LNG gasification system and method based on double cold storage circulation

Abstract

The invention provides an LNG gasification system and method based on double cold accumulation circulation, and belongs to the technical field of ocean engineering, the LNG gasification system comprises a first gasification cold accumulation unit, a second gasification cold accumulation unit and a third open type gasification unit, and a controller of a cold accumulation distribution control system is connected with instruments on the first gasification cold accumulation unit and the second gasification cold accumulation unit. LNG heating carriers of the first gasification cold storage unit and the second gasification cold storage unit are liquid cold storage carriers from a cold storage cabin, and an LNG heating carrier of the third open gasification unit is environmental seawater. According to different LNG gasification cold storage function requirements and the requirement for LNG gasification flow fluctuation, the flow of the cold storage carrier is adjusted, the series-parallel connection mode of the first gasification cold storage unit and the second gasification cold storage unit is controlled, the cold storage function matching problem and the gasification function matching problem are solved, the cold storage carrier after cold storage is stabilized within the specified temperature range, and the LNG gasification flow fluctuation requirement is met. And high efficiency and safety of cold storage are realized.

Description

Technical Field

[0001] The present invention belongs to the field of marine engineering technology, and in particular relates to an LNG gasification system and method based on a double cold storage cycle. Background Art

[0002] LNG, as a highly efficient energy source, contains a large amount of cold energy. Developing efficient cold storage and transportation functions during LNG gasification is particularly important for remote cold use.

[0003] At present, the technology based on LNG gasification cold storage is to store the cold energy generated when LNG is gasified through a cold storage carrier, and store the cold storage carrier in a cold storage cabin according to different temperature qualities to supply it to remote users who need cold energy, thereby providing cold energy of different temperature qualities for users in need of cold energy.

[0004] Fluctuations in the LNG gasification process often cause fluctuations in the generated cold energy. In the LNG gasification cold storage operation, the cold energy extraction and cold storage efficiency is low due to the passive influence of the high and low fluctuations in the LNG flow rate. Failure to properly control the temperature of the cold carrier will also cause safety hazards to the cold storage system and cold storage tank.

[0005] In view of the operational requirements of LNG gasification cold storage, it is necessary not only to ensure the efficient cold storage performance of a large number of cold storage carriers, but also to achieve the volatility of LNG gasification and accurately control the low temperature of the cold storage carrier entering the cold storage tank. However, it is difficult to adapt to the volatility of LNG gasification by simply controlling the flow of the cold storage carrier passing through the LNG gasification cold storage unit, and it is also impossible to accurately control the output temperature of the cold storage carrier and ensure the safety of system operation.

[0006] Therefore, a fast and efficient cold storage system and method that can adapt to the fluctuation of LNG input is needed. This system and method should ensure that the LNG cold energy is stably extracted and accurately controlled when the LNG liquid input fluctuates during the LNG gasification process, so as to achieve fast and efficient recovery of LNG cold energy. At the same time, the efficiency, safety and flexibility of LNG energy utilization should be further considered. Summary of the invention

[0007] The problem to be solved by the present invention is to provide an LNG gasification system and method based on a dual cold storage cycle.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: an LNG gasification system based on a dual cold storage cycle, including an LNG gasification module, a cold storage tank and a cold storage distribution control system, the LNG gasification module includes a first gasification cold storage unit, a second gasification cold storage unit and a third open gasification unit; the inlets of the first gasification cold storage unit and the second gasification cold storage unit are connected to the LNG input port, the outlets of the first gasification cold storage unit and the second gasification cold storage unit are connected to the inlet of the third open gasification unit, and the outlet of the third open gasification unit is connected to the natural gas output port; the first gasification cold storage unit and the second gasification cold storage unit are connected through a function The conversion valve group performs series-parallel conversion; the first gasification cold storage unit and the second gasification cold storage unit are respectively connected to a number of cold storage tanks through pipelines, and the cold storage carrier is transferred to the adjacent cold storage tank or the gasification cold storage unit through the cold storage tank pump of each cold storage tank, forming an independent first cold storage carrier circulation loop and a second cold storage carrier circulation loop respectively; the cold storage distribution control system adjusts the cold storage carrier flow entering the first gasification cold storage unit or the second gasification cold storage unit and controls the first gasification cold storage unit and the second gasification cold storage unit to perform series-parallel mode conversion according to the monitored cold storage carrier flow, temperature signal and LNG flow, temperature signal, so as to realize the control of the temperature of the cold storage carrier entering the cold storage tank.

[0009] Furthermore, the first gasification cold storage unit and the second gasification cold storage unit are LNG closed gasifiers, and the LNG gasification heat medium is a cold storage carrier from the cold storage tank; the third open gasification unit is an open gasifier, and the heating medium is ambient seawater.

[0010] Furthermore, the adjacent cold storage tanks of the first cold storage carrier circulation loop or the second cold storage carrier circulation loop realize the transmission of the cold storage carrier through the cold storage tank pump and the overflow pipeline, until it is transmitted to the first gasification cold storage unit or the second gasification cold storage unit for cold storage and then output to the cold storage tank to complete the cold storage carrier circulation loop, and the cold storage tank pump draws the cold storage carrier from the upper part of the cold storage tank and injects it into the bottom of the adjacent cold storage tank or the gasification cold storage unit. The advantage of the overflow cold storage method of the cold storage carrier is that it utilizes the different densities of the hot and cold carriers in the cold storage tank and the stratification of the cold storage carrier in the tank, and the high and low temperature cold storage carriers are quickly expelled and replaced by tank-by-tank transfer to achieve effective cold storage. The replacement of cold storage in all cold storage tanks is completed in a short time, and at the same time, the stability and draft difference of the ship are not changed, and the local strength of the ship is less affected, and it is easy to operate.

