Dry-ice blockage removal
The method of routing warmed CO2 vapour streams from both sides of the pipeline effectively addresses dry ice blockages in liquefied gas carriers, ensuring safe and efficient operation by equalizing pressure and temperature, thus preventing hazardous situations.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- LGE IP MANAGEMENT CO LTD
- Filing Date
- 2025-11-04
- Publication Date
- 2026-06-18
AI Technical Summary
The formation of dry ice (solid CO2) blockages in liquefied gas carriers poses a risk to the functionality of the cargo handling system due to reduced operating margins between transportation conditions and the triple point of CO2, leading to hazardous situations.
A method involving the extraction of CO2 vapour from a liquefied CO2 source, heating it to create warmer CO2 vapour streams, and routing these streams through the affected pipeline from both upstream and downstream directions to melt or sublime the dry ice blockage, using tie-in pipes and compression to increase pressure and temperature.
This method effectively removes dry ice blockages safely and quickly, restoring normal operation by equalizing pressure and temperature around the blockage, reducing the risk of pipe damage and ensuring safe functionality of the liquefied gas carrier.
Smart Images
Figure EP2025081839_18062026_PF_FP_ABST
Abstract
Description
[0001] DRY-ICE BLOCKAGE REMOVAL
[0002] FIELD OF THE INVENTION
[0003] The present invention relates to a method of removing a dry-ice (solid CO2) blockage which has formed in a pipeline on a liquefied gas carrier having one or more liquified CO2 (LCO2) cargo tanks.
[0004] BACKGROUND OF THE INVENTION
[0005] In general, carbon dioxide (CO2) is liquefied and then transported to destinations by gas carriers while stored in cargo tanks. At present the number of existing LCO2 carriers is small and the transportation vessels / ships are also small with LCO2 being transported as a high purity product for the food and beverage industries.
[0006] One method to transport large quantities of CO2 typically in quantities of 7,500 m3or greater is in liquid / liquefied form. This can be achieved by transporting the LCO2 at low pressure e.g., pressure in the region of 6 to 10 bar g and low temperature e.g., -50°C. These conditions have been found to increase cargo capacity and to reduce the cost associated with transporting larger quantities of CO2.
[0007] The triple point of CO2 (where CO2 can coexist as a solid, a liquid and a gas) occurs at a pressure of approximately 4.2 barg and temperature of approximately -56.6 °C. As such a low pressure and low temperature design as described above compared with medium to high pressure systems reduces the operating margin to the triple point.
[0008] The triple point characteristics of CO2 combined with a low pressure and low temperature cargo handling and reliquefaction plant results in a reduced operating margin between transportation conditions and triple point conditions. This presents risks and challenges during the design and operation of the cargo handling system. An example of a risk is the formation of dry ice (solid CO2). This could be hazardous and would undoubtedly affect functionality of the liquefied gas carrier.
[0009] SUMMARY
[0010] The present invention provides a method of removing a dry-ice (solid CO2) blockage, which is affecting flow through one or more pipelines in a liquified gas carrier having one or more liquefied CO2 cargo tanks, the method comprising at least the steps of: extracting CO2 vapour from a liquefied CO2 source; heating the CO2 vapour to provide a warmer CO2 vapour stream; creating two working CO2 vapour streams and routing each working CO2 vapour stream through the affected pipeline towards the dry-ice blockage simultaneously from both an upstream and downstream direction towards the dry-ice blockage.
[0011] The step of routing the working CO2 vapour streams into the affected pipeline may compress the working CO2 vapour streams thereby increasing pressure and temperature of the working CO2 vapour streams flowing toward the dry-ice blockage.
[0012] The step of extracting CO2 vapour may extract CO2 vapour from a cargo tank containing liquid CO2. Alternatively, the step of extracting CO2 vapour may extract CO2 vapour from a deck tank or pressure vessel containing liquid CO2.
[0013] The method may comprise routing the extracted CO2 vapour to a heating source, wherein the extracted CO2 vapour is heated thereby producing the warmer CO2 stream.
[0014] The extracted CO2 vapour may be warmed against a heat exchanger to produce the warmed CO2 vapour stream.
[0015] The extracted CO2 may be heated via a suction heater where the vapour is warmed against a heat exchanger to produce the warmed CO2 vapour stream. The method may further comprise routing the warmed CO2 vapour stream to a pressurisation line, wherein the pressurisation line facilitates creating a first and a second working CO2 vapour stream, which are routed to two opposing direction flow paths.
