Carbon dioxide reliquefaction system for FSIU

Abstract

A carbon dioxide reliquefaction system for an FSIU is provided with a CO2 liquid cargo tank, the CO2 liquid cargo tank is connected with a refrigerant economizer through a pipeline, after an outlet of the refrigerant economizer is sequentially connected with a liquid cargo condenser, a liquid cargo receiver and the liquid cargo economizer, the top of the liquid cargo economizer conveys CO2 back to a CO2 compressor through a pipeline, and a circulation pipeline is formed. The bottom of the liquid cargo economizer conveys the CO2 liquid cargo back to the CO2 liquid cargo tank through a pipeline; and a gas phase pipeline is arranged at the top of the CO2 liquid cargo tank, and the CO2 liquid cargo tank is connected with the buffer tank and a filling station on the FSIU through the gas phase pipeline. According to the method, the problem that the cabin pressure of the CO2 liquid cargo cabin is increased due to CO2 liquid cargo evaporation in the operation process of the FSIU liquid cargo system can be effectively solved, and the problems that in FSIU conventional operation, the cabin pressure is increased, and CO2 gas is discharged, so that environment pollution is caused, and the CO2 storage efficiency is reduced are solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of offshore ship design and construction, and particularly relates to a carbon dioxide reliquefaction system for FSIU. BACKGROUND

[0002] Carbon capture and storage (CCS) is increasingly recognized for its role in achieving carbon emission reduction, and is one of the key technologies for achieving low-cost net zero emissions. Floating carbon dioxide storage and injection unit (FSIU) is a new type of CO2 offshore receiving station, which has developed rapidly in recent years and has huge market potential. The liquid cargo system is a key system of FSIU, which should meet the functional requirements of loading, storing and unloading liquefied CO2.

[0003] A large amount of CO2 gas is generated in the CO2 storage tank of the FSIU liquid cargo system during operation. In the traditional FSIU process, the BOG generated in the storage tank is usually subjected to pressure build-up treatment, or the gas phase valve is opened to release the CO2 gas to the air when the pressure in the storage tank rises to a certain pressure. Although this method saves costs, on the one hand, it may cause the safety valve to trip due to improper control, which poses a certain safety hazard to the system operation and personnel; on the other hand, since the purpose of FSIU project is to store and inject CO2 into the seabed, if the CO2 gas generated in the storage tank during operation is discharged back to the atmosphere, it will reduce the efficiency of CO2 seabed storage in the CCS project and pollute the marine environment.

[0004] Therefore, it is necessary to develop a CO2 reliquefaction system suitable for use on FSIU, which can economically and efficiently recover and utilize the BOG gas generated in the storage tank. SUMMARY

[0005] To solve the above problems, the present application provides a carbon dioxide reliquefaction system for FSIU, which aims to reliquify and recycle the CO2 gas generated in the storage tank in the CO2 liquid cargo system process of FSIU, effectively maintain the tank pressure and improve the storage efficiency of CO2, and the technical scheme adopted is:

[0006] A carbon dioxide reliquefaction system for FSIU, comprising a CO2 liquid cargo tank, the CO2 liquid cargo tank is connected with a buffer tank, a CO2 compressor, a liquid cargo condenser, a refrigerant compressor, a refrigerant condenser, a refrigerant receiver and a refrigerant economizer through pipelines in sequence, the outlet of the refrigerant economizer is connected with the liquid cargo condenser, a liquid cargo receiver and a liquid cargo economizer in sequence, the top of the liquid cargo economizer is connected with the CO2 compressor through a pipeline to form a circulating pipeline, and the bottom of the liquid cargo economizer is connected with the CO2 liquid cargo tank through a pipeline.

[0007] The CO2 liquid cargo tank is provided with a gas phase pipeline on the top, and a gas phase pipeline valve is arranged on the gas phase pipeline, and the CO2 liquid cargo tank is connected with the buffer tank and the filling station on the FSIU through the gas phase pipeline.