[0011] Furthermore, the cold storage distribution control system completes the series-parallel conversion by controlling the function conversion valve group between the first gasification cold storage unit and the second gasification cold storage unit, the function conversion valve group includes a first function conversion valve, a second function conversion valve and a third function conversion valve, the first function conversion valve is installed on the pipeline between the LNG input port and the inlet of the second gasification cold storage unit, the second function conversion valve is installed on the pipeline between the outlet of the first gasification cold storage unit and the outlet of the second gasification cold storage unit, and the third function conversion valve is installed on the pipeline between the outlet of the first gasification cold storage unit and the inlet of the second gasification cold storage unit.

[0012] Furthermore, when the first gasification cold storage unit and the second gasification cold storage unit are operated in series, the cold storage distribution control system controls the closing of the first function conversion valve and the second function conversion valve, and the opening of the third function conversion valve; the cold storage carrier passes through the first cold storage carrier circulation loop and the second cold storage carrier circulation loop respectively, the first gasification cold storage unit sets a relatively low temperature first gasification cold storage cycle, and the second gasification cold storage unit sets a relatively high temperature second gasification cold storage cycle. In the series mode, the cold storage carrier flow rate in the series gasification mode is relatively low, which maximizes the utilization efficiency of LNG gasification heat. When the first gasification cold storage unit and the second gasification cold storage unit are operated in parallel, the cold storage distribution control system controls the opening of the first function conversion valve and the second function conversion valve and the closing of the third function conversion valve; the inlets of the first gasification cold storage unit and the second gasification cold storage unit are simultaneously connected to the liquid LNG, and the natural gas after gasification by the first gasification cold storage unit and the second gasification cold storage unit enters the third open gasification unit through the gas phase manifold outlet, and the natural gas reaches normal temperature after passing through the third open gasification unit and is connected to the shore end user. In parallel mode, it can meet the demand for larger LNG gasification volume, and realize the cold storage operation of relatively large flow cold storage carrier at the same time, so as to maximize the LNG gasification and cold storage speed. Parallel operation is generally used in the peak period of LNG gasification volume or when the cold storage speed demand is higher.

[0013] Furthermore, after the cold storage carrier passes through the first gasification cold storage unit and the second gasification cold storage unit, it is distributed to the respective cold storage compartments through independent closed cycles. In the combination mode of the dual gasification cold storage unit having the first gasification cold storage unit and the second gasification cold storage unit, the different temperatures of the output cold storage carrier can be controlled according to the cold storage needs and stored in different cold storage compartments. The adopted combination modes include single gasification cold storage unit operation (first gasification cold storage unit or second gasification cold storage unit operation), series operation of the first gasification cold storage unit and the second gasification cold storage unit, and parallel operation of the first gasification cold storage unit and the second gasification cold storage unit.

[0014] Due to the use of the above three combination modes and the cold storage distribution control system, single, series and parallel conversion can be performed to respond to changes in LNG flow in real time. The cold energy storage of the cold storage carrier is not limited by the volatility or passivity of the LNG gasification flow, which improves the cold energy utilization efficiency, improves the flexibility of the temperature adjustment of the cold storage carrier, increases the gasification operation volume and the operation time efficiency of the cold storage carrier, enables the temperature of the cold storage carrier to be accurately controlled, and the cold storage speed is improved, which can respond to fluctuations in the LNG gasification volume, making the cold storage gasification selection more convenient.

[0015] Furthermore, there is an isolation valve in front of each cold storage tank. When the overflow cold storage cycle is implemented, after monitoring that the cold storage in the cold storage tank has reached the set cold storage temperature, the cold storage distribution control system opens the isolation valve, isolates and bypasses the cold storage tank from the circulation loop, and closes the cold storage tank to improve the overall operating efficiency.

[0016] Furthermore, the cold storage distribution control system of the present invention is also provided with a remote data monitoring and operation platform to realize real-time monitoring and remote control of the cold storage capacity and effect of the cold storage compartment. The remote data monitoring and operation platform is provided with a switch for switching between a manual mode and an automatic mode of cold storage operation to realize the switching between the manual mode and the automatic mode of cold storage operation.

[0017] The present invention also provides an LNG gasification method based on a dual cold storage cycle, comprising the following steps: S1. Determine whether all the cold storage compartments are in a full cold storage carrier state through a cold storage distribution control system; S2. After determining that the tank is full, implement overflow circulation of the cold storage carrier; For the first cold storage carrier circulation loop and the second cold storage carrier circulation loop, the pipelines connecting the cold storage tanks are opened, the cold storage tank pumps of the cold storage tanks in the same cold storage carrier circulation loop are turned on, and the cold storage carrier is transferred to the upper adjacent cold storage tank in the same loop; S3, when LNG gasification begins, the first gasification cold storage unit and the second gasification cold storage unit are initially connected in parallel to operate the cold storage operation of the cold storage carrier, LNG is injected from the inlet of the first gasification cold storage unit and the second gasification cold storage unit, and the gasification cold storage operation is performed in parallel. When the cold storage distribution control system determines that the LNG injection amount is continuously stable, the cold storage tank pump flow of each cold storage tank is controlled to control the temperature of the cold storage carrier passing through the first gasification cold storage unit and the second gasification cold storage unit; S4. During the cold storage operation, the cold storage distribution control system monitors the liquid level, flow rate and temperature of each cold storage tank in real time, as well as the change of LNG injection flow rate, and adjusts the optimal flow control rate of the cold storage tank pump of each cold storage tank in manual or automatic mode according to the change of LNG injection flow rate, and implements the cold storage operation until the average temperature of the cold storage carrier of the farthest cold storage tank reaches a certain low temperature setting value. The cold storage distribution control system determines that the cold storage of the cold storage tank is completed, opens its isolation valve, and seals the farthest cold storage tank at the same time, and performs the cold storage operation of the next tank; S5. When all cold storage compartments reach the low temperature setting value, all compartments are sealed and the cold storage operation is completed.

