensate before reducing the condensate pressure below the cargo tank pressure.

The steam not processed by the reliquefaction unit 130 flows via the steam line 2 which is also connected to additional reliquefaction units arranged in parallel, not shown.

Any number of reliquefaction units can be used but generally two to four reliquefaction units are common.

In the cargo tanks 100, 110, 120, the steam flowing through the steam line 2 enters the cargo compressor 200, where the steam is generally at a medium pressure in the range of 3 bar g to 5 bar g. Is compressed. The compressed steam exits the cargo compressor 200 and passes through line 3 to the combined superheater / flash economizer 210. No liquid flow occurs through the line 6 supplied to the combined superheater / flash economizer 210, and the combined superheater / flash via line 4 is in the same state as the vapor entered. It is sent out of the economizer 210.

Steam also flows to the cargo compressor 220, where the vapor is compressed to a pressure at least corresponding to the saturation pressure based on the temperature obtainable at the downstream condenser 170. The cooling medium used in the condenser 170 is sea water or any water / glycol mixture, not shown in FIG. 3. The vapor exits the cargo compressor 220 and enters the condenser 170 where it condenses via line 5. Isolation valve 267 is closed and isolation valve 268 is open, allowing hot condensate to flow to deck tank 160 via line 16. Regulating valve 370 ensures sufficient backpressure for cargo compressor 220. Isolation valve 380 is open.

Another operating configuration is to bypass the combined desuperheater / flash economizer. Compressed steam exits cargo compressor 220 and passes through line 3 but bypasses combined superheater / flash economizer 210 via line 3b (see FIG. 10). Bypass is provided by closing the isolation valve 380 and opening the isolation valve 390. Line 3b is connected with line 4.

Only steam flows through the combined superheater / flash economizer 210. Thus, each reliquefaction unit operates in a non-freezing manner in which all steam is only compressed and condensed.

Hot condensate in other reliquefaction units operating in parallel enters line 16 via line 13. Valve 380 isolates deck tank 160 from the liquid line and prevents overfilling. The valve 350 of the line 17 enables the filling of the cold condensate 10. Line 17 branches from condensate return line 9 and connects with liquid line 10. Steam from deck tank 160 flows back through line 14 to the cargo compressor section of the reliquefaction unit, and the steam is sent to other reliquefaction units operating in parallel. The valve 360 regulates the vapor pressure in the deck tank 160.

In the prior art solutions, the deck tank is filled with LPG, whereas in the present invention the deck tank is filled with condensate. An important difference between the LPG grades of propane, for example with 5 mol% ethane, is that the condensate is in the gaseous phase in equilibrium composition and generally has a ethane content of 26 mol%.

The vapor from the cargo tank is formed by the elements described above but with the same proportions as specified below.

Steam generated when loading cargo: 5 to 10%,

Flash steam from loaded cargo: 35 to 65%

Steam from condensate return from reliquefaction unit: 0 to 1%

Flash steam from returned condensate: 15 to 30%

Steam generated by adding heat to cargo tanks: 25 to 35%

Depending on the cargo grade, the content of volatile components in the LPG, the temperature and work type, and the distribution ratio may differ from those described above.

The steam handling capacity set for each LPG carrier is determined by the capacity of the cargo compressor and the number of reliquefaction units that can operate in parallel at the same time. By sending all the condensate to the deck tank 160, the steam portion produced by the condensate flash is removed from the entire steam and thus increasing the loading rate.

Steam from deck tank 160 may be treated by the following description.

1. sending it back to the suction side of the cargo compressor 200 (see FIG. 3)

2. Sending back to the discharge side of the cargo compressor (200). The steam line 14 is connected to the discharge side of the cargo compressor 200 (see FIG. 4).

3. Sending back to the suction side of a third cargo compressor to which three stage compression stages are applied. The steam line 14 is connected to the discharge side of the cargo compressor 200 (see FIG. 5).

4. Mix with loaded LPG. Steam exiting deck tank 160 flows through line 17 to cargo liquid line 1 where steam is completely or partially absorbed by the liquid stream.

3 to 6 is a reciprocating cargo compressor which usually compresses in two or three stage compression stages. Other cargo compressors may also be used, such as screw cargo compressors or centrifugal cargo compressors.

