Cyclic tolerance determination method and system for flash iterative computation

Abstract

The embodiment of the invention provides a cyclic tolerance determination method and system for flash evaporation iterative computation.The cyclic tolerance determination method comprises the steps that the total error amplification coefficient is determined based on different component proportions corresponding to a plurality of to-be-processed flash evaporation devices and the error amplification coefficient of each flash evaporation, the different components corresponding to the plurality of to-be-treated flash evaporation devices are component proportions of different gas phases of the plurality of to-be-treated flash evaporation devices or component proportions of different liquid phases of the plurality of to-be-treated flash evaporation devices; and based on the error total amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed and the effective component fraction of the tearing stream, utilizing a preset cycle tolerance calculation formula to determine the cycle tolerance of the tearing stream after one cycle.

Description

Technical Field

[0001] The embodiments of the present application belong to the technical field of process simulation flash iterative calculation, and in particular, to a method and system for determining a cycle tolerance for flash iterative calculation. Background Art

[0002] Chemical process simulation is an important tool in the field of chemical engineering, which is used to predict and optimize the behavior of industrial production processes. Chemical process simulation can be applied to a variety of chemical processes from laboratory scale to large-scale production.

[0003] At present, in chemical process simulation, it is necessary to manually specify the loop iteration tolerance of the process software. Although this method of manually specifying the loop iteration tolerance can give a default tolerance value, the default value will be too large for processes with a small number of two-phase devices and too small for processes with a large number of two-phase devices. Therefore, users are required to make gradual adjustments based on their usage experience, and ordinary users cannot adjust the default value according to the process they have built.

[0004] Based on this, a method for determining the cycle tolerance for flash iterative calculation is needed. Summary of the invention

[0005] The embodiments of this specification provide a method and system for determining the loop tolerance for flash iterative calculation to solve some or all of the problems: At present, in chemical process simulation, it is necessary to manually specify the loop iteration tolerance of the process software. Although this method of manually specifying the loop iteration tolerance can give a default tolerance value, the default value will be too large for processes with a small number of two-phase devices and too small for processes with a large number of two-phase devices. Therefore, users are required to make gradual adjustments based on their usage experience, and ordinary users cannot adjust the default value according to the processes they have built.

[0006] To solve the above technical problems, the embodiments of this specification are implemented as follows:

[0007] The embodiment of this specification provides a cycle tolerance determination method for flash iterative calculation, and the cycle tolerance determination method includes:

[0008] Determining a total error amplification factor based on different component proportions corresponding to the plurality of flash evaporation devices to be processed and an error amplification factor of each flash evaporation, wherein the different component proportions corresponding to the plurality of flash evaporation devices to be processed are component proportions of different gas phases of the plurality of flash evaporation devices to be processed, or component proportions of different liquid phases of the plurality of flash evaporation devices to be processed;

[0009] Based on the total error amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed and the effective component number of the tear stream, a preset cycle tolerance calculation formula is used to determine the cycle tolerance of the tear stream after one cycle.

[0010] The embodiment of this specification also provides a cycle tolerance determination system for flash evaporation iterative calculation, and the cycle tolerance determination system includes:

[0011] The total error amplification coefficient determination module determines the total error amplification coefficient based on the different component proportions corresponding to the plurality of flash evaporation devices to be processed and the error amplification coefficient of each flash evaporation, wherein the different component proportions corresponding to the plurality of flash evaporation devices to be processed are the component proportions of different gas phases of the plurality of flash evaporation devices to be processed, or the component proportions of different liquid phases of the plurality of flash evaporation devices to be processed;

[0012] The cycle tolerance calculation module determines the cycle tolerance of the tear stream after one cycle using a preset cycle tolerance calculation formula based on the total error amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed, and the effective component number of the tear stream.

[0013] At least one of the above-mentioned technical solutions adopted in the embodiments of this specification can achieve the following beneficial effects: based on the different component proportions corresponding to the several flash evaporation devices to be processed and the error magnification coefficient of each flash evaporation, the total error magnification coefficient is determined, and the different component proportions corresponding to the several flash evaporation devices to be processed are the component proportions of different gas phases of the several flash evaporation devices to be processed, or the component proportions of different liquid phases of the several flash evaporation devices to be processed; based on the total error magnification coefficient, the gasification fraction corresponding to the several flash evaporation devices to be processed and the effective component number of the tear flow stock, the preset cycle tolerance calculation formula is used to determine the cycle tolerance of the tear flow stock after one cycle, which can be applied to the tear flow stock in the process simulation with circulation to realize automatic setting of the cycle tolerance and can realize the optimal tolerance calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. Some specific embodiments of the present application will be described in detail in an illustrative and non-restrictive manner with reference to the drawings. The same reference numerals in the drawings indicate the same or similar components or parts. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings:

