Method for determining the switching point of multiple ORV vaporizers in an LNG station

Abstract

This invention discloses a method for determining the switching point of multiple ORV vaporizers in an LNG terminal, belonging to the technical field of ORV vaporizer switching point determination. The method includes: establishing an LNG vaporization system based on n identical ORVs connected in parallel; obtaining the temperature difference between seawater entering and exiting the ORVs when k ORVs are running and the temperature difference between seawater entering and exiting the ORVs when k+1 ORVs are running; calculating the LNG flow rate at the switching point based on the temperature differences between seawater entering and exiting the ORVs when k ORVs are running and the temperature difference between seawater entering and exiting the ORVs when k+1 ORVs are running; and switching the number of ORVs in operation based on the LNG flow rate at the switching point. This invention provides a method for determining the switching point of multiple ORV vaporizers in an LNG terminal, and the measures taken by this method are clear and executable.

Description

Technical Field

[0001] This invention belongs to the technical field of ORV vaporizer switching point determination, and particularly relates to a method for determining the switching point of multiple ORV vaporizers in an LNG station. Background Technology

[0002] In liquefied natural gas (LNG) terminals, the three commonly used vaporizers are open-frame vaporizers (ORV), intermediate medium vaporizers (IFV), and submerged combustion vaporizers (SCV). LNG terminals use ORV, IFV, and SCV vaporizers to vaporize LNG and convert it into natural gas (NG) for export. SCVs use natural gas combustion as the heat input to vaporize LNG, which is very costly. ORV and IFV vaporizers use seawater and warm seawater discharged from power plants as the heat input to vaporize LNG. This is because seawater heat is a free energy source in nature, and warm seawater discharged from power plants is a free waste containing heat energy; only the seawater discharged by the ORV needs to meet environmental protection requirements. Many large LNG terminals are built in coastal areas, utilizing free heat energy such as seawater and warm seawater discharged from factories to provide heat for the ORV and IFV vaporizers, which can significantly reduce the operating costs of LNG terminals.

[0003] LNG vaporization is a comprehensive system utilizing thermal, cold, and electrical energy. LNG vaporization requires heat, the transport of the hot and cold media requires electricity, and LNG itself contains a significant amount of cold energy. Optimizing the balance among these three elements, and rationally utilizing seawater, power plant warm seawater, geothermal energy, or other resources, while ensuring efficient transport of the hot and cold media, is crucial to achieving efficient utilization of thermal and cold energy, thereby minimizing total system energy consumption, CO2 emissions, and pollutants. In the context of a "dual-carbon" environment, research on these issues is becoming increasingly widespread.

[0004] Utilizing seawater pumping stations to supply water to multiple ORV vaporizers is currently the most common method for LNG vaporization. Since seawater heat is free, research has primarily focused on matching pump sets to reduce station power consumption. These studies have combined the optimization of multiple vaporizers with the optimization of seawater pumping stations composed of multiple pump sets, and tentatively summarized various optimal pump combination methods, resulting in differing conclusions from different companies. Essentially, these are two separate issues: first, determining the seawater heat input required for LNG vaporization and the minimum seawater flow rate to meet vaporizer constraints by optimizing the number of operating vaporizers and load allocation; and second, optimizing the number of operating pump sets and load allocation for each pump set to minimize the overall power consumption of the seawater pumping station. Currently, there is no clear path to determine the optimal switching point for multiple ORV vaporizers in an LNG station. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for determining the switching point of multiple ORV vaporizers in an LNG station, thereby resolving the issues present in the prior art.

[0006] To achieve the above objectives, the present invention provides a method for determining the switching point of multiple ORV vaporizers in an LNG station, comprising: An LNG gasification system is formed by connecting n identical ORVs in parallel. Obtain the temperature difference between seawater entering and exiting the ORV when k ORVs are running in the LNG gasification system and the temperature difference between seawater entering and exiting the ORV when k+1 ORVs are running. The LNG flow rate at the switching point is calculated based on the temperature difference between seawater entering and exiting the ORV when the k ORVs are running and the temperature difference between seawater entering and exiting the ORV when the k+1 ORVs are running. The number of ORVs in operation is switched based on the LNG flow rate at the switching point.