[0016] The two flow paths may be operable to direct the working CO2 vapour stream towards two normally closed tie-in pipes or hoses, which connect the pressurisation line to the affected pipe at a location on each side of the dry-ice blockage, thereby routing the first working CO2 vapour stream and the second working CO2 vapour stream to opposite sides of the dry-ice blockage simultaneously.
[0017] The normally closed tie-in pipes or hoses may be opened manually or automatically in the event of a dry-ice blockage being detected in a pipeline.
[0018] The method may further comprise monitoring pressure upstream and downstream of the dryice blockage.
[0019] Monitoring pressure may be done by one or more pressure gauges associated with points in the affected pipeline upstream and downstream of the dry-ice blockage.
[0020] Subsequent to heating the extracted CO2 vapour the warmed CO2 vapour stream may undergo one or more stages of compression to provide a pre-working CO2 vapour stream.
[0021] The pre-working CO2 vapour stream may be cooled to produce the working CO2 vapour stream.
[0022] The pre-working CO2 vapour stream may be cooled by a condenser. The condenser may be a liquid petroleum gas condenser. Therefore, the pre-working CO2 vapour stream may be cooled by a liquid petroleum gas condenser.
[0023] The pre-working CO2 vapour stream may be routed through a condensate accumulator to produce the working CO2 vapour streams.
[0024] The method may further comprise routing vapour from upstream and downstream of the dryice blockage from the affected pipe to the cargo tank. Tie-in pipes or hoses connecting the affected blocked pipe, and an adjacent unblocked pipe may facilitate routing the vapour from the affected pipe to the adjacent unblocked pipe, wherein the unblocked pipe routes the vapour to the cargo tank.
[0025] Condensate produced via the step of routing the pre-working CO2 vapour stream through a condensate accumulator may be routed to the cargo tank via the condensate line and a condensate connection at the cargo tank.
[0026] A further aspect of the invention provides a cargo handling system comprising a first tie-in pipe between a first point of a pressurisation line and a connection to a cargo tank containing liquefied CO2, where the connection directly links the cargo tank to a pipe at risk of containing a dry-ice blockage; and a second tie in pipe extending between a second point of the pressurisation line directly to or indirectly to the pipe at risk of containing a dry-ice blockage.
[0027] The second tie-in point may extend between the pressurisation line and a liquid manifold that serves the pipe at risk of containing a dry-ice blockage.
[0028] DRAWINGS
[0029] The present invention will now be further described in detail and with reference to the following figures:
[0030] Fig. 1 is a diagram of an example of a liquefied gas carrier containing three cargo tanks, wherein at least one of the cargo tanks is configured to contain liquefied CO2;
[0031] Fig. 2 is a diagram summarising the main facilities within a liquefied gas carrier;
[0032] Fig. 3 shows a schematic diagram of an example CO2 handling equipment on the liquefied gas carrier of Fig. 2, the handling equipment includes three cargo tanks, which includes at least one tank for liquefied CO2, associated pipework and ancillary equipment operable to maintain the CO2 cargo in a liquefied state; Fig. 4 shows the schematic diagram of Fig. 3, annotated to include a dry-ice blockage in a liquid line and is annotated to show an example of how the dry-ice blockage can be removed with CO2 vapour;
[0033] Fig. 5 shows the schematic diagram of Fig. 3, annotated to include a dry-ice blockage in a stripping line and is annotated to show an example of how the dry-ice blockage can be removed with CO2 vapour;
[0034] Fig. 6 shows the schematic diagram of Fig. 3, annotated to include a dry-ice blockage in a condensate line and is annotated to show an example of how the dry-ice blockage can be removed with CO2 vapour;
[0035] Fig. 7 shows the schematic diagram of Fig. 3, annotated to include a dry-ice blockage in the liquid line utilising a cargo compressor to create an unblocking flow;
[0036] Fig. 8 represents the arrangement of Fig. 7 with the addition of recirculation of LCO2 to the cargo tank; and
[0037] Fig. 9 shows the schematic diagram of Fig. 7 with the addition of a condensate from the condensation stage being routed to the cargo tank.
[0038] DETAILED DESCRIPTION
[0039] Fig. 1 shows an example of a liquefied gas carrier 2 incorporating a reliquefaction plant (see Fig. 2 to 7) and three cargo tanks 6A, 6B, 6C.
[0040] In this example one of the cargo tanks 6C is configured to transport liquefied carbon dioxide (LCO2) at low pressure and low temperature as discussed further below. It will be appreciated that any or all three tanks 6A, 6B, 6C could be configured to transport LCO2.
