Method for assisting oil removal of oil sludge based on freeze-thaw method

Abstract

The invention provides a method for assisting in oil sludge deoiling based on a freeze-thaw method. The method comprises the following steps: replenishing water for saturation, freezing, thawing and washing, collecting a leaching solution, repeatedly leaching, deionizing and leaching and the like. As the viscosity of the oil sludge is extremely high, the eluting agent is combined with a one-way freezing and thawing method, so that the structural framework of the oil-containing sludge can be effectively destroyed, full contact of the eluting agent and the oil sludge is promoted, the acting force between an oil layer in the oil sludge and solid particles is broken, oil desorption on the surface of the oil sludge is promoted, and the purpose of deoiling is achieved. The residual oil content in the oil sludge treated by the oil removal method is lower than the national standard, the removal rate of colloid, aromatic hydrocarbon, saturated hydrocarbon and other components in the oil sludge is high, three wastes are not generated in the process, and the oil sludge can be used for roads, building materials and the like. Therefore, the method for assisting in oil sludge deoiling based on the freeze-thaw method provided by the invention has the characteristics of small dosage of the eluting agent, high total deoiling rate, high colloid removal rate, high aromatic hydrocarbon removal rate, high saturated hydrocarbon removal rate and the like.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection, and in particular to a method for deoiling sludge assisted by freeze-thaw method. Background Art

[0002] In recent years, with the continuous development of the global economy, the demand for energy has also increased. Among them, oil is one of the most important energy sources. However, the extraction and processing of oil will also produce a large amount of waste, including oily sludge. Oil sludge not only has a huge impact on the environment, but also poses a huge safety hazard to the ecological environment after long-term accumulation. It is urgent to maximize the resource utilization of oil sludge.

[0003] Oil sludge is one of the solid wastes generated during the process of oilfield development, oil refining, transportation and storage. It is a complex mixture of oil, water and solid, containing a variety of organic pollutants and heavy metal pollutants, and has strong biological toxicity. With the rapid development of domestic and foreign economies, the amount of oil production is increasing, and the amount of oil sludge produced by the oil industry is also increasing. The annual output of solid waste oil sludge in my country is as high as 5 million tons. Due to insufficient processing capacity, most of the oil sludge is stored in the form of simple stacking or landfill, resulting in a waste of resources.

[0004] Commonly used methods for treating oily sludge include solvent extraction, incineration, biological treatment, coking, oily sludge profile control, and comprehensive utilization of oily sludge. However, these methods have certain limitations and challenges in practical applications, and factors such as technical feasibility, economic cost, and environmental impact need to be considered comprehensively.

[0005] Oily sludge has complex chemical composition, special physical properties, high stability, serious environmental hazards and difficulty in treatment; which makes it difficult to draw on some mature processes, technologies and equipment in other fields for its comprehensive utilization. At present, there is no effective method for the utilization of red mud. Summary of the invention

[0006] In view of this, the main purpose of the present invention is to provide a method for deoiling sludge based on freeze-thaw method, which mainly adopts eluent combined with unidirectional freeze-thaw method to achieve deoiling of sludge to solve the above technical problems.

[0007] Specifically, the technical solution provided by the present invention is as follows: A method for deoiling oil sludge based on freeze-thaw method, comprising the steps of: Water replenishment and saturation: adding eluent to the oil sludge until the oil sludge reaches a saturated state to form an oil sludge saturated mixture; Freezing and freezing: using a one-way freeze-thaw method to cool the sludge saturated mixture, while continuously adding an eluent to the low-temperature part of the sludge saturated mixture, until the eluent in the sludge saturated mixture is converted into a solid state and is frozen with the sludge saturated mixture as a whole, forming frozen sludge; Melting and flushing: using the eluent to elute the low-temperature part of the frozen sludge, instantly melting the frozen sludge until it is completely melted to form melted sludge; Collecting the leachate: collecting the leachate in the melted oil sludge by filtering, wherein the leachate contains components of the eluent and crude oil; Repeat elution: repeat the freezing step to the step of collecting the elution until the crude oil content in the collected elution is stable and less than 2%, thereby obtaining a deoiled sludge semi-finished product; Deionized elution: Repeat the freezing step to the step of collecting the eluted liquid to treat the deoiled sludge semi-finished product, and replace the eluent therein with deionized water to obtain the deoiled sludge finished product.

