Method and system for calculating oil mixing quantity in dead oil section of product oil transportation

Abstract

The invention provides a method and a system for calculating the oil mixing quantity of a dead oil section in product oil conveying, and belongs to the technical field of product oil sequential conveying pipelines. The method comprises the following steps: (1) measuring the density, viscosity and flow velocity of front and rear oil products and the concentration gradient of the rear oil product in the axial direction of a blind pipe section in the replacement process; and (2) calculating a turbulence diffusion coefficient by using a turbulence diffusion coefficient calculation formula considering the flow velocity of the main pipe and the properties of the front and back oil products, and obtaining the oil mixing amount by a common oil mixing formula according to the Fischer's law of diffusion. According to the calculation method, factors such as the mixed oil kinematic viscosity, the mixed oil flow state, the hydraulic friction resistance and the mixed oil flow speed are considered, and the calculation precision of the diffusion coefficient and the mixed oil amount can be improved; and the mixed oil quantity calculation system measures the density difference of the oil products at the upper end and the lower end of the blind pipe, converts the density difference into the mass concentration difference of the subsequent oil products at the moment, and calculates the measured parameters through a computer to obtain the mixed oil quantity generated by the switching, so that the process is clear, the operability is high, and the mixed oil quantity calculation system is convenient for personnel in the technical field to use.

Description

Technical Field

[0001] The invention belongs to the technical field of finished oil sequential transportation pipelines, and in particular relates to a method and system for calculating the mixed oil amount in a dead oil section of finished oil transportation. Background Art

[0002] There is a blind end in the process flow of the station for the sequential transportation of finished oil, and the preceding oil products are piled up to form a dead oil section; the succeeding oil products carry the preceding oil products retained in the dead corner section, which causes a considerable amount of mixed oil, so that the oil products are contaminated and the oil quality is reduced. In the actual working process of sequential transportation, the amount of mixed oil within a certain concentration range will be determined according to the relationship between the change of oil product concentration at the end of the pipeline with time, so as to cut the mixed oil section. The turbulent diffusion coefficient Dt combines the influence of various factors on the diffusion rate during the oil product alternation process. The current diffusion coefficient calculation formula is mainly summarized from experiments, but the existing empirical formulas such as the Jabolonsky-Schitskirov formula, the Asaturian formula and the Nechvalya-Jaboslonki formula mainly study the relationship between the turbulent diffusion coefficient and the viscosity, flow state and local resistance loss of the preceding and succeeding oil products. However, the influence of the main flow velocity on the diffusion degree of the succeeding oil products under turbulent conditions is not considered enough, resulting in limited calculation accuracy. Experimental results also show that the calculated values ​​obtained by them deviate greatly from the actual values. Therefore, the applicability and accuracy of the existing empirical formula of the turbulent diffusion coefficient Dt still have a lot of room for improvement. In order to monitor the oil mixing in the finished oil pipeline, reduce the oil mixing tail and facilitate the cutting of the oil mixing section, a more accurate calculation method of the turbulent diffusion coefficient is needed.

[0003] According to experiments, the present invention establishes a difference fitting formula, modifies the original formula, and obtains a turbulent diffusion coefficient calculation formula that takes into account the main flow velocity and the properties of the preceding and succeeding oil products. Compared with the existing empirical formula, the calculation formula has higher prediction accuracy. Summary of the invention

[0004] The present invention is to correct the formula to solve the problem that the general oil mixing formula has poor applicability and the prediction accuracy needs to be improved, as well as the statistical system structure of the oil mixing amount generated by the blind pipe section replacing the preceding oil product when the finished oil is transported in sequence. 1. The present invention is realized by the following technical solutions:

[0005] (1) Use instruments such as viscometers, flow meters, and pressure densitometers to measure the density and viscosity of the oil products in the front and rear lines, the flow rate of the oil products in the pipe, and the concentration gradient of the oil products in the front and rear lines in the blind pipe.