[0015] Figure 1 A schematic flow chart of a method for determining cycle tolerance for flash iterative calculation provided in an embodiment of this specification;

[0016] Figure 2 A schematic diagram of a single flash evaporation device provided for an embodiment of this specification;

[0017] Figure 3 A schematic diagram of a process for determining the component proportions of different gas phases and the component proportions of different liquid phases of a flash evaporation device provided in an embodiment of this specification;

[0018] Figure 4 A schematic diagram of a cyclic iteration of a process simulation provided in an embodiment of this specification;

[0019] Figure 5 A schematic diagram of a cycle tolerance determination system for flash iterative calculation provided in accordance with an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0021] Figure 1 The flowchart of a method for determining the cycle tolerance of flash iterative calculation provided in the embodiment of this specification is as follows. From the program perspective, the execution subject of the method for determining the cycle tolerance of flash iterative calculation is a program installed on an application server or an application terminal. It can be understood that the method can be executed by any device, equipment, platform, or device cluster with computing and processing capabilities. Figure 1 As shown, the cycle tolerance determination method includes:

[0022] Step S101: Determine the total error amplification coefficient based on the different component proportions corresponding to the several flash evaporation devices to be processed and the error amplification coefficient of each flash evaporation, where the different component proportions corresponding to the several flash evaporation devices to be processed are the component proportions of different gas phases of the several flash evaporation devices to be processed, or the component proportions of different liquid phases of the several flash evaporation devices to be processed.

[0023] In the embodiment of this specification, the method for obtaining the proportions of different components corresponding to the several flash evaporation equipments to be processed includes:

[0024] Determining a phase equilibrium constant based on the temperature, pressure and composition of flash streams of a plurality of flash devices to be processed;

[0025] Based on the phase equilibrium constant and the initial gasification fraction, determining the component proportions of different gas phases of the plurality of flash evaporation devices to be processed;

[0026] Determining a flash evaporation convergence judgment function based on the component proportions of different gas phases of the plurality of flash evaporation devices to be processed;

[0027] If the flash evaporation convergence judgment function satisfies the flash evaporation tolerance, the component proportions of different liquid phases of the plurality of flash evaporation equipments to be processed are determined.

[0028] In the embodiment of this specification, the calculation formula for the component proportions of different gas phases of the several flash evaporation devices to be processed is:

[0029]

[0030] in,

[0031] y i represents the gas phase proportion of component i;

[0032] K i represents the phase equilibrium constant of component i;

[0033] e j represents the initial gasification fraction;

[0034] The calculation formula of the flash steam convergence judgment function is:

[0035]

[0036] in,

[0037] f(e) represents the flash evaporation convergence judgment function;

[0038] y i represents the gas phase proportion of component i;

[0039] K i represents the phase equilibrium constant of component i;

[0040] z i represents the proportion of component i;

[0041] e j represents the initial gasification fraction;

[0042] The calculation formula for the component proportions of different liquid phases of the several flash evaporation devices to be processed is:

[0043]

[0044] in,

[0045] x i represents the liquid phase proportion of component i;

[0046] K i represents the phase equilibrium constant of component i;

[0047] e j represents the initial gasification fraction.

[0048] In a specific embodiment, the phase equilibrium constant can be obtained by looking up a chart or an empirical formula, which will not be described in detail here.

[0049] In the embodiment of this specification, the method further comprises:

[0050] If the flash evaporation convergence judgment function does not satisfy the flash evaporation tolerance, adjusting the initial gasification fraction to an updated initial gasification fraction, and then determining the component proportions of different gas phases of the plurality of flash evaporation devices to be processed;

[0051] in,

[0052] The adjusting the initial gasification fraction to an updated initial gasification fraction specifically includes:

[0053]

[0054] in,

[0055] e j+1 represents the updated initial gasification fraction;

[0056] e j represents the initial gasification fraction;

[0057] f(e) represents the flash evaporation convergence judgment function;

[0058] f′(e) represents the updated flash convergence judgment function,

[0059] Figure 2 Schematic diagram of a single flash evaporation device provided in the embodiment of this specification. In the process of chemical process simulation calculation, the temperature, pressure and feed composition of the product calculated for the tank and other equipment have been determined, and the gas-liquid phase composition and vaporization fraction after flash evaporation need to be calculated.