[0007] Preferably, among the n identical ORVs, each ORV has the same minimum seawater film formation flow rate, the same maximum seawater flow rate, the same maximum LNG flow rate, the same required seawater heat, the same LNG inlet and outlet temperature difference, and the same seawater flow rate.

[0008] Preferably, the formula for calculating the required seawater heat is: W SW-ORVi =xQ LNG-ORVi ΔT LNG-ORVi / (a-bQ LNG-ORVi ); Among them, W SW-ORVi This is the seawater thermal energy required by the i-th ORV, ΔT LNG-ORVi Q is the difference between the NG outlet temperature and the LNG inlet temperature of the i-th ORV, where a and b are constants, x is the density of LNG, and Q is the density of LNG. LNG-ORVi It is the LNG flow rate of the i-th ORV.

[0009] Preferably, the expression for calculating the seawater flow rate is: Q SW-ORV1 =W LNG-ORV / (k*c*d*ΔT SW-ORV1 ); Among them, Q SW-ORV1 It is the flow rate of seawater for each operating ORV, W LNG-ORV Here, c is the heat of seawater required by the ORV, d is the specific heat capacity of seawater, k is the density of seawater, and k is the number of ORVs. ΔT SW-ORV1 This refers to the temperature difference between seawater entering and exiting the ORV.

[0010] Preferably, the value of 'a' ranges from 1440 to 1466, and the value of 'b' ranges from 1 to 1.04.

[0011] Preferably, the expression for calculating the LNG flow rate at the switching point is: Q LNG(K,K+1) =(a / b)(ΔT SW-ORV-K -ΔT SW-ORV-（K+1） ) / (ΔT SW-ORV-K / k-ΔT SW-ORV-（K+1） / (k+1)); Among them, Q LNG(K,K+1) ΔT represents the LNG flow rate at the switching point. SW-ORV-K Let ΔT be the temperature difference between seawater entering and exiting the ORV during the operation of k ORVs. SW-ORV-（K+1） Let K+1 be the temperature difference between seawater entering and exiting the ORV during operation.

[0012] Preferably, the process of switching the number of ORVs operating based on the LNG flow rate at the switching point includes: When k ORVs are running, if the total LNG flow rate is greater than the LNG flow rate at the switching point, then switch from running k ORVs to running k+1 ORVs. When k+1 ORVs are running, if the total LNG flow rate is less than the LNG flow rate at the switching point, then switch from running k+1 ORVs to running k ORVs.

[0013] Compared with the prior art, the present invention has the following advantages and technical effects: This invention provides a method for determining the switching point of multiple ORV vaporizers in an LNG station. The measures taken by this method are clear and feasible, and the switching point determined by this invention requires the lowest seawater flow rate and the least power consumption of the seawater pumping station. Attached Figure Description

[0014] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of multiple ORV vaporizers in an LNG station according to an embodiment of the present invention, wherein 1 is the first ORV vaporizer, 2 is the second ORV vaporizer, 3 is the third ORV vaporizer, 4 is the fourth ORV vaporizer, 5 is the seawater inlet pipe, 6 is the seawater return channel, 7 is the LNG inlet pipe, and 8 is the NG outlet pipe. Detailed Implementation

[0015] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0016] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0017] Example 1 This embodiment provides a method for determining the switching point of multiple ORV vaporizers in an LNG station, including: An LNG gasification system is formed by connecting n identical ORVs in parallel. Obtain the temperature difference between seawater entering and exiting the ORV when k ORVs are running in the LNG gasification system and the temperature difference between seawater entering and exiting the ORV when k+1 ORVs are running. The LNG flow rate at the switching point is calculated based on the temperature difference between seawater entering and exiting the ORV when the k ORVs are running and the temperature difference between seawater entering and exiting the ORV when the k+1 ORVs are running. The number of ORVs in operation is switched based on the LNG flow rate at the switching point.