[0006] (2) Based on the measured parameters, the turbulent diffusion system calculation formula (1.2.1) considering the main flow velocity and the properties of the upstream and downstream oil products, Fick's diffusion law (1.2.2) and the oil mixing formula (1.2.3) are used to calculate the oil mixing amount G in the dead oil section under different main flow velocities and oil products:

[0007]

[0008]

[0009] G=WFdt (1.2.3)

[0010] Where D t m is the turbulent diffusion coefficient considering the main flow velocity and the properties of the oil in front and behind. 2 / s;

[0011] s is the main pipe flow rate, m / s;

[0012] v 50 To calculate the kinematic viscosity of the mixed oil, m 2 / s, And v1>v2, m 2 / s;

[0013] v1 and v2 are the kinematic viscosities of the oils in the front and rear rows, respectively;

[0014] Re is in ν 50 The calculated Reynolds number, a dimensionless quantity;

[0015] λ is the hydraulic friction coefficient, dimensionless quantity;

[0016] W is the diffusion velocity, m / s;

[0017] F is the cross-sectional area of ​​the pipe, m 2 ;

[0018] G is the amount of a certain oil product diffused into another oil product through the pipeline cross section within dt time, m 3 ;

[0019] is the concentration gradient along the line.

[0020] 2. The present invention considers the turbulent diffusion coefficient D of the main flow velocity and the properties of the oil products in the front and rear lines. t The calculation formula is implemented through the following technical solutions:

[0021] (1) First, determine the fluid components in the oil mixing section and their sequence of flow;

[0022] (2) Establish a physical model of the blind pipe section and perform mesh division;

[0023] (3) Formulate boundary conditions and oil parameters;

[0024] (4) Finally, the experimental results are fitted into “flow rate-D t The experimental results are plotted as a curve and the "flow rate-D" calculated by the existing empirical formulat The calculation formula of turbulent diffusion coefficient considering the main flow velocity and the properties of the upstream and downstream oils was finally obtained by differential fitting.

[0025] Based on the general oil mixing formula and Fick's diffusion law, the experimental results at different average flow rates were collected and sorted to obtain the turbulent diffusion coefficient D of each experiment. t :

[0026]

[0027] The conditions for establishing the turbulent diffusion coefficient calculation formula model and calculating the settings considering the main pipe flow velocity and the properties of the leading and trailing oils include: 1) Determining that the model meets or is close to the revised use conditions, the inner diameter of the main pipe is 306mm, the outer diameter of the blind pipe is 255mm, and the length of the blind pipe is 1000mm; 2) Determining the properties of the leading and trailing oils, the properties of the leading oil are close to diesel, and the properties of the trailing oil are close to gasoline.

[0028] Through the calculation results, it is found that under the condition of flow rate of 1m / s, the D t The value fluctuates slightly. Considering the calculation time and data volume, the 20th second is selected as the data processing point. Change the main flow velocity and select a series of data points with a velocity interval of 0.05 m / s from 0.9 to 1.6 m / s to perform experimental simulation to obtain D t .

[0029] After a series of experimental results were fitted with curves, they were compared with the Nechivaliya-Yabsolonki formula (4.3). It was found that there was a large difference between the two, but the difference decreased as the flow rate of the main pipe increased, and the two gradually fit in the later period.

[0030]

[0031] Based on the Niechwala-Yabschluss formula, a difference fitting formula was established by fitting the curve. The original formula was added with the difference fitting formula to obtain the turbulent diffusion coefficient calculation formula (4.4) that takes into account the main flow velocity and the properties of the upstream and downstream oils.

[0032]

[0033] Where: D tx is the corrected turbulent diffusion coefficient considering the main flow velocity and the properties of the oil in front and behind, m 2 / s.

[0034] After checking and calculating, the calculation results using this formula are basically consistent with the experimental results.