[0008] Among them, the composition of the oil sludge includes 18-20% oil phase, 31-33% solid phase, and the balance is water phase, calculated by mass percentage. Among them, the oil phase is composed of the following components: 48-49.8% saturated hydrocarbons, 23-24.5% aromatic hydrocarbons, 16-17.2% colloids, and the balance is asphaltene. The solid phase is mainly mineral particles, the main component of which is quartz, and also includes trace amounts of feldspar minerals (CaAl2Si2O8, NaAlSi3O8 and KAlSi3O8).

[0009] The step of replenishing water and saturation includes: pre-treating the oil sludge raw material to remove impurities therein, and then replenishing the eluent to form the oil sludge saturated mixture.

[0010] Based on the above, the eluent includes sodium dodecylbenzene sulfonate (SDBS) with a concentration of 200-1000 mg / L and an alkali with a concentration of 2-5 wt%, wherein the alkali is at least one of potassium hydroxide (KOH), sodium carbonate (Na2CO3) and sodium silicate (Na2SiO3). Preferably, the alkali is Na2SiO3. In order to further improve the oil sludge deoiling rate, the eluent includes 600-900 mg / L SDBS and 2.5-5 wt% Na2SiO3.

[0011] The solid-liquid ratio of the oil sludge to the eluent may be 1: (1-7) g / mL. Taking all factors into consideration, the solid-liquid ratio of the oil sludge to the eluent may be 1: (1-4) g / mL. The eluent volume in the solid-liquid ratio described in the present invention refers to the total volume of the eluent used in the entire oil sludge deoiling process.

[0012] Based on the above, the freezing step includes: using a unidirectional freeze-thaw method to freeze the sludge saturated mixture to form a temperature difference between the upper surface and the lower surface of the sludge saturated mixture, controlling the cooling rate, ensuring the movement speed of the freezing front, and continuously replenishing the eluent from the unfrozen area of ​​the sludge saturated mixture to the frozen area until the sludge saturated mixture is frozen as a whole to form the frozen sludge.

[0013] During the freezing process, the upper surface temperature of the saturated oil sludge mixture gradually decreases from -2°C to 2°C and then keeps a constant temperature for 4 to 6 hours; the lower surface temperature of the saturated oil sludge mixture first gradually decreases from 8°C to 12°C to -2°C to 2°C, then instantly decreases to -12°C to -8°C and then keeps a constant temperature for 4 to 6 hours, so that the saturated oil sludge mixture is completely frozen to form the frozen oil sludge.

[0014] Since an appropriate cooling rate can cause the moisture in the soil to migrate to the low temperature zone and condense into ice at the freezing front, causing the soil volume to expand, the cooling rate during the freezing process is preferably 0.1-0.3 ℃ / h.

[0015] In the freezing step, the eluent is supplemented by pressureless supplementation through the freezing suction force generated by the frost heave effect.

[0016] Based on the above, the melting and washing step includes: instantly raising the temperature of the upper and lower surfaces of the frozen sludge to 8°C to 12°C at the same time, and keeping the temperature constant for 8 to 12 hours, so that the eluent and sludge in the frozen sludge melt, and at the same time, the melted eluent again washes the surface of the frozen sludge particles from top to bottom under the action of gravity to form the melted mixed sludge. Among them, since the separated oil layer can be quickly discharged without secondary adsorption by rapid heating, the frozen sludge is heated by instantaneous heating during the melting and washing process, and the melting heating rate is 1 to 2°C / min.

