Method for determining switching points of multiple ORV gasifiers in LNG station

Abstract

The invention discloses a switching point determination method for multiple ORV vaporizers in an LNG station, and belongs to the technical field of switching point determination of ORV vaporizers. The switching point determination method comprises the steps that n identical ORVs are connected in parallel to form an LNG gasification system; the temperature difference of seawater entering and exiting from the ORV when k ORVs in the LNG gasification system operate and the temperature difference of seawater entering and exiting from the ORV when k + 1 ORVs operate are obtained; on the basis of the temperature difference of seawater entering and exiting from the ORV when k ORVs operate and the temperature difference of seawater entering and exiting from the ORV when k + 1 ORVs operate, the LNG flow of a switching point is obtained through calculation; and switching the number of the ORV operation based on the LNG flow at the switching point. The invention provides a method for determining switching points of multiple ORV gasifiers of an LNG station. The measures adopted by the method are clear and executable.

Description

Technical Field

[0001] The invention belongs to the technical field of switching point determination of ORV gasifiers, and in particular relates to a method for determining switching points of multiple ORV gasifiers in an LNG station. Background Art

[0002] In liquefied natural gas (LNG) stations, the three commonly used vaporizers are open rack vaporizers (ORV), intermediate medium vaporizers (IFV) and submerged combustion vaporizers (SCV). LNG stations use ORV, IFV, and SCV vaporizers to gasify LNG and convert it into natural gas (NG) for external transmission. SCV uses natural gas combustion as heat input to gasify LNG, which is very expensive. ORV and IFV vaporizers use seawater and warm seawater discharged from power plants as heat input to gasify LNG, because seawater heat is free energy in nature, and warm seawater discharged from power plants is free waste containing heat energy. It only needs the seawater discharged by ORV to meet environmental protection requirements. Many large LNG stations are built in coastal areas. Using free heat energy such as seawater and warm seawater discharged from factories to provide heat for ORV and IFV vaporizers can greatly reduce the operating costs of LNG stations.

[0003] The LNG gasification process is a comprehensive utilization system of heat energy, cold energy and electric energy. LNG gasification requires heat, and the transportation of hot and cold media requires electric energy. LNG itself contains a large amount of cold energy. How to optimize and balance the relationship between the three, and rationally utilize seawater, warm seawater from power plants, geothermal energy or other resources, while ensuring the efficient transportation of hot and cold media, to achieve efficient utilization of heat energy and full utilization of cold energy, thereby minimizing the total energy consumption of the system, minimizing CO2 emissions, and minimizing pollutants. In the context of "dual carbon", research on these issues is becoming more and more extensive.

[0004] Using seawater pumping stations to supply water to multiple ORV vaporizers is currently the most common method for LNG gasification. Since seawater heat is free, research work has mainly focused on how to match pump groups to reduce the power consumption of pump stations. These studies mixed the optimization of multiple vaporizers with the optimization of seawater pumping stations composed of multiple pump groups, and tentatively summarized the optimization combination methods of various water pumps, so the conclusions of various companies are not the same. In fact, these are two problems. One is to determine the seawater heat energy input required for LNG gasification and the minimum seawater flow rate that meets the constraints of the vaporizer by optimizing the number of operating vaporizers and load distribution; the other is how to optimize the number of operating pump groups and distribute the load of each pump group for this minimum seawater flow rate, so that the power consumption of the entire seawater pump station is minimized. There is currently no clear path to determine the optimal operating switching point for multiple ORV vaporizers in an LNG station. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a method for determining the switching points of multiple ORV gasifiers in an LNG station to solve the above problems in the prior art.

[0006] To achieve the above object, the present invention provides a method for determining a switching point of multiple ORV gasifiers in an LNG station, comprising:

[0007] Based on n identical ORVs connected in parallel to form an LNG gasification system;

[0008] Obtaining the temperature difference of seawater entering and exiting the ORV when k ORVs are in operation and the temperature difference of seawater entering and exiting the ORV when k+1 ORVs are in operation in the LNG gasification system;

[0009] The LNG flow rate at the switching point is calculated based on the temperature difference of the seawater entering and leaving the ORV when the k ORV is in operation and the temperature difference of the seawater entering and leaving the ORV when the k+1 ORV is in operation;

[0010] The number of ORV operations is switched based on the switch point LNG flow rate.

