Process for pressure filtration treatment of oily sludge
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHENGDU NAMAGNESIUM CHEM CO LTD
- Filing Date
- 2026-04-08
- Publication Date
- 2026-06-19
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Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention belongs to the field of oil and gas field waste treatment technology, specifically a depressurization process for oily sludge. Background Technology
[0002] During oil and gas field extraction, the resulting sludge naturally carries silica particles from the formation. Simultaneously, chemical additives such as demulsifiers and corrosion inhibitors, added to ensure smooth extraction operations, interact with the silica particles, crude oil, and water, ultimately forming oily sludge. This type of oily sludge is classified as hazardous waste. If not properly disposed of promptly, it can easily lead to crude oil leakage, polluting soil and groundwater, and damaging the surrounding ecosystem. Therefore, it requires harmless and volume-reducing treatment. Filtration is a crucial process for achieving solid-liquid separation of oily sludge and ensuring that subsequent treatment meets standards, and it is widely used in the field of oily sludge disposal.
[0003] Existing conventional pressure filtration processes typically employ ambient temperature and pressure feeding, the addition of conventional filter aids (such as polyaluminum chloride and polyacrylamide), and high-pressure compression filtration. This process is widely used in the treatment of oily sludge from ordinary oil and gas fields, suitable for conventional operating conditions with ambient temperature, atmospheric pressure, and low silica particle content. However, in high-altitude oil and gas fields (≥3000 meters) (such as Qinghai Oilfield, Sebei Gas Field, and the Lunpola Basin in northern Tibet), the sludge produced differs from that of ordinary oil and gas fields due to the unique geological structure and intense weathering of the plateau siliceous strata. This leads to several technical shortcomings in the practical application of pressure filtration processes, which are originally suitable for conventional scenarios, in high-altitude oil and gas fields. These shortcomings are detailed below:
[0004] Firstly, the ambient temperature in high-altitude areas is maintained at -15℃ to 10℃ year-round. The low temperature environment easily causes oily sludge to freeze or become a high-viscosity semi-solid, which in turn causes blockage of the feed port during feeding. At the same time, the low temperature reduces the fluidity of the sludge, resulting in uneven distribution of sludge on the surface of the filter cloth, with local dry blockage and local filter cloth idling, reducing the filtration efficiency. In addition, the low temperature reduces the toughness of the filter cloth. During high-pressure filtration (compression pressure ≥20 bar), the filter cloth is prone to damage, and it also reduces the demulsification and flocculation activity of conventional filter aids, weakening their effect.
[0005] Secondly, the unique silica particles in high-altitude oily sludge (originating from the special structure and strong weathering of the plateau silica strata in high-altitude areas, with a SiO2 mass fraction ≥25%, of which particles with a diameter ≤5μm account for ≥60%) interact with demulsifiers, corrosion inhibitors and other chemical additives, crude oil and water added during the mining process to form a stable emulsion system of "oil-water-silica particles", which further exacerbates the difficulty of pressure filtration: conventional filter aids are prone to adsorption reactions with silica particles, making it difficult to effectively demulsify and flocculate and break the stable system. Moreover, the viscous substance formed by the reaction between the two will clog the filter cloth and the flow channel of the pressure filtration equipment, resulting in frequent shutdowns for cleaning and increased operation and maintenance costs.
[0006] Third, the air pressure in high-altitude areas is usually below 0.7 atm. Low air pressure will lower the boiling point of water in sludge, indirectly weakening the dewatering efficiency of filter cake. In addition, the synergistic interference of fine silica particles and chemical additives further aggravates the filter cloth clogging problem. The pore size of conventional filter cloth is usually ≥10μm. Fine silica particles can easily penetrate the pores of the filter cloth or quickly form a dense silica filter cake layer on the surface of the filter cloth, resulting in a decrease in the permeability of the filter cloth. This leads to an increase in filtration pressure, a decrease in filtration rate, and even a "filtration standstill" phenomenon, affecting the progress of oily sludge treatment.
[0007] Therefore, it is of great practical significance to provide a filter press treatment process for oily sludge that can be adapted to complex working conditions at high altitudes. Summary of the Invention
[0008] The purpose of this invention is to provide a pressure filtration process for treating oily sludge, which effectively solves the technical problems of conventional pressure filtration processes in high-altitude oil and gas fields, such as sludge agglomeration, difficulty in breaking up emulsion systems, equipment blockage, filter cloth damage, and low pressure filtration efficiency, under the combined conditions of low temperature, low pressure, and high silica fine particles. This enables efficient, harmless, and reduced-volume treatment of oily sludge from high-altitude oil and gas fields, and improves the stability and practicality of the pressure filtration process.