[0017] Since the viscosity of the sludge is extremely large, the conventional elution method requires a large amount of eluent and the eluent is not easy to fully react with the sludge. The above-mentioned method for assisted sludge deoiling based on the freeze-thaw method provided by the present invention uses an eluent combined with a one-way freeze-thaw method to effectively destroy the structural framework of the oil-containing sludge, promote the eluent to fully contact with the sludge, break the interaction between the oil layer inside the sludge and the solid particles, and promote the desorption of oil on the surface of the sludge, thereby achieving the purpose of deoiling. The residual oil content in the sludge treated by the above-mentioned deoiling method is lower than the national standard, and the removal rate of components such as colloids, aromatic hydrocarbons and saturated hydrocarbons in the sludge is relatively high, and no three wastes are generated in the process, so it can be used for roads, building materials, etc. Therefore, the above-mentioned method for assisted sludge deoiling based on the freeze-thaw method provided by the present invention has the characteristics of small amount of eluent, high total deoiling rate, high colloid removal rate, high aromatic hydrocarbon removal rate and high saturated hydrocarbon removal rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a one-way freeze-thaw device used in an embodiment of the present invention; wherein, the component symbols in the figure are: cylinder 1, lower low-temperature circulation unit 2, upper low-temperature circulation unit 3, sample chamber 4, permeable stone 5, temperature sensor 6, leachate collection unit 7, water replenishment container 81, electronic balance 82, load unit 9, displacement sensor 10; Figure 2 A temperature control curve diagram used in the freeze-thaw assisted sludge deoiling method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0020] Unless otherwise specified in the present invention, the amount, content and removal rate of each raw material all refer to "weight", and the terms used are all commonly used terms in the relevant field. The preparation processes, testing methods, etc. used in each embodiment are conventional means well known to those skilled in the art unless otherwise specified, and the raw materials and equipment used can be obtained from public commercial channels.

[0021] The basic properties of the sludge used in the following tests and examples are shown in Table 1.

[0022] Table 1 Basic properties of sludge

[0023] The main purpose of the present invention is to achieve oil sludge deoiling by combining a one-way freeze-thaw method with an eluent, wherein one of the important factors affecting oil sludge deoiling is the eluent. The effect of the eluent on the oil sludge deoiling rate is further illustrated by the following experiment.

[0024] Through the oscillation elution test, the effects of different eluents on the removal efficiency of sludge and petroleum components were analyzed. The surfactant and alkali screening test scheme is shown in Table 2, where the surfactants SDBS and HTAC in Table 2 refer to sodium dodecylbenzene sulfonate and hexadecyltrimethylammonium chloride, respectively. First, 5 g of sludge was placed in a 50 ml centrifuge tube, and eluents were added according to the solid-liquid ratio and different concentrations, and then placed in a constant temperature oscillating box with a speed of 250 rpm and a temperature of 25°C for 12 hours. After oscillation elution, the sample was placed in a centrifuge and centrifuged at 4000 rpm for 15 minutes to detect the residual oil rate, removal rate and petroleum components after solid-liquid separation. The detection method refers to the standard analysis of soluble organic matter and crude oil group components in rocks, SY / T5119-2008. Among them, the solid-liquid ratio refers to the volume ratio of sludge mass and eluent; all experiments were repeated three times, and the average value was calculated. The results are shown in Tables 3-7.

[0025] Table 2 Surfactant and alkali screening test plan

[0026] Table 3 Solid-liquid ratio screening results

[0027] It can be seen from Table 3 that the removal effect of each eluent increases first and then decreases with the increase of the solid-liquid ratio, and the best elution effect is achieved when the solid-liquid ratio is 1:3. Specifically, the removal rates of rhamnolipids, SDBS and HTAC reached 62.50%, 64.93% and 63.54%, respectively. Too low a solid-liquid ratio may lead to poor fluidity of oil molecules, which is not conducive to the separation of oil and solid particles, resulting in reduced removal efficiency. An increase in the solid-liquid ratio can improve the washing effect to a certain extent, but it will also increase the amount of eluent and the washing cost. In addition, the elution efficiency of the oil sludge is reduced, which is not convenient for subsequent elution treatment. From the perspective of economy and elution, the optimal solid-liquid ratio is 1:3.

