Method for predicting supercritical carbon dioxide extraction oily sludge conditions and components

Abstract

The invention discloses a method for predicting supercritical carbon dioxide extraction oily sludge conditions and components, and relates to the technical field of oily sludge treatment. Comprising the following steps: determining the content of each component of crude oil in the oily sludge; based on the carbon number of each component of the crude oil and a characterization method, merging the components of the crude oil to obtain a virtual component, and determining a critical condition of the virtual component; calculating the viscosity of the supercritical carbon dioxide / crude oil mixture by taking the critical condition of the supercritical carbon dioxide as a reference and adopting a gradient rising method, and taking the turning point of the viscosity change as the optimal injection amount of the supercritical carbon dioxide under different conditions; and on the basis of the critical condition of the supercritical carbon dioxide, the optimal extraction condition and component are calculated by combining the optimal injection amount of the supercritical carbon dioxide. By means of the method, the optimal conditions of supercritical carbon dioxide extraction of different oily sludge and extracted components can be predicted, and technical guidance is provided for design of an actual extraction process.

Description

Technical Field

[0001] The invention relates to the technical field of oily sludge treatment, in particular to a method for predicting conditions and components of supercritical carbon dioxide extraction of oily sludge. Background Art

[0002] According to statistics, my country's petrochemical industry generates an average of approximately 800,000 tons of oily solid waste annually. These wastes typically have an oil-based content between 10% and 50%, and are characterized by good emulsification, high viscosity, and high treatment costs. If these oily solid wastes are discharged without treatment, they will not only occupy a large amount of arable land but also cause serious pollution to soil, water, and air. Recycling the oil-based components of these wastes offers enormous economic potential. Currently, the commonly used oily solid waste treatment technologies in the petrochemical industry include containment and degradation technologies. However, these technologies suffer from limitations such as difficulty in reducing pollution, long treatment cycles, and susceptibility to climate change. Supercritical CO2 extraction (SCCO2) utilizes the low viscosity, low surface tension, high solubility, and high diffusion coefficient of SCCO2 to extract the oil-based components from sludge, enabling efficient separation of oil from rock and soil minerals and resource recovery of oil-based products. Therefore, utilizing SCCO2 extraction to achieve comprehensive treatment of oily solid waste, including harmless and clean treatment and resource recovery, is of vital importance to environmental protection.

[0003] At present, when extracting oil base from oily sludge by supercritical carbon dioxide, the optimal extraction temperature and pressure are mainly determined by experiments combined with response surface optimization method and orthogonal experimental method. However, the cycle of determining the optimal extraction conditions by experiments is long and costly, and it is impossible to predict the extraction components and extraction amount. In addition, although there are reports in the literature that use theoretical methods to predict the optimal extraction pressure and temperature, the corresponding component changes and extraction amount during the extraction process cannot be predicted, which has limitations. In view of the shortcomings of the existing technology that cannot predict the optimal extraction conditions and components during the supercritical carbon dioxide extraction of oily sludge, based on the variation law of the liquid phase mole fraction and the component distribution of the extraction system, and taking full account of the influencing factors of the extraction process, a method for predicting the conditions and components of supercritical carbon dioxide extraction of oily sludge is proposed. The method can predict the extraction temperature, pressure, carbon dioxide content and oil base extraction amount of oily sludge of different properties under different carbon dioxide contents, thereby providing guidance for the design of the extraction process. Summary of the Invention

[0004] To solve at least one of the above problems, the present invention provides a method for predicting the conditions and components of supercritical carbon dioxide extraction of oily sludge.

