A system and method for transfer of LNG from a cargo tank of an LNG carrier during a gas trial

Abstract

The application discloses a liquid cargo tank LNG unloading system for LNG ship gas test process, which comprises a liquid cargo main pipe, a liquid cargo branch pipe, a scavenging main pipe and a scavenging branch pipe, the liquid cargo main pipe is connected with the liquid cargo branch pipe, the scavenging main pipe is connected with the scavenging branch pipe, the liquid cargo branch pipe and the scavenging branch pipe are arranged in each LNG tank respectively, the liquid cargo branch pipes in each LNG tank are connected in parallel, the scavenging branch pipes in each LNG tank are connected in parallel, an injection pipe is further arranged in the LNG tank, the injection pipe is connected with the liquid cargo main pipe and the scavenging main pipe respectively, a liquid cargo pump is arranged at the bottom of the liquid cargo branch pipe, a scavenging pump is arranged at the bottom of the scavenging branch pipe, and valves are arranged on the liquid cargo branch pipe, the scavenging branch pipe and the injection pipe; and valves are arranged on the liquid cargo main pipe and the scavenging main pipe. The liquid cargo tank gas test and LNG pumping are simultaneously carried out, the problem of low efficiency of the scavenging pump when pumping LNG is avoided, the LNG pumping efficiency is improved, the liquid cargo tank gas test is completed, the gas test period is shortened, and the cost of the trial voyage is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of shipbuilding, and particularly relates to a liquid cargo tank LNG transfer system and method for LNG ship gas trial process. BACKGROUND

[0002] The gas trial stage is also one of the difficult stages in the overall construction process, and is also a stage in which a large amount of cost is spent in the entire shipbuilding stage.

[0003] The main purpose of the liquid cargo tank transfer stage is to test the performance of each pump in the LNG ship cargo tank. Generally, there are two liquid cargo pumps and one scavenging pump in the cargo tank. The liquid cargo pump is used to quickly transfer the LNG liquid in the cargo tank, so the starting liquid level (hereinafter referred to as the starting liquid level) is relatively high, but the transfer liquid speed is fast and the transfer time is short. The scavenging pump is used to remove the LNG liquid that cannot be transferred by other pumps in the tank, so the starting liquid level required is low, but the transfer liquid speed is slow and the transfer time is long. Before starting each pump, each pump needs to be completely immersed in LNG liquid for more than one and a half hours. Therefore, the starting liquid level is also referred to as the liquid level at which the pump is completely immersed (hereinafter referred to as the immersion liquid level). Therefore, the total time of the transfer process between the liquid cargo tanks includes the transfer time between each cargo tank and the immersion time before starting the pump.

[0004] The present application changes the previous transfer process and changes the idea. The present application does not need to completely transfer the liquid in one tank to another tank, but instead transfers the target tank to the immersion liquid level and then transfers the remaining liquid to the next target liquid level. That is, first transfer from tank 1 to tank 4, and then transfer the remaining liquid to tank 2 when tank 4 reaches the immersion liquid level. In this way, the immersion pump time and the pump test time can be overlapped with the time of transferring the remaining liquid to the next target tank, so as to reduce the transfer time increased due to the slow speed of the scavenging pump, thereby reducing the overall transfer time and improving the transfer quality. SUMMARY

[0005] The present application aims to overcome the deficiencies in the prior art and provide a liquid cargo tank LNG transfer system and method for LNG ship gas trial process. The present application simultaneously performs the gas trial test of the liquid cargo tank and the LNG pumping, avoids the low efficiency problem of the scavenging pump when pumping LNG, improves the LNG pumping efficiency, completes the gas trial test of the liquid cargo tank, shortens the gas trial period, and reduces the cost of the trial voyage.

[0006] In order to achieve the above-mentioned application purposes, the technical solutions provided by the present application patent are as follows:

[0007] A kind of liquid cargo tank LNG of LNG ship gas test process's transfer system, the system includes liquid cargo main pipe, liquid cargo branch pipe, scavenging main pipe and scavenging branch pipe, the liquid cargo main pipe is connected with liquid cargo branch pipe, the scavenging main pipe is connected with scavenging branch pipe, liquid cargo branch pipe and scavenging branch pipe are respectively arranged in LNG tank, the liquid cargo branch pipe in each LNG tank is parallelly connected, the scavenging branch pipe in each LNG tank is parallelly connected, injection pipe is also provided in the LNG tank, injection pipe is connected with liquid cargo main pipe and scavenging main pipe respectively, the bottom of the liquid cargo branch pipe is provided with liquid cargo pump, the bottom of the scavenging branch pipe is provided with scavenging pump, valve is arranged on the liquid cargo branch pipe, scavenging branch pipe and injection pipe;Valve is arranged on the liquid cargo main pipe and scavenging main pipe.