[0028] Table 4 Surfactant screening results

[0029] Table 4 shows that there are significant differences in the deoiling efficiency of rhamnolipid, SDBS and HTAC for oil sludge at different concentrations. Their optimal elution concentrations are 600 mg / L, 800 mg / L and 800 mg / L, respectively, and the corresponding optimal removal rates are 70.14%, 72.39% and 66.66%, respectively. It can be observed that the elution effect of HTAC is poor, which may be due to the strong adsorption capacity of soil solids for cationic surfactants, which is not conducive to the effective removal of oil sludge. Due to the presence of clay minerals and humus in the soil, soil aggregates usually have negative charges, and cationic groups are adsorbed on the surface of soil particles in the form of monolayers through electrostatic interactions, thereby inhibiting the release of petroleum hydrocarbons from the soil. Therefore, the cationic surfactant HTAC has a lower removal efficiency than the anionic surfactants SDBS and rhamnolipid. The experimental results also show that as the concentration of HTAC increases, its removal rate decreases when a certain threshold is reached. It may be that a large number of HTAC surfactant molecules are adsorbed on the surface of soil particles or fill the internal pore space, resulting in poor fluidity of oil. When the HTAC concentration further increases and exceeds the threshold, the removal rate increases. It is possible that the large amount of HTAC surfactant molecules in solution will bring the oil out of the soil again.

[0030] During the surfactant elution process, as the surfactant concentration increases, the surfactant molecules in the solution form micelle structures, which help to remove oil from the soil surface. When the concentration of anionic surfactants rhamnolipids and SDBS increases, the elution efficiency will be significantly improved. However, if the surfactant concentration is too high, the adsorption of surfactant molecules in the soil is inevitable, which will significantly affect the residue of oil in the soil. The adsorbed surfactants may redistribute the petroleum hydrocarbons in the soil, thereby reducing its solubility and, in turn, the removal efficiency.

[0031] Table 5 Effect of surfactant on petroleum components at the optimal solid-liquid ratio and concentration

[0032] As can be seen from Table 5, the addition of surfactants has a significant effect on the removal of the four components of crude oil. Rhamnolipids performed outstandingly in the removal of asphaltene, with a removal rate of 52.21%, and the removal rates of colloids, saturated hydrocarbons and aromatic hydrocarbons were 67.69%, 66.67% and 67.69% respectively. Compared with other surfactants, SDBS performed well in the removal of colloids and aromatic hydrocarbons, with removal rates of 71.96% and 78.86% respectively; the removal rates of asphaltene and saturated hydrocarbons were 45.45% and 66.34% respectively. Compared with other surfactants, HTAC has a better removal effect on saturated hydrocarbons, with a removal rate of up to 75.42%; the removal rates of asphaltene, colloids and aromatic hydrocarbons were 42.09%, 57.38% and 55.74% respectively.

[0033] Therefore, choosing the appropriate surfactant concentration is crucial to improving elution efficiency. This not only ensures efficient oil removal, but also takes into account the actual engineering application cost. Therefore, after comprehensive consideration, SDBS is the best surfactant, and 800 mg / L SDBS is the better surfactant, which will be used as the subsequent test.

[0034] Table 6 Alkali screening results

[0035] Table 6 shows that the addition of alkaline substances can significantly affect the leaching effect of surfactants on oil sludge. When KOH, Na2CO3 and Na2SiO3 were added at 3%, 3% and 2% respectively, the oil removal rates increased to 78.82%, 81.77% and 76.65% respectively. With the addition of alkali, the leaching effect of oil sludge showed a trend of first increasing and then decreasing. This shows that low concentration of alkali has a positive effect on the leaching effect, while high concentration may have a negative impact on the removal rate of oil sludge. The addition of alkali increases the Na in the aqueous phase. + and K + Concentration, these ions can increase the negative charge of the soil surface, which is conducive to breaking the bond between oil and soil particles. However, excessive Na + and K + It may reduce the concentration of petroleum hydrocarbons in the aqueous phase, thus negatively affecting the desorption of petroleum from solid particles.

[0036] The combination of surfactant and alkali improves the leaching efficiency of oily sludge, which can be attributed to two aspects: first, the surfactant solution can solubilize and remove hydrophobic pollutants in the soil; second, the alkaline substance can react with the natural organic acid in the crude oil to form an in-situ surfactant, which reduces the interfacial tension between the crude oil and the alkaline solution, and may integrate the oil pollutants associated with it into the water phase, thereby enhancing the removal effect of crude oil. Alkali will also react with SiO2 in the soil to form HSiO3⁻, which will prevent the re-adsorption of oil droplets. Therefore, the combination of surfactant and appropriate amount of alkali can significantly improve the leaching efficiency.

