Method for treating oil field oil sludge through supercritical carbon dioxide

Abstract

The invention discloses a method for treating oil field oil sludge by supercritical carbon dioxide, and aims to solve the problems that an organic solvent needs to be used in an existing oil sludge treatment process, and the treatment period of a biological method is long. The method for treating the oil field oil sludge comprises the following steps: 1, mixing the oil field oil sludge with deionized water to obtain an oil sludge mixture, freezing the oil sludge mixture at-50 to-60 DEG C for 6-10 hours, unfreezing in a water bath at the temperature of 40-45 DEG C, heating in a water bath at the temperature of 40-45 DEG C, and repeating freezing-heating treatment for multiple times; 2, putting the pretreated oil field oil sludge into an extraction kettle and sealing; 3, pressurizing the liquid carbon dioxide through a high-pressure pump to obtain supercritical carbon dioxide, controlling the extraction temperature, the extraction pressure and the extraction time, and introducing the supercritical carbon dioxide into the extraction kettle for supercritical extraction treatment; and 4, the extracted oil sludge mixture enters a separation kettle. The supercritical carbon dioxide extraction process is optimized, oil extraction is achieved, and the extraction rate can reach about 75%.

Description

Technical Field

[0001] The invention relates to a method for treating oilfield sludge. Background Art

[0002] More than 50% of the oil fields are distributed in the middle and high latitudes. At the same time, this area is the main area of ​​perennial frozen soil and seasonal frozen soil. Perennial frozen soil and seasonal frozen soil are mainly distributed in the middle and high latitudes outside 30 degrees north and south latitude. The climate characteristics of these areas make it common for the soil to experience freezing and thawing. Many large oil fields such as the Ural-Volga oil field and the Tyumen oil field, the Alaska Gulf oil field, the North Sea oil field in Northern Europe, and China's Daqing, Liaohe, Karamay oil fields are all distributed here. Oil sludge contains various highly persistent, difficult to degrade, carcinogenic, teratogenic, and mutagenic petroleum hydrocarbons. It is a type of hazardous waste that needs to be highly valued and treated with priority. Improper disposal can easily lead to environmental pollution and pose a serious threat to human health.

[0003] The composition and properties of oily sludge are affected by the type of oil field, soil and storage conditions. Refinery sludge contains chemical agents such as flocculants and emulsifiers; tank bottom sludge has a high content of heavy hydrocarbons and asphaltene; ground sludge is in contact with exposed soil, has a low oil content and is easily affected by soil conditions and soil freeze-thaw effects. Traditional sludge treatment technologies include incineration, solidification, bioremediation, pyrolysis and organic solvent extraction. Incineration can remove more than 95% of sludge, but it will cause secondary pollution caused by dioxin emissions. The residual oil content after solidification of sludge can be as low as 5%, but this method occupies land space and has the risk of seepage pollution. Biotechnology focuses on the degradation of oil hydrocarbons and soil remediation, which is environmentally friendly and low-cost. For example, the use of composite biological agents can achieve an oil hydrocarbon degradation rate of 96.6% within 60 days, but its treatment cycle is long and is limited by environmental factors such as temperature and humidity. Solvent extraction technology can separate and recover hydrocarbons in oil sludge. For example, 67.5% of PHCs in oil sludge were recovered by extracting hexane and xylene. However, the large consumption of expensive and toxic chemicals has limited its development. It is a general trend to seek green, non-toxic, pollution-free and recyclable oil sludge treatment solvents. Summary of the invention

[0004] The purpose of the present invention is to solve the problems that the existing sludge treatment process needs to use organic solvents and the biological treatment cycle is long, and to provide a method for treating oilfield sludge with supercritical carbon dioxide.