[0041] Fig. 2 is a diagram summarising the main facilities within and onboard the liquefied gas carrier
[0042] 2 illustrated in Fig. 1. The facilities relevant to the present invention are the Cargo Handling System (CHS) 8 and the Cargo Ancillary System (CAS) 10. In this example, the illustrated CHS 8 includes, three cargo tanks 6A, 6B, 6C located in the hull of the liquefied gas carrier 2 (see Fig. 1).
[0043] The illustrated CHS 8 represents a system for a liquefied gas carrier 2 configured to carry liquid petroleum gas (LPG), e.g., Ammonia, Butane, Propane I Butane mixtures, Propane, Propylene and Vinyl chloride monomer etc, and LCO2. In the following, the description is concerned only with handling LCO2.
[0044] The CHS 8 comprises vapour and liquid handling stages i.e., compression, condensation, refrigeration, heating / vaporisation, loading and offloading. From the illustrated CAS 10 a Glycol / freshwater unit 4 is utilised with the CHS 8 as described further below.
[0045] Fig. 3 shows a schematic diagram of the cargo handling system and the cargo tanks 6A, 6B, 6C. The cargo handling system includes a network of pipes and associated ancillary equipment. The network of pipes includes a liquid manifold 13, that serves a liquid system / liquid line 12 and a stripping line 14. The liquid line 12 and the stripping line 14 serve the cargo tank 6C.
[0046] The network of pipes also includes a vapour manifold 15 that serves a vapour line 16.
[0047] In this example, the liquid and vapour manifolds 13, 15 and associated lines facilitate loading liquefied CO2 into the cargo tank 6C and discharge from the cargo tank 6C. It will be appreciated that the liquid and vapour manifolds 13, 15 and associated lines facilitate loading liquefied CO2 or other liquefied cargoes to all tanks 6A, 6B, 6C.
[0048] Other pipelines forming part of the cargo handling system include condensate lines 18, pressurisation line 19 etc.
[0049] In the illustrated example, components of the cargo handling system 8 which includes the reliquefaction plant, include a refrigeration skid 20, a reliquefaction skid 21 , a compressor skid 22 and a CO2 vaporiser system 24. These components, the associated pipework and ancillary equipment i.e., valves, pressure control valves, temperature gauges, pressure gauges etc., facilitate the various operational stages e.g., loading, unloading, compression, condensation, heating, vaporising, monitoring etc, of the cargo handling system 8. The reliquefaction process described further below maintains the CO2 in the liquid phase in the cargo tank 6C.
[0050] The process of loading the cargo tank 6C with liquid CO2 involves a multi-stage process and then an ongoing reliquefaction process to maintain the CO2 contained in the cargo tank 6C at the correct pressure / temperature.
[0051] Before loading the cargo tank 6C with liquid CCh the cargo tank 6C is primed. The process, known as gassing-up, adds CO2 vapour to the cargo tank 6C before adding the LCO2 cargo to the cargo tank 6C.
[0052] In the gassing-up process, CO2 vapour is added to the cargo tank6C through the liquid loading line 12. The CO2 vapour can be sourced as direct vapour from shore or liquid which is vaporised, using the onboard CO2 vaporiser system 24. The CO2 vapour is fed to the cargo tank 6C via the liquid manifold 13 and the liquid loading lines 12.
[0053] A vapour outlet connection 30 at the top of the cargo tank 6C facilitates displacement of air / nitrogen through the vapour line 16 during gassing-up. The vapour outlet connection 30 also facilitates release of CO2 vapour as boil off gas from the loaded cargo tank 6C during transportation to maintain the liquefied CO2 cargo in a liquid state.
[0054] In preparation for loading the cargo tank 6C with liquid CO2, after gassing-up, the cargo tank 6C is pressurised to above the triple point pressure.
[0055] The pipework serving the cargo tank 6C is similarly prepared with CO2 vapour and is pressurised before LCO2 is introduced to the system.
[0056] A final step of preparing the cargo tank 6C for LCO2, is where after pressurising the cargo tank 6C the cargo tank 6C is cooled to prevent excessive thermal stresses and to reduce the rate of flash vapour generation. Cooling is done by adding liquid CO2 to the cargo tank 6C e.g., via the stripping lines 14 and a condensate connection 31 at the cargo tank 6C. The addition of liquid CO2 displaces the CO2 vapour to the reliquefaction system 21 . The displaced CO2 vapour is reliquefied and fed back to the cargo tank 6C as liquid CCh via the condensate line 18.
[0057] After conditioning the cargo tank 6C as described above, formal loading can commence.
[0058] Loading is the process of adding additional liquid CO2 to a prescribed level, which is less than 100% e.g. 90 to 98% of capacity in the cargo tank 6C.
[0059] The cargo tank 6C is loaded via the liquid manifold 13 and the liquid loading lines 12.
