TW202406639A - Process of oily sludge washing and remediation - Google Patents

Abstract

A process of oily sludge washing and remediation is provided. The process includes the following steps. (1) Hot water and biodegradable surfactants were added to the oily sludge and followed by stir and ultrasonic oscillation to wash the oil pollutant from the soil surface. (2) The sludge was centrifuged and dewatered to low water content and low oil content before been backfilled. The surfactant was degraded by itself and no chemical pollution was left behind. (3) The sewage is purified by electrocoagulation and is reused. The present invention can achieve zero pollutant discharge.

Description

Process flow of oily sludge leaching and purification

The invention relates to a technological process for leaching and purifying oily sludge.

Residual oil, waste oil, oil-based mud, oily garbage, tank cleaning sludge from refineries, landing oil sludge, and tanker bilge sludge generated from oil or natural gas extraction must all be recycled and processed. The total petroleum hydrocarbon (TPH) content of the treated soil should be less than 1,000 mg/kg or 1,000 ppm, 0.1%.

Oily sludge treatment and disposal technologies include: landfill, profile control injection into the formation, solidification treatment, solvent extraction, incineration, coking and pyrolysis, thermal analysis, thermal desorption, biological treatment, comprehensive utilization and soil leaching. Most of these technologies are hindered by serious secondary pollution. Among them, the most thorough, fast, economical, environmentally friendly and effective way is soil leaching.

Soil leaching generally only focuses on washing the sludge. However, there is no clear process on how to completely desorb oil (especially aged oil) from the surface of the sediment and then separate the mud and water to achieve low moisture content and low oil content. After cleaning, sewage treatment is even more critical. No one can figure out how to prevent sewage from being discharged, not causing secondary pollution, and reusing reclaimed water to save water resources, so that oily sludge leaching can become a zero-pollution and zero-discharge process.

After the existing oily sludge is treated through the leaching and purification process, there is still secondary pollution. This is because clean water used to clean the sludge becomes sewage, which cannot be reused and can only be discharged. Not only is the resource utilization rate low, but it also pollutes the environment.

In order to solve the above technical problems, the present invention provides a process flow for leaching and purifying oily sludge, which includes the following steps: Step (1), if the oil content of the sludge is high, about >0.5% - 20%, add hot water to the sludge, stir at high speed, and vibrate with ultrasonic waves to rinse, so that the oil stains can be desorbed from the surface of the sediment and float to the surface. The surface of the water; after the floating oil is scraped off, the oil and water can be separated and can be recovered and refined. This step can be repeated 1-2 times; Step (2): If the oil content is low, add hot water and biodegradable surfactant to the oil sludge, then stir at high speed, vibrate with ultrasonic waves, and rinse to desorb the oil stain from the surface of the sand; Step (3): Wash the soil and then perform centrifugal dehydration, adding flocculant and polymer coagulant to make the washed soil and sewage easy to separate; Step (4): The sewage is treated by electric coagulation, so that the dissolved oil, organic matter COD, and heavy metals in the water are oxidized, degraded, flocculated, and filtered to obtain clean water, which is also sterilized and deodorized. The clean water is reused to clean the sludge. The oil sludge is cleaned to obtain floating oil, which can be recovered and refined after oil and water separation.

In some embodiments, the vibration uses ultrasonic vibration.

In some embodiments, the centrifugal dehydration is performed using a vertical centrifuge (spin dryer) and a horizontal centrifuge, and centrifugal dehydration is performed respectively according to the particle size to achieve the lowest average moisture content and oil content.

In some embodiments, the surfactant is a biodegradable surfactant.

In some embodiments, the flocculant is polyaluminum and polyiron, and the polymer coagulant is polyacrylamide.

In some embodiments, the electrocoagulation treatment is implemented by energizing conductive electrode sheets in series to generate an electrochemical reaction.

Compared with the existing technology, the beneficial effects of the present invention are as follows: high oil content is desorbed from sludge and recovered and refined; low oil content sludge is heated with water and biodegradable surfactant through high-speed stirring and ultrasonic waves. The sludge is washed by vibration; multi-stage centrifugation is used to separate the sludge according to particle size to achieve the lowest moisture content and oil content; the washed soil is backfilled, and the surfactant will naturally degrade within a few weeks, leaving no secondary pollution; the sewage is After electrocoagulation purification, it becomes clean water, which can be reused to clean the sludge, forming a complete cycle without any sewage discharge problems; and, the oil separated from the sludge can be recycled and refined after oil-water separation. Through the present invention, the entire oily sludge leaching and purification becomes a zero-pollution and zero-emission process.