[0018] Furthermore, in step S3, when the outlet temperature of the cold storage carrier is too low, the cold storage carrier flow rate increases to a certain value, and the cold storage carrier still continues to be lower than the set temperature value, the cold storage distribution control system will change the parallel mode of the first gasification cold storage unit and the second gasification cold storage unit to a series mode.

[0019] Due to the adoption of the above technical solution, the present invention has the following beneficial effects: (1) The present invention implements an intelligent control strategy. According to the data analysis results, the cold storage distribution control system automatically adjusts the flow of the cold storage carrier to adapt to the fluctuation of the LNG liquid inlet. When the LNG liquid inlet increases, the cold storage distribution control system automatically increases the flow of the cold storage carrier to maintain the temperature stability in the first gasification cold storage unit and the second gasification cold storage unit to ensure that the gasification effect is not affected; when the LNG liquid inlet decreases, the cold storage distribution control system automatically reduces the flow of the cold storage carrier to avoid energy waste, while maintaining the temperature stability in the first gasification cold storage unit and the second gasification cold storage unit. It can be seen that the cold energy storage of the present invention is not passively restricted by the fluctuation of the LNG gasification operation, which improves the utilization efficiency of LNG cold storage.

[0020] (2) The present invention integrates multiple combination control methods and priority control strategies of the gasification cold storage unit. The cold storage distribution control system performs feedback adjustment according to the real-time cold storage effect, and continuously optimizes the control strategies of the three combinations of the first gasification cold storage unit and the second gasification cold storage unit to ensure that a stable cold storage effect can be maintained when the LNG inlet volume fluctuates greatly.

[0021] (3) The temperature of the cold storage carrier of the present invention can be precisely controlled. The inlet and outlet flow and temperature of the first gasification cold storage unit and the second gasification cold storage unit are monitored in real time. Flow meters and temperature meters (or flow sensors and temperature sensors) are set at the inlet and outlet of the cold storage carrier of the first gasification cold storage unit and the second gasification cold storage unit to collect the flow data and temperature data of the cold storage carrier in real time, and transmit the data to the cold storage distribution control system for system judgment, processing and analysis of the data.

[0022] (4) The present invention not only makes LNG gasification cold storage operable, but also adjusts the coordinated flow balance control of each cold storage tank, and at the same time makes the synergy between the cold storage tanks balanced.

[0023] (5) The matching degree and synergy of LNG gasification and cold energy cold storage are improved in the present invention, and the cold storage distribution control system monitors and receives the cold storage carrier flow and temperature data in real time.

[0024] (6) The present invention effectively enhances the stability and flexibility of the cold storage control process of the LNG gasification cold storage carrier and significantly improves the cold storage efficiency.

[0025] (7) The use of the cold storage distribution control system of the present invention can flexibly and accurately control the temperature of the cold storage carrier, and the first gasification cold storage unit and the second gasification cold storage unit can be quickly switched in series and parallel, which can realize the functional conversion of timely adaptive cold storage temperature priority and large flow cold storage priority according to the gasification volume requirements.

[0026] (8) The cold storage distribution control system of the present invention improves the cold storage efficiency of the first gasification cold storage unit and the second gasification cold storage unit, so that LNG cold energy is efficiently utilized, fundamentally solving the problem of the impact of traditional LNG gasification methods on seawater resources.

[0027] (9) The present invention realizes efficient coordination of LNG gasification and cold storage, is environmentally friendly, and can realize sustainable utilization of LNG cold energy.

[0028] In summary, the present invention adjusts the flow and temperature of the cold storage carriers of the first gasification cold storage unit and the second gasification cold storage unit, and controls the series-parallel mode of the first gasification cold storage unit and the second gasification cold storage unit according to the different functional requirements of LNG gasification cold storage and the need to cope with the volatility of the LNG gasification flow. Intelligently adjusting the flow of the cold storage carrier can adapt to the requirements of efficient, fast and flexible cold energy storage and transportation on water, and ensure that when the LNG liquid intake fluctuates during the LNG gasification process, the stable extraction and precise control of the LNG cold energy makes the cold storage carrier after cold storage reach the specified temperature, so as to realize the rapid and efficient recovery of LNG cold energy. The present invention solves the problem of matching the cold storage of the cold storage carrier and the LNG gasification control. The cold storage carrier after cold storage is stable within the specified temperature range, and the high efficiency and safety of cold storage are achieved. The cold storage effect is guaranteed, and the safety of the overall system is guaranteed at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in combination with examples, and the advantages and implementation methods of the present invention will become more obvious. The contents shown in the accompanying drawings are only used to explain the present invention and do not constitute any limitation to the present invention in any sense. In the accompanying drawings: Figure 1 It is a structural schematic diagram of the LNG gasification system based on the dual cold storage cycle of the present invention.

[0030] In the figure: 1. The first gasification cold storage unit; 2. The second gasification cold storage unit; 3. The third open gasification unit; 4. The first cold storage chamber; 5. The second cold storage chamber; 6. The third cold storage chamber; 7. The first cold storage chamber pump; 8. The second cold storage chamber pump; 9. The third cold storage chamber pump; 10. The fourth cold storage chamber; 11. The fifth cold storage chamber; 12. The sixth cold storage chamber; 13. The fourth cold storage chamber pump; 14. The fifth cold storage chamber pump; 15. The sixth cold storage chamber pump; 16. The overflow pipeline; 17. The first function conversion valve; 18. The second function conversion valve; 19. The third function conversion valve; 20. The isolation valve. DETAILED DESCRIPTION

[0031] like Figure 1 As shown, the present invention provides an LNG gasification system based on a dual cold storage cycle, including an LNG gasification module, a cold storage tank and a cold storage distribution control system.

