An LNG and LPG storage tank system

Abstract

The utility model relates to a LNG and LPG storage tank system, including LPG storage tank and LNG storage tank, through main pipeline and the import connection of gasifier at LNG storage tank export, be equipped with valve V1 and the branch with valve V1 parallelly connected on main pipeline, set up valve V2 and a LNG heat exchanger on parallel branch, the outer wall of LPG storage tank is equipped with the jacketed heat exchanger, the import of jacketed heat exchanger is connected with the coolant outlet of LNG heat exchanger through coolant pump and valve V3, the coolant import of LNG heat exchanger is connected with the coolant storage tank of jacketed heat exchanger export. The utility model is based on the core logic of "LNG cold energy shunt recovery-coolant circulation heat exchange-temperature interlock regulation", under the prerequisite of not interfering LNG gasification station main body delivery and distribution function, utilize LNG cold energy to cool LPG storage tank outer surface, reduce LPG storage tank evaporation loss.

Description

Technical Field

[0001] This utility model relates to the field of energy-saving technology for oil and gas storage and transportation. Specifically, it relates to the coupling technology of cold energy recovery of liquefied natural gas (LNG) and evaporation loss control of liquefied petroleum gas (LPG) full-pressure storage tanks. It is particularly suitable for scenarios in urban gas hubs where LNG gasification stations and LPG storage and distribution stations are built together or located adjacent to each other. Background Technology In urban gas supply systems, LNG, as a clean, efficient, and low-carbon energy source, has become one of the core gas sources due to its flexible transportation and high storage density. LNG regasification stations, as the end-of-supply hub, undertake key functions such as LNG receiving, cryogenic storage, vaporization and reheating, and distribution. After flowing out of cryogenic storage tanks, liquid LNG needs to be vaporized by exchanging heat with the surrounding medium in a vaporizer, converting it into ambient-temperature gaseous natural gas (NG). It then undergoes pressure regulation, metering, and odorization processes before being sent to the city's pipeline network or supplied to end users. This vaporization process involves the release of a large amount of high-quality cold energy. Taking an LNG regasification station with a daily processing capacity of 100,000 Nm³ as an example, the recoverable cold power can reach up to 680 kW (equivalent to approximately 2.45 × 10⁻⁶ kW released per hour). 6 (kJ cold energy), but in existing projects, most of this cold energy is directly emitted into the environment through gasifiers, without being effectively recycled and utilized, resulting in significant energy waste and energy efficiency loss.

[0002] LPG full-pressure storage tanks are widely used in urban gas storage and distribution due to their compact structure and ease of operation. However, this method has inherent technical drawbacks. Ambient heat continuously penetrates the tank through tank wall radiation, atmospheric convection, and solar radiation, causing liquid LPG to absorb heat and vaporize, forming evaporative gas. When the pressure inside the tank rises to the safety valve's set value, the gaseous LPG must be forcibly released to ensure equipment safety, resulting in material loss. Industry data shows that the daily evaporation rate of conventional full-pressure storage tanks reaches 0.06% to 0.1%. Taking a 1000m³ LPG storage tank (LPG density 520kg / m³) as an example, the annual loss can reach more than 187 tons, resulting in direct economic losses. In addition, the released gaseous LPG also poses risks of combustion and explosion, as well as environmental hazards.

[0003] To address the aforementioned issues, this method utilizes the cold energy of LNG to cool the outer surface of the LPG storage tank, thereby reducing evaporation losses in the LPG storage tank. Utility Model Content

[0004] The problem to be solved by this invention is to provide an LNG and LPG storage tank system that can reduce evaporation losses in LPG storage tanks.

[0005] The technical solution provided by this utility model is: an LNG and LPG storage tank system, including an LPG storage tank and an LNG storage tank. The cryogenic liquid outlet of the LNG storage tank is connected to the inlet of the vaporizer through a main pipeline. The main pipeline is equipped with a valve V1 and a branch connected in parallel with valve V1. A valve V2 and an LNG heat exchanger are installed on the parallel branch. The outer wall of the LPG storage tank is equipped with a jacketed heat exchanger. The inlet of the jacketed heat exchanger is connected to the refrigerant outlet of the LNG heat exchanger through a refrigerant pump and valve V3. The outlet of the jacketed heat exchanger is connected to the refrigerant inlet of the LNG heat exchanger through a refrigerant storage tank.

[0006] This utility model also includes a PLC controller. The liquid phase zone of the LPG storage tank is equipped with a temperature sensor one, and a temperature sensor two is equipped on the branch line. Both valves V1 and V2 are electric valves. Temperature sensor one, temperature sensor two, valves V1 and V2 are electrically connected to the PLC controller.

[0007] This invention is based on the core logic of "LNG cold energy diversion and recovery - refrigerant circulation and heat exchange - temperature interlock control". Without interfering with the main transmission and distribution function of the LNG gasification station, it uses LNG cold energy to cool the outer surface of the LPG storage tank, thereby reducing the evaporation loss of the LPG storage tank. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the structure of this utility model. Detailed Implementation