[0060] As described above with regard to the cooling step, CO2 vapour produced from the tank 6C during loading undergoes reliquefaction 21 and is fed back to the cargo tank 6C as liquid CO2 via the condensate line 18, to maintain optimal tank conditions during the loading process.
[0061] The cargo tank 6C includes connections that facilitate loading and unloading the liquid CO2 into and from the tank 6C. Due to the reliquefaction plant and the cargo tank 6C being configured to transport liquefied CO2 it will be appreciated that during loading, unloading and transportation CO2 will be present in the tank 6C in liquid and in vapour form and that pressure within the tank 6C will fluctuate.
[0062] To avoid significant pressure changes within the tank 6C, the vapour outlet connection 30 is used to remove boil of gas (BOG) from the cargo tank 6C to prevent pressure increase during loading and transportation. The vapour outlet connection 30 can also be used to add CO2 gas to the tank 6C during unloading to prevent a significant pressure drop and to prevent deposition of the CO2 in the tank during unloading.
[0063] The liquefied CO2 cargo may be high purity CO2 (as used in the food and beverage industries), but most likely will be a composition of CO2 and other components e.g. water (H2O), Nitrogen (N2), Oxygen (O2) etc. i.e. , CO2 rich gas (for example >95 mol% of CO2). In this regard, the liquefied cargo CO2 may include captured CO2, e.g., from various emitters, for environmental reasons.
[0064] The composition of the CCh rich gas will be dependent on the source of the gas e.g., captured gas. Examples of CO2 rich gas specifications are provided in table 1 below.
[0065] Table 1 *ppm - parts per million by mol
[0066] As noted above, the illustrated system is designed to liquefy and transport CO2 rich gas at low pressure and low temperature, which is considered to be the optimum way to transport large quantities of CO2. In this example, large means a quantity in excess of 20,000 m3.
[0067] As noted above, a decrease in pressure in the cargo tank 6C during loading and unloading can result in solidification of CO2 within the tank. This is a concern for liquefied CO2 at low- pressure levels because there is a lower margin to the triple point, which increases the risk of the formation of dry-ice (solid CO2). The transportation condition of the cargo tank 6C, and the system described and illustrated above, is low pressure and low temperature at which CO2 is in liquid / liquefied form. The low pressure being around 6 to 7 barg and the low temperature of around -50°C.
[0068] It was noted above that a drop in pressure in the tank 6C during loading and unloading can cause dry-ice formation within the tanks.
[0069] As described above in respect of loading, maintaining and unloading the tank 6C, it will be appreciated that the liquid lines 12, stripping lines 14, and condensate lines 18 in the cargo handling system, are all configured to carry CO2 in vapour or liquid form. A low pressure and low temperature combination maintains the CO2 in liquid form. A reduction in pressure within these lines or associated equipment could result in dry-ice formation, which could be hazardous and affect functionality of the liquefied gas carrier 2.
[0070] In Figs. 4 to 7, the system illustrated in Fig.3 is adapted to allow removal of a dry-ice blockage within an affected pipe.
[0071] The process adopted is creating a working CO2 vapour stream and routing the working CO2 vapour stream through the affected pipe towards the dry-ice blockage such that the dry-ice blockage is melted (to liquid) or sublimed (to vapour) due to contact between the dry-ice blockage and the warmer working CO2 vapour stream.
[0072] The adaptation of the system 8 includes adding, permanently or temporarily additional tie-in pipe or hose connections and ancillary equipment e.g., valves, pressure gauges, temperature gauges etc. to facilitate routing a working CO2 vapour stream towards a dry-ice blockage in an affected pipe.
[0073] Fig. 4 to 7 each represent separate situations, where dry-ice has formed in a section of the pipework, and each illustrate the creation of a working CO2 vapour stream that can be used to clear the dry-ice blockage. It is expected that the formed CO2 solid will be at an approximate temperature of -78°C. In each of the examples, the dry-ice blockage blocks flow in the system through the affected section of pipework.
[0074] A dry-ice blockage 32 may be identified by a change in pressure or temperature (as noted above) in the system causing alarms and automatic shutdowns to take effect. At which time the dry-ice blockage 32 needs to be removed to restore normal operation.
[0075] In the illustrated system 8, the pipelines prone to blockage are the liquid line 12, the stripping line 14 and the condensate line 18.
[0076] Fig.4 represents a dry-ice blockage 32 in the liquid line 12.
[0077] Fig. 5 represents a dry-ice blockage 32 in the stripping line 14.
[0078] Fig. 6 represents a dry-ice blockage 32 in the condensate line 18.