[0018] Among the n identical ORVs, each ORV has the same minimum seawater film formation flow rate, the same maximum seawater flow rate, the same maximum LNG flow rate, the same required seawater heat, the same LNG inlet and outlet temperature difference, and the same seawater flow rate.

[0019] Specifically: An LNG gasification system consisting of n identical ORVs connected in parallel, where the minimum seawater film formation flow rate of each ORV is equal to Q. SW-ORV1-MIN (m 3 / h), the maximum seawater flow rate of each ORV is equal to Q. SW-ORV1-MAX (m 3 / h), the maximum LNG flow rate of each ORV is equal to Q. LNG-ORV1-MAX (m 3 ( / h), the LNG inlets flowing through all ORVs are connected together, the NG outlets flowing through all ORVs are connected together, k ORVs are in operation, and the seawater thermal energy required for the i-th ORV to operate is W. SW-ORVi =xQ LNG-ORVi ΔT LNG-ORVi / (a-bQ LNG-ORVi ), W SW-ORVi This represents the seawater thermal energy required for the i-th ORV, where x is the density of LNG (t / m³). 3 ), Q LNG-ORVi ΔT is the LNG flow rate of the i-th ORV. LNG-ORVi Let be the difference (°C) between the NG outlet temperature and the LNG inlet temperature of the i-th ORV. All operating ORVs have the same LNG inlet and outlet temperature difference. Let a and b be constants, and the total LNG flow rate be Q. LNG-ORV (m3 / h), Q LNG-ORV-k =Q LNG-ORV1 + Q LNG-ORV2 +…+Q LNG-ORVk The traffic of each ORV is equal to Q. LNG-ORV1 =Q LNG-ORV / k, each ORV requires the same amount of seawater heat (W). SW-ORV1 The total heat (W) of seawater required for k ORVs LNG-ORV-k =W LNG-ORV1 + W LNG-ORV2 +…+ W LNG-ORVk The specific heat capacity of seawater is c (MW / (tk), and the total flow rate of seawater is Q. SW-ORV (m 3 / h), seawater density is d (t / m 3 The seawater flow rate for each operating ORV is equal to Q. SW-ORV1 (m 3 / h), calculate Q SW-ORV1 =W LNG-ORV-K / (k*c*d*ΔT SW-ORV1 ), ΔT SW-ORV1 The temperature difference (°C) between seawater entering and exiting the ORV is required by environmental regulations. The seawater temperature difference ΔT SW-ORV1 The maximum is 5°C. If the calculated Q... SW-ORV1 SW-ORV1-MIN Then Q SW-ORV1 =Q SW-ORV1-MIN If the calculated Q SW-ORV1 Q SW-ORV1-MAX Then Q SW-ORV1 =Q SW-ORV1-MAX Calculate the total seawater flow Q SW-ORV-k = Q LNG-ORV1 +Q LNG-ORV2 +…+ Q LNG-ORVk The value range of constant a is 1440-1466, with a preferred value of 1453. The value range of b is 1-1.04, with a preferred value of 1.02.

[0020] k ORVs are operating, with a total LNG flow rate of Q. LNG-ORV-k The total seawater flow rate is Q. SW-ORV-k The temperature difference between LNG entering and exiting the ORV is ΔT. LNG-ORV-K The temperature difference between seawater entering and exiting the ORV is ΔT. SW-ORV-K With k+1 ORVs operating, the total LNG flow rate is Q. LNG-ORV-(k+1) The total seawater flow rate is Q. SW-ORV-(k+1) The temperature difference between LNG entering and exiting the ORV is ΔT. LNG-ORV-（K+1） The temperature difference between seawater entering and exiting the ORV is ΔT. SW-ORV-（K+1） a and b are both constants.

[0021] ​The process of switching the number of ORVs in operation based on the LNG flow rate at the switching point includes: When k ORVs are running, if the total LNG flow rate is greater than the LNG flow rate at the switching point, then switch from running k ORVs to running k+1 ORVs. When k+1 ORVs are running, if the total LNG flow rate is less than the LNG flow rate at the switching point, the operation will switch from k+1 ORVs to k ORVs.