[0008] Further, when the injection pipe in the LNG tank is communicated with the scavenging main pipe, the injection pipe is parallelly connected with the scavenging branch pipe, and when the injection pipe in the LNG tank is communicated with the liquid cargo main pipe, the injection pipe is parallelly connected with the liquid cargo branch pipe.

[0009] A kind of liquid cargo tank LNG of LNG ship gas test process's transfer method, the method specifically includes the following steps:

[0010] S1, prepare a kind of liquid cargo tank LNG of LNG ship gas test process's transfer system, the system includes liquid cargo main pipe, liquid cargo branch pipe, scavenging main pipe and scavenging branch pipe, the liquid cargo main pipe is connected with liquid cargo branch pipe, the scavenging main pipe is connected with scavenging branch pipe, liquid cargo branch pipe and scavenging branch pipe are respectively arranged in LNG tank, the liquid cargo branch pipe in each LNG tank is parallelly connected, the scavenging branch pipe in each LNG tank is parallelly connected, injection pipe is also provided in the LNG tank, injection pipe is connected with liquid cargo main pipe and scavenging main pipe respectively, the bottom of the liquid cargo branch pipe is provided with liquid cargo pump, the bottom of the scavenging branch pipe is provided with scavenging pump, valve is arranged on the liquid cargo branch pipe, scavenging branch pipe and injection pipe;Valve is arranged on the liquid cargo main pipe and scavenging main pipe;

[0011] S2, pump into the LNG used for testing to first liquid cargo tank, when the LNG pumped in first liquid cargo tank completely submerges liquid cargo pump and scavenging pump in first liquid cargo tank, stop pumping LNG to first liquid cargo tank, start the gas test of first liquid cargo tank;

[0012] S3, when the gas test of first liquid cargo tank is completed, open the valve on the liquid cargo branch pipe in first liquid cargo tank, start the valve of liquid cargo main pipe, start the liquid cargo pump in first liquid cargo tank, LNG in first liquid cargo tank is injected into fourth liquid cargo tank through injection pipe in fourth liquid cargo tank by liquid cargo main pipe by liquid cargo pump;

[0013] S4, when the LNG in the fourth liquid cargo tank completely submerges the liquid cargo pump and the scavenging pump in the fourth liquid cargo tank, the valve on the injection pipe in the fourth liquid cargo tank is closed, the valve on the injection pipe in the second liquid cargo tank is opened, and the LNG in the first liquid cargo tank is pumped to the second liquid cargo tank by the liquid cargo pump and the scavenging pump; the fourth liquid cargo tank is subjected to a gas test;

[0014] S5, when the gas test of the fourth liquid cargo tank is completed, the liquid cargo pump in the fourth liquid cargo tank pumps the LNG to the second liquid cargo tank, when the LNG in the second liquid cargo tank completely submerges the liquid cargo pump and the scavenging pump in the second liquid cargo tank, the valve on the injection pipe in the second liquid cargo tank is closed, the valve on the injection pipe in the third liquid cargo tank is opened, and the LNG in the fourth liquid cargo tank is pumped to the second liquid cargo tank by the liquid cargo pump and the scavenging pump; the second liquid cargo tank is subjected to a gas test;

[0015] S6, when the gas test of the second liquid cargo tank is completed, the liquid cargo pump and the scavenging pump in the second liquid cargo tank pump all the LNG in the second liquid cargo tank to the third liquid cargo tank, when the LNG in the third liquid cargo tank completely submerges the liquid cargo pump and the scavenging pump in the third liquid cargo tank, the third liquid cargo tank is subjected to a gas test, and the gas test of all the liquid cargo tanks is completed.

[0016] Further, when the liquid cargo pump cannot pump the LNG in the liquid cargo tank to another liquid cargo tank during LNG pumping, the liquid cargo pump is closed, the scavenging pump is started, and the valve on the scavenging main pipe is opened, so that the LNG in the liquid cargo tank is completely pumped to another liquid cargo tank by the scavenging pump.

[0017] Further, after the gas test of the liquid cargo tank is completed, all the LNG is transported back to the shore station.