[0008] The carbon dioxide reliquefaction system for the FSIU further utilizes seawater and refrigerant for heat exchange.

[0009] The carbon dioxide reliquefaction system for the FSIU further utilizes seawater and refrigerant for heat exchange.

[0010] The carbon dioxide reliquefaction system for the FSIU further utilizes seawater and refrigerant for heat exchange.

[0011] 1) The application can effectively solve the problem of the increase of the cabin pressure of the CO2 liquid cargo cabin caused by the evaporation of the CO2 liquid cargo during the operation of the FSIU liquid cargo system, and the cabin BOG is completely reliquefied by adopting the method of combining open liquid cargo circulation and closed refrigerant circulation, so that the BOG is reasonably recycled to maintain the cabin pressure and improve the safety and stability of the operation of the FSIU liquid cargo system.

[0012] 2) The application can avoid the environmental pollution and the reduction of the CO2 storage efficiency caused by the discharge of CO2 gas due to the increase of the cabin pressure during the normal operation of the FSIU by reasonably recycling the BOG gas, and the cabin is cooled by the backflow CO2 liquid cargo, thereby reducing the local stress of the CO2 storage cabin caused by the temperature difference during the loading and unloading process, and improving the economy and safety of the CO2 liquid cargo system during the operation.

[0013] 3) Compared with the traditional land conventional refrigeration cycle, the application adds a gas phase backflow pipeline on the top of the liquid cargo economizer in combination with the working characteristics and liquid cargo parameters of the FSIU offshore operation, so as to recycle the incomplete liquefied gas phase CO2 to improve the liquefaction efficiency. The state parameters of the gas on the top of the liquid cargo economizer are calculated by ASPEN HYSYS, and the feasibility and necessity of the secondary backflow and pressurization of the incomplete liquefied CO2 are verified. By recycling the incomplete liquefied CO2 gas, the working efficiency of the reliquefaction system can be improved while maintaining the stable pressure of the liquid cargo economizer. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The system schematic diagram of the application is shown in the figure;

[0015] Figure 2 The BOG reliquefaction system HYSYS software calculation is shown in the figure;

[0016] Among them, 01-CO2 liquid cargo tank; 02-buffer tank; 03-CO2 compressor; 04-liquid cargo condenser; 05-liquid cargo receiver; 06-liquid cargo economizer; 07-refrigerant compressor; 08-refrigerant condenser; 09-refrigerant receiver; 10-refrigerant economizer. Detailed Implementation

[0017] The invention will be further described with reference to the accompanying drawings. Example

[0018] like Figure 1 As shown, a CO2 reliquefaction system for an FSIU (Freestanding Integrated Tank Unit) involves a CO2 carrier delivering liquid CO2 to a CO2 cargo tank via a refueling station on the FSIU. The liquid CO2 is transported through pipeline 001 to pipeline 002, and then sprayed onto the tank via a spray pipe at the top of the CO2 cargo tank for cooling. During this process, a large amount of BOG (Boiled Air Gas) is generated in the CO2 cargo tank. The valve on the top vapor phase pipeline is opened, and the BOG flows back along vapor phase pipeline 003. The valve connecting the vapor phase pipeline to the refueling station is closed, and the valve on pipeline 004 is opened, allowing the BOG to be transported through pipeline 004 to a buffer tank for temperature, pressure, and flow buffering. The BOG is then transported along the buffer tank outlet pipeline to the CO2 compressor for initial pressurization. The pressurized BOG is then transported along the CO2 compressor outlet pipeline 005 to the cargo condenser, where it participates in the refrigeration cycle. The liquid refrigerant is liquefied through heat exchange. The resulting liquid CO2 is transported to the liquid cargo receiver via condenser outlet pipeline 006, and then to the liquid cargo economizer via pipeline 007 for throttling. The CO2 gas at the top of the economizer is transported back to the CO2 compressor via top gas phase pipe along pipeline 015 for secondary pressurization and recirculation. The liquid CO2 at the bottom of the economizer is transported back to the CO2 liquid cargo tank via bottom liquid phase pipeline 008, and merges with the liquid CO2 transported from the refueling station at pipeline 002. The liquid CO2 is then transported to the spray pipeline at the top of the liquid cargo tank for spray cooling of the tank. On the other hand, during the refrigerant cycle, the refrigerant is pressurized by the refrigerant compressor and then transported to the refrigerant condenser through outlet pipeline 011. After exchanging heat with seawater, the refrigerant liquefies. The liquefied refrigerant is then transported to the refrigerant receiver and the refrigerant economizer through pipelines 012 and 013. After that, it is transported to the liquid cargo condenser through the liquid phase outlet pipeline 009 of the refrigerant economizer. It exchanges heat with the gaseous CO2 from the CO2 compressor in the liquid cargo condenser and then vaporizes. The vaporized refrigerant is transported back to the refrigerant compressor along pipeline 010 and mixes with the gaseous refrigerant transported back by the gaseous pipeline 014 at the top of the refrigerant economizer. It then enters the refrigerant compressor and is pressurized repeatedly to form a closed cycle, continuously providing cold energy for the CO2 condensation cycle.