[0037] Table 7 Effect of alkali and SDBS on petroleum components under optimal conditions

[0038] Comparing Table 7 with Table 5, the addition of alkali can significantly improve the removal effect of asphaltene, colloid, saturated hydrocarbons and aromatic hydrocarbons. The removal effect of eluent on asphaltene is poor. Since colloid and asphaltene in the oily layer mainly coexist at the bottom, their high viscosity makes it relatively difficult to remove them. Anionic surfactants and alkaline salts in the solution can produce an ionization effect to form negatively charged ions in the system. Solid particles are also negatively charged, which produces a mutual repulsion effect in the entire system, so that the combination of colloid and asphaltene can be separated. Therefore, compared with cationic surfactants, anionic surfactants and alkaline salts are better in removing asphaltene and colloid, but for heavier components such as asphaltene, their removal effect is relatively poor compared to other components. Saturated hydrocarbons and aromatic hydrocarbons are mainly concentrated in the middle and surface of the oily layer and are relatively easy to be separated, so all eluents have a good removal effect on them. Among them, the combination of surfactant and alkali can significantly improve the removal effect of the four components of petroleum, especially the combination of SDBS and Na2SiO3 has the most significant removal effect on the four components of petroleum. Therefore, considering the synergistic effect of surfactant and alkali and the cost of practical application in future engineering projects, 800 mg / L SDBS combined with 3% Na2SiO3 was selected as the eluent for the subsequent freeze-thaw test.

[0039] The methods for deoiling sludge assisted by freeze-thaw method provided in the following embodiments are mainly based on Figure 1 The unidirectional freeze-thaw test device shown is implemented.

[0040] The unidirectional freeze-thaw test device includes an acrylic cylinder 1, a lower low-temperature circulation unit 2, an upper low-temperature circulation unit 3, a permeable stone 5, a temperature sensor 6, a leachate collection unit 7, an automatic water replenishment unit, a load unit 9 and a displacement sensor 10.

[0041] The cylinder 1 is provided with a sample cavity 4 for filling the sample, the lower end of the sample cavity 4 is connected to the lower low-temperature circulation unit 2, and the upper end of the sample cavity 4 is connected to the upper low-temperature circulation unit 3. A permeable stone 5 is provided at the upper and lower ends of the sample cavity 4, and the permeable stone 5 is respectively arranged in accordance with the corresponding low-temperature circulation unit. A temperature sensor 6 is respectively installed on the permeable stone 5. The lower end of the sample cavity 4 is connected to the leachate collection unit 7 through a pipeline, and the leachate collection unit 7 includes a leachate collection bottle connected to the sample cavity 4 and a balance for weighing the leachate collection bottle and its contents. A detachable insulation board is installed on the outer surface of the cylinder 1. The lower low-temperature circulation unit 2 and the upper low-temperature circulation unit 3 respectively include a coolant and a cooling container for filling the coolant, and the cooling containers are respectively connected to the corresponding permeable stones 5, and the temperature of the refrigerant in the upper low-temperature circulation unit 3 is lower than the temperature of the refrigerant in the lower low-temperature circulation unit 2, that is, the lower low-temperature circulation unit 2 is a warm end, and the upper low-temperature circulation unit 4 is a cold end. The temperature control curves used in the following embodiments and comparative examples are as follows: Figure 2 Freeze-thaw treatments were performed as indicated for a total of 75 h.

[0042] The lower end of the sample chamber 4 is also connected to an automatic water replenishment unit through a pipeline. The automatic water replenishment unit includes a water replenishment container 81 and an electronic balance 82 for weighing the weight of the water replenishment container 81 and its contents. The load unit 9 is arranged above the sample chamber 4 and is connected to the upper low-temperature circulation unit 3, and is used to apply a load to the sample loaded in the sample chamber 4, so as to avoid the sample from expanding due to absorbing water, so that a vacuum layer is generated in the sample during the freezing process, affecting the overall freezing performance of the sample; applying pressure through the load unit 9 can enable water to fully penetrate into the sample, expel air, and avoid the generation of a vacuum layer. The displacement sensor 10 is installed on the load unit 9 and is used to measure the height of the sample in the sample chamber 4.