[0009] The objective of this invention is achieved through the following technical solution:
[0010] A filter press treatment process for oily sludge includes the following steps:
[0011] S1 Sludge Preheating Treatment: Oily sludge from oil and gas fields is sent into a preheating conditioning tank, and surface modifiers alkyl glycosides and amorphous silica powder are added. Then, gradient heating and stirring treatment is carried out. After stirring, pretreated sludge is obtained.
[0012] S2 Filter Aid Addition and Demulsification: The pretreated sludge is fed into a mixing reactor and a composite modified filter aid is added. Then, it is subjected to stirring and ultrasonic treatment to obtain demulsified sludge.
[0013] The composite modified filter aid is made by mixing hydrophobically modified diatomaceous earth, quaternized modified chitosan, aminated modified graphene oxide, trisodium citrate, sodium dodecylbenzene sulfonate and polyoxyethylene sorbitan monooleate (Tween-80).
[0014] S3 Gradient Filtration: The demulsified sludge is fed into the filter press, first with a pressure of ≤0.5 bar, and then the pressure is gradually increased to the set pressure for continuous filtration; during the filtration process, dry nitrogen gas with temperature and humidity control is introduced into the filter chamber of the filter press; wherein, the filter plate flow channel of the filter press is pre-coated with a porous non-hydrophobic diatomaceous earth pre-coating, and the filter press adopts a double-layer structure air-permeable gradient pore size filter cloth;
[0015] S4 Cake Discharge and Filter Cloth Cleaning: After the filter press is completed, instantaneous high-pressure nitrogen is introduced into the filter chamber of the filter press, and micro-backflushing is used to complete the cake discharge. After cleaning the filter cloth, the single filter press operation is completed.
[0016] Preferably, in step S1, the initial temperature of the oily sludge is -15℃ to 10℃, and the temperature is gradually increased to 15℃ to 20℃ at a rate of 1℃ to 2℃ / min; the alkyl glycoside accounts for 0.1% to 0.3% of the sludge mass, the amorphous silica powder accounts for 0.3% to 1.2% of the silica fine particles mass, and the particle size is 1 to 2 μm; the settling time is 5 to 10 min.
[0017] Preferably, in step S2, the preparation process of the quaternized modified chitosan is as follows: first, the chitosan is grafted with quaternary ammonium salt groups; after the grafting is completed, 0.1% to 0.2% of citric acid by weight of chitosan is added to improve the demulsification stability of the quaternized chitosan under low temperature conditions; then, it is activated by microwave at 55 to 65°C to finally obtain the quaternized modified chitosan. In this scheme, chitosan is first grafted with quaternary ammonium salt groups, which endows it with good demulsification ability. After grafting, citric acid is added to improve the stability of quaternized chitosan in high-altitude and low-temperature environments, prevent its activity from decreasing under subsequent drying nitrogen, reduce the chance of it being washed onto the filter cloth surface by nitrogen, and reduce the probability of adhesion to fine silica particles, thereby improving the utilization rate of filter aid and reducing filter cloth adhesion. Subsequently, microwave low-temperature activation at 55~65℃ can further enhance the activity of quaternized chitosan, ensuring that it continues to play a demulsification and adsorption role under high-altitude, low-temperature, nitrogen-assisted pressure filtration conditions.
[0018] Preferably, in step S2, the aminated modified graphene oxide is obtained by intercalating graphene oxide with ethylenediamine. In this scheme, the ethylenediamine intercalation treatment of graphene oxide can effectively improve the dispersibility of the aminated modified graphene oxide itself, reduce its agglomeration with high-silica fine particles under low-temperature conditions, and enhance its adsorption capacity for oil droplets and fine particles in sludge, thus better assisting the quaternized modified chitosan in completing the demulsification operation and further optimizing the demulsification effect.
[0019] Preferably, in step S2, the hydrophobically modified diatomaceous earth is obtained by grafting diatomaceous earth with methyltrimethoxysilane. In this scheme, by grafting diatomaceous earth with methyltrimethoxysilane, good hydrophobicity can be imparted to the diatomaceous earth, enabling it to adsorb oil droplets in oily sludge, while effectively repelling fine silica particles, preventing the fine silica particles from mixing with filter aids and oil droplets to form a viscous mixture, thus reducing equipment clogging problems at the source.
[0020] Preferably, the composite modified filter aid comprises the following components in parts by weight:
[0021] 40-50 parts of hydrophobically modified diatomaceous earth, 25-35 parts of quaternized modified chitosan, 5-10 parts of aminated modified graphene oxide, 5-10 parts of trisodium citrate, 3-5 parts of sodium dodecylbenzene sulfonate, and 0.5-1 parts of polyoxyethylene sorbitan monooleate (Tween-80).