[0019] To verify the feasibility of this solution, the above process was built and data calculations were performed using ASPEN HYSYS V11. The process and key node calculation parameters in HYSYS are as follows: Figure 2 As shown.

[0020] Based on the design input of the 50,000 cubic meter FSIU research project upon which this invention is based, the BOG generated in the CO2 liquid cargo tank is... Figure 2 The temperature of the 004 unit is -30℃, the pressure is 820kPa, and the flow rate is 1000kg / h. Based on the actual working conditions, the parameters of each device in the circulation process are set. The software calculates that under these conditions, the temperature of the gaseous CO2 separated from the top of the liquid cargo economizer is -48.5℃, the pressure is 700kPa, and the flow rate is 72.28kg / h. Figure 2 As shown in the table, the flow rate is not zero, and the flow rate accounts for approximately 7.2% of the initial gaseous CO2. Therefore, the BOG generated by the storage tank during the operation of the FSIU liquid cargo system cannot be completely liquefied after the traditional open-loop reliquefaction process. This proves the feasibility of introducing a gas phase pipeline above the liquid cargo economizer in this scheme to return the incompletely liquefied gaseous CO2 for secondary compression.

Claims

1. A carbon dioxide reliquefaction system for FSIU, characterized in that, There is a CO2 liquid cargo tank. The CO2 liquid cargo tank is connected in sequence to a buffer tank, a CO2 compressor, a liquid cargo condenser, a refrigerant compressor, a refrigerant condenser, a refrigerant receiver, and a refrigerant economizer via pipelines. After the outlet of the refrigerant economizer is connected in sequence to the liquid cargo condenser, the liquid cargo receiver, and the liquid cargo economizer, the top of the liquid cargo economizer sends CO2 back to the CO2 compressor through pipelines to form a circulation pipeline. The bottom of the liquid cargo economizer sends CO2 liquid cargo back to the CO2 liquid cargo tank through pipelines. The CO2 liquid cargo tank is equipped with a vapor phase pipeline on the top, and a vapor phase pipeline valve is installed on the vapor phase pipeline. The CO2 liquid cargo tank is connected to the buffer tank and the filling station on the FSIU via the vapor phase pipeline.

2. The carbon dioxide reliquefaction system for FSIU according to claim 1, characterized in that, The refrigerant condenser uses seawater and refrigerant for heat exchange.

3. The carbon dioxide reliquefaction system for FSIU according to claim 1, characterized in that, The top of the CO2 cargo tank is equipped with a spray pipe. CO2 carriers deliver liquid CO2 to the CO2 cargo tank through the refueling station on the FSIU and connect it to the spray pipe to spray and cool the CO2 cargo tank.

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