[0032] The LNG gasification module includes a first gasification cold storage unit 1, a second gasification cold storage unit 2 and a third open gasification unit 3. The first gasification cold storage unit 1 and the second gasification cold storage unit 2 are LNG closed gasifiers, and the LNG gasification heat medium is a cold storage carrier from the cold storage tank. The third open gasification unit 3 is an open gasifier, and the heating medium is ambient seawater.

[0033] The first gasification cold storage unit 1 and the second gasification cold storage unit 2 are arranged in parallel and can be switched in series and parallel by a function switching valve group.

[0034] The first gasification cold storage unit 1 and the second gasification cold storage unit 2 are respectively connected to a number of cold storage tanks through pipelines, and the cold storage carrier is transferred to the adjacent cold storage tank or the gasification cold storage unit through the cold storage tank pump of each cold storage tank, forming an independent first cold storage carrier circulation loop and a second cold storage carrier circulation loop. After the cold storage carrier from each cold storage tank is gasified into LNG in the first gasification cold storage unit 1 and the second gasification cold storage unit 2, a closed cold storage cycle is performed according to the overflow cold storage method.

[0035] In this embodiment, the first gasification cold storage unit 1 is connected to the first cold storage tank 4, the second cold storage tank 5 and the third cold storage tank 6 through a pipeline, and the cold storage carrier is transported by the first cold storage tank pump 7, the second cold storage tank pump 8 and the third cold storage tank pump 9, and the first gasification cold storage unit 1, the first cold storage tank 4, the second cold storage tank 5 and the third cold storage tank 6 form an independent first cold storage carrier circulation loop; the second gasification cold storage unit 2 is connected to the fourth cold storage tank 10, the fifth cold storage tank 11 and the sixth cold storage tank 12 through a pipeline, and the cold storage carrier is transported by the fourth cold storage tank pump 13, the fifth cold storage tank pump 14 and the sixth cold storage tank pump 15, and the second gasification cold storage unit 2, the fourth cold storage tank 10, the fifth cold storage tank 11 and the sixth cold storage tank 12 form an independent second cold storage carrier circulation loop; The overflow cold storage method of the cold storage carrier is as follows: in the first cold storage carrier circulation loop and the second cold storage carrier circulation loop, respectively, when the cold storage carrier of the cold storage compartment is in a full compartment state, the adjacent cold storage compartments realize the transmission of the cold storage carrier through the cold storage compartment pump and the overflow pipeline 16, until the cold storage carrier is transmitted to the first gasification cold storage unit 1 or the second gasification cold storage unit 2 for cold storage and then output to the cold storage compartment, realizing a closed cold storage carrier overflow cycle and completing the cold storage carrier circulation loop. The cold storage compartment pump of each cold storage compartment is turned on and the overflow pipeline 16 is opened, and the cold storage compartment pump draws the cold storage carrier from the upper part of the cold storage compartment and injects it into the bottom of the adjacent cold storage compartment or the gasification cold storage unit.

[0036] The corresponding cold storage tanks are connected through the overflow pipeline 16, and the reflux carrier liquid is injected from the bottom of the tank. In this embodiment, in the first cold storage carrier circulation loop, the first cold storage tank 4 is closest to and adjacent to the first gasification cold storage unit 1. After starting, the third cold storage tank pump 9 of the farthest third cold storage tank 6 transfers the cold storage carrier to the second cold storage tank 5 through the overflow pipeline 16 between the third cold storage tank 6 and the second cold storage tank 5. Similarly, the second cold storage tank pump 8 of the second cold storage tank 5 transfers the cold storage carrier to the first cold storage tank 4, and the first cold storage tank pump 7 of the first cold storage tank 4 transfers the cold storage carrier to the first gasification cold storage unit 1. The cold storage carrier after being stored in the first gasification cold storage unit 1 returns to the third cold storage tank 6, realizing a closed cold storage carrier overflow cycle, and completing the first cold storage carrier circulation loop. The circulation mode of the second cold storage carrier circulation loop is the same as above.

[0037] The advantage of the overflow cold storage method of the cold storage carrier is that it utilizes the different densities of the hot and cold carriers in the cold storage compartment and the stratification of the cold storage carrier in the compartment. The high and low temperature cold storage carriers are quickly expelled and replaced by transshipment from compartment to compartment to achieve effective cold storage. The cold storage replacement of all cold storage compartments is completed in a short time. At the same time, it does not change the stability and draft difference of the ship, has little impact on the local strength of the ship, and is easy to operate.

[0038] The inlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 is connected to the LNG input port, the outlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 is connected to the inlet of the third open gasification unit 3, and the outlet of the third open gasification unit 3 is connected to the natural gas output port.

[0039] The final process of LNG gasification is completed by the third open gasification unit 3, and the heating carrier is provided by the seawater system. Since the LNG has passed through the first gasification cold storage unit 1 and the second gasification cold storage unit 2, the natural gas temperature is only increased in the third open gasification unit 3. Therefore, the seawater consumption of the third open gasification unit 3 will be greatly reduced, reducing dependence on and adverse effects on the environment.

[0040] The cold storage distribution control system monitors the cold storage carrier flow, temperature signal and LNG flow and temperature signal, and adjusts the cold storage carrier flow entering the first gasification cold storage unit 1 or the second gasification cold storage unit 2 according to the gasification cold storage model control strategy, and controls the first gasification cold storage unit 1 or the second gasification cold storage unit 2 to perform series-parallel mode conversion, thereby controlling the temperature of the cold storage carrier entering the cold storage compartment, solving the problem of coordinated matching of the cold storage carrier and LNG gasification function.

[0041] The cold storage distribution control system completes the series-parallel conversion by controlling the function conversion valve group between the first gasification cold storage unit 1 and the second gasification cold storage unit 2. The function conversion valve group is a number of control valves on the LNG pipeline. The function conversion valve group includes a first function conversion valve 17, a second function conversion valve 18 and a third function conversion valve 19, wherein the first function conversion valve 17 is installed on the pipeline between the LNG input port and the inlet of the second gasification cold storage unit 2, the second function conversion valve 18 is installed on the pipeline between the outlet of the first gasification cold storage unit 1 and the outlet of the second gasification cold storage unit 2, and the third function conversion valve 19 is installed on the pipeline between the outlet of the first gasification cold storage unit 1 and the inlet of the second gasification cold storage unit 2.