The invention provides a process flow for leaching and purifying oily sludge, which includes the following steps:

Step (1): If the oil content of the sludge is high, add hot water to the sludge and rinse it. At this time, stir at high speed and use ultrasonic vibration to use the friction and cavitation effect on the surface of the sediment to desorb the oil, heavy metals, and microorganisms adsorbed on the surface of the oil sludge from the soil surface and dissolve them in the water. When the water is saturated with oil, the oil floats to the surface of the water and becomes floating oil. After these floating oils are scraped off, they can be recovered and refined through oil-water separation. Ultrasound also has a solubilizing effect, increasing the solubility of oil in water.

Although the general oil sludge at the bottom of the tank has a high oil content, it is easier to separate. Landed oil sludge often undergoes years or decades of drying. The alkanes, naphthenes and aromatic hydrocarbons in the oil molecules are closely combined with the gaps in the sediment and are difficult to separate. Therefore, it is necessary to soak in hot water at 70°C to 85°C to soften it, and use the shear force of high-speed stirring and the cavitation effect of ultrasonic waves to easily desorb the oil molecules from the surface of the sediment. Otherwise, even if 5% to 10% of the oil molecules cannot be desorbed, it will be difficult to achieve an oil content of 0.1%.

Step (2): If the oil content of the sludge is low, or when cleaning the second pass, add hot water and biodegradable surfactant to the sludge and rinse. Surfactants can reduce the surface tension of water and reduce its adsorption force on the surface of sediment through a rollup mechanism. Surfactant monomers accumulate in large quantities at the soil/water and oil/water interfaces, greatly reducing the interfacial tension between soil/water and oil/water, prompting water to wet the surface of soil and oil molecules, and increasing the contact between oil and soil. angle, reducing the adsorption force of oil on the soil surface, causing the oil droplets to gradually shrink and break away from the soil surface. . At this time, it is heated, stirred, and vibrated with ultrasonic waves to desorb a small amount of oil, heavy metals, and microorganisms remaining on the surface of the sludge from the soil surface and dissolve them in water. Surfactant also has a solubilizing effect, increasing the solubility of oil pollution in water, so that the oil pollution can be completely dissolved in water. After leaching and dehydration, some surfactants still remain in the soil, which will cause secondary pollution. The present invention uses biodegradable surfactant, which is extracted from tropical vegetable oil. It is a purely natural substance and does not contain any synthetic petrochemical components. Therefore, the surfactant remaining in the soil can be naturally degraded within a few weeks. , without any harmful residues and no concerns about secondary pollution.

Step (3): Separate the washed soil and sewage, and then add flocculants and polymer coagulants to make the soil and sewage easy to separate; first use a vertical centrifuge for centrifugation, the diameter of the vertical centrifuge is larger (greater than 150 cm), with a rotation speed of 1200 rpm, a gravitational acceleration of 565 G is generated. With the help of high G accelerated centrifugation, most of the larger particle size sediment (larger than 0.3mm) is dried to a moisture content of 15% to 18% or lower. At this time, the sediment is very dry, the moisture content is low, and there is little residual oil in the water, so the oil content is less than 0.1%. Fine mud with small particle size in sewage (particle size less than 0.3 mm and greater than 5 μm) can be separated from water using horizontal centrifugation, and its moisture content is about 30% to 40%. After adding flocculants such as polyaluminum and polyiron and the polymer coagulant polyacrylamide, the finer mud is flocculated into larger particles and then filtered out using a filter press. Due to the large specific surface area and high moisture content of these fine mud, the residual oil pollution may be >0.1%; but the coarse mud has a large volume and a low oil content, while the fine mud has a relatively small volume and a high oil content. After mixing, the soil with an average oil content of less than 0.1% can be obtained and can be backfilled.