[0011] Preferably, among the n identical ORVs, each ORV has an equal minimum seawater film flow rate, an equal maximum seawater flow rate, an equal maximum LNG flow rate, an equal required seawater heat, an equal LNG inlet and outlet temperature difference, and an equal seawater flow rate.

[0012] Preferably, the required seawater heat is calculated as follows:

[0013] W SW-ORVi =xQ LNG-ORVi ΔT LNG-ORVi / (a-bQ LNG-ORVi );

[0014] Among them, W SW-ORVi is the seawater thermal energy required by the i-th ORV, ΔT LNG-ORVi is the difference between the NG outlet temperature and the LNG inlet temperature of the i-th ORV, a and b are constants, x is the density of LNG, Q LNG-ORVi is the LNG flow rate of the i-th ORV.

[0015] Preferably, the calculation expression of the flow rate of seawater is:

[0016] Q SW-ORV1 =W LNG-ORV / (k*c*d*ΔT SW-ORV1 );

[0017] Among them, Q SW-ORV1 is the flow rate of seawater per operating ORV, W LNG-ORV is the seawater heat required by the ORV, c is the specific heat capacity of seawater, d is the density of seawater, k is the number of ORVs, ΔTSW-ORV1 is the temperature difference of seawater entering and leaving the ORV.

[0018] Preferably, the value range of a is 1440-1466, and the value range of b is 1-1.04.

[0019] Preferably, the calculation expression of the switching point LNG flow is:

[0020] 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));

[0021] Among them, Q LNG(K,K+1) is the LNG flow rate at the switching point, ΔT SW-ORV-K is the temperature difference of seawater entering and leaving the ORV when k ORVs are in operation, ΔT SW-ORV-(K+1) is the temperature difference of seawater entering and leaving the ORV when k+1 ORV is in operation.

[0022] Preferably, the process of switching the number of ORV operations based on the switching point LNG flow rate includes:

[0023] When k ORVs are in operation, if the total LNG flow is greater than the LNG flow at the switching point, the operation of k ORVs is switched to k+1 ORVs;

[0024] When the k+1 ORV is in operation, if the total LNG flow is less than the LNG flow at the switching point, the operation of the k+1 ORV is switched to the k ORV.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The present invention provides a method for determining the switching points of multiple ORV gasifiers of an LNG station. Since the measures taken by the method are clear and executable, and the switching points determined by the present invention require the lowest seawater flow rate, the seawater pump station requires the least power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0028] 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. a first ORV vaporizer; 2. a second ORV vaporizer; 3. a third ORV vaporizer; 4. a fourth ORV vaporizer; 5. a seawater inlet pipe; 6. a seawater return channel; 7. a LNG inlet pipe; and 8. a NG outlet pipe. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0031] Embodiment 1

[0032] This embodiment provides a method for determining the switching points of multiple ORV vaporizers in an LNG station, including:

[0033] Based on n identical ORVs connected in parallel to form an LNG gasification system;

[0034] Obtaining the temperature difference of seawater entering and exiting the ORV when k ORVs are in operation and the temperature difference of seawater entering and exiting the ORV when k+1 ORVs are in operation in the LNG gasification system;

[0035] The LNG flow rate at the switching point is calculated based on the temperature difference of the seawater entering and leaving the ORV when the k ORV is in operation and the temperature difference of the seawater entering and leaving the ORV when the k+1 ORV is in operation;

[0036] The number of ORV operations is switched based on the switch point LNG flow rate.

[0037] Among the n identical ORVs, each ORV has an equal minimum seawater film flow rate, an equal maximum seawater flow rate, an equal maximum LNG flow rate, an equal required seawater heat, an equal LNG inlet and outlet temperature difference, and an equal seawater flow rate.