[0009] See Figure 1 This utility model includes an LPG storage tank 5, an LNG storage tank 1, and a PLC controller 10. The cryogenic liquid outlet of the LNG storage tank 1 is connected to the inlet of a vaporizer 2 via a main pipeline. The main pipeline 2 is equipped with an electric valve V1 and a branch line connected in parallel with electric valve V1. The parallel branch line is equipped with an electric valve V2, a second temperature sensor 9, and an LNG heat exchanger 4. Switching between "conventional vaporization" and "cold energy recovery" modes is achieved by switching between electric valves V1 and V2. A temperature sensor 8 is installed in the liquid phase zone of the LPG storage tank. A jacketed heat exchanger 11 is installed on the outer wall of the LPG storage tank 5. The inlet of the jacketed heat exchanger 11 is connected to the refrigerant outlet of the LNG heat exchanger 4 via a refrigerant pump 7 and an electric valve V3. The outlet of the jacketed heat exchanger 11 is connected to the refrigerant inlet of the LNG heat exchanger 4 via a refrigerant storage tank 6. Temperature sensors 8 and 9, valves V1 and V2 are electrically connected to the PLC controller 10. The outlet of gasifier 2 is connected to the inlet of pressure regulating, metering and odorizing equipment 3. Natural gas is then transported to the city pipeline network after being regulated, metered and odorized by pressure regulating, metering and odorizing equipment 3.

[0010] This invention achieves precise transfer of cold energy to the LPG storage tank by adding a modular heat exchange and control unit. The specific technical solution is as follows:

[0011] Based on the existing processes of the LNG regasification station, three new key functional units have been added to work in synergy with existing equipment: LNG cold energy diversion unit: An LNG heat exchanger 4 is connected in parallel on the main pipeline from the cryogenic liquid outlet of the LNG storage tank to the vaporizer. The main pipeline is equipped with valve V1, and the parallel branch is equipped with valve V2. The switching between "conventional vaporization" and "cold energy recovery" modes is achieved by switching between V1 and V2. The refrigerant circulation unit includes a refrigerant storage tank 6, a refrigerant pump 7, and a jacketed heat exchanger 11 on the outer wall of the LPG storage tank. The jacketed heat exchanger is closely attached to the outer wall of the LPG storage tank, forming a closed loop of "LNG heat exchanger → jacketed heat exchanger → refrigerant storage tank". Temperature interlock control unit: A temperature sensor 8 is installed in the liquid phase zone of the LPG storage tank, and an outlet temperature sensor (9) is installed in the refrigerant circulation pipeline. Both are electrically connected to the PLC control system (10). The PLC automatically controls the switching status of V1 and V2 and the start and stop of the refrigerant pump by collecting the LPG temperature signal.

[0012] This method includes two operating modes: "cold energy recovery cooling mode" and "conventional gasification mode," which are automatically switched based on temperature thresholds. ① Cold energy recovery cooling mode (triggered when LPG temperature T≥25℃) Valve control: The PLC control system (10) receives the signal from the temperature sensor (8), automatically closes the main pipeline valve V1, and opens the parallel branch valve V2, so that the -162℃ liquid LNG flowing out of the LNG storage tank enters the LNG heat exchanger 4 first. Cold energy transfer: Liquid LNG exchanges heat with the refrigerant in the LNG heat exchanger - the refrigerant absorbs cold energy and cools down to -10℃~-5℃, and is sent into the jacketed heat exchanger (11) by the refrigerant pump 7; the refrigerant flows along the spiral guide plate close to the outer wall of the LPG storage tank, efficiently absorbing the ambient heat intruded into the tank wall, so that the LPG temperature in the tank gradually drops to the range of 15℃~25℃; the refrigerant that has been heated to 5℃~10℃ after heat exchange flows back to the refrigerant storage tank (6) to complete the cycle; LNG post-processing: After initial heat exchange in the LNG heat exchanger, the LNG is fed into the main process of the vaporizer from the parallel branch, where it undergoes secondary heat exchange with the ambient medium and is finally vaporized into ambient temperature gaseous natural gas (NG). After pressure regulation, metering, and odorization processes, it is sent to the city pipeline network.

[0013] ② Conventional gasification mode (triggered when LPG temperature T≤15℃) Valve reset: The PLC control system (10) receives the signal from the temperature sensor (8), automatically opens the main pipeline valve 1 (V1), closes the parallel branch valve 2 (V2), and the liquid LNG directly enters the vaporizer; System standby: The refrigerant pump (7) stops running, and the refrigerant in the jacketed heat exchanger remains static, with the help of the external insulation layer to reduce the loss of cold energy; if the LPG temperature rises to above 25°C, the system will automatically restart the cold energy recovery cooling mode.

[0014] ③ Safety Redundancy Control If the LNG heat exchanger malfunctions, valve 1 (V1) will automatically open and valve (V2) will automatically close, ensuring the normal transmission and distribution of LNG at the LNG regasification station and not affecting the town's gas supply.

Claims

1. An LNG and LPG storage tank system, characterized in that: It includes LPG storage tanks and LNG storage tanks; the cryogenic liquid outlet of the LNG storage tank is connected to the inlet of the vaporizer through a main pipeline. The main pipeline is equipped with valve V1 and a branch line connected in parallel with valve V1. Valve V2 and an LNG heat exchanger are installed on the branch line; the outer wall of the LPG storage tank is equipped with a jacketed heat exchanger. The inlet of the jacketed heat exchanger is connected to the refrigerant outlet of the LNG heat exchanger through a refrigerant pump and valve V3. The outlet of the jacketed heat exchanger is connected to the refrigerant inlet of the LNG heat exchanger through a refrigerant storage tank.

2. The LNG and LPG storage tank system according to claim 1, characterized in that: The system includes a PLC controller, a temperature sensor 1 in the liquid phase zone of the LPG storage tank, a temperature sensor 2 on the branch line, and valves V1 and V2, which are both electric valves. Temperature sensor 1, temperature sensor 2, valves V1 and V2 are electrically connected to the PLC controller.

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