[0022] The amount of composite modified filter aid added is 0.3% to 0.45% of the total dry weight of oily sludge.
[0023] Preferably, in step S2, the temperature of the mixing reaction is 15~20℃, and the reaction time is 10~15min; the temperature of the ultrasonic treatment is ≤25℃.
[0024] Preferably, in step S3, the air-permeable gradient pore size filter cloth has a double-layer structure, with the outer layer in contact with the sludge having a pore size of 10~15μm and the inner layer in contact with the filter plate having a pore size of 5~8μm; the thickness of the non-hydrophobic diatomaceous earth pre-coating layer is 0.2~0.3mm. In this application, by setting a double-layer gradient pore size filter cloth, graded interception can be achieved. The outer layer intercepts larger particles, and the inner layer intercepts fine silicon particles, ensuring the permeability of the filter cloth while preventing fine silicon particles from penetrating the filter cloth; limiting the pre-coating parameters can intercept undispersed micro-agglomerates without affecting nitrogen permeation and water discharge, forming a synergistic interception effect with the filter cloth, further reducing equipment blockage and "pressure filtration stagnation" phenomenon, and improving pressure filtration efficiency and stability.
[0025] Preferably, in step S3, the pressure of the low-pressure fabric is 0.3~0.5 bar, and the duration is 5~8 min; the rate of gradient pressurization is 0.5~1 bar / min, the final pressure is 20~25 bar, and the continuous pressurization time is 20~30 min; the initial pressure of the drying nitrogen is 0.8~1.0 bar, and the temperature after temperature and humidity control is 20~25℃, and the relative humidity is 15%~20%.
[0026] Preferably, in step S4, the instantaneous high-pressure nitrogen pressure is 5~8 atm, and the micro-backflushing time is 0.5~1 min.
[0027] Compared with the prior art, the beneficial effects of the present invention are:
[0028] The process of this invention can effectively solve the technical problems of pressure filtration in high-altitude oil and gas fields under the combined conditions of low temperature, low pressure, and high silica fine particles, as follows:
[0029] In step S1, pretreatment of oily sludge from oil and gas fields by first feeding and then gradually heating and stirring improves the dispersion of the sludge at low temperatures, providing a stable material basis for subsequent demulsification and filtration. Specifically, alkyl glycosides can significantly reduce sludge viscosity, improve its fluidity at low temperatures, and reduce sludge agglomeration, creating favorable conditions for the uniform mixing and demulsification flocculation of subsequent filter aids; amorphous silica powder, as a dispersion medium, can effectively alleviate the low-temperature agglomeration of aminated modified graphene oxide and high-silica fine particles, reduce secondary clogging of the filter plate channels by agglomerates, and since it is homologous to formation silica fine particles, it will not introduce heterogeneous impurities.
[0030] In step S2, by mixing the pretreated sludge with the composite modified filter aid in the reactor and combining it with stirring and ultrasonic treatment, the uniformity of filter aid dispersion can be improved, the demulsification effect can be enhanced, and the stability of the system can be improved. Specifically, hydrophobically modified diatomaceous earth can adsorb oil droplets while repelling fine silica particles, effectively preventing the formation of a viscous mixture by mixing with filter aids and oil droplets, thus aiding in demulsification; quaternized modified chitosan can still efficiently break down the stable emulsion system formed by "oil-water-fine silica particles" in oily sludge at low temperatures, and it also has a certain adsorption capacity, which can help adsorb small oil droplets and particles in sludge, improving the filtration performance of the material after demulsification; aminated modified graphene oxide enhances the overall adsorption performance of the composite filter aid by improving its own dispersibility, and can assist quaternized modified chitosan in completing demulsification; sodium dodecylbenzenesulfonate can reduce the oil-water interfacial tension, which not only assists in demulsification but also improves the filter cake formation effect; Tween-80 can alleviate the microphase separation phenomenon between hydrophobic diatomaceous earth and sodium dodecylbenzenesulfonate at low temperatures, ensuring the stability of the filter aid system.