[0042] When the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are operated in series, the cold storage distribution control system controls the closing of the first function conversion valve 17 and the second function conversion valve 18, and opens the third function conversion valve 19, so as to realize the series mode of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 of LNG gasification. The inlet (LNG pipe interface) of the first gasification cold storage unit 1 is connected to the LNG input port (liquid LNG interface) externally. After the first gasification of the first gasification cold storage unit 1, the low-temperature natural gas enters the second gasification cold storage unit 2. The natural gas after passing through the second gasification cold storage unit 2 enters the third open gasification unit 3 through the gas phase pipe outlet for heating. After passing through the third open gasification unit 3, the natural gas reaches the normal temperature and is connected to the shore end user. The corresponding cold storage carrier passes through the first cold storage carrier circulation loop and the second cold storage carrier circulation loop respectively, wherein the first gasification cold storage unit 1 sets the first gasification cold storage cycle with a relatively low temperature, and the second gasification cold storage unit 2 sets the second gasification cold storage cycle with a relatively high temperature. In the series mode, the flow rate of the cold storage carrier in the series gasification mode is relatively low, which maximizes the utilization efficiency of the LNG gasification heat.

[0043] When the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are operated in parallel, the cold storage distribution control system controls the opening of the first function conversion valve 17 and the second function conversion valve 18, and the closing of the third function conversion valve 19, so as to realize the parallel mode of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 for LNG gasification. The inlets of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are simultaneously connected to the liquid LNG. The natural gas after the LNG is gasified by the first gasification cold storage unit 1 and the second gasification cold storage unit 2 enters the third open gasification unit 3 through the gas phase manifold outlet. After passing through the third open gasification unit 3, the natural gas reaches the normal temperature and is connected to the shore end user. In the parallel mode, the demand for a large LNG gasification volume is met, and the cold storage operation of a relatively large flow cold storage carrier is realized at the same time (the cold storage distribution control system will adjust the cold storage tank pump to output a relatively large flow), so as to maximize the LNG gasification and cold storage speed. The parallel operation is generally used during the peak period of LNG gasification volume or when the cold storage speed is high.

[0044] The cold storage distribution control system includes a controller, which is connected to the flow meter and temperature meter at the inlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2, as well as the temperature meter at the inlet and outlet of the cold storage carrier, and the temperature meter and flow meter in each cold storage tank pump and each cold storage tank. The temperature signals monitored by the cold storage distribution control system include: the temperature signal at the inlet and outlet of the cold storage carrier on the first gasification cold storage unit 1 and the second gasification cold storage unit 2, and the temperature signal in each cold storage tank; the flow signals monitored by the cold storage distribution control system include: the LNG flow signal at the inlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2, and the cold storage carrier flow signal of each cold storage tank. The cold storage distribution control system controls the flow and temperature of the cold storage carrier entering the first gasification cold storage unit 1 and the second gasification cold storage unit 2 through the above-mentioned temperature and flow data information collection and control strategy.

[0045] After the cold storage carrier passes through the first gasification cold storage unit 1 and the second gasification cold storage unit 2, it is distributed to the respective cold storage compartments through independent closed cycles. In the combination mode of the dual gasification cold storage unit with the first gasification cold storage unit 1 and the second gasification cold storage unit 2, the different temperatures of the output cold storage carrier can be controlled according to the cold storage needs and stored in different cold storage compartments. The combination modes used include single gasification cold storage unit operation (first gasification cold storage unit 1 or second gasification cold storage unit 2 operation), first gasification cold storage unit 1 and second gasification cold storage unit 2 series operation, and first gasification cold storage unit 1 and second gasification cold storage unit 2 parallel operation. The characteristics of different combination modes are: In the single gasification cold storage mode: to cope with the demand for LNG gasification with a small flow rate, the cold storage carrier temperature control accuracy is high. For example, the cold storage carrier temperature output is controlled at -60°~-35°, and the cold storage speed is controlled at 400 cubic meters / hour. According to the LNG flow rate and the set cold storage carrier temperature, the cold storage carrier flow rate is adjusted in real time. When the LNG inflow is stable, the outlet temperature of the first gasification cold storage unit 1 or the second gasification cold storage unit 2 is adaptively feedback-adjusted. When the outlet temperature of the cold storage carrier pipeline is too high, the cold storage carrier flow value is increased and the flow is monitored.

[0046] In the series operation mode: the cold storage carrier has a wide storage temperature range, high cold storage efficiency, low cold energy loss, and the cold storage temperature can be precisely controlled. The cold storage carriers passing through the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are graded to implement high and low temperature cold storage. For example, the temperature output of the cold storage carrier of the first gasification cold storage unit 1 is controlled at -65°~-30°, and the output of the cold storage carrier of the second gasification cold storage unit 2 is controlled at -35°~-20°. The cold storage speed can be controlled at 300~500 cubic meters / hour.

[0047] In parallel operation mode: it can meet the demand for high-flow LNG gasification, and at the same time, the cold storage capacity of the cold storage carrier increases, which improves the cold energy storage speed. For example, the temperature output of the cold storage carrier of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 is controlled at -60°~-35° respectively, and the cold storage speed can be controlled at 800 cubic meters / hour.

[0048] After LNG is gasified and stored in cold, it changes from liquid to gaseous natural gas, and the third open gasification unit 3 completes the natural gas heating process. The cold storage distribution control system can adjust the seawater flow rate according to the natural gas outlet temperature. At the same time, due to the high efficiency of cold energy utilization when passing through the first gasification cold storage unit 1 and the second gasification cold storage unit 2, the amount of seawater used through the third open gasification unit 3 is reduced. Compared with the traditional receiving station that directly uses seawater to gasify LNG, the amount of seawater used is small, which reduces the dependence of LNG gasification on seawater and alleviates the adverse effects of low temperature on the marine environment caused by LNG gasification.