Emptying the deck tank 160 is carried out through the liquid line 9 during the unloading of the LPG carrier and the LPG contents of the deck tank 16 flow by the pressure through the spray cooling nozzles 50, 60 in the cargo tank. (See FIG. 7, where appropriate connections to each reliquefaction unit are not shown). By sending the condensate stored in the deck tank 160 into the LPG cargo tanks 100, 110, 120, the following advantages are obtained.

Flashing through the spray nozzle will compensate for the pressure drop during the unloading operation. Thus, operations such as pressure formation by vaporization of the pumped cargo and heating of the vapor space will not be necessary.

• Unloading can start with more relaxed tank pressure. In other words, it is not necessary to increase the pressure at the end of the voyage.

LPG carrier cargo carrying capacity is increased by the volume of the deck tank.

The rate of evaporation from the cargo tank is significantly higher in the first few days than in the second half of the sailing period. This high evaporation rate is due to the fact that the cargo containment system did not reach a stable temperature corresponding to the cargo during shipment.

The amount of steam required to replace the volume pumped during cargo unloading can be supplied by flashing hot condensate from deck tank 160. However, depending on the cargo temperature loaded, the amount of condensate sent to deck tank 160 may not meet the steam requirements during unloading. Therefore, by sending hot condensate to deck tank 160 during the first few days of sailing, the entire available steam by flashing the condensate back to the cargo tank during unloading maintains the pressure in the cargo tanks 100, 110, 120. In order to be at least balanced with the total amount of vaporized LPG. Since this change in operation requires fewer reliquefaction units to operate, this change in operation reduces the pumping force for seawater used for example in the cargo evaporator 190 shown in FIG. This will reduce fuel use during the first few days of transportation. Requiring less operation of the reliquefaction unit means that approximately 20-35% of the condensate that is returned back to the cargo tanks 100, 110, 120 is flashed into steam and sent back to the cargo compressor unit for recycling. It is based.

3, 4, 5 and 6 show a prior art reliquefaction unit with connections to a proposed deck tank according to the invention.

Operation on LPG carriers during voyage often involves intermittent operation of the reliquefaction unit, i.e. some reliquefaction units do not operate and the cargo tank pressure can rise to a high level and then to reduce the cargo tank pressure. That means running one or two of the reliquefaction units during the day. By using a new connection to the deck tank 160, the advantages described below are obtained.

During the day, especially during the hottest days, two reliquefaction units are often used for operation. If hot condensate is sent to deck tank 160 via line 16, only one working reliquefaction unit will suffice for most of the voyage. By doing so, the total steam treatment capacity of one operational reliquefaction unit is increased. During periods of moderate temperature, the condensate filled in the deck tank 160 may be sent back to the cargo tank via line 16 or alternatively line 10. Thus, deck tank 160 can be actively used for peaks with high steam rates during the hottest times, thus reducing the number of operational reliquefaction units required.

Yes

A typical LPG carrier with a capacity of 35000 m ³ is loaded with a light propane mixture at a temperature of -37.5 ° C. The cargo tank pressure during loading is 0.22 bar g and the corresponding saturation pressure for LPG is 0.45 bar g.

The vapor flow from the cargo tank during loading is formed by the following elements.

1-6.6% volume of steam generated during loading

2-20.8% flash from reliquefaction

3-0.4% of the volume of vapor resulting from reliquefaction

4-Flash 42.0% from loaded cargo

5-Evaporation due to heat inflow 30.2%

100% overall

By removing all the condensate in the hot state from the reliquefaction unit, contributing to the flash from the condensate is eliminated and the vapor flow from the cargo tank is reduced. This reduction in the overall vapor flow rate offers the possibility of increasing the loading rate in order to maintain the same initial vapor flow rate. For the same conditions as described above, the contribution ratio of the individual vapor elements is as follows.

1-9.8% of the volume of steam generated during loading

2-0.0% flash from reliquefaction

3-0.0% vapor volume resulting from reliquefaction

4-Flash 62.6% from loaded cargo

5-Evaporation by heat inflow 27.6%

100% overall

From this example, one can simply conclude that significantly increased loading speeds are possible through the present invention.

In this case, the LPG may be one having a content of the volatile components in the above-described general range which causes the saturation pressure in the deck tank 160 to be higher than the design pressure. Also, high contributions of more volatile components can lead to unacceptable emission temperatures. In addition, some operating aspects cause saturation pressures that exceed the design pressure of the deck tank.