[0005] The technical solution of the present invention is: a method for predicting the conditions and components of supercritical carbon dioxide extraction of oily sludge, comprising the following steps:

[0006] S1. Determine the content of each component of crude oil in oily sludge;

[0007] S2. Based on the carbon number of each crude oil component and the characterization method, the crude oil components are combined to obtain virtual components, and the critical conditions of the virtual components are determined;

[0008] S3. Based on the critical conditions of supercritical carbon dioxide, the viscosity of supercritical carbon dioxide / crude oil mixtures under different conditions and at different addition ratios is calculated using a gradient rise method, and the turning point of the viscosity change is used as the optimal injection amount of supercritical carbon dioxide under different conditions;

[0009] S4. Taking the critical condition of supercritical carbon dioxide as the benchmark and the injection amount of supercritical carbon dioxide as the optimal injection amount, combined with the virtual components and their critical conditions of S2, the optimal extraction conditions are obtained according to multiphase equilibrium calculation.

[0010] Beneficial effects: The method of the present invention can predict the optimal conditions for supercritical carbon dioxide extraction of different oily sludges, providing technical guidance for the design of actual extraction processes. DETAILED DESCRIPTION

[0011] The specific implementation methods of the present invention will be clearly and completely described below with reference to examples. Obviously, the examples described are only part of the embodiments of the present invention, rather than all the embodiments.

[0012] A method for predicting supercritical carbon dioxide extraction conditions and components of oily sludge, comprising the following steps:

[0013] S1. Determine the content of each component of crude oil in oily sludge;

[0014] It is known to those skilled in the art that the crude oil in oily sludge is the same as conventional crude oil, which is a mixture of various hydrocarbons. Among them, hydrocarbons with a carbon number of less than 6, such as components such as n-pentane and ethane, boil and vaporize under normal temperature conditions (methane, ethane, etc.) or slightly higher temperature conditions (n-pentane, boiling point 36°C). At the same time, combined with the actual work experience of the inventors, in the crude oil of oily sludge, the content of hydrocarbons with a carbon number of less than 6 is extremely small or basically non-existent. Therefore, in the actual process summary, the "various components" we usually determine refer to hydrocarbons with a carbon number greater than or equal to 6.

[0015] The existing methods for determining crude oil components mainly include gas-phase mass spectrometry chromatography or distillation. Gas-phase mass spectrometry chromatography is chosen in this embodiment to determine the content of each component in crude oil due to its high accuracy.

[0016] In particular, conventional gas-phase mass spectrometry, due to its inherent performance limitations, is generally only able to effectively detect the content of hydrocarbons with a carbon number of 40 or less. However, those skilled in the art are aware that, for crude oil in oily sludge, the heavy components have a greater impact on the sludge. Research by the inventors has revealed that for hydrocarbons with larger carbon numbers, the logarithm of the expected mole fraction of their carbon number distribution has an approximately linear relationship.

[0017] Therefore, we can use the least square method to fit the content of hydrocarbons with a carbon number not greater than 40 with the following formula. The obtained formula can calculate the content of hydrocarbons with a carbon number greater than 40: C N =A+Blnz N , where C N represents the carbon number, z N C N The corresponding mole fractions, A and B are the coefficients of the relationship.

[0018] In this embodiment, the carbon number range of the calculated hydrocarbons is 6 to 80. Of course, those skilled in the art can choose other carbon number ranges, such as 6 to 60.

[0019] S2. Based on the carbon number of each crude oil component and the characterization method, the crude oil components are combined to obtain virtual components, and the critical conditions of the virtual components are determined;

[0020] In this step, the calculation of virtual components and their critical conditions primarily provides data support for subsequent phase equilibrium calculations. As previously mentioned, this example obtained the content distribution of 75 hydrocarbons with carbon numbers ranging from 6 to 80. Directly performing phase equilibrium calculations on these 75 hydrocarbons would result in excessively large data sets and be extremely time-consuming. Therefore, the inventors considered combining hydrocarbons with different carbon numbers to simplify the calculation steps for phase equilibrium calculations.

[0021] The method for obtaining a virtual component and determining its critical condition comprises the following steps:

[0022] S21. Calculate the supercritical conditions of each component in crude oil: Where, T N represents the critical temperature of the Nth component in crude oil; ρ N Indicates the density of the Nth component in crude oil; MW N The molecular weight of the Nth component in crude oil; P N represents the critical pressure of the Nth component in crude oil; c1, c2, c3, c4, d1, d2, d3, d4 and d5 are coefficients; since the critical conditions of the virtual components need to be determined, in this step, we first determine the critical conditions of each single component.