[0022] At the optimal switching point between operating k ORVs and operating k+1 ORVs, the LNG flow rate is equal to Q. LNG-ORV-k =Q LNG-ORV-(k+1) =Q LNG(K,K+1) Q LNG(K,K+1) The LNG flow rate at the switching point; the LNG temperature difference ΔT is the same. LNG-ORV-K =ΔT LNG-ORV-（K+1） The flow rate of seawater is equal to Q. SW-ORV-k =Q SW-ORV-(k+1) = Q SW（K,K+1） Q SW(K,K+1) The seawater flow rate at the switching point is equal, but this does not necessarily mean a seawater temperature difference ΔT. SW-ORV-K and ΔT SW-ORV-（K+1） They are equal because the thermal efficiency of the ORV varies at different points; if there are currently k ORVs running, Q LNG-ORV-k When traffic increases, the system switches from running on k ORV servers to running on k+1 servers. If currently running on k+1 ORV servers, Q... LNG-ORV-(k+1) If traffic decreases, switch from running on k+1 ORV servers to running on k servers. The optimal switch point Q between running on k ORV servers and running on k+1 ORV servers is... LNG(K,K+1) =(a / b)(ΔT SW-ORV-K -ΔT SW-ORV-（K+1） ) / (ΔT SW-ORV-K / k-ΔT SW-ORV-（K+1） / (k+1)).

[0023] Example 2 like Figure 1 As shown in the figure, this embodiment provides a method for determining the switching point of multiple ORV vaporizers in an LNG station, including: The LNG vaporizer station has four ORV vaporizers: ORV vaporizer 1, ORV vaporizer 2, ORV vaporizer 3, and ORV vaporizer 4, n=4. Seawater enters the top of the four ORV vaporizers through seawater inlet pipe 5. The seawater temperature is 7°C. The minimum film formation flow rate Q for each vaporizer is... SW-ORV1-MIN =3660 (m 3 / h), maximum seawater flow rate Q SW-ORV1-MAX =8500 (m 3 / h), the low-temperature seawater return water flowing from the vaporizer enters the seawater return water channel 6. According to environmental protection requirements, the seawater return water temperature must not be lower than 2°C. The maximum LNG flow rate Q for each ORV is... LNG-ORV1-MAX =900 (m) 3 LNG is fed into each operating ORV vaporizer through LNG inlet pipe 7. The LNG entering the ORV vaporizer has a temperature of -130°C and a density of 0.444 (t / m³). 3 Natural gas is delivered through NG outlet pipe 8, and the temperature of NG is 5°C. Optimal values ​​are taken as a=1453, b=1.02, and seawater density d=1.031 (t / m³). 3 The specific heat capacity of seawater is c = 0.0011083 (MW / (tk)).

[0024] The optimal switching point Q between running k ORVs and running k+1 ORVs. LNG(K,K+1) =(a / b)(ΔT SW-ORV-K -ΔT SW-ORV-（K+1） ) / (ΔT SW-ORV-K / k-ΔT SW-ORV-（K+1） / (k+1)).

[0025] The switching point for the ORV vaporizer is calculated as follows: 1. The temperature difference between LNG and NG remains unchanged at 135°C, Q LNG-ORV-K =588.46 is the switching point between k=1 and k=2, where the total seawater flow is the same for both, which is 7320 (m³). 3 / h), the seawater temperature difference is different, the seawater temperature difference for k=1 is 5 (°C), and the seawater temperature difference for k=2 is 3.7 (°C).

[0026] 2. The temperature difference between LNG and NG remains unchanged at 135°C. Q LNG-ORV-K =984.33 is the switching point between k=2 and k=3, where the total seawater discharge is the same for both, equal to 10980 (m³). 3 / h), the seawater temperature difference is different, the seawater temperature difference for k=2 is 5 (°C), and the seawater temperature difference for k=3 is 4.25 (°C).