[0018] Based on the above technical solution, the LNG tank LNG unloading system and method for the gas test process of an LNG ship have the following technical advantages after practical application:

[0019] 1. The LNG tank LNG unloading method for the gas test process of an LNG ship simultaneously performs the gas test of the liquid cargo tank and LNG pumping, avoids the low efficiency problem of the scavenging pump during LNG pumping, improves the LNG pumping efficiency, completes the gas test of the liquid cargo tank, shortens the gas test period, and reduces the cost of the trial voyage.

[0020] 2. The LNG tank LNG unloading method for the gas test process of an LNG ship realizes the shortening of the unloading gas test and saves the gas test period and cost without changing the original unloading pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1It is a kind of structure diagram of transfer pipeline in the liquid cargo tank LNG transfer system for the gas test process of LNG ship. DETAILED DESCRIPTION

[0022] To make the objects, technical solutions and advantages of the present application clearer, the present application will be described below in detail with specific examples shown in the drawings. However, it should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present application.

[0023] As Figure 1 The present application belongs to a kind of liquid cargo tank LNG transfer system for the gas test process of LNG ship, which comprises a liquid cargo main pipe 31, a liquid cargo branch pipe 32, a scavenging main pipe 41 and a scavenging branch pipe 42, the liquid cargo main pipe 31 is connected with the liquid cargo branch pipe 32, the scavenging main pipe 41 is connected with the scavenging branch pipe 42, the liquid cargo branch pipe 32 and the scavenging branch pipe 42 are arranged in the LNG tank respectively, the liquid cargo branch pipe 32 in each LNG tank is connected in parallel, the scavenging branch pipe 42 in each LNG tank is connected in parallel, the LNG tank is also provided with an injection pipe 5, the injection pipe 5 is connected with the liquid cargo main pipe 31 and the scavenging main pipe 41 respectively, the bottom of the liquid cargo branch pipe 32 is provided with a liquid cargo pump 1, the bottom of the scavenging branch pipe 42 is provided with a scavenging pump 2, and the liquid cargo branch pipe 32, the scavenging branch pipe 42 and the injection pipe 5 are all provided with a valve 6; the liquid cargo main pipe 31 and the scavenging main pipe 41 are provided with a valve 6.

[0024] Further, when the injection pipe 5 in the LNG tank is communicated with the scavenging main pipe 41, the injection pipe 5 is connected in parallel with the scavenging branch pipe 42, and when the injection pipe 5 in the LNG tank is communicated with the liquid cargo main pipe 31, the injection pipe 5 is connected in parallel with the liquid cargo branch pipe 32.

[0025] A kind of liquid cargo tank LNG transfer method for the gas test process of LNG ship, which specifically comprises the following steps:

[0026] S1, prepare a LNG ship gas test process of LNG cargo tank unloading system, the system includes liquid cargo main pipe 31, liquid cargo branch pipe 32, scavenging main pipe 41 and scavenging branch pipe 42, the liquid cargo main pipe 31 is connected with liquid cargo branch pipe 32, the scavenging main pipe 41 is connected with scavenging branch pipe 42, liquid cargo branch pipe 32 and scavenging branch pipe 42 are respectively arranged in LNG tank, liquid cargo branch pipe 32 in each LNG tank is connected in parallel, scavenging branch pipe 42 in each LNG tank is connected in parallel, injection pipe 5 is further arranged in the LNG tank, injection pipe 5 is connected with liquid cargo main pipe 31 and scavenging main pipe 41 respectively, liquid cargo pump 1 is arranged at the bottom of liquid cargo branch pipe 32, scavenging pump 2 is arranged at the bottom of scavenging branch pipe 42, valve 6 is arranged on liquid cargo branch pipe 32, scavenging branch pipe 42 and injection pipe 5;Valve 6 is arranged on liquid cargo main pipe 31 and scavenging main pipe 41;

[0027] S2, pump 71 into the first liquid cargo tank LNG for test use, when the LNG pumped into the first liquid cargo tank completely immerses liquid cargo pump 1 and scavenging pump 2 in the first liquid cargo tank, stop pumping LNG into the first liquid cargo tank, start the gas test of the first liquid cargo tank;