[0038] Specifically:

[0039] The LNG gasification system consists of n identical ORVs connected in parallel. The minimum seawater film 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 W required for the operation of the i-th ORV is SW-ORVi =xQ LNG-ORVi ΔTLNG-ORVi / (a-bQ LNG-ORVi ), W SW-ORVi is the seawater thermal energy required by the i-th ORV, x is the density of LNG (t / m 3 ), Q LNG-ORVi is the LNG flow rate of the i-th ORV, ΔT LNG-ORVi is the difference between the NG outlet temperature and the LNG inlet temperature of the i-th ORV (°C). The LNG inlet and outlet temperature differences of all running ORVs are equal. a and b are constants. The total LNG flow rate is Q LNG-ORV (m 3 / h), Q LNG-ORV-k =Q LNG-ORV1 +Q LNG-ORV2 +…+Q LNG-ORVk , the flow rate of each ORV is equal to Q LNG-ORV1 =Q LNG-ORV / k, the seawater heat required by each ORV is equal to W SW-ORV1 , the total heat of seawater required by k ORVs W 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), the density of seawater is d(t / m 3 ), the flow rate of seawater for each operating ORV is equal to Q SW-ORV1 (m 3 / h), find Q SW-ORV1 =W LNG-ORV / (k*c*d*ΔT SW-ORV1 ), ΔT SW-ORV1 is the temperature difference of seawater entering and leaving the ORV (℃), and the environmental protection requirement is the seawater temperature difference ΔT SW-ORV1 The maximum is 5°C. If the Q SW-ORV1 SW-ORV1-MIN , then Q SW-ORV1 =Q SW-ORV1-MIN , if the 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, the preferred value is 1453, and the value range of b is 1-1.04, the preferred value is 1.02.

[0040] k ORVs are in operation, and the total LNG flow is Q LNG-ORV-k , the total seawater flow is Q​SW-ORV-k , the temperature difference between LNG entering and leaving the ORV is ΔT LNG-ORV-K , the temperature difference between seawater entering and leaving the ORV is ΔT SW-ORV-K ; k+1 ORVs are in operation, and the total LNG flow is Q LNG-ORV-(k+1) , the total seawater flow is Q SW-ORV-(k+1) , the temperature difference between LNG entering and leaving the ORV is ΔT LNG-ORV-(K+1) , the temperature difference between seawater entering and leaving the ORV is ΔT SW-ORV-(K+1) ; a and b are both constants.

[0041] The process of switching the number of ORV operations based on the switching point LNG flow rate includes:

[0042] When k ORVs are in operation, if the total LNG flow is greater than the LNG flow at the switching point, the operation of k ORVs is switched to k+1 ORVs;

[0043] When the k+1 ORV is in operation, if the total LNG flow is less than the LNG flow at the switching point, the operation of the k+1 ORV is switched to the k ORV.

[0044] At the optimal switching point between k ORV operation and k+1 ORV operation, 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) is the LNG flow rate at the switching point; the temperature difference of LNG is equal to ΔT 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) is the seawater flow rate at the switching point. Equal seawater flow rate does not mean a seawater temperature difference of ΔT SW-ORV-K and ΔT SW-ORV-(K+1) equal, because the thermal efficiency of ORV is different at different points; if k ORVs are currently in operation, Q LNG-ORV-k When the traffic increases, the operation of ORV k is switched to ORV k+1. If ORV k+1 is currently in operation, Q LNG-ORV-(k+1) When the flow rate decreases, the operation of ORV k+1 is switched to ORV k. The optimal switching point Q between ORV k and ORV k+1 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)).

[0045] Embodiment 2

[0046] like Figure 1As shown, this embodiment provides a method for determining the switching points of multiple ORV gasifiers in an LNG station, including:

[0047] LNG vaporizer station, there are 4 ORV vaporizers, the first ORV vaporizer 1, the second ORV vaporizer 2, the third ORV vaporizer 3 and the fourth ORV vaporizer 4, n = 4, seawater enters the top of the 4 ORV vaporizers from the seawater inlet pipe 5, the seawater temperature is 7 ° C, the minimum film flow rate of each vaporizer Q 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 from the vaporizer enters the seawater return channel 6. According to environmental protection requirements, the seawater return temperature shall not be lower than 2°C. The maximum LNG flow rate of each ORV is Q LNG-ORV1-MAX =900(m 3 / h), LNG is fed into each running ORV vaporizer through LNG inlet pipe 7. The temperature of LNG entering the ORV vaporizer is -130℃ and the density of LNG is 0.444 (t / m 3 ), the natural gas is sent out through the NG outlet pipe 8, and the temperature of the NG is 5°C. The preferred values ​​are a=1453, b=1.02, and the density of seawater d=1.031(t / m 3 ), the specific heat capacity of seawater c = 0.0011083 (MW / (tk)).