[0023] S22. Combine the carbon numbers of the components in the crude oil at intervals of a certain carbon number to obtain virtual components. During the merging process, those skilled in the art can select different carbon number intervals for merging according to actual conditions. For example, the interval is 15 carbon numbers, 20 carbon numbers, 25 carbon numbers, etc. Since the maximum carbon number in this embodiment is 80, the interval is set to 20 carbon numbers for the convenience of calculation. In particular, since hydrocarbons with a carbon number less than 6 are not considered in this embodiment, when setting the first virtual component, it is necessary to start from 6. In this embodiment, the virtual components set are as follows: C6~C20, C21~C40, C41~C60, C61~C80.

[0024] S23. Calculate the supercritical conditions of the virtual components: Where, T ck and P ck Respectively represent the critical temperature of the virtual component; M is the lower limit of the carbon number of the virtual component, L is the upper limit of the carbon number of the virtual component, i is the component with carbon number i in the virtual component; z i is the molar fraction of the component with carbon number i; M i represents the molecular weight of the component with carbon number i; T ci and P ci are the critical temperature and critical pressure of the component with carbon number i. The supercritical condition of each virtual component can be calculated using the formula in this step.

[0025] S3. Based on the critical conditions of supercritical carbon dioxide, the viscosity of supercritical carbon dioxide / crude oil mixtures under different conditions and at different addition ratios is calculated using a gradient rise method, and the turning point of the viscosity change is used as the optimal injection amount of supercritical carbon dioxide under different conditions;

[0026] In this step, the purpose is to calculate the optimal injection rate of supercritical carbon dioxide under different conditions. Since supercritical carbon dioxide itself has its critical conditions (31.1°C, 7.38MPa), and in the extraction process, only supercritical carbon dioxide can be used for extraction. Therefore, the "different conditions" in this step need to be no less than the critical conditions of supercritical carbon dioxide.

[0027] S31. Determine the total content range and initial amount of supercritical carbon dioxide. Using the critical pressure and critical temperature of supercritical carbon dioxide as a benchmark, use a gradient rise method to calculate the solubility of the dissolved gas crude oil under different conditions according to the following formula:

[0028] Where Rs represents solubility; y g is the gas mole fraction; △o represents the relative density of crude oil; Mo represents the average molecular weight of degassed crude oil; p is absolute pressure; T is temperature; △g represents the molecular weight of carbon dioxide;

[0029] In this step, the initial conditions are the critical conditions of supercritical carbon dioxide, that is, the temperature is 31.1° C., the pressure is 7.38 MPa, the initial addition amount of carbon dioxide is 1 wt%, and the addition amount of crude oil is 99 wt%.

[0030] S32. Based on the solubility of the crude oil in the gas solution, calculate the viscosity of the crude oil after it dissolves in the gas: Where μ′ O 、 are the viscosities of dissolved gas and degassed crude oil at the same temperature, respectively;

[0031] S33. As the amount of gas dissolved in crude oil increases, the viscosity of the crude oil will decrease. When a turning point appears in its viscosity change, the supercritical carbon dioxide content at the turning point is the optimal injection amount of supercritical carbon dioxide. By changing the pressure and temperature, the optimal injection amount of supercritical carbon dioxide under different conditions can be calculated.

[0032] In this step, the extraction conditions—temperature and pressure—are fixed, and the viscosity of the crude oil is calculated under these conditions for different CO2 dosages. As the CO2 content increases, the amount of CO2 dissolved in the crude oil increases, and the viscosity of the crude oil decreases. However, at a certain point, the supercritical CO2's ability to reduce the viscosity of the crude oil reaches its limit, resulting in minimal changes in the crude oil's viscosity even with further increases in the CO2 dosage. The CO2 dosage that reaches this turning point in the viscosity change is the optimal dosage under these conditions.