[0060] Figure 3 A schematic diagram of a process for determining the component proportions of different gas phases and different liquid phases of a flash evaporation device provided in an embodiment of this specification. Figure 3 As shown, based on the temperature T, pressure P and composition z of the flash streams of several flash equipment to be processed i ; Determine the phase equilibrium constant K of different components i at temperature T and pressure P i (T,P); Determine the initial gasification fraction e j ; Calculate the component proportion y of different gas phases of several flash evaporation equipment to be processed i ; Calculate the flash evaporation convergence judgment function f(e); if |f(e)|<ε flash , then calculate the component proportion x of different liquid phases of several flash evaporation equipment to be processed i ; If |f(e)|≥εflash , then according to Adjustments are made to update the initial vaporization fraction.

[0061] The process calculation is composed of multiple devices. The calculation of each device is mainly composed of flash calculation. The target value of the calculation equation should be 0 in theory, but due to the characteristics of iterative solution, the target equation cannot reach absolute 0. Usually, the convergence condition is set to a minimum value, such as 1e-6, which is recorded as ε here. flash Then the composition x calculated by flash evaporation is i With y i It is not an absolutely accurate value, but a value with a certain error, expressed as:

[0062]

[0063] In the above formula Indicates the true value calculated when the target equation is 0, x i ,y i They represent the values ​​actually calculated and solved due to the set tolerance, Represents the error carried by the true value.

[0064] The process simulation usually involves calculations for multiple devices, and loops are often formed between the devices. Products that do not meet the requirements are usually processed and reprocessed as feed. Figure 4 This is a schematic diagram of the iterative cycle of the process simulation provided in the embodiment of this specification. Figure 4 As shown in the figure, when there is a cycle, one of the flows in the cycle is usually torn, which is called "tear flow". The cycle needs to be iterated to converge, and it is usually required that the flow rates of all components calculated twice before and after the tear are consistent. When using computer iterative calculations, absolute equality cannot be achieved, and it is also required that the error of the two calculations of the tear flow is less than the tolerance.

[0065] z i -z i-1 <ε 撕裂流

[0066] Since the tear flow is also an intermediate calculation flow, the composition of the tear flow is erroneous: in, Indicates the composition z i The error is found in the flash calculation formula. After each flash calculation, the error will be amplified. When there are fewer devices in the cycle, ε 撕裂流 A relatively small value can be specified. When there are many devices in the loop, the tear flow error at the inlet is amplified. When the user specifies a smaller ε 撕裂流 , which will cause the loop to fail to converge.

[0067] In the embodiment of this specification, the total error amplification factor specifically includes:

[0068] The component proportions of the different gas phases are: And the ideal component ratio of different gas phases The error of the component proportions of different gas phases is: Then the error magnification factor of each flash evaporation is The total error amplification factor is: Wherein, n represents the flash evaporation equipment n;

[0069] Or the composition ratio of the different liquid phases is:

[0070] And the ideal component ratio of different liquid phases The error of the component proportions of different liquid phases is: Then the error magnification factor of each flash evaporation is The total error amplification factor is: Wherein, n represents the flash evaporation equipment n.

[0071] In order to understand the total error amplification factor s, the derivation process of the formula is introduced below. Assume that the flow composition z at the tearing flow i With error

[0072]

[0073] y calculated by flash evaporation i for

[0074]

[0075] make

[0076]

[0077] Then y i Simplified to

[0078]

[0079] make

[0080]

[0081] From the above formula we can see yes s i times, i It is called the error magnification factor of each flash. After each flash, the tolerance will be magnified by s itimes. After multiple flash evaporations, the error magnification is:

[0082]

[0083] Similarly, x calculated by flash evaporation i for make And the ideal component ratio of different liquid phases Then the error of the component proportion of different liquid phases is:

[0084] make

[0085] From the above formula we can see yes s i times, i It is called the error magnification factor of each flash. After each flash, the tolerance will be magnified by s i times. After multiple flash evaporations, the error magnification is:

[0086] It can be seen that in the flash evaporation process, whether for the liquid phase component or the gas phase component, after multiple flash evaporations, the error magnification factor is:

[0087] In the embodiment of this specification, the total error amplification factor s and the phase equilibrium constant K i , the gas phase fraction e and the number of two-phase devices e, and s i =1 / e j ;

[0088] Then the total magnification factor s is:

[0089] in,

[0090] s represents the total amplification factor;

[0091] e j represents the initial gasification fraction;

[0092] j represents the gas phase component;

[0093] n represents the flash evaporation equipment n.

[0094] Since the total error amplification factor s and the phase equilibrium constant K i , gas phase fraction e and the number of two-phase devices e. Different variables have different effects on the total error amplification factor s, which will be explained below. Phase equilibrium constant K i Impact: When K iWhen K is 0, s is 0, the error is not amplified, and i As increases, the error coefficient gradually approaches 1 / e.