[0005] The method for treating oilfield sludge with supercritical carbon dioxide of the present invention is implemented according to the following steps:

[0006] 1. Mixing oilfield sludge and deionized water to obtain an oil sludge mixture, freezing the oil sludge mixture at -50 to -60°C for 6 to 10 hours, thawing it in a water bath at 40 to 45°C, and heating it in a water bath at 40 to 45°C for 3 to 5 hours to complete a freezing-heating treatment, repeating the freezing-heating treatment for multiple times, and finally obtaining the pretreated oilfield sludge after fully drying;

[0007] 2. Place the pretreated oilfield sludge in a barrel, then install the barrel into the extraction kettle and seal it;

[0008] 3. The CO2 supplied from the CO2 cylinder is cooled in a chiller and then sent to a high-pressure pump. The liquid carbon dioxide is pressurized by the high-pressure pump to obtain supercritical carbon dioxide. The extraction kettle is heated to an extraction temperature of 40-60°C. The supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 70-100 minutes. The extraction pressure is controlled at 22-32MPa to obtain an extracted oil sludge mixture.

[0009] Fourth, the extracted oil sludge mixture enters the separation kettle, and the supercritical carbon dioxide is converted into carbon dioxide gas in the separation kettle, and the oil phase is discharged from the bottom of the separation kettle, thereby completing the method of treating oilfield sludge with supercritical carbon dioxide.

[0010] The present invention first performs multiple freezing-heating treatments on oilfield sludge. During the multiple freezing-heating cycles, the oil phase (oil substances) in the sludge migrates to the freezing interface, promoting the separation of the oil substances. Then, a supercritical carbon dioxide extraction process is used to extract the oil.

[0011] The method for treating oilfield sludge with supercritical carbon dioxide of the present invention also optimizes the factors of temperature, pressure and time in the supercritical carbon dioxide extraction process, determines that the extraction temperature is 55°C, the extraction pressure is 25MPa, the extraction time is 90min, and the extraction rate can reach about 75%. This extraction condition not only ensures a higher extraction rate, but also takes into account energy consumption and cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The schematic diagram of the process of the method for treating oilfield sludge with supercritical carbon dioxide of the present invention;

[0013] Figure 2 This is a test chart showing the effects of temperature, pressure and time on extraction efficiency in a supercritical carbon dioxide extraction process according to an embodiment. DETAILED DESCRIPTION

[0014] Specific implementation method 1: The method for treating oilfield sludge with supercritical carbon dioxide in this implementation method is implemented according to the following steps:

[0015] 1. Mixing oilfield sludge and deionized water to obtain an oil sludge mixture, freezing the oil sludge mixture at -50 to -60°C for 6 to 10 hours, thawing it in a water bath at 40 to 45°C, and heating it in a water bath at 40 to 45°C for 3 to 5 hours to complete a freezing-heating treatment, repeating the freezing-heating treatment for multiple times, and finally obtaining the pretreated oilfield sludge after fully drying;

[0016] 2. Place the pretreated oilfield sludge in a barrel, then install the barrel into the extraction kettle and seal it;

[0017] 3. The CO2 supplied from the CO2 cylinder is cooled in a chiller and then sent to a high-pressure pump. The liquid carbon dioxide is pressurized by the high-pressure pump to obtain supercritical carbon dioxide. The extraction kettle is heated to an extraction temperature of 40-60°C. The supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 70-100 minutes. The extraction pressure is controlled at 22-32MPa to obtain an extracted oil sludge mixture.

[0018] Fourth, the extracted oil sludge mixture enters the separation kettle, and the supercritical carbon dioxide is converted into carbon dioxide gas in the separation kettle, and the oil phase is discharged from the bottom of the separation kettle, thereby completing the method of treating oilfield sludge with supercritical carbon dioxide.

[0019] The matrix of the oilfield sludge in this embodiment is chernozem.

[0020] Specific embodiment 2: The difference between this embodiment and specific embodiment 1 is that in step 1, oilfield sludge and deionized water are mixed to obtain a sludge mixture, the sludge mixture is frozen at -55°C for 8 hours, then thawed in a water bath at 45°C, and heated in a water bath at 45°C for 4 hours to complete a freeze-heating treatment.