[0049] Due to the use of the above three combination modes and the cold storage distribution control system, single, series and parallel conversion can be performed to respond to changes in LNG flow in real time. The cold energy storage of the cold storage carrier is not limited by the volatility or passivity of the LNG gasification flow, which improves the cold energy utilization efficiency, improves the flexibility of the temperature adjustment of the cold storage carrier, increases the gasification operation volume and the operation time efficiency of the cold storage carrier, enables the temperature of the cold storage carrier to be accurately controlled, and the cold storage speed is improved, which can respond to fluctuations in the LNG gasification volume, making the cold storage gasification selection more convenient.

[0050] The cold storage carrier circulation of the present invention has low temperature and flow balance protection functions. The cold storage distribution control system monitors the outlet temperature of the cold storage carrier of the first gasification cold storage unit 1 and the second gasification cold storage unit 2, and the flow balance of each cold storage tank pump. When the temperature is lower than the temperature setting and the cold storage tank pump flow of each cold storage tank is unbalanced, an alarm and adjustment will be issued to protect the structure of the cold storage tank. The cold storage distribution control system monitors the flow of the cold storage carrier of each cold storage tank in a distributed manner, and monitors the balance of the flow of each cold storage tank in real time; the cold storage distribution control system has a temperature monitoring function. If the temperature of the cold storage carrier is lower than the set value or the flow of the cold storage carrier is unbalanced, the cold storage distribution control system implements over-low temperature protection, flow protection and other alarm protection measures to protect the performance of the cold storage carrier and the structure of the cold storage tank.

[0051] There is an isolation valve 20 in front of each cold storage tank. When the overflow cold storage cycle is implemented, after monitoring that the cold storage tank has reached the set cold storage temperature, the cold storage distribution control system opens the isolation valve 20, isolates and bypasses the cold storage tank from the circulation loop, and closes the cold storage tank to improve the overall operation efficiency. For example, when the temperature of the first cold storage tank 4 reaches the cold storage set temperature, the isolation valve 20 on the first cold storage tank 4 is opened to isolate and bypass the first cold storage tank 4, and at the same time, the inlet and outlet valves of the first cold storage tank 4 are closed to achieve closure.

[0052] The cold storage distribution control system of the present invention has a remote data monitoring and operation platform to realize real-time monitoring and remote control of the cold storage capacity and effect of the cold storage tank. The cold storage and cold release working conditions can be understood at any time through data collection of LNG gasification volume and cold storage carrier temperature information, and through data collection, data measurement includes the cumulative LNG gasification volume of the cold storage carrier, the cumulative cold storage heat, and the cold storage efficiency, and remote operation and adjustment are performed according to the above results.

[0053] The cold storage distribution control system measures the cold storage value and cold storage efficiency of the present invention during the cold storage operation. The present invention establishes a cold storage calculation model, and converts the cold energy reserve and the corresponding time efficiency according to the heat capacity value of the cold storage carrier, the temperature change and flow rate of the cold storage carrier after gasification cold storage collected per unit time. The calculation formula is: Q1=ΔT1×R1×M1+ΔT2×R1×M2 Among them, Q1 is the calorific value of cold storage per unit time; ΔT1 is the temperature change value of the cold storage carrier of the first gasification cold storage unit 1 per unit time; R1 is the heat capacity value of the cold storage carrier; M1 is the flow rate of the cold storage carrier passing through the first gasification cold storage unit 1 per unit time; ΔT2 is the temperature change value of the cold storage carrier of the second gasification cold storage unit 2 per unit time; M2 is the flow rate of the cold storage carrier passing through the second gasification cold storage unit 2 per unit time.

[0054] Q2=M3×R2 Among them, Q2 is the LNG vaporization calorific value per unit time; M3 is the sum of the LNG flow rates passing through the first gasification cold storage unit 1 or the second gasification cold storage unit 2 per unit time, and R2 is the LNG vaporization calorific value.

[0055] N=Q1 / Q2×100% Where N is the thermal efficiency of the system.

[0056] The remote data monitoring and operation platform of the present invention has a switch for converting the manual mode and the automatic mode of the cold storage operation, so as to realize the conversion of the manual mode and the automatic mode of the cold storage operation of the present invention.

[0057] Manual mode control method: When the LNG flow rate flowing through the first gasification cold storage unit 1 and the second gasification cold storage unit 2 monitored by the cold storage distribution control system is stable within the rated value range, the cold storage carrier cold storage priority control is implemented, including three combination schemes to choose from, and the first gasification cold storage unit 1 and the second gasification cold storage unit 2 can be adjusted as needed to be a series cycle, giving priority to ensuring the maximum cold storage efficiency, maximizing the use of LNG gasification potential, and realizing graded cold storage in two high and low temperature ranges; if the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are selected for parallel circulation, it can meet the large flow rate of cold storage carriers and quickly store cold, giving priority to fast cold storage, and realizing fast and large flow rate cold storage of cold storage media, and the first gasification cold storage unit 1 and the second gasification cold storage unit 2 perform gasification cold storage at the same level. If a single gasification cold storage unit is selected for operation, the cold storage demand for a smaller LNG flow rate can be achieved.

[0058] Automatic mode control method: When the LNG flow rate flowing through the first gasification cold storage unit 1 and the second gasification cold storage unit 2 monitored by the cold storage distribution control system is in a certain fluctuation state or judged according to the total flow rate of the LNG inlet, the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are automatically switched in series and parallel, and the adaptive adjustment function switches the valve group state, that is, through the flow meter installed at the inlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2, when it is judged that the total LNG injection flow rate is less than 60% of the set rated flow rate, the single gasification cold storage mode is automatically started; when the total LNG flow rate is between 60% and 80%, it is adjusted to the series operation mode, and when the flow rate is judged to be greater than 80% or the total LNG flow rate fluctuation exceeds 20%, it is adjusted to the parallel operation mode. The present invention fully responds to the LNG gasification demand, responds to the impact of LNG injection fluctuations, takes intelligent control measures, and improves the overall efficiency of cold energy utilization.