[0031] In step S3, by using a pre-coated diatomaceous earth layer, combined with a double-layer gradient pore size filter cloth, and employing a pressure filtration method that integrates low-pressure cloth, gradient pressurization, and temperature and humidity controlled nitrogen introduction, the stability and dehydration efficiency of the pressure filtration process can be improved, while reducing equipment blockage and filter cloth damage. Specifically, the low-pressure cloth (≤0.5 bar) effectively prevents filter cloth breakage due to high pressure at low temperatures, while the gradient pressurization mode compensates for insufficient pressure difference caused by low air pressure, ensuring dehydration efficiency. The temperature and humidity controlled nitrogen introduction reduces the activity decay of quaternized chitosan, preventing it from forming adsorption complexes with fine silica particles, thereby improving the utilization rate of the filter aid. The porous, non-hydrophobic diatomaceous earth pre-coating can intercept small aggregates without affecting the passage of nitrogen and water. Together with the double-layer gradient pore size filter cloth, it forms a graded interception system, effectively preventing equipment blockage and "pressure filtration stagnation."
[0032] In summary, the process of this invention effectively solves the problems of low-temperature agglomeration, system instability, equipment blockage and filter cloth damage in the pressure filtration treatment of oily sludge in high-altitude oil and gas fields, and is suitable for the complex working conditions of high altitude, low temperature, low air pressure and high silica fine particles. Detailed Implementation
[0033] Example 1
[0034] 1. Preparation method of non-commercially available components.
[0035] (1) Quaternized modified chitosan: Take 100g of chitosan (degree of deacetylation ≥90%), add 1000mL of deionized water, stir until swollen, then add 30g of 3-chloro-2-hydroxypropyltrimethylammonium chloride, adjust the pH to 8.5 with 1mol / L NaOH solution, stir at 50℃ for 4h to complete the grafting of quaternary ammonium salt groups; then add 0.15g of citric acid (0.15% of chitosan mass) to the above system, stir at 30℃ for 30min; finally place the product in a microwave reactor, microwave activate at 58℃ for 12min, vacuum dry at 60℃ to constant weight, pulverize and pass through an 80-mesh sieve to obtain quaternized modified chitosan.
[0036] (2) Aminated graphene oxide: Take 10g of graphene oxide (sheet thickness 1~3nm), add 500mL of deionized water, and ultrasonically disperse for 30min to form a suspension; then add 20g of ethylenediamine (purity 99%), stir at 80℃ for 6h, centrifuge and wash until neutral, vacuum dry at 60℃ to constant weight, grind and pass through a 100-mesh sieve to obtain aminated graphene oxide.
[0037] (3) Hydrophobic modified diatomaceous earth: Take 100g of diatomaceous earth (specific surface area 200~300m² / g), calcine at 600℃ for 2h, cool and add 500mL of anhydrous ethanol, and ultrasonically disperse for 20min; then add 15g of methyltrimethoxysilane (purity 98%), stir at 70℃ for 3h, filter and wash, vacuum dry at 80℃ to constant weight, grind and pass through a 100-mesh sieve to obtain hydrophobic modified diatomaceous earth.
[0038] (4) Composite modified filter aid: Weigh 45 parts of hydrophobically modified diatomaceous earth, 30 parts of quaternized modified chitosan, 8 parts of aminated modified graphene oxide, 7 parts of trisodium citrate, 4 parts of sodium dodecylbenzene sulfonate, and 0.8 parts of polyoxyethylene sorbitan monooleate (Tween-80) according to the weight ratio, place them in a high-speed mixer, mix at 2000r / min for 10min to obtain the composite modified filter aid product.
[0039] 2. Oily sludge depressurization process.
[0040] S1 Sludge Preheating Treatment: 100 kg of high-altitude oily sludge (collected from Qinghai Oilfield at an altitude of 3200 m, with an initial sludge temperature of 8℃, a dry basis content of 30%, an oil content of 12.5%, a water content of 65.3%, and a SiO2 mass fraction of 28.6%, of which 65.2% are fine silica particles with a particle size ≤5μm; the sludge contains residues of polyoxyethylene polyoxypropylene ether demulsifier and imidazoline corrosion inhibitor added during the mining process, with a total residue of 0.8% of the sludge dry basis) was sent to a preheating conditioning tank. 0.2 kg of alkyl glycoside and 0.095 kg of amorphous silica powder (particle size 1~2μm, industrial grade) were added. Stirring was started (stirring speed 300 r / min), and the temperature was gradually increased to 18℃ at a rate of 1.5℃ / min. After stirring for 30 min, the mixture was allowed to stand for 8 min to obtain pretreated sludge.
[0041] S2 Filter Aid Addition and Demulsification: The pretreated sludge is fed into a mixing reactor (with an ultrasonic device, power 300W, frequency 28kHz), 0.105kg of composite modified filter aid is added, the reactor temperature is adjusted to 18℃, and after stirring at 250r / min for 5min, ultrasonic treatment is started (temperature 22℃), and stirring-ultrasonic co-treatment is carried out for 12min to obtain demulsified sludge.