[0021] Specific implementation method three: This implementation method is different from specific implementation method two in that the freezing-heating treatment is repeated 4 to 6 times in step one.

[0022] Specific embodiment 4: This embodiment is different from specific embodiments 1 to 3 in that the drying temperature in step 1 is 50-80°C.

[0023] Specific implementation mode 5: This implementation mode is different from any one of specific implementation modes 1 to 4 in that in step 3, the volume mass ratio of supercritical carbon dioxide to oilfield sludge in the extraction kettle is controlled to be (800-1200) mL: (350-450) g.

[0024] Specific embodiment six: The difference between this embodiment and any one of specific embodiments one to five is that in step two, liquid carbon dioxide is pressurized by a high-pressure pump to obtain supercritical carbon dioxide, the extraction kettle is heated to an extraction temperature of 50-60°C, and supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 90-100 minutes, and the extraction pressure is controlled to 25-31 MPa.

[0025] Specific embodiment seven: This embodiment differs from specific embodiment six in that in step two, liquid carbon dioxide is pressurized by a high-pressure pump to obtain supercritical carbon dioxide, the extraction kettle is heated to an extraction temperature of 55°C, and supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 90 minutes, and the extraction pressure is controlled to 25 MPa.

[0026] Specific implementation eight: This implementation differs from any one of specific implementations one to seven in that the carbon dioxide gas converted from supercritical carbon dioxide in step three flows back to the CO2 gas cylinder through a circulation pipeline.

[0027] Embodiment: The method for treating oilfield sludge with supercritical carbon dioxide in this embodiment is implemented according to the following steps:

[0028] 1. Mixing oilfield sludge and deionized water to obtain an oil sludge mixture, freezing the oil sludge mixture at -55°C for 8 hours, thawing it in a water bath at 45°C, and heating it in a water bath at 45°C for 4 hours to complete a freezing-heating treatment, repeating the freezing-heating treatment for 5 times, and finally fully drying it to obtain the pretreated oilfield sludge;

[0029] Second, the pretreated oilfield sludge is placed in a barrel, and then the barrel is installed in an extraction kettle and sealed. This embodiment uses a HA-121-50-C supercritical extraction device (Nantong Yichuang Experimental Instrument Co., Ltd., China);

[0030] 3. The CO2 supplied from the CO2 cylinder is cooled in a chiller and then sent to a high-pressure pump. The liquid carbon dioxide is pressurized by the high-pressure pump to obtain supercritical carbon dioxide. The extraction temperature is controlled, and the supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment. The extraction pressure is controlled. The volume mass ratio of supercritical carbon dioxide to oilfield sludge in the extraction kettle is 1L:400g. The total amount of carbon dioxide in the system is about 30L. 80% of the carbon dioxide can be reused to obtain an extracted sludge mixture.

[0031] Fourth, the extracted oil sludge mixture enters the separation kettle, the supercritical carbon dioxide is converted into carbon dioxide gas, and the oil phase is discharged from the bottom of the separation kettle, thereby completing the method of treating oilfield sludge with supercritical carbon dioxide.

[0032] In step 1 of this embodiment, the oil sludge mixture is first subjected to multiple freezing-heating treatments to optimize the freezing and heating time to promote the separation of oil substances in the oil field sludge, and then the supercritical carbon dioxide extraction process is used to extract the oil in the oil sludge.