[0028] S3, when the gas test of the first liquid cargo tank is completed, open the valve 6 on the liquid cargo branch pipe 32 in the first liquid cargo tank, start the valve 6 of liquid cargo main pipe 31, start liquid cargo pump 1 in the first liquid cargo tank, liquid cargo pump 1 injects LNG in the first liquid cargo tank into the fourth liquid cargo tank 74 through liquid cargo main pipe 31 through injection pipe 5 in the fourth liquid cargo tank 74;

[0029] S4, when the LNG in the fourth liquid cargo tank 74 completely immerses liquid cargo pump 1 and scavenging pump 2 in the fourth liquid cargo tank 74, close the valve 6 on the injection pipe 5 of the fourth liquid cargo tank 74, open the valve 6 on the injection pipe 5 in the second liquid cargo tank 72, LNG in the first liquid cargo tank is pumped into the second liquid cargo tank 72 by liquid cargo pump 1 and scavenging pump 2;The fourth liquid cargo tank 74 carries out gas test;

[0030] S5, when the gas test of the fourth liquid cargo tank 74 is completed, liquid cargo pump 1 in the fourth liquid cargo tank 74 pumps LNG into the second liquid cargo tank 72, when the LNG in the second liquid cargo tank 72 completely immerses liquid cargo pump 1 and scavenging pump 2 in the second liquid cargo tank 72, close the valve 6 on the injection pipe 5 in the second liquid cargo tank 72, open the valve 6 on the injection pipe 5 in the third liquid cargo tank 73, LNG in the fourth liquid cargo tank 74 is pumped into the second liquid cargo tank 72 by liquid cargo pump 1 and scavenging pump 2;The second liquid cargo tank 72 carries out gas test;

[0031] S6, when the second liquid cargo tank 72 gas test is completed, the second liquid cargo tank 72 in the liquid cargo pump 1 and the cleaning pump 2 will be pumped to the second liquid cargo tank 72 LNG in the third liquid cargo tank 73, when the LNG in the third liquid cargo tank 73 will be completely immersed in the third liquid cargo tank 73, the liquid cargo pump 1 and the cleaning pump 2 in the third liquid cargo tank 73, the third liquid cargo tank 73 is tested, and the gas test of all liquid cargo tanks is completed.

[0032] The liquid cargo pump 1 is pumped when the liquid cargo pump 1 cannot pump the LNG in the liquid cargo tank to another liquid cargo tank, the liquid cargo pump 1 is closed, the cleaning pump 2 is started and the valve 6 on the cleaning pump 2 is opened, and the LNG in the liquid cargo tank is pumped to another liquid cargo tank by the cleaning pump 2.

[0033] After the gas test of the liquid cargo tank is completed, the LNG is all shipped back to the shore station.

[0034] Embodiment

[0035] Step 1, taking a large LNG ship of 173 million cubic meters commonly used in China as an example, during the loading of LNG into the liquid cargo tank, because the capacity of the 1 tank is small, it can achieve the required liquid level of all pumps in the tank with less liquid, so the LNG is preferentially loaded into the 1 tank, and finally 300m 3 ;

[0036] Step 2, when the test of all pumps in the 1 tank is completed, the liquid is shipped to the 4 tank by the liquid cargo pump 1;

[0037] Step 3, when the liquid is shipped to the 4 tank by the liquid cargo pump 1 and reaches the specified liquid level of 1.94m, and the liquid level in the 1 tank is lower than 1m, start the cleaning pump 2, and ship the liquid shipped by the cleaning pump 2 to the 2 tank instead of continuing to ship to the 4 tank.

[0038] Step 4, in the same way, when the pump test of the 4 tank is completed, the liquid in the 4 tank is shipped to the 2 tank, and the excess liquid is shipped to the 3 tank;

[0039] Step 5. Finally, all the liquid in the 2 tank is shipped to the 3 tank.

[0040] Table 1 traditional liquid cargo tank gas test time

[0041]

[0042]

[0043] Table 2 liquid cargo tank gas test time of the embodiment

[0044] Project Time (h) 1st tank pump immersion 1.5 1st tank pump test 0.5 1st tank barge to 4th and 2nd tank 1 4th tank pump immersion 1.5 4th tank pump test 0.5 4th tank barge to 2nd and 3rd tank 1 2nd tank pump immersion 1.5 2nd tank pump test 0.5 2nd tank remaining barge to 3rd tank 1 3rd tank pump immersion 1.5 3rd tank pump test 0.5 3rd tank barge to gas station 1 Total 12

[0045] From table 1 and table 2, it can be seen that the trial method of the barge transportation air test according to the present application can reduce the time required by more than four hours compared with the traditional scheme, save the trial cost, and improve the trial efficiency.