[0095] Influence of gas phase fraction e: When e is 0, the error amplification factor is K i , when e is 1, the error amplification factor is 1.

[0096] Impact of the number of two-phase devices n: As the number of two-phase devices increases, the error amplification factor increases exponentially.

[0097] From the influence of the above variables, it can be concluded that device n has the greatest impact on the error amplification factor, which is an exponential relationship. Assume K i If the value is large, s i =1 / e j .

[0098] Based on this, the total error amplification factor is:

[0099] Step S103: Based on the total error amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed and the effective component number of the tear stream, a preset cycle tolerance calculation formula is used to determine the cycle tolerance of the tear stream after one cycle.

[0100] Continuing the previous derivation process, when the flash tolerance is ε flash , then the average tolerance of each component is Where m is the number of components. Assume that the initial tolerance of the tear flow is After calculating one cycle, the cycle tolerance should be set to

[0101] In the embodiment of this specification, the preset cycle tolerance calculation formula is:

[0102] in,

[0103] ε 撕裂流 represents the cyclic tolerance of the tear stream;

[0104] ε flash represents the flash tolerance;

[0105] m represents the number of groups;

[0106] s represents the total error amplification factor.

[0107] In the embodiments of this specification, ε flash Set to 1e-6.

[0108] In order to further understand the method for determining the cycle tolerance for flash iterative calculation provided by the embodiments of this specification, it will be described below in conjunction with specific embodiments.

[0109] The tearing flow of a certain device is shown below. There are three two-phase flash evaporation devices involved in the device, and the flash evaporation calculation tolerance is 0.000001.

[0110] The tear flow components are as follows:

[0111] serial number Components Molar ratio 1 C1 0.84326 2 C2 0.10412 3 C3 0.00145 4 IC4 0.00001 5 NC4 0 6 IC5 0 7 NC5 0 8 NC6 0 9 NC7 0 10 NC8 0 11 NC9 0 12 NC10 0 13 H2O 0 14 CO2 0.05034 15 N2 0.00081 16 H2S 0 17 MDEA 0

[0112] It can be seen that the tearing stream has 6 effective components, so m = 6. After the initial cycle calculation, the vaporization fractions of the three flash evaporation equipment are e1 = 0.90979, e2 = 0.84956, e3 = 0.95463,

[0113] so

[0114]

[0115] The convergence error of the initial tearing flow calculated by the present invention is 0.000000226.

[0116] The embodiment of the present specification provides a method for determining a cycle tolerance for flash evaporation iterative calculation. Based on the temperature, pressure and composition of the flash evaporation streams of the several flash evaporation devices to be processed, the component proportions of different gas phases and the component proportions of different liquid phases of the several flash evaporation devices to be processed are determined, and the component proportions of different gas phases of the several flash evaporation devices to be processed meet the flash evaporation tolerance; based on the component proportions of the different gas phases and the error magnification coefficient of each flash evaporation, the total error magnification coefficient is determined; based on the gasification fraction corresponding to the several flash evaporation devices to be processed, the effective component number of the tear stream and the total error magnification coefficient, the cycle tolerance of the tear stream after one cycle is determined using a preset cycle tolerance calculation formula. The method can be applied to the tear stream in the process simulation with circulation to realize automatic setting of the cycle tolerance and can realize the optimal tolerance calculation.

[0117] The foregoing embodiment of this specification provides a method for determining a cycle tolerance for flash iterative calculation. Based on the same idea, the embodiment of this specification also provides a system for determining a cycle tolerance for flash iterative calculation. Figure 5 A schematic diagram of a cycle tolerance determination system for flash iterative calculation provided in this embodiment. Figure 5 As shown, the cycle tolerance determination system includes:

[0118] The total error magnification coefficient determination module 501 determines the total error magnification coefficient based on the different component proportions corresponding to the plurality of flash evaporation devices to be processed and the error magnification coefficient of each flash evaporation, wherein the different component proportions corresponding to the plurality of flash evaporation devices to be processed are the component proportions of different gas phases of the plurality of flash evaporation devices to be processed, or the component proportions of different liquid phases of the plurality of flash evaporation devices to be processed;

[0119] The cycle tolerance calculation module 503 determines the cycle tolerance of the tear stream after one cycle using a preset cycle tolerance calculation formula based on the total error magnification coefficient, the gasification fraction corresponding to the plurality of flash evaporation devices to be processed and the effective component number of the tear stream.