[0035] 3. By setting a flow meter on the main pipe section, the average flow rate and volume flow rate of the rear oil product when switching oil products are obtained; a pressure density meter is set on the blind pipe section, and the density difference between the two oil products along the axial direction of the blind pipe section when the front and rear oil products are replaced is converted into the concentration gradient of the rear oil product along the axial direction of the blind pipe at this time. The density and viscosity of the front and rear oil products, the density and viscosity of the mixed oil, the volume flow rate of the main pipe section, and the basic dimensions of the dead oil section including the diameter and length of the main pipe and the blind pipe are substituted into the above turbulent diffusion coefficient calculation formula considering the main pipe flow rate and the properties of the front and rear oil products, and the turbulent diffusion coefficient D under the corresponding flow rate and oil product properties is calculated by computer. t , and then use Fick's diffusion law and the general oil mixing formula to calculate the amount of mixed oil generated during the replacement process.

[0036] The present invention adopts the above technical solution, and can achieve the following beneficial effects:

[0037] (1) The dead oil section mixed oil amount calculation method provided by the present invention introduces a fitting difference on the basis of the existing turbulence coefficient empirical formula, thereby improving the calculation accuracy of the turbulence diffusion coefficient;

[0038] (2) The method for calculating the amount of mixed oil in the dead oil section provided by the present invention has a clear calculation process and strong operability, and is convenient for use by personnel in the field of technology;

[0039] (3) The oil mixing amount calculation system structure provided by the present invention can be used to collect the density and viscosity of the front and rear oil products, the density and viscosity of the mixed oil, and the volume flow of the main pipe section when the oil products are switched, and upload them to the computer to calculate the oil mixing amount generated after the front and rear oil products of the batch are replaced. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A flow chart of a method for calculating the amount of mixed oil in a dead oil section of finished oil transportation provided by the present invention;

[0041] Figure 2 A schematic diagram of the structure and oil mixing process of a system for calculating the amount of mixed oil in a dead oil section of finished oil transportation provided by the present invention; DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with the accompanying drawings, but the present invention is not limited to the following embodiments.

[0043] Considering the turbulent diffusion coefficient calculation formula of the main pipe flow velocity and the properties of the upstream and downstream oil products, the turbulent diffusion coefficient in the dead oil section under different main pipe flow velocities and oil properties is calculated. The specific calculation formula is as follows:

[0044]

[0045] Implementation Taking this model as an example, the turbulent diffusion coefficient values ​​at the intersection of the main pipe and blind pipe with main pipe velocities of 1.005m / s, 1.305m / s, and 1.605m / s are predicted. The definitions of relative deviation (RD) and average relative difference (ARD) are as follows:

[0046]

[0047] In the formula, G tcal The amount of mixed oil is calculated based on the turbulent diffusion coefficient calculation formula related to the main flow velocity and the properties of the preceding and following oil products;

[0048] G texp is the amount of mixed oil obtained in the experiment.

[0049] The steps for calculating the amount of mixed oil based on the turbulent diffusion coefficient calculation formula considering the main flow velocity and the properties of the upstream and downstream oils are shown in Figure 1 As shown, the steps include:

[0050] 1) Make sure the model meets or is close to the revised usage conditions. The inner diameter of the main pipe is 306mm, the outer diameter of the blind pipe is 255mm, and the length of the blind pipe is

[0051] 1000mm;

[0052] 2) Determine the properties of the front and rear oils. The front oil is close to diesel, while the rear oil is close to gasoline, both of which meet the oil property requirements;

[0053] 3) Collect data such as oil flow velocity in the dead oil section and blind pipe concentration gradient through post-processing, and process the data.

[0054] Based on the method of the present invention, the turbulent diffusion coefficient D under different main pipe flow velocities in the blind pipe mixing section is calculated. t Make predictions and compare the predicted values ​​with the experimental results, as shown in the following table:

[0055]

[0056] Table 1 Prediction results of turbulent diffusion coefficient under main flow conditions

[0057] It can be seen from the above table that the relative deviations (RD) between the predicted values ​​and the experimental values ​​of the three groups of turbulent diffusion coefficient calculation formulas related to the main flow velocity and the properties of the upstream and downstream oils are within 4% to 33%, and the average relative deviation (ARD) is only 17.13%. Compared with the average relative deviation (ARD) of 100.27% of the original formula, the calculation method of the present invention has a higher prediction accuracy.