[0033] In the process of adjusting the amount of carbon dioxide added, the gradient of addition is 1wt%. Since the total amount of crude oil and carbon dioxide added is 100%, the amount of crude oil added is correspondingly reduced by 1wt%. Of course, those skilled in the art can also use different gradients to adjust the amount of carbon dioxide added.

[0034] After calculating the optimal amount of carbon dioxide added under initial conditions, it is necessary to further calculate the optimal amount of carbon dioxide added under different conditions. When adjusting the temperature and pressure, a gradient ramp method is also used, with a temperature gradient of 1°C and a pressure gradient of 0.5 MPa. Similarly, those skilled in the art can adjust the conditions using different gradients.

[0035] Regarding the upper limit of the gradient, especially the upper limits of temperature and pressure, in this embodiment, the upper limit of pressure is set to 30 MPa and the upper limit of temperature is set to 100° C. Those skilled in the art can set different upper limits.

[0036] S4. Taking the critical condition of supercritical carbon dioxide as the benchmark and the injection amount of supercritical carbon dioxide as the optimal injection amount, combined with the virtual components and their critical conditions of S2, the optimal extraction conditions are obtained according to multiphase equilibrium calculation.

[0037] In this step, since supercritical carbon dioxide is soluble in the oil phase, supercritical carbon dioxide can be regarded as a liquid phase, and the oil product itself belongs to the liquid phase under such conditions. Therefore, the molar fraction of the liquid phase can be used as an important parameter for judging the extraction conditions; since the purpose of the embodiment of the present invention is to predict and judge the extraction conditions of supercritical carbon dioxide, another key condition is the oil content in the liquid phase.

[0038] S41. Based on the critical pressure and critical temperature of supercritical carbon dioxide, the optimal injection amount of supercritical carbon dioxide in S3 and the virtual components in S2 are used to perform phase equilibrium calculations.

[0039] Phase equilibrium calculation is a conventional method in this field. Phase simulation software or the method described in the reference "A New Algorithm for Rachford-Rice for Multiphase Compositional Simulation" can be used for calculation. Therefore, the specific operation process will not be described in detail here.

[0040] At the same time, in this step, the initial conditions for phase equilibrium calculation are: the critical conditions of carbon dioxide, and the initial parameters for phase equilibrium calculation are: the optimal injection amount of supercritical carbon dioxide calculated by S3, and the virtual components, the content of the virtual components, and the critical conditions of the virtual components calculated by S2.

[0041] S42. Based on the calculation results, determine the mole fraction of the liquid phase and the oil content in the liquid phase in the system under the current conditions; as mentioned above, these two parameters are important parameters for determining the effect of supercritical carbon dioxide extraction.

[0042] S43. Use the gradient rise method to change the pressure, temperature and the optimal injection amount of supercritical carbon dioxide under the current pressure and temperature conditions, repeat S41 to S42 until the mole fraction of the liquid phase in the system and the oil content in the liquid phase under all conditions are obtained, and use the mole fraction of the liquid phase in the system and the oil content in the liquid phase as indicators to screen the optimal extraction conditions.

[0043] Similar to S33, this step also uses the gradient rise method. Since the virtual component, the content of the virtual component, and the critical condition of the virtual component are fixed values, the variables in this step are temperature, pressure, and the optimal injection rate of supercritical carbon dioxide. When setting the gradients of these three parameters, the temperature gradient is 1°C and the pressure gradient is 0.5MPa. As for the optimal injection rate of supercritical carbon dioxide, when the temperature and pressure are determined, the optimal injection rate is also determined, so there is no need to set a gradient.