[0027] 3. The temperature difference between LNG and NG remains unchanged at 135°C. LNG-ORV-K =1364.84 is the switching point between k=3 and k=4, where the total seawater discharge is the same for both, equal to 14640 (m³). 3 / h), the seawater temperature difference is different, the seawater temperature difference for k=3 is 5 (°C), and the seawater temperature difference for k=4 is 4.48 (°C).

[0028] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for determining the switching point of multiple ORV vaporizers in an LNG station, characterized in that, Includes the following steps: An LNG gasification system is formed by connecting n identical ORVs in parallel. Obtain the temperature difference between seawater entering and exiting the ORV when k ORVs are running in the LNG gasification system and the temperature difference between seawater entering and exiting the ORV when k+1 ORVs are running. At the optimal switching point between operating k ORVs and operating k+1 ORVs, the LNG flow rate is equal to Q. LNG-ORV-k =Q LNG-ORV-(k+1) =Q LNG(K,K+1) Q LNG(K,K+1) The LNG flow rate at the switching point; the LNG temperature difference ΔT is the same. LNG-ORV-K =ΔT LNG-ORV-（K+1） The flow rate of seawater is equal to Q. SW-ORV-k =Q SW-ORV-(k+1) = Q SW（K,K+1） Q SW(K,K+1) The seawater flow rate at the switching point; The LNG flow rate at the switching point is calculated based on the temperature difference between seawater entering and exiting the ORV during the operation of the k ORVs and the temperature difference between seawater entering and exiting the ORV during the operation of the k+1 ORVs. The calculation expression is as follows: Q LNG(K,K+1) =(a / b)(ΔT SW-ORV-K -ΔT SW-ORV-（K+1） ) / (ΔT SW-ORV-K / k-ΔT SW-ORV-（K+1） / (k+1)); Among them, Q LNG(K,K+1) ΔT represents the LNG flow rate at the switching point. SW-ORV-K Let ΔT be the temperature difference between seawater entering and exiting the ORV during the operation of k ORVs. SW-ORV-（K+1） The temperature difference between seawater entering and exiting the ORV during the operation of unit k+1; The value of 'a' ranges from 1440 to 1466, and the value of 'b' ranges from 1 to 1.

04. The number of ORVs in operation is switched based on the LNG flow rate at the switching point. When k ORVs are in operation, if the total LNG flow rate is greater than the LNG flow rate at the switching point, the operation is switched from k ORVs to k+1 ORVs. When k+1 ORVs are running, if the total LNG flow rate is less than the LNG flow rate at the switching point, the operation will switch from k+1 ORVs to k ORVs.

2. The method for determining the switching point of multiple ORV vaporizers in an LNG station according to claim 1, characterized in that, Among the n identical ORVs, each ORV has the same minimum seawater film formation flow rate, the same maximum seawater flow rate, the same maximum LNG flow rate, the same required seawater heat, the same LNG inlet and outlet temperature difference, and the same seawater flow rate for each operating ORV.

3. The method for determining the switching point of multiple ORV vaporizers in an LNG station according to claim 2, characterized in that, The formula for calculating the required seawater heat is as follows: W SW-ORVi =xQ LNG-ORVi ΔT LNG-ORVi / (a-bQ LNG-ORVi ); Among them, W SW-ORVi This is the amount of seawater heat required for the i-th ORV, ΔT LNG-ORVi Q is the difference between the NG outlet temperature and the LNG inlet temperature of the i-th ORV, where a and b are constants, x is the density of LNG, and Q is the density of LNG. LNG-ORVi It is the LNG flow rate of the i-th ORV.

4. The method for determining the switching point of multiple ORV vaporizers in an LNG station according to claim 2, characterized in that, The expression for calculating the flow rate of the seawater is: Q SW-ORV1 =W LNG-ORV-K / (k*c*d*ΔT SW-ORV1 ); Among them, Q SW-ORV1 It is the flow rate of seawater for each operating ORV, W LNG-ORV-K ΔT is the total heat required by seawater for k ORVs, where c is the specific heat capacity of seawater, d is the density of seawater, k is the number of ORVs, and ΔT is the total heat required by seawater for k ORVs. SW-ORV1 This refers to the temperature difference between seawater entering and exiting the ORV.

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