[0042] S3 Gradient Filtration: The demulsified sludge is fed into a plate and frame filter press. The filter plates of this filter press are pre-coated with a 0.25mm thick porous, non-hydrophobic diatomaceous earth pre-coating (diatomaceous earth, specific surface area 200~300m² / g, pore size 4μm). A double-layer structure of air-permeable gradient pore size filter cloth is used (the outer layer in contact with the sludge has a pore size of 12μm, and the inner layer in contact with the filter plate has a pore size of 6μm; both the inner and outer layers of the double-layer structure of air-permeable gradient pore size filter cloth are made of polypropylene monofilaments through a double weaving process). First, the cloth is pressed at a low pressure of 0.4 bar for 6 minutes; then the pressure is gradually increased to 22 bar at a rate of 0.8 bar / min and pressed for 25 minutes. During the filtration process, dry nitrogen gas with temperature and humidity control is introduced into the filter chamber through a nitrogen generator (with a temperature and humidity control unit). The initial nitrogen pressure is 0.9 bar, and the temperature after control is 22℃ and the relative humidity is 18%.
[0043] S4 Cake Discharge and Filter Cloth Cleaning: After the filter press is completed, 6 atm of instantaneous high-pressure nitrogen is introduced into the filter chamber of the filter press, and the cake is discharged by micro-backblowing for 0.8 minutes. Then, the filter cloth is purged with room temperature dry nitrogen for 2 minutes to complete a single filter press operation.
[0044] Example 2
[0045] Based on Example 1, only some parameters were adjusted. The preparation methods and operating steps of the remaining raw materials, non-commercial components, and other unmentioned raw materials were the same as in Example 1. The specific parameter adjustments are as follows:
[0046] S1 sludge preheating treatment: Alkyl glycoside addition amount 0.1kg.
[0047] S2 filter aid addition and demulsification: The amount of composite modified filter aid added is 0.09 kg, and the composition ratio is as follows: 40 parts of hydrophobically modified diatomaceous earth, 25 parts of quaternized modified chitosan, 5 parts of aminated modified graphene oxide, 5 parts of trisodium citrate, 3 parts of sodium dodecylbenzenesulfonate, and 0.5 parts of Tween-80.
[0048] S3 gradient pressure filtration: unhydrophobic diatomaceous earth pre-coating thickness 0.2mm, filter cloth outer layer 10μm, inner layer 5μm; low pressure cloth 0.3bar, continuous for 5min; gradient pressure increase rate 0.5bar / min, final pressure 20bar, continuous pressure filtration for 20min; initial pressure of dry nitrogen 0.8bar, temperature 20℃ after temperature and humidity control, relative humidity 15%.
[0049] S4 cake unloading and filter cloth cleaning: instantaneous high-pressure nitrogen 5 atm, micro backflushing for 0.5 min.
[0050] Example 3
[0051] Based on Example 1, only some parameters were adjusted. The preparation methods and operating steps of the remaining raw materials, non-commercial components, and other unmentioned raw materials were the same as in Example 1. The specific parameter adjustments are as follows:
[0052] S1 sludge preheating treatment: alkyl glycoside addition amount 0.3kg, heating rate 2℃ / min, heating to 20℃.
[0053] S2 filter aid addition and demulsification: The amount of composite modified filter aid added is 0.135 kg, and the component ratio is as follows: 50 parts of hydrophobically modified diatomaceous earth, 35 parts of quaternized modified chitosan, 10 parts of aminated modified graphene oxide, 10 parts of trisodium citrate, 5 parts of sodium dodecylbenzenesulfonate, and 1 part of Tween-80; the mixing reaction temperature is 20℃, the time is 15 min, and the ultrasonic treatment temperature is 25℃.
[0054] S3 gradient pressure filtration: unhydrophobic diatomaceous earth pre-coating thickness 0.3mm, filter cloth outer layer 15μm, inner layer 8μm; low pressure cloth 0.5bar, continuous for 8min; gradient pressure increase rate 1bar / min, final pressure 25bar, continuous pressure filtration for 30min; initial pressure of dry nitrogen 1.0bar, temperature 25℃ after temperature and humidity control, relative humidity 20%.
[0055] S4 cake unloading and filter cloth cleaning: instantaneous high-pressure nitrogen 8 atm, slight backflushing for 1 min.
[0056] Comparative Example 1
[0057] Compared to Example 1, during the preheating treatment of S1 sludge, the addition of amorphous silica powder was omitted, and only alkyl glycosides were added. The remaining stirring and heating parameters were completely consistent with those of Example 1.