[0044] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention is disclosed above with reference to the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make slight changes or modifications to the technical contents disclosed above into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for predicting the conditions and components of supercritical carbon dioxide extraction of oily sludge, characterized in that: The following steps are included: S1. Determine the content of each component of crude oil in oily sludge; S2. Based on the carbon number of each crude oil component and the characterization method, the crude oil components are combined to obtain virtual components, and the critical conditions of the virtual components are determined; S3. Based on the critical conditions of supercritical carbon dioxide, the viscosity of supercritical carbon dioxide / crude oil mixtures under different conditions and at different addition ratios is calculated using a gradient rise method, and the turning point of the viscosity change is used as the optimal injection amount of supercritical carbon dioxide under different conditions; S4. Taking the critical condition of supercritical carbon dioxide as the benchmark and the injection amount of supercritical carbon dioxide as the optimal injection amount, combined with the virtual components and their critical conditions of S2, the optimal extraction conditions are obtained according to multiphase equilibrium calculation.

2. The method according to claim 1, characterized in that In S1, the content of each component of crude oil is obtained by the following steps: using gas phase mass spectrometry to obtain the component content of C6-C40 in crude oil, then fitting it, and extending it to C80 based on the relationship obtained by fitting to obtain the component content of C41-C80.

3. The method according to claim 2, characterized in that The fitting formula is as follows: C N =A+Blnz N , where C N represents the carbon number, z N C N The corresponding mole fractions, A and B are the coefficients of the relationship.

4. The method according to claim 1, wherein In S2, the method for determining the critical conditions for merging components includes the following steps: S21. Calculate the supercritical conditions of each component in crude oil: Where, T N represents the critical temperature of the Nth component in crude oil; ρ N Indicates the density of the Nth component in crude oil; MW N The molecular weight of the Nth component in crude oil; P N represents the critical pressure of the Nth component in crude oil; c1, c2, c3, c4, d1, d2, d3, d4 and d5 are coefficients; S22, combining the carbon numbers of the components in the crude oil at intervals of a certain carbon number to obtain virtual components; S23. Calculate the supercritical conditions of the virtual components: Where, T ck and P ck Respectively represent the critical temperature of the virtual component; M is the lower limit of the carbon number of the virtual component, L is the upper limit of the carbon number of the virtual component, i is the component with carbon number i in the virtual component; z i is the molar fraction of the component with carbon number i; M i represents the molecular weight of the component with carbon number i; T ci and P ci are the critical temperature and critical pressure of the component with carbon number i, respectively.

5. The method according to claim 1, wherein S3 includes the following steps: S31. Determine the total content range and initial amount of supercritical carbon dioxide. Using the critical pressure and critical temperature of supercritical carbon dioxide as a benchmark, use a gradient rise method to calculate the solubility of the dissolved gas crude oil under different conditions according to the following formula: Where Rs represents solubility; y g is the gas mole fraction; △o represents the relative density of crude oil; Mo represents the average molecular weight of degassed crude oil; p is absolute pressure; T is temperature; △g represents the molecular weight of carbon dioxide; S32. Based on the solubility of the crude oil in the gas solution, calculate the viscosity of the crude oil after it dissolves in the gas: Where μ′ O 、 are the viscosities of dissolved gas and degassed crude oil at the same temperature, respectively; S33. As the amount of gas dissolved in crude oil increases, the viscosity of the crude oil will decrease. When a turning point appears in its viscosity change, the supercritical carbon dioxide content at the turning point is the optimal injection amount of supercritical carbon dioxide. By changing the pressure and temperature, the optimal injection amount of supercritical carbon dioxide under different conditions can be calculated.

6. The method according to claim 1, characterized in that In S4, The following steps are included: S41. Based on the critical pressure and critical temperature of supercritical carbon dioxide, the optimal injection amount of supercritical carbon dioxide in S3 and the virtual components in S2 are used to perform phase equilibrium calculations. S42. Based on the calculation results, determine the mole fraction of the liquid phase and the oil content in the liquid phase in the system under the current conditions; S43. Use the gradient rise method to change the pressure, temperature and the optimal injection amount of supercritical carbon dioxide under the current pressure and temperature conditions, repeat S41 to S42 until the mole fraction of the liquid phase in the system and the oil content in the liquid phase under all conditions are obtained, and use the mole fraction of the liquid phase in the system and the oil content in the liquid phase as indicators to screen the optimal extraction conditions.

Images