How to dehydrate to a low moisture content is the key to achieving a low oil content, because the oil enters the water or liquid phase from the surface of the sediment; if the dehydration is not clean, the water content will be high, and the natural oil content will be high. For example, the oil content in the water after cleaning is 3,000 mg/L (kg). If it is dehydrated to a water content of 40%, the oil content will be approximately 3,000 mg/L (kg) * 40% = 1,200 mg/kg, which cannot reach 1,000 mg/kg. standards. If dehydrated to 25%, the oil content will be 3,000 mg/L(kg) * 25% = 750 mg/kg, which is safe and up to standard.

This oil content can also be adjusted by the proportion of cleaning water. If the water/soil ratio is large during cleaning, such as 5:1 to 20:1, the washing will be cleaner, but there will be relatively more muddy water, and the energy consumption for muddy water separation and sewage purification will be higher. Therefore, in conjunction with the low moisture content of the vertical centrifuge and the water/soil ratio during cleaning, the soil oil content is adjusted to less than 0.1% and energy consumption is reduced.

If the required soil oil content cannot be achieved in one rinse, it can be washed a second or third time, but multiple sets of mixing and mixing rinse equipment, mud-water separation equipment and water purification equipment need to be prepared.

The flocculant is polyaluminum and polyiron, and the polymer coagulant is polyacrylamide.

Step (4): The sewage is treated by electric coagulation, so that the dissolved oil, organic matter COD, and heavy metals in the water are oxidized, degraded, flocculated, and filtered to obtain clean water, which is also sterilized and deodorized. The purified water is reused to clean the sludge and realize water recycling. Only a small amount of water lost with the soil needs to be replenished, so there is no sewage discharge problem. At the same time, the floating oil obtained by sludge cleaning can be sent again for refining after oil and water separation, so there is no solid waste discharge problem.

The electrocoagulation treatment is achieved by energizing conductive electrode sheets in series to produce an electrochemical reaction.

Please refer to Figure 1, which is a schematic diagram of the electrocoagulation principle. When two parallel electrode plates are placed in an aqueous solution and DC current is applied, an electrochemical reaction will occur. If an iron electrode sheet is used, the anode produces iron ions Fe ⁺³ and ferrous ions Fe ⁺² , which have strong chemical activity and can convert heavy metals in the water into oxides; the cathode produces hydroxyl radicals OH ^- and Hydrogen H ₂ . Iron hydroxide Fe(OH) ₃ has a flocculation effect and can adsorb tiny particles to form larger particles, which are easy to remove by filtration. Hydroxyl radical (•OH) is the strongest oxidant and can degrade organic matter such as COD and oil pollution.

The method of electrocoagulation treatment is to place two or more conductive electrode sheets in the water. The material can be iron, aluminum, stainless steel, copper, titanium and other metal sheets or graphite. The electrode pads are connected to the DC power supply, as shown in Figure 1. Taking the iron sheet as an example, when direct current is applied to the metal electrode sheet, the anode produces iron ions (Fe ⁺³ ) and ferrous ions (Fe ⁺² ), which have strong chemical activity and can convert heavy metals in the water into oxides, such as Cadmium oxide CdO, chromium oxide Cr ₂ O ₃ , lead oxide PbO, arsenic oxide As ₂ O ₃ , As ₂ O ₅ , etc. These heavy metal oxides have low solubility in water, so they precipitate from the water.

The cathode produces hydroxyl radicals (OH ^- ). As the core of agglomeration, iron hydroxide can change the electron distribution or polarity on the surface of nearby small particles, thereby adsorbing nearby small particles together and flocculating into larger particles. When the particles flocculate to sub-micrometers or above, or even millimeters, they float or settle and are easily filtered out by the filter.

Hydroxyl radicals (•OH hydroxyl group) are generated between the electrodes, which are the strongest oxidants available. They can break the long-chain carbon bonds of organic matter, facilitate flocculation, and even completely oxidize them into carbon dioxide and water. Therefore, it is very effective in degrading oil pollution and organic matter COD in water.

Electric coagulation can also absorb organic matter, chlorides, pesticides, and oil stains, and has functions such as bleaching, sterilization, and deodorization.

Figure 2 is a schematic diagram of the series connection results of several electrodes in electrocoagulation. The first electrode is connected to the positive electrode, and the last electrode is connected to the negative electrode. The middle electrode plate does not need to be connected to the power supply. Water is used as the medium, and the voltage is naturally distributed to all electrode plates. The voltage is the voltage V between each pair of electrode plates multiplied by the number of intervals n, the current is the current I between each pair of electrode plates, and the power consumption is (nV)I.