[0058] Comparative Example 2
[0059] Compared to Example 1, the composite modified filter aid was replaced with an equal mass of conventional oil and gas field sludge filter aid (polyaluminum chloride (industrial grade): polyacrylamide (industrial grade, molecular weight 8 million) = 4:1, mass ratio), and the remaining steps, equipment, and parameters were completely consistent with Example 1.
[0060] Comparative Example 3
[0061] Compared to Example 1, the quaternized chitosan only undergoes quaternary ammonium salt group grafting, eliminating the subsequent steps of adding citric acid (food grade) and microwave activation. The preparation of other components, process steps, and parameters are completely consistent with Example 1.
[0062] Comparative Example 4
[0063] Compared to Example 1, the hydrophobically modified diatomaceous earth was replaced with an equal mass of unmodified diatomaceous earth, while the preparation of the remaining components, process steps, and parameters were completely consistent with Example 1.
[0064] Comparative Example 5
[0065] Compared to Example 1, the aminated modified graphene oxide was replaced with an equal mass of unmodified graphene oxide, while the preparation of the remaining components, process steps, and parameters were completely consistent with Example 1.
[0066] Comparative Example 6
[0067] Compared to Example 1, when preparing the composite modified filter aid, the addition of Tween-80 (food grade) was omitted, while the proportions of the remaining components and the preparation method remained unchanged. The entire process steps, equipment, and parameters were completely consistent with those of Example 1.
[0068] Comparative Example 7
[0069] Compared to Example 1, the filter press is not coated with diatomaceous earth pre-coating, and the double-layer filter cloth is replaced with a conventional single-layer filter cloth. The rest of the filter press equipment, parameters, and steps are completely the same as in Example 1.
[0070] Comparative Example 8
[0071] Compared to Example 1, dry nitrogen gas at room temperature was directly introduced during pressure filtration (without temperature and humidity control), while the other pressure filtration parameters, equipment, and steps were completely consistent with Example 1.
[0072] Experimental Example
[0073] To verify the effectiveness of the oily sludge pressure filtration treatment process of this invention in treating oily sludge from high-altitude oil and gas fields, experiments were conducted on Examples 1-3 and Comparative Examples 1-8. All experiments were repeated three times in parallel, with a relative standard deviation (RSD) ≤ 5%. The average value was taken as the final result (as shown in Table 1). Specific detection indicators and methods are as follows:
[0074] (1) Demulsification effect test.
[0075] ① Demulsification rate: The bottle test method is adopted. Take 20 mL of demulsified sludge and place it in a stoppered graduated test tube. After standing for 30 min, measure the volume of the precipitated oil phase. Calculate according to the formula: Demulsification rate = (volume of precipitated oil phase / total oil phase volume in sludge) × 100%. The higher the value, the better the demulsification effect.
[0076] ② Aqueous phase transmittance: The aqueous phase of the demulsified sludge was centrifuged at 3000 r / min for 10 min. The transmittance was measured using a 722 spectrophotometer at a wavelength of 550 nm and a 1 cm cuvette, with deionized water as a reference.
[0077] (2) Filter cake detection:
[0078] ① Moisture content of filter cake: Using the 105℃ constant temperature drying method, take 5g of filter cake and dry it in the oven until constant weight. Calculate according to the formula: Moisture content = (mass before drying - mass after drying) / mass before drying × 100%.
[0079] ② Oil content of filter cake: Soxhlet extraction method is adopted, with carbon tetrachloride as the extractant. The crude oil in the filter cake is continuously extracted by reflux. The oil content is calculated according to the formula: oil content = (mass of crude oil after extraction / initial mass of filter cake) × 100%.
[0080] (3) Process efficiency testing:
[0081] ① Filtration rate: Record the amount of filtrate that passes through the filter cloth per unit time and per unit area. Calculate it according to the formula: Filtration rate = filtrate volume / (effective area of filter cloth × filtration time), in mL / (m²·min).
[0082] ② Filter cloth breakage rate: After a single filtration, the filter cloth (the effective area is the same in all embodiments and comparative examples) is divided into several uniform grids of 1cm×1cm (greater than or equal to 500). Each grid is inspected using a 10x magnifying glass, with each grid as the counting unit. If there is a visible breakage point (including pinholes and tears) with a diameter ≥0.1mm in each grid, it is counted as 1 broken grid. The number of broken points on the filter cloth = the total number of broken grids. The filter cloth breakage rate is calculated according to the formula: Filter cloth breakage rate = (total number of broken grids / total number of filter cloth grids) × 100%.
[0083] (4) Equipment blockage frequency detection: Record the number of times the equipment is shut down for cleaning due to blockage of the filter cloth and filter plate flow channels during the processing of 200kg of oily sludge, in units of times / 200kg.