The more volatile components may include propane having a higher ethane content than that acceptable for commercial propane. Then the cargo compressor discharge pressure will increase and the discharge temperature will correspondingly increase.

The operating pattern may be that the sea water temperature exceeds the design limit causing higher condensation pressure.

In this case, the section of the reliquefaction unit including both the superheater / flash economizer 210 such that the initial saturation pressure of the condensate sent to the deck tank 160 is much lower than the maximum working pressure of the deck tank 160. It is necessary to work. Heat leakage into the deck tank 160 will gradually increase the pressure in the deck tank and at some time the steam line 14 must be open. This situation will generally occur after shipment when the LPG carriers are sailing.

8 schematically shows how to be processed. Isolation valve 268 is closed and isolation valve 267 is opened to allow hot condensate to flow through combined line 7 to combined superheater / flash economizer 210. A small portion of the condensate is sent through line 6 to provide the necessary condensate subcooling and interstage cooling. Isolation valves 264, 265, 266, 320 are all closed. Isolation valve 350 is opened to allow the supercooled condensate to flow via line 7 connected to line 10. The subcooling temperature is generally less than 10 ° C.

At some time after the end of filling, the temperature of the deck tank 160 reaches a level at which the corresponding saturation pressure is set to the maximum allowable working pressure. At this point the control valve 360 is open and maintains this pressure.

Steam from the deck tank 160 is sent back to the compressor unit 400 via line 14 for recompression. The steam sent to another reliquefaction unit is branched in line 14.

To be a more flexible device for deck tanks, a transfer pump 460 is arranged in line 16 to counteract the frictional pressure loss in the lines connected to the deck tank (see FIG. 11).

Although shipping is by far the most carbon-efficient way of commercial transport, its size has a significant impact of approximately 3% of global carbon dioxide emissions.

The shipping industry thus suggested that the carbon reduction targets should be at least equal to future carbon reductions agreed under the new United Nations climate change agreement.

One alternative for the maritime industry to meet its carbon goals is to switch to fuels with less carbon impact. In the case of LPG carriers, it is generally possible to reduce the carbon impact by installing a dual fuel engine and running primarily propane.

Dual fuel low speed diesel engines running on propane will require fuel tanks of adequate capacity. Deck tank 160 achieves several advantages by maintaining a sufficient volume of propane during most of the operation and combining deck tank functionality to be a fuel tank.

1. No additional tank required.

2. No additional fuel filling system is needed.

3. The fuel tank can be filled from the reliquefaction unit during navigation.

Emptying deck tank 160 is accomplished by a low pressure pump providing a high pressure pump that presses the condensate to a sufficiently high pressure. The final feed pressure will generally be between 350 and 550 bar g. Low pressure fuel pump 450 draws from fuel tank 160 through line 20 connected to line 16. The valve 455 isolates the fuel system when the LPG carrier is not running on propane. Fuel feed pump 450 delivers the condensate via line 21 to a downstream high pressure fuel supply system, not shown.

During voyage, natural evaporated vapors can be sent to deck tanks as hot condensate, so deck tanks do not need to be sized for trade transactions over long distances. The descriptions given during cargo unloading may be maintained. 9 shows a combined device.

As described above, deck tank 160 is on an LPG carrier, but this does not preclude the use of one or more tanks to replace or supplement conventional deck tanks.

Claims (20)