[0033] The CO2 supplied by the gas cylinder of this embodiment is sent to the high-pressure pump after being cooled in the chiller, and the liquid carbon dioxide is pressurized to achieve the pressure required for supercriticality, and then the extraction kettle is heated by the heating sleeve to reach the preset extraction temperature. The flow meter is used to monitor the system carbon dioxide circulation flow and estimate the reuse amount. For each group of experiments, 400±0.05g of oil sludge is placed in a stainless steel barrel, and absorbent cotton and filter screen are placed in turn to prevent fine soil particles from being entrained and blocking the pipeline. The barrel containing oil sludge is then placed in the extraction kettle, the kettle cover is tightened, and supercritical carbon dioxide is introduced. According to the preset process parameters, the temperature and pressure are adjusted and the timing is started. At the same time, the output flow of the carbon dioxide pump is controlled to be 20.0±0.05L / h. When the required time is reached, the CO2 pump is turned off and the valve below the separation kettle is opened to manually recover the oil product. After the pressure of the extraction kettle drops to 0.0MPa, the barrel is taken out, and the residual soil after extraction is collected and analyzed. Each sample is measured in parallel twice to reduce the error.

[0034] Temperature and pressure are key supercritical state parameters, while extraction time is important for process efficiency and energy consumption. In this example, a single factor experiment was conducted with chernozem as the matrix under extraction conditions of 40–60°C, 10–30 MPa, and 0–180 min to investigate the effects of extraction temperature, pressure, and time on the removal efficiency of oily sludge.

[0035] Based on the in-depth analysis using the response surface methodology (RSM), the maximum value of the model was solved using the solutions module of the Design expert software. Through this method, the process parameters corresponding to the maximum value of the extraction rate were determined: the extraction temperature was 57.0°C, the extraction pressure was 30.1MPa, and the extraction time was 98.3min. Under this optimized condition, the extraction rate reached 76.33%. However, compared with the previous experimental conditions (55°C, 25MPa and 90min), the extraction time increased by 8.3 minutes, which means that the equipment needs to run longer, resulting in an increase in energy consumption of about 9.2%. The extraction temperature increased by 2°C, which is about 5.7% compared to the calculation starting from the normal temperature of 20°C. Increasing the temperature requires more energy to maintain the temperature of the extraction kettle and cool the circulating gas, so the energy consumption will also increase. The extraction pressure increased by 5.1MPa, accounting for about 20.4% of the original. Higher pressure will increase the maintenance cost of the extraction system. The present invention has made a comprehensive comparison and analysis. By weighing the process energy consumption and sludge removal efficiency, the extraction conditions of 55°C, 25MPa and 90min were determined to ensure a high extraction rate while taking into account energy consumption and cost-effectiveness.

[0036] The effect of temperature on the extraction efficiency is as follows Figure 2 As shown in Figure 1, the extraction rate is positively correlated with the temperature in the range of 40℃–55℃, and the highest extraction rate (74.12%) is achieved at 55℃. The extraction efficiency of oil is affected by the combined effect of its saturated vapor pressure and supercritical phase density. When the temperature rises, the saturated vapor pressure of the oil increases accordingly. This effect helps the oil volatilize into the supercritical phase, thereby significantly improving the extraction rate. However, the increase in temperature also inhibits the solubility of CO2. In particular, in the temperature range of 40-55℃, the effect of increasing the saturated vapor pressure of the oil dominates and promotes the increase in the extraction rate. However, once the temperature exceeds 55℃, the negative impact of the decrease in supercritical phase density on the solubility of CO2 begins to become prominent, resulting in a downward trend in the extraction rate. For the black calcium clay sludge studied in this experiment, 55℃ is the key temperature point to achieve the highest extraction efficiency, because it happens to be the equilibrium point where the above two opposite effects offset each other.

[0037] like Figure 2As shown in Figure 2b, pressure has a significant effect on the extraction efficiency. When the pressure increases from 10MPa to 15MPa, the extraction rate increases rapidly; in the range of 15-25MPa, the extraction rate increases but the growth rate slows down; especially from 20MPa to 25MPa, the extraction rate increases by 3%, but when it further increases to 30MPa, the extraction rate only increases by 0.54%. The increase in pressure increases the density of supercritical CO2 and enhances its solubility. However, as the density and solubility of pressurized CO2 no longer increase significantly, the extraction rate tends to stabilize. In summary, within the range of investigation, 25MPa is the optimal pressure value to achieve the highest extraction efficiency.