[0084] (5) Others:
[0085] ① Average particle size of aggregates: After adding the composite modified filter aid in step S2, the mixed sludge system was stirred at low speed of 120r / min for 4min and then allowed to stand for 10min (without ultrasound). The volume average particle size of the aggregates in the mixed sludge was determined using a Malvern Mastersizer 3000 laser particle size analyzer under wet dispersion conditions, in μm.
[0086] ② Stratification rate of the filter aid system: Take 50 mL of the mixed sludge system (without ultrasound) after adding the composite modified filter aid in step S2 and stirring at low speed of 120 r / min for 4 min, and place it in a stoppered graduated test tube. After standing for 10 min, directly read the volume of the supernatant (unmixed filter aid components / water) in the test tube, which is the volume of the stratified liquid layer. If there is no obvious stratification of the system, the volume of the stratified liquid layer is recorded as 0. Calculate the stratification rate according to the formula: Stratification rate = (Separated liquid layer volume / Total volume of the mixed system) × 100%.
[0087] ③Silicon fine particle interception efficiency:
[0088] Detection subject: Inductively coupled plasma atomic emission spectrometry was used to determine the SiO2 mass concentration in the filtrate obtained from gradient pressure filtration in step S3 and the original oily sludge, respectively. The SiO2 interception efficiency was calculated according to the formula: SiO2 concentration in the original sludge - SiO2 concentration in the filtrate) / SiO2 concentration in the original sludge × 100%.
[0089] Table 1:
[0090]
[0091] Note: "-" in Table 1 indicates that the experimental group has not performed well in the tested items and is not suitable for the working conditions of high-altitude oil and gas fields, so the experiment is not necessary.
[0092] As can be seen from Table 1:
[0093] Examples 1-3 effectively solve problems such as low-temperature agglomeration, system instability, equipment blockage and filter cloth damage in the pressure filtration treatment of oily sludge in high-altitude oil and gas fields, and are suitable for the complex working conditions of high altitude, low temperature, low air pressure and high silica fine particles. Among these, the demulsification rate was ≥97.8% and the aqueous phase transmittance was ≥90.5%, effectively breaking the stable emulsion system of "oil-water-silica fine particles"; the filter cake moisture content was ≤57.8% and the oil content was ≤2.9%, achieving the requirements for harmless and reduced-volume treatment of oily sludge; the filtration rate was ≥82.3mL / (m²・min), the filter cloth damage rate was ≤0.3%, and the equipment clogging frequency was ≤1 time / 200kg, ensuring the high efficiency and stability of the filtration process; the average particle size of the aggregates was ≤20.3μm and the stratification rate of the filter aid system was ≤0.5%, effectively alleviating the problems of low-temperature agglomeration and microphase separation in the system; and the silica fine particle interception efficiency was ≥99.7%, achieving efficient interception of silica fine particles and avoiding the phenomenon of "filtration stagnation".
[0094] In Comparative Example 1, the removal of amorphous silica powder prevented the steric hindrance effect from mitigating the low-temperature agglomeration of aminated modified graphene oxide and high-silica fine particles, resulting in a significant increase in the average particle size of the agglomerates. This led to a decrease in demulsification efficiency and an increase in equipment clogging frequency. In Comparative Example 2, replacing the composite modified filter aid with a conventional filter aid failed to break down the stable emulsion system of oily sludge from high altitudes and lacked anti-agglomeration and system-stabilizing effects, resulting in poor performance across all indicators. In Comparative Example 3, the removal of citric acid addition and microwave activation steps from the quaternized modified chitosan resulted in decreased demulsification stability and activity under low-temperature nitrogen conditions, leading to reduced demulsification efficiency and pressure filtration efficiency. In Comparative Example 4, replacing the hydrophobically modified diatomaceous earth with unmodified diatomaceous earth caused the diatomaceous earth to lose its "oil-absorbing and silica-repelling" properties, making it prone to combining with silica fine particles to form viscous substances. This resulted in increased agglomerate particle size, decreased demulsification efficiency, and equipment clogging. In Comparative Example 5, replacing the aminated modified graphene oxide with unmodified graphene oxide significantly reduced its dispersibility and intensified low-temperature agglomeration with silica particles, leading to a decrease in demulsification and filtration efficiency. In Comparative Example 6, the removal of Tween-80 failed to alleviate the microphase separation phenomenon between hydrophobic diatomaceous earth and sodium dodecylbenzenesulfonate at low temperatures, resulting in increased stratification rate and decreased system stability in the filter aid system. In Comparative Example 7, the removal of the diatomaceous earth pre-coating and its replacement with conventional single-layer filter cloth eliminated the synergistic effect of the graded interception system, significantly reducing the silica particle interception efficiency. Silica particles easily penetrated the filter cloth to form a dense filter cake layer, leading to a decrease in filtration rate and an increase in filter cloth breakage rate. In Comparative Example 8, the introduction of room-temperature dry nitrogen gas without temperature and humidity control during filtration accelerated the activity decay of quaternized chitosan and exacerbated the low-temperature embrittlement of the filter cloth, resulting in a decrease in demulsification and an increase in filter cloth breakage rate.