[0058] According to Fick's diffusion law and the general oil mixing formula, the predicted value of the oil mixing amount in this section under different main pipe flow rates is further obtained and compared with the experimental results, as shown in the following table:

[0059]

[0060] Table 2 Prediction results of diffusion velocity under main flow rate conditions

[0061]

[0062] Table 3 Prediction results of oil mixing amount under main flow velocity conditions

[0063] It can be seen from the above table that the relative deviations (RD) of the three groups of predicted values ​​of mixed oil content and the experimental values ​​are within 4% to 33%, and the average relative deviation (ARD) is only 17.15%. Compared with the average relative deviation (ARD) of 100.31% of the uncorrected empirical formula, the calculation method of the present invention has a higher prediction accuracy.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method and system for calculating the amount of mixed oil in the dead oil section of finished oil transportation, characterized in that: The following steps are involved: (1) Use instruments such as viscometers, flow meters, and pressure densitometers to measure the density and viscosity of the oil products in the front and rear lines, the flow rate of the oil products in the pipe, and the concentration gradient of the oil products in the front and rear lines in the blind pipe; (2) Based on the measured parameters, the turbulent diffusion coefficient calculation formula considering the main flow velocity and the properties of the upstream and downstream oil products, Fick's diffusion law (1.2.1) and the oil mixing formula (1.2.2) are used to calculate the oil mixing amount G in the dead oil section under different main flow velocities and oil products: G=WFdt (1.2.2) Where W is the diffusion velocity, m / s; F is the cross-sectional area of ​​the pipe, m 2 ; G is the amount of a certain oil product diffused into another oil product through the pipeline cross section within dt time, m 3 ; is the concentration gradient along the line.

2. The turbulent diffusion coefficient calculation formula considering the main flow velocity and the properties of the preceding and succeeding oil products according to claim 1 is characterized in that: Taking into account the influence of factors such as the kinematic viscosity of the mixed oil, the mixed oil flow state in the blind pipe section, the hydraulic friction and the mixed oil flow rate on the diffusion degree of the rear oil mixed into the front oil, the diffusion coefficient calculation term related to the flow rate is established, that is, the 2nd, 3rd and 4th items on the right side of formula (2.1); using this formula, a more accurate relationship between the turbulent diffusion coefficient and the main flow velocity can be obtained. The specific formula is as follows: Where D t m is the turbulent diffusion coefficient considering the main flow velocity and the properties of the oil in front and behind. 2 / s; s is the main pipe flow rate, m / s; v 50 To calculate the kinematic viscosity of the mixed oil, m 2 / s, And v1>v2, m 2 / s; v1 and v2 are the kinematic viscosities of the oils in the front and rear rows, respectively; Re is press v 50 The calculated Reynolds number, a dimensionless quantity; λ is the hydraulic friction coefficient, Dimensionless quantity.

3. The system for calculating the amount of mixed oil in the dead oil section of finished oil transportation according to claim 1 is characterized in that A flow meter is provided in the main pipe section to measure the average flow rate of the rear oil product in the main pipe when the oil product is switched; a pressure density meter is provided in the blind pipe section to measure the density difference of the rear oil product during a period of time when the blind pipe section is replaced, and convert it into the mass concentration difference of the rear oil product in the blind pipe at this time through the relationship between density and mass concentration; the density and viscosity of the front and rear oil products, the density and viscosity of the mixed oil, the volume flow rate of the main pipe section and the basic size of the dead oil section measured by the above-mentioned instruments are collected, including the diameter and length of the main pipe and the blind pipe, and the above-mentioned parameters are substituted into the turbulent diffusion coefficient calculation formula considering the main pipe flow rate and the properties of the front and rear oil products, Fick's diffusion law and the general oil mixing formula described in claim 1 by computer, and the calculation is completed in the computer in sequence according to the three formulas, and finally the mixed oil amount during the oil product switching is obtained.

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