[0038] Figure 2 c shows the effect of extraction time on extraction efficiency. Within 0-180 min, the extraction rate and extraction time showed a significant positive correlation trend. In a very short 10 min, the extraction process showed significant results, and the extraction rate quickly exceeded 40%. Subsequently, in the time period of 10-30 min, the extraction rate continued to increase rapidly, showing the characteristics of the rapid extraction stage. However, when the time was extended to 30-90 min, although the extraction rate still maintained an upward trend, its growth rate slowed down significantly and entered the transition extraction stage. When the extraction time exceeded 90 min, the growth of the extraction rate became particularly slow, and it almost stopped changing after 150 minutes, indicating that it entered the slow extraction stage until it reached equilibrium. After the extraction time reached 150 minutes, the solute reached a dissolution equilibrium state in CO2, and the extraction efficiency of the system no longer changed significantly. Therefore, combined with the comprehensive consideration of energy consumption and extraction rate, this embodiment determines 90 minutes as the time point for achieving the best extraction efficiency.

Claims

1. A method for treating oilfield sludge with supercritical carbon dioxide, characterized in that The method for treating oilfield sludge with supercritical carbon dioxide is implemented according to the following steps:

1. Mixing oilfield sludge and deionized water to obtain an oil sludge mixture, freezing the oil sludge mixture at -50 to -60°C for 6 to 10 hours, thawing it in a water bath at 40 to 45°C, and heating it in a water bath at 40 to 45°C for 3 to 5 hours to complete a freezing-heating treatment, repeating the freezing-heating treatment for multiple times, and finally obtaining the pretreated oilfield sludge after fully drying; 2. Place the pretreated oilfield sludge in a barrel, then install the barrel into the extraction kettle and seal it; 3. The CO2 supplied from the CO2 cylinder is cooled in a chiller and then sent to a high-pressure pump. The liquid carbon dioxide is pressurized by the high-pressure pump to obtain supercritical carbon dioxide. The extraction kettle is heated to an extraction temperature of 40-60°C. The supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 70-100 minutes. The extraction pressure is controlled at 22-32MPa to obtain an extracted oil sludge mixture. Fourth, the extracted oil sludge mixture enters the separation kettle, and the supercritical carbon dioxide is converted into carbon dioxide gas in the separation kettle, and the oil phase is discharged from the bottom of the separation kettle, thereby completing the method of treating oilfield sludge with supercritical carbon dioxide.

2. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 1, characterized in that In step 1, the oilfield sludge and deionized water are mixed to obtain a sludge mixture, which is frozen at -55°C for 8 hours, then thawed in a water bath at 45°C, and heated in a water bath at 45°C for 4 hours to complete a freeze-heating treatment.

3. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 2, characterized in that Repeat the freezing-heating treatment in step 1 4 to 6 times.

4. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 1, characterized in that The drying temperature in step 1 is 50-80°C.

5. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 1, characterized in that In step 3, the volume mass ratio of supercritical carbon dioxide to oilfield sludge in the extraction kettle is controlled to be (800-1200) mL: (350-450) g.

6. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 1, characterized in that In step three, liquid carbon dioxide is pressurized by a high-pressure pump to obtain supercritical carbon dioxide, the extraction kettle is heated to an extraction temperature of 50-60°C, and supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 90-100 minutes, and the extraction pressure is controlled to be 25-31MPa.

7. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 6, characterized in that In step 2, liquid carbon dioxide is pressurized by a high-pressure pump to obtain supercritical carbon dioxide, the extraction kettle is heated to an extraction temperature of 55° C., and supercritical carbon dioxide is introduced into the extraction kettle for supercritical extraction treatment for 90 minutes, and the extraction pressure is controlled to be 25 MPa.

8. The method for treating oilfield sludge with supercritical carbon dioxide according to claim 1, characterized in that The carbon dioxide gas converted from supercritical carbon dioxide in step 3 flows back to the CO2 cylinder through the circulation pipeline.

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