[0043] Embodiment 1 This embodiment provides a method for deoiling sludge assisted by freeze-thaw method, comprising the following steps: Water replenishment and saturation: firstly, 500 g of the oil sludge raw material is stirred to remove impurities in the oil sludge raw material, and then loaded into the sample chamber 4, and the eluent is continuously added to the low-temperature part of the oil sludge through the automatic water replenishment unit 8 until it reaches a saturated state to form an oil sludge saturated mixture; at the same time, in this process, the lower low-temperature circulation unit 2 and the upper low-temperature circulation unit 3 are started, so that the lower surface of the oil sludge in the sample chamber 4 is kept at a constant temperature of 10°C for 10 hours, and the upper surface temperature is kept at a constant temperature of 0°C for 10 hours; Freezing and freezing: cooling the saturated oil sludge mixture, the upper surface of the saturated oil sludge mixture is cooled from 0°C at a rate of -0.2°C / h to -10°C and then kept at a constant temperature for 5 hours, and the lower surface is cooled from 10°C to 0°C at a rate of -0.2°C / h and then instantly cooled to -10°C and kept at a constant temperature for 5 hours, so that a temperature difference is formed between the upper and lower surfaces of the saturated mixture to ensure the moving speed of the freezing front; at the same time, the freezing suction force generated by the frost heave effect continuously replenishes the eluent to the low-temperature part of the saturated mixture; freezing the sludge saturated mixture through a low-temperature circulation unit until the eluent in the saturated oil sludge mixture is converted into a solid state and is frozen as a whole with the saturated oil sludge mixture therein to form frozen oil sludge; Melting and flushing: the temperature of each low-temperature circulation unit is increased, so that the upper and lower surfaces of the frozen sludge are heated from -10°C to 10°C at a heating rate of 1°C / min and then kept at a constant temperature for 10 hours. At the same time, the melted eluent will again elute the surface of the frozen sludge particles from top to bottom under the action of gravity until the solid eluent and sludge raw material mixture in the frozen sludge is completely melted as a whole to form melted sludge; Collecting the leachate: opening the leachate collecting unit 7, collecting the leachate in the melted oil sludge through the leachate collecting unit 7, and closing the leachate collecting unit 7 after the collection is completed, wherein the leachate contains components of the eluent and crude oil; Repeat elution: repeat the freezing step to the step of collecting the elution for 6 times, until the crude oil content in the collected elution is stable and less than 2%, to obtain a deoiled sludge semi-finished product; Deionized elution: Repeat the freezing step to the step of collecting the eluted liquid to treat the deoiled sludge semi-finished product, and replace the eluent therein with deionized H2O pure water to obtain the deoiled sludge finished product. In this embodiment, the eluent is mainly composed of 800 mg / L SDBS and 3% Na2SiO3.

[0044] Comparative Example 1 This comparative example provides a method for deoiling sludge, which is basically the same as the method provided in Example 1, with the main difference being that this comparative example adopts a non-freeze-thaw method and uses water as an eluent to deoil the sludge, with the same number of repeated elutions.

[0045] Comparative Example 2 This comparative example provides a method for deoiling oil sludge, which is basically the same as the method provided in Example 1, with the main difference being that this comparative example adopts a non-freeze-thaw method, and the other steps are the same.

[0046] Comparative Example 3 This comparative example provides a method for deoiling sludge based on freeze-thaw method, which is basically the same as the method provided in Example 1, with the main difference being that deionized water is used instead of eluent for elution in this comparative example.

[0047] Comparative Example 4 This comparative example provides a method for assisted sludge deoiling based on freeze-thaw method, which is different from the method provided in Example 1. The main difference is that this comparative example uses -20°C constant temperature freeze-thaw instead of unidirectional freeze-thaw for elution.

[0048] The residual oil rate, oil removal rate and removed crude oil components in the deoiled sludge treated by Example 1 and Comparative Examples 1 to 4 were tested, and the results are shown in Tables 8 and 9.