[0059] The present invention also provides an LNG gasification method based on a dual cold storage cycle, comprising the following steps: S1. Determine whether all the cold storage compartments are in a full cold storage carrier state through a cold storage distribution control system.

[0060] S2. After determining that the tank is full, implement overflow circulation of the cold storage carrier; For the first cold storage carrier circulation loop and the second cold storage carrier circulation loop, the pipelines connecting the cold storage tanks are opened, the cold storage tank pumps of the cold storage tanks in the same cold storage carrier circulation loop are turned on, and the cold storage carrier is transferred to the previous cold storage tank in the same loop; In this embodiment, in the first cold storage carrier circulation loop, the first chamber closest to and adjacent to the first gasification cold storage unit 1 is the first cold storage chamber 4. After startup, the third cold storage chamber pump 9 of the farthest third cold storage chamber 6 transfers the cold storage carrier to the second cold storage chamber 5 through the overflow pipeline 16 between the third cold storage chamber 6 and the second cold storage chamber 5. Similarly, the second cold storage chamber pump 8 of the second cold storage chamber 5 transfers the cold storage carrier to the first cold storage chamber 4, and the first cold storage chamber pump 7 of the first cold storage chamber 4 transfers the cold storage carrier to the first gasification cold storage unit 1. The cold storage carrier after being stored in the first gasification cold storage unit 1 returns to the third cold storage chamber 6, realizing a closed cold storage carrier overflow cycle, and completing the first cold storage carrier circulation loop. The circulation mode of the second cold storage carrier circulation loop is the same as above.

[0061] S3, when LNG gasification begins, the first gasification cold storage unit 1 and the second gasification cold storage unit 2 are initially connected in parallel to operate the cold storage operation of the cold storage carrier, LNG is injected from the inlet of the first gasification cold storage unit 1 and the second gasification cold storage unit 2, and the gasification cold storage operation is performed in parallel. When the cold storage distribution control system determines that the LNG injection amount is continuously stable, the cold storage tank pump flow of each cold storage tank is controlled to control the temperature of the cold storage carrier passing through the first gasification cold storage unit 1 and the second gasification cold storage unit 2; During the implementation process, the cold storage distribution control system monitors the temperature and flow of the cold storage carrier, and automatically provides feedback based on the outlet temperature of the cold storage carrier measured in the first gasification cold storage unit 1 and the second gasification cold storage unit 2. When the outlet temperature of the cold storage carrier is too low and lower than the design value, the cold storage distribution control system increases the flow of the cold storage carrier. When the outlet temperature of the cold storage carrier is too high and higher than the set value, the flow of the cold storage carrier is reduced.

[0062] When the outlet temperature of the cold storage carrier is too low, the flow rate of the cold storage carrier increases to a certain value, such as 85-90% of the rated flow rate, and the cold storage carrier still continues to be lower than the set temperature value, the cold storage distribution control system will adaptively change the parallel mode of the first gasification cold storage unit 1 and the second gasification cold storage unit 2 to the series mode.

[0063] S4. During the cold storage operation, the cold storage distribution control system monitors the liquid level, flow rate and temperature of each cold storage tank, as well as the change of LNG injection flow rate in real time, and adjusts the optimal flow control rate of the cold storage tank pump of each cold storage tank in manual mode or automatic mode according to the change of LNG injection flow rate, and implements the cold storage operation until the average temperature of the cold storage carrier of the farthest third cold storage tank 6 reaches a certain low temperature set value. The cold storage distribution control system determines that the cold storage of the cold storage tank is completed, opens its isolation valve 20, and at the same time seals the third cold storage tank 6, closes the cold storage tank, and performs the cold storage operation of the next tank.

[0064] S5. When all cold storage compartments reach the low temperature setting value, all compartments are sealed and the cold storage operation is completed.

[0065] The embodiments of the present invention are described in detail above, but the contents are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. An LNG gasification system based on a dual cold storage cycle, characterized in that: The invention comprises an LNG gasification module, a cold storage tank and a cold storage distribution control system, wherein the LNG gasification module comprises a first gasification cold storage unit, a second gasification cold storage unit and a third open gasification unit; the inlets of the first gasification cold storage unit and the second gasification cold storage unit are connected to the LNG input port, the outlets of the first gasification cold storage unit and the second gasification cold storage unit are connected to the inlet of the third open gasification unit, and the outlet of the third open gasification unit is connected to the natural gas output port; the first gasification cold storage unit and the second gasification cold storage unit are connected to the series-parallel conversion through the function conversion valve group; the first gasification cold storage unit The unit and the second gasification cold storage unit are respectively connected to several cold storage tanks through pipelines, and the cold storage carrier is transferred to the adjacent cold storage tank or the gasification cold storage unit through the cold storage tank pump of each cold storage tank, forming an independent first cold storage carrier circulation loop and a second cold storage carrier circulation loop respectively; the cold storage distribution control system is used to monitor the cold storage carrier flow, temperature signal and LNG flow, temperature signal, adjust the cold storage carrier flow entering the first gasification cold storage unit or the second gasification cold storage unit, and control the first gasification cold storage unit and the second gasification cold storage unit to perform series-parallel mode conversion, so as to realize the control of the temperature of the cold storage carrier entering the cold storage tank.

2. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: The first gasification cold storage unit and the second gasification cold storage unit are LNG closed gasifiers, and the LNG gasification heat medium is the cold storage carrier from the cold storage tank; the third open gasification unit is an open gasifier, and the heating medium is ambient seawater.

3. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: The first cold storage carrier circulation loop or the second cold storage carrier circulation loop has adjacent cold storage tanks that transfer the cold storage carrier through a cold storage tank pump and an overflow pipeline until the cold storage carrier is transferred to the first gasification cold storage unit or the second gasification cold storage unit for cold storage and then output to the cold storage tank to complete the cold storage carrier circulation loop. The cold storage tank pump draws the cold storage carrier from the upper part of the cold storage tank and injects it into the bottom of the adjacent cold storage tank or the gasification cold storage unit.

4. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: The cold storage distribution control system completes the series-parallel conversion by controlling the function conversion valve group between the first gasification cold storage unit and the second gasification cold storage unit. The function conversion valve group includes a first function conversion valve, a second function conversion valve and a third function conversion valve. The first function conversion valve is installed on the pipeline between the LNG input port and the inlet of the second gasification cold storage unit, the second function conversion valve is installed on the pipeline between the outlet of the first gasification cold storage unit and the outlet of the second gasification cold storage unit, and the third function conversion valve is installed on the pipeline between the outlet of the first gasification cold storage unit and the inlet of the second gasification cold storage unit.

5. The LNG gasification system based on dual cold storage cycle according to claim 4 is characterized in that: When the first gasification cold storage unit and the second gasification cold storage unit are operated in series, the cold storage distribution control system controls the closing of the first function conversion valve and the second function conversion valve, and opens the third function conversion valve; the cold storage carrier passes through the first cold storage carrier circulation loop and the second cold storage carrier circulation loop respectively, the first gasification cold storage unit sets a relatively low temperature first gasification cold storage cycle, and the second gasification cold storage unit sets a relatively high temperature second gasification cold storage cycle; when the first gasification cold storage unit and the second gasification cold storage unit are operated in parallel, the cold storage distribution control system controls the opening of the first function conversion valve and the second function conversion valve and the closing of the third function conversion valve; the inlets of the first gasification cold storage unit and the second gasification cold storage unit are simultaneously connected to liquid LNG, and the natural gas gasified by the first gasification cold storage unit and the second gasification cold storage unit enters the third open gasification unit through the gas phase manifold outlet, and the natural gas reaches normal temperature after passing through the third open gasification unit and is connected to the shore user.

6. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: After the cold storage carrier passes through the first gasification cold storage unit and the second gasification cold storage unit, it is distributed to the respective cold storage compartments through independent closed cycles. In the combination mode of the dual gasification cold storage unit having the first gasification cold storage unit and the second gasification cold storage unit, the different temperatures of the output cold storage carrier can be controlled according to the cold storage needs and stored in different cold storage compartments. The adopted combination modes include three modes: single gasification cold storage unit operation, first gasification cold storage unit and second gasification cold storage unit series operation, and first gasification cold storage unit and second gasification cold storage unit parallel operation.

7. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: There is an isolation valve in front of each cold storage tank. When the overflow cold storage cycle is implemented, after monitoring that the cold storage in the cold storage tank reaches the set cold storage temperature, the cold storage distribution control system opens the isolation valve, isolates and bypasses the cold storage tank from the circulation loop, and closes the cold storage tank.

8. The LNG gasification system based on dual cold storage cycle according to claim 1 is characterized in that: The cold storage distribution control system is also provided with a remote data monitoring and operation platform to realize real-time monitoring and remote control of the cold storage capacity and effect of the cold storage compartment. The remote data monitoring and operation platform is provided with a cold storage operation manual mode and automatic mode conversion switch to realize the conversion of the cold storage operation manual mode and automatic mode.

9. An LNG gasification method based on a dual cold storage cycle, implemented by the LNG gasification system based on a dual cold storage cycle according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1. Determine whether all the cold storage compartments are in a full cold storage carrier state through a cold storage distribution control system; S2. After determining that the tank is full, implement overflow circulation of the cold storage carrier; For the first cold storage carrier circulation loop and the second cold storage carrier circulation loop, the pipelines connecting the cold storage tanks are opened, the cold storage tank pumps of the cold storage tanks in the same cold storage carrier circulation loop are turned on, and the cold storage carrier is transferred to the adjacent cold storage tanks in the same loop; S3, when LNG gasification begins, the first gasification cold storage unit and the second gasification cold storage unit are initially connected in parallel to operate the cold storage operation of the cold storage carrier, LNG is injected from the inlet of the first gasification cold storage unit and the second gasification cold storage unit, and the gasification cold storage operation is performed in parallel. When the cold storage distribution control system determines that the LNG injection amount is continuously stable, the cold storage tank pump flow of each cold storage tank is controlled to control the temperature of the cold storage carrier passing through the first gasification cold storage unit and the second gasification cold storage unit; S4. During the cold storage operation, the cold storage distribution control system monitors the liquid level, flow rate and temperature of each cold storage tank in real time, as well as the change of LNG injection flow rate, and adjusts the optimal flow control rate of the cold storage tank pump of each cold storage tank in manual mode or automatic mode according to the change of LNG injection flow rate, and implements the cold storage operation until the average temperature of the cold storage carrier of the farthest cold storage tank reaches a certain low temperature setting value. The cold storage distribution control system determines that the cold storage of the cold storage tank is completed, opens its isolation valve, and seals the farthest cold storage tank at the same time, and performs the cold storage operation of the next tank; S5. When all cold storage compartments reach the low temperature setting value, all compartments are sealed and the cold storage operation is completed.

10. The LNG gasification method based on dual cold storage cycle according to claim 9, characterized in that: In step S3, when the outlet temperature of the cold storage carrier is too low, the cold storage carrier flow rate increases to a certain value, and the cold storage carrier still continues to be lower than the set temperature value, the cold storage distribution control system will change the parallel mode of the first gasification cold storage unit and the second gasification cold storage unit to a series mode.

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