[0048] The optimal switching point Q between k ORVs and 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)).

[0049] The switch point of the ORV vaporizer is calculated as follows:

[0050] 1. The temperature difference between LNG and NG remains unchanged at 135℃, Q LNG-ORV-K =588.46 is the switching point between k=1 and k=2. The total seawater flow rate of both at this point is the same, which is 7320 (m 3 / h), the seawater temperature difference is different, the seawater temperature difference when k=1 is 5(℃), and the seawater temperature difference when k=2 is 3.7(℃).

[0051] 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. The total seawater flow rate of both at this point is the same, which is equal to 10980 (m 3 / h), the seawater temperature difference is different, the seawater temperature difference when k=2 is 5(℃), and the seawater temperature difference when k=3 is 4.25(℃).

[0052] 3. The temperature difference between LNG and NG remains unchanged at 135°C, Q LNG-ORV-K =1364.84 is the switching point between k=3 and k=4. The total seawater flow rate of both at this point is the same, which is equal to 14640 (m 3 / h), the seawater temperature difference is different, the seawater temperature difference when k=3 is 5(℃), and the seawater temperature difference when k=4 is 4.48(℃).

[0053] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for determining the switching point of multiple ORV vaporizers in an LNG station, characterized in that: The following steps are involved: Based on n identical ORVs connected in parallel to form an LNG gasification system; Obtaining the temperature difference of seawater entering and exiting the ORV when k ORVs are in operation and the temperature difference of seawater entering and exiting the ORV when k+1 ORVs are in operation in the LNG gasification system; The LNG flow rate at the switching point is calculated based on the temperature difference of the seawater entering and leaving the ORV when the k ORV is in operation and the temperature difference of the seawater entering and leaving the ORV when the k+1 ORV is in operation; The number of ORV operations is switched based on the switch point LNG flow rate.

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

3. The method for determining the switching points of multiple ORV gasifiers in an LNG station according to claim 2, characterized in that: The calculation expression of the required seawater heat is: W SW-ORVi =xQ LNG-ORVi ΔT LNG-ORVi / (a-bQ LNG-ORVi ); Among them, W SW-ORVi is the seawater thermal energy required by the i-th ORV, ΔT LNG-ORVi is the difference between the NG outlet temperature and the LNG inlet temperature of the i-th ORV, a and b are constants, x is the density of LNG, Q LNG-ORVi is the LNG flow rate of the i-th ORV.

4. The method for determining the switching points of multiple ORV gasifiers in an LNG station according to claim 2, characterized in that: The calculation expression of the flow rate of the seawater is: Q SW-ORV1 =W LNG-ORV / (k*c*d*ΔT SW-ORV1 ); Among them, Q SW-ORV1 is the flow rate of seawater per operating ORV, W LNG-ORV is the seawater heat required by the ORV, c is the specific heat capacity of seawater, d is the density of seawater, k is the number of ORVs, ΔT SW-ORV1 is the temperature difference of seawater entering and leaving the ORV.

5. The method for determining the switching points of multiple ORV gasifiers in an LNG station according to claim 3, characterized in that: The value range of a is 1440-1466, and the value range of b is 1-1.

04.

6. The method for determining the switching points of multiple ORV gasifiers in an LNG station according to claim 1, characterized in that: The calculation expression of the switching point LNG flow 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) is the LNG flow rate at the switching point, ΔT SW-ORV-K is the temperature difference of seawater entering and leaving the ORV when k ORVs are in operation, ΔT SW-ORV-(K+1) is the temperature difference of seawater entering and leaving the ORV when k+1 ORV is in operation.

7. The method for determining the switching points of multiple ORV gasifiers in an LNG station according to claim 1, characterized in that: The process of switching the number of ORV operations based on the switching point LNG flow rate includes: When k ORVs are in operation, if the total LNG flow is greater than the LNG flow at the switching point, the operation of k ORVs is switched to k+1 ORVs; When the k+1 ORV is in operation, if the total LNG flow is less than the LNG flow at the switching point, the operation of the k+1 ORV is switched to the k ORV.

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