Claims
1. A filter press treatment process for oily sludge, characterized in that, Includes the following steps: S1 Sludge Preheating Treatment: Oily sludge from oil and gas fields is sent into a preheating conditioning tank, and surface modifiers alkyl glycosides and amorphous silica powder are added. Then, gradient heating and stirring treatment is carried out. After stirring, pretreated sludge is obtained. S2 Filter Aid Addition and Demulsification: The pretreated sludge is fed into a mixing reactor and a composite modified filter aid is added. Then, it is subjected to stirring and ultrasonic treatment to obtain demulsified sludge. The composite modified filter aid is made by mixing hydrophobically modified diatomaceous earth, quaternized modified chitosan, aminated modified graphene oxide, trisodium citrate, sodium dodecylbenzene sulfonate and polyoxyethylene sorbitan monooleate. The quaternized modified chitosan is prepared by first grafting chitosan with quaternary ammonium salt groups, then adding 0.1% to 0.2% citric acid by weight of chitosan after grafting, and then activating it by microwave at 55 to 65°C. S3 Gradient Filtration: Demulsified sludge is fed into a filter press, initially distributed at a pressure of ≤0.5 bar, then gradually increased to a set pressure for continuous filtration. During filtration, dry nitrogen gas, regulated by temperature and humidity, is introduced into the filter chamber. The filter plates of the filter press are pre-coated with a porous, non-hydrophobic diatomaceous earth pre-coating, and the filter press uses a double-layer structure of permeable gradient pore size filter cloth. The initial pressure of the dry nitrogen gas is 0.8~1.0 bar, and the temperature after temperature and humidity regulation is 20~25℃, with a relative humidity of 15%~20%. S4 Cake Discharge and Filter Cloth Cleaning: After the filter press is completed, instantaneous high-pressure nitrogen is introduced into the filter chamber of the filter press, and micro-backflushing is used to complete the cake discharge. After cleaning the filter cloth, the single filter press operation is completed.
2. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S1, the initial temperature of the oily sludge is -15℃ to 10℃, and the temperature is gradually increased to 15℃ to 20℃ at a rate of 1℃ to 2℃ / min; the alkyl glycoside accounts for 0.1% to 0.3% of the sludge mass, the amorphous silica powder accounts for 0.3% to 1.2% of the silica fine particles mass, and the particle size is 1 to 2 μm; the settling time is 5 to 10 min.
3. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S2, the aminated modified graphene oxide is obtained by intercalating graphene oxide with ethylenediamine.
4. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S2, the hydrophobically modified diatomaceous earth is obtained by grafting diatomaceous earth with methyltrimethoxysilane.
5. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, The composite modified filter aid comprises the following components in parts by weight: 40-50 parts of hydrophobically modified diatomaceous earth, 25-35 parts of quaternized modified chitosan, 5-10 parts of aminated modified graphene oxide, 5-10 parts of trisodium citrate, 3-5 parts of sodium dodecylbenzene sulfonate, and 0.5-1 parts of polyoxyethylene sorbitan monooleate. The amount of composite modified filter aid added is 0.3% to 0.45% of the total dry weight of oily sludge.
6. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S2, the temperature of the mixing reaction is 15~20℃, and the reaction time is 10~15min; the temperature of the ultrasonic treatment is ≤25℃.
7. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S3, the air-permeable gradient pore size filter cloth has a double-layer structure, with the outer layer in contact with the sludge having a pore size of 10~15μm and the inner layer in contact with the filter plate having a pore size of 5~8μm; the thickness of the unhydrophobic diatomaceous earth pre-coating is 0.2~0.3mm.
8. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S3, the pressure of the low-pressure fabric is 0.3~0.5 bar, and the duration is 5~8 min; the rate of gradient pressurization is 0.5~1 bar / min, the final pressure is 20~25 bar, and the continuous pressurization time is 20~30 min.
9. The oily sludge pressure filtration treatment process according to claim 1, characterized in that, In step S4, the instantaneous high-pressure nitrogen gas pressure is 5~8 atm, and the micro-backflushing time is 0.5~1 min.