[0049] Table 8 Sludge desludging effect table project Embodiment 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Residual oil rate 1.82% 8.89% 6.98% 7.52% 5.46% Removal rate 90.52% 53.69% 63.65% 60.83% 71.52% Table 9 Composition of crude oil after treatment in Example 1 and Comparative Examples 3-4

[0050] It can be seen from Table 9 that the removal rate of colloid and aromatic hydrocarbons in the crude oil components is the highest, reaching more than 92%, and the other two components also reach more than 85%. Compared with Example 1, Comparative Example 3 only uses water elution, and Comparative Example 4 uses constant temperature freeze-thaw method. The removal rate of aromatic hydrocarbons in the crude oil components of these two comparative examples is the highest, followed by saturated hydrocarbons. In the method provided in Example 1, the removal rate of the four components of crude oil is significantly higher than that of the comparative example.

[0051] In summary, the method for deoiling sludge based on freeze-thaw method provided in the embodiment of the present invention adopts a combination of slow unidirectional freeze-thaw and eluent, which can effectively improve the deoiling effect of sludge and make the crude oil removal rate of sludge reach more than 90%.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A method for deoiling sludge based on freeze-thaw method, comprising the steps of: Water replenishment and saturation: adding eluent to the oil sludge until the oil sludge reaches a saturated state to form an oil sludge saturated mixture; Freezing and freezing: using a one-way freeze-thaw method to cool the sludge saturated mixture, while continuously adding the eluent to the low-temperature part of the sludge saturated mixture, until the eluent in the sludge saturated mixture is converted into a solid state and is frozen with the sludge saturated mixture as a whole, forming frozen sludge; Melting and flushing: using the eluent to elute the low-temperature part of the frozen sludge, instantly melting the frozen sludge until it is completely melted to form melted sludge; Collecting the leachate: The leachate in the melted sludge is collected by filtering, wherein: The eluate contains components of the eluent and crude oil; Repeat elution: repeat the freezing step to the step of collecting the elution until the crude oil content in the collected elution is stable and less than 2%, thereby obtaining a deoiled sludge semi-finished product; Deionized elution: Repeat the freezing step to the step of collecting the eluted liquid to treat the deoiled sludge semi-finished product, and replace the eluent therein with deionized water to obtain the deoiled sludge finished product.

2. The method according to claim 1, characterized in that The eluent comprises sodium dodecylbenzene sulfonate with a concentration of 200 to 1000 mg / L and a base with a concentration of 2 to 5 wt%.

3. The method according to claim 2, characterized in that The alkali is at least one of potassium hydroxide, sodium carbonate and sodium silicate.

4. The method according to claim 3, characterized in that The eluent includes 600-900 mg / L SDBS and 2.5-5 wt% Na2SiO3.

5. The method according to any one of claims 1 to 4, characterized in that: The solid-to-liquid ratio of the oil sludge to the eluent may be 1: (1-7) g / mL.

6. The method according to claim 5, characterized in that The freezing step includes: freezing and freezing the sludge saturated mixture by a one-way freeze-thaw method to form a temperature difference between the upper surface and the lower surface of the sludge saturated mixture, controlling the cooling rate to ensure the movement speed of the freezing front, and continuously replenishing the eluent from the unfrozen area of ​​the sludge saturated mixture to the frozen area until the sludge saturated mixture is frozen as a whole to form the frozen sludge.

7. The method according to claim 6, characterized in that In the freezing step, the upper surface temperature of the sludge saturated mixture is gradually reduced from -2°C to 2°C to -12°C to -8°C and then kept constant for 4 to 6 hours; the lower surface temperature of the sludge saturated mixture is first gradually reduced from 8°C to 12°C to -2°C to 2°C, then instantly cooled to -12°C to -8°C and then kept constant for 4 to 6 hours, so that the sludge saturated mixture is completely frozen.

8. The method according to claim 7, characterized in that In the freezing step, the temperature of the sludge saturated mixture is reduced at a rate of 0.1-0.3°C / h.

9. The method according to claim 7 or 8, characterized in that The melting and flushing step includes: instantly raising the temperature of the upper surface and the lower surface of the frozen sludge to 8°C to 12°C at the same time, and keeping the temperature constant for 8 to 12 hours, so that the eluent and sludge in the frozen sludge are melted, and at the same time, the melted eluent rinses the surface of the frozen sludge particles from top to bottom again under the action of gravity to form the melted mixed sludge.

10. The method according to claim 9, characterized in that In the melting and flushing step, the melting temperature rise rate of the frozen sludge is 1-2°C / min.

Images