[0079] In each of these examples the location of the dry-ice blockage 32 is indicated by a black oval overlaying the affected line in the figure representing the affected line.
[0080] Common to each of the examples illustrated in Fig. 4 to 6, CO2 vapour is extracted from the cargo tank 6C through the vapour outlet connection 30 from the liquefied CO2 cargo tank 6C.
[0081] The extracted vapour is routed (see black line and white arrows) to a suction heater 40 where the vapour is warmed against the freshwater / glycol heat exchanger.
[0082] The extracted vapour is warmed to produce a warmed CO2 vapour stream, at a predetermined temperature e.g. +20°C. The maximum temperature of the warmed CO2 vapour stream being driven by the glycol setpoint temperature, which is a max of +35°C.
[0083] In the examples illustrated in Fig. 4 to Fig. 6, the warmed CO2 vapour stream is routed to a hot gas line 42 via a first tie-in pipe or hose 44 and associated valves etc. As noted above, tie-in pipes or hoses are added to the system illustrated in Fig. 3 to facilitate transporting a working CO2 vapour stream towards the dry-ice blockage 32. In this example, the first tie-in pipe or hose 44 extends from the suction heater 40 to the hot gas line 42.
[0084] The warmed CO2 vapour stream is routed along the hot gas line 42, via existing pipework to a junction 46 with the pressurisation line 19.
[0085] In the pressurisation line 19, the warmed CO2 vapour stream is divided into first and second working CO2 vapour streams where each working CO2 vapour stream is routed along one of two flow paths 48, 50. The working CO2 vapour streams being those that flow towards the dry-ice blockage in the affected pipe.
[0086] Each flow path 48, 50 (indicated by black and grey arrows) routes the working CO2 vapour streams in opposing directions along the pressurisation line 19. The first flow path 48 (grey arrows) directs the first working CO2 vapour stream towards the cargo tank 6C and the second flow path 50 (black arrows) directs the second working CO2 vapour stream towards the CO2 liquid manifold 13.
[0087] The first and second flow paths 48, 50 facilitate routing the first and second working CO2 vapour streams towards the dry-ice blockage from opposite sides (i.e. , from both an upstream and downstream direction) in the affected pipe.
[0088] Routing the working CO2 vapour streams directly towards the dry-ice blockage is further facilitated by the addition of two further tie-in pipe or hoses (a second tie-in pipe or hose 52 and a third tie in pipe 54).
[0089] The second tie-in pipe or hose 52 extends between the pressurisation line 19 and a connection at the cargo tank 6C, where the connection at the cargo tank 6C directly links the cargo tank 6C to the affected pipe.
[0090] Connection of the second tie-in pipe or hose 52 is described further below with reference to the specific affected pipe as illustrated by Fig. 4 to Fig. 6. Connection of the third tie-in pipe or hose 54 is between the pressurisation pipe 19 and the affected pipe directly or indirectly as described further below with regard to Fig. 4 to 6.
[0091] In the examples illustrated in Fig. 4 to 6, the second and third tie-in pipes or hoses 52, 54 ensure the working CO2 vapour streams are routed simultaneously towards the dry-ice blockage 32 from two directions.
[0092] The process of creating the warmed CO2 vapour stream and the working CO2 vapour streams, as described above, is common to the examples illustrated in Figs. 4, 5 and 6. The differences between each of the illustrated examples is the pipe in which the dry-ice blockage 32 is located and the source and destination of the second and third tie-in pipes or hoses 52, 54.
[0093] In these examples, the working CO2 vapour stream may undergo compression in the pressurisation pipe and in the affected pipe thereby further increasing the temperature of the working CO2 vapour streams as they are directed towards the upstream and downstream side of the dry-ice blockage 32.
[0094] The configuration of the system is such that during normal operation the pressure in the pipes 12, 14, 18 will be lower (approximately ambient) than the pressure in the cargo tank 6C (approximately 6 barg) during normal operation. However, in the event of a dry-ice blockage 32 occurring and routing the working CO2 vapour streams into the affected pipe 12, 14, 18, pressure within the affected pipe 12, 14, 18 will increase and equalise out at tank pressure. As this is above the triple point, the working CO2 vapour streams assist in removing the dryice blockage 32 from two sides.
[0095] To assist the flow of the working CO2 vapour streams in the affected pipe any associated pressure control valves will be set to open. The system is configured such that the working CO2 vapour streams supplying CO2 vapour to the dry-ice blockage will be at a pressure above the triple point.