[0120] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining cycle tolerance for flash iterative calculation, characterized in that: The cycle tolerance determination method comprises: Determining a total error amplification factor based on different component proportions corresponding to the plurality of flash evaporation devices to be processed and an error amplification factor of each flash evaporation, wherein the different component proportions corresponding to the plurality of flash evaporation devices to be processed are component proportions of different gas phases of the plurality of flash evaporation devices to be processed, or component proportions of different liquid phases of the plurality of flash evaporation devices to be processed; Based on the total error amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed and the effective component number of the tear stream, a preset cycle tolerance calculation formula is used to determine the cycle tolerance of the tear stream after one cycle.

2. The method for determining cycle tolerance according to claim 1, wherein: The method for obtaining the proportions of different components corresponding to the plurality of flash evaporation devices to be processed includes: Determining a phase equilibrium constant based on the temperature, pressure and composition of flash streams of a plurality of flash devices to be processed; Based on the phase equilibrium constant and the initial gasification fraction, determining the component proportions of different gas phases of the plurality of flash evaporation devices to be processed; Determining a flash evaporation convergence judgment function based on the component proportions of different gas phases of the plurality of flash evaporation devices to be processed; If the flash evaporation convergence judgment function satisfies the flash evaporation tolerance, the component proportions of different liquid phases of the plurality of flash evaporation equipments to be processed are determined.

3. The method for determining cycle tolerance according to claim 1, wherein: The calculation formula for the component proportions of different gas phases of the several flash evaporation devices to be processed is: in, y i represents the gas phase proportion of component i; K i represents the phase equilibrium constant of component i; e j represents the initial gasification fraction; The calculation formula of the flash steam convergence judgment function is: in, f(e) represents the flash evaporation convergence judgment function; y i represents the gas phase proportion of component i; K i represents the phase equilibrium constant of component i; z i represents the proportion of component i; e j represents the initial gasification fraction; The calculation formula for the component proportions of different liquid phases of the several flash evaporation devices to be processed is: in, x i represents the liquid phase proportion of component i; K i represents the phase equilibrium constant of component i; e j represents the initial gasification fraction.

4. The method for determining cycle tolerance according to claim 3, characterized in that: The method further comprises: If the flash evaporation convergence judgment function does not satisfy the flash evaporation tolerance, adjusting the initial gasification fraction to an updated initial gasification fraction, and then determining the component proportions of different gas phases of the plurality of flash evaporation devices to be processed; in, The adjusting the initial gasification fraction to an updated initial gasification fraction specifically includes: in, e j+1 represents the updated initial gasification fraction; e j represents the initial gasification fraction; f(e) represents the flash evaporation convergence judgment function; f′(e) represents the updated flash convergence judgment function, 5. The method for determining cycle tolerance according to claim 1, wherein: The total error amplification factor specifically includes: The component proportions of the different gas phases are: And the ideal component ratio of different gas phases The error of the component proportions of different gas phases is: Then the error magnification factor of each flash evaporation is The total error amplification factor is: Wherein, n represents the flash evaporation equipment n; Or the composition ratio of the different liquid phases is: And the ideal component ratio of different gas phases The error of the component proportions of different liquid phases is: Then the error magnification factor of each flash evaporation is The total error amplification factor is: Wherein, n represents the flash evaporation equipment n.

6. The method for determining cycle tolerance according to claim 5, characterized in that: The total error amplification factor s and the phase equilibrium constant K i , the gas phase fraction e and the number of two-phase devices e, and s i =1 / e j ; Then the total magnification factor s is: in, s represents the total amplification factor; e j represents the initial gasification fraction; j represents the gas phase component; n represents the flash evaporation equipment n.

7. The cycle tolerance determination method according to claim 1, characterized in that: The preset cycle tolerance calculation formula is: in, ε 撕裂流 represents the cyclic tolerance of the tear stream; ε flash represents the flash tolerance; m represents the number of groups; s represents the total error amplification factor.

8. A cycle tolerance determination system for flash iterative calculation, characterized in that: The cycle tolerance determination system comprises: The total error amplification coefficient determination module determines the total error amplification coefficient based on the different component proportions corresponding to the plurality of flash evaporation devices to be processed and the error amplification coefficient of each flash evaporation, wherein the different component proportions corresponding to the plurality of flash evaporation devices to be processed are the component proportions of different gas phases of the plurality of flash evaporation devices to be processed, or the component proportions of different liquid phases of the plurality of flash evaporation devices to be processed; The cycle tolerance calculation module determines the cycle tolerance of the tear stream after one cycle using a preset cycle tolerance calculation formula based on the total error amplification coefficient, the gasification fractions corresponding to the plurality of flash evaporation devices to be processed, and the effective component number of the tear stream.

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