[0046] It should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit the same; although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the specific embodiments of the present application can be modified or some technical features can be replaced by equivalent ones without departing from the spirit of the technical solutions of the present application, and all of them should be covered in the technical solution range of the present application claimed.

Claims

1. A method for transferring LNG from a liquid cargo tank during a gas test of an LNG ship, characterized in that: The method specifically comprises the following steps: S1. Prepare a LNG transfer system for a liquid cargo tank during a gas trial of an LNG ship, the system comprising a liquid cargo main pipe, a liquid cargo branch pipe, a tank stripping main pipe, and a tank stripping branch pipe. The liquid cargo main pipe is connected to the liquid cargo branch pipe, and the tank stripping main pipe is connected to the tank stripping branch pipe. Liquid cargo branch pipes and tank stripping branch pipes are respectively provided in the LNG tanks. The liquid cargo branch pipes in each LNG tank are connected in parallel, and the tank stripping branch pipes in each LNG tank are connected in parallel. The LNG tanks are further provided with injection pipes, which are respectively connected to the liquid cargo main pipe and the tank stripping main pipe. A liquid cargo pump is provided at the bottom of the liquid cargo branch pipe, and a tank stripping pump is provided at the bottom of the tank stripping branch pipe. Valves are provided on the liquid cargo branch pipe, the tank stripping branch pipe, and the injection pipe; and valves are provided on the liquid cargo main pipe and the tank stripping main pipe. S2, pumping LNG for test into the first cargo tank. When the LNG pumped into the first cargo tank completely submerges the cargo pump and stripping pump in the first cargo tank, stop pumping LNG into the first cargo tank and start the gas test of the first cargo tank. S3, after the gas test of the first liquid cargo tank is completed, the valve on the liquid cargo branch pipe in the first liquid cargo tank is opened, the valve of the liquid cargo main pipe is started, and the liquid cargo pump in the first liquid cargo tank is started. The liquid cargo pump injects the LNG in the first liquid cargo tank into the fourth liquid cargo tank through the liquid cargo main pipe and the injection pipe in the fourth liquid cargo tank; S4, when the LNG in the fourth cargo tank completely submerges the cargo pump and stripping pump in the fourth cargo tank, close the valve on the injection pipe in the fourth cargo tank, open the valve on the injection pipe in the second cargo tank, and pump the LNG in the first cargo tank to the second cargo tank through the cargo pump and stripping pump; and conduct a gas test on the fourth cargo tank; S5, after the gas test of the fourth cargo tank is completed, the cargo pump in the fourth cargo tank pumps LNG into the second cargo tank. When the LNG in the second cargo tank completely submerges the cargo pump and the stripping pump in the second cargo tank, the valve on the injection pipe in the second cargo tank is closed, and the valve on the injection pipe in the third cargo tank is opened. The LNG in the fourth cargo tank is pumped into the second cargo tank by the cargo pump and the stripping pump; the gas test of the second cargo tank is carried out; S6. After the gas test of the second cargo tank is completed, the cargo pump and stripping pump in the second cargo tank pump all the LNG in the second cargo tank to the third cargo tank. When the LNG in the third cargo tank completely immerses the cargo pump and stripping pump in the third cargo tank, the third cargo tank is gas tested to complete the gas test of all cargo tanks.

2. The method for transferring LNG from a liquid cargo tank during a gas test of an LNG ship according to claim 1, characterized in that: When the liquid cargo pump is pumping LNG, if the liquid cargo pump cannot pump the LNG in the liquid cargo tank to another liquid cargo tank, the liquid cargo pump is shut down, the stripping pump is started, and the valve on the stripping main pipe is opened, and all the LNG in the liquid cargo tank is pumped into another liquid cargo tank through the stripping pump.

3. The method for transferring LNG from a liquid cargo tank during a gas test of an LNG ship according to claim 1, characterized in that: After the gas test of the liquid cargo tank is completed, all the LNG is transported back to the shore station.

4. The method for transferring LNG from a liquid cargo tank during a gas test of an LNG ship according to claim 1, characterized in that: When the injection pipe in the LNG tank is connected to the stripping main pipe, the injection pipe and the stripping branch pipe are connected in parallel; when the injection pipe in the LNG tank is connected to the liquid cargo main pipe, the injection pipe and the liquid cargo branch pipe are connected in parallel.

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