[0096] Fig. 4 represents the system of Fig. 3, experiencing a dry-ice blockage in the liquid line 12. To remove the dry-ice blockage 32 from the liquid line 12, the second tie-in pipe or hose 52 is connected between the pressurisation line 19 and a connection 56 at the cargo tank 6C (the connection is a valve / pipe that connects the cargo tank 6C directly to the liquid line 12 during normal operation. This second tie in pipe or hose 52 routes the working CO2 vapour stream along the liquid line 12 towards the dry-ice blockage 32, as illustrated by the grey arrows pointing in a direction from the right.
[0097] In Fig. 4, the third tie-in pipe or hose 54 extends between the pressurisation line 19 and the CO2 liquid manifold 13 such that the working CO2 vapour stream is routed via an existing connection of the liquid line 12 and the CO2 liquid manifold 13 towards the dry-ice blockage 32, as illustrated by the black arrows pointing in a direction from the left.
[0098] Fig. 5 represents the system of Fig. 3, experiencing a dry-ice blockage in the stripping line 14.
[0099] To remove the dry-ice blockage 32 from the stripping line 14, the second tie-in pipe or hose 52 is connected between the pressurisation line 19 and a connection 56 at the cargo tank 6C (the connection is a valve / pipe that connects the cargo tank 6C directly to the stripping line 12 during normal operation). This second tie in pipe or hose 52 routes the working CO2 vapour stream along the stripping line 14 towards the dry-ice blockage 32, as illustrated by the grey arrows pointing in a direction from the right.
[0100] In Fig. 5, the third tie-in pipe or hose 54 extends between the pressurisation line 19 and the CO2 liquid manifold 13 such that the working CO2 vapour stream is routed via an existing connection of the stripping line 14 and the CO2 liquid manifold 13 towards the dry-ice blockage 32, as illustrated by the black arrows pointing in a direction from the left.
[0101] Fig. 6 represents the system of Fig. 3, experiencing a dry-ice blockage in the condensate line 18.
[0102] To remove the dry-ice blockage 32 from the condensate line 18, the second tie-in pipe or hose 52 is connected between the pressurisation line 19 and a connection 56 at the cargo tank 6C (the connection is a valve / pipe that connects the cargo tank 6C directly to the condensate line 18 during normal operation). This second tie in pipe or hose 52 routes the working CO2 vapour stream along the condensate line 18 towards the dry-ice blockage 32, as illustrated by the grey arrows pointing in a direction from the right.
[0103] In Fig. 6, the third tie-in pipe or hose 54 extends directly between the pressurisation line 19 and the condensate line 18. The working CO2 vapour stream is routed towards the second side of the dry-ice blockage 32, as illustrated by the black arrows pointing in a direction from the right.
[0104] In each of the examples illustrated in Fig. 4 to Fig. 6, the second and third tie-in pipes or hoses 52, 54 facilitate directing the working CO2 vapour stream towards the dry-ice blockage 32 from two directions.
[0105] By feeding the working CO2 vapour stream towards the dry-ice blockage 32 from two directions the speed at which the dry-ice blockage 32 is removed is expected to be quicker and safer than compared with feeding the working CO2 vapour stream towards the dry-ice blockage 32 from only one direction. The two-direction approach is considered safer because pressure on each side of the dry-ice blockage 32 is equalised and the risk of a dry-ice blockage being propelled along the pipe is reduced. This reduces the risk of damage to the pipe or any of the ancillary equipment.
[0106] Fig. 7 represents a further example of the system of Fig. 3, experiencing a dry-ice blockage 32 in the liquid line 12. This example differs from the one illustrated in Fig. 4 in that the working CO2 vapour stream is created differently. In this example the compressor skid 22 is utilised to create the working CO2 vapour stream.
[0107] In this example, CO2 vapour is extracted from the cargo tank 6C and is directed to the suction heater 40 where the extracted CO2 vapour is heated to create a warmed CO2 vapour stream.
[0108] The warmed CO2 vapour stream then passes to the compression skid 22, where the warmed CO2 vapour stream undergoes one or more compression stages 60 to compress the warmed CO2 vapour stream, thereby creating a pre-working CO2 vapour stream. At this stage of the process, the temperature and pressure of the pre-working CO2 vapour stream are above the triple point.
[0109] To manage the temperature of the compressed pre-working CO2 vapour stream, before it reaches the blocked pipe, the pre-working CO2 vapour stream is routed through existing pipework from the final compression stage 60 into the reliquefaction skid 21 where the preworking CO2 vapour stream is cooled by a condenser e.g., a liquid petroleum gas (LPG) condenser 62. Cooling produces the working CO2 vapour stream, which is routed to the hot gas line 42 via a condensate accumulator 63.
[0110] As described above with reference to Fig. 4 to 6, the working CO2 vapour stream is routed along the hot gas line 42 via existing pipework to a T-junction with the pressurisation line 19.
[0111] In the pressurisation line 19, the working CO2 vapour stream 46 is divided into two flow paths 48, 50, i.e., first and second working CO2 vapour streams each flow path routing the working CO2 vapour streams in opposing directions along the pressurisation line 19.
[0112] The first flow path 48 directs the first working CO2 vapour stream towards the cargo tank 6C and the second flow path directs the second working CO2 vapour stream towards the CO2 liquid manifold 13.
[0113] The first and second flow paths 48, 50 facilitate routing the working CO2 vapour streams towards the dry-ice blockage 32 from opposite sides (i.e., from both an upstream and downstream direction) in the affected pipe.
[0114] Routing the working CO2 vapour stream directly towards the dry-ice blockage 32 is further facilitated by the addition of two tie-in pipes or hoses.
[0115] In this example, to remove the dry-ice blockage 32 from the liquid line 12, a tie-in pipe or hose 52 is connected between the pressurisation line 19 and a connection 56 at the cargo tank 60 (the connection is a valve / pipe that connects the cargo tank 60 directly to the liquid line 12 during normal operation). This tie in pipe 52 routes the working CO2 vapour stream along the liquid line 12 towards the dry-ice blockage 32, as illustrated by the grey arrows pointing in a direction from the right.
[0116] In Fig. 7, a further tie-in pipe or hose 54 extends between the pressurisation line 19 and the CO2 liquid manifold 13 such that the working CO2 vapour stream is routed via an existing connection of the liquid line 12 and the CO2 liquid manifold 13 towards the dry-ice blockage 32, as illustrated by the black arrows pointing in a direction from the left.
[0117] Regarding Fig. 7 and with further reference to Fig. 5 and 6, it will be appreciated that the process to create a working CO2 vapour stream using the compressor skid 22 can similarly be applied to dry-ice blockages 32 in the stripping lines 14 and condensate line 18 as indicated in Fig. 5 and 6.
[0118] The routing of the working CO2 vapour stream from the pressurisation line 19 will include two tie-in pipes or hoses 52, 54 and associated components to route the working CO2 vapour stream in two directions towards the dry-ice blockage 32. For a dry-ice blockage in the stripping line 14 and a dry-ice blockage in the condensate line 18, the configuration of the tie- in pipes or hoses 52, 54 and routing the working CO2 vapour streams are described above with reference to Fig. 5 and 6 respectively.
[0119] It will be appreciated that normal flow through the reliquefaction plant / pipework is unidirectional. However, as described above the system can be adapted in a manner that does not affect normal operation, but the adaptation can be utilised to create and route working CO2 vapour streams simultaneously from opposite sides of and towards a dry-ice blockage such that normal operation can be resumed quickly and safely.
[0120] Fig. 8 represents the system of Fig. 7, but with the addition of additional tie-ins 70, 72 between the blocked pipe e.g., the liquid line 12 and a neighbouring pipe e.g., the stripping line 14. These tie-ins 70, 72 may include flexible hose, valves etc. and they are configured to facilitate recirculation of condensate / liquefied CO2 back to the cargo tank 6C. It will be appreciated that a similar arrangement can be applied, where tie-ins are provided between the affected pipe is the stripping line 14 or the condensate line 18.
[0121] The location of the tie-ins will be variable depending on where the dry-ice blockage 32 is identified to minimise the effect of dead legs between the tie-in location and the dry-ice blockage 32. Sensors attached to and monitoring conditions of the affected pipe 12 may be useful in identifying the location of the dry-ice blockage 32.
[0122] As noted above, with reference to Fig. 7 to manage the temperature of the compressed preworking CO2 vapour stream, before it reaches the blocked pipe, the pre-working CO2 vapour stream is routed through existing pipework from the final compression stage 60 into the reliquefaction skid 21 where the pre-working CO2 vapour stream is cooled by a condenser e.g., a liquid petroleum gas (LPG) condenser 62. Cooling produces the working CO2 vapour stream, which is routed to the hot gas line 42 via the condensate accumulator 63. It will be appreciated that cooling the CO2 vapour may also generate condensate which settles at the bottom of the accumulator 63. Fig. 9 represents the system of Fig. 7, including utilising the condensate accumulator 63 and existing condensate lines 18 to return CO2 condensate back to the cargo tank 6C via the condensate connection 31 . The flow path of the condensate from the condensate accumulator 63 to the cargo tank 60 is indicated by the grey-filled arrows. Fig.9 includes a partial flow path of the CO2 vapour, indicated by white filled arrows; the complete CO2 vapour flow path is shown in Fig. 7 and described above.
[0123] Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention.
Claims
CLAIMS1. A method of removing a dry-ice (solid CO2) blockage, which is affecting flow through one or more pipelines in a liquified gas carrier having one or more liquefied CO2 cargo tanks, the method comprising at least the steps of: extracting CO2 vapour from a liquefied CO2 source; heating the CO2 vapour to provide a warmer CO2 vapour stream; creating two working CO2 vapour streams and routing each working CO2 vapour stream through the affected pipeline towards the dry-ice blockage simultaneously from both an upstream and downstream direction towards the solid CCh to remove the dry-ice blockage.
2. The method as claimed in claim 1 , wherein the step of routing the working CO2 vapour streams into the affected pipeline compresses the working CO2 vapour streams thereby increasing pressure and temperature of the working CO2 vapour streams flowing toward the dry-ice blockage.
3. The method as claimed in claim 1 or 2, wherein the step of extracting CO2 vapour extracts CO2 vapour from a cargo tank containing liquid CO2.
4. The method as claimed in claim 1 or 2, wherein the step of extracting CO2 vapour extracts CO2 vapour from a deck tank or a pressure vessel containing liquid CO2.
5. The method as claimed in any preceding claim, comprising routing the extracted CO2 vapour to a heating source, wherein the extracted CO2 vapour is heated to thereby producing the warmer CO2 stream.
6. The method as claimed in claim 5, wherein the extracted CO2 vapour is warmed against a heat exchanger to produce the warmed CO2 vapour stream.
7. The method as claimed in claim 5, wherein the extracted CO2 is heated via a suction heater where the vapour is warmed against a heat exchanger to produce the warmed CO2 vapour stream.
8. The method as claimed in any preceding claim, further comprising routing the warmed CO2 vapour stream to a pressurisation line, wherein the pressurisation line facilitates creating a first and a second working CO2 vapour stream, which are routed to two opposing direction flow paths.
9. The method as claimed in 8, wherein the two flow paths are operable to direct the working CO2 vapour stream towards two normally closed tie-in pipes, which connect the pressurisation line to the affected pipe at a location on each side of the dry-ice blockage, thereby routing the first working CO2 vapour stream and the second working CO2 vapour stream to opposite sides of the dry-ice blockage simultaneously.
10. The method as claimed in claim 9, wherein the normally closed tie-in pipes are opened manually or automatically in the event of a dry-ice blockage being detected in a pipeline.11 . The method as claimed in any preceding claim, further comprising monitoring pressure upstream and downstream of the dry-ice blockage.
12. The method as claimed in claim 11 , wherein monitoring pressure is done by one or more pressure gauges associated with points in the affected pipeline upstream and downstream of the dry-ice blockage.
13. A method as claimed in any preceding claim, wherein subsequent to heating the extracted CO2 vapour the warmed CO2 vapour stream undergoes one or more stages of compression to provide a pre-working CO2 vapour stream.
14. A method as claimed in claim 13, wherein the pre-working CO2 vapour stream is cooled to produce the working CO2 vapour stream.
15. A method as claimed in claim 14, wherein the pre-working CO2 vapour stream is cooled by a condenser.
16. A method as claimed in claim 14 or claim 15, wherein the pre-working CO2 vapour stream is cooled by a liquid petroleum gas condenser.
17. A method as claimed in claim 14, 15 or 16, wherein the pre-working CO2 vapour stream is routed through a condensate accumulator to produce the working CO2 vapour streams.
18. A method as claimed in claim 17, further comprising routing vapour from the affected pipe to an adjacent unblocked pipe, via tie-in pipes routed between the affected blocked pipe and an adjacent unblocked pipe and routing the vapour to the cargo tank via the unblocked Pipe.
19. A method as claimed in any of claims 17, further comprising routing condensate from the condensate accumulator to the cargo tank.
20. A method as claimed in claim 19, wherein condensate produced via the step routing the pre-working CO2 vapour stream through a condensate accumulator is routed to the cargo tank via the condensate line and the condensate connection at the tank.21 . A cargo handling system comprising a first tie-in pipe between a first point of a pressurisation line and a connection to a cargo tank containing liquefied CO2, where the connection directly links the cargo tank to a pipe at risk of containing a dry-ice blockage; and a second tie in pipe extending between a second point of the pressurisation line directly to or indirectly to the pipe at risk of containing a dry-ice blockage.
22. The cargo handling system of claim 21 , wherein the second tie-in point extends between the pressurisation line and a liquid manifold that serves the pipe at risk of containing a dry-ice blockage.