In order to increase treatment efficiency, multiple electrode pads are commonly used in electrocoagulation equipment. There are three ways to connect several electrodes: series, parallel, and series plus parallel. Series connection is high voltage and low current, parallel connection is low voltage and high current, series plus parallel connection is medium voltage and medium current. In water treatment equipment, electrodes connected in series usually only require a few hundred volts of voltage and hundreds of amperes of current, and the power supply is easy. Therefore, a large number of electrode sheets with a large area can be used to treat a large amount of water. Even if the large electrode plates are bent and come into contact, they will not cause a short circuit. Therefore, the distance between the electrode plates can be shortened, the resistance between the electrode plates is smaller, and the energy consumption is less, so the energy efficiency is improved.

If the electrodes are connected in parallel, the voltage will be low and the current will be large for the same power, which may require thousands or tens of thousands of amperes. The power supply is difficult, so it can only be used for applications with small water volumes. Moreover, the distance between the electrode plates is large, the ohmic resistance is large, more electric energy is consumed, and the energy efficiency is low. The present invention adopts electrode series connection, so it is possible to process a large amount of water and has high energy efficiency.

During the electrocoagulation reaction, some impurities in the water will be deposited on the electrode plate, causing electrode passivation or even short circuit. Therefore, the positive and negative electrodes are reversed every few minutes to prevent impurities from depositing on the electrode sheets and solve the problem of electrode passivation.

When the impurities in the water are flocculated into micrometer μm or even millimeter-sized particles, the particles will be separated from the water through air flotation or sedimentation; these particles can be removed by centrifugation or pressure filtration, thereby removing the impurities in the water and obtaining clean water.

The above are only examples to illustrate the preferred embodiments of the present invention, and are not intended to limit the scope of implementation. All simple substitutions and equivalent changes made based on the patent scope of the present invention and the contents of the patent specification belong to the patent of the present invention. Application scope.

Figure 1 is a schematic diagram of the electrocoagulation principle; Figure 2 is a schematic diagram of the series connection results of several electrodes in electrocoagulation.

Claims (7)

A process flow for leaching and purifying oily sludge, including the following steps: Step (1): If the oil content of the oil sludge is high, add hot water to the oil sludge, stir at high speed and vibrate with ultrasonic waves to rinse, so that the oil stains are desorbed from the surface of the sand and float to the water surface, and then the floating oil is scraped off. After quality, the oil and water can be separated and can be recycled and refined; Step (2): If the oil content of the sludge is low, add hot water and biodegradable surfactant to the sludge, then stir at high speed, vibrate with ultrasonic waves, and rinse to desorb the oil and sediment from the surface; Step (3): After washing the soil, separate it according to particle size and perform centrifugal dehydration to obtain the lowest moisture content and oil content. Adding flocculants and polymer coagulants can make the washed soil and sewage easy to separate. come out; and Step (4): The sewage is treated by electric coagulation, so that the dissolved oil, organic matter COD, and heavy metals in the water are oxidized, degraded, flocculated, and filtered to obtain clean water, which is also sterilized and deodorized. In the process flow of leaching and purifying oily sludge as described in claim 1, the clean water is reused to clean the oil sludge, and the floating oil obtained during the oil sludge cleaning can be recovered and refined after the oil and water are separated. For the process flow of leaching and purifying oily sludge as described in claim 1, the vibration adopts ultrasonic vibration. In the process flow for leaching and purifying oily sludge as described in claim 1, the surfactant is a biodegradable surfactant. For the process flow of leaching and purifying oily sludge as described in claim 1, the centrifugal dehydration uses a vertical centrifuge (spin dryer) and a horizontal centrifuge to perform centrifugal dehydration respectively according to the particle size. Reach the lowest average moisture content and oil content. As described in claim 1, for the process flow of leaching and purifying oily sludge, the flocculant is polyaluminum and polyiron, and the polymer coagulant is polyacrylamide. As in the process flow of leaching and purifying oily sludge described in claim 1, the electrocoagulation treatment is achieved by energizing conductive electrode sheets in series to produce an electrochemical reaction.