At least one reliquefaction unit 130 comprising a condenser 170 as a method for processing hot LPG cargo in at least one cargo tank 100, 110, 120 installed in an LPG carrier for processing, preferably during shipment. Re-liquefying vapors discharged from the cargo in at least one cargo tank (100, 110, 120) to the at least one cargo tank (100, 110, 120). In the method comprising the step of sending,
The method comprises operating the at least one reliquefaction unit 130, 140, 150 and the condenser 170 in a non-freezing manner that only compresses and condenses steam and the hot condensate from the condenser 170 to the deck tank. And a flow to (160). The method of claim 1,
The method also includes compressing the vapor to a compressor device (400) in the at least one resupply unit (130, 140, 150), wherein the condenser (170) condenses the hot condensate and the deck tank Wherein the compressor is connected to the compressor device for flow into the compressor. The method of claim 2,
The method also includes bypassing the combined superheater and flash economizer (210) when passing the compressed steam into the condenser (170). The method according to any of the preceding claims,
The method comprises:
Iii) sending steam back to the suction side of the cargo compressor 200,
ii) sending steam back to the discharge side of the cargo compressor 200,
Iii) sending steam back to the suction side of a third cargo compressor 225 to which the three stage compression stages are applied,
Iii) returning steam from the deck tank by one of mixing steam with the loaded LPG. The method according to any of the preceding claims,
The method also includes emptying the deck tank 160 into at least one cargo tank 1, 2, 3 during unloading, wherein hot steam is spray cooled nozzles 50, arranged in the at least one cargo tank. Hot LPG cargo handling method characterized in that flow by the pressure through 60). The method according to any of the preceding claims,
The method comprises at least one reliquefaction unit 130, 140, comprising both combined superheater and flash economizer 210, such that the initial saturation pressure of the condensate introduced into the deck tank is below the maximum working pressure of the deck tank. And operating the section of 150). The method according to any of the preceding claims,
The method further includes using LPG generated from the hot condensate in the deck tank 160 as a fuel to propel the LPG carrier engine by the low pressure fuel pump 450. A system for processing hot LPG cargo in at least one cargo tank (100, 110, 120) installed on an LPG carrier, preferably during shipment, from cargo in at least one cargo tank (100, 110, 120). The released steam is re-liquefied to at least one reliquefaction unit (130, 140, 150) comprising a condenser (170), and the re-liquefied vapor is returned to the at least one cargo tank (100, 110, 120). In the system,
The at least one reliquefaction unit 130, 140, 150 and the condenser 170 are operated in a non-freezing manner to compress and condense steam only,
Hot LPG cargo handling system, characterized in that the hot condensate from the condenser (170) is introduced into the deck tank (160). The method of claim 8,
Hot LPG cargo handling system, characterized in that hot condensate from condenser (170) is introduced into the deck tank via a line (16) comprising control and isolation valves (370, 380). The method according to claim 8 and 9,
Vapor is compressed into a compressor device 400 in the at least one reliquefaction unit 130, 140, 150, and a condenser 170 condenses the hot condensate and flows it into the deck tank 160. High temperature LPG cargo handling system, characterized in that arranged in conjunction with. The method of claim 10,
The compressed steam enters the combined superheater and flash economizer 210 via line 3 and passes through line 4 from the combined superheater and flash economizer via line 4. . The method of claim 10,
High temperature LPG cargo handling system, characterized in that when passing the compressed steam into the condenser (170), the combined superheater and flash economizer (210) are bypassed. The method of claim 12,
The combined desuperheater and flash economizer 210 are bypassed by a line 3a connecting lines 3 and 4, wherein lines 3 and 3b comprise isolation valves 380 and 390, respectively. High temperature LPG cargo handling system. The method according to any one of claims 8 to 13,
Iii) the steam is sent back to the suction side of the cargo compressor 200,
ii) the steam is sent back to the discharge side of the cargo compressor 200,
Iii) steam is sent back to the suction side of the third cargo compressor 225 to which the three stage compression stages are applied,
And v) steam is returned from the deck tank by one of mixing with loaded LPG. 15. The method of claim 14,
The steam is sent back to each side of the compressor apparatus by a steam line (14) comprising a control valve (360). 16. The method of claim 15,
The vapor further comprises mixing with LPG loaded via a steam line (17) comprising a control valve (360). The method according to any one of claims 8 to 16,
Deck tank 160 is emptied into at least one cargo tank 1, 2, 3 during unloading, and hot steam is caused by pressure through spray cooling nozzles 50, 60 arranged in the at least one cargo tank. A high temperature LPG cargo handling system characterized by flowing. The method according to any one of claims 8 to 17,
Of the at least one reliquefaction unit 130, 140, 150 including both the combined desuperheater and flash economizer 210 such that the initial saturation pressure of the condensate introduced into the deck tank is below the maximum working pressure of the deck tank. Hot LPG cargo handling system, characterized in that the section is operated. The method according to any one of claims 8 to 18,
The high temperature LPG cargo handling system, characterized in that LPG generated from the hot condensate in the deck tank (160) is used as fuel for propelling the LPG carrier engine by the low pressure fuel pump (450). 20. The method of claim 19,
The low pressure fuel pump is a high temperature LPG cargo handling system, characterized in that the supply via the line (21) to the high pressure pump included in the